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129.\" ======================================================================== 133.\" ========================================================================
130.\" 134.\"
131.IX Title ""<STANDARD INPUT>" 1" 135.IX Title "LIBEV 3"
132.TH "<STANDARD INPUT>" 1 "2007-11-27" "perl v5.8.8" "User Contributed Perl Documentation" 136.TH LIBEV 3 "2019-06-22" "libev-4.25" "libev - high performance full featured event loop"
137.\" For nroff, turn off justification. Always turn off hyphenation; it makes
138.\" way too many mistakes in technical documents.
139.if n .ad l
140.nh
133.SH "NAME" 141.SH "NAME"
134libev \- a high performance full\-featured event loop written in C 142libev \- a high performance full\-featured event loop written in C
135.SH "SYNOPSIS" 143.SH "SYNOPSIS"
136.IX Header "SYNOPSIS" 144.IX Header "SYNOPSIS"
137.Vb 1 145.Vb 1
138\& #include <ev.h> 146\& #include <ev.h>
139.Ve 147.Ve
140.SH "DESCRIPTION" 148.SS "\s-1EXAMPLE PROGRAM\s0"
141.IX Header "DESCRIPTION" 149.IX Subsection "EXAMPLE PROGRAM"
150.Vb 2
151\& // a single header file is required
152\& #include <ev.h>
153\&
154\& #include <stdio.h> // for puts
155\&
156\& // every watcher type has its own typedef\*(Aqd struct
157\& // with the name ev_TYPE
158\& ev_io stdin_watcher;
159\& ev_timer timeout_watcher;
160\&
161\& // all watcher callbacks have a similar signature
162\& // this callback is called when data is readable on stdin
163\& static void
164\& stdin_cb (EV_P_ ev_io *w, int revents)
165\& {
166\& puts ("stdin ready");
167\& // for one\-shot events, one must manually stop the watcher
168\& // with its corresponding stop function.
169\& ev_io_stop (EV_A_ w);
170\&
171\& // this causes all nested ev_run\*(Aqs to stop iterating
172\& ev_break (EV_A_ EVBREAK_ALL);
173\& }
174\&
175\& // another callback, this time for a time\-out
176\& static void
177\& timeout_cb (EV_P_ ev_timer *w, int revents)
178\& {
179\& puts ("timeout");
180\& // this causes the innermost ev_run to stop iterating
181\& ev_break (EV_A_ EVBREAK_ONE);
182\& }
183\&
184\& int
185\& main (void)
186\& {
187\& // use the default event loop unless you have special needs
188\& struct ev_loop *loop = EV_DEFAULT;
189\&
190\& // initialise an io watcher, then start it
191\& // this one will watch for stdin to become readable
192\& ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
193\& ev_io_start (loop, &stdin_watcher);
194\&
195\& // initialise a timer watcher, then start it
196\& // simple non\-repeating 5.5 second timeout
197\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
198\& ev_timer_start (loop, &timeout_watcher);
199\&
200\& // now wait for events to arrive
201\& ev_run (loop, 0);
202\&
203\& // break was called, so exit
204\& return 0;
205\& }
206.Ve
207.SH "ABOUT THIS DOCUMENT"
208.IX Header "ABOUT THIS DOCUMENT"
209This document documents the libev software package.
210.PP
211The newest version of this document is also available as an html-formatted
212web page you might find easier to navigate when reading it for the first
213time: <http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
214.PP
215While this document tries to be as complete as possible in documenting
216libev, its usage and the rationale behind its design, it is not a tutorial
217on event-based programming, nor will it introduce event-based programming
218with libev.
219.PP
220Familiarity with event based programming techniques in general is assumed
221throughout this document.
222.SH "WHAT TO READ WHEN IN A HURRY"
223.IX Header "WHAT TO READ WHEN IN A HURRY"
224This manual tries to be very detailed, but unfortunately, this also makes
225it very long. If you just want to know the basics of libev, I suggest
226reading \*(L"\s-1ANATOMY OF A WATCHER\*(R"\s0, then the \*(L"\s-1EXAMPLE PROGRAM\*(R"\s0 above and
227look up the missing functions in \*(L"\s-1GLOBAL FUNCTIONS\*(R"\s0 and the \f(CW\*(C`ev_io\*(C'\fR and
228\&\f(CW\*(C`ev_timer\*(C'\fR sections in \*(L"\s-1WATCHER TYPES\*(R"\s0.
229.SH "ABOUT LIBEV"
230.IX Header "ABOUT LIBEV"
142Libev is an event loop: you register interest in certain events (such as a 231Libev is an event loop: you register interest in certain events (such as a
143file descriptor being readable or a timeout occuring), and it will manage 232file descriptor being readable or a timeout occurring), and it will manage
144these event sources and provide your program with events. 233these event sources and provide your program with events.
145.PP 234.PP
146To do this, it must take more or less complete control over your process 235To do this, it must take more or less complete control over your process
147(or thread) by executing the \fIevent loop\fR handler, and will then 236(or thread) by executing the \fIevent loop\fR handler, and will then
148communicate events via a callback mechanism. 237communicate events via a callback mechanism.
149.PP 238.PP
150You register interest in certain events by registering so-called \fIevent 239You register interest in certain events by registering so-called \fIevent
151watchers\fR, which are relatively small C structures you initialise with the 240watchers\fR, which are relatively small C structures you initialise with the
152details of the event, and then hand it over to libev by \fIstarting\fR the 241details of the event, and then hand it over to libev by \fIstarting\fR the
153watcher. 242watcher.
154.SH "FEATURES" 243.SS "\s-1FEATURES\s0"
155.IX Header "FEATURES" 244.IX Subsection "FEATURES"
156Libev supports select, poll, the linux-specific epoll and the bsd-specific 245Libev supports \f(CW\*(C`select\*(C'\fR, \f(CW\*(C`poll\*(C'\fR, the Linux-specific aio and \f(CW\*(C`epoll\*(C'\fR
157kqueue mechanisms for file descriptor events, relative timers, absolute 246interfaces, the BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port
158timers with customised rescheduling, signal events, process status change 247mechanisms for file descriptor events (\f(CW\*(C`ev_io\*(C'\fR), the Linux \f(CW\*(C`inotify\*(C'\fR
159events (related to \s-1SIGCHLD\s0), and event watchers dealing with the event 248interface (for \f(CW\*(C`ev_stat\*(C'\fR), Linux eventfd/signalfd (for faster and cleaner
160loop mechanism itself (idle, prepare and check watchers). It also is quite 249inter-thread wakeup (\f(CW\*(C`ev_async\*(C'\fR)/signal handling (\f(CW\*(C`ev_signal\*(C'\fR)) relative
161fast (see this benchmark comparing 250timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers with customised rescheduling
162it to libevent for example). 251(\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals (\f(CW\*(C`ev_signal\*(C'\fR), process status
252change events (\f(CW\*(C`ev_child\*(C'\fR), and event watchers dealing with the event
253loop mechanism itself (\f(CW\*(C`ev_idle\*(C'\fR, \f(CW\*(C`ev_embed\*(C'\fR, \f(CW\*(C`ev_prepare\*(C'\fR and
254\&\f(CW\*(C`ev_check\*(C'\fR watchers) as well as file watchers (\f(CW\*(C`ev_stat\*(C'\fR) and even
255limited support for fork events (\f(CW\*(C`ev_fork\*(C'\fR).
256.PP
257It also is quite fast (see this
258benchmark <http://libev.schmorp.de/bench.html> comparing it to libevent
259for example).
163.SH "CONVENTIONS" 260.SS "\s-1CONVENTIONS\s0"
164.IX Header "CONVENTIONS" 261.IX Subsection "CONVENTIONS"
165Libev is very configurable. In this manual the default configuration 262Libev is very configurable. In this manual the default (and most common)
166will be described, which supports multiple event loops. For more info 263configuration will be described, which supports multiple event loops. For
167about various configuration options please have a look at the file 264more info about various configuration options please have a look at
168\&\fI\s-1README\s0.embed\fR in the libev distribution. If libev was configured without 265\&\fB\s-1EMBED\s0\fR section in this manual. If libev was configured without support
169support for multiple event loops, then all functions taking an initial 266for multiple event loops, then all functions taking an initial argument of
170argument of name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) 267name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) will not have
171will not have this argument. 268this argument.
172.SH "TIME REPRESENTATION" 269.SS "\s-1TIME REPRESENTATION\s0"
173.IX Header "TIME REPRESENTATION" 270.IX Subsection "TIME REPRESENTATION"
174Libev represents time as a single floating point number, representing the 271Libev represents time as a single floating point number, representing
175(fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere near 272the (fractional) number of seconds since the (\s-1POSIX\s0) epoch (in practice
176the beginning of 1970, details are complicated, don't ask). This type is 273somewhere near the beginning of 1970, details are complicated, don't
177called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use too. It usually aliases 274ask). This type is called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use
178to the \f(CW\*(C`double\*(C'\fR type in C, and when you need to do any calculations on 275too. It usually aliases to the \f(CW\*(C`double\*(C'\fR type in C. When you need to do
179it, you should treat it as such. 276any calculations on it, you should treat it as some floating point value.
277.PP
278Unlike the name component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for
279time differences (e.g. delays) throughout libev.
280.SH "ERROR HANDLING"
281.IX Header "ERROR HANDLING"
282Libev knows three classes of errors: operating system errors, usage errors
283and internal errors (bugs).
284.PP
285When libev catches an operating system error it cannot handle (for example
286a system call indicating a condition libev cannot fix), it calls the callback
287set via \f(CW\*(C`ev_set_syserr_cb\*(C'\fR, which is supposed to fix the problem or
288abort. The default is to print a diagnostic message and to call \f(CW\*(C`abort
289()\*(C'\fR.
290.PP
291When libev detects a usage error such as a negative timer interval, then
292it will print a diagnostic message and abort (via the \f(CW\*(C`assert\*(C'\fR mechanism,
293so \f(CW\*(C`NDEBUG\*(C'\fR will disable this checking): these are programming errors in
294the libev caller and need to be fixed there.
295.PP
296Libev also has a few internal error-checking \f(CW\*(C`assert\*(C'\fRions, and also has
297extensive consistency checking code. These do not trigger under normal
298circumstances, as they indicate either a bug in libev or worse.
180.SH "GLOBAL FUNCTIONS" 299.SH "GLOBAL FUNCTIONS"
181.IX Header "GLOBAL FUNCTIONS" 300.IX Header "GLOBAL FUNCTIONS"
182These functions can be called anytime, even before initialising the 301These functions can be called anytime, even before initialising the
183library in any way. 302library in any way.
184.IP "ev_tstamp ev_time ()" 4 303.IP "ev_tstamp ev_time ()" 4
185.IX Item "ev_tstamp ev_time ()" 304.IX Item "ev_tstamp ev_time ()"
186Returns the current time as libev would use it. Please note that the 305Returns the current time as libev would use it. Please note that the
187\&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp 306\&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp
188you actually want to know. 307you actually want to know. Also interesting is the combination of
308\&\f(CW\*(C`ev_now_update\*(C'\fR and \f(CW\*(C`ev_now\*(C'\fR.
309.IP "ev_sleep (ev_tstamp interval)" 4
310.IX Item "ev_sleep (ev_tstamp interval)"
311Sleep for the given interval: The current thread will be blocked
312until either it is interrupted or the given time interval has
313passed (approximately \- it might return a bit earlier even if not
314interrupted). Returns immediately if \f(CW\*(C`interval <= 0\*(C'\fR.
315.Sp
316Basically this is a sub-second-resolution \f(CW\*(C`sleep ()\*(C'\fR.
317.Sp
318The range of the \f(CW\*(C`interval\*(C'\fR is limited \- libev only guarantees to work
319with sleep times of up to one day (\f(CW\*(C`interval <= 86400\*(C'\fR).
189.IP "int ev_version_major ()" 4 320.IP "int ev_version_major ()" 4
190.IX Item "int ev_version_major ()" 321.IX Item "int ev_version_major ()"
191.PD 0 322.PD 0
192.IP "int ev_version_minor ()" 4 323.IP "int ev_version_minor ()" 4
193.IX Item "int ev_version_minor ()" 324.IX Item "int ev_version_minor ()"
194.PD 325.PD
195You can find out the major and minor version numbers of the library 326You can find out the major and minor \s-1ABI\s0 version numbers of the library
196you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and 327you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and
197\&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global 328\&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global
198symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the 329symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the
199version of the library your program was compiled against. 330version of the library your program was compiled against.
200.Sp 331.Sp
332These version numbers refer to the \s-1ABI\s0 version of the library, not the
333release version.
334.Sp
201Usually, it's a good idea to terminate if the major versions mismatch, 335Usually, it's a good idea to terminate if the major versions mismatch,
202as this indicates an incompatible change. Minor versions are usually 336as this indicates an incompatible change. Minor versions are usually
203compatible to older versions, so a larger minor version alone is usually 337compatible to older versions, so a larger minor version alone is usually
204not a problem. 338not a problem.
205.Sp 339.Sp
206Example: make sure we haven't accidentally been linked against the wrong 340Example: Make sure we haven't accidentally been linked against the wrong
207version: 341version (note, however, that this will not detect other \s-1ABI\s0 mismatches,
342such as \s-1LFS\s0 or reentrancy).
208.Sp 343.Sp
209.Vb 3 344.Vb 3
210\& assert (("libev version mismatch", 345\& assert (("libev version mismatch",
211\& ev_version_major () == EV_VERSION_MAJOR 346\& ev_version_major () == EV_VERSION_MAJOR
212\& && ev_version_minor () >= EV_VERSION_MINOR)); 347\& && ev_version_minor () >= EV_VERSION_MINOR));
213.Ve 348.Ve
214.IP "unsigned int ev_supported_backends ()" 4 349.IP "unsigned int ev_supported_backends ()" 4
215.IX Item "unsigned int ev_supported_backends ()" 350.IX Item "unsigned int ev_supported_backends ()"
216Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR 351Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR
217value) compiled into this binary of libev (independent of their 352value) compiled into this binary of libev (independent of their
… …
220.Sp 355.Sp
221Example: make sure we have the epoll method, because yeah this is cool and 356Example: make sure we have the epoll method, because yeah this is cool and
222a must have and can we have a torrent of it please!!!11 357a must have and can we have a torrent of it please!!!11
223.Sp 358.Sp
224.Vb 2 359.Vb 2
225\& assert (("sorry, no epoll, no sex", 360\& assert (("sorry, no epoll, no sex",
226\& ev_supported_backends () & EVBACKEND_EPOLL)); 361\& ev_supported_backends () & EVBACKEND_EPOLL));
227.Ve 362.Ve
228.IP "unsigned int ev_recommended_backends ()" 4 363.IP "unsigned int ev_recommended_backends ()" 4
229.IX Item "unsigned int ev_recommended_backends ()" 364.IX Item "unsigned int ev_recommended_backends ()"
230Return the set of all backends compiled into this binary of libev and also 365Return the set of all backends compiled into this binary of libev and
231recommended for this platform. This set is often smaller than the one 366also recommended for this platform, meaning it will work for most file
367descriptor types. This set is often smaller than the one returned by
232returned by \f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on 368\&\f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on most BSDs
233most BSDs and will not be autodetected unless you explicitly request it 369and will not be auto-detected unless you explicitly request it (assuming
234(assuming you know what you are doing). This is the set of backends that 370you know what you are doing). This is the set of backends that libev will
235libev will probe for if you specify no backends explicitly. 371probe for if you specify no backends explicitly.
236.IP "unsigned int ev_embeddable_backends ()" 4 372.IP "unsigned int ev_embeddable_backends ()" 4
237.IX Item "unsigned int ev_embeddable_backends ()" 373.IX Item "unsigned int ev_embeddable_backends ()"
238Returns the set of backends that are embeddable in other event loops. This 374Returns the set of backends that are embeddable in other event loops. This
239is the theoretical, all\-platform, value. To find which backends 375value is platform-specific but can include backends not available on the
240might be supported on the current system, you would need to look at 376current system. To find which embeddable backends might be supported on
241\&\f(CW\*(C`ev_embeddable_backends () & ev_supported_backends ()\*(C'\fR, likewise for 377the current system, you would need to look at \f(CW\*(C`ev_embeddable_backends ()
242recommended ones. 378& ev_supported_backends ()\*(C'\fR, likewise for recommended ones.
243.Sp 379.Sp
244See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info. 380See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
245.IP "ev_set_allocator (void *(*cb)(void *ptr, size_t size))" 4 381.IP "ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())" 4
246.IX Item "ev_set_allocator (void *(*cb)(void *ptr, size_t size))" 382.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())"
247Sets the allocation function to use (the prototype and semantics are 383Sets the allocation function to use (the prototype is similar \- the
248identical to the realloc C function). It is used to allocate and free 384semantics are identical to the \f(CW\*(C`realloc\*(C'\fR C89/SuS/POSIX function). It is
249memory (no surprises here). If it returns zero when memory needs to be 385used to allocate and free memory (no surprises here). If it returns zero
250allocated, the library might abort or take some potentially destructive 386when memory needs to be allocated (\f(CW\*(C`size != 0\*(C'\fR), the library might abort
251action. The default is your system realloc function. 387or take some potentially destructive action.
388.Sp
389Since some systems (at least OpenBSD and Darwin) fail to implement
390correct \f(CW\*(C`realloc\*(C'\fR semantics, libev will use a wrapper around the system
391\&\f(CW\*(C`realloc\*(C'\fR and \f(CW\*(C`free\*(C'\fR functions by default.
252.Sp 392.Sp
253You could override this function in high-availability programs to, say, 393You could override this function in high-availability programs to, say,
254free some memory if it cannot allocate memory, to use a special allocator, 394free some memory if it cannot allocate memory, to use a special allocator,
255or even to sleep a while and retry until some memory is available. 395or even to sleep a while and retry until some memory is available.
256.Sp 396.Sp
397Example: The following is the \f(CW\*(C`realloc\*(C'\fR function that libev itself uses
398which should work with \f(CW\*(C`realloc\*(C'\fR and \f(CW\*(C`free\*(C'\fR functions of all kinds and
399is probably a good basis for your own implementation.
400.Sp
401.Vb 5
402\& static void *
403\& ev_realloc_emul (void *ptr, long size) EV_NOEXCEPT
404\& {
405\& if (size)
406\& return realloc (ptr, size);
407\&
408\& free (ptr);
409\& return 0;
410\& }
411.Ve
412.Sp
257Example: replace the libev allocator with one that waits a bit and then 413Example: Replace the libev allocator with one that waits a bit and then
258retries: better than mine). 414retries.
259.Sp 415.Sp
260.Vb 6 416.Vb 8
261\& static void * 417\& static void *
262\& persistent_realloc (void *ptr, size_t size) 418\& persistent_realloc (void *ptr, size_t size)
263\& { 419\& {
420\& if (!size)
421\& {
422\& free (ptr);
423\& return 0;
424\& }
425\&
264\& for (;;) 426\& for (;;)
265\& { 427\& {
266\& void *newptr = realloc (ptr, size); 428\& void *newptr = realloc (ptr, size);
267.Ve 429\&
268.Sp
269.Vb 2
270\& if (newptr) 430\& if (newptr)
271\& return newptr; 431\& return newptr;
272.Ve 432\&
273.Sp
274.Vb 3
275\& sleep (60); 433\& sleep (60);
276\& } 434\& }
277\& } 435\& }
278.Ve 436\&
279.Sp
280.Vb 2
281\& ... 437\& ...
282\& ev_set_allocator (persistent_realloc); 438\& ev_set_allocator (persistent_realloc);
283.Ve 439.Ve
284.IP "ev_set_syserr_cb (void (*cb)(const char *msg));" 4 440.IP "ev_set_syserr_cb (void (*cb)(const char *msg) throw ())" 4
285.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg));" 441.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg) throw ())"
286Set the callback function to call on a retryable syscall error (such 442Set the callback function to call on a retryable system call error (such
287as failed select, poll, epoll_wait). The message is a printable string 443as failed select, poll, epoll_wait). The message is a printable string
288indicating the system call or subsystem causing the problem. If this 444indicating the system call or subsystem causing the problem. If this
289callback is set, then libev will expect it to remedy the sitution, no 445callback is set, then libev will expect it to remedy the situation, no
290matter what, when it returns. That is, libev will generally retry the 446matter what, when it returns. That is, libev will generally retry the
291requested operation, or, if the condition doesn't go away, do bad stuff 447requested operation, or, if the condition doesn't go away, do bad stuff
292(such as abort). 448(such as abort).
293.Sp 449.Sp
294Example: do the same thing as libev does internally: 450Example: This is basically the same thing that libev does internally, too.
295.Sp 451.Sp
296.Vb 6 452.Vb 6
297\& static void 453\& static void
298\& fatal_error (const char *msg) 454\& fatal_error (const char *msg)
299\& { 455\& {
300\& perror (msg); 456\& perror (msg);
301\& abort (); 457\& abort ();
302\& } 458\& }
303.Ve 459\&
304.Sp
305.Vb 2
306\& ... 460\& ...
307\& ev_set_syserr_cb (fatal_error); 461\& ev_set_syserr_cb (fatal_error);
308.Ve 462.Ve
463.IP "ev_feed_signal (int signum)" 4
464.IX Item "ev_feed_signal (int signum)"
465This function can be used to \*(L"simulate\*(R" a signal receive. It is completely
466safe to call this function at any time, from any context, including signal
467handlers or random threads.
468.Sp
469Its main use is to customise signal handling in your process, especially
470in the presence of threads. For example, you could block signals
471by default in all threads (and specifying \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when
472creating any loops), and in one thread, use \f(CW\*(C`sigwait\*(C'\fR or any other
473mechanism to wait for signals, then \*(L"deliver\*(R" them to libev by calling
474\&\f(CW\*(C`ev_feed_signal\*(C'\fR.
309.SH "FUNCTIONS CONTROLLING THE EVENT LOOP" 475.SH "FUNCTIONS CONTROLLING EVENT LOOPS"
310.IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP" 476.IX Header "FUNCTIONS CONTROLLING EVENT LOOPS"
311An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR. The library knows two 477An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR (the \f(CW\*(C`struct\*(C'\fR is
312types of such loops, the \fIdefault\fR loop, which supports signals and child 478\&\fInot\fR optional in this case unless libev 3 compatibility is disabled, as
313events, and dynamically created loops which do not. 479libev 3 had an \f(CW\*(C`ev_loop\*(C'\fR function colliding with the struct name).
314.PP 480.PP
315If you use threads, a common model is to run the default event loop 481The library knows two types of such loops, the \fIdefault\fR loop, which
316in your main thread (or in a separate thread) and for each thread you 482supports child process events, and dynamically created event loops which
317create, you also create another event loop. Libev itself does no locking 483do not.
318whatsoever, so if you mix calls to the same event loop in different
319threads, make sure you lock (this is usually a bad idea, though, even if
320done correctly, because it's hideous and inefficient).
321.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4 484.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
322.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)" 485.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
323This will initialise the default event loop if it hasn't been initialised 486This returns the \*(L"default\*(R" event loop object, which is what you should
324yet and return it. If the default loop could not be initialised, returns 487normally use when you just need \*(L"the event loop\*(R". Event loop objects and
325false. If it already was initialised it simply returns it (and ignores the 488the \f(CW\*(C`flags\*(C'\fR parameter are described in more detail in the entry for
326flags. If that is troubling you, check \f(CW\*(C`ev_backend ()\*(C'\fR afterwards). 489\&\f(CW\*(C`ev_loop_new\*(C'\fR.
490.Sp
491If the default loop is already initialised then this function simply
492returns it (and ignores the flags. If that is troubling you, check
493\&\f(CW\*(C`ev_backend ()\*(C'\fR afterwards). Otherwise it will create it with the given
494flags, which should almost always be \f(CW0\fR, unless the caller is also the
495one calling \f(CW\*(C`ev_run\*(C'\fR or otherwise qualifies as \*(L"the main program\*(R".
327.Sp 496.Sp
328If you don't know what event loop to use, use the one returned from this 497If you don't know what event loop to use, use the one returned from this
329function. 498function (or via the \f(CW\*(C`EV_DEFAULT\*(C'\fR macro).
499.Sp
500Note that this function is \fInot\fR thread-safe, so if you want to use it
501from multiple threads, you have to employ some kind of mutex (note also
502that this case is unlikely, as loops cannot be shared easily between
503threads anyway).
504.Sp
505The default loop is the only loop that can handle \f(CW\*(C`ev_child\*(C'\fR watchers,
506and to do this, it always registers a handler for \f(CW\*(C`SIGCHLD\*(C'\fR. If this is
507a problem for your application you can either create a dynamic loop with
508\&\f(CW\*(C`ev_loop_new\*(C'\fR which doesn't do that, or you can simply overwrite the
509\&\f(CW\*(C`SIGCHLD\*(C'\fR signal handler \fIafter\fR calling \f(CW\*(C`ev_default_init\*(C'\fR.
510.Sp
511Example: This is the most typical usage.
512.Sp
513.Vb 2
514\& if (!ev_default_loop (0))
515\& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
516.Ve
517.Sp
518Example: Restrict libev to the select and poll backends, and do not allow
519environment settings to be taken into account:
520.Sp
521.Vb 1
522\& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
523.Ve
524.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
525.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
526This will create and initialise a new event loop object. If the loop
527could not be initialised, returns false.
528.Sp
529This function is thread-safe, and one common way to use libev with
530threads is indeed to create one loop per thread, and using the default
531loop in the \*(L"main\*(R" or \*(L"initial\*(R" thread.
330.Sp 532.Sp
331The flags argument can be used to specify special behaviour or specific 533The flags argument can be used to specify special behaviour or specific
332backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). 534backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).
333.Sp 535.Sp
334The following flags are supported: 536The following flags are supported:
… …
339The default flags value. Use this if you have no clue (it's the right 541The default flags value. Use this if you have no clue (it's the right
340thing, believe me). 542thing, believe me).
341.ie n .IP """EVFLAG_NOENV""" 4 543.ie n .IP """EVFLAG_NOENV""" 4
342.el .IP "\f(CWEVFLAG_NOENV\fR" 4 544.el .IP "\f(CWEVFLAG_NOENV\fR" 4
343.IX Item "EVFLAG_NOENV" 545.IX Item "EVFLAG_NOENV"
344If this flag bit is ored into the flag value (or the program runs setuid 546If this flag bit is or'ed into the flag value (or the program runs setuid
345or setgid) then libev will \fInot\fR look at the environment variable 547or setgid) then libev will \fInot\fR look at the environment variable
346\&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will 548\&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will
347override the flags completely if it is found in the environment. This is 549override the flags completely if it is found in the environment. This is
348useful to try out specific backends to test their performance, or to work 550useful to try out specific backends to test their performance, to work
349around bugs. 551around bugs, or to make libev threadsafe (accessing environment variables
552cannot be done in a threadsafe way, but usually it works if no other
553thread modifies them).
554.ie n .IP """EVFLAG_FORKCHECK""" 4
555.el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4
556.IX Item "EVFLAG_FORKCHECK"
557Instead of calling \f(CW\*(C`ev_loop_fork\*(C'\fR manually after a fork, you can also
558make libev check for a fork in each iteration by enabling this flag.
559.Sp
560This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop,
561and thus this might slow down your event loop if you do a lot of loop
562iterations and little real work, but is usually not noticeable (on my
563GNU/Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn
564sequence without a system call and thus \fIvery\fR fast, but my GNU/Linux
565system also has \f(CW\*(C`pthread_atfork\*(C'\fR which is even faster). (Update: glibc
566versions 2.25 apparently removed the \f(CW\*(C`getpid\*(C'\fR optimisation again).
567.Sp
568The big advantage of this flag is that you can forget about fork (and
569forget about forgetting to tell libev about forking, although you still
570have to ignore \f(CW\*(C`SIGPIPE\*(C'\fR) when you use this flag.
571.Sp
572This flag setting cannot be overridden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR
573environment variable.
574.ie n .IP """EVFLAG_NOINOTIFY""" 4
575.el .IP "\f(CWEVFLAG_NOINOTIFY\fR" 4
576.IX Item "EVFLAG_NOINOTIFY"
577When this flag is specified, then libev will not attempt to use the
578\&\fIinotify\fR \s-1API\s0 for its \f(CW\*(C`ev_stat\*(C'\fR watchers. Apart from debugging and
579testing, this flag can be useful to conserve inotify file descriptors, as
580otherwise each loop using \f(CW\*(C`ev_stat\*(C'\fR watchers consumes one inotify handle.
581.ie n .IP """EVFLAG_SIGNALFD""" 4
582.el .IP "\f(CWEVFLAG_SIGNALFD\fR" 4
583.IX Item "EVFLAG_SIGNALFD"
584When this flag is specified, then libev will attempt to use the
585\&\fIsignalfd\fR \s-1API\s0 for its \f(CW\*(C`ev_signal\*(C'\fR (and \f(CW\*(C`ev_child\*(C'\fR) watchers. This \s-1API\s0
586delivers signals synchronously, which makes it both faster and might make
587it possible to get the queued signal data. It can also simplify signal
588handling with threads, as long as you properly block signals in your
589threads that are not interested in handling them.
590.Sp
591Signalfd will not be used by default as this changes your signal mask, and
592there are a lot of shoddy libraries and programs (glib's threadpool for
593example) that can't properly initialise their signal masks.
594.ie n .IP """EVFLAG_NOSIGMASK""" 4
595.el .IP "\f(CWEVFLAG_NOSIGMASK\fR" 4
596.IX Item "EVFLAG_NOSIGMASK"
597When this flag is specified, then libev will avoid to modify the signal
598mask. Specifically, this means you have to make sure signals are unblocked
599when you want to receive them.
600.Sp
601This behaviour is useful when you want to do your own signal handling, or
602want to handle signals only in specific threads and want to avoid libev
603unblocking the signals.
604.Sp
605It's also required by \s-1POSIX\s0 in a threaded program, as libev calls
606\&\f(CW\*(C`sigprocmask\*(C'\fR, whose behaviour is officially unspecified.
607.Sp
608This flag's behaviour will become the default in future versions of libev.
350.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4 609.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
351.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4 610.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
352.IX Item "EVBACKEND_SELECT (value 1, portable select backend)" 611.IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
353This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as 612This is your standard \fBselect\fR\|(2) backend. Not \fIcompletely\fR standard, as
354libev tries to roll its own fd_set with no limits on the number of fds, 613libev tries to roll its own fd_set with no limits on the number of fds,
355but if that fails, expect a fairly low limit on the number of fds when 614but if that fails, expect a fairly low limit on the number of fds when
356using this backend. It doesn't scale too well (O(highest_fd)), but its usually 615using this backend. It doesn't scale too well (O(highest_fd)), but its
357the fastest backend for a low number of fds. 616usually the fastest backend for a low number of (low-numbered :) fds.
617.Sp
618To get good performance out of this backend you need a high amount of
619parallelism (most of the file descriptors should be busy). If you are
620writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many
621connections as possible during one iteration. You might also want to have
622a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of
623readiness notifications you get per iteration.
624.Sp
625This backend maps \f(CW\*(C`EV_READ\*(C'\fR to the \f(CW\*(C`readfds\*(C'\fR set and \f(CW\*(C`EV_WRITE\*(C'\fR to the
626\&\f(CW\*(C`writefds\*(C'\fR set (and to work around Microsoft Windows bugs, also onto the
627\&\f(CW\*(C`exceptfds\*(C'\fR set on that platform).
358.ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4 628.ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4
359.el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4 629.el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4
360.IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)" 630.IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)"
361And this is your standard \fIpoll\fR\|(2) backend. It's more complicated than 631And this is your standard \fBpoll\fR\|(2) backend. It's more complicated
362select, but handles sparse fds better and has no artificial limit on the 632than select, but handles sparse fds better and has no artificial
363number of fds you can use (except it will slow down considerably with a 633limit on the number of fds you can use (except it will slow down
364lot of inactive fds). It scales similarly to select, i.e. O(total_fds). 634considerably with a lot of inactive fds). It scales similarly to select,
635i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for
636performance tips.
637.Sp
638This backend maps \f(CW\*(C`EV_READ\*(C'\fR to \f(CW\*(C`POLLIN | POLLERR | POLLHUP\*(C'\fR, and
639\&\f(CW\*(C`EV_WRITE\*(C'\fR to \f(CW\*(C`POLLOUT | POLLERR | POLLHUP\*(C'\fR.
365.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4 640.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
366.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4 641.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
367.IX Item "EVBACKEND_EPOLL (value 4, Linux)" 642.IX Item "EVBACKEND_EPOLL (value 4, Linux)"
643Use the linux-specific \fBepoll\fR\|(7) interface (for both pre\- and post\-2.6.9
644kernels).
645.Sp
368For few fds, this backend is a bit little slower than poll and select, 646For few fds, this backend is a bit little slower than poll and select, but
369but it scales phenomenally better. While poll and select usually scale like 647it scales phenomenally better. While poll and select usually scale like
370O(total_fds) where n is the total number of fds (or the highest fd), epoll scales 648O(total_fds) where total_fds is the total number of fds (or the highest
371either O(1) or O(active_fds). 649fd), epoll scales either O(1) or O(active_fds).
372.Sp 650.Sp
651The epoll mechanism deserves honorable mention as the most misdesigned
652of the more advanced event mechanisms: mere annoyances include silently
653dropping file descriptors, requiring a system call per change per file
654descriptor (and unnecessary guessing of parameters), problems with dup,
655returning before the timeout value, resulting in additional iterations
656(and only giving 5ms accuracy while select on the same platform gives
6570.1ms) and so on. The biggest issue is fork races, however \- if a program
658forks then \fIboth\fR parent and child process have to recreate the epoll
659set, which can take considerable time (one syscall per file descriptor)
660and is of course hard to detect.
661.Sp
662Epoll is also notoriously buggy \- embedding epoll fds \fIshould\fR work,
663but of course \fIdoesn't\fR, and epoll just loves to report events for
664totally \fIdifferent\fR file descriptors (even already closed ones, so
665one cannot even remove them from the set) than registered in the set
666(especially on \s-1SMP\s0 systems). Libev tries to counter these spurious
667notifications by employing an additional generation counter and comparing
668that against the events to filter out spurious ones, recreating the set
669when required. Epoll also erroneously rounds down timeouts, but gives you
670no way to know when and by how much, so sometimes you have to busy-wait
671because epoll returns immediately despite a nonzero timeout. And last
672not least, it also refuses to work with some file descriptors which work
673perfectly fine with \f(CW\*(C`select\*(C'\fR (files, many character devices...).
674.Sp
675Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
676cobbled together in a hurry, no thought to design or interaction with
677others. Oh, the pain, will it ever stop...
678.Sp
373While stopping and starting an I/O watcher in the same iteration will 679While stopping, setting and starting an I/O watcher in the same iteration
374result in some caching, there is still a syscall per such incident 680will result in some caching, there is still a system call per such
375(because the fd could point to a different file description now), so its 681incident (because the same \fIfile descriptor\fR could point to a different
376best to avoid that. Also, \fIdup()\fRed file descriptors might not work very 682\&\fIfile description\fR now), so its best to avoid that. Also, \f(CW\*(C`dup ()\*(C'\fR'ed
377well if you register events for both fds. 683file descriptors might not work very well if you register events for both
684file descriptors.
378.Sp 685.Sp
379Please note that epoll sometimes generates spurious notifications, so you 686Best performance from this backend is achieved by not unregistering all
380need to use non-blocking I/O or other means to avoid blocking when no data 687watchers for a file descriptor until it has been closed, if possible,
381(or space) is available. 688i.e. keep at least one watcher active per fd at all times. Stopping and
689starting a watcher (without re-setting it) also usually doesn't cause
690extra overhead. A fork can both result in spurious notifications as well
691as in libev having to destroy and recreate the epoll object, which can
692take considerable time and thus should be avoided.
693.Sp
694All this means that, in practice, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR can be as fast or
695faster than epoll for maybe up to a hundred file descriptors, depending on
696the usage. So sad.
697.Sp
698While nominally embeddable in other event loops, this feature is broken in
699a lot of kernel revisions, but probably(!) works in current versions.
700.Sp
701This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
702\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
703.ie n .IP """EVBACKEND_LINUXAIO"" (value 64, Linux)" 4
704.el .IP "\f(CWEVBACKEND_LINUXAIO\fR (value 64, Linux)" 4
705.IX Item "EVBACKEND_LINUXAIO (value 64, Linux)"
706Use the linux-specific linux aio (\fInot\fR \f(CWaio(7)\fR) event interface
707available in post\-4.18 kernels.
708.Sp
709If this backend works for you (as of this writing, it was very
710experimental and only supports a subset of file types), it is the best
711event interface available on linux and might be well worth it enabling it
712\&\- if it isn't available in your kernel this will be detected and another
713backend will be chosen.
714.Sp
715This backend can batch oneshot requests and uses a user-space ring buffer
716to receive events. It also doesn't suffer from most of the design problems
717of epoll (such as not being able to remove event sources from the epoll
718set), and generally sounds too good to be true. Because, this being the
719linux kernel, of course it suffers from a whole new set of limitations.
720.Sp
721For one, it is not easily embeddable (but probably could be done using
722an event fd at some extra overhead). It also is subject to various
723arbitrary limits that can be configured in \fI/proc/sys/fs/aio\-max\-nr\fR
724and \fI/proc/sys/fs/aio\-nr\fR), which could lead to it being skipped during
725initialisation.
726.Sp
727Most problematic in practise, however, is that, like kqueue, it requires
728special support from drivers, and, not surprisingly, not all drivers
729implement it. For example, in linux 4.19, tcp sockets, pipes, event fds,
730files, \fI/dev/null\fR and a few others are supported, but ttys are not, so
731this is not (yet?) a generic event polling interface but is probably still
732be very useful in a web server or similar program.
733.Sp
734This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
735\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
382.ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4 736.ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4
383.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4 737.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
384.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)" 738.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
385Kqueue deserves special mention, as at the time of this writing, it 739Kqueue deserves special mention, as at the time of this writing, it
386was broken on all BSDs except NetBSD (usually it doesn't work with 740was broken on all BSDs except NetBSD (usually it doesn't work reliably
387anything but sockets and pipes, except on Darwin, where of course its 741with anything but sockets and pipes, except on Darwin, where of course
388completely useless). For this reason its not being \*(L"autodetected\*(R" 742it's completely useless). Unlike epoll, however, whose brokenness
743is by design, these kqueue bugs can (and eventually will) be fixed
744without \s-1API\s0 changes to existing programs. For this reason it's not being
389unless you explicitly specify it explicitly in the flags (i.e. using 745\&\*(L"auto-detected\*(R" unless you explicitly specify it in the flags (i.e. using
390\&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR). 746\&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a known-to-be-good (\-enough)
747system like NetBSD.
748.Sp
749You still can embed kqueue into a normal poll or select backend and use it
750only for sockets (after having made sure that sockets work with kqueue on
751the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
391.Sp 752.Sp
392It scales in the same way as the epoll backend, but the interface to the 753It scales in the same way as the epoll backend, but the interface to the
393kernel is more efficient (which says nothing about its actual speed, of 754kernel is more efficient (which says nothing about its actual speed, of
394course). While starting and stopping an I/O watcher does not cause an 755course). While stopping, setting and starting an I/O watcher does never
395extra syscall as with epoll, it still adds up to four event changes per 756cause an extra system call as with \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to
396incident, so its best to avoid that. 757two event changes per incident. Support for \f(CW\*(C`fork ()\*(C'\fR is very bad (you
758might have to leak fd's on fork, but it's more sane than epoll) and it
759drops fds silently in similarly hard-to-detect cases.
760.Sp
761This backend usually performs well under most conditions.
762.Sp
763While nominally embeddable in other event loops, this doesn't work
764everywhere, so you might need to test for this. And since it is broken
765almost everywhere, you should only use it when you have a lot of sockets
766(for which it usually works), by embedding it into another event loop
767(e.g. \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR (but \f(CW\*(C`poll\*(C'\fR is of course
768also broken on \s-1OS X\s0)) and, did I mention it, using it only for sockets.
769.Sp
770This backend maps \f(CW\*(C`EV_READ\*(C'\fR into an \f(CW\*(C`EVFILT_READ\*(C'\fR kevent with
771\&\f(CW\*(C`NOTE_EOF\*(C'\fR, and \f(CW\*(C`EV_WRITE\*(C'\fR into an \f(CW\*(C`EVFILT_WRITE\*(C'\fR kevent with
772\&\f(CW\*(C`NOTE_EOF\*(C'\fR.
397.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4 773.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
398.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4 774.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
399.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)" 775.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
400This is not implemented yet (and might never be). 776This is not implemented yet (and might never be, unless you send me an
777implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets
778and is not embeddable, which would limit the usefulness of this backend
779immensely.
401.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4 780.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
402.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4 781.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
403.IX Item "EVBACKEND_PORT (value 32, Solaris 10)" 782.IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
404This uses the Solaris 10 port mechanism. As with everything on Solaris, 783This uses the Solaris 10 event port mechanism. As with everything on Solaris,
405it's really slow, but it still scales very well (O(active_fds)). 784it's really slow, but it still scales very well (O(active_fds)).
406.Sp 785.Sp
407Please note that solaris ports can result in a lot of spurious 786While this backend scales well, it requires one system call per active
408notifications, so you need to use non-blocking I/O or other means to avoid 787file descriptor per loop iteration. For small and medium numbers of file
409blocking when no data (or space) is available. 788descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend
789might perform better.
790.Sp
791On the positive side, this backend actually performed fully to
792specification in all tests and is fully embeddable, which is a rare feat
793among the OS-specific backends (I vastly prefer correctness over speed
794hacks).
795.Sp
796On the negative side, the interface is \fIbizarre\fR \- so bizarre that
797even sun itself gets it wrong in their code examples: The event polling
798function sometimes returns events to the caller even though an error
799occurred, but with no indication whether it has done so or not (yes, it's
800even documented that way) \- deadly for edge-triggered interfaces where you
801absolutely have to know whether an event occurred or not because you have
802to re-arm the watcher.
803.Sp
804Fortunately libev seems to be able to work around these idiocies.
805.Sp
806This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
807\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
410.ie n .IP """EVBACKEND_ALL""" 4 808.ie n .IP """EVBACKEND_ALL""" 4
411.el .IP "\f(CWEVBACKEND_ALL\fR" 4 809.el .IP "\f(CWEVBACKEND_ALL\fR" 4
412.IX Item "EVBACKEND_ALL" 810.IX Item "EVBACKEND_ALL"
413Try all backends (even potentially broken ones that wouldn't be tried 811Try all backends (even potentially broken ones that wouldn't be tried
414with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as 812with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as
415\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR. 813\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR.
814.Sp
815It is definitely not recommended to use this flag, use whatever
816\&\f(CW\*(C`ev_recommended_backends ()\*(C'\fR returns, or simply do not specify a backend
817at all.
818.ie n .IP """EVBACKEND_MASK""" 4
819.el .IP "\f(CWEVBACKEND_MASK\fR" 4
820.IX Item "EVBACKEND_MASK"
821Not a backend at all, but a mask to select all backend bits from a
822\&\f(CW\*(C`flags\*(C'\fR value, in case you want to mask out any backends from a flags
823value (e.g. when modifying the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR environment variable).
