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129.\" ======================================================================== 133.\" ========================================================================
130.\" 134.\"
131.IX Title ""<STANDARD INPUT>" 1" 135.IX Title "LIBEV 3"
132.TH "<STANDARD INPUT>" 1 "2007-11-24" "perl v5.8.8" "User Contributed Perl Documentation" 136.TH LIBEV 3 "2015-12-20" "libev-4.20" "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 \f(CW\*(C`epoll\*(C'\fR, the
157kqueue mechanisms for file descriptor events, relative timers, absolute 246BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port mechanisms
158timers with customised rescheduling, signal events, process status change 247for file descriptor events (\f(CW\*(C`ev_io\*(C'\fR), the Linux \f(CW\*(C`inotify\*(C'\fR interface
159events (related to \s-1SIGCHLD\s0), and event watchers dealing with the event 248(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: Replace the libev allocator with one that waits a bit and then
258retries: better than mine). 398retries (example requires a standards-compliant \f(CW\*(C`realloc\*(C'\fR).
259.Sp 399.Sp
260.Vb 6 400.Vb 6
261\& static void * 401\& static void *
262\& persistent_realloc (void *ptr, long size) 402\& persistent_realloc (void *ptr, size_t size)
263\& { 403\& {
264\& for (;;) 404\& for (;;)
265\& { 405\& {
266\& void *newptr = realloc (ptr, size); 406\& void *newptr = realloc (ptr, size);
267.Ve 407\&
268.Sp
269.Vb 2
270\& if (newptr) 408\& if (newptr)
271\& return newptr; 409\& return newptr;
272.Ve 410\&
273.Sp
274.Vb 3
275\& sleep (60); 411\& sleep (60);
276\& } 412\& }
277\& } 413\& }
278.Ve 414\&
279.Sp
280.Vb 2
281\& ... 415\& ...
282\& ev_set_allocator (persistent_realloc); 416\& ev_set_allocator (persistent_realloc);
283.Ve 417.Ve
284.IP "ev_set_syserr_cb (void (*cb)(const char *msg));" 4 418.IP "ev_set_syserr_cb (void (*cb)(const char *msg) throw ())" 4
285.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg));" 419.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg) throw ())"
286Set the callback function to call on a retryable syscall error (such 420Set the callback function to call on a retryable system call error (such
287as failed select, poll, epoll_wait). The message is a printable string 421as failed select, poll, epoll_wait). The message is a printable string
288indicating the system call or subsystem causing the problem. If this 422indicating the system call or subsystem causing the problem. If this
289callback is set, then libev will expect it to remedy the sitution, no 423callback is set, then libev will expect it to remedy the situation, no
290matter what, when it returns. That is, libev will generally retry the 424matter what, when it returns. That is, libev will generally retry the
291requested operation, or, if the condition doesn't go away, do bad stuff 425requested operation, or, if the condition doesn't go away, do bad stuff
292(such as abort). 426(such as abort).
293.Sp 427.Sp
294Example: do the same thing as libev does internally: 428Example: This is basically the same thing that libev does internally, too.
295.Sp 429.Sp
296.Vb 6 430.Vb 6
297\& static void 431\& static void
298\& fatal_error (const char *msg) 432\& fatal_error (const char *msg)
299\& { 433\& {
300\& perror (msg); 434\& perror (msg);
301\& abort (); 435\& abort ();
302\& } 436\& }
303.Ve 437\&
304.Sp
305.Vb 2
306\& ... 438\& ...
307\& ev_set_syserr_cb (fatal_error); 439\& ev_set_syserr_cb (fatal_error);
308.Ve 440.Ve
441.IP "ev_feed_signal (int signum)" 4
442.IX Item "ev_feed_signal (int signum)"
443This function can be used to \*(L"simulate\*(R" a signal receive. It is completely
444safe to call this function at any time, from any context, including signal
445handlers or random threads.
446.Sp
447Its main use is to customise signal handling in your process, especially
448in the presence of threads. For example, you could block signals
449by default in all threads (and specifying \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when
450creating any loops), and in one thread, use \f(CW\*(C`sigwait\*(C'\fR or any other
451mechanism to wait for signals, then \*(L"deliver\*(R" them to libev by calling
452\&\f(CW\*(C`ev_feed_signal\*(C'\fR.
309.SH "FUNCTIONS CONTROLLING THE EVENT LOOP" 453.SH "FUNCTIONS CONTROLLING EVENT LOOPS"
310.IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP" 454.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 455An 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 456\&\fInot\fR optional in this case unless libev 3 compatibility is disabled, as
313events, and dynamically created loops which do not. 457libev 3 had an \f(CW\*(C`ev_loop\*(C'\fR function colliding with the struct name).
314.PP 458.PP
315If you use threads, a common model is to run the default event loop 459The 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 460supports child process events, and dynamically created event loops which
317create, you also create another event loop. Libev itself does no locking 461do 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)" 4 462.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
322.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)" 463.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
323This will initialise the default event loop if it hasn't been initialised 464This 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 465normally 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 466the \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). 467\&\f(CW\*(C`ev_loop_new\*(C'\fR.
468.Sp
469If the default loop is already initialised then this function simply
470returns it (and ignores the flags. If that is troubling you, check
471\&\f(CW\*(C`ev_backend ()\*(C'\fR afterwards). Otherwise it will create it with the given
472flags, which should almost always be \f(CW0\fR, unless the caller is also the
473one calling \f(CW\*(C`ev_run\*(C'\fR or otherwise qualifies as \*(L"the main program\*(R".
327.Sp 474.Sp
328If you don't know what event loop to use, use the one returned from this 475If you don't know what event loop to use, use the one returned from this
329function. 476function (or via the \f(CW\*(C`EV_DEFAULT\*(C'\fR macro).
477.Sp
478Note that this function is \fInot\fR thread-safe, so if you want to use it
479from multiple threads, you have to employ some kind of mutex (note also
480that this case is unlikely, as loops cannot be shared easily between
481threads anyway).
482.Sp
483The default loop is the only loop that can handle \f(CW\*(C`ev_child\*(C'\fR watchers,
484and to do this, it always registers a handler for \f(CW\*(C`SIGCHLD\*(C'\fR. If this is
485a problem for your application you can either create a dynamic loop with
486\&\f(CW\*(C`ev_loop_new\*(C'\fR which doesn't do that, or you can simply overwrite the
487\&\f(CW\*(C`SIGCHLD\*(C'\fR signal handler \fIafter\fR calling \f(CW\*(C`ev_default_init\*(C'\fR.
488.Sp
489Example: This is the most typical usage.
490.Sp
491.Vb 2
492\& if (!ev_default_loop (0))
493\& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
494.Ve
495.Sp
496Example: Restrict libev to the select and poll backends, and do not allow
497environment settings to be taken into account:
498.Sp
499.Vb 1
500\& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
501.Ve
502.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
503.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
504This will create and initialise a new event loop object. If the loop
505could not be initialised, returns false.
506.Sp
507This function is thread-safe, and one common way to use libev with
508threads is indeed to create one loop per thread, and using the default
509loop in the \*(L"main\*(R" or \*(L"initial\*(R" thread.
330.Sp 510.Sp
331The flags argument can be used to specify special behaviour or specific 511The 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). 512backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).
333.Sp 513.Sp
334The following flags are supported: 514The following flags are supported:
… …
339The default flags value. Use this if you have no clue (it's the right 519The default flags value. Use this if you have no clue (it's the right
340thing, believe me). 520thing, believe me).
341.ie n .IP """EVFLAG_NOENV""" 4 521.ie n .IP """EVFLAG_NOENV""" 4
342.el .IP "\f(CWEVFLAG_NOENV\fR" 4 522.el .IP "\f(CWEVFLAG_NOENV\fR" 4
343.IX Item "EVFLAG_NOENV" 523.IX Item "EVFLAG_NOENV"
344If this flag bit is ored into the flag value (or the program runs setuid 524If 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 525or 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 526\&\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 527override 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 528useful to try out specific backends to test their performance, to work
349around bugs. 529around bugs, or to make libev threadsafe (accessing environment variables
530cannot be done in a threadsafe way, but usually it works if no other
531thread modifies them).
532.ie n .IP """EVFLAG_FORKCHECK""" 4
533.el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4
534.IX Item "EVFLAG_FORKCHECK"
535Instead of calling \f(CW\*(C`ev_loop_fork\*(C'\fR manually after a fork, you can also
536make libev check for a fork in each iteration by enabling this flag.
537.Sp
538This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop,
539and thus this might slow down your event loop if you do a lot of loop
540iterations and little real work, but is usually not noticeable (on my
541GNU/Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn sequence
542without a system call and thus \fIvery\fR fast, but my GNU/Linux system also has
543\&\f(CW\*(C`pthread_atfork\*(C'\fR which is even faster).
544.Sp
545The big advantage of this flag is that you can forget about fork (and
546forget about forgetting to tell libev about forking, although you still
547have to ignore \f(CW\*(C`SIGPIPE\*(C'\fR) when you use this flag.
548.Sp
549This flag setting cannot be overridden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR
550environment variable.
551.ie n .IP """EVFLAG_NOINOTIFY""" 4
552.el .IP "\f(CWEVFLAG_NOINOTIFY\fR" 4
553.IX Item "EVFLAG_NOINOTIFY"
554When this flag is specified, then libev will not attempt to use the
555\&\fIinotify\fR \s-1API\s0 for its \f(CW\*(C`ev_stat\*(C'\fR watchers. Apart from debugging and
556testing, this flag can be useful to conserve inotify file descriptors, as
557otherwise each loop using \f(CW\*(C`ev_stat\*(C'\fR watchers consumes one inotify handle.
558.ie n .IP """EVFLAG_SIGNALFD""" 4
559.el .IP "\f(CWEVFLAG_SIGNALFD\fR" 4
560.IX Item "EVFLAG_SIGNALFD"
561When this flag is specified, then libev will attempt to use the
562\&\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
563delivers signals synchronously, which makes it both faster and might make
564it possible to get the queued signal data. It can also simplify signal
565handling with threads, as long as you properly block signals in your
566threads that are not interested in handling them.
567.Sp
568Signalfd will not be used by default as this changes your signal mask, and
569there are a lot of shoddy libraries and programs (glib's threadpool for
570example) that can't properly initialise their signal masks.
571.ie n .IP """EVFLAG_NOSIGMASK""" 4
572.el .IP "\f(CWEVFLAG_NOSIGMASK\fR" 4
573.IX Item "EVFLAG_NOSIGMASK"
574When this flag is specified, then libev will avoid to modify the signal
575mask. Specifically, this means you have to make sure signals are unblocked
576when you want to receive them.
577.Sp
578This behaviour is useful when you want to do your own signal handling, or
579want to handle signals only in specific threads and want to avoid libev
580unblocking the signals.
581.Sp
582It's also required by \s-1POSIX\s0 in a threaded program, as libev calls
583\&\f(CW\*(C`sigprocmask\*(C'\fR, whose behaviour is officially unspecified.
584.Sp
585This flag's behaviour will become the default in future versions of libev.
350.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4 586.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
351.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4 587.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
352.IX Item "EVBACKEND_SELECT (value 1, portable select backend)" 588.IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
353This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as 589This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as
354libev tries to roll its own fd_set with no limits on the number of fds, 590libev 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 591but 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 592using this backend. It doesn't scale too well (O(highest_fd)), but its
357the fastest backend for a low number of fds. 593usually the fastest backend for a low number of (low-numbered :) fds.
594.Sp
595To get good performance out of this backend you need a high amount of
596parallelism (most of the file descriptors should be busy). If you are
597writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many
598connections as possible during one iteration. You might also want to have
599a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of
600readiness notifications you get per iteration.
601.Sp
602This 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
603\&\f(CW\*(C`writefds\*(C'\fR set (and to work around Microsoft Windows bugs, also onto the
604\&\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)" 4 605.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)" 4 606.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)" 607.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 608And this is your standard \fIpoll\fR\|(2) backend. It's more complicated
362select, but handles sparse fds better and has no artificial limit on the 609than select, but handles sparse fds better and has no artificial
363number of fds you can use (except it will slow down considerably with a 610limit 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). 611considerably with a lot of inactive fds). It scales similarly to select,
612i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for
613performance tips.
614.Sp
615This backend maps \f(CW\*(C`EV_READ\*(C'\fR to \f(CW\*(C`POLLIN | POLLERR | POLLHUP\*(C'\fR, and
616\&\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)" 4 617.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
366.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4 618.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
367.IX Item "EVBACKEND_EPOLL (value 4, Linux)" 619.IX Item "EVBACKEND_EPOLL (value 4, Linux)"
620Use the linux-specific \fIepoll\fR\|(7) interface (for both pre\- and post\-2.6.9
621kernels).
622.Sp
368For few fds, this backend is a bit little slower than poll and select, 623For 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 624it 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 625O(total_fds) where total_fds is the total number of fds (or the highest
371either O(1) or O(active_fds). 626fd), epoll scales either O(1) or O(active_fds).
372.Sp 627.Sp
628The epoll mechanism deserves honorable mention as the most misdesigned
629of the more advanced event mechanisms: mere annoyances include silently
630dropping file descriptors, requiring a system call per change per file
631descriptor (and unnecessary guessing of parameters), problems with dup,
632returning before the timeout value, resulting in additional iterations
633(and only giving 5ms accuracy while select on the same platform gives
6340.1ms) and so on. The biggest issue is fork races, however \- if a program
635forks then \fIboth\fR parent and child process have to recreate the epoll
636set, which can take considerable time (one syscall per file descriptor)
637and is of course hard to detect.
638.Sp
639Epoll is also notoriously buggy \- embedding epoll fds \fIshould\fR work,
640but of course \fIdoesn't\fR, and epoll just loves to report events for
641totally \fIdifferent\fR file descriptors (even already closed ones, so
642one cannot even remove them from the set) than registered in the set
643(especially on \s-1SMP\s0 systems). Libev tries to counter these spurious
644notifications by employing an additional generation counter and comparing
645that against the events to filter out spurious ones, recreating the set
646when required. Epoll also erroneously rounds down timeouts, but gives you
647no way to know when and by how much, so sometimes you have to busy-wait
648because epoll returns immediately despite a nonzero timeout. And last
649not least, it also refuses to work with some file descriptors which work
650perfectly fine with \f(CW\*(C`select\*(C'\fR (files, many character devices...).
651.Sp
652Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
653cobbled together in a hurry, no thought to design or interaction with
654others. Oh, the pain, will it ever stop...
655.Sp
373While stopping and starting an I/O watcher in the same iteration will 656While stopping, setting and starting an I/O watcher in the same iteration
374result in some caching, there is still a syscall per such incident 657will 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 658incident (because the same \fIfile descriptor\fR could point to a different
376best to avoid that. Also, \fIdup()\fRed file descriptors might not work very 659\&\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. 660file descriptors might not work very well if you register events for both
661file descriptors.
378.Sp 662.Sp
379Please note that epoll sometimes generates spurious notifications, so you 663Best 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 664watchers for a file descriptor until it has been closed, if possible,
381(or space) is available. 665i.e. keep at least one watcher active per fd at all times. Stopping and
666starting a watcher (without re-setting it) also usually doesn't cause
667extra overhead. A fork can both result in spurious notifications as well
668as in libev having to destroy and recreate the epoll object, which can
669take considerable time and thus should be avoided.
670.Sp
671All this means that, in practice, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR can be as fast or
672faster than epoll for maybe up to a hundred file descriptors, depending on
673the usage. So sad.
674.Sp
675While nominally embeddable in other event loops, this feature is broken in
676all kernel versions tested so far.
677.Sp
678This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
679\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
382.ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4 680.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)" 4 681.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
384.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)" 682.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
385Kqueue deserves special mention, as at the time of this writing, it 683Kqueue deserves special mention, as at the time of this writing, it
386was broken on all BSDs except NetBSD (usually it doesn't work with 684was broken on all BSDs except NetBSD (usually it doesn't work reliably
387anything but sockets and pipes, except on Darwin, where of course its 685with anything but sockets and pipes, except on Darwin, where of course
388completely useless). For this reason its not being \*(L"autodetected\*(R" 686it's completely useless). Unlike epoll, however, whose brokenness
687is by design, these kqueue bugs can (and eventually will) be fixed
688without \s-1API\s0 changes to existing programs. For this reason it's not being
389unless you explicitly specify it explicitly in the flags (i.e. using 689\&\*(L"auto-detected\*(R" unless you explicitly specify it in the flags (i.e. using
390\&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR). 690\&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a known-to-be-good (\-enough)
691system like NetBSD.
692.Sp
693You still can embed kqueue into a normal poll or select backend and use it
694only for sockets (after having made sure that sockets work with kqueue on
695the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
391.Sp 696.Sp
392It scales in the same way as the epoll backend, but the interface to the 697It 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 698kernel is more efficient (which says nothing about its actual speed, of
394course). While starting and stopping an I/O watcher does not cause an 699course). 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 700cause 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. 701two event changes per incident. Support for \f(CW\*(C`fork ()\*(C'\fR is very bad (you
702might have to leak fd's on fork, but it's more sane than epoll) and it
703drops fds silently in similarly hard-to-detect cases.
704.Sp
705This backend usually performs well under most conditions.
706.Sp
707While nominally embeddable in other event loops, this doesn't work
708everywhere, so you might need to test for this. And since it is broken
709almost everywhere, you should only use it when you have a lot of sockets
710(for which it usually works), by embedding it into another event loop
711(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
712also broken on \s-1OS X\s0)) and, did I mention it, using it only for sockets.
713.Sp
714This backend maps \f(CW\*(C`EV_READ\*(C'\fR into an \f(CW\*(C`EVFILT_READ\*(C'\fR kevent with
715\&\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
716\&\f(CW\*(C`NOTE_EOF\*(C'\fR.
397.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4 717.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
398.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4 718.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
399.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)" 719.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
400This is not implemented yet (and might never be). 720This is not implemented yet (and might never be, unless you send me an
721implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets
722and is not embeddable, which would limit the usefulness of this backend
723immensely.
401.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4 724.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
402.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4 725.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
403.IX Item "EVBACKEND_PORT (value 32, Solaris 10)" 726.IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
404This uses the Solaris 10 port mechanism. As with everything on Solaris, 727This 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)). 728it's really slow, but it still scales very well (O(active_fds)).
406.Sp 729.Sp
407Please note that solaris ports can result in a lot of spurious 730While 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 731file descriptor per loop iteration. For small and medium numbers of file
409blocking when no data (or space) is available. 732descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend
733might perform better.
734.Sp
735On the positive side, this backend actually performed fully to
736specification in all tests and is fully embeddable, which is a rare feat
737among the OS-specific backends (I vastly prefer correctness over speed
738hacks).
739.Sp
740On the negative side, the interface is \fIbizarre\fR \- so bizarre that
741even sun itself gets it wrong in their code examples: The event polling
742function sometimes returns events to the caller even though an error
743occurred, but with no indication whether it has done so or not (yes, it's
744even documented that way) \- deadly for edge-triggered interfaces where you
745absolutely have to know whether an event occurred or not because you have
746to re-arm the watcher.
747.Sp
748Fortunately libev seems to be able to work around these idiocies.
749.Sp
750This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
751\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
410.ie n .IP """EVBACKEND_ALL""" 4 752.ie n .IP """EVBACKEND_ALL""" 4
411.el .IP "\f(CWEVBACKEND_ALL\fR" 4 753.el .IP "\f(CWEVBACKEND_ALL\fR" 4
412.IX Item "EVBACKEND_ALL" 754.IX Item "EVBACKEND_ALL"
413Try all backends (even potentially broken ones that wouldn't be tried 755Try 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 756with \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. 757\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR.
758.Sp
759It is definitely not recommended to use this flag, use whatever
760\&\f(CW\*(C`ev_recommended_backends ()\*(C'\fR returns, or simply do not specify a backend
761at all.
762.ie n .IP """EVBACKEND_MASK""" 4
763.el .IP "\f(CWEVBACKEND_MASK\fR" 4
764.IX Item "EVBACKEND_MASK"
765Not a backend at all, but a mask to select all backend bits from a
766\&\f(CW\*(C`flags\*(C'\fR value, in case you want to mask out any backends from a flags
767value (e.g. when modifying the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR environment variable).
416.RE 768.RE
417.RS 4 769.RS 4
418.Sp 770.Sp
419If one or more of these are ored into the flags value, then only these 771If 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 772then only these backends will be tried (in the reverse order as listed
421specified, most compiled-in backend will be tried, usually in reverse 773here). If none are specified, all backends in \f(CW\*(C`ev_recommended_backends
422order of their flag values :) 774()\*(C'\fR will be tried.
423.Sp 775.Sp
424The most typical usage is like this: 776Example: Try to create a event loop that uses epoll and nothing else.
425.Sp 777.Sp
426.Vb 2 778.Vb 3
427\& if (!ev_default_loop (0)) 779\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
428\& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?"); 780\& if (!epoller)
781\& fatal ("no epoll found here, maybe it hides under your chair");
429.Ve 782.Ve
430.Sp 783.Sp
431Restrict libev to the select and poll backends, and do not allow 784Example: Use whatever libev has to offer, but make sure that kqueue is
432environment settings to be taken into account: 785used if available.
433.Sp 786.Sp
434.Vb 1 787.Vb 1
435\& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
436.Ve
437.Sp
438Use whatever libev has to offer, but make sure that kqueue is used if
439available (warning, breaks stuff, best use only with your own private
440event loop and only if you know the \s-1OS\s0 supports your types of fds):
441.Sp
442.Vb 1
443\& ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE); 788\& struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
444.Ve 789.Ve
445.RE 790.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 ()" 4 791.IP "ev_loop_destroy (loop)" 4
461.IX Item "ev_default_destroy ()" 792.IX Item "ev_loop_destroy (loop)"
462Destroys the default loop again (frees all memory and kernel state 793Destroys an event loop object (frees all memory and kernel state
463etc.). None of the active event watchers will be stopped in the normal 794etc.). 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 795sense, 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 796responsibility to either stop all watchers cleanly yourself \fIbefore\fR
466calling this function, or cope with the fact afterwards (which is usually 797calling 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 798the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them
468for example). 799for 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 800.Sp
480You \fImust\fR call this function in the child process after forking if and 801Note 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 802handlers), will not be freed by this function, and related watchers (such
482fork+exec, you don't have to call it. 803as signal and child watchers) would need to be stopped manually.
483.Sp 804.Sp
484The function itself is quite fast and it's usually not a problem to call 805This 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 806\&\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: 807\&\f(CW\*(C`ev_default_loop\*(C'\fR, in which case it is not thread-safe.
487.Sp 808.Sp
488.Vb 1 809Note that it is not advisable to call this function on the default loop
489\& pthread_atfork (0, 0, ev_default_fork); 810except in the rare occasion where you really need to free its resources.
490.Ve 811If you need dynamically allocated loops it is better to use \f(CW\*(C`ev_loop_new\*(C'\fR
491.Sp 812and \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)" 4 813.IP "ev_loop_fork (loop)" 4
496.IX Item "ev_loop_fork (loop)" 814.IX Item "ev_loop_fork (loop)"
497Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by 815This 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 816to reinitialise the kernel state for backends that have one. Despite
499after fork, and how you do this is entirely your own problem. 817the name, you can call it anytime you are allowed to start or stop
818watchers (except inside an \f(CW\*(C`ev_prepare\*(C'\fR callback), but it makes most
819sense after forking, in the child process. You \fImust\fR call it (or use
820\&\f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR) in the child before resuming or calling \f(CW\*(C`ev_run\*(C'\fR.
821.Sp
822In addition, if you want to reuse a loop (via this function or
823\&\f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR), you \fIalso\fR have to ignore \f(CW\*(C`SIGPIPE\*(C'\fR.
824.Sp
825Again, you \fIhave\fR to call it on \fIany\fR loop that you want to re-use after
826a fork, \fIeven if you do not plan to use the loop in the parent\fR. This is
827because some kernel interfaces *cough* \fIkqueue\fR *cough* do funny things
828during fork.
829.Sp
830On the other hand, you only need to call this function in the child
831process if and only if you want to use the event loop in the child. If
832you just fork+exec or create a new loop in the child, you don't have to
833call it at all (in fact, \f(CW\*(C`epoll\*(C'\fR is so badly broken that it makes a
834difference, but libev will usually detect this case on its own and do a
835costly reset of the backend).
836.Sp
837The function itself is quite fast and it's usually not a problem to call
838it just in case after a fork.
839.Sp
840Example: Automate calling \f(CW\*(C`ev_loop_fork\*(C'\fR on the default loop when
841using pthreads.
842.Sp
843.Vb 5
844\& static void
845\& post_fork_child (void)
846\& {
847\& ev_loop_fork (EV_DEFAULT);
848\& }
849\&
850\& ...
851\& pthread_atfork (0, 0, post_fork_child);
852.Ve
853.IP "int ev_is_default_loop (loop)" 4
854.IX Item "int ev_is_default_loop (loop)"
855Returns true when the given loop is, in fact, the default loop, and false
856otherwise.
857.IP "unsigned int ev_iteration (loop)" 4
858.IX Item "unsigned int ev_iteration (loop)"
859Returns the current iteration count for the event loop, which is identical
860to the number of times libev did poll for new events. It starts at \f(CW0\fR
861and happily wraps around with enough iterations.
862.Sp
863This value can sometimes be useful as a generation counter of sorts (it
864\&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with
865\&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls \- and is incremented between the
866prepare and check phases.
867.IP "unsigned int ev_depth (loop)" 4
868.IX Item "unsigned int ev_depth (loop)"
869Returns the number of times \f(CW\*(C`ev_run\*(C'\fR was entered minus the number of
870times \f(CW\*(C`ev_run\*(C'\fR was exited normally, in other words, the recursion depth.
871.Sp
872Outside \f(CW\*(C`ev_run\*(C'\fR, this number is zero. In a callback, this number is
873\&\f(CW1\fR, unless \f(CW\*(C`ev_run\*(C'\fR was invoked recursively (or from another thread),
874in which case it is higher.
875.Sp
876Leaving \f(CW\*(C`ev_run\*(C'\fR abnormally (setjmp/longjmp, cancelling the thread,
877throwing an exception etc.), doesn't count as \*(L"exit\*(R" \- consider this
878as a hint to avoid such ungentleman-like behaviour unless it's really
879convenient, in which case it is fully supported.
500.IP "unsigned int ev_backend (loop)" 4 880.IP "unsigned int ev_backend (loop)" 4
501.IX Item "unsigned int ev_backend (loop)" 881.IX Item "unsigned int ev_backend (loop)"
502Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in 882Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
503use. 883use.
504.IP "ev_tstamp ev_now (loop)" 4 884.IP "ev_tstamp ev_now (loop)" 4
505.IX Item "ev_tstamp ev_now (loop)" 885.IX Item "ev_tstamp ev_now (loop)"
506Returns the current \*(L"event loop time\*(R", which is the time the event loop 886Returns the current \*(L"event loop time\*(R", which is the time the event loop
507received events and started processing them. This timestamp does not 887received events and started processing them. This timestamp does not
508change as long as callbacks are being processed, and this is also the base 888change 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 889time used for relative timers. You can treat it as the timestamp of the
510event occuring (or more correctly, libev finding out about it). 890event occurring (or more correctly, libev finding out about it).
891.IP "ev_now_update (loop)" 4
892.IX Item "ev_now_update (loop)"
893Establishes the current time by querying the kernel, updating the time
894returned by \f(CW\*(C`ev_now ()\*(C'\fR in the progress. This is a costly operation and
895is usually done automatically within \f(CW\*(C`ev_run ()\*(C'\fR.
896.Sp
897This function is rarely useful, but when some event callback runs for a
898very long time without entering the event loop, updating libev's idea of
899the current time is a good idea.
900.Sp
901See also \*(L"The special problem of time updates\*(R" in the \f(CW\*(C`ev_timer\*(C'\fR section.
902.IP "ev_suspend (loop)" 4
903.IX Item "ev_suspend (loop)"
904.PD 0
905.IP "ev_resume (loop)" 4
906.IX Item "ev_resume (loop)"
907.PD
908These two functions suspend and resume an event loop, for use when the
909loop is not used for a while and timeouts should not be processed.
910.Sp
911A typical use case would be an interactive program such as a game: When
912the user presses \f(CW\*(C`^Z\*(C'\fR to suspend the game and resumes it an hour later it
913would be best to handle timeouts as if no time had actually passed while
914the program was suspended. This can be achieved by calling \f(CW\*(C`ev_suspend\*(C'\fR
915in your \f(CW\*(C`SIGTSTP\*(C'\fR handler, sending yourself a \f(CW\*(C`SIGSTOP\*(C'\fR and calling
916\&\f(CW\*(C`ev_resume\*(C'\fR directly afterwards to resume timer processing.
917.Sp
918Effectively, all \f(CW\*(C`ev_timer\*(C'\fR watchers will be delayed by the time spend
919between \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
920will be rescheduled (that is, they will lose any events that would have
921occurred while suspended).
922.Sp
923After calling \f(CW\*(C`ev_suspend\*(C'\fR you \fBmust not\fR call \fIany\fR function on the
924given loop other than \f(CW\*(C`ev_resume\*(C'\fR, and you \fBmust not\fR call \f(CW\*(C`ev_resume\*(C'\fR
925without a previous call to \f(CW\*(C`ev_suspend\*(C'\fR.
926.Sp
927Calling \f(CW\*(C`ev_suspend\*(C'\fR/\f(CW\*(C`ev_resume\*(C'\fR has the side effect of updating the
928event loop time (see \f(CW\*(C`ev_now_update\*(C'\fR).
511.IP "ev_loop (loop, int flags)" 4 929.IP "bool ev_run (loop, int flags)" 4
512.IX Item "ev_loop (loop, int flags)" 930.IX Item "bool ev_run (loop, int flags)"
513Finally, this is it, the event handler. This function usually is called 931Finally, this is it, the event handler. This function usually is called
514after you initialised all your watchers and you want to start handling 932after you have initialised all your watchers and you want to start
515events. 933handling events. It will ask the operating system for any new events, call
934the watcher callbacks, and then repeat the whole process indefinitely: This
935is why event loops are called \fIloops\fR.
516.Sp 936.Sp
517If the flags argument is specified as \f(CW0\fR, it will not return until 937If 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. 938until either no event watchers are active anymore or \f(CW\*(C`ev_break\*(C'\fR was
939called.
519.Sp 940.Sp
941The return value is false if there are no more active watchers (which
942usually means \*(L"all jobs done\*(R" or \*(L"deadlock\*(R"), and true in all other cases
943(which usually means " you should call \f(CW\*(C`ev_run\*(C'\fR again").
944.Sp
520Please note that an explicit \f(CW\*(C`ev_unloop\*(C'\fR is usually better than 945Please 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 946relying on all watchers to be stopped when deciding when a program has
522finished (especially in interactive programs), but having a program that 947finished (especially in interactive programs), but having a program
523automatically loops as long as it has to and no longer by virtue of 948that automatically loops as long as it has to and no longer by virtue
524relying on its watchers stopping correctly is a thing of beauty. 949of relying on its watchers stopping correctly, that is truly a thing of
950beauty.
525.Sp 951.Sp
952This function is \fImostly\fR exception-safe \- you can break out of a
953\&\f(CW\*(C`ev_run\*(C'\fR call by calling \f(CW\*(C`longjmp\*(C'\fR in a callback, throwing a \*(C+
954exception and so on. This does not decrement the \f(CW\*(C`ev_depth\*(C'\fR value, nor
955will it clear any outstanding \f(CW\*(C`EVBREAK_ONE\*(C'\fR breaks.
956.Sp
526A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle 957A 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 958those 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. 959block your process in case there are no events and will return after one
960iteration of the loop. This is sometimes useful to poll and handle new
961events while doing lengthy calculations, to keep the program responsive.
529.Sp 962.Sp
530A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if 963A 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 964necessary) and will handle those and any already outstanding ones. It
532your process until at least one new event arrives, and will return after 965will 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 966be an event internal to libev itself, so there is no guarantee that a
534external event in conjunction with something not expressible using other 967user-registered callback will be called), and will return after one
968iteration of the loop.
969.Sp
970This is useful if you are waiting for some external event in conjunction
971with 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 972own \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. 973usually a better approach for this kind of thing.
537.Sp 974.Sp
538Here are the gory details of what \f(CW\*(C`ev_loop\*(C'\fR does: 975Here are the gory details of what \f(CW\*(C`ev_run\*(C'\fR does (this is for your
976understanding, not a guarantee that things will work exactly like this in
977future versions):
539.Sp 978.Sp
540.Vb 18 979.Vb 10
541\& * If there are no active watchers (reference count is zero), return. 980\& \- Increment loop depth.
542\& - Queue prepare watchers and then call all outstanding watchers. 981\& \- Reset the ev_break status.
982\& \- Before the first iteration, call any pending watchers.
983\& LOOP:
984\& \- If EVFLAG_FORKCHECK was used, check for a fork.
985\& \- If a fork was detected (by any means), queue and call all fork watchers.
986\& \- Queue and call all prepare watchers.
987\& \- If ev_break was called, goto FINISH.
543\& - If we have been forked, recreate the kernel state. 988\& \- If we have been forked, detach and recreate the kernel state
989\& as to not disturb the other process.
544\& - Update the kernel state with all outstanding changes. 990\& \- Update the kernel state with all outstanding changes.
545\& - Update the "event loop time". 991\& \- Update the "event loop time" (ev_now ()).
546\& - Calculate for how long to block. 992\& \- Calculate for how long to sleep or block, if at all
993\& (active idle watchers, EVRUN_NOWAIT or not having
994\& any active watchers at all will result in not sleeping).
995\& \- Sleep if the I/O and timer collect interval say so.
996\& \- Increment loop iteration counter.
547\& - Block the process, waiting for any events. 997\& \- Block the process, waiting for any events.
548\& - Queue all outstanding I/O (fd) events. 998\& \- Queue all outstanding I/O (fd) events.
549\& - Update the "event loop time" and do time jump handling. 999\& \- Update the "event loop time" (ev_now ()), and do time jump adjustments.
550\& - Queue all outstanding timers. 1000\& \- Queue all expired timers.
551\& - Queue all outstanding periodics. 1001\& \- Queue all expired periodics.
552\& - If no events are pending now, queue all idle watchers. 1002\& \- Queue all idle watchers with priority higher than that of pending events.
553\& - Queue all check watchers. 1003\& \- Queue all check watchers.
554\& - Call all queued watchers in reverse order (i.e. check watchers first). 1004\& \- 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 1005\& Signals and child watchers are implemented as I/O watchers, and will
556\& be handled here by queueing them when their watcher gets executed. 1006\& be handled here by queueing them when their watcher gets executed.
557\& - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK 1007\& \- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
558\& were used, return, otherwise continue with step *. 1008\& were used, or there are no active watchers, goto FINISH, otherwise
1009\& continue with step LOOP.
1010\& FINISH:
1011\& \- Reset the ev_break status iff it was EVBREAK_ONE.
1012\& \- Decrement the loop depth.
1013\& \- Return.
559.Ve 1014.Ve
560.Sp 1015.Sp
561Example: queue some jobs and then loop until no events are outsanding 1016Example: Queue some jobs and then loop until no events are outstanding
562anymore. 1017anymore.
563.Sp 1018.Sp
564.Vb 4 1019.Vb 4
565\& ... queue jobs here, make sure they register event watchers as long 1020\& ... 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..) 1021\& ... as they still have work to do (even an idle watcher will do..)
567\& ev_loop (my_loop, 0); 1022\& ev_run (my_loop, 0);
568\& ... jobs done. yeah! 1023\& ... jobs done or somebody called break. yeah!
569.Ve 1024.Ve
570.IP "ev_unloop (loop, how)" 4 1025.IP "ev_break (loop, how)" 4
571.IX Item "ev_unloop (loop, how)" 1026.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 1027Can 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 1028has 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 1029\&\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. 1030\&\f(CW\*(C`EVBREAK_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_run\*(C'\fR calls return.
1031.Sp
1032This \*(L"break state\*(R" will be cleared on the next call to \f(CW\*(C`ev_run\*(C'\fR.
1033.Sp
1034It is safe to call \f(CW\*(C`ev_break\*(C'\fR from outside any \f(CW\*(C`ev_run\*(C'\fR calls, too, in
1035which case it will have no effect.
576.IP "ev_ref (loop)" 4 1036.IP "ev_ref (loop)" 4
577.IX Item "ev_ref (loop)" 1037.IX Item "ev_ref (loop)"
578.PD 0 1038.PD 0
579.IP "ev_unref (loop)" 4 1039.IP "ev_unref (loop)" 4
580.IX Item "ev_unref (loop)" 1040.IX Item "ev_unref (loop)"
581.PD 1041.PD
582Ref/unref can be used to add or remove a reference count on the event 1042Ref/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 1043loop: 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 1044count 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 1045.Sp
586returning, \fIev_unref()\fR after starting, and \fIev_ref()\fR before stopping it. For 1046This is useful when you have a watcher that you never intend to
1047unregister, but that nevertheless should not keep \f(CW\*(C`ev_run\*(C'\fR from
1048returning. In such a case, call \f(CW\*(C`ev_unref\*(C'\fR after starting, and \f(CW\*(C`ev_ref\*(C'\fR
1049before stopping it.
