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129.\" ======================================================================== 133.\" ========================================================================
130.\" 134.\"
131.IX Title ""<STANDARD INPUT>" 1" 135.IX Title "LIBEV 3"
132.TH "<STANDARD INPUT>" 1 "2007-11-23" "perl v5.8.8" "User Contributed Perl Documentation" 136.TH LIBEV 3 "2020-01-22" "libev-4.31" "libev - high performance full featured event loop"
137.\" For nroff, turn off justification. Always turn off hyphenation; it makes
138.\" way too many mistakes in technical documents.
139.if n .ad l
140.nh
133.SH "NAME" 141.SH "NAME"
134libev \- a high performance full\-featured event loop written in C 142libev \- a high performance full\-featured event loop written in C
135.SH "SYNOPSIS" 143.SH "SYNOPSIS"
136.IX Header "SYNOPSIS" 144.IX Header "SYNOPSIS"
137.Vb 1 145.Vb 1
138\& #include <ev.h> 146\& #include <ev.h>
139.Ve 147.Ve
140.SH "DESCRIPTION" 148.SS "\s-1EXAMPLE PROGRAM\s0"
141.IX Header "DESCRIPTION" 149.IX Subsection "EXAMPLE PROGRAM"
150.Vb 2
151\& // a single header file is required
152\& #include <ev.h>
153\&
154\& #include <stdio.h> // for puts
155\&
156\& // every watcher type has its own typedef\*(Aqd struct
157\& // with the name ev_TYPE
158\& ev_io stdin_watcher;
159\& ev_timer timeout_watcher;
160\&
161\& // all watcher callbacks have a similar signature
162\& // this callback is called when data is readable on stdin
163\& static void
164\& stdin_cb (EV_P_ ev_io *w, int revents)
165\& {
166\& puts ("stdin ready");
167\& // for one\-shot events, one must manually stop the watcher
168\& // with its corresponding stop function.
169\& ev_io_stop (EV_A_ w);
170\&
171\& // this causes all nested ev_run\*(Aqs to stop iterating
172\& ev_break (EV_A_ EVBREAK_ALL);
173\& }
174\&
175\& // another callback, this time for a time\-out
176\& static void
177\& timeout_cb (EV_P_ ev_timer *w, int revents)
178\& {
179\& puts ("timeout");
180\& // this causes the innermost ev_run to stop iterating
181\& ev_break (EV_A_ EVBREAK_ONE);
182\& }
183\&
184\& int
185\& main (void)
186\& {
187\& // use the default event loop unless you have special needs
188\& struct ev_loop *loop = EV_DEFAULT;
189\&
190\& // initialise an io watcher, then start it
191\& // this one will watch for stdin to become readable
192\& ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
193\& ev_io_start (loop, &stdin_watcher);
194\&
195\& // initialise a timer watcher, then start it
196\& // simple non\-repeating 5.5 second timeout
197\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
198\& ev_timer_start (loop, &timeout_watcher);
199\&
200\& // now wait for events to arrive
201\& ev_run (loop, 0);
202\&
203\& // break was called, so exit
204\& return 0;
205\& }
206.Ve
207.SH "ABOUT THIS DOCUMENT"
208.IX Header "ABOUT THIS DOCUMENT"
209This document documents the libev software package.
210.PP
211The newest version of this document is also available as an html-formatted
212web page you might find easier to navigate when reading it for the first
213time: <http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
214.PP
215While this document tries to be as complete as possible in documenting
216libev, its usage and the rationale behind its design, it is not a tutorial
217on event-based programming, nor will it introduce event-based programming
218with libev.
219.PP
220Familiarity with event based programming techniques in general is assumed
221throughout this document.
222.SH "WHAT TO READ WHEN IN A HURRY"
223.IX Header "WHAT TO READ WHEN IN A HURRY"
224This manual tries to be very detailed, but unfortunately, this also makes
225it very long. If you just want to know the basics of libev, I suggest
226reading \*(L"\s-1ANATOMY OF A WATCHER\*(R"\s0, then the \*(L"\s-1EXAMPLE PROGRAM\*(R"\s0 above and
227look up the missing functions in \*(L"\s-1GLOBAL FUNCTIONS\*(R"\s0 and the \f(CW\*(C`ev_io\*(C'\fR and
228\&\f(CW\*(C`ev_timer\*(C'\fR sections in \*(L"\s-1WATCHER TYPES\*(R"\s0.
229.SH "ABOUT LIBEV"
230.IX Header "ABOUT LIBEV"
142Libev is an event loop: you register interest in certain events (such as a 231Libev is an event loop: you register interest in certain events (such as a
143file descriptor being readable or a timeout occuring), and it will manage 232file descriptor being readable or a timeout occurring), and it will manage
144these event sources and provide your program with events. 233these event sources and provide your program with events.
145.PP 234.PP
146To do this, it must take more or less complete control over your process 235To do this, it must take more or less complete control over your process
147(or thread) by executing the \fIevent loop\fR handler, and will then 236(or thread) by executing the \fIevent loop\fR handler, and will then
148communicate events via a callback mechanism. 237communicate events via a callback mechanism.
149.PP 238.PP
150You register interest in certain events by registering so-called \fIevent 239You register interest in certain events by registering so-called \fIevent
151watchers\fR, which are relatively small C structures you initialise with the 240watchers\fR, which are relatively small C structures you initialise with the
152details of the event, and then hand it over to libev by \fIstarting\fR the 241details of the event, and then hand it over to libev by \fIstarting\fR the
153watcher. 242watcher.
154.SH "FEATURES" 243.SS "\s-1FEATURES\s0"
155.IX Header "FEATURES" 244.IX Subsection "FEATURES"
156Libev supports select, poll, the linux-specific epoll and the bsd-specific 245Libev supports \f(CW\*(C`select\*(C'\fR, \f(CW\*(C`poll\*(C'\fR, the Linux-specific aio and \f(CW\*(C`epoll\*(C'\fR
157kqueue mechanisms for file descriptor events, relative timers, absolute 246interfaces, the BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port
158timers with customised rescheduling, signal events, process status change 247mechanisms for file descriptor events (\f(CW\*(C`ev_io\*(C'\fR), the Linux \f(CW\*(C`inotify\*(C'\fR
159events (related to \s-1SIGCHLD\s0), and event watchers dealing with the event 248interface (for \f(CW\*(C`ev_stat\*(C'\fR), Linux eventfd/signalfd (for faster and cleaner
160loop mechanism itself (idle, prepare and check watchers). It also is quite 249inter-thread wakeup (\f(CW\*(C`ev_async\*(C'\fR)/signal handling (\f(CW\*(C`ev_signal\*(C'\fR)) relative
161fast (see this benchmark comparing 250timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers with customised rescheduling
162it to libevent for example). 251(\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals (\f(CW\*(C`ev_signal\*(C'\fR), process status
252change events (\f(CW\*(C`ev_child\*(C'\fR), and event watchers dealing with the event
253loop mechanism itself (\f(CW\*(C`ev_idle\*(C'\fR, \f(CW\*(C`ev_embed\*(C'\fR, \f(CW\*(C`ev_prepare\*(C'\fR and
254\&\f(CW\*(C`ev_check\*(C'\fR watchers) as well as file watchers (\f(CW\*(C`ev_stat\*(C'\fR) and even
255limited support for fork events (\f(CW\*(C`ev_fork\*(C'\fR).
256.PP
257It also is quite fast (see this
258benchmark <http://libev.schmorp.de/bench.html> comparing it to libevent
259for example).
163.SH "CONVENTIONS" 260.SS "\s-1CONVENTIONS\s0"
164.IX Header "CONVENTIONS" 261.IX Subsection "CONVENTIONS"
165Libev is very configurable. In this manual the default configuration 262Libev is very configurable. In this manual the default (and most common)
166will be described, which supports multiple event loops. For more info 263configuration will be described, which supports multiple event loops. For
167about various configuration options please have a look at the file 264more info about various configuration options please have a look at
168\&\fI\s-1README\s0.embed\fR in the libev distribution. If libev was configured without 265\&\fB\s-1EMBED\s0\fR section in this manual. If libev was configured without support
169support for multiple event loops, then all functions taking an initial 266for multiple event loops, then all functions taking an initial argument of
170argument of name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) 267name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) will not have
171will not have this argument. 268this argument.
172.SH "TIME REPRESENTATION" 269.SS "\s-1TIME REPRESENTATION\s0"
173.IX Header "TIME REPRESENTATION" 270.IX Subsection "TIME REPRESENTATION"
174Libev represents time as a single floating point number, representing the 271Libev represents time as a single floating point number, representing
175(fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere near 272the (fractional) number of seconds since the (\s-1POSIX\s0) epoch (in practice
176the beginning of 1970, details are complicated, don't ask). This type is 273somewhere near the beginning of 1970, details are complicated, don't
177called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use too. It usually aliases 274ask). This type is called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use
178to the \f(CW\*(C`double\*(C'\fR type in C, and when you need to do any calculations on 275too. It usually aliases to the \f(CW\*(C`double\*(C'\fR type in C. When you need to do
179it, you should treat it as such. 276any calculations on it, you should treat it as some floating point value.
277.PP
278Unlike the name component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for
279time differences (e.g. delays) throughout libev.
280.SH "ERROR HANDLING"
281.IX Header "ERROR HANDLING"
282Libev knows three classes of errors: operating system errors, usage errors
283and internal errors (bugs).
284.PP
285When libev catches an operating system error it cannot handle (for example
286a system call indicating a condition libev cannot fix), it calls the callback
287set via \f(CW\*(C`ev_set_syserr_cb\*(C'\fR, which is supposed to fix the problem or
288abort. The default is to print a diagnostic message and to call \f(CW\*(C`abort
289()\*(C'\fR.
290.PP
291When libev detects a usage error such as a negative timer interval, then
292it will print a diagnostic message and abort (via the \f(CW\*(C`assert\*(C'\fR mechanism,
293so \f(CW\*(C`NDEBUG\*(C'\fR will disable this checking): these are programming errors in
294the libev caller and need to be fixed there.
295.PP
296Via the \f(CW\*(C`EV_FREQUENT\*(C'\fR macro you can compile in and/or enable extensive
297consistency checking code inside libev that can be used to check for
298internal inconsistencies, suually caused by application bugs.
299.PP
300Libev also has a few internal error-checking \f(CW\*(C`assert\*(C'\fRions. These do not
301trigger under normal circumstances, as they indicate either a bug in libev
302or worse.
180.SH "GLOBAL FUNCTIONS" 303.SH "GLOBAL FUNCTIONS"
181.IX Header "GLOBAL FUNCTIONS" 304.IX Header "GLOBAL FUNCTIONS"
182These functions can be called anytime, even before initialising the 305These functions can be called anytime, even before initialising the
183library in any way. 306library in any way.
184.IP "ev_tstamp ev_time ()" 4 307.IP "ev_tstamp ev_time ()" 4
185.IX Item "ev_tstamp ev_time ()" 308.IX Item "ev_tstamp ev_time ()"
186Returns the current time as libev would use it. Please note that the 309Returns 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 310\&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp
188you actually want to know. 311you actually want to know. Also interesting is the combination of
312\&\f(CW\*(C`ev_now_update\*(C'\fR and \f(CW\*(C`ev_now\*(C'\fR.
313.IP "ev_sleep (ev_tstamp interval)" 4
314.IX Item "ev_sleep (ev_tstamp interval)"
315Sleep for the given interval: The current thread will be blocked
316until either it is interrupted or the given time interval has
317passed (approximately \- it might return a bit earlier even if not
318interrupted). Returns immediately if \f(CW\*(C`interval <= 0\*(C'\fR.
319.Sp
320Basically this is a sub-second-resolution \f(CW\*(C`sleep ()\*(C'\fR.
321.Sp
322The range of the \f(CW\*(C`interval\*(C'\fR is limited \- libev only guarantees to work
323with sleep times of up to one day (\f(CW\*(C`interval <= 86400\*(C'\fR).
189.IP "int ev_version_major ()" 4 324.IP "int ev_version_major ()" 4
190.IX Item "int ev_version_major ()" 325.IX Item "int ev_version_major ()"
191.PD 0 326.PD 0
192.IP "int ev_version_minor ()" 4 327.IP "int ev_version_minor ()" 4
193.IX Item "int ev_version_minor ()" 328.IX Item "int ev_version_minor ()"
194.PD 329.PD
195You can find out the major and minor version numbers of the library 330You 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 331you 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 332\&\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 333symbols \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. 334version of the library your program was compiled against.
200.Sp 335.Sp
336These version numbers refer to the \s-1ABI\s0 version of the library, not the
337release version.
338.Sp
201Usually, it's a good idea to terminate if the major versions mismatch, 339Usually, it's a good idea to terminate if the major versions mismatch,
202as this indicates an incompatible change. Minor versions are usually 340as this indicates an incompatible change. Minor versions are usually
203compatible to older versions, so a larger minor version alone is usually 341compatible to older versions, so a larger minor version alone is usually
204not a problem. 342not a problem.
205.Sp 343.Sp
206Example: make sure we haven't accidentally been linked against the wrong 344Example: Make sure we haven't accidentally been linked against the wrong
207version: 345version (note, however, that this will not detect other \s-1ABI\s0 mismatches,
346such as \s-1LFS\s0 or reentrancy).
208.Sp 347.Sp
209.Vb 3 348.Vb 3
210\& assert (("libev version mismatch", 349\& assert (("libev version mismatch",
211\& ev_version_major () == EV_VERSION_MAJOR 350\& ev_version_major () == EV_VERSION_MAJOR
212\& && ev_version_minor () >= EV_VERSION_MINOR)); 351\& && ev_version_minor () >= EV_VERSION_MINOR));
213.Ve 352.Ve
214.IP "unsigned int ev_supported_backends ()" 4 353.IP "unsigned int ev_supported_backends ()" 4
215.IX Item "unsigned int ev_supported_backends ()" 354.IX Item "unsigned int ev_supported_backends ()"
216Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR 355Return 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 356value) compiled into this binary of libev (independent of their
… …
220.Sp 359.Sp
221Example: make sure we have the epoll method, because yeah this is cool and 360Example: 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 361a must have and can we have a torrent of it please!!!11
223.Sp 362.Sp
224.Vb 2 363.Vb 2
225\& assert (("sorry, no epoll, no sex", 364\& assert (("sorry, no epoll, no sex",
226\& ev_supported_backends () & EVBACKEND_EPOLL)); 365\& ev_supported_backends () & EVBACKEND_EPOLL));
227.Ve 366.Ve
228.IP "unsigned int ev_recommended_backends ()" 4 367.IP "unsigned int ev_recommended_backends ()" 4
229.IX Item "unsigned int ev_recommended_backends ()" 368.IX Item "unsigned int ev_recommended_backends ()"
230Return the set of all backends compiled into this binary of libev and also 369Return the set of all backends compiled into this binary of libev and
231recommended for this platform. This set is often smaller than the one 370also recommended for this platform, meaning it will work for most file
371descriptor 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 372\&\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 373and 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 374you know what you are doing). This is the set of backends that libev will
235libev will probe for if you specify no backends explicitly. 375probe for if you specify no backends explicitly.
376.IP "unsigned int ev_embeddable_backends ()" 4
377.IX Item "unsigned int ev_embeddable_backends ()"
378Returns the set of backends that are embeddable in other event loops. This
379value is platform-specific but can include backends not available on the
380current system. To find which embeddable backends might be supported on
381the current system, you would need to look at \f(CW\*(C`ev_embeddable_backends ()
382& ev_supported_backends ()\*(C'\fR, likewise for recommended ones.
383.Sp
384See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
236.IP "ev_set_allocator (void *(*cb)(void *ptr, long size))" 4 385.IP "ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())" 4
237.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))" 386.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())"
238Sets the allocation function to use (the prototype is similar to the 387Sets the allocation function to use (the prototype is similar \- the
239realloc C function, the semantics are identical). It is used to allocate 388semantics are identical to the \f(CW\*(C`realloc\*(C'\fR C89/SuS/POSIX function). It is
240and free memory (no surprises here). If it returns zero when memory 389used to allocate and free memory (no surprises here). If it returns zero
241needs to be allocated, the library might abort or take some potentially 390when memory needs to be allocated (\f(CW\*(C`size != 0\*(C'\fR), the library might abort
242destructive action. The default is your system realloc function. 391or take some potentially destructive action.
392.Sp
393Since some systems (at least OpenBSD and Darwin) fail to implement
394correct \f(CW\*(C`realloc\*(C'\fR semantics, libev will use a wrapper around the system
395\&\f(CW\*(C`realloc\*(C'\fR and \f(CW\*(C`free\*(C'\fR functions by default.
243.Sp 396.Sp
244You could override this function in high-availability programs to, say, 397You could override this function in high-availability programs to, say,
245free some memory if it cannot allocate memory, to use a special allocator, 398free some memory if it cannot allocate memory, to use a special allocator,
246or even to sleep a while and retry until some memory is available. 399or even to sleep a while and retry until some memory is available.
247.Sp 400.Sp
248Example: replace the libev allocator with one that waits a bit and then 401Example: The following is the \f(CW\*(C`realloc\*(C'\fR function that libev itself uses
249retries: better than mine). 402which should work with \f(CW\*(C`realloc\*(C'\fR and \f(CW\*(C`free\*(C'\fR functions of all kinds and
403is probably a good basis for your own implementation.
250.Sp 404.Sp
251.Vb 6 405.Vb 5
252\& static void * 406\& static void *
253\& persistent_realloc (void *ptr, long size) 407\& ev_realloc_emul (void *ptr, long size) EV_NOEXCEPT
254\& { 408\& {
409\& if (size)
410\& return realloc (ptr, size);
411\&
412\& free (ptr);
413\& return 0;
414\& }
415.Ve
416.Sp
417Example: Replace the libev allocator with one that waits a bit and then
418retries.
419.Sp
420.Vb 8
421\& static void *
422\& persistent_realloc (void *ptr, size_t size)
423\& {
424\& if (!size)
425\& {
426\& free (ptr);
427\& return 0;
428\& }
429\&
255\& for (;;) 430\& for (;;)
256\& { 431\& {
257\& void *newptr = realloc (ptr, size); 432\& void *newptr = realloc (ptr, size);
258.Ve 433\&
259.Sp
260.Vb 2
261\& if (newptr) 434\& if (newptr)
262\& return newptr; 435\& return newptr;
263.Ve 436\&
264.Sp
265.Vb 3
266\& sleep (60); 437\& sleep (60);
267\& } 438\& }
268\& } 439\& }
269.Ve 440\&
270.Sp
271.Vb 2
272\& ... 441\& ...
273\& ev_set_allocator (persistent_realloc); 442\& ev_set_allocator (persistent_realloc);
274.Ve 443.Ve
275.IP "ev_set_syserr_cb (void (*cb)(const char *msg));" 4 444.IP "ev_set_syserr_cb (void (*cb)(const char *msg) throw ())" 4
276.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg));" 445.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg) throw ())"
277Set the callback function to call on a retryable syscall error (such 446Set the callback function to call on a retryable system call error (such
278as failed select, poll, epoll_wait). The message is a printable string 447as failed select, poll, epoll_wait). The message is a printable string
279indicating the system call or subsystem causing the problem. If this 448indicating the system call or subsystem causing the problem. If this
280callback is set, then libev will expect it to remedy the sitution, no 449callback is set, then libev will expect it to remedy the situation, no
281matter what, when it returns. That is, libev will generally retry the 450matter what, when it returns. That is, libev will generally retry the
282requested operation, or, if the condition doesn't go away, do bad stuff 451requested operation, or, if the condition doesn't go away, do bad stuff
283(such as abort). 452(such as abort).
284.Sp 453.Sp
285Example: do the same thing as libev does internally: 454Example: This is basically the same thing that libev does internally, too.
286.Sp 455.Sp
287.Vb 6 456.Vb 6
288\& static void 457\& static void
289\& fatal_error (const char *msg) 458\& fatal_error (const char *msg)
290\& { 459\& {
291\& perror (msg); 460\& perror (msg);
292\& abort (); 461\& abort ();
293\& } 462\& }
294.Ve 463\&
295.Sp
296.Vb 2
297\& ... 464\& ...
298\& ev_set_syserr_cb (fatal_error); 465\& ev_set_syserr_cb (fatal_error);
299.Ve 466.Ve
467.IP "ev_feed_signal (int signum)" 4
468.IX Item "ev_feed_signal (int signum)"
469This function can be used to \*(L"simulate\*(R" a signal receive. It is completely
470safe to call this function at any time, from any context, including signal
471handlers or random threads.
472.Sp
473Its main use is to customise signal handling in your process, especially
474in the presence of threads. For example, you could block signals
475by default in all threads (and specifying \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when
476creating any loops), and in one thread, use \f(CW\*(C`sigwait\*(C'\fR or any other
477mechanism to wait for signals, then \*(L"deliver\*(R" them to libev by calling
478\&\f(CW\*(C`ev_feed_signal\*(C'\fR.
300.SH "FUNCTIONS CONTROLLING THE EVENT LOOP" 479.SH "FUNCTIONS CONTROLLING EVENT LOOPS"
301.IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP" 480.IX Header "FUNCTIONS CONTROLLING EVENT LOOPS"
302An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR. The library knows two 481An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR (the \f(CW\*(C`struct\*(C'\fR is
303types of such loops, the \fIdefault\fR loop, which supports signals and child 482\&\fInot\fR optional in this case unless libev 3 compatibility is disabled, as
304events, and dynamically created loops which do not. 483libev 3 had an \f(CW\*(C`ev_loop\*(C'\fR function colliding with the struct name).
305.PP 484.PP
306If you use threads, a common model is to run the default event loop 485The library knows two types of such loops, the \fIdefault\fR loop, which
307in your main thread (or in a separate thread) and for each thread you 486supports child process events, and dynamically created event loops which
308create, you also create another event loop. Libev itself does no locking 487do not.
309whatsoever, so if you mix calls to the same event loop in different
310threads, make sure you lock (this is usually a bad idea, though, even if
311done correctly, because it's hideous and inefficient).
312.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4 488.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
313.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)" 489.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
314This will initialise the default event loop if it hasn't been initialised 490This returns the \*(L"default\*(R" event loop object, which is what you should
315yet and return it. If the default loop could not be initialised, returns 491normally use when you just need \*(L"the event loop\*(R". Event loop objects and
316false. If it already was initialised it simply returns it (and ignores the 492the \f(CW\*(C`flags\*(C'\fR parameter are described in more detail in the entry for
317flags. If that is troubling you, check \f(CW\*(C`ev_backend ()\*(C'\fR afterwards). 493\&\f(CW\*(C`ev_loop_new\*(C'\fR.
494.Sp
495If the default loop is already initialised then this function simply
496returns it (and ignores the flags. If that is troubling you, check
497\&\f(CW\*(C`ev_backend ()\*(C'\fR afterwards). Otherwise it will create it with the given
498flags, which should almost always be \f(CW0\fR, unless the caller is also the
499one calling \f(CW\*(C`ev_run\*(C'\fR or otherwise qualifies as \*(L"the main program\*(R".
318.Sp 500.Sp
319If you don't know what event loop to use, use the one returned from this 501If you don't know what event loop to use, use the one returned from this
320function. 502function (or via the \f(CW\*(C`EV_DEFAULT\*(C'\fR macro).
503.Sp
504Note that this function is \fInot\fR thread-safe, so if you want to use it
505from multiple threads, you have to employ some kind of mutex (note also
506that this case is unlikely, as loops cannot be shared easily between
507threads anyway).
508.Sp
509The default loop is the only loop that can handle \f(CW\*(C`ev_child\*(C'\fR watchers,
510and to do this, it always registers a handler for \f(CW\*(C`SIGCHLD\*(C'\fR. If this is
511a problem for your application you can either create a dynamic loop with
512\&\f(CW\*(C`ev_loop_new\*(C'\fR which doesn't do that, or you can simply overwrite the
513\&\f(CW\*(C`SIGCHLD\*(C'\fR signal handler \fIafter\fR calling \f(CW\*(C`ev_default_init\*(C'\fR.
514.Sp
515Example: This is the most typical usage.
516.Sp
517.Vb 2
518\& if (!ev_default_loop (0))
519\& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
520.Ve
521.Sp
522Example: Restrict libev to the select and poll backends, and do not allow
523environment settings to be taken into account:
524.Sp
525.Vb 1
526\& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
527.Ve
528.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
529.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
530This will create and initialise a new event loop object. If the loop
531could not be initialised, returns false.
532.Sp
533This function is thread-safe, and one common way to use libev with
534threads is indeed to create one loop per thread, and using the default
535loop in the \*(L"main\*(R" or \*(L"initial\*(R" thread.
321.Sp 536.Sp
322The flags argument can be used to specify special behaviour or specific 537The flags argument can be used to specify special behaviour or specific
323backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). 538backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).
324.Sp 539.Sp
325The following flags are supported: 540The following flags are supported:
… …
330The default flags value. Use this if you have no clue (it's the right 545The default flags value. Use this if you have no clue (it's the right
331thing, believe me). 546thing, believe me).
332.ie n .IP """EVFLAG_NOENV""" 4 547.ie n .IP """EVFLAG_NOENV""" 4
333.el .IP "\f(CWEVFLAG_NOENV\fR" 4 548.el .IP "\f(CWEVFLAG_NOENV\fR" 4
334.IX Item "EVFLAG_NOENV" 549.IX Item "EVFLAG_NOENV"
335If this flag bit is ored into the flag value (or the program runs setuid 550If this flag bit is or'ed into the flag value (or the program runs setuid
336or setgid) then libev will \fInot\fR look at the environment variable 551or setgid) then libev will \fInot\fR look at the environment variable
337\&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will 552\&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will
338override the flags completely if it is found in the environment. This is 553override the flags completely if it is found in the environment. This is
339useful to try out specific backends to test their performance, or to work 554useful to try out specific backends to test their performance, to work
340around bugs. 555around bugs, or to make libev threadsafe (accessing environment variables
556cannot be done in a threadsafe way, but usually it works if no other
557thread modifies them).
558.ie n .IP """EVFLAG_FORKCHECK""" 4
559.el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4
560.IX Item "EVFLAG_FORKCHECK"
561Instead of calling \f(CW\*(C`ev_loop_fork\*(C'\fR manually after a fork, you can also
562make libev check for a fork in each iteration by enabling this flag.
563.Sp
564This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop,
565and thus this might slow down your event loop if you do a lot of loop
566iterations and little real work, but is usually not noticeable (on my
567GNU/Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn
568sequence without a system call and thus \fIvery\fR fast, but my GNU/Linux
569system also has \f(CW\*(C`pthread_atfork\*(C'\fR which is even faster). (Update: glibc
570versions 2.25 apparently removed the \f(CW\*(C`getpid\*(C'\fR optimisation again).
571.Sp
572The big advantage of this flag is that you can forget about fork (and
573forget about forgetting to tell libev about forking, although you still
574have to ignore \f(CW\*(C`SIGPIPE\*(C'\fR) when you use this flag.
575.Sp
576This flag setting cannot be overridden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR
577environment variable.
578.ie n .IP """EVFLAG_NOINOTIFY""" 4
579.el .IP "\f(CWEVFLAG_NOINOTIFY\fR" 4
580.IX Item "EVFLAG_NOINOTIFY"
581When this flag is specified, then libev will not attempt to use the
582\&\fIinotify\fR \s-1API\s0 for its \f(CW\*(C`ev_stat\*(C'\fR watchers. Apart from debugging and
583testing, this flag can be useful to conserve inotify file descriptors, as
584otherwise each loop using \f(CW\*(C`ev_stat\*(C'\fR watchers consumes one inotify handle.
585.ie n .IP """EVFLAG_SIGNALFD""" 4
586.el .IP "\f(CWEVFLAG_SIGNALFD\fR" 4
587.IX Item "EVFLAG_SIGNALFD"
588When this flag is specified, then libev will attempt to use the
589\&\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
590delivers signals synchronously, which makes it both faster and might make
591it possible to get the queued signal data. It can also simplify signal
592handling with threads, as long as you properly block signals in your
593threads that are not interested in handling them.
594.Sp
595Signalfd will not be used by default as this changes your signal mask, and
596there are a lot of shoddy libraries and programs (glib's threadpool for
597example) that can't properly initialise their signal masks.
598.ie n .IP """EVFLAG_NOSIGMASK""" 4
599.el .IP "\f(CWEVFLAG_NOSIGMASK\fR" 4
600.IX Item "EVFLAG_NOSIGMASK"
601When this flag is specified, then libev will avoid to modify the signal
602mask. Specifically, this means you have to make sure signals are unblocked
603when you want to receive them.
604.Sp
605This behaviour is useful when you want to do your own signal handling, or
606want to handle signals only in specific threads and want to avoid libev
607unblocking the signals.
608.Sp
609It's also required by \s-1POSIX\s0 in a threaded program, as libev calls
610\&\f(CW\*(C`sigprocmask\*(C'\fR, whose behaviour is officially unspecified.
611.ie n .IP """EVFLAG_NOTIMERFD""" 4
612.el .IP "\f(CWEVFLAG_NOTIMERFD\fR" 4
613.IX Item "EVFLAG_NOTIMERFD"
614When this flag is specified, the libev will avoid using a \f(CW\*(C`timerfd\*(C'\fR to
615detect time jumps. It will still be able to detect time jumps, but takes
616longer and has a lower accuracy in doing so, but saves a file descriptor
617per loop.
618.Sp
619The current implementation only tries to use a \f(CW\*(C`timerfd\*(C'\fR when the first
620\&\f(CW\*(C`ev_periodic\*(C'\fR watcher is started and falls back on other methods if it
621cannot be created, but this behaviour might change in the future.
341.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4 622.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
342.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4 623.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
343.IX Item "EVBACKEND_SELECT (value 1, portable select backend)" 624.IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
344This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as 625This is your standard \fBselect\fR\|(2) backend. Not \fIcompletely\fR standard, as
345libev tries to roll its own fd_set with no limits on the number of fds, 626libev tries to roll its own fd_set with no limits on the number of fds,
346but if that fails, expect a fairly low limit on the number of fds when 627but if that fails, expect a fairly low limit on the number of fds when
347using this backend. It doesn't scale too well (O(highest_fd)), but its usually 628using this backend. It doesn't scale too well (O(highest_fd)), but its
348the fastest backend for a low number of fds. 629usually the fastest backend for a low number of (low-numbered :) fds.
630.Sp
631To get good performance out of this backend you need a high amount of
632parallelism (most of the file descriptors should be busy). If you are
633writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many
634connections as possible during one iteration. You might also want to have
635a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of
636readiness notifications you get per iteration.
637.Sp
638This 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
639\&\f(CW\*(C`writefds\*(C'\fR set (and to work around Microsoft Windows bugs, also onto the
640\&\f(CW\*(C`exceptfds\*(C'\fR set on that platform).
349.ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4 641.ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4
350.el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4 642.el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4
351.IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)" 643.IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)"
352And this is your standard \fIpoll\fR\|(2) backend. It's more complicated than 644And this is your standard \fBpoll\fR\|(2) backend. It's more complicated
353select, but handles sparse fds better and has no artificial limit on the 645than select, but handles sparse fds better and has no artificial
354number of fds you can use (except it will slow down considerably with a 646limit on the number of fds you can use (except it will slow down
355lot of inactive fds). It scales similarly to select, i.e. O(total_fds). 647considerably with a lot of inactive fds). It scales similarly to select,
648i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for
649performance tips.
650.Sp
651This backend maps \f(CW\*(C`EV_READ\*(C'\fR to \f(CW\*(C`POLLIN | POLLERR | POLLHUP\*(C'\fR, and
652\&\f(CW\*(C`EV_WRITE\*(C'\fR to \f(CW\*(C`POLLOUT | POLLERR | POLLHUP\*(C'\fR.
356.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4 653.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
357.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4 654.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
358.IX Item "EVBACKEND_EPOLL (value 4, Linux)" 655.IX Item "EVBACKEND_EPOLL (value 4, Linux)"
656Use the Linux-specific \fBepoll\fR\|(7) interface (for both pre\- and post\-2.6.9
657kernels).
658.Sp
359For few fds, this backend is a bit little slower than poll and select, 659For few fds, this backend is a bit little slower than poll and select, but
360but it scales phenomenally better. While poll and select usually scale like 660it scales phenomenally better. While poll and select usually scale like
361O(total_fds) where n is the total number of fds (or the highest fd), epoll scales 661O(total_fds) where total_fds is the total number of fds (or the highest
362either O(1) or O(active_fds). 662fd), epoll scales either O(1) or O(active_fds).
363.Sp 663.Sp
664The epoll mechanism deserves honorable mention as the most misdesigned
665of the more advanced event mechanisms: mere annoyances include silently
666dropping file descriptors, requiring a system call per change per file
667descriptor (and unnecessary guessing of parameters), problems with dup,
668returning before the timeout value, resulting in additional iterations
669(and only giving 5ms accuracy while select on the same platform gives
6700.1ms) and so on. The biggest issue is fork races, however \- if a program
671forks then \fIboth\fR parent and child process have to recreate the epoll
672set, which can take considerable time (one syscall per file descriptor)
673and is of course hard to detect.
674.Sp
675Epoll is also notoriously buggy \- embedding epoll fds \fIshould\fR work,
676but of course \fIdoesn't\fR, and epoll just loves to report events for
677totally \fIdifferent\fR file descriptors (even already closed ones, so
678one cannot even remove them from the set) than registered in the set
679(especially on \s-1SMP\s0 systems). Libev tries to counter these spurious
680notifications by employing an additional generation counter and comparing
681that against the events to filter out spurious ones, recreating the set
682when required. Epoll also erroneously rounds down timeouts, but gives you
683no way to know when and by how much, so sometimes you have to busy-wait
684because epoll returns immediately despite a nonzero timeout. And last
685not least, it also refuses to work with some file descriptors which work
686perfectly fine with \f(CW\*(C`select\*(C'\fR (files, many character devices...).
687.Sp
688Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
689cobbled together in a hurry, no thought to design or interaction with
690others. Oh, the pain, will it ever stop...
691.Sp
364While stopping and starting an I/O watcher in the same iteration will 692While stopping, setting and starting an I/O watcher in the same iteration
365result in some caching, there is still a syscall per such incident 693will result in some caching, there is still a system call per such
366(because the fd could point to a different file description now), so its 694incident (because the same \fIfile descriptor\fR could point to a different
367best to avoid that. Also, \fIdup()\fRed file descriptors might not work very 695\&\fIfile description\fR now), so its best to avoid that. Also, \f(CW\*(C`dup ()\*(C'\fR'ed
368well if you register events for both fds. 696file descriptors might not work very well if you register events for both
697file descriptors.
369.Sp 698.Sp
370Please note that epoll sometimes generates spurious notifications, so you 699Best performance from this backend is achieved by not unregistering all
371need to use non-blocking I/O or other means to avoid blocking when no data 700watchers for a file descriptor until it has been closed, if possible,
372(or space) is available. 701i.e. keep at least one watcher active per fd at all times. Stopping and
702starting a watcher (without re-setting it) also usually doesn't cause
703extra overhead. A fork can both result in spurious notifications as well
704as in libev having to destroy and recreate the epoll object, which can
705take considerable time and thus should be avoided.
706.Sp
707All this means that, in practice, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR can be as fast or
708faster than epoll for maybe up to a hundred file descriptors, depending on
709the usage. So sad.
710.Sp
711While nominally embeddable in other event loops, this feature is broken in
712a lot of kernel revisions, but probably(!) works in current versions.
713.Sp
714This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
715\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
716.ie n .IP """EVBACKEND_LINUXAIO"" (value 64, Linux)" 4
717.el .IP "\f(CWEVBACKEND_LINUXAIO\fR (value 64, Linux)" 4
718.IX Item "EVBACKEND_LINUXAIO (value 64, Linux)"
719Use the Linux-specific Linux \s-1AIO\s0 (\fInot\fR \f(CWaio(7)\fR but \f(CWio_submit(2)\fR) event interface available in post\-4.18 kernels (but libev
720only tries to use it in 4.19+).
721.Sp
722This is another Linux train wreck of an event interface.
723.Sp
724If this backend works for you (as of this writing, it was very
725experimental), it is the best event interface available on Linux and might
726be well worth enabling it \- if it isn't available in your kernel this will
727be detected and this backend will be skipped.
728.Sp
729This backend can batch oneshot requests and supports a user-space ring
730buffer to receive events. It also doesn't suffer from most of the design
731problems of epoll (such as not being able to remove event sources from
732the epoll set), and generally sounds too good to be true. Because, this
733being the Linux kernel, of course it suffers from a whole new set of
734limitations, forcing you to fall back to epoll, inheriting all its design
735issues.
736.Sp
737For one, it is not easily embeddable (but probably could be done using
738an event fd at some extra overhead). It also is subject to a system wide
739limit that can be configured in \fI/proc/sys/fs/aio\-max\-nr\fR. If no \s-1AIO\s0
740requests are left, this backend will be skipped during initialisation, and
741will switch to epoll when the loop is active.
742.Sp
743Most problematic in practice, however, is that not all file descriptors
744work with it. For example, in Linux 5.1, \s-1TCP\s0 sockets, pipes, event fds,
745files, \fI/dev/null\fR and many others are supported, but ttys do not work
746properly (a known bug that the kernel developers don't care about, see
747<https://lore.kernel.org/patchwork/patch/1047453/>), so this is not
748(yet?) a generic event polling interface.
749.Sp
750Overall, it seems the Linux developers just don't want it to have a
751generic event handling mechanism other than \f(CW\*(C`select\*(C'\fR or \f(CW\*(C`poll\*(C'\fR.
752.Sp
753To work around all these problem, the current version of libev uses its
754epoll backend as a fallback for file descriptor types that do not work. Or
755falls back completely to epoll if the kernel acts up.
756.Sp
757This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
758\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
373.ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4 759.ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4
374.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4 760.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
375.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)" 761.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
376Kqueue deserves special mention, as at the time of this writing, it 762Kqueue deserves special mention, as at the time this backend was
377was broken on all BSDs except NetBSD (usually it doesn't work with 763implemented, it was broken on all BSDs except NetBSD (usually it doesn't
378anything but sockets and pipes, except on Darwin, where of course its 764work reliably with anything but sockets and pipes, except on Darwin,
379completely useless). For this reason its not being \*(L"autodetected\*(R" 765where of course it's completely useless). Unlike epoll, however, whose
380unless you explicitly specify it explicitly in the flags (i.e. using 766brokenness is by design, these kqueue bugs can be (and mostly have been)
381\&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR). 767fixed without \s-1API\s0 changes to existing programs. For this reason it's not
768being \*(L"auto-detected\*(R" on all platforms unless you explicitly specify it
769in the flags (i.e. using \f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a
770known-to-be-good (\-enough) system like NetBSD.
