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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 "2023-05-15" "libev-4.33" "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 double type in C. 275too. It usually aliases to the \f(CW\*(C`double\*(C'\fR type in C. When you need to do
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.
179.SH "GLOBAL FUNCTIONS" 303.SH "GLOBAL FUNCTIONS"
180.IX Header "GLOBAL FUNCTIONS" 304.IX Header "GLOBAL FUNCTIONS"
181These functions can be called anytime, even before initialising the 305These functions can be called anytime, even before initialising the
182library in any way. 306library in any way.
183.IP "ev_tstamp ev_time ()" 4 307.IP "ev_tstamp ev_time ()" 4
184.IX Item "ev_tstamp ev_time ()" 308.IX Item "ev_tstamp ev_time ()"
185Returns 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
186\&\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
187you 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).
188.IP "int ev_version_major ()" 4 324.IP "int ev_version_major ()" 4
189.IX Item "int ev_version_major ()" 325.IX Item "int ev_version_major ()"
190.PD 0 326.PD 0
191.IP "int ev_version_minor ()" 4 327.IP "int ev_version_minor ()" 4
192.IX Item "int ev_version_minor ()" 328.IX Item "int ev_version_minor ()"
193.PD 329.PD
194You 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
195you 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
196\&\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
197symbols \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
198version of the library your program was compiled against. 334version of the library your program was compiled against.
199.Sp 335.Sp
336These version numbers refer to the \s-1ABI\s0 version of the library, not the
337release version.
338.Sp
200Usually, 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,
201as this indicates an incompatible change. Minor versions are usually 340as this indicates an incompatible change. Minor versions are usually
202compatible to older versions, so a larger minor version alone is usually 341compatible to older versions, so a larger minor version alone is usually
203not a problem. 342not a problem.
343.Sp
344Example: Make sure we haven't accidentally been linked against the wrong
345version (note, however, that this will not detect other \s-1ABI\s0 mismatches,
346such as \s-1LFS\s0 or reentrancy).
347.Sp
348.Vb 3
349\& assert (("libev version mismatch",
350\& ev_version_major () == EV_VERSION_MAJOR
351\& && ev_version_minor () >= EV_VERSION_MINOR));
352.Ve
353.IP "unsigned int ev_supported_backends ()" 4
354.IX Item "unsigned int ev_supported_backends ()"
355Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR
356value) compiled into this binary of libev (independent of their
357availability on the system you are running on). See \f(CW\*(C`ev_default_loop\*(C'\fR for
358a description of the set values.
359.Sp
360Example: make sure we have the epoll method, because yeah this is cool and
361a must have and can we have a torrent of it please!!!11
362.Sp
363.Vb 2
364\& assert (("sorry, no epoll, no sex",
365\& ev_supported_backends () & EVBACKEND_EPOLL));
366.Ve
367.IP "unsigned int ev_recommended_backends ()" 4
368.IX Item "unsigned int ev_recommended_backends ()"
369Return the set of all backends compiled into this binary of libev and
370also recommended for this platform, meaning it will work for most file
371descriptor types. This set is often smaller than the one returned by
372\&\f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on most BSDs
373and will not be auto-detected unless you explicitly request it (assuming
374you know what you are doing). This is the set of backends that libev will
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.
204.IP "ev_set_allocator (void *(*cb)(void *ptr, long size))" 4 385.IP "ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())" 4
205.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))" 386.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())"
206Sets the allocation function to use (the prototype is similar to the 387Sets the allocation function to use (the prototype is similar \- the
207realloc 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
208and free memory (no surprises here). If it returns zero when memory 389used to allocate and free memory (no surprises here). If it returns zero
209needs 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
210destructive 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.
211.Sp 396.Sp
212You could override this function in high-availability programs to, say, 397You could override this function in high-availability programs to, say,
213free 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,
214or 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.
400.Sp
401Example: The following is the \f(CW\*(C`realloc\*(C'\fR function that libev itself uses
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.
404.Sp
405.Vb 5
406\& static void *
407\& ev_realloc_emul (void *ptr, long size) EV_NOEXCEPT
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\&
430\& for (;;)
431\& {
432\& void *newptr = realloc (ptr, size);
433\&
434\& if (newptr)
435\& return newptr;
436\&
437\& sleep (60);
438\& }
439\& }
440\&
441\& ...
442\& ev_set_allocator (persistent_realloc);
443.Ve
215.IP "ev_set_syserr_cb (void (*cb)(const char *msg));" 4 444.IP "ev_set_syserr_cb (void (*cb)(const char *msg) throw ())" 4
216.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg));" 445.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg) throw ())"
217Set the callback function to call on a retryable syscall error (such 446Set the callback function to call on a retryable system call error (such
218as failed select, poll, epoll_wait). The message is a printable string 447as failed select, poll, epoll_wait). The message is a printable string
219indicating the system call or subsystem causing the problem. If this 448indicating the system call or subsystem causing the problem. If this
220callback 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
221matter what, when it returns. That is, libev will generally retry the 450matter what, when it returns. That is, libev will generally retry the
222requested 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
223(such as abort). 452(such as abort).
453.Sp
454Example: This is basically the same thing that libev does internally, too.
455.Sp
456.Vb 6
457\& static void
458\& fatal_error (const char *msg)
459\& {
460\& perror (msg);
461\& abort ();
462\& }
463\&
464\& ...
465\& ev_set_syserr_cb (fatal_error);
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.
224.SH "FUNCTIONS CONTROLLING THE EVENT LOOP" 479.SH "FUNCTIONS CONTROLLING EVENT LOOPS"
225.IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP" 480.IX Header "FUNCTIONS CONTROLLING EVENT LOOPS"
226An 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
227types 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
228events, and dynamically created loops which do not. 483libev 3 had an \f(CW\*(C`ev_loop\*(C'\fR function colliding with the struct name).
229.PP 484.PP
230If 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
231in your main thread (or in a separate thread) and for each thread you 486supports child process events, and dynamically created event loops which
232create, you also create another event loop. Libev itself does no locking 487do not.
233whatsoever, so if you mix calls to the same event loop in different
234threads, make sure you lock (this is usually a bad idea, though, even if
235done correctly, because it's hideous and inefficient).
236.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4 488.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
237.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)" 489.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
238This 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
239yet 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
240false. 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
241flags). 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".
242.Sp 500.Sp
243If 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
244function. 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.
245.Sp 536.Sp
246The flags argument can be used to specify special behaviour or specific 537The flags argument can be used to specify special behaviour or specific
247backends to use, and is usually specified as 0 (or \s-1EVFLAG_AUTO\s0). 538backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).
248.Sp 539.Sp
249It supports the following flags: 540The following flags are supported:
250.RS 4 541.RS 4
251.ie n .IP """EVFLAG_AUTO""" 4 542.ie n .IP """EVFLAG_AUTO""" 4
252.el .IP "\f(CWEVFLAG_AUTO\fR" 4 543.el .IP "\f(CWEVFLAG_AUTO\fR" 4
253.IX Item "EVFLAG_AUTO" 544.IX Item "EVFLAG_AUTO"
254The 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
255thing, believe me). 546thing, believe me).
256.ie n .IP """EVFLAG_NOENV""" 4 547.ie n .IP """EVFLAG_NOENV""" 4
257.el .IP "\f(CWEVFLAG_NOENV\fR" 4 548.el .IP "\f(CWEVFLAG_NOENV\fR" 4
258.IX Item "EVFLAG_NOENV" 549.IX Item "EVFLAG_NOENV"
259If 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
260or setgid) then libev will \fInot\fR look at the environment variable 551or setgid) then libev will \fInot\fR look at the environment variable
261\&\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
262override 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
263useful to try out specific backends to test their performance, or to work 554useful to try out specific backends to test their performance, to work
264around 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.
265.ie n .IP """EVMETHOD_SELECT"" (value 1, portable select backend)" 4 622.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
266.el .IP "\f(CWEVMETHOD_SELECT\fR (value 1, portable select backend)" 4 623.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
267.IX Item "EVMETHOD_SELECT (value 1, portable select backend)" 624.IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
268This 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
269libev 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,
270but 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
271using 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
272the 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).
273.ie n .IP """EVMETHOD_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
274.el .IP "\f(CWEVMETHOD_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
275.IX Item "EVMETHOD_POLL (value 2, poll backend, available everywhere except on windows)" 643.IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)"
276And 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
277select, but handles sparse fds better and has no artificial limit on the 645than select, but handles sparse fds better and has no artificial
278number 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
279lot 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.
280.ie n .IP """EVMETHOD_EPOLL"" (value 4, Linux)" 4 653.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
281.el .IP "\f(CWEVMETHOD_EPOLL\fR (value 4, Linux)" 4 654.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
282.IX Item "EVMETHOD_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
283For 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
284but it scales phenomenally better. While poll and select usually scale like 660it scales phenomenally better. While poll and select usually scale like
285O(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
286either O(1) or O(active_fds). 662fd), epoll scales either O(1) or O(active_fds).
287.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
288While 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
289result in some caching, there is still a syscall per such incident 693will result in some caching, there is still a system call per such
290(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
291best 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
292well if you register events for both fds. 696file descriptors might not work very well if you register events for both
697file descriptors.
698.Sp
699Best performance from this backend is achieved by not unregistering all
700watchers for a file descriptor until it has been closed, if possible,
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.
293.ie n .IP """EVMETHOD_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4 759.ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4
294.el .IP "\f(CWEVMETHOD_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
295.IX Item "EVMETHOD_KQUEUE (value 8, most BSD clones)" 761.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
296Kqueue deserves special mention, as at the time of this writing, it 762Kqueue deserves special mention, as at the time this backend was
297was 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
298anything but sockets and pipes, except on Darwin, where of course its 764work reliably with anything but sockets and pipes, except on Darwin,
299completely useless). For this reason its not being \*(L"autodetected\*(R" unless 765where of course it's completely useless). Unlike epoll, however, whose
300you explicitly specify the flags (i.e. you don't use \s-1EVFLAG_AUTO\s0). 766brokenness is by design, these kqueue bugs can be (and mostly have been)
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.
301.Sp 775.Sp
302It 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
303kernel is more efficient (which says nothing about its actual speed, of 777kernel is more efficient (which says nothing about its actual speed, of
304course). While starting and stopping an I/O watcher does not cause an 778course). While stopping, setting and starting an I/O watcher does never
305extra 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
306incident, 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.
307.ie n .IP """EVMETHOD_DEVPOLL"" (value 16, Solaris 8)" 4 796.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
308.el .IP "\f(CWEVMETHOD_DEVPOLL\fR (value 16, Solaris 8)" 4 797.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
309.IX Item "EVMETHOD_DEVPOLL (value 16, Solaris 8)" 798.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
310This 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.
311.ie n .IP """EVMETHOD_PORT"" (value 32, Solaris 10)" 4 803.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
312.el .IP "\f(CWEVMETHOD_PORT\fR (value 32, Solaris 10)" 4 804.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
313.IX Item "EVMETHOD_PORT (value 32, Solaris 10)" 805.IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
314This uses the Solaris 10 port mechanism. As with everything on Solaris, 806This uses the Solaris 10 event port mechanism. As with everything on
315it's really slow, but it still scales very well (O(active_fds)). 807Solaris, it's really slow, but it still scales very well (O(active_fds)).
808.Sp
809While this backend scales well, it requires one system call per active
810file descriptor per loop iteration. For small and medium numbers of file
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.
316.ie n .IP """EVMETHOD_ALL""" 4 831.ie n .IP """EVBACKEND_ALL""" 4
317.el .IP "\f(CWEVMETHOD_ALL\fR" 4 832.el .IP "\f(CWEVBACKEND_ALL\fR" 4
318.IX Item "EVMETHOD_ALL" 833.IX Item "EVBACKEND_ALL"
319Try all backends (even potentially broken ones that wouldn't be tried 834Try all backends (even potentially broken ones that wouldn't be tried
320with \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
321\&\f(CW\*(C`EVMETHOD_ALL & ~EVMETHOD_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).
322.RE 847.RE
323.RS 4 848.RS 4
324.Sp 849.Sp
325If 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,
326backends 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
327specified, most compiled-in backend will be tried, usually in reverse 852here). If none are specified, all backends in \f(CW\*(C`ev_recommended_backends
328order of their flag values :) 853()\*(C'\fR will be tried.
854.Sp
855Example: Try to create a event loop that uses epoll and nothing else.
856.Sp
857.Vb 3
858\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
859\& if (!epoller)
860\& fatal ("no epoll found here, maybe it hides under your chair");
861.Ve
862.Sp
863Example: Use whatever libev has to offer, but make sure that kqueue is
864used if available.
865.Sp
866.Vb 1
867\& struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
868.Ve
869.Sp
870Example: Similarly, on linux, you mgiht want to take advantage of the
871linux aio backend if possible, but fall back to something else if that
872isn't available.
873.Sp
874.Vb 1
875\& struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_LINUXAIO);
876.Ve
329.RE 877.RE
330.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
331.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
332Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is
333always distinct from the default loop. Unlike the default loop, it cannot
334handle signal and child watchers, and attempts to do so will be greeted by
335undefined behaviour (or a failed assertion if assertions are enabled).
336.IP "ev_default_destroy ()" 4
337.IX Item "ev_default_destroy ()"
338Destroys the default loop again (frees all memory and kernel state
339etc.). This stops all registered event watchers (by not touching them in
340any way whatsoever, although you cannot rely on this :).
341.IP "ev_loop_destroy (loop)" 4 878.IP "ev_loop_destroy (loop)" 4
342.IX Item "ev_loop_destroy (loop)" 879.IX Item "ev_loop_destroy (loop)"
343Like \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
344earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR. 881etc.). None of the active event watchers will be stopped in the normal
345.IP "ev_default_fork ()" 4 882sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your
346.IX Item "ev_default_fork ()" 883responsibility to either stop all watchers cleanly yourself \fIbefore\fR
347This function reinitialises the kernel state for backends that have 884calling this function, or cope with the fact afterwards (which is usually
348one. 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
349after forking, in either the parent or child process (or both, but that 886for example).
350again makes little sense).
351.Sp 887.Sp
352You \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
353only 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
354fork+exec, you don't have to call it. 890as signal and child watchers) would need to be stopped manually.
355.Sp 891.Sp
356The function itself is quite fast and it's usually not a problem to call 892This function is normally used on loop objects allocated by
357it 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
358quite 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.
359.Sp 895.Sp
360.Vb 1 896Note that it is not advisable to call this function on the default loop
361\& pthread_atfork (0, 0, ev_default_fork); 897except in the rare occasion where you really need to free its resources.
362.Ve 898If you need dynamically allocated loops it is better to use \f(CW\*(C`ev_loop_new\*(C'\fR
899and \f(CW\*(C`ev_loop_destroy\*(C'\fR.
363.IP "ev_loop_fork (loop)" 4 900.IP "ev_loop_fork (loop)" 4
364.IX Item "ev_loop_fork (loop)" 901.IX Item "ev_loop_fork (loop)"
365Like \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
366\&\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
367after 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.
368.IP "unsigned int ev_method (loop)" 4 954.IP "unsigned int ev_depth (loop)" 4
369.IX Item "unsigned int ev_method (loop)" 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.
967.IP "unsigned int ev_backend (loop)" 4
968.IX Item "unsigned int ev_backend (loop)"
370Returns one of the \f(CW\*(C`EVMETHOD_*\*(C'\fR flags indicating the event backend in 969Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
371use. 970use.
372.IP "ev_tstamp ev_now (loop)" 4 971.IP "ev_tstamp ev_now (loop)" 4
373.IX Item "ev_tstamp ev_now (loop)" 972.IX Item "ev_tstamp ev_now (loop)"
374Returns 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
375got events and started processing them. This timestamp does not change 974received events and started processing them. This timestamp does not
376as long as callbacks are being processed, and this is also the base time 975change as long as callbacks are being processed, and this is also the base
377used for relative timers. You can treat it as the timestamp of the event 976time used for relative timers. You can treat it as the timestamp of the
378occuring (or more correctly, the mainloop 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).
379.IP "ev_loop (loop, int flags)" 4 1016.IP "bool ev_run (loop, int flags)" 4
380.IX Item "ev_loop (loop, int flags)" 1017.IX Item "bool ev_run (loop, int flags)"
381Finally, this is it, the event handler. This function usually is called 1018Finally, this is it, the event handler. This function usually is called
382after you initialised all your watchers and you want to start handling 1019after you have initialised all your watchers and you want to start
383events. 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.
384.Sp 1023.Sp
385If the flags argument is specified as 0, it will not return until either 1024If the flags argument is specified as \f(CW0\fR, it will keep handling events
386no 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.
387.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
1032Please note that an explicit \f(CW\*(C`ev_break\*(C'\fR is usually better than
1033relying on all watchers to be stopped when deciding when a program has
1034finished (especially in interactive programs), but having a program
1035that automatically loops as long as it has to and no longer by virtue
1036of relying on its watchers stopping correctly, that is truly a thing of
1037beauty.
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
388A 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
389those events and any outstanding ones, but will not block your process in 1045those events and any already outstanding ones, but will not wait and
390case 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.
391.Sp 1049.Sp
392A 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
393neccessary) and will handle those and any outstanding ones. It will block 1051necessary) and will handle those and any already outstanding ones. It
394your 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
1053be an event internal to libev itself, so there is no guarantee that a
1054user-registered callback will be called), and will return after one
395one iteration of the loop. 1055iteration of the loop.
396.Sp 1056.Sp
397This flags value could be used to implement alternative looping 1057This is useful if you are waiting for some external event in conjunction
398constructs, but the \f(CW\*(C`prepare\*(C'\fR and \f(CW\*(C`check\*(C'\fR watchers provide a better and 1058with something not expressible using other libev watchers (i.e. "roll your
399more generic mechanism. 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
1060usually a better approach for this kind of thing.
400.Sp 1061.Sp
401Here are the gory details of what ev_loop 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):
402.Sp 1065.Sp
403.Vb 15 1066.Vb 10
404\& 1. If there are no active watchers (reference count is zero), return. 1067\& \- Increment loop depth.
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.
405\& 2. Queue and immediately call all prepare watchers. 1073\& \- Queue and call all prepare watchers.
1074\& \- If ev_break was called, goto FINISH.
406\& 3. 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.
407\& 4. Update the kernel state with all outstanding changes. 1077\& \- Update the kernel state with all outstanding changes.
408\& 5. Update the "event loop time". 1078\& \- Update the "event loop time" (ev_now ()).
409\& 6. 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.
410\& 7. Block the process, waiting for events. 1084\& \- Block the process, waiting for any events.
1085\& \- Queue all outstanding I/O (fd) events.
411\& 8. Update the "event loop time" and do time jump handling. 1086\& \- Update the "event loop time" (ev_now ()), and do time jump adjustments.
412\& 9. Queue all outstanding timers. 1087\& \- Queue all expired timers.
413\& 10. Queue all outstanding periodics. 1088\& \- Queue all expired periodics.
414\& 11. If no events are pending now, queue all idle watchers. 1089\& \- Queue all idle watchers with priority higher than that of pending events.
415\& 12. Queue all check watchers. 1090\& \- Queue all check watchers.
416\& 13. 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).
417\& 14. If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK 1092\& Signals, async and child watchers are implemented as I/O watchers, and
418\& was used, return, otherwise continue with step #1. 1093\& will be handled here by queueing them when their watcher gets executed.
1094\& \- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
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.
419.Ve 1101.Ve
1102.Sp
1103Example: Queue some jobs and then loop until no events are outstanding
1104anymore.
1105.Sp
1106.Vb 4
1107\& ... queue jobs here, make sure they register event watchers as long
1108\& ... as they still have work to do (even an idle watcher will do..)
1109\& ev_run (my_loop, 0);
1110\& ... jobs done or somebody called break. yeah!
1111.Ve
420.IP "ev_unloop (loop, how)" 4 1112.IP "ev_break (loop, how)" 4
421.IX Item "ev_unloop (loop, how)" 1113.IX Item "ev_break (loop, how)"
422Can 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
423has 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
424\&\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
425\&\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.
426.IP "ev_ref (loop)" 4 1123.IP "ev_ref (loop)" 4
427.IX Item "ev_ref (loop)" 1124.IX Item "ev_ref (loop)"
428.PD 0 1125.PD 0
429.IP "ev_unref (loop)" 4 1126.IP "ev_unref (loop)" 4
430.IX Item "ev_unref (loop)" 1127.IX Item "ev_unref (loop)"
431.PD 1128.PD
432Ref/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
433loop: Every watcher keeps one reference, and as long as the reference 1130loop: Every watcher keeps one reference, and as long as the reference
434count 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.
435a watcher you never unregister that should not keep \f(CW\*(C`ev_loop\*(C'\fR from 1132.Sp
436returning, \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
437example, 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
438visible 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
439no 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
440way to do this for generic recurring timers or from within third-party 1141excellent way to do this for generic recurring timers or from within
441libraries. 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).
1147.Sp
1148Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_run\*(C'\fR
1149running when nothing else is active.
1150.Sp
1151.Vb 4
1152\& ev_signal exitsig;
1153\& ev_signal_init (&exitsig, sig_cb, SIGINT);
1154\& ev_signal_start (loop, &exitsig);
1155\& ev_unref (loop);
1156.Ve
1157.Sp
1158Example: For some weird reason, unregister the above signal handler again.
1159.Sp
1160.Vb 2
1161\& ev_ref (loop);
1162\& ev_signal_stop (loop, &exitsig);
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.
442.SH "ANATOMY OF A WATCHER" 1302.SH "ANATOMY OF A WATCHER"
443.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
444A 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
445interest 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
446become 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:
447.PP 1312.PP
448.Vb 5 1313.Vb 5
449\& 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)
450\& { 1315\& {
451\& ev_io_stop (w); 1316\& ev_io_stop (w);
452\& ev_unloop (loop, EVUNLOOP_ALL); 1317\& ev_break (loop, EVBREAK_ALL);
453\& } 1318\& }
454.Ve 1319\&
455.PP
456.Vb 6
457\& struct ev_loop *loop = ev_default_loop (0); 1320\& struct ev_loop *loop = ev_default_loop (0);
1321\&
458\& struct ev_io stdin_watcher; 1322\& ev_io stdin_watcher;
1323\&
459\& ev_init (&stdin_watcher, my_cb); 1324\& ev_init (&stdin_watcher, my_cb);
460\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); 1325\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
461\& ev_io_start (loop, &stdin_watcher); 1326\& ev_io_start (loop, &stdin_watcher);
1327\&
462\& ev_loop (loop, 0); 1328\& ev_run (loop, 0);
463.Ve 1329.Ve
464.PP 1330.PP
465As 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
466watcher 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
467although this can sometimes be quite valid). 1333stack).
468.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
469Each 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
470(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
471callback 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
472watchers, each time the event loop detects that the file descriptor given 1341time the event loop detects that the file descriptor given is readable
473is readable and/or writable). 1342and/or writable).
474.PP 1343.PP
475Each 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
476with arguments specific to this watcher type. There is also a macro 1345macro to configure it, with arguments specific to the watcher type. There
477to 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.
478(watcher *, callback, ...)\*(C'\fR.
479.PP 1347.PP
480To 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
481with 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
482*)\*(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
483corresponding 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.
484.PP 1352.PP
485As 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
486must not touch the values stored in it. Most specifically you must never 1354must not touch the values stored in it except when explicitly documented
487reinitialise it or call its set method. 1355otherwise. Most specifically you must never reinitialise it or call its
488.PP 1356\&\f(CW\*(C`ev_TYPE_set\*(C'\fR macro.
489You can check whether an event is active by calling the \f(CW\*(C`ev_is_active
490(watcher *)\*(C'\fR macro. To see whether an event is outstanding (but the
491callback for it has not been called yet) you can use the \f(CW\*(C`ev_is_pending
492(watcher *)\*(C'\fR macro.
493.PP 1357.PP
494Each and every callback receives the event loop pointer as first, the 1358Each and every callback receives the event loop pointer as first, the
495registered watcher structure as second, and a bitset of received events as 1359registered watcher structure as second, and a bitset of received events as
496third argument. 1360third argument.
497.PP 1361.PP
… …
506.el .IP "\f(CWEV_WRITE\fR" 4 1370.el .IP "\f(CWEV_WRITE\fR" 4
507.IX Item "EV_WRITE" 1371.IX Item "EV_WRITE"
508.PD 1372.PD
509The 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
510writable. 1374writable.
511.ie n .IP """EV_TIMEOUT""" 4 1375.ie n .IP """EV_TIMER""" 4
512.el .IP "\f(CWEV_TIMEOUT\fR" 4 1376.el .IP "\f(CWEV_TIMER\fR" 4
513.IX Item "EV_TIMEOUT" 1377.IX Item "EV_TIMER"
514The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out. 1378The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
515.ie n .IP """EV_PERIODIC""" 4 1379.ie n .IP """EV_PERIODIC""" 4
516.el .IP "\f(CWEV_PERIODIC\fR" 4 1380.el .IP "\f(CWEV_PERIODIC\fR" 4
517.IX Item "EV_PERIODIC" 1381.IX Item "EV_PERIODIC"
518The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out. 1382The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
… …
522The 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.
523.ie n .IP """EV_CHILD""" 4 1387.ie n .IP """EV_CHILD""" 4
524.el .IP "\f(CWEV_CHILD\fR" 4 1388.el .IP "\f(CWEV_CHILD\fR" 4
525.IX Item "EV_CHILD" 1389.IX Item "EV_CHILD"
526The 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.
527.ie n .IP """EV_IDLE""" 4 1395.ie n .IP """EV_IDLE""" 4
528.el .IP "\f(CWEV_IDLE\fR" 4 1396.el .IP "\f(CWEV_IDLE\fR" 4
529.IX Item "EV_IDLE" 1397.IX Item "EV_IDLE"
530The \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.
531.ie n .IP """EV_PREPARE""" 4 1399.ie n .IP """EV_PREPARE""" 4
… …
534.PD 0 1402.PD 0
535.ie n .IP """EV_CHECK""" 4 1403.ie n .IP """EV_CHECK""" 4
536.el .IP "\f(CWEV_CHECK\fR" 4 1404.el .IP "\f(CWEV_CHECK\fR" 4
537.IX Item "EV_CHECK" 1405.IX Item "EV_CHECK"
538.PD 1406.PD
539All \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
540to 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)
541\&\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
542received events. Callbacks of both watcher types can start and stop as 1415Callbacks of both watcher types can start and stop as many watchers as
543many 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
544(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
545\&\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).
546.ie n .IP """EV_ERROR""" 4 1441.ie n .IP """EV_ERROR""" 4
547.el .IP "\f(CWEV_ERROR\fR" 4 1442.el .IP "\f(CWEV_ERROR\fR" 4
548.IX Item "EV_ERROR" 1443.IX Item "EV_ERROR"
549An unspecified error has occured, the watcher has been stopped. This might 1444An unspecified error has occurred, the watcher has been stopped. This might
550happen because the watcher could not be properly started because libev 1445happen because the watcher could not be properly started because libev
551ran 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
552problem. 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
553with 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.
554.Sp 1453.Sp
555Libev 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
556for 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
557your 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
558with 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
559programs, though, so beware. 1458programs, though, as the fd could already be closed and reused for another
560.Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0" 1459thing, so beware.
561.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER" 1460.SS "\s-1GENERIC WATCHER FUNCTIONS\s0"
562Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change 1461.IX Subsection "GENERIC WATCHER FUNCTIONS"
563and read at any time, libev will completely ignore it. This can be used 1462.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
564to associate arbitrary data with your watcher. If you need more data and 1463.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
565don't want to allocate memory and store a pointer to it in that data 1464.IX Item "ev_init (ev_TYPE *watcher, callback)"
566member, you can also \*(L"subclass\*(R" the watcher type and provide your own 1465This macro initialises the generic portion of a watcher. The contents
567data: 1466of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
568.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
569.Vb 7 1480.Vb 3
570\& 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 unless documented otherwise.
1538.Sp
1539Obviously, it is safe to call this on an active watcher, or actually any
1540watcher that is initialised.
1541.IP "bool ev_is_pending (ev_TYPE *watcher)" 4
1542.IX Item "bool ev_is_pending (ev_TYPE *watcher)"
1543Returns a true value iff the watcher is pending, (i.e. it has outstanding
1544events but its callback has not yet been invoked). As long as a watcher
1545is pending (but not active) you must not call an init function on it (but
1546\&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe), you must not change its priority, and you must
1547make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR
1548it).
1549.Sp
1550It is safe to call this on any watcher in any state as long as it is
1551initialised.
1552.IP "callback ev_cb (ev_TYPE *watcher)" 4
1553.IX Item "callback ev_cb (ev_TYPE *watcher)"
1554Returns the callback currently set on the watcher.
1555.IP "ev_set_cb (ev_TYPE *watcher, callback)" 4
1556.IX Item "ev_set_cb (ev_TYPE *watcher, callback)"
1557Change the callback. You can change the callback at virtually any time
1558(modulo threads).
1559.IP "ev_set_priority (ev_TYPE *watcher, int priority)" 4
1560.IX Item "ev_set_priority (ev_TYPE *watcher, int priority)"
1561.PD 0
1562.IP "int ev_priority (ev_TYPE *watcher)" 4
1563.IX Item "int ev_priority (ev_TYPE *watcher)"
1564.PD
1565Set and query the priority of the watcher. The priority is a small
1566integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR
1567(default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked
1568before watchers with lower priority, but priority will not keep watchers
1569from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
1570.Sp
1571If you need to suppress invocation when higher priority events are pending
1572you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
1573.Sp
1574You \fImust not\fR change the priority of a watcher as long as it is active
1575or pending. Reading the priority with \f(CW\*(C`ev_priority\*(C'\fR is fine in any state.
1576.Sp
1577Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
1578fine, as long as you do not mind that the priority value you query might
1579or might not have been clamped to the valid range.
1580.Sp
1581The default priority used by watchers when no priority has been set is
1582always \f(CW0\fR, which is supposed to not be too high and not be too low :).
1583.Sp
1584See \*(L"\s-1WATCHER PRIORITY MODELS\*(R"\s0, below, for a more thorough treatment of
1585priorities.
1586.IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
1587.IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
1588Invoke the \f(CW\*(C`watcher\*(C'\fR with the given \f(CW\*(C`loop\*(C'\fR and \f(CW\*(C`revents\*(C'\fR. Neither
1589\&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback
1590can deal with that fact, as both are simply passed through to the
1591callback.
1592.IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
1593.IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
1594If the watcher is pending, this function clears its pending status and
1595returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the
1596watcher isn't pending it does nothing and returns \f(CW0\fR.
