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1.\" Automatically generated by Pod::Man v1.37, Pod::Parser v1.35 1.\" Automatically generated by Pod::Man 2.22 (Pod::Simple 3.07)
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129.\" ======================================================================== 124.\" ========================================================================
130.\" 125.\"
131.IX Title ""<STANDARD INPUT>" 1" 126.IX Title "LIBEV 3"
132.TH "<STANDARD INPUT>" 1 "2007-11-23" "perl v5.8.8" "User Contributed Perl Documentation" 127.TH LIBEV 3 "2009-12-31" "libev-3.9" "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_loop\*(Aqs to stop iterating
163\& ev_unloop (EV_A_ EVUNLOOP_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_loop to stop iterating
172\& ev_unloop (EV_A_ EVUNLOOP_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_loop (0);
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_loop (loop, 0);
193\&
194\& // unloop 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
211Familarity with event based programming techniques in general is assumed
212throughout this document.
213.SH "ABOUT LIBEV"
214.IX Header "ABOUT LIBEV"
142Libev is an event loop: you register interest in certain events (such as a 215Libev 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 216file descriptor being readable or a timeout occurring), and it will manage
144these event sources and provide your program with events. 217these event sources and provide your program with events.
145.PP 218.PP
146To do this, it must take more or less complete control over your process 219To 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 220(or thread) by executing the \fIevent loop\fR handler, and will then
148communicate events via a callback mechanism. 221communicate events via a callback mechanism.
149.PP 222.PP
150You register interest in certain events by registering so-called \fIevent 223You register interest in certain events by registering so-called \fIevent
151watchers\fR, which are relatively small C structures you initialise with the 224watchers\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 225details of the event, and then hand it over to libev by \fIstarting\fR the
153watcher. 226watcher.
154.SH "FEATURES" 227.SS "\s-1FEATURES\s0"
155.IX Header "FEATURES" 228.IX Subsection "FEATURES"
156Libev supports select, poll, the linux-specific epoll and the bsd-specific 229Libev 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 230BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port mechanisms
158timers with customised rescheduling, signal events, process status change 231for 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 232(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 233inter-thread wakeup (\f(CW\*(C`ev_async\*(C'\fR)/signal handling (\f(CW\*(C`ev_signal\*(C'\fR)) relative
161fast (see this benchmark comparing 234timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers with customised rescheduling
162it to libevent for example). 235(\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals (\f(CW\*(C`ev_signal\*(C'\fR), process status
236change events (\f(CW\*(C`ev_child\*(C'\fR), and event watchers dealing with the event
237loop mechanism itself (\f(CW\*(C`ev_idle\*(C'\fR, \f(CW\*(C`ev_embed\*(C'\fR, \f(CW\*(C`ev_prepare\*(C'\fR and
238\&\f(CW\*(C`ev_check\*(C'\fR watchers) as well as file watchers (\f(CW\*(C`ev_stat\*(C'\fR) and even
239limited support for fork events (\f(CW\*(C`ev_fork\*(C'\fR).
240.PP
241It also is quite fast (see this
242<benchmark> comparing it to libevent
243for example).
163.SH "CONVENTIONS" 244.SS "\s-1CONVENTIONS\s0"
164.IX Header "CONVENTIONS" 245.IX Subsection "CONVENTIONS"
165Libev is very configurable. In this manual the default configuration 246Libev is very configurable. In this manual the default (and most common)
166will be described, which supports multiple event loops. For more info 247configuration will be described, which supports multiple event loops. For
167about various configuration options please have a look at the file 248more 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 249\&\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 250for 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) 251name \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. 252this argument.
172.SH "TIME REPRESENTATION" 253.SS "\s-1TIME\s0 \s-1REPRESENTATION\s0"
173.IX Header "TIME REPRESENTATION" 254.IX Subsection "TIME REPRESENTATION"
174Libev represents time as a single floating point number, representing the 255Libev represents time as a single floating point number, representing
175(fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere near 256the (fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere
176the beginning of 1970, details are complicated, don't ask). This type is 257near the beginning of 1970, details are complicated, don't ask). This
177called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use too. It usually aliases 258type is called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use too. It usually
178to the double type in C. 259aliases to the \f(CW\*(C`double\*(C'\fR type in C. When you need to do any calculations
260on it, you should treat it as some floating point value. Unlike the name
261component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for time differences
262throughout libev.
263.SH "ERROR HANDLING"
264.IX Header "ERROR HANDLING"
265Libev knows three classes of errors: operating system errors, usage errors
266and internal errors (bugs).
267.PP
268When libev catches an operating system error it cannot handle (for example
269a system call indicating a condition libev cannot fix), it calls the callback
270set via \f(CW\*(C`ev_set_syserr_cb\*(C'\fR, which is supposed to fix the problem or
271abort. The default is to print a diagnostic message and to call \f(CW\*(C`abort
272()\*(C'\fR.
273.PP
274When libev detects a usage error such as a negative timer interval, then
275it will print a diagnostic message and abort (via the \f(CW\*(C`assert\*(C'\fR mechanism,
276so \f(CW\*(C`NDEBUG\*(C'\fR will disable this checking): these are programming errors in
277the libev caller and need to be fixed there.
278.PP
279Libev also has a few internal error-checking \f(CW\*(C`assert\*(C'\fRions, and also has
280extensive consistency checking code. These do not trigger under normal
281circumstances, as they indicate either a bug in libev or worse.
179.SH "GLOBAL FUNCTIONS" 282.SH "GLOBAL FUNCTIONS"
180.IX Header "GLOBAL FUNCTIONS" 283.IX Header "GLOBAL FUNCTIONS"
181These functions can be called anytime, even before initialising the 284These functions can be called anytime, even before initialising the
182library in any way. 285library in any way.
183.IP "ev_tstamp ev_time ()" 4 286.IP "ev_tstamp ev_time ()" 4
184.IX Item "ev_tstamp ev_time ()" 287.IX Item "ev_tstamp ev_time ()"
185Returns the current time as libev would use it. Please note that the 288Returns 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 289\&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp
187you actually want to know. 290you actually want to know.
291.IP "ev_sleep (ev_tstamp interval)" 4
292.IX Item "ev_sleep (ev_tstamp interval)"
293Sleep for the given interval: The current thread will be blocked until
294either it is interrupted or the given time interval has passed. Basically
295this is a sub-second-resolution \f(CW\*(C`sleep ()\*(C'\fR.
188.IP "int ev_version_major ()" 4 296.IP "int ev_version_major ()" 4
189.IX Item "int ev_version_major ()" 297.IX Item "int ev_version_major ()"
190.PD 0 298.PD 0
191.IP "int ev_version_minor ()" 4 299.IP "int ev_version_minor ()" 4
192.IX Item "int ev_version_minor ()" 300.IX Item "int ev_version_minor ()"
193.PD 301.PD
194You can find out the major and minor version numbers of the library 302You 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 303you 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 304\&\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 305symbols \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. 306version of the library your program was compiled against.
199.Sp 307.Sp
308These version numbers refer to the \s-1ABI\s0 version of the library, not the
309release version.
310.Sp
200Usually, it's a good idea to terminate if the major versions mismatch, 311Usually, it's a good idea to terminate if the major versions mismatch,
201as this indicates an incompatible change. Minor versions are usually 312as this indicates an incompatible change. Minor versions are usually
202compatible to older versions, so a larger minor version alone is usually 313compatible to older versions, so a larger minor version alone is usually
203not a problem. 314not a problem.
315.Sp
316Example: Make sure we haven't accidentally been linked against the wrong
317version.
318.Sp
319.Vb 3
320\& assert (("libev version mismatch",
321\& ev_version_major () == EV_VERSION_MAJOR
322\& && ev_version_minor () >= EV_VERSION_MINOR));
323.Ve
204.IP "unsigned int ev_supported_backends ()" 4 324.IP "unsigned int ev_supported_backends ()" 4
205.IX Item "unsigned int ev_supported_backends ()" 325.IX Item "unsigned int ev_supported_backends ()"
206Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR 326Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR
207value) compiled into this binary of libev (independent of their 327value) compiled into this binary of libev (independent of their
208availability on the system you are running on). See \f(CW\*(C`ev_default_loop\*(C'\fR for 328availability on the system you are running on). See \f(CW\*(C`ev_default_loop\*(C'\fR for
209a description of the set values. 329a description of the set values.
330.Sp
331Example: make sure we have the epoll method, because yeah this is cool and
332a must have and can we have a torrent of it please!!!11
333.Sp
334.Vb 2
335\& assert (("sorry, no epoll, no sex",
336\& ev_supported_backends () & EVBACKEND_EPOLL));
337.Ve
210.IP "unsigned int ev_recommended_backends ()" 4 338.IP "unsigned int ev_recommended_backends ()" 4
211.IX Item "unsigned int ev_recommended_backends ()" 339.IX Item "unsigned int ev_recommended_backends ()"
212Return the set of all backends compiled into this binary of libev and also 340Return the set of all backends compiled into this binary of libev and also
213recommended for this platform. This set is often smaller than the one 341recommended for this platform. This set is often smaller than the one
214returned by \f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on 342returned by \f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on
215most BSDs and will not be autodetected unless you explicitly request it 343most BSDs and will not be auto-detected unless you explicitly request it
216(assuming you know what you are doing). This is the set of backends that 344(assuming you know what you are doing). This is the set of backends that
217\&\f(CW\*(C`EVFLAG_AUTO\*(C'\fR will probe for. 345libev will probe for if you specify no backends explicitly.
346.IP "unsigned int ev_embeddable_backends ()" 4
347.IX Item "unsigned int ev_embeddable_backends ()"
348Returns the set of backends that are embeddable in other event loops. This
349is the theoretical, all-platform, value. To find which backends
350might be supported on the current system, you would need to look at
351\&\f(CW\*(C`ev_embeddable_backends () & ev_supported_backends ()\*(C'\fR, likewise for
352recommended ones.
353.Sp
354See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
218.IP "ev_set_allocator (void *(*cb)(void *ptr, long size))" 4 355.IP "ev_set_allocator (void *(*cb)(void *ptr, long size)) [\s-1NOT\s0 \s-1REENTRANT\s0]" 4
219.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))" 356.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]"
220Sets the allocation function to use (the prototype is similar to the 357Sets the allocation function to use (the prototype is similar \- the
221realloc C function, the semantics are identical). It is used to allocate 358semantics are identical to the \f(CW\*(C`realloc\*(C'\fR C89/SuS/POSIX function). It is
222and free memory (no surprises here). If it returns zero when memory 359used to allocate and free memory (no surprises here). If it returns zero
223needs to be allocated, the library might abort or take some potentially 360when memory needs to be allocated (\f(CW\*(C`size != 0\*(C'\fR), the library might abort
224destructive action. The default is your system realloc function. 361or take some potentially destructive action.
362.Sp
363Since some systems (at least OpenBSD and Darwin) fail to implement
364correct \f(CW\*(C`realloc\*(C'\fR semantics, libev will use a wrapper around the system
365\&\f(CW\*(C`realloc\*(C'\fR and \f(CW\*(C`free\*(C'\fR functions by default.
225.Sp 366.Sp
226You could override this function in high-availability programs to, say, 367You could override this function in high-availability programs to, say,
227free some memory if it cannot allocate memory, to use a special allocator, 368free some memory if it cannot allocate memory, to use a special allocator,
228or even to sleep a while and retry until some memory is available. 369or even to sleep a while and retry until some memory is available.
370.Sp
371Example: Replace the libev allocator with one that waits a bit and then
372retries (example requires a standards-compliant \f(CW\*(C`realloc\*(C'\fR).
373.Sp
374.Vb 6
375\& static void *
376\& persistent_realloc (void *ptr, size_t size)
377\& {
378\& for (;;)
379\& {
380\& void *newptr = realloc (ptr, size);
381\&
382\& if (newptr)
383\& return newptr;
384\&
385\& sleep (60);
386\& }
387\& }
388\&
389\& ...
390\& ev_set_allocator (persistent_realloc);
391.Ve
229.IP "ev_set_syserr_cb (void (*cb)(const char *msg));" 4 392.IP "ev_set_syserr_cb (void (*cb)(const char *msg)); [\s-1NOT\s0 \s-1REENTRANT\s0]" 4
230.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg));" 393.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]"
231Set the callback function to call on a retryable syscall error (such 394Set the callback function to call on a retryable system call error (such
232as failed select, poll, epoll_wait). The message is a printable string 395as failed select, poll, epoll_wait). The message is a printable string
233indicating the system call or subsystem causing the problem. If this 396indicating the system call or subsystem causing the problem. If this
234callback is set, then libev will expect it to remedy the sitution, no 397callback is set, then libev will expect it to remedy the situation, no
235matter what, when it returns. That is, libev will generally retry the 398matter what, when it returns. That is, libev will generally retry the
236requested operation, or, if the condition doesn't go away, do bad stuff 399requested operation, or, if the condition doesn't go away, do bad stuff
237(such as abort). 400(such as abort).
401.Sp
402Example: This is basically the same thing that libev does internally, too.
403.Sp
404.Vb 6
405\& static void
406\& fatal_error (const char *msg)
407\& {
408\& perror (msg);
409\& abort ();
410\& }
411\&
412\& ...
413\& ev_set_syserr_cb (fatal_error);
414.Ve
238.SH "FUNCTIONS CONTROLLING THE EVENT LOOP" 415.SH "FUNCTIONS CONTROLLING THE EVENT LOOP"
239.IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP" 416.IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP"
240An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR. The library knows two 417An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR (the \f(CW\*(C`struct\*(C'\fR
241types of such loops, the \fIdefault\fR loop, which supports signals and child 418is \fInot\fR optional in this case, as there is also an \f(CW\*(C`ev_loop\*(C'\fR
242events, and dynamically created loops which do not. 419\&\fIfunction\fR).
243.PP 420.PP
244If you use threads, a common model is to run the default event loop 421The library knows two types of such loops, the \fIdefault\fR loop, which
245in your main thread (or in a separate thread) and for each thread you 422supports signals and child events, and dynamically created loops which do
246create, you also create another event loop. Libev itself does no locking 423not.
247whatsoever, so if you mix calls to the same event loop in different
248threads, make sure you lock (this is usually a bad idea, though, even if
249done correctly, because it's hideous and inefficient).
250.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4 424.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
251.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)" 425.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
252This will initialise the default event loop if it hasn't been initialised 426This will initialise the default event loop if it hasn't been initialised
253yet and return it. If the default loop could not be initialised, returns 427yet and return it. If the default loop could not be initialised, returns
254false. If it already was initialised it simply returns it (and ignores the 428false. If it already was initialised it simply returns it (and ignores the
255flags. If that is troubling you, check \f(CW\*(C`ev_backend ()\*(C'\fR afterwards). 429flags. If that is troubling you, check \f(CW\*(C`ev_backend ()\*(C'\fR afterwards).
256.Sp 430.Sp
257If you don't know what event loop to use, use the one returned from this 431If you don't know what event loop to use, use the one returned from this
258function. 432function.
259.Sp 433.Sp
434Note that this function is \fInot\fR thread-safe, so if you want to use it
435from multiple threads, you have to lock (note also that this is unlikely,
436as loops cannot be shared easily between threads anyway).
437.Sp
438The default loop is the only loop that can handle \f(CW\*(C`ev_signal\*(C'\fR and
439\&\f(CW\*(C`ev_child\*(C'\fR watchers, and to do this, it always registers a handler
440for \f(CW\*(C`SIGCHLD\*(C'\fR. If this is a problem for your application you can either
441create a dynamic loop with \f(CW\*(C`ev_loop_new\*(C'\fR that doesn't do that, or you
442can simply overwrite the \f(CW\*(C`SIGCHLD\*(C'\fR signal handler \fIafter\fR calling
443\&\f(CW\*(C`ev_default_init\*(C'\fR.
444.Sp
260The flags argument can be used to specify special behaviour or specific 445The flags argument can be used to specify special behaviour or specific
261backends to use, and is usually specified as \f(CW0\fR (or \s-1EVFLAG_AUTO\s0). 446backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).
262.Sp 447.Sp
263It supports the following flags: 448The following flags are supported:
264.RS 4 449.RS 4
265.ie n .IP """EVFLAG_AUTO""" 4 450.ie n .IP """EVFLAG_AUTO""" 4
266.el .IP "\f(CWEVFLAG_AUTO\fR" 4 451.el .IP "\f(CWEVFLAG_AUTO\fR" 4
267.IX Item "EVFLAG_AUTO" 452.IX Item "EVFLAG_AUTO"
268The default flags value. Use this if you have no clue (it's the right 453The default flags value. Use this if you have no clue (it's the right
269thing, believe me). 454thing, believe me).
270.ie n .IP """EVFLAG_NOENV""" 4 455.ie n .IP """EVFLAG_NOENV""" 4
271.el .IP "\f(CWEVFLAG_NOENV\fR" 4 456.el .IP "\f(CWEVFLAG_NOENV\fR" 4
272.IX Item "EVFLAG_NOENV" 457.IX Item "EVFLAG_NOENV"
273If this flag bit is ored into the flag value (or the program runs setuid 458If this flag bit is or'ed into the flag value (or the program runs setuid
274or setgid) then libev will \fInot\fR look at the environment variable 459or setgid) then libev will \fInot\fR look at the environment variable
275\&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will 460\&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will
276override the flags completely if it is found in the environment. This is 461override the flags completely if it is found in the environment. This is
277useful to try out specific backends to test their performance, or to work 462useful to try out specific backends to test their performance, or to work
278around bugs. 463around bugs.
464.ie n .IP """EVFLAG_FORKCHECK""" 4
465.el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4
466.IX Item "EVFLAG_FORKCHECK"
467Instead of calling \f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR manually after
468a fork, you can also make libev check for a fork in each iteration by
469enabling this flag.
470.Sp
471This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop,
472and thus this might slow down your event loop if you do a lot of loop
473iterations and little real work, but is usually not noticeable (on my
474GNU/Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn sequence
475without a system call and thus \fIvery\fR fast, but my GNU/Linux system also has
476\&\f(CW\*(C`pthread_atfork\*(C'\fR which is even faster).
477.Sp
478The big advantage of this flag is that you can forget about fork (and
479forget about forgetting to tell libev about forking) when you use this
480flag.
481.Sp
482This flag setting cannot be overridden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR
483environment variable.
484.ie n .IP """EVFLAG_NOINOTIFY""" 4
485.el .IP "\f(CWEVFLAG_NOINOTIFY\fR" 4
486.IX Item "EVFLAG_NOINOTIFY"
487When this flag is specified, then libev will not attempt to use the
488\&\fIinotify\fR \s-1API\s0 for it's \f(CW\*(C`ev_stat\*(C'\fR watchers. Apart from debugging and
489testing, this flag can be useful to conserve inotify file descriptors, as
490otherwise each loop using \f(CW\*(C`ev_stat\*(C'\fR watchers consumes one inotify handle.
491.ie n .IP """EVFLAG_SIGNALFD""" 4
492.el .IP "\f(CWEVFLAG_SIGNALFD\fR" 4
493.IX Item "EVFLAG_SIGNALFD"
494When this flag is specified, then libev will attempt to use the
495\&\fIsignalfd\fR \s-1API\s0 for it's \f(CW\*(C`ev_signal\*(C'\fR (and \f(CW\*(C`ev_child\*(C'\fR) watchers. This \s-1API\s0
496delivers signals synchronously, which makes it both faster and might make
497it possible to get the queued signal data. It can also simplify signal
498handling with threads, as long as you properly block signals in your
499threads that are not interested in handling them.
500.Sp
501Signalfd will not be used by default as this changes your signal mask, and
502there are a lot of shoddy libraries and programs (glib's threadpool for
503example) that can't properly initialise their signal masks.
279.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4 504.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
280.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4 505.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
281.IX Item "EVBACKEND_SELECT (value 1, portable select backend)" 506.IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
282This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as 507This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as
283libev tries to roll its own fd_set with no limits on the number of fds, 508libev tries to roll its own fd_set with no limits on the number of fds,
284but if that fails, expect a fairly low limit on the number of fds when 509but if that fails, expect a fairly low limit on the number of fds when
285using this backend. It doesn't scale too well (O(highest_fd)), but its usually 510using this backend. It doesn't scale too well (O(highest_fd)), but its
286the fastest backend for a low number of fds. 511usually the fastest backend for a low number of (low-numbered :) fds.
512.Sp
513To get good performance out of this backend you need a high amount of
514parallelism (most of the file descriptors should be busy). If you are
515writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many
516connections as possible during one iteration. You might also want to have
517a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of
518readiness notifications you get per iteration.
519.Sp
520This 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
521\&\f(CW\*(C`writefds\*(C'\fR set (and to work around Microsoft Windows bugs, also onto the
522\&\f(CW\*(C`exceptfds\*(C'\fR set on that platform).
287.ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4 523.ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4
288.el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4 524.el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4
289.IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)" 525.IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)"
290And this is your standard \fIpoll\fR\|(2) backend. It's more complicated than 526And this is your standard \fIpoll\fR\|(2) backend. It's more complicated
291select, but handles sparse fds better and has no artificial limit on the 527than select, but handles sparse fds better and has no artificial
292number of fds you can use (except it will slow down considerably with a 528limit on the number of fds you can use (except it will slow down
293lot of inactive fds). It scales similarly to select, i.e. O(total_fds). 529considerably with a lot of inactive fds). It scales similarly to select,
530i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for
531performance tips.
532.Sp
533This backend maps \f(CW\*(C`EV_READ\*(C'\fR to \f(CW\*(C`POLLIN | POLLERR | POLLHUP\*(C'\fR, and
534\&\f(CW\*(C`EV_WRITE\*(C'\fR to \f(CW\*(C`POLLOUT | POLLERR | POLLHUP\*(C'\fR.
294.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4 535.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
295.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4 536.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
296.IX Item "EVBACKEND_EPOLL (value 4, Linux)" 537.IX Item "EVBACKEND_EPOLL (value 4, Linux)"
538Use the linux-specific \fIepoll\fR\|(7) interface (for both pre\- and post\-2.6.9
539kernels).
540.Sp
297For few fds, this backend is a bit little slower than poll and select, 541For few fds, this backend is a bit little slower than poll and select,
298but it scales phenomenally better. While poll and select usually scale like 542but it scales phenomenally better. While poll and select usually scale
299O(total_fds) where n is the total number of fds (or the highest fd), epoll scales 543like O(total_fds) where n is the total number of fds (or the highest fd),
300either O(1) or O(active_fds). 544epoll scales either O(1) or O(active_fds).
301.Sp 545.Sp
546The epoll mechanism deserves honorable mention as the most misdesigned
547of the more advanced event mechanisms: mere annoyances include silently
548dropping file descriptors, requiring a system call per change per file
549descriptor (and unnecessary guessing of parameters), problems with dup and
550so on. The biggest issue is fork races, however \- if a program forks then
551\&\fIboth\fR parent and child process have to recreate the epoll set, which can
552take considerable time (one syscall per file descriptor) and is of course
553hard to detect.
554.Sp
555Epoll is also notoriously buggy \- embedding epoll fds \fIshould\fR work, but
556of course \fIdoesn't\fR, and epoll just loves to report events for totally
557\&\fIdifferent\fR file descriptors (even already closed ones, so one cannot
558even remove them from the set) than registered in the set (especially
559on \s-1SMP\s0 systems). Libev tries to counter these spurious notifications by
560employing an additional generation counter and comparing that against the
561events to filter out spurious ones, recreating the set when required.
562.Sp
302While stopping and starting an I/O watcher in the same iteration will 563While stopping, setting and starting an I/O watcher in the same iteration
303result in some caching, there is still a syscall per such incident 564will result in some caching, there is still a system call per such
304(because the fd could point to a different file description now), so its 565incident (because the same \fIfile descriptor\fR could point to a different
305best to avoid that. Also, \fIdup()\fRed file descriptors might not work very 566\&\fIfile description\fR now), so its best to avoid that. Also, \f(CW\*(C`dup ()\*(C'\fR'ed
306well if you register events for both fds. 567file descriptors might not work very well if you register events for both
568file descriptors.
307.Sp 569.Sp
308Please note that epoll sometimes generates spurious notifications, so you 570Best performance from this backend is achieved by not unregistering all
309need to use non-blocking I/O or other means to avoid blocking when no data 571watchers for a file descriptor until it has been closed, if possible,
310(or space) is available. 572i.e. keep at least one watcher active per fd at all times. Stopping and
573starting a watcher (without re-setting it) also usually doesn't cause
574extra overhead. A fork can both result in spurious notifications as well
575as in libev having to destroy and recreate the epoll object, which can
576take considerable time and thus should be avoided.
577.Sp
578All this means that, in practice, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR can be as fast or
579faster than epoll for maybe up to a hundred file descriptors, depending on
580the usage. So sad.
581.Sp
582While nominally embeddable in other event loops, this feature is broken in
583all kernel versions tested so far.
584.Sp
585This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
586\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
311.ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4 587.ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4
312.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4 588.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
313.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)" 589.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
314Kqueue deserves special mention, as at the time of this writing, it 590Kqueue deserves special mention, as at the time of this writing, it
315was broken on all BSDs except NetBSD (usually it doesn't work with 591was broken on all BSDs except NetBSD (usually it doesn't work reliably
316anything but sockets and pipes, except on Darwin, where of course its 592with anything but sockets and pipes, except on Darwin, where of course
317completely useless). For this reason its not being \*(L"autodetected\*(R" unless 593it's completely useless). Unlike epoll, however, whose brokenness
318you explicitly specify the flags (i.e. you don't use \s-1EVFLAG_AUTO\s0). 594is by design, these kqueue bugs can (and eventually will) be fixed
595without \s-1API\s0 changes to existing programs. For this reason it's not being
596\&\*(L"auto-detected\*(R" unless you explicitly specify it in the flags (i.e. using
597\&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a known-to-be-good (\-enough)
598system like NetBSD.
599.Sp
600You still can embed kqueue into a normal poll or select backend and use it
601only for sockets (after having made sure that sockets work with kqueue on
602the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
319.Sp 603.Sp
320It scales in the same way as the epoll backend, but the interface to the 604It scales in the same way as the epoll backend, but the interface to the
321kernel is more efficient (which says nothing about its actual speed, of 605kernel is more efficient (which says nothing about its actual speed, of
322course). While starting and stopping an I/O watcher does not cause an 606course). While stopping, setting and starting an I/O watcher does never
323extra syscall as with epoll, it still adds up to four event changes per 607cause an extra system call as with \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to
324incident, so its best to avoid that. 608two event changes per incident. Support for \f(CW\*(C`fork ()\*(C'\fR is very bad (but
609sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
610cases
611.Sp
612This backend usually performs well under most conditions.
613.Sp
614While nominally embeddable in other event loops, this doesn't work
615everywhere, so you might need to test for this. And since it is broken
616almost everywhere, you should only use it when you have a lot of sockets
617(for which it usually works), by embedding it into another event loop
618(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
619also broken on \s-1OS\s0 X)) and, did I mention it, using it only for sockets.
620.Sp
621This backend maps \f(CW\*(C`EV_READ\*(C'\fR into an \f(CW\*(C`EVFILT_READ\*(C'\fR kevent with
622\&\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
623\&\f(CW\*(C`NOTE_EOF\*(C'\fR.
325.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4 624.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
326.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4 625.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
327.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)" 626.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
328This is not implemented yet (and might never be). 627This is not implemented yet (and might never be, unless you send me an
628implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets
629and is not embeddable, which would limit the usefulness of this backend
630immensely.
329.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4 631.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
330.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4 632.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
331.IX Item "EVBACKEND_PORT (value 32, Solaris 10)" 633.IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
332This uses the Solaris 10 port mechanism. As with everything on Solaris, 634This uses the Solaris 10 event port mechanism. As with everything on Solaris,
333it's really slow, but it still scales very well (O(active_fds)). 635it's really slow, but it still scales very well (O(active_fds)).
334.Sp 636.Sp
335Please note that solaris ports can result in a lot of spurious 637Please note that Solaris event ports can deliver a lot of spurious
336notifications, so you need to use non-blocking I/O or other means to avoid 638notifications, so you need to use non-blocking I/O or other means to avoid
337blocking when no data (or space) is available. 639blocking when no data (or space) is available.
640.Sp
641While this backend scales well, it requires one system call per active
642file descriptor per loop iteration. For small and medium numbers of file
643descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend
644might perform better.
645.Sp
646On the positive side, with the exception of the spurious readiness
647notifications, this backend actually performed fully to specification
648in all tests and is fully embeddable, which is a rare feat among the
649OS-specific backends (I vastly prefer correctness over speed hacks).
650.Sp
651This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
652\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
338.ie n .IP """EVBACKEND_ALL""" 4 653.ie n .IP """EVBACKEND_ALL""" 4
339.el .IP "\f(CWEVBACKEND_ALL\fR" 4 654.el .IP "\f(CWEVBACKEND_ALL\fR" 4
340.IX Item "EVBACKEND_ALL" 655.IX Item "EVBACKEND_ALL"
341Try all backends (even potentially broken ones that wouldn't be tried 656Try all backends (even potentially broken ones that wouldn't be tried
342with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as 657with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as
343\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR. 658\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR.
659.Sp
660It is definitely not recommended to use this flag.
