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129.\" ======================================================================== 132.\" ========================================================================
130.\" 133.\"
131.IX Title ""<STANDARD INPUT>" 1" 134.IX Title "LIBEV 3"
132.TH "<STANDARD INPUT>" 1 "2007-11-23" "perl v5.8.8" "User Contributed Perl Documentation" 135.TH LIBEV 3 "2008-09-29" "libev-3.44" "libev - high performance full featured event loop"
136.\" For nroff, turn off justification. Always turn off hyphenation; it makes
137.\" way too many mistakes in technical documents.
138.if n .ad l
139.nh
133.SH "NAME" 140.SH "NAME"
134libev \- a high performance full\-featured event loop written in C 141libev \- a high performance full\-featured event loop written in C
135.SH "SYNOPSIS" 142.SH "SYNOPSIS"
136.IX Header "SYNOPSIS" 143.IX Header "SYNOPSIS"
137.Vb 1 144.Vb 1
138\& #include <ev.h> 145\& #include <ev.h>
146.Ve
147.Sh "\s-1EXAMPLE\s0 \s-1PROGRAM\s0"
148.IX Subsection "EXAMPLE PROGRAM"
149.Vb 2
150\& // a single header file is required
151\& #include <ev.h>
152\&
153\& // every watcher type has its own typedef\*(Aqd struct
154\& // with the name ev_<type>
155\& ev_io stdin_watcher;
156\& ev_timer timeout_watcher;
157\&
158\& // all watcher callbacks have a similar signature
159\& // this callback is called when data is readable on stdin
160\& static void
161\& stdin_cb (EV_P_ struct ev_io *w, int revents)
162\& {
163\& puts ("stdin ready");
164\& // for one\-shot events, one must manually stop the watcher
165\& // with its corresponding stop function.
166\& ev_io_stop (EV_A_ w);
167\&
168\& // this causes all nested ev_loop\*(Aqs to stop iterating
169\& ev_unloop (EV_A_ EVUNLOOP_ALL);
170\& }
171\&
172\& // another callback, this time for a time\-out
173\& static void
174\& timeout_cb (EV_P_ struct ev_timer *w, int revents)
175\& {
176\& puts ("timeout");
177\& // this causes the innermost ev_loop to stop iterating
178\& ev_unloop (EV_A_ EVUNLOOP_ONE);
179\& }
180\&
181\& int
182\& main (void)
183\& {
184\& // use the default event loop unless you have special needs
185\& struct ev_loop *loop = ev_default_loop (0);
186\&
187\& // initialise an io watcher, then start it
188\& // this one will watch for stdin to become readable
189\& ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
190\& ev_io_start (loop, &stdin_watcher);
191\&
192\& // initialise a timer watcher, then start it
193\& // simple non\-repeating 5.5 second timeout
194\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
195\& ev_timer_start (loop, &timeout_watcher);
196\&
197\& // now wait for events to arrive
198\& ev_loop (loop, 0);
199\&
200\& // unloop was called, so exit
201\& return 0;
202\& }
139.Ve 203.Ve
140.SH "DESCRIPTION" 204.SH "DESCRIPTION"
141.IX Header "DESCRIPTION" 205.IX Header "DESCRIPTION"
206The newest version of this document is also available as an html-formatted
207web page you might find easier to navigate when reading it for the first
208time: <http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
209.PP
142Libev is an event loop: you register interest in certain events (such as a 210Libev 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 211file descriptor being readable or a timeout occurring), and it will manage
144these event sources and provide your program with events. 212these event sources and provide your program with events.
145.PP 213.PP
146To do this, it must take more or less complete control over your process 214To 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 215(or thread) by executing the \fIevent loop\fR handler, and will then
148communicate events via a callback mechanism. 216communicate events via a callback mechanism.
149.PP 217.PP
150You register interest in certain events by registering so-called \fIevent 218You register interest in certain events by registering so-called \fIevent
151watchers\fR, which are relatively small C structures you initialise with the 219watchers\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 220details of the event, and then hand it over to libev by \fIstarting\fR the
153watcher. 221watcher.
154.SH "FEATURES" 222.Sh "\s-1FEATURES\s0"
155.IX Header "FEATURES" 223.IX Subsection "FEATURES"
156Libev supports select, poll, the linux-specific epoll and the bsd-specific 224Libev 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 225BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port mechanisms
158timers with customised rescheduling, signal events, process status change 226for 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 227(for \f(CW\*(C`ev_stat\*(C'\fR), relative timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers
160loop mechanism itself (idle, prepare and check watchers). It also is quite 228with customised rescheduling (\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals
161fast (see this benchmark comparing 229(\f(CW\*(C`ev_signal\*(C'\fR), process status change events (\f(CW\*(C`ev_child\*(C'\fR), and event
162it to libevent for example). 230watchers dealing with the event loop mechanism itself (\f(CW\*(C`ev_idle\*(C'\fR,
231\&\f(CW\*(C`ev_embed\*(C'\fR, \f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR watchers) as well as
232file watchers (\f(CW\*(C`ev_stat\*(C'\fR) and even limited support for fork events
233(\f(CW\*(C`ev_fork\*(C'\fR).
234.PP
235It also is quite fast (see this
236benchmark comparing it to libevent
237for example).
163.SH "CONVENTIONS" 238.Sh "\s-1CONVENTIONS\s0"
164.IX Header "CONVENTIONS" 239.IX Subsection "CONVENTIONS"
165Libev is very configurable. In this manual the default configuration 240Libev is very configurable. In this manual the default (and most common)
166will be described, which supports multiple event loops. For more info 241configuration will be described, which supports multiple event loops. For
167about various configuration options please have a look at the file 242more 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 243\&\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 244for 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) 245name \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. 246this argument.
172.SH "TIME REPRESENTATION" 247.Sh "\s-1TIME\s0 \s-1REPRESENTATION\s0"
173.IX Header "TIME REPRESENTATION" 248.IX Subsection "TIME REPRESENTATION"
174Libev represents time as a single floating point number, representing the 249Libev represents time as a single floating point number, representing the
175(fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere near 250(fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere near
176the beginning of 1970, details are complicated, don't ask). This type is 251the beginning of 1970, details are complicated, don't ask). This type is
177called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use too. It usually aliases 252called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use too. It usually aliases
178to the double type in C. 253to the \f(CW\*(C`double\*(C'\fR type in C, and when you need to do any calculations on
254it, you should treat it as some floating point value. Unlike the name
255component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for time differences
256throughout libev.
257.SH "ERROR HANDLING"
258.IX Header "ERROR HANDLING"
259Libev knows three classes of errors: operating system errors, usage errors
260and internal errors (bugs).
261.PP
262When libev catches an operating system error it cannot handle (for example
263a system call indicating a condition libev cannot fix), it calls the callback
264set via \f(CW\*(C`ev_set_syserr_cb\*(C'\fR, which is supposed to fix the problem or
265abort. The default is to print a diagnostic message and to call \f(CW\*(C`abort
266()\*(C'\fR.
267.PP
268When libev detects a usage error such as a negative timer interval, then
269it will print a diagnostic message and abort (via the \f(CW\*(C`assert\*(C'\fR mechanism,
270so \f(CW\*(C`NDEBUG\*(C'\fR will disable this checking): these are programming errors in
271the libev caller and need to be fixed there.
272.PP
273Libev also has a few internal error-checking \f(CW\*(C`assert\*(C'\fRions, and also has
274extensive consistency checking code. These do not trigger under normal
275circumstances, as they indicate either a bug in libev or worse.
179.SH "GLOBAL FUNCTIONS" 276.SH "GLOBAL FUNCTIONS"
180.IX Header "GLOBAL FUNCTIONS" 277.IX Header "GLOBAL FUNCTIONS"
181These functions can be called anytime, even before initialising the 278These functions can be called anytime, even before initialising the
182library in any way. 279library in any way.
183.IP "ev_tstamp ev_time ()" 4 280.IP "ev_tstamp ev_time ()" 4
184.IX Item "ev_tstamp ev_time ()" 281.IX Item "ev_tstamp ev_time ()"
185Returns the current time as libev would use it. Please note that the 282Returns 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 283\&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp
187you actually want to know. 284you actually want to know.
285.IP "ev_sleep (ev_tstamp interval)" 4
286.IX Item "ev_sleep (ev_tstamp interval)"
287Sleep for the given interval: The current thread will be blocked until
288either it is interrupted or the given time interval has passed. Basically
289this is a sub-second-resolution \f(CW\*(C`sleep ()\*(C'\fR.
188.IP "int ev_version_major ()" 4 290.IP "int ev_version_major ()" 4
189.IX Item "int ev_version_major ()" 291.IX Item "int ev_version_major ()"
190.PD 0 292.PD 0
191.IP "int ev_version_minor ()" 4 293.IP "int ev_version_minor ()" 4
192.IX Item "int ev_version_minor ()" 294.IX Item "int ev_version_minor ()"
193.PD 295.PD
194You can find out the major and minor version numbers of the library 296You 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 297you 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 298\&\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 299symbols \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. 300version of the library your program was compiled against.
199.Sp 301.Sp
302These version numbers refer to the \s-1ABI\s0 version of the library, not the
303release version.
304.Sp
200Usually, it's a good idea to terminate if the major versions mismatch, 305Usually, it's a good idea to terminate if the major versions mismatch,
201as this indicates an incompatible change. Minor versions are usually 306as this indicates an incompatible change. Minor versions are usually
202compatible to older versions, so a larger minor version alone is usually 307compatible to older versions, so a larger minor version alone is usually
203not a problem. 308not a problem.
309.Sp
310Example: Make sure we haven't accidentally been linked against the wrong
311version.
312.Sp
313.Vb 3
314\& assert (("libev version mismatch",
315\& ev_version_major () == EV_VERSION_MAJOR
316\& && ev_version_minor () >= EV_VERSION_MINOR));
317.Ve
204.IP "unsigned int ev_supported_backends ()" 4 318.IP "unsigned int ev_supported_backends ()" 4
205.IX Item "unsigned int ev_supported_backends ()" 319.IX Item "unsigned int ev_supported_backends ()"
206Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR 320Return 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 321value) 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 322availability on the system you are running on). See \f(CW\*(C`ev_default_loop\*(C'\fR for
209a description of the set values. 323a description of the set values.
324.Sp
325Example: make sure we have the epoll method, because yeah this is cool and
326a must have and can we have a torrent of it please!!!11
327.Sp
328.Vb 2
329\& assert (("sorry, no epoll, no sex",
330\& ev_supported_backends () & EVBACKEND_EPOLL));
331.Ve
210.IP "unsigned int ev_recommended_backends ()" 4 332.IP "unsigned int ev_recommended_backends ()" 4
211.IX Item "unsigned int ev_recommended_backends ()" 333.IX Item "unsigned int ev_recommended_backends ()"
212Return the set of all backends compiled into this binary of libev and also 334Return 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 335recommended 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 336returned 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 337most 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 338(assuming you know what you are doing). This is the set of backends that
217libev will probe for if you specify no backends explicitly. 339libev will probe for if you specify no backends explicitly.
340.IP "unsigned int ev_embeddable_backends ()" 4
341.IX Item "unsigned int ev_embeddable_backends ()"
342Returns the set of backends that are embeddable in other event loops. This
343is the theoretical, all-platform, value. To find which backends
344might be supported on the current system, you would need to look at
345\&\f(CW\*(C`ev_embeddable_backends () & ev_supported_backends ()\*(C'\fR, likewise for
346recommended ones.
347.Sp
348See 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))" 4 349.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))" 350.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 351Sets the allocation function to use (the prototype is similar \- the
221realloc C function, the semantics are identical). It is used to allocate 352semantics 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 353used to allocate and free memory (no surprises here). If it returns zero
223needs to be allocated, the library might abort or take some potentially 354when 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. 355or take some potentially destructive action.
356.Sp
357Since some systems (at least OpenBSD and Darwin) fail to implement
358correct \f(CW\*(C`realloc\*(C'\fR semantics, libev will use a wrapper around the system
359\&\f(CW\*(C`realloc\*(C'\fR and \f(CW\*(C`free\*(C'\fR functions by default.
225.Sp 360.Sp
226You could override this function in high-availability programs to, say, 361You could override this function in high-availability programs to, say,
227free some memory if it cannot allocate memory, to use a special allocator, 362free 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. 363or even to sleep a while and retry until some memory is available.
364.Sp
365Example: Replace the libev allocator with one that waits a bit and then
366retries (example requires a standards-compliant \f(CW\*(C`realloc\*(C'\fR).
367.Sp
368.Vb 6
369\& static void *
370\& persistent_realloc (void *ptr, size_t size)
371\& {
372\& for (;;)
373\& {
374\& void *newptr = realloc (ptr, size);
375\&
376\& if (newptr)
377\& return newptr;
378\&
379\& sleep (60);
380\& }
381\& }
382\&
383\& ...
384\& ev_set_allocator (persistent_realloc);
385.Ve
229.IP "ev_set_syserr_cb (void (*cb)(const char *msg));" 4 386.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));" 387.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 388Set the callback function to call on a retryable system call error (such
232as failed select, poll, epoll_wait). The message is a printable string 389as failed select, poll, epoll_wait). The message is a printable string
233indicating the system call or subsystem causing the problem. If this 390indicating the system call or subsystem causing the problem. If this
234callback is set, then libev will expect it to remedy the sitution, no 391callback is set, then libev will expect it to remedy the situation, no
235matter what, when it returns. That is, libev will generally retry the 392matter what, when it returns. That is, libev will generally retry the
236requested operation, or, if the condition doesn't go away, do bad stuff 393requested operation, or, if the condition doesn't go away, do bad stuff
237(such as abort). 394(such as abort).
395.Sp
396Example: This is basically the same thing that libev does internally, too.
397.Sp
398.Vb 6
399\& static void
400\& fatal_error (const char *msg)
401\& {
402\& perror (msg);
403\& abort ();
404\& }
405\&
406\& ...
407\& ev_set_syserr_cb (fatal_error);
408.Ve
238.SH "FUNCTIONS CONTROLLING THE EVENT LOOP" 409.SH "FUNCTIONS CONTROLLING THE EVENT LOOP"
239.IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP" 410.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 411An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR. The library knows two
241types of such loops, the \fIdefault\fR loop, which supports signals and child 412types of such loops, the \fIdefault\fR loop, which supports signals and child
242events, and dynamically created loops which do not. 413events, and dynamically created loops which do not.
243.PP
244If you use threads, a common model is to run the default event loop
245in your main thread (or in a separate thread) and for each thread you
246create, you also create another event loop. Libev itself does no locking
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)" 4 414.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
251.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)" 415.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
252This will initialise the default event loop if it hasn't been initialised 416This 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 417yet 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 418false. 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). 419flags. If that is troubling you, check \f(CW\*(C`ev_backend ()\*(C'\fR afterwards).
256.Sp 420.Sp
257If you don't know what event loop to use, use the one returned from this 421If you don't know what event loop to use, use the one returned from this
258function. 422function.
423.Sp
424Note that this function is \fInot\fR thread-safe, so if you want to use it
425from multiple threads, you have to lock (note also that this is unlikely,
426as loops cannot bes hared easily between threads anyway).
427.Sp
428The default loop is the only loop that can handle \f(CW\*(C`ev_signal\*(C'\fR and
429\&\f(CW\*(C`ev_child\*(C'\fR watchers, and to do this, it always registers a handler
430for \f(CW\*(C`SIGCHLD\*(C'\fR. If this is a problem for your application you can either
431create a dynamic loop with \f(CW\*(C`ev_loop_new\*(C'\fR that doesn't do that, or you
432can simply overwrite the \f(CW\*(C`SIGCHLD\*(C'\fR signal handler \fIafter\fR calling
433\&\f(CW\*(C`ev_default_init\*(C'\fR.
259.Sp 434.Sp
260The flags argument can be used to specify special behaviour or specific 435The flags argument can be used to specify special behaviour or specific
261backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). 436backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).
262.Sp 437.Sp
263The following flags are supported: 438The following flags are supported:
… …
268The default flags value. Use this if you have no clue (it's the right 443The default flags value. Use this if you have no clue (it's the right
269thing, believe me). 444thing, believe me).
270.ie n .IP """EVFLAG_NOENV""" 4 445.ie n .IP """EVFLAG_NOENV""" 4
271.el .IP "\f(CWEVFLAG_NOENV\fR" 4 446.el .IP "\f(CWEVFLAG_NOENV\fR" 4
272.IX Item "EVFLAG_NOENV" 447.IX Item "EVFLAG_NOENV"
273If this flag bit is ored into the flag value (or the program runs setuid 448If 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 449or 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 450\&\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 451override 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 452useful to try out specific backends to test their performance, or to work
278around bugs. 453around bugs.
454.ie n .IP """EVFLAG_FORKCHECK""" 4
455.el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4
456.IX Item "EVFLAG_FORKCHECK"
457Instead of calling \f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR manually after
458a fork, you can also make libev check for a fork in each iteration by
459enabling this flag.
460.Sp
461This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop,
462and thus this might slow down your event loop if you do a lot of loop
463iterations and little real work, but is usually not noticeable (on my
464GNU/Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn sequence
465without a system call and thus \fIvery\fR fast, but my GNU/Linux system also has
466\&\f(CW\*(C`pthread_atfork\*(C'\fR which is even faster).
467.Sp
468The big advantage of this flag is that you can forget about fork (and
469forget about forgetting to tell libev about forking) when you use this
470flag.
471.Sp
472This flag setting cannot be overridden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR
473environment variable.
279.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4 474.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
280.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4 475.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
281.IX Item "EVBACKEND_SELECT (value 1, portable select backend)" 476.IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
282This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as 477This 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, 478libev 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 479but 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 480using this backend. It doesn't scale too well (O(highest_fd)), but its
286the fastest backend for a low number of fds. 481usually the fastest backend for a low number of (low-numbered :) fds.
482.Sp
483To get good performance out of this backend you need a high amount of
484parallelism (most of the file descriptors should be busy). If you are
485writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many
486connections as possible during one iteration. You might also want to have
487a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of
488readiness notifications you get per iteration.
489.Sp
490This 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
491\&\f(CW\*(C`writefds\*(C'\fR set (and to work around Microsoft Windows bugs, also onto the
492\&\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)" 4 493.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)" 4 494.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)" 495.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 496And 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 497than select, but handles sparse fds better and has no artificial
292number of fds you can use (except it will slow down considerably with a 498limit 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). 499considerably with a lot of inactive fds). It scales similarly to select,
500i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for
501performance tips.
502.Sp
503This backend maps \f(CW\*(C`EV_READ\*(C'\fR to \f(CW\*(C`POLLIN | POLLERR | POLLHUP\*(C'\fR, and
504\&\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)" 4 505.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
295.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4 506.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
296.IX Item "EVBACKEND_EPOLL (value 4, Linux)" 507.IX Item "EVBACKEND_EPOLL (value 4, Linux)"
297For few fds, this backend is a bit little slower than poll and select, 508For 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 509but 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 510like O(total_fds) where n is the total number of fds (or the highest fd),
300either O(1) or O(active_fds). 511epoll scales either O(1) or O(active_fds). The epoll design has a number
512of shortcomings, such as silently dropping events in some hard-to-detect
513cases and requiring a system call per fd change, no fork support and bad
514support for dup.
301.Sp 515.Sp
302While stopping and starting an I/O watcher in the same iteration will 516While stopping, setting and starting an I/O watcher in the same iteration
303result in some caching, there is still a syscall per such incident 517will result in some caching, there is still a system call per such incident
304(because the fd could point to a different file description now), so its 518(because the fd could point to a different file description now), so its
305best to avoid that. Also, \fIdup()\fRed file descriptors might not work very 519best to avoid that. Also, \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors might not work
306well if you register events for both fds. 520very well if you register events for both fds.
307.Sp 521.Sp
308Please note that epoll sometimes generates spurious notifications, so you 522Please note that epoll sometimes generates spurious notifications, so you
309need to use non-blocking I/O or other means to avoid blocking when no data 523need to use non-blocking I/O or other means to avoid blocking when no data
310(or space) is available. 524(or space) is available.
525.Sp
526Best performance from this backend is achieved by not unregistering all
527watchers for a file descriptor until it has been closed, if possible,
528i.e. keep at least one watcher active per fd at all times. Stopping and
529starting a watcher (without re-setting it) also usually doesn't cause
530extra overhead.
531.Sp
532While nominally embeddable in other event loops, this feature is broken in
533all kernel versions tested so far.
534.Sp
535This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
536\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
311.ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4 537.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)" 4 538.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
313.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)" 539.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
314Kqueue deserves special mention, as at the time of this writing, it 540Kqueue deserves special mention, as at the time of this writing, it was
315was broken on all BSDs except NetBSD (usually it doesn't work with 541broken on all BSDs except NetBSD (usually it doesn't work reliably with
316anything but sockets and pipes, except on Darwin, where of course its 542anything but sockets and pipes, except on Darwin, where of course it's
317completely useless). For this reason its not being \*(L"autodetected\*(R" 543completely useless). For this reason it's not being \*(L"auto-detected\*(R" unless
318unless you explicitly specify it explicitly in the flags (i.e. using 544you explicitly specify it in the flags (i.e. using \f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or
319\&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR). 545libev was compiled on a known-to-be-good (\-enough) system like NetBSD.
546.Sp
547You still can embed kqueue into a normal poll or select backend and use it
548only for sockets (after having made sure that sockets work with kqueue on
549the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
320.Sp 550.Sp
321It scales in the same way as the epoll backend, but the interface to the 551It scales in the same way as the epoll backend, but the interface to the
322kernel is more efficient (which says nothing about its actual speed, of 552kernel is more efficient (which says nothing about its actual speed, of
323course). While starting and stopping an I/O watcher does not cause an 553course). While stopping, setting and starting an I/O watcher does never
324extra syscall as with epoll, it still adds up to four event changes per 554cause an extra system call as with \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to
325incident, so its best to avoid that. 555two event changes per incident. Support for \f(CW\*(C`fork ()\*(C'\fR is very bad and it
556drops fds silently in similarly hard-to-detect cases.
557.Sp
558This backend usually performs well under most conditions.
559.Sp
560While nominally embeddable in other event loops, this doesn't work
561everywhere, so you might need to test for this. And since it is broken
562almost everywhere, you should only use it when you have a lot of sockets
563(for which it usually works), by embedding it into another event loop
564(e.g. \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR) and, did I mention it,
565using it only for sockets.
566.Sp
567This backend maps \f(CW\*(C`EV_READ\*(C'\fR into an \f(CW\*(C`EVFILT_READ\*(C'\fR kevent with
568\&\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
569\&\f(CW\*(C`NOTE_EOF\*(C'\fR.
326.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4 570.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
327.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4 571.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
328.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)" 572.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
329This is not implemented yet (and might never be). 573This is not implemented yet (and might never be, unless you send me an
574implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets
575and is not embeddable, which would limit the usefulness of this backend
576immensely.