1597.Sp
1598Sometimes it can be useful to \*(L"poll\*(R" a watcher instead of waiting for its
1599callback to be invoked, which can be accomplished with this function.
1600.IP "ev_feed_event (loop, ev_TYPE *watcher, int revents)" 4
1601.IX Item "ev_feed_event (loop, ev_TYPE *watcher, int revents)"
1602Feeds the given event set into the event loop, as if the specified event
1603had happened for the specified watcher (which must be a pointer to an
1604initialised but not necessarily started event watcher, though it can be
1605active). Obviously you must not free the watcher as long as it has pending
1606events.
1607.Sp
1608Stopping the watcher, letting libev invoke it, or calling
1609\&\f(CW\*(C`ev_clear_pending\*(C'\fR will clear the pending event, even if the watcher was
1610not started in the first place.
1611.Sp
1612See also \f(CW\*(C`ev_feed_fd_event\*(C'\fR and \f(CW\*(C`ev_feed_signal_event\*(C'\fR for related
1613functions that do not need a watcher.
1614.PP
1615See also the \*(L"\s-1ASSOCIATING CUSTOM DATA WITH A WATCHER\*(R"\s0 and \*(L"\s-1BUILDING YOUR
1616OWN COMPOSITE WATCHERS\*(R"\s0 idioms.
1617.SS "\s-1WATCHER STATES\s0"
1618.IX Subsection "WATCHER STATES"
1619There are various watcher states mentioned throughout this manual \-
1620active, pending and so on. In this section these states and the rules to
1621transition between them will be described in more detail \- and while these
1622rules might look complicated, they usually do \*(L"the right thing\*(R".
1623.IP "initialised" 4
1624.IX Item "initialised"
1625Before a watcher can be registered with the event loop it has to be
1626initialised. This can be done with a call to \f(CW\*(C`ev_TYPE_init\*(C'\fR, or calls to
1627\&\f(CW\*(C`ev_init\*(C'\fR followed by the watcher-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR function.
1628.Sp
1629In this state it is simply some block of memory that is suitable for
1630use in an event loop. It can be moved around, freed, reused etc. at
1631will \- as long as you either keep the memory contents intact, or call
1632\&\f(CW\*(C`ev_TYPE_init\*(C'\fR again.
1633.IP "started/running/active" 4
1634.IX Item "started/running/active"
1635Once a watcher has been started with a call to \f(CW\*(C`ev_TYPE_start\*(C'\fR it becomes
1636property of the event loop, and is actively waiting for events. While in
1637this state it cannot be accessed (except in a few documented ways, such as
1638stoping it), moved, freed or anything else \- the only legal thing is to
1639keep a pointer to it, and call libev functions on it that are documented
1640to work on active watchers.
1641.Sp
1642As a rule of thumb, before accessing a member or calling any function on
1643a watcher, it should be stopped (or freshly initialised). If that is not
1644convenient, you can check the documentation for that function or member to
1645see if it is safe to use on an active watcher.
1646.IP "pending" 4
1647.IX Item "pending"
1648If a watcher is active and libev determines that an event it is interested
1649in has occurred (such as a timer expiring), it will become pending. It
1650will stay in this pending state until either it is explicitly stopped or
1651its callback is about to be invoked, so it is not normally pending inside
1652the watcher callback.
1653.Sp
1654Generally, the watcher might or might not be active while it is pending
1655(for example, an expired non-repeating timer can be pending but no longer
1656active). If it is pending but not active, it can be freely accessed (e.g.
1657by calling \f(CW\*(C`ev_TYPE_set\*(C'\fR), but it is still property of the event loop at
1658this time, so cannot be moved, freed or reused. And if it is active the
1659rules described in the previous item still apply.
1660.Sp
1661Explicitly stopping a watcher will also clear the pending state
1662unconditionally, so it is safe to stop a watcher and then free it.
1663.Sp
1664It is also possible to feed an event on a watcher that is not active (e.g.
1665via \f(CW\*(C`ev_feed_event\*(C'\fR), in which case it becomes pending without being
1666active.
1667.IP "stopped" 4
1668.IX Item "stopped"
1669A watcher can be stopped implicitly by libev (in which case it might still
1670be pending), or explicitly by calling its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. The
1671latter will clear any pending state the watcher might be in, regardless
1672of whether it was active or not, so stopping a watcher explicitly before
1673freeing it is often a good idea.
1674.Sp
1675While stopped (and not pending) the watcher is essentially in the
1676initialised state, that is, it can be reused, moved, modified in any way
1677you wish (but when you trash the memory block, you need to \f(CW\*(C`ev_TYPE_init\*(C'\fR
1678it again).
1679.SS "\s-1WATCHER PRIORITY MODELS\s0"
1680.IX Subsection "WATCHER PRIORITY MODELS"
1681Many event loops support \fIwatcher priorities\fR, which are usually small
1682integers that influence the ordering of event callback invocation
1683between watchers in some way, all else being equal.
1684.PP
1685In libev, watcher priorities can be set using \f(CW\*(C`ev_set_priority\*(C'\fR. See its
1686description for the more technical details such as the actual priority
1687range.
1688.PP
1689There are two common ways how these these priorities are being interpreted
1690by event loops:
1691.PP
1692In the more common lock-out model, higher priorities \*(L"lock out\*(R" invocation
1693of lower priority watchers, which means as long as higher priority
1694watchers receive events, lower priority watchers are not being invoked.
1695.PP
1696The less common only-for-ordering model uses priorities solely to order
1697callback invocation within a single event loop iteration: Higher priority
1698watchers are invoked before lower priority ones, but they all get invoked
1699before polling for new events.
1700.PP
1701Libev uses the second (only-for-ordering) model for all its watchers
1702except for idle watchers (which use the lock-out model).
1703.PP
1704The rationale behind this is that implementing the lock-out model for
1705watchers is not well supported by most kernel interfaces, and most event
1706libraries will just poll for the same events again and again as long as
1707their callbacks have not been executed, which is very inefficient in the
1708common case of one high-priority watcher locking out a mass of lower
1709priority ones.
1710.PP
1711Static (ordering) priorities are most useful when you have two or more
1712watchers handling the same resource: a typical usage example is having an
1713\&\f(CW\*(C`ev_io\*(C'\fR watcher to receive data, and an associated \f(CW\*(C`ev_timer\*(C'\fR to handle
1714timeouts. Under load, data might be received while the program handles
1715other jobs, but since timers normally get invoked first, the timeout
1716handler will be executed before checking for data. In that case, giving
1717the timer a lower priority than the I/O watcher ensures that I/O will be
1718handled first even under adverse conditions (which is usually, but not
1719always, what you want).
1720.PP
1721Since idle watchers use the \*(L"lock-out\*(R" model, meaning that idle watchers
1722will only be executed when no same or higher priority watchers have
1723received events, they can be used to implement the \*(L"lock-out\*(R" model when
1724required.
1725.PP
1726For example, to emulate how many other event libraries handle priorities,
1727you can associate an \f(CW\*(C`ev_idle\*(C'\fR watcher to each such watcher, and in
1728the normal watcher callback, you just start the idle watcher. The real
1729processing is done in the idle watcher callback. This causes libev to
1730continuously poll and process kernel event data for the watcher, but when
1731the lock-out case is known to be rare (which in turn is rare :), this is
1732workable.
1733.PP
1734Usually, however, the lock-out model implemented that way will perform
1735miserably under the type of load it was designed to handle. In that case,
1736it might be preferable to stop the real watcher before starting the
1737idle watcher, so the kernel will not have to process the event in case
1738the actual processing will be delayed for considerable time.
1739.PP
1740Here is an example of an I/O watcher that should run at a strictly lower
1741priority than the default, and which should only process data when no
1742other events are pending:
1743.PP
1744.Vb 2
1745\& ev_idle idle; // actual processing watcher
1746\& ev_io io; // actual event watcher
1747\&
1748\& static void
1749\& io_cb (EV_P_ ev_io *w, int revents)
571\& { 1750\& {
572\& struct ev_io io; 1751\& // stop the I/O watcher, we received the event, but
573\& int otherfd; 1752\& // are not yet ready to handle it.
574\& void *somedata; 1753\& ev_io_stop (EV_A_ w);
575\& struct whatever *mostinteresting; 1754\&
1755\& // start the idle watcher to handle the actual event.
1756\& // it will not be executed as long as other watchers
1757\& // with the default priority are receiving events.
1758\& ev_idle_start (EV_A_ &idle);
576\& } 1759\& }
577.Ve 1760\&
578.PP 1761\& static void
579And since your callback will be called with a pointer to the watcher, you 1762\& idle_cb (EV_P_ ev_idle *w, int revents)
580can cast it back to your own type:
581.PP
582.Vb 5
583\& static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
584\& { 1763\& {
585\& struct my_io *w = (struct my_io *)w_; 1764\& // actual processing
586\& ... 1765\& read (STDIN_FILENO, ...);
1766\&
1767\& // have to start the I/O watcher again, as
1768\& // we have handled the event
1769\& ev_io_start (EV_P_ &io);
587\& } 1770\& }
1771\&
1772\& // initialisation
1773\& ev_idle_init (&idle, idle_cb);
1774\& ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
1775\& ev_io_start (EV_DEFAULT_ &io);
588.Ve 1776.Ve
589.PP 1777.PP
590More interesting and less C\-conformant ways of catsing your callback type 1778In the \*(L"real\*(R" world, it might also be beneficial to start a timer, so that
591have been omitted.... 1779low-priority connections can not be locked out forever under load. This
1780enables your program to keep a lower latency for important connections
1781during short periods of high load, while not completely locking out less
1782important ones.
592.SH "WATCHER TYPES" 1783.SH "WATCHER TYPES"
593.IX Header "WATCHER TYPES" 1784.IX Header "WATCHER TYPES"
594This section describes each watcher in detail, but will not repeat 1785This section describes each watcher in detail, but will not repeat
595information given in the last section. 1786information given in the last section. Any initialisation/set macros,
1787functions and members specific to the watcher type are explained.
1788.PP
1789Most members are additionally marked with either \fI[read\-only]\fR, meaning
1790that, while the watcher is active, you can look at the member and expect
1791some sensible content, but you must not modify it (you can modify it while
1792the watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
1793means you can expect it to have some sensible content while the watcher is
1794active, but you can also modify it (within the same thread as the event
1795loop, i.e. without creating data races). Modifying it may not do something
1796sensible or take immediate effect (or do anything at all), but libev will
1797not crash or malfunction in any way.
1798.PP
1799In any case, the documentation for each member will explain what the
1800effects are, and if there are any additional access restrictions.
596.ie n .Sh """ev_io"" \- is this file descriptor readable or writable" 1801.ie n .SS """ev_io"" \- is this file descriptor readable or writable?"
597.el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable" 1802.el .SS "\f(CWev_io\fP \- is this file descriptor readable or writable?"
598.IX Subsection "ev_io - is this file descriptor readable or writable" 1803.IX Subsection "ev_io - is this file descriptor readable or writable?"
599I/O watchers check whether a file descriptor is readable or writable 1804I/O watchers check whether a file descriptor is readable or writable
600in each iteration of the event loop (This behaviour is called 1805in each iteration of the event loop, or, more precisely, when reading
601level-triggering because you keep receiving events as long as the 1806would not block the process and writing would at least be able to write
602condition persists. Remember you can stop the watcher if you don't want to 1807some data. This behaviour is called level-triggering because you keep
603act on the event and neither want to receive future events). 1808receiving events as long as the condition persists. Remember you can stop
1809the watcher if you don't want to act on the event and neither want to
1810receive future events.
604.PP 1811.PP
605In general you can register as many read and/or write event watchers per 1812In general you can register as many read and/or write event watchers per
606fd as you want (as long as you don't confuse yourself). Setting all file 1813fd as you want (as long as you don't confuse yourself). Setting all file
607descriptors to non-blocking mode is also usually a good idea (but not 1814descriptors to non-blocking mode is also usually a good idea (but not
608required if you know what you are doing). 1815required if you know what you are doing).
609.PP 1816.PP
610You have to be careful with dup'ed file descriptors, though. Some backends 1817Another thing you have to watch out for is that it is quite easy to
611(the linux epoll backend is a notable example) cannot handle dup'ed file 1818receive \*(L"spurious\*(R" readiness notifications, that is, your callback might
612descriptors correctly if you register interest in two or more fds pointing 1819be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block
613to the same underlying file/socket etc. description (that is, they share 1820because there is no data. It is very easy to get into this situation even
614the same underlying \*(L"file open\*(R"). 1821with a relatively standard program structure. Thus it is best to always
1822use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning \f(CW\*(C`EAGAIN\*(C'\fR is far
1823preferable to a program hanging until some data arrives.
615.PP 1824.PP
616If you must do this, then force the use of a known-to-be-good backend 1825If you cannot run the fd in non-blocking mode (for example you should
617(at the time of this writing, this includes only \s-1EVMETHOD_SELECT\s0 and 1826not play around with an Xlib connection), then you have to separately
618\&\s-1EVMETHOD_POLL\s0). 1827re-test whether a file descriptor is really ready with a known-to-be good
1828interface such as poll (fortunately in the case of Xlib, it already does
1829this on its own, so its quite safe to use). Some people additionally
1830use \f(CW\*(C`SIGALRM\*(C'\fR and an interval timer, just to be sure you won't block
1831indefinitely.
1832.PP
1833But really, best use non-blocking mode.
1834.PP
1835\fIThe special problem of disappearing file descriptors\fR
1836.IX Subsection "The special problem of disappearing file descriptors"
1837.PP
1838Some backends (e.g. kqueue, epoll, linuxaio) need to be told about closing
1839a file descriptor (either due to calling \f(CW\*(C`close\*(C'\fR explicitly or any other
1840means, such as \f(CW\*(C`dup2\*(C'\fR). The reason is that you register interest in some
1841file descriptor, but when it goes away, the operating system will silently
1842drop this interest. If another file descriptor with the same number then
1843is registered with libev, there is no efficient way to see that this is,
1844in fact, a different file descriptor.
1845.PP
1846To avoid having to explicitly tell libev about such cases, libev follows
1847the following policy: Each time \f(CW\*(C`ev_io_set\*(C'\fR is being called, libev
1848will assume that this is potentially a new file descriptor, otherwise
1849it is assumed that the file descriptor stays the same. That means that
1850you \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
1851descriptor even if the file descriptor number itself did not change.
1852.PP
1853This is how one would do it normally anyway, the important point is that
1854the libev application should not optimise around libev but should leave
1855optimisations to libev.
1856.PP
1857\fIThe special problem of dup'ed file descriptors\fR
1858.IX Subsection "The special problem of dup'ed file descriptors"
1859.PP
1860Some backends (e.g. epoll), cannot register events for file descriptors,
1861but only events for the underlying file descriptions. That means when you
1862have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register
1863events for them, only one file descriptor might actually receive events.
1864.PP
1865There is no workaround possible except not registering events
1866for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
1867\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1868.PP
1869\fIThe special problem of files\fR
1870.IX Subsection "The special problem of files"
1871.PP
1872Many people try to use \f(CW\*(C`select\*(C'\fR (or libev) on file descriptors
1873representing files, and expect it to become ready when their program
1874doesn't block on disk accesses (which can take a long time on their own).
1875.PP
1876However, this cannot ever work in the \*(L"expected\*(R" way \- you get a readiness
1877notification as soon as the kernel knows whether and how much data is
1878there, and in the case of open files, that's always the case, so you
1879always get a readiness notification instantly, and your read (or possibly
1880write) will still block on the disk I/O.
1881.PP
1882Another way to view it is that in the case of sockets, pipes, character
1883devices and so on, there is another party (the sender) that delivers data
1884on its own, but in the case of files, there is no such thing: the disk
1885will not send data on its own, simply because it doesn't know what you
1886wish to read \- you would first have to request some data.
1887.PP
1888Since files are typically not-so-well supported by advanced notification
1889mechanism, libev tries hard to emulate \s-1POSIX\s0 behaviour with respect
1890to files, even though you should not use it. The reason for this is
1891convenience: sometimes you want to watch \s-1STDIN\s0 or \s-1STDOUT,\s0 which is
1892usually a tty, often a pipe, but also sometimes files or special devices
1893(for example, \f(CW\*(C`epoll\*(C'\fR on Linux works with \fI/dev/random\fR but not with
1894\&\fI/dev/urandom\fR), and even though the file might better be served with
1895asynchronous I/O instead of with non-blocking I/O, it is still useful when
1896it \*(L"just works\*(R" instead of freezing.
1897.PP
1898So avoid file descriptors pointing to files when you know it (e.g. use
1899libeio), but use them when it is convenient, e.g. for \s-1STDIN/STDOUT,\s0 or
1900when you rarely read from a file instead of from a socket, and want to
1901reuse the same code path.
1902.PP
1903\fIThe special problem of fork\fR
1904.IX Subsection "The special problem of fork"
1905.PP
1906Some backends (epoll, kqueue, linuxaio, iouring) do not support \f(CW\*(C`fork ()\*(C'\fR
1907at all or exhibit useless behaviour. Libev fully supports fork, but needs
1908to be told about it in the child if you want to continue to use it in the
1909child.
1910.PP
1911To support fork in your child processes, you have to call \f(CW\*(C`ev_loop_fork
1912()\*(C'\fR after a fork in the child, enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to
1913\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1914.PP
1915\fIThe special problem of \s-1SIGPIPE\s0\fR
1916.IX Subsection "The special problem of SIGPIPE"
1917.PP
1918While not really specific to libev, it is easy to forget about \f(CW\*(C`SIGPIPE\*(C'\fR:
1919when writing to a pipe whose other end has been closed, your program gets
1920sent a \s-1SIGPIPE,\s0 which, by default, aborts your program. For most programs
1921this is sensible behaviour, for daemons, this is usually undesirable.
1922.PP
1923So when you encounter spurious, unexplained daemon exits, make sure you
1924ignore \s-1SIGPIPE\s0 (and maybe make sure you log the exit status of your daemon
1925somewhere, as that would have given you a big clue).
1926.PP
1927\fIThe special problem of \f(BIaccept()\fIing when you can't\fR
1928.IX Subsection "The special problem of accept()ing when you can't"
1929.PP
1930Many implementations of the \s-1POSIX\s0 \f(CW\*(C`accept\*(C'\fR function (for example,
1931found in post\-2004 Linux) have the peculiar behaviour of not removing a
1932connection from the pending queue in all error cases.
1933.PP
1934For example, larger servers often run out of file descriptors (because
1935of resource limits), causing \f(CW\*(C`accept\*(C'\fR to fail with \f(CW\*(C`ENFILE\*(C'\fR but not
1936rejecting the connection, leading to libev signalling readiness on
1937the next iteration again (the connection still exists after all), and
1938typically causing the program to loop at 100% \s-1CPU\s0 usage.
1939.PP
1940Unfortunately, the set of errors that cause this issue differs between
1941operating systems, there is usually little the app can do to remedy the
1942situation, and no known thread-safe method of removing the connection to
1943cope with overload is known (to me).
1944.PP
1945One of the easiest ways to handle this situation is to just ignore it
1946\&\- when the program encounters an overload, it will just loop until the
1947situation is over. While this is a form of busy waiting, no \s-1OS\s0 offers an
1948event-based way to handle this situation, so it's the best one can do.
1949.PP
1950A better way to handle the situation is to log any errors other than
1951\&\f(CW\*(C`EAGAIN\*(C'\fR and \f(CW\*(C`EWOULDBLOCK\*(C'\fR, making sure not to flood the log with such
1952messages, and continue as usual, which at least gives the user an idea of
1953what could be wrong (\*(L"raise the ulimit!\*(R"). For extra points one could stop
1954the \f(CW\*(C`ev_io\*(C'\fR watcher on the listening fd \*(L"for a while\*(R", which reduces \s-1CPU\s0
1955usage.
1956.PP
1957If your program is single-threaded, then you could also keep a dummy file
1958descriptor for overload situations (e.g. by opening \fI/dev/null\fR), and
1959when 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,
1960close that fd, and create a new dummy fd. This will gracefully refuse
1961clients under typical overload conditions.
1962.PP
1963The last way to handle it is to simply log the error and \f(CW\*(C`exit\*(C'\fR, as
1964is often done with \f(CW\*(C`malloc\*(C'\fR failures, but this results in an easy
1965opportunity for a DoS attack.
1966.PP
1967\fIWatcher-Specific Functions\fR
1968.IX Subsection "Watcher-Specific Functions"
619.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4 1969.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
620.IX Item "ev_io_init (ev_io *, callback, int fd, int events)" 1970.IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
621.PD 0 1971.PD 0
622.IP "ev_io_set (ev_io *, int fd, int events)" 4 1972.IP "ev_io_set (ev_io *, int fd, int events)" 4
623.IX Item "ev_io_set (ev_io *, int fd, int events)" 1973.IX Item "ev_io_set (ev_io *, int fd, int events)"
624.PD 1974.PD
625Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The fd is the file descriptor to rceeive 1975Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to
626events 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 | 1976receive 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
627EV_WRITE\*(C'\fR to receive the given events. 1977\&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR or \f(CW0\fR, to express the desire to receive the given
1978events.
1979.Sp
1980Note that setting the \f(CW\*(C`events\*(C'\fR to \f(CW0\fR and starting the watcher is
1981supported, but not specially optimized \- if your program sometimes happens
1982to generate this combination this is fine, but if it is easy to avoid
1983starting an io watcher watching for no events you should do so.
1984.IP "ev_io_modify (ev_io *, int events)" 4
1985.IX Item "ev_io_modify (ev_io *, int events)"
1986Similar to \f(CW\*(C`ev_io_set\*(C'\fR, but only changes the requested events. Using this
1987might be faster with some backends, as libev can assume that the \f(CW\*(C`fd\*(C'\fR
1988still refers to the same underlying file description, something it cannot
1989do when using \f(CW\*(C`ev_io_set\*(C'\fR.
1990.IP "int fd [no\-modify]" 4
1991.IX Item "int fd [no-modify]"
1992The file descriptor being watched. While it can be read at any time, you
1993must not modify this member even when the watcher is stopped \- always use
1994\&\f(CW\*(C`ev_io_set\*(C'\fR for that.
1995.IP "int events [no\-modify]" 4
1996.IX Item "int events [no-modify]"
1997The set of events the fd is being watched for, among other flags. Remember
1998that this is a bit set \- to test for \f(CW\*(C`EV_READ\*(C'\fR, use \f(CW\*(C`w\->events &
1999EV_READ\*(C'\fR, and similarly for \f(CW\*(C`EV_WRITE\*(C'\fR.
2000.Sp
2001As with \f(CW\*(C`fd\*(C'\fR, you must not modify this member even when the watcher is
2002stopped, always use \f(CW\*(C`ev_io_set\*(C'\fR or \f(CW\*(C`ev_io_modify\*(C'\fR for that.
2003.PP
2004\fIExamples\fR
2005.IX Subsection "Examples"
2006.PP
2007Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
2008readable, but only once. Since it is likely line-buffered, you could
2009attempt to read a whole line in the callback.
2010.PP
2011.Vb 6
2012\& static void
2013\& stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
2014\& {
2015\& ev_io_stop (loop, w);
2016\& .. read from stdin here (or from w\->fd) and handle any I/O errors
2017\& }
2018\&
2019\& ...
2020\& struct ev_loop *loop = ev_default_init (0);
2021\& ev_io stdin_readable;
2022\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
2023\& ev_io_start (loop, &stdin_readable);
2024\& ev_run (loop, 0);
2025.Ve
628.ie n .Sh """ev_timer"" \- relative and optionally recurring timeouts" 2026.ie n .SS """ev_timer"" \- relative and optionally repeating timeouts"
629.el .Sh "\f(CWev_timer\fP \- relative and optionally recurring timeouts" 2027.el .SS "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
630.IX Subsection "ev_timer - relative and optionally recurring timeouts" 2028.IX Subsection "ev_timer - relative and optionally repeating timeouts"
631Timer watchers are simple relative timers that generate an event after a 2029Timer watchers are simple relative timers that generate an event after a
632given time, and optionally repeating in regular intervals after that. 2030given time, and optionally repeating in regular intervals after that.
633.PP 2031.PP
634The timers are based on real time, that is, if you register an event that 2032The timers are based on real time, that is, if you register an event that
635times out after an hour and you reset your system clock to last years 2033times out after an hour and you reset your system clock to January last
636time, it will still time out after (roughly) and hour. \*(L"Roughly\*(R" because 2034year, it will still time out after (roughly) one hour. \*(L"Roughly\*(R" because
637detecting time jumps is hard, and some inaccuracies are unavoidable (the 2035detecting time jumps is hard, and some inaccuracies are unavoidable (the
638monotonic clock option helps a lot here). 2036monotonic clock option helps a lot here).
2037.PP
2038The callback is guaranteed to be invoked only \fIafter\fR its timeout has
2039passed (not \fIat\fR, so on systems with very low-resolution clocks this
2040might introduce a small delay, see \*(L"the special problem of being too
2041early\*(R", below). If multiple timers become ready during the same loop
2042iteration then the ones with earlier time-out values are invoked before
2043ones of the same priority with later time-out values (but this is no
2044longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
2045.PP
2046\fIBe smart about timeouts\fR
2047.IX Subsection "Be smart about timeouts"
2048.PP
2049Many real-world problems involve some kind of timeout, usually for error
2050recovery. A typical example is an \s-1HTTP\s0 request \- if the other side hangs,
2051you want to raise some error after a while.
2052.PP
2053What follows are some ways to handle this problem, from obvious and
2054inefficient to smart and efficient.
2055.PP
2056In the following, a 60 second activity timeout is assumed \- a timeout that
2057gets reset to 60 seconds each time there is activity (e.g. each time some
2058data or other life sign was received).
2059.IP "1. Use a timer and stop, reinitialise and start it on activity." 4
2060.IX Item "1. Use a timer and stop, reinitialise and start it on activity."
2061This is the most obvious, but not the most simple way: In the beginning,
2062start the watcher:
2063.Sp
2064.Vb 2
2065\& ev_timer_init (timer, callback, 60., 0.);
2066\& ev_timer_start (loop, timer);
2067.Ve
2068.Sp
2069Then, each time there is some activity, \f(CW\*(C`ev_timer_stop\*(C'\fR it, initialise it
2070and start it again:
2071.Sp
2072.Vb 3
2073\& ev_timer_stop (loop, timer);
2074\& ev_timer_set (timer, 60., 0.);
2075\& ev_timer_start (loop, timer);
2076.Ve
2077.Sp
2078This is relatively simple to implement, but means that each time there is
2079some activity, libev will first have to remove the timer from its internal
2080data structure and then add it again. Libev tries to be fast, but it's
2081still not a constant-time operation.
2082.ie n .IP "2. Use a timer and re-start it with ""ev_timer_again"" inactivity." 4
2083.el .IP "2. Use a timer and re-start it with \f(CWev_timer_again\fR inactivity." 4
2084.IX Item "2. Use a timer and re-start it with ev_timer_again inactivity."
2085This is the easiest way, and involves using \f(CW\*(C`ev_timer_again\*(C'\fR instead of
2086\&\f(CW\*(C`ev_timer_start\*(C'\fR.
2087.Sp
2088To implement this, configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value
2089of \f(CW60\fR and then call \f(CW\*(C`ev_timer_again\*(C'\fR at start and each time you
2090successfully read or write some data. If you go into an idle state where
2091you do not expect data to travel on the socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR
2092the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will automatically restart it if need be.
2093.Sp
2094That means you can ignore both the \f(CW\*(C`ev_timer_start\*(C'\fR function and the
2095\&\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
2096member and \f(CW\*(C`ev_timer_again\*(C'\fR.
2097.Sp
2098At start:
2099.Sp
2100.Vb 3
2101\& ev_init (timer, callback);
2102\& timer\->repeat = 60.;
2103\& ev_timer_again (loop, timer);
2104.Ve
2105.Sp
2106Each time there is some activity:
2107.Sp
2108.Vb 1
2109\& ev_timer_again (loop, timer);
2110.Ve
2111.Sp
2112It is even possible to change the time-out on the fly, regardless of
2113whether the watcher is active or not:
2114.Sp
2115.Vb 2
2116\& timer\->repeat = 30.;
2117\& ev_timer_again (loop, timer);
2118.Ve
2119.Sp
2120This is slightly more efficient then stopping/starting the timer each time
2121you want to modify its timeout value, as libev does not have to completely
2122remove and re-insert the timer from/into its internal data structure.
2123.Sp
2124It is, however, even simpler than the \*(L"obvious\*(R" way to do it.
2125.IP "3. Let the timer time out, but then re-arm it as required." 4
2126.IX Item "3. Let the timer time out, but then re-arm it as required."
2127This method is more tricky, but usually most efficient: Most timeouts are
2128relatively long compared to the intervals between other activity \- in
2129our example, within 60 seconds, there are usually many I/O events with
2130associated activity resets.
2131.Sp
2132In this case, it would be more efficient to leave the \f(CW\*(C`ev_timer\*(C'\fR alone,
2133but remember the time of last activity, and check for a real timeout only
2134within the callback:
2135.Sp
2136.Vb 3
2137\& ev_tstamp timeout = 60.;
2138\& ev_tstamp last_activity; // time of last activity
2139\& ev_timer timer;
2140\&
2141\& static void
2142\& callback (EV_P_ ev_timer *w, int revents)
2143\& {
2144\& // calculate when the timeout would happen
2145\& ev_tstamp after = last_activity \- ev_now (EV_A) + timeout;
2146\&
2147\& // if negative, it means we the timeout already occurred
2148\& if (after < 0.)
2149\& {
2150\& // timeout occurred, take action
2151\& }
2152\& else
2153\& {
2154\& // callback was invoked, but there was some recent
2155\& // activity. simply restart the timer to time out
2156\& // after "after" seconds, which is the earliest time
2157\& // the timeout can occur.
2158\& ev_timer_set (w, after, 0.);
2159\& ev_timer_start (EV_A_ w);
2160\& }
2161\& }
2162.Ve
2163.Sp
2164To summarise the callback: first calculate in how many seconds the
2165timeout will occur (by calculating the absolute time when it would occur,
2166\&\f(CW\*(C`last_activity + timeout\*(C'\fR, and subtracting the current time, \f(CW\*(C`ev_now
2167(EV_A)\*(C'\fR from that).
2168.Sp
2169If this value is negative, then we are already past the timeout, i.e. we
2170timed out, and need to do whatever is needed in this case.
2171.Sp
2172Otherwise, we now the earliest time at which the timeout would trigger,
2173and simply start the timer with this timeout value.
