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129.\" ======================================================================== 132.\" ========================================================================
130.\" 133.\"
131.IX Title ""<STANDARD INPUT>" 1" 134.IX Title "LIBEV 3"
132.TH "<STANDARD INPUT>" 1 "2007-11-22" "perl v5.8.8" "User Contributed Perl Documentation" 135.TH LIBEV 3 "2008-05-11" "libev-3.33" "libev - high perfromance 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>
139.Ve 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\& }
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 floatingpoint value. Unlike the name
255component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for time differences
256throughout libev.
179.SH "GLOBAL FUNCTIONS" 257.SH "GLOBAL FUNCTIONS"
180.IX Header "GLOBAL FUNCTIONS" 258.IX Header "GLOBAL FUNCTIONS"
181These functions can be called anytime, even before initialising the 259These functions can be called anytime, even before initialising the
182library in any way. 260library in any way.
183.IP "ev_tstamp ev_time ()" 4 261.IP "ev_tstamp ev_time ()" 4
184.IX Item "ev_tstamp ev_time ()" 262.IX Item "ev_tstamp ev_time ()"
185Returns the current time as libev would use it. Please note that the 263Returns 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 264\&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp
187you actually want to know. 265you actually want to know.
266.IP "ev_sleep (ev_tstamp interval)" 4
267.IX Item "ev_sleep (ev_tstamp interval)"
268Sleep for the given interval: The current thread will be blocked until
269either it is interrupted or the given time interval has passed. Basically
270this is a subsecond-resolution \f(CW\*(C`sleep ()\*(C'\fR.
188.IP "int ev_version_major ()" 4 271.IP "int ev_version_major ()" 4
189.IX Item "int ev_version_major ()" 272.IX Item "int ev_version_major ()"
190.PD 0 273.PD 0
191.IP "int ev_version_minor ()" 4 274.IP "int ev_version_minor ()" 4
192.IX Item "int ev_version_minor ()" 275.IX Item "int ev_version_minor ()"
193.PD 276.PD
194You can find out the major and minor version numbers of the library 277You 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 278you 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 279\&\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 280symbols \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. 281version of the library your program was compiled against.
199.Sp 282.Sp
283These version numbers refer to the \s-1ABI\s0 version of the library, not the
284release version.
285.Sp
200Usually, it's a good idea to terminate if the major versions mismatch, 286Usually, it's a good idea to terminate if the major versions mismatch,
201as this indicates an incompatible change. Minor versions are usually 287as this indicates an incompatible change. Minor versions are usually
202compatible to older versions, so a larger minor version alone is usually 288compatible to older versions, so a larger minor version alone is usually
203not a problem. 289not a problem.
290.Sp
291Example: Make sure we haven't accidentally been linked against the wrong
292version.
293.Sp
294.Vb 3
295\& assert (("libev version mismatch",
296\& ev_version_major () == EV_VERSION_MAJOR
297\& && ev_version_minor () >= EV_VERSION_MINOR));
298.Ve
299.IP "unsigned int ev_supported_backends ()" 4
300.IX Item "unsigned int ev_supported_backends ()"
301Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR
302value) compiled into this binary of libev (independent of their
303availability on the system you are running on). See \f(CW\*(C`ev_default_loop\*(C'\fR for
304a description of the set values.
305.Sp
306Example: make sure we have the epoll method, because yeah this is cool and
307a must have and can we have a torrent of it please!!!11
308.Sp
309.Vb 2
310\& assert (("sorry, no epoll, no sex",
311\& ev_supported_backends () & EVBACKEND_EPOLL));
312.Ve
313.IP "unsigned int ev_recommended_backends ()" 4
314.IX Item "unsigned int ev_recommended_backends ()"
315Return the set of all backends compiled into this binary of libev and also
316recommended for this platform. This set is often smaller than the one
317returned by \f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on
318most BSDs and will not be autodetected unless you explicitly request it
319(assuming you know what you are doing). This is the set of backends that
320libev will probe for if you specify no backends explicitly.
321.IP "unsigned int ev_embeddable_backends ()" 4
322.IX Item "unsigned int ev_embeddable_backends ()"
323Returns the set of backends that are embeddable in other event loops. This
324is the theoretical, all-platform, value. To find which backends
325might be supported on the current system, you would need to look at
326\&\f(CW\*(C`ev_embeddable_backends () & ev_supported_backends ()\*(C'\fR, likewise for
327recommended ones.
