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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 "2019-06-25" "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, long 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, long size))" 382.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())"
247Sets the allocation function to use (the prototype is similar to the 383Sets the allocation function to use (the prototype is similar \- the
248realloc C function, the semantics are identical). It is used to allocate 384semantics are identical to the \f(CW\*(C`realloc\*(C'\fR C89/SuS/POSIX function). It is
249and free memory (no surprises here). If it returns zero when memory 385used to allocate and free memory (no surprises here). If it returns zero
250needs to be allocated, the library might abort or take some potentially 386when memory needs to be allocated (\f(CW\*(C`size != 0\*(C'\fR), the library might abort
251destructive action. 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
257Example: replace the libev allocator with one that waits a bit and then 397Example: The following is the \f(CW\*(C`realloc\*(C'\fR function that libev itself uses
258retries: better than mine). 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.
259.Sp 400.Sp
260.Vb 6 401.Vb 5
261\& static void * 402\& static void *
262\& persistent_realloc (void *ptr, long size) 403\& ev_realloc_emul (void *ptr, long size) EV_NOEXCEPT
263\& { 404\& {
405\& if (size)
406\& return realloc (ptr, size);
407\&
408\& free (ptr);
409\& return 0;
410\& }
411.Ve
412.Sp
413Example: Replace the libev allocator with one that waits a bit and then
414retries.
415.Sp
416.Vb 8
417\& static void *
418\& persistent_realloc (void *ptr, size_t size)
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 \s-1AIO\s0 (\fInot\fR \f(CWaio(7)\fR but \f(CWio_submit(2)\fR) event interface available in post\-4.18 kernels (but libev
707only tries to use it in 4.19+).
708.Sp
709This is another Linux train wreck of an event interface.
710.Sp
711If this backend works for you (as of this writing, it was very
712experimental), it is the best event interface available on Linux and might
713be well worth enabling it \- if it isn't available in your kernel this will
714be detected and this backend will be skipped.
715.Sp
716This backend can batch oneshot requests and supports a user-space ring
717buffer to receive events. It also doesn't suffer from most of the design
718problems of epoll (such as not being able to remove event sources from
719the epoll set), and generally sounds too good to be true. Because, this
720being the Linux kernel, of course it suffers from a whole new set of
721limitations, forcing you to fall back to epoll, inheriting all its design
722issues.
723.Sp
724For one, it is not easily embeddable (but probably could be done using
725an event fd at some extra overhead). It also is subject to a system wide
726limit that can be configured in \fI/proc/sys/fs/aio\-max\-nr\fR. If no \s-1AIO\s0
727requests are left, this backend will be skipped during initialisation, and
728will switch to epoll when the loop is active.
729.Sp
730Most problematic in practice, however, is that not all file descriptors
731work with it. For example, in Linux 5.1, \s-1TCP\s0 sockets, pipes, event fds,
732files, \fI/dev/null\fR and many others are supported, but ttys do not work
733properly (a known bug that the kernel developers don't care about, see
734<https://lore.kernel.org/patchwork/patch/1047453/>), so this is not
735(yet?) a generic event polling interface.
736.Sp
737Overall, it seems the Linux developers just don't want it to have a
738generic event handling mechanism other than \f(CW\*(C`select\*(C'\fR or \f(CW\*(C`poll\*(C'\fR.
739.Sp
740To work around all these problem, the current version of libev uses its
741epoll backend as a fallback for file descriptor types that do not work. Or
742falls back completely to epoll if the kernel acts up.
743.Sp
744This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
745\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
382.ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4 746.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)" 4 747.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
384.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)" 748.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
385Kqueue deserves special mention, as at the time of this writing, it 749Kqueue deserves special mention, as at the time this backend was
386was broken on all BSDs except NetBSD (usually it doesn't work with 750implemented, it was broken on all BSDs except NetBSD (usually it doesn't
387anything but sockets and pipes, except on Darwin, where of course its 751work reliably with anything but sockets and pipes, except on Darwin,
388completely useless). For this reason its not being \*(L"autodetected\*(R" 752where of course it's completely useless). Unlike epoll, however, whose
389unless you explicitly specify it explicitly in the flags (i.e. using 753brokenness is by design, these kqueue bugs can be (and mostly have been)
390\&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR). 754fixed without \s-1API\s0 changes to existing programs. For this reason it's not
755being \*(L"auto-detected\*(R" on all platforms unless you explicitly specify it
756in the flags (i.e. using \f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a
757known-to-be-good (\-enough) system like NetBSD.
758.Sp
759You still can embed kqueue into a normal poll or select backend and use it
760only for sockets (after having made sure that sockets work with kqueue on
761the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
391.Sp 762.Sp
392It scales in the same way as the epoll backend, but the interface to the 763It 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 764kernel is more efficient (which says nothing about its actual speed, of
394course). While starting and stopping an I/O watcher does not cause an 765course). 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 766cause 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. 767two event changes per incident. Support for \f(CW\*(C`fork ()\*(C'\fR is very bad (you
768might have to leak fds on fork, but it's more sane than epoll) and it
769drops fds silently in similarly hard-to-detect cases.
770.Sp
771This backend usually performs well under most conditions.
772.Sp
773While nominally embeddable in other event loops, this doesn't work
774everywhere, so you might need to test for this. And since it is broken
775almost everywhere, you should only use it when you have a lot of sockets
776(for which it usually works), by embedding it into another event loop
777(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
778also broken on \s-1OS X\s0)) and, did I mention it, using it only for sockets.
779.Sp
780This backend maps \f(CW\*(C`EV_READ\*(C'\fR into an \f(CW\*(C`EVFILT_READ\*(C'\fR kevent with
781\&\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
782\&\f(CW\*(C`NOTE_EOF\*(C'\fR.
397.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4 783.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
398.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4 784.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
399.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)" 785.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
400This is not implemented yet (and might never be). 786This is not implemented yet (and might never be, unless you send me an
787implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets
788and is not embeddable, which would limit the usefulness of this backend
789immensely.
401.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4 790.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
402.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4 791.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
403.IX Item "EVBACKEND_PORT (value 32, Solaris 10)" 792.IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
404This uses the Solaris 10 port mechanism. As with everything on Solaris, 793This 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)). 794it's really slow, but it still scales very well (O(active_fds)).
406.Sp 795.Sp
407Please note that solaris ports can result in a lot of spurious 796While 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 797file descriptor per loop iteration. For small and medium numbers of file
409blocking when no data (or space) is available. 798descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend
799might perform better.
800.Sp
801On the positive side, this backend actually performed fully to
802specification in all tests and is fully embeddable, which is a rare feat
803among the OS-specific backends (I vastly prefer correctness over speed
804hacks).
805.Sp
806On the negative side, the interface is \fIbizarre\fR \- so bizarre that
807even sun itself gets it wrong in their code examples: The event polling
808function sometimes returns events to the caller even though an error
809occurred, but with no indication whether it has done so or not (yes, it's
810even documented that way) \- deadly for edge-triggered interfaces where you
811absolutely have to know whether an event occurred or not because you have
812to re-arm the watcher.
813.Sp
814Fortunately libev seems to be able to work around these idiocies.
815.Sp
816This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
817\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
410.ie n .IP """EVBACKEND_ALL""" 4 818.ie n .IP """EVBACKEND_ALL""" 4
411.el .IP "\f(CWEVBACKEND_ALL\fR" 4 819.el .IP "\f(CWEVBACKEND_ALL\fR" 4
412.IX Item "EVBACKEND_ALL" 820.IX Item "EVBACKEND_ALL"
413Try all backends (even potentially broken ones that wouldn't be tried 821Try 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 822with \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. 823\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR.
824.Sp
825It is definitely not recommended to use this flag, use whatever
826\&\f(CW\*(C`ev_recommended_backends ()\*(C'\fR returns, or simply do not specify a backend
827at all.
828.ie n .IP """EVBACKEND_MASK""" 4
829.el .IP "\f(CWEVBACKEND_MASK\fR" 4
830.IX Item "EVBACKEND_MASK"
831Not a backend at all, but a mask to select all backend bits from a
832\&\f(CW\*(C`flags\*(C'\fR value, in case you want to mask out any backends from a flags
833value (e.g. when modifying the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR environment variable).
416.RE 834.RE
417.RS 4 835.RS 4
418.Sp 836.Sp
419If one or more of these are ored into the flags value, then only these 837If 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 838then only these backends will be tried (in the reverse order as listed
421specified, most compiled-in backend will be tried, usually in reverse 839here). If none are specified, all backends in \f(CW\*(C`ev_recommended_backends
422order of their flag values :) 840()\*(C'\fR will be tried.
423.Sp 841.Sp
424The most typical usage is like this: 842Example: Try to create a event loop that uses epoll and nothing else.
425.Sp 843.Sp
426.Vb 2 844.Vb 3
427\& if (!ev_default_loop (0)) 845\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
428\& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?"); 846\& if (!epoller)
847\& fatal ("no epoll found here, maybe it hides under your chair");
429.Ve 848.Ve
430.Sp 849.Sp
431Restrict libev to the select and poll backends, and do not allow 850Example: Use whatever libev has to offer, but make sure that kqueue is
432environment settings to be taken into account: 851used if available.
433.Sp 852.Sp
434.Vb 1 853.Vb 1
435\& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV); 854\& struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
436.Ve 855.Ve
437.Sp 856.Sp
438Use whatever libev has to offer, but make sure that kqueue is used if 857Example: Similarly, on linux, you mgiht want to take advantage of the
439available (warning, breaks stuff, best use only with your own private 858linux 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): 859isn't available.
441.Sp 860.Sp
442.Vb 1 861.Vb 1
443\& ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE); 862\& struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_LINUXAIO);
444.Ve 863.Ve
445.RE 864.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 ()" 4 865.IP "ev_loop_destroy (loop)" 4
461.IX Item "ev_default_destroy ()" 866.IX Item "ev_loop_destroy (loop)"
462Destroys the default loop again (frees all memory and kernel state 867Destroys an event loop object (frees all memory and kernel state
463etc.). None of the active event watchers will be stopped in the normal 868etc.). 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 869sense, 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 870responsibility to either stop all watchers cleanly yourself \fIbefore\fR
466calling this function, or cope with the fact afterwards (which is usually 871calling 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 872the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them
468for example). 873for 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 874.Sp
480You \fImust\fR call this function in the child process after forking if and 875Note 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 876handlers), will not be freed by this function, and related watchers (such
482fork+exec, you don't have to call it. 877as signal and child watchers) would need to be stopped manually.
483.Sp 878.Sp
484The function itself is quite fast and it's usually not a problem to call 879This 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 880\&\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: 881\&\f(CW\*(C`ev_default_loop\*(C'\fR, in which case it is not thread-safe.
487.Sp 882.Sp
488.Vb 1 883Note that it is not advisable to call this function on the default loop
489\& pthread_atfork (0, 0, ev_default_fork); 884except in the rare occasion where you really need to free its resources.
490.Ve 885If you need dynamically allocated loops it is better to use \f(CW\*(C`ev_loop_new\*(C'\fR
491.Sp 886and \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)" 4 887.IP "ev_loop_fork (loop)" 4
496.IX Item "ev_loop_fork (loop)" 888.IX Item "ev_loop_fork (loop)"
497Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by 889This 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 890to reinitialise the kernel state for backends that have one. Despite
499after fork, and how you do this is entirely your own problem. 891the name, you can call it anytime you are allowed to start or stop
892watchers (except inside an \f(CW\*(C`ev_prepare\*(C'\fR callback), but it makes most
893sense after forking, in the child process. You \fImust\fR call it (or use
894\&\f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR) in the child before resuming or calling \f(CW\*(C`ev_run\*(C'\fR.
895.Sp
896In addition, if you want to reuse a loop (via this function or
897\&\f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR), you \fIalso\fR have to ignore \f(CW\*(C`SIGPIPE\*(C'\fR.
898.Sp
899Again, you \fIhave\fR to call it on \fIany\fR loop that you want to re-use after
900a fork, \fIeven if you do not plan to use the loop in the parent\fR. This is
901because some kernel interfaces *cough* \fIkqueue\fR *cough* do funny things
902during fork.
903.Sp
904On the other hand, you only need to call this function in the child
905process if and only if you want to use the event loop in the child. If
906you just fork+exec or create a new loop in the child, you don't have to
907call it at all (in fact, \f(CW\*(C`epoll\*(C'\fR is so badly broken that it makes a
908difference, but libev will usually detect this case on its own and do a
909costly reset of the backend).
910.Sp
911The function itself is quite fast and it's usually not a problem to call
912it just in case after a fork.
913.Sp
914Example: Automate calling \f(CW\*(C`ev_loop_fork\*(C'\fR on the default loop when
915using pthreads.
916.Sp
917.Vb 5
918\& static void
919\& post_fork_child (void)
920\& {
921\& ev_loop_fork (EV_DEFAULT);
922\& }
923\&
924\& ...
925\& pthread_atfork (0, 0, post_fork_child);
926.Ve
927.IP "int ev_is_default_loop (loop)" 4
928.IX Item "int ev_is_default_loop (loop)"
929Returns true when the given loop is, in fact, the default loop, and false
930otherwise.
931.IP "unsigned int ev_iteration (loop)" 4
932.IX Item "unsigned int ev_iteration (loop)"
933Returns the current iteration count for the event loop, which is identical
934to the number of times libev did poll for new events. It starts at \f(CW0\fR
935and happily wraps around with enough iterations.
936.Sp
937This value can sometimes be useful as a generation counter of sorts (it
938\&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with
939\&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls \- and is incremented between the
940prepare and check phases.
941.IP "unsigned int ev_depth (loop)" 4
942.IX Item "unsigned int ev_depth (loop)"
943Returns the number of times \f(CW\*(C`ev_run\*(C'\fR was entered minus the number of
944times \f(CW\*(C`ev_run\*(C'\fR was exited normally, in other words, the recursion depth.
945.Sp
946Outside \f(CW\*(C`ev_run\*(C'\fR, this number is zero. In a callback, this number is
947\&\f(CW1\fR, unless \f(CW\*(C`ev_run\*(C'\fR was invoked recursively (or from another thread),
948in which case it is higher.
949.Sp
950Leaving \f(CW\*(C`ev_run\*(C'\fR abnormally (setjmp/longjmp, cancelling the thread,
951throwing an exception etc.), doesn't count as \*(L"exit\*(R" \- consider this
952as a hint to avoid such ungentleman-like behaviour unless it's really
953convenient, in which case it is fully supported.
500.IP "unsigned int ev_backend (loop)" 4 954.IP "unsigned int ev_backend (loop)" 4
501.IX Item "unsigned int ev_backend (loop)" 955.IX Item "unsigned int ev_backend (loop)"
502Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in 956Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
503use. 957use.
504.IP "ev_tstamp ev_now (loop)" 4 958.IP "ev_tstamp ev_now (loop)" 4
505.IX Item "ev_tstamp ev_now (loop)" 959.IX Item "ev_tstamp ev_now (loop)"
506Returns the current \*(L"event loop time\*(R", which is the time the event loop 960Returns the current \*(L"event loop time\*(R", which is the time the event loop
507received events and started processing them. This timestamp does not 961received events and started processing them. This timestamp does not
508change as long as callbacks are being processed, and this is also the base 962change 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 963time used for relative timers. You can treat it as the timestamp of the
510event occuring (or more correctly, libev finding out about it). 964event occurring (or more correctly, libev finding out about it).
965.IP "ev_now_update (loop)" 4
966.IX Item "ev_now_update (loop)"
967Establishes the current time by querying the kernel, updating the time
968returned by \f(CW\*(C`ev_now ()\*(C'\fR in the progress. This is a costly operation and
969is usually done automatically within \f(CW\*(C`ev_run ()\*(C'\fR.
970.Sp
971This function is rarely useful, but when some event callback runs for a
972very long time without entering the event loop, updating libev's idea of
973the current time is a good idea.
974.Sp
975See also \*(L"The special problem of time updates\*(R" in the \f(CW\*(C`ev_timer\*(C'\fR section.
976.IP "ev_suspend (loop)" 4
977.IX Item "ev_suspend (loop)"
978.PD 0
979.IP "ev_resume (loop)" 4
980.IX Item "ev_resume (loop)"
981.PD
982These two functions suspend and resume an event loop, for use when the
983loop is not used for a while and timeouts should not be processed.
984.Sp
985A typical use case would be an interactive program such as a game: When
986the user presses \f(CW\*(C`^Z\*(C'\fR to suspend the game and resumes it an hour later it
987would be best to handle timeouts as if no time had actually passed while
988the program was suspended. This can be achieved by calling \f(CW\*(C`ev_suspend\*(C'\fR
989in your \f(CW\*(C`SIGTSTP\*(C'\fR handler, sending yourself a \f(CW\*(C`SIGSTOP\*(C'\fR and calling
990\&\f(CW\*(C`ev_resume\*(C'\fR directly afterwards to resume timer processing.
991.Sp
992Effectively, all \f(CW\*(C`ev_timer\*(C'\fR watchers will be delayed by the time spend
993between \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
994will be rescheduled (that is, they will lose any events that would have
995occurred while suspended).
996.Sp
997After calling \f(CW\*(C`ev_suspend\*(C'\fR you \fBmust not\fR call \fIany\fR function on the
998given loop other than \f(CW\*(C`ev_resume\*(C'\fR, and you \fBmust not\fR call \f(CW\*(C`ev_resume\*(C'\fR
999without a previous call to \f(CW\*(C`ev_suspend\*(C'\fR.
1000.Sp
1001Calling \f(CW\*(C`ev_suspend\*(C'\fR/\f(CW\*(C`ev_resume\*(C'\fR has the side effect of updating the
1002event loop time (see \f(CW\*(C`ev_now_update\*(C'\fR).
511.IP "ev_loop (loop, int flags)" 4 1003.IP "bool ev_run (loop, int flags)" 4
512.IX Item "ev_loop (loop, int flags)" 1004.IX Item "bool ev_run (loop, int flags)"
513Finally, this is it, the event handler. This function usually is called 1005Finally, this is it, the event handler. This function usually is called
514after you initialised all your watchers and you want to start handling 1006after you have initialised all your watchers and you want to start
515events. 1007handling events. It will ask the operating system for any new events, call
1008the watcher callbacks, and then repeat the whole process indefinitely: This
1009is why event loops are called \fIloops\fR.
516.Sp 1010.Sp
517If the flags argument is specified as \f(CW0\fR, it will not return until 1011If 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. 1012until either no event watchers are active anymore or \f(CW\*(C`ev_break\*(C'\fR was
1013called.
519.Sp 1014.Sp
1015The return value is false if there are no more active watchers (which
1016usually means \*(L"all jobs done\*(R" or \*(L"deadlock\*(R"), and true in all other cases
1017(which usually means " you should call \f(CW\*(C`ev_run\*(C'\fR again").
1018.Sp
520Please note that an explicit \f(CW\*(C`ev_unloop\*(C'\fR is usually better than 1019Please 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 1020relying on all watchers to be stopped when deciding when a program has
522finished (especially in interactive programs), but having a program that 1021finished (especially in interactive programs), but having a program
523automatically loops as long as it has to and no longer by virtue of 1022that automatically loops as long as it has to and no longer by virtue
524relying on its watchers stopping correctly is a thing of beauty. 1023of relying on its watchers stopping correctly, that is truly a thing of
1024beauty.
525.Sp 1025.Sp
1026This function is \fImostly\fR exception-safe \- you can break out of a
1027\&\f(CW\*(C`ev_run\*(C'\fR call by calling \f(CW\*(C`longjmp\*(C'\fR in a callback, throwing a \*(C+
1028exception and so on. This does not decrement the \f(CW\*(C`ev_depth\*(C'\fR value, nor
1029will it clear any outstanding \f(CW\*(C`EVBREAK_ONE\*(C'\fR breaks.
1030.Sp
526A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle 1031A 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 1032those 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. 1033block your process in case there are no events and will return after one
1034iteration of the loop. This is sometimes useful to poll and handle new
1035events while doing lengthy calculations, to keep the program responsive.
529.Sp 1036.Sp
530A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if 1037A 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 1038necessary) and will handle those and any already outstanding ones. It
532your process until at least one new event arrives, and will return after 1039will 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 1040be an event internal to libev itself, so there is no guarantee that a
534external event in conjunction with something not expressible using other 1041user-registered callback will be called), and will return after one
1042iteration of the loop.
1043.Sp
1044This is useful if you are waiting for some external event in conjunction
1045with 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 1046own \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. 1047usually a better approach for this kind of thing.
537.Sp 1048.Sp
538Here are the gory details of what \f(CW\*(C`ev_loop\*(C'\fR does: 1049Here are the gory details of what \f(CW\*(C`ev_run\*(C'\fR does (this is for your
1050understanding, not a guarantee that things will work exactly like this in
1051future versions):
539.Sp 1052.Sp
540.Vb 18 1053.Vb 10
541\& * If there are no active watchers (reference count is zero), return. 1054\& \- Increment loop depth.
542\& - Queue prepare watchers and then call all outstanding watchers. 1055\& \- Reset the ev_break status.
1056\& \- Before the first iteration, call any pending watchers.
1057\& LOOP:
1058\& \- If EVFLAG_FORKCHECK was used, check for a fork.
1059\& \- If a fork was detected (by any means), queue and call all fork watchers.
1060\& \- Queue and call all prepare watchers.
1061\& \- If ev_break was called, goto FINISH.
543\& - If we have been forked, recreate the kernel state. 1062\& \- If we have been forked, detach and recreate the kernel state
1063\& as to not disturb the other process.
544\& - Update the kernel state with all outstanding changes. 1064\& \- Update the kernel state with all outstanding changes.
545\& - Update the "event loop time". 1065\& \- Update the "event loop time" (ev_now ()).
546\& - Calculate for how long to block. 1066\& \- Calculate for how long to sleep or block, if at all
1067\& (active idle watchers, EVRUN_NOWAIT or not having
1068\& any active watchers at all will result in not sleeping).
1069\& \- Sleep if the I/O and timer collect interval say so.
1070\& \- Increment loop iteration counter.
547\& - Block the process, waiting for any events. 1071\& \- Block the process, waiting for any events.
548\& - Queue all outstanding I/O (fd) events. 1072\& \- Queue all outstanding I/O (fd) events.
549\& - Update the "event loop time" and do time jump handling. 1073\& \- Update the "event loop time" (ev_now ()), and do time jump adjustments.
550\& - Queue all outstanding timers. 1074\& \- Queue all expired timers.
551\& - Queue all outstanding periodics. 1075\& \- Queue all expired periodics.
552\& - If no events are pending now, queue all idle watchers. 1076\& \- Queue all idle watchers with priority higher than that of pending events.
553\& - Queue all check watchers. 1077\& \- Queue all check watchers.
554\& - Call all queued watchers in reverse order (i.e. check watchers first). 1078\& \- 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 1079\& Signals and child watchers are implemented as I/O watchers, and will
556\& be handled here by queueing them when their watcher gets executed. 1080\& be handled here by queueing them when their watcher gets executed.
557\& - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK 1081\& \- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
558\& were used, return, otherwise continue with step *. 1082\& were used, or there are no active watchers, goto FINISH, otherwise
1083\& continue with step LOOP.
1084\& FINISH:
1085\& \- Reset the ev_break status iff it was EVBREAK_ONE.
1086\& \- Decrement the loop depth.
1087\& \- Return.
559.Ve 1088.Ve
560.Sp 1089.Sp
561Example: queue some jobs and then loop until no events are outsanding 1090Example: Queue some jobs and then loop until no events are outstanding
562anymore. 1091anymore.
563.Sp 1092.Sp
564.Vb 4 1093.Vb 4
565\& ... queue jobs here, make sure they register event watchers as long 1094\& ... 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..) 1095\& ... as they still have work to do (even an idle watcher will do..)
567\& ev_loop (my_loop, 0); 1096\& ev_run (my_loop, 0);
568\& ... jobs done. yeah! 1097\& ... jobs done or somebody called break. yeah!
569.Ve 1098.Ve
570.IP "ev_unloop (loop, how)" 4 1099.IP "ev_break (loop, how)" 4
571.IX Item "ev_unloop (loop, how)" 1100.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 1101Can 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 1102has 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 1103\&\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. 1104\&\f(CW\*(C`EVBREAK_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_run\*(C'\fR calls return.
1105.Sp
1106This \*(L"break state\*(R" will be cleared on the next call to \f(CW\*(C`ev_run\*(C'\fR.
1107.Sp
1108It is safe to call \f(CW\*(C`ev_break\*(C'\fR from outside any \f(CW\*(C`ev_run\*(C'\fR calls, too, in
1109which case it will have no effect.
576.IP "ev_ref (loop)" 4 1110.IP "ev_ref (loop)" 4
577.IX Item "ev_ref (loop)" 1111.IX Item "ev_ref (loop)"
578.PD 0 1112.PD 0
579.IP "ev_unref (loop)" 4 1113.IP "ev_unref (loop)" 4
580.IX Item "ev_unref (loop)" 1114.IX Item "ev_unref (loop)"
581.PD 1115.PD
582Ref/unref can be used to add or remove a reference count on the event 1116Ref/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 1117loop: 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 1118count 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 1119.Sp
586returning, \fIev_unref()\fR after starting, and \fIev_ref()\fR before stopping it. For 1120This is useful when you have a watcher that you never intend to
1121unregister, but that nevertheless should not keep \f(CW\*(C`ev_run\*(C'\fR from
1122returning. In such a case, call \f(CW\*(C`ev_unref\*(C'\fR after starting, and \f(CW\*(C`ev_ref\*(C'\fR
1123before stopping it.
1124.Sp
587example, libev itself uses this for its internal signal pipe: It is not 1125As 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 1126is 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 1127exiting 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 1128excellent way to do this for generic recurring timers or from within
591libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR. 1129third-party libraries. Just remember to \fIunref after start\fR and \fIref
1130before stop\fR (but only if the watcher wasn't active before, or was active
1131before, respectively. Note also that libev might stop watchers itself
1132(e.g. non-repeating timers) in which case you have to \f(CW\*(C`ev_ref\*(C'\fR
1133in the callback).
592.Sp 1134.Sp
593Example: create a signal watcher, but keep it from keeping \f(CW\*(C`ev_loop\*(C'\fR 1135Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_run\*(C'\fR
594running when nothing else is active. 1136running when nothing else is active.
595.Sp 1137.Sp
596.Vb 4 1138.Vb 4
597\& struct dv_signal exitsig; 1139\& ev_signal exitsig;
598\& ev_signal_init (&exitsig, sig_cb, SIGINT); 1140\& ev_signal_init (&exitsig, sig_cb, SIGINT);
599\& ev_signal_start (myloop, &exitsig); 1141\& ev_signal_start (loop, &exitsig);
600\& evf_unref (myloop); 1142\& ev_unref (loop);
601.Ve 1143.Ve
602.Sp 1144.Sp
603Example: for some weird reason, unregister the above signal handler again. 1145Example: For some weird reason, unregister the above signal handler again.
604.Sp 1146.Sp
605.Vb 2 1147.Vb 2
606\& ev_ref (myloop); 1148\& ev_ref (loop);
607\& ev_signal_stop (myloop, &exitsig); 1149\& ev_signal_stop (loop, &exitsig);
608.Ve 1150.Ve
1151.IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4
1152.IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"
1153.PD 0
1154.IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4
1155.IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"
1156.PD
1157These advanced functions influence the time that libev will spend waiting
1158for events. Both time intervals are by default \f(CW0\fR, meaning that libev
1159will try to invoke timer/periodic callbacks and I/O callbacks with minimum
1160latency.
1161.Sp
1162Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR)
1163allows libev to delay invocation of I/O and timer/periodic callbacks
1164to increase efficiency of loop iterations (or to increase power-saving
1165opportunities).
1166.Sp
1167The idea is that sometimes your program runs just fast enough to handle
1168one (or very few) event(s) per loop iteration. While this makes the
1169program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new
1170events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high
1171overhead for the actual polling but can deliver many events at once.
1172.Sp
1173By setting a higher \fIio collect interval\fR you allow libev to spend more
1174time collecting I/O events, so you can handle more events per iteration,
1175at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and
1176\&\f(CW\*(C`ev_timer\*(C'\fR) will not be affected. Setting this to a non-null value will
1177introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations. The
1178sleep time ensures that libev will not poll for I/O events more often then
1179once per this interval, on average (as long as the host time resolution is
1180good enough).
1181.Sp
1182Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
1183to spend more time collecting timeouts, at the expense of increased
1184latency/jitter/inexactness (the watcher callback will be called
1185later). \f(CW\*(C`ev_io\*(C'\fR watchers will not be affected. Setting this to a non-null
1186value will not introduce any overhead in libev.
1187.Sp
1188Many (busy) programs can usually benefit by setting the I/O collect
1189interval to a value near \f(CW0.1\fR or so, which is often enough for
1190interactive servers (of course not for games), likewise for timeouts. It
1191usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR,
1192as this approaches the timing granularity of most systems. Note that if
1193you do transactions with the outside world and you can't increase the
1194parallelity, then this setting will limit your transaction rate (if you
1195need to poll once per transaction and the I/O collect interval is 0.01,
1196then you can't do more than 100 transactions per second).
1197.Sp
1198Setting the \fItimeout collect interval\fR can improve the opportunity for
1199saving power, as the program will \*(L"bundle\*(R" timer callback invocations that
1200are \*(L"near\*(R" in time together, by delaying some, thus reducing the number of
1201times the process sleeps and wakes up again. Another useful technique to
1202reduce iterations/wake\-ups is to use \f(CW\*(C`ev_periodic\*(C'\fR watchers and make sure
1203they fire on, say, one-second boundaries only.
1204.Sp
1205Example: we only need 0.1s timeout granularity, and we wish not to poll
1206more often than 100 times per second:
1207.Sp
1208.Vb 2
1209\& ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
1210\& ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
1211.Ve
1212.IP "ev_invoke_pending (loop)" 4
1213.IX Item "ev_invoke_pending (loop)"
1214This call will simply invoke all pending watchers while resetting their
1215pending state. Normally, \f(CW\*(C`ev_run\*(C'\fR does this automatically when required,
1216but when overriding the invoke callback this call comes handy. This
1217function can be invoked from a watcher \- this can be useful for example
1218when you want to do some lengthy calculation and want to pass further
1219event handling to another thread (you still have to make sure only one
1220thread executes within \f(CW\*(C`ev_invoke_pending\*(C'\fR or \f(CW\*(C`ev_run\*(C'\fR of course).
1221.IP "int ev_pending_count (loop)" 4
1222.IX Item "int ev_pending_count (loop)"
1223Returns the number of pending watchers \- zero indicates that no watchers
1224are pending.
1225.IP "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(\s-1EV_P\s0))" 4
1226.IX Item "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))"
1227This overrides the invoke pending functionality of the loop: Instead of
1228invoking all pending watchers when there are any, \f(CW\*(C`ev_run\*(C'\fR will call
1229this callback instead. This is useful, for example, when you want to
1230invoke the actual watchers inside another context (another thread etc.).
1231.Sp
1232If you want to reset the callback, use \f(CW\*(C`ev_invoke_pending\*(C'\fR as new
1233callback.
1234.IP "ev_set_loop_release_cb (loop, void (*release)(\s-1EV_P\s0) throw (), void (*acquire)(\s-1EV_P\s0) throw ())" 4
1235.IX Item "ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())"
1236Sometimes you want to share the same loop between multiple threads. This
1237can be done relatively simply by putting mutex_lock/unlock calls around
1238each call to a libev function.
1239.Sp
1240However, \f(CW\*(C`ev_run\*(C'\fR can run an indefinite time, so it is not feasible
1241to wait for it to return. One way around this is to wake up the event
1242loop via \f(CW\*(C`ev_break\*(C'\fR and \f(CW\*(C`ev_async_send\*(C'\fR, another way is to set these
1243\&\fIrelease\fR and \fIacquire\fR callbacks on the loop.
1244.Sp
1245When set, then \f(CW\*(C`release\*(C'\fR will be called just before the thread is
1246suspended waiting for new events, and \f(CW\*(C`acquire\*(C'\fR is called just
1247afterwards.
1248.Sp
1249Ideally, \f(CW\*(C`release\*(C'\fR will just call your mutex_unlock function, and
1250\&\f(CW\*(C`acquire\*(C'\fR will just call the mutex_lock function again.
1251.Sp
1252While event loop modifications are allowed between invocations of
1253\&\f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR (that's their only purpose after all), no
1254modifications done will affect the event loop, i.e. adding watchers will
1255have no effect on the set of file descriptors being watched, or the time
1256waited. Use an \f(CW\*(C`ev_async\*(C'\fR watcher to wake up \f(CW\*(C`ev_run\*(C'\fR when you want it
1257to take note of any changes you made.
1258.Sp
1259In theory, threads executing \f(CW\*(C`ev_run\*(C'\fR will be async-cancel safe between
1260invocations of \f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR.
1261.Sp
1262See also the locking example in the \f(CW\*(C`THREADS\*(C'\fR section later in this
1263document.
1264.IP "ev_set_userdata (loop, void *data)" 4
1265.IX Item "ev_set_userdata (loop, void *data)"
1266.PD 0
1267.IP "void *ev_userdata (loop)" 4
1268.IX Item "void *ev_userdata (loop)"
1269.PD
1270Set and retrieve a single \f(CW\*(C`void *\*(C'\fR associated with a loop. When
1271\&\f(CW\*(C`ev_set_userdata\*(C'\fR has never been called, then \f(CW\*(C`ev_userdata\*(C'\fR returns
1272\&\f(CW0\fR.
1273.Sp
1274These two functions can be used to associate arbitrary data with a loop,
1275and are intended solely for the \f(CW\*(C`invoke_pending_cb\*(C'\fR, \f(CW\*(C`release\*(C'\fR and
1276\&\f(CW\*(C`acquire\*(C'\fR callbacks described above, but of course can be (ab\-)used for
1277any other purpose as well.
1278.IP "ev_verify (loop)" 4
1279.IX Item "ev_verify (loop)"
1280This function only does something when \f(CW\*(C`EV_VERIFY\*(C'\fR support has been
1281compiled in, which is the default for non-minimal builds. It tries to go
1282through all internal structures and checks them for validity. If anything
1283is found to be inconsistent, it will print an error message to standard
1284error and call \f(CW\*(C`abort ()\*(C'\fR.
1285.Sp
1286This can be used to catch bugs inside libev itself: under normal
1287circumstances, this function will never abort as of course libev keeps its
1288data structures consistent.
609.SH "ANATOMY OF A WATCHER" 1289.SH "ANATOMY OF A WATCHER"
610.IX Header "ANATOMY OF A WATCHER" 1290.IX Header "ANATOMY OF A WATCHER"
1291In the following description, uppercase \f(CW\*(C`TYPE\*(C'\fR in names stands for the
1292watcher type, e.g. \f(CW\*(C`ev_TYPE_start\*(C'\fR can mean \f(CW\*(C`ev_timer_start\*(C'\fR for timer
1293watchers and \f(CW\*(C`ev_io_start\*(C'\fR for I/O watchers.
1294.PP
611A watcher is a structure that you create and register to record your 1295A 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 1296your 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: 1297to wait for \s-1STDIN\s0 to become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher
1298for that:
614.PP 1299.PP
615.Vb 5 1300.Vb 5
616\& static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) 1301\& static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
617\& { 1302\& {
618\& ev_io_stop (w); 1303\& ev_io_stop (w);
619\& ev_unloop (loop, EVUNLOOP_ALL); 1304\& ev_break (loop, EVBREAK_ALL);
620\& } 1305\& }
621.Ve 1306\&
622.PP
623.Vb 6
624\& struct ev_loop *loop = ev_default_loop (0); 1307\& struct ev_loop *loop = ev_default_loop (0);
1308\&
625\& struct ev_io stdin_watcher; 1309\& ev_io stdin_watcher;
1310\&
626\& ev_init (&stdin_watcher, my_cb); 1311\& ev_init (&stdin_watcher, my_cb);
627\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); 1312\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
628\& ev_io_start (loop, &stdin_watcher); 1313\& ev_io_start (loop, &stdin_watcher);
1314\&
629\& ev_loop (loop, 0); 1315\& ev_run (loop, 0);
630.Ve 1316.Ve
631.PP 1317.PP
632As you can see, you are responsible for allocating the memory for your 1318As 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, 1319watcher structures (and it is \fIusually\fR a bad idea to do this on the
634although this can sometimes be quite valid). 1320stack).
635.PP 1321.PP
1322Each watcher has an associated watcher structure (called \f(CW\*(C`struct ev_TYPE\*(C'\fR
1323or simply \f(CW\*(C`ev_TYPE\*(C'\fR, as typedefs are provided for all watcher structs).
1324.PP
636Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init 1325Each 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 1326*, 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 1327invoked 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 1328time the event loop detects that the file descriptor given is readable
640is readable and/or writable). 1329and/or writable).