2174.Sp
2175In other words, each time the callback is invoked it will check whether
2176the timeout occurred. If not, it will simply reschedule itself to check
2177again at the earliest time it could time out. Rinse. Repeat.
2178.Sp
2179This scheme causes more callback invocations (about one every 60 seconds
2180minus half the average time between activity), but virtually no calls to
2181libev to change the timeout.
2182.Sp
2183To start the machinery, simply initialise the watcher and set
2184\&\f(CW\*(C`last_activity\*(C'\fR to the current time (meaning there was some activity just
2185now), then call the callback, which will \*(L"do the right thing\*(R" and start
2186the timer:
2187.Sp
2188.Vb 3
2189\& last_activity = ev_now (EV_A);
2190\& ev_init (&timer, callback);
2191\& callback (EV_A_ &timer, 0);
2192.Ve
2193.Sp
2194When there is some activity, simply store the current time in
2195\&\f(CW\*(C`last_activity\*(C'\fR, no libev calls at all:
2196.Sp
2197.Vb 2
2198\& if (activity detected)
2199\& last_activity = ev_now (EV_A);
2200.Ve
2201.Sp
2202When your timeout value changes, then the timeout can be changed by simply
2203providing a new value, stopping the timer and calling the callback, which
2204will again do the right thing (for example, time out immediately :).
2205.Sp
2206.Vb 3
2207\& timeout = new_value;
2208\& ev_timer_stop (EV_A_ &timer);
2209\& callback (EV_A_ &timer, 0);
2210.Ve
2211.Sp
2212This technique is slightly more complex, but in most cases where the
2213time-out is unlikely to be triggered, much more efficient.
2214.IP "4. Wee, just use a double-linked list for your timeouts." 4
2215.IX Item "4. Wee, just use a double-linked list for your timeouts."
2216If there is not one request, but many thousands (millions...), all
2217employing some kind of timeout with the same timeout value, then one can
2218do even better:
2219.Sp
2220When starting the timeout, calculate the timeout value and put the timeout
2221at the \fIend\fR of the list.
2222.Sp
2223Then use an \f(CW\*(C`ev_timer\*(C'\fR to fire when the timeout at the \fIbeginning\fR of
2224the list is expected to fire (for example, using the technique #3).
2225.Sp
2226When there is some activity, remove the timer from the list, recalculate
2227the timeout, append it to the end of the list again, and make sure to
2228update the \f(CW\*(C`ev_timer\*(C'\fR if it was taken from the beginning of the list.
2229.Sp
2230This way, one can manage an unlimited number of timeouts in O(1) time for
2231starting, stopping and updating the timers, at the expense of a major
2232complication, and having to use a constant timeout. The constant timeout
2233ensures that the list stays sorted.
2234.PP
2235So which method the best?
2236.PP
2237Method #2 is a simple no-brain-required solution that is adequate in most
2238situations. Method #3 requires a bit more thinking, but handles many cases
2239better, and isn't very complicated either. In most case, choosing either
2240one is fine, with #3 being better in typical situations.
2241.PP
2242Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
2243rather complicated, but extremely efficient, something that really pays
2244off after the first million or so of active timers, i.e. it's usually
2245overkill :)
2246.PP
2247\fIThe special problem of being too early\fR
2248.IX Subsection "The special problem of being too early"
2249.PP
2250If you ask a timer to call your callback after three seconds, then
2251you expect it to be invoked after three seconds \- but of course, this
2252cannot be guaranteed to infinite precision. Less obviously, it cannot be
2253guaranteed to any precision by libev \- imagine somebody suspending the
2254process with a \s-1STOP\s0 signal for a few hours for example.
2255.PP
2256So, libev tries to invoke your callback as soon as possible \fIafter\fR the
2257delay has occurred, but cannot guarantee this.
2258.PP
2259A less obvious failure mode is calling your callback too early: many event
2260loops compare timestamps with a \*(L"elapsed delay >= requested delay\*(R", but
2261this can cause your callback to be invoked much earlier than you would
2262expect.
2263.PP
2264To see why, imagine a system with a clock that only offers full second
2265resolution (think windows if you can't come up with a broken enough \s-1OS\s0
2266yourself). If you schedule a one-second timer at the time 500.9, then the
2267event loop will schedule your timeout to elapse at a system time of 500
2268(500.9 truncated to the resolution) + 1, or 501.
2269.PP
2270If an event library looks at the timeout 0.1s later, it will see \*(L"501 >=
2271501\*(R" and invoke the callback 0.1s after it was started, even though a
2272one-second delay was requested \- this is being \*(L"too early\*(R", despite best
2273intentions.
2274.PP
2275This is the reason why libev will never invoke the callback if the elapsed
2276delay equals the requested delay, but only when the elapsed delay is
2277larger than the requested delay. In the example above, libev would only invoke
2278the callback at system time 502, or 1.1s after the timer was started.
2279.PP
2280So, while libev cannot guarantee that your callback will be invoked
2281exactly when requested, it \fIcan\fR and \fIdoes\fR guarantee that the requested
2282delay has actually elapsed, or in other words, it always errs on the \*(L"too
2283late\*(R" side of things.
2284.PP
2285\fIThe special problem of time updates\fR
2286.IX Subsection "The special problem of time updates"
2287.PP
2288Establishing the current time is a costly operation (it usually takes
2289at least one system call): \s-1EV\s0 therefore updates its idea of the current
2290time only before and after \f(CW\*(C`ev_run\*(C'\fR collects new events, which causes a
2291growing difference between \f(CW\*(C`ev_now ()\*(C'\fR and \f(CW\*(C`ev_time ()\*(C'\fR when handling
2292lots of events in one iteration.
639.PP 2293.PP
640The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR 2294The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
641time. This is usually the right thing as this timestamp refers to the time 2295time. This is usually the right thing as this timestamp refers to the time
642of the event triggering whatever timeout you are modifying/starting. If 2296of the event triggering whatever timeout you are modifying/starting. If
643you suspect event processing to be delayed and you \fIneed\fR to base the timeout 2297you suspect event processing to be delayed and you \fIneed\fR to base the
644on the current time, use something like this to adjust for this: 2298timeout on the current time, use something like the following to adjust
2299for it:
645.PP 2300.PP
646.Vb 1 2301.Vb 1
647\& ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); 2302\& ev_timer_set (&timer, after + (ev_time () \- ev_now ()), 0.);
648.Ve 2303.Ve
649.PP 2304.PP
650The callback is guarenteed to be invoked only when its timeout has passed, 2305If the event loop is suspended for a long time, you can also force an
651but if multiple timers become ready during the same loop iteration then 2306update of the time returned by \f(CW\*(C`ev_now ()\*(C'\fR by calling \f(CW\*(C`ev_now_update
652order of execution is undefined. 2307()\*(C'\fR, although that will push the event time of all outstanding events
2308further into the future.
2309.PP
2310\fIThe special problem of unsynchronised clocks\fR
2311.IX Subsection "The special problem of unsynchronised clocks"
2312.PP
2313Modern systems have a variety of clocks \- libev itself uses the normal
2314\&\*(L"wall clock\*(R" clock and, if available, the monotonic clock (to avoid time
2315jumps).
2316.PP
2317Neither of these clocks is synchronised with each other or any other clock
2318on the system, so \f(CW\*(C`ev_time ()\*(C'\fR might return a considerably different time
2319than \f(CW\*(C`gettimeofday ()\*(C'\fR or \f(CW\*(C`time ()\*(C'\fR. On a GNU/Linux system, for example,
2320a call to \f(CW\*(C`gettimeofday\*(C'\fR might return a second count that is one higher
2321than a directly following call to \f(CW\*(C`time\*(C'\fR.
2322.PP
2323The moral of this is to only compare libev-related timestamps with
2324\&\f(CW\*(C`ev_time ()\*(C'\fR and \f(CW\*(C`ev_now ()\*(C'\fR, at least if you want better precision than
2325a second or so.
2326.PP
2327One more problem arises due to this lack of synchronisation: if libev uses
2328the system monotonic clock and you compare timestamps from \f(CW\*(C`ev_time\*(C'\fR
2329or \f(CW\*(C`ev_now\*(C'\fR from when you started your timer and when your callback is
2330invoked, you will find that sometimes the callback is a bit \*(L"early\*(R".
2331.PP
2332This is because \f(CW\*(C`ev_timer\*(C'\fRs work in real time, not wall clock time, so
2333libev makes sure your callback is not invoked before the delay happened,
2334\&\fImeasured according to the real time\fR, not the system clock.
2335.PP
2336If your timeouts are based on a physical timescale (e.g. \*(L"time out this
2337connection after 100 seconds\*(R") then this shouldn't bother you as it is
2338exactly the right behaviour.
2339.PP
2340If you want to compare wall clock/system timestamps to your timers, then
2341you need to use \f(CW\*(C`ev_periodic\*(C'\fRs, as these are based on the wall clock
2342time, where your comparisons will always generate correct results.
2343.PP
2344\fIThe special problems of suspended animation\fR
2345.IX Subsection "The special problems of suspended animation"
2346.PP
2347When you leave the server world it is quite customary to hit machines that
2348can suspend/hibernate \- what happens to the clocks during such a suspend?
2349.PP
2350Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
2351all processes, while the clocks (\f(CW\*(C`times\*(C'\fR, \f(CW\*(C`CLOCK_MONOTONIC\*(C'\fR) continue
2352to run until the system is suspended, but they will not advance while the
2353system is suspended. That means, on resume, it will be as if the program
2354was frozen for a few seconds, but the suspend time will not be counted
2355towards \f(CW\*(C`ev_timer\*(C'\fR when a monotonic clock source is used. The real time
2356clock advanced as expected, but if it is used as sole clocksource, then a
2357long suspend would be detected as a time jump by libev, and timers would
2358be adjusted accordingly.
2359.PP
2360I would not be surprised to see different behaviour in different between
2361operating systems, \s-1OS\s0 versions or even different hardware.
2362.PP
2363The other form of suspend (job control, or sending a \s-1SIGSTOP\s0) will see a
2364time jump in the monotonic clocks and the realtime clock. If the program
2365is suspended for a very long time, and monotonic clock sources are in use,
2366then you can expect \f(CW\*(C`ev_timer\*(C'\fRs to expire as the full suspension time
2367will be counted towards the timers. When no monotonic clock source is in
2368use, then libev will again assume a timejump and adjust accordingly.
2369.PP
2370It might be beneficial for this latter case to call \f(CW\*(C`ev_suspend\*(C'\fR
2371and \f(CW\*(C`ev_resume\*(C'\fR in code that handles \f(CW\*(C`SIGTSTP\*(C'\fR, to at least get
2372deterministic behaviour in this case (you can do nothing against
2373\&\f(CW\*(C`SIGSTOP\*(C'\fR).
2374.PP
2375\fIWatcher-Specific Functions and Data Members\fR
2376.IX Subsection "Watcher-Specific Functions and Data Members"
653.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4 2377.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
654.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 2378.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
655.PD 0 2379.PD 0
656.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4 2380.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
657.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 2381.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
658.PD 2382.PD
659Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR is 2383Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds (fractional and
660\&\f(CW0.\fR, then it will automatically be stopped. If it is positive, then the 2384negative values are supported). If \f(CW\*(C`repeat\*(C'\fR is \f(CW0.\fR, then it will
2385automatically be stopped once the timeout is reached. If it is positive,
661timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds 2386then the timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR
662later, again, and again, until stopped manually. 2387seconds later, again, and again, until stopped manually.
663.Sp 2388.Sp
664The timer itself will do a best-effort at avoiding drift, that is, if you 2389The timer itself will do a best-effort at avoiding drift, that is, if
665configure a timer to trigger every 10 seconds, then it will trigger at 2390you configure a timer to trigger every 10 seconds, then it will normally
666exactly 10 second intervals. If, however, your program cannot keep up with 2391trigger at exactly 10 second intervals. If, however, your program cannot
667the timer (because it takes longer than those 10 seconds to do stuff) the 2392keep up with the timer (because it takes longer than those 10 seconds to
668timer will not fire more than once per event loop iteration. 2393do stuff) the timer will not fire more than once per event loop iteration.
669.IP "ev_timer_again (loop)" 4 2394.IP "ev_timer_again (loop, ev_timer *)" 4
670.IX Item "ev_timer_again (loop)" 2395.IX Item "ev_timer_again (loop, ev_timer *)"
671This will act as if the timer timed out and restart it again if it is 2396This will act as if the timer timed out, and restarts it again if it is
672repeating. The exact semantics are: 2397repeating. It basically works like calling \f(CW\*(C`ev_timer_stop\*(C'\fR, updating the
2398timeout to the \f(CW\*(C`repeat\*(C'\fR value and calling \f(CW\*(C`ev_timer_start\*(C'\fR.
673.Sp 2399.Sp
674If the timer is started but nonrepeating, stop it. 2400The exact semantics are as in the following rules, all of which will be
2401applied to the watcher:
2402.RS 4
2403.IP "If the timer is pending, the pending status is always cleared." 4
2404.IX Item "If the timer is pending, the pending status is always cleared."
2405.PD 0
2406.IP "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)." 4
2407.IX Item "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)."
2408.ie n .IP "If the timer is repeating, make the ""repeat"" value the new timeout and start the timer, if necessary." 4
2409.el .IP "If the timer is repeating, make the \f(CWrepeat\fR value the new timeout and start the timer, if necessary." 4
2410.IX Item "If the timer is repeating, make the repeat value the new timeout and start the timer, if necessary."
2411.RE
2412.RS 4
2413.PD
675.Sp 2414.Sp
676If the timer is repeating, either start it if necessary (with the repeat 2415This sounds a bit complicated, see \*(L"Be smart about timeouts\*(R", above, for a
677value), or reset the running timer to the repeat value. 2416usage example.
2417.RE
2418.IP "ev_tstamp ev_timer_remaining (loop, ev_timer *)" 4
2419.IX Item "ev_tstamp ev_timer_remaining (loop, ev_timer *)"
2420Returns the remaining time until a timer fires. If the timer is active,
2421then this time is relative to the current event loop time, otherwise it's
2422the timeout value currently configured.
678.Sp 2423.Sp
679This sounds a bit complicated, but here is a useful and typical 2424That is, after an \f(CW\*(C`ev_timer_set (w, 5, 7)\*(C'\fR, \f(CW\*(C`ev_timer_remaining\*(C'\fR returns
680example: Imagine you have a tcp connection and you want a so-called idle 2425\&\f(CW5\fR. When the timer is started and one second passes, \f(CW\*(C`ev_timer_remaining\*(C'\fR
681timeout, that is, you want to be called when there have been, say, 60 2426will return \f(CW4\fR. When the timer expires and is restarted, it will return
682seconds of inactivity on the socket. The easiest way to do this is to 2427roughly \f(CW7\fR (likely slightly less as callback invocation takes some time,
683configure an \f(CW\*(C`ev_timer\*(C'\fR with after=repeat=60 and calling ev_timer_again each 2428too), and so on.
684time you successfully read or write some data. If you go into an idle 2429.IP "ev_tstamp repeat [read\-write]" 4
685state where you do not expect data to travel on the socket, you can stop 2430.IX Item "ev_tstamp repeat [read-write]"
686the timer, and again will automatically restart it if need be. 2431The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
2432or \f(CW\*(C`ev_timer_again\*(C'\fR is called, and determines the next timeout (if any),
2433which is also when any modifications are taken into account.
2434.PP
2435\fIExamples\fR
2436.IX Subsection "Examples"
2437.PP
2438Example: Create a timer that fires after 60 seconds.
2439.PP
2440.Vb 5
2441\& static void
2442\& one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
2443\& {
2444\& .. one minute over, w is actually stopped right here
2445\& }
2446\&
2447\& ev_timer mytimer;
2448\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
2449\& ev_timer_start (loop, &mytimer);
2450.Ve
2451.PP
2452Example: Create a timeout timer that times out after 10 seconds of
2453inactivity.
2454.PP
2455.Vb 5
2456\& static void
2457\& timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
2458\& {
2459\& .. ten seconds without any activity
2460\& }
2461\&
2462\& ev_timer mytimer;
2463\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
2464\& ev_timer_again (&mytimer); /* start timer */
2465\& ev_run (loop, 0);
2466\&
2467\& // and in some piece of code that gets executed on any "activity":
2468\& // reset the timeout to start ticking again at 10 seconds
2469\& ev_timer_again (&mytimer);
2470.Ve
687.ie n .Sh """ev_periodic"" \- to cron or not to cron" 2471.ie n .SS """ev_periodic"" \- to cron or not to cron?"
688.el .Sh "\f(CWev_periodic\fP \- to cron or not to cron" 2472.el .SS "\f(CWev_periodic\fP \- to cron or not to cron?"
689.IX Subsection "ev_periodic - to cron or not to cron" 2473.IX Subsection "ev_periodic - to cron or not to cron?"
690Periodic watchers are also timers of a kind, but they are very versatile 2474Periodic watchers are also timers of a kind, but they are very versatile
691(and unfortunately a bit complex). 2475(and unfortunately a bit complex).
692.PP 2476.PP
693Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time) 2477Unlike \f(CW\*(C`ev_timer\*(C'\fR, periodic watchers are not based on real time (or
694but on wallclock time (absolute time). You can tell a periodic watcher 2478relative time, the physical time that passes) but on wall clock time
695to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a 2479(absolute time, the thing you can read on your calendar or clock). The
696periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now () 2480difference is that wall clock time can run faster or slower than real
697+ 10.>) and then reset your system clock to the last year, then it will 2481time, and time jumps are not uncommon (e.g. when you adjust your
698take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger 2482wrist-watch).
699roughly 10 seconds later and of course not if you reset your system time
700again).
701.PP 2483.PP
702They can also be used to implement vastly more complex timers, such as 2484You can tell a periodic watcher to trigger after some specific point
703triggering an event on eahc midnight, local time. 2485in time: for example, if you tell a periodic watcher to trigger \*(L"in 10
2486seconds\*(R" (by specifying e.g. \f(CW\*(C`ev_now () + 10.\*(C'\fR, that is, an absolute time
2487not a delay) and then reset your system clock to January of the previous
2488year, then it will take a year or more to trigger the event (unlike an
2489\&\f(CW\*(C`ev_timer\*(C'\fR, which would still trigger roughly 10 seconds after starting
2490it, as it uses a relative timeout).
704.PP 2491.PP
2492\&\f(CW\*(C`ev_periodic\*(C'\fR watchers can also be used to implement vastly more complex
2493timers, such as triggering an event on each \*(L"midnight, local time\*(R", or
2494other complicated rules. This cannot easily be done with \f(CW\*(C`ev_timer\*(C'\fR
2495watchers, as those cannot react to time jumps.
2496.PP
705As with timers, the callback is guarenteed to be invoked only when the 2497As with timers, the callback is guaranteed to be invoked only when the
706time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready 2498point in time where it is supposed to trigger has passed. If multiple
707during the same loop iteration then order of execution is undefined. 2499timers become ready during the same loop iteration then the ones with
2500earlier time-out values are invoked before ones with later time-out values
2501(but this is no longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
2502.PP
2503\fIWatcher-Specific Functions and Data Members\fR
2504.IX Subsection "Watcher-Specific Functions and Data Members"
708.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4 2505.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
709.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 2506.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
710.PD 0 2507.PD 0
711.IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4 2508.IP "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
712.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 2509.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
713.PD 2510.PD
714Lots of arguments, lets sort it out... There are basically three modes of 2511Lots of arguments, let's sort it out... There are basically three modes of
715operation, and we will explain them from simplest to complex: 2512operation, and we will explain them from simplest to most complex:
716.RS 4 2513.RS 4
717.IP "* absolute timer (interval = reschedule_cb = 0)" 4 2514.IP "\(bu" 4
718.IX Item "absolute timer (interval = reschedule_cb = 0)" 2515absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
2516.Sp
719In this configuration the watcher triggers an event at the wallclock time 2517In this configuration the watcher triggers an event after the wall clock
720\&\f(CW\*(C`at\*(C'\fR and doesn't repeat. It will not adjust when a time jump occurs, 2518time \f(CW\*(C`offset\*(C'\fR has passed. It will not repeat and will not adjust when a
721that is, if it is to be run at January 1st 2011 then it will run when the 2519time jump occurs, that is, if it is to be run at January 1st 2011 then it
722system time reaches or surpasses this time. 2520will be stopped and invoked when the system clock reaches or surpasses
723.IP "* non-repeating interval timer (interval > 0, reschedule_cb = 0)" 4 2521this point in time.
724.IX Item "non-repeating interval timer (interval > 0, reschedule_cb = 0)" 2522.IP "\(bu" 4
2523repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
2524.Sp
725In this mode the watcher will always be scheduled to time out at the next 2525In this mode the watcher will always be scheduled to time out at the next
726\&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N) and then repeat, regardless 2526\&\f(CW\*(C`offset + N * interval\*(C'\fR time (for some integer N, which can also be
727of any time jumps. 2527negative) and then repeat, regardless of any time jumps. The \f(CW\*(C`offset\*(C'\fR
2528argument is merely an offset into the \f(CW\*(C`interval\*(C'\fR periods.
728.Sp 2529.Sp
729This can be used to create timers that do not drift with respect to system 2530This can be used to create timers that do not drift with respect to the
730time: 2531system clock, for example, here is an \f(CW\*(C`ev_periodic\*(C'\fR that triggers each
2532hour, on the hour (with respect to \s-1UTC\s0):
731.Sp 2533.Sp
732.Vb 1 2534.Vb 1
733\& ev_periodic_set (&periodic, 0., 3600., 0); 2535\& ev_periodic_set (&periodic, 0., 3600., 0);
734.Ve 2536.Ve
735.Sp 2537.Sp
736This doesn't mean there will always be 3600 seconds in between triggers, 2538This doesn't mean there will always be 3600 seconds in between triggers,
737but only that the the callback will be called when the system time shows a 2539but only that the callback will be called when the system time shows a
738full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible 2540full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
739by 3600. 2541by 3600.
740.Sp 2542.Sp
741Another way to think about it (for the mathematically inclined) is that 2543Another way to think about it (for the mathematically inclined) is that
742\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible 2544\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
743time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps. 2545time where \f(CW\*(C`time = offset (mod interval)\*(C'\fR, regardless of any time jumps.
744.IP "* manual reschedule mode (reschedule_cb = callback)" 4 2546.Sp
745.IX Item "manual reschedule mode (reschedule_cb = callback)" 2547The \f(CW\*(C`interval\*(C'\fR \fI\s-1MUST\s0\fR be positive, and for numerical stability, the
2548interval value should be higher than \f(CW\*(C`1/8192\*(C'\fR (which is around 100
2549microseconds) and \f(CW\*(C`offset\*(C'\fR should be higher than \f(CW0\fR and should have
2550at most a similar magnitude as the current time (say, within a factor of
2551ten). Typical values for offset are, in fact, \f(CW0\fR or something between
2552\&\f(CW0\fR and \f(CW\*(C`interval\*(C'\fR, which is also the recommended range.
2553.Sp
2554Note also that there is an upper limit to how often a timer can fire (\s-1CPU\s0
2555speed for example), so if \f(CW\*(C`interval\*(C'\fR is very small then timing stability
2556will of course deteriorate. Libev itself tries to be exact to be about one
2557millisecond (if the \s-1OS\s0 supports it and the machine is fast enough).
2558.IP "\(bu" 4
2559manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
2560.Sp
746In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being 2561In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`offset\*(C'\fR are both being
747ignored. Instead, each time the periodic watcher gets scheduled, the 2562ignored. Instead, each time the periodic watcher gets scheduled, the
748reschedule callback will be called with the watcher as first, and the 2563reschedule callback will be called with the watcher as first, and the
749current time as second argument. 2564current time as second argument.
750.Sp 2565.Sp
751\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, 2566\&\s-1NOTE:\s0 \fIThis callback \s-1MUST NOT\s0 stop or destroy any periodic watcher, ever,
752ever, or make any event loop modifications\fR. If you need to stop it, 2567or make \s-1ANY\s0 other event loop modifications whatsoever, unless explicitly
753return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by 2568allowed by documentation here\fR.
754starting a prepare watcher).
755.Sp 2569.Sp
2570If you need to stop it, return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop
2571it afterwards (e.g. by starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is the
2572only event loop modification you are allowed to do).
2573.Sp
756Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w, 2574The callback prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(ev_periodic
757ev_tstamp now)\*(C'\fR, e.g.: 2575*w, ev_tstamp now)\*(C'\fR, e.g.:
758.Sp 2576.Sp
759.Vb 4 2577.Vb 5
2578\& static ev_tstamp
760\& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) 2579\& my_rescheduler (ev_periodic *w, ev_tstamp now)
761\& { 2580\& {
762\& return now + 60.; 2581\& return now + 60.;
763\& } 2582\& }
764.Ve 2583.Ve
765.Sp 2584.Sp
766It must return the next time to trigger, based on the passed time value 2585It must return the next time to trigger, based on the passed time value
767(that is, the lowest time value larger than to the second argument). It 2586(that is, the lowest time value larger than to the second argument). It
768will usually be called just before the callback will be triggered, but 2587will usually be called just before the callback will be triggered, but
769might be called at other times, too. 2588might be called at other times, too.
770.Sp 2589.Sp
771\&\s-1NOTE:\s0 \fIThis callback must always return a time that is later than the 2590\&\s-1NOTE:\s0 \fIThis callback must always return a time that is higher than or
772passed \f(CI\*(C`now\*(C'\fI value\fR. Not even \f(CW\*(C`now\*(C'\fR itself will do, it \fImust\fR be larger. 2591equal to the passed \f(CI\*(C`now\*(C'\fI value\fR.
773.Sp 2592.Sp
774This can be used to create very complex timers, such as a timer that 2593This can be used to create very complex timers, such as a timer that
775triggers on each midnight, local time. To do this, you would calculate the 2594triggers on \*(L"next midnight, local time\*(R". To do this, you would calculate
776next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How 2595the next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for
777you do this is, again, up to you (but it is not trivial, which is the main 2596this. Here is a (completely untested, no error checking) example on how to
778reason I omitted it as an example). 2597do this:
2598.Sp
2599.Vb 1
2600\& #include <time.h>
2601\&
2602\& static ev_tstamp
2603\& my_rescheduler (ev_periodic *w, ev_tstamp now)
2604\& {
2605\& time_t tnow = (time_t)now;
2606\& struct tm tm;
2607\& localtime_r (&tnow, &tm);
2608\&
2609\& tm.tm_sec = tm.tm_min = tm.tm_hour = 0; // midnight current day
2610\& ++tm.tm_mday; // midnight next day
2611\&
2612\& return mktime (&tm);
2613\& }
2614.Ve
2615.Sp
2616Note: this code might run into trouble on days that have more then two
2617midnights (beginning and end).
779.RE 2618.RE
780.RS 4 2619.RS 4
781.RE 2620.RE
782.IP "ev_periodic_again (loop, ev_periodic *)" 4 2621.IP "ev_periodic_again (loop, ev_periodic *)" 4
783.IX Item "ev_periodic_again (loop, ev_periodic *)" 2622.IX Item "ev_periodic_again (loop, ev_periodic *)"
784Simply stops and restarts the periodic watcher again. This is only useful 2623Simply stops and restarts the periodic watcher again. This is only useful
785when you changed some parameters or the reschedule callback would return 2624when you changed some parameters or the reschedule callback would return
786a different time than the last time it was called (e.g. in a crond like 2625a different time than the last time it was called (e.g. in a crond like
787program when the crontabs have changed). 2626program when the crontabs have changed).
2627.IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4
2628.IX Item "ev_tstamp ev_periodic_at (ev_periodic *)"
2629When active, returns the absolute time that the watcher is supposed
2630to trigger next. This is not the same as the \f(CW\*(C`offset\*(C'\fR argument to
2631\&\f(CW\*(C`ev_periodic_set\*(C'\fR, but indeed works even in interval and manual
2632rescheduling modes.
2633.IP "ev_tstamp offset [read\-write]" 4
2634.IX Item "ev_tstamp offset [read-write]"
2635When repeating, this contains the offset value, otherwise this is the
2636absolute point in time (the \f(CW\*(C`offset\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR,
2637although libev might modify this value for better numerical stability).
2638.Sp
2639Can be modified any time, but changes only take effect when the periodic
2640timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
2641.IP "ev_tstamp interval [read\-write]" 4
2642.IX Item "ev_tstamp interval [read-write]"
2643The current interval value. Can be modified any time, but changes only
2644take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
2645called.
2646.IP "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read\-write]" 4
2647.IX Item "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]"
2648The current reschedule callback, or \f(CW0\fR, if this functionality is
2649switched off. Can be changed any time, but changes only take effect when
2650the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
2651.PP
2652\fIExamples\fR
2653.IX Subsection "Examples"
2654.PP
2655Example: Call a callback every hour, or, more precisely, whenever the
2656system time is divisible by 3600. The callback invocation times have
2657potentially a lot of jitter, but good long-term stability.
2658.PP
2659.Vb 5
2660\& static void
2661\& clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
2662\& {
2663\& ... its now a full hour (UTC, or TAI or whatever your clock follows)
2664\& }
2665\&
2666\& ev_periodic hourly_tick;
2667\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
2668\& ev_periodic_start (loop, &hourly_tick);
2669.Ve
2670.PP
2671Example: The same as above, but use a reschedule callback to do it:
2672.PP
2673.Vb 1
2674\& #include <math.h>
2675\&
2676\& static ev_tstamp
2677\& my_scheduler_cb (ev_periodic *w, ev_tstamp now)
2678\& {
2679\& return now + (3600. \- fmod (now, 3600.));
2680\& }
2681\&
2682\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
2683.Ve
2684.PP
2685Example: Call a callback every hour, starting now:
2686.PP
2687.Vb 4
2688\& ev_periodic hourly_tick;
2689\& ev_periodic_init (&hourly_tick, clock_cb,
2690\& fmod (ev_now (loop), 3600.), 3600., 0);
2691\& ev_periodic_start (loop, &hourly_tick);
2692.Ve
788.ie n .Sh """ev_signal"" \- signal me when a signal gets signalled" 2693.ie n .SS """ev_signal"" \- signal me when a signal gets signalled!"
789.el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled" 2694.el .SS "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
790.IX Subsection "ev_signal - signal me when a signal gets signalled" 2695.IX Subsection "ev_signal - signal me when a signal gets signalled!"