344.RE 661.RE
345.RS 4 662.RS 4
346.Sp 663.Sp
347If one or more of these are ored into the flags value, then only these 664If one or more of the backend flags are or'ed into the flags value,
348backends will be tried (in the reverse order as given here). If none are 665then only these backends will be tried (in the reverse order as listed
349specified, most compiled-in backend will be tried, usually in reverse 666here). If none are specified, all backends in \f(CW\*(C`ev_recommended_backends
350order of their flag values :) 667()\*(C'\fR will be tried.
668.Sp
669Example: This is the most typical usage.
670.Sp
671.Vb 2
672\& if (!ev_default_loop (0))
673\& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
674.Ve
675.Sp
676Example: Restrict libev to the select and poll backends, and do not allow
677environment settings to be taken into account:
678.Sp
679.Vb 1
680\& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
681.Ve
682.Sp
683Example: Use whatever libev has to offer, but make sure that kqueue is
684used if available (warning, breaks stuff, best use only with your own
685private event loop and only if you know the \s-1OS\s0 supports your types of
686fds):
687.Sp
688.Vb 1
689\& ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
690.Ve
351.RE 691.RE
352.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4 692.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
353.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)" 693.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
354Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is 694Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is
355always distinct from the default loop. Unlike the default loop, it cannot 695always distinct from the default loop. Unlike the default loop, it cannot
356handle signal and child watchers, and attempts to do so will be greeted by 696handle signal and child watchers, and attempts to do so will be greeted by
357undefined behaviour (or a failed assertion if assertions are enabled). 697undefined behaviour (or a failed assertion if assertions are enabled).
698.Sp
699Note that this function \fIis\fR thread-safe, and the recommended way to use
700libev with threads is indeed to create one loop per thread, and using the
701default loop in the \*(L"main\*(R" or \*(L"initial\*(R" thread.
702.Sp
703Example: Try to create a event loop that uses epoll and nothing else.
704.Sp
705.Vb 3
706\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
707\& if (!epoller)
708\& fatal ("no epoll found here, maybe it hides under your chair");
709.Ve
358.IP "ev_default_destroy ()" 4 710.IP "ev_default_destroy ()" 4
359.IX Item "ev_default_destroy ()" 711.IX Item "ev_default_destroy ()"
360Destroys the default loop again (frees all memory and kernel state 712Destroys the default loop again (frees all memory and kernel state
361etc.). This stops all registered event watchers (by not touching them in 713etc.). None of the active event watchers will be stopped in the normal
362any way whatsoever, although you cannot rely on this :). 714sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your
715responsibility to either stop all watchers cleanly yourself \fIbefore\fR
716calling this function, or cope with the fact afterwards (which is usually
717the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them
718for example).
719.Sp
720Note that certain global state, such as signal state (and installed signal
721handlers), will not be freed by this function, and related watchers (such
722as signal and child watchers) would need to be stopped manually.
723.Sp
724In general it is not advisable to call this function except in the
725rare occasion where you really need to free e.g. the signal handling
726pipe fds. If you need dynamically allocated loops it is better to use
727\&\f(CW\*(C`ev_loop_new\*(C'\fR and \f(CW\*(C`ev_loop_destroy\*(C'\fR.
363.IP "ev_loop_destroy (loop)" 4 728.IP "ev_loop_destroy (loop)" 4
364.IX Item "ev_loop_destroy (loop)" 729.IX Item "ev_loop_destroy (loop)"
365Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an 730Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an
366earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR. 731earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR.
367.IP "ev_default_fork ()" 4 732.IP "ev_default_fork ()" 4
368.IX Item "ev_default_fork ()" 733.IX Item "ev_default_fork ()"
734This function sets a flag that causes subsequent \f(CW\*(C`ev_loop\*(C'\fR iterations
369This function reinitialises the kernel state for backends that have 735to reinitialise the kernel state for backends that have one. Despite the
370one. Despite the name, you can call it anytime, but it makes most sense 736name, you can call it anytime, but it makes most sense after forking, in
371after forking, in either the parent or child process (or both, but that 737the child process (or both child and parent, but that again makes little
372again makes little sense). 738sense). You \fImust\fR call it in the child before using any of the libev
739functions, and it will only take effect at the next \f(CW\*(C`ev_loop\*(C'\fR iteration.
373.Sp 740.Sp
374You \fImust\fR call this function in the child process after forking if and 741On the other hand, you only need to call this function in the child
375only if you want to use the event library in both processes. If you just 742process if and only if you want to use the event library in the child. If
376fork+exec, you don't have to call it. 743you just fork+exec, you don't have to call it at all.
377.Sp 744.Sp
378The function itself is quite fast and it's usually not a problem to call 745The function itself is quite fast and it's usually not a problem to call
379it just in case after a fork. To make this easy, the function will fit in 746it just in case after a fork. To make this easy, the function will fit in
380quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR: 747quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR:
381.Sp 748.Sp
382.Vb 1 749.Vb 1
383\& pthread_atfork (0, 0, ev_default_fork); 750\& pthread_atfork (0, 0, ev_default_fork);
384.Ve 751.Ve
385.Sp
386At the moment, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and \f(CW\*(C`EVBACKEND_POLL\*(C'\fR are safe to use
387without calling this function, so if you force one of those backends you
388do not need to care.
389.IP "ev_loop_fork (loop)" 4 752.IP "ev_loop_fork (loop)" 4
390.IX Item "ev_loop_fork (loop)" 753.IX Item "ev_loop_fork (loop)"
391Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by 754Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by
392\&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop 755\&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop
393after fork, and how you do this is entirely your own problem. 756after fork that you want to re-use in the child, and how you do this is
757entirely your own problem.
758.IP "int ev_is_default_loop (loop)" 4
759.IX Item "int ev_is_default_loop (loop)"
760Returns true when the given loop is, in fact, the default loop, and false
761otherwise.
762.IP "unsigned int ev_loop_count (loop)" 4
763.IX Item "unsigned int ev_loop_count (loop)"
764Returns the count of loop iterations for the loop, which is identical to
765the number of times libev did poll for new events. It starts at \f(CW0\fR and
766happily wraps around with enough iterations.
767.Sp
768This value can sometimes be useful as a generation counter of sorts (it
769\&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with
770\&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls.
771.IP "unsigned int ev_loop_depth (loop)" 4
772.IX Item "unsigned int ev_loop_depth (loop)"
773Returns the number of times \f(CW\*(C`ev_loop\*(C'\fR was entered minus the number of
774times \f(CW\*(C`ev_loop\*(C'\fR was exited, in other words, the recursion depth.
775.Sp
776Outside \f(CW\*(C`ev_loop\*(C'\fR, this number is zero. In a callback, this number is
777\&\f(CW1\fR, unless \f(CW\*(C`ev_loop\*(C'\fR was invoked recursively (or from another thread),
778in which case it is higher.
779.Sp
780Leaving \f(CW\*(C`ev_loop\*(C'\fR abnormally (setjmp/longjmp, cancelling the thread
781etc.), doesn't count as exit.
394.IP "unsigned int ev_backend (loop)" 4 782.IP "unsigned int ev_backend (loop)" 4
395.IX Item "unsigned int ev_backend (loop)" 783.IX Item "unsigned int ev_backend (loop)"
396Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in 784Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
397use. 785use.
398.IP "ev_tstamp ev_now (loop)" 4 786.IP "ev_tstamp ev_now (loop)" 4
399.IX Item "ev_tstamp ev_now (loop)" 787.IX Item "ev_tstamp ev_now (loop)"
400Returns the current \*(L"event loop time\*(R", which is the time the event loop 788Returns the current \*(L"event loop time\*(R", which is the time the event loop
401got events and started processing them. This timestamp does not change 789received events and started processing them. This timestamp does not
402as long as callbacks are being processed, and this is also the base time 790change as long as callbacks are being processed, and this is also the base
403used for relative timers. You can treat it as the timestamp of the event 791time used for relative timers. You can treat it as the timestamp of the
404occuring (or more correctly, the mainloop finding out about it). 792event occurring (or more correctly, libev finding out about it).
793.IP "ev_now_update (loop)" 4
794.IX Item "ev_now_update (loop)"
795Establishes the current time by querying the kernel, updating the time
796returned by \f(CW\*(C`ev_now ()\*(C'\fR in the progress. This is a costly operation and
797is usually done automatically within \f(CW\*(C`ev_loop ()\*(C'\fR.
798.Sp
799This function is rarely useful, but when some event callback runs for a
800very long time without entering the event loop, updating libev's idea of
801the current time is a good idea.
802.Sp
803See also \*(L"The special problem of time updates\*(R" in the \f(CW\*(C`ev_timer\*(C'\fR section.
804.IP "ev_suspend (loop)" 4
805.IX Item "ev_suspend (loop)"
806.PD 0
807.IP "ev_resume (loop)" 4
808.IX Item "ev_resume (loop)"
809.PD
810These two functions suspend and resume a loop, for use when the loop is
811not used for a while and timeouts should not be processed.
812.Sp
813A typical use case would be an interactive program such as a game: When
814the user presses \f(CW\*(C`^Z\*(C'\fR to suspend the game and resumes it an hour later it
815would be best to handle timeouts as if no time had actually passed while
816the program was suspended. This can be achieved by calling \f(CW\*(C`ev_suspend\*(C'\fR
817in your \f(CW\*(C`SIGTSTP\*(C'\fR handler, sending yourself a \f(CW\*(C`SIGSTOP\*(C'\fR and calling
818\&\f(CW\*(C`ev_resume\*(C'\fR directly afterwards to resume timer processing.
819.Sp
820Effectively, all \f(CW\*(C`ev_timer\*(C'\fR watchers will be delayed by the time spend
821between \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
822will be rescheduled (that is, they will lose any events that would have
823occured while suspended).
824.Sp
825After calling \f(CW\*(C`ev_suspend\*(C'\fR you \fBmust not\fR call \fIany\fR function on the
826given loop other than \f(CW\*(C`ev_resume\*(C'\fR, and you \fBmust not\fR call \f(CW\*(C`ev_resume\*(C'\fR
827without a previous call to \f(CW\*(C`ev_suspend\*(C'\fR.
828.Sp
829Calling \f(CW\*(C`ev_suspend\*(C'\fR/\f(CW\*(C`ev_resume\*(C'\fR has the side effect of updating the
830event loop time (see \f(CW\*(C`ev_now_update\*(C'\fR).
405.IP "ev_loop (loop, int flags)" 4 831.IP "ev_loop (loop, int flags)" 4
406.IX Item "ev_loop (loop, int flags)" 832.IX Item "ev_loop (loop, int flags)"
407Finally, this is it, the event handler. This function usually is called 833Finally, this is it, the event handler. This function usually is called
408after you initialised all your watchers and you want to start handling 834after you have initialised all your watchers and you want to start
409events. 835handling events.
410.Sp 836.Sp
411If the flags argument is specified as 0, it will not return until either 837If the flags argument is specified as \f(CW0\fR, it will not return until
412no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called. 838either no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called.
839.Sp
840Please note that an explicit \f(CW\*(C`ev_unloop\*(C'\fR is usually better than
841relying on all watchers to be stopped when deciding when a program has
842finished (especially in interactive programs), but having a program
843that automatically loops as long as it has to and no longer by virtue
844of relying on its watchers stopping correctly, that is truly a thing of
845beauty.
413.Sp 846.Sp
414A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle 847A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle
415those events and any outstanding ones, but will not block your process in 848those events and any already outstanding ones, but will not block your
416case there are no events and will return after one iteration of the loop. 849process in case there are no events and will return after one iteration of
850the loop.
417.Sp 851.Sp
418A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if 852A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if
419neccessary) and will handle those and any outstanding ones. It will block 853necessary) and will handle those and any already outstanding ones. It
420your process until at least one new event arrives, and will return after 854will block your process until at least one new event arrives (which could
855be an event internal to libev itself, so there is no guarantee that a
856user-registered callback will be called), and will return after one
421one iteration of the loop. 857iteration of the loop.
422.Sp 858.Sp
423This flags value could be used to implement alternative looping 859This is useful if you are waiting for some external event in conjunction
424constructs, but the \f(CW\*(C`prepare\*(C'\fR and \f(CW\*(C`check\*(C'\fR watchers provide a better and 860with something not expressible using other libev watchers (i.e. "roll your
425more generic mechanism. 861own \f(CW\*(C`ev_loop\*(C'\fR"). However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is
862usually a better approach for this kind of thing.
426.Sp 863.Sp
427Here are the gory details of what ev_loop does: 864Here are the gory details of what \f(CW\*(C`ev_loop\*(C'\fR does:
428.Sp 865.Sp
429.Vb 15 866.Vb 10
430\& 1. If there are no active watchers (reference count is zero), return. 867\& \- Before the first iteration, call any pending watchers.
868\& * If EVFLAG_FORKCHECK was used, check for a fork.
869\& \- If a fork was detected (by any means), queue and call all fork watchers.
431\& 2. Queue and immediately call all prepare watchers. 870\& \- Queue and call all prepare watchers.
432\& 3. If we have been forked, recreate the kernel state. 871\& \- If we have been forked, detach and recreate the kernel state
872\& as to not disturb the other process.
433\& 4. Update the kernel state with all outstanding changes. 873\& \- Update the kernel state with all outstanding changes.
434\& 5. Update the "event loop time". 874\& \- Update the "event loop time" (ev_now ()).
435\& 6. Calculate for how long to block. 875\& \- Calculate for how long to sleep or block, if at all
876\& (active idle watchers, EVLOOP_NONBLOCK or not having
877\& any active watchers at all will result in not sleeping).
878\& \- Sleep if the I/O and timer collect interval say so.
436\& 7. Block the process, waiting for events. 879\& \- Block the process, waiting for any events.
880\& \- Queue all outstanding I/O (fd) events.
437\& 8. Update the "event loop time" and do time jump handling. 881\& \- Update the "event loop time" (ev_now ()), and do time jump adjustments.
438\& 9. Queue all outstanding timers. 882\& \- Queue all expired timers.
439\& 10. Queue all outstanding periodics. 883\& \- Queue all expired periodics.
440\& 11. If no events are pending now, queue all idle watchers. 884\& \- Unless any events are pending now, queue all idle watchers.
441\& 12. Queue all check watchers. 885\& \- Queue all check watchers.
442\& 13. Call all queued watchers in reverse order (i.e. check watchers first). 886\& \- Call all queued watchers in reverse order (i.e. check watchers first).
887\& Signals and child watchers are implemented as I/O watchers, and will
888\& be handled here by queueing them when their watcher gets executed.
443\& 14. If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK 889\& \- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
444\& was used, return, otherwise continue with step #1. 890\& were used, or there are no active watchers, return, otherwise
891\& continue with step *.
892.Ve
893.Sp
894Example: Queue some jobs and then loop until no events are outstanding
895anymore.
896.Sp
897.Vb 4
898\& ... queue jobs here, make sure they register event watchers as long
899\& ... as they still have work to do (even an idle watcher will do..)
900\& ev_loop (my_loop, 0);
901\& ... jobs done or somebody called unloop. yeah!
445.Ve 902.Ve
446.IP "ev_unloop (loop, how)" 4 903.IP "ev_unloop (loop, how)" 4
447.IX Item "ev_unloop (loop, how)" 904.IX Item "ev_unloop (loop, how)"
448Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it 905Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it
449has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either 906has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
450\&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or 907\&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or
451\&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return. 908\&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return.
909.Sp
910This \*(L"unloop state\*(R" will be cleared when entering \f(CW\*(C`ev_loop\*(C'\fR again.
911.Sp
912It is safe to call \f(CW\*(C`ev_unloop\*(C'\fR from otuside any \f(CW\*(C`ev_loop\*(C'\fR calls.
452.IP "ev_ref (loop)" 4 913.IP "ev_ref (loop)" 4
453.IX Item "ev_ref (loop)" 914.IX Item "ev_ref (loop)"
454.PD 0 915.PD 0
455.IP "ev_unref (loop)" 4 916.IP "ev_unref (loop)" 4
456.IX Item "ev_unref (loop)" 917.IX Item "ev_unref (loop)"
457.PD 918.PD
458Ref/unref can be used to add or remove a reference count on the event 919Ref/unref can be used to add or remove a reference count on the event
459loop: Every watcher keeps one reference, and as long as the reference 920loop: Every watcher keeps one reference, and as long as the reference
460count is nonzero, \f(CW\*(C`ev_loop\*(C'\fR will not return on its own. If you have 921count is nonzero, \f(CW\*(C`ev_loop\*(C'\fR will not return on its own.
922.Sp
923This is useful when you have a watcher that you never intend to
461a watcher you never unregister that should not keep \f(CW\*(C`ev_loop\*(C'\fR from 924unregister, but that nevertheless should not keep \f(CW\*(C`ev_loop\*(C'\fR from
462returning, \fIev_unref()\fR after starting, and \fIev_ref()\fR before stopping it. For 925returning. In such a case, call \f(CW\*(C`ev_unref\*(C'\fR after starting, and \f(CW\*(C`ev_ref\*(C'\fR
926before stopping it.
927.Sp
463example, libev itself uses this for its internal signal pipe: It is not 928As an example, libev itself uses this for its internal signal pipe: It
464visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from exiting if 929is not visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from
465no event watchers registered by it are active. It is also an excellent 930exiting if no event watchers registered by it are active. It is also an
466way to do this for generic recurring timers or from within third-party 931excellent way to do this for generic recurring timers or from within
467libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR. 932third-party libraries. Just remember to \fIunref after start\fR and \fIref
933before stop\fR (but only if the watcher wasn't active before, or was active
934before, respectively. Note also that libev might stop watchers itself
935(e.g. non-repeating timers) in which case you have to \f(CW\*(C`ev_ref\*(C'\fR
936in the callback).
937.Sp
938Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_loop\*(C'\fR
939running when nothing else is active.
940.Sp
941.Vb 4
942\& ev_signal exitsig;
943\& ev_signal_init (&exitsig, sig_cb, SIGINT);
944\& ev_signal_start (loop, &exitsig);
945\& evf_unref (loop);
946.Ve
947.Sp
948Example: For some weird reason, unregister the above signal handler again.
949.Sp
950.Vb 2
951\& ev_ref (loop);
952\& ev_signal_stop (loop, &exitsig);
953.Ve
954.IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4
955.IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"
956.PD 0
957.IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4
958.IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"
959.PD
960These advanced functions influence the time that libev will spend waiting
961for events. Both time intervals are by default \f(CW0\fR, meaning that libev
962will try to invoke timer/periodic callbacks and I/O callbacks with minimum
963latency.
964.Sp
965Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR)
966allows libev to delay invocation of I/O and timer/periodic callbacks
967to increase efficiency of loop iterations (or to increase power-saving
968opportunities).
969.Sp
970The idea is that sometimes your program runs just fast enough to handle
971one (or very few) event(s) per loop iteration. While this makes the
972program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new
973events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high
974overhead for the actual polling but can deliver many events at once.
975.Sp
976By setting a higher \fIio collect interval\fR you allow libev to spend more
977time collecting I/O events, so you can handle more events per iteration,
978at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and
979\&\f(CW\*(C`ev_timer\*(C'\fR) will be not affected. Setting this to a non-null value will
980introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations. The
981sleep time ensures that libev will not poll for I/O events more often then
982once per this interval, on average.
983.Sp
984Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
985to spend more time collecting timeouts, at the expense of increased
986latency/jitter/inexactness (the watcher callback will be called
987later). \f(CW\*(C`ev_io\*(C'\fR watchers will not be affected. Setting this to a non-null
988value will not introduce any overhead in libev.
989.Sp
990Many (busy) programs can usually benefit by setting the I/O collect
991interval to a value near \f(CW0.1\fR or so, which is often enough for
992interactive servers (of course not for games), likewise for timeouts. It
993usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR,
994as this approaches the timing granularity of most systems. Note that if
995you do transactions with the outside world and you can't increase the
996parallelity, then this setting will limit your transaction rate (if you
997need to poll once per transaction and the I/O collect interval is 0.01,
998then you can't do more than 100 transations per second).
999.Sp
1000Setting the \fItimeout collect interval\fR can improve the opportunity for
1001saving power, as the program will \*(L"bundle\*(R" timer callback invocations that
1002are \*(L"near\*(R" in time together, by delaying some, thus reducing the number of
1003times the process sleeps and wakes up again. Another useful technique to
1004reduce iterations/wake\-ups is to use \f(CW\*(C`ev_periodic\*(C'\fR watchers and make sure
1005they fire on, say, one-second boundaries only.
1006.Sp
1007Example: we only need 0.1s timeout granularity, and we wish not to poll
1008more often than 100 times per second:
1009.Sp
1010.Vb 2
1011\& ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
1012\& ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
1013.Ve
1014.IP "ev_invoke_pending (loop)" 4
1015.IX Item "ev_invoke_pending (loop)"
1016This call will simply invoke all pending watchers while resetting their
1017pending state. Normally, \f(CW\*(C`ev_loop\*(C'\fR does this automatically when required,
1018but when overriding the invoke callback this call comes handy.
1019.IP "int ev_pending_count (loop)" 4
1020.IX Item "int ev_pending_count (loop)"
1021Returns the number of pending watchers \- zero indicates that no watchers
1022are pending.
1023.IP "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(\s-1EV_P\s0))" 4
1024.IX Item "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))"
1025This overrides the invoke pending functionality of the loop: Instead of
1026invoking all pending watchers when there are any, \f(CW\*(C`ev_loop\*(C'\fR will call
1027this callback instead. This is useful, for example, when you want to
1028invoke the actual watchers inside another context (another thread etc.).
1029.Sp
1030If you want to reset the callback, use \f(CW\*(C`ev_invoke_pending\*(C'\fR as new
1031callback.
1032.IP "ev_set_loop_release_cb (loop, void (*release)(\s-1EV_P\s0), void (*acquire)(\s-1EV_P\s0))" 4
1033.IX Item "ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))"
1034Sometimes you want to share the same loop between multiple threads. This
1035can be done relatively simply by putting mutex_lock/unlock calls around
1036each call to a libev function.
1037.Sp
1038However, \f(CW\*(C`ev_loop\*(C'\fR can run an indefinite time, so it is not feasible to
1039wait for it to return. One way around this is to wake up the loop via
1040\&\f(CW\*(C`ev_unloop\*(C'\fR and \f(CW\*(C`av_async_send\*(C'\fR, another way is to set these \fIrelease\fR
1041and \fIacquire\fR callbacks on the loop.
1042.Sp
1043When set, then \f(CW\*(C`release\*(C'\fR will be called just before the thread is
1044suspended waiting for new events, and \f(CW\*(C`acquire\*(C'\fR is called just
1045afterwards.
1046.Sp
1047Ideally, \f(CW\*(C`release\*(C'\fR will just call your mutex_unlock function, and
1048\&\f(CW\*(C`acquire\*(C'\fR will just call the mutex_lock function again.
1049.Sp
1050While event loop modifications are allowed between invocations of
1051\&\f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR (that's their only purpose after all), no
1052modifications done will affect the event loop, i.e. adding watchers will
1053have no effect on the set of file descriptors being watched, or the time
1054waited. Use an \f(CW\*(C`ev_async\*(C'\fR watcher to wake up \f(CW\*(C`ev_loop\*(C'\fR when you want it
1055to take note of any changes you made.
1056.Sp
1057In theory, threads executing \f(CW\*(C`ev_loop\*(C'\fR will be async-cancel safe between
1058invocations of \f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR.
1059.Sp
1060See also the locking example in the \f(CW\*(C`THREADS\*(C'\fR section later in this
1061document.
1062.IP "ev_set_userdata (loop, void *data)" 4
1063.IX Item "ev_set_userdata (loop, void *data)"
1064.PD 0
1065.IP "ev_userdata (loop)" 4
1066.IX Item "ev_userdata (loop)"
1067.PD
1068Set and retrieve a single \f(CW\*(C`void *\*(C'\fR associated with a loop. When
1069\&\f(CW\*(C`ev_set_userdata\*(C'\fR has never been called, then \f(CW\*(C`ev_userdata\*(C'\fR returns
1070\&\f(CW0.\fR
1071.Sp
1072These two functions can be used to associate arbitrary data with a loop,
1073and are intended solely for the \f(CW\*(C`invoke_pending_cb\*(C'\fR, \f(CW\*(C`release\*(C'\fR and
1074\&\f(CW\*(C`acquire\*(C'\fR callbacks described above, but of course can be (ab\-)used for
1075any other purpose as well.
1076.IP "ev_loop_verify (loop)" 4
1077.IX Item "ev_loop_verify (loop)"
1078This function only does something when \f(CW\*(C`EV_VERIFY\*(C'\fR support has been
1079compiled in, which is the default for non-minimal builds. It tries to go
1080through all internal structures and checks them for validity. If anything
1081is found to be inconsistent, it will print an error message to standard
1082error and call \f(CW\*(C`abort ()\*(C'\fR.
1083.Sp
1084This can be used to catch bugs inside libev itself: under normal
1085circumstances, this function will never abort as of course libev keeps its
1086data structures consistent.
468.SH "ANATOMY OF A WATCHER" 1087.SH "ANATOMY OF A WATCHER"
469.IX Header "ANATOMY OF A WATCHER" 1088.IX Header "ANATOMY OF A WATCHER"
1089In the following description, uppercase \f(CW\*(C`TYPE\*(C'\fR in names stands for the
1090watcher type, e.g. \f(CW\*(C`ev_TYPE_start\*(C'\fR can mean \f(CW\*(C`ev_timer_start\*(C'\fR for timer
1091watchers and \f(CW\*(C`ev_io_start\*(C'\fR for I/O watchers.
1092.PP
470A watcher is a structure that you create and register to record your 1093A watcher is a structure that you create and register to record your
471interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to 1094interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to
472become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that: 1095become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that:
473.PP 1096.PP
474.Vb 5 1097.Vb 5
475\& static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) 1098\& static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
476\& { 1099\& {
477\& ev_io_stop (w); 1100\& ev_io_stop (w);
478\& ev_unloop (loop, EVUNLOOP_ALL); 1101\& ev_unloop (loop, EVUNLOOP_ALL);
479\& } 1102\& }
480.Ve 1103\&
481.PP
482.Vb 6
483\& struct ev_loop *loop = ev_default_loop (0); 1104\& struct ev_loop *loop = ev_default_loop (0);
1105\&
484\& struct ev_io stdin_watcher; 1106\& ev_io stdin_watcher;
1107\&
485\& ev_init (&stdin_watcher, my_cb); 1108\& ev_init (&stdin_watcher, my_cb);
486\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); 1109\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
487\& ev_io_start (loop, &stdin_watcher); 1110\& ev_io_start (loop, &stdin_watcher);
1111\&
488\& ev_loop (loop, 0); 1112\& ev_loop (loop, 0);
489.Ve 1113.Ve
490.PP 1114.PP
491As you can see, you are responsible for allocating the memory for your 1115As you can see, you are responsible for allocating the memory for your
492watcher structures (and it is usually a bad idea to do this on the stack, 1116watcher structures (and it is \fIusually\fR a bad idea to do this on the
493although this can sometimes be quite valid). 1117stack).
1118.PP
1119Each watcher has an associated watcher structure (called \f(CW\*(C`struct ev_TYPE\*(C'\fR
1120or simply \f(CW\*(C`ev_TYPE\*(C'\fR, as typedefs are provided for all watcher structs).
494.PP 1121.PP
495Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init 1122Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init
496(watcher *, callback)\*(C'\fR, which expects a callback to be provided. This 1123(watcher *, callback)\*(C'\fR, which expects a callback to be provided. This
497callback gets invoked each time the event occurs (or, in the case of io 1124callback gets invoked each time the event occurs (or, in the case of I/O
498watchers, each time the event loop detects that the file descriptor given 1125watchers, each time the event loop detects that the file descriptor given
499is readable and/or writable). 1126is readable and/or writable).
500.PP 1127.PP
501Each watcher type has its own \f(CW\*(C`ev_<type>_set (watcher *, ...)\*(C'\fR macro 1128Each watcher type further has its own \f(CW\*(C`ev_TYPE_set (watcher *, ...)\*(C'\fR
502with arguments specific to this watcher type. There is also a macro 1129macro to configure it, with arguments specific to the watcher type. There
503to combine initialisation and setting in one call: \f(CW\*(C`ev_<type>_init 1130is also a macro to combine initialisation and setting in one call: \f(CW\*(C`ev_TYPE_init (watcher *, callback, ...)\*(C'\fR.
504(watcher *, callback, ...)\*(C'\fR.
505.PP 1131.PP
506To make the watcher actually watch out for events, you have to start it 1132To make the watcher actually watch out for events, you have to start it
507with a watcher-specific start function (\f(CW\*(C`ev_<type>_start (loop, watcher 1133with a watcher-specific start function (\f(CW\*(C`ev_TYPE_start (loop, watcher
508*)\*(C'\fR), and you can stop watching for events at any time by calling the 1134*)\*(C'\fR), and you can stop watching for events at any time by calling the
509corresponding stop function (\f(CW\*(C`ev_<type>_stop (loop, watcher *)\*(C'\fR. 1135corresponding stop function (\f(CW\*(C`ev_TYPE_stop (loop, watcher *)\*(C'\fR.