641.PP 1330.PP
642Each watcher type has its own \f(CW\*(C`ev_<type>_set (watcher *, ...)\*(C'\fR macro 1331Each 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 1332macro 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 1333is 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 1334.PP
647To make the watcher actually watch out for events, you have to start it 1335To 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 1336with 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 1337*)\*(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. 1338corresponding stop function (\f(CW\*(C`ev_TYPE_stop (loop, watcher *)\*(C'\fR.
651.PP 1339.PP
652As long as your watcher is active (has been started but not stopped) you 1340As 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 1341must not touch the values stored in it. Most specifically you must never
654reinitialise it or call its \f(CW\*(C`set\*(C'\fR macro. 1342reinitialise it or call its \f(CW\*(C`ev_TYPE_set\*(C'\fR macro.
655.PP 1343.PP
656Each and every callback receives the event loop pointer as first, the 1344Each and every callback receives the event loop pointer as first, the
657registered watcher structure as second, and a bitset of received events as 1345registered watcher structure as second, and a bitset of received events as
658third argument. 1346third argument.
659.PP 1347.PP
… …
668.el .IP "\f(CWEV_WRITE\fR" 4 1356.el .IP "\f(CWEV_WRITE\fR" 4
669.IX Item "EV_WRITE" 1357.IX Item "EV_WRITE"
670.PD 1358.PD
671The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or 1359The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
672writable. 1360writable.
673.ie n .IP """EV_TIMEOUT""" 4 1361.ie n .IP """EV_TIMER""" 4
674.el .IP "\f(CWEV_TIMEOUT\fR" 4 1362.el .IP "\f(CWEV_TIMER\fR" 4
675.IX Item "EV_TIMEOUT" 1363.IX Item "EV_TIMER"
676The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out. 1364The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
677.ie n .IP """EV_PERIODIC""" 4 1365.ie n .IP """EV_PERIODIC""" 4
678.el .IP "\f(CWEV_PERIODIC\fR" 4 1366.el .IP "\f(CWEV_PERIODIC\fR" 4
679.IX Item "EV_PERIODIC" 1367.IX Item "EV_PERIODIC"
680The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out. 1368The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
… …
700.PD 0 1388.PD 0
701.ie n .IP """EV_CHECK""" 4 1389.ie n .IP """EV_CHECK""" 4
702.el .IP "\f(CWEV_CHECK\fR" 4 1390.el .IP "\f(CWEV_CHECK\fR" 4
703.IX Item "EV_CHECK" 1391.IX Item "EV_CHECK"
704.PD 1392.PD
705All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_loop\*(C'\fR starts 1393All \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 1394gather 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 1395just after \f(CW\*(C`ev_run\*(C'\fR has gathered them, but before it queues any callbacks
1396for any received events. That means \f(CW\*(C`ev_prepare\*(C'\fR watchers are the last
1397watchers invoked before the event loop sleeps or polls for new events, and
1398\&\f(CW\*(C`ev_check\*(C'\fR watchers will be invoked before any other watchers of the same
1399or lower priority within an event loop iteration.
1400.Sp
708received events. Callbacks of both watcher types can start and stop as 1401Callbacks 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 1402they 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 1403\&\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). 1404blocking).
1405.ie n .IP """EV_EMBED""" 4
1406.el .IP "\f(CWEV_EMBED\fR" 4
1407.IX Item "EV_EMBED"
1408The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.
1409.ie n .IP """EV_FORK""" 4
1410.el .IP "\f(CWEV_FORK\fR" 4
1411.IX Item "EV_FORK"
1412The event loop has been resumed in the child process after fork (see
1413\&\f(CW\*(C`ev_fork\*(C'\fR).
1414.ie n .IP """EV_CLEANUP""" 4
1415.el .IP "\f(CWEV_CLEANUP\fR" 4
1416.IX Item "EV_CLEANUP"
1417The event loop is about to be destroyed (see \f(CW\*(C`ev_cleanup\*(C'\fR).
1418.ie n .IP """EV_ASYNC""" 4
1419.el .IP "\f(CWEV_ASYNC\fR" 4
1420.IX Item "EV_ASYNC"
1421The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR).
1422.ie n .IP """EV_CUSTOM""" 4
1423.el .IP "\f(CWEV_CUSTOM\fR" 4
1424.IX Item "EV_CUSTOM"
1425Not ever sent (or otherwise used) by libev itself, but can be freely used
1426by libev users to signal watchers (e.g. via \f(CW\*(C`ev_feed_event\*(C'\fR).
712.ie n .IP """EV_ERROR""" 4 1427.ie n .IP """EV_ERROR""" 4
713.el .IP "\f(CWEV_ERROR\fR" 4 1428.el .IP "\f(CWEV_ERROR\fR" 4
714.IX Item "EV_ERROR" 1429.IX Item "EV_ERROR"
715An unspecified error has occured, the watcher has been stopped. This might 1430An unspecified error has occurred, the watcher has been stopped. This might
716happen because the watcher could not be properly started because libev 1431happen because the watcher could not be properly started because libev
717ran out of memory, a file descriptor was found to be closed or any other 1432ran out of memory, a file descriptor was found to be closed or any other
1433problem. Libev considers these application bugs.
1434.Sp
718problem. You best act on it by reporting the problem and somehow coping 1435You best act on it by reporting the problem and somehow coping with the
719with the watcher being stopped. 1436watcher being stopped. Note that well-written programs should not receive
1437an error ever, so when your watcher receives it, this usually indicates a
1438bug in your program.
720.Sp 1439.Sp
721Libev will usually signal a few \*(L"dummy\*(R" events together with an error, 1440Libev will usually signal a few \*(L"dummy\*(R" events together with an error, for
722for example it might indicate that a fd is readable or writable, and if 1441example it might indicate that a fd is readable or writable, and if your
723your callbacks is well-written it can just attempt the operation and cope 1442callbacks is well-written it can just attempt the operation and cope with
724with the error from \fIread()\fR or \fIwrite()\fR. This will not work in multithreaded 1443the error from \fBread()\fR or \fBwrite()\fR. This will not work in multi-threaded
725programs, though, so beware. 1444programs, though, as the fd could already be closed and reused for another
1445thing, so beware.
726.Sh "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0" 1446.SS "\s-1GENERIC WATCHER FUNCTIONS\s0"
727.IX Subsection "GENERIC WATCHER FUNCTIONS" 1447.IX Subsection "GENERIC WATCHER FUNCTIONS"
728In the following description, \f(CW\*(C`TYPE\*(C'\fR stands for the watcher type,
729e.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.
730.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4 1448.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
731.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4 1449.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
732.IX Item "ev_init (ev_TYPE *watcher, callback)" 1450.IX Item "ev_init (ev_TYPE *watcher, callback)"
733This macro initialises the generic portion of a watcher. The contents 1451This macro initialises the generic portion of a watcher. The contents
734of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only 1452of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
… …
738which rolls both calls into one. 1456which rolls both calls into one.
739.Sp 1457.Sp
740You can reinitialise a watcher at any time as long as it has been stopped 1458You can reinitialise a watcher at any time as long as it has been stopped
741(or never started) and there are no pending events outstanding. 1459(or never started) and there are no pending events outstanding.
742.Sp 1460.Sp
743The callback is always of type \f(CW\*(C`void (*)(ev_loop *loop, ev_TYPE *watcher, 1461The callback is always of type \f(CW\*(C`void (*)(struct ev_loop *loop, ev_TYPE *watcher,
744int revents)\*(C'\fR. 1462int revents)\*(C'\fR.
1463.Sp
1464Example: Initialise an \f(CW\*(C`ev_io\*(C'\fR watcher in two steps.
1465.Sp
1466.Vb 3
1467\& ev_io w;
1468\& ev_init (&w, my_cb);
1469\& ev_io_set (&w, STDIN_FILENO, EV_READ);
1470.Ve
745.ie n .IP """ev_TYPE_set"" (ev_TYPE *, [args])" 4 1471.ie n .IP """ev_TYPE_set"" (ev_TYPE *watcher, [args])" 4
746.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *, [args])" 4 1472.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *watcher, [args])" 4
747.IX Item "ev_TYPE_set (ev_TYPE *, [args])" 1473.IX Item "ev_TYPE_set (ev_TYPE *watcher, [args])"
748This macro initialises the type-specific parts of a watcher. You need to 1474This macro initialises the type-specific parts of a watcher. You need to
749call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can 1475call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
750call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this 1476call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
751macro on a watcher that is active (it can be pending, however, which is a 1477macro on a watcher that is active (it can be pending, however, which is a
752difference to the \f(CW\*(C`ev_init\*(C'\fR macro). 1478difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
753.Sp 1479.Sp
754Although some watcher types do not have type-specific arguments 1480Although some watcher types do not have type-specific arguments
755(e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro. 1481(e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
1482.Sp
1483See \f(CW\*(C`ev_init\*(C'\fR, above, for an example.
756.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4 1484.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
757.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4 1485.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
758.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])" 1486.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
759This convinience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro 1487This convenience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
760calls into a single call. This is the most convinient method to initialise 1488calls into a single call. This is the most convenient method to initialise
761a watcher. The same limitations apply, of course. 1489a watcher. The same limitations apply, of course.
1490.Sp
1491Example: Initialise and set an \f(CW\*(C`ev_io\*(C'\fR watcher in one step.
1492.Sp
1493.Vb 1
1494\& ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1495.Ve
762.ie n .IP """ev_TYPE_start"" (loop *, ev_TYPE *watcher)" 4 1496.ie n .IP """ev_TYPE_start"" (loop, ev_TYPE *watcher)" 4
763.el .IP "\f(CWev_TYPE_start\fR (loop *, ev_TYPE *watcher)" 4 1497.el .IP "\f(CWev_TYPE_start\fR (loop, ev_TYPE *watcher)" 4
764.IX Item "ev_TYPE_start (loop *, ev_TYPE *watcher)" 1498.IX Item "ev_TYPE_start (loop, ev_TYPE *watcher)"
765Starts (activates) the given watcher. Only active watchers will receive 1499Starts (activates) the given watcher. Only active watchers will receive
766events. If the watcher is already active nothing will happen. 1500events. If the watcher is already active nothing will happen.
1501.Sp
1502Example: Start the \f(CW\*(C`ev_io\*(C'\fR watcher that is being abused as example in this
1503whole section.
1504.Sp
1505.Vb 1
1506\& ev_io_start (EV_DEFAULT_UC, &w);
1507.Ve
767.ie n .IP """ev_TYPE_stop"" (loop *, ev_TYPE *watcher)" 4 1508.ie n .IP """ev_TYPE_stop"" (loop, ev_TYPE *watcher)" 4
768.el .IP "\f(CWev_TYPE_stop\fR (loop *, ev_TYPE *watcher)" 4 1509.el .IP "\f(CWev_TYPE_stop\fR (loop, ev_TYPE *watcher)" 4
769.IX Item "ev_TYPE_stop (loop *, ev_TYPE *watcher)" 1510.IX Item "ev_TYPE_stop (loop, ev_TYPE *watcher)"
770Stops the given watcher again (if active) and clears the pending 1511Stops the given watcher if active, and clears the pending status (whether
1512the watcher was active or not).
1513.Sp
771status. It is possible that stopped watchers are pending (for example, 1514It is possible that stopped watchers are pending \- for example,
772non-repeating timers are being stopped when they become pending), but 1515non-repeating timers are being stopped when they become pending \- but
773\&\f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor pending. If 1516calling \f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor
774you want to free or reuse the memory used by the watcher it is therefore a 1517pending. If you want to free or reuse the memory used by the watcher it is
775good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. 1518therefore a good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
776.IP "bool ev_is_active (ev_TYPE *watcher)" 4 1519.IP "bool ev_is_active (ev_TYPE *watcher)" 4
777.IX Item "bool ev_is_active (ev_TYPE *watcher)" 1520.IX Item "bool ev_is_active (ev_TYPE *watcher)"
778Returns a true value iff the watcher is active (i.e. it has been started 1521Returns a true value iff the watcher is active (i.e. it has been started
779and not yet been stopped). As long as a watcher is active you must not modify 1522and not yet been stopped). As long as a watcher is active you must not modify
780it. 1523it.
781.IP "bool ev_is_pending (ev_TYPE *watcher)" 4 1524.IP "bool ev_is_pending (ev_TYPE *watcher)" 4
782.IX Item "bool ev_is_pending (ev_TYPE *watcher)" 1525.IX Item "bool ev_is_pending (ev_TYPE *watcher)"
783Returns a true value iff the watcher is pending, (i.e. it has outstanding 1526Returns a true value iff the watcher is pending, (i.e. it has outstanding
784events but its callback has not yet been invoked). As long as a watcher 1527events but its callback has not yet been invoked). As long as a watcher
785is pending (but not active) you must not call an init function on it (but 1528is pending (but not active) you must not call an init function on it (but
786\&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe) and you must make sure the watcher is available to 1529\&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe), you must not change its priority, and you must
787libev (e.g. you cnanot \f(CW\*(C`free ()\*(C'\fR it). 1530make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR
1531it).
788.IP "callback = ev_cb (ev_TYPE *watcher)" 4 1532.IP "callback ev_cb (ev_TYPE *watcher)" 4
789.IX Item "callback = ev_cb (ev_TYPE *watcher)" 1533.IX Item "callback ev_cb (ev_TYPE *watcher)"
790Returns the callback currently set on the watcher. 1534Returns the callback currently set on the watcher.
791.IP "ev_cb_set (ev_TYPE *watcher, callback)" 4 1535.IP "ev_set_cb (ev_TYPE *watcher, callback)" 4
792.IX Item "ev_cb_set (ev_TYPE *watcher, callback)" 1536.IX Item "ev_set_cb (ev_TYPE *watcher, callback)"
793Change the callback. You can change the callback at virtually any time 1537Change the callback. You can change the callback at virtually any time
794(modulo threads). 1538(modulo threads).
795.Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0" 1539.IP "ev_set_priority (ev_TYPE *watcher, int priority)" 4
796.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER" 1540.IX Item "ev_set_priority (ev_TYPE *watcher, int priority)"
797Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change 1541.PD 0
798and read at any time, libev will completely ignore it. This can be used 1542.IP "int ev_priority (ev_TYPE *watcher)" 4
799to associate arbitrary data with your watcher. If you need more data and 1543.IX Item "int ev_priority (ev_TYPE *watcher)"
800don't want to allocate memory and store a pointer to it in that data 1544.PD
801member, you can also \*(L"subclass\*(R" the watcher type and provide your own 1545Set and query the priority of the watcher. The priority is a small
802data: 1546integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR
1547(default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked
1548before watchers with lower priority, but priority will not keep watchers
1549from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
1550.Sp
1551If you need to suppress invocation when higher priority events are pending
1552you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
1553.Sp
1554You \fImust not\fR change the priority of a watcher as long as it is active or
1555pending.
1556.Sp
1557Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
1558fine, as long as you do not mind that the priority value you query might
1559or might not have been clamped to the valid range.
1560.Sp
1561The default priority used by watchers when no priority has been set is
1562always \f(CW0\fR, which is supposed to not be too high and not be too low :).
1563.Sp
1564See \*(L"\s-1WATCHER PRIORITY MODELS\*(R"\s0, below, for a more thorough treatment of
1565priorities.
1566.IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
1567.IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
1568Invoke the \f(CW\*(C`watcher\*(C'\fR with the given \f(CW\*(C`loop\*(C'\fR and \f(CW\*(C`revents\*(C'\fR. Neither
1569\&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback
1570can deal with that fact, as both are simply passed through to the
1571callback.
1572.IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
1573.IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
1574If the watcher is pending, this function clears its pending status and
1575returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the
1576watcher isn't pending it does nothing and returns \f(CW0\fR.
1577.Sp
1578Sometimes it can be useful to \*(L"poll\*(R" a watcher instead of waiting for its
1579callback to be invoked, which can be accomplished with this function.
1580.IP "ev_feed_event (loop, ev_TYPE *watcher, int revents)" 4
1581.IX Item "ev_feed_event (loop, ev_TYPE *watcher, int revents)"
1582Feeds the given event set into the event loop, as if the specified event
1583had happened for the specified watcher (which must be a pointer to an
1584initialised but not necessarily started event watcher). Obviously you must
1585not free the watcher as long as it has pending events.
1586.Sp
1587Stopping the watcher, letting libev invoke it, or calling
1588\&\f(CW\*(C`ev_clear_pending\*(C'\fR will clear the pending event, even if the watcher was
1589not started in the first place.
1590.Sp
1591See also \f(CW\*(C`ev_feed_fd_event\*(C'\fR and \f(CW\*(C`ev_feed_signal_event\*(C'\fR for related
1592functions that do not need a watcher.
803.PP 1593.PP
1594See also the \*(L"\s-1ASSOCIATING CUSTOM DATA WITH A WATCHER\*(R"\s0 and \*(L"\s-1BUILDING YOUR
1595OWN COMPOSITE WATCHERS\*(R"\s0 idioms.
1596.SS "\s-1WATCHER STATES\s0"
1597.IX Subsection "WATCHER STATES"
1598There are various watcher states mentioned throughout this manual \-
1599active, pending and so on. In this section these states and the rules to
1600transition between them will be described in more detail \- and while these
1601rules might look complicated, they usually do \*(L"the right thing\*(R".
1602.IP "initialised" 4
1603.IX Item "initialised"
1604Before a watcher can be registered with the event loop it has to be
1605initialised. This can be done with a call to \f(CW\*(C`ev_TYPE_init\*(C'\fR, or calls to
1606\&\f(CW\*(C`ev_init\*(C'\fR followed by the watcher-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR function.
1607.Sp
1608In this state it is simply some block of memory that is suitable for
1609use in an event loop. It can be moved around, freed, reused etc. at
1610will \- as long as you either keep the memory contents intact, or call
1611\&\f(CW\*(C`ev_TYPE_init\*(C'\fR again.
1612.IP "started/running/active" 4
1613.IX Item "started/running/active"
1614Once a watcher has been started with a call to \f(CW\*(C`ev_TYPE_start\*(C'\fR it becomes
1615property of the event loop, and is actively waiting for events. While in
1616this state it cannot be accessed (except in a few documented ways), moved,
1617freed or anything else \- the only legal thing is to keep a pointer to it,
1618and call libev functions on it that are documented to work on active watchers.
1619.IP "pending" 4
1620.IX Item "pending"
1621If a watcher is active and libev determines that an event it is interested
1622in has occurred (such as a timer expiring), it will become pending. It will
1623stay in this pending state until either it is stopped or its callback is
1624about to be invoked, so it is not normally pending inside the watcher
1625callback.
1626.Sp
1627The watcher might or might not be active while it is pending (for example,
1628an expired non-repeating timer can be pending but no longer active). If it
1629is stopped, it can be freely accessed (e.g. by calling \f(CW\*(C`ev_TYPE_set\*(C'\fR),
1630but it is still property of the event loop at this time, so cannot be
1631moved, freed or reused. And if it is active the rules described in the
1632previous item still apply.
1633.Sp
1634It is also possible to feed an event on a watcher that is not active (e.g.
1635via \f(CW\*(C`ev_feed_event\*(C'\fR), in which case it becomes pending without being
1636active.
1637.IP "stopped" 4
1638.IX Item "stopped"
1639A watcher can be stopped implicitly by libev (in which case it might still
1640be pending), or explicitly by calling its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. The
1641latter will clear any pending state the watcher might be in, regardless
1642of whether it was active or not, so stopping a watcher explicitly before
1643freeing it is often a good idea.
1644.Sp
1645While stopped (and not pending) the watcher is essentially in the
1646initialised state, that is, it can be reused, moved, modified in any way
1647you wish (but when you trash the memory block, you need to \f(CW\*(C`ev_TYPE_init\*(C'\fR
1648it again).
1649.SS "\s-1WATCHER PRIORITY MODELS\s0"
1650.IX Subsection "WATCHER PRIORITY MODELS"
1651Many event loops support \fIwatcher priorities\fR, which are usually small
1652integers that influence the ordering of event callback invocation
1653between watchers in some way, all else being equal.
1654.PP
1655In libev, Watcher priorities can be set using \f(CW\*(C`ev_set_priority\*(C'\fR. See its
1656description for the more technical details such as the actual priority
1657range.
1658.PP
1659There are two common ways how these these priorities are being interpreted
1660by event loops:
1661.PP
1662In the more common lock-out model, higher priorities \*(L"lock out\*(R" invocation
1663of lower priority watchers, which means as long as higher priority
1664watchers receive events, lower priority watchers are not being invoked.
1665.PP
1666The less common only-for-ordering model uses priorities solely to order
1667callback invocation within a single event loop iteration: Higher priority
1668watchers are invoked before lower priority ones, but they all get invoked
1669before polling for new events.
1670.PP
1671Libev uses the second (only-for-ordering) model for all its watchers
1672except for idle watchers (which use the lock-out model).
1673.PP
1674The rationale behind this is that implementing the lock-out model for
1675watchers is not well supported by most kernel interfaces, and most event
1676libraries will just poll for the same events again and again as long as
1677their callbacks have not been executed, which is very inefficient in the
1678common case of one high-priority watcher locking out a mass of lower
1679priority ones.
1680.PP
1681Static (ordering) priorities are most useful when you have two or more
1682watchers handling the same resource: a typical usage example is having an
1683\&\f(CW\*(C`ev_io\*(C'\fR watcher to receive data, and an associated \f(CW\*(C`ev_timer\*(C'\fR to handle
1684timeouts. Under load, data might be received while the program handles
1685other jobs, but since timers normally get invoked first, the timeout
1686handler will be executed before checking for data. In that case, giving
1687the timer a lower priority than the I/O watcher ensures that I/O will be
1688handled first even under adverse conditions (which is usually, but not
1689always, what you want).
1690.PP
1691Since idle watchers use the \*(L"lock-out\*(R" model, meaning that idle watchers
1692will only be executed when no same or higher priority watchers have
1693received events, they can be used to implement the \*(L"lock-out\*(R" model when
1694required.
1695.PP
1696For example, to emulate how many other event libraries handle priorities,
1697you can associate an \f(CW\*(C`ev_idle\*(C'\fR watcher to each such watcher, and in
1698the normal watcher callback, you just start the idle watcher. The real
1699processing is done in the idle watcher callback. This causes libev to
1700continuously poll and process kernel event data for the watcher, but when
1701the lock-out case is known to be rare (which in turn is rare :), this is
1702workable.
1703.PP
1704Usually, however, the lock-out model implemented that way will perform
1705miserably under the type of load it was designed to handle. In that case,
1706it might be preferable to stop the real watcher before starting the
1707idle watcher, so the kernel will not have to process the event in case
1708the actual processing will be delayed for considerable time.
1709.PP
1710Here is an example of an I/O watcher that should run at a strictly lower
1711priority than the default, and which should only process data when no
1712other events are pending:
1713.PP
804.Vb 7 1714.Vb 2
805\& struct my_io 1715\& ev_idle idle; // actual processing watcher
1716\& ev_io io; // actual event watcher
1717\&
1718\& static void
1719\& io_cb (EV_P_ ev_io *w, int revents)
806\& { 1720\& {
807\& struct ev_io io; 1721\& // stop the I/O watcher, we received the event, but
808\& int otherfd; 1722\& // are not yet ready to handle it.
809\& void *somedata; 1723\& ev_io_stop (EV_A_ w);
810\& struct whatever *mostinteresting; 1724\&
1725\& // start the idle watcher to handle the actual event.
1726\& // it will not be executed as long as other watchers
1727\& // with the default priority are receiving events.
1728\& ev_idle_start (EV_A_ &idle);
811\& } 1729\& }
812.Ve 1730\&
813.PP 1731\& static void
814And since your callback will be called with a pointer to the watcher, you 1732\& idle_cb (EV_P_ ev_idle *w, int revents)
815can cast it back to your own type:
816.PP
817.Vb 5
818\& static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
819\& { 1733\& {
820\& struct my_io *w = (struct my_io *)w_; 1734\& // actual processing
821\& ... 1735\& read (STDIN_FILENO, ...);
1736\&
1737\& // have to start the I/O watcher again, as
1738\& // we have handled the event
1739\& ev_io_start (EV_P_ &io);
822\& } 1740\& }
1741\&
1742\& // initialisation
1743\& ev_idle_init (&idle, idle_cb);
1744\& ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
1745\& ev_io_start (EV_DEFAULT_ &io);
823.Ve 1746.Ve
824.PP 1747.PP
825More interesting and less C\-conformant ways of catsing your callback type 1748In the \*(L"real\*(R" world, it might also be beneficial to start a timer, so that
826have been omitted.... 1749low-priority connections can not be locked out forever under load. This
1750enables your program to keep a lower latency for important connections
1751during short periods of high load, while not completely locking out less
1752important ones.
827.SH "WATCHER TYPES" 1753.SH "WATCHER TYPES"
828.IX Header "WATCHER TYPES" 1754.IX Header "WATCHER TYPES"
829This section describes each watcher in detail, but will not repeat 1755This section describes each watcher in detail, but will not repeat
830information given in the last section. Any initialisation/set macros, 1756information given in the last section. Any initialisation/set macros,
831functions and members specific to the watcher type are explained. 1757functions and members specific to the watcher type are explained.
… …
836watcher is stopped to your hearts content), or \fI[read\-write]\fR, which 1762watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
837means you can expect it to have some sensible content while the watcher 1763means you can expect it to have some sensible content while the watcher
838is active, but you can also modify it. Modifying it may not do something 1764is active, but you can also modify it. Modifying it may not do something
839sensible or take immediate effect (or do anything at all), but libev will 1765sensible or take immediate effect (or do anything at all), but libev will
840not crash or malfunction in any way. 1766not crash or malfunction in any way.
841.ie n .Sh """ev_io"" \- is this file descriptor readable or writable?" 1767.ie n .SS """ev_io"" \- is this file descriptor readable or writable?"
842.el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable?" 1768.el .SS "\f(CWev_io\fP \- is this file descriptor readable or writable?"
843.IX Subsection "ev_io - is this file descriptor readable or writable?" 1769.IX Subsection "ev_io - is this file descriptor readable or writable?"
844I/O watchers check whether a file descriptor is readable or writable 1770I/O watchers check whether a file descriptor is readable or writable
845in each iteration of the event loop, or, more precisely, when reading 1771in each iteration of the event loop, or, more precisely, when reading
846would not block the process and writing would at least be able to write 1772would not block the process and writing would at least be able to write
847some data. This behaviour is called level-triggering because you keep 1773some data. This behaviour is called level-triggering because you keep
… …
852In general you can register as many read and/or write event watchers per 1778In general you can register as many read and/or write event watchers per
853fd as you want (as long as you don't confuse yourself). Setting all file 1779fd as you want (as long as you don't confuse yourself). Setting all file
854descriptors to non-blocking mode is also usually a good idea (but not 1780descriptors to non-blocking mode is also usually a good idea (but not
855required if you know what you are doing). 1781required if you know what you are doing).
856.PP 1782.PP
857You have to be careful with dup'ed file descriptors, though. Some backends
858(the linux epoll backend is a notable example) cannot handle dup'ed file
859descriptors correctly if you register interest in two or more fds pointing
860to the same underlying file/socket/etc. description (that is, they share
861the same underlying \*(L"file open\*(R").
862.PP
863If you must do this, then force the use of a known-to-be-good backend
864(at the time of this writing, this includes only \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and
865\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR).
866.PP
867Another thing you have to watch out for is that it is quite easy to 1783Another thing you have to watch out for is that it is quite easy to
868receive \*(L"spurious\*(R" readyness notifications, that is your callback might 1784receive \*(L"spurious\*(R" readiness notifications, that is, your callback might
869be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block 1785be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block
870because there is no data. Not only are some backends known to create a 1786because there is no data. It is very easy to get into this situation even
871lot of those (for example solaris ports), it is very easy to get into 1787with a relatively standard program structure. Thus it is best to always
872this situation even with a relatively standard program structure. Thus 1788use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning \f(CW\*(C`EAGAIN\*(C'\fR is far
873it is best to always use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning
874\&\f(CW\*(C`EAGAIN\*(C'\fR is far preferable to a program hanging until some data arrives. 1789preferable to a program hanging until some data arrives.
875.PP 1790.PP
876If you cannot run the fd in non-blocking mode (for example you should not 1791If you cannot run the fd in non-blocking mode (for example you should
877play around with an Xlib connection), then you have to seperately re-test 1792not play around with an Xlib connection), then you have to separately
878wether a file descriptor is really ready with a known-to-be good interface 1793re-test whether a file descriptor is really ready with a known-to-be good
879such as poll (fortunately in our Xlib example, Xlib already does this on 1794interface such as poll (fortunately in the case of Xlib, it already does
880its own, so its quite safe to use). 1795this on its own, so its quite safe to use). Some people additionally
1796use \f(CW\*(C`SIGALRM\*(C'\fR and an interval timer, just to be sure you won't block
1797indefinitely.
1798.PP
1799But really, best use non-blocking mode.
1800.PP
1801\fIThe special problem of disappearing file descriptors\fR
1802.IX Subsection "The special problem of disappearing file descriptors"
1803.PP
1804Some backends (e.g. kqueue, epoll, linuxaio) need to be told about closing
1805a file descriptor (either due to calling \f(CW\*(C`close\*(C'\fR explicitly or any other
1806means, such as \f(CW\*(C`dup2\*(C'\fR). The reason is that you register interest in some
1807file descriptor, but when it goes away, the operating system will silently
1808drop this interest. If another file descriptor with the same number then
1809is registered with libev, there is no efficient way to see that this is,
1810in fact, a different file descriptor.
1811.PP
1812To avoid having to explicitly tell libev about such cases, libev follows
1813the following policy: Each time \f(CW\*(C`ev_io_set\*(C'\fR is being called, libev
1814will assume that this is potentially a new file descriptor, otherwise
1815it is assumed that the file descriptor stays the same. That means that
1816you \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
1817descriptor even if the file descriptor number itself did not change.
1818.PP
1819This is how one would do it normally anyway, the important point is that
1820the libev application should not optimise around libev but should leave
1821optimisations to libev.
1822.PP
1823\fIThe special problem of dup'ed file descriptors\fR
1824.IX Subsection "The special problem of dup'ed file descriptors"
1825.PP
1826Some backends (e.g. epoll), cannot register events for file descriptors,
1827but only events for the underlying file descriptions. That means when you
1828have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register
1829events for them, only one file descriptor might actually receive events.
1830.PP
1831There is no workaround possible except not registering events
1832for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
1833\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1834.PP
1835\fIThe special problem of files\fR
1836.IX Subsection "The special problem of files"
1837.PP
1838Many people try to use \f(CW\*(C`select\*(C'\fR (or libev) on file descriptors
1839representing files, and expect it to become ready when their program
1840doesn't block on disk accesses (which can take a long time on their own).
1841.PP
1842However, this cannot ever work in the \*(L"expected\*(R" way \- you get a readiness
1843notification as soon as the kernel knows whether and how much data is
1844there, and in the case of open files, that's always the case, so you
1845always get a readiness notification instantly, and your read (or possibly
1846write) will still block on the disk I/O.
1847.PP
1848Another way to view it is that in the case of sockets, pipes, character
1849devices and so on, there is another party (the sender) that delivers data
1850on its own, but in the case of files, there is no such thing: the disk
1851will not send data on its own, simply because it doesn't know what you
1852wish to read \- you would first have to request some data.
1853.PP
1854Since files are typically not-so-well supported by advanced notification
1855mechanism, libev tries hard to emulate \s-1POSIX\s0 behaviour with respect
1856to files, even though you should not use it. The reason for this is
1857convenience: sometimes you want to watch \s-1STDIN\s0 or \s-1STDOUT,\s0 which is
1858usually a tty, often a pipe, but also sometimes files or special devices
1859(for example, \f(CW\*(C`epoll\*(C'\fR on Linux works with \fI/dev/random\fR but not with
1860\&\fI/dev/urandom\fR), and even though the file might better be served with
1861asynchronous I/O instead of with non-blocking I/O, it is still useful when
1862it \*(L"just works\*(R" instead of freezing.
1863.PP
1864So avoid file descriptors pointing to files when you know it (e.g. use
1865libeio), but use them when it is convenient, e.g. for \s-1STDIN/STDOUT,\s0 or
1866when you rarely read from a file instead of from a socket, and want to
1867reuse the same code path.
1868.PP
1869\fIThe special problem of fork\fR
1870.IX Subsection "The special problem of fork"
1871.PP
1872Some backends (epoll, kqueue, probably linuxaio) do not support \f(CW\*(C`fork ()\*(C'\fR
1873at all or exhibit useless behaviour. Libev fully supports fork, but needs
1874to be told about it in the child if you want to continue to use it in the
1875child.
1876.PP
1877To support fork in your child processes, you have to call \f(CW\*(C`ev_loop_fork
1878()\*(C'\fR after a fork in the child, enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to
1879\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1880.PP
1881\fIThe special problem of \s-1SIGPIPE\s0\fR
1882.IX Subsection "The special problem of SIGPIPE"
1883.PP
1884While not really specific to libev, it is easy to forget about \f(CW\*(C`SIGPIPE\*(C'\fR:
1885when writing to a pipe whose other end has been closed, your program gets
1886sent a \s-1SIGPIPE,\s0 which, by default, aborts your program. For most programs
1887this is sensible behaviour, for daemons, this is usually undesirable.
1888.PP
1889So when you encounter spurious, unexplained daemon exits, make sure you
1890ignore \s-1SIGPIPE\s0 (and maybe make sure you log the exit status of your daemon
1891somewhere, as that would have given you a big clue).
1892.PP
1893\fIThe special problem of \f(BIaccept()\fIing when you can't\fR
1894.IX Subsection "The special problem of accept()ing when you can't"
1895.PP
1896Many implementations of the \s-1POSIX\s0 \f(CW\*(C`accept\*(C'\fR function (for example,
1897found in post\-2004 Linux) have the peculiar behaviour of not removing a
1898connection from the pending queue in all error cases.
1899.PP
1900For example, larger servers often run out of file descriptors (because
1901of resource limits), causing \f(CW\*(C`accept\*(C'\fR to fail with \f(CW\*(C`ENFILE\*(C'\fR but not
1902rejecting the connection, leading to libev signalling readiness on
1903the next iteration again (the connection still exists after all), and
1904typically causing the program to loop at 100% \s-1CPU\s0 usage.
1905.PP
1906Unfortunately, the set of errors that cause this issue differs between
1907operating systems, there is usually little the app can do to remedy the
1908situation, and no known thread-safe method of removing the connection to
1909cope with overload is known (to me).
1910.PP
1911One of the easiest ways to handle this situation is to just ignore it
1912\&\- when the program encounters an overload, it will just loop until the
1913situation is over. While this is a form of busy waiting, no \s-1OS\s0 offers an
1914event-based way to handle this situation, so it's the best one can do.
1915.PP
1916A better way to handle the situation is to log any errors other than
1917\&\f(CW\*(C`EAGAIN\*(C'\fR and \f(CW\*(C`EWOULDBLOCK\*(C'\fR, making sure not to flood the log with such
1918messages, and continue as usual, which at least gives the user an idea of
1919what could be wrong (\*(L"raise the ulimit!\*(R"). For extra points one could stop
1920the \f(CW\*(C`ev_io\*(C'\fR watcher on the listening fd \*(L"for a while\*(R", which reduces \s-1CPU\s0
1921usage.
1922.PP
1923If your program is single-threaded, then you could also keep a dummy file
1924descriptor for overload situations (e.g. by opening \fI/dev/null\fR), and
1925when 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,
1926close that fd, and create a new dummy fd. This will gracefully refuse
1927clients under typical overload conditions.
1928.PP
1929The last way to handle it is to simply log the error and \f(CW\*(C`exit\*(C'\fR, as
1930is often done with \f(CW\*(C`malloc\*(C'\fR failures, but this results in an easy
1931opportunity for a DoS attack.
1932.PP
1933\fIWatcher-Specific Functions\fR
1934.IX Subsection "Watcher-Specific Functions"
881.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4 1935.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
882.IX Item "ev_io_init (ev_io *, callback, int fd, int events)" 1936.IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
883.PD 0 1937.PD 0
884.IP "ev_io_set (ev_io *, int fd, int events)" 4 1938.IP "ev_io_set (ev_io *, int fd, int events)" 4
885.IX Item "ev_io_set (ev_io *, int fd, int events)" 1939.IX Item "ev_io_set (ev_io *, int fd, int events)"
886.PD 1940.PD
887Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to 1941Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to
888rceeive events for and events is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or 1942receive 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
889\&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR to receive the given events. 1943\&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR, to express the desire to receive the given events.
890.IP "int fd [read\-only]" 4 1944.IP "int fd [read\-only]" 4
891.IX Item "int fd [read-only]" 1945.IX Item "int fd [read-only]"
892The file descriptor being watched. 1946The file descriptor being watched.
893.IP "int events [read\-only]" 4 1947.IP "int events [read\-only]" 4
894.IX Item "int events [read-only]" 1948.IX Item "int events [read-only]"
895The events being watched. 1949The events being watched.