791Signal watchers will trigger an event when the process receives a specific 2696Signal watchers will trigger an event when the process receives a specific
792signal one or more times. Even though signals are very asynchronous, libev 2697signal one or more times. Even though signals are very asynchronous, libev
793will try it's best to deliver signals synchronously, i.e. as part of the 2698will try its best to deliver signals synchronously, i.e. as part of the
794normal event processing, like any other event. 2699normal event processing, like any other event.
795.PP 2700.PP
2701If you want signals to be delivered truly asynchronously, just use
2702\&\f(CW\*(C`sigaction\*(C'\fR as you would do without libev and forget about sharing
2703the signal. You can even use \f(CW\*(C`ev_async\*(C'\fR from a signal handler to
2704synchronously wake up an event loop.
2705.PP
796You can configure as many watchers as you like per signal. Only when the 2706You can configure as many watchers as you like for the same signal, but
797first watcher gets started will libev actually register a signal watcher 2707only within the same loop, i.e. you can watch for \f(CW\*(C`SIGINT\*(C'\fR in your
798with the kernel (thus it coexists with your own signal handlers as long 2708default loop and for \f(CW\*(C`SIGIO\*(C'\fR in another loop, but you cannot watch for
799as you don't register any with libev). Similarly, when the last signal 2709\&\f(CW\*(C`SIGINT\*(C'\fR in both the default loop and another loop at the same time. At
800watcher for a signal is stopped libev will reset the signal handler to 2710the moment, \f(CW\*(C`SIGCHLD\*(C'\fR is permanently tied to the default loop.
801\&\s-1SIG_DFL\s0 (regardless of what it was set to before). 2711.PP
2712Only after the first watcher for a signal is started will libev actually
2713register something with the kernel. It thus coexists with your own signal
2714handlers as long as you don't register any with libev for the same signal.
2715.PP
2716If possible and supported, libev will install its handlers with
2717\&\f(CW\*(C`SA_RESTART\*(C'\fR (or equivalent) behaviour enabled, so system calls should
2718not be unduly interrupted. If you have a problem with system calls getting
2719interrupted by signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher
2720and unblock them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher.
2721.PP
2722\fIThe special problem of inheritance over fork/execve/pthread_create\fR
2723.IX Subsection "The special problem of inheritance over fork/execve/pthread_create"
2724.PP
2725Both the signal mask (\f(CW\*(C`sigprocmask\*(C'\fR) and the signal disposition
2726(\f(CW\*(C`sigaction\*(C'\fR) are unspecified after starting a signal watcher (and after
2727stopping it again), that is, libev might or might not block the signal,
2728and might or might not set or restore the installed signal handler (but
2729see \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR).
2730.PP
2731While this does not matter for the signal disposition (libev never
2732sets signals to \f(CW\*(C`SIG_IGN\*(C'\fR, so handlers will be reset to \f(CW\*(C`SIG_DFL\*(C'\fR on
2733\&\f(CW\*(C`execve\*(C'\fR), this matters for the signal mask: many programs do not expect
2734certain signals to be blocked.
2735.PP
2736This means that before calling \f(CW\*(C`exec\*(C'\fR (from the child) you should reset
2737the signal mask to whatever \*(L"default\*(R" you expect (all clear is a good
2738choice usually).
2739.PP
2740The simplest way to ensure that the signal mask is reset in the child is
2741to install a fork handler with \f(CW\*(C`pthread_atfork\*(C'\fR that resets it. That will
2742catch fork calls done by libraries (such as the libc) as well.
2743.PP
2744In current versions of libev, the signal will not be blocked indefinitely
2745unless you use the \f(CW\*(C`signalfd\*(C'\fR \s-1API\s0 (\f(CW\*(C`EV_SIGNALFD\*(C'\fR). While this reduces
2746the window of opportunity for problems, it will not go away, as libev
2747\&\fIhas\fR to modify the signal mask, at least temporarily.
2748.PP
2749So I can't stress this enough: \fIIf you do not reset your signal mask when
2750you expect it to be empty, you have a race condition in your code\fR. This
2751is not a libev-specific thing, this is true for most event libraries.
2752.PP
2753\fIThe special problem of threads signal handling\fR
2754.IX Subsection "The special problem of threads signal handling"
2755.PP
2756\&\s-1POSIX\s0 threads has problematic signal handling semantics, specifically,
2757a lot of functionality (sigfd, sigwait etc.) only really works if all
2758threads in a process block signals, which is hard to achieve.
2759.PP
2760When you want to use sigwait (or mix libev signal handling with your own
2761for the same signals), you can tackle this problem by globally blocking
2762all signals before creating any threads (or creating them with a fully set
2763sigprocmask) and also specifying the \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when creating
2764loops. Then designate one thread as \*(L"signal receiver thread\*(R" which handles
2765these signals. You can pass on any signals that libev might be interested
2766in by calling \f(CW\*(C`ev_feed_signal\*(C'\fR.
2767.PP
2768\fIWatcher-Specific Functions and Data Members\fR
2769.IX Subsection "Watcher-Specific Functions and Data Members"
802.IP "ev_signal_init (ev_signal *, callback, int signum)" 4 2770.IP "ev_signal_init (ev_signal *, callback, int signum)" 4
803.IX Item "ev_signal_init (ev_signal *, callback, int signum)" 2771.IX Item "ev_signal_init (ev_signal *, callback, int signum)"
804.PD 0 2772.PD 0
805.IP "ev_signal_set (ev_signal *, int signum)" 4 2773.IP "ev_signal_set (ev_signal *, int signum)" 4
806.IX Item "ev_signal_set (ev_signal *, int signum)" 2774.IX Item "ev_signal_set (ev_signal *, int signum)"
807.PD 2775.PD
808Configures the watcher to trigger on the given signal number (usually one 2776Configures the watcher to trigger on the given signal number (usually one
809of the \f(CW\*(C`SIGxxx\*(C'\fR constants). 2777of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
2778.IP "int signum [read\-only]" 4
2779.IX Item "int signum [read-only]"
2780The signal the watcher watches out for.
2781.PP
2782\fIExamples\fR
2783.IX Subsection "Examples"
2784.PP
2785Example: Try to exit cleanly on \s-1SIGINT.\s0
2786.PP
2787.Vb 5
2788\& static void
2789\& sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
2790\& {
2791\& ev_break (loop, EVBREAK_ALL);
2792\& }
2793\&
2794\& ev_signal signal_watcher;
2795\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
2796\& ev_signal_start (loop, &signal_watcher);
2797.Ve
810.ie n .Sh """ev_child"" \- wait for pid status changes" 2798.ie n .SS """ev_child"" \- watch out for process status changes"
811.el .Sh "\f(CWev_child\fP \- wait for pid status changes" 2799.el .SS "\f(CWev_child\fP \- watch out for process status changes"
812.IX Subsection "ev_child - wait for pid status changes" 2800.IX Subsection "ev_child - watch out for process status changes"
813Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to 2801Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
814some child status changes (most typically when a child of yours dies). 2802some child status changes (most typically when a child of yours dies or
2803exits). It is permissible to install a child watcher \fIafter\fR the child
2804has been forked (which implies it might have already exited), as long
2805as the event loop isn't entered (or is continued from a watcher), i.e.,
2806forking and then immediately registering a watcher for the child is fine,
2807but forking and registering a watcher a few event loop iterations later or
2808in the next callback invocation is not.
2809.PP
2810Only the default event loop is capable of handling signals, and therefore
2811you can only register child watchers in the default event loop.
2812.PP
2813Due to some design glitches inside libev, child watchers will always be
2814handled at maximum priority (their priority is set to \f(CW\*(C`EV_MAXPRI\*(C'\fR by
2815libev)
2816.PP
2817\fIProcess Interaction\fR
2818.IX Subsection "Process Interaction"
2819.PP
2820Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is
2821initialised. This is necessary to guarantee proper behaviour even if the
2822first child watcher is started after the child exits. The occurrence
2823of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done
2824synchronously as part of the event loop processing. Libev always reaps all
2825children, even ones not watched.
2826.PP
2827\fIOverriding the Built-In Processing\fR
2828.IX Subsection "Overriding the Built-In Processing"
2829.PP
2830Libev offers no special support for overriding the built-in child
2831processing, but if your application collides with libev's default child
2832handler, you can override it easily by installing your own handler for
2833\&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the
2834default loop never gets destroyed. You are encouraged, however, to use an
2835event-based approach to child reaping and thus use libev's support for
2836that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely.
2837.PP
2838\fIStopping the Child Watcher\fR
2839.IX Subsection "Stopping the Child Watcher"
2840.PP
2841Currently, the child watcher never gets stopped, even when the
2842child terminates, so normally one needs to stop the watcher in the
2843callback. Future versions of libev might stop the watcher automatically
2844when a child exit is detected (calling \f(CW\*(C`ev_child_stop\*(C'\fR twice is not a
2845problem).
2846.PP
2847\fIWatcher-Specific Functions and Data Members\fR
2848.IX Subsection "Watcher-Specific Functions and Data Members"
815.IP "ev_child_init (ev_child *, callback, int pid)" 4 2849.IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4
816.IX Item "ev_child_init (ev_child *, callback, int pid)" 2850.IX Item "ev_child_init (ev_child *, callback, int pid, int trace)"
817.PD 0 2851.PD 0
818.IP "ev_child_set (ev_child *, int pid)" 4 2852.IP "ev_child_set (ev_child *, int pid, int trace)" 4
819.IX Item "ev_child_set (ev_child *, int pid)" 2853.IX Item "ev_child_set (ev_child *, int pid, int trace)"
820.PD 2854.PD
821Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or 2855Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
822\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look 2856\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
823at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see 2857at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
824the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems 2858the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
825\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the 2859\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
826process causing the status change. 2860process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only
2861activate the watcher when the process terminates) or \f(CW1\fR (additionally
2862activate the watcher when the process is stopped or continued).
2863.IP "int pid [read\-only]" 4
2864.IX Item "int pid [read-only]"
2865The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
2866.IP "int rpid [read\-write]" 4
2867.IX Item "int rpid [read-write]"
2868The process id that detected a status change.
2869.IP "int rstatus [read\-write]" 4
2870.IX Item "int rstatus [read-write]"
2871The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
2872\&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
2873.PP
2874\fIExamples\fR
2875.IX Subsection "Examples"
2876.PP
2877Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for
2878its completion.
2879.PP
2880.Vb 1
2881\& ev_child cw;
2882\&
2883\& static void
2884\& child_cb (EV_P_ ev_child *w, int revents)
2885\& {
2886\& ev_child_stop (EV_A_ w);
2887\& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus);
2888\& }
2889\&
2890\& pid_t pid = fork ();
2891\&
2892\& if (pid < 0)
2893\& // error
2894\& else if (pid == 0)
2895\& {
2896\& // the forked child executes here
2897\& exit (1);
2898\& }
2899\& else
2900\& {
2901\& ev_child_init (&cw, child_cb, pid, 0);
2902\& ev_child_start (EV_DEFAULT_ &cw);
2903\& }
2904.Ve
2905.ie n .SS """ev_stat"" \- did the file attributes just change?"
2906.el .SS "\f(CWev_stat\fP \- did the file attributes just change?"
2907.IX Subsection "ev_stat - did the file attributes just change?"
2908This watches a file system path for attribute changes. That is, it calls
2909\&\f(CW\*(C`stat\*(C'\fR on that path in regular intervals (or when the \s-1OS\s0 says it changed)
2910and sees if it changed compared to the last time, invoking the callback
2911if it did. Starting the watcher \f(CW\*(C`stat\*(C'\fR's the file, so only changes that
2912happen after the watcher has been started will be reported.
2913.PP
2914The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does
2915not exist\*(R" is a status change like any other. The condition \*(L"path does not
2916exist\*(R" (or more correctly \*(L"path cannot be stat'ed\*(R") is signified by the
2917\&\f(CW\*(C`st_nlink\*(C'\fR field being zero (which is otherwise always forced to be at
2918least one) and all the other fields of the stat buffer having unspecified
2919contents.
2920.PP
2921The path \fImust not\fR end in a slash or contain special components such as
2922\&\f(CW\*(C`.\*(C'\fR or \f(CW\*(C`..\*(C'\fR. The path \fIshould\fR be absolute: If it is relative and
2923your working directory changes, then the behaviour is undefined.
2924.PP
2925Since there is no portable change notification interface available, the
2926portable implementation simply calls \f(CWstat(2)\fR regularly on the path
2927to see if it changed somehow. You can specify a recommended polling
2928interval for this case. If you specify a polling interval of \f(CW0\fR (highly
2929recommended!) then a \fIsuitable, unspecified default\fR value will be used
2930(which you can expect to be around five seconds, although this might
2931change dynamically). Libev will also impose a minimum interval which is
2932currently around \f(CW0.1\fR, but that's usually overkill.
2933.PP
2934This watcher type is not meant for massive numbers of stat watchers,
2935as even with OS-supported change notifications, this can be
2936resource-intensive.
2937.PP
2938At the time of this writing, the only OS-specific interface implemented
2939is the Linux inotify interface (implementing kqueue support is left as an
2940exercise for the reader. Note, however, that the author sees no way of
2941implementing \f(CW\*(C`ev_stat\*(C'\fR semantics with kqueue, except as a hint).
2942.PP
2943\fI\s-1ABI\s0 Issues (Largefile Support)\fR
2944.IX Subsection "ABI Issues (Largefile Support)"
2945.PP
2946Libev by default (unless the user overrides this) uses the default
2947compilation environment, which means that on systems with large file
2948support disabled by default, you get the 32 bit version of the stat
2949structure. When using the library from programs that change the \s-1ABI\s0 to
2950use 64 bit file offsets the programs will fail. In that case you have to
2951compile libev with the same flags to get binary compatibility. This is
2952obviously the case with any flags that change the \s-1ABI,\s0 but the problem is
2953most noticeably displayed with ev_stat and large file support.
2954.PP
2955The solution for this is to lobby your distribution maker to make large
2956file interfaces available by default (as e.g. FreeBSD does) and not
2957optional. Libev cannot simply switch on large file support because it has
2958to exchange stat structures with application programs compiled using the
2959default compilation environment.
2960.PP
2961\fIInotify and Kqueue\fR
2962.IX Subsection "Inotify and Kqueue"
2963.PP
2964When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev and present at
2965runtime, it will be used to speed up change detection where possible. The
2966inotify descriptor will be created lazily when the first \f(CW\*(C`ev_stat\*(C'\fR
2967watcher is being started.
2968.PP
2969Inotify presence does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
2970except that changes might be detected earlier, and in some cases, to avoid
2971making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presence of inotify support
2972there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling,
2973but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
2974many bugs), the path exists (i.e. stat succeeds), and the path resides on
2975a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
2976xfs are fully working) libev usually gets away without polling.
2977.PP
2978There is no support for kqueue, as apparently it cannot be used to
2979implement this functionality, due to the requirement of having a file
2980descriptor open on the object at all times, and detecting renames, unlinks
2981etc. is difficult.
2982.PP
2983\fI\f(CI\*(C`stat ()\*(C'\fI is a synchronous operation\fR
2984.IX Subsection "stat () is a synchronous operation"
2985.PP
2986Libev doesn't normally do any kind of I/O itself, and so is not blocking
2987the process. The exception are \f(CW\*(C`ev_stat\*(C'\fR watchers \- those call \f(CW\*(C`stat
2988()\*(C'\fR, which is a synchronous operation.
2989.PP
2990For local paths, this usually doesn't matter: unless the system is very
2991busy or the intervals between stat's are large, a stat call will be fast,
2992as the path data is usually in memory already (except when starting the
2993watcher).
2994.PP
2995For networked file systems, calling \f(CW\*(C`stat ()\*(C'\fR can block an indefinite
2996time due to network issues, and even under good conditions, a stat call
2997often takes multiple milliseconds.
2998.PP
2999Therefore, it is best to avoid using \f(CW\*(C`ev_stat\*(C'\fR watchers on networked
3000paths, although this is fully supported by libev.
3001.PP
3002\fIThe special problem of stat time resolution\fR
3003.IX Subsection "The special problem of stat time resolution"
3004.PP
3005The \f(CW\*(C`stat ()\*(C'\fR system call only supports full-second resolution portably,
3006and even on systems where the resolution is higher, most file systems
3007still only support whole seconds.
3008.PP
3009That means that, if the time is the only thing that changes, you can
3010easily miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and
3011calls your callback, which does something. When there is another update
3012within the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect unless the
3013stat data does change in other ways (e.g. file size).
3014.PP
3015The solution to this is to delay acting on a change for slightly more
3016than a second (or till slightly after the next full second boundary), using
3017a roughly one-second-delay \f(CW\*(C`ev_timer\*(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02);
3018ev_timer_again (loop, w)\*(C'\fR).
3019.PP
3020The \f(CW.02\fR offset is added to work around small timing inconsistencies
3021of some operating systems (where the second counter of the current time
3022might be be delayed. One such system is the Linux kernel, where a call to
3023\&\f(CW\*(C`gettimeofday\*(C'\fR might return a timestamp with a full second later than
3024a subsequent \f(CW\*(C`time\*(C'\fR call \- if the equivalent of \f(CW\*(C`time ()\*(C'\fR is used to
3025update file times then there will be a small window where the kernel uses
3026the previous second to update file times but libev might already execute
3027the timer callback).
3028.PP
3029\fIWatcher-Specific Functions and Data Members\fR
3030.IX Subsection "Watcher-Specific Functions and Data Members"
3031.IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
3032.IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
3033.PD 0
3034.IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4
3035.IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)"
3036.PD
3037Configures the watcher to wait for status changes of the given
3038\&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to
3039be detected and should normally be specified as \f(CW0\fR to let libev choose
3040a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same
3041path for as long as the watcher is active.
3042.Sp
3043The callback will receive an \f(CW\*(C`EV_STAT\*(C'\fR event when a change was detected,
3044relative to the attributes at the time the watcher was started (or the
3045last change was detected).
3046.IP "ev_stat_stat (loop, ev_stat *)" 4
3047.IX Item "ev_stat_stat (loop, ev_stat *)"
3048Updates the stat buffer immediately with new values. If you change the
3049watched path in your callback, you could call this function to avoid
3050detecting this change (while introducing a race condition if you are not
3051the only one changing the path). Can also be useful simply to find out the
3052new values.
3053.IP "ev_statdata attr [read\-only]" 4
3054.IX Item "ev_statdata attr [read-only]"
3055The most-recently detected attributes of the file. Although the type is
3056\&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
3057suitable for your system, but you can only rely on the POSIX-standardised
3058members to be present. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there was
3059some error while \f(CW\*(C`stat\*(C'\fRing the file.
3060.IP "ev_statdata prev [read\-only]" 4
3061.IX Item "ev_statdata prev [read-only]"
3062The previous attributes of the file. The callback gets invoked whenever
3063\&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR, or, more precisely, one or more of these members
3064differ: \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,
3065\&\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.
3066.IP "ev_tstamp interval [read\-only]" 4
3067.IX Item "ev_tstamp interval [read-only]"
3068The specified interval.
3069.IP "const char *path [read\-only]" 4
3070.IX Item "const char *path [read-only]"
3071The file system path that is being watched.
3072.PP
3073\fIExamples\fR
3074.IX Subsection "Examples"
3075.PP
3076Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
3077.PP
3078.Vb 10
3079\& static void
3080\& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
3081\& {
3082\& /* /etc/passwd changed in some way */
3083\& if (w\->attr.st_nlink)
3084\& {
3085\& printf ("passwd current size %ld\en", (long)w\->attr.st_size);
3086\& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime);
3087\& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime);
3088\& }
3089\& else
3090\& /* you shalt not abuse printf for puts */
3091\& puts ("wow, /etc/passwd is not there, expect problems. "
3092\& "if this is windows, they already arrived\en");
3093\& }
3094\&
3095\& ...
3096\& ev_stat passwd;
3097\&
3098\& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
3099\& ev_stat_start (loop, &passwd);
3100.Ve
3101.PP
3102Example: Like above, but additionally use a one-second delay so we do not
3103miss updates (however, frequent updates will delay processing, too, so
3104one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
3105\&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
3106.PP
3107.Vb 2
3108\& static ev_stat passwd;
3109\& static ev_timer timer;
3110\&
3111\& static void
3112\& timer_cb (EV_P_ ev_timer *w, int revents)
3113\& {
3114\& ev_timer_stop (EV_A_ w);
3115\&
3116\& /* now it\*(Aqs one second after the most recent passwd change */
3117\& }
3118\&
3119\& static void
3120\& stat_cb (EV_P_ ev_stat *w, int revents)
3121\& {
3122\& /* reset the one\-second timer */
3123\& ev_timer_again (EV_A_ &timer);
3124\& }
3125\&
3126\& ...
3127\& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
3128\& ev_stat_start (loop, &passwd);
3129\& ev_timer_init (&timer, timer_cb, 0., 1.02);
3130.Ve
827.ie n .Sh """ev_idle"" \- when you've got nothing better to do" 3131.ie n .SS """ev_idle"" \- when you've got nothing better to do..."
828.el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do" 3132.el .SS "\f(CWev_idle\fP \- when you've got nothing better to do..."
829.IX Subsection "ev_idle - when you've got nothing better to do" 3133.IX Subsection "ev_idle - when you've got nothing better to do..."
830Idle watchers trigger events when there are no other events are pending 3134Idle watchers trigger events when no other events of the same or higher
831(prepare, check and other idle watchers do not count). That is, as long 3135priority are pending (prepare, check and other idle watchers do not count
832as your process is busy handling sockets or timeouts (or even signals, 3136as receiving \*(L"events\*(R").
833imagine) it will not be triggered. But when your process is idle all idle 3137.PP
834watchers are being called again and again, once per event loop iteration \- 3138That is, as long as your process is busy handling sockets or timeouts
3139(or even signals, imagine) of the same or higher priority it will not be
3140triggered. But when your process is idle (or only lower-priority watchers
3141are pending), the idle watchers are being called once per event loop
835until stopped, that is, or your process receives more events and becomes 3142iteration \- until stopped, that is, or your process receives more events
836busy. 3143and becomes busy again with higher priority stuff.
837.PP 3144.PP
838The most noteworthy effect is that as long as any idle watchers are 3145The most noteworthy effect is that as long as any idle watchers are
839active, the process will not block when waiting for new events. 3146active, the process will not block when waiting for new events.
840.PP 3147.PP
841Apart from keeping your process non-blocking (which is a useful 3148Apart from keeping your process non-blocking (which is a useful
842effect on its own sometimes), idle watchers are a good place to do 3149effect on its own sometimes), idle watchers are a good place to do
843\&\*(L"pseudo\-background processing\*(R", or delay processing stuff to after the 3150\&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the
844event loop has handled all outstanding events. 3151event loop has handled all outstanding events.
3152.PP
3153\fIAbusing an \f(CI\*(C`ev_idle\*(C'\fI watcher for its side-effect\fR
3154.IX Subsection "Abusing an ev_idle watcher for its side-effect"
3155.PP
3156As long as there is at least one active idle watcher, libev will never
3157sleep unnecessarily. Or in other words, it will loop as fast as possible.
3158For this to work, the idle watcher doesn't need to be invoked at all \- the
3159lowest priority will do.
3160.PP
3161This mode of operation can be useful together with an \f(CW\*(C`ev_check\*(C'\fR watcher,
3162to do something on each event loop iteration \- for example to balance load
3163between different connections.
3164.PP
3165See \*(L"Abusing an ev_check watcher for its side-effect\*(R" for a longer
3166example.
3167.PP
3168\fIWatcher-Specific Functions and Data Members\fR
3169.IX Subsection "Watcher-Specific Functions and Data Members"
845.IP "ev_idle_init (ev_signal *, callback)" 4 3170.IP "ev_idle_init (ev_idle *, callback)" 4
846.IX Item "ev_idle_init (ev_signal *, callback)" 3171.IX Item "ev_idle_init (ev_idle *, callback)"
847Initialises and configures the idle watcher \- it has no parameters of any 3172Initialises and configures the idle watcher \- it has no parameters of any
848kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless, 3173kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
849believe me. 3174believe me.
3175.PP
3176\fIExamples\fR
3177.IX Subsection "Examples"
3178.PP
3179Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the
3180callback, free it. Also, use no error checking, as usual.
3181.PP
3182.Vb 5
3183\& static void
3184\& idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
3185\& {
3186\& // stop the watcher
3187\& ev_idle_stop (loop, w);
3188\&
3189\& // now we can free it
3190\& free (w);
3191\&
3192\& // now do something you wanted to do when the program has
3193\& // no longer anything immediate to do.
3194\& }
3195\&
3196\& ev_idle *idle_watcher = malloc (sizeof (ev_idle));
3197\& ev_idle_init (idle_watcher, idle_cb);
3198\& ev_idle_start (loop, idle_watcher);
3199.Ve
850.ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop" 3200.ie n .SS """ev_prepare"" and ""ev_check"" \- customise your event loop!"
851.el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop" 3201.el .SS "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
852.IX Subsection "ev_prepare and ev_check - customise your event loop" 3202.IX Subsection "ev_prepare and ev_check - customise your event loop!"
853Prepare and check watchers are usually (but not always) used in tandem: 3203Prepare and check watchers are often (but not always) used in pairs:
854prepare watchers get invoked before the process blocks and check watchers 3204prepare watchers get invoked before the process blocks and check watchers
855afterwards. 3205afterwards.
856.PP 3206.PP
3207You \fImust not\fR call \f(CW\*(C`ev_run\*(C'\fR (or similar functions that enter the
3208current event loop) or \f(CW\*(C`ev_loop_fork\*(C'\fR from either \f(CW\*(C`ev_prepare\*(C'\fR or
3209\&\f(CW\*(C`ev_check\*(C'\fR watchers. Other loops than the current one are fine,
3210however. The rationale behind this is that you do not need to check
3211for recursion in those watchers, i.e. the sequence will always be
3212\&\f(CW\*(C`ev_prepare\*(C'\fR, blocking, \f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each
3213kind they will always be called in pairs bracketing the blocking call.
3214.PP
857Their main purpose is to integrate other event mechanisms into libev. This 3215Their main purpose is to integrate other event mechanisms into libev and
858could be used, for example, to track variable changes, implement your own 3216their use is somewhat advanced. They could be used, for example, to track
859watchers, integrate net-snmp or a coroutine library and lots more. 3217variable changes, implement your own watchers, integrate net-snmp or a
3218coroutine library and lots more. They are also occasionally useful if
3219you cache some data and want to flush it before blocking (for example,
3220in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
3221watcher).
860.PP 3222.PP
861This is done by examining in each prepare call which file descriptors need 3223This is done by examining in each prepare call which file descriptors
862to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers for 3224need to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers
863them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many libraries 3225for them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many
864provide just this functionality). Then, in the check watcher you check for 3226libraries provide exactly this functionality). Then, in the check watcher,
865any events that occured (by checking the pending status of all watchers 3227you check for any events that occurred (by checking the pending status
866and stopping them) and call back into the library. The I/O and timer 3228of all watchers and stopping them) and call back into the library. The
867callbacks will never actually be called (but must be valid nevertheless, 3229I/O and timer callbacks will never actually be called (but must be valid
868because you never know, you know?). 3230nevertheless, because you never know, you know?).
869.PP 3231.PP
870As another example, the Perl Coro module uses these hooks to integrate 3232As another example, the Perl Coro module uses these hooks to integrate
871coroutines into libev programs, by yielding to other active coroutines 3233coroutines into libev programs, by yielding to other active coroutines
872during each prepare and only letting the process block if no coroutines 3234during each prepare and only letting the process block if no coroutines
873are ready to run (it's actually more complicated: it only runs coroutines 3235are ready to run (it's actually more complicated: it only runs coroutines
874with priority higher than or equal to the event loop and one coroutine 3236with priority higher than or equal to the event loop and one coroutine
875of lower priority, but only once, using idle watchers to keep the event 3237of lower priority, but only once, using idle watchers to keep the event
876loop from blocking if lower-priority coroutines are active, thus mapping 3238loop from blocking if lower-priority coroutines are active, thus mapping
877low-priority coroutines to idle/background tasks). 3239low-priority coroutines to idle/background tasks).
3240.PP
3241When used for this purpose, it is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers
3242highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR) priority, to ensure that they are being run before
3243any other watchers after the poll (this doesn't matter for \f(CW\*(C`ev_prepare\*(C'\fR
3244watchers).
3245.PP
3246Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, too) should not
3247activate (\*(L"feed\*(R") events into libev. While libev fully supports this, they
3248might get executed before other \f(CW\*(C`ev_check\*(C'\fR watchers did their job. As
3249\&\f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other (non-libev) event
3250loops those other event loops might be in an unusable state until their
3251\&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with
3252others).
3253.PP
3254\fIAbusing an \f(CI\*(C`ev_check\*(C'\fI watcher for its side-effect\fR
3255.IX Subsection "Abusing an ev_check watcher for its side-effect"
3256.PP
3257\&\f(CW\*(C`ev_check\*(C'\fR (and less often also \f(CW\*(C`ev_prepare\*(C'\fR) watchers can also be
3258useful because they are called once per event loop iteration. For
3259example, if you want to handle a large number of connections fairly, you
3260normally only do a bit of work for each active connection, and if there
3261is more work to do, you wait for the next event loop iteration, so other
3262connections have a chance of making progress.
3263.PP
3264Using an \f(CW\*(C`ev_check\*(C'\fR watcher is almost enough: it will be called on the
3265next event loop iteration. However, that isn't as soon as possible \-
3266without external events, your \f(CW\*(C`ev_check\*(C'\fR watcher will not be invoked.
3267.PP
3268This is where \f(CW\*(C`ev_idle\*(C'\fR watchers come in handy \- all you need is a
3269single global idle watcher that is active as long as you have one active
3270\&\f(CW\*(C`ev_check\*(C'\fR watcher. The \f(CW\*(C`ev_idle\*(C'\fR watcher makes sure the event loop
3271will not sleep, and the \f(CW\*(C`ev_check\*(C'\fR watcher makes sure a callback gets
3272invoked. Neither watcher alone can do that.
3273.PP
3274\fIWatcher-Specific Functions and Data Members\fR
3275.IX Subsection "Watcher-Specific Functions and Data Members"
878.IP "ev_prepare_init (ev_prepare *, callback)" 4 3276.IP "ev_prepare_init (ev_prepare *, callback)" 4
879.IX Item "ev_prepare_init (ev_prepare *, callback)" 3277.IX Item "ev_prepare_init (ev_prepare *, callback)"
880.PD 0 3278.PD 0
881.IP "ev_check_init (ev_check *, callback)" 4 3279.IP "ev_check_init (ev_check *, callback)" 4
882.IX Item "ev_check_init (ev_check *, callback)" 3280.IX Item "ev_check_init (ev_check *, callback)"
883.PD 3281.PD
884Initialises and configures the prepare or check watcher \- they have no 3282Initialises and configures the prepare or check watcher \- they have no
885parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR 3283parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
886macros, but using them is utterly, utterly and completely pointless. 3284macros, but using them is utterly, utterly, utterly and completely
3285pointless.