771.Sp
772You still can embed kqueue into a normal poll or select backend and use it
773only for sockets (after having made sure that sockets work with kqueue on
774the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
382.Sp 775.Sp
383It scales in the same way as the epoll backend, but the interface to the 776It scales in the same way as the epoll backend, but the interface to the
384kernel is more efficient (which says nothing about its actual speed, of 777kernel is more efficient (which says nothing about its actual speed, of
385course). While starting and stopping an I/O watcher does not cause an 778course). While stopping, setting and starting an I/O watcher does never
386extra syscall as with epoll, it still adds up to four event changes per 779cause an extra system call as with \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to
387incident, so its best to avoid that. 780two event changes per incident. Support for \f(CW\*(C`fork ()\*(C'\fR is very bad (you
781might have to leak fds on fork, but it's more sane than epoll) and it
782drops fds silently in similarly hard-to-detect cases.
783.Sp
784This backend usually performs well under most conditions.
785.Sp
786While nominally embeddable in other event loops, this doesn't work
787everywhere, so you might need to test for this. And since it is broken
788almost everywhere, you should only use it when you have a lot of sockets
789(for which it usually works), by embedding it into another event loop
790(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
791also broken on \s-1OS X\s0)) and, did I mention it, using it only for sockets.
792.Sp
793This backend maps \f(CW\*(C`EV_READ\*(C'\fR into an \f(CW\*(C`EVFILT_READ\*(C'\fR kevent with
794\&\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
795\&\f(CW\*(C`NOTE_EOF\*(C'\fR.
388.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4 796.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
389.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4 797.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
390.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)" 798.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
391This is not implemented yet (and might never be). 799This is not implemented yet (and might never be, unless you send me an
800implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets
801and is not embeddable, which would limit the usefulness of this backend
802immensely.
392.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4 803.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
393.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4 804.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
394.IX Item "EVBACKEND_PORT (value 32, Solaris 10)" 805.IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
395This uses the Solaris 10 port mechanism. As with everything on Solaris, 806This uses the Solaris 10 event port mechanism. As with everything on Solaris,
396it's really slow, but it still scales very well (O(active_fds)). 807it's really slow, but it still scales very well (O(active_fds)).
397.Sp 808.Sp
398Please note that solaris ports can result in a lot of spurious 809While this backend scales well, it requires one system call per active
399notifications, so you need to use non-blocking I/O or other means to avoid 810file descriptor per loop iteration. For small and medium numbers of file
400blocking when no data (or space) is available. 811descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend
812might perform better.
813.Sp
814On the positive side, this backend actually performed fully to
815specification in all tests and is fully embeddable, which is a rare feat
816among the OS-specific backends (I vastly prefer correctness over speed
817hacks).
818.Sp
819On the negative side, the interface is \fIbizarre\fR \- so bizarre that
820even sun itself gets it wrong in their code examples: The event polling
821function sometimes returns events to the caller even though an error
822occurred, but with no indication whether it has done so or not (yes, it's
823even documented that way) \- deadly for edge-triggered interfaces where you
824absolutely have to know whether an event occurred or not because you have
825to re-arm the watcher.
826.Sp
827Fortunately libev seems to be able to work around these idiocies.
828.Sp
829This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
830\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
401.ie n .IP """EVBACKEND_ALL""" 4 831.ie n .IP """EVBACKEND_ALL""" 4
402.el .IP "\f(CWEVBACKEND_ALL\fR" 4 832.el .IP "\f(CWEVBACKEND_ALL\fR" 4
403.IX Item "EVBACKEND_ALL" 833.IX Item "EVBACKEND_ALL"
404Try all backends (even potentially broken ones that wouldn't be tried 834Try all backends (even potentially broken ones that wouldn't be tried
405with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as 835with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as
406\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR. 836\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR.
837.Sp
838It is definitely not recommended to use this flag, use whatever
839\&\f(CW\*(C`ev_recommended_backends ()\*(C'\fR returns, or simply do not specify a backend
840at all.
841.ie n .IP """EVBACKEND_MASK""" 4
842.el .IP "\f(CWEVBACKEND_MASK\fR" 4
843.IX Item "EVBACKEND_MASK"
844Not a backend at all, but a mask to select all backend bits from a
845\&\f(CW\*(C`flags\*(C'\fR value, in case you want to mask out any backends from a flags
846value (e.g. when modifying the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR environment variable).
407.RE 847.RE
408.RS 4 848.RS 4
409.Sp 849.Sp
410If one or more of these are ored into the flags value, then only these 850If one or more of the backend flags are or'ed into the flags value,
411backends will be tried (in the reverse order as given here). If none are 851then only these backends will be tried (in the reverse order as listed
412specified, most compiled-in backend will be tried, usually in reverse 852here). If none are specified, all backends in \f(CW\*(C`ev_recommended_backends
413order of their flag values :) 853()\*(C'\fR will be tried.
414.Sp 854.Sp
415The most typical usage is like this: 855Example: Try to create a event loop that uses epoll and nothing else.
416.Sp 856.Sp
417.Vb 2 857.Vb 3
418\& if (!ev_default_loop (0)) 858\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
419\& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?"); 859\& if (!epoller)
860\& fatal ("no epoll found here, maybe it hides under your chair");
420.Ve 861.Ve
421.Sp 862.Sp
422Restrict libev to the select and poll backends, and do not allow 863Example: Use whatever libev has to offer, but make sure that kqueue is
423environment settings to be taken into account: 864used if available.
424.Sp 865.Sp
425.Vb 1 866.Vb 1
426\& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV); 867\& struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
427.Ve 868.Ve
428.Sp 869.Sp
429Use whatever libev has to offer, but make sure that kqueue is used if 870Example: Similarly, on linux, you mgiht want to take advantage of the
430available (warning, breaks stuff, best use only with your own private 871linux aio backend if possible, but fall back to something else if that
431event loop and only if you know the \s-1OS\s0 supports your types of fds): 872isn't available.
432.Sp 873.Sp
433.Vb 1 874.Vb 1
434\& ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE); 875\& struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_LINUXAIO);
435.Ve 876.Ve
436.RE 877.RE
437.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
438.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
439Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is
440always distinct from the default loop. Unlike the default loop, it cannot
441handle signal and child watchers, and attempts to do so will be greeted by
442undefined behaviour (or a failed assertion if assertions are enabled).
443.Sp
444Example: try to create a event loop that uses epoll and nothing else.
445.Sp
446.Vb 3
447\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
448\& if (!epoller)
449\& fatal ("no epoll found here, maybe it hides under your chair");
450.Ve
451.IP "ev_default_destroy ()" 4
452.IX Item "ev_default_destroy ()"
453Destroys the default loop again (frees all memory and kernel state
454etc.). This stops all registered event watchers (by not touching them in
455any way whatsoever, although you cannot rely on this :).
456.IP "ev_loop_destroy (loop)" 4 878.IP "ev_loop_destroy (loop)" 4
457.IX Item "ev_loop_destroy (loop)" 879.IX Item "ev_loop_destroy (loop)"
458Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an 880Destroys an event loop object (frees all memory and kernel state
459earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR. 881etc.). None of the active event watchers will be stopped in the normal
460.IP "ev_default_fork ()" 4 882sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your
461.IX Item "ev_default_fork ()" 883responsibility to either stop all watchers cleanly yourself \fIbefore\fR
462This function reinitialises the kernel state for backends that have 884calling this function, or cope with the fact afterwards (which is usually
463one. Despite the name, you can call it anytime, but it makes most sense 885the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them
464after forking, in either the parent or child process (or both, but that 886for example).
465again makes little sense).
466.Sp 887.Sp
467You \fImust\fR call this function in the child process after forking if and 888Note that certain global state, such as signal state (and installed signal
468only if you want to use the event library in both processes. If you just 889handlers), will not be freed by this function, and related watchers (such
469fork+exec, you don't have to call it. 890as signal and child watchers) would need to be stopped manually.
470.Sp 891.Sp
471The function itself is quite fast and it's usually not a problem to call 892This function is normally used on loop objects allocated by
472it just in case after a fork. To make this easy, the function will fit in 893\&\f(CW\*(C`ev_loop_new\*(C'\fR, but it can also be used on the default loop returned by
473quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR: 894\&\f(CW\*(C`ev_default_loop\*(C'\fR, in which case it is not thread-safe.
474.Sp 895.Sp
475.Vb 1 896Note that it is not advisable to call this function on the default loop
476\& pthread_atfork (0, 0, ev_default_fork); 897except in the rare occasion where you really need to free its resources.
477.Ve 898If you need dynamically allocated loops it is better to use \f(CW\*(C`ev_loop_new\*(C'\fR
478.Sp 899and \f(CW\*(C`ev_loop_destroy\*(C'\fR.
479At the moment, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and \f(CW\*(C`EVBACKEND_POLL\*(C'\fR are safe to use
480without calling this function, so if you force one of those backends you
481do not need to care.
482.IP "ev_loop_fork (loop)" 4 900.IP "ev_loop_fork (loop)" 4
483.IX Item "ev_loop_fork (loop)" 901.IX Item "ev_loop_fork (loop)"
484Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by 902This function sets a flag that causes subsequent \f(CW\*(C`ev_run\*(C'\fR iterations
485\&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop 903to reinitialise the kernel state for backends that have one. Despite
486after fork, and how you do this is entirely your own problem. 904the name, you can call it anytime you are allowed to start or stop
905watchers (except inside an \f(CW\*(C`ev_prepare\*(C'\fR callback), but it makes most
906sense after forking, in the child process. You \fImust\fR call it (or use
907\&\f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR) in the child before resuming or calling \f(CW\*(C`ev_run\*(C'\fR.
908.Sp
909In addition, if you want to reuse a loop (via this function or
910\&\f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR), you \fIalso\fR have to ignore \f(CW\*(C`SIGPIPE\*(C'\fR.
911.Sp
912Again, you \fIhave\fR to call it on \fIany\fR loop that you want to re-use after
913a fork, \fIeven if you do not plan to use the loop in the parent\fR. This is
914because some kernel interfaces *cough* \fIkqueue\fR *cough* do funny things
915during fork.
916.Sp
917On the other hand, you only need to call this function in the child
918process if and only if you want to use the event loop in the child. If
919you just fork+exec or create a new loop in the child, you don't have to
920call it at all (in fact, \f(CW\*(C`epoll\*(C'\fR is so badly broken that it makes a
921difference, but libev will usually detect this case on its own and do a
922costly reset of the backend).
923.Sp
924The function itself is quite fast and it's usually not a problem to call
925it just in case after a fork.
926.Sp
927Example: Automate calling \f(CW\*(C`ev_loop_fork\*(C'\fR on the default loop when
928using pthreads.
929.Sp
930.Vb 5
931\& static void
932\& post_fork_child (void)
933\& {
934\& ev_loop_fork (EV_DEFAULT);
935\& }
936\&
937\& ...
938\& pthread_atfork (0, 0, post_fork_child);
939.Ve
940.IP "int ev_is_default_loop (loop)" 4
941.IX Item "int ev_is_default_loop (loop)"
942Returns true when the given loop is, in fact, the default loop, and false
943otherwise.
944.IP "unsigned int ev_iteration (loop)" 4
945.IX Item "unsigned int ev_iteration (loop)"
946Returns the current iteration count for the event loop, which is identical
947to the number of times libev did poll for new events. It starts at \f(CW0\fR
948and happily wraps around with enough iterations.
949.Sp
950This value can sometimes be useful as a generation counter of sorts (it
951\&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with
952\&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls \- and is incremented between the
953prepare and check phases.
954.IP "unsigned int ev_depth (loop)" 4
955.IX Item "unsigned int ev_depth (loop)"
956Returns the number of times \f(CW\*(C`ev_run\*(C'\fR was entered minus the number of
957times \f(CW\*(C`ev_run\*(C'\fR was exited normally, in other words, the recursion depth.
958.Sp
959Outside \f(CW\*(C`ev_run\*(C'\fR, this number is zero. In a callback, this number is
960\&\f(CW1\fR, unless \f(CW\*(C`ev_run\*(C'\fR was invoked recursively (or from another thread),
961in which case it is higher.
962.Sp
963Leaving \f(CW\*(C`ev_run\*(C'\fR abnormally (setjmp/longjmp, cancelling the thread,
964throwing an exception etc.), doesn't count as \*(L"exit\*(R" \- consider this
965as a hint to avoid such ungentleman-like behaviour unless it's really
966convenient, in which case it is fully supported.
487.IP "unsigned int ev_backend (loop)" 4 967.IP "unsigned int ev_backend (loop)" 4
488.IX Item "unsigned int ev_backend (loop)" 968.IX Item "unsigned int ev_backend (loop)"
489Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in 969Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
490use. 970use.
491.IP "ev_tstamp ev_now (loop)" 4 971.IP "ev_tstamp ev_now (loop)" 4
492.IX Item "ev_tstamp ev_now (loop)" 972.IX Item "ev_tstamp ev_now (loop)"
493Returns the current \*(L"event loop time\*(R", which is the time the event loop 973Returns the current \*(L"event loop time\*(R", which is the time the event loop
494received events and started processing them. This timestamp does not 974received events and started processing them. This timestamp does not
495change as long as callbacks are being processed, and this is also the base 975change as long as callbacks are being processed, and this is also the base
496time used for relative timers. You can treat it as the timestamp of the 976time used for relative timers. You can treat it as the timestamp of the
497event occuring (or more correctly, libev finding out about it). 977event occurring (or more correctly, libev finding out about it).
978.IP "ev_now_update (loop)" 4
979.IX Item "ev_now_update (loop)"
980Establishes the current time by querying the kernel, updating the time
981returned by \f(CW\*(C`ev_now ()\*(C'\fR in the progress. This is a costly operation and
982is usually done automatically within \f(CW\*(C`ev_run ()\*(C'\fR.
983.Sp
984This function is rarely useful, but when some event callback runs for a
985very long time without entering the event loop, updating libev's idea of
986the current time is a good idea.
987.Sp
988See also \*(L"The special problem of time updates\*(R" in the \f(CW\*(C`ev_timer\*(C'\fR section.
989.IP "ev_suspend (loop)" 4
990.IX Item "ev_suspend (loop)"
991.PD 0
992.IP "ev_resume (loop)" 4
993.IX Item "ev_resume (loop)"
994.PD
995These two functions suspend and resume an event loop, for use when the
996loop is not used for a while and timeouts should not be processed.
997.Sp
998A typical use case would be an interactive program such as a game: When
999the user presses \f(CW\*(C`^Z\*(C'\fR to suspend the game and resumes it an hour later it
1000would be best to handle timeouts as if no time had actually passed while
1001the program was suspended. This can be achieved by calling \f(CW\*(C`ev_suspend\*(C'\fR
1002in your \f(CW\*(C`SIGTSTP\*(C'\fR handler, sending yourself a \f(CW\*(C`SIGSTOP\*(C'\fR and calling
1003\&\f(CW\*(C`ev_resume\*(C'\fR directly afterwards to resume timer processing.
1004.Sp
1005Effectively, all \f(CW\*(C`ev_timer\*(C'\fR watchers will be delayed by the time spend
1006between \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
1007will be rescheduled (that is, they will lose any events that would have
1008occurred while suspended).
1009.Sp
1010After calling \f(CW\*(C`ev_suspend\*(C'\fR you \fBmust not\fR call \fIany\fR function on the
1011given loop other than \f(CW\*(C`ev_resume\*(C'\fR, and you \fBmust not\fR call \f(CW\*(C`ev_resume\*(C'\fR
1012without a previous call to \f(CW\*(C`ev_suspend\*(C'\fR.
1013.Sp
1014Calling \f(CW\*(C`ev_suspend\*(C'\fR/\f(CW\*(C`ev_resume\*(C'\fR has the side effect of updating the
1015event loop time (see \f(CW\*(C`ev_now_update\*(C'\fR).
498.IP "ev_loop (loop, int flags)" 4 1016.IP "bool ev_run (loop, int flags)" 4
499.IX Item "ev_loop (loop, int flags)" 1017.IX Item "bool ev_run (loop, int flags)"
500Finally, this is it, the event handler. This function usually is called 1018Finally, this is it, the event handler. This function usually is called
501after you initialised all your watchers and you want to start handling 1019after you have initialised all your watchers and you want to start
502events. 1020handling events. It will ask the operating system for any new events, call
1021the watcher callbacks, and then repeat the whole process indefinitely: This
1022is why event loops are called \fIloops\fR.
503.Sp 1023.Sp
504If the flags argument is specified as \f(CW0\fR, it will not return until 1024If the flags argument is specified as \f(CW0\fR, it will keep handling events
505either no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called. 1025until either no event watchers are active anymore or \f(CW\*(C`ev_break\*(C'\fR was
1026called.
506.Sp 1027.Sp
1028The return value is false if there are no more active watchers (which
1029usually means \*(L"all jobs done\*(R" or \*(L"deadlock\*(R"), and true in all other cases
1030(which usually means " you should call \f(CW\*(C`ev_run\*(C'\fR again").
1031.Sp
507Please note that an explicit \f(CW\*(C`ev_unloop\*(C'\fR is usually better than 1032Please note that an explicit \f(CW\*(C`ev_break\*(C'\fR is usually better than
508relying on all watchers to be stopped when deciding when a program has 1033relying on all watchers to be stopped when deciding when a program has
509finished (especially in interactive programs), but having a program that 1034finished (especially in interactive programs), but having a program
510automatically loops as long as it has to and no longer by virtue of 1035that automatically loops as long as it has to and no longer by virtue
511relying on its watchers stopping correctly is a thing of beauty. 1036of relying on its watchers stopping correctly, that is truly a thing of
1037beauty.
512.Sp 1038.Sp
1039This function is \fImostly\fR exception-safe \- you can break out of a
1040\&\f(CW\*(C`ev_run\*(C'\fR call by calling \f(CW\*(C`longjmp\*(C'\fR in a callback, throwing a \*(C+
1041exception and so on. This does not decrement the \f(CW\*(C`ev_depth\*(C'\fR value, nor
1042will it clear any outstanding \f(CW\*(C`EVBREAK_ONE\*(C'\fR breaks.
1043.Sp
513A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle 1044A flags value of \f(CW\*(C`EVRUN_NOWAIT\*(C'\fR will look for new events, will handle
514those events and any outstanding ones, but will not block your process in 1045those events and any already outstanding ones, but will not wait and
515case there are no events and will return after one iteration of the loop. 1046block your process in case there are no events and will return after one
1047iteration of the loop. This is sometimes useful to poll and handle new
1048events while doing lengthy calculations, to keep the program responsive.
516.Sp 1049.Sp
517A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if 1050A flags value of \f(CW\*(C`EVRUN_ONCE\*(C'\fR will look for new events (waiting if
518neccessary) and will handle those and any outstanding ones. It will block 1051necessary) and will handle those and any already outstanding ones. It
519your process until at least one new event arrives, and will return after 1052will block your process until at least one new event arrives (which could
520one iteration of the loop. This is useful if you are waiting for some 1053be an event internal to libev itself, so there is no guarantee that a
521external event in conjunction with something not expressible using other 1054user-registered callback will be called), and will return after one
1055iteration of the loop.
1056.Sp
1057This is useful if you are waiting for some external event in conjunction
1058with something not expressible using other libev watchers (i.e. "roll your
522libev watchers. However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is 1059own \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
523usually a better approach for this kind of thing. 1060usually a better approach for this kind of thing.
524.Sp 1061.Sp
525Here are the gory details of what \f(CW\*(C`ev_loop\*(C'\fR does: 1062Here are the gory details of what \f(CW\*(C`ev_run\*(C'\fR does (this is for your
1063understanding, not a guarantee that things will work exactly like this in
1064future versions):
526.Sp 1065.Sp
527.Vb 18 1066.Vb 10
528\& * If there are no active watchers (reference count is zero), return. 1067\& \- Increment loop depth.
529\& - Queue prepare watchers and then call all outstanding watchers. 1068\& \- Reset the ev_break status.
1069\& \- Before the first iteration, call any pending watchers.
1070\& LOOP:
1071\& \- If EVFLAG_FORKCHECK was used, check for a fork.
1072\& \- If a fork was detected (by any means), queue and call all fork watchers.
1073\& \- Queue and call all prepare watchers.
1074\& \- If ev_break was called, goto FINISH.
530\& - If we have been forked, recreate the kernel state. 1075\& \- If we have been forked, detach and recreate the kernel state
1076\& as to not disturb the other process.
531\& - Update the kernel state with all outstanding changes. 1077\& \- Update the kernel state with all outstanding changes.
532\& - Update the "event loop time". 1078\& \- Update the "event loop time" (ev_now ()).
533\& - Calculate for how long to block. 1079\& \- Calculate for how long to sleep or block, if at all
1080\& (active idle watchers, EVRUN_NOWAIT or not having
1081\& any active watchers at all will result in not sleeping).
1082\& \- Sleep if the I/O and timer collect interval say so.
1083\& \- Increment loop iteration counter.
534\& - Block the process, waiting for any events. 1084\& \- Block the process, waiting for any events.
535\& - Queue all outstanding I/O (fd) events. 1085\& \- Queue all outstanding I/O (fd) events.
536\& - Update the "event loop time" and do time jump handling. 1086\& \- Update the "event loop time" (ev_now ()), and do time jump adjustments.
537\& - Queue all outstanding timers. 1087\& \- Queue all expired timers.
538\& - Queue all outstanding periodics. 1088\& \- Queue all expired periodics.
539\& - If no events are pending now, queue all idle watchers. 1089\& \- Queue all idle watchers with priority higher than that of pending events.
540\& - Queue all check watchers. 1090\& \- Queue all check watchers.
541\& - Call all queued watchers in reverse order (i.e. check watchers first). 1091\& \- Call all queued watchers in reverse order (i.e. check watchers first).
542\& Signals and child watchers are implemented as I/O watchers, and will 1092\& Signals and child watchers are implemented as I/O watchers, and will
543\& be handled here by queueing them when their watcher gets executed. 1093\& be handled here by queueing them when their watcher gets executed.
544\& - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK 1094\& \- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
545\& were used, return, otherwise continue with step *. 1095\& were used, or there are no active watchers, goto FINISH, otherwise
1096\& continue with step LOOP.
1097\& FINISH:
1098\& \- Reset the ev_break status iff it was EVBREAK_ONE.
1099\& \- Decrement the loop depth.
1100\& \- Return.
546.Ve 1101.Ve
547.Sp 1102.Sp
548Example: queue some jobs and then loop until no events are outsanding 1103Example: Queue some jobs and then loop until no events are outstanding
549anymore. 1104anymore.
550.Sp 1105.Sp
551.Vb 4 1106.Vb 4
552\& ... queue jobs here, make sure they register event watchers as long 1107\& ... queue jobs here, make sure they register event watchers as long
553\& ... as they still have work to do (even an idle watcher will do..) 1108\& ... as they still have work to do (even an idle watcher will do..)
554\& ev_loop (my_loop, 0); 1109\& ev_run (my_loop, 0);
555\& ... jobs done. yeah! 1110\& ... jobs done or somebody called break. yeah!
556.Ve 1111.Ve
557.IP "ev_unloop (loop, how)" 4 1112.IP "ev_break (loop, how)" 4
558.IX Item "ev_unloop (loop, how)" 1113.IX Item "ev_break (loop, how)"
559Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it 1114Can be used to make a call to \f(CW\*(C`ev_run\*(C'\fR return early (but only after it
560has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either 1115has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
561\&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or 1116\&\f(CW\*(C`EVBREAK_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_run\*(C'\fR call return, or
562\&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return. 1117\&\f(CW\*(C`EVBREAK_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_run\*(C'\fR calls return.
1118.Sp
1119This \*(L"break state\*(R" will be cleared on the next call to \f(CW\*(C`ev_run\*(C'\fR.
1120.Sp
1121It is safe to call \f(CW\*(C`ev_break\*(C'\fR from outside any \f(CW\*(C`ev_run\*(C'\fR calls, too, in
1122which case it will have no effect.
563.IP "ev_ref (loop)" 4 1123.IP "ev_ref (loop)" 4
564.IX Item "ev_ref (loop)" 1124.IX Item "ev_ref (loop)"
565.PD 0 1125.PD 0
566.IP "ev_unref (loop)" 4 1126.IP "ev_unref (loop)" 4
567.IX Item "ev_unref (loop)" 1127.IX Item "ev_unref (loop)"
568.PD 1128.PD
569Ref/unref can be used to add or remove a reference count on the event 1129Ref/unref can be used to add or remove a reference count on the event
570loop: Every watcher keeps one reference, and as long as the reference 1130loop: Every watcher keeps one reference, and as long as the reference
571count is nonzero, \f(CW\*(C`ev_loop\*(C'\fR will not return on its own. If you have 1131count is nonzero, \f(CW\*(C`ev_run\*(C'\fR will not return on its own.
572a watcher you never unregister that should not keep \f(CW\*(C`ev_loop\*(C'\fR from 1132.Sp
573returning, \fIev_unref()\fR after starting, and \fIev_ref()\fR before stopping it. For 1133This is useful when you have a watcher that you never intend to
1134unregister, but that nevertheless should not keep \f(CW\*(C`ev_run\*(C'\fR from
1135returning. In such a case, call \f(CW\*(C`ev_unref\*(C'\fR after starting, and \f(CW\*(C`ev_ref\*(C'\fR
1136before stopping it.
1137.Sp
574example, libev itself uses this for its internal signal pipe: It is not 1138As an example, libev itself uses this for its internal signal pipe: It
575visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from exiting if 1139is not visible to the libev user and should not keep \f(CW\*(C`ev_run\*(C'\fR from
576no event watchers registered by it are active. It is also an excellent 1140exiting if no event watchers registered by it are active. It is also an
577way to do this for generic recurring timers or from within third-party 1141excellent way to do this for generic recurring timers or from within
578libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR. 1142third-party libraries. Just remember to \fIunref after start\fR and \fIref
1143before stop\fR (but only if the watcher wasn't active before, or was active
1144before, respectively. Note also that libev might stop watchers itself
1145(e.g. non-repeating timers) in which case you have to \f(CW\*(C`ev_ref\*(C'\fR
1146in the callback).
579.Sp 1147.Sp
580Example: create a signal watcher, but keep it from keeping \f(CW\*(C`ev_loop\*(C'\fR 1148Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_run\*(C'\fR
581running when nothing else is active. 1149running when nothing else is active.
582.Sp 1150.Sp
583.Vb 4 1151.Vb 4
584\& struct dv_signal exitsig; 1152\& ev_signal exitsig;
585\& ev_signal_init (&exitsig, sig_cb, SIGINT); 1153\& ev_signal_init (&exitsig, sig_cb, SIGINT);
586\& ev_signal_start (myloop, &exitsig); 1154\& ev_signal_start (loop, &exitsig);
587\& evf_unref (myloop); 1155\& ev_unref (loop);
588.Ve 1156.Ve
589.Sp 1157.Sp
590Example: for some weird reason, unregister the above signal handler again. 1158Example: For some weird reason, unregister the above signal handler again.
591.Sp 1159.Sp
592.Vb 2 1160.Vb 2
593\& ev_ref (myloop); 1161\& ev_ref (loop);
594\& ev_signal_stop (myloop, &exitsig); 1162\& ev_signal_stop (loop, &exitsig);
595.Ve 1163.Ve
1164.IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4
1165.IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"
1166.PD 0
1167.IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4
1168.IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"
1169.PD
1170These advanced functions influence the time that libev will spend waiting
1171for events. Both time intervals are by default \f(CW0\fR, meaning that libev
1172will try to invoke timer/periodic callbacks and I/O callbacks with minimum
1173latency.
1174.Sp
1175Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR)
1176allows libev to delay invocation of I/O and timer/periodic callbacks
1177to increase efficiency of loop iterations (or to increase power-saving
1178opportunities).
1179.Sp
1180The idea is that sometimes your program runs just fast enough to handle
1181one (or very few) event(s) per loop iteration. While this makes the
1182program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new
1183events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high
1184overhead for the actual polling but can deliver many events at once.
1185.Sp
1186By setting a higher \fIio collect interval\fR you allow libev to spend more
1187time collecting I/O events, so you can handle more events per iteration,
1188at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and
1189\&\f(CW\*(C`ev_timer\*(C'\fR) will not be affected. Setting this to a non-null value will
1190introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations. The
1191sleep time ensures that libev will not poll for I/O events more often then
1192once per this interval, on average (as long as the host time resolution is
1193good enough).
1194.Sp
1195Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
1196to spend more time collecting timeouts, at the expense of increased
1197latency/jitter/inexactness (the watcher callback will be called
1198later). \f(CW\*(C`ev_io\*(C'\fR watchers will not be affected. Setting this to a non-null
1199value will not introduce any overhead in libev.
1200.Sp
1201Many (busy) programs can usually benefit by setting the I/O collect
1202interval to a value near \f(CW0.1\fR or so, which is often enough for
1203interactive servers (of course not for games), likewise for timeouts. It
1204usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR,
1205as this approaches the timing granularity of most systems. Note that if
1206you do transactions with the outside world and you can't increase the
1207parallelity, then this setting will limit your transaction rate (if you
1208need to poll once per transaction and the I/O collect interval is 0.01,
1209then you can't do more than 100 transactions per second).
1210.Sp
1211Setting the \fItimeout collect interval\fR can improve the opportunity for
1212saving power, as the program will \*(L"bundle\*(R" timer callback invocations that
1213are \*(L"near\*(R" in time together, by delaying some, thus reducing the number of
1214times the process sleeps and wakes up again. Another useful technique to
1215reduce iterations/wake\-ups is to use \f(CW\*(C`ev_periodic\*(C'\fR watchers and make sure
1216they fire on, say, one-second boundaries only.
1217.Sp
1218Example: we only need 0.1s timeout granularity, and we wish not to poll
1219more often than 100 times per second:
1220.Sp
1221.Vb 2
1222\& ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
1223\& ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
1224.Ve
1225.IP "ev_invoke_pending (loop)" 4
1226.IX Item "ev_invoke_pending (loop)"
1227This call will simply invoke all pending watchers while resetting their
1228pending state. Normally, \f(CW\*(C`ev_run\*(C'\fR does this automatically when required,
1229but when overriding the invoke callback this call comes handy. This
1230function can be invoked from a watcher \- this can be useful for example
1231when you want to do some lengthy calculation and want to pass further
1232event handling to another thread (you still have to make sure only one
1233thread executes within \f(CW\*(C`ev_invoke_pending\*(C'\fR or \f(CW\*(C`ev_run\*(C'\fR of course).
1234.IP "int ev_pending_count (loop)" 4
1235.IX Item "int ev_pending_count (loop)"
1236Returns the number of pending watchers \- zero indicates that no watchers
1237are pending.
1238.IP "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(\s-1EV_P\s0))" 4
1239.IX Item "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))"
1240This overrides the invoke pending functionality of the loop: Instead of
1241invoking all pending watchers when there are any, \f(CW\*(C`ev_run\*(C'\fR will call
1242this callback instead. This is useful, for example, when you want to
1243invoke the actual watchers inside another context (another thread etc.).
1244.Sp
1245If you want to reset the callback, use \f(CW\*(C`ev_invoke_pending\*(C'\fR as new
1246callback.
1247.IP "ev_set_loop_release_cb (loop, void (*release)(\s-1EV_P\s0) throw (), void (*acquire)(\s-1EV_P\s0) throw ())" 4
1248.IX Item "ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())"
1249Sometimes you want to share the same loop between multiple threads. This
1250can be done relatively simply by putting mutex_lock/unlock calls around
1251each call to a libev function.
1252.Sp
1253However, \f(CW\*(C`ev_run\*(C'\fR can run an indefinite time, so it is not feasible
1254to wait for it to return. One way around this is to wake up the event
1255loop via \f(CW\*(C`ev_break\*(C'\fR and \f(CW\*(C`ev_async_send\*(C'\fR, another way is to set these
1256\&\fIrelease\fR and \fIacquire\fR callbacks on the loop.
1257.Sp
1258When set, then \f(CW\*(C`release\*(C'\fR will be called just before the thread is
1259suspended waiting for new events, and \f(CW\*(C`acquire\*(C'\fR is called just
1260afterwards.
1261.Sp
1262Ideally, \f(CW\*(C`release\*(C'\fR will just call your mutex_unlock function, and
1263\&\f(CW\*(C`acquire\*(C'\fR will just call the mutex_lock function again.
1264.Sp
1265While event loop modifications are allowed between invocations of
1266\&\f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR (that's their only purpose after all), no
1267modifications done will affect the event loop, i.e. adding watchers will
1268have no effect on the set of file descriptors being watched, or the time
1269waited. Use an \f(CW\*(C`ev_async\*(C'\fR watcher to wake up \f(CW\*(C`ev_run\*(C'\fR when you want it
1270to take note of any changes you made.
1271.Sp
1272In theory, threads executing \f(CW\*(C`ev_run\*(C'\fR will be async-cancel safe between
1273invocations of \f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR.
1274.Sp
1275See also the locking example in the \f(CW\*(C`THREADS\*(C'\fR section later in this
1276document.
1277.IP "ev_set_userdata (loop, void *data)" 4
1278.IX Item "ev_set_userdata (loop, void *data)"
1279.PD 0
1280.IP "void *ev_userdata (loop)" 4
1281.IX Item "void *ev_userdata (loop)"
1282.PD
1283Set and retrieve a single \f(CW\*(C`void *\*(C'\fR associated with a loop. When
1284\&\f(CW\*(C`ev_set_userdata\*(C'\fR has never been called, then \f(CW\*(C`ev_userdata\*(C'\fR returns
1285\&\f(CW0\fR.
1286.Sp
1287These two functions can be used to associate arbitrary data with a loop,
1288and are intended solely for the \f(CW\*(C`invoke_pending_cb\*(C'\fR, \f(CW\*(C`release\*(C'\fR and
1289\&\f(CW\*(C`acquire\*(C'\fR callbacks described above, but of course can be (ab\-)used for
1290any other purpose as well.
1291.IP "ev_verify (loop)" 4
1292.IX Item "ev_verify (loop)"
1293This function only does something when \f(CW\*(C`EV_VERIFY\*(C'\fR support has been
1294compiled in, which is the default for non-minimal builds. It tries to go
1295through all internal structures and checks them for validity. If anything
1296is found to be inconsistent, it will print an error message to standard
1297error and call \f(CW\*(C`abort ()\*(C'\fR.
1298.Sp
1299This can be used to catch bugs inside libev itself: under normal
1300circumstances, this function will never abort as of course libev keeps its
1301data structures consistent.
596.SH "ANATOMY OF A WATCHER" 1302.SH "ANATOMY OF A WATCHER"
597.IX Header "ANATOMY OF A WATCHER" 1303.IX Header "ANATOMY OF A WATCHER"
1304In the following description, uppercase \f(CW\*(C`TYPE\*(C'\fR in names stands for the
1305watcher type, e.g. \f(CW\*(C`ev_TYPE_start\*(C'\fR can mean \f(CW\*(C`ev_timer_start\*(C'\fR for timer
1306watchers and \f(CW\*(C`ev_io_start\*(C'\fR for I/O watchers.
1307.PP
598A watcher is a structure that you create and register to record your 1308A watcher is an opaque structure that you allocate and register to record
599interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to 1309your interest in some event. To make a concrete example, imagine you want
600become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that: 1310to wait for \s-1STDIN\s0 to become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher
1311for that:
601.PP 1312.PP
602.Vb 5 1313.Vb 5
603\& static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) 1314\& static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
604\& { 1315\& {
605\& ev_io_stop (w); 1316\& ev_io_stop (w);
606\& ev_unloop (loop, EVUNLOOP_ALL); 1317\& ev_break (loop, EVBREAK_ALL);
607\& } 1318\& }
608.Ve 1319\&
609.PP
610.Vb 6
611\& struct ev_loop *loop = ev_default_loop (0); 1320\& struct ev_loop *loop = ev_default_loop (0);
1321\&
612\& struct ev_io stdin_watcher; 1322\& ev_io stdin_watcher;
1323\&
613\& ev_init (&stdin_watcher, my_cb); 1324\& ev_init (&stdin_watcher, my_cb);
614\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); 1325\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
615\& ev_io_start (loop, &stdin_watcher); 1326\& ev_io_start (loop, &stdin_watcher);
1327\&
616\& ev_loop (loop, 0); 1328\& ev_run (loop, 0);
617.Ve 1329.Ve
618.PP 1330.PP
619As you can see, you are responsible for allocating the memory for your 1331As you can see, you are responsible for allocating the memory for your
620watcher structures (and it is usually a bad idea to do this on the stack, 1332watcher structures (and it is \fIusually\fR a bad idea to do this on the
621although this can sometimes be quite valid). 1333stack).
622.PP 1334.PP
1335Each watcher has an associated watcher structure (called \f(CW\*(C`struct ev_TYPE\*(C'\fR
1336or simply \f(CW\*(C`ev_TYPE\*(C'\fR, as typedefs are provided for all watcher structs).
1337.PP
623Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init 1338Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init (watcher
624(watcher *, callback)\*(C'\fR, which expects a callback to be provided. This 1339*, callback)\*(C'\fR, which expects a callback to be provided. This callback is
625callback gets invoked each time the event occurs (or, in the case of io 1340invoked each time the event occurs (or, in the case of I/O watchers, each
626watchers, each time the event loop detects that the file descriptor given 1341time the event loop detects that the file descriptor given is readable
627is readable and/or writable). 1342and/or writable).
628.PP 1343.PP
629Each watcher type has its own \f(CW\*(C`ev_<type>_set (watcher *, ...)\*(C'\fR macro 1344Each watcher type further has its own \f(CW\*(C`ev_TYPE_set (watcher *, ...)\*(C'\fR
630with arguments specific to this watcher type. There is also a macro 1345macro to configure it, with arguments specific to the watcher type. There
631to combine initialisation and setting in one call: \f(CW\*(C`ev_<type>_init 1346is also a macro to combine initialisation and setting in one call: \f(CW\*(C`ev_TYPE_init (watcher *, callback, ...)\*(C'\fR.
632(watcher *, callback, ...)\*(C'\fR.
633.PP 1347.PP
634To make the watcher actually watch out for events, you have to start it 1348To make the watcher actually watch out for events, you have to start it
635with a watcher-specific start function (\f(CW\*(C`ev_<type>_start (loop, watcher 1349with a watcher-specific start function (\f(CW\*(C`ev_TYPE_start (loop, watcher
636*)\*(C'\fR), and you can stop watching for events at any time by calling the 1350*)\*(C'\fR), and you can stop watching for events at any time by calling the
637corresponding stop function (\f(CW\*(C`ev_<type>_stop (loop, watcher *)\*(C'\fR. 1351corresponding stop function (\f(CW\*(C`ev_TYPE_stop (loop, watcher *)\*(C'\fR.
