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1.\" Automatically generated by Pod::Man v1.37, Pod::Parser v1.35 1.\" Automatically generated by Pod::Man 2.23 (Pod::Simple 3.14)
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129.\" ======================================================================== 124.\" ========================================================================
130.\" 125.\"
131.IX Title ""<STANDARD INPUT>" 1" 126.IX Title "LIBEV 3"
132.TH "<STANDARD INPUT>" 1 "2007-11-22" "perl v5.8.8" "User Contributed Perl Documentation" 127.TH LIBEV 3 "2012-05-06" "libev-4.11" "libev - high performance full featured event loop"
128.\" For nroff, turn off justification. Always turn off hyphenation; it makes
129.\" way too many mistakes in technical documents.
130.if n .ad l
131.nh
133.SH "NAME" 132.SH "NAME"
134libev \- a high performance full\-featured event loop written in C 133libev \- a high performance full\-featured event loop written in C
135.SH "SYNOPSIS" 134.SH "SYNOPSIS"
136.IX Header "SYNOPSIS" 135.IX Header "SYNOPSIS"
137.Vb 1 136.Vb 1
138\& #include <ev.h> 137\& #include <ev.h>
139.Ve 138.Ve
140.SH "DESCRIPTION" 139.SS "\s-1EXAMPLE\s0 \s-1PROGRAM\s0"
141.IX Header "DESCRIPTION" 140.IX Subsection "EXAMPLE PROGRAM"
141.Vb 2
142\& // a single header file is required
143\& #include <ev.h>
144\&
145\& #include <stdio.h> // for puts
146\&
147\& // every watcher type has its own typedef\*(Aqd struct
148\& // with the name ev_TYPE
149\& ev_io stdin_watcher;
150\& ev_timer timeout_watcher;
151\&
152\& // all watcher callbacks have a similar signature
153\& // this callback is called when data is readable on stdin
154\& static void
155\& stdin_cb (EV_P_ ev_io *w, int revents)
156\& {
157\& puts ("stdin ready");
158\& // for one\-shot events, one must manually stop the watcher
159\& // with its corresponding stop function.
160\& ev_io_stop (EV_A_ w);
161\&
162\& // this causes all nested ev_run\*(Aqs to stop iterating
163\& ev_break (EV_A_ EVBREAK_ALL);
164\& }
165\&
166\& // another callback, this time for a time\-out
167\& static void
168\& timeout_cb (EV_P_ ev_timer *w, int revents)
169\& {
170\& puts ("timeout");
171\& // this causes the innermost ev_run to stop iterating
172\& ev_break (EV_A_ EVBREAK_ONE);
173\& }
174\&
175\& int
176\& main (void)
177\& {
178\& // use the default event loop unless you have special needs
179\& struct ev_loop *loop = EV_DEFAULT;
180\&
181\& // initialise an io watcher, then start it
182\& // this one will watch for stdin to become readable
183\& ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
184\& ev_io_start (loop, &stdin_watcher);
185\&
186\& // initialise a timer watcher, then start it
187\& // simple non\-repeating 5.5 second timeout
188\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
189\& ev_timer_start (loop, &timeout_watcher);
190\&
191\& // now wait for events to arrive
192\& ev_run (loop, 0);
193\&
194\& // break was called, so exit
195\& return 0;
196\& }
197.Ve
198.SH "ABOUT THIS DOCUMENT"
199.IX Header "ABOUT THIS DOCUMENT"
200This document documents the libev software package.
201.PP
202The newest version of this document is also available as an html-formatted
203web page you might find easier to navigate when reading it for the first
204time: <http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
205.PP
206While this document tries to be as complete as possible in documenting
207libev, its usage and the rationale behind its design, it is not a tutorial
208on event-based programming, nor will it introduce event-based programming
209with libev.
210.PP
211Familiarity with event based programming techniques in general is assumed
212throughout this document.
213.SH "WHAT TO READ WHEN IN A HURRY"
214.IX Header "WHAT TO READ WHEN IN A HURRY"
215This manual tries to be very detailed, but unfortunately, this also makes
216it very long. If you just want to know the basics of libev, I suggest
217reading \*(L"\s-1ANATOMY\s0 \s-1OF\s0 A \s-1WATCHER\s0\*(R", then the \*(L"\s-1EXAMPLE\s0 \s-1PROGRAM\s0\*(R" above and
218look up the missing functions in \*(L"\s-1GLOBAL\s0 \s-1FUNCTIONS\s0\*(R" and the \f(CW\*(C`ev_io\*(C'\fR and
219\&\f(CW\*(C`ev_timer\*(C'\fR sections in \*(L"\s-1WATCHER\s0 \s-1TYPES\s0\*(R".
220.SH "ABOUT LIBEV"
221.IX Header "ABOUT LIBEV"
142Libev is an event loop: you register interest in certain events (such as a 222Libev 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 223file descriptor being readable or a timeout occurring), and it will manage
144these event sources and provide your program with events. 224these event sources and provide your program with events.
145.PP 225.PP
146To do this, it must take more or less complete control over your process 226To 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 227(or thread) by executing the \fIevent loop\fR handler, and will then
148communicate events via a callback mechanism. 228communicate events via a callback mechanism.
149.PP 229.PP
150You register interest in certain events by registering so-called \fIevent 230You register interest in certain events by registering so-called \fIevent
151watchers\fR, which are relatively small C structures you initialise with the 231watchers\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 232details of the event, and then hand it over to libev by \fIstarting\fR the
153watcher. 233watcher.
154.SH "FEATURES" 234.SS "\s-1FEATURES\s0"
155.IX Header "FEATURES" 235.IX Subsection "FEATURES"
156Libev supports select, poll, the linux-specific epoll and the bsd-specific 236Libev supports \f(CW\*(C`select\*(C'\fR, \f(CW\*(C`poll\*(C'\fR, the Linux-specific \f(CW\*(C`epoll\*(C'\fR, the
157kqueue mechanisms for file descriptor events, relative timers, absolute 237BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port mechanisms
158timers with customised rescheduling, signal events, process status change 238for file descriptor events (\f(CW\*(C`ev_io\*(C'\fR), the Linux \f(CW\*(C`inotify\*(C'\fR interface
159events (related to \s-1SIGCHLD\s0), and event watchers dealing with the event 239(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 240inter-thread wakeup (\f(CW\*(C`ev_async\*(C'\fR)/signal handling (\f(CW\*(C`ev_signal\*(C'\fR)) relative
161fast (see this benchmark comparing 241timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers with customised rescheduling
162it to libevent for example). 242(\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals (\f(CW\*(C`ev_signal\*(C'\fR), process status
243change events (\f(CW\*(C`ev_child\*(C'\fR), and event watchers dealing with the event
244loop mechanism itself (\f(CW\*(C`ev_idle\*(C'\fR, \f(CW\*(C`ev_embed\*(C'\fR, \f(CW\*(C`ev_prepare\*(C'\fR and
245\&\f(CW\*(C`ev_check\*(C'\fR watchers) as well as file watchers (\f(CW\*(C`ev_stat\*(C'\fR) and even
246limited support for fork events (\f(CW\*(C`ev_fork\*(C'\fR).
247.PP
248It also is quite fast (see this
249benchmark <http://libev.schmorp.de/bench.html> comparing it to libevent
250for example).
163.SH "CONVENTIONS" 251.SS "\s-1CONVENTIONS\s0"
164.IX Header "CONVENTIONS" 252.IX Subsection "CONVENTIONS"
165Libev is very configurable. In this manual the default configuration 253Libev is very configurable. In this manual the default (and most common)
166will be described, which supports multiple event loops. For more info 254configuration will be described, which supports multiple event loops. For
167about various configuration options please have a look at the file 255more 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 256\&\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 257for 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) 258name \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. 259this argument.
172.SH "TIME REPRESENTATION" 260.SS "\s-1TIME\s0 \s-1REPRESENTATION\s0"
173.IX Header "TIME REPRESENTATION" 261.IX Subsection "TIME REPRESENTATION"
174Libev represents time as a single floating point number, representing the 262Libev represents time as a single floating point number, representing
175(fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere near 263the (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 264somewhere 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 265ask). This type is called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use
178to the double type in C. 266too. It usually aliases to the \f(CW\*(C`double\*(C'\fR type in C. When you need to do
267any calculations on it, you should treat it as some floating point value.
268.PP
269Unlike the name component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for
270time differences (e.g. delays) throughout libev.
271.SH "ERROR HANDLING"
272.IX Header "ERROR HANDLING"
273Libev knows three classes of errors: operating system errors, usage errors
274and internal errors (bugs).
275.PP
276When libev catches an operating system error it cannot handle (for example
277a system call indicating a condition libev cannot fix), it calls the callback
278set via \f(CW\*(C`ev_set_syserr_cb\*(C'\fR, which is supposed to fix the problem or
279abort. The default is to print a diagnostic message and to call \f(CW\*(C`abort
280()\*(C'\fR.
281.PP
282When libev detects a usage error such as a negative timer interval, then
283it will print a diagnostic message and abort (via the \f(CW\*(C`assert\*(C'\fR mechanism,
284so \f(CW\*(C`NDEBUG\*(C'\fR will disable this checking): these are programming errors in
285the libev caller and need to be fixed there.
286.PP
287Libev also has a few internal error-checking \f(CW\*(C`assert\*(C'\fRions, and also has
288extensive consistency checking code. These do not trigger under normal
289circumstances, as they indicate either a bug in libev or worse.
179.SH "GLOBAL FUNCTIONS" 290.SH "GLOBAL FUNCTIONS"
180.IX Header "GLOBAL FUNCTIONS" 291.IX Header "GLOBAL FUNCTIONS"
181These functions can be called anytime, even before initialising the 292These functions can be called anytime, even before initialising the
182library in any way. 293library in any way.
183.IP "ev_tstamp ev_time ()" 4 294.IP "ev_tstamp ev_time ()" 4
184.IX Item "ev_tstamp ev_time ()" 295.IX Item "ev_tstamp ev_time ()"
185Returns the current time as libev would use it. Please note that the 296Returns 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 297\&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp
187you actually want to know. 298you actually want to know. Also interesting is the combination of
299\&\f(CW\*(C`ev_now_update\*(C'\fR and \f(CW\*(C`ev_now\*(C'\fR.
300.IP "ev_sleep (ev_tstamp interval)" 4
301.IX Item "ev_sleep (ev_tstamp interval)"
302Sleep for the given interval: The current thread will be blocked
303until either it is interrupted or the given time interval has
304passed (approximately \- it might return a bit earlier even if not
305interrupted). Returns immediately if \f(CW\*(C`interval <= 0\*(C'\fR.
306.Sp
307Basically this is a sub-second-resolution \f(CW\*(C`sleep ()\*(C'\fR.
308.Sp
309The range of the \f(CW\*(C`interval\*(C'\fR is limited \- libev only guarantees to work
310with sleep times of up to one day (\f(CW\*(C`interval <= 86400\*(C'\fR).
188.IP "int ev_version_major ()" 4 311.IP "int ev_version_major ()" 4
189.IX Item "int ev_version_major ()" 312.IX Item "int ev_version_major ()"
190.PD 0 313.PD 0
191.IP "int ev_version_minor ()" 4 314.IP "int ev_version_minor ()" 4
192.IX Item "int ev_version_minor ()" 315.IX Item "int ev_version_minor ()"
193.PD 316.PD
194You can find out the major and minor version numbers of the library 317You 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 318you 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 319\&\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 320symbols \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. 321version of the library your program was compiled against.
199.Sp 322.Sp
323These version numbers refer to the \s-1ABI\s0 version of the library, not the
324release version.
325.Sp
200Usually, it's a good idea to terminate if the major versions mismatch, 326Usually, it's a good idea to terminate if the major versions mismatch,
201as this indicates an incompatible change. Minor versions are usually 327as this indicates an incompatible change. Minor versions are usually
202compatible to older versions, so a larger minor version alone is usually 328compatible to older versions, so a larger minor version alone is usually
203not a problem. 329not a problem.
330.Sp
331Example: Make sure we haven't accidentally been linked against the wrong
332version (note, however, that this will not detect other \s-1ABI\s0 mismatches,
333such as \s-1LFS\s0 or reentrancy).
334.Sp
335.Vb 3
336\& assert (("libev version mismatch",
337\& ev_version_major () == EV_VERSION_MAJOR
338\& && ev_version_minor () >= EV_VERSION_MINOR));
339.Ve
340.IP "unsigned int ev_supported_backends ()" 4
341.IX Item "unsigned int ev_supported_backends ()"
342Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR
343value) compiled into this binary of libev (independent of their
344availability on the system you are running on). See \f(CW\*(C`ev_default_loop\*(C'\fR for
345a description of the set values.
346.Sp
347Example: make sure we have the epoll method, because yeah this is cool and
348a must have and can we have a torrent of it please!!!11
349.Sp
350.Vb 2
351\& assert (("sorry, no epoll, no sex",
352\& ev_supported_backends () & EVBACKEND_EPOLL));
353.Ve
354.IP "unsigned int ev_recommended_backends ()" 4
355.IX Item "unsigned int ev_recommended_backends ()"
356Return the set of all backends compiled into this binary of libev and
357also recommended for this platform, meaning it will work for most file
358descriptor types. This set is often smaller than the one returned by
359\&\f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on most BSDs
360and will not be auto-detected unless you explicitly request it (assuming
361you know what you are doing). This is the set of backends that libev will
362probe for if you specify no backends explicitly.
363.IP "unsigned int ev_embeddable_backends ()" 4
364.IX Item "unsigned int ev_embeddable_backends ()"
365Returns the set of backends that are embeddable in other event loops. This
366value is platform-specific but can include backends not available on the
367current system. To find which embeddable backends might be supported on
368the current system, you would need to look at \f(CW\*(C`ev_embeddable_backends ()
369& ev_supported_backends ()\*(C'\fR, likewise for recommended ones.
370.Sp
371See 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))" 4 372.IP "ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())" 4
205.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))" 373.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())"
206Sets the allocation function to use (the prototype is similar to the 374Sets the allocation function to use (the prototype is similar \- the
207realloc C function, the semantics are identical). It is used to allocate 375semantics 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 376used to allocate and free memory (no surprises here). If it returns zero
209needs to be allocated, the library might abort or take some potentially 377when 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. 378or take some potentially destructive action.
379.Sp
380Since some systems (at least OpenBSD and Darwin) fail to implement
381correct \f(CW\*(C`realloc\*(C'\fR semantics, libev will use a wrapper around the system
382\&\f(CW\*(C`realloc\*(C'\fR and \f(CW\*(C`free\*(C'\fR functions by default.
211.Sp 383.Sp
212You could override this function in high-availability programs to, say, 384You could override this function in high-availability programs to, say,
213free some memory if it cannot allocate memory, to use a special allocator, 385free 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. 386or even to sleep a while and retry until some memory is available.
387.Sp
388Example: Replace the libev allocator with one that waits a bit and then
389retries (example requires a standards-compliant \f(CW\*(C`realloc\*(C'\fR).
390.Sp
391.Vb 6
392\& static void *
393\& persistent_realloc (void *ptr, size_t size)
394\& {
395\& for (;;)
396\& {
397\& void *newptr = realloc (ptr, size);
398\&
399\& if (newptr)
400\& return newptr;
401\&
402\& sleep (60);
403\& }
404\& }
405\&
406\& ...
407\& ev_set_allocator (persistent_realloc);
408.Ve
215.IP "ev_set_syserr_cb (void (*cb)(const char *msg));" 4 409.IP "ev_set_syserr_cb (void (*cb)(const char *msg) throw ())" 4
216.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg));" 410.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg) throw ())"
217Set the callback function to call on a retryable syscall error (such 411Set the callback function to call on a retryable system call error (such
218as failed select, poll, epoll_wait). The message is a printable string 412as failed select, poll, epoll_wait). The message is a printable string
219indicating the system call or subsystem causing the problem. If this 413indicating the system call or subsystem causing the problem. If this
220callback is set, then libev will expect it to remedy the sitution, no 414callback is set, then libev will expect it to remedy the situation, no
221matter what, when it returns. That is, libev will generally retry the 415matter what, when it returns. That is, libev will generally retry the
222requested operation, or, if the condition doesn't go away, do bad stuff 416requested operation, or, if the condition doesn't go away, do bad stuff
223(such as abort). 417(such as abort).
418.Sp
419Example: This is basically the same thing that libev does internally, too.
420.Sp
421.Vb 6
422\& static void
423\& fatal_error (const char *msg)
424\& {
425\& perror (msg);
426\& abort ();
427\& }
428\&
429\& ...
430\& ev_set_syserr_cb (fatal_error);
431.Ve
432.IP "ev_feed_signal (int signum)" 4
433.IX Item "ev_feed_signal (int signum)"
434This function can be used to \*(L"simulate\*(R" a signal receive. It is completely
435safe to call this function at any time, from any context, including signal
436handlers or random threads.
437.Sp
438Its main use is to customise signal handling in your process, especially
439in the presence of threads. For example, you could block signals
440by default in all threads (and specifying \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when
441creating any loops), and in one thread, use \f(CW\*(C`sigwait\*(C'\fR or any other
442mechanism to wait for signals, then \*(L"deliver\*(R" them to libev by calling
443\&\f(CW\*(C`ev_feed_signal\*(C'\fR.
224.SH "FUNCTIONS CONTROLLING THE EVENT LOOP" 444.SH "FUNCTIONS CONTROLLING EVENT LOOPS"
225.IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP" 445.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 446An 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 447\&\fInot\fR optional in this case unless libev 3 compatibility is disabled, as
228events, and dynamically created loops which do not. 448libev 3 had an \f(CW\*(C`ev_loop\*(C'\fR function colliding with the struct name).
229.PP 449.PP
230If you use threads, a common model is to run the default event loop 450The 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 451supports child process events, and dynamically created event loops which
232create, you also create another event loop. Libev itself does no locking 452do 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)" 4 453.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
237.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)" 454.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
238This will initialise the default event loop if it hasn't been initialised 455This 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 456normally 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 457the \f(CW\*(C`flags\*(C'\fR parameter are described in more detail in the entry for
241flags). 458\&\f(CW\*(C`ev_loop_new\*(C'\fR.
459.Sp
460If the default loop is already initialised then this function simply
461returns it (and ignores the flags. If that is troubling you, check
462\&\f(CW\*(C`ev_backend ()\*(C'\fR afterwards). Otherwise it will create it with the given
463flags, which should almost always be \f(CW0\fR, unless the caller is also the
464one calling \f(CW\*(C`ev_run\*(C'\fR or otherwise qualifies as \*(L"the main program\*(R".
242.Sp 465.Sp
243If you don't know what event loop to use, use the one returned from this 466If you don't know what event loop to use, use the one returned from this
244function. 467function (or via the \f(CW\*(C`EV_DEFAULT\*(C'\fR macro).
468.Sp
469Note that this function is \fInot\fR thread-safe, so if you want to use it
470from multiple threads, you have to employ some kind of mutex (note also
471that this case is unlikely, as loops cannot be shared easily between
472threads anyway).
473.Sp
474The default loop is the only loop that can handle \f(CW\*(C`ev_child\*(C'\fR watchers,
475and to do this, it always registers a handler for \f(CW\*(C`SIGCHLD\*(C'\fR. If this is
476a problem for your application you can either create a dynamic loop with
477\&\f(CW\*(C`ev_loop_new\*(C'\fR which doesn't do that, or you can simply overwrite the
478\&\f(CW\*(C`SIGCHLD\*(C'\fR signal handler \fIafter\fR calling \f(CW\*(C`ev_default_init\*(C'\fR.
479.Sp
480Example: This is the most typical usage.
481.Sp
482.Vb 2
483\& if (!ev_default_loop (0))
484\& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
485.Ve
486.Sp
487Example: Restrict libev to the select and poll backends, and do not allow
488environment settings to be taken into account:
489.Sp
490.Vb 1
491\& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
492.Ve
493.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
494.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
495This will create and initialise a new event loop object. If the loop
496could not be initialised, returns false.
497.Sp
498This function is thread-safe, and one common way to use libev with
499threads is indeed to create one loop per thread, and using the default
500loop in the \*(L"main\*(R" or \*(L"initial\*(R" thread.
245.Sp 501.Sp
246The flags argument can be used to specify special behaviour or specific 502The 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). 503backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).
248.Sp 504.Sp
249It supports the following flags: 505The following flags are supported:
250.RS 4 506.RS 4
251.ie n .IP """EVFLAG_AUTO""" 4 507.ie n .IP """EVFLAG_AUTO""" 4
252.el .IP "\f(CWEVFLAG_AUTO\fR" 4 508.el .IP "\f(CWEVFLAG_AUTO\fR" 4
253.IX Item "EVFLAG_AUTO" 509.IX Item "EVFLAG_AUTO"
254The default flags value. Use this if you have no clue (it's the right 510The default flags value. Use this if you have no clue (it's the right
255thing, believe me). 511thing, believe me).
256.ie n .IP """EVFLAG_NOENV""" 4 512.ie n .IP """EVFLAG_NOENV""" 4
257.el .IP "\f(CWEVFLAG_NOENV\fR" 4 513.el .IP "\f(CWEVFLAG_NOENV\fR" 4
258.IX Item "EVFLAG_NOENV" 514.IX Item "EVFLAG_NOENV"
259If this flag bit is ored into the flag value (or the program runs setuid 515If 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 516or 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 517\&\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 518override 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 519useful to try out specific backends to test their performance, or to work
264around bugs. 520around bugs.
521.ie n .IP """EVFLAG_FORKCHECK""" 4
522.el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4
523.IX Item "EVFLAG_FORKCHECK"
524Instead of calling \f(CW\*(C`ev_loop_fork\*(C'\fR manually after a fork, you can also
525make libev check for a fork in each iteration by enabling this flag.
526.Sp
527This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop,
528and thus this might slow down your event loop if you do a lot of loop
529iterations and little real work, but is usually not noticeable (on my
530GNU/Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn sequence
531without a system call and thus \fIvery\fR fast, but my GNU/Linux system also has
532\&\f(CW\*(C`pthread_atfork\*(C'\fR which is even faster).
533.Sp
534The big advantage of this flag is that you can forget about fork (and
535forget about forgetting to tell libev about forking) when you use this
536flag.
537.Sp
538This flag setting cannot be overridden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR
539environment variable.
540.ie n .IP """EVFLAG_NOINOTIFY""" 4
541.el .IP "\f(CWEVFLAG_NOINOTIFY\fR" 4
542.IX Item "EVFLAG_NOINOTIFY"
543When this flag is specified, then libev will not attempt to use the
544\&\fIinotify\fR \s-1API\s0 for its \f(CW\*(C`ev_stat\*(C'\fR watchers. Apart from debugging and
545testing, this flag can be useful to conserve inotify file descriptors, as
546otherwise each loop using \f(CW\*(C`ev_stat\*(C'\fR watchers consumes one inotify handle.
547.ie n .IP """EVFLAG_SIGNALFD""" 4
548.el .IP "\f(CWEVFLAG_SIGNALFD\fR" 4
549.IX Item "EVFLAG_SIGNALFD"
550When this flag is specified, then libev will attempt to use the
551\&\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
552delivers signals synchronously, which makes it both faster and might make
553it possible to get the queued signal data. It can also simplify signal
554handling with threads, as long as you properly block signals in your
555threads that are not interested in handling them.
556.Sp
557Signalfd will not be used by default as this changes your signal mask, and
558there are a lot of shoddy libraries and programs (glib's threadpool for
559example) that can't properly initialise their signal masks.
560.ie n .IP """EVFLAG_NOSIGMASK""" 4
561.el .IP "\f(CWEVFLAG_NOSIGMASK\fR" 4
562.IX Item "EVFLAG_NOSIGMASK"
563When this flag is specified, then libev will avoid to modify the signal
564mask. Specifically, this means you have to make sure signals are unblocked
565when you want to receive them.
566.Sp
567This behaviour is useful when you want to do your own signal handling, or
568want to handle signals only in specific threads and want to avoid libev
569unblocking the signals.
570.Sp
571It's also required by \s-1POSIX\s0 in a threaded program, as libev calls
572\&\f(CW\*(C`sigprocmask\*(C'\fR, whose behaviour is officially unspecified.
573.Sp
574This flag's behaviour will become the default in future versions of libev.
265.ie n .IP """EVMETHOD_SELECT"" (value 1, portable select backend)" 4 575.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
266.el .IP "\f(CWEVMETHOD_SELECT\fR (value 1, portable select backend)" 4 576.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
267.IX Item "EVMETHOD_SELECT (value 1, portable select backend)" 577.IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
268This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as 578This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as
269libev tries to roll its own fd_set with no limits on the number of fds, 579libev 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 580but 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 581using this backend. It doesn't scale too well (O(highest_fd)), but its
272the fastest backend for a low number of fds. 582usually the fastest backend for a low number of (low-numbered :) fds.
583.Sp
584To get good performance out of this backend you need a high amount of
585parallelism (most of the file descriptors should be busy). If you are
586writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many
587connections as possible during one iteration. You might also want to have
588a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of
589readiness notifications you get per iteration.
590.Sp
591This 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
592\&\f(CW\*(C`writefds\*(C'\fR set (and to work around Microsoft Windows bugs, also onto the
593\&\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)" 4 594.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)" 4 595.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)" 596.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 597And this is your standard \fIpoll\fR\|(2) backend. It's more complicated
277select, but handles sparse fds better and has no artificial limit on the 598than select, but handles sparse fds better and has no artificial
278number of fds you can use (except it will slow down considerably with a 599limit 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). 600considerably with a lot of inactive fds). It scales similarly to select,
601i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for
602performance tips.
603.Sp
604This backend maps \f(CW\*(C`EV_READ\*(C'\fR to \f(CW\*(C`POLLIN | POLLERR | POLLHUP\*(C'\fR, and
605\&\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)" 4 606.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
281.el .IP "\f(CWEVMETHOD_EPOLL\fR (value 4, Linux)" 4 607.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
282.IX Item "EVMETHOD_EPOLL (value 4, Linux)" 608.IX Item "EVBACKEND_EPOLL (value 4, Linux)"
609Use the linux-specific \fIepoll\fR\|(7) interface (for both pre\- and post\-2.6.9
610kernels).
611.Sp
283For few fds, this backend is a bit little slower than poll and select, 612For 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 613it 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 614O(total_fds) where total_fds is the total number of fds (or the highest
286either O(1) or O(active_fds). 615fd), epoll scales either O(1) or O(active_fds).
287.Sp 616.Sp
617The epoll mechanism deserves honorable mention as the most misdesigned
618of the more advanced event mechanisms: mere annoyances include silently
619dropping file descriptors, requiring a system call per change per file
620descriptor (and unnecessary guessing of parameters), problems with dup,
621returning before the timeout value, resulting in additional iterations
622(and only giving 5ms accuracy while select on the same platform gives
6230.1ms) and so on. The biggest issue is fork races, however \- if a program
624forks then \fIboth\fR parent and child process have to recreate the epoll
625set, which can take considerable time (one syscall per file descriptor)
626and is of course hard to detect.
627.Sp
628Epoll is also notoriously buggy \- embedding epoll fds \fIshould\fR work,
629but of course \fIdoesn't\fR, and epoll just loves to report events for
630totally \fIdifferent\fR file descriptors (even already closed ones, so
631one cannot even remove them from the set) than registered in the set
632(especially on \s-1SMP\s0 systems). Libev tries to counter these spurious
633notifications by employing an additional generation counter and comparing
634that against the events to filter out spurious ones, recreating the set
635when required. Epoll also erroneously rounds down timeouts, but gives you
636no way to know when and by how much, so sometimes you have to busy-wait
637because epoll returns immediately despite a nonzero timeout. And last
638not least, it also refuses to work with some file descriptors which work
639perfectly fine with \f(CW\*(C`select\*(C'\fR (files, many character devices...).
640.Sp
641Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
642cobbled together in a hurry, no thought to design or interaction with
643others. Oh, the pain, will it ever stop...
644.Sp
288While stopping and starting an I/O watcher in the same iteration will 645While stopping, setting and starting an I/O watcher in the same iteration
289result in some caching, there is still a syscall per such incident 646will 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 647incident (because the same \fIfile descriptor\fR could point to a different
291best to avoid that. Also, \fIdup()\fRed file descriptors might not work very 648\&\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. 649file descriptors might not work very well if you register events for both
650file descriptors.
651.Sp
652Best performance from this backend is achieved by not unregistering all
653watchers for a file descriptor until it has been closed, if possible,
654i.e. keep at least one watcher active per fd at all times. Stopping and
655starting a watcher (without re-setting it) also usually doesn't cause
656extra overhead. A fork can both result in spurious notifications as well
657as in libev having to destroy and recreate the epoll object, which can
658take considerable time and thus should be avoided.
659.Sp
660All this means that, in practice, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR can be as fast or
661faster than epoll for maybe up to a hundred file descriptors, depending on
662the usage. So sad.
663.Sp
664While nominally embeddable in other event loops, this feature is broken in
665all kernel versions tested so far.
666.Sp
667This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
668\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
293.ie n .IP """EVMETHOD_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4 669.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)" 4 670.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
295.IX Item "EVMETHOD_KQUEUE (value 8, most BSD clones)" 671.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
296Kqueue deserves special mention, as at the time of this writing, it 672Kqueue deserves special mention, as at the time of this writing, it
297was broken on all BSDs except NetBSD (usually it doesn't work with 673was broken on all BSDs except NetBSD (usually it doesn't work reliably
298anything but sockets and pipes, except on Darwin, where of course its 674with anything but sockets and pipes, except on Darwin, where of course
299completely useless). For this reason its not being \*(L"autodetected\*(R" unless 675it's completely useless). Unlike epoll, however, whose brokenness
300you explicitly specify the flags (i.e. you don't use \s-1EVFLAG_AUTO\s0). 676is by design, these kqueue bugs can (and eventually will) be fixed
677without \s-1API\s0 changes to existing programs. For this reason it's not being
678\&\*(L"auto-detected\*(R" unless you explicitly specify it in the flags (i.e. using
679\&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a known-to-be-good (\-enough)
680system like NetBSD.
681.Sp
682You still can embed kqueue into a normal poll or select backend and use it
683only for sockets (after having made sure that sockets work with kqueue on
684the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
301.Sp 685.Sp
302It scales in the same way as the epoll backend, but the interface to the 686It 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 687kernel is more efficient (which says nothing about its actual speed, of
304course). While starting and stopping an I/O watcher does not cause an 688course). 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 689cause 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. 690two event changes per incident. Support for \f(CW\*(C`fork ()\*(C'\fR is very bad (you
691might have to leak fd's on fork, but it's more sane than epoll) and it
692drops fds silently in similarly hard-to-detect cases
693.Sp
694This backend usually performs well under most conditions.
695.Sp
696While nominally embeddable in other event loops, this doesn't work
697everywhere, so you might need to test for this. And since it is broken
698almost everywhere, you should only use it when you have a lot of sockets
699(for which it usually works), by embedding it into another event loop
700(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
701also broken on \s-1OS\s0 X)) and, did I mention it, using it only for sockets.
702.Sp
703This backend maps \f(CW\*(C`EV_READ\*(C'\fR into an \f(CW\*(C`EVFILT_READ\*(C'\fR kevent with
704\&\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
705\&\f(CW\*(C`NOTE_EOF\*(C'\fR.
307.ie n .IP """EVMETHOD_DEVPOLL"" (value 16, Solaris 8)" 4 706.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
308.el .IP "\f(CWEVMETHOD_DEVPOLL\fR (value 16, Solaris 8)" 4 707.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
309.IX Item "EVMETHOD_DEVPOLL (value 16, Solaris 8)" 708.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
310This is not implemented yet (and might never be). 709This is not implemented yet (and might never be, unless you send me an
710implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets
711and is not embeddable, which would limit the usefulness of this backend
712immensely.
311.ie n .IP """EVMETHOD_PORT"" (value 32, Solaris 10)" 4 713.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
312.el .IP "\f(CWEVMETHOD_PORT\fR (value 32, Solaris 10)" 4 714.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
313.IX Item "EVMETHOD_PORT (value 32, Solaris 10)" 715.IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
314This uses the Solaris 10 port mechanism. As with everything on Solaris, 716This uses the Solaris 10 event port mechanism. As with everything on Solaris,
315it's really slow, but it still scales very well (O(active_fds)). 717it's really slow, but it still scales very well (O(active_fds)).
718.Sp
719While this backend scales well, it requires one system call per active
720file descriptor per loop iteration. For small and medium numbers of file
721descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend
722might perform better.
723.Sp
724On the positive side, this backend actually performed fully to
725specification in all tests and is fully embeddable, which is a rare feat
726among the OS-specific backends (I vastly prefer correctness over speed
727hacks).
728.Sp
729On the negative side, the interface is \fIbizarre\fR \- so bizarre that
730even sun itself gets it wrong in their code examples: The event polling
731function sometimes returns events to the caller even though an error
732occurred, but with no indication whether it has done so or not (yes, it's
733even documented that way) \- deadly for edge-triggered interfaces where you
734absolutely have to know whether an event occurred or not because you have
735to re-arm the watcher.
736.Sp
737Fortunately libev seems to be able to work around these idiocies.
738.Sp
739This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
740\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
316.ie n .IP """EVMETHOD_ALL""" 4 741.ie n .IP """EVBACKEND_ALL""" 4
317.el .IP "\f(CWEVMETHOD_ALL\fR" 4 742.el .IP "\f(CWEVBACKEND_ALL\fR" 4
318.IX Item "EVMETHOD_ALL" 743.IX Item "EVBACKEND_ALL"
319Try all backends (even potentially broken ones that wouldn't be tried 744Try 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 745with \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. 746\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR.
747.Sp
748It is definitely not recommended to use this flag, use whatever
749\&\f(CW\*(C`ev_recommended_backends ()\*(C'\fR returns, or simply do not specify a backend
750at all.
751.ie n .IP """EVBACKEND_MASK""" 4
752.el .IP "\f(CWEVBACKEND_MASK\fR" 4
753.IX Item "EVBACKEND_MASK"
754Not a backend at all, but a mask to select all backend bits from a
755\&\f(CW\*(C`flags\*(C'\fR value, in case you want to mask out any backends from a flags
756value (e.g. when modifying the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR environment variable).