416.RE 824.RE
417.RS 4 825.RS 4
418.Sp 826.Sp
419If one or more of these are ored into the flags value, then only these 827If one or more of the backend flags are or'ed into the flags value,
420backends will be tried (in the reverse order as given here). If none are 828then only these backends will be tried (in the reverse order as listed
421specified, most compiled-in backend will be tried, usually in reverse 829here). If none are specified, all backends in \f(CW\*(C`ev_recommended_backends
422order of their flag values :) 830()\*(C'\fR will be tried.
423.Sp 831.Sp
424The most typical usage is like this: 832Example: Try to create a event loop that uses epoll and nothing else.
425.Sp 833.Sp
426.Vb 2 834.Vb 3
427\& if (!ev_default_loop (0)) 835\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
428\& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?"); 836\& if (!epoller)
837\& fatal ("no epoll found here, maybe it hides under your chair");
429.Ve 838.Ve
430.Sp 839.Sp
431Restrict libev to the select and poll backends, and do not allow 840Example: Use whatever libev has to offer, but make sure that kqueue is
432environment settings to be taken into account: 841used if available.
433.Sp 842.Sp
434.Vb 1 843.Vb 1
435\& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV); 844\& struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
436.Ve 845.Ve
437.Sp 846.Sp
438Use whatever libev has to offer, but make sure that kqueue is used if 847Example: Similarly, on linux, you mgiht want to take advantage of the
439available (warning, breaks stuff, best use only with your own private 848linux aio backend if possible, but fall back to something else if that
440event loop and only if you know the \s-1OS\s0 supports your types of fds): 849isn't available.
441.Sp 850.Sp
442.Vb 1 851.Vb 1
443\& ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE); 852\& struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_LINUXAIO);
444.Ve 853.Ve
445.RE 854.RE
446.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
447.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
448Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is
449always distinct from the default loop. Unlike the default loop, it cannot
450handle signal and child watchers, and attempts to do so will be greeted by
451undefined behaviour (or a failed assertion if assertions are enabled).
452.Sp
453Example: try to create a event loop that uses epoll and nothing else.
454.Sp
455.Vb 3
456\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
457\& if (!epoller)
458\& fatal ("no epoll found here, maybe it hides under your chair");
459.Ve
460.IP "ev_default_destroy ()" 4 855.IP "ev_loop_destroy (loop)" 4
461.IX Item "ev_default_destroy ()" 856.IX Item "ev_loop_destroy (loop)"
462Destroys the default loop again (frees all memory and kernel state 857Destroys an event loop object (frees all memory and kernel state
463etc.). None of the active event watchers will be stopped in the normal 858etc.). None of the active event watchers will be stopped in the normal
464sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your 859sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your
465responsibility to either stop all watchers cleanly yoursef \fIbefore\fR 860responsibility to either stop all watchers cleanly yourself \fIbefore\fR
466calling this function, or cope with the fact afterwards (which is usually 861calling this function, or cope with the fact afterwards (which is usually
467the easiest thing, youc na just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them 862the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them
468for example). 863for example).
469.IP "ev_loop_destroy (loop)" 4
470.IX Item "ev_loop_destroy (loop)"
471Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an
472earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR.
473.IP "ev_default_fork ()" 4
474.IX Item "ev_default_fork ()"
475This function reinitialises the kernel state for backends that have
476one. Despite the name, you can call it anytime, but it makes most sense
477after forking, in either the parent or child process (or both, but that
478again makes little sense).
479.Sp 864.Sp
480You \fImust\fR call this function in the child process after forking if and 865Note that certain global state, such as signal state (and installed signal
481only if you want to use the event library in both processes. If you just 866handlers), will not be freed by this function, and related watchers (such
482fork+exec, you don't have to call it. 867as signal and child watchers) would need to be stopped manually.
483.Sp 868.Sp
484The function itself is quite fast and it's usually not a problem to call 869This function is normally used on loop objects allocated by
485it just in case after a fork. To make this easy, the function will fit in 870\&\f(CW\*(C`ev_loop_new\*(C'\fR, but it can also be used on the default loop returned by
486quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR: 871\&\f(CW\*(C`ev_default_loop\*(C'\fR, in which case it is not thread-safe.
487.Sp 872.Sp
488.Vb 1 873Note that it is not advisable to call this function on the default loop
489\& pthread_atfork (0, 0, ev_default_fork); 874except in the rare occasion where you really need to free its resources.
490.Ve 875If you need dynamically allocated loops it is better to use \f(CW\*(C`ev_loop_new\*(C'\fR
491.Sp 876and \f(CW\*(C`ev_loop_destroy\*(C'\fR.
492At the moment, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and \f(CW\*(C`EVBACKEND_POLL\*(C'\fR are safe to use
493without calling this function, so if you force one of those backends you
494do not need to care.
495.IP "ev_loop_fork (loop)" 4 877.IP "ev_loop_fork (loop)" 4
496.IX Item "ev_loop_fork (loop)" 878.IX Item "ev_loop_fork (loop)"
497Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by 879This function sets a flag that causes subsequent \f(CW\*(C`ev_run\*(C'\fR iterations
498\&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop 880to reinitialise the kernel state for backends that have one. Despite
499after fork, and how you do this is entirely your own problem. 881the name, you can call it anytime you are allowed to start or stop
882watchers (except inside an \f(CW\*(C`ev_prepare\*(C'\fR callback), but it makes most
883sense after forking, in the child process. You \fImust\fR call it (or use
884\&\f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR) in the child before resuming or calling \f(CW\*(C`ev_run\*(C'\fR.
885.Sp
886In addition, if you want to reuse a loop (via this function or
887\&\f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR), you \fIalso\fR have to ignore \f(CW\*(C`SIGPIPE\*(C'\fR.
888.Sp
889Again, you \fIhave\fR to call it on \fIany\fR loop that you want to re-use after
890a fork, \fIeven if you do not plan to use the loop in the parent\fR. This is
891because some kernel interfaces *cough* \fIkqueue\fR *cough* do funny things
892during fork.
893.Sp
894On the other hand, you only need to call this function in the child
895process if and only if you want to use the event loop in the child. If
896you just fork+exec or create a new loop in the child, you don't have to
897call it at all (in fact, \f(CW\*(C`epoll\*(C'\fR is so badly broken that it makes a
898difference, but libev will usually detect this case on its own and do a
899costly reset of the backend).
900.Sp
901The function itself is quite fast and it's usually not a problem to call
902it just in case after a fork.
903.Sp
904Example: Automate calling \f(CW\*(C`ev_loop_fork\*(C'\fR on the default loop when
905using pthreads.
906.Sp
907.Vb 5
908\& static void
909\& post_fork_child (void)
910\& {
911\& ev_loop_fork (EV_DEFAULT);
912\& }
913\&
914\& ...
915\& pthread_atfork (0, 0, post_fork_child);
916.Ve
917.IP "int ev_is_default_loop (loop)" 4
918.IX Item "int ev_is_default_loop (loop)"
919Returns true when the given loop is, in fact, the default loop, and false
920otherwise.
921.IP "unsigned int ev_iteration (loop)" 4
922.IX Item "unsigned int ev_iteration (loop)"
923Returns the current iteration count for the event loop, which is identical
924to the number of times libev did poll for new events. It starts at \f(CW0\fR
925and happily wraps around with enough iterations.
926.Sp
927This value can sometimes be useful as a generation counter of sorts (it
928\&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with
929\&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls \- and is incremented between the
930prepare and check phases.
931.IP "unsigned int ev_depth (loop)" 4
932.IX Item "unsigned int ev_depth (loop)"
933Returns the number of times \f(CW\*(C`ev_run\*(C'\fR was entered minus the number of
934times \f(CW\*(C`ev_run\*(C'\fR was exited normally, in other words, the recursion depth.
935.Sp
936Outside \f(CW\*(C`ev_run\*(C'\fR, this number is zero. In a callback, this number is
937\&\f(CW1\fR, unless \f(CW\*(C`ev_run\*(C'\fR was invoked recursively (or from another thread),
938in which case it is higher.
939.Sp
940Leaving \f(CW\*(C`ev_run\*(C'\fR abnormally (setjmp/longjmp, cancelling the thread,
941throwing an exception etc.), doesn't count as \*(L"exit\*(R" \- consider this
942as a hint to avoid such ungentleman-like behaviour unless it's really
943convenient, in which case it is fully supported.
500.IP "unsigned int ev_backend (loop)" 4 944.IP "unsigned int ev_backend (loop)" 4
501.IX Item "unsigned int ev_backend (loop)" 945.IX Item "unsigned int ev_backend (loop)"
502Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in 946Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
503use. 947use.
504.IP "ev_tstamp ev_now (loop)" 4 948.IP "ev_tstamp ev_now (loop)" 4
505.IX Item "ev_tstamp ev_now (loop)" 949.IX Item "ev_tstamp ev_now (loop)"
506Returns the current \*(L"event loop time\*(R", which is the time the event loop 950Returns the current \*(L"event loop time\*(R", which is the time the event loop
507received events and started processing them. This timestamp does not 951received events and started processing them. This timestamp does not
508change as long as callbacks are being processed, and this is also the base 952change as long as callbacks are being processed, and this is also the base
509time used for relative timers. You can treat it as the timestamp of the 953time used for relative timers. You can treat it as the timestamp of the
510event occuring (or more correctly, libev finding out about it). 954event occurring (or more correctly, libev finding out about it).
955.IP "ev_now_update (loop)" 4
956.IX Item "ev_now_update (loop)"
957Establishes the current time by querying the kernel, updating the time
958returned by \f(CW\*(C`ev_now ()\*(C'\fR in the progress. This is a costly operation and
959is usually done automatically within \f(CW\*(C`ev_run ()\*(C'\fR.
960.Sp
961This function is rarely useful, but when some event callback runs for a
962very long time without entering the event loop, updating libev's idea of
963the current time is a good idea.
964.Sp
965See also \*(L"The special problem of time updates\*(R" in the \f(CW\*(C`ev_timer\*(C'\fR section.
966.IP "ev_suspend (loop)" 4
967.IX Item "ev_suspend (loop)"
968.PD 0
969.IP "ev_resume (loop)" 4
970.IX Item "ev_resume (loop)"
971.PD
972These two functions suspend and resume an event loop, for use when the
973loop is not used for a while and timeouts should not be processed.
974.Sp
975A typical use case would be an interactive program such as a game: When
976the user presses \f(CW\*(C`^Z\*(C'\fR to suspend the game and resumes it an hour later it
977would be best to handle timeouts as if no time had actually passed while
978the program was suspended. This can be achieved by calling \f(CW\*(C`ev_suspend\*(C'\fR
979in your \f(CW\*(C`SIGTSTP\*(C'\fR handler, sending yourself a \f(CW\*(C`SIGSTOP\*(C'\fR and calling
980\&\f(CW\*(C`ev_resume\*(C'\fR directly afterwards to resume timer processing.
981.Sp
982Effectively, all \f(CW\*(C`ev_timer\*(C'\fR watchers will be delayed by the time spend
983between \f(CW\*(C`ev_suspend\*(C'\fR and \f(CW\*(C`ev_resume\*(C'\fR, and all \f(CW\*(C`ev_periodic\*(C'\fR watchers
984will be rescheduled (that is, they will lose any events that would have
985occurred while suspended).
986.Sp
987After calling \f(CW\*(C`ev_suspend\*(C'\fR you \fBmust not\fR call \fIany\fR function on the
988given loop other than \f(CW\*(C`ev_resume\*(C'\fR, and you \fBmust not\fR call \f(CW\*(C`ev_resume\*(C'\fR
989without a previous call to \f(CW\*(C`ev_suspend\*(C'\fR.
990.Sp
991Calling \f(CW\*(C`ev_suspend\*(C'\fR/\f(CW\*(C`ev_resume\*(C'\fR has the side effect of updating the
992event loop time (see \f(CW\*(C`ev_now_update\*(C'\fR).
511.IP "ev_loop (loop, int flags)" 4 993.IP "bool ev_run (loop, int flags)" 4
512.IX Item "ev_loop (loop, int flags)" 994.IX Item "bool ev_run (loop, int flags)"
513Finally, this is it, the event handler. This function usually is called 995Finally, this is it, the event handler. This function usually is called
514after you initialised all your watchers and you want to start handling 996after you have initialised all your watchers and you want to start
515events. 997handling events. It will ask the operating system for any new events, call
998the watcher callbacks, and then repeat the whole process indefinitely: This
999is why event loops are called \fIloops\fR.
516.Sp 1000.Sp
517If the flags argument is specified as \f(CW0\fR, it will not return until 1001If the flags argument is specified as \f(CW0\fR, it will keep handling events
518either no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called. 1002until either no event watchers are active anymore or \f(CW\*(C`ev_break\*(C'\fR was
1003called.
519.Sp 1004.Sp
1005The return value is false if there are no more active watchers (which
1006usually means \*(L"all jobs done\*(R" or \*(L"deadlock\*(R"), and true in all other cases
1007(which usually means " you should call \f(CW\*(C`ev_run\*(C'\fR again").
1008.Sp
520Please note that an explicit \f(CW\*(C`ev_unloop\*(C'\fR is usually better than 1009Please note that an explicit \f(CW\*(C`ev_break\*(C'\fR is usually better than
521relying on all watchers to be stopped when deciding when a program has 1010relying on all watchers to be stopped when deciding when a program has
522finished (especially in interactive programs), but having a program that 1011finished (especially in interactive programs), but having a program
523automatically loops as long as it has to and no longer by virtue of 1012that automatically loops as long as it has to and no longer by virtue
524relying on its watchers stopping correctly is a thing of beauty. 1013of relying on its watchers stopping correctly, that is truly a thing of
1014beauty.
525.Sp 1015.Sp
1016This function is \fImostly\fR exception-safe \- you can break out of a
1017\&\f(CW\*(C`ev_run\*(C'\fR call by calling \f(CW\*(C`longjmp\*(C'\fR in a callback, throwing a \*(C+
1018exception and so on. This does not decrement the \f(CW\*(C`ev_depth\*(C'\fR value, nor
1019will it clear any outstanding \f(CW\*(C`EVBREAK_ONE\*(C'\fR breaks.
1020.Sp
526A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle 1021A flags value of \f(CW\*(C`EVRUN_NOWAIT\*(C'\fR will look for new events, will handle
527those events and any outstanding ones, but will not block your process in 1022those events and any already outstanding ones, but will not wait and
528case there are no events and will return after one iteration of the loop. 1023block your process in case there are no events and will return after one
1024iteration of the loop. This is sometimes useful to poll and handle new
1025events while doing lengthy calculations, to keep the program responsive.
529.Sp 1026.Sp
530A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if 1027A flags value of \f(CW\*(C`EVRUN_ONCE\*(C'\fR will look for new events (waiting if
531neccessary) and will handle those and any outstanding ones. It will block 1028necessary) and will handle those and any already outstanding ones. It
532your process until at least one new event arrives, and will return after 1029will block your process until at least one new event arrives (which could
533one iteration of the loop. This is useful if you are waiting for some 1030be an event internal to libev itself, so there is no guarantee that a
534external event in conjunction with something not expressible using other 1031user-registered callback will be called), and will return after one
1032iteration of the loop.
1033.Sp
1034This is useful if you are waiting for some external event in conjunction
1035with something not expressible using other libev watchers (i.e. "roll your
535libev watchers. However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is 1036own \f(CW\*(C`ev_run\*(C'\fR"). However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is
536usually a better approach for this kind of thing. 1037usually a better approach for this kind of thing.
537.Sp 1038.Sp
538Here are the gory details of what \f(CW\*(C`ev_loop\*(C'\fR does: 1039Here are the gory details of what \f(CW\*(C`ev_run\*(C'\fR does (this is for your
1040understanding, not a guarantee that things will work exactly like this in
1041future versions):
539.Sp 1042.Sp
540.Vb 18 1043.Vb 10
541\& * If there are no active watchers (reference count is zero), return. 1044\& \- Increment loop depth.
542\& - Queue prepare watchers and then call all outstanding watchers. 1045\& \- Reset the ev_break status.
1046\& \- Before the first iteration, call any pending watchers.
1047\& LOOP:
1048\& \- If EVFLAG_FORKCHECK was used, check for a fork.
1049\& \- If a fork was detected (by any means), queue and call all fork watchers.
1050\& \- Queue and call all prepare watchers.
1051\& \- If ev_break was called, goto FINISH.
543\& - If we have been forked, recreate the kernel state. 1052\& \- If we have been forked, detach and recreate the kernel state
1053\& as to not disturb the other process.
544\& - Update the kernel state with all outstanding changes. 1054\& \- Update the kernel state with all outstanding changes.
545\& - Update the "event loop time". 1055\& \- Update the "event loop time" (ev_now ()).
546\& - Calculate for how long to block. 1056\& \- Calculate for how long to sleep or block, if at all
1057\& (active idle watchers, EVRUN_NOWAIT or not having
1058\& any active watchers at all will result in not sleeping).
1059\& \- Sleep if the I/O and timer collect interval say so.
1060\& \- Increment loop iteration counter.
547\& - Block the process, waiting for any events. 1061\& \- Block the process, waiting for any events.
548\& - Queue all outstanding I/O (fd) events. 1062\& \- Queue all outstanding I/O (fd) events.
549\& - Update the "event loop time" and do time jump handling. 1063\& \- Update the "event loop time" (ev_now ()), and do time jump adjustments.
550\& - Queue all outstanding timers. 1064\& \- Queue all expired timers.
551\& - Queue all outstanding periodics. 1065\& \- Queue all expired periodics.
552\& - If no events are pending now, queue all idle watchers. 1066\& \- Queue all idle watchers with priority higher than that of pending events.
553\& - Queue all check watchers. 1067\& \- Queue all check watchers.
554\& - Call all queued watchers in reverse order (i.e. check watchers first). 1068\& \- Call all queued watchers in reverse order (i.e. check watchers first).
555\& Signals and child watchers are implemented as I/O watchers, and will 1069\& Signals and child watchers are implemented as I/O watchers, and will
556\& be handled here by queueing them when their watcher gets executed. 1070\& be handled here by queueing them when their watcher gets executed.
557\& - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK 1071\& \- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
558\& were used, return, otherwise continue with step *. 1072\& were used, or there are no active watchers, goto FINISH, otherwise
1073\& continue with step LOOP.
1074\& FINISH:
1075\& \- Reset the ev_break status iff it was EVBREAK_ONE.
1076\& \- Decrement the loop depth.
1077\& \- Return.
559.Ve 1078.Ve
560.Sp 1079.Sp
561Example: queue some jobs and then loop until no events are outsanding 1080Example: Queue some jobs and then loop until no events are outstanding
562anymore. 1081anymore.
563.Sp 1082.Sp
564.Vb 4 1083.Vb 4
565\& ... queue jobs here, make sure they register event watchers as long 1084\& ... queue jobs here, make sure they register event watchers as long
566\& ... as they still have work to do (even an idle watcher will do..) 1085\& ... as they still have work to do (even an idle watcher will do..)
567\& ev_loop (my_loop, 0); 1086\& ev_run (my_loop, 0);
568\& ... jobs done. yeah! 1087\& ... jobs done or somebody called break. yeah!
569.Ve 1088.Ve
570.IP "ev_unloop (loop, how)" 4 1089.IP "ev_break (loop, how)" 4
571.IX Item "ev_unloop (loop, how)" 1090.IX Item "ev_break (loop, how)"
572Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it 1091Can be used to make a call to \f(CW\*(C`ev_run\*(C'\fR return early (but only after it
573has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either 1092has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
574\&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or 1093\&\f(CW\*(C`EVBREAK_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_run\*(C'\fR call return, or
575\&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return. 1094\&\f(CW\*(C`EVBREAK_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_run\*(C'\fR calls return.
1095.Sp
1096This \*(L"break state\*(R" will be cleared on the next call to \f(CW\*(C`ev_run\*(C'\fR.
1097.Sp
1098It is safe to call \f(CW\*(C`ev_break\*(C'\fR from outside any \f(CW\*(C`ev_run\*(C'\fR calls, too, in
1099which case it will have no effect.
576.IP "ev_ref (loop)" 4 1100.IP "ev_ref (loop)" 4
577.IX Item "ev_ref (loop)" 1101.IX Item "ev_ref (loop)"
578.PD 0 1102.PD 0
579.IP "ev_unref (loop)" 4 1103.IP "ev_unref (loop)" 4
580.IX Item "ev_unref (loop)" 1104.IX Item "ev_unref (loop)"
581.PD 1105.PD
582Ref/unref can be used to add or remove a reference count on the event 1106Ref/unref can be used to add or remove a reference count on the event
583loop: Every watcher keeps one reference, and as long as the reference 1107loop: Every watcher keeps one reference, and as long as the reference
584count is nonzero, \f(CW\*(C`ev_loop\*(C'\fR will not return on its own. If you have 1108count is nonzero, \f(CW\*(C`ev_run\*(C'\fR will not return on its own.
585a watcher you never unregister that should not keep \f(CW\*(C`ev_loop\*(C'\fR from 1109.Sp
586returning, \fIev_unref()\fR after starting, and \fIev_ref()\fR before stopping it. For 1110This is useful when you have a watcher that you never intend to
1111unregister, but that nevertheless should not keep \f(CW\*(C`ev_run\*(C'\fR from
1112returning. In such a case, call \f(CW\*(C`ev_unref\*(C'\fR after starting, and \f(CW\*(C`ev_ref\*(C'\fR
1113before stopping it.
1114.Sp
587example, libev itself uses this for its internal signal pipe: It is not 1115As an example, libev itself uses this for its internal signal pipe: It
588visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from exiting if 1116is not visible to the libev user and should not keep \f(CW\*(C`ev_run\*(C'\fR from
589no event watchers registered by it are active. It is also an excellent 1117exiting if no event watchers registered by it are active. It is also an
590way to do this for generic recurring timers or from within third-party 1118excellent way to do this for generic recurring timers or from within
591libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR. 1119third-party libraries. Just remember to \fIunref after start\fR and \fIref
1120before stop\fR (but only if the watcher wasn't active before, or was active
1121before, respectively. Note also that libev might stop watchers itself
1122(e.g. non-repeating timers) in which case you have to \f(CW\*(C`ev_ref\*(C'\fR
1123in the callback).
592.Sp 1124.Sp
593Example: create a signal watcher, but keep it from keeping \f(CW\*(C`ev_loop\*(C'\fR 1125Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_run\*(C'\fR
594running when nothing else is active. 1126running when nothing else is active.
595.Sp 1127.Sp
596.Vb 4 1128.Vb 4
597\& struct dv_signal exitsig; 1129\& ev_signal exitsig;
598\& ev_signal_init (&exitsig, sig_cb, SIGINT); 1130\& ev_signal_init (&exitsig, sig_cb, SIGINT);
599\& ev_signal_start (myloop, &exitsig); 1131\& ev_signal_start (loop, &exitsig);
600\& evf_unref (myloop); 1132\& ev_unref (loop);
601.Ve 1133.Ve
602.Sp 1134.Sp
603Example: for some weird reason, unregister the above signal handler again. 1135Example: For some weird reason, unregister the above signal handler again.
604.Sp 1136.Sp
605.Vb 2 1137.Vb 2
606\& ev_ref (myloop); 1138\& ev_ref (loop);
607\& ev_signal_stop (myloop, &exitsig); 1139\& ev_signal_stop (loop, &exitsig);
608.Ve 1140.Ve
1141.IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4
1142.IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"
1143.PD 0
1144.IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4
1145.IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"
1146.PD
1147These advanced functions influence the time that libev will spend waiting
1148for events. Both time intervals are by default \f(CW0\fR, meaning that libev
1149will try to invoke timer/periodic callbacks and I/O callbacks with minimum
1150latency.
1151.Sp
1152Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR)
1153allows libev to delay invocation of I/O and timer/periodic callbacks
1154to increase efficiency of loop iterations (or to increase power-saving
1155opportunities).
1156.Sp
1157The idea is that sometimes your program runs just fast enough to handle
1158one (or very few) event(s) per loop iteration. While this makes the
1159program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new
1160events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high
1161overhead for the actual polling but can deliver many events at once.
1162.Sp
1163By setting a higher \fIio collect interval\fR you allow libev to spend more
1164time collecting I/O events, so you can handle more events per iteration,
1165at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and
1166\&\f(CW\*(C`ev_timer\*(C'\fR) will not be affected. Setting this to a non-null value will
1167introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations. The
1168sleep time ensures that libev will not poll for I/O events more often then
1169once per this interval, on average (as long as the host time resolution is
1170good enough).
1171.Sp
1172Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
1173to spend more time collecting timeouts, at the expense of increased
1174latency/jitter/inexactness (the watcher callback will be called
1175later). \f(CW\*(C`ev_io\*(C'\fR watchers will not be affected. Setting this to a non-null
1176value will not introduce any overhead in libev.
1177.Sp
1178Many (busy) programs can usually benefit by setting the I/O collect
1179interval to a value near \f(CW0.1\fR or so, which is often enough for
1180interactive servers (of course not for games), likewise for timeouts. It
1181usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR,
1182as this approaches the timing granularity of most systems. Note that if
1183you do transactions with the outside world and you can't increase the
1184parallelity, then this setting will limit your transaction rate (if you
1185need to poll once per transaction and the I/O collect interval is 0.01,
1186then you can't do more than 100 transactions per second).
1187.Sp
1188Setting the \fItimeout collect interval\fR can improve the opportunity for
1189saving power, as the program will \*(L"bundle\*(R" timer callback invocations that
1190are \*(L"near\*(R" in time together, by delaying some, thus reducing the number of
1191times the process sleeps and wakes up again. Another useful technique to
1192reduce iterations/wake\-ups is to use \f(CW\*(C`ev_periodic\*(C'\fR watchers and make sure
1193they fire on, say, one-second boundaries only.
1194.Sp
1195Example: we only need 0.1s timeout granularity, and we wish not to poll
1196more often than 100 times per second:
1197.Sp
1198.Vb 2
1199\& ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
1200\& ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
1201.Ve
1202.IP "ev_invoke_pending (loop)" 4
1203.IX Item "ev_invoke_pending (loop)"
1204This call will simply invoke all pending watchers while resetting their
1205pending state. Normally, \f(CW\*(C`ev_run\*(C'\fR does this automatically when required,
1206but when overriding the invoke callback this call comes handy. This
1207function can be invoked from a watcher \- this can be useful for example
1208when you want to do some lengthy calculation and want to pass further
1209event handling to another thread (you still have to make sure only one
1210thread executes within \f(CW\*(C`ev_invoke_pending\*(C'\fR or \f(CW\*(C`ev_run\*(C'\fR of course).
1211.IP "int ev_pending_count (loop)" 4
1212.IX Item "int ev_pending_count (loop)"
1213Returns the number of pending watchers \- zero indicates that no watchers
1214are pending.
1215.IP "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(\s-1EV_P\s0))" 4
1216.IX Item "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))"
1217This overrides the invoke pending functionality of the loop: Instead of
1218invoking all pending watchers when there are any, \f(CW\*(C`ev_run\*(C'\fR will call
1219this callback instead. This is useful, for example, when you want to
1220invoke the actual watchers inside another context (another thread etc.).
1221.Sp
1222If you want to reset the callback, use \f(CW\*(C`ev_invoke_pending\*(C'\fR as new
1223callback.
1224.IP "ev_set_loop_release_cb (loop, void (*release)(\s-1EV_P\s0) throw (), void (*acquire)(\s-1EV_P\s0) throw ())" 4
1225.IX Item "ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())"
1226Sometimes you want to share the same loop between multiple threads. This
1227can be done relatively simply by putting mutex_lock/unlock calls around
1228each call to a libev function.
1229.Sp
1230However, \f(CW\*(C`ev_run\*(C'\fR can run an indefinite time, so it is not feasible
1231to wait for it to return. One way around this is to wake up the event
1232loop via \f(CW\*(C`ev_break\*(C'\fR and \f(CW\*(C`ev_async_send\*(C'\fR, another way is to set these
1233\&\fIrelease\fR and \fIacquire\fR callbacks on the loop.
1234.Sp
1235When set, then \f(CW\*(C`release\*(C'\fR will be called just before the thread is
1236suspended waiting for new events, and \f(CW\*(C`acquire\*(C'\fR is called just
1237afterwards.
1238.Sp
1239Ideally, \f(CW\*(C`release\*(C'\fR will just call your mutex_unlock function, and
1240\&\f(CW\*(C`acquire\*(C'\fR will just call the mutex_lock function again.
1241.Sp
1242While event loop modifications are allowed between invocations of
1243\&\f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR (that's their only purpose after all), no
1244modifications done will affect the event loop, i.e. adding watchers will
1245have no effect on the set of file descriptors being watched, or the time
1246waited. Use an \f(CW\*(C`ev_async\*(C'\fR watcher to wake up \f(CW\*(C`ev_run\*(C'\fR when you want it
1247to take note of any changes you made.
1248.Sp
1249In theory, threads executing \f(CW\*(C`ev_run\*(C'\fR will be async-cancel safe between
1250invocations of \f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR.
1251.Sp
1252See also the locking example in the \f(CW\*(C`THREADS\*(C'\fR section later in this
1253document.
1254.IP "ev_set_userdata (loop, void *data)" 4
1255.IX Item "ev_set_userdata (loop, void *data)"
1256.PD 0
1257.IP "void *ev_userdata (loop)" 4
1258.IX Item "void *ev_userdata (loop)"
1259.PD
1260Set and retrieve a single \f(CW\*(C`void *\*(C'\fR associated with a loop. When
1261\&\f(CW\*(C`ev_set_userdata\*(C'\fR has never been called, then \f(CW\*(C`ev_userdata\*(C'\fR returns
1262\&\f(CW0\fR.
1263.Sp
1264These two functions can be used to associate arbitrary data with a loop,
1265and are intended solely for the \f(CW\*(C`invoke_pending_cb\*(C'\fR, \f(CW\*(C`release\*(C'\fR and
1266\&\f(CW\*(C`acquire\*(C'\fR callbacks described above, but of course can be (ab\-)used for
1267any other purpose as well.
1268.IP "ev_verify (loop)" 4
1269.IX Item "ev_verify (loop)"
1270This function only does something when \f(CW\*(C`EV_VERIFY\*(C'\fR support has been
1271compiled in, which is the default for non-minimal builds. It tries to go
1272through all internal structures and checks them for validity. If anything
1273is found to be inconsistent, it will print an error message to standard
1274error and call \f(CW\*(C`abort ()\*(C'\fR.
1275.Sp
1276This can be used to catch bugs inside libev itself: under normal
1277circumstances, this function will never abort as of course libev keeps its
1278data structures consistent.
609.SH "ANATOMY OF A WATCHER" 1279.SH "ANATOMY OF A WATCHER"
610.IX Header "ANATOMY OF A WATCHER" 1280.IX Header "ANATOMY OF A WATCHER"
1281In the following description, uppercase \f(CW\*(C`TYPE\*(C'\fR in names stands for the
1282watcher type, e.g. \f(CW\*(C`ev_TYPE_start\*(C'\fR can mean \f(CW\*(C`ev_timer_start\*(C'\fR for timer
1283watchers and \f(CW\*(C`ev_io_start\*(C'\fR for I/O watchers.
1284.PP
611A watcher is a structure that you create and register to record your 1285A watcher is an opaque structure that you allocate and register to record
612interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to 1286your interest in some event. To make a concrete example, imagine you want
613become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that: 1287to wait for \s-1STDIN\s0 to become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher
1288for that:
614.PP 1289.PP
615.Vb 5 1290.Vb 5
616\& static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) 1291\& static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
617\& { 1292\& {
618\& ev_io_stop (w); 1293\& ev_io_stop (w);
619\& ev_unloop (loop, EVUNLOOP_ALL); 1294\& ev_break (loop, EVBREAK_ALL);
620\& } 1295\& }
621.Ve 1296\&
622.PP
623.Vb 6
624\& struct ev_loop *loop = ev_default_loop (0); 1297\& struct ev_loop *loop = ev_default_loop (0);
1298\&
625\& struct ev_io stdin_watcher; 1299\& ev_io stdin_watcher;
1300\&
626\& ev_init (&stdin_watcher, my_cb); 1301\& ev_init (&stdin_watcher, my_cb);
627\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); 1302\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
628\& ev_io_start (loop, &stdin_watcher); 1303\& ev_io_start (loop, &stdin_watcher);
1304\&
629\& ev_loop (loop, 0); 1305\& ev_run (loop, 0);
630.Ve 1306.Ve
631.PP 1307.PP
632As you can see, you are responsible for allocating the memory for your 1308As you can see, you are responsible for allocating the memory for your
633watcher structures (and it is usually a bad idea to do this on the stack, 1309watcher structures (and it is \fIusually\fR a bad idea to do this on the
634although this can sometimes be quite valid). 1310stack).
635.PP 1311.PP
1312Each watcher has an associated watcher structure (called \f(CW\*(C`struct ev_TYPE\*(C'\fR
1313or simply \f(CW\*(C`ev_TYPE\*(C'\fR, as typedefs are provided for all watcher structs).
1314.PP
636Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init 1315Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init (watcher
637(watcher *, callback)\*(C'\fR, which expects a callback to be provided. This 1316*, callback)\*(C'\fR, which expects a callback to be provided. This callback is
638callback gets invoked each time the event occurs (or, in the case of io 1317invoked each time the event occurs (or, in the case of I/O watchers, each
639watchers, each time the event loop detects that the file descriptor given 1318time the event loop detects that the file descriptor given is readable
640is readable and/or writable). 1319and/or writable).
641.PP 1320.PP
642Each watcher type has its own \f(CW\*(C`ev_<type>_set (watcher *, ...)\*(C'\fR macro 1321Each watcher type further has its own \f(CW\*(C`ev_TYPE_set (watcher *, ...)\*(C'\fR
643with arguments specific to this watcher type. There is also a macro 1322macro to configure it, with arguments specific to the watcher type. There
644to combine initialisation and setting in one call: \f(CW\*(C`ev_<type>_init 1323is also a macro to combine initialisation and setting in one call: \f(CW\*(C`ev_TYPE_init (watcher *, callback, ...)\*(C'\fR.
645(watcher *, callback, ...)\*(C'\fR.
646.PP 1324.PP
647To make the watcher actually watch out for events, you have to start it 1325To make the watcher actually watch out for events, you have to start it
648with a watcher-specific start function (\f(CW\*(C`ev_<type>_start (loop, watcher 1326with a watcher-specific start function (\f(CW\*(C`ev_TYPE_start (loop, watcher
649*)\*(C'\fR), and you can stop watching for events at any time by calling the 1327*)\*(C'\fR), and you can stop watching for events at any time by calling the
650corresponding stop function (\f(CW\*(C`ev_<type>_stop (loop, watcher *)\*(C'\fR. 1328corresponding stop function (\f(CW\*(C`ev_TYPE_stop (loop, watcher *)\*(C'\fR.
651.PP 1329.PP
652As long as your watcher is active (has been started but not stopped) you 1330As long as your watcher is active (has been started but not stopped) you
653must not touch the values stored in it. Most specifically you must never 1331must not touch the values stored in it. Most specifically you must never
654reinitialise it or call its \f(CW\*(C`set\*(C'\fR macro. 1332reinitialise it or call its \f(CW\*(C`ev_TYPE_set\*(C'\fR macro.
655.PP 1333.PP
656Each and every callback receives the event loop pointer as first, the 1334Each and every callback receives the event loop pointer as first, the
657registered watcher structure as second, and a bitset of received events as 1335registered watcher structure as second, and a bitset of received events as
658third argument. 1336third argument.
659.PP 1337.PP
… …
668.el .IP "\f(CWEV_WRITE\fR" 4 1346.el .IP "\f(CWEV_WRITE\fR" 4
669.IX Item "EV_WRITE" 1347.IX Item "EV_WRITE"
670.PD 1348.PD
671The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or 1349The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
672writable. 1350writable.
673.ie n .IP """EV_TIMEOUT""" 4 1351.ie n .IP """EV_TIMER""" 4
674.el .IP "\f(CWEV_TIMEOUT\fR" 4 1352.el .IP "\f(CWEV_TIMER\fR" 4
675.IX Item "EV_TIMEOUT" 1353.IX Item "EV_TIMER"
676The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out. 1354The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
677.ie n .IP """EV_PERIODIC""" 4 1355.ie n .IP """EV_PERIODIC""" 4
678.el .IP "\f(CWEV_PERIODIC\fR" 4 1356.el .IP "\f(CWEV_PERIODIC\fR" 4
679.IX Item "EV_PERIODIC" 1357.IX Item "EV_PERIODIC"
680The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out. 1358The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
… …
700.PD 0 1378.PD 0
701.ie n .IP """EV_CHECK""" 4 1379.ie n .IP """EV_CHECK""" 4
702.el .IP "\f(CWEV_CHECK\fR" 4 1380.el .IP "\f(CWEV_CHECK\fR" 4
703.IX Item "EV_CHECK" 1381.IX Item "EV_CHECK"
704.PD 1382.PD
705All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_loop\*(C'\fR starts 1383All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_run\*(C'\fR starts to
706to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after 1384gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are queued (not invoked)
707\&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any 1385just after \f(CW\*(C`ev_run\*(C'\fR has gathered them, but before it queues any callbacks
1386for any received events. That means \f(CW\*(C`ev_prepare\*(C'\fR watchers are the last
1387watchers invoked before the event loop sleeps or polls for new events, and
1388\&\f(CW\*(C`ev_check\*(C'\fR watchers will be invoked before any other watchers of the same
1389or lower priority within an event loop iteration.
1390.Sp
708received events. Callbacks of both watcher types can start and stop as 1391Callbacks of both watcher types can start and stop as many watchers as
709many watchers as they want, and all of them will be taken into account 1392they want, and all of them will be taken into account (for example, a
710(for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep 1393\&\f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep \f(CW\*(C`ev_run\*(C'\fR from
711\&\f(CW\*(C`ev_loop\*(C'\fR from blocking). 1394blocking).
712.ie n .IP """EV_EMBED""" 4 1395.ie n .IP """EV_EMBED""" 4
713.el .IP "\f(CWEV_EMBED\fR" 4 1396.el .IP "\f(CWEV_EMBED\fR" 4
714.IX Item "EV_EMBED" 1397.IX Item "EV_EMBED"
715The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention. 1398The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.
716.ie n .IP """EV_FORK""" 4 1399.ie n .IP """EV_FORK""" 4
717.el .IP "\f(CWEV_FORK\fR" 4 1400.el .IP "\f(CWEV_FORK\fR" 4
718.IX Item "EV_FORK" 1401.IX Item "EV_FORK"
719The event loop has been resumed in the child process after fork (see 1402The event loop has been resumed in the child process after fork (see
720\&\f(CW\*(C`ev_fork\*(C'\fR). 1403\&\f(CW\*(C`ev_fork\*(C'\fR).
1404.ie n .IP """EV_CLEANUP""" 4
1405.el .IP "\f(CWEV_CLEANUP\fR" 4
1406.IX Item "EV_CLEANUP"
1407The event loop is about to be destroyed (see \f(CW\*(C`ev_cleanup\*(C'\fR).
1408.ie n .IP """EV_ASYNC""" 4
1409.el .IP "\f(CWEV_ASYNC\fR" 4
1410.IX Item "EV_ASYNC"
1411The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR).
1412.ie n .IP """EV_CUSTOM""" 4
1413.el .IP "\f(CWEV_CUSTOM\fR" 4
1414.IX Item "EV_CUSTOM"
1415Not ever sent (or otherwise used) by libev itself, but can be freely used
1416by libev users to signal watchers (e.g. via \f(CW\*(C`ev_feed_event\*(C'\fR).
721.ie n .IP """EV_ERROR""" 4 1417.ie n .IP """EV_ERROR""" 4
722.el .IP "\f(CWEV_ERROR\fR" 4 1418.el .IP "\f(CWEV_ERROR\fR" 4
723.IX Item "EV_ERROR" 1419.IX Item "EV_ERROR"
724An unspecified error has occured, the watcher has been stopped. This might 1420An unspecified error has occurred, the watcher has been stopped. This might
725happen because the watcher could not be properly started because libev 1421happen because the watcher could not be properly started because libev
726ran out of memory, a file descriptor was found to be closed or any other 1422ran out of memory, a file descriptor was found to be closed or any other
1423problem. Libev considers these application bugs.
1424.Sp
727problem. You best act on it by reporting the problem and somehow coping 1425You best act on it by reporting the problem and somehow coping with the
728with the watcher being stopped. 1426watcher being stopped. Note that well-written programs should not receive
1427an error ever, so when your watcher receives it, this usually indicates a
1428bug in your program.
729.Sp 1429.Sp
730Libev will usually signal a few \*(L"dummy\*(R" events together with an error, 1430Libev will usually signal a few \*(L"dummy\*(R" events together with an error, for
731for example it might indicate that a fd is readable or writable, and if 1431example it might indicate that a fd is readable or writable, and if your
732your callbacks is well-written it can just attempt the operation and cope 1432callbacks is well-written it can just attempt the operation and cope with
733with the error from \fIread()\fR or \fIwrite()\fR. This will not work in multithreaded 1433the error from \fBread()\fR or \fBwrite()\fR. This will not work in multi-threaded
734programs, though, so beware. 1434programs, though, as the fd could already be closed and reused for another
1435thing, so beware.
735.Sh "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0" 1436.SS "\s-1GENERIC WATCHER FUNCTIONS\s0"
736.IX Subsection "GENERIC WATCHER FUNCTIONS" 1437.IX Subsection "GENERIC WATCHER FUNCTIONS"
737In the following description, \f(CW\*(C`TYPE\*(C'\fR stands for the watcher type,
738e.g. \f(CW\*(C`timer\*(C'\fR for \f(CW\*(C`ev_timer\*(C'\fR watchers and \f(CW\*(C`io\*(C'\fR for \f(CW\*(C`ev_io\*(C'\fR watchers.
739.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4 1438.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
740.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4 1439.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
741.IX Item "ev_init (ev_TYPE *watcher, callback)" 1440.IX Item "ev_init (ev_TYPE *watcher, callback)"
742This macro initialises the generic portion of a watcher. The contents 1441This macro initialises the generic portion of a watcher. The contents
743of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only 1442of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
… …
747which rolls both calls into one. 1446which rolls both calls into one.
748.Sp 1447.Sp
749You can reinitialise a watcher at any time as long as it has been stopped 1448You can reinitialise a watcher at any time as long as it has been stopped
750(or never started) and there are no pending events outstanding. 1449(or never started) and there are no pending events outstanding.
751.Sp 1450.Sp
752The callback is always of type \f(CW\*(C`void (*)(ev_loop *loop, ev_TYPE *watcher, 1451The callback is always of type \f(CW\*(C`void (*)(struct ev_loop *loop, ev_TYPE *watcher,
753int revents)\*(C'\fR. 1452int revents)\*(C'\fR.
1453.Sp
1454Example: Initialise an \f(CW\*(C`ev_io\*(C'\fR watcher in two steps.