328.Sp
329See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
204.IP "ev_set_allocator (void *(*cb)(void *ptr, long size))" 4 330.IP "ev_set_allocator (void *(*cb)(void *ptr, long size))" 4
205.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))" 331.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))"
206Sets the allocation function to use (the prototype is similar to the 332Sets the allocation function to use (the prototype is similar \- the
207realloc C function, the semantics are identical). It is used to allocate 333semantics are identical to the \f(CW\*(C`realloc\*(C'\fR C89/SuS/POSIX function). It is
208and free memory (no surprises here). If it returns zero when memory 334used to allocate and free memory (no surprises here). If it returns zero
209needs to be allocated, the library might abort or take some potentially 335when memory needs to be allocated (\f(CW\*(C`size != 0\*(C'\fR), the library might abort
210destructive action. The default is your system realloc function. 336or take some potentially destructive action.
337.Sp
338Since some systems (at least OpenBSD and Darwin) fail to implement
339correct \f(CW\*(C`realloc\*(C'\fR semantics, libev will use a wrapper around the system
340\&\f(CW\*(C`realloc\*(C'\fR and \f(CW\*(C`free\*(C'\fR functions by default.
211.Sp 341.Sp
212You could override this function in high-availability programs to, say, 342You could override this function in high-availability programs to, say,
213free some memory if it cannot allocate memory, to use a special allocator, 343free some memory if it cannot allocate memory, to use a special allocator,
214or even to sleep a while and retry until some memory is available. 344or even to sleep a while and retry until some memory is available.
345.Sp
346Example: Replace the libev allocator with one that waits a bit and then
347retries (example requires a standards-compliant \f(CW\*(C`realloc\*(C'\fR).
348.Sp
349.Vb 6
350\& static void *
351\& persistent_realloc (void *ptr, size_t size)
352\& {
353\& for (;;)
354\& {
355\& void *newptr = realloc (ptr, size);
356\&
357\& if (newptr)
358\& return newptr;
359\&
360\& sleep (60);
361\& }
362\& }
363\&
364\& ...
365\& ev_set_allocator (persistent_realloc);
366.Ve
215.IP "ev_set_syserr_cb (void (*cb)(const char *msg));" 4 367.IP "ev_set_syserr_cb (void (*cb)(const char *msg));" 4
216.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg));" 368.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg));"
217Set the callback function to call on a retryable syscall error (such 369Set the callback function to call on a retryable syscall error (such
218as failed select, poll, epoll_wait). The message is a printable string 370as failed select, poll, epoll_wait). The message is a printable string
219indicating the system call or subsystem causing the problem. If this 371indicating the system call or subsystem causing the problem. If this
220callback is set, then libev will expect it to remedy the sitution, no 372callback is set, then libev will expect it to remedy the sitution, no
221matter what, when it returns. That is, libev will generally retry the 373matter what, when it returns. That is, libev will generally retry the
222requested operation, or, if the condition doesn't go away, do bad stuff 374requested operation, or, if the condition doesn't go away, do bad stuff
223(such as abort). 375(such as abort).
376.Sp
377Example: This is basically the same thing that libev does internally, too.
378.Sp
379.Vb 6
380\& static void
381\& fatal_error (const char *msg)
382\& {
383\& perror (msg);
384\& abort ();
385\& }
386\&
387\& ...
388\& ev_set_syserr_cb (fatal_error);
389.Ve
224.SH "FUNCTIONS CONTROLLING THE EVENT LOOP" 390.SH "FUNCTIONS CONTROLLING THE EVENT LOOP"
225.IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP" 391.IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP"
226An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR. The library knows two 392An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR. The library knows two
227types of such loops, the \fIdefault\fR loop, which supports signals and child 393types of such loops, the \fIdefault\fR loop, which supports signals and child
228events, and dynamically created loops which do not. 394events, and dynamically created loops which do not.