896.PP 1950.PP
1951\fIExamples\fR
1952.IX Subsection "Examples"
1953.PP
897Example: call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well 1954Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
898readable, but only once. Since it is likely line\-buffered, you could 1955readable, but only once. Since it is likely line-buffered, you could
899attempt to read a whole line in the callback: 1956attempt to read a whole line in the callback.
900.PP 1957.PP
901.Vb 6 1958.Vb 6
902\& static void 1959\& static void
903\& stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents) 1960\& stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
904\& { 1961\& {
905\& ev_io_stop (loop, w); 1962\& ev_io_stop (loop, w);
906\& .. read from stdin here (or from w->fd) and haqndle any I/O errors 1963\& .. read from stdin here (or from w\->fd) and handle any I/O errors
907\& } 1964\& }
908.Ve 1965\&
909.PP
910.Vb 6
911\& ... 1966\& ...
912\& struct ev_loop *loop = ev_default_init (0); 1967\& struct ev_loop *loop = ev_default_init (0);
913\& struct ev_io stdin_readable; 1968\& ev_io stdin_readable;
914\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ); 1969\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
915\& ev_io_start (loop, &stdin_readable); 1970\& ev_io_start (loop, &stdin_readable);
916\& ev_loop (loop, 0); 1971\& ev_run (loop, 0);
917.Ve 1972.Ve
918.ie n .Sh """ev_timer"" \- relative and optionally repeating timeouts" 1973.ie n .SS """ev_timer"" \- relative and optionally repeating timeouts"
919.el .Sh "\f(CWev_timer\fP \- relative and optionally repeating timeouts" 1974.el .SS "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
920.IX Subsection "ev_timer - relative and optionally repeating timeouts" 1975.IX Subsection "ev_timer - relative and optionally repeating timeouts"
921Timer watchers are simple relative timers that generate an event after a 1976Timer watchers are simple relative timers that generate an event after a
922given time, and optionally repeating in regular intervals after that. 1977given time, and optionally repeating in regular intervals after that.
923.PP 1978.PP
924The timers are based on real time, that is, if you register an event that 1979The timers are based on real time, that is, if you register an event that
925times out after an hour and you reset your system clock to last years 1980times out after an hour and you reset your system clock to January last
926time, it will still time out after (roughly) and hour. \*(L"Roughly\*(R" because 1981year, it will still time out after (roughly) one hour. \*(L"Roughly\*(R" because
927detecting time jumps is hard, and some inaccuracies are unavoidable (the 1982detecting time jumps is hard, and some inaccuracies are unavoidable (the
928monotonic clock option helps a lot here). 1983monotonic clock option helps a lot here).
1984.PP
1985The callback is guaranteed to be invoked only \fIafter\fR its timeout has
1986passed (not \fIat\fR, so on systems with very low-resolution clocks this
1987might introduce a small delay, see \*(L"the special problem of being too
1988early\*(R", below). If multiple timers become ready during the same loop
1989iteration then the ones with earlier time-out values are invoked before
1990ones of the same priority with later time-out values (but this is no
1991longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
1992.PP
1993\fIBe smart about timeouts\fR
1994.IX Subsection "Be smart about timeouts"
1995.PP
1996Many real-world problems involve some kind of timeout, usually for error
1997recovery. A typical example is an \s-1HTTP\s0 request \- if the other side hangs,
1998you want to raise some error after a while.
1999.PP
2000What follows are some ways to handle this problem, from obvious and
2001inefficient to smart and efficient.
2002.PP
2003In the following, a 60 second activity timeout is assumed \- a timeout that
2004gets reset to 60 seconds each time there is activity (e.g. each time some
2005data or other life sign was received).
2006.IP "1. Use a timer and stop, reinitialise and start it on activity." 4
2007.IX Item "1. Use a timer and stop, reinitialise and start it on activity."
2008This is the most obvious, but not the most simple way: In the beginning,
2009start the watcher:
2010.Sp
2011.Vb 2
2012\& ev_timer_init (timer, callback, 60., 0.);
2013\& ev_timer_start (loop, timer);
2014.Ve
2015.Sp
2016Then, each time there is some activity, \f(CW\*(C`ev_timer_stop\*(C'\fR it, initialise it
2017and start it again:
2018.Sp
2019.Vb 3
2020\& ev_timer_stop (loop, timer);
2021\& ev_timer_set (timer, 60., 0.);
2022\& ev_timer_start (loop, timer);
2023.Ve
2024.Sp
2025This is relatively simple to implement, but means that each time there is
2026some activity, libev will first have to remove the timer from its internal
2027data structure and then add it again. Libev tries to be fast, but it's
2028still not a constant-time operation.
2029.ie n .IP "2. Use a timer and re-start it with ""ev_timer_again"" inactivity." 4
2030.el .IP "2. Use a timer and re-start it with \f(CWev_timer_again\fR inactivity." 4
2031.IX Item "2. Use a timer and re-start it with ev_timer_again inactivity."
2032This is the easiest way, and involves using \f(CW\*(C`ev_timer_again\*(C'\fR instead of
2033\&\f(CW\*(C`ev_timer_start\*(C'\fR.
2034.Sp
2035To implement this, configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value
2036of \f(CW60\fR and then call \f(CW\*(C`ev_timer_again\*(C'\fR at start and each time you
2037successfully read or write some data. If you go into an idle state where
2038you do not expect data to travel on the socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR
2039the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will automatically restart it if need be.
2040.Sp
2041That means you can ignore both the \f(CW\*(C`ev_timer_start\*(C'\fR function and the
2042\&\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
2043member and \f(CW\*(C`ev_timer_again\*(C'\fR.
2044.Sp
2045At start:
2046.Sp
2047.Vb 3
2048\& ev_init (timer, callback);
2049\& timer\->repeat = 60.;
2050\& ev_timer_again (loop, timer);
2051.Ve
2052.Sp
2053Each time there is some activity:
2054.Sp
2055.Vb 1
2056\& ev_timer_again (loop, timer);
2057.Ve
2058.Sp
2059It is even possible to change the time-out on the fly, regardless of
2060whether the watcher is active or not:
2061.Sp
2062.Vb 2
2063\& timer\->repeat = 30.;
2064\& ev_timer_again (loop, timer);
2065.Ve
2066.Sp
2067This is slightly more efficient then stopping/starting the timer each time
2068you want to modify its timeout value, as libev does not have to completely
2069remove and re-insert the timer from/into its internal data structure.
2070.Sp
2071It is, however, even simpler than the \*(L"obvious\*(R" way to do it.
2072.IP "3. Let the timer time out, but then re-arm it as required." 4
2073.IX Item "3. Let the timer time out, but then re-arm it as required."
2074This method is more tricky, but usually most efficient: Most timeouts are
2075relatively long compared to the intervals between other activity \- in
2076our example, within 60 seconds, there are usually many I/O events with
2077associated activity resets.
2078.Sp
2079In this case, it would be more efficient to leave the \f(CW\*(C`ev_timer\*(C'\fR alone,
2080but remember the time of last activity, and check for a real timeout only
2081within the callback:
2082.Sp
2083.Vb 3
2084\& ev_tstamp timeout = 60.;
2085\& ev_tstamp last_activity; // time of last activity
2086\& ev_timer timer;
2087\&
2088\& static void
2089\& callback (EV_P_ ev_timer *w, int revents)
2090\& {
2091\& // calculate when the timeout would happen
2092\& ev_tstamp after = last_activity \- ev_now (EV_A) + timeout;
2093\&
2094\& // if negative, it means we the timeout already occurred
2095\& if (after < 0.)
2096\& {
2097\& // timeout occurred, take action
2098\& }
2099\& else
2100\& {
2101\& // callback was invoked, but there was some recent
2102\& // activity. simply restart the timer to time out
2103\& // after "after" seconds, which is the earliest time
2104\& // the timeout can occur.
2105\& ev_timer_set (w, after, 0.);
2106\& ev_timer_start (EV_A_ w);
2107\& }
2108\& }
2109.Ve
2110.Sp
2111To summarise the callback: first calculate in how many seconds the
2112timeout will occur (by calculating the absolute time when it would occur,
2113\&\f(CW\*(C`last_activity + timeout\*(C'\fR, and subtracting the current time, \f(CW\*(C`ev_now
2114(EV_A)\*(C'\fR from that).
2115.Sp
2116If this value is negative, then we are already past the timeout, i.e. we
2117timed out, and need to do whatever is needed in this case.
2118.Sp
2119Otherwise, we now the earliest time at which the timeout would trigger,
2120and simply start the timer with this timeout value.
2121.Sp
2122In other words, each time the callback is invoked it will check whether
2123the timeout occurred. If not, it will simply reschedule itself to check
2124again at the earliest time it could time out. Rinse. Repeat.
2125.Sp
2126This scheme causes more callback invocations (about one every 60 seconds
2127minus half the average time between activity), but virtually no calls to
2128libev to change the timeout.
2129.Sp
2130To start the machinery, simply initialise the watcher and set
2131\&\f(CW\*(C`last_activity\*(C'\fR to the current time (meaning there was some activity just
2132now), then call the callback, which will \*(L"do the right thing\*(R" and start
2133the timer:
2134.Sp
2135.Vb 3
2136\& last_activity = ev_now (EV_A);
2137\& ev_init (&timer, callback);
2138\& callback (EV_A_ &timer, 0);
2139.Ve
2140.Sp
2141When there is some activity, simply store the current time in
2142\&\f(CW\*(C`last_activity\*(C'\fR, no libev calls at all:
2143.Sp
2144.Vb 2
2145\& if (activity detected)
2146\& last_activity = ev_now (EV_A);
2147.Ve
2148.Sp
2149When your timeout value changes, then the timeout can be changed by simply
2150providing a new value, stopping the timer and calling the callback, which
2151will again do the right thing (for example, time out immediately :).
2152.Sp
2153.Vb 3
2154\& timeout = new_value;
2155\& ev_timer_stop (EV_A_ &timer);
2156\& callback (EV_A_ &timer, 0);
2157.Ve
2158.Sp
2159This technique is slightly more complex, but in most cases where the
2160time-out is unlikely to be triggered, much more efficient.
2161.IP "4. Wee, just use a double-linked list for your timeouts." 4
2162.IX Item "4. Wee, just use a double-linked list for your timeouts."
2163If there is not one request, but many thousands (millions...), all
2164employing some kind of timeout with the same timeout value, then one can
2165do even better:
2166.Sp
2167When starting the timeout, calculate the timeout value and put the timeout
2168at the \fIend\fR of the list.
2169.Sp
2170Then use an \f(CW\*(C`ev_timer\*(C'\fR to fire when the timeout at the \fIbeginning\fR of
2171the list is expected to fire (for example, using the technique #3).
2172.Sp
2173When there is some activity, remove the timer from the list, recalculate
2174the timeout, append it to the end of the list again, and make sure to
2175update the \f(CW\*(C`ev_timer\*(C'\fR if it was taken from the beginning of the list.
2176.Sp
2177This way, one can manage an unlimited number of timeouts in O(1) time for
2178starting, stopping and updating the timers, at the expense of a major
2179complication, and having to use a constant timeout. The constant timeout
2180ensures that the list stays sorted.
2181.PP
2182So which method the best?
2183.PP
2184Method #2 is a simple no-brain-required solution that is adequate in most
2185situations. Method #3 requires a bit more thinking, but handles many cases
2186better, and isn't very complicated either. In most case, choosing either
2187one is fine, with #3 being better in typical situations.
2188.PP
2189Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
2190rather complicated, but extremely efficient, something that really pays
2191off after the first million or so of active timers, i.e. it's usually
2192overkill :)
2193.PP
2194\fIThe special problem of being too early\fR
2195.IX Subsection "The special problem of being too early"
2196.PP
2197If you ask a timer to call your callback after three seconds, then
2198you expect it to be invoked after three seconds \- but of course, this
2199cannot be guaranteed to infinite precision. Less obviously, it cannot be
2200guaranteed to any precision by libev \- imagine somebody suspending the
2201process with a \s-1STOP\s0 signal for a few hours for example.
2202.PP
2203So, libev tries to invoke your callback as soon as possible \fIafter\fR the
2204delay has occurred, but cannot guarantee this.
2205.PP
2206A less obvious failure mode is calling your callback too early: many event
2207loops compare timestamps with a \*(L"elapsed delay >= requested delay\*(R", but
2208this can cause your callback to be invoked much earlier than you would
2209expect.
2210.PP
2211To see why, imagine a system with a clock that only offers full second
2212resolution (think windows if you can't come up with a broken enough \s-1OS\s0
2213yourself). If you schedule a one-second timer at the time 500.9, then the
2214event loop will schedule your timeout to elapse at a system time of 500
2215(500.9 truncated to the resolution) + 1, or 501.
2216.PP
2217If an event library looks at the timeout 0.1s later, it will see \*(L"501 >=
2218501\*(R" and invoke the callback 0.1s after it was started, even though a
2219one-second delay was requested \- this is being \*(L"too early\*(R", despite best
2220intentions.
2221.PP
2222This is the reason why libev will never invoke the callback if the elapsed
2223delay equals the requested delay, but only when the elapsed delay is
2224larger than the requested delay. In the example above, libev would only invoke
2225the callback at system time 502, or 1.1s after the timer was started.
2226.PP
2227So, while libev cannot guarantee that your callback will be invoked
2228exactly when requested, it \fIcan\fR and \fIdoes\fR guarantee that the requested
2229delay has actually elapsed, or in other words, it always errs on the \*(L"too
2230late\*(R" side of things.
2231.PP
2232\fIThe special problem of time updates\fR
2233.IX Subsection "The special problem of time updates"
2234.PP
2235Establishing the current time is a costly operation (it usually takes
2236at least one system call): \s-1EV\s0 therefore updates its idea of the current
2237time only before and after \f(CW\*(C`ev_run\*(C'\fR collects new events, which causes a
2238growing difference between \f(CW\*(C`ev_now ()\*(C'\fR and \f(CW\*(C`ev_time ()\*(C'\fR when handling
2239lots of events in one iteration.
929.PP 2240.PP
930The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR 2241The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
931time. This is usually the right thing as this timestamp refers to the time 2242time. This is usually the right thing as this timestamp refers to the time
932of the event triggering whatever timeout you are modifying/starting. If 2243of the event triggering whatever timeout you are modifying/starting. If
933you suspect event processing to be delayed and you \fIneed\fR to base the timeout 2244you suspect event processing to be delayed and you \fIneed\fR to base the
934on the current time, use something like this to adjust for this: 2245timeout on the current time, use something like the following to adjust
2246for it:
935.PP 2247.PP
936.Vb 1 2248.Vb 1
937\& ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); 2249\& ev_timer_set (&timer, after + (ev_time () \- ev_now ()), 0.);
938.Ve 2250.Ve
939.PP 2251.PP
940The callback is guarenteed to be invoked only when its timeout has passed, 2252If the event loop is suspended for a long time, you can also force an
941but if multiple timers become ready during the same loop iteration then 2253update of the time returned by \f(CW\*(C`ev_now ()\*(C'\fR by calling \f(CW\*(C`ev_now_update
942order of execution is undefined. 2254()\*(C'\fR, although that will push the event time of all outstanding events
2255further into the future.
2256.PP
2257\fIThe special problem of unsynchronised clocks\fR
2258.IX Subsection "The special problem of unsynchronised clocks"
2259.PP
2260Modern systems have a variety of clocks \- libev itself uses the normal
2261\&\*(L"wall clock\*(R" clock and, if available, the monotonic clock (to avoid time
2262jumps).
2263.PP
2264Neither of these clocks is synchronised with each other or any other clock
2265on the system, so \f(CW\*(C`ev_time ()\*(C'\fR might return a considerably different time
2266than \f(CW\*(C`gettimeofday ()\*(C'\fR or \f(CW\*(C`time ()\*(C'\fR. On a GNU/Linux system, for example,
2267a call to \f(CW\*(C`gettimeofday\*(C'\fR might return a second count that is one higher
2268than a directly following call to \f(CW\*(C`time\*(C'\fR.
2269.PP
2270The moral of this is to only compare libev-related timestamps with
2271\&\f(CW\*(C`ev_time ()\*(C'\fR and \f(CW\*(C`ev_now ()\*(C'\fR, at least if you want better precision than
2272a second or so.
2273.PP
2274One more problem arises due to this lack of synchronisation: if libev uses
2275the system monotonic clock and you compare timestamps from \f(CW\*(C`ev_time\*(C'\fR
2276or \f(CW\*(C`ev_now\*(C'\fR from when you started your timer and when your callback is
2277invoked, you will find that sometimes the callback is a bit \*(L"early\*(R".
2278.PP
2279This is because \f(CW\*(C`ev_timer\*(C'\fRs work in real time, not wall clock time, so
2280libev makes sure your callback is not invoked before the delay happened,
2281\&\fImeasured according to the real time\fR, not the system clock.
2282.PP
2283If your timeouts are based on a physical timescale (e.g. \*(L"time out this
2284connection after 100 seconds\*(R") then this shouldn't bother you as it is
2285exactly the right behaviour.
2286.PP
2287If you want to compare wall clock/system timestamps to your timers, then
2288you need to use \f(CW\*(C`ev_periodic\*(C'\fRs, as these are based on the wall clock
2289time, where your comparisons will always generate correct results.
2290.PP
2291\fIThe special problems of suspended animation\fR
2292.IX Subsection "The special problems of suspended animation"
2293.PP
2294When you leave the server world it is quite customary to hit machines that
2295can suspend/hibernate \- what happens to the clocks during such a suspend?
2296.PP
2297Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
2298all processes, while the clocks (\f(CW\*(C`times\*(C'\fR, \f(CW\*(C`CLOCK_MONOTONIC\*(C'\fR) continue
2299to run until the system is suspended, but they will not advance while the
2300system is suspended. That means, on resume, it will be as if the program
2301was frozen for a few seconds, but the suspend time will not be counted
2302towards \f(CW\*(C`ev_timer\*(C'\fR when a monotonic clock source is used. The real time
2303clock advanced as expected, but if it is used as sole clocksource, then a
2304long suspend would be detected as a time jump by libev, and timers would
2305be adjusted accordingly.
2306.PP
2307I would not be surprised to see different behaviour in different between
2308operating systems, \s-1OS\s0 versions or even different hardware.
2309.PP
2310The other form of suspend (job control, or sending a \s-1SIGSTOP\s0) will see a
2311time jump in the monotonic clocks and the realtime clock. If the program
2312is suspended for a very long time, and monotonic clock sources are in use,
2313then you can expect \f(CW\*(C`ev_timer\*(C'\fRs to expire as the full suspension time
2314will be counted towards the timers. When no monotonic clock source is in
2315use, then libev will again assume a timejump and adjust accordingly.
2316.PP
2317It might be beneficial for this latter case to call \f(CW\*(C`ev_suspend\*(C'\fR
2318and \f(CW\*(C`ev_resume\*(C'\fR in code that handles \f(CW\*(C`SIGTSTP\*(C'\fR, to at least get
2319deterministic behaviour in this case (you can do nothing against
2320\&\f(CW\*(C`SIGSTOP\*(C'\fR).
2321.PP
2322\fIWatcher-Specific Functions and Data Members\fR
2323.IX Subsection "Watcher-Specific Functions and Data Members"
943.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4 2324.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
944.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 2325.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
945.PD 0 2326.PD 0
946.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4 2327.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
947.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 2328.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
948.PD 2329.PD
949Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR is 2330Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds (fractional and
950\&\f(CW0.\fR, then it will automatically be stopped. If it is positive, then the 2331negative values are supported). If \f(CW\*(C`repeat\*(C'\fR is \f(CW0.\fR, then it will
2332automatically be stopped once the timeout is reached. If it is positive,
951timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds 2333then the timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR
952later, again, and again, until stopped manually. 2334seconds later, again, and again, until stopped manually.
953.Sp 2335.Sp
954The timer itself will do a best-effort at avoiding drift, that is, if you 2336The timer itself will do a best-effort at avoiding drift, that is, if
955configure a timer to trigger every 10 seconds, then it will trigger at 2337you configure a timer to trigger every 10 seconds, then it will normally
956exactly 10 second intervals. If, however, your program cannot keep up with 2338trigger at exactly 10 second intervals. If, however, your program cannot
957the timer (because it takes longer than those 10 seconds to do stuff) the 2339keep up with the timer (because it takes longer than those 10 seconds to
958timer will not fire more than once per event loop iteration. 2340do stuff) the timer will not fire more than once per event loop iteration.
959.IP "ev_timer_again (loop)" 4 2341.IP "ev_timer_again (loop, ev_timer *)" 4
960.IX Item "ev_timer_again (loop)" 2342.IX Item "ev_timer_again (loop, ev_timer *)"
961This will act as if the timer timed out and restart it again if it is 2343This will act as if the timer timed out, and restarts it again if it is
962repeating. The exact semantics are: 2344repeating. It basically works like calling \f(CW\*(C`ev_timer_stop\*(C'\fR, updating the
2345timeout to the \f(CW\*(C`repeat\*(C'\fR value and calling \f(CW\*(C`ev_timer_start\*(C'\fR.
963.Sp 2346.Sp
964If the timer is started but nonrepeating, stop it. 2347The exact semantics are as in the following rules, all of which will be
2348applied to the watcher:
2349.RS 4
2350.IP "If the timer is pending, the pending status is always cleared." 4
2351.IX Item "If the timer is pending, the pending status is always cleared."
2352.PD 0
2353.IP "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)." 4
2354.IX Item "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)."
2355.ie n .IP "If the timer is repeating, make the ""repeat"" value the new timeout and start the timer, if necessary." 4
2356.el .IP "If the timer is repeating, make the \f(CWrepeat\fR value the new timeout and start the timer, if necessary." 4
2357.IX Item "If the timer is repeating, make the repeat value the new timeout and start the timer, if necessary."
2358.RE
2359.RS 4
2360.PD
965.Sp 2361.Sp
966If the timer is repeating, either start it if necessary (with the repeat 2362This sounds a bit complicated, see \*(L"Be smart about timeouts\*(R", above, for a
967value), or reset the running timer to the repeat value. 2363usage example.
2364.RE
2365.IP "ev_tstamp ev_timer_remaining (loop, ev_timer *)" 4
2366.IX Item "ev_tstamp ev_timer_remaining (loop, ev_timer *)"
2367Returns the remaining time until a timer fires. If the timer is active,
2368then this time is relative to the current event loop time, otherwise it's
2369the timeout value currently configured.
968.Sp 2370.Sp
969This sounds a bit complicated, but here is a useful and typical 2371That is, after an \f(CW\*(C`ev_timer_set (w, 5, 7)\*(C'\fR, \f(CW\*(C`ev_timer_remaining\*(C'\fR returns
970example: Imagine you have a tcp connection and you want a so-called 2372\&\f(CW5\fR. When the timer is started and one second passes, \f(CW\*(C`ev_timer_remaining\*(C'\fR
971idle timeout, that is, you want to be called when there have been, 2373will return \f(CW4\fR. When the timer expires and is restarted, it will return
972say, 60 seconds of inactivity on the socket. The easiest way to do 2374roughly \f(CW7\fR (likely slightly less as callback invocation takes some time,
973this 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 2375too), and so on.
974\&\f(CW\*(C`ev_timer_again\*(C'\fR each time you successfully read or write some data. If
975you go into an idle state where you do not expect data to travel on the
976socket, you can stop the timer, and again will automatically restart it if
977need be.
978.Sp
979You can also ignore the \f(CW\*(C`after\*(C'\fR value and \f(CW\*(C`ev_timer_start\*(C'\fR altogether
980and only ever use the \f(CW\*(C`repeat\*(C'\fR value:
981.Sp
982.Vb 8
983\& ev_timer_init (timer, callback, 0., 5.);
984\& ev_timer_again (loop, timer);
985\& ...
986\& timer->again = 17.;
987\& ev_timer_again (loop, timer);
988\& ...
989\& timer->again = 10.;
990\& ev_timer_again (loop, timer);
991.Ve
992.Sp
993This is more efficient then stopping/starting the timer eahc time you want
994to modify its timeout value.
995.IP "ev_tstamp repeat [read\-write]" 4 2376.IP "ev_tstamp repeat [read\-write]" 4
996.IX Item "ev_tstamp repeat [read-write]" 2377.IX Item "ev_tstamp repeat [read-write]"
997The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out 2378The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
998or \f(CW\*(C`ev_timer_again\*(C'\fR is called and determines the next timeout (if any), 2379or \f(CW\*(C`ev_timer_again\*(C'\fR is called, and determines the next timeout (if any),
999which is also when any modifications are taken into account. 2380which is also when any modifications are taken into account.
1000.PP 2381.PP
2382\fIExamples\fR
2383.IX Subsection "Examples"
2384.PP
1001Example: create a timer that fires after 60 seconds. 2385Example: Create a timer that fires after 60 seconds.
1002.PP 2386.PP
1003.Vb 5 2387.Vb 5
1004\& static void 2388\& static void
1005\& one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents) 2389\& one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1006\& { 2390\& {
1007\& .. one minute over, w is actually stopped right here 2391\& .. one minute over, w is actually stopped right here
1008\& } 2392\& }
1009.Ve 2393\&
1010.PP
1011.Vb 3
1012\& struct ev_timer mytimer; 2394\& ev_timer mytimer;
1013\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.); 2395\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1014\& ev_timer_start (loop, &mytimer); 2396\& ev_timer_start (loop, &mytimer);
1015.Ve 2397.Ve
1016.PP 2398.PP
1017Example: create a timeout timer that times out after 10 seconds of 2399Example: Create a timeout timer that times out after 10 seconds of
1018inactivity. 2400inactivity.
1019.PP 2401.PP
1020.Vb 5 2402.Vb 5
1021\& static void 2403\& static void
1022\& timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents) 2404\& timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1023\& { 2405\& {
1024\& .. ten seconds without any activity 2406\& .. ten seconds without any activity
1025\& } 2407\& }
1026.Ve 2408\&
1027.PP
1028.Vb 4
1029\& struct ev_timer mytimer; 2409\& ev_timer mytimer;
1030\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */ 2410\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1031\& ev_timer_again (&mytimer); /* start timer */ 2411\& ev_timer_again (&mytimer); /* start timer */
1032\& ev_loop (loop, 0); 2412\& ev_run (loop, 0);
1033.Ve 2413\&
1034.PP
1035.Vb 3
1036\& // and in some piece of code that gets executed on any "activity": 2414\& // and in some piece of code that gets executed on any "activity":
1037\& // reset the timeout to start ticking again at 10 seconds 2415\& // reset the timeout to start ticking again at 10 seconds
1038\& ev_timer_again (&mytimer); 2416\& ev_timer_again (&mytimer);
1039.Ve 2417.Ve
1040.ie n .Sh """ev_periodic"" \- to cron or not to cron?" 2418.ie n .SS """ev_periodic"" \- to cron or not to cron?"
1041.el .Sh "\f(CWev_periodic\fP \- to cron or not to cron?" 2419.el .SS "\f(CWev_periodic\fP \- to cron or not to cron?"
1042.IX Subsection "ev_periodic - to cron or not to cron?" 2420.IX Subsection "ev_periodic - to cron or not to cron?"
1043Periodic watchers are also timers of a kind, but they are very versatile 2421Periodic watchers are also timers of a kind, but they are very versatile
1044(and unfortunately a bit complex). 2422(and unfortunately a bit complex).
1045.PP 2423.PP
1046Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time) 2424Unlike \f(CW\*(C`ev_timer\*(C'\fR, periodic watchers are not based on real time (or
1047but on wallclock time (absolute time). You can tell a periodic watcher 2425relative time, the physical time that passes) but on wall clock time
1048to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a 2426(absolute time, the thing you can read on your calendar or clock). The
1049periodic watcher to trigger in 10 seconds (by specifiying e.g. \f(CW\*(C`ev_now () 2427difference is that wall clock time can run faster or slower than real
1050+ 10.\*(C'\fR) and then reset your system clock to the last year, then it will 2428time, and time jumps are not uncommon (e.g. when you adjust your
1051take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger 2429wrist-watch).
1052roughly 10 seconds later and of course not if you reset your system time
1053again).
1054.PP 2430.PP
1055They can also be used to implement vastly more complex timers, such as 2431You can tell a periodic watcher to trigger after some specific point
1056triggering an event on eahc midnight, local time. 2432in time: for example, if you tell a periodic watcher to trigger \*(L"in 10
2433seconds\*(R" (by specifying e.g. \f(CW\*(C`ev_now () + 10.\*(C'\fR, that is, an absolute time
2434not a delay) and then reset your system clock to January of the previous
2435year, then it will take a year or more to trigger the event (unlike an
2436\&\f(CW\*(C`ev_timer\*(C'\fR, which would still trigger roughly 10 seconds after starting
2437it, as it uses a relative timeout).
1057.PP 2438.PP
2439\&\f(CW\*(C`ev_periodic\*(C'\fR watchers can also be used to implement vastly more complex
2440timers, such as triggering an event on each \*(L"midnight, local time\*(R", or
2441other complicated rules. This cannot easily be done with \f(CW\*(C`ev_timer\*(C'\fR
2442watchers, as those cannot react to time jumps.
2443.PP
1058As with timers, the callback is guarenteed to be invoked only when the 2444As with timers, the callback is guaranteed to be invoked only when the
1059time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready 2445point in time where it is supposed to trigger has passed. If multiple
1060during the same loop iteration then order of execution is undefined. 2446timers become ready during the same loop iteration then the ones with
2447earlier time-out values are invoked before ones with later time-out values
2448(but this is no longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
2449.PP
2450\fIWatcher-Specific Functions and Data Members\fR
2451.IX Subsection "Watcher-Specific Functions and Data Members"
1061.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4 2452.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
1062.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 2453.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
1063.PD 0 2454.PD 0
1064.IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4 2455.IP "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
1065.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 2456.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
1066.PD 2457.PD
1067Lots of arguments, lets sort it out... There are basically three modes of 2458Lots of arguments, let's sort it out... There are basically three modes of
1068operation, and we will explain them from simplest to complex: 2459operation, and we will explain them from simplest to most complex:
1069.RS 4 2460.RS 4
1070.IP "* absolute timer (interval = reschedule_cb = 0)" 4 2461.IP "\(bu" 4
1071.IX Item "absolute timer (interval = reschedule_cb = 0)" 2462absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
2463.Sp
1072In this configuration the watcher triggers an event at the wallclock time 2464In this configuration the watcher triggers an event after the wall clock
1073\&\f(CW\*(C`at\*(C'\fR and doesn't repeat. It will not adjust when a time jump occurs, 2465time \f(CW\*(C`offset\*(C'\fR has passed. It will not repeat and will not adjust when a
1074that is, if it is to be run at January 1st 2011 then it will run when the 2466time jump occurs, that is, if it is to be run at January 1st 2011 then it
1075system time reaches or surpasses this time. 2467will be stopped and invoked when the system clock reaches or surpasses
1076.IP "* non-repeating interval timer (interval > 0, reschedule_cb = 0)" 4 2468this point in time.
1077.IX Item "non-repeating interval timer (interval > 0, reschedule_cb = 0)" 2469.IP "\(bu" 4
2470repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
2471.Sp
1078In this mode the watcher will always be scheduled to time out at the next 2472In this mode the watcher will always be scheduled to time out at the next
1079\&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N) and then repeat, regardless 2473\&\f(CW\*(C`offset + N * interval\*(C'\fR time (for some integer N, which can also be
1080of any time jumps. 2474negative) and then repeat, regardless of any time jumps. The \f(CW\*(C`offset\*(C'\fR
2475argument is merely an offset into the \f(CW\*(C`interval\*(C'\fR periods.
1081.Sp 2476.Sp
1082This can be used to create timers that do not drift with respect to system 2477This can be used to create timers that do not drift with respect to the
1083time: 2478system clock, for example, here is an \f(CW\*(C`ev_periodic\*(C'\fR that triggers each
2479hour, on the hour (with respect to \s-1UTC\s0):
1084.Sp 2480.Sp
1085.Vb 1 2481.Vb 1
1086\& ev_periodic_set (&periodic, 0., 3600., 0); 2482\& ev_periodic_set (&periodic, 0., 3600., 0);
1087.Ve 2483.Ve
1088.Sp 2484.Sp
1089This doesn't mean there will always be 3600 seconds in between triggers, 2485This doesn't mean there will always be 3600 seconds in between triggers,
1090but only that the the callback will be called when the system time shows a 2486but only that the callback will be called when the system time shows a
1091full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible 2487full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
1092by 3600. 2488by 3600.
1093.Sp 2489.Sp
1094Another way to think about it (for the mathematically inclined) is that 2490Another way to think about it (for the mathematically inclined) is that
1095\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible 2491\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
1096time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps. 2492time where \f(CW\*(C`time = offset (mod interval)\*(C'\fR, regardless of any time jumps.
1097.IP "* manual reschedule mode (reschedule_cb = callback)" 4 2493.Sp
1098.IX Item "manual reschedule mode (reschedule_cb = callback)" 2494The \f(CW\*(C`interval\*(C'\fR \fI\s-1MUST\s0\fR be positive, and for numerical stability, the
2495interval value should be higher than \f(CW\*(C`1/8192\*(C'\fR (which is around 100
2496microseconds) and \f(CW\*(C`offset\*(C'\fR should be higher than \f(CW0\fR and should have
2497at most a similar magnitude as the current time (say, within a factor of
2498ten). Typical values for offset are, in fact, \f(CW0\fR or something between
2499\&\f(CW0\fR and \f(CW\*(C`interval\*(C'\fR, which is also the recommended range.
2500.Sp
2501Note also that there is an upper limit to how often a timer can fire (\s-1CPU\s0
2502speed for example), so if \f(CW\*(C`interval\*(C'\fR is very small then timing stability
2503will of course deteriorate. Libev itself tries to be exact to be about one
2504millisecond (if the \s-1OS\s0 supports it and the machine is fast enough).
2505.IP "\(bu" 4
2506manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
2507.Sp
1099In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being 2508In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`offset\*(C'\fR are both being
1100ignored. Instead, each time the periodic watcher gets scheduled, the 2509ignored. Instead, each time the periodic watcher gets scheduled, the
1101reschedule callback will be called with the watcher as first, and the 2510reschedule callback will be called with the watcher as first, and the
1102current time as second argument. 2511current time as second argument.
1103.Sp 2512.Sp
1104\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, 2513\&\s-1NOTE:\s0 \fIThis callback \s-1MUST NOT\s0 stop or destroy any periodic watcher, ever,
1105ever, or make any event loop modifications\fR. If you need to stop it, 2514or make \s-1ANY\s0 other event loop modifications whatsoever, unless explicitly
1106return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by 2515allowed by documentation here\fR.
1107starting a prepare watcher).
1108.Sp 2516.Sp
2517If you need to stop it, return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop
2518it afterwards (e.g. by starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is the
2519only event loop modification you are allowed to do).
2520.Sp
1109Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w, 2521The callback prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(ev_periodic
1110ev_tstamp now)\*(C'\fR, e.g.: 2522*w, ev_tstamp now)\*(C'\fR, e.g.:
1111.Sp 2523.Sp
1112.Vb 4 2524.Vb 5
2525\& static ev_tstamp
1113\& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) 2526\& my_rescheduler (ev_periodic *w, ev_tstamp now)
1114\& { 2527\& {
1115\& return now + 60.; 2528\& return now + 60.;
1116\& } 2529\& }
1117.Ve 2530.Ve
1118.Sp 2531.Sp
1119It must return the next time to trigger, based on the passed time value 2532It must return the next time to trigger, based on the passed time value
1120(that is, the lowest time value larger than to the second argument). It 2533(that is, the lowest time value larger than to the second argument). It
1121will usually be called just before the callback will be triggered, but 2534will usually be called just before the callback will be triggered, but
1122might be called at other times, too. 2535might be called at other times, too.
1123.Sp 2536.Sp
1124\&\s-1NOTE:\s0 \fIThis callback must always return a time that is later than the 2537\&\s-1NOTE:\s0 \fIThis callback must always return a time that is higher than or
1125passed \f(CI\*(C`now\*(C'\fI value\fR. Not even \f(CW\*(C`now\*(C'\fR itself will do, it \fImust\fR be larger. 2538equal to the passed \f(CI\*(C`now\*(C'\fI value\fR.
1126.Sp 2539.Sp
1127This can be used to create very complex timers, such as a timer that 2540This can be used to create very complex timers, such as a timer that
1128triggers on each midnight, local time. To do this, you would calculate the 2541triggers on \*(L"next midnight, local time\*(R". To do this, you would calculate
1129next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How 2542the next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for
1130you do this is, again, up to you (but it is not trivial, which is the main 2543this. Here is a (completely untested, no error checking) example on how to
1131reason I omitted it as an example). 2544do this:
2545.Sp
2546.Vb 1
2547\& #include <time.h>
2548\&
2549\& static ev_tstamp
2550\& my_rescheduler (ev_periodic *w, ev_tstamp now)
2551\& {
2552\& time_t tnow = (time_t)now;
2553\& struct tm tm;
2554\& localtime_r (&tnow, &tm);
2555\&
2556\& tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
2557\& ++tm.tm_mday; // midnight next day
2558\&
2559\& return mktime (&tm);
2560\& }
2561.Ve
2562.Sp
2563Note: this code might run into trouble on days that have more then two
2564midnights (beginning and end).