1455.Sp
1456.Vb 3
1457\& ev_io w;
1458\& ev_init (&w, my_cb);
1459\& ev_io_set (&w, STDIN_FILENO, EV_READ);
1460.Ve
754.ie n .IP """ev_TYPE_set"" (ev_TYPE *, [args])" 4 1461.ie n .IP """ev_TYPE_set"" (ev_TYPE *watcher, [args])" 4
755.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *, [args])" 4 1462.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *watcher, [args])" 4
756.IX Item "ev_TYPE_set (ev_TYPE *, [args])" 1463.IX Item "ev_TYPE_set (ev_TYPE *watcher, [args])"
757This macro initialises the type-specific parts of a watcher. You need to 1464This macro initialises the type-specific parts of a watcher. You need to
758call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can 1465call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
759call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this 1466call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
760macro on a watcher that is active (it can be pending, however, which is a 1467macro on a watcher that is active (it can be pending, however, which is a
761difference to the \f(CW\*(C`ev_init\*(C'\fR macro). 1468difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
762.Sp 1469.Sp
763Although some watcher types do not have type-specific arguments 1470Although some watcher types do not have type-specific arguments
764(e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro. 1471(e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
1472.Sp
1473See \f(CW\*(C`ev_init\*(C'\fR, above, for an example.
765.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4 1474.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
766.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4 1475.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
767.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])" 1476.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
768This convinience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro 1477This convenience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
769calls into a single call. This is the most convinient method to initialise 1478calls into a single call. This is the most convenient method to initialise
770a watcher. The same limitations apply, of course. 1479a watcher. The same limitations apply, of course.
1480.Sp
1481Example: Initialise and set an \f(CW\*(C`ev_io\*(C'\fR watcher in one step.
1482.Sp
1483.Vb 1
1484\& ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1485.Ve
771.ie n .IP """ev_TYPE_start"" (loop *, ev_TYPE *watcher)" 4 1486.ie n .IP """ev_TYPE_start"" (loop, ev_TYPE *watcher)" 4
772.el .IP "\f(CWev_TYPE_start\fR (loop *, ev_TYPE *watcher)" 4 1487.el .IP "\f(CWev_TYPE_start\fR (loop, ev_TYPE *watcher)" 4
773.IX Item "ev_TYPE_start (loop *, ev_TYPE *watcher)" 1488.IX Item "ev_TYPE_start (loop, ev_TYPE *watcher)"
774Starts (activates) the given watcher. Only active watchers will receive 1489Starts (activates) the given watcher. Only active watchers will receive
775events. If the watcher is already active nothing will happen. 1490events. If the watcher is already active nothing will happen.
1491.Sp
1492Example: Start the \f(CW\*(C`ev_io\*(C'\fR watcher that is being abused as example in this
1493whole section.
1494.Sp
1495.Vb 1
1496\& ev_io_start (EV_DEFAULT_UC, &w);
1497.Ve
776.ie n .IP """ev_TYPE_stop"" (loop *, ev_TYPE *watcher)" 4 1498.ie n .IP """ev_TYPE_stop"" (loop, ev_TYPE *watcher)" 4
777.el .IP "\f(CWev_TYPE_stop\fR (loop *, ev_TYPE *watcher)" 4 1499.el .IP "\f(CWev_TYPE_stop\fR (loop, ev_TYPE *watcher)" 4
778.IX Item "ev_TYPE_stop (loop *, ev_TYPE *watcher)" 1500.IX Item "ev_TYPE_stop (loop, ev_TYPE *watcher)"
779Stops the given watcher again (if active) and clears the pending 1501Stops the given watcher if active, and clears the pending status (whether
1502the watcher was active or not).
1503.Sp
780status. It is possible that stopped watchers are pending (for example, 1504It is possible that stopped watchers are pending \- for example,
781non-repeating timers are being stopped when they become pending), but 1505non-repeating timers are being stopped when they become pending \- but
782\&\f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor pending. If 1506calling \f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor
783you want to free or reuse the memory used by the watcher it is therefore a 1507pending. If you want to free or reuse the memory used by the watcher it is
784good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. 1508therefore a good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
785.IP "bool ev_is_active (ev_TYPE *watcher)" 4 1509.IP "bool ev_is_active (ev_TYPE *watcher)" 4
786.IX Item "bool ev_is_active (ev_TYPE *watcher)" 1510.IX Item "bool ev_is_active (ev_TYPE *watcher)"
787Returns a true value iff the watcher is active (i.e. it has been started 1511Returns a true value iff the watcher is active (i.e. it has been started
788and not yet been stopped). As long as a watcher is active you must not modify 1512and not yet been stopped). As long as a watcher is active you must not modify
789it. 1513it.
790.IP "bool ev_is_pending (ev_TYPE *watcher)" 4 1514.IP "bool ev_is_pending (ev_TYPE *watcher)" 4
791.IX Item "bool ev_is_pending (ev_TYPE *watcher)" 1515.IX Item "bool ev_is_pending (ev_TYPE *watcher)"
792Returns a true value iff the watcher is pending, (i.e. it has outstanding 1516Returns a true value iff the watcher is pending, (i.e. it has outstanding
793events but its callback has not yet been invoked). As long as a watcher 1517events but its callback has not yet been invoked). As long as a watcher
794is pending (but not active) you must not call an init function on it (but 1518is pending (but not active) you must not call an init function on it (but
795\&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe) and you must make sure the watcher is available to 1519\&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe), you must not change its priority, and you must
796libev (e.g. you cnanot \f(CW\*(C`free ()\*(C'\fR it). 1520make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR
1521it).
797.IP "callback = ev_cb (ev_TYPE *watcher)" 4 1522.IP "callback ev_cb (ev_TYPE *watcher)" 4
798.IX Item "callback = ev_cb (ev_TYPE *watcher)" 1523.IX Item "callback ev_cb (ev_TYPE *watcher)"
799Returns the callback currently set on the watcher. 1524Returns the callback currently set on the watcher.
800.IP "ev_cb_set (ev_TYPE *watcher, callback)" 4 1525.IP "ev_set_cb (ev_TYPE *watcher, callback)" 4
801.IX Item "ev_cb_set (ev_TYPE *watcher, callback)" 1526.IX Item "ev_set_cb (ev_TYPE *watcher, callback)"
802Change the callback. You can change the callback at virtually any time 1527Change the callback. You can change the callback at virtually any time
803(modulo threads). 1528(modulo threads).
804.Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0" 1529.IP "ev_set_priority (ev_TYPE *watcher, int priority)" 4
805.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER" 1530.IX Item "ev_set_priority (ev_TYPE *watcher, int priority)"
806Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change 1531.PD 0
807and read at any time, libev will completely ignore it. This can be used 1532.IP "int ev_priority (ev_TYPE *watcher)" 4
808to associate arbitrary data with your watcher. If you need more data and 1533.IX Item "int ev_priority (ev_TYPE *watcher)"
809don't want to allocate memory and store a pointer to it in that data 1534.PD
810member, you can also \*(L"subclass\*(R" the watcher type and provide your own 1535Set and query the priority of the watcher. The priority is a small
811data: 1536integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR
1537(default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked
1538before watchers with lower priority, but priority will not keep watchers
1539from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
1540.Sp
1541If you need to suppress invocation when higher priority events are pending
1542you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
1543.Sp
1544You \fImust not\fR change the priority of a watcher as long as it is active or
1545pending.
1546.Sp
1547Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
1548fine, as long as you do not mind that the priority value you query might
1549or might not have been clamped to the valid range.
1550.Sp
1551The default priority used by watchers when no priority has been set is
1552always \f(CW0\fR, which is supposed to not be too high and not be too low :).
1553.Sp
1554See \*(L"\s-1WATCHER PRIORITY MODELS\*(R"\s0, below, for a more thorough treatment of
1555priorities.
1556.IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
1557.IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
1558Invoke the \f(CW\*(C`watcher\*(C'\fR with the given \f(CW\*(C`loop\*(C'\fR and \f(CW\*(C`revents\*(C'\fR. Neither
1559\&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback
1560can deal with that fact, as both are simply passed through to the
1561callback.
1562.IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
1563.IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
1564If the watcher is pending, this function clears its pending status and
1565returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the
1566watcher isn't pending it does nothing and returns \f(CW0\fR.
1567.Sp
1568Sometimes it can be useful to \*(L"poll\*(R" a watcher instead of waiting for its
1569callback to be invoked, which can be accomplished with this function.
1570.IP "ev_feed_event (loop, ev_TYPE *watcher, int revents)" 4
1571.IX Item "ev_feed_event (loop, ev_TYPE *watcher, int revents)"
1572Feeds the given event set into the event loop, as if the specified event
1573had happened for the specified watcher (which must be a pointer to an
1574initialised but not necessarily started event watcher). Obviously you must
1575not free the watcher as long as it has pending events.
1576.Sp
1577Stopping the watcher, letting libev invoke it, or calling
1578\&\f(CW\*(C`ev_clear_pending\*(C'\fR will clear the pending event, even if the watcher was
1579not started in the first place.
1580.Sp
1581See also \f(CW\*(C`ev_feed_fd_event\*(C'\fR and \f(CW\*(C`ev_feed_signal_event\*(C'\fR for related
1582functions that do not need a watcher.
812.PP 1583.PP
1584See also the \*(L"\s-1ASSOCIATING CUSTOM DATA WITH A WATCHER\*(R"\s0 and \*(L"\s-1BUILDING YOUR
1585OWN COMPOSITE WATCHERS\*(R"\s0 idioms.
1586.SS "\s-1WATCHER STATES\s0"
1587.IX Subsection "WATCHER STATES"
1588There are various watcher states mentioned throughout this manual \-
1589active, pending and so on. In this section these states and the rules to
1590transition between them will be described in more detail \- and while these
1591rules might look complicated, they usually do \*(L"the right thing\*(R".
1592.IP "initialised" 4
1593.IX Item "initialised"
1594Before a watcher can be registered with the event loop it has to be
1595initialised. This can be done with a call to \f(CW\*(C`ev_TYPE_init\*(C'\fR, or calls to
1596\&\f(CW\*(C`ev_init\*(C'\fR followed by the watcher-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR function.
1597.Sp
1598In this state it is simply some block of memory that is suitable for
1599use in an event loop. It can be moved around, freed, reused etc. at
1600will \- as long as you either keep the memory contents intact, or call
1601\&\f(CW\*(C`ev_TYPE_init\*(C'\fR again.
1602.IP "started/running/active" 4
1603.IX Item "started/running/active"
1604Once a watcher has been started with a call to \f(CW\*(C`ev_TYPE_start\*(C'\fR it becomes
1605property of the event loop, and is actively waiting for events. While in
1606this state it cannot be accessed (except in a few documented ways), moved,
1607freed or anything else \- the only legal thing is to keep a pointer to it,
1608and call libev functions on it that are documented to work on active watchers.
1609.IP "pending" 4
1610.IX Item "pending"
1611If a watcher is active and libev determines that an event it is interested
1612in has occurred (such as a timer expiring), it will become pending. It will
1613stay in this pending state until either it is stopped or its callback is
1614about to be invoked, so it is not normally pending inside the watcher
1615callback.
1616.Sp
1617The watcher might or might not be active while it is pending (for example,
1618an expired non-repeating timer can be pending but no longer active). If it
1619is stopped, it can be freely accessed (e.g. by calling \f(CW\*(C`ev_TYPE_set\*(C'\fR),
1620but it is still property of the event loop at this time, so cannot be
1621moved, freed or reused. And if it is active the rules described in the
1622previous item still apply.
1623.Sp
1624It is also possible to feed an event on a watcher that is not active (e.g.
1625via \f(CW\*(C`ev_feed_event\*(C'\fR), in which case it becomes pending without being
1626active.
1627.IP "stopped" 4
1628.IX Item "stopped"
1629A watcher can be stopped implicitly by libev (in which case it might still
1630be pending), or explicitly by calling its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. The
1631latter will clear any pending state the watcher might be in, regardless
1632of whether it was active or not, so stopping a watcher explicitly before
1633freeing it is often a good idea.
1634.Sp
1635While stopped (and not pending) the watcher is essentially in the
1636initialised state, that is, it can be reused, moved, modified in any way
1637you wish (but when you trash the memory block, you need to \f(CW\*(C`ev_TYPE_init\*(C'\fR
1638it again).
1639.SS "\s-1WATCHER PRIORITY MODELS\s0"
1640.IX Subsection "WATCHER PRIORITY MODELS"
1641Many event loops support \fIwatcher priorities\fR, which are usually small
1642integers that influence the ordering of event callback invocation
1643between watchers in some way, all else being equal.
1644.PP
1645In libev, Watcher priorities can be set using \f(CW\*(C`ev_set_priority\*(C'\fR. See its
1646description for the more technical details such as the actual priority
1647range.
1648.PP
1649There are two common ways how these these priorities are being interpreted
1650by event loops:
1651.PP
1652In the more common lock-out model, higher priorities \*(L"lock out\*(R" invocation
1653of lower priority watchers, which means as long as higher priority
1654watchers receive events, lower priority watchers are not being invoked.
1655.PP
1656The less common only-for-ordering model uses priorities solely to order
1657callback invocation within a single event loop iteration: Higher priority
1658watchers are invoked before lower priority ones, but they all get invoked
1659before polling for new events.
1660.PP
1661Libev uses the second (only-for-ordering) model for all its watchers
1662except for idle watchers (which use the lock-out model).
1663.PP
1664The rationale behind this is that implementing the lock-out model for
1665watchers is not well supported by most kernel interfaces, and most event
1666libraries will just poll for the same events again and again as long as
1667their callbacks have not been executed, which is very inefficient in the
1668common case of one high-priority watcher locking out a mass of lower
1669priority ones.
1670.PP
1671Static (ordering) priorities are most useful when you have two or more
1672watchers handling the same resource: a typical usage example is having an
1673\&\f(CW\*(C`ev_io\*(C'\fR watcher to receive data, and an associated \f(CW\*(C`ev_timer\*(C'\fR to handle
1674timeouts. Under load, data might be received while the program handles
1675other jobs, but since timers normally get invoked first, the timeout
1676handler will be executed before checking for data. In that case, giving
1677the timer a lower priority than the I/O watcher ensures that I/O will be
1678handled first even under adverse conditions (which is usually, but not
1679always, what you want).
1680.PP
1681Since idle watchers use the \*(L"lock-out\*(R" model, meaning that idle watchers
1682will only be executed when no same or higher priority watchers have
1683received events, they can be used to implement the \*(L"lock-out\*(R" model when
1684required.
1685.PP
1686For example, to emulate how many other event libraries handle priorities,
1687you can associate an \f(CW\*(C`ev_idle\*(C'\fR watcher to each such watcher, and in
1688the normal watcher callback, you just start the idle watcher. The real
1689processing is done in the idle watcher callback. This causes libev to
1690continuously poll and process kernel event data for the watcher, but when
1691the lock-out case is known to be rare (which in turn is rare :), this is
1692workable.
1693.PP
1694Usually, however, the lock-out model implemented that way will perform
1695miserably under the type of load it was designed to handle. In that case,
1696it might be preferable to stop the real watcher before starting the
1697idle watcher, so the kernel will not have to process the event in case
1698the actual processing will be delayed for considerable time.
1699.PP
1700Here is an example of an I/O watcher that should run at a strictly lower
1701priority than the default, and which should only process data when no
1702other events are pending:
1703.PP
813.Vb 7 1704.Vb 2
814\& struct my_io 1705\& ev_idle idle; // actual processing watcher
1706\& ev_io io; // actual event watcher
1707\&
1708\& static void
1709\& io_cb (EV_P_ ev_io *w, int revents)
815\& { 1710\& {
816\& struct ev_io io; 1711\& // stop the I/O watcher, we received the event, but
817\& int otherfd; 1712\& // are not yet ready to handle it.
818\& void *somedata; 1713\& ev_io_stop (EV_A_ w);
819\& struct whatever *mostinteresting; 1714\&
1715\& // start the idle watcher to handle the actual event.
1716\& // it will not be executed as long as other watchers
1717\& // with the default priority are receiving events.
1718\& ev_idle_start (EV_A_ &idle);
820\& } 1719\& }
821.Ve 1720\&
822.PP 1721\& static void
823And since your callback will be called with a pointer to the watcher, you 1722\& idle_cb (EV_P_ ev_idle *w, int revents)
824can cast it back to your own type:
825.PP
826.Vb 5
827\& static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
828\& { 1723\& {
829\& struct my_io *w = (struct my_io *)w_; 1724\& // actual processing
830\& ... 1725\& read (STDIN_FILENO, ...);
1726\&
1727\& // have to start the I/O watcher again, as
1728\& // we have handled the event
1729\& ev_io_start (EV_P_ &io);
831\& } 1730\& }
1731\&
1732\& // initialisation
1733\& ev_idle_init (&idle, idle_cb);
1734\& ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
1735\& ev_io_start (EV_DEFAULT_ &io);
832.Ve 1736.Ve
833.PP 1737.PP
834More interesting and less C\-conformant ways of catsing your callback type 1738In the \*(L"real\*(R" world, it might also be beneficial to start a timer, so that
835have been omitted.... 1739low-priority connections can not be locked out forever under load. This
1740enables your program to keep a lower latency for important connections
1741during short periods of high load, while not completely locking out less
1742important ones.
836.SH "WATCHER TYPES" 1743.SH "WATCHER TYPES"
837.IX Header "WATCHER TYPES" 1744.IX Header "WATCHER TYPES"
838This section describes each watcher in detail, but will not repeat 1745This section describes each watcher in detail, but will not repeat
839information given in the last section. Any initialisation/set macros, 1746information given in the last section. Any initialisation/set macros,
840functions and members specific to the watcher type are explained. 1747functions and members specific to the watcher type are explained.
… …
845watcher is stopped to your hearts content), or \fI[read\-write]\fR, which 1752watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
846means you can expect it to have some sensible content while the watcher 1753means you can expect it to have some sensible content while the watcher
847is active, but you can also modify it. Modifying it may not do something 1754is active, but you can also modify it. Modifying it may not do something
848sensible or take immediate effect (or do anything at all), but libev will 1755sensible or take immediate effect (or do anything at all), but libev will
849not crash or malfunction in any way. 1756not crash or malfunction in any way.
850.ie n .Sh """ev_io"" \- is this file descriptor readable or writable?" 1757.ie n .SS """ev_io"" \- is this file descriptor readable or writable?"
851.el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable?" 1758.el .SS "\f(CWev_io\fP \- is this file descriptor readable or writable?"
852.IX Subsection "ev_io - is this file descriptor readable or writable?" 1759.IX Subsection "ev_io - is this file descriptor readable or writable?"
853I/O watchers check whether a file descriptor is readable or writable 1760I/O watchers check whether a file descriptor is readable or writable
854in each iteration of the event loop, or, more precisely, when reading 1761in each iteration of the event loop, or, more precisely, when reading
855would not block the process and writing would at least be able to write 1762would not block the process and writing would at least be able to write
856some data. This behaviour is called level-triggering because you keep 1763some data. This behaviour is called level-triggering because you keep
… …
861In general you can register as many read and/or write event watchers per 1768In general you can register as many read and/or write event watchers per
862fd as you want (as long as you don't confuse yourself). Setting all file 1769fd as you want (as long as you don't confuse yourself). Setting all file
863descriptors to non-blocking mode is also usually a good idea (but not 1770descriptors to non-blocking mode is also usually a good idea (but not
864required if you know what you are doing). 1771required if you know what you are doing).
865.PP 1772.PP
866You have to be careful with dup'ed file descriptors, though. Some backends
867(the linux epoll backend is a notable example) cannot handle dup'ed file
868descriptors correctly if you register interest in two or more fds pointing
869to the same underlying file/socket/etc. description (that is, they share
870the same underlying \*(L"file open\*(R").
871.PP
872If you must do this, then force the use of a known-to-be-good backend
873(at the time of this writing, this includes only \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and
874\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR).
875.PP
876Another thing you have to watch out for is that it is quite easy to 1773Another thing you have to watch out for is that it is quite easy to
877receive \*(L"spurious\*(R" readyness notifications, that is your callback might 1774receive \*(L"spurious\*(R" readiness notifications, that is, your callback might
878be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block 1775be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block
879because there is no data. Not only are some backends known to create a 1776because there is no data. It is very easy to get into this situation even
880lot of those (for example solaris ports), it is very easy to get into 1777with a relatively standard program structure. Thus it is best to always
881this situation even with a relatively standard program structure. Thus 1778use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning \f(CW\*(C`EAGAIN\*(C'\fR is far
882it is best to always use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning
883\&\f(CW\*(C`EAGAIN\*(C'\fR is far preferable to a program hanging until some data arrives. 1779preferable to a program hanging until some data arrives.
884.PP 1780.PP
885If you cannot run the fd in non-blocking mode (for example you should not 1781If you cannot run the fd in non-blocking mode (for example you should
886play around with an Xlib connection), then you have to seperately re-test 1782not play around with an Xlib connection), then you have to separately
887wether a file descriptor is really ready with a known-to-be good interface 1783re-test whether a file descriptor is really ready with a known-to-be good
888such as poll (fortunately in our Xlib example, Xlib already does this on 1784interface such as poll (fortunately in the case of Xlib, it already does
889its own, so its quite safe to use). 1785this on its own, so its quite safe to use). Some people additionally
1786use \f(CW\*(C`SIGALRM\*(C'\fR and an interval timer, just to be sure you won't block
1787indefinitely.
1788.PP
1789But really, best use non-blocking mode.
1790.PP
1791\fIThe special problem of disappearing file descriptors\fR
1792.IX Subsection "The special problem of disappearing file descriptors"
1793.PP
1794Some backends (e.g. kqueue, epoll, linuxaio) need to be told about closing
1795a file descriptor (either due to calling \f(CW\*(C`close\*(C'\fR explicitly or any other
1796means, such as \f(CW\*(C`dup2\*(C'\fR). The reason is that you register interest in some
1797file descriptor, but when it goes away, the operating system will silently
1798drop this interest. If another file descriptor with the same number then
1799is registered with libev, there is no efficient way to see that this is,
1800in fact, a different file descriptor.
1801.PP
1802To avoid having to explicitly tell libev about such cases, libev follows
1803the following policy: Each time \f(CW\*(C`ev_io_set\*(C'\fR is being called, libev
1804will assume that this is potentially a new file descriptor, otherwise
1805it is assumed that the file descriptor stays the same. That means that
1806you \fIhave\fR to call \f(CW\*(C`ev_io_set\*(C'\fR (or \f(CW\*(C`ev_io_init\*(C'\fR) when you change the
1807descriptor even if the file descriptor number itself did not change.
1808.PP
1809This is how one would do it normally anyway, the important point is that
1810the libev application should not optimise around libev but should leave
1811optimisations to libev.
1812.PP
1813\fIThe special problem of dup'ed file descriptors\fR
1814.IX Subsection "The special problem of dup'ed file descriptors"
1815.PP
1816Some backends (e.g. epoll), cannot register events for file descriptors,
1817but only events for the underlying file descriptions. That means when you
1818have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register
1819events for them, only one file descriptor might actually receive events.
1820.PP
1821There is no workaround possible except not registering events
1822for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
1823\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1824.PP
1825\fIThe special problem of files\fR
1826.IX Subsection "The special problem of files"
1827.PP
1828Many people try to use \f(CW\*(C`select\*(C'\fR (or libev) on file descriptors
1829representing files, and expect it to become ready when their program
1830doesn't block on disk accesses (which can take a long time on their own).
1831.PP
1832However, this cannot ever work in the \*(L"expected\*(R" way \- you get a readiness
1833notification as soon as the kernel knows whether and how much data is
1834there, and in the case of open files, that's always the case, so you
1835always get a readiness notification instantly, and your read (or possibly
1836write) will still block on the disk I/O.
1837.PP
1838Another way to view it is that in the case of sockets, pipes, character
1839devices and so on, there is another party (the sender) that delivers data
1840on its own, but in the case of files, there is no such thing: the disk
1841will not send data on its own, simply because it doesn't know what you
1842wish to read \- you would first have to request some data.
1843.PP
1844Since files are typically not-so-well supported by advanced notification
1845mechanism, libev tries hard to emulate \s-1POSIX\s0 behaviour with respect
1846to files, even though you should not use it. The reason for this is
1847convenience: sometimes you want to watch \s-1STDIN\s0 or \s-1STDOUT,\s0 which is
1848usually a tty, often a pipe, but also sometimes files or special devices
1849(for example, \f(CW\*(C`epoll\*(C'\fR on Linux works with \fI/dev/random\fR but not with
1850\&\fI/dev/urandom\fR), and even though the file might better be served with
1851asynchronous I/O instead of with non-blocking I/O, it is still useful when
1852it \*(L"just works\*(R" instead of freezing.
1853.PP
1854So avoid file descriptors pointing to files when you know it (e.g. use
1855libeio), but use them when it is convenient, e.g. for \s-1STDIN/STDOUT,\s0 or
1856when you rarely read from a file instead of from a socket, and want to
1857reuse the same code path.
1858.PP
1859\fIThe special problem of fork\fR
1860.IX Subsection "The special problem of fork"
1861.PP
1862Some backends (epoll, kqueue, probably linuxaio) do not support \f(CW\*(C`fork ()\*(C'\fR
1863at all or exhibit useless behaviour. Libev fully supports fork, but needs
1864to be told about it in the child if you want to continue to use it in the
1865child.
1866.PP
1867To support fork in your child processes, you have to call \f(CW\*(C`ev_loop_fork
1868()\*(C'\fR after a fork in the child, enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to
1869\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1870.PP
1871\fIThe special problem of \s-1SIGPIPE\s0\fR
1872.IX Subsection "The special problem of SIGPIPE"
1873.PP
1874While not really specific to libev, it is easy to forget about \f(CW\*(C`SIGPIPE\*(C'\fR:
1875when writing to a pipe whose other end has been closed, your program gets
1876sent a \s-1SIGPIPE,\s0 which, by default, aborts your program. For most programs
1877this is sensible behaviour, for daemons, this is usually undesirable.
1878.PP
1879So when you encounter spurious, unexplained daemon exits, make sure you
1880ignore \s-1SIGPIPE\s0 (and maybe make sure you log the exit status of your daemon
1881somewhere, as that would have given you a big clue).
1882.PP
1883\fIThe special problem of \f(BIaccept()\fIing when you can't\fR
1884.IX Subsection "The special problem of accept()ing when you can't"
1885.PP
1886Many implementations of the \s-1POSIX\s0 \f(CW\*(C`accept\*(C'\fR function (for example,
1887found in post\-2004 Linux) have the peculiar behaviour of not removing a
1888connection from the pending queue in all error cases.
1889.PP
1890For example, larger servers often run out of file descriptors (because
1891of resource limits), causing \f(CW\*(C`accept\*(C'\fR to fail with \f(CW\*(C`ENFILE\*(C'\fR but not
1892rejecting the connection, leading to libev signalling readiness on
1893the next iteration again (the connection still exists after all), and
1894typically causing the program to loop at 100% \s-1CPU\s0 usage.
1895.PP
1896Unfortunately, the set of errors that cause this issue differs between
1897operating systems, there is usually little the app can do to remedy the
1898situation, and no known thread-safe method of removing the connection to
1899cope with overload is known (to me).
1900.PP
1901One of the easiest ways to handle this situation is to just ignore it
1902\&\- when the program encounters an overload, it will just loop until the
1903situation is over. While this is a form of busy waiting, no \s-1OS\s0 offers an
1904event-based way to handle this situation, so it's the best one can do.
1905.PP
1906A better way to handle the situation is to log any errors other than
1907\&\f(CW\*(C`EAGAIN\*(C'\fR and \f(CW\*(C`EWOULDBLOCK\*(C'\fR, making sure not to flood the log with such
1908messages, and continue as usual, which at least gives the user an idea of
1909what could be wrong (\*(L"raise the ulimit!\*(R"). For extra points one could stop
1910the \f(CW\*(C`ev_io\*(C'\fR watcher on the listening fd \*(L"for a while\*(R", which reduces \s-1CPU\s0
1911usage.
1912.PP
1913If your program is single-threaded, then you could also keep a dummy file
1914descriptor for overload situations (e.g. by opening \fI/dev/null\fR), and
1915when you run into \f(CW\*(C`ENFILE\*(C'\fR or \f(CW\*(C`EMFILE\*(C'\fR, close it, run \f(CW\*(C`accept\*(C'\fR,
1916close that fd, and create a new dummy fd. This will gracefully refuse
1917clients under typical overload conditions.
1918.PP
1919The last way to handle it is to simply log the error and \f(CW\*(C`exit\*(C'\fR, as
1920is often done with \f(CW\*(C`malloc\*(C'\fR failures, but this results in an easy
1921opportunity for a DoS attack.
1922.PP
1923\fIWatcher-Specific Functions\fR
1924.IX Subsection "Watcher-Specific Functions"
890.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4 1925.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
891.IX Item "ev_io_init (ev_io *, callback, int fd, int events)" 1926.IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
892.PD 0 1927.PD 0
893.IP "ev_io_set (ev_io *, int fd, int events)" 4 1928.IP "ev_io_set (ev_io *, int fd, int events)" 4
894.IX Item "ev_io_set (ev_io *, int fd, int events)" 1929.IX Item "ev_io_set (ev_io *, int fd, int events)"
895.PD 1930.PD
896Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to 1931Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to
897rceeive events for and events is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or 1932receive events for and \f(CW\*(C`events\*(C'\fR is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or
898\&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR to receive the given events. 1933\&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR, to express the desire to receive the given events.
899.IP "int fd [read\-only]" 4 1934.IP "int fd [read\-only]" 4
900.IX Item "int fd [read-only]" 1935.IX Item "int fd [read-only]"
901The file descriptor being watched. 1936The file descriptor being watched.
902.IP "int events [read\-only]" 4 1937.IP "int events [read\-only]" 4
903.IX Item "int events [read-only]" 1938.IX Item "int events [read-only]"
904The events being watched. 1939The events being watched.
905.PP 1940.PP
1941\fIExamples\fR
1942.IX Subsection "Examples"
1943.PP
906Example: call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well 1944Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
907readable, but only once. Since it is likely line\-buffered, you could 1945readable, but only once. Since it is likely line-buffered, you could
908attempt to read a whole line in the callback: 1946attempt to read a whole line in the callback.
909.PP 1947.PP
910.Vb 6 1948.Vb 6
911\& static void 1949\& static void
912\& stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents) 1950\& stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
913\& { 1951\& {
914\& ev_io_stop (loop, w); 1952\& ev_io_stop (loop, w);
915\& .. read from stdin here (or from w->fd) and haqndle any I/O errors 1953\& .. read from stdin here (or from w\->fd) and handle any I/O errors
916\& } 1954\& }
917.Ve 1955\&
918.PP
919.Vb 6
920\& ... 1956\& ...
921\& struct ev_loop *loop = ev_default_init (0); 1957\& struct ev_loop *loop = ev_default_init (0);
922\& struct ev_io stdin_readable; 1958\& ev_io stdin_readable;
923\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ); 1959\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
924\& ev_io_start (loop, &stdin_readable); 1960\& ev_io_start (loop, &stdin_readable);
925\& ev_loop (loop, 0); 1961\& ev_run (loop, 0);
926.Ve 1962.Ve
927.ie n .Sh """ev_timer"" \- relative and optionally repeating timeouts" 1963.ie n .SS """ev_timer"" \- relative and optionally repeating timeouts"
928.el .Sh "\f(CWev_timer\fP \- relative and optionally repeating timeouts" 1964.el .SS "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
929.IX Subsection "ev_timer - relative and optionally repeating timeouts" 1965.IX Subsection "ev_timer - relative and optionally repeating timeouts"
930Timer watchers are simple relative timers that generate an event after a 1966Timer watchers are simple relative timers that generate an event after a
931given time, and optionally repeating in regular intervals after that. 1967given time, and optionally repeating in regular intervals after that.
932.PP 1968.PP
933The timers are based on real time, that is, if you register an event that 1969The timers are based on real time, that is, if you register an event that
934times out after an hour and you reset your system clock to last years 1970times out after an hour and you reset your system clock to January last
935time, it will still time out after (roughly) and hour. \*(L"Roughly\*(R" because 1971year, it will still time out after (roughly) one hour. \*(L"Roughly\*(R" because
936detecting time jumps is hard, and some inaccuracies are unavoidable (the 1972detecting time jumps is hard, and some inaccuracies are unavoidable (the
937monotonic clock option helps a lot here). 1973monotonic clock option helps a lot here).
1974.PP
1975The callback is guaranteed to be invoked only \fIafter\fR its timeout has
1976passed (not \fIat\fR, so on systems with very low-resolution clocks this
1977might introduce a small delay, see \*(L"the special problem of being too
1978early\*(R", below). If multiple timers become ready during the same loop
1979iteration then the ones with earlier time-out values are invoked before
1980ones of the same priority with later time-out values (but this is no
1981longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
1982.PP
1983\fIBe smart about timeouts\fR
1984.IX Subsection "Be smart about timeouts"
1985.PP
1986Many real-world problems involve some kind of timeout, usually for error
1987recovery. A typical example is an \s-1HTTP\s0 request \- if the other side hangs,
1988you want to raise some error after a while.
1989.PP
1990What follows are some ways to handle this problem, from obvious and
1991inefficient to smart and efficient.
1992.PP
1993In the following, a 60 second activity timeout is assumed \- a timeout that
1994gets reset to 60 seconds each time there is activity (e.g. each time some
1995data or other life sign was received).
1996.IP "1. Use a timer and stop, reinitialise and start it on activity." 4
1997.IX Item "1. Use a timer and stop, reinitialise and start it on activity."
1998This is the most obvious, but not the most simple way: In the beginning,
1999start the watcher:
2000.Sp
2001.Vb 2
2002\& ev_timer_init (timer, callback, 60., 0.);
2003\& ev_timer_start (loop, timer);
2004.Ve
2005.Sp
2006Then, each time there is some activity, \f(CW\*(C`ev_timer_stop\*(C'\fR it, initialise it
2007and start it again:
2008.Sp
2009.Vb 3
2010\& ev_timer_stop (loop, timer);
2011\& ev_timer_set (timer, 60., 0.);
2012\& ev_timer_start (loop, timer);
2013.Ve
2014.Sp
2015This is relatively simple to implement, but means that each time there is
2016some activity, libev will first have to remove the timer from its internal
2017data structure and then add it again. Libev tries to be fast, but it's
2018still not a constant-time operation.
2019.ie n .IP "2. Use a timer and re-start it with ""ev_timer_again"" inactivity." 4
2020.el .IP "2. Use a timer and re-start it with \f(CWev_timer_again\fR inactivity." 4
2021.IX Item "2. Use a timer and re-start it with ev_timer_again inactivity."
2022This is the easiest way, and involves using \f(CW\*(C`ev_timer_again\*(C'\fR instead of
2023\&\f(CW\*(C`ev_timer_start\*(C'\fR.
2024.Sp
2025To implement this, configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value
2026of \f(CW60\fR and then call \f(CW\*(C`ev_timer_again\*(C'\fR at start and each time you
2027successfully read or write some data. If you go into an idle state where
2028you do not expect data to travel on the socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR
2029the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will automatically restart it if need be.
2030.Sp
2031That means you can ignore both the \f(CW\*(C`ev_timer_start\*(C'\fR function and the
2032\&\f(CW\*(C`after\*(C'\fR argument to \f(CW\*(C`ev_timer_set\*(C'\fR, and only ever use the \f(CW\*(C`repeat\*(C'\fR
2033member and \f(CW\*(C`ev_timer_again\*(C'\fR.
2034.Sp
2035At start:
2036.Sp
2037.Vb 3
2038\& ev_init (timer, callback);
2039\& timer\->repeat = 60.;
2040\& ev_timer_again (loop, timer);
2041.Ve
2042.Sp
2043Each time there is some activity:
2044.Sp
2045.Vb 1
2046\& ev_timer_again (loop, timer);
2047.Ve
2048.Sp
2049It is even possible to change the time-out on the fly, regardless of
2050whether the watcher is active or not:
2051.Sp
2052.Vb 2
2053\& timer\->repeat = 30.;
2054\& ev_timer_again (loop, timer);
2055.Ve
2056.Sp
2057This is slightly more efficient then stopping/starting the timer each time
2058you want to modify its timeout value, as libev does not have to completely
2059remove and re-insert the timer from/into its internal data structure.
2060.Sp
2061It is, however, even simpler than the \*(L"obvious\*(R" way to do it.
2062.IP "3. Let the timer time out, but then re-arm it as required." 4
2063.IX Item "3. Let the timer time out, but then re-arm it as required."
2064This method is more tricky, but usually most efficient: Most timeouts are
2065relatively long compared to the intervals between other activity \- in
2066our example, within 60 seconds, there are usually many I/O events with
2067associated activity resets.
2068.Sp
2069In this case, it would be more efficient to leave the \f(CW\*(C`ev_timer\*(C'\fR alone,
2070but remember the time of last activity, and check for a real timeout only
2071within the callback:
2072.Sp
2073.Vb 3
2074\& ev_tstamp timeout = 60.;
2075\& ev_tstamp last_activity; // time of last activity
2076\& ev_timer timer;
2077\&
2078\& static void
2079\& callback (EV_P_ ev_timer *w, int revents)
2080\& {
2081\& // calculate when the timeout would happen
2082\& ev_tstamp after = last_activity \- ev_now (EV_A) + timeout;
2083\&
2084\& // if negative, it means we the timeout already occurred
2085\& if (after < 0.)
2086\& {
2087\& // timeout occurred, take action
2088\& }
2089\& else
2090\& {
2091\& // callback was invoked, but there was some recent
2092\& // activity. simply restart the timer to time out
2093\& // after "after" seconds, which is the earliest time
2094\& // the timeout can occur.
2095\& ev_timer_set (w, after, 0.);
2096\& ev_timer_start (EV_A_ w);
2097\& }
2098\& }
2099.Ve
2100.Sp
2101To summarise the callback: first calculate in how many seconds the
2102timeout will occur (by calculating the absolute time when it would occur,
2103\&\f(CW\*(C`last_activity + timeout\*(C'\fR, and subtracting the current time, \f(CW\*(C`ev_now
2104(EV_A)\*(C'\fR from that).
2105.Sp
2106If this value is negative, then we are already past the timeout, i.e. we
2107timed out, and need to do whatever is needed in this case.
2108.Sp
2109Otherwise, we now the earliest time at which the timeout would trigger,
2110and simply start the timer with this timeout value.
2111.Sp
2112In other words, each time the callback is invoked it will check whether
2113the timeout occurred. If not, it will simply reschedule itself to check
2114again at the earliest time it could time out. Rinse. Repeat.
2115.Sp
2116This scheme causes more callback invocations (about one every 60 seconds
2117minus half the average time between activity), but virtually no calls to
2118libev to change the timeout.
2119.Sp
2120To start the machinery, simply initialise the watcher and set
2121\&\f(CW\*(C`last_activity\*(C'\fR to the current time (meaning there was some activity just
2122now), then call the callback, which will \*(L"do the right thing\*(R" and start
2123the timer:
2124.Sp
2125.Vb 3
2126\& last_activity = ev_now (EV_A);
2127\& ev_init (&timer, callback);
2128\& callback (EV_A_ &timer, 0);
2129.Ve
2130.Sp
2131When there is some activity, simply store the current time in
2132\&\f(CW\*(C`last_activity\*(C'\fR, no libev calls at all:
2133.Sp
2134.Vb 2
2135\& if (activity detected)
2136\& last_activity = ev_now (EV_A);
2137.Ve
2138.Sp
2139When your timeout value changes, then the timeout can be changed by simply
2140providing a new value, stopping the timer and calling the callback, which
2141will again do the right thing (for example, time out immediately :).
2142.Sp
2143.Vb 3
2144\& timeout = new_value;
2145\& ev_timer_stop (EV_A_ &timer);
2146\& callback (EV_A_ &timer, 0);
2147.Ve
2148.Sp
2149This technique is slightly more complex, but in most cases where the
2150time-out is unlikely to be triggered, much more efficient.
2151.IP "4. Wee, just use a double-linked list for your timeouts." 4
2152.IX Item "4. Wee, just use a double-linked list for your timeouts."
2153If there is not one request, but many thousands (millions...), all
2154employing some kind of timeout with the same timeout value, then one can
2155do even better:
2156.Sp
2157When starting the timeout, calculate the timeout value and put the timeout
2158at the \fIend\fR of the list.
2159.Sp
2160Then use an \f(CW\*(C`ev_timer\*(C'\fR to fire when the timeout at the \fIbeginning\fR of
2161the list is expected to fire (for example, using the technique #3).
2162.Sp
2163When there is some activity, remove the timer from the list, recalculate
2164the timeout, append it to the end of the list again, and make sure to
2165update the \f(CW\*(C`ev_timer\*(C'\fR if it was taken from the beginning of the list.
2166.Sp
2167This way, one can manage an unlimited number of timeouts in O(1) time for
2168starting, stopping and updating the timers, at the expense of a major
2169complication, and having to use a constant timeout. The constant timeout
2170ensures that the list stays sorted.
2171.PP
2172So which method the best?
2173.PP
2174Method #2 is a simple no-brain-required solution that is adequate in most
2175situations. Method #3 requires a bit more thinking, but handles many cases
2176better, and isn't very complicated either. In most case, choosing either
2177one is fine, with #3 being better in typical situations.
2178.PP
2179Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
2180rather complicated, but extremely efficient, something that really pays
2181off after the first million or so of active timers, i.e. it's usually
2182overkill :)
2183.PP
2184\fIThe special problem of being too early\fR
2185.IX Subsection "The special problem of being too early"
2186.PP
2187If you ask a timer to call your callback after three seconds, then
2188you expect it to be invoked after three seconds \- but of course, this
2189cannot be guaranteed to infinite precision. Less obviously, it cannot be
2190guaranteed to any precision by libev \- imagine somebody suspending the
2191process with a \s-1STOP\s0 signal for a few hours for example.
2192.PP
2193So, libev tries to invoke your callback as soon as possible \fIafter\fR the
2194delay has occurred, but cannot guarantee this.
2195.PP
2196A less obvious failure mode is calling your callback too early: many event
2197loops compare timestamps with a \*(L"elapsed delay >= requested delay\*(R", but
2198this can cause your callback to be invoked much earlier than you would
2199expect.
2200.PP
2201To see why, imagine a system with a clock that only offers full second
2202resolution (think windows if you can't come up with a broken enough \s-1OS\s0
2203yourself). If you schedule a one-second timer at the time 500.9, then the
2204event loop will schedule your timeout to elapse at a system time of 500
2205(500.9 truncated to the resolution) + 1, or 501.
2206.PP
2207If an event library looks at the timeout 0.1s later, it will see \*(L"501 >=
2208501\*(R" and invoke the callback 0.1s after it was started, even though a
2209one-second delay was requested \- this is being \*(L"too early\*(R", despite best
2210intentions.
2211.PP
2212This is the reason why libev will never invoke the callback if the elapsed
2213delay equals the requested delay, but only when the elapsed delay is
2214larger than the requested delay. In the example above, libev would only invoke
2215the callback at system time 502, or 1.1s after the timer was started.