229.PP
230If you use threads, a common model is to run the default event loop
231in your main thread (or in a separate thread) and for each thread you
232create, you also create another event loop. Libev itself does no locking
233whatsoever, so if you mix calls to the same event loop in different
234threads, make sure you lock (this is usually a bad idea, though, even if
235done correctly, because it's hideous and inefficient).
236.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4 395.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
237.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)" 396.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
238This will initialise the default event loop if it hasn't been initialised 397This will initialise the default event loop if it hasn't been initialised
239yet and return it. If the default loop could not be initialised, returns 398yet and return it. If the default loop could not be initialised, returns
240false. If it already was initialised it simply returns it (and ignores the 399false. If it already was initialised it simply returns it (and ignores the
241flags). 400flags. If that is troubling you, check \f(CW\*(C`ev_backend ()\*(C'\fR afterwards).
242.Sp 401.Sp
243If you don't know what event loop to use, use the one returned from this 402If you don't know what event loop to use, use the one returned from this
244function. 403function.
245.Sp 404.Sp
405Note that this function is \fInot\fR thread-safe, so if you want to use it
406from multiple threads, you have to lock (note also that this is unlikely,
407as loops cannot bes hared easily between threads anyway).
408.Sp
409The default loop is the only loop that can handle \f(CW\*(C`ev_signal\*(C'\fR and
410\&\f(CW\*(C`ev_child\*(C'\fR watchers, and to do this, it always registers a handler
411for \f(CW\*(C`SIGCHLD\*(C'\fR. If this is a problem for your app you can either
412create a dynamic loop with \f(CW\*(C`ev_loop_new\*(C'\fR that doesn't do that, or you
413can simply overwrite the \f(CW\*(C`SIGCHLD\*(C'\fR signal handler \fIafter\fR calling
414\&\f(CW\*(C`ev_default_init\*(C'\fR.
415.Sp
246The flags argument can be used to specify special behaviour or specific 416The flags argument can be used to specify special behaviour or specific
247backends to use, and is usually specified as 0 (or \s-1EVFLAG_AUTO\s0). 417backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).
248.Sp 418.Sp
249It supports the following flags: 419The following flags are supported:
250.RS 4 420.RS 4
251.ie n .IP """EVFLAG_AUTO""" 4 421.ie n .IP """EVFLAG_AUTO""" 4
252.el .IP "\f(CWEVFLAG_AUTO\fR" 4 422.el .IP "\f(CWEVFLAG_AUTO\fR" 4
253.IX Item "EVFLAG_AUTO" 423.IX Item "EVFLAG_AUTO"
254The default flags value. Use this if you have no clue (it's the right 424The default flags value. Use this if you have no clue (it's the right
… …
260or setgid) then libev will \fInot\fR look at the environment variable 430or setgid) then libev will \fInot\fR look at the environment variable
261\&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will 431\&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will
262override the flags completely if it is found in the environment. This is 432override the flags completely if it is found in the environment. This is
263useful to try out specific backends to test their performance, or to work 433useful to try out specific backends to test their performance, or to work
264around bugs. 434around bugs.
435.ie n .IP """EVFLAG_FORKCHECK""" 4
436.el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4
437.IX Item "EVFLAG_FORKCHECK"
438Instead of calling \f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR manually after
439a fork, you can also make libev check for a fork in each iteration by
440enabling this flag.
441.Sp
442This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop,
443and thus this might slow down your event loop if you do a lot of loop
444iterations and little real work, but is usually not noticeable (on my
445GNU/Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn sequence
446without a syscall and thus \fIvery\fR fast, but my GNU/Linux system also has
447\&\f(CW\*(C`pthread_atfork\*(C'\fR which is even faster).
448.Sp
449The big advantage of this flag is that you can forget about fork (and
450forget about forgetting to tell libev about forking) when you use this
451flag.
452.Sp
453This flag setting cannot be overriden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR
454environment variable.
265.ie n .IP """EVMETHOD_SELECT"" (value 1, portable select backend)" 4 455.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
266.el .IP "\f(CWEVMETHOD_SELECT\fR (value 1, portable select backend)" 4 456.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
267.IX Item "EVMETHOD_SELECT (value 1, portable select backend)" 457.IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
268This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as 458This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as
269libev tries to roll its own fd_set with no limits on the number of fds, 459libev tries to roll its own fd_set with no limits on the number of fds,
270but if that fails, expect a fairly low limit on the number of fds when 460but if that fails, expect a fairly low limit on the number of fds when
271using this backend. It doesn't scale too well (O(highest_fd)), but its usually 461using this backend. It doesn't scale too well (O(highest_fd)), but its
272the fastest backend for a low number of fds. 462usually the fastest backend for a low number of (low-numbered :) fds.