510.PP 1136.PP
511As long as your watcher is active (has been started but not stopped) you 1137As long as your watcher is active (has been started but not stopped) you
512must not touch the values stored in it. Most specifically you must never 1138must not touch the values stored in it. Most specifically you must never
513reinitialise it or call its set macro. 1139reinitialise it or call its \f(CW\*(C`ev_TYPE_set\*(C'\fR macro.
514.PP
515You can check whether an event is active by calling the \f(CW\*(C`ev_is_active
516(watcher *)\*(C'\fR macro. To see whether an event is outstanding (but the
517callback for it has not been called yet) you can use the \f(CW\*(C`ev_is_pending
518(watcher *)\*(C'\fR macro.
519.PP 1140.PP
520Each and every callback receives the event loop pointer as first, the 1141Each and every callback receives the event loop pointer as first, the
521registered watcher structure as second, and a bitset of received events as 1142registered watcher structure as second, and a bitset of received events as
522third argument. 1143third argument.
523.PP 1144.PP
… …
548The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread. 1169The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread.
549.ie n .IP """EV_CHILD""" 4 1170.ie n .IP """EV_CHILD""" 4
550.el .IP "\f(CWEV_CHILD\fR" 4 1171.el .IP "\f(CWEV_CHILD\fR" 4
551.IX Item "EV_CHILD" 1172.IX Item "EV_CHILD"
552The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change. 1173The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change.
1174.ie n .IP """EV_STAT""" 4
1175.el .IP "\f(CWEV_STAT\fR" 4
1176.IX Item "EV_STAT"
1177The path specified in the \f(CW\*(C`ev_stat\*(C'\fR watcher changed its attributes somehow.
553.ie n .IP """EV_IDLE""" 4 1178.ie n .IP """EV_IDLE""" 4
554.el .IP "\f(CWEV_IDLE\fR" 4 1179.el .IP "\f(CWEV_IDLE\fR" 4
555.IX Item "EV_IDLE" 1180.IX Item "EV_IDLE"
556The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do. 1181The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do.
557.ie n .IP """EV_PREPARE""" 4 1182.ie n .IP """EV_PREPARE""" 4
… …
567\&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any 1192\&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any
568received events. Callbacks of both watcher types can start and stop as 1193received events. Callbacks of both watcher types can start and stop as
569many watchers as they want, and all of them will be taken into account 1194many watchers as they want, and all of them will be taken into account
570(for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep 1195(for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep
571\&\f(CW\*(C`ev_loop\*(C'\fR from blocking). 1196\&\f(CW\*(C`ev_loop\*(C'\fR from blocking).
1197.ie n .IP """EV_EMBED""" 4
1198.el .IP "\f(CWEV_EMBED\fR" 4
1199.IX Item "EV_EMBED"
1200The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.
1201.ie n .IP """EV_FORK""" 4
1202.el .IP "\f(CWEV_FORK\fR" 4
1203.IX Item "EV_FORK"
1204The event loop has been resumed in the child process after fork (see
1205\&\f(CW\*(C`ev_fork\*(C'\fR).
1206.ie n .IP """EV_ASYNC""" 4
1207.el .IP "\f(CWEV_ASYNC\fR" 4
1208.IX Item "EV_ASYNC"
1209The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR).
1210.ie n .IP """EV_CUSTOM""" 4
1211.el .IP "\f(CWEV_CUSTOM\fR" 4
1212.IX Item "EV_CUSTOM"
1213Not ever sent (or otherwise used) by libev itself, but can be freely used
1214by libev users to signal watchers (e.g. via \f(CW\*(C`ev_feed_event\*(C'\fR).
572.ie n .IP """EV_ERROR""" 4 1215.ie n .IP """EV_ERROR""" 4
573.el .IP "\f(CWEV_ERROR\fR" 4 1216.el .IP "\f(CWEV_ERROR\fR" 4
574.IX Item "EV_ERROR" 1217.IX Item "EV_ERROR"
575An unspecified error has occured, the watcher has been stopped. This might 1218An unspecified error has occurred, the watcher has been stopped. This might
576happen because the watcher could not be properly started because libev 1219happen because the watcher could not be properly started because libev
577ran out of memory, a file descriptor was found to be closed or any other 1220ran out of memory, a file descriptor was found to be closed or any other
1221problem. Libev considers these application bugs.
1222.Sp
578problem. You best act on it by reporting the problem and somehow coping 1223You best act on it by reporting the problem and somehow coping with the
579with the watcher being stopped. 1224watcher being stopped. Note that well-written programs should not receive
1225an error ever, so when your watcher receives it, this usually indicates a
1226bug in your program.
580.Sp 1227.Sp
581Libev will usually signal a few \*(L"dummy\*(R" events together with an error, 1228Libev will usually signal a few \*(L"dummy\*(R" events together with an error, for
582for example it might indicate that a fd is readable or writable, and if 1229example it might indicate that a fd is readable or writable, and if your
583your callbacks is well-written it can just attempt the operation and cope 1230callbacks is well-written it can just attempt the operation and cope with
584with the error from \fIread()\fR or \fIwrite()\fR. This will not work in multithreaded 1231the error from \fIread()\fR or \fIwrite()\fR. This will not work in multi-threaded
585programs, though, so beware. 1232programs, though, as the fd could already be closed and reused for another
1233thing, so beware.
1234.SS "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0"
1235.IX Subsection "GENERIC WATCHER FUNCTIONS"
1236.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
1237.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
1238.IX Item "ev_init (ev_TYPE *watcher, callback)"
1239This macro initialises the generic portion of a watcher. The contents
1240of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
1241the generic parts of the watcher are initialised, you \fIneed\fR to call
1242the type-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR macro afterwards to initialise the
1243type-specific parts. For each type there is also a \f(CW\*(C`ev_TYPE_init\*(C'\fR macro
1244which rolls both calls into one.
1245.Sp
1246You can reinitialise a watcher at any time as long as it has been stopped
1247(or never started) and there are no pending events outstanding.
1248.Sp
1249The callback is always of type \f(CW\*(C`void (*)(struct ev_loop *loop, ev_TYPE *watcher,
1250int revents)\*(C'\fR.
1251.Sp
1252Example: Initialise an \f(CW\*(C`ev_io\*(C'\fR watcher in two steps.
1253.Sp
1254.Vb 3
1255\& ev_io w;
1256\& ev_init (&w, my_cb);
1257\& ev_io_set (&w, STDIN_FILENO, EV_READ);
1258.Ve
1259.ie n .IP """ev_TYPE_set"" (ev_TYPE *watcher, [args])" 4
1260.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *watcher, [args])" 4
1261.IX Item "ev_TYPE_set (ev_TYPE *watcher, [args])"
1262This macro initialises the type-specific parts of a watcher. You need to
1263call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
1264call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
1265macro on a watcher that is active (it can be pending, however, which is a
1266difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
1267.Sp
1268Although some watcher types do not have type-specific arguments
1269(e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
1270.Sp
1271See \f(CW\*(C`ev_init\*(C'\fR, above, for an example.
1272.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
1273.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
1274.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
1275This convenience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
1276calls into a single call. This is the most convenient method to initialise
1277a watcher. The same limitations apply, of course.
1278.Sp
1279Example: Initialise and set an \f(CW\*(C`ev_io\*(C'\fR watcher in one step.
1280.Sp
1281.Vb 1
1282\& ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1283.Ve
1284.ie n .IP """ev_TYPE_start"" (loop, ev_TYPE *watcher)" 4
1285.el .IP "\f(CWev_TYPE_start\fR (loop, ev_TYPE *watcher)" 4
1286.IX Item "ev_TYPE_start (loop, ev_TYPE *watcher)"
1287Starts (activates) the given watcher. Only active watchers will receive
1288events. If the watcher is already active nothing will happen.
1289.Sp
1290Example: Start the \f(CW\*(C`ev_io\*(C'\fR watcher that is being abused as example in this
1291whole section.
1292.Sp
1293.Vb 1
1294\& ev_io_start (EV_DEFAULT_UC, &w);
1295.Ve
1296.ie n .IP """ev_TYPE_stop"" (loop, ev_TYPE *watcher)" 4
1297.el .IP "\f(CWev_TYPE_stop\fR (loop, ev_TYPE *watcher)" 4
1298.IX Item "ev_TYPE_stop (loop, ev_TYPE *watcher)"
1299Stops the given watcher if active, and clears the pending status (whether
1300the watcher was active or not).
1301.Sp
1302It is possible that stopped watchers are pending \- for example,
1303non-repeating timers are being stopped when they become pending \- but
1304calling \f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor
1305pending. If you want to free or reuse the memory used by the watcher it is
1306therefore a good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
1307.IP "bool ev_is_active (ev_TYPE *watcher)" 4
1308.IX Item "bool ev_is_active (ev_TYPE *watcher)"
1309Returns a true value iff the watcher is active (i.e. it has been started
1310and not yet been stopped). As long as a watcher is active you must not modify
1311it.
1312.IP "bool ev_is_pending (ev_TYPE *watcher)" 4
1313.IX Item "bool ev_is_pending (ev_TYPE *watcher)"
1314Returns a true value iff the watcher is pending, (i.e. it has outstanding
1315events but its callback has not yet been invoked). As long as a watcher
1316is pending (but not active) you must not call an init function on it (but
1317\&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe), you must not change its priority, and you must
1318make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR
1319it).
1320.IP "callback ev_cb (ev_TYPE *watcher)" 4
1321.IX Item "callback ev_cb (ev_TYPE *watcher)"
1322Returns the callback currently set on the watcher.
1323.IP "ev_cb_set (ev_TYPE *watcher, callback)" 4
1324.IX Item "ev_cb_set (ev_TYPE *watcher, callback)"
1325Change the callback. You can change the callback at virtually any time
1326(modulo threads).
1327.IP "ev_set_priority (ev_TYPE *watcher, int priority)" 4
1328.IX Item "ev_set_priority (ev_TYPE *watcher, int priority)"
1329.PD 0
1330.IP "int ev_priority (ev_TYPE *watcher)" 4
1331.IX Item "int ev_priority (ev_TYPE *watcher)"
1332.PD
1333Set and query the priority of the watcher. The priority is a small
1334integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR
1335(default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked
1336before watchers with lower priority, but priority will not keep watchers
1337from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
1338.Sp
1339If you need to suppress invocation when higher priority events are pending
1340you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
1341.Sp
1342You \fImust not\fR change the priority of a watcher as long as it is active or
1343pending.
1344.Sp
1345Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
1346fine, as long as you do not mind that the priority value you query might
1347or might not have been clamped to the valid range.
1348.Sp
1349The default priority used by watchers when no priority has been set is
1350always \f(CW0\fR, which is supposed to not be too high and not be too low :).
1351.Sp
1352See \*(L"\s-1WATCHER\s0 \s-1PRIORITY\s0 \s-1MODELS\s0\*(R", below, for a more thorough treatment of
1353priorities.
1354.IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
1355.IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
1356Invoke the \f(CW\*(C`watcher\*(C'\fR with the given \f(CW\*(C`loop\*(C'\fR and \f(CW\*(C`revents\*(C'\fR. Neither
1357\&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback
1358can deal with that fact, as both are simply passed through to the
1359callback.
1360.IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
1361.IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
1362If the watcher is pending, this function clears its pending status and
1363returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the
1364watcher isn't pending it does nothing and returns \f(CW0\fR.
1365.Sp
1366Sometimes it can be useful to \*(L"poll\*(R" a watcher instead of waiting for its
1367callback to be invoked, which can be accomplished with this function.
1368.IP "ev_feed_event (loop, ev_TYPE *watcher, int revents)" 4
1369.IX Item "ev_feed_event (loop, ev_TYPE *watcher, int revents)"
1370Feeds the given event set into the event loop, as if the specified event
1371had happened for the specified watcher (which must be a pointer to an
1372initialised but not necessarily started event watcher). Obviously you must
1373not free the watcher as long as it has pending events.
1374.Sp
1375Stopping the watcher, letting libev invoke it, or calling
1376\&\f(CW\*(C`ev_clear_pending\*(C'\fR will clear the pending event, even if the watcher was
1377not started in the first place.
1378.Sp
1379See also \f(CW\*(C`ev_feed_fd_event\*(C'\fR and \f(CW\*(C`ev_feed_signal_event\*(C'\fR for related
1380functions that do not need a watcher.
586.Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0" 1381.SS "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0"
587.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER" 1382.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
588Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change 1383Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change
589and read at any time, libev will completely ignore it. This can be used 1384and read at any time: libev will completely ignore it. This can be used
590to associate arbitrary data with your watcher. If you need more data and 1385to associate arbitrary data with your watcher. If you need more data and
591don't want to allocate memory and store a pointer to it in that data 1386don't want to allocate memory and store a pointer to it in that data
592member, you can also \*(L"subclass\*(R" the watcher type and provide your own 1387member, you can also \*(L"subclass\*(R" the watcher type and provide your own
593data: 1388data:
594.PP 1389.PP
595.Vb 7 1390.Vb 7
596\& struct my_io 1391\& struct my_io
597\& { 1392\& {
598\& struct ev_io io; 1393\& ev_io io;
599\& int otherfd; 1394\& int otherfd;
600\& void *somedata; 1395\& void *somedata;
601\& struct whatever *mostinteresting; 1396\& struct whatever *mostinteresting;
602\& } 1397\& };
1398\&
1399\& ...
1400\& struct my_io w;
1401\& ev_io_init (&w.io, my_cb, fd, EV_READ);
603.Ve 1402.Ve
604.PP 1403.PP
605And since your callback will be called with a pointer to the watcher, you 1404And since your callback will be called with a pointer to the watcher, you
606can cast it back to your own type: 1405can cast it back to your own type:
607.PP 1406.PP
608.Vb 5 1407.Vb 5
609\& static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents) 1408\& static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
610\& { 1409\& {
611\& struct my_io *w = (struct my_io *)w_; 1410\& struct my_io *w = (struct my_io *)w_;
612\& ... 1411\& ...
613\& } 1412\& }
614.Ve 1413.Ve
615.PP 1414.PP
616More interesting and less C\-conformant ways of catsing your callback type 1415More interesting and less C\-conformant ways of casting your callback type
617have been omitted.... 1416instead have been omitted.
1417.PP
1418Another common scenario is to use some data structure with multiple
1419embedded watchers:
1420.PP
1421.Vb 6
1422\& struct my_biggy
1423\& {
1424\& int some_data;
1425\& ev_timer t1;
1426\& ev_timer t2;
1427\& }
1428.Ve
1429.PP
1430In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more
1431complicated: Either you store the address of your \f(CW\*(C`my_biggy\*(C'\fR struct
1432in the \f(CW\*(C`data\*(C'\fR member of the watcher (for woozies), or you need to use
1433some pointer arithmetic using \f(CW\*(C`offsetof\*(C'\fR inside your watchers (for real
1434programmers):
1435.PP
1436.Vb 1
1437\& #include <stddef.h>
1438\&
1439\& static void
1440\& t1_cb (EV_P_ ev_timer *w, int revents)
1441\& {
1442\& struct my_biggy big = (struct my_biggy *)
1443\& (((char *)w) \- offsetof (struct my_biggy, t1));
1444\& }
1445\&
1446\& static void
1447\& t2_cb (EV_P_ ev_timer *w, int revents)
1448\& {
1449\& struct my_biggy big = (struct my_biggy *)
1450\& (((char *)w) \- offsetof (struct my_biggy, t2));
1451\& }
1452.Ve
1453.SS "\s-1WATCHER\s0 \s-1PRIORITY\s0 \s-1MODELS\s0"
1454.IX Subsection "WATCHER PRIORITY MODELS"
1455Many event loops support \fIwatcher priorities\fR, which are usually small
1456integers that influence the ordering of event callback invocation
1457between watchers in some way, all else being equal.
1458.PP
1459In libev, Watcher priorities can be set using \f(CW\*(C`ev_set_priority\*(C'\fR. See its
1460description for the more technical details such as the actual priority
1461range.
1462.PP
1463There are two common ways how these these priorities are being interpreted
1464by event loops:
1465.PP
1466In the more common lock-out model, higher priorities \*(L"lock out\*(R" invocation
1467of lower priority watchers, which means as long as higher priority
1468watchers receive events, lower priority watchers are not being invoked.
1469.PP
1470The less common only-for-ordering model uses priorities solely to order
1471callback invocation within a single event loop iteration: Higher priority
1472watchers are invoked before lower priority ones, but they all get invoked
1473before polling for new events.
1474.PP
1475Libev uses the second (only-for-ordering) model for all its watchers
1476except for idle watchers (which use the lock-out model).
1477.PP
1478The rationale behind this is that implementing the lock-out model for
1479watchers is not well supported by most kernel interfaces, and most event
1480libraries will just poll for the same events again and again as long as
1481their callbacks have not been executed, which is very inefficient in the
1482common case of one high-priority watcher locking out a mass of lower
1483priority ones.
1484.PP
1485Static (ordering) priorities are most useful when you have two or more
1486watchers handling the same resource: a typical usage example is having an
1487\&\f(CW\*(C`ev_io\*(C'\fR watcher to receive data, and an associated \f(CW\*(C`ev_timer\*(C'\fR to handle
1488timeouts. Under load, data might be received while the program handles
1489other jobs, but since timers normally get invoked first, the timeout
1490handler will be executed before checking for data. In that case, giving
1491the timer a lower priority than the I/O watcher ensures that I/O will be
1492handled first even under adverse conditions (which is usually, but not
1493always, what you want).
1494.PP
1495Since idle watchers use the \*(L"lock-out\*(R" model, meaning that idle watchers
1496will only be executed when no same or higher priority watchers have
1497received events, they can be used to implement the \*(L"lock-out\*(R" model when
1498required.
1499.PP
1500For example, to emulate how many other event libraries handle priorities,
1501you can associate an \f(CW\*(C`ev_idle\*(C'\fR watcher to each such watcher, and in
1502the normal watcher callback, you just start the idle watcher. The real
1503processing is done in the idle watcher callback. This causes libev to
1504continously poll and process kernel event data for the watcher, but when
1505the lock-out case is known to be rare (which in turn is rare :), this is
1506workable.
1507.PP
1508Usually, however, the lock-out model implemented that way will perform
1509miserably under the type of load it was designed to handle. In that case,
1510it might be preferable to stop the real watcher before starting the
1511idle watcher, so the kernel will not have to process the event in case
1512the actual processing will be delayed for considerable time.
1513.PP
1514Here is an example of an I/O watcher that should run at a strictly lower
1515priority than the default, and which should only process data when no
1516other events are pending:
1517.PP
1518.Vb 2
1519\& ev_idle idle; // actual processing watcher
1520\& ev_io io; // actual event watcher
1521\&
1522\& static void
1523\& io_cb (EV_P_ ev_io *w, int revents)
1524\& {
1525\& // stop the I/O watcher, we received the event, but
1526\& // are not yet ready to handle it.
1527\& ev_io_stop (EV_A_ w);
1528\&
1529\& // start the idle watcher to ahndle the actual event.
1530\& // it will not be executed as long as other watchers
1531\& // with the default priority are receiving events.
1532\& ev_idle_start (EV_A_ &idle);
1533\& }
1534\&
1535\& static void
1536\& idle_cb (EV_P_ ev_idle *w, int revents)
1537\& {
1538\& // actual processing
1539\& read (STDIN_FILENO, ...);
1540\&
1541\& // have to start the I/O watcher again, as
1542\& // we have handled the event
1543\& ev_io_start (EV_P_ &io);
1544\& }
1545\&
1546\& // initialisation
1547\& ev_idle_init (&idle, idle_cb);
1548\& ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
1549\& ev_io_start (EV_DEFAULT_ &io);
1550.Ve
1551.PP
1552In the \*(L"real\*(R" world, it might also be beneficial to start a timer, so that
1553low-priority connections can not be locked out forever under load. This
1554enables your program to keep a lower latency for important connections
1555during short periods of high load, while not completely locking out less
1556important ones.
618.SH "WATCHER TYPES" 1557.SH "WATCHER TYPES"
619.IX Header "WATCHER TYPES" 1558.IX Header "WATCHER TYPES"
620This section describes each watcher in detail, but will not repeat 1559This section describes each watcher in detail, but will not repeat
621information given in the last section. 1560information given in the last section. Any initialisation/set macros,
1561functions and members specific to the watcher type are explained.
1562.PP
1563Members are additionally marked with either \fI[read\-only]\fR, meaning that,
1564while the watcher is active, you can look at the member and expect some
1565sensible content, but you must not modify it (you can modify it while the
1566watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
1567means you can expect it to have some sensible content while the watcher
1568is active, but you can also modify it. Modifying it may not do something
1569sensible or take immediate effect (or do anything at all), but libev will
1570not crash or malfunction in any way.
622.ie n .Sh """ev_io"" \- is this file descriptor readable or writable" 1571.ie n .SS """ev_io"" \- is this file descriptor readable or writable?"
623.el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable" 1572.el .SS "\f(CWev_io\fP \- is this file descriptor readable or writable?"
624.IX Subsection "ev_io - is this file descriptor readable or writable" 1573.IX Subsection "ev_io - is this file descriptor readable or writable?"
625I/O watchers check whether a file descriptor is readable or writable 1574I/O watchers check whether a file descriptor is readable or writable
626in each iteration of the event loop (This behaviour is called 1575in each iteration of the event loop, or, more precisely, when reading
627level-triggering because you keep receiving events as long as the 1576would not block the process and writing would at least be able to write
628condition persists. Remember you can stop the watcher if you don't want to 1577some data. This behaviour is called level-triggering because you keep
629act on the event and neither want to receive future events). 1578receiving events as long as the condition persists. Remember you can stop
1579the watcher if you don't want to act on the event and neither want to
1580receive future events.
630.PP 1581.PP
631In general you can register as many read and/or write event watchers per 1582In general you can register as many read and/or write event watchers per
632fd as you want (as long as you don't confuse yourself). Setting all file 1583fd as you want (as long as you don't confuse yourself). Setting all file
633descriptors to non-blocking mode is also usually a good idea (but not 1584descriptors to non-blocking mode is also usually a good idea (but not
634required if you know what you are doing). 1585required if you know what you are doing).
635.PP 1586.PP
636You have to be careful with dup'ed file descriptors, though. Some backends 1587If you cannot use non-blocking mode, then force the use of a
637(the linux epoll backend is a notable example) cannot handle dup'ed file 1588known-to-be-good backend (at the time of this writing, this includes only
638descriptors correctly if you register interest in two or more fds pointing 1589\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and \f(CW\*(C`EVBACKEND_POLL\*(C'\fR). The same applies to file
639to the same underlying file/socket etc. description (that is, they share 1590descriptors for which non-blocking operation makes no sense (such as
640the same underlying \*(L"file open\*(R"). 1591files) \- libev doesn't guarentee any specific behaviour in that case.
641.PP 1592.PP
642If you must do this, then force the use of a known-to-be-good backend 1593Another thing you have to watch out for is that it is quite easy to
643(at the time of this writing, this includes only \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and 1594receive \*(L"spurious\*(R" readiness notifications, that is your callback might
1595be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block
1596because there is no data. Not only are some backends known to create a
1597lot of those (for example Solaris ports), it is very easy to get into
1598this situation even with a relatively standard program structure. Thus
1599it is best to always use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning
1600\&\f(CW\*(C`EAGAIN\*(C'\fR is far preferable to a program hanging until some data arrives.
1601.PP
1602If you cannot run the fd in non-blocking mode (for example you should
1603not play around with an Xlib connection), then you have to separately
1604re-test whether a file descriptor is really ready with a known-to-be good
1605interface such as poll (fortunately in our Xlib example, Xlib already
1606does this on its own, so its quite safe to use). Some people additionally
1607use \f(CW\*(C`SIGALRM\*(C'\fR and an interval timer, just to be sure you won't block
1608indefinitely.
1609.PP
1610But really, best use non-blocking mode.
1611.PP
1612\fIThe special problem of disappearing file descriptors\fR
1613.IX Subsection "The special problem of disappearing file descriptors"
1614.PP
1615Some backends (e.g. kqueue, epoll) need to be told about closing a file
1616descriptor (either due to calling \f(CW\*(C`close\*(C'\fR explicitly or any other means,
1617such as \f(CW\*(C`dup2\*(C'\fR). The reason is that you register interest in some file
1618descriptor, but when it goes away, the operating system will silently drop
1619this interest. If another file descriptor with the same number then is
1620registered with libev, there is no efficient way to see that this is, in
1621fact, a different file descriptor.
1622.PP
1623To avoid having to explicitly tell libev about such cases, libev follows
1624the following policy: Each time \f(CW\*(C`ev_io_set\*(C'\fR is being called, libev
1625will assume that this is potentially a new file descriptor, otherwise
1626it is assumed that the file descriptor stays the same. That means that
1627you \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
1628descriptor even if the file descriptor number itself did not change.
1629.PP
1630This is how one would do it normally anyway, the important point is that
1631the libev application should not optimise around libev but should leave
1632optimisations to libev.
1633.PP
1634\fIThe special problem of dup'ed file descriptors\fR
1635.IX Subsection "The special problem of dup'ed file descriptors"
1636.PP
1637Some backends (e.g. epoll), cannot register events for file descriptors,
1638but only events for the underlying file descriptions. That means when you
1639have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register
1640events for them, only one file descriptor might actually receive events.
1641.PP
1642There is no workaround possible except not registering events
1643for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
1644\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1645.PP
1646\fIThe special problem of fork\fR
1647.IX Subsection "The special problem of fork"
1648.PP
1649Some backends (epoll, kqueue) do not support \f(CW\*(C`fork ()\*(C'\fR at all or exhibit
1650useless behaviour. Libev fully supports fork, but needs to be told about
1651it in the child.
1652.PP
1653To support fork in your programs, you either have to call
1654\&\f(CW\*(C`ev_default_fork ()\*(C'\fR or \f(CW\*(C`ev_loop_fork ()\*(C'\fR after a fork in the child,
1655enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or
644\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR). 1656\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1657.PP
1658\fIThe special problem of \s-1SIGPIPE\s0\fR
1659.IX Subsection "The special problem of SIGPIPE"
1660.PP
1661While not really specific to libev, it is easy to forget about \f(CW\*(C`SIGPIPE\*(C'\fR:
1662when writing to a pipe whose other end has been closed, your program gets
1663sent a \s-1SIGPIPE\s0, which, by default, aborts your program. For most programs
1664this is sensible behaviour, for daemons, this is usually undesirable.
1665.PP
1666So when you encounter spurious, unexplained daemon exits, make sure you
1667ignore \s-1SIGPIPE\s0 (and maybe make sure you log the exit status of your daemon
1668somewhere, as that would have given you a big clue).
1669.PP
1670\fIWatcher-Specific Functions\fR
1671.IX Subsection "Watcher-Specific Functions"
645.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4 1672.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
646.IX Item "ev_io_init (ev_io *, callback, int fd, int events)" 1673.IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
647.PD 0 1674.PD 0
648.IP "ev_io_set (ev_io *, int fd, int events)" 4 1675.IP "ev_io_set (ev_io *, int fd, int events)" 4
649.IX Item "ev_io_set (ev_io *, int fd, int events)" 1676.IX Item "ev_io_set (ev_io *, int fd, int events)"
650.PD 1677.PD
651Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The fd is the file descriptor to rceeive 1678Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to
652events 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 | 1679receive 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
653EV_WRITE\*(C'\fR to receive the given events. 1680\&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR, to express the desire to receive the given events.
654.Sp 1681.IP "int fd [read\-only]" 4
655Please note that most of the more scalable backend mechanisms (for example 1682.IX Item "int fd [read-only]"
656epoll and solaris ports) can result in spurious readyness notifications 1683The file descriptor being watched.
657for file descriptors, so you practically need to use non-blocking I/O (and 1684.IP "int events [read\-only]" 4
658treat callback invocation as hint only), or retest separately with a safe 1685.IX Item "int events [read-only]"
659interface before doing I/O (XLib can do this), or force the use of either 1686The events being watched.
660\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR, which don't suffer from this 1687.PP
661problem. Also note that it is quite easy to have your callback invoked 1688\fIExamples\fR
662when the readyness condition is no longer valid even when employing 1689.IX Subsection "Examples"
663typical ways of handling events, so its a good idea to use non-blocking 1690.PP
664I/O unconditionally. 1691Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
1692readable, but only once. Since it is likely line-buffered, you could
1693attempt to read a whole line in the callback.
1694.PP
1695.Vb 6
1696\& static void
1697\& stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1698\& {
1699\& ev_io_stop (loop, w);
1700\& .. read from stdin here (or from w\->fd) and handle any I/O errors
1701\& }
1702\&
1703\& ...
1704\& struct ev_loop *loop = ev_default_init (0);
1705\& ev_io stdin_readable;
1706\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1707\& ev_io_start (loop, &stdin_readable);
1708\& ev_loop (loop, 0);
1709.Ve
665.ie n .Sh """ev_timer"" \- relative and optionally recurring timeouts" 1710.ie n .SS """ev_timer"" \- relative and optionally repeating timeouts"
666.el .Sh "\f(CWev_timer\fP \- relative and optionally recurring timeouts" 1711.el .SS "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
667.IX Subsection "ev_timer - relative and optionally recurring timeouts" 1712.IX Subsection "ev_timer - relative and optionally repeating timeouts"
668Timer watchers are simple relative timers that generate an event after a 1713Timer watchers are simple relative timers that generate an event after a
669given time, and optionally repeating in regular intervals after that. 1714given time, and optionally repeating in regular intervals after that.