1050.Sp
587example, libev itself uses this for its internal signal pipe: It is not 1051As 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 1052is 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 1053exiting 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 1054excellent way to do this for generic recurring timers or from within
591libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR. 1055third-party libraries. Just remember to \fIunref after start\fR and \fIref
1056before stop\fR (but only if the watcher wasn't active before, or was active
1057before, respectively. Note also that libev might stop watchers itself
1058(e.g. non-repeating timers) in which case you have to \f(CW\*(C`ev_ref\*(C'\fR
1059in the callback).
592.Sp 1060.Sp
593Example: create a signal watcher, but keep it from keeping \f(CW\*(C`ev_loop\*(C'\fR 1061Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_run\*(C'\fR
594running when nothing else is active. 1062running when nothing else is active.
595.Sp 1063.Sp
596.Vb 4 1064.Vb 4
597\& struct dv_signal exitsig; 1065\& ev_signal exitsig;
598\& ev_signal_init (&exitsig, sig_cb, SIGINT); 1066\& ev_signal_init (&exitsig, sig_cb, SIGINT);
599\& ev_signal_start (myloop, &exitsig); 1067\& ev_signal_start (loop, &exitsig);
600\& evf_unref (myloop); 1068\& ev_unref (loop);
601.Ve 1069.Ve
602.Sp 1070.Sp
603Example: for some weird reason, unregister the above signal handler again. 1071Example: For some weird reason, unregister the above signal handler again.
604.Sp 1072.Sp
605.Vb 2 1073.Vb 2
606\& ev_ref (myloop); 1074\& ev_ref (loop);
607\& ev_signal_stop (myloop, &exitsig); 1075\& ev_signal_stop (loop, &exitsig);
608.Ve 1076.Ve
1077.IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4
1078.IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"
1079.PD 0
1080.IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4
1081.IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"
1082.PD
1083These advanced functions influence the time that libev will spend waiting
1084for events. Both time intervals are by default \f(CW0\fR, meaning that libev
1085will try to invoke timer/periodic callbacks and I/O callbacks with minimum
1086latency.
1087.Sp
1088Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR)
1089allows libev to delay invocation of I/O and timer/periodic callbacks
1090to increase efficiency of loop iterations (or to increase power-saving
1091opportunities).
1092.Sp
1093The idea is that sometimes your program runs just fast enough to handle
1094one (or very few) event(s) per loop iteration. While this makes the
1095program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new
1096events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high
1097overhead for the actual polling but can deliver many events at once.
1098.Sp
1099By setting a higher \fIio collect interval\fR you allow libev to spend more
1100time collecting I/O events, so you can handle more events per iteration,
1101at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and
1102\&\f(CW\*(C`ev_timer\*(C'\fR) will not be affected. Setting this to a non-null value will
1103introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations. The
1104sleep time ensures that libev will not poll for I/O events more often then
1105once per this interval, on average (as long as the host time resolution is
1106good enough).
1107.Sp
1108Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
1109to spend more time collecting timeouts, at the expense of increased
1110latency/jitter/inexactness (the watcher callback will be called
1111later). \f(CW\*(C`ev_io\*(C'\fR watchers will not be affected. Setting this to a non-null
1112value will not introduce any overhead in libev.
1113.Sp
1114Many (busy) programs can usually benefit by setting the I/O collect
1115interval to a value near \f(CW0.1\fR or so, which is often enough for
1116interactive servers (of course not for games), likewise for timeouts. It
1117usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR,
1118as this approaches the timing granularity of most systems. Note that if
1119you do transactions with the outside world and you can't increase the
1120parallelity, then this setting will limit your transaction rate (if you
1121need to poll once per transaction and the I/O collect interval is 0.01,
1122then you can't do more than 100 transactions per second).
1123.Sp
1124Setting the \fItimeout collect interval\fR can improve the opportunity for
1125saving power, as the program will \*(L"bundle\*(R" timer callback invocations that
1126are \*(L"near\*(R" in time together, by delaying some, thus reducing the number of
1127times the process sleeps and wakes up again. Another useful technique to
1128reduce iterations/wake\-ups is to use \f(CW\*(C`ev_periodic\*(C'\fR watchers and make sure
1129they fire on, say, one-second boundaries only.
1130.Sp
1131Example: we only need 0.1s timeout granularity, and we wish not to poll
1132more often than 100 times per second:
1133.Sp
1134.Vb 2
1135\& ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
1136\& ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
1137.Ve
1138.IP "ev_invoke_pending (loop)" 4
1139.IX Item "ev_invoke_pending (loop)"
1140This call will simply invoke all pending watchers while resetting their
1141pending state. Normally, \f(CW\*(C`ev_run\*(C'\fR does this automatically when required,
1142but when overriding the invoke callback this call comes handy. This
1143function can be invoked from a watcher \- this can be useful for example
1144when you want to do some lengthy calculation and want to pass further
1145event handling to another thread (you still have to make sure only one
1146thread executes within \f(CW\*(C`ev_invoke_pending\*(C'\fR or \f(CW\*(C`ev_run\*(C'\fR of course).
1147.IP "int ev_pending_count (loop)" 4
1148.IX Item "int ev_pending_count (loop)"
1149Returns the number of pending watchers \- zero indicates that no watchers
1150are pending.
1151.IP "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(\s-1EV_P\s0))" 4
1152.IX Item "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))"
1153This overrides the invoke pending functionality of the loop: Instead of
1154invoking all pending watchers when there are any, \f(CW\*(C`ev_run\*(C'\fR will call
1155this callback instead. This is useful, for example, when you want to
1156invoke the actual watchers inside another context (another thread etc.).
1157.Sp
1158If you want to reset the callback, use \f(CW\*(C`ev_invoke_pending\*(C'\fR as new
1159callback.
1160.IP "ev_set_loop_release_cb (loop, void (*release)(\s-1EV_P\s0) throw (), void (*acquire)(\s-1EV_P\s0) throw ())" 4
1161.IX Item "ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())"
1162Sometimes you want to share the same loop between multiple threads. This
1163can be done relatively simply by putting mutex_lock/unlock calls around
1164each call to a libev function.
1165.Sp
1166However, \f(CW\*(C`ev_run\*(C'\fR can run an indefinite time, so it is not feasible
1167to wait for it to return. One way around this is to wake up the event
1168loop via \f(CW\*(C`ev_break\*(C'\fR and \f(CW\*(C`ev_async_send\*(C'\fR, another way is to set these
1169\&\fIrelease\fR and \fIacquire\fR callbacks on the loop.
1170.Sp
1171When set, then \f(CW\*(C`release\*(C'\fR will be called just before the thread is
1172suspended waiting for new events, and \f(CW\*(C`acquire\*(C'\fR is called just
1173afterwards.
1174.Sp
1175Ideally, \f(CW\*(C`release\*(C'\fR will just call your mutex_unlock function, and
1176\&\f(CW\*(C`acquire\*(C'\fR will just call the mutex_lock function again.
1177.Sp
1178While event loop modifications are allowed between invocations of
1179\&\f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR (that's their only purpose after all), no
1180modifications done will affect the event loop, i.e. adding watchers will
1181have no effect on the set of file descriptors being watched, or the time
1182waited. Use an \f(CW\*(C`ev_async\*(C'\fR watcher to wake up \f(CW\*(C`ev_run\*(C'\fR when you want it
1183to take note of any changes you made.
1184.Sp
1185In theory, threads executing \f(CW\*(C`ev_run\*(C'\fR will be async-cancel safe between
1186invocations of \f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR.
1187.Sp
1188See also the locking example in the \f(CW\*(C`THREADS\*(C'\fR section later in this
1189document.
1190.IP "ev_set_userdata (loop, void *data)" 4
1191.IX Item "ev_set_userdata (loop, void *data)"
1192.PD 0
1193.IP "void *ev_userdata (loop)" 4
1194.IX Item "void *ev_userdata (loop)"
1195.PD
1196Set and retrieve a single \f(CW\*(C`void *\*(C'\fR associated with a loop. When
1197\&\f(CW\*(C`ev_set_userdata\*(C'\fR has never been called, then \f(CW\*(C`ev_userdata\*(C'\fR returns
1198\&\f(CW0\fR.
1199.Sp
1200These two functions can be used to associate arbitrary data with a loop,
1201and are intended solely for the \f(CW\*(C`invoke_pending_cb\*(C'\fR, \f(CW\*(C`release\*(C'\fR and
1202\&\f(CW\*(C`acquire\*(C'\fR callbacks described above, but of course can be (ab\-)used for
1203any other purpose as well.
1204.IP "ev_verify (loop)" 4
1205.IX Item "ev_verify (loop)"
1206This function only does something when \f(CW\*(C`EV_VERIFY\*(C'\fR support has been
1207compiled in, which is the default for non-minimal builds. It tries to go
1208through all internal structures and checks them for validity. If anything
1209is found to be inconsistent, it will print an error message to standard
1210error and call \f(CW\*(C`abort ()\*(C'\fR.
1211.Sp
1212This can be used to catch bugs inside libev itself: under normal
1213circumstances, this function will never abort as of course libev keeps its
1214data structures consistent.
609.SH "ANATOMY OF A WATCHER" 1215.SH "ANATOMY OF A WATCHER"
610.IX Header "ANATOMY OF A WATCHER" 1216.IX Header "ANATOMY OF A WATCHER"
1217In the following description, uppercase \f(CW\*(C`TYPE\*(C'\fR in names stands for the
1218watcher type, e.g. \f(CW\*(C`ev_TYPE_start\*(C'\fR can mean \f(CW\*(C`ev_timer_start\*(C'\fR for timer
1219watchers and \f(CW\*(C`ev_io_start\*(C'\fR for I/O watchers.
1220.PP
611A watcher is a structure that you create and register to record your 1221A 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 1222your 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: 1223to wait for \s-1STDIN\s0 to become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher
1224for that:
614.PP 1225.PP
615.Vb 5 1226.Vb 5
616\& static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) 1227\& static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
617\& { 1228\& {
618\& ev_io_stop (w); 1229\& ev_io_stop (w);
619\& ev_unloop (loop, EVUNLOOP_ALL); 1230\& ev_break (loop, EVBREAK_ALL);
620\& } 1231\& }
621.Ve 1232\&
622.PP
623.Vb 6
624\& struct ev_loop *loop = ev_default_loop (0); 1233\& struct ev_loop *loop = ev_default_loop (0);
1234\&
625\& struct ev_io stdin_watcher; 1235\& ev_io stdin_watcher;
1236\&
626\& ev_init (&stdin_watcher, my_cb); 1237\& ev_init (&stdin_watcher, my_cb);
627\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); 1238\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
628\& ev_io_start (loop, &stdin_watcher); 1239\& ev_io_start (loop, &stdin_watcher);
1240\&
629\& ev_loop (loop, 0); 1241\& ev_run (loop, 0);
630.Ve 1242.Ve
631.PP 1243.PP
632As you can see, you are responsible for allocating the memory for your 1244As 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, 1245watcher structures (and it is \fIusually\fR a bad idea to do this on the
634although this can sometimes be quite valid). 1246stack).
635.PP 1247.PP
1248Each watcher has an associated watcher structure (called \f(CW\*(C`struct ev_TYPE\*(C'\fR
1249or simply \f(CW\*(C`ev_TYPE\*(C'\fR, as typedefs are provided for all watcher structs).
1250.PP
636Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init 1251Each 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 1252*, 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 1253invoked 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 1254time the event loop detects that the file descriptor given is readable
640is readable and/or writable). 1255and/or writable).
641.PP 1256.PP
642Each watcher type has its own \f(CW\*(C`ev_<type>_set (watcher *, ...)\*(C'\fR macro 1257Each 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 1258macro 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 1259is 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 1260.PP
647To make the watcher actually watch out for events, you have to start it 1261To 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 1262with 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 1263*)\*(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. 1264corresponding stop function (\f(CW\*(C`ev_TYPE_stop (loop, watcher *)\*(C'\fR.
651.PP 1265.PP
652As long as your watcher is active (has been started but not stopped) you 1266As 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 1267must not touch the values stored in it. Most specifically you must never
654reinitialise it or call its \f(CW\*(C`set\*(C'\fR macro. 1268reinitialise it or call its \f(CW\*(C`ev_TYPE_set\*(C'\fR macro.
655.PP 1269.PP
656Each and every callback receives the event loop pointer as first, the 1270Each and every callback receives the event loop pointer as first, the
657registered watcher structure as second, and a bitset of received events as 1271registered watcher structure as second, and a bitset of received events as
658third argument. 1272third argument.
659.PP 1273.PP
… …
668.el .IP "\f(CWEV_WRITE\fR" 4 1282.el .IP "\f(CWEV_WRITE\fR" 4
669.IX Item "EV_WRITE" 1283.IX Item "EV_WRITE"
670.PD 1284.PD
671The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or 1285The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
672writable. 1286writable.
673.ie n .IP """EV_TIMEOUT""" 4 1287.ie n .IP """EV_TIMER""" 4
674.el .IP "\f(CWEV_TIMEOUT\fR" 4 1288.el .IP "\f(CWEV_TIMER\fR" 4
675.IX Item "EV_TIMEOUT" 1289.IX Item "EV_TIMER"
676The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out. 1290The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
677.ie n .IP """EV_PERIODIC""" 4 1291.ie n .IP """EV_PERIODIC""" 4
678.el .IP "\f(CWEV_PERIODIC\fR" 4 1292.el .IP "\f(CWEV_PERIODIC\fR" 4
679.IX Item "EV_PERIODIC" 1293.IX Item "EV_PERIODIC"
680The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out. 1294The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
… …
684The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread. 1298The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread.
685.ie n .IP """EV_CHILD""" 4 1299.ie n .IP """EV_CHILD""" 4
686.el .IP "\f(CWEV_CHILD\fR" 4 1300.el .IP "\f(CWEV_CHILD\fR" 4
687.IX Item "EV_CHILD" 1301.IX Item "EV_CHILD"
688The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change. 1302The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change.
1303.ie n .IP """EV_STAT""" 4
1304.el .IP "\f(CWEV_STAT\fR" 4
1305.IX Item "EV_STAT"
1306The path specified in the \f(CW\*(C`ev_stat\*(C'\fR watcher changed its attributes somehow.
689.ie n .IP """EV_IDLE""" 4 1307.ie n .IP """EV_IDLE""" 4
690.el .IP "\f(CWEV_IDLE\fR" 4 1308.el .IP "\f(CWEV_IDLE\fR" 4
691.IX Item "EV_IDLE" 1309.IX Item "EV_IDLE"
692The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do. 1310The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do.
693.ie n .IP """EV_PREPARE""" 4 1311.ie n .IP """EV_PREPARE""" 4
… …
696.PD 0 1314.PD 0
697.ie n .IP """EV_CHECK""" 4 1315.ie n .IP """EV_CHECK""" 4
698.el .IP "\f(CWEV_CHECK\fR" 4 1316.el .IP "\f(CWEV_CHECK\fR" 4
699.IX Item "EV_CHECK" 1317.IX Item "EV_CHECK"
700.PD 1318.PD
701All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_loop\*(C'\fR starts 1319All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_run\*(C'\fR starts to
702to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after 1320gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are queued (not invoked)
703\&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any 1321just after \f(CW\*(C`ev_run\*(C'\fR has gathered them, but before it queues any callbacks
1322for any received events. That means \f(CW\*(C`ev_prepare\*(C'\fR watchers are the last
1323watchers invoked before the event loop sleeps or polls for new events, and
1324\&\f(CW\*(C`ev_check\*(C'\fR watchers will be invoked before any other watchers of the same
1325or lower priority within an event loop iteration.
1326.Sp
704received events. Callbacks of both watcher types can start and stop as 1327Callbacks of both watcher types can start and stop as many watchers as
705many watchers as they want, and all of them will be taken into account 1328they want, and all of them will be taken into account (for example, a
706(for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep 1329\&\f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep \f(CW\*(C`ev_run\*(C'\fR from
707\&\f(CW\*(C`ev_loop\*(C'\fR from blocking). 1330blocking).
1331.ie n .IP """EV_EMBED""" 4
1332.el .IP "\f(CWEV_EMBED\fR" 4
1333.IX Item "EV_EMBED"
1334The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.
1335.ie n .IP """EV_FORK""" 4
1336.el .IP "\f(CWEV_FORK\fR" 4
1337.IX Item "EV_FORK"
1338The event loop has been resumed in the child process after fork (see
1339\&\f(CW\*(C`ev_fork\*(C'\fR).
1340.ie n .IP """EV_CLEANUP""" 4
1341.el .IP "\f(CWEV_CLEANUP\fR" 4
1342.IX Item "EV_CLEANUP"
1343The event loop is about to be destroyed (see \f(CW\*(C`ev_cleanup\*(C'\fR).
1344.ie n .IP """EV_ASYNC""" 4
1345.el .IP "\f(CWEV_ASYNC\fR" 4
1346.IX Item "EV_ASYNC"
1347The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR).
1348.ie n .IP """EV_CUSTOM""" 4
1349.el .IP "\f(CWEV_CUSTOM\fR" 4
1350.IX Item "EV_CUSTOM"
1351Not ever sent (or otherwise used) by libev itself, but can be freely used
1352by libev users to signal watchers (e.g. via \f(CW\*(C`ev_feed_event\*(C'\fR).
708.ie n .IP """EV_ERROR""" 4 1353.ie n .IP """EV_ERROR""" 4
709.el .IP "\f(CWEV_ERROR\fR" 4 1354.el .IP "\f(CWEV_ERROR\fR" 4
710.IX Item "EV_ERROR" 1355.IX Item "EV_ERROR"
711An unspecified error has occured, the watcher has been stopped. This might 1356An unspecified error has occurred, the watcher has been stopped. This might
712happen because the watcher could not be properly started because libev 1357happen because the watcher could not be properly started because libev
713ran out of memory, a file descriptor was found to be closed or any other 1358ran out of memory, a file descriptor was found to be closed or any other
1359problem. Libev considers these application bugs.
1360.Sp
714problem. You best act on it by reporting the problem and somehow coping 1361You best act on it by reporting the problem and somehow coping with the
715with the watcher being stopped. 1362watcher being stopped. Note that well-written programs should not receive
1363an error ever, so when your watcher receives it, this usually indicates a
1364bug in your program.
716.Sp 1365.Sp
717Libev will usually signal a few \*(L"dummy\*(R" events together with an error, 1366Libev will usually signal a few \*(L"dummy\*(R" events together with an error, for
718for example it might indicate that a fd is readable or writable, and if 1367example it might indicate that a fd is readable or writable, and if your
719your callbacks is well-written it can just attempt the operation and cope 1368callbacks is well-written it can just attempt the operation and cope with
720with the error from \fIread()\fR or \fIwrite()\fR. This will not work in multithreaded 1369the error from \fIread()\fR or \fIwrite()\fR. This will not work in multi-threaded
721programs, though, so beware. 1370programs, though, as the fd could already be closed and reused for another
722.Sh "\s-1SUMMARY\s0 \s-1OF\s0 \s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0" 1371thing, so beware.
1372.SS "\s-1GENERIC WATCHER FUNCTIONS\s0"
723.IX Subsection "SUMMARY OF GENERIC WATCHER FUNCTIONS" 1373.IX Subsection "GENERIC WATCHER FUNCTIONS"
724In the following description, \f(CW\*(C`TYPE\*(C'\fR stands for the watcher type,
725e.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.
726.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4 1374.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
727.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4 1375.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
728.IX Item "ev_init (ev_TYPE *watcher, callback)" 1376.IX Item "ev_init (ev_TYPE *watcher, callback)"
729This macro initialises the generic portion of a watcher. The contents 1377This macro initialises the generic portion of a watcher. The contents
730of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only 1378of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
… …
734which rolls both calls into one. 1382which rolls both calls into one.
735.Sp 1383.Sp
736You can reinitialise a watcher at any time as long as it has been stopped 1384You can reinitialise a watcher at any time as long as it has been stopped
737(or never started) and there are no pending events outstanding. 1385(or never started) and there are no pending events outstanding.
738.Sp 1386.Sp
739The callbakc is always of type \f(CW\*(C`void (*)(ev_loop *loop, ev_TYPE *watcher, 1387The callback is always of type \f(CW\*(C`void (*)(struct ev_loop *loop, ev_TYPE *watcher,
740int revents)\*(C'\fR. 1388int revents)\*(C'\fR.
1389.Sp
1390Example: Initialise an \f(CW\*(C`ev_io\*(C'\fR watcher in two steps.
1391.Sp
1392.Vb 3
1393\& ev_io w;
1394\& ev_init (&w, my_cb);
1395\& ev_io_set (&w, STDIN_FILENO, EV_READ);
1396.Ve
741.ie n .IP """ev_TYPE_set"" (ev_TYPE *, [args])" 4 1397.ie n .IP """ev_TYPE_set"" (ev_TYPE *watcher, [args])" 4
742.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *, [args])" 4 1398.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *watcher, [args])" 4
743.IX Item "ev_TYPE_set (ev_TYPE *, [args])" 1399.IX Item "ev_TYPE_set (ev_TYPE *watcher, [args])"
744This macro initialises the type-specific parts of a watcher. You need to 1400This macro initialises the type-specific parts of a watcher. You need to
745call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can 1401call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
746call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this 1402call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
747macro on a watcher that is active (it can be pending, however, which is a 1403macro on a watcher that is active (it can be pending, however, which is a
748difference to the \f(CW\*(C`ev_init\*(C'\fR macro). 1404difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
749.Sp 1405.Sp
750Although some watcher types do not have type-specific arguments 1406Although some watcher types do not have type-specific arguments
751(e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro. 1407(e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
1408.Sp
1409See \f(CW\*(C`ev_init\*(C'\fR, above, for an example.
752.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4 1410.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
753.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4 1411.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
754.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])" 1412.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
755This convinience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro 1413This convenience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
756calls into a single call. This is the most convinient method to initialise 1414calls into a single call. This is the most convenient method to initialise
757a watcher. The same limitations apply, of course. 1415a watcher. The same limitations apply, of course.
1416.Sp
1417Example: Initialise and set an \f(CW\*(C`ev_io\*(C'\fR watcher in one step.
1418.Sp
1419.Vb 1
1420\& ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1421.Ve
758.ie n .IP """ev_TYPE_start"" (loop *, ev_TYPE *watcher)" 4 1422.ie n .IP """ev_TYPE_start"" (loop, ev_TYPE *watcher)" 4
759.el .IP "\f(CWev_TYPE_start\fR (loop *, ev_TYPE *watcher)" 4 1423.el .IP "\f(CWev_TYPE_start\fR (loop, ev_TYPE *watcher)" 4
760.IX Item "ev_TYPE_start (loop *, ev_TYPE *watcher)" 1424.IX Item "ev_TYPE_start (loop, ev_TYPE *watcher)"
761Starts (activates) the given watcher. Only active watchers will receive 1425Starts (activates) the given watcher. Only active watchers will receive
762events. If the watcher is already active nothing will happen. 1426events. If the watcher is already active nothing will happen.
1427.Sp
1428Example: Start the \f(CW\*(C`ev_io\*(C'\fR watcher that is being abused as example in this
1429whole section.
1430.Sp
1431.Vb 1
1432\& ev_io_start (EV_DEFAULT_UC, &w);
1433.Ve
763.ie n .IP """ev_TYPE_stop"" (loop *, ev_TYPE *watcher)" 4 1434.ie n .IP """ev_TYPE_stop"" (loop, ev_TYPE *watcher)" 4
764.el .IP "\f(CWev_TYPE_stop\fR (loop *, ev_TYPE *watcher)" 4 1435.el .IP "\f(CWev_TYPE_stop\fR (loop, ev_TYPE *watcher)" 4
765.IX Item "ev_TYPE_stop (loop *, ev_TYPE *watcher)" 1436.IX Item "ev_TYPE_stop (loop, ev_TYPE *watcher)"
766Stops the given watcher again (if active) and clears the pending 1437Stops the given watcher if active, and clears the pending status (whether
1438the watcher was active or not).
1439.Sp
767status. It is possible that stopped watchers are pending (for example, 1440It is possible that stopped watchers are pending \- for example,
768non-repeating timers are being stopped when they become pending), but 1441non-repeating timers are being stopped when they become pending \- but
769\&\f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor pending. If 1442calling \f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor
770you want to free or reuse the memory used by the watcher it is therefore a 1443pending. If you want to free or reuse the memory used by the watcher it is
771good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. 1444therefore a good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
772.IP "bool ev_is_active (ev_TYPE *watcher)" 4 1445.IP "bool ev_is_active (ev_TYPE *watcher)" 4
773.IX Item "bool ev_is_active (ev_TYPE *watcher)" 1446.IX Item "bool ev_is_active (ev_TYPE *watcher)"
774Returns a true value iff the watcher is active (i.e. it has been started 1447Returns a true value iff the watcher is active (i.e. it has been started
775and not yet been stopped). As long as a watcher is active you must not modify 1448and not yet been stopped). As long as a watcher is active you must not modify
776it. 1449it.
777.IP "bool ev_is_pending (ev_TYPE *watcher)" 4 1450.IP "bool ev_is_pending (ev_TYPE *watcher)" 4
778.IX Item "bool ev_is_pending (ev_TYPE *watcher)" 1451.IX Item "bool ev_is_pending (ev_TYPE *watcher)"
779Returns a true value iff the watcher is pending, (i.e. it has outstanding 1452Returns a true value iff the watcher is pending, (i.e. it has outstanding
780events but its callback has not yet been invoked). As long as a watcher 1453events but its callback has not yet been invoked). As long as a watcher
781is pending (but not active) you must not call an init function on it (but 1454is pending (but not active) you must not call an init function on it (but
782\&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe) and you must make sure the watcher is available to 1455\&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe), you must not change its priority, and you must
783libev (e.g. you cnanot \f(CW\*(C`free ()\*(C'\fR it). 1456make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR
1457it).
784.IP "callback = ev_cb (ev_TYPE *watcher)" 4 1458.IP "callback ev_cb (ev_TYPE *watcher)" 4
785.IX Item "callback = ev_cb (ev_TYPE *watcher)" 1459.IX Item "callback ev_cb (ev_TYPE *watcher)"
786Returns the callback currently set on the watcher. 1460Returns the callback currently set on the watcher.
787.IP "ev_cb_set (ev_TYPE *watcher, callback)" 4 1461.IP "ev_set_cb (ev_TYPE *watcher, callback)" 4
788.IX Item "ev_cb_set (ev_TYPE *watcher, callback)" 1462.IX Item "ev_set_cb (ev_TYPE *watcher, callback)"
789Change the callback. You can change the callback at virtually any time 1463Change the callback. You can change the callback at virtually any time
790(modulo threads). 1464(modulo threads).
791.Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0" 1465.IP "ev_set_priority (ev_TYPE *watcher, int priority)" 4
792.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER" 1466.IX Item "ev_set_priority (ev_TYPE *watcher, int priority)"
793Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change 1467.PD 0
794and read at any time, libev will completely ignore it. This can be used 1468.IP "int ev_priority (ev_TYPE *watcher)" 4
795to associate arbitrary data with your watcher. If you need more data and 1469.IX Item "int ev_priority (ev_TYPE *watcher)"
796don't want to allocate memory and store a pointer to it in that data 1470.PD
797member, you can also \*(L"subclass\*(R" the watcher type and provide your own 1471Set and query the priority of the watcher. The priority is a small
798data: 1472integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR
1473(default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked
1474before watchers with lower priority, but priority will not keep watchers
1475from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
1476.Sp
1477If you need to suppress invocation when higher priority events are pending
1478you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
1479.Sp
1480You \fImust not\fR change the priority of a watcher as long as it is active or
1481pending.
1482.Sp
1483Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
1484fine, as long as you do not mind that the priority value you query might
1485or might not have been clamped to the valid range.
1486.Sp
1487The default priority used by watchers when no priority has been set is
1488always \f(CW0\fR, which is supposed to not be too high and not be too low :).
1489.Sp
1490See \*(L"\s-1WATCHER PRIORITY MODELS\*(R"\s0, below, for a more thorough treatment of
1491priorities.
1492.IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
1493.IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
1494Invoke the \f(CW\*(C`watcher\*(C'\fR with the given \f(CW\*(C`loop\*(C'\fR and \f(CW\*(C`revents\*(C'\fR. Neither
1495\&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback
1496can deal with that fact, as both are simply passed through to the
1497callback.
1498.IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
1499.IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
1500If the watcher is pending, this function clears its pending status and
1501returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the
1502watcher isn't pending it does nothing and returns \f(CW0\fR.
1503.Sp
1504Sometimes it can be useful to \*(L"poll\*(R" a watcher instead of waiting for its
1505callback to be invoked, which can be accomplished with this function.
1506.IP "ev_feed_event (loop, ev_TYPE *watcher, int revents)" 4
1507.IX Item "ev_feed_event (loop, ev_TYPE *watcher, int revents)"
1508Feeds the given event set into the event loop, as if the specified event
1509had happened for the specified watcher (which must be a pointer to an
1510initialised but not necessarily started event watcher). Obviously you must
1511not free the watcher as long as it has pending events.
1512.Sp
1513Stopping the watcher, letting libev invoke it, or calling
1514\&\f(CW\*(C`ev_clear_pending\*(C'\fR will clear the pending event, even if the watcher was
1515not started in the first place.
1516.Sp
1517See also \f(CW\*(C`ev_feed_fd_event\*(C'\fR and \f(CW\*(C`ev_feed_signal_event\*(C'\fR for related
1518functions that do not need a watcher.
799.PP 1519.PP
1520See also the \*(L"\s-1ASSOCIATING CUSTOM DATA WITH A WATCHER\*(R"\s0 and \*(L"\s-1BUILDING YOUR
1521OWN COMPOSITE WATCHERS\*(R"\s0 idioms.
1522.SS "\s-1WATCHER STATES\s0"
1523.IX Subsection "WATCHER STATES"
1524There are various watcher states mentioned throughout this manual \-
1525active, pending and so on. In this section these states and the rules to
1526transition between them will be described in more detail \- and while these
1527rules might look complicated, they usually do \*(L"the right thing\*(R".
1528.IP "initialised" 4
1529.IX Item "initialised"
1530Before a watcher can be registered with the event loop it has to be
1531initialised. This can be done with a call to \f(CW\*(C`ev_TYPE_init\*(C'\fR, or calls to
1532\&\f(CW\*(C`ev_init\*(C'\fR followed by the watcher-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR function.
1533.Sp
1534In this state it is simply some block of memory that is suitable for
1535use in an event loop. It can be moved around, freed, reused etc. at
1536will \- as long as you either keep the memory contents intact, or call
1537\&\f(CW\*(C`ev_TYPE_init\*(C'\fR again.
1538.IP "started/running/active" 4
1539.IX Item "started/running/active"
1540Once a watcher has been started with a call to \f(CW\*(C`ev_TYPE_start\*(C'\fR it becomes
1541property of the event loop, and is actively waiting for events. While in
1542this state it cannot be accessed (except in a few documented ways), moved,
1543freed or anything else \- the only legal thing is to keep a pointer to it,
1544and call libev functions on it that are documented to work on active watchers.
1545.IP "pending" 4
1546.IX Item "pending"
1547If a watcher is active and libev determines that an event it is interested
1548in has occurred (such as a timer expiring), it will become pending. It will
1549stay in this pending state until either it is stopped or its callback is
1550about to be invoked, so it is not normally pending inside the watcher
1551callback.
1552.Sp
1553The watcher might or might not be active while it is pending (for example,
1554an expired non-repeating timer can be pending but no longer active). If it
1555is stopped, it can be freely accessed (e.g. by calling \f(CW\*(C`ev_TYPE_set\*(C'\fR),
1556but it is still property of the event loop at this time, so cannot be
1557moved, freed or reused. And if it is active the rules described in the
1558previous item still apply.
1559.Sp
1560It is also possible to feed an event on a watcher that is not active (e.g.
1561via \f(CW\*(C`ev_feed_event\*(C'\fR), in which case it becomes pending without being
1562active.
1563.IP "stopped" 4
1564.IX Item "stopped"
1565A watcher can be stopped implicitly by libev (in which case it might still
1566be pending), or explicitly by calling its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. The
1567latter will clear any pending state the watcher might be in, regardless
1568of whether it was active or not, so stopping a watcher explicitly before
1569freeing it is often a good idea.
1570.Sp
1571While stopped (and not pending) the watcher is essentially in the
1572initialised state, that is, it can be reused, moved, modified in any way
1573you wish (but when you trash the memory block, you need to \f(CW\*(C`ev_TYPE_init\*(C'\fR
1574it again).
1575.SS "\s-1WATCHER PRIORITY MODELS\s0"
1576.IX Subsection "WATCHER PRIORITY MODELS"
1577Many event loops support \fIwatcher priorities\fR, which are usually small
1578integers that influence the ordering of event callback invocation
1579between watchers in some way, all else being equal.
1580.PP
1581In libev, Watcher priorities can be set using \f(CW\*(C`ev_set_priority\*(C'\fR. See its
1582description for the more technical details such as the actual priority
1583range.
1584.PP
1585There are two common ways how these these priorities are being interpreted
1586by event loops:
1587.PP
1588In the more common lock-out model, higher priorities \*(L"lock out\*(R" invocation
1589of lower priority watchers, which means as long as higher priority
1590watchers receive events, lower priority watchers are not being invoked.
1591.PP
1592The less common only-for-ordering model uses priorities solely to order
1593callback invocation within a single event loop iteration: Higher priority
1594watchers are invoked before lower priority ones, but they all get invoked
1595before polling for new events.
1596.PP
1597Libev uses the second (only-for-ordering) model for all its watchers
1598except for idle watchers (which use the lock-out model).
1599.PP
1600The rationale behind this is that implementing the lock-out model for
1601watchers is not well supported by most kernel interfaces, and most event
1602libraries will just poll for the same events again and again as long as
1603their callbacks have not been executed, which is very inefficient in the
1604common case of one high-priority watcher locking out a mass of lower
1605priority ones.
1606.PP
1607Static (ordering) priorities are most useful when you have two or more
1608watchers handling the same resource: a typical usage example is having an
1609\&\f(CW\*(C`ev_io\*(C'\fR watcher to receive data, and an associated \f(CW\*(C`ev_timer\*(C'\fR to handle
1610timeouts. Under load, data might be received while the program handles
1611other jobs, but since timers normally get invoked first, the timeout
1612handler will be executed before checking for data. In that case, giving
1613the timer a lower priority than the I/O watcher ensures that I/O will be
1614handled first even under adverse conditions (which is usually, but not
1615always, what you want).
1616.PP
1617Since idle watchers use the \*(L"lock-out\*(R" model, meaning that idle watchers
1618will only be executed when no same or higher priority watchers have
1619received events, they can be used to implement the \*(L"lock-out\*(R" model when
1620required.
1621.PP
1622For example, to emulate how many other event libraries handle priorities,
1623you can associate an \f(CW\*(C`ev_idle\*(C'\fR watcher to each such watcher, and in
1624the normal watcher callback, you just start the idle watcher. The real
1625processing is done in the idle watcher callback. This causes libev to
1626continuously poll and process kernel event data for the watcher, but when
1627the lock-out case is known to be rare (which in turn is rare :), this is
1628workable.
1629.PP
1630Usually, however, the lock-out model implemented that way will perform
1631miserably under the type of load it was designed to handle. In that case,
1632it might be preferable to stop the real watcher before starting the
1633idle watcher, so the kernel will not have to process the event in case
1634the actual processing will be delayed for considerable time.
1635.PP
1636Here is an example of an I/O watcher that should run at a strictly lower
1637priority than the default, and which should only process data when no
1638other events are pending:
1639.PP
800.Vb 7 1640.Vb 2
801\& struct my_io 1641\& ev_idle idle; // actual processing watcher
1642\& ev_io io; // actual event watcher
1643\&
1644\& static void
1645\& io_cb (EV_P_ ev_io *w, int revents)
802\& { 1646\& {
803\& struct ev_io io; 1647\& // stop the I/O watcher, we received the event, but
804\& int otherfd; 1648\& // are not yet ready to handle it.
805\& void *somedata; 1649\& ev_io_stop (EV_A_ w);
806\& struct whatever *mostinteresting; 1650\&
1651\& // start the idle watcher to handle the actual event.
1652\& // it will not be executed as long as other watchers
1653\& // with the default priority are receiving events.
1654\& ev_idle_start (EV_A_ &idle);
807\& } 1655\& }
808.Ve 1656\&
809.PP 1657\& static void
810And since your callback will be called with a pointer to the watcher, you 1658\& idle_cb (EV_P_ ev_idle *w, int revents)
811can cast it back to your own type:
812.PP
813.Vb 5
814\& static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
815\& { 1659\& {
816\& struct my_io *w = (struct my_io *)w_; 1660\& // actual processing
817\& ... 1661\& read (STDIN_FILENO, ...);
1662\&
1663\& // have to start the I/O watcher again, as
1664\& // we have handled the event
1665\& ev_io_start (EV_P_ &io);
818\& } 1666\& }
1667\&
1668\& // initialisation
1669\& ev_idle_init (&idle, idle_cb);
1670\& ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
1671\& ev_io_start (EV_DEFAULT_ &io);
819.Ve 1672.Ve
820.PP 1673.PP
821More interesting and less C\-conformant ways of catsing your callback type 1674In the \*(L"real\*(R" world, it might also be beneficial to start a timer, so that
822have been omitted.... 1675low-priority connections can not be locked out forever under load. This
1676enables your program to keep a lower latency for important connections
1677during short periods of high load, while not completely locking out less
1678important ones.