330.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4 577.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
331.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4 578.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
332.IX Item "EVBACKEND_PORT (value 32, Solaris 10)" 579.IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
333This uses the Solaris 10 port mechanism. As with everything on Solaris, 580This uses the Solaris 10 event port mechanism. As with everything on Solaris,
334it's really slow, but it still scales very well (O(active_fds)). 581it's really slow, but it still scales very well (O(active_fds)).
335.Sp 582.Sp
336Please note that solaris ports can result in a lot of spurious 583Please note that Solaris event ports can deliver a lot of spurious
337notifications, so you need to use non-blocking I/O or other means to avoid 584notifications, so you need to use non-blocking I/O or other means to avoid
338blocking when no data (or space) is available. 585blocking when no data (or space) is available.
586.Sp
587While this backend scales well, it requires one system call per active
588file descriptor per loop iteration. For small and medium numbers of file
589descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend
590might perform better.
591.Sp
592On the positive side, with the exception of the spurious readiness
593notifications, this backend actually performed fully to specification
594in all tests and is fully embeddable, which is a rare feat among the
595OS-specific backends.
596.Sp
597This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
598\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
339.ie n .IP """EVBACKEND_ALL""" 4 599.ie n .IP """EVBACKEND_ALL""" 4
340.el .IP "\f(CWEVBACKEND_ALL\fR" 4 600.el .IP "\f(CWEVBACKEND_ALL\fR" 4
341.IX Item "EVBACKEND_ALL" 601.IX Item "EVBACKEND_ALL"
342Try all backends (even potentially broken ones that wouldn't be tried 602Try all backends (even potentially broken ones that wouldn't be tried
343with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as 603with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as
344\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR. 604\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR.
605.Sp
606It is definitely not recommended to use this flag.
345.RE 607.RE
346.RS 4 608.RS 4
347.Sp 609.Sp
348If one or more of these are ored into the flags value, then only these 610If one or more of these are or'ed into the flags value, then only these
349backends will be tried (in the reverse order as given here). If none are 611backends will be tried (in the reverse order as listed here). If none are
350specified, most compiled-in backend will be tried, usually in reverse 612specified, all backends in \f(CW\*(C`ev_recommended_backends ()\*(C'\fR will be tried.
351order of their flag values :)
352.Sp 613.Sp
353The most typical usage is like this: 614Example: This is the most typical usage.
354.Sp 615.Sp
355.Vb 2 616.Vb 2
356\& if (!ev_default_loop (0)) 617\& if (!ev_default_loop (0))
357\& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?"); 618\& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
358.Ve 619.Ve
359.Sp 620.Sp
360Restrict libev to the select and poll backends, and do not allow 621Example: Restrict libev to the select and poll backends, and do not allow
361environment settings to be taken into account: 622environment settings to be taken into account:
362.Sp 623.Sp
363.Vb 1 624.Vb 1
364\& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV); 625\& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
365.Ve 626.Ve
366.Sp 627.Sp
367Use whatever libev has to offer, but make sure that kqueue is used if 628Example: Use whatever libev has to offer, but make sure that kqueue is
368available (warning, breaks stuff, best use only with your own private 629used if available (warning, breaks stuff, best use only with your own
369event loop and only if you know the \s-1OS\s0 supports your types of fds): 630private event loop and only if you know the \s-1OS\s0 supports your types of
631fds):
370.Sp 632.Sp
371.Vb 1 633.Vb 1
372\& ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE); 634\& ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
373.Ve 635.Ve
374.RE 636.RE
375.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4 637.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
376.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)" 638.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
377Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is 639Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is
378always distinct from the default loop. Unlike the default loop, it cannot 640always distinct from the default loop. Unlike the default loop, it cannot
379handle signal and child watchers, and attempts to do so will be greeted by 641handle signal and child watchers, and attempts to do so will be greeted by
380undefined behaviour (or a failed assertion if assertions are enabled). 642undefined behaviour (or a failed assertion if assertions are enabled).
643.Sp
644Note that this function \fIis\fR thread-safe, and the recommended way to use
645libev with threads is indeed to create one loop per thread, and using the
646default loop in the \*(L"main\*(R" or \*(L"initial\*(R" thread.
647.Sp
648Example: Try to create a event loop that uses epoll and nothing else.
649.Sp
650.Vb 3
651\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
652\& if (!epoller)
653\& fatal ("no epoll found here, maybe it hides under your chair");
654.Ve
381.IP "ev_default_destroy ()" 4 655.IP "ev_default_destroy ()" 4
382.IX Item "ev_default_destroy ()" 656.IX Item "ev_default_destroy ()"
383Destroys the default loop again (frees all memory and kernel state 657Destroys the default loop again (frees all memory and kernel state
384etc.). This stops all registered event watchers (by not touching them in 658etc.). None of the active event watchers will be stopped in the normal
385any way whatsoever, although you cannot rely on this :). 659sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your
660responsibility to either stop all watchers cleanly yourself \fIbefore\fR
661calling this function, or cope with the fact afterwards (which is usually
662the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them
663for example).
664.Sp
665Note that certain global state, such as signal state, will not be freed by
666this function, and related watchers (such as signal and child watchers)
667would need to be stopped manually.
668.Sp
669In general it is not advisable to call this function except in the
670rare occasion where you really need to free e.g. the signal handling
671pipe fds. If you need dynamically allocated loops it is better to use
672\&\f(CW\*(C`ev_loop_new\*(C'\fR and \f(CW\*(C`ev_loop_destroy\*(C'\fR).
386.IP "ev_loop_destroy (loop)" 4 673.IP "ev_loop_destroy (loop)" 4
387.IX Item "ev_loop_destroy (loop)" 674.IX Item "ev_loop_destroy (loop)"
388Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an 675Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an
389earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR. 676earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR.
390.IP "ev_default_fork ()" 4 677.IP "ev_default_fork ()" 4
391.IX Item "ev_default_fork ()" 678.IX Item "ev_default_fork ()"
679This function sets a flag that causes subsequent \f(CW\*(C`ev_loop\*(C'\fR iterations
392This function reinitialises the kernel state for backends that have 680to reinitialise the kernel state for backends that have one. Despite the
393one. Despite the name, you can call it anytime, but it makes most sense 681name, you can call it anytime, but it makes most sense after forking, in
394after forking, in either the parent or child process (or both, but that 682the child process (or both child and parent, but that again makes little
395again makes little sense). 683sense). You \fImust\fR call it in the child before using any of the libev
684functions, and it will only take effect at the next \f(CW\*(C`ev_loop\*(C'\fR iteration.
396.Sp 685.Sp
397You \fImust\fR call this function in the child process after forking if and 686On the other hand, you only need to call this function in the child
398only if you want to use the event library in both processes. If you just 687process if and only if you want to use the event library in the child. If
399fork+exec, you don't have to call it. 688you just fork+exec, you don't have to call it at all.
400.Sp 689.Sp
401The function itself is quite fast and it's usually not a problem to call 690The function itself is quite fast and it's usually not a problem to call
402it just in case after a fork. To make this easy, the function will fit in 691it just in case after a fork. To make this easy, the function will fit in
403quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR: 692quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR:
404.Sp 693.Sp
405.Vb 1 694.Vb 1
406\& pthread_atfork (0, 0, ev_default_fork); 695\& pthread_atfork (0, 0, ev_default_fork);
407.Ve 696.Ve
408.Sp
409At the moment, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and \f(CW\*(C`EVBACKEND_POLL\*(C'\fR are safe to use
410without calling this function, so if you force one of those backends you
411do not need to care.
412.IP "ev_loop_fork (loop)" 4 697.IP "ev_loop_fork (loop)" 4
413.IX Item "ev_loop_fork (loop)" 698.IX Item "ev_loop_fork (loop)"
414Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by 699Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by
415\&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop 700\&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop
416after fork, and how you do this is entirely your own problem. 701after fork that you want to re-use in the child, and how you do this is
702entirely your own problem.
703.IP "int ev_is_default_loop (loop)" 4
704.IX Item "int ev_is_default_loop (loop)"
705Returns true when the given loop is, in fact, the default loop, and false
706otherwise.
707.IP "unsigned int ev_loop_count (loop)" 4
708.IX Item "unsigned int ev_loop_count (loop)"
709Returns the count of loop iterations for the loop, which is identical to
710the number of times libev did poll for new events. It starts at \f(CW0\fR and
711happily wraps around with enough iterations.
712.Sp
713This value can sometimes be useful as a generation counter of sorts (it
714\&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with
715\&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls.
417.IP "unsigned int ev_backend (loop)" 4 716.IP "unsigned int ev_backend (loop)" 4
418.IX Item "unsigned int ev_backend (loop)" 717.IX Item "unsigned int ev_backend (loop)"
419Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in 718Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
420use. 719use.
421.IP "ev_tstamp ev_now (loop)" 4 720.IP "ev_tstamp ev_now (loop)" 4
422.IX Item "ev_tstamp ev_now (loop)" 721.IX Item "ev_tstamp ev_now (loop)"
423Returns the current \*(L"event loop time\*(R", which is the time the event loop 722Returns the current \*(L"event loop time\*(R", which is the time the event loop
424got events and started processing them. This timestamp does not change 723received events and started processing them. This timestamp does not
425as long as callbacks are being processed, and this is also the base time 724change as long as callbacks are being processed, and this is also the base
426used for relative timers. You can treat it as the timestamp of the event 725time used for relative timers. You can treat it as the timestamp of the
427occuring (or more correctly, the mainloop finding out about it). 726event occurring (or more correctly, libev finding out about it).
727.IP "ev_now_update (loop)" 4
728.IX Item "ev_now_update (loop)"
729Establishes the current time by querying the kernel, updating the time
730returned by \f(CW\*(C`ev_now ()\*(C'\fR in the progress. This is a costly operation and
731is usually done automatically within \f(CW\*(C`ev_loop ()\*(C'\fR.
732.Sp
733This function is rarely useful, but when some event callback runs for a
734very long time without entering the event loop, updating libev's idea of
735the current time is a good idea.
736.Sp
737See also \*(L"The special problem of time updates\*(R" in the \f(CW\*(C`ev_timer\*(C'\fR section.
428.IP "ev_loop (loop, int flags)" 4 738.IP "ev_loop (loop, int flags)" 4
429.IX Item "ev_loop (loop, int flags)" 739.IX Item "ev_loop (loop, int flags)"
430Finally, this is it, the event handler. This function usually is called 740Finally, this is it, the event handler. This function usually is called
431after you initialised all your watchers and you want to start handling 741after you initialised all your watchers and you want to start handling
432events. 742events.
433.Sp 743.Sp
434If the flags argument is specified as \f(CW0\fR, it will not return until 744If the flags argument is specified as \f(CW0\fR, it will not return until
435either no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called. 745either no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called.
436.Sp 746.Sp
747Please note that an explicit \f(CW\*(C`ev_unloop\*(C'\fR is usually better than
748relying on all watchers to be stopped when deciding when a program has
749finished (especially in interactive programs), but having a program
750that automatically loops as long as it has to and no longer by virtue
751of relying on its watchers stopping correctly, that is truly a thing of
752beauty.
753.Sp
437A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle 754A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle
438those events and any outstanding ones, but will not block your process in 755those events and any already outstanding ones, but will not block your
439case there are no events and will return after one iteration of the loop. 756process in case there are no events and will return after one iteration of
757the loop.
440.Sp 758.Sp
441A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if 759A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if
442neccessary) and will handle those and any outstanding ones. It will block 760necessary) and will handle those and any already outstanding ones. It
443your process until at least one new event arrives, and will return after 761will block your process until at least one new event arrives (which could
444one iteration of the loop. This is useful if you are waiting for some 762be an event internal to libev itself, so there is no guarentee that a
445external event in conjunction with something not expressible using other 763user-registered callback will be called), and will return after one
764iteration of the loop.
765.Sp
766This is useful if you are waiting for some external event in conjunction
767with something not expressible using other libev watchers (i.e. "roll your
446libev watchers. However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is 768own \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
447usually a better approach for this kind of thing. 769usually a better approach for this kind of thing.
448.Sp 770.Sp
449Here are the gory details of what \f(CW\*(C`ev_loop\*(C'\fR does: 771Here are the gory details of what \f(CW\*(C`ev_loop\*(C'\fR does:
450.Sp 772.Sp
451.Vb 18 773.Vb 10
452\& * If there are no active watchers (reference count is zero), return. 774\& \- Before the first iteration, call any pending watchers.
453\& - Queue prepare watchers and then call all outstanding watchers. 775\& * If EVFLAG_FORKCHECK was used, check for a fork.
776\& \- If a fork was detected (by any means), queue and call all fork watchers.
777\& \- Queue and call all prepare watchers.
454\& - If we have been forked, recreate the kernel state. 778\& \- If we have been forked, detach and recreate the kernel state
779\& as to not disturb the other process.
455\& - Update the kernel state with all outstanding changes. 780\& \- Update the kernel state with all outstanding changes.
456\& - Update the "event loop time". 781\& \- Update the "event loop time" (ev_now ()).
457\& - Calculate for how long to block. 782\& \- Calculate for how long to sleep or block, if at all
783\& (active idle watchers, EVLOOP_NONBLOCK or not having
784\& any active watchers at all will result in not sleeping).
785\& \- Sleep if the I/O and timer collect interval say so.
458\& - Block the process, waiting for any events. 786\& \- Block the process, waiting for any events.
459\& - Queue all outstanding I/O (fd) events. 787\& \- Queue all outstanding I/O (fd) events.
460\& - Update the "event loop time" and do time jump handling. 788\& \- Update the "event loop time" (ev_now ()), and do time jump adjustments.
461\& - Queue all outstanding timers. 789\& \- Queue all expired timers.
462\& - Queue all outstanding periodics. 790\& \- Queue all expired periodics.
463\& - If no events are pending now, queue all idle watchers. 791\& \- Unless any events are pending now, queue all idle watchers.
464\& - Queue all check watchers. 792\& \- Queue all check watchers.
465\& - Call all queued watchers in reverse order (i.e. check watchers first). 793\& \- Call all queued watchers in reverse order (i.e. check watchers first).
466\& Signals and child watchers are implemented as I/O watchers, and will 794\& Signals and child watchers are implemented as I/O watchers, and will
467\& be handled here by queueing them when their watcher gets executed. 795\& be handled here by queueing them when their watcher gets executed.
468\& - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK 796\& \- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
469\& were used, return, otherwise continue with step *. 797\& were used, or there are no active watchers, return, otherwise
798\& continue with step *.
799.Ve
800.Sp
801Example: Queue some jobs and then loop until no events are outstanding
802anymore.
803.Sp
804.Vb 4
805\& ... queue jobs here, make sure they register event watchers as long
806\& ... as they still have work to do (even an idle watcher will do..)
807\& ev_loop (my_loop, 0);
808\& ... jobs done or somebody called unloop. yeah!
470.Ve 809.Ve
471.IP "ev_unloop (loop, how)" 4 810.IP "ev_unloop (loop, how)" 4
472.IX Item "ev_unloop (loop, how)" 811.IX Item "ev_unloop (loop, how)"
473Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it 812Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it
474has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either 813has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
475\&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or 814\&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or
476\&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return. 815\&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return.
816.Sp
817This \*(L"unloop state\*(R" will be cleared when entering \f(CW\*(C`ev_loop\*(C'\fR again.
477.IP "ev_ref (loop)" 4 818.IP "ev_ref (loop)" 4
478.IX Item "ev_ref (loop)" 819.IX Item "ev_ref (loop)"
479.PD 0 820.PD 0
480.IP "ev_unref (loop)" 4 821.IP "ev_unref (loop)" 4
481.IX Item "ev_unref (loop)" 822.IX Item "ev_unref (loop)"
482.PD 823.PD
483Ref/unref can be used to add or remove a reference count on the event 824Ref/unref can be used to add or remove a reference count on the event
484loop: Every watcher keeps one reference, and as long as the reference 825loop: Every watcher keeps one reference, and as long as the reference
485count is nonzero, \f(CW\*(C`ev_loop\*(C'\fR will not return on its own. If you have 826count is nonzero, \f(CW\*(C`ev_loop\*(C'\fR will not return on its own.
827.Sp
486a watcher you never unregister that should not keep \f(CW\*(C`ev_loop\*(C'\fR from 828If you have a watcher you never unregister that should not keep \f(CW\*(C`ev_loop\*(C'\fR
487returning, \fIev_unref()\fR after starting, and \fIev_ref()\fR before stopping it. For 829from returning, call \fIev_unref()\fR after starting, and \fIev_ref()\fR before
830stopping it.
831.Sp
488example, libev itself uses this for its internal signal pipe: It is not 832As an example, libev itself uses this for its internal signal pipe: It is
489visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from exiting if 833not visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from exiting
490no event watchers registered by it are active. It is also an excellent 834if no event watchers registered by it are active. It is also an excellent
491way to do this for generic recurring timers or from within third-party 835way to do this for generic recurring timers or from within third-party
492libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR. 836libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR
837(but only if the watcher wasn't active before, or was active before,
838respectively).
839.Sp
840Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_loop\*(C'\fR
841running when nothing else is active.
842.Sp
843.Vb 4
844\& struct ev_signal exitsig;
845\& ev_signal_init (&exitsig, sig_cb, SIGINT);
846\& ev_signal_start (loop, &exitsig);
847\& evf_unref (loop);
848.Ve
849.Sp
850Example: For some weird reason, unregister the above signal handler again.
851.Sp
852.Vb 2
853\& ev_ref (loop);
854\& ev_signal_stop (loop, &exitsig);
855.Ve
856.IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4
857.IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"
858.PD 0
859.IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4
860.IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"
861.PD
862These advanced functions influence the time that libev will spend waiting
863for events. Both time intervals are by default \f(CW0\fR, meaning that libev
864will try to invoke timer/periodic callbacks and I/O callbacks with minimum
865latency.
866.Sp
867Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR)
868allows libev to delay invocation of I/O and timer/periodic callbacks
869to increase efficiency of loop iterations (or to increase power-saving
870opportunities).
871.Sp
872The idea is that sometimes your program runs just fast enough to handle
873one (or very few) event(s) per loop iteration. While this makes the
874program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new
875events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high
876overhead for the actual polling but can deliver many events at once.
877.Sp
878By setting a higher \fIio collect interval\fR you allow libev to spend more
879time collecting I/O events, so you can handle more events per iteration,
880at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and
881\&\f(CW\*(C`ev_timer\*(C'\fR) will be not affected. Setting this to a non-null value will
882introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations.
883.Sp
884Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
885to spend more time collecting timeouts, at the expense of increased
886latency/jitter/inexactness (the watcher callback will be called
887later). \f(CW\*(C`ev_io\*(C'\fR watchers will not be affected. Setting this to a non-null
888value will not introduce any overhead in libev.
889.Sp
890Many (busy) programs can usually benefit by setting the I/O collect
891interval to a value near \f(CW0.1\fR or so, which is often enough for
892interactive servers (of course not for games), likewise for timeouts. It
893usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR,
894as this approaches the timing granularity of most systems.
895.Sp
896Setting the \fItimeout collect interval\fR can improve the opportunity for
897saving power, as the program will \*(L"bundle\*(R" timer callback invocations that
898are \*(L"near\*(R" in time together, by delaying some, thus reducing the number of
899times the process sleeps and wakes up again. Another useful technique to
900reduce iterations/wake\-ups is to use \f(CW\*(C`ev_periodic\*(C'\fR watchers and make sure
901they fire on, say, one-second boundaries only.
902.IP "ev_loop_verify (loop)" 4
903.IX Item "ev_loop_verify (loop)"
904This function only does something when \f(CW\*(C`EV_VERIFY\*(C'\fR support has been
905compiled in. which is the default for non-minimal builds. It tries to go
906through all internal structures and checks them for validity. If anything
907is found to be inconsistent, it will print an error message to standard
908error and call \f(CW\*(C`abort ()\*(C'\fR.
909.Sp
910This can be used to catch bugs inside libev itself: under normal
911circumstances, this function will never abort as of course libev keeps its
912data structures consistent.
493.SH "ANATOMY OF A WATCHER" 913.SH "ANATOMY OF A WATCHER"
494.IX Header "ANATOMY OF A WATCHER" 914.IX Header "ANATOMY OF A WATCHER"
495A watcher is a structure that you create and register to record your 915A watcher is a structure that you create and register to record your
496interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to 916interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to
497become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that: 917become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that:
498.PP 918.PP
499.Vb 5 919.Vb 5
500\& static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) 920\& static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
501\& { 921\& {
502\& ev_io_stop (w); 922\& ev_io_stop (w);
503\& ev_unloop (loop, EVUNLOOP_ALL); 923\& ev_unloop (loop, EVUNLOOP_ALL);
504\& } 924\& }
505.Ve 925\&
506.PP
507.Vb 6
508\& struct ev_loop *loop = ev_default_loop (0); 926\& struct ev_loop *loop = ev_default_loop (0);
509\& struct ev_io stdin_watcher; 927\& struct ev_io stdin_watcher;
510\& ev_init (&stdin_watcher, my_cb); 928\& ev_init (&stdin_watcher, my_cb);
511\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); 929\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
512\& ev_io_start (loop, &stdin_watcher); 930\& ev_io_start (loop, &stdin_watcher);
513\& ev_loop (loop, 0); 931\& ev_loop (loop, 0);
514.Ve 932.Ve
515.PP 933.PP
516As you can see, you are responsible for allocating the memory for your 934As you can see, you are responsible for allocating the memory for your
517watcher structures (and it is usually a bad idea to do this on the stack, 935watcher structures (and it is usually a bad idea to do this on the stack,
518although this can sometimes be quite valid). 936although this can sometimes be quite valid).
519.PP 937.PP
520Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init 938Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init
521(watcher *, callback)\*(C'\fR, which expects a callback to be provided. This 939(watcher *, callback)\*(C'\fR, which expects a callback to be provided. This
522callback gets invoked each time the event occurs (or, in the case of io 940callback gets invoked each time the event occurs (or, in the case of I/O
523watchers, each time the event loop detects that the file descriptor given 941watchers, each time the event loop detects that the file descriptor given
524is readable and/or writable). 942is readable and/or writable).
525.PP 943.PP
526Each watcher type has its own \f(CW\*(C`ev_<type>_set (watcher *, ...)\*(C'\fR macro 944Each watcher type has its own \f(CW\*(C`ev_<type>_set (watcher *, ...)\*(C'\fR macro
527with arguments specific to this watcher type. There is also a macro 945with arguments specific to this watcher type. There is also a macro
… …
533*)\*(C'\fR), and you can stop watching for events at any time by calling the 951*)\*(C'\fR), and you can stop watching for events at any time by calling the
534corresponding stop function (\f(CW\*(C`ev_<type>_stop (loop, watcher *)\*(C'\fR. 952corresponding stop function (\f(CW\*(C`ev_<type>_stop (loop, watcher *)\*(C'\fR.
535.PP 953.PP
536As long as your watcher is active (has been started but not stopped) you 954As long as your watcher is active (has been started but not stopped) you
537must not touch the values stored in it. Most specifically you must never 955must not touch the values stored in it. Most specifically you must never
538reinitialise it or call its set macro. 956reinitialise it or call its \f(CW\*(C`set\*(C'\fR macro.