1132.RE 2565.RE
1133.RS 4 2566.RS 4
1134.RE 2567.RE
1135.IP "ev_periodic_again (loop, ev_periodic *)" 4 2568.IP "ev_periodic_again (loop, ev_periodic *)" 4
1136.IX Item "ev_periodic_again (loop, ev_periodic *)" 2569.IX Item "ev_periodic_again (loop, ev_periodic *)"
1137Simply stops and restarts the periodic watcher again. This is only useful 2570Simply stops and restarts the periodic watcher again. This is only useful
1138when you changed some parameters or the reschedule callback would return 2571when you changed some parameters or the reschedule callback would return
1139a different time than the last time it was called (e.g. in a crond like 2572a different time than the last time it was called (e.g. in a crond like
1140program when the crontabs have changed). 2573program when the crontabs have changed).
2574.IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4
2575.IX Item "ev_tstamp ev_periodic_at (ev_periodic *)"
2576When active, returns the absolute time that the watcher is supposed
2577to trigger next. This is not the same as the \f(CW\*(C`offset\*(C'\fR argument to
2578\&\f(CW\*(C`ev_periodic_set\*(C'\fR, but indeed works even in interval and manual
2579rescheduling modes.
2580.IP "ev_tstamp offset [read\-write]" 4
2581.IX Item "ev_tstamp offset [read-write]"
2582When repeating, this contains the offset value, otherwise this is the
2583absolute point in time (the \f(CW\*(C`offset\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR,
2584although libev might modify this value for better numerical stability).
2585.Sp
2586Can be modified any time, but changes only take effect when the periodic
2587timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1141.IP "ev_tstamp interval [read\-write]" 4 2588.IP "ev_tstamp interval [read\-write]" 4
1142.IX Item "ev_tstamp interval [read-write]" 2589.IX Item "ev_tstamp interval [read-write]"
1143The current interval value. Can be modified any time, but changes only 2590The current interval value. Can be modified any time, but changes only
1144take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being 2591take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
1145called. 2592called.
1146.IP "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read\-write]" 4 2593.IP "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read\-write]" 4
1147.IX Item "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]" 2594.IX Item "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]"
1148The current reschedule callback, or \f(CW0\fR, if this functionality is 2595The current reschedule callback, or \f(CW0\fR, if this functionality is
1149switched off. Can be changed any time, but changes only take effect when 2596switched off. Can be changed any time, but changes only take effect when
1150the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called. 2597the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1151.PP 2598.PP
2599\fIExamples\fR
2600.IX Subsection "Examples"
2601.PP
1152Example: call a callback every hour, or, more precisely, whenever the 2602Example: Call a callback every hour, or, more precisely, whenever the
1153system clock is divisible by 3600. The callback invocation times have 2603system time is divisible by 3600. The callback invocation times have
1154potentially a lot of jittering, but good long-term stability. 2604potentially a lot of jitter, but good long-term stability.
1155.PP 2605.PP
1156.Vb 5 2606.Vb 5
1157\& static void 2607\& static void
1158\& clock_cb (struct ev_loop *loop, struct ev_io *w, int revents) 2608\& clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1159\& { 2609\& {
1160\& ... its now a full hour (UTC, or TAI or whatever your clock follows) 2610\& ... its now a full hour (UTC, or TAI or whatever your clock follows)
1161\& } 2611\& }
1162.Ve 2612\&
1163.PP
1164.Vb 3
1165\& struct ev_periodic hourly_tick; 2613\& ev_periodic hourly_tick;
1166\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0); 2614\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1167\& ev_periodic_start (loop, &hourly_tick); 2615\& ev_periodic_start (loop, &hourly_tick);
1168.Ve 2616.Ve
1169.PP 2617.PP
1170Example: the same as above, but use a reschedule callback to do it: 2618Example: The same as above, but use a reschedule callback to do it:
1171.PP 2619.PP
1172.Vb 1 2620.Vb 1
1173\& #include <math.h> 2621\& #include <math.h>
1174.Ve 2622\&
1175.PP
1176.Vb 5
1177\& static ev_tstamp 2623\& static ev_tstamp
1178\& my_scheduler_cb (struct ev_periodic *w, ev_tstamp now) 2624\& my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1179\& { 2625\& {
1180\& return fmod (now, 3600.) + 3600.; 2626\& return now + (3600. \- fmod (now, 3600.));
1181\& } 2627\& }
1182.Ve 2628\&
1183.PP
1184.Vb 1
1185\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb); 2629\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1186.Ve 2630.Ve
1187.PP 2631.PP
1188Example: call a callback every hour, starting now: 2632Example: Call a callback every hour, starting now:
1189.PP 2633.PP
1190.Vb 4 2634.Vb 4
1191\& struct ev_periodic hourly_tick; 2635\& ev_periodic hourly_tick;
1192\& ev_periodic_init (&hourly_tick, clock_cb, 2636\& ev_periodic_init (&hourly_tick, clock_cb,
1193\& fmod (ev_now (loop), 3600.), 3600., 0); 2637\& fmod (ev_now (loop), 3600.), 3600., 0);
1194\& ev_periodic_start (loop, &hourly_tick); 2638\& ev_periodic_start (loop, &hourly_tick);
1195.Ve 2639.Ve
1196.ie n .Sh """ev_signal"" \- signal me when a signal gets signalled!" 2640.ie n .SS """ev_signal"" \- signal me when a signal gets signalled!"
1197.el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled!" 2641.el .SS "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
1198.IX Subsection "ev_signal - signal me when a signal gets signalled!" 2642.IX Subsection "ev_signal - signal me when a signal gets signalled!"
1199Signal watchers will trigger an event when the process receives a specific 2643Signal watchers will trigger an event when the process receives a specific
1200signal one or more times. Even though signals are very asynchronous, libev 2644signal one or more times. Even though signals are very asynchronous, libev
1201will try it's best to deliver signals synchronously, i.e. as part of the 2645will try its best to deliver signals synchronously, i.e. as part of the
1202normal event processing, like any other event. 2646normal event processing, like any other event.
1203.PP 2647.PP
2648If you want signals to be delivered truly asynchronously, just use
2649\&\f(CW\*(C`sigaction\*(C'\fR as you would do without libev and forget about sharing
2650the signal. You can even use \f(CW\*(C`ev_async\*(C'\fR from a signal handler to
2651synchronously wake up an event loop.
2652.PP
1204You can configure as many watchers as you like per signal. Only when the 2653You can configure as many watchers as you like for the same signal, but
1205first watcher gets started will libev actually register a signal watcher 2654only within the same loop, i.e. you can watch for \f(CW\*(C`SIGINT\*(C'\fR in your
1206with the kernel (thus it coexists with your own signal handlers as long 2655default loop and for \f(CW\*(C`SIGIO\*(C'\fR in another loop, but you cannot watch for
1207as you don't register any with libev). Similarly, when the last signal 2656\&\f(CW\*(C`SIGINT\*(C'\fR in both the default loop and another loop at the same time. At
1208watcher for a signal is stopped libev will reset the signal handler to 2657the moment, \f(CW\*(C`SIGCHLD\*(C'\fR is permanently tied to the default loop.
1209\&\s-1SIG_DFL\s0 (regardless of what it was set to before). 2658.PP
2659Only after the first watcher for a signal is started will libev actually
2660register something with the kernel. It thus coexists with your own signal
2661handlers as long as you don't register any with libev for the same signal.
2662.PP
2663If possible and supported, libev will install its handlers with
2664\&\f(CW\*(C`SA_RESTART\*(C'\fR (or equivalent) behaviour enabled, so system calls should
2665not be unduly interrupted. If you have a problem with system calls getting
2666interrupted by signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher
2667and unblock them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher.
2668.PP
2669\fIThe special problem of inheritance over fork/execve/pthread_create\fR
2670.IX Subsection "The special problem of inheritance over fork/execve/pthread_create"
2671.PP
2672Both the signal mask (\f(CW\*(C`sigprocmask\*(C'\fR) and the signal disposition
2673(\f(CW\*(C`sigaction\*(C'\fR) are unspecified after starting a signal watcher (and after
2674stopping it again), that is, libev might or might not block the signal,
2675and might or might not set or restore the installed signal handler (but
2676see \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR).
2677.PP
2678While this does not matter for the signal disposition (libev never
2679sets signals to \f(CW\*(C`SIG_IGN\*(C'\fR, so handlers will be reset to \f(CW\*(C`SIG_DFL\*(C'\fR on
2680\&\f(CW\*(C`execve\*(C'\fR), this matters for the signal mask: many programs do not expect
2681certain signals to be blocked.
2682.PP
2683This means that before calling \f(CW\*(C`exec\*(C'\fR (from the child) you should reset
2684the signal mask to whatever \*(L"default\*(R" you expect (all clear is a good
2685choice usually).
2686.PP
2687The simplest way to ensure that the signal mask is reset in the child is
2688to install a fork handler with \f(CW\*(C`pthread_atfork\*(C'\fR that resets it. That will
2689catch fork calls done by libraries (such as the libc) as well.
2690.PP
2691In current versions of libev, the signal will not be blocked indefinitely
2692unless you use the \f(CW\*(C`signalfd\*(C'\fR \s-1API\s0 (\f(CW\*(C`EV_SIGNALFD\*(C'\fR). While this reduces
2693the window of opportunity for problems, it will not go away, as libev
2694\&\fIhas\fR to modify the signal mask, at least temporarily.
2695.PP
2696So I can't stress this enough: \fIIf you do not reset your signal mask when
2697you expect it to be empty, you have a race condition in your code\fR. This
2698is not a libev-specific thing, this is true for most event libraries.
2699.PP
2700\fIThe special problem of threads signal handling\fR
2701.IX Subsection "The special problem of threads signal handling"
2702.PP
2703\&\s-1POSIX\s0 threads has problematic signal handling semantics, specifically,
2704a lot of functionality (sigfd, sigwait etc.) only really works if all
2705threads in a process block signals, which is hard to achieve.
2706.PP
2707When you want to use sigwait (or mix libev signal handling with your own
2708for the same signals), you can tackle this problem by globally blocking
2709all signals before creating any threads (or creating them with a fully set
2710sigprocmask) and also specifying the \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when creating
2711loops. Then designate one thread as \*(L"signal receiver thread\*(R" which handles
2712these signals. You can pass on any signals that libev might be interested
2713in by calling \f(CW\*(C`ev_feed_signal\*(C'\fR.
2714.PP
2715\fIWatcher-Specific Functions and Data Members\fR
2716.IX Subsection "Watcher-Specific Functions and Data Members"
1210.IP "ev_signal_init (ev_signal *, callback, int signum)" 4 2717.IP "ev_signal_init (ev_signal *, callback, int signum)" 4
1211.IX Item "ev_signal_init (ev_signal *, callback, int signum)" 2718.IX Item "ev_signal_init (ev_signal *, callback, int signum)"
1212.PD 0 2719.PD 0
1213.IP "ev_signal_set (ev_signal *, int signum)" 4 2720.IP "ev_signal_set (ev_signal *, int signum)" 4
1214.IX Item "ev_signal_set (ev_signal *, int signum)" 2721.IX Item "ev_signal_set (ev_signal *, int signum)"
… …
1216Configures the watcher to trigger on the given signal number (usually one 2723Configures the watcher to trigger on the given signal number (usually one
1217of the \f(CW\*(C`SIGxxx\*(C'\fR constants). 2724of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
1218.IP "int signum [read\-only]" 4 2725.IP "int signum [read\-only]" 4
1219.IX Item "int signum [read-only]" 2726.IX Item "int signum [read-only]"
1220The signal the watcher watches out for. 2727The signal the watcher watches out for.
2728.PP
2729\fIExamples\fR
2730.IX Subsection "Examples"
2731.PP
2732Example: Try to exit cleanly on \s-1SIGINT.\s0
2733.PP
2734.Vb 5
2735\& static void
2736\& sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
2737\& {
2738\& ev_break (loop, EVBREAK_ALL);
2739\& }
2740\&
2741\& ev_signal signal_watcher;
2742\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
2743\& ev_signal_start (loop, &signal_watcher);
2744.Ve
1221.ie n .Sh """ev_child"" \- watch out for process status changes" 2745.ie n .SS """ev_child"" \- watch out for process status changes"
1222.el .Sh "\f(CWev_child\fP \- watch out for process status changes" 2746.el .SS "\f(CWev_child\fP \- watch out for process status changes"
1223.IX Subsection "ev_child - watch out for process status changes" 2747.IX Subsection "ev_child - watch out for process status changes"
1224Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to 2748Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
1225some child status changes (most typically when a child of yours dies). 2749some child status changes (most typically when a child of yours dies or
2750exits). It is permissible to install a child watcher \fIafter\fR the child
2751has been forked (which implies it might have already exited), as long
2752as the event loop isn't entered (or is continued from a watcher), i.e.,
2753forking and then immediately registering a watcher for the child is fine,
2754but forking and registering a watcher a few event loop iterations later or
2755in the next callback invocation is not.
2756.PP
2757Only the default event loop is capable of handling signals, and therefore
2758you can only register child watchers in the default event loop.
2759.PP
2760Due to some design glitches inside libev, child watchers will always be
2761handled at maximum priority (their priority is set to \f(CW\*(C`EV_MAXPRI\*(C'\fR by
2762libev)
2763.PP
2764\fIProcess Interaction\fR
2765.IX Subsection "Process Interaction"
2766.PP
2767Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is
2768initialised. This is necessary to guarantee proper behaviour even if the
2769first child watcher is started after the child exits. The occurrence
2770of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done
2771synchronously as part of the event loop processing. Libev always reaps all
2772children, even ones not watched.
2773.PP
2774\fIOverriding the Built-In Processing\fR
2775.IX Subsection "Overriding the Built-In Processing"
2776.PP
2777Libev offers no special support for overriding the built-in child
2778processing, but if your application collides with libev's default child
2779handler, you can override it easily by installing your own handler for
2780\&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the
2781default loop never gets destroyed. You are encouraged, however, to use an
2782event-based approach to child reaping and thus use libev's support for
2783that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely.
2784.PP
2785\fIStopping the Child Watcher\fR
2786.IX Subsection "Stopping the Child Watcher"
2787.PP
2788Currently, the child watcher never gets stopped, even when the
2789child terminates, so normally one needs to stop the watcher in the
2790callback. Future versions of libev might stop the watcher automatically
2791when a child exit is detected (calling \f(CW\*(C`ev_child_stop\*(C'\fR twice is not a
2792problem).
2793.PP
2794\fIWatcher-Specific Functions and Data Members\fR
2795.IX Subsection "Watcher-Specific Functions and Data Members"
1226.IP "ev_child_init (ev_child *, callback, int pid)" 4 2796.IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4
1227.IX Item "ev_child_init (ev_child *, callback, int pid)" 2797.IX Item "ev_child_init (ev_child *, callback, int pid, int trace)"
1228.PD 0 2798.PD 0
1229.IP "ev_child_set (ev_child *, int pid)" 4 2799.IP "ev_child_set (ev_child *, int pid, int trace)" 4
1230.IX Item "ev_child_set (ev_child *, int pid)" 2800.IX Item "ev_child_set (ev_child *, int pid, int trace)"
1231.PD 2801.PD
1232Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or 2802Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
1233\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look 2803\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
1234at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see 2804at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
1235the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems 2805the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
1236\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the 2806\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
1237process causing the status change. 2807process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only
2808activate the watcher when the process terminates) or \f(CW1\fR (additionally
2809activate the watcher when the process is stopped or continued).
1238.IP "int pid [read\-only]" 4 2810.IP "int pid [read\-only]" 4
1239.IX Item "int pid [read-only]" 2811.IX Item "int pid [read-only]"
1240The process id this watcher watches out for, or \f(CW0\fR, meaning any process id. 2812The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
1241.IP "int rpid [read\-write]" 4 2813.IP "int rpid [read\-write]" 4
1242.IX Item "int rpid [read-write]" 2814.IX Item "int rpid [read-write]"
… …
1244.IP "int rstatus [read\-write]" 4 2816.IP "int rstatus [read\-write]" 4
1245.IX Item "int rstatus [read-write]" 2817.IX Item "int rstatus [read-write]"
1246The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems 2818The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
1247\&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details). 2819\&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
1248.PP 2820.PP
1249Example: try to exit cleanly on \s-1SIGINT\s0 and \s-1SIGTERM\s0. 2821\fIExamples\fR
2822.IX Subsection "Examples"
1250.PP 2823.PP
2824Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for
2825its completion.
2826.PP
1251.Vb 5 2827.Vb 1
2828\& ev_child cw;
2829\&
1252\& static void 2830\& static void
1253\& sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents) 2831\& child_cb (EV_P_ ev_child *w, int revents)
1254\& { 2832\& {
1255\& ev_unloop (loop, EVUNLOOP_ALL); 2833\& ev_child_stop (EV_A_ w);
2834\& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus);
1256\& } 2835\& }
2836\&
2837\& pid_t pid = fork ();
2838\&
2839\& if (pid < 0)
2840\& // error
2841\& else if (pid == 0)
2842\& {
2843\& // the forked child executes here
2844\& exit (1);
2845\& }
2846\& else
2847\& {
2848\& ev_child_init (&cw, child_cb, pid, 0);
2849\& ev_child_start (EV_DEFAULT_ &cw);
2850\& }
1257.Ve 2851.Ve
1258.PP
1259.Vb 3
1260\& struct ev_signal signal_watcher;
1261\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1262\& ev_signal_start (loop, &sigint_cb);
1263.Ve
1264.ie n .Sh """ev_stat"" \- did the file attributes just change?" 2852.ie n .SS """ev_stat"" \- did the file attributes just change?"
1265.el .Sh "\f(CWev_stat\fP \- did the file attributes just change?" 2853.el .SS "\f(CWev_stat\fP \- did the file attributes just change?"
1266.IX Subsection "ev_stat - did the file attributes just change?" 2854.IX Subsection "ev_stat - did the file attributes just change?"
1267This watches a filesystem path for attribute changes. That is, it calls 2855This watches a file system path for attribute changes. That is, it calls
1268\&\f(CW\*(C`stat\*(C'\fR regularly (or when the \s-1OS\s0 says it changed) and sees if it changed 2856\&\f(CW\*(C`stat\*(C'\fR on that path in regular intervals (or when the \s-1OS\s0 says it changed)
1269compared to the last time, invoking the callback if it did. 2857and sees if it changed compared to the last time, invoking the callback
2858if it did. Starting the watcher \f(CW\*(C`stat\*(C'\fR's the file, so only changes that
2859happen after the watcher has been started will be reported.
1270.PP 2860.PP
1271The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does 2861The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does
1272not exist\*(R" is a status change like any other. The condition \*(L"path does 2862not exist\*(R" is a status change like any other. The condition \*(L"path does not
1273not exist\*(R" is signified by the \f(CW\*(C`st_nlink\*(C'\fR field being zero (which is 2863exist\*(R" (or more correctly \*(L"path cannot be stat'ed\*(R") is signified by the
1274otherwise always forced to be at least one) and all the other fields of 2864\&\f(CW\*(C`st_nlink\*(C'\fR field being zero (which is otherwise always forced to be at
1275the stat buffer having unspecified contents. 2865least one) and all the other fields of the stat buffer having unspecified
2866contents.
1276.PP 2867.PP
1277Since there is no standard to do this, the portable implementation simply 2868The path \fImust not\fR end in a slash or contain special components such as
1278calls \f(CW\*(C`stat (2)\*(C'\fR regulalry on the path to see if it changed somehow. You 2869\&\f(CW\*(C`.\*(C'\fR or \f(CW\*(C`..\*(C'\fR. The path \fIshould\fR be absolute: If it is relative and
1279can specify a recommended polling interval for this case. If you specify 2870your working directory changes, then the behaviour is undefined.
1280a polling interval of \f(CW0\fR (highly recommended!) then a \fIsuitable, 2871.PP
1281unspecified default\fR value will be used (which you can expect to be around 2872Since there is no portable change notification interface available, the
1282five seconds, although this might change dynamically). Libev will also 2873portable implementation simply calls \f(CWstat(2)\fR regularly on the path
1283impose a minimum interval which is currently around \f(CW0.1\fR, but thats 2874to see if it changed somehow. You can specify a recommended polling
1284usually overkill. 2875interval for this case. If you specify a polling interval of \f(CW0\fR (highly
2876recommended!) then a \fIsuitable, unspecified default\fR value will be used
2877(which you can expect to be around five seconds, although this might
2878change dynamically). Libev will also impose a minimum interval which is
2879currently around \f(CW0.1\fR, but that's usually overkill.
1285.PP 2880.PP
1286This watcher type is not meant for massive numbers of stat watchers, 2881This watcher type is not meant for massive numbers of stat watchers,
1287as even with OS-supported change notifications, this can be 2882as even with OS-supported change notifications, this can be
1288resource\-intensive. 2883resource-intensive.
1289.PP 2884.PP
1290At the time of this writing, no specific \s-1OS\s0 backends are implemented, but 2885At the time of this writing, the only OS-specific interface implemented
1291if demand increases, at least a kqueue and inotify backend will be added. 2886is the Linux inotify interface (implementing kqueue support is left as an
2887exercise for the reader. Note, however, that the author sees no way of
2888implementing \f(CW\*(C`ev_stat\*(C'\fR semantics with kqueue, except as a hint).
2889.PP
2890\fI\s-1ABI\s0 Issues (Largefile Support)\fR
2891.IX Subsection "ABI Issues (Largefile Support)"
2892.PP
2893Libev by default (unless the user overrides this) uses the default
2894compilation environment, which means that on systems with large file
2895support disabled by default, you get the 32 bit version of the stat
2896structure. When using the library from programs that change the \s-1ABI\s0 to
2897use 64 bit file offsets the programs will fail. In that case you have to
2898compile libev with the same flags to get binary compatibility. This is
2899obviously the case with any flags that change the \s-1ABI,\s0 but the problem is
2900most noticeably displayed with ev_stat and large file support.
2901.PP
2902The solution for this is to lobby your distribution maker to make large
2903file interfaces available by default (as e.g. FreeBSD does) and not
2904optional. Libev cannot simply switch on large file support because it has
2905to exchange stat structures with application programs compiled using the
2906default compilation environment.
2907.PP
2908\fIInotify and Kqueue\fR
2909.IX Subsection "Inotify and Kqueue"
2910.PP
2911When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev and present at
2912runtime, it will be used to speed up change detection where possible. The
2913inotify descriptor will be created lazily when the first \f(CW\*(C`ev_stat\*(C'\fR
2914watcher is being started.
2915.PP
2916Inotify presence does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
2917except that changes might be detected earlier, and in some cases, to avoid
2918making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presence of inotify support
2919there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling,
2920but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
2921many bugs), the path exists (i.e. stat succeeds), and the path resides on
2922a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
2923xfs are fully working) libev usually gets away without polling.
2924.PP
2925There is no support for kqueue, as apparently it cannot be used to
2926implement this functionality, due to the requirement of having a file
2927descriptor open on the object at all times, and detecting renames, unlinks
2928etc. is difficult.
2929.PP
2930\fI\f(CI\*(C`stat ()\*(C'\fI is a synchronous operation\fR
2931.IX Subsection "stat () is a synchronous operation"
2932.PP
2933Libev doesn't normally do any kind of I/O itself, and so is not blocking
2934the process. The exception are \f(CW\*(C`ev_stat\*(C'\fR watchers \- those call \f(CW\*(C`stat
2935()\*(C'\fR, which is a synchronous operation.
2936.PP
2937For local paths, this usually doesn't matter: unless the system is very
2938busy or the intervals between stat's are large, a stat call will be fast,
2939as the path data is usually in memory already (except when starting the
2940watcher).
2941.PP
2942For networked file systems, calling \f(CW\*(C`stat ()\*(C'\fR can block an indefinite
2943time due to network issues, and even under good conditions, a stat call
2944often takes multiple milliseconds.
2945.PP
2946Therefore, it is best to avoid using \f(CW\*(C`ev_stat\*(C'\fR watchers on networked
2947paths, although this is fully supported by libev.
2948.PP
2949\fIThe special problem of stat time resolution\fR
2950.IX Subsection "The special problem of stat time resolution"
2951.PP
2952The \f(CW\*(C`stat ()\*(C'\fR system call only supports full-second resolution portably,
2953and even on systems where the resolution is higher, most file systems
2954still only support whole seconds.
2955.PP
2956That means that, if the time is the only thing that changes, you can
2957easily miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and
2958calls your callback, which does something. When there is another update
2959within the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect unless the
2960stat data does change in other ways (e.g. file size).
2961.PP
2962The solution to this is to delay acting on a change for slightly more
2963than a second (or till slightly after the next full second boundary), using
2964a roughly one-second-delay \f(CW\*(C`ev_timer\*(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02);
2965ev_timer_again (loop, w)\*(C'\fR).
2966.PP
2967The \f(CW.02\fR offset is added to work around small timing inconsistencies
2968of some operating systems (where the second counter of the current time
2969might be be delayed. One such system is the Linux kernel, where a call to
2970\&\f(CW\*(C`gettimeofday\*(C'\fR might return a timestamp with a full second later than
2971a subsequent \f(CW\*(C`time\*(C'\fR call \- if the equivalent of \f(CW\*(C`time ()\*(C'\fR is used to
2972update file times then there will be a small window where the kernel uses
2973the previous second to update file times but libev might already execute
2974the timer callback).
2975.PP
2976\fIWatcher-Specific Functions and Data Members\fR
2977.IX Subsection "Watcher-Specific Functions and Data Members"
1292.IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4 2978.IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
1293.IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 2979.IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
1294.PD 0 2980.PD 0
1295.IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4 2981.IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4
1296.IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 2982.IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)"
… …
1299\&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to 2985\&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to
1300be detected and should normally be specified as \f(CW0\fR to let libev choose 2986be detected and should normally be specified as \f(CW0\fR to let libev choose
1301a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same 2987a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same
1302path for as long as the watcher is active. 2988path for as long as the watcher is active.
1303.Sp 2989.Sp
1304The callback will be receive \f(CW\*(C`EV_STAT\*(C'\fR when a change was detected, 2990The callback will receive an \f(CW\*(C`EV_STAT\*(C'\fR event when a change was detected,
1305relative to the attributes at the time the watcher was started (or the 2991relative to the attributes at the time the watcher was started (or the
1306last change was detected). 2992last change was detected).
1307.IP "ev_stat_stat (ev_stat *)" 4 2993.IP "ev_stat_stat (loop, ev_stat *)" 4
1308.IX Item "ev_stat_stat (ev_stat *)" 2994.IX Item "ev_stat_stat (loop, ev_stat *)"
1309Updates the stat buffer immediately with new values. If you change the 2995Updates the stat buffer immediately with new values. If you change the
1310watched path in your callback, you could call this fucntion to avoid 2996watched path in your callback, you could call this function to avoid
1311detecting this change (while introducing a race condition). Can also be 2997detecting this change (while introducing a race condition if you are not
1312useful simply to find out the new values. 2998the only one changing the path). Can also be useful simply to find out the
2999new values.
1313.IP "ev_statdata attr [read\-only]" 4 3000.IP "ev_statdata attr [read\-only]" 4
1314.IX Item "ev_statdata attr [read-only]" 3001.IX Item "ev_statdata attr [read-only]"
1315The most-recently detected attributes of the file. Although the type is of 3002The most-recently detected attributes of the file. Although the type is
1316\&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types 3003\&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
3004suitable for your system, but you can only rely on the POSIX-standardised
1317suitable for your system. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there 3005members to be present. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there was
1318was some error while \f(CW\*(C`stat\*(C'\fRing the file. 3006some error while \f(CW\*(C`stat\*(C'\fRing the file.
1319.IP "ev_statdata prev [read\-only]" 4 3007.IP "ev_statdata prev [read\-only]" 4
1320.IX Item "ev_statdata prev [read-only]" 3008.IX Item "ev_statdata prev [read-only]"
1321The previous attributes of the file. The callback gets invoked whenever 3009The previous attributes of the file. The callback gets invoked whenever
1322\&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR. 3010\&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR, or, more precisely, one or more of these members
3011differ: \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,
3012\&\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.
1323.IP "ev_tstamp interval [read\-only]" 4 3013.IP "ev_tstamp interval [read\-only]" 4
1324.IX Item "ev_tstamp interval [read-only]" 3014.IX Item "ev_tstamp interval [read-only]"
1325The specified interval. 3015The specified interval.
1326.IP "const char *path [read\-only]" 4 3016.IP "const char *path [read\-only]" 4
1327.IX Item "const char *path [read-only]" 3017.IX Item "const char *path [read-only]"
1328The filesystem path that is being watched. 3018The file system path that is being watched.
3019.PP
3020\fIExamples\fR
3021.IX Subsection "Examples"
1329.PP 3022.PP
1330Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes. 3023Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
1331.PP 3024.PP
1332.Vb 15 3025.Vb 10
1333\& static void 3026\& static void
1334\& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents) 3027\& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1335\& { 3028\& {
1336\& /* /etc/passwd changed in some way */ 3029\& /* /etc/passwd changed in some way */
1337\& if (w->attr.st_nlink) 3030\& if (w\->attr.st_nlink)
1338\& { 3031\& {
1339\& printf ("passwd current size %ld\en", (long)w->attr.st_size); 3032\& printf ("passwd current size %ld\en", (long)w\->attr.st_size);
1340\& printf ("passwd current atime %ld\en", (long)w->attr.st_mtime); 3033\& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime);
1341\& printf ("passwd current mtime %ld\en", (long)w->attr.st_mtime); 3034\& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime);
1342\& } 3035\& }
1343\& else 3036\& else
1344\& /* you shalt not abuse printf for puts */ 3037\& /* you shalt not abuse printf for puts */
1345\& puts ("wow, /etc/passwd is not there, expect problems. " 3038\& puts ("wow, /etc/passwd is not there, expect problems. "
1346\& "if this is windows, they already arrived\en"); 3039\& "if this is windows, they already arrived\en");
1347\& } 3040\& }
3041\&
3042\& ...
3043\& ev_stat passwd;
3044\&
3045\& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
3046\& ev_stat_start (loop, &passwd);
1348.Ve 3047.Ve
3048.PP
3049Example: Like above, but additionally use a one-second delay so we do not
3050miss updates (however, frequent updates will delay processing, too, so
3051one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
3052\&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
1349.PP 3053.PP
1350.Vb 2 3054.Vb 2
3055\& static ev_stat passwd;
3056\& static ev_timer timer;
3057\&
3058\& static void
3059\& timer_cb (EV_P_ ev_timer *w, int revents)
3060\& {
3061\& ev_timer_stop (EV_A_ w);
3062\&
3063\& /* now it\*(Aqs one second after the most recent passwd change */
3064\& }
3065\&
3066\& static void
3067\& stat_cb (EV_P_ ev_stat *w, int revents)
3068\& {
3069\& /* reset the one\-second timer */
3070\& ev_timer_again (EV_A_ &timer);
3071\& }
3072\&
1351\& ... 3073\& ...
1352\& ev_stat passwd;
1353.Ve
1354.PP
1355.Vb 2
1356\& ev_stat_init (&passwd, passwd_cb, "/etc/passwd"); 3074\& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1357\& ev_stat_start (loop, &passwd); 3075\& ev_stat_start (loop, &passwd);
3076\& ev_timer_init (&timer, timer_cb, 0., 1.02);
1358.Ve 3077.Ve
1359.ie n .Sh """ev_idle"" \- when you've got nothing better to do..." 3078.ie n .SS """ev_idle"" \- when you've got nothing better to do..."
1360.el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do..." 3079.el .SS "\f(CWev_idle\fP \- when you've got nothing better to do..."
1361.IX Subsection "ev_idle - when you've got nothing better to do..." 3080.IX Subsection "ev_idle - when you've got nothing better to do..."
1362Idle watchers trigger events when there are no other events are pending 3081Idle watchers trigger events when no other events of the same or higher
1363(prepare, check and other idle watchers do not count). That is, as long 3082priority are pending (prepare, check and other idle watchers do not count
1364as your process is busy handling sockets or timeouts (or even signals, 3083as receiving \*(L"events\*(R").
1365imagine) it will not be triggered. But when your process is idle all idle 3084.PP
1366watchers are being called again and again, once per event loop iteration \- 3085That is, as long as your process is busy handling sockets or timeouts
3086(or even signals, imagine) of the same or higher priority it will not be
3087triggered. But when your process is idle (or only lower-priority watchers
3088are pending), the idle watchers are being called once per event loop
1367until stopped, that is, or your process receives more events and becomes 3089iteration \- until stopped, that is, or your process receives more events
1368busy. 3090and becomes busy again with higher priority stuff.
1369.PP 3091.PP
1370The most noteworthy effect is that as long as any idle watchers are 3092The most noteworthy effect is that as long as any idle watchers are
1371active, the process will not block when waiting for new events. 3093active, the process will not block when waiting for new events.
1372.PP 3094.PP
1373Apart from keeping your process non-blocking (which is a useful 3095Apart from keeping your process non-blocking (which is a useful
1374effect on its own sometimes), idle watchers are a good place to do 3096effect on its own sometimes), idle watchers are a good place to do
1375\&\*(L"pseudo\-background processing\*(R", or delay processing stuff to after the 3097\&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the
1376event loop has handled all outstanding events. 3098event loop has handled all outstanding events.
3099.PP
3100\fIAbusing an \f(CI\*(C`ev_idle\*(C'\fI watcher for its side-effect\fR
3101.IX Subsection "Abusing an ev_idle watcher for its side-effect"
3102.PP
3103As long as there is at least one active idle watcher, libev will never
3104sleep unnecessarily. Or in other words, it will loop as fast as possible.
3105For this to work, the idle watcher doesn't need to be invoked at all \- the
3106lowest priority will do.
3107.PP
3108This mode of operation can be useful together with an \f(CW\*(C`ev_check\*(C'\fR watcher,
3109to do something on each event loop iteration \- for example to balance load
3110between different connections.
3111.PP
3112See \*(L"Abusing an ev_check watcher for its side-effect\*(R" for a longer
3113example.
3114.PP
3115\fIWatcher-Specific Functions and Data Members\fR
3116.IX Subsection "Watcher-Specific Functions and Data Members"
1377.IP "ev_idle_init (ev_signal *, callback)" 4 3117.IP "ev_idle_init (ev_idle *, callback)" 4
1378.IX Item "ev_idle_init (ev_signal *, callback)" 3118.IX Item "ev_idle_init (ev_idle *, callback)"
1379Initialises and configures the idle watcher \- it has no parameters of any 3119Initialises and configures the idle watcher \- it has no parameters of any
1380kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless, 3120kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
1381believe me. 3121believe me.
1382.PP 3122.PP
3123\fIExamples\fR
3124.IX Subsection "Examples"
3125.PP
1383Example: dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR, start it, and in the 3126Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the
1384callback, free it. Alos, use no error checking, as usual. 3127callback, free it. Also, use no error checking, as usual.
1385.PP 3128.PP
1386.Vb 7 3129.Vb 5
1387\& static void 3130\& static void
1388\& idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents) 3131\& idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1389\& { 3132\& {
3133\& // stop the watcher
3134\& ev_idle_stop (loop, w);
3135\&
3136\& // now we can free it
1390\& free (w); 3137\& free (w);
3138\&
1391\& // now do something you wanted to do when the program has 3139\& // now do something you wanted to do when the program has
1392\& // no longer asnything immediate to do. 3140\& // no longer anything immediate to do.
1393\& } 3141\& }
1394.Ve 3142\&
1395.PP
1396.Vb 3
1397\& struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle)); 3143\& ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1398\& ev_idle_init (idle_watcher, idle_cb); 3144\& ev_idle_init (idle_watcher, idle_cb);
1399\& ev_idle_start (loop, idle_cb); 3145\& ev_idle_start (loop, idle_watcher);
1400.Ve 3146.Ve
1401.ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop!" 3147.ie n .SS """ev_prepare"" and ""ev_check"" \- customise your event loop!"
1402.el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!" 3148.el .SS "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
1403.IX Subsection "ev_prepare and ev_check - customise your event loop!" 3149.IX Subsection "ev_prepare and ev_check - customise your event loop!"
1404Prepare and check watchers are usually (but not always) used in tandem: 3150Prepare and check watchers are often (but not always) used in pairs:
1405prepare watchers get invoked before the process blocks and check watchers 3151prepare watchers get invoked before the process blocks and check watchers
1406afterwards. 3152afterwards.