823.SH "WATCHER TYPES" 1679.SH "WATCHER TYPES"
824.IX Header "WATCHER TYPES" 1680.IX Header "WATCHER TYPES"
825This section describes each watcher in detail, but will not repeat 1681This section describes each watcher in detail, but will not repeat
826information given in the last section. 1682information given in the last section. Any initialisation/set macros,
1683functions and members specific to the watcher type are explained.
1684.PP
1685Members are additionally marked with either \fI[read\-only]\fR, meaning that,
1686while the watcher is active, you can look at the member and expect some
1687sensible content, but you must not modify it (you can modify it while the
1688watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
1689means you can expect it to have some sensible content while the watcher
1690is active, but you can also modify it. Modifying it may not do something
1691sensible or take immediate effect (or do anything at all), but libev will
1692not crash or malfunction in any way.
827.ie n .Sh """ev_io"" \- is this file descriptor readable or writable" 1693.ie n .SS """ev_io"" \- is this file descriptor readable or writable?"
828.el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable" 1694.el .SS "\f(CWev_io\fP \- is this file descriptor readable or writable?"
829.IX Subsection "ev_io - is this file descriptor readable or writable" 1695.IX Subsection "ev_io - is this file descriptor readable or writable?"
830I/O watchers check whether a file descriptor is readable or writable 1696I/O watchers check whether a file descriptor is readable or writable
831in each iteration of the event loop (This behaviour is called 1697in each iteration of the event loop, or, more precisely, when reading
832level-triggering because you keep receiving events as long as the 1698would not block the process and writing would at least be able to write
833condition persists. Remember you can stop the watcher if you don't want to 1699some data. This behaviour is called level-triggering because you keep
834act on the event and neither want to receive future events). 1700receiving events as long as the condition persists. Remember you can stop
1701the watcher if you don't want to act on the event and neither want to
1702receive future events.
835.PP 1703.PP
836In general you can register as many read and/or write event watchers per 1704In general you can register as many read and/or write event watchers per
837fd as you want (as long as you don't confuse yourself). Setting all file 1705fd as you want (as long as you don't confuse yourself). Setting all file
838descriptors to non-blocking mode is also usually a good idea (but not 1706descriptors to non-blocking mode is also usually a good idea (but not
839required if you know what you are doing). 1707required if you know what you are doing).
840.PP 1708.PP
841You have to be careful with dup'ed file descriptors, though. Some backends 1709Another thing you have to watch out for is that it is quite easy to
842(the linux epoll backend is a notable example) cannot handle dup'ed file 1710receive \*(L"spurious\*(R" readiness notifications, that is, your callback might
843descriptors correctly if you register interest in two or more fds pointing 1711be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block
844to the same underlying file/socket etc. description (that is, they share 1712because there is no data. It is very easy to get into this situation even
845the same underlying \*(L"file open\*(R"). 1713with a relatively standard program structure. Thus it is best to always
1714use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning \f(CW\*(C`EAGAIN\*(C'\fR is far
1715preferable to a program hanging until some data arrives.
846.PP 1716.PP
847If you must do this, then force the use of a known-to-be-good backend 1717If you cannot run the fd in non-blocking mode (for example you should
848(at the time of this writing, this includes only \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and 1718not play around with an Xlib connection), then you have to separately
849\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR). 1719re-test whether a file descriptor is really ready with a known-to-be good
1720interface such as poll (fortunately in the case of Xlib, it already does
1721this on its own, so its quite safe to use). Some people additionally
1722use \f(CW\*(C`SIGALRM\*(C'\fR and an interval timer, just to be sure you won't block
1723indefinitely.
1724.PP
1725But really, best use non-blocking mode.
1726.PP
1727\fIThe special problem of disappearing file descriptors\fR
1728.IX Subsection "The special problem of disappearing file descriptors"
1729.PP
1730Some backends (e.g. kqueue, epoll) need to be told about closing a file
1731descriptor (either due to calling \f(CW\*(C`close\*(C'\fR explicitly or any other means,
1732such as \f(CW\*(C`dup2\*(C'\fR). The reason is that you register interest in some file
1733descriptor, but when it goes away, the operating system will silently drop
1734this interest. If another file descriptor with the same number then is
1735registered with libev, there is no efficient way to see that this is, in
1736fact, a different file descriptor.
1737.PP
1738To avoid having to explicitly tell libev about such cases, libev follows
1739the following policy: Each time \f(CW\*(C`ev_io_set\*(C'\fR is being called, libev
1740will assume that this is potentially a new file descriptor, otherwise
1741it is assumed that the file descriptor stays the same. That means that
1742you \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
1743descriptor even if the file descriptor number itself did not change.
1744.PP
1745This is how one would do it normally anyway, the important point is that
1746the libev application should not optimise around libev but should leave
1747optimisations to libev.
1748.PP
1749\fIThe special problem of dup'ed file descriptors\fR
1750.IX Subsection "The special problem of dup'ed file descriptors"
1751.PP
1752Some backends (e.g. epoll), cannot register events for file descriptors,
1753but only events for the underlying file descriptions. That means when you
1754have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register
1755events for them, only one file descriptor might actually receive events.
1756.PP
1757There is no workaround possible except not registering events
1758for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
1759\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1760.PP
1761\fIThe special problem of files\fR
1762.IX Subsection "The special problem of files"
1763.PP
1764Many people try to use \f(CW\*(C`select\*(C'\fR (or libev) on file descriptors
1765representing files, and expect it to become ready when their program
1766doesn't block on disk accesses (which can take a long time on their own).
1767.PP
1768However, this cannot ever work in the \*(L"expected\*(R" way \- you get a readiness
1769notification as soon as the kernel knows whether and how much data is
1770there, and in the case of open files, that's always the case, so you
1771always get a readiness notification instantly, and your read (or possibly
1772write) will still block on the disk I/O.
1773.PP
1774Another way to view it is that in the case of sockets, pipes, character
1775devices and so on, there is another party (the sender) that delivers data
1776on its own, but in the case of files, there is no such thing: the disk
1777will not send data on its own, simply because it doesn't know what you
1778wish to read \- you would first have to request some data.
1779.PP
1780Since files are typically not-so-well supported by advanced notification
1781mechanism, libev tries hard to emulate \s-1POSIX\s0 behaviour with respect
1782to files, even though you should not use it. The reason for this is
1783convenience: sometimes you want to watch \s-1STDIN\s0 or \s-1STDOUT,\s0 which is
1784usually a tty, often a pipe, but also sometimes files or special devices
1785(for example, \f(CW\*(C`epoll\*(C'\fR on Linux works with \fI/dev/random\fR but not with
1786\&\fI/dev/urandom\fR), and even though the file might better be served with
1787asynchronous I/O instead of with non-blocking I/O, it is still useful when
1788it \*(L"just works\*(R" instead of freezing.
1789.PP
1790So avoid file descriptors pointing to files when you know it (e.g. use
1791libeio), but use them when it is convenient, e.g. for \s-1STDIN/STDOUT,\s0 or
1792when you rarely read from a file instead of from a socket, and want to
1793reuse the same code path.
1794.PP
1795\fIThe special problem of fork\fR
1796.IX Subsection "The special problem of fork"
1797.PP
1798Some backends (epoll, kqueue) do not support \f(CW\*(C`fork ()\*(C'\fR at all or exhibit
1799useless behaviour. Libev fully supports fork, but needs to be told about
1800it in the child if you want to continue to use it in the child.
1801.PP
1802To support fork in your child processes, you have to call \f(CW\*(C`ev_loop_fork
1803()\*(C'\fR after a fork in the child, enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to
1804\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1805.PP
1806\fIThe special problem of \s-1SIGPIPE\s0\fR
1807.IX Subsection "The special problem of SIGPIPE"
1808.PP
1809While not really specific to libev, it is easy to forget about \f(CW\*(C`SIGPIPE\*(C'\fR:
1810when writing to a pipe whose other end has been closed, your program gets
1811sent a \s-1SIGPIPE,\s0 which, by default, aborts your program. For most programs
1812this is sensible behaviour, for daemons, this is usually undesirable.
1813.PP
1814So when you encounter spurious, unexplained daemon exits, make sure you
1815ignore \s-1SIGPIPE \s0(and maybe make sure you log the exit status of your daemon
1816somewhere, as that would have given you a big clue).
1817.PP
1818\fIThe special problem of \fIaccept()\fIing when you can't\fR
1819.IX Subsection "The special problem of accept()ing when you can't"
1820.PP
1821Many implementations of the \s-1POSIX \s0\f(CW\*(C`accept\*(C'\fR function (for example,
1822found in post\-2004 Linux) have the peculiar behaviour of not removing a
1823connection from the pending queue in all error cases.
1824.PP
1825For example, larger servers often run out of file descriptors (because
1826of resource limits), causing \f(CW\*(C`accept\*(C'\fR to fail with \f(CW\*(C`ENFILE\*(C'\fR but not
1827rejecting the connection, leading to libev signalling readiness on
1828the next iteration again (the connection still exists after all), and
1829typically causing the program to loop at 100% \s-1CPU\s0 usage.
1830.PP
1831Unfortunately, the set of errors that cause this issue differs between
1832operating systems, there is usually little the app can do to remedy the
1833situation, and no known thread-safe method of removing the connection to
1834cope with overload is known (to me).
1835.PP
1836One of the easiest ways to handle this situation is to just ignore it
1837\&\- when the program encounters an overload, it will just loop until the
1838situation is over. While this is a form of busy waiting, no \s-1OS\s0 offers an
1839event-based way to handle this situation, so it's the best one can do.
1840.PP
1841A better way to handle the situation is to log any errors other than
1842\&\f(CW\*(C`EAGAIN\*(C'\fR and \f(CW\*(C`EWOULDBLOCK\*(C'\fR, making sure not to flood the log with such
1843messages, and continue as usual, which at least gives the user an idea of
1844what could be wrong (\*(L"raise the ulimit!\*(R"). For extra points one could stop
1845the \f(CW\*(C`ev_io\*(C'\fR watcher on the listening fd \*(L"for a while\*(R", which reduces \s-1CPU\s0
1846usage.
1847.PP
1848If your program is single-threaded, then you could also keep a dummy file
1849descriptor for overload situations (e.g. by opening \fI/dev/null\fR), and
1850when 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,
1851close that fd, and create a new dummy fd. This will gracefully refuse
1852clients under typical overload conditions.
1853.PP
1854The last way to handle it is to simply log the error and \f(CW\*(C`exit\*(C'\fR, as
1855is often done with \f(CW\*(C`malloc\*(C'\fR failures, but this results in an easy
1856opportunity for a DoS attack.
1857.PP
1858\fIWatcher-Specific Functions\fR
1859.IX Subsection "Watcher-Specific Functions"
850.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4 1860.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
851.IX Item "ev_io_init (ev_io *, callback, int fd, int events)" 1861.IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
852.PD 0 1862.PD 0
853.IP "ev_io_set (ev_io *, int fd, int events)" 4 1863.IP "ev_io_set (ev_io *, int fd, int events)" 4
854.IX Item "ev_io_set (ev_io *, int fd, int events)" 1864.IX Item "ev_io_set (ev_io *, int fd, int events)"
855.PD 1865.PD
856Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The fd is the file descriptor to rceeive 1866Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to
857events for and events is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or \f(CW\*(C`EV_READ | 1867receive 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
858EV_WRITE\*(C'\fR to receive the given events. 1868\&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR, to express the desire to receive the given events.
859.Sp 1869.IP "int fd [read\-only]" 4
860Please note that most of the more scalable backend mechanisms (for example 1870.IX Item "int fd [read-only]"
861epoll and solaris ports) can result in spurious readyness notifications 1871The file descriptor being watched.
862for file descriptors, so you practically need to use non-blocking I/O (and 1872.IP "int events [read\-only]" 4
863treat callback invocation as hint only), or retest separately with a safe 1873.IX Item "int events [read-only]"
864interface before doing I/O (XLib can do this), or force the use of either 1874The events being watched.
865\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR, which don't suffer from this
866problem. Also note that it is quite easy to have your callback invoked
867when the readyness condition is no longer valid even when employing
868typical ways of handling events, so its a good idea to use non-blocking
869I/O unconditionally.
870.PP 1875.PP
1876\fIExamples\fR
1877.IX Subsection "Examples"
1878.PP
871Example: call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well 1879Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
872readable, but only once. Since it is likely line\-buffered, you could 1880readable, but only once. Since it is likely line-buffered, you could
873attempt to read a whole line in the callback: 1881attempt to read a whole line in the callback.
874.PP 1882.PP
875.Vb 6 1883.Vb 6
876\& static void 1884\& static void
877\& stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents) 1885\& stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
878\& { 1886\& {
879\& ev_io_stop (loop, w); 1887\& ev_io_stop (loop, w);
880\& .. read from stdin here (or from w->fd) and haqndle any I/O errors 1888\& .. read from stdin here (or from w\->fd) and handle any I/O errors
881\& } 1889\& }
882.Ve 1890\&
883.PP
884.Vb 6
885\& ... 1891\& ...
886\& struct ev_loop *loop = ev_default_init (0); 1892\& struct ev_loop *loop = ev_default_init (0);
887\& struct ev_io stdin_readable; 1893\& ev_io stdin_readable;
888\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ); 1894\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
889\& ev_io_start (loop, &stdin_readable); 1895\& ev_io_start (loop, &stdin_readable);
890\& ev_loop (loop, 0); 1896\& ev_run (loop, 0);
891.Ve 1897.Ve
892.ie n .Sh """ev_timer"" \- relative and optionally recurring timeouts" 1898.ie n .SS """ev_timer"" \- relative and optionally repeating timeouts"
893.el .Sh "\f(CWev_timer\fP \- relative and optionally recurring timeouts" 1899.el .SS "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
894.IX Subsection "ev_timer - relative and optionally recurring timeouts" 1900.IX Subsection "ev_timer - relative and optionally repeating timeouts"
895Timer watchers are simple relative timers that generate an event after a 1901Timer watchers are simple relative timers that generate an event after a
896given time, and optionally repeating in regular intervals after that. 1902given time, and optionally repeating in regular intervals after that.
897.PP 1903.PP
898The timers are based on real time, that is, if you register an event that 1904The timers are based on real time, that is, if you register an event that
899times out after an hour and you reset your system clock to last years 1905times out after an hour and you reset your system clock to January last
900time, it will still time out after (roughly) and hour. \*(L"Roughly\*(R" because 1906year, it will still time out after (roughly) one hour. \*(L"Roughly\*(R" because
901detecting time jumps is hard, and some inaccuracies are unavoidable (the 1907detecting time jumps is hard, and some inaccuracies are unavoidable (the
902monotonic clock option helps a lot here). 1908monotonic clock option helps a lot here).
1909.PP
1910The callback is guaranteed to be invoked only \fIafter\fR its timeout has
1911passed (not \fIat\fR, so on systems with very low-resolution clocks this
1912might introduce a small delay, see \*(L"the special problem of being too
1913early\*(R", below). If multiple timers become ready during the same loop
1914iteration then the ones with earlier time-out values are invoked before
1915ones of the same priority with later time-out values (but this is no
1916longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
1917.PP
1918\fIBe smart about timeouts\fR
1919.IX Subsection "Be smart about timeouts"
1920.PP
1921Many real-world problems involve some kind of timeout, usually for error
1922recovery. A typical example is an \s-1HTTP\s0 request \- if the other side hangs,
1923you want to raise some error after a while.
1924.PP
1925What follows are some ways to handle this problem, from obvious and
1926inefficient to smart and efficient.
1927.PP
1928In the following, a 60 second activity timeout is assumed \- a timeout that
1929gets reset to 60 seconds each time there is activity (e.g. each time some
1930data or other life sign was received).
1931.IP "1. Use a timer and stop, reinitialise and start it on activity." 4
1932.IX Item "1. Use a timer and stop, reinitialise and start it on activity."
1933This is the most obvious, but not the most simple way: In the beginning,
1934start the watcher:
1935.Sp
1936.Vb 2
1937\& ev_timer_init (timer, callback, 60., 0.);
1938\& ev_timer_start (loop, timer);
1939.Ve
1940.Sp
1941Then, each time there is some activity, \f(CW\*(C`ev_timer_stop\*(C'\fR it, initialise it
1942and start it again:
1943.Sp
1944.Vb 3
1945\& ev_timer_stop (loop, timer);
1946\& ev_timer_set (timer, 60., 0.);
1947\& ev_timer_start (loop, timer);
1948.Ve
1949.Sp
1950This is relatively simple to implement, but means that each time there is
1951some activity, libev will first have to remove the timer from its internal
1952data structure and then add it again. Libev tries to be fast, but it's
1953still not a constant-time operation.
1954.ie n .IP "2. Use a timer and re-start it with ""ev_timer_again"" inactivity." 4
1955.el .IP "2. Use a timer and re-start it with \f(CWev_timer_again\fR inactivity." 4
1956.IX Item "2. Use a timer and re-start it with ev_timer_again inactivity."
1957This is the easiest way, and involves using \f(CW\*(C`ev_timer_again\*(C'\fR instead of
1958\&\f(CW\*(C`ev_timer_start\*(C'\fR.
1959.Sp
1960To implement this, configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value
1961of \f(CW60\fR and then call \f(CW\*(C`ev_timer_again\*(C'\fR at start and each time you
1962successfully read or write some data. If you go into an idle state where
1963you do not expect data to travel on the socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR
1964the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will automatically restart it if need be.
1965.Sp
1966That means you can ignore both the \f(CW\*(C`ev_timer_start\*(C'\fR function and the
1967\&\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
1968member and \f(CW\*(C`ev_timer_again\*(C'\fR.
1969.Sp
1970At start:
1971.Sp
1972.Vb 3
1973\& ev_init (timer, callback);
1974\& timer\->repeat = 60.;
1975\& ev_timer_again (loop, timer);
1976.Ve
1977.Sp
1978Each time there is some activity:
1979.Sp
1980.Vb 1
1981\& ev_timer_again (loop, timer);
1982.Ve
1983.Sp
1984It is even possible to change the time-out on the fly, regardless of
1985whether the watcher is active or not:
1986.Sp
1987.Vb 2
1988\& timer\->repeat = 30.;
1989\& ev_timer_again (loop, timer);
1990.Ve
1991.Sp
1992This is slightly more efficient then stopping/starting the timer each time
1993you want to modify its timeout value, as libev does not have to completely
1994remove and re-insert the timer from/into its internal data structure.
1995.Sp
1996It is, however, even simpler than the \*(L"obvious\*(R" way to do it.
1997.IP "3. Let the timer time out, but then re-arm it as required." 4
1998.IX Item "3. Let the timer time out, but then re-arm it as required."
1999This method is more tricky, but usually most efficient: Most timeouts are
2000relatively long compared to the intervals between other activity \- in
2001our example, within 60 seconds, there are usually many I/O events with
2002associated activity resets.
2003.Sp
2004In this case, it would be more efficient to leave the \f(CW\*(C`ev_timer\*(C'\fR alone,
2005but remember the time of last activity, and check for a real timeout only
2006within the callback:
2007.Sp
2008.Vb 3
2009\& ev_tstamp timeout = 60.;
2010\& ev_tstamp last_activity; // time of last activity
2011\& ev_timer timer;
2012\&
2013\& static void
2014\& callback (EV_P_ ev_timer *w, int revents)
2015\& {
2016\& // calculate when the timeout would happen
2017\& ev_tstamp after = last_activity \- ev_now (EV_A) + timeout;
2018\&
2019\& // if negative, it means we the timeout already occurred
2020\& if (after < 0.)
2021\& {
2022\& // timeout occurred, take action
2023\& }
2024\& else
2025\& {
2026\& // callback was invoked, but there was some recent
2027\& // activity. simply restart the timer to time out
2028\& // after "after" seconds, which is the earliest time
2029\& // the timeout can occur.
2030\& ev_timer_set (w, after, 0.);
2031\& ev_timer_start (EV_A_ w);
2032\& }
2033\& }
2034.Ve
2035.Sp
2036To summarise the callback: first calculate in how many seconds the
2037timeout will occur (by calculating the absolute time when it would occur,
2038\&\f(CW\*(C`last_activity + timeout\*(C'\fR, and subtracting the current time, \f(CW\*(C`ev_now
2039(EV_A)\*(C'\fR from that).
2040.Sp
2041If this value is negative, then we are already past the timeout, i.e. we
2042timed out, and need to do whatever is needed in this case.
2043.Sp
2044Otherwise, we now the earliest time at which the timeout would trigger,
2045and simply start the timer with this timeout value.
2046.Sp
2047In other words, each time the callback is invoked it will check whether
2048the timeout occurred. If not, it will simply reschedule itself to check
2049again at the earliest time it could time out. Rinse. Repeat.
2050.Sp
2051This scheme causes more callback invocations (about one every 60 seconds
2052minus half the average time between activity), but virtually no calls to
2053libev to change the timeout.
2054.Sp
2055To start the machinery, simply initialise the watcher and set
2056\&\f(CW\*(C`last_activity\*(C'\fR to the current time (meaning there was some activity just
2057now), then call the callback, which will \*(L"do the right thing\*(R" and start
2058the timer:
2059.Sp
2060.Vb 3
2061\& last_activity = ev_now (EV_A);
2062\& ev_init (&timer, callback);
2063\& callback (EV_A_ &timer, 0);
2064.Ve
2065.Sp
2066When there is some activity, simply store the current time in
2067\&\f(CW\*(C`last_activity\*(C'\fR, no libev calls at all:
2068.Sp
2069.Vb 2
2070\& if (activity detected)
2071\& last_activity = ev_now (EV_A);
2072.Ve
2073.Sp
2074When your timeout value changes, then the timeout can be changed by simply
2075providing a new value, stopping the timer and calling the callback, which
2076will again do the right thing (for example, time out immediately :).
2077.Sp
2078.Vb 3
2079\& timeout = new_value;
2080\& ev_timer_stop (EV_A_ &timer);
2081\& callback (EV_A_ &timer, 0);
2082.Ve
2083.Sp
2084This technique is slightly more complex, but in most cases where the
2085time-out is unlikely to be triggered, much more efficient.
2086.IP "4. Wee, just use a double-linked list for your timeouts." 4
2087.IX Item "4. Wee, just use a double-linked list for your timeouts."
2088If there is not one request, but many thousands (millions...), all
2089employing some kind of timeout with the same timeout value, then one can
2090do even better:
2091.Sp
2092When starting the timeout, calculate the timeout value and put the timeout
2093at the \fIend\fR of the list.
2094.Sp
2095Then use an \f(CW\*(C`ev_timer\*(C'\fR to fire when the timeout at the \fIbeginning\fR of
2096the list is expected to fire (for example, using the technique #3).
2097.Sp
2098When there is some activity, remove the timer from the list, recalculate
2099the timeout, append it to the end of the list again, and make sure to
2100update the \f(CW\*(C`ev_timer\*(C'\fR if it was taken from the beginning of the list.
2101.Sp
2102This way, one can manage an unlimited number of timeouts in O(1) time for
2103starting, stopping and updating the timers, at the expense of a major
2104complication, and having to use a constant timeout. The constant timeout
2105ensures that the list stays sorted.
2106.PP
2107So which method the best?
2108.PP
2109Method #2 is a simple no-brain-required solution that is adequate in most
2110situations. Method #3 requires a bit more thinking, but handles many cases
2111better, and isn't very complicated either. In most case, choosing either
2112one is fine, with #3 being better in typical situations.
2113.PP
2114Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
2115rather complicated, but extremely efficient, something that really pays
2116off after the first million or so of active timers, i.e. it's usually
2117overkill :)
2118.PP
2119\fIThe special problem of being too early\fR
2120.IX Subsection "The special problem of being too early"
2121.PP
2122If you ask a timer to call your callback after three seconds, then
2123you expect it to be invoked after three seconds \- but of course, this
2124cannot be guaranteed to infinite precision. Less obviously, it cannot be
2125guaranteed to any precision by libev \- imagine somebody suspending the
2126process with a \s-1STOP\s0 signal for a few hours for example.
2127.PP
2128So, libev tries to invoke your callback as soon as possible \fIafter\fR the
2129delay has occurred, but cannot guarantee this.
2130.PP
2131A less obvious failure mode is calling your callback too early: many event
2132loops compare timestamps with a \*(L"elapsed delay >= requested delay\*(R", but
2133this can cause your callback to be invoked much earlier than you would
2134expect.
2135.PP
2136To see why, imagine a system with a clock that only offers full second
2137resolution (think windows if you can't come up with a broken enough \s-1OS\s0
2138yourself). If you schedule a one-second timer at the time 500.9, then the
2139event loop will schedule your timeout to elapse at a system time of 500
2140(500.9 truncated to the resolution) + 1, or 501.
2141.PP
2142If an event library looks at the timeout 0.1s later, it will see \*(L"501 >=
2143501\*(R" and invoke the callback 0.1s after it was started, even though a
2144one-second delay was requested \- this is being \*(L"too early\*(R", despite best
2145intentions.
2146.PP
2147This is the reason why libev will never invoke the callback if the elapsed
2148delay equals the requested delay, but only when the elapsed delay is
2149larger than the requested delay. In the example above, libev would only invoke
2150the callback at system time 502, or 1.1s after the timer was started.
2151.PP
2152So, while libev cannot guarantee that your callback will be invoked
2153exactly when requested, it \fIcan\fR and \fIdoes\fR guarantee that the requested
2154delay has actually elapsed, or in other words, it always errs on the \*(L"too
2155late\*(R" side of things.
2156.PP
2157\fIThe special problem of time updates\fR
2158.IX Subsection "The special problem of time updates"
2159.PP
2160Establishing the current time is a costly operation (it usually takes
2161at least one system call): \s-1EV\s0 therefore updates its idea of the current
2162time only before and after \f(CW\*(C`ev_run\*(C'\fR collects new events, which causes a
2163growing difference between \f(CW\*(C`ev_now ()\*(C'\fR and \f(CW\*(C`ev_time ()\*(C'\fR when handling
2164lots of events in one iteration.
903.PP 2165.PP
904The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR 2166The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
905time. This is usually the right thing as this timestamp refers to the time 2167time. This is usually the right thing as this timestamp refers to the time
906of the event triggering whatever timeout you are modifying/starting. If 2168of the event triggering whatever timeout you are modifying/starting. If
907you suspect event processing to be delayed and you \fIneed\fR to base the timeout 2169you suspect event processing to be delayed and you \fIneed\fR to base the
908on the current time, use something like this to adjust for this: 2170timeout on the current time, use something like the following to adjust
2171for it:
909.PP 2172.PP
910.Vb 1 2173.Vb 1
911\& ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); 2174\& ev_timer_set (&timer, after + (ev_time () \- ev_now ()), 0.);
912.Ve 2175.Ve
913.PP 2176.PP
914The callback is guarenteed to be invoked only when its timeout has passed, 2177If the event loop is suspended for a long time, you can also force an
915but if multiple timers become ready during the same loop iteration then 2178update of the time returned by \f(CW\*(C`ev_now ()\*(C'\fR by calling \f(CW\*(C`ev_now_update
916order of execution is undefined. 2179()\*(C'\fR, although that will push the event time of all outstanding events
2180further into the future.
2181.PP
2182\fIThe special problem of unsynchronised clocks\fR
2183.IX Subsection "The special problem of unsynchronised clocks"
2184.PP
2185Modern systems have a variety of clocks \- libev itself uses the normal
2186\&\*(L"wall clock\*(R" clock and, if available, the monotonic clock (to avoid time
2187jumps).
2188.PP
2189Neither of these clocks is synchronised with each other or any other clock
2190on the system, so \f(CW\*(C`ev_time ()\*(C'\fR might return a considerably different time
2191than \f(CW\*(C`gettimeofday ()\*(C'\fR or \f(CW\*(C`time ()\*(C'\fR. On a GNU/Linux system, for example,
2192a call to \f(CW\*(C`gettimeofday\*(C'\fR might return a second count that is one higher
2193than a directly following call to \f(CW\*(C`time\*(C'\fR.
2194.PP
2195The moral of this is to only compare libev-related timestamps with
2196\&\f(CW\*(C`ev_time ()\*(C'\fR and \f(CW\*(C`ev_now ()\*(C'\fR, at least if you want better precision than
2197a second or so.
2198.PP
2199One more problem arises due to this lack of synchronisation: if libev uses
2200the system monotonic clock and you compare timestamps from \f(CW\*(C`ev_time\*(C'\fR
2201or \f(CW\*(C`ev_now\*(C'\fR from when you started your timer and when your callback is
2202invoked, you will find that sometimes the callback is a bit \*(L"early\*(R".
2203.PP
2204This is because \f(CW\*(C`ev_timer\*(C'\fRs work in real time, not wall clock time, so
2205libev makes sure your callback is not invoked before the delay happened,
2206\&\fImeasured according to the real time\fR, not the system clock.
2207.PP
2208If your timeouts are based on a physical timescale (e.g. \*(L"time out this
2209connection after 100 seconds\*(R") then this shouldn't bother you as it is
2210exactly the right behaviour.
2211.PP
2212If you want to compare wall clock/system timestamps to your timers, then
2213you need to use \f(CW\*(C`ev_periodic\*(C'\fRs, as these are based on the wall clock
2214time, where your comparisons will always generate correct results.
2215.PP
2216\fIThe special problems of suspended animation\fR
2217.IX Subsection "The special problems of suspended animation"
2218.PP
2219When you leave the server world it is quite customary to hit machines that
2220can suspend/hibernate \- what happens to the clocks during such a suspend?
2221.PP
2222Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
2223all processes, while the clocks (\f(CW\*(C`times\*(C'\fR, \f(CW\*(C`CLOCK_MONOTONIC\*(C'\fR) continue
2224to run until the system is suspended, but they will not advance while the
2225system is suspended. That means, on resume, it will be as if the program
2226was frozen for a few seconds, but the suspend time will not be counted
2227towards \f(CW\*(C`ev_timer\*(C'\fR when a monotonic clock source is used. The real time
2228clock advanced as expected, but if it is used as sole clocksource, then a
2229long suspend would be detected as a time jump by libev, and timers would
2230be adjusted accordingly.
2231.PP
2232I would not be surprised to see different behaviour in different between
2233operating systems, \s-1OS\s0 versions or even different hardware.
2234.PP
2235The other form of suspend (job control, or sending a \s-1SIGSTOP\s0) will see a
2236time jump in the monotonic clocks and the realtime clock. If the program
2237is suspended for a very long time, and monotonic clock sources are in use,
2238then you can expect \f(CW\*(C`ev_timer\*(C'\fRs to expire as the full suspension time
2239will be counted towards the timers. When no monotonic clock source is in
2240use, then libev will again assume a timejump and adjust accordingly.
2241.PP
2242It might be beneficial for this latter case to call \f(CW\*(C`ev_suspend\*(C'\fR
2243and \f(CW\*(C`ev_resume\*(C'\fR in code that handles \f(CW\*(C`SIGTSTP\*(C'\fR, to at least get
2244deterministic behaviour in this case (you can do nothing against
2245\&\f(CW\*(C`SIGSTOP\*(C'\fR).
2246.PP
2247\fIWatcher-Specific Functions and Data Members\fR
2248.IX Subsection "Watcher-Specific Functions and Data Members"
917.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4 2249.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
918.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 2250.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
919.PD 0 2251.PD 0
920.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4 2252.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
921.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 2253.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
922.PD 2254.PD
923Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR is 2255Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR
924\&\f(CW0.\fR, then it will automatically be stopped. If it is positive, then the 2256is \f(CW0.\fR, then it will automatically be stopped once the timeout is
925timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds 2257reached. If it is positive, then the timer will automatically be
926later, again, and again, until stopped manually. 2258configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds later, again, and again,
2259until stopped manually.
927.Sp 2260.Sp
928The timer itself will do a best-effort at avoiding drift, that is, if you 2261The timer itself will do a best-effort at avoiding drift, that is, if
929configure a timer to trigger every 10 seconds, then it will trigger at 2262you configure a timer to trigger every 10 seconds, then it will normally
930exactly 10 second intervals. If, however, your program cannot keep up with 2263trigger at exactly 10 second intervals. If, however, your program cannot
931the timer (because it takes longer than those 10 seconds to do stuff) the 2264keep up with the timer (because it takes longer than those 10 seconds to
932timer will not fire more than once per event loop iteration. 2265do stuff) the timer will not fire more than once per event loop iteration.
933.IP "ev_timer_again (loop)" 4 2266.IP "ev_timer_again (loop, ev_timer *)" 4
934.IX Item "ev_timer_again (loop)" 2267.IX Item "ev_timer_again (loop, ev_timer *)"
935This will act as if the timer timed out and restart it again if it is 2268This will act as if the timer timed out, and restarts it again if it is
936repeating. The exact semantics are: 2269repeating. It basically works like calling \f(CW\*(C`ev_timer_stop\*(C'\fR, updating the
2270timeout to the \f(CW\*(C`repeat\*(C'\fR value and calling \f(CW\*(C`ev_timer_start\*(C'\fR.
937.Sp 2271.Sp
938If the timer is started but nonrepeating, stop it. 2272The exact semantics are as in the following rules, all of which will be
2273applied to the watcher:
2274.RS 4
2275.IP "If the timer is pending, the pending status is always cleared." 4
2276.IX Item "If the timer is pending, the pending status is always cleared."
2277.PD 0
2278.IP "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)." 4
2279.IX Item "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)."
2280.ie n .IP "If the timer is repeating, make the ""repeat"" value the new timeout and start the timer, if necessary." 4
2281.el .IP "If the timer is repeating, make the \f(CWrepeat\fR value the new timeout and start the timer, if necessary." 4
2282.IX Item "If the timer is repeating, make the repeat value the new timeout and start the timer, if necessary."
2283.RE
2284.RS 4
2285.PD
939.Sp 2286.Sp
940If the timer is repeating, either start it if necessary (with the repeat 2287This sounds a bit complicated, see \*(L"Be smart about timeouts\*(R", above, for a
941value), or reset the running timer to the repeat value. 2288usage example.
2289.RE
2290.IP "ev_tstamp ev_timer_remaining (loop, ev_timer *)" 4
2291.IX Item "ev_tstamp ev_timer_remaining (loop, ev_timer *)"
2292Returns the remaining time until a timer fires. If the timer is active,
2293then this time is relative to the current event loop time, otherwise it's
2294the timeout value currently configured.
942.Sp 2295.Sp
943This sounds a bit complicated, but here is a useful and typical 2296That is, after an \f(CW\*(C`ev_timer_set (w, 5, 7)\*(C'\fR, \f(CW\*(C`ev_timer_remaining\*(C'\fR returns
944example: Imagine you have a tcp connection and you want a so-called idle 2297\&\f(CW5\fR. When the timer is started and one second passes, \f(CW\*(C`ev_timer_remaining\*(C'\fR
945timeout, that is, you want to be called when there have been, say, 60 2298will return \f(CW4\fR. When the timer expires and is restarted, it will return
946seconds of inactivity on the socket. The easiest way to do this is to 2299roughly \f(CW7\fR (likely slightly less as callback invocation takes some time,
947configure an \f(CW\*(C`ev_timer\*(C'\fR with after=repeat=60 and calling ev_timer_again each 2300too), and so on.
948time you successfully read or write some data. If you go into an idle 2301.IP "ev_tstamp repeat [read\-write]" 4
949state where you do not expect data to travel on the socket, you can stop 2302.IX Item "ev_tstamp repeat [read-write]"
950the timer, and again will automatically restart it if need be. 2303The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
2304or \f(CW\*(C`ev_timer_again\*(C'\fR is called, and determines the next timeout (if any),
2305which is also when any modifications are taken into account.
951.PP 2306.PP
2307\fIExamples\fR
2308.IX Subsection "Examples"
2309.PP
952Example: create a timer that fires after 60 seconds. 2310Example: Create a timer that fires after 60 seconds.
953.PP 2311.PP
954.Vb 5 2312.Vb 5
955\& static void 2313\& static void
956\& one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents) 2314\& one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
957\& { 2315\& {
958\& .. one minute over, w is actually stopped right here 2316\& .. one minute over, w is actually stopped right here
959\& } 2317\& }
960.Ve 2318\&
961.PP
962.Vb 3
963\& struct ev_timer mytimer; 2319\& ev_timer mytimer;
964\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.); 2320\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
965\& ev_timer_start (loop, &mytimer); 2321\& ev_timer_start (loop, &mytimer);
966.Ve 2322.Ve
967.PP 2323.PP
968Example: create a timeout timer that times out after 10 seconds of 2324Example: Create a timeout timer that times out after 10 seconds of
969inactivity. 2325inactivity.