539.PP
540You can check whether an event is active by calling the \f(CW\*(C`ev_is_active
541(watcher *)\*(C'\fR macro. To see whether an event is outstanding (but the
542callback for it has not been called yet) you can use the \f(CW\*(C`ev_is_pending
543(watcher *)\*(C'\fR macro.
544.PP 957.PP
545Each and every callback receives the event loop pointer as first, the 958Each and every callback receives the event loop pointer as first, the
546registered watcher structure as second, and a bitset of received events as 959registered watcher structure as second, and a bitset of received events as
547third argument. 960third argument.
548.PP 961.PP
… …
573The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread. 986The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread.
574.ie n .IP """EV_CHILD""" 4 987.ie n .IP """EV_CHILD""" 4
575.el .IP "\f(CWEV_CHILD\fR" 4 988.el .IP "\f(CWEV_CHILD\fR" 4
576.IX Item "EV_CHILD" 989.IX Item "EV_CHILD"
577The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change. 990The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change.
991.ie n .IP """EV_STAT""" 4
992.el .IP "\f(CWEV_STAT\fR" 4
993.IX Item "EV_STAT"
994The path specified in the \f(CW\*(C`ev_stat\*(C'\fR watcher changed its attributes somehow.
578.ie n .IP """EV_IDLE""" 4 995.ie n .IP """EV_IDLE""" 4
579.el .IP "\f(CWEV_IDLE\fR" 4 996.el .IP "\f(CWEV_IDLE\fR" 4
580.IX Item "EV_IDLE" 997.IX Item "EV_IDLE"
581The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do. 998The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do.
582.ie n .IP """EV_PREPARE""" 4 999.ie n .IP """EV_PREPARE""" 4
… …
592\&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any 1009\&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any
593received events. Callbacks of both watcher types can start and stop as 1010received events. Callbacks of both watcher types can start and stop as
594many watchers as they want, and all of them will be taken into account 1011many watchers as they want, and all of them will be taken into account
595(for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep 1012(for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep
596\&\f(CW\*(C`ev_loop\*(C'\fR from blocking). 1013\&\f(CW\*(C`ev_loop\*(C'\fR from blocking).
1014.ie n .IP """EV_EMBED""" 4
1015.el .IP "\f(CWEV_EMBED\fR" 4
1016.IX Item "EV_EMBED"
1017The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.
1018.ie n .IP """EV_FORK""" 4
1019.el .IP "\f(CWEV_FORK\fR" 4
1020.IX Item "EV_FORK"
1021The event loop has been resumed in the child process after fork (see
1022\&\f(CW\*(C`ev_fork\*(C'\fR).
1023.ie n .IP """EV_ASYNC""" 4
1024.el .IP "\f(CWEV_ASYNC\fR" 4
1025.IX Item "EV_ASYNC"
1026The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR).
597.ie n .IP """EV_ERROR""" 4 1027.ie n .IP """EV_ERROR""" 4
598.el .IP "\f(CWEV_ERROR\fR" 4 1028.el .IP "\f(CWEV_ERROR\fR" 4
599.IX Item "EV_ERROR" 1029.IX Item "EV_ERROR"
600An unspecified error has occured, the watcher has been stopped. This might 1030An unspecified error has occurred, the watcher has been stopped. This might
601happen because the watcher could not be properly started because libev 1031happen because the watcher could not be properly started because libev
602ran out of memory, a file descriptor was found to be closed or any other 1032ran out of memory, a file descriptor was found to be closed or any other
603problem. You best act on it by reporting the problem and somehow coping 1033problem. You best act on it by reporting the problem and somehow coping
604with the watcher being stopped. 1034with the watcher being stopped.
605.Sp 1035.Sp
606Libev will usually signal a few \*(L"dummy\*(R" events together with an error, 1036Libev will usually signal a few \*(L"dummy\*(R" events together with an error, for
607for example it might indicate that a fd is readable or writable, and if 1037example it might indicate that a fd is readable or writable, and if your
608your callbacks is well-written it can just attempt the operation and cope 1038callbacks is well-written it can just attempt the operation and cope with
609with the error from \fIread()\fR or \fIwrite()\fR. This will not work in multithreaded 1039the error from \fIread()\fR or \fIwrite()\fR. This will not work in multi-threaded
610programs, though, so beware. 1040programs, though, as the fd could already be closed and reused for another
1041thing, so beware.
1042.Sh "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0"
1043.IX Subsection "GENERIC WATCHER FUNCTIONS"
1044In the following description, \f(CW\*(C`TYPE\*(C'\fR stands for the watcher type,
1045e.g. \f(CW\*(C`timer\*(C'\fR for \f(CW\*(C`ev_timer\*(C'\fR watchers and \f(CW\*(C`io\*(C'\fR for \f(CW\*(C`ev_io\*(C'\fR watchers.
1046.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
1047.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
1048.IX Item "ev_init (ev_TYPE *watcher, callback)"
1049This macro initialises the generic portion of a watcher. The contents
1050of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
1051the generic parts of the watcher are initialised, you \fIneed\fR to call
1052the type-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR macro afterwards to initialise the
1053type-specific parts. For each type there is also a \f(CW\*(C`ev_TYPE_init\*(C'\fR macro
1054which rolls both calls into one.
1055.Sp
1056You can reinitialise a watcher at any time as long as it has been stopped
1057(or never started) and there are no pending events outstanding.
1058.Sp
1059The callback is always of type \f(CW\*(C`void (*)(ev_loop *loop, ev_TYPE *watcher,
1060int revents)\*(C'\fR.
1061.Sp
1062Example: Initialise an \f(CW\*(C`ev_io\*(C'\fR watcher in two steps.
1063.Sp
1064.Vb 3
1065\& ev_io w;
1066\& ev_init (&w, my_cb);
1067\& ev_io_set (&w, STDIN_FILENO, EV_READ);
1068.Ve
1069.ie n .IP """ev_TYPE_set"" (ev_TYPE *, [args])" 4
1070.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *, [args])" 4
1071.IX Item "ev_TYPE_set (ev_TYPE *, [args])"
1072This macro initialises the type-specific parts of a watcher. You need to
1073call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
1074call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
1075macro on a watcher that is active (it can be pending, however, which is a
1076difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
1077.Sp
1078Although some watcher types do not have type-specific arguments
1079(e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
1080.Sp
1081See \f(CW\*(C`ev_init\*(C'\fR, above, for an example.
1082.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
1083.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
1084.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
1085This convenience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
1086calls into a single call. This is the most convenient method to initialise
1087a watcher. The same limitations apply, of course.
1088.Sp
1089Example: Initialise and set an \f(CW\*(C`ev_io\*(C'\fR watcher in one step.
1090.Sp
1091.Vb 1
1092\& ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1093.Ve
1094.ie n .IP """ev_TYPE_start"" (loop *, ev_TYPE *watcher)" 4
1095.el .IP "\f(CWev_TYPE_start\fR (loop *, ev_TYPE *watcher)" 4
1096.IX Item "ev_TYPE_start (loop *, ev_TYPE *watcher)"
1097Starts (activates) the given watcher. Only active watchers will receive
1098events. If the watcher is already active nothing will happen.
1099.Sp
1100Example: Start the \f(CW\*(C`ev_io\*(C'\fR watcher that is being abused as example in this
1101whole section.
1102.Sp
1103.Vb 1
1104\& ev_io_start (EV_DEFAULT_UC, &w);
1105.Ve
1106.ie n .IP """ev_TYPE_stop"" (loop *, ev_TYPE *watcher)" 4
1107.el .IP "\f(CWev_TYPE_stop\fR (loop *, ev_TYPE *watcher)" 4
1108.IX Item "ev_TYPE_stop (loop *, ev_TYPE *watcher)"
1109Stops the given watcher again (if active) and clears the pending
1110status. It is possible that stopped watchers are pending (for example,
1111non-repeating timers are being stopped when they become pending), but
1112\&\f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor pending. If
1113you want to free or reuse the memory used by the watcher it is therefore a
1114good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
1115.IP "bool ev_is_active (ev_TYPE *watcher)" 4
1116.IX Item "bool ev_is_active (ev_TYPE *watcher)"
1117Returns a true value iff the watcher is active (i.e. it has been started
1118and not yet been stopped). As long as a watcher is active you must not modify
1119it.
1120.IP "bool ev_is_pending (ev_TYPE *watcher)" 4
1121.IX Item "bool ev_is_pending (ev_TYPE *watcher)"
1122Returns a true value iff the watcher is pending, (i.e. it has outstanding
1123events but its callback has not yet been invoked). As long as a watcher
1124is pending (but not active) you must not call an init function on it (but
1125\&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe), you must not change its priority, and you must
1126make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR
1127it).
1128.IP "callback ev_cb (ev_TYPE *watcher)" 4
1129.IX Item "callback ev_cb (ev_TYPE *watcher)"
1130Returns the callback currently set on the watcher.
1131.IP "ev_cb_set (ev_TYPE *watcher, callback)" 4
1132.IX Item "ev_cb_set (ev_TYPE *watcher, callback)"
1133Change the callback. You can change the callback at virtually any time
1134(modulo threads).
1135.IP "ev_set_priority (ev_TYPE *watcher, priority)" 4
1136.IX Item "ev_set_priority (ev_TYPE *watcher, priority)"
1137.PD 0
1138.IP "int ev_priority (ev_TYPE *watcher)" 4
1139.IX Item "int ev_priority (ev_TYPE *watcher)"
1140.PD
1141Set and query the priority of the watcher. The priority is a small
1142integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR
1143(default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked
1144before watchers with lower priority, but priority will not keep watchers
1145from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
1146.Sp
1147This means that priorities are \fIonly\fR used for ordering callback
1148invocation after new events have been received. This is useful, for
1149example, to reduce latency after idling, or more often, to bind two
1150watchers on the same event and make sure one is called first.
1151.Sp
1152If you need to suppress invocation when higher priority events are pending
1153you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
1154.Sp
1155You \fImust not\fR change the priority of a watcher as long as it is active or
1156pending.
1157.Sp
1158The default priority used by watchers when no priority has been set is
1159always \f(CW0\fR, which is supposed to not be too high and not be too low :).
1160.Sp
1161Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
1162fine, as long as you do not mind that the priority value you query might
1163or might not have been adjusted to be within valid range.
1164.IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
1165.IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
1166Invoke the \f(CW\*(C`watcher\*(C'\fR with the given \f(CW\*(C`loop\*(C'\fR and \f(CW\*(C`revents\*(C'\fR. Neither
1167\&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback
1168can deal with that fact, as both are simply passed through to the
1169callback.
1170.IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
1171.IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
1172If the watcher is pending, this function clears its pending status and
1173returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the
1174watcher isn't pending it does nothing and returns \f(CW0\fR.
1175.Sp
1176Sometimes it can be useful to \*(L"poll\*(R" a watcher instead of waiting for its
1177callback to be invoked, which can be accomplished with this function.
611.Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0" 1178.Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0"
612.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER" 1179.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
613Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change 1180Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change
614and read at any time, libev will completely ignore it. This can be used 1181and read at any time: libev will completely ignore it. This can be used
615to associate arbitrary data with your watcher. If you need more data and 1182to associate arbitrary data with your watcher. If you need more data and
616don't want to allocate memory and store a pointer to it in that data 1183don't want to allocate memory and store a pointer to it in that data
617member, you can also \*(L"subclass\*(R" the watcher type and provide your own 1184member, you can also \*(L"subclass\*(R" the watcher type and provide your own
618data: 1185data:
619.PP 1186.PP
620.Vb 7 1187.Vb 7
621\& struct my_io 1188\& struct my_io
622\& { 1189\& {
623\& struct ev_io io; 1190\& struct ev_io io;
624\& int otherfd; 1191\& int otherfd;
625\& void *somedata; 1192\& void *somedata;
626\& struct whatever *mostinteresting; 1193\& struct whatever *mostinteresting;
627\& } 1194\& };
1195\&
1196\& ...
1197\& struct my_io w;
1198\& ev_io_init (&w.io, my_cb, fd, EV_READ);
628.Ve 1199.Ve
629.PP 1200.PP
630And since your callback will be called with a pointer to the watcher, you 1201And since your callback will be called with a pointer to the watcher, you
631can cast it back to your own type: 1202can cast it back to your own type:
632.PP 1203.PP
633.Vb 5 1204.Vb 5
634\& static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents) 1205\& static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
635\& { 1206\& {
636\& struct my_io *w = (struct my_io *)w_; 1207\& struct my_io *w = (struct my_io *)w_;
637\& ... 1208\& ...
638\& } 1209\& }
639.Ve 1210.Ve
640.PP 1211.PP
641More interesting and less C\-conformant ways of catsing your callback type 1212More interesting and less C\-conformant ways of casting your callback type
642have been omitted.... 1213instead have been omitted.
1214.PP
1215Another common scenario is to use some data structure with multiple
1216embedded watchers:
1217.PP
1218.Vb 6
1219\& struct my_biggy
1220\& {
1221\& int some_data;
1222\& ev_timer t1;
1223\& ev_timer t2;
1224\& }
1225.Ve
1226.PP
1227In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more
1228complicated: Either you store the address of your \f(CW\*(C`my_biggy\*(C'\fR struct
1229in the \f(CW\*(C`data\*(C'\fR member of the watcher (for woozies), or you need to use
1230some pointer arithmetic using \f(CW\*(C`offsetof\*(C'\fR inside your watchers (for real
1231programmers):
1232.PP
1233.Vb 1
1234\& #include <stddef.h>
1235\&
1236\& static void
1237\& t1_cb (EV_P_ struct ev_timer *w, int revents)
1238\& {
1239\& struct my_biggy big = (struct my_biggy *
1240\& (((char *)w) \- offsetof (struct my_biggy, t1));
1241\& }
1242\&
1243\& static void
1244\& t2_cb (EV_P_ struct ev_timer *w, int revents)
1245\& {
1246\& struct my_biggy big = (struct my_biggy *
1247\& (((char *)w) \- offsetof (struct my_biggy, t2));
1248\& }
1249.Ve
643.SH "WATCHER TYPES" 1250.SH "WATCHER TYPES"
644.IX Header "WATCHER TYPES" 1251.IX Header "WATCHER TYPES"
645This section describes each watcher in detail, but will not repeat 1252This section describes each watcher in detail, but will not repeat
646information given in the last section. 1253information given in the last section. Any initialisation/set macros,
1254functions and members specific to the watcher type are explained.
1255.PP
1256Members are additionally marked with either \fI[read\-only]\fR, meaning that,
1257while the watcher is active, you can look at the member and expect some
1258sensible content, but you must not modify it (you can modify it while the
1259watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
1260means you can expect it to have some sensible content while the watcher
1261is active, but you can also modify it. Modifying it may not do something
1262sensible or take immediate effect (or do anything at all), but libev will
1263not crash or malfunction in any way.
647.ie n .Sh """ev_io"" \- is this file descriptor readable or writable" 1264.ie n .Sh """ev_io"" \- is this file descriptor readable or writable?"
648.el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable" 1265.el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable?"
649.IX Subsection "ev_io - is this file descriptor readable or writable" 1266.IX Subsection "ev_io - is this file descriptor readable or writable?"
650I/O watchers check whether a file descriptor is readable or writable 1267I/O watchers check whether a file descriptor is readable or writable
651in each iteration of the event loop (This behaviour is called 1268in each iteration of the event loop, or, more precisely, when reading
652level-triggering because you keep receiving events as long as the 1269would not block the process and writing would at least be able to write
653condition persists. Remember you can stop the watcher if you don't want to 1270some data. This behaviour is called level-triggering because you keep
654act on the event and neither want to receive future events). 1271receiving events as long as the condition persists. Remember you can stop
1272the watcher if you don't want to act on the event and neither want to
1273receive future events.
655.PP 1274.PP
656In general you can register as many read and/or write event watchers per 1275In general you can register as many read and/or write event watchers per
657fd as you want (as long as you don't confuse yourself). Setting all file 1276fd as you want (as long as you don't confuse yourself). Setting all file
658descriptors to non-blocking mode is also usually a good idea (but not 1277descriptors to non-blocking mode is also usually a good idea (but not
659required if you know what you are doing). 1278required if you know what you are doing).
660.PP 1279.PP
661You have to be careful with dup'ed file descriptors, though. Some backends 1280If you cannot use non-blocking mode, then force the use of a
662(the linux epoll backend is a notable example) cannot handle dup'ed file 1281known-to-be-good backend (at the time of this writing, this includes only
663descriptors correctly if you register interest in two or more fds pointing 1282\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and \f(CW\*(C`EVBACKEND_POLL\*(C'\fR).
664to the same underlying file/socket etc. description (that is, they share
665the same underlying \*(L"file open\*(R").
666.PP 1283.PP
667If you must do this, then force the use of a known-to-be-good backend 1284Another thing you have to watch out for is that it is quite easy to
668(at the time of this writing, this includes only \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and 1285receive \*(L"spurious\*(R" readiness notifications, that is your callback might
1286be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block
1287because there is no data. Not only are some backends known to create a
1288lot of those (for example Solaris ports), it is very easy to get into
1289this situation even with a relatively standard program structure. Thus
1290it is best to always use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning
1291\&\f(CW\*(C`EAGAIN\*(C'\fR is far preferable to a program hanging until some data arrives.
1292.PP
1293If you cannot run the fd in non-blocking mode (for example you should
1294not play around with an Xlib connection), then you have to separately
1295re-test whether a file descriptor is really ready with a known-to-be good
1296interface such as poll (fortunately in our Xlib example, Xlib already
1297does this on its own, so its quite safe to use). Some people additionally
1298use \f(CW\*(C`SIGALRM\*(C'\fR and an interval timer, just to be sure you won't block
1299indefinitely.
1300.PP
1301But really, best use non-blocking mode.
1302.PP
1303\fIThe special problem of disappearing file descriptors\fR
1304.IX Subsection "The special problem of disappearing file descriptors"
1305.PP
1306Some backends (e.g. kqueue, epoll) need to be told about closing a file
1307descriptor (either due to calling \f(CW\*(C`close\*(C'\fR explicitly or any other means,
1308such as \f(CW\*(C`dup2\*(C'\fR). The reason is that you register interest in some file
1309descriptor, but when it goes away, the operating system will silently drop
1310this interest. If another file descriptor with the same number then is
1311registered with libev, there is no efficient way to see that this is, in
1312fact, a different file descriptor.
1313.PP
1314To avoid having to explicitly tell libev about such cases, libev follows
1315the following policy: Each time \f(CW\*(C`ev_io_set\*(C'\fR is being called, libev
1316will assume that this is potentially a new file descriptor, otherwise
1317it is assumed that the file descriptor stays the same. That means that
1318you \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
1319descriptor even if the file descriptor number itself did not change.
1320.PP
1321This is how one would do it normally anyway, the important point is that
1322the libev application should not optimise around libev but should leave
1323optimisations to libev.
1324.PP
1325\fIThe special problem of dup'ed file descriptors\fR
1326.IX Subsection "The special problem of dup'ed file descriptors"
1327.PP
1328Some backends (e.g. epoll), cannot register events for file descriptors,
1329but only events for the underlying file descriptions. That means when you
1330have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register
1331events for them, only one file descriptor might actually receive events.
1332.PP
1333There is no workaround possible except not registering events
1334for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
1335\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1336.PP
1337\fIThe special problem of fork\fR
1338.IX Subsection "The special problem of fork"
1339.PP
1340Some backends (epoll, kqueue) do not support \f(CW\*(C`fork ()\*(C'\fR at all or exhibit
1341useless behaviour. Libev fully supports fork, but needs to be told about
1342it in the child.
1343.PP
1344To support fork in your programs, you either have to call
1345\&\f(CW\*(C`ev_default_fork ()\*(C'\fR or \f(CW\*(C`ev_loop_fork ()\*(C'\fR after a fork in the child,
1346enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or
669\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR). 1347\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1348.PP
1349\fIThe special problem of \s-1SIGPIPE\s0\fR
1350.IX Subsection "The special problem of SIGPIPE"
1351.PP
1352While not really specific to libev, it is easy to forget about \f(CW\*(C`SIGPIPE\*(C'\fR:
1353when writing to a pipe whose other end has been closed, your program gets
1354sent a \s-1SIGPIPE\s0, which, by default, aborts your program. For most programs
1355this is sensible behaviour, for daemons, this is usually undesirable.
1356.PP
1357So when you encounter spurious, unexplained daemon exits, make sure you
1358ignore \s-1SIGPIPE\s0 (and maybe make sure you log the exit status of your daemon
1359somewhere, as that would have given you a big clue).
1360.PP
1361\fIWatcher-Specific Functions\fR
1362.IX Subsection "Watcher-Specific Functions"
670.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4 1363.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
671.IX Item "ev_io_init (ev_io *, callback, int fd, int events)" 1364.IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
672.PD 0 1365.PD 0
673.IP "ev_io_set (ev_io *, int fd, int events)" 4 1366.IP "ev_io_set (ev_io *, int fd, int events)" 4
674.IX Item "ev_io_set (ev_io *, int fd, int events)" 1367.IX Item "ev_io_set (ev_io *, int fd, int events)"
675.PD 1368.PD
676Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The fd is the file descriptor to rceeive 1369Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to
677events 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 | 1370receive 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
678EV_WRITE\*(C'\fR to receive the given events. 1371\&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR, to express the desire to receive the given events.
679.Sp 1372.IP "int fd [read\-only]" 4
680Please note that most of the more scalable backend mechanisms (for example 1373.IX Item "int fd [read-only]"
681epoll and solaris ports) can result in spurious readyness notifications 1374The file descriptor being watched.
682for file descriptors, so you practically need to use non-blocking I/O (and 1375.IP "int events [read\-only]" 4
683treat callback invocation as hint only), or retest separately with a safe 1376.IX Item "int events [read-only]"
684interface before doing I/O (XLib can do this), or force the use of either 1377The events being watched.
685\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR, which don't suffer from this 1378.PP
686problem. Also note that it is quite easy to have your callback invoked 1379\fIExamples\fR
687when the readyness condition is no longer valid even when employing 1380.IX Subsection "Examples"
688typical ways of handling events, so its a good idea to use non-blocking 1381.PP
689I/O unconditionally. 1382Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
1383readable, but only once. Since it is likely line-buffered, you could
1384attempt to read a whole line in the callback.
1385.PP
1386.Vb 6
1387\& static void
1388\& stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
1389\& {
1390\& ev_io_stop (loop, w);
1391\& .. read from stdin here (or from w\->fd) and handle any I/O errors
1392\& }
1393\&
1394\& ...