322.RE 757.RE
323.RS 4 758.RS 4
324.Sp 759.Sp
325If one or more of these are ored into the flags value, then only these 760If 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 761then only these backends will be tried (in the reverse order as listed
327specified, most compiled-in backend will be tried, usually in reverse 762here). If none are specified, all backends in \f(CW\*(C`ev_recommended_backends
328order of their flag values :) 763()\*(C'\fR will be tried.
764.Sp
765Example: Try to create a event loop that uses epoll and nothing else.
766.Sp
767.Vb 3
768\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
769\& if (!epoller)
770\& fatal ("no epoll found here, maybe it hides under your chair");
771.Ve
772.Sp
773Example: Use whatever libev has to offer, but make sure that kqueue is
774used if available.
775.Sp
776.Vb 1
777\& struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
778.Ve
329.RE 779.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)" 4 780.IP "ev_loop_destroy (loop)" 4
342.IX Item "ev_loop_destroy (loop)" 781.IX Item "ev_loop_destroy (loop)"
343Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an 782Destroys an event loop object (frees all memory and kernel state
344earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR. 783etc.). None of the active event watchers will be stopped in the normal
345.IP "ev_default_fork ()" 4 784sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your
346.IX Item "ev_default_fork ()" 785responsibility to either stop all watchers cleanly yourself \fIbefore\fR
347This function reinitialises the kernel state for backends that have 786calling 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 787the 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 788for example).
350again makes little sense).
351.Sp 789.Sp
352You \fImust\fR call this function after forking if and only if you want to 790Note that certain global state, such as signal state (and installed signal
353use the event library in both processes. If you just fork+exec, you don't 791handlers), will not be freed by this function, and related watchers (such
354have to call it. 792as signal and child watchers) would need to be stopped manually.
355.Sp 793.Sp
356The function itself is quite fast and it's usually not a problem to call 794This 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 795\&\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: 796\&\f(CW\*(C`ev_default_loop\*(C'\fR, in which case it is not thread-safe.
359.Sp 797.Sp
360.Vb 1 798Note that it is not advisable to call this function on the default loop
361\& pthread_atfork (0, 0, ev_default_fork); 799except in the rare occasion where you really need to free its resources.
362.Ve 800If you need dynamically allocated loops it is better to use \f(CW\*(C`ev_loop_new\*(C'\fR
801and \f(CW\*(C`ev_loop_destroy\*(C'\fR.
363.IP "ev_loop_fork (loop)" 4 802.IP "ev_loop_fork (loop)" 4
364.IX Item "ev_loop_fork (loop)" 803.IX Item "ev_loop_fork (loop)"
365Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by 804This function sets a flag that causes subsequent \f(CW\*(C`ev_run\*(C'\fR iterations to
366\&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop 805reinitialise the kernel state for backends that have one. Despite the
367after fork, and how you do this is entirely your own problem. 806name, you can call it anytime, but it makes most sense after forking, in
807the child process. You \fImust\fR call it (or use \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR) in the
808child before resuming or calling \f(CW\*(C`ev_run\*(C'\fR.
809.Sp
810Again, you \fIhave\fR to call it on \fIany\fR loop that you want to re-use after
811a fork, \fIeven if you do not plan to use the loop in the parent\fR. This is
812because some kernel interfaces *cough* \fIkqueue\fR *cough* do funny things
813during fork.
814.Sp
815On the other hand, you only need to call this function in the child
816process if and only if you want to use the event loop in the child. If
817you just fork+exec or create a new loop in the child, you don't have to
818call it at all (in fact, \f(CW\*(C`epoll\*(C'\fR is so badly broken that it makes a
819difference, but libev will usually detect this case on its own and do a
820costly reset of the backend).
821.Sp
822The function itself is quite fast and it's usually not a problem to call
823it just in case after a fork.
824.Sp
825Example: Automate calling \f(CW\*(C`ev_loop_fork\*(C'\fR on the default loop when
826using pthreads.
827.Sp
828.Vb 5
829\& static void
830\& post_fork_child (void)
831\& {
832\& ev_loop_fork (EV_DEFAULT);
833\& }
834\&
835\& ...
836\& pthread_atfork (0, 0, post_fork_child);
837.Ve
838.IP "int ev_is_default_loop (loop)" 4
839.IX Item "int ev_is_default_loop (loop)"
840Returns true when the given loop is, in fact, the default loop, and false
841otherwise.
842.IP "unsigned int ev_iteration (loop)" 4
843.IX Item "unsigned int ev_iteration (loop)"
844Returns the current iteration count for the event loop, which is identical
845to the number of times libev did poll for new events. It starts at \f(CW0\fR
846and happily wraps around with enough iterations.
847.Sp
848This value can sometimes be useful as a generation counter of sorts (it
849\&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with
850\&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls \- and is incremented between the
851prepare and check phases.
368.IP "unsigned int ev_method (loop)" 4 852.IP "unsigned int ev_depth (loop)" 4
369.IX Item "unsigned int ev_method (loop)" 853.IX Item "unsigned int ev_depth (loop)"
854Returns the number of times \f(CW\*(C`ev_run\*(C'\fR was entered minus the number of
855times \f(CW\*(C`ev_run\*(C'\fR was exited normally, in other words, the recursion depth.
856.Sp
857Outside \f(CW\*(C`ev_run\*(C'\fR, this number is zero. In a callback, this number is
858\&\f(CW1\fR, unless \f(CW\*(C`ev_run\*(C'\fR was invoked recursively (or from another thread),
859in which case it is higher.
860.Sp
861Leaving \f(CW\*(C`ev_run\*(C'\fR abnormally (setjmp/longjmp, cancelling the thread,
862throwing an exception etc.), doesn't count as \*(L"exit\*(R" \- consider this
863as a hint to avoid such ungentleman-like behaviour unless it's really
864convenient, in which case it is fully supported.
865.IP "unsigned int ev_backend (loop)" 4
866.IX Item "unsigned int ev_backend (loop)"
370Returns one of the \f(CW\*(C`EVMETHOD_*\*(C'\fR flags indicating the event backend in 867Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
371use. 868use.
372.IP "ev_tstamp ev_now (loop)" 4 869.IP "ev_tstamp ev_now (loop)" 4
373.IX Item "ev_tstamp ev_now (loop)" 870.IX Item "ev_tstamp ev_now (loop)"
374Returns the current \*(L"event loop time\*(R", which is the time the event loop 871Returns 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 872received events and started processing them. This timestamp does not
376as long as callbacks are being processed, and this is also the base time 873change 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 874time used for relative timers. You can treat it as the timestamp of the
378occuring (or more correctly, the mainloop finding out about it). 875event occurring (or more correctly, libev finding out about it).
876.IP "ev_now_update (loop)" 4
877.IX Item "ev_now_update (loop)"
878Establishes the current time by querying the kernel, updating the time
879returned by \f(CW\*(C`ev_now ()\*(C'\fR in the progress. This is a costly operation and
880is usually done automatically within \f(CW\*(C`ev_run ()\*(C'\fR.
881.Sp
882This function is rarely useful, but when some event callback runs for a
883very long time without entering the event loop, updating libev's idea of
884the current time is a good idea.
885.Sp
886See also \*(L"The special problem of time updates\*(R" in the \f(CW\*(C`ev_timer\*(C'\fR section.
887.IP "ev_suspend (loop)" 4
888.IX Item "ev_suspend (loop)"
889.PD 0
890.IP "ev_resume (loop)" 4
891.IX Item "ev_resume (loop)"
892.PD
893These two functions suspend and resume an event loop, for use when the
894loop is not used for a while and timeouts should not be processed.
895.Sp
896A typical use case would be an interactive program such as a game: When
897the user presses \f(CW\*(C`^Z\*(C'\fR to suspend the game and resumes it an hour later it
898would be best to handle timeouts as if no time had actually passed while
899the program was suspended. This can be achieved by calling \f(CW\*(C`ev_suspend\*(C'\fR
900in your \f(CW\*(C`SIGTSTP\*(C'\fR handler, sending yourself a \f(CW\*(C`SIGSTOP\*(C'\fR and calling
901\&\f(CW\*(C`ev_resume\*(C'\fR directly afterwards to resume timer processing.
902.Sp
903Effectively, all \f(CW\*(C`ev_timer\*(C'\fR watchers will be delayed by the time spend
904between \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
905will be rescheduled (that is, they will lose any events that would have
906occurred while suspended).
907.Sp
908After calling \f(CW\*(C`ev_suspend\*(C'\fR you \fBmust not\fR call \fIany\fR function on the
909given loop other than \f(CW\*(C`ev_resume\*(C'\fR, and you \fBmust not\fR call \f(CW\*(C`ev_resume\*(C'\fR
910without a previous call to \f(CW\*(C`ev_suspend\*(C'\fR.
911.Sp
912Calling \f(CW\*(C`ev_suspend\*(C'\fR/\f(CW\*(C`ev_resume\*(C'\fR has the side effect of updating the
913event loop time (see \f(CW\*(C`ev_now_update\*(C'\fR).
379.IP "ev_loop (loop, int flags)" 4 914.IP "bool ev_run (loop, int flags)" 4
380.IX Item "ev_loop (loop, int flags)" 915.IX Item "bool ev_run (loop, int flags)"
381Finally, this is it, the event handler. This function usually is called 916Finally, this is it, the event handler. This function usually is called
382after you initialised all your watchers and you want to start handling 917after you have initialised all your watchers and you want to start
383events. 918handling events. It will ask the operating system for any new events, call
919the watcher callbacks, and then repeat the whole process indefinitely: This
920is why event loops are called \fIloops\fR.
384.Sp 921.Sp
385If the flags argument is specified as 0, it will not return until either 922If 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. 923until either no event watchers are active anymore or \f(CW\*(C`ev_break\*(C'\fR was
924called.
387.Sp 925.Sp
926The return value is false if there are no more active watchers (which
927usually means \*(L"all jobs done\*(R" or \*(L"deadlock\*(R"), and true in all other cases
928(which usually means " you should call \f(CW\*(C`ev_run\*(C'\fR again").
929.Sp
930Please note that an explicit \f(CW\*(C`ev_break\*(C'\fR is usually better than
931relying on all watchers to be stopped when deciding when a program has
932finished (especially in interactive programs), but having a program
933that automatically loops as long as it has to and no longer by virtue
934of relying on its watchers stopping correctly, that is truly a thing of
935beauty.
936.Sp
937This function is \fImostly\fR exception-safe \- you can break out of a
938\&\f(CW\*(C`ev_run\*(C'\fR call by calling \f(CW\*(C`longjmp\*(C'\fR in a callback, throwing a \*(C+
939exception and so on. This does not decrement the \f(CW\*(C`ev_depth\*(C'\fR value, nor
940will it clear any outstanding \f(CW\*(C`EVBREAK_ONE\*(C'\fR breaks.
941.Sp
388A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle 942A 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 943those 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. 944block your process in case there are no events and will return after one
945iteration of the loop. This is sometimes useful to poll and handle new
946events while doing lengthy calculations, to keep the program responsive.
391.Sp 947.Sp
392A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if 948A 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 949necessary) and will handle those and any already outstanding ones. It
394your process until at least one new event arrives, and will return after 950will block your process until at least one new event arrives (which could
951be an event internal to libev itself, so there is no guarantee that a
952user-registered callback will be called), and will return after one
395one iteration of the loop. 953iteration of the loop.
396.Sp 954.Sp
397This flags value could be used to implement alternative looping 955This 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 956with something not expressible using other libev watchers (i.e. "roll your
399more generic mechanism. 957own \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
958usually a better approach for this kind of thing.
400.Sp 959.Sp
401Here are the gory details of what ev_loop does: 960Here are the gory details of what \f(CW\*(C`ev_run\*(C'\fR does (this is for your
961understanding, not a guarantee that things will work exactly like this in
962future versions):
402.Sp 963.Sp
403.Vb 15 964.Vb 10
404\& 1. If there are no active watchers (reference count is zero), return. 965\& \- Increment loop depth.
966\& \- Reset the ev_break status.
967\& \- Before the first iteration, call any pending watchers.
968\& LOOP:
969\& \- If EVFLAG_FORKCHECK was used, check for a fork.
970\& \- If a fork was detected (by any means), queue and call all fork watchers.
405\& 2. Queue and immediately call all prepare watchers. 971\& \- Queue and call all prepare watchers.
972\& \- If ev_break was called, goto FINISH.
406\& 3. If we have been forked, recreate the kernel state. 973\& \- If we have been forked, detach and recreate the kernel state
974\& as to not disturb the other process.
407\& 4. Update the kernel state with all outstanding changes. 975\& \- Update the kernel state with all outstanding changes.
408\& 5. Update the "event loop time". 976\& \- Update the "event loop time" (ev_now ()).
409\& 6. Calculate for how long to block. 977\& \- Calculate for how long to sleep or block, if at all
978\& (active idle watchers, EVRUN_NOWAIT or not having
979\& any active watchers at all will result in not sleeping).
980\& \- Sleep if the I/O and timer collect interval say so.
981\& \- Increment loop iteration counter.
410\& 7. Block the process, waiting for events. 982\& \- Block the process, waiting for any events.
983\& \- Queue all outstanding I/O (fd) events.
411\& 8. Update the "event loop time" and do time jump handling. 984\& \- Update the "event loop time" (ev_now ()), and do time jump adjustments.
412\& 9. Queue all outstanding timers. 985\& \- Queue all expired timers.
413\& 10. Queue all outstanding periodics. 986\& \- Queue all expired periodics.
414\& 11. If no events are pending now, queue all idle watchers. 987\& \- Queue all idle watchers with priority higher than that of pending events.
415\& 12. Queue all check watchers. 988\& \- Queue all check watchers.
416\& 13. Call all queued watchers in reverse order (i.e. check watchers first). 989\& \- 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 990\& Signals and child watchers are implemented as I/O watchers, and will
418\& was used, return, otherwise continue with step #1. 991\& be handled here by queueing them when their watcher gets executed.
992\& \- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
993\& were used, or there are no active watchers, goto FINISH, otherwise
994\& continue with step LOOP.
995\& FINISH:
996\& \- Reset the ev_break status iff it was EVBREAK_ONE.
997\& \- Decrement the loop depth.
998\& \- Return.
419.Ve 999.Ve
1000.Sp
1001Example: Queue some jobs and then loop until no events are outstanding
1002anymore.
1003.Sp
1004.Vb 4
1005\& ... queue jobs here, make sure they register event watchers as long
1006\& ... as they still have work to do (even an idle watcher will do..)
1007\& ev_run (my_loop, 0);
1008\& ... jobs done or somebody called break. yeah!
1009.Ve
420.IP "ev_unloop (loop, how)" 4 1010.IP "ev_break (loop, how)" 4
421.IX Item "ev_unloop (loop, how)" 1011.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 1012Can 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 1013has 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 1014\&\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. 1015\&\f(CW\*(C`EVBREAK_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_run\*(C'\fR calls return.
1016.Sp
1017This \*(L"break state\*(R" will be cleared on the next call to \f(CW\*(C`ev_run\*(C'\fR.
1018.Sp
1019It is safe to call \f(CW\*(C`ev_break\*(C'\fR from outside any \f(CW\*(C`ev_run\*(C'\fR calls, too, in
1020which case it will have no effect.
426.IP "ev_ref (loop)" 4 1021.IP "ev_ref (loop)" 4
427.IX Item "ev_ref (loop)" 1022.IX Item "ev_ref (loop)"
428.PD 0 1023.PD 0
429.IP "ev_unref (loop)" 4 1024.IP "ev_unref (loop)" 4
430.IX Item "ev_unref (loop)" 1025.IX Item "ev_unref (loop)"
431.PD 1026.PD
432Ref/unref can be used to add or remove a reference count on the event 1027Ref/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 1028loop: 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 1029count 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 1030.Sp
436returning, \fIev_unref()\fR after starting, and \fIev_ref()\fR before stopping it. For 1031This is useful when you have a watcher that you never intend to
1032unregister, but that nevertheless should not keep \f(CW\*(C`ev_run\*(C'\fR from
1033returning. In such a case, call \f(CW\*(C`ev_unref\*(C'\fR after starting, and \f(CW\*(C`ev_ref\*(C'\fR
1034before stopping it.
1035.Sp
437example, libev itself uses this for its internal signal pipe: It is not 1036As 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 1037is 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 1038exiting 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 1039excellent way to do this for generic recurring timers or from within
441libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR. 1040third-party libraries. Just remember to \fIunref after start\fR and \fIref
1041before stop\fR (but only if the watcher wasn't active before, or was active
1042before, respectively. Note also that libev might stop watchers itself
1043(e.g. non-repeating timers) in which case you have to \f(CW\*(C`ev_ref\*(C'\fR
1044in the callback).
1045.Sp
1046Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_run\*(C'\fR
1047running when nothing else is active.
1048.Sp
1049.Vb 4
1050\& ev_signal exitsig;
1051\& ev_signal_init (&exitsig, sig_cb, SIGINT);
1052\& ev_signal_start (loop, &exitsig);
1053\& ev_unref (loop);
1054.Ve
1055.Sp
1056Example: For some weird reason, unregister the above signal handler again.
1057.Sp
1058.Vb 2
1059\& ev_ref (loop);
1060\& ev_signal_stop (loop, &exitsig);
1061.Ve
1062.IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4
1063.IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"
1064.PD 0
1065.IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4
1066.IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"
1067.PD
1068These advanced functions influence the time that libev will spend waiting
1069for events. Both time intervals are by default \f(CW0\fR, meaning that libev
1070will try to invoke timer/periodic callbacks and I/O callbacks with minimum
1071latency.
1072.Sp
1073Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR)
1074allows libev to delay invocation of I/O and timer/periodic callbacks
1075to increase efficiency of loop iterations (or to increase power-saving
1076opportunities).
1077.Sp
1078The idea is that sometimes your program runs just fast enough to handle
1079one (or very few) event(s) per loop iteration. While this makes the
1080program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new
1081events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high
1082overhead for the actual polling but can deliver many events at once.
1083.Sp
1084By setting a higher \fIio collect interval\fR you allow libev to spend more
1085time collecting I/O events, so you can handle more events per iteration,
1086at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and
1087\&\f(CW\*(C`ev_timer\*(C'\fR) will not be affected. Setting this to a non-null value will
1088introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations. The
1089sleep time ensures that libev will not poll for I/O events more often then
1090once per this interval, on average (as long as the host time resolution is
1091good enough).
1092.Sp
1093Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
1094to spend more time collecting timeouts, at the expense of increased
1095latency/jitter/inexactness (the watcher callback will be called
1096later). \f(CW\*(C`ev_io\*(C'\fR watchers will not be affected. Setting this to a non-null
1097value will not introduce any overhead in libev.
1098.Sp
1099Many (busy) programs can usually benefit by setting the I/O collect
1100interval to a value near \f(CW0.1\fR or so, which is often enough for
1101interactive servers (of course not for games), likewise for timeouts. It
1102usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR,
1103as this approaches the timing granularity of most systems. Note that if
1104you do transactions with the outside world and you can't increase the
1105parallelity, then this setting will limit your transaction rate (if you
1106need to poll once per transaction and the I/O collect interval is 0.01,
1107then you can't do more than 100 transactions per second).
1108.Sp
1109Setting the \fItimeout collect interval\fR can improve the opportunity for
1110saving power, as the program will \*(L"bundle\*(R" timer callback invocations that
1111are \*(L"near\*(R" in time together, by delaying some, thus reducing the number of
1112times the process sleeps and wakes up again. Another useful technique to
1113reduce iterations/wake\-ups is to use \f(CW\*(C`ev_periodic\*(C'\fR watchers and make sure
1114they fire on, say, one-second boundaries only.
1115.Sp
1116Example: we only need 0.1s timeout granularity, and we wish not to poll
1117more often than 100 times per second:
1118.Sp
1119.Vb 2
1120\& ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
1121\& ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
1122.Ve
1123.IP "ev_invoke_pending (loop)" 4
1124.IX Item "ev_invoke_pending (loop)"
1125This call will simply invoke all pending watchers while resetting their
1126pending state. Normally, \f(CW\*(C`ev_run\*(C'\fR does this automatically when required,
1127but when overriding the invoke callback this call comes handy. This
1128function can be invoked from a watcher \- this can be useful for example
1129when you want to do some lengthy calculation and want to pass further
1130event handling to another thread (you still have to make sure only one
1131thread executes within \f(CW\*(C`ev_invoke_pending\*(C'\fR or \f(CW\*(C`ev_run\*(C'\fR of course).
1132.IP "int ev_pending_count (loop)" 4
1133.IX Item "int ev_pending_count (loop)"
1134Returns the number of pending watchers \- zero indicates that no watchers
1135are pending.
1136.IP "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(\s-1EV_P\s0))" 4
1137.IX Item "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))"
1138This overrides the invoke pending functionality of the loop: Instead of
1139invoking all pending watchers when there are any, \f(CW\*(C`ev_run\*(C'\fR will call
1140this callback instead. This is useful, for example, when you want to
1141invoke the actual watchers inside another context (another thread etc.).
1142.Sp
1143If you want to reset the callback, use \f(CW\*(C`ev_invoke_pending\*(C'\fR as new
1144callback.
1145.IP "ev_set_loop_release_cb (loop, void (*release)(\s-1EV_P\s0) throw (), void (*acquire)(\s-1EV_P\s0) throw ())" 4
1146.IX Item "ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())"
1147Sometimes you want to share the same loop between multiple threads. This
1148can be done relatively simply by putting mutex_lock/unlock calls around
1149each call to a libev function.
1150.Sp
1151However, \f(CW\*(C`ev_run\*(C'\fR can run an indefinite time, so it is not feasible
1152to wait for it to return. One way around this is to wake up the event
1153loop via \f(CW\*(C`ev_break\*(C'\fR and \f(CW\*(C`ev_async_send\*(C'\fR, another way is to set these
1154\&\fIrelease\fR and \fIacquire\fR callbacks on the loop.
1155.Sp
1156When set, then \f(CW\*(C`release\*(C'\fR will be called just before the thread is
1157suspended waiting for new events, and \f(CW\*(C`acquire\*(C'\fR is called just
1158afterwards.
1159.Sp
1160Ideally, \f(CW\*(C`release\*(C'\fR will just call your mutex_unlock function, and
1161\&\f(CW\*(C`acquire\*(C'\fR will just call the mutex_lock function again.
1162.Sp
1163While event loop modifications are allowed between invocations of
1164\&\f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR (that's their only purpose after all), no
1165modifications done will affect the event loop, i.e. adding watchers will
1166have no effect on the set of file descriptors being watched, or the time
1167waited. Use an \f(CW\*(C`ev_async\*(C'\fR watcher to wake up \f(CW\*(C`ev_run\*(C'\fR when you want it
1168to take note of any changes you made.
1169.Sp
1170In theory, threads executing \f(CW\*(C`ev_run\*(C'\fR will be async-cancel safe between
1171invocations of \f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR.
1172.Sp
1173See also the locking example in the \f(CW\*(C`THREADS\*(C'\fR section later in this
1174document.
1175.IP "ev_set_userdata (loop, void *data)" 4
1176.IX Item "ev_set_userdata (loop, void *data)"
1177.PD 0
1178.IP "void *ev_userdata (loop)" 4
1179.IX Item "void *ev_userdata (loop)"
1180.PD
1181Set and retrieve a single \f(CW\*(C`void *\*(C'\fR associated with a loop. When
1182\&\f(CW\*(C`ev_set_userdata\*(C'\fR has never been called, then \f(CW\*(C`ev_userdata\*(C'\fR returns
1183\&\f(CW0\fR.
1184.Sp
1185These two functions can be used to associate arbitrary data with a loop,
1186and are intended solely for the \f(CW\*(C`invoke_pending_cb\*(C'\fR, \f(CW\*(C`release\*(C'\fR and
1187\&\f(CW\*(C`acquire\*(C'\fR callbacks described above, but of course can be (ab\-)used for
1188any other purpose as well.
1189.IP "ev_verify (loop)" 4
1190.IX Item "ev_verify (loop)"
1191This function only does something when \f(CW\*(C`EV_VERIFY\*(C'\fR support has been
1192compiled in, which is the default for non-minimal builds. It tries to go
1193through all internal structures and checks them for validity. If anything
1194is found to be inconsistent, it will print an error message to standard
1195error and call \f(CW\*(C`abort ()\*(C'\fR.
1196.Sp
1197This can be used to catch bugs inside libev itself: under normal
1198circumstances, this function will never abort as of course libev keeps its
1199data structures consistent.
442.SH "ANATOMY OF A WATCHER" 1200.SH "ANATOMY OF A WATCHER"
443.IX Header "ANATOMY OF A WATCHER" 1201.IX Header "ANATOMY OF A WATCHER"
1202In the following description, uppercase \f(CW\*(C`TYPE\*(C'\fR in names stands for the
1203watcher type, e.g. \f(CW\*(C`ev_TYPE_start\*(C'\fR can mean \f(CW\*(C`ev_timer_start\*(C'\fR for timer
1204watchers and \f(CW\*(C`ev_io_start\*(C'\fR for I/O watchers.
1205.PP
444A watcher is a structure that you create and register to record your 1206A 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 1207your 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: 1208to wait for \s-1STDIN\s0 to become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher
1209for that:
447.PP 1210.PP
448.Vb 5 1211.Vb 5
449\& static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) 1212\& static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
450\& { 1213\& {
451\& ev_io_stop (w); 1214\& ev_io_stop (w);
452\& ev_unloop (loop, EVUNLOOP_ALL); 1215\& ev_break (loop, EVBREAK_ALL);
453\& } 1216\& }
454.Ve 1217\&
455.PP
456.Vb 6
457\& struct ev_loop *loop = ev_default_loop (0); 1218\& struct ev_loop *loop = ev_default_loop (0);
1219\&
458\& struct ev_io stdin_watcher; 1220\& ev_io stdin_watcher;
1221\&
459\& ev_init (&stdin_watcher, my_cb); 1222\& ev_init (&stdin_watcher, my_cb);
460\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); 1223\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
461\& ev_io_start (loop, &stdin_watcher); 1224\& ev_io_start (loop, &stdin_watcher);
1225\&
462\& ev_loop (loop, 0); 1226\& ev_run (loop, 0);
463.Ve 1227.Ve
464.PP 1228.PP
465As you can see, you are responsible for allocating the memory for your 1229As 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, 1230watcher structures (and it is \fIusually\fR a bad idea to do this on the
467although this can sometimes be quite valid). 1231stack).
468.PP 1232.PP
1233Each watcher has an associated watcher structure (called \f(CW\*(C`struct ev_TYPE\*(C'\fR
1234or simply \f(CW\*(C`ev_TYPE\*(C'\fR, as typedefs are provided for all watcher structs).
1235.PP
469Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init 1236Each 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 1237*, 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 1238invoked 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 1239time the event loop detects that the file descriptor given is readable
473is readable and/or writable). 1240and/or writable).
474.PP 1241.PP
475Each watcher type has its own \f(CW\*(C`ev_<type>_set (watcher *, ...)\*(C'\fR macro 1242Each 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 1243macro 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 1244is 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 1245.PP
480To make the watcher actually watch out for events, you have to start it 1246To 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 1247with 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 1248*)\*(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. 1249corresponding stop function (\f(CW\*(C`ev_TYPE_stop (loop, watcher *)\*(C'\fR.
484.PP 1250.PP
485As long as your watcher is active (has been started but not stopped) you 1251As 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 1252must not touch the values stored in it. Most specifically you must never
487reinitialise it or call its set method. 1253reinitialise it or call its \f(CW\*(C`ev_TYPE_set\*(C'\fR macro.
488.PP
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 1254.PP
494Each and every callback receives the event loop pointer as first, the 1255Each and every callback receives the event loop pointer as first, the
495registered watcher structure as second, and a bitset of received events as 1256registered watcher structure as second, and a bitset of received events as
496third argument. 1257third argument.
497.PP 1258.PP
… …
506.el .IP "\f(CWEV_WRITE\fR" 4 1267.el .IP "\f(CWEV_WRITE\fR" 4
507.IX Item "EV_WRITE" 1268.IX Item "EV_WRITE"
508.PD 1269.PD
509The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or 1270The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
510writable. 1271writable.
511.ie n .IP """EV_TIMEOUT""" 4 1272.ie n .IP """EV_TIMER""" 4
512.el .IP "\f(CWEV_TIMEOUT\fR" 4 1273.el .IP "\f(CWEV_TIMER\fR" 4
513.IX Item "EV_TIMEOUT" 1274.IX Item "EV_TIMER"
514The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out. 1275The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
515.ie n .IP """EV_PERIODIC""" 4 1276.ie n .IP """EV_PERIODIC""" 4
516.el .IP "\f(CWEV_PERIODIC\fR" 4 1277.el .IP "\f(CWEV_PERIODIC\fR" 4
517.IX Item "EV_PERIODIC" 1278.IX Item "EV_PERIODIC"
518The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out. 1279The \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. 1283The 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 1284.ie n .IP """EV_CHILD""" 4
524.el .IP "\f(CWEV_CHILD\fR" 4 1285.el .IP "\f(CWEV_CHILD\fR" 4
525.IX Item "EV_CHILD" 1286.IX Item "EV_CHILD"
526The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change. 1287The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change.
1288.ie n .IP """EV_STAT""" 4
1289.el .IP "\f(CWEV_STAT\fR" 4
1290.IX Item "EV_STAT"
1291The path specified in the \f(CW\*(C`ev_stat\*(C'\fR watcher changed its attributes somehow.
527.ie n .IP """EV_IDLE""" 4 1292.ie n .IP """EV_IDLE""" 4
528.el .IP "\f(CWEV_IDLE\fR" 4 1293.el .IP "\f(CWEV_IDLE\fR" 4
529.IX Item "EV_IDLE" 1294.IX Item "EV_IDLE"
530The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do. 1295The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do.
531.ie n .IP """EV_PREPARE""" 4 1296.ie n .IP """EV_PREPARE""" 4
… …
534.PD 0 1299.PD 0
535.ie n .IP """EV_CHECK""" 4 1300.ie n .IP """EV_CHECK""" 4
536.el .IP "\f(CWEV_CHECK\fR" 4 1301.el .IP "\f(CWEV_CHECK\fR" 4
537.IX Item "EV_CHECK" 1302.IX Item "EV_CHECK"
538.PD 1303.PD
539All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_loop\*(C'\fR starts 1304All \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 1305gather 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 1306just after \f(CW\*(C`ev_run\*(C'\fR has gathered them, but before it queues any callbacks
1307for any received events. That means \f(CW\*(C`ev_prepare\*(C'\fR watchers are the last
1308watchers invoked before the event loop sleeps or polls for new events, and
1309\&\f(CW\*(C`ev_check\*(C'\fR watchers will be invoked before any other watchers of the same
1310or lower priority within an event loop iteration.
1311.Sp
542received events. Callbacks of both watcher types can start and stop as 1312Callbacks 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 1313they 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 1314\&\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). 1315blocking).
1316.ie n .IP """EV_EMBED""" 4
1317.el .IP "\f(CWEV_EMBED\fR" 4
1318.IX Item "EV_EMBED"
1319The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.
1320.ie n .IP """EV_FORK""" 4
1321.el .IP "\f(CWEV_FORK\fR" 4
1322.IX Item "EV_FORK"
1323The event loop has been resumed in the child process after fork (see
1324\&\f(CW\*(C`ev_fork\*(C'\fR).
1325.ie n .IP """EV_CLEANUP""" 4
1326.el .IP "\f(CWEV_CLEANUP\fR" 4
1327.IX Item "EV_CLEANUP"
1328The event loop is about to be destroyed (see \f(CW\*(C`ev_cleanup\*(C'\fR).
1329.ie n .IP """EV_ASYNC""" 4
1330.el .IP "\f(CWEV_ASYNC\fR" 4
1331.IX Item "EV_ASYNC"
1332The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR).
1333.ie n .IP """EV_CUSTOM""" 4
1334.el .IP "\f(CWEV_CUSTOM\fR" 4
1335.IX Item "EV_CUSTOM"
1336Not ever sent (or otherwise used) by libev itself, but can be freely used
1337by libev users to signal watchers (e.g. via \f(CW\*(C`ev_feed_event\*(C'\fR).
546.ie n .IP """EV_ERROR""" 4 1338.ie n .IP """EV_ERROR""" 4
547.el .IP "\f(CWEV_ERROR\fR" 4 1339.el .IP "\f(CWEV_ERROR\fR" 4
548.IX Item "EV_ERROR" 1340.IX Item "EV_ERROR"
549An unspecified error has occured, the watcher has been stopped. This might 1341An unspecified error has occurred, the watcher has been stopped. This might
550happen because the watcher could not be properly started because libev 1342happen 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 1343ran out of memory, a file descriptor was found to be closed or any other
1344problem. Libev considers these application bugs.
1345.Sp
552problem. You best act on it by reporting the problem and somehow coping 1346You best act on it by reporting the problem and somehow coping with the
553with the watcher being stopped. 1347watcher being stopped. Note that well-written programs should not receive
1348an error ever, so when your watcher receives it, this usually indicates a
1349bug in your program.
554.Sp 1350.Sp
555Libev will usually signal a few \*(L"dummy\*(R" events together with an error, 1351Libev 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 1352example 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 1353callbacks 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 1354the error from \fIread()\fR or \fIwrite()\fR. This will not work in multi-threaded
559programs, though, so beware. 1355programs, 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" 1356thing, so beware.
561.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER" 1357.SS "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0"
562Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change 1358.IX Subsection "GENERIC WATCHER FUNCTIONS"
563and read at any time, libev will completely ignore it. This can be used 1359.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
564to associate arbitrary data with your watcher. If you need more data and 1360.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 1361.IX Item "ev_init (ev_TYPE *watcher, callback)"
566member, you can also \*(L"subclass\*(R" the watcher type and provide your own 1362This macro initialises the generic portion of a watcher. The contents
567data: 1363of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
568.PP 1364the generic parts of the watcher are initialised, you \fIneed\fR to call
1365the type-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR macro afterwards to initialise the
1366type-specific parts. For each type there is also a \f(CW\*(C`ev_TYPE_init\*(C'\fR macro
1367which rolls both calls into one.
1368.Sp
1369You can reinitialise a watcher at any time as long as it has been stopped
1370(or never started) and there are no pending events outstanding.
1371.Sp
1372The callback is always of type \f(CW\*(C`void (*)(struct ev_loop *loop, ev_TYPE *watcher,
1373int revents)\*(C'\fR.