970.PP 2326.PP
971.Vb 5 2327.Vb 5
972\& static void 2328\& static void
973\& timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents) 2329\& timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
974\& { 2330\& {
975\& .. ten seconds without any activity 2331\& .. ten seconds without any activity
976\& } 2332\& }
977.Ve 2333\&
978.PP
979.Vb 4
980\& struct ev_timer mytimer; 2334\& ev_timer mytimer;
981\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */ 2335\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
982\& ev_timer_again (&mytimer); /* start timer */ 2336\& ev_timer_again (&mytimer); /* start timer */
983\& ev_loop (loop, 0); 2337\& ev_run (loop, 0);
984.Ve 2338\&
985.PP
986.Vb 3
987\& // and in some piece of code that gets executed on any "activity": 2339\& // and in some piece of code that gets executed on any "activity":
988\& // reset the timeout to start ticking again at 10 seconds 2340\& // reset the timeout to start ticking again at 10 seconds
989\& ev_timer_again (&mytimer); 2341\& ev_timer_again (&mytimer);
990.Ve 2342.Ve
991.ie n .Sh """ev_periodic"" \- to cron or not to cron" 2343.ie n .SS """ev_periodic"" \- to cron or not to cron?"
992.el .Sh "\f(CWev_periodic\fP \- to cron or not to cron" 2344.el .SS "\f(CWev_periodic\fP \- to cron or not to cron?"
993.IX Subsection "ev_periodic - to cron or not to cron" 2345.IX Subsection "ev_periodic - to cron or not to cron?"
994Periodic watchers are also timers of a kind, but they are very versatile 2346Periodic watchers are also timers of a kind, but they are very versatile
995(and unfortunately a bit complex). 2347(and unfortunately a bit complex).
996.PP 2348.PP
997Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time) 2349Unlike \f(CW\*(C`ev_timer\*(C'\fR, periodic watchers are not based on real time (or
998but on wallclock time (absolute time). You can tell a periodic watcher 2350relative time, the physical time that passes) but on wall clock time
999to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a 2351(absolute time, the thing you can read on your calender or clock). The
1000periodic watcher to trigger in 10 seconds (by specifiying e.g. \f(CW\*(C`ev_now () 2352difference is that wall clock time can run faster or slower than real
1001+ 10.\*(C'\fR) and then reset your system clock to the last year, then it will 2353time, and time jumps are not uncommon (e.g. when you adjust your
1002take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger 2354wrist-watch).
1003roughly 10 seconds later and of course not if you reset your system time
1004again).
1005.PP 2355.PP
1006They can also be used to implement vastly more complex timers, such as 2356You can tell a periodic watcher to trigger after some specific point
1007triggering an event on eahc midnight, local time. 2357in time: for example, if you tell a periodic watcher to trigger \*(L"in 10
2358seconds\*(R" (by specifying e.g. \f(CW\*(C`ev_now () + 10.\*(C'\fR, that is, an absolute time
2359not a delay) and then reset your system clock to January of the previous
2360year, then it will take a year or more to trigger the event (unlike an
2361\&\f(CW\*(C`ev_timer\*(C'\fR, which would still trigger roughly 10 seconds after starting
2362it, as it uses a relative timeout).
1008.PP 2363.PP
2364\&\f(CW\*(C`ev_periodic\*(C'\fR watchers can also be used to implement vastly more complex
2365timers, such as triggering an event on each \*(L"midnight, local time\*(R", or
2366other complicated rules. This cannot be done with \f(CW\*(C`ev_timer\*(C'\fR watchers, as
2367those cannot react to time jumps.
2368.PP
1009As with timers, the callback is guarenteed to be invoked only when the 2369As with timers, the callback is guaranteed to be invoked only when the
1010time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready 2370point in time where it is supposed to trigger has passed. If multiple
1011during the same loop iteration then order of execution is undefined. 2371timers become ready during the same loop iteration then the ones with
2372earlier time-out values are invoked before ones with later time-out values
2373(but this is no longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
2374.PP
2375\fIWatcher-Specific Functions and Data Members\fR
2376.IX Subsection "Watcher-Specific Functions and Data Members"
1012.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4 2377.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
1013.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 2378.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
1014.PD 0 2379.PD 0
1015.IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4 2380.IP "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
1016.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 2381.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
1017.PD 2382.PD
1018Lots of arguments, lets sort it out... There are basically three modes of 2383Lots of arguments, let's sort it out... There are basically three modes of
1019operation, and we will explain them from simplest to complex: 2384operation, and we will explain them from simplest to most complex:
1020.RS 4 2385.RS 4
1021.IP "* absolute timer (interval = reschedule_cb = 0)" 4 2386.IP "\(bu" 4
1022.IX Item "absolute timer (interval = reschedule_cb = 0)" 2387absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
2388.Sp
1023In this configuration the watcher triggers an event at the wallclock time 2389In this configuration the watcher triggers an event after the wall clock
1024\&\f(CW\*(C`at\*(C'\fR and doesn't repeat. It will not adjust when a time jump occurs, 2390time \f(CW\*(C`offset\*(C'\fR has passed. It will not repeat and will not adjust when a
1025that is, if it is to be run at January 1st 2011 then it will run when the 2391time jump occurs, that is, if it is to be run at January 1st 2011 then it
1026system time reaches or surpasses this time. 2392will be stopped and invoked when the system clock reaches or surpasses
1027.IP "* non-repeating interval timer (interval > 0, reschedule_cb = 0)" 4 2393this point in time.
1028.IX Item "non-repeating interval timer (interval > 0, reschedule_cb = 0)" 2394.IP "\(bu" 4
2395repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
2396.Sp
1029In this mode the watcher will always be scheduled to time out at the next 2397In this mode the watcher will always be scheduled to time out at the next
1030\&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N) and then repeat, regardless 2398\&\f(CW\*(C`offset + N * interval\*(C'\fR time (for some integer N, which can also be
1031of any time jumps. 2399negative) and then repeat, regardless of any time jumps. The \f(CW\*(C`offset\*(C'\fR
2400argument is merely an offset into the \f(CW\*(C`interval\*(C'\fR periods.
1032.Sp 2401.Sp
1033This can be used to create timers that do not drift with respect to system 2402This can be used to create timers that do not drift with respect to the
1034time: 2403system clock, for example, here is an \f(CW\*(C`ev_periodic\*(C'\fR that triggers each
2404hour, on the hour (with respect to \s-1UTC\s0):
1035.Sp 2405.Sp
1036.Vb 1 2406.Vb 1
1037\& ev_periodic_set (&periodic, 0., 3600., 0); 2407\& ev_periodic_set (&periodic, 0., 3600., 0);
1038.Ve 2408.Ve
1039.Sp 2409.Sp
1040This doesn't mean there will always be 3600 seconds in between triggers, 2410This doesn't mean there will always be 3600 seconds in between triggers,
1041but only that the the callback will be called when the system time shows a 2411but only that the callback will be called when the system time shows a
1042full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible 2412full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
1043by 3600. 2413by 3600.
1044.Sp 2414.Sp
1045Another way to think about it (for the mathematically inclined) is that 2415Another way to think about it (for the mathematically inclined) is that
1046\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible 2416\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
1047time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps. 2417time where \f(CW\*(C`time = offset (mod interval)\*(C'\fR, regardless of any time jumps.
1048.IP "* manual reschedule mode (reschedule_cb = callback)" 4 2418.Sp
1049.IX Item "manual reschedule mode (reschedule_cb = callback)" 2419The \f(CW\*(C`interval\*(C'\fR \fI\s-1MUST\s0\fR be positive, and for numerical stability, the
2420interval value should be higher than \f(CW\*(C`1/8192\*(C'\fR (which is around 100
2421microseconds) and \f(CW\*(C`offset\*(C'\fR should be higher than \f(CW0\fR and should have
2422at most a similar magnitude as the current time (say, within a factor of
2423ten). Typical values for offset are, in fact, \f(CW0\fR or something between
2424\&\f(CW0\fR and \f(CW\*(C`interval\*(C'\fR, which is also the recommended range.
2425.Sp
2426Note also that there is an upper limit to how often a timer can fire (\s-1CPU\s0
2427speed for example), so if \f(CW\*(C`interval\*(C'\fR is very small then timing stability
2428will of course deteriorate. Libev itself tries to be exact to be about one
2429millisecond (if the \s-1OS\s0 supports it and the machine is fast enough).
2430.IP "\(bu" 4
2431manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
2432.Sp
1050In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being 2433In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`offset\*(C'\fR are both being
1051ignored. Instead, each time the periodic watcher gets scheduled, the 2434ignored. Instead, each time the periodic watcher gets scheduled, the
1052reschedule callback will be called with the watcher as first, and the 2435reschedule callback will be called with the watcher as first, and the
1053current time as second argument. 2436current time as second argument.
1054.Sp 2437.Sp
1055\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, 2438\&\s-1NOTE: \s0\fIThis callback \s-1MUST NOT\s0 stop or destroy any periodic watcher, ever,
1056ever, or make any event loop modifications\fR. If you need to stop it, 2439or make \s-1ANY\s0 other event loop modifications whatsoever, unless explicitly
1057return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by 2440allowed by documentation here\fR.
1058starting a prepare watcher).
1059.Sp 2441.Sp
2442If you need to stop it, return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop
2443it afterwards (e.g. by starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is the
2444only event loop modification you are allowed to do).
2445.Sp
1060Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w, 2446The callback prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(ev_periodic
1061ev_tstamp now)\*(C'\fR, e.g.: 2447*w, ev_tstamp now)\*(C'\fR, e.g.:
1062.Sp 2448.Sp
1063.Vb 4 2449.Vb 5
2450\& static ev_tstamp
1064\& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) 2451\& my_rescheduler (ev_periodic *w, ev_tstamp now)
1065\& { 2452\& {
1066\& return now + 60.; 2453\& return now + 60.;
1067\& } 2454\& }
1068.Ve 2455.Ve
1069.Sp 2456.Sp
1070It must return the next time to trigger, based on the passed time value 2457It must return the next time to trigger, based on the passed time value
1071(that is, the lowest time value larger than to the second argument). It 2458(that is, the lowest time value larger than to the second argument). It
1072will usually be called just before the callback will be triggered, but 2459will usually be called just before the callback will be triggered, but
1073might be called at other times, too. 2460might be called at other times, too.
1074.Sp 2461.Sp
1075\&\s-1NOTE:\s0 \fIThis callback must always return a time that is later than the 2462\&\s-1NOTE: \s0\fIThis callback must always return a time that is higher than or
1076passed \f(CI\*(C`now\*(C'\fI value\fR. Not even \f(CW\*(C`now\*(C'\fR itself will do, it \fImust\fR be larger. 2463equal to the passed \f(CI\*(C`now\*(C'\fI value\fR.
1077.Sp 2464.Sp
1078This can be used to create very complex timers, such as a timer that 2465This can be used to create very complex timers, such as a timer that
1079triggers on each midnight, local time. To do this, you would calculate the 2466triggers on \*(L"next midnight, local time\*(R". To do this, you would calculate the
1080next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How 2467next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How
1081you do this is, again, up to you (but it is not trivial, which is the main 2468you do this is, again, up to you (but it is not trivial, which is the main
1082reason I omitted it as an example). 2469reason I omitted it as an example).
1083.RE 2470.RE
1084.RS 4 2471.RS 4
… …
1087.IX Item "ev_periodic_again (loop, ev_periodic *)" 2474.IX Item "ev_periodic_again (loop, ev_periodic *)"
1088Simply stops and restarts the periodic watcher again. This is only useful 2475Simply stops and restarts the periodic watcher again. This is only useful
1089when you changed some parameters or the reschedule callback would return 2476when you changed some parameters or the reschedule callback would return
1090a different time than the last time it was called (e.g. in a crond like 2477a different time than the last time it was called (e.g. in a crond like
1091program when the crontabs have changed). 2478program when the crontabs have changed).
2479.IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4
2480.IX Item "ev_tstamp ev_periodic_at (ev_periodic *)"
2481When active, returns the absolute time that the watcher is supposed
2482to trigger next. This is not the same as the \f(CW\*(C`offset\*(C'\fR argument to
2483\&\f(CW\*(C`ev_periodic_set\*(C'\fR, but indeed works even in interval and manual
2484rescheduling modes.
2485.IP "ev_tstamp offset [read\-write]" 4
2486.IX Item "ev_tstamp offset [read-write]"
2487When repeating, this contains the offset value, otherwise this is the
2488absolute point in time (the \f(CW\*(C`offset\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR,
2489although libev might modify this value for better numerical stability).
2490.Sp
2491Can be modified any time, but changes only take effect when the periodic
2492timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
2493.IP "ev_tstamp interval [read\-write]" 4
2494.IX Item "ev_tstamp interval [read-write]"
2495The current interval value. Can be modified any time, but changes only
2496take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
2497called.
2498.IP "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read\-write]" 4
2499.IX Item "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]"
2500The current reschedule callback, or \f(CW0\fR, if this functionality is
2501switched off. Can be changed any time, but changes only take effect when
2502the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1092.PP 2503.PP
2504\fIExamples\fR
2505.IX Subsection "Examples"
2506.PP
1093Example: call a callback every hour, or, more precisely, whenever the 2507Example: Call a callback every hour, or, more precisely, whenever the
1094system clock is divisible by 3600. The callback invocation times have 2508system time is divisible by 3600. The callback invocation times have
1095potentially a lot of jittering, but good long-term stability. 2509potentially a lot of jitter, but good long-term stability.
1096.PP 2510.PP
1097.Vb 5 2511.Vb 5
1098\& static void 2512\& static void
1099\& clock_cb (struct ev_loop *loop, struct ev_io *w, int revents) 2513\& clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1100\& { 2514\& {
1101\& ... its now a full hour (UTC, or TAI or whatever your clock follows) 2515\& ... its now a full hour (UTC, or TAI or whatever your clock follows)
1102\& } 2516\& }
1103.Ve 2517\&
1104.PP
1105.Vb 3
1106\& struct ev_periodic hourly_tick; 2518\& ev_periodic hourly_tick;
1107\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0); 2519\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1108\& ev_periodic_start (loop, &hourly_tick); 2520\& ev_periodic_start (loop, &hourly_tick);
1109.Ve 2521.Ve
1110.PP 2522.PP
1111Example: the same as above, but use a reschedule callback to do it: 2523Example: The same as above, but use a reschedule callback to do it:
1112.PP 2524.PP
1113.Vb 1 2525.Vb 1
1114\& #include <math.h> 2526\& #include <math.h>
1115.Ve 2527\&
1116.PP
1117.Vb 5
1118\& static ev_tstamp 2528\& static ev_tstamp
1119\& my_scheduler_cb (struct ev_periodic *w, ev_tstamp now) 2529\& my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1120\& { 2530\& {
1121\& return fmod (now, 3600.) + 3600.; 2531\& return now + (3600. \- fmod (now, 3600.));
1122\& } 2532\& }
1123.Ve 2533\&
1124.PP
1125.Vb 1
1126\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb); 2534\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1127.Ve 2535.Ve
1128.PP 2536.PP
1129Example: call a callback every hour, starting now: 2537Example: Call a callback every hour, starting now:
1130.PP 2538.PP
1131.Vb 4 2539.Vb 4
1132\& struct ev_periodic hourly_tick; 2540\& ev_periodic hourly_tick;
1133\& ev_periodic_init (&hourly_tick, clock_cb, 2541\& ev_periodic_init (&hourly_tick, clock_cb,
1134\& fmod (ev_now (loop), 3600.), 3600., 0); 2542\& fmod (ev_now (loop), 3600.), 3600., 0);
1135\& ev_periodic_start (loop, &hourly_tick); 2543\& ev_periodic_start (loop, &hourly_tick);
1136.Ve 2544.Ve
1137.ie n .Sh """ev_signal"" \- signal me when a signal gets signalled" 2545.ie n .SS """ev_signal"" \- signal me when a signal gets signalled!"
1138.el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled" 2546.el .SS "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
1139.IX Subsection "ev_signal - signal me when a signal gets signalled" 2547.IX Subsection "ev_signal - signal me when a signal gets signalled!"
1140Signal watchers will trigger an event when the process receives a specific 2548Signal watchers will trigger an event when the process receives a specific
1141signal one or more times. Even though signals are very asynchronous, libev 2549signal one or more times. Even though signals are very asynchronous, libev
1142will try it's best to deliver signals synchronously, i.e. as part of the 2550will try its best to deliver signals synchronously, i.e. as part of the
1143normal event processing, like any other event. 2551normal event processing, like any other event.
1144.PP 2552.PP
2553If you want signals to be delivered truly asynchronously, just use
2554\&\f(CW\*(C`sigaction\*(C'\fR as you would do without libev and forget about sharing
2555the signal. You can even use \f(CW\*(C`ev_async\*(C'\fR from a signal handler to
2556synchronously wake up an event loop.
2557.PP
1145You can configure as many watchers as you like per signal. Only when the 2558You can configure as many watchers as you like for the same signal, but
1146first watcher gets started will libev actually register a signal watcher 2559only within the same loop, i.e. you can watch for \f(CW\*(C`SIGINT\*(C'\fR in your
1147with the kernel (thus it coexists with your own signal handlers as long 2560default loop and for \f(CW\*(C`SIGIO\*(C'\fR in another loop, but you cannot watch for
1148as you don't register any with libev). Similarly, when the last signal 2561\&\f(CW\*(C`SIGINT\*(C'\fR in both the default loop and another loop at the same time. At
1149watcher for a signal is stopped libev will reset the signal handler to 2562the moment, \f(CW\*(C`SIGCHLD\*(C'\fR is permanently tied to the default loop.
1150\&\s-1SIG_DFL\s0 (regardless of what it was set to before). 2563.PP
2564Only after the first watcher for a signal is started will libev actually
2565register something with the kernel. It thus coexists with your own signal
2566handlers as long as you don't register any with libev for the same signal.
2567.PP
2568If possible and supported, libev will install its handlers with
2569\&\f(CW\*(C`SA_RESTART\*(C'\fR (or equivalent) behaviour enabled, so system calls should
2570not be unduly interrupted. If you have a problem with system calls getting
2571interrupted by signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher
2572and unblock them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher.
2573.PP
2574\fIThe special problem of inheritance over fork/execve/pthread_create\fR
2575.IX Subsection "The special problem of inheritance over fork/execve/pthread_create"
2576.PP
2577Both the signal mask (\f(CW\*(C`sigprocmask\*(C'\fR) and the signal disposition
2578(\f(CW\*(C`sigaction\*(C'\fR) are unspecified after starting a signal watcher (and after
2579stopping it again), that is, libev might or might not block the signal,
2580and might or might not set or restore the installed signal handler (but
2581see \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR).
2582.PP
2583While this does not matter for the signal disposition (libev never
2584sets signals to \f(CW\*(C`SIG_IGN\*(C'\fR, so handlers will be reset to \f(CW\*(C`SIG_DFL\*(C'\fR on
2585\&\f(CW\*(C`execve\*(C'\fR), this matters for the signal mask: many programs do not expect
2586certain signals to be blocked.
2587.PP
2588This means that before calling \f(CW\*(C`exec\*(C'\fR (from the child) you should reset
2589the signal mask to whatever \*(L"default\*(R" you expect (all clear is a good
2590choice usually).
2591.PP
2592The simplest way to ensure that the signal mask is reset in the child is
2593to install a fork handler with \f(CW\*(C`pthread_atfork\*(C'\fR that resets it. That will
2594catch fork calls done by libraries (such as the libc) as well.
2595.PP
2596In current versions of libev, the signal will not be blocked indefinitely
2597unless you use the \f(CW\*(C`signalfd\*(C'\fR \s-1API \s0(\f(CW\*(C`EV_SIGNALFD\*(C'\fR). While this reduces
2598the window of opportunity for problems, it will not go away, as libev
2599\&\fIhas\fR to modify the signal mask, at least temporarily.
2600.PP
2601So I can't stress this enough: \fIIf you do not reset your signal mask when
2602you expect it to be empty, you have a race condition in your code\fR. This
2603is not a libev-specific thing, this is true for most event libraries.
2604.PP
2605\fIThe special problem of threads signal handling\fR
2606.IX Subsection "The special problem of threads signal handling"
2607.PP
2608\&\s-1POSIX\s0 threads has problematic signal handling semantics, specifically,
2609a lot of functionality (sigfd, sigwait etc.) only really works if all
2610threads in a process block signals, which is hard to achieve.
2611.PP
2612When you want to use sigwait (or mix libev signal handling with your own
2613for the same signals), you can tackle this problem by globally blocking
2614all signals before creating any threads (or creating them with a fully set
2615sigprocmask) and also specifying the \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when creating
2616loops. Then designate one thread as \*(L"signal receiver thread\*(R" which handles
2617these signals. You can pass on any signals that libev might be interested
2618in by calling \f(CW\*(C`ev_feed_signal\*(C'\fR.
2619.PP
2620\fIWatcher-Specific Functions and Data Members\fR
2621.IX Subsection "Watcher-Specific Functions and Data Members"
1151.IP "ev_signal_init (ev_signal *, callback, int signum)" 4 2622.IP "ev_signal_init (ev_signal *, callback, int signum)" 4
1152.IX Item "ev_signal_init (ev_signal *, callback, int signum)" 2623.IX Item "ev_signal_init (ev_signal *, callback, int signum)"
1153.PD 0 2624.PD 0
1154.IP "ev_signal_set (ev_signal *, int signum)" 4 2625.IP "ev_signal_set (ev_signal *, int signum)" 4
1155.IX Item "ev_signal_set (ev_signal *, int signum)" 2626.IX Item "ev_signal_set (ev_signal *, int signum)"
1156.PD 2627.PD
1157Configures the watcher to trigger on the given signal number (usually one 2628Configures the watcher to trigger on the given signal number (usually one
1158of the \f(CW\*(C`SIGxxx\*(C'\fR constants). 2629of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
2630.IP "int signum [read\-only]" 4
2631.IX Item "int signum [read-only]"
2632The signal the watcher watches out for.
2633.PP
2634\fIExamples\fR
2635.IX Subsection "Examples"
2636.PP
2637Example: Try to exit cleanly on \s-1SIGINT.\s0
2638.PP
2639.Vb 5
2640\& static void
2641\& sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
2642\& {
2643\& ev_break (loop, EVBREAK_ALL);
2644\& }
2645\&
2646\& ev_signal signal_watcher;
2647\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
2648\& ev_signal_start (loop, &signal_watcher);
2649.Ve
1159.ie n .Sh """ev_child"" \- wait for pid status changes" 2650.ie n .SS """ev_child"" \- watch out for process status changes"
1160.el .Sh "\f(CWev_child\fP \- wait for pid status changes" 2651.el .SS "\f(CWev_child\fP \- watch out for process status changes"
1161.IX Subsection "ev_child - wait for pid status changes" 2652.IX Subsection "ev_child - watch out for process status changes"
1162Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to 2653Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
1163some child status changes (most typically when a child of yours dies). 2654some child status changes (most typically when a child of yours dies or
2655exits). It is permissible to install a child watcher \fIafter\fR the child
2656has been forked (which implies it might have already exited), as long
2657as the event loop isn't entered (or is continued from a watcher), i.e.,
2658forking and then immediately registering a watcher for the child is fine,
2659but forking and registering a watcher a few event loop iterations later or
2660in the next callback invocation is not.
2661.PP
2662Only the default event loop is capable of handling signals, and therefore
2663you can only register child watchers in the default event loop.
2664.PP
2665Due to some design glitches inside libev, child watchers will always be
2666handled at maximum priority (their priority is set to \f(CW\*(C`EV_MAXPRI\*(C'\fR by
2667libev)
2668.PP
2669\fIProcess Interaction\fR
2670.IX Subsection "Process Interaction"
2671.PP
2672Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is
2673initialised. This is necessary to guarantee proper behaviour even if the
2674first child watcher is started after the child exits. The occurrence
2675of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done
2676synchronously as part of the event loop processing. Libev always reaps all
2677children, even ones not watched.
2678.PP
2679\fIOverriding the Built-In Processing\fR
2680.IX Subsection "Overriding the Built-In Processing"
2681.PP
2682Libev offers no special support for overriding the built-in child
2683processing, but if your application collides with libev's default child
2684handler, you can override it easily by installing your own handler for
2685\&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the
2686default loop never gets destroyed. You are encouraged, however, to use an
2687event-based approach to child reaping and thus use libev's support for
2688that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely.
2689.PP
2690\fIStopping the Child Watcher\fR
2691.IX Subsection "Stopping the Child Watcher"
2692.PP
2693Currently, the child watcher never gets stopped, even when the
2694child terminates, so normally one needs to stop the watcher in the
2695callback. Future versions of libev might stop the watcher automatically
2696when a child exit is detected (calling \f(CW\*(C`ev_child_stop\*(C'\fR twice is not a
2697problem).
2698.PP
2699\fIWatcher-Specific Functions and Data Members\fR
2700.IX Subsection "Watcher-Specific Functions and Data Members"
1164.IP "ev_child_init (ev_child *, callback, int pid)" 4 2701.IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4
1165.IX Item "ev_child_init (ev_child *, callback, int pid)" 2702.IX Item "ev_child_init (ev_child *, callback, int pid, int trace)"
1166.PD 0 2703.PD 0
1167.IP "ev_child_set (ev_child *, int pid)" 4 2704.IP "ev_child_set (ev_child *, int pid, int trace)" 4
1168.IX Item "ev_child_set (ev_child *, int pid)" 2705.IX Item "ev_child_set (ev_child *, int pid, int trace)"
1169.PD 2706.PD
1170Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or 2707Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
1171\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look 2708\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
1172at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see 2709at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
1173the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems 2710the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
1174\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the 2711\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
1175process causing the status change. 2712process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only
2713activate the watcher when the process terminates) or \f(CW1\fR (additionally
2714activate the watcher when the process is stopped or continued).
2715.IP "int pid [read\-only]" 4
2716.IX Item "int pid [read-only]"
2717The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
2718.IP "int rpid [read\-write]" 4
2719.IX Item "int rpid [read-write]"
2720The process id that detected a status change.
2721.IP "int rstatus [read\-write]" 4
2722.IX Item "int rstatus [read-write]"
2723The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
2724\&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
1176.PP 2725.PP
1177Example: try to exit cleanly on \s-1SIGINT\s0 and \s-1SIGTERM\s0. 2726\fIExamples\fR
2727.IX Subsection "Examples"
1178.PP 2728.PP
2729Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for
2730its completion.
2731.PP
1179.Vb 5 2732.Vb 1
2733\& ev_child cw;
2734\&
1180\& static void 2735\& static void
1181\& sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents) 2736\& child_cb (EV_P_ ev_child *w, int revents)
1182\& { 2737\& {
1183\& ev_unloop (loop, EVUNLOOP_ALL); 2738\& ev_child_stop (EV_A_ w);
2739\& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus);
1184\& } 2740\& }
2741\&
2742\& pid_t pid = fork ();
2743\&
2744\& if (pid < 0)
2745\& // error
2746\& else if (pid == 0)
2747\& {
2748\& // the forked child executes here
2749\& exit (1);
2750\& }
2751\& else
2752\& {
2753\& ev_child_init (&cw, child_cb, pid, 0);
2754\& ev_child_start (EV_DEFAULT_ &cw);
2755\& }
1185.Ve 2756.Ve
2757.ie n .SS """ev_stat"" \- did the file attributes just change?"
2758.el .SS "\f(CWev_stat\fP \- did the file attributes just change?"
2759.IX Subsection "ev_stat - did the file attributes just change?"
2760This watches a file system path for attribute changes. That is, it calls
2761\&\f(CW\*(C`stat\*(C'\fR on that path in regular intervals (or when the \s-1OS\s0 says it changed)
2762and sees if it changed compared to the last time, invoking the callback
2763if it did. Starting the watcher \f(CW\*(C`stat\*(C'\fR's the file, so only changes that
2764happen after the watcher has been started will be reported.
1186.PP 2765.PP
2766The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does
2767not exist\*(R" is a status change like any other. The condition \*(L"path does not
2768exist\*(R" (or more correctly \*(L"path cannot be stat'ed\*(R") is signified by the
2769\&\f(CW\*(C`st_nlink\*(C'\fR field being zero (which is otherwise always forced to be at
2770least one) and all the other fields of the stat buffer having unspecified
2771contents.
2772.PP
2773The path \fImust not\fR end in a slash or contain special components such as
2774\&\f(CW\*(C`.\*(C'\fR or \f(CW\*(C`..\*(C'\fR. The path \fIshould\fR be absolute: If it is relative and
2775your working directory changes, then the behaviour is undefined.
2776.PP
2777Since there is no portable change notification interface available, the
2778portable implementation simply calls \f(CWstat(2)\fR regularly on the path
2779to see if it changed somehow. You can specify a recommended polling
2780interval for this case. If you specify a polling interval of \f(CW0\fR (highly
2781recommended!) then a \fIsuitable, unspecified default\fR value will be used
2782(which you can expect to be around five seconds, although this might
2783change dynamically). Libev will also impose a minimum interval which is
2784currently around \f(CW0.1\fR, but that's usually overkill.
2785.PP
2786This watcher type is not meant for massive numbers of stat watchers,
2787as even with OS-supported change notifications, this can be
2788resource-intensive.
2789.PP
2790At the time of this writing, the only OS-specific interface implemented
2791is the Linux inotify interface (implementing kqueue support is left as an
2792exercise for the reader. Note, however, that the author sees no way of
2793implementing \f(CW\*(C`ev_stat\*(C'\fR semantics with kqueue, except as a hint).
2794.PP
2795\fI\s-1ABI\s0 Issues (Largefile Support)\fR
2796.IX Subsection "ABI Issues (Largefile Support)"
2797.PP
2798Libev by default (unless the user overrides this) uses the default
2799compilation environment, which means that on systems with large file
2800support disabled by default, you get the 32 bit version of the stat
2801structure. When using the library from programs that change the \s-1ABI\s0 to
2802use 64 bit file offsets the programs will fail. In that case you have to
2803compile libev with the same flags to get binary compatibility. This is
2804obviously the case with any flags that change the \s-1ABI,\s0 but the problem is
2805most noticeably displayed with ev_stat and large file support.
2806.PP
2807The solution for this is to lobby your distribution maker to make large
2808file interfaces available by default (as e.g. FreeBSD does) and not
2809optional. Libev cannot simply switch on large file support because it has
2810to exchange stat structures with application programs compiled using the
2811default compilation environment.
2812.PP
2813\fIInotify and Kqueue\fR
2814.IX Subsection "Inotify and Kqueue"
2815.PP
2816When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev and present at
2817runtime, it will be used to speed up change detection where possible. The
2818inotify descriptor will be created lazily when the first \f(CW\*(C`ev_stat\*(C'\fR
2819watcher is being started.
2820.PP
2821Inotify presence does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
2822except that changes might be detected earlier, and in some cases, to avoid
2823making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presence of inotify support
2824there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling,
2825but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
2826many bugs), the path exists (i.e. stat succeeds), and the path resides on
2827a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
2828xfs are fully working) libev usually gets away without polling.
2829.PP
2830There is no support for kqueue, as apparently it cannot be used to
2831implement this functionality, due to the requirement of having a file
2832descriptor open on the object at all times, and detecting renames, unlinks
2833etc. is difficult.
2834.PP
2835\fI\f(CI\*(C`stat ()\*(C'\fI is a synchronous operation\fR
2836.IX Subsection "stat () is a synchronous operation"
2837.PP
2838Libev doesn't normally do any kind of I/O itself, and so is not blocking
2839the process. The exception are \f(CW\*(C`ev_stat\*(C'\fR watchers \- those call \f(CW\*(C`stat
2840()\*(C'\fR, which is a synchronous operation.
2841.PP
2842For local paths, this usually doesn't matter: unless the system is very
2843busy or the intervals between stat's are large, a stat call will be fast,
2844as the path data is usually in memory already (except when starting the
2845watcher).
2846.PP
2847For networked file systems, calling \f(CW\*(C`stat ()\*(C'\fR can block an indefinite
2848time due to network issues, and even under good conditions, a stat call
2849often takes multiple milliseconds.
2850.PP
2851Therefore, it is best to avoid using \f(CW\*(C`ev_stat\*(C'\fR watchers on networked
2852paths, although this is fully supported by libev.
2853.PP
2854\fIThe special problem of stat time resolution\fR
2855.IX Subsection "The special problem of stat time resolution"
2856.PP
2857The \f(CW\*(C`stat ()\*(C'\fR system call only supports full-second resolution portably,
2858and even on systems where the resolution is higher, most file systems
2859still only support whole seconds.
2860.PP
2861That means that, if the time is the only thing that changes, you can
2862easily miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and
2863calls your callback, which does something. When there is another update
2864within the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect unless the
2865stat data does change in other ways (e.g. file size).
2866.PP
2867The solution to this is to delay acting on a change for slightly more
2868than a second (or till slightly after the next full second boundary), using
2869a roughly one-second-delay \f(CW\*(C`ev_timer\*(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02);
2870ev_timer_again (loop, w)\*(C'\fR).
2871.PP
2872The \f(CW.02\fR offset is added to work around small timing inconsistencies
2873of some operating systems (where the second counter of the current time
2874might be be delayed. One such system is the Linux kernel, where a call to
2875\&\f(CW\*(C`gettimeofday\*(C'\fR might return a timestamp with a full second later than
2876a subsequent \f(CW\*(C`time\*(C'\fR call \- if the equivalent of \f(CW\*(C`time ()\*(C'\fR is used to
2877update file times then there will be a small window where the kernel uses
2878the previous second to update file times but libev might already execute
2879the timer callback).
2880.PP
2881\fIWatcher-Specific Functions and Data Members\fR
2882.IX Subsection "Watcher-Specific Functions and Data Members"
2883.IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
2884.IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
2885.PD 0
2886.IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4
2887.IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)"
2888.PD
2889Configures the watcher to wait for status changes of the given
2890\&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to
2891be detected and should normally be specified as \f(CW0\fR to let libev choose
2892a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same
2893path for as long as the watcher is active.
2894.Sp
2895The callback will receive an \f(CW\*(C`EV_STAT\*(C'\fR event when a change was detected,
2896relative to the attributes at the time the watcher was started (or the
2897last change was detected).
2898.IP "ev_stat_stat (loop, ev_stat *)" 4
2899.IX Item "ev_stat_stat (loop, ev_stat *)"
2900Updates the stat buffer immediately with new values. If you change the
2901watched path in your callback, you could call this function to avoid
2902detecting this change (while introducing a race condition if you are not
2903the only one changing the path). Can also be useful simply to find out the
2904new values.
2905.IP "ev_statdata attr [read\-only]" 4
2906.IX Item "ev_statdata attr [read-only]"
2907The most-recently detected attributes of the file. Although the type is
2908\&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
2909suitable for your system, but you can only rely on the POSIX-standardised
2910members to be present. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there was
2911some error while \f(CW\*(C`stat\*(C'\fRing the file.
2912.IP "ev_statdata prev [read\-only]" 4
2913.IX Item "ev_statdata prev [read-only]"
2914The previous attributes of the file. The callback gets invoked whenever
2915\&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR, or, more precisely, one or more of these members
2916differ: \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,
2917\&\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.
2918.IP "ev_tstamp interval [read\-only]" 4
2919.IX Item "ev_tstamp interval [read-only]"
2920The specified interval.
2921.IP "const char *path [read\-only]" 4
2922.IX Item "const char *path [read-only]"
2923The file system path that is being watched.
2924.PP
2925\fIExamples\fR
2926.IX Subsection "Examples"
2927.PP
2928Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
2929.PP
2930.Vb 10
2931\& static void
2932\& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
2933\& {
2934\& /* /etc/passwd changed in some way */
2935\& if (w\->attr.st_nlink)
2936\& {
2937\& printf ("passwd current size %ld\en", (long)w\->attr.st_size);
2938\& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime);
2939\& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime);
2940\& }
2941\& else
2942\& /* you shalt not abuse printf for puts */
2943\& puts ("wow, /etc/passwd is not there, expect problems. "
2944\& "if this is windows, they already arrived\en");
2945\& }
2946\&
2947\& ...
2948\& ev_stat passwd;
2949\&
2950\& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
2951\& ev_stat_start (loop, &passwd);
2952.Ve
2953.PP
2954Example: Like above, but additionally use a one-second delay so we do not
2955miss updates (however, frequent updates will delay processing, too, so
2956one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
2957\&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
2958.PP
1187.Vb 3 2959.Vb 2
1188\& struct ev_signal signal_watcher; 2960\& static ev_stat passwd;
1189\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT); 2961\& static ev_timer timer;
1190\& ev_signal_start (loop, &sigint_cb); 2962\&
2963\& static void
2964\& timer_cb (EV_P_ ev_timer *w, int revents)
2965\& {
2966\& ev_timer_stop (EV_A_ w);
2967\&
2968\& /* now it\*(Aqs one second after the most recent passwd change */
2969\& }
2970\&
2971\& static void
2972\& stat_cb (EV_P_ ev_stat *w, int revents)
2973\& {
2974\& /* reset the one\-second timer */
2975\& ev_timer_again (EV_A_ &timer);
2976\& }
2977\&
2978\& ...