1395\& struct ev_loop *loop = ev_default_init (0);
1396\& struct ev_io stdin_readable;
1397\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1398\& ev_io_start (loop, &stdin_readable);
1399\& ev_loop (loop, 0);
1400.Ve
690.ie n .Sh """ev_timer"" \- relative and optionally recurring timeouts" 1401.ie n .Sh """ev_timer"" \- relative and optionally repeating timeouts"
691.el .Sh "\f(CWev_timer\fP \- relative and optionally recurring timeouts" 1402.el .Sh "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
692.IX Subsection "ev_timer - relative and optionally recurring timeouts" 1403.IX Subsection "ev_timer - relative and optionally repeating timeouts"
693Timer watchers are simple relative timers that generate an event after a 1404Timer watchers are simple relative timers that generate an event after a
694given time, and optionally repeating in regular intervals after that. 1405given time, and optionally repeating in regular intervals after that.
695.PP 1406.PP
696The timers are based on real time, that is, if you register an event that 1407The timers are based on real time, that is, if you register an event that
697times out after an hour and you reset your system clock to last years 1408times out after an hour and you reset your system clock to January last
698time, it will still time out after (roughly) and hour. \*(L"Roughly\*(R" because 1409year, it will still time out after (roughly) one hour. \*(L"Roughly\*(R" because
699detecting time jumps is hard, and some inaccuracies are unavoidable (the 1410detecting time jumps is hard, and some inaccuracies are unavoidable (the
700monotonic clock option helps a lot here). 1411monotonic clock option helps a lot here).
1412.PP
1413The callback is guaranteed to be invoked only \fIafter\fR its timeout has
1414passed, but if multiple timers become ready during the same loop iteration
1415then order of execution is undefined.
1416.PP
1417\fIThe special problem of time updates\fR
1418.IX Subsection "The special problem of time updates"
1419.PP
1420Establishing the current time is a costly operation (it usually takes at
1421least two system calls): \s-1EV\s0 therefore updates its idea of the current
1422time only before and after \f(CW\*(C`ev_loop\*(C'\fR collects new events, which causes a
1423growing difference between \f(CW\*(C`ev_now ()\*(C'\fR and \f(CW\*(C`ev_time ()\*(C'\fR when handling
1424lots of events in one iteration.
701.PP 1425.PP
702The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR 1426The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
703time. This is usually the right thing as this timestamp refers to the time 1427time. This is usually the right thing as this timestamp refers to the time
704of the event triggering whatever timeout you are modifying/starting. If 1428of the event triggering whatever timeout you are modifying/starting. If
705you suspect event processing to be delayed and you \fIneed\fR to base the timeout 1429you suspect event processing to be delayed and you \fIneed\fR to base the
706on the current time, use something like this to adjust for this: 1430timeout on the current time, use something like this to adjust for this:
707.PP 1431.PP
708.Vb 1 1432.Vb 1
709\& ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); 1433\& ev_timer_set (&timer, after + ev_now () \- ev_time (), 0.);
710.Ve 1434.Ve
711.PP 1435.PP
712The callback is guarenteed to be invoked only when its timeout has passed, 1436If the event loop is suspended for a long time, you can also force an
713but if multiple timers become ready during the same loop iteration then 1437update of the time returned by \f(CW\*(C`ev_now ()\*(C'\fR by calling \f(CW\*(C`ev_now_update
714order of execution is undefined. 1438()\*(C'\fR.
1439.PP
1440\fIWatcher-Specific Functions and Data Members\fR
1441.IX Subsection "Watcher-Specific Functions and Data Members"
715.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4 1442.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
716.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 1443.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
717.PD 0 1444.PD 0
718.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4 1445.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
719.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 1446.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
720.PD 1447.PD
721Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR is 1448Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR
722\&\f(CW0.\fR, then it will automatically be stopped. If it is positive, then the 1449is \f(CW0.\fR, then it will automatically be stopped once the timeout is
723timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds 1450reached. If it is positive, then the timer will automatically be
724later, again, and again, until stopped manually. 1451configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds later, again, and again,
1452until stopped manually.
725.Sp 1453.Sp
726The timer itself will do a best-effort at avoiding drift, that is, if you 1454The timer itself will do a best-effort at avoiding drift, that is, if
727configure a timer to trigger every 10 seconds, then it will trigger at 1455you configure a timer to trigger every 10 seconds, then it will normally
728exactly 10 second intervals. If, however, your program cannot keep up with 1456trigger at exactly 10 second intervals. If, however, your program cannot
729the timer (because it takes longer than those 10 seconds to do stuff) the 1457keep up with the timer (because it takes longer than those 10 seconds to
730timer will not fire more than once per event loop iteration. 1458do stuff) the timer will not fire more than once per event loop iteration.
731.IP "ev_timer_again (loop)" 4 1459.IP "ev_timer_again (loop, ev_timer *)" 4
732.IX Item "ev_timer_again (loop)" 1460.IX Item "ev_timer_again (loop, ev_timer *)"
733This will act as if the timer timed out and restart it again if it is 1461This will act as if the timer timed out and restart it again if it is
734repeating. The exact semantics are: 1462repeating. The exact semantics are:
735.Sp 1463.Sp
1464If the timer is pending, its pending status is cleared.
1465.Sp
736If the timer is started but nonrepeating, stop it. 1466If the timer is started but non-repeating, stop it (as if it timed out).
737.Sp 1467.Sp
738If the timer is repeating, either start it if necessary (with the repeat 1468If the timer is repeating, either start it if necessary (with the
739value), or reset the running timer to the repeat value. 1469\&\f(CW\*(C`repeat\*(C'\fR value), or reset the running timer to the \f(CW\*(C`repeat\*(C'\fR value.
740.Sp 1470.Sp
741This sounds a bit complicated, but here is a useful and typical 1471This sounds a bit complicated, but here is a useful and typical
742example: Imagine you have a tcp connection and you want a so-called idle 1472example: Imagine you have a \s-1TCP\s0 connection and you want a so-called idle
743timeout, that is, you want to be called when there have been, say, 60 1473timeout, that is, you want to be called when there have been, say, 60
744seconds of inactivity on the socket. The easiest way to do this is to 1474seconds of inactivity on the socket. The easiest way to do this is to
745configure an \f(CW\*(C`ev_timer\*(C'\fR with after=repeat=60 and calling ev_timer_again each 1475configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value of \f(CW60\fR and then call
746time you successfully read or write some data. If you go into an idle 1476\&\f(CW\*(C`ev_timer_again\*(C'\fR each time you successfully read or write some data. If
747state where you do not expect data to travel on the socket, you can stop 1477you go into an idle state where you do not expect data to travel on the
748the timer, and again will automatically restart it if need be. 1478socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will
1479automatically restart it if need be.
1480.Sp
1481That means you can ignore the \f(CW\*(C`after\*(C'\fR value and \f(CW\*(C`ev_timer_start\*(C'\fR
1482altogether and only ever use the \f(CW\*(C`repeat\*(C'\fR value and \f(CW\*(C`ev_timer_again\*(C'\fR:
1483.Sp
1484.Vb 8
1485\& ev_timer_init (timer, callback, 0., 5.);
1486\& ev_timer_again (loop, timer);
1487\& ...
1488\& timer\->again = 17.;
1489\& ev_timer_again (loop, timer);
1490\& ...
1491\& timer\->again = 10.;
1492\& ev_timer_again (loop, timer);
1493.Ve
1494.Sp
1495This is more slightly efficient then stopping/starting the timer each time
1496you want to modify its timeout value.
1497.Sp
1498Note, however, that it is often even more efficient to remember the
1499time of the last activity and let the timer time-out naturally. In the
1500callback, you then check whether the time-out is real, or, if there was
1501some activity, you reschedule the watcher to time-out in \*(L"last_activity +
1502timeout \- ev_now ()\*(R" seconds.
1503.IP "ev_tstamp repeat [read\-write]" 4
1504.IX Item "ev_tstamp repeat [read-write]"
1505The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
1506or \f(CW\*(C`ev_timer_again\*(C'\fR is called, and determines the next timeout (if any),
1507which is also when any modifications are taken into account.
1508.PP
1509\fIExamples\fR
1510.IX Subsection "Examples"
1511.PP
1512Example: Create a timer that fires after 60 seconds.
1513.PP
1514.Vb 5
1515\& static void
1516\& one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
1517\& {
1518\& .. one minute over, w is actually stopped right here
1519\& }
1520\&
1521\& struct ev_timer mytimer;
1522\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1523\& ev_timer_start (loop, &mytimer);
1524.Ve
1525.PP
1526Example: Create a timeout timer that times out after 10 seconds of
1527inactivity.
1528.PP
1529.Vb 5
1530\& static void
1531\& timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
1532\& {
1533\& .. ten seconds without any activity
1534\& }
1535\&
1536\& struct ev_timer mytimer;
1537\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1538\& ev_timer_again (&mytimer); /* start timer */
1539\& ev_loop (loop, 0);
1540\&
1541\& // and in some piece of code that gets executed on any "activity":
1542\& // reset the timeout to start ticking again at 10 seconds
1543\& ev_timer_again (&mytimer);
1544.Ve
749.ie n .Sh """ev_periodic"" \- to cron or not to cron" 1545.ie n .Sh """ev_periodic"" \- to cron or not to cron?"
750.el .Sh "\f(CWev_periodic\fP \- to cron or not to cron" 1546.el .Sh "\f(CWev_periodic\fP \- to cron or not to cron?"
751.IX Subsection "ev_periodic - to cron or not to cron" 1547.IX Subsection "ev_periodic - to cron or not to cron?"
752Periodic watchers are also timers of a kind, but they are very versatile 1548Periodic watchers are also timers of a kind, but they are very versatile
753(and unfortunately a bit complex). 1549(and unfortunately a bit complex).
754.PP 1550.PP
755Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time) 1551Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time)
756but on wallclock time (absolute time). You can tell a periodic watcher 1552but on wall clock time (absolute time). You can tell a periodic watcher
757to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a 1553to trigger after some specific point in time. For example, if you tell a
758periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now () 1554periodic watcher to trigger in 10 seconds (by specifying e.g. \f(CW\*(C`ev_now ()
759+ 10.>) and then reset your system clock to the last year, then it will 1555+ 10.\*(C'\fR, that is, an absolute time not a delay) and then reset your system
1556clock to January of the previous year, then it will take more than year
760take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger 1557to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would still trigger
761roughly 10 seconds later and of course not if you reset your system time 1558roughly 10 seconds later as it uses a relative timeout).
762again).
763.PP 1559.PP
764They can also be used to implement vastly more complex timers, such as 1560\&\f(CW\*(C`ev_periodic\*(C'\fRs can also be used to implement vastly more complex timers,
765triggering an event on eahc midnight, local time. 1561such as triggering an event on each \*(L"midnight, local time\*(R", or other
1562complicated rules.
766.PP 1563.PP
767As with timers, the callback is guarenteed to be invoked only when the 1564As with timers, the callback is guaranteed to be invoked only when the
768time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready 1565time (\f(CW\*(C`at\*(C'\fR) has passed, but if multiple periodic timers become ready
769during the same loop iteration then order of execution is undefined. 1566during the same loop iteration, then order of execution is undefined.
1567.PP
1568\fIWatcher-Specific Functions and Data Members\fR
1569.IX Subsection "Watcher-Specific Functions and Data Members"
770.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4 1570.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4
771.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 1571.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)"
772.PD 0 1572.PD 0
773.IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4 1573.IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4
774.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 1574.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)"
775.PD 1575.PD
776Lots of arguments, lets sort it out... There are basically three modes of 1576Lots of arguments, lets sort it out... There are basically three modes of
777operation, and we will explain them from simplest to complex: 1577operation, and we will explain them from simplest to most complex:
778.RS 4 1578.RS 4
1579.IP "\(bu" 4
779.IP "* absolute timer (interval = reschedule_cb = 0)" 4 1580absolute timer (at = time, interval = reschedule_cb = 0)
780.IX Item "absolute timer (interval = reschedule_cb = 0)" 1581.Sp
781In this configuration the watcher triggers an event at the wallclock time 1582In this configuration the watcher triggers an event after the wall clock
782\&\f(CW\*(C`at\*(C'\fR and doesn't repeat. It will not adjust when a time jump occurs, 1583time \f(CW\*(C`at\*(C'\fR has passed. It will not repeat and will not adjust when a time
783that is, if it is to be run at January 1st 2011 then it will run when the 1584jump occurs, that is, if it is to be run at January 1st 2011 then it will
784system time reaches or surpasses this time. 1585only run when the system clock reaches or surpasses this time.
1586.IP "\(bu" 4
785.IP "* non-repeating interval timer (interval > 0, reschedule_cb = 0)" 4 1587repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
786.IX Item "non-repeating interval timer (interval > 0, reschedule_cb = 0)" 1588.Sp
787In this mode the watcher will always be scheduled to time out at the next 1589In this mode the watcher will always be scheduled to time out at the next
788\&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N) and then repeat, regardless 1590\&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N, which can also be negative)
789of any time jumps. 1591and then repeat, regardless of any time jumps.
790.Sp 1592.Sp
791This can be used to create timers that do not drift with respect to system 1593This can be used to create timers that do not drift with respect to the
792time: 1594system clock, for example, here is a \f(CW\*(C`ev_periodic\*(C'\fR that triggers each
1595hour, on the hour:
793.Sp 1596.Sp
794.Vb 1 1597.Vb 1
795\& ev_periodic_set (&periodic, 0., 3600., 0); 1598\& ev_periodic_set (&periodic, 0., 3600., 0);
796.Ve 1599.Ve
797.Sp 1600.Sp
798This doesn't mean there will always be 3600 seconds in between triggers, 1601This doesn't mean there will always be 3600 seconds in between triggers,
799but only that the the callback will be called when the system time shows a 1602but only that the callback will be called when the system time shows a
800full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible 1603full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
801by 3600. 1604by 3600.
802.Sp 1605.Sp
803Another way to think about it (for the mathematically inclined) is that 1606Another way to think about it (for the mathematically inclined) is that
804\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible 1607\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
805time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps. 1608time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps.
806.IP "* manual reschedule mode (reschedule_cb = callback)" 4 1609.Sp
807.IX Item "manual reschedule mode (reschedule_cb = callback)" 1610For numerical stability it is preferable that the \f(CW\*(C`at\*(C'\fR value is near
1611\&\f(CW\*(C`ev_now ()\*(C'\fR (the current time), but there is no range requirement for
1612this value, and in fact is often specified as zero.
1613.Sp
1614Note also that there is an upper limit to how often a timer can fire (\s-1CPU\s0
1615speed for example), so if \f(CW\*(C`interval\*(C'\fR is very small then timing stability
1616will of course deteriorate. Libev itself tries to be exact to be about one
1617millisecond (if the \s-1OS\s0 supports it and the machine is fast enough).
1618.IP "\(bu" 4
1619manual reschedule mode (at and interval ignored, reschedule_cb = callback)
1620.Sp
808In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being 1621In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being
809ignored. Instead, each time the periodic watcher gets scheduled, the 1622ignored. Instead, each time the periodic watcher gets scheduled, the
810reschedule callback will be called with the watcher as first, and the 1623reschedule callback will be called with the watcher as first, and the
811current time as second argument. 1624current time as second argument.
812.Sp 1625.Sp
813\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, 1626\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher,
814ever, or make any event loop modifications\fR. If you need to stop it, 1627ever, or make \s-1ANY\s0 event loop modifications whatsoever\fR.
815return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by
816starting a prepare watcher).
817.Sp 1628.Sp
1629If you need to stop it, return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop
1630it afterwards (e.g. by starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is the
1631only event loop modification you are allowed to do).
1632.Sp
818Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w, 1633The callback prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic
819ev_tstamp now)\*(C'\fR, e.g.: 1634*w, ev_tstamp now)\*(C'\fR, e.g.:
820.Sp 1635.Sp
821.Vb 4 1636.Vb 4
822\& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) 1637\& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
823\& { 1638\& {
824\& return now + 60.; 1639\& return now + 60.;
… …
828It must return the next time to trigger, based on the passed time value 1643It must return the next time to trigger, based on the passed time value
829(that is, the lowest time value larger than to the second argument). It 1644(that is, the lowest time value larger than to the second argument). It
830will usually be called just before the callback will be triggered, but 1645will usually be called just before the callback will be triggered, but
831might be called at other times, too. 1646might be called at other times, too.
832.Sp 1647.Sp
833\&\s-1NOTE:\s0 \fIThis callback must always return a time that is later than the 1648\&\s-1NOTE:\s0 \fIThis callback must always return a time that is higher than or
834passed \f(CI\*(C`now\*(C'\fI value\fR. Not even \f(CW\*(C`now\*(C'\fR itself will do, it \fImust\fR be larger. 1649equal to the passed \f(CI\*(C`now\*(C'\fI value\fR.
835.Sp 1650.Sp
836This can be used to create very complex timers, such as a timer that 1651This can be used to create very complex timers, such as a timer that
837triggers on each midnight, local time. To do this, you would calculate the 1652triggers on \*(L"next midnight, local time\*(R". To do this, you would calculate the
838next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How 1653next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How
839you do this is, again, up to you (but it is not trivial, which is the main 1654you do this is, again, up to you (but it is not trivial, which is the main
840reason I omitted it as an example). 1655reason I omitted it as an example).
841.RE 1656.RE
842.RS 4 1657.RS 4
… …
845.IX Item "ev_periodic_again (loop, ev_periodic *)" 1660.IX Item "ev_periodic_again (loop, ev_periodic *)"
846Simply stops and restarts the periodic watcher again. This is only useful 1661Simply stops and restarts the periodic watcher again. This is only useful
847when you changed some parameters or the reschedule callback would return 1662when you changed some parameters or the reschedule callback would return
848a different time than the last time it was called (e.g. in a crond like 1663a different time than the last time it was called (e.g. in a crond like
849program when the crontabs have changed). 1664program when the crontabs have changed).
1665.IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4
1666.IX Item "ev_tstamp ev_periodic_at (ev_periodic *)"
1667When active, returns the absolute time that the watcher is supposed to
1668trigger next.
1669.IP "ev_tstamp offset [read\-write]" 4
1670.IX Item "ev_tstamp offset [read-write]"
1671When repeating, this contains the offset value, otherwise this is the
1672absolute point in time (the \f(CW\*(C`at\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR).
1673.Sp
1674Can be modified any time, but changes only take effect when the periodic
1675timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1676.IP "ev_tstamp interval [read\-write]" 4
1677.IX Item "ev_tstamp interval [read-write]"
1678The current interval value. Can be modified any time, but changes only
1679take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
1680called.
1681.IP "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read\-write]" 4
1682.IX Item "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]"
1683The current reschedule callback, or \f(CW0\fR, if this functionality is
1684switched off. Can be changed any time, but changes only take effect when
1685the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1686.PP
1687\fIExamples\fR
1688.IX Subsection "Examples"
1689.PP
1690Example: Call a callback every hour, or, more precisely, whenever the
1691system time is divisible by 3600. The callback invocation times have
1692potentially a lot of jitter, but good long-term stability.
1693.PP
1694.Vb 5
1695\& static void
1696\& clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
1697\& {
1698\& ... its now a full hour (UTC, or TAI or whatever your clock follows)
1699\& }
1700\&
1701\& struct ev_periodic hourly_tick;
1702\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1703\& ev_periodic_start (loop, &hourly_tick);
1704.Ve
1705.PP
1706Example: The same as above, but use a reschedule callback to do it:
1707.PP
1708.Vb 1
1709\& #include <math.h>
1710\&
1711\& static ev_tstamp
1712\& my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
1713\& {
1714\& return now + (3600. \- fmod (now, 3600.));
1715\& }
1716\&
1717\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1718.Ve
1719.PP
1720Example: Call a callback every hour, starting now:
1721.PP
1722.Vb 4
1723\& struct ev_periodic hourly_tick;
1724\& ev_periodic_init (&hourly_tick, clock_cb,
1725\& fmod (ev_now (loop), 3600.), 3600., 0);
1726\& ev_periodic_start (loop, &hourly_tick);
1727.Ve
850.ie n .Sh """ev_signal"" \- signal me when a signal gets signalled" 1728.ie n .Sh """ev_signal"" \- signal me when a signal gets signalled!"
851.el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled" 1729.el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
852.IX Subsection "ev_signal - signal me when a signal gets signalled" 1730.IX Subsection "ev_signal - signal me when a signal gets signalled!"
853Signal watchers will trigger an event when the process receives a specific 1731Signal watchers will trigger an event when the process receives a specific
854signal one or more times. Even though signals are very asynchronous, libev 1732signal one or more times. Even though signals are very asynchronous, libev
855will try it's best to deliver signals synchronously, i.e. as part of the 1733will try it's best to deliver signals synchronously, i.e. as part of the
856normal event processing, like any other event. 1734normal event processing, like any other event.
857.PP 1735.PP
1736If you want signals asynchronously, just use \f(CW\*(C`sigaction\*(C'\fR as you would
1737do without libev and forget about sharing the signal. You can even use
1738\&\f(CW\*(C`ev_async\*(C'\fR from a signal handler to synchronously wake up an event loop.
1739.PP
858You can configure as many watchers as you like per signal. Only when the 1740You can configure as many watchers as you like per signal. Only when the
859first watcher gets started will libev actually register a signal watcher 1741first watcher gets started will libev actually register a signal handler
860with the kernel (thus it coexists with your own signal handlers as long 1742with the kernel (thus it coexists with your own signal handlers as long as
861as you don't register any with libev). Similarly, when the last signal 1743you don't register any with libev for the same signal). Similarly, when
862watcher for a signal is stopped libev will reset the signal handler to 1744the last signal watcher for a signal is stopped, libev will reset the
863\&\s-1SIG_DFL\s0 (regardless of what it was set to before). 1745signal handler to \s-1SIG_DFL\s0 (regardless of what it was set to before).
1746.PP
1747If possible and supported, libev will install its handlers with
1748\&\f(CW\*(C`SA_RESTART\*(C'\fR behaviour enabled, so system calls should not be unduly
1749interrupted. If you have a problem with system calls getting interrupted by
1750signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher and unblock
1751them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher.
1752.PP
1753\fIWatcher-Specific Functions and Data Members\fR
1754.IX Subsection "Watcher-Specific Functions and Data Members"
864.IP "ev_signal_init (ev_signal *, callback, int signum)" 4 1755.IP "ev_signal_init (ev_signal *, callback, int signum)" 4
865.IX Item "ev_signal_init (ev_signal *, callback, int signum)" 1756.IX Item "ev_signal_init (ev_signal *, callback, int signum)"
866.PD 0 1757.PD 0
867.IP "ev_signal_set (ev_signal *, int signum)" 4 1758.IP "ev_signal_set (ev_signal *, int signum)" 4
868.IX Item "ev_signal_set (ev_signal *, int signum)" 1759.IX Item "ev_signal_set (ev_signal *, int signum)"
869.PD 1760.PD
870Configures the watcher to trigger on the given signal number (usually one 1761Configures the watcher to trigger on the given signal number (usually one
871of the \f(CW\*(C`SIGxxx\*(C'\fR constants). 1762of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
1763.IP "int signum [read\-only]" 4
1764.IX Item "int signum [read-only]"
1765The signal the watcher watches out for.