463.Sp
464To get good performance out of this backend you need a high amount of
465parallelity (most of the file descriptors should be busy). If you are
466writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many
467connections as possible during one iteration. You might also want to have
468a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of
469readyness notifications you get per iteration.
273.ie n .IP """EVMETHOD_POLL"" (value 2, poll backend, available everywhere except on windows)" 4 470.ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4
274.el .IP "\f(CWEVMETHOD_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4 471.el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4
275.IX Item "EVMETHOD_POLL (value 2, poll backend, available everywhere except on windows)" 472.IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)"
276And this is your standard \fIpoll\fR\|(2) backend. It's more complicated than 473And this is your standard \fIpoll\fR\|(2) backend. It's more complicated
277select, but handles sparse fds better and has no artificial limit on the 474than select, but handles sparse fds better and has no artificial
278number of fds you can use (except it will slow down considerably with a 475limit on the number of fds you can use (except it will slow down
279lot of inactive fds). It scales similarly to select, i.e. O(total_fds). 476considerably with a lot of inactive fds). It scales similarly to select,
477i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for
478performance tips.
280.ie n .IP """EVMETHOD_EPOLL"" (value 4, Linux)" 4 479.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
281.el .IP "\f(CWEVMETHOD_EPOLL\fR (value 4, Linux)" 4 480.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
282.IX Item "EVMETHOD_EPOLL (value 4, Linux)" 481.IX Item "EVBACKEND_EPOLL (value 4, Linux)"
283For few fds, this backend is a bit little slower than poll and select, 482For few fds, this backend is a bit little slower than poll and select,
284but it scales phenomenally better. While poll and select usually scale like 483but it scales phenomenally better. While poll and select usually scale
285O(total_fds) where n is the total number of fds (or the highest fd), epoll scales 484like O(total_fds) where n is the total number of fds (or the highest fd),
286either O(1) or O(active_fds). 485epoll scales either O(1) or O(active_fds). The epoll design has a number
486of shortcomings, such as silently dropping events in some hard-to-detect
487cases and requiring a syscall per fd change, no fork support and bad
488support for dup.
287.Sp 489.Sp
288While stopping and starting an I/O watcher in the same iteration will 490While stopping, setting and starting an I/O watcher in the same iteration
289result in some caching, there is still a syscall per such incident 491will result in some caching, there is still a syscall per such incident
290(because the fd could point to a different file description now), so its 492(because the fd could point to a different file description now), so its
291best to avoid that. Also, \fIdup()\fRed file descriptors might not work very 493best to avoid that. Also, \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors might not work
292well if you register events for both fds. 494very well if you register events for both fds.
495.Sp
496Please note that epoll sometimes generates spurious notifications, so you
497need to use non-blocking I/O or other means to avoid blocking when no data
498(or space) is available.
499.Sp
500Best performance from this backend is achieved by not unregistering all
501watchers for a file descriptor until it has been closed, if possible, i.e.
502keep at least one watcher active per fd at all times.
503.Sp
504While nominally embeddeble in other event loops, this feature is broken in
505all kernel versions tested so far.
293.ie n .IP """EVMETHOD_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4 506.ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4
294.el .IP "\f(CWEVMETHOD_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4 507.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
295.IX Item "EVMETHOD_KQUEUE (value 8, most BSD clones)" 508.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
296Kqueue deserves special mention, as at the time of this writing, it 509Kqueue deserves special mention, as at the time of this writing, it
297was broken on all BSDs except NetBSD (usually it doesn't work with 510was broken on all BSDs except NetBSD (usually it doesn't work reliably
298anything but sockets and pipes, except on Darwin, where of course its 511with anything but sockets and pipes, except on Darwin, where of course
299completely useless). For this reason its not being \*(L"autodetected\*(R" unless 512it's completely useless). For this reason it's not being \*(L"autodetected\*(R"
300you explicitly specify the flags (i.e. you don't use \s-1EVFLAG_AUTO\s0). 513unless you explicitly specify it explicitly in the flags (i.e. using
514\&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a known-to-be-good (\-enough)
515system like NetBSD.