1407.PP 3153.PP
1408You \fImust not\fR call \f(CW\*(C`ev_loop\*(C'\fR or similar functions that enter 3154You \fImust not\fR call \f(CW\*(C`ev_run\*(C'\fR (or similar functions that enter the
1409the current event loop from either \f(CW\*(C`ev_prepare\*(C'\fR or \f(CW\*(C`ev_check\*(C'\fR 3155current event loop) or \f(CW\*(C`ev_loop_fork\*(C'\fR from either \f(CW\*(C`ev_prepare\*(C'\fR or
1410watchers. Other loops than the current one are fine, however. The 3156\&\f(CW\*(C`ev_check\*(C'\fR watchers. Other loops than the current one are fine,
1411rationale behind this is that you do not need to check for recursion in 3157however. The rationale behind this is that you do not need to check
1412those watchers, i.e. the sequence will always be \f(CW\*(C`ev_prepare\*(C'\fR, blocking, 3158for recursion in those watchers, i.e. the sequence will always be
1413\&\f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each kind they will always be 3159\&\f(CW\*(C`ev_prepare\*(C'\fR, blocking, \f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each
1414called in pairs bracketing the blocking call. 3160kind they will always be called in pairs bracketing the blocking call.
1415.PP 3161.PP
1416Their main purpose is to integrate other event mechanisms into libev and 3162Their main purpose is to integrate other event mechanisms into libev and
1417their use is somewhat advanced. This could be used, for example, to track 3163their use is somewhat advanced. They could be used, for example, to track
1418variable changes, implement your own watchers, integrate net-snmp or a 3164variable changes, implement your own watchers, integrate net-snmp or a
1419coroutine library and lots more. They are also occasionally useful if 3165coroutine library and lots more. They are also occasionally useful if
1420you cache some data and want to flush it before blocking (for example, 3166you cache some data and want to flush it before blocking (for example,
1421in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR 3167in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
1422watcher). 3168watcher).
1423.PP 3169.PP
1424This is done by examining in each prepare call which file descriptors need 3170This is done by examining in each prepare call which file descriptors
1425to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers for 3171need to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers
1426them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many libraries 3172for them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many
1427provide just this functionality). Then, in the check watcher you check for 3173libraries provide exactly this functionality). Then, in the check watcher,
1428any events that occured (by checking the pending status of all watchers 3174you check for any events that occurred (by checking the pending status
1429and stopping them) and call back into the library. The I/O and timer 3175of all watchers and stopping them) and call back into the library. The
1430callbacks will never actually be called (but must be valid nevertheless, 3176I/O and timer callbacks will never actually be called (but must be valid
1431because you never know, you know?). 3177nevertheless, because you never know, you know?).
1432.PP 3178.PP
1433As another example, the Perl Coro module uses these hooks to integrate 3179As another example, the Perl Coro module uses these hooks to integrate
1434coroutines into libev programs, by yielding to other active coroutines 3180coroutines into libev programs, by yielding to other active coroutines
1435during each prepare and only letting the process block if no coroutines 3181during each prepare and only letting the process block if no coroutines
1436are ready to run (it's actually more complicated: it only runs coroutines 3182are ready to run (it's actually more complicated: it only runs coroutines
1437with priority higher than or equal to the event loop and one coroutine 3183with priority higher than or equal to the event loop and one coroutine
1438of lower priority, but only once, using idle watchers to keep the event 3184of lower priority, but only once, using idle watchers to keep the event
1439loop from blocking if lower-priority coroutines are active, thus mapping 3185loop from blocking if lower-priority coroutines are active, thus mapping
1440low-priority coroutines to idle/background tasks). 3186low-priority coroutines to idle/background tasks).
3187.PP
3188When used for this purpose, it is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers
3189highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR) priority, to ensure that they are being run before
3190any other watchers after the poll (this doesn't matter for \f(CW\*(C`ev_prepare\*(C'\fR
3191watchers).
3192.PP
3193Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, too) should not
3194activate (\*(L"feed\*(R") events into libev. While libev fully supports this, they
3195might get executed before other \f(CW\*(C`ev_check\*(C'\fR watchers did their job. As
3196\&\f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other (non-libev) event
3197loops those other event loops might be in an unusable state until their
3198\&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with
3199others).
3200.PP
3201\fIAbusing an \f(CI\*(C`ev_check\*(C'\fI watcher for its side-effect\fR
3202.IX Subsection "Abusing an ev_check watcher for its side-effect"
3203.PP
3204\&\f(CW\*(C`ev_check\*(C'\fR (and less often also \f(CW\*(C`ev_prepare\*(C'\fR) watchers can also be
3205useful because they are called once per event loop iteration. For
3206example, if you want to handle a large number of connections fairly, you
3207normally only do a bit of work for each active connection, and if there
3208is more work to do, you wait for the next event loop iteration, so other
3209connections have a chance of making progress.
3210.PP
3211Using an \f(CW\*(C`ev_check\*(C'\fR watcher is almost enough: it will be called on the
3212next event loop iteration. However, that isn't as soon as possible \-
3213without external events, your \f(CW\*(C`ev_check\*(C'\fR watcher will not be invoked.
3214.PP
3215This is where \f(CW\*(C`ev_idle\*(C'\fR watchers come in handy \- all you need is a
3216single global idle watcher that is active as long as you have one active
3217\&\f(CW\*(C`ev_check\*(C'\fR watcher. The \f(CW\*(C`ev_idle\*(C'\fR watcher makes sure the event loop
3218will not sleep, and the \f(CW\*(C`ev_check\*(C'\fR watcher makes sure a callback gets
3219invoked. Neither watcher alone can do that.
3220.PP
3221\fIWatcher-Specific Functions and Data Members\fR
3222.IX Subsection "Watcher-Specific Functions and Data Members"
1441.IP "ev_prepare_init (ev_prepare *, callback)" 4 3223.IP "ev_prepare_init (ev_prepare *, callback)" 4
1442.IX Item "ev_prepare_init (ev_prepare *, callback)" 3224.IX Item "ev_prepare_init (ev_prepare *, callback)"
1443.PD 0 3225.PD 0
1444.IP "ev_check_init (ev_check *, callback)" 4 3226.IP "ev_check_init (ev_check *, callback)" 4
1445.IX Item "ev_check_init (ev_check *, callback)" 3227.IX Item "ev_check_init (ev_check *, callback)"
1446.PD 3228.PD
1447Initialises and configures the prepare or check watcher \- they have no 3229Initialises and configures the prepare or check watcher \- they have no
1448parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR 3230parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
1449macros, but using them is utterly, utterly and completely pointless. 3231macros, but using them is utterly, utterly, utterly and completely
3232pointless.
1450.PP 3233.PP
1451Example: To include a library such as adns, you would add \s-1IO\s0 watchers 3234\fIExamples\fR
1452and a timeout watcher in a prepare handler, as required by libadns, and 3235.IX Subsection "Examples"
3236.PP
3237There are a number of principal ways to embed other event loops or modules
3238into libev. Here are some ideas on how to include libadns into libev
3239(there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could
3240use as a working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR embeds a
3241Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 into the
3242Glib event loop).
3243.PP
3244Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
1453in a check watcher, destroy them and call into libadns. What follows is 3245and in a check watcher, destroy them and call into libadns. What follows
1454pseudo-code only of course: 3246is pseudo-code only of course. This requires you to either use a low
3247priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as
3248the callbacks for the IO/timeout watchers might not have been called yet.
1455.PP 3249.PP
1456.Vb 2 3250.Vb 2
1457\& static ev_io iow [nfd]; 3251\& static ev_io iow [nfd];
1458\& static ev_timer tw; 3252\& static ev_timer tw;
1459.Ve 3253\&
1460.PP
1461.Vb 9
1462\& static void 3254\& static void
1463\& io_cb (ev_loop *loop, ev_io *w, int revents) 3255\& io_cb (struct ev_loop *loop, ev_io *w, int revents)
1464\& { 3256\& {
1465\& // set the relevant poll flags
1466\& // could also call adns_processreadable etc. here
1467\& struct pollfd *fd = (struct pollfd *)w->data;
1468\& if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1469\& if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1470\& } 3257\& }
1471.Ve 3258\&
1472.PP
1473.Vb 7
1474\& // create io watchers for each fd and a timer before blocking 3259\& // create io watchers for each fd and a timer before blocking
1475\& static void 3260\& static void
1476\& adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents) 3261\& adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1477\& { 3262\& {
1478\& int timeout = 3600000;truct pollfd fds [nfd]; 3263\& int timeout = 3600000;
3264\& struct pollfd fds [nfd];
1479\& // actual code will need to loop here and realloc etc. 3265\& // actual code will need to loop here and realloc etc.
1480\& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ())); 3266\& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1481.Ve 3267\&
1482.PP
1483.Vb 3
1484\& /* the callback is illegal, but won't be called as we stop during check */ 3268\& /* the callback is illegal, but won\*(Aqt be called as we stop during check */
1485\& ev_timer_init (&tw, 0, timeout * 1e-3); 3269\& ev_timer_init (&tw, 0, timeout * 1e\-3, 0.);
1486\& ev_timer_start (loop, &tw); 3270\& ev_timer_start (loop, &tw);
1487.Ve 3271\&
1488.PP
1489.Vb 6
1490\& // create on ev_io per pollfd 3272\& // create one ev_io per pollfd
1491\& for (int i = 0; i < nfd; ++i) 3273\& for (int i = 0; i < nfd; ++i)
1492\& { 3274\& {
1493\& ev_io_init (iow + i, io_cb, fds [i].fd, 3275\& ev_io_init (iow + i, io_cb, fds [i].fd,
1494\& ((fds [i].events & POLLIN ? EV_READ : 0) 3276\& ((fds [i].events & POLLIN ? EV_READ : 0)
1495\& | (fds [i].events & POLLOUT ? EV_WRITE : 0))); 3277\& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
3278\&
3279\& fds [i].revents = 0;
3280\& ev_io_start (loop, iow + i);
3281\& }
3282\& }
3283\&
3284\& // stop all watchers after blocking
3285\& static void
3286\& adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
3287\& {
3288\& ev_timer_stop (loop, &tw);
3289\&
3290\& for (int i = 0; i < nfd; ++i)
3291\& {
3292\& // set the relevant poll flags
3293\& // could also call adns_processreadable etc. here
3294\& struct pollfd *fd = fds + i;
3295\& int revents = ev_clear_pending (iow + i);
3296\& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN;
3297\& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT;
3298\&
3299\& // now stop the watcher
3300\& ev_io_stop (loop, iow + i);
3301\& }
3302\&
3303\& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
3304\& }
1496.Ve 3305.Ve
3306.PP
3307Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR
3308in the prepare watcher and would dispose of the check watcher.
3309.PP
3310Method 3: If the module to be embedded supports explicit event
3311notification (libadns does), you can also make use of the actual watcher
3312callbacks, and only destroy/create the watchers in the prepare watcher.
1497.PP 3313.PP
1498.Vb 5 3314.Vb 5
1499\& fds [i].revents = 0;
1500\& iow [i].data = fds + i;
1501\& ev_io_start (loop, iow + i);
1502\& }
1503\& }
1504.Ve
1505.PP
1506.Vb 5
1507\& // stop all watchers after blocking
1508\& static void 3315\& static void
1509\& adns_check_cb (ev_loop *loop, ev_check *w, int revents) 3316\& timer_cb (EV_P_ ev_timer *w, int revents)
1510\& { 3317\& {
1511\& ev_timer_stop (loop, &tw); 3318\& adns_state ads = (adns_state)w\->data;
1512.Ve 3319\& update_now (EV_A);
1513.PP 3320\&
1514.Vb 2 3321\& adns_processtimeouts (ads, &tv_now);
1515\& for (int i = 0; i < nfd; ++i)
1516\& ev_io_stop (loop, iow + i);
1517.Ve
1518.PP
1519.Vb 2
1520\& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1521\& } 3322\& }
3323\&
3324\& static void
3325\& io_cb (EV_P_ ev_io *w, int revents)
3326\& {
3327\& adns_state ads = (adns_state)w\->data;
3328\& update_now (EV_A);
3329\&
3330\& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now);
3331\& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now);
3332\& }
3333\&
3334\& // do not ever call adns_afterpoll
1522.Ve 3335.Ve
3336.PP
3337Method 4: Do not use a prepare or check watcher because the module you
3338want to embed is not flexible enough to support it. Instead, you can
3339override their poll function. The drawback with this solution is that the
3340main loop is now no longer controllable by \s-1EV.\s0 The \f(CW\*(C`Glib::EV\*(C'\fR module uses
3341this approach, effectively embedding \s-1EV\s0 as a client into the horrible
3342libglib event loop.
3343.PP
3344.Vb 4
3345\& static gint
3346\& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
3347\& {
3348\& int got_events = 0;
3349\&
3350\& for (n = 0; n < nfds; ++n)
3351\& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
3352\&
3353\& if (timeout >= 0)
3354\& // create/start timer
3355\&
3356\& // poll
3357\& ev_run (EV_A_ 0);
3358\&
3359\& // stop timer again
3360\& if (timeout >= 0)
3361\& ev_timer_stop (EV_A_ &to);
3362\&
3363\& // stop io watchers again \- their callbacks should have set
3364\& for (n = 0; n < nfds; ++n)
3365\& ev_io_stop (EV_A_ iow [n]);
3366\&
3367\& return got_events;
3368\& }
3369.Ve
1523.ie n .Sh """ev_embed"" \- when one backend isn't enough..." 3370.ie n .SS """ev_embed"" \- when one backend isn't enough..."
1524.el .Sh "\f(CWev_embed\fP \- when one backend isn't enough..." 3371.el .SS "\f(CWev_embed\fP \- when one backend isn't enough..."
1525.IX Subsection "ev_embed - when one backend isn't enough..." 3372.IX Subsection "ev_embed - when one backend isn't enough..."
1526This is a rather advanced watcher type that lets you embed one event loop 3373This is a rather advanced watcher type that lets you embed one event loop
1527into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded 3374into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
1528loop, other types of watchers might be handled in a delayed or incorrect 3375loop, other types of watchers might be handled in a delayed or incorrect
1529fashion and must not be used). 3376fashion and must not be used).
… …
1532prioritise I/O. 3379prioritise I/O.
1533.PP 3380.PP
1534As an example for a bug workaround, the kqueue backend might only support 3381As an example for a bug workaround, the kqueue backend might only support
1535sockets on some platform, so it is unusable as generic backend, but you 3382sockets on some platform, so it is unusable as generic backend, but you
1536still want to make use of it because you have many sockets and it scales 3383still want to make use of it because you have many sockets and it scales
1537so nicely. In this case, you would create a kqueue-based loop and embed it 3384so nicely. In this case, you would create a kqueue-based loop and embed
1538into your default loop (which might use e.g. poll). Overall operation will 3385it into your default loop (which might use e.g. poll). Overall operation
1539be a bit slower because first libev has to poll and then call kevent, but 3386will be a bit slower because first libev has to call \f(CW\*(C`poll\*(C'\fR and then
1540at least you can use both at what they are best. 3387\&\f(CW\*(C`kevent\*(C'\fR, but at least you can use both mechanisms for what they are
3388best: \f(CW\*(C`kqueue\*(C'\fR for scalable sockets and \f(CW\*(C`poll\*(C'\fR if you want it to work :)
1541.PP 3389.PP
1542As for prioritising I/O: rarely you have the case where some fds have 3390As for prioritising I/O: under rare circumstances you have the case where
1543to be watched and handled very quickly (with low latency), and even 3391some fds have to be watched and handled very quickly (with low latency),
1544priorities and idle watchers might have too much overhead. In this case 3392and even priorities and idle watchers might have too much overhead. In
1545you would put all the high priority stuff in one loop and all the rest in 3393this case you would put all the high priority stuff in one loop and all
1546a second one, and embed the second one in the first. 3394the rest in a second one, and embed the second one in the first.
1547.PP 3395.PP
1548As long as the watcher is active, the callback will be invoked every time 3396As long as the watcher is active, the callback will be invoked every
1549there might be events pending in the embedded loop. The callback must then 3397time there might be events pending in the embedded loop. The callback
1550call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single sweep and invoke 3398must then call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single
1551their callbacks (you could also start an idle watcher to give the embedded 3399sweep and invoke their callbacks (the callback doesn't need to invoke the
1552loop strictly lower priority for example). You can also set the callback 3400\&\f(CW\*(C`ev_embed_sweep\*(C'\fR function directly, it could also start an idle watcher
1553to \f(CW0\fR, in which case the embed watcher will automatically execute the 3401to give the embedded loop strictly lower priority for example).
1554embedded loop sweep.
1555.PP 3402.PP
1556As long as the watcher is started it will automatically handle events. The 3403You can also set the callback to \f(CW0\fR, in which case the embed watcher
1557callback will be invoked whenever some events have been handled. You can 3404will automatically execute the embedded loop sweep whenever necessary.
1558set the callback to \f(CW0\fR to avoid having to specify one if you are not
1559interested in that.
1560.PP 3405.PP
1561Also, there have not currently been made special provisions for forking: 3406Fork detection will be handled transparently while the \f(CW\*(C`ev_embed\*(C'\fR watcher
1562when you fork, you not only have to call \f(CW\*(C`ev_loop_fork\*(C'\fR on both loops, 3407is active, i.e., the embedded loop will automatically be forked when the
1563but you will also have to stop and restart any \f(CW\*(C`ev_embed\*(C'\fR watchers 3408embedding loop forks. In other cases, the user is responsible for calling
1564yourself. 3409\&\f(CW\*(C`ev_loop_fork\*(C'\fR on the embedded loop.
1565.PP 3410.PP
1566Unfortunately, not all backends are embeddable, only the ones returned by 3411Unfortunately, not all backends are embeddable: only the ones returned by
1567\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any 3412\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
1568portable one. 3413portable one.
1569.PP 3414.PP
1570So when you want to use this feature you will always have to be prepared 3415So when you want to use this feature you will always have to be prepared
1571that you cannot get an embeddable loop. The recommended way to get around 3416that you cannot get an embeddable loop. The recommended way to get around
1572this is to have a separate variables for your embeddable loop, try to 3417this is to have a separate variables for your embeddable loop, try to
1573create it, and if that fails, use the normal loop for everything: 3418create it, and if that fails, use the normal loop for everything.
1574.PP 3419.PP
1575.Vb 3 3420\fI\f(CI\*(C`ev_embed\*(C'\fI and fork\fR
1576\& struct ev_loop *loop_hi = ev_default_init (0); 3421.IX Subsection "ev_embed and fork"
1577\& struct ev_loop *loop_lo = 0;
1578\& struct ev_embed embed;
1579.Ve
1580.PP 3422.PP
1581.Vb 5 3423While the \f(CW\*(C`ev_embed\*(C'\fR watcher is running, forks in the embedding loop will
1582\& // see if there is a chance of getting one that works 3424automatically be applied to the embedded loop as well, so no special
1583\& // (remember that a flags value of 0 means autodetection) 3425fork handling is required in that case. When the watcher is not running,
1584\& loop_lo = ev_embeddable_backends () & ev_recommended_backends () 3426however, it is still the task of the libev user to call \f(CW\*(C`ev_loop_fork ()\*(C'\fR
1585\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ()) 3427as applicable.
1586\& : 0;
1587.Ve
1588.PP 3428.PP
1589.Vb 8 3429\fIWatcher-Specific Functions and Data Members\fR
1590\& // if we got one, then embed it, otherwise default to loop_hi 3430.IX Subsection "Watcher-Specific Functions and Data Members"
1591\& if (loop_lo)
1592\& {
1593\& ev_embed_init (&embed, 0, loop_lo);
1594\& ev_embed_start (loop_hi, &embed);
1595\& }
1596\& else
1597\& loop_lo = loop_hi;
1598.Ve
1599.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4 3431.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
1600.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 3432.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
1601.PD 0 3433.PD 0
1602.IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4 3434.IP "ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)" 4
1603.IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 3435.IX Item "ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)"
1604.PD 3436.PD
1605Configures the watcher to embed the given loop, which must be 3437Configures the watcher to embed the given loop, which must be
1606embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be 3438embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
1607invoked automatically, otherwise it is the responsibility of the callback 3439invoked automatically, otherwise it is the responsibility of the callback
1608to invoke it (it will continue to be called until the sweep has been done, 3440to invoke it (it will continue to be called until the sweep has been done,
1609if you do not want thta, you need to temporarily stop the embed watcher). 3441if you do not want that, you need to temporarily stop the embed watcher).
1610.IP "ev_embed_sweep (loop, ev_embed *)" 4 3442.IP "ev_embed_sweep (loop, ev_embed *)" 4
1611.IX Item "ev_embed_sweep (loop, ev_embed *)" 3443.IX Item "ev_embed_sweep (loop, ev_embed *)"
1612Make a single, non-blocking sweep over the embedded loop. This works 3444Make a single, non-blocking sweep over the embedded loop. This works
1613similarly to \f(CW\*(C`ev_loop (embedded_loop, EVLOOP_NONBLOCK)\*(C'\fR, but in the most 3445similarly to \f(CW\*(C`ev_run (embedded_loop, EVRUN_NOWAIT)\*(C'\fR, but in the most
1614apropriate way for embedded loops. 3446appropriate way for embedded loops.
1615.IP "struct ev_loop *loop [read\-only]" 4 3447.IP "struct ev_loop *other [read\-only]" 4
1616.IX Item "struct ev_loop *loop [read-only]" 3448.IX Item "struct ev_loop *other [read-only]"
1617The embedded event loop. 3449The embedded event loop.
3450.PP
3451\fIExamples\fR
3452.IX Subsection "Examples"
3453.PP
3454Example: Try to get an embeddable event loop and embed it into the default
3455event loop. If that is not possible, use the default loop. The default
3456loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the embeddable loop is stored in
3457\&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the case no embeddable loop can be
3458used).
3459.PP
3460.Vb 3
3461\& struct ev_loop *loop_hi = ev_default_init (0);
3462\& struct ev_loop *loop_lo = 0;
3463\& ev_embed embed;
3464\&
3465\& // see if there is a chance of getting one that works
3466\& // (remember that a flags value of 0 means autodetection)
3467\& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3468\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3469\& : 0;
3470\&
3471\& // if we got one, then embed it, otherwise default to loop_hi
3472\& if (loop_lo)
3473\& {
3474\& ev_embed_init (&embed, 0, loop_lo);
3475\& ev_embed_start (loop_hi, &embed);
3476\& }
3477\& else
3478\& loop_lo = loop_hi;
3479.Ve
3480.PP
3481Example: Check if kqueue is available but not recommended and create
3482a kqueue backend for use with sockets (which usually work with any
3483kqueue implementation). Store the kqueue/socket\-only event loop in
3484\&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too).
3485.PP
3486.Vb 3
3487\& struct ev_loop *loop = ev_default_init (0);
3488\& struct ev_loop *loop_socket = 0;
3489\& ev_embed embed;
3490\&
3491\& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3492\& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3493\& {
3494\& ev_embed_init (&embed, 0, loop_socket);
3495\& ev_embed_start (loop, &embed);
3496\& }
3497\&
3498\& if (!loop_socket)
3499\& loop_socket = loop;
3500\&
3501\& // now use loop_socket for all sockets, and loop for everything else
3502.Ve
3503.ie n .SS """ev_fork"" \- the audacity to resume the event loop after a fork"
3504.el .SS "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
3505.IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
3506Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
3507whoever is a good citizen cared to tell libev about it by calling
3508\&\f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the event loop blocks next
3509and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called, and only in the child
3510after the fork. If whoever good citizen calling \f(CW\*(C`ev_default_fork\*(C'\fR cheats
3511and calls it in the wrong process, the fork handlers will be invoked, too,
3512of course.
3513.PP
3514\fIThe special problem of life after fork \- how is it possible?\fR
3515.IX Subsection "The special problem of life after fork - how is it possible?"
3516.PP
3517Most uses of \f(CW\*(C`fork ()\*(C'\fR consist of forking, then some simple calls to set
3518up/change the process environment, followed by a call to \f(CW\*(C`exec()\*(C'\fR. This
3519sequence should be handled by libev without any problems.
3520.PP
3521This changes when the application actually wants to do event handling
3522in the child, or both parent in child, in effect \*(L"continuing\*(R" after the
3523fork.
3524.PP
3525The default mode of operation (for libev, with application help to detect
3526forks) is to duplicate all the state in the child, as would be expected
3527when \fIeither\fR the parent \fIor\fR the child process continues.
3528.PP
3529When both processes want to continue using libev, then this is usually the
3530wrong result. In that case, usually one process (typically the parent) is
3531supposed to continue with all watchers in place as before, while the other
3532process typically wants to start fresh, i.e. without any active watchers.
3533.PP
3534The cleanest and most efficient way to achieve that with libev is to
3535simply create a new event loop, which of course will be \*(L"empty\*(R", and
3536use that for new watchers. This has the advantage of not touching more
3537memory than necessary, and thus avoiding the copy-on-write, and the
3538disadvantage of having to use multiple event loops (which do not support
3539signal watchers).
3540.PP
3541When this is not possible, or you want to use the default loop for
3542other reasons, then in the process that wants to start \*(L"fresh\*(R", call
3543\&\f(CW\*(C`ev_loop_destroy (EV_DEFAULT)\*(C'\fR followed by \f(CW\*(C`ev_default_loop (...)\*(C'\fR.
3544Destroying the default loop will \*(L"orphan\*(R" (not stop) all registered
3545watchers, so you have to be careful not to execute code that modifies
3546those watchers. Note also that in that case, you have to re-register any
3547signal watchers.
3548.PP
3549\fIWatcher-Specific Functions and Data Members\fR
3550.IX Subsection "Watcher-Specific Functions and Data Members"
3551.IP "ev_fork_init (ev_fork *, callback)" 4
3552.IX Item "ev_fork_init (ev_fork *, callback)"
3553Initialises and configures the fork watcher \- it has no parameters of any
3554kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
3555really.
3556.ie n .SS """ev_cleanup"" \- even the best things end"
3557.el .SS "\f(CWev_cleanup\fP \- even the best things end"
3558.IX Subsection "ev_cleanup - even the best things end"
3559Cleanup watchers are called just before the event loop is being destroyed
3560by a call to \f(CW\*(C`ev_loop_destroy\*(C'\fR.
3561.PP
3562While there is no guarantee that the event loop gets destroyed, cleanup
3563watchers provide a convenient method to install cleanup hooks for your
3564program, worker threads and so on \- you just to make sure to destroy the
3565loop when you want them to be invoked.
3566.PP
3567Cleanup watchers are invoked in the same way as any other watcher. Unlike
3568all other watchers, they do not keep a reference to the event loop (which
3569makes a lot of sense if you think about it). Like all other watchers, you
3570can call libev functions in the callback, except \f(CW\*(C`ev_cleanup_start\*(C'\fR.
3571.PP
3572\fIWatcher-Specific Functions and Data Members\fR
3573.IX Subsection "Watcher-Specific Functions and Data Members"
3574.IP "ev_cleanup_init (ev_cleanup *, callback)" 4
3575.IX Item "ev_cleanup_init (ev_cleanup *, callback)"
3576Initialises and configures the cleanup watcher \- it has no parameters of
3577any kind. There is a \f(CW\*(C`ev_cleanup_set\*(C'\fR macro, but using it is utterly
3578pointless, I assure you.
3579.PP
3580Example: Register an atexit handler to destroy the default loop, so any
3581cleanup functions are called.
3582.PP
3583.Vb 5
3584\& static void
3585\& program_exits (void)
3586\& {
3587\& ev_loop_destroy (EV_DEFAULT_UC);
3588\& }
3589\&
3590\& ...
3591\& atexit (program_exits);
3592.Ve
3593.ie n .SS """ev_async"" \- how to wake up an event loop"
3594.el .SS "\f(CWev_async\fP \- how to wake up an event loop"
3595.IX Subsection "ev_async - how to wake up an event loop"
3596In general, you cannot use an \f(CW\*(C`ev_loop\*(C'\fR from multiple threads or other
3597asynchronous sources such as signal handlers (as opposed to multiple event
3598loops \- those are of course safe to use in different threads).
3599.PP
3600Sometimes, however, you need to wake up an event loop you do not control,
3601for example because it belongs to another thread. This is what \f(CW\*(C`ev_async\*(C'\fR
3602watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you can signal
3603it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal safe.
3604.PP
3605This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals,
3606too, are asynchronous in nature, and signals, too, will be compressed
3607(i.e. the number of callback invocations may be less than the number of
3608\&\f(CW\*(C`ev_async_send\*(C'\fR calls). In fact, you could use signal watchers as a kind
3609of \*(L"global async watchers\*(R" by using a watcher on an otherwise unused
3610signal, and \f(CW\*(C`ev_feed_signal\*(C'\fR to signal this watcher from another thread,
3611even without knowing which loop owns the signal.
3612.PP
3613\fIQueueing\fR
3614.IX Subsection "Queueing"
3615.PP
3616\&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason
3617is that the author does not know of a simple (or any) algorithm for a
3618multiple-writer-single-reader queue that works in all cases and doesn't
3619need elaborate support such as pthreads or unportable memory access
3620semantics.
3621.PP
3622That means that if you want to queue data, you have to provide your own
3623queue. But at least I can tell you how to implement locking around your
3624queue:
3625.IP "queueing from a signal handler context" 4
3626.IX Item "queueing from a signal handler context"
3627To implement race-free queueing, you simply add to the queue in the signal
3628handler but you block the signal handler in the watcher callback. Here is
3629an example that does that for some fictitious \s-1SIGUSR1\s0 handler:
3630.Sp
3631.Vb 1
3632\& static ev_async mysig;
3633\&
3634\& static void
3635\& sigusr1_handler (void)
3636\& {
3637\& sometype data;
3638\&
3639\& // no locking etc.
3640\& queue_put (data);
3641\& ev_async_send (EV_DEFAULT_ &mysig);
3642\& }
3643\&
3644\& static void
3645\& mysig_cb (EV_P_ ev_async *w, int revents)
3646\& {
3647\& sometype data;
3648\& sigset_t block, prev;
3649\&
3650\& sigemptyset (&block);
3651\& sigaddset (&block, SIGUSR1);
3652\& sigprocmask (SIG_BLOCK, &block, &prev);
3653\&
3654\& while (queue_get (&data))
3655\& process (data);
3656\&
3657\& if (sigismember (&prev, SIGUSR1)
3658\& sigprocmask (SIG_UNBLOCK, &block, 0);
3659\& }
3660.Ve
3661.Sp
3662(Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR
3663instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it
3664either...).
3665.IP "queueing from a thread context" 4
3666.IX Item "queueing from a thread context"
3667The strategy for threads is different, as you cannot (easily) block
3668threads but you can easily preempt them, so to queue safely you need to
3669employ a traditional mutex lock, such as in this pthread example:
3670.Sp
3671.Vb 2
3672\& static ev_async mysig;
3673\& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
3674\&
3675\& static void
3676\& otherthread (void)
3677\& {
3678\& // only need to lock the actual queueing operation
3679\& pthread_mutex_lock (&mymutex);
3680\& queue_put (data);
3681\& pthread_mutex_unlock (&mymutex);
3682\&
3683\& ev_async_send (EV_DEFAULT_ &mysig);
3684\& }
3685\&
3686\& static void
3687\& mysig_cb (EV_P_ ev_async *w, int revents)
3688\& {
3689\& pthread_mutex_lock (&mymutex);
3690\&
3691\& while (queue_get (&data))
3692\& process (data);
3693\&
3694\& pthread_mutex_unlock (&mymutex);
3695\& }
3696.Ve
3697.PP
3698\fIWatcher-Specific Functions and Data Members\fR
3699.IX Subsection "Watcher-Specific Functions and Data Members"
3700.IP "ev_async_init (ev_async *, callback)" 4
3701.IX Item "ev_async_init (ev_async *, callback)"
3702Initialises and configures the async watcher \- it has no parameters of any
3703kind. There is a \f(CW\*(C`ev_async_set\*(C'\fR macro, but using it is utterly pointless,
3704trust me.
3705.IP "ev_async_send (loop, ev_async *)" 4
3706.IX Item "ev_async_send (loop, ev_async *)"
3707Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds
3708an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop, and instantly
3709returns.
3710.Sp
3711Unlike \f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do from other threads,
3712signal or similar contexts (see the discussion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the
3713embedding section below on what exactly this means).
3714.Sp
3715Note that, as with other watchers in libev, multiple events might get
3716compressed into a single callback invocation (another way to look at
3717this is that \f(CW\*(C`ev_async\*(C'\fR watchers are level-triggered: they are set on
3718\&\f(CW\*(C`ev_async_send\*(C'\fR, reset when the event loop detects that).
3719.Sp
3720This call incurs the overhead of at most one extra system call per event
3721loop iteration, if the event loop is blocked, and no syscall at all if
3722the event loop (or your program) is processing events. That means that
3723repeated calls are basically free (there is no need to avoid calls for
3724performance reasons) and that the overhead becomes smaller (typically
3725zero) under load.
3726.IP "bool = ev_async_pending (ev_async *)" 4
3727.IX Item "bool = ev_async_pending (ev_async *)"
3728Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the
3729watcher but the event has not yet been processed (or even noted) by the
3730event loop.
3731.Sp
3732\&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When
3733the loop iterates next and checks for the watcher to have become active,
3734it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very
3735quickly check whether invoking the loop might be a good idea.
3736.Sp
3737Not that this does \fInot\fR check whether the watcher itself is pending,
3738only whether it has been requested to make this watcher pending: there
3739is a time window between the event loop checking and resetting the async
3740notification, and the callback being invoked.
1618.SH "OTHER FUNCTIONS" 3741.SH "OTHER FUNCTIONS"
1619.IX Header "OTHER FUNCTIONS" 3742.IX Header "OTHER FUNCTIONS"
1620There are some other functions of possible interest. Described. Here. Now. 3743There are some other functions of possible interest. Described. Here. Now.
1621.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4 3744.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)" 4
1622.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 3745.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)"
1623This function combines a simple timer and an I/O watcher, calls your 3746This function combines a simple timer and an I/O watcher, calls your
1624callback on whichever event happens first and automatically stop both 3747callback on whichever event happens first and automatically stops both
1625watchers. This is useful if you want to wait for a single event on an fd 3748watchers. This is useful if you want to wait for a single event on an fd
1626or timeout without having to allocate/configure/start/stop/free one or 3749or timeout without having to allocate/configure/start/stop/free one or
1627more watchers yourself. 3750more watchers yourself.
1628.Sp 3751.Sp
1629If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and events 3752If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and the
1630is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for the given \f(CW\*(C`fd\*(C'\fR and 3753\&\f(CW\*(C`events\*(C'\fR argument is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for
1631\&\f(CW\*(C`events\*(C'\fR set will be craeted and started. 3754the given \f(CW\*(C`fd\*(C'\fR and \f(CW\*(C`events\*(C'\fR set will be created and started.
1632.Sp 3755.Sp
1633If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be 3756If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
1634started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and 3757started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
1635repeat = 0) will be started. While \f(CW0\fR is a valid timeout, it is of 3758repeat = 0) will be started. \f(CW0\fR is a valid timeout.
1636dubious value.
1637.Sp 3759.Sp
1638The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets 3760The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and is
1639passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of 3761passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
1640\&\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 3762\&\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
1641value passed to \f(CW\*(C`ev_once\*(C'\fR: 3763value passed to \f(CW\*(C`ev_once\*(C'\fR. Note that it is possible to receive \fIboth\fR
3764a timeout and an io event at the same time \- you probably should give io
3765events precedence.
3766.Sp
3767Example: wait up to ten seconds for data to appear on \s-1STDIN_FILENO.\s0
1642.Sp 3768.Sp
1643.Vb 7 3769.Vb 7
1644\& static void stdin_ready (int revents, void *arg) 3770\& static void stdin_ready (int revents, void *arg)
3771\& {
3772\& if (revents & EV_READ)
3773\& /* stdin might have data for us, joy! */;
3774\& else if (revents & EV_TIMER)
3775\& /* doh, nothing entered */;
3776\& }
3777\&
3778\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3779.Ve
3780.IP "ev_feed_fd_event (loop, int fd, int revents)" 4
3781.IX Item "ev_feed_fd_event (loop, int fd, int revents)"
3782Feed an event on the given fd, as if a file descriptor backend detected
3783the given events.
3784.IP "ev_feed_signal_event (loop, int signum)" 4
3785.IX Item "ev_feed_signal_event (loop, int signum)"
3786Feed an event as if the given signal occurred. See also \f(CW\*(C`ev_feed_signal\*(C'\fR,
3787which is async-safe.
3788.SH "COMMON OR USEFUL IDIOMS (OR BOTH)"
3789.IX Header "COMMON OR USEFUL IDIOMS (OR BOTH)"
3790This section explains some common idioms that are not immediately
3791obvious. Note that examples are sprinkled over the whole manual, and this
3792section only contains stuff that wouldn't fit anywhere else.
3793.SS "\s-1ASSOCIATING CUSTOM DATA WITH A WATCHER\s0"
3794.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
3795Each watcher has, by default, a \f(CW\*(C`void *data\*(C'\fR member that you can read
3796or modify at any time: libev will completely ignore it. This can be used
3797to associate arbitrary data with your watcher. If you need more data and
3798don't want to allocate memory separately and store a pointer to it in that
3799data member, you can also \*(L"subclass\*(R" the watcher type and provide your own
3800data:
3801.PP
3802.Vb 7
3803\& struct my_io
3804\& {
3805\& ev_io io;
3806\& int otherfd;
3807\& void *somedata;
3808\& struct whatever *mostinteresting;
3809\& };
3810\&
3811\& ...