2216.PP
2217So, while libev cannot guarantee that your callback will be invoked
2218exactly when requested, it \fIcan\fR and \fIdoes\fR guarantee that the requested
2219delay has actually elapsed, or in other words, it always errs on the \*(L"too
2220late\*(R" side of things.
2221.PP
2222\fIThe special problem of time updates\fR
2223.IX Subsection "The special problem of time updates"
2224.PP
2225Establishing the current time is a costly operation (it usually takes
2226at least one system call): \s-1EV\s0 therefore updates its idea of the current
2227time only before and after \f(CW\*(C`ev_run\*(C'\fR collects new events, which causes a
2228growing difference between \f(CW\*(C`ev_now ()\*(C'\fR and \f(CW\*(C`ev_time ()\*(C'\fR when handling
2229lots of events in one iteration.
938.PP 2230.PP
939The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR 2231The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
940time. This is usually the right thing as this timestamp refers to the time 2232time. This is usually the right thing as this timestamp refers to the time
941of the event triggering whatever timeout you are modifying/starting. If 2233of the event triggering whatever timeout you are modifying/starting. If
942you suspect event processing to be delayed and you \fIneed\fR to base the timeout 2234you suspect event processing to be delayed and you \fIneed\fR to base the
943on the current time, use something like this to adjust for this: 2235timeout on the current time, use something like the following to adjust
2236for it:
944.PP 2237.PP
945.Vb 1 2238.Vb 1
946\& ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); 2239\& ev_timer_set (&timer, after + (ev_time () \- ev_now ()), 0.);
947.Ve 2240.Ve
948.PP 2241.PP
949The callback is guarenteed to be invoked only when its timeout has passed, 2242If the event loop is suspended for a long time, you can also force an
950but if multiple timers become ready during the same loop iteration then 2243update of the time returned by \f(CW\*(C`ev_now ()\*(C'\fR by calling \f(CW\*(C`ev_now_update
951order of execution is undefined. 2244()\*(C'\fR, although that will push the event time of all outstanding events
2245further into the future.
2246.PP
2247\fIThe special problem of unsynchronised clocks\fR
2248.IX Subsection "The special problem of unsynchronised clocks"
2249.PP
2250Modern systems have a variety of clocks \- libev itself uses the normal
2251\&\*(L"wall clock\*(R" clock and, if available, the monotonic clock (to avoid time
2252jumps).
2253.PP
2254Neither of these clocks is synchronised with each other or any other clock
2255on the system, so \f(CW\*(C`ev_time ()\*(C'\fR might return a considerably different time
2256than \f(CW\*(C`gettimeofday ()\*(C'\fR or \f(CW\*(C`time ()\*(C'\fR. On a GNU/Linux system, for example,
2257a call to \f(CW\*(C`gettimeofday\*(C'\fR might return a second count that is one higher
2258than a directly following call to \f(CW\*(C`time\*(C'\fR.
2259.PP
2260The moral of this is to only compare libev-related timestamps with
2261\&\f(CW\*(C`ev_time ()\*(C'\fR and \f(CW\*(C`ev_now ()\*(C'\fR, at least if you want better precision than
2262a second or so.
2263.PP
2264One more problem arises due to this lack of synchronisation: if libev uses
2265the system monotonic clock and you compare timestamps from \f(CW\*(C`ev_time\*(C'\fR
2266or \f(CW\*(C`ev_now\*(C'\fR from when you started your timer and when your callback is
2267invoked, you will find that sometimes the callback is a bit \*(L"early\*(R".
2268.PP
2269This is because \f(CW\*(C`ev_timer\*(C'\fRs work in real time, not wall clock time, so
2270libev makes sure your callback is not invoked before the delay happened,
2271\&\fImeasured according to the real time\fR, not the system clock.
2272.PP
2273If your timeouts are based on a physical timescale (e.g. \*(L"time out this
2274connection after 100 seconds\*(R") then this shouldn't bother you as it is
2275exactly the right behaviour.
2276.PP
2277If you want to compare wall clock/system timestamps to your timers, then
2278you need to use \f(CW\*(C`ev_periodic\*(C'\fRs, as these are based on the wall clock
2279time, where your comparisons will always generate correct results.
2280.PP
2281\fIThe special problems of suspended animation\fR
2282.IX Subsection "The special problems of suspended animation"
2283.PP
2284When you leave the server world it is quite customary to hit machines that
2285can suspend/hibernate \- what happens to the clocks during such a suspend?
2286.PP
2287Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
2288all processes, while the clocks (\f(CW\*(C`times\*(C'\fR, \f(CW\*(C`CLOCK_MONOTONIC\*(C'\fR) continue
2289to run until the system is suspended, but they will not advance while the
2290system is suspended. That means, on resume, it will be as if the program
2291was frozen for a few seconds, but the suspend time will not be counted
2292towards \f(CW\*(C`ev_timer\*(C'\fR when a monotonic clock source is used. The real time
2293clock advanced as expected, but if it is used as sole clocksource, then a
2294long suspend would be detected as a time jump by libev, and timers would
2295be adjusted accordingly.
2296.PP
2297I would not be surprised to see different behaviour in different between
2298operating systems, \s-1OS\s0 versions or even different hardware.
2299.PP
2300The other form of suspend (job control, or sending a \s-1SIGSTOP\s0) will see a
2301time jump in the monotonic clocks and the realtime clock. If the program
2302is suspended for a very long time, and monotonic clock sources are in use,
2303then you can expect \f(CW\*(C`ev_timer\*(C'\fRs to expire as the full suspension time
2304will be counted towards the timers. When no monotonic clock source is in
2305use, then libev will again assume a timejump and adjust accordingly.
2306.PP
2307It might be beneficial for this latter case to call \f(CW\*(C`ev_suspend\*(C'\fR
2308and \f(CW\*(C`ev_resume\*(C'\fR in code that handles \f(CW\*(C`SIGTSTP\*(C'\fR, to at least get
2309deterministic behaviour in this case (you can do nothing against
2310\&\f(CW\*(C`SIGSTOP\*(C'\fR).
2311.PP
2312\fIWatcher-Specific Functions and Data Members\fR
2313.IX Subsection "Watcher-Specific Functions and Data Members"
952.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4 2314.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
953.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 2315.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
954.PD 0 2316.PD 0
955.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4 2317.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
956.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 2318.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
957.PD 2319.PD
958Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR is 2320Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds (fractional and
959\&\f(CW0.\fR, then it will automatically be stopped. If it is positive, then the 2321negative values are supported). If \f(CW\*(C`repeat\*(C'\fR is \f(CW0.\fR, then it will
2322automatically be stopped once the timeout is reached. If it is positive,
960timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds 2323then the timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR
961later, again, and again, until stopped manually. 2324seconds later, again, and again, until stopped manually.
962.Sp 2325.Sp
963The timer itself will do a best-effort at avoiding drift, that is, if you 2326The timer itself will do a best-effort at avoiding drift, that is, if
964configure a timer to trigger every 10 seconds, then it will trigger at 2327you configure a timer to trigger every 10 seconds, then it will normally
965exactly 10 second intervals. If, however, your program cannot keep up with 2328trigger at exactly 10 second intervals. If, however, your program cannot
966the timer (because it takes longer than those 10 seconds to do stuff) the 2329keep up with the timer (because it takes longer than those 10 seconds to
967timer will not fire more than once per event loop iteration. 2330do stuff) the timer will not fire more than once per event loop iteration.
968.IP "ev_timer_again (loop)" 4 2331.IP "ev_timer_again (loop, ev_timer *)" 4
969.IX Item "ev_timer_again (loop)" 2332.IX Item "ev_timer_again (loop, ev_timer *)"
970This will act as if the timer timed out and restart it again if it is 2333This will act as if the timer timed out, and restarts it again if it is
971repeating. The exact semantics are: 2334repeating. It basically works like calling \f(CW\*(C`ev_timer_stop\*(C'\fR, updating the
2335timeout to the \f(CW\*(C`repeat\*(C'\fR value and calling \f(CW\*(C`ev_timer_start\*(C'\fR.
972.Sp 2336.Sp
973If the timer is started but nonrepeating, stop it. 2337The exact semantics are as in the following rules, all of which will be
2338applied to the watcher:
2339.RS 4
2340.IP "If the timer is pending, the pending status is always cleared." 4
2341.IX Item "If the timer is pending, the pending status is always cleared."
2342.PD 0
2343.IP "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)." 4
2344.IX Item "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)."
2345.ie n .IP "If the timer is repeating, make the ""repeat"" value the new timeout and start the timer, if necessary." 4
2346.el .IP "If the timer is repeating, make the \f(CWrepeat\fR value the new timeout and start the timer, if necessary." 4
2347.IX Item "If the timer is repeating, make the repeat value the new timeout and start the timer, if necessary."
2348.RE
2349.RS 4
2350.PD
974.Sp 2351.Sp
975If the timer is repeating, either start it if necessary (with the repeat 2352This sounds a bit complicated, see \*(L"Be smart about timeouts\*(R", above, for a
976value), or reset the running timer to the repeat value. 2353usage example.
2354.RE
2355.IP "ev_tstamp ev_timer_remaining (loop, ev_timer *)" 4
2356.IX Item "ev_tstamp ev_timer_remaining (loop, ev_timer *)"
2357Returns the remaining time until a timer fires. If the timer is active,
2358then this time is relative to the current event loop time, otherwise it's
2359the timeout value currently configured.
977.Sp 2360.Sp
978This sounds a bit complicated, but here is a useful and typical 2361That is, after an \f(CW\*(C`ev_timer_set (w, 5, 7)\*(C'\fR, \f(CW\*(C`ev_timer_remaining\*(C'\fR returns
979example: Imagine you have a tcp connection and you want a so-called 2362\&\f(CW5\fR. When the timer is started and one second passes, \f(CW\*(C`ev_timer_remaining\*(C'\fR
980idle timeout, that is, you want to be called when there have been, 2363will return \f(CW4\fR. When the timer expires and is restarted, it will return
981say, 60 seconds of inactivity on the socket. The easiest way to do 2364roughly \f(CW7\fR (likely slightly less as callback invocation takes some time,
982this is to configure an \f(CW\*(C`ev_timer\*(C'\fR with \f(CW\*(C`after\*(C'\fR=\f(CW\*(C`repeat\*(C'\fR=\f(CW60\fR and calling 2365too), and so on.
983\&\f(CW\*(C`ev_timer_again\*(C'\fR each time you successfully read or write some data. If
984you go into an idle state where you do not expect data to travel on the
985socket, you can stop the timer, and again will automatically restart it if
986need be.
987.Sp
988You can also ignore the \f(CW\*(C`after\*(C'\fR value and \f(CW\*(C`ev_timer_start\*(C'\fR altogether
989and only ever use the \f(CW\*(C`repeat\*(C'\fR value:
990.Sp
991.Vb 8
992\& ev_timer_init (timer, callback, 0., 5.);
993\& ev_timer_again (loop, timer);
994\& ...
995\& timer->again = 17.;
996\& ev_timer_again (loop, timer);
997\& ...
998\& timer->again = 10.;
999\& ev_timer_again (loop, timer);
1000.Ve
1001.Sp
1002This is more efficient then stopping/starting the timer eahc time you want
1003to modify its timeout value.
1004.IP "ev_tstamp repeat [read\-write]" 4 2366.IP "ev_tstamp repeat [read\-write]" 4
1005.IX Item "ev_tstamp repeat [read-write]" 2367.IX Item "ev_tstamp repeat [read-write]"
1006The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out 2368The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
1007or \f(CW\*(C`ev_timer_again\*(C'\fR is called and determines the next timeout (if any), 2369or \f(CW\*(C`ev_timer_again\*(C'\fR is called, and determines the next timeout (if any),
1008which is also when any modifications are taken into account. 2370which is also when any modifications are taken into account.
1009.PP 2371.PP
2372\fIExamples\fR
2373.IX Subsection "Examples"
2374.PP
1010Example: create a timer that fires after 60 seconds. 2375Example: Create a timer that fires after 60 seconds.
1011.PP 2376.PP
1012.Vb 5 2377.Vb 5
1013\& static void 2378\& static void
1014\& one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents) 2379\& one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1015\& { 2380\& {
1016\& .. one minute over, w is actually stopped right here 2381\& .. one minute over, w is actually stopped right here
1017\& } 2382\& }
1018.Ve 2383\&
1019.PP
1020.Vb 3
1021\& struct ev_timer mytimer; 2384\& ev_timer mytimer;
1022\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.); 2385\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1023\& ev_timer_start (loop, &mytimer); 2386\& ev_timer_start (loop, &mytimer);
1024.Ve 2387.Ve
1025.PP 2388.PP
1026Example: create a timeout timer that times out after 10 seconds of 2389Example: Create a timeout timer that times out after 10 seconds of
1027inactivity. 2390inactivity.
1028.PP 2391.PP
1029.Vb 5 2392.Vb 5
1030\& static void 2393\& static void
1031\& timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents) 2394\& timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1032\& { 2395\& {
1033\& .. ten seconds without any activity 2396\& .. ten seconds without any activity
1034\& } 2397\& }
1035.Ve 2398\&
1036.PP
1037.Vb 4
1038\& struct ev_timer mytimer; 2399\& ev_timer mytimer;
1039\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */ 2400\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1040\& ev_timer_again (&mytimer); /* start timer */ 2401\& ev_timer_again (&mytimer); /* start timer */
1041\& ev_loop (loop, 0); 2402\& ev_run (loop, 0);
1042.Ve 2403\&
1043.PP
1044.Vb 3
1045\& // and in some piece of code that gets executed on any "activity": 2404\& // and in some piece of code that gets executed on any "activity":
1046\& // reset the timeout to start ticking again at 10 seconds 2405\& // reset the timeout to start ticking again at 10 seconds
1047\& ev_timer_again (&mytimer); 2406\& ev_timer_again (&mytimer);
1048.Ve 2407.Ve
1049.ie n .Sh """ev_periodic"" \- to cron or not to cron?" 2408.ie n .SS """ev_periodic"" \- to cron or not to cron?"
1050.el .Sh "\f(CWev_periodic\fP \- to cron or not to cron?" 2409.el .SS "\f(CWev_periodic\fP \- to cron or not to cron?"
1051.IX Subsection "ev_periodic - to cron or not to cron?" 2410.IX Subsection "ev_periodic - to cron or not to cron?"
1052Periodic watchers are also timers of a kind, but they are very versatile 2411Periodic watchers are also timers of a kind, but they are very versatile
1053(and unfortunately a bit complex). 2412(and unfortunately a bit complex).
1054.PP 2413.PP
1055Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time) 2414Unlike \f(CW\*(C`ev_timer\*(C'\fR, periodic watchers are not based on real time (or
1056but on wallclock time (absolute time). You can tell a periodic watcher 2415relative time, the physical time that passes) but on wall clock time
1057to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a 2416(absolute time, the thing you can read on your calendar or clock). The
1058periodic watcher to trigger in 10 seconds (by specifiying e.g. \f(CW\*(C`ev_now () 2417difference is that wall clock time can run faster or slower than real
1059+ 10.\*(C'\fR) and then reset your system clock to the last year, then it will 2418time, and time jumps are not uncommon (e.g. when you adjust your
1060take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger 2419wrist-watch).
1061roughly 10 seconds later and of course not if you reset your system time
1062again).
1063.PP 2420.PP
1064They can also be used to implement vastly more complex timers, such as 2421You can tell a periodic watcher to trigger after some specific point
1065triggering an event on eahc midnight, local time. 2422in time: for example, if you tell a periodic watcher to trigger \*(L"in 10
2423seconds\*(R" (by specifying e.g. \f(CW\*(C`ev_now () + 10.\*(C'\fR, that is, an absolute time
2424not a delay) and then reset your system clock to January of the previous
2425year, then it will take a year or more to trigger the event (unlike an
2426\&\f(CW\*(C`ev_timer\*(C'\fR, which would still trigger roughly 10 seconds after starting
2427it, as it uses a relative timeout).
1066.PP 2428.PP
2429\&\f(CW\*(C`ev_periodic\*(C'\fR watchers can also be used to implement vastly more complex
2430timers, such as triggering an event on each \*(L"midnight, local time\*(R", or
2431other complicated rules. This cannot easily be done with \f(CW\*(C`ev_timer\*(C'\fR
2432watchers, as those cannot react to time jumps.
2433.PP
1067As with timers, the callback is guarenteed to be invoked only when the 2434As with timers, the callback is guaranteed to be invoked only when the
1068time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready 2435point in time where it is supposed to trigger has passed. If multiple
1069during the same loop iteration then order of execution is undefined. 2436timers become ready during the same loop iteration then the ones with
2437earlier time-out values are invoked before ones with later time-out values
2438(but this is no longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
2439.PP
2440\fIWatcher-Specific Functions and Data Members\fR
2441.IX Subsection "Watcher-Specific Functions and Data Members"
1070.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4 2442.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
1071.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 2443.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
1072.PD 0 2444.PD 0
1073.IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4 2445.IP "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
1074.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 2446.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
1075.PD 2447.PD
1076Lots of arguments, lets sort it out... There are basically three modes of 2448Lots of arguments, let's sort it out... There are basically three modes of
1077operation, and we will explain them from simplest to complex: 2449operation, and we will explain them from simplest to most complex:
1078.RS 4 2450.RS 4
1079.IP "* absolute timer (interval = reschedule_cb = 0)" 4 2451.IP "\(bu" 4
1080.IX Item "absolute timer (interval = reschedule_cb = 0)" 2452absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
2453.Sp
1081In this configuration the watcher triggers an event at the wallclock time 2454In this configuration the watcher triggers an event after the wall clock
1082\&\f(CW\*(C`at\*(C'\fR and doesn't repeat. It will not adjust when a time jump occurs, 2455time \f(CW\*(C`offset\*(C'\fR has passed. It will not repeat and will not adjust when a
1083that is, if it is to be run at January 1st 2011 then it will run when the 2456time jump occurs, that is, if it is to be run at January 1st 2011 then it
1084system time reaches or surpasses this time. 2457will be stopped and invoked when the system clock reaches or surpasses
1085.IP "* non-repeating interval timer (interval > 0, reschedule_cb = 0)" 4 2458this point in time.
1086.IX Item "non-repeating interval timer (interval > 0, reschedule_cb = 0)" 2459.IP "\(bu" 4
2460repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
2461.Sp
1087In this mode the watcher will always be scheduled to time out at the next 2462In this mode the watcher will always be scheduled to time out at the next
1088\&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N) and then repeat, regardless 2463\&\f(CW\*(C`offset + N * interval\*(C'\fR time (for some integer N, which can also be
1089of any time jumps. 2464negative) and then repeat, regardless of any time jumps. The \f(CW\*(C`offset\*(C'\fR
2465argument is merely an offset into the \f(CW\*(C`interval\*(C'\fR periods.
1090.Sp 2466.Sp
1091This can be used to create timers that do not drift with respect to system 2467This can be used to create timers that do not drift with respect to the
1092time: 2468system clock, for example, here is an \f(CW\*(C`ev_periodic\*(C'\fR that triggers each
2469hour, on the hour (with respect to \s-1UTC\s0):
1093.Sp 2470.Sp
1094.Vb 1 2471.Vb 1
1095\& ev_periodic_set (&periodic, 0., 3600., 0); 2472\& ev_periodic_set (&periodic, 0., 3600., 0);
1096.Ve 2473.Ve
1097.Sp 2474.Sp
1098This doesn't mean there will always be 3600 seconds in between triggers, 2475This doesn't mean there will always be 3600 seconds in between triggers,
1099but only that the the callback will be called when the system time shows a 2476but only that the callback will be called when the system time shows a
1100full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible 2477full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
1101by 3600. 2478by 3600.
1102.Sp 2479.Sp
1103Another way to think about it (for the mathematically inclined) is that 2480Another way to think about it (for the mathematically inclined) is that
1104\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible 2481\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
1105time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps. 2482time where \f(CW\*(C`time = offset (mod interval)\*(C'\fR, regardless of any time jumps.
1106.IP "* manual reschedule mode (reschedule_cb = callback)" 4 2483.Sp
1107.IX Item "manual reschedule mode (reschedule_cb = callback)" 2484The \f(CW\*(C`interval\*(C'\fR \fI\s-1MUST\s0\fR be positive, and for numerical stability, the
2485interval value should be higher than \f(CW\*(C`1/8192\*(C'\fR (which is around 100
2486microseconds) and \f(CW\*(C`offset\*(C'\fR should be higher than \f(CW0\fR and should have
2487at most a similar magnitude as the current time (say, within a factor of
2488ten). Typical values for offset are, in fact, \f(CW0\fR or something between
2489\&\f(CW0\fR and \f(CW\*(C`interval\*(C'\fR, which is also the recommended range.
2490.Sp
2491Note also that there is an upper limit to how often a timer can fire (\s-1CPU\s0
2492speed for example), so if \f(CW\*(C`interval\*(C'\fR is very small then timing stability
2493will of course deteriorate. Libev itself tries to be exact to be about one
2494millisecond (if the \s-1OS\s0 supports it and the machine is fast enough).
2495.IP "\(bu" 4
2496manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
2497.Sp
1108In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being 2498In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`offset\*(C'\fR are both being
1109ignored. Instead, each time the periodic watcher gets scheduled, the 2499ignored. Instead, each time the periodic watcher gets scheduled, the
1110reschedule callback will be called with the watcher as first, and the 2500reschedule callback will be called with the watcher as first, and the
1111current time as second argument. 2501current time as second argument.
1112.Sp 2502.Sp
1113\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, 2503\&\s-1NOTE:\s0 \fIThis callback \s-1MUST NOT\s0 stop or destroy any periodic watcher, ever,
1114ever, or make any event loop modifications\fR. If you need to stop it, 2504or make \s-1ANY\s0 other event loop modifications whatsoever, unless explicitly
1115return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by 2505allowed by documentation here\fR.
1116starting a prepare watcher).
1117.Sp 2506.Sp
2507If you need to stop it, return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop
2508it afterwards (e.g. by starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is the
2509only event loop modification you are allowed to do).
2510.Sp
1118Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w, 2511The callback prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(ev_periodic
1119ev_tstamp now)\*(C'\fR, e.g.: 2512*w, ev_tstamp now)\*(C'\fR, e.g.:
1120.Sp 2513.Sp
1121.Vb 4 2514.Vb 5
2515\& static ev_tstamp
1122\& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) 2516\& my_rescheduler (ev_periodic *w, ev_tstamp now)
1123\& { 2517\& {
1124\& return now + 60.; 2518\& return now + 60.;
1125\& } 2519\& }
1126.Ve 2520.Ve
1127.Sp 2521.Sp
1128It must return the next time to trigger, based on the passed time value 2522It must return the next time to trigger, based on the passed time value
1129(that is, the lowest time value larger than to the second argument). It 2523(that is, the lowest time value larger than to the second argument). It
1130will usually be called just before the callback will be triggered, but 2524will usually be called just before the callback will be triggered, but
1131might be called at other times, too. 2525might be called at other times, too.
1132.Sp 2526.Sp
1133\&\s-1NOTE:\s0 \fIThis callback must always return a time that is later than the 2527\&\s-1NOTE:\s0 \fIThis callback must always return a time that is higher than or
1134passed \f(CI\*(C`now\*(C'\fI value\fR. Not even \f(CW\*(C`now\*(C'\fR itself will do, it \fImust\fR be larger. 2528equal to the passed \f(CI\*(C`now\*(C'\fI value\fR.
1135.Sp 2529.Sp
1136This can be used to create very complex timers, such as a timer that 2530This can be used to create very complex timers, such as a timer that
1137triggers on each midnight, local time. To do this, you would calculate the 2531triggers on \*(L"next midnight, local time\*(R". To do this, you would calculate
1138next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How 2532the next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for
1139you do this is, again, up to you (but it is not trivial, which is the main 2533this. Here is a (completely untested, no error checking) example on how to
1140reason I omitted it as an example). 2534do this:
2535.Sp
2536.Vb 1
2537\& #include <time.h>
2538\&
2539\& static ev_tstamp
2540\& my_rescheduler (ev_periodic *w, ev_tstamp now)
2541\& {
2542\& time_t tnow = (time_t)now;
2543\& struct tm tm;
2544\& localtime_r (&tnow, &tm);
2545\&
2546\& tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
2547\& ++tm.tm_mday; // midnight next day
2548\&
2549\& return mktime (&tm);
2550\& }
2551.Ve
2552.Sp
2553Note: this code might run into trouble on days that have more then two
2554midnights (beginning and end).
1141.RE 2555.RE
1142.RS 4 2556.RS 4
1143.RE 2557.RE
1144.IP "ev_periodic_again (loop, ev_periodic *)" 4 2558.IP "ev_periodic_again (loop, ev_periodic *)" 4
1145.IX Item "ev_periodic_again (loop, ev_periodic *)" 2559.IX Item "ev_periodic_again (loop, ev_periodic *)"
1146Simply stops and restarts the periodic watcher again. This is only useful 2560Simply stops and restarts the periodic watcher again. This is only useful
1147when you changed some parameters or the reschedule callback would return 2561when you changed some parameters or the reschedule callback would return
1148a different time than the last time it was called (e.g. in a crond like 2562a different time than the last time it was called (e.g. in a crond like
1149program when the crontabs have changed). 2563program when the crontabs have changed).
2564.IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4
2565.IX Item "ev_tstamp ev_periodic_at (ev_periodic *)"
2566When active, returns the absolute time that the watcher is supposed
2567to trigger next. This is not the same as the \f(CW\*(C`offset\*(C'\fR argument to
2568\&\f(CW\*(C`ev_periodic_set\*(C'\fR, but indeed works even in interval and manual
2569rescheduling modes.
2570.IP "ev_tstamp offset [read\-write]" 4
2571.IX Item "ev_tstamp offset [read-write]"
2572When repeating, this contains the offset value, otherwise this is the
2573absolute point in time (the \f(CW\*(C`offset\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR,
2574although libev might modify this value for better numerical stability).
2575.Sp
2576Can be modified any time, but changes only take effect when the periodic
2577timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1150.IP "ev_tstamp interval [read\-write]" 4 2578.IP "ev_tstamp interval [read\-write]" 4
1151.IX Item "ev_tstamp interval [read-write]" 2579.IX Item "ev_tstamp interval [read-write]"
1152The current interval value. Can be modified any time, but changes only 2580The current interval value. Can be modified any time, but changes only
1153take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being 2581take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
1154called. 2582called.
1155.IP "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read\-write]" 4 2583.IP "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read\-write]" 4
1156.IX Item "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]" 2584.IX Item "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]"
1157The current reschedule callback, or \f(CW0\fR, if this functionality is 2585The current reschedule callback, or \f(CW0\fR, if this functionality is
1158switched off. Can be changed any time, but changes only take effect when 2586switched off. Can be changed any time, but changes only take effect when
1159the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called. 2587the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1160.PP 2588.PP
2589\fIExamples\fR
2590.IX Subsection "Examples"
2591.PP
1161Example: call a callback every hour, or, more precisely, whenever the 2592Example: Call a callback every hour, or, more precisely, whenever the
1162system clock is divisible by 3600. The callback invocation times have 2593system time is divisible by 3600. The callback invocation times have
1163potentially a lot of jittering, but good long-term stability. 2594potentially a lot of jitter, but good long-term stability.
1164.PP 2595.PP
1165.Vb 5 2596.Vb 5
1166\& static void 2597\& static void
1167\& clock_cb (struct ev_loop *loop, struct ev_io *w, int revents) 2598\& clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1168\& { 2599\& {
1169\& ... its now a full hour (UTC, or TAI or whatever your clock follows) 2600\& ... its now a full hour (UTC, or TAI or whatever your clock follows)
1170\& } 2601\& }
1171.Ve 2602\&
1172.PP
1173.Vb 3
1174\& struct ev_periodic hourly_tick; 2603\& ev_periodic hourly_tick;
1175\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0); 2604\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1176\& ev_periodic_start (loop, &hourly_tick); 2605\& ev_periodic_start (loop, &hourly_tick);
1177.Ve 2606.Ve
1178.PP 2607.PP
1179Example: the same as above, but use a reschedule callback to do it: 2608Example: The same as above, but use a reschedule callback to do it:
1180.PP 2609.PP
1181.Vb 1 2610.Vb 1
1182\& #include <math.h> 2611\& #include <math.h>
1183.Ve 2612\&
1184.PP
1185.Vb 5
1186\& static ev_tstamp 2613\& static ev_tstamp
1187\& my_scheduler_cb (struct ev_periodic *w, ev_tstamp now) 2614\& my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1188\& { 2615\& {
1189\& return fmod (now, 3600.) + 3600.; 2616\& return now + (3600. \- fmod (now, 3600.));
1190\& } 2617\& }
1191.Ve 2618\&
1192.PP
1193.Vb 1
1194\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb); 2619\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1195.Ve 2620.Ve
1196.PP 2621.PP
1197Example: call a callback every hour, starting now: 2622Example: Call a callback every hour, starting now:
1198.PP 2623.PP
1199.Vb 4 2624.Vb 4
1200\& struct ev_periodic hourly_tick; 2625\& ev_periodic hourly_tick;
1201\& ev_periodic_init (&hourly_tick, clock_cb, 2626\& ev_periodic_init (&hourly_tick, clock_cb,
1202\& fmod (ev_now (loop), 3600.), 3600., 0); 2627\& fmod (ev_now (loop), 3600.), 3600., 0);
1203\& ev_periodic_start (loop, &hourly_tick); 2628\& ev_periodic_start (loop, &hourly_tick);
1204.Ve 2629.Ve
1205.ie n .Sh """ev_signal"" \- signal me when a signal gets signalled!" 2630.ie n .SS """ev_signal"" \- signal me when a signal gets signalled!"
1206.el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled!" 2631.el .SS "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
1207.IX Subsection "ev_signal - signal me when a signal gets signalled!" 2632.IX Subsection "ev_signal - signal me when a signal gets signalled!"
1208Signal watchers will trigger an event when the process receives a specific 2633Signal watchers will trigger an event when the process receives a specific
1209signal one or more times. Even though signals are very asynchronous, libev 2634signal one or more times. Even though signals are very asynchronous, libev
1210will try it's best to deliver signals synchronously, i.e. as part of the 2635will try its best to deliver signals synchronously, i.e. as part of the
1211normal event processing, like any other event. 2636normal event processing, like any other event.
1212.PP 2637.PP
2638If you want signals to be delivered truly asynchronously, just use
2639\&\f(CW\*(C`sigaction\*(C'\fR as you would do without libev and forget about sharing
2640the signal. You can even use \f(CW\*(C`ev_async\*(C'\fR from a signal handler to
2641synchronously wake up an event loop.
2642.PP
1213You can configure as many watchers as you like per signal. Only when the 2643You can configure as many watchers as you like for the same signal, but
1214first watcher gets started will libev actually register a signal watcher 2644only within the same loop, i.e. you can watch for \f(CW\*(C`SIGINT\*(C'\fR in your
1215with the kernel (thus it coexists with your own signal handlers as long 2645default loop and for \f(CW\*(C`SIGIO\*(C'\fR in another loop, but you cannot watch for
1216as you don't register any with libev). Similarly, when the last signal 2646\&\f(CW\*(C`SIGINT\*(C'\fR in both the default loop and another loop at the same time. At
1217watcher for a signal is stopped libev will reset the signal handler to 2647the moment, \f(CW\*(C`SIGCHLD\*(C'\fR is permanently tied to the default loop.
1218\&\s-1SIG_DFL\s0 (regardless of what it was set to before). 2648.PP
2649Only after the first watcher for a signal is started will libev actually
2650register something with the kernel. It thus coexists with your own signal
2651handlers as long as you don't register any with libev for the same signal.
2652.PP
2653If possible and supported, libev will install its handlers with
2654\&\f(CW\*(C`SA_RESTART\*(C'\fR (or equivalent) behaviour enabled, so system calls should
2655not be unduly interrupted. If you have a problem with system calls getting
2656interrupted by signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher
2657and unblock them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher.
2658.PP
2659\fIThe special problem of inheritance over fork/execve/pthread_create\fR
2660.IX Subsection "The special problem of inheritance over fork/execve/pthread_create"
2661.PP
2662Both the signal mask (\f(CW\*(C`sigprocmask\*(C'\fR) and the signal disposition
2663(\f(CW\*(C`sigaction\*(C'\fR) are unspecified after starting a signal watcher (and after
2664stopping it again), that is, libev might or might not block the signal,
2665and might or might not set or restore the installed signal handler (but
2666see \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR).
2667.PP
2668While this does not matter for the signal disposition (libev never
2669sets signals to \f(CW\*(C`SIG_IGN\*(C'\fR, so handlers will be reset to \f(CW\*(C`SIG_DFL\*(C'\fR on
2670\&\f(CW\*(C`execve\*(C'\fR), this matters for the signal mask: many programs do not expect
2671certain signals to be blocked.
2672.PP
2673This means that before calling \f(CW\*(C`exec\*(C'\fR (from the child) you should reset
2674the signal mask to whatever \*(L"default\*(R" you expect (all clear is a good
2675choice usually).
2676.PP
2677The simplest way to ensure that the signal mask is reset in the child is
2678to install a fork handler with \f(CW\*(C`pthread_atfork\*(C'\fR that resets it. That will
2679catch fork calls done by libraries (such as the libc) as well.
2680.PP
2681In current versions of libev, the signal will not be blocked indefinitely
2682unless you use the \f(CW\*(C`signalfd\*(C'\fR \s-1API\s0 (\f(CW\*(C`EV_SIGNALFD\*(C'\fR). While this reduces
2683the window of opportunity for problems, it will not go away, as libev
2684\&\fIhas\fR to modify the signal mask, at least temporarily.
2685.PP
2686So I can't stress this enough: \fIIf you do not reset your signal mask when
2687you expect it to be empty, you have a race condition in your code\fR. This
2688is not a libev-specific thing, this is true for most event libraries.
2689.PP
2690\fIThe special problem of threads signal handling\fR
2691.IX Subsection "The special problem of threads signal handling"
2692.PP
2693\&\s-1POSIX\s0 threads has problematic signal handling semantics, specifically,
2694a lot of functionality (sigfd, sigwait etc.) only really works if all
2695threads in a process block signals, which is hard to achieve.
2696.PP
2697When you want to use sigwait (or mix libev signal handling with your own
2698for the same signals), you can tackle this problem by globally blocking
2699all signals before creating any threads (or creating them with a fully set
2700sigprocmask) and also specifying the \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when creating
2701loops. Then designate one thread as \*(L"signal receiver thread\*(R" which handles
2702these signals. You can pass on any signals that libev might be interested
2703in by calling \f(CW\*(C`ev_feed_signal\*(C'\fR.
2704.PP
2705\fIWatcher-Specific Functions and Data Members\fR
2706.IX Subsection "Watcher-Specific Functions and Data Members"
1219.IP "ev_signal_init (ev_signal *, callback, int signum)" 4 2707.IP "ev_signal_init (ev_signal *, callback, int signum)" 4
1220.IX Item "ev_signal_init (ev_signal *, callback, int signum)" 2708.IX Item "ev_signal_init (ev_signal *, callback, int signum)"
1221.PD 0 2709.PD 0
1222.IP "ev_signal_set (ev_signal *, int signum)" 4 2710.IP "ev_signal_set (ev_signal *, int signum)" 4
1223.IX Item "ev_signal_set (ev_signal *, int signum)" 2711.IX Item "ev_signal_set (ev_signal *, int signum)"
… …
1225Configures the watcher to trigger on the given signal number (usually one 2713Configures the watcher to trigger on the given signal number (usually one
1226of the \f(CW\*(C`SIGxxx\*(C'\fR constants). 2714of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
1227.IP "int signum [read\-only]" 4 2715.IP "int signum [read\-only]" 4
1228.IX Item "int signum [read-only]" 2716.IX Item "int signum [read-only]"
1229The signal the watcher watches out for. 2717The signal the watcher watches out for.
2718.PP
2719\fIExamples\fR
2720.IX Subsection "Examples"
2721.PP
2722Example: Try to exit cleanly on \s-1SIGINT.\s0
2723.PP
2724.Vb 5
2725\& static void
2726\& sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
2727\& {
2728\& ev_break (loop, EVBREAK_ALL);
2729\& }
2730\&
2731\& ev_signal signal_watcher;
2732\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
2733\& ev_signal_start (loop, &signal_watcher);
2734.Ve
1230.ie n .Sh """ev_child"" \- watch out for process status changes" 2735.ie n .SS """ev_child"" \- watch out for process status changes"
1231.el .Sh "\f(CWev_child\fP \- watch out for process status changes" 2736.el .SS "\f(CWev_child\fP \- watch out for process status changes"
1232.IX Subsection "ev_child - watch out for process status changes" 2737.IX Subsection "ev_child - watch out for process status changes"
1233Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to 2738Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
1234some child status changes (most typically when a child of yours dies). 2739some child status changes (most typically when a child of yours dies or
2740exits). It is permissible to install a child watcher \fIafter\fR the child
2741has been forked (which implies it might have already exited), as long
2742as the event loop isn't entered (or is continued from a watcher), i.e.,
2743forking and then immediately registering a watcher for the child is fine,
2744but forking and registering a watcher a few event loop iterations later or
2745in the next callback invocation is not.
2746.PP
2747Only the default event loop is capable of handling signals, and therefore
2748you can only register child watchers in the default event loop.
2749.PP
2750Due to some design glitches inside libev, child watchers will always be
2751handled at maximum priority (their priority is set to \f(CW\*(C`EV_MAXPRI\*(C'\fR by
2752libev)
2753.PP
2754\fIProcess Interaction\fR
2755.IX Subsection "Process Interaction"
2756.PP
2757Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is
2758initialised. This is necessary to guarantee proper behaviour even if the
2759first child watcher is started after the child exits. The occurrence
2760of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done
2761synchronously as part of the event loop processing. Libev always reaps all
2762children, even ones not watched.
2763.PP
2764\fIOverriding the Built-In Processing\fR
2765.IX Subsection "Overriding the Built-In Processing"
2766.PP
2767Libev offers no special support for overriding the built-in child
2768processing, but if your application collides with libev's default child
2769handler, you can override it easily by installing your own handler for
2770\&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the
2771default loop never gets destroyed. You are encouraged, however, to use an
2772event-based approach to child reaping and thus use libev's support for
2773that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely.
2774.PP
2775\fIStopping the Child Watcher\fR
2776.IX Subsection "Stopping the Child Watcher"
2777.PP
2778Currently, the child watcher never gets stopped, even when the
2779child terminates, so normally one needs to stop the watcher in the
2780callback. Future versions of libev might stop the watcher automatically
2781when a child exit is detected (calling \f(CW\*(C`ev_child_stop\*(C'\fR twice is not a
2782problem).
2783.PP
2784\fIWatcher-Specific Functions and Data Members\fR
2785.IX Subsection "Watcher-Specific Functions and Data Members"
1235.IP "ev_child_init (ev_child *, callback, int pid)" 4 2786.IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4
1236.IX Item "ev_child_init (ev_child *, callback, int pid)" 2787.IX Item "ev_child_init (ev_child *, callback, int pid, int trace)"
1237.PD 0 2788.PD 0
1238.IP "ev_child_set (ev_child *, int pid)" 4 2789.IP "ev_child_set (ev_child *, int pid, int trace)" 4
1239.IX Item "ev_child_set (ev_child *, int pid)" 2790.IX Item "ev_child_set (ev_child *, int pid, int trace)"
1240.PD 2791.PD
1241Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or 2792Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
1242\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look 2793\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
1243at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see 2794at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
1244the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems 2795the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
1245\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the 2796\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
1246process causing the status change. 2797process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only
2798activate the watcher when the process terminates) or \f(CW1\fR (additionally
2799activate the watcher when the process is stopped or continued).
1247.IP "int pid [read\-only]" 4 2800.IP "int pid [read\-only]" 4
1248.IX Item "int pid [read-only]" 2801.IX Item "int pid [read-only]"
1249The process id this watcher watches out for, or \f(CW0\fR, meaning any process id. 2802The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
1250.IP "int rpid [read\-write]" 4 2803.IP "int rpid [read\-write]" 4
1251.IX Item "int rpid [read-write]" 2804.IX Item "int rpid [read-write]"
… …
1253.IP "int rstatus [read\-write]" 4 2806.IP "int rstatus [read\-write]" 4
1254.IX Item "int rstatus [read-write]" 2807.IX Item "int rstatus [read-write]"
1255The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems 2808The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
1256\&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details). 2809\&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
1257.PP 2810.PP
1258Example: try to exit cleanly on \s-1SIGINT\s0 and \s-1SIGTERM\s0. 2811\fIExamples\fR
2812.IX Subsection "Examples"
1259.PP 2813.PP
2814Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for
2815its completion.
2816.PP
1260.Vb 5 2817.Vb 1
2818\& ev_child cw;
2819\&
1261\& static void 2820\& static void
1262\& sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents) 2821\& child_cb (EV_P_ ev_child *w, int revents)
1263\& { 2822\& {
1264\& ev_unloop (loop, EVUNLOOP_ALL); 2823\& ev_child_stop (EV_A_ w);
2824\& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus);
1265\& } 2825\& }
2826\&
2827\& pid_t pid = fork ();
2828\&
2829\& if (pid < 0)
2830\& // error
2831\& else if (pid == 0)
2832\& {
2833\& // the forked child executes here
2834\& exit (1);
2835\& }
2836\& else
2837\& {
2838\& ev_child_init (&cw, child_cb, pid, 0);
2839\& ev_child_start (EV_DEFAULT_ &cw);
2840\& }
1266.Ve 2841.Ve
1267.PP
1268.Vb 3
1269\& struct ev_signal signal_watcher;
1270\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1271\& ev_signal_start (loop, &sigint_cb);
1272.Ve
1273.ie n .Sh """ev_stat"" \- did the file attributes just change?" 2842.ie n .SS """ev_stat"" \- did the file attributes just change?"
1274.el .Sh "\f(CWev_stat\fP \- did the file attributes just change?" 2843.el .SS "\f(CWev_stat\fP \- did the file attributes just change?"
1275.IX Subsection "ev_stat - did the file attributes just change?" 2844.IX Subsection "ev_stat - did the file attributes just change?"
1276This watches a filesystem path for attribute changes. That is, it calls 2845This watches a file system path for attribute changes. That is, it calls
1277\&\f(CW\*(C`stat\*(C'\fR regularly (or when the \s-1OS\s0 says it changed) and sees if it changed 2846\&\f(CW\*(C`stat\*(C'\fR on that path in regular intervals (or when the \s-1OS\s0 says it changed)
1278compared to the last time, invoking the callback if it did. 2847and sees if it changed compared to the last time, invoking the callback
2848if it did. Starting the watcher \f(CW\*(C`stat\*(C'\fR's the file, so only changes that
2849happen after the watcher has been started will be reported.
1279.PP 2850.PP
1280The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does 2851The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does
1281not exist\*(R" is a status change like any other. The condition \*(L"path does 2852not exist\*(R" is a status change like any other. The condition \*(L"path does not
1282not exist\*(R" is signified by the \f(CW\*(C`st_nlink\*(C'\fR field being zero (which is 2853exist\*(R" (or more correctly \*(L"path cannot be stat'ed\*(R") is signified by the
1283otherwise always forced to be at least one) and all the other fields of 2854\&\f(CW\*(C`st_nlink\*(C'\fR field being zero (which is otherwise always forced to be at
1284the stat buffer having unspecified contents. 2855least one) and all the other fields of the stat buffer having unspecified
2856contents.