638.PP 1352.PP
639As long as your watcher is active (has been started but not stopped) you 1353As long as your watcher is active (has been started but not stopped) you
640must not touch the values stored in it. Most specifically you must never 1354must not touch the values stored in it except when explicitly documented
641reinitialise it or call its set macro. 1355otherwise. Most specifically you must never reinitialise it or call its
642.PP 1356\&\f(CW\*(C`ev_TYPE_set\*(C'\fR macro.
643You can check whether an event is active by calling the \f(CW\*(C`ev_is_active
644(watcher *)\*(C'\fR macro. To see whether an event is outstanding (but the
645callback for it has not been called yet) you can use the \f(CW\*(C`ev_is_pending
646(watcher *)\*(C'\fR macro.
647.PP 1357.PP
648Each and every callback receives the event loop pointer as first, the 1358Each and every callback receives the event loop pointer as first, the
649registered watcher structure as second, and a bitset of received events as 1359registered watcher structure as second, and a bitset of received events as
650third argument. 1360third argument.
651.PP 1361.PP
… …
660.el .IP "\f(CWEV_WRITE\fR" 4 1370.el .IP "\f(CWEV_WRITE\fR" 4
661.IX Item "EV_WRITE" 1371.IX Item "EV_WRITE"
662.PD 1372.PD
663The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or 1373The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
664writable. 1374writable.
665.ie n .IP """EV_TIMEOUT""" 4 1375.ie n .IP """EV_TIMER""" 4
666.el .IP "\f(CWEV_TIMEOUT\fR" 4 1376.el .IP "\f(CWEV_TIMER\fR" 4
667.IX Item "EV_TIMEOUT" 1377.IX Item "EV_TIMER"
668The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out. 1378The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
669.ie n .IP """EV_PERIODIC""" 4 1379.ie n .IP """EV_PERIODIC""" 4
670.el .IP "\f(CWEV_PERIODIC\fR" 4 1380.el .IP "\f(CWEV_PERIODIC\fR" 4
671.IX Item "EV_PERIODIC" 1381.IX Item "EV_PERIODIC"
672The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out. 1382The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
… …
676The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread. 1386The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread.
677.ie n .IP """EV_CHILD""" 4 1387.ie n .IP """EV_CHILD""" 4
678.el .IP "\f(CWEV_CHILD\fR" 4 1388.el .IP "\f(CWEV_CHILD\fR" 4
679.IX Item "EV_CHILD" 1389.IX Item "EV_CHILD"
680The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change. 1390The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change.
1391.ie n .IP """EV_STAT""" 4
1392.el .IP "\f(CWEV_STAT\fR" 4
1393.IX Item "EV_STAT"
1394The path specified in the \f(CW\*(C`ev_stat\*(C'\fR watcher changed its attributes somehow.
681.ie n .IP """EV_IDLE""" 4 1395.ie n .IP """EV_IDLE""" 4
682.el .IP "\f(CWEV_IDLE\fR" 4 1396.el .IP "\f(CWEV_IDLE\fR" 4
683.IX Item "EV_IDLE" 1397.IX Item "EV_IDLE"
684The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do. 1398The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do.
685.ie n .IP """EV_PREPARE""" 4 1399.ie n .IP """EV_PREPARE""" 4
… …
688.PD 0 1402.PD 0
689.ie n .IP """EV_CHECK""" 4 1403.ie n .IP """EV_CHECK""" 4
690.el .IP "\f(CWEV_CHECK\fR" 4 1404.el .IP "\f(CWEV_CHECK\fR" 4
691.IX Item "EV_CHECK" 1405.IX Item "EV_CHECK"
692.PD 1406.PD
693All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_loop\*(C'\fR starts 1407All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_run\*(C'\fR starts to
694to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after 1408gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are queued (not invoked)
695\&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any 1409just after \f(CW\*(C`ev_run\*(C'\fR has gathered them, but before it queues any callbacks
1410for any received events. That means \f(CW\*(C`ev_prepare\*(C'\fR watchers are the last
1411watchers invoked before the event loop sleeps or polls for new events, and
1412\&\f(CW\*(C`ev_check\*(C'\fR watchers will be invoked before any other watchers of the same
1413or lower priority within an event loop iteration.
1414.Sp
696received events. Callbacks of both watcher types can start and stop as 1415Callbacks of both watcher types can start and stop as many watchers as
697many watchers as they want, and all of them will be taken into account 1416they want, and all of them will be taken into account (for example, a
698(for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep 1417\&\f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep \f(CW\*(C`ev_run\*(C'\fR from
699\&\f(CW\*(C`ev_loop\*(C'\fR from blocking). 1418blocking).
1419.ie n .IP """EV_EMBED""" 4
1420.el .IP "\f(CWEV_EMBED\fR" 4
1421.IX Item "EV_EMBED"
1422The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.
1423.ie n .IP """EV_FORK""" 4
1424.el .IP "\f(CWEV_FORK\fR" 4
1425.IX Item "EV_FORK"
1426The event loop has been resumed in the child process after fork (see
1427\&\f(CW\*(C`ev_fork\*(C'\fR).
1428.ie n .IP """EV_CLEANUP""" 4
1429.el .IP "\f(CWEV_CLEANUP\fR" 4
1430.IX Item "EV_CLEANUP"
1431The event loop is about to be destroyed (see \f(CW\*(C`ev_cleanup\*(C'\fR).
1432.ie n .IP """EV_ASYNC""" 4
1433.el .IP "\f(CWEV_ASYNC\fR" 4
1434.IX Item "EV_ASYNC"
1435The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR).
1436.ie n .IP """EV_CUSTOM""" 4
1437.el .IP "\f(CWEV_CUSTOM\fR" 4
1438.IX Item "EV_CUSTOM"
1439Not ever sent (or otherwise used) by libev itself, but can be freely used
1440by libev users to signal watchers (e.g. via \f(CW\*(C`ev_feed_event\*(C'\fR).
700.ie n .IP """EV_ERROR""" 4 1441.ie n .IP """EV_ERROR""" 4
701.el .IP "\f(CWEV_ERROR\fR" 4 1442.el .IP "\f(CWEV_ERROR\fR" 4
702.IX Item "EV_ERROR" 1443.IX Item "EV_ERROR"
703An unspecified error has occured, the watcher has been stopped. This might 1444An unspecified error has occurred, the watcher has been stopped. This might
704happen because the watcher could not be properly started because libev 1445happen because the watcher could not be properly started because libev
705ran out of memory, a file descriptor was found to be closed or any other 1446ran out of memory, a file descriptor was found to be closed or any other
1447problem. Libev considers these application bugs.
1448.Sp
706problem. You best act on it by reporting the problem and somehow coping 1449You best act on it by reporting the problem and somehow coping with the
707with the watcher being stopped. 1450watcher being stopped. Note that well-written programs should not receive
1451an error ever, so when your watcher receives it, this usually indicates a
1452bug in your program.
708.Sp 1453.Sp
709Libev will usually signal a few \*(L"dummy\*(R" events together with an error, 1454Libev will usually signal a few \*(L"dummy\*(R" events together with an error, for
710for example it might indicate that a fd is readable or writable, and if 1455example it might indicate that a fd is readable or writable, and if your
711your callbacks is well-written it can just attempt the operation and cope 1456callbacks is well-written it can just attempt the operation and cope with
712with the error from \fIread()\fR or \fIwrite()\fR. This will not work in multithreaded 1457the error from \fBread()\fR or \fBwrite()\fR. This will not work in multi-threaded
713programs, though, so beware. 1458programs, though, as the fd could already be closed and reused for another
714.Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0" 1459thing, so beware.
715.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER" 1460.SS "\s-1GENERIC WATCHER FUNCTIONS\s0"
716Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change 1461.IX Subsection "GENERIC WATCHER FUNCTIONS"
717and read at any time, libev will completely ignore it. This can be used 1462.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
718to associate arbitrary data with your watcher. If you need more data and 1463.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
719don't want to allocate memory and store a pointer to it in that data 1464.IX Item "ev_init (ev_TYPE *watcher, callback)"
720member, you can also \*(L"subclass\*(R" the watcher type and provide your own 1465This macro initialises the generic portion of a watcher. The contents
721data: 1466of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
722.PP 1467the generic parts of the watcher are initialised, you \fIneed\fR to call
1468the type-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR macro afterwards to initialise the
1469type-specific parts. For each type there is also a \f(CW\*(C`ev_TYPE_init\*(C'\fR macro
1470which rolls both calls into one.
1471.Sp
1472You can reinitialise a watcher at any time as long as it has been stopped
1473(or never started) and there are no pending events outstanding.
1474.Sp
1475The callback is always of type \f(CW\*(C`void (*)(struct ev_loop *loop, ev_TYPE *watcher,
1476int revents)\*(C'\fR.
1477.Sp
1478Example: Initialise an \f(CW\*(C`ev_io\*(C'\fR watcher in two steps.
1479.Sp
723.Vb 7 1480.Vb 3
724\& struct my_io 1481\& ev_io w;
1482\& ev_init (&w, my_cb);
1483\& ev_io_set (&w, STDIN_FILENO, EV_READ);
1484.Ve
1485.ie n .IP """ev_TYPE_set"" (ev_TYPE *watcher, [args])" 4
1486.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *watcher, [args])" 4
1487.IX Item "ev_TYPE_set (ev_TYPE *watcher, [args])"
1488This macro initialises the type-specific parts of a watcher. You need to
1489call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
1490call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
1491macro on a watcher that is active (it can be pending, however, which is a
1492difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
1493.Sp
1494Although some watcher types do not have type-specific arguments
1495(e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
1496.Sp
1497See \f(CW\*(C`ev_init\*(C'\fR, above, for an example.
1498.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
1499.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
1500.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
1501This convenience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
1502calls into a single call. This is the most convenient method to initialise
1503a watcher. The same limitations apply, of course.
1504.Sp
1505Example: Initialise and set an \f(CW\*(C`ev_io\*(C'\fR watcher in one step.
1506.Sp
1507.Vb 1
1508\& ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1509.Ve
1510.ie n .IP """ev_TYPE_start"" (loop, ev_TYPE *watcher)" 4
1511.el .IP "\f(CWev_TYPE_start\fR (loop, ev_TYPE *watcher)" 4
1512.IX Item "ev_TYPE_start (loop, ev_TYPE *watcher)"
1513Starts (activates) the given watcher. Only active watchers will receive
1514events. If the watcher is already active nothing will happen.
1515.Sp
1516Example: Start the \f(CW\*(C`ev_io\*(C'\fR watcher that is being abused as example in this
1517whole section.
1518.Sp
1519.Vb 1
1520\& ev_io_start (EV_DEFAULT_UC, &w);
1521.Ve
1522.ie n .IP """ev_TYPE_stop"" (loop, ev_TYPE *watcher)" 4
1523.el .IP "\f(CWev_TYPE_stop\fR (loop, ev_TYPE *watcher)" 4
1524.IX Item "ev_TYPE_stop (loop, ev_TYPE *watcher)"
1525Stops the given watcher if active, and clears the pending status (whether
1526the watcher was active or not).
1527.Sp
1528It is possible that stopped watchers are pending \- for example,
1529non-repeating timers are being stopped when they become pending \- but
1530calling \f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor
1531pending. If you want to free or reuse the memory used by the watcher it is
1532therefore a good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
1533.IP "bool ev_is_active (ev_TYPE *watcher)" 4
1534.IX Item "bool ev_is_active (ev_TYPE *watcher)"
1535Returns a true value iff the watcher is active (i.e. it has been started
1536and not yet been stopped). As long as a watcher is active you must not modify
1537it.
1538.IP "bool ev_is_pending (ev_TYPE *watcher)" 4
1539.IX Item "bool ev_is_pending (ev_TYPE *watcher)"
1540Returns a true value iff the watcher is pending, (i.e. it has outstanding
1541events but its callback has not yet been invoked). As long as a watcher
1542is pending (but not active) you must not call an init function on it (but
1543\&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe), you must not change its priority, and you must
1544make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR
1545it).
1546.IP "callback ev_cb (ev_TYPE *watcher)" 4
1547.IX Item "callback ev_cb (ev_TYPE *watcher)"
1548Returns the callback currently set on the watcher.
1549.IP "ev_set_cb (ev_TYPE *watcher, callback)" 4
1550.IX Item "ev_set_cb (ev_TYPE *watcher, callback)"
1551Change the callback. You can change the callback at virtually any time
1552(modulo threads).
1553.IP "ev_set_priority (ev_TYPE *watcher, int priority)" 4
1554.IX Item "ev_set_priority (ev_TYPE *watcher, int priority)"
1555.PD 0
1556.IP "int ev_priority (ev_TYPE *watcher)" 4
1557.IX Item "int ev_priority (ev_TYPE *watcher)"
1558.PD
1559Set and query the priority of the watcher. The priority is a small
1560integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR
1561(default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked
1562before watchers with lower priority, but priority will not keep watchers
1563from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
1564.Sp
1565If you need to suppress invocation when higher priority events are pending
1566you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
1567.Sp
1568You \fImust not\fR change the priority of a watcher as long as it is active or
1569pending.
1570.Sp
1571Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
1572fine, as long as you do not mind that the priority value you query might
1573or might not have been clamped to the valid range.
1574.Sp
1575The default priority used by watchers when no priority has been set is
1576always \f(CW0\fR, which is supposed to not be too high and not be too low :).
1577.Sp
1578See \*(L"\s-1WATCHER PRIORITY MODELS\*(R"\s0, below, for a more thorough treatment of
1579priorities.
1580.IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
1581.IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
1582Invoke the \f(CW\*(C`watcher\*(C'\fR with the given \f(CW\*(C`loop\*(C'\fR and \f(CW\*(C`revents\*(C'\fR. Neither
1583\&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback
1584can deal with that fact, as both are simply passed through to the
1585callback.
1586.IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
1587.IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
1588If the watcher is pending, this function clears its pending status and
1589returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the
1590watcher isn't pending it does nothing and returns \f(CW0\fR.
1591.Sp
1592Sometimes it can be useful to \*(L"poll\*(R" a watcher instead of waiting for its
1593callback to be invoked, which can be accomplished with this function.
1594.IP "ev_feed_event (loop, ev_TYPE *watcher, int revents)" 4
1595.IX Item "ev_feed_event (loop, ev_TYPE *watcher, int revents)"
1596Feeds the given event set into the event loop, as if the specified event
1597had happened for the specified watcher (which must be a pointer to an
1598initialised but not necessarily started event watcher). Obviously you must
1599not free the watcher as long as it has pending events.
1600.Sp
1601Stopping the watcher, letting libev invoke it, or calling
1602\&\f(CW\*(C`ev_clear_pending\*(C'\fR will clear the pending event, even if the watcher was
1603not started in the first place.
1604.Sp
1605See also \f(CW\*(C`ev_feed_fd_event\*(C'\fR and \f(CW\*(C`ev_feed_signal_event\*(C'\fR for related
1606functions that do not need a watcher.
1607.PP
1608See also the \*(L"\s-1ASSOCIATING CUSTOM DATA WITH A WATCHER\*(R"\s0 and \*(L"\s-1BUILDING YOUR
1609OWN COMPOSITE WATCHERS\*(R"\s0 idioms.
1610.SS "\s-1WATCHER STATES\s0"
1611.IX Subsection "WATCHER STATES"
1612There are various watcher states mentioned throughout this manual \-
1613active, pending and so on. In this section these states and the rules to
1614transition between them will be described in more detail \- and while these
1615rules might look complicated, they usually do \*(L"the right thing\*(R".
1616.IP "initialised" 4
1617.IX Item "initialised"
1618Before a watcher can be registered with the event loop it has to be
1619initialised. This can be done with a call to \f(CW\*(C`ev_TYPE_init\*(C'\fR, or calls to
1620\&\f(CW\*(C`ev_init\*(C'\fR followed by the watcher-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR function.
1621.Sp
1622In this state it is simply some block of memory that is suitable for
1623use in an event loop. It can be moved around, freed, reused etc. at
1624will \- as long as you either keep the memory contents intact, or call
1625\&\f(CW\*(C`ev_TYPE_init\*(C'\fR again.
1626.IP "started/running/active" 4
1627.IX Item "started/running/active"
1628Once a watcher has been started with a call to \f(CW\*(C`ev_TYPE_start\*(C'\fR it becomes
1629property of the event loop, and is actively waiting for events. While in
1630this state it cannot be accessed (except in a few documented ways), moved,
1631freed or anything else \- the only legal thing is to keep a pointer to it,
1632and call libev functions on it that are documented to work on active watchers.
1633.IP "pending" 4
1634.IX Item "pending"
1635If a watcher is active and libev determines that an event it is interested
1636in has occurred (such as a timer expiring), it will become pending. It will
1637stay in this pending state until either it is stopped or its callback is
1638about to be invoked, so it is not normally pending inside the watcher
1639callback.
1640.Sp
1641The watcher might or might not be active while it is pending (for example,
1642an expired non-repeating timer can be pending but no longer active). If it
1643is stopped, it can be freely accessed (e.g. by calling \f(CW\*(C`ev_TYPE_set\*(C'\fR),
1644but it is still property of the event loop at this time, so cannot be
1645moved, freed or reused. And if it is active the rules described in the
1646previous item still apply.
1647.Sp
1648It is also possible to feed an event on a watcher that is not active (e.g.
1649via \f(CW\*(C`ev_feed_event\*(C'\fR), in which case it becomes pending without being
1650active.
1651.IP "stopped" 4
1652.IX Item "stopped"
1653A watcher can be stopped implicitly by libev (in which case it might still
1654be pending), or explicitly by calling its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. The
1655latter will clear any pending state the watcher might be in, regardless
1656of whether it was active or not, so stopping a watcher explicitly before
1657freeing it is often a good idea.
1658.Sp
1659While stopped (and not pending) the watcher is essentially in the
1660initialised state, that is, it can be reused, moved, modified in any way
1661you wish (but when you trash the memory block, you need to \f(CW\*(C`ev_TYPE_init\*(C'\fR
1662it again).
1663.SS "\s-1WATCHER PRIORITY MODELS\s0"
1664.IX Subsection "WATCHER PRIORITY MODELS"
1665Many event loops support \fIwatcher priorities\fR, which are usually small
1666integers that influence the ordering of event callback invocation
1667between watchers in some way, all else being equal.
1668.PP
1669In libev, watcher priorities can be set using \f(CW\*(C`ev_set_priority\*(C'\fR. See its
1670description for the more technical details such as the actual priority
1671range.
1672.PP
1673There are two common ways how these these priorities are being interpreted
1674by event loops:
1675.PP
1676In the more common lock-out model, higher priorities \*(L"lock out\*(R" invocation
1677of lower priority watchers, which means as long as higher priority
1678watchers receive events, lower priority watchers are not being invoked.
1679.PP
1680The less common only-for-ordering model uses priorities solely to order
1681callback invocation within a single event loop iteration: Higher priority
1682watchers are invoked before lower priority ones, but they all get invoked
1683before polling for new events.
1684.PP
1685Libev uses the second (only-for-ordering) model for all its watchers
1686except for idle watchers (which use the lock-out model).
1687.PP
1688The rationale behind this is that implementing the lock-out model for
1689watchers is not well supported by most kernel interfaces, and most event
1690libraries will just poll for the same events again and again as long as
1691their callbacks have not been executed, which is very inefficient in the
1692common case of one high-priority watcher locking out a mass of lower
1693priority ones.
1694.PP
1695Static (ordering) priorities are most useful when you have two or more
1696watchers handling the same resource: a typical usage example is having an
1697\&\f(CW\*(C`ev_io\*(C'\fR watcher to receive data, and an associated \f(CW\*(C`ev_timer\*(C'\fR to handle
1698timeouts. Under load, data might be received while the program handles
1699other jobs, but since timers normally get invoked first, the timeout
1700handler will be executed before checking for data. In that case, giving
1701the timer a lower priority than the I/O watcher ensures that I/O will be
1702handled first even under adverse conditions (which is usually, but not
1703always, what you want).
1704.PP
1705Since idle watchers use the \*(L"lock-out\*(R" model, meaning that idle watchers
1706will only be executed when no same or higher priority watchers have
1707received events, they can be used to implement the \*(L"lock-out\*(R" model when
1708required.
1709.PP
1710For example, to emulate how many other event libraries handle priorities,
1711you can associate an \f(CW\*(C`ev_idle\*(C'\fR watcher to each such watcher, and in
1712the normal watcher callback, you just start the idle watcher. The real
1713processing is done in the idle watcher callback. This causes libev to
1714continuously poll and process kernel event data for the watcher, but when
1715the lock-out case is known to be rare (which in turn is rare :), this is
1716workable.
1717.PP
1718Usually, however, the lock-out model implemented that way will perform
1719miserably under the type of load it was designed to handle. In that case,
1720it might be preferable to stop the real watcher before starting the
1721idle watcher, so the kernel will not have to process the event in case
1722the actual processing will be delayed for considerable time.
1723.PP
1724Here is an example of an I/O watcher that should run at a strictly lower
1725priority than the default, and which should only process data when no
1726other events are pending:
1727.PP
1728.Vb 2
1729\& ev_idle idle; // actual processing watcher
1730\& ev_io io; // actual event watcher
1731\&
1732\& static void
1733\& io_cb (EV_P_ ev_io *w, int revents)
725\& { 1734\& {
726\& struct ev_io io; 1735\& // stop the I/O watcher, we received the event, but
727\& int otherfd; 1736\& // are not yet ready to handle it.
728\& void *somedata; 1737\& ev_io_stop (EV_A_ w);
729\& struct whatever *mostinteresting; 1738\&
1739\& // start the idle watcher to handle the actual event.
1740\& // it will not be executed as long as other watchers
1741\& // with the default priority are receiving events.
1742\& ev_idle_start (EV_A_ &idle);
730\& } 1743\& }
731.Ve 1744\&
732.PP 1745\& static void
733And since your callback will be called with a pointer to the watcher, you 1746\& idle_cb (EV_P_ ev_idle *w, int revents)
734can cast it back to your own type:
735.PP
736.Vb 5
737\& static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
738\& { 1747\& {
739\& struct my_io *w = (struct my_io *)w_; 1748\& // actual processing
740\& ... 1749\& read (STDIN_FILENO, ...);
1750\&
1751\& // have to start the I/O watcher again, as
1752\& // we have handled the event
1753\& ev_io_start (EV_P_ &io);
741\& } 1754\& }
1755\&
1756\& // initialisation
1757\& ev_idle_init (&idle, idle_cb);
1758\& ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
1759\& ev_io_start (EV_DEFAULT_ &io);
742.Ve 1760.Ve
743.PP 1761.PP
744More interesting and less C\-conformant ways of catsing your callback type 1762In the \*(L"real\*(R" world, it might also be beneficial to start a timer, so that
745have been omitted.... 1763low-priority connections can not be locked out forever under load. This
1764enables your program to keep a lower latency for important connections
1765during short periods of high load, while not completely locking out less
1766important ones.
746.SH "WATCHER TYPES" 1767.SH "WATCHER TYPES"
747.IX Header "WATCHER TYPES" 1768.IX Header "WATCHER TYPES"
748This section describes each watcher in detail, but will not repeat 1769This section describes each watcher in detail, but will not repeat
749information given in the last section. 1770information given in the last section. Any initialisation/set macros,
1771functions and members specific to the watcher type are explained.
1772.PP
1773Most members are additionally marked with either \fI[read\-only]\fR, meaning
1774that, while the watcher is active, you can look at the member and expect
1775some sensible content, but you must not modify it (you can modify it while
1776the watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
1777means you can expect it to have some sensible content while the watcher
1778is active, but you can also modify it. Modifying it may not do something
1779sensible or take immediate effect (or do anything at all), but libev will
1780not crash or malfunction in any way.
1781.PP
1782In any case, the documentation for each member will explain what the
1783effects are, and if there are any additional access restrictions.
750.ie n .Sh """ev_io"" \- is this file descriptor readable or writable" 1784.ie n .SS """ev_io"" \- is this file descriptor readable or writable?"
751.el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable" 1785.el .SS "\f(CWev_io\fP \- is this file descriptor readable or writable?"
752.IX Subsection "ev_io - is this file descriptor readable or writable" 1786.IX Subsection "ev_io - is this file descriptor readable or writable?"
753I/O watchers check whether a file descriptor is readable or writable 1787I/O watchers check whether a file descriptor is readable or writable
754in each iteration of the event loop (This behaviour is called 1788in each iteration of the event loop, or, more precisely, when reading
755level-triggering because you keep receiving events as long as the 1789would not block the process and writing would at least be able to write
756condition persists. Remember you can stop the watcher if you don't want to 1790some data. This behaviour is called level-triggering because you keep
757act on the event and neither want to receive future events). 1791receiving events as long as the condition persists. Remember you can stop
1792the watcher if you don't want to act on the event and neither want to
1793receive future events.
758.PP 1794.PP
759In general you can register as many read and/or write event watchers per 1795In general you can register as many read and/or write event watchers per
760fd as you want (as long as you don't confuse yourself). Setting all file 1796fd as you want (as long as you don't confuse yourself). Setting all file
761descriptors to non-blocking mode is also usually a good idea (but not 1797descriptors to non-blocking mode is also usually a good idea (but not
762required if you know what you are doing). 1798required if you know what you are doing).
763.PP 1799.PP
764You have to be careful with dup'ed file descriptors, though. Some backends 1800Another thing you have to watch out for is that it is quite easy to
765(the linux epoll backend is a notable example) cannot handle dup'ed file 1801receive \*(L"spurious\*(R" readiness notifications, that is, your callback might
766descriptors correctly if you register interest in two or more fds pointing 1802be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block
767to the same underlying file/socket etc. description (that is, they share 1803because there is no data. It is very easy to get into this situation even
768the same underlying \*(L"file open\*(R"). 1804with a relatively standard program structure. Thus it is best to always
1805use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning \f(CW\*(C`EAGAIN\*(C'\fR is far
1806preferable to a program hanging until some data arrives.
769.PP 1807.PP
770If you must do this, then force the use of a known-to-be-good backend 1808If you cannot run the fd in non-blocking mode (for example you should
771(at the time of this writing, this includes only \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and 1809not play around with an Xlib connection), then you have to separately
772\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR). 1810re-test whether a file descriptor is really ready with a known-to-be good
1811interface such as poll (fortunately in the case of Xlib, it already does
1812this on its own, so its quite safe to use). Some people additionally
1813use \f(CW\*(C`SIGALRM\*(C'\fR and an interval timer, just to be sure you won't block
1814indefinitely.
1815.PP
1816But really, best use non-blocking mode.
1817.PP
1818\fIThe special problem of disappearing file descriptors\fR
1819.IX Subsection "The special problem of disappearing file descriptors"
1820.PP
1821Some backends (e.g. kqueue, epoll, linuxaio) need to be told about closing
1822a file descriptor (either due to calling \f(CW\*(C`close\*(C'\fR explicitly or any other
1823means, such as \f(CW\*(C`dup2\*(C'\fR). The reason is that you register interest in some
1824file descriptor, but when it goes away, the operating system will silently
1825drop this interest. If another file descriptor with the same number then
1826is registered with libev, there is no efficient way to see that this is,
1827in fact, a different file descriptor.
1828.PP
1829To avoid having to explicitly tell libev about such cases, libev follows
1830the following policy: Each time \f(CW\*(C`ev_io_set\*(C'\fR is being called, libev
1831will assume that this is potentially a new file descriptor, otherwise
1832it is assumed that the file descriptor stays the same. That means that
1833you \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
1834descriptor even if the file descriptor number itself did not change.
1835.PP
1836This is how one would do it normally anyway, the important point is that
1837the libev application should not optimise around libev but should leave
1838optimisations to libev.
1839.PP
1840\fIThe special problem of dup'ed file descriptors\fR
1841.IX Subsection "The special problem of dup'ed file descriptors"
1842.PP
1843Some backends (e.g. epoll), cannot register events for file descriptors,
1844but only events for the underlying file descriptions. That means when you
1845have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register
1846events for them, only one file descriptor might actually receive events.
1847.PP
1848There is no workaround possible except not registering events
1849for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
1850\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1851.PP
1852\fIThe special problem of files\fR
1853.IX Subsection "The special problem of files"
1854.PP
1855Many people try to use \f(CW\*(C`select\*(C'\fR (or libev) on file descriptors
1856representing files, and expect it to become ready when their program
1857doesn't block on disk accesses (which can take a long time on their own).
1858.PP
1859However, this cannot ever work in the \*(L"expected\*(R" way \- you get a readiness
1860notification as soon as the kernel knows whether and how much data is
1861there, and in the case of open files, that's always the case, so you
1862always get a readiness notification instantly, and your read (or possibly
1863write) will still block on the disk I/O.
1864.PP
1865Another way to view it is that in the case of sockets, pipes, character
1866devices and so on, there is another party (the sender) that delivers data
1867on its own, but in the case of files, there is no such thing: the disk
1868will not send data on its own, simply because it doesn't know what you
1869wish to read \- you would first have to request some data.
1870.PP
1871Since files are typically not-so-well supported by advanced notification
1872mechanism, libev tries hard to emulate \s-1POSIX\s0 behaviour with respect
1873to files, even though you should not use it. The reason for this is
1874convenience: sometimes you want to watch \s-1STDIN\s0 or \s-1STDOUT,\s0 which is
1875usually a tty, often a pipe, but also sometimes files or special devices
1876(for example, \f(CW\*(C`epoll\*(C'\fR on Linux works with \fI/dev/random\fR but not with
1877\&\fI/dev/urandom\fR), and even though the file might better be served with
1878asynchronous I/O instead of with non-blocking I/O, it is still useful when
1879it \*(L"just works\*(R" instead of freezing.
1880.PP
1881So avoid file descriptors pointing to files when you know it (e.g. use
1882libeio), but use them when it is convenient, e.g. for \s-1STDIN/STDOUT,\s0 or
1883when you rarely read from a file instead of from a socket, and want to
1884reuse the same code path.
1885.PP
1886\fIThe special problem of fork\fR
1887.IX Subsection "The special problem of fork"
1888.PP
1889Some backends (epoll, kqueue, linuxaio, iouring) do not support \f(CW\*(C`fork ()\*(C'\fR
1890at all or exhibit useless behaviour. Libev fully supports fork, but needs
1891to be told about it in the child if you want to continue to use it in the
1892child.
1893.PP
1894To support fork in your child processes, you have to call \f(CW\*(C`ev_loop_fork
1895()\*(C'\fR after a fork in the child, enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to
1896\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1897.PP
1898\fIThe special problem of \s-1SIGPIPE\s0\fR
1899.IX Subsection "The special problem of SIGPIPE"
1900.PP
1901While not really specific to libev, it is easy to forget about \f(CW\*(C`SIGPIPE\*(C'\fR:
1902when writing to a pipe whose other end has been closed, your program gets
1903sent a \s-1SIGPIPE,\s0 which, by default, aborts your program. For most programs
1904this is sensible behaviour, for daemons, this is usually undesirable.
1905.PP
1906So when you encounter spurious, unexplained daemon exits, make sure you
1907ignore \s-1SIGPIPE\s0 (and maybe make sure you log the exit status of your daemon
1908somewhere, as that would have given you a big clue).
1909.PP
1910\fIThe special problem of \f(BIaccept()\fIing when you can't\fR
1911.IX Subsection "The special problem of accept()ing when you can't"
1912.PP
1913Many implementations of the \s-1POSIX\s0 \f(CW\*(C`accept\*(C'\fR function (for example,
1914found in post\-2004 Linux) have the peculiar behaviour of not removing a
1915connection from the pending queue in all error cases.
1916.PP
1917For example, larger servers often run out of file descriptors (because
1918of resource limits), causing \f(CW\*(C`accept\*(C'\fR to fail with \f(CW\*(C`ENFILE\*(C'\fR but not
1919rejecting the connection, leading to libev signalling readiness on
1920the next iteration again (the connection still exists after all), and
1921typically causing the program to loop at 100% \s-1CPU\s0 usage.
1922.PP
1923Unfortunately, the set of errors that cause this issue differs between
1924operating systems, there is usually little the app can do to remedy the
1925situation, and no known thread-safe method of removing the connection to
1926cope with overload is known (to me).
1927.PP
1928One of the easiest ways to handle this situation is to just ignore it
1929\&\- when the program encounters an overload, it will just loop until the
1930situation is over. While this is a form of busy waiting, no \s-1OS\s0 offers an
1931event-based way to handle this situation, so it's the best one can do.
1932.PP
1933A better way to handle the situation is to log any errors other than
1934\&\f(CW\*(C`EAGAIN\*(C'\fR and \f(CW\*(C`EWOULDBLOCK\*(C'\fR, making sure not to flood the log with such
1935messages, and continue as usual, which at least gives the user an idea of
1936what could be wrong (\*(L"raise the ulimit!\*(R"). For extra points one could stop
1937the \f(CW\*(C`ev_io\*(C'\fR watcher on the listening fd \*(L"for a while\*(R", which reduces \s-1CPU\s0
1938usage.
1939.PP
1940If your program is single-threaded, then you could also keep a dummy file
1941descriptor for overload situations (e.g. by opening \fI/dev/null\fR), and
1942when 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,
1943close that fd, and create a new dummy fd. This will gracefully refuse
1944clients under typical overload conditions.
1945.PP
1946The last way to handle it is to simply log the error and \f(CW\*(C`exit\*(C'\fR, as
1947is often done with \f(CW\*(C`malloc\*(C'\fR failures, but this results in an easy
1948opportunity for a DoS attack.
1949.PP
1950\fIWatcher-Specific Functions\fR
1951.IX Subsection "Watcher-Specific Functions"
773.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4 1952.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
774.IX Item "ev_io_init (ev_io *, callback, int fd, int events)" 1953.IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
775.PD 0 1954.PD 0
776.IP "ev_io_set (ev_io *, int fd, int events)" 4 1955.IP "ev_io_set (ev_io *, int fd, int events)" 4
777.IX Item "ev_io_set (ev_io *, int fd, int events)" 1956.IX Item "ev_io_set (ev_io *, int fd, int events)"
778.PD 1957.PD
779Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The fd is the file descriptor to rceeive 1958Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to
780events 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 | 1959receive 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, both
781EV_WRITE\*(C'\fR to receive the given events. 1960\&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR or \f(CW0\fR, to express the desire to receive the given
1961events.
782.Sp 1962.Sp
783Please note that most of the more scalable backend mechanisms (for example 1963Note that setting the \f(CW\*(C`events\*(C'\fR to \f(CW0\fR and starting the watcher is
784epoll and solaris ports) can result in spurious readyness notifications 1964supported, but not specially optimized \- if your program sometimes happens
785for file descriptors, so you practically need to use non-blocking I/O (and 1965to generate this combination this is fine, but if it is easy to avoid
786treat callback invocation as hint only), or retest separately with a safe 1966starting an io watcher watching for no events you should do so.
787interface before doing I/O (XLib can do this), or force the use of either 1967.IP "ev_io_modify (ev_io *, int events)" 4
788\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR, which don't suffer from this 1968.IX Item "ev_io_modify (ev_io *, int events)"
789problem. Also note that it is quite easy to have your callback invoked 1969Similar to \f(CW\*(C`ev_io_set\*(C'\fR, but only changes the event mask. Using this might
790when the readyness condition is no longer valid even when employing 1970be faster with some backends, as libev can assume that the \f(CW\*(C`fd\*(C'\fR still
791typical ways of handling events, so its a good idea to use non-blocking 1971refers to the same underlying file description, something it cannot do
792I/O unconditionally. 1972when using \f(CW\*(C`ev_io_set\*(C'\fR.
1973.IP "int fd [no\-modify]" 4
1974.IX Item "int fd [no-modify]"
1975The file descriptor being watched. While it can be read at any time, you
1976must not modify this member even when the watcher is stopped \- always use
1977\&\f(CW\*(C`ev_io_set\*(C'\fR for that.
1978.IP "int events [no\-modify]" 4
1979.IX Item "int events [no-modify]"
1980The set of events the fd is being watched for, among other flags. Remember
1981that this is a bit set \- to test for \f(CW\*(C`EV_READ\*(C'\fR, use \f(CW\*(C`w\->events &
1982EV_READ\*(C'\fR, and similarly for \f(CW\*(C`EV_WRITE\*(C'\fR.
1983.Sp
1984As with \f(CW\*(C`fd\*(C'\fR, you must not modify this member even when the watcher is
1985stopped, always use \f(CW\*(C`ev_io_set\*(C'\fR or \f(CW\*(C`ev_io_modify\*(C'\fR for that.
793.PP 1986.PP
1987\fIExamples\fR
1988.IX Subsection "Examples"
1989.PP
794Example: call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well 1990Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
795readable, but only once. Since it is likely line\-buffered, you could 1991readable, but only once. Since it is likely line-buffered, you could
796attempt to read a whole line in the callback: 1992attempt to read a whole line in the callback.
797.PP 1993.PP
798.Vb 6 1994.Vb 6
799\& static void 1995\& static void
800\& stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents) 1996\& stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
801\& { 1997\& {
802\& ev_io_stop (loop, w); 1998\& ev_io_stop (loop, w);
803\& .. read from stdin here (or from w->fd) and haqndle any I/O errors 1999\& .. read from stdin here (or from w\->fd) and handle any I/O errors
804\& } 2000\& }
805.Ve 2001\&
806.PP
807.Vb 6
808\& ... 2002\& ...
809\& struct ev_loop *loop = ev_default_init (0); 2003\& struct ev_loop *loop = ev_default_init (0);
810\& struct ev_io stdin_readable; 2004\& ev_io stdin_readable;
811\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ); 2005\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
812\& ev_io_start (loop, &stdin_readable); 2006\& ev_io_start (loop, &stdin_readable);
813\& ev_loop (loop, 0); 2007\& ev_run (loop, 0);
814.Ve 2008.Ve
815.ie n .Sh """ev_timer"" \- relative and optionally recurring timeouts" 2009.ie n .SS """ev_timer"" \- relative and optionally repeating timeouts"
816.el .Sh "\f(CWev_timer\fP \- relative and optionally recurring timeouts" 2010.el .SS "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
817.IX Subsection "ev_timer - relative and optionally recurring timeouts" 2011.IX Subsection "ev_timer - relative and optionally repeating timeouts"
818Timer watchers are simple relative timers that generate an event after a 2012Timer watchers are simple relative timers that generate an event after a
819given time, and optionally repeating in regular intervals after that. 2013given time, and optionally repeating in regular intervals after that.