3286.PP
3287\fIExamples\fR
3288.IX Subsection "Examples"
3289.PP
3290There are a number of principal ways to embed other event loops or modules
3291into libev. Here are some ideas on how to include libadns into libev
3292(there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could
3293use as a working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR embeds a
3294Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 into the
3295Glib event loop).
3296.PP
3297Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
3298and in a check watcher, destroy them and call into libadns. What follows
3299is pseudo-code only of course. This requires you to either use a low
3300priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as
3301the callbacks for the IO/timeout watchers might not have been called yet.
3302.PP
3303.Vb 2
3304\& static ev_io iow [nfd];
3305\& static ev_timer tw;
3306\&
3307\& static void
3308\& io_cb (struct ev_loop *loop, ev_io *w, int revents)
3309\& {
3310\& }
3311\&
3312\& // create io watchers for each fd and a timer before blocking
3313\& static void
3314\& adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
3315\& {
3316\& int timeout = 3600000;
3317\& struct pollfd fds [nfd];
3318\& // actual code will need to loop here and realloc etc.
3319\& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
3320\&
3321\& /* the callback is illegal, but won\*(Aqt be called as we stop during check */
3322\& ev_timer_init (&tw, 0, timeout * 1e\-3, 0.);
3323\& ev_timer_start (loop, &tw);
3324\&
3325\& // create one ev_io per pollfd
3326\& for (int i = 0; i < nfd; ++i)
3327\& {
3328\& ev_io_init (iow + i, io_cb, fds [i].fd,
3329\& ((fds [i].events & POLLIN ? EV_READ : 0)
3330\& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
3331\&
3332\& fds [i].revents = 0;
3333\& ev_io_start (loop, iow + i);
3334\& }
3335\& }
3336\&
3337\& // stop all watchers after blocking
3338\& static void
3339\& adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
3340\& {
3341\& ev_timer_stop (loop, &tw);
3342\&
3343\& for (int i = 0; i < nfd; ++i)
3344\& {
3345\& // set the relevant poll flags
3346\& // could also call adns_processreadable etc. here
3347\& struct pollfd *fd = fds + i;
3348\& int revents = ev_clear_pending (iow + i);
3349\& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN;
3350\& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT;
3351\&
3352\& // now stop the watcher
3353\& ev_io_stop (loop, iow + i);
3354\& }
3355\&
3356\& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
3357\& }
3358.Ve
3359.PP
3360Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR
3361in the prepare watcher and would dispose of the check watcher.
3362.PP
3363Method 3: If the module to be embedded supports explicit event
3364notification (libadns does), you can also make use of the actual watcher
3365callbacks, and only destroy/create the watchers in the prepare watcher.
3366.PP
3367.Vb 5
3368\& static void
3369\& timer_cb (EV_P_ ev_timer *w, int revents)
3370\& {
3371\& adns_state ads = (adns_state)w\->data;
3372\& update_now (EV_A);
3373\&
3374\& adns_processtimeouts (ads, &tv_now);
3375\& }
3376\&
3377\& static void
3378\& io_cb (EV_P_ ev_io *w, int revents)
3379\& {
3380\& adns_state ads = (adns_state)w\->data;
3381\& update_now (EV_A);
3382\&
3383\& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now);
3384\& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now);
3385\& }
3386\&
3387\& // do not ever call adns_afterpoll
3388.Ve
3389.PP
3390Method 4: Do not use a prepare or check watcher because the module you
3391want to embed is not flexible enough to support it. Instead, you can
3392override their poll function. The drawback with this solution is that the
3393main loop is now no longer controllable by \s-1EV.\s0 The \f(CW\*(C`Glib::EV\*(C'\fR module uses
3394this approach, effectively embedding \s-1EV\s0 as a client into the horrible
3395libglib event loop.
3396.PP
3397.Vb 4
3398\& static gint
3399\& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
3400\& {
3401\& int got_events = 0;
3402\&
3403\& for (n = 0; n < nfds; ++n)
3404\& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
3405\&
3406\& if (timeout >= 0)
3407\& // create/start timer
3408\&
3409\& // poll
3410\& ev_run (EV_A_ 0);
3411\&
3412\& // stop timer again
3413\& if (timeout >= 0)
3414\& ev_timer_stop (EV_A_ &to);
3415\&
3416\& // stop io watchers again \- their callbacks should have set
3417\& for (n = 0; n < nfds; ++n)
3418\& ev_io_stop (EV_A_ iow [n]);
3419\&
3420\& return got_events;
3421\& }
3422.Ve
3423.ie n .SS """ev_embed"" \- when one backend isn't enough..."
3424.el .SS "\f(CWev_embed\fP \- when one backend isn't enough..."
3425.IX Subsection "ev_embed - when one backend isn't enough..."
3426This is a rather advanced watcher type that lets you embed one event loop
3427into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
3428loop, other types of watchers might be handled in a delayed or incorrect
3429fashion and must not be used).
3430.PP
3431There are primarily two reasons you would want that: work around bugs and
3432prioritise I/O.
3433.PP
3434As an example for a bug workaround, the kqueue backend might only support
3435sockets on some platform, so it is unusable as generic backend, but you
3436still want to make use of it because you have many sockets and it scales
3437so nicely. In this case, you would create a kqueue-based loop and embed
3438it into your default loop (which might use e.g. poll). Overall operation
3439will be a bit slower because first libev has to call \f(CW\*(C`poll\*(C'\fR and then
3440\&\f(CW\*(C`kevent\*(C'\fR, but at least you can use both mechanisms for what they are
3441best: \f(CW\*(C`kqueue\*(C'\fR for scalable sockets and \f(CW\*(C`poll\*(C'\fR if you want it to work :)
3442.PP
3443As for prioritising I/O: under rare circumstances you have the case where
3444some fds have to be watched and handled very quickly (with low latency),
3445and even priorities and idle watchers might have too much overhead. In
3446this case you would put all the high priority stuff in one loop and all
3447the rest in a second one, and embed the second one in the first.
3448.PP
3449As long as the watcher is active, the callback will be invoked every
3450time there might be events pending in the embedded loop. The callback
3451must then call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single
3452sweep and invoke their callbacks (the callback doesn't need to invoke the
3453\&\f(CW\*(C`ev_embed_sweep\*(C'\fR function directly, it could also start an idle watcher
3454to give the embedded loop strictly lower priority for example).
3455.PP
3456You can also set the callback to \f(CW0\fR, in which case the embed watcher
3457will automatically execute the embedded loop sweep whenever necessary.
3458.PP
3459Fork detection will be handled transparently while the \f(CW\*(C`ev_embed\*(C'\fR watcher
3460is active, i.e., the embedded loop will automatically be forked when the
3461embedding loop forks. In other cases, the user is responsible for calling
3462\&\f(CW\*(C`ev_loop_fork\*(C'\fR on the embedded loop.
3463.PP
3464Unfortunately, not all backends are embeddable: only the ones returned by
3465\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
3466portable one.
3467.PP
3468So when you want to use this feature you will always have to be prepared
3469that you cannot get an embeddable loop. The recommended way to get around
3470this is to have a separate variables for your embeddable loop, try to
3471create it, and if that fails, use the normal loop for everything.
3472.PP
3473\fI\f(CI\*(C`ev_embed\*(C'\fI and fork\fR
3474.IX Subsection "ev_embed and fork"
3475.PP
3476While the \f(CW\*(C`ev_embed\*(C'\fR watcher is running, forks in the embedding loop will
3477automatically be applied to the embedded loop as well, so no special
3478fork handling is required in that case. When the watcher is not running,
3479however, it is still the task of the libev user to call \f(CW\*(C`ev_loop_fork ()\*(C'\fR
3480as applicable.
3481.PP
3482\fIWatcher-Specific Functions and Data Members\fR
3483.IX Subsection "Watcher-Specific Functions and Data Members"
3484.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
3485.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
3486.PD 0
3487.IP "ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)" 4
3488.IX Item "ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)"
3489.PD
3490Configures the watcher to embed the given loop, which must be
3491embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
3492invoked automatically, otherwise it is the responsibility of the callback
3493to invoke it (it will continue to be called until the sweep has been done,
3494if you do not want that, you need to temporarily stop the embed watcher).
3495.IP "ev_embed_sweep (loop, ev_embed *)" 4
3496.IX Item "ev_embed_sweep (loop, ev_embed *)"
3497Make a single, non-blocking sweep over the embedded loop. This works
3498similarly to \f(CW\*(C`ev_run (embedded_loop, EVRUN_NOWAIT)\*(C'\fR, but in the most
3499appropriate way for embedded loops.
3500.IP "struct ev_loop *other [read\-only]" 4
3501.IX Item "struct ev_loop *other [read-only]"
3502The embedded event loop.
3503.PP
3504\fIExamples\fR
3505.IX Subsection "Examples"
3506.PP
3507Example: Try to get an embeddable event loop and embed it into the default
3508event loop. If that is not possible, use the default loop. The default
3509loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the embeddable loop is stored in
3510\&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the case no embeddable loop can be
3511used).
3512.PP
3513.Vb 3
3514\& struct ev_loop *loop_hi = ev_default_init (0);
3515\& struct ev_loop *loop_lo = 0;
3516\& ev_embed embed;
3517\&
3518\& // see if there is a chance of getting one that works
3519\& // (remember that a flags value of 0 means autodetection)
3520\& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3521\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3522\& : 0;
3523\&
3524\& // if we got one, then embed it, otherwise default to loop_hi
3525\& if (loop_lo)
3526\& {
3527\& ev_embed_init (&embed, 0, loop_lo);
3528\& ev_embed_start (loop_hi, &embed);
3529\& }
3530\& else
3531\& loop_lo = loop_hi;
3532.Ve
3533.PP
3534Example: Check if kqueue is available but not recommended and create
3535a kqueue backend for use with sockets (which usually work with any
3536kqueue implementation). Store the kqueue/socket\-only event loop in
3537\&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too).
3538.PP
3539.Vb 3
3540\& struct ev_loop *loop = ev_default_init (0);
3541\& struct ev_loop *loop_socket = 0;
3542\& ev_embed embed;
3543\&
3544\& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3545\& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3546\& {
3547\& ev_embed_init (&embed, 0, loop_socket);
3548\& ev_embed_start (loop, &embed);
3549\& }
3550\&
3551\& if (!loop_socket)
3552\& loop_socket = loop;
3553\&
3554\& // now use loop_socket for all sockets, and loop for everything else
3555.Ve
3556.ie n .SS """ev_fork"" \- the audacity to resume the event loop after a fork"
3557.el .SS "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
3558.IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
3559Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
3560whoever is a good citizen cared to tell libev about it by calling
3561\&\f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the event loop blocks next
3562and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called, and only in the child
3563after the fork. If whoever good citizen calling \f(CW\*(C`ev_default_fork\*(C'\fR cheats
3564and calls it in the wrong process, the fork handlers will be invoked, too,
3565of course.
3566.PP
3567\fIThe special problem of life after fork \- how is it possible?\fR
3568.IX Subsection "The special problem of life after fork - how is it possible?"
3569.PP
3570Most uses of \f(CW\*(C`fork ()\*(C'\fR consist of forking, then some simple calls to set
3571up/change the process environment, followed by a call to \f(CW\*(C`exec()\*(C'\fR. This
3572sequence should be handled by libev without any problems.
3573.PP
3574This changes when the application actually wants to do event handling
3575in the child, or both parent in child, in effect \*(L"continuing\*(R" after the
3576fork.
3577.PP
3578The default mode of operation (for libev, with application help to detect
3579forks) is to duplicate all the state in the child, as would be expected
3580when \fIeither\fR the parent \fIor\fR the child process continues.
3581.PP
3582When both processes want to continue using libev, then this is usually the
3583wrong result. In that case, usually one process (typically the parent) is
3584supposed to continue with all watchers in place as before, while the other
3585process typically wants to start fresh, i.e. without any active watchers.
3586.PP
3587The cleanest and most efficient way to achieve that with libev is to
3588simply create a new event loop, which of course will be \*(L"empty\*(R", and
3589use that for new watchers. This has the advantage of not touching more
3590memory than necessary, and thus avoiding the copy-on-write, and the
3591disadvantage of having to use multiple event loops (which do not support
3592signal watchers).
3593.PP
3594When this is not possible, or you want to use the default loop for
3595other reasons, then in the process that wants to start \*(L"fresh\*(R", call
3596\&\f(CW\*(C`ev_loop_destroy (EV_DEFAULT)\*(C'\fR followed by \f(CW\*(C`ev_default_loop (...)\*(C'\fR.
3597Destroying the default loop will \*(L"orphan\*(R" (not stop) all registered
3598watchers, so you have to be careful not to execute code that modifies
3599those watchers. Note also that in that case, you have to re-register any
3600signal watchers.
3601.PP
3602\fIWatcher-Specific Functions and Data Members\fR
3603.IX Subsection "Watcher-Specific Functions and Data Members"
3604.IP "ev_fork_init (ev_fork *, callback)" 4
3605.IX Item "ev_fork_init (ev_fork *, callback)"
3606Initialises and configures the fork watcher \- it has no parameters of any
3607kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
3608really.
3609.ie n .SS """ev_cleanup"" \- even the best things end"
3610.el .SS "\f(CWev_cleanup\fP \- even the best things end"
3611.IX Subsection "ev_cleanup - even the best things end"
3612Cleanup watchers are called just before the event loop is being destroyed
3613by a call to \f(CW\*(C`ev_loop_destroy\*(C'\fR.
3614.PP
3615While there is no guarantee that the event loop gets destroyed, cleanup
3616watchers provide a convenient method to install cleanup hooks for your
3617program, worker threads and so on \- you just to make sure to destroy the
3618loop when you want them to be invoked.
3619.PP
3620Cleanup watchers are invoked in the same way as any other watcher. Unlike
3621all other watchers, they do not keep a reference to the event loop (which
3622makes a lot of sense if you think about it). Like all other watchers, you
3623can call libev functions in the callback, except \f(CW\*(C`ev_cleanup_start\*(C'\fR.
3624.PP
3625\fIWatcher-Specific Functions and Data Members\fR
3626.IX Subsection "Watcher-Specific Functions and Data Members"
3627.IP "ev_cleanup_init (ev_cleanup *, callback)" 4
3628.IX Item "ev_cleanup_init (ev_cleanup *, callback)"
3629Initialises and configures the cleanup watcher \- it has no parameters of
3630any kind. There is a \f(CW\*(C`ev_cleanup_set\*(C'\fR macro, but using it is utterly
3631pointless, I assure you.
3632.PP
3633Example: Register an atexit handler to destroy the default loop, so any
3634cleanup functions are called.
3635.PP
3636.Vb 5
3637\& static void
3638\& program_exits (void)
3639\& {
3640\& ev_loop_destroy (EV_DEFAULT_UC);
3641\& }
3642\&
3643\& ...
3644\& atexit (program_exits);
3645.Ve
3646.ie n .SS """ev_async"" \- how to wake up an event loop"
3647.el .SS "\f(CWev_async\fP \- how to wake up an event loop"
3648.IX Subsection "ev_async - how to wake up an event loop"
3649In general, you cannot use an \f(CW\*(C`ev_loop\*(C'\fR from multiple threads or other
3650asynchronous sources such as signal handlers (as opposed to multiple event
3651loops \- those are of course safe to use in different threads).
3652.PP
3653Sometimes, however, you need to wake up an event loop you do not control,
3654for example because it belongs to another thread. This is what \f(CW\*(C`ev_async\*(C'\fR
3655watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you can signal
3656it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal safe.
3657.PP
3658This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals,
3659too, are asynchronous in nature, and signals, too, will be compressed
3660(i.e. the number of callback invocations may be less than the number of
3661\&\f(CW\*(C`ev_async_send\*(C'\fR calls). In fact, you could use signal watchers as a kind
3662of \*(L"global async watchers\*(R" by using a watcher on an otherwise unused
3663signal, and \f(CW\*(C`ev_feed_signal\*(C'\fR to signal this watcher from another thread,
3664even without knowing which loop owns the signal.
3665.PP
3666\fIQueueing\fR
3667.IX Subsection "Queueing"
3668.PP
3669\&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason
3670is that the author does not know of a simple (or any) algorithm for a
3671multiple-writer-single-reader queue that works in all cases and doesn't
3672need elaborate support such as pthreads or unportable memory access
3673semantics.
3674.PP
3675That means that if you want to queue data, you have to provide your own
3676queue. But at least I can tell you how to implement locking around your
3677queue:
3678.IP "queueing from a signal handler context" 4
3679.IX Item "queueing from a signal handler context"
3680To implement race-free queueing, you simply add to the queue in the signal
3681handler but you block the signal handler in the watcher callback. Here is
3682an example that does that for some fictitious \s-1SIGUSR1\s0 handler:
3683.Sp
3684.Vb 1
3685\& static ev_async mysig;
3686\&
3687\& static void
3688\& sigusr1_handler (void)
3689\& {
3690\& sometype data;
3691\&
3692\& // no locking etc.
3693\& queue_put (data);
3694\& ev_async_send (EV_DEFAULT_ &mysig);
3695\& }
3696\&
3697\& static void
3698\& mysig_cb (EV_P_ ev_async *w, int revents)
3699\& {
3700\& sometype data;
3701\& sigset_t block, prev;
3702\&
3703\& sigemptyset (&block);
3704\& sigaddset (&block, SIGUSR1);
3705\& sigprocmask (SIG_BLOCK, &block, &prev);
3706\&
3707\& while (queue_get (&data))
3708\& process (data);
3709\&
3710\& if (sigismember (&prev, SIGUSR1)
3711\& sigprocmask (SIG_UNBLOCK, &block, 0);
3712\& }
3713.Ve
3714.Sp
3715(Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR
3716instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it
3717either...).
3718.IP "queueing from a thread context" 4
3719.IX Item "queueing from a thread context"
3720The strategy for threads is different, as you cannot (easily) block
3721threads but you can easily preempt them, so to queue safely you need to
3722employ a traditional mutex lock, such as in this pthread example:
3723.Sp
3724.Vb 2
3725\& static ev_async mysig;
3726\& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
3727\&
3728\& static void
3729\& otherthread (void)
3730\& {
3731\& // only need to lock the actual queueing operation
3732\& pthread_mutex_lock (&mymutex);
3733\& queue_put (data);
3734\& pthread_mutex_unlock (&mymutex);
3735\&
3736\& ev_async_send (EV_DEFAULT_ &mysig);
3737\& }
3738\&
3739\& static void
3740\& mysig_cb (EV_P_ ev_async *w, int revents)
3741\& {
3742\& pthread_mutex_lock (&mymutex);
3743\&
3744\& while (queue_get (&data))
3745\& process (data);
3746\&
3747\& pthread_mutex_unlock (&mymutex);
3748\& }
3749.Ve
3750.PP
3751\fIWatcher-Specific Functions and Data Members\fR
3752.IX Subsection "Watcher-Specific Functions and Data Members"
3753.IP "ev_async_init (ev_async *, callback)" 4
3754.IX Item "ev_async_init (ev_async *, callback)"
3755Initialises and configures the async watcher \- it has no parameters of any
3756kind. There is a \f(CW\*(C`ev_async_set\*(C'\fR macro, but using it is utterly pointless,
3757trust me.
3758.IP "ev_async_send (loop, ev_async *)" 4
3759.IX Item "ev_async_send (loop, ev_async *)"
3760Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds
3761an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop, and instantly
3762returns.
3763.Sp
3764Unlike \f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do from other threads,
3765signal or similar contexts (see the discussion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the
3766embedding section below on what exactly this means).
3767.Sp
3768Note that, as with other watchers in libev, multiple events might get
3769compressed into a single callback invocation (another way to look at
3770this is that \f(CW\*(C`ev_async\*(C'\fR watchers are level-triggered: they are set on
3771\&\f(CW\*(C`ev_async_send\*(C'\fR, reset when the event loop detects that).
3772.Sp
3773This call incurs the overhead of at most one extra system call per event
3774loop iteration, if the event loop is blocked, and no syscall at all if
3775the event loop (or your program) is processing events. That means that
3776repeated calls are basically free (there is no need to avoid calls for
3777performance reasons) and that the overhead becomes smaller (typically
3778zero) under load.
3779.IP "bool = ev_async_pending (ev_async *)" 4
3780.IX Item "bool = ev_async_pending (ev_async *)"
3781Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the
3782watcher but the event has not yet been processed (or even noted) by the
3783event loop.
3784.Sp
3785\&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When
3786the loop iterates next and checks for the watcher to have become active,
3787it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very
3788quickly check whether invoking the loop might be a good idea.
3789.Sp
3790Not that this does \fInot\fR check whether the watcher itself is pending,
3791only whether it has been requested to make this watcher pending: there
3792is a time window between the event loop checking and resetting the async
3793notification, and the callback being invoked.
887.SH "OTHER FUNCTIONS" 3794.SH "OTHER FUNCTIONS"
888.IX Header "OTHER FUNCTIONS" 3795.IX Header "OTHER FUNCTIONS"
889There are some other functions of possible interest. Described. Here. Now. 3796There are some other functions of possible interest. Described. Here. Now.
890.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4 3797.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)" 4
891.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 3798.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback, arg)"
892This function combines a simple timer and an I/O watcher, calls your 3799This function combines a simple timer and an I/O watcher, calls your
893callback on whichever event happens first and automatically stop both 3800callback on whichever event happens first and automatically stops both
894watchers. This is useful if you want to wait for a single event on an fd 3801watchers. This is useful if you want to wait for a single event on an fd
895or timeout without having to allocate/configure/start/stop/free one or 3802or timeout without having to allocate/configure/start/stop/free one or
896more watchers yourself. 3803more watchers yourself.
897.Sp 3804.Sp
898If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and events 3805If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and the
899is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for the given \f(CW\*(C`fd\*(C'\fR and 3806\&\f(CW\*(C`events\*(C'\fR argument is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for
900\&\f(CW\*(C`events\*(C'\fR set will be craeted and started. 3807the given \f(CW\*(C`fd\*(C'\fR and \f(CW\*(C`events\*(C'\fR set will be created and started.
901.Sp 3808.Sp
902If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be 3809If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
903started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and 3810started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
904repeat = 0) will be started. While \f(CW0\fR is a valid timeout, it is of 3811repeat = 0) will be started. \f(CW0\fR is a valid timeout.
905dubious value.
906.Sp 3812.Sp
907The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets 3813The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and is
908passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of 3814passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
909\&\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 3815\&\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
910value passed to \f(CW\*(C`ev_once\*(C'\fR: 3816value passed to \f(CW\*(C`ev_once\*(C'\fR. Note that it is possible to receive \fIboth\fR
3817a timeout and an io event at the same time \- you probably should give io
3818events precedence.
3819.Sp
3820Example: wait up to ten seconds for data to appear on \s-1STDIN_FILENO.\s0
911.Sp 3821.Sp
912.Vb 7 3822.Vb 7
913\& static void stdin_ready (int revents, void *arg) 3823\& static void stdin_ready (int revents, void *arg)
914\& { 3824\& {
915\& if (revents & EV_TIMEOUT)
916\& /* doh, nothing entered */;
917\& else if (revents & EV_READ) 3825\& if (revents & EV_READ)
918\& /* stdin might have data for us, joy! */; 3826\& /* stdin might have data for us, joy! */;
3827\& else if (revents & EV_TIMER)
3828\& /* doh, nothing entered */;
919\& } 3829\& }
920.Ve 3830\&
921.Sp
922.Vb 1
923\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); 3831\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
924.Ve 3832.Ve
925.IP "ev_feed_event (loop, watcher, int events)" 4
926.IX Item "ev_feed_event (loop, watcher, int events)"
927Feeds the given event set into the event loop, as if the specified event
928had happened for the specified watcher (which must be a pointer to an
929initialised but not necessarily started event watcher).
930.IP "ev_feed_fd_event (loop, int fd, int revents)" 4 3833.IP "ev_feed_fd_event (loop, int fd, int revents)" 4
931.IX Item "ev_feed_fd_event (loop, int fd, int revents)" 3834.IX Item "ev_feed_fd_event (loop, int fd, int revents)"
932Feed an event on the given fd, as if a file descriptor backend detected 3835Feed an event on the given fd, as if a file descriptor backend detected
933the given events it. 3836the given events.
934.IP "ev_feed_signal_event (loop, int signum)" 4 3837.IP "ev_feed_signal_event (loop, int signum)" 4
935.IX Item "ev_feed_signal_event (loop, int signum)" 3838.IX Item "ev_feed_signal_event (loop, int signum)"
936Feed an event as if the given signal occured (loop must be the default loop!). 3839Feed an event as if the given signal occurred. See also \f(CW\*(C`ev_feed_signal\*(C'\fR,
3840which is async-safe.
3841.SH "COMMON OR USEFUL IDIOMS (OR BOTH)"
3842.IX Header "COMMON OR USEFUL IDIOMS (OR BOTH)"
3843This section explains some common idioms that are not immediately
3844obvious. Note that examples are sprinkled over the whole manual, and this
3845section only contains stuff that wouldn't fit anywhere else.
3846.SS "\s-1ASSOCIATING CUSTOM DATA WITH A WATCHER\s0"
3847.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
3848Each watcher has, by default, a \f(CW\*(C`void *data\*(C'\fR member that you can read
3849or modify at any time: libev will completely ignore it. This can be used
3850to associate arbitrary data with your watcher. If you need more data and
3851don't want to allocate memory separately and store a pointer to it in that
3852data member, you can also \*(L"subclass\*(R" the watcher type and provide your own
3853data:
3854.PP
3855.Vb 7
3856\& struct my_io
3857\& {
3858\& ev_io io;
3859\& int otherfd;
3860\& void *somedata;
3861\& struct whatever *mostinteresting;
3862\& };
3863\&
3864\& ...
3865\& struct my_io w;
3866\& ev_io_init (&w.io, my_cb, fd, EV_READ);
3867.Ve
3868.PP
3869And since your callback will be called with a pointer to the watcher, you
3870can cast it back to your own type:
3871.PP
3872.Vb 5
3873\& static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
3874\& {
3875\& struct my_io *w = (struct my_io *)w_;
3876\& ...
3877\& }
3878.Ve
3879.PP
3880More interesting and less C\-conformant ways of casting your callback
3881function type instead have been omitted.
3882.SS "\s-1BUILDING YOUR OWN COMPOSITE WATCHERS\s0"
3883.IX Subsection "BUILDING YOUR OWN COMPOSITE WATCHERS"
3884Another common scenario is to use some data structure with multiple
3885embedded watchers, in effect creating your own watcher that combines
3886multiple libev event sources into one \*(L"super-watcher\*(R":
3887.PP
3888.Vb 6
3889\& struct my_biggy
3890\& {
3891\& int some_data;
3892\& ev_timer t1;
3893\& ev_timer t2;
3894\& }
3895.Ve
3896.PP
3897In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more
3898complicated: Either you store the address of your \f(CW\*(C`my_biggy\*(C'\fR struct in
3899the \f(CW\*(C`data\*(C'\fR member of the watcher (for woozies or \*(C+ coders), or you need
3900to use some pointer arithmetic using \f(CW\*(C`offsetof\*(C'\fR inside your watchers (for
3901real programmers):
3902.PP
3903.Vb 1
3904\& #include <stddef.h>
3905\&
3906\& static void
3907\& t1_cb (EV_P_ ev_timer *w, int revents)
3908\& {
3909\& struct my_biggy big = (struct my_biggy *)
3910\& (((char *)w) \- offsetof (struct my_biggy, t1));
3911\& }
3912\&
3913\& static void
3914\& t2_cb (EV_P_ ev_timer *w, int revents)
3915\& {
3916\& struct my_biggy big = (struct my_biggy *)
3917\& (((char *)w) \- offsetof (struct my_biggy, t2));
3918\& }
3919.Ve
3920.SS "\s-1AVOIDING FINISHING BEFORE RETURNING\s0"
3921.IX Subsection "AVOIDING FINISHING BEFORE RETURNING"
3922Often you have structures like this in event-based programs:
3923.PP
3924.Vb 4
3925\& callback ()
3926\& {
3927\& free (request);
3928\& }
3929\&
3930\& request = start_new_request (..., callback);
3931.Ve
3932.PP
3933The intent is to start some \*(L"lengthy\*(R" operation. The \f(CW\*(C`request\*(C'\fR could be
3934used to cancel the operation, or do other things with it.
3935.PP
3936It's not uncommon to have code paths in \f(CW\*(C`start_new_request\*(C'\fR that
3937immediately invoke the callback, for example, to report errors. Or you add
3938some caching layer that finds that it can skip the lengthy aspects of the
3939operation and simply invoke the callback with the result.
3940.PP
3941The problem here is that this will happen \fIbefore\fR \f(CW\*(C`start_new_request\*(C'\fR
3942has returned, so \f(CW\*(C`request\*(C'\fR is not set.
3943.PP
3944Even if you pass the request by some safer means to the callback, you
3945might want to do something to the request after starting it, such as
3946canceling it, which probably isn't working so well when the callback has
3947already been invoked.
3948.PP
3949A common way around all these issues is to make sure that
3950\&\f(CW\*(C`start_new_request\*(C'\fR \fIalways\fR returns before the callback is invoked. If
3951\&\f(CW\*(C`start_new_request\*(C'\fR immediately knows the result, it can artificially
3952delay invoking the callback by using a \f(CW\*(C`prepare\*(C'\fR or \f(CW\*(C`idle\*(C'\fR watcher for
3953example, or more sneakily, by reusing an existing (stopped) watcher and
3954pushing it into the pending queue:
3955.PP
3956.Vb 2
3957\& ev_set_cb (watcher, callback);
3958\& ev_feed_event (EV_A_ watcher, 0);
3959.Ve
3960.PP
3961This way, \f(CW\*(C`start_new_request\*(C'\fR can safely return before the callback is
3962invoked, while not delaying callback invocation too much.
3963.SS "\s-1MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS\s0"
3964.IX Subsection "MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS"
3965Often (especially in \s-1GUI\s0 toolkits) there are places where you have
3966\&\fImodal\fR interaction, which is most easily implemented by recursively
3967invoking \f(CW\*(C`ev_run\*(C'\fR.