516.Sp
517You still can embed kqueue into a normal poll or select backend and use it
518only for sockets (after having made sure that sockets work with kqueue on
519the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
301.Sp 520.Sp
302It scales in the same way as the epoll backend, but the interface to the 521It scales in the same way as the epoll backend, but the interface to the
303kernel is more efficient (which says nothing about its actual speed, of 522kernel is more efficient (which says nothing about its actual speed, of
304course). While starting and stopping an I/O watcher does not cause an 523course). While stopping, setting and starting an I/O watcher does never
305extra syscall as with epoll, it still adds up to four event changes per 524cause an extra syscall as with \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to
306incident, so its best to avoid that. 525two event changes per incident, support for \f(CW\*(C`fork ()\*(C'\fR is very bad and it
526drops fds silently in similarly hard-to-detect cases.
527.Sp
528This backend usually performs well under most conditions.
529.Sp
530While nominally embeddable in other event loops, this doesn't work
531everywhere, so you might need to test for this. And since it is broken
532almost everywhere, you should only use it when you have a lot of sockets
533(for which it usually works), by embedding it into another event loop
534(e.g. \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR) and using it only for
535sockets.
307.ie n .IP """EVMETHOD_DEVPOLL"" (value 16, Solaris 8)" 4 536.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
308.el .IP "\f(CWEVMETHOD_DEVPOLL\fR (value 16, Solaris 8)" 4 537.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
309.IX Item "EVMETHOD_DEVPOLL (value 16, Solaris 8)" 538.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
310This is not implemented yet (and might never be). 539This is not implemented yet (and might never be, unless you send me an
540implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets
541and is not embeddable, which would limit the usefulness of this backend
542immensely.
311.ie n .IP """EVMETHOD_PORT"" (value 32, Solaris 10)" 4 543.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
312.el .IP "\f(CWEVMETHOD_PORT\fR (value 32, Solaris 10)" 4 544.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
313.IX Item "EVMETHOD_PORT (value 32, Solaris 10)" 545.IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
314This uses the Solaris 10 port mechanism. As with everything on Solaris, 546This uses the Solaris 10 event port mechanism. As with everything on Solaris,
315it's really slow, but it still scales very well (O(active_fds)). 547it's really slow, but it still scales very well (O(active_fds)).
548.Sp
549Please note that solaris event ports can deliver a lot of spurious
550notifications, so you need to use non-blocking I/O or other means to avoid
551blocking when no data (or space) is available.
552.Sp
553While this backend scales well, it requires one system call per active
554file descriptor per loop iteration. For small and medium numbers of file
555descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend
556might perform better.
557.Sp
558On the positive side, ignoring the spurious readyness notifications, this
559backend actually performed to specification in all tests and is fully
560embeddable, which is a rare feat among the OS-specific backends.
316.ie n .IP """EVMETHOD_ALL""" 4 561.ie n .IP """EVBACKEND_ALL""" 4
317.el .IP "\f(CWEVMETHOD_ALL\fR" 4 562.el .IP "\f(CWEVBACKEND_ALL\fR" 4
318.IX Item "EVMETHOD_ALL" 563.IX Item "EVBACKEND_ALL"
319Try all backends (even potentially broken ones). Since this is a mask, you 564Try all backends (even potentially broken ones that wouldn't be tried
320can do stuff like \f(CW\*(C`EVMETHOD_ALL & ~EVMETHOD_KQUEUE\*(C'\fR. 565with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as
566\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR.
567.Sp
568It is definitely not recommended to use this flag.
321.RE 569.RE
322.RS 4 570.RS 4
323.Sp 571.Sp
324If one or more of these are ored into the flags value, then only these 572If one or more of these are ored into the flags value, then only these
325backends will be tried (in the reverse order as given here). If none are 573backends will be tried (in the reverse order as listed here). If none are
326specified, most compiled-in backend will be tried, usually in reverse 574specified, all backends in \f(CW\*(C`ev_recommended_backends ()\*(C'\fR will be tried.