670.PP 1715.PP
671The timers are based on real time, that is, if you register an event that 1716The timers are based on real time, that is, if you register an event that
672times out after an hour and you reset your system clock to last years 1717times out after an hour and you reset your system clock to January last
673time, it will still time out after (roughly) and hour. \*(L"Roughly\*(R" because 1718year, it will still time out after (roughly) one hour. \*(L"Roughly\*(R" because
674detecting time jumps is hard, and some inaccuracies are unavoidable (the 1719detecting time jumps is hard, and some inaccuracies are unavoidable (the
675monotonic clock option helps a lot here). 1720monotonic clock option helps a lot here).
1721.PP
1722The callback is guaranteed to be invoked only \fIafter\fR its timeout has
1723passed (not \fIat\fR, so on systems with very low-resolution clocks this
1724might introduce a small delay). If multiple timers become ready during the
1725same loop iteration then the ones with earlier time-out values are invoked
1726before ones of the same priority with later time-out values (but this is
1727no longer true when a callback calls \f(CW\*(C`ev_loop\*(C'\fR recursively).
1728.PP
1729\fIBe smart about timeouts\fR
1730.IX Subsection "Be smart about timeouts"
1731.PP
1732Many real-world problems involve some kind of timeout, usually for error
1733recovery. A typical example is an \s-1HTTP\s0 request \- if the other side hangs,
1734you want to raise some error after a while.
1735.PP
1736What follows are some ways to handle this problem, from obvious and
1737inefficient to smart and efficient.
1738.PP
1739In the following, a 60 second activity timeout is assumed \- a timeout that
1740gets reset to 60 seconds each time there is activity (e.g. each time some
1741data or other life sign was received).
1742.IP "1. Use a timer and stop, reinitialise and start it on activity." 4
1743.IX Item "1. Use a timer and stop, reinitialise and start it on activity."
1744This is the most obvious, but not the most simple way: In the beginning,
1745start the watcher:
1746.Sp
1747.Vb 2
1748\& ev_timer_init (timer, callback, 60., 0.);
1749\& ev_timer_start (loop, timer);
1750.Ve
1751.Sp
1752Then, each time there is some activity, \f(CW\*(C`ev_timer_stop\*(C'\fR it, initialise it
1753and start it again:
1754.Sp
1755.Vb 3
1756\& ev_timer_stop (loop, timer);
1757\& ev_timer_set (timer, 60., 0.);
1758\& ev_timer_start (loop, timer);
1759.Ve
1760.Sp
1761This is relatively simple to implement, but means that each time there is
1762some activity, libev will first have to remove the timer from its internal
1763data structure and then add it again. Libev tries to be fast, but it's
1764still not a constant-time operation.
1765.ie n .IP "2. Use a timer and re-start it with ""ev_timer_again"" inactivity." 4
1766.el .IP "2. Use a timer and re-start it with \f(CWev_timer_again\fR inactivity." 4
1767.IX Item "2. Use a timer and re-start it with ev_timer_again inactivity."
1768This is the easiest way, and involves using \f(CW\*(C`ev_timer_again\*(C'\fR instead of
1769\&\f(CW\*(C`ev_timer_start\*(C'\fR.
1770.Sp
1771To implement this, configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value
1772of \f(CW60\fR and then call \f(CW\*(C`ev_timer_again\*(C'\fR at start and each time you
1773successfully read or write some data. If you go into an idle state where
1774you do not expect data to travel on the socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR
1775the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will automatically restart it if need be.
1776.Sp
1777That means you can ignore both the \f(CW\*(C`ev_timer_start\*(C'\fR function and the
1778\&\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
1779member and \f(CW\*(C`ev_timer_again\*(C'\fR.
1780.Sp
1781At start:
1782.Sp
1783.Vb 3
1784\& ev_init (timer, callback);
1785\& timer\->repeat = 60.;
1786\& ev_timer_again (loop, timer);
1787.Ve
1788.Sp
1789Each time there is some activity:
1790.Sp
1791.Vb 1
1792\& ev_timer_again (loop, timer);
1793.Ve
1794.Sp
1795It is even possible to change the time-out on the fly, regardless of
1796whether the watcher is active or not:
1797.Sp
1798.Vb 2
1799\& timer\->repeat = 30.;
1800\& ev_timer_again (loop, timer);
1801.Ve
1802.Sp
1803This is slightly more efficient then stopping/starting the timer each time
1804you want to modify its timeout value, as libev does not have to completely
1805remove and re-insert the timer from/into its internal data structure.
1806.Sp
1807It is, however, even simpler than the \*(L"obvious\*(R" way to do it.
1808.IP "3. Let the timer time out, but then re-arm it as required." 4
1809.IX Item "3. Let the timer time out, but then re-arm it as required."
1810This method is more tricky, but usually most efficient: Most timeouts are
1811relatively long compared to the intervals between other activity \- in
1812our example, within 60 seconds, there are usually many I/O events with
1813associated activity resets.
1814.Sp
1815In this case, it would be more efficient to leave the \f(CW\*(C`ev_timer\*(C'\fR alone,
1816but remember the time of last activity, and check for a real timeout only
1817within the callback:
1818.Sp
1819.Vb 1
1820\& ev_tstamp last_activity; // time of last activity
1821\&
1822\& static void
1823\& callback (EV_P_ ev_timer *w, int revents)
1824\& {
1825\& ev_tstamp now = ev_now (EV_A);
1826\& ev_tstamp timeout = last_activity + 60.;
1827\&
1828\& // if last_activity + 60. is older than now, we did time out
1829\& if (timeout < now)
1830\& {
1831\& // timeout occured, take action
1832\& }
1833\& else
1834\& {
1835\& // callback was invoked, but there was some activity, re\-arm
1836\& // the watcher to fire in last_activity + 60, which is
1837\& // guaranteed to be in the future, so "again" is positive:
1838\& w\->repeat = timeout \- now;
1839\& ev_timer_again (EV_A_ w);
1840\& }
1841\& }
1842.Ve
1843.Sp
1844To summarise the callback: first calculate the real timeout (defined
1845as \*(L"60 seconds after the last activity\*(R"), then check if that time has
1846been reached, which means something \fIdid\fR, in fact, time out. Otherwise
1847the callback was invoked too early (\f(CW\*(C`timeout\*(C'\fR is in the future), so
1848re-schedule the timer to fire at that future time, to see if maybe we have
1849a timeout then.
1850.Sp
1851Note how \f(CW\*(C`ev_timer_again\*(C'\fR is used, taking advantage of the
1852\&\f(CW\*(C`ev_timer_again\*(C'\fR optimisation when the timer is already running.
1853.Sp
1854This scheme causes more callback invocations (about one every 60 seconds
1855minus half the average time between activity), but virtually no calls to
1856libev to change the timeout.
1857.Sp
1858To start the timer, simply initialise the watcher and set \f(CW\*(C`last_activity\*(C'\fR
1859to the current time (meaning we just have some activity :), then call the
1860callback, which will \*(L"do the right thing\*(R" and start the timer:
1861.Sp
1862.Vb 3
1863\& ev_init (timer, callback);
1864\& last_activity = ev_now (loop);
1865\& callback (loop, timer, EV_TIMEOUT);
1866.Ve
1867.Sp
1868And when there is some activity, simply store the current time in
1869\&\f(CW\*(C`last_activity\*(C'\fR, no libev calls at all:
1870.Sp
1871.Vb 1
1872\& last_actiivty = ev_now (loop);
1873.Ve
1874.Sp
1875This technique is slightly more complex, but in most cases where the
1876time-out is unlikely to be triggered, much more efficient.
1877.Sp
1878Changing the timeout is trivial as well (if it isn't hard-coded in the
1879callback :) \- just change the timeout and invoke the callback, which will
1880fix things for you.
1881.IP "4. Wee, just use a double-linked list for your timeouts." 4
1882.IX Item "4. Wee, just use a double-linked list for your timeouts."
1883If there is not one request, but many thousands (millions...), all
1884employing some kind of timeout with the same timeout value, then one can
1885do even better:
1886.Sp
1887When starting the timeout, calculate the timeout value and put the timeout
1888at the \fIend\fR of the list.
1889.Sp
1890Then use an \f(CW\*(C`ev_timer\*(C'\fR to fire when the timeout at the \fIbeginning\fR of
1891the list is expected to fire (for example, using the technique #3).
1892.Sp
1893When there is some activity, remove the timer from the list, recalculate
1894the timeout, append it to the end of the list again, and make sure to
1895update the \f(CW\*(C`ev_timer\*(C'\fR if it was taken from the beginning of the list.
1896.Sp
1897This way, one can manage an unlimited number of timeouts in O(1) time for
1898starting, stopping and updating the timers, at the expense of a major
1899complication, and having to use a constant timeout. The constant timeout
1900ensures that the list stays sorted.
1901.PP
1902So which method the best?
1903.PP
1904Method #2 is a simple no-brain-required solution that is adequate in most
1905situations. Method #3 requires a bit more thinking, but handles many cases
1906better, and isn't very complicated either. In most case, choosing either
1907one is fine, with #3 being better in typical situations.
1908.PP
1909Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
1910rather complicated, but extremely efficient, something that really pays
1911off after the first million or so of active timers, i.e. it's usually
1912overkill :)
1913.PP
1914\fIThe special problem of time updates\fR
1915.IX Subsection "The special problem of time updates"
1916.PP
1917Establishing the current time is a costly operation (it usually takes at
1918least two system calls): \s-1EV\s0 therefore updates its idea of the current
1919time only before and after \f(CW\*(C`ev_loop\*(C'\fR collects new events, which causes a
1920growing difference between \f(CW\*(C`ev_now ()\*(C'\fR and \f(CW\*(C`ev_time ()\*(C'\fR when handling
1921lots of events in one iteration.
676.PP 1922.PP
677The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR 1923The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
678time. This is usually the right thing as this timestamp refers to the time 1924time. This is usually the right thing as this timestamp refers to the time
679of the event triggering whatever timeout you are modifying/starting. If 1925of the event triggering whatever timeout you are modifying/starting. If
680you suspect event processing to be delayed and you \fIneed\fR to base the timeout 1926you suspect event processing to be delayed and you \fIneed\fR to base the
681on the current time, use something like this to adjust for this: 1927timeout on the current time, use something like this to adjust for this:
682.PP 1928.PP
683.Vb 1 1929.Vb 1
684\& ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); 1930\& ev_timer_set (&timer, after + ev_now () \- ev_time (), 0.);
685.Ve 1931.Ve
686.PP 1932.PP
687The callback is guarenteed to be invoked only when its timeout has passed, 1933If the event loop is suspended for a long time, you can also force an
688but if multiple timers become ready during the same loop iteration then 1934update of the time returned by \f(CW\*(C`ev_now ()\*(C'\fR by calling \f(CW\*(C`ev_now_update
689order of execution is undefined. 1935()\*(C'\fR.
1936.PP
1937\fIThe special problems of suspended animation\fR
1938.IX Subsection "The special problems of suspended animation"
1939.PP
1940When you leave the server world it is quite customary to hit machines that
1941can suspend/hibernate \- what happens to the clocks during such a suspend?
1942.PP
1943Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
1944all processes, while the clocks (\f(CW\*(C`times\*(C'\fR, \f(CW\*(C`CLOCK_MONOTONIC\*(C'\fR) continue
1945to run until the system is suspended, but they will not advance while the
1946system is suspended. That means, on resume, it will be as if the program
1947was frozen for a few seconds, but the suspend time will not be counted
1948towards \f(CW\*(C`ev_timer\*(C'\fR when a monotonic clock source is used. The real time
1949clock advanced as expected, but if it is used as sole clocksource, then a
1950long suspend would be detected as a time jump by libev, and timers would
1951be adjusted accordingly.
1952.PP
1953I would not be surprised to see different behaviour in different between
1954operating systems, \s-1OS\s0 versions or even different hardware.
1955.PP
1956The other form of suspend (job control, or sending a \s-1SIGSTOP\s0) will see a
1957time jump in the monotonic clocks and the realtime clock. If the program
1958is suspended for a very long time, and monotonic clock sources are in use,
1959then you can expect \f(CW\*(C`ev_timer\*(C'\fRs to expire as the full suspension time
1960will be counted towards the timers. When no monotonic clock source is in
1961use, then libev will again assume a timejump and adjust accordingly.
1962.PP
1963It might be beneficial for this latter case to call \f(CW\*(C`ev_suspend\*(C'\fR
1964and \f(CW\*(C`ev_resume\*(C'\fR in code that handles \f(CW\*(C`SIGTSTP\*(C'\fR, to at least get
1965deterministic behaviour in this case (you can do nothing against
1966\&\f(CW\*(C`SIGSTOP\*(C'\fR).
1967.PP
1968\fIWatcher-Specific Functions and Data Members\fR
1969.IX Subsection "Watcher-Specific Functions and Data Members"
690.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4 1970.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
691.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 1971.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
692.PD 0 1972.PD 0
693.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4 1973.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
694.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 1974.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
695.PD 1975.PD
696Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR is 1976Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR
697\&\f(CW0.\fR, then it will automatically be stopped. If it is positive, then the 1977is \f(CW0.\fR, then it will automatically be stopped once the timeout is
698timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds 1978reached. If it is positive, then the timer will automatically be
699later, again, and again, until stopped manually. 1979configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds later, again, and again,
1980until stopped manually.
700.Sp 1981.Sp
701The timer itself will do a best-effort at avoiding drift, that is, if you 1982The timer itself will do a best-effort at avoiding drift, that is, if
702configure a timer to trigger every 10 seconds, then it will trigger at 1983you configure a timer to trigger every 10 seconds, then it will normally
703exactly 10 second intervals. If, however, your program cannot keep up with 1984trigger at exactly 10 second intervals. If, however, your program cannot
704the timer (because it takes longer than those 10 seconds to do stuff) the 1985keep up with the timer (because it takes longer than those 10 seconds to
705timer will not fire more than once per event loop iteration. 1986do stuff) the timer will not fire more than once per event loop iteration.
706.IP "ev_timer_again (loop)" 4 1987.IP "ev_timer_again (loop, ev_timer *)" 4
707.IX Item "ev_timer_again (loop)" 1988.IX Item "ev_timer_again (loop, ev_timer *)"
708This will act as if the timer timed out and restart it again if it is 1989This will act as if the timer timed out and restart it again if it is
709repeating. The exact semantics are: 1990repeating. The exact semantics are:
710.Sp 1991.Sp
1992If the timer is pending, its pending status is cleared.
1993.Sp
711If the timer is started but nonrepeating, stop it. 1994If the timer is started but non-repeating, stop it (as if it timed out).
712.Sp 1995.Sp
713If the timer is repeating, either start it if necessary (with the repeat 1996If the timer is repeating, either start it if necessary (with the
714value), or reset the running timer to the repeat value. 1997\&\f(CW\*(C`repeat\*(C'\fR value), or reset the running timer to the \f(CW\*(C`repeat\*(C'\fR value.
715.Sp 1998.Sp
716This sounds a bit complicated, but here is a useful and typical 1999This sounds a bit complicated, see \*(L"Be smart about timeouts\*(R", above, for a
717example: Imagine you have a tcp connection and you want a so-called idle 2000usage example.
718timeout, that is, you want to be called when there have been, say, 60 2001.IP "ev_tstamp ev_timer_remaining (loop, ev_timer *)" 4
719seconds of inactivity on the socket. The easiest way to do this is to 2002.IX Item "ev_tstamp ev_timer_remaining (loop, ev_timer *)"
720configure an \f(CW\*(C`ev_timer\*(C'\fR with after=repeat=60 and calling ev_timer_again each 2003Returns the remaining time until a timer fires. If the timer is active,
721time you successfully read or write some data. If you go into an idle 2004then this time is relative to the current event loop time, otherwise it's
722state where you do not expect data to travel on the socket, you can stop 2005the timeout value currently configured.
723the timer, and again will automatically restart it if need be. 2006.Sp
2007That is, after an \f(CW\*(C`ev_timer_set (w, 5, 7)\*(C'\fR, \f(CW\*(C`ev_timer_remaining\*(C'\fR returns
2008\&\f(CW5\fR. When the timer is started and one second passes, \f(CW\*(C`ev_timer_remain\*(C'\fR
2009will return \f(CW4\fR. When the timer expires and is restarted, it will return
2010roughly \f(CW7\fR (likely slightly less as callback invocation takes some time,
2011too), and so on.
2012.IP "ev_tstamp repeat [read\-write]" 4
2013.IX Item "ev_tstamp repeat [read-write]"
2014The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
2015or \f(CW\*(C`ev_timer_again\*(C'\fR is called, and determines the next timeout (if any),
2016which is also when any modifications are taken into account.
2017.PP
2018\fIExamples\fR
2019.IX Subsection "Examples"
2020.PP
2021Example: Create a timer that fires after 60 seconds.
2022.PP
2023.Vb 5
2024\& static void
2025\& one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
2026\& {
2027\& .. one minute over, w is actually stopped right here
2028\& }
2029\&
2030\& ev_timer mytimer;
2031\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
2032\& ev_timer_start (loop, &mytimer);
2033.Ve
2034.PP
2035Example: Create a timeout timer that times out after 10 seconds of
2036inactivity.
2037.PP
2038.Vb 5
2039\& static void
2040\& timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
2041\& {
2042\& .. ten seconds without any activity
2043\& }
2044\&
2045\& ev_timer mytimer;
2046\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
2047\& ev_timer_again (&mytimer); /* start timer */
2048\& ev_loop (loop, 0);
2049\&
2050\& // and in some piece of code that gets executed on any "activity":
2051\& // reset the timeout to start ticking again at 10 seconds
2052\& ev_timer_again (&mytimer);
2053.Ve
724.ie n .Sh """ev_periodic"" \- to cron or not to cron" 2054.ie n .SS """ev_periodic"" \- to cron or not to cron?"
725.el .Sh "\f(CWev_periodic\fP \- to cron or not to cron" 2055.el .SS "\f(CWev_periodic\fP \- to cron or not to cron?"
726.IX Subsection "ev_periodic - to cron or not to cron" 2056.IX Subsection "ev_periodic - to cron or not to cron?"
727Periodic watchers are also timers of a kind, but they are very versatile 2057Periodic watchers are also timers of a kind, but they are very versatile
728(and unfortunately a bit complex). 2058(and unfortunately a bit complex).
729.PP 2059.PP
730Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time) 2060Unlike \f(CW\*(C`ev_timer\*(C'\fR, periodic watchers are not based on real time (or
731but on wallclock time (absolute time). You can tell a periodic watcher 2061relative time, the physical time that passes) but on wall clock time
732to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a 2062(absolute time, the thing you can read on your calender or clock). The
733periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now () 2063difference is that wall clock time can run faster or slower than real
734+ 10.>) and then reset your system clock to the last year, then it will 2064time, and time jumps are not uncommon (e.g. when you adjust your
735take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger 2065wrist-watch).
736roughly 10 seconds later and of course not if you reset your system time
737again).
738.PP 2066.PP
739They can also be used to implement vastly more complex timers, such as 2067You can tell a periodic watcher to trigger after some specific point
740triggering an event on eahc midnight, local time. 2068in time: for example, if you tell a periodic watcher to trigger \*(L"in 10
2069seconds\*(R" (by specifying e.g. \f(CW\*(C`ev_now () + 10.\*(C'\fR, that is, an absolute time
2070not a delay) and then reset your system clock to January of the previous
2071year, then it will take a year or more to trigger the event (unlike an
2072\&\f(CW\*(C`ev_timer\*(C'\fR, which would still trigger roughly 10 seconds after starting
2073it, as it uses a relative timeout).
741.PP 2074.PP
2075\&\f(CW\*(C`ev_periodic\*(C'\fR watchers can also be used to implement vastly more complex
2076timers, such as triggering an event on each \*(L"midnight, local time\*(R", or
2077other complicated rules. This cannot be done with \f(CW\*(C`ev_timer\*(C'\fR watchers, as
2078those cannot react to time jumps.
2079.PP
742As with timers, the callback is guarenteed to be invoked only when the 2080As with timers, the callback is guaranteed to be invoked only when the
743time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready 2081point in time where it is supposed to trigger has passed. If multiple
744during the same loop iteration then order of execution is undefined. 2082timers become ready during the same loop iteration then the ones with
2083earlier time-out values are invoked before ones with later time-out values
2084(but this is no longer true when a callback calls \f(CW\*(C`ev_loop\*(C'\fR recursively).
2085.PP
2086\fIWatcher-Specific Functions and Data Members\fR
2087.IX Subsection "Watcher-Specific Functions and Data Members"
745.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4 2088.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
746.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 2089.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
747.PD 0 2090.PD 0
748.IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4 2091.IP "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
749.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 2092.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
750.PD 2093.PD
751Lots of arguments, lets sort it out... There are basically three modes of 2094Lots of arguments, let's sort it out... There are basically three modes of
752operation, and we will explain them from simplest to complex: 2095operation, and we will explain them from simplest to most complex:
753.RS 4 2096.RS 4
754.IP "* absolute timer (interval = reschedule_cb = 0)" 4 2097.IP "\(bu" 4
755.IX Item "absolute timer (interval = reschedule_cb = 0)" 2098absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
2099.Sp
756In this configuration the watcher triggers an event at the wallclock time 2100In this configuration the watcher triggers an event after the wall clock
757\&\f(CW\*(C`at\*(C'\fR and doesn't repeat. It will not adjust when a time jump occurs, 2101time \f(CW\*(C`offset\*(C'\fR has passed. It will not repeat and will not adjust when a
758that is, if it is to be run at January 1st 2011 then it will run when the 2102time jump occurs, that is, if it is to be run at January 1st 2011 then it
759system time reaches or surpasses this time. 2103will be stopped and invoked when the system clock reaches or surpasses
760.IP "* non-repeating interval timer (interval > 0, reschedule_cb = 0)" 4 2104this point in time.
761.IX Item "non-repeating interval timer (interval > 0, reschedule_cb = 0)" 2105.IP "\(bu" 4
2106repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
2107.Sp
762In this mode the watcher will always be scheduled to time out at the next 2108In this mode the watcher will always be scheduled to time out at the next
763\&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N) and then repeat, regardless 2109\&\f(CW\*(C`offset + N * interval\*(C'\fR time (for some integer N, which can also be
764of any time jumps. 2110negative) and then repeat, regardless of any time jumps. The \f(CW\*(C`offset\*(C'\fR
2111argument is merely an offset into the \f(CW\*(C`interval\*(C'\fR periods.
765.Sp 2112.Sp
766This can be used to create timers that do not drift with respect to system 2113This can be used to create timers that do not drift with respect to the
767time: 2114system clock, for example, here is an \f(CW\*(C`ev_periodic\*(C'\fR that triggers each
2115hour, on the hour (with respect to \s-1UTC\s0):
768.Sp 2116.Sp
769.Vb 1 2117.Vb 1
770\& ev_periodic_set (&periodic, 0., 3600., 0); 2118\& ev_periodic_set (&periodic, 0., 3600., 0);
771.Ve 2119.Ve
772.Sp 2120.Sp
773This doesn't mean there will always be 3600 seconds in between triggers, 2121This doesn't mean there will always be 3600 seconds in between triggers,
774but only that the the callback will be called when the system time shows a 2122but only that the callback will be called when the system time shows a
775full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible 2123full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
776by 3600. 2124by 3600.
777.Sp 2125.Sp
778Another way to think about it (for the mathematically inclined) is that 2126Another way to think about it (for the mathematically inclined) is that
779\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible 2127\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
780time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps. 2128time where \f(CW\*(C`time = offset (mod interval)\*(C'\fR, regardless of any time jumps.
781.IP "* manual reschedule mode (reschedule_cb = callback)" 4 2129.Sp
782.IX Item "manual reschedule mode (reschedule_cb = callback)" 2130For numerical stability it is preferable that the \f(CW\*(C`offset\*(C'\fR value is near
2131\&\f(CW\*(C`ev_now ()\*(C'\fR (the current time), but there is no range requirement for
2132this value, and in fact is often specified as zero.
2133.Sp
2134Note also that there is an upper limit to how often a timer can fire (\s-1CPU\s0
2135speed for example), so if \f(CW\*(C`interval\*(C'\fR is very small then timing stability
2136will of course deteriorate. Libev itself tries to be exact to be about one
2137millisecond (if the \s-1OS\s0 supports it and the machine is fast enough).
2138.IP "\(bu" 4
2139manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
2140.Sp
783In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being 2141In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`offset\*(C'\fR are both being
784ignored. Instead, each time the periodic watcher gets scheduled, the 2142ignored. Instead, each time the periodic watcher gets scheduled, the
785reschedule callback will be called with the watcher as first, and the 2143reschedule callback will be called with the watcher as first, and the
786current time as second argument. 2144current time as second argument.
787.Sp 2145.Sp
788\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, 2146\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, ever,
789ever, or make any event loop modifications\fR. If you need to stop it, 2147or make \s-1ANY\s0 other event loop modifications whatsoever, unless explicitly
790return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by 2148allowed by documentation here\fR.
791starting a prepare watcher).
792.Sp 2149.Sp
2150If you need to stop it, return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop
2151it afterwards (e.g. by starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is the
2152only event loop modification you are allowed to do).
2153.Sp
793Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w, 2154The callback prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(ev_periodic
794ev_tstamp now)\*(C'\fR, e.g.: 2155*w, ev_tstamp now)\*(C'\fR, e.g.:
795.Sp 2156.Sp
796.Vb 4 2157.Vb 5
2158\& static ev_tstamp
797\& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) 2159\& my_rescheduler (ev_periodic *w, ev_tstamp now)
798\& { 2160\& {
799\& return now + 60.; 2161\& return now + 60.;
800\& } 2162\& }
801.Ve 2163.Ve
802.Sp 2164.Sp
803It must return the next time to trigger, based on the passed time value 2165It must return the next time to trigger, based on the passed time value
804(that is, the lowest time value larger than to the second argument). It 2166(that is, the lowest time value larger than to the second argument). It
805will usually be called just before the callback will be triggered, but 2167will usually be called just before the callback will be triggered, but
806might be called at other times, too. 2168might be called at other times, too.
807.Sp 2169.Sp
808\&\s-1NOTE:\s0 \fIThis callback must always return a time that is later than the 2170\&\s-1NOTE:\s0 \fIThis callback must always return a time that is higher than or
809passed \f(CI\*(C`now\*(C'\fI value\fR. Not even \f(CW\*(C`now\*(C'\fR itself will do, it \fImust\fR be larger. 2171equal to the passed \f(CI\*(C`now\*(C'\fI value\fR.
810.Sp 2172.Sp
811This can be used to create very complex timers, such as a timer that 2173This can be used to create very complex timers, such as a timer that
812triggers on each midnight, local time. To do this, you would calculate the 2174triggers on \*(L"next midnight, local time\*(R". To do this, you would calculate the
813next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How 2175next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How
814you do this is, again, up to you (but it is not trivial, which is the main 2176you do this is, again, up to you (but it is not trivial, which is the main
815reason I omitted it as an example). 2177reason I omitted it as an example).
816.RE 2178.RE
817.RS 4 2179.RS 4
… …
820.IX Item "ev_periodic_again (loop, ev_periodic *)" 2182.IX Item "ev_periodic_again (loop, ev_periodic *)"
821Simply stops and restarts the periodic watcher again. This is only useful 2183Simply stops and restarts the periodic watcher again. This is only useful
822when you changed some parameters or the reschedule callback would return 2184when you changed some parameters or the reschedule callback would return
823a different time than the last time it was called (e.g. in a crond like 2185a different time than the last time it was called (e.g. in a crond like
824program when the crontabs have changed). 2186program when the crontabs have changed).
2187.IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4
2188.IX Item "ev_tstamp ev_periodic_at (ev_periodic *)"
2189When active, returns the absolute time that the watcher is supposed
2190to trigger next. This is not the same as the \f(CW\*(C`offset\*(C'\fR argument to
2191\&\f(CW\*(C`ev_periodic_set\*(C'\fR, but indeed works even in interval and manual
2192rescheduling modes.
2193.IP "ev_tstamp offset [read\-write]" 4
2194.IX Item "ev_tstamp offset [read-write]"
2195When repeating, this contains the offset value, otherwise this is the
2196absolute point in time (the \f(CW\*(C`offset\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR,
2197although libev might modify this value for better numerical stability).
2198.Sp
2199Can be modified any time, but changes only take effect when the periodic
2200timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
2201.IP "ev_tstamp interval [read\-write]" 4
2202.IX Item "ev_tstamp interval [read-write]"
2203The current interval value. Can be modified any time, but changes only
2204take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
2205called.
2206.IP "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read\-write]" 4
2207.IX Item "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]"
2208The current reschedule callback, or \f(CW0\fR, if this functionality is
2209switched off. Can be changed any time, but changes only take effect when
2210the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
2211.PP
2212\fIExamples\fR
2213.IX Subsection "Examples"
2214.PP
2215Example: Call a callback every hour, or, more precisely, whenever the
2216system time is divisible by 3600. The callback invocation times have
2217potentially a lot of jitter, but good long-term stability.