2979\& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
2980\& ev_stat_start (loop, &passwd);
2981\& ev_timer_init (&timer, timer_cb, 0., 1.02);
1191.Ve 2982.Ve
1192.ie n .Sh """ev_idle"" \- when you've got nothing better to do" 2983.ie n .SS """ev_idle"" \- when you've got nothing better to do..."
1193.el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do" 2984.el .SS "\f(CWev_idle\fP \- when you've got nothing better to do..."
1194.IX Subsection "ev_idle - when you've got nothing better to do" 2985.IX Subsection "ev_idle - when you've got nothing better to do..."
1195Idle watchers trigger events when there are no other events are pending 2986Idle watchers trigger events when no other events of the same or higher
1196(prepare, check and other idle watchers do not count). That is, as long 2987priority are pending (prepare, check and other idle watchers do not count
1197as your process is busy handling sockets or timeouts (or even signals, 2988as receiving \*(L"events\*(R").
1198imagine) it will not be triggered. But when your process is idle all idle 2989.PP
1199watchers are being called again and again, once per event loop iteration \- 2990That is, as long as your process is busy handling sockets or timeouts
2991(or even signals, imagine) of the same or higher priority it will not be
2992triggered. But when your process is idle (or only lower-priority watchers
2993are pending), the idle watchers are being called once per event loop
1200until stopped, that is, or your process receives more events and becomes 2994iteration \- until stopped, that is, or your process receives more events
1201busy. 2995and becomes busy again with higher priority stuff.
1202.PP 2996.PP
1203The most noteworthy effect is that as long as any idle watchers are 2997The most noteworthy effect is that as long as any idle watchers are
1204active, the process will not block when waiting for new events. 2998active, the process will not block when waiting for new events.
1205.PP 2999.PP
1206Apart from keeping your process non-blocking (which is a useful 3000Apart from keeping your process non-blocking (which is a useful
1207effect on its own sometimes), idle watchers are a good place to do 3001effect on its own sometimes), idle watchers are a good place to do
1208\&\*(L"pseudo\-background processing\*(R", or delay processing stuff to after the 3002\&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the
1209event loop has handled all outstanding events. 3003event loop has handled all outstanding events.
3004.PP
3005\fIAbusing an \f(CI\*(C`ev_idle\*(C'\fI watcher for its side-effect\fR
3006.IX Subsection "Abusing an ev_idle watcher for its side-effect"
3007.PP
3008As long as there is at least one active idle watcher, libev will never
3009sleep unnecessarily. Or in other words, it will loop as fast as possible.
3010For this to work, the idle watcher doesn't need to be invoked at all \- the
3011lowest priority will do.
3012.PP
3013This mode of operation can be useful together with an \f(CW\*(C`ev_check\*(C'\fR watcher,
3014to do something on each event loop iteration \- for example to balance load
3015between different connections.
3016.PP
3017See \*(L"Abusing an ev_check watcher for its side-effect\*(R" for a longer
3018example.
3019.PP
3020\fIWatcher-Specific Functions and Data Members\fR
3021.IX Subsection "Watcher-Specific Functions and Data Members"
1210.IP "ev_idle_init (ev_signal *, callback)" 4 3022.IP "ev_idle_init (ev_idle *, callback)" 4
1211.IX Item "ev_idle_init (ev_signal *, callback)" 3023.IX Item "ev_idle_init (ev_idle *, callback)"
1212Initialises and configures the idle watcher \- it has no parameters of any 3024Initialises and configures the idle watcher \- it has no parameters of any
1213kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless, 3025kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
1214believe me. 3026believe me.
1215.PP 3027.PP
3028\fIExamples\fR
3029.IX Subsection "Examples"
3030.PP
1216Example: dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR, start it, and in the 3031Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the
1217callback, free it. Alos, use no error checking, as usual. 3032callback, free it. Also, use no error checking, as usual.
1218.PP 3033.PP
1219.Vb 7 3034.Vb 5
1220\& static void 3035\& static void
1221\& idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents) 3036\& idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1222\& { 3037\& {
3038\& // stop the watcher
3039\& ev_idle_stop (loop, w);
3040\&
3041\& // now we can free it
1223\& free (w); 3042\& free (w);
3043\&
1224\& // now do something you wanted to do when the program has 3044\& // now do something you wanted to do when the program has
1225\& // no longer asnything immediate to do. 3045\& // no longer anything immediate to do.
1226\& } 3046\& }
1227.Ve 3047\&
1228.PP
1229.Vb 3
1230\& struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle)); 3048\& ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1231\& ev_idle_init (idle_watcher, idle_cb); 3049\& ev_idle_init (idle_watcher, idle_cb);
1232\& ev_idle_start (loop, idle_cb); 3050\& ev_idle_start (loop, idle_watcher);
1233.Ve 3051.Ve
1234.ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop" 3052.ie n .SS """ev_prepare"" and ""ev_check"" \- customise your event loop!"
1235.el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop" 3053.el .SS "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
1236.IX Subsection "ev_prepare and ev_check - customise your event loop" 3054.IX Subsection "ev_prepare and ev_check - customise your event loop!"
1237Prepare and check watchers are usually (but not always) used in tandem: 3055Prepare and check watchers are often (but not always) used in pairs:
1238prepare watchers get invoked before the process blocks and check watchers 3056prepare watchers get invoked before the process blocks and check watchers
1239afterwards. 3057afterwards.
1240.PP 3058.PP
3059You \fImust not\fR call \f(CW\*(C`ev_run\*(C'\fR (or similar functions that enter the
3060current event loop) or \f(CW\*(C`ev_loop_fork\*(C'\fR from either \f(CW\*(C`ev_prepare\*(C'\fR or
3061\&\f(CW\*(C`ev_check\*(C'\fR watchers. Other loops than the current one are fine,
3062however. The rationale behind this is that you do not need to check
3063for recursion in those watchers, i.e. the sequence will always be
3064\&\f(CW\*(C`ev_prepare\*(C'\fR, blocking, \f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each
3065kind they will always be called in pairs bracketing the blocking call.
3066.PP
1241Their main purpose is to integrate other event mechanisms into libev and 3067Their main purpose is to integrate other event mechanisms into libev and
1242their use is somewhat advanced. This could be used, for example, to track 3068their use is somewhat advanced. They could be used, for example, to track
1243variable changes, implement your own watchers, integrate net-snmp or a 3069variable changes, implement your own watchers, integrate net-snmp or a
1244coroutine library and lots more. 3070coroutine library and lots more. They are also occasionally useful if
3071you cache some data and want to flush it before blocking (for example,
3072in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
3073watcher).
1245.PP 3074.PP
1246This is done by examining in each prepare call which file descriptors need 3075This is done by examining in each prepare call which file descriptors
1247to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers for 3076need to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers
1248them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many libraries 3077for them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many
1249provide just this functionality). Then, in the check watcher you check for 3078libraries provide exactly this functionality). Then, in the check watcher,
1250any events that occured (by checking the pending status of all watchers 3079you check for any events that occurred (by checking the pending status
1251and stopping them) and call back into the library. The I/O and timer 3080of all watchers and stopping them) and call back into the library. The
1252callbacks will never actually be called (but must be valid nevertheless, 3081I/O and timer callbacks will never actually be called (but must be valid
1253because you never know, you know?). 3082nevertheless, because you never know, you know?).
1254.PP 3083.PP
1255As another example, the Perl Coro module uses these hooks to integrate 3084As another example, the Perl Coro module uses these hooks to integrate
1256coroutines into libev programs, by yielding to other active coroutines 3085coroutines into libev programs, by yielding to other active coroutines
1257during each prepare and only letting the process block if no coroutines 3086during each prepare and only letting the process block if no coroutines
1258are ready to run (it's actually more complicated: it only runs coroutines 3087are ready to run (it's actually more complicated: it only runs coroutines
1259with priority higher than or equal to the event loop and one coroutine 3088with priority higher than or equal to the event loop and one coroutine
1260of lower priority, but only once, using idle watchers to keep the event 3089of lower priority, but only once, using idle watchers to keep the event
1261loop from blocking if lower-priority coroutines are active, thus mapping 3090loop from blocking if lower-priority coroutines are active, thus mapping
1262low-priority coroutines to idle/background tasks). 3091low-priority coroutines to idle/background tasks).
3092.PP
3093When used for this purpose, it is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers
3094highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR) priority, to ensure that they are being run before
3095any other watchers after the poll (this doesn't matter for \f(CW\*(C`ev_prepare\*(C'\fR
3096watchers).
3097.PP
3098Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, too) should not
3099activate (\*(L"feed\*(R") events into libev. While libev fully supports this, they
3100might get executed before other \f(CW\*(C`ev_check\*(C'\fR watchers did their job. As
3101\&\f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other (non-libev) event
3102loops those other event loops might be in an unusable state until their
3103\&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with
3104others).
3105.PP
3106\fIAbusing an \f(CI\*(C`ev_check\*(C'\fI watcher for its side-effect\fR
3107.IX Subsection "Abusing an ev_check watcher for its side-effect"
3108.PP
3109\&\f(CW\*(C`ev_check\*(C'\fR (and less often also \f(CW\*(C`ev_prepare\*(C'\fR) watchers can also be
3110useful because they are called once per event loop iteration. For
3111example, if you want to handle a large number of connections fairly, you
3112normally only do a bit of work for each active connection, and if there
3113is more work to do, you wait for the next event loop iteration, so other
3114connections have a chance of making progress.
3115.PP
3116Using an \f(CW\*(C`ev_check\*(C'\fR watcher is almost enough: it will be called on the
3117next event loop iteration. However, that isn't as soon as possible \-
3118without external events, your \f(CW\*(C`ev_check\*(C'\fR watcher will not be invoked.
3119.PP
3120This is where \f(CW\*(C`ev_idle\*(C'\fR watchers come in handy \- all you need is a
3121single global idle watcher that is active as long as you have one active
3122\&\f(CW\*(C`ev_check\*(C'\fR watcher. The \f(CW\*(C`ev_idle\*(C'\fR watcher makes sure the event loop
3123will not sleep, and the \f(CW\*(C`ev_check\*(C'\fR watcher makes sure a callback gets
3124invoked. Neither watcher alone can do that.
3125.PP
3126\fIWatcher-Specific Functions and Data Members\fR
3127.IX Subsection "Watcher-Specific Functions and Data Members"
1263.IP "ev_prepare_init (ev_prepare *, callback)" 4 3128.IP "ev_prepare_init (ev_prepare *, callback)" 4
1264.IX Item "ev_prepare_init (ev_prepare *, callback)" 3129.IX Item "ev_prepare_init (ev_prepare *, callback)"
1265.PD 0 3130.PD 0
1266.IP "ev_check_init (ev_check *, callback)" 4 3131.IP "ev_check_init (ev_check *, callback)" 4
1267.IX Item "ev_check_init (ev_check *, callback)" 3132.IX Item "ev_check_init (ev_check *, callback)"
1268.PD 3133.PD
1269Initialises and configures the prepare or check watcher \- they have no 3134Initialises and configures the prepare or check watcher \- they have no
1270parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR 3135parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
1271macros, but using them is utterly, utterly and completely pointless. 3136macros, but using them is utterly, utterly, utterly and completely
3137pointless.
1272.PP 3138.PP
1273Example: *TODO*. 3139\fIExamples\fR
3140.IX Subsection "Examples"
3141.PP
3142There are a number of principal ways to embed other event loops or modules
3143into libev. Here are some ideas on how to include libadns into libev
3144(there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could
3145use as a working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR embeds a
3146Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 into the
3147Glib event loop).
3148.PP
3149Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
3150and in a check watcher, destroy them and call into libadns. What follows
3151is pseudo-code only of course. This requires you to either use a low
3152priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as
3153the callbacks for the IO/timeout watchers might not have been called yet.
3154.PP
3155.Vb 2
3156\& static ev_io iow [nfd];
3157\& static ev_timer tw;
3158\&
3159\& static void
3160\& io_cb (struct ev_loop *loop, ev_io *w, int revents)
3161\& {
3162\& }
3163\&
3164\& // create io watchers for each fd and a timer before blocking
3165\& static void
3166\& adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
3167\& {
3168\& int timeout = 3600000;
3169\& struct pollfd fds [nfd];
3170\& // actual code will need to loop here and realloc etc.
3171\& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
3172\&
3173\& /* the callback is illegal, but won\*(Aqt be called as we stop during check */
3174\& ev_timer_init (&tw, 0, timeout * 1e\-3, 0.);
3175\& ev_timer_start (loop, &tw);
3176\&
3177\& // create one ev_io per pollfd
3178\& for (int i = 0; i < nfd; ++i)
3179\& {
3180\& ev_io_init (iow + i, io_cb, fds [i].fd,
3181\& ((fds [i].events & POLLIN ? EV_READ : 0)
3182\& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
3183\&
3184\& fds [i].revents = 0;
3185\& ev_io_start (loop, iow + i);
3186\& }
3187\& }
3188\&
3189\& // stop all watchers after blocking
3190\& static void
3191\& adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
3192\& {
3193\& ev_timer_stop (loop, &tw);
3194\&
3195\& for (int i = 0; i < nfd; ++i)
3196\& {
3197\& // set the relevant poll flags
3198\& // could also call adns_processreadable etc. here
3199\& struct pollfd *fd = fds + i;
3200\& int revents = ev_clear_pending (iow + i);
3201\& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN;
3202\& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT;
3203\&
3204\& // now stop the watcher
3205\& ev_io_stop (loop, iow + i);
3206\& }
3207\&
3208\& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
3209\& }
3210.Ve
3211.PP
3212Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR
3213in the prepare watcher and would dispose of the check watcher.
3214.PP
3215Method 3: If the module to be embedded supports explicit event
3216notification (libadns does), you can also make use of the actual watcher
3217callbacks, and only destroy/create the watchers in the prepare watcher.
3218.PP
3219.Vb 5
3220\& static void
3221\& timer_cb (EV_P_ ev_timer *w, int revents)
3222\& {
3223\& adns_state ads = (adns_state)w\->data;
3224\& update_now (EV_A);
3225\&
3226\& adns_processtimeouts (ads, &tv_now);
3227\& }
3228\&
3229\& static void
3230\& io_cb (EV_P_ ev_io *w, int revents)
3231\& {
3232\& adns_state ads = (adns_state)w\->data;
3233\& update_now (EV_A);
3234\&
3235\& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now);
3236\& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now);
3237\& }
3238\&
3239\& // do not ever call adns_afterpoll
3240.Ve
3241.PP
3242Method 4: Do not use a prepare or check watcher because the module you
3243want to embed is not flexible enough to support it. Instead, you can
3244override their poll function. The drawback with this solution is that the
3245main loop is now no longer controllable by \s-1EV.\s0 The \f(CW\*(C`Glib::EV\*(C'\fR module uses
3246this approach, effectively embedding \s-1EV\s0 as a client into the horrible
3247libglib event loop.
3248.PP
3249.Vb 4
3250\& static gint
3251\& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
3252\& {
3253\& int got_events = 0;
3254\&
3255\& for (n = 0; n < nfds; ++n)
3256\& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
3257\&
3258\& if (timeout >= 0)
3259\& // create/start timer
3260\&
3261\& // poll
3262\& ev_run (EV_A_ 0);
3263\&
3264\& // stop timer again
3265\& if (timeout >= 0)
3266\& ev_timer_stop (EV_A_ &to);
3267\&
3268\& // stop io watchers again \- their callbacks should have set
3269\& for (n = 0; n < nfds; ++n)
3270\& ev_io_stop (EV_A_ iow [n]);
3271\&
3272\& return got_events;
3273\& }
3274.Ve
1274.ie n .Sh """ev_embed"" \- when one backend isn't enough" 3275.ie n .SS """ev_embed"" \- when one backend isn't enough..."
1275.el .Sh "\f(CWev_embed\fP \- when one backend isn't enough" 3276.el .SS "\f(CWev_embed\fP \- when one backend isn't enough..."
1276.IX Subsection "ev_embed - when one backend isn't enough" 3277.IX Subsection "ev_embed - when one backend isn't enough..."
1277This is a rather advanced watcher type that lets you embed one event loop 3278This is a rather advanced watcher type that lets you embed one event loop
1278into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded 3279into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
1279loop, other types of watchers might be handled in a delayed or incorrect 3280loop, other types of watchers might be handled in a delayed or incorrect
1280fashion and must not be used). 3281fashion and must not be used).
1281.PP 3282.PP
… …
1283prioritise I/O. 3284prioritise I/O.
1284.PP 3285.PP
1285As an example for a bug workaround, the kqueue backend might only support 3286As an example for a bug workaround, the kqueue backend might only support
1286sockets on some platform, so it is unusable as generic backend, but you 3287sockets on some platform, so it is unusable as generic backend, but you
1287still want to make use of it because you have many sockets and it scales 3288still want to make use of it because you have many sockets and it scales
1288so nicely. In this case, you would create a kqueue-based loop and embed it 3289so nicely. In this case, you would create a kqueue-based loop and embed
1289into your default loop (which might use e.g. poll). Overall operation will 3290it into your default loop (which might use e.g. poll). Overall operation
1290be a bit slower because first libev has to poll and then call kevent, but 3291will be a bit slower because first libev has to call \f(CW\*(C`poll\*(C'\fR and then
1291at least you can use both at what they are best. 3292\&\f(CW\*(C`kevent\*(C'\fR, but at least you can use both mechanisms for what they are
3293best: \f(CW\*(C`kqueue\*(C'\fR for scalable sockets and \f(CW\*(C`poll\*(C'\fR if you want it to work :)
1292.PP 3294.PP
1293As for prioritising I/O: rarely you have the case where some fds have 3295As for prioritising I/O: under rare circumstances you have the case where
1294to be watched and handled very quickly (with low latency), and even 3296some fds have to be watched and handled very quickly (with low latency),
1295priorities and idle watchers might have too much overhead. In this case 3297and even priorities and idle watchers might have too much overhead. In
1296you would put all the high priority stuff in one loop and all the rest in 3298this case you would put all the high priority stuff in one loop and all
1297a second one, and embed the second one in the first. 3299the rest in a second one, and embed the second one in the first.
1298.PP 3300.PP
1299As long as the watcher is active, the callback will be invoked every time 3301As long as the watcher is active, the callback will be invoked every
1300there might be events pending in the embedded loop. The callback must then 3302time there might be events pending in the embedded loop. The callback
1301call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single sweep and invoke 3303must then call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single
1302their callbacks (you could also start an idle watcher to give the embedded 3304sweep and invoke their callbacks (the callback doesn't need to invoke the
1303loop strictly lower priority for example). You can also set the callback 3305\&\f(CW\*(C`ev_embed_sweep\*(C'\fR function directly, it could also start an idle watcher
1304to \f(CW0\fR, in which case the embed watcher will automatically execute the 3306to give the embedded loop strictly lower priority for example).
1305embedded loop sweep.
1306.PP 3307.PP
1307As long as the watcher is started it will automatically handle events. The 3308You can also set the callback to \f(CW0\fR, in which case the embed watcher
1308callback will be invoked whenever some events have been handled. You can 3309will automatically execute the embedded loop sweep whenever necessary.
1309set the callback to \f(CW0\fR to avoid having to specify one if you are not
1310interested in that.
1311.PP 3310.PP
1312Also, there have not currently been made special provisions for forking: 3311Fork detection will be handled transparently while the \f(CW\*(C`ev_embed\*(C'\fR watcher
1313when you fork, you not only have to call \f(CW\*(C`ev_loop_fork\*(C'\fR on both loops, 3312is active, i.e., the embedded loop will automatically be forked when the
1314but you will also have to stop and restart any \f(CW\*(C`ev_embed\*(C'\fR watchers 3313embedding loop forks. In other cases, the user is responsible for calling
1315yourself. 3314\&\f(CW\*(C`ev_loop_fork\*(C'\fR on the embedded loop.
1316.PP 3315.PP
1317Unfortunately, not all backends are embeddable, only the ones returned by 3316Unfortunately, not all backends are embeddable: only the ones returned by
1318\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any 3317\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
1319portable one. 3318portable one.
1320.PP 3319.PP
1321So when you want to use this feature you will always have to be prepared 3320So when you want to use this feature you will always have to be prepared
1322that you cannot get an embeddable loop. The recommended way to get around 3321that you cannot get an embeddable loop. The recommended way to get around
1323this is to have a separate variables for your embeddable loop, try to 3322this is to have a separate variables for your embeddable loop, try to
1324create it, and if that fails, use the normal loop for everything: 3323create it, and if that fails, use the normal loop for everything.
1325.PP 3324.PP
1326.Vb 3 3325\fI\f(CI\*(C`ev_embed\*(C'\fI and fork\fR
1327\& struct ev_loop *loop_hi = ev_default_init (0); 3326.IX Subsection "ev_embed and fork"
1328\& struct ev_loop *loop_lo = 0;
1329\& struct ev_embed embed;
1330.Ve
1331.PP 3327.PP
1332.Vb 5 3328While the \f(CW\*(C`ev_embed\*(C'\fR watcher is running, forks in the embedding loop will
1333\& // see if there is a chance of getting one that works 3329automatically be applied to the embedded loop as well, so no special
1334\& // (remember that a flags value of 0 means autodetection) 3330fork handling is required in that case. When the watcher is not running,
1335\& loop_lo = ev_embeddable_backends () & ev_recommended_backends () 3331however, it is still the task of the libev user to call \f(CW\*(C`ev_loop_fork ()\*(C'\fR
1336\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ()) 3332as applicable.
1337\& : 0;
1338.Ve
1339.PP 3333.PP
1340.Vb 8 3334\fIWatcher-Specific Functions and Data Members\fR
1341\& // if we got one, then embed it, otherwise default to loop_hi 3335.IX Subsection "Watcher-Specific Functions and Data Members"
1342\& if (loop_lo)
1343\& {
1344\& ev_embed_init (&embed, 0, loop_lo);
1345\& ev_embed_start (loop_hi, &embed);
1346\& }
1347\& else
1348\& loop_lo = loop_hi;
1349.Ve
1350.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4 3336.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
1351.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 3337.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
1352.PD 0 3338.PD 0
1353.IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4 3339.IP "ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)" 4
1354.IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 3340.IX Item "ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)"
1355.PD 3341.PD
1356Configures the watcher to embed the given loop, which must be 3342Configures the watcher to embed the given loop, which must be
1357embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be 3343embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
1358invoked automatically, otherwise it is the responsibility of the callback 3344invoked automatically, otherwise it is the responsibility of the callback
1359to invoke it (it will continue to be called until the sweep has been done, 3345to invoke it (it will continue to be called until the sweep has been done,
1360if you do not want thta, you need to temporarily stop the embed watcher). 3346if you do not want that, you need to temporarily stop the embed watcher).
1361.IP "ev_embed_sweep (loop, ev_embed *)" 4 3347.IP "ev_embed_sweep (loop, ev_embed *)" 4
1362.IX Item "ev_embed_sweep (loop, ev_embed *)" 3348.IX Item "ev_embed_sweep (loop, ev_embed *)"
1363Make a single, non-blocking sweep over the embedded loop. This works 3349Make a single, non-blocking sweep over the embedded loop. This works
1364similarly to \f(CW\*(C`ev_loop (embedded_loop, EVLOOP_NONBLOCK)\*(C'\fR, but in the most 3350similarly to \f(CW\*(C`ev_run (embedded_loop, EVRUN_NOWAIT)\*(C'\fR, but in the most
1365apropriate way for embedded loops. 3351appropriate way for embedded loops.
3352.IP "struct ev_loop *other [read\-only]" 4
3353.IX Item "struct ev_loop *other [read-only]"
3354The embedded event loop.
3355.PP
3356\fIExamples\fR
3357.IX Subsection "Examples"
3358.PP
3359Example: Try to get an embeddable event loop and embed it into the default
3360event loop. If that is not possible, use the default loop. The default
3361loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the embeddable loop is stored in
3362\&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the case no embeddable loop can be
3363used).
3364.PP
3365.Vb 3
3366\& struct ev_loop *loop_hi = ev_default_init (0);
3367\& struct ev_loop *loop_lo = 0;
3368\& ev_embed embed;
3369\&
3370\& // see if there is a chance of getting one that works
3371\& // (remember that a flags value of 0 means autodetection)
3372\& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3373\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3374\& : 0;
3375\&
3376\& // if we got one, then embed it, otherwise default to loop_hi
3377\& if (loop_lo)
3378\& {
3379\& ev_embed_init (&embed, 0, loop_lo);
3380\& ev_embed_start (loop_hi, &embed);
3381\& }
3382\& else
3383\& loop_lo = loop_hi;
3384.Ve
3385.PP
3386Example: Check if kqueue is available but not recommended and create
3387a kqueue backend for use with sockets (which usually work with any
3388kqueue implementation). Store the kqueue/socket\-only event loop in
3389\&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too).
3390.PP
3391.Vb 3
3392\& struct ev_loop *loop = ev_default_init (0);
3393\& struct ev_loop *loop_socket = 0;
3394\& ev_embed embed;
3395\&
3396\& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3397\& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3398\& {
3399\& ev_embed_init (&embed, 0, loop_socket);
3400\& ev_embed_start (loop, &embed);
3401\& }
3402\&
3403\& if (!loop_socket)
3404\& loop_socket = loop;
3405\&
3406\& // now use loop_socket for all sockets, and loop for everything else
3407.Ve
3408.ie n .SS """ev_fork"" \- the audacity to resume the event loop after a fork"
3409.el .SS "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
3410.IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
3411Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
3412whoever is a good citizen cared to tell libev about it by calling
3413\&\f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the event loop blocks next
3414and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called, and only in the child
3415after the fork. If whoever good citizen calling \f(CW\*(C`ev_default_fork\*(C'\fR cheats
3416and calls it in the wrong process, the fork handlers will be invoked, too,
3417of course.
3418.PP
3419\fIThe special problem of life after fork \- how is it possible?\fR
3420.IX Subsection "The special problem of life after fork - how is it possible?"
3421.PP
3422Most uses of \f(CW\*(C`fork ()\*(C'\fR consist of forking, then some simple calls to set
3423up/change the process environment, followed by a call to \f(CW\*(C`exec()\*(C'\fR. This
3424sequence should be handled by libev without any problems.
3425.PP
3426This changes when the application actually wants to do event handling
3427in the child, or both parent in child, in effect \*(L"continuing\*(R" after the
3428fork.
3429.PP
3430The default mode of operation (for libev, with application help to detect
3431forks) is to duplicate all the state in the child, as would be expected
3432when \fIeither\fR the parent \fIor\fR the child process continues.
3433.PP
3434When both processes want to continue using libev, then this is usually the
3435wrong result. In that case, usually one process (typically the parent) is
3436supposed to continue with all watchers in place as before, while the other
3437process typically wants to start fresh, i.e. without any active watchers.
3438.PP
3439The cleanest and most efficient way to achieve that with libev is to
3440simply create a new event loop, which of course will be \*(L"empty\*(R", and
3441use that for new watchers. This has the advantage of not touching more
3442memory than necessary, and thus avoiding the copy-on-write, and the
3443disadvantage of having to use multiple event loops (which do not support
3444signal watchers).
3445.PP
3446When this is not possible, or you want to use the default loop for
3447other reasons, then in the process that wants to start \*(L"fresh\*(R", call
3448\&\f(CW\*(C`ev_loop_destroy (EV_DEFAULT)\*(C'\fR followed by \f(CW\*(C`ev_default_loop (...)\*(C'\fR.
3449Destroying the default loop will \*(L"orphan\*(R" (not stop) all registered
3450watchers, so you have to be careful not to execute code that modifies
3451those watchers. Note also that in that case, you have to re-register any
3452signal watchers.
3453.PP
3454\fIWatcher-Specific Functions and Data Members\fR
3455.IX Subsection "Watcher-Specific Functions and Data Members"
3456.IP "ev_fork_init (ev_fork *, callback)" 4
3457.IX Item "ev_fork_init (ev_fork *, callback)"
3458Initialises and configures the fork watcher \- it has no parameters of any
3459kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
3460really.
3461.ie n .SS """ev_cleanup"" \- even the best things end"
3462.el .SS "\f(CWev_cleanup\fP \- even the best things end"
3463.IX Subsection "ev_cleanup - even the best things end"
3464Cleanup watchers are called just before the event loop is being destroyed
3465by a call to \f(CW\*(C`ev_loop_destroy\*(C'\fR.
3466.PP
3467While there is no guarantee that the event loop gets destroyed, cleanup
3468watchers provide a convenient method to install cleanup hooks for your
3469program, worker threads and so on \- you just to make sure to destroy the
3470loop when you want them to be invoked.
3471.PP
3472Cleanup watchers are invoked in the same way as any other watcher. Unlike
3473all other watchers, they do not keep a reference to the event loop (which
3474makes a lot of sense if you think about it). Like all other watchers, you
3475can call libev functions in the callback, except \f(CW\*(C`ev_cleanup_start\*(C'\fR.
3476.PP
3477\fIWatcher-Specific Functions and Data Members\fR
3478.IX Subsection "Watcher-Specific Functions and Data Members"
3479.IP "ev_cleanup_init (ev_cleanup *, callback)" 4
3480.IX Item "ev_cleanup_init (ev_cleanup *, callback)"
3481Initialises and configures the cleanup watcher \- it has no parameters of
3482any kind. There is a \f(CW\*(C`ev_cleanup_set\*(C'\fR macro, but using it is utterly
3483pointless, I assure you.
3484.PP
3485Example: Register an atexit handler to destroy the default loop, so any
3486cleanup functions are called.
3487.PP
3488.Vb 5
3489\& static void
3490\& program_exits (void)
3491\& {
3492\& ev_loop_destroy (EV_DEFAULT_UC);
3493\& }
3494\&
3495\& ...
3496\& atexit (program_exits);
3497.Ve
3498.ie n .SS """ev_async"" \- how to wake up an event loop"
3499.el .SS "\f(CWev_async\fP \- how to wake up an event loop"
3500.IX Subsection "ev_async - how to wake up an event loop"
3501In general, you cannot use an \f(CW\*(C`ev_loop\*(C'\fR from multiple threads or other
3502asynchronous sources such as signal handlers (as opposed to multiple event
3503loops \- those are of course safe to use in different threads).
3504.PP
3505Sometimes, however, you need to wake up an event loop you do not control,
3506for example because it belongs to another thread. This is what \f(CW\*(C`ev_async\*(C'\fR
3507watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you can signal
3508it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal safe.
3509.PP
3510This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals,
3511too, are asynchronous in nature, and signals, too, will be compressed
3512(i.e. the number of callback invocations may be less than the number of
3513\&\f(CW\*(C`ev_async_send\*(C'\fR calls). In fact, you could use signal watchers as a kind
3514of \*(L"global async watchers\*(R" by using a watcher on an otherwise unused
3515signal, and \f(CW\*(C`ev_feed_signal\*(C'\fR to signal this watcher from another thread,
3516even without knowing which loop owns the signal.
3517.PP
3518\fIQueueing\fR
3519.IX Subsection "Queueing"
3520.PP
3521\&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason
3522is that the author does not know of a simple (or any) algorithm for a
3523multiple-writer-single-reader queue that works in all cases and doesn't
3524need elaborate support such as pthreads or unportable memory access
3525semantics.
3526.PP
3527That means that if you want to queue data, you have to provide your own
3528queue. But at least I can tell you how to implement locking around your
3529queue:
3530.IP "queueing from a signal handler context" 4
3531.IX Item "queueing from a signal handler context"
3532To implement race-free queueing, you simply add to the queue in the signal
3533handler but you block the signal handler in the watcher callback. Here is
3534an example that does that for some fictitious \s-1SIGUSR1\s0 handler:
3535.Sp
3536.Vb 1
3537\& static ev_async mysig;
3538\&
3539\& static void
3540\& sigusr1_handler (void)
3541\& {
3542\& sometype data;
3543\&
3544\& // no locking etc.
3545\& queue_put (data);
3546\& ev_async_send (EV_DEFAULT_ &mysig);
3547\& }
3548\&
3549\& static void
3550\& mysig_cb (EV_P_ ev_async *w, int revents)
3551\& {
3552\& sometype data;
3553\& sigset_t block, prev;
3554\&
3555\& sigemptyset (&block);
3556\& sigaddset (&block, SIGUSR1);
3557\& sigprocmask (SIG_BLOCK, &block, &prev);
3558\&
3559\& while (queue_get (&data))
3560\& process (data);
3561\&
3562\& if (sigismember (&prev, SIGUSR1)
3563\& sigprocmask (SIG_UNBLOCK, &block, 0);
3564\& }
3565.Ve
3566.Sp
3567(Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR
3568instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it
3569either...).
3570.IP "queueing from a thread context" 4
3571.IX Item "queueing from a thread context"
3572The strategy for threads is different, as you cannot (easily) block
3573threads but you can easily preempt them, so to queue safely you need to
3574employ a traditional mutex lock, such as in this pthread example:
3575.Sp
3576.Vb 2
3577\& static ev_async mysig;
3578\& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
3579\&
3580\& static void
3581\& otherthread (void)
3582\& {
3583\& // only need to lock the actual queueing operation
3584\& pthread_mutex_lock (&mymutex);
3585\& queue_put (data);
3586\& pthread_mutex_unlock (&mymutex);
3587\&
3588\& ev_async_send (EV_DEFAULT_ &mysig);
3589\& }
3590\&
3591\& static void
3592\& mysig_cb (EV_P_ ev_async *w, int revents)
3593\& {
3594\& pthread_mutex_lock (&mymutex);
3595\&
3596\& while (queue_get (&data))
3597\& process (data);
3598\&
3599\& pthread_mutex_unlock (&mymutex);
3600\& }
3601.Ve
3602.PP
3603\fIWatcher-Specific Functions and Data Members\fR
3604.IX Subsection "Watcher-Specific Functions and Data Members"
3605.IP "ev_async_init (ev_async *, callback)" 4
3606.IX Item "ev_async_init (ev_async *, callback)"
3607Initialises and configures the async watcher \- it has no parameters of any
3608kind. There is a \f(CW\*(C`ev_async_set\*(C'\fR macro, but using it is utterly pointless,
3609trust me.
3610.IP "ev_async_send (loop, ev_async *)" 4
3611.IX Item "ev_async_send (loop, ev_async *)"
3612Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds
3613an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop, and instantly
3614returns.
3615.Sp
3616Unlike \f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do from other threads,
3617signal or similar contexts (see the discussion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the
3618embedding section below on what exactly this means).
3619.Sp
3620Note that, as with other watchers in libev, multiple events might get
3621compressed into a single callback invocation (another way to look at
3622this is that \f(CW\*(C`ev_async\*(C'\fR watchers are level-triggered: they are set on
3623\&\f(CW\*(C`ev_async_send\*(C'\fR, reset when the event loop detects that).
3624.Sp
3625This call incurs the overhead of at most one extra system call per event
3626loop iteration, if the event loop is blocked, and no syscall at all if
3627the event loop (or your program) is processing events. That means that
3628repeated calls are basically free (there is no need to avoid calls for
3629performance reasons) and that the overhead becomes smaller (typically
3630zero) under load.
3631.IP "bool = ev_async_pending (ev_async *)" 4
3632.IX Item "bool = ev_async_pending (ev_async *)"
3633Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the
3634watcher but the event has not yet been processed (or even noted) by the
3635event loop.
3636.Sp
3637\&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When
3638the loop iterates next and checks for the watcher to have become active,
3639it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very
3640quickly check whether invoking the loop might be a good idea.
3641.Sp
3642Not that this does \fInot\fR check whether the watcher itself is pending,
3643only whether it has been requested to make this watcher pending: there
3644is a time window between the event loop checking and resetting the async
3645notification, and the callback being invoked.
1366.SH "OTHER FUNCTIONS" 3646.SH "OTHER FUNCTIONS"
1367.IX Header "OTHER FUNCTIONS" 3647.IX Header "OTHER FUNCTIONS"
1368There are some other functions of possible interest. Described. Here. Now. 3648There are some other functions of possible interest. Described. Here. Now.
1369.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4 3649.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
1370.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 3650.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"
1371This function combines a simple timer and an I/O watcher, calls your 3651This function combines a simple timer and an I/O watcher, calls your
1372callback on whichever event happens first and automatically stop both 3652callback on whichever event happens first and automatically stops both
1373watchers. This is useful if you want to wait for a single event on an fd 3653watchers. This is useful if you want to wait for a single event on an fd
1374or timeout without having to allocate/configure/start/stop/free one or 3654or timeout without having to allocate/configure/start/stop/free one or
1375more watchers yourself. 3655more watchers yourself.
1376.Sp 3656.Sp
1377If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and events 3657If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and the
1378is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for the given \f(CW\*(C`fd\*(C'\fR and 3658\&\f(CW\*(C`events\*(C'\fR argument is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for
1379\&\f(CW\*(C`events\*(C'\fR set will be craeted and started. 3659the given \f(CW\*(C`fd\*(C'\fR and \f(CW\*(C`events\*(C'\fR set will be created and started.