1374.Sp
1375Example: Initialise an \f(CW\*(C`ev_io\*(C'\fR watcher in two steps.
1376.Sp
569.Vb 7 1377.Vb 3
570\& struct my_io 1378\& ev_io w;
1379\& ev_init (&w, my_cb);
1380\& ev_io_set (&w, STDIN_FILENO, EV_READ);
1381.Ve
1382.ie n .IP """ev_TYPE_set"" (ev_TYPE *watcher, [args])" 4
1383.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *watcher, [args])" 4
1384.IX Item "ev_TYPE_set (ev_TYPE *watcher, [args])"
1385This macro initialises the type-specific parts of a watcher. You need to
1386call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
1387call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
1388macro on a watcher that is active (it can be pending, however, which is a
1389difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
1390.Sp
1391Although some watcher types do not have type-specific arguments
1392(e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
1393.Sp
1394See \f(CW\*(C`ev_init\*(C'\fR, above, for an example.
1395.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
1396.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
1397.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
1398This convenience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
1399calls into a single call. This is the most convenient method to initialise
1400a watcher. The same limitations apply, of course.
1401.Sp
1402Example: Initialise and set an \f(CW\*(C`ev_io\*(C'\fR watcher in one step.
1403.Sp
1404.Vb 1
1405\& ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1406.Ve
1407.ie n .IP """ev_TYPE_start"" (loop, ev_TYPE *watcher)" 4
1408.el .IP "\f(CWev_TYPE_start\fR (loop, ev_TYPE *watcher)" 4
1409.IX Item "ev_TYPE_start (loop, ev_TYPE *watcher)"
1410Starts (activates) the given watcher. Only active watchers will receive
1411events. If the watcher is already active nothing will happen.
1412.Sp
1413Example: Start the \f(CW\*(C`ev_io\*(C'\fR watcher that is being abused as example in this
1414whole section.
1415.Sp
1416.Vb 1
1417\& ev_io_start (EV_DEFAULT_UC, &w);
1418.Ve
1419.ie n .IP """ev_TYPE_stop"" (loop, ev_TYPE *watcher)" 4
1420.el .IP "\f(CWev_TYPE_stop\fR (loop, ev_TYPE *watcher)" 4
1421.IX Item "ev_TYPE_stop (loop, ev_TYPE *watcher)"
1422Stops the given watcher if active, and clears the pending status (whether
1423the watcher was active or not).
1424.Sp
1425It is possible that stopped watchers are pending \- for example,
1426non-repeating timers are being stopped when they become pending \- but
1427calling \f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor
1428pending. If you want to free or reuse the memory used by the watcher it is
1429therefore a good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
1430.IP "bool ev_is_active (ev_TYPE *watcher)" 4
1431.IX Item "bool ev_is_active (ev_TYPE *watcher)"
1432Returns a true value iff the watcher is active (i.e. it has been started
1433and not yet been stopped). As long as a watcher is active you must not modify
1434it.
1435.IP "bool ev_is_pending (ev_TYPE *watcher)" 4
1436.IX Item "bool ev_is_pending (ev_TYPE *watcher)"
1437Returns a true value iff the watcher is pending, (i.e. it has outstanding
1438events but its callback has not yet been invoked). As long as a watcher
1439is pending (but not active) you must not call an init function on it (but
1440\&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe), you must not change its priority, and you must
1441make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR
1442it).
1443.IP "callback ev_cb (ev_TYPE *watcher)" 4
1444.IX Item "callback ev_cb (ev_TYPE *watcher)"
1445Returns the callback currently set on the watcher.
1446.IP "ev_set_cb (ev_TYPE *watcher, callback)" 4
1447.IX Item "ev_set_cb (ev_TYPE *watcher, callback)"
1448Change the callback. You can change the callback at virtually any time
1449(modulo threads).
1450.IP "ev_set_priority (ev_TYPE *watcher, int priority)" 4
1451.IX Item "ev_set_priority (ev_TYPE *watcher, int priority)"
1452.PD 0
1453.IP "int ev_priority (ev_TYPE *watcher)" 4
1454.IX Item "int ev_priority (ev_TYPE *watcher)"
1455.PD
1456Set and query the priority of the watcher. The priority is a small
1457integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR
1458(default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked
1459before watchers with lower priority, but priority will not keep watchers
1460from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
1461.Sp
1462If you need to suppress invocation when higher priority events are pending
1463you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
1464.Sp
1465You \fImust not\fR change the priority of a watcher as long as it is active or
1466pending.
1467.Sp
1468Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
1469fine, as long as you do not mind that the priority value you query might
1470or might not have been clamped to the valid range.
1471.Sp
1472The default priority used by watchers when no priority has been set is
1473always \f(CW0\fR, which is supposed to not be too high and not be too low :).
1474.Sp
1475See \*(L"\s-1WATCHER\s0 \s-1PRIORITY\s0 \s-1MODELS\s0\*(R", below, for a more thorough treatment of
1476priorities.
1477.IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
1478.IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
1479Invoke the \f(CW\*(C`watcher\*(C'\fR with the given \f(CW\*(C`loop\*(C'\fR and \f(CW\*(C`revents\*(C'\fR. Neither
1480\&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback
1481can deal with that fact, as both are simply passed through to the
1482callback.
1483.IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
1484.IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
1485If the watcher is pending, this function clears its pending status and
1486returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the
1487watcher isn't pending it does nothing and returns \f(CW0\fR.
1488.Sp
1489Sometimes it can be useful to \*(L"poll\*(R" a watcher instead of waiting for its
1490callback to be invoked, which can be accomplished with this function.
1491.IP "ev_feed_event (loop, ev_TYPE *watcher, int revents)" 4
1492.IX Item "ev_feed_event (loop, ev_TYPE *watcher, int revents)"
1493Feeds the given event set into the event loop, as if the specified event
1494had happened for the specified watcher (which must be a pointer to an
1495initialised but not necessarily started event watcher). Obviously you must
1496not free the watcher as long as it has pending events.
1497.Sp
1498Stopping the watcher, letting libev invoke it, or calling
1499\&\f(CW\*(C`ev_clear_pending\*(C'\fR will clear the pending event, even if the watcher was
1500not started in the first place.
1501.Sp
1502See also \f(CW\*(C`ev_feed_fd_event\*(C'\fR and \f(CW\*(C`ev_feed_signal_event\*(C'\fR for related
1503functions that do not need a watcher.
1504.PP
1505See also the \*(L"\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0\*(R" and \*(L"\s-1BUILDING\s0 \s-1YOUR\s0
1506\&\s-1OWN\s0 \s-1COMPOSITE\s0 \s-1WATCHERS\s0\*(R" idioms.
1507.SS "\s-1WATCHER\s0 \s-1STATES\s0"
1508.IX Subsection "WATCHER STATES"
1509There are various watcher states mentioned throughout this manual \-
1510active, pending and so on. In this section these states and the rules to
1511transition between them will be described in more detail \- and while these
1512rules might look complicated, they usually do \*(L"the right thing\*(R".
1513.IP "initialiased" 4
1514.IX Item "initialiased"
1515Before a watcher can be registered with the event loop it has to be
1516initialised. This can be done with a call to \f(CW\*(C`ev_TYPE_init\*(C'\fR, or calls to
1517\&\f(CW\*(C`ev_init\*(C'\fR followed by the watcher-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR function.
1518.Sp
1519In this state it is simply some block of memory that is suitable for
1520use in an event loop. It can be moved around, freed, reused etc. at
1521will \- as long as you either keep the memory contents intact, or call
1522\&\f(CW\*(C`ev_TYPE_init\*(C'\fR again.
1523.IP "started/running/active" 4
1524.IX Item "started/running/active"
1525Once a watcher has been started with a call to \f(CW\*(C`ev_TYPE_start\*(C'\fR it becomes
1526property of the event loop, and is actively waiting for events. While in
1527this state it cannot be accessed (except in a few documented ways), moved,
1528freed or anything else \- the only legal thing is to keep a pointer to it,
1529and call libev functions on it that are documented to work on active watchers.
1530.IP "pending" 4
1531.IX Item "pending"
1532If a watcher is active and libev determines that an event it is interested
1533in has occurred (such as a timer expiring), it will become pending. It will
1534stay in this pending state until either it is stopped or its callback is
1535about to be invoked, so it is not normally pending inside the watcher
1536callback.
1537.Sp
1538The watcher might or might not be active while it is pending (for example,
1539an expired non-repeating timer can be pending but no longer active). If it
1540is stopped, it can be freely accessed (e.g. by calling \f(CW\*(C`ev_TYPE_set\*(C'\fR),
1541but it is still property of the event loop at this time, so cannot be
1542moved, freed or reused. And if it is active the rules described in the
1543previous item still apply.
1544.Sp
1545It is also possible to feed an event on a watcher that is not active (e.g.
1546via \f(CW\*(C`ev_feed_event\*(C'\fR), in which case it becomes pending without being
1547active.
1548.IP "stopped" 4
1549.IX Item "stopped"
1550A watcher can be stopped implicitly by libev (in which case it might still
1551be pending), or explicitly by calling its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. The
1552latter will clear any pending state the watcher might be in, regardless
1553of whether it was active or not, so stopping a watcher explicitly before
1554freeing it is often a good idea.
1555.Sp
1556While stopped (and not pending) the watcher is essentially in the
1557initialised state, that is, it can be reused, moved, modified in any way
1558you wish (but when you trash the memory block, you need to \f(CW\*(C`ev_TYPE_init\*(C'\fR
1559it again).
1560.SS "\s-1WATCHER\s0 \s-1PRIORITY\s0 \s-1MODELS\s0"
1561.IX Subsection "WATCHER PRIORITY MODELS"
1562Many event loops support \fIwatcher priorities\fR, which are usually small
1563integers that influence the ordering of event callback invocation
1564between watchers in some way, all else being equal.
1565.PP
1566In libev, Watcher priorities can be set using \f(CW\*(C`ev_set_priority\*(C'\fR. See its
1567description for the more technical details such as the actual priority
1568range.
1569.PP
1570There are two common ways how these these priorities are being interpreted
1571by event loops:
1572.PP
1573In the more common lock-out model, higher priorities \*(L"lock out\*(R" invocation
1574of lower priority watchers, which means as long as higher priority
1575watchers receive events, lower priority watchers are not being invoked.
1576.PP
1577The less common only-for-ordering model uses priorities solely to order
1578callback invocation within a single event loop iteration: Higher priority
1579watchers are invoked before lower priority ones, but they all get invoked
1580before polling for new events.
1581.PP
1582Libev uses the second (only-for-ordering) model for all its watchers
1583except for idle watchers (which use the lock-out model).
1584.PP
1585The rationale behind this is that implementing the lock-out model for
1586watchers is not well supported by most kernel interfaces, and most event
1587libraries will just poll for the same events again and again as long as
1588their callbacks have not been executed, which is very inefficient in the
1589common case of one high-priority watcher locking out a mass of lower
1590priority ones.
1591.PP
1592Static (ordering) priorities are most useful when you have two or more
1593watchers handling the same resource: a typical usage example is having an
1594\&\f(CW\*(C`ev_io\*(C'\fR watcher to receive data, and an associated \f(CW\*(C`ev_timer\*(C'\fR to handle
1595timeouts. Under load, data might be received while the program handles
1596other jobs, but since timers normally get invoked first, the timeout
1597handler will be executed before checking for data. In that case, giving
1598the timer a lower priority than the I/O watcher ensures that I/O will be
1599handled first even under adverse conditions (which is usually, but not
1600always, what you want).
1601.PP
1602Since idle watchers use the \*(L"lock-out\*(R" model, meaning that idle watchers
1603will only be executed when no same or higher priority watchers have
1604received events, they can be used to implement the \*(L"lock-out\*(R" model when
1605required.
1606.PP
1607For example, to emulate how many other event libraries handle priorities,
1608you can associate an \f(CW\*(C`ev_idle\*(C'\fR watcher to each such watcher, and in
1609the normal watcher callback, you just start the idle watcher. The real
1610processing is done in the idle watcher callback. This causes libev to
1611continuously poll and process kernel event data for the watcher, but when
1612the lock-out case is known to be rare (which in turn is rare :), this is
1613workable.
1614.PP
1615Usually, however, the lock-out model implemented that way will perform
1616miserably under the type of load it was designed to handle. In that case,
1617it might be preferable to stop the real watcher before starting the
1618idle watcher, so the kernel will not have to process the event in case
1619the actual processing will be delayed for considerable time.
1620.PP
1621Here is an example of an I/O watcher that should run at a strictly lower
1622priority than the default, and which should only process data when no
1623other events are pending:
1624.PP
1625.Vb 2
1626\& ev_idle idle; // actual processing watcher
1627\& ev_io io; // actual event watcher
1628\&
1629\& static void
1630\& io_cb (EV_P_ ev_io *w, int revents)
571\& { 1631\& {
572\& struct ev_io io; 1632\& // stop the I/O watcher, we received the event, but
573\& int otherfd; 1633\& // are not yet ready to handle it.
574\& void *somedata; 1634\& ev_io_stop (EV_A_ w);
575\& struct whatever *mostinteresting; 1635\&
1636\& // start the idle watcher to handle the actual event.
1637\& // it will not be executed as long as other watchers
1638\& // with the default priority are receiving events.
1639\& ev_idle_start (EV_A_ &idle);
576\& } 1640\& }
577.Ve 1641\&
578.PP 1642\& static void
579And since your callback will be called with a pointer to the watcher, you 1643\& 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\& { 1644\& {
585\& struct my_io *w = (struct my_io *)w_; 1645\& // actual processing
586\& ... 1646\& read (STDIN_FILENO, ...);
1647\&
1648\& // have to start the I/O watcher again, as
1649\& // we have handled the event
1650\& ev_io_start (EV_P_ &io);
587\& } 1651\& }
1652\&
1653\& // initialisation
1654\& ev_idle_init (&idle, idle_cb);
1655\& ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
1656\& ev_io_start (EV_DEFAULT_ &io);
588.Ve 1657.Ve
589.PP 1658.PP
590More interesting and less C\-conformant ways of catsing your callback type 1659In the \*(L"real\*(R" world, it might also be beneficial to start a timer, so that
591have been omitted.... 1660low-priority connections can not be locked out forever under load. This
1661enables your program to keep a lower latency for important connections
1662during short periods of high load, while not completely locking out less
1663important ones.
592.SH "WATCHER TYPES" 1664.SH "WATCHER TYPES"
593.IX Header "WATCHER TYPES" 1665.IX Header "WATCHER TYPES"
594This section describes each watcher in detail, but will not repeat 1666This section describes each watcher in detail, but will not repeat
595information given in the last section. 1667information given in the last section. Any initialisation/set macros,
1668functions and members specific to the watcher type are explained.
1669.PP
1670Members are additionally marked with either \fI[read\-only]\fR, meaning that,
1671while the watcher is active, you can look at the member and expect some
1672sensible content, but you must not modify it (you can modify it while the
1673watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
1674means you can expect it to have some sensible content while the watcher
1675is active, but you can also modify it. Modifying it may not do something
1676sensible or take immediate effect (or do anything at all), but libev will
1677not crash or malfunction in any way.
596.ie n .Sh """ev_io"" \- is this file descriptor readable or writable" 1678.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" 1679.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" 1680.IX Subsection "ev_io - is this file descriptor readable or writable?"
599I/O watchers check whether a file descriptor is readable or writable 1681I/O watchers check whether a file descriptor is readable or writable
600in each iteration of the event loop (This behaviour is called 1682in each iteration of the event loop, or, more precisely, when reading
601level-triggering because you keep receiving events as long as the 1683would 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 1684some data. This behaviour is called level-triggering because you keep
603act on the event and neither want to receive future events). 1685receiving events as long as the condition persists. Remember you can stop
1686the watcher if you don't want to act on the event and neither want to
1687receive future events.
604.PP 1688.PP
605In general you can register as many read and/or write event watchers per 1689In 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 1690fd 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 1691descriptors to non-blocking mode is also usually a good idea (but not
608required if you know what you are doing). 1692required if you know what you are doing).
609.PP 1693.PP
610You have to be careful with dup'ed file descriptors, though. Some backends 1694Another 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 1695receive \*(L"spurious\*(R" readiness notifications, that is, your callback might
612descriptors correctly if you register interest in two or more fds pointing 1696be 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 1697because there is no data. It is very easy to get into this situation even
614the same underlying \*(L"file open\*(R"). 1698with a relatively standard program structure. Thus it is best to always
1699use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning \f(CW\*(C`EAGAIN\*(C'\fR is far
1700preferable to a program hanging until some data arrives.
615.PP 1701.PP
616If you must do this, then force the use of a known-to-be-good backend 1702If 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 1703not play around with an Xlib connection), then you have to separately
618\&\s-1EVMETHOD_POLL\s0). 1704re-test whether a file descriptor is really ready with a known-to-be good
1705interface such as poll (fortunately in the case of Xlib, it already does
1706this on its own, so its quite safe to use). Some people additionally
1707use \f(CW\*(C`SIGALRM\*(C'\fR and an interval timer, just to be sure you won't block
1708indefinitely.
1709.PP
1710But really, best use non-blocking mode.
1711.PP
1712\fIThe special problem of disappearing file descriptors\fR
1713.IX Subsection "The special problem of disappearing file descriptors"
1714.PP
1715Some backends (e.g. kqueue, epoll) need to be told about closing a file
1716descriptor (either due to calling \f(CW\*(C`close\*(C'\fR explicitly or any other means,
1717such as \f(CW\*(C`dup2\*(C'\fR). The reason is that you register interest in some file
1718descriptor, but when it goes away, the operating system will silently drop
1719this interest. If another file descriptor with the same number then is
1720registered with libev, there is no efficient way to see that this is, in
1721fact, a different file descriptor.
1722.PP
1723To avoid having to explicitly tell libev about such cases, libev follows
1724the following policy: Each time \f(CW\*(C`ev_io_set\*(C'\fR is being called, libev
1725will assume that this is potentially a new file descriptor, otherwise
1726it is assumed that the file descriptor stays the same. That means that
1727you \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
1728descriptor even if the file descriptor number itself did not change.
1729.PP
1730This is how one would do it normally anyway, the important point is that
1731the libev application should not optimise around libev but should leave
1732optimisations to libev.
1733.PP
1734\fIThe special problem of dup'ed file descriptors\fR
1735.IX Subsection "The special problem of dup'ed file descriptors"
1736.PP
1737Some backends (e.g. epoll), cannot register events for file descriptors,
1738but only events for the underlying file descriptions. That means when you
1739have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register
1740events for them, only one file descriptor might actually receive events.
1741.PP
1742There is no workaround possible except not registering events
1743for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
1744\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1745.PP
1746\fIThe special problem of files\fR
1747.IX Subsection "The special problem of files"
1748.PP
1749Many people try to use \f(CW\*(C`select\*(C'\fR (or libev) on file descriptors
1750representing files, and expect it to become ready when their program
1751doesn't block on disk accesses (which can take a long time on their own).
1752.PP
1753However, this cannot ever work in the \*(L"expected\*(R" way \- you get a readiness
1754notification as soon as the kernel knows whether and how much data is
1755there, and in the case of open files, that's always the case, so you
1756always get a readiness notification instantly, and your read (or possibly
1757write) will still block on the disk I/O.
1758.PP
1759Another way to view it is that in the case of sockets, pipes, character
1760devices and so on, there is another party (the sender) that delivers data
1761on its own, but in the case of files, there is no such thing: the disk
1762will not send data on its own, simply because it doesn't know what you
1763wish to read \- you would first have to request some data.
1764.PP
1765Since files are typically not-so-well supported by advanced notification
1766mechanism, libev tries hard to emulate \s-1POSIX\s0 behaviour with respect
1767to files, even though you should not use it. The reason for this is
1768convenience: sometimes you want to watch \s-1STDIN\s0 or \s-1STDOUT\s0, which is
1769usually a tty, often a pipe, but also sometimes files or special devices
1770(for example, \f(CW\*(C`epoll\*(C'\fR on Linux works with \fI/dev/random\fR but not with
1771\&\fI/dev/urandom\fR), and even though the file might better be served with
1772asynchronous I/O instead of with non-blocking I/O, it is still useful when
1773it \*(L"just works\*(R" instead of freezing.
1774.PP
1775So avoid file descriptors pointing to files when you know it (e.g. use
1776libeio), but use them when it is convenient, e.g. for \s-1STDIN/STDOUT\s0, or
1777when you rarely read from a file instead of from a socket, and want to
1778reuse the same code path.
1779.PP
1780\fIThe special problem of fork\fR
1781.IX Subsection "The special problem of fork"
1782.PP
1783Some backends (epoll, kqueue) do not support \f(CW\*(C`fork ()\*(C'\fR at all or exhibit
1784useless behaviour. Libev fully supports fork, but needs to be told about
1785it in the child if you want to continue to use it in the child.
1786.PP
1787To support fork in your child processes, you have to call \f(CW\*(C`ev_loop_fork
1788()\*(C'\fR after a fork in the child, enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to
1789\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1790.PP
1791\fIThe special problem of \s-1SIGPIPE\s0\fR
1792.IX Subsection "The special problem of SIGPIPE"
1793.PP
1794While not really specific to libev, it is easy to forget about \f(CW\*(C`SIGPIPE\*(C'\fR:
1795when writing to a pipe whose other end has been closed, your program gets
1796sent a \s-1SIGPIPE\s0, which, by default, aborts your program. For most programs
1797this is sensible behaviour, for daemons, this is usually undesirable.
1798.PP
1799So when you encounter spurious, unexplained daemon exits, make sure you
1800ignore \s-1SIGPIPE\s0 (and maybe make sure you log the exit status of your daemon
1801somewhere, as that would have given you a big clue).
1802.PP
1803\fIThe special problem of \fIaccept()\fIing when you can't\fR
1804.IX Subsection "The special problem of accept()ing when you can't"
1805.PP
1806Many implementations of the \s-1POSIX\s0 \f(CW\*(C`accept\*(C'\fR function (for example,
1807found in post\-2004 Linux) have the peculiar behaviour of not removing a
1808connection from the pending queue in all error cases.
1809.PP
1810For example, larger servers often run out of file descriptors (because
1811of resource limits), causing \f(CW\*(C`accept\*(C'\fR to fail with \f(CW\*(C`ENFILE\*(C'\fR but not
1812rejecting the connection, leading to libev signalling readiness on
1813the next iteration again (the connection still exists after all), and
1814typically causing the program to loop at 100% \s-1CPU\s0 usage.
1815.PP
1816Unfortunately, the set of errors that cause this issue differs between
1817operating systems, there is usually little the app can do to remedy the
1818situation, and no known thread-safe method of removing the connection to
1819cope with overload is known (to me).
1820.PP
1821One of the easiest ways to handle this situation is to just ignore it
1822\&\- when the program encounters an overload, it will just loop until the
1823situation is over. While this is a form of busy waiting, no \s-1OS\s0 offers an
1824event-based way to handle this situation, so it's the best one can do.
1825.PP
1826A better way to handle the situation is to log any errors other than
1827\&\f(CW\*(C`EAGAIN\*(C'\fR and \f(CW\*(C`EWOULDBLOCK\*(C'\fR, making sure not to flood the log with such
1828messages, and continue as usual, which at least gives the user an idea of
1829what could be wrong (\*(L"raise the ulimit!\*(R"). For extra points one could stop
1830the \f(CW\*(C`ev_io\*(C'\fR watcher on the listening fd \*(L"for a while\*(R", which reduces \s-1CPU\s0
1831usage.
1832.PP
1833If your program is single-threaded, then you could also keep a dummy file
1834descriptor for overload situations (e.g. by opening \fI/dev/null\fR), and
1835when 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,
1836close that fd, and create a new dummy fd. This will gracefully refuse
1837clients under typical overload conditions.
1838.PP
1839The last way to handle it is to simply log the error and \f(CW\*(C`exit\*(C'\fR, as
1840is often done with \f(CW\*(C`malloc\*(C'\fR failures, but this results in an easy
1841opportunity for a DoS attack.
1842.PP
1843\fIWatcher-Specific Functions\fR
1844.IX Subsection "Watcher-Specific Functions"
619.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4 1845.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)" 1846.IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
621.PD 0 1847.PD 0
622.IP "ev_io_set (ev_io *, int fd, int events)" 4 1848.IP "ev_io_set (ev_io *, int fd, int events)" 4
623.IX Item "ev_io_set (ev_io *, int fd, int events)" 1849.IX Item "ev_io_set (ev_io *, int fd, int events)"
624.PD 1850.PD
625Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The fd is the file descriptor to rceeive 1851Configures 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 | 1852receive events for and \f(CW\*(C`events\*(C'\fR is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or
627EV_WRITE\*(C'\fR to receive the given events. 1853\&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR, to express the desire to receive the given events.
1854.IP "int fd [read\-only]" 4
1855.IX Item "int fd [read-only]"
1856The file descriptor being watched.
1857.IP "int events [read\-only]" 4
1858.IX Item "int events [read-only]"
1859The events being watched.
1860.PP
1861\fIExamples\fR
1862.IX Subsection "Examples"
1863.PP
1864Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
1865readable, but only once. Since it is likely line-buffered, you could
1866attempt to read a whole line in the callback.
1867.PP
1868.Vb 6
1869\& static void
1870\& stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1871\& {
1872\& ev_io_stop (loop, w);
1873\& .. read from stdin here (or from w\->fd) and handle any I/O errors
1874\& }
1875\&
1876\& ...
1877\& struct ev_loop *loop = ev_default_init (0);
1878\& ev_io stdin_readable;
1879\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1880\& ev_io_start (loop, &stdin_readable);
1881\& ev_run (loop, 0);
1882.Ve
628.ie n .Sh """ev_timer"" \- relative and optionally recurring timeouts" 1883.ie n .SS """ev_timer"" \- relative and optionally repeating timeouts"
629.el .Sh "\f(CWev_timer\fP \- relative and optionally recurring timeouts" 1884.el .SS "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
630.IX Subsection "ev_timer - relative and optionally recurring timeouts" 1885.IX Subsection "ev_timer - relative and optionally repeating timeouts"
631Timer watchers are simple relative timers that generate an event after a 1886Timer watchers are simple relative timers that generate an event after a
632given time, and optionally repeating in regular intervals after that. 1887given time, and optionally repeating in regular intervals after that.
633.PP 1888.PP
634The timers are based on real time, that is, if you register an event that 1889The 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 1890times 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 1891year, it will still time out after (roughly) one hour. \*(L"Roughly\*(R" because
637detecting time jumps is hard, and some inaccuracies are unavoidable (the 1892detecting time jumps is hard, and some inaccuracies are unavoidable (the
638monotonic clock option helps a lot here). 1893monotonic clock option helps a lot here).
1894.PP
1895The callback is guaranteed to be invoked only \fIafter\fR its timeout has
1896passed (not \fIat\fR, so on systems with very low-resolution clocks this
1897might introduce a small delay, see \*(L"the special problem of being too
1898early\*(R", below). If multiple timers become ready during the same loop
1899iteration then the ones with earlier time-out values are invoked before
1900ones of the same priority with later time-out values (but this is no
1901longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
1902.PP
1903\fIBe smart about timeouts\fR
1904.IX Subsection "Be smart about timeouts"
1905.PP
1906Many real-world problems involve some kind of timeout, usually for error
1907recovery. A typical example is an \s-1HTTP\s0 request \- if the other side hangs,
1908you want to raise some error after a while.
1909.PP
1910What follows are some ways to handle this problem, from obvious and
1911inefficient to smart and efficient.
1912.PP
1913In the following, a 60 second activity timeout is assumed \- a timeout that
1914gets reset to 60 seconds each time there is activity (e.g. each time some
1915data or other life sign was received).
1916.IP "1. Use a timer and stop, reinitialise and start it on activity." 4
1917.IX Item "1. Use a timer and stop, reinitialise and start it on activity."
1918This is the most obvious, but not the most simple way: In the beginning,
1919start the watcher:
1920.Sp
1921.Vb 2
1922\& ev_timer_init (timer, callback, 60., 0.);
1923\& ev_timer_start (loop, timer);
1924.Ve
1925.Sp
1926Then, each time there is some activity, \f(CW\*(C`ev_timer_stop\*(C'\fR it, initialise it
1927and start it again:
1928.Sp
1929.Vb 3
1930\& ev_timer_stop (loop, timer);
1931\& ev_timer_set (timer, 60., 0.);
1932\& ev_timer_start (loop, timer);
1933.Ve
1934.Sp
1935This is relatively simple to implement, but means that each time there is
1936some activity, libev will first have to remove the timer from its internal
1937data structure and then add it again. Libev tries to be fast, but it's
1938still not a constant-time operation.
1939.ie n .IP "2. Use a timer and re-start it with ""ev_timer_again"" inactivity." 4
1940.el .IP "2. Use a timer and re-start it with \f(CWev_timer_again\fR inactivity." 4
1941.IX Item "2. Use a timer and re-start it with ev_timer_again inactivity."
1942This is the easiest way, and involves using \f(CW\*(C`ev_timer_again\*(C'\fR instead of
1943\&\f(CW\*(C`ev_timer_start\*(C'\fR.
1944.Sp
1945To implement this, configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value
1946of \f(CW60\fR and then call \f(CW\*(C`ev_timer_again\*(C'\fR at start and each time you
1947successfully read or write some data. If you go into an idle state where
1948you do not expect data to travel on the socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR
1949the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will automatically restart it if need be.
1950.Sp
1951That means you can ignore both the \f(CW\*(C`ev_timer_start\*(C'\fR function and the
1952\&\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
1953member and \f(CW\*(C`ev_timer_again\*(C'\fR.
1954.Sp
1955At start:
1956.Sp
1957.Vb 3
1958\& ev_init (timer, callback);
1959\& timer\->repeat = 60.;
1960\& ev_timer_again (loop, timer);
1961.Ve
1962.Sp
1963Each time there is some activity:
1964.Sp
1965.Vb 1
1966\& ev_timer_again (loop, timer);
1967.Ve
1968.Sp
1969It is even possible to change the time-out on the fly, regardless of
1970whether the watcher is active or not:
1971.Sp
1972.Vb 2
1973\& timer\->repeat = 30.;
1974\& ev_timer_again (loop, timer);
1975.Ve
1976.Sp
1977This is slightly more efficient then stopping/starting the timer each time
1978you want to modify its timeout value, as libev does not have to completely
1979remove and re-insert the timer from/into its internal data structure.
1980.Sp
1981It is, however, even simpler than the \*(L"obvious\*(R" way to do it.
1982.IP "3. Let the timer time out, but then re-arm it as required." 4
1983.IX Item "3. Let the timer time out, but then re-arm it as required."
1984This method is more tricky, but usually most efficient: Most timeouts are
1985relatively long compared to the intervals between other activity \- in
1986our example, within 60 seconds, there are usually many I/O events with
1987associated activity resets.
1988.Sp
1989In this case, it would be more efficient to leave the \f(CW\*(C`ev_timer\*(C'\fR alone,
1990but remember the time of last activity, and check for a real timeout only
1991within the callback:
1992.Sp
1993.Vb 3
1994\& ev_tstamp timeout = 60.;
1995\& ev_tstamp last_activity; // time of last activity
1996\& ev_timer timer;
1997\&
1998\& static void
1999\& callback (EV_P_ ev_timer *w, int revents)
2000\& {
2001\& // calculate when the timeout would happen
2002\& ev_tstamp after = last_activity \- ev_now (EV_A) + timeout;
2003\&
2004\& // if negative, it means we the timeout already occurred
2005\& if (after < 0.)
2006\& {
2007\& // timeout occurred, take action
2008\& }
2009\& else
2010\& {
2011\& // callback was invoked, but there was some recent
2012\& // activity. simply restart the timer to time out
2013\& // after "after" seconds, which is the earliest time
2014\& // the timeout can occur.
2015\& ev_timer_set (w, after, 0.);
2016\& ev_timer_start (EV_A_ w);
2017\& }
2018\& }
2019.Ve
2020.Sp
2021To summarise the callback: first calculate in how many seconds the
2022timeout will occur (by calculating the absolute time when it would occur,
2023\&\f(CW\*(C`last_activity + timeout\*(C'\fR, and subtracting the current time, \f(CW\*(C`ev_now
2024(EV_A)\*(C'\fR from that).
2025.Sp
2026If this value is negative, then we are already past the timeout, i.e. we
2027timed out, and need to do whatever is needed in this case.
2028.Sp
2029Otherwise, we now the earliest time at which the timeout would trigger,
2030and simply start the timer with this timeout value.
2031.Sp
2032In other words, each time the callback is invoked it will check whether
2033the timeout occurred. If not, it will simply reschedule itself to check
2034again at the earliest time it could time out. Rinse. Repeat.
2035.Sp
2036This scheme causes more callback invocations (about one every 60 seconds
2037minus half the average time between activity), but virtually no calls to
2038libev to change the timeout.
2039.Sp
2040To start the machinery, simply initialise the watcher and set
2041\&\f(CW\*(C`last_activity\*(C'\fR to the current time (meaning there was some activity just
2042now), then call the callback, which will \*(L"do the right thing\*(R" and start
2043the timer:
2044.Sp
2045.Vb 3
2046\& last_activity = ev_now (EV_A);
2047\& ev_init (&timer, callback);
2048\& callback (EV_A_ &timer, 0);
2049.Ve
2050.Sp
2051When there is some activity, simply store the current time in
2052\&\f(CW\*(C`last_activity\*(C'\fR, no libev calls at all:
2053.Sp
2054.Vb 2
2055\& if (activity detected)
2056\& last_activity = ev_now (EV_A);
2057.Ve
2058.Sp
2059When your timeout value changes, then the timeout can be changed by simply
2060providing a new value, stopping the timer and calling the callback, which
2061will again do the right thing (for example, time out immediately :).
2062.Sp
2063.Vb 3
2064\& timeout = new_value;
2065\& ev_timer_stop (EV_A_ &timer);
2066\& callback (EV_A_ &timer, 0);
2067.Ve
2068.Sp
2069This technique is slightly more complex, but in most cases where the
2070time-out is unlikely to be triggered, much more efficient.
2071.IP "4. Wee, just use a double-linked list for your timeouts." 4
2072.IX Item "4. Wee, just use a double-linked list for your timeouts."