820.PP 2014.PP
821The timers are based on real time, that is, if you register an event that 2015The timers are based on real time, that is, if you register an event that
822times out after an hour and you reset your system clock to last years 2016times out after an hour and you reset your system clock to January last
823time, it will still time out after (roughly) and hour. \*(L"Roughly\*(R" because 2017year, it will still time out after (roughly) one hour. \*(L"Roughly\*(R" because
824detecting time jumps is hard, and some inaccuracies are unavoidable (the 2018detecting time jumps is hard, and some inaccuracies are unavoidable (the
825monotonic clock option helps a lot here). 2019monotonic clock option helps a lot here).
2020.PP
2021The callback is guaranteed to be invoked only \fIafter\fR its timeout has
2022passed (not \fIat\fR, so on systems with very low-resolution clocks this
2023might introduce a small delay, see \*(L"the special problem of being too
2024early\*(R", below). If multiple timers become ready during the same loop
2025iteration then the ones with earlier time-out values are invoked before
2026ones of the same priority with later time-out values (but this is no
2027longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
2028.PP
2029\fIBe smart about timeouts\fR
2030.IX Subsection "Be smart about timeouts"
2031.PP
2032Many real-world problems involve some kind of timeout, usually for error
2033recovery. A typical example is an \s-1HTTP\s0 request \- if the other side hangs,
2034you want to raise some error after a while.
2035.PP
2036What follows are some ways to handle this problem, from obvious and
2037inefficient to smart and efficient.
2038.PP
2039In the following, a 60 second activity timeout is assumed \- a timeout that
2040gets reset to 60 seconds each time there is activity (e.g. each time some
2041data or other life sign was received).
2042.IP "1. Use a timer and stop, reinitialise and start it on activity." 4
2043.IX Item "1. Use a timer and stop, reinitialise and start it on activity."
2044This is the most obvious, but not the most simple way: In the beginning,
2045start the watcher:
2046.Sp
2047.Vb 2
2048\& ev_timer_init (timer, callback, 60., 0.);
2049\& ev_timer_start (loop, timer);
2050.Ve
2051.Sp
2052Then, each time there is some activity, \f(CW\*(C`ev_timer_stop\*(C'\fR it, initialise it
2053and start it again:
2054.Sp
2055.Vb 3
2056\& ev_timer_stop (loop, timer);
2057\& ev_timer_set (timer, 60., 0.);
2058\& ev_timer_start (loop, timer);
2059.Ve
2060.Sp
2061This is relatively simple to implement, but means that each time there is
2062some activity, libev will first have to remove the timer from its internal
2063data structure and then add it again. Libev tries to be fast, but it's
2064still not a constant-time operation.
2065.ie n .IP "2. Use a timer and re-start it with ""ev_timer_again"" inactivity." 4
2066.el .IP "2. Use a timer and re-start it with \f(CWev_timer_again\fR inactivity." 4
2067.IX Item "2. Use a timer and re-start it with ev_timer_again inactivity."
2068This is the easiest way, and involves using \f(CW\*(C`ev_timer_again\*(C'\fR instead of
2069\&\f(CW\*(C`ev_timer_start\*(C'\fR.
2070.Sp
2071To implement this, configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value
2072of \f(CW60\fR and then call \f(CW\*(C`ev_timer_again\*(C'\fR at start and each time you
2073successfully read or write some data. If you go into an idle state where
2074you do not expect data to travel on the socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR
2075the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will automatically restart it if need be.
2076.Sp
2077That means you can ignore both the \f(CW\*(C`ev_timer_start\*(C'\fR function and the
2078\&\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
2079member and \f(CW\*(C`ev_timer_again\*(C'\fR.
2080.Sp
2081At start:
2082.Sp
2083.Vb 3
2084\& ev_init (timer, callback);
2085\& timer\->repeat = 60.;
2086\& ev_timer_again (loop, timer);
2087.Ve
2088.Sp
2089Each time there is some activity:
2090.Sp
2091.Vb 1
2092\& ev_timer_again (loop, timer);
2093.Ve
2094.Sp
2095It is even possible to change the time-out on the fly, regardless of
2096whether the watcher is active or not:
2097.Sp
2098.Vb 2
2099\& timer\->repeat = 30.;
2100\& ev_timer_again (loop, timer);
2101.Ve
2102.Sp
2103This is slightly more efficient then stopping/starting the timer each time
2104you want to modify its timeout value, as libev does not have to completely
2105remove and re-insert the timer from/into its internal data structure.
2106.Sp
2107It is, however, even simpler than the \*(L"obvious\*(R" way to do it.
2108.IP "3. Let the timer time out, but then re-arm it as required." 4
2109.IX Item "3. Let the timer time out, but then re-arm it as required."
2110This method is more tricky, but usually most efficient: Most timeouts are
2111relatively long compared to the intervals between other activity \- in
2112our example, within 60 seconds, there are usually many I/O events with
2113associated activity resets.
2114.Sp
2115In this case, it would be more efficient to leave the \f(CW\*(C`ev_timer\*(C'\fR alone,
2116but remember the time of last activity, and check for a real timeout only
2117within the callback:
2118.Sp
2119.Vb 3
2120\& ev_tstamp timeout = 60.;
2121\& ev_tstamp last_activity; // time of last activity
2122\& ev_timer timer;
2123\&
2124\& static void
2125\& callback (EV_P_ ev_timer *w, int revents)
2126\& {
2127\& // calculate when the timeout would happen
2128\& ev_tstamp after = last_activity \- ev_now (EV_A) + timeout;
2129\&
2130\& // if negative, it means we the timeout already occurred
2131\& if (after < 0.)
2132\& {
2133\& // timeout occurred, take action
2134\& }
2135\& else
2136\& {
2137\& // callback was invoked, but there was some recent
2138\& // activity. simply restart the timer to time out
2139\& // after "after" seconds, which is the earliest time
2140\& // the timeout can occur.
2141\& ev_timer_set (w, after, 0.);
2142\& ev_timer_start (EV_A_ w);
2143\& }
2144\& }
2145.Ve
2146.Sp
2147To summarise the callback: first calculate in how many seconds the
2148timeout will occur (by calculating the absolute time when it would occur,
2149\&\f(CW\*(C`last_activity + timeout\*(C'\fR, and subtracting the current time, \f(CW\*(C`ev_now
2150(EV_A)\*(C'\fR from that).
2151.Sp
2152If this value is negative, then we are already past the timeout, i.e. we
2153timed out, and need to do whatever is needed in this case.
2154.Sp
2155Otherwise, we now the earliest time at which the timeout would trigger,
2156and simply start the timer with this timeout value.
2157.Sp
2158In other words, each time the callback is invoked it will check whether
2159the timeout occurred. If not, it will simply reschedule itself to check
2160again at the earliest time it could time out. Rinse. Repeat.
2161.Sp
2162This scheme causes more callback invocations (about one every 60 seconds
2163minus half the average time between activity), but virtually no calls to
2164libev to change the timeout.
2165.Sp
2166To start the machinery, simply initialise the watcher and set
2167\&\f(CW\*(C`last_activity\*(C'\fR to the current time (meaning there was some activity just
2168now), then call the callback, which will \*(L"do the right thing\*(R" and start
2169the timer:
2170.Sp
2171.Vb 3
2172\& last_activity = ev_now (EV_A);
2173\& ev_init (&timer, callback);
2174\& callback (EV_A_ &timer, 0);
2175.Ve
2176.Sp
2177When there is some activity, simply store the current time in
2178\&\f(CW\*(C`last_activity\*(C'\fR, no libev calls at all:
2179.Sp
2180.Vb 2
2181\& if (activity detected)
2182\& last_activity = ev_now (EV_A);
2183.Ve
2184.Sp
2185When your timeout value changes, then the timeout can be changed by simply
2186providing a new value, stopping the timer and calling the callback, which
2187will again do the right thing (for example, time out immediately :).
2188.Sp
2189.Vb 3
2190\& timeout = new_value;
2191\& ev_timer_stop (EV_A_ &timer);
2192\& callback (EV_A_ &timer, 0);
2193.Ve
2194.Sp
2195This technique is slightly more complex, but in most cases where the
2196time-out is unlikely to be triggered, much more efficient.
2197.IP "4. Wee, just use a double-linked list for your timeouts." 4
2198.IX Item "4. Wee, just use a double-linked list for your timeouts."
2199If there is not one request, but many thousands (millions...), all
2200employing some kind of timeout with the same timeout value, then one can
2201do even better:
2202.Sp
2203When starting the timeout, calculate the timeout value and put the timeout
2204at the \fIend\fR of the list.
2205.Sp
2206Then use an \f(CW\*(C`ev_timer\*(C'\fR to fire when the timeout at the \fIbeginning\fR of
2207the list is expected to fire (for example, using the technique #3).
2208.Sp
2209When there is some activity, remove the timer from the list, recalculate
2210the timeout, append it to the end of the list again, and make sure to
2211update the \f(CW\*(C`ev_timer\*(C'\fR if it was taken from the beginning of the list.
2212.Sp
2213This way, one can manage an unlimited number of timeouts in O(1) time for
2214starting, stopping and updating the timers, at the expense of a major
2215complication, and having to use a constant timeout. The constant timeout
2216ensures that the list stays sorted.
2217.PP
2218So which method the best?
2219.PP
2220Method #2 is a simple no-brain-required solution that is adequate in most
2221situations. Method #3 requires a bit more thinking, but handles many cases
2222better, and isn't very complicated either. In most case, choosing either
2223one is fine, with #3 being better in typical situations.
2224.PP
2225Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
2226rather complicated, but extremely efficient, something that really pays
2227off after the first million or so of active timers, i.e. it's usually
2228overkill :)
2229.PP
2230\fIThe special problem of being too early\fR
2231.IX Subsection "The special problem of being too early"
2232.PP
2233If you ask a timer to call your callback after three seconds, then
2234you expect it to be invoked after three seconds \- but of course, this
2235cannot be guaranteed to infinite precision. Less obviously, it cannot be
2236guaranteed to any precision by libev \- imagine somebody suspending the
2237process with a \s-1STOP\s0 signal for a few hours for example.
2238.PP
2239So, libev tries to invoke your callback as soon as possible \fIafter\fR the
2240delay has occurred, but cannot guarantee this.
2241.PP
2242A less obvious failure mode is calling your callback too early: many event
2243loops compare timestamps with a \*(L"elapsed delay >= requested delay\*(R", but
2244this can cause your callback to be invoked much earlier than you would
2245expect.
2246.PP
2247To see why, imagine a system with a clock that only offers full second
2248resolution (think windows if you can't come up with a broken enough \s-1OS\s0
2249yourself). If you schedule a one-second timer at the time 500.9, then the
2250event loop will schedule your timeout to elapse at a system time of 500
2251(500.9 truncated to the resolution) + 1, or 501.
2252.PP
2253If an event library looks at the timeout 0.1s later, it will see \*(L"501 >=
2254501\*(R" and invoke the callback 0.1s after it was started, even though a
2255one-second delay was requested \- this is being \*(L"too early\*(R", despite best
2256intentions.
2257.PP
2258This is the reason why libev will never invoke the callback if the elapsed
2259delay equals the requested delay, but only when the elapsed delay is
2260larger than the requested delay. In the example above, libev would only invoke
2261the callback at system time 502, or 1.1s after the timer was started.
2262.PP
2263So, while libev cannot guarantee that your callback will be invoked
2264exactly when requested, it \fIcan\fR and \fIdoes\fR guarantee that the requested
2265delay has actually elapsed, or in other words, it always errs on the \*(L"too
2266late\*(R" side of things.
2267.PP
2268\fIThe special problem of time updates\fR
2269.IX Subsection "The special problem of time updates"
2270.PP
2271Establishing the current time is a costly operation (it usually takes
2272at least one system call): \s-1EV\s0 therefore updates its idea of the current
2273time only before and after \f(CW\*(C`ev_run\*(C'\fR collects new events, which causes a
2274growing difference between \f(CW\*(C`ev_now ()\*(C'\fR and \f(CW\*(C`ev_time ()\*(C'\fR when handling
2275lots of events in one iteration.
826.PP 2276.PP
827The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR 2277The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
828time. This is usually the right thing as this timestamp refers to the time 2278time. This is usually the right thing as this timestamp refers to the time
829of the event triggering whatever timeout you are modifying/starting. If 2279of the event triggering whatever timeout you are modifying/starting. If
830you suspect event processing to be delayed and you \fIneed\fR to base the timeout 2280you suspect event processing to be delayed and you \fIneed\fR to base the
831on the current time, use something like this to adjust for this: 2281timeout on the current time, use something like the following to adjust
2282for it:
832.PP 2283.PP
833.Vb 1 2284.Vb 1
834\& ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); 2285\& ev_timer_set (&timer, after + (ev_time () \- ev_now ()), 0.);
835.Ve 2286.Ve
836.PP 2287.PP
837The callback is guarenteed to be invoked only when its timeout has passed, 2288If the event loop is suspended for a long time, you can also force an
838but if multiple timers become ready during the same loop iteration then 2289update of the time returned by \f(CW\*(C`ev_now ()\*(C'\fR by calling \f(CW\*(C`ev_now_update
839order of execution is undefined. 2290()\*(C'\fR, although that will push the event time of all outstanding events
2291further into the future.
2292.PP
2293\fIThe special problem of unsynchronised clocks\fR
2294.IX Subsection "The special problem of unsynchronised clocks"
2295.PP
2296Modern systems have a variety of clocks \- libev itself uses the normal
2297\&\*(L"wall clock\*(R" clock and, if available, the monotonic clock (to avoid time
2298jumps).
2299.PP
2300Neither of these clocks is synchronised with each other or any other clock
2301on the system, so \f(CW\*(C`ev_time ()\*(C'\fR might return a considerably different time
2302than \f(CW\*(C`gettimeofday ()\*(C'\fR or \f(CW\*(C`time ()\*(C'\fR. On a GNU/Linux system, for example,
2303a call to \f(CW\*(C`gettimeofday\*(C'\fR might return a second count that is one higher
2304than a directly following call to \f(CW\*(C`time\*(C'\fR.
2305.PP
2306The moral of this is to only compare libev-related timestamps with
2307\&\f(CW\*(C`ev_time ()\*(C'\fR and \f(CW\*(C`ev_now ()\*(C'\fR, at least if you want better precision than
2308a second or so.
2309.PP
2310One more problem arises due to this lack of synchronisation: if libev uses
2311the system monotonic clock and you compare timestamps from \f(CW\*(C`ev_time\*(C'\fR
2312or \f(CW\*(C`ev_now\*(C'\fR from when you started your timer and when your callback is
2313invoked, you will find that sometimes the callback is a bit \*(L"early\*(R".
2314.PP
2315This is because \f(CW\*(C`ev_timer\*(C'\fRs work in real time, not wall clock time, so
2316libev makes sure your callback is not invoked before the delay happened,
2317\&\fImeasured according to the real time\fR, not the system clock.
2318.PP
2319If your timeouts are based on a physical timescale (e.g. \*(L"time out this
2320connection after 100 seconds\*(R") then this shouldn't bother you as it is
2321exactly the right behaviour.
2322.PP
2323If you want to compare wall clock/system timestamps to your timers, then
2324you need to use \f(CW\*(C`ev_periodic\*(C'\fRs, as these are based on the wall clock
2325time, where your comparisons will always generate correct results.
2326.PP
2327\fIThe special problems of suspended animation\fR
2328.IX Subsection "The special problems of suspended animation"
2329.PP
2330When you leave the server world it is quite customary to hit machines that
2331can suspend/hibernate \- what happens to the clocks during such a suspend?
2332.PP
2333Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
2334all processes, while the clocks (\f(CW\*(C`times\*(C'\fR, \f(CW\*(C`CLOCK_MONOTONIC\*(C'\fR) continue
2335to run until the system is suspended, but they will not advance while the
2336system is suspended. That means, on resume, it will be as if the program
2337was frozen for a few seconds, but the suspend time will not be counted
2338towards \f(CW\*(C`ev_timer\*(C'\fR when a monotonic clock source is used. The real time
2339clock advanced as expected, but if it is used as sole clocksource, then a
2340long suspend would be detected as a time jump by libev, and timers would
2341be adjusted accordingly.
2342.PP
2343I would not be surprised to see different behaviour in different between
2344operating systems, \s-1OS\s0 versions or even different hardware.
2345.PP
2346The other form of suspend (job control, or sending a \s-1SIGSTOP\s0) will see a
2347time jump in the monotonic clocks and the realtime clock. If the program
2348is suspended for a very long time, and monotonic clock sources are in use,
2349then you can expect \f(CW\*(C`ev_timer\*(C'\fRs to expire as the full suspension time
2350will be counted towards the timers. When no monotonic clock source is in
2351use, then libev will again assume a timejump and adjust accordingly.
2352.PP
2353It might be beneficial for this latter case to call \f(CW\*(C`ev_suspend\*(C'\fR
2354and \f(CW\*(C`ev_resume\*(C'\fR in code that handles \f(CW\*(C`SIGTSTP\*(C'\fR, to at least get
2355deterministic behaviour in this case (you can do nothing against
2356\&\f(CW\*(C`SIGSTOP\*(C'\fR).
2357.PP
2358\fIWatcher-Specific Functions and Data Members\fR
2359.IX Subsection "Watcher-Specific Functions and Data Members"
840.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4 2360.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
841.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 2361.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
842.PD 0 2362.PD 0
843.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4 2363.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
844.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 2364.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
845.PD 2365.PD
846Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR is 2366Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds (fractional and
847\&\f(CW0.\fR, then it will automatically be stopped. If it is positive, then the 2367negative values are supported). If \f(CW\*(C`repeat\*(C'\fR is \f(CW0.\fR, then it will
2368automatically be stopped once the timeout is reached. If it is positive,
848timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds 2369then the timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR
849later, again, and again, until stopped manually. 2370seconds later, again, and again, until stopped manually.
850.Sp 2371.Sp
851The timer itself will do a best-effort at avoiding drift, that is, if you 2372The timer itself will do a best-effort at avoiding drift, that is, if
852configure a timer to trigger every 10 seconds, then it will trigger at 2373you configure a timer to trigger every 10 seconds, then it will normally
853exactly 10 second intervals. If, however, your program cannot keep up with 2374trigger at exactly 10 second intervals. If, however, your program cannot
854the timer (because it takes longer than those 10 seconds to do stuff) the 2375keep up with the timer (because it takes longer than those 10 seconds to
855timer will not fire more than once per event loop iteration. 2376do stuff) the timer will not fire more than once per event loop iteration.
856.IP "ev_timer_again (loop)" 4 2377.IP "ev_timer_again (loop, ev_timer *)" 4
857.IX Item "ev_timer_again (loop)" 2378.IX Item "ev_timer_again (loop, ev_timer *)"
858This will act as if the timer timed out and restart it again if it is 2379This will act as if the timer timed out, and restarts it again if it is
859repeating. The exact semantics are: 2380repeating. It basically works like calling \f(CW\*(C`ev_timer_stop\*(C'\fR, updating the
2381timeout to the \f(CW\*(C`repeat\*(C'\fR value and calling \f(CW\*(C`ev_timer_start\*(C'\fR.
860.Sp 2382.Sp
861If the timer is started but nonrepeating, stop it. 2383The exact semantics are as in the following rules, all of which will be
2384applied to the watcher:
2385.RS 4
2386.IP "If the timer is pending, the pending status is always cleared." 4
2387.IX Item "If the timer is pending, the pending status is always cleared."
2388.PD 0
2389.IP "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)." 4
2390.IX Item "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)."
2391.ie n .IP "If the timer is repeating, make the ""repeat"" value the new timeout and start the timer, if necessary." 4
2392.el .IP "If the timer is repeating, make the \f(CWrepeat\fR value the new timeout and start the timer, if necessary." 4
2393.IX Item "If the timer is repeating, make the repeat value the new timeout and start the timer, if necessary."
2394.RE
2395.RS 4
2396.PD
862.Sp 2397.Sp
863If the timer is repeating, either start it if necessary (with the repeat 2398This sounds a bit complicated, see \*(L"Be smart about timeouts\*(R", above, for a
864value), or reset the running timer to the repeat value. 2399usage example.
2400.RE
2401.IP "ev_tstamp ev_timer_remaining (loop, ev_timer *)" 4
2402.IX Item "ev_tstamp ev_timer_remaining (loop, ev_timer *)"
2403Returns the remaining time until a timer fires. If the timer is active,
2404then this time is relative to the current event loop time, otherwise it's
2405the timeout value currently configured.
865.Sp 2406.Sp
866This sounds a bit complicated, but here is a useful and typical 2407That is, after an \f(CW\*(C`ev_timer_set (w, 5, 7)\*(C'\fR, \f(CW\*(C`ev_timer_remaining\*(C'\fR returns
867example: Imagine you have a tcp connection and you want a so-called idle 2408\&\f(CW5\fR. When the timer is started and one second passes, \f(CW\*(C`ev_timer_remaining\*(C'\fR
868timeout, that is, you want to be called when there have been, say, 60 2409will return \f(CW4\fR. When the timer expires and is restarted, it will return
869seconds of inactivity on the socket. The easiest way to do this is to 2410roughly \f(CW7\fR (likely slightly less as callback invocation takes some time,
870configure an \f(CW\*(C`ev_timer\*(C'\fR with after=repeat=60 and calling ev_timer_again each 2411too), and so on.
871time you successfully read or write some data. If you go into an idle 2412.IP "ev_tstamp repeat [read\-write]" 4
872state where you do not expect data to travel on the socket, you can stop 2413.IX Item "ev_tstamp repeat [read-write]"
873the timer, and again will automatically restart it if need be. 2414The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
2415or \f(CW\*(C`ev_timer_again\*(C'\fR is called, and determines the next timeout (if any),
2416which is also when any modifications are taken into account.
874.PP 2417.PP
2418\fIExamples\fR
2419.IX Subsection "Examples"
2420.PP
875Example: create a timer that fires after 60 seconds. 2421Example: Create a timer that fires after 60 seconds.
876.PP 2422.PP
877.Vb 5 2423.Vb 5
878\& static void 2424\& static void
879\& one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents) 2425\& one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
880\& { 2426\& {
881\& .. one minute over, w is actually stopped right here 2427\& .. one minute over, w is actually stopped right here
882\& } 2428\& }
883.Ve 2429\&
884.PP
885.Vb 3
886\& struct ev_timer mytimer; 2430\& ev_timer mytimer;
887\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.); 2431\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
888\& ev_timer_start (loop, &mytimer); 2432\& ev_timer_start (loop, &mytimer);
889.Ve 2433.Ve
890.PP 2434.PP
891Example: create a timeout timer that times out after 10 seconds of 2435Example: Create a timeout timer that times out after 10 seconds of
892inactivity. 2436inactivity.
893.PP 2437.PP
894.Vb 5 2438.Vb 5
895\& static void 2439\& static void
896\& timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents) 2440\& timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
897\& { 2441\& {
898\& .. ten seconds without any activity 2442\& .. ten seconds without any activity
899\& } 2443\& }
900.Ve 2444\&
901.PP
902.Vb 4
903\& struct ev_timer mytimer; 2445\& ev_timer mytimer;
904\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */ 2446\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
905\& ev_timer_again (&mytimer); /* start timer */ 2447\& ev_timer_again (&mytimer); /* start timer */
906\& ev_loop (loop, 0); 2448\& ev_run (loop, 0);
907.Ve 2449\&
908.PP
909.Vb 3
910\& // and in some piece of code that gets executed on any "activity": 2450\& // and in some piece of code that gets executed on any "activity":
911\& // reset the timeout to start ticking again at 10 seconds 2451\& // reset the timeout to start ticking again at 10 seconds
912\& ev_timer_again (&mytimer); 2452\& ev_timer_again (&mytimer);
913.Ve 2453.Ve
914.ie n .Sh """ev_periodic"" \- to cron or not to cron" 2454.ie n .SS """ev_periodic"" \- to cron or not to cron?"
915.el .Sh "\f(CWev_periodic\fP \- to cron or not to cron" 2455.el .SS "\f(CWev_periodic\fP \- to cron or not to cron?"
916.IX Subsection "ev_periodic - to cron or not to cron" 2456.IX Subsection "ev_periodic - to cron or not to cron?"
917Periodic watchers are also timers of a kind, but they are very versatile 2457Periodic watchers are also timers of a kind, but they are very versatile
918(and unfortunately a bit complex). 2458(and unfortunately a bit complex).
919.PP 2459.PP
920Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time) 2460Unlike \f(CW\*(C`ev_timer\*(C'\fR, periodic watchers are not based on real time (or
921but on wallclock time (absolute time). You can tell a periodic watcher 2461relative time, the physical time that passes) but on wall clock time
922to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a 2462(absolute time, the thing you can read on your calendar or clock). The
923periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now () 2463difference is that wall clock time can run faster or slower than real
924+ 10.>) and then reset your system clock to the last year, then it will 2464time, and time jumps are not uncommon (e.g. when you adjust your
925take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger 2465wrist-watch).
926roughly 10 seconds later and of course not if you reset your system time
927again).
928.PP 2466.PP
929They can also be used to implement vastly more complex timers, such as 2467You can tell a periodic watcher to trigger after some specific point
930triggering an event on eahc midnight, local time. 2468in time: for example, if you tell a periodic watcher to trigger \*(L"in 10
2469seconds\*(R" (by specifying e.g. \f(CW\*(C`ev_now () + 10.\*(C'\fR, that is, an absolute time
2470not a delay) and then reset your system clock to January of the previous
2471year, then it will take a year or more to trigger the event (unlike an
2472\&\f(CW\*(C`ev_timer\*(C'\fR, which would still trigger roughly 10 seconds after starting
2473it, as it uses a relative timeout).
931.PP 2474.PP
2475\&\f(CW\*(C`ev_periodic\*(C'\fR watchers can also be used to implement vastly more complex
2476timers, such as triggering an event on each \*(L"midnight, local time\*(R", or
2477other complicated rules. This cannot easily be done with \f(CW\*(C`ev_timer\*(C'\fR
2478watchers, as those cannot react to time jumps.
2479.PP
932As with timers, the callback is guarenteed to be invoked only when the 2480As with timers, the callback is guaranteed to be invoked only when the
933time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready 2481point in time where it is supposed to trigger has passed. If multiple
934during the same loop iteration then order of execution is undefined. 2482timers become ready during the same loop iteration then the ones with
2483earlier time-out values are invoked before ones with later time-out values
2484(but this is no longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
2485.PP
2486\fIWatcher-Specific Functions and Data Members\fR
2487.IX Subsection "Watcher-Specific Functions and Data Members"
935.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4 2488.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
936.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 2489.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
937.PD 0 2490.PD 0
938.IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4 2491.IP "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
939.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 2492.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
940.PD 2493.PD
941Lots of arguments, lets sort it out... There are basically three modes of 2494Lots of arguments, let's sort it out... There are basically three modes of
942operation, and we will explain them from simplest to complex: 2495operation, and we will explain them from simplest to most complex:
943.RS 4 2496.RS 4
944.IP "* absolute timer (interval = reschedule_cb = 0)" 4 2497.IP "\(bu" 4
945.IX Item "absolute timer (interval = reschedule_cb = 0)" 2498absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
2499.Sp
946In this configuration the watcher triggers an event at the wallclock time 2500In this configuration the watcher triggers an event after the wall clock
947\&\f(CW\*(C`at\*(C'\fR and doesn't repeat. It will not adjust when a time jump occurs, 2501time \f(CW\*(C`offset\*(C'\fR has passed. It will not repeat and will not adjust when a
948that is, if it is to be run at January 1st 2011 then it will run when the 2502time jump occurs, that is, if it is to be run at January 1st 2011 then it
949system time reaches or surpasses this time. 2503will be stopped and invoked when the system clock reaches or surpasses
950.IP "* non-repeating interval timer (interval > 0, reschedule_cb = 0)" 4 2504this point in time.
951.IX Item "non-repeating interval timer (interval > 0, reschedule_cb = 0)" 2505.IP "\(bu" 4
2506repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
2507.Sp
952In this mode the watcher will always be scheduled to time out at the next 2508In this mode the watcher will always be scheduled to time out at the next
953\&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N) and then repeat, regardless 2509\&\f(CW\*(C`offset + N * interval\*(C'\fR time (for some integer N, which can also be
954of any time jumps. 2510negative) and then repeat, regardless of any time jumps. The \f(CW\*(C`offset\*(C'\fR
2511argument is merely an offset into the \f(CW\*(C`interval\*(C'\fR periods.
955.Sp 2512.Sp
956This can be used to create timers that do not drift with respect to system 2513This can be used to create timers that do not drift with respect to the
957time: 2514system clock, for example, here is an \f(CW\*(C`ev_periodic\*(C'\fR that triggers each
2515hour, on the hour (with respect to \s-1UTC\s0):
958.Sp 2516.Sp
959.Vb 1 2517.Vb 1
960\& ev_periodic_set (&periodic, 0., 3600., 0); 2518\& ev_periodic_set (&periodic, 0., 3600., 0);
961.Ve 2519.Ve
962.Sp 2520.Sp
963This doesn't mean there will always be 3600 seconds in between triggers, 2521This doesn't mean there will always be 3600 seconds in between triggers,
964but only that the the callback will be called when the system time shows a 2522but only that the callback will be called when the system time shows a
965full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible 2523full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
966by 3600. 2524by 3600.
967.Sp 2525.Sp
968Another way to think about it (for the mathematically inclined) is that 2526Another way to think about it (for the mathematically inclined) is that
969\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible 2527\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
970time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps. 2528time where \f(CW\*(C`time = offset (mod interval)\*(C'\fR, regardless of any time jumps.
971.IP "* manual reschedule mode (reschedule_cb = callback)" 4 2529.Sp
972.IX Item "manual reschedule mode (reschedule_cb = callback)" 2530The \f(CW\*(C`interval\*(C'\fR \fI\s-1MUST\s0\fR be positive, and for numerical stability, the
2531interval value should be higher than \f(CW\*(C`1/8192\*(C'\fR (which is around 100
2532microseconds) and \f(CW\*(C`offset\*(C'\fR should be higher than \f(CW0\fR and should have
2533at most a similar magnitude as the current time (say, within a factor of
2534ten). Typical values for offset are, in fact, \f(CW0\fR or something between
2535\&\f(CW0\fR and \f(CW\*(C`interval\*(C'\fR, which is also the recommended range.
2536.Sp
2537Note also that there is an upper limit to how often a timer can fire (\s-1CPU\s0
2538speed for example), so if \f(CW\*(C`interval\*(C'\fR is very small then timing stability
2539will of course deteriorate. Libev itself tries to be exact to be about one
2540millisecond (if the \s-1OS\s0 supports it and the machine is fast enough).
2541.IP "\(bu" 4
2542manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
2543.Sp
973In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being 2544In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`offset\*(C'\fR are both being
974ignored. Instead, each time the periodic watcher gets scheduled, the 2545ignored. Instead, each time the periodic watcher gets scheduled, the
975reschedule callback will be called with the watcher as first, and the 2546reschedule callback will be called with the watcher as first, and the
976current time as second argument. 2547current time as second argument.
977.Sp 2548.Sp
978\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, 2549\&\s-1NOTE:\s0 \fIThis callback \s-1MUST NOT\s0 stop or destroy any periodic watcher, ever,
979ever, or make any event loop modifications\fR. If you need to stop it, 2550or make \s-1ANY\s0 other event loop modifications whatsoever, unless explicitly
980return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by 2551allowed by documentation here\fR.
981starting a prepare watcher).
982.Sp 2552.Sp
2553If you need to stop it, return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop
2554it afterwards (e.g. by starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is the
2555only event loop modification you are allowed to do).
2556.Sp
983Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w, 2557The callback prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(ev_periodic
984ev_tstamp now)\*(C'\fR, e.g.: 2558*w, ev_tstamp now)\*(C'\fR, e.g.:
985.Sp 2559.Sp
986.Vb 4 2560.Vb 5
2561\& static ev_tstamp
987\& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) 2562\& my_rescheduler (ev_periodic *w, ev_tstamp now)
988\& { 2563\& {
989\& return now + 60.; 2564\& return now + 60.;
990\& } 2565\& }
991.Ve 2566.Ve
992.Sp 2567.Sp
993It must return the next time to trigger, based on the passed time value 2568It must return the next time to trigger, based on the passed time value
994(that is, the lowest time value larger than to the second argument). It 2569(that is, the lowest time value larger than to the second argument). It
995will usually be called just before the callback will be triggered, but 2570will usually be called just before the callback will be triggered, but
996might be called at other times, too. 2571might be called at other times, too.
997.Sp 2572.Sp
998\&\s-1NOTE:\s0 \fIThis callback must always return a time that is later than the 2573\&\s-1NOTE:\s0 \fIThis callback must always return a time that is higher than or
999passed \f(CI\*(C`now\*(C'\fI value\fR. Not even \f(CW\*(C`now\*(C'\fR itself will do, it \fImust\fR be larger. 2574equal to the passed \f(CI\*(C`now\*(C'\fI value\fR.
1000.Sp 2575.Sp
1001This can be used to create very complex timers, such as a timer that 2576This can be used to create very complex timers, such as a timer that
1002triggers on each midnight, local time. To do this, you would calculate the 2577triggers on \*(L"next midnight, local time\*(R". To do this, you would calculate
1003next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How 2578the next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for
1004you do this is, again, up to you (but it is not trivial, which is the main 2579this. Here is a (completely untested, no error checking) example on how to
1005reason I omitted it as an example). 2580do this:
2581.Sp
2582.Vb 1
2583\& #include <time.h>
2584\&
2585\& static ev_tstamp
2586\& my_rescheduler (ev_periodic *w, ev_tstamp now)
2587\& {
2588\& time_t tnow = (time_t)now;
2589\& struct tm tm;
2590\& localtime_r (&tnow, &tm);
2591\&
2592\& tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
2593\& ++tm.tm_mday; // midnight next day
2594\&
2595\& return mktime (&tm);
2596\& }
2597.Ve
2598.Sp
2599Note: this code might run into trouble on days that have more then two
2600midnights (beginning and end).
1006.RE 2601.RE
1007.RS 4 2602.RS 4
1008.RE 2603.RE
1009.IP "ev_periodic_again (loop, ev_periodic *)" 4 2604.IP "ev_periodic_again (loop, ev_periodic *)" 4
1010.IX Item "ev_periodic_again (loop, ev_periodic *)" 2605.IX Item "ev_periodic_again (loop, ev_periodic *)"
1011Simply stops and restarts the periodic watcher again. This is only useful 2606Simply stops and restarts the periodic watcher again. This is only useful
1012when you changed some parameters or the reschedule callback would return 2607when you changed some parameters or the reschedule callback would return
1013a different time than the last time it was called (e.g. in a crond like 2608a different time than the last time it was called (e.g. in a crond like
1014program when the crontabs have changed). 2609program when the crontabs have changed).
2610.IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4
2611.IX Item "ev_tstamp ev_periodic_at (ev_periodic *)"
2612When active, returns the absolute time that the watcher is supposed
2613to trigger next. This is not the same as the \f(CW\*(C`offset\*(C'\fR argument to
2614\&\f(CW\*(C`ev_periodic_set\*(C'\fR, but indeed works even in interval and manual
2615rescheduling modes.
2616.IP "ev_tstamp offset [read\-write]" 4
2617.IX Item "ev_tstamp offset [read-write]"
2618When repeating, this contains the offset value, otherwise this is the
2619absolute point in time (the \f(CW\*(C`offset\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR,
2620although libev might modify this value for better numerical stability).
2621.Sp
2622Can be modified any time, but changes only take effect when the periodic
2623timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
2624.IP "ev_tstamp interval [read\-write]" 4
2625.IX Item "ev_tstamp interval [read-write]"
2626The current interval value. Can be modified any time, but changes only
2627take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
2628called.
2629.IP "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read\-write]" 4
2630.IX Item "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]"
2631The current reschedule callback, or \f(CW0\fR, if this functionality is
2632switched off. Can be changed any time, but changes only take effect when
2633the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1015.PP 2634.PP
2635\fIExamples\fR
2636.IX Subsection "Examples"
2637.PP
1016Example: call a callback every hour, or, more precisely, whenever the 2638Example: Call a callback every hour, or, more precisely, whenever the
1017system clock is divisible by 3600. The callback invocation times have 2639system time is divisible by 3600. The callback invocation times have
1018potentially a lot of jittering, but good long-term stability. 2640potentially a lot of jitter, but good long-term stability.
1019.PP 2641.PP
1020.Vb 5 2642.Vb 5
1021\& static void 2643\& static void
1022\& clock_cb (struct ev_loop *loop, struct ev_io *w, int revents) 2644\& clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1023\& { 2645\& {
1024\& ... its now a full hour (UTC, or TAI or whatever your clock follows) 2646\& ... its now a full hour (UTC, or TAI or whatever your clock follows)
1025\& } 2647\& }
1026.Ve 2648\&
1027.PP
1028.Vb 3
1029\& struct ev_periodic hourly_tick; 2649\& ev_periodic hourly_tick;
1030\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0); 2650\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1031\& ev_periodic_start (loop, &hourly_tick); 2651\& ev_periodic_start (loop, &hourly_tick);
1032.Ve 2652.Ve
1033.PP 2653.PP
1034Example: the same as above, but use a reschedule callback to do it: 2654Example: The same as above, but use a reschedule callback to do it:
1035.PP 2655.PP
1036.Vb 1 2656.Vb 1
1037\& #include <math.h> 2657\& #include <math.h>
1038.Ve 2658\&
1039.PP
1040.Vb 5
1041\& static ev_tstamp 2659\& static ev_tstamp
1042\& my_scheduler_cb (struct ev_periodic *w, ev_tstamp now) 2660\& my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1043\& { 2661\& {
1044\& return fmod (now, 3600.) + 3600.; 2662\& return now + (3600. \- fmod (now, 3600.));
1045\& } 2663\& }
1046.Ve 2664\&
1047.PP
1048.Vb 1
1049\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb); 2665\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1050.Ve 2666.Ve
1051.PP 2667.PP
1052Example: call a callback every hour, starting now: 2668Example: Call a callback every hour, starting now:
1053.PP 2669.PP
1054.Vb 4 2670.Vb 4
1055\& struct ev_periodic hourly_tick; 2671\& ev_periodic hourly_tick;
1056\& ev_periodic_init (&hourly_tick, clock_cb, 2672\& ev_periodic_init (&hourly_tick, clock_cb,
1057\& fmod (ev_now (loop), 3600.), 3600., 0); 2673\& fmod (ev_now (loop), 3600.), 3600., 0);
1058\& ev_periodic_start (loop, &hourly_tick); 2674\& ev_periodic_start (loop, &hourly_tick);
1059.Ve 2675.Ve
1060.ie n .Sh """ev_signal"" \- signal me when a signal gets signalled" 2676.ie n .SS """ev_signal"" \- signal me when a signal gets signalled!"