1380.Sp 3660.Sp
1381If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be 3661If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
1382started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and 3662started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
1383repeat = 0) will be started. While \f(CW0\fR is a valid timeout, it is of 3663repeat = 0) will be started. \f(CW0\fR is a valid timeout.
1384dubious value.
1385.Sp 3664.Sp
1386The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets 3665The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and is
1387passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of 3666passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
1388\&\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 3667\&\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
1389value passed to \f(CW\*(C`ev_once\*(C'\fR: 3668value passed to \f(CW\*(C`ev_once\*(C'\fR. Note that it is possible to receive \fIboth\fR
3669a timeout and an io event at the same time \- you probably should give io
3670events precedence.
3671.Sp
3672Example: wait up to ten seconds for data to appear on \s-1STDIN_FILENO.\s0
1390.Sp 3673.Sp
1391.Vb 7 3674.Vb 7
1392\& static void stdin_ready (int revents, void *arg) 3675\& static void stdin_ready (int revents, void *arg)
3676\& {
3677\& if (revents & EV_READ)
3678\& /* stdin might have data for us, joy! */;
3679\& else if (revents & EV_TIMER)
3680\& /* doh, nothing entered */;
3681\& }
3682\&
3683\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3684.Ve
3685.IP "ev_feed_fd_event (loop, int fd, int revents)" 4
3686.IX Item "ev_feed_fd_event (loop, int fd, int revents)"
3687Feed an event on the given fd, as if a file descriptor backend detected
3688the given events.
3689.IP "ev_feed_signal_event (loop, int signum)" 4
3690.IX Item "ev_feed_signal_event (loop, int signum)"
3691Feed an event as if the given signal occurred. See also \f(CW\*(C`ev_feed_signal\*(C'\fR,
3692which is async-safe.
3693.SH "COMMON OR USEFUL IDIOMS (OR BOTH)"
3694.IX Header "COMMON OR USEFUL IDIOMS (OR BOTH)"
3695This section explains some common idioms that are not immediately
3696obvious. Note that examples are sprinkled over the whole manual, and this
3697section only contains stuff that wouldn't fit anywhere else.
3698.SS "\s-1ASSOCIATING CUSTOM DATA WITH A WATCHER\s0"
3699.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
3700Each watcher has, by default, a \f(CW\*(C`void *data\*(C'\fR member that you can read
3701or modify at any time: libev will completely ignore it. This can be used
3702to associate arbitrary data with your watcher. If you need more data and
3703don't want to allocate memory separately and store a pointer to it in that
3704data member, you can also \*(L"subclass\*(R" the watcher type and provide your own
3705data:
3706.PP
3707.Vb 7
3708\& struct my_io
3709\& {
3710\& ev_io io;
3711\& int otherfd;
3712\& void *somedata;
3713\& struct whatever *mostinteresting;
3714\& };
3715\&
3716\& ...
3717\& struct my_io w;
3718\& ev_io_init (&w.io, my_cb, fd, EV_READ);
3719.Ve
3720.PP
3721And since your callback will be called with a pointer to the watcher, you
3722can cast it back to your own type:
3723.PP
3724.Vb 5
3725\& static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
3726\& {
3727\& struct my_io *w = (struct my_io *)w_;
3728\& ...
3729\& }
3730.Ve
3731.PP
3732More interesting and less C\-conformant ways of casting your callback
3733function type instead have been omitted.
3734.SS "\s-1BUILDING YOUR OWN COMPOSITE WATCHERS\s0"
3735.IX Subsection "BUILDING YOUR OWN COMPOSITE WATCHERS"
3736Another common scenario is to use some data structure with multiple
3737embedded watchers, in effect creating your own watcher that combines
3738multiple libev event sources into one \*(L"super-watcher\*(R":
3739.PP
3740.Vb 6
3741\& struct my_biggy
3742\& {
3743\& int some_data;
3744\& ev_timer t1;
3745\& ev_timer t2;
3746\& }
3747.Ve
3748.PP
3749In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more
3750complicated: Either you store the address of your \f(CW\*(C`my_biggy\*(C'\fR struct in
3751the \f(CW\*(C`data\*(C'\fR member of the watcher (for woozies or \*(C+ coders), or you need
3752to use some pointer arithmetic using \f(CW\*(C`offsetof\*(C'\fR inside your watchers (for
3753real programmers):
3754.PP
3755.Vb 1
3756\& #include <stddef.h>
3757\&
3758\& static void
3759\& t1_cb (EV_P_ ev_timer *w, int revents)
3760\& {
3761\& struct my_biggy big = (struct my_biggy *)
3762\& (((char *)w) \- offsetof (struct my_biggy, t1));
3763\& }
3764\&
3765\& static void
3766\& t2_cb (EV_P_ ev_timer *w, int revents)
3767\& {
3768\& struct my_biggy big = (struct my_biggy *)
3769\& (((char *)w) \- offsetof (struct my_biggy, t2));
3770\& }
3771.Ve
3772.SS "\s-1AVOIDING FINISHING BEFORE RETURNING\s0"
3773.IX Subsection "AVOIDING FINISHING BEFORE RETURNING"
3774Often you have structures like this in event-based programs:
3775.PP
3776.Vb 4
3777\& callback ()
1393\& { 3778\& {
1394\& if (revents & EV_TIMEOUT) 3779\& free (request);
1395\& /* doh, nothing entered */;
1396\& else if (revents & EV_READ)
1397\& /* stdin might have data for us, joy! */;
1398\& } 3780\& }
3781\&
3782\& request = start_new_request (..., callback);
1399.Ve 3783.Ve
1400.Sp 3784.PP
3785The intent is to start some \*(L"lengthy\*(R" operation. The \f(CW\*(C`request\*(C'\fR could be
3786used to cancel the operation, or do other things with it.
3787.PP
3788It's not uncommon to have code paths in \f(CW\*(C`start_new_request\*(C'\fR that
3789immediately invoke the callback, for example, to report errors. Or you add
3790some caching layer that finds that it can skip the lengthy aspects of the
3791operation and simply invoke the callback with the result.
3792.PP
3793The problem here is that this will happen \fIbefore\fR \f(CW\*(C`start_new_request\*(C'\fR
3794has returned, so \f(CW\*(C`request\*(C'\fR is not set.
3795.PP
3796Even if you pass the request by some safer means to the callback, you
3797might want to do something to the request after starting it, such as
3798canceling it, which probably isn't working so well when the callback has
3799already been invoked.
3800.PP
3801A common way around all these issues is to make sure that
3802\&\f(CW\*(C`start_new_request\*(C'\fR \fIalways\fR returns before the callback is invoked. If
3803\&\f(CW\*(C`start_new_request\*(C'\fR immediately knows the result, it can artificially
3804delay invoking the callback by using a \f(CW\*(C`prepare\*(C'\fR or \f(CW\*(C`idle\*(C'\fR watcher for
3805example, or more sneakily, by reusing an existing (stopped) watcher and
3806pushing it into the pending queue:
3807.PP
1401.Vb 1 3808.Vb 2
1402\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); 3809\& ev_set_cb (watcher, callback);
3810\& ev_feed_event (EV_A_ watcher, 0);
1403.Ve 3811.Ve
1404.IP "ev_feed_event (ev_loop *, watcher *, int revents)" 4 3812.PP
1405.IX Item "ev_feed_event (ev_loop *, watcher *, int revents)" 3813This way, \f(CW\*(C`start_new_request\*(C'\fR can safely return before the callback is
1406Feeds the given event set into the event loop, as if the specified event 3814invoked, while not delaying callback invocation too much.
1407had happened for the specified watcher (which must be a pointer to an 3815.SS "\s-1MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS\s0"
1408initialised but not necessarily started event watcher). 3816.IX Subsection "MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS"
1409.IP "ev_feed_fd_event (ev_loop *, int fd, int revents)" 4 3817Often (especially in \s-1GUI\s0 toolkits) there are places where you have
1410.IX Item "ev_feed_fd_event (ev_loop *, int fd, int revents)" 3818\&\fImodal\fR interaction, which is most easily implemented by recursively
1411Feed an event on the given fd, as if a file descriptor backend detected 3819invoking \f(CW\*(C`ev_run\*(C'\fR.
1412the given events it. 3820.PP
1413.IP "ev_feed_signal_event (ev_loop *loop, int signum)" 4 3821This brings the problem of exiting \- a callback might want to finish the
1414.IX Item "ev_feed_signal_event (ev_loop *loop, int signum)" 3822main \f(CW\*(C`ev_run\*(C'\fR call, but not the nested one (e.g. user clicked \*(L"Quit\*(R", but
1415Feed an event as if the given signal occured (\f(CW\*(C`loop\*(C'\fR must be the default 3823a modal \*(L"Are you sure?\*(R" dialog is still waiting), or just the nested one
1416loop!). 3824and not the main one (e.g. user clocked \*(L"Ok\*(R" in a modal dialog), or some
3825other combination: In these cases, a simple \f(CW\*(C`ev_break\*(C'\fR will not work.
3826.PP
3827The solution is to maintain \*(L"break this loop\*(R" variable for each \f(CW\*(C`ev_run\*(C'\fR
3828invocation, and use a loop around \f(CW\*(C`ev_run\*(C'\fR until the condition is
3829triggered, using \f(CW\*(C`EVRUN_ONCE\*(C'\fR:
3830.PP
3831.Vb 2
3832\& // main loop
3833\& int exit_main_loop = 0;
3834\&
3835\& while (!exit_main_loop)
3836\& ev_run (EV_DEFAULT_ EVRUN_ONCE);
3837\&
3838\& // in a modal watcher
3839\& int exit_nested_loop = 0;
3840\&
3841\& while (!exit_nested_loop)
3842\& ev_run (EV_A_ EVRUN_ONCE);
3843.Ve
3844.PP
3845To exit from any of these loops, just set the corresponding exit variable:
3846.PP
3847.Vb 2
3848\& // exit modal loop
3849\& exit_nested_loop = 1;
3850\&
3851\& // exit main program, after modal loop is finished
3852\& exit_main_loop = 1;
3853\&
3854\& // exit both
3855\& exit_main_loop = exit_nested_loop = 1;
3856.Ve
3857.SS "\s-1THREAD LOCKING EXAMPLE\s0"
3858.IX Subsection "THREAD LOCKING EXAMPLE"
3859Here is a fictitious example of how to run an event loop in a different
3860thread from where callbacks are being invoked and watchers are
3861created/added/removed.
3862.PP
3863For a real-world example, see the \f(CW\*(C`EV::Loop::Async\*(C'\fR perl module,
3864which uses exactly this technique (which is suited for many high-level
3865languages).
3866.PP
3867The example uses a pthread mutex to protect the loop data, a condition
3868variable to wait for callback invocations, an async watcher to notify the
3869event loop thread and an unspecified mechanism to wake up the main thread.
3870.PP
3871First, you need to associate some data with the event loop:
3872.PP
3873.Vb 6
3874\& typedef struct {
3875\& mutex_t lock; /* global loop lock */
3876\& ev_async async_w;
3877\& thread_t tid;
3878\& cond_t invoke_cv;
3879\& } userdata;
3880\&
3881\& void prepare_loop (EV_P)
3882\& {
3883\& // for simplicity, we use a static userdata struct.
3884\& static userdata u;
3885\&
3886\& ev_async_init (&u\->async_w, async_cb);
3887\& ev_async_start (EV_A_ &u\->async_w);
3888\&
3889\& pthread_mutex_init (&u\->lock, 0);
3890\& pthread_cond_init (&u\->invoke_cv, 0);
3891\&
3892\& // now associate this with the loop
3893\& ev_set_userdata (EV_A_ u);
3894\& ev_set_invoke_pending_cb (EV_A_ l_invoke);
3895\& ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
3896\&
3897\& // then create the thread running ev_run
3898\& pthread_create (&u\->tid, 0, l_run, EV_A);
3899\& }
3900.Ve
3901.PP
3902The callback for the \f(CW\*(C`ev_async\*(C'\fR watcher does nothing: the watcher is used
3903solely to wake up the event loop so it takes notice of any new watchers
3904that might have been added:
3905.PP
3906.Vb 5
3907\& static void
3908\& async_cb (EV_P_ ev_async *w, int revents)
3909\& {
3910\& // just used for the side effects
3911\& }
3912.Ve
3913.PP
3914The \f(CW\*(C`l_release\*(C'\fR and \f(CW\*(C`l_acquire\*(C'\fR callbacks simply unlock/lock the mutex
3915protecting the loop data, respectively.
3916.PP
3917.Vb 6
3918\& static void
3919\& l_release (EV_P)
3920\& {
3921\& userdata *u = ev_userdata (EV_A);
3922\& pthread_mutex_unlock (&u\->lock);
3923\& }
3924\&
3925\& static void
3926\& l_acquire (EV_P)
3927\& {
3928\& userdata *u = ev_userdata (EV_A);
3929\& pthread_mutex_lock (&u\->lock);
3930\& }
3931.Ve
3932.PP
3933The event loop thread first acquires the mutex, and then jumps straight
3934into \f(CW\*(C`ev_run\*(C'\fR:
3935.PP
3936.Vb 4
3937\& void *
3938\& l_run (void *thr_arg)
3939\& {
3940\& struct ev_loop *loop = (struct ev_loop *)thr_arg;
3941\&
3942\& l_acquire (EV_A);
3943\& pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
3944\& ev_run (EV_A_ 0);
3945\& l_release (EV_A);
3946\&
3947\& return 0;
3948\& }
3949.Ve
3950.PP
3951Instead of invoking all pending watchers, the \f(CW\*(C`l_invoke\*(C'\fR callback will
3952signal the main thread via some unspecified mechanism (signals? pipe
3953writes? \f(CW\*(C`Async::Interrupt\*(C'\fR?) and then waits until all pending watchers
3954have been called (in a while loop because a) spurious wakeups are possible
3955and b) skipping inter-thread-communication when there are no pending
3956watchers is very beneficial):
3957.PP
3958.Vb 4
3959\& static void
3960\& l_invoke (EV_P)
3961\& {
3962\& userdata *u = ev_userdata (EV_A);
3963\&
3964\& while (ev_pending_count (EV_A))
3965\& {
3966\& wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
3967\& pthread_cond_wait (&u\->invoke_cv, &u\->lock);
3968\& }
3969\& }
3970.Ve
3971.PP
3972Now, whenever the main thread gets told to invoke pending watchers, it
3973will grab the lock, call \f(CW\*(C`ev_invoke_pending\*(C'\fR and then signal the loop
3974thread to continue:
3975.PP
3976.Vb 4
3977\& static void
3978\& real_invoke_pending (EV_P)
3979\& {
3980\& userdata *u = ev_userdata (EV_A);
3981\&
3982\& pthread_mutex_lock (&u\->lock);
3983\& ev_invoke_pending (EV_A);
3984\& pthread_cond_signal (&u\->invoke_cv);
3985\& pthread_mutex_unlock (&u\->lock);
3986\& }
3987.Ve
3988.PP
3989Whenever you want to start/stop a watcher or do other modifications to an
3990event loop, you will now have to lock:
3991.PP
3992.Vb 2
3993\& ev_timer timeout_watcher;
3994\& userdata *u = ev_userdata (EV_A);
3995\&
3996\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
3997\&
3998\& pthread_mutex_lock (&u\->lock);
3999\& ev_timer_start (EV_A_ &timeout_watcher);
4000\& ev_async_send (EV_A_ &u\->async_w);
4001\& pthread_mutex_unlock (&u\->lock);
4002.Ve
4003.PP
4004Note that sending the \f(CW\*(C`ev_async\*(C'\fR watcher is required because otherwise
4005an event loop currently blocking in the kernel will have no knowledge
4006about the newly added timer. By waking up the loop it will pick up any new
4007watchers in the next event loop iteration.
4008.SS "\s-1THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS\s0"
4009.IX Subsection "THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS"
4010While the overhead of a callback that e.g. schedules a thread is small, it
4011is still an overhead. If you embed libev, and your main usage is with some
4012kind of threads or coroutines, you might want to customise libev so that
4013doesn't need callbacks anymore.
4014.PP
4015Imagine you have coroutines that you can switch to using a function
4016\&\f(CW\*(C`switch_to (coro)\*(C'\fR, that libev runs in a coroutine called \f(CW\*(C`libev_coro\*(C'\fR
4017and that due to some magic, the currently active coroutine is stored in a
4018global called \f(CW\*(C`current_coro\*(C'\fR. Then you can build your own \*(L"wait for libev
4019event\*(R" primitive by changing \f(CW\*(C`EV_CB_DECLARE\*(C'\fR and \f(CW\*(C`EV_CB_INVOKE\*(C'\fR (note
4020the differing \f(CW\*(C`;\*(C'\fR conventions):
4021.PP
4022.Vb 2
4023\& #define EV_CB_DECLARE(type) struct my_coro *cb;
4024\& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb)
4025.Ve
4026.PP
4027That means instead of having a C callback function, you store the
4028coroutine to switch to in each watcher, and instead of having libev call
4029your callback, you instead have it switch to that coroutine.
4030.PP
4031A coroutine might now wait for an event with a function called
4032\&\f(CW\*(C`wait_for_event\*(C'\fR. (the watcher needs to be started, as always, but it doesn't
4033matter when, or whether the watcher is active or not when this function is
4034called):
4035.PP
4036.Vb 6
4037\& void
4038\& wait_for_event (ev_watcher *w)
4039\& {
4040\& ev_set_cb (w, current_coro);
4041\& switch_to (libev_coro);
4042\& }
4043.Ve
4044.PP
4045That basically suspends the coroutine inside \f(CW\*(C`wait_for_event\*(C'\fR and
4046continues the libev coroutine, which, when appropriate, switches back to
4047this or any other coroutine.
4048.PP
4049You can do similar tricks if you have, say, threads with an event queue \-
4050instead of storing a coroutine, you store the queue object and instead of
4051switching to a coroutine, you push the watcher onto the queue and notify
4052any waiters.
4053.PP
4054To embed libev, see \*(L"\s-1EMBEDDING\*(R"\s0, but in short, it's easiest to create two
4055files, \fImy_ev.h\fR and \fImy_ev.c\fR that include the respective libev files:
4056.PP
4057.Vb 4
4058\& // my_ev.h
4059\& #define EV_CB_DECLARE(type) struct my_coro *cb;
4060\& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb)
4061\& #include "../libev/ev.h"
4062\&
4063\& // my_ev.c
4064\& #define EV_H "my_ev.h"
4065\& #include "../libev/ev.c"
4066.Ve
4067.PP
4068And then use \fImy_ev.h\fR when you would normally use \fIev.h\fR, and compile
4069\&\fImy_ev.c\fR into your project. When properly specifying include paths, you
4070can even use \fIev.h\fR as header file name directly.
1417.SH "LIBEVENT EMULATION" 4071.SH "LIBEVENT EMULATION"
1418.IX Header "LIBEVENT EMULATION" 4072.IX Header "LIBEVENT EMULATION"
1419Libev offers a compatibility emulation layer for libevent. It cannot 4073Libev offers a compatibility emulation layer for libevent. It cannot
1420emulate the internals of libevent, so here are some usage hints: 4074emulate the internals of libevent, so here are some usage hints:
4075.IP "\(bu" 4
4076Only the libevent\-1.4.1\-beta \s-1API\s0 is being emulated.
4077.Sp
4078This was the newest libevent version available when libev was implemented,
4079and is still mostly unchanged in 2010.
4080.IP "\(bu" 4
1421.IP "* Use it by including <event.h>, as usual." 4 4081Use it by including <event.h>, as usual.
1422.IX Item "Use it by including <event.h>, as usual." 4082.IP "\(bu" 4
1423.PD 0 4083The following members are fully supported: ev_base, ev_callback,
1424.IP "* The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4 4084ev_arg, ev_fd, ev_res, ev_events.
1425.IX Item "The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4085.IP "\(bu" 4
1426.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 4086Avoid using ev_flags and the EVLIST_*\-macros, while it is
1427.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)." 4087maintained by libev, it does not work exactly the same way as in libevent (consider
1428.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 4088it a private \s-1API\s0).
1429.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." 4089.IP "\(bu" 4
4090Priorities are not currently supported. Initialising priorities
4091will fail and all watchers will have the same priority, even though there
4092is an ev_pri field.
4093.IP "\(bu" 4
4094In libevent, the last base created gets the signals, in libev, the
4095base that registered the signal gets the signals.
4096.IP "\(bu" 4
1430.IP "* Other members are not supported." 4 4097Other members are not supported.
1431.IX Item "Other members are not supported." 4098.IP "\(bu" 4
1432.IP "* The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need to use the libev header file and library." 4 4099The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need
1433.IX Item "The libev emulation is not ABI compatible to libevent, you need to use the libev header file and library." 4100to use the libev header file and library.
1434.PD
1435.SH "\*(C+ SUPPORT" 4101.SH "\*(C+ SUPPORT"
1436.IX Header " SUPPORT" 4102.IX Header " SUPPORT"
4103.SS "C \s-1API\s0"
4104.IX Subsection "C API"
4105The normal C \s-1API\s0 should work fine when used from \*(C+: both ev.h and the
4106libev sources can be compiled as \*(C+. Therefore, code that uses the C \s-1API\s0
4107will work fine.
4108.PP
4109Proper exception specifications might have to be added to callbacks passed
4110to libev: exceptions may be thrown only from watcher callbacks, all
4111other callbacks (allocator, syserr, loop acquire/release and periodic
4112reschedule callbacks) must not throw exceptions, and might need a \f(CW\*(C`throw
4113()\*(C'\fR specification. If you have code that needs to be compiled as both C
4114and \*(C+ you can use the \f(CW\*(C`EV_THROW\*(C'\fR macro for this:
4115.PP
4116.Vb 6
4117\& static void
4118\& fatal_error (const char *msg) EV_THROW
4119\& {
4120\& perror (msg);
4121\& abort ();
4122\& }
4123\&
4124\& ...
4125\& ev_set_syserr_cb (fatal_error);
4126.Ve
4127.PP
4128The only \s-1API\s0 functions that can currently throw exceptions are \f(CW\*(C`ev_run\*(C'\fR,
4129\&\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
4130because it runs cleanup watchers).
4131.PP
4132Throwing exceptions in watcher callbacks is only supported if libev itself
4133is compiled with a \*(C+ compiler or your C and \*(C+ environments allow
4134throwing exceptions through C libraries (most do).
4135.SS "\*(C+ \s-1API\s0"
4136.IX Subsection " API"
1437Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow 4137Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
1438you to use some convinience methods to start/stop watchers and also change 4138you to use some convenience methods to start/stop watchers and also change
1439the callback model to a model using method callbacks on objects. 4139the callback model to a model using method callbacks on objects.
1440.PP 4140.PP
1441To use it, 4141To use it,
1442.PP 4142.PP
1443.Vb 1 4143.Vb 1
1444\& #include <ev++.h> 4144\& #include <ev++.h>
1445.Ve 4145.Ve
1446.PP 4146.PP
1447(it is not installed by default). This automatically includes \fIev.h\fR 4147This automatically includes \fIev.h\fR and puts all of its definitions (many
1448and puts all of its definitions (many of them macros) into the global 4148of them macros) into the global namespace. All \*(C+ specific things are
1449namespace. All \*(C+ specific things are put into the \f(CW\*(C`ev\*(C'\fR namespace. 4149put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding
4150options as \fIev.h\fR, most notably \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR.
1450.PP 4151.PP
1451It should support all the same embedding options as \fIev.h\fR, most notably 4152Care has been taken to keep the overhead low. The only data member the \*(C+
1452\&\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. 4153classes add (compared to plain C\-style watchers) is the event loop pointer
4154that the watcher is associated with (or no additional members at all if
4155you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
4156.PP
4157Currently, functions, static and non-static member functions and classes
4158with \f(CW\*(C`operator ()\*(C'\fR can be used as callbacks. Other types should be easy
4159to add as long as they only need one additional pointer for context. If
4160you need support for other types of functors please contact the author
4161(preferably after implementing it).
4162.PP
4163For all this to work, your \*(C+ compiler either has to use the same calling
4164conventions as your C compiler (for static member functions), or you have
4165to embed libev and compile libev itself as \*(C+.
1453.PP 4166.PP
1454Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace: 4167Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
1455.ie n .IP """ev::READ""\fR, \f(CW""ev::WRITE"" etc." 4 4168.ie n .IP """ev::READ"", ""ev::WRITE"" etc." 4
1456.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4 4169.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
1457.IX Item "ev::READ, ev::WRITE etc." 4170.IX Item "ev::READ, ev::WRITE etc."
1458These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc. 4171These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
1459macros from \fIev.h\fR. 4172macros from \fIev.h\fR.
1460.ie n .IP """ev::tstamp""\fR, \f(CW""ev::now""" 4 4173.ie n .IP """ev::tstamp"", ""ev::now""" 4
1461.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4 4174.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
1462.IX Item "ev::tstamp, ev::now" 4175.IX Item "ev::tstamp, ev::now"
1463Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix. 4176Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
1464.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 4177.ie n .IP """ev::io"", ""ev::timer"", ""ev::periodic"", ""ev::idle"", ""ev::sig"" etc." 4
1465.el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4 4178.el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
1466.IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc." 4179.IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
1467For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of 4180For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
1468the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR 4181the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
1469which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro 4182which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
1470defines by many implementations. 4183defined by many implementations.
1471.Sp 4184.Sp
1472All of those classes have these methods: 4185All of those classes have these methods:
1473.RS 4 4186.RS 4
1474.IP "ev::TYPE::TYPE (object *, object::method *)" 4 4187.IP "ev::TYPE::TYPE ()" 4
1475.IX Item "ev::TYPE::TYPE (object *, object::method *)" 4188.IX Item "ev::TYPE::TYPE ()"
1476.PD 0 4189.PD 0
1477.IP "ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)" 4 4190.IP "ev::TYPE::TYPE (loop)" 4
1478.IX Item "ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)" 4191.IX Item "ev::TYPE::TYPE (loop)"
1479.IP "ev::TYPE::~TYPE" 4 4192.IP "ev::TYPE::~TYPE" 4
1480.IX Item "ev::TYPE::~TYPE" 4193.IX Item "ev::TYPE::~TYPE"
1481.PD 4194.PD
1482The constructor takes a pointer to an object and a method pointer to 4195The constructor (optionally) takes an event loop to associate the watcher
1483the event handler callback to call in this class. The constructor calls 4196with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR.
1484\&\f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the \f(CW\*(C`set\*(C'\fR method 4197.Sp
1485before starting it. If you do not specify a loop then the constructor 4198The constructor calls \f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the
1486automatically associates the default loop with this watcher. 4199\&\f(CW\*(C`set\*(C'\fR method before starting it.
4200.Sp
4201It will not set a callback, however: You have to call the templated \f(CW\*(C`set\*(C'\fR
4202method to set a callback before you can start the watcher.
4203.Sp
4204(The reason why you have to use a method is a limitation in \*(C+ which does
4205not allow explicit template arguments for constructors).
1487.Sp 4206.Sp
1488The destructor automatically stops the watcher if it is active. 4207The destructor automatically stops the watcher if it is active.
4208.IP "w\->set<class, &class::method> (object *)" 4
4209.IX Item "w->set<class, &class::method> (object *)"
4210This method sets the callback method to call. The method has to have a
4211signature of \f(CW\*(C`void (*)(ev_TYPE &, int)\*(C'\fR, it receives the watcher as
4212first argument and the \f(CW\*(C`revents\*(C'\fR as second. The object must be given as
4213parameter and is stored in the \f(CW\*(C`data\*(C'\fR member of the watcher.
4214.Sp
4215This method synthesizes efficient thunking code to call your method from
4216the C callback that libev requires. If your compiler can inline your
4217callback (i.e. it is visible to it at the place of the \f(CW\*(C`set\*(C'\fR call and
4218your compiler is good :), then the method will be fully inlined into the
4219thunking function, making it as fast as a direct C callback.
4220.Sp
4221Example: simple class declaration and watcher initialisation
4222.Sp
4223.Vb 4
4224\& struct myclass
4225\& {
4226\& void io_cb (ev::io &w, int revents) { }
4227\& }
4228\&
4229\& myclass obj;
4230\& ev::io iow;
4231\& iow.set <myclass, &myclass::io_cb> (&obj);
4232.Ve
4233.IP "w\->set (object *)" 4
4234.IX Item "w->set (object *)"
4235This is a variation of a method callback \- leaving out the method to call
4236will default the method to \f(CW\*(C`operator ()\*(C'\fR, which makes it possible to use
4237functor objects without having to manually specify the \f(CW\*(C`operator ()\*(C'\fR all
4238the time. Incidentally, you can then also leave out the template argument
4239list.
4240.Sp
4241The \f(CW\*(C`operator ()\*(C'\fR method prototype must be \f(CW\*(C`void operator ()(watcher &w,
4242int revents)\*(C'\fR.
4243.Sp
4244See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
4245.Sp
4246Example: use a functor object as callback.
4247.Sp
4248.Vb 7
4249\& struct myfunctor
4250\& {
4251\& void operator() (ev::io &w, int revents)
4252\& {
4253\& ...
4254\& }
4255\& }
4256\&
4257\& myfunctor f;
4258\&
4259\& ev::io w;
4260\& w.set (&f);
4261.Ve
4262.IP "w\->set<function> (void *data = 0)" 4
4263.IX Item "w->set<function> (void *data = 0)"
4264Also sets a callback, but uses a static method or plain function as
4265callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
4266\&\f(CW\*(C`data\*(C'\fR member and is free for you to use.
4267.Sp
4268The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
4269.Sp
4270See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
4271.Sp
4272Example: Use a plain function as callback.
4273.Sp
4274.Vb 2
4275\& static void io_cb (ev::io &w, int revents) { }
4276\& iow.set <io_cb> ();
4277.Ve
1489.IP "w\->set (struct ev_loop *)" 4 4278.IP "w\->set (loop)" 4
1490.IX Item "w->set (struct ev_loop *)" 4279.IX Item "w->set (loop)"
1491Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only 4280Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
1492do this when the watcher is inactive (and not pending either). 4281do this when the watcher is inactive (and not pending either).
1493.IP "w\->set ([args])" 4 4282.IP "w\->set ([arguments])" 4
1494.IX Item "w->set ([args])" 4283.IX Item "w->set ([arguments])"
1495Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same args. Must be 4284Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR (except for \f(CW\*(C`ev::embed\*(C'\fR watchers>),
4285with the same arguments. Either this method or a suitable start method
1496called at least once. Unlike the C counterpart, an active watcher gets 4286must be called at least once. Unlike the C counterpart, an active watcher
1497automatically stopped and restarted. 4287gets automatically stopped and restarted when reconfiguring it with this
4288method.
4289.Sp
4290For \f(CW\*(C`ev::embed\*(C'\fR watchers this method is called \f(CW\*(C`set_embed\*(C'\fR, to avoid
4291clashing with the \f(CW\*(C`set (loop)\*(C'\fR method.
1498.IP "w\->start ()" 4 4292.IP "w\->start ()" 4
1499.IX Item "w->start ()" 4293.IX Item "w->start ()"
1500Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument as the 4294Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
1501constructor already takes the loop. 4295constructor already stores the event loop.
4296.IP "w\->start ([arguments])" 4
4297.IX Item "w->start ([arguments])"
4298Instead of calling \f(CW\*(C`set\*(C'\fR and \f(CW\*(C`start\*(C'\fR methods separately, it is often
4299convenient to wrap them in one call. Uses the same type of arguments as
4300the configure \f(CW\*(C`set\*(C'\fR method of the watcher.
1502.IP "w\->stop ()" 4 4301.IP "w\->stop ()" 4
1503.IX Item "w->stop ()" 4302.IX Item "w->stop ()"
1504Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument. 4303Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
1505.ie n .IP "w\->again () ""ev::timer""\fR, \f(CW""ev::periodic"" only" 4 4304.ie n .IP "w\->again () (""ev::timer"", ""ev::periodic"" only)" 4
1506.el .IP "w\->again () \f(CWev::timer\fR, \f(CWev::periodic\fR only" 4 4305.el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
1507.IX Item "w->again () ev::timer, ev::periodic only" 4306.IX Item "w->again () (ev::timer, ev::periodic only)"
1508For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding 4307For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
1509\&\f(CW\*(C`ev_TYPE_again\*(C'\fR function. 4308\&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
1510.ie n .IP "w\->sweep () ""ev::embed"" only" 4 4309.ie n .IP "w\->sweep () (""ev::embed"" only)" 4
1511.el .IP "w\->sweep () \f(CWev::embed\fR only" 4 4310.el .IP "w\->sweep () (\f(CWev::embed\fR only)" 4
1512.IX Item "w->sweep () ev::embed only" 4311.IX Item "w->sweep () (ev::embed only)"
1513Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR. 4312Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR.
4313.ie n .IP "w\->update () (""ev::stat"" only)" 4
4314.el .IP "w\->update () (\f(CWev::stat\fR only)" 4
4315.IX Item "w->update () (ev::stat only)"
4316Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
1514.RE 4317.RE
1515.RS 4 4318.RS 4
1516.RE 4319.RE
1517.PP 4320.PP
1518Example: Define a class with an \s-1IO\s0 and idle watcher, start one of them in 4321Example: Define a class with two I/O and idle watchers, start the I/O
1519the constructor. 4322watchers in the constructor.
1520.PP 4323.PP
1521.Vb 4 4324.Vb 5
1522\& class myclass 4325\& class myclass
1523\& { 4326\& {
1524\& ev_io io; void io_cb (ev::io &w, int revents); 4327\& ev::io io ; void io_cb (ev::io &w, int revents);
4328\& ev::io io2 ; void io2_cb (ev::io &w, int revents);
1525\& ev_idle idle void idle_cb (ev::idle &w, int revents); 4329\& ev::idle idle; void idle_cb (ev::idle &w, int revents);
4330\&
4331\& myclass (int fd)
4332\& {
4333\& io .set <myclass, &myclass::io_cb > (this);
4334\& io2 .set <myclass, &myclass::io2_cb > (this);
4335\& idle.set <myclass, &myclass::idle_cb> (this);
4336\&
4337\& io.set (fd, ev::WRITE); // configure the watcher
4338\& io.start (); // start it whenever convenient
4339\&
4340\& io2.start (fd, ev::READ); // set + start in one call
4341\& }
4342\& };
1526.Ve 4343.Ve
4344.SH "OTHER LANGUAGE BINDINGS"
4345.IX Header "OTHER LANGUAGE BINDINGS"
4346Libev does not offer other language bindings itself, but bindings for a
4347number of languages exist in the form of third-party packages. If you know
4348any interesting language binding in addition to the ones listed here, drop
4349me a note.
4350.IP "Perl" 4
4351.IX Item "Perl"
4352The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test
4353libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module,
4354there are additional modules that implement libev-compatible interfaces
4355to \f(CW\*(C`libadns\*(C'\fR (\f(CW\*(C`EV::ADNS\*(C'\fR, but \f(CW\*(C`AnyEvent::DNS\*(C'\fR is preferred nowadays),
4356\&\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
4357and \f(CW\*(C`EV::Glib\*(C'\fR).
4358.Sp
4359It can be found and installed via \s-1CPAN,\s0 its homepage is at
4360<http://software.schmorp.de/pkg/EV>.
4361.IP "Python" 4
4362.IX Item "Python"
4363Python bindings can be found at <http://code.google.com/p/pyev/>. It
4364seems to be quite complete and well-documented.
4365.IP "Ruby" 4
4366.IX Item "Ruby"
4367Tony Arcieri has written a ruby extension that offers access to a subset
4368of the libev \s-1API\s0 and adds file handle abstractions, asynchronous \s-1DNS\s0 and
4369more on top of it. It can be found via gem servers. Its homepage is at
4370<http://rev.rubyforge.org/>.
4371.Sp
4372Roger Pack reports that using the link order \f(CW\*(C`\-lws2_32 \-lmsvcrt\-ruby\-190\*(C'\fR
4373makes rev work even on mingw.
4374.IP "Haskell" 4
4375.IX Item "Haskell"
4376A haskell binding to libev is available at
4377<http://hackage.haskell.org/cgi\-bin/hackage\-scripts/package/hlibev>.
4378.IP "D" 4
4379.IX Item "D"
4380Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
4381be found at <http://www.llucax.com.ar/proj/ev.d/index.html>.
4382.IP "Ocaml" 4
4383.IX Item "Ocaml"
4384Erkki Seppala has written Ocaml bindings for libev, to be found at
4385<http://modeemi.cs.tut.fi/~flux/software/ocaml\-ev/>.
4386.IP "Lua" 4
4387.IX Item "Lua"
4388Brian Maher has written a partial interface to libev for lua (at the
4389time of this writing, only \f(CW\*(C`ev_io\*(C'\fR and \f(CW\*(C`ev_timer\*(C'\fR), to be found at
4390<http://github.com/brimworks/lua\-ev>.
4391.IP "Javascript" 4
4392.IX Item "Javascript"
4393Node.js (<http://nodejs.org>) uses libev as the underlying event library.
4394.IP "Others" 4
4395.IX Item "Others"
4396There are others, and I stopped counting.