1285.PP 2857.PP
1286Since there is no standard to do this, the portable implementation simply 2858The path \fImust not\fR end in a slash or contain special components such as
1287calls \f(CW\*(C`stat (2)\*(C'\fR regulalry on the path to see if it changed somehow. You 2859\&\f(CW\*(C`.\*(C'\fR or \f(CW\*(C`..\*(C'\fR. The path \fIshould\fR be absolute: If it is relative and
1288can specify a recommended polling interval for this case. If you specify 2860your working directory changes, then the behaviour is undefined.
1289a polling interval of \f(CW0\fR (highly recommended!) then a \fIsuitable, 2861.PP
1290unspecified default\fR value will be used (which you can expect to be around 2862Since there is no portable change notification interface available, the
1291five seconds, although this might change dynamically). Libev will also 2863portable implementation simply calls \f(CWstat(2)\fR regularly on the path
1292impose a minimum interval which is currently around \f(CW0.1\fR, but thats 2864to see if it changed somehow. You can specify a recommended polling
1293usually overkill. 2865interval for this case. If you specify a polling interval of \f(CW0\fR (highly
2866recommended!) then a \fIsuitable, unspecified default\fR value will be used
2867(which you can expect to be around five seconds, although this might
2868change dynamically). Libev will also impose a minimum interval which is
2869currently around \f(CW0.1\fR, but that's usually overkill.
1294.PP 2870.PP
1295This watcher type is not meant for massive numbers of stat watchers, 2871This watcher type is not meant for massive numbers of stat watchers,
1296as even with OS-supported change notifications, this can be 2872as even with OS-supported change notifications, this can be
1297resource\-intensive. 2873resource-intensive.
1298.PP 2874.PP
1299At the time of this writing, no specific \s-1OS\s0 backends are implemented, but 2875At the time of this writing, the only OS-specific interface implemented
1300if demand increases, at least a kqueue and inotify backend will be added. 2876is the Linux inotify interface (implementing kqueue support is left as an
2877exercise for the reader. Note, however, that the author sees no way of
2878implementing \f(CW\*(C`ev_stat\*(C'\fR semantics with kqueue, except as a hint).
2879.PP
2880\fI\s-1ABI\s0 Issues (Largefile Support)\fR
2881.IX Subsection "ABI Issues (Largefile Support)"
2882.PP
2883Libev by default (unless the user overrides this) uses the default
2884compilation environment, which means that on systems with large file
2885support disabled by default, you get the 32 bit version of the stat
2886structure. When using the library from programs that change the \s-1ABI\s0 to
2887use 64 bit file offsets the programs will fail. In that case you have to
2888compile libev with the same flags to get binary compatibility. This is
2889obviously the case with any flags that change the \s-1ABI,\s0 but the problem is
2890most noticeably displayed with ev_stat and large file support.
2891.PP
2892The solution for this is to lobby your distribution maker to make large
2893file interfaces available by default (as e.g. FreeBSD does) and not
2894optional. Libev cannot simply switch on large file support because it has
2895to exchange stat structures with application programs compiled using the
2896default compilation environment.
2897.PP
2898\fIInotify and Kqueue\fR
2899.IX Subsection "Inotify and Kqueue"
2900.PP
2901When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev and present at
2902runtime, it will be used to speed up change detection where possible. The
2903inotify descriptor will be created lazily when the first \f(CW\*(C`ev_stat\*(C'\fR
2904watcher is being started.
2905.PP
2906Inotify presence does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
2907except that changes might be detected earlier, and in some cases, to avoid
2908making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presence of inotify support
2909there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling,
2910but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
2911many bugs), the path exists (i.e. stat succeeds), and the path resides on
2912a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
2913xfs are fully working) libev usually gets away without polling.
2914.PP
2915There is no support for kqueue, as apparently it cannot be used to
2916implement this functionality, due to the requirement of having a file
2917descriptor open on the object at all times, and detecting renames, unlinks
2918etc. is difficult.
2919.PP
2920\fI\f(CI\*(C`stat ()\*(C'\fI is a synchronous operation\fR
2921.IX Subsection "stat () is a synchronous operation"
2922.PP
2923Libev doesn't normally do any kind of I/O itself, and so is not blocking
2924the process. The exception are \f(CW\*(C`ev_stat\*(C'\fR watchers \- those call \f(CW\*(C`stat
2925()\*(C'\fR, which is a synchronous operation.
2926.PP
2927For local paths, this usually doesn't matter: unless the system is very
2928busy or the intervals between stat's are large, a stat call will be fast,
2929as the path data is usually in memory already (except when starting the
2930watcher).
2931.PP
2932For networked file systems, calling \f(CW\*(C`stat ()\*(C'\fR can block an indefinite
2933time due to network issues, and even under good conditions, a stat call
2934often takes multiple milliseconds.
2935.PP
2936Therefore, it is best to avoid using \f(CW\*(C`ev_stat\*(C'\fR watchers on networked
2937paths, although this is fully supported by libev.
2938.PP
2939\fIThe special problem of stat time resolution\fR
2940.IX Subsection "The special problem of stat time resolution"
2941.PP
2942The \f(CW\*(C`stat ()\*(C'\fR system call only supports full-second resolution portably,
2943and even on systems where the resolution is higher, most file systems
2944still only support whole seconds.
2945.PP
2946That means that, if the time is the only thing that changes, you can
2947easily miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and
2948calls your callback, which does something. When there is another update
2949within the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect unless the
2950stat data does change in other ways (e.g. file size).
2951.PP
2952The solution to this is to delay acting on a change for slightly more
2953than a second (or till slightly after the next full second boundary), using
2954a roughly one-second-delay \f(CW\*(C`ev_timer\*(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02);
2955ev_timer_again (loop, w)\*(C'\fR).
2956.PP
2957The \f(CW.02\fR offset is added to work around small timing inconsistencies
2958of some operating systems (where the second counter of the current time
2959might be be delayed. One such system is the Linux kernel, where a call to
2960\&\f(CW\*(C`gettimeofday\*(C'\fR might return a timestamp with a full second later than
2961a subsequent \f(CW\*(C`time\*(C'\fR call \- if the equivalent of \f(CW\*(C`time ()\*(C'\fR is used to
2962update file times then there will be a small window where the kernel uses
2963the previous second to update file times but libev might already execute
2964the timer callback).
2965.PP
2966\fIWatcher-Specific Functions and Data Members\fR
2967.IX Subsection "Watcher-Specific Functions and Data Members"
1301.IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4 2968.IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
1302.IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 2969.IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
1303.PD 0 2970.PD 0
1304.IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4 2971.IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4
1305.IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 2972.IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)"
… …
1308\&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to 2975\&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to
1309be detected and should normally be specified as \f(CW0\fR to let libev choose 2976be detected and should normally be specified as \f(CW0\fR to let libev choose
1310a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same 2977a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same
1311path for as long as the watcher is active. 2978path for as long as the watcher is active.
1312.Sp 2979.Sp
1313The callback will be receive \f(CW\*(C`EV_STAT\*(C'\fR when a change was detected, 2980The callback will receive an \f(CW\*(C`EV_STAT\*(C'\fR event when a change was detected,
1314relative to the attributes at the time the watcher was started (or the 2981relative to the attributes at the time the watcher was started (or the
1315last change was detected). 2982last change was detected).
1316.IP "ev_stat_stat (ev_stat *)" 4 2983.IP "ev_stat_stat (loop, ev_stat *)" 4
1317.IX Item "ev_stat_stat (ev_stat *)" 2984.IX Item "ev_stat_stat (loop, ev_stat *)"
1318Updates the stat buffer immediately with new values. If you change the 2985Updates the stat buffer immediately with new values. If you change the
1319watched path in your callback, you could call this fucntion to avoid 2986watched path in your callback, you could call this function to avoid
1320detecting this change (while introducing a race condition). Can also be 2987detecting this change (while introducing a race condition if you are not
1321useful simply to find out the new values. 2988the only one changing the path). Can also be useful simply to find out the
2989new values.
1322.IP "ev_statdata attr [read\-only]" 4 2990.IP "ev_statdata attr [read\-only]" 4
1323.IX Item "ev_statdata attr [read-only]" 2991.IX Item "ev_statdata attr [read-only]"
1324The most-recently detected attributes of the file. Although the type is of 2992The most-recently detected attributes of the file. Although the type is
1325\&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types 2993\&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
2994suitable for your system, but you can only rely on the POSIX-standardised
1326suitable for your system. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there 2995members to be present. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there was
1327was some error while \f(CW\*(C`stat\*(C'\fRing the file. 2996some error while \f(CW\*(C`stat\*(C'\fRing the file.
1328.IP "ev_statdata prev [read\-only]" 4 2997.IP "ev_statdata prev [read\-only]" 4
1329.IX Item "ev_statdata prev [read-only]" 2998.IX Item "ev_statdata prev [read-only]"
1330The previous attributes of the file. The callback gets invoked whenever 2999The previous attributes of the file. The callback gets invoked whenever
1331\&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR. 3000\&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR, or, more precisely, one or more of these members
3001differ: \f(CW\*(C`st_dev\*(C'\fR, \f(CW\*(C`st_ino\*(C'\fR, \f(CW\*(C`st_mode\*(C'\fR, \f(CW\*(C`st_nlink\*(C'\fR, \f(CW\*(C`st_uid\*(C'\fR,
3002\&\f(CW\*(C`st_gid\*(C'\fR, \f(CW\*(C`st_rdev\*(C'\fR, \f(CW\*(C`st_size\*(C'\fR, \f(CW\*(C`st_atime\*(C'\fR, \f(CW\*(C`st_mtime\*(C'\fR, \f(CW\*(C`st_ctime\*(C'\fR.
1332.IP "ev_tstamp interval [read\-only]" 4 3003.IP "ev_tstamp interval [read\-only]" 4
1333.IX Item "ev_tstamp interval [read-only]" 3004.IX Item "ev_tstamp interval [read-only]"
1334The specified interval. 3005The specified interval.
1335.IP "const char *path [read\-only]" 4 3006.IP "const char *path [read\-only]" 4
1336.IX Item "const char *path [read-only]" 3007.IX Item "const char *path [read-only]"
1337The filesystem path that is being watched. 3008The file system path that is being watched.
3009.PP
3010\fIExamples\fR
3011.IX Subsection "Examples"
1338.PP 3012.PP
1339Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes. 3013Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
1340.PP 3014.PP
1341.Vb 15 3015.Vb 10
1342\& static void 3016\& static void
1343\& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents) 3017\& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1344\& { 3018\& {
1345\& /* /etc/passwd changed in some way */ 3019\& /* /etc/passwd changed in some way */
1346\& if (w->attr.st_nlink) 3020\& if (w\->attr.st_nlink)
1347\& { 3021\& {
1348\& printf ("passwd current size %ld\en", (long)w->attr.st_size); 3022\& printf ("passwd current size %ld\en", (long)w\->attr.st_size);
1349\& printf ("passwd current atime %ld\en", (long)w->attr.st_mtime); 3023\& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime);
1350\& printf ("passwd current mtime %ld\en", (long)w->attr.st_mtime); 3024\& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime);
1351\& } 3025\& }
1352\& else 3026\& else
1353\& /* you shalt not abuse printf for puts */ 3027\& /* you shalt not abuse printf for puts */
1354\& puts ("wow, /etc/passwd is not there, expect problems. " 3028\& puts ("wow, /etc/passwd is not there, expect problems. "
1355\& "if this is windows, they already arrived\en"); 3029\& "if this is windows, they already arrived\en");
1356\& } 3030\& }
3031\&
3032\& ...
3033\& ev_stat passwd;
3034\&
3035\& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
3036\& ev_stat_start (loop, &passwd);
1357.Ve 3037.Ve
3038.PP
3039Example: Like above, but additionally use a one-second delay so we do not
3040miss updates (however, frequent updates will delay processing, too, so
3041one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
3042\&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
1358.PP 3043.PP
1359.Vb 2 3044.Vb 2
3045\& static ev_stat passwd;
3046\& static ev_timer timer;
3047\&
3048\& static void
3049\& timer_cb (EV_P_ ev_timer *w, int revents)
3050\& {
3051\& ev_timer_stop (EV_A_ w);
3052\&
3053\& /* now it\*(Aqs one second after the most recent passwd change */
3054\& }
3055\&
3056\& static void
3057\& stat_cb (EV_P_ ev_stat *w, int revents)
3058\& {
3059\& /* reset the one\-second timer */
3060\& ev_timer_again (EV_A_ &timer);
3061\& }
3062\&
1360\& ... 3063\& ...
1361\& ev_stat passwd;
1362.Ve
1363.PP
1364.Vb 2
1365\& ev_stat_init (&passwd, passwd_cb, "/etc/passwd"); 3064\& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1366\& ev_stat_start (loop, &passwd); 3065\& ev_stat_start (loop, &passwd);
3066\& ev_timer_init (&timer, timer_cb, 0., 1.02);
1367.Ve 3067.Ve
1368.ie n .Sh """ev_idle"" \- when you've got nothing better to do..." 3068.ie n .SS """ev_idle"" \- when you've got nothing better to do..."
1369.el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do..." 3069.el .SS "\f(CWev_idle\fP \- when you've got nothing better to do..."
1370.IX Subsection "ev_idle - when you've got nothing better to do..." 3070.IX Subsection "ev_idle - when you've got nothing better to do..."
1371Idle watchers trigger events when there are no other events are pending 3071Idle watchers trigger events when no other events of the same or higher
1372(prepare, check and other idle watchers do not count). That is, as long 3072priority are pending (prepare, check and other idle watchers do not count
1373as your process is busy handling sockets or timeouts (or even signals, 3073as receiving \*(L"events\*(R").
1374imagine) it will not be triggered. But when your process is idle all idle 3074.PP
1375watchers are being called again and again, once per event loop iteration \- 3075That is, as long as your process is busy handling sockets or timeouts
3076(or even signals, imagine) of the same or higher priority it will not be
3077triggered. But when your process is idle (or only lower-priority watchers
3078are pending), the idle watchers are being called once per event loop
1376until stopped, that is, or your process receives more events and becomes 3079iteration \- until stopped, that is, or your process receives more events
1377busy. 3080and becomes busy again with higher priority stuff.
1378.PP 3081.PP
1379The most noteworthy effect is that as long as any idle watchers are 3082The most noteworthy effect is that as long as any idle watchers are
1380active, the process will not block when waiting for new events. 3083active, the process will not block when waiting for new events.
1381.PP 3084.PP
1382Apart from keeping your process non-blocking (which is a useful 3085Apart from keeping your process non-blocking (which is a useful
1383effect on its own sometimes), idle watchers are a good place to do 3086effect on its own sometimes), idle watchers are a good place to do
1384\&\*(L"pseudo\-background processing\*(R", or delay processing stuff to after the 3087\&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the
1385event loop has handled all outstanding events. 3088event loop has handled all outstanding events.
3089.PP
3090\fIAbusing an \f(CI\*(C`ev_idle\*(C'\fI watcher for its side-effect\fR
3091.IX Subsection "Abusing an ev_idle watcher for its side-effect"
3092.PP
3093As long as there is at least one active idle watcher, libev will never
3094sleep unnecessarily. Or in other words, it will loop as fast as possible.
3095For this to work, the idle watcher doesn't need to be invoked at all \- the
3096lowest priority will do.
3097.PP
3098This mode of operation can be useful together with an \f(CW\*(C`ev_check\*(C'\fR watcher,
3099to do something on each event loop iteration \- for example to balance load
3100between different connections.
3101.PP
3102See \*(L"Abusing an ev_check watcher for its side-effect\*(R" for a longer
3103example.
3104.PP
3105\fIWatcher-Specific Functions and Data Members\fR
3106.IX Subsection "Watcher-Specific Functions and Data Members"
1386.IP "ev_idle_init (ev_signal *, callback)" 4 3107.IP "ev_idle_init (ev_idle *, callback)" 4
1387.IX Item "ev_idle_init (ev_signal *, callback)" 3108.IX Item "ev_idle_init (ev_idle *, callback)"
1388Initialises and configures the idle watcher \- it has no parameters of any 3109Initialises and configures the idle watcher \- it has no parameters of any
1389kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless, 3110kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
1390believe me. 3111believe me.
1391.PP 3112.PP
3113\fIExamples\fR
3114.IX Subsection "Examples"
3115.PP
1392Example: dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR, start it, and in the 3116Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the
1393callback, free it. Alos, use no error checking, as usual. 3117callback, free it. Also, use no error checking, as usual.
1394.PP 3118.PP
1395.Vb 7 3119.Vb 5
1396\& static void 3120\& static void
1397\& idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents) 3121\& idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1398\& { 3122\& {
3123\& // stop the watcher
3124\& ev_idle_stop (loop, w);
3125\&
3126\& // now we can free it
1399\& free (w); 3127\& free (w);
3128\&
1400\& // now do something you wanted to do when the program has 3129\& // now do something you wanted to do when the program has
1401\& // no longer asnything immediate to do. 3130\& // no longer anything immediate to do.
1402\& } 3131\& }
1403.Ve 3132\&
1404.PP
1405.Vb 3
1406\& struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle)); 3133\& ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1407\& ev_idle_init (idle_watcher, idle_cb); 3134\& ev_idle_init (idle_watcher, idle_cb);
1408\& ev_idle_start (loop, idle_cb); 3135\& ev_idle_start (loop, idle_watcher);
1409.Ve 3136.Ve
1410.ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop!" 3137.ie n .SS """ev_prepare"" and ""ev_check"" \- customise your event loop!"
1411.el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!" 3138.el .SS "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
1412.IX Subsection "ev_prepare and ev_check - customise your event loop!" 3139.IX Subsection "ev_prepare and ev_check - customise your event loop!"
1413Prepare and check watchers are usually (but not always) used in tandem: 3140Prepare and check watchers are often (but not always) used in pairs:
1414prepare watchers get invoked before the process blocks and check watchers 3141prepare watchers get invoked before the process blocks and check watchers
1415afterwards. 3142afterwards.
1416.PP 3143.PP
1417You \fImust not\fR call \f(CW\*(C`ev_loop\*(C'\fR or similar functions that enter 3144You \fImust not\fR call \f(CW\*(C`ev_run\*(C'\fR (or similar functions that enter the
1418the current event loop from either \f(CW\*(C`ev_prepare\*(C'\fR or \f(CW\*(C`ev_check\*(C'\fR 3145current event loop) or \f(CW\*(C`ev_loop_fork\*(C'\fR from either \f(CW\*(C`ev_prepare\*(C'\fR or
1419watchers. Other loops than the current one are fine, however. The 3146\&\f(CW\*(C`ev_check\*(C'\fR watchers. Other loops than the current one are fine,
1420rationale behind this is that you do not need to check for recursion in 3147however. The rationale behind this is that you do not need to check
1421those watchers, i.e. the sequence will always be \f(CW\*(C`ev_prepare\*(C'\fR, blocking, 3148for recursion in those watchers, i.e. the sequence will always be
1422\&\f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each kind they will always be 3149\&\f(CW\*(C`ev_prepare\*(C'\fR, blocking, \f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each
1423called in pairs bracketing the blocking call. 3150kind they will always be called in pairs bracketing the blocking call.
1424.PP 3151.PP
1425Their main purpose is to integrate other event mechanisms into libev and 3152Their main purpose is to integrate other event mechanisms into libev and
1426their use is somewhat advanced. This could be used, for example, to track 3153their use is somewhat advanced. They could be used, for example, to track
1427variable changes, implement your own watchers, integrate net-snmp or a 3154variable changes, implement your own watchers, integrate net-snmp or a
1428coroutine library and lots more. They are also occasionally useful if 3155coroutine library and lots more. They are also occasionally useful if
1429you cache some data and want to flush it before blocking (for example, 3156you cache some data and want to flush it before blocking (for example,
1430in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR 3157in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
1431watcher). 3158watcher).
1432.PP 3159.PP
1433This is done by examining in each prepare call which file descriptors need 3160This is done by examining in each prepare call which file descriptors
1434to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers for 3161need to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers
1435them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many libraries 3162for them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many
1436provide just this functionality). Then, in the check watcher you check for 3163libraries provide exactly this functionality). Then, in the check watcher,
1437any events that occured (by checking the pending status of all watchers 3164you check for any events that occurred (by checking the pending status
1438and stopping them) and call back into the library. The I/O and timer 3165of all watchers and stopping them) and call back into the library. The
1439callbacks will never actually be called (but must be valid nevertheless, 3166I/O and timer callbacks will never actually be called (but must be valid
1440because you never know, you know?). 3167nevertheless, because you never know, you know?).
1441.PP 3168.PP
1442As another example, the Perl Coro module uses these hooks to integrate 3169As another example, the Perl Coro module uses these hooks to integrate
1443coroutines into libev programs, by yielding to other active coroutines 3170coroutines into libev programs, by yielding to other active coroutines
1444during each prepare and only letting the process block if no coroutines 3171during each prepare and only letting the process block if no coroutines
1445are ready to run (it's actually more complicated: it only runs coroutines 3172are ready to run (it's actually more complicated: it only runs coroutines
1446with priority higher than or equal to the event loop and one coroutine 3173with priority higher than or equal to the event loop and one coroutine
1447of lower priority, but only once, using idle watchers to keep the event 3174of lower priority, but only once, using idle watchers to keep the event
1448loop from blocking if lower-priority coroutines are active, thus mapping 3175loop from blocking if lower-priority coroutines are active, thus mapping
1449low-priority coroutines to idle/background tasks). 3176low-priority coroutines to idle/background tasks).
3177.PP
3178When used for this purpose, it is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers
3179highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR) priority, to ensure that they are being run before
3180any other watchers after the poll (this doesn't matter for \f(CW\*(C`ev_prepare\*(C'\fR
3181watchers).
3182.PP
3183Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, too) should not
3184activate (\*(L"feed\*(R") events into libev. While libev fully supports this, they
3185might get executed before other \f(CW\*(C`ev_check\*(C'\fR watchers did their job. As
3186\&\f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other (non-libev) event
3187loops those other event loops might be in an unusable state until their
3188\&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with
3189others).
3190.PP
3191\fIAbusing an \f(CI\*(C`ev_check\*(C'\fI watcher for its side-effect\fR
3192.IX Subsection "Abusing an ev_check watcher for its side-effect"
3193.PP
3194\&\f(CW\*(C`ev_check\*(C'\fR (and less often also \f(CW\*(C`ev_prepare\*(C'\fR) watchers can also be
3195useful because they are called once per event loop iteration. For
3196example, if you want to handle a large number of connections fairly, you
3197normally only do a bit of work for each active connection, and if there
3198is more work to do, you wait for the next event loop iteration, so other
3199connections have a chance of making progress.
3200.PP
3201Using an \f(CW\*(C`ev_check\*(C'\fR watcher is almost enough: it will be called on the
3202next event loop iteration. However, that isn't as soon as possible \-
3203without external events, your \f(CW\*(C`ev_check\*(C'\fR watcher will not be invoked.
3204.PP
3205This is where \f(CW\*(C`ev_idle\*(C'\fR watchers come in handy \- all you need is a
3206single global idle watcher that is active as long as you have one active
3207\&\f(CW\*(C`ev_check\*(C'\fR watcher. The \f(CW\*(C`ev_idle\*(C'\fR watcher makes sure the event loop
3208will not sleep, and the \f(CW\*(C`ev_check\*(C'\fR watcher makes sure a callback gets
3209invoked. Neither watcher alone can do that.
3210.PP
3211\fIWatcher-Specific Functions and Data Members\fR
3212.IX Subsection "Watcher-Specific Functions and Data Members"
1450.IP "ev_prepare_init (ev_prepare *, callback)" 4 3213.IP "ev_prepare_init (ev_prepare *, callback)" 4
1451.IX Item "ev_prepare_init (ev_prepare *, callback)" 3214.IX Item "ev_prepare_init (ev_prepare *, callback)"
1452.PD 0 3215.PD 0
1453.IP "ev_check_init (ev_check *, callback)" 4 3216.IP "ev_check_init (ev_check *, callback)" 4
1454.IX Item "ev_check_init (ev_check *, callback)" 3217.IX Item "ev_check_init (ev_check *, callback)"
1455.PD 3218.PD
1456Initialises and configures the prepare or check watcher \- they have no 3219Initialises and configures the prepare or check watcher \- they have no
1457parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR 3220parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
1458macros, but using them is utterly, utterly and completely pointless. 3221macros, but using them is utterly, utterly, utterly and completely
3222pointless.
1459.PP 3223.PP
1460Example: To include a library such as adns, you would add \s-1IO\s0 watchers 3224\fIExamples\fR
1461and a timeout watcher in a prepare handler, as required by libadns, and 3225.IX Subsection "Examples"
3226.PP
3227There are a number of principal ways to embed other event loops or modules
3228into libev. Here are some ideas on how to include libadns into libev
3229(there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could
3230use as a working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR embeds a
3231Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 into the
3232Glib event loop).
3233.PP
3234Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
1462in a check watcher, destroy them and call into libadns. What follows is 3235and in a check watcher, destroy them and call into libadns. What follows
1463pseudo-code only of course: 3236is pseudo-code only of course. This requires you to either use a low
3237priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as
3238the callbacks for the IO/timeout watchers might not have been called yet.
1464.PP 3239.PP
1465.Vb 2 3240.Vb 2
1466\& static ev_io iow [nfd]; 3241\& static ev_io iow [nfd];
1467\& static ev_timer tw; 3242\& static ev_timer tw;
1468.Ve 3243\&
1469.PP
1470.Vb 9
1471\& static void 3244\& static void
1472\& io_cb (ev_loop *loop, ev_io *w, int revents) 3245\& io_cb (struct ev_loop *loop, ev_io *w, int revents)
1473\& { 3246\& {
1474\& // set the relevant poll flags
1475\& // could also call adns_processreadable etc. here
1476\& struct pollfd *fd = (struct pollfd *)w->data;
1477\& if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1478\& if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1479\& } 3247\& }
1480.Ve 3248\&
1481.PP
1482.Vb 7
1483\& // create io watchers for each fd and a timer before blocking 3249\& // create io watchers for each fd and a timer before blocking
1484\& static void 3250\& static void
1485\& adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents) 3251\& adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1486\& { 3252\& {
1487\& int timeout = 3600000;truct pollfd fds [nfd]; 3253\& int timeout = 3600000;
3254\& struct pollfd fds [nfd];
1488\& // actual code will need to loop here and realloc etc. 3255\& // actual code will need to loop here and realloc etc.
1489\& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ())); 3256\& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1490.Ve 3257\&
1491.PP
1492.Vb 3
1493\& /* the callback is illegal, but won't be called as we stop during check */ 3258\& /* the callback is illegal, but won\*(Aqt be called as we stop during check */
1494\& ev_timer_init (&tw, 0, timeout * 1e-3); 3259\& ev_timer_init (&tw, 0, timeout * 1e\-3, 0.);
1495\& ev_timer_start (loop, &tw); 3260\& ev_timer_start (loop, &tw);
1496.Ve 3261\&
1497.PP
1498.Vb 6
1499\& // create on ev_io per pollfd 3262\& // create one ev_io per pollfd
1500\& for (int i = 0; i < nfd; ++i) 3263\& for (int i = 0; i < nfd; ++i)
1501\& { 3264\& {
1502\& ev_io_init (iow + i, io_cb, fds [i].fd, 3265\& ev_io_init (iow + i, io_cb, fds [i].fd,
1503\& ((fds [i].events & POLLIN ? EV_READ : 0) 3266\& ((fds [i].events & POLLIN ? EV_READ : 0)
1504\& | (fds [i].events & POLLOUT ? EV_WRITE : 0))); 3267\& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
3268\&
3269\& fds [i].revents = 0;
3270\& ev_io_start (loop, iow + i);
3271\& }
3272\& }
3273\&
3274\& // stop all watchers after blocking
3275\& static void
3276\& adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
3277\& {
3278\& ev_timer_stop (loop, &tw);
3279\&
3280\& for (int i = 0; i < nfd; ++i)
3281\& {
3282\& // set the relevant poll flags
3283\& // could also call adns_processreadable etc. here
3284\& struct pollfd *fd = fds + i;
3285\& int revents = ev_clear_pending (iow + i);
3286\& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN;
3287\& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT;
3288\&
3289\& // now stop the watcher
3290\& ev_io_stop (loop, iow + i);
3291\& }
3292\&
3293\& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
3294\& }
1505.Ve 3295.Ve
3296.PP
3297Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR
3298in the prepare watcher and would dispose of the check watcher.
3299.PP
3300Method 3: If the module to be embedded supports explicit event
3301notification (libadns does), you can also make use of the actual watcher
3302callbacks, and only destroy/create the watchers in the prepare watcher.
1506.PP 3303.PP
1507.Vb 5 3304.Vb 5
1508\& fds [i].revents = 0;
1509\& iow [i].data = fds + i;
1510\& ev_io_start (loop, iow + i);
1511\& }
1512\& }
1513.Ve
1514.PP
1515.Vb 5
1516\& // stop all watchers after blocking
1517\& static void 3305\& static void
1518\& adns_check_cb (ev_loop *loop, ev_check *w, int revents) 3306\& timer_cb (EV_P_ ev_timer *w, int revents)
1519\& { 3307\& {
1520\& ev_timer_stop (loop, &tw); 3308\& adns_state ads = (adns_state)w\->data;
1521.Ve 3309\& update_now (EV_A);
1522.PP 3310\&
1523.Vb 2 3311\& adns_processtimeouts (ads, &tv_now);
1524\& for (int i = 0; i < nfd; ++i)
1525\& ev_io_stop (loop, iow + i);
1526.Ve
1527.PP
1528.Vb 2
1529\& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1530\& } 3312\& }
3313\&
3314\& static void
3315\& io_cb (EV_P_ ev_io *w, int revents)
3316\& {
3317\& adns_state ads = (adns_state)w\->data;
3318\& update_now (EV_A);
3319\&
3320\& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now);
3321\& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now);
3322\& }
3323\&
3324\& // do not ever call adns_afterpoll
1531.Ve 3325.Ve
3326.PP
3327Method 4: Do not use a prepare or check watcher because the module you
3328want to embed is not flexible enough to support it. Instead, you can
3329override their poll function. The drawback with this solution is that the
3330main loop is now no longer controllable by \s-1EV.\s0 The \f(CW\*(C`Glib::EV\*(C'\fR module uses
3331this approach, effectively embedding \s-1EV\s0 as a client into the horrible
3332libglib event loop.
3333.PP
3334.Vb 4
3335\& static gint
3336\& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
3337\& {
3338\& int got_events = 0;
3339\&
3340\& for (n = 0; n < nfds; ++n)
3341\& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
3342\&
3343\& if (timeout >= 0)
3344\& // create/start timer
3345\&
3346\& // poll
3347\& ev_run (EV_A_ 0);
3348\&
3349\& // stop timer again
3350\& if (timeout >= 0)
3351\& ev_timer_stop (EV_A_ &to);
3352\&
3353\& // stop io watchers again \- their callbacks should have set
3354\& for (n = 0; n < nfds; ++n)
3355\& ev_io_stop (EV_A_ iow [n]);
3356\&
3357\& return got_events;
3358\& }
3359.Ve
1532.ie n .Sh """ev_embed"" \- when one backend isn't enough..." 3360.ie n .SS """ev_embed"" \- when one backend isn't enough..."
1533.el .Sh "\f(CWev_embed\fP \- when one backend isn't enough..." 3361.el .SS "\f(CWev_embed\fP \- when one backend isn't enough..."
1534.IX Subsection "ev_embed - when one backend isn't enough..." 3362.IX Subsection "ev_embed - when one backend isn't enough..."
1535This is a rather advanced watcher type that lets you embed one event loop 3363This is a rather advanced watcher type that lets you embed one event loop
1536into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded 3364into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
1537loop, other types of watchers might be handled in a delayed or incorrect 3365loop, other types of watchers might be handled in a delayed or incorrect
1538fashion and must not be used). 3366fashion and must not be used).
… …
1541prioritise I/O. 3369prioritise I/O.
1542.PP 3370.PP
1543As an example for a bug workaround, the kqueue backend might only support 3371As an example for a bug workaround, the kqueue backend might only support
1544sockets on some platform, so it is unusable as generic backend, but you 3372sockets on some platform, so it is unusable as generic backend, but you
1545still want to make use of it because you have many sockets and it scales 3373still want to make use of it because you have many sockets and it scales
1546so nicely. In this case, you would create a kqueue-based loop and embed it 3374so nicely. In this case, you would create a kqueue-based loop and embed
1547into your default loop (which might use e.g. poll). Overall operation will 3375it into your default loop (which might use e.g. poll). Overall operation
1548be a bit slower because first libev has to poll and then call kevent, but 3376will be a bit slower because first libev has to call \f(CW\*(C`poll\*(C'\fR and then
1549at least you can use both at what they are best. 3377\&\f(CW\*(C`kevent\*(C'\fR, but at least you can use both mechanisms for what they are
3378best: \f(CW\*(C`kqueue\*(C'\fR for scalable sockets and \f(CW\*(C`poll\*(C'\fR if you want it to work :)
1550.PP 3379.PP
1551As for prioritising I/O: rarely you have the case where some fds have 3380As for prioritising I/O: under rare circumstances you have the case where
1552to be watched and handled very quickly (with low latency), and even 3381some fds have to be watched and handled very quickly (with low latency),
1553priorities and idle watchers might have too much overhead. In this case 3382and even priorities and idle watchers might have too much overhead. In
1554you would put all the high priority stuff in one loop and all the rest in 3383this case you would put all the high priority stuff in one loop and all
1555a second one, and embed the second one in the first. 3384the rest in a second one, and embed the second one in the first.
1556.PP 3385.PP
1557As long as the watcher is active, the callback will be invoked every time 3386As long as the watcher is active, the callback will be invoked every
1558there might be events pending in the embedded loop. The callback must then 3387time there might be events pending in the embedded loop. The callback
1559call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single sweep and invoke 3388must then call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single
1560their callbacks (you could also start an idle watcher to give the embedded 3389sweep and invoke their callbacks (the callback doesn't need to invoke the
1561loop strictly lower priority for example). You can also set the callback 3390\&\f(CW\*(C`ev_embed_sweep\*(C'\fR function directly, it could also start an idle watcher
1562to \f(CW0\fR, in which case the embed watcher will automatically execute the 3391to give the embedded loop strictly lower priority for example).
1563embedded loop sweep.
1564.PP 3392.PP
1565As long as the watcher is started it will automatically handle events. The 3393You can also set the callback to \f(CW0\fR, in which case the embed watcher
1566callback will be invoked whenever some events have been handled. You can 3394will automatically execute the embedded loop sweep whenever necessary.
1567set the callback to \f(CW0\fR to avoid having to specify one if you are not
1568interested in that.
1569.PP 3395.PP
1570Also, there have not currently been made special provisions for forking: 3396Fork detection will be handled transparently while the \f(CW\*(C`ev_embed\*(C'\fR watcher
1571when you fork, you not only have to call \f(CW\*(C`ev_loop_fork\*(C'\fR on both loops, 3397is active, i.e., the embedded loop will automatically be forked when the
1572but you will also have to stop and restart any \f(CW\*(C`ev_embed\*(C'\fR watchers 3398embedding loop forks. In other cases, the user is responsible for calling
1573yourself. 3399\&\f(CW\*(C`ev_loop_fork\*(C'\fR on the embedded loop.
1574.PP 3400.PP
1575Unfortunately, not all backends are embeddable, only the ones returned by 3401Unfortunately, not all backends are embeddable: only the ones returned by
1576\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any 3402\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
1577portable one. 3403portable one.
1578.PP 3404.PP
1579So when you want to use this feature you will always have to be prepared 3405So when you want to use this feature you will always have to be prepared
1580that you cannot get an embeddable loop. The recommended way to get around 3406that you cannot get an embeddable loop. The recommended way to get around
1581this is to have a separate variables for your embeddable loop, try to 3407this is to have a separate variables for your embeddable loop, try to
1582create it, and if that fails, use the normal loop for everything: 3408create it, and if that fails, use the normal loop for everything.
1583.PP 3409.PP
1584.Vb 3 3410\fI\f(CI\*(C`ev_embed\*(C'\fI and fork\fR
1585\& struct ev_loop *loop_hi = ev_default_init (0); 3411.IX Subsection "ev_embed and fork"
1586\& struct ev_loop *loop_lo = 0;
1587\& struct ev_embed embed;
1588.Ve
1589.PP 3412.PP
1590.Vb 5 3413While the \f(CW\*(C`ev_embed\*(C'\fR watcher is running, forks in the embedding loop will
1591\& // see if there is a chance of getting one that works 3414automatically be applied to the embedded loop as well, so no special
1592\& // (remember that a flags value of 0 means autodetection) 3415fork handling is required in that case. When the watcher is not running,
1593\& loop_lo = ev_embeddable_backends () & ev_recommended_backends () 3416however, it is still the task of the libev user to call \f(CW\*(C`ev_loop_fork ()\*(C'\fR
1594\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ()) 3417as applicable.
1595\& : 0;
1596.Ve
1597.PP 3418.PP
1598.Vb 8 3419\fIWatcher-Specific Functions and Data Members\fR
1599\& // if we got one, then embed it, otherwise default to loop_hi 3420.IX Subsection "Watcher-Specific Functions and Data Members"
1600\& if (loop_lo)
1601\& {
1602\& ev_embed_init (&embed, 0, loop_lo);
1603\& ev_embed_start (loop_hi, &embed);
1604\& }
1605\& else
1606\& loop_lo = loop_hi;
1607.Ve
1608.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4 3421.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
1609.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 3422.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
1610.PD 0 3423.PD 0
1611.IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4 3424.IP "ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)" 4
1612.IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 3425.IX Item "ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)"
1613.PD 3426.PD
1614Configures the watcher to embed the given loop, which must be 3427Configures the watcher to embed the given loop, which must be
1615embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be 3428embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
1616invoked automatically, otherwise it is the responsibility of the callback 3429invoked automatically, otherwise it is the responsibility of the callback
1617to invoke it (it will continue to be called until the sweep has been done, 3430to invoke it (it will continue to be called until the sweep has been done,
1618if you do not want thta, you need to temporarily stop the embed watcher). 3431if you do not want that, you need to temporarily stop the embed watcher).
1619.IP "ev_embed_sweep (loop, ev_embed *)" 4 3432.IP "ev_embed_sweep (loop, ev_embed *)" 4
1620.IX Item "ev_embed_sweep (loop, ev_embed *)" 3433.IX Item "ev_embed_sweep (loop, ev_embed *)"
1621Make a single, non-blocking sweep over the embedded loop. This works 3434Make a single, non-blocking sweep over the embedded loop. This works
1622similarly to \f(CW\*(C`ev_loop (embedded_loop, EVLOOP_NONBLOCK)\*(C'\fR, but in the most 3435similarly to \f(CW\*(C`ev_run (embedded_loop, EVRUN_NOWAIT)\*(C'\fR, but in the most
1623apropriate way for embedded loops. 3436appropriate way for embedded loops.
1624.IP "struct ev_loop *loop [read\-only]" 4 3437.IP "struct ev_loop *other [read\-only]" 4
1625.IX Item "struct ev_loop *loop [read-only]" 3438.IX Item "struct ev_loop *other [read-only]"
1626The embedded event loop. 3439The embedded event loop.
3440.PP
3441\fIExamples\fR
3442.IX Subsection "Examples"
3443.PP
3444Example: Try to get an embeddable event loop and embed it into the default
3445event loop. If that is not possible, use the default loop. The default
3446loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the embeddable loop is stored in
3447\&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the case no embeddable loop can be
3448used).
3449.PP
3450.Vb 3
3451\& struct ev_loop *loop_hi = ev_default_init (0);
3452\& struct ev_loop *loop_lo = 0;
3453\& ev_embed embed;
3454\&
3455\& // see if there is a chance of getting one that works
3456\& // (remember that a flags value of 0 means autodetection)
3457\& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3458\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3459\& : 0;
3460\&
3461\& // if we got one, then embed it, otherwise default to loop_hi
3462\& if (loop_lo)
3463\& {
3464\& ev_embed_init (&embed, 0, loop_lo);
3465\& ev_embed_start (loop_hi, &embed);
3466\& }
3467\& else
3468\& loop_lo = loop_hi;
3469.Ve
3470.PP
3471Example: Check if kqueue is available but not recommended and create
3472a kqueue backend for use with sockets (which usually work with any
3473kqueue implementation). Store the kqueue/socket\-only event loop in
3474\&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too).
3475.PP
3476.Vb 3
3477\& struct ev_loop *loop = ev_default_init (0);
3478\& struct ev_loop *loop_socket = 0;
3479\& ev_embed embed;
3480\&
3481\& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3482\& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3483\& {
3484\& ev_embed_init (&embed, 0, loop_socket);
3485\& ev_embed_start (loop, &embed);
3486\& }
3487\&
3488\& if (!loop_socket)
3489\& loop_socket = loop;
3490\&
3491\& // now use loop_socket for all sockets, and loop for everything else
3492.Ve
1627.ie n .Sh """ev_fork"" \- the audacity to resume the event loop after a fork" 3493.ie n .SS """ev_fork"" \- the audacity to resume the event loop after a fork"
1628.el .Sh "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork" 3494.el .SS "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
1629.IX Subsection "ev_fork - the audacity to resume the event loop after a fork" 3495.IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
1630Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because 3496Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
1631whoever is a good citizen cared to tell libev about it by calling 3497whoever is a good citizen cared to tell libev about it by calling
1632\&\f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the 3498\&\f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the event loop blocks next
1633event loop blocks next and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called, 3499and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called, and only in the child
1634and only in the child after the fork. If whoever good citizen calling 3500after the fork. If whoever good citizen calling \f(CW\*(C`ev_default_fork\*(C'\fR cheats
1635\&\f(CW\*(C`ev_default_fork\*(C'\fR cheats and calls it in the wrong process, the fork 3501and calls it in the wrong process, the fork handlers will be invoked, too,
1636handlers will be invoked, too, of course. 3502of course.
3503.PP
3504\fIThe special problem of life after fork \- how is it possible?\fR
3505.IX Subsection "The special problem of life after fork - how is it possible?"
3506.PP
3507Most uses of \f(CW\*(C`fork ()\*(C'\fR consist of forking, then some simple calls to set
3508up/change the process environment, followed by a call to \f(CW\*(C`exec()\*(C'\fR. This
3509sequence should be handled by libev without any problems.
3510.PP
3511This changes when the application actually wants to do event handling
3512in the child, or both parent in child, in effect \*(L"continuing\*(R" after the
3513fork.
3514.PP
3515The default mode of operation (for libev, with application help to detect
3516forks) is to duplicate all the state in the child, as would be expected
3517when \fIeither\fR the parent \fIor\fR the child process continues.