2073If there is not one request, but many thousands (millions...), all
2074employing some kind of timeout with the same timeout value, then one can
2075do even better:
2076.Sp
2077When starting the timeout, calculate the timeout value and put the timeout
2078at the \fIend\fR of the list.
2079.Sp
2080Then use an \f(CW\*(C`ev_timer\*(C'\fR to fire when the timeout at the \fIbeginning\fR of
2081the list is expected to fire (for example, using the technique #3).
2082.Sp
2083When there is some activity, remove the timer from the list, recalculate
2084the timeout, append it to the end of the list again, and make sure to
2085update the \f(CW\*(C`ev_timer\*(C'\fR if it was taken from the beginning of the list.
2086.Sp
2087This way, one can manage an unlimited number of timeouts in O(1) time for
2088starting, stopping and updating the timers, at the expense of a major
2089complication, and having to use a constant timeout. The constant timeout
2090ensures that the list stays sorted.
2091.PP
2092So which method the best?
2093.PP
2094Method #2 is a simple no-brain-required solution that is adequate in most
2095situations. Method #3 requires a bit more thinking, but handles many cases
2096better, and isn't very complicated either. In most case, choosing either
2097one is fine, with #3 being better in typical situations.
2098.PP
2099Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
2100rather complicated, but extremely efficient, something that really pays
2101off after the first million or so of active timers, i.e. it's usually
2102overkill :)
2103.PP
2104\fIThe special problem of being too early\fR
2105.IX Subsection "The special problem of being too early"
2106.PP
2107If you ask a timer to call your callback after three seconds, then
2108you expect it to be invoked after three seconds \- but of course, this
2109cannot be guaranteed to infinite precision. Less obviously, it cannot be
2110guaranteed to any precision by libev \- imagine somebody suspending the
2111process with a \s-1STOP\s0 signal for a few hours for example.
2112.PP
2113So, libev tries to invoke your callback as soon as possible \fIafter\fR the
2114delay has occurred, but cannot guarantee this.
2115.PP
2116A less obvious failure mode is calling your callback too early: many event
2117loops compare timestamps with a \*(L"elapsed delay >= requested delay\*(R", but
2118this can cause your callback to be invoked much earlier than you would
2119expect.
2120.PP
2121To see why, imagine a system with a clock that only offers full second
2122resolution (think windows if you can't come up with a broken enough \s-1OS\s0
2123yourself). If you schedule a one-second timer at the time 500.9, then the
2124event loop will schedule your timeout to elapse at a system time of 500
2125(500.9 truncated to the resolution) + 1, or 501.
2126.PP
2127If an event library looks at the timeout 0.1s later, it will see \*(L"501 >=
2128501\*(R" and invoke the callback 0.1s after it was started, even though a
2129one-second delay was requested \- this is being \*(L"too early\*(R", despite best
2130intentions.
2131.PP
2132This is the reason why libev will never invoke the callback if the elapsed
2133delay equals the requested delay, but only when the elapsed delay is
2134larger than the requested delay. In the example above, libev would only invoke
2135the callback at system time 502, or 1.1s after the timer was started.
2136.PP
2137So, while libev cannot guarantee that your callback will be invoked
2138exactly when requested, it \fIcan\fR and \fIdoes\fR guarantee that the requested
2139delay has actually elapsed, or in other words, it always errs on the \*(L"too
2140late\*(R" side of things.
2141.PP
2142\fIThe special problem of time updates\fR
2143.IX Subsection "The special problem of time updates"
2144.PP
2145Establishing the current time is a costly operation (it usually takes
2146at least one system call): \s-1EV\s0 therefore updates its idea of the current
2147time only before and after \f(CW\*(C`ev_run\*(C'\fR collects new events, which causes a
2148growing difference between \f(CW\*(C`ev_now ()\*(C'\fR and \f(CW\*(C`ev_time ()\*(C'\fR when handling
2149lots of events in one iteration.
639.PP 2150.PP
640The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR 2151The 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 2152time. This is usually the right thing as this timestamp refers to the time
642of the event triggering whatever timeout you are modifying/starting. If 2153of 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 2154you 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: 2155timeout on the current time, use something like this to adjust for this:
645.PP 2156.PP
646.Vb 1 2157.Vb 1
647\& ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); 2158\& ev_timer_set (&timer, after + ev_now () \- ev_time (), 0.);
648.Ve 2159.Ve
649.PP 2160.PP
650The callback is guarenteed to be invoked only when its timeout has passed, 2161If 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 2162update 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. 2163()\*(C'\fR.
2164.PP
2165\fIThe special problem of unsynchronised clocks\fR
2166.IX Subsection "The special problem of unsynchronised clocks"
2167.PP
2168Modern systems have a variety of clocks \- libev itself uses the normal
2169\&\*(L"wall clock\*(R" clock and, if available, the monotonic clock (to avoid time
2170jumps).
2171.PP
2172Neither of these clocks is synchronised with each other or any other clock
2173on the system, so \f(CW\*(C`ev_time ()\*(C'\fR might return a considerably different time
2174than \f(CW\*(C`gettimeofday ()\*(C'\fR or \f(CW\*(C`time ()\*(C'\fR. On a GNU/Linux system, for example,
2175a call to \f(CW\*(C`gettimeofday\*(C'\fR might return a second count that is one higher
2176than a directly following call to \f(CW\*(C`time\*(C'\fR.
2177.PP
2178The moral of this is to only compare libev-related timestamps with
2179\&\f(CW\*(C`ev_time ()\*(C'\fR and \f(CW\*(C`ev_now ()\*(C'\fR, at least if you want better precision than
2180a second or so.
2181.PP
2182One more problem arises due to this lack of synchronisation: if libev uses
2183the system monotonic clock and you compare timestamps from \f(CW\*(C`ev_time\*(C'\fR
2184or \f(CW\*(C`ev_now\*(C'\fR from when you started your timer and when your callback is
2185invoked, you will find that sometimes the callback is a bit \*(L"early\*(R".
2186.PP
2187This is because \f(CW\*(C`ev_timer\*(C'\fRs work in real time, not wall clock time, so
2188libev makes sure your callback is not invoked before the delay happened,
2189\&\fImeasured according to the real time\fR, not the system clock.
2190.PP
2191If your timeouts are based on a physical timescale (e.g. \*(L"time out this
2192connection after 100 seconds\*(R") then this shouldn't bother you as it is
2193exactly the right behaviour.
2194.PP
2195If you want to compare wall clock/system timestamps to your timers, then
2196you need to use \f(CW\*(C`ev_periodic\*(C'\fRs, as these are based on the wall clock
2197time, where your comparisons will always generate correct results.
2198.PP
2199\fIThe special problems of suspended animation\fR
2200.IX Subsection "The special problems of suspended animation"
2201.PP
2202When you leave the server world it is quite customary to hit machines that
2203can suspend/hibernate \- what happens to the clocks during such a suspend?
2204.PP
2205Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
2206all processes, while the clocks (\f(CW\*(C`times\*(C'\fR, \f(CW\*(C`CLOCK_MONOTONIC\*(C'\fR) continue
2207to run until the system is suspended, but they will not advance while the
2208system is suspended. That means, on resume, it will be as if the program
2209was frozen for a few seconds, but the suspend time will not be counted
2210towards \f(CW\*(C`ev_timer\*(C'\fR when a monotonic clock source is used. The real time
2211clock advanced as expected, but if it is used as sole clocksource, then a
2212long suspend would be detected as a time jump by libev, and timers would
2213be adjusted accordingly.
2214.PP
2215I would not be surprised to see different behaviour in different between
2216operating systems, \s-1OS\s0 versions or even different hardware.
2217.PP
2218The other form of suspend (job control, or sending a \s-1SIGSTOP\s0) will see a
2219time jump in the monotonic clocks and the realtime clock. If the program
2220is suspended for a very long time, and monotonic clock sources are in use,
2221then you can expect \f(CW\*(C`ev_timer\*(C'\fRs to expire as the full suspension time
2222will be counted towards the timers. When no monotonic clock source is in
2223use, then libev will again assume a timejump and adjust accordingly.
2224.PP
2225It might be beneficial for this latter case to call \f(CW\*(C`ev_suspend\*(C'\fR
2226and \f(CW\*(C`ev_resume\*(C'\fR in code that handles \f(CW\*(C`SIGTSTP\*(C'\fR, to at least get
2227deterministic behaviour in this case (you can do nothing against
2228\&\f(CW\*(C`SIGSTOP\*(C'\fR).
2229.PP
2230\fIWatcher-Specific Functions and Data Members\fR
2231.IX Subsection "Watcher-Specific Functions and Data Members"
653.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4 2232.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)" 2233.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
655.PD 0 2234.PD 0
656.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4 2235.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)" 2236.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
658.PD 2237.PD
659Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR is 2238Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR
660\&\f(CW0.\fR, then it will automatically be stopped. If it is positive, then the 2239is \f(CW0.\fR, then it will automatically be stopped once the timeout is
661timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds 2240reached. If it is positive, then the timer will automatically be
662later, again, and again, until stopped manually. 2241configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds later, again, and again,
2242until stopped manually.
663.Sp 2243.Sp
664The timer itself will do a best-effort at avoiding drift, that is, if you 2244The 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 2245you configure a timer to trigger every 10 seconds, then it will normally
666exactly 10 second intervals. If, however, your program cannot keep up with 2246trigger at exactly 10 second intervals. If, however, your program cannot
667the timer (because it takes longer than those 10 seconds to do stuff) the 2247keep up with the timer (because it takes longer than those 10 seconds to
668timer will not fire more than once per event loop iteration. 2248do stuff) the timer will not fire more than once per event loop iteration.
669.IP "ev_timer_again (loop)" 4 2249.IP "ev_timer_again (loop, ev_timer *)" 4
670.IX Item "ev_timer_again (loop)" 2250.IX Item "ev_timer_again (loop, ev_timer *)"
671This will act as if the timer timed out and restart it again if it is 2251This will act as if the timer timed out, and restarts it again if it is
672repeating. The exact semantics are: 2252repeating. It basically works like calling \f(CW\*(C`ev_timer_stop\*(C'\fR, updating the
2253timeout to the \f(CW\*(C`repeat\*(C'\fR value and calling \f(CW\*(C`ev_timer_start\*(C'\fR.
673.Sp 2254.Sp
674If the timer is started but nonrepeating, stop it. 2255The exact semantics are as in the following rules, all of which will be
2256applied to the watcher:
2257.RS 4
2258.IP "If the timer is pending, the pending status is always cleared." 4
2259.IX Item "If the timer is pending, the pending status is always cleared."
2260.PD 0
2261.IP "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)." 4
2262.IX Item "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)."
2263.ie n .IP "If the timer is repeating, make the ""repeat"" value the new timeout and start the timer, if necessary." 4
2264.el .IP "If the timer is repeating, make the \f(CWrepeat\fR value the new timeout and start the timer, if necessary." 4
2265.IX Item "If the timer is repeating, make the repeat value the new timeout and start the timer, if necessary."
2266.RE
2267.RS 4
2268.PD
675.Sp 2269.Sp
676If the timer is repeating, either start it if necessary (with the repeat 2270This sounds a bit complicated, see \*(L"Be smart about timeouts\*(R", above, for a
677value), or reset the running timer to the repeat value. 2271usage example.
2272.RE
2273.IP "ev_tstamp ev_timer_remaining (loop, ev_timer *)" 4
2274.IX Item "ev_tstamp ev_timer_remaining (loop, ev_timer *)"
2275Returns the remaining time until a timer fires. If the timer is active,
2276then this time is relative to the current event loop time, otherwise it's
2277the timeout value currently configured.
678.Sp 2278.Sp
679This sounds a bit complicated, but here is a useful and typical 2279That 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 2280\&\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 2281will 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 2282roughly \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 2283too), and so on.
684time you successfully read or write some data. If you go into an idle 2284.IP "ev_tstamp repeat [read\-write]" 4
685state where you do not expect data to travel on the socket, you can stop 2285.IX Item "ev_tstamp repeat [read-write]"
686the timer, and again will automatically restart it if need be. 2286The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
2287or \f(CW\*(C`ev_timer_again\*(C'\fR is called, and determines the next timeout (if any),
2288which is also when any modifications are taken into account.
2289.PP
2290\fIExamples\fR
2291.IX Subsection "Examples"
2292.PP
2293Example: Create a timer that fires after 60 seconds.
2294.PP
2295.Vb 5
2296\& static void
2297\& one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
2298\& {
2299\& .. one minute over, w is actually stopped right here
2300\& }
2301\&
2302\& ev_timer mytimer;
2303\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
2304\& ev_timer_start (loop, &mytimer);
2305.Ve
2306.PP
2307Example: Create a timeout timer that times out after 10 seconds of
2308inactivity.
2309.PP
2310.Vb 5
2311\& static void
2312\& timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
2313\& {
2314\& .. ten seconds without any activity
2315\& }
2316\&
2317\& ev_timer mytimer;
2318\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
2319\& ev_timer_again (&mytimer); /* start timer */
2320\& ev_run (loop, 0);
2321\&
2322\& // and in some piece of code that gets executed on any "activity":
2323\& // reset the timeout to start ticking again at 10 seconds
2324\& ev_timer_again (&mytimer);
2325.Ve
687.ie n .Sh """ev_periodic"" \- to cron or not to cron" 2326.ie n .SS """ev_periodic"" \- to cron or not to cron?"
688.el .Sh "\f(CWev_periodic\fP \- to cron or not to cron" 2327.el .SS "\f(CWev_periodic\fP \- to cron or not to cron?"
689.IX Subsection "ev_periodic - to cron or not to cron" 2328.IX Subsection "ev_periodic - to cron or not to cron?"
690Periodic watchers are also timers of a kind, but they are very versatile 2329Periodic watchers are also timers of a kind, but they are very versatile
691(and unfortunately a bit complex). 2330(and unfortunately a bit complex).
692.PP 2331.PP
693Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time) 2332Unlike \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 2333relative 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 2334(absolute time, the thing you can read on your calender or clock). The
696periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now () 2335difference 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 2336time, 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 2337wrist-watch).
699roughly 10 seconds later and of course not if you reset your system time
700again).
701.PP 2338.PP
702They can also be used to implement vastly more complex timers, such as 2339You can tell a periodic watcher to trigger after some specific point
703triggering an event on eahc midnight, local time. 2340in time: for example, if you tell a periodic watcher to trigger \*(L"in 10
2341seconds\*(R" (by specifying e.g. \f(CW\*(C`ev_now () + 10.\*(C'\fR, that is, an absolute time
2342not a delay) and then reset your system clock to January of the previous
2343year, then it will take a year or more to trigger the event (unlike an
2344\&\f(CW\*(C`ev_timer\*(C'\fR, which would still trigger roughly 10 seconds after starting
2345it, as it uses a relative timeout).
704.PP 2346.PP
2347\&\f(CW\*(C`ev_periodic\*(C'\fR watchers can also be used to implement vastly more complex
2348timers, such as triggering an event on each \*(L"midnight, local time\*(R", or
2349other complicated rules. This cannot be done with \f(CW\*(C`ev_timer\*(C'\fR watchers, as
2350those cannot react to time jumps.
2351.PP
705As with timers, the callback is guarenteed to be invoked only when the 2352As 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 2353point in time where it is supposed to trigger has passed. If multiple
707during the same loop iteration then order of execution is undefined. 2354timers become ready during the same loop iteration then the ones with
2355earlier time-out values are invoked before ones with later time-out values
2356(but this is no longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
2357.PP
2358\fIWatcher-Specific Functions and Data Members\fR
2359.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 2360.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)" 2361.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
710.PD 0 2362.PD 0
711.IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4 2363.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)" 2364.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
713.PD 2365.PD
714Lots of arguments, lets sort it out... There are basically three modes of 2366Lots of arguments, let's sort it out... There are basically three modes of
715operation, and we will explain them from simplest to complex: 2367operation, and we will explain them from simplest to most complex:
716.RS 4 2368.RS 4
717.IP "* absolute timer (interval = reschedule_cb = 0)" 4 2369.IP "\(bu" 4
718.IX Item "absolute timer (interval = reschedule_cb = 0)" 2370absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
2371.Sp
719In this configuration the watcher triggers an event at the wallclock time 2372In 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, 2373time \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 2374time jump occurs, that is, if it is to be run at January 1st 2011 then it
722system time reaches or surpasses this time. 2375will be stopped and invoked when the system clock reaches or surpasses
723.IP "* non-repeating interval timer (interval > 0, reschedule_cb = 0)" 4 2376this point in time.
724.IX Item "non-repeating interval timer (interval > 0, reschedule_cb = 0)" 2377.IP "\(bu" 4
2378repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
2379.Sp
725In this mode the watcher will always be scheduled to time out at the next 2380In 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 2381\&\f(CW\*(C`offset + N * interval\*(C'\fR time (for some integer N, which can also be
727of any time jumps. 2382negative) and then repeat, regardless of any time jumps. The \f(CW\*(C`offset\*(C'\fR
2383argument is merely an offset into the \f(CW\*(C`interval\*(C'\fR periods.
728.Sp 2384.Sp
729This can be used to create timers that do not drift with respect to system 2385This can be used to create timers that do not drift with respect to the
730time: 2386system clock, for example, here is an \f(CW\*(C`ev_periodic\*(C'\fR that triggers each
2387hour, on the hour (with respect to \s-1UTC\s0):
731.Sp 2388.Sp
732.Vb 1 2389.Vb 1
733\& ev_periodic_set (&periodic, 0., 3600., 0); 2390\& ev_periodic_set (&periodic, 0., 3600., 0);
734.Ve 2391.Ve
735.Sp 2392.Sp
736This doesn't mean there will always be 3600 seconds in between triggers, 2393This 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 2394but 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 2395full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
739by 3600. 2396by 3600.
740.Sp 2397.Sp
741Another way to think about it (for the mathematically inclined) is that 2398Another 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 2399\&\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. 2400time where \f(CW\*(C`time = offset (mod interval)\*(C'\fR, regardless of any time jumps.
744.IP "* manual reschedule mode (reschedule_cb = callback)" 4 2401.Sp
745.IX Item "manual reschedule mode (reschedule_cb = callback)" 2402The \f(CW\*(C`interval\*(C'\fR \fI\s-1MUST\s0\fR be positive, and for numerical stability, the
2403interval value should be higher than \f(CW\*(C`1/8192\*(C'\fR (which is around 100
2404microseconds) and \f(CW\*(C`offset\*(C'\fR should be higher than \f(CW0\fR and should have
2405at most a similar magnitude as the current time (say, within a factor of
2406ten). Typical values for offset are, in fact, \f(CW0\fR or something between
2407\&\f(CW0\fR and \f(CW\*(C`interval\*(C'\fR, which is also the recommended range.
2408.Sp
2409Note also that there is an upper limit to how often a timer can fire (\s-1CPU\s0
2410speed for example), so if \f(CW\*(C`interval\*(C'\fR is very small then timing stability
2411will of course deteriorate. Libev itself tries to be exact to be about one
2412millisecond (if the \s-1OS\s0 supports it and the machine is fast enough).
2413.IP "\(bu" 4
2414manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
2415.Sp
746In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being 2416In 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 2417ignored. Instead, each time the periodic watcher gets scheduled, the
748reschedule callback will be called with the watcher as first, and the 2418reschedule callback will be called with the watcher as first, and the
749current time as second argument. 2419current time as second argument.
750.Sp 2420.Sp
751\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, 2421\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, ever,
752ever, or make any event loop modifications\fR. If you need to stop it, 2422or 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 2423allowed by documentation here\fR.
754starting a prepare watcher).
755.Sp 2424.Sp
2425If you need to stop it, return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop
2426it afterwards (e.g. by starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is the
2427only event loop modification you are allowed to do).
2428.Sp
756Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w, 2429The callback prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(ev_periodic
757ev_tstamp now)\*(C'\fR, e.g.: 2430*w, ev_tstamp now)\*(C'\fR, e.g.:
758.Sp 2431.Sp
759.Vb 4 2432.Vb 5
2433\& static ev_tstamp
760\& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) 2434\& my_rescheduler (ev_periodic *w, ev_tstamp now)
761\& { 2435\& {
762\& return now + 60.; 2436\& return now + 60.;
763\& } 2437\& }
764.Ve 2438.Ve
765.Sp 2439.Sp
766It must return the next time to trigger, based on the passed time value 2440It 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 2441(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 2442will usually be called just before the callback will be triggered, but
769might be called at other times, too. 2443might be called at other times, too.
770.Sp 2444.Sp
771\&\s-1NOTE:\s0 \fIThis callback must always return a time that is later than the 2445\&\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. 2446equal to the passed \f(CI\*(C`now\*(C'\fI value\fR.
773.Sp 2447.Sp
774This can be used to create very complex timers, such as a timer that 2448This 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 2449triggers on \*(L"next midnight, local time\*(R". To do this, you would calculate the
776next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How 2450next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How
777you do this is, again, up to you (but it is not trivial, which is the main 2451you do this is, again, up to you (but it is not trivial, which is the main
778reason I omitted it as an example). 2452reason I omitted it as an example).
779.RE 2453.RE
780.RS 4 2454.RS 4
… …
783.IX Item "ev_periodic_again (loop, ev_periodic *)" 2457.IX Item "ev_periodic_again (loop, ev_periodic *)"
784Simply stops and restarts the periodic watcher again. This is only useful 2458Simply stops and restarts the periodic watcher again. This is only useful
785when you changed some parameters or the reschedule callback would return 2459when 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 2460a different time than the last time it was called (e.g. in a crond like
787program when the crontabs have changed). 2461program when the crontabs have changed).
2462.IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4
2463.IX Item "ev_tstamp ev_periodic_at (ev_periodic *)"
2464When active, returns the absolute time that the watcher is supposed
2465to trigger next. This is not the same as the \f(CW\*(C`offset\*(C'\fR argument to
2466\&\f(CW\*(C`ev_periodic_set\*(C'\fR, but indeed works even in interval and manual
2467rescheduling modes.
2468.IP "ev_tstamp offset [read\-write]" 4
2469.IX Item "ev_tstamp offset [read-write]"
2470When repeating, this contains the offset value, otherwise this is the
2471absolute point in time (the \f(CW\*(C`offset\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR,
2472although libev might modify this value for better numerical stability).
2473.Sp
2474Can be modified any time, but changes only take effect when the periodic
2475timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
2476.IP "ev_tstamp interval [read\-write]" 4
2477.IX Item "ev_tstamp interval [read-write]"
2478The current interval value. Can be modified any time, but changes only
2479take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
2480called.
2481.IP "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read\-write]" 4
2482.IX Item "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]"
2483The current reschedule callback, or \f(CW0\fR, if this functionality is
2484switched off. Can be changed any time, but changes only take effect when
2485the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
2486.PP
2487\fIExamples\fR
2488.IX Subsection "Examples"
2489.PP
2490Example: Call a callback every hour, or, more precisely, whenever the
2491system time is divisible by 3600. The callback invocation times have
2492potentially a lot of jitter, but good long-term stability.
2493.PP
2494.Vb 5
2495\& static void
2496\& clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
2497\& {
2498\& ... its now a full hour (UTC, or TAI or whatever your clock follows)
2499\& }
2500\&
2501\& ev_periodic hourly_tick;
2502\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
2503\& ev_periodic_start (loop, &hourly_tick);
2504.Ve
2505.PP
2506Example: The same as above, but use a reschedule callback to do it:
2507.PP
2508.Vb 1
2509\& #include <math.h>
2510\&
2511\& static ev_tstamp
2512\& my_scheduler_cb (ev_periodic *w, ev_tstamp now)
2513\& {
2514\& return now + (3600. \- fmod (now, 3600.));
2515\& }
2516\&
2517\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
2518.Ve
2519.PP
2520Example: Call a callback every hour, starting now:
2521.PP
2522.Vb 4
2523\& ev_periodic hourly_tick;
2524\& ev_periodic_init (&hourly_tick, clock_cb,
2525\& fmod (ev_now (loop), 3600.), 3600., 0);
2526\& ev_periodic_start (loop, &hourly_tick);
2527.Ve
788.ie n .Sh """ev_signal"" \- signal me when a signal gets signalled" 2528.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" 2529.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" 2530.IX Subsection "ev_signal - signal me when a signal gets signalled!"
791Signal watchers will trigger an event when the process receives a specific 2531Signal watchers will trigger an event when the process receives a specific
792signal one or more times. Even though signals are very asynchronous, libev 2532signal 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 2533will try its best to deliver signals synchronously, i.e. as part of the
794normal event processing, like any other event. 2534normal event processing, like any other event.
795.PP 2535.PP
2536If you want signals to be delivered truly asynchronously, just use
2537\&\f(CW\*(C`sigaction\*(C'\fR as you would do without libev and forget about sharing
2538the signal. You can even use \f(CW\*(C`ev_async\*(C'\fR from a signal handler to
2539synchronously wake up an event loop.
2540.PP
796You can configure as many watchers as you like per signal. Only when the 2541You can configure as many watchers as you like for the same signal, but
2542only within the same loop, i.e. you can watch for \f(CW\*(C`SIGINT\*(C'\fR in your
2543default loop and for \f(CW\*(C`SIGIO\*(C'\fR in another loop, but you cannot watch for
2544\&\f(CW\*(C`SIGINT\*(C'\fR in both the default loop and another loop at the same time. At
2545the moment, \f(CW\*(C`SIGCHLD\*(C'\fR is permanently tied to the default loop.
2546.PP
797first watcher gets started will libev actually register a signal watcher 2547When the first watcher gets started will libev actually register something
798with the kernel (thus it coexists with your own signal handlers as long 2548with the kernel (thus it coexists with your own signal handlers as long as
799as you don't register any with libev). Similarly, when the last signal 2549you don't register any with libev for the same signal).
800watcher for a signal is stopped libev will reset the signal handler to 2550.PP
801\&\s-1SIG_DFL\s0 (regardless of what it was set to before). 2551If possible and supported, libev will install its handlers with
2552\&\f(CW\*(C`SA_RESTART\*(C'\fR (or equivalent) behaviour enabled, so system calls should
2553not be unduly interrupted. If you have a problem with system calls getting
2554interrupted by signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher
2555and unblock them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher.
2556.PP
2557\fIThe special problem of inheritance over fork/execve/pthread_create\fR
2558.IX Subsection "The special problem of inheritance over fork/execve/pthread_create"
2559.PP
2560Both the signal mask (\f(CW\*(C`sigprocmask\*(C'\fR) and the signal disposition
2561(\f(CW\*(C`sigaction\*(C'\fR) are unspecified after starting a signal watcher (and after
2562stopping it again), that is, libev might or might not block the signal,
2563and might or might not set or restore the installed signal handler (but
2564see \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR).
2565.PP
2566While this does not matter for the signal disposition (libev never
2567sets signals to \f(CW\*(C`SIG_IGN\*(C'\fR, so handlers will be reset to \f(CW\*(C`SIG_DFL\*(C'\fR on
2568\&\f(CW\*(C`execve\*(C'\fR), this matters for the signal mask: many programs do not expect
2569certain signals to be blocked.
2570.PP
2571This means that before calling \f(CW\*(C`exec\*(C'\fR (from the child) you should reset
2572the signal mask to whatever \*(L"default\*(R" you expect (all clear is a good
2573choice usually).
2574.PP
2575The simplest way to ensure that the signal mask is reset in the child is
2576to install a fork handler with \f(CW\*(C`pthread_atfork\*(C'\fR that resets it. That will
2577catch fork calls done by libraries (such as the libc) as well.
2578.PP
2579In current versions of libev, the signal will not be blocked indefinitely
2580unless you use the \f(CW\*(C`signalfd\*(C'\fR \s-1API\s0 (\f(CW\*(C`EV_SIGNALFD\*(C'\fR). While this reduces
2581the window of opportunity for problems, it will not go away, as libev
2582\&\fIhas\fR to modify the signal mask, at least temporarily.
2583.PP
2584So I can't stress this enough: \fIIf you do not reset your signal mask when
2585you expect it to be empty, you have a race condition in your code\fR. This
2586is not a libev-specific thing, this is true for most event libraries.
2587.PP
2588\fIThe special problem of threads signal handling\fR
2589.IX Subsection "The special problem of threads signal handling"
2590.PP
2591\&\s-1POSIX\s0 threads has problematic signal handling semantics, specifically,
2592a lot of functionality (sigfd, sigwait etc.) only really works if all
2593threads in a process block signals, which is hard to achieve.
2594.PP
2595When you want to use sigwait (or mix libev signal handling with your own
2596for the same signals), you can tackle this problem by globally blocking
2597all signals before creating any threads (or creating them with a fully set
2598sigprocmask) and also specifying the \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when creating
2599loops. Then designate one thread as \*(L"signal receiver thread\*(R" which handles
2600these signals. You can pass on any signals that libev might be interested
2601in by calling \f(CW\*(C`ev_feed_signal\*(C'\fR.
2602.PP
2603\fIWatcher-Specific Functions and Data Members\fR
2604.IX Subsection "Watcher-Specific Functions and Data Members"
802.IP "ev_signal_init (ev_signal *, callback, int signum)" 4 2605.IP "ev_signal_init (ev_signal *, callback, int signum)" 4
803.IX Item "ev_signal_init (ev_signal *, callback, int signum)" 2606.IX Item "ev_signal_init (ev_signal *, callback, int signum)"
804.PD 0 2607.PD 0
805.IP "ev_signal_set (ev_signal *, int signum)" 4 2608.IP "ev_signal_set (ev_signal *, int signum)" 4
806.IX Item "ev_signal_set (ev_signal *, int signum)" 2609.IX Item "ev_signal_set (ev_signal *, int signum)"
807.PD 2610.PD
808Configures the watcher to trigger on the given signal number (usually one 2611Configures the watcher to trigger on the given signal number (usually one
809of the \f(CW\*(C`SIGxxx\*(C'\fR constants). 2612of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
2613.IP "int signum [read\-only]" 4
2614.IX Item "int signum [read-only]"
2615The signal the watcher watches out for.
2616.PP
2617\fIExamples\fR
2618.IX Subsection "Examples"
2619.PP
2620Example: Try to exit cleanly on \s-1SIGINT\s0.
2621.PP
2622.Vb 5
2623\& static void
2624\& sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
2625\& {
2626\& ev_break (loop, EVBREAK_ALL);
2627\& }
2628\&
2629\& ev_signal signal_watcher;
2630\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
2631\& ev_signal_start (loop, &signal_watcher);
2632.Ve
810.ie n .Sh """ev_child"" \- wait for pid status changes" 2633.ie n .SS """ev_child"" \- watch out for process status changes"
811.el .Sh "\f(CWev_child\fP \- wait for pid status changes" 2634.el .SS "\f(CWev_child\fP \- watch out for process status changes"
812.IX Subsection "ev_child - wait for pid status changes" 2635.IX Subsection "ev_child - watch out for process status changes"
813Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to 2636Child 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). 2637some child status changes (most typically when a child of yours dies or
2638exits). It is permissible to install a child watcher \fIafter\fR the child
2639has been forked (which implies it might have already exited), as long
2640as the event loop isn't entered (or is continued from a watcher), i.e.,
2641forking and then immediately registering a watcher for the child is fine,
2642but forking and registering a watcher a few event loop iterations later or
2643in the next callback invocation is not.
2644.PP
2645Only the default event loop is capable of handling signals, and therefore
2646you can only register child watchers in the default event loop.
2647.PP
2648Due to some design glitches inside libev, child watchers will always be
2649handled at maximum priority (their priority is set to \f(CW\*(C`EV_MAXPRI\*(C'\fR by
2650libev)
2651.PP
2652\fIProcess Interaction\fR
2653.IX Subsection "Process Interaction"
2654.PP
2655Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is
2656initialised. This is necessary to guarantee proper behaviour even if the
2657first child watcher is started after the child exits. The occurrence
2658of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done
2659synchronously as part of the event loop processing. Libev always reaps all
2660children, even ones not watched.
2661.PP
2662\fIOverriding the Built-In Processing\fR
2663.IX Subsection "Overriding the Built-In Processing"
2664.PP
2665Libev offers no special support for overriding the built-in child
2666processing, but if your application collides with libev's default child
2667handler, you can override it easily by installing your own handler for
2668\&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the
2669default loop never gets destroyed. You are encouraged, however, to use an
2670event-based approach to child reaping and thus use libev's support for
2671that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely.
2672.PP
2673\fIStopping the Child Watcher\fR
2674.IX Subsection "Stopping the Child Watcher"
2675.PP
2676Currently, the child watcher never gets stopped, even when the
2677child terminates, so normally one needs to stop the watcher in the
2678callback. Future versions of libev might stop the watcher automatically
2679when a child exit is detected (calling \f(CW\*(C`ev_child_stop\*(C'\fR twice is not a
2680problem).
2681.PP
2682\fIWatcher-Specific Functions and Data Members\fR
2683.IX Subsection "Watcher-Specific Functions and Data Members"
815.IP "ev_child_init (ev_child *, callback, int pid)" 4 2684.IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4
816.IX Item "ev_child_init (ev_child *, callback, int pid)" 2685.IX Item "ev_child_init (ev_child *, callback, int pid, int trace)"
817.PD 0 2686.PD 0
818.IP "ev_child_set (ev_child *, int pid)" 4 2687.IP "ev_child_set (ev_child *, int pid, int trace)" 4
819.IX Item "ev_child_set (ev_child *, int pid)" 2688.IX Item "ev_child_set (ev_child *, int pid, int trace)"
820.PD 2689.PD
821Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or 2690Configures 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 2691\&\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 2692at 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 2693the 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 2694\&\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. 2695process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only
2696activate the watcher when the process terminates) or \f(CW1\fR (additionally
2697activate the watcher when the process is stopped or continued).
2698.IP "int pid [read\-only]" 4
2699.IX Item "int pid [read-only]"
2700The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
2701.IP "int rpid [read\-write]" 4
2702.IX Item "int rpid [read-write]"
2703The process id that detected a status change.
2704.IP "int rstatus [read\-write]" 4
2705.IX Item "int rstatus [read-write]"
2706The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
2707\&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
2708.PP
2709\fIExamples\fR
2710.IX Subsection "Examples"
2711.PP
2712Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for
2713its completion.