2218.PP
2219.Vb 5
2220\& static void
2221\& clock_cb (struct ev_loop *loop, ev_io *w, int revents)
2222\& {
2223\& ... its now a full hour (UTC, or TAI or whatever your clock follows)
2224\& }
2225\&
2226\& ev_periodic hourly_tick;
2227\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
2228\& ev_periodic_start (loop, &hourly_tick);
2229.Ve
2230.PP
2231Example: The same as above, but use a reschedule callback to do it:
2232.PP
2233.Vb 1
2234\& #include <math.h>
2235\&
2236\& static ev_tstamp
2237\& my_scheduler_cb (ev_periodic *w, ev_tstamp now)
2238\& {
2239\& return now + (3600. \- fmod (now, 3600.));
2240\& }
2241\&
2242\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
2243.Ve
2244.PP
2245Example: Call a callback every hour, starting now:
2246.PP
2247.Vb 4
2248\& ev_periodic hourly_tick;
2249\& ev_periodic_init (&hourly_tick, clock_cb,
2250\& fmod (ev_now (loop), 3600.), 3600., 0);
2251\& ev_periodic_start (loop, &hourly_tick);
2252.Ve
825.ie n .Sh """ev_signal"" \- signal me when a signal gets signalled" 2253.ie n .SS """ev_signal"" \- signal me when a signal gets signalled!"
826.el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled" 2254.el .SS "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
827.IX Subsection "ev_signal - signal me when a signal gets signalled" 2255.IX Subsection "ev_signal - signal me when a signal gets signalled!"
828Signal watchers will trigger an event when the process receives a specific 2256Signal watchers will trigger an event when the process receives a specific
829signal one or more times. Even though signals are very asynchronous, libev 2257signal one or more times. Even though signals are very asynchronous, libev
830will try it's best to deliver signals synchronously, i.e. as part of the 2258will try it's best to deliver signals synchronously, i.e. as part of the
831normal event processing, like any other event. 2259normal event processing, like any other event.
832.PP 2260.PP
2261If you want signals to be delivered truly asynchronously, just use
2262\&\f(CW\*(C`sigaction\*(C'\fR as you would do without libev and forget about sharing
2263the signal. You can even use \f(CW\*(C`ev_async\*(C'\fR from a signal handler to
2264synchronously wake up an event loop.
2265.PP
833You can configure as many watchers as you like per signal. Only when the 2266You can configure as many watchers as you like for the same signal, but
2267only within the same loop, i.e. you can watch for \f(CW\*(C`SIGINT\*(C'\fR in your
2268default loop and for \f(CW\*(C`SIGIO\*(C'\fR in another loop, but you cannot watch for
2269\&\f(CW\*(C`SIGINT\*(C'\fR in both the default loop and another loop at the same time. At
2270the moment, \f(CW\*(C`SIGCHLD\*(C'\fR is permanently tied to the default loop.
2271.PP
834first watcher gets started will libev actually register a signal watcher 2272When the first watcher gets started will libev actually register something
835with the kernel (thus it coexists with your own signal handlers as long 2273with the kernel (thus it coexists with your own signal handlers as long as
836as you don't register any with libev). Similarly, when the last signal 2274you don't register any with libev for the same signal).
837watcher for a signal is stopped libev will reset the signal handler to 2275.PP
838\&\s-1SIG_DFL\s0 (regardless of what it was set to before). 2276If possible and supported, libev will install its handlers with
2277\&\f(CW\*(C`SA_RESTART\*(C'\fR (or equivalent) behaviour enabled, so system calls should
2278not be unduly interrupted. If you have a problem with system calls getting
2279interrupted by signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher
2280and unblock them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher.
2281.PP
2282\fIThe special problem of inheritance over fork/execve/pthread_create\fR
2283.IX Subsection "The special problem of inheritance over fork/execve/pthread_create"
2284.PP
2285Both the signal mask (\f(CW\*(C`sigprocmask\*(C'\fR) and the signal disposition
2286(\f(CW\*(C`sigaction\*(C'\fR) are unspecified after starting a signal watcher (and after
2287stopping it again), that is, libev might or might not block the signal,
2288and might or might not set or restore the installed signal handler.
2289.PP
2290While this does not matter for the signal disposition (libev never
2291sets signals to \f(CW\*(C`SIG_IGN\*(C'\fR, so handlers will be reset to \f(CW\*(C`SIG_DFL\*(C'\fR on
2292\&\f(CW\*(C`execve\*(C'\fR), this matters for the signal mask: many programs do not expect
2293certain signals to be blocked.
2294.PP
2295This means that before calling \f(CW\*(C`exec\*(C'\fR (from the child) you should reset
2296the signal mask to whatever \*(L"default\*(R" you expect (all clear is a good
2297choice usually).
2298.PP
2299The simplest way to ensure that the signal mask is reset in the child is
2300to install a fork handler with \f(CW\*(C`pthread_atfork\*(C'\fR that resets it. That will
2301catch fork calls done by libraries (such as the libc) as well.
2302.PP
2303In current versions of libev, the signal will not be blocked indefinitely
2304unless you use the \f(CW\*(C`signalfd\*(C'\fR \s-1API\s0 (\f(CW\*(C`EV_SIGNALFD\*(C'\fR). While this reduces
2305the window of opportunity for problems, it will not go away, as libev
2306\&\fIhas\fR to modify the signal mask, at least temporarily.
2307.PP
2308So I can't stress this enough: \fIIf you do not reset your signal mask when
2309you expect it to be empty, you have a race condition in your code\fR. This
2310is not a libev-specific thing, this is true for most event libraries.
2311.PP
2312\fIWatcher-Specific Functions and Data Members\fR
2313.IX Subsection "Watcher-Specific Functions and Data Members"
839.IP "ev_signal_init (ev_signal *, callback, int signum)" 4 2314.IP "ev_signal_init (ev_signal *, callback, int signum)" 4
840.IX Item "ev_signal_init (ev_signal *, callback, int signum)" 2315.IX Item "ev_signal_init (ev_signal *, callback, int signum)"
841.PD 0 2316.PD 0
842.IP "ev_signal_set (ev_signal *, int signum)" 4 2317.IP "ev_signal_set (ev_signal *, int signum)" 4
843.IX Item "ev_signal_set (ev_signal *, int signum)" 2318.IX Item "ev_signal_set (ev_signal *, int signum)"
844.PD 2319.PD
845Configures the watcher to trigger on the given signal number (usually one 2320Configures the watcher to trigger on the given signal number (usually one
846of the \f(CW\*(C`SIGxxx\*(C'\fR constants). 2321of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
2322.IP "int signum [read\-only]" 4
2323.IX Item "int signum [read-only]"
2324The signal the watcher watches out for.
2325.PP
2326\fIExamples\fR
2327.IX Subsection "Examples"
2328.PP
2329Example: Try to exit cleanly on \s-1SIGINT\s0.
2330.PP
2331.Vb 5
2332\& static void
2333\& sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
2334\& {
2335\& ev_unloop (loop, EVUNLOOP_ALL);
2336\& }
2337\&
2338\& ev_signal signal_watcher;
2339\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
2340\& ev_signal_start (loop, &signal_watcher);
2341.Ve
847.ie n .Sh """ev_child"" \- wait for pid status changes" 2342.ie n .SS """ev_child"" \- watch out for process status changes"
848.el .Sh "\f(CWev_child\fP \- wait for pid status changes" 2343.el .SS "\f(CWev_child\fP \- watch out for process status changes"
849.IX Subsection "ev_child - wait for pid status changes" 2344.IX Subsection "ev_child - watch out for process status changes"
850Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to 2345Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
851some child status changes (most typically when a child of yours dies). 2346some child status changes (most typically when a child of yours dies or
2347exits). It is permissible to install a child watcher \fIafter\fR the child
2348has been forked (which implies it might have already exited), as long
2349as the event loop isn't entered (or is continued from a watcher), i.e.,
2350forking and then immediately registering a watcher for the child is fine,
2351but forking and registering a watcher a few event loop iterations later or
2352in the next callback invocation is not.
2353.PP
2354Only the default event loop is capable of handling signals, and therefore
2355you can only register child watchers in the default event loop.
2356.PP
2357Due to some design glitches inside libev, child watchers will always be
2358handled at maximum priority (their priority is set to \f(CW\*(C`EV_MAXPRI\*(C'\fR by
2359libev)
2360.PP
2361\fIProcess Interaction\fR
2362.IX Subsection "Process Interaction"
2363.PP
2364Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is
2365initialised. This is necessary to guarantee proper behaviour even if the
2366first child watcher is started after the child exits. The occurrence
2367of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done
2368synchronously as part of the event loop processing. Libev always reaps all
2369children, even ones not watched.
2370.PP
2371\fIOverriding the Built-In Processing\fR
2372.IX Subsection "Overriding the Built-In Processing"
2373.PP
2374Libev offers no special support for overriding the built-in child
2375processing, but if your application collides with libev's default child
2376handler, you can override it easily by installing your own handler for
2377\&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the
2378default loop never gets destroyed. You are encouraged, however, to use an
2379event-based approach to child reaping and thus use libev's support for
2380that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely.
2381.PP
2382\fIStopping the Child Watcher\fR
2383.IX Subsection "Stopping the Child Watcher"
2384.PP
2385Currently, the child watcher never gets stopped, even when the
2386child terminates, so normally one needs to stop the watcher in the
2387callback. Future versions of libev might stop the watcher automatically
2388when a child exit is detected (calling \f(CW\*(C`ev_child_stop\*(C'\fR twice is not a
2389problem).
2390.PP
2391\fIWatcher-Specific Functions and Data Members\fR
2392.IX Subsection "Watcher-Specific Functions and Data Members"
852.IP "ev_child_init (ev_child *, callback, int pid)" 4 2393.IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4
853.IX Item "ev_child_init (ev_child *, callback, int pid)" 2394.IX Item "ev_child_init (ev_child *, callback, int pid, int trace)"
854.PD 0 2395.PD 0
855.IP "ev_child_set (ev_child *, int pid)" 4 2396.IP "ev_child_set (ev_child *, int pid, int trace)" 4
856.IX Item "ev_child_set (ev_child *, int pid)" 2397.IX Item "ev_child_set (ev_child *, int pid, int trace)"
857.PD 2398.PD
858Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or 2399Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
859\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look 2400\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
860at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see 2401at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
861the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems 2402the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
862\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the 2403\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
863process causing the status change. 2404process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only
2405activate the watcher when the process terminates) or \f(CW1\fR (additionally
2406activate the watcher when the process is stopped or continued).
2407.IP "int pid [read\-only]" 4
2408.IX Item "int pid [read-only]"
2409The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
2410.IP "int rpid [read\-write]" 4
2411.IX Item "int rpid [read-write]"
2412The process id that detected a status change.
2413.IP "int rstatus [read\-write]" 4
2414.IX Item "int rstatus [read-write]"
2415The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
2416\&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
2417.PP
2418\fIExamples\fR
2419.IX Subsection "Examples"
2420.PP
2421Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for
2422its completion.
2423.PP
2424.Vb 1
2425\& ev_child cw;
2426\&
2427\& static void
2428\& child_cb (EV_P_ ev_child *w, int revents)
2429\& {
2430\& ev_child_stop (EV_A_ w);
2431\& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus);
2432\& }
2433\&
2434\& pid_t pid = fork ();
2435\&
2436\& if (pid < 0)
2437\& // error
2438\& else if (pid == 0)
2439\& {
2440\& // the forked child executes here
2441\& exit (1);
2442\& }
2443\& else
2444\& {
2445\& ev_child_init (&cw, child_cb, pid, 0);
2446\& ev_child_start (EV_DEFAULT_ &cw);
2447\& }
2448.Ve
2449.ie n .SS """ev_stat"" \- did the file attributes just change?"
2450.el .SS "\f(CWev_stat\fP \- did the file attributes just change?"
2451.IX Subsection "ev_stat - did the file attributes just change?"
2452This watches a file system path for attribute changes. That is, it calls
2453\&\f(CW\*(C`stat\*(C'\fR on that path in regular intervals (or when the \s-1OS\s0 says it changed)
2454and sees if it changed compared to the last time, invoking the callback if
2455it did.
2456.PP
2457The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does
2458not exist\*(R" is a status change like any other. The condition \*(L"path does not
2459exist\*(R" (or more correctly \*(L"path cannot be stat'ed\*(R") is signified by the
2460\&\f(CW\*(C`st_nlink\*(C'\fR field being zero (which is otherwise always forced to be at
2461least one) and all the other fields of the stat buffer having unspecified
2462contents.
2463.PP
2464The path \fImust not\fR end in a slash or contain special components such as
2465\&\f(CW\*(C`.\*(C'\fR or \f(CW\*(C`..\*(C'\fR. The path \fIshould\fR be absolute: If it is relative and
2466your working directory changes, then the behaviour is undefined.
2467.PP
2468Since there is no portable change notification interface available, the
2469portable implementation simply calls \f(CWstat(2)\fR regularly on the path
2470to see if it changed somehow. You can specify a recommended polling
2471interval for this case. If you specify a polling interval of \f(CW0\fR (highly
2472recommended!) then a \fIsuitable, unspecified default\fR value will be used
2473(which you can expect to be around five seconds, although this might
2474change dynamically). Libev will also impose a minimum interval which is
2475currently around \f(CW0.1\fR, but that's usually overkill.
2476.PP
2477This watcher type is not meant for massive numbers of stat watchers,
2478as even with OS-supported change notifications, this can be
2479resource-intensive.
2480.PP
2481At the time of this writing, the only OS-specific interface implemented
2482is the Linux inotify interface (implementing kqueue support is left as an
2483exercise for the reader. Note, however, that the author sees no way of
2484implementing \f(CW\*(C`ev_stat\*(C'\fR semantics with kqueue, except as a hint).
2485.PP
2486\fI\s-1ABI\s0 Issues (Largefile Support)\fR
2487.IX Subsection "ABI Issues (Largefile Support)"
2488.PP
2489Libev by default (unless the user overrides this) uses the default
2490compilation environment, which means that on systems with large file
2491support disabled by default, you get the 32 bit version of the stat
2492structure. When using the library from programs that change the \s-1ABI\s0 to
2493use 64 bit file offsets the programs will fail. In that case you have to
2494compile libev with the same flags to get binary compatibility. This is
2495obviously the case with any flags that change the \s-1ABI\s0, but the problem is
2496most noticeably displayed with ev_stat and large file support.
2497.PP
2498The solution for this is to lobby your distribution maker to make large
2499file interfaces available by default (as e.g. FreeBSD does) and not
2500optional. Libev cannot simply switch on large file support because it has
2501to exchange stat structures with application programs compiled using the
2502default compilation environment.
2503.PP
2504\fIInotify and Kqueue\fR
2505.IX Subsection "Inotify and Kqueue"
2506.PP
2507When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev and present at
2508runtime, it will be used to speed up change detection where possible. The
2509inotify descriptor will be created lazily when the first \f(CW\*(C`ev_stat\*(C'\fR
2510watcher is being started.
2511.PP
2512Inotify presence does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
2513except that changes might be detected earlier, and in some cases, to avoid
2514making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presence of inotify support
2515there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling,
2516but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
2517many bugs), the path exists (i.e. stat succeeds), and the path resides on
2518a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
2519xfs are fully working) libev usually gets away without polling.
2520.PP
2521There is no support for kqueue, as apparently it cannot be used to
2522implement this functionality, due to the requirement of having a file
2523descriptor open on the object at all times, and detecting renames, unlinks
2524etc. is difficult.
2525.PP
2526\fI\f(CI\*(C`stat ()\*(C'\fI is a synchronous operation\fR
2527.IX Subsection "stat () is a synchronous operation"
2528.PP
2529Libev doesn't normally do any kind of I/O itself, and so is not blocking
2530the process. The exception are \f(CW\*(C`ev_stat\*(C'\fR watchers \- those call \f(CW\*(C`stat
2531()\*(C'\fR, which is a synchronous operation.
2532.PP
2533For local paths, this usually doesn't matter: unless the system is very
2534busy or the intervals between stat's are large, a stat call will be fast,
2535as the path data is usually in memory already (except when starting the
2536watcher).
2537.PP
2538For networked file systems, calling \f(CW\*(C`stat ()\*(C'\fR can block an indefinite
2539time due to network issues, and even under good conditions, a stat call
2540often takes multiple milliseconds.
2541.PP
2542Therefore, it is best to avoid using \f(CW\*(C`ev_stat\*(C'\fR watchers on networked
2543paths, although this is fully supported by libev.
2544.PP
2545\fIThe special problem of stat time resolution\fR
2546.IX Subsection "The special problem of stat time resolution"
2547.PP
2548The \f(CW\*(C`stat ()\*(C'\fR system call only supports full-second resolution portably,
2549and even on systems where the resolution is higher, most file systems
2550still only support whole seconds.
2551.PP
2552That means that, if the time is the only thing that changes, you can
2553easily miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and
2554calls your callback, which does something. When there is another update
2555within the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect unless the
2556stat data does change in other ways (e.g. file size).
2557.PP
2558The solution to this is to delay acting on a change for slightly more
2559than a second (or till slightly after the next full second boundary), using
2560a roughly one-second-delay \f(CW\*(C`ev_timer\*(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02);
2561ev_timer_again (loop, w)\*(C'\fR).
2562.PP
2563The \f(CW.02\fR offset is added to work around small timing inconsistencies
2564of some operating systems (where the second counter of the current time
2565might be be delayed. One such system is the Linux kernel, where a call to
2566\&\f(CW\*(C`gettimeofday\*(C'\fR might return a timestamp with a full second later than
2567a subsequent \f(CW\*(C`time\*(C'\fR call \- if the equivalent of \f(CW\*(C`time ()\*(C'\fR is used to
2568update file times then there will be a small window where the kernel uses
2569the previous second to update file times but libev might already execute
2570the timer callback).
2571.PP
2572\fIWatcher-Specific Functions and Data Members\fR
2573.IX Subsection "Watcher-Specific Functions and Data Members"
2574.IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
2575.IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
2576.PD 0
2577.IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4
2578.IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)"
2579.PD
2580Configures the watcher to wait for status changes of the given
2581\&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to
2582be detected and should normally be specified as \f(CW0\fR to let libev choose
2583a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same
2584path for as long as the watcher is active.
2585.Sp
2586The callback will receive an \f(CW\*(C`EV_STAT\*(C'\fR event when a change was detected,
2587relative to the attributes at the time the watcher was started (or the
2588last change was detected).
2589.IP "ev_stat_stat (loop, ev_stat *)" 4
2590.IX Item "ev_stat_stat (loop, ev_stat *)"
2591Updates the stat buffer immediately with new values. If you change the
2592watched path in your callback, you could call this function to avoid
2593detecting this change (while introducing a race condition if you are not
2594the only one changing the path). Can also be useful simply to find out the
2595new values.
2596.IP "ev_statdata attr [read\-only]" 4
2597.IX Item "ev_statdata attr [read-only]"
2598The most-recently detected attributes of the file. Although the type is
2599\&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
2600suitable for your system, but you can only rely on the POSIX-standardised
2601members to be present. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there was
2602some error while \f(CW\*(C`stat\*(C'\fRing the file.
2603.IP "ev_statdata prev [read\-only]" 4
2604.IX Item "ev_statdata prev [read-only]"
2605The previous attributes of the file. The callback gets invoked whenever
2606\&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR, or, more precisely, one or more of these members
2607differ: \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,
2608\&\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.
2609.IP "ev_tstamp interval [read\-only]" 4
2610.IX Item "ev_tstamp interval [read-only]"
2611The specified interval.
2612.IP "const char *path [read\-only]" 4
2613.IX Item "const char *path [read-only]"
2614The file system path that is being watched.
2615.PP
2616\fIExamples\fR
2617.IX Subsection "Examples"
2618.PP
2619Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
2620.PP
2621.Vb 10
2622\& static void
2623\& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
2624\& {
2625\& /* /etc/passwd changed in some way */
2626\& if (w\->attr.st_nlink)
2627\& {
2628\& printf ("passwd current size %ld\en", (long)w\->attr.st_size);
2629\& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime);
2630\& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime);
2631\& }
2632\& else
2633\& /* you shalt not abuse printf for puts */
2634\& puts ("wow, /etc/passwd is not there, expect problems. "
2635\& "if this is windows, they already arrived\en");
2636\& }
2637\&
2638\& ...
2639\& ev_stat passwd;
2640\&
2641\& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
2642\& ev_stat_start (loop, &passwd);
2643.Ve
2644.PP
2645Example: Like above, but additionally use a one-second delay so we do not
2646miss updates (however, frequent updates will delay processing, too, so
2647one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
2648\&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
2649.PP
2650.Vb 2
2651\& static ev_stat passwd;
2652\& static ev_timer timer;
2653\&
2654\& static void
2655\& timer_cb (EV_P_ ev_timer *w, int revents)
2656\& {
2657\& ev_timer_stop (EV_A_ w);
2658\&
2659\& /* now it\*(Aqs one second after the most recent passwd change */
2660\& }
2661\&
2662\& static void
2663\& stat_cb (EV_P_ ev_stat *w, int revents)
2664\& {
2665\& /* reset the one\-second timer */
2666\& ev_timer_again (EV_A_ &timer);
2667\& }
2668\&
2669\& ...
2670\& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
2671\& ev_stat_start (loop, &passwd);
2672\& ev_timer_init (&timer, timer_cb, 0., 1.02);
2673.Ve
864.ie n .Sh """ev_idle"" \- when you've got nothing better to do" 2674.ie n .SS """ev_idle"" \- when you've got nothing better to do..."
865.el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do" 2675.el .SS "\f(CWev_idle\fP \- when you've got nothing better to do..."
866.IX Subsection "ev_idle - when you've got nothing better to do" 2676.IX Subsection "ev_idle - when you've got nothing better to do..."
867Idle watchers trigger events when there are no other events are pending 2677Idle watchers trigger events when no other events of the same or higher
868(prepare, check and other idle watchers do not count). That is, as long 2678priority are pending (prepare, check and other idle watchers do not count
869as your process is busy handling sockets or timeouts (or even signals, 2679as receiving \*(L"events\*(R").
870imagine) it will not be triggered. But when your process is idle all idle 2680.PP
871watchers are being called again and again, once per event loop iteration \- 2681That is, as long as your process is busy handling sockets or timeouts
2682(or even signals, imagine) of the same or higher priority it will not be
2683triggered. But when your process is idle (or only lower-priority watchers
2684are pending), the idle watchers are being called once per event loop
872until stopped, that is, or your process receives more events and becomes 2685iteration \- until stopped, that is, or your process receives more events
873busy. 2686and becomes busy again with higher priority stuff.
874.PP 2687.PP
875The most noteworthy effect is that as long as any idle watchers are 2688The most noteworthy effect is that as long as any idle watchers are
876active, the process will not block when waiting for new events. 2689active, the process will not block when waiting for new events.
877.PP 2690.PP
878Apart from keeping your process non-blocking (which is a useful 2691Apart from keeping your process non-blocking (which is a useful
879effect on its own sometimes), idle watchers are a good place to do 2692effect on its own sometimes), idle watchers are a good place to do
880\&\*(L"pseudo\-background processing\*(R", or delay processing stuff to after the 2693\&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the
881event loop has handled all outstanding events. 2694event loop has handled all outstanding events.
2695.PP
2696\fIWatcher-Specific Functions and Data Members\fR
2697.IX Subsection "Watcher-Specific Functions and Data Members"
882.IP "ev_idle_init (ev_signal *, callback)" 4 2698.IP "ev_idle_init (ev_idle *, callback)" 4
883.IX Item "ev_idle_init (ev_signal *, callback)" 2699.IX Item "ev_idle_init (ev_idle *, callback)"
884Initialises and configures the idle watcher \- it has no parameters of any 2700Initialises and configures the idle watcher \- it has no parameters of any
885kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless, 2701kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
886believe me. 2702believe me.
2703.PP
2704\fIExamples\fR
2705.IX Subsection "Examples"
2706.PP
2707Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the
2708callback, free it. Also, use no error checking, as usual.
2709.PP
2710.Vb 7
2711\& static void
2712\& idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2713\& {
2714\& free (w);
2715\& // now do something you wanted to do when the program has
2716\& // no longer anything immediate to do.
2717\& }
2718\&
2719\& ev_idle *idle_watcher = malloc (sizeof (ev_idle));
2720\& ev_idle_init (idle_watcher, idle_cb);
2721\& ev_idle_start (loop, idle_watcher);
2722.Ve
887.ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop" 2723.ie n .SS """ev_prepare"" and ""ev_check"" \- customise your event loop!"
888.el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop" 2724.el .SS "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
889.IX Subsection "ev_prepare and ev_check - customise your event loop" 2725.IX Subsection "ev_prepare and ev_check - customise your event loop!"
890Prepare and check watchers are usually (but not always) used in tandem: 2726Prepare and check watchers are usually (but not always) used in pairs:
891prepare watchers get invoked before the process blocks and check watchers 2727prepare watchers get invoked before the process blocks and check watchers
892afterwards. 2728afterwards.
893.PP 2729.PP
2730You \fImust not\fR call \f(CW\*(C`ev_loop\*(C'\fR or similar functions that enter
2731the current event loop from either \f(CW\*(C`ev_prepare\*(C'\fR or \f(CW\*(C`ev_check\*(C'\fR
2732watchers. Other loops than the current one are fine, however. The
2733rationale behind this is that you do not need to check for recursion in
2734those watchers, i.e. the sequence will always be \f(CW\*(C`ev_prepare\*(C'\fR, blocking,
2735\&\f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each kind they will always be
2736called in pairs bracketing the blocking call.
2737.PP
894Their main purpose is to integrate other event mechanisms into libev. This 2738Their main purpose is to integrate other event mechanisms into libev and
895could be used, for example, to track variable changes, implement your own 2739their use is somewhat advanced. They could be used, for example, to track
896watchers, integrate net-snmp or a coroutine library and lots more. 2740variable changes, implement your own watchers, integrate net-snmp or a
2741coroutine library and lots more. They are also occasionally useful if
2742you cache some data and want to flush it before blocking (for example,
2743in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
2744watcher).
897.PP 2745.PP
898This is done by examining in each prepare call which file descriptors need 2746This is done by examining in each prepare call which file descriptors
899to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers for 2747need to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers
900them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many libraries 2748for them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many
901provide just this functionality). Then, in the check watcher you check for 2749libraries provide exactly this functionality). Then, in the check watcher,
902any events that occured (by checking the pending status of all watchers 2750you check for any events that occurred (by checking the pending status
903and stopping them) and call back into the library. The I/O and timer 2751of all watchers and stopping them) and call back into the library. The
904callbacks will never actually be called (but must be valid nevertheless, 2752I/O and timer callbacks will never actually be called (but must be valid
905because you never know, you know?). 2753nevertheless, because you never know, you know?).
906.PP 2754.PP
907As another example, the Perl Coro module uses these hooks to integrate 2755As another example, the Perl Coro module uses these hooks to integrate
908coroutines into libev programs, by yielding to other active coroutines 2756coroutines into libev programs, by yielding to other active coroutines
909during each prepare and only letting the process block if no coroutines 2757during each prepare and only letting the process block if no coroutines
910are ready to run (it's actually more complicated: it only runs coroutines 2758are ready to run (it's actually more complicated: it only runs coroutines
911with priority higher than or equal to the event loop and one coroutine 2759with priority higher than or equal to the event loop and one coroutine
912of lower priority, but only once, using idle watchers to keep the event 2760of lower priority, but only once, using idle watchers to keep the event
913loop from blocking if lower-priority coroutines are active, thus mapping 2761loop from blocking if lower-priority coroutines are active, thus mapping
914low-priority coroutines to idle/background tasks). 2762low-priority coroutines to idle/background tasks).
2763.PP
2764It is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR)
2765priority, to ensure that they are being run before any other watchers
2766after the poll (this doesn't matter for \f(CW\*(C`ev_prepare\*(C'\fR watchers).
2767.PP
2768Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, too) should not
2769activate (\*(L"feed\*(R") events into libev. While libev fully supports this, they
2770might get executed before other \f(CW\*(C`ev_check\*(C'\fR watchers did their job. As
2771\&\f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other (non-libev) event
2772loops those other event loops might be in an unusable state until their
2773\&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with
2774others).
2775.PP
2776\fIWatcher-Specific Functions and Data Members\fR
2777.IX Subsection "Watcher-Specific Functions and Data Members"
915.IP "ev_prepare_init (ev_prepare *, callback)" 4 2778.IP "ev_prepare_init (ev_prepare *, callback)" 4
916.IX Item "ev_prepare_init (ev_prepare *, callback)" 2779.IX Item "ev_prepare_init (ev_prepare *, callback)"
917.PD 0 2780.PD 0
918.IP "ev_check_init (ev_check *, callback)" 4 2781.IP "ev_check_init (ev_check *, callback)" 4
919.IX Item "ev_check_init (ev_check *, callback)" 2782.IX Item "ev_check_init (ev_check *, callback)"
920.PD 2783.PD
921Initialises and configures the prepare or check watcher \- they have no 2784Initialises and configures the prepare or check watcher \- they have no
922parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR 2785parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
923macros, but using them is utterly, utterly and completely pointless. 2786macros, but using them is utterly, utterly, utterly and completely
2787pointless.