4397.SH "MACRO MAGIC"
4398.IX Header "MACRO MAGIC"
4399Libev can be compiled with a variety of options, the most fundamental
4400of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most)
4401functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
1527.PP 4402.PP
4403To make it easier to write programs that cope with either variant, the
4404following macros are defined:
4405.ie n .IP """EV_A"", ""EV_A_""" 4
4406.el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
4407.IX Item "EV_A, EV_A_"
4408This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
4409loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
4410\&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
4411.Sp
4412.Vb 3
4413\& ev_unref (EV_A);
4414\& ev_timer_add (EV_A_ watcher);
4415\& ev_run (EV_A_ 0);
4416.Ve
4417.Sp
4418It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
4419which is often provided by the following macro.
4420.ie n .IP """EV_P"", ""EV_P_""" 4
4421.el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
4422.IX Item "EV_P, EV_P_"
4423This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
4424loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
4425\&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
4426.Sp
1528.Vb 2 4427.Vb 2
1529\& myclass (); 4428\& // this is how ev_unref is being declared
1530\& } 4429\& static void ev_unref (EV_P);
4430\&
4431\& // this is how you can declare your typical callback
4432\& static void cb (EV_P_ ev_timer *w, int revents)
1531.Ve 4433.Ve
4434.Sp
4435It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
4436suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
4437.ie n .IP """EV_DEFAULT"", ""EV_DEFAULT_""" 4
4438.el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
4439.IX Item "EV_DEFAULT, EV_DEFAULT_"
4440Similar to the other two macros, this gives you the value of the default
4441loop, if multiple loops are supported (\*(L"ev loop default\*(R"). The default loop
4442will be initialised if it isn't already initialised.
4443.Sp
4444For non-multiplicity builds, these macros do nothing, so you always have
4445to initialise the loop somewhere.
4446.ie n .IP """EV_DEFAULT_UC"", ""EV_DEFAULT_UC_""" 4
4447.el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
4448.IX Item "EV_DEFAULT_UC, EV_DEFAULT_UC_"
4449Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the
4450default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour
4451is undefined when the default loop has not been initialised by a previous
4452execution of \f(CW\*(C`EV_DEFAULT\*(C'\fR, \f(CW\*(C`EV_DEFAULT_\*(C'\fR or \f(CW\*(C`ev_default_init (...)\*(C'\fR.
4453.Sp
4454It is often prudent to use \f(CW\*(C`EV_DEFAULT\*(C'\fR when initialising the first
4455watcher in a function but use \f(CW\*(C`EV_DEFAULT_UC\*(C'\fR afterwards.
1532.PP 4456.PP
4457Example: Declare and initialise a check watcher, utilising the above
4458macros so it will work regardless of whether multiple loops are supported
4459or not.
4460.PP
1533.Vb 6 4461.Vb 5
1534\& myclass::myclass (int fd) 4462\& static void
1535\& : io (this, &myclass::io_cb), 4463\& check_cb (EV_P_ ev_timer *w, int revents)
1536\& idle (this, &myclass::idle_cb)
1537\& { 4464\& {
1538\& io.start (fd, ev::READ); 4465\& ev_check_stop (EV_A_ w);
1539\& } 4466\& }
4467\&
4468\& ev_check check;
4469\& ev_check_init (&check, check_cb);
4470\& ev_check_start (EV_DEFAULT_ &check);
4471\& ev_run (EV_DEFAULT_ 0);
1540.Ve 4472.Ve
1541.SH "EMBEDDING" 4473.SH "EMBEDDING"
1542.IX Header "EMBEDDING" 4474.IX Header "EMBEDDING"
1543Libev can (and often is) directly embedded into host 4475Libev can (and often is) directly embedded into host
1544applications. Examples of applications that embed it include the Deliantra 4476applications. Examples of applications that embed it include the Deliantra
1545Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe) 4477Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
1546and rxvt\-unicode. 4478and rxvt-unicode.
1547.PP 4479.PP
1548The goal is to enable you to just copy the neecssary files into your 4480The goal is to enable you to just copy the necessary files into your
1549source directory without having to change even a single line in them, so 4481source directory without having to change even a single line in them, so
1550you can easily upgrade by simply copying (or having a checked-out copy of 4482you can easily upgrade by simply copying (or having a checked-out copy of
1551libev somewhere in your source tree). 4483libev somewhere in your source tree).
1552.Sh "\s-1FILESETS\s0" 4484.SS "\s-1FILESETS\s0"
1553.IX Subsection "FILESETS" 4485.IX Subsection "FILESETS"
1554Depending on what features you need you need to include one or more sets of files 4486Depending on what features you need you need to include one or more sets of files
1555in your app. 4487in your application.
1556.PP 4488.PP
1557\fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR 4489\fI\s-1CORE EVENT LOOP\s0\fR
1558.IX Subsection "CORE EVENT LOOP" 4490.IX Subsection "CORE EVENT LOOP"
1559.PP 4491.PP
1560To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual 4492To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
1561configuration (no autoconf): 4493configuration (no autoconf):
1562.PP 4494.PP
1563.Vb 2 4495.Vb 2
1564\& #define EV_STANDALONE 1 4496\& #define EV_STANDALONE 1
1565\& #include "ev.c" 4497\& #include "ev.c"
1566.Ve 4498.Ve
1567.PP 4499.PP
1568This will automatically include \fIev.h\fR, too, and should be done in a 4500This will automatically include \fIev.h\fR, too, and should be done in a
1569single C source file only to provide the function implementations. To use 4501single C source file only to provide the function implementations. To use
1570it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best 4502it, do the same for \fIev.h\fR in all files wishing to use this \s-1API \s0(best
1571done by writing a wrapper around \fIev.h\fR that you can include instead and 4503done by writing a wrapper around \fIev.h\fR that you can include instead and
1572where you can put other configuration options): 4504where you can put other configuration options):
1573.PP 4505.PP
1574.Vb 2 4506.Vb 2
1575\& #define EV_STANDALONE 1 4507\& #define EV_STANDALONE 1
1576\& #include "ev.h" 4508\& #include "ev.h"
1577.Ve 4509.Ve
1578.PP 4510.PP
1579Both header files and implementation files can be compiled with a \*(C+ 4511Both header files and implementation files can be compiled with a \*(C+
1580compiler (at least, thats a stated goal, and breakage will be treated 4512compiler (at least, that's a stated goal, and breakage will be treated
1581as a bug). 4513as a bug).
1582.PP 4514.PP
1583You need the following files in your source tree, or in a directory 4515You need the following files in your source tree, or in a directory
1584in your include path (e.g. in libev/ when using \-Ilibev): 4516in your include path (e.g. in libev/ when using \-Ilibev):
1585.PP 4517.PP
1586.Vb 4 4518.Vb 4
1587\& ev.h 4519\& ev.h
1588\& ev.c 4520\& ev.c
1589\& ev_vars.h 4521\& ev_vars.h
1590\& ev_wrap.h 4522\& ev_wrap.h
4523\&
4524\& ev_win32.c required on win32 platforms only
4525\&
4526\& ev_select.c only when select backend is enabled (which is enabled by default)
4527\& ev_poll.c only when poll backend is enabled (disabled by default)
4528\& ev_epoll.c only when the epoll backend is enabled (disabled by default)
4529\& ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
4530\& ev_port.c only when the solaris port backend is enabled (disabled by default)
1591.Ve 4531.Ve
4532.PP
4533\&\fIev.c\fR includes the backend files directly when enabled, so you only need
4534to compile this single file.
4535.PP
4536\fI\s-1LIBEVENT COMPATIBILITY API\s0\fR
4537.IX Subsection "LIBEVENT COMPATIBILITY API"
4538.PP
4539To include the libevent compatibility \s-1API,\s0 also include:
1592.PP 4540.PP
1593.Vb 1 4541.Vb 1
1594\& ev_win32.c required on win32 platforms only 4542\& #include "event.c"
1595.Ve 4543.Ve
1596.PP 4544.PP
1597.Vb 5 4545in the file including \fIev.c\fR, and:
1598\& ev_select.c only when select backend is enabled (which is is by default)
1599\& ev_poll.c only when poll backend is enabled (disabled by default)
1600\& ev_epoll.c only when the epoll backend is enabled (disabled by default)
1601\& ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
1602\& ev_port.c only when the solaris port backend is enabled (disabled by default)
1603.Ve
1604.PP
1605\&\fIev.c\fR includes the backend files directly when enabled, so you only need
1606to compile a single file.
1607.PP
1608\fI\s-1LIBEVENT\s0 \s-1COMPATIBILITY\s0 \s-1API\s0\fR
1609.IX Subsection "LIBEVENT COMPATIBILITY API"
1610.PP
1611To include the libevent compatibility \s-1API\s0, also include:
1612.PP 4546.PP
1613.Vb 1 4547.Vb 1
1614\& #include "event.c" 4548\& #include "event.h"
1615.Ve 4549.Ve
1616.PP 4550.PP
1617in the file including \fIev.c\fR, and: 4551in the files that want to use the libevent \s-1API.\s0 This also includes \fIev.h\fR.
4552.PP
4553You need the following additional files for this:
4554.PP
4555.Vb 2
4556\& event.h
4557\& event.c
4558.Ve
4559.PP
4560\fI\s-1AUTOCONF SUPPORT\s0\fR
4561.IX Subsection "AUTOCONF SUPPORT"
4562.PP
4563Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your configuration in
4564whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
4565\&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then
4566include \fIconfig.h\fR and configure itself accordingly.
4567.PP
4568For this of course you need the m4 file:
1618.PP 4569.PP
1619.Vb 1 4570.Vb 1
1620\& #include "event.h"
1621.Ve
1622.PP
1623in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR.
1624.PP
1625You need the following additional files for this:
1626.PP
1627.Vb 2
1628\& event.h
1629\& event.c
1630.Ve
1631.PP
1632\fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR
1633.IX Subsection "AUTOCONF SUPPORT"
1634.PP
1635Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your config in
1636whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
1637\&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR off. \fIev.c\fR will then include
1638\&\fIconfig.h\fR and configure itself accordingly.
1639.PP
1640For this of course you need the m4 file:
1641.PP
1642.Vb 1
1643\& libev.m4 4571\& libev.m4
1644.Ve 4572.Ve
1645.Sh "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0" 4573.SS "\s-1PREPROCESSOR SYMBOLS/MACROS\s0"
1646.IX Subsection "PREPROCESSOR SYMBOLS/MACROS" 4574.IX Subsection "PREPROCESSOR SYMBOLS/MACROS"
1647Libev can be configured via a variety of preprocessor symbols you have to define 4575Libev can be configured via a variety of preprocessor symbols you have to
1648before including any of its files. The default is not to build for multiplicity 4576define before including (or compiling) any of its files. The default in
1649and only include the select backend. 4577the absence of autoconf is documented for every option.
4578.PP
4579Symbols marked with \*(L"(h)\*(R" do not change the \s-1ABI,\s0 and can have different
4580values when compiling libev vs. including \fIev.h\fR, so it is permissible
4581to redefine them before including \fIev.h\fR without breaking compatibility
4582to a compiled library. All other symbols change the \s-1ABI,\s0 which means all
4583users of libev and the libev code itself must be compiled with compatible
4584settings.
4585.IP "\s-1EV_COMPAT3 \s0(h)" 4
4586.IX Item "EV_COMPAT3 (h)"
4587Backwards compatibility is a major concern for libev. This is why this
4588release of libev comes with wrappers for the functions and symbols that
4589have been renamed between libev version 3 and 4.
4590.Sp
4591You can disable these wrappers (to test compatibility with future
4592versions) by defining \f(CW\*(C`EV_COMPAT3\*(C'\fR to \f(CW0\fR when compiling your
4593sources. This has the additional advantage that you can drop the \f(CW\*(C`struct\*(C'\fR
4594from \f(CW\*(C`struct ev_loop\*(C'\fR declarations, as libev will provide an \f(CW\*(C`ev_loop\*(C'\fR
4595typedef in that case.
4596.Sp
4597In some future version, the default for \f(CW\*(C`EV_COMPAT3\*(C'\fR will become \f(CW0\fR,
4598and in some even more future version the compatibility code will be
4599removed completely.
1650.IP "\s-1EV_STANDALONE\s0" 4 4600.IP "\s-1EV_STANDALONE \s0(h)" 4
1651.IX Item "EV_STANDALONE" 4601.IX Item "EV_STANDALONE (h)"
1652Must always be \f(CW1\fR if you do not use autoconf configuration, which 4602Must always be \f(CW1\fR if you do not use autoconf configuration, which
1653keeps libev from including \fIconfig.h\fR, and it also defines dummy 4603keeps libev from including \fIconfig.h\fR, and it also defines dummy
1654implementations for some libevent functions (such as logging, which is not 4604implementations for some libevent functions (such as logging, which is not
1655supported). It will also not define any of the structs usually found in 4605supported). It will also not define any of the structs usually found in
1656\&\fIevent.h\fR that are not directly supported by the libev core alone. 4606\&\fIevent.h\fR that are not directly supported by the libev core alone.
4607.Sp
4608In standalone mode, libev will still try to automatically deduce the
4609configuration, but has to be more conservative.
4610.IP "\s-1EV_USE_FLOOR\s0" 4
4611.IX Item "EV_USE_FLOOR"
4612If defined to be \f(CW1\fR, libev will use the \f(CW\*(C`floor ()\*(C'\fR function for its
4613periodic reschedule calculations, otherwise libev will fall back on a
4614portable (slower) implementation. If you enable this, you usually have to
4615link against libm or something equivalent. Enabling this when the \f(CW\*(C`floor\*(C'\fR
4616function is not available will fail, so the safe default is to not enable
4617this.
1657.IP "\s-1EV_USE_MONOTONIC\s0" 4 4618.IP "\s-1EV_USE_MONOTONIC\s0" 4
1658.IX Item "EV_USE_MONOTONIC" 4619.IX Item "EV_USE_MONOTONIC"
1659If defined to be \f(CW1\fR, libev will try to detect the availability of the 4620If defined to be \f(CW1\fR, libev will try to detect the availability of the
1660monotonic clock option at both compiletime and runtime. Otherwise no use 4621monotonic clock option at both compile time and runtime. Otherwise no
1661of the monotonic clock option will be attempted. If you enable this, you 4622use of the monotonic clock option will be attempted. If you enable this,
1662usually have to link against librt or something similar. Enabling it when 4623you usually have to link against librt or something similar. Enabling it
1663the functionality isn't available is safe, though, althoguh you have 4624when the functionality isn't available is safe, though, although you have
1664to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR 4625to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
1665function is hiding in (often \fI\-lrt\fR). 4626function is hiding in (often \fI\-lrt\fR). See also \f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
1666.IP "\s-1EV_USE_REALTIME\s0" 4 4627.IP "\s-1EV_USE_REALTIME\s0" 4
1667.IX Item "EV_USE_REALTIME" 4628.IX Item "EV_USE_REALTIME"
1668If defined to be \f(CW1\fR, libev will try to detect the availability of the 4629If defined to be \f(CW1\fR, libev will try to detect the availability of the
1669realtime clock option at compiletime (and assume its availability at 4630real-time clock option at compile time (and assume its availability
1670runtime if successful). Otherwise no use of the realtime clock option will 4631at runtime if successful). Otherwise no use of the real-time clock
1671be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR by \f(CW\*(C`clock_get 4632option will be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR
1672(CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect correctness. See tzhe note about libraries 4633by \f(CW\*(C`clock_get (CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect
1673in the description of \f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. 4634correctness. See the note about libraries in the description of
4635\&\f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. Defaults to the opposite value of
4636\&\f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
4637.IP "\s-1EV_USE_CLOCK_SYSCALL\s0" 4
4638.IX Item "EV_USE_CLOCK_SYSCALL"
4639If defined to be \f(CW1\fR, libev will try to use a direct syscall instead
4640of calling the system-provided \f(CW\*(C`clock_gettime\*(C'\fR function. This option
4641exists 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
4642unconditionally pulls in \f(CW\*(C`libpthread\*(C'\fR, slowing down single-threaded
4643programs needlessly. Using a direct syscall is slightly slower (in
4644theory), because no optimised vdso implementation can be used, but avoids
4645the pthread dependency. Defaults to \f(CW1\fR on GNU/Linux with glibc 2.x or
4646higher, as it simplifies linking (no need for \f(CW\*(C`\-lrt\*(C'\fR).
4647.IP "\s-1EV_USE_NANOSLEEP\s0" 4
4648.IX Item "EV_USE_NANOSLEEP"
4649If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available
4650and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR.
4651.IP "\s-1EV_USE_EVENTFD\s0" 4
4652.IX Item "EV_USE_EVENTFD"
4653If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
4654available and will probe for kernel support at runtime. This will improve
4655\&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
4656If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
46572.7 or newer, otherwise disabled.
1674.IP "\s-1EV_USE_SELECT\s0" 4 4658.IP "\s-1EV_USE_SELECT\s0" 4
1675.IX Item "EV_USE_SELECT" 4659.IX Item "EV_USE_SELECT"
1676If undefined or defined to be \f(CW1\fR, libev will compile in support for the 4660If undefined or defined to be \f(CW1\fR, libev will compile in support for the
1677\&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at autodetection will be done: if no 4661\&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at auto-detection will be done: if no
1678other method takes over, select will be it. Otherwise the select backend 4662other method takes over, select will be it. Otherwise the select backend
1679will not be compiled in. 4663will not be compiled in.
1680.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4 4664.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
1681.IX Item "EV_SELECT_USE_FD_SET" 4665.IX Item "EV_SELECT_USE_FD_SET"
1682If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR 4666If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR
1683structure. This is useful if libev doesn't compile due to a missing 4667structure. This is useful if libev doesn't compile due to a missing
1684\&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it misguesses the bitset layout on 4668\&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it mis-guesses the bitset layout
1685exotic systems. This usually limits the range of file descriptors to some 4669on exotic systems. This usually limits the range of file descriptors to
1686low limit such as 1024 or might have other limitations (winsocket only 4670some low limit such as 1024 or might have other limitations (winsocket
1687allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation, might 4671only allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation,
1688influence the size of the \f(CW\*(C`fd_set\*(C'\fR used. 4672configures the maximum size of the \f(CW\*(C`fd_set\*(C'\fR.
1689.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4 4673.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
1690.IX Item "EV_SELECT_IS_WINSOCKET" 4674.IX Item "EV_SELECT_IS_WINSOCKET"
1691When defined to \f(CW1\fR, the select backend will assume that 4675When defined to \f(CW1\fR, the select backend will assume that
1692select/socket/connect etc. don't understand file descriptors but 4676select/socket/connect etc. don't understand file descriptors but
1693wants osf handles on win32 (this is the case when the select to 4677wants osf handles on win32 (this is the case when the select to
1694be used is the winsock select). This means that it will call 4678be used is the winsock select). This means that it will call
1695\&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise, 4679\&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
1696it is assumed that all these functions actually work on fds, even 4680it is assumed that all these functions actually work on fds, even
1697on win32. Should not be defined on non\-win32 platforms. 4681on win32. Should not be defined on non\-win32 platforms.
4682.IP "\s-1EV_FD_TO_WIN32_HANDLE\s0(fd)" 4
4683.IX Item "EV_FD_TO_WIN32_HANDLE(fd)"
4684If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map
4685file descriptors to socket handles. When not defining this symbol (the
4686default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually
4687correct. In some cases, programs use their own file descriptor management,
4688in which case they can provide this function to map fds to socket handles.
4689.IP "\s-1EV_WIN32_HANDLE_TO_FD\s0(handle)" 4
4690.IX Item "EV_WIN32_HANDLE_TO_FD(handle)"
4691If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR then libev maps handles to file descriptors
4692using the standard \f(CW\*(C`_open_osfhandle\*(C'\fR function. For programs implementing
4693their own fd to handle mapping, overwriting this function makes it easier
4694to do so. This can be done by defining this macro to an appropriate value.
4695.IP "\s-1EV_WIN32_CLOSE_FD\s0(fd)" 4
4696.IX Item "EV_WIN32_CLOSE_FD(fd)"
4697If programs implement their own fd to handle mapping on win32, then this
4698macro can be used to override the \f(CW\*(C`close\*(C'\fR function, useful to unregister
4699file descriptors again. Note that the replacement function has to close
4700the underlying \s-1OS\s0 handle.
4701.IP "\s-1EV_USE_WSASOCKET\s0" 4
4702.IX Item "EV_USE_WSASOCKET"
4703If defined to be \f(CW1\fR, libev will use \f(CW\*(C`WSASocket\*(C'\fR to create its internal
4704communication socket, which works better in some environments. Otherwise,
4705the normal \f(CW\*(C`socket\*(C'\fR function will be used, which works better in other
4706environments.
1698.IP "\s-1EV_USE_POLL\s0" 4 4707.IP "\s-1EV_USE_POLL\s0" 4
1699.IX Item "EV_USE_POLL" 4708.IX Item "EV_USE_POLL"
1700If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2) 4709If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2)
1701backend. Otherwise it will be enabled on non\-win32 platforms. It 4710backend. Otherwise it will be enabled on non\-win32 platforms. It
1702takes precedence over select. 4711takes precedence over select.
1703.IP "\s-1EV_USE_EPOLL\s0" 4 4712.IP "\s-1EV_USE_EPOLL\s0" 4
1704.IX Item "EV_USE_EPOLL" 4713.IX Item "EV_USE_EPOLL"
1705If defined to be \f(CW1\fR, libev will compile in support for the Linux 4714If defined to be \f(CW1\fR, libev will compile in support for the Linux
1706\&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime, 4715\&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime,
1707otherwise another method will be used as fallback. This is the 4716otherwise another method will be used as fallback. This is the preferred
1708preferred backend for GNU/Linux systems. 4717backend for GNU/Linux systems. If undefined, it will be enabled if the
4718headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
1709.IP "\s-1EV_USE_KQUEUE\s0" 4 4719.IP "\s-1EV_USE_KQUEUE\s0" 4
1710.IX Item "EV_USE_KQUEUE" 4720.IX Item "EV_USE_KQUEUE"
1711If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style 4721If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
1712\&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime, 4722\&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime,
1713otherwise another method will be used as fallback. This is the preferred 4723otherwise another method will be used as fallback. This is the preferred
… …
172310 port style backend. Its availability will be detected at runtime, 473310 port style backend. Its availability will be detected at runtime,
1724otherwise another method will be used as fallback. This is the preferred 4734otherwise another method will be used as fallback. This is the preferred
1725backend for Solaris 10 systems. 4735backend for Solaris 10 systems.
1726.IP "\s-1EV_USE_DEVPOLL\s0" 4 4736.IP "\s-1EV_USE_DEVPOLL\s0" 4
1727.IX Item "EV_USE_DEVPOLL" 4737.IX Item "EV_USE_DEVPOLL"
1728reserved for future expansion, works like the \s-1USE\s0 symbols above. 4738Reserved for future expansion, works like the \s-1USE\s0 symbols above.
4739.IP "\s-1EV_USE_INOTIFY\s0" 4
4740.IX Item "EV_USE_INOTIFY"
4741If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
4742interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
4743be detected at runtime. If undefined, it will be enabled if the headers
4744indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4745.IP "\s-1EV_NO_SMP\s0" 4
4746.IX Item "EV_NO_SMP"
4747If defined to be \f(CW1\fR, libev will assume that memory is always coherent
4748between threads, that is, threads can be used, but threads never run on
4749different cpus (or different cpu cores). This reduces dependencies
4750and makes libev faster.
4751.IP "\s-1EV_NO_THREADS\s0" 4
4752.IX Item "EV_NO_THREADS"
4753If defined to be \f(CW1\fR, libev will assume that it will never be called from
4754different threads (that includes signal handlers), which is a stronger
4755assumption than \f(CW\*(C`EV_NO_SMP\*(C'\fR, above. This reduces dependencies and makes
4756libev faster.
4757.IP "\s-1EV_ATOMIC_T\s0" 4
4758.IX Item "EV_ATOMIC_T"
4759Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
4760access is atomic with respect to other threads or signal contexts. No
4761such type is easily found in the C language, so you can provide your own
4762type that you know is safe for your purposes. It is used both for signal
4763handler \*(L"locking\*(R" as well as for signal and thread safety in \f(CW\*(C`ev_async\*(C'\fR
4764watchers.
4765.Sp
4766In the absence of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR
4767(from \fIsignal.h\fR), which is usually good enough on most platforms.
1729.IP "\s-1EV_H\s0" 4 4768.IP "\s-1EV_H \s0(h)" 4
1730.IX Item "EV_H" 4769.IX Item "EV_H (h)"
1731The name of the \fIev.h\fR header file used to include it. The default if 4770The name of the \fIev.h\fR header file used to include it. The default if
1732undefined is \f(CW\*(C`<ev.h>\*(C'\fR in \fIevent.h\fR and \f(CW"ev.h"\fR in \fIev.c\fR. This 4771undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be
1733can be used to virtually rename the \fIev.h\fR header file in case of conflicts. 4772used to virtually rename the \fIev.h\fR header file in case of conflicts.
1734.IP "\s-1EV_CONFIG_H\s0" 4 4773.IP "\s-1EV_CONFIG_H \s0(h)" 4
1735.IX Item "EV_CONFIG_H" 4774.IX Item "EV_CONFIG_H (h)"
1736If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override 4775If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
1737\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to 4776\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
1738\&\f(CW\*(C`EV_H\*(C'\fR, above. 4777\&\f(CW\*(C`EV_H\*(C'\fR, above.
1739.IP "\s-1EV_EVENT_H\s0" 4 4778.IP "\s-1EV_EVENT_H \s0(h)" 4
1740.IX Item "EV_EVENT_H" 4779.IX Item "EV_EVENT_H (h)"
1741Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea 4780Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea
1742of how the \fIevent.h\fR header can be found. 4781of how the \fIevent.h\fR header can be found, the default is \f(CW"event.h"\fR.
1743.IP "\s-1EV_PROTOTYPES\s0" 4 4782.IP "\s-1EV_PROTOTYPES \s0(h)" 4
1744.IX Item "EV_PROTOTYPES" 4783.IX Item "EV_PROTOTYPES (h)"
1745If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function 4784If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
1746prototypes, but still define all the structs and other symbols. This is 4785prototypes, but still define all the structs and other symbols. This is
1747occasionally useful if you want to provide your own wrapper functions 4786occasionally useful if you want to provide your own wrapper functions
1748around libev functions. 4787around libev functions.
1749.IP "\s-1EV_MULTIPLICITY\s0" 4 4788.IP "\s-1EV_MULTIPLICITY\s0" 4
… …
1751If undefined or defined to \f(CW1\fR, then all event-loop-specific functions 4790If undefined or defined to \f(CW1\fR, then all event-loop-specific functions
1752will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create 4791will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create
1753additional independent event loops. Otherwise there will be no support 4792additional independent event loops. Otherwise there will be no support
1754for multiple event loops and there is no first event loop pointer 4793for multiple event loops and there is no first event loop pointer
1755argument. Instead, all functions act on the single default loop. 4794argument. Instead, all functions act on the single default loop.
4795.Sp
4796Note that \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR will no longer provide a
4797default loop when multiplicity is switched off \- you always have to
4798initialise the loop manually in this case.
1756.IP "\s-1EV_PERIODICS\s0" 4 4799.IP "\s-1EV_MINPRI\s0" 4
1757.IX Item "EV_PERIODICS" 4800.IX Item "EV_MINPRI"
1758If undefined or defined to be \f(CW1\fR, then periodic timers are supported, 4801.PD 0
1759otherwise not. This saves a few kb of code. 4802.IP "\s-1EV_MAXPRI\s0" 4
4803.IX Item "EV_MAXPRI"
4804.PD
4805The range of allowed priorities. \f(CW\*(C`EV_MINPRI\*(C'\fR must be smaller or equal to
4806\&\f(CW\*(C`EV_MAXPRI\*(C'\fR, but otherwise there are no non-obvious limitations. You can
4807provide for more priorities by overriding those symbols (usually defined
4808to be \f(CW\*(C`\-2\*(C'\fR and \f(CW2\fR, respectively).
4809.Sp
4810When doing priority-based operations, libev usually has to linearly search
4811all the priorities, so having many of them (hundreds) uses a lot of space
4812and time, so using the defaults of five priorities (\-2 .. +2) is usually
4813fine.
4814.Sp
4815If your embedding application does not need any priorities, defining these
4816both to \f(CW0\fR will save some memory and \s-1CPU.\s0
4817.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
4818.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."
4819If undefined or defined to be \f(CW1\fR (and the platform supports it), then
4820the respective watcher type is supported. If defined to be \f(CW0\fR, then it
4821is not. Disabling watcher types mainly saves code size.
4822.IP "\s-1EV_FEATURES\s0" 4
4823.IX Item "EV_FEATURES"
4824If you need to shave off some kilobytes of code at the expense of some
4825speed (but with the full \s-1API\s0), you can define this symbol to request
4826certain subsets of functionality. The default is to enable all features
4827that can be enabled on the platform.
4828.Sp
4829A typical way to use this symbol is to define it to \f(CW0\fR (or to a bitset
4830with some broad features you want) and then selectively re-enable
4831additional parts you want, for example if you want everything minimal,
4832but multiple event loop support, async and child watchers and the poll
4833backend, use this:
4834.Sp
4835.Vb 5
4836\& #define EV_FEATURES 0
4837\& #define EV_MULTIPLICITY 1
4838\& #define EV_USE_POLL 1
4839\& #define EV_CHILD_ENABLE 1
4840\& #define EV_ASYNC_ENABLE 1
4841.Ve
4842.Sp
4843The actual value is a bitset, it can be a combination of the following
4844values (by default, all of these are enabled):
4845.RS 4
4846.ie n .IP "1 \- faster/larger code" 4
4847.el .IP "\f(CW1\fR \- faster/larger code" 4
4848.IX Item "1 - faster/larger code"
4849Use larger code to speed up some operations.
4850.Sp
4851Currently this is used to override some inlining decisions (enlarging the
4852code size by roughly 30% on amd64).
4853.Sp
4854When optimising for size, use of compiler flags such as \f(CW\*(C`\-Os\*(C'\fR with
4855gcc is recommended, as well as \f(CW\*(C`\-DNDEBUG\*(C'\fR, as libev contains a number of
4856assertions.
4857.Sp
4858The default is off when \f(CW\*(C`_\|_OPTIMIZE_SIZE_\|_\*(C'\fR is defined by your compiler
4859(e.g. gcc with \f(CW\*(C`\-Os\*(C'\fR).
4860.ie n .IP "2 \- faster/larger data structures" 4
4861.el .IP "\f(CW2\fR \- faster/larger data structures" 4
4862.IX Item "2 - faster/larger data structures"
4863Replaces the small 2\-heap for timer management by a faster 4\-heap, larger
4864hash table sizes and so on. This will usually further increase code size
4865and can additionally have an effect on the size of data structures at
4866runtime.
4867.Sp
4868The default is off when \f(CW\*(C`_\|_OPTIMIZE_SIZE_\|_\*(C'\fR is defined by your compiler
4869(e.g. gcc with \f(CW\*(C`\-Os\*(C'\fR).
4870.ie n .IP "4 \- full \s-1API\s0 configuration" 4
4871.el .IP "\f(CW4\fR \- full \s-1API\s0 configuration" 4
4872.IX Item "4 - full API configuration"
4873This enables priorities (sets \f(CW\*(C`EV_MAXPRI\*(C'\fR=2 and \f(CW\*(C`EV_MINPRI\*(C'\fR=\-2), and
4874enables multiplicity (\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR=1).
4875.ie n .IP "8 \- full \s-1API\s0" 4
4876.el .IP "\f(CW8\fR \- full \s-1API\s0" 4
4877.IX Item "8 - full API"
4878This enables a lot of the \*(L"lesser used\*(R" \s-1API\s0 functions. See \f(CW\*(C`ev.h\*(C'\fR for
4879details on which parts of the \s-1API\s0 are still available without this
4880feature, and do not complain if this subset changes over time.
4881.ie n .IP "16 \- enable all optional watcher types" 4
4882.el .IP "\f(CW16\fR \- enable all optional watcher types" 4
4883.IX Item "16 - enable all optional watcher types"
4884Enables all optional watcher types. If you want to selectively enable
4885only some watcher types other than I/O and timers (e.g. prepare,
4886embed, async, child...) you can enable them manually by defining
4887\&\f(CW\*(C`EV_watchertype_ENABLE\*(C'\fR to \f(CW1\fR instead.
4888.ie n .IP "32 \- enable all backends" 4
4889.el .IP "\f(CW32\fR \- enable all backends" 4
4890.IX Item "32 - enable all backends"
4891This enables all backends \- without this feature, you need to enable at
4892least one backend manually (\f(CW\*(C`EV_USE_SELECT\*(C'\fR is a good choice).
4893.ie n .IP "64 \- enable OS-specific ""helper"" APIs" 4
4894.el .IP "\f(CW64\fR \- enable OS-specific ``helper'' APIs" 4
4895.IX Item "64 - enable OS-specific helper APIs"
4896Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
4897default.
4898.RE
4899.RS 4
4900.Sp
4901Compiling with \f(CW\*(C`gcc \-Os \-DEV_STANDALONE \-DEV_USE_EPOLL=1 \-DEV_FEATURES=0\*(C'\fR
4902reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
4903code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
4904watchers, timers and monotonic clock support.
4905.Sp
4906With an intelligent-enough linker (gcc+binutils are intelligent enough
4907when you use \f(CW\*(C`\-Wl,\-\-gc\-sections \-ffunction\-sections\*(C'\fR) functions unused by
4908your program might be left out as well \- a binary starting a timer and an
4909I/O watcher then might come out at only 5Kb.
4910.RE
4911.IP "\s-1EV_API_STATIC\s0" 4
4912.IX Item "EV_API_STATIC"
4913If this symbol is defined (by default it is not), then all identifiers
4914will have static linkage. This means that libev will not export any
4915identifiers, and you cannot link against libev anymore. This can be useful
4916when you embed libev, only want to use libev functions in a single file,
4917and do not want its identifiers to be visible.
4918.Sp
4919To use this, define \f(CW\*(C`EV_API_STATIC\*(C'\fR and include \fIev.c\fR in the file that
4920wants to use libev.
4921.Sp
4922This option only works when libev is compiled with a C compiler, as \*(C+
4923doesn't support the required declaration syntax.
4924.IP "\s-1EV_AVOID_STDIO\s0" 4
4925.IX Item "EV_AVOID_STDIO"
4926If this is set to \f(CW1\fR at compiletime, then libev will avoid using stdio
4927functions (printf, scanf, perror etc.). This will increase the code size
4928somewhat, but if your program doesn't otherwise depend on stdio and your
4929libc allows it, this avoids linking in the stdio library which is quite
4930big.
4931.Sp
4932Note that error messages might become less precise when this option is
4933enabled.
4934.IP "\s-1EV_NSIG\s0" 4
4935.IX Item "EV_NSIG"
4936The highest supported signal number, +1 (or, the number of
4937signals): Normally, libev tries to deduce the maximum number of signals
4938automatically, but sometimes this fails, in which case it can be
4939specified. Also, using a lower number than detected (\f(CW32\fR should be
4940good for about any system in existence) can save some memory, as libev
4941statically allocates some 12\-24 bytes per signal number.
4942.IP "\s-1EV_PID_HASHSIZE\s0" 4
4943.IX Item "EV_PID_HASHSIZE"
4944\&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by
4945pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR disabled),
4946usually more than enough. If you need to manage thousands of children you
4947might want to increase this value (\fImust\fR be a power of two).
4948.IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4
4949.IX Item "EV_INOTIFY_HASHSIZE"
4950\&\f(CW\*(C`ev_stat\*(C'\fR watchers use a small hash table to distribute workload by
4951inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR
4952disabled), usually more than enough. If you need to manage thousands of
4953\&\f(CW\*(C`ev_stat\*(C'\fR watchers you might want to increase this value (\fImust\fR be a
4954power of two).
4955.IP "\s-1EV_USE_4HEAP\s0" 4
4956.IX Item "EV_USE_4HEAP"
4957Heaps are not very cache-efficient. To improve the cache-efficiency of the
4958timer and periodics heaps, libev uses a 4\-heap when this symbol is defined
4959to \f(CW1\fR. The 4\-heap uses more complicated (longer) code but has noticeably
4960faster performance with many (thousands) of watchers.
4961.Sp
4962The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4963will be \f(CW0\fR.
4964.IP "\s-1EV_HEAP_CACHE_AT\s0" 4
4965.IX Item "EV_HEAP_CACHE_AT"
4966Heaps are not very cache-efficient. To improve the cache-efficiency of the
4967timer and periodics heaps, libev can cache the timestamp (\fIat\fR) within
4968the heap structure (selected by defining \f(CW\*(C`EV_HEAP_CACHE_AT\*(C'\fR to \f(CW1\fR),
4969which uses 8\-12 bytes more per watcher and a few hundred bytes more code,
4970but avoids random read accesses on heap changes. This improves performance
4971noticeably with many (hundreds) of watchers.
4972.Sp
4973The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4974will be \f(CW0\fR.