1766.PP
1767\fIExamples\fR
1768.IX Subsection "Examples"
1769.PP
1770Example: Try to exit cleanly on \s-1SIGINT\s0 and \s-1SIGTERM\s0.
1771.PP
1772.Vb 5
1773\& static void
1774\& sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
1775\& {
1776\& ev_unloop (loop, EVUNLOOP_ALL);
1777\& }
1778\&
1779\& struct ev_signal signal_watcher;
1780\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1781\& ev_signal_start (loop, &sigint_cb);
1782.Ve
872.ie n .Sh """ev_child"" \- wait for pid status changes" 1783.ie n .Sh """ev_child"" \- watch out for process status changes"
873.el .Sh "\f(CWev_child\fP \- wait for pid status changes" 1784.el .Sh "\f(CWev_child\fP \- watch out for process status changes"
874.IX Subsection "ev_child - wait for pid status changes" 1785.IX Subsection "ev_child - watch out for process status changes"
875Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to 1786Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
876some child status changes (most typically when a child of yours dies). 1787some child status changes (most typically when a child of yours dies or
1788exits). It is permissible to install a child watcher \fIafter\fR the child
1789has been forked (which implies it might have already exited), as long
1790as the event loop isn't entered (or is continued from a watcher), i.e.,
1791forking and then immediately registering a watcher for the child is fine,
1792but forking and registering a watcher a few event loop iterations later is
1793not.
1794.PP
1795Only the default event loop is capable of handling signals, and therefore
1796you can only register child watchers in the default event loop.
1797.PP
1798\fIProcess Interaction\fR
1799.IX Subsection "Process Interaction"
1800.PP
1801Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is
1802initialised. This is necessary to guarantee proper behaviour even if
1803the first child watcher is started after the child exits. The occurrence
1804of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done
1805synchronously as part of the event loop processing. Libev always reaps all
1806children, even ones not watched.
1807.PP
1808\fIOverriding the Built-In Processing\fR
1809.IX Subsection "Overriding the Built-In Processing"
1810.PP
1811Libev offers no special support for overriding the built-in child
1812processing, but if your application collides with libev's default child
1813handler, you can override it easily by installing your own handler for
1814\&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the
1815default loop never gets destroyed. You are encouraged, however, to use an
1816event-based approach to child reaping and thus use libev's support for
1817that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely.
1818.PP
1819\fIStopping the Child Watcher\fR
1820.IX Subsection "Stopping the Child Watcher"
1821.PP
1822Currently, the child watcher never gets stopped, even when the
1823child terminates, so normally one needs to stop the watcher in the
1824callback. Future versions of libev might stop the watcher automatically
1825when a child exit is detected.
1826.PP
1827\fIWatcher-Specific Functions and Data Members\fR
1828.IX Subsection "Watcher-Specific Functions and Data Members"
877.IP "ev_child_init (ev_child *, callback, int pid)" 4 1829.IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4
878.IX Item "ev_child_init (ev_child *, callback, int pid)" 1830.IX Item "ev_child_init (ev_child *, callback, int pid, int trace)"
879.PD 0 1831.PD 0
880.IP "ev_child_set (ev_child *, int pid)" 4 1832.IP "ev_child_set (ev_child *, int pid, int trace)" 4
881.IX Item "ev_child_set (ev_child *, int pid)" 1833.IX Item "ev_child_set (ev_child *, int pid, int trace)"
882.PD 1834.PD
883Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or 1835Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
884\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look 1836\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
885at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see 1837at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
886the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems 1838the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
887\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the 1839\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
888process causing the status change. 1840process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only
1841activate the watcher when the process terminates) or \f(CW1\fR (additionally
1842activate the watcher when the process is stopped or continued).
1843.IP "int pid [read\-only]" 4
1844.IX Item "int pid [read-only]"
1845The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
1846.IP "int rpid [read\-write]" 4
1847.IX Item "int rpid [read-write]"
1848The process id that detected a status change.
1849.IP "int rstatus [read\-write]" 4
1850.IX Item "int rstatus [read-write]"
1851The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
1852\&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
1853.PP
1854\fIExamples\fR
1855.IX Subsection "Examples"
1856.PP
1857Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for
1858its completion.
1859.PP
1860.Vb 1
1861\& ev_child cw;
1862\&
1863\& static void
1864\& child_cb (EV_P_ struct ev_child *w, int revents)
1865\& {
1866\& ev_child_stop (EV_A_ w);
1867\& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus);
1868\& }
1869\&
1870\& pid_t pid = fork ();
1871\&
1872\& if (pid < 0)
1873\& // error
1874\& else if (pid == 0)
1875\& {
1876\& // the forked child executes here
1877\& exit (1);
1878\& }
1879\& else
1880\& {
1881\& ev_child_init (&cw, child_cb, pid, 0);
1882\& ev_child_start (EV_DEFAULT_ &cw);
1883\& }
1884.Ve
1885.ie n .Sh """ev_stat"" \- did the file attributes just change?"
1886.el .Sh "\f(CWev_stat\fP \- did the file attributes just change?"
1887.IX Subsection "ev_stat - did the file attributes just change?"
1888This watches a file system path for attribute changes. That is, it calls
1889\&\f(CW\*(C`stat\*(C'\fR regularly (or when the \s-1OS\s0 says it changed) and sees if it changed
1890compared to the last time, invoking the callback if it did.
1891.PP
1892The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does
1893not exist\*(R" is a status change like any other. The condition \*(L"path does
1894not exist\*(R" is signified by the \f(CW\*(C`st_nlink\*(C'\fR field being zero (which is
1895otherwise always forced to be at least one) and all the other fields of
1896the stat buffer having unspecified contents.
1897.PP
1898The path \fIshould\fR be absolute and \fImust not\fR end in a slash. If it is
1899relative and your working directory changes, the behaviour is undefined.
1900.PP
1901Since there is no standard kernel interface to do this, the portable
1902implementation simply calls \f(CW\*(C`stat (2)\*(C'\fR regularly on the path to see if
1903it changed somehow. You can specify a recommended polling interval for
1904this case. If you specify a polling interval of \f(CW0\fR (highly recommended!)
1905then a \fIsuitable, unspecified default\fR value will be used (which
1906you can expect to be around five seconds, although this might change
1907dynamically). Libev will also impose a minimum interval which is currently
1908around \f(CW0.1\fR, but thats usually overkill.
1909.PP
1910This watcher type is not meant for massive numbers of stat watchers,
1911as even with OS-supported change notifications, this can be
1912resource-intensive.
1913.PP
1914At the time of this writing, the only OS-specific interface implemented
1915is the Linux inotify interface (implementing kqueue support is left as
1916an exercise for the reader. Note, however, that the author sees no way
1917of implementing \f(CW\*(C`ev_stat\*(C'\fR semantics with kqueue).
1918.PP
1919\fI\s-1ABI\s0 Issues (Largefile Support)\fR
1920.IX Subsection "ABI Issues (Largefile Support)"
1921.PP
1922Libev by default (unless the user overrides this) uses the default
1923compilation environment, which means that on systems with large file
1924support disabled by default, you get the 32 bit version of the stat
1925structure. When using the library from programs that change the \s-1ABI\s0 to
1926use 64 bit file offsets the programs will fail. In that case you have to
1927compile libev with the same flags to get binary compatibility. This is
1928obviously the case with any flags that change the \s-1ABI\s0, but the problem is
1929most noticeably disabled with ev_stat and large file support.
1930.PP
1931The solution for this is to lobby your distribution maker to make large
1932file interfaces available by default (as e.g. FreeBSD does) and not
1933optional. Libev cannot simply switch on large file support because it has
1934to exchange stat structures with application programs compiled using the
1935default compilation environment.
1936.PP
1937\fIInotify and Kqueue\fR
1938.IX Subsection "Inotify and Kqueue"
1939.PP
1940When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev (generally only
1941available with Linux) and present at runtime, it will be used to speed up
1942change detection where possible. The inotify descriptor will be created lazily
1943when the first \f(CW\*(C`ev_stat\*(C'\fR watcher is being started.
1944.PP
1945Inotify presence does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
1946except that changes might be detected earlier, and in some cases, to avoid
1947making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presence of inotify support
1948there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling,
1949but as long as the path exists, libev usually gets away without polling.
1950.PP
1951There is no support for kqueue, as apparently it cannot be used to
1952implement this functionality, due to the requirement of having a file
1953descriptor open on the object at all times, and detecting renames, unlinks
1954etc. is difficult.
1955.PP
1956\fIThe special problem of stat time resolution\fR
1957.IX Subsection "The special problem of stat time resolution"
1958.PP
1959The \f(CW\*(C`stat ()\*(C'\fR system call only supports full-second resolution portably, and
1960even on systems where the resolution is higher, most file systems still
1961only support whole seconds.
1962.PP
1963That means that, if the time is the only thing that changes, you can
1964easily miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and
1965calls your callback, which does something. When there is another update
1966within the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect unless the
1967stat data does change in other ways (e.g. file size).
1968.PP
1969The solution to this is to delay acting on a change for slightly more
1970than a second (or till slightly after the next full second boundary), using
1971a roughly one-second-delay \f(CW\*(C`ev_timer\*(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02);
1972ev_timer_again (loop, w)\*(C'\fR).
1973.PP
1974The \f(CW.02\fR offset is added to work around small timing inconsistencies
1975of some operating systems (where the second counter of the current time
1976might be be delayed. One such system is the Linux kernel, where a call to
1977\&\f(CW\*(C`gettimeofday\*(C'\fR might return a timestamp with a full second later than
1978a subsequent \f(CW\*(C`time\*(C'\fR call \- if the equivalent of \f(CW\*(C`time ()\*(C'\fR is used to
1979update file times then there will be a small window where the kernel uses
1980the previous second to update file times but libev might already execute
1981the timer callback).
1982.PP
1983\fIWatcher-Specific Functions and Data Members\fR
1984.IX Subsection "Watcher-Specific Functions and Data Members"
1985.IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
1986.IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
1987.PD 0
1988.IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4
1989.IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)"
1990.PD
1991Configures the watcher to wait for status changes of the given
1992\&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to
1993be detected and should normally be specified as \f(CW0\fR to let libev choose
1994a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same
1995path for as long as the watcher is active.
1996.Sp
1997The callback will receive an \f(CW\*(C`EV_STAT\*(C'\fR event when a change was detected,
1998relative to the attributes at the time the watcher was started (or the
1999last change was detected).
2000.IP "ev_stat_stat (loop, ev_stat *)" 4
2001.IX Item "ev_stat_stat (loop, ev_stat *)"
2002Updates the stat buffer immediately with new values. If you change the
2003watched path in your callback, you could call this function to avoid
2004detecting this change (while introducing a race condition if you are not
2005the only one changing the path). Can also be useful simply to find out the
2006new values.
2007.IP "ev_statdata attr [read\-only]" 4
2008.IX Item "ev_statdata attr [read-only]"
2009The most-recently detected attributes of the file. Although the type is
2010\&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
2011suitable for your system, but you can only rely on the POSIX-standardised
2012members to be present. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there was
2013some error while \f(CW\*(C`stat\*(C'\fRing the file.
2014.IP "ev_statdata prev [read\-only]" 4
2015.IX Item "ev_statdata prev [read-only]"
2016The previous attributes of the file. The callback gets invoked whenever
2017\&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR, or, more precisely, one or more of these members
2018differ: \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,
2019\&\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.
2020.IP "ev_tstamp interval [read\-only]" 4
2021.IX Item "ev_tstamp interval [read-only]"
2022The specified interval.
2023.IP "const char *path [read\-only]" 4
2024.IX Item "const char *path [read-only]"
2025The file system path that is being watched.
2026.PP
2027\fIExamples\fR
2028.IX Subsection "Examples"
2029.PP
2030Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
2031.PP
2032.Vb 10
2033\& static void
2034\& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
2035\& {
2036\& /* /etc/passwd changed in some way */
2037\& if (w\->attr.st_nlink)
2038\& {
2039\& printf ("passwd current size %ld\en", (long)w\->attr.st_size);
2040\& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime);
2041\& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime);
2042\& }
2043\& else
2044\& /* you shalt not abuse printf for puts */
2045\& puts ("wow, /etc/passwd is not there, expect problems. "
2046\& "if this is windows, they already arrived\en");
2047\& }
2048\&
2049\& ...
2050\& ev_stat passwd;
2051\&
2052\& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
2053\& ev_stat_start (loop, &passwd);
2054.Ve
2055.PP
2056Example: Like above, but additionally use a one-second delay so we do not
2057miss updates (however, frequent updates will delay processing, too, so
2058one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
2059\&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
2060.PP
2061.Vb 2
2062\& static ev_stat passwd;
2063\& static ev_timer timer;
2064\&
2065\& static void
2066\& timer_cb (EV_P_ ev_timer *w, int revents)
2067\& {
2068\& ev_timer_stop (EV_A_ w);
2069\&
2070\& /* now it\*(Aqs one second after the most recent passwd change */
2071\& }
2072\&
2073\& static void
2074\& stat_cb (EV_P_ ev_stat *w, int revents)
2075\& {
2076\& /* reset the one\-second timer */
2077\& ev_timer_again (EV_A_ &timer);
2078\& }
2079\&
2080\& ...
2081\& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
2082\& ev_stat_start (loop, &passwd);
2083\& ev_timer_init (&timer, timer_cb, 0., 1.02);
2084.Ve
889.ie n .Sh """ev_idle"" \- when you've got nothing better to do" 2085.ie n .Sh """ev_idle"" \- when you've got nothing better to do..."
890.el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do" 2086.el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do..."
891.IX Subsection "ev_idle - when you've got nothing better to do" 2087.IX Subsection "ev_idle - when you've got nothing better to do..."
892Idle watchers trigger events when there are no other events are pending 2088Idle watchers trigger events when no other events of the same or higher
893(prepare, check and other idle watchers do not count). That is, as long 2089priority are pending (prepare, check and other idle watchers do not count
894as your process is busy handling sockets or timeouts (or even signals, 2090as receiving \*(L"events\*(R").
895imagine) it will not be triggered. But when your process is idle all idle 2091.PP
896watchers are being called again and again, once per event loop iteration \- 2092That is, as long as your process is busy handling sockets or timeouts
2093(or even signals, imagine) of the same or higher priority it will not be
2094triggered. But when your process is idle (or only lower-priority watchers
2095are pending), the idle watchers are being called once per event loop
897until stopped, that is, or your process receives more events and becomes 2096iteration \- until stopped, that is, or your process receives more events
898busy. 2097and becomes busy again with higher priority stuff.
899.PP 2098.PP
900The most noteworthy effect is that as long as any idle watchers are 2099The most noteworthy effect is that as long as any idle watchers are
901active, the process will not block when waiting for new events. 2100active, the process will not block when waiting for new events.
902.PP 2101.PP
903Apart from keeping your process non-blocking (which is a useful 2102Apart from keeping your process non-blocking (which is a useful
904effect on its own sometimes), idle watchers are a good place to do 2103effect on its own sometimes), idle watchers are a good place to do
905\&\*(L"pseudo\-background processing\*(R", or delay processing stuff to after the 2104\&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the
906event loop has handled all outstanding events. 2105event loop has handled all outstanding events.
2106.PP
2107\fIWatcher-Specific Functions and Data Members\fR
2108.IX Subsection "Watcher-Specific Functions and Data Members"
907.IP "ev_idle_init (ev_signal *, callback)" 4 2109.IP "ev_idle_init (ev_signal *, callback)" 4
908.IX Item "ev_idle_init (ev_signal *, callback)" 2110.IX Item "ev_idle_init (ev_signal *, callback)"
909Initialises and configures the idle watcher \- it has no parameters of any 2111Initialises and configures the idle watcher \- it has no parameters of any
910kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless, 2112kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
911believe me. 2113believe me.
2114.PP
2115\fIExamples\fR
2116.IX Subsection "Examples"
2117.PP
2118Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the
2119callback, free it. Also, use no error checking, as usual.
2120.PP
2121.Vb 7
2122\& static void
2123\& idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
2124\& {
2125\& free (w);
2126\& // now do something you wanted to do when the program has
2127\& // no longer anything immediate to do.
2128\& }
2129\&
2130\& struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
2131\& ev_idle_init (idle_watcher, idle_cb);
2132\& ev_idle_start (loop, idle_cb);
2133.Ve
912.ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop" 2134.ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop!"
913.el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop" 2135.el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
914.IX Subsection "ev_prepare and ev_check - customise your event loop" 2136.IX Subsection "ev_prepare and ev_check - customise your event loop!"
915Prepare and check watchers are usually (but not always) used in tandem: 2137Prepare and check watchers are usually (but not always) used in pairs:
916prepare watchers get invoked before the process blocks and check watchers 2138prepare watchers get invoked before the process blocks and check watchers
917afterwards. 2139afterwards.
918.PP 2140.PP
2141You \fImust not\fR call \f(CW\*(C`ev_loop\*(C'\fR or similar functions that enter
2142the current event loop from either \f(CW\*(C`ev_prepare\*(C'\fR or \f(CW\*(C`ev_check\*(C'\fR
2143watchers. Other loops than the current one are fine, however. The
2144rationale behind this is that you do not need to check for recursion in
2145those watchers, i.e. the sequence will always be \f(CW\*(C`ev_prepare\*(C'\fR, blocking,
2146\&\f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each kind they will always be
2147called in pairs bracketing the blocking call.
2148.PP
919Their main purpose is to integrate other event mechanisms into libev. This 2149Their main purpose is to integrate other event mechanisms into libev and
920could be used, for example, to track variable changes, implement your own 2150their use is somewhat advanced. They could be used, for example, to track
921watchers, integrate net-snmp or a coroutine library and lots more. 2151variable changes, implement your own watchers, integrate net-snmp or a
2152coroutine library and lots more. They are also occasionally useful if
2153you cache some data and want to flush it before blocking (for example,
2154in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
2155watcher).
922.PP 2156.PP
923This is done by examining in each prepare call which file descriptors need 2157This is done by examining in each prepare call which file descriptors
924to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers for 2158need to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers
925them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many libraries 2159for them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many
926provide just this functionality). Then, in the check watcher you check for 2160libraries provide exactly this functionality). Then, in the check watcher,
927any events that occured (by checking the pending status of all watchers 2161you check for any events that occurred (by checking the pending status
928and stopping them) and call back into the library. The I/O and timer 2162of all watchers and stopping them) and call back into the library. The
929callbacks will never actually be called (but must be valid nevertheless, 2163I/O and timer callbacks will never actually be called (but must be valid
930because you never know, you know?). 2164nevertheless, because you never know, you know?).
931.PP 2165.PP
932As another example, the Perl Coro module uses these hooks to integrate 2166As another example, the Perl Coro module uses these hooks to integrate
933coroutines into libev programs, by yielding to other active coroutines 2167coroutines into libev programs, by yielding to other active coroutines
934during each prepare and only letting the process block if no coroutines 2168during each prepare and only letting the process block if no coroutines
935are ready to run (it's actually more complicated: it only runs coroutines 2169are ready to run (it's actually more complicated: it only runs coroutines
936with priority higher than or equal to the event loop and one coroutine 2170with priority higher than or equal to the event loop and one coroutine
937of lower priority, but only once, using idle watchers to keep the event 2171of lower priority, but only once, using idle watchers to keep the event
938loop from blocking if lower-priority coroutines are active, thus mapping 2172loop from blocking if lower-priority coroutines are active, thus mapping
939low-priority coroutines to idle/background tasks). 2173low-priority coroutines to idle/background tasks).
2174.PP
2175It is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR)
2176priority, to ensure that they are being run before any other watchers
2177after the poll (this doesn't matter for \f(CW\*(C`ev_prepare\*(C'\fR watchers).
2178.PP
2179Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, too) should not
2180activate (\*(L"feed\*(R") events into libev. While libev fully supports this, they
2181might get executed before other \f(CW\*(C`ev_check\*(C'\fR watchers did their job. As
2182\&\f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other (non-libev) event
2183loops those other event loops might be in an unusable state until their
2184\&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with
2185others).
2186.PP
2187\fIWatcher-Specific Functions and Data Members\fR
2188.IX Subsection "Watcher-Specific Functions and Data Members"
940.IP "ev_prepare_init (ev_prepare *, callback)" 4 2189.IP "ev_prepare_init (ev_prepare *, callback)" 4
941.IX Item "ev_prepare_init (ev_prepare *, callback)" 2190.IX Item "ev_prepare_init (ev_prepare *, callback)"
942.PD 0 2191.PD 0
943.IP "ev_check_init (ev_check *, callback)" 4 2192.IP "ev_check_init (ev_check *, callback)" 4
944.IX Item "ev_check_init (ev_check *, callback)" 2193.IX Item "ev_check_init (ev_check *, callback)"
945.PD 2194.PD
946Initialises and configures the prepare or check watcher \- they have no 2195Initialises and configures the prepare or check watcher \- they have no
947parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR 2196parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
948macros, but using them is utterly, utterly and completely pointless. 2197macros, but using them is utterly, utterly, utterly and completely
2198pointless.
2199.PP
2200\fIExamples\fR
2201.IX Subsection "Examples"
2202.PP
2203There are a number of principal ways to embed other event loops or modules
2204into libev. Here are some ideas on how to include libadns into libev
2205(there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could
2206use as a working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR embeds a
2207Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 into the
2208Glib event loop).
2209.PP
2210Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
2211and in a check watcher, destroy them and call into libadns. What follows
2212is pseudo-code only of course. This requires you to either use a low
2213priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as
2214the callbacks for the IO/timeout watchers might not have been called yet.
2215.PP
2216.Vb 2
2217\& static ev_io iow [nfd];
2218\& static ev_timer tw;
2219\&
2220\& static void
2221\& io_cb (ev_loop *loop, ev_io *w, int revents)
2222\& {
2223\& }
2224\&
2225\& // create io watchers for each fd and a timer before blocking
2226\& static void
2227\& adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
2228\& {
2229\& int timeout = 3600000;
2230\& struct pollfd fds [nfd];
2231\& // actual code will need to loop here and realloc etc.
2232\& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2233\&
2234\& /* the callback is illegal, but won\*(Aqt be called as we stop during check */
2235\& ev_timer_init (&tw, 0, timeout * 1e\-3);
2236\& ev_timer_start (loop, &tw);
2237\&
2238\& // create one ev_io per pollfd
2239\& for (int i = 0; i < nfd; ++i)
2240\& {
2241\& ev_io_init (iow + i, io_cb, fds [i].fd,
2242\& ((fds [i].events & POLLIN ? EV_READ : 0)
2243\& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
2244\&
2245\& fds [i].revents = 0;
2246\& ev_io_start (loop, iow + i);
2247\& }
2248\& }
2249\&
2250\& // stop all watchers after blocking
2251\& static void
2252\& adns_check_cb (ev_loop *loop, ev_check *w, int revents)
2253\& {
2254\& ev_timer_stop (loop, &tw);
2255\&
2256\& for (int i = 0; i < nfd; ++i)
2257\& {
2258\& // set the relevant poll flags
2259\& // could also call adns_processreadable etc. here
2260\& struct pollfd *fd = fds + i;
2261\& int revents = ev_clear_pending (iow + i);
2262\& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN;
2263\& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT;
2264\&
2265\& // now stop the watcher
2266\& ev_io_stop (loop, iow + i);
2267\& }
2268\&
2269\& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
2270\& }
2271.Ve
2272.PP
2273Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR
2274in the prepare watcher and would dispose of the check watcher.