2714.PP
2715.Vb 1
2716\& ev_child cw;
2717\&
2718\& static void
2719\& child_cb (EV_P_ ev_child *w, int revents)
2720\& {
2721\& ev_child_stop (EV_A_ w);
2722\& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus);
2723\& }
2724\&
2725\& pid_t pid = fork ();
2726\&
2727\& if (pid < 0)
2728\& // error
2729\& else if (pid == 0)
2730\& {
2731\& // the forked child executes here
2732\& exit (1);
2733\& }
2734\& else
2735\& {
2736\& ev_child_init (&cw, child_cb, pid, 0);
2737\& ev_child_start (EV_DEFAULT_ &cw);
2738\& }
2739.Ve
2740.ie n .SS """ev_stat"" \- did the file attributes just change?"
2741.el .SS "\f(CWev_stat\fP \- did the file attributes just change?"
2742.IX Subsection "ev_stat - did the file attributes just change?"
2743This watches a file system path for attribute changes. That is, it calls
2744\&\f(CW\*(C`stat\*(C'\fR on that path in regular intervals (or when the \s-1OS\s0 says it changed)
2745and sees if it changed compared to the last time, invoking the callback if
2746it did.
2747.PP
2748The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does
2749not exist\*(R" is a status change like any other. The condition \*(L"path does not
2750exist\*(R" (or more correctly \*(L"path cannot be stat'ed\*(R") is signified by the
2751\&\f(CW\*(C`st_nlink\*(C'\fR field being zero (which is otherwise always forced to be at
2752least one) and all the other fields of the stat buffer having unspecified
2753contents.
2754.PP
2755The path \fImust not\fR end in a slash or contain special components such as
2756\&\f(CW\*(C`.\*(C'\fR or \f(CW\*(C`..\*(C'\fR. The path \fIshould\fR be absolute: If it is relative and
2757your working directory changes, then the behaviour is undefined.
2758.PP
2759Since there is no portable change notification interface available, the
2760portable implementation simply calls \f(CWstat(2)\fR regularly on the path
2761to see if it changed somehow. You can specify a recommended polling
2762interval for this case. If you specify a polling interval of \f(CW0\fR (highly
2763recommended!) then a \fIsuitable, unspecified default\fR value will be used
2764(which you can expect to be around five seconds, although this might
2765change dynamically). Libev will also impose a minimum interval which is
2766currently around \f(CW0.1\fR, but that's usually overkill.
2767.PP
2768This watcher type is not meant for massive numbers of stat watchers,
2769as even with OS-supported change notifications, this can be
2770resource-intensive.
2771.PP
2772At the time of this writing, the only OS-specific interface implemented
2773is the Linux inotify interface (implementing kqueue support is left as an
2774exercise for the reader. Note, however, that the author sees no way of
2775implementing \f(CW\*(C`ev_stat\*(C'\fR semantics with kqueue, except as a hint).
2776.PP
2777\fI\s-1ABI\s0 Issues (Largefile Support)\fR
2778.IX Subsection "ABI Issues (Largefile Support)"
2779.PP
2780Libev by default (unless the user overrides this) uses the default
2781compilation environment, which means that on systems with large file
2782support disabled by default, you get the 32 bit version of the stat
2783structure. When using the library from programs that change the \s-1ABI\s0 to
2784use 64 bit file offsets the programs will fail. In that case you have to
2785compile libev with the same flags to get binary compatibility. This is
2786obviously the case with any flags that change the \s-1ABI\s0, but the problem is
2787most noticeably displayed with ev_stat and large file support.
2788.PP
2789The solution for this is to lobby your distribution maker to make large
2790file interfaces available by default (as e.g. FreeBSD does) and not
2791optional. Libev cannot simply switch on large file support because it has
2792to exchange stat structures with application programs compiled using the
2793default compilation environment.
2794.PP
2795\fIInotify and Kqueue\fR
2796.IX Subsection "Inotify and Kqueue"
2797.PP
2798When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev and present at
2799runtime, it will be used to speed up change detection where possible. The
2800inotify descriptor will be created lazily when the first \f(CW\*(C`ev_stat\*(C'\fR
2801watcher is being started.
2802.PP
2803Inotify presence does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
2804except that changes might be detected earlier, and in some cases, to avoid
2805making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presence of inotify support
2806there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling,
2807but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
2808many bugs), the path exists (i.e. stat succeeds), and the path resides on
2809a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
2810xfs are fully working) libev usually gets away without polling.
2811.PP
2812There is no support for kqueue, as apparently it cannot be used to
2813implement this functionality, due to the requirement of having a file
2814descriptor open on the object at all times, and detecting renames, unlinks
2815etc. is difficult.
2816.PP
2817\fI\f(CI\*(C`stat ()\*(C'\fI is a synchronous operation\fR
2818.IX Subsection "stat () is a synchronous operation"
2819.PP
2820Libev doesn't normally do any kind of I/O itself, and so is not blocking
2821the process. The exception are \f(CW\*(C`ev_stat\*(C'\fR watchers \- those call \f(CW\*(C`stat
2822()\*(C'\fR, which is a synchronous operation.
2823.PP
2824For local paths, this usually doesn't matter: unless the system is very
2825busy or the intervals between stat's are large, a stat call will be fast,
2826as the path data is usually in memory already (except when starting the
2827watcher).
2828.PP
2829For networked file systems, calling \f(CW\*(C`stat ()\*(C'\fR can block an indefinite
2830time due to network issues, and even under good conditions, a stat call
2831often takes multiple milliseconds.
2832.PP
2833Therefore, it is best to avoid using \f(CW\*(C`ev_stat\*(C'\fR watchers on networked
2834paths, although this is fully supported by libev.
2835.PP
2836\fIThe special problem of stat time resolution\fR
2837.IX Subsection "The special problem of stat time resolution"
2838.PP
2839The \f(CW\*(C`stat ()\*(C'\fR system call only supports full-second resolution portably,
2840and even on systems where the resolution is higher, most file systems
2841still only support whole seconds.
2842.PP
2843That means that, if the time is the only thing that changes, you can
2844easily miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and
2845calls your callback, which does something. When there is another update
2846within the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect unless the
2847stat data does change in other ways (e.g. file size).
2848.PP
2849The solution to this is to delay acting on a change for slightly more
2850than a second (or till slightly after the next full second boundary), using
2851a roughly one-second-delay \f(CW\*(C`ev_timer\*(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02);
2852ev_timer_again (loop, w)\*(C'\fR).
2853.PP
2854The \f(CW.02\fR offset is added to work around small timing inconsistencies
2855of some operating systems (where the second counter of the current time
2856might be be delayed. One such system is the Linux kernel, where a call to
2857\&\f(CW\*(C`gettimeofday\*(C'\fR might return a timestamp with a full second later than
2858a subsequent \f(CW\*(C`time\*(C'\fR call \- if the equivalent of \f(CW\*(C`time ()\*(C'\fR is used to
2859update file times then there will be a small window where the kernel uses
2860the previous second to update file times but libev might already execute
2861the timer callback).
2862.PP
2863\fIWatcher-Specific Functions and Data Members\fR
2864.IX Subsection "Watcher-Specific Functions and Data Members"
2865.IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
2866.IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
2867.PD 0
2868.IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4
2869.IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)"
2870.PD
2871Configures the watcher to wait for status changes of the given
2872\&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to
2873be detected and should normally be specified as \f(CW0\fR to let libev choose
2874a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same
2875path for as long as the watcher is active.
2876.Sp
2877The callback will receive an \f(CW\*(C`EV_STAT\*(C'\fR event when a change was detected,
2878relative to the attributes at the time the watcher was started (or the
2879last change was detected).
2880.IP "ev_stat_stat (loop, ev_stat *)" 4
2881.IX Item "ev_stat_stat (loop, ev_stat *)"
2882Updates the stat buffer immediately with new values. If you change the
2883watched path in your callback, you could call this function to avoid
2884detecting this change (while introducing a race condition if you are not
2885the only one changing the path). Can also be useful simply to find out the
2886new values.
2887.IP "ev_statdata attr [read\-only]" 4
2888.IX Item "ev_statdata attr [read-only]"
2889The most-recently detected attributes of the file. Although the type is
2890\&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
2891suitable for your system, but you can only rely on the POSIX-standardised
2892members to be present. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there was
2893some error while \f(CW\*(C`stat\*(C'\fRing the file.
2894.IP "ev_statdata prev [read\-only]" 4
2895.IX Item "ev_statdata prev [read-only]"
2896The previous attributes of the file. The callback gets invoked whenever
2897\&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR, or, more precisely, one or more of these members
2898differ: \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,
2899\&\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.
2900.IP "ev_tstamp interval [read\-only]" 4
2901.IX Item "ev_tstamp interval [read-only]"
2902The specified interval.
2903.IP "const char *path [read\-only]" 4
2904.IX Item "const char *path [read-only]"
2905The file system path that is being watched.
2906.PP
2907\fIExamples\fR
2908.IX Subsection "Examples"
2909.PP
2910Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
2911.PP
2912.Vb 10
2913\& static void
2914\& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
2915\& {
2916\& /* /etc/passwd changed in some way */
2917\& if (w\->attr.st_nlink)
2918\& {
2919\& printf ("passwd current size %ld\en", (long)w\->attr.st_size);
2920\& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime);
2921\& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime);
2922\& }
2923\& else
2924\& /* you shalt not abuse printf for puts */
2925\& puts ("wow, /etc/passwd is not there, expect problems. "
2926\& "if this is windows, they already arrived\en");
2927\& }
2928\&
2929\& ...
2930\& ev_stat passwd;
2931\&
2932\& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
2933\& ev_stat_start (loop, &passwd);
2934.Ve
2935.PP
2936Example: Like above, but additionally use a one-second delay so we do not
2937miss updates (however, frequent updates will delay processing, too, so
2938one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
2939\&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
2940.PP
2941.Vb 2
2942\& static ev_stat passwd;
2943\& static ev_timer timer;
2944\&
2945\& static void
2946\& timer_cb (EV_P_ ev_timer *w, int revents)
2947\& {
2948\& ev_timer_stop (EV_A_ w);
2949\&
2950\& /* now it\*(Aqs one second after the most recent passwd change */
2951\& }
2952\&
2953\& static void
2954\& stat_cb (EV_P_ ev_stat *w, int revents)
2955\& {
2956\& /* reset the one\-second timer */
2957\& ev_timer_again (EV_A_ &timer);
2958\& }
2959\&
2960\& ...
2961\& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
2962\& ev_stat_start (loop, &passwd);
2963\& ev_timer_init (&timer, timer_cb, 0., 1.02);
2964.Ve
827.ie n .Sh """ev_idle"" \- when you've got nothing better to do" 2965.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" 2966.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" 2967.IX Subsection "ev_idle - when you've got nothing better to do..."
830Idle watchers trigger events when there are no other events are pending 2968Idle 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 2969priority are pending (prepare, check and other idle watchers do not count
832as your process is busy handling sockets or timeouts (or even signals, 2970as receiving \*(L"events\*(R").
833imagine) it will not be triggered. But when your process is idle all idle 2971.PP
834watchers are being called again and again, once per event loop iteration \- 2972That is, as long as your process is busy handling sockets or timeouts
2973(or even signals, imagine) of the same or higher priority it will not be
2974triggered. But when your process is idle (or only lower-priority watchers
2975are pending), the idle watchers are being called once per event loop
835until stopped, that is, or your process receives more events and becomes 2976iteration \- until stopped, that is, or your process receives more events
836busy. 2977and becomes busy again with higher priority stuff.
837.PP 2978.PP
838The most noteworthy effect is that as long as any idle watchers are 2979The most noteworthy effect is that as long as any idle watchers are
839active, the process will not block when waiting for new events. 2980active, the process will not block when waiting for new events.
840.PP 2981.PP
841Apart from keeping your process non-blocking (which is a useful 2982Apart from keeping your process non-blocking (which is a useful
842effect on its own sometimes), idle watchers are a good place to do 2983effect 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 2984\&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the
844event loop has handled all outstanding events. 2985event loop has handled all outstanding events.
2986.PP
2987\fIAbusing an \f(CI\*(C`ev_idle\*(C'\fI watcher for its side-effect\fR
2988.IX Subsection "Abusing an ev_idle watcher for its side-effect"
2989.PP
2990As long as there is at least one active idle watcher, libev will never
2991sleep unnecessarily. Or in other words, it will loop as fast as possible.
2992For this to work, the idle watcher doesn't need to be invoked at all \- the
2993lowest priority will do.
2994.PP
2995This mode of operation can be useful together with an \f(CW\*(C`ev_check\*(C'\fR watcher,
2996to do something on each event loop iteration \- for example to balance load
2997between different connections.
2998.PP
2999See \*(L"Abusing an ev_check watcher for its side-effect\*(R" for a longer
3000example.
3001.PP
3002\fIWatcher-Specific Functions and Data Members\fR
3003.IX Subsection "Watcher-Specific Functions and Data Members"
845.IP "ev_idle_init (ev_signal *, callback)" 4 3004.IP "ev_idle_init (ev_idle *, callback)" 4
846.IX Item "ev_idle_init (ev_signal *, callback)" 3005.IX Item "ev_idle_init (ev_idle *, callback)"
847Initialises and configures the idle watcher \- it has no parameters of any 3006Initialises 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, 3007kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
849believe me. 3008believe me.
3009.PP
3010\fIExamples\fR
3011.IX Subsection "Examples"
3012.PP
3013Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the
3014callback, free it. Also, use no error checking, as usual.
3015.PP
3016.Vb 5
3017\& static void
3018\& idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
3019\& {
3020\& // stop the watcher
3021\& ev_idle_stop (loop, w);
3022\&
3023\& // now we can free it
3024\& free (w);
3025\&
3026\& // now do something you wanted to do when the program has
3027\& // no longer anything immediate to do.
3028\& }
3029\&
3030\& ev_idle *idle_watcher = malloc (sizeof (ev_idle));
3031\& ev_idle_init (idle_watcher, idle_cb);
3032\& ev_idle_start (loop, idle_watcher);
3033.Ve
850.ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop" 3034.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" 3035.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" 3036.IX Subsection "ev_prepare and ev_check - customise your event loop!"
853Prepare and check watchers are usually (but not always) used in tandem: 3037Prepare and check watchers are often (but not always) used in pairs:
854prepare watchers get invoked before the process blocks and check watchers 3038prepare watchers get invoked before the process blocks and check watchers
855afterwards. 3039afterwards.
856.PP 3040.PP
3041You \fImust not\fR call \f(CW\*(C`ev_run\*(C'\fR or similar functions that enter
3042the current event loop from either \f(CW\*(C`ev_prepare\*(C'\fR or \f(CW\*(C`ev_check\*(C'\fR
3043watchers. Other loops than the current one are fine, however. The
3044rationale behind this is that you do not need to check for recursion in
3045those watchers, i.e. the sequence will always be \f(CW\*(C`ev_prepare\*(C'\fR, blocking,
3046\&\f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each kind they will always be
3047called in pairs bracketing the blocking call.
3048.PP
857Their main purpose is to integrate other event mechanisms into libev. This 3049Their main purpose is to integrate other event mechanisms into libev and
858could be used, for example, to track variable changes, implement your own 3050their use is somewhat advanced. They could be used, for example, to track
859watchers, integrate net-snmp or a coroutine library and lots more. 3051variable changes, implement your own watchers, integrate net-snmp or a
3052coroutine library and lots more. They are also occasionally useful if
3053you cache some data and want to flush it before blocking (for example,
3054in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
3055watcher).
860.PP 3056.PP
861This is done by examining in each prepare call which file descriptors need 3057This 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 3058need 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 3059for 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 3060libraries provide exactly this functionality). Then, in the check watcher,
865any events that occured (by checking the pending status of all watchers 3061you 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 3062of all watchers and stopping them) and call back into the library. The
867callbacks will never actually be called (but must be valid nevertheless, 3063I/O and timer callbacks will never actually be called (but must be valid
868because you never know, you know?). 3064nevertheless, because you never know, you know?).
869.PP 3065.PP
870As another example, the Perl Coro module uses these hooks to integrate 3066As another example, the Perl Coro module uses these hooks to integrate
871coroutines into libev programs, by yielding to other active coroutines 3067coroutines into libev programs, by yielding to other active coroutines
872during each prepare and only letting the process block if no coroutines 3068during each prepare and only letting the process block if no coroutines
873are ready to run (it's actually more complicated: it only runs coroutines 3069are 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 3070with 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 3071of lower priority, but only once, using idle watchers to keep the event
876loop from blocking if lower-priority coroutines are active, thus mapping 3072loop from blocking if lower-priority coroutines are active, thus mapping
877low-priority coroutines to idle/background tasks). 3073low-priority coroutines to idle/background tasks).
3074.PP
3075When used for this purpose, it is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers
3076highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR) priority, to ensure that they are being run before
3077any other watchers after the poll (this doesn't matter for \f(CW\*(C`ev_prepare\*(C'\fR
3078watchers).
3079.PP
3080Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, too) should not
3081activate (\*(L"feed\*(R") events into libev. While libev fully supports this, they
3082might get executed before other \f(CW\*(C`ev_check\*(C'\fR watchers did their job. As
3083\&\f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other (non-libev) event
3084loops those other event loops might be in an unusable state until their
3085\&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with
3086others).
3087.PP
3088\fIAbusing an \f(CI\*(C`ev_check\*(C'\fI watcher for its side-effect\fR
3089.IX Subsection "Abusing an ev_check watcher for its side-effect"
3090.PP
3091\&\f(CW\*(C`ev_check\*(C'\fR (and less often also \f(CW\*(C`ev_prepare\*(C'\fR) watchers can also be
3092useful because they are called once per event loop iteration. For
3093example, if you want to handle a large number of connections fairly, you
3094normally only do a bit of work for each active connection, and if there
3095is more work to do, you wait for the next event loop iteration, so other
3096connections have a chance of making progress.
3097.PP
3098Using an \f(CW\*(C`ev_check\*(C'\fR watcher is almost enough: it will be called on the
3099next event loop iteration. However, that isn't as soon as possible \-
3100without external events, your \f(CW\*(C`ev_check\*(C'\fR watcher will not be invoked.
3101.PP
3102This is where \f(CW\*(C`ev_idle\*(C'\fR watchers come in handy \- all you need is a
3103single global idle watcher that is active as long as you have one active
3104\&\f(CW\*(C`ev_check\*(C'\fR watcher. The \f(CW\*(C`ev_idle\*(C'\fR watcher makes sure the event loop
3105will not sleep, and the \f(CW\*(C`ev_check\*(C'\fR watcher makes sure a callback gets
3106invoked. Neither watcher alone can do that.
3107.PP
3108\fIWatcher-Specific Functions and Data Members\fR
3109.IX Subsection "Watcher-Specific Functions and Data Members"
878.IP "ev_prepare_init (ev_prepare *, callback)" 4 3110.IP "ev_prepare_init (ev_prepare *, callback)" 4
879.IX Item "ev_prepare_init (ev_prepare *, callback)" 3111.IX Item "ev_prepare_init (ev_prepare *, callback)"
880.PD 0 3112.PD 0
881.IP "ev_check_init (ev_check *, callback)" 4 3113.IP "ev_check_init (ev_check *, callback)" 4
882.IX Item "ev_check_init (ev_check *, callback)" 3114.IX Item "ev_check_init (ev_check *, callback)"
883.PD 3115.PD
884Initialises and configures the prepare or check watcher \- they have no 3116Initialises 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 3117parameters 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. 3118macros, but using them is utterly, utterly, utterly and completely
3119pointless.
3120.PP
3121\fIExamples\fR
3122.IX Subsection "Examples"
3123.PP
3124There are a number of principal ways to embed other event loops or modules
3125into libev. Here are some ideas on how to include libadns into libev
3126(there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could
3127use as a working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR embeds a
3128Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 into the
3129Glib event loop).
3130.PP
3131Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
3132and in a check watcher, destroy them and call into libadns. What follows
3133is pseudo-code only of course. This requires you to either use a low
3134priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as
3135the callbacks for the IO/timeout watchers might not have been called yet.
3136.PP
3137.Vb 2
3138\& static ev_io iow [nfd];
3139\& static ev_timer tw;
3140\&
3141\& static void
3142\& io_cb (struct ev_loop *loop, ev_io *w, int revents)
3143\& {
3144\& }
3145\&
3146\& // create io watchers for each fd and a timer before blocking
3147\& static void
3148\& adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
3149\& {
3150\& int timeout = 3600000;
3151\& struct pollfd fds [nfd];
3152\& // actual code will need to loop here and realloc etc.
3153\& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
3154\&
3155\& /* the callback is illegal, but won\*(Aqt be called as we stop during check */
3156\& ev_timer_init (&tw, 0, timeout * 1e\-3, 0.);
3157\& ev_timer_start (loop, &tw);
3158\&
3159\& // create one ev_io per pollfd
3160\& for (int i = 0; i < nfd; ++i)
3161\& {
3162\& ev_io_init (iow + i, io_cb, fds [i].fd,
3163\& ((fds [i].events & POLLIN ? EV_READ : 0)
3164\& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
3165\&
3166\& fds [i].revents = 0;
3167\& ev_io_start (loop, iow + i);
3168\& }
3169\& }
3170\&
3171\& // stop all watchers after blocking
3172\& static void
3173\& adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
3174\& {
3175\& ev_timer_stop (loop, &tw);
3176\&
3177\& for (int i = 0; i < nfd; ++i)
3178\& {
3179\& // set the relevant poll flags
3180\& // could also call adns_processreadable etc. here
3181\& struct pollfd *fd = fds + i;
3182\& int revents = ev_clear_pending (iow + i);
3183\& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN;
3184\& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT;
3185\&
3186\& // now stop the watcher
3187\& ev_io_stop (loop, iow + i);
3188\& }
3189\&
3190\& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
3191\& }
3192.Ve
3193.PP
3194Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR
3195in the prepare watcher and would dispose of the check watcher.
3196.PP
3197Method 3: If the module to be embedded supports explicit event
3198notification (libadns does), you can also make use of the actual watcher
3199callbacks, and only destroy/create the watchers in the prepare watcher.
3200.PP
3201.Vb 5
3202\& static void
3203\& timer_cb (EV_P_ ev_timer *w, int revents)
3204\& {
3205\& adns_state ads = (adns_state)w\->data;
3206\& update_now (EV_A);
3207\&
3208\& adns_processtimeouts (ads, &tv_now);
3209\& }
3210\&
3211\& static void
3212\& io_cb (EV_P_ ev_io *w, int revents)
3213\& {
3214\& adns_state ads = (adns_state)w\->data;
3215\& update_now (EV_A);
3216\&
3217\& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now);
3218\& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now);
3219\& }
3220\&
3221\& // do not ever call adns_afterpoll
3222.Ve
3223.PP
3224Method 4: Do not use a prepare or check watcher because the module you
3225want to embed is not flexible enough to support it. Instead, you can
3226override their poll function. The drawback with this solution is that the
3227main loop is now no longer controllable by \s-1EV\s0. The \f(CW\*(C`Glib::EV\*(C'\fR module uses
3228this approach, effectively embedding \s-1EV\s0 as a client into the horrible
3229libglib event loop.
3230.PP
3231.Vb 4
3232\& static gint
3233\& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
3234\& {
3235\& int got_events = 0;
3236\&
3237\& for (n = 0; n < nfds; ++n)
3238\& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
3239\&
3240\& if (timeout >= 0)
3241\& // create/start timer
3242\&
3243\& // poll
3244\& ev_run (EV_A_ 0);
3245\&
3246\& // stop timer again
3247\& if (timeout >= 0)
3248\& ev_timer_stop (EV_A_ &to);
3249\&
3250\& // stop io watchers again \- their callbacks should have set
3251\& for (n = 0; n < nfds; ++n)
3252\& ev_io_stop (EV_A_ iow [n]);
3253\&
3254\& return got_events;
3255\& }
3256.Ve
3257.ie n .SS """ev_embed"" \- when one backend isn't enough..."
3258.el .SS "\f(CWev_embed\fP \- when one backend isn't enough..."
3259.IX Subsection "ev_embed - when one backend isn't enough..."
3260This is a rather advanced watcher type that lets you embed one event loop
3261into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
3262loop, other types of watchers might be handled in a delayed or incorrect
3263fashion and must not be used).
3264.PP
3265There are primarily two reasons you would want that: work around bugs and
3266prioritise I/O.
3267.PP
3268As an example for a bug workaround, the kqueue backend might only support
3269sockets on some platform, so it is unusable as generic backend, but you
3270still want to make use of it because you have many sockets and it scales
3271so nicely. In this case, you would create a kqueue-based loop and embed
3272it into your default loop (which might use e.g. poll). Overall operation
3273will be a bit slower because first libev has to call \f(CW\*(C`poll\*(C'\fR and then
3274\&\f(CW\*(C`kevent\*(C'\fR, but at least you can use both mechanisms for what they are
3275best: \f(CW\*(C`kqueue\*(C'\fR for scalable sockets and \f(CW\*(C`poll\*(C'\fR if you want it to work :)
3276.PP
3277As for prioritising I/O: under rare circumstances you have the case where
3278some fds have to be watched and handled very quickly (with low latency),
3279and even priorities and idle watchers might have too much overhead. In
3280this case you would put all the high priority stuff in one loop and all
3281the rest in a second one, and embed the second one in the first.
3282.PP
3283As long as the watcher is active, the callback will be invoked every
3284time there might be events pending in the embedded loop. The callback
3285must then call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single
3286sweep and invoke their callbacks (the callback doesn't need to invoke the
3287\&\f(CW\*(C`ev_embed_sweep\*(C'\fR function directly, it could also start an idle watcher
3288to give the embedded loop strictly lower priority for example).
3289.PP
3290You can also set the callback to \f(CW0\fR, in which case the embed watcher
3291will automatically execute the embedded loop sweep whenever necessary.
3292.PP
3293Fork detection will be handled transparently while the \f(CW\*(C`ev_embed\*(C'\fR watcher
3294is active, i.e., the embedded loop will automatically be forked when the
3295embedding loop forks. In other cases, the user is responsible for calling
3296\&\f(CW\*(C`ev_loop_fork\*(C'\fR on the embedded loop.
3297.PP
3298Unfortunately, not all backends are embeddable: only the ones returned by
3299\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
3300portable one.
3301.PP
3302So when you want to use this feature you will always have to be prepared
3303that you cannot get an embeddable loop. The recommended way to get around
3304this is to have a separate variables for your embeddable loop, try to
3305create it, and if that fails, use the normal loop for everything.
3306.PP
3307\fI\f(CI\*(C`ev_embed\*(C'\fI and fork\fR
3308.IX Subsection "ev_embed and fork"
3309.PP
3310While the \f(CW\*(C`ev_embed\*(C'\fR watcher is running, forks in the embedding loop will
3311automatically be applied to the embedded loop as well, so no special
3312fork handling is required in that case. When the watcher is not running,
3313however, it is still the task of the libev user to call \f(CW\*(C`ev_loop_fork ()\*(C'\fR
3314as applicable.
3315.PP
3316\fIWatcher-Specific Functions and Data Members\fR
3317.IX Subsection "Watcher-Specific Functions and Data Members"
3318.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
3319.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
3320.PD 0
3321.IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
3322.IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)"
3323.PD
3324Configures the watcher to embed the given loop, which must be
3325embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
3326invoked automatically, otherwise it is the responsibility of the callback
3327to invoke it (it will continue to be called until the sweep has been done,
3328if you do not want that, you need to temporarily stop the embed watcher).
3329.IP "ev_embed_sweep (loop, ev_embed *)" 4
3330.IX Item "ev_embed_sweep (loop, ev_embed *)"
3331Make a single, non-blocking sweep over the embedded loop. This works
3332similarly to \f(CW\*(C`ev_run (embedded_loop, EVRUN_NOWAIT)\*(C'\fR, but in the most
3333appropriate way for embedded loops.
3334.IP "struct ev_loop *other [read\-only]" 4
3335.IX Item "struct ev_loop *other [read-only]"
3336The embedded event loop.
3337.PP
3338\fIExamples\fR
3339.IX Subsection "Examples"
3340.PP
3341Example: Try to get an embeddable event loop and embed it into the default
3342event loop. If that is not possible, use the default loop. The default
3343loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the embeddable loop is stored in
3344\&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the case no embeddable loop can be
3345used).
3346.PP
3347.Vb 3
3348\& struct ev_loop *loop_hi = ev_default_init (0);
3349\& struct ev_loop *loop_lo = 0;
3350\& ev_embed embed;
3351\&
3352\& // see if there is a chance of getting one that works
3353\& // (remember that a flags value of 0 means autodetection)
3354\& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3355\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3356\& : 0;
3357\&
3358\& // if we got one, then embed it, otherwise default to loop_hi
3359\& if (loop_lo)
3360\& {
3361\& ev_embed_init (&embed, 0, loop_lo);
3362\& ev_embed_start (loop_hi, &embed);
3363\& }
3364\& else
3365\& loop_lo = loop_hi;
3366.Ve
3367.PP
3368Example: Check if kqueue is available but not recommended and create
3369a kqueue backend for use with sockets (which usually work with any
3370kqueue implementation). Store the kqueue/socket\-only event loop in
3371\&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too).
3372.PP
3373.Vb 3
3374\& struct ev_loop *loop = ev_default_init (0);
3375\& struct ev_loop *loop_socket = 0;
3376\& ev_embed embed;
3377\&
3378\& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3379\& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3380\& {
3381\& ev_embed_init (&embed, 0, loop_socket);
3382\& ev_embed_start (loop, &embed);
3383\& }
3384\&
3385\& if (!loop_socket)
3386\& loop_socket = loop;
3387\&
3388\& // now use loop_socket for all sockets, and loop for everything else
3389.Ve
3390.ie n .SS """ev_fork"" \- the audacity to resume the event loop after a fork"
3391.el .SS "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
3392.IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
3393Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
3394whoever is a good citizen cared to tell libev about it by calling
3395\&\f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the
3396event loop blocks next and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called,
3397and only in the child after the fork. If whoever good citizen calling
3398\&\f(CW\*(C`ev_default_fork\*(C'\fR cheats and calls it in the wrong process, the fork
3399handlers will be invoked, too, of course.
3400.PP
3401\fIThe special problem of life after fork \- how is it possible?\fR
3402.IX Subsection "The special problem of life after fork - how is it possible?"
3403.PP
3404Most uses of \f(CW\*(C`fork()\*(C'\fR consist of forking, then some simple calls to set
3405up/change the process environment, followed by a call to \f(CW\*(C`exec()\*(C'\fR. This
3406sequence should be handled by libev without any problems.
3407.PP
3408This changes when the application actually wants to do event handling
3409in the child, or both parent in child, in effect \*(L"continuing\*(R" after the
3410fork.
3411.PP
3412The default mode of operation (for libev, with application help to detect
3413forks) is to duplicate all the state in the child, as would be expected
3414when \fIeither\fR the parent \fIor\fR the child process continues.
3415.PP
3416When both processes want to continue using libev, then this is usually the
3417wrong result. In that case, usually one process (typically the parent) is
3418supposed to continue with all watchers in place as before, while the other
3419process typically wants to start fresh, i.e. without any active watchers.
3420.PP
3421The cleanest and most efficient way to achieve that with libev is to
3422simply create a new event loop, which of course will be \*(L"empty\*(R", and
3423use that for new watchers. This has the advantage of not touching more
3424memory than necessary, and thus avoiding the copy-on-write, and the
3425disadvantage of having to use multiple event loops (which do not support
3426signal watchers).
3427.PP
3428When this is not possible, or you want to use the default loop for
3429other reasons, then in the process that wants to start \*(L"fresh\*(R", call
3430\&\f(CW\*(C`ev_loop_destroy (EV_DEFAULT)\*(C'\fR followed by \f(CW\*(C`ev_default_loop (...)\*(C'\fR.
3431Destroying the default loop will \*(L"orphan\*(R" (not stop) all registered
3432watchers, so you have to be careful not to execute code that modifies
3433those watchers. Note also that in that case, you have to re-register any
3434signal watchers.
3435.PP
3436\fIWatcher-Specific Functions and Data Members\fR
3437.IX Subsection "Watcher-Specific Functions and Data Members"
3438.IP "ev_fork_init (ev_fork *, callback)" 4
3439.IX Item "ev_fork_init (ev_fork *, callback)"
3440Initialises and configures the fork watcher \- it has no parameters of any
3441kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
3442really.
3443.ie n .SS """ev_cleanup"" \- even the best things end"
3444.el .SS "\f(CWev_cleanup\fP \- even the best things end"
3445.IX Subsection "ev_cleanup - even the best things end"
3446Cleanup watchers are called just before the event loop is being destroyed
3447by a call to \f(CW\*(C`ev_loop_destroy\*(C'\fR.
3448.PP
3449While there is no guarantee that the event loop gets destroyed, cleanup
3450watchers provide a convenient method to install cleanup hooks for your
3451program, worker threads and so on \- you just to make sure to destroy the
3452loop when you want them to be invoked.
3453.PP
3454Cleanup watchers are invoked in the same way as any other watcher. Unlike
3455all other watchers, they do not keep a reference to the event loop (which
3456makes a lot of sense if you think about it). Like all other watchers, you
3457can call libev functions in the callback, except \f(CW\*(C`ev_cleanup_start\*(C'\fR.
3458.PP
3459\fIWatcher-Specific Functions and Data Members\fR
3460.IX Subsection "Watcher-Specific Functions and Data Members"
3461.IP "ev_cleanup_init (ev_cleanup *, callback)" 4
3462.IX Item "ev_cleanup_init (ev_cleanup *, callback)"
3463Initialises and configures the cleanup watcher \- it has no parameters of
3464any kind. There is a \f(CW\*(C`ev_cleanup_set\*(C'\fR macro, but using it is utterly
3465pointless, I assure you.
3466.PP
3467Example: Register an atexit handler to destroy the default loop, so any
3468cleanup functions are called.
3469.PP
3470.Vb 5
3471\& static void
3472\& program_exits (void)
3473\& {
3474\& ev_loop_destroy (EV_DEFAULT_UC);
3475\& }
3476\&
3477\& ...
3478\& atexit (program_exits);
3479.Ve
3480.ie n .SS """ev_async"" \- how to wake up an event loop"
3481.el .SS "\f(CWev_async\fP \- how to wake up an event loop"
3482.IX Subsection "ev_async - how to wake up an event loop"
3483In general, you cannot use an \f(CW\*(C`ev_loop\*(C'\fR from multiple threads or other
3484asynchronous sources such as signal handlers (as opposed to multiple event
3485loops \- those are of course safe to use in different threads).