1061.el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled" 2677.el .SS "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
1062.IX Subsection "ev_signal - signal me when a signal gets signalled" 2678.IX Subsection "ev_signal - signal me when a signal gets signalled!"
1063Signal watchers will trigger an event when the process receives a specific 2679Signal watchers will trigger an event when the process receives a specific
1064signal one or more times. Even though signals are very asynchronous, libev 2680signal one or more times. Even though signals are very asynchronous, libev
1065will try it's best to deliver signals synchronously, i.e. as part of the 2681will try its best to deliver signals synchronously, i.e. as part of the
1066normal event processing, like any other event. 2682normal event processing, like any other event.
1067.PP 2683.PP
2684If you want signals to be delivered truly asynchronously, just use
2685\&\f(CW\*(C`sigaction\*(C'\fR as you would do without libev and forget about sharing
2686the signal. You can even use \f(CW\*(C`ev_async\*(C'\fR from a signal handler to
2687synchronously wake up an event loop.
2688.PP
1068You can configure as many watchers as you like per signal. Only when the 2689You can configure as many watchers as you like for the same signal, but
1069first watcher gets started will libev actually register a signal watcher 2690only within the same loop, i.e. you can watch for \f(CW\*(C`SIGINT\*(C'\fR in your
1070with the kernel (thus it coexists with your own signal handlers as long 2691default loop and for \f(CW\*(C`SIGIO\*(C'\fR in another loop, but you cannot watch for
1071as you don't register any with libev). Similarly, when the last signal 2692\&\f(CW\*(C`SIGINT\*(C'\fR in both the default loop and another loop at the same time. At
1072watcher for a signal is stopped libev will reset the signal handler to 2693the moment, \f(CW\*(C`SIGCHLD\*(C'\fR is permanently tied to the default loop.
1073\&\s-1SIG_DFL\s0 (regardless of what it was set to before). 2694.PP
2695Only after the first watcher for a signal is started will libev actually
2696register something with the kernel. It thus coexists with your own signal
2697handlers as long as you don't register any with libev for the same signal.
2698.PP
2699If possible and supported, libev will install its handlers with
2700\&\f(CW\*(C`SA_RESTART\*(C'\fR (or equivalent) behaviour enabled, so system calls should
2701not be unduly interrupted. If you have a problem with system calls getting
2702interrupted by signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher
2703and unblock them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher.
2704.PP
2705\fIThe special problem of inheritance over fork/execve/pthread_create\fR
2706.IX Subsection "The special problem of inheritance over fork/execve/pthread_create"
2707.PP
2708Both the signal mask (\f(CW\*(C`sigprocmask\*(C'\fR) and the signal disposition
2709(\f(CW\*(C`sigaction\*(C'\fR) are unspecified after starting a signal watcher (and after
2710stopping it again), that is, libev might or might not block the signal,
2711and might or might not set or restore the installed signal handler (but
2712see \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR).
2713.PP
2714While this does not matter for the signal disposition (libev never
2715sets signals to \f(CW\*(C`SIG_IGN\*(C'\fR, so handlers will be reset to \f(CW\*(C`SIG_DFL\*(C'\fR on
2716\&\f(CW\*(C`execve\*(C'\fR), this matters for the signal mask: many programs do not expect
2717certain signals to be blocked.
2718.PP
2719This means that before calling \f(CW\*(C`exec\*(C'\fR (from the child) you should reset
2720the signal mask to whatever \*(L"default\*(R" you expect (all clear is a good
2721choice usually).
2722.PP
2723The simplest way to ensure that the signal mask is reset in the child is
2724to install a fork handler with \f(CW\*(C`pthread_atfork\*(C'\fR that resets it. That will
2725catch fork calls done by libraries (such as the libc) as well.
2726.PP
2727In current versions of libev, the signal will not be blocked indefinitely
2728unless you use the \f(CW\*(C`signalfd\*(C'\fR \s-1API\s0 (\f(CW\*(C`EV_SIGNALFD\*(C'\fR). While this reduces
2729the window of opportunity for problems, it will not go away, as libev
2730\&\fIhas\fR to modify the signal mask, at least temporarily.
2731.PP
2732So I can't stress this enough: \fIIf you do not reset your signal mask when
2733you expect it to be empty, you have a race condition in your code\fR. This
2734is not a libev-specific thing, this is true for most event libraries.
2735.PP
2736\fIThe special problem of threads signal handling\fR
2737.IX Subsection "The special problem of threads signal handling"
2738.PP
2739\&\s-1POSIX\s0 threads has problematic signal handling semantics, specifically,
2740a lot of functionality (sigfd, sigwait etc.) only really works if all
2741threads in a process block signals, which is hard to achieve.
2742.PP
2743When you want to use sigwait (or mix libev signal handling with your own
2744for the same signals), you can tackle this problem by globally blocking
2745all signals before creating any threads (or creating them with a fully set
2746sigprocmask) and also specifying the \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when creating
2747loops. Then designate one thread as \*(L"signal receiver thread\*(R" which handles
2748these signals. You can pass on any signals that libev might be interested
2749in by calling \f(CW\*(C`ev_feed_signal\*(C'\fR.
2750.PP
2751\fIWatcher-Specific Functions and Data Members\fR
2752.IX Subsection "Watcher-Specific Functions and Data Members"
1074.IP "ev_signal_init (ev_signal *, callback, int signum)" 4 2753.IP "ev_signal_init (ev_signal *, callback, int signum)" 4
1075.IX Item "ev_signal_init (ev_signal *, callback, int signum)" 2754.IX Item "ev_signal_init (ev_signal *, callback, int signum)"
1076.PD 0 2755.PD 0
1077.IP "ev_signal_set (ev_signal *, int signum)" 4 2756.IP "ev_signal_set (ev_signal *, int signum)" 4
1078.IX Item "ev_signal_set (ev_signal *, int signum)" 2757.IX Item "ev_signal_set (ev_signal *, int signum)"
1079.PD 2758.PD
1080Configures the watcher to trigger on the given signal number (usually one 2759Configures the watcher to trigger on the given signal number (usually one
1081of the \f(CW\*(C`SIGxxx\*(C'\fR constants). 2760of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
2761.IP "int signum [read\-only]" 4
2762.IX Item "int signum [read-only]"
2763The signal the watcher watches out for.
2764.PP
2765\fIExamples\fR
2766.IX Subsection "Examples"
2767.PP
2768Example: Try to exit cleanly on \s-1SIGINT.\s0
2769.PP
2770.Vb 5
2771\& static void
2772\& sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
2773\& {
2774\& ev_break (loop, EVBREAK_ALL);
2775\& }
2776\&
2777\& ev_signal signal_watcher;
2778\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
2779\& ev_signal_start (loop, &signal_watcher);
2780.Ve
1082.ie n .Sh """ev_child"" \- wait for pid status changes" 2781.ie n .SS """ev_child"" \- watch out for process status changes"
1083.el .Sh "\f(CWev_child\fP \- wait for pid status changes" 2782.el .SS "\f(CWev_child\fP \- watch out for process status changes"
1084.IX Subsection "ev_child - wait for pid status changes" 2783.IX Subsection "ev_child - watch out for process status changes"
1085Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to 2784Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
1086some child status changes (most typically when a child of yours dies). 2785some child status changes (most typically when a child of yours dies or
2786exits). It is permissible to install a child watcher \fIafter\fR the child
2787has been forked (which implies it might have already exited), as long
2788as the event loop isn't entered (or is continued from a watcher), i.e.,
2789forking and then immediately registering a watcher for the child is fine,
2790but forking and registering a watcher a few event loop iterations later or
2791in the next callback invocation is not.
2792.PP
2793Only the default event loop is capable of handling signals, and therefore
2794you can only register child watchers in the default event loop.
2795.PP
2796Due to some design glitches inside libev, child watchers will always be
2797handled at maximum priority (their priority is set to \f(CW\*(C`EV_MAXPRI\*(C'\fR by
2798libev)
2799.PP
2800\fIProcess Interaction\fR
2801.IX Subsection "Process Interaction"
2802.PP
2803Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is
2804initialised. This is necessary to guarantee proper behaviour even if the
2805first child watcher is started after the child exits. The occurrence
2806of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done
2807synchronously as part of the event loop processing. Libev always reaps all
2808children, even ones not watched.
2809.PP
2810\fIOverriding the Built-In Processing\fR
2811.IX Subsection "Overriding the Built-In Processing"
2812.PP
2813Libev offers no special support for overriding the built-in child
2814processing, but if your application collides with libev's default child
2815handler, you can override it easily by installing your own handler for
2816\&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the
2817default loop never gets destroyed. You are encouraged, however, to use an
2818event-based approach to child reaping and thus use libev's support for
2819that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely.
2820.PP
2821\fIStopping the Child Watcher\fR
2822.IX Subsection "Stopping the Child Watcher"
2823.PP
2824Currently, the child watcher never gets stopped, even when the
2825child terminates, so normally one needs to stop the watcher in the
2826callback. Future versions of libev might stop the watcher automatically
2827when a child exit is detected (calling \f(CW\*(C`ev_child_stop\*(C'\fR twice is not a
2828problem).
2829.PP
2830\fIWatcher-Specific Functions and Data Members\fR
2831.IX Subsection "Watcher-Specific Functions and Data Members"
1087.IP "ev_child_init (ev_child *, callback, int pid)" 4 2832.IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4
1088.IX Item "ev_child_init (ev_child *, callback, int pid)" 2833.IX Item "ev_child_init (ev_child *, callback, int pid, int trace)"
1089.PD 0 2834.PD 0
1090.IP "ev_child_set (ev_child *, int pid)" 4 2835.IP "ev_child_set (ev_child *, int pid, int trace)" 4
1091.IX Item "ev_child_set (ev_child *, int pid)" 2836.IX Item "ev_child_set (ev_child *, int pid, int trace)"
1092.PD 2837.PD
1093Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or 2838Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
1094\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look 2839\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
1095at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see 2840at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
1096the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems 2841the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
1097\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the 2842\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
1098process causing the status change. 2843process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only
2844activate the watcher when the process terminates) or \f(CW1\fR (additionally
2845activate the watcher when the process is stopped or continued).
2846.IP "int pid [read\-only]" 4
2847.IX Item "int pid [read-only]"
2848The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
2849.IP "int rpid [read\-write]" 4
2850.IX Item "int rpid [read-write]"
2851The process id that detected a status change.
2852.IP "int rstatus [read\-write]" 4
2853.IX Item "int rstatus [read-write]"
2854The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
2855\&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
1099.PP 2856.PP
1100Example: try to exit cleanly on \s-1SIGINT\s0 and \s-1SIGTERM\s0. 2857\fIExamples\fR
2858.IX Subsection "Examples"
1101.PP 2859.PP
2860Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for
2861its completion.
2862.PP
1102.Vb 5 2863.Vb 1
2864\& ev_child cw;
2865\&
1103\& static void 2866\& static void
1104\& sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents) 2867\& child_cb (EV_P_ ev_child *w, int revents)
1105\& { 2868\& {
1106\& ev_unloop (loop, EVUNLOOP_ALL); 2869\& ev_child_stop (EV_A_ w);
2870\& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus);
1107\& } 2871\& }
2872\&
2873\& pid_t pid = fork ();
2874\&
2875\& if (pid < 0)
2876\& // error
2877\& else if (pid == 0)
2878\& {
2879\& // the forked child executes here
2880\& exit (1);
2881\& }
2882\& else
2883\& {
2884\& ev_child_init (&cw, child_cb, pid, 0);
2885\& ev_child_start (EV_DEFAULT_ &cw);
2886\& }
1108.Ve 2887.Ve
2888.ie n .SS """ev_stat"" \- did the file attributes just change?"
2889.el .SS "\f(CWev_stat\fP \- did the file attributes just change?"
2890.IX Subsection "ev_stat - did the file attributes just change?"
2891This watches a file system path for attribute changes. That is, it calls
2892\&\f(CW\*(C`stat\*(C'\fR on that path in regular intervals (or when the \s-1OS\s0 says it changed)
2893and sees if it changed compared to the last time, invoking the callback
2894if it did. Starting the watcher \f(CW\*(C`stat\*(C'\fR's the file, so only changes that
2895happen after the watcher has been started will be reported.
1109.PP 2896.PP
2897The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does
2898not exist\*(R" is a status change like any other. The condition \*(L"path does not
2899exist\*(R" (or more correctly \*(L"path cannot be stat'ed\*(R") is signified by the
2900\&\f(CW\*(C`st_nlink\*(C'\fR field being zero (which is otherwise always forced to be at
2901least one) and all the other fields of the stat buffer having unspecified
2902contents.
2903.PP
2904The path \fImust not\fR end in a slash or contain special components such as
2905\&\f(CW\*(C`.\*(C'\fR or \f(CW\*(C`..\*(C'\fR. The path \fIshould\fR be absolute: If it is relative and
2906your working directory changes, then the behaviour is undefined.
2907.PP
2908Since there is no portable change notification interface available, the
2909portable implementation simply calls \f(CWstat(2)\fR regularly on the path
2910to see if it changed somehow. You can specify a recommended polling
2911interval for this case. If you specify a polling interval of \f(CW0\fR (highly
2912recommended!) then a \fIsuitable, unspecified default\fR value will be used
2913(which you can expect to be around five seconds, although this might
2914change dynamically). Libev will also impose a minimum interval which is
2915currently around \f(CW0.1\fR, but that's usually overkill.
2916.PP
2917This watcher type is not meant for massive numbers of stat watchers,
2918as even with OS-supported change notifications, this can be
2919resource-intensive.
2920.PP
2921At the time of this writing, the only OS-specific interface implemented
2922is the Linux inotify interface (implementing kqueue support is left as an
2923exercise for the reader. Note, however, that the author sees no way of
2924implementing \f(CW\*(C`ev_stat\*(C'\fR semantics with kqueue, except as a hint).
2925.PP
2926\fI\s-1ABI\s0 Issues (Largefile Support)\fR
2927.IX Subsection "ABI Issues (Largefile Support)"
2928.PP
2929Libev by default (unless the user overrides this) uses the default
2930compilation environment, which means that on systems with large file
2931support disabled by default, you get the 32 bit version of the stat
2932structure. When using the library from programs that change the \s-1ABI\s0 to
2933use 64 bit file offsets the programs will fail. In that case you have to
2934compile libev with the same flags to get binary compatibility. This is
2935obviously the case with any flags that change the \s-1ABI,\s0 but the problem is
2936most noticeably displayed with ev_stat and large file support.
2937.PP
2938The solution for this is to lobby your distribution maker to make large
2939file interfaces available by default (as e.g. FreeBSD does) and not
2940optional. Libev cannot simply switch on large file support because it has
2941to exchange stat structures with application programs compiled using the
2942default compilation environment.
2943.PP
2944\fIInotify and Kqueue\fR
2945.IX Subsection "Inotify and Kqueue"
2946.PP
2947When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev and present at
2948runtime, it will be used to speed up change detection where possible. The
2949inotify descriptor will be created lazily when the first \f(CW\*(C`ev_stat\*(C'\fR
2950watcher is being started.
2951.PP
2952Inotify presence does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
2953except that changes might be detected earlier, and in some cases, to avoid
2954making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presence of inotify support
2955there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling,
2956but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
2957many bugs), the path exists (i.e. stat succeeds), and the path resides on
2958a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
2959xfs are fully working) libev usually gets away without polling.
2960.PP
2961There is no support for kqueue, as apparently it cannot be used to
2962implement this functionality, due to the requirement of having a file
2963descriptor open on the object at all times, and detecting renames, unlinks
2964etc. is difficult.
2965.PP
2966\fI\f(CI\*(C`stat ()\*(C'\fI is a synchronous operation\fR
2967.IX Subsection "stat () is a synchronous operation"
2968.PP
2969Libev doesn't normally do any kind of I/O itself, and so is not blocking
2970the process. The exception are \f(CW\*(C`ev_stat\*(C'\fR watchers \- those call \f(CW\*(C`stat
2971()\*(C'\fR, which is a synchronous operation.
2972.PP
2973For local paths, this usually doesn't matter: unless the system is very
2974busy or the intervals between stat's are large, a stat call will be fast,
2975as the path data is usually in memory already (except when starting the
2976watcher).
2977.PP
2978For networked file systems, calling \f(CW\*(C`stat ()\*(C'\fR can block an indefinite
2979time due to network issues, and even under good conditions, a stat call
2980often takes multiple milliseconds.
2981.PP
2982Therefore, it is best to avoid using \f(CW\*(C`ev_stat\*(C'\fR watchers on networked
2983paths, although this is fully supported by libev.
2984.PP
2985\fIThe special problem of stat time resolution\fR
2986.IX Subsection "The special problem of stat time resolution"
2987.PP
2988The \f(CW\*(C`stat ()\*(C'\fR system call only supports full-second resolution portably,
2989and even on systems where the resolution is higher, most file systems
2990still only support whole seconds.
2991.PP
2992That means that, if the time is the only thing that changes, you can
2993easily miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and
2994calls your callback, which does something. When there is another update
2995within the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect unless the
2996stat data does change in other ways (e.g. file size).
2997.PP
2998The solution to this is to delay acting on a change for slightly more
2999than a second (or till slightly after the next full second boundary), using
3000a roughly one-second-delay \f(CW\*(C`ev_timer\*(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02);
3001ev_timer_again (loop, w)\*(C'\fR).
3002.PP
3003The \f(CW.02\fR offset is added to work around small timing inconsistencies
3004of some operating systems (where the second counter of the current time
3005might be be delayed. One such system is the Linux kernel, where a call to
3006\&\f(CW\*(C`gettimeofday\*(C'\fR might return a timestamp with a full second later than
3007a subsequent \f(CW\*(C`time\*(C'\fR call \- if the equivalent of \f(CW\*(C`time ()\*(C'\fR is used to
3008update file times then there will be a small window where the kernel uses
3009the previous second to update file times but libev might already execute
3010the timer callback).
3011.PP
3012\fIWatcher-Specific Functions and Data Members\fR
3013.IX Subsection "Watcher-Specific Functions and Data Members"
3014.IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
3015.IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
3016.PD 0
3017.IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4
3018.IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)"
3019.PD
3020Configures the watcher to wait for status changes of the given
3021\&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to
3022be detected and should normally be specified as \f(CW0\fR to let libev choose
3023a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same
3024path for as long as the watcher is active.
3025.Sp
3026The callback will receive an \f(CW\*(C`EV_STAT\*(C'\fR event when a change was detected,
3027relative to the attributes at the time the watcher was started (or the
3028last change was detected).
3029.IP "ev_stat_stat (loop, ev_stat *)" 4
3030.IX Item "ev_stat_stat (loop, ev_stat *)"
3031Updates the stat buffer immediately with new values. If you change the
3032watched path in your callback, you could call this function to avoid
3033detecting this change (while introducing a race condition if you are not
3034the only one changing the path). Can also be useful simply to find out the
3035new values.
3036.IP "ev_statdata attr [read\-only]" 4
3037.IX Item "ev_statdata attr [read-only]"
3038The most-recently detected attributes of the file. Although the type is
3039\&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
3040suitable for your system, but you can only rely on the POSIX-standardised
3041members to be present. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there was
3042some error while \f(CW\*(C`stat\*(C'\fRing the file.
3043.IP "ev_statdata prev [read\-only]" 4
3044.IX Item "ev_statdata prev [read-only]"
3045The previous attributes of the file. The callback gets invoked whenever
3046\&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR, or, more precisely, one or more of these members
3047differ: \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,
3048\&\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.
3049.IP "ev_tstamp interval [read\-only]" 4
3050.IX Item "ev_tstamp interval [read-only]"
3051The specified interval.
3052.IP "const char *path [read\-only]" 4
3053.IX Item "const char *path [read-only]"
3054The file system path that is being watched.
3055.PP
3056\fIExamples\fR
3057.IX Subsection "Examples"
3058.PP
3059Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
3060.PP
3061.Vb 10
3062\& static void
3063\& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
3064\& {
3065\& /* /etc/passwd changed in some way */
3066\& if (w\->attr.st_nlink)
3067\& {
3068\& printf ("passwd current size %ld\en", (long)w\->attr.st_size);
3069\& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime);
3070\& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime);
3071\& }
3072\& else
3073\& /* you shalt not abuse printf for puts */
3074\& puts ("wow, /etc/passwd is not there, expect problems. "
3075\& "if this is windows, they already arrived\en");
3076\& }
3077\&
3078\& ...
3079\& ev_stat passwd;
3080\&
3081\& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
3082\& ev_stat_start (loop, &passwd);
3083.Ve
3084.PP
3085Example: Like above, but additionally use a one-second delay so we do not
3086miss updates (however, frequent updates will delay processing, too, so
3087one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
3088\&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
3089.PP
1110.Vb 3 3090.Vb 2
1111\& struct ev_signal signal_watcher; 3091\& static ev_stat passwd;
1112\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT); 3092\& static ev_timer timer;
1113\& ev_signal_start (loop, &sigint_cb); 3093\&
3094\& static void
3095\& timer_cb (EV_P_ ev_timer *w, int revents)
3096\& {
3097\& ev_timer_stop (EV_A_ w);
3098\&
3099\& /* now it\*(Aqs one second after the most recent passwd change */
3100\& }
3101\&
3102\& static void
3103\& stat_cb (EV_P_ ev_stat *w, int revents)
3104\& {
3105\& /* reset the one\-second timer */
3106\& ev_timer_again (EV_A_ &timer);
3107\& }
3108\&
3109\& ...
3110\& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
3111\& ev_stat_start (loop, &passwd);
3112\& ev_timer_init (&timer, timer_cb, 0., 1.02);
1114.Ve 3113.Ve
1115.ie n .Sh """ev_idle"" \- when you've got nothing better to do" 3114.ie n .SS """ev_idle"" \- when you've got nothing better to do..."
1116.el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do" 3115.el .SS "\f(CWev_idle\fP \- when you've got nothing better to do..."
1117.IX Subsection "ev_idle - when you've got nothing better to do" 3116.IX Subsection "ev_idle - when you've got nothing better to do..."
1118Idle watchers trigger events when there are no other events are pending 3117Idle watchers trigger events when no other events of the same or higher
1119(prepare, check and other idle watchers do not count). That is, as long 3118priority are pending (prepare, check and other idle watchers do not count
1120as your process is busy handling sockets or timeouts (or even signals, 3119as receiving \*(L"events\*(R").
1121imagine) it will not be triggered. But when your process is idle all idle 3120.PP
1122watchers are being called again and again, once per event loop iteration \- 3121That is, as long as your process is busy handling sockets or timeouts
3122(or even signals, imagine) of the same or higher priority it will not be
3123triggered. But when your process is idle (or only lower-priority watchers
3124are pending), the idle watchers are being called once per event loop
1123until stopped, that is, or your process receives more events and becomes 3125iteration \- until stopped, that is, or your process receives more events
1124busy. 3126and becomes busy again with higher priority stuff.
1125.PP 3127.PP
1126The most noteworthy effect is that as long as any idle watchers are 3128The most noteworthy effect is that as long as any idle watchers are
1127active, the process will not block when waiting for new events. 3129active, the process will not block when waiting for new events.
1128.PP 3130.PP
1129Apart from keeping your process non-blocking (which is a useful 3131Apart from keeping your process non-blocking (which is a useful
1130effect on its own sometimes), idle watchers are a good place to do 3132effect on its own sometimes), idle watchers are a good place to do
1131\&\*(L"pseudo\-background processing\*(R", or delay processing stuff to after the 3133\&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the
1132event loop has handled all outstanding events. 3134event loop has handled all outstanding events.
3135.PP
3136\fIAbusing an \f(CI\*(C`ev_idle\*(C'\fI watcher for its side-effect\fR
3137.IX Subsection "Abusing an ev_idle watcher for its side-effect"
3138.PP
3139As long as there is at least one active idle watcher, libev will never
3140sleep unnecessarily. Or in other words, it will loop as fast as possible.
3141For this to work, the idle watcher doesn't need to be invoked at all \- the
3142lowest priority will do.
3143.PP
3144This mode of operation can be useful together with an \f(CW\*(C`ev_check\*(C'\fR watcher,
3145to do something on each event loop iteration \- for example to balance load
3146between different connections.
3147.PP
3148See \*(L"Abusing an ev_check watcher for its side-effect\*(R" for a longer
3149example.
3150.PP
3151\fIWatcher-Specific Functions and Data Members\fR
3152.IX Subsection "Watcher-Specific Functions and Data Members"
1133.IP "ev_idle_init (ev_signal *, callback)" 4 3153.IP "ev_idle_init (ev_idle *, callback)" 4
1134.IX Item "ev_idle_init (ev_signal *, callback)" 3154.IX Item "ev_idle_init (ev_idle *, callback)"
1135Initialises and configures the idle watcher \- it has no parameters of any 3155Initialises and configures the idle watcher \- it has no parameters of any
1136kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless, 3156kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
1137believe me. 3157believe me.
1138.PP 3158.PP
3159\fIExamples\fR
3160.IX Subsection "Examples"
3161.PP
1139Example: dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR, start it, and in the 3162Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the
1140callback, free it. Alos, use no error checking, as usual. 3163callback, free it. Also, use no error checking, as usual.
1141.PP 3164.PP
1142.Vb 7 3165.Vb 5
1143\& static void 3166\& static void
1144\& idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents) 3167\& idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1145\& { 3168\& {
3169\& // stop the watcher
3170\& ev_idle_stop (loop, w);
3171\&
3172\& // now we can free it
1146\& free (w); 3173\& free (w);
3174\&
1147\& // now do something you wanted to do when the program has 3175\& // now do something you wanted to do when the program has
1148\& // no longer asnything immediate to do. 3176\& // no longer anything immediate to do.
1149\& } 3177\& }
1150.Ve 3178\&
1151.PP
1152.Vb 3
1153\& struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle)); 3179\& ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1154\& ev_idle_init (idle_watcher, idle_cb); 3180\& ev_idle_init (idle_watcher, idle_cb);
1155\& ev_idle_start (loop, idle_cb); 3181\& ev_idle_start (loop, idle_watcher);
1156.Ve 3182.Ve
1157.ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop" 3183.ie n .SS """ev_prepare"" and ""ev_check"" \- customise your event loop!"
1158.el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop" 3184.el .SS "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
1159.IX Subsection "ev_prepare and ev_check - customise your event loop" 3185.IX Subsection "ev_prepare and ev_check - customise your event loop!"
1160Prepare and check watchers are usually (but not always) used in tandem: 3186Prepare and check watchers are often (but not always) used in pairs:
1161prepare watchers get invoked before the process blocks and check watchers 3187prepare watchers get invoked before the process blocks and check watchers
1162afterwards. 3188afterwards.
1163.PP 3189.PP
3190You \fImust not\fR call \f(CW\*(C`ev_run\*(C'\fR (or similar functions that enter the
3191current event loop) or \f(CW\*(C`ev_loop_fork\*(C'\fR from either \f(CW\*(C`ev_prepare\*(C'\fR or
3192\&\f(CW\*(C`ev_check\*(C'\fR watchers. Other loops than the current one are fine,
3193however. The rationale behind this is that you do not need to check
3194for recursion in those watchers, i.e. the sequence will always be
3195\&\f(CW\*(C`ev_prepare\*(C'\fR, blocking, \f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each
3196kind they will always be called in pairs bracketing the blocking call.
3197.PP
1164Their main purpose is to integrate other event mechanisms into libev. This 3198Their main purpose is to integrate other event mechanisms into libev and
1165could be used, for example, to track variable changes, implement your own 3199their use is somewhat advanced. They could be used, for example, to track
1166watchers, integrate net-snmp or a coroutine library and lots more. 3200variable changes, implement your own watchers, integrate net-snmp or a
3201coroutine library and lots more. They are also occasionally useful if
3202you cache some data and want to flush it before blocking (for example,
3203in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
3204watcher).
1167.PP 3205.PP
1168This is done by examining in each prepare call which file descriptors need 3206This is done by examining in each prepare call which file descriptors
1169to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers for 3207need to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers
1170them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many libraries 3208for them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many
1171provide just this functionality). Then, in the check watcher you check for 3209libraries provide exactly this functionality). Then, in the check watcher,
1172any events that occured (by checking the pending status of all watchers 3210you check for any events that occurred (by checking the pending status
1173and stopping them) and call back into the library. The I/O and timer 3211of all watchers and stopping them) and call back into the library. The
1174callbacks will never actually be called (but must be valid nevertheless, 3212I/O and timer callbacks will never actually be called (but must be valid
1175because you never know, you know?). 3213nevertheless, because you never know, you know?).
1176.PP 3214.PP
1177As another example, the Perl Coro module uses these hooks to integrate 3215As another example, the Perl Coro module uses these hooks to integrate
1178coroutines into libev programs, by yielding to other active coroutines 3216coroutines into libev programs, by yielding to other active coroutines
1179during each prepare and only letting the process block if no coroutines 3217during each prepare and only letting the process block if no coroutines
1180are ready to run (it's actually more complicated: it only runs coroutines 3218are ready to run (it's actually more complicated: it only runs coroutines
1181with priority higher than or equal to the event loop and one coroutine 3219with priority higher than or equal to the event loop and one coroutine
1182of lower priority, but only once, using idle watchers to keep the event 3220of lower priority, but only once, using idle watchers to keep the event
1183loop from blocking if lower-priority coroutines are active, thus mapping 3221loop from blocking if lower-priority coroutines are active, thus mapping
1184low-priority coroutines to idle/background tasks). 3222low-priority coroutines to idle/background tasks).
3223.PP
3224When used for this purpose, it is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers
3225highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR) priority, to ensure that they are being run before
3226any other watchers after the poll (this doesn't matter for \f(CW\*(C`ev_prepare\*(C'\fR
3227watchers).
3228.PP
3229Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, too) should not
3230activate (\*(L"feed\*(R") events into libev. While libev fully supports this, they
3231might get executed before other \f(CW\*(C`ev_check\*(C'\fR watchers did their job. As
3232\&\f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other (non-libev) event
3233loops those other event loops might be in an unusable state until their
3234\&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with
3235others).
3236.PP
3237\fIAbusing an \f(CI\*(C`ev_check\*(C'\fI watcher for its side-effect\fR
3238.IX Subsection "Abusing an ev_check watcher for its side-effect"
3239.PP
3240\&\f(CW\*(C`ev_check\*(C'\fR (and less often also \f(CW\*(C`ev_prepare\*(C'\fR) watchers can also be
3241useful because they are called once per event loop iteration. For
3242example, if you want to handle a large number of connections fairly, you
3243normally only do a bit of work for each active connection, and if there
3244is more work to do, you wait for the next event loop iteration, so other
3245connections have a chance of making progress.
3246.PP
3247Using an \f(CW\*(C`ev_check\*(C'\fR watcher is almost enough: it will be called on the
3248next event loop iteration. However, that isn't as soon as possible \-
3249without external events, your \f(CW\*(C`ev_check\*(C'\fR watcher will not be invoked.
3250.PP
3251This is where \f(CW\*(C`ev_idle\*(C'\fR watchers come in handy \- all you need is a
3252single global idle watcher that is active as long as you have one active
3253\&\f(CW\*(C`ev_check\*(C'\fR watcher. The \f(CW\*(C`ev_idle\*(C'\fR watcher makes sure the event loop
3254will not sleep, and the \f(CW\*(C`ev_check\*(C'\fR watcher makes sure a callback gets
3255invoked. Neither watcher alone can do that.
3256.PP
3257\fIWatcher-Specific Functions and Data Members\fR
3258.IX Subsection "Watcher-Specific Functions and Data Members"
1185.IP "ev_prepare_init (ev_prepare *, callback)" 4 3259.IP "ev_prepare_init (ev_prepare *, callback)" 4
1186.IX Item "ev_prepare_init (ev_prepare *, callback)" 3260.IX Item "ev_prepare_init (ev_prepare *, callback)"
1187.PD 0 3261.PD 0
1188.IP "ev_check_init (ev_check *, callback)" 4 3262.IP "ev_check_init (ev_check *, callback)" 4
1189.IX Item "ev_check_init (ev_check *, callback)" 3263.IX Item "ev_check_init (ev_check *, callback)"
1190.PD 3264.PD
1191Initialises and configures the prepare or check watcher \- they have no 3265Initialises and configures the prepare or check watcher \- they have no
1192parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR 3266parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
1193macros, but using them is utterly, utterly and completely pointless. 3267macros, but using them is utterly, utterly, utterly and completely
3268pointless.
1194.PP 3269.PP
1195Example: *TODO*. 3270\fIExamples\fR
3271.IX Subsection "Examples"
3272.PP
3273There are a number of principal ways to embed other event loops or modules
3274into libev. Here are some ideas on how to include libadns into libev
3275(there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could
3276use as a working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR embeds a
3277Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 into the
3278Glib event loop).
3279.PP
3280Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
3281and in a check watcher, destroy them and call into libadns. What follows
3282is pseudo-code only of course. This requires you to either use a low
3283priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as
3284the callbacks for the IO/timeout watchers might not have been called yet.
3285.PP
3286.Vb 2
3287\& static ev_io iow [nfd];
3288\& static ev_timer tw;
3289\&
3290\& static void
3291\& io_cb (struct ev_loop *loop, ev_io *w, int revents)
3292\& {
3293\& }
3294\&
3295\& // create io watchers for each fd and a timer before blocking
3296\& static void
3297\& adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
3298\& {
3299\& int timeout = 3600000;
3300\& struct pollfd fds [nfd];
3301\& // actual code will need to loop here and realloc etc.
3302\& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
3303\&
3304\& /* the callback is illegal, but won\*(Aqt be called as we stop during check */
3305\& ev_timer_init (&tw, 0, timeout * 1e\-3, 0.);
3306\& ev_timer_start (loop, &tw);
3307\&
3308\& // create one ev_io per pollfd
3309\& for (int i = 0; i < nfd; ++i)
3310\& {
3311\& ev_io_init (iow + i, io_cb, fds [i].fd,
3312\& ((fds [i].events & POLLIN ? EV_READ : 0)
3313\& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
3314\&
3315\& fds [i].revents = 0;
3316\& ev_io_start (loop, iow + i);
3317\& }
3318\& }
3319\&
3320\& // stop all watchers after blocking
3321\& static void
3322\& adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
3323\& {
3324\& ev_timer_stop (loop, &tw);
3325\&
3326\& for (int i = 0; i < nfd; ++i)
3327\& {
3328\& // set the relevant poll flags
3329\& // could also call adns_processreadable etc. here
3330\& struct pollfd *fd = fds + i;
3331\& int revents = ev_clear_pending (iow + i);
3332\& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN;
3333\& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT;
3334\&
3335\& // now stop the watcher
3336\& ev_io_stop (loop, iow + i);
3337\& }
3338\&
3339\& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
3340\& }
3341.Ve
3342.PP
3343Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR
3344in the prepare watcher and would dispose of the check watcher.
3345.PP
3346Method 3: If the module to be embedded supports explicit event
3347notification (libadns does), you can also make use of the actual watcher
3348callbacks, and only destroy/create the watchers in the prepare watcher.
3349.PP
3350.Vb 5
3351\& static void
3352\& timer_cb (EV_P_ ev_timer *w, int revents)
3353\& {
3354\& adns_state ads = (adns_state)w\->data;
3355\& update_now (EV_A);
3356\&
3357\& adns_processtimeouts (ads, &tv_now);
3358\& }
3359\&
3360\& static void
3361\& io_cb (EV_P_ ev_io *w, int revents)
3362\& {
3363\& adns_state ads = (adns_state)w\->data;
3364\& update_now (EV_A);
3365\&
3366\& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now);
3367\& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now);
3368\& }
3369\&
3370\& // do not ever call adns_afterpoll
3371.Ve
3372.PP
3373Method 4: Do not use a prepare or check watcher because the module you
3374want to embed is not flexible enough to support it. Instead, you can
3375override their poll function. The drawback with this solution is that the
3376main loop is now no longer controllable by \s-1EV.\s0 The \f(CW\*(C`Glib::EV\*(C'\fR module uses
3377this approach, effectively embedding \s-1EV\s0 as a client into the horrible
3378libglib event loop.
3379.PP
3380.Vb 4
3381\& static gint
3382\& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
3383\& {
3384\& int got_events = 0;
3385\&
3386\& for (n = 0; n < nfds; ++n)
3387\& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
3388\&
3389\& if (timeout >= 0)
3390\& // create/start timer
3391\&
3392\& // poll
3393\& ev_run (EV_A_ 0);
3394\&
3395\& // stop timer again
3396\& if (timeout >= 0)
3397\& ev_timer_stop (EV_A_ &to);
3398\&
3399\& // stop io watchers again \- their callbacks should have set
3400\& for (n = 0; n < nfds; ++n)
3401\& ev_io_stop (EV_A_ iow [n]);
3402\&
3403\& return got_events;
3404\& }
3405.Ve
3406.ie n .SS """ev_embed"" \- when one backend isn't enough..."
3407.el .SS "\f(CWev_embed\fP \- when one backend isn't enough..."
3408.IX Subsection "ev_embed - when one backend isn't enough..."
3409This is a rather advanced watcher type that lets you embed one event loop
3410into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
3411loop, other types of watchers might be handled in a delayed or incorrect
3412fashion and must not be used).
3413.PP
3414There are primarily two reasons you would want that: work around bugs and
3415prioritise I/O.
3416.PP
3417As an example for a bug workaround, the kqueue backend might only support
3418sockets on some platform, so it is unusable as generic backend, but you
3419still want to make use of it because you have many sockets and it scales
3420so nicely. In this case, you would create a kqueue-based loop and embed
3421it into your default loop (which might use e.g. poll). Overall operation
3422will be a bit slower because first libev has to call \f(CW\*(C`poll\*(C'\fR and then
3423\&\f(CW\*(C`kevent\*(C'\fR, but at least you can use both mechanisms for what they are
3424best: \f(CW\*(C`kqueue\*(C'\fR for scalable sockets and \f(CW\*(C`poll\*(C'\fR if you want it to work :)
3425.PP
3426As for prioritising I/O: under rare circumstances you have the case where
3427some fds have to be watched and handled very quickly (with low latency),
3428and even priorities and idle watchers might have too much overhead. In
3429this case you would put all the high priority stuff in one loop and all
3430the rest in a second one, and embed the second one in the first.