4975.IP "\s-1EV_VERIFY\s0" 4
4976.IX Item "EV_VERIFY"
4977Controls how much internal verification (see \f(CW\*(C`ev_verify ()\*(C'\fR) will
4978be done: If set to \f(CW0\fR, no internal verification code will be compiled
4979in. If set to \f(CW1\fR, then verification code will be compiled in, but not
4980called. If set to \f(CW2\fR, then the internal verification code will be
4981called once per loop, which can slow down libev. If set to \f(CW3\fR, then the
4982verification code will be called very frequently, which will slow down
4983libev considerably.
4984.Sp
4985The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4986will be \f(CW0\fR.
1760.IP "\s-1EV_COMMON\s0" 4 4987.IP "\s-1EV_COMMON\s0" 4
1761.IX Item "EV_COMMON" 4988.IX Item "EV_COMMON"
1762By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining 4989By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining
1763this macro to a something else you can include more and other types of 4990this macro to something else you can include more and other types of
1764members. You have to define it each time you include one of the files, 4991members. You have to define it each time you include one of the files,
1765though, and it must be identical each time. 4992though, and it must be identical each time.
1766.Sp 4993.Sp
1767For example, the perl \s-1EV\s0 module uses something like this: 4994For example, the perl \s-1EV\s0 module uses something like this:
1768.Sp 4995.Sp
1769.Vb 3 4996.Vb 3
1770\& #define EV_COMMON \e 4997\& #define EV_COMMON \e
1771\& SV *self; /* contains this struct */ \e 4998\& SV *self; /* contains this struct */ \e
1772\& SV *cb_sv, *fh /* note no trailing ";" */ 4999\& SV *cb_sv, *fh /* note no trailing ";" */
1773.Ve 5000.Ve
1774.IP "\s-1EV_CB_DECLARE\s0(type)" 4 5001.IP "\s-1EV_CB_DECLARE \s0(type)" 4
1775.IX Item "EV_CB_DECLARE(type)" 5002.IX Item "EV_CB_DECLARE (type)"
1776.PD 0 5003.PD 0
1777.IP "\s-1EV_CB_INVOKE\s0(watcher,revents)" 4 5004.IP "\s-1EV_CB_INVOKE \s0(watcher, revents)" 4
1778.IX Item "EV_CB_INVOKE(watcher,revents)" 5005.IX Item "EV_CB_INVOKE (watcher, revents)"
1779.IP "ev_set_cb(ev,cb)" 4 5006.IP "ev_set_cb (ev, cb)" 4
1780.IX Item "ev_set_cb(ev,cb)" 5007.IX Item "ev_set_cb (ev, cb)"
1781.PD 5008.PD
1782Can be used to change the callback member declaration in each watcher, 5009Can be used to change the callback member declaration in each watcher,
1783and the way callbacks are invoked and set. Must expand to a struct member 5010and the way callbacks are invoked and set. Must expand to a struct member
1784definition and a statement, respectively. See the \fIev.v\fR header file for 5011definition and a statement, respectively. See the \fIev.h\fR header file for
1785their default definitions. One possible use for overriding these is to 5012their default definitions. One possible use for overriding these is to
1786avoid the ev_loop pointer as first argument in all cases, or to use method 5013avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use
1787calls instead of plain function calls in \*(C+. 5014method calls instead of plain function calls in \*(C+.
5015.SS "\s-1EXPORTED API SYMBOLS\s0"
5016.IX Subsection "EXPORTED API SYMBOLS"
5017If you need to re-export the \s-1API \s0(e.g. via a \s-1DLL\s0) and you need a list of
5018exported symbols, you can use the provided \fISymbol.*\fR files which list
5019all public symbols, one per line:
5020.PP
5021.Vb 2
5022\& Symbols.ev for libev proper
5023\& Symbols.event for the libevent emulation
5024.Ve
5025.PP
5026This can also be used to rename all public symbols to avoid clashes with
5027multiple versions of libev linked together (which is obviously bad in
5028itself, but sometimes it is inconvenient to avoid this).
5029.PP
5030A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to
5031include before including \fIev.h\fR:
5032.PP
5033.Vb 1
5034\& <Symbols.ev sed \-e "s/.*/#define & myprefix_&/" >wrap.h
5035.Ve
5036.PP
5037This would create a file \fIwrap.h\fR which essentially looks like this:
5038.PP
5039.Vb 4
5040\& #define ev_backend myprefix_ev_backend
5041\& #define ev_check_start myprefix_ev_check_start
5042\& #define ev_check_stop myprefix_ev_check_stop
5043\& ...
5044.Ve
1788.Sh "\s-1EXAMPLES\s0" 5045.SS "\s-1EXAMPLES\s0"
1789.IX Subsection "EXAMPLES" 5046.IX Subsection "EXAMPLES"
1790For a real-world example of a program the includes libev 5047For a real-world example of a program the includes libev
1791verbatim, you can have a look at the \s-1EV\s0 perl module 5048verbatim, you can have a look at the \s-1EV\s0 perl module
1792(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in 5049(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
1793the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public 5050the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public
1794interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file 5051interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file
1795will be compiled. It is pretty complex because it provides its own header 5052will be compiled. It is pretty complex because it provides its own header
1796file. 5053file.
1797.Sp 5054.PP
1798The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file 5055The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file
1799that everybody includes and which overrides some autoconf choices: 5056that everybody includes and which overrides some configure choices:
1800.Sp 5057.PP
1801.Vb 4 5058.Vb 8
5059\& #define EV_FEATURES 8
5060\& #define EV_USE_SELECT 1
5061\& #define EV_PREPARE_ENABLE 1
5062\& #define EV_IDLE_ENABLE 1
5063\& #define EV_SIGNAL_ENABLE 1
5064\& #define EV_CHILD_ENABLE 1
1802\& #define EV_USE_POLL 0 5065\& #define EV_USE_STDEXCEPT 0
1803\& #define EV_MULTIPLICITY 0
1804\& #define EV_PERIODICS 0
1805\& #define EV_CONFIG_H <config.h> 5066\& #define EV_CONFIG_H <config.h>
1806.Ve 5067\&
1807.Sp
1808.Vb 1
1809\& #include "ev++.h" 5068\& #include "ev++.h"
1810.Ve 5069.Ve
1811.Sp 5070.PP
1812And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled: 5071And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled:
1813.Sp 5072.PP
1814.Vb 2 5073.Vb 2
1815\& #include "ev_cpp.h" 5074\& #include "ev_cpp.h"
1816\& #include "ev.c" 5075\& #include "ev.c"
1817.Ve 5076.Ve
5077.SH "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT"
5078.IX Header "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT"
5079.SS "\s-1THREADS AND COROUTINES\s0"
5080.IX Subsection "THREADS AND COROUTINES"
5081\fI\s-1THREADS\s0\fR
5082.IX Subsection "THREADS"
5083.PP
5084All libev functions are reentrant and thread-safe unless explicitly
5085documented otherwise, but libev implements no locking itself. This means
5086that you can use as many loops as you want in parallel, as long as there
5087are no concurrent calls into any libev function with the same loop
5088parameter (\f(CW\*(C`ev_default_*\*(C'\fR calls have an implicit default loop parameter,
5089of course): libev guarantees that different event loops share no data
5090structures that need any locking.
5091.PP
5092Or to put it differently: calls with different loop parameters can be done
5093concurrently from multiple threads, calls with the same loop parameter
5094must be done serially (but can be done from different threads, as long as
5095only one thread ever is inside a call at any point in time, e.g. by using
5096a mutex per loop).
5097.PP
5098Specifically to support threads (and signal handlers), libev implements
5099so-called \f(CW\*(C`ev_async\*(C'\fR watchers, which allow some limited form of
5100concurrency on the same event loop, namely waking it up \*(L"from the
5101outside\*(R".
5102.PP
5103If you want to know which design (one loop, locking, or multiple loops
5104without or something else still) is best for your problem, then I cannot
5105help you, but here is some generic advice:
5106.IP "\(bu" 4
5107most applications have a main thread: use the default libev loop
5108in that thread, or create a separate thread running only the default loop.
5109.Sp
5110This helps integrating other libraries or software modules that use libev
5111themselves and don't care/know about threading.
5112.IP "\(bu" 4
5113one loop per thread is usually a good model.
5114.Sp
5115Doing this is almost never wrong, sometimes a better-performance model
5116exists, but it is always a good start.
5117.IP "\(bu" 4
5118other models exist, such as the leader/follower pattern, where one
5119loop is handed through multiple threads in a kind of round-robin fashion.
5120.Sp
5121Choosing a model is hard \- look around, learn, know that usually you can do
5122better than you currently do :\-)
5123.IP "\(bu" 4
5124often you need to talk to some other thread which blocks in the
5125event loop.
5126.Sp
5127\&\f(CW\*(C`ev_async\*(C'\fR watchers can be used to wake them up from other threads safely
5128(or from signal contexts...).
5129.Sp
5130An example use would be to communicate signals or other events that only
5131work in the default loop by registering the signal watcher with the
5132default loop and triggering an \f(CW\*(C`ev_async\*(C'\fR watcher from the default loop
5133watcher callback into the event loop interested in the signal.
5134.PP
5135See also \*(L"\s-1THREAD LOCKING EXAMPLE\*(R"\s0.
5136.PP
5137\fI\s-1COROUTINES\s0\fR
5138.IX Subsection "COROUTINES"
5139.PP
5140Libev is very accommodating to coroutines (\*(L"cooperative threads\*(R"):
5141libev fully supports nesting calls to its functions from different
5142coroutines (e.g. you can call \f(CW\*(C`ev_run\*(C'\fR on the same loop from two
5143different coroutines, and switch freely between both coroutines running
5144the loop, as long as you don't confuse yourself). The only exception is
5145that you must not do this from \f(CW\*(C`ev_periodic\*(C'\fR reschedule callbacks.
5146.PP
5147Care has been taken to ensure that libev does not keep local state inside
5148\&\f(CW\*(C`ev_run\*(C'\fR, and other calls do not usually allow for coroutine switches as
5149they do not call any callbacks.
5150.SS "\s-1COMPILER WARNINGS\s0"
5151.IX Subsection "COMPILER WARNINGS"
5152Depending on your compiler and compiler settings, you might get no or a
5153lot of warnings when compiling libev code. Some people are apparently
5154scared by this.
5155.PP
5156However, these are unavoidable for many reasons. For one, each compiler
5157has different warnings, and each user has different tastes regarding
5158warning options. \*(L"Warn-free\*(R" code therefore cannot be a goal except when
5159targeting a specific compiler and compiler-version.
5160.PP
5161Another reason is that some compiler warnings require elaborate
5162workarounds, or other changes to the code that make it less clear and less
5163maintainable.
5164.PP
5165And of course, some compiler warnings are just plain stupid, or simply
5166wrong (because they don't actually warn about the condition their message
5167seems to warn about). For example, certain older gcc versions had some
5168warnings that resulted in an extreme number of false positives. These have
5169been fixed, but some people still insist on making code warn-free with
5170such buggy versions.
5171.PP
5172While libev is written to generate as few warnings as possible,
5173\&\*(L"warn-free\*(R" code is not a goal, and it is recommended not to build libev
5174with any compiler warnings enabled unless you are prepared to cope with
5175them (e.g. by ignoring them). Remember that warnings are just that:
5176warnings, not errors, or proof of bugs.
5177.SS "\s-1VALGRIND\s0"
5178.IX Subsection "VALGRIND"
5179Valgrind has a special section here because it is a popular tool that is
5180highly useful. Unfortunately, valgrind reports are very hard to interpret.
5181.PP
5182If you think you found a bug (memory leak, uninitialised data access etc.)
5183in libev, then check twice: If valgrind reports something like:
5184.PP
5185.Vb 3
5186\& ==2274== definitely lost: 0 bytes in 0 blocks.
5187\& ==2274== possibly lost: 0 bytes in 0 blocks.
5188\& ==2274== still reachable: 256 bytes in 1 blocks.
5189.Ve
5190.PP
5191Then there is no memory leak, just as memory accounted to global variables
5192is not a memleak \- the memory is still being referenced, and didn't leak.
5193.PP
5194Similarly, under some circumstances, valgrind might report kernel bugs
5195as if it were a bug in libev (e.g. in realloc or in the poll backend,
5196although an acceptable workaround has been found here), or it might be
5197confused.
5198.PP
5199Keep in mind that valgrind is a very good tool, but only a tool. Don't
5200make it into some kind of religion.
5201.PP
5202If you are unsure about something, feel free to contact the mailing list
5203with the full valgrind report and an explanation on why you think this
5204is a bug in libev (best check the archives, too :). However, don't be
5205annoyed when you get a brisk \*(L"this is no bug\*(R" answer and take the chance
5206of learning how to interpret valgrind properly.
5207.PP
5208If you need, for some reason, empty reports from valgrind for your project
5209I suggest using suppression lists.
5210.SH "PORTABILITY NOTES"
5211.IX Header "PORTABILITY NOTES"
5212.SS "\s-1GNU/LINUX 32 BIT LIMITATIONS\s0"
5213.IX Subsection "GNU/LINUX 32 BIT LIMITATIONS"
5214GNU/Linux is the only common platform that supports 64 bit file/large file
5215interfaces but \fIdisables\fR them by default.
5216.PP
5217That means that libev compiled in the default environment doesn't support
5218files larger than 2GiB or so, which mainly affects \f(CW\*(C`ev_stat\*(C'\fR watchers.
5219.PP
5220Unfortunately, many programs try to work around this GNU/Linux issue
5221by enabling the large file \s-1API,\s0 which makes them incompatible with the
5222standard libev compiled for their system.
5223.PP
5224Likewise, libev cannot enable the large file \s-1API\s0 itself as this would
5225suddenly make it incompatible to the default compile time environment,
5226i.e. all programs not using special compile switches.
5227.SS "\s-1OS/X AND DARWIN BUGS\s0"
5228.IX Subsection "OS/X AND DARWIN BUGS"
5229The whole thing is a bug if you ask me \- basically any system interface
5230you touch is broken, whether it is locales, poll, kqueue or even the
5231OpenGL drivers.
5232.PP
5233\fI\f(CI\*(C`kqueue\*(C'\fI is buggy\fR
5234.IX Subsection "kqueue is buggy"
5235.PP
5236The kqueue syscall is broken in all known versions \- most versions support
5237only sockets, many support pipes.
5238.PP
5239Libev tries to work around this by not using \f(CW\*(C`kqueue\*(C'\fR by default on this
5240rotten platform, but of course you can still ask for it when creating a
5241loop \- embedding a socket-only kqueue loop into a select-based one is
5242probably going to work well.
5243.PP
5244\fI\f(CI\*(C`poll\*(C'\fI is buggy\fR
5245.IX Subsection "poll is buggy"
5246.PP
5247Instead of fixing \f(CW\*(C`kqueue\*(C'\fR, Apple replaced their (working) \f(CW\*(C`poll\*(C'\fR
5248implementation by something calling \f(CW\*(C`kqueue\*(C'\fR internally around the 10.5.6
5249release, so now \f(CW\*(C`kqueue\*(C'\fR \fIand\fR \f(CW\*(C`poll\*(C'\fR are broken.
5250.PP
5251Libev tries to work around this by not using \f(CW\*(C`poll\*(C'\fR by default on
5252this rotten platform, but of course you can still ask for it when creating
5253a loop.
5254.PP
5255\fI\f(CI\*(C`select\*(C'\fI is buggy\fR
5256.IX Subsection "select is buggy"
5257.PP
5258All that's left is \f(CW\*(C`select\*(C'\fR, and of course Apple found a way to fuck this
5259one up as well: On \s-1OS/X, \s0\f(CW\*(C`select\*(C'\fR actively limits the number of file
5260descriptors you can pass in to 1024 \- your program suddenly crashes when
5261you use more.
5262.PP
5263There is an undocumented \*(L"workaround\*(R" for this \- defining
5264\&\f(CW\*(C`_DARWIN_UNLIMITED_SELECT\*(C'\fR, which libev tries to use, so select \fIshould\fR
5265work on \s-1OS/X.\s0
5266.SS "\s-1SOLARIS PROBLEMS AND WORKAROUNDS\s0"
5267.IX Subsection "SOLARIS PROBLEMS AND WORKAROUNDS"
5268\fI\f(CI\*(C`errno\*(C'\fI reentrancy\fR
5269.IX Subsection "errno reentrancy"
5270.PP
5271The default compile environment on Solaris is unfortunately so
5272thread-unsafe that you can't even use components/libraries compiled
5273without \f(CW\*(C`\-D_REENTRANT\*(C'\fR in a threaded program, which, of course, isn't
5274defined by default. A valid, if stupid, implementation choice.
5275.PP
5276If you want to use libev in threaded environments you have to make sure
5277it's compiled with \f(CW\*(C`_REENTRANT\*(C'\fR defined.
5278.PP
5279\fIEvent port backend\fR
5280.IX Subsection "Event port backend"
5281.PP
5282The scalable event interface for Solaris is called \*(L"event
5283ports\*(R". Unfortunately, this mechanism is very buggy in all major
5284releases. If you run into high \s-1CPU\s0 usage, your program freezes or you get
5285a large number of spurious wakeups, make sure you have all the relevant
5286and latest kernel patches applied. No, I don't know which ones, but there
5287are multiple ones to apply, and afterwards, event ports actually work
5288great.
5289.PP
5290If you can't get it to work, you can try running the program by setting
5291the environment variable \f(CW\*(C`LIBEV_FLAGS=3\*(C'\fR to only allow \f(CW\*(C`poll\*(C'\fR and
5292\&\f(CW\*(C`select\*(C'\fR backends.
5293.SS "\s-1AIX POLL BUG\s0"
5294.IX Subsection "AIX POLL BUG"
5295\&\s-1AIX\s0 unfortunately has a broken \f(CW\*(C`poll.h\*(C'\fR header. Libev works around
5296this by trying to avoid the poll backend altogether (i.e. it's not even
5297compiled in), which normally isn't a big problem as \f(CW\*(C`select\*(C'\fR works fine
5298with large bitsets on \s-1AIX,\s0 and \s-1AIX\s0 is dead anyway.
5299.SS "\s-1WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS\s0"
5300.IX Subsection "WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS"
5301\fIGeneral issues\fR
5302.IX Subsection "General issues"
5303.PP
5304Win32 doesn't support any of the standards (e.g. \s-1POSIX\s0) that libev
5305requires, and its I/O model is fundamentally incompatible with the \s-1POSIX\s0
5306model. Libev still offers limited functionality on this platform in
5307the form of the \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR backend, and only supports socket
5308descriptors. This only applies when using Win32 natively, not when using
5309e.g. cygwin. Actually, it only applies to the microsofts own compilers,
5310as every compiler comes with a slightly differently broken/incompatible
5311environment.
5312.PP
5313Lifting these limitations would basically require the full
5314re-implementation of the I/O system. If you are into this kind of thing,
5315then note that glib does exactly that for you in a very portable way (note
5316also that glib is the slowest event library known to man).
5317.PP
5318There is no supported compilation method available on windows except
5319embedding it into other applications.
5320.PP
5321Sensible signal handling is officially unsupported by Microsoft \- libev
5322tries its best, but under most conditions, signals will simply not work.
5323.PP
5324Not a libev limitation but worth mentioning: windows apparently doesn't
5325accept large writes: instead of resulting in a partial write, windows will
5326either accept everything or return \f(CW\*(C`ENOBUFS\*(C'\fR if the buffer is too large,
5327so make sure you only write small amounts into your sockets (less than a
5328megabyte seems safe, but this apparently depends on the amount of memory
5329available).
5330.PP
5331Due to the many, low, and arbitrary limits on the win32 platform and
5332the abysmal performance of winsockets, using a large number of sockets
5333is not recommended (and not reasonable). If your program needs to use
5334more than a hundred or so sockets, then likely it needs to use a totally
5335different implementation for windows, as libev offers the \s-1POSIX\s0 readiness
5336notification model, which cannot be implemented efficiently on windows
5337(due to Microsoft monopoly games).
5338.PP
5339A typical way to use libev under windows is to embed it (see the embedding
5340section for details) and use the following \fIevwrap.h\fR header file instead
5341of \fIev.h\fR:
5342.PP
5343.Vb 2
5344\& #define EV_STANDALONE /* keeps ev from requiring config.h */
5345\& #define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
5346\&
5347\& #include "ev.h"
5348.Ve
5349.PP
5350And compile the following \fIevwrap.c\fR file into your project (make sure
5351you do \fInot\fR compile the \fIev.c\fR or any other embedded source files!):
5352.PP
5353.Vb 2
5354\& #include "evwrap.h"
5355\& #include "ev.c"
5356.Ve
5357.PP
5358\fIThe winsocket \f(CI\*(C`select\*(C'\fI function\fR
5359.IX Subsection "The winsocket select function"
5360.PP
5361The winsocket \f(CW\*(C`select\*(C'\fR function doesn't follow \s-1POSIX\s0 in that it
5362requires socket \fIhandles\fR and not socket \fIfile descriptors\fR (it is
5363also extremely buggy). This makes select very inefficient, and also
5364requires a mapping from file descriptors to socket handles (the Microsoft
5365C runtime provides the function \f(CW\*(C`_open_osfhandle\*(C'\fR for this). See the
5366discussion of the \f(CW\*(C`EV_SELECT_USE_FD_SET\*(C'\fR, \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR and
5367\&\f(CW\*(C`EV_FD_TO_WIN32_HANDLE\*(C'\fR preprocessor symbols for more info.
5368.PP
5369The configuration for a \*(L"naked\*(R" win32 using the Microsoft runtime
5370libraries and raw winsocket select is:
5371.PP
5372.Vb 2
5373\& #define EV_USE_SELECT 1
5374\& #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
5375.Ve
5376.PP
5377Note that winsockets handling of fd sets is O(n), so you can easily get a
5378complexity in the O(nX) range when using win32.
5379.PP
5380\fILimited number of file descriptors\fR
5381.IX Subsection "Limited number of file descriptors"
5382.PP
5383Windows has numerous arbitrary (and low) limits on things.
5384.PP
5385Early versions of winsocket's select only supported waiting for a maximum
5386of \f(CW64\fR handles (probably owning to the fact that all windows kernels
5387can only wait for \f(CW64\fR things at the same time internally; Microsoft
5388recommends spawning a chain of threads and wait for 63 handles and the
5389previous thread in each. Sounds great!).
5390.PP
5391Newer versions support more handles, but you need to define \f(CW\*(C`FD_SETSIZE\*(C'\fR
5392to some high number (e.g. \f(CW2048\fR) before compiling the winsocket select
5393call (which might be in libev or elsewhere, for example, perl and many
5394other interpreters do their own select emulation on windows).
5395.PP
5396Another limit is the number of file descriptors in the Microsoft runtime
5397libraries, which by default is \f(CW64\fR (there must be a hidden \fI64\fR
5398fetish or something like this inside Microsoft). You can increase this
5399by calling \f(CW\*(C`_setmaxstdio\*(C'\fR, which can increase this limit to \f(CW2048\fR
5400(another arbitrary limit), but is broken in many versions of the Microsoft
5401runtime libraries. This might get you to about \f(CW512\fR or \f(CW2048\fR sockets
5402(depending on windows version and/or the phase of the moon). To get more,
5403you need to wrap all I/O functions and provide your own fd management, but
5404the cost of calling select (O(nX)) will likely make this unworkable.
5405.SS "\s-1PORTABILITY REQUIREMENTS\s0"
5406.IX Subsection "PORTABILITY REQUIREMENTS"
5407In addition to a working ISO-C implementation and of course the
5408backend-specific APIs, libev relies on a few additional extensions:
5409.ie n .IP """void (*)(ev_watcher_type *, int revents)"" must have compatible calling conventions regardless of ""ev_watcher_type *""." 4
5410.el .IP "\f(CWvoid (*)(ev_watcher_type *, int revents)\fR must have compatible calling conventions regardless of \f(CWev_watcher_type *\fR." 4
5411.IX Item "void (*)(ev_watcher_type *, int revents) must have compatible calling conventions regardless of ev_watcher_type *."
5412Libev assumes not only that all watcher pointers have the same internal
5413structure (guaranteed by \s-1POSIX\s0 but not by \s-1ISO C\s0 for example), but it also
5414assumes that the same (machine) code can be used to call any watcher
5415callback: The watcher callbacks have different type signatures, but libev
5416calls them using an \f(CW\*(C`ev_watcher *\*(C'\fR internally.
5417.IP "pointer accesses must be thread-atomic" 4
5418.IX Item "pointer accesses must be thread-atomic"
5419Accessing a pointer value must be atomic, it must both be readable and
5420writable in one piece \- this is the case on all current architectures.
5421.ie n .IP """sig_atomic_t volatile"" must be thread-atomic as well" 4
5422.el .IP "\f(CWsig_atomic_t volatile\fR must be thread-atomic as well" 4
5423.IX Item "sig_atomic_t volatile must be thread-atomic as well"
5424The type \f(CW\*(C`sig_atomic_t volatile\*(C'\fR (or whatever is defined as
5425\&\f(CW\*(C`EV_ATOMIC_T\*(C'\fR) must be atomic with respect to accesses from different
5426threads. This is not part of the specification for \f(CW\*(C`sig_atomic_t\*(C'\fR, but is
5427believed to be sufficiently portable.
5428.ie n .IP """sigprocmask"" must work in a threaded environment" 4
5429.el .IP "\f(CWsigprocmask\fR must work in a threaded environment" 4
5430.IX Item "sigprocmask must work in a threaded environment"
5431Libev uses \f(CW\*(C`sigprocmask\*(C'\fR to temporarily block signals. This is not
5432allowed in a threaded program (\f(CW\*(C`pthread_sigmask\*(C'\fR has to be used). Typical
5433pthread implementations will either allow \f(CW\*(C`sigprocmask\*(C'\fR in the \*(L"main
5434thread\*(R" or will block signals process-wide, both behaviours would
5435be compatible with libev. Interaction between \f(CW\*(C`sigprocmask\*(C'\fR and
5436\&\f(CW\*(C`pthread_sigmask\*(C'\fR could complicate things, however.
5437.Sp
5438The most portable way to handle signals is to block signals in all threads
5439except the initial one, and run the signal handling loop in the initial
5440thread as well.
5441.ie n .IP """long"" must be large enough for common memory allocation sizes" 4
5442.el .IP "\f(CWlong\fR must be large enough for common memory allocation sizes" 4
5443.IX Item "long must be large enough for common memory allocation sizes"
5444To improve portability and simplify its \s-1API,\s0 libev uses \f(CW\*(C`long\*(C'\fR internally
5445instead of \f(CW\*(C`size_t\*(C'\fR when allocating its data structures. On non-POSIX
5446systems (Microsoft...) this might be unexpectedly low, but is still at
5447least 31 bits everywhere, which is enough for hundreds of millions of
5448watchers.
5449.ie n .IP """double"" must hold a time value in seconds with enough accuracy" 4
5450.el .IP "\f(CWdouble\fR must hold a time value in seconds with enough accuracy" 4
5451.IX Item "double must hold a time value in seconds with enough accuracy"
5452The type \f(CW\*(C`double\*(C'\fR is used to represent timestamps. It is required to
5453have at least 51 bits of mantissa (and 9 bits of exponent), which is
5454good enough for at least into the year 4000 with millisecond accuracy
5455(the design goal for libev). This requirement is overfulfilled by
5456implementations using \s-1IEEE 754,\s0 which is basically all existing ones.
5457.Sp
5458With \s-1IEEE 754\s0 doubles, you get microsecond accuracy until at least the
5459year 2255 (and millisecond accuracy till the year 287396 \- by then, libev
5460is either obsolete or somebody patched it to use \f(CW\*(C`long double\*(C'\fR or
5461something like that, just kidding).
5462.PP
5463If you know of other additional requirements drop me a note.
5464.SH "ALGORITHMIC COMPLEXITIES"
5465.IX Header "ALGORITHMIC COMPLEXITIES"
5466In this section the complexities of (many of) the algorithms used inside
5467libev will be documented. For complexity discussions about backends see
5468the documentation for \f(CW\*(C`ev_default_init\*(C'\fR.
5469.PP
5470All of the following are about amortised time: If an array needs to be
5471extended, libev needs to realloc and move the whole array, but this
5472happens asymptotically rarer with higher number of elements, so O(1) might
5473mean that libev does a lengthy realloc operation in rare cases, but on
5474average it is much faster and asymptotically approaches constant time.
5475.IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4
5476.IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)"
5477This means that, when you have a watcher that triggers in one hour and
5478there are 100 watchers that would trigger before that, then inserting will
5479have to skip roughly seven (\f(CW\*(C`ld 100\*(C'\fR) of these watchers.
5480.IP "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 4
5481.IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)"
5482That means that changing a timer costs less than removing/adding them,
5483as only the relative motion in the event queue has to be paid for.
5484.IP "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)" 4
5485.IX Item "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)"
5486These just add the watcher into an array or at the head of a list.
5487.IP "Stopping check/prepare/idle/fork/async watchers: O(1)" 4
5488.IX Item "Stopping check/prepare/idle/fork/async watchers: O(1)"
5489.PD 0
5490.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4
5491.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))"
5492.PD
5493These watchers are stored in lists, so they need to be walked to find the
5494correct watcher to remove. The lists are usually short (you don't usually
5495have many watchers waiting for the same fd or signal: one is typical, two
5496is rare).
5497.IP "Finding the next timer in each loop iteration: O(1)" 4
5498.IX Item "Finding the next timer in each loop iteration: O(1)"
5499By virtue of using a binary or 4\-heap, the next timer is always found at a
5500fixed position in the storage array.
5501.IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4
5502.IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)"
5503A change means an I/O watcher gets started or stopped, which requires
5504libev to recalculate its status (and possibly tell the kernel, depending
5505on backend and whether \f(CW\*(C`ev_io_set\*(C'\fR was used).
5506.IP "Activating one watcher (putting it into the pending state): O(1)" 4
5507.IX Item "Activating one watcher (putting it into the pending state): O(1)"
5508.PD 0
5509.IP "Priority handling: O(number_of_priorities)" 4
5510.IX Item "Priority handling: O(number_of_priorities)"
5511.PD
5512Priorities are implemented by allocating some space for each
5513priority. When doing priority-based operations, libev usually has to
5514linearly search all the priorities, but starting/stopping and activating
5515watchers becomes O(1) with respect to priority handling.
5516.IP "Sending an ev_async: O(1)" 4
5517.IX Item "Sending an ev_async: O(1)"
5518.PD 0
5519.IP "Processing ev_async_send: O(number_of_async_watchers)" 4
5520.IX Item "Processing ev_async_send: O(number_of_async_watchers)"
5521.IP "Processing signals: O(max_signal_number)" 4
5522.IX Item "Processing signals: O(max_signal_number)"
5523.PD
5524Sending involves a system call \fIiff\fR there were no other \f(CW\*(C`ev_async_send\*(C'\fR
5525calls in the current loop iteration and the loop is currently
5526blocked. Checking for async and signal events involves iterating over all
5527running async watchers or all signal numbers.
5528.SH "PORTING FROM LIBEV 3.X TO 4.X"
5529.IX Header "PORTING FROM LIBEV 3.X TO 4.X"
5530The major version 4 introduced some incompatible changes to the \s-1API.\s0
5531.PP
5532At the moment, the \f(CW\*(C`ev.h\*(C'\fR header file provides compatibility definitions
5533for all changes, so most programs should still compile. The compatibility
5534layer might be removed in later versions of libev, so better update to the
5535new \s-1API\s0 early than late.
5536.ie n .IP """EV_COMPAT3"" backwards compatibility mechanism" 4
5537.el .IP "\f(CWEV_COMPAT3\fR backwards compatibility mechanism" 4
5538.IX Item "EV_COMPAT3 backwards compatibility mechanism"
5539The backward compatibility mechanism can be controlled by
5540\&\f(CW\*(C`EV_COMPAT3\*(C'\fR. See \*(L"\s-1PREPROCESSOR SYMBOLS/MACROS\*(R"\s0 in the \*(L"\s-1EMBEDDING\*(R"\s0
5541section.
5542.ie n .IP """ev_default_destroy"" and ""ev_default_fork"" have been removed" 4
5543.el .IP "\f(CWev_default_destroy\fR and \f(CWev_default_fork\fR have been removed" 4
5544.IX Item "ev_default_destroy and ev_default_fork have been removed"
5545These calls can be replaced easily by their \f(CW\*(C`ev_loop_xxx\*(C'\fR counterparts:
5546.Sp
5547.Vb 2
5548\& ev_loop_destroy (EV_DEFAULT_UC);
5549\& ev_loop_fork (EV_DEFAULT);
5550.Ve
5551.IP "function/symbol renames" 4
5552.IX Item "function/symbol renames"
5553A number of functions and symbols have been renamed:
5554.Sp
5555.Vb 3
5556\& ev_loop => ev_run
5557\& EVLOOP_NONBLOCK => EVRUN_NOWAIT
5558\& EVLOOP_ONESHOT => EVRUN_ONCE
5559\&
5560\& ev_unloop => ev_break
5561\& EVUNLOOP_CANCEL => EVBREAK_CANCEL
5562\& EVUNLOOP_ONE => EVBREAK_ONE
5563\& EVUNLOOP_ALL => EVBREAK_ALL
5564\&
5565\& EV_TIMEOUT => EV_TIMER
5566\&
5567\& ev_loop_count => ev_iteration
5568\& ev_loop_depth => ev_depth
5569\& ev_loop_verify => ev_verify
5570.Ve
5571.Sp
5572Most functions working on \f(CW\*(C`struct ev_loop\*(C'\fR objects don't have an
5573\&\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
5574associated constants have been renamed to not collide with the \f(CW\*(C`struct
5575ev_loop\*(C'\fR anymore and \f(CW\*(C`EV_TIMER\*(C'\fR now follows the same naming scheme
5576as all other watcher types. Note that \f(CW\*(C`ev_loop_fork\*(C'\fR is still called
5577\&\f(CW\*(C`ev_loop_fork\*(C'\fR because it would otherwise clash with the \f(CW\*(C`ev_fork\*(C'\fR
5578typedef.
5579.ie n .IP """EV_MINIMAL"" mechanism replaced by ""EV_FEATURES""" 4
5580.el .IP "\f(CWEV_MINIMAL\fR mechanism replaced by \f(CWEV_FEATURES\fR" 4
5581.IX Item "EV_MINIMAL mechanism replaced by EV_FEATURES"
5582The preprocessor symbol \f(CW\*(C`EV_MINIMAL\*(C'\fR has been replaced by a different
5583mechanism, \f(CW\*(C`EV_FEATURES\*(C'\fR. Programs using \f(CW\*(C`EV_MINIMAL\*(C'\fR usually compile
5584and work, but the library code will of course be larger.
5585.SH "GLOSSARY"
5586.IX Header "GLOSSARY"
5587.IP "active" 4
5588.IX Item "active"
5589A watcher is active as long as it has been started and not yet stopped.
5590See \*(L"\s-1WATCHER STATES\*(R"\s0 for details.
5591.IP "application" 4
5592.IX Item "application"
5593In this document, an application is whatever is using libev.
5594.IP "backend" 4
5595.IX Item "backend"
5596The part of the code dealing with the operating system interfaces.
5597.IP "callback" 4
5598.IX Item "callback"
5599The address of a function that is called when some event has been
5600detected. Callbacks are being passed the event loop, the watcher that
5601received the event, and the actual event bitset.
5602.IP "callback/watcher invocation" 4
5603.IX Item "callback/watcher invocation"
5604The act of calling the callback associated with a watcher.
5605.IP "event" 4
5606.IX Item "event"
5607A change of state of some external event, such as data now being available
5608for reading on a file descriptor, time having passed or simply not having
5609any other events happening anymore.
5610.Sp
5611In libev, events are represented as single bits (such as \f(CW\*(C`EV_READ\*(C'\fR or
5612\&\f(CW\*(C`EV_TIMER\*(C'\fR).
5613.IP "event library" 4
5614.IX Item "event library"
5615A software package implementing an event model and loop.
5616.IP "event loop" 4
5617.IX Item "event loop"
5618An entity that handles and processes external events and converts them
5619into callback invocations.
5620.IP "event model" 4
5621.IX Item "event model"
5622The model used to describe how an event loop handles and processes
5623watchers and events.
5624.IP "pending" 4
5625.IX Item "pending"
5626A watcher is pending as soon as the corresponding event has been
5627detected. See \*(L"\s-1WATCHER STATES\*(R"\s0 for details.
5628.IP "real time" 4
5629.IX Item "real time"
5630The physical time that is observed. It is apparently strictly monotonic :)
5631.IP "wall-clock time" 4
5632.IX Item "wall-clock time"
5633The time and date as shown on clocks. Unlike real time, it can actually
5634be wrong and jump forwards and backwards, e.g. when you adjust your
5635clock.
5636.IP "watcher" 4
5637.IX Item "watcher"
5638A data structure that describes interest in certain events. Watchers need
5639to be started (attached to an event loop) before they can receive events.
1818.SH "AUTHOR" 5640.SH "AUTHOR"
1819.IX Header "AUTHOR" 5641.IX Header "AUTHOR"
1820Marc Lehmann <libev@schmorp.de>. 5642Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5643Magnusson and Emanuele Giaquinta, and minor corrections by many others.

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