3486.PP
3487Sometimes, however, you need to wake up an event loop you do not control,
3488for example because it belongs to another thread. This is what \f(CW\*(C`ev_async\*(C'\fR
3489watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you can signal
3490it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal safe.
3491.PP
3492This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals,
3493too, are asynchronous in nature, and signals, too, will be compressed
3494(i.e. the number of callback invocations may be less than the number of
3495\&\f(CW\*(C`ev_async_send\*(C'\fR calls). In fact, you could use signal watchers as a kind
3496of \*(L"global async watchers\*(R" by using a watcher on an otherwise unused
3497signal, and \f(CW\*(C`ev_feed_signal\*(C'\fR to signal this watcher from another thread,
3498even without knowing which loop owns the signal.
3499.PP
3500\fIQueueing\fR
3501.IX Subsection "Queueing"
3502.PP
3503\&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason
3504is that the author does not know of a simple (or any) algorithm for a
3505multiple-writer-single-reader queue that works in all cases and doesn't
3506need elaborate support such as pthreads or unportable memory access
3507semantics.
3508.PP
3509That means that if you want to queue data, you have to provide your own
3510queue. But at least I can tell you how to implement locking around your
3511queue:
3512.IP "queueing from a signal handler context" 4
3513.IX Item "queueing from a signal handler context"
3514To implement race-free queueing, you simply add to the queue in the signal
3515handler but you block the signal handler in the watcher callback. Here is
3516an example that does that for some fictitious \s-1SIGUSR1\s0 handler:
3517.Sp
3518.Vb 1
3519\& static ev_async mysig;
3520\&
3521\& static void
3522\& sigusr1_handler (void)
3523\& {
3524\& sometype data;
3525\&
3526\& // no locking etc.
3527\& queue_put (data);
3528\& ev_async_send (EV_DEFAULT_ &mysig);
3529\& }
3530\&
3531\& static void
3532\& mysig_cb (EV_P_ ev_async *w, int revents)
3533\& {
3534\& sometype data;
3535\& sigset_t block, prev;
3536\&
3537\& sigemptyset (&block);
3538\& sigaddset (&block, SIGUSR1);
3539\& sigprocmask (SIG_BLOCK, &block, &prev);
3540\&
3541\& while (queue_get (&data))
3542\& process (data);
3543\&
3544\& if (sigismember (&prev, SIGUSR1)
3545\& sigprocmask (SIG_UNBLOCK, &block, 0);
3546\& }
3547.Ve
3548.Sp
3549(Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR
3550instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it
3551either...).
3552.IP "queueing from a thread context" 4
3553.IX Item "queueing from a thread context"
3554The strategy for threads is different, as you cannot (easily) block
3555threads but you can easily preempt them, so to queue safely you need to
3556employ a traditional mutex lock, such as in this pthread example:
3557.Sp
3558.Vb 2
3559\& static ev_async mysig;
3560\& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
3561\&
3562\& static void
3563\& otherthread (void)
3564\& {
3565\& // only need to lock the actual queueing operation
3566\& pthread_mutex_lock (&mymutex);
3567\& queue_put (data);
3568\& pthread_mutex_unlock (&mymutex);
3569\&
3570\& ev_async_send (EV_DEFAULT_ &mysig);
3571\& }
3572\&
3573\& static void
3574\& mysig_cb (EV_P_ ev_async *w, int revents)
3575\& {
3576\& pthread_mutex_lock (&mymutex);
3577\&
3578\& while (queue_get (&data))
3579\& process (data);
3580\&
3581\& pthread_mutex_unlock (&mymutex);
3582\& }
3583.Ve
3584.PP
3585\fIWatcher-Specific Functions and Data Members\fR
3586.IX Subsection "Watcher-Specific Functions and Data Members"
3587.IP "ev_async_init (ev_async *, callback)" 4
3588.IX Item "ev_async_init (ev_async *, callback)"
3589Initialises and configures the async watcher \- it has no parameters of any
3590kind. There is a \f(CW\*(C`ev_async_set\*(C'\fR macro, but using it is utterly pointless,
3591trust me.
3592.IP "ev_async_send (loop, ev_async *)" 4
3593.IX Item "ev_async_send (loop, ev_async *)"
3594Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds
3595an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop, and instantly
3596returns.
3597.Sp
3598Unlike \f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do from other threads,
3599signal or similar contexts (see the discussion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the
3600embedding section below on what exactly this means).
3601.Sp
3602Note that, as with other watchers in libev, multiple events might get
3603compressed into a single callback invocation (another way to look at
3604this is that \f(CW\*(C`ev_async\*(C'\fR watchers are level-triggered: they are set on
3605\&\f(CW\*(C`ev_async_send\*(C'\fR, reset when the event loop detects that).
3606.Sp
3607This call incurs the overhead of at most one extra system call per event
3608loop iteration, if the event loop is blocked, and no syscall at all if
3609the event loop (or your program) is processing events. That means that
3610repeated calls are basically free (there is no need to avoid calls for
3611performance reasons) and that the overhead becomes smaller (typically
3612zero) under load.
3613.IP "bool = ev_async_pending (ev_async *)" 4
3614.IX Item "bool = ev_async_pending (ev_async *)"
3615Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the
3616watcher but the event has not yet been processed (or even noted) by the
3617event loop.
3618.Sp
3619\&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When
3620the loop iterates next and checks for the watcher to have become active,
3621it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very
3622quickly check whether invoking the loop might be a good idea.
3623.Sp
3624Not that this does \fInot\fR check whether the watcher itself is pending,
3625only whether it has been requested to make this watcher pending: there
3626is a time window between the event loop checking and resetting the async
3627notification, and the callback being invoked.
887.SH "OTHER FUNCTIONS" 3628.SH "OTHER FUNCTIONS"
888.IX Header "OTHER FUNCTIONS" 3629.IX Header "OTHER FUNCTIONS"
889There are some other functions of possible interest. Described. Here. Now. 3630There are some other functions of possible interest. Described. Here. Now.
890.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4 3631.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
891.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 3632.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"
892This function combines a simple timer and an I/O watcher, calls your 3633This function combines a simple timer and an I/O watcher, calls your
893callback on whichever event happens first and automatically stop both 3634callback 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 3635watchers. 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 3636or timeout without having to allocate/configure/start/stop/free one or
896more watchers yourself. 3637more watchers yourself.
897.Sp 3638.Sp
898If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and events 3639If \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 3640\&\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. 3641the given \f(CW\*(C`fd\*(C'\fR and \f(CW\*(C`events\*(C'\fR set will be created and started.
901.Sp 3642.Sp
902If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be 3643If \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 3644started. 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 3645repeat = 0) will be started. \f(CW0\fR is a valid timeout.
905dubious value.
906.Sp 3646.Sp
907The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets 3647The 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 3648passed 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 3649\&\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: 3650value passed to \f(CW\*(C`ev_once\*(C'\fR. Note that it is possible to receive \fIboth\fR
3651a timeout and an io event at the same time \- you probably should give io
3652events precedence.
3653.Sp
3654Example: wait up to ten seconds for data to appear on \s-1STDIN_FILENO\s0.
911.Sp 3655.Sp
912.Vb 7 3656.Vb 7
913\& static void stdin_ready (int revents, void *arg) 3657\& static void stdin_ready (int revents, void *arg)
914\& { 3658\& {
915\& if (revents & EV_TIMEOUT)
916\& /* doh, nothing entered */;
917\& else if (revents & EV_READ) 3659\& if (revents & EV_READ)
918\& /* stdin might have data for us, joy! */; 3660\& /* stdin might have data for us, joy! */;
3661\& else if (revents & EV_TIMER)
3662\& /* doh, nothing entered */;
919\& } 3663\& }
920.Ve 3664\&
921.Sp
922.Vb 1
923\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); 3665\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
924.Ve 3666.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 3667.IP "ev_feed_fd_event (loop, int fd, int revents)" 4
931.IX Item "ev_feed_fd_event (loop, int fd, int revents)" 3668.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 3669Feed an event on the given fd, as if a file descriptor backend detected
933the given events it. 3670the given events.
934.IP "ev_feed_signal_event (loop, int signum)" 4 3671.IP "ev_feed_signal_event (loop, int signum)" 4
935.IX Item "ev_feed_signal_event (loop, int signum)" 3672.IX Item "ev_feed_signal_event (loop, int signum)"
936Feed an event as if the given signal occured (loop must be the default loop!). 3673Feed an event as if the given signal occurred. See also \f(CW\*(C`ev_feed_signal\*(C'\fR,
3674which is async-safe.
3675.SH "COMMON OR USEFUL IDIOMS (OR BOTH)"
3676.IX Header "COMMON OR USEFUL IDIOMS (OR BOTH)"
3677This section explains some common idioms that are not immediately
3678obvious. Note that examples are sprinkled over the whole manual, and this
3679section only contains stuff that wouldn't fit anywhere else.
3680.SS "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0"
3681.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
3682Each watcher has, by default, a \f(CW\*(C`void *data\*(C'\fR member that you can read
3683or modify at any time: libev will completely ignore it. This can be used
3684to associate arbitrary data with your watcher. If you need more data and
3685don't want to allocate memory separately and store a pointer to it in that
3686data member, you can also \*(L"subclass\*(R" the watcher type and provide your own
3687data:
3688.PP
3689.Vb 7
3690\& struct my_io
3691\& {
3692\& ev_io io;
3693\& int otherfd;
3694\& void *somedata;
3695\& struct whatever *mostinteresting;
3696\& };
3697\&
3698\& ...
3699\& struct my_io w;
3700\& ev_io_init (&w.io, my_cb, fd, EV_READ);
3701.Ve
3702.PP
3703And since your callback will be called with a pointer to the watcher, you
3704can cast it back to your own type:
3705.PP
3706.Vb 5
3707\& static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
3708\& {
3709\& struct my_io *w = (struct my_io *)w_;
3710\& ...
3711\& }
3712.Ve
3713.PP
3714More interesting and less C\-conformant ways of casting your callback
3715function type instead have been omitted.
3716.SS "\s-1BUILDING\s0 \s-1YOUR\s0 \s-1OWN\s0 \s-1COMPOSITE\s0 \s-1WATCHERS\s0"
3717.IX Subsection "BUILDING YOUR OWN COMPOSITE WATCHERS"
3718Another common scenario is to use some data structure with multiple
3719embedded watchers, in effect creating your own watcher that combines
3720multiple libev event sources into one \*(L"super-watcher\*(R":
3721.PP
3722.Vb 6
3723\& struct my_biggy
3724\& {
3725\& int some_data;
3726\& ev_timer t1;
3727\& ev_timer t2;
3728\& }
3729.Ve
3730.PP
3731In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more
3732complicated: Either you store the address of your \f(CW\*(C`my_biggy\*(C'\fR struct in
3733the \f(CW\*(C`data\*(C'\fR member of the watcher (for woozies or \*(C+ coders), or you need
3734to use some pointer arithmetic using \f(CW\*(C`offsetof\*(C'\fR inside your watchers (for
3735real programmers):
3736.PP
3737.Vb 1
3738\& #include <stddef.h>
3739\&
3740\& static void
3741\& t1_cb (EV_P_ ev_timer *w, int revents)
3742\& {
3743\& struct my_biggy big = (struct my_biggy *)
3744\& (((char *)w) \- offsetof (struct my_biggy, t1));
3745\& }
3746\&
3747\& static void
3748\& t2_cb (EV_P_ ev_timer *w, int revents)
3749\& {
3750\& struct my_biggy big = (struct my_biggy *)
3751\& (((char *)w) \- offsetof (struct my_biggy, t2));
3752\& }
3753.Ve
3754.SS "\s-1AVOIDING\s0 \s-1FINISHING\s0 \s-1BEFORE\s0 \s-1RETURNING\s0"
3755.IX Subsection "AVOIDING FINISHING BEFORE RETURNING"
3756Often you have structures like this in event-based programs:
3757.PP
3758.Vb 4
3759\& callback ()
3760\& {
3761\& free (request);
3762\& }
3763\&
3764\& request = start_new_request (..., callback);
3765.Ve
3766.PP
3767The intent is to start some \*(L"lengthy\*(R" operation. The \f(CW\*(C`request\*(C'\fR could be
3768used to cancel the operation, or do other things with it.
3769.PP
3770It's not uncommon to have code paths in \f(CW\*(C`start_new_request\*(C'\fR that
3771immediately invoke the callback, for example, to report errors. Or you add
3772some caching layer that finds that it can skip the lengthy aspects of the
3773operation and simply invoke the callback with the result.
3774.PP
3775The problem here is that this will happen \fIbefore\fR \f(CW\*(C`start_new_request\*(C'\fR
3776has returned, so \f(CW\*(C`request\*(C'\fR is not set.
3777.PP
3778Even if you pass the request by some safer means to the callback, you
3779might want to do something to the request after starting it, such as
3780canceling it, which probably isn't working so well when the callback has
3781already been invoked.
3782.PP
3783A common way around all these issues is to make sure that
3784\&\f(CW\*(C`start_new_request\*(C'\fR \fIalways\fR returns before the callback is invoked. If
3785\&\f(CW\*(C`start_new_request\*(C'\fR immediately knows the result, it can artificially
3786delay invoking the callback by e.g. using a \f(CW\*(C`prepare\*(C'\fR or \f(CW\*(C`idle\*(C'\fR watcher
3787for example, or more sneakily, by reusing an existing (stopped) watcher
3788and pushing it into the pending queue:
3789.PP
3790.Vb 2
3791\& ev_set_cb (watcher, callback);
3792\& ev_feed_event (EV_A_ watcher, 0);
3793.Ve
3794.PP
3795This way, \f(CW\*(C`start_new_request\*(C'\fR can safely return before the callback is
3796invoked, while not delaying callback invocation too much.
3797.SS "\s-1MODEL/NESTED\s0 \s-1EVENT\s0 \s-1LOOP\s0 \s-1INVOCATIONS\s0 \s-1AND\s0 \s-1EXIT\s0 \s-1CONDITIONS\s0"
3798.IX Subsection "MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS"
3799Often (especially in \s-1GUI\s0 toolkits) there are places where you have
3800\&\fImodal\fR interaction, which is most easily implemented by recursively
3801invoking \f(CW\*(C`ev_run\*(C'\fR.
3802.PP
3803This brings the problem of exiting \- a callback might want to finish the
3804main \f(CW\*(C`ev_run\*(C'\fR call, but not the nested one (e.g. user clicked \*(L"Quit\*(R", but
3805a modal \*(L"Are you sure?\*(R" dialog is still waiting), or just the nested one
3806and not the main one (e.g. user clocked \*(L"Ok\*(R" in a modal dialog), or some
3807other combination: In these cases, \f(CW\*(C`ev_break\*(C'\fR will not work alone.
3808.PP
3809The solution is to maintain \*(L"break this loop\*(R" variable for each \f(CW\*(C`ev_run\*(C'\fR
3810invocation, and use a loop around \f(CW\*(C`ev_run\*(C'\fR until the condition is
3811triggered, using \f(CW\*(C`EVRUN_ONCE\*(C'\fR:
3812.PP
3813.Vb 2
3814\& // main loop
3815\& int exit_main_loop = 0;
3816\&
3817\& while (!exit_main_loop)
3818\& ev_run (EV_DEFAULT_ EVRUN_ONCE);
3819\&
3820\& // in a modal watcher
3821\& int exit_nested_loop = 0;
3822\&
3823\& while (!exit_nested_loop)
3824\& ev_run (EV_A_ EVRUN_ONCE);
3825.Ve
3826.PP
3827To exit from any of these loops, just set the corresponding exit variable:
3828.PP
3829.Vb 2
3830\& // exit modal loop
3831\& exit_nested_loop = 1;
3832\&
3833\& // exit main program, after modal loop is finished
3834\& exit_main_loop = 1;
3835\&
3836\& // exit both
3837\& exit_main_loop = exit_nested_loop = 1;
3838.Ve
3839.SS "\s-1THREAD\s0 \s-1LOCKING\s0 \s-1EXAMPLE\s0"
3840.IX Subsection "THREAD LOCKING EXAMPLE"
3841Here is a fictitious example of how to run an event loop in a different
3842thread from where callbacks are being invoked and watchers are
3843created/added/removed.
3844.PP
3845For a real-world example, see the \f(CW\*(C`EV::Loop::Async\*(C'\fR perl module,
3846which uses exactly this technique (which is suited for many high-level
3847languages).
3848.PP
3849The example uses a pthread mutex to protect the loop data, a condition
3850variable to wait for callback invocations, an async watcher to notify the
3851event loop thread and an unspecified mechanism to wake up the main thread.
3852.PP
3853First, you need to associate some data with the event loop:
3854.PP
3855.Vb 6
3856\& typedef struct {
3857\& mutex_t lock; /* global loop lock */
3858\& ev_async async_w;
3859\& thread_t tid;
3860\& cond_t invoke_cv;
3861\& } userdata;
3862\&
3863\& void prepare_loop (EV_P)
3864\& {
3865\& // for simplicity, we use a static userdata struct.
3866\& static userdata u;
3867\&
3868\& ev_async_init (&u\->async_w, async_cb);
3869\& ev_async_start (EV_A_ &u\->async_w);
3870\&
3871\& pthread_mutex_init (&u\->lock, 0);
3872\& pthread_cond_init (&u\->invoke_cv, 0);
3873\&
3874\& // now associate this with the loop
3875\& ev_set_userdata (EV_A_ u);
3876\& ev_set_invoke_pending_cb (EV_A_ l_invoke);
3877\& ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
3878\&
3879\& // then create the thread running ev_run
3880\& pthread_create (&u\->tid, 0, l_run, EV_A);
3881\& }
3882.Ve
3883.PP
3884The callback for the \f(CW\*(C`ev_async\*(C'\fR watcher does nothing: the watcher is used
3885solely to wake up the event loop so it takes notice of any new watchers
3886that might have been added:
3887.PP
3888.Vb 5
3889\& static void
3890\& async_cb (EV_P_ ev_async *w, int revents)
3891\& {
3892\& // just used for the side effects
3893\& }
3894.Ve
3895.PP
3896The \f(CW\*(C`l_release\*(C'\fR and \f(CW\*(C`l_acquire\*(C'\fR callbacks simply unlock/lock the mutex
3897protecting the loop data, respectively.
3898.PP
3899.Vb 6
3900\& static void
3901\& l_release (EV_P)
3902\& {
3903\& userdata *u = ev_userdata (EV_A);
3904\& pthread_mutex_unlock (&u\->lock);
3905\& }
3906\&
3907\& static void
3908\& l_acquire (EV_P)
3909\& {
3910\& userdata *u = ev_userdata (EV_A);
3911\& pthread_mutex_lock (&u\->lock);
3912\& }
3913.Ve
3914.PP
3915The event loop thread first acquires the mutex, and then jumps straight
3916into \f(CW\*(C`ev_run\*(C'\fR:
3917.PP
3918.Vb 4
3919\& void *
3920\& l_run (void *thr_arg)
3921\& {
3922\& struct ev_loop *loop = (struct ev_loop *)thr_arg;
3923\&
3924\& l_acquire (EV_A);
3925\& pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
3926\& ev_run (EV_A_ 0);
3927\& l_release (EV_A);
3928\&
3929\& return 0;
3930\& }
3931.Ve
3932.PP
3933Instead of invoking all pending watchers, the \f(CW\*(C`l_invoke\*(C'\fR callback will
3934signal the main thread via some unspecified mechanism (signals? pipe
3935writes? \f(CW\*(C`Async::Interrupt\*(C'\fR?) and then waits until all pending watchers
3936have been called (in a while loop because a) spurious wakeups are possible
3937and b) skipping inter-thread-communication when there are no pending
3938watchers is very beneficial):
3939.PP
3940.Vb 4
3941\& static void
3942\& l_invoke (EV_P)
3943\& {
3944\& userdata *u = ev_userdata (EV_A);
3945\&
3946\& while (ev_pending_count (EV_A))
3947\& {
3948\& wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
3949\& pthread_cond_wait (&u\->invoke_cv, &u\->lock);
3950\& }
3951\& }
3952.Ve
3953.PP
3954Now, whenever the main thread gets told to invoke pending watchers, it
3955will grab the lock, call \f(CW\*(C`ev_invoke_pending\*(C'\fR and then signal the loop
3956thread to continue:
3957.PP
3958.Vb 4
3959\& static void
3960\& real_invoke_pending (EV_P)
3961\& {
3962\& userdata *u = ev_userdata (EV_A);
3963\&
3964\& pthread_mutex_lock (&u\->lock);
3965\& ev_invoke_pending (EV_A);
3966\& pthread_cond_signal (&u\->invoke_cv);
3967\& pthread_mutex_unlock (&u\->lock);
3968\& }
3969.Ve
3970.PP
3971Whenever you want to start/stop a watcher or do other modifications to an
3972event loop, you will now have to lock:
3973.PP
3974.Vb 2
3975\& ev_timer timeout_watcher;
3976\& userdata *u = ev_userdata (EV_A);
3977\&
3978\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
3979\&
3980\& pthread_mutex_lock (&u\->lock);
3981\& ev_timer_start (EV_A_ &timeout_watcher);
3982\& ev_async_send (EV_A_ &u\->async_w);
3983\& pthread_mutex_unlock (&u\->lock);
3984.Ve
3985.PP
3986Note that sending the \f(CW\*(C`ev_async\*(C'\fR watcher is required because otherwise
3987an event loop currently blocking in the kernel will have no knowledge
3988about the newly added timer. By waking up the loop it will pick up any new
3989watchers in the next event loop iteration.
3990.SS "\s-1THREADS\s0, \s-1COROUTINES\s0, \s-1CONTINUATIONS\s0, \s-1QUEUES\s0... \s-1INSTEAD\s0 \s-1OF\s0 \s-1CALLBACKS\s0"
3991.IX Subsection "THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS"
3992While the overhead of a callback that e.g. schedules a thread is small, it
3993is still an overhead. If you embed libev, and your main usage is with some
3994kind of threads or coroutines, you might want to customise libev so that
3995doesn't need callbacks anymore.
3996.PP
3997Imagine you have coroutines that you can switch to using a function
3998\&\f(CW\*(C`switch_to (coro)\*(C'\fR, that libev runs in a coroutine called \f(CW\*(C`libev_coro\*(C'\fR
3999and that due to some magic, the currently active coroutine is stored in a
4000global called \f(CW\*(C`current_coro\*(C'\fR. Then you can build your own \*(L"wait for libev
4001event\*(R" primitive by changing \f(CW\*(C`EV_CB_DECLARE\*(C'\fR and \f(CW\*(C`EV_CB_INVOKE\*(C'\fR (note
4002the differing \f(CW\*(C`;\*(C'\fR conventions):
4003.PP
4004.Vb 2
4005\& #define EV_CB_DECLARE(type) struct my_coro *cb;
4006\& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb)
4007.Ve
4008.PP
4009That means instead of having a C callback function, you store the
4010coroutine to switch to in each watcher, and instead of having libev call
4011your callback, you instead have it switch to that coroutine.
4012.PP
4013A coroutine might now wait for an event with a function called
4014\&\f(CW\*(C`wait_for_event\*(C'\fR. (the watcher needs to be started, as always, but it doesn't
4015matter when, or whether the watcher is active or not when this function is
4016called):
4017.PP
4018.Vb 6
4019\& void
4020\& wait_for_event (ev_watcher *w)
4021\& {
4022\& ev_set_cb (w, current_coro);
4023\& switch_to (libev_coro);
4024\& }
4025.Ve
4026.PP
4027That basically suspends the coroutine inside \f(CW\*(C`wait_for_event\*(C'\fR and
4028continues the libev coroutine, which, when appropriate, switches back to
4029this or any other coroutine.
4030.PP
4031You can do similar tricks if you have, say, threads with an event queue \-
4032instead of storing a coroutine, you store the queue object and instead of
4033switching to a coroutine, you push the watcher onto the queue and notify
4034any waiters.
4035.PP
4036To embed libev, see \*(L"\s-1EMBEDDING\s0\*(R", but in short, it's easiest to create two
4037files, \fImy_ev.h\fR and \fImy_ev.c\fR that include the respective libev files:
4038.PP
4039.Vb 4
4040\& // my_ev.h
4041\& #define EV_CB_DECLARE(type) struct my_coro *cb;
4042\& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb);
4043\& #include "../libev/ev.h"
4044\&
4045\& // my_ev.c
4046\& #define EV_H "my_ev.h"
4047\& #include "../libev/ev.c"
4048.Ve
4049.PP
4050And then use \fImy_ev.h\fR when you would normally use \fIev.h\fR, and compile
4051\&\fImy_ev.c\fR into your project. When properly specifying include paths, you
4052can even use \fIev.h\fR as header file name directly.
937.SH "LIBEVENT EMULATION" 4053.SH "LIBEVENT EMULATION"
938.IX Header "LIBEVENT EMULATION" 4054.IX Header "LIBEVENT EMULATION"
939Libev offers a compatibility emulation layer for libevent. It cannot 4055Libev offers a compatibility emulation layer for libevent. It cannot
940emulate the internals of libevent, so here are some usage hints: 4056emulate the internals of libevent, so here are some usage hints:
4057.IP "\(bu" 4
4058Only the libevent\-1.4.1\-beta \s-1API\s0 is being emulated.
4059.Sp
4060This was the newest libevent version available when libev was implemented,
4061and is still mostly unchanged in 2010.
4062.IP "\(bu" 4
941.IP "* Use it by including <event.h>, as usual." 4 4063Use it by including <event.h>, as usual.
942.IX Item "Use it by including <event.h>, as usual." 4064.IP "\(bu" 4
943.PD 0 4065The 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 4066ev_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." 4067.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 4068Avoid 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)." 4069maintained 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 4070it 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." 4071.IP "\(bu" 4
4072Priorities are not currently supported. Initialising priorities
4073will fail and all watchers will have the same priority, even though there
4074is an ev_pri field.
4075.IP "\(bu" 4
4076In libevent, the last base created gets the signals, in libev, the
4077base that registered the signal gets the signals.
4078.IP "\(bu" 4
950.IP "* Other members are not supported." 4 4079Other members are not supported.
951.IX Item "Other members are not supported." 4080.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 4081The 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." 4082to use the libev header file and library.
954.PD
955.SH "\*(C+ SUPPORT" 4083.SH "\*(C+ SUPPORT"
956.IX Header " SUPPORT" 4084.IX Header " SUPPORT"
957\&\s-1TBD\s0. 4085.SS "C \s-1API\s0"
4086.IX Subsection "C API"
4087The normal C \s-1API\s0 should work fine when used from \*(C+: both ev.h and the
4088libev sources can be compiled as \*(C+. Therefore, code that uses the C \s-1API\s0
4089will work fine.
4090.PP
4091Proper exception specifications might have to be added to callbacks passed
4092to libev: exceptions may be thrown only from watcher callbacks, all
4093other callbacks (allocator, syserr, loop acquire/release and periodioc
4094reschedule callbacks) must not throw exceptions, and might need a \f(CW\*(C`throw
4095()\*(C'\fR specification. If you have code that needs to be compiled as both C
4096and \*(C+ you can use the \f(CW\*(C`EV_THROW\*(C'\fR macro for this:
4097.PP
4098.Vb 6
4099\& static void
4100\& fatal_error (const char *msg) EV_THROW
4101\& {
4102\& perror (msg);
4103\& abort ();
4104\& }
4105\&
4106\& ...
4107\& ev_set_syserr_cb (fatal_error);
4108.Ve
4109.PP
4110The only \s-1API\s0 functions that can currently throw exceptions are \f(CW\*(C`ev_run\*(C'\fR,
4111\&\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
4112because it runs cleanup watchers).
4113.PP
4114Throwing exceptions in watcher callbacks is only supported if libev itself
4115is compiled with a \*(C+ compiler or your C and \*(C+ environments allow
4116throwing exceptions through C libraries (most do).
4117.SS "\*(C+ \s-1API\s0"
4118.IX Subsection " API"
4119Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
4120you to use some convenience methods to start/stop watchers and also change
4121the callback model to a model using method callbacks on objects.
4122.PP
4123To use it,
4124.PP
4125.Vb 1
4126\& #include <ev++.h>
4127.Ve
4128.PP
4129This automatically includes \fIev.h\fR and puts all of its definitions (many
4130of them macros) into the global namespace. All \*(C+ specific things are
4131put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding
4132options as \fIev.h\fR, most notably \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR.
4133.PP
4134Care has been taken to keep the overhead low. The only data member the \*(C+
4135classes add (compared to plain C\-style watchers) is the event loop pointer
4136that the watcher is associated with (or no additional members at all if
4137you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
4138.PP
4139Currently, functions, static and non-static member functions and classes
4140with \f(CW\*(C`operator ()\*(C'\fR can be used as callbacks. Other types should be easy
4141to add as long as they only need one additional pointer for context. If
4142you need support for other types of functors please contact the author
4143(preferably after implementing it).
4144.PP
4145For all this to work, your \*(C+ compiler either has to use the same calling
4146conventions as your C compiler (for static member functions), or you have
4147to embed libev and compile libev itself as \*(C+.
4148.PP
4149Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
4150.ie n .IP """ev::READ"", ""ev::WRITE"" etc." 4
4151.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
4152.IX Item "ev::READ, ev::WRITE etc."
4153These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
4154macros from \fIev.h\fR.
4155.ie n .IP """ev::tstamp"", ""ev::now""" 4
4156.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
4157.IX Item "ev::tstamp, ev::now"
4158Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
4159.ie n .IP """ev::io"", ""ev::timer"", ""ev::periodic"", ""ev::idle"", ""ev::sig"" etc." 4
4160.el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
4161.IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
4162For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
4163the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
4164which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
4165defined by many implementations.
4166.Sp
4167All of those classes have these methods:
4168.RS 4
4169.IP "ev::TYPE::TYPE ()" 4
4170.IX Item "ev::TYPE::TYPE ()"
4171.PD 0
4172.IP "ev::TYPE::TYPE (loop)" 4
4173.IX Item "ev::TYPE::TYPE (loop)"
4174.IP "ev::TYPE::~TYPE" 4
4175.IX Item "ev::TYPE::~TYPE"
4176.PD
4177The constructor (optionally) takes an event loop to associate the watcher
4178with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR.
4179.Sp
4180The constructor calls \f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the
4181\&\f(CW\*(C`set\*(C'\fR method before starting it.
4182.Sp
4183It will not set a callback, however: You have to call the templated \f(CW\*(C`set\*(C'\fR
4184method to set a callback before you can start the watcher.
4185.Sp
4186(The reason why you have to use a method is a limitation in \*(C+ which does
4187not allow explicit template arguments for constructors).
4188.Sp
4189The destructor automatically stops the watcher if it is active.
4190.IP "w\->set<class, &class::method> (object *)" 4
4191.IX Item "w->set<class, &class::method> (object *)"
4192This method sets the callback method to call. The method has to have a
4193signature of \f(CW\*(C`void (*)(ev_TYPE &, int)\*(C'\fR, it receives the watcher as
4194first argument and the \f(CW\*(C`revents\*(C'\fR as second. The object must be given as
4195parameter and is stored in the \f(CW\*(C`data\*(C'\fR member of the watcher.
4196.Sp
4197This method synthesizes efficient thunking code to call your method from
4198the C callback that libev requires. If your compiler can inline your
4199callback (i.e. it is visible to it at the place of the \f(CW\*(C`set\*(C'\fR call and
4200your compiler is good :), then the method will be fully inlined into the
4201thunking function, making it as fast as a direct C callback.
4202.Sp
4203Example: simple class declaration and watcher initialisation
4204.Sp
4205.Vb 4
4206\& struct myclass
4207\& {
4208\& void io_cb (ev::io &w, int revents) { }
4209\& }
4210\&
4211\& myclass obj;
4212\& ev::io iow;
4213\& iow.set <myclass, &myclass::io_cb> (&obj);
4214.Ve
4215.IP "w\->set (object *)" 4
4216.IX Item "w->set (object *)"
4217This is a variation of a method callback \- leaving out the method to call
4218will default the method to \f(CW\*(C`operator ()\*(C'\fR, which makes it possible to use
4219functor objects without having to manually specify the \f(CW\*(C`operator ()\*(C'\fR all
4220the time. Incidentally, you can then also leave out the template argument
4221list.
4222.Sp
4223The \f(CW\*(C`operator ()\*(C'\fR method prototype must be \f(CW\*(C`void operator ()(watcher &w,
4224int revents)\*(C'\fR.
4225.Sp
4226See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
4227.Sp
4228Example: use a functor object as callback.
4229.Sp
4230.Vb 7
4231\& struct myfunctor
4232\& {
4233\& void operator() (ev::io &w, int revents)
4234\& {
4235\& ...
4236\& }
4237\& }
4238\&
4239\& myfunctor f;
4240\&
4241\& ev::io w;
4242\& w.set (&f);
4243.Ve
4244.IP "w\->set<function> (void *data = 0)" 4
4245.IX Item "w->set<function> (void *data = 0)"
4246Also sets a callback, but uses a static method or plain function as
4247callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
4248\&\f(CW\*(C`data\*(C'\fR member and is free for you to use.
4249.Sp
4250The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
4251.Sp
4252See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
4253.Sp
4254Example: Use a plain function as callback.
4255.Sp
4256.Vb 2
4257\& static void io_cb (ev::io &w, int revents) { }
4258\& iow.set <io_cb> ();
4259.Ve
4260.IP "w\->set (loop)" 4
4261.IX Item "w->set (loop)"
4262Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
4263do this when the watcher is inactive (and not pending either).
4264.IP "w\->set ([arguments])" 4
4265.IX Item "w->set ([arguments])"
4266Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same arguments. Either this
4267method or a suitable start method must be called at least once. Unlike the
4268C counterpart, an active watcher gets automatically stopped and restarted
4269when reconfiguring it with this method.
4270.IP "w\->start ()" 4
4271.IX Item "w->start ()"
4272Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
4273constructor already stores the event loop.
4274.IP "w\->start ([arguments])" 4
4275.IX Item "w->start ([arguments])"
4276Instead of calling \f(CW\*(C`set\*(C'\fR and \f(CW\*(C`start\*(C'\fR methods separately, it is often
4277convenient to wrap them in one call. Uses the same type of arguments as
4278the configure \f(CW\*(C`set\*(C'\fR method of the watcher.