3431.PP
3432As long as the watcher is active, the callback will be invoked every
3433time there might be events pending in the embedded loop. The callback
3434must then call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single
3435sweep and invoke their callbacks (the callback doesn't need to invoke the
3436\&\f(CW\*(C`ev_embed_sweep\*(C'\fR function directly, it could also start an idle watcher
3437to give the embedded loop strictly lower priority for example).
3438.PP
3439You can also set the callback to \f(CW0\fR, in which case the embed watcher
3440will automatically execute the embedded loop sweep whenever necessary.
3441.PP
3442Fork detection will be handled transparently while the \f(CW\*(C`ev_embed\*(C'\fR watcher
3443is active, i.e., the embedded loop will automatically be forked when the
3444embedding loop forks. In other cases, the user is responsible for calling
3445\&\f(CW\*(C`ev_loop_fork\*(C'\fR on the embedded loop.
3446.PP
3447Unfortunately, not all backends are embeddable: only the ones returned by
3448\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
3449portable one.
3450.PP
3451So when you want to use this feature you will always have to be prepared
3452that you cannot get an embeddable loop. The recommended way to get around
3453this is to have a separate variables for your embeddable loop, try to
3454create it, and if that fails, use the normal loop for everything.
3455.PP
3456\fI\f(CI\*(C`ev_embed\*(C'\fI and fork\fR
3457.IX Subsection "ev_embed and fork"
3458.PP
3459While the \f(CW\*(C`ev_embed\*(C'\fR watcher is running, forks in the embedding loop will
3460automatically be applied to the embedded loop as well, so no special
3461fork handling is required in that case. When the watcher is not running,
3462however, it is still the task of the libev user to call \f(CW\*(C`ev_loop_fork ()\*(C'\fR
3463as applicable.
3464.PP
3465\fIWatcher-Specific Functions and Data Members\fR
3466.IX Subsection "Watcher-Specific Functions and Data Members"
3467.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
3468.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
3469.PD 0
3470.IP "ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)" 4
3471.IX Item "ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)"
3472.PD
3473Configures the watcher to embed the given loop, which must be
3474embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
3475invoked automatically, otherwise it is the responsibility of the callback
3476to invoke it (it will continue to be called until the sweep has been done,
3477if you do not want that, you need to temporarily stop the embed watcher).
3478.IP "ev_embed_sweep (loop, ev_embed *)" 4
3479.IX Item "ev_embed_sweep (loop, ev_embed *)"
3480Make a single, non-blocking sweep over the embedded loop. This works
3481similarly to \f(CW\*(C`ev_run (embedded_loop, EVRUN_NOWAIT)\*(C'\fR, but in the most
3482appropriate way for embedded loops.
3483.IP "struct ev_loop *other [read\-only]" 4
3484.IX Item "struct ev_loop *other [read-only]"
3485The embedded event loop.
3486.PP
3487\fIExamples\fR
3488.IX Subsection "Examples"
3489.PP
3490Example: Try to get an embeddable event loop and embed it into the default
3491event loop. If that is not possible, use the default loop. The default
3492loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the embeddable loop is stored in
3493\&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the case no embeddable loop can be
3494used).
3495.PP
3496.Vb 3
3497\& struct ev_loop *loop_hi = ev_default_init (0);
3498\& struct ev_loop *loop_lo = 0;
3499\& ev_embed embed;
3500\&
3501\& // see if there is a chance of getting one that works
3502\& // (remember that a flags value of 0 means autodetection)
3503\& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3504\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3505\& : 0;
3506\&
3507\& // if we got one, then embed it, otherwise default to loop_hi
3508\& if (loop_lo)
3509\& {
3510\& ev_embed_init (&embed, 0, loop_lo);
3511\& ev_embed_start (loop_hi, &embed);
3512\& }
3513\& else
3514\& loop_lo = loop_hi;
3515.Ve
3516.PP
3517Example: Check if kqueue is available but not recommended and create
3518a kqueue backend for use with sockets (which usually work with any
3519kqueue implementation). Store the kqueue/socket\-only event loop in
3520\&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too).
3521.PP
3522.Vb 3
3523\& struct ev_loop *loop = ev_default_init (0);
3524\& struct ev_loop *loop_socket = 0;
3525\& ev_embed embed;
3526\&
3527\& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3528\& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3529\& {
3530\& ev_embed_init (&embed, 0, loop_socket);
3531\& ev_embed_start (loop, &embed);
3532\& }
3533\&
3534\& if (!loop_socket)
3535\& loop_socket = loop;
3536\&
3537\& // now use loop_socket for all sockets, and loop for everything else
3538.Ve
3539.ie n .SS """ev_fork"" \- the audacity to resume the event loop after a fork"
3540.el .SS "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
3541.IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
3542Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
3543whoever is a good citizen cared to tell libev about it by calling
3544\&\f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the event loop blocks next
3545and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called, and only in the child
3546after the fork. If whoever good citizen calling \f(CW\*(C`ev_default_fork\*(C'\fR cheats
3547and calls it in the wrong process, the fork handlers will be invoked, too,
3548of course.
3549.PP
3550\fIThe special problem of life after fork \- how is it possible?\fR
3551.IX Subsection "The special problem of life after fork - how is it possible?"
3552.PP
3553Most uses of \f(CW\*(C`fork ()\*(C'\fR consist of forking, then some simple calls to set
3554up/change the process environment, followed by a call to \f(CW\*(C`exec()\*(C'\fR. This
3555sequence should be handled by libev without any problems.
3556.PP
3557This changes when the application actually wants to do event handling
3558in the child, or both parent in child, in effect \*(L"continuing\*(R" after the
3559fork.
3560.PP
3561The default mode of operation (for libev, with application help to detect
3562forks) is to duplicate all the state in the child, as would be expected
3563when \fIeither\fR the parent \fIor\fR the child process continues.
3564.PP
3565When both processes want to continue using libev, then this is usually the
3566wrong result. In that case, usually one process (typically the parent) is
3567supposed to continue with all watchers in place as before, while the other
3568process typically wants to start fresh, i.e. without any active watchers.
3569.PP
3570The cleanest and most efficient way to achieve that with libev is to
3571simply create a new event loop, which of course will be \*(L"empty\*(R", and
3572use that for new watchers. This has the advantage of not touching more
3573memory than necessary, and thus avoiding the copy-on-write, and the
3574disadvantage of having to use multiple event loops (which do not support
3575signal watchers).
3576.PP
3577When this is not possible, or you want to use the default loop for
3578other reasons, then in the process that wants to start \*(L"fresh\*(R", call
3579\&\f(CW\*(C`ev_loop_destroy (EV_DEFAULT)\*(C'\fR followed by \f(CW\*(C`ev_default_loop (...)\*(C'\fR.
3580Destroying the default loop will \*(L"orphan\*(R" (not stop) all registered
3581watchers, so you have to be careful not to execute code that modifies
3582those watchers. Note also that in that case, you have to re-register any
3583signal watchers.
3584.PP
3585\fIWatcher-Specific Functions and Data Members\fR
3586.IX Subsection "Watcher-Specific Functions and Data Members"
3587.IP "ev_fork_init (ev_fork *, callback)" 4
3588.IX Item "ev_fork_init (ev_fork *, callback)"
3589Initialises and configures the fork watcher \- it has no parameters of any
3590kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
3591really.
3592.ie n .SS """ev_cleanup"" \- even the best things end"
3593.el .SS "\f(CWev_cleanup\fP \- even the best things end"
3594.IX Subsection "ev_cleanup - even the best things end"
3595Cleanup watchers are called just before the event loop is being destroyed
3596by a call to \f(CW\*(C`ev_loop_destroy\*(C'\fR.
3597.PP
3598While there is no guarantee that the event loop gets destroyed, cleanup
3599watchers provide a convenient method to install cleanup hooks for your
3600program, worker threads and so on \- you just to make sure to destroy the
3601loop when you want them to be invoked.
3602.PP
3603Cleanup watchers are invoked in the same way as any other watcher. Unlike
3604all other watchers, they do not keep a reference to the event loop (which
3605makes a lot of sense if you think about it). Like all other watchers, you
3606can call libev functions in the callback, except \f(CW\*(C`ev_cleanup_start\*(C'\fR.
3607.PP
3608\fIWatcher-Specific Functions and Data Members\fR
3609.IX Subsection "Watcher-Specific Functions and Data Members"
3610.IP "ev_cleanup_init (ev_cleanup *, callback)" 4
3611.IX Item "ev_cleanup_init (ev_cleanup *, callback)"
3612Initialises and configures the cleanup watcher \- it has no parameters of
3613any kind. There is a \f(CW\*(C`ev_cleanup_set\*(C'\fR macro, but using it is utterly
3614pointless, I assure you.
3615.PP
3616Example: Register an atexit handler to destroy the default loop, so any
3617cleanup functions are called.
3618.PP
3619.Vb 5
3620\& static void
3621\& program_exits (void)
3622\& {
3623\& ev_loop_destroy (EV_DEFAULT_UC);
3624\& }
3625\&
3626\& ...
3627\& atexit (program_exits);
3628.Ve
3629.ie n .SS """ev_async"" \- how to wake up an event loop"
3630.el .SS "\f(CWev_async\fP \- how to wake up an event loop"
3631.IX Subsection "ev_async - how to wake up an event loop"
3632In general, you cannot use an \f(CW\*(C`ev_loop\*(C'\fR from multiple threads or other
3633asynchronous sources such as signal handlers (as opposed to multiple event
3634loops \- those are of course safe to use in different threads).
3635.PP
3636Sometimes, however, you need to wake up an event loop you do not control,
3637for example because it belongs to another thread. This is what \f(CW\*(C`ev_async\*(C'\fR
3638watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you can signal
3639it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal safe.
3640.PP
3641This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals,
3642too, are asynchronous in nature, and signals, too, will be compressed
3643(i.e. the number of callback invocations may be less than the number of
3644\&\f(CW\*(C`ev_async_send\*(C'\fR calls). In fact, you could use signal watchers as a kind
3645of \*(L"global async watchers\*(R" by using a watcher on an otherwise unused
3646signal, and \f(CW\*(C`ev_feed_signal\*(C'\fR to signal this watcher from another thread,
3647even without knowing which loop owns the signal.
3648.PP
3649\fIQueueing\fR
3650.IX Subsection "Queueing"
3651.PP
3652\&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason
3653is that the author does not know of a simple (or any) algorithm for a
3654multiple-writer-single-reader queue that works in all cases and doesn't
3655need elaborate support such as pthreads or unportable memory access
3656semantics.
3657.PP
3658That means that if you want to queue data, you have to provide your own
3659queue. But at least I can tell you how to implement locking around your
3660queue:
3661.IP "queueing from a signal handler context" 4
3662.IX Item "queueing from a signal handler context"
3663To implement race-free queueing, you simply add to the queue in the signal
3664handler but you block the signal handler in the watcher callback. Here is
3665an example that does that for some fictitious \s-1SIGUSR1\s0 handler:
3666.Sp
3667.Vb 1
3668\& static ev_async mysig;
3669\&
3670\& static void
3671\& sigusr1_handler (void)
3672\& {
3673\& sometype data;
3674\&
3675\& // no locking etc.
3676\& queue_put (data);
3677\& ev_async_send (EV_DEFAULT_ &mysig);
3678\& }
3679\&
3680\& static void
3681\& mysig_cb (EV_P_ ev_async *w, int revents)
3682\& {
3683\& sometype data;
3684\& sigset_t block, prev;
3685\&
3686\& sigemptyset (&block);
3687\& sigaddset (&block, SIGUSR1);
3688\& sigprocmask (SIG_BLOCK, &block, &prev);
3689\&
3690\& while (queue_get (&data))
3691\& process (data);
3692\&
3693\& if (sigismember (&prev, SIGUSR1)
3694\& sigprocmask (SIG_UNBLOCK, &block, 0);
3695\& }
3696.Ve
3697.Sp
3698(Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR
3699instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it
3700either...).
3701.IP "queueing from a thread context" 4
3702.IX Item "queueing from a thread context"
3703The strategy for threads is different, as you cannot (easily) block
3704threads but you can easily preempt them, so to queue safely you need to
3705employ a traditional mutex lock, such as in this pthread example:
3706.Sp
3707.Vb 2
3708\& static ev_async mysig;
3709\& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
3710\&
3711\& static void
3712\& otherthread (void)
3713\& {
3714\& // only need to lock the actual queueing operation
3715\& pthread_mutex_lock (&mymutex);
3716\& queue_put (data);
3717\& pthread_mutex_unlock (&mymutex);
3718\&
3719\& ev_async_send (EV_DEFAULT_ &mysig);
3720\& }
3721\&
3722\& static void
3723\& mysig_cb (EV_P_ ev_async *w, int revents)
3724\& {
3725\& pthread_mutex_lock (&mymutex);
3726\&
3727\& while (queue_get (&data))
3728\& process (data);
3729\&
3730\& pthread_mutex_unlock (&mymutex);
3731\& }
3732.Ve
3733.PP
3734\fIWatcher-Specific Functions and Data Members\fR
3735.IX Subsection "Watcher-Specific Functions and Data Members"
3736.IP "ev_async_init (ev_async *, callback)" 4
3737.IX Item "ev_async_init (ev_async *, callback)"
3738Initialises and configures the async watcher \- it has no parameters of any
3739kind. There is a \f(CW\*(C`ev_async_set\*(C'\fR macro, but using it is utterly pointless,
3740trust me.
3741.IP "ev_async_send (loop, ev_async *)" 4
3742.IX Item "ev_async_send (loop, ev_async *)"
3743Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds
3744an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop, and instantly
3745returns.
3746.Sp
3747Unlike \f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do from other threads,
3748signal or similar contexts (see the discussion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the
3749embedding section below on what exactly this means).
3750.Sp
3751Note that, as with other watchers in libev, multiple events might get
3752compressed into a single callback invocation (another way to look at
3753this is that \f(CW\*(C`ev_async\*(C'\fR watchers are level-triggered: they are set on
3754\&\f(CW\*(C`ev_async_send\*(C'\fR, reset when the event loop detects that).
3755.Sp
3756This call incurs the overhead of at most one extra system call per event
3757loop iteration, if the event loop is blocked, and no syscall at all if
3758the event loop (or your program) is processing events. That means that
3759repeated calls are basically free (there is no need to avoid calls for
3760performance reasons) and that the overhead becomes smaller (typically
3761zero) under load.
3762.IP "bool = ev_async_pending (ev_async *)" 4
3763.IX Item "bool = ev_async_pending (ev_async *)"
3764Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the
3765watcher but the event has not yet been processed (or even noted) by the
3766event loop.
3767.Sp
3768\&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When
3769the loop iterates next and checks for the watcher to have become active,
3770it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very
3771quickly check whether invoking the loop might be a good idea.
3772.Sp
3773Not that this does \fInot\fR check whether the watcher itself is pending,
3774only whether it has been requested to make this watcher pending: there
3775is a time window between the event loop checking and resetting the async
3776notification, and the callback being invoked.
1196.SH "OTHER FUNCTIONS" 3777.SH "OTHER FUNCTIONS"
1197.IX Header "OTHER FUNCTIONS" 3778.IX Header "OTHER FUNCTIONS"
1198There are some other functions of possible interest. Described. Here. Now. 3779There are some other functions of possible interest. Described. Here. Now.
1199.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4 3780.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)" 4
1200.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 3781.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)"
1201This function combines a simple timer and an I/O watcher, calls your 3782This function combines a simple timer and an I/O watcher, calls your
1202callback on whichever event happens first and automatically stop both 3783callback on whichever event happens first and automatically stops both
1203watchers. This is useful if you want to wait for a single event on an fd 3784watchers. This is useful if you want to wait for a single event on an fd
1204or timeout without having to allocate/configure/start/stop/free one or 3785or timeout without having to allocate/configure/start/stop/free one or
1205more watchers yourself. 3786more watchers yourself.
1206.Sp 3787.Sp
1207If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and events 3788If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and the
1208is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for the given \f(CW\*(C`fd\*(C'\fR and 3789\&\f(CW\*(C`events\*(C'\fR argument is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for
1209\&\f(CW\*(C`events\*(C'\fR set will be craeted and started. 3790the given \f(CW\*(C`fd\*(C'\fR and \f(CW\*(C`events\*(C'\fR set will be created and started.
1210.Sp 3791.Sp
1211If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be 3792If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
1212started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and 3793started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
1213repeat = 0) will be started. While \f(CW0\fR is a valid timeout, it is of 3794repeat = 0) will be started. \f(CW0\fR is a valid timeout.
1214dubious value.
1215.Sp 3795.Sp
1216The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets 3796The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and is
1217passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of 3797passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
1218\&\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 3798\&\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
1219value passed to \f(CW\*(C`ev_once\*(C'\fR: 3799value passed to \f(CW\*(C`ev_once\*(C'\fR. Note that it is possible to receive \fIboth\fR
3800a timeout and an io event at the same time \- you probably should give io
3801events precedence.
3802.Sp
3803Example: wait up to ten seconds for data to appear on \s-1STDIN_FILENO.\s0
1220.Sp 3804.Sp
1221.Vb 7 3805.Vb 7
1222\& static void stdin_ready (int revents, void *arg) 3806\& static void stdin_ready (int revents, void *arg)
1223\& { 3807\& {
1224\& if (revents & EV_TIMEOUT)
1225\& /* doh, nothing entered */;
1226\& else if (revents & EV_READ) 3808\& if (revents & EV_READ)
1227\& /* stdin might have data for us, joy! */; 3809\& /* stdin might have data for us, joy! */;
3810\& else if (revents & EV_TIMER)
3811\& /* doh, nothing entered */;
1228\& } 3812\& }
1229.Ve 3813\&
1230.Sp
1231.Vb 1
1232\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); 3814\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1233.Ve 3815.Ve
1234.IP "ev_feed_event (loop, watcher, int events)" 4
1235.IX Item "ev_feed_event (loop, watcher, int events)"
1236Feeds the given event set into the event loop, as if the specified event
1237had happened for the specified watcher (which must be a pointer to an
1238initialised but not necessarily started event watcher).
1239.IP "ev_feed_fd_event (loop, int fd, int revents)" 4 3816.IP "ev_feed_fd_event (loop, int fd, int revents)" 4
1240.IX Item "ev_feed_fd_event (loop, int fd, int revents)" 3817.IX Item "ev_feed_fd_event (loop, int fd, int revents)"
1241Feed an event on the given fd, as if a file descriptor backend detected 3818Feed an event on the given fd, as if a file descriptor backend detected
1242the given events it. 3819the given events.
1243.IP "ev_feed_signal_event (loop, int signum)" 4 3820.IP "ev_feed_signal_event (loop, int signum)" 4
1244.IX Item "ev_feed_signal_event (loop, int signum)" 3821.IX Item "ev_feed_signal_event (loop, int signum)"
1245Feed an event as if the given signal occured (loop must be the default loop!). 3822Feed an event as if the given signal occurred. See also \f(CW\*(C`ev_feed_signal\*(C'\fR,
3823which is async-safe.
3824.SH "COMMON OR USEFUL IDIOMS (OR BOTH)"
3825.IX Header "COMMON OR USEFUL IDIOMS (OR BOTH)"
3826This section explains some common idioms that are not immediately
3827obvious. Note that examples are sprinkled over the whole manual, and this
3828section only contains stuff that wouldn't fit anywhere else.
3829.SS "\s-1ASSOCIATING CUSTOM DATA WITH A WATCHER\s0"
3830.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
3831Each watcher has, by default, a \f(CW\*(C`void *data\*(C'\fR member that you can read
3832or modify at any time: libev will completely ignore it. This can be used
3833to associate arbitrary data with your watcher. If you need more data and
3834don't want to allocate memory separately and store a pointer to it in that
3835data member, you can also \*(L"subclass\*(R" the watcher type and provide your own
3836data:
3837.PP
3838.Vb 7
3839\& struct my_io
3840\& {
3841\& ev_io io;
3842\& int otherfd;
3843\& void *somedata;
3844\& struct whatever *mostinteresting;
3845\& };
3846\&
3847\& ...
3848\& struct my_io w;
3849\& ev_io_init (&w.io, my_cb, fd, EV_READ);
3850.Ve
3851.PP
3852And since your callback will be called with a pointer to the watcher, you
3853can cast it back to your own type:
3854.PP
3855.Vb 5
3856\& static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
3857\& {
3858\& struct my_io *w = (struct my_io *)w_;
3859\& ...
3860\& }
3861.Ve
3862.PP
3863More interesting and less C\-conformant ways of casting your callback
3864function type instead have been omitted.
3865.SS "\s-1BUILDING YOUR OWN COMPOSITE WATCHERS\s0"
3866.IX Subsection "BUILDING YOUR OWN COMPOSITE WATCHERS"
3867Another common scenario is to use some data structure with multiple
3868embedded watchers, in effect creating your own watcher that combines
3869multiple libev event sources into one \*(L"super-watcher\*(R":
3870.PP
3871.Vb 6
3872\& struct my_biggy
3873\& {
3874\& int some_data;
3875\& ev_timer t1;
3876\& ev_timer t2;
3877\& }
3878.Ve
3879.PP
3880In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more
3881complicated: Either you store the address of your \f(CW\*(C`my_biggy\*(C'\fR struct in
3882the \f(CW\*(C`data\*(C'\fR member of the watcher (for woozies or \*(C+ coders), or you need
3883to use some pointer arithmetic using \f(CW\*(C`offsetof\*(C'\fR inside your watchers (for
3884real programmers):
3885.PP
3886.Vb 1
3887\& #include <stddef.h>
3888\&
3889\& static void
3890\& t1_cb (EV_P_ ev_timer *w, int revents)
3891\& {
3892\& struct my_biggy big = (struct my_biggy *)
3893\& (((char *)w) \- offsetof (struct my_biggy, t1));
3894\& }
3895\&
3896\& static void
3897\& t2_cb (EV_P_ ev_timer *w, int revents)
3898\& {
3899\& struct my_biggy big = (struct my_biggy *)
3900\& (((char *)w) \- offsetof (struct my_biggy, t2));
3901\& }
3902.Ve
3903.SS "\s-1AVOIDING FINISHING BEFORE RETURNING\s0"
3904.IX Subsection "AVOIDING FINISHING BEFORE RETURNING"
3905Often you have structures like this in event-based programs:
3906.PP
3907.Vb 4
3908\& callback ()
3909\& {
3910\& free (request);
3911\& }
3912\&
3913\& request = start_new_request (..., callback);
3914.Ve
3915.PP
3916The intent is to start some \*(L"lengthy\*(R" operation. The \f(CW\*(C`request\*(C'\fR could be
3917used to cancel the operation, or do other things with it.
3918.PP
3919It's not uncommon to have code paths in \f(CW\*(C`start_new_request\*(C'\fR that
3920immediately invoke the callback, for example, to report errors. Or you add
3921some caching layer that finds that it can skip the lengthy aspects of the
3922operation and simply invoke the callback with the result.
3923.PP
3924The problem here is that this will happen \fIbefore\fR \f(CW\*(C`start_new_request\*(C'\fR
3925has returned, so \f(CW\*(C`request\*(C'\fR is not set.
3926.PP
3927Even if you pass the request by some safer means to the callback, you
3928might want to do something to the request after starting it, such as
3929canceling it, which probably isn't working so well when the callback has
3930already been invoked.
3931.PP
3932A common way around all these issues is to make sure that
3933\&\f(CW\*(C`start_new_request\*(C'\fR \fIalways\fR returns before the callback is invoked. If
3934\&\f(CW\*(C`start_new_request\*(C'\fR immediately knows the result, it can artificially
3935delay invoking the callback by using a \f(CW\*(C`prepare\*(C'\fR or \f(CW\*(C`idle\*(C'\fR watcher for
3936example, or more sneakily, by reusing an existing (stopped) watcher and
3937pushing it into the pending queue:
3938.PP
3939.Vb 2
3940\& ev_set_cb (watcher, callback);
3941\& ev_feed_event (EV_A_ watcher, 0);
3942.Ve
3943.PP
3944This way, \f(CW\*(C`start_new_request\*(C'\fR can safely return before the callback is
3945invoked, while not delaying callback invocation too much.
3946.SS "\s-1MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS\s0"
3947.IX Subsection "MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS"
3948Often (especially in \s-1GUI\s0 toolkits) there are places where you have
3949\&\fImodal\fR interaction, which is most easily implemented by recursively
3950invoking \f(CW\*(C`ev_run\*(C'\fR.
3951.PP
3952This brings the problem of exiting \- a callback might want to finish the
3953main \f(CW\*(C`ev_run\*(C'\fR call, but not the nested one (e.g. user clicked \*(L"Quit\*(R", but
3954a modal \*(L"Are you sure?\*(R" dialog is still waiting), or just the nested one
3955and not the main one (e.g. user clocked \*(L"Ok\*(R" in a modal dialog), or some
3956other combination: In these cases, a simple \f(CW\*(C`ev_break\*(C'\fR will not work.
3957.PP
3958The solution is to maintain \*(L"break this loop\*(R" variable for each \f(CW\*(C`ev_run\*(C'\fR
3959invocation, and use a loop around \f(CW\*(C`ev_run\*(C'\fR until the condition is
3960triggered, using \f(CW\*(C`EVRUN_ONCE\*(C'\fR:
3961.PP
3962.Vb 2
3963\& // main loop
3964\& int exit_main_loop = 0;
3965\&
3966\& while (!exit_main_loop)
3967\& ev_run (EV_DEFAULT_ EVRUN_ONCE);
3968\&
3969\& // in a modal watcher
3970\& int exit_nested_loop = 0;
3971\&
3972\& while (!exit_nested_loop)
3973\& ev_run (EV_A_ EVRUN_ONCE);
3974.Ve
3975.PP
3976To exit from any of these loops, just set the corresponding exit variable:
3977.PP
3978.Vb 2
3979\& // exit modal loop
3980\& exit_nested_loop = 1;
3981\&
3982\& // exit main program, after modal loop is finished
3983\& exit_main_loop = 1;
3984\&
3985\& // exit both
3986\& exit_main_loop = exit_nested_loop = 1;
3987.Ve
3988.SS "\s-1THREAD LOCKING EXAMPLE\s0"
3989.IX Subsection "THREAD LOCKING EXAMPLE"
3990Here is a fictitious example of how to run an event loop in a different
3991thread from where callbacks are being invoked and watchers are
3992created/added/removed.
3993.PP
3994For a real-world example, see the \f(CW\*(C`EV::Loop::Async\*(C'\fR perl module,
3995which uses exactly this technique (which is suited for many high-level
3996languages).
3997.PP
3998The example uses a pthread mutex to protect the loop data, a condition
3999variable to wait for callback invocations, an async watcher to notify the
4000event loop thread and an unspecified mechanism to wake up the main thread.
4001.PP
4002First, you need to associate some data with the event loop:
4003.PP
4004.Vb 6
4005\& typedef struct {
4006\& mutex_t lock; /* global loop lock */
4007\& ev_async async_w;
4008\& thread_t tid;
4009\& cond_t invoke_cv;
4010\& } userdata;
4011\&
4012\& void prepare_loop (EV_P)
4013\& {
4014\& // for simplicity, we use a static userdata struct.
4015\& static userdata u;
4016\&
4017\& ev_async_init (&u\->async_w, async_cb);
4018\& ev_async_start (EV_A_ &u\->async_w);
4019\&
4020\& pthread_mutex_init (&u\->lock, 0);
4021\& pthread_cond_init (&u\->invoke_cv, 0);
4022\&
4023\& // now associate this with the loop
4024\& ev_set_userdata (EV_A_ u);
4025\& ev_set_invoke_pending_cb (EV_A_ l_invoke);
4026\& ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4027\&
4028\& // then create the thread running ev_run
4029\& pthread_create (&u\->tid, 0, l_run, EV_A);
4030\& }
4031.Ve
4032.PP
4033The callback for the \f(CW\*(C`ev_async\*(C'\fR watcher does nothing: the watcher is used
4034solely to wake up the event loop so it takes notice of any new watchers
4035that might have been added:
4036.PP
4037.Vb 5
4038\& static void
4039\& async_cb (EV_P_ ev_async *w, int revents)
4040\& {
4041\& // just used for the side effects
4042\& }
4043.Ve
4044.PP
4045The \f(CW\*(C`l_release\*(C'\fR and \f(CW\*(C`l_acquire\*(C'\fR callbacks simply unlock/lock the mutex
4046protecting the loop data, respectively.
4047.PP
4048.Vb 6
4049\& static void
4050\& l_release (EV_P)
4051\& {
4052\& userdata *u = ev_userdata (EV_A);
4053\& pthread_mutex_unlock (&u\->lock);
4054\& }
4055\&
4056\& static void
4057\& l_acquire (EV_P)
4058\& {
4059\& userdata *u = ev_userdata (EV_A);
4060\& pthread_mutex_lock (&u\->lock);
4061\& }
4062.Ve
4063.PP
4064The event loop thread first acquires the mutex, and then jumps straight
4065into \f(CW\*(C`ev_run\*(C'\fR:
4066.PP
4067.Vb 4
4068\& void *
4069\& l_run (void *thr_arg)
4070\& {
4071\& struct ev_loop *loop = (struct ev_loop *)thr_arg;
4072\&
4073\& l_acquire (EV_A);
4074\& pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4075\& ev_run (EV_A_ 0);
4076\& l_release (EV_A);
4077\&
4078\& return 0;
4079\& }
4080.Ve
4081.PP
4082Instead of invoking all pending watchers, the \f(CW\*(C`l_invoke\*(C'\fR callback will
4083signal the main thread via some unspecified mechanism (signals? pipe
4084writes? \f(CW\*(C`Async::Interrupt\*(C'\fR?) and then waits until all pending watchers
4085have been called (in a while loop because a) spurious wakeups are possible
4086and b) skipping inter-thread-communication when there are no pending
4087watchers is very beneficial):
4088.PP
4089.Vb 4
4090\& static void
4091\& l_invoke (EV_P)
4092\& {
4093\& userdata *u = ev_userdata (EV_A);
4094\&
4095\& while (ev_pending_count (EV_A))
4096\& {
4097\& wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4098\& pthread_cond_wait (&u\->invoke_cv, &u\->lock);
4099\& }
4100\& }
4101.Ve
4102.PP
4103Now, whenever the main thread gets told to invoke pending watchers, it
4104will grab the lock, call \f(CW\*(C`ev_invoke_pending\*(C'\fR and then signal the loop
4105thread to continue:
4106.PP
4107.Vb 4
4108\& static void
4109\& real_invoke_pending (EV_P)
4110\& {
4111\& userdata *u = ev_userdata (EV_A);
4112\&
4113\& pthread_mutex_lock (&u\->lock);
4114\& ev_invoke_pending (EV_A);
4115\& pthread_cond_signal (&u\->invoke_cv);
4116\& pthread_mutex_unlock (&u\->lock);
4117\& }
4118.Ve
4119.PP
4120Whenever you want to start/stop a watcher or do other modifications to an
4121event loop, you will now have to lock:
4122.PP
4123.Vb 2
4124\& ev_timer timeout_watcher;
4125\& userdata *u = ev_userdata (EV_A);
4126\&
4127\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4128\&
4129\& pthread_mutex_lock (&u\->lock);
4130\& ev_timer_start (EV_A_ &timeout_watcher);
4131\& ev_async_send (EV_A_ &u\->async_w);
4132\& pthread_mutex_unlock (&u\->lock);
4133.Ve
4134.PP
4135Note that sending the \f(CW\*(C`ev_async\*(C'\fR watcher is required because otherwise
4136an event loop currently blocking in the kernel will have no knowledge
4137about the newly added timer. By waking up the loop it will pick up any new
4138watchers in the next event loop iteration.
4139.SS "\s-1THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS\s0"
4140.IX Subsection "THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS"
4141While the overhead of a callback that e.g. schedules a thread is small, it
4142is still an overhead. If you embed libev, and your main usage is with some
4143kind of threads or coroutines, you might want to customise libev so that
4144doesn't need callbacks anymore.
4145.PP
4146Imagine you have coroutines that you can switch to using a function
4147\&\f(CW\*(C`switch_to (coro)\*(C'\fR, that libev runs in a coroutine called \f(CW\*(C`libev_coro\*(C'\fR
4148and that due to some magic, the currently active coroutine is stored in a
4149global called \f(CW\*(C`current_coro\*(C'\fR. Then you can build your own \*(L"wait for libev
4150event\*(R" primitive by changing \f(CW\*(C`EV_CB_DECLARE\*(C'\fR and \f(CW\*(C`EV_CB_INVOKE\*(C'\fR (note
4151the differing \f(CW\*(C`;\*(C'\fR conventions):
4152.PP
4153.Vb 2
4154\& #define EV_CB_DECLARE(type) struct my_coro *cb;
4155\& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb)
4156.Ve
4157.PP
4158That means instead of having a C callback function, you store the
4159coroutine to switch to in each watcher, and instead of having libev call
4160your callback, you instead have it switch to that coroutine.
4161.PP
4162A coroutine might now wait for an event with a function called
4163\&\f(CW\*(C`wait_for_event\*(C'\fR. (the watcher needs to be started, as always, but it doesn't
4164matter when, or whether the watcher is active or not when this function is
4165called):
4166.PP
4167.Vb 6
4168\& void
4169\& wait_for_event (ev_watcher *w)
4170\& {
4171\& ev_set_cb (w, current_coro);
4172\& switch_to (libev_coro);
4173\& }
4174.Ve
4175.PP
4176That basically suspends the coroutine inside \f(CW\*(C`wait_for_event\*(C'\fR and
4177continues the libev coroutine, which, when appropriate, switches back to
4178this or any other coroutine.
4179.PP
4180You can do similar tricks if you have, say, threads with an event queue \-
4181instead of storing a coroutine, you store the queue object and instead of
4182switching to a coroutine, you push the watcher onto the queue and notify
4183any waiters.
4184.PP
4185To embed libev, see \*(L"\s-1EMBEDDING\*(R"\s0, but in short, it's easiest to create two
4186files, \fImy_ev.h\fR and \fImy_ev.c\fR that include the respective libev files:
4187.PP
4188.Vb 4
4189\& // my_ev.h
4190\& #define EV_CB_DECLARE(type) struct my_coro *cb;
4191\& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb)
4192\& #include "../libev/ev.h"
4193\&
4194\& // my_ev.c
4195\& #define EV_H "my_ev.h"
4196\& #include "../libev/ev.c"
4197.Ve
4198.PP
4199And then use \fImy_ev.h\fR when you would normally use \fIev.h\fR, and compile
4200\&\fImy_ev.c\fR into your project. When properly specifying include paths, you
4201can even use \fIev.h\fR as header file name directly.
1246.SH "LIBEVENT EMULATION" 4202.SH "LIBEVENT EMULATION"
1247.IX Header "LIBEVENT EMULATION" 4203.IX Header "LIBEVENT EMULATION"
1248Libev offers a compatibility emulation layer for libevent. It cannot 4204Libev offers a compatibility emulation layer for libevent. It cannot
1249emulate the internals of libevent, so here are some usage hints: 4205emulate the internals of libevent, so here are some usage hints:
4206.IP "\(bu" 4
4207Only the libevent\-1.4.1\-beta \s-1API\s0 is being emulated.
4208.Sp
4209This was the newest libevent version available when libev was implemented,
4210and is still mostly unchanged in 2010.
4211.IP "\(bu" 4
1250.IP "* Use it by including <event.h>, as usual." 4 4212Use it by including <event.h>, as usual.
1251.IX Item "Use it by including <event.h>, as usual." 4213.IP "\(bu" 4
1252.PD 0 4214The following members are fully supported: ev_base, ev_callback,
1253.IP "* The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4 4215ev_arg, ev_fd, ev_res, ev_events.
1254.IX Item "The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4216.IP "\(bu" 4
1255.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 4217Avoid using ev_flags and the EVLIST_*\-macros, while it is
1256.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)." 4218maintained by libev, it does not work exactly the same way as in libevent (consider
1257.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 4219it a private \s-1API\s0).
1258.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." 4220.IP "\(bu" 4
4221Priorities are not currently supported. Initialising priorities
4222will fail and all watchers will have the same priority, even though there
4223is an ev_pri field.
4224.IP "\(bu" 4
4225In libevent, the last base created gets the signals, in libev, the
4226base that registered the signal gets the signals.
4227.IP "\(bu" 4
1259.IP "* Other members are not supported." 4 4228Other members are not supported.
1260.IX Item "Other members are not supported." 4229.IP "\(bu" 4
1261.IP "* The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need to use the libev header file and library." 4 4230The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need
1262.IX Item "The libev emulation is not ABI compatible to libevent, you need to use the libev header file and library." 4231to use the libev header file and library.
1263.PD
1264.SH "\*(C+ SUPPORT" 4232.SH "\*(C+ SUPPORT"
1265.IX Header " SUPPORT" 4233.IX Header " SUPPORT"
1266\&\s-1TBD\s0. 4234.SS "C \s-1API\s0"
4235.IX Subsection "C API"
4236The normal C \s-1API\s0 should work fine when used from \*(C+: both ev.h and the
4237libev sources can be compiled as \*(C+. Therefore, code that uses the C \s-1API\s0
4238will work fine.
4239.PP
4240Proper exception specifications might have to be added to callbacks passed
4241to libev: exceptions may be thrown only from watcher callbacks, all other
4242callbacks (allocator, syserr, loop acquire/release and periodic reschedule
4243callbacks) must not throw exceptions, and might need a \f(CW\*(C`noexcept\*(C'\fR
4244specification. If you have code that needs to be compiled as both C and
4245\&\*(C+ you can use the \f(CW\*(C`EV_NOEXCEPT\*(C'\fR macro for this:
4246.PP
4247.Vb 6
4248\& static void
4249\& fatal_error (const char *msg) EV_NOEXCEPT
4250\& {
4251\& perror (msg);
4252\& abort ();
4253\& }
4254\&
4255\& ...
4256\& ev_set_syserr_cb (fatal_error);
4257.Ve
4258.PP
4259The only \s-1API\s0 functions that can currently throw exceptions are \f(CW\*(C`ev_run\*(C'\fR,
4260\&\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
4261because it runs cleanup watchers).
4262.PP
4263Throwing exceptions in watcher callbacks is only supported if libev itself
4264is compiled with a \*(C+ compiler or your C and \*(C+ environments allow
4265throwing exceptions through C libraries (most do).
4266.SS "\*(C+ \s-1API\s0"
4267.IX Subsection " API"
4268Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
4269you to use some convenience methods to start/stop watchers and also change
4270the callback model to a model using method callbacks on objects.