2788.PP
2789\fIExamples\fR
2790.IX Subsection "Examples"
2791.PP
2792There are a number of principal ways to embed other event loops or modules
2793into libev. Here are some ideas on how to include libadns into libev
2794(there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could
2795use as a working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR embeds a
2796Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 into the
2797Glib event loop).
2798.PP
2799Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
2800and in a check watcher, destroy them and call into libadns. What follows
2801is pseudo-code only of course. This requires you to either use a low
2802priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as
2803the callbacks for the IO/timeout watchers might not have been called yet.
2804.PP
2805.Vb 2
2806\& static ev_io iow [nfd];
2807\& static ev_timer tw;
2808\&
2809\& static void
2810\& io_cb (struct ev_loop *loop, ev_io *w, int revents)
2811\& {
2812\& }
2813\&
2814\& // create io watchers for each fd and a timer before blocking
2815\& static void
2816\& adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
2817\& {
2818\& int timeout = 3600000;
2819\& struct pollfd fds [nfd];
2820\& // actual code will need to loop here and realloc etc.
2821\& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2822\&
2823\& /* the callback is illegal, but won\*(Aqt be called as we stop during check */
2824\& ev_timer_init (&tw, 0, timeout * 1e\-3, 0.);
2825\& ev_timer_start (loop, &tw);
2826\&
2827\& // create one ev_io per pollfd
2828\& for (int i = 0; i < nfd; ++i)
2829\& {
2830\& ev_io_init (iow + i, io_cb, fds [i].fd,
2831\& ((fds [i].events & POLLIN ? EV_READ : 0)
2832\& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
2833\&
2834\& fds [i].revents = 0;
2835\& ev_io_start (loop, iow + i);
2836\& }
2837\& }
2838\&
2839\& // stop all watchers after blocking
2840\& static void
2841\& adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
2842\& {
2843\& ev_timer_stop (loop, &tw);
2844\&
2845\& for (int i = 0; i < nfd; ++i)
2846\& {
2847\& // set the relevant poll flags
2848\& // could also call adns_processreadable etc. here
2849\& struct pollfd *fd = fds + i;
2850\& int revents = ev_clear_pending (iow + i);
2851\& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN;
2852\& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT;
2853\&
2854\& // now stop the watcher
2855\& ev_io_stop (loop, iow + i);
2856\& }
2857\&
2858\& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
2859\& }
2860.Ve
2861.PP
2862Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR
2863in the prepare watcher and would dispose of the check watcher.
2864.PP
2865Method 3: If the module to be embedded supports explicit event
2866notification (libadns does), you can also make use of the actual watcher
2867callbacks, and only destroy/create the watchers in the prepare watcher.
2868.PP
2869.Vb 5
2870\& static void
2871\& timer_cb (EV_P_ ev_timer *w, int revents)
2872\& {
2873\& adns_state ads = (adns_state)w\->data;
2874\& update_now (EV_A);
2875\&
2876\& adns_processtimeouts (ads, &tv_now);
2877\& }
2878\&
2879\& static void
2880\& io_cb (EV_P_ ev_io *w, int revents)
2881\& {
2882\& adns_state ads = (adns_state)w\->data;
2883\& update_now (EV_A);
2884\&
2885\& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now);
2886\& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now);
2887\& }
2888\&
2889\& // do not ever call adns_afterpoll
2890.Ve
2891.PP
2892Method 4: Do not use a prepare or check watcher because the module you
2893want to embed is not flexible enough to support it. Instead, you can
2894override their poll function. The drawback with this solution is that the
2895main loop is now no longer controllable by \s-1EV\s0. The \f(CW\*(C`Glib::EV\*(C'\fR module uses
2896this approach, effectively embedding \s-1EV\s0 as a client into the horrible
2897libglib event loop.
2898.PP
2899.Vb 4
2900\& static gint
2901\& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
2902\& {
2903\& int got_events = 0;
2904\&
2905\& for (n = 0; n < nfds; ++n)
2906\& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
2907\&
2908\& if (timeout >= 0)
2909\& // create/start timer
2910\&
2911\& // poll
2912\& ev_loop (EV_A_ 0);
2913\&
2914\& // stop timer again
2915\& if (timeout >= 0)
2916\& ev_timer_stop (EV_A_ &to);
2917\&
2918\& // stop io watchers again \- their callbacks should have set
2919\& for (n = 0; n < nfds; ++n)
2920\& ev_io_stop (EV_A_ iow [n]);
2921\&
2922\& return got_events;
2923\& }
2924.Ve
2925.ie n .SS """ev_embed"" \- when one backend isn't enough..."
2926.el .SS "\f(CWev_embed\fP \- when one backend isn't enough..."
2927.IX Subsection "ev_embed - when one backend isn't enough..."
2928This is a rather advanced watcher type that lets you embed one event loop
2929into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
2930loop, other types of watchers might be handled in a delayed or incorrect
2931fashion and must not be used).
2932.PP
2933There are primarily two reasons you would want that: work around bugs and
2934prioritise I/O.
2935.PP
2936As an example for a bug workaround, the kqueue backend might only support
2937sockets on some platform, so it is unusable as generic backend, but you
2938still want to make use of it because you have many sockets and it scales
2939so nicely. In this case, you would create a kqueue-based loop and embed
2940it into your default loop (which might use e.g. poll). Overall operation
2941will be a bit slower because first libev has to call \f(CW\*(C`poll\*(C'\fR and then
2942\&\f(CW\*(C`kevent\*(C'\fR, but at least you can use both mechanisms for what they are
2943best: \f(CW\*(C`kqueue\*(C'\fR for scalable sockets and \f(CW\*(C`poll\*(C'\fR if you want it to work :)
2944.PP
2945As for prioritising I/O: under rare circumstances you have the case where
2946some fds have to be watched and handled very quickly (with low latency),
2947and even priorities and idle watchers might have too much overhead. In
2948this case you would put all the high priority stuff in one loop and all
2949the rest in a second one, and embed the second one in the first.
2950.PP
2951As long as the watcher is active, the callback will be invoked every
2952time there might be events pending in the embedded loop. The callback
2953must then call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single
2954sweep and invoke their callbacks (the callback doesn't need to invoke the
2955\&\f(CW\*(C`ev_embed_sweep\*(C'\fR function directly, it could also start an idle watcher
2956to give the embedded loop strictly lower priority for example).
2957.PP
2958You can also set the callback to \f(CW0\fR, in which case the embed watcher
2959will automatically execute the embedded loop sweep whenever necessary.
2960.PP
2961Fork detection will be handled transparently while the \f(CW\*(C`ev_embed\*(C'\fR watcher
2962is active, i.e., the embedded loop will automatically be forked when the
2963embedding loop forks. In other cases, the user is responsible for calling
2964\&\f(CW\*(C`ev_loop_fork\*(C'\fR on the embedded loop.
2965.PP
2966Unfortunately, not all backends are embeddable: only the ones returned by
2967\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
2968portable one.
2969.PP
2970So when you want to use this feature you will always have to be prepared
2971that you cannot get an embeddable loop. The recommended way to get around
2972this is to have a separate variables for your embeddable loop, try to
2973create it, and if that fails, use the normal loop for everything.
2974.PP
2975\fI\f(CI\*(C`ev_embed\*(C'\fI and fork\fR
2976.IX Subsection "ev_embed and fork"
2977.PP
2978While the \f(CW\*(C`ev_embed\*(C'\fR watcher is running, forks in the embedding loop will
2979automatically be applied to the embedded loop as well, so no special
2980fork handling is required in that case. When the watcher is not running,
2981however, it is still the task of the libev user to call \f(CW\*(C`ev_loop_fork ()\*(C'\fR
2982as applicable.
2983.PP
2984\fIWatcher-Specific Functions and Data Members\fR
2985.IX Subsection "Watcher-Specific Functions and Data Members"
2986.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
2987.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
2988.PD 0
2989.IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
2990.IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)"
2991.PD
2992Configures the watcher to embed the given loop, which must be
2993embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
2994invoked automatically, otherwise it is the responsibility of the callback
2995to invoke it (it will continue to be called until the sweep has been done,
2996if you do not want that, you need to temporarily stop the embed watcher).
2997.IP "ev_embed_sweep (loop, ev_embed *)" 4
2998.IX Item "ev_embed_sweep (loop, ev_embed *)"
2999Make a single, non-blocking sweep over the embedded loop. This works
3000similarly to \f(CW\*(C`ev_loop (embedded_loop, EVLOOP_NONBLOCK)\*(C'\fR, but in the most
3001appropriate way for embedded loops.
3002.IP "struct ev_loop *other [read\-only]" 4
3003.IX Item "struct ev_loop *other [read-only]"
3004The embedded event loop.
3005.PP
3006\fIExamples\fR
3007.IX Subsection "Examples"
3008.PP
3009Example: Try to get an embeddable event loop and embed it into the default
3010event loop. If that is not possible, use the default loop. The default
3011loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the embeddable loop is stored in
3012\&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the case no embeddable loop can be
3013used).
3014.PP
3015.Vb 3
3016\& struct ev_loop *loop_hi = ev_default_init (0);
3017\& struct ev_loop *loop_lo = 0;
3018\& ev_embed embed;
3019\&
3020\& // see if there is a chance of getting one that works
3021\& // (remember that a flags value of 0 means autodetection)
3022\& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3023\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3024\& : 0;
3025\&
3026\& // if we got one, then embed it, otherwise default to loop_hi
3027\& if (loop_lo)
3028\& {
3029\& ev_embed_init (&embed, 0, loop_lo);
3030\& ev_embed_start (loop_hi, &embed);
3031\& }
3032\& else
3033\& loop_lo = loop_hi;
3034.Ve
3035.PP
3036Example: Check if kqueue is available but not recommended and create
3037a kqueue backend for use with sockets (which usually work with any
3038kqueue implementation). Store the kqueue/socket\-only event loop in
3039\&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too).
3040.PP
3041.Vb 3
3042\& struct ev_loop *loop = ev_default_init (0);
3043\& struct ev_loop *loop_socket = 0;
3044\& ev_embed embed;
3045\&
3046\& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3047\& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3048\& {
3049\& ev_embed_init (&embed, 0, loop_socket);
3050\& ev_embed_start (loop, &embed);
3051\& }
3052\&
3053\& if (!loop_socket)
3054\& loop_socket = loop;
3055\&
3056\& // now use loop_socket for all sockets, and loop for everything else
3057.Ve
3058.ie n .SS """ev_fork"" \- the audacity to resume the event loop after a fork"
3059.el .SS "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
3060.IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
3061Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
3062whoever is a good citizen cared to tell libev about it by calling
3063\&\f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the
3064event loop blocks next and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called,
3065and only in the child after the fork. If whoever good citizen calling
3066\&\f(CW\*(C`ev_default_fork\*(C'\fR cheats and calls it in the wrong process, the fork
3067handlers will be invoked, too, of course.
3068.PP
3069\fIThe special problem of life after fork \- how is it possible?\fR
3070.IX Subsection "The special problem of life after fork - how is it possible?"
3071.PP
3072Most uses of \f(CW\*(C`fork()\*(C'\fR consist of forking, then some simple calls to ste
3073up/change the process environment, followed by a call to \f(CW\*(C`exec()\*(C'\fR. This
3074sequence should be handled by libev without any problems.
3075.PP
3076This changes when the application actually wants to do event handling
3077in the child, or both parent in child, in effect \*(L"continuing\*(R" after the
3078fork.
3079.PP
3080The default mode of operation (for libev, with application help to detect
3081forks) is to duplicate all the state in the child, as would be expected
3082when \fIeither\fR the parent \fIor\fR the child process continues.
3083.PP
3084When both processes want to continue using libev, then this is usually the
3085wrong result. In that case, usually one process (typically the parent) is
3086supposed to continue with all watchers in place as before, while the other
3087process typically wants to start fresh, i.e. without any active watchers.
3088.PP
3089The cleanest and most efficient way to achieve that with libev is to
3090simply create a new event loop, which of course will be \*(L"empty\*(R", and
3091use that for new watchers. This has the advantage of not touching more
3092memory than necessary, and thus avoiding the copy-on-write, and the
3093disadvantage of having to use multiple event loops (which do not support
3094signal watchers).
3095.PP
3096When this is not possible, or you want to use the default loop for
3097other reasons, then in the process that wants to start \*(L"fresh\*(R", call
3098\&\f(CW\*(C`ev_default_destroy ()\*(C'\fR followed by \f(CW\*(C`ev_default_loop (...)\*(C'\fR. Destroying
3099the default loop will \*(L"orphan\*(R" (not stop) all registered watchers, so you
3100have to be careful not to execute code that modifies those watchers. Note
3101also that in that case, you have to re-register any signal watchers.
3102.PP
3103\fIWatcher-Specific Functions and Data Members\fR
3104.IX Subsection "Watcher-Specific Functions and Data Members"
3105.IP "ev_fork_init (ev_signal *, callback)" 4
3106.IX Item "ev_fork_init (ev_signal *, callback)"
3107Initialises and configures the fork watcher \- it has no parameters of any
3108kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
3109believe me.
3110.ie n .SS """ev_async"" \- how to wake up another event loop"
3111.el .SS "\f(CWev_async\fP \- how to wake up another event loop"
3112.IX Subsection "ev_async - how to wake up another event loop"
3113In general, you cannot use an \f(CW\*(C`ev_loop\*(C'\fR from multiple threads or other
3114asynchronous sources such as signal handlers (as opposed to multiple event
3115loops \- those are of course safe to use in different threads).
3116.PP
3117Sometimes, however, you need to wake up another event loop you do not
3118control, for example because it belongs to another thread. This is what
3119\&\f(CW\*(C`ev_async\*(C'\fR watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you
3120can signal it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal
3121safe.
3122.PP
3123This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals,
3124too, are asynchronous in nature, and signals, too, will be compressed
3125(i.e. the number of callback invocations may be less than the number of
3126\&\f(CW\*(C`ev_async_sent\*(C'\fR calls).
3127.PP
3128Unlike \f(CW\*(C`ev_signal\*(C'\fR watchers, \f(CW\*(C`ev_async\*(C'\fR works with any event loop, not
3129just the default loop.
3130.PP
3131\fIQueueing\fR
3132.IX Subsection "Queueing"
3133.PP
3134\&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason
3135is that the author does not know of a simple (or any) algorithm for a
3136multiple-writer-single-reader queue that works in all cases and doesn't
3137need elaborate support such as pthreads or unportable memory access
3138semantics.
3139.PP
3140That means that if you want to queue data, you have to provide your own
3141queue. But at least I can tell you how to implement locking around your
3142queue:
3143.IP "queueing from a signal handler context" 4
3144.IX Item "queueing from a signal handler context"
3145To implement race-free queueing, you simply add to the queue in the signal
3146handler but you block the signal handler in the watcher callback. Here is
3147an example that does that for some fictitious \s-1SIGUSR1\s0 handler:
3148.Sp
3149.Vb 1
3150\& static ev_async mysig;
3151\&
3152\& static void
3153\& sigusr1_handler (void)
3154\& {
3155\& sometype data;
3156\&
3157\& // no locking etc.
3158\& queue_put (data);
3159\& ev_async_send (EV_DEFAULT_ &mysig);
3160\& }
3161\&
3162\& static void
3163\& mysig_cb (EV_P_ ev_async *w, int revents)
3164\& {
3165\& sometype data;
3166\& sigset_t block, prev;
3167\&
3168\& sigemptyset (&block);
3169\& sigaddset (&block, SIGUSR1);
3170\& sigprocmask (SIG_BLOCK, &block, &prev);
3171\&
3172\& while (queue_get (&data))
3173\& process (data);
3174\&
3175\& if (sigismember (&prev, SIGUSR1)
3176\& sigprocmask (SIG_UNBLOCK, &block, 0);
3177\& }
3178.Ve
3179.Sp
3180(Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR
3181instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it
3182either...).
3183.IP "queueing from a thread context" 4
3184.IX Item "queueing from a thread context"
3185The strategy for threads is different, as you cannot (easily) block
3186threads but you can easily preempt them, so to queue safely you need to
3187employ a traditional mutex lock, such as in this pthread example:
3188.Sp
3189.Vb 2
3190\& static ev_async mysig;
3191\& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
3192\&
3193\& static void
3194\& otherthread (void)
3195\& {
3196\& // only need to lock the actual queueing operation
3197\& pthread_mutex_lock (&mymutex);
3198\& queue_put (data);
3199\& pthread_mutex_unlock (&mymutex);
3200\&
3201\& ev_async_send (EV_DEFAULT_ &mysig);
3202\& }
3203\&
3204\& static void
3205\& mysig_cb (EV_P_ ev_async *w, int revents)
3206\& {
3207\& pthread_mutex_lock (&mymutex);
3208\&
3209\& while (queue_get (&data))
3210\& process (data);
3211\&
3212\& pthread_mutex_unlock (&mymutex);
3213\& }
3214.Ve
3215.PP
3216\fIWatcher-Specific Functions and Data Members\fR
3217.IX Subsection "Watcher-Specific Functions and Data Members"
3218.IP "ev_async_init (ev_async *, callback)" 4
3219.IX Item "ev_async_init (ev_async *, callback)"
3220Initialises and configures the async watcher \- it has no parameters of any
3221kind. There is a \f(CW\*(C`ev_async_set\*(C'\fR macro, but using it is utterly pointless,
3222trust me.
3223.IP "ev_async_send (loop, ev_async *)" 4
3224.IX Item "ev_async_send (loop, ev_async *)"
3225Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds
3226an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop. Unlike
3227\&\f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do from other threads, signal or
3228similar contexts (see the discussion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the embedding
3229section below on what exactly this means).
3230.Sp
3231Note that, as with other watchers in libev, multiple events might get
3232compressed into a single callback invocation (another way to look at this
3233is that \f(CW\*(C`ev_async\*(C'\fR watchers are level-triggered, set on \f(CW\*(C`ev_async_send\*(C'\fR,
3234reset when the event loop detects that).
3235.Sp
3236This call incurs the overhead of a system call only once per event loop
3237iteration, so while the overhead might be noticeable, it doesn't apply to
3238repeated calls to \f(CW\*(C`ev_async_send\*(C'\fR for the same event loop.
3239.IP "bool = ev_async_pending (ev_async *)" 4
3240.IX Item "bool = ev_async_pending (ev_async *)"
3241Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the
3242watcher but the event has not yet been processed (or even noted) by the
3243event loop.
3244.Sp
3245\&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When
3246the loop iterates next and checks for the watcher to have become active,
3247it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very
3248quickly check whether invoking the loop might be a good idea.
3249.Sp
3250Not that this does \fInot\fR check whether the watcher itself is pending,
3251only whether it has been requested to make this watcher pending: there
3252is a time window between the event loop checking and resetting the async
3253notification, and the callback being invoked.
924.SH "OTHER FUNCTIONS" 3254.SH "OTHER FUNCTIONS"
925.IX Header "OTHER FUNCTIONS" 3255.IX Header "OTHER FUNCTIONS"
926There are some other functions of possible interest. Described. Here. Now. 3256There are some other functions of possible interest. Described. Here. Now.
927.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4 3257.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
928.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 3258.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"
929This function combines a simple timer and an I/O watcher, calls your 3259This function combines a simple timer and an I/O watcher, calls your
930callback on whichever event happens first and automatically stop both 3260callback on whichever event happens first and automatically stops both
931watchers. This is useful if you want to wait for a single event on an fd 3261watchers. This is useful if you want to wait for a single event on an fd
932or timeout without having to allocate/configure/start/stop/free one or 3262or timeout without having to allocate/configure/start/stop/free one or
933more watchers yourself. 3263more watchers yourself.
934.Sp 3264.Sp
935If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and events 3265If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and the
936is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for the given \f(CW\*(C`fd\*(C'\fR and 3266\&\f(CW\*(C`events\*(C'\fR argument is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for
937\&\f(CW\*(C`events\*(C'\fR set will be craeted and started. 3267the given \f(CW\*(C`fd\*(C'\fR and \f(CW\*(C`events\*(C'\fR set will be created and started.
938.Sp 3268.Sp
939If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be 3269If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
940started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and 3270started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
941repeat = 0) will be started. While \f(CW0\fR is a valid timeout, it is of 3271repeat = 0) will be started. \f(CW0\fR is a valid timeout.
942dubious value.
943.Sp 3272.Sp
944The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets 3273The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets
945passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of 3274passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
946\&\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 3275\&\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
947value passed to \f(CW\*(C`ev_once\*(C'\fR: 3276value passed to \f(CW\*(C`ev_once\*(C'\fR. Note that it is possible to receive \fIboth\fR
3277a timeout and an io event at the same time \- you probably should give io
3278events precedence.
3279.Sp
3280Example: wait up to ten seconds for data to appear on \s-1STDIN_FILENO\s0.
948.Sp 3281.Sp
949.Vb 7 3282.Vb 7
950\& static void stdin_ready (int revents, void *arg) 3283\& static void stdin_ready (int revents, void *arg)
951\& { 3284\& {
952\& if (revents & EV_TIMEOUT)
953\& /* doh, nothing entered */;
954\& else if (revents & EV_READ) 3285\& if (revents & EV_READ)
955\& /* stdin might have data for us, joy! */; 3286\& /* stdin might have data for us, joy! */;
3287\& else if (revents & EV_TIMEOUT)
3288\& /* doh, nothing entered */;
956\& } 3289\& }
957.Ve 3290\&
958.Sp
959.Vb 1
960\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); 3291\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
961.Ve 3292.Ve
962.IP "ev_feed_event (loop, watcher, int events)" 4
963.IX Item "ev_feed_event (loop, watcher, int events)"
964Feeds the given event set into the event loop, as if the specified event
965had happened for the specified watcher (which must be a pointer to an
966initialised but not necessarily started event watcher).
967.IP "ev_feed_fd_event (loop, int fd, int revents)" 4 3293.IP "ev_feed_fd_event (loop, int fd, int revents)" 4
968.IX Item "ev_feed_fd_event (loop, int fd, int revents)" 3294.IX Item "ev_feed_fd_event (loop, int fd, int revents)"
969Feed an event on the given fd, as if a file descriptor backend detected 3295Feed an event on the given fd, as if a file descriptor backend detected
970the given events it. 3296the given events it.
971.IP "ev_feed_signal_event (loop, int signum)" 4 3297.IP "ev_feed_signal_event (loop, int signum)" 4
972.IX Item "ev_feed_signal_event (loop, int signum)" 3298.IX Item "ev_feed_signal_event (loop, int signum)"
973Feed an event as if the given signal occured (loop must be the default loop!). 3299Feed an event as if the given signal occurred (\f(CW\*(C`loop\*(C'\fR must be the default
3300loop!).
974.SH "LIBEVENT EMULATION" 3301.SH "LIBEVENT EMULATION"
975.IX Header "LIBEVENT EMULATION" 3302.IX Header "LIBEVENT EMULATION"
976Libev offers a compatibility emulation layer for libevent. It cannot 3303Libev offers a compatibility emulation layer for libevent. It cannot
977emulate the internals of libevent, so here are some usage hints: 3304emulate the internals of libevent, so here are some usage hints:
3305.IP "\(bu" 4
978.IP "* Use it by including <event.h>, as usual." 4 3306Use it by including <event.h>, as usual.
979.IX Item "Use it by including <event.h>, as usual." 3307.IP "\(bu" 4
980.PD 0 3308The following members are fully supported: ev_base, ev_callback,
981.IP "* The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4 3309ev_arg, ev_fd, ev_res, ev_events.
982.IX Item "The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 3310.IP "\(bu" 4
983.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 3311Avoid using ev_flags and the EVLIST_*\-macros, while it is
984.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)." 3312maintained by libev, it does not work exactly the same way as in libevent (consider
985.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 3313it a private \s-1API\s0).
986.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." 3314.IP "\(bu" 4
3315Priorities are not currently supported. Initialising priorities
3316will fail and all watchers will have the same priority, even though there
3317is an ev_pri field.
3318.IP "\(bu" 4
3319In libevent, the last base created gets the signals, in libev, the
3320first base created (== the default loop) gets the signals.
3321.IP "\(bu" 4
987.IP "* Other members are not supported." 4 3322Other members are not supported.
988.IX Item "Other members are not supported." 3323.IP "\(bu" 4
989.IP "* The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need to use the libev header file and library." 4 3324The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need
990.IX Item "The libev emulation is not ABI compatible to libevent, you need to use the libev header file and library." 3325to use the libev header file and library.
991.PD
992.SH "\*(C+ SUPPORT" 3326.SH "\*(C+ SUPPORT"
993.IX Header " SUPPORT" 3327.IX Header " SUPPORT"
994\&\s-1TBD\s0. 3328Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
3329you to use some convenience methods to start/stop watchers and also change
3330the callback model to a model using method callbacks on objects.
3331.PP
3332To use it,
3333.PP
3334.Vb 1
3335\& #include <ev++.h>
3336.Ve
3337.PP
3338This automatically includes \fIev.h\fR and puts all of its definitions (many
3339of them macros) into the global namespace. All \*(C+ specific things are
3340put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding
3341options as \fIev.h\fR, most notably \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR.
3342.PP
3343Care has been taken to keep the overhead low. The only data member the \*(C+
3344classes add (compared to plain C\-style watchers) is the event loop pointer
3345that the watcher is associated with (or no additional members at all if
3346you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
3347.PP
3348Currently, functions, and static and non-static member functions can be
3349used as callbacks. Other types should be easy to add as long as they only
3350need one additional pointer for context. If you need support for other
3351types of functors please contact the author (preferably after implementing
3352it).
3353.PP
3354Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
3355.ie n .IP """ev::READ"", ""ev::WRITE"" etc." 4
3356.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
3357.IX Item "ev::READ, ev::WRITE etc."
3358These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
3359macros from \fIev.h\fR.
3360.ie n .IP """ev::tstamp"", ""ev::now""" 4
3361.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
3362.IX Item "ev::tstamp, ev::now"
3363Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
3364.ie n .IP """ev::io"", ""ev::timer"", ""ev::periodic"", ""ev::idle"", ""ev::sig"" etc." 4
3365.el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
3366.IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
3367For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
3368the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
3369which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
3370defines by many implementations.
3371.Sp
3372All of those classes have these methods:
3373.RS 4
3374.IP "ev::TYPE::TYPE ()" 4
3375.IX Item "ev::TYPE::TYPE ()"
3376.PD 0
3377.IP "ev::TYPE::TYPE (loop)" 4
3378.IX Item "ev::TYPE::TYPE (loop)"
3379.IP "ev::TYPE::~TYPE" 4
3380.IX Item "ev::TYPE::~TYPE"
3381.PD
3382The constructor (optionally) takes an event loop to associate the watcher
3383with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR.
3384.Sp
3385The constructor calls \f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the
3386\&\f(CW\*(C`set\*(C'\fR method before starting it.
3387.Sp
3388It will not set a callback, however: You have to call the templated \f(CW\*(C`set\*(C'\fR
3389method to set a callback before you can start the watcher.
3390.Sp
3391(The reason why you have to use a method is a limitation in \*(C+ which does
3392not allow explicit template arguments for constructors).
3393.Sp
3394The destructor automatically stops the watcher if it is active.
3395.IP "w\->set<class, &class::method> (object *)" 4
3396.IX Item "w->set<class, &class::method> (object *)"
3397This method sets the callback method to call. The method has to have a
3398signature of \f(CW\*(C`void (*)(ev_TYPE &, int)\*(C'\fR, it receives the watcher as
3399first argument and the \f(CW\*(C`revents\*(C'\fR as second. The object must be given as
3400parameter and is stored in the \f(CW\*(C`data\*(C'\fR member of the watcher.
3401.Sp
3402This method synthesizes efficient thunking code to call your method from
3403the C callback that libev requires. If your compiler can inline your
3404callback (i.e. it is visible to it at the place of the \f(CW\*(C`set\*(C'\fR call and
3405your compiler is good :), then the method will be fully inlined into the
3406thunking function, making it as fast as a direct C callback.
3407.Sp
3408Example: simple class declaration and watcher initialisation
3409.Sp
3410.Vb 4
3411\& struct myclass
3412\& {
3413\& void io_cb (ev::io &w, int revents) { }
3414\& }
3415\&
3416\& myclass obj;
3417\& ev::io iow;
3418\& iow.set <myclass, &myclass::io_cb> (&obj);
3419.Ve
3420.IP "w\->set (object *)" 4
3421.IX Item "w->set (object *)"
3422This is an \fBexperimental\fR feature that might go away in a future version.
3423.Sp
3424This is a variation of a method callback \- leaving out the method to call
3425will default the method to \f(CW\*(C`operator ()\*(C'\fR, which makes it possible to use
3426functor objects without having to manually specify the \f(CW\*(C`operator ()\*(C'\fR all
3427the time. Incidentally, you can then also leave out the template argument
3428list.