327order of their flag values :) 575.Sp
576The most typical usage is like this:
577.Sp
578.Vb 2
579\& if (!ev_default_loop (0))
580\& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
581.Ve
582.Sp
583Restrict libev to the select and poll backends, and do not allow
584environment settings to be taken into account:
585.Sp
586.Vb 1
587\& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
588.Ve
589.Sp
590Use whatever libev has to offer, but make sure that kqueue is used if
591available (warning, breaks stuff, best use only with your own private
592event loop and only if you know the \s-1OS\s0 supports your types of fds):
593.Sp
594.Vb 1
595\& ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
596.Ve
328.RE 597.RE
329.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4 598.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
330.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)" 599.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
331Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is 600Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is
332always distinct from the default loop. Unlike the default loop, it cannot 601always distinct from the default loop. Unlike the default loop, it cannot
333handle signal and child watchers, and attempts to do so will be greeted by 602handle signal and child watchers, and attempts to do so will be greeted by
334undefined behaviour (or a failed assertion if assertions are enabled). 603undefined behaviour (or a failed assertion if assertions are enabled).
604.Sp
605Note that this function \fIis\fR thread-safe, and the recommended way to use
606libev with threads is indeed to create one loop per thread, and using the
607default loop in the \*(L"main\*(R" or \*(L"initial\*(R" thread.
608.Sp
609Example: Try to create a event loop that uses epoll and nothing else.
610.Sp
611.Vb 3
612\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
613\& if (!epoller)
614\& fatal ("no epoll found here, maybe it hides under your chair");
615.Ve
335.IP "ev_default_destroy ()" 4 616.IP "ev_default_destroy ()" 4
336.IX Item "ev_default_destroy ()" 617.IX Item "ev_default_destroy ()"
337Destroys the default loop again (frees all memory and kernel state 618Destroys the default loop again (frees all memory and kernel state
338etc.). This stops all registered event watchers (by not touching them in 619etc.). None of the active event watchers will be stopped in the normal
339any way whatsoever, although you cannot rely on this :). 620sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your
621responsibility to either stop all watchers cleanly yoursef \fIbefore\fR
622calling this function, or cope with the fact afterwards (which is usually
623the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them
624for example).
625.Sp
626Note that certain global state, such as signal state, will not be freed by
627this function, and related watchers (such as signal and child watchers)
628would need to be stopped manually.
629.Sp
630In general it is not advisable to call this function except in the
631rare occasion where you really need to free e.g. the signal handling
632pipe fds. If you need dynamically allocated loops it is better to use
633\&\f(CW\*(C`ev_loop_new\*(C'\fR and \f(CW\*(C`ev_loop_destroy\*(C'\fR).
340.IP "ev_loop_destroy (loop)" 4 634.IP "ev_loop_destroy (loop)" 4
341.IX Item "ev_loop_destroy (loop)" 635.IX Item "ev_loop_destroy (loop)"
342Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an 636Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an
343earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR. 637earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR.
344.IP "ev_default_fork ()" 4 638.IP "ev_default_fork ()" 4
345.IX Item "ev_default_fork ()" 639.IX Item "ev_default_fork ()"
640This function sets a flag that causes subsequent \f(CW\*(C`ev_loop\*(C'\fR iterations
346This function reinitialises the kernel state for backends that have 641to reinitialise the kernel state for backends that have one. Despite the
347one. Despite the name, you can call it anytime, but it makes most sense 642name, you can call it anytime, but it makes most sense after forking, in
348after forking, in either the parent or child process (or both, but that 643the child process (or both child and parent, but that again makes little
349again makes little sense). 644sense). You \fImust\fR call it in the child before using any of the libev
645functions, and it will only take effect at the next \f(CW\*(C`ev_loop\*(C'\fR iteration.
350.Sp 646.Sp
351You \fImust\fR call this function after forking if and only if you want to 647On the other hand, you only need to call this function in the child
352use the event library in both processes. If you just fork+exec, you don't 648process if and only if you want to use the event library in the child. If
353have to call it. 649you just fork+exec, you don't have to call it at all.