3518.PP
3519When both processes want to continue using libev, then this is usually the
3520wrong result. In that case, usually one process (typically the parent) is
3521supposed to continue with all watchers in place as before, while the other
3522process typically wants to start fresh, i.e. without any active watchers.
3523.PP
3524The cleanest and most efficient way to achieve that with libev is to
3525simply create a new event loop, which of course will be \*(L"empty\*(R", and
3526use that for new watchers. This has the advantage of not touching more
3527memory than necessary, and thus avoiding the copy-on-write, and the
3528disadvantage of having to use multiple event loops (which do not support
3529signal watchers).
3530.PP
3531When this is not possible, or you want to use the default loop for
3532other reasons, then in the process that wants to start \*(L"fresh\*(R", call
3533\&\f(CW\*(C`ev_loop_destroy (EV_DEFAULT)\*(C'\fR followed by \f(CW\*(C`ev_default_loop (...)\*(C'\fR.
3534Destroying the default loop will \*(L"orphan\*(R" (not stop) all registered
3535watchers, so you have to be careful not to execute code that modifies
3536those watchers. Note also that in that case, you have to re-register any
3537signal watchers.
3538.PP
3539\fIWatcher-Specific Functions and Data Members\fR
3540.IX Subsection "Watcher-Specific Functions and Data Members"
1637.IP "ev_fork_init (ev_signal *, callback)" 4 3541.IP "ev_fork_init (ev_fork *, callback)" 4
1638.IX Item "ev_fork_init (ev_signal *, callback)" 3542.IX Item "ev_fork_init (ev_fork *, callback)"
1639Initialises and configures the fork watcher \- it has no parameters of any 3543Initialises and configures the fork watcher \- it has no parameters of any
1640kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless, 3544kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
1641believe me. 3545really.
3546.ie n .SS """ev_cleanup"" \- even the best things end"
3547.el .SS "\f(CWev_cleanup\fP \- even the best things end"
3548.IX Subsection "ev_cleanup - even the best things end"
3549Cleanup watchers are called just before the event loop is being destroyed
3550by a call to \f(CW\*(C`ev_loop_destroy\*(C'\fR.
3551.PP
3552While there is no guarantee that the event loop gets destroyed, cleanup
3553watchers provide a convenient method to install cleanup hooks for your
3554program, worker threads and so on \- you just to make sure to destroy the
3555loop when you want them to be invoked.
3556.PP
3557Cleanup watchers are invoked in the same way as any other watcher. Unlike
3558all other watchers, they do not keep a reference to the event loop (which
3559makes a lot of sense if you think about it). Like all other watchers, you
3560can call libev functions in the callback, except \f(CW\*(C`ev_cleanup_start\*(C'\fR.
3561.PP
3562\fIWatcher-Specific Functions and Data Members\fR
3563.IX Subsection "Watcher-Specific Functions and Data Members"
3564.IP "ev_cleanup_init (ev_cleanup *, callback)" 4
3565.IX Item "ev_cleanup_init (ev_cleanup *, callback)"
3566Initialises and configures the cleanup watcher \- it has no parameters of
3567any kind. There is a \f(CW\*(C`ev_cleanup_set\*(C'\fR macro, but using it is utterly
3568pointless, I assure you.
3569.PP
3570Example: Register an atexit handler to destroy the default loop, so any
3571cleanup functions are called.
3572.PP
3573.Vb 5
3574\& static void
3575\& program_exits (void)
3576\& {
3577\& ev_loop_destroy (EV_DEFAULT_UC);
3578\& }
3579\&
3580\& ...
3581\& atexit (program_exits);
3582.Ve
3583.ie n .SS """ev_async"" \- how to wake up an event loop"
3584.el .SS "\f(CWev_async\fP \- how to wake up an event loop"
3585.IX Subsection "ev_async - how to wake up an event loop"
3586In general, you cannot use an \f(CW\*(C`ev_loop\*(C'\fR from multiple threads or other
3587asynchronous sources such as signal handlers (as opposed to multiple event
3588loops \- those are of course safe to use in different threads).
3589.PP
3590Sometimes, however, you need to wake up an event loop you do not control,
3591for example because it belongs to another thread. This is what \f(CW\*(C`ev_async\*(C'\fR
3592watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you can signal
3593it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal safe.
3594.PP
3595This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals,
3596too, are asynchronous in nature, and signals, too, will be compressed
3597(i.e. the number of callback invocations may be less than the number of
3598\&\f(CW\*(C`ev_async_send\*(C'\fR calls). In fact, you could use signal watchers as a kind
3599of \*(L"global async watchers\*(R" by using a watcher on an otherwise unused
3600signal, and \f(CW\*(C`ev_feed_signal\*(C'\fR to signal this watcher from another thread,
3601even without knowing which loop owns the signal.
3602.PP
3603\fIQueueing\fR
3604.IX Subsection "Queueing"
3605.PP
3606\&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason
3607is that the author does not know of a simple (or any) algorithm for a
3608multiple-writer-single-reader queue that works in all cases and doesn't
3609need elaborate support such as pthreads or unportable memory access
3610semantics.
3611.PP
3612That means that if you want to queue data, you have to provide your own
3613queue. But at least I can tell you how to implement locking around your
3614queue:
3615.IP "queueing from a signal handler context" 4
3616.IX Item "queueing from a signal handler context"
3617To implement race-free queueing, you simply add to the queue in the signal
3618handler but you block the signal handler in the watcher callback. Here is
3619an example that does that for some fictitious \s-1SIGUSR1\s0 handler:
3620.Sp
3621.Vb 1
3622\& static ev_async mysig;
3623\&
3624\& static void
3625\& sigusr1_handler (void)
3626\& {
3627\& sometype data;
3628\&
3629\& // no locking etc.
3630\& queue_put (data);
3631\& ev_async_send (EV_DEFAULT_ &mysig);
3632\& }
3633\&
3634\& static void
3635\& mysig_cb (EV_P_ ev_async *w, int revents)
3636\& {
3637\& sometype data;
3638\& sigset_t block, prev;
3639\&
3640\& sigemptyset (&block);
3641\& sigaddset (&block, SIGUSR1);
3642\& sigprocmask (SIG_BLOCK, &block, &prev);
3643\&
3644\& while (queue_get (&data))
3645\& process (data);
3646\&
3647\& if (sigismember (&prev, SIGUSR1)
3648\& sigprocmask (SIG_UNBLOCK, &block, 0);
3649\& }
3650.Ve
3651.Sp
3652(Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR
3653instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it
3654either...).
3655.IP "queueing from a thread context" 4
3656.IX Item "queueing from a thread context"
3657The strategy for threads is different, as you cannot (easily) block
3658threads but you can easily preempt them, so to queue safely you need to
3659employ a traditional mutex lock, such as in this pthread example:
3660.Sp
3661.Vb 2
3662\& static ev_async mysig;
3663\& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
3664\&
3665\& static void
3666\& otherthread (void)
3667\& {
3668\& // only need to lock the actual queueing operation
3669\& pthread_mutex_lock (&mymutex);
3670\& queue_put (data);
3671\& pthread_mutex_unlock (&mymutex);
3672\&
3673\& ev_async_send (EV_DEFAULT_ &mysig);
3674\& }
3675\&
3676\& static void
3677\& mysig_cb (EV_P_ ev_async *w, int revents)
3678\& {
3679\& pthread_mutex_lock (&mymutex);
3680\&
3681\& while (queue_get (&data))
3682\& process (data);
3683\&
3684\& pthread_mutex_unlock (&mymutex);
3685\& }
3686.Ve
3687.PP
3688\fIWatcher-Specific Functions and Data Members\fR
3689.IX Subsection "Watcher-Specific Functions and Data Members"
3690.IP "ev_async_init (ev_async *, callback)" 4
3691.IX Item "ev_async_init (ev_async *, callback)"
3692Initialises and configures the async watcher \- it has no parameters of any
3693kind. There is a \f(CW\*(C`ev_async_set\*(C'\fR macro, but using it is utterly pointless,
3694trust me.
3695.IP "ev_async_send (loop, ev_async *)" 4
3696.IX Item "ev_async_send (loop, ev_async *)"
3697Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds
3698an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop, and instantly
3699returns.
3700.Sp
3701Unlike \f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do from other threads,
3702signal or similar contexts (see the discussion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the
3703embedding section below on what exactly this means).
3704.Sp
3705Note that, as with other watchers in libev, multiple events might get
3706compressed into a single callback invocation (another way to look at
3707this is that \f(CW\*(C`ev_async\*(C'\fR watchers are level-triggered: they are set on
3708\&\f(CW\*(C`ev_async_send\*(C'\fR, reset when the event loop detects that).
3709.Sp
3710This call incurs the overhead of at most one extra system call per event
3711loop iteration, if the event loop is blocked, and no syscall at all if
3712the event loop (or your program) is processing events. That means that
3713repeated calls are basically free (there is no need to avoid calls for
3714performance reasons) and that the overhead becomes smaller (typically
3715zero) under load.
3716.IP "bool = ev_async_pending (ev_async *)" 4
3717.IX Item "bool = ev_async_pending (ev_async *)"
3718Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the
3719watcher but the event has not yet been processed (or even noted) by the
3720event loop.
3721.Sp
3722\&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When
3723the loop iterates next and checks for the watcher to have become active,
3724it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very
3725quickly check whether invoking the loop might be a good idea.
3726.Sp
3727Not that this does \fInot\fR check whether the watcher itself is pending,
3728only whether it has been requested to make this watcher pending: there
3729is a time window between the event loop checking and resetting the async
3730notification, and the callback being invoked.
1642.SH "OTHER FUNCTIONS" 3731.SH "OTHER FUNCTIONS"
1643.IX Header "OTHER FUNCTIONS" 3732.IX Header "OTHER FUNCTIONS"
1644There are some other functions of possible interest. Described. Here. Now. 3733There are some other functions of possible interest. Described. Here. Now.
1645.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4 3734.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)" 4
1646.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 3735.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)"
1647This function combines a simple timer and an I/O watcher, calls your 3736This function combines a simple timer and an I/O watcher, calls your
1648callback on whichever event happens first and automatically stop both 3737callback on whichever event happens first and automatically stops both
1649watchers. This is useful if you want to wait for a single event on an fd 3738watchers. This is useful if you want to wait for a single event on an fd
1650or timeout without having to allocate/configure/start/stop/free one or 3739or timeout without having to allocate/configure/start/stop/free one or
1651more watchers yourself. 3740more watchers yourself.
1652.Sp 3741.Sp
1653If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and events 3742If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and the
1654is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for the given \f(CW\*(C`fd\*(C'\fR and 3743\&\f(CW\*(C`events\*(C'\fR argument is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for
1655\&\f(CW\*(C`events\*(C'\fR set will be craeted and started. 3744the given \f(CW\*(C`fd\*(C'\fR and \f(CW\*(C`events\*(C'\fR set will be created and started.
1656.Sp 3745.Sp
1657If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be 3746If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
1658started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and 3747started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
1659repeat = 0) will be started. While \f(CW0\fR is a valid timeout, it is of 3748repeat = 0) will be started. \f(CW0\fR is a valid timeout.
1660dubious value.
1661.Sp 3749.Sp
1662The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets 3750The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and is
1663passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of 3751passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
1664\&\f(CW\*(C`EV_ERROR\*(C'\fR, \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or \f(CW\*(C`EV_TIMEOUT\*(C'\fR) and the \f(CW\*(C`arg\*(C'\fR 3752\&\f(CW\*(C`EV_ERROR\*(C'\fR, \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or \f(CW\*(C`EV_TIMER\*(C'\fR) and the \f(CW\*(C`arg\*(C'\fR
1665value passed to \f(CW\*(C`ev_once\*(C'\fR: 3753value passed to \f(CW\*(C`ev_once\*(C'\fR. Note that it is possible to receive \fIboth\fR
3754a timeout and an io event at the same time \- you probably should give io
3755events precedence.
3756.Sp
3757Example: wait up to ten seconds for data to appear on \s-1STDIN_FILENO.\s0
1666.Sp 3758.Sp
1667.Vb 7 3759.Vb 7
1668\& static void stdin_ready (int revents, void *arg) 3760\& static void stdin_ready (int revents, void *arg)
3761\& {
3762\& if (revents & EV_READ)
3763\& /* stdin might have data for us, joy! */;
3764\& else if (revents & EV_TIMER)
3765\& /* doh, nothing entered */;
3766\& }
3767\&
3768\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3769.Ve
3770.IP "ev_feed_fd_event (loop, int fd, int revents)" 4
3771.IX Item "ev_feed_fd_event (loop, int fd, int revents)"
3772Feed an event on the given fd, as if a file descriptor backend detected
3773the given events.
3774.IP "ev_feed_signal_event (loop, int signum)" 4
3775.IX Item "ev_feed_signal_event (loop, int signum)"
3776Feed an event as if the given signal occurred. See also \f(CW\*(C`ev_feed_signal\*(C'\fR,
3777which is async-safe.
3778.SH "COMMON OR USEFUL IDIOMS (OR BOTH)"
3779.IX Header "COMMON OR USEFUL IDIOMS (OR BOTH)"
3780This section explains some common idioms that are not immediately
3781obvious. Note that examples are sprinkled over the whole manual, and this
3782section only contains stuff that wouldn't fit anywhere else.
3783.SS "\s-1ASSOCIATING CUSTOM DATA WITH A WATCHER\s0"
3784.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
3785Each watcher has, by default, a \f(CW\*(C`void *data\*(C'\fR member that you can read
3786or modify at any time: libev will completely ignore it. This can be used
3787to associate arbitrary data with your watcher. If you need more data and
3788don't want to allocate memory separately and store a pointer to it in that
3789data member, you can also \*(L"subclass\*(R" the watcher type and provide your own
3790data:
3791.PP
3792.Vb 7
3793\& struct my_io
3794\& {
3795\& ev_io io;
3796\& int otherfd;
3797\& void *somedata;
3798\& struct whatever *mostinteresting;
3799\& };
3800\&
3801\& ...
3802\& struct my_io w;
3803\& ev_io_init (&w.io, my_cb, fd, EV_READ);
3804.Ve
3805.PP
3806And since your callback will be called with a pointer to the watcher, you
3807can cast it back to your own type:
3808.PP
3809.Vb 5
3810\& static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
3811\& {
3812\& struct my_io *w = (struct my_io *)w_;
3813\& ...
3814\& }
3815.Ve
3816.PP
3817More interesting and less C\-conformant ways of casting your callback
3818function type instead have been omitted.
3819.SS "\s-1BUILDING YOUR OWN COMPOSITE WATCHERS\s0"
3820.IX Subsection "BUILDING YOUR OWN COMPOSITE WATCHERS"
3821Another common scenario is to use some data structure with multiple
3822embedded watchers, in effect creating your own watcher that combines
3823multiple libev event sources into one \*(L"super-watcher\*(R":
3824.PP
3825.Vb 6
3826\& struct my_biggy
3827\& {
3828\& int some_data;
3829\& ev_timer t1;
3830\& ev_timer t2;
3831\& }
3832.Ve
3833.PP
3834In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more
3835complicated: Either you store the address of your \f(CW\*(C`my_biggy\*(C'\fR struct in
3836the \f(CW\*(C`data\*(C'\fR member of the watcher (for woozies or \*(C+ coders), or you need
3837to use some pointer arithmetic using \f(CW\*(C`offsetof\*(C'\fR inside your watchers (for
3838real programmers):
3839.PP
3840.Vb 1
3841\& #include <stddef.h>
3842\&
3843\& static void
3844\& t1_cb (EV_P_ ev_timer *w, int revents)
3845\& {
3846\& struct my_biggy big = (struct my_biggy *)
3847\& (((char *)w) \- offsetof (struct my_biggy, t1));
3848\& }
3849\&
3850\& static void
3851\& t2_cb (EV_P_ ev_timer *w, int revents)
3852\& {
3853\& struct my_biggy big = (struct my_biggy *)
3854\& (((char *)w) \- offsetof (struct my_biggy, t2));
3855\& }
3856.Ve
3857.SS "\s-1AVOIDING FINISHING BEFORE RETURNING\s0"
3858.IX Subsection "AVOIDING FINISHING BEFORE RETURNING"
3859Often you have structures like this in event-based programs:
3860.PP
3861.Vb 4
3862\& callback ()
1669\& { 3863\& {
1670\& if (revents & EV_TIMEOUT) 3864\& free (request);
1671\& /* doh, nothing entered */;
1672\& else if (revents & EV_READ)
1673\& /* stdin might have data for us, joy! */;
1674\& } 3865\& }
3866\&
3867\& request = start_new_request (..., callback);
1675.Ve 3868.Ve
1676.Sp 3869.PP
3870The intent is to start some \*(L"lengthy\*(R" operation. The \f(CW\*(C`request\*(C'\fR could be
3871used to cancel the operation, or do other things with it.
3872.PP
3873It's not uncommon to have code paths in \f(CW\*(C`start_new_request\*(C'\fR that
3874immediately invoke the callback, for example, to report errors. Or you add
3875some caching layer that finds that it can skip the lengthy aspects of the
3876operation and simply invoke the callback with the result.
3877.PP
3878The problem here is that this will happen \fIbefore\fR \f(CW\*(C`start_new_request\*(C'\fR
3879has returned, so \f(CW\*(C`request\*(C'\fR is not set.
3880.PP
3881Even if you pass the request by some safer means to the callback, you
3882might want to do something to the request after starting it, such as
3883canceling it, which probably isn't working so well when the callback has
3884already been invoked.
3885.PP
3886A common way around all these issues is to make sure that
3887\&\f(CW\*(C`start_new_request\*(C'\fR \fIalways\fR returns before the callback is invoked. If
3888\&\f(CW\*(C`start_new_request\*(C'\fR immediately knows the result, it can artificially
3889delay invoking the callback by using a \f(CW\*(C`prepare\*(C'\fR or \f(CW\*(C`idle\*(C'\fR watcher for
3890example, or more sneakily, by reusing an existing (stopped) watcher and
3891pushing it into the pending queue:
3892.PP
1677.Vb 1 3893.Vb 2
1678\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); 3894\& ev_set_cb (watcher, callback);
3895\& ev_feed_event (EV_A_ watcher, 0);
1679.Ve 3896.Ve
1680.IP "ev_feed_event (ev_loop *, watcher *, int revents)" 4 3897.PP
1681.IX Item "ev_feed_event (ev_loop *, watcher *, int revents)" 3898This way, \f(CW\*(C`start_new_request\*(C'\fR can safely return before the callback is
1682Feeds the given event set into the event loop, as if the specified event 3899invoked, while not delaying callback invocation too much.
1683had happened for the specified watcher (which must be a pointer to an 3900.SS "\s-1MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS\s0"
1684initialised but not necessarily started event watcher). 3901.IX Subsection "MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS"
1685.IP "ev_feed_fd_event (ev_loop *, int fd, int revents)" 4 3902Often (especially in \s-1GUI\s0 toolkits) there are places where you have
1686.IX Item "ev_feed_fd_event (ev_loop *, int fd, int revents)" 3903\&\fImodal\fR interaction, which is most easily implemented by recursively
1687Feed an event on the given fd, as if a file descriptor backend detected 3904invoking \f(CW\*(C`ev_run\*(C'\fR.
1688the given events it. 3905.PP
1689.IP "ev_feed_signal_event (ev_loop *loop, int signum)" 4 3906This brings the problem of exiting \- a callback might want to finish the
1690.IX Item "ev_feed_signal_event (ev_loop *loop, int signum)" 3907main \f(CW\*(C`ev_run\*(C'\fR call, but not the nested one (e.g. user clicked \*(L"Quit\*(R", but
1691Feed an event as if the given signal occured (\f(CW\*(C`loop\*(C'\fR must be the default 3908a modal \*(L"Are you sure?\*(R" dialog is still waiting), or just the nested one
1692loop!). 3909and not the main one (e.g. user clocked \*(L"Ok\*(R" in a modal dialog), or some
3910other combination: In these cases, a simple \f(CW\*(C`ev_break\*(C'\fR will not work.
3911.PP
3912The solution is to maintain \*(L"break this loop\*(R" variable for each \f(CW\*(C`ev_run\*(C'\fR
3913invocation, and use a loop around \f(CW\*(C`ev_run\*(C'\fR until the condition is
3914triggered, using \f(CW\*(C`EVRUN_ONCE\*(C'\fR:
3915.PP
3916.Vb 2
3917\& // main loop
3918\& int exit_main_loop = 0;
3919\&
3920\& while (!exit_main_loop)
3921\& ev_run (EV_DEFAULT_ EVRUN_ONCE);
3922\&
3923\& // in a modal watcher
3924\& int exit_nested_loop = 0;
3925\&
3926\& while (!exit_nested_loop)
3927\& ev_run (EV_A_ EVRUN_ONCE);
3928.Ve
3929.PP
3930To exit from any of these loops, just set the corresponding exit variable:
3931.PP
3932.Vb 2
3933\& // exit modal loop
3934\& exit_nested_loop = 1;
3935\&
3936\& // exit main program, after modal loop is finished
3937\& exit_main_loop = 1;
3938\&
3939\& // exit both
3940\& exit_main_loop = exit_nested_loop = 1;
3941.Ve
3942.SS "\s-1THREAD LOCKING EXAMPLE\s0"
3943.IX Subsection "THREAD LOCKING EXAMPLE"
3944Here is a fictitious example of how to run an event loop in a different
3945thread from where callbacks are being invoked and watchers are
3946created/added/removed.
3947.PP
3948For a real-world example, see the \f(CW\*(C`EV::Loop::Async\*(C'\fR perl module,
3949which uses exactly this technique (which is suited for many high-level
3950languages).
3951.PP
3952The example uses a pthread mutex to protect the loop data, a condition
3953variable to wait for callback invocations, an async watcher to notify the
3954event loop thread and an unspecified mechanism to wake up the main thread.
3955.PP
3956First, you need to associate some data with the event loop:
3957.PP
3958.Vb 6
3959\& typedef struct {
3960\& mutex_t lock; /* global loop lock */
3961\& ev_async async_w;
3962\& thread_t tid;
3963\& cond_t invoke_cv;
3964\& } userdata;
3965\&
3966\& void prepare_loop (EV_P)
3967\& {
3968\& // for simplicity, we use a static userdata struct.
3969\& static userdata u;
3970\&
3971\& ev_async_init (&u\->async_w, async_cb);
3972\& ev_async_start (EV_A_ &u\->async_w);
3973\&
3974\& pthread_mutex_init (&u\->lock, 0);
3975\& pthread_cond_init (&u\->invoke_cv, 0);
3976\&
3977\& // now associate this with the loop
3978\& ev_set_userdata (EV_A_ u);
3979\& ev_set_invoke_pending_cb (EV_A_ l_invoke);
3980\& ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
3981\&
3982\& // then create the thread running ev_run
3983\& pthread_create (&u\->tid, 0, l_run, EV_A);
3984\& }
3985.Ve
3986.PP
3987The callback for the \f(CW\*(C`ev_async\*(C'\fR watcher does nothing: the watcher is used
3988solely to wake up the event loop so it takes notice of any new watchers
3989that might have been added:
3990.PP
3991.Vb 5
3992\& static void
3993\& async_cb (EV_P_ ev_async *w, int revents)
3994\& {
3995\& // just used for the side effects
3996\& }
3997.Ve
3998.PP
3999The \f(CW\*(C`l_release\*(C'\fR and \f(CW\*(C`l_acquire\*(C'\fR callbacks simply unlock/lock the mutex
4000protecting the loop data, respectively.
4001.PP
4002.Vb 6
4003\& static void
4004\& l_release (EV_P)
4005\& {
4006\& userdata *u = ev_userdata (EV_A);
4007\& pthread_mutex_unlock (&u\->lock);
4008\& }
4009\&
4010\& static void
4011\& l_acquire (EV_P)
4012\& {
4013\& userdata *u = ev_userdata (EV_A);
4014\& pthread_mutex_lock (&u\->lock);
4015\& }
4016.Ve
4017.PP
4018The event loop thread first acquires the mutex, and then jumps straight
4019into \f(CW\*(C`ev_run\*(C'\fR:
4020.PP
4021.Vb 4
4022\& void *
4023\& l_run (void *thr_arg)
4024\& {
4025\& struct ev_loop *loop = (struct ev_loop *)thr_arg;
4026\&
4027\& l_acquire (EV_A);
4028\& pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4029\& ev_run (EV_A_ 0);
4030\& l_release (EV_A);
4031\&
4032\& return 0;
4033\& }
4034.Ve
4035.PP
4036Instead of invoking all pending watchers, the \f(CW\*(C`l_invoke\*(C'\fR callback will
4037signal the main thread via some unspecified mechanism (signals? pipe
4038writes? \f(CW\*(C`Async::Interrupt\*(C'\fR?) and then waits until all pending watchers
4039have been called (in a while loop because a) spurious wakeups are possible
4040and b) skipping inter-thread-communication when there are no pending
4041watchers is very beneficial):
4042.PP
4043.Vb 4
4044\& static void
4045\& l_invoke (EV_P)
4046\& {
4047\& userdata *u = ev_userdata (EV_A);
4048\&
4049\& while (ev_pending_count (EV_A))
4050\& {
4051\& wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4052\& pthread_cond_wait (&u\->invoke_cv, &u\->lock);
4053\& }
4054\& }
4055.Ve
4056.PP
4057Now, whenever the main thread gets told to invoke pending watchers, it
4058will grab the lock, call \f(CW\*(C`ev_invoke_pending\*(C'\fR and then signal the loop
4059thread to continue:
4060.PP
4061.Vb 4
4062\& static void
4063\& real_invoke_pending (EV_P)
4064\& {
4065\& userdata *u = ev_userdata (EV_A);
4066\&
4067\& pthread_mutex_lock (&u\->lock);
4068\& ev_invoke_pending (EV_A);
4069\& pthread_cond_signal (&u\->invoke_cv);
4070\& pthread_mutex_unlock (&u\->lock);
4071\& }
4072.Ve
4073.PP
4074Whenever you want to start/stop a watcher or do other modifications to an
4075event loop, you will now have to lock:
4076.PP
4077.Vb 2
4078\& ev_timer timeout_watcher;
4079\& userdata *u = ev_userdata (EV_A);
4080\&
4081\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4082\&
4083\& pthread_mutex_lock (&u\->lock);
4084\& ev_timer_start (EV_A_ &timeout_watcher);
4085\& ev_async_send (EV_A_ &u\->async_w);
4086\& pthread_mutex_unlock (&u\->lock);
4087.Ve
4088.PP
4089Note that sending the \f(CW\*(C`ev_async\*(C'\fR watcher is required because otherwise
4090an event loop currently blocking in the kernel will have no knowledge
4091about the newly added timer. By waking up the loop it will pick up any new
4092watchers in the next event loop iteration.
4093.SS "\s-1THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS\s0"
4094.IX Subsection "THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS"
4095While the overhead of a callback that e.g. schedules a thread is small, it
4096is still an overhead. If you embed libev, and your main usage is with some
4097kind of threads or coroutines, you might want to customise libev so that
4098doesn't need callbacks anymore.
4099.PP
4100Imagine you have coroutines that you can switch to using a function
4101\&\f(CW\*(C`switch_to (coro)\*(C'\fR, that libev runs in a coroutine called \f(CW\*(C`libev_coro\*(C'\fR
4102and that due to some magic, the currently active coroutine is stored in a
4103global called \f(CW\*(C`current_coro\*(C'\fR. Then you can build your own \*(L"wait for libev
4104event\*(R" primitive by changing \f(CW\*(C`EV_CB_DECLARE\*(C'\fR and \f(CW\*(C`EV_CB_INVOKE\*(C'\fR (note
4105the differing \f(CW\*(C`;\*(C'\fR conventions):
4106.PP
4107.Vb 2
4108\& #define EV_CB_DECLARE(type) struct my_coro *cb;
4109\& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb)
4110.Ve
4111.PP
4112That means instead of having a C callback function, you store the
4113coroutine to switch to in each watcher, and instead of having libev call
4114your callback, you instead have it switch to that coroutine.
4115.PP
4116A coroutine might now wait for an event with a function called
4117\&\f(CW\*(C`wait_for_event\*(C'\fR. (the watcher needs to be started, as always, but it doesn't
4118matter when, or whether the watcher is active or not when this function is
4119called):
4120.PP
4121.Vb 6
4122\& void
4123\& wait_for_event (ev_watcher *w)
4124\& {
4125\& ev_set_cb (w, current_coro);
4126\& switch_to (libev_coro);
4127\& }
4128.Ve
4129.PP
4130That basically suspends the coroutine inside \f(CW\*(C`wait_for_event\*(C'\fR and
4131continues the libev coroutine, which, when appropriate, switches back to
4132this or any other coroutine.
4133.PP
4134You can do similar tricks if you have, say, threads with an event queue \-
4135instead of storing a coroutine, you store the queue object and instead of
4136switching to a coroutine, you push the watcher onto the queue and notify
4137any waiters.
4138.PP
4139To embed libev, see \*(L"\s-1EMBEDDING\*(R"\s0, but in short, it's easiest to create two
4140files, \fImy_ev.h\fR and \fImy_ev.c\fR that include the respective libev files:
4141.PP
4142.Vb 4
4143\& // my_ev.h
4144\& #define EV_CB_DECLARE(type) struct my_coro *cb;
4145\& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb)
4146\& #include "../libev/ev.h"
4147\&
4148\& // my_ev.c
4149\& #define EV_H "my_ev.h"
4150\& #include "../libev/ev.c"
4151.Ve
4152.PP
4153And then use \fImy_ev.h\fR when you would normally use \fIev.h\fR, and compile
4154\&\fImy_ev.c\fR into your project. When properly specifying include paths, you
4155can even use \fIev.h\fR as header file name directly.
1693.SH "LIBEVENT EMULATION" 4156.SH "LIBEVENT EMULATION"
1694.IX Header "LIBEVENT EMULATION" 4157.IX Header "LIBEVENT EMULATION"
1695Libev offers a compatibility emulation layer for libevent. It cannot 4158Libev offers a compatibility emulation layer for libevent. It cannot
1696emulate the internals of libevent, so here are some usage hints: 4159emulate the internals of libevent, so here are some usage hints:
4160.IP "\(bu" 4
4161Only the libevent\-1.4.1\-beta \s-1API\s0 is being emulated.
4162.Sp
4163This was the newest libevent version available when libev was implemented,
4164and is still mostly unchanged in 2010.
4165.IP "\(bu" 4
1697.IP "* Use it by including <event.h>, as usual." 4 4166Use it by including <event.h>, as usual.
1698.IX Item "Use it by including <event.h>, as usual." 4167.IP "\(bu" 4
1699.PD 0 4168The following members are fully supported: ev_base, ev_callback,
1700.IP "* The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4 4169ev_arg, ev_fd, ev_res, ev_events.
1701.IX Item "The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4170.IP "\(bu" 4
1702.IP "* Avoid using ev_flags and the EVLIST_*\-macros, while it is maintained by libev, it does not work exactly the same way as in libevent (consider it a private \s-1API\s0)." 4 4171Avoid using ev_flags and the EVLIST_*\-macros, while it is
1703.IX Item "Avoid using ev_flags and the EVLIST_*-macros, while it is maintained by libev, it does not work exactly the same way as in libevent (consider it a private API)." 4172maintained by libev, it does not work exactly the same way as in libevent (consider
1704.IP "* Priorities are not currently supported. Initialising priorities will fail and all watchers will have the same priority, even though there is an ev_pri field." 4 4173it a private \s-1API\s0).
1705.IX Item "Priorities are not currently supported. Initialising priorities will fail and all watchers will have the same priority, even though there is an ev_pri field." 4174.IP "\(bu" 4
4175Priorities are not currently supported. Initialising priorities
4176will fail and all watchers will have the same priority, even though there
4177is an ev_pri field.
4178.IP "\(bu" 4
4179In libevent, the last base created gets the signals, in libev, the
4180base that registered the signal gets the signals.
4181.IP "\(bu" 4
1706.IP "* Other members are not supported." 4 4182Other members are not supported.
1707.IX Item "Other members are not supported." 4183.IP "\(bu" 4
1708.IP "* The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need to use the libev header file and library." 4 4184The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need
1709.IX Item "The libev emulation is not ABI compatible to libevent, you need to use the libev header file and library." 4185to use the libev header file and library.
1710.PD
1711.SH "\*(C+ SUPPORT" 4186.SH "\*(C+ SUPPORT"
1712.IX Header " SUPPORT" 4187.IX Header " SUPPORT"
4188.SS "C \s-1API\s0"
4189.IX Subsection "C API"
4190The normal C \s-1API\s0 should work fine when used from \*(C+: both ev.h and the
4191libev sources can be compiled as \*(C+. Therefore, code that uses the C \s-1API\s0
4192will work fine.
4193.PP
4194Proper exception specifications might have to be added to callbacks passed
4195to libev: exceptions may be thrown only from watcher callbacks, all other
4196callbacks (allocator, syserr, loop acquire/release and periodic reschedule
4197callbacks) must not throw exceptions, and might need a \f(CW\*(C`noexcept\*(C'\fR
4198specification. If you have code that needs to be compiled as both C and
4199\&\*(C+ you can use the \f(CW\*(C`EV_NOEXCEPT\*(C'\fR macro for this:
4200.PP
4201.Vb 6
4202\& static void
4203\& fatal_error (const char *msg) EV_NOEXCEPT
4204\& {
4205\& perror (msg);
4206\& abort ();
4207\& }
4208\&
4209\& ...
4210\& ev_set_syserr_cb (fatal_error);
4211.Ve
4212.PP
4213The only \s-1API\s0 functions that can currently throw exceptions are \f(CW\*(C`ev_run\*(C'\fR,
4214\&\f(CW\*(C`ev_invoke\*(C'\fR, \f(CW\*(C`ev_invoke_pending\*(C'\fR and \f(CW\*(C`ev_loop_destroy\*(C'\fR (the latter
4215because it runs cleanup watchers).
4216.PP
4217Throwing exceptions in watcher callbacks is only supported if libev itself
4218is compiled with a \*(C+ compiler or your C and \*(C+ environments allow
4219throwing exceptions through C libraries (most do).
4220.SS "\*(C+ \s-1API\s0"
4221.IX Subsection " API"
1713Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow 4222Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
1714you to use some convinience methods to start/stop watchers and also change 4223you to use some convenience methods to start/stop watchers and also change
1715the callback model to a model using method callbacks on objects. 4224the callback model to a model using method callbacks on objects.
1716.PP 4225.PP
1717To use it, 4226To use it,
1718.PP 4227.PP
1719.Vb 1 4228.Vb 1
1720\& #include <ev++.h> 4229\& #include <ev++.h>
1721.Ve 4230.Ve
1722.PP 4231.PP
1723(it is not installed by default). This automatically includes \fIev.h\fR 4232This automatically includes \fIev.h\fR and puts all of its definitions (many
1724and puts all of its definitions (many of them macros) into the global 4233of them macros) into the global namespace. All \*(C+ specific things are
1725namespace. All \*(C+ specific things are put into the \f(CW\*(C`ev\*(C'\fR namespace. 4234put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding
4235options as \fIev.h\fR, most notably \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR.
1726.PP 4236.PP
1727It should support all the same embedding options as \fIev.h\fR, most notably 4237Care has been taken to keep the overhead low. The only data member the \*(C+
1728\&\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. 4238classes add (compared to plain C\-style watchers) is the event loop pointer
4239that the watcher is associated with (or no additional members at all if
4240you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
4241.PP
4242Currently, functions, static and non-static member functions and classes
4243with \f(CW\*(C`operator ()\*(C'\fR can be used as callbacks. Other types should be easy
4244to add as long as they only need one additional pointer for context. If
4245you need support for other types of functors please contact the author
4246(preferably after implementing it).
4247.PP
4248For all this to work, your \*(C+ compiler either has to use the same calling
4249conventions as your C compiler (for static member functions), or you have
4250to embed libev and compile libev itself as \*(C+.
1729.PP 4251.PP
1730Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace: 4252Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
1731.ie n .IP """ev::READ""\fR, \f(CW""ev::WRITE"" etc." 4 4253.ie n .IP """ev::READ"", ""ev::WRITE"" etc." 4
1732.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4 4254.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
1733.IX Item "ev::READ, ev::WRITE etc." 4255.IX Item "ev::READ, ev::WRITE etc."
1734These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc. 4256These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
1735macros from \fIev.h\fR. 4257macros from \fIev.h\fR.
1736.ie n .IP """ev::tstamp""\fR, \f(CW""ev::now""" 4 4258.ie n .IP """ev::tstamp"", ""ev::now""" 4
1737.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4 4259.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
1738.IX Item "ev::tstamp, ev::now" 4260.IX Item "ev::tstamp, ev::now"
1739Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix. 4261Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
1740.ie n .IP """ev::io""\fR, \f(CW""ev::timer""\fR, \f(CW""ev::periodic""\fR, \f(CW""ev::idle""\fR, \f(CW""ev::sig"" etc." 4 4262.ie n .IP """ev::io"", ""ev::timer"", ""ev::periodic"", ""ev::idle"", ""ev::sig"" etc." 4
1741.el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4 4263.el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
1742.IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc." 4264.IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
1743For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of 4265For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
1744the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR 4266the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
1745which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro 4267which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
1746defines by many implementations. 4268defined by many implementations.
1747.Sp 4269.Sp
1748All of those classes have these methods: 4270All of those classes have these methods:
1749.RS 4 4271.RS 4
1750.IP "ev::TYPE::TYPE (object *, object::method *)" 4 4272.IP "ev::TYPE::TYPE ()" 4
1751.IX Item "ev::TYPE::TYPE (object *, object::method *)" 4273.IX Item "ev::TYPE::TYPE ()"
1752.PD 0 4274.PD 0
1753.IP "ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)" 4 4275.IP "ev::TYPE::TYPE (loop)" 4
1754.IX Item "ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)" 4276.IX Item "ev::TYPE::TYPE (loop)"
1755.IP "ev::TYPE::~TYPE" 4 4277.IP "ev::TYPE::~TYPE" 4
1756.IX Item "ev::TYPE::~TYPE" 4278.IX Item "ev::TYPE::~TYPE"
1757.PD 4279.PD
1758The constructor takes a pointer to an object and a method pointer to 4280The constructor (optionally) takes an event loop to associate the watcher
1759the event handler callback to call in this class. The constructor calls 4281with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR.
1760\&\f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the \f(CW\*(C`set\*(C'\fR method 4282.Sp
1761before starting it. If you do not specify a loop then the constructor 4283The constructor calls \f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the
1762automatically associates the default loop with this watcher. 4284\&\f(CW\*(C`set\*(C'\fR method before starting it.
4285.Sp
4286It will not set a callback, however: You have to call the templated \f(CW\*(C`set\*(C'\fR
4287method to set a callback before you can start the watcher.
4288.Sp
4289(The reason why you have to use a method is a limitation in \*(C+ which does
4290not allow explicit template arguments for constructors).
1763.Sp 4291.Sp
1764The destructor automatically stops the watcher if it is active. 4292The destructor automatically stops the watcher if it is active.
4293.IP "w\->set<class, &class::method> (object *)" 4
4294.IX Item "w->set<class, &class::method> (object *)"
4295This method sets the callback method to call. The method has to have a
4296signature of \f(CW\*(C`void (*)(ev_TYPE &, int)\*(C'\fR, it receives the watcher as
4297first argument and the \f(CW\*(C`revents\*(C'\fR as second. The object must be given as
4298parameter and is stored in the \f(CW\*(C`data\*(C'\fR member of the watcher.
4299.Sp
4300This method synthesizes efficient thunking code to call your method from
4301the C callback that libev requires. If your compiler can inline your
4302callback (i.e. it is visible to it at the place of the \f(CW\*(C`set\*(C'\fR call and
4303your compiler is good :), then the method will be fully inlined into the
4304thunking function, making it as fast as a direct C callback.
4305.Sp
4306Example: simple class declaration and watcher initialisation
4307.Sp
4308.Vb 4
4309\& struct myclass
4310\& {
4311\& void io_cb (ev::io &w, int revents) { }
4312\& }
4313\&
4314\& myclass obj;
4315\& ev::io iow;
4316\& iow.set <myclass, &myclass::io_cb> (&obj);
4317.Ve
4318.IP "w\->set (object *)" 4
4319.IX Item "w->set (object *)"
4320This is a variation of a method callback \- leaving out the method to call
4321will default the method to \f(CW\*(C`operator ()\*(C'\fR, which makes it possible to use
4322functor objects without having to manually specify the \f(CW\*(C`operator ()\*(C'\fR all
4323the time. Incidentally, you can then also leave out the template argument
4324list.
4325.Sp
4326The \f(CW\*(C`operator ()\*(C'\fR method prototype must be \f(CW\*(C`void operator ()(watcher &w,
4327int revents)\*(C'\fR.
4328.Sp
4329See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
4330.Sp
4331Example: use a functor object as callback.
4332.Sp
4333.Vb 7
4334\& struct myfunctor
4335\& {
4336\& void operator() (ev::io &w, int revents)
4337\& {
4338\& ...
4339\& }
4340\& }
4341\&
4342\& myfunctor f;
4343\&
4344\& ev::io w;
4345\& w.set (&f);
4346.Ve
4347.IP "w\->set<function> (void *data = 0)" 4
4348.IX Item "w->set<function> (void *data = 0)"
4349Also sets a callback, but uses a static method or plain function as
4350callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
4351\&\f(CW\*(C`data\*(C'\fR member and is free for you to use.
4352.Sp
4353The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
4354.Sp
4355See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
4356.Sp
4357Example: Use a plain function as callback.
4358.Sp
4359.Vb 2
4360\& static void io_cb (ev::io &w, int revents) { }
4361\& iow.set <io_cb> ();
4362.Ve
1765.IP "w\->set (struct ev_loop *)" 4 4363.IP "w\->set (loop)" 4
1766.IX Item "w->set (struct ev_loop *)" 4364.IX Item "w->set (loop)"
1767Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only 4365Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
1768do this when the watcher is inactive (and not pending either). 4366do this when the watcher is inactive (and not pending either).
1769.IP "w\->set ([args])" 4 4367.IP "w\->set ([arguments])" 4
1770.IX Item "w->set ([args])" 4368.IX Item "w->set ([arguments])"
1771Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same args. Must be 4369Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR (except for \f(CW\*(C`ev::embed\*(C'\fR watchers>),
4370with the same arguments. Either this method or a suitable start method
1772called at least once. Unlike the C counterpart, an active watcher gets 4371must be called at least once. Unlike the C counterpart, an active watcher
1773automatically stopped and restarted. 4372gets automatically stopped and restarted when reconfiguring it with this
4373method.
4374.Sp
4375For \f(CW\*(C`ev::embed\*(C'\fR watchers this method is called \f(CW\*(C`set_embed\*(C'\fR, to avoid
4376clashing with the \f(CW\*(C`set (loop)\*(C'\fR method.
1774.IP "w\->start ()" 4 4377.IP "w\->start ()" 4
1775.IX Item "w->start ()" 4378.IX Item "w->start ()"
1776Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument as the 4379Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
1777constructor already takes the loop. 4380constructor already stores the event loop.