3429.Sp
3430The \f(CW\*(C`operator ()\*(C'\fR method prototype must be \f(CW\*(C`void operator ()(watcher &w,
3431int revents)\*(C'\fR.
3432.Sp
3433See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
3434.Sp
3435Example: use a functor object as callback.
3436.Sp
3437.Vb 7
3438\& struct myfunctor
3439\& {
3440\& void operator() (ev::io &w, int revents)
3441\& {
3442\& ...
3443\& }
3444\& }
3445\&
3446\& myfunctor f;
3447\&
3448\& ev::io w;
3449\& w.set (&f);
3450.Ve
3451.IP "w\->set<function> (void *data = 0)" 4
3452.IX Item "w->set<function> (void *data = 0)"
3453Also sets a callback, but uses a static method or plain function as
3454callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
3455\&\f(CW\*(C`data\*(C'\fR member and is free for you to use.
3456.Sp
3457The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
3458.Sp
3459See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
3460.Sp
3461Example: Use a plain function as callback.
3462.Sp
3463.Vb 2
3464\& static void io_cb (ev::io &w, int revents) { }
3465\& iow.set <io_cb> ();
3466.Ve
3467.IP "w\->set (loop)" 4
3468.IX Item "w->set (loop)"
3469Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
3470do this when the watcher is inactive (and not pending either).
3471.IP "w\->set ([arguments])" 4
3472.IX Item "w->set ([arguments])"
3473Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same arguments. Must be
3474called at least once. Unlike the C counterpart, an active watcher gets
3475automatically stopped and restarted when reconfiguring it with this
3476method.
3477.IP "w\->start ()" 4
3478.IX Item "w->start ()"
3479Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
3480constructor already stores the event loop.
3481.IP "w\->stop ()" 4
3482.IX Item "w->stop ()"
3483Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
3484.ie n .IP "w\->again () (""ev::timer"", ""ev::periodic"" only)" 4
3485.el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
3486.IX Item "w->again () (ev::timer, ev::periodic only)"
3487For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
3488\&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
3489.ie n .IP "w\->sweep () (""ev::embed"" only)" 4
3490.el .IP "w\->sweep () (\f(CWev::embed\fR only)" 4
3491.IX Item "w->sweep () (ev::embed only)"
3492Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR.
3493.ie n .IP "w\->update () (""ev::stat"" only)" 4
3494.el .IP "w\->update () (\f(CWev::stat\fR only)" 4
3495.IX Item "w->update () (ev::stat only)"
3496Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
3497.RE
3498.RS 4
3499.RE
3500.PP
3501Example: Define a class with an \s-1IO\s0 and idle watcher, start one of them in
3502the constructor.
3503.PP
3504.Vb 4
3505\& class myclass
3506\& {
3507\& ev::io io ; void io_cb (ev::io &w, int revents);
3508\& ev::idle idle; void idle_cb (ev::idle &w, int revents);
3509\&
3510\& myclass (int fd)
3511\& {
3512\& io .set <myclass, &myclass::io_cb > (this);
3513\& idle.set <myclass, &myclass::idle_cb> (this);
3514\&
3515\& io.start (fd, ev::READ);
3516\& }
3517\& };
3518.Ve
3519.SH "OTHER LANGUAGE BINDINGS"
3520.IX Header "OTHER LANGUAGE BINDINGS"
3521Libev does not offer other language bindings itself, but bindings for a
3522number of languages exist in the form of third-party packages. If you know
3523any interesting language binding in addition to the ones listed here, drop
3524me a note.
3525.IP "Perl" 4
3526.IX Item "Perl"
3527The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test
3528libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module,
3529there are additional modules that implement libev-compatible interfaces
3530to \f(CW\*(C`libadns\*(C'\fR (\f(CW\*(C`EV::ADNS\*(C'\fR, but \f(CW\*(C`AnyEvent::DNS\*(C'\fR is preferred nowadays),
3531\&\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
3532and \f(CW\*(C`EV::Glib\*(C'\fR).
3533.Sp
3534It can be found and installed via \s-1CPAN\s0, its homepage is at
3535<http://software.schmorp.de/pkg/EV>.
3536.IP "Python" 4
3537.IX Item "Python"
3538Python bindings can be found at <http://code.google.com/p/pyev/>. It
3539seems to be quite complete and well-documented.
3540.IP "Ruby" 4
3541.IX Item "Ruby"
3542Tony Arcieri has written a ruby extension that offers access to a subset
3543of the libev \s-1API\s0 and adds file handle abstractions, asynchronous \s-1DNS\s0 and
3544more on top of it. It can be found via gem servers. Its homepage is at
3545<http://rev.rubyforge.org/>.
3546.Sp
3547Roger Pack reports that using the link order \f(CW\*(C`\-lws2_32 \-lmsvcrt\-ruby\-190\*(C'\fR
3548makes rev work even on mingw.
3549.IP "Haskell" 4
3550.IX Item "Haskell"
3551A haskell binding to libev is available at
3552<http://hackage.haskell.org/cgi\-bin/hackage\-scripts/package/hlibev>.
3553.IP "D" 4
3554.IX Item "D"
3555Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
3556be found at <http://proj.llucax.com.ar/wiki/evd>.
3557.IP "Ocaml" 4
3558.IX Item "Ocaml"
3559Erkki Seppala has written Ocaml bindings for libev, to be found at
3560<http://modeemi.cs.tut.fi/~flux/software/ocaml\-ev/>.
3561.IP "Lua" 4
3562.IX Item "Lua"
3563Brian Maher has written a partial interface to libev
3564for lua (only \f(CW\*(C`ev_io\*(C'\fR and \f(CW\*(C`ev_timer\*(C'\fR), to be found at
3565<http://github.com/brimworks/lua\-ev>.
3566.SH "MACRO MAGIC"
3567.IX Header "MACRO MAGIC"
3568Libev can be compiled with a variety of options, the most fundamental
3569of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most)
3570functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
3571.PP
3572To make it easier to write programs that cope with either variant, the
3573following macros are defined:
3574.ie n .IP """EV_A"", ""EV_A_""" 4
3575.el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
3576.IX Item "EV_A, EV_A_"
3577This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
3578loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
3579\&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
3580.Sp
3581.Vb 3
3582\& ev_unref (EV_A);
3583\& ev_timer_add (EV_A_ watcher);
3584\& ev_loop (EV_A_ 0);
3585.Ve
3586.Sp
3587It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
3588which is often provided by the following macro.
3589.ie n .IP """EV_P"", ""EV_P_""" 4
3590.el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
3591.IX Item "EV_P, EV_P_"
3592This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
3593loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
3594\&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
3595.Sp
3596.Vb 2
3597\& // this is how ev_unref is being declared
3598\& static void ev_unref (EV_P);
3599\&
3600\& // this is how you can declare your typical callback
3601\& static void cb (EV_P_ ev_timer *w, int revents)
3602.Ve
3603.Sp
3604It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
3605suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
3606.ie n .IP """EV_DEFAULT"", ""EV_DEFAULT_""" 4
3607.el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
3608.IX Item "EV_DEFAULT, EV_DEFAULT_"
3609Similar to the other two macros, this gives you the value of the default
3610loop, if multiple loops are supported (\*(L"ev loop default\*(R").
3611.ie n .IP """EV_DEFAULT_UC"", ""EV_DEFAULT_UC_""" 4
3612.el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
3613.IX Item "EV_DEFAULT_UC, EV_DEFAULT_UC_"
3614Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the
3615default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour
3616is undefined when the default loop has not been initialised by a previous
3617execution of \f(CW\*(C`EV_DEFAULT\*(C'\fR, \f(CW\*(C`EV_DEFAULT_\*(C'\fR or \f(CW\*(C`ev_default_init (...)\*(C'\fR.
3618.Sp
3619It is often prudent to use \f(CW\*(C`EV_DEFAULT\*(C'\fR when initialising the first
3620watcher in a function but use \f(CW\*(C`EV_DEFAULT_UC\*(C'\fR afterwards.
3621.PP
3622Example: Declare and initialise a check watcher, utilising the above
3623macros so it will work regardless of whether multiple loops are supported
3624or not.
3625.PP
3626.Vb 5
3627\& static void
3628\& check_cb (EV_P_ ev_timer *w, int revents)
3629\& {
3630\& ev_check_stop (EV_A_ w);
3631\& }
3632\&
3633\& ev_check check;
3634\& ev_check_init (&check, check_cb);
3635\& ev_check_start (EV_DEFAULT_ &check);
3636\& ev_loop (EV_DEFAULT_ 0);
3637.Ve
3638.SH "EMBEDDING"
3639.IX Header "EMBEDDING"
3640Libev can (and often is) directly embedded into host
3641applications. Examples of applications that embed it include the Deliantra
3642Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
3643and rxvt-unicode.
3644.PP
3645The goal is to enable you to just copy the necessary files into your
3646source directory without having to change even a single line in them, so
3647you can easily upgrade by simply copying (or having a checked-out copy of
3648libev somewhere in your source tree).
3649.SS "\s-1FILESETS\s0"
3650.IX Subsection "FILESETS"
3651Depending on what features you need you need to include one or more sets of files
3652in your application.
3653.PP
3654\fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR
3655.IX Subsection "CORE EVENT LOOP"
3656.PP
3657To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
3658configuration (no autoconf):
3659.PP
3660.Vb 2
3661\& #define EV_STANDALONE 1
3662\& #include "ev.c"
3663.Ve
3664.PP
3665This will automatically include \fIev.h\fR, too, and should be done in a
3666single C source file only to provide the function implementations. To use
3667it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best
3668done by writing a wrapper around \fIev.h\fR that you can include instead and
3669where you can put other configuration options):
3670.PP
3671.Vb 2
3672\& #define EV_STANDALONE 1
3673\& #include "ev.h"
3674.Ve
3675.PP
3676Both header files and implementation files can be compiled with a \*(C+
3677compiler (at least, that's a stated goal, and breakage will be treated
3678as a bug).
3679.PP
3680You need the following files in your source tree, or in a directory
3681in your include path (e.g. in libev/ when using \-Ilibev):
3682.PP
3683.Vb 4
3684\& ev.h
3685\& ev.c
3686\& ev_vars.h
3687\& ev_wrap.h
3688\&
3689\& ev_win32.c required on win32 platforms only
3690\&
3691\& ev_select.c only when select backend is enabled (which is enabled by default)
3692\& ev_poll.c only when poll backend is enabled (disabled by default)
3693\& ev_epoll.c only when the epoll backend is enabled (disabled by default)
3694\& ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
3695\& ev_port.c only when the solaris port backend is enabled (disabled by default)
3696.Ve
3697.PP
3698\&\fIev.c\fR includes the backend files directly when enabled, so you only need
3699to compile this single file.
3700.PP
3701\fI\s-1LIBEVENT\s0 \s-1COMPATIBILITY\s0 \s-1API\s0\fR
3702.IX Subsection "LIBEVENT COMPATIBILITY API"
3703.PP
3704To include the libevent compatibility \s-1API\s0, also include:
3705.PP
3706.Vb 1
3707\& #include "event.c"
3708.Ve
3709.PP
3710in the file including \fIev.c\fR, and:
3711.PP
3712.Vb 1
3713\& #include "event.h"
3714.Ve
3715.PP
3716in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR.
3717.PP
3718You need the following additional files for this:
3719.PP
3720.Vb 2
3721\& event.h
3722\& event.c
3723.Ve
3724.PP
3725\fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR
3726.IX Subsection "AUTOCONF SUPPORT"
3727.PP
3728Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your configuration in
3729whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
3730\&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then
3731include \fIconfig.h\fR and configure itself accordingly.
3732.PP
3733For this of course you need the m4 file:
3734.PP
3735.Vb 1
3736\& libev.m4
3737.Ve
3738.SS "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0"
3739.IX Subsection "PREPROCESSOR SYMBOLS/MACROS"
3740Libev can be configured via a variety of preprocessor symbols you have to
3741define before including any of its files. The default in the absence of
3742autoconf is documented for every option.
3743.IP "\s-1EV_STANDALONE\s0" 4
3744.IX Item "EV_STANDALONE"
3745Must always be \f(CW1\fR if you do not use autoconf configuration, which
3746keeps libev from including \fIconfig.h\fR, and it also defines dummy
3747implementations for some libevent functions (such as logging, which is not
3748supported). It will also not define any of the structs usually found in
3749\&\fIevent.h\fR that are not directly supported by the libev core alone.
3750.Sp
3751In standalone mode, libev will still try to automatically deduce the
3752configuration, but has to be more conservative.
3753.IP "\s-1EV_USE_MONOTONIC\s0" 4
3754.IX Item "EV_USE_MONOTONIC"
3755If defined to be \f(CW1\fR, libev will try to detect the availability of the
3756monotonic clock option at both compile time and runtime. Otherwise no
3757use of the monotonic clock option will be attempted. If you enable this,
3758you usually have to link against librt or something similar. Enabling it
3759when the functionality isn't available is safe, though, although you have
3760to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
3761function is hiding in (often \fI\-lrt\fR). See also \f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
3762.IP "\s-1EV_USE_REALTIME\s0" 4
3763.IX Item "EV_USE_REALTIME"
3764If defined to be \f(CW1\fR, libev will try to detect the availability of the
3765real-time clock option at compile time (and assume its availability
3766at runtime if successful). Otherwise no use of the real-time clock
3767option will be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR
3768by \f(CW\*(C`clock_get (CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect
3769correctness. See the note about libraries in the description of
3770\&\f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. Defaults to the opposite value of
3771\&\f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
3772.IP "\s-1EV_USE_CLOCK_SYSCALL\s0" 4
3773.IX Item "EV_USE_CLOCK_SYSCALL"
3774If defined to be \f(CW1\fR, libev will try to use a direct syscall instead
3775of calling the system-provided \f(CW\*(C`clock_gettime\*(C'\fR function. This option
3776exists 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
3777unconditionally pulls in \f(CW\*(C`libpthread\*(C'\fR, slowing down single-threaded
3778programs needlessly. Using a direct syscall is slightly slower (in
3779theory), because no optimised vdso implementation can be used, but avoids
3780the pthread dependency. Defaults to \f(CW1\fR on GNU/Linux with glibc 2.x or
3781higher, as it simplifies linking (no need for \f(CW\*(C`\-lrt\*(C'\fR).
3782.IP "\s-1EV_USE_NANOSLEEP\s0" 4
3783.IX Item "EV_USE_NANOSLEEP"
3784If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available
3785and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR.
3786.IP "\s-1EV_USE_EVENTFD\s0" 4
3787.IX Item "EV_USE_EVENTFD"
3788If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
3789available and will probe for kernel support at runtime. This will improve
3790\&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
3791If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
37922.7 or newer, otherwise disabled.
3793.IP "\s-1EV_USE_SELECT\s0" 4
3794.IX Item "EV_USE_SELECT"
3795If undefined or defined to be \f(CW1\fR, libev will compile in support for the
3796\&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at auto-detection will be done: if no
3797other method takes over, select will be it. Otherwise the select backend
3798will not be compiled in.
3799.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
3800.IX Item "EV_SELECT_USE_FD_SET"
3801If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR
3802structure. This is useful if libev doesn't compile due to a missing
3803\&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it mis-guesses the bitset layout
3804on exotic systems. This usually limits the range of file descriptors to
3805some low limit such as 1024 or might have other limitations (winsocket
3806only allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation,
3807configures the maximum size of the \f(CW\*(C`fd_set\*(C'\fR.
3808.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
3809.IX Item "EV_SELECT_IS_WINSOCKET"
3810When defined to \f(CW1\fR, the select backend will assume that
3811select/socket/connect etc. don't understand file descriptors but
3812wants osf handles on win32 (this is the case when the select to
3813be used is the winsock select). This means that it will call
3814\&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
3815it is assumed that all these functions actually work on fds, even
3816on win32. Should not be defined on non\-win32 platforms.
3817.IP "\s-1EV_FD_TO_WIN32_HANDLE\s0(fd)" 4
3818.IX Item "EV_FD_TO_WIN32_HANDLE(fd)"
3819If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map
3820file descriptors to socket handles. When not defining this symbol (the
3821default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually
3822correct. In some cases, programs use their own file descriptor management,
3823in which case they can provide this function to map fds to socket handles.
3824.IP "\s-1EV_WIN32_HANDLE_TO_FD\s0(handle)" 4
3825.IX Item "EV_WIN32_HANDLE_TO_FD(handle)"
3826If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR then libev maps handles to file descriptors
3827using the standard \f(CW\*(C`_open_osfhandle\*(C'\fR function. For programs implementing
3828their own fd to handle mapping, overwriting this function makes it easier
3829to do so. This can be done by defining this macro to an appropriate value.
3830.IP "\s-1EV_WIN32_CLOSE_FD\s0(fd)" 4
3831.IX Item "EV_WIN32_CLOSE_FD(fd)"
3832If programs implement their own fd to handle mapping on win32, then this
3833macro can be used to override the \f(CW\*(C`close\*(C'\fR function, useful to unregister
3834file descriptors again. Note that the replacement function has to close
3835the underlying \s-1OS\s0 handle.
3836.IP "\s-1EV_USE_POLL\s0" 4
3837.IX Item "EV_USE_POLL"
3838If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2)
3839backend. Otherwise it will be enabled on non\-win32 platforms. It
3840takes precedence over select.
3841.IP "\s-1EV_USE_EPOLL\s0" 4
3842.IX Item "EV_USE_EPOLL"
3843If defined to be \f(CW1\fR, libev will compile in support for the Linux
3844\&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime,
3845otherwise another method will be used as fallback. This is the preferred
3846backend for GNU/Linux systems. If undefined, it will be enabled if the
3847headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3848.IP "\s-1EV_USE_KQUEUE\s0" 4
3849.IX Item "EV_USE_KQUEUE"
3850If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
3851\&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime,
3852otherwise another method will be used as fallback. This is the preferred
3853backend for \s-1BSD\s0 and BSD-like systems, although on most BSDs kqueue only
3854supports some types of fds correctly (the only platform we found that
3855supports ptys for example was NetBSD), so kqueue might be compiled in, but
3856not be used unless explicitly requested. The best way to use it is to find
3857out whether kqueue supports your type of fd properly and use an embedded
3858kqueue loop.
3859.IP "\s-1EV_USE_PORT\s0" 4
3860.IX Item "EV_USE_PORT"
3861If defined to be \f(CW1\fR, libev will compile in support for the Solaris
386210 port style backend. Its availability will be detected at runtime,
3863otherwise another method will be used as fallback. This is the preferred
3864backend for Solaris 10 systems.
3865.IP "\s-1EV_USE_DEVPOLL\s0" 4
3866.IX Item "EV_USE_DEVPOLL"
3867Reserved for future expansion, works like the \s-1USE\s0 symbols above.
3868.IP "\s-1EV_USE_INOTIFY\s0" 4
3869.IX Item "EV_USE_INOTIFY"
3870If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
3871interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
3872be detected at runtime. If undefined, it will be enabled if the headers
3873indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3874.IP "\s-1EV_ATOMIC_T\s0" 4
3875.IX Item "EV_ATOMIC_T"
3876Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
3877access is atomic with respect to other threads or signal contexts. No such
3878type is easily found in the C language, so you can provide your own type
3879that you know is safe for your purposes. It is used both for signal handler \*(L"locking\*(R"
3880as well as for signal and thread safety in \f(CW\*(C`ev_async\*(C'\fR watchers.
3881.Sp
3882In the absence of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR
3883(from \fIsignal.h\fR), which is usually good enough on most platforms.
3884.IP "\s-1EV_H\s0" 4
3885.IX Item "EV_H"
3886The name of the \fIev.h\fR header file used to include it. The default if
3887undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be
3888used to virtually rename the \fIev.h\fR header file in case of conflicts.
3889.IP "\s-1EV_CONFIG_H\s0" 4
3890.IX Item "EV_CONFIG_H"
3891If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
3892\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
3893\&\f(CW\*(C`EV_H\*(C'\fR, above.
3894.IP "\s-1EV_EVENT_H\s0" 4
3895.IX Item "EV_EVENT_H"
3896Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea
3897of how the \fIevent.h\fR header can be found, the default is \f(CW"event.h"\fR.
3898.IP "\s-1EV_PROTOTYPES\s0" 4
3899.IX Item "EV_PROTOTYPES"
3900If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
3901prototypes, but still define all the structs and other symbols. This is
3902occasionally useful if you want to provide your own wrapper functions
3903around libev functions.
3904.IP "\s-1EV_MULTIPLICITY\s0" 4
3905.IX Item "EV_MULTIPLICITY"
3906If undefined or defined to \f(CW1\fR, then all event-loop-specific functions
3907will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create
3908additional independent event loops. Otherwise there will be no support
3909for multiple event loops and there is no first event loop pointer
3910argument. Instead, all functions act on the single default loop.
3911.IP "\s-1EV_MINPRI\s0" 4
3912.IX Item "EV_MINPRI"
3913.PD 0
3914.IP "\s-1EV_MAXPRI\s0" 4
3915.IX Item "EV_MAXPRI"
3916.PD
3917The range of allowed priorities. \f(CW\*(C`EV_MINPRI\*(C'\fR must be smaller or equal to
3918\&\f(CW\*(C`EV_MAXPRI\*(C'\fR, but otherwise there are no non-obvious limitations. You can
3919provide for more priorities by overriding those symbols (usually defined
3920to be \f(CW\*(C`\-2\*(C'\fR and \f(CW2\fR, respectively).
3921.Sp
3922When doing priority-based operations, libev usually has to linearly search
3923all the priorities, so having many of them (hundreds) uses a lot of space
3924and time, so using the defaults of five priorities (\-2 .. +2) is usually
3925fine.
3926.Sp
3927If your embedding application does not need any priorities, defining these
3928both to \f(CW0\fR will save some memory and \s-1CPU\s0.
3929.IP "\s-1EV_PERIODIC_ENABLE\s0" 4
3930.IX Item "EV_PERIODIC_ENABLE"
3931If undefined or defined to be \f(CW1\fR, then periodic timers are supported. If
3932defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of
3933code.
3934.IP "\s-1EV_IDLE_ENABLE\s0" 4
3935.IX Item "EV_IDLE_ENABLE"
3936If undefined or defined to be \f(CW1\fR, then idle watchers are supported. If
3937defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of
3938code.
3939.IP "\s-1EV_EMBED_ENABLE\s0" 4
3940.IX Item "EV_EMBED_ENABLE"
3941If undefined or defined to be \f(CW1\fR, then embed watchers are supported. If
3942defined to be \f(CW0\fR, then they are not. Embed watchers rely on most other
3943watcher types, which therefore must not be disabled.
3944.IP "\s-1EV_STAT_ENABLE\s0" 4
3945.IX Item "EV_STAT_ENABLE"
3946If undefined or defined to be \f(CW1\fR, then stat watchers are supported. If
3947defined to be \f(CW0\fR, then they are not.
3948.IP "\s-1EV_FORK_ENABLE\s0" 4
3949.IX Item "EV_FORK_ENABLE"
3950If undefined or defined to be \f(CW1\fR, then fork watchers are supported. If
3951defined to be \f(CW0\fR, then they are not.
3952.IP "\s-1EV_ASYNC_ENABLE\s0" 4
3953.IX Item "EV_ASYNC_ENABLE"
3954If undefined or defined to be \f(CW1\fR, then async watchers are supported. If
3955defined to be \f(CW0\fR, then they are not.
3956.IP "\s-1EV_MINIMAL\s0" 4
3957.IX Item "EV_MINIMAL"
3958If you need to shave off some kilobytes of code at the expense of some
3959speed (but with the full \s-1API\s0), define this symbol to \f(CW1\fR. Currently this
3960is used to override some inlining decisions, saves roughly 30% code size
3961on amd64. It also selects a much smaller 2\-heap for timer management over
3962the default 4\-heap.
3963.Sp
3964You can save even more by disabling watcher types you do not need
3965and setting \f(CW\*(C`EV_MAXPRI\*(C'\fR == \f(CW\*(C`EV_MINPRI\*(C'\fR. Also, disabling \f(CW\*(C`assert\*(C'\fR
3966(\f(CW\*(C`\-DNDEBUG\*(C'\fR) will usually reduce code size a lot.
3967.Sp
3968Defining \f(CW\*(C`EV_MINIMAL\*(C'\fR to \f(CW2\fR will additionally reduce the core \s-1API\s0 to
3969provide a bare-bones event library. See \f(CW\*(C`ev.h\*(C'\fR for details on what parts
3970of the \s-1API\s0 are still available, and do not complain if this subset changes
3971over time.
3972.IP "\s-1EV_NSIG\s0" 4
3973.IX Item "EV_NSIG"
3974The highest supported signal number, +1 (or, the number of
3975signals): Normally, libev tries to deduce the maximum number of signals
3976automatically, but sometimes this fails, in which case it can be
3977specified. Also, using a lower number than detected (\f(CW32\fR should be
3978good for about any system in existance) can save some memory, as libev
3979statically allocates some 12\-24 bytes per signal number.
3980.IP "\s-1EV_PID_HASHSIZE\s0" 4
3981.IX Item "EV_PID_HASHSIZE"
3982\&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by
3983pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR), usually more
3984than enough. If you need to manage thousands of children you might want to
3985increase this value (\fImust\fR be a power of two).
3986.IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4
3987.IX Item "EV_INOTIFY_HASHSIZE"
3988\&\f(CW\*(C`ev_stat\*(C'\fR watchers use a small hash table to distribute workload by
3989inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR),
3990usually more than enough. If you need to manage thousands of \f(CW\*(C`ev_stat\*(C'\fR
3991watchers you might want to increase this value (\fImust\fR be a power of
3992two).
3993.IP "\s-1EV_USE_4HEAP\s0" 4
3994.IX Item "EV_USE_4HEAP"
3995Heaps are not very cache-efficient. To improve the cache-efficiency of the
3996timer and periodics heaps, libev uses a 4\-heap when this symbol is defined
3997to \f(CW1\fR. The 4\-heap uses more complicated (longer) code but has noticeably
3998faster performance with many (thousands) of watchers.
3999.Sp
4000The default is \f(CW1\fR unless \f(CW\*(C`EV_MINIMAL\*(C'\fR is set in which case it is \f(CW0\fR
4001(disabled).
4002.IP "\s-1EV_HEAP_CACHE_AT\s0" 4
4003.IX Item "EV_HEAP_CACHE_AT"
4004Heaps are not very cache-efficient. To improve the cache-efficiency of the
4005timer and periodics heaps, libev can cache the timestamp (\fIat\fR) within
4006the heap structure (selected by defining \f(CW\*(C`EV_HEAP_CACHE_AT\*(C'\fR to \f(CW1\fR),
4007which uses 8\-12 bytes more per watcher and a few hundred bytes more code,
4008but avoids random read accesses on heap changes. This improves performance
4009noticeably with many (hundreds) of watchers.
4010.Sp
4011The default is \f(CW1\fR unless \f(CW\*(C`EV_MINIMAL\*(C'\fR is set in which case it is \f(CW0\fR
4012(disabled).
4013.IP "\s-1EV_VERIFY\s0" 4
4014.IX Item "EV_VERIFY"
4015Controls how much internal verification (see \f(CW\*(C`ev_loop_verify ()\*(C'\fR) will
4016be done: If set to \f(CW0\fR, no internal verification code will be compiled
4017in. If set to \f(CW1\fR, then verification code will be compiled in, but not
4018called. If set to \f(CW2\fR, then the internal verification code will be
4019called once per loop, which can slow down libev. If set to \f(CW3\fR, then the
4020verification code will be called very frequently, which will slow down
4021libev considerably.
4022.Sp
4023The default is \f(CW1\fR, unless \f(CW\*(C`EV_MINIMAL\*(C'\fR is set, in which case it will be
4024\&\f(CW0\fR.
4025.IP "\s-1EV_COMMON\s0" 4
4026.IX Item "EV_COMMON"
4027By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining
4028this macro to a something else you can include more and other types of
4029members. You have to define it each time you include one of the files,
4030though, and it must be identical each time.
4031.Sp
4032For example, the perl \s-1EV\s0 module uses something like this:
4033.Sp
4034.Vb 3
4035\& #define EV_COMMON \e
4036\& SV *self; /* contains this struct */ \e
4037\& SV *cb_sv, *fh /* note no trailing ";" */
4038.Ve
4039.IP "\s-1EV_CB_DECLARE\s0 (type)" 4
4040.IX Item "EV_CB_DECLARE (type)"
4041.PD 0
4042.IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4
4043.IX Item "EV_CB_INVOKE (watcher, revents)"
4044.IP "ev_set_cb (ev, cb)" 4
4045.IX Item "ev_set_cb (ev, cb)"
4046.PD
4047Can be used to change the callback member declaration in each watcher,
4048and the way callbacks are invoked and set. Must expand to a struct member
4049definition and a statement, respectively. See the \fIev.h\fR header file for
4050their default definitions. One possible use for overriding these is to
4051avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use
4052method calls instead of plain function calls in \*(C+.