3968.PP
3969This brings the problem of exiting \- a callback might want to finish the
3970main \f(CW\*(C`ev_run\*(C'\fR call, but not the nested one (e.g. user clicked \*(L"Quit\*(R", but
3971a modal \*(L"Are you sure?\*(R" dialog is still waiting), or just the nested one
3972and not the main one (e.g. user clocked \*(L"Ok\*(R" in a modal dialog), or some
3973other combination: In these cases, a simple \f(CW\*(C`ev_break\*(C'\fR will not work.
3974.PP
3975The solution is to maintain \*(L"break this loop\*(R" variable for each \f(CW\*(C`ev_run\*(C'\fR
3976invocation, and use a loop around \f(CW\*(C`ev_run\*(C'\fR until the condition is
3977triggered, using \f(CW\*(C`EVRUN_ONCE\*(C'\fR:
3978.PP
3979.Vb 2
3980\& // main loop
3981\& int exit_main_loop = 0;
3982\&
3983\& while (!exit_main_loop)
3984\& ev_run (EV_DEFAULT_ EVRUN_ONCE);
3985\&
3986\& // in a modal watcher
3987\& int exit_nested_loop = 0;
3988\&
3989\& while (!exit_nested_loop)
3990\& ev_run (EV_A_ EVRUN_ONCE);
3991.Ve
3992.PP
3993To exit from any of these loops, just set the corresponding exit variable:
3994.PP
3995.Vb 2
3996\& // exit modal loop
3997\& exit_nested_loop = 1;
3998\&
3999\& // exit main program, after modal loop is finished
4000\& exit_main_loop = 1;
4001\&
4002\& // exit both
4003\& exit_main_loop = exit_nested_loop = 1;
4004.Ve
4005.SS "\s-1THREAD LOCKING EXAMPLE\s0"
4006.IX Subsection "THREAD LOCKING EXAMPLE"
4007Here is a fictitious example of how to run an event loop in a different
4008thread from where callbacks are being invoked and watchers are
4009created/added/removed.
4010.PP
4011For a real-world example, see the \f(CW\*(C`EV::Loop::Async\*(C'\fR perl module,
4012which uses exactly this technique (which is suited for many high-level
4013languages).
4014.PP
4015The example uses a pthread mutex to protect the loop data, a condition
4016variable to wait for callback invocations, an async watcher to notify the
4017event loop thread and an unspecified mechanism to wake up the main thread.
4018.PP
4019First, you need to associate some data with the event loop:
4020.PP
4021.Vb 6
4022\& typedef struct {
4023\& pthread_mutex_t lock; /* global loop lock */
4024\& pthread_t tid;
4025\& pthread_cond_t invoke_cv;
4026\& ev_async async_w;
4027\& } userdata;
4028\&
4029\& void prepare_loop (EV_P)
4030\& {
4031\& // for simplicity, we use a static userdata struct.
4032\& static userdata u;
4033\&
4034\& ev_async_init (&u.async_w, async_cb);
4035\& ev_async_start (EV_A_ &u.async_w);
4036\&
4037\& pthread_mutex_init (&u.lock, 0);
4038\& pthread_cond_init (&u.invoke_cv, 0);
4039\&
4040\& // now associate this with the loop
4041\& ev_set_userdata (EV_A_ &u);
4042\& ev_set_invoke_pending_cb (EV_A_ l_invoke);
4043\& ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4044\&
4045\& // then create the thread running ev_run
4046\& pthread_create (&u.tid, 0, l_run, EV_A);
4047\& }
4048.Ve
4049.PP
4050The callback for the \f(CW\*(C`ev_async\*(C'\fR watcher does nothing: the watcher is used
4051solely to wake up the event loop so it takes notice of any new watchers
4052that might have been added:
4053.PP
4054.Vb 5
4055\& static void
4056\& async_cb (EV_P_ ev_async *w, int revents)
4057\& {
4058\& // just used for the side effects
4059\& }
4060.Ve
4061.PP
4062The \f(CW\*(C`l_release\*(C'\fR and \f(CW\*(C`l_acquire\*(C'\fR callbacks simply unlock/lock the mutex
4063protecting the loop data, respectively.
4064.PP
4065.Vb 6
4066\& static void
4067\& l_release (EV_P)
4068\& {
4069\& userdata *u = ev_userdata (EV_A);
4070\& pthread_mutex_unlock (&u\->lock);
4071\& }
4072\&
4073\& static void
4074\& l_acquire (EV_P)
4075\& {
4076\& userdata *u = ev_userdata (EV_A);
4077\& pthread_mutex_lock (&u\->lock);
4078\& }
4079.Ve
4080.PP
4081The event loop thread first acquires the mutex, and then jumps straight
4082into \f(CW\*(C`ev_run\*(C'\fR:
4083.PP
4084.Vb 4
4085\& void *
4086\& l_run (void *thr_arg)
4087\& {
4088\& struct ev_loop *loop = (struct ev_loop *)thr_arg;
4089\&
4090\& l_acquire (EV_A);
4091\& pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4092\& ev_run (EV_A_ 0);
4093\& l_release (EV_A);
4094\&
4095\& return 0;
4096\& }
4097.Ve
4098.PP
4099Instead of invoking all pending watchers, the \f(CW\*(C`l_invoke\*(C'\fR callback will
4100signal the main thread via some unspecified mechanism (signals? pipe
4101writes? \f(CW\*(C`Async::Interrupt\*(C'\fR?) and then waits until all pending watchers
4102have been called (in a while loop because a) spurious wakeups are possible
4103and b) skipping inter-thread-communication when there are no pending
4104watchers is very beneficial):
4105.PP
4106.Vb 4
4107\& static void
4108\& l_invoke (EV_P)
4109\& {
4110\& userdata *u = ev_userdata (EV_A);
4111\&
4112\& while (ev_pending_count (EV_A))
4113\& {
4114\& wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4115\& pthread_cond_wait (&u\->invoke_cv, &u\->lock);
4116\& }
4117\& }
4118.Ve
4119.PP
4120Now, whenever the main thread gets told to invoke pending watchers, it
4121will grab the lock, call \f(CW\*(C`ev_invoke_pending\*(C'\fR and then signal the loop
4122thread to continue:
4123.PP
4124.Vb 4
4125\& static void
4126\& real_invoke_pending (EV_P)
4127\& {
4128\& userdata *u = ev_userdata (EV_A);
4129\&
4130\& pthread_mutex_lock (&u\->lock);
4131\& ev_invoke_pending (EV_A);
4132\& pthread_cond_signal (&u\->invoke_cv);
4133\& pthread_mutex_unlock (&u\->lock);
4134\& }
4135.Ve
4136.PP
4137Whenever you want to start/stop a watcher or do other modifications to an
4138event loop, you will now have to lock:
4139.PP
4140.Vb 2
4141\& ev_timer timeout_watcher;
4142\& userdata *u = ev_userdata (EV_A);
4143\&
4144\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4145\&
4146\& pthread_mutex_lock (&u\->lock);
4147\& ev_timer_start (EV_A_ &timeout_watcher);
4148\& ev_async_send (EV_A_ &u\->async_w);
4149\& pthread_mutex_unlock (&u\->lock);
4150.Ve
4151.PP
4152Note that sending the \f(CW\*(C`ev_async\*(C'\fR watcher is required because otherwise
4153an event loop currently blocking in the kernel will have no knowledge
4154about the newly added timer. By waking up the loop it will pick up any new
4155watchers in the next event loop iteration.
4156.SS "\s-1THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS\s0"
4157.IX Subsection "THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS"
4158While the overhead of a callback that e.g. schedules a thread is small, it
4159is still an overhead. If you embed libev, and your main usage is with some
4160kind of threads or coroutines, you might want to customise libev so that
4161doesn't need callbacks anymore.
4162.PP
4163Imagine you have coroutines that you can switch to using a function
4164\&\f(CW\*(C`switch_to (coro)\*(C'\fR, that libev runs in a coroutine called \f(CW\*(C`libev_coro\*(C'\fR
4165and that due to some magic, the currently active coroutine is stored in a
4166global called \f(CW\*(C`current_coro\*(C'\fR. Then you can build your own \*(L"wait for libev
4167event\*(R" primitive by changing \f(CW\*(C`EV_CB_DECLARE\*(C'\fR and \f(CW\*(C`EV_CB_INVOKE\*(C'\fR (note
4168the differing \f(CW\*(C`;\*(C'\fR conventions):
4169.PP
4170.Vb 2
4171\& #define EV_CB_DECLARE(type) struct my_coro *cb;
4172\& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb)
4173.Ve
4174.PP
4175That means instead of having a C callback function, you store the
4176coroutine to switch to in each watcher, and instead of having libev call
4177your callback, you instead have it switch to that coroutine.
4178.PP
4179A coroutine might now wait for an event with a function called
4180\&\f(CW\*(C`wait_for_event\*(C'\fR. (the watcher needs to be started, as always, but it doesn't
4181matter when, or whether the watcher is active or not when this function is
4182called):
4183.PP
4184.Vb 6
4185\& void
4186\& wait_for_event (ev_watcher *w)
4187\& {
4188\& ev_set_cb (w, current_coro);
4189\& switch_to (libev_coro);
4190\& }
4191.Ve
4192.PP
4193That basically suspends the coroutine inside \f(CW\*(C`wait_for_event\*(C'\fR and
4194continues the libev coroutine, which, when appropriate, switches back to
4195this or any other coroutine.
4196.PP
4197You can do similar tricks if you have, say, threads with an event queue \-
4198instead of storing a coroutine, you store the queue object and instead of
4199switching to a coroutine, you push the watcher onto the queue and notify
4200any waiters.
4201.PP
4202To embed libev, see \*(L"\s-1EMBEDDING\*(R"\s0, but in short, it's easiest to create two
4203files, \fImy_ev.h\fR and \fImy_ev.c\fR that include the respective libev files:
4204.PP
4205.Vb 4
4206\& // my_ev.h
4207\& #define EV_CB_DECLARE(type) struct my_coro *cb;
4208\& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb)
4209\& #include "../libev/ev.h"
4210\&
4211\& // my_ev.c
4212\& #define EV_H "my_ev.h"
4213\& #include "../libev/ev.c"
4214.Ve
4215.PP
4216And then use \fImy_ev.h\fR when you would normally use \fIev.h\fR, and compile
4217\&\fImy_ev.c\fR into your project. When properly specifying include paths, you
4218can even use \fIev.h\fR as header file name directly.
937.SH "LIBEVENT EMULATION" 4219.SH "LIBEVENT EMULATION"
938.IX Header "LIBEVENT EMULATION" 4220.IX Header "LIBEVENT EMULATION"
939Libev offers a compatibility emulation layer for libevent. It cannot 4221Libev offers a compatibility emulation layer for libevent. It cannot
940emulate the internals of libevent, so here are some usage hints: 4222emulate the internals of libevent, so here are some usage hints:
4223.IP "\(bu" 4
4224Only the libevent\-1.4.1\-beta \s-1API\s0 is being emulated.
4225.Sp
4226This was the newest libevent version available when libev was implemented,
4227and is still mostly unchanged in 2010.
4228.IP "\(bu" 4
941.IP "* Use it by including <event.h>, as usual." 4 4229Use it by including <event.h>, as usual.
942.IX Item "Use it by including <event.h>, as usual." 4230.IP "\(bu" 4
943.PD 0 4231The following members are fully supported: ev_base, ev_callback,
944.IP "* The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4 4232ev_arg, ev_fd, ev_res, ev_events.
945.IX Item "The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4233.IP "\(bu" 4
946.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 4234Avoid using ev_flags and the EVLIST_*\-macros, while it is
947.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)." 4235maintained by libev, it does not work exactly the same way as in libevent (consider
948.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 4236it a private \s-1API\s0).
949.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." 4237.IP "\(bu" 4
4238Priorities are not currently supported. Initialising priorities
4239will fail and all watchers will have the same priority, even though there
4240is an ev_pri field.
4241.IP "\(bu" 4
4242In libevent, the last base created gets the signals, in libev, the
4243base that registered the signal gets the signals.
4244.IP "\(bu" 4
950.IP "* Other members are not supported." 4 4245Other members are not supported.
951.IX Item "Other members are not supported." 4246.IP "\(bu" 4
952.IP "* The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need to use the libev header file and library." 4 4247The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need
953.IX Item "The libev emulation is not ABI compatible to libevent, you need to use the libev header file and library." 4248to use the libev header file and library.
954.PD
955.SH "\*(C+ SUPPORT" 4249.SH "\*(C+ SUPPORT"
956.IX Header " SUPPORT" 4250.IX Header " SUPPORT"
957\&\s-1TBD\s0. 4251.SS "C \s-1API\s0"
4252.IX Subsection "C API"
4253The normal C \s-1API\s0 should work fine when used from \*(C+: both ev.h and the
4254libev sources can be compiled as \*(C+. Therefore, code that uses the C \s-1API\s0
4255will work fine.
4256.PP
4257Proper exception specifications might have to be added to callbacks passed
4258to libev: exceptions may be thrown only from watcher callbacks, all other
4259callbacks (allocator, syserr, loop acquire/release and periodic reschedule
4260callbacks) must not throw exceptions, and might need a \f(CW\*(C`noexcept\*(C'\fR
4261specification. If you have code that needs to be compiled as both C and
4262\&\*(C+ you can use the \f(CW\*(C`EV_NOEXCEPT\*(C'\fR macro for this:
4263.PP
4264.Vb 6
4265\& static void
4266\& fatal_error (const char *msg) EV_NOEXCEPT
4267\& {
4268\& perror (msg);
4269\& abort ();
4270\& }
4271\&
4272\& ...
4273\& ev_set_syserr_cb (fatal_error);
4274.Ve
4275.PP
4276The only \s-1API\s0 functions that can currently throw exceptions are \f(CW\*(C`ev_run\*(C'\fR,
4277\&\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
4278because it runs cleanup watchers).
4279.PP
4280Throwing exceptions in watcher callbacks is only supported if libev itself
4281is compiled with a \*(C+ compiler or your C and \*(C+ environments allow
4282throwing exceptions through C libraries (most do).
4283.SS "\*(C+ \s-1API\s0"
4284.IX Subsection " API"
4285Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
4286you to use some convenience methods to start/stop watchers and also change
4287the callback model to a model using method callbacks on objects.
4288.PP
4289To use it,
4290.PP
4291.Vb 1
4292\& #include <ev++.h>
4293.Ve
4294.PP
4295This automatically includes \fIev.h\fR and puts all of its definitions (many
4296of them macros) into the global namespace. All \*(C+ specific things are
4297put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding
4298options as \fIev.h\fR, most notably \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR.
4299.PP
4300Care has been taken to keep the overhead low. The only data member the \*(C+
4301classes add (compared to plain C\-style watchers) is the event loop pointer
4302that the watcher is associated with (or no additional members at all if
4303you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
4304.PP
4305Currently, functions, static and non-static member functions and classes
4306with \f(CW\*(C`operator ()\*(C'\fR can be used as callbacks. Other types should be easy
4307to add as long as they only need one additional pointer for context. If
4308you need support for other types of functors please contact the author
4309(preferably after implementing it).
4310.PP
4311For all this to work, your \*(C+ compiler either has to use the same calling
4312conventions as your C compiler (for static member functions), or you have
4313to embed libev and compile libev itself as \*(C+.
4314.PP
4315Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
4316.ie n .IP """ev::READ"", ""ev::WRITE"" etc." 4
4317.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
4318.IX Item "ev::READ, ev::WRITE etc."
4319These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
4320macros from \fIev.h\fR.
4321.ie n .IP """ev::tstamp"", ""ev::now""" 4
4322.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
4323.IX Item "ev::tstamp, ev::now"
4324Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
4325.ie n .IP """ev::io"", ""ev::timer"", ""ev::periodic"", ""ev::idle"", ""ev::sig"" etc." 4
4326.el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
4327.IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
4328For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
4329the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
4330which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
4331defined by many implementations.
4332.Sp
4333All of those classes have these methods:
4334.RS 4
4335.IP "ev::TYPE::TYPE ()" 4
4336.IX Item "ev::TYPE::TYPE ()"
4337.PD 0
4338.IP "ev::TYPE::TYPE (loop)" 4
4339.IX Item "ev::TYPE::TYPE (loop)"
4340.IP "ev::TYPE::~TYPE" 4
4341.IX Item "ev::TYPE::~TYPE"
4342.PD
4343The constructor (optionally) takes an event loop to associate the watcher
4344with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR.
4345.Sp
4346The constructor calls \f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the
4347\&\f(CW\*(C`set\*(C'\fR method before starting it.
4348.Sp
4349It will not set a callback, however: You have to call the templated \f(CW\*(C`set\*(C'\fR
4350method to set a callback before you can start the watcher.
4351.Sp
4352(The reason why you have to use a method is a limitation in \*(C+ which does
4353not allow explicit template arguments for constructors).
4354.Sp
4355The destructor automatically stops the watcher if it is active.
4356.IP "w\->set<class, &class::method> (object *)" 4
4357.IX Item "w->set<class, &class::method> (object *)"
4358This method sets the callback method to call. The method has to have a
4359signature of \f(CW\*(C`void (*)(ev_TYPE &, int)\*(C'\fR, it receives the watcher as
4360first argument and the \f(CW\*(C`revents\*(C'\fR as second. The object must be given as
4361parameter and is stored in the \f(CW\*(C`data\*(C'\fR member of the watcher.
4362.Sp
4363This method synthesizes efficient thunking code to call your method from
4364the C callback that libev requires. If your compiler can inline your
4365callback (i.e. it is visible to it at the place of the \f(CW\*(C`set\*(C'\fR call and
4366your compiler is good :), then the method will be fully inlined into the
4367thunking function, making it as fast as a direct C callback.
4368.Sp
4369Example: simple class declaration and watcher initialisation
4370.Sp
4371.Vb 4
4372\& struct myclass
4373\& {
4374\& void io_cb (ev::io &w, int revents) { }
4375\& }
4376\&
4377\& myclass obj;
4378\& ev::io iow;
4379\& iow.set <myclass, &myclass::io_cb> (&obj);
4380.Ve
4381.IP "w\->set (object *)" 4
4382.IX Item "w->set (object *)"
4383This is a variation of a method callback \- leaving out the method to call
4384will default the method to \f(CW\*(C`operator ()\*(C'\fR, which makes it possible to use
4385functor objects without having to manually specify the \f(CW\*(C`operator ()\*(C'\fR all
4386the time. Incidentally, you can then also leave out the template argument
4387list.
4388.Sp
4389The \f(CW\*(C`operator ()\*(C'\fR method prototype must be \f(CW\*(C`void operator ()(watcher &w,
4390int revents)\*(C'\fR.
4391.Sp
4392See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
4393.Sp
4394Example: use a functor object as callback.
4395.Sp
4396.Vb 7
4397\& struct myfunctor
4398\& {
4399\& void operator() (ev::io &w, int revents)
4400\& {
4401\& ...
4402\& }
4403\& }
4404\&
4405\& myfunctor f;
4406\&
4407\& ev::io w;
4408\& w.set (&f);
4409.Ve
4410.IP "w\->set<function> (void *data = 0)" 4
4411.IX Item "w->set<function> (void *data = 0)"
4412Also sets a callback, but uses a static method or plain function as
4413callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
4414\&\f(CW\*(C`data\*(C'\fR member and is free for you to use.
4415.Sp
4416The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
4417.Sp
4418See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
4419.Sp
4420Example: Use a plain function as callback.
4421.Sp
4422.Vb 2
4423\& static void io_cb (ev::io &w, int revents) { }
4424\& iow.set <io_cb> ();
4425.Ve
4426.IP "w\->set (loop)" 4
4427.IX Item "w->set (loop)"
4428Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
4429do this when the watcher is inactive (and not pending either).
4430.IP "w\->set ([arguments])" 4
4431.IX Item "w->set ([arguments])"
4432Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR (except for \f(CW\*(C`ev::embed\*(C'\fR watchers>),
4433with the same arguments. Either this method or a suitable start method
4434must be called at least once. Unlike the C counterpart, an active watcher
4435gets automatically stopped and restarted when reconfiguring it with this
4436method.
4437.Sp
4438For \f(CW\*(C`ev::embed\*(C'\fR watchers this method is called \f(CW\*(C`set_embed\*(C'\fR, to avoid
4439clashing with the \f(CW\*(C`set (loop)\*(C'\fR method.
4440.Sp
4441For \f(CW\*(C`ev::io\*(C'\fR watchers there is an additional \f(CW\*(C`set\*(C'\fR method that acepts a
4442new event mask only, and internally calls \f(CW\*(C`ev_io_modify\*(C'\fR.
4443.IP "w\->start ()" 4
4444.IX Item "w->start ()"
4445Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
4446constructor already stores the event loop.
4447.IP "w\->start ([arguments])" 4
4448.IX Item "w->start ([arguments])"
4449Instead of calling \f(CW\*(C`set\*(C'\fR and \f(CW\*(C`start\*(C'\fR methods separately, it is often
4450convenient to wrap them in one call. Uses the same type of arguments as
4451the configure \f(CW\*(C`set\*(C'\fR method of the watcher.
4452.IP "w\->stop ()" 4
4453.IX Item "w->stop ()"
4454Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
4455.ie n .IP "w\->again () (""ev::timer"", ""ev::periodic"" only)" 4
4456.el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
4457.IX Item "w->again () (ev::timer, ev::periodic only)"
4458For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
4459\&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
4460.ie n .IP "w\->sweep () (""ev::embed"" only)" 4
4461.el .IP "w\->sweep () (\f(CWev::embed\fR only)" 4
4462.IX Item "w->sweep () (ev::embed only)"
4463Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR.
4464.ie n .IP "w\->update () (""ev::stat"" only)" 4
4465.el .IP "w\->update () (\f(CWev::stat\fR only)" 4
4466.IX Item "w->update () (ev::stat only)"
4467Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
4468.RE
4469.RS 4
4470.RE
4471.PP
4472Example: Define a class with two I/O and idle watchers, start the I/O
4473watchers in the constructor.
4474.PP
4475.Vb 5
4476\& class myclass
4477\& {
4478\& ev::io io ; void io_cb (ev::io &w, int revents);
4479\& ev::io io2 ; void io2_cb (ev::io &w, int revents);
4480\& ev::idle idle; void idle_cb (ev::idle &w, int revents);
4481\&
4482\& myclass (int fd)
4483\& {
4484\& io .set <myclass, &myclass::io_cb > (this);
4485\& io2 .set <myclass, &myclass::io2_cb > (this);
4486\& idle.set <myclass, &myclass::idle_cb> (this);
4487\&
4488\& io.set (fd, ev::WRITE); // configure the watcher
4489\& io.start (); // start it whenever convenient
4490\&
4491\& io2.start (fd, ev::READ); // set + start in one call
4492\& }
4493\& };
4494.Ve
4495.SH "OTHER LANGUAGE BINDINGS"
4496.IX Header "OTHER LANGUAGE BINDINGS"
4497Libev does not offer other language bindings itself, but bindings for a
4498number of languages exist in the form of third-party packages. If you know
4499any interesting language binding in addition to the ones listed here, drop
4500me a note.
4501.IP "Perl" 4
4502.IX Item "Perl"
4503The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test
4504libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module,
4505there are additional modules that implement libev-compatible interfaces
4506to \f(CW\*(C`libadns\*(C'\fR (\f(CW\*(C`EV::ADNS\*(C'\fR, but \f(CW\*(C`AnyEvent::DNS\*(C'\fR is preferred nowadays),
4507\&\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
4508and \f(CW\*(C`EV::Glib\*(C'\fR).
4509.Sp
4510It can be found and installed via \s-1CPAN,\s0 its homepage is at
4511<http://software.schmorp.de/pkg/EV>.
4512.IP "Python" 4
4513.IX Item "Python"
4514Python bindings can be found at <http://code.google.com/p/pyev/>. It
4515seems to be quite complete and well-documented.
4516.IP "Ruby" 4
4517.IX Item "Ruby"
4518Tony Arcieri has written a ruby extension that offers access to a subset
4519of the libev \s-1API\s0 and adds file handle abstractions, asynchronous \s-1DNS\s0 and
4520more on top of it. It can be found via gem servers. Its homepage is at
4521<http://rev.rubyforge.org/>.
4522.Sp
4523Roger Pack reports that using the link order \f(CW\*(C`\-lws2_32 \-lmsvcrt\-ruby\-190\*(C'\fR
4524makes rev work even on mingw.
4525.IP "Haskell" 4
4526.IX Item "Haskell"
4527A haskell binding to libev is available at
4528<http://hackage.haskell.org/cgi\-bin/hackage\-scripts/package/hlibev>.
4529.IP "D" 4
4530.IX Item "D"
4531Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
4532be found at <http://www.llucax.com.ar/proj/ev.d/index.html>.
4533.IP "Ocaml" 4
4534.IX Item "Ocaml"
4535Erkki Seppala has written Ocaml bindings for libev, to be found at
4536<http://modeemi.cs.tut.fi/~flux/software/ocaml\-ev/>.
4537.IP "Lua" 4
4538.IX Item "Lua"
4539Brian Maher has written a partial interface to libev for lua (at the
4540time of this writing, only \f(CW\*(C`ev_io\*(C'\fR and \f(CW\*(C`ev_timer\*(C'\fR), to be found at
4541<http://github.com/brimworks/lua\-ev>.
4542.IP "Javascript" 4
4543.IX Item "Javascript"
4544Node.js (<http://nodejs.org>) uses libev as the underlying event library.
4545.IP "Others" 4
4546.IX Item "Others"
4547There are others, and I stopped counting.
4548.SH "MACRO MAGIC"
4549.IX Header "MACRO MAGIC"
4550Libev can be compiled with a variety of options, the most fundamental
4551of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most)
4552functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
4553.PP
4554To make it easier to write programs that cope with either variant, the
4555following macros are defined:
4556.ie n .IP """EV_A"", ""EV_A_""" 4
4557.el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
4558.IX Item "EV_A, EV_A_"
4559This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
4560loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
4561\&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
4562.Sp
4563.Vb 3
4564\& ev_unref (EV_A);
4565\& ev_timer_add (EV_A_ watcher);
4566\& ev_run (EV_A_ 0);
4567.Ve
4568.Sp
4569It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
4570which is often provided by the following macro.
4571.ie n .IP """EV_P"", ""EV_P_""" 4
4572.el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
4573.IX Item "EV_P, EV_P_"
4574This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
4575loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
4576\&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
4577.Sp
4578.Vb 2
4579\& // this is how ev_unref is being declared
4580\& static void ev_unref (EV_P);
4581\&
4582\& // this is how you can declare your typical callback
4583\& static void cb (EV_P_ ev_timer *w, int revents)
4584.Ve
4585.Sp
4586It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
4587suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
4588.ie n .IP """EV_DEFAULT"", ""EV_DEFAULT_""" 4
4589.el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
4590.IX Item "EV_DEFAULT, EV_DEFAULT_"
4591Similar to the other two macros, this gives you the value of the default
4592loop, if multiple loops are supported (\*(L"ev loop default\*(R"). The default loop
4593will be initialised if it isn't already initialised.
4594.Sp
4595For non-multiplicity builds, these macros do nothing, so you always have
4596to initialise the loop somewhere.
4597.ie n .IP """EV_DEFAULT_UC"", ""EV_DEFAULT_UC_""" 4
4598.el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
4599.IX Item "EV_DEFAULT_UC, EV_DEFAULT_UC_"
4600Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the
4601default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour
4602is undefined when the default loop has not been initialised by a previous
4603execution of \f(CW\*(C`EV_DEFAULT\*(C'\fR, \f(CW\*(C`EV_DEFAULT_\*(C'\fR or \f(CW\*(C`ev_default_init (...)\*(C'\fR.
4604.Sp
4605It is often prudent to use \f(CW\*(C`EV_DEFAULT\*(C'\fR when initialising the first
4606watcher in a function but use \f(CW\*(C`EV_DEFAULT_UC\*(C'\fR afterwards.
4607.PP
4608Example: Declare and initialise a check watcher, utilising the above
4609macros so it will work regardless of whether multiple loops are supported
4610or not.
4611.PP
4612.Vb 5
4613\& static void
4614\& check_cb (EV_P_ ev_timer *w, int revents)
4615\& {
4616\& ev_check_stop (EV_A_ w);
4617\& }
4618\&
4619\& ev_check check;
4620\& ev_check_init (&check, check_cb);
4621\& ev_check_start (EV_DEFAULT_ &check);
4622\& ev_run (EV_DEFAULT_ 0);
4623.Ve
4624.SH "EMBEDDING"
4625.IX Header "EMBEDDING"
4626Libev can (and often is) directly embedded into host
4627applications. Examples of applications that embed it include the Deliantra
4628Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
4629and rxvt-unicode.
4630.PP
4631The goal is to enable you to just copy the necessary files into your
4632source directory without having to change even a single line in them, so
4633you can easily upgrade by simply copying (or having a checked-out copy of
4634libev somewhere in your source tree).
4635.SS "\s-1FILESETS\s0"
4636.IX Subsection "FILESETS"
4637Depending on what features you need you need to include one or more sets of files
4638in your application.
4639.PP
4640\fI\s-1CORE EVENT LOOP\s0\fR
4641.IX Subsection "CORE EVENT LOOP"
4642.PP
4643To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
4644configuration (no autoconf):
4645.PP
4646.Vb 2
4647\& #define EV_STANDALONE 1
4648\& #include "ev.c"
4649.Ve
4650.PP
4651This will automatically include \fIev.h\fR, too, and should be done in a
4652single C source file only to provide the function implementations. To use
4653it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best
4654done by writing a wrapper around \fIev.h\fR that you can include instead and
4655where you can put other configuration options):
4656.PP
4657.Vb 2
4658\& #define EV_STANDALONE 1
4659\& #include "ev.h"
4660.Ve
4661.PP
4662Both header files and implementation files can be compiled with a \*(C+
4663compiler (at least, that's a stated goal, and breakage will be treated
4664as a bug).
4665.PP
4666You need the following files in your source tree, or in a directory
4667in your include path (e.g. in libev/ when using \-Ilibev):
4668.PP
4669.Vb 4
4670\& ev.h
4671\& ev.c
4672\& ev_vars.h
4673\& ev_wrap.h
4674\&
4675\& ev_win32.c required on win32 platforms only
4676\&
4677\& ev_select.c only when select backend is enabled
4678\& ev_poll.c only when poll backend is enabled
4679\& ev_epoll.c only when the epoll backend is enabled
4680\& ev_linuxaio.c only when the linux aio backend is enabled
4681\& ev_iouring.c only when the linux io_uring backend is enabled
4682\& ev_kqueue.c only when the kqueue backend is enabled
4683\& ev_port.c only when the solaris port backend is enabled
4684.Ve
4685.PP
4686\&\fIev.c\fR includes the backend files directly when enabled, so you only need
4687to compile this single file.