2275.PP
2276Method 3: If the module to be embedded supports explicit event
2277notification (libadns does), you can also make use of the actual watcher
2278callbacks, and only destroy/create the watchers in the prepare watcher.
2279.PP
2280.Vb 5
2281\& static void
2282\& timer_cb (EV_P_ ev_timer *w, int revents)
2283\& {
2284\& adns_state ads = (adns_state)w\->data;
2285\& update_now (EV_A);
2286\&
2287\& adns_processtimeouts (ads, &tv_now);
2288\& }
2289\&
2290\& static void
2291\& io_cb (EV_P_ ev_io *w, int revents)
2292\& {
2293\& adns_state ads = (adns_state)w\->data;
2294\& update_now (EV_A);
2295\&
2296\& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now);
2297\& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now);
2298\& }
2299\&
2300\& // do not ever call adns_afterpoll
2301.Ve
2302.PP
2303Method 4: Do not use a prepare or check watcher because the module you
2304want to embed is not flexible enough to support it. Instead, you can
2305override their poll function. The drawback with this solution is that the
2306main loop is now no longer controllable by \s-1EV\s0. The \f(CW\*(C`Glib::EV\*(C'\fR module uses
2307this approach, effectively embedding \s-1EV\s0 as a client into the horrible
2308libglib event loop.
2309.PP
2310.Vb 4
2311\& static gint
2312\& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
2313\& {
2314\& int got_events = 0;
2315\&
2316\& for (n = 0; n < nfds; ++n)
2317\& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
2318\&
2319\& if (timeout >= 0)
2320\& // create/start timer
2321\&
2322\& // poll
2323\& ev_loop (EV_A_ 0);
2324\&
2325\& // stop timer again
2326\& if (timeout >= 0)
2327\& ev_timer_stop (EV_A_ &to);
2328\&
2329\& // stop io watchers again \- their callbacks should have set
2330\& for (n = 0; n < nfds; ++n)
2331\& ev_io_stop (EV_A_ iow [n]);
2332\&
2333\& return got_events;
2334\& }
2335.Ve
2336.ie n .Sh """ev_embed"" \- when one backend isn't enough..."
2337.el .Sh "\f(CWev_embed\fP \- when one backend isn't enough..."
2338.IX Subsection "ev_embed - when one backend isn't enough..."
2339This is a rather advanced watcher type that lets you embed one event loop
2340into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
2341loop, other types of watchers might be handled in a delayed or incorrect
2342fashion and must not be used).
2343.PP
2344There are primarily two reasons you would want that: work around bugs and
2345prioritise I/O.
2346.PP
2347As an example for a bug workaround, the kqueue backend might only support
2348sockets on some platform, so it is unusable as generic backend, but you
2349still want to make use of it because you have many sockets and it scales
2350so nicely. In this case, you would create a kqueue-based loop and embed
2351it into your default loop (which might use e.g. poll). Overall operation
2352will be a bit slower because first libev has to call \f(CW\*(C`poll\*(C'\fR and then
2353\&\f(CW\*(C`kevent\*(C'\fR, but at least you can use both mechanisms for what they are
2354best: \f(CW\*(C`kqueue\*(C'\fR for scalable sockets and \f(CW\*(C`poll\*(C'\fR if you want it to work :)
2355.PP
2356As for prioritising I/O: under rare circumstances you have the case where
2357some fds have to be watched and handled very quickly (with low latency),
2358and even priorities and idle watchers might have too much overhead. In
2359this case you would put all the high priority stuff in one loop and all
2360the rest in a second one, and embed the second one in the first.
2361.PP
2362As long as the watcher is active, the callback will be invoked every time
2363there might be events pending in the embedded loop. The callback must then
2364call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single sweep and invoke
2365their callbacks (you could also start an idle watcher to give the embedded
2366loop strictly lower priority for example). You can also set the callback
2367to \f(CW0\fR, in which case the embed watcher will automatically execute the
2368embedded loop sweep.
2369.PP
2370As long as the watcher is started it will automatically handle events. The
2371callback will be invoked whenever some events have been handled. You can
2372set the callback to \f(CW0\fR to avoid having to specify one if you are not
2373interested in that.
2374.PP
2375Also, there have not currently been made special provisions for forking:
2376when you fork, you not only have to call \f(CW\*(C`ev_loop_fork\*(C'\fR on both loops,
2377but you will also have to stop and restart any \f(CW\*(C`ev_embed\*(C'\fR watchers
2378yourself \- but you can use a fork watcher to handle this automatically,
2379and future versions of libev might do just that.
2380.PP
2381Unfortunately, not all backends are embeddable: only the ones returned by
2382\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
2383portable one.
2384.PP
2385So when you want to use this feature you will always have to be prepared
2386that you cannot get an embeddable loop. The recommended way to get around
2387this is to have a separate variables for your embeddable loop, try to
2388create it, and if that fails, use the normal loop for everything.
2389.PP
2390\fI\f(CI\*(C`ev_embed\*(C'\fI and fork\fR
2391.IX Subsection "ev_embed and fork"
2392.PP
2393While the \f(CW\*(C`ev_embed\*(C'\fR watcher is running, forks in the embedding loop will
2394automatically be applied to the embedded loop as well, so no special
2395fork handling is required in that case. When the watcher is not running,
2396however, it is still the task of the libev user to call \f(CW\*(C`ev_loop_fork ()\*(C'\fR
2397as applicable.
2398.PP
2399\fIWatcher-Specific Functions and Data Members\fR
2400.IX Subsection "Watcher-Specific Functions and Data Members"
2401.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
2402.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
2403.PD 0
2404.IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
2405.IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)"
2406.PD
2407Configures the watcher to embed the given loop, which must be
2408embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
2409invoked automatically, otherwise it is the responsibility of the callback
2410to invoke it (it will continue to be called until the sweep has been done,
2411if you do not want that, you need to temporarily stop the embed watcher).
2412.IP "ev_embed_sweep (loop, ev_embed *)" 4
2413.IX Item "ev_embed_sweep (loop, ev_embed *)"
2414Make a single, non-blocking sweep over the embedded loop. This works
2415similarly to \f(CW\*(C`ev_loop (embedded_loop, EVLOOP_NONBLOCK)\*(C'\fR, but in the most
2416appropriate way for embedded loops.
2417.IP "struct ev_loop *other [read\-only]" 4
2418.IX Item "struct ev_loop *other [read-only]"
2419The embedded event loop.
2420.PP
2421\fIExamples\fR
2422.IX Subsection "Examples"
2423.PP
2424Example: Try to get an embeddable event loop and embed it into the default
2425event loop. If that is not possible, use the default loop. The default
2426loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the embeddable loop is stored in
2427\&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the case no embeddable loop can be
2428used).
2429.PP
2430.Vb 3
2431\& struct ev_loop *loop_hi = ev_default_init (0);
2432\& struct ev_loop *loop_lo = 0;
2433\& struct ev_embed embed;
2434\&
2435\& // see if there is a chance of getting one that works
2436\& // (remember that a flags value of 0 means autodetection)
2437\& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2438\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
2439\& : 0;
2440\&
2441\& // if we got one, then embed it, otherwise default to loop_hi
2442\& if (loop_lo)
2443\& {
2444\& ev_embed_init (&embed, 0, loop_lo);
2445\& ev_embed_start (loop_hi, &embed);
2446\& }
2447\& else
2448\& loop_lo = loop_hi;
2449.Ve
2450.PP
2451Example: Check if kqueue is available but not recommended and create
2452a kqueue backend for use with sockets (which usually work with any
2453kqueue implementation). Store the kqueue/socket\-only event loop in
2454\&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too).
2455.PP
2456.Vb 3
2457\& struct ev_loop *loop = ev_default_init (0);
2458\& struct ev_loop *loop_socket = 0;
2459\& struct ev_embed embed;
2460\&
2461\& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2462\& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2463\& {
2464\& ev_embed_init (&embed, 0, loop_socket);
2465\& ev_embed_start (loop, &embed);
2466\& }
2467\&
2468\& if (!loop_socket)
2469\& loop_socket = loop;
2470\&
2471\& // now use loop_socket for all sockets, and loop for everything else
2472.Ve
2473.ie n .Sh """ev_fork"" \- the audacity to resume the event loop after a fork"
2474.el .Sh "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
2475.IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
2476Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
2477whoever is a good citizen cared to tell libev about it by calling
2478\&\f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the
2479event loop blocks next and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called,
2480and only in the child after the fork. If whoever good citizen calling
2481\&\f(CW\*(C`ev_default_fork\*(C'\fR cheats and calls it in the wrong process, the fork
2482handlers will be invoked, too, of course.
2483.PP
2484\fIWatcher-Specific Functions and Data Members\fR
2485.IX Subsection "Watcher-Specific Functions and Data Members"
2486.IP "ev_fork_init (ev_signal *, callback)" 4
2487.IX Item "ev_fork_init (ev_signal *, callback)"
2488Initialises and configures the fork watcher \- it has no parameters of any
2489kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
2490believe me.
2491.ie n .Sh """ev_async"" \- how to wake up another event loop"
2492.el .Sh "\f(CWev_async\fP \- how to wake up another event loop"
2493.IX Subsection "ev_async - how to wake up another event loop"
2494In general, you cannot use an \f(CW\*(C`ev_loop\*(C'\fR from multiple threads or other
2495asynchronous sources such as signal handlers (as opposed to multiple event
2496loops \- those are of course safe to use in different threads).
2497.PP
2498Sometimes, however, you need to wake up another event loop you do not
2499control, for example because it belongs to another thread. This is what
2500\&\f(CW\*(C`ev_async\*(C'\fR watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you
2501can signal it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal
2502safe.
2503.PP
2504This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals,
2505too, are asynchronous in nature, and signals, too, will be compressed
2506(i.e. the number of callback invocations may be less than the number of
2507\&\f(CW\*(C`ev_async_sent\*(C'\fR calls).
2508.PP
2509Unlike \f(CW\*(C`ev_signal\*(C'\fR watchers, \f(CW\*(C`ev_async\*(C'\fR works with any event loop, not
2510just the default loop.
2511.PP
2512\fIQueueing\fR
2513.IX Subsection "Queueing"
2514.PP
2515\&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason
2516is that the author does not know of a simple (or any) algorithm for a
2517multiple-writer-single-reader queue that works in all cases and doesn't
2518need elaborate support such as pthreads.
2519.PP
2520That means that if you want to queue data, you have to provide your own
2521queue. But at least I can tell you how to implement locking around your
2522queue:
2523.IP "queueing from a signal handler context" 4
2524.IX Item "queueing from a signal handler context"
2525To implement race-free queueing, you simply add to the queue in the signal
2526handler but you block the signal handler in the watcher callback. Here is an example that does that for
2527some fictitious \s-1SIGUSR1\s0 handler:
2528.Sp
2529.Vb 1
2530\& static ev_async mysig;
2531\&
2532\& static void
2533\& sigusr1_handler (void)
2534\& {
2535\& sometype data;
2536\&
2537\& // no locking etc.
2538\& queue_put (data);
2539\& ev_async_send (EV_DEFAULT_ &mysig);
2540\& }
2541\&
2542\& static void
2543\& mysig_cb (EV_P_ ev_async *w, int revents)
2544\& {
2545\& sometype data;
2546\& sigset_t block, prev;
2547\&
2548\& sigemptyset (&block);
2549\& sigaddset (&block, SIGUSR1);
2550\& sigprocmask (SIG_BLOCK, &block, &prev);
2551\&
2552\& while (queue_get (&data))
2553\& process (data);
2554\&
2555\& if (sigismember (&prev, SIGUSR1)
2556\& sigprocmask (SIG_UNBLOCK, &block, 0);
2557\& }
2558.Ve
2559.Sp
2560(Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR
2561instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it
2562either...).
2563.IP "queueing from a thread context" 4
2564.IX Item "queueing from a thread context"
2565The strategy for threads is different, as you cannot (easily) block
2566threads but you can easily preempt them, so to queue safely you need to
2567employ a traditional mutex lock, such as in this pthread example:
2568.Sp
2569.Vb 2
2570\& static ev_async mysig;
2571\& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
2572\&
2573\& static void
2574\& otherthread (void)
2575\& {
2576\& // only need to lock the actual queueing operation
2577\& pthread_mutex_lock (&mymutex);
2578\& queue_put (data);
2579\& pthread_mutex_unlock (&mymutex);
2580\&
2581\& ev_async_send (EV_DEFAULT_ &mysig);
2582\& }
2583\&
2584\& static void
2585\& mysig_cb (EV_P_ ev_async *w, int revents)
2586\& {
2587\& pthread_mutex_lock (&mymutex);
2588\&
2589\& while (queue_get (&data))
2590\& process (data);
2591\&
2592\& pthread_mutex_unlock (&mymutex);
2593\& }
2594.Ve
2595.PP
2596\fIWatcher-Specific Functions and Data Members\fR
2597.IX Subsection "Watcher-Specific Functions and Data Members"
2598.IP "ev_async_init (ev_async *, callback)" 4
2599.IX Item "ev_async_init (ev_async *, callback)"
2600Initialises and configures the async watcher \- it has no parameters of any
2601kind. There is a \f(CW\*(C`ev_asynd_set\*(C'\fR macro, but using it is utterly pointless,
2602trust me.
2603.IP "ev_async_send (loop, ev_async *)" 4
2604.IX Item "ev_async_send (loop, ev_async *)"
2605Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds
2606an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop. Unlike
2607\&\f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do from other threads, signal or
2608similar contexts (see the discussion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the embedding
2609section below on what exactly this means).
2610.Sp
2611This call incurs the overhead of a system call only once per loop iteration,
2612so while the overhead might be noticeable, it doesn't apply to repeated
2613calls to \f(CW\*(C`ev_async_send\*(C'\fR.
2614.IP "bool = ev_async_pending (ev_async *)" 4
2615.IX Item "bool = ev_async_pending (ev_async *)"
2616Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the
2617watcher but the event has not yet been processed (or even noted) by the
2618event loop.
2619.Sp
2620\&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When
2621the loop iterates next and checks for the watcher to have become active,
2622it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very
2623quickly check whether invoking the loop might be a good idea.
2624.Sp
2625Not that this does \fInot\fR check whether the watcher itself is pending, only
2626whether it has been requested to make this watcher pending.
949.SH "OTHER FUNCTIONS" 2627.SH "OTHER FUNCTIONS"
950.IX Header "OTHER FUNCTIONS" 2628.IX Header "OTHER FUNCTIONS"
951There are some other functions of possible interest. Described. Here. Now. 2629There are some other functions of possible interest. Described. Here. Now.
952.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4 2630.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
953.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 2631.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"
… …
957or timeout without having to allocate/configure/start/stop/free one or 2635or timeout without having to allocate/configure/start/stop/free one or
958more watchers yourself. 2636more watchers yourself.
959.Sp 2637.Sp
960If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and events 2638If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and events
961is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for the given \f(CW\*(C`fd\*(C'\fR and 2639is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for the given \f(CW\*(C`fd\*(C'\fR and
962\&\f(CW\*(C`events\*(C'\fR set will be craeted and started. 2640\&\f(CW\*(C`events\*(C'\fR set will be created and started.
963.Sp 2641.Sp
964If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be 2642If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
965started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and 2643started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
966repeat = 0) will be started. While \f(CW0\fR is a valid timeout, it is of 2644repeat = 0) will be started. While \f(CW0\fR is a valid timeout, it is of
967dubious value. 2645dubious value.
… …
970passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of 2648passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
971\&\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 2649\&\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
972value passed to \f(CW\*(C`ev_once\*(C'\fR: 2650value passed to \f(CW\*(C`ev_once\*(C'\fR:
973.Sp 2651.Sp
974.Vb 7 2652.Vb 7
975\& static void stdin_ready (int revents, void *arg) 2653\& static void stdin_ready (int revents, void *arg)
976\& { 2654\& {
977\& if (revents & EV_TIMEOUT) 2655\& if (revents & EV_TIMEOUT)
978\& /* doh, nothing entered */; 2656\& /* doh, nothing entered */;
979\& else if (revents & EV_READ) 2657\& else if (revents & EV_READ)
980\& /* stdin might have data for us, joy! */; 2658\& /* stdin might have data for us, joy! */;
981\& } 2659\& }
982.Ve 2660\&
983.Sp
984.Vb 1
985\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); 2661\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
986.Ve 2662.Ve
987.IP "ev_feed_event (loop, watcher, int events)" 4 2663.IP "ev_feed_event (ev_loop *, watcher *, int revents)" 4
988.IX Item "ev_feed_event (loop, watcher, int events)" 2664.IX Item "ev_feed_event (ev_loop *, watcher *, int revents)"
989Feeds the given event set into the event loop, as if the specified event 2665Feeds the given event set into the event loop, as if the specified event
990had happened for the specified watcher (which must be a pointer to an 2666had happened for the specified watcher (which must be a pointer to an
991initialised but not necessarily started event watcher). 2667initialised but not necessarily started event watcher).
992.IP "ev_feed_fd_event (loop, int fd, int revents)" 4 2668.IP "ev_feed_fd_event (ev_loop *, int fd, int revents)" 4
993.IX Item "ev_feed_fd_event (loop, int fd, int revents)" 2669.IX Item "ev_feed_fd_event (ev_loop *, int fd, int revents)"
994Feed an event on the given fd, as if a file descriptor backend detected 2670Feed an event on the given fd, as if a file descriptor backend detected
995the given events it. 2671the given events it.
996.IP "ev_feed_signal_event (loop, int signum)" 4 2672.IP "ev_feed_signal_event (ev_loop *loop, int signum)" 4
997.IX Item "ev_feed_signal_event (loop, int signum)" 2673.IX Item "ev_feed_signal_event (ev_loop *loop, int signum)"
998Feed an event as if the given signal occured (loop must be the default loop!). 2674Feed an event as if the given signal occurred (\f(CW\*(C`loop\*(C'\fR must be the default
2675loop!).
999.SH "LIBEVENT EMULATION" 2676.SH "LIBEVENT EMULATION"
1000.IX Header "LIBEVENT EMULATION" 2677.IX Header "LIBEVENT EMULATION"
1001Libev offers a compatibility emulation layer for libevent. It cannot 2678Libev offers a compatibility emulation layer for libevent. It cannot
1002emulate the internals of libevent, so here are some usage hints: 2679emulate the internals of libevent, so here are some usage hints:
2680.IP "\(bu" 4
1003.IP "* Use it by including <event.h>, as usual." 4 2681Use it by including <event.h>, as usual.
1004.IX Item "Use it by including <event.h>, as usual." 2682.IP "\(bu" 4
1005.PD 0 2683The following members are fully supported: ev_base, ev_callback,
1006.IP "* The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4 2684ev_arg, ev_fd, ev_res, ev_events.
1007.IX Item "The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 2685.IP "\(bu" 4
1008.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 2686Avoid using ev_flags and the EVLIST_*\-macros, while it is
1009.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)." 2687maintained by libev, it does not work exactly the same way as in libevent (consider
1010.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 2688it a private \s-1API\s0).
1011.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." 2689.IP "\(bu" 4
2690Priorities are not currently supported. Initialising priorities
2691will fail and all watchers will have the same priority, even though there
2692is an ev_pri field.
2693.IP "\(bu" 4
2694In libevent, the last base created gets the signals, in libev, the
2695first base created (== the default loop) gets the signals.
2696.IP "\(bu" 4
1012.IP "* Other members are not supported." 4 2697Other members are not supported.
1013.IX Item "Other members are not supported." 2698.IP "\(bu" 4
1014.IP "* The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need to use the libev header file and library." 4 2699The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need
1015.IX Item "The libev emulation is not ABI compatible to libevent, you need to use the libev header file and library." 2700to use the libev header file and library.
1016.PD
1017.SH "\*(C+ SUPPORT" 2701.SH "\*(C+ SUPPORT"
1018.IX Header " SUPPORT" 2702.IX Header " SUPPORT"
1019\&\s-1TBD\s0. 2703Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
2704you to use some convenience methods to start/stop watchers and also change
2705the callback model to a model using method callbacks on objects.
2706.PP
2707To use it,
2708.PP
2709.Vb 1
2710\& #include <ev++.h>
2711.Ve
2712.PP
2713This automatically includes \fIev.h\fR and puts all of its definitions (many
2714of them macros) into the global namespace. All \*(C+ specific things are
2715put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding
2716options as \fIev.h\fR, most notably \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR.
2717.PP
2718Care has been taken to keep the overhead low. The only data member the \*(C+
2719classes add (compared to plain C\-style watchers) is the event loop pointer
2720that the watcher is associated with (or no additional members at all if
2721you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
2722.PP
2723Currently, functions, and static and non-static member functions can be
2724used as callbacks. Other types should be easy to add as long as they only
2725need one additional pointer for context. If you need support for other
2726types of functors please contact the author (preferably after implementing
2727it).
2728.PP
2729Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
2730.ie n .IP """ev::READ""\fR, \f(CW""ev::WRITE"" etc." 4
2731.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
2732.IX Item "ev::READ, ev::WRITE etc."
2733These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
2734macros from \fIev.h\fR.
2735.ie n .IP """ev::tstamp""\fR, \f(CW""ev::now""" 4
2736.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
2737.IX Item "ev::tstamp, ev::now"
2738Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
2739.ie n .IP """ev::io""\fR, \f(CW""ev::timer""\fR, \f(CW""ev::periodic""\fR, \f(CW""ev::idle""\fR, \f(CW""ev::sig"" etc." 4
2740.el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
2741.IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
2742For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
2743the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
2744which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
2745defines by many implementations.
2746.Sp
2747All of those classes have these methods:
2748.RS 4
2749.IP "ev::TYPE::TYPE ()" 4
2750.IX Item "ev::TYPE::TYPE ()"
2751.PD 0
2752.IP "ev::TYPE::TYPE (struct ev_loop *)" 4
2753.IX Item "ev::TYPE::TYPE (struct ev_loop *)"
2754.IP "ev::TYPE::~TYPE" 4
2755.IX Item "ev::TYPE::~TYPE"
2756.PD
2757The constructor (optionally) takes an event loop to associate the watcher
2758with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR.
2759.Sp
2760The constructor calls \f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the
2761\&\f(CW\*(C`set\*(C'\fR method before starting it.
2762.Sp
2763It will not set a callback, however: You have to call the templated \f(CW\*(C`set\*(C'\fR
2764method to set a callback before you can start the watcher.
2765.Sp
2766(The reason why you have to use a method is a limitation in \*(C+ which does
2767not allow explicit template arguments for constructors).
2768.Sp
2769The destructor automatically stops the watcher if it is active.