4053.SS "\s-1EXPORTED\s0 \s-1API\s0 \s-1SYMBOLS\s0"
4054.IX Subsection "EXPORTED API SYMBOLS"
4055If you need to re-export the \s-1API\s0 (e.g. via a \s-1DLL\s0) and you need a list of
4056exported symbols, you can use the provided \fISymbol.*\fR files which list
4057all public symbols, one per line:
4058.PP
4059.Vb 2
4060\& Symbols.ev for libev proper
4061\& Symbols.event for the libevent emulation
4062.Ve
4063.PP
4064This can also be used to rename all public symbols to avoid clashes with
4065multiple versions of libev linked together (which is obviously bad in
4066itself, but sometimes it is inconvenient to avoid this).
4067.PP
4068A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to
4069include before including \fIev.h\fR:
4070.PP
4071.Vb 1
4072\& <Symbols.ev sed \-e "s/.*/#define & myprefix_&/" >wrap.h
4073.Ve
4074.PP
4075This would create a file \fIwrap.h\fR which essentially looks like this:
4076.PP
4077.Vb 4
4078\& #define ev_backend myprefix_ev_backend
4079\& #define ev_check_start myprefix_ev_check_start
4080\& #define ev_check_stop myprefix_ev_check_stop
4081\& ...
4082.Ve
4083.SS "\s-1EXAMPLES\s0"
4084.IX Subsection "EXAMPLES"
4085For a real-world example of a program the includes libev
4086verbatim, you can have a look at the \s-1EV\s0 perl module
4087(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
4088the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public
4089interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file
4090will be compiled. It is pretty complex because it provides its own header
4091file.
4092.PP
4093The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file
4094that everybody includes and which overrides some configure choices:
4095.PP
4096.Vb 9
4097\& #define EV_MINIMAL 1
4098\& #define EV_USE_POLL 0
4099\& #define EV_MULTIPLICITY 0
4100\& #define EV_PERIODIC_ENABLE 0
4101\& #define EV_STAT_ENABLE 0
4102\& #define EV_FORK_ENABLE 0
4103\& #define EV_CONFIG_H <config.h>
4104\& #define EV_MINPRI 0
4105\& #define EV_MAXPRI 0
4106\&
4107\& #include "ev++.h"
4108.Ve
4109.PP
4110And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled:
4111.PP
4112.Vb 2
4113\& #include "ev_cpp.h"
4114\& #include "ev.c"
4115.Ve
4116.SH "INTERACTION WITH OTHER PROGRAMS OR LIBRARIES"
4117.IX Header "INTERACTION WITH OTHER PROGRAMS OR LIBRARIES"
4118.SS "\s-1THREADS\s0 \s-1AND\s0 \s-1COROUTINES\s0"
4119.IX Subsection "THREADS AND COROUTINES"
4120\fI\s-1THREADS\s0\fR
4121.IX Subsection "THREADS"
4122.PP
4123All libev functions are reentrant and thread-safe unless explicitly
4124documented otherwise, but libev implements no locking itself. This means
4125that you can use as many loops as you want in parallel, as long as there
4126are no concurrent calls into any libev function with the same loop
4127parameter (\f(CW\*(C`ev_default_*\*(C'\fR calls have an implicit default loop parameter,
4128of course): libev guarantees that different event loops share no data
4129structures that need any locking.
4130.PP
4131Or to put it differently: calls with different loop parameters can be done
4132concurrently from multiple threads, calls with the same loop parameter
4133must be done serially (but can be done from different threads, as long as
4134only one thread ever is inside a call at any point in time, e.g. by using
4135a mutex per loop).
4136.PP
4137Specifically to support threads (and signal handlers), libev implements
4138so-called \f(CW\*(C`ev_async\*(C'\fR watchers, which allow some limited form of
4139concurrency on the same event loop, namely waking it up \*(L"from the
4140outside\*(R".
4141.PP
4142If you want to know which design (one loop, locking, or multiple loops
4143without or something else still) is best for your problem, then I cannot
4144help you, but here is some generic advice:
4145.IP "\(bu" 4
4146most applications have a main thread: use the default libev loop
4147in that thread, or create a separate thread running only the default loop.
4148.Sp
4149This helps integrating other libraries or software modules that use libev
4150themselves and don't care/know about threading.
4151.IP "\(bu" 4
4152one loop per thread is usually a good model.
4153.Sp
4154Doing this is almost never wrong, sometimes a better-performance model
4155exists, but it is always a good start.
4156.IP "\(bu" 4
4157other models exist, such as the leader/follower pattern, where one
4158loop is handed through multiple threads in a kind of round-robin fashion.
4159.Sp
4160Choosing a model is hard \- look around, learn, know that usually you can do
4161better than you currently do :\-)
4162.IP "\(bu" 4
4163often you need to talk to some other thread which blocks in the
4164event loop.
4165.Sp
4166\&\f(CW\*(C`ev_async\*(C'\fR watchers can be used to wake them up from other threads safely
4167(or from signal contexts...).
4168.Sp
4169An example use would be to communicate signals or other events that only
4170work in the default loop by registering the signal watcher with the
4171default loop and triggering an \f(CW\*(C`ev_async\*(C'\fR watcher from the default loop
4172watcher callback into the event loop interested in the signal.
4173.PP
4174\s-1THREAD\s0 \s-1LOCKING\s0 \s-1EXAMPLE\s0
4175.IX Subsection "THREAD LOCKING EXAMPLE"
4176.PP
4177Here is a fictitious example of how to run an event loop in a different
4178thread than where callbacks are being invoked and watchers are
4179created/added/removed.
4180.PP
4181For a real-world example, see the \f(CW\*(C`EV::Loop::Async\*(C'\fR perl module,
4182which uses exactly this technique (which is suited for many high-level
4183languages).
4184.PP
4185The example uses a pthread mutex to protect the loop data, a condition
4186variable to wait for callback invocations, an async watcher to notify the
4187event loop thread and an unspecified mechanism to wake up the main thread.
4188.PP
4189First, you need to associate some data with the event loop:
4190.PP
4191.Vb 6
4192\& typedef struct {
4193\& mutex_t lock; /* global loop lock */
4194\& ev_async async_w;
4195\& thread_t tid;
4196\& cond_t invoke_cv;
4197\& } userdata;
4198\&
4199\& void prepare_loop (EV_P)
4200\& {
4201\& // for simplicity, we use a static userdata struct.
4202\& static userdata u;
4203\&
4204\& ev_async_init (&u\->async_w, async_cb);
4205\& ev_async_start (EV_A_ &u\->async_w);
4206\&
4207\& pthread_mutex_init (&u\->lock, 0);
4208\& pthread_cond_init (&u\->invoke_cv, 0);
4209\&
4210\& // now associate this with the loop
4211\& ev_set_userdata (EV_A_ u);
4212\& ev_set_invoke_pending_cb (EV_A_ l_invoke);
4213\& ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4214\&
4215\& // then create the thread running ev_loop
4216\& pthread_create (&u\->tid, 0, l_run, EV_A);
4217\& }
4218.Ve
4219.PP
4220The callback for the \f(CW\*(C`ev_async\*(C'\fR watcher does nothing: the watcher is used
4221solely to wake up the event loop so it takes notice of any new watchers
4222that might have been added:
4223.PP
4224.Vb 5
4225\& static void
4226\& async_cb (EV_P_ ev_async *w, int revents)
4227\& {
4228\& // just used for the side effects
4229\& }
4230.Ve
4231.PP
4232The \f(CW\*(C`l_release\*(C'\fR and \f(CW\*(C`l_acquire\*(C'\fR callbacks simply unlock/lock the mutex
4233protecting the loop data, respectively.
4234.PP
4235.Vb 6
4236\& static void
4237\& l_release (EV_P)
4238\& {
4239\& userdata *u = ev_userdata (EV_A);
4240\& pthread_mutex_unlock (&u\->lock);
4241\& }
4242\&
4243\& static void
4244\& l_acquire (EV_P)
4245\& {
4246\& userdata *u = ev_userdata (EV_A);
4247\& pthread_mutex_lock (&u\->lock);
4248\& }
4249.Ve
4250.PP
4251The event loop thread first acquires the mutex, and then jumps straight
4252into \f(CW\*(C`ev_loop\*(C'\fR:
4253.PP
4254.Vb 4
4255\& void *
4256\& l_run (void *thr_arg)
4257\& {
4258\& struct ev_loop *loop = (struct ev_loop *)thr_arg;
4259\&
4260\& l_acquire (EV_A);
4261\& pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4262\& ev_loop (EV_A_ 0);
4263\& l_release (EV_A);
4264\&
4265\& return 0;
4266\& }
4267.Ve
4268.PP
4269Instead of invoking all pending watchers, the \f(CW\*(C`l_invoke\*(C'\fR callback will
4270signal the main thread via some unspecified mechanism (signals? pipe
4271writes? \f(CW\*(C`Async::Interrupt\*(C'\fR?) and then waits until all pending watchers
4272have been called (in a while loop because a) spurious wakeups are possible
4273and b) skipping inter-thread-communication when there are no pending
4274watchers is very beneficial):
4275.PP
4276.Vb 4
4277\& static void
4278\& l_invoke (EV_P)
4279\& {
4280\& userdata *u = ev_userdata (EV_A);
4281\&
4282\& while (ev_pending_count (EV_A))
4283\& {
4284\& wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4285\& pthread_cond_wait (&u\->invoke_cv, &u\->lock);
4286\& }
4287\& }
4288.Ve
4289.PP
4290Now, whenever the main thread gets told to invoke pending watchers, it
4291will grab the lock, call \f(CW\*(C`ev_invoke_pending\*(C'\fR and then signal the loop
4292thread to continue:
4293.PP
4294.Vb 4
4295\& static void
4296\& real_invoke_pending (EV_P)
4297\& {
4298\& userdata *u = ev_userdata (EV_A);
4299\&
4300\& pthread_mutex_lock (&u\->lock);
4301\& ev_invoke_pending (EV_A);
4302\& pthread_cond_signal (&u\->invoke_cv);
4303\& pthread_mutex_unlock (&u\->lock);
4304\& }
4305.Ve
4306.PP
4307Whenever you want to start/stop a watcher or do other modifications to an
4308event loop, you will now have to lock:
4309.PP
4310.Vb 2
4311\& ev_timer timeout_watcher;
4312\& userdata *u = ev_userdata (EV_A);
4313\&
4314\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4315\&
4316\& pthread_mutex_lock (&u\->lock);
4317\& ev_timer_start (EV_A_ &timeout_watcher);
4318\& ev_async_send (EV_A_ &u\->async_w);
4319\& pthread_mutex_unlock (&u\->lock);
4320.Ve
4321.PP
4322Note that sending the \f(CW\*(C`ev_async\*(C'\fR watcher is required because otherwise
4323an event loop currently blocking in the kernel will have no knowledge
4324about the newly added timer. By waking up the loop it will pick up any new
4325watchers in the next event loop iteration.
4326.PP
4327\fI\s-1COROUTINES\s0\fR
4328.IX Subsection "COROUTINES"
4329.PP
4330Libev is very accommodating to coroutines (\*(L"cooperative threads\*(R"):
4331libev fully supports nesting calls to its functions from different
4332coroutines (e.g. you can call \f(CW\*(C`ev_loop\*(C'\fR on the same loop from two
4333different coroutines, and switch freely between both coroutines running
4334the loop, as long as you don't confuse yourself). The only exception is
4335that you must not do this from \f(CW\*(C`ev_periodic\*(C'\fR reschedule callbacks.
4336.PP
4337Care has been taken to ensure that libev does not keep local state inside
4338\&\f(CW\*(C`ev_loop\*(C'\fR, and other calls do not usually allow for coroutine switches as
4339they do not call any callbacks.
4340.SS "\s-1COMPILER\s0 \s-1WARNINGS\s0"
4341.IX Subsection "COMPILER WARNINGS"
4342Depending on your compiler and compiler settings, you might get no or a
4343lot of warnings when compiling libev code. Some people are apparently
4344scared by this.
4345.PP
4346However, these are unavoidable for many reasons. For one, each compiler
4347has different warnings, and each user has different tastes regarding
4348warning options. \*(L"Warn-free\*(R" code therefore cannot be a goal except when
4349targeting a specific compiler and compiler-version.
4350.PP
4351Another reason is that some compiler warnings require elaborate
4352workarounds, or other changes to the code that make it less clear and less
4353maintainable.
4354.PP
4355And of course, some compiler warnings are just plain stupid, or simply
4356wrong (because they don't actually warn about the condition their message
4357seems to warn about). For example, certain older gcc versions had some
4358warnings that resulted an extreme number of false positives. These have
4359been fixed, but some people still insist on making code warn-free with
4360such buggy versions.
4361.PP
4362While libev is written to generate as few warnings as possible,
4363\&\*(L"warn-free\*(R" code is not a goal, and it is recommended not to build libev
4364with any compiler warnings enabled unless you are prepared to cope with
4365them (e.g. by ignoring them). Remember that warnings are just that:
4366warnings, not errors, or proof of bugs.
4367.SS "\s-1VALGRIND\s0"
4368.IX Subsection "VALGRIND"
4369Valgrind has a special section here because it is a popular tool that is
4370highly useful. Unfortunately, valgrind reports are very hard to interpret.
4371.PP
4372If you think you found a bug (memory leak, uninitialised data access etc.)
4373in libev, then check twice: If valgrind reports something like:
4374.PP
4375.Vb 3
4376\& ==2274== definitely lost: 0 bytes in 0 blocks.
4377\& ==2274== possibly lost: 0 bytes in 0 blocks.
4378\& ==2274== still reachable: 256 bytes in 1 blocks.
4379.Ve
4380.PP
4381Then there is no memory leak, just as memory accounted to global variables
4382is not a memleak \- the memory is still being referenced, and didn't leak.
4383.PP
4384Similarly, under some circumstances, valgrind might report kernel bugs
4385as if it were a bug in libev (e.g. in realloc or in the poll backend,
4386although an acceptable workaround has been found here), or it might be
4387confused.
4388.PP
4389Keep in mind that valgrind is a very good tool, but only a tool. Don't
4390make it into some kind of religion.
4391.PP
4392If you are unsure about something, feel free to contact the mailing list
4393with the full valgrind report and an explanation on why you think this
4394is a bug in libev (best check the archives, too :). However, don't be
4395annoyed when you get a brisk \*(L"this is no bug\*(R" answer and take the chance
4396of learning how to interpret valgrind properly.
4397.PP
4398If you need, for some reason, empty reports from valgrind for your project
4399I suggest using suppression lists.
4400.SH "PORTABILITY NOTES"
4401.IX Header "PORTABILITY NOTES"
4402.SS "\s-1WIN32\s0 \s-1PLATFORM\s0 \s-1LIMITATIONS\s0 \s-1AND\s0 \s-1WORKAROUNDS\s0"
4403.IX Subsection "WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS"
4404Win32 doesn't support any of the standards (e.g. \s-1POSIX\s0) that libev
4405requires, and its I/O model is fundamentally incompatible with the \s-1POSIX\s0
4406model. Libev still offers limited functionality on this platform in
4407the form of the \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR backend, and only supports socket
4408descriptors. This only applies when using Win32 natively, not when using
4409e.g. cygwin.
4410.PP
4411Lifting these limitations would basically require the full
4412re-implementation of the I/O system. If you are into these kinds of
4413things, then note that glib does exactly that for you in a very portable
4414way (note also that glib is the slowest event library known to man).
4415.PP
4416There is no supported compilation method available on windows except
4417embedding it into other applications.
4418.PP
4419Sensible signal handling is officially unsupported by Microsoft \- libev
4420tries its best, but under most conditions, signals will simply not work.
4421.PP
4422Not a libev limitation but worth mentioning: windows apparently doesn't
4423accept large writes: instead of resulting in a partial write, windows will
4424either accept everything or return \f(CW\*(C`ENOBUFS\*(C'\fR if the buffer is too large,
4425so make sure you only write small amounts into your sockets (less than a
4426megabyte seems safe, but this apparently depends on the amount of memory
4427available).
4428.PP
4429Due to the many, low, and arbitrary limits on the win32 platform and
4430the abysmal performance of winsockets, using a large number of sockets
4431is not recommended (and not reasonable). If your program needs to use
4432more than a hundred or so sockets, then likely it needs to use a totally
4433different implementation for windows, as libev offers the \s-1POSIX\s0 readiness
4434notification model, which cannot be implemented efficiently on windows
4435(due to Microsoft monopoly games).
4436.PP
4437A typical way to use libev under windows is to embed it (see the embedding
4438section for details) and use the following \fIevwrap.h\fR header file instead
4439of \fIev.h\fR:
4440.PP
4441.Vb 2
4442\& #define EV_STANDALONE /* keeps ev from requiring config.h */
4443\& #define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
4444\&
4445\& #include "ev.h"
4446.Ve
4447.PP
4448And compile the following \fIevwrap.c\fR file into your project (make sure
4449you do \fInot\fR compile the \fIev.c\fR or any other embedded source files!):
4450.PP
4451.Vb 2
4452\& #include "evwrap.h"
4453\& #include "ev.c"
4454.Ve
4455.IP "The winsocket select function" 4
4456.IX Item "The winsocket select function"
4457The winsocket \f(CW\*(C`select\*(C'\fR function doesn't follow \s-1POSIX\s0 in that it
4458requires socket \fIhandles\fR and not socket \fIfile descriptors\fR (it is
4459also extremely buggy). This makes select very inefficient, and also
4460requires a mapping from file descriptors to socket handles (the Microsoft
4461C runtime provides the function \f(CW\*(C`_open_osfhandle\*(C'\fR for this). See the
4462discussion of the \f(CW\*(C`EV_SELECT_USE_FD_SET\*(C'\fR, \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR and
4463\&\f(CW\*(C`EV_FD_TO_WIN32_HANDLE\*(C'\fR preprocessor symbols for more info.
4464.Sp
4465The configuration for a \*(L"naked\*(R" win32 using the Microsoft runtime
4466libraries and raw winsocket select is:
4467.Sp
4468.Vb 2
4469\& #define EV_USE_SELECT 1
4470\& #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
4471.Ve
4472.Sp
4473Note that winsockets handling of fd sets is O(n), so you can easily get a
4474complexity in the O(nA\*^X) range when using win32.
4475.IP "Limited number of file descriptors" 4
4476.IX Item "Limited number of file descriptors"
4477Windows has numerous arbitrary (and low) limits on things.
4478.Sp
4479Early versions of winsocket's select only supported waiting for a maximum
4480of \f(CW64\fR handles (probably owning to the fact that all windows kernels
4481can only wait for \f(CW64\fR things at the same time internally; Microsoft
4482recommends spawning a chain of threads and wait for 63 handles and the
4483previous thread in each. Sounds great!).
4484.Sp
4485Newer versions support more handles, but you need to define \f(CW\*(C`FD_SETSIZE\*(C'\fR
4486to some high number (e.g. \f(CW2048\fR) before compiling the winsocket select
4487call (which might be in libev or elsewhere, for example, perl and many
4488other interpreters do their own select emulation on windows).
4489.Sp
4490Another limit is the number of file descriptors in the Microsoft runtime
4491libraries, which by default is \f(CW64\fR (there must be a hidden \fI64\fR
4492fetish or something like this inside Microsoft). You can increase this
4493by calling \f(CW\*(C`_setmaxstdio\*(C'\fR, which can increase this limit to \f(CW2048\fR
4494(another arbitrary limit), but is broken in many versions of the Microsoft
4495runtime libraries. This might get you to about \f(CW512\fR or \f(CW2048\fR sockets
4496(depending on windows version and/or the phase of the moon). To get more,
4497you need to wrap all I/O functions and provide your own fd management, but
4498the cost of calling select (O(nA\*^X)) will likely make this unworkable.
4499.SS "\s-1PORTABILITY\s0 \s-1REQUIREMENTS\s0"
4500.IX Subsection "PORTABILITY REQUIREMENTS"
4501In addition to a working ISO-C implementation and of course the
4502backend-specific APIs, libev relies on a few additional extensions:
4503.ie n .IP """void (*)(ev_watcher_type *, int revents)"" must have compatible calling conventions regardless of ""ev_watcher_type *""." 4
4504.el .IP "\f(CWvoid (*)(ev_watcher_type *, int revents)\fR must have compatible calling conventions regardless of \f(CWev_watcher_type *\fR." 4
4505.IX Item "void (*)(ev_watcher_type *, int revents) must have compatible calling conventions regardless of ev_watcher_type *."
4506Libev assumes not only that all watcher pointers have the same internal
4507structure (guaranteed by \s-1POSIX\s0 but not by \s-1ISO\s0 C for example), but it also
4508assumes that the same (machine) code can be used to call any watcher
4509callback: The watcher callbacks have different type signatures, but libev
4510calls them using an \f(CW\*(C`ev_watcher *\*(C'\fR internally.
4511.ie n .IP """sig_atomic_t volatile"" must be thread-atomic as well" 4
4512.el .IP "\f(CWsig_atomic_t volatile\fR must be thread-atomic as well" 4
4513.IX Item "sig_atomic_t volatile must be thread-atomic as well"
4514The type \f(CW\*(C`sig_atomic_t volatile\*(C'\fR (or whatever is defined as
4515\&\f(CW\*(C`EV_ATOMIC_T\*(C'\fR) must be atomic with respect to accesses from different
4516threads. This is not part of the specification for \f(CW\*(C`sig_atomic_t\*(C'\fR, but is
4517believed to be sufficiently portable.
4518.ie n .IP """sigprocmask"" must work in a threaded environment" 4
4519.el .IP "\f(CWsigprocmask\fR must work in a threaded environment" 4
4520.IX Item "sigprocmask must work in a threaded environment"
4521Libev uses \f(CW\*(C`sigprocmask\*(C'\fR to temporarily block signals. This is not
4522allowed in a threaded program (\f(CW\*(C`pthread_sigmask\*(C'\fR has to be used). Typical
4523pthread implementations will either allow \f(CW\*(C`sigprocmask\*(C'\fR in the \*(L"main
4524thread\*(R" or will block signals process-wide, both behaviours would
4525be compatible with libev. Interaction between \f(CW\*(C`sigprocmask\*(C'\fR and
4526\&\f(CW\*(C`pthread_sigmask\*(C'\fR could complicate things, however.
4527.Sp
4528The most portable way to handle signals is to block signals in all threads
4529except the initial one, and run the default loop in the initial thread as
4530well.
4531.ie n .IP """long"" must be large enough for common memory allocation sizes" 4
4532.el .IP "\f(CWlong\fR must be large enough for common memory allocation sizes" 4
4533.IX Item "long must be large enough for common memory allocation sizes"
4534To improve portability and simplify its \s-1API\s0, libev uses \f(CW\*(C`long\*(C'\fR internally
4535instead of \f(CW\*(C`size_t\*(C'\fR when allocating its data structures. On non-POSIX
4536systems (Microsoft...) this might be unexpectedly low, but is still at
4537least 31 bits everywhere, which is enough for hundreds of millions of
4538watchers.
4539.ie n .IP """double"" must hold a time value in seconds with enough accuracy" 4
4540.el .IP "\f(CWdouble\fR must hold a time value in seconds with enough accuracy" 4
4541.IX Item "double must hold a time value in seconds with enough accuracy"
4542The type \f(CW\*(C`double\*(C'\fR is used to represent timestamps. It is required to
4543have at least 51 bits of mantissa (and 9 bits of exponent), which is good
4544enough for at least into the year 4000. This requirement is fulfilled by
4545implementations implementing \s-1IEEE\s0 754, which is basically all existing
4546ones. With \s-1IEEE\s0 754 doubles, you get microsecond accuracy until at least
45472200.
4548.PP
4549If you know of other additional requirements drop me a note.
4550.SH "ALGORITHMIC COMPLEXITIES"
4551.IX Header "ALGORITHMIC COMPLEXITIES"
4552In this section the complexities of (many of) the algorithms used inside
4553libev will be documented. For complexity discussions about backends see
4554the documentation for \f(CW\*(C`ev_default_init\*(C'\fR.
4555.PP
4556All of the following are about amortised time: If an array needs to be
4557extended, libev needs to realloc and move the whole array, but this
4558happens asymptotically rarer with higher number of elements, so O(1) might
4559mean that libev does a lengthy realloc operation in rare cases, but on
4560average it is much faster and asymptotically approaches constant time.
4561.IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4
4562.IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)"
4563This means that, when you have a watcher that triggers in one hour and
4564there are 100 watchers that would trigger before that, then inserting will
4565have to skip roughly seven (\f(CW\*(C`ld 100\*(C'\fR) of these watchers.
4566.IP "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 4
4567.IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)"
4568That means that changing a timer costs less than removing/adding them,
4569as only the relative motion in the event queue has to be paid for.
4570.IP "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)" 4
4571.IX Item "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)"
4572These just add the watcher into an array or at the head of a list.
4573.IP "Stopping check/prepare/idle/fork/async watchers: O(1)" 4
4574.IX Item "Stopping check/prepare/idle/fork/async watchers: O(1)"
4575.PD 0
4576.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4
4577.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))"
4578.PD
4579These watchers are stored in lists, so they need to be walked to find the
4580correct watcher to remove. The lists are usually short (you don't usually
4581have many watchers waiting for the same fd or signal: one is typical, two
4582is rare).
4583.IP "Finding the next timer in each loop iteration: O(1)" 4
4584.IX Item "Finding the next timer in each loop iteration: O(1)"
4585By virtue of using a binary or 4\-heap, the next timer is always found at a
4586fixed position in the storage array.
4587.IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4
4588.IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)"
4589A change means an I/O watcher gets started or stopped, which requires
4590libev to recalculate its status (and possibly tell the kernel, depending
4591on backend and whether \f(CW\*(C`ev_io_set\*(C'\fR was used).
4592.IP "Activating one watcher (putting it into the pending state): O(1)" 4
4593.IX Item "Activating one watcher (putting it into the pending state): O(1)"
4594.PD 0
4595.IP "Priority handling: O(number_of_priorities)" 4
4596.IX Item "Priority handling: O(number_of_priorities)"
4597.PD
4598Priorities are implemented by allocating some space for each
4599priority. When doing priority-based operations, libev usually has to
4600linearly search all the priorities, but starting/stopping and activating
4601watchers becomes O(1) with respect to priority handling.
4602.IP "Sending an ev_async: O(1)" 4
4603.IX Item "Sending an ev_async: O(1)"
4604.PD 0
4605.IP "Processing ev_async_send: O(number_of_async_watchers)" 4
4606.IX Item "Processing ev_async_send: O(number_of_async_watchers)"
4607.IP "Processing signals: O(max_signal_number)" 4
4608.IX Item "Processing signals: O(max_signal_number)"
4609.PD
4610Sending involves a system call \fIiff\fR there were no other \f(CW\*(C`ev_async_send\*(C'\fR
4611calls in the current loop iteration. Checking for async and signal events
4612involves iterating over all running async watchers or all signal numbers.
4613.SH "GLOSSARY"
4614.IX Header "GLOSSARY"
4615.IP "active" 4
4616.IX Item "active"
4617A watcher is active as long as it has been started (has been attached to
4618an event loop) but not yet stopped (disassociated from the event loop).
4619.IP "application" 4
4620.IX Item "application"
4621In this document, an application is whatever is using libev.
4622.IP "callback" 4
4623.IX Item "callback"
4624The address of a function that is called when some event has been
4625detected. Callbacks are being passed the event loop, the watcher that
4626received the event, and the actual event bitset.
4627.IP "callback invocation" 4
4628.IX Item "callback invocation"
4629The act of calling the callback associated with a watcher.
4630.IP "event" 4
4631.IX Item "event"
4632A change of state of some external event, such as data now being available
4633for reading on a file descriptor, time having passed or simply not having
4634any other events happening anymore.
4635.Sp
4636In libev, events are represented as single bits (such as \f(CW\*(C`EV_READ\*(C'\fR or
4637\&\f(CW\*(C`EV_TIMEOUT\*(C'\fR).
4638.IP "event library" 4
4639.IX Item "event library"
4640A software package implementing an event model and loop.
4641.IP "event loop" 4
4642.IX Item "event loop"
4643An entity that handles and processes external events and converts them
4644into callback invocations.
4645.IP "event model" 4
4646.IX Item "event model"
4647The model used to describe how an event loop handles and processes
4648watchers and events.
4649.IP "pending" 4
4650.IX Item "pending"
4651A watcher is pending as soon as the corresponding event has been detected,
4652and stops being pending as soon as the watcher will be invoked or its
4653pending status is explicitly cleared by the application.
4654.Sp
4655A watcher can be pending, but not active. Stopping a watcher also clears
4656its pending status.
4657.IP "real time" 4
4658.IX Item "real time"
4659The physical time that is observed. It is apparently strictly monotonic :)
4660.IP "wall-clock time" 4
4661.IX Item "wall-clock time"
4662The time and date as shown on clocks. Unlike real time, it can actually
4663be wrong and jump forwards and backwards, e.g. when the you adjust your
4664clock.
4665.IP "watcher" 4
4666.IX Item "watcher"
4667A data structure that describes interest in certain events. Watchers need
4668to be started (attached to an event loop) before they can receive events.
4669.IP "watcher invocation" 4
4670.IX Item "watcher invocation"
4671The act of calling the callback associated with a watcher.
995.SH "AUTHOR" 4672.SH "AUTHOR"
996.IX Header "AUTHOR" 4673.IX Header "AUTHOR"
997Marc Lehmann <libev@schmorp.de>. 4674Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.

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