4688.PP
4689\fI\s-1LIBEVENT COMPATIBILITY API\s0\fR
4690.IX Subsection "LIBEVENT COMPATIBILITY API"
4691.PP
4692To include the libevent compatibility \s-1API,\s0 also include:
4693.PP
4694.Vb 1
4695\& #include "event.c"
4696.Ve
4697.PP
4698in the file including \fIev.c\fR, and:
4699.PP
4700.Vb 1
4701\& #include "event.h"
4702.Ve
4703.PP
4704in the files that want to use the libevent \s-1API.\s0 This also includes \fIev.h\fR.
4705.PP
4706You need the following additional files for this:
4707.PP
4708.Vb 2
4709\& event.h
4710\& event.c
4711.Ve
4712.PP
4713\fI\s-1AUTOCONF SUPPORT\s0\fR
4714.IX Subsection "AUTOCONF SUPPORT"
4715.PP
4716Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your configuration in
4717whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
4718\&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then
4719include \fIconfig.h\fR and configure itself accordingly.
4720.PP
4721For this of course you need the m4 file:
4722.PP
4723.Vb 1
4724\& libev.m4
4725.Ve
4726.SS "\s-1PREPROCESSOR SYMBOLS/MACROS\s0"
4727.IX Subsection "PREPROCESSOR SYMBOLS/MACROS"
4728Libev can be configured via a variety of preprocessor symbols you have to
4729define before including (or compiling) any of its files. The default in
4730the absence of autoconf is documented for every option.
4731.PP
4732Symbols marked with \*(L"(h)\*(R" do not change the \s-1ABI,\s0 and can have different
4733values when compiling libev vs. including \fIev.h\fR, so it is permissible
4734to redefine them before including \fIev.h\fR without breaking compatibility
4735to a compiled library. All other symbols change the \s-1ABI,\s0 which means all
4736users of libev and the libev code itself must be compiled with compatible
4737settings.
4738.IP "\s-1EV_COMPAT3\s0 (h)" 4
4739.IX Item "EV_COMPAT3 (h)"
4740Backwards compatibility is a major concern for libev. This is why this
4741release of libev comes with wrappers for the functions and symbols that
4742have been renamed between libev version 3 and 4.
4743.Sp
4744You can disable these wrappers (to test compatibility with future
4745versions) by defining \f(CW\*(C`EV_COMPAT3\*(C'\fR to \f(CW0\fR when compiling your
4746sources. This has the additional advantage that you can drop the \f(CW\*(C`struct\*(C'\fR
4747from \f(CW\*(C`struct ev_loop\*(C'\fR declarations, as libev will provide an \f(CW\*(C`ev_loop\*(C'\fR
4748typedef in that case.
4749.Sp
4750In some future version, the default for \f(CW\*(C`EV_COMPAT3\*(C'\fR will become \f(CW0\fR,
4751and in some even more future version the compatibility code will be
4752removed completely.
4753.IP "\s-1EV_STANDALONE\s0 (h)" 4
4754.IX Item "EV_STANDALONE (h)"
4755Must always be \f(CW1\fR if you do not use autoconf configuration, which
4756keeps libev from including \fIconfig.h\fR, and it also defines dummy
4757implementations for some libevent functions (such as logging, which is not
4758supported). It will also not define any of the structs usually found in
4759\&\fIevent.h\fR that are not directly supported by the libev core alone.
4760.Sp
4761In standalone mode, libev will still try to automatically deduce the
4762configuration, but has to be more conservative.
4763.IP "\s-1EV_USE_FLOOR\s0" 4
4764.IX Item "EV_USE_FLOOR"
4765If defined to be \f(CW1\fR, libev will use the \f(CW\*(C`floor ()\*(C'\fR function for its
4766periodic reschedule calculations, otherwise libev will fall back on a
4767portable (slower) implementation. If you enable this, you usually have to
4768link against libm or something equivalent. Enabling this when the \f(CW\*(C`floor\*(C'\fR
4769function is not available will fail, so the safe default is to not enable
4770this.
4771.IP "\s-1EV_USE_MONOTONIC\s0" 4
4772.IX Item "EV_USE_MONOTONIC"
4773If defined to be \f(CW1\fR, libev will try to detect the availability of the
4774monotonic clock option at both compile time and runtime. Otherwise no
4775use of the monotonic clock option will be attempted. If you enable this,
4776you usually have to link against librt or something similar. Enabling it
4777when the functionality isn't available is safe, though, although you have
4778to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
4779function is hiding in (often \fI\-lrt\fR). See also \f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
4780.IP "\s-1EV_USE_REALTIME\s0" 4
4781.IX Item "EV_USE_REALTIME"
4782If defined to be \f(CW1\fR, libev will try to detect the availability of the
4783real-time clock option at compile time (and assume its availability
4784at runtime if successful). Otherwise no use of the real-time clock
4785option will be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR
4786by \f(CW\*(C`clock_get (CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect
4787correctness. See the note about libraries in the description of
4788\&\f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. Defaults to the opposite value of
4789\&\f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
4790.IP "\s-1EV_USE_CLOCK_SYSCALL\s0" 4
4791.IX Item "EV_USE_CLOCK_SYSCALL"
4792If defined to be \f(CW1\fR, libev will try to use a direct syscall instead
4793of calling the system-provided \f(CW\*(C`clock_gettime\*(C'\fR function. This option
4794exists 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
4795unconditionally pulls in \f(CW\*(C`libpthread\*(C'\fR, slowing down single-threaded
4796programs needlessly. Using a direct syscall is slightly slower (in
4797theory), because no optimised vdso implementation can be used, but avoids
4798the pthread dependency. Defaults to \f(CW1\fR on GNU/Linux with glibc 2.x or
4799higher, as it simplifies linking (no need for \f(CW\*(C`\-lrt\*(C'\fR).
4800.IP "\s-1EV_USE_NANOSLEEP\s0" 4
4801.IX Item "EV_USE_NANOSLEEP"
4802If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available
4803and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR.
4804.IP "\s-1EV_USE_EVENTFD\s0" 4
4805.IX Item "EV_USE_EVENTFD"
4806If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
4807available and will probe for kernel support at runtime. This will improve
4808\&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
4809If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
48102.7 or newer, otherwise disabled.
4811.IP "\s-1EV_USE_SIGNALFD\s0" 4
4812.IX Item "EV_USE_SIGNALFD"
4813If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`signalfd ()\*(C'\fR is
4814available and will probe for kernel support at runtime. This enables
4815the use of \s-1EVFLAG_SIGNALFD\s0 for faster and simpler signal handling. If
4816undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
48172.7 or newer, otherwise disabled.
4818.IP "\s-1EV_USE_TIMERFD\s0" 4
4819.IX Item "EV_USE_TIMERFD"
4820If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`timerfd ()\*(C'\fR is
4821available and will probe for kernel support at runtime. This allows
4822libev to detect time jumps accurately. If undefined, it will be enabled
4823if the headers indicate GNU/Linux + Glibc 2.8 or newer and define
4824\&\f(CW\*(C`TFD_TIMER_CANCEL_ON_SET\*(C'\fR, otherwise disabled.
4825.IP "\s-1EV_USE_EVENTFD\s0" 4
4826.IX Item "EV_USE_EVENTFD"
4827If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
4828available and will probe for kernel support at runtime. This will improve
4829\&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
4830If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
48312.7 or newer, otherwise disabled.
4832.IP "\s-1EV_USE_SELECT\s0" 4
4833.IX Item "EV_USE_SELECT"
4834If undefined or defined to be \f(CW1\fR, libev will compile in support for the
4835\&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at auto-detection will be done: if no
4836other method takes over, select will be it. Otherwise the select backend
4837will not be compiled in.
4838.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
4839.IX Item "EV_SELECT_USE_FD_SET"
4840If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR
4841structure. This is useful if libev doesn't compile due to a missing
4842\&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it mis-guesses the bitset layout
4843on exotic systems. This usually limits the range of file descriptors to
4844some low limit such as 1024 or might have other limitations (winsocket
4845only allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation,
4846configures the maximum size of the \f(CW\*(C`fd_set\*(C'\fR.
4847.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
4848.IX Item "EV_SELECT_IS_WINSOCKET"
4849When defined to \f(CW1\fR, the select backend will assume that
4850select/socket/connect etc. don't understand file descriptors but
4851wants osf handles on win32 (this is the case when the select to
4852be used is the winsock select). This means that it will call
4853\&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
4854it is assumed that all these functions actually work on fds, even
4855on win32. Should not be defined on non\-win32 platforms.
4856.IP "\s-1EV_FD_TO_WIN32_HANDLE\s0(fd)" 4
4857.IX Item "EV_FD_TO_WIN32_HANDLE(fd)"
4858If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map
4859file descriptors to socket handles. When not defining this symbol (the
4860default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually
4861correct. In some cases, programs use their own file descriptor management,
4862in which case they can provide this function to map fds to socket handles.
4863.IP "\s-1EV_WIN32_HANDLE_TO_FD\s0(handle)" 4
4864.IX Item "EV_WIN32_HANDLE_TO_FD(handle)"
4865If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR then libev maps handles to file descriptors
4866using the standard \f(CW\*(C`_open_osfhandle\*(C'\fR function. For programs implementing
4867their own fd to handle mapping, overwriting this function makes it easier
4868to do so. This can be done by defining this macro to an appropriate value.
4869.IP "\s-1EV_WIN32_CLOSE_FD\s0(fd)" 4
4870.IX Item "EV_WIN32_CLOSE_FD(fd)"
4871If programs implement their own fd to handle mapping on win32, then this
4872macro can be used to override the \f(CW\*(C`close\*(C'\fR function, useful to unregister
4873file descriptors again. Note that the replacement function has to close
4874the underlying \s-1OS\s0 handle.
4875.IP "\s-1EV_USE_WSASOCKET\s0" 4
4876.IX Item "EV_USE_WSASOCKET"
4877If defined to be \f(CW1\fR, libev will use \f(CW\*(C`WSASocket\*(C'\fR to create its internal
4878communication socket, which works better in some environments. Otherwise,
4879the normal \f(CW\*(C`socket\*(C'\fR function will be used, which works better in other
4880environments.
4881.IP "\s-1EV_USE_POLL\s0" 4
4882.IX Item "EV_USE_POLL"
4883If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2)
4884backend. Otherwise it will be enabled on non\-win32 platforms. It
4885takes precedence over select.
4886.IP "\s-1EV_USE_EPOLL\s0" 4
4887.IX Item "EV_USE_EPOLL"
4888If defined to be \f(CW1\fR, libev will compile in support for the Linux
4889\&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime,
4890otherwise another method will be used as fallback. This is the preferred
4891backend for GNU/Linux systems. If undefined, it will be enabled if the
4892headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4893.IP "\s-1EV_USE_LINUXAIO\s0" 4
4894.IX Item "EV_USE_LINUXAIO"
4895If defined to be \f(CW1\fR, libev will compile in support for the Linux aio
4896backend (\f(CW\*(C`EV_USE_EPOLL\*(C'\fR must also be enabled). If undefined, it will be
4897enabled on linux, otherwise disabled.
4898.IP "\s-1EV_USE_IOURING\s0" 4
4899.IX Item "EV_USE_IOURING"
4900If defined to be \f(CW1\fR, libev will compile in support for the Linux
4901io_uring backend (\f(CW\*(C`EV_USE_EPOLL\*(C'\fR must also be enabled). Due to it's
4902current limitations it has to be requested explicitly. If undefined, it
4903will be enabled on linux, otherwise disabled.
4904.IP "\s-1EV_USE_KQUEUE\s0" 4
4905.IX Item "EV_USE_KQUEUE"
4906If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
4907\&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime,
4908otherwise another method will be used as fallback. This is the preferred
4909backend for \s-1BSD\s0 and BSD-like systems, although on most BSDs kqueue only
4910supports some types of fds correctly (the only platform we found that
4911supports ptys for example was NetBSD), so kqueue might be compiled in, but
4912not be used unless explicitly requested. The best way to use it is to find
4913out whether kqueue supports your type of fd properly and use an embedded
4914kqueue loop.
4915.IP "\s-1EV_USE_PORT\s0" 4
4916.IX Item "EV_USE_PORT"
4917If defined to be \f(CW1\fR, libev will compile in support for the Solaris
491810 port style backend. Its availability will be detected at runtime,
4919otherwise another method will be used as fallback. This is the preferred
4920backend for Solaris 10 systems.
4921.IP "\s-1EV_USE_DEVPOLL\s0" 4
4922.IX Item "EV_USE_DEVPOLL"
4923Reserved for future expansion, works like the \s-1USE\s0 symbols above.
4924.IP "\s-1EV_USE_INOTIFY\s0" 4
4925.IX Item "EV_USE_INOTIFY"
4926If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
4927interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
4928be detected at runtime. If undefined, it will be enabled if the headers
4929indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4930.IP "\s-1EV_NO_SMP\s0" 4
4931.IX Item "EV_NO_SMP"
4932If defined to be \f(CW1\fR, libev will assume that memory is always coherent
4933between threads, that is, threads can be used, but threads never run on
4934different cpus (or different cpu cores). This reduces dependencies
4935and makes libev faster.
4936.IP "\s-1EV_NO_THREADS\s0" 4
4937.IX Item "EV_NO_THREADS"
4938If defined to be \f(CW1\fR, libev will assume that it will never be called from
4939different threads (that includes signal handlers), which is a stronger
4940assumption than \f(CW\*(C`EV_NO_SMP\*(C'\fR, above. This reduces dependencies and makes
4941libev faster.
4942.IP "\s-1EV_ATOMIC_T\s0" 4
4943.IX Item "EV_ATOMIC_T"
4944Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
4945access is atomic with respect to other threads or signal contexts. No
4946such type is easily found in the C language, so you can provide your own
4947type that you know is safe for your purposes. It is used both for signal
4948handler \*(L"locking\*(R" as well as for signal and thread safety in \f(CW\*(C`ev_async\*(C'\fR
4949watchers.
4950.Sp
4951In the absence of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR
4952(from \fIsignal.h\fR), which is usually good enough on most platforms.
4953.IP "\s-1EV_H\s0 (h)" 4
4954.IX Item "EV_H (h)"
4955The name of the \fIev.h\fR header file used to include it. The default if
4956undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be
4957used to virtually rename the \fIev.h\fR header file in case of conflicts.
4958.IP "\s-1EV_CONFIG_H\s0 (h)" 4
4959.IX Item "EV_CONFIG_H (h)"
4960If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
4961\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
4962\&\f(CW\*(C`EV_H\*(C'\fR, above.
4963.IP "\s-1EV_EVENT_H\s0 (h)" 4
4964.IX Item "EV_EVENT_H (h)"
4965Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea
4966of how the \fIevent.h\fR header can be found, the default is \f(CW"event.h"\fR.
4967.IP "\s-1EV_PROTOTYPES\s0 (h)" 4
4968.IX Item "EV_PROTOTYPES (h)"
4969If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
4970prototypes, but still define all the structs and other symbols. This is
4971occasionally useful if you want to provide your own wrapper functions
4972around libev functions.
4973.IP "\s-1EV_MULTIPLICITY\s0" 4
4974.IX Item "EV_MULTIPLICITY"
4975If undefined or defined to \f(CW1\fR, then all event-loop-specific functions
4976will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create
4977additional independent event loops. Otherwise there will be no support
4978for multiple event loops and there is no first event loop pointer
4979argument. Instead, all functions act on the single default loop.
4980.Sp
4981Note that \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR will no longer provide a
4982default loop when multiplicity is switched off \- you always have to
4983initialise the loop manually in this case.
4984.IP "\s-1EV_MINPRI\s0" 4
4985.IX Item "EV_MINPRI"
4986.PD 0
4987.IP "\s-1EV_MAXPRI\s0" 4
4988.IX Item "EV_MAXPRI"
4989.PD
4990The range of allowed priorities. \f(CW\*(C`EV_MINPRI\*(C'\fR must be smaller or equal to
4991\&\f(CW\*(C`EV_MAXPRI\*(C'\fR, but otherwise there are no non-obvious limitations. You can
4992provide for more priorities by overriding those symbols (usually defined
4993to be \f(CW\*(C`\-2\*(C'\fR and \f(CW2\fR, respectively).
4994.Sp
4995When doing priority-based operations, libev usually has to linearly search
4996all the priorities, so having many of them (hundreds) uses a lot of space
4997and time, so using the defaults of five priorities (\-2 .. +2) is usually
4998fine.
4999.Sp
5000If your embedding application does not need any priorities, defining these
5001both to \f(CW0\fR will save some memory and \s-1CPU.\s0
5002.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
5003.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."
5004If undefined or defined to be \f(CW1\fR (and the platform supports it), then
5005the respective watcher type is supported. If defined to be \f(CW0\fR, then it
5006is not. Disabling watcher types mainly saves code size.
5007.IP "\s-1EV_FEATURES\s0" 4
5008.IX Item "EV_FEATURES"
5009If you need to shave off some kilobytes of code at the expense of some
5010speed (but with the full \s-1API\s0), you can define this symbol to request
5011certain subsets of functionality. The default is to enable all features
5012that can be enabled on the platform.
5013.Sp
5014A typical way to use this symbol is to define it to \f(CW0\fR (or to a bitset
5015with some broad features you want) and then selectively re-enable
5016additional parts you want, for example if you want everything minimal,
5017but multiple event loop support, async and child watchers and the poll
5018backend, use this:
5019.Sp
5020.Vb 5
5021\& #define EV_FEATURES 0
5022\& #define EV_MULTIPLICITY 1
5023\& #define EV_USE_POLL 1
5024\& #define EV_CHILD_ENABLE 1
5025\& #define EV_ASYNC_ENABLE 1
5026.Ve
5027.Sp
5028The actual value is a bitset, it can be a combination of the following
5029values (by default, all of these are enabled):
5030.RS 4
5031.ie n .IP "1 \- faster/larger code" 4
5032.el .IP "\f(CW1\fR \- faster/larger code" 4
5033.IX Item "1 - faster/larger code"
5034Use larger code to speed up some operations.
5035.Sp
5036Currently this is used to override some inlining decisions (enlarging the
5037code size by roughly 30% on amd64).
5038.Sp
5039When optimising for size, use of compiler flags such as \f(CW\*(C`\-Os\*(C'\fR with
5040gcc is recommended, as well as \f(CW\*(C`\-DNDEBUG\*(C'\fR, as libev contains a number of
5041assertions.
5042.Sp
5043The default is off when \f(CW\*(C`_\|_OPTIMIZE_SIZE_\|_\*(C'\fR is defined by your compiler
5044(e.g. gcc with \f(CW\*(C`\-Os\*(C'\fR).
5045.ie n .IP "2 \- faster/larger data structures" 4
5046.el .IP "\f(CW2\fR \- faster/larger data structures" 4
5047.IX Item "2 - faster/larger data structures"
5048Replaces the small 2\-heap for timer management by a faster 4\-heap, larger
5049hash table sizes and so on. This will usually further increase code size
5050and can additionally have an effect on the size of data structures at
5051runtime.
5052.Sp
5053The default is off when \f(CW\*(C`_\|_OPTIMIZE_SIZE_\|_\*(C'\fR is defined by your compiler
5054(e.g. gcc with \f(CW\*(C`\-Os\*(C'\fR).
5055.ie n .IP "4 \- full \s-1API\s0 configuration" 4
5056.el .IP "\f(CW4\fR \- full \s-1API\s0 configuration" 4
5057.IX Item "4 - full API configuration"
5058This enables priorities (sets \f(CW\*(C`EV_MAXPRI\*(C'\fR=2 and \f(CW\*(C`EV_MINPRI\*(C'\fR=\-2), and
5059enables multiplicity (\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR=1).
5060.ie n .IP "8 \- full \s-1API\s0" 4
5061.el .IP "\f(CW8\fR \- full \s-1API\s0" 4
5062.IX Item "8 - full API"
5063This enables a lot of the \*(L"lesser used\*(R" \s-1API\s0 functions. See \f(CW\*(C`ev.h\*(C'\fR for
5064details on which parts of the \s-1API\s0 are still available without this
5065feature, and do not complain if this subset changes over time.
5066.ie n .IP "16 \- enable all optional watcher types" 4
5067.el .IP "\f(CW16\fR \- enable all optional watcher types" 4
5068.IX Item "16 - enable all optional watcher types"
5069Enables all optional watcher types. If you want to selectively enable
5070only some watcher types other than I/O and timers (e.g. prepare,
5071embed, async, child...) you can enable them manually by defining
5072\&\f(CW\*(C`EV_watchertype_ENABLE\*(C'\fR to \f(CW1\fR instead.
5073.ie n .IP "32 \- enable all backends" 4
5074.el .IP "\f(CW32\fR \- enable all backends" 4
5075.IX Item "32 - enable all backends"
5076This enables all backends \- without this feature, you need to enable at
5077least one backend manually (\f(CW\*(C`EV_USE_SELECT\*(C'\fR is a good choice).
5078.ie n .IP "64 \- enable OS-specific ""helper"" APIs" 4
5079.el .IP "\f(CW64\fR \- enable OS-specific ``helper'' APIs" 4
5080.IX Item "64 - enable OS-specific helper APIs"
5081Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
5082default.
5083.RE
5084.RS 4
5085.Sp
5086Compiling with \f(CW\*(C`gcc \-Os \-DEV_STANDALONE \-DEV_USE_EPOLL=1 \-DEV_FEATURES=0\*(C'\fR
5087reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
5088code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
5089watchers, timers and monotonic clock support.
5090.Sp
5091With an intelligent-enough linker (gcc+binutils are intelligent enough
5092when you use \f(CW\*(C`\-Wl,\-\-gc\-sections \-ffunction\-sections\*(C'\fR) functions unused by
5093your program might be left out as well \- a binary starting a timer and an
5094I/O watcher then might come out at only 5Kb.
5095.RE
5096.IP "\s-1EV_API_STATIC\s0" 4
5097.IX Item "EV_API_STATIC"
5098If this symbol is defined (by default it is not), then all identifiers
5099will have static linkage. This means that libev will not export any
5100identifiers, and you cannot link against libev anymore. This can be useful
5101when you embed libev, only want to use libev functions in a single file,
5102and do not want its identifiers to be visible.
5103.Sp
5104To use this, define \f(CW\*(C`EV_API_STATIC\*(C'\fR and include \fIev.c\fR in the file that
5105wants to use libev.
5106.Sp
5107This option only works when libev is compiled with a C compiler, as \*(C+
5108doesn't support the required declaration syntax.
5109.IP "\s-1EV_AVOID_STDIO\s0" 4
5110.IX Item "EV_AVOID_STDIO"
5111If this is set to \f(CW1\fR at compiletime, then libev will avoid using stdio
5112functions (printf, scanf, perror etc.). This will increase the code size
5113somewhat, but if your program doesn't otherwise depend on stdio and your
5114libc allows it, this avoids linking in the stdio library which is quite
5115big.
5116.Sp
5117Note that error messages might become less precise when this option is
5118enabled.
5119.IP "\s-1EV_NSIG\s0" 4
5120.IX Item "EV_NSIG"
5121The highest supported signal number, +1 (or, the number of
5122signals): Normally, libev tries to deduce the maximum number of signals
5123automatically, but sometimes this fails, in which case it can be
5124specified. Also, using a lower number than detected (\f(CW32\fR should be
5125good for about any system in existence) can save some memory, as libev
5126statically allocates some 12\-24 bytes per signal number.
5127.IP "\s-1EV_PID_HASHSIZE\s0" 4
5128.IX Item "EV_PID_HASHSIZE"
5129\&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by
5130pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR disabled),
5131usually more than enough. If you need to manage thousands of children you
5132might want to increase this value (\fImust\fR be a power of two).
5133.IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4
5134.IX Item "EV_INOTIFY_HASHSIZE"
5135\&\f(CW\*(C`ev_stat\*(C'\fR watchers use a small hash table to distribute workload by
5136inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR
5137disabled), usually more than enough. If you need to manage thousands of
5138\&\f(CW\*(C`ev_stat\*(C'\fR watchers you might want to increase this value (\fImust\fR be a
5139power of two).
5140.IP "\s-1EV_USE_4HEAP\s0" 4
5141.IX Item "EV_USE_4HEAP"
5142Heaps are not very cache-efficient. To improve the cache-efficiency of the
5143timer and periodics heaps, libev uses a 4\-heap when this symbol is defined
5144to \f(CW1\fR. The 4\-heap uses more complicated (longer) code but has noticeably
5145faster performance with many (thousands) of watchers.
5146.Sp
5147The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
5148will be \f(CW0\fR.
5149.IP "\s-1EV_HEAP_CACHE_AT\s0" 4
5150.IX Item "EV_HEAP_CACHE_AT"
5151Heaps are not very cache-efficient. To improve the cache-efficiency of the
5152timer and periodics heaps, libev can cache the timestamp (\fIat\fR) within
5153the heap structure (selected by defining \f(CW\*(C`EV_HEAP_CACHE_AT\*(C'\fR to \f(CW1\fR),
5154which uses 8\-12 bytes more per watcher and a few hundred bytes more code,
5155but avoids random read accesses on heap changes. This improves performance
5156noticeably with many (hundreds) of watchers.
5157.Sp
5158The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
5159will be \f(CW0\fR.
5160.IP "\s-1EV_VERIFY\s0" 4
5161.IX Item "EV_VERIFY"
5162Controls how much internal verification (see \f(CW\*(C`ev_verify ()\*(C'\fR) will
5163be done: If set to \f(CW0\fR, no internal verification code will be compiled
5164in. If set to \f(CW1\fR, then verification code will be compiled in, but not
5165called. If set to \f(CW2\fR, then the internal verification code will be
5166called once per loop, which can slow down libev. If set to \f(CW3\fR, then the
5167verification code will be called very frequently, which will slow down
5168libev considerably.
5169.Sp
5170Verification errors are reported via C's \f(CW\*(C`assert\*(C'\fR mechanism, so if you
5171disable that (e.g. by defining \f(CW\*(C`NDEBUG\*(C'\fR) then no errors will be reported.
5172.Sp
5173The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
5174will be \f(CW0\fR.
5175.IP "\s-1EV_COMMON\s0" 4
5176.IX Item "EV_COMMON"
5177By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining
5178this macro to something else you can include more and other types of
5179members. You have to define it each time you include one of the files,
5180though, and it must be identical each time.
5181.Sp
5182For example, the perl \s-1EV\s0 module uses something like this:
5183.Sp
5184.Vb 3
5185\& #define EV_COMMON \e
5186\& SV *self; /* contains this struct */ \e
5187\& SV *cb_sv, *fh /* note no trailing ";" */
5188.Ve
5189.IP "\s-1EV_CB_DECLARE\s0 (type)" 4
5190.IX Item "EV_CB_DECLARE (type)"
5191.PD 0
5192.IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4
5193.IX Item "EV_CB_INVOKE (watcher, revents)"
5194.IP "ev_set_cb (ev, cb)" 4
5195.IX Item "ev_set_cb (ev, cb)"
5196.PD
5197Can be used to change the callback member declaration in each watcher,
5198and the way callbacks are invoked and set. Must expand to a struct member
5199definition and a statement, respectively. See the \fIev.h\fR header file for
5200their default definitions. One possible use for overriding these is to
5201avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use
5202method calls instead of plain function calls in \*(C+.
5203.SS "\s-1EXPORTED API SYMBOLS\s0"
5204.IX Subsection "EXPORTED API SYMBOLS"
5205If you need to re-export the \s-1API\s0 (e.g. via a \s-1DLL\s0) and you need a list of
5206exported symbols, you can use the provided \fISymbol.*\fR files which list
5207all public symbols, one per line:
5208.PP
5209.Vb 2
5210\& Symbols.ev for libev proper
5211\& Symbols.event for the libevent emulation
5212.Ve
5213.PP
5214This can also be used to rename all public symbols to avoid clashes with
5215multiple versions of libev linked together (which is obviously bad in
5216itself, but sometimes it is inconvenient to avoid this).
5217.PP
5218A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to
5219include before including \fIev.h\fR:
5220.PP
5221.Vb 1
5222\& <Symbols.ev sed \-e "s/.*/#define & myprefix_&/" >wrap.h
5223.Ve
5224.PP
5225This would create a file \fIwrap.h\fR which essentially looks like this:
5226.PP
5227.Vb 4
5228\& #define ev_backend myprefix_ev_backend
5229\& #define ev_check_start myprefix_ev_check_start
5230\& #define ev_check_stop myprefix_ev_check_stop
5231\& ...
5232.Ve
5233.SS "\s-1EXAMPLES\s0"
5234.IX Subsection "EXAMPLES"
5235For a real-world example of a program the includes libev
5236verbatim, you can have a look at the \s-1EV\s0 perl module
5237(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
5238the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public
5239interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file
5240will be compiled. It is pretty complex because it provides its own header
5241file.
5242.PP
5243The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file
5244that everybody includes and which overrides some configure choices:
5245.PP
5246.Vb 8
5247\& #define EV_FEATURES 8
5248\& #define EV_USE_SELECT 1
5249\& #define EV_PREPARE_ENABLE 1
5250\& #define EV_IDLE_ENABLE 1
5251\& #define EV_SIGNAL_ENABLE 1
5252\& #define EV_CHILD_ENABLE 1
5253\& #define EV_USE_STDEXCEPT 0
5254\& #define EV_CONFIG_H <config.h>
5255\&
5256\& #include "ev++.h"
5257.Ve
5258.PP
5259And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled:
5260.PP
5261.Vb 2
5262\& #include "ev_cpp.h"
5263\& #include "ev.c"
5264.Ve
5265.SH "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT"
5266.IX Header "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT"
5267.SS "\s-1THREADS AND COROUTINES\s0"
5268.IX Subsection "THREADS AND COROUTINES"
5269\fI\s-1THREADS\s0\fR
5270.IX Subsection "THREADS"
5271.PP
5272All libev functions are reentrant and thread-safe unless explicitly
5273documented otherwise, but libev implements no locking itself. This means
5274that you can use as many loops as you want in parallel, as long as there
5275are no concurrent calls into any libev function with the same loop
5276parameter (\f(CW\*(C`ev_default_*\*(C'\fR calls have an implicit default loop parameter,
5277of course): libev guarantees that different event loops share no data
5278structures that need any locking.