3812\& struct my_io w;
3813\& ev_io_init (&w.io, my_cb, fd, EV_READ);
3814.Ve
3815.PP
3816And since your callback will be called with a pointer to the watcher, you
3817can cast it back to your own type:
3818.PP
3819.Vb 5
3820\& static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
3821\& {
3822\& struct my_io *w = (struct my_io *)w_;
3823\& ...
3824\& }
3825.Ve
3826.PP
3827More interesting and less C\-conformant ways of casting your callback
3828function type instead have been omitted.
3829.SS "\s-1BUILDING YOUR OWN COMPOSITE WATCHERS\s0"
3830.IX Subsection "BUILDING YOUR OWN COMPOSITE WATCHERS"
3831Another common scenario is to use some data structure with multiple
3832embedded watchers, in effect creating your own watcher that combines
3833multiple libev event sources into one \*(L"super-watcher\*(R":
3834.PP
3835.Vb 6
3836\& struct my_biggy
3837\& {
3838\& int some_data;
3839\& ev_timer t1;
3840\& ev_timer t2;
3841\& }
3842.Ve
3843.PP
3844In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more
3845complicated: Either you store the address of your \f(CW\*(C`my_biggy\*(C'\fR struct in
3846the \f(CW\*(C`data\*(C'\fR member of the watcher (for woozies or \*(C+ coders), or you need
3847to use some pointer arithmetic using \f(CW\*(C`offsetof\*(C'\fR inside your watchers (for
3848real programmers):
3849.PP
3850.Vb 1
3851\& #include <stddef.h>
3852\&
3853\& static void
3854\& t1_cb (EV_P_ ev_timer *w, int revents)
3855\& {
3856\& struct my_biggy big = (struct my_biggy *)
3857\& (((char *)w) \- offsetof (struct my_biggy, t1));
3858\& }
3859\&
3860\& static void
3861\& t2_cb (EV_P_ ev_timer *w, int revents)
3862\& {
3863\& struct my_biggy big = (struct my_biggy *)
3864\& (((char *)w) \- offsetof (struct my_biggy, t2));
3865\& }
3866.Ve
3867.SS "\s-1AVOIDING FINISHING BEFORE RETURNING\s0"
3868.IX Subsection "AVOIDING FINISHING BEFORE RETURNING"
3869Often you have structures like this in event-based programs:
3870.PP
3871.Vb 4
3872\& callback ()
1645\& { 3873\& {
1646\& if (revents & EV_TIMEOUT) 3874\& free (request);
1647\& /* doh, nothing entered */;
1648\& else if (revents & EV_READ)
1649\& /* stdin might have data for us, joy! */;
1650\& } 3875\& }
3876\&
3877\& request = start_new_request (..., callback);
1651.Ve 3878.Ve
1652.Sp 3879.PP
3880The intent is to start some \*(L"lengthy\*(R" operation. The \f(CW\*(C`request\*(C'\fR could be
3881used to cancel the operation, or do other things with it.
3882.PP
3883It's not uncommon to have code paths in \f(CW\*(C`start_new_request\*(C'\fR that
3884immediately invoke the callback, for example, to report errors. Or you add
3885some caching layer that finds that it can skip the lengthy aspects of the
3886operation and simply invoke the callback with the result.
3887.PP
3888The problem here is that this will happen \fIbefore\fR \f(CW\*(C`start_new_request\*(C'\fR
3889has returned, so \f(CW\*(C`request\*(C'\fR is not set.
3890.PP
3891Even if you pass the request by some safer means to the callback, you
3892might want to do something to the request after starting it, such as
3893canceling it, which probably isn't working so well when the callback has
3894already been invoked.
3895.PP
3896A common way around all these issues is to make sure that
3897\&\f(CW\*(C`start_new_request\*(C'\fR \fIalways\fR returns before the callback is invoked. If
3898\&\f(CW\*(C`start_new_request\*(C'\fR immediately knows the result, it can artificially
3899delay invoking the callback by using a \f(CW\*(C`prepare\*(C'\fR or \f(CW\*(C`idle\*(C'\fR watcher for
3900example, or more sneakily, by reusing an existing (stopped) watcher and
3901pushing it into the pending queue:
3902.PP
1653.Vb 1 3903.Vb 2
1654\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); 3904\& ev_set_cb (watcher, callback);
3905\& ev_feed_event (EV_A_ watcher, 0);
1655.Ve 3906.Ve
1656.IP "ev_feed_event (ev_loop *, watcher *, int revents)" 4 3907.PP
1657.IX Item "ev_feed_event (ev_loop *, watcher *, int revents)" 3908This way, \f(CW\*(C`start_new_request\*(C'\fR can safely return before the callback is
1658Feeds the given event set into the event loop, as if the specified event 3909invoked, while not delaying callback invocation too much.
1659had happened for the specified watcher (which must be a pointer to an 3910.SS "\s-1MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS\s0"
1660initialised but not necessarily started event watcher). 3911.IX Subsection "MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS"
1661.IP "ev_feed_fd_event (ev_loop *, int fd, int revents)" 4 3912Often (especially in \s-1GUI\s0 toolkits) there are places where you have
1662.IX Item "ev_feed_fd_event (ev_loop *, int fd, int revents)" 3913\&\fImodal\fR interaction, which is most easily implemented by recursively
1663Feed an event on the given fd, as if a file descriptor backend detected 3914invoking \f(CW\*(C`ev_run\*(C'\fR.
1664the given events it. 3915.PP
1665.IP "ev_feed_signal_event (ev_loop *loop, int signum)" 4 3916This brings the problem of exiting \- a callback might want to finish the
1666.IX Item "ev_feed_signal_event (ev_loop *loop, int signum)" 3917main \f(CW\*(C`ev_run\*(C'\fR call, but not the nested one (e.g. user clicked \*(L"Quit\*(R", but
1667Feed an event as if the given signal occured (\f(CW\*(C`loop\*(C'\fR must be the default 3918a modal \*(L"Are you sure?\*(R" dialog is still waiting), or just the nested one
1668loop!). 3919and not the main one (e.g. user clocked \*(L"Ok\*(R" in a modal dialog), or some
3920other combination: In these cases, a simple \f(CW\*(C`ev_break\*(C'\fR will not work.
3921.PP
3922The solution is to maintain \*(L"break this loop\*(R" variable for each \f(CW\*(C`ev_run\*(C'\fR
3923invocation, and use a loop around \f(CW\*(C`ev_run\*(C'\fR until the condition is
3924triggered, using \f(CW\*(C`EVRUN_ONCE\*(C'\fR:
3925.PP
3926.Vb 2
3927\& // main loop
3928\& int exit_main_loop = 0;
3929\&
3930\& while (!exit_main_loop)
3931\& ev_run (EV_DEFAULT_ EVRUN_ONCE);
3932\&
3933\& // in a modal watcher
3934\& int exit_nested_loop = 0;
3935\&
3936\& while (!exit_nested_loop)
3937\& ev_run (EV_A_ EVRUN_ONCE);
3938.Ve
3939.PP
3940To exit from any of these loops, just set the corresponding exit variable:
3941.PP
3942.Vb 2
3943\& // exit modal loop
3944\& exit_nested_loop = 1;
3945\&
3946\& // exit main program, after modal loop is finished
3947\& exit_main_loop = 1;
3948\&
3949\& // exit both
3950\& exit_main_loop = exit_nested_loop = 1;
3951.Ve
3952.SS "\s-1THREAD LOCKING EXAMPLE\s0"
3953.IX Subsection "THREAD LOCKING EXAMPLE"
3954Here is a fictitious example of how to run an event loop in a different
3955thread from where callbacks are being invoked and watchers are
3956created/added/removed.
3957.PP
3958For a real-world example, see the \f(CW\*(C`EV::Loop::Async\*(C'\fR perl module,
3959which uses exactly this technique (which is suited for many high-level
3960languages).
3961.PP
3962The example uses a pthread mutex to protect the loop data, a condition
3963variable to wait for callback invocations, an async watcher to notify the
3964event loop thread and an unspecified mechanism to wake up the main thread.
3965.PP
3966First, you need to associate some data with the event loop:
3967.PP
3968.Vb 6
3969\& typedef struct {
3970\& mutex_t lock; /* global loop lock */
3971\& ev_async async_w;
3972\& thread_t tid;
3973\& cond_t invoke_cv;
3974\& } userdata;
3975\&
3976\& void prepare_loop (EV_P)
3977\& {
3978\& // for simplicity, we use a static userdata struct.
3979\& static userdata u;
3980\&
3981\& ev_async_init (&u\->async_w, async_cb);
3982\& ev_async_start (EV_A_ &u\->async_w);
3983\&
3984\& pthread_mutex_init (&u\->lock, 0);
3985\& pthread_cond_init (&u\->invoke_cv, 0);
3986\&
3987\& // now associate this with the loop
3988\& ev_set_userdata (EV_A_ u);
3989\& ev_set_invoke_pending_cb (EV_A_ l_invoke);
3990\& ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
3991\&
3992\& // then create the thread running ev_run
3993\& pthread_create (&u\->tid, 0, l_run, EV_A);
3994\& }
3995.Ve
3996.PP
3997The callback for the \f(CW\*(C`ev_async\*(C'\fR watcher does nothing: the watcher is used
3998solely to wake up the event loop so it takes notice of any new watchers
3999that might have been added:
4000.PP
4001.Vb 5
4002\& static void
4003\& async_cb (EV_P_ ev_async *w, int revents)
4004\& {
4005\& // just used for the side effects
4006\& }
4007.Ve
4008.PP
4009The \f(CW\*(C`l_release\*(C'\fR and \f(CW\*(C`l_acquire\*(C'\fR callbacks simply unlock/lock the mutex
4010protecting the loop data, respectively.
4011.PP
4012.Vb 6
4013\& static void
4014\& l_release (EV_P)
4015\& {
4016\& userdata *u = ev_userdata (EV_A);
4017\& pthread_mutex_unlock (&u\->lock);
4018\& }
4019\&
4020\& static void
4021\& l_acquire (EV_P)
4022\& {
4023\& userdata *u = ev_userdata (EV_A);
4024\& pthread_mutex_lock (&u\->lock);
4025\& }
4026.Ve
4027.PP
4028The event loop thread first acquires the mutex, and then jumps straight
4029into \f(CW\*(C`ev_run\*(C'\fR:
4030.PP
4031.Vb 4
4032\& void *
4033\& l_run (void *thr_arg)
4034\& {
4035\& struct ev_loop *loop = (struct ev_loop *)thr_arg;
4036\&
4037\& l_acquire (EV_A);
4038\& pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4039\& ev_run (EV_A_ 0);
4040\& l_release (EV_A);
4041\&
4042\& return 0;
4043\& }
4044.Ve
4045.PP
4046Instead of invoking all pending watchers, the \f(CW\*(C`l_invoke\*(C'\fR callback will
4047signal the main thread via some unspecified mechanism (signals? pipe
4048writes? \f(CW\*(C`Async::Interrupt\*(C'\fR?) and then waits until all pending watchers
4049have been called (in a while loop because a) spurious wakeups are possible
4050and b) skipping inter-thread-communication when there are no pending
4051watchers is very beneficial):
4052.PP
4053.Vb 4
4054\& static void
4055\& l_invoke (EV_P)
4056\& {
4057\& userdata *u = ev_userdata (EV_A);
4058\&
4059\& while (ev_pending_count (EV_A))
4060\& {
4061\& wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4062\& pthread_cond_wait (&u\->invoke_cv, &u\->lock);
4063\& }
4064\& }
4065.Ve
4066.PP
4067Now, whenever the main thread gets told to invoke pending watchers, it
4068will grab the lock, call \f(CW\*(C`ev_invoke_pending\*(C'\fR and then signal the loop
4069thread to continue:
4070.PP
4071.Vb 4
4072\& static void
4073\& real_invoke_pending (EV_P)
4074\& {
4075\& userdata *u = ev_userdata (EV_A);
4076\&
4077\& pthread_mutex_lock (&u\->lock);
4078\& ev_invoke_pending (EV_A);
4079\& pthread_cond_signal (&u\->invoke_cv);
4080\& pthread_mutex_unlock (&u\->lock);
4081\& }
4082.Ve
4083.PP
4084Whenever you want to start/stop a watcher or do other modifications to an
4085event loop, you will now have to lock:
4086.PP
4087.Vb 2
4088\& ev_timer timeout_watcher;
4089\& userdata *u = ev_userdata (EV_A);
4090\&
4091\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4092\&
4093\& pthread_mutex_lock (&u\->lock);
4094\& ev_timer_start (EV_A_ &timeout_watcher);
4095\& ev_async_send (EV_A_ &u\->async_w);
4096\& pthread_mutex_unlock (&u\->lock);
4097.Ve
4098.PP
4099Note that sending the \f(CW\*(C`ev_async\*(C'\fR watcher is required because otherwise
4100an event loop currently blocking in the kernel will have no knowledge
4101about the newly added timer. By waking up the loop it will pick up any new
4102watchers in the next event loop iteration.
4103.SS "\s-1THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS\s0"
4104.IX Subsection "THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS"
4105While the overhead of a callback that e.g. schedules a thread is small, it
4106is still an overhead. If you embed libev, and your main usage is with some
4107kind of threads or coroutines, you might want to customise libev so that
4108doesn't need callbacks anymore.
4109.PP
4110Imagine you have coroutines that you can switch to using a function
4111\&\f(CW\*(C`switch_to (coro)\*(C'\fR, that libev runs in a coroutine called \f(CW\*(C`libev_coro\*(C'\fR
4112and that due to some magic, the currently active coroutine is stored in a
4113global called \f(CW\*(C`current_coro\*(C'\fR. Then you can build your own \*(L"wait for libev
4114event\*(R" primitive by changing \f(CW\*(C`EV_CB_DECLARE\*(C'\fR and \f(CW\*(C`EV_CB_INVOKE\*(C'\fR (note
4115the differing \f(CW\*(C`;\*(C'\fR conventions):
4116.PP
4117.Vb 2
4118\& #define EV_CB_DECLARE(type) struct my_coro *cb;
4119\& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb)
4120.Ve
4121.PP
4122That means instead of having a C callback function, you store the
4123coroutine to switch to in each watcher, and instead of having libev call
4124your callback, you instead have it switch to that coroutine.
4125.PP
4126A coroutine might now wait for an event with a function called
4127\&\f(CW\*(C`wait_for_event\*(C'\fR. (the watcher needs to be started, as always, but it doesn't
4128matter when, or whether the watcher is active or not when this function is
4129called):
4130.PP
4131.Vb 6
4132\& void
4133\& wait_for_event (ev_watcher *w)
4134\& {
4135\& ev_set_cb (w, current_coro);
4136\& switch_to (libev_coro);
4137\& }
4138.Ve
4139.PP
4140That basically suspends the coroutine inside \f(CW\*(C`wait_for_event\*(C'\fR and
4141continues the libev coroutine, which, when appropriate, switches back to
4142this or any other coroutine.
4143.PP
4144You can do similar tricks if you have, say, threads with an event queue \-
4145instead of storing a coroutine, you store the queue object and instead of
4146switching to a coroutine, you push the watcher onto the queue and notify
4147any waiters.
4148.PP
4149To embed libev, see \*(L"\s-1EMBEDDING\*(R"\s0, but in short, it's easiest to create two
4150files, \fImy_ev.h\fR and \fImy_ev.c\fR that include the respective libev files:
4151.PP
4152.Vb 4
4153\& // my_ev.h
4154\& #define EV_CB_DECLARE(type) struct my_coro *cb;
4155\& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb)
4156\& #include "../libev/ev.h"
4157\&
4158\& // my_ev.c
4159\& #define EV_H "my_ev.h"
4160\& #include "../libev/ev.c"
4161.Ve
4162.PP
4163And then use \fImy_ev.h\fR when you would normally use \fIev.h\fR, and compile
4164\&\fImy_ev.c\fR into your project. When properly specifying include paths, you
4165can even use \fIev.h\fR as header file name directly.
1669.SH "LIBEVENT EMULATION" 4166.SH "LIBEVENT EMULATION"
1670.IX Header "LIBEVENT EMULATION" 4167.IX Header "LIBEVENT EMULATION"
1671Libev offers a compatibility emulation layer for libevent. It cannot 4168Libev offers a compatibility emulation layer for libevent. It cannot
1672emulate the internals of libevent, so here are some usage hints: 4169emulate the internals of libevent, so here are some usage hints:
4170.IP "\(bu" 4
4171Only the libevent\-1.4.1\-beta \s-1API\s0 is being emulated.
4172.Sp
4173This was the newest libevent version available when libev was implemented,
4174and is still mostly unchanged in 2010.
4175.IP "\(bu" 4
1673.IP "* Use it by including <event.h>, as usual." 4 4176Use it by including <event.h>, as usual.
1674.IX Item "Use it by including <event.h>, as usual." 4177.IP "\(bu" 4
1675.PD 0 4178The following members are fully supported: ev_base, ev_callback,
1676.IP "* The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4 4179ev_arg, ev_fd, ev_res, ev_events.
1677.IX Item "The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4180.IP "\(bu" 4
1678.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 4181Avoid using ev_flags and the EVLIST_*\-macros, while it is
1679.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)." 4182maintained by libev, it does not work exactly the same way as in libevent (consider
1680.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 4183it a private \s-1API\s0).
1681.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." 4184.IP "\(bu" 4
4185Priorities are not currently supported. Initialising priorities
4186will fail and all watchers will have the same priority, even though there
4187is an ev_pri field.
4188.IP "\(bu" 4
4189In libevent, the last base created gets the signals, in libev, the
4190base that registered the signal gets the signals.
4191.IP "\(bu" 4
1682.IP "* Other members are not supported." 4 4192Other members are not supported.
1683.IX Item "Other members are not supported." 4193.IP "\(bu" 4
1684.IP "* The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need to use the libev header file and library." 4 4194The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need
1685.IX Item "The libev emulation is not ABI compatible to libevent, you need to use the libev header file and library." 4195to use the libev header file and library.
1686.PD
1687.SH "\*(C+ SUPPORT" 4196.SH "\*(C+ SUPPORT"
1688.IX Header " SUPPORT" 4197.IX Header " SUPPORT"
4198.SS "C \s-1API\s0"
4199.IX Subsection "C API"
4200The normal C \s-1API\s0 should work fine when used from \*(C+: both ev.h and the
4201libev sources can be compiled as \*(C+. Therefore, code that uses the C \s-1API\s0
4202will work fine.
4203.PP
4204Proper exception specifications might have to be added to callbacks passed
4205to libev: exceptions may be thrown only from watcher callbacks, all other
4206callbacks (allocator, syserr, loop acquire/release and periodic reschedule
4207callbacks) must not throw exceptions, and might need a \f(CW\*(C`noexcept\*(C'\fR
4208specification. If you have code that needs to be compiled as both C and
4209\&\*(C+ you can use the \f(CW\*(C`EV_NOEXCEPT\*(C'\fR macro for this:
4210.PP
4211.Vb 6
4212\& static void
4213\& fatal_error (const char *msg) EV_NOEXCEPT
4214\& {
4215\& perror (msg);
4216\& abort ();
4217\& }
4218\&
4219\& ...
4220\& ev_set_syserr_cb (fatal_error);
4221.Ve
4222.PP
4223The only \s-1API\s0 functions that can currently throw exceptions are \f(CW\*(C`ev_run\*(C'\fR,
4224\&\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
4225because it runs cleanup watchers).
4226.PP
4227Throwing exceptions in watcher callbacks is only supported if libev itself
4228is compiled with a \*(C+ compiler or your C and \*(C+ environments allow
4229throwing exceptions through C libraries (most do).
4230.SS "\*(C+ \s-1API\s0"
4231.IX Subsection " API"
1689Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow 4232Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
1690you to use some convinience methods to start/stop watchers and also change 4233you to use some convenience methods to start/stop watchers and also change
1691the callback model to a model using method callbacks on objects. 4234the callback model to a model using method callbacks on objects.
1692.PP 4235.PP
1693To use it, 4236To use it,
1694.PP 4237.PP
1695.Vb 1 4238.Vb 1
1696\& #include <ev++.h> 4239\& #include <ev++.h>
1697.Ve 4240.Ve
1698.PP 4241.PP
1699(it is not installed by default). This automatically includes \fIev.h\fR 4242This automatically includes \fIev.h\fR and puts all of its definitions (many
1700and puts all of its definitions (many of them macros) into the global 4243of them macros) into the global namespace. All \*(C+ specific things are
1701namespace. All \*(C+ specific things are put into the \f(CW\*(C`ev\*(C'\fR namespace. 4244put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding
4245options as \fIev.h\fR, most notably \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR.
1702.PP 4246.PP
1703It should support all the same embedding options as \fIev.h\fR, most notably 4247Care has been taken to keep the overhead low. The only data member the \*(C+
1704\&\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. 4248classes add (compared to plain C\-style watchers) is the event loop pointer
4249that the watcher is associated with (or no additional members at all if
4250you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
4251.PP
4252Currently, functions, static and non-static member functions and classes
4253with \f(CW\*(C`operator ()\*(C'\fR can be used as callbacks. Other types should be easy
4254to add as long as they only need one additional pointer for context. If
4255you need support for other types of functors please contact the author
4256(preferably after implementing it).
4257.PP
4258For all this to work, your \*(C+ compiler either has to use the same calling
4259conventions as your C compiler (for static member functions), or you have
4260to embed libev and compile libev itself as \*(C+.
1705.PP 4261.PP
1706Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace: 4262Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
1707.ie n .IP """ev::READ""\fR, \f(CW""ev::WRITE"" etc." 4 4263.ie n .IP """ev::READ"", ""ev::WRITE"" etc." 4
1708.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4 4264.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
1709.IX Item "ev::READ, ev::WRITE etc." 4265.IX Item "ev::READ, ev::WRITE etc."
1710These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc. 4266These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
1711macros from \fIev.h\fR. 4267macros from \fIev.h\fR.
1712.ie n .IP """ev::tstamp""\fR, \f(CW""ev::now""" 4 4268.ie n .IP """ev::tstamp"", ""ev::now""" 4
1713.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4 4269.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
1714.IX Item "ev::tstamp, ev::now" 4270.IX Item "ev::tstamp, ev::now"
1715Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix. 4271Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
1716.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 4272.ie n .IP """ev::io"", ""ev::timer"", ""ev::periodic"", ""ev::idle"", ""ev::sig"" etc." 4
1717.el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4 4273.el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
1718.IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc." 4274.IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
1719For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of 4275For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
1720the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR 4276the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
1721which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro 4277which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
1722defines by many implementations. 4278defined by many implementations.
1723.Sp 4279.Sp
1724All of those classes have these methods: 4280All of those classes have these methods:
1725.RS 4 4281.RS 4
1726.IP "ev::TYPE::TYPE (object *, object::method *)" 4 4282.IP "ev::TYPE::TYPE ()" 4
1727.IX Item "ev::TYPE::TYPE (object *, object::method *)" 4283.IX Item "ev::TYPE::TYPE ()"
1728.PD 0 4284.PD 0
1729.IP "ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)" 4 4285.IP "ev::TYPE::TYPE (loop)" 4
1730.IX Item "ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)" 4286.IX Item "ev::TYPE::TYPE (loop)"
1731.IP "ev::TYPE::~TYPE" 4 4287.IP "ev::TYPE::~TYPE" 4
1732.IX Item "ev::TYPE::~TYPE" 4288.IX Item "ev::TYPE::~TYPE"
1733.PD 4289.PD
1734The constructor takes a pointer to an object and a method pointer to 4290The constructor (optionally) takes an event loop to associate the watcher
1735the event handler callback to call in this class. The constructor calls 4291with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR.
1736\&\f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the \f(CW\*(C`set\*(C'\fR method 4292.Sp
1737before starting it. If you do not specify a loop then the constructor 4293The constructor calls \f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the
1738automatically associates the default loop with this watcher. 4294\&\f(CW\*(C`set\*(C'\fR method before starting it.
4295.Sp
4296It will not set a callback, however: You have to call the templated \f(CW\*(C`set\*(C'\fR
4297method to set a callback before you can start the watcher.
4298.Sp
4299(The reason why you have to use a method is a limitation in \*(C+ which does
4300not allow explicit template arguments for constructors).
1739.Sp 4301.Sp
1740The destructor automatically stops the watcher if it is active. 4302The destructor automatically stops the watcher if it is active.
4303.IP "w\->set<class, &class::method> (object *)" 4
4304.IX Item "w->set<class, &class::method> (object *)"
4305This method sets the callback method to call. The method has to have a
4306signature of \f(CW\*(C`void (*)(ev_TYPE &, int)\*(C'\fR, it receives the watcher as
4307first argument and the \f(CW\*(C`revents\*(C'\fR as second. The object must be given as
4308parameter and is stored in the \f(CW\*(C`data\*(C'\fR member of the watcher.
4309.Sp
4310This method synthesizes efficient thunking code to call your method from
4311the C callback that libev requires. If your compiler can inline your
4312callback (i.e. it is visible to it at the place of the \f(CW\*(C`set\*(C'\fR call and
4313your compiler is good :), then the method will be fully inlined into the
4314thunking function, making it as fast as a direct C callback.
4315.Sp
4316Example: simple class declaration and watcher initialisation
4317.Sp
4318.Vb 4
4319\& struct myclass
4320\& {
4321\& void io_cb (ev::io &w, int revents) { }
4322\& }
4323\&
4324\& myclass obj;
4325\& ev::io iow;
4326\& iow.set <myclass, &myclass::io_cb> (&obj);
4327.Ve
4328.IP "w\->set (object *)" 4
4329.IX Item "w->set (object *)"
4330This is a variation of a method callback \- leaving out the method to call
4331will default the method to \f(CW\*(C`operator ()\*(C'\fR, which makes it possible to use
4332functor objects without having to manually specify the \f(CW\*(C`operator ()\*(C'\fR all
4333the time. Incidentally, you can then also leave out the template argument
4334list.
4335.Sp
4336The \f(CW\*(C`operator ()\*(C'\fR method prototype must be \f(CW\*(C`void operator ()(watcher &w,
4337int revents)\*(C'\fR.
4338.Sp
4339See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
4340.Sp
4341Example: use a functor object as callback.
4342.Sp
4343.Vb 7
4344\& struct myfunctor
4345\& {
4346\& void operator() (ev::io &w, int revents)
4347\& {
4348\& ...
4349\& }
4350\& }
4351\&
4352\& myfunctor f;
4353\&
4354\& ev::io w;
4355\& w.set (&f);
4356.Ve
4357.IP "w\->set<function> (void *data = 0)" 4
4358.IX Item "w->set<function> (void *data = 0)"
4359Also sets a callback, but uses a static method or plain function as
4360callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
4361\&\f(CW\*(C`data\*(C'\fR member and is free for you to use.
4362.Sp
4363The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
4364.Sp
4365See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
4366.Sp
4367Example: Use a plain function as callback.
4368.Sp
4369.Vb 2
4370\& static void io_cb (ev::io &w, int revents) { }
4371\& iow.set <io_cb> ();
4372.Ve
1741.IP "w\->set (struct ev_loop *)" 4 4373.IP "w\->set (loop)" 4
1742.IX Item "w->set (struct ev_loop *)" 4374.IX Item "w->set (loop)"
1743Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only 4375Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
1744do this when the watcher is inactive (and not pending either). 4376do this when the watcher is inactive (and not pending either).
1745.IP "w\->set ([args])" 4 4377.IP "w\->set ([arguments])" 4
1746.IX Item "w->set ([args])" 4378.IX Item "w->set ([arguments])"
1747Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same args. Must be 4379Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR (except for \f(CW\*(C`ev::embed\*(C'\fR watchers>),
4380with the same arguments. Either this method or a suitable start method
1748called at least once. Unlike the C counterpart, an active watcher gets 4381must be called at least once. Unlike the C counterpart, an active watcher
1749automatically stopped and restarted. 4382gets automatically stopped and restarted when reconfiguring it with this
4383method.
4384.Sp
4385For \f(CW\*(C`ev::embed\*(C'\fR watchers this method is called \f(CW\*(C`set_embed\*(C'\fR, to avoid
4386clashing with the \f(CW\*(C`set (loop)\*(C'\fR method.
1750.IP "w\->start ()" 4 4387.IP "w\->start ()" 4
1751.IX Item "w->start ()" 4388.IX Item "w->start ()"
1752Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument as the 4389Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
1753constructor already takes the loop. 4390constructor already stores the event loop.
4391.IP "w\->start ([arguments])" 4
4392.IX Item "w->start ([arguments])"
4393Instead of calling \f(CW\*(C`set\*(C'\fR and \f(CW\*(C`start\*(C'\fR methods separately, it is often
4394convenient to wrap them in one call. Uses the same type of arguments as
4395the configure \f(CW\*(C`set\*(C'\fR method of the watcher.
1754.IP "w\->stop ()" 4 4396.IP "w\->stop ()" 4
1755.IX Item "w->stop ()" 4397.IX Item "w->stop ()"
1756Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument. 4398Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
1757.ie n .IP "w\->again () ""ev::timer""\fR, \f(CW""ev::periodic"" only" 4 4399.ie n .IP "w\->again () (""ev::timer"", ""ev::periodic"" only)" 4
1758.el .IP "w\->again () \f(CWev::timer\fR, \f(CWev::periodic\fR only" 4 4400.el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
1759.IX Item "w->again () ev::timer, ev::periodic only" 4401.IX Item "w->again () (ev::timer, ev::periodic only)"
1760For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding 4402For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
1761\&\f(CW\*(C`ev_TYPE_again\*(C'\fR function. 4403\&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
1762.ie n .IP "w\->sweep () ""ev::embed"" only" 4 4404.ie n .IP "w\->sweep () (""ev::embed"" only)" 4
1763.el .IP "w\->sweep () \f(CWev::embed\fR only" 4 4405.el .IP "w\->sweep () (\f(CWev::embed\fR only)" 4
1764.IX Item "w->sweep () ev::embed only" 4406.IX Item "w->sweep () (ev::embed only)"
1765Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR. 4407Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR.
1766.ie n .IP "w\->update () ""ev::stat"" only" 4 4408.ie n .IP "w\->update () (""ev::stat"" only)" 4
1767.el .IP "w\->update () \f(CWev::stat\fR only" 4 4409.el .IP "w\->update () (\f(CWev::stat\fR only)" 4
1768.IX Item "w->update () ev::stat only" 4410.IX Item "w->update () (ev::stat only)"
1769Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR. 4411Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
1770.RE 4412.RE
1771.RS 4 4413.RS 4
1772.RE 4414.RE
1773.PP 4415.PP
1774Example: Define a class with an \s-1IO\s0 and idle watcher, start one of them in 4416Example: Define a class with two I/O and idle watchers, start the I/O
1775the constructor. 4417watchers in the constructor.
1776.PP 4418.PP
1777.Vb 4 4419.Vb 5
1778\& class myclass 4420\& class myclass
1779\& { 4421\& {
1780\& ev_io io; void io_cb (ev::io &w, int revents); 4422\& ev::io io ; void io_cb (ev::io &w, int revents);
4423\& ev::io io2 ; void io2_cb (ev::io &w, int revents);
1781\& ev_idle idle void idle_cb (ev::idle &w, int revents); 4424\& ev::idle idle; void idle_cb (ev::idle &w, int revents);
4425\&
4426\& myclass (int fd)
4427\& {
4428\& io .set <myclass, &myclass::io_cb > (this);
4429\& io2 .set <myclass, &myclass::io2_cb > (this);
4430\& idle.set <myclass, &myclass::idle_cb> (this);
4431\&
4432\& io.set (fd, ev::WRITE); // configure the watcher
4433\& io.start (); // start it whenever convenient
4434\&
4435\& io2.start (fd, ev::READ); // set + start in one call
4436\& }
4437\& };
1782.Ve 4438.Ve
4439.SH "OTHER LANGUAGE BINDINGS"
4440.IX Header "OTHER LANGUAGE BINDINGS"
4441Libev does not offer other language bindings itself, but bindings for a
4442number of languages exist in the form of third-party packages. If you know
4443any interesting language binding in addition to the ones listed here, drop
4444me a note.
4445.IP "Perl" 4
4446.IX Item "Perl"
4447The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test
4448libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module,
4449there are additional modules that implement libev-compatible interfaces
4450to \f(CW\*(C`libadns\*(C'\fR (\f(CW\*(C`EV::ADNS\*(C'\fR, but \f(CW\*(C`AnyEvent::DNS\*(C'\fR is preferred nowadays),
4451\&\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
4452and \f(CW\*(C`EV::Glib\*(C'\fR).
4453.Sp
4454It can be found and installed via \s-1CPAN,\s0 its homepage is at
4455<http://software.schmorp.de/pkg/EV>.
4456.IP "Python" 4
4457.IX Item "Python"
4458Python bindings can be found at <http://code.google.com/p/pyev/>. It
4459seems to be quite complete and well-documented.
4460.IP "Ruby" 4
4461.IX Item "Ruby"
4462Tony Arcieri has written a ruby extension that offers access to a subset
4463of the libev \s-1API\s0 and adds file handle abstractions, asynchronous \s-1DNS\s0 and
4464more on top of it. It can be found via gem servers. Its homepage is at
4465<http://rev.rubyforge.org/>.
4466.Sp
4467Roger Pack reports that using the link order \f(CW\*(C`\-lws2_32 \-lmsvcrt\-ruby\-190\*(C'\fR
4468makes rev work even on mingw.
4469.IP "Haskell" 4
4470.IX Item "Haskell"
4471A haskell binding to libev is available at
4472<http://hackage.haskell.org/cgi\-bin/hackage\-scripts/package/hlibev>.
4473.IP "D" 4
4474.IX Item "D"
4475Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
4476be found at <http://www.llucax.com.ar/proj/ev.d/index.html>.
4477.IP "Ocaml" 4
4478.IX Item "Ocaml"
4479Erkki Seppala has written Ocaml bindings for libev, to be found at
4480<http://modeemi.cs.tut.fi/~flux/software/ocaml\-ev/>.
4481.IP "Lua" 4
4482.IX Item "Lua"
4483Brian Maher has written a partial interface to libev for lua (at the
4484time of this writing, only \f(CW\*(C`ev_io\*(C'\fR and \f(CW\*(C`ev_timer\*(C'\fR), to be found at
4485<http://github.com/brimworks/lua\-ev>.
4486.IP "Javascript" 4
4487.IX Item "Javascript"
4488Node.js (<http://nodejs.org>) uses libev as the underlying event library.
4489.IP "Others" 4
4490.IX Item "Others"
4491There are others, and I stopped counting.
4492.SH "MACRO MAGIC"
4493.IX Header "MACRO MAGIC"
4494Libev can be compiled with a variety of options, the most fundamental
4495of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most)
4496functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
1783.PP 4497.PP
4498To make it easier to write programs that cope with either variant, the
4499following macros are defined:
4500.ie n .IP """EV_A"", ""EV_A_""" 4
4501.el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
4502.IX Item "EV_A, EV_A_"
4503This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
4504loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
4505\&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
4506.Sp
4507.Vb 3
4508\& ev_unref (EV_A);
4509\& ev_timer_add (EV_A_ watcher);
4510\& ev_run (EV_A_ 0);
4511.Ve
4512.Sp
4513It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
4514which is often provided by the following macro.
4515.ie n .IP """EV_P"", ""EV_P_""" 4
4516.el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
4517.IX Item "EV_P, EV_P_"
4518This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
4519loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
4520\&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
4521.Sp
1784.Vb 2 4522.Vb 2
1785\& myclass (); 4523\& // this is how ev_unref is being declared
1786\& } 4524\& static void ev_unref (EV_P);
4525\&
4526\& // this is how you can declare your typical callback
4527\& static void cb (EV_P_ ev_timer *w, int revents)
1787.Ve 4528.Ve
4529.Sp
4530It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
4531suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
4532.ie n .IP """EV_DEFAULT"", ""EV_DEFAULT_""" 4
4533.el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
4534.IX Item "EV_DEFAULT, EV_DEFAULT_"
4535Similar to the other two macros, this gives you the value of the default
4536loop, if multiple loops are supported (\*(L"ev loop default\*(R"). The default loop
4537will be initialised if it isn't already initialised.
4538.Sp
4539For non-multiplicity builds, these macros do nothing, so you always have
4540to initialise the loop somewhere.
4541.ie n .IP """EV_DEFAULT_UC"", ""EV_DEFAULT_UC_""" 4
4542.el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
4543.IX Item "EV_DEFAULT_UC, EV_DEFAULT_UC_"
4544Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the
4545default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour
4546is undefined when the default loop has not been initialised by a previous
4547execution of \f(CW\*(C`EV_DEFAULT\*(C'\fR, \f(CW\*(C`EV_DEFAULT_\*(C'\fR or \f(CW\*(C`ev_default_init (...)\*(C'\fR.