4271.PP
4272To use it,
4273.PP
4274.Vb 1
4275\& #include <ev++.h>
4276.Ve
4277.PP
4278This automatically includes \fIev.h\fR and puts all of its definitions (many
4279of them macros) into the global namespace. All \*(C+ specific things are
4280put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding
4281options as \fIev.h\fR, most notably \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR.
4282.PP
4283Care has been taken to keep the overhead low. The only data member the \*(C+
4284classes add (compared to plain C\-style watchers) is the event loop pointer
4285that the watcher is associated with (or no additional members at all if
4286you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
4287.PP
4288Currently, functions, static and non-static member functions and classes
4289with \f(CW\*(C`operator ()\*(C'\fR can be used as callbacks. Other types should be easy
4290to add as long as they only need one additional pointer for context. If
4291you need support for other types of functors please contact the author
4292(preferably after implementing it).
4293.PP
4294For all this to work, your \*(C+ compiler either has to use the same calling
4295conventions as your C compiler (for static member functions), or you have
4296to embed libev and compile libev itself as \*(C+.
4297.PP
4298Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
4299.ie n .IP """ev::READ"", ""ev::WRITE"" etc." 4
4300.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
4301.IX Item "ev::READ, ev::WRITE etc."
4302These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
4303macros from \fIev.h\fR.
4304.ie n .IP """ev::tstamp"", ""ev::now""" 4
4305.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
4306.IX Item "ev::tstamp, ev::now"
4307Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
4308.ie n .IP """ev::io"", ""ev::timer"", ""ev::periodic"", ""ev::idle"", ""ev::sig"" etc." 4
4309.el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
4310.IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
4311For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
4312the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
4313which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
4314defined by many implementations.
4315.Sp
4316All of those classes have these methods:
4317.RS 4
4318.IP "ev::TYPE::TYPE ()" 4
4319.IX Item "ev::TYPE::TYPE ()"
4320.PD 0
4321.IP "ev::TYPE::TYPE (loop)" 4
4322.IX Item "ev::TYPE::TYPE (loop)"
4323.IP "ev::TYPE::~TYPE" 4
4324.IX Item "ev::TYPE::~TYPE"
4325.PD
4326The constructor (optionally) takes an event loop to associate the watcher
4327with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR.
4328.Sp
4329The constructor calls \f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the
4330\&\f(CW\*(C`set\*(C'\fR method before starting it.
4331.Sp
4332It will not set a callback, however: You have to call the templated \f(CW\*(C`set\*(C'\fR
4333method to set a callback before you can start the watcher.
4334.Sp
4335(The reason why you have to use a method is a limitation in \*(C+ which does
4336not allow explicit template arguments for constructors).
4337.Sp
4338The destructor automatically stops the watcher if it is active.
4339.IP "w\->set<class, &class::method> (object *)" 4
4340.IX Item "w->set<class, &class::method> (object *)"
4341This method sets the callback method to call. The method has to have a
4342signature of \f(CW\*(C`void (*)(ev_TYPE &, int)\*(C'\fR, it receives the watcher as
4343first argument and the \f(CW\*(C`revents\*(C'\fR as second. The object must be given as
4344parameter and is stored in the \f(CW\*(C`data\*(C'\fR member of the watcher.
4345.Sp
4346This method synthesizes efficient thunking code to call your method from
4347the C callback that libev requires. If your compiler can inline your
4348callback (i.e. it is visible to it at the place of the \f(CW\*(C`set\*(C'\fR call and
4349your compiler is good :), then the method will be fully inlined into the
4350thunking function, making it as fast as a direct C callback.
4351.Sp
4352Example: simple class declaration and watcher initialisation
4353.Sp
4354.Vb 4
4355\& struct myclass
4356\& {
4357\& void io_cb (ev::io &w, int revents) { }
4358\& }
4359\&
4360\& myclass obj;
4361\& ev::io iow;
4362\& iow.set <myclass, &myclass::io_cb> (&obj);
4363.Ve
4364.IP "w\->set (object *)" 4
4365.IX Item "w->set (object *)"
4366This is a variation of a method callback \- leaving out the method to call
4367will default the method to \f(CW\*(C`operator ()\*(C'\fR, which makes it possible to use
4368functor objects without having to manually specify the \f(CW\*(C`operator ()\*(C'\fR all
4369the time. Incidentally, you can then also leave out the template argument
4370list.
4371.Sp
4372The \f(CW\*(C`operator ()\*(C'\fR method prototype must be \f(CW\*(C`void operator ()(watcher &w,
4373int revents)\*(C'\fR.
4374.Sp
4375See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
4376.Sp
4377Example: use a functor object as callback.
4378.Sp
4379.Vb 7
4380\& struct myfunctor
4381\& {
4382\& void operator() (ev::io &w, int revents)
4383\& {
4384\& ...
4385\& }
4386\& }
4387\&
4388\& myfunctor f;
4389\&
4390\& ev::io w;
4391\& w.set (&f);
4392.Ve
4393.IP "w\->set<function> (void *data = 0)" 4
4394.IX Item "w->set<function> (void *data = 0)"
4395Also sets a callback, but uses a static method or plain function as
4396callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
4397\&\f(CW\*(C`data\*(C'\fR member and is free for you to use.
4398.Sp
4399The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
4400.Sp
4401See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
4402.Sp
4403Example: Use a plain function as callback.
4404.Sp
4405.Vb 2
4406\& static void io_cb (ev::io &w, int revents) { }
4407\& iow.set <io_cb> ();
4408.Ve
4409.IP "w\->set (loop)" 4
4410.IX Item "w->set (loop)"
4411Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
4412do this when the watcher is inactive (and not pending either).
4413.IP "w\->set ([arguments])" 4
4414.IX Item "w->set ([arguments])"
4415Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR (except for \f(CW\*(C`ev::embed\*(C'\fR watchers>),
4416with the same arguments. Either this method or a suitable start method
4417must be called at least once. Unlike the C counterpart, an active watcher
4418gets automatically stopped and restarted when reconfiguring it with this
4419method.
4420.Sp
4421For \f(CW\*(C`ev::embed\*(C'\fR watchers this method is called \f(CW\*(C`set_embed\*(C'\fR, to avoid
4422clashing with the \f(CW\*(C`set (loop)\*(C'\fR method.
4423.Sp
4424For \f(CW\*(C`ev::io\*(C'\fR watchers there is an additional \f(CW\*(C`set\*(C'\fR method that acepts a
4425new event mask only, and internally calls \f(CW\*(C`ev_io_modfify\*(C'\fR.
4426.IP "w\->start ()" 4
4427.IX Item "w->start ()"
4428Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
4429constructor already stores the event loop.
4430.IP "w\->start ([arguments])" 4
4431.IX Item "w->start ([arguments])"
4432Instead of calling \f(CW\*(C`set\*(C'\fR and \f(CW\*(C`start\*(C'\fR methods separately, it is often
4433convenient to wrap them in one call. Uses the same type of arguments as
4434the configure \f(CW\*(C`set\*(C'\fR method of the watcher.
4435.IP "w\->stop ()" 4
4436.IX Item "w->stop ()"
4437Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
4438.ie n .IP "w\->again () (""ev::timer"", ""ev::periodic"" only)" 4
4439.el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
4440.IX Item "w->again () (ev::timer, ev::periodic only)"
4441For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
4442\&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
4443.ie n .IP "w\->sweep () (""ev::embed"" only)" 4
4444.el .IP "w\->sweep () (\f(CWev::embed\fR only)" 4
4445.IX Item "w->sweep () (ev::embed only)"
4446Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR.
4447.ie n .IP "w\->update () (""ev::stat"" only)" 4
4448.el .IP "w\->update () (\f(CWev::stat\fR only)" 4
4449.IX Item "w->update () (ev::stat only)"
4450Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
4451.RE
4452.RS 4
4453.RE
4454.PP
4455Example: Define a class with two I/O and idle watchers, start the I/O
4456watchers in the constructor.
4457.PP
4458.Vb 5
4459\& class myclass
4460\& {
4461\& ev::io io ; void io_cb (ev::io &w, int revents);
4462\& ev::io io2 ; void io2_cb (ev::io &w, int revents);
4463\& ev::idle idle; void idle_cb (ev::idle &w, int revents);
4464\&
4465\& myclass (int fd)
4466\& {
4467\& io .set <myclass, &myclass::io_cb > (this);
4468\& io2 .set <myclass, &myclass::io2_cb > (this);
4469\& idle.set <myclass, &myclass::idle_cb> (this);
4470\&
4471\& io.set (fd, ev::WRITE); // configure the watcher
4472\& io.start (); // start it whenever convenient
4473\&
4474\& io2.start (fd, ev::READ); // set + start in one call
4475\& }
4476\& };
4477.Ve
4478.SH "OTHER LANGUAGE BINDINGS"
4479.IX Header "OTHER LANGUAGE BINDINGS"
4480Libev does not offer other language bindings itself, but bindings for a
4481number of languages exist in the form of third-party packages. If you know
4482any interesting language binding in addition to the ones listed here, drop
4483me a note.
4484.IP "Perl" 4
4485.IX Item "Perl"
4486The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test
4487libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module,
4488there are additional modules that implement libev-compatible interfaces
4489to \f(CW\*(C`libadns\*(C'\fR (\f(CW\*(C`EV::ADNS\*(C'\fR, but \f(CW\*(C`AnyEvent::DNS\*(C'\fR is preferred nowadays),
4490\&\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
4491and \f(CW\*(C`EV::Glib\*(C'\fR).
4492.Sp
4493It can be found and installed via \s-1CPAN,\s0 its homepage is at
4494<http://software.schmorp.de/pkg/EV>.
4495.IP "Python" 4
4496.IX Item "Python"
4497Python bindings can be found at <http://code.google.com/p/pyev/>. It
4498seems to be quite complete and well-documented.
4499.IP "Ruby" 4
4500.IX Item "Ruby"
4501Tony Arcieri has written a ruby extension that offers access to a subset
4502of the libev \s-1API\s0 and adds file handle abstractions, asynchronous \s-1DNS\s0 and
4503more on top of it. It can be found via gem servers. Its homepage is at
4504<http://rev.rubyforge.org/>.
4505.Sp
4506Roger Pack reports that using the link order \f(CW\*(C`\-lws2_32 \-lmsvcrt\-ruby\-190\*(C'\fR
4507makes rev work even on mingw.
4508.IP "Haskell" 4
4509.IX Item "Haskell"
4510A haskell binding to libev is available at
4511<http://hackage.haskell.org/cgi\-bin/hackage\-scripts/package/hlibev>.
4512.IP "D" 4
4513.IX Item "D"
4514Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
4515be found at <http://www.llucax.com.ar/proj/ev.d/index.html>.
4516.IP "Ocaml" 4
4517.IX Item "Ocaml"
4518Erkki Seppala has written Ocaml bindings for libev, to be found at
4519<http://modeemi.cs.tut.fi/~flux/software/ocaml\-ev/>.
4520.IP "Lua" 4
4521.IX Item "Lua"
4522Brian Maher has written a partial interface to libev for lua (at the
4523time of this writing, only \f(CW\*(C`ev_io\*(C'\fR and \f(CW\*(C`ev_timer\*(C'\fR), to be found at
4524<http://github.com/brimworks/lua\-ev>.
4525.IP "Javascript" 4
4526.IX Item "Javascript"
4527Node.js (<http://nodejs.org>) uses libev as the underlying event library.
4528.IP "Others" 4
4529.IX Item "Others"
4530There are others, and I stopped counting.
4531.SH "MACRO MAGIC"
4532.IX Header "MACRO MAGIC"
4533Libev can be compiled with a variety of options, the most fundamental
4534of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most)
4535functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
4536.PP
4537To make it easier to write programs that cope with either variant, the
4538following macros are defined:
4539.ie n .IP """EV_A"", ""EV_A_""" 4
4540.el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
4541.IX Item "EV_A, EV_A_"
4542This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
4543loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
4544\&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
4545.Sp
4546.Vb 3
4547\& ev_unref (EV_A);
4548\& ev_timer_add (EV_A_ watcher);
4549\& ev_run (EV_A_ 0);
4550.Ve
4551.Sp
4552It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
4553which is often provided by the following macro.
4554.ie n .IP """EV_P"", ""EV_P_""" 4
4555.el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
4556.IX Item "EV_P, EV_P_"
4557This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
4558loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
4559\&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
4560.Sp
4561.Vb 2
4562\& // this is how ev_unref is being declared
4563\& static void ev_unref (EV_P);
4564\&
4565\& // this is how you can declare your typical callback
4566\& static void cb (EV_P_ ev_timer *w, int revents)
4567.Ve
4568.Sp
4569It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
4570suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
4571.ie n .IP """EV_DEFAULT"", ""EV_DEFAULT_""" 4
4572.el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
4573.IX Item "EV_DEFAULT, EV_DEFAULT_"
4574Similar to the other two macros, this gives you the value of the default
4575loop, if multiple loops are supported (\*(L"ev loop default\*(R"). The default loop
4576will be initialised if it isn't already initialised.
4577.Sp
4578For non-multiplicity builds, these macros do nothing, so you always have
4579to initialise the loop somewhere.
4580.ie n .IP """EV_DEFAULT_UC"", ""EV_DEFAULT_UC_""" 4
4581.el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
4582.IX Item "EV_DEFAULT_UC, EV_DEFAULT_UC_"
4583Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the
4584default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour
4585is undefined when the default loop has not been initialised by a previous
4586execution of \f(CW\*(C`EV_DEFAULT\*(C'\fR, \f(CW\*(C`EV_DEFAULT_\*(C'\fR or \f(CW\*(C`ev_default_init (...)\*(C'\fR.
4587.Sp
4588It is often prudent to use \f(CW\*(C`EV_DEFAULT\*(C'\fR when initialising the first
4589watcher in a function but use \f(CW\*(C`EV_DEFAULT_UC\*(C'\fR afterwards.
4590.PP
4591Example: Declare and initialise a check watcher, utilising the above
4592macros so it will work regardless of whether multiple loops are supported
4593or not.
4594.PP
4595.Vb 5
4596\& static void
4597\& check_cb (EV_P_ ev_timer *w, int revents)
4598\& {
4599\& ev_check_stop (EV_A_ w);
4600\& }
4601\&
4602\& ev_check check;
4603\& ev_check_init (&check, check_cb);
4604\& ev_check_start (EV_DEFAULT_ &check);
4605\& ev_run (EV_DEFAULT_ 0);
4606.Ve
4607.SH "EMBEDDING"
4608.IX Header "EMBEDDING"
4609Libev can (and often is) directly embedded into host
4610applications. Examples of applications that embed it include the Deliantra
4611Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
4612and rxvt-unicode.
4613.PP
4614The goal is to enable you to just copy the necessary files into your
4615source directory without having to change even a single line in them, so
4616you can easily upgrade by simply copying (or having a checked-out copy of
4617libev somewhere in your source tree).
4618.SS "\s-1FILESETS\s0"
4619.IX Subsection "FILESETS"
4620Depending on what features you need you need to include one or more sets of files
4621in your application.
4622.PP
4623\fI\s-1CORE EVENT LOOP\s0\fR
4624.IX Subsection "CORE EVENT LOOP"
4625.PP
4626To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
4627configuration (no autoconf):
4628.PP
4629.Vb 2
4630\& #define EV_STANDALONE 1
4631\& #include "ev.c"
4632.Ve
4633.PP
4634This will automatically include \fIev.h\fR, too, and should be done in a
4635single C source file only to provide the function implementations. To use
4636it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best
4637done by writing a wrapper around \fIev.h\fR that you can include instead and
4638where you can put other configuration options):
4639.PP
4640.Vb 2
4641\& #define EV_STANDALONE 1
4642\& #include "ev.h"
4643.Ve
4644.PP
4645Both header files and implementation files can be compiled with a \*(C+
4646compiler (at least, that's a stated goal, and breakage will be treated
4647as a bug).
4648.PP
4649You need the following files in your source tree, or in a directory
4650in your include path (e.g. in libev/ when using \-Ilibev):
4651.PP
4652.Vb 4
4653\& ev.h
4654\& ev.c
4655\& ev_vars.h
4656\& ev_wrap.h
4657\&
4658\& ev_win32.c required on win32 platforms only
4659\&
4660\& ev_select.c only when select backend is enabled
4661\& ev_poll.c only when poll backend is enabled
4662\& ev_epoll.c only when the epoll backend is enabled
4663\& ev_linuxaio.c only when the linux aio backend is enabled
4664\& ev_iouring.c only when the linux io_uring backend is enabled
4665\& ev_kqueue.c only when the kqueue backend is enabled
4666\& ev_port.c only when the solaris port backend is enabled
4667.Ve
4668.PP
4669\&\fIev.c\fR includes the backend files directly when enabled, so you only need
4670to compile this single file.
4671.PP
4672\fI\s-1LIBEVENT COMPATIBILITY API\s0\fR
4673.IX Subsection "LIBEVENT COMPATIBILITY API"
4674.PP
4675To include the libevent compatibility \s-1API,\s0 also include:
4676.PP
4677.Vb 1
4678\& #include "event.c"
4679.Ve
4680.PP
4681in the file including \fIev.c\fR, and:
4682.PP
4683.Vb 1
4684\& #include "event.h"
4685.Ve
4686.PP
4687in the files that want to use the libevent \s-1API.\s0 This also includes \fIev.h\fR.
4688.PP
4689You need the following additional files for this:
4690.PP
4691.Vb 2
4692\& event.h
4693\& event.c
4694.Ve
4695.PP
4696\fI\s-1AUTOCONF SUPPORT\s0\fR
4697.IX Subsection "AUTOCONF SUPPORT"
4698.PP
4699Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your configuration in
4700whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
4701\&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then
4702include \fIconfig.h\fR and configure itself accordingly.
4703.PP
4704For this of course you need the m4 file:
4705.PP
4706.Vb 1
4707\& libev.m4
4708.Ve
4709.SS "\s-1PREPROCESSOR SYMBOLS/MACROS\s0"
4710.IX Subsection "PREPROCESSOR SYMBOLS/MACROS"
4711Libev can be configured via a variety of preprocessor symbols you have to
4712define before including (or compiling) any of its files. The default in
4713the absence of autoconf is documented for every option.
4714.PP
4715Symbols marked with \*(L"(h)\*(R" do not change the \s-1ABI,\s0 and can have different
4716values when compiling libev vs. including \fIev.h\fR, so it is permissible
4717to redefine them before including \fIev.h\fR without breaking compatibility
4718to a compiled library. All other symbols change the \s-1ABI,\s0 which means all
4719users of libev and the libev code itself must be compiled with compatible
4720settings.
4721.IP "\s-1EV_COMPAT3\s0 (h)" 4
4722.IX Item "EV_COMPAT3 (h)"
4723Backwards compatibility is a major concern for libev. This is why this
4724release of libev comes with wrappers for the functions and symbols that
4725have been renamed between libev version 3 and 4.
4726.Sp
4727You can disable these wrappers (to test compatibility with future
4728versions) by defining \f(CW\*(C`EV_COMPAT3\*(C'\fR to \f(CW0\fR when compiling your
4729sources. This has the additional advantage that you can drop the \f(CW\*(C`struct\*(C'\fR
4730from \f(CW\*(C`struct ev_loop\*(C'\fR declarations, as libev will provide an \f(CW\*(C`ev_loop\*(C'\fR
4731typedef in that case.
4732.Sp
4733In some future version, the default for \f(CW\*(C`EV_COMPAT3\*(C'\fR will become \f(CW0\fR,
4734and in some even more future version the compatibility code will be
4735removed completely.
4736.IP "\s-1EV_STANDALONE\s0 (h)" 4
4737.IX Item "EV_STANDALONE (h)"
4738Must always be \f(CW1\fR if you do not use autoconf configuration, which
4739keeps libev from including \fIconfig.h\fR, and it also defines dummy
4740implementations for some libevent functions (such as logging, which is not
4741supported). It will also not define any of the structs usually found in
4742\&\fIevent.h\fR that are not directly supported by the libev core alone.
4743.Sp
4744In standalone mode, libev will still try to automatically deduce the
4745configuration, but has to be more conservative.
4746.IP "\s-1EV_USE_FLOOR\s0" 4
4747.IX Item "EV_USE_FLOOR"
4748If defined to be \f(CW1\fR, libev will use the \f(CW\*(C`floor ()\*(C'\fR function for its
4749periodic reschedule calculations, otherwise libev will fall back on a
4750portable (slower) implementation. If you enable this, you usually have to
4751link against libm or something equivalent. Enabling this when the \f(CW\*(C`floor\*(C'\fR
4752function is not available will fail, so the safe default is to not enable
4753this.
4754.IP "\s-1EV_USE_MONOTONIC\s0" 4
4755.IX Item "EV_USE_MONOTONIC"
4756If defined to be \f(CW1\fR, libev will try to detect the availability of the
4757monotonic clock option at both compile time and runtime. Otherwise no
4758use of the monotonic clock option will be attempted. If you enable this,
4759you usually have to link against librt or something similar. Enabling it
4760when the functionality isn't available is safe, though, although you have
4761to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
4762function is hiding in (often \fI\-lrt\fR). See also \f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
4763.IP "\s-1EV_USE_REALTIME\s0" 4
4764.IX Item "EV_USE_REALTIME"
4765If defined to be \f(CW1\fR, libev will try to detect the availability of the
4766real-time clock option at compile time (and assume its availability
4767at runtime if successful). Otherwise no use of the real-time clock
4768option will be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR
4769by \f(CW\*(C`clock_get (CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect
4770correctness. See the note about libraries in the description of
4771\&\f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. Defaults to the opposite value of
4772\&\f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
4773.IP "\s-1EV_USE_CLOCK_SYSCALL\s0" 4
4774.IX Item "EV_USE_CLOCK_SYSCALL"
4775If defined to be \f(CW1\fR, libev will try to use a direct syscall instead
4776of calling the system-provided \f(CW\*(C`clock_gettime\*(C'\fR function. This option
4777exists 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
4778unconditionally pulls in \f(CW\*(C`libpthread\*(C'\fR, slowing down single-threaded
4779programs needlessly. Using a direct syscall is slightly slower (in
4780theory), because no optimised vdso implementation can be used, but avoids
4781the pthread dependency. Defaults to \f(CW1\fR on GNU/Linux with glibc 2.x or
4782higher, as it simplifies linking (no need for \f(CW\*(C`\-lrt\*(C'\fR).
4783.IP "\s-1EV_USE_NANOSLEEP\s0" 4
4784.IX Item "EV_USE_NANOSLEEP"
4785If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available
4786and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR.
4787.IP "\s-1EV_USE_EVENTFD\s0" 4
4788.IX Item "EV_USE_EVENTFD"
4789If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
4790available and will probe for kernel support at runtime. This will improve
4791\&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
4792If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
47932.7 or newer, otherwise disabled.
4794.IP "\s-1EV_USE_SIGNALFD\s0" 4
4795.IX Item "EV_USE_SIGNALFD"
4796If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`signalfd ()\*(C'\fR is
4797available and will probe for kernel support at runtime. This enables
4798the use of \s-1EVFLAG_SIGNALFD\s0 for faster and simpler signal handling. If
4799undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
48002.7 or newer, otherwise disabled.
4801.IP "\s-1EV_USE_TIMERFD\s0" 4
4802.IX Item "EV_USE_TIMERFD"
4803If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`timerfd ()\*(C'\fR is
4804available and will probe for kernel support at runtime. This allows
4805libev to detect time jumps accurately. If undefined, it will be enabled
4806if the headers indicate GNU/Linux + Glibc 2.8 or newer and define
4807\&\f(CW\*(C`TFD_TIMER_CANCEL_ON_SET\*(C'\fR, otherwise disabled.
4808.IP "\s-1EV_USE_EVENTFD\s0" 4
4809.IX Item "EV_USE_EVENTFD"
4810If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
4811available and will probe for kernel support at runtime. This will improve
4812\&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
4813If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
48142.7 or newer, otherwise disabled.
4815.IP "\s-1EV_USE_SELECT\s0" 4
4816.IX Item "EV_USE_SELECT"
4817If undefined or defined to be \f(CW1\fR, libev will compile in support for the
4818\&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at auto-detection will be done: if no
4819other method takes over, select will be it. Otherwise the select backend
4820will not be compiled in.
4821.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
4822.IX Item "EV_SELECT_USE_FD_SET"
4823If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR
4824structure. This is useful if libev doesn't compile due to a missing
4825\&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it mis-guesses the bitset layout
4826on exotic systems. This usually limits the range of file descriptors to
4827some low limit such as 1024 or might have other limitations (winsocket
4828only allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation,
4829configures the maximum size of the \f(CW\*(C`fd_set\*(C'\fR.
4830.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
4831.IX Item "EV_SELECT_IS_WINSOCKET"
4832When defined to \f(CW1\fR, the select backend will assume that
4833select/socket/connect etc. don't understand file descriptors but
4834wants osf handles on win32 (this is the case when the select to
4835be used is the winsock select). This means that it will call
4836\&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
4837it is assumed that all these functions actually work on fds, even
4838on win32. Should not be defined on non\-win32 platforms.
4839.IP "\s-1EV_FD_TO_WIN32_HANDLE\s0(fd)" 4
4840.IX Item "EV_FD_TO_WIN32_HANDLE(fd)"
4841If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map
4842file descriptors to socket handles. When not defining this symbol (the
4843default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually
4844correct. In some cases, programs use their own file descriptor management,
4845in which case they can provide this function to map fds to socket handles.
4846.IP "\s-1EV_WIN32_HANDLE_TO_FD\s0(handle)" 4
4847.IX Item "EV_WIN32_HANDLE_TO_FD(handle)"
4848If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR then libev maps handles to file descriptors
4849using the standard \f(CW\*(C`_open_osfhandle\*(C'\fR function. For programs implementing
4850their own fd to handle mapping, overwriting this function makes it easier
4851to do so. This can be done by defining this macro to an appropriate value.
4852.IP "\s-1EV_WIN32_CLOSE_FD\s0(fd)" 4
4853.IX Item "EV_WIN32_CLOSE_FD(fd)"
4854If programs implement their own fd to handle mapping on win32, then this
4855macro can be used to override the \f(CW\*(C`close\*(C'\fR function, useful to unregister
4856file descriptors again. Note that the replacement function has to close
4857the underlying \s-1OS\s0 handle.
4858.IP "\s-1EV_USE_WSASOCKET\s0" 4
4859.IX Item "EV_USE_WSASOCKET"
4860If defined to be \f(CW1\fR, libev will use \f(CW\*(C`WSASocket\*(C'\fR to create its internal
4861communication socket, which works better in some environments. Otherwise,
4862the normal \f(CW\*(C`socket\*(C'\fR function will be used, which works better in other
4863environments.
4864.IP "\s-1EV_USE_POLL\s0" 4
4865.IX Item "EV_USE_POLL"
4866If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2)
4867backend. Otherwise it will be enabled on non\-win32 platforms. It
4868takes precedence over select.
4869.IP "\s-1EV_USE_EPOLL\s0" 4
4870.IX Item "EV_USE_EPOLL"
4871If defined to be \f(CW1\fR, libev will compile in support for the Linux
4872\&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime,
4873otherwise another method will be used as fallback. This is the preferred
4874backend for GNU/Linux systems. If undefined, it will be enabled if the
4875headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4876.IP "\s-1EV_USE_LINUXAIO\s0" 4
4877.IX Item "EV_USE_LINUXAIO"
4878If defined to be \f(CW1\fR, libev will compile in support for the Linux aio
4879backend (\f(CW\*(C`EV_USE_EPOLL\*(C'\fR must also be enabled). If undefined, it will be
4880enabled on linux, otherwise disabled.
4881.IP "\s-1EV_USE_IOURING\s0" 4
4882.IX Item "EV_USE_IOURING"
4883If defined to be \f(CW1\fR, libev will compile in support for the Linux
4884io_uring backend (\f(CW\*(C`EV_USE_EPOLL\*(C'\fR must also be enabled). Due to it's
4885current limitations it has to be requested explicitly. If undefined, it
4886will be enabled on linux, otherwise disabled.
4887.IP "\s-1EV_USE_KQUEUE\s0" 4
4888.IX Item "EV_USE_KQUEUE"
4889If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
4890\&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime,
4891otherwise another method will be used as fallback. This is the preferred
4892backend for \s-1BSD\s0 and BSD-like systems, although on most BSDs kqueue only
4893supports some types of fds correctly (the only platform we found that
4894supports ptys for example was NetBSD), so kqueue might be compiled in, but
4895not be used unless explicitly requested. The best way to use it is to find
4896out whether kqueue supports your type of fd properly and use an embedded
4897kqueue loop.
4898.IP "\s-1EV_USE_PORT\s0" 4
4899.IX Item "EV_USE_PORT"
4900If defined to be \f(CW1\fR, libev will compile in support for the Solaris
490110 port style backend. Its availability will be detected at runtime,
4902otherwise another method will be used as fallback. This is the preferred
4903backend for Solaris 10 systems.
4904.IP "\s-1EV_USE_DEVPOLL\s0" 4
4905.IX Item "EV_USE_DEVPOLL"
4906Reserved for future expansion, works like the \s-1USE\s0 symbols above.
4907.IP "\s-1EV_USE_INOTIFY\s0" 4
4908.IX Item "EV_USE_INOTIFY"
4909If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
4910interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
4911be detected at runtime. If undefined, it will be enabled if the headers
4912indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4913.IP "\s-1EV_NO_SMP\s0" 4
4914.IX Item "EV_NO_SMP"
4915If defined to be \f(CW1\fR, libev will assume that memory is always coherent
4916between threads, that is, threads can be used, but threads never run on
4917different cpus (or different cpu cores). This reduces dependencies
4918and makes libev faster.
4919.IP "\s-1EV_NO_THREADS\s0" 4
4920.IX Item "EV_NO_THREADS"
4921If defined to be \f(CW1\fR, libev will assume that it will never be called from
4922different threads (that includes signal handlers), which is a stronger
4923assumption than \f(CW\*(C`EV_NO_SMP\*(C'\fR, above. This reduces dependencies and makes
4924libev faster.
4925.IP "\s-1EV_ATOMIC_T\s0" 4
4926.IX Item "EV_ATOMIC_T"
4927Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
4928access is atomic with respect to other threads or signal contexts. No
4929such type is easily found in the C language, so you can provide your own
4930type that you know is safe for your purposes. It is used both for signal
4931handler \*(L"locking\*(R" as well as for signal and thread safety in \f(CW\*(C`ev_async\*(C'\fR
4932watchers.
4933.Sp
4934In the absence of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR
4935(from \fIsignal.h\fR), which is usually good enough on most platforms.
4936.IP "\s-1EV_H\s0 (h)" 4
4937.IX Item "EV_H (h)"
4938The name of the \fIev.h\fR header file used to include it. The default if
4939undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be
4940used to virtually rename the \fIev.h\fR header file in case of conflicts.
4941.IP "\s-1EV_CONFIG_H\s0 (h)" 4
4942.IX Item "EV_CONFIG_H (h)"
4943If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
4944\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
4945\&\f(CW\*(C`EV_H\*(C'\fR, above.
4946.IP "\s-1EV_EVENT_H\s0 (h)" 4
4947.IX Item "EV_EVENT_H (h)"
4948Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea
4949of how the \fIevent.h\fR header can be found, the default is \f(CW"event.h"\fR.
4950.IP "\s-1EV_PROTOTYPES\s0 (h)" 4
4951.IX Item "EV_PROTOTYPES (h)"
4952If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
4953prototypes, but still define all the structs and other symbols. This is
4954occasionally useful if you want to provide your own wrapper functions
4955around libev functions.
4956.IP "\s-1EV_MULTIPLICITY\s0" 4
4957.IX Item "EV_MULTIPLICITY"
4958If undefined or defined to \f(CW1\fR, then all event-loop-specific functions
4959will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create
4960additional independent event loops. Otherwise there will be no support
4961for multiple event loops and there is no first event loop pointer
4962argument. Instead, all functions act on the single default loop.
4963.Sp
4964Note that \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR will no longer provide a
4965default loop when multiplicity is switched off \- you always have to
4966initialise the loop manually in this case.
4967.IP "\s-1EV_MINPRI\s0" 4
4968.IX Item "EV_MINPRI"
4969.PD 0
4970.IP "\s-1EV_MAXPRI\s0" 4
4971.IX Item "EV_MAXPRI"
4972.PD
4973The range of allowed priorities. \f(CW\*(C`EV_MINPRI\*(C'\fR must be smaller or equal to
4974\&\f(CW\*(C`EV_MAXPRI\*(C'\fR, but otherwise there are no non-obvious limitations. You can
4975provide for more priorities by overriding those symbols (usually defined
4976to be \f(CW\*(C`\-2\*(C'\fR and \f(CW2\fR, respectively).
4977.Sp
4978When doing priority-based operations, libev usually has to linearly search
4979all the priorities, so having many of them (hundreds) uses a lot of space
4980and time, so using the defaults of five priorities (\-2 .. +2) is usually
4981fine.
4982.Sp
4983If your embedding application does not need any priorities, defining these
4984both to \f(CW0\fR will save some memory and \s-1CPU.\s0
4985.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
4986.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."
4987If undefined or defined to be \f(CW1\fR (and the platform supports it), then
4988the respective watcher type is supported. If defined to be \f(CW0\fR, then it
4989is not. Disabling watcher types mainly saves code size.
4990.IP "\s-1EV_FEATURES\s0" 4
4991.IX Item "EV_FEATURES"
4992If you need to shave off some kilobytes of code at the expense of some
4993speed (but with the full \s-1API\s0), you can define this symbol to request
4994certain subsets of functionality. The default is to enable all features
4995that can be enabled on the platform.
4996.Sp
4997A typical way to use this symbol is to define it to \f(CW0\fR (or to a bitset
4998with some broad features you want) and then selectively re-enable
4999additional parts you want, for example if you want everything minimal,
5000but multiple event loop support, async and child watchers and the poll
5001backend, use this:
5002.Sp
5003.Vb 5
5004\& #define EV_FEATURES 0
5005\& #define EV_MULTIPLICITY 1
5006\& #define EV_USE_POLL 1
5007\& #define EV_CHILD_ENABLE 1
5008\& #define EV_ASYNC_ENABLE 1
5009.Ve
5010.Sp
5011The actual value is a bitset, it can be a combination of the following
5012values (by default, all of these are enabled):
5013.RS 4
5014.ie n .IP "1 \- faster/larger code" 4
5015.el .IP "\f(CW1\fR \- faster/larger code" 4
5016.IX Item "1 - faster/larger code"
5017Use larger code to speed up some operations.
5018.Sp
5019Currently this is used to override some inlining decisions (enlarging the
5020code size by roughly 30% on amd64).
5021.Sp
5022When optimising for size, use of compiler flags such as \f(CW\*(C`\-Os\*(C'\fR with
5023gcc is recommended, as well as \f(CW\*(C`\-DNDEBUG\*(C'\fR, as libev contains a number of
5024assertions.
5025.Sp
5026The default is off when \f(CW\*(C`_\|_OPTIMIZE_SIZE_\|_\*(C'\fR is defined by your compiler
5027(e.g. gcc with \f(CW\*(C`\-Os\*(C'\fR).
5028.ie n .IP "2 \- faster/larger data structures" 4
5029.el .IP "\f(CW2\fR \- faster/larger data structures" 4
5030.IX Item "2 - faster/larger data structures"
5031Replaces the small 2\-heap for timer management by a faster 4\-heap, larger
5032hash table sizes and so on. This will usually further increase code size
5033and can additionally have an effect on the size of data structures at
5034runtime.
5035.Sp
5036The default is off when \f(CW\*(C`_\|_OPTIMIZE_SIZE_\|_\*(C'\fR is defined by your compiler
5037(e.g. gcc with \f(CW\*(C`\-Os\*(C'\fR).
5038.ie n .IP "4 \- full \s-1API\s0 configuration" 4
5039.el .IP "\f(CW4\fR \- full \s-1API\s0 configuration" 4
5040.IX Item "4 - full API configuration"
5041This enables priorities (sets \f(CW\*(C`EV_MAXPRI\*(C'\fR=2 and \f(CW\*(C`EV_MINPRI\*(C'\fR=\-2), and
5042enables multiplicity (\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR=1).
5043.ie n .IP "8 \- full \s-1API\s0" 4
5044.el .IP "\f(CW8\fR \- full \s-1API\s0" 4
5045.IX Item "8 - full API"
5046This enables a lot of the \*(L"lesser used\*(R" \s-1API\s0 functions. See \f(CW\*(C`ev.h\*(C'\fR for
5047details on which parts of the \s-1API\s0 are still available without this
5048feature, and do not complain if this subset changes over time.
5049.ie n .IP "16 \- enable all optional watcher types" 4
5050.el .IP "\f(CW16\fR \- enable all optional watcher types" 4
5051.IX Item "16 - enable all optional watcher types"
5052Enables all optional watcher types. If you want to selectively enable
5053only some watcher types other than I/O and timers (e.g. prepare,
5054embed, async, child...) you can enable them manually by defining
5055\&\f(CW\*(C`EV_watchertype_ENABLE\*(C'\fR to \f(CW1\fR instead.
5056.ie n .IP "32 \- enable all backends" 4
5057.el .IP "\f(CW32\fR \- enable all backends" 4
5058.IX Item "32 - enable all backends"
5059This enables all backends \- without this feature, you need to enable at
5060least one backend manually (\f(CW\*(C`EV_USE_SELECT\*(C'\fR is a good choice).
5061.ie n .IP "64 \- enable OS-specific ""helper"" APIs" 4
5062.el .IP "\f(CW64\fR \- enable OS-specific ``helper'' APIs" 4
5063.IX Item "64 - enable OS-specific helper APIs"
5064Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
5065default.
5066.RE
5067.RS 4
5068.Sp
5069Compiling with \f(CW\*(C`gcc \-Os \-DEV_STANDALONE \-DEV_USE_EPOLL=1 \-DEV_FEATURES=0\*(C'\fR
5070reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
5071code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
5072watchers, timers and monotonic clock support.
5073.Sp
5074With an intelligent-enough linker (gcc+binutils are intelligent enough
5075when you use \f(CW\*(C`\-Wl,\-\-gc\-sections \-ffunction\-sections\*(C'\fR) functions unused by
5076your program might be left out as well \- a binary starting a timer and an
5077I/O watcher then might come out at only 5Kb.
5078.RE
5079.IP "\s-1EV_API_STATIC\s0" 4
5080.IX Item "EV_API_STATIC"
5081If this symbol is defined (by default it is not), then all identifiers
5082will have static linkage. This means that libev will not export any
5083identifiers, and you cannot link against libev anymore. This can be useful
5084when you embed libev, only want to use libev functions in a single file,
5085and do not want its identifiers to be visible.