2770.IP "w\->set<class, &class::method> (object *)" 4
2771.IX Item "w->set<class, &class::method> (object *)"
2772This method sets the callback method to call. The method has to have a
2773signature of \f(CW\*(C`void (*)(ev_TYPE &, int)\*(C'\fR, it receives the watcher as
2774first argument and the \f(CW\*(C`revents\*(C'\fR as second. The object must be given as
2775parameter and is stored in the \f(CW\*(C`data\*(C'\fR member of the watcher.
2776.Sp
2777This method synthesizes efficient thunking code to call your method from
2778the C callback that libev requires. If your compiler can inline your
2779callback (i.e. it is visible to it at the place of the \f(CW\*(C`set\*(C'\fR call and
2780your compiler is good :), then the method will be fully inlined into the
2781thunking function, making it as fast as a direct C callback.
2782.Sp
2783Example: simple class declaration and watcher initialisation
2784.Sp
2785.Vb 4
2786\& struct myclass
2787\& {
2788\& void io_cb (ev::io &w, int revents) { }
2789\& }
2790\&
2791\& myclass obj;
2792\& ev::io iow;
2793\& iow.set <myclass, &myclass::io_cb> (&obj);
2794.Ve
2795.IP "w\->set<function> (void *data = 0)" 4
2796.IX Item "w->set<function> (void *data = 0)"
2797Also sets a callback, but uses a static method or plain function as
2798callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
2799\&\f(CW\*(C`data\*(C'\fR member and is free for you to use.
2800.Sp
2801The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
2802.Sp
2803See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
2804.Sp
2805Example: Use a plain function as callback.
2806.Sp
2807.Vb 2
2808\& static void io_cb (ev::io &w, int revents) { }
2809\& iow.set <io_cb> ();
2810.Ve
2811.IP "w\->set (struct ev_loop *)" 4
2812.IX Item "w->set (struct ev_loop *)"
2813Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
2814do this when the watcher is inactive (and not pending either).
2815.IP "w\->set ([arguments])" 4
2816.IX Item "w->set ([arguments])"
2817Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same arguments. Must be
2818called at least once. Unlike the C counterpart, an active watcher gets
2819automatically stopped and restarted when reconfiguring it with this
2820method.
2821.IP "w\->start ()" 4
2822.IX Item "w->start ()"
2823Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
2824constructor already stores the event loop.
2825.IP "w\->stop ()" 4
2826.IX Item "w->stop ()"
2827Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
2828.ie n .IP "w\->again () (""ev::timer""\fR, \f(CW""ev::periodic"" only)" 4
2829.el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
2830.IX Item "w->again () (ev::timer, ev::periodic only)"
2831For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
2832\&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
2833.ie n .IP "w\->sweep () (""ev::embed"" only)" 4
2834.el .IP "w\->sweep () (\f(CWev::embed\fR only)" 4
2835.IX Item "w->sweep () (ev::embed only)"
2836Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR.
2837.ie n .IP "w\->update () (""ev::stat"" only)" 4
2838.el .IP "w\->update () (\f(CWev::stat\fR only)" 4
2839.IX Item "w->update () (ev::stat only)"
2840Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
2841.RE
2842.RS 4
2843.RE
2844.PP
2845Example: Define a class with an \s-1IO\s0 and idle watcher, start one of them in
2846the constructor.
2847.PP
2848.Vb 4
2849\& class myclass
2850\& {
2851\& ev::io io ; void io_cb (ev::io &w, int revents);
2852\& ev::idle idle; void idle_cb (ev::idle &w, int revents);
2853\&
2854\& myclass (int fd)
2855\& {
2856\& io .set <myclass, &myclass::io_cb > (this);
2857\& idle.set <myclass, &myclass::idle_cb> (this);
2858\&
2859\& io.start (fd, ev::READ);
2860\& }
2861\& };
2862.Ve
2863.SH "OTHER LANGUAGE BINDINGS"
2864.IX Header "OTHER LANGUAGE BINDINGS"
2865Libev does not offer other language bindings itself, but bindings for a
2866number of languages exist in the form of third-party packages. If you know
2867any interesting language binding in addition to the ones listed here, drop
2868me a note.
2869.IP "Perl" 4
2870.IX Item "Perl"
2871The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test
2872libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module,
2873there are additional modules that implement libev-compatible interfaces
2874to \f(CW\*(C`libadns\*(C'\fR (\f(CW\*(C`EV::ADNS\*(C'\fR, but \f(CW\*(C`AnyEvent::DNS\*(C'\fR is preferred nowadays),
2875\&\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
2876and \f(CW\*(C`EV::Glib\*(C'\fR).
2877.Sp
2878It can be found and installed via \s-1CPAN\s0, its homepage is at
2879<http://software.schmorp.de/pkg/EV>.
2880.IP "Python" 4
2881.IX Item "Python"
2882Python bindings can be found at <http://code.google.com/p/pyev/>. It
2883seems to be quite complete and well-documented. Note, however, that the
2884patch they require for libev is outright dangerous as it breaks the \s-1ABI\s0
2885for everybody else, and therefore, should never be applied in an installed
2886libev (if python requires an incompatible \s-1ABI\s0 then it needs to embed
2887libev).
2888.IP "Ruby" 4
2889.IX Item "Ruby"
2890Tony Arcieri has written a ruby extension that offers access to a subset
2891of the libev \s-1API\s0 and adds file handle abstractions, asynchronous \s-1DNS\s0 and
2892more on top of it. It can be found via gem servers. Its homepage is at
2893<http://rev.rubyforge.org/>.
2894.IP "D" 4
2895.IX Item "D"
2896Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
2897be found at <http://proj.llucax.com.ar/wiki/evd>.
2898.SH "MACRO MAGIC"
2899.IX Header "MACRO MAGIC"
2900Libev can be compiled with a variety of options, the most fundamental
2901of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most)
2902functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
2903.PP
2904To make it easier to write programs that cope with either variant, the
2905following macros are defined:
2906.ie n .IP """EV_A""\fR, \f(CW""EV_A_""" 4
2907.el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
2908.IX Item "EV_A, EV_A_"
2909This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
2910loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
2911\&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
2912.Sp
2913.Vb 3
2914\& ev_unref (EV_A);
2915\& ev_timer_add (EV_A_ watcher);
2916\& ev_loop (EV_A_ 0);
2917.Ve
2918.Sp
2919It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
2920which is often provided by the following macro.
2921.ie n .IP """EV_P""\fR, \f(CW""EV_P_""" 4
2922.el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
2923.IX Item "EV_P, EV_P_"
2924This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
2925loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
2926\&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
2927.Sp
2928.Vb 2
2929\& // this is how ev_unref is being declared
2930\& static void ev_unref (EV_P);
2931\&
2932\& // this is how you can declare your typical callback
2933\& static void cb (EV_P_ ev_timer *w, int revents)
2934.Ve
2935.Sp
2936It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
2937suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
2938.ie n .IP """EV_DEFAULT""\fR, \f(CW""EV_DEFAULT_""" 4
2939.el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
2940.IX Item "EV_DEFAULT, EV_DEFAULT_"
2941Similar to the other two macros, this gives you the value of the default
2942loop, if multiple loops are supported (\*(L"ev loop default\*(R").
2943.ie n .IP """EV_DEFAULT_UC""\fR, \f(CW""EV_DEFAULT_UC_""" 4
2944.el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
2945.IX Item "EV_DEFAULT_UC, EV_DEFAULT_UC_"
2946Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the
2947default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour
2948is undefined when the default loop has not been initialised by a previous
2949execution of \f(CW\*(C`EV_DEFAULT\*(C'\fR, \f(CW\*(C`EV_DEFAULT_\*(C'\fR or \f(CW\*(C`ev_default_init (...)\*(C'\fR.
2950.Sp
2951It is often prudent to use \f(CW\*(C`EV_DEFAULT\*(C'\fR when initialising the first
2952watcher in a function but use \f(CW\*(C`EV_DEFAULT_UC\*(C'\fR afterwards.
2953.PP
2954Example: Declare and initialise a check watcher, utilising the above
2955macros so it will work regardless of whether multiple loops are supported
2956or not.
2957.PP
2958.Vb 5
2959\& static void
2960\& check_cb (EV_P_ ev_timer *w, int revents)
2961\& {
2962\& ev_check_stop (EV_A_ w);
2963\& }
2964\&
2965\& ev_check check;
2966\& ev_check_init (&check, check_cb);
2967\& ev_check_start (EV_DEFAULT_ &check);
2968\& ev_loop (EV_DEFAULT_ 0);
2969.Ve
2970.SH "EMBEDDING"
2971.IX Header "EMBEDDING"
2972Libev can (and often is) directly embedded into host
2973applications. Examples of applications that embed it include the Deliantra
2974Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
2975and rxvt-unicode.
2976.PP
2977The goal is to enable you to just copy the necessary files into your
2978source directory without having to change even a single line in them, so
2979you can easily upgrade by simply copying (or having a checked-out copy of
2980libev somewhere in your source tree).
2981.Sh "\s-1FILESETS\s0"
2982.IX Subsection "FILESETS"
2983Depending on what features you need you need to include one or more sets of files
2984in your application.
2985.PP
2986\fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR
2987.IX Subsection "CORE EVENT LOOP"
2988.PP
2989To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
2990configuration (no autoconf):
2991.PP
2992.Vb 2
2993\& #define EV_STANDALONE 1
2994\& #include "ev.c"
2995.Ve
2996.PP
2997This will automatically include \fIev.h\fR, too, and should be done in a
2998single C source file only to provide the function implementations. To use
2999it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best
3000done by writing a wrapper around \fIev.h\fR that you can include instead and
3001where you can put other configuration options):
3002.PP
3003.Vb 2
3004\& #define EV_STANDALONE 1
3005\& #include "ev.h"
3006.Ve
3007.PP
3008Both header files and implementation files can be compiled with a \*(C+
3009compiler (at least, thats a stated goal, and breakage will be treated
3010as a bug).
3011.PP
3012You need the following files in your source tree, or in a directory
3013in your include path (e.g. in libev/ when using \-Ilibev):
3014.PP
3015.Vb 4
3016\& ev.h
3017\& ev.c
3018\& ev_vars.h
3019\& ev_wrap.h
3020\&
3021\& ev_win32.c required on win32 platforms only
3022\&
3023\& ev_select.c only when select backend is enabled (which is enabled by default)
3024\& ev_poll.c only when poll backend is enabled (disabled by default)
3025\& ev_epoll.c only when the epoll backend is enabled (disabled by default)
3026\& ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
3027\& ev_port.c only when the solaris port backend is enabled (disabled by default)
3028.Ve
3029.PP
3030\&\fIev.c\fR includes the backend files directly when enabled, so you only need
3031to compile this single file.
3032.PP
3033\fI\s-1LIBEVENT\s0 \s-1COMPATIBILITY\s0 \s-1API\s0\fR
3034.IX Subsection "LIBEVENT COMPATIBILITY API"
3035.PP
3036To include the libevent compatibility \s-1API\s0, also include:
3037.PP
3038.Vb 1
3039\& #include "event.c"
3040.Ve
3041.PP
3042in the file including \fIev.c\fR, and:
3043.PP
3044.Vb 1
3045\& #include "event.h"
3046.Ve
3047.PP
3048in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR.
3049.PP
3050You need the following additional files for this:
3051.PP
3052.Vb 2
3053\& event.h
3054\& event.c
3055.Ve
3056.PP
3057\fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR
3058.IX Subsection "AUTOCONF SUPPORT"
3059.PP
3060Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your configuration in
3061whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
3062\&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then
3063include \fIconfig.h\fR and configure itself accordingly.
3064.PP
3065For this of course you need the m4 file:
3066.PP
3067.Vb 1
3068\& libev.m4
3069.Ve
3070.Sh "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0"
3071.IX Subsection "PREPROCESSOR SYMBOLS/MACROS"
3072Libev can be configured via a variety of preprocessor symbols you have to
3073define before including any of its files. The default in the absence of
3074autoconf is documented for every option.
3075.IP "\s-1EV_STANDALONE\s0" 4
3076.IX Item "EV_STANDALONE"
3077Must always be \f(CW1\fR if you do not use autoconf configuration, which
3078keeps libev from including \fIconfig.h\fR, and it also defines dummy
3079implementations for some libevent functions (such as logging, which is not
3080supported). It will also not define any of the structs usually found in
3081\&\fIevent.h\fR that are not directly supported by the libev core alone.
3082.IP "\s-1EV_USE_MONOTONIC\s0" 4
3083.IX Item "EV_USE_MONOTONIC"
3084If defined to be \f(CW1\fR, libev will try to detect the availability of the
3085monotonic clock option at both compile time and runtime. Otherwise no use
3086of the monotonic clock option will be attempted. If you enable this, you
3087usually have to link against librt or something similar. Enabling it when
3088the functionality isn't available is safe, though, although you have
3089to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
3090function is hiding in (often \fI\-lrt\fR).
3091.IP "\s-1EV_USE_REALTIME\s0" 4
3092.IX Item "EV_USE_REALTIME"
3093If defined to be \f(CW1\fR, libev will try to detect the availability of the
3094real-time clock option at compile time (and assume its availability at
3095runtime if successful). Otherwise no use of the real-time clock option will
3096be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR by \f(CW\*(C`clock_get
3097(CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect correctness. See the
3098note about libraries in the description of \f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though.
3099.IP "\s-1EV_USE_NANOSLEEP\s0" 4
3100.IX Item "EV_USE_NANOSLEEP"
3101If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available
3102and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR.
3103.IP "\s-1EV_USE_EVENTFD\s0" 4
3104.IX Item "EV_USE_EVENTFD"
3105If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
3106available and will probe for kernel support at runtime. This will improve
3107\&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
3108If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
31092.7 or newer, otherwise disabled.
3110.IP "\s-1EV_USE_SELECT\s0" 4
3111.IX Item "EV_USE_SELECT"
3112If undefined or defined to be \f(CW1\fR, libev will compile in support for the
3113\&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at auto-detection will be done: if no
3114other method takes over, select will be it. Otherwise the select backend
3115will not be compiled in.
3116.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
3117.IX Item "EV_SELECT_USE_FD_SET"
3118If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR
3119structure. This is useful if libev doesn't compile due to a missing
3120\&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it mis-guesses the bitset layout on
3121exotic systems. This usually limits the range of file descriptors to some
3122low limit such as 1024 or might have other limitations (winsocket only
3123allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation, might
3124influence the size of the \f(CW\*(C`fd_set\*(C'\fR used.
3125.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
3126.IX Item "EV_SELECT_IS_WINSOCKET"
3127When defined to \f(CW1\fR, the select backend will assume that
3128select/socket/connect etc. don't understand file descriptors but
3129wants osf handles on win32 (this is the case when the select to
3130be used is the winsock select). This means that it will call
3131\&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
3132it is assumed that all these functions actually work on fds, even
3133on win32. Should not be defined on non\-win32 platforms.
3134.IP "\s-1EV_FD_TO_WIN32_HANDLE\s0" 4
3135.IX Item "EV_FD_TO_WIN32_HANDLE"
3136If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map
3137file descriptors to socket handles. When not defining this symbol (the
3138default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually
3139correct. In some cases, programs use their own file descriptor management,
3140in which case they can provide this function to map fds to socket handles.
3141.IP "\s-1EV_USE_POLL\s0" 4
3142.IX Item "EV_USE_POLL"
3143If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2)
3144backend. Otherwise it will be enabled on non\-win32 platforms. It
3145takes precedence over select.
3146.IP "\s-1EV_USE_EPOLL\s0" 4
3147.IX Item "EV_USE_EPOLL"
3148If defined to be \f(CW1\fR, libev will compile in support for the Linux
3149\&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime,
3150otherwise another method will be used as fallback. This is the preferred
3151backend for GNU/Linux systems. If undefined, it will be enabled if the
3152headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3153.IP "\s-1EV_USE_KQUEUE\s0" 4
3154.IX Item "EV_USE_KQUEUE"
3155If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
3156\&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime,
3157otherwise another method will be used as fallback. This is the preferred
3158backend for \s-1BSD\s0 and BSD-like systems, although on most BSDs kqueue only
3159supports some types of fds correctly (the only platform we found that
3160supports ptys for example was NetBSD), so kqueue might be compiled in, but
3161not be used unless explicitly requested. The best way to use it is to find
3162out whether kqueue supports your type of fd properly and use an embedded
3163kqueue loop.
3164.IP "\s-1EV_USE_PORT\s0" 4
3165.IX Item "EV_USE_PORT"
3166If defined to be \f(CW1\fR, libev will compile in support for the Solaris
316710 port style backend. Its availability will be detected at runtime,
3168otherwise another method will be used as fallback. This is the preferred
3169backend for Solaris 10 systems.
3170.IP "\s-1EV_USE_DEVPOLL\s0" 4
3171.IX Item "EV_USE_DEVPOLL"
3172Reserved for future expansion, works like the \s-1USE\s0 symbols above.
3173.IP "\s-1EV_USE_INOTIFY\s0" 4
3174.IX Item "EV_USE_INOTIFY"
3175If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
3176interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
3177be detected at runtime. If undefined, it will be enabled if the headers
3178indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3179.IP "\s-1EV_ATOMIC_T\s0" 4
3180.IX Item "EV_ATOMIC_T"
3181Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
3182access is atomic with respect to other threads or signal contexts. No such
3183type is easily found in the C language, so you can provide your own type
3184that you know is safe for your purposes. It is used both for signal handler \*(L"locking\*(R"
3185as well as for signal and thread safety in \f(CW\*(C`ev_async\*(C'\fR watchers.
3186.Sp
3187In the absence of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR
3188(from \fIsignal.h\fR), which is usually good enough on most platforms.
3189.IP "\s-1EV_H\s0" 4
3190.IX Item "EV_H"
3191The name of the \fIev.h\fR header file used to include it. The default if
3192undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be
3193used to virtually rename the \fIev.h\fR header file in case of conflicts.
3194.IP "\s-1EV_CONFIG_H\s0" 4
3195.IX Item "EV_CONFIG_H"
3196If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
3197\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
3198\&\f(CW\*(C`EV_H\*(C'\fR, above.
3199.IP "\s-1EV_EVENT_H\s0" 4
3200.IX Item "EV_EVENT_H"
3201Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea
3202of how the \fIevent.h\fR header can be found, the default is \f(CW"event.h"\fR.
3203.IP "\s-1EV_PROTOTYPES\s0" 4
3204.IX Item "EV_PROTOTYPES"
3205If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
3206prototypes, but still define all the structs and other symbols. This is
3207occasionally useful if you want to provide your own wrapper functions
3208around libev functions.
3209.IP "\s-1EV_MULTIPLICITY\s0" 4
3210.IX Item "EV_MULTIPLICITY"
3211If undefined or defined to \f(CW1\fR, then all event-loop-specific functions
3212will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create
3213additional independent event loops. Otherwise there will be no support
3214for multiple event loops and there is no first event loop pointer
3215argument. Instead, all functions act on the single default loop.
3216.IP "\s-1EV_MINPRI\s0" 4
3217.IX Item "EV_MINPRI"
3218.PD 0
3219.IP "\s-1EV_MAXPRI\s0" 4
3220.IX Item "EV_MAXPRI"
3221.PD
3222The range of allowed priorities. \f(CW\*(C`EV_MINPRI\*(C'\fR must be smaller or equal to
3223\&\f(CW\*(C`EV_MAXPRI\*(C'\fR, but otherwise there are no non-obvious limitations. You can
3224provide for more priorities by overriding those symbols (usually defined
3225to be \f(CW\*(C`\-2\*(C'\fR and \f(CW2\fR, respectively).
3226.Sp
3227When doing priority-based operations, libev usually has to linearly search
3228all the priorities, so having many of them (hundreds) uses a lot of space
3229and time, so using the defaults of five priorities (\-2 .. +2) is usually
3230fine.
3231.Sp
3232If your embedding application does not need any priorities, defining these
3233both to \f(CW0\fR will save some memory and \s-1CPU\s0.
3234.IP "\s-1EV_PERIODIC_ENABLE\s0" 4
3235.IX Item "EV_PERIODIC_ENABLE"
3236If undefined or defined to be \f(CW1\fR, then periodic timers are supported. If
3237defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of
3238code.
3239.IP "\s-1EV_IDLE_ENABLE\s0" 4
3240.IX Item "EV_IDLE_ENABLE"
3241If undefined or defined to be \f(CW1\fR, then idle watchers are supported. If
3242defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of
3243code.
3244.IP "\s-1EV_EMBED_ENABLE\s0" 4
3245.IX Item "EV_EMBED_ENABLE"
3246If undefined or defined to be \f(CW1\fR, then embed watchers are supported. If
3247defined to be \f(CW0\fR, then they are not. Embed watchers rely on most other
3248watcher types, which therefore must not be disabled.
3249.IP "\s-1EV_STAT_ENABLE\s0" 4
3250.IX Item "EV_STAT_ENABLE"
3251If undefined or defined to be \f(CW1\fR, then stat watchers are supported. If
3252defined to be \f(CW0\fR, then they are not.
3253.IP "\s-1EV_FORK_ENABLE\s0" 4
3254.IX Item "EV_FORK_ENABLE"
3255If undefined or defined to be \f(CW1\fR, then fork watchers are supported. If
3256defined to be \f(CW0\fR, then they are not.
3257.IP "\s-1EV_ASYNC_ENABLE\s0" 4
3258.IX Item "EV_ASYNC_ENABLE"
3259If undefined or defined to be \f(CW1\fR, then async watchers are supported. If
3260defined to be \f(CW0\fR, then they are not.
3261.IP "\s-1EV_MINIMAL\s0" 4
3262.IX Item "EV_MINIMAL"
3263If you need to shave off some kilobytes of code at the expense of some
3264speed, define this symbol to \f(CW1\fR. Currently this is used to override some
3265inlining decisions, saves roughly 30% code size on amd64. It also selects a
3266much smaller 2\-heap for timer management over the default 4\-heap.
3267.IP "\s-1EV_PID_HASHSIZE\s0" 4
3268.IX Item "EV_PID_HASHSIZE"
3269\&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by
3270pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR), usually more
3271than enough. If you need to manage thousands of children you might want to
3272increase this value (\fImust\fR be a power of two).
3273.IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4
3274.IX Item "EV_INOTIFY_HASHSIZE"
3275\&\f(CW\*(C`ev_stat\*(C'\fR watchers use a small hash table to distribute workload by
3276inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR),
3277usually more than enough. If you need to manage thousands of \f(CW\*(C`ev_stat\*(C'\fR
3278watchers you might want to increase this value (\fImust\fR be a power of
3279two).
3280.IP "\s-1EV_USE_4HEAP\s0" 4
3281.IX Item "EV_USE_4HEAP"
3282Heaps are not very cache-efficient. To improve the cache-efficiency of the
3283timer and periodics heaps, libev uses a 4\-heap when this symbol is defined
3284to \f(CW1\fR. The 4\-heap uses more complicated (longer) code but has noticeably
3285faster performance with many (thousands) of watchers.