4548.Sp
4549It is often prudent to use \f(CW\*(C`EV_DEFAULT\*(C'\fR when initialising the first
4550watcher in a function but use \f(CW\*(C`EV_DEFAULT_UC\*(C'\fR afterwards.
1788.PP 4551.PP
4552Example: Declare and initialise a check watcher, utilising the above
4553macros so it will work regardless of whether multiple loops are supported
4554or not.
4555.PP
1789.Vb 6 4556.Vb 5
1790\& myclass::myclass (int fd) 4557\& static void
1791\& : io (this, &myclass::io_cb), 4558\& check_cb (EV_P_ ev_timer *w, int revents)
1792\& idle (this, &myclass::idle_cb)
1793\& { 4559\& {
1794\& io.start (fd, ev::READ); 4560\& ev_check_stop (EV_A_ w);
1795\& } 4561\& }
4562\&
4563\& ev_check check;
4564\& ev_check_init (&check, check_cb);
4565\& ev_check_start (EV_DEFAULT_ &check);
4566\& ev_run (EV_DEFAULT_ 0);
1796.Ve 4567.Ve
1797.SH "EMBEDDING" 4568.SH "EMBEDDING"
1798.IX Header "EMBEDDING" 4569.IX Header "EMBEDDING"
1799Libev can (and often is) directly embedded into host 4570Libev can (and often is) directly embedded into host
1800applications. Examples of applications that embed it include the Deliantra 4571applications. Examples of applications that embed it include the Deliantra
1801Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe) 4572Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
1802and rxvt\-unicode. 4573and rxvt-unicode.
1803.PP 4574.PP
1804The goal is to enable you to just copy the neecssary files into your 4575The goal is to enable you to just copy the necessary files into your
1805source directory without having to change even a single line in them, so 4576source directory without having to change even a single line in them, so
1806you can easily upgrade by simply copying (or having a checked-out copy of 4577you can easily upgrade by simply copying (or having a checked-out copy of
1807libev somewhere in your source tree). 4578libev somewhere in your source tree).
1808.Sh "\s-1FILESETS\s0" 4579.SS "\s-1FILESETS\s0"
1809.IX Subsection "FILESETS" 4580.IX Subsection "FILESETS"
1810Depending on what features you need you need to include one or more sets of files 4581Depending on what features you need you need to include one or more sets of files
1811in your app. 4582in your application.
1812.PP 4583.PP
1813\fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR 4584\fI\s-1CORE EVENT LOOP\s0\fR
1814.IX Subsection "CORE EVENT LOOP" 4585.IX Subsection "CORE EVENT LOOP"
1815.PP 4586.PP
1816To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual 4587To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
1817configuration (no autoconf): 4588configuration (no autoconf):
1818.PP 4589.PP
1819.Vb 2 4590.Vb 2
1820\& #define EV_STANDALONE 1 4591\& #define EV_STANDALONE 1
1821\& #include "ev.c" 4592\& #include "ev.c"
1822.Ve 4593.Ve
1823.PP 4594.PP
1824This will automatically include \fIev.h\fR, too, and should be done in a 4595This will automatically include \fIev.h\fR, too, and should be done in a
1825single C source file only to provide the function implementations. To use 4596single C source file only to provide the function implementations. To use
1826it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best 4597it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best
1827done by writing a wrapper around \fIev.h\fR that you can include instead and 4598done by writing a wrapper around \fIev.h\fR that you can include instead and
1828where you can put other configuration options): 4599where you can put other configuration options):
1829.PP 4600.PP
1830.Vb 2 4601.Vb 2
1831\& #define EV_STANDALONE 1 4602\& #define EV_STANDALONE 1
1832\& #include "ev.h" 4603\& #include "ev.h"
1833.Ve 4604.Ve
1834.PP 4605.PP
1835Both header files and implementation files can be compiled with a \*(C+ 4606Both header files and implementation files can be compiled with a \*(C+
1836compiler (at least, thats a stated goal, and breakage will be treated 4607compiler (at least, that's a stated goal, and breakage will be treated
1837as a bug). 4608as a bug).
1838.PP 4609.PP
1839You need the following files in your source tree, or in a directory 4610You need the following files in your source tree, or in a directory
1840in your include path (e.g. in libev/ when using \-Ilibev): 4611in your include path (e.g. in libev/ when using \-Ilibev):
1841.PP 4612.PP
1842.Vb 4 4613.Vb 4
1843\& ev.h 4614\& ev.h
1844\& ev.c 4615\& ev.c
1845\& ev_vars.h 4616\& ev_vars.h
1846\& ev_wrap.h 4617\& ev_wrap.h
1847.Ve 4618\&
1848.PP
1849.Vb 1
1850\& ev_win32.c required on win32 platforms only 4619\& ev_win32.c required on win32 platforms only
1851.Ve 4620\&
1852.PP
1853.Vb 5
1854\& ev_select.c only when select backend is enabled (which is by default) 4621\& ev_select.c only when select backend is enabled
1855\& ev_poll.c only when poll backend is enabled (disabled by default) 4622\& ev_poll.c only when poll backend is enabled
1856\& ev_epoll.c only when the epoll backend is enabled (disabled by default) 4623\& ev_epoll.c only when the epoll backend is enabled
4624\& ev_linuxaio.c only when the linux aio backend is enabled
1857\& ev_kqueue.c only when the kqueue backend is enabled (disabled by default) 4625\& ev_kqueue.c only when the kqueue backend is enabled
1858\& ev_port.c only when the solaris port backend is enabled (disabled by default) 4626\& ev_port.c only when the solaris port backend is enabled
1859.Ve 4627.Ve
1860.PP 4628.PP
1861\&\fIev.c\fR includes the backend files directly when enabled, so you only need 4629\&\fIev.c\fR includes the backend files directly when enabled, so you only need
1862to compile this single file. 4630to compile this single file.
1863.PP 4631.PP
1864\fI\s-1LIBEVENT\s0 \s-1COMPATIBILITY\s0 \s-1API\s0\fR 4632\fI\s-1LIBEVENT COMPATIBILITY API\s0\fR
1865.IX Subsection "LIBEVENT COMPATIBILITY API" 4633.IX Subsection "LIBEVENT COMPATIBILITY API"
1866.PP 4634.PP
1867To include the libevent compatibility \s-1API\s0, also include: 4635To include the libevent compatibility \s-1API,\s0 also include:
1868.PP 4636.PP
1869.Vb 1 4637.Vb 1
1870\& #include "event.c" 4638\& #include "event.c"
1871.Ve 4639.Ve
1872.PP 4640.PP
1873in the file including \fIev.c\fR, and: 4641in the file including \fIev.c\fR, and:
1874.PP 4642.PP
1875.Vb 1 4643.Vb 1
1876\& #include "event.h" 4644\& #include "event.h"
1877.Ve 4645.Ve
1878.PP 4646.PP
1879in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR. 4647in the files that want to use the libevent \s-1API.\s0 This also includes \fIev.h\fR.
1880.PP 4648.PP
1881You need the following additional files for this: 4649You need the following additional files for this:
1882.PP 4650.PP
1883.Vb 2 4651.Vb 2
1884\& event.h 4652\& event.h
1885\& event.c 4653\& event.c
1886.Ve 4654.Ve
1887.PP 4655.PP
1888\fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR 4656\fI\s-1AUTOCONF SUPPORT\s0\fR
1889.IX Subsection "AUTOCONF SUPPORT" 4657.IX Subsection "AUTOCONF SUPPORT"
1890.PP 4658.PP
1891Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your config in 4659Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your configuration in
1892whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your 4660whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
1893\&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then 4661\&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then
1894include \fIconfig.h\fR and configure itself accordingly. 4662include \fIconfig.h\fR and configure itself accordingly.
1895.PP 4663.PP
1896For this of course you need the m4 file: 4664For this of course you need the m4 file:
1897.PP 4665.PP
1898.Vb 1 4666.Vb 1
1899\& libev.m4 4667\& libev.m4
1900.Ve 4668.Ve
1901.Sh "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0" 4669.SS "\s-1PREPROCESSOR SYMBOLS/MACROS\s0"
1902.IX Subsection "PREPROCESSOR SYMBOLS/MACROS" 4670.IX Subsection "PREPROCESSOR SYMBOLS/MACROS"
1903Libev can be configured via a variety of preprocessor symbols you have to define 4671Libev can be configured via a variety of preprocessor symbols you have to
1904before including any of its files. The default is not to build for multiplicity 4672define before including (or compiling) any of its files. The default in
1905and only include the select backend. 4673the absence of autoconf is documented for every option.
4674.PP
4675Symbols marked with \*(L"(h)\*(R" do not change the \s-1ABI,\s0 and can have different
4676values when compiling libev vs. including \fIev.h\fR, so it is permissible
4677to redefine them before including \fIev.h\fR without breaking compatibility
4678to a compiled library. All other symbols change the \s-1ABI,\s0 which means all
4679users of libev and the libev code itself must be compiled with compatible
4680settings.
4681.IP "\s-1EV_COMPAT3\s0 (h)" 4
4682.IX Item "EV_COMPAT3 (h)"
4683Backwards compatibility is a major concern for libev. This is why this
4684release of libev comes with wrappers for the functions and symbols that
4685have been renamed between libev version 3 and 4.
4686.Sp
4687You can disable these wrappers (to test compatibility with future
4688versions) by defining \f(CW\*(C`EV_COMPAT3\*(C'\fR to \f(CW0\fR when compiling your
4689sources. This has the additional advantage that you can drop the \f(CW\*(C`struct\*(C'\fR
4690from \f(CW\*(C`struct ev_loop\*(C'\fR declarations, as libev will provide an \f(CW\*(C`ev_loop\*(C'\fR
4691typedef in that case.
4692.Sp
4693In some future version, the default for \f(CW\*(C`EV_COMPAT3\*(C'\fR will become \f(CW0\fR,
4694and in some even more future version the compatibility code will be
4695removed completely.
1906.IP "\s-1EV_STANDALONE\s0" 4 4696.IP "\s-1EV_STANDALONE\s0 (h)" 4
1907.IX Item "EV_STANDALONE" 4697.IX Item "EV_STANDALONE (h)"
1908Must always be \f(CW1\fR if you do not use autoconf configuration, which 4698Must always be \f(CW1\fR if you do not use autoconf configuration, which
1909keeps libev from including \fIconfig.h\fR, and it also defines dummy 4699keeps libev from including \fIconfig.h\fR, and it also defines dummy
1910implementations for some libevent functions (such as logging, which is not 4700implementations for some libevent functions (such as logging, which is not
1911supported). It will also not define any of the structs usually found in 4701supported). It will also not define any of the structs usually found in
1912\&\fIevent.h\fR that are not directly supported by the libev core alone. 4702\&\fIevent.h\fR that are not directly supported by the libev core alone.
4703.Sp
4704In standalone mode, libev will still try to automatically deduce the
4705configuration, but has to be more conservative.
4706.IP "\s-1EV_USE_FLOOR\s0" 4
4707.IX Item "EV_USE_FLOOR"
4708If defined to be \f(CW1\fR, libev will use the \f(CW\*(C`floor ()\*(C'\fR function for its
4709periodic reschedule calculations, otherwise libev will fall back on a
4710portable (slower) implementation. If you enable this, you usually have to
4711link against libm or something equivalent. Enabling this when the \f(CW\*(C`floor\*(C'\fR
4712function is not available will fail, so the safe default is to not enable
4713this.
1913.IP "\s-1EV_USE_MONOTONIC\s0" 4 4714.IP "\s-1EV_USE_MONOTONIC\s0" 4
1914.IX Item "EV_USE_MONOTONIC" 4715.IX Item "EV_USE_MONOTONIC"
1915If defined to be \f(CW1\fR, libev will try to detect the availability of the 4716If defined to be \f(CW1\fR, libev will try to detect the availability of the
1916monotonic clock option at both compiletime and runtime. Otherwise no use 4717monotonic clock option at both compile time and runtime. Otherwise no
1917of the monotonic clock option will be attempted. If you enable this, you 4718use of the monotonic clock option will be attempted. If you enable this,
1918usually have to link against librt or something similar. Enabling it when 4719you usually have to link against librt or something similar. Enabling it
1919the functionality isn't available is safe, though, althoguh you have 4720when the functionality isn't available is safe, though, although you have
1920to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR 4721to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
1921function is hiding in (often \fI\-lrt\fR). 4722function is hiding in (often \fI\-lrt\fR). See also \f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
1922.IP "\s-1EV_USE_REALTIME\s0" 4 4723.IP "\s-1EV_USE_REALTIME\s0" 4
1923.IX Item "EV_USE_REALTIME" 4724.IX Item "EV_USE_REALTIME"
1924If defined to be \f(CW1\fR, libev will try to detect the availability of the 4725If defined to be \f(CW1\fR, libev will try to detect the availability of the
1925realtime clock option at compiletime (and assume its availability at 4726real-time clock option at compile time (and assume its availability
1926runtime if successful). Otherwise no use of the realtime clock option will 4727at runtime if successful). Otherwise no use of the real-time clock
1927be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR by \f(CW\*(C`clock_get 4728option will be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR
1928(CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect correctness. See tzhe note about libraries 4729by \f(CW\*(C`clock_get (CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect
1929in the description of \f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. 4730correctness. See the note about libraries in the description of
4731\&\f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. Defaults to the opposite value of
4732\&\f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
4733.IP "\s-1EV_USE_CLOCK_SYSCALL\s0" 4
4734.IX Item "EV_USE_CLOCK_SYSCALL"
4735If defined to be \f(CW1\fR, libev will try to use a direct syscall instead
4736of calling the system-provided \f(CW\*(C`clock_gettime\*(C'\fR function. This option
4737exists 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
4738unconditionally pulls in \f(CW\*(C`libpthread\*(C'\fR, slowing down single-threaded
4739programs needlessly. Using a direct syscall is slightly slower (in
4740theory), because no optimised vdso implementation can be used, but avoids
4741the pthread dependency. Defaults to \f(CW1\fR on GNU/Linux with glibc 2.x or
4742higher, as it simplifies linking (no need for \f(CW\*(C`\-lrt\*(C'\fR).
4743.IP "\s-1EV_USE_NANOSLEEP\s0" 4
4744.IX Item "EV_USE_NANOSLEEP"
4745If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available
4746and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR.
4747.IP "\s-1EV_USE_EVENTFD\s0" 4
4748.IX Item "EV_USE_EVENTFD"
4749If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
4750available and will probe for kernel support at runtime. This will improve
4751\&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
4752If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
47532.7 or newer, otherwise disabled.
1930.IP "\s-1EV_USE_SELECT\s0" 4 4754.IP "\s-1EV_USE_SELECT\s0" 4
1931.IX Item "EV_USE_SELECT" 4755.IX Item "EV_USE_SELECT"
1932If undefined or defined to be \f(CW1\fR, libev will compile in support for the 4756If undefined or defined to be \f(CW1\fR, libev will compile in support for the
1933\&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at autodetection will be done: if no 4757\&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at auto-detection will be done: if no
1934other method takes over, select will be it. Otherwise the select backend 4758other method takes over, select will be it. Otherwise the select backend
1935will not be compiled in. 4759will not be compiled in.
1936.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4 4760.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
1937.IX Item "EV_SELECT_USE_FD_SET" 4761.IX Item "EV_SELECT_USE_FD_SET"
1938If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR 4762If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR
1939structure. This is useful if libev doesn't compile due to a missing 4763structure. This is useful if libev doesn't compile due to a missing
1940\&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it misguesses the bitset layout on 4764\&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it mis-guesses the bitset layout
1941exotic systems. This usually limits the range of file descriptors to some 4765on exotic systems. This usually limits the range of file descriptors to
1942low limit such as 1024 or might have other limitations (winsocket only 4766some low limit such as 1024 or might have other limitations (winsocket
1943allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation, might 4767only allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation,
1944influence the size of the \f(CW\*(C`fd_set\*(C'\fR used. 4768configures the maximum size of the \f(CW\*(C`fd_set\*(C'\fR.
1945.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4 4769.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
1946.IX Item "EV_SELECT_IS_WINSOCKET" 4770.IX Item "EV_SELECT_IS_WINSOCKET"
1947When defined to \f(CW1\fR, the select backend will assume that 4771When defined to \f(CW1\fR, the select backend will assume that
1948select/socket/connect etc. don't understand file descriptors but 4772select/socket/connect etc. don't understand file descriptors but
1949wants osf handles on win32 (this is the case when the select to 4773wants osf handles on win32 (this is the case when the select to
1950be used is the winsock select). This means that it will call 4774be used is the winsock select). This means that it will call
1951\&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise, 4775\&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
1952it is assumed that all these functions actually work on fds, even 4776it is assumed that all these functions actually work on fds, even
1953on win32. Should not be defined on non\-win32 platforms. 4777on win32. Should not be defined on non\-win32 platforms.
4778.IP "\s-1EV_FD_TO_WIN32_HANDLE\s0(fd)" 4
4779.IX Item "EV_FD_TO_WIN32_HANDLE(fd)"
4780If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map
4781file descriptors to socket handles. When not defining this symbol (the
4782default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually
4783correct. In some cases, programs use their own file descriptor management,
4784in which case they can provide this function to map fds to socket handles.
4785.IP "\s-1EV_WIN32_HANDLE_TO_FD\s0(handle)" 4
4786.IX Item "EV_WIN32_HANDLE_TO_FD(handle)"
4787If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR then libev maps handles to file descriptors
4788using the standard \f(CW\*(C`_open_osfhandle\*(C'\fR function. For programs implementing
4789their own fd to handle mapping, overwriting this function makes it easier
4790to do so. This can be done by defining this macro to an appropriate value.
4791.IP "\s-1EV_WIN32_CLOSE_FD\s0(fd)" 4
4792.IX Item "EV_WIN32_CLOSE_FD(fd)"
4793If programs implement their own fd to handle mapping on win32, then this
4794macro can be used to override the \f(CW\*(C`close\*(C'\fR function, useful to unregister
4795file descriptors again. Note that the replacement function has to close
4796the underlying \s-1OS\s0 handle.
4797.IP "\s-1EV_USE_WSASOCKET\s0" 4
4798.IX Item "EV_USE_WSASOCKET"
4799If defined to be \f(CW1\fR, libev will use \f(CW\*(C`WSASocket\*(C'\fR to create its internal
4800communication socket, which works better in some environments. Otherwise,
4801the normal \f(CW\*(C`socket\*(C'\fR function will be used, which works better in other
4802environments.
1954.IP "\s-1EV_USE_POLL\s0" 4 4803.IP "\s-1EV_USE_POLL\s0" 4
1955.IX Item "EV_USE_POLL" 4804.IX Item "EV_USE_POLL"
1956If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2) 4805If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2)
1957backend. Otherwise it will be enabled on non\-win32 platforms. It 4806backend. Otherwise it will be enabled on non\-win32 platforms. It
1958takes precedence over select. 4807takes precedence over select.
1959.IP "\s-1EV_USE_EPOLL\s0" 4 4808.IP "\s-1EV_USE_EPOLL\s0" 4
1960.IX Item "EV_USE_EPOLL" 4809.IX Item "EV_USE_EPOLL"
1961If defined to be \f(CW1\fR, libev will compile in support for the Linux 4810If defined to be \f(CW1\fR, libev will compile in support for the Linux
1962\&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime, 4811\&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime,
1963otherwise another method will be used as fallback. This is the 4812otherwise another method will be used as fallback. This is the preferred
1964preferred backend for GNU/Linux systems. 4813backend for GNU/Linux systems. If undefined, it will be enabled if the
4814headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4815.IP "\s-1EV_USE_LINUXAIO\s0" 4
4816.IX Item "EV_USE_LINUXAIO"
4817If defined to be \f(CW1\fR, libev will compile in support for the Linux
4818aio backend. Due to it's currenbt limitations it has to be requested
4819explicitly. If undefined, it will be enabled on linux, otherwise
4820disabled.
1965.IP "\s-1EV_USE_KQUEUE\s0" 4 4821.IP "\s-1EV_USE_KQUEUE\s0" 4
1966.IX Item "EV_USE_KQUEUE" 4822.IX Item "EV_USE_KQUEUE"
1967If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style 4823If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
1968\&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime, 4824\&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime,
1969otherwise another method will be used as fallback. This is the preferred 4825otherwise another method will be used as fallback. This is the preferred
… …
197910 port style backend. Its availability will be detected at runtime, 483510 port style backend. Its availability will be detected at runtime,
1980otherwise another method will be used as fallback. This is the preferred 4836otherwise another method will be used as fallback. This is the preferred
1981backend for Solaris 10 systems. 4837backend for Solaris 10 systems.
1982.IP "\s-1EV_USE_DEVPOLL\s0" 4 4838.IP "\s-1EV_USE_DEVPOLL\s0" 4
1983.IX Item "EV_USE_DEVPOLL" 4839.IX Item "EV_USE_DEVPOLL"
1984reserved for future expansion, works like the \s-1USE\s0 symbols above. 4840Reserved for future expansion, works like the \s-1USE\s0 symbols above.
4841.IP "\s-1EV_USE_INOTIFY\s0" 4
4842.IX Item "EV_USE_INOTIFY"
4843If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
4844interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
4845be detected at runtime. If undefined, it will be enabled if the headers
4846indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4847.IP "\s-1EV_NO_SMP\s0" 4
4848.IX Item "EV_NO_SMP"
4849If defined to be \f(CW1\fR, libev will assume that memory is always coherent
4850between threads, that is, threads can be used, but threads never run on
4851different cpus (or different cpu cores). This reduces dependencies
4852and makes libev faster.
4853.IP "\s-1EV_NO_THREADS\s0" 4
4854.IX Item "EV_NO_THREADS"
4855If defined to be \f(CW1\fR, libev will assume that it will never be called from
4856different threads (that includes signal handlers), which is a stronger
4857assumption than \f(CW\*(C`EV_NO_SMP\*(C'\fR, above. This reduces dependencies and makes
4858libev faster.
4859.IP "\s-1EV_ATOMIC_T\s0" 4
4860.IX Item "EV_ATOMIC_T"
4861Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
4862access is atomic with respect to other threads or signal contexts. No
4863such type is easily found in the C language, so you can provide your own
4864type that you know is safe for your purposes. It is used both for signal
4865handler \*(L"locking\*(R" as well as for signal and thread safety in \f(CW\*(C`ev_async\*(C'\fR
4866watchers.
4867.Sp
4868In the absence of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR
4869(from \fIsignal.h\fR), which is usually good enough on most platforms.
1985.IP "\s-1EV_H\s0" 4 4870.IP "\s-1EV_H\s0 (h)" 4
1986.IX Item "EV_H" 4871.IX Item "EV_H (h)"
1987The name of the \fIev.h\fR header file used to include it. The default if 4872The name of the \fIev.h\fR header file used to include it. The default if
1988undefined is \f(CW\*(C`<ev.h>\*(C'\fR in \fIevent.h\fR and \f(CW"ev.h"\fR in \fIev.c\fR. This 4873undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be
1989can be used to virtually rename the \fIev.h\fR header file in case of conflicts. 4874used to virtually rename the \fIev.h\fR header file in case of conflicts.
1990.IP "\s-1EV_CONFIG_H\s0" 4 4875.IP "\s-1EV_CONFIG_H\s0 (h)" 4
1991.IX Item "EV_CONFIG_H" 4876.IX Item "EV_CONFIG_H (h)"
1992If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override 4877If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
1993\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to 4878\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
1994\&\f(CW\*(C`EV_H\*(C'\fR, above. 4879\&\f(CW\*(C`EV_H\*(C'\fR, above.
1995.IP "\s-1EV_EVENT_H\s0" 4 4880.IP "\s-1EV_EVENT_H\s0 (h)" 4
1996.IX Item "EV_EVENT_H" 4881.IX Item "EV_EVENT_H (h)"
1997Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea 4882Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea
1998of how the \fIevent.h\fR header can be found. 4883of how the \fIevent.h\fR header can be found, the default is \f(CW"event.h"\fR.
1999.IP "\s-1EV_PROTOTYPES\s0" 4 4884.IP "\s-1EV_PROTOTYPES\s0 (h)" 4
2000.IX Item "EV_PROTOTYPES" 4885.IX Item "EV_PROTOTYPES (h)"
2001If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function 4886If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
2002prototypes, but still define all the structs and other symbols. This is 4887prototypes, but still define all the structs and other symbols. This is
2003occasionally useful if you want to provide your own wrapper functions 4888occasionally useful if you want to provide your own wrapper functions
2004around libev functions. 4889around libev functions.
2005.IP "\s-1EV_MULTIPLICITY\s0" 4 4890.IP "\s-1EV_MULTIPLICITY\s0" 4
… …
2007If undefined or defined to \f(CW1\fR, then all event-loop-specific functions 4892If undefined or defined to \f(CW1\fR, then all event-loop-specific functions
2008will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create 4893will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create
2009additional independent event loops. Otherwise there will be no support 4894additional independent event loops. Otherwise there will be no support
2010for multiple event loops and there is no first event loop pointer 4895for multiple event loops and there is no first event loop pointer
2011argument. Instead, all functions act on the single default loop. 4896argument. Instead, all functions act on the single default loop.
2012.IP "\s-1EV_PERIODIC_ENABLE\s0" 4 4897.Sp
2013.IX Item "EV_PERIODIC_ENABLE" 4898Note that \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR will no longer provide a
2014If undefined or defined to be \f(CW1\fR, then periodic timers are supported. If 4899default loop when multiplicity is switched off \- you always have to
2015defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of 4900initialise the loop manually in this case.
2016code.
2017.IP "\s-1EV_EMBED_ENABLE\s0" 4
2018.IX Item "EV_EMBED_ENABLE"
2019If undefined or defined to be \f(CW1\fR, then embed watchers are supported. If
2020defined to be \f(CW0\fR, then they are not.
2021.IP "\s-1EV_STAT_ENABLE\s0" 4
2022.IX Item "EV_STAT_ENABLE"
2023If undefined or defined to be \f(CW1\fR, then stat watchers are supported. If
2024defined to be \f(CW0\fR, then they are not.
2025.IP "\s-1EV_MINIMAL\s0" 4 4901.IP "\s-1EV_MINPRI\s0" 4
2026.IX Item "EV_MINIMAL" 4902.IX Item "EV_MINPRI"
4903.PD 0
4904.IP "\s-1EV_MAXPRI\s0" 4
4905.IX Item "EV_MAXPRI"
4906.PD
4907The range of allowed priorities. \f(CW\*(C`EV_MINPRI\*(C'\fR must be smaller or equal to
4908\&\f(CW\*(C`EV_MAXPRI\*(C'\fR, but otherwise there are no non-obvious limitations. You can
4909provide for more priorities by overriding those symbols (usually defined
4910to be \f(CW\*(C`\-2\*(C'\fR and \f(CW2\fR, respectively).
4911.Sp
4912When doing priority-based operations, libev usually has to linearly search
4913all the priorities, so having many of them (hundreds) uses a lot of space
4914and time, so using the defaults of five priorities (\-2 .. +2) is usually
4915fine.
4916.Sp
4917If your embedding application does not need any priorities, defining these
4918both to \f(CW0\fR will save some memory and \s-1CPU.\s0
4919.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
4920.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."
4921If undefined or defined to be \f(CW1\fR (and the platform supports it), then
4922the respective watcher type is supported. If defined to be \f(CW0\fR, then it
4923is not. Disabling watcher types mainly saves code size.
4924.IP "\s-1EV_FEATURES\s0" 4
4925.IX Item "EV_FEATURES"
2027If you need to shave off some kilobytes of code at the expense of some 4926If you need to shave off some kilobytes of code at the expense of some
2028speed, define this symbol to \f(CW1\fR. Currently only used for gcc to override 4927speed (but with the full \s-1API\s0), you can define this symbol to request
2029some inlining decisions, saves roughly 30% codesize of amd64. 4928certain subsets of functionality. The default is to enable all features
4929that can be enabled on the platform.
4930.Sp
4931A typical way to use this symbol is to define it to \f(CW0\fR (or to a bitset
4932with some broad features you want) and then selectively re-enable
4933additional parts you want, for example if you want everything minimal,
4934but multiple event loop support, async and child watchers and the poll
4935backend, use this:
4936.Sp
4937.Vb 5
4938\& #define EV_FEATURES 0
4939\& #define EV_MULTIPLICITY 1
4940\& #define EV_USE_POLL 1
4941\& #define EV_CHILD_ENABLE 1
4942\& #define EV_ASYNC_ENABLE 1
4943.Ve
4944.Sp
4945The actual value is a bitset, it can be a combination of the following
4946values (by default, all of these are enabled):
4947.RS 4
4948.ie n .IP "1 \- faster/larger code" 4
4949.el .IP "\f(CW1\fR \- faster/larger code" 4
4950.IX Item "1 - faster/larger code"
4951Use larger code to speed up some operations.
4952.Sp
4953Currently this is used to override some inlining decisions (enlarging the
4954code size by roughly 30% on amd64).
4955.Sp
4956When optimising for size, use of compiler flags such as \f(CW\*(C`\-Os\*(C'\fR with
4957gcc is recommended, as well as \f(CW\*(C`\-DNDEBUG\*(C'\fR, as libev contains a number of
4958assertions.
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 "2 \- faster/larger data structures" 4
4963.el .IP "\f(CW2\fR \- faster/larger data structures" 4
4964.IX Item "2 - faster/larger data structures"
4965Replaces the small 2\-heap for timer management by a faster 4\-heap, larger
4966hash table sizes and so on. This will usually further increase code size
4967and can additionally have an effect on the size of data structures at
4968runtime.
4969.Sp
4970The default is off when \f(CW\*(C`_\|_OPTIMIZE_SIZE_\|_\*(C'\fR is defined by your compiler
4971(e.g. gcc with \f(CW\*(C`\-Os\*(C'\fR).
4972.ie n .IP "4 \- full \s-1API\s0 configuration" 4
4973.el .IP "\f(CW4\fR \- full \s-1API\s0 configuration" 4
4974.IX Item "4 - full API configuration"
4975This enables priorities (sets \f(CW\*(C`EV_MAXPRI\*(C'\fR=2 and \f(CW\*(C`EV_MINPRI\*(C'\fR=\-2), and
4976enables multiplicity (\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR=1).
4977.ie n .IP "8 \- full \s-1API\s0" 4
4978.el .IP "\f(CW8\fR \- full \s-1API\s0" 4
4979.IX Item "8 - full API"
4980This enables a lot of the \*(L"lesser used\*(R" \s-1API\s0 functions. See \f(CW\*(C`ev.h\*(C'\fR for
4981details on which parts of the \s-1API\s0 are still available without this
4982feature, and do not complain if this subset changes over time.
4983.ie n .IP "16 \- enable all optional watcher types" 4
4984.el .IP "\f(CW16\fR \- enable all optional watcher types" 4
4985.IX Item "16 - enable all optional watcher types"
4986Enables all optional watcher types. If you want to selectively enable
4987only some watcher types other than I/O and timers (e.g. prepare,
4988embed, async, child...) you can enable them manually by defining
4989\&\f(CW\*(C`EV_watchertype_ENABLE\*(C'\fR to \f(CW1\fR instead.
4990.ie n .IP "32 \- enable all backends" 4
4991.el .IP "\f(CW32\fR \- enable all backends" 4
4992.IX Item "32 - enable all backends"
4993This enables all backends \- without this feature, you need to enable at
4994least one backend manually (\f(CW\*(C`EV_USE_SELECT\*(C'\fR is a good choice).
4995.ie n .IP "64 \- enable OS-specific ""helper"" APIs" 4
4996.el .IP "\f(CW64\fR \- enable OS-specific ``helper'' APIs" 4
4997.IX Item "64 - enable OS-specific helper APIs"
4998Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
4999default.
5000.RE
5001.RS 4
5002.Sp
5003Compiling with \f(CW\*(C`gcc \-Os \-DEV_STANDALONE \-DEV_USE_EPOLL=1 \-DEV_FEATURES=0\*(C'\fR
5004reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
5005code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
5006watchers, timers and monotonic clock support.
5007.Sp
5008With an intelligent-enough linker (gcc+binutils are intelligent enough
5009when you use \f(CW\*(C`\-Wl,\-\-gc\-sections \-ffunction\-sections\*(C'\fR) functions unused by
5010your program might be left out as well \- a binary starting a timer and an
5011I/O watcher then might come out at only 5Kb.
5012.RE
5013.IP "\s-1EV_API_STATIC\s0" 4
5014.IX Item "EV_API_STATIC"
5015If this symbol is defined (by default it is not), then all identifiers
5016will have static linkage. This means that libev will not export any
5017identifiers, and you cannot link against libev anymore. This can be useful
5018when you embed libev, only want to use libev functions in a single file,
5019and do not want its identifiers to be visible.
5020.Sp
5021To use this, define \f(CW\*(C`EV_API_STATIC\*(C'\fR and include \fIev.c\fR in the file that
5022wants to use libev.
5023.Sp
5024This option only works when libev is compiled with a C compiler, as \*(C+
5025doesn't support the required declaration syntax.
5026.IP "\s-1EV_AVOID_STDIO\s0" 4
5027.IX Item "EV_AVOID_STDIO"
5028If this is set to \f(CW1\fR at compiletime, then libev will avoid using stdio
5029functions (printf, scanf, perror etc.). This will increase the code size
5030somewhat, but if your program doesn't otherwise depend on stdio and your
5031libc allows it, this avoids linking in the stdio library which is quite
5032big.
5033.Sp
5034Note that error messages might become less precise when this option is
5035enabled.
5036.IP "\s-1EV_NSIG\s0" 4
5037.IX Item "EV_NSIG"
5038The highest supported signal number, +1 (or, the number of
5039signals): Normally, libev tries to deduce the maximum number of signals
5040automatically, but sometimes this fails, in which case it can be
5041specified. Also, using a lower number than detected (\f(CW32\fR should be
5042good for about any system in existence) can save some memory, as libev
5043statically allocates some 12\-24 bytes per signal number.
5044.IP "\s-1EV_PID_HASHSIZE\s0" 4
5045.IX Item "EV_PID_HASHSIZE"
5046\&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by
5047pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR disabled),
5048usually more than enough. If you need to manage thousands of children you
5049might want to increase this value (\fImust\fR be a power of two).
5050.IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4
5051.IX Item "EV_INOTIFY_HASHSIZE"
5052\&\f(CW\*(C`ev_stat\*(C'\fR watchers use a small hash table to distribute workload by
5053inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR
5054disabled), usually more than enough. If you need to manage thousands of
5055\&\f(CW\*(C`ev_stat\*(C'\fR watchers you might want to increase this value (\fImust\fR be a
5056power of two).
5057.IP "\s-1EV_USE_4HEAP\s0" 4
5058.IX Item "EV_USE_4HEAP"
5059Heaps are not very cache-efficient. To improve the cache-efficiency of the
5060timer and periodics heaps, libev uses a 4\-heap when this symbol is defined
5061to \f(CW1\fR. The 4\-heap uses more complicated (longer) code but has noticeably
5062faster performance with many (thousands) of watchers.
5063.Sp
5064The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
5065will be \f(CW0\fR.
5066.IP "\s-1EV_HEAP_CACHE_AT\s0" 4
5067.IX Item "EV_HEAP_CACHE_AT"
5068Heaps are not very cache-efficient. To improve the cache-efficiency of the
5069timer and periodics heaps, libev can cache the timestamp (\fIat\fR) within
5070the heap structure (selected by defining \f(CW\*(C`EV_HEAP_CACHE_AT\*(C'\fR to \f(CW1\fR),
5071which uses 8\-12 bytes more per watcher and a few hundred bytes more code,
5072but avoids random read accesses on heap changes. This improves performance
5073noticeably with many (hundreds) of watchers.
5074.Sp
5075The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
5076will be \f(CW0\fR.
5077.IP "\s-1EV_VERIFY\s0" 4
5078.IX Item "EV_VERIFY"
5079Controls how much internal verification (see \f(CW\*(C`ev_verify ()\*(C'\fR) will
5080be done: If set to \f(CW0\fR, no internal verification code will be compiled
5081in. If set to \f(CW1\fR, then verification code will be compiled in, but not
5082called. If set to \f(CW2\fR, then the internal verification code will be
5083called once per loop, which can slow down libev. If set to \f(CW3\fR, then the
5084verification code will be called very frequently, which will slow down
5085libev considerably.
5086.Sp
5087The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
5088will be \f(CW0\fR.
2030.IP "\s-1EV_COMMON\s0" 4 5089.IP "\s-1EV_COMMON\s0" 4
2031.IX Item "EV_COMMON" 5090.IX Item "EV_COMMON"
2032By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining 5091By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining
2033this macro to a something else you can include more and other types of 5092this macro to something else you can include more and other types of
2034members. You have to define it each time you include one of the files, 5093members. You have to define it each time you include one of the files,
2035though, and it must be identical each time. 5094though, and it must be identical each time.