4279.IP "w\->stop ()" 4
4280.IX Item "w->stop ()"
4281Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
4282.ie n .IP "w\->again () (""ev::timer"", ""ev::periodic"" only)" 4
4283.el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
4284.IX Item "w->again () (ev::timer, ev::periodic only)"
4285For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
4286\&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
4287.ie n .IP "w\->sweep () (""ev::embed"" only)" 4
4288.el .IP "w\->sweep () (\f(CWev::embed\fR only)" 4
4289.IX Item "w->sweep () (ev::embed only)"
4290Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR.
4291.ie n .IP "w\->update () (""ev::stat"" only)" 4
4292.el .IP "w\->update () (\f(CWev::stat\fR only)" 4
4293.IX Item "w->update () (ev::stat only)"
4294Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
4295.RE
4296.RS 4
4297.RE
4298.PP
4299Example: Define a class with two I/O and idle watchers, start the I/O
4300watchers in the constructor.
4301.PP
4302.Vb 5
4303\& class myclass
4304\& {
4305\& ev::io io ; void io_cb (ev::io &w, int revents);
4306\& ev::io io2 ; void io2_cb (ev::io &w, int revents);
4307\& ev::idle idle; void idle_cb (ev::idle &w, int revents);
4308\&
4309\& myclass (int fd)
4310\& {
4311\& io .set <myclass, &myclass::io_cb > (this);
4312\& io2 .set <myclass, &myclass::io2_cb > (this);
4313\& idle.set <myclass, &myclass::idle_cb> (this);
4314\&
4315\& io.set (fd, ev::WRITE); // configure the watcher
4316\& io.start (); // start it whenever convenient
4317\&
4318\& io2.start (fd, ev::READ); // set + start in one call
4319\& }
4320\& };
4321.Ve
4322.SH "OTHER LANGUAGE BINDINGS"
4323.IX Header "OTHER LANGUAGE BINDINGS"
4324Libev does not offer other language bindings itself, but bindings for a
4325number of languages exist in the form of third-party packages. If you know
4326any interesting language binding in addition to the ones listed here, drop
4327me a note.
4328.IP "Perl" 4
4329.IX Item "Perl"
4330The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test
4331libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module,
4332there are additional modules that implement libev-compatible interfaces
4333to \f(CW\*(C`libadns\*(C'\fR (\f(CW\*(C`EV::ADNS\*(C'\fR, but \f(CW\*(C`AnyEvent::DNS\*(C'\fR is preferred nowadays),
4334\&\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
4335and \f(CW\*(C`EV::Glib\*(C'\fR).
4336.Sp
4337It can be found and installed via \s-1CPAN\s0, its homepage is at
4338<http://software.schmorp.de/pkg/EV>.
4339.IP "Python" 4
4340.IX Item "Python"
4341Python bindings can be found at <http://code.google.com/p/pyev/>. It
4342seems to be quite complete and well-documented.
4343.IP "Ruby" 4
4344.IX Item "Ruby"
4345Tony Arcieri has written a ruby extension that offers access to a subset
4346of the libev \s-1API\s0 and adds file handle abstractions, asynchronous \s-1DNS\s0 and
4347more on top of it. It can be found via gem servers. Its homepage is at
4348<http://rev.rubyforge.org/>.
4349.Sp
4350Roger Pack reports that using the link order \f(CW\*(C`\-lws2_32 \-lmsvcrt\-ruby\-190\*(C'\fR
4351makes rev work even on mingw.
4352.IP "Haskell" 4
4353.IX Item "Haskell"
4354A haskell binding to libev is available at
4355http://hackage.haskell.org/cgi\-bin/hackage\-scripts/package/hlibev <http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
4356.IP "D" 4
4357.IX Item "D"
4358Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
4359be found at <http://www.llucax.com.ar/proj/ev.d/index.html>.
4360.IP "Ocaml" 4
4361.IX Item "Ocaml"
4362Erkki Seppala has written Ocaml bindings for libev, to be found at
4363http://modeemi.cs.tut.fi/~flux/software/ocaml\-ev/ <http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
4364.IP "Lua" 4
4365.IX Item "Lua"
4366Brian Maher has written a partial interface to libev for lua (at the
4367time of this writing, only \f(CW\*(C`ev_io\*(C'\fR and \f(CW\*(C`ev_timer\*(C'\fR), to be found at
4368http://github.com/brimworks/lua\-ev <http://github.com/brimworks/lua-ev>.
4369.IP "Javascript" 4
4370.IX Item "Javascript"
4371Node.js (<http://nodejs.org>) uses libev as the underlying event library.
4372.IP "Others" 4
4373.IX Item "Others"
4374There are others, and I stopped counting.
4375.SH "MACRO MAGIC"
4376.IX Header "MACRO MAGIC"
4377Libev can be compiled with a variety of options, the most fundamental
4378of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most)
4379functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
4380.PP
4381To make it easier to write programs that cope with either variant, the
4382following macros are defined:
4383.ie n .IP """EV_A"", ""EV_A_""" 4
4384.el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
4385.IX Item "EV_A, EV_A_"
4386This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
4387loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
4388\&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
4389.Sp
4390.Vb 3
4391\& ev_unref (EV_A);
4392\& ev_timer_add (EV_A_ watcher);
4393\& ev_run (EV_A_ 0);
4394.Ve
4395.Sp
4396It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
4397which is often provided by the following macro.
4398.ie n .IP """EV_P"", ""EV_P_""" 4
4399.el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
4400.IX Item "EV_P, EV_P_"
4401This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
4402loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
4403\&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
4404.Sp
4405.Vb 2
4406\& // this is how ev_unref is being declared
4407\& static void ev_unref (EV_P);
4408\&
4409\& // this is how you can declare your typical callback
4410\& static void cb (EV_P_ ev_timer *w, int revents)
4411.Ve
4412.Sp
4413It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
4414suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
4415.ie n .IP """EV_DEFAULT"", ""EV_DEFAULT_""" 4
4416.el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
4417.IX Item "EV_DEFAULT, EV_DEFAULT_"
4418Similar to the other two macros, this gives you the value of the default
4419loop, if multiple loops are supported (\*(L"ev loop default\*(R"). The default loop
4420will be initialised if it isn't already initialised.
4421.Sp
4422For non-multiplicity builds, these macros do nothing, so you always have
4423to initialise the loop somewhere.
4424.ie n .IP """EV_DEFAULT_UC"", ""EV_DEFAULT_UC_""" 4
4425.el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
4426.IX Item "EV_DEFAULT_UC, EV_DEFAULT_UC_"
4427Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the
4428default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour
4429is undefined when the default loop has not been initialised by a previous
4430execution of \f(CW\*(C`EV_DEFAULT\*(C'\fR, \f(CW\*(C`EV_DEFAULT_\*(C'\fR or \f(CW\*(C`ev_default_init (...)\*(C'\fR.
4431.Sp
4432It is often prudent to use \f(CW\*(C`EV_DEFAULT\*(C'\fR when initialising the first
4433watcher in a function but use \f(CW\*(C`EV_DEFAULT_UC\*(C'\fR afterwards.
4434.PP
4435Example: Declare and initialise a check watcher, utilising the above
4436macros so it will work regardless of whether multiple loops are supported
4437or not.
4438.PP
4439.Vb 5
4440\& static void
4441\& check_cb (EV_P_ ev_timer *w, int revents)
4442\& {
4443\& ev_check_stop (EV_A_ w);
4444\& }
4445\&
4446\& ev_check check;
4447\& ev_check_init (&check, check_cb);
4448\& ev_check_start (EV_DEFAULT_ &check);
4449\& ev_run (EV_DEFAULT_ 0);
4450.Ve
4451.SH "EMBEDDING"
4452.IX Header "EMBEDDING"
4453Libev can (and often is) directly embedded into host
4454applications. Examples of applications that embed it include the Deliantra
4455Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
4456and rxvt-unicode.
4457.PP
4458The goal is to enable you to just copy the necessary files into your
4459source directory without having to change even a single line in them, so
4460you can easily upgrade by simply copying (or having a checked-out copy of
4461libev somewhere in your source tree).
4462.SS "\s-1FILESETS\s0"
4463.IX Subsection "FILESETS"
4464Depending on what features you need you need to include one or more sets of files
4465in your application.
4466.PP
4467\fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR
4468.IX Subsection "CORE EVENT LOOP"
4469.PP
4470To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
4471configuration (no autoconf):
4472.PP
4473.Vb 2
4474\& #define EV_STANDALONE 1
4475\& #include "ev.c"
4476.Ve
4477.PP
4478This will automatically include \fIev.h\fR, too, and should be done in a
4479single C source file only to provide the function implementations. To use
4480it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best
4481done by writing a wrapper around \fIev.h\fR that you can include instead and
4482where you can put other configuration options):
4483.PP
4484.Vb 2
4485\& #define EV_STANDALONE 1
4486\& #include "ev.h"
4487.Ve
4488.PP
4489Both header files and implementation files can be compiled with a \*(C+
4490compiler (at least, that's a stated goal, and breakage will be treated
4491as a bug).
4492.PP
4493You need the following files in your source tree, or in a directory
4494in your include path (e.g. in libev/ when using \-Ilibev):
4495.PP
4496.Vb 4
4497\& ev.h
4498\& ev.c
4499\& ev_vars.h
4500\& ev_wrap.h
4501\&
4502\& ev_win32.c required on win32 platforms only
4503\&
4504\& ev_select.c only when select backend is enabled (which is enabled by default)
4505\& ev_poll.c only when poll backend is enabled (disabled by default)
4506\& ev_epoll.c only when the epoll backend is enabled (disabled by default)
4507\& ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
4508\& ev_port.c only when the solaris port backend is enabled (disabled by default)
4509.Ve
4510.PP
4511\&\fIev.c\fR includes the backend files directly when enabled, so you only need
4512to compile this single file.
4513.PP
4514\fI\s-1LIBEVENT\s0 \s-1COMPATIBILITY\s0 \s-1API\s0\fR
4515.IX Subsection "LIBEVENT COMPATIBILITY API"
4516.PP
4517To include the libevent compatibility \s-1API\s0, also include:
4518.PP
4519.Vb 1
4520\& #include "event.c"
4521.Ve
4522.PP
4523in the file including \fIev.c\fR, and:
4524.PP
4525.Vb 1
4526\& #include "event.h"
4527.Ve
4528.PP
4529in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR.
4530.PP
4531You need the following additional files for this:
4532.PP
4533.Vb 2
4534\& event.h
4535\& event.c
4536.Ve
4537.PP
4538\fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR
4539.IX Subsection "AUTOCONF SUPPORT"
4540.PP
4541Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your configuration in
4542whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
4543\&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then
4544include \fIconfig.h\fR and configure itself accordingly.
4545.PP
4546For this of course you need the m4 file:
4547.PP
4548.Vb 1
4549\& libev.m4
4550.Ve
4551.SS "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0"
4552.IX Subsection "PREPROCESSOR SYMBOLS/MACROS"
4553Libev can be configured via a variety of preprocessor symbols you have to
4554define before including (or compiling) any of its files. The default in
4555the absence of autoconf is documented for every option.
4556.PP
4557Symbols marked with \*(L"(h)\*(R" do not change the \s-1ABI\s0, and can have different
4558values when compiling libev vs. including \fIev.h\fR, so it is permissible
4559to redefine them before including \fIev.h\fR without breaking compatibility
4560to a compiled library. All other symbols change the \s-1ABI\s0, which means all
4561users of libev and the libev code itself must be compiled with compatible
4562settings.
4563.IP "\s-1EV_COMPAT3\s0 (h)" 4
4564.IX Item "EV_COMPAT3 (h)"
4565Backwards compatibility is a major concern for libev. This is why this
4566release of libev comes with wrappers for the functions and symbols that
4567have been renamed between libev version 3 and 4.
4568.Sp
4569You can disable these wrappers (to test compatibility with future
4570versions) by defining \f(CW\*(C`EV_COMPAT3\*(C'\fR to \f(CW0\fR when compiling your
4571sources. This has the additional advantage that you can drop the \f(CW\*(C`struct\*(C'\fR
4572from \f(CW\*(C`struct ev_loop\*(C'\fR declarations, as libev will provide an \f(CW\*(C`ev_loop\*(C'\fR
4573typedef in that case.
4574.Sp
4575In some future version, the default for \f(CW\*(C`EV_COMPAT3\*(C'\fR will become \f(CW0\fR,
4576and in some even more future version the compatibility code will be
4577removed completely.
4578.IP "\s-1EV_STANDALONE\s0 (h)" 4
4579.IX Item "EV_STANDALONE (h)"
4580Must always be \f(CW1\fR if you do not use autoconf configuration, which
4581keeps libev from including \fIconfig.h\fR, and it also defines dummy
4582implementations for some libevent functions (such as logging, which is not
4583supported). It will also not define any of the structs usually found in
4584\&\fIevent.h\fR that are not directly supported by the libev core alone.
4585.Sp
4586In standalone mode, libev will still try to automatically deduce the
4587configuration, but has to be more conservative.
4588.IP "\s-1EV_USE_FLOOR\s0" 4
4589.IX Item "EV_USE_FLOOR"
4590If defined to be \f(CW1\fR, libev will use the \f(CW\*(C`floor ()\*(C'\fR function for its
4591periodic reschedule calculations, otherwise libev will fall back on a
4592portable (slower) implementation. If you enable this, you usually have to
4593link against libm or something equivalent. Enabling this when the \f(CW\*(C`floor\*(C'\fR
4594function is not available will fail, so the safe default is to not enable
4595this.
4596.IP "\s-1EV_USE_MONOTONIC\s0" 4
4597.IX Item "EV_USE_MONOTONIC"
4598If defined to be \f(CW1\fR, libev will try to detect the availability of the
4599monotonic clock option at both compile time and runtime. Otherwise no
4600use of the monotonic clock option will be attempted. If you enable this,
4601you usually have to link against librt or something similar. Enabling it
4602when the functionality isn't available is safe, though, although you have
4603to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
4604function is hiding in (often \fI\-lrt\fR). See also \f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
4605.IP "\s-1EV_USE_REALTIME\s0" 4
4606.IX Item "EV_USE_REALTIME"
4607If defined to be \f(CW1\fR, libev will try to detect the availability of the
4608real-time clock option at compile time (and assume its availability
4609at runtime if successful). Otherwise no use of the real-time clock
4610option will be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR
4611by \f(CW\*(C`clock_get (CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect
4612correctness. See the note about libraries in the description of
4613\&\f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. Defaults to the opposite value of
4614\&\f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
4615.IP "\s-1EV_USE_CLOCK_SYSCALL\s0" 4
4616.IX Item "EV_USE_CLOCK_SYSCALL"
4617If defined to be \f(CW1\fR, libev will try to use a direct syscall instead
4618of calling the system-provided \f(CW\*(C`clock_gettime\*(C'\fR function. This option
4619exists 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
4620unconditionally pulls in \f(CW\*(C`libpthread\*(C'\fR, slowing down single-threaded
4621programs needlessly. Using a direct syscall is slightly slower (in
4622theory), because no optimised vdso implementation can be used, but avoids
4623the pthread dependency. Defaults to \f(CW1\fR on GNU/Linux with glibc 2.x or
4624higher, as it simplifies linking (no need for \f(CW\*(C`\-lrt\*(C'\fR).
4625.IP "\s-1EV_USE_NANOSLEEP\s0" 4
4626.IX Item "EV_USE_NANOSLEEP"
4627If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available
4628and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR.
4629.IP "\s-1EV_USE_EVENTFD\s0" 4
4630.IX Item "EV_USE_EVENTFD"
4631If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
4632available and will probe for kernel support at runtime. This will improve
4633\&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
4634If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
46352.7 or newer, otherwise disabled.
4636.IP "\s-1EV_USE_SELECT\s0" 4
4637.IX Item "EV_USE_SELECT"
4638If undefined or defined to be \f(CW1\fR, libev will compile in support for the
4639\&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at auto-detection will be done: if no
4640other method takes over, select will be it. Otherwise the select backend
4641will not be compiled in.
4642.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
4643.IX Item "EV_SELECT_USE_FD_SET"
4644If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR
4645structure. This is useful if libev doesn't compile due to a missing
4646\&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it mis-guesses the bitset layout
4647on exotic systems. This usually limits the range of file descriptors to
4648some low limit such as 1024 or might have other limitations (winsocket
4649only allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation,
4650configures the maximum size of the \f(CW\*(C`fd_set\*(C'\fR.
4651.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
4652.IX Item "EV_SELECT_IS_WINSOCKET"
4653When defined to \f(CW1\fR, the select backend will assume that
4654select/socket/connect etc. don't understand file descriptors but
4655wants osf handles on win32 (this is the case when the select to
4656be used is the winsock select). This means that it will call
4657\&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
4658it is assumed that all these functions actually work on fds, even
4659on win32. Should not be defined on non\-win32 platforms.
4660.IP "\s-1EV_FD_TO_WIN32_HANDLE\s0(fd)" 4
4661.IX Item "EV_FD_TO_WIN32_HANDLE(fd)"
4662If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map
4663file descriptors to socket handles. When not defining this symbol (the
4664default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually
4665correct. In some cases, programs use their own file descriptor management,
4666in which case they can provide this function to map fds to socket handles.
4667.IP "\s-1EV_WIN32_HANDLE_TO_FD\s0(handle)" 4
4668.IX Item "EV_WIN32_HANDLE_TO_FD(handle)"
4669If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR then libev maps handles to file descriptors
4670using the standard \f(CW\*(C`_open_osfhandle\*(C'\fR function. For programs implementing
4671their own fd to handle mapping, overwriting this function makes it easier
4672to do so. This can be done by defining this macro to an appropriate value.
4673.IP "\s-1EV_WIN32_CLOSE_FD\s0(fd)" 4
4674.IX Item "EV_WIN32_CLOSE_FD(fd)"
4675If programs implement their own fd to handle mapping on win32, then this
4676macro can be used to override the \f(CW\*(C`close\*(C'\fR function, useful to unregister
4677file descriptors again. Note that the replacement function has to close
4678the underlying \s-1OS\s0 handle.
4679.IP "\s-1EV_USE_WSASOCKET\s0" 4
4680.IX Item "EV_USE_WSASOCKET"
4681If defined to be \f(CW1\fR, libev will use \f(CW\*(C`WSASocket\*(C'\fR to create its internal
4682communication socket, which works better in some environments. Otherwise,
4683the normal \f(CW\*(C`socket\*(C'\fR function will be used, which works better in other
4684enviornments.
4685.IP "\s-1EV_USE_POLL\s0" 4
4686.IX Item "EV_USE_POLL"
4687If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2)
4688backend. Otherwise it will be enabled on non\-win32 platforms. It
4689takes precedence over select.
4690.IP "\s-1EV_USE_EPOLL\s0" 4
4691.IX Item "EV_USE_EPOLL"
4692If defined to be \f(CW1\fR, libev will compile in support for the Linux
4693\&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime,
4694otherwise another method will be used as fallback. This is the preferred
4695backend for GNU/Linux systems. If undefined, it will be enabled if the
4696headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4697.IP "\s-1EV_USE_KQUEUE\s0" 4
4698.IX Item "EV_USE_KQUEUE"
4699If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
4700\&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime,
4701otherwise another method will be used as fallback. This is the preferred
4702backend for \s-1BSD\s0 and BSD-like systems, although on most BSDs kqueue only
4703supports some types of fds correctly (the only platform we found that
4704supports ptys for example was NetBSD), so kqueue might be compiled in, but
4705not be used unless explicitly requested. The best way to use it is to find
4706out whether kqueue supports your type of fd properly and use an embedded
4707kqueue loop.
4708.IP "\s-1EV_USE_PORT\s0" 4
4709.IX Item "EV_USE_PORT"
4710If defined to be \f(CW1\fR, libev will compile in support for the Solaris
471110 port style backend. Its availability will be detected at runtime,
4712otherwise another method will be used as fallback. This is the preferred
4713backend for Solaris 10 systems.
4714.IP "\s-1EV_USE_DEVPOLL\s0" 4
4715.IX Item "EV_USE_DEVPOLL"
4716Reserved for future expansion, works like the \s-1USE\s0 symbols above.
4717.IP "\s-1EV_USE_INOTIFY\s0" 4
4718.IX Item "EV_USE_INOTIFY"
4719If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
4720interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
4721be detected at runtime. If undefined, it will be enabled if the headers
4722indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4723.IP "\s-1EV_NO_SMP\s0" 4
4724.IX Item "EV_NO_SMP"
4725If defined to be \f(CW1\fR, libev will assume that memory is always coherent
4726between threads, that is, threads can be used, but threads never run on
4727different cpus (or different cpu cores). This reduces dependencies
4728and makes libev faster.
4729.IP "\s-1EV_NO_THREADS\s0" 4
4730.IX Item "EV_NO_THREADS"
4731If defined to be \f(CW1\fR, libev will assume that it will never be called
4732from different threads, which is a stronger assumption than \f(CW\*(C`EV_NO_SMP\*(C'\fR,
4733above. This reduces dependencies and makes libev faster.
4734.IP "\s-1EV_ATOMIC_T\s0" 4
4735.IX Item "EV_ATOMIC_T"
4736Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
4737access is atomic and serialised with respect to other threads or signal
4738contexts. No such type is easily found in the C language, so you can
4739provide your own type that you know is safe for your purposes. It is used
4740both for signal handler \*(L"locking\*(R" as well as for signal and thread safety
4741in \f(CW\*(C`ev_async\*(C'\fR watchers.
4742.Sp
4743In the absence of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR
4744(from \fIsignal.h\fR), which is usually good enough on most platforms,
4745although strictly speaking using a type that also implies a memory fence
4746is required.
4747.IP "\s-1EV_H\s0 (h)" 4
4748.IX Item "EV_H (h)"
4749The name of the \fIev.h\fR header file used to include it. The default if
4750undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be
4751used to virtually rename the \fIev.h\fR header file in case of conflicts.
4752.IP "\s-1EV_CONFIG_H\s0 (h)" 4
4753.IX Item "EV_CONFIG_H (h)"
4754If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
4755\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
4756\&\f(CW\*(C`EV_H\*(C'\fR, above.
4757.IP "\s-1EV_EVENT_H\s0 (h)" 4
4758.IX Item "EV_EVENT_H (h)"
4759Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea
4760of how the \fIevent.h\fR header can be found, the default is \f(CW"event.h"\fR.
4761.IP "\s-1EV_PROTOTYPES\s0 (h)" 4
4762.IX Item "EV_PROTOTYPES (h)"
4763If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
4764prototypes, but still define all the structs and other symbols. This is
4765occasionally useful if you want to provide your own wrapper functions
4766around libev functions.
4767.IP "\s-1EV_MULTIPLICITY\s0" 4
4768.IX Item "EV_MULTIPLICITY"
4769If undefined or defined to \f(CW1\fR, then all event-loop-specific functions
4770will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create
4771additional independent event loops. Otherwise there will be no support
4772for multiple event loops and there is no first event loop pointer
4773argument. Instead, all functions act on the single default loop.
4774.Sp
4775Note that \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR will no longer provide a
4776default loop when multiplicity is switched off \- you always have to
4777initialise the loop manually in this case.
4778.IP "\s-1EV_MINPRI\s0" 4
4779.IX Item "EV_MINPRI"
4780.PD 0
4781.IP "\s-1EV_MAXPRI\s0" 4
4782.IX Item "EV_MAXPRI"
4783.PD
4784The range of allowed priorities. \f(CW\*(C`EV_MINPRI\*(C'\fR must be smaller or equal to
4785\&\f(CW\*(C`EV_MAXPRI\*(C'\fR, but otherwise there are no non-obvious limitations. You can
4786provide for more priorities by overriding those symbols (usually defined
4787to be \f(CW\*(C`\-2\*(C'\fR and \f(CW2\fR, respectively).
4788.Sp
4789When doing priority-based operations, libev usually has to linearly search
4790all the priorities, so having many of them (hundreds) uses a lot of space
4791and time, so using the defaults of five priorities (\-2 .. +2) is usually
4792fine.
4793.Sp
4794If your embedding application does not need any priorities, defining these
4795both to \f(CW0\fR will save some memory and \s-1CPU\s0.
4796.IP "\s-1EV_PERIODIC_ENABLE\s0, \s-1EV_IDLE_ENABLE\s0, \s-1EV_EMBED_ENABLE\s0, \s-1EV_STAT_ENABLE\s0, \s-1EV_PREPARE_ENABLE\s0, \s-1EV_CHECK_ENABLE\s0, \s-1EV_FORK_ENABLE\s0, \s-1EV_SIGNAL_ENABLE\s0, \s-1EV_ASYNC_ENABLE\s0, \s-1EV_CHILD_ENABLE\s0." 4
4797.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."
4798If undefined or defined to be \f(CW1\fR (and the platform supports it), then
4799the respective watcher type is supported. If defined to be \f(CW0\fR, then it
4800is not. Disabling watcher types mainly saves code size.
4801.IP "\s-1EV_FEATURES\s0" 4
4802.IX Item "EV_FEATURES"
4803If you need to shave off some kilobytes of code at the expense of some
4804speed (but with the full \s-1API\s0), you can define this symbol to request
4805certain subsets of functionality. The default is to enable all features
4806that can be enabled on the platform.
4807.Sp
4808A typical way to use this symbol is to define it to \f(CW0\fR (or to a bitset
4809with some broad features you want) and then selectively re-enable
4810additional parts you want, for example if you want everything minimal,
4811but multiple event loop support, async and child watchers and the poll
4812backend, use this:
4813.Sp
4814.Vb 5
4815\& #define EV_FEATURES 0
4816\& #define EV_MULTIPLICITY 1
4817\& #define EV_USE_POLL 1
4818\& #define EV_CHILD_ENABLE 1
4819\& #define EV_ASYNC_ENABLE 1
4820.Ve
4821.Sp
4822The actual value is a bitset, it can be a combination of the following
4823values (by default, all of these are enabled):
4824.RS 4
4825.ie n .IP "1 \- faster/larger code" 4
4826.el .IP "\f(CW1\fR \- faster/larger code" 4
4827.IX Item "1 - faster/larger code"
4828Use larger code to speed up some operations.
4829.Sp
4830Currently this is used to override some inlining decisions (enlarging the
4831code size by roughly 30% on amd64).
4832.Sp
4833When optimising for size, use of compiler flags such as \f(CW\*(C`\-Os\*(C'\fR with
4834gcc is recommended, as well as \f(CW\*(C`\-DNDEBUG\*(C'\fR, as libev contains a number of
4835assertions.
4836.Sp
4837The default is off when \f(CW\*(C`_\|_OPTIMIZE_SIZE_\|_\*(C'\fR is defined by your compiler
4838(e.g. gcc with \f(CW\*(C`\-Os\*(C'\fR).
4839.ie n .IP "2 \- faster/larger data structures" 4
4840.el .IP "\f(CW2\fR \- faster/larger data structures" 4
4841.IX Item "2 - faster/larger data structures"
4842Replaces the small 2\-heap for timer management by a faster 4\-heap, larger
4843hash table sizes and so on. This will usually further increase code size
4844and can additionally have an effect on the size of data structures at
4845runtime.
4846.Sp
4847The default is off when \f(CW\*(C`_\|_OPTIMIZE_SIZE_\|_\*(C'\fR is defined by your compiler
4848(e.g. gcc with \f(CW\*(C`\-Os\*(C'\fR).
4849.ie n .IP "4 \- full \s-1API\s0 configuration" 4
4850.el .IP "\f(CW4\fR \- full \s-1API\s0 configuration" 4
4851.IX Item "4 - full API configuration"
4852This enables priorities (sets \f(CW\*(C`EV_MAXPRI\*(C'\fR=2 and \f(CW\*(C`EV_MINPRI\*(C'\fR=\-2), and
4853enables multiplicity (\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR=1).
4854.ie n .IP "8 \- full \s-1API\s0" 4
4855.el .IP "\f(CW8\fR \- full \s-1API\s0" 4
4856.IX Item "8 - full API"
4857This enables a lot of the \*(L"lesser used\*(R" \s-1API\s0 functions. See \f(CW\*(C`ev.h\*(C'\fR for
4858details on which parts of the \s-1API\s0 are still available without this
4859feature, and do not complain if this subset changes over time.
4860.ie n .IP "16 \- enable all optional watcher types" 4
4861.el .IP "\f(CW16\fR \- enable all optional watcher types" 4
4862.IX Item "16 - enable all optional watcher types"
4863Enables all optional watcher types. If you want to selectively enable
4864only some watcher types other than I/O and timers (e.g. prepare,
4865embed, async, child...) you can enable them manually by defining
4866\&\f(CW\*(C`EV_watchertype_ENABLE\*(C'\fR to \f(CW1\fR instead.
4867.ie n .IP "32 \- enable all backends" 4
4868.el .IP "\f(CW32\fR \- enable all backends" 4
4869.IX Item "32 - enable all backends"
4870This enables all backends \- without this feature, you need to enable at
4871least one backend manually (\f(CW\*(C`EV_USE_SELECT\*(C'\fR is a good choice).
4872.ie n .IP "64 \- enable OS-specific ""helper"" APIs" 4
4873.el .IP "\f(CW64\fR \- enable OS-specific ``helper'' APIs" 4
4874.IX Item "64 - enable OS-specific helper APIs"
4875Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
4876default.
4877.RE
4878.RS 4
4879.Sp
4880Compiling with \f(CW\*(C`gcc \-Os \-DEV_STANDALONE \-DEV_USE_EPOLL=1 \-DEV_FEATURES=0\*(C'\fR
4881reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
4882code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
4883watchers, timers and monotonic clock support.
4884.Sp
4885With an intelligent-enough linker (gcc+binutils are intelligent enough
4886when you use \f(CW\*(C`\-Wl,\-\-gc\-sections \-ffunction\-sections\*(C'\fR) functions unused by
4887your program might be left out as well \- a binary starting a timer and an
4888I/O watcher then might come out at only 5Kb.
4889.RE
4890.IP "\s-1EV_API_STATIC\s0" 4
4891.IX Item "EV_API_STATIC"
4892If this symbol is defined (by default it is not), then all identifiers
4893will have static linkage. This means that libev will not export any
4894identifiers, and you cannot link against libev anymore. This can be useful
4895when you embed libev, only want to use libev functions in a single file,
4896and do not want its identifiers to be visible.
4897.Sp
4898To use this, define \f(CW\*(C`EV_API_STATIC\*(C'\fR and include \fIev.c\fR in the file that
4899wants to use libev.
4900.Sp
4901This option only works when libev is compiled with a C compiler, as \*(C+
4902doesn't support the required declaration syntax.
4903.IP "\s-1EV_AVOID_STDIO\s0" 4
4904.IX Item "EV_AVOID_STDIO"
4905If this is set to \f(CW1\fR at compiletime, then libev will avoid using stdio
4906functions (printf, scanf, perror etc.). This will increase the code size
4907somewhat, but if your program doesn't otherwise depend on stdio and your
4908libc allows it, this avoids linking in the stdio library which is quite
4909big.
4910.Sp
4911Note that error messages might become less precise when this option is
4912enabled.
4913.IP "\s-1EV_NSIG\s0" 4
4914.IX Item "EV_NSIG"
4915The highest supported signal number, +1 (or, the number of
4916signals): Normally, libev tries to deduce the maximum number of signals
4917automatically, but sometimes this fails, in which case it can be
4918specified. Also, using a lower number than detected (\f(CW32\fR should be
4919good for about any system in existence) can save some memory, as libev
4920statically allocates some 12\-24 bytes per signal number.
4921.IP "\s-1EV_PID_HASHSIZE\s0" 4
4922.IX Item "EV_PID_HASHSIZE"
4923\&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by
4924pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR disabled),
4925usually more than enough. If you need to manage thousands of children you
4926might want to increase this value (\fImust\fR be a power of two).
4927.IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4
4928.IX Item "EV_INOTIFY_HASHSIZE"
4929\&\f(CW\*(C`ev_stat\*(C'\fR watchers use a small hash table to distribute workload by
4930inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR
4931disabled), usually more than enough. If you need to manage thousands of
4932\&\f(CW\*(C`ev_stat\*(C'\fR watchers you might want to increase this value (\fImust\fR be a
4933power of two).
4934.IP "\s-1EV_USE_4HEAP\s0" 4
4935.IX Item "EV_USE_4HEAP"
4936Heaps are not very cache-efficient. To improve the cache-efficiency of the
4937timer and periodics heaps, libev uses a 4\-heap when this symbol is defined
4938to \f(CW1\fR. The 4\-heap uses more complicated (longer) code but has noticeably
4939faster performance with many (thousands) of watchers.
4940.Sp
4941The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4942will be \f(CW0\fR.
4943.IP "\s-1EV_HEAP_CACHE_AT\s0" 4
4944.IX Item "EV_HEAP_CACHE_AT"
4945Heaps are not very cache-efficient. To improve the cache-efficiency of the
4946timer and periodics heaps, libev can cache the timestamp (\fIat\fR) within
4947the heap structure (selected by defining \f(CW\*(C`EV_HEAP_CACHE_AT\*(C'\fR to \f(CW1\fR),
4948which uses 8\-12 bytes more per watcher and a few hundred bytes more code,
4949but avoids random read accesses on heap changes. This improves performance
4950noticeably with many (hundreds) of watchers.
4951.Sp
4952The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4953will be \f(CW0\fR.
4954.IP "\s-1EV_VERIFY\s0" 4
4955.IX Item "EV_VERIFY"
4956Controls how much internal verification (see \f(CW\*(C`ev_verify ()\*(C'\fR) will
4957be done: If set to \f(CW0\fR, no internal verification code will be compiled
4958in. If set to \f(CW1\fR, then verification code will be compiled in, but not
4959called. If set to \f(CW2\fR, then the internal verification code will be
4960called once per loop, which can slow down libev. If set to \f(CW3\fR, then the
4961verification code will be called very frequently, which will slow down
4962libev considerably.
4963.Sp
4964The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4965will be \f(CW0\fR.
4966.IP "\s-1EV_COMMON\s0" 4
4967.IX Item "EV_COMMON"
4968By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining
4969this macro to something else you can include more and other types of
4970members. You have to define it each time you include one of the files,
4971though, and it must be identical each time.