4381.IP "w\->start ([arguments])" 4
4382.IX Item "w->start ([arguments])"
4383Instead of calling \f(CW\*(C`set\*(C'\fR and \f(CW\*(C`start\*(C'\fR methods separately, it is often
4384convenient to wrap them in one call. Uses the same type of arguments as
4385the configure \f(CW\*(C`set\*(C'\fR method of the watcher.
1778.IP "w\->stop ()" 4 4386.IP "w\->stop ()" 4
1779.IX Item "w->stop ()" 4387.IX Item "w->stop ()"
1780Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument. 4388Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
1781.ie n .IP "w\->again () ""ev::timer""\fR, \f(CW""ev::periodic"" only" 4 4389.ie n .IP "w\->again () (""ev::timer"", ""ev::periodic"" only)" 4
1782.el .IP "w\->again () \f(CWev::timer\fR, \f(CWev::periodic\fR only" 4 4390.el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
1783.IX Item "w->again () ev::timer, ev::periodic only" 4391.IX Item "w->again () (ev::timer, ev::periodic only)"
1784For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding 4392For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
1785\&\f(CW\*(C`ev_TYPE_again\*(C'\fR function. 4393\&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
1786.ie n .IP "w\->sweep () ""ev::embed"" only" 4 4394.ie n .IP "w\->sweep () (""ev::embed"" only)" 4
1787.el .IP "w\->sweep () \f(CWev::embed\fR only" 4 4395.el .IP "w\->sweep () (\f(CWev::embed\fR only)" 4
1788.IX Item "w->sweep () ev::embed only" 4396.IX Item "w->sweep () (ev::embed only)"
1789Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR. 4397Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR.
1790.ie n .IP "w\->update () ""ev::stat"" only" 4 4398.ie n .IP "w\->update () (""ev::stat"" only)" 4
1791.el .IP "w\->update () \f(CWev::stat\fR only" 4 4399.el .IP "w\->update () (\f(CWev::stat\fR only)" 4
1792.IX Item "w->update () ev::stat only" 4400.IX Item "w->update () (ev::stat only)"
1793Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR. 4401Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
1794.RE 4402.RE
1795.RS 4 4403.RS 4
1796.RE 4404.RE
1797.PP 4405.PP
1798Example: Define a class with an \s-1IO\s0 and idle watcher, start one of them in 4406Example: Define a class with two I/O and idle watchers, start the I/O
1799the constructor. 4407watchers in the constructor.
1800.PP 4408.PP
1801.Vb 4 4409.Vb 5
1802\& class myclass 4410\& class myclass
1803\& { 4411\& {
1804\& ev_io io; void io_cb (ev::io &w, int revents); 4412\& ev::io io ; void io_cb (ev::io &w, int revents);
4413\& ev::io io2 ; void io2_cb (ev::io &w, int revents);
1805\& ev_idle idle void idle_cb (ev::idle &w, int revents); 4414\& ev::idle idle; void idle_cb (ev::idle &w, int revents);
1806.Ve 4415\&
1807.PP
1808.Vb 2
1809\& myclass (); 4416\& myclass (int fd)
4417\& {
4418\& io .set <myclass, &myclass::io_cb > (this);
4419\& io2 .set <myclass, &myclass::io2_cb > (this);
4420\& idle.set <myclass, &myclass::idle_cb> (this);
4421\&
4422\& io.set (fd, ev::WRITE); // configure the watcher
4423\& io.start (); // start it whenever convenient
4424\&
4425\& io2.start (fd, ev::READ); // set + start in one call
4426\& }
1810\& } 4427\& };
1811.Ve 4428.Ve
1812.PP 4429.SH "OTHER LANGUAGE BINDINGS"
1813.Vb 6 4430.IX Header "OTHER LANGUAGE BINDINGS"
1814\& myclass::myclass (int fd) 4431Libev does not offer other language bindings itself, but bindings for a
1815\& : io (this, &myclass::io_cb), 4432number of languages exist in the form of third-party packages. If you know
1816\& idle (this, &myclass::idle_cb) 4433any interesting language binding in addition to the ones listed here, drop
1817\& { 4434me a note.
1818\& io.start (fd, ev::READ); 4435.IP "Perl" 4
1819\& } 4436.IX Item "Perl"
1820.Ve 4437The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test
4438libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module,
4439there are additional modules that implement libev-compatible interfaces
4440to \f(CW\*(C`libadns\*(C'\fR (\f(CW\*(C`EV::ADNS\*(C'\fR, but \f(CW\*(C`AnyEvent::DNS\*(C'\fR is preferred nowadays),
4441\&\f(CW\*(C`Net::SNMP\*(C'\fR (\f(CW\*(C`Net::SNMP::EV\*(C'\fR) and the \f(CW\*(C`libglib\*(C'\fR event core (\f(CW\*(C`Glib::EV\*(C'\fR
4442and \f(CW\*(C`EV::Glib\*(C'\fR).
4443.Sp
4444It can be found and installed via \s-1CPAN,\s0 its homepage is at
4445<http://software.schmorp.de/pkg/EV>.
4446.IP "Python" 4
4447.IX Item "Python"
4448Python bindings can be found at <http://code.google.com/p/pyev/>. It
4449seems to be quite complete and well-documented.
4450.IP "Ruby" 4
4451.IX Item "Ruby"
4452Tony Arcieri has written a ruby extension that offers access to a subset
4453of the libev \s-1API\s0 and adds file handle abstractions, asynchronous \s-1DNS\s0 and
4454more on top of it. It can be found via gem servers. Its homepage is at
4455<http://rev.rubyforge.org/>.
4456.Sp
4457Roger Pack reports that using the link order \f(CW\*(C`\-lws2_32 \-lmsvcrt\-ruby\-190\*(C'\fR
4458makes rev work even on mingw.
4459.IP "Haskell" 4
4460.IX Item "Haskell"
4461A haskell binding to libev is available at
4462<http://hackage.haskell.org/cgi\-bin/hackage\-scripts/package/hlibev>.
4463.IP "D" 4
4464.IX Item "D"
4465Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
4466be found at <http://www.llucax.com.ar/proj/ev.d/index.html>.
4467.IP "Ocaml" 4
4468.IX Item "Ocaml"
4469Erkki Seppala has written Ocaml bindings for libev, to be found at
4470<http://modeemi.cs.tut.fi/~flux/software/ocaml\-ev/>.
4471.IP "Lua" 4
4472.IX Item "Lua"
4473Brian Maher has written a partial interface to libev for lua (at the
4474time of this writing, only \f(CW\*(C`ev_io\*(C'\fR and \f(CW\*(C`ev_timer\*(C'\fR), to be found at
4475<http://github.com/brimworks/lua\-ev>.
4476.IP "Javascript" 4
4477.IX Item "Javascript"
4478Node.js (<http://nodejs.org>) uses libev as the underlying event library.
4479.IP "Others" 4
4480.IX Item "Others"
4481There are others, and I stopped counting.
1821.SH "MACRO MAGIC" 4482.SH "MACRO MAGIC"
1822.IX Header "MACRO MAGIC" 4483.IX Header "MACRO MAGIC"
1823Libev can be compiled with a variety of options, the most fundemantal is 4484Libev can be compiled with a variety of options, the most fundamental
1824\&\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines wether (most) functions and 4485of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most)
1825callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument. 4486functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
1826.PP 4487.PP
1827To make it easier to write programs that cope with either variant, the 4488To make it easier to write programs that cope with either variant, the
1828following macros are defined: 4489following macros are defined:
1829.ie n .IP """EV_A""\fR, \f(CW""EV_A_""" 4 4490.ie n .IP """EV_A"", ""EV_A_""" 4
1830.el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4 4491.el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
1831.IX Item "EV_A, EV_A_" 4492.IX Item "EV_A, EV_A_"
1832This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev 4493This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
1833loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument, 4494loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
1834\&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example: 4495\&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
1835.Sp 4496.Sp
1836.Vb 3 4497.Vb 3
1837\& ev_unref (EV_A); 4498\& ev_unref (EV_A);
1838\& ev_timer_add (EV_A_ watcher); 4499\& ev_timer_add (EV_A_ watcher);
1839\& ev_loop (EV_A_ 0); 4500\& ev_run (EV_A_ 0);
1840.Ve 4501.Ve
1841.Sp 4502.Sp
1842It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope, 4503It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
1843which is often provided by the following macro. 4504which is often provided by the following macro.
1844.ie n .IP """EV_P""\fR, \f(CW""EV_P_""" 4 4505.ie n .IP """EV_P"", ""EV_P_""" 4
1845.el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4 4506.el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
1846.IX Item "EV_P, EV_P_" 4507.IX Item "EV_P, EV_P_"
1847This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev 4508This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
1848loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter, 4509loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
1849\&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example: 4510\&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
1850.Sp 4511.Sp
1851.Vb 2 4512.Vb 2
1852\& // this is how ev_unref is being declared 4513\& // this is how ev_unref is being declared
1853\& static void ev_unref (EV_P); 4514\& static void ev_unref (EV_P);
1854.Ve 4515\&
1855.Sp
1856.Vb 2
1857\& // this is how you can declare your typical callback 4516\& // this is how you can declare your typical callback
1858\& static void cb (EV_P_ ev_timer *w, int revents) 4517\& static void cb (EV_P_ ev_timer *w, int revents)
1859.Ve 4518.Ve
1860.Sp 4519.Sp
1861It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite 4520It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
1862suitable for use with \f(CW\*(C`EV_A\*(C'\fR. 4521suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
1863.ie n .IP """EV_DEFAULT""\fR, \f(CW""EV_DEFAULT_""" 4 4522.ie n .IP """EV_DEFAULT"", ""EV_DEFAULT_""" 4
1864.el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4 4523.el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
1865.IX Item "EV_DEFAULT, EV_DEFAULT_" 4524.IX Item "EV_DEFAULT, EV_DEFAULT_"
1866Similar to the other two macros, this gives you the value of the default 4525Similar to the other two macros, this gives you the value of the default
1867loop, if multiple loops are supported (\*(L"ev loop default\*(R"). 4526loop, if multiple loops are supported (\*(L"ev loop default\*(R"). The default loop
4527will be initialised if it isn't already initialised.
4528.Sp
4529For non-multiplicity builds, these macros do nothing, so you always have
4530to initialise the loop somewhere.
4531.ie n .IP """EV_DEFAULT_UC"", ""EV_DEFAULT_UC_""" 4
4532.el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
4533.IX Item "EV_DEFAULT_UC, EV_DEFAULT_UC_"
4534Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the
4535default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour
4536is undefined when the default loop has not been initialised by a previous
4537execution of \f(CW\*(C`EV_DEFAULT\*(C'\fR, \f(CW\*(C`EV_DEFAULT_\*(C'\fR or \f(CW\*(C`ev_default_init (...)\*(C'\fR.
4538.Sp
4539It is often prudent to use \f(CW\*(C`EV_DEFAULT\*(C'\fR when initialising the first
4540watcher in a function but use \f(CW\*(C`EV_DEFAULT_UC\*(C'\fR afterwards.
1868.PP 4541.PP
1869Example: Declare and initialise a check watcher, working regardless of 4542Example: Declare and initialise a check watcher, utilising the above
1870wether multiple loops are supported or not. 4543macros so it will work regardless of whether multiple loops are supported
4544or not.
1871.PP 4545.PP
1872.Vb 5 4546.Vb 5
1873\& static void 4547\& static void
1874\& check_cb (EV_P_ ev_timer *w, int revents) 4548\& check_cb (EV_P_ ev_timer *w, int revents)
1875\& { 4549\& {
1876\& ev_check_stop (EV_A_ w); 4550\& ev_check_stop (EV_A_ w);
1877\& } 4551\& }
1878.Ve 4552\&
1879.PP
1880.Vb 4
1881\& ev_check check; 4553\& ev_check check;
1882\& ev_check_init (&check, check_cb); 4554\& ev_check_init (&check, check_cb);
1883\& ev_check_start (EV_DEFAULT_ &check); 4555\& ev_check_start (EV_DEFAULT_ &check);
1884\& ev_loop (EV_DEFAULT_ 0); 4556\& ev_run (EV_DEFAULT_ 0);
1885.Ve 4557.Ve
1886.SH "EMBEDDING" 4558.SH "EMBEDDING"
1887.IX Header "EMBEDDING" 4559.IX Header "EMBEDDING"
1888Libev can (and often is) directly embedded into host 4560Libev can (and often is) directly embedded into host
1889applications. Examples of applications that embed it include the Deliantra 4561applications. Examples of applications that embed it include the Deliantra
1890Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe) 4562Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
1891and rxvt\-unicode. 4563and rxvt-unicode.
1892.PP 4564.PP
1893The goal is to enable you to just copy the neecssary files into your 4565The goal is to enable you to just copy the necessary files into your
1894source directory without having to change even a single line in them, so 4566source directory without having to change even a single line in them, so
1895you can easily upgrade by simply copying (or having a checked-out copy of 4567you can easily upgrade by simply copying (or having a checked-out copy of
1896libev somewhere in your source tree). 4568libev somewhere in your source tree).
1897.Sh "\s-1FILESETS\s0" 4569.SS "\s-1FILESETS\s0"
1898.IX Subsection "FILESETS" 4570.IX Subsection "FILESETS"
1899Depending on what features you need you need to include one or more sets of files 4571Depending on what features you need you need to include one or more sets of files
1900in your app. 4572in your application.
1901.PP 4573.PP
1902\fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR 4574\fI\s-1CORE EVENT LOOP\s0\fR
1903.IX Subsection "CORE EVENT LOOP" 4575.IX Subsection "CORE EVENT LOOP"
1904.PP 4576.PP
1905To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual 4577To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
1906configuration (no autoconf): 4578configuration (no autoconf):
1907.PP 4579.PP
1908.Vb 2 4580.Vb 2
1909\& #define EV_STANDALONE 1 4581\& #define EV_STANDALONE 1
1910\& #include "ev.c" 4582\& #include "ev.c"
1911.Ve 4583.Ve
1912.PP 4584.PP
1913This will automatically include \fIev.h\fR, too, and should be done in a 4585This will automatically include \fIev.h\fR, too, and should be done in a
1914single C source file only to provide the function implementations. To use 4586single C source file only to provide the function implementations. To use
1915it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best 4587it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best
1916done by writing a wrapper around \fIev.h\fR that you can include instead and 4588done by writing a wrapper around \fIev.h\fR that you can include instead and
1917where you can put other configuration options): 4589where you can put other configuration options):
1918.PP 4590.PP
1919.Vb 2 4591.Vb 2
1920\& #define EV_STANDALONE 1 4592\& #define EV_STANDALONE 1
1921\& #include "ev.h" 4593\& #include "ev.h"
1922.Ve 4594.Ve
1923.PP 4595.PP
1924Both header files and implementation files can be compiled with a \*(C+ 4596Both header files and implementation files can be compiled with a \*(C+
1925compiler (at least, thats a stated goal, and breakage will be treated 4597compiler (at least, that's a stated goal, and breakage will be treated
1926as a bug). 4598as a bug).
1927.PP 4599.PP
1928You need the following files in your source tree, or in a directory 4600You need the following files in your source tree, or in a directory
1929in your include path (e.g. in libev/ when using \-Ilibev): 4601in your include path (e.g. in libev/ when using \-Ilibev):
1930.PP 4602.PP
1931.Vb 4 4603.Vb 4
1932\& ev.h 4604\& ev.h
1933\& ev.c 4605\& ev.c
1934\& ev_vars.h 4606\& ev_vars.h
1935\& ev_wrap.h 4607\& ev_wrap.h
1936.Ve 4608\&
1937.PP
1938.Vb 1
1939\& ev_win32.c required on win32 platforms only 4609\& ev_win32.c required on win32 platforms only
1940.Ve 4610\&
1941.PP
1942.Vb 5
1943\& ev_select.c only when select backend is enabled (which is by default) 4611\& ev_select.c only when select backend is enabled
1944\& ev_poll.c only when poll backend is enabled (disabled by default) 4612\& ev_poll.c only when poll backend is enabled
1945\& ev_epoll.c only when the epoll backend is enabled (disabled by default) 4613\& ev_epoll.c only when the epoll backend is enabled
4614\& ev_linuxaio.c only when the linux aio backend is enabled
1946\& ev_kqueue.c only when the kqueue backend is enabled (disabled by default) 4615\& ev_kqueue.c only when the kqueue backend is enabled
1947\& ev_port.c only when the solaris port backend is enabled (disabled by default) 4616\& ev_port.c only when the solaris port backend is enabled
1948.Ve 4617.Ve
1949.PP 4618.PP
1950\&\fIev.c\fR includes the backend files directly when enabled, so you only need 4619\&\fIev.c\fR includes the backend files directly when enabled, so you only need
1951to compile this single file. 4620to compile this single file.
1952.PP 4621.PP
1953\fI\s-1LIBEVENT\s0 \s-1COMPATIBILITY\s0 \s-1API\s0\fR 4622\fI\s-1LIBEVENT COMPATIBILITY API\s0\fR
1954.IX Subsection "LIBEVENT COMPATIBILITY API" 4623.IX Subsection "LIBEVENT COMPATIBILITY API"
1955.PP 4624.PP
1956To include the libevent compatibility \s-1API\s0, also include: 4625To include the libevent compatibility \s-1API,\s0 also include:
1957.PP 4626.PP
1958.Vb 1 4627.Vb 1
1959\& #include "event.c" 4628\& #include "event.c"
1960.Ve 4629.Ve
1961.PP 4630.PP
1962in the file including \fIev.c\fR, and: 4631in the file including \fIev.c\fR, and:
1963.PP 4632.PP
1964.Vb 1 4633.Vb 1
1965\& #include "event.h" 4634\& #include "event.h"
1966.Ve 4635.Ve
1967.PP 4636.PP
1968in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR. 4637in the files that want to use the libevent \s-1API.\s0 This also includes \fIev.h\fR.
1969.PP 4638.PP
1970You need the following additional files for this: 4639You need the following additional files for this:
1971.PP 4640.PP
1972.Vb 2 4641.Vb 2
1973\& event.h 4642\& event.h
1974\& event.c 4643\& event.c
1975.Ve 4644.Ve
1976.PP 4645.PP
1977\fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR 4646\fI\s-1AUTOCONF SUPPORT\s0\fR
1978.IX Subsection "AUTOCONF SUPPORT" 4647.IX Subsection "AUTOCONF SUPPORT"
1979.PP 4648.PP
1980Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your config in 4649Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your configuration in
1981whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your 4650whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
1982\&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then 4651\&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then
1983include \fIconfig.h\fR and configure itself accordingly. 4652include \fIconfig.h\fR and configure itself accordingly.
1984.PP 4653.PP
1985For this of course you need the m4 file: 4654For this of course you need the m4 file:
1986.PP 4655.PP
1987.Vb 1 4656.Vb 1
1988\& libev.m4 4657\& libev.m4
1989.Ve 4658.Ve
1990.Sh "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0" 4659.SS "\s-1PREPROCESSOR SYMBOLS/MACROS\s0"
1991.IX Subsection "PREPROCESSOR SYMBOLS/MACROS" 4660.IX Subsection "PREPROCESSOR SYMBOLS/MACROS"
1992Libev can be configured via a variety of preprocessor symbols you have to define 4661Libev can be configured via a variety of preprocessor symbols you have to
1993before including any of its files. The default is not to build for multiplicity 4662define before including (or compiling) any of its files. The default in
1994and only include the select backend. 4663the absence of autoconf is documented for every option.
4664.PP
4665Symbols marked with \*(L"(h)\*(R" do not change the \s-1ABI,\s0 and can have different
4666values when compiling libev vs. including \fIev.h\fR, so it is permissible
4667to redefine them before including \fIev.h\fR without breaking compatibility
4668to a compiled library. All other symbols change the \s-1ABI,\s0 which means all
4669users of libev and the libev code itself must be compiled with compatible
4670settings.
4671.IP "\s-1EV_COMPAT3\s0 (h)" 4
4672.IX Item "EV_COMPAT3 (h)"
4673Backwards compatibility is a major concern for libev. This is why this
4674release of libev comes with wrappers for the functions and symbols that
4675have been renamed between libev version 3 and 4.
4676.Sp
4677You can disable these wrappers (to test compatibility with future
4678versions) by defining \f(CW\*(C`EV_COMPAT3\*(C'\fR to \f(CW0\fR when compiling your
4679sources. This has the additional advantage that you can drop the \f(CW\*(C`struct\*(C'\fR
4680from \f(CW\*(C`struct ev_loop\*(C'\fR declarations, as libev will provide an \f(CW\*(C`ev_loop\*(C'\fR
4681typedef in that case.
4682.Sp
4683In some future version, the default for \f(CW\*(C`EV_COMPAT3\*(C'\fR will become \f(CW0\fR,
4684and in some even more future version the compatibility code will be
4685removed completely.
1995.IP "\s-1EV_STANDALONE\s0" 4 4686.IP "\s-1EV_STANDALONE\s0 (h)" 4
1996.IX Item "EV_STANDALONE" 4687.IX Item "EV_STANDALONE (h)"
1997Must always be \f(CW1\fR if you do not use autoconf configuration, which 4688Must always be \f(CW1\fR if you do not use autoconf configuration, which
1998keeps libev from including \fIconfig.h\fR, and it also defines dummy 4689keeps libev from including \fIconfig.h\fR, and it also defines dummy
1999implementations for some libevent functions (such as logging, which is not 4690implementations for some libevent functions (such as logging, which is not
2000supported). It will also not define any of the structs usually found in 4691supported). It will also not define any of the structs usually found in
2001\&\fIevent.h\fR that are not directly supported by the libev core alone. 4692\&\fIevent.h\fR that are not directly supported by the libev core alone.
4693.Sp
4694In standalone mode, libev will still try to automatically deduce the
4695configuration, but has to be more conservative.
4696.IP "\s-1EV_USE_FLOOR\s0" 4
4697.IX Item "EV_USE_FLOOR"
4698If defined to be \f(CW1\fR, libev will use the \f(CW\*(C`floor ()\*(C'\fR function for its
4699periodic reschedule calculations, otherwise libev will fall back on a
4700portable (slower) implementation. If you enable this, you usually have to
4701link against libm or something equivalent. Enabling this when the \f(CW\*(C`floor\*(C'\fR
4702function is not available will fail, so the safe default is to not enable
4703this.
2002.IP "\s-1EV_USE_MONOTONIC\s0" 4 4704.IP "\s-1EV_USE_MONOTONIC\s0" 4
2003.IX Item "EV_USE_MONOTONIC" 4705.IX Item "EV_USE_MONOTONIC"
2004If defined to be \f(CW1\fR, libev will try to detect the availability of the 4706If defined to be \f(CW1\fR, libev will try to detect the availability of the
2005monotonic clock option at both compiletime and runtime. Otherwise no use 4707monotonic clock option at both compile time and runtime. Otherwise no
2006of the monotonic clock option will be attempted. If you enable this, you 4708use of the monotonic clock option will be attempted. If you enable this,
2007usually have to link against librt or something similar. Enabling it when 4709you usually have to link against librt or something similar. Enabling it
2008the functionality isn't available is safe, though, althoguh you have 4710when the functionality isn't available is safe, though, although you have
2009to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR 4711to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
2010function is hiding in (often \fI\-lrt\fR). 4712function is hiding in (often \fI\-lrt\fR). See also \f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
2011.IP "\s-1EV_USE_REALTIME\s0" 4 4713.IP "\s-1EV_USE_REALTIME\s0" 4
2012.IX Item "EV_USE_REALTIME" 4714.IX Item "EV_USE_REALTIME"
2013If defined to be \f(CW1\fR, libev will try to detect the availability of the 4715If defined to be \f(CW1\fR, libev will try to detect the availability of the
2014realtime clock option at compiletime (and assume its availability at 4716real-time clock option at compile time (and assume its availability
2015runtime if successful). Otherwise no use of the realtime clock option will 4717at runtime if successful). Otherwise no use of the real-time clock
2016be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR by \f(CW\*(C`clock_get 4718option will be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR
2017(CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect correctness. See tzhe note about libraries 4719by \f(CW\*(C`clock_get (CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect
2018in the description of \f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. 4720correctness. See the note about libraries in the description of
4721\&\f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. Defaults to the opposite value of
4722\&\f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
4723.IP "\s-1EV_USE_CLOCK_SYSCALL\s0" 4
4724.IX Item "EV_USE_CLOCK_SYSCALL"
4725If defined to be \f(CW1\fR, libev will try to use a direct syscall instead
4726of calling the system-provided \f(CW\*(C`clock_gettime\*(C'\fR function. This option
4727exists because on GNU/Linux, \f(CW\*(C`clock_gettime\*(C'\fR is in \f(CW\*(C`librt\*(C'\fR, but \f(CW\*(C`librt\*(C'\fR
4728unconditionally pulls in \f(CW\*(C`libpthread\*(C'\fR, slowing down single-threaded
4729programs needlessly. Using a direct syscall is slightly slower (in
4730theory), because no optimised vdso implementation can be used, but avoids
4731the pthread dependency. Defaults to \f(CW1\fR on GNU/Linux with glibc 2.x or
4732higher, as it simplifies linking (no need for \f(CW\*(C`\-lrt\*(C'\fR).
4733.IP "\s-1EV_USE_NANOSLEEP\s0" 4
4734.IX Item "EV_USE_NANOSLEEP"
4735If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available
4736and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR.
4737.IP "\s-1EV_USE_EVENTFD\s0" 4
4738.IX Item "EV_USE_EVENTFD"
4739If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
4740available and will probe for kernel support at runtime. This will improve
4741\&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
4742If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
47432.7 or newer, otherwise disabled.
2019.IP "\s-1EV_USE_SELECT\s0" 4 4744.IP "\s-1EV_USE_SELECT\s0" 4
2020.IX Item "EV_USE_SELECT" 4745.IX Item "EV_USE_SELECT"
2021If undefined or defined to be \f(CW1\fR, libev will compile in support for the 4746If undefined or defined to be \f(CW1\fR, libev will compile in support for the
2022\&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at autodetection will be done: if no 4747\&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at auto-detection will be done: if no
2023other method takes over, select will be it. Otherwise the select backend 4748other method takes over, select will be it. Otherwise the select backend
2024will not be compiled in. 4749will not be compiled in.
2025.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4 4750.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
2026.IX Item "EV_SELECT_USE_FD_SET" 4751.IX Item "EV_SELECT_USE_FD_SET"
2027If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR 4752If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR
2028structure. This is useful if libev doesn't compile due to a missing 4753structure. This is useful if libev doesn't compile due to a missing
2029\&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it misguesses the bitset layout on 4754\&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it mis-guesses the bitset layout
2030exotic systems. This usually limits the range of file descriptors to some 4755on exotic systems. This usually limits the range of file descriptors to
2031low limit such as 1024 or might have other limitations (winsocket only 4756some low limit such as 1024 or might have other limitations (winsocket
2032allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation, might 4757only allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation,
2033influence the size of the \f(CW\*(C`fd_set\*(C'\fR used. 4758configures the maximum size of the \f(CW\*(C`fd_set\*(C'\fR.
2034.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4 4759.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
2035.IX Item "EV_SELECT_IS_WINSOCKET" 4760.IX Item "EV_SELECT_IS_WINSOCKET"
2036When defined to \f(CW1\fR, the select backend will assume that 4761When defined to \f(CW1\fR, the select backend will assume that
2037select/socket/connect etc. don't understand file descriptors but 4762select/socket/connect etc. don't understand file descriptors but
2038wants osf handles on win32 (this is the case when the select to 4763wants osf handles on win32 (this is the case when the select to
2039be used is the winsock select). This means that it will call 4764be used is the winsock select). This means that it will call
2040\&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise, 4765\&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
2041it is assumed that all these functions actually work on fds, even 4766it is assumed that all these functions actually work on fds, even
2042on win32. Should not be defined on non\-win32 platforms. 4767on win32. Should not be defined on non\-win32 platforms.
4768.IP "\s-1EV_FD_TO_WIN32_HANDLE\s0(fd)" 4
4769.IX Item "EV_FD_TO_WIN32_HANDLE(fd)"
4770If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map
4771file descriptors to socket handles. When not defining this symbol (the
4772default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually
4773correct. In some cases, programs use their own file descriptor management,
4774in which case they can provide this function to map fds to socket handles.
4775.IP "\s-1EV_WIN32_HANDLE_TO_FD\s0(handle)" 4
4776.IX Item "EV_WIN32_HANDLE_TO_FD(handle)"
4777If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR then libev maps handles to file descriptors
4778using the standard \f(CW\*(C`_open_osfhandle\*(C'\fR function. For programs implementing
4779their own fd to handle mapping, overwriting this function makes it easier
4780to do so. This can be done by defining this macro to an appropriate value.
4781.IP "\s-1EV_WIN32_CLOSE_FD\s0(fd)" 4
4782.IX Item "EV_WIN32_CLOSE_FD(fd)"
4783If programs implement their own fd to handle mapping on win32, then this
4784macro can be used to override the \f(CW\*(C`close\*(C'\fR function, useful to unregister
4785file descriptors again. Note that the replacement function has to close
4786the underlying \s-1OS\s0 handle.
4787.IP "\s-1EV_USE_WSASOCKET\s0" 4
4788.IX Item "EV_USE_WSASOCKET"
4789If defined to be \f(CW1\fR, libev will use \f(CW\*(C`WSASocket\*(C'\fR to create its internal
4790communication socket, which works better in some environments. Otherwise,
4791the normal \f(CW\*(C`socket\*(C'\fR function will be used, which works better in other
4792environments.
2043.IP "\s-1EV_USE_POLL\s0" 4 4793.IP "\s-1EV_USE_POLL\s0" 4
2044.IX Item "EV_USE_POLL" 4794.IX Item "EV_USE_POLL"
2045If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2) 4795If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2)
2046backend. Otherwise it will be enabled on non\-win32 platforms. It 4796backend. Otherwise it will be enabled on non\-win32 platforms. It
2047takes precedence over select. 4797takes precedence over select.
2048.IP "\s-1EV_USE_EPOLL\s0" 4 4798.IP "\s-1EV_USE_EPOLL\s0" 4
2049.IX Item "EV_USE_EPOLL" 4799.IX Item "EV_USE_EPOLL"
2050If defined to be \f(CW1\fR, libev will compile in support for the Linux 4800If defined to be \f(CW1\fR, libev will compile in support for the Linux
2051\&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime, 4801\&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime,
2052otherwise another method will be used as fallback. This is the 4802otherwise another method will be used as fallback. This is the preferred
2053preferred backend for GNU/Linux systems. 4803backend for GNU/Linux systems. If undefined, it will be enabled if the
4804headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4805.IP "\s-1EV_USE_LINUXAIO\s0" 4
4806.IX Item "EV_USE_LINUXAIO"
4807If defined to be \f(CW1\fR, libev will compile in support for the Linux
4808aio backend. Due to it's currenbt limitations it has to be requested
4809explicitly. If undefined, it will be enabled on linux, otherwise
4810disabled.
2054.IP "\s-1EV_USE_KQUEUE\s0" 4 4811.IP "\s-1EV_USE_KQUEUE\s0" 4
2055.IX Item "EV_USE_KQUEUE" 4812.IX Item "EV_USE_KQUEUE"
2056If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style 4813If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
2057\&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime, 4814\&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime,
2058otherwise another method will be used as fallback. This is the preferred 4815otherwise another method will be used as fallback. This is the preferred
… …
206810 port style backend. Its availability will be detected at runtime, 482510 port style backend. Its availability will be detected at runtime,
2069otherwise another method will be used as fallback. This is the preferred 4826otherwise another method will be used as fallback. This is the preferred
2070backend for Solaris 10 systems. 4827backend for Solaris 10 systems.
2071.IP "\s-1EV_USE_DEVPOLL\s0" 4 4828.IP "\s-1EV_USE_DEVPOLL\s0" 4
2072.IX Item "EV_USE_DEVPOLL" 4829.IX Item "EV_USE_DEVPOLL"
2073reserved for future expansion, works like the \s-1USE\s0 symbols above. 4830Reserved for future expansion, works like the \s-1USE\s0 symbols above.
4831.IP "\s-1EV_USE_INOTIFY\s0" 4
4832.IX Item "EV_USE_INOTIFY"
4833If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
4834interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
4835be detected at runtime. If undefined, it will be enabled if the headers
4836indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4837.IP "\s-1EV_NO_SMP\s0" 4
4838.IX Item "EV_NO_SMP"
4839If defined to be \f(CW1\fR, libev will assume that memory is always coherent
4840between threads, that is, threads can be used, but threads never run on
4841different cpus (or different cpu cores). This reduces dependencies
4842and makes libev faster.
4843.IP "\s-1EV_NO_THREADS\s0" 4
4844.IX Item "EV_NO_THREADS"
4845If defined to be \f(CW1\fR, libev will assume that it will never be called from
4846different threads (that includes signal handlers), which is a stronger
4847assumption than \f(CW\*(C`EV_NO_SMP\*(C'\fR, above. This reduces dependencies and makes
4848libev faster.
4849.IP "\s-1EV_ATOMIC_T\s0" 4
4850.IX Item "EV_ATOMIC_T"
4851Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
4852access is atomic with respect to other threads or signal contexts. No
4853such type is easily found in the C language, so you can provide your own
4854type that you know is safe for your purposes. It is used both for signal
4855handler \*(L"locking\*(R" as well as for signal and thread safety in \f(CW\*(C`ev_async\*(C'\fR
4856watchers.
4857.Sp
4858In the absence of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR
4859(from \fIsignal.h\fR), which is usually good enough on most platforms.
2074.IP "\s-1EV_H\s0" 4 4860.IP "\s-1EV_H\s0 (h)" 4
2075.IX Item "EV_H" 4861.IX Item "EV_H (h)"
2076The name of the \fIev.h\fR header file used to include it. The default if 4862The name of the \fIev.h\fR header file used to include it. The default if
2077undefined is \f(CW\*(C`<ev.h>\*(C'\fR in \fIevent.h\fR and \f(CW"ev.h"\fR in \fIev.c\fR. This 4863undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be
2078can be used to virtually rename the \fIev.h\fR header file in case of conflicts. 4864used to virtually rename the \fIev.h\fR header file in case of conflicts.
2079.IP "\s-1EV_CONFIG_H\s0" 4 4865.IP "\s-1EV_CONFIG_H\s0 (h)" 4
2080.IX Item "EV_CONFIG_H" 4866.IX Item "EV_CONFIG_H (h)"
2081If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override 4867If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
2082\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to 4868\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
2083\&\f(CW\*(C`EV_H\*(C'\fR, above. 4869\&\f(CW\*(C`EV_H\*(C'\fR, above.
2084.IP "\s-1EV_EVENT_H\s0" 4 4870.IP "\s-1EV_EVENT_H\s0 (h)" 4
2085.IX Item "EV_EVENT_H" 4871.IX Item "EV_EVENT_H (h)"
2086Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea 4872Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea
2087of how the \fIevent.h\fR header can be found. 4873of how the \fIevent.h\fR header can be found, the default is \f(CW"event.h"\fR.
2088.IP "\s-1EV_PROTOTYPES\s0" 4 4874.IP "\s-1EV_PROTOTYPES\s0 (h)" 4
2089.IX Item "EV_PROTOTYPES" 4875.IX Item "EV_PROTOTYPES (h)"
2090If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function 4876If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
2091prototypes, but still define all the structs and other symbols. This is 4877prototypes, but still define all the structs and other symbols. This is
2092occasionally useful if you want to provide your own wrapper functions 4878occasionally useful if you want to provide your own wrapper functions
2093around libev functions. 4879around libev functions.
2094.IP "\s-1EV_MULTIPLICITY\s0" 4 4880.IP "\s-1EV_MULTIPLICITY\s0" 4
… …
2096If undefined or defined to \f(CW1\fR, then all event-loop-specific functions 4882If undefined or defined to \f(CW1\fR, then all event-loop-specific functions
2097will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create 4883will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create
2098additional independent event loops. Otherwise there will be no support 4884additional independent event loops. Otherwise there will be no support
2099for multiple event loops and there is no first event loop pointer 4885for multiple event loops and there is no first event loop pointer
2100argument. Instead, all functions act on the single default loop. 4886argument. Instead, all functions act on the single default loop.
2101.IP "\s-1EV_PERIODIC_ENABLE\s0" 4 4887.Sp
2102.IX Item "EV_PERIODIC_ENABLE" 4888Note that \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR will no longer provide a
2103If undefined or defined to be \f(CW1\fR, then periodic timers are supported. If 4889default loop when multiplicity is switched off \- you always have to
2104defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of 4890initialise the loop manually in this case.
2105code.
2106.IP "\s-1EV_EMBED_ENABLE\s0" 4
2107.IX Item "EV_EMBED_ENABLE"
2108If undefined or defined to be \f(CW1\fR, then embed watchers are supported. If
2109defined to be \f(CW0\fR, then they are not.
2110.IP "\s-1EV_STAT_ENABLE\s0" 4
2111.IX Item "EV_STAT_ENABLE"
2112If undefined or defined to be \f(CW1\fR, then stat watchers are supported. If
2113defined to be \f(CW0\fR, then they are not.
2114.IP "\s-1EV_FORK_ENABLE\s0" 4
2115.IX Item "EV_FORK_ENABLE"
2116If undefined or defined to be \f(CW1\fR, then fork watchers are supported. If
2117defined to be \f(CW0\fR, then they are not.
2118.IP "\s-1EV_MINIMAL\s0" 4 4891.IP "\s-1EV_MINPRI\s0" 4
2119.IX Item "EV_MINIMAL" 4892.IX Item "EV_MINPRI"
4893.PD 0
4894.IP "\s-1EV_MAXPRI\s0" 4
4895.IX Item "EV_MAXPRI"
4896.PD
4897The range of allowed priorities. \f(CW\*(C`EV_MINPRI\*(C'\fR must be smaller or equal to
4898\&\f(CW\*(C`EV_MAXPRI\*(C'\fR, but otherwise there are no non-obvious limitations. You can
4899provide for more priorities by overriding those symbols (usually defined
4900to be \f(CW\*(C`\-2\*(C'\fR and \f(CW2\fR, respectively).
4901.Sp
4902When doing priority-based operations, libev usually has to linearly search
4903all the priorities, so having many of them (hundreds) uses a lot of space
4904and time, so using the defaults of five priorities (\-2 .. +2) is usually
4905fine.
4906.Sp
4907If your embedding application does not need any priorities, defining these
4908both to \f(CW0\fR will save some memory and \s-1CPU.\s0
4909.IP "\s-1EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE, EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE, EV_ASYNC_ENABLE, EV_CHILD_ENABLE.\s0" 4
4910.IX Item "EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE, EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE, EV_ASYNC_ENABLE, EV_CHILD_ENABLE."
4911If undefined or defined to be \f(CW1\fR (and the platform supports it), then
4912the respective watcher type is supported. If defined to be \f(CW0\fR, then it
4913is not. Disabling watcher types mainly saves code size.
4914.IP "\s-1EV_FEATURES\s0" 4
4915.IX Item "EV_FEATURES"
2120If you need to shave off some kilobytes of code at the expense of some 4916If you need to shave off some kilobytes of code at the expense of some
2121speed, define this symbol to \f(CW1\fR. Currently only used for gcc to override 4917speed (but with the full \s-1API\s0), you can define this symbol to request
2122some inlining decisions, saves roughly 30% codesize of amd64. 4918certain subsets of functionality. The default is to enable all features
4919that can be enabled on the platform.
4920.Sp
4921A typical way to use this symbol is to define it to \f(CW0\fR (or to a bitset
4922with some broad features you want) and then selectively re-enable
4923additional parts you want, for example if you want everything minimal,
4924but multiple event loop support, async and child watchers and the poll
4925backend, use this:
4926.Sp
4927.Vb 5
4928\& #define EV_FEATURES 0
4929\& #define EV_MULTIPLICITY 1
4930\& #define EV_USE_POLL 1
4931\& #define EV_CHILD_ENABLE 1
4932\& #define EV_ASYNC_ENABLE 1
4933.Ve
4934.Sp
4935The actual value is a bitset, it can be a combination of the following
4936values (by default, all of these are enabled):
4937.RS 4
4938.ie n .IP "1 \- faster/larger code" 4
4939.el .IP "\f(CW1\fR \- faster/larger code" 4
4940.IX Item "1 - faster/larger code"
4941Use larger code to speed up some operations.
4942.Sp
4943Currently this is used to override some inlining decisions (enlarging the
4944code size by roughly 30% on amd64).
4945.Sp
4946When optimising for size, use of compiler flags such as \f(CW\*(C`\-Os\*(C'\fR with
4947gcc is recommended, as well as \f(CW\*(C`\-DNDEBUG\*(C'\fR, as libev contains a number of
4948assertions.
4949.Sp
4950The default is off when \f(CW\*(C`_\|_OPTIMIZE_SIZE_\|_\*(C'\fR is defined by your compiler
4951(e.g. gcc with \f(CW\*(C`\-Os\*(C'\fR).
4952.ie n .IP "2 \- faster/larger data structures" 4
4953.el .IP "\f(CW2\fR \- faster/larger data structures" 4
4954.IX Item "2 - faster/larger data structures"
4955Replaces the small 2\-heap for timer management by a faster 4\-heap, larger
4956hash table sizes and so on. This will usually further increase code size
4957and can additionally have an effect on the size of data structures at
4958runtime.
4959.Sp
4960The default is off when \f(CW\*(C`_\|_OPTIMIZE_SIZE_\|_\*(C'\fR is defined by your compiler
4961(e.g. gcc with \f(CW\*(C`\-Os\*(C'\fR).
4962.ie n .IP "4 \- full \s-1API\s0 configuration" 4
4963.el .IP "\f(CW4\fR \- full \s-1API\s0 configuration" 4
4964.IX Item "4 - full API configuration"
4965This enables priorities (sets \f(CW\*(C`EV_MAXPRI\*(C'\fR=2 and \f(CW\*(C`EV_MINPRI\*(C'\fR=\-2), and
4966enables multiplicity (\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR=1).
4967.ie n .IP "8 \- full \s-1API\s0" 4
4968.el .IP "\f(CW8\fR \- full \s-1API\s0" 4
4969.IX Item "8 - full API"
4970This enables a lot of the \*(L"lesser used\*(R" \s-1API\s0 functions. See \f(CW\*(C`ev.h\*(C'\fR for
4971details on which parts of the \s-1API\s0 are still available without this
4972feature, and do not complain if this subset changes over time.
4973.ie n .IP "16 \- enable all optional watcher types" 4
4974.el .IP "\f(CW16\fR \- enable all optional watcher types" 4
4975.IX Item "16 - enable all optional watcher types"
4976Enables all optional watcher types. If you want to selectively enable
4977only some watcher types other than I/O and timers (e.g. prepare,
4978embed, async, child...) you can enable them manually by defining
4979\&\f(CW\*(C`EV_watchertype_ENABLE\*(C'\fR to \f(CW1\fR instead.
4980.ie n .IP "32 \- enable all backends" 4
4981.el .IP "\f(CW32\fR \- enable all backends" 4
4982.IX Item "32 - enable all backends"
4983This enables all backends \- without this feature, you need to enable at
4984least one backend manually (\f(CW\*(C`EV_USE_SELECT\*(C'\fR is a good choice).