5086.Sp
5087To use this, define \f(CW\*(C`EV_API_STATIC\*(C'\fR and include \fIev.c\fR in the file that
5088wants to use libev.
5089.Sp
5090This option only works when libev is compiled with a C compiler, as \*(C+
5091doesn't support the required declaration syntax.
5092.IP "\s-1EV_AVOID_STDIO\s0" 4
5093.IX Item "EV_AVOID_STDIO"
5094If this is set to \f(CW1\fR at compiletime, then libev will avoid using stdio
5095functions (printf, scanf, perror etc.). This will increase the code size
5096somewhat, but if your program doesn't otherwise depend on stdio and your
5097libc allows it, this avoids linking in the stdio library which is quite
5098big.
5099.Sp
5100Note that error messages might become less precise when this option is
5101enabled.
5102.IP "\s-1EV_NSIG\s0" 4
5103.IX Item "EV_NSIG"
5104The highest supported signal number, +1 (or, the number of
5105signals): Normally, libev tries to deduce the maximum number of signals
5106automatically, but sometimes this fails, in which case it can be
5107specified. Also, using a lower number than detected (\f(CW32\fR should be
5108good for about any system in existence) can save some memory, as libev
5109statically allocates some 12\-24 bytes per signal number.
5110.IP "\s-1EV_PID_HASHSIZE\s0" 4
5111.IX Item "EV_PID_HASHSIZE"
5112\&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by
5113pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR disabled),
5114usually more than enough. If you need to manage thousands of children you
5115might want to increase this value (\fImust\fR be a power of two).
5116.IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4
5117.IX Item "EV_INOTIFY_HASHSIZE"
5118\&\f(CW\*(C`ev_stat\*(C'\fR watchers use a small hash table to distribute workload by
5119inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR
5120disabled), usually more than enough. If you need to manage thousands of
5121\&\f(CW\*(C`ev_stat\*(C'\fR watchers you might want to increase this value (\fImust\fR be a
5122power of two).
5123.IP "\s-1EV_USE_4HEAP\s0" 4
5124.IX Item "EV_USE_4HEAP"
5125Heaps are not very cache-efficient. To improve the cache-efficiency of the
5126timer and periodics heaps, libev uses a 4\-heap when this symbol is defined
5127to \f(CW1\fR. The 4\-heap uses more complicated (longer) code but has noticeably
5128faster performance with many (thousands) of watchers.
5129.Sp
5130The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
5131will be \f(CW0\fR.
5132.IP "\s-1EV_HEAP_CACHE_AT\s0" 4
5133.IX Item "EV_HEAP_CACHE_AT"
5134Heaps are not very cache-efficient. To improve the cache-efficiency of the
5135timer and periodics heaps, libev can cache the timestamp (\fIat\fR) within
5136the heap structure (selected by defining \f(CW\*(C`EV_HEAP_CACHE_AT\*(C'\fR to \f(CW1\fR),
5137which uses 8\-12 bytes more per watcher and a few hundred bytes more code,
5138but avoids random read accesses on heap changes. This improves performance
5139noticeably with many (hundreds) of watchers.
5140.Sp
5141The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
5142will be \f(CW0\fR.
5143.IP "\s-1EV_VERIFY\s0" 4
5144.IX Item "EV_VERIFY"
5145Controls how much internal verification (see \f(CW\*(C`ev_verify ()\*(C'\fR) will
5146be done: If set to \f(CW0\fR, no internal verification code will be compiled
5147in. If set to \f(CW1\fR, then verification code will be compiled in, but not
5148called. If set to \f(CW2\fR, then the internal verification code will be
5149called once per loop, which can slow down libev. If set to \f(CW3\fR, then the
5150verification code will be called very frequently, which will slow down
5151libev considerably.
5152.Sp
5153Verification errors are reported via C's \f(CW\*(C`assert\*(C'\fR mechanism, so if you
5154disable that (e.g. by defining \f(CW\*(C`NDEBUG\*(C'\fR) then no errors will be reported.
5155.Sp
5156The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
5157will be \f(CW0\fR.
5158.IP "\s-1EV_COMMON\s0" 4
5159.IX Item "EV_COMMON"
5160By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining
5161this macro to something else you can include more and other types of
5162members. You have to define it each time you include one of the files,
5163though, and it must be identical each time.
5164.Sp
5165For example, the perl \s-1EV\s0 module uses something like this:
5166.Sp
5167.Vb 3
5168\& #define EV_COMMON \e
5169\& SV *self; /* contains this struct */ \e
5170\& SV *cb_sv, *fh /* note no trailing ";" */
5171.Ve
5172.IP "\s-1EV_CB_DECLARE\s0 (type)" 4
5173.IX Item "EV_CB_DECLARE (type)"
5174.PD 0
5175.IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4
5176.IX Item "EV_CB_INVOKE (watcher, revents)"
5177.IP "ev_set_cb (ev, cb)" 4
5178.IX Item "ev_set_cb (ev, cb)"
5179.PD
5180Can be used to change the callback member declaration in each watcher,
5181and the way callbacks are invoked and set. Must expand to a struct member
5182definition and a statement, respectively. See the \fIev.h\fR header file for
5183their default definitions. One possible use for overriding these is to
5184avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use
5185method calls instead of plain function calls in \*(C+.
5186.SS "\s-1EXPORTED API SYMBOLS\s0"
5187.IX Subsection "EXPORTED API SYMBOLS"
5188If you need to re-export the \s-1API\s0 (e.g. via a \s-1DLL\s0) and you need a list of
5189exported symbols, you can use the provided \fISymbol.*\fR files which list
5190all public symbols, one per line:
5191.PP
5192.Vb 2
5193\& Symbols.ev for libev proper
5194\& Symbols.event for the libevent emulation
5195.Ve
5196.PP
5197This can also be used to rename all public symbols to avoid clashes with
5198multiple versions of libev linked together (which is obviously bad in
5199itself, but sometimes it is inconvenient to avoid this).
5200.PP
5201A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to
5202include before including \fIev.h\fR:
5203.PP
5204.Vb 1
5205\& <Symbols.ev sed \-e "s/.*/#define & myprefix_&/" >wrap.h
5206.Ve
5207.PP
5208This would create a file \fIwrap.h\fR which essentially looks like this:
5209.PP
5210.Vb 4
5211\& #define ev_backend myprefix_ev_backend
5212\& #define ev_check_start myprefix_ev_check_start
5213\& #define ev_check_stop myprefix_ev_check_stop
5214\& ...
5215.Ve
5216.SS "\s-1EXAMPLES\s0"
5217.IX Subsection "EXAMPLES"
5218For a real-world example of a program the includes libev
5219verbatim, you can have a look at the \s-1EV\s0 perl module
5220(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
5221the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public
5222interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file
5223will be compiled. It is pretty complex because it provides its own header
5224file.
5225.PP
5226The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file
5227that everybody includes and which overrides some configure choices:
5228.PP
5229.Vb 8
5230\& #define EV_FEATURES 8
5231\& #define EV_USE_SELECT 1
5232\& #define EV_PREPARE_ENABLE 1
5233\& #define EV_IDLE_ENABLE 1
5234\& #define EV_SIGNAL_ENABLE 1
5235\& #define EV_CHILD_ENABLE 1
5236\& #define EV_USE_STDEXCEPT 0
5237\& #define EV_CONFIG_H <config.h>
5238\&
5239\& #include "ev++.h"
5240.Ve
5241.PP
5242And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled:
5243.PP
5244.Vb 2
5245\& #include "ev_cpp.h"
5246\& #include "ev.c"
5247.Ve
5248.SH "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT"
5249.IX Header "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT"
5250.SS "\s-1THREADS AND COROUTINES\s0"
5251.IX Subsection "THREADS AND COROUTINES"
5252\fI\s-1THREADS\s0\fR
5253.IX Subsection "THREADS"
5254.PP
5255All libev functions are reentrant and thread-safe unless explicitly
5256documented otherwise, but libev implements no locking itself. This means
5257that you can use as many loops as you want in parallel, as long as there
5258are no concurrent calls into any libev function with the same loop
5259parameter (\f(CW\*(C`ev_default_*\*(C'\fR calls have an implicit default loop parameter,
5260of course): libev guarantees that different event loops share no data
5261structures that need any locking.
5262.PP
5263Or to put it differently: calls with different loop parameters can be done
5264concurrently from multiple threads, calls with the same loop parameter
5265must be done serially (but can be done from different threads, as long as
5266only one thread ever is inside a call at any point in time, e.g. by using
5267a mutex per loop).
5268.PP
5269Specifically to support threads (and signal handlers), libev implements
5270so-called \f(CW\*(C`ev_async\*(C'\fR watchers, which allow some limited form of
5271concurrency on the same event loop, namely waking it up \*(L"from the
5272outside\*(R".
5273.PP
5274If you want to know which design (one loop, locking, or multiple loops
5275without or something else still) is best for your problem, then I cannot
5276help you, but here is some generic advice:
5277.IP "\(bu" 4
5278most applications have a main thread: use the default libev loop
5279in that thread, or create a separate thread running only the default loop.
5280.Sp
5281This helps integrating other libraries or software modules that use libev
5282themselves and don't care/know about threading.
5283.IP "\(bu" 4
5284one loop per thread is usually a good model.
5285.Sp
5286Doing this is almost never wrong, sometimes a better-performance model
5287exists, but it is always a good start.
5288.IP "\(bu" 4
5289other models exist, such as the leader/follower pattern, where one
5290loop is handed through multiple threads in a kind of round-robin fashion.
5291.Sp
5292Choosing a model is hard \- look around, learn, know that usually you can do
5293better than you currently do :\-)
5294.IP "\(bu" 4
5295often you need to talk to some other thread which blocks in the
5296event loop.
5297.Sp
5298\&\f(CW\*(C`ev_async\*(C'\fR watchers can be used to wake them up from other threads safely
5299(or from signal contexts...).
5300.Sp
5301An example use would be to communicate signals or other events that only
5302work in the default loop by registering the signal watcher with the
5303default loop and triggering an \f(CW\*(C`ev_async\*(C'\fR watcher from the default loop
5304watcher callback into the event loop interested in the signal.
5305.PP
5306See also \*(L"\s-1THREAD LOCKING EXAMPLE\*(R"\s0.
5307.PP
5308\fI\s-1COROUTINES\s0\fR
5309.IX Subsection "COROUTINES"
5310.PP
5311Libev is very accommodating to coroutines (\*(L"cooperative threads\*(R"):
5312libev fully supports nesting calls to its functions from different
5313coroutines (e.g. you can call \f(CW\*(C`ev_run\*(C'\fR on the same loop from two
5314different coroutines, and switch freely between both coroutines running
5315the loop, as long as you don't confuse yourself). The only exception is
5316that you must not do this from \f(CW\*(C`ev_periodic\*(C'\fR reschedule callbacks.
5317.PP
5318Care has been taken to ensure that libev does not keep local state inside
5319\&\f(CW\*(C`ev_run\*(C'\fR, and other calls do not usually allow for coroutine switches as
5320they do not call any callbacks.
5321.SS "\s-1COMPILER WARNINGS\s0"
5322.IX Subsection "COMPILER WARNINGS"
5323Depending on your compiler and compiler settings, you might get no or a
5324lot of warnings when compiling libev code. Some people are apparently
5325scared by this.
5326.PP
5327However, these are unavoidable for many reasons. For one, each compiler
5328has different warnings, and each user has different tastes regarding
5329warning options. \*(L"Warn-free\*(R" code therefore cannot be a goal except when
5330targeting a specific compiler and compiler-version.
5331.PP
5332Another reason is that some compiler warnings require elaborate
5333workarounds, or other changes to the code that make it less clear and less
5334maintainable.
5335.PP
5336And of course, some compiler warnings are just plain stupid, or simply
5337wrong (because they don't actually warn about the condition their message
5338seems to warn about). For example, certain older gcc versions had some
5339warnings that resulted in an extreme number of false positives. These have
5340been fixed, but some people still insist on making code warn-free with
5341such buggy versions.
5342.PP
5343While libev is written to generate as few warnings as possible,
5344\&\*(L"warn-free\*(R" code is not a goal, and it is recommended not to build libev
5345with any compiler warnings enabled unless you are prepared to cope with
5346them (e.g. by ignoring them). Remember that warnings are just that:
5347warnings, not errors, or proof of bugs.
5348.SS "\s-1VALGRIND\s0"
5349.IX Subsection "VALGRIND"
5350Valgrind has a special section here because it is a popular tool that is
5351highly useful. Unfortunately, valgrind reports are very hard to interpret.
5352.PP
5353If you think you found a bug (memory leak, uninitialised data access etc.)
5354in libev, then check twice: If valgrind reports something like:
5355.PP
5356.Vb 3
5357\& ==2274== definitely lost: 0 bytes in 0 blocks.
5358\& ==2274== possibly lost: 0 bytes in 0 blocks.
5359\& ==2274== still reachable: 256 bytes in 1 blocks.
5360.Ve
5361.PP
5362Then there is no memory leak, just as memory accounted to global variables
5363is not a memleak \- the memory is still being referenced, and didn't leak.
5364.PP
5365Similarly, under some circumstances, valgrind might report kernel bugs
5366as if it were a bug in libev (e.g. in realloc or in the poll backend,
5367although an acceptable workaround has been found here), or it might be
5368confused.
5369.PP
5370Keep in mind that valgrind is a very good tool, but only a tool. Don't
5371make it into some kind of religion.
5372.PP
5373If you are unsure about something, feel free to contact the mailing list
5374with the full valgrind report and an explanation on why you think this
5375is a bug in libev (best check the archives, too :). However, don't be
5376annoyed when you get a brisk \*(L"this is no bug\*(R" answer and take the chance
5377of learning how to interpret valgrind properly.
5378.PP
5379If you need, for some reason, empty reports from valgrind for your project
5380I suggest using suppression lists.
5381.SH "PORTABILITY NOTES"
5382.IX Header "PORTABILITY NOTES"
5383.SS "\s-1GNU/LINUX 32 BIT LIMITATIONS\s0"
5384.IX Subsection "GNU/LINUX 32 BIT LIMITATIONS"
5385GNU/Linux is the only common platform that supports 64 bit file/large file
5386interfaces but \fIdisables\fR them by default.
5387.PP
5388That means that libev compiled in the default environment doesn't support
5389files larger than 2GiB or so, which mainly affects \f(CW\*(C`ev_stat\*(C'\fR watchers.
5390.PP
5391Unfortunately, many programs try to work around this GNU/Linux issue
5392by enabling the large file \s-1API,\s0 which makes them incompatible with the
5393standard libev compiled for their system.
5394.PP
5395Likewise, libev cannot enable the large file \s-1API\s0 itself as this would
5396suddenly make it incompatible to the default compile time environment,
5397i.e. all programs not using special compile switches.
5398.SS "\s-1OS/X AND DARWIN BUGS\s0"
5399.IX Subsection "OS/X AND DARWIN BUGS"
5400The whole thing is a bug if you ask me \- basically any system interface
5401you touch is broken, whether it is locales, poll, kqueue or even the
5402OpenGL drivers.
5403.PP
5404\fI\f(CI\*(C`kqueue\*(C'\fI is buggy\fR
5405.IX Subsection "kqueue is buggy"
5406.PP
5407The kqueue syscall is broken in all known versions \- most versions support
5408only sockets, many support pipes.
5409.PP
5410Libev tries to work around this by not using \f(CW\*(C`kqueue\*(C'\fR by default on this
5411rotten platform, but of course you can still ask for it when creating a
5412loop \- embedding a socket-only kqueue loop into a select-based one is
5413probably going to work well.
5414.PP
5415\fI\f(CI\*(C`poll\*(C'\fI is buggy\fR
5416.IX Subsection "poll is buggy"
5417.PP
5418Instead of fixing \f(CW\*(C`kqueue\*(C'\fR, Apple replaced their (working) \f(CW\*(C`poll\*(C'\fR
5419implementation by something calling \f(CW\*(C`kqueue\*(C'\fR internally around the 10.5.6
5420release, so now \f(CW\*(C`kqueue\*(C'\fR \fIand\fR \f(CW\*(C`poll\*(C'\fR are broken.
5421.PP
5422Libev tries to work around this by not using \f(CW\*(C`poll\*(C'\fR by default on
5423this rotten platform, but of course you can still ask for it when creating
5424a loop.
5425.PP
5426\fI\f(CI\*(C`select\*(C'\fI is buggy\fR
5427.IX Subsection "select is buggy"
5428.PP
5429All that's left is \f(CW\*(C`select\*(C'\fR, and of course Apple found a way to fuck this
5430one up as well: On \s-1OS/X,\s0 \f(CW\*(C`select\*(C'\fR actively limits the number of file
5431descriptors you can pass in to 1024 \- your program suddenly crashes when
5432you use more.
5433.PP
5434There is an undocumented \*(L"workaround\*(R" for this \- defining
5435\&\f(CW\*(C`_DARWIN_UNLIMITED_SELECT\*(C'\fR, which libev tries to use, so select \fIshould\fR
5436work on \s-1OS/X.\s0
5437.SS "\s-1SOLARIS PROBLEMS AND WORKAROUNDS\s0"
5438.IX Subsection "SOLARIS PROBLEMS AND WORKAROUNDS"
5439\fI\f(CI\*(C`errno\*(C'\fI reentrancy\fR
5440.IX Subsection "errno reentrancy"
5441.PP
5442The default compile environment on Solaris is unfortunately so
5443thread-unsafe that you can't even use components/libraries compiled
5444without \f(CW\*(C`\-D_REENTRANT\*(C'\fR in a threaded program, which, of course, isn't
5445defined by default. A valid, if stupid, implementation choice.
5446.PP
5447If you want to use libev in threaded environments you have to make sure
5448it's compiled with \f(CW\*(C`_REENTRANT\*(C'\fR defined.
5449.PP
5450\fIEvent port backend\fR
5451.IX Subsection "Event port backend"
5452.PP
5453The scalable event interface for Solaris is called \*(L"event
5454ports\*(R". Unfortunately, this mechanism is very buggy in all major
5455releases. If you run into high \s-1CPU\s0 usage, your program freezes or you get
5456a large number of spurious wakeups, make sure you have all the relevant
5457and latest kernel patches applied. No, I don't know which ones, but there
5458are multiple ones to apply, and afterwards, event ports actually work
5459great.
5460.PP
5461If you can't get it to work, you can try running the program by setting
5462the environment variable \f(CW\*(C`LIBEV_FLAGS=3\*(C'\fR to only allow \f(CW\*(C`poll\*(C'\fR and
5463\&\f(CW\*(C`select\*(C'\fR backends.
5464.SS "\s-1AIX POLL BUG\s0"
5465.IX Subsection "AIX POLL BUG"
5466\&\s-1AIX\s0 unfortunately has a broken \f(CW\*(C`poll.h\*(C'\fR header. Libev works around
5467this by trying to avoid the poll backend altogether (i.e. it's not even
5468compiled in), which normally isn't a big problem as \f(CW\*(C`select\*(C'\fR works fine
5469with large bitsets on \s-1AIX,\s0 and \s-1AIX\s0 is dead anyway.
5470.SS "\s-1WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS\s0"
5471.IX Subsection "WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS"
5472\fIGeneral issues\fR
5473.IX Subsection "General issues"
5474.PP
5475Win32 doesn't support any of the standards (e.g. \s-1POSIX\s0) that libev
5476requires, and its I/O model is fundamentally incompatible with the \s-1POSIX\s0
5477model. Libev still offers limited functionality on this platform in
5478the form of the \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR backend, and only supports socket
5479descriptors. This only applies when using Win32 natively, not when using
5480e.g. cygwin. Actually, it only applies to the microsofts own compilers,
5481as every compiler comes with a slightly differently broken/incompatible
5482environment.
5483.PP
5484Lifting these limitations would basically require the full
5485re-implementation of the I/O system. If you are into this kind of thing,
5486then note that glib does exactly that for you in a very portable way (note
5487also that glib is the slowest event library known to man).
5488.PP
5489There is no supported compilation method available on windows except
5490embedding it into other applications.
5491.PP
5492Sensible signal handling is officially unsupported by Microsoft \- libev
5493tries its best, but under most conditions, signals will simply not work.
5494.PP
5495Not a libev limitation but worth mentioning: windows apparently doesn't
5496accept large writes: instead of resulting in a partial write, windows will
5497either accept everything or return \f(CW\*(C`ENOBUFS\*(C'\fR if the buffer is too large,
5498so make sure you only write small amounts into your sockets (less than a
5499megabyte seems safe, but this apparently depends on the amount of memory
5500available).
5501.PP
5502Due to the many, low, and arbitrary limits on the win32 platform and
5503the abysmal performance of winsockets, using a large number of sockets
5504is not recommended (and not reasonable). If your program needs to use
5505more than a hundred or so sockets, then likely it needs to use a totally
5506different implementation for windows, as libev offers the \s-1POSIX\s0 readiness
5507notification model, which cannot be implemented efficiently on windows
5508(due to Microsoft monopoly games).
5509.PP
5510A typical way to use libev under windows is to embed it (see the embedding
5511section for details) and use the following \fIevwrap.h\fR header file instead
5512of \fIev.h\fR:
5513.PP
5514.Vb 2
5515\& #define EV_STANDALONE /* keeps ev from requiring config.h */
5516\& #define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
5517\&
5518\& #include "ev.h"
5519.Ve
5520.PP
5521And compile the following \fIevwrap.c\fR file into your project (make sure
5522you do \fInot\fR compile the \fIev.c\fR or any other embedded source files!):
5523.PP
5524.Vb 2
5525\& #include "evwrap.h"
5526\& #include "ev.c"
5527.Ve
5528.PP
5529\fIThe winsocket \f(CI\*(C`select\*(C'\fI function\fR
5530.IX Subsection "The winsocket select function"
5531.PP
5532The winsocket \f(CW\*(C`select\*(C'\fR function doesn't follow \s-1POSIX\s0 in that it
5533requires socket \fIhandles\fR and not socket \fIfile descriptors\fR (it is
5534also extremely buggy). This makes select very inefficient, and also
5535requires a mapping from file descriptors to socket handles (the Microsoft
5536C runtime provides the function \f(CW\*(C`_open_osfhandle\*(C'\fR for this). See the
5537discussion of the \f(CW\*(C`EV_SELECT_USE_FD_SET\*(C'\fR, \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR and
5538\&\f(CW\*(C`EV_FD_TO_WIN32_HANDLE\*(C'\fR preprocessor symbols for more info.
5539.PP
5540The configuration for a \*(L"naked\*(R" win32 using the Microsoft runtime
5541libraries and raw winsocket select is:
5542.PP
5543.Vb 2
5544\& #define EV_USE_SELECT 1
5545\& #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
5546.Ve
5547.PP
5548Note that winsockets handling of fd sets is O(n), so you can easily get a
5549complexity in the O(nX) range when using win32.
5550.PP
5551\fILimited number of file descriptors\fR
5552.IX Subsection "Limited number of file descriptors"
5553.PP
5554Windows has numerous arbitrary (and low) limits on things.
5555.PP
5556Early versions of winsocket's select only supported waiting for a maximum
5557of \f(CW64\fR handles (probably owning to the fact that all windows kernels
5558can only wait for \f(CW64\fR things at the same time internally; Microsoft
5559recommends spawning a chain of threads and wait for 63 handles and the
5560previous thread in each. Sounds great!).
5561.PP
5562Newer versions support more handles, but you need to define \f(CW\*(C`FD_SETSIZE\*(C'\fR
5563to some high number (e.g. \f(CW2048\fR) before compiling the winsocket select
5564call (which might be in libev or elsewhere, for example, perl and many
5565other interpreters do their own select emulation on windows).
5566.PP
5567Another limit is the number of file descriptors in the Microsoft runtime
5568libraries, which by default is \f(CW64\fR (there must be a hidden \fI64\fR
5569fetish or something like this inside Microsoft). You can increase this
5570by calling \f(CW\*(C`_setmaxstdio\*(C'\fR, which can increase this limit to \f(CW2048\fR
5571(another arbitrary limit), but is broken in many versions of the Microsoft
5572runtime libraries. This might get you to about \f(CW512\fR or \f(CW2048\fR sockets
5573(depending on windows version and/or the phase of the moon). To get more,
5574you need to wrap all I/O functions and provide your own fd management, but
5575the cost of calling select (O(nX)) will likely make this unworkable.
5576.SS "\s-1PORTABILITY REQUIREMENTS\s0"
5577.IX Subsection "PORTABILITY REQUIREMENTS"
5578In addition to a working ISO-C implementation and of course the
5579backend-specific APIs, libev relies on a few additional extensions:
5580.ie n .IP """void (*)(ev_watcher_type *, int revents)"" must have compatible calling conventions regardless of ""ev_watcher_type *""." 4
5581.el .IP "\f(CWvoid (*)(ev_watcher_type *, int revents)\fR must have compatible calling conventions regardless of \f(CWev_watcher_type *\fR." 4
5582.IX Item "void (*)(ev_watcher_type *, int revents) must have compatible calling conventions regardless of ev_watcher_type *."
5583Libev assumes not only that all watcher pointers have the same internal
5584structure (guaranteed by \s-1POSIX\s0 but not by \s-1ISO C\s0 for example), but it also
5585assumes that the same (machine) code can be used to call any watcher
5586callback: The watcher callbacks have different type signatures, but libev
5587calls them using an \f(CW\*(C`ev_watcher *\*(C'\fR internally.
5588.IP "null pointers and integer zero are represented by 0 bytes" 4
5589.IX Item "null pointers and integer zero are represented by 0 bytes"
5590Libev uses \f(CW\*(C`memset\*(C'\fR to initialise structs and arrays to \f(CW0\fR bytes, and
5591relies on this setting pointers and integers to null.
5592.IP "pointer accesses must be thread-atomic" 4
5593.IX Item "pointer accesses must be thread-atomic"
5594Accessing a pointer value must be atomic, it must both be readable and
5595writable in one piece \- this is the case on all current architectures.
5596.ie n .IP """sig_atomic_t volatile"" must be thread-atomic as well" 4
5597.el .IP "\f(CWsig_atomic_t volatile\fR must be thread-atomic as well" 4
5598.IX Item "sig_atomic_t volatile must be thread-atomic as well"
5599The type \f(CW\*(C`sig_atomic_t volatile\*(C'\fR (or whatever is defined as
5600\&\f(CW\*(C`EV_ATOMIC_T\*(C'\fR) must be atomic with respect to accesses from different
5601threads. This is not part of the specification for \f(CW\*(C`sig_atomic_t\*(C'\fR, but is
5602believed to be sufficiently portable.
5603.ie n .IP """sigprocmask"" must work in a threaded environment" 4
5604.el .IP "\f(CWsigprocmask\fR must work in a threaded environment" 4
5605.IX Item "sigprocmask must work in a threaded environment"
5606Libev uses \f(CW\*(C`sigprocmask\*(C'\fR to temporarily block signals. This is not
5607allowed in a threaded program (\f(CW\*(C`pthread_sigmask\*(C'\fR has to be used). Typical
5608pthread implementations will either allow \f(CW\*(C`sigprocmask\*(C'\fR in the \*(L"main
5609thread\*(R" or will block signals process-wide, both behaviours would
5610be compatible with libev. Interaction between \f(CW\*(C`sigprocmask\*(C'\fR and
5611\&\f(CW\*(C`pthread_sigmask\*(C'\fR could complicate things, however.
5612.Sp
5613The most portable way to handle signals is to block signals in all threads
5614except the initial one, and run the signal handling loop in the initial
5615thread as well.
5616.ie n .IP """long"" must be large enough for common memory allocation sizes" 4
5617.el .IP "\f(CWlong\fR must be large enough for common memory allocation sizes" 4
5618.IX Item "long must be large enough for common memory allocation sizes"
5619To improve portability and simplify its \s-1API,\s0 libev uses \f(CW\*(C`long\*(C'\fR internally
5620instead of \f(CW\*(C`size_t\*(C'\fR when allocating its data structures. On non-POSIX
5621systems (Microsoft...) this might be unexpectedly low, but is still at
5622least 31 bits everywhere, which is enough for hundreds of millions of
5623watchers.
5624.ie n .IP """double"" must hold a time value in seconds with enough accuracy" 4
5625.el .IP "\f(CWdouble\fR must hold a time value in seconds with enough accuracy" 4
5626.IX Item "double must hold a time value in seconds with enough accuracy"
5627The type \f(CW\*(C`double\*(C'\fR is used to represent timestamps. It is required to
5628have at least 51 bits of mantissa (and 9 bits of exponent), which is
5629good enough for at least into the year 4000 with millisecond accuracy
5630(the design goal for libev). This requirement is overfulfilled by
5631implementations using \s-1IEEE 754,\s0 which is basically all existing ones.
5632.Sp
5633With \s-1IEEE 754\s0 doubles, you get microsecond accuracy until at least the
5634year 2255 (and millisecond accuracy till the year 287396 \- by then, libev
5635is either obsolete or somebody patched it to use \f(CW\*(C`long double\*(C'\fR or
5636something like that, just kidding).
5637.PP
5638If you know of other additional requirements drop me a note.
5639.SH "ALGORITHMIC COMPLEXITIES"
5640.IX Header "ALGORITHMIC COMPLEXITIES"
5641In this section the complexities of (many of) the algorithms used inside
5642libev will be documented. For complexity discussions about backends see
5643the documentation for \f(CW\*(C`ev_default_init\*(C'\fR.
5644.PP
5645All of the following are about amortised time: If an array needs to be
5646extended, libev needs to realloc and move the whole array, but this
5647happens asymptotically rarer with higher number of elements, so O(1) might
5648mean that libev does a lengthy realloc operation in rare cases, but on
5649average it is much faster and asymptotically approaches constant time.
5650.IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4
5651.IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)"
5652This means that, when you have a watcher that triggers in one hour and
5653there are 100 watchers that would trigger before that, then inserting will
5654have to skip roughly seven (\f(CW\*(C`ld 100\*(C'\fR) of these watchers.
5655.IP "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 4
5656.IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)"
5657That means that changing a timer costs less than removing/adding them,
5658as only the relative motion in the event queue has to be paid for.
5659.IP "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)" 4
5660.IX Item "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)"
5661These just add the watcher into an array or at the head of a list.
5662.IP "Stopping check/prepare/idle/fork/async watchers: O(1)" 4
5663.IX Item "Stopping check/prepare/idle/fork/async watchers: O(1)"
5664.PD 0
5665.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4
5666.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))"
5667.PD
5668These watchers are stored in lists, so they need to be walked to find the
5669correct watcher to remove. The lists are usually short (you don't usually
5670have many watchers waiting for the same fd or signal: one is typical, two
5671is rare).
5672.IP "Finding the next timer in each loop iteration: O(1)" 4
5673.IX Item "Finding the next timer in each loop iteration: O(1)"
5674By virtue of using a binary or 4\-heap, the next timer is always found at a
5675fixed position in the storage array.
5676.IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4
5677.IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)"
5678A change means an I/O watcher gets started or stopped, which requires
5679libev to recalculate its status (and possibly tell the kernel, depending
5680on backend and whether \f(CW\*(C`ev_io_set\*(C'\fR was used).
5681.IP "Activating one watcher (putting it into the pending state): O(1)" 4
5682.IX Item "Activating one watcher (putting it into the pending state): O(1)"
5683.PD 0
5684.IP "Priority handling: O(number_of_priorities)" 4
5685.IX Item "Priority handling: O(number_of_priorities)"
5686.PD
5687Priorities are implemented by allocating some space for each
5688priority. When doing priority-based operations, libev usually has to
5689linearly search all the priorities, but starting/stopping and activating
5690watchers becomes O(1) with respect to priority handling.
5691.IP "Sending an ev_async: O(1)" 4
5692.IX Item "Sending an ev_async: O(1)"
5693.PD 0
5694.IP "Processing ev_async_send: O(number_of_async_watchers)" 4
5695.IX Item "Processing ev_async_send: O(number_of_async_watchers)"
5696.IP "Processing signals: O(max_signal_number)" 4
5697.IX Item "Processing signals: O(max_signal_number)"
5698.PD
5699Sending involves a system call \fIiff\fR there were no other \f(CW\*(C`ev_async_send\*(C'\fR
5700calls in the current loop iteration and the loop is currently
5701blocked. Checking for async and signal events involves iterating over all
5702running async watchers or all signal numbers.
5703.SH "PORTING FROM LIBEV 3.X TO 4.X"
5704.IX Header "PORTING FROM LIBEV 3.X TO 4.X"
5705The major version 4 introduced some incompatible changes to the \s-1API.\s0
5706.PP
5707At the moment, the \f(CW\*(C`ev.h\*(C'\fR header file provides compatibility definitions
5708for all changes, so most programs should still compile. The compatibility
5709layer might be removed in later versions of libev, so better update to the
5710new \s-1API\s0 early than late.
5711.ie n .IP """EV_COMPAT3"" backwards compatibility mechanism" 4
5712.el .IP "\f(CWEV_COMPAT3\fR backwards compatibility mechanism" 4
5713.IX Item "EV_COMPAT3 backwards compatibility mechanism"
5714The backward compatibility mechanism can be controlled by
5715\&\f(CW\*(C`EV_COMPAT3\*(C'\fR. See \*(L"\s-1PREPROCESSOR SYMBOLS/MACROS\*(R"\s0 in the \*(L"\s-1EMBEDDING\*(R"\s0
5716section.
5717.ie n .IP """ev_default_destroy"" and ""ev_default_fork"" have been removed" 4
5718.el .IP "\f(CWev_default_destroy\fR and \f(CWev_default_fork\fR have been removed" 4
5719.IX Item "ev_default_destroy and ev_default_fork have been removed"
5720These calls can be replaced easily by their \f(CW\*(C`ev_loop_xxx\*(C'\fR counterparts:
5721.Sp
5722.Vb 2
5723\& ev_loop_destroy (EV_DEFAULT_UC);
5724\& ev_loop_fork (EV_DEFAULT);
5725.Ve
5726.IP "function/symbol renames" 4
5727.IX Item "function/symbol renames"
5728A number of functions and symbols have been renamed:
5729.Sp
5730.Vb 3
5731\& ev_loop => ev_run
5732\& EVLOOP_NONBLOCK => EVRUN_NOWAIT
5733\& EVLOOP_ONESHOT => EVRUN_ONCE
5734\&
5735\& ev_unloop => ev_break
5736\& EVUNLOOP_CANCEL => EVBREAK_CANCEL
5737\& EVUNLOOP_ONE => EVBREAK_ONE
5738\& EVUNLOOP_ALL => EVBREAK_ALL
5739\&
5740\& EV_TIMEOUT => EV_TIMER
5741\&
5742\& ev_loop_count => ev_iteration
5743\& ev_loop_depth => ev_depth
5744\& ev_loop_verify => ev_verify
5745.Ve
5746.Sp
5747Most functions working on \f(CW\*(C`struct ev_loop\*(C'\fR objects don't have an
5748\&\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
5749associated constants have been renamed to not collide with the \f(CW\*(C`struct
5750ev_loop\*(C'\fR anymore and \f(CW\*(C`EV_TIMER\*(C'\fR now follows the same naming scheme
5751as all other watcher types. Note that \f(CW\*(C`ev_loop_fork\*(C'\fR is still called
5752\&\f(CW\*(C`ev_loop_fork\*(C'\fR because it would otherwise clash with the \f(CW\*(C`ev_fork\*(C'\fR
5753typedef.
5754.ie n .IP """EV_MINIMAL"" mechanism replaced by ""EV_FEATURES""" 4
5755.el .IP "\f(CWEV_MINIMAL\fR mechanism replaced by \f(CWEV_FEATURES\fR" 4
5756.IX Item "EV_MINIMAL mechanism replaced by EV_FEATURES"
5757The preprocessor symbol \f(CW\*(C`EV_MINIMAL\*(C'\fR has been replaced by a different
5758mechanism, \f(CW\*(C`EV_FEATURES\*(C'\fR. Programs using \f(CW\*(C`EV_MINIMAL\*(C'\fR usually compile
5759and work, but the library code will of course be larger.
5760.SH "GLOSSARY"
5761.IX Header "GLOSSARY"
5762.IP "active" 4
5763.IX Item "active"
5764A watcher is active as long as it has been started and not yet stopped.
5765See \*(L"\s-1WATCHER STATES\*(R"\s0 for details.
5766.IP "application" 4
5767.IX Item "application"
5768In this document, an application is whatever is using libev.
5769.IP "backend" 4
5770.IX Item "backend"
5771The part of the code dealing with the operating system interfaces.
5772.IP "callback" 4
5773.IX Item "callback"
5774The address of a function that is called when some event has been
5775detected. Callbacks are being passed the event loop, the watcher that
5776received the event, and the actual event bitset.
5777.IP "callback/watcher invocation" 4
5778.IX Item "callback/watcher invocation"
5779The act of calling the callback associated with a watcher.
5780.IP "event" 4
5781.IX Item "event"
5782A change of state of some external event, such as data now being available
5783for reading on a file descriptor, time having passed or simply not having
5784any other events happening anymore.
5785.Sp
5786In libev, events are represented as single bits (such as \f(CW\*(C`EV_READ\*(C'\fR or
5787\&\f(CW\*(C`EV_TIMER\*(C'\fR).
5788.IP "event library" 4
5789.IX Item "event library"
5790A software package implementing an event model and loop.
5791.IP "event loop" 4
5792.IX Item "event loop"
5793An entity that handles and processes external events and converts them
5794into callback invocations.
5795.IP "event model" 4
5796.IX Item "event model"
5797The model used to describe how an event loop handles and processes
5798watchers and events.
5799.IP "pending" 4
5800.IX Item "pending"
5801A watcher is pending as soon as the corresponding event has been
5802detected. See \*(L"\s-1WATCHER STATES\*(R"\s0 for details.
5803.IP "real time" 4
5804.IX Item "real time"
5805The physical time that is observed. It is apparently strictly monotonic :)
5806.IP "wall-clock time" 4
5807.IX Item "wall-clock time"
5808The time and date as shown on clocks. Unlike real time, it can actually
5809be wrong and jump forwards and backwards, e.g. when you adjust your
5810clock.
5811.IP "watcher" 4
5812.IX Item "watcher"
5813A data structure that describes interest in certain events. Watchers need
5814to be started (attached to an event loop) before they can receive events.
1267.SH "AUTHOR" 5815.SH "AUTHOR"
1268.IX Header "AUTHOR" 5816.IX Header "AUTHOR"
1269Marc Lehmann <libev@schmorp.de>. 5817Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5818Magnusson and Emanuele Giaquinta, and minor corrections by many others.

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