4972.Sp
4973For example, the perl \s-1EV\s0 module uses something like this:
4974.Sp
4975.Vb 3
4976\& #define EV_COMMON \e
4977\& SV *self; /* contains this struct */ \e
4978\& SV *cb_sv, *fh /* note no trailing ";" */
4979.Ve
4980.IP "\s-1EV_CB_DECLARE\s0 (type)" 4
4981.IX Item "EV_CB_DECLARE (type)"
4982.PD 0
4983.IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4
4984.IX Item "EV_CB_INVOKE (watcher, revents)"
4985.IP "ev_set_cb (ev, cb)" 4
4986.IX Item "ev_set_cb (ev, cb)"
4987.PD
4988Can be used to change the callback member declaration in each watcher,
4989and the way callbacks are invoked and set. Must expand to a struct member
4990definition and a statement, respectively. See the \fIev.h\fR header file for
4991their default definitions. One possible use for overriding these is to
4992avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use
4993method calls instead of plain function calls in \*(C+.
4994.SS "\s-1EXPORTED\s0 \s-1API\s0 \s-1SYMBOLS\s0"
4995.IX Subsection "EXPORTED API SYMBOLS"
4996If you need to re-export the \s-1API\s0 (e.g. via a \s-1DLL\s0) and you need a list of
4997exported symbols, you can use the provided \fISymbol.*\fR files which list
4998all public symbols, one per line:
4999.PP
5000.Vb 2
5001\& Symbols.ev for libev proper
5002\& Symbols.event for the libevent emulation
5003.Ve
5004.PP
5005This can also be used to rename all public symbols to avoid clashes with
5006multiple versions of libev linked together (which is obviously bad in
5007itself, but sometimes it is inconvenient to avoid this).
5008.PP
5009A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to
5010include before including \fIev.h\fR:
5011.PP
5012.Vb 1
5013\& <Symbols.ev sed \-e "s/.*/#define & myprefix_&/" >wrap.h
5014.Ve
5015.PP
5016This would create a file \fIwrap.h\fR which essentially looks like this:
5017.PP
5018.Vb 4
5019\& #define ev_backend myprefix_ev_backend
5020\& #define ev_check_start myprefix_ev_check_start
5021\& #define ev_check_stop myprefix_ev_check_stop
5022\& ...
5023.Ve
5024.SS "\s-1EXAMPLES\s0"
5025.IX Subsection "EXAMPLES"
5026For a real-world example of a program the includes libev
5027verbatim, you can have a look at the \s-1EV\s0 perl module
5028(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
5029the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public
5030interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file
5031will be compiled. It is pretty complex because it provides its own header
5032file.
5033.PP
5034The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file
5035that everybody includes and which overrides some configure choices:
5036.PP
5037.Vb 8
5038\& #define EV_FEATURES 8
5039\& #define EV_USE_SELECT 1
5040\& #define EV_PREPARE_ENABLE 1
5041\& #define EV_IDLE_ENABLE 1
5042\& #define EV_SIGNAL_ENABLE 1
5043\& #define EV_CHILD_ENABLE 1
5044\& #define EV_USE_STDEXCEPT 0
5045\& #define EV_CONFIG_H <config.h>
5046\&
5047\& #include "ev++.h"
5048.Ve
5049.PP
5050And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled:
5051.PP
5052.Vb 2
5053\& #include "ev_cpp.h"
5054\& #include "ev.c"
5055.Ve
5056.SH "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT"
5057.IX Header "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT"
5058.SS "\s-1THREADS\s0 \s-1AND\s0 \s-1COROUTINES\s0"
5059.IX Subsection "THREADS AND COROUTINES"
5060\fI\s-1THREADS\s0\fR
5061.IX Subsection "THREADS"
5062.PP
5063All libev functions are reentrant and thread-safe unless explicitly
5064documented otherwise, but libev implements no locking itself. This means
5065that you can use as many loops as you want in parallel, as long as there
5066are no concurrent calls into any libev function with the same loop
5067parameter (\f(CW\*(C`ev_default_*\*(C'\fR calls have an implicit default loop parameter,
5068of course): libev guarantees that different event loops share no data
5069structures that need any locking.
5070.PP
5071Or to put it differently: calls with different loop parameters can be done
5072concurrently from multiple threads, calls with the same loop parameter
5073must be done serially (but can be done from different threads, as long as
5074only one thread ever is inside a call at any point in time, e.g. by using
5075a mutex per loop).
5076.PP
5077Specifically to support threads (and signal handlers), libev implements
5078so-called \f(CW\*(C`ev_async\*(C'\fR watchers, which allow some limited form of
5079concurrency on the same event loop, namely waking it up \*(L"from the
5080outside\*(R".
5081.PP
5082If you want to know which design (one loop, locking, or multiple loops
5083without or something else still) is best for your problem, then I cannot
5084help you, but here is some generic advice:
5085.IP "\(bu" 4
5086most applications have a main thread: use the default libev loop
5087in that thread, or create a separate thread running only the default loop.
5088.Sp
5089This helps integrating other libraries or software modules that use libev
5090themselves and don't care/know about threading.
5091.IP "\(bu" 4
5092one loop per thread is usually a good model.
5093.Sp
5094Doing this is almost never wrong, sometimes a better-performance model
5095exists, but it is always a good start.
5096.IP "\(bu" 4
5097other models exist, such as the leader/follower pattern, where one
5098loop is handed through multiple threads in a kind of round-robin fashion.
5099.Sp
5100Choosing a model is hard \- look around, learn, know that usually you can do
5101better than you currently do :\-)
5102.IP "\(bu" 4
5103often you need to talk to some other thread which blocks in the
5104event loop.
5105.Sp
5106\&\f(CW\*(C`ev_async\*(C'\fR watchers can be used to wake them up from other threads safely
5107(or from signal contexts...).
5108.Sp
5109An example use would be to communicate signals or other events that only
5110work in the default loop by registering the signal watcher with the
5111default loop and triggering an \f(CW\*(C`ev_async\*(C'\fR watcher from the default loop
5112watcher callback into the event loop interested in the signal.
5113.PP
5114See also \*(L"\s-1THREAD\s0 \s-1LOCKING\s0 \s-1EXAMPLE\s0\*(R".
5115.PP
5116\fI\s-1COROUTINES\s0\fR
5117.IX Subsection "COROUTINES"
5118.PP
5119Libev is very accommodating to coroutines (\*(L"cooperative threads\*(R"):
5120libev fully supports nesting calls to its functions from different
5121coroutines (e.g. you can call \f(CW\*(C`ev_run\*(C'\fR on the same loop from two
5122different coroutines, and switch freely between both coroutines running
5123the loop, as long as you don't confuse yourself). The only exception is
5124that you must not do this from \f(CW\*(C`ev_periodic\*(C'\fR reschedule callbacks.
5125.PP
5126Care has been taken to ensure that libev does not keep local state inside
5127\&\f(CW\*(C`ev_run\*(C'\fR, and other calls do not usually allow for coroutine switches as
5128they do not call any callbacks.
5129.SS "\s-1COMPILER\s0 \s-1WARNINGS\s0"
5130.IX Subsection "COMPILER WARNINGS"
5131Depending on your compiler and compiler settings, you might get no or a
5132lot of warnings when compiling libev code. Some people are apparently
5133scared by this.
5134.PP
5135However, these are unavoidable for many reasons. For one, each compiler
5136has different warnings, and each user has different tastes regarding
5137warning options. \*(L"Warn-free\*(R" code therefore cannot be a goal except when
5138targeting a specific compiler and compiler-version.
5139.PP
5140Another reason is that some compiler warnings require elaborate
5141workarounds, or other changes to the code that make it less clear and less
5142maintainable.
5143.PP
5144And of course, some compiler warnings are just plain stupid, or simply
5145wrong (because they don't actually warn about the condition their message
5146seems to warn about). For example, certain older gcc versions had some
5147warnings that resulted in an extreme number of false positives. These have
5148been fixed, but some people still insist on making code warn-free with
5149such buggy versions.
5150.PP
5151While libev is written to generate as few warnings as possible,
5152\&\*(L"warn-free\*(R" code is not a goal, and it is recommended not to build libev
5153with any compiler warnings enabled unless you are prepared to cope with
5154them (e.g. by ignoring them). Remember that warnings are just that:
5155warnings, not errors, or proof of bugs.
5156.SS "\s-1VALGRIND\s0"
5157.IX Subsection "VALGRIND"
5158Valgrind has a special section here because it is a popular tool that is
5159highly useful. Unfortunately, valgrind reports are very hard to interpret.
5160.PP
5161If you think you found a bug (memory leak, uninitialised data access etc.)
5162in libev, then check twice: If valgrind reports something like:
5163.PP
5164.Vb 3
5165\& ==2274== definitely lost: 0 bytes in 0 blocks.
5166\& ==2274== possibly lost: 0 bytes in 0 blocks.
5167\& ==2274== still reachable: 256 bytes in 1 blocks.
5168.Ve
5169.PP
5170Then there is no memory leak, just as memory accounted to global variables
5171is not a memleak \- the memory is still being referenced, and didn't leak.
5172.PP
5173Similarly, under some circumstances, valgrind might report kernel bugs
5174as if it were a bug in libev (e.g. in realloc or in the poll backend,
5175although an acceptable workaround has been found here), or it might be
5176confused.
5177.PP
5178Keep in mind that valgrind is a very good tool, but only a tool. Don't
5179make it into some kind of religion.
5180.PP
5181If you are unsure about something, feel free to contact the mailing list
5182with the full valgrind report and an explanation on why you think this
5183is a bug in libev (best check the archives, too :). However, don't be
5184annoyed when you get a brisk \*(L"this is no bug\*(R" answer and take the chance
5185of learning how to interpret valgrind properly.
5186.PP
5187If you need, for some reason, empty reports from valgrind for your project
5188I suggest using suppression lists.
5189.SH "PORTABILITY NOTES"
5190.IX Header "PORTABILITY NOTES"
5191.SS "\s-1GNU/LINUX\s0 32 \s-1BIT\s0 \s-1LIMITATIONS\s0"
5192.IX Subsection "GNU/LINUX 32 BIT LIMITATIONS"
5193GNU/Linux is the only common platform that supports 64 bit file/large file
5194interfaces but \fIdisables\fR them by default.
5195.PP
5196That means that libev compiled in the default environment doesn't support
5197files larger than 2GiB or so, which mainly affects \f(CW\*(C`ev_stat\*(C'\fR watchers.
5198.PP
5199Unfortunately, many programs try to work around this GNU/Linux issue
5200by enabling the large file \s-1API\s0, which makes them incompatible with the
5201standard libev compiled for their system.
5202.PP
5203Likewise, libev cannot enable the large file \s-1API\s0 itself as this would
5204suddenly make it incompatible to the default compile time environment,
5205i.e. all programs not using special compile switches.
5206.SS "\s-1OS/X\s0 \s-1AND\s0 \s-1DARWIN\s0 \s-1BUGS\s0"
5207.IX Subsection "OS/X AND DARWIN BUGS"
5208The whole thing is a bug if you ask me \- basically any system interface
5209you touch is broken, whether it is locales, poll, kqueue or even the
5210OpenGL drivers.
5211.PP
5212\fI\f(CI\*(C`kqueue\*(C'\fI is buggy\fR
5213.IX Subsection "kqueue is buggy"
5214.PP
5215The kqueue syscall is broken in all known versions \- most versions support
5216only sockets, many support pipes.
5217.PP
5218Libev tries to work around this by not using \f(CW\*(C`kqueue\*(C'\fR by default on this
5219rotten platform, but of course you can still ask for it when creating a
5220loop \- embedding a socket-only kqueue loop into a select-based one is
5221probably going to work well.
5222.PP
5223\fI\f(CI\*(C`poll\*(C'\fI is buggy\fR
5224.IX Subsection "poll is buggy"
5225.PP
5226Instead of fixing \f(CW\*(C`kqueue\*(C'\fR, Apple replaced their (working) \f(CW\*(C`poll\*(C'\fR
5227implementation by something calling \f(CW\*(C`kqueue\*(C'\fR internally around the 10.5.6
5228release, so now \f(CW\*(C`kqueue\*(C'\fR \fIand\fR \f(CW\*(C`poll\*(C'\fR are broken.
5229.PP
5230Libev tries to work around this by not using \f(CW\*(C`poll\*(C'\fR by default on
5231this rotten platform, but of course you can still ask for it when creating
5232a loop.
5233.PP
5234\fI\f(CI\*(C`select\*(C'\fI is buggy\fR
5235.IX Subsection "select is buggy"
5236.PP
5237All that's left is \f(CW\*(C`select\*(C'\fR, and of course Apple found a way to fuck this
5238one up as well: On \s-1OS/X\s0, \f(CW\*(C`select\*(C'\fR actively limits the number of file
5239descriptors you can pass in to 1024 \- your program suddenly crashes when
5240you use more.
5241.PP
5242There is an undocumented \*(L"workaround\*(R" for this \- defining
5243\&\f(CW\*(C`_DARWIN_UNLIMITED_SELECT\*(C'\fR, which libev tries to use, so select \fIshould\fR
5244work on \s-1OS/X\s0.
5245.SS "\s-1SOLARIS\s0 \s-1PROBLEMS\s0 \s-1AND\s0 \s-1WORKAROUNDS\s0"
5246.IX Subsection "SOLARIS PROBLEMS AND WORKAROUNDS"
5247\fI\f(CI\*(C`errno\*(C'\fI reentrancy\fR
5248.IX Subsection "errno reentrancy"
5249.PP
5250The default compile environment on Solaris is unfortunately so
5251thread-unsafe that you can't even use components/libraries compiled
5252without \f(CW\*(C`\-D_REENTRANT\*(C'\fR in a threaded program, which, of course, isn't
5253defined by default. A valid, if stupid, implementation choice.
5254.PP
5255If you want to use libev in threaded environments you have to make sure
5256it's compiled with \f(CW\*(C`_REENTRANT\*(C'\fR defined.
5257.PP
5258\fIEvent port backend\fR
5259.IX Subsection "Event port backend"
5260.PP
5261The scalable event interface for Solaris is called \*(L"event
5262ports\*(R". Unfortunately, this mechanism is very buggy in all major
5263releases. If you run into high \s-1CPU\s0 usage, your program freezes or you get
5264a large number of spurious wakeups, make sure you have all the relevant
5265and latest kernel patches applied. No, I don't know which ones, but there
5266are multiple ones to apply, and afterwards, event ports actually work
5267great.
5268.PP
5269If you can't get it to work, you can try running the program by setting
5270the environment variable \f(CW\*(C`LIBEV_FLAGS=3\*(C'\fR to only allow \f(CW\*(C`poll\*(C'\fR and
5271\&\f(CW\*(C`select\*(C'\fR backends.
5272.SS "\s-1AIX\s0 \s-1POLL\s0 \s-1BUG\s0"
5273.IX Subsection "AIX POLL BUG"
5274\&\s-1AIX\s0 unfortunately has a broken \f(CW\*(C`poll.h\*(C'\fR header. Libev works around
5275this by trying to avoid the poll backend altogether (i.e. it's not even
5276compiled in), which normally isn't a big problem as \f(CW\*(C`select\*(C'\fR works fine
5277with large bitsets on \s-1AIX\s0, and \s-1AIX\s0 is dead anyway.
5278.SS "\s-1WIN32\s0 \s-1PLATFORM\s0 \s-1LIMITATIONS\s0 \s-1AND\s0 \s-1WORKAROUNDS\s0"
5279.IX Subsection "WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS"
5280\fIGeneral issues\fR
5281.IX Subsection "General issues"
5282.PP
5283Win32 doesn't support any of the standards (e.g. \s-1POSIX\s0) that libev
5284requires, and its I/O model is fundamentally incompatible with the \s-1POSIX\s0
5285model. Libev still offers limited functionality on this platform in
5286the form of the \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR backend, and only supports socket
5287descriptors. This only applies when using Win32 natively, not when using
5288e.g. cygwin. Actually, it only applies to the microsofts own compilers,
5289as every compiler comes with a slightly differently broken/incompatible
5290environment.
5291.PP
5292Lifting these limitations would basically require the full
5293re-implementation of the I/O system. If you are into this kind of thing,
5294then note that glib does exactly that for you in a very portable way (note
5295also that glib is the slowest event library known to man).
5296.PP
5297There is no supported compilation method available on windows except
5298embedding it into other applications.
5299.PP
5300Sensible signal handling is officially unsupported by Microsoft \- libev
5301tries its best, but under most conditions, signals will simply not work.
5302.PP
5303Not a libev limitation but worth mentioning: windows apparently doesn't
5304accept large writes: instead of resulting in a partial write, windows will
5305either accept everything or return \f(CW\*(C`ENOBUFS\*(C'\fR if the buffer is too large,
5306so make sure you only write small amounts into your sockets (less than a
5307megabyte seems safe, but this apparently depends on the amount of memory
5308available).
5309.PP
5310Due to the many, low, and arbitrary limits on the win32 platform and
5311the abysmal performance of winsockets, using a large number of sockets
5312is not recommended (and not reasonable). If your program needs to use
5313more than a hundred or so sockets, then likely it needs to use a totally
5314different implementation for windows, as libev offers the \s-1POSIX\s0 readiness
5315notification model, which cannot be implemented efficiently on windows
5316(due to Microsoft monopoly games).
5317.PP
5318A typical way to use libev under windows is to embed it (see the embedding
5319section for details) and use the following \fIevwrap.h\fR header file instead
5320of \fIev.h\fR:
5321.PP
5322.Vb 2
5323\& #define EV_STANDALONE /* keeps ev from requiring config.h */
5324\& #define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
5325\&
5326\& #include "ev.h"
5327.Ve
5328.PP
5329And compile the following \fIevwrap.c\fR file into your project (make sure
5330you do \fInot\fR compile the \fIev.c\fR or any other embedded source files!):
5331.PP
5332.Vb 2
5333\& #include "evwrap.h"
5334\& #include "ev.c"
5335.Ve
5336.PP
5337\fIThe winsocket \f(CI\*(C`select\*(C'\fI function\fR
5338.IX Subsection "The winsocket select function"
5339.PP
5340The winsocket \f(CW\*(C`select\*(C'\fR function doesn't follow \s-1POSIX\s0 in that it
5341requires socket \fIhandles\fR and not socket \fIfile descriptors\fR (it is
5342also extremely buggy). This makes select very inefficient, and also
5343requires a mapping from file descriptors to socket handles (the Microsoft
5344C runtime provides the function \f(CW\*(C`_open_osfhandle\*(C'\fR for this). See the
5345discussion of the \f(CW\*(C`EV_SELECT_USE_FD_SET\*(C'\fR, \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR and
5346\&\f(CW\*(C`EV_FD_TO_WIN32_HANDLE\*(C'\fR preprocessor symbols for more info.
5347.PP
5348The configuration for a \*(L"naked\*(R" win32 using the Microsoft runtime
5349libraries and raw winsocket select is:
5350.PP
5351.Vb 2
5352\& #define EV_USE_SELECT 1
5353\& #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
5354.Ve
5355.PP
5356Note that winsockets handling of fd sets is O(n), so you can easily get a
5357complexity in the O(nA\*^X) range when using win32.
5358.PP
5359\fILimited number of file descriptors\fR
5360.IX Subsection "Limited number of file descriptors"
5361.PP
5362Windows has numerous arbitrary (and low) limits on things.
5363.PP
5364Early versions of winsocket's select only supported waiting for a maximum
5365of \f(CW64\fR handles (probably owning to the fact that all windows kernels
5366can only wait for \f(CW64\fR things at the same time internally; Microsoft
5367recommends spawning a chain of threads and wait for 63 handles and the
5368previous thread in each. Sounds great!).
5369.PP
5370Newer versions support more handles, but you need to define \f(CW\*(C`FD_SETSIZE\*(C'\fR
5371to some high number (e.g. \f(CW2048\fR) before compiling the winsocket select
5372call (which might be in libev or elsewhere, for example, perl and many
5373other interpreters do their own select emulation on windows).
5374.PP
5375Another limit is the number of file descriptors in the Microsoft runtime
5376libraries, which by default is \f(CW64\fR (there must be a hidden \fI64\fR
5377fetish or something like this inside Microsoft). You can increase this
5378by calling \f(CW\*(C`_setmaxstdio\*(C'\fR, which can increase this limit to \f(CW2048\fR
5379(another arbitrary limit), but is broken in many versions of the Microsoft
5380runtime libraries. This might get you to about \f(CW512\fR or \f(CW2048\fR sockets
5381(depending on windows version and/or the phase of the moon). To get more,
5382you need to wrap all I/O functions and provide your own fd management, but
5383the cost of calling select (O(nA\*^X)) will likely make this unworkable.
5384.SS "\s-1PORTABILITY\s0 \s-1REQUIREMENTS\s0"
5385.IX Subsection "PORTABILITY REQUIREMENTS"
5386In addition to a working ISO-C implementation and of course the
5387backend-specific APIs, libev relies on a few additional extensions:
5388.ie n .IP """void (*)(ev_watcher_type *, int revents)"" must have compatible calling conventions regardless of ""ev_watcher_type *""." 4
5389.el .IP "\f(CWvoid (*)(ev_watcher_type *, int revents)\fR must have compatible calling conventions regardless of \f(CWev_watcher_type *\fR." 4
5390.IX Item "void (*)(ev_watcher_type *, int revents) must have compatible calling conventions regardless of ev_watcher_type *."
5391Libev assumes not only that all watcher pointers have the same internal
5392structure (guaranteed by \s-1POSIX\s0 but not by \s-1ISO\s0 C for example), but it also
5393assumes that the same (machine) code can be used to call any watcher
5394callback: The watcher callbacks have different type signatures, but libev
5395calls them using an \f(CW\*(C`ev_watcher *\*(C'\fR internally.
5396.IP "pointer accesses must be thread-atomic" 4
5397.IX Item "pointer accesses must be thread-atomic"
5398Accessing a pointer value must be atomic, it must both be readable and
5399writable in one piece \- this is the case on all current architectures.
5400.ie n .IP """sig_atomic_t volatile"" must be thread-atomic as well" 4
5401.el .IP "\f(CWsig_atomic_t volatile\fR must be thread-atomic as well" 4
5402.IX Item "sig_atomic_t volatile must be thread-atomic as well"
5403The type \f(CW\*(C`sig_atomic_t volatile\*(C'\fR (or whatever is defined as
5404\&\f(CW\*(C`EV_ATOMIC_T\*(C'\fR) must be atomic with respect to accesses from different
5405threads. This is not part of the specification for \f(CW\*(C`sig_atomic_t\*(C'\fR, but is
5406believed to be sufficiently portable.
5407.ie n .IP """sigprocmask"" must work in a threaded environment" 4
5408.el .IP "\f(CWsigprocmask\fR must work in a threaded environment" 4
5409.IX Item "sigprocmask must work in a threaded environment"
5410Libev uses \f(CW\*(C`sigprocmask\*(C'\fR to temporarily block signals. This is not
5411allowed in a threaded program (\f(CW\*(C`pthread_sigmask\*(C'\fR has to be used). Typical
5412pthread implementations will either allow \f(CW\*(C`sigprocmask\*(C'\fR in the \*(L"main
5413thread\*(R" or will block signals process-wide, both behaviours would
5414be compatible with libev. Interaction between \f(CW\*(C`sigprocmask\*(C'\fR and
5415\&\f(CW\*(C`pthread_sigmask\*(C'\fR could complicate things, however.
5416.Sp
5417The most portable way to handle signals is to block signals in all threads
5418except the initial one, and run the default loop in the initial thread as
5419well.
5420.ie n .IP """long"" must be large enough for common memory allocation sizes" 4
5421.el .IP "\f(CWlong\fR must be large enough for common memory allocation sizes" 4
5422.IX Item "long must be large enough for common memory allocation sizes"
5423To improve portability and simplify its \s-1API\s0, libev uses \f(CW\*(C`long\*(C'\fR internally
5424instead of \f(CW\*(C`size_t\*(C'\fR when allocating its data structures. On non-POSIX
5425systems (Microsoft...) this might be unexpectedly low, but is still at
5426least 31 bits everywhere, which is enough for hundreds of millions of
5427watchers.
5428.ie n .IP """double"" must hold a time value in seconds with enough accuracy" 4
5429.el .IP "\f(CWdouble\fR must hold a time value in seconds with enough accuracy" 4
5430.IX Item "double must hold a time value in seconds with enough accuracy"
5431The type \f(CW\*(C`double\*(C'\fR is used to represent timestamps. It is required to
5432have at least 51 bits of mantissa (and 9 bits of exponent), which is
5433good enough for at least into the year 4000 with millisecond accuracy
5434(the design goal for libev). This requirement is overfulfilled by
5435implementations using \s-1IEEE\s0 754, which is basically all existing ones.
5436.Sp
5437With \s-1IEEE\s0 754 doubles, you get microsecond accuracy until at least the
5438year 2255 (and millisecond accuracy till the year 287396 \- by then, libev
5439is either obsolete or somebody patched it to use \f(CW\*(C`long double\*(C'\fR or
5440something like that, just kidding).
5441.PP
5442If you know of other additional requirements drop me a note.
5443.SH "ALGORITHMIC COMPLEXITIES"
5444.IX Header "ALGORITHMIC COMPLEXITIES"
5445In this section the complexities of (many of) the algorithms used inside
5446libev will be documented. For complexity discussions about backends see
5447the documentation for \f(CW\*(C`ev_default_init\*(C'\fR.
5448.PP
5449All of the following are about amortised time: If an array needs to be
5450extended, libev needs to realloc and move the whole array, but this
5451happens asymptotically rarer with higher number of elements, so O(1) might
5452mean that libev does a lengthy realloc operation in rare cases, but on
5453average it is much faster and asymptotically approaches constant time.
5454.IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4
5455.IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)"
5456This means that, when you have a watcher that triggers in one hour and
5457there are 100 watchers that would trigger before that, then inserting will
5458have to skip roughly seven (\f(CW\*(C`ld 100\*(C'\fR) of these watchers.
5459.IP "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 4
5460.IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)"
5461That means that changing a timer costs less than removing/adding them,
5462as only the relative motion in the event queue has to be paid for.
5463.IP "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)" 4
5464.IX Item "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)"
5465These just add the watcher into an array or at the head of a list.
5466.IP "Stopping check/prepare/idle/fork/async watchers: O(1)" 4
5467.IX Item "Stopping check/prepare/idle/fork/async watchers: O(1)"
5468.PD 0
5469.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4
5470.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))"
5471.PD
5472These watchers are stored in lists, so they need to be walked to find the
5473correct watcher to remove. The lists are usually short (you don't usually
5474have many watchers waiting for the same fd or signal: one is typical, two
5475is rare).
5476.IP "Finding the next timer in each loop iteration: O(1)" 4
5477.IX Item "Finding the next timer in each loop iteration: O(1)"
5478By virtue of using a binary or 4\-heap, the next timer is always found at a
5479fixed position in the storage array.
5480.IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4
5481.IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)"
5482A change means an I/O watcher gets started or stopped, which requires
5483libev to recalculate its status (and possibly tell the kernel, depending
5484on backend and whether \f(CW\*(C`ev_io_set\*(C'\fR was used).
5485.IP "Activating one watcher (putting it into the pending state): O(1)" 4
5486.IX Item "Activating one watcher (putting it into the pending state): O(1)"
5487.PD 0
5488.IP "Priority handling: O(number_of_priorities)" 4
5489.IX Item "Priority handling: O(number_of_priorities)"
5490.PD
5491Priorities are implemented by allocating some space for each
5492priority. When doing priority-based operations, libev usually has to
5493linearly search all the priorities, but starting/stopping and activating
5494watchers becomes O(1) with respect to priority handling.
5495.IP "Sending an ev_async: O(1)" 4
5496.IX Item "Sending an ev_async: O(1)"
5497.PD 0
5498.IP "Processing ev_async_send: O(number_of_async_watchers)" 4
5499.IX Item "Processing ev_async_send: O(number_of_async_watchers)"
5500.IP "Processing signals: O(max_signal_number)" 4
5501.IX Item "Processing signals: O(max_signal_number)"
5502.PD
5503Sending involves a system call \fIiff\fR there were no other \f(CW\*(C`ev_async_send\*(C'\fR
5504calls in the current loop iteration and the loop is currently
5505blocked. Checking for async and signal events involves iterating over all
5506running async watchers or all signal numbers.
5507.SH "PORTING FROM LIBEV 3.X TO 4.X"
5508.IX Header "PORTING FROM LIBEV 3.X TO 4.X"
5509The major version 4 introduced some incompatible changes to the \s-1API\s0.
5510.PP
5511At the moment, the \f(CW\*(C`ev.h\*(C'\fR header file provides compatibility definitions
5512for all changes, so most programs should still compile. The compatibility
5513layer might be removed in later versions of libev, so better update to the
5514new \s-1API\s0 early than late.
5515.ie n .IP """EV_COMPAT3"" backwards compatibility mechanism" 4
5516.el .IP "\f(CWEV_COMPAT3\fR backwards compatibility mechanism" 4
5517.IX Item "EV_COMPAT3 backwards compatibility mechanism"
5518The backward compatibility mechanism can be controlled by
5519\&\f(CW\*(C`EV_COMPAT3\*(C'\fR. See \*(L"\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0\*(R" in the \*(L"\s-1EMBEDDING\s0\*(R"
5520section.
5521.ie n .IP """ev_default_destroy"" and ""ev_default_fork"" have been removed" 4
5522.el .IP "\f(CWev_default_destroy\fR and \f(CWev_default_fork\fR have been removed" 4
5523.IX Item "ev_default_destroy and ev_default_fork have been removed"
5524These calls can be replaced easily by their \f(CW\*(C`ev_loop_xxx\*(C'\fR counterparts:
5525.Sp
5526.Vb 2
5527\& ev_loop_destroy (EV_DEFAULT_UC);
5528\& ev_loop_fork (EV_DEFAULT);
5529.Ve
5530.IP "function/symbol renames" 4
5531.IX Item "function/symbol renames"
5532A number of functions and symbols have been renamed:
5533.Sp
5534.Vb 3
5535\& ev_loop => ev_run
5536\& EVLOOP_NONBLOCK => EVRUN_NOWAIT
5537\& EVLOOP_ONESHOT => EVRUN_ONCE
5538\&
5539\& ev_unloop => ev_break
5540\& EVUNLOOP_CANCEL => EVBREAK_CANCEL
5541\& EVUNLOOP_ONE => EVBREAK_ONE
5542\& EVUNLOOP_ALL => EVBREAK_ALL
5543\&
5544\& EV_TIMEOUT => EV_TIMER
5545\&
5546\& ev_loop_count => ev_iteration
5547\& ev_loop_depth => ev_depth
5548\& ev_loop_verify => ev_verify
5549.Ve
5550.Sp
5551Most functions working on \f(CW\*(C`struct ev_loop\*(C'\fR objects don't have an
5552\&\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
5553associated constants have been renamed to not collide with the \f(CW\*(C`struct
5554ev_loop\*(C'\fR anymore and \f(CW\*(C`EV_TIMER\*(C'\fR now follows the same naming scheme
5555as all other watcher types. Note that \f(CW\*(C`ev_loop_fork\*(C'\fR is still called
5556\&\f(CW\*(C`ev_loop_fork\*(C'\fR because it would otherwise clash with the \f(CW\*(C`ev_fork\*(C'\fR
5557typedef.
5558.ie n .IP """EV_MINIMAL"" mechanism replaced by ""EV_FEATURES""" 4
5559.el .IP "\f(CWEV_MINIMAL\fR mechanism replaced by \f(CWEV_FEATURES\fR" 4
5560.IX Item "EV_MINIMAL mechanism replaced by EV_FEATURES"
5561The preprocessor symbol \f(CW\*(C`EV_MINIMAL\*(C'\fR has been replaced by a different
5562mechanism, \f(CW\*(C`EV_FEATURES\*(C'\fR. Programs using \f(CW\*(C`EV_MINIMAL\*(C'\fR usually compile
5563and work, but the library code will of course be larger.
5564.SH "GLOSSARY"
5565.IX Header "GLOSSARY"
5566.IP "active" 4
5567.IX Item "active"
5568A watcher is active as long as it has been started and not yet stopped.
5569See \*(L"\s-1WATCHER\s0 \s-1STATES\s0\*(R" for details.
5570.IP "application" 4
5571.IX Item "application"
5572In this document, an application is whatever is using libev.
5573.IP "backend" 4
5574.IX Item "backend"
5575The part of the code dealing with the operating system interfaces.
5576.IP "callback" 4
5577.IX Item "callback"
5578The address of a function that is called when some event has been
5579detected. Callbacks are being passed the event loop, the watcher that
5580received the event, and the actual event bitset.
5581.IP "callback/watcher invocation" 4
5582.IX Item "callback/watcher invocation"
5583The act of calling the callback associated with a watcher.
5584.IP "event" 4
5585.IX Item "event"
5586A change of state of some external event, such as data now being available
5587for reading on a file descriptor, time having passed or simply not having
5588any other events happening anymore.
5589.Sp
5590In libev, events are represented as single bits (such as \f(CW\*(C`EV_READ\*(C'\fR or
5591\&\f(CW\*(C`EV_TIMER\*(C'\fR).
5592.IP "event library" 4
5593.IX Item "event library"
5594A software package implementing an event model and loop.
5595.IP "event loop" 4
5596.IX Item "event loop"
5597An entity that handles and processes external events and converts them
5598into callback invocations.
5599.IP "event model" 4
5600.IX Item "event model"
5601The model used to describe how an event loop handles and processes
5602watchers and events.
5603.IP "pending" 4
5604.IX Item "pending"
5605A watcher is pending as soon as the corresponding event has been
5606detected. See \*(L"\s-1WATCHER\s0 \s-1STATES\s0\*(R" for details.
5607.IP "real time" 4
5608.IX Item "real time"
5609The physical time that is observed. It is apparently strictly monotonic :)
5610.IP "wall-clock time" 4
5611.IX Item "wall-clock time"
5612The time and date as shown on clocks. Unlike real time, it can actually
5613be wrong and jump forwards and backwards, e.g. when you adjust your
5614clock.
5615.IP "watcher" 4
5616.IX Item "watcher"
5617A data structure that describes interest in certain events. Watchers need
5618to be started (attached to an event loop) before they can receive events.
958.SH "AUTHOR" 5619.SH "AUTHOR"
959.IX Header "AUTHOR" 5620.IX Header "AUTHOR"
960Marc Lehmann <libev@schmorp.de>. 5621Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5622Magnusson and Emanuele Giaquinta, and minor corrections by many others.

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