2036.Sp 5095.Sp
2037For example, the perl \s-1EV\s0 module uses something like this: 5096For example, the perl \s-1EV\s0 module uses something like this:
2038.Sp 5097.Sp
2039.Vb 3 5098.Vb 3
2040\& #define EV_COMMON \e 5099\& #define EV_COMMON \e
2041\& SV *self; /* contains this struct */ \e 5100\& SV *self; /* contains this struct */ \e
2042\& SV *cb_sv, *fh /* note no trailing ";" */ 5101\& SV *cb_sv, *fh /* note no trailing ";" */
2043.Ve 5102.Ve
2044.IP "\s-1EV_CB_DECLARE\s0 (type)" 4 5103.IP "\s-1EV_CB_DECLARE\s0 (type)" 4
2045.IX Item "EV_CB_DECLARE (type)" 5104.IX Item "EV_CB_DECLARE (type)"
2046.PD 0 5105.PD 0
2047.IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4 5106.IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4
… …
2049.IP "ev_set_cb (ev, cb)" 4 5108.IP "ev_set_cb (ev, cb)" 4
2050.IX Item "ev_set_cb (ev, cb)" 5109.IX Item "ev_set_cb (ev, cb)"
2051.PD 5110.PD
2052Can be used to change the callback member declaration in each watcher, 5111Can be used to change the callback member declaration in each watcher,
2053and the way callbacks are invoked and set. Must expand to a struct member 5112and the way callbacks are invoked and set. Must expand to a struct member
2054definition and a statement, respectively. See the \fIev.v\fR header file for 5113definition and a statement, respectively. See the \fIev.h\fR header file for
2055their default definitions. One possible use for overriding these is to 5114their default definitions. One possible use for overriding these is to
2056avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use 5115avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use
2057method calls instead of plain function calls in \*(C+. 5116method calls instead of plain function calls in \*(C+.
5117.SS "\s-1EXPORTED API SYMBOLS\s0"
5118.IX Subsection "EXPORTED API SYMBOLS"
5119If you need to re-export the \s-1API\s0 (e.g. via a \s-1DLL\s0) and you need a list of
5120exported symbols, you can use the provided \fISymbol.*\fR files which list
5121all public symbols, one per line:
5122.PP
5123.Vb 2
5124\& Symbols.ev for libev proper
5125\& Symbols.event for the libevent emulation
5126.Ve
5127.PP
5128This can also be used to rename all public symbols to avoid clashes with
5129multiple versions of libev linked together (which is obviously bad in
5130itself, but sometimes it is inconvenient to avoid this).
5131.PP
5132A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to
5133include before including \fIev.h\fR:
5134.PP
5135.Vb 1
5136\& <Symbols.ev sed \-e "s/.*/#define & myprefix_&/" >wrap.h
5137.Ve
5138.PP
5139This would create a file \fIwrap.h\fR which essentially looks like this:
5140.PP
5141.Vb 4
5142\& #define ev_backend myprefix_ev_backend
5143\& #define ev_check_start myprefix_ev_check_start
5144\& #define ev_check_stop myprefix_ev_check_stop
5145\& ...
5146.Ve
2058.Sh "\s-1EXAMPLES\s0" 5147.SS "\s-1EXAMPLES\s0"
2059.IX Subsection "EXAMPLES" 5148.IX Subsection "EXAMPLES"
2060For a real-world example of a program the includes libev 5149For a real-world example of a program the includes libev
2061verbatim, you can have a look at the \s-1EV\s0 perl module 5150verbatim, you can have a look at the \s-1EV\s0 perl module
2062(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in 5151(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
2063the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public 5152the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public
2064interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file 5153interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file
2065will be compiled. It is pretty complex because it provides its own header 5154will be compiled. It is pretty complex because it provides its own header
2066file. 5155file.
2067.Sp 5156.PP
2068The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file 5157The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file
2069that everybody includes and which overrides some autoconf choices: 5158that everybody includes and which overrides some configure choices:
2070.Sp 5159.PP
2071.Vb 4 5160.Vb 8
5161\& #define EV_FEATURES 8
5162\& #define EV_USE_SELECT 1
5163\& #define EV_PREPARE_ENABLE 1
5164\& #define EV_IDLE_ENABLE 1
5165\& #define EV_SIGNAL_ENABLE 1
5166\& #define EV_CHILD_ENABLE 1
2072\& #define EV_USE_POLL 0 5167\& #define EV_USE_STDEXCEPT 0
2073\& #define EV_MULTIPLICITY 0
2074\& #define EV_PERIODICS 0
2075\& #define EV_CONFIG_H <config.h> 5168\& #define EV_CONFIG_H <config.h>
2076.Ve 5169\&
2077.Sp
2078.Vb 1
2079\& #include "ev++.h" 5170\& #include "ev++.h"
2080.Ve 5171.Ve
2081.Sp 5172.PP
2082And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled: 5173And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled:
2083.Sp 5174.PP
2084.Vb 2 5175.Vb 2
2085\& #include "ev_cpp.h" 5176\& #include "ev_cpp.h"
2086\& #include "ev.c" 5177\& #include "ev.c"
2087.Ve 5178.Ve
5179.SH "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT"
5180.IX Header "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT"
5181.SS "\s-1THREADS AND COROUTINES\s0"
5182.IX Subsection "THREADS AND COROUTINES"
5183\fI\s-1THREADS\s0\fR
5184.IX Subsection "THREADS"
5185.PP
5186All libev functions are reentrant and thread-safe unless explicitly
5187documented otherwise, but libev implements no locking itself. This means
5188that you can use as many loops as you want in parallel, as long as there
5189are no concurrent calls into any libev function with the same loop
5190parameter (\f(CW\*(C`ev_default_*\*(C'\fR calls have an implicit default loop parameter,
5191of course): libev guarantees that different event loops share no data
5192structures that need any locking.
5193.PP
5194Or to put it differently: calls with different loop parameters can be done
5195concurrently from multiple threads, calls with the same loop parameter
5196must be done serially (but can be done from different threads, as long as
5197only one thread ever is inside a call at any point in time, e.g. by using
5198a mutex per loop).
5199.PP
5200Specifically to support threads (and signal handlers), libev implements
5201so-called \f(CW\*(C`ev_async\*(C'\fR watchers, which allow some limited form of
5202concurrency on the same event loop, namely waking it up \*(L"from the
5203outside\*(R".
5204.PP
5205If you want to know which design (one loop, locking, or multiple loops
5206without or something else still) is best for your problem, then I cannot
5207help you, but here is some generic advice:
5208.IP "\(bu" 4
5209most applications have a main thread: use the default libev loop
5210in that thread, or create a separate thread running only the default loop.
5211.Sp
5212This helps integrating other libraries or software modules that use libev
5213themselves and don't care/know about threading.
5214.IP "\(bu" 4
5215one loop per thread is usually a good model.
5216.Sp
5217Doing this is almost never wrong, sometimes a better-performance model
5218exists, but it is always a good start.
5219.IP "\(bu" 4
5220other models exist, such as the leader/follower pattern, where one
5221loop is handed through multiple threads in a kind of round-robin fashion.
5222.Sp
5223Choosing a model is hard \- look around, learn, know that usually you can do
5224better than you currently do :\-)
5225.IP "\(bu" 4
5226often you need to talk to some other thread which blocks in the
5227event loop.
5228.Sp
5229\&\f(CW\*(C`ev_async\*(C'\fR watchers can be used to wake them up from other threads safely
5230(or from signal contexts...).
5231.Sp
5232An example use would be to communicate signals or other events that only
5233work in the default loop by registering the signal watcher with the
5234default loop and triggering an \f(CW\*(C`ev_async\*(C'\fR watcher from the default loop
5235watcher callback into the event loop interested in the signal.
5236.PP
5237See also \*(L"\s-1THREAD LOCKING EXAMPLE\*(R"\s0.
5238.PP
5239\fI\s-1COROUTINES\s0\fR
5240.IX Subsection "COROUTINES"
5241.PP
5242Libev is very accommodating to coroutines (\*(L"cooperative threads\*(R"):
5243libev fully supports nesting calls to its functions from different
5244coroutines (e.g. you can call \f(CW\*(C`ev_run\*(C'\fR on the same loop from two
5245different coroutines, and switch freely between both coroutines running
5246the loop, as long as you don't confuse yourself). The only exception is
5247that you must not do this from \f(CW\*(C`ev_periodic\*(C'\fR reschedule callbacks.
5248.PP
5249Care has been taken to ensure that libev does not keep local state inside
5250\&\f(CW\*(C`ev_run\*(C'\fR, and other calls do not usually allow for coroutine switches as
5251they do not call any callbacks.
5252.SS "\s-1COMPILER WARNINGS\s0"
5253.IX Subsection "COMPILER WARNINGS"
5254Depending on your compiler and compiler settings, you might get no or a
5255lot of warnings when compiling libev code. Some people are apparently
5256scared by this.
5257.PP
5258However, these are unavoidable for many reasons. For one, each compiler
5259has different warnings, and each user has different tastes regarding
5260warning options. \*(L"Warn-free\*(R" code therefore cannot be a goal except when
5261targeting a specific compiler and compiler-version.
5262.PP
5263Another reason is that some compiler warnings require elaborate
5264workarounds, or other changes to the code that make it less clear and less
5265maintainable.
5266.PP
5267And of course, some compiler warnings are just plain stupid, or simply
5268wrong (because they don't actually warn about the condition their message
5269seems to warn about). For example, certain older gcc versions had some
5270warnings that resulted in an extreme number of false positives. These have
5271been fixed, but some people still insist on making code warn-free with
5272such buggy versions.
5273.PP
5274While libev is written to generate as few warnings as possible,
5275\&\*(L"warn-free\*(R" code is not a goal, and it is recommended not to build libev
5276with any compiler warnings enabled unless you are prepared to cope with
5277them (e.g. by ignoring them). Remember that warnings are just that:
5278warnings, not errors, or proof of bugs.
5279.SS "\s-1VALGRIND\s0"
5280.IX Subsection "VALGRIND"
5281Valgrind has a special section here because it is a popular tool that is
5282highly useful. Unfortunately, valgrind reports are very hard to interpret.
5283.PP
5284If you think you found a bug (memory leak, uninitialised data access etc.)
5285in libev, then check twice: If valgrind reports something like:
5286.PP
5287.Vb 3
5288\& ==2274== definitely lost: 0 bytes in 0 blocks.
5289\& ==2274== possibly lost: 0 bytes in 0 blocks.
5290\& ==2274== still reachable: 256 bytes in 1 blocks.
5291.Ve
5292.PP
5293Then there is no memory leak, just as memory accounted to global variables
5294is not a memleak \- the memory is still being referenced, and didn't leak.
5295.PP
5296Similarly, under some circumstances, valgrind might report kernel bugs
5297as if it were a bug in libev (e.g. in realloc or in the poll backend,
5298although an acceptable workaround has been found here), or it might be
5299confused.
5300.PP
5301Keep in mind that valgrind is a very good tool, but only a tool. Don't
5302make it into some kind of religion.
5303.PP
5304If you are unsure about something, feel free to contact the mailing list
5305with the full valgrind report and an explanation on why you think this
5306is a bug in libev (best check the archives, too :). However, don't be
5307annoyed when you get a brisk \*(L"this is no bug\*(R" answer and take the chance
5308of learning how to interpret valgrind properly.
5309.PP
5310If you need, for some reason, empty reports from valgrind for your project
5311I suggest using suppression lists.
5312.SH "PORTABILITY NOTES"
5313.IX Header "PORTABILITY NOTES"
5314.SS "\s-1GNU/LINUX 32 BIT LIMITATIONS\s0"
5315.IX Subsection "GNU/LINUX 32 BIT LIMITATIONS"
5316GNU/Linux is the only common platform that supports 64 bit file/large file
5317interfaces but \fIdisables\fR them by default.
5318.PP
5319That means that libev compiled in the default environment doesn't support
5320files larger than 2GiB or so, which mainly affects \f(CW\*(C`ev_stat\*(C'\fR watchers.
5321.PP
5322Unfortunately, many programs try to work around this GNU/Linux issue
5323by enabling the large file \s-1API,\s0 which makes them incompatible with the
5324standard libev compiled for their system.
5325.PP
5326Likewise, libev cannot enable the large file \s-1API\s0 itself as this would
5327suddenly make it incompatible to the default compile time environment,
5328i.e. all programs not using special compile switches.
5329.SS "\s-1OS/X AND DARWIN BUGS\s0"
5330.IX Subsection "OS/X AND DARWIN BUGS"
5331The whole thing is a bug if you ask me \- basically any system interface
5332you touch is broken, whether it is locales, poll, kqueue or even the
5333OpenGL drivers.
5334.PP
5335\fI\f(CI\*(C`kqueue\*(C'\fI is buggy\fR
5336.IX Subsection "kqueue is buggy"
5337.PP
5338The kqueue syscall is broken in all known versions \- most versions support
5339only sockets, many support pipes.
5340.PP
5341Libev tries to work around this by not using \f(CW\*(C`kqueue\*(C'\fR by default on this
5342rotten platform, but of course you can still ask for it when creating a
5343loop \- embedding a socket-only kqueue loop into a select-based one is
5344probably going to work well.
5345.PP
5346\fI\f(CI\*(C`poll\*(C'\fI is buggy\fR
5347.IX Subsection "poll is buggy"
5348.PP
5349Instead of fixing \f(CW\*(C`kqueue\*(C'\fR, Apple replaced their (working) \f(CW\*(C`poll\*(C'\fR
5350implementation by something calling \f(CW\*(C`kqueue\*(C'\fR internally around the 10.5.6
5351release, so now \f(CW\*(C`kqueue\*(C'\fR \fIand\fR \f(CW\*(C`poll\*(C'\fR are broken.
5352.PP
5353Libev tries to work around this by not using \f(CW\*(C`poll\*(C'\fR by default on
5354this rotten platform, but of course you can still ask for it when creating
5355a loop.
5356.PP
5357\fI\f(CI\*(C`select\*(C'\fI is buggy\fR
5358.IX Subsection "select is buggy"
5359.PP
5360All that's left is \f(CW\*(C`select\*(C'\fR, and of course Apple found a way to fuck this
5361one up as well: On \s-1OS/X,\s0 \f(CW\*(C`select\*(C'\fR actively limits the number of file
5362descriptors you can pass in to 1024 \- your program suddenly crashes when
5363you use more.
5364.PP
5365There is an undocumented \*(L"workaround\*(R" for this \- defining
5366\&\f(CW\*(C`_DARWIN_UNLIMITED_SELECT\*(C'\fR, which libev tries to use, so select \fIshould\fR
5367work on \s-1OS/X.\s0
5368.SS "\s-1SOLARIS PROBLEMS AND WORKAROUNDS\s0"
5369.IX Subsection "SOLARIS PROBLEMS AND WORKAROUNDS"
5370\fI\f(CI\*(C`errno\*(C'\fI reentrancy\fR
5371.IX Subsection "errno reentrancy"
5372.PP
5373The default compile environment on Solaris is unfortunately so
5374thread-unsafe that you can't even use components/libraries compiled
5375without \f(CW\*(C`\-D_REENTRANT\*(C'\fR in a threaded program, which, of course, isn't
5376defined by default. A valid, if stupid, implementation choice.
5377.PP
5378If you want to use libev in threaded environments you have to make sure
5379it's compiled with \f(CW\*(C`_REENTRANT\*(C'\fR defined.
5380.PP
5381\fIEvent port backend\fR
5382.IX Subsection "Event port backend"
5383.PP
5384The scalable event interface for Solaris is called \*(L"event
5385ports\*(R". Unfortunately, this mechanism is very buggy in all major
5386releases. If you run into high \s-1CPU\s0 usage, your program freezes or you get
5387a large number of spurious wakeups, make sure you have all the relevant
5388and latest kernel patches applied. No, I don't know which ones, but there
5389are multiple ones to apply, and afterwards, event ports actually work
5390great.
5391.PP
5392If you can't get it to work, you can try running the program by setting
5393the environment variable \f(CW\*(C`LIBEV_FLAGS=3\*(C'\fR to only allow \f(CW\*(C`poll\*(C'\fR and
5394\&\f(CW\*(C`select\*(C'\fR backends.
5395.SS "\s-1AIX POLL BUG\s0"
5396.IX Subsection "AIX POLL BUG"
5397\&\s-1AIX\s0 unfortunately has a broken \f(CW\*(C`poll.h\*(C'\fR header. Libev works around
5398this by trying to avoid the poll backend altogether (i.e. it's not even
5399compiled in), which normally isn't a big problem as \f(CW\*(C`select\*(C'\fR works fine
5400with large bitsets on \s-1AIX,\s0 and \s-1AIX\s0 is dead anyway.
5401.SS "\s-1WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS\s0"
5402.IX Subsection "WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS"
5403\fIGeneral issues\fR
5404.IX Subsection "General issues"
5405.PP
5406Win32 doesn't support any of the standards (e.g. \s-1POSIX\s0) that libev
5407requires, and its I/O model is fundamentally incompatible with the \s-1POSIX\s0
5408model. Libev still offers limited functionality on this platform in
5409the form of the \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR backend, and only supports socket
5410descriptors. This only applies when using Win32 natively, not when using
5411e.g. cygwin. Actually, it only applies to the microsofts own compilers,
5412as every compiler comes with a slightly differently broken/incompatible
5413environment.
5414.PP
5415Lifting these limitations would basically require the full
5416re-implementation of the I/O system. If you are into this kind of thing,
5417then note that glib does exactly that for you in a very portable way (note
5418also that glib is the slowest event library known to man).
5419.PP
5420There is no supported compilation method available on windows except
5421embedding it into other applications.
5422.PP
5423Sensible signal handling is officially unsupported by Microsoft \- libev
5424tries its best, but under most conditions, signals will simply not work.
5425.PP
5426Not a libev limitation but worth mentioning: windows apparently doesn't
5427accept large writes: instead of resulting in a partial write, windows will
5428either accept everything or return \f(CW\*(C`ENOBUFS\*(C'\fR if the buffer is too large,
5429so make sure you only write small amounts into your sockets (less than a
5430megabyte seems safe, but this apparently depends on the amount of memory
5431available).
5432.PP
5433Due to the many, low, and arbitrary limits on the win32 platform and
5434the abysmal performance of winsockets, using a large number of sockets
5435is not recommended (and not reasonable). If your program needs to use
5436more than a hundred or so sockets, then likely it needs to use a totally
5437different implementation for windows, as libev offers the \s-1POSIX\s0 readiness
5438notification model, which cannot be implemented efficiently on windows
5439(due to Microsoft monopoly games).
5440.PP
5441A typical way to use libev under windows is to embed it (see the embedding
5442section for details) and use the following \fIevwrap.h\fR header file instead
5443of \fIev.h\fR:
5444.PP
5445.Vb 2
5446\& #define EV_STANDALONE /* keeps ev from requiring config.h */
5447\& #define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
5448\&
5449\& #include "ev.h"
5450.Ve
5451.PP
5452And compile the following \fIevwrap.c\fR file into your project (make sure
5453you do \fInot\fR compile the \fIev.c\fR or any other embedded source files!):
5454.PP
5455.Vb 2
5456\& #include "evwrap.h"
5457\& #include "ev.c"
5458.Ve
5459.PP
5460\fIThe winsocket \f(CI\*(C`select\*(C'\fI function\fR
5461.IX Subsection "The winsocket select function"
5462.PP
5463The winsocket \f(CW\*(C`select\*(C'\fR function doesn't follow \s-1POSIX\s0 in that it
5464requires socket \fIhandles\fR and not socket \fIfile descriptors\fR (it is
5465also extremely buggy). This makes select very inefficient, and also
5466requires a mapping from file descriptors to socket handles (the Microsoft
5467C runtime provides the function \f(CW\*(C`_open_osfhandle\*(C'\fR for this). See the
5468discussion of the \f(CW\*(C`EV_SELECT_USE_FD_SET\*(C'\fR, \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR and
5469\&\f(CW\*(C`EV_FD_TO_WIN32_HANDLE\*(C'\fR preprocessor symbols for more info.
5470.PP
5471The configuration for a \*(L"naked\*(R" win32 using the Microsoft runtime
5472libraries and raw winsocket select is:
5473.PP
5474.Vb 2
5475\& #define EV_USE_SELECT 1
5476\& #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
5477.Ve
5478.PP
5479Note that winsockets handling of fd sets is O(n), so you can easily get a
5480complexity in the O(nX) range when using win32.
5481.PP
5482\fILimited number of file descriptors\fR
5483.IX Subsection "Limited number of file descriptors"
5484.PP
5485Windows has numerous arbitrary (and low) limits on things.
5486.PP
5487Early versions of winsocket's select only supported waiting for a maximum
5488of \f(CW64\fR handles (probably owning to the fact that all windows kernels
5489can only wait for \f(CW64\fR things at the same time internally; Microsoft
5490recommends spawning a chain of threads and wait for 63 handles and the
5491previous thread in each. Sounds great!).
5492.PP
5493Newer versions support more handles, but you need to define \f(CW\*(C`FD_SETSIZE\*(C'\fR
5494to some high number (e.g. \f(CW2048\fR) before compiling the winsocket select
5495call (which might be in libev or elsewhere, for example, perl and many
5496other interpreters do their own select emulation on windows).
5497.PP
5498Another limit is the number of file descriptors in the Microsoft runtime
5499libraries, which by default is \f(CW64\fR (there must be a hidden \fI64\fR
5500fetish or something like this inside Microsoft). You can increase this
5501by calling \f(CW\*(C`_setmaxstdio\*(C'\fR, which can increase this limit to \f(CW2048\fR
5502(another arbitrary limit), but is broken in many versions of the Microsoft
5503runtime libraries. This might get you to about \f(CW512\fR or \f(CW2048\fR sockets
5504(depending on windows version and/or the phase of the moon). To get more,
5505you need to wrap all I/O functions and provide your own fd management, but
5506the cost of calling select (O(nX)) will likely make this unworkable.
5507.SS "\s-1PORTABILITY REQUIREMENTS\s0"
5508.IX Subsection "PORTABILITY REQUIREMENTS"
5509In addition to a working ISO-C implementation and of course the
5510backend-specific APIs, libev relies on a few additional extensions:
5511.ie n .IP """void (*)(ev_watcher_type *, int revents)"" must have compatible calling conventions regardless of ""ev_watcher_type *""." 4
5512.el .IP "\f(CWvoid (*)(ev_watcher_type *, int revents)\fR must have compatible calling conventions regardless of \f(CWev_watcher_type *\fR." 4
5513.IX Item "void (*)(ev_watcher_type *, int revents) must have compatible calling conventions regardless of ev_watcher_type *."
5514Libev assumes not only that all watcher pointers have the same internal
5515structure (guaranteed by \s-1POSIX\s0 but not by \s-1ISO C\s0 for example), but it also
5516assumes that the same (machine) code can be used to call any watcher
5517callback: The watcher callbacks have different type signatures, but libev
5518calls them using an \f(CW\*(C`ev_watcher *\*(C'\fR internally.
5519.IP "null pointers and integer zero are represented by 0 bytes" 4
5520.IX Item "null pointers and integer zero are represented by 0 bytes"
5521Libev uses \f(CW\*(C`memset\*(C'\fR to initialise structs and arrays to \f(CW0\fR bytes, and
5522relies on this setting pointers and integers to null.
5523.IP "pointer accesses must be thread-atomic" 4
5524.IX Item "pointer accesses must be thread-atomic"
5525Accessing a pointer value must be atomic, it must both be readable and
5526writable in one piece \- this is the case on all current architectures.
5527.ie n .IP """sig_atomic_t volatile"" must be thread-atomic as well" 4
5528.el .IP "\f(CWsig_atomic_t volatile\fR must be thread-atomic as well" 4
5529.IX Item "sig_atomic_t volatile must be thread-atomic as well"
5530The type \f(CW\*(C`sig_atomic_t volatile\*(C'\fR (or whatever is defined as
5531\&\f(CW\*(C`EV_ATOMIC_T\*(C'\fR) must be atomic with respect to accesses from different
5532threads. This is not part of the specification for \f(CW\*(C`sig_atomic_t\*(C'\fR, but is
5533believed to be sufficiently portable.
5534.ie n .IP """sigprocmask"" must work in a threaded environment" 4
5535.el .IP "\f(CWsigprocmask\fR must work in a threaded environment" 4
5536.IX Item "sigprocmask must work in a threaded environment"
5537Libev uses \f(CW\*(C`sigprocmask\*(C'\fR to temporarily block signals. This is not
5538allowed in a threaded program (\f(CW\*(C`pthread_sigmask\*(C'\fR has to be used). Typical
5539pthread implementations will either allow \f(CW\*(C`sigprocmask\*(C'\fR in the \*(L"main
5540thread\*(R" or will block signals process-wide, both behaviours would
5541be compatible with libev. Interaction between \f(CW\*(C`sigprocmask\*(C'\fR and
5542\&\f(CW\*(C`pthread_sigmask\*(C'\fR could complicate things, however.
5543.Sp
5544The most portable way to handle signals is to block signals in all threads
5545except the initial one, and run the signal handling loop in the initial
5546thread as well.
5547.ie n .IP """long"" must be large enough for common memory allocation sizes" 4
5548.el .IP "\f(CWlong\fR must be large enough for common memory allocation sizes" 4
5549.IX Item "long must be large enough for common memory allocation sizes"
5550To improve portability and simplify its \s-1API,\s0 libev uses \f(CW\*(C`long\*(C'\fR internally
5551instead of \f(CW\*(C`size_t\*(C'\fR when allocating its data structures. On non-POSIX
5552systems (Microsoft...) this might be unexpectedly low, but is still at
5553least 31 bits everywhere, which is enough for hundreds of millions of
5554watchers.
5555.ie n .IP """double"" must hold a time value in seconds with enough accuracy" 4
5556.el .IP "\f(CWdouble\fR must hold a time value in seconds with enough accuracy" 4
5557.IX Item "double must hold a time value in seconds with enough accuracy"
5558The type \f(CW\*(C`double\*(C'\fR is used to represent timestamps. It is required to
5559have at least 51 bits of mantissa (and 9 bits of exponent), which is
5560good enough for at least into the year 4000 with millisecond accuracy
5561(the design goal for libev). This requirement is overfulfilled by
5562implementations using \s-1IEEE 754,\s0 which is basically all existing ones.
5563.Sp
5564With \s-1IEEE 754\s0 doubles, you get microsecond accuracy until at least the
5565year 2255 (and millisecond accuracy till the year 287396 \- by then, libev
5566is either obsolete or somebody patched it to use \f(CW\*(C`long double\*(C'\fR or
5567something like that, just kidding).
5568.PP
5569If you know of other additional requirements drop me a note.
2088.SH "COMPLEXITIES" 5570.SH "ALGORITHMIC COMPLEXITIES"
2089.IX Header "COMPLEXITIES" 5571.IX Header "ALGORITHMIC COMPLEXITIES"
2090In this section the complexities of (many of) the algorithms used inside 5572In this section the complexities of (many of) the algorithms used inside
2091libev will be explained. For complexity discussions about backends see the 5573libev will be documented. For complexity discussions about backends see
2092documentation for \f(CW\*(C`ev_default_init\*(C'\fR. 5574the documentation for \f(CW\*(C`ev_default_init\*(C'\fR.
2093.RS 4 5575.PP
5576All of the following are about amortised time: If an array needs to be
5577extended, libev needs to realloc and move the whole array, but this
5578happens asymptotically rarer with higher number of elements, so O(1) might
5579mean that libev does a lengthy realloc operation in rare cases, but on
5580average it is much faster and asymptotically approaches constant time.
2094.IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4 5581.IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4
2095.IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 5582.IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)"
5583This means that, when you have a watcher that triggers in one hour and
5584there are 100 watchers that would trigger before that, then inserting will
5585have to skip roughly seven (\f(CW\*(C`ld 100\*(C'\fR) of these watchers.
5586.IP "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 4
5587.IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)"
5588That means that changing a timer costs less than removing/adding them,
5589as only the relative motion in the event queue has to be paid for.
5590.IP "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)" 4
5591.IX Item "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)"
5592These just add the watcher into an array or at the head of a list.
5593.IP "Stopping check/prepare/idle/fork/async watchers: O(1)" 4
5594.IX Item "Stopping check/prepare/idle/fork/async watchers: O(1)"
2096.PD 0 5595.PD 0
2097.IP "Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)" 4
2098.IX Item "Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)"
2099.IP "Starting io/check/prepare/idle/signal/child watchers: O(1)" 4
2100.IX Item "Starting io/check/prepare/idle/signal/child watchers: O(1)"
2101.IP "Stopping check/prepare/idle watchers: O(1)" 4
2102.IX Item "Stopping check/prepare/idle watchers: O(1)"
2103.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % 16))" 4 5596.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4
2104.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % 16))" 5597.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))"
5598.PD
5599These watchers are stored in lists, so they need to be walked to find the
5600correct watcher to remove. The lists are usually short (you don't usually
5601have many watchers waiting for the same fd or signal: one is typical, two
5602is rare).
2105.IP "Finding the next timer per loop iteration: O(1)" 4 5603.IP "Finding the next timer in each loop iteration: O(1)" 4
2106.IX Item "Finding the next timer per loop iteration: O(1)" 5604.IX Item "Finding the next timer in each loop iteration: O(1)"
5605By virtue of using a binary or 4\-heap, the next timer is always found at a
5606fixed position in the storage array.
2107.IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4 5607.IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4
2108.IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 5608.IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)"
2109.IP "Activating one watcher: O(1)" 4 5609A change means an I/O watcher gets started or stopped, which requires
2110.IX Item "Activating one watcher: O(1)" 5610libev to recalculate its status (and possibly tell the kernel, depending
2111.RE 5611on backend and whether \f(CW\*(C`ev_io_set\*(C'\fR was used).
2112.RS 4 5612.IP "Activating one watcher (putting it into the pending state): O(1)" 4
5613.IX Item "Activating one watcher (putting it into the pending state): O(1)"
5614.PD 0
5615.IP "Priority handling: O(number_of_priorities)" 4
5616.IX Item "Priority handling: O(number_of_priorities)"
2113.PD 5617.PD
5618Priorities are implemented by allocating some space for each
5619priority. When doing priority-based operations, libev usually has to
5620linearly search all the priorities, but starting/stopping and activating
5621watchers becomes O(1) with respect to priority handling.
5622.IP "Sending an ev_async: O(1)" 4
5623.IX Item "Sending an ev_async: O(1)"
5624.PD 0
5625.IP "Processing ev_async_send: O(number_of_async_watchers)" 4
5626.IX Item "Processing ev_async_send: O(number_of_async_watchers)"
5627.IP "Processing signals: O(max_signal_number)" 4
5628.IX Item "Processing signals: O(max_signal_number)"
5629.PD
5630Sending involves a system call \fIiff\fR there were no other \f(CW\*(C`ev_async_send\*(C'\fR
5631calls in the current loop iteration and the loop is currently
5632blocked. Checking for async and signal events involves iterating over all
5633running async watchers or all signal numbers.
5634.SH "PORTING FROM LIBEV 3.X TO 4.X"
5635.IX Header "PORTING FROM LIBEV 3.X TO 4.X"
5636The major version 4 introduced some incompatible changes to the \s-1API.\s0
5637.PP
5638At the moment, the \f(CW\*(C`ev.h\*(C'\fR header file provides compatibility definitions
5639for all changes, so most programs should still compile. The compatibility
5640layer might be removed in later versions of libev, so better update to the
5641new \s-1API\s0 early than late.
5642.ie n .IP """EV_COMPAT3"" backwards compatibility mechanism" 4
5643.el .IP "\f(CWEV_COMPAT3\fR backwards compatibility mechanism" 4
5644.IX Item "EV_COMPAT3 backwards compatibility mechanism"
5645The backward compatibility mechanism can be controlled by
5646\&\f(CW\*(C`EV_COMPAT3\*(C'\fR. See \*(L"\s-1PREPROCESSOR SYMBOLS/MACROS\*(R"\s0 in the \*(L"\s-1EMBEDDING\*(R"\s0
5647section.
5648.ie n .IP """ev_default_destroy"" and ""ev_default_fork"" have been removed" 4
5649.el .IP "\f(CWev_default_destroy\fR and \f(CWev_default_fork\fR have been removed" 4
5650.IX Item "ev_default_destroy and ev_default_fork have been removed"
5651These calls can be replaced easily by their \f(CW\*(C`ev_loop_xxx\*(C'\fR counterparts:
5652.Sp
5653.Vb 2
5654\& ev_loop_destroy (EV_DEFAULT_UC);
5655\& ev_loop_fork (EV_DEFAULT);
5656.Ve
5657.IP "function/symbol renames" 4
5658.IX Item "function/symbol renames"
5659A number of functions and symbols have been renamed:
5660.Sp
5661.Vb 3
5662\& ev_loop => ev_run
5663\& EVLOOP_NONBLOCK => EVRUN_NOWAIT
5664\& EVLOOP_ONESHOT => EVRUN_ONCE
5665\&
5666\& ev_unloop => ev_break
5667\& EVUNLOOP_CANCEL => EVBREAK_CANCEL
5668\& EVUNLOOP_ONE => EVBREAK_ONE
5669\& EVUNLOOP_ALL => EVBREAK_ALL
5670\&
5671\& EV_TIMEOUT => EV_TIMER
5672\&
5673\& ev_loop_count => ev_iteration
5674\& ev_loop_depth => ev_depth
5675\& ev_loop_verify => ev_verify
5676.Ve
5677.Sp
5678Most functions working on \f(CW\*(C`struct ev_loop\*(C'\fR objects don't have an
5679\&\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
5680associated constants have been renamed to not collide with the \f(CW\*(C`struct
5681ev_loop\*(C'\fR anymore and \f(CW\*(C`EV_TIMER\*(C'\fR now follows the same naming scheme
5682as all other watcher types. Note that \f(CW\*(C`ev_loop_fork\*(C'\fR is still called
5683\&\f(CW\*(C`ev_loop_fork\*(C'\fR because it would otherwise clash with the \f(CW\*(C`ev_fork\*(C'\fR
5684typedef.
5685.ie n .IP """EV_MINIMAL"" mechanism replaced by ""EV_FEATURES""" 4
5686.el .IP "\f(CWEV_MINIMAL\fR mechanism replaced by \f(CWEV_FEATURES\fR" 4
5687.IX Item "EV_MINIMAL mechanism replaced by EV_FEATURES"
5688The preprocessor symbol \f(CW\*(C`EV_MINIMAL\*(C'\fR has been replaced by a different
5689mechanism, \f(CW\*(C`EV_FEATURES\*(C'\fR. Programs using \f(CW\*(C`EV_MINIMAL\*(C'\fR usually compile
5690and work, but the library code will of course be larger.
5691.SH "GLOSSARY"
5692.IX Header "GLOSSARY"
5693.IP "active" 4
5694.IX Item "active"
5695A watcher is active as long as it has been started and not yet stopped.
5696See \*(L"\s-1WATCHER STATES\*(R"\s0 for details.
5697.IP "application" 4
5698.IX Item "application"
5699In this document, an application is whatever is using libev.
5700.IP "backend" 4
5701.IX Item "backend"
5702The part of the code dealing with the operating system interfaces.
5703.IP "callback" 4
5704.IX Item "callback"
5705The address of a function that is called when some event has been
5706detected. Callbacks are being passed the event loop, the watcher that
5707received the event, and the actual event bitset.
5708.IP "callback/watcher invocation" 4
5709.IX Item "callback/watcher invocation"
5710The act of calling the callback associated with a watcher.
5711.IP "event" 4
5712.IX Item "event"
5713A change of state of some external event, such as data now being available
5714for reading on a file descriptor, time having passed or simply not having
5715any other events happening anymore.
5716.Sp
5717In libev, events are represented as single bits (such as \f(CW\*(C`EV_READ\*(C'\fR or
5718\&\f(CW\*(C`EV_TIMER\*(C'\fR).
5719.IP "event library" 4
5720.IX Item "event library"
5721A software package implementing an event model and loop.
5722.IP "event loop" 4
5723.IX Item "event loop"
5724An entity that handles and processes external events and converts them
5725into callback invocations.
5726.IP "event model" 4
5727.IX Item "event model"
5728The model used to describe how an event loop handles and processes
5729watchers and events.
5730.IP "pending" 4
5731.IX Item "pending"
5732A watcher is pending as soon as the corresponding event has been
5733detected. See \*(L"\s-1WATCHER STATES\*(R"\s0 for details.
5734.IP "real time" 4
5735.IX Item "real time"
5736The physical time that is observed. It is apparently strictly monotonic :)
5737.IP "wall-clock time" 4
5738.IX Item "wall-clock time"
5739The time and date as shown on clocks. Unlike real time, it can actually
5740be wrong and jump forwards and backwards, e.g. when you adjust your
5741clock.
5742.IP "watcher" 4
5743.IX Item "watcher"
5744A data structure that describes interest in certain events. Watchers need
5745to be started (attached to an event loop) before they can receive events.
2114.SH "AUTHOR" 5746.SH "AUTHOR"
2115.IX Header "AUTHOR" 5747.IX Header "AUTHOR"
2116Marc Lehmann <libev@schmorp.de>. 5748Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5749Magnusson and Emanuele Giaquinta, and minor corrections by many others.

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