5279.PP
5280Or to put it differently: calls with different loop parameters can be done
5281concurrently from multiple threads, calls with the same loop parameter
5282must be done serially (but can be done from different threads, as long as
5283only one thread ever is inside a call at any point in time, e.g. by using
5284a mutex per loop).
5285.PP
5286Specifically to support threads (and signal handlers), libev implements
5287so-called \f(CW\*(C`ev_async\*(C'\fR watchers, which allow some limited form of
5288concurrency on the same event loop, namely waking it up \*(L"from the
5289outside\*(R".
5290.PP
5291If you want to know which design (one loop, locking, or multiple loops
5292without or something else still) is best for your problem, then I cannot
5293help you, but here is some generic advice:
5294.IP "\(bu" 4
5295most applications have a main thread: use the default libev loop
5296in that thread, or create a separate thread running only the default loop.
5297.Sp
5298This helps integrating other libraries or software modules that use libev
5299themselves and don't care/know about threading.
5300.IP "\(bu" 4
5301one loop per thread is usually a good model.
5302.Sp
5303Doing this is almost never wrong, sometimes a better-performance model
5304exists, but it is always a good start.
5305.IP "\(bu" 4
5306other models exist, such as the leader/follower pattern, where one
5307loop is handed through multiple threads in a kind of round-robin fashion.
5308.Sp
5309Choosing a model is hard \- look around, learn, know that usually you can do
5310better than you currently do :\-)
5311.IP "\(bu" 4
5312often you need to talk to some other thread which blocks in the
5313event loop.
5314.Sp
5315\&\f(CW\*(C`ev_async\*(C'\fR watchers can be used to wake them up from other threads safely
5316(or from signal contexts...).
5317.Sp
5318An example use would be to communicate signals or other events that only
5319work in the default loop by registering the signal watcher with the
5320default loop and triggering an \f(CW\*(C`ev_async\*(C'\fR watcher from the default loop
5321watcher callback into the event loop interested in the signal.
5322.PP
5323See also \*(L"\s-1THREAD LOCKING EXAMPLE\*(R"\s0.
5324.PP
5325\fI\s-1COROUTINES\s0\fR
5326.IX Subsection "COROUTINES"
5327.PP
5328Libev is very accommodating to coroutines (\*(L"cooperative threads\*(R"):
5329libev fully supports nesting calls to its functions from different
5330coroutines (e.g. you can call \f(CW\*(C`ev_run\*(C'\fR on the same loop from two
5331different coroutines, and switch freely between both coroutines running
5332the loop, as long as you don't confuse yourself). The only exception is
5333that you must not do this from \f(CW\*(C`ev_periodic\*(C'\fR reschedule callbacks.
5334.PP
5335Care has been taken to ensure that libev does not keep local state inside
5336\&\f(CW\*(C`ev_run\*(C'\fR, and other calls do not usually allow for coroutine switches as
5337they do not call any callbacks.
5338.SS "\s-1COMPILER WARNINGS\s0"
5339.IX Subsection "COMPILER WARNINGS"
5340Depending on your compiler and compiler settings, you might get no or a
5341lot of warnings when compiling libev code. Some people are apparently
5342scared by this.
5343.PP
5344However, these are unavoidable for many reasons. For one, each compiler
5345has different warnings, and each user has different tastes regarding
5346warning options. \*(L"Warn-free\*(R" code therefore cannot be a goal except when
5347targeting a specific compiler and compiler-version.
5348.PP
5349Another reason is that some compiler warnings require elaborate
5350workarounds, or other changes to the code that make it less clear and less
5351maintainable.
5352.PP
5353And of course, some compiler warnings are just plain stupid, or simply
5354wrong (because they don't actually warn about the condition their message
5355seems to warn about). For example, certain older gcc versions had some
5356warnings that resulted in an extreme number of false positives. These have
5357been fixed, but some people still insist on making code warn-free with
5358such buggy versions.
5359.PP
5360While libev is written to generate as few warnings as possible,
5361\&\*(L"warn-free\*(R" code is not a goal, and it is recommended not to build libev
5362with any compiler warnings enabled unless you are prepared to cope with
5363them (e.g. by ignoring them). Remember that warnings are just that:
5364warnings, not errors, or proof of bugs.
5365.SS "\s-1VALGRIND\s0"
5366.IX Subsection "VALGRIND"
5367Valgrind has a special section here because it is a popular tool that is
5368highly useful. Unfortunately, valgrind reports are very hard to interpret.
5369.PP
5370If you think you found a bug (memory leak, uninitialised data access etc.)
5371in libev, then check twice: If valgrind reports something like:
5372.PP
5373.Vb 3
5374\& ==2274== definitely lost: 0 bytes in 0 blocks.
5375\& ==2274== possibly lost: 0 bytes in 0 blocks.
5376\& ==2274== still reachable: 256 bytes in 1 blocks.
5377.Ve
5378.PP
5379Then there is no memory leak, just as memory accounted to global variables
5380is not a memleak \- the memory is still being referenced, and didn't leak.
5381.PP
5382Similarly, under some circumstances, valgrind might report kernel bugs
5383as if it were a bug in libev (e.g. in realloc or in the poll backend,
5384although an acceptable workaround has been found here), or it might be
5385confused.
5386.PP
5387Keep in mind that valgrind is a very good tool, but only a tool. Don't
5388make it into some kind of religion.
5389.PP
5390If you are unsure about something, feel free to contact the mailing list
5391with the full valgrind report and an explanation on why you think this
5392is a bug in libev (best check the archives, too :). However, don't be
5393annoyed when you get a brisk \*(L"this is no bug\*(R" answer and take the chance
5394of learning how to interpret valgrind properly.
5395.PP
5396If you need, for some reason, empty reports from valgrind for your project
5397I suggest using suppression lists.
5398.SH "PORTABILITY NOTES"
5399.IX Header "PORTABILITY NOTES"
5400.SS "\s-1GNU/LINUX 32 BIT LIMITATIONS\s0"
5401.IX Subsection "GNU/LINUX 32 BIT LIMITATIONS"
5402GNU/Linux is the only common platform that supports 64 bit file/large file
5403interfaces but \fIdisables\fR them by default.
5404.PP
5405That means that libev compiled in the default environment doesn't support
5406files larger than 2GiB or so, which mainly affects \f(CW\*(C`ev_stat\*(C'\fR watchers.
5407.PP
5408Unfortunately, many programs try to work around this GNU/Linux issue
5409by enabling the large file \s-1API,\s0 which makes them incompatible with the
5410standard libev compiled for their system.
5411.PP
5412Likewise, libev cannot enable the large file \s-1API\s0 itself as this would
5413suddenly make it incompatible to the default compile time environment,
5414i.e. all programs not using special compile switches.
5415.SS "\s-1OS/X AND DARWIN BUGS\s0"
5416.IX Subsection "OS/X AND DARWIN BUGS"
5417The whole thing is a bug if you ask me \- basically any system interface
5418you touch is broken, whether it is locales, poll, kqueue or even the
5419OpenGL drivers.
5420.PP
5421\fI\f(CI\*(C`kqueue\*(C'\fI is buggy\fR
5422.IX Subsection "kqueue is buggy"
5423.PP
5424The kqueue syscall is broken in all known versions \- most versions support
5425only sockets, many support pipes.
5426.PP
5427Libev tries to work around this by not using \f(CW\*(C`kqueue\*(C'\fR by default on this
5428rotten platform, but of course you can still ask for it when creating a
5429loop \- embedding a socket-only kqueue loop into a select-based one is
5430probably going to work well.
5431.PP
5432\fI\f(CI\*(C`poll\*(C'\fI is buggy\fR
5433.IX Subsection "poll is buggy"
5434.PP
5435Instead of fixing \f(CW\*(C`kqueue\*(C'\fR, Apple replaced their (working) \f(CW\*(C`poll\*(C'\fR
5436implementation by something calling \f(CW\*(C`kqueue\*(C'\fR internally around the 10.5.6
5437release, so now \f(CW\*(C`kqueue\*(C'\fR \fIand\fR \f(CW\*(C`poll\*(C'\fR are broken.
5438.PP
5439Libev tries to work around this by not using \f(CW\*(C`poll\*(C'\fR by default on
5440this rotten platform, but of course you can still ask for it when creating
5441a loop.
5442.PP
5443\fI\f(CI\*(C`select\*(C'\fI is buggy\fR
5444.IX Subsection "select is buggy"
5445.PP
5446All that's left is \f(CW\*(C`select\*(C'\fR, and of course Apple found a way to fuck this
5447one up as well: On \s-1OS/X,\s0 \f(CW\*(C`select\*(C'\fR actively limits the number of file
5448descriptors you can pass in to 1024 \- your program suddenly crashes when
5449you use more.
5450.PP
5451There is an undocumented \*(L"workaround\*(R" for this \- defining
5452\&\f(CW\*(C`_DARWIN_UNLIMITED_SELECT\*(C'\fR, which libev tries to use, so select \fIshould\fR
5453work on \s-1OS/X.\s0
5454.SS "\s-1SOLARIS PROBLEMS AND WORKAROUNDS\s0"
5455.IX Subsection "SOLARIS PROBLEMS AND WORKAROUNDS"
5456\fI\f(CI\*(C`errno\*(C'\fI reentrancy\fR
5457.IX Subsection "errno reentrancy"
5458.PP
5459The default compile environment on Solaris is unfortunately so
5460thread-unsafe that you can't even use components/libraries compiled
5461without \f(CW\*(C`\-D_REENTRANT\*(C'\fR in a threaded program, which, of course, isn't
5462defined by default. A valid, if stupid, implementation choice.
5463.PP
5464If you want to use libev in threaded environments you have to make sure
5465it's compiled with \f(CW\*(C`_REENTRANT\*(C'\fR defined.
5466.PP
5467\fIEvent port backend\fR
5468.IX Subsection "Event port backend"
5469.PP
5470The scalable event interface for Solaris is called \*(L"event
5471ports\*(R". Unfortunately, this mechanism is very buggy in all major
5472releases. If you run into high \s-1CPU\s0 usage, your program freezes or you get
5473a large number of spurious wakeups, make sure you have all the relevant
5474and latest kernel patches applied. No, I don't know which ones, but there
5475are multiple ones to apply, and afterwards, event ports actually work
5476great.
5477.PP
5478If you can't get it to work, you can try running the program by setting
5479the environment variable \f(CW\*(C`LIBEV_FLAGS=3\*(C'\fR to only allow \f(CW\*(C`poll\*(C'\fR and
5480\&\f(CW\*(C`select\*(C'\fR backends.
5481.SS "\s-1AIX POLL BUG\s0"
5482.IX Subsection "AIX POLL BUG"
5483\&\s-1AIX\s0 unfortunately has a broken \f(CW\*(C`poll.h\*(C'\fR header. Libev works around
5484this by trying to avoid the poll backend altogether (i.e. it's not even
5485compiled in), which normally isn't a big problem as \f(CW\*(C`select\*(C'\fR works fine
5486with large bitsets on \s-1AIX,\s0 and \s-1AIX\s0 is dead anyway.
5487.SS "\s-1WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS\s0"
5488.IX Subsection "WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS"
5489\fIGeneral issues\fR
5490.IX Subsection "General issues"
5491.PP
5492Win32 doesn't support any of the standards (e.g. \s-1POSIX\s0) that libev
5493requires, and its I/O model is fundamentally incompatible with the \s-1POSIX\s0
5494model. Libev still offers limited functionality on this platform in
5495the form of the \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR backend, and only supports socket
5496descriptors. This only applies when using Win32 natively, not when using
5497e.g. cygwin. Actually, it only applies to the microsofts own compilers,
5498as every compiler comes with a slightly differently broken/incompatible
5499environment.
5500.PP
5501Lifting these limitations would basically require the full
5502re-implementation of the I/O system. If you are into this kind of thing,
5503then note that glib does exactly that for you in a very portable way (note
5504also that glib is the slowest event library known to man).
5505.PP
5506There is no supported compilation method available on windows except
5507embedding it into other applications.
5508.PP
5509Sensible signal handling is officially unsupported by Microsoft \- libev
5510tries its best, but under most conditions, signals will simply not work.
5511.PP
5512Not a libev limitation but worth mentioning: windows apparently doesn't
5513accept large writes: instead of resulting in a partial write, windows will
5514either accept everything or return \f(CW\*(C`ENOBUFS\*(C'\fR if the buffer is too large,
5515so make sure you only write small amounts into your sockets (less than a
5516megabyte seems safe, but this apparently depends on the amount of memory
5517available).
5518.PP
5519Due to the many, low, and arbitrary limits on the win32 platform and
5520the abysmal performance of winsockets, using a large number of sockets
5521is not recommended (and not reasonable). If your program needs to use
5522more than a hundred or so sockets, then likely it needs to use a totally
5523different implementation for windows, as libev offers the \s-1POSIX\s0 readiness
5524notification model, which cannot be implemented efficiently on windows
5525(due to Microsoft monopoly games).
5526.PP
5527A typical way to use libev under windows is to embed it (see the embedding
5528section for details) and use the following \fIevwrap.h\fR header file instead
5529of \fIev.h\fR:
5530.PP
5531.Vb 2
5532\& #define EV_STANDALONE /* keeps ev from requiring config.h */
5533\& #define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
5534\&
5535\& #include "ev.h"
5536.Ve
5537.PP
5538And compile the following \fIevwrap.c\fR file into your project (make sure
5539you do \fInot\fR compile the \fIev.c\fR or any other embedded source files!):
5540.PP
5541.Vb 2
5542\& #include "evwrap.h"
5543\& #include "ev.c"
5544.Ve
5545.PP
5546\fIThe winsocket \f(CI\*(C`select\*(C'\fI function\fR
5547.IX Subsection "The winsocket select function"
5548.PP
5549The winsocket \f(CW\*(C`select\*(C'\fR function doesn't follow \s-1POSIX\s0 in that it
5550requires socket \fIhandles\fR and not socket \fIfile descriptors\fR (it is
5551also extremely buggy). This makes select very inefficient, and also
5552requires a mapping from file descriptors to socket handles (the Microsoft
5553C runtime provides the function \f(CW\*(C`_open_osfhandle\*(C'\fR for this). See the
5554discussion of the \f(CW\*(C`EV_SELECT_USE_FD_SET\*(C'\fR, \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR and
5555\&\f(CW\*(C`EV_FD_TO_WIN32_HANDLE\*(C'\fR preprocessor symbols for more info.
5556.PP
5557The configuration for a \*(L"naked\*(R" win32 using the Microsoft runtime
5558libraries and raw winsocket select is:
5559.PP
5560.Vb 2
5561\& #define EV_USE_SELECT 1
5562\& #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
5563.Ve
5564.PP
5565Note that winsockets handling of fd sets is O(n), so you can easily get a
5566complexity in the O(nX) range when using win32.
5567.PP
5568\fILimited number of file descriptors\fR
5569.IX Subsection "Limited number of file descriptors"
5570.PP
5571Windows has numerous arbitrary (and low) limits on things.
5572.PP
5573Early versions of winsocket's select only supported waiting for a maximum
5574of \f(CW64\fR handles (probably owning to the fact that all windows kernels
5575can only wait for \f(CW64\fR things at the same time internally; Microsoft
5576recommends spawning a chain of threads and wait for 63 handles and the
5577previous thread in each. Sounds great!).
5578.PP
5579Newer versions support more handles, but you need to define \f(CW\*(C`FD_SETSIZE\*(C'\fR
5580to some high number (e.g. \f(CW2048\fR) before compiling the winsocket select
5581call (which might be in libev or elsewhere, for example, perl and many
5582other interpreters do their own select emulation on windows).
5583.PP
5584Another limit is the number of file descriptors in the Microsoft runtime
5585libraries, which by default is \f(CW64\fR (there must be a hidden \fI64\fR
5586fetish or something like this inside Microsoft). You can increase this
5587by calling \f(CW\*(C`_setmaxstdio\*(C'\fR, which can increase this limit to \f(CW2048\fR
5588(another arbitrary limit), but is broken in many versions of the Microsoft
5589runtime libraries. This might get you to about \f(CW512\fR or \f(CW2048\fR sockets
5590(depending on windows version and/or the phase of the moon). To get more,
5591you need to wrap all I/O functions and provide your own fd management, but
5592the cost of calling select (O(nX)) will likely make this unworkable.
5593.SS "\s-1PORTABILITY REQUIREMENTS\s0"
5594.IX Subsection "PORTABILITY REQUIREMENTS"
5595In addition to a working ISO-C implementation and of course the
5596backend-specific APIs, libev relies on a few additional extensions:
5597.ie n .IP """void (*)(ev_watcher_type *, int revents)"" must have compatible calling conventions regardless of ""ev_watcher_type *""." 4
5598.el .IP "\f(CWvoid (*)(ev_watcher_type *, int revents)\fR must have compatible calling conventions regardless of \f(CWev_watcher_type *\fR." 4
5599.IX Item "void (*)(ev_watcher_type *, int revents) must have compatible calling conventions regardless of ev_watcher_type *."
5600Libev assumes not only that all watcher pointers have the same internal
5601structure (guaranteed by \s-1POSIX\s0 but not by \s-1ISO C\s0 for example), but it also
5602assumes that the same (machine) code can be used to call any watcher
5603callback: The watcher callbacks have different type signatures, but libev
5604calls them using an \f(CW\*(C`ev_watcher *\*(C'\fR internally.
5605.IP "null pointers and integer zero are represented by 0 bytes" 4
5606.IX Item "null pointers and integer zero are represented by 0 bytes"
5607Libev uses \f(CW\*(C`memset\*(C'\fR to initialise structs and arrays to \f(CW0\fR bytes, and
5608relies on this setting pointers and integers to null.
5609.IP "pointer accesses must be thread-atomic" 4
5610.IX Item "pointer accesses must be thread-atomic"
5611Accessing a pointer value must be atomic, it must both be readable and
5612writable in one piece \- this is the case on all current architectures.
5613.ie n .IP """sig_atomic_t volatile"" must be thread-atomic as well" 4
5614.el .IP "\f(CWsig_atomic_t volatile\fR must be thread-atomic as well" 4
5615.IX Item "sig_atomic_t volatile must be thread-atomic as well"
5616The type \f(CW\*(C`sig_atomic_t volatile\*(C'\fR (or whatever is defined as
5617\&\f(CW\*(C`EV_ATOMIC_T\*(C'\fR) must be atomic with respect to accesses from different
5618threads. This is not part of the specification for \f(CW\*(C`sig_atomic_t\*(C'\fR, but is
5619believed to be sufficiently portable.
5620.ie n .IP """sigprocmask"" must work in a threaded environment" 4
5621.el .IP "\f(CWsigprocmask\fR must work in a threaded environment" 4
5622.IX Item "sigprocmask must work in a threaded environment"
5623Libev uses \f(CW\*(C`sigprocmask\*(C'\fR to temporarily block signals. This is not
5624allowed in a threaded program (\f(CW\*(C`pthread_sigmask\*(C'\fR has to be used). Typical
5625pthread implementations will either allow \f(CW\*(C`sigprocmask\*(C'\fR in the \*(L"main
5626thread\*(R" or will block signals process-wide, both behaviours would
5627be compatible with libev. Interaction between \f(CW\*(C`sigprocmask\*(C'\fR and
5628\&\f(CW\*(C`pthread_sigmask\*(C'\fR could complicate things, however.
5629.Sp
5630The most portable way to handle signals is to block signals in all threads
5631except the initial one, and run the signal handling loop in the initial
5632thread as well.
5633.ie n .IP """long"" must be large enough for common memory allocation sizes" 4
5634.el .IP "\f(CWlong\fR must be large enough for common memory allocation sizes" 4
5635.IX Item "long must be large enough for common memory allocation sizes"
5636To improve portability and simplify its \s-1API,\s0 libev uses \f(CW\*(C`long\*(C'\fR internally
5637instead of \f(CW\*(C`size_t\*(C'\fR when allocating its data structures. On non-POSIX
5638systems (Microsoft...) this might be unexpectedly low, but is still at
5639least 31 bits everywhere, which is enough for hundreds of millions of
5640watchers.
5641.ie n .IP """double"" must hold a time value in seconds with enough accuracy" 4
5642.el .IP "\f(CWdouble\fR must hold a time value in seconds with enough accuracy" 4
5643.IX Item "double must hold a time value in seconds with enough accuracy"
5644The type \f(CW\*(C`double\*(C'\fR is used to represent timestamps. It is required to
5645have at least 51 bits of mantissa (and 9 bits of exponent), which is
5646good enough for at least into the year 4000 with millisecond accuracy
5647(the design goal for libev). This requirement is overfulfilled by
5648implementations using \s-1IEEE 754,\s0 which is basically all existing ones.
5649.Sp
5650With \s-1IEEE 754\s0 doubles, you get microsecond accuracy until at least the
5651year 2255 (and millisecond accuracy till the year 287396 \- by then, libev
5652is either obsolete or somebody patched it to use \f(CW\*(C`long double\*(C'\fR or
5653something like that, just kidding).
5654.PP
5655If you know of other additional requirements drop me a note.
5656.SH "ALGORITHMIC COMPLEXITIES"
5657.IX Header "ALGORITHMIC COMPLEXITIES"
5658In this section the complexities of (many of) the algorithms used inside
5659libev will be documented. For complexity discussions about backends see
5660the documentation for \f(CW\*(C`ev_default_init\*(C'\fR.
5661.PP
5662All of the following are about amortised time: If an array needs to be
5663extended, libev needs to realloc and move the whole array, but this
5664happens asymptotically rarer with higher number of elements, so O(1) might
5665mean that libev does a lengthy realloc operation in rare cases, but on
5666average it is much faster and asymptotically approaches constant time.
5667.IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4
5668.IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)"
5669This means that, when you have a watcher that triggers in one hour and
5670there are 100 watchers that would trigger before that, then inserting will
5671have to skip roughly seven (\f(CW\*(C`ld 100\*(C'\fR) of these watchers.
5672.IP "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 4
5673.IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)"
5674That means that changing a timer costs less than removing/adding them,
5675as only the relative motion in the event queue has to be paid for.
5676.IP "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)" 4
5677.IX Item "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)"
5678These just add the watcher into an array or at the head of a list.
5679.IP "Stopping check/prepare/idle/fork/async watchers: O(1)" 4
5680.IX Item "Stopping check/prepare/idle/fork/async watchers: O(1)"
5681.PD 0
5682.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4
5683.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))"
5684.PD
5685These watchers are stored in lists, so they need to be walked to find the
5686correct watcher to remove. The lists are usually short (you don't usually
5687have many watchers waiting for the same fd or signal: one is typical, two
5688is rare).
5689.IP "Finding the next timer in each loop iteration: O(1)" 4
5690.IX Item "Finding the next timer in each loop iteration: O(1)"
5691By virtue of using a binary or 4\-heap, the next timer is always found at a
5692fixed position in the storage array.
5693.IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4
5694.IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)"
5695A change means an I/O watcher gets started or stopped, which requires
5696libev to recalculate its status (and possibly tell the kernel, depending
5697on backend and whether \f(CW\*(C`ev_io_set\*(C'\fR was used).
5698.IP "Activating one watcher (putting it into the pending state): O(1)" 4
5699.IX Item "Activating one watcher (putting it into the pending state): O(1)"
5700.PD 0
5701.IP "Priority handling: O(number_of_priorities)" 4
5702.IX Item "Priority handling: O(number_of_priorities)"
5703.PD
5704Priorities are implemented by allocating some space for each
5705priority. When doing priority-based operations, libev usually has to
5706linearly search all the priorities, but starting/stopping and activating
5707watchers becomes O(1) with respect to priority handling.
5708.IP "Sending an ev_async: O(1)" 4
5709.IX Item "Sending an ev_async: O(1)"
5710.PD 0
5711.IP "Processing ev_async_send: O(number_of_async_watchers)" 4
5712.IX Item "Processing ev_async_send: O(number_of_async_watchers)"
5713.IP "Processing signals: O(max_signal_number)" 4
5714.IX Item "Processing signals: O(max_signal_number)"
5715.PD
5716Sending involves a system call \fIiff\fR there were no other \f(CW\*(C`ev_async_send\*(C'\fR
5717calls in the current loop iteration and the loop is currently
5718blocked. Checking for async and signal events involves iterating over all
5719running async watchers or all signal numbers.
5720.SH "PORTING FROM LIBEV 3.X TO 4.X"
5721.IX Header "PORTING FROM LIBEV 3.X TO 4.X"
5722The major version 4 introduced some incompatible changes to the \s-1API.\s0
5723.PP
5724At the moment, the \f(CW\*(C`ev.h\*(C'\fR header file provides compatibility definitions
5725for all changes, so most programs should still compile. The compatibility
5726layer might be removed in later versions of libev, so better update to the
5727new \s-1API\s0 early than late.
5728.ie n .IP """EV_COMPAT3"" backwards compatibility mechanism" 4
5729.el .IP "\f(CWEV_COMPAT3\fR backwards compatibility mechanism" 4
5730.IX Item "EV_COMPAT3 backwards compatibility mechanism"
5731The backward compatibility mechanism can be controlled by
5732\&\f(CW\*(C`EV_COMPAT3\*(C'\fR. See \*(L"\s-1PREPROCESSOR SYMBOLS/MACROS\*(R"\s0 in the \*(L"\s-1EMBEDDING\*(R"\s0
5733section.
5734.ie n .IP """ev_default_destroy"" and ""ev_default_fork"" have been removed" 4
5735.el .IP "\f(CWev_default_destroy\fR and \f(CWev_default_fork\fR have been removed" 4
5736.IX Item "ev_default_destroy and ev_default_fork have been removed"
5737These calls can be replaced easily by their \f(CW\*(C`ev_loop_xxx\*(C'\fR counterparts:
5738.Sp
5739.Vb 2
5740\& ev_loop_destroy (EV_DEFAULT_UC);
5741\& ev_loop_fork (EV_DEFAULT);
5742.Ve
5743.IP "function/symbol renames" 4
5744.IX Item "function/symbol renames"
5745A number of functions and symbols have been renamed:
5746.Sp
5747.Vb 3
5748\& ev_loop => ev_run
5749\& EVLOOP_NONBLOCK => EVRUN_NOWAIT
5750\& EVLOOP_ONESHOT => EVRUN_ONCE
5751\&
5752\& ev_unloop => ev_break
5753\& EVUNLOOP_CANCEL => EVBREAK_CANCEL
5754\& EVUNLOOP_ONE => EVBREAK_ONE
5755\& EVUNLOOP_ALL => EVBREAK_ALL
5756\&
5757\& EV_TIMEOUT => EV_TIMER
5758\&
5759\& ev_loop_count => ev_iteration
5760\& ev_loop_depth => ev_depth
5761\& ev_loop_verify => ev_verify
5762.Ve
5763.Sp
5764Most functions working on \f(CW\*(C`struct ev_loop\*(C'\fR objects don't have an
5765\&\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
5766associated constants have been renamed to not collide with the \f(CW\*(C`struct
5767ev_loop\*(C'\fR anymore and \f(CW\*(C`EV_TIMER\*(C'\fR now follows the same naming scheme
5768as all other watcher types. Note that \f(CW\*(C`ev_loop_fork\*(C'\fR is still called
5769\&\f(CW\*(C`ev_loop_fork\*(C'\fR because it would otherwise clash with the \f(CW\*(C`ev_fork\*(C'\fR
5770typedef.
5771.ie n .IP """EV_MINIMAL"" mechanism replaced by ""EV_FEATURES""" 4
5772.el .IP "\f(CWEV_MINIMAL\fR mechanism replaced by \f(CWEV_FEATURES\fR" 4
5773.IX Item "EV_MINIMAL mechanism replaced by EV_FEATURES"
5774The preprocessor symbol \f(CW\*(C`EV_MINIMAL\*(C'\fR has been replaced by a different
5775mechanism, \f(CW\*(C`EV_FEATURES\*(C'\fR. Programs using \f(CW\*(C`EV_MINIMAL\*(C'\fR usually compile
5776and work, but the library code will of course be larger.
5777.SH "GLOSSARY"
5778.IX Header "GLOSSARY"
5779.IP "active" 4
5780.IX Item "active"
5781A watcher is active as long as it has been started and not yet stopped.
5782See \*(L"\s-1WATCHER STATES\*(R"\s0 for details.
5783.IP "application" 4
5784.IX Item "application"
5785In this document, an application is whatever is using libev.
5786.IP "backend" 4
5787.IX Item "backend"
5788The part of the code dealing with the operating system interfaces.
5789.IP "callback" 4
5790.IX Item "callback"
5791The address of a function that is called when some event has been
5792detected. Callbacks are being passed the event loop, the watcher that
5793received the event, and the actual event bitset.
5794.IP "callback/watcher invocation" 4
5795.IX Item "callback/watcher invocation"
5796The act of calling the callback associated with a watcher.
5797.IP "event" 4
5798.IX Item "event"
5799A change of state of some external event, such as data now being available
5800for reading on a file descriptor, time having passed or simply not having
5801any other events happening anymore.
5802.Sp
5803In libev, events are represented as single bits (such as \f(CW\*(C`EV_READ\*(C'\fR or
5804\&\f(CW\*(C`EV_TIMER\*(C'\fR).
5805.IP "event library" 4
5806.IX Item "event library"
5807A software package implementing an event model and loop.
5808.IP "event loop" 4
5809.IX Item "event loop"
5810An entity that handles and processes external events and converts them
5811into callback invocations.
5812.IP "event model" 4
5813.IX Item "event model"
5814The model used to describe how an event loop handles and processes
5815watchers and events.
5816.IP "pending" 4
5817.IX Item "pending"
5818A watcher is pending as soon as the corresponding event has been
5819detected. See \*(L"\s-1WATCHER STATES\*(R"\s0 for details.
5820.IP "real time" 4
5821.IX Item "real time"
5822The physical time that is observed. It is apparently strictly monotonic :)
5823.IP "wall-clock time" 4
5824.IX Item "wall-clock time"
5825The time and date as shown on clocks. Unlike real time, it can actually
5826be wrong and jump forwards and backwards, e.g. when you adjust your
5827clock.
5828.IP "watcher" 4
5829.IX Item "watcher"
5830A data structure that describes interest in certain events. Watchers need
5831to be started (attached to an event loop) before they can receive events.
958.SH "AUTHOR" 5832.SH "AUTHOR"
959.IX Header "AUTHOR" 5833.IX Header "AUTHOR"
960Marc Lehmann <libev@schmorp.de>. 5834Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5835Magnusson and Emanuele Giaquinta, and minor corrections by many others.

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