3286.Sp
3287The default is \f(CW1\fR unless \f(CW\*(C`EV_MINIMAL\*(C'\fR is set in which case it is \f(CW0\fR
3288(disabled).
3289.IP "\s-1EV_HEAP_CACHE_AT\s0" 4
3290.IX Item "EV_HEAP_CACHE_AT"
3291Heaps are not very cache-efficient. To improve the cache-efficiency of the
3292timer and periodics heaps, libev can cache the timestamp (\fIat\fR) within
3293the heap structure (selected by defining \f(CW\*(C`EV_HEAP_CACHE_AT\*(C'\fR to \f(CW1\fR),
3294which uses 8\-12 bytes more per watcher and a few hundred bytes more code,
3295but avoids random read accesses on heap changes. This improves performance
3296noticeably with many (hundreds) of watchers.
3297.Sp
3298The default is \f(CW1\fR unless \f(CW\*(C`EV_MINIMAL\*(C'\fR is set in which case it is \f(CW0\fR
3299(disabled).
3300.IP "\s-1EV_VERIFY\s0" 4
3301.IX Item "EV_VERIFY"
3302Controls how much internal verification (see \f(CW\*(C`ev_loop_verify ()\*(C'\fR) will
3303be done: If set to \f(CW0\fR, no internal verification code will be compiled
3304in. If set to \f(CW1\fR, then verification code will be compiled in, but not
3305called. If set to \f(CW2\fR, then the internal verification code will be
3306called once per loop, which can slow down libev. If set to \f(CW3\fR, then the
3307verification code will be called very frequently, which will slow down
3308libev considerably.
3309.Sp
3310The default is \f(CW1\fR, unless \f(CW\*(C`EV_MINIMAL\*(C'\fR is set, in which case it will be
3311\&\f(CW0\fR.
3312.IP "\s-1EV_COMMON\s0" 4
3313.IX Item "EV_COMMON"
3314By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining
3315this macro to a something else you can include more and other types of
3316members. You have to define it each time you include one of the files,
3317though, and it must be identical each time.
3318.Sp
3319For example, the perl \s-1EV\s0 module uses something like this:
3320.Sp
3321.Vb 3
3322\& #define EV_COMMON \e
3323\& SV *self; /* contains this struct */ \e
3324\& SV *cb_sv, *fh /* note no trailing ";" */
3325.Ve
3326.IP "\s-1EV_CB_DECLARE\s0 (type)" 4
3327.IX Item "EV_CB_DECLARE (type)"
3328.PD 0
3329.IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4
3330.IX Item "EV_CB_INVOKE (watcher, revents)"
3331.IP "ev_set_cb (ev, cb)" 4
3332.IX Item "ev_set_cb (ev, cb)"
3333.PD
3334Can be used to change the callback member declaration in each watcher,
3335and the way callbacks are invoked and set. Must expand to a struct member
3336definition and a statement, respectively. See the \fIev.h\fR header file for
3337their default definitions. One possible use for overriding these is to
3338avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use
3339method calls instead of plain function calls in \*(C+.
3340.Sh "\s-1EXPORTED\s0 \s-1API\s0 \s-1SYMBOLS\s0"
3341.IX Subsection "EXPORTED API SYMBOLS"
3342If you need to re-export the \s-1API\s0 (e.g. via a \s-1DLL\s0) and you need a list of
3343exported symbols, you can use the provided \fISymbol.*\fR files which list
3344all public symbols, one per line:
3345.PP
3346.Vb 2
3347\& Symbols.ev for libev proper
3348\& Symbols.event for the libevent emulation
3349.Ve
3350.PP
3351This can also be used to rename all public symbols to avoid clashes with
3352multiple versions of libev linked together (which is obviously bad in
3353itself, but sometimes it is inconvenient to avoid this).
3354.PP
3355A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to
3356include before including \fIev.h\fR:
3357.PP
3358.Vb 1
3359\& <Symbols.ev sed \-e "s/.*/#define & myprefix_&/" >wrap.h
3360.Ve
3361.PP
3362This would create a file \fIwrap.h\fR which essentially looks like this:
3363.PP
3364.Vb 4
3365\& #define ev_backend myprefix_ev_backend
3366\& #define ev_check_start myprefix_ev_check_start
3367\& #define ev_check_stop myprefix_ev_check_stop
3368\& ...
3369.Ve
3370.Sh "\s-1EXAMPLES\s0"
3371.IX Subsection "EXAMPLES"
3372For a real-world example of a program the includes libev
3373verbatim, you can have a look at the \s-1EV\s0 perl module
3374(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
3375the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public
3376interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file
3377will be compiled. It is pretty complex because it provides its own header
3378file.
3379.PP
3380The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file
3381that everybody includes and which overrides some configure choices:
3382.PP
3383.Vb 9
3384\& #define EV_MINIMAL 1
3385\& #define EV_USE_POLL 0
3386\& #define EV_MULTIPLICITY 0
3387\& #define EV_PERIODIC_ENABLE 0
3388\& #define EV_STAT_ENABLE 0
3389\& #define EV_FORK_ENABLE 0
3390\& #define EV_CONFIG_H <config.h>
3391\& #define EV_MINPRI 0
3392\& #define EV_MAXPRI 0
3393\&
3394\& #include "ev++.h"
3395.Ve
3396.PP
3397And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled:
3398.PP
3399.Vb 2
3400\& #include "ev_cpp.h"
3401\& #include "ev.c"
3402.Ve
3403.SH "THREADS AND COROUTINES"
3404.IX Header "THREADS AND COROUTINES"
3405.Sh "\s-1THREADS\s0"
3406.IX Subsection "THREADS"
3407All libev functions are reentrant and thread-safe unless explicitly
3408documented otherwise, but it uses no locking itself. This means that you
3409can use as many loops as you want in parallel, as long as there are no
3410concurrent calls into any libev function with the same loop parameter
3411(\f(CW\*(C`ev_default_*\*(C'\fR calls have an implicit default loop parameter, of
3412course): libev guarantees that different event loops share no data
3413structures that need any locking.
3414.PP
3415Or to put it differently: calls with different loop parameters can be done
3416concurrently from multiple threads, calls with the same loop parameter
3417must be done serially (but can be done from different threads, as long as
3418only one thread ever is inside a call at any point in time, e.g. by using
3419a mutex per loop).
3420.PP
3421Specifically to support threads (and signal handlers), libev implements
3422so-called \f(CW\*(C`ev_async\*(C'\fR watchers, which allow some limited form of
3423concurrency on the same event loop, namely waking it up \*(L"from the
3424outside\*(R".
3425.PP
3426If you want to know which design (one loop, locking, or multiple loops
3427without or something else still) is best for your problem, then I cannot
3428help you, but here is some generic advice:
3429.IP "\(bu" 4
3430most applications have a main thread: use the default libev loop
3431in that thread, or create a separate thread running only the default loop.
3432.Sp
3433This helps integrating other libraries or software modules that use libev
3434themselves and don't care/know about threading.
3435.IP "\(bu" 4
3436one loop per thread is usually a good model.
3437.Sp
3438Doing this is almost never wrong, sometimes a better-performance model
3439exists, but it is always a good start.
3440.IP "\(bu" 4
3441other models exist, such as the leader/follower pattern, where one
3442loop is handed through multiple threads in a kind of round-robin fashion.
3443.Sp
3444Choosing a model is hard \- look around, learn, know that usually you can do
3445better than you currently do :\-)
3446.IP "\(bu" 4
3447often you need to talk to some other thread which blocks in the
3448event loop.
3449.Sp
3450\&\f(CW\*(C`ev_async\*(C'\fR watchers can be used to wake them up from other threads safely
3451(or from signal contexts...).
3452.Sp
3453An example use would be to communicate signals or other events that only
3454work in the default loop by registering the signal watcher with the
3455default loop and triggering an \f(CW\*(C`ev_async\*(C'\fR watcher from the default loop
3456watcher callback into the event loop interested in the signal.
3457.Sh "\s-1COROUTINES\s0"
3458.IX Subsection "COROUTINES"
3459Libev is much more accommodating to coroutines (\*(L"cooperative threads\*(R"):
3460libev fully supports nesting calls to it's functions from different
3461coroutines (e.g. you can call \f(CW\*(C`ev_loop\*(C'\fR on the same loop from two
3462different coroutines and switch freely between both coroutines running the
3463loop, as long as you don't confuse yourself). The only exception is that
3464you must not do this from \f(CW\*(C`ev_periodic\*(C'\fR reschedule callbacks.
3465.PP
3466Care has been taken to ensure that libev does not keep local state inside
3467\&\f(CW\*(C`ev_loop\*(C'\fR, and other calls do not usually allow coroutine switches.
3468.SH "COMPLEXITIES"
3469.IX Header "COMPLEXITIES"
3470In this section the complexities of (many of) the algorithms used inside
3471libev will be explained. For complexity discussions about backends see the
3472documentation for \f(CW\*(C`ev_default_init\*(C'\fR.
3473.PP
3474All of the following are about amortised time: If an array needs to be
3475extended, libev needs to realloc and move the whole array, but this
3476happens asymptotically never with higher number of elements, so O(1) might
3477mean it might do a lengthy realloc operation in rare cases, but on average
3478it is much faster and asymptotically approaches constant time.
3479.IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4
3480.IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)"
3481This means that, when you have a watcher that triggers in one hour and
3482there are 100 watchers that would trigger before that then inserting will
3483have to skip roughly seven (\f(CW\*(C`ld 100\*(C'\fR) of these watchers.
3484.IP "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 4
3485.IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)"
3486That means that changing a timer costs less than removing/adding them
3487as only the relative motion in the event queue has to be paid for.
3488.IP "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)" 4
3489.IX Item "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)"
3490These just add the watcher into an array or at the head of a list.
3491.IP "Stopping check/prepare/idle/fork/async watchers: O(1)" 4
3492.IX Item "Stopping check/prepare/idle/fork/async watchers: O(1)"
3493.PD 0
3494.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4
3495.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))"
3496.PD
3497These watchers are stored in lists then need to be walked to find the
3498correct watcher to remove. The lists are usually short (you don't usually
3499have many watchers waiting for the same fd or signal).
3500.IP "Finding the next timer in each loop iteration: O(1)" 4
3501.IX Item "Finding the next timer in each loop iteration: O(1)"
3502By virtue of using a binary or 4\-heap, the next timer is always found at a
3503fixed position in the storage array.
3504.IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4
3505.IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)"
3506A change means an I/O watcher gets started or stopped, which requires
3507libev to recalculate its status (and possibly tell the kernel, depending
3508on backend and whether \f(CW\*(C`ev_io_set\*(C'\fR was used).
3509.IP "Activating one watcher (putting it into the pending state): O(1)" 4
3510.IX Item "Activating one watcher (putting it into the pending state): O(1)"
3511.PD 0
3512.IP "Priority handling: O(number_of_priorities)" 4
3513.IX Item "Priority handling: O(number_of_priorities)"
3514.PD
3515Priorities are implemented by allocating some space for each
3516priority. When doing priority-based operations, libev usually has to
3517linearly search all the priorities, but starting/stopping and activating
3518watchers becomes O(1) with respect to priority handling.
3519.IP "Sending an ev_async: O(1)" 4
3520.IX Item "Sending an ev_async: O(1)"
3521.PD 0
3522.IP "Processing ev_async_send: O(number_of_async_watchers)" 4
3523.IX Item "Processing ev_async_send: O(number_of_async_watchers)"
3524.IP "Processing signals: O(max_signal_number)" 4
3525.IX Item "Processing signals: O(max_signal_number)"
3526.PD
3527Sending involves a system call \fIiff\fR there were no other \f(CW\*(C`ev_async_send\*(C'\fR
3528calls in the current loop iteration. Checking for async and signal events
3529involves iterating over all running async watchers or all signal numbers.
3530.SH "WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS"
3531.IX Header "WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS"
3532Win32 doesn't support any of the standards (e.g. \s-1POSIX\s0) that libev
3533requires, and its I/O model is fundamentally incompatible with the \s-1POSIX\s0
3534model. Libev still offers limited functionality on this platform in
3535the form of the \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR backend, and only supports socket
3536descriptors. This only applies when using Win32 natively, not when using
3537e.g. cygwin.
3538.PP
3539Lifting these limitations would basically require the full
3540re-implementation of the I/O system. If you are into these kinds of
3541things, then note that glib does exactly that for you in a very portable
3542way (note also that glib is the slowest event library known to man).
3543.PP
3544There is no supported compilation method available on windows except
3545embedding it into other applications.
3546.PP
3547Not a libev limitation but worth mentioning: windows apparently doesn't
3548accept large writes: instead of resulting in a partial write, windows will
3549either accept everything or return \f(CW\*(C`ENOBUFS\*(C'\fR if the buffer is too large,
3550so make sure you only write small amounts into your sockets (less than a
3551megabyte seems safe, but this apparently depends on the amount of memory
3552available).
3553.PP
3554Due to the many, low, and arbitrary limits on the win32 platform and
3555the abysmal performance of winsockets, using a large number of sockets
3556is not recommended (and not reasonable). If your program needs to use
3557more than a hundred or so sockets, then likely it needs to use a totally
3558different implementation for windows, as libev offers the \s-1POSIX\s0 readiness
3559notification model, which cannot be implemented efficiently on windows
3560(Microsoft monopoly games).
3561.PP
3562A typical way to use libev under windows is to embed it (see the embedding
3563section for details) and use the following \fIevwrap.h\fR header file instead
3564of \fIev.h\fR:
3565.PP
3566.Vb 2
3567\& #define EV_STANDALONE /* keeps ev from requiring config.h */
3568\& #define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
3569\&
3570\& #include "ev.h"
3571.Ve
3572.PP
3573And compile the following \fIevwrap.c\fR file into your project (make sure
3574you do \fInot\fR compile the \fIev.c\fR or any other embedded source files!):
3575.PP
3576.Vb 2
3577\& #include "evwrap.h"
3578\& #include "ev.c"
3579.Ve
3580.IP "The winsocket select function" 4
3581.IX Item "The winsocket select function"
3582The winsocket \f(CW\*(C`select\*(C'\fR function doesn't follow \s-1POSIX\s0 in that it
3583requires socket \fIhandles\fR and not socket \fIfile descriptors\fR (it is
3584also extremely buggy). This makes select very inefficient, and also
3585requires a mapping from file descriptors to socket handles (the Microsoft
3586C runtime provides the function \f(CW\*(C`_open_osfhandle\*(C'\fR for this). See the
3587discussion of the \f(CW\*(C`EV_SELECT_USE_FD_SET\*(C'\fR, \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR and
3588\&\f(CW\*(C`EV_FD_TO_WIN32_HANDLE\*(C'\fR preprocessor symbols for more info.
3589.Sp
3590The configuration for a \*(L"naked\*(R" win32 using the Microsoft runtime
3591libraries and raw winsocket select is:
3592.Sp
3593.Vb 2
3594\& #define EV_USE_SELECT 1
3595\& #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
3596.Ve
3597.Sp
3598Note that winsockets handling of fd sets is O(n), so you can easily get a
3599complexity in the O(nA\*^X) range when using win32.
3600.IP "Limited number of file descriptors" 4
3601.IX Item "Limited number of file descriptors"
3602Windows has numerous arbitrary (and low) limits on things.
3603.Sp
3604Early versions of winsocket's select only supported waiting for a maximum
3605of \f(CW64\fR handles (probably owning to the fact that all windows kernels
3606can only wait for \f(CW64\fR things at the same time internally; Microsoft
3607recommends spawning a chain of threads and wait for 63 handles and the
3608previous thread in each. Great).
3609.Sp
3610Newer versions support more handles, but you need to define \f(CW\*(C`FD_SETSIZE\*(C'\fR
3611to some high number (e.g. \f(CW2048\fR) before compiling the winsocket select
3612call (which might be in libev or elsewhere, for example, perl does its own
3613select emulation on windows).
3614.Sp
3615Another limit is the number of file descriptors in the Microsoft runtime
3616libraries, which by default is \f(CW64\fR (there must be a hidden \fI64\fR fetish
3617or something like this inside Microsoft). You can increase this by calling
3618\&\f(CW\*(C`_setmaxstdio\*(C'\fR, which can increase this limit to \f(CW2048\fR (another
3619arbitrary limit), but is broken in many versions of the Microsoft runtime
3620libraries.
3621.Sp
3622This might get you to about \f(CW512\fR or \f(CW2048\fR sockets (depending on
3623windows version and/or the phase of the moon). To get more, you need to
3624wrap all I/O functions and provide your own fd management, but the cost of
3625calling select (O(nA\*^X)) will likely make this unworkable.
3626.SH "PORTABILITY REQUIREMENTS"
3627.IX Header "PORTABILITY REQUIREMENTS"
3628In addition to a working ISO-C implementation, libev relies on a few
3629additional extensions:
3630.ie n .IP """void (*)(ev_watcher_type *, int revents)""\fR must have compatible calling conventions regardless of \f(CW""ev_watcher_type *""." 4
3631.el .IP "\f(CWvoid (*)(ev_watcher_type *, int revents)\fR must have compatible calling conventions regardless of \f(CWev_watcher_type *\fR." 4
3632.IX Item "void (*)(ev_watcher_type *, int revents) must have compatible calling conventions regardless of ev_watcher_type *."
3633Libev assumes not only that all watcher pointers have the same internal
3634structure (guaranteed by \s-1POSIX\s0 but not by \s-1ISO\s0 C for example), but it also
3635assumes that the same (machine) code can be used to call any watcher
3636callback: The watcher callbacks have different type signatures, but libev
3637calls them using an \f(CW\*(C`ev_watcher *\*(C'\fR internally.
3638.ie n .IP """sig_atomic_t volatile"" must be thread-atomic as well" 4
3639.el .IP "\f(CWsig_atomic_t volatile\fR must be thread-atomic as well" 4
3640.IX Item "sig_atomic_t volatile must be thread-atomic as well"
3641The type \f(CW\*(C`sig_atomic_t volatile\*(C'\fR (or whatever is defined as
3642\&\f(CW\*(C`EV_ATOMIC_T\*(C'\fR) must be atomic with respect to accesses from different
3643threads. This is not part of the specification for \f(CW\*(C`sig_atomic_t\*(C'\fR, but is
3644believed to be sufficiently portable.
3645.ie n .IP """sigprocmask"" must work in a threaded environment" 4
3646.el .IP "\f(CWsigprocmask\fR must work in a threaded environment" 4
3647.IX Item "sigprocmask must work in a threaded environment"
3648Libev uses \f(CW\*(C`sigprocmask\*(C'\fR to temporarily block signals. This is not
3649allowed in a threaded program (\f(CW\*(C`pthread_sigmask\*(C'\fR has to be used). Typical
3650pthread implementations will either allow \f(CW\*(C`sigprocmask\*(C'\fR in the \*(L"main
3651thread\*(R" or will block signals process-wide, both behaviours would
3652be compatible with libev. Interaction between \f(CW\*(C`sigprocmask\*(C'\fR and
3653\&\f(CW\*(C`pthread_sigmask\*(C'\fR could complicate things, however.
3654.Sp
3655The most portable way to handle signals is to block signals in all threads
3656except the initial one, and run the default loop in the initial thread as
3657well.
3658.ie n .IP """long"" must be large enough for common memory allocation sizes" 4
3659.el .IP "\f(CWlong\fR must be large enough for common memory allocation sizes" 4
3660.IX Item "long must be large enough for common memory allocation sizes"
3661To improve portability and simplify using libev, libev uses \f(CW\*(C`long\*(C'\fR
3662internally instead of \f(CW\*(C`size_t\*(C'\fR when allocating its data structures. On
3663non-POSIX systems (Microsoft...) this might be unexpectedly low, but
3664is still at least 31 bits everywhere, which is enough for hundreds of
3665millions of watchers.
3666.ie n .IP """double"" must hold a time value in seconds with enough accuracy" 4
3667.el .IP "\f(CWdouble\fR must hold a time value in seconds with enough accuracy" 4
3668.IX Item "double must hold a time value in seconds with enough accuracy"
3669The type \f(CW\*(C`double\*(C'\fR is used to represent timestamps. It is required to
3670have at least 51 bits of mantissa (and 9 bits of exponent), which is good
3671enough for at least into the year 4000. This requirement is fulfilled by
3672implementations implementing \s-1IEEE\s0 754 (basically all existing ones).
3673.PP
3674If you know of other additional requirements drop me a note.
3675.SH "COMPILER WARNINGS"
3676.IX Header "COMPILER WARNINGS"
3677Depending on your compiler and compiler settings, you might get no or a
3678lot of warnings when compiling libev code. Some people are apparently
3679scared by this.
3680.PP
3681However, these are unavoidable for many reasons. For one, each compiler
3682has different warnings, and each user has different tastes regarding
3683warning options. \*(L"Warn-free\*(R" code therefore cannot be a goal except when
3684targeting a specific compiler and compiler-version.
3685.PP
3686Another reason is that some compiler warnings require elaborate
3687workarounds, or other changes to the code that make it less clear and less
3688maintainable.
3689.PP
3690And of course, some compiler warnings are just plain stupid, or simply
3691wrong (because they don't actually warn about the condition their message
3692seems to warn about).
3693.PP
3694While libev is written to generate as few warnings as possible,
3695\&\*(L"warn-free\*(R" code is not a goal, and it is recommended not to build libev
3696with any compiler warnings enabled unless you are prepared to cope with
3697them (e.g. by ignoring them). Remember that warnings are just that:
3698warnings, not errors, or proof of bugs.
3699.SH "VALGRIND"
3700.IX Header "VALGRIND"
3701Valgrind has a special section here because it is a popular tool that is
3702highly useful, but valgrind reports are very hard to interpret.
3703.PP
3704If you think you found a bug (memory leak, uninitialised data access etc.)
3705in libev, then check twice: If valgrind reports something like:
3706.PP
3707.Vb 3
3708\& ==2274== definitely lost: 0 bytes in 0 blocks.
3709\& ==2274== possibly lost: 0 bytes in 0 blocks.
3710\& ==2274== still reachable: 256 bytes in 1 blocks.
3711.Ve
3712.PP
3713Then there is no memory leak. Similarly, under some circumstances,
3714valgrind might report kernel bugs as if it were a bug in libev, or it
3715might be confused (it is a very good tool, but only a tool).
3716.PP
3717If you are unsure about something, feel free to contact the mailing list
3718with the full valgrind report and an explanation on why you think this is
3719a bug in libev. However, don't be annoyed when you get a brisk \*(L"this is
3720no bug\*(R" answer and take the chance of learning how to interpret valgrind
3721properly.
3722.PP
3723If you need, for some reason, empty reports from valgrind for your project
3724I suggest using suppression lists.
1020.SH "AUTHOR" 3725.SH "AUTHOR"
1021.IX Header "AUTHOR" 3726.IX Header "AUTHOR"
1022Marc Lehmann <libev@schmorp.de>. 3727Marc Lehmann <libev@schmorp.de>.

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