4985.ie n .IP "64 \- enable OS-specific ""helper"" APIs" 4
4986.el .IP "\f(CW64\fR \- enable OS-specific ``helper'' APIs" 4
4987.IX Item "64 - enable OS-specific helper APIs"
4988Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
4989default.
4990.RE
4991.RS 4
4992.Sp
4993Compiling with \f(CW\*(C`gcc \-Os \-DEV_STANDALONE \-DEV_USE_EPOLL=1 \-DEV_FEATURES=0\*(C'\fR
4994reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
4995code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
4996watchers, timers and monotonic clock support.
4997.Sp
4998With an intelligent-enough linker (gcc+binutils are intelligent enough
4999when you use \f(CW\*(C`\-Wl,\-\-gc\-sections \-ffunction\-sections\*(C'\fR) functions unused by
5000your program might be left out as well \- a binary starting a timer and an
5001I/O watcher then might come out at only 5Kb.
5002.RE
5003.IP "\s-1EV_API_STATIC\s0" 4
5004.IX Item "EV_API_STATIC"
5005If this symbol is defined (by default it is not), then all identifiers
5006will have static linkage. This means that libev will not export any
5007identifiers, and you cannot link against libev anymore. This can be useful
5008when you embed libev, only want to use libev functions in a single file,
5009and do not want its identifiers to be visible.
5010.Sp
5011To use this, define \f(CW\*(C`EV_API_STATIC\*(C'\fR and include \fIev.c\fR in the file that
5012wants to use libev.
5013.Sp
5014This option only works when libev is compiled with a C compiler, as \*(C+
5015doesn't support the required declaration syntax.
5016.IP "\s-1EV_AVOID_STDIO\s0" 4
5017.IX Item "EV_AVOID_STDIO"
5018If this is set to \f(CW1\fR at compiletime, then libev will avoid using stdio
5019functions (printf, scanf, perror etc.). This will increase the code size
5020somewhat, but if your program doesn't otherwise depend on stdio and your
5021libc allows it, this avoids linking in the stdio library which is quite
5022big.
5023.Sp
5024Note that error messages might become less precise when this option is
5025enabled.
5026.IP "\s-1EV_NSIG\s0" 4
5027.IX Item "EV_NSIG"
5028The highest supported signal number, +1 (or, the number of
5029signals): Normally, libev tries to deduce the maximum number of signals
5030automatically, but sometimes this fails, in which case it can be
5031specified. Also, using a lower number than detected (\f(CW32\fR should be
5032good for about any system in existence) can save some memory, as libev
5033statically allocates some 12\-24 bytes per signal number.
2123.IP "\s-1EV_PID_HASHSIZE\s0" 4 5034.IP "\s-1EV_PID_HASHSIZE\s0" 4
2124.IX Item "EV_PID_HASHSIZE" 5035.IX Item "EV_PID_HASHSIZE"
2125\&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by 5036\&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by
2126pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR), usually more 5037pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR disabled),
2127than enough. If you need to manage thousands of children you might want to 5038usually more than enough. If you need to manage thousands of children you
2128increase this value. 5039might want to increase this value (\fImust\fR be a power of two).
5040.IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4
5041.IX Item "EV_INOTIFY_HASHSIZE"
5042\&\f(CW\*(C`ev_stat\*(C'\fR watchers use a small hash table to distribute workload by
5043inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR
5044disabled), usually more than enough. If you need to manage thousands of
5045\&\f(CW\*(C`ev_stat\*(C'\fR watchers you might want to increase this value (\fImust\fR be a
5046power of two).
5047.IP "\s-1EV_USE_4HEAP\s0" 4
5048.IX Item "EV_USE_4HEAP"
5049Heaps are not very cache-efficient. To improve the cache-efficiency of the
5050timer and periodics heaps, libev uses a 4\-heap when this symbol is defined
5051to \f(CW1\fR. The 4\-heap uses more complicated (longer) code but has noticeably
5052faster performance with many (thousands) of watchers.
5053.Sp
5054The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
5055will be \f(CW0\fR.
5056.IP "\s-1EV_HEAP_CACHE_AT\s0" 4
5057.IX Item "EV_HEAP_CACHE_AT"
5058Heaps are not very cache-efficient. To improve the cache-efficiency of the
5059timer and periodics heaps, libev can cache the timestamp (\fIat\fR) within
5060the heap structure (selected by defining \f(CW\*(C`EV_HEAP_CACHE_AT\*(C'\fR to \f(CW1\fR),
5061which uses 8\-12 bytes more per watcher and a few hundred bytes more code,
5062but avoids random read accesses on heap changes. This improves performance
5063noticeably with many (hundreds) of watchers.
5064.Sp
5065The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
5066will be \f(CW0\fR.
5067.IP "\s-1EV_VERIFY\s0" 4
5068.IX Item "EV_VERIFY"
5069Controls how much internal verification (see \f(CW\*(C`ev_verify ()\*(C'\fR) will
5070be done: If set to \f(CW0\fR, no internal verification code will be compiled
5071in. If set to \f(CW1\fR, then verification code will be compiled in, but not
5072called. If set to \f(CW2\fR, then the internal verification code will be
5073called once per loop, which can slow down libev. If set to \f(CW3\fR, then the
5074verification code will be called very frequently, which will slow down
5075libev considerably.
5076.Sp
5077The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
5078will be \f(CW0\fR.
2129.IP "\s-1EV_COMMON\s0" 4 5079.IP "\s-1EV_COMMON\s0" 4
2130.IX Item "EV_COMMON" 5080.IX Item "EV_COMMON"
2131By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining 5081By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining
2132this macro to a something else you can include more and other types of 5082this macro to something else you can include more and other types of
2133members. You have to define it each time you include one of the files, 5083members. You have to define it each time you include one of the files,
2134though, and it must be identical each time. 5084though, and it must be identical each time.
2135.Sp 5085.Sp
2136For example, the perl \s-1EV\s0 module uses something like this: 5086For example, the perl \s-1EV\s0 module uses something like this:
2137.Sp 5087.Sp
2138.Vb 3 5088.Vb 3
2139\& #define EV_COMMON \e 5089\& #define EV_COMMON \e
2140\& SV *self; /* contains this struct */ \e 5090\& SV *self; /* contains this struct */ \e
2141\& SV *cb_sv, *fh /* note no trailing ";" */ 5091\& SV *cb_sv, *fh /* note no trailing ";" */
2142.Ve 5092.Ve
2143.IP "\s-1EV_CB_DECLARE\s0 (type)" 4 5093.IP "\s-1EV_CB_DECLARE\s0 (type)" 4
2144.IX Item "EV_CB_DECLARE (type)" 5094.IX Item "EV_CB_DECLARE (type)"
2145.PD 0 5095.PD 0
2146.IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4 5096.IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4
… …
2148.IP "ev_set_cb (ev, cb)" 4 5098.IP "ev_set_cb (ev, cb)" 4
2149.IX Item "ev_set_cb (ev, cb)" 5099.IX Item "ev_set_cb (ev, cb)"
2150.PD 5100.PD
2151Can be used to change the callback member declaration in each watcher, 5101Can be used to change the callback member declaration in each watcher,
2152and the way callbacks are invoked and set. Must expand to a struct member 5102and the way callbacks are invoked and set. Must expand to a struct member
2153definition and a statement, respectively. See the \fIev.v\fR header file for 5103definition and a statement, respectively. See the \fIev.h\fR header file for
2154their default definitions. One possible use for overriding these is to 5104their default definitions. One possible use for overriding these is to
2155avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use 5105avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use
2156method calls instead of plain function calls in \*(C+. 5106method calls instead of plain function calls in \*(C+.
5107.SS "\s-1EXPORTED API SYMBOLS\s0"
5108.IX Subsection "EXPORTED API SYMBOLS"
5109If you need to re-export the \s-1API\s0 (e.g. via a \s-1DLL\s0) and you need a list of
5110exported symbols, you can use the provided \fISymbol.*\fR files which list
5111all public symbols, one per line:
5112.PP
5113.Vb 2
5114\& Symbols.ev for libev proper
5115\& Symbols.event for the libevent emulation
5116.Ve
5117.PP
5118This can also be used to rename all public symbols to avoid clashes with
5119multiple versions of libev linked together (which is obviously bad in
5120itself, but sometimes it is inconvenient to avoid this).
5121.PP
5122A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to
5123include before including \fIev.h\fR:
5124.PP
5125.Vb 1
5126\& <Symbols.ev sed \-e "s/.*/#define & myprefix_&/" >wrap.h
5127.Ve
5128.PP
5129This would create a file \fIwrap.h\fR which essentially looks like this:
5130.PP
5131.Vb 4
5132\& #define ev_backend myprefix_ev_backend
5133\& #define ev_check_start myprefix_ev_check_start
5134\& #define ev_check_stop myprefix_ev_check_stop
5135\& ...
5136.Ve
2157.Sh "\s-1EXAMPLES\s0" 5137.SS "\s-1EXAMPLES\s0"
2158.IX Subsection "EXAMPLES" 5138.IX Subsection "EXAMPLES"
2159For a real-world example of a program the includes libev 5139For a real-world example of a program the includes libev
2160verbatim, you can have a look at the \s-1EV\s0 perl module 5140verbatim, you can have a look at the \s-1EV\s0 perl module
2161(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in 5141(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
2162the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public 5142the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public
2163interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file 5143interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file
2164will be compiled. It is pretty complex because it provides its own header 5144will be compiled. It is pretty complex because it provides its own header
2165file. 5145file.
2166.Sp 5146.PP
2167The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file 5147The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file
2168that everybody includes and which overrides some autoconf choices: 5148that everybody includes and which overrides some configure choices:
2169.Sp 5149.PP
2170.Vb 4 5150.Vb 8
5151\& #define EV_FEATURES 8
5152\& #define EV_USE_SELECT 1
5153\& #define EV_PREPARE_ENABLE 1
5154\& #define EV_IDLE_ENABLE 1
5155\& #define EV_SIGNAL_ENABLE 1
5156\& #define EV_CHILD_ENABLE 1
2171\& #define EV_USE_POLL 0 5157\& #define EV_USE_STDEXCEPT 0
2172\& #define EV_MULTIPLICITY 0
2173\& #define EV_PERIODICS 0
2174\& #define EV_CONFIG_H <config.h> 5158\& #define EV_CONFIG_H <config.h>
2175.Ve 5159\&
2176.Sp
2177.Vb 1
2178\& #include "ev++.h" 5160\& #include "ev++.h"
2179.Ve 5161.Ve
2180.Sp 5162.PP
2181And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled: 5163And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled:
2182.Sp 5164.PP
2183.Vb 2 5165.Vb 2
2184\& #include "ev_cpp.h" 5166\& #include "ev_cpp.h"
2185\& #include "ev.c" 5167\& #include "ev.c"
2186.Ve 5168.Ve
5169.SH "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT"
5170.IX Header "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT"
5171.SS "\s-1THREADS AND COROUTINES\s0"
5172.IX Subsection "THREADS AND COROUTINES"
5173\fI\s-1THREADS\s0\fR
5174.IX Subsection "THREADS"
5175.PP
5176All libev functions are reentrant and thread-safe unless explicitly
5177documented otherwise, but libev implements no locking itself. This means
5178that you can use as many loops as you want in parallel, as long as there
5179are no concurrent calls into any libev function with the same loop
5180parameter (\f(CW\*(C`ev_default_*\*(C'\fR calls have an implicit default loop parameter,
5181of course): libev guarantees that different event loops share no data
5182structures that need any locking.
5183.PP
5184Or to put it differently: calls with different loop parameters can be done
5185concurrently from multiple threads, calls with the same loop parameter
5186must be done serially (but can be done from different threads, as long as
5187only one thread ever is inside a call at any point in time, e.g. by using
5188a mutex per loop).
5189.PP
5190Specifically to support threads (and signal handlers), libev implements
5191so-called \f(CW\*(C`ev_async\*(C'\fR watchers, which allow some limited form of
5192concurrency on the same event loop, namely waking it up \*(L"from the
5193outside\*(R".
5194.PP
5195If you want to know which design (one loop, locking, or multiple loops
5196without or something else still) is best for your problem, then I cannot
5197help you, but here is some generic advice:
5198.IP "\(bu" 4
5199most applications have a main thread: use the default libev loop
5200in that thread, or create a separate thread running only the default loop.
5201.Sp
5202This helps integrating other libraries or software modules that use libev
5203themselves and don't care/know about threading.
5204.IP "\(bu" 4
5205one loop per thread is usually a good model.
5206.Sp
5207Doing this is almost never wrong, sometimes a better-performance model
5208exists, but it is always a good start.
5209.IP "\(bu" 4
5210other models exist, such as the leader/follower pattern, where one
5211loop is handed through multiple threads in a kind of round-robin fashion.
5212.Sp
5213Choosing a model is hard \- look around, learn, know that usually you can do
5214better than you currently do :\-)
5215.IP "\(bu" 4
5216often you need to talk to some other thread which blocks in the
5217event loop.
5218.Sp
5219\&\f(CW\*(C`ev_async\*(C'\fR watchers can be used to wake them up from other threads safely
5220(or from signal contexts...).
5221.Sp
5222An example use would be to communicate signals or other events that only
5223work in the default loop by registering the signal watcher with the
5224default loop and triggering an \f(CW\*(C`ev_async\*(C'\fR watcher from the default loop
5225watcher callback into the event loop interested in the signal.
5226.PP
5227See also \*(L"\s-1THREAD LOCKING EXAMPLE\*(R"\s0.
5228.PP
5229\fI\s-1COROUTINES\s0\fR
5230.IX Subsection "COROUTINES"
5231.PP
5232Libev is very accommodating to coroutines (\*(L"cooperative threads\*(R"):
5233libev fully supports nesting calls to its functions from different
5234coroutines (e.g. you can call \f(CW\*(C`ev_run\*(C'\fR on the same loop from two
5235different coroutines, and switch freely between both coroutines running
5236the loop, as long as you don't confuse yourself). The only exception is
5237that you must not do this from \f(CW\*(C`ev_periodic\*(C'\fR reschedule callbacks.
5238.PP
5239Care has been taken to ensure that libev does not keep local state inside
5240\&\f(CW\*(C`ev_run\*(C'\fR, and other calls do not usually allow for coroutine switches as
5241they do not call any callbacks.
5242.SS "\s-1COMPILER WARNINGS\s0"
5243.IX Subsection "COMPILER WARNINGS"
5244Depending on your compiler and compiler settings, you might get no or a
5245lot of warnings when compiling libev code. Some people are apparently
5246scared by this.
5247.PP
5248However, these are unavoidable for many reasons. For one, each compiler
5249has different warnings, and each user has different tastes regarding
5250warning options. \*(L"Warn-free\*(R" code therefore cannot be a goal except when
5251targeting a specific compiler and compiler-version.
5252.PP
5253Another reason is that some compiler warnings require elaborate
5254workarounds, or other changes to the code that make it less clear and less
5255maintainable.
5256.PP
5257And of course, some compiler warnings are just plain stupid, or simply
5258wrong (because they don't actually warn about the condition their message
5259seems to warn about). For example, certain older gcc versions had some
5260warnings that resulted in an extreme number of false positives. These have
5261been fixed, but some people still insist on making code warn-free with
5262such buggy versions.
5263.PP
5264While libev is written to generate as few warnings as possible,
5265\&\*(L"warn-free\*(R" code is not a goal, and it is recommended not to build libev
5266with any compiler warnings enabled unless you are prepared to cope with
5267them (e.g. by ignoring them). Remember that warnings are just that:
5268warnings, not errors, or proof of bugs.
5269.SS "\s-1VALGRIND\s0"
5270.IX Subsection "VALGRIND"
5271Valgrind has a special section here because it is a popular tool that is
5272highly useful. Unfortunately, valgrind reports are very hard to interpret.
5273.PP
5274If you think you found a bug (memory leak, uninitialised data access etc.)
5275in libev, then check twice: If valgrind reports something like:
5276.PP
5277.Vb 3
5278\& ==2274== definitely lost: 0 bytes in 0 blocks.
5279\& ==2274== possibly lost: 0 bytes in 0 blocks.
5280\& ==2274== still reachable: 256 bytes in 1 blocks.
5281.Ve
5282.PP
5283Then there is no memory leak, just as memory accounted to global variables
5284is not a memleak \- the memory is still being referenced, and didn't leak.
5285.PP
5286Similarly, under some circumstances, valgrind might report kernel bugs
5287as if it were a bug in libev (e.g. in realloc or in the poll backend,
5288although an acceptable workaround has been found here), or it might be
5289confused.
5290.PP
5291Keep in mind that valgrind is a very good tool, but only a tool. Don't
5292make it into some kind of religion.
5293.PP
5294If you are unsure about something, feel free to contact the mailing list
5295with the full valgrind report and an explanation on why you think this
5296is a bug in libev (best check the archives, too :). However, don't be
5297annoyed when you get a brisk \*(L"this is no bug\*(R" answer and take the chance
5298of learning how to interpret valgrind properly.
5299.PP
5300If you need, for some reason, empty reports from valgrind for your project
5301I suggest using suppression lists.
5302.SH "PORTABILITY NOTES"
5303.IX Header "PORTABILITY NOTES"
5304.SS "\s-1GNU/LINUX 32 BIT LIMITATIONS\s0"
5305.IX Subsection "GNU/LINUX 32 BIT LIMITATIONS"
5306GNU/Linux is the only common platform that supports 64 bit file/large file
5307interfaces but \fIdisables\fR them by default.
5308.PP
5309That means that libev compiled in the default environment doesn't support
5310files larger than 2GiB or so, which mainly affects \f(CW\*(C`ev_stat\*(C'\fR watchers.
5311.PP
5312Unfortunately, many programs try to work around this GNU/Linux issue
5313by enabling the large file \s-1API,\s0 which makes them incompatible with the
5314standard libev compiled for their system.
5315.PP
5316Likewise, libev cannot enable the large file \s-1API\s0 itself as this would
5317suddenly make it incompatible to the default compile time environment,
5318i.e. all programs not using special compile switches.
5319.SS "\s-1OS/X AND DARWIN BUGS\s0"
5320.IX Subsection "OS/X AND DARWIN BUGS"
5321The whole thing is a bug if you ask me \- basically any system interface
5322you touch is broken, whether it is locales, poll, kqueue or even the
5323OpenGL drivers.
5324.PP
5325\fI\f(CI\*(C`kqueue\*(C'\fI is buggy\fR
5326.IX Subsection "kqueue is buggy"
5327.PP
5328The kqueue syscall is broken in all known versions \- most versions support
5329only sockets, many support pipes.
5330.PP
5331Libev tries to work around this by not using \f(CW\*(C`kqueue\*(C'\fR by default on this
5332rotten platform, but of course you can still ask for it when creating a
5333loop \- embedding a socket-only kqueue loop into a select-based one is
5334probably going to work well.
5335.PP
5336\fI\f(CI\*(C`poll\*(C'\fI is buggy\fR
5337.IX Subsection "poll is buggy"
5338.PP
5339Instead of fixing \f(CW\*(C`kqueue\*(C'\fR, Apple replaced their (working) \f(CW\*(C`poll\*(C'\fR
5340implementation by something calling \f(CW\*(C`kqueue\*(C'\fR internally around the 10.5.6
5341release, so now \f(CW\*(C`kqueue\*(C'\fR \fIand\fR \f(CW\*(C`poll\*(C'\fR are broken.
5342.PP
5343Libev tries to work around this by not using \f(CW\*(C`poll\*(C'\fR by default on
5344this rotten platform, but of course you can still ask for it when creating
5345a loop.
5346.PP
5347\fI\f(CI\*(C`select\*(C'\fI is buggy\fR
5348.IX Subsection "select is buggy"
5349.PP
5350All that's left is \f(CW\*(C`select\*(C'\fR, and of course Apple found a way to fuck this
5351one up as well: On \s-1OS/X,\s0 \f(CW\*(C`select\*(C'\fR actively limits the number of file
5352descriptors you can pass in to 1024 \- your program suddenly crashes when
5353you use more.
5354.PP
5355There is an undocumented \*(L"workaround\*(R" for this \- defining
5356\&\f(CW\*(C`_DARWIN_UNLIMITED_SELECT\*(C'\fR, which libev tries to use, so select \fIshould\fR
5357work on \s-1OS/X.\s0
5358.SS "\s-1SOLARIS PROBLEMS AND WORKAROUNDS\s0"
5359.IX Subsection "SOLARIS PROBLEMS AND WORKAROUNDS"
5360\fI\f(CI\*(C`errno\*(C'\fI reentrancy\fR
5361.IX Subsection "errno reentrancy"
5362.PP
5363The default compile environment on Solaris is unfortunately so
5364thread-unsafe that you can't even use components/libraries compiled
5365without \f(CW\*(C`\-D_REENTRANT\*(C'\fR in a threaded program, which, of course, isn't
5366defined by default. A valid, if stupid, implementation choice.
5367.PP
5368If you want to use libev in threaded environments you have to make sure
5369it's compiled with \f(CW\*(C`_REENTRANT\*(C'\fR defined.
5370.PP
5371\fIEvent port backend\fR
5372.IX Subsection "Event port backend"
5373.PP
5374The scalable event interface for Solaris is called \*(L"event
5375ports\*(R". Unfortunately, this mechanism is very buggy in all major
5376releases. If you run into high \s-1CPU\s0 usage, your program freezes or you get
5377a large number of spurious wakeups, make sure you have all the relevant
5378and latest kernel patches applied. No, I don't know which ones, but there
5379are multiple ones to apply, and afterwards, event ports actually work
5380great.
5381.PP
5382If you can't get it to work, you can try running the program by setting
5383the environment variable \f(CW\*(C`LIBEV_FLAGS=3\*(C'\fR to only allow \f(CW\*(C`poll\*(C'\fR and
5384\&\f(CW\*(C`select\*(C'\fR backends.
5385.SS "\s-1AIX POLL BUG\s0"
5386.IX Subsection "AIX POLL BUG"
5387\&\s-1AIX\s0 unfortunately has a broken \f(CW\*(C`poll.h\*(C'\fR header. Libev works around
5388this by trying to avoid the poll backend altogether (i.e. it's not even
5389compiled in), which normally isn't a big problem as \f(CW\*(C`select\*(C'\fR works fine
5390with large bitsets on \s-1AIX,\s0 and \s-1AIX\s0 is dead anyway.
5391.SS "\s-1WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS\s0"
5392.IX Subsection "WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS"
5393\fIGeneral issues\fR
5394.IX Subsection "General issues"
5395.PP
5396Win32 doesn't support any of the standards (e.g. \s-1POSIX\s0) that libev
5397requires, and its I/O model is fundamentally incompatible with the \s-1POSIX\s0
5398model. Libev still offers limited functionality on this platform in
5399the form of the \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR backend, and only supports socket
5400descriptors. This only applies when using Win32 natively, not when using
5401e.g. cygwin. Actually, it only applies to the microsofts own compilers,
5402as every compiler comes with a slightly differently broken/incompatible
5403environment.
5404.PP
5405Lifting these limitations would basically require the full
5406re-implementation of the I/O system. If you are into this kind of thing,
5407then note that glib does exactly that for you in a very portable way (note
5408also that glib is the slowest event library known to man).
5409.PP
5410There is no supported compilation method available on windows except
5411embedding it into other applications.
5412.PP
5413Sensible signal handling is officially unsupported by Microsoft \- libev
5414tries its best, but under most conditions, signals will simply not work.
5415.PP
5416Not a libev limitation but worth mentioning: windows apparently doesn't
5417accept large writes: instead of resulting in a partial write, windows will
5418either accept everything or return \f(CW\*(C`ENOBUFS\*(C'\fR if the buffer is too large,
5419so make sure you only write small amounts into your sockets (less than a
5420megabyte seems safe, but this apparently depends on the amount of memory
5421available).
5422.PP
5423Due to the many, low, and arbitrary limits on the win32 platform and
5424the abysmal performance of winsockets, using a large number of sockets
5425is not recommended (and not reasonable). If your program needs to use
5426more than a hundred or so sockets, then likely it needs to use a totally
5427different implementation for windows, as libev offers the \s-1POSIX\s0 readiness
5428notification model, which cannot be implemented efficiently on windows
5429(due to Microsoft monopoly games).
5430.PP
5431A typical way to use libev under windows is to embed it (see the embedding
5432section for details) and use the following \fIevwrap.h\fR header file instead
5433of \fIev.h\fR:
5434.PP
5435.Vb 2
5436\& #define EV_STANDALONE /* keeps ev from requiring config.h */
5437\& #define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
5438\&
5439\& #include "ev.h"
5440.Ve
5441.PP
5442And compile the following \fIevwrap.c\fR file into your project (make sure
5443you do \fInot\fR compile the \fIev.c\fR or any other embedded source files!):
5444.PP
5445.Vb 2
5446\& #include "evwrap.h"
5447\& #include "ev.c"
5448.Ve
5449.PP
5450\fIThe winsocket \f(CI\*(C`select\*(C'\fI function\fR
5451.IX Subsection "The winsocket select function"
5452.PP
5453The winsocket \f(CW\*(C`select\*(C'\fR function doesn't follow \s-1POSIX\s0 in that it
5454requires socket \fIhandles\fR and not socket \fIfile descriptors\fR (it is
5455also extremely buggy). This makes select very inefficient, and also
5456requires a mapping from file descriptors to socket handles (the Microsoft
5457C runtime provides the function \f(CW\*(C`_open_osfhandle\*(C'\fR for this). See the
5458discussion of the \f(CW\*(C`EV_SELECT_USE_FD_SET\*(C'\fR, \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR and
5459\&\f(CW\*(C`EV_FD_TO_WIN32_HANDLE\*(C'\fR preprocessor symbols for more info.
5460.PP
5461The configuration for a \*(L"naked\*(R" win32 using the Microsoft runtime
5462libraries and raw winsocket select is:
5463.PP
5464.Vb 2
5465\& #define EV_USE_SELECT 1
5466\& #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
5467.Ve
5468.PP
5469Note that winsockets handling of fd sets is O(n), so you can easily get a
5470complexity in the O(nX) range when using win32.
5471.PP
5472\fILimited number of file descriptors\fR
5473.IX Subsection "Limited number of file descriptors"
5474.PP
5475Windows has numerous arbitrary (and low) limits on things.
5476.PP
5477Early versions of winsocket's select only supported waiting for a maximum
5478of \f(CW64\fR handles (probably owning to the fact that all windows kernels
5479can only wait for \f(CW64\fR things at the same time internally; Microsoft
5480recommends spawning a chain of threads and wait for 63 handles and the
5481previous thread in each. Sounds great!).
5482.PP
5483Newer versions support more handles, but you need to define \f(CW\*(C`FD_SETSIZE\*(C'\fR
5484to some high number (e.g. \f(CW2048\fR) before compiling the winsocket select
5485call (which might be in libev or elsewhere, for example, perl and many
5486other interpreters do their own select emulation on windows).
5487.PP
5488Another limit is the number of file descriptors in the Microsoft runtime
5489libraries, which by default is \f(CW64\fR (there must be a hidden \fI64\fR
5490fetish or something like this inside Microsoft). You can increase this
5491by calling \f(CW\*(C`_setmaxstdio\*(C'\fR, which can increase this limit to \f(CW2048\fR
5492(another arbitrary limit), but is broken in many versions of the Microsoft
5493runtime libraries. This might get you to about \f(CW512\fR or \f(CW2048\fR sockets
5494(depending on windows version and/or the phase of the moon). To get more,
5495you need to wrap all I/O functions and provide your own fd management, but
5496the cost of calling select (O(nX)) will likely make this unworkable.
5497.SS "\s-1PORTABILITY REQUIREMENTS\s0"
5498.IX Subsection "PORTABILITY REQUIREMENTS"
5499In addition to a working ISO-C implementation and of course the
5500backend-specific APIs, libev relies on a few additional extensions:
5501.ie n .IP """void (*)(ev_watcher_type *, int revents)"" must have compatible calling conventions regardless of ""ev_watcher_type *""." 4
5502.el .IP "\f(CWvoid (*)(ev_watcher_type *, int revents)\fR must have compatible calling conventions regardless of \f(CWev_watcher_type *\fR." 4
5503.IX Item "void (*)(ev_watcher_type *, int revents) must have compatible calling conventions regardless of ev_watcher_type *."
5504Libev assumes not only that all watcher pointers have the same internal
5505structure (guaranteed by \s-1POSIX\s0 but not by \s-1ISO C\s0 for example), but it also
5506assumes that the same (machine) code can be used to call any watcher
5507callback: The watcher callbacks have different type signatures, but libev
5508calls them using an \f(CW\*(C`ev_watcher *\*(C'\fR internally.
5509.IP "null pointers and integer zero are represented by 0 bytes" 4
5510.IX Item "null pointers and integer zero are represented by 0 bytes"
5511Libev uses \f(CW\*(C`memset\*(C'\fR to initialise structs and arrays to \f(CW0\fR bytes, and
5512relies on this setting pointers and integers to null.
5513.IP "pointer accesses must be thread-atomic" 4
5514.IX Item "pointer accesses must be thread-atomic"
5515Accessing a pointer value must be atomic, it must both be readable and
5516writable in one piece \- this is the case on all current architectures.
5517.ie n .IP """sig_atomic_t volatile"" must be thread-atomic as well" 4
5518.el .IP "\f(CWsig_atomic_t volatile\fR must be thread-atomic as well" 4
5519.IX Item "sig_atomic_t volatile must be thread-atomic as well"
5520The type \f(CW\*(C`sig_atomic_t volatile\*(C'\fR (or whatever is defined as
5521\&\f(CW\*(C`EV_ATOMIC_T\*(C'\fR) must be atomic with respect to accesses from different
5522threads. This is not part of the specification for \f(CW\*(C`sig_atomic_t\*(C'\fR, but is
5523believed to be sufficiently portable.
5524.ie n .IP """sigprocmask"" must work in a threaded environment" 4
5525.el .IP "\f(CWsigprocmask\fR must work in a threaded environment" 4
5526.IX Item "sigprocmask must work in a threaded environment"
5527Libev uses \f(CW\*(C`sigprocmask\*(C'\fR to temporarily block signals. This is not
5528allowed in a threaded program (\f(CW\*(C`pthread_sigmask\*(C'\fR has to be used). Typical
5529pthread implementations will either allow \f(CW\*(C`sigprocmask\*(C'\fR in the \*(L"main
5530thread\*(R" or will block signals process-wide, both behaviours would
5531be compatible with libev. Interaction between \f(CW\*(C`sigprocmask\*(C'\fR and
5532\&\f(CW\*(C`pthread_sigmask\*(C'\fR could complicate things, however.
5533.Sp
5534The most portable way to handle signals is to block signals in all threads
5535except the initial one, and run the signal handling loop in the initial
5536thread as well.
5537.ie n .IP """long"" must be large enough for common memory allocation sizes" 4
5538.el .IP "\f(CWlong\fR must be large enough for common memory allocation sizes" 4
5539.IX Item "long must be large enough for common memory allocation sizes"
5540To improve portability and simplify its \s-1API,\s0 libev uses \f(CW\*(C`long\*(C'\fR internally
5541instead of \f(CW\*(C`size_t\*(C'\fR when allocating its data structures. On non-POSIX
5542systems (Microsoft...) this might be unexpectedly low, but is still at
5543least 31 bits everywhere, which is enough for hundreds of millions of
5544watchers.
5545.ie n .IP """double"" must hold a time value in seconds with enough accuracy" 4
5546.el .IP "\f(CWdouble\fR must hold a time value in seconds with enough accuracy" 4
5547.IX Item "double must hold a time value in seconds with enough accuracy"
5548The type \f(CW\*(C`double\*(C'\fR is used to represent timestamps. It is required to
5549have at least 51 bits of mantissa (and 9 bits of exponent), which is
5550good enough for at least into the year 4000 with millisecond accuracy
5551(the design goal for libev). This requirement is overfulfilled by
5552implementations using \s-1IEEE 754,\s0 which is basically all existing ones.
5553.Sp
5554With \s-1IEEE 754\s0 doubles, you get microsecond accuracy until at least the
5555year 2255 (and millisecond accuracy till the year 287396 \- by then, libev
5556is either obsolete or somebody patched it to use \f(CW\*(C`long double\*(C'\fR or
5557something like that, just kidding).
5558.PP
5559If you know of other additional requirements drop me a note.
2187.SH "COMPLEXITIES" 5560.SH "ALGORITHMIC COMPLEXITIES"
2188.IX Header "COMPLEXITIES" 5561.IX Header "ALGORITHMIC COMPLEXITIES"
2189In this section the complexities of (many of) the algorithms used inside 5562In this section the complexities of (many of) the algorithms used inside
2190libev will be explained. For complexity discussions about backends see the 5563libev will be documented. For complexity discussions about backends see
2191documentation for \f(CW\*(C`ev_default_init\*(C'\fR. 5564the documentation for \f(CW\*(C`ev_default_init\*(C'\fR.
2192.RS 4 5565.PP
5566All of the following are about amortised time: If an array needs to be
5567extended, libev needs to realloc and move the whole array, but this
5568happens asymptotically rarer with higher number of elements, so O(1) might
5569mean that libev does a lengthy realloc operation in rare cases, but on
5570average it is much faster and asymptotically approaches constant time.
2193.IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4 5571.IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4
2194.IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 5572.IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)"
5573This means that, when you have a watcher that triggers in one hour and
5574there are 100 watchers that would trigger before that, then inserting will
5575have to skip roughly seven (\f(CW\*(C`ld 100\*(C'\fR) of these watchers.
5576.IP "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 4
5577.IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)"
5578That means that changing a timer costs less than removing/adding them,
5579as only the relative motion in the event queue has to be paid for.
5580.IP "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)" 4
5581.IX Item "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)"
5582These just add the watcher into an array or at the head of a list.
5583.IP "Stopping check/prepare/idle/fork/async watchers: O(1)" 4
5584.IX Item "Stopping check/prepare/idle/fork/async watchers: O(1)"
2195.PD 0 5585.PD 0
2196.IP "Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)" 4
2197.IX Item "Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)"
2198.IP "Starting io/check/prepare/idle/signal/child watchers: O(1)" 4
2199.IX Item "Starting io/check/prepare/idle/signal/child watchers: O(1)"
2200.IP "Stopping check/prepare/idle watchers: O(1)" 4
2201.IX Item "Stopping check/prepare/idle watchers: O(1)"
2202.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % 16))" 4 5586.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4
2203.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % 16))" 5587.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))"
5588.PD
5589These watchers are stored in lists, so they need to be walked to find the
5590correct watcher to remove. The lists are usually short (you don't usually
5591have many watchers waiting for the same fd or signal: one is typical, two
5592is rare).
2204.IP "Finding the next timer per loop iteration: O(1)" 4 5593.IP "Finding the next timer in each loop iteration: O(1)" 4
2205.IX Item "Finding the next timer per loop iteration: O(1)" 5594.IX Item "Finding the next timer in each loop iteration: O(1)"
5595By virtue of using a binary or 4\-heap, the next timer is always found at a
5596fixed position in the storage array.
2206.IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4 5597.IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4
2207.IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 5598.IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)"
2208.IP "Activating one watcher: O(1)" 4 5599A change means an I/O watcher gets started or stopped, which requires
2209.IX Item "Activating one watcher: O(1)" 5600libev to recalculate its status (and possibly tell the kernel, depending
2210.RE 5601on backend and whether \f(CW\*(C`ev_io_set\*(C'\fR was used).
2211.RS 4 5602.IP "Activating one watcher (putting it into the pending state): O(1)" 4
5603.IX Item "Activating one watcher (putting it into the pending state): O(1)"
5604.PD 0
5605.IP "Priority handling: O(number_of_priorities)" 4
5606.IX Item "Priority handling: O(number_of_priorities)"
2212.PD 5607.PD
5608Priorities are implemented by allocating some space for each
5609priority. When doing priority-based operations, libev usually has to
5610linearly search all the priorities, but starting/stopping and activating
5611watchers becomes O(1) with respect to priority handling.
5612.IP "Sending an ev_async: O(1)" 4
5613.IX Item "Sending an ev_async: O(1)"
5614.PD 0
5615.IP "Processing ev_async_send: O(number_of_async_watchers)" 4
5616.IX Item "Processing ev_async_send: O(number_of_async_watchers)"
5617.IP "Processing signals: O(max_signal_number)" 4
5618.IX Item "Processing signals: O(max_signal_number)"
5619.PD
5620Sending involves a system call \fIiff\fR there were no other \f(CW\*(C`ev_async_send\*(C'\fR
5621calls in the current loop iteration and the loop is currently
5622blocked. Checking for async and signal events involves iterating over all
5623running async watchers or all signal numbers.
5624.SH "PORTING FROM LIBEV 3.X TO 4.X"
5625.IX Header "PORTING FROM LIBEV 3.X TO 4.X"
5626The major version 4 introduced some incompatible changes to the \s-1API.\s0
5627.PP
5628At the moment, the \f(CW\*(C`ev.h\*(C'\fR header file provides compatibility definitions
5629for all changes, so most programs should still compile. The compatibility
5630layer might be removed in later versions of libev, so better update to the
5631new \s-1API\s0 early than late.
5632.ie n .IP """EV_COMPAT3"" backwards compatibility mechanism" 4
5633.el .IP "\f(CWEV_COMPAT3\fR backwards compatibility mechanism" 4
5634.IX Item "EV_COMPAT3 backwards compatibility mechanism"
5635The backward compatibility mechanism can be controlled by
5636\&\f(CW\*(C`EV_COMPAT3\*(C'\fR. See \*(L"\s-1PREPROCESSOR SYMBOLS/MACROS\*(R"\s0 in the \*(L"\s-1EMBEDDING\*(R"\s0
5637section.
5638.ie n .IP """ev_default_destroy"" and ""ev_default_fork"" have been removed" 4
5639.el .IP "\f(CWev_default_destroy\fR and \f(CWev_default_fork\fR have been removed" 4
5640.IX Item "ev_default_destroy and ev_default_fork have been removed"
5641These calls can be replaced easily by their \f(CW\*(C`ev_loop_xxx\*(C'\fR counterparts:
5642.Sp
5643.Vb 2
5644\& ev_loop_destroy (EV_DEFAULT_UC);
5645\& ev_loop_fork (EV_DEFAULT);
5646.Ve
5647.IP "function/symbol renames" 4
5648.IX Item "function/symbol renames"
5649A number of functions and symbols have been renamed:
5650.Sp
5651.Vb 3
5652\& ev_loop => ev_run
5653\& EVLOOP_NONBLOCK => EVRUN_NOWAIT
5654\& EVLOOP_ONESHOT => EVRUN_ONCE
5655\&
5656\& ev_unloop => ev_break
5657\& EVUNLOOP_CANCEL => EVBREAK_CANCEL
5658\& EVUNLOOP_ONE => EVBREAK_ONE
5659\& EVUNLOOP_ALL => EVBREAK_ALL
5660\&
5661\& EV_TIMEOUT => EV_TIMER
5662\&
5663\& ev_loop_count => ev_iteration
5664\& ev_loop_depth => ev_depth
5665\& ev_loop_verify => ev_verify
5666.Ve
5667.Sp
5668Most functions working on \f(CW\*(C`struct ev_loop\*(C'\fR objects don't have an
5669\&\f(CW\*(C`ev_loop_\*(C'\fR prefix, so it was removed; \f(CW\*(C`ev_loop\*(C'\fR, \f(CW\*(C`ev_unloop\*(C'\fR and
5670associated constants have been renamed to not collide with the \f(CW\*(C`struct
5671ev_loop\*(C'\fR anymore and \f(CW\*(C`EV_TIMER\*(C'\fR now follows the same naming scheme
5672as all other watcher types. Note that \f(CW\*(C`ev_loop_fork\*(C'\fR is still called
5673\&\f(CW\*(C`ev_loop_fork\*(C'\fR because it would otherwise clash with the \f(CW\*(C`ev_fork\*(C'\fR
5674typedef.
5675.ie n .IP """EV_MINIMAL"" mechanism replaced by ""EV_FEATURES""" 4
5676.el .IP "\f(CWEV_MINIMAL\fR mechanism replaced by \f(CWEV_FEATURES\fR" 4
5677.IX Item "EV_MINIMAL mechanism replaced by EV_FEATURES"
5678The preprocessor symbol \f(CW\*(C`EV_MINIMAL\*(C'\fR has been replaced by a different
5679mechanism, \f(CW\*(C`EV_FEATURES\*(C'\fR. Programs using \f(CW\*(C`EV_MINIMAL\*(C'\fR usually compile
5680and work, but the library code will of course be larger.
5681.SH "GLOSSARY"
5682.IX Header "GLOSSARY"
5683.IP "active" 4
5684.IX Item "active"
5685A watcher is active as long as it has been started and not yet stopped.
5686See \*(L"\s-1WATCHER STATES\*(R"\s0 for details.
5687.IP "application" 4
5688.IX Item "application"
5689In this document, an application is whatever is using libev.
5690.IP "backend" 4
5691.IX Item "backend"
5692The part of the code dealing with the operating system interfaces.
5693.IP "callback" 4
5694.IX Item "callback"
5695The address of a function that is called when some event has been
5696detected. Callbacks are being passed the event loop, the watcher that
5697received the event, and the actual event bitset.
5698.IP "callback/watcher invocation" 4
5699.IX Item "callback/watcher invocation"
5700The act of calling the callback associated with a watcher.
5701.IP "event" 4
5702.IX Item "event"
5703A change of state of some external event, such as data now being available
5704for reading on a file descriptor, time having passed or simply not having
5705any other events happening anymore.
5706.Sp
5707In libev, events are represented as single bits (such as \f(CW\*(C`EV_READ\*(C'\fR or
5708\&\f(CW\*(C`EV_TIMER\*(C'\fR).
5709.IP "event library" 4
5710.IX Item "event library"
5711A software package implementing an event model and loop.
5712.IP "event loop" 4
5713.IX Item "event loop"
5714An entity that handles and processes external events and converts them
5715into callback invocations.
5716.IP "event model" 4
5717.IX Item "event model"
5718The model used to describe how an event loop handles and processes
5719watchers and events.
5720.IP "pending" 4
5721.IX Item "pending"
5722A watcher is pending as soon as the corresponding event has been
5723detected. See \*(L"\s-1WATCHER STATES\*(R"\s0 for details.
5724.IP "real time" 4
5725.IX Item "real time"
5726The physical time that is observed. It is apparently strictly monotonic :)
5727.IP "wall-clock time" 4
5728.IX Item "wall-clock time"
5729The time and date as shown on clocks. Unlike real time, it can actually
5730be wrong and jump forwards and backwards, e.g. when you adjust your
5731clock.
5732.IP "watcher" 4
5733.IX Item "watcher"
5734A data structure that describes interest in certain events. Watchers need
5735to be started (attached to an event loop) before they can receive events.
2213.SH "AUTHOR" 5736.SH "AUTHOR"
2214.IX Header "AUTHOR" 5737.IX Header "AUTHOR"
2215Marc Lehmann <libev@schmorp.de>. 5738Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5739Magnusson and Emanuele Giaquinta, and minor corrections by many others.

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