354.Sp 650.Sp
355The function itself is quite fast and it's usually not a problem to call 651The function itself is quite fast and it's usually not a problem to call
356it just in case after a fork. To make this easy, the function will fit in 652it just in case after a fork. To make this easy, the function will fit in
357quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR: 653quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR:
358.Sp 654.Sp
… …
362.IP "ev_loop_fork (loop)" 4 658.IP "ev_loop_fork (loop)" 4
363.IX Item "ev_loop_fork (loop)" 659.IX Item "ev_loop_fork (loop)"
364Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by 660Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by
365\&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop 661\&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop
366after fork, and how you do this is entirely your own problem. 662after fork, and how you do this is entirely your own problem.
663.IP "int ev_is_default_loop (loop)" 4
664.IX Item "int ev_is_default_loop (loop)"
665Returns true when the given loop actually is the default loop, false otherwise.
666.IP "unsigned int ev_loop_count (loop)" 4
667.IX Item "unsigned int ev_loop_count (loop)"
668Returns the count of loop iterations for the loop, which is identical to
669the number of times libev did poll for new events. It starts at \f(CW0\fR and
670happily wraps around with enough iterations.
671.Sp
672This value can sometimes be useful as a generation counter of sorts (it
673\&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with
674\&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls.
367.IP "unsigned int ev_method (loop)" 4 675.IP "unsigned int ev_backend (loop)" 4
368.IX Item "unsigned int ev_method (loop)" 676.IX Item "unsigned int ev_backend (loop)"
369Returns one of the \f(CW\*(C`EVMETHOD_*\*(C'\fR flags indicating the event backend in 677Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
370use. 678use.
371.IP "ev_tstamp ev_now (loop)" 4 679.IP "ev_tstamp ev_now (loop)" 4
372.IX Item "ev_tstamp ev_now (loop)" 680.IX Item "ev_tstamp ev_now (loop)"
373Returns the current \*(L"event loop time\*(R", which is the time the event loop 681Returns the current \*(L"event loop time\*(R", which is the time the event loop
374got events and started processing them. This timestamp does not change 682received events and started processing them. This timestamp does not
375as long as callbacks are being processed, and this is also the base time 683change as long as callbacks are being processed, and this is also the base
376used for relative timers. You can treat it as the timestamp of the event 684time used for relative timers. You can treat it as the timestamp of the
377occuring (or more correctly, the mainloop finding out about it). 685event occurring (or more correctly, libev finding out about it).
378.IP "ev_loop (loop, int flags)" 4 686.IP "ev_loop (loop, int flags)" 4
379.IX Item "ev_loop (loop, int flags)" 687.IX Item "ev_loop (loop, int flags)"
380Finally, this is it, the event handler. This function usually is called 688Finally, this is it, the event handler. This function usually is called
381after you initialised all your watchers and you want to start handling 689after you initialised all your watchers and you want to start handling
382events. 690events.
383.Sp 691.Sp
384If the flags argument is specified as 0, it will not return until either 692If the flags argument is specified as \f(CW0\fR, it will not return until
385no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called. 693either no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called.
694.Sp
695Please note that an explicit \f(CW\*(C`ev_unloop\*(C'\fR is usually better than
696relying on all watchers to be stopped when deciding when a program has
697finished (especially in interactive programs), but having a program that
698automatically loops as long as it has to and no longer by virtue of
699relying on its watchers stopping correctly is a thing of beauty.
386.Sp 700.Sp
387A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle 701A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle
388those events and any outstanding ones, but will not block your process in 702those events and any outstanding ones, but will not block your process in
389case there are no events and will return after one iteration of the loop. 703case there are no events and will return after one iteration of the loop.
390.Sp 704.Sp
391A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if 705A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if
392neccessary) and will handle those and any outstanding ones. It will block 706neccessary) and will handle those and any outstanding ones. It will block
393your process until at least one new event arrives, and will return after 707your process until at least one new event arrives, and will return after
394one iteration of the loop. 708one iteration of the loop. This is useful if you are waiting for some
709external event in conjunction with something not expressible using other
710libev watchers. However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is
711usually a better approach for this kind of thing.
395.Sp 712.Sp
396This flags value could be used to implement alternative looping
397constructs, but the \f(CW\*(C`prepare\*(C'\fR and \f(CW\*(C`check\*(C'\fR watchers provide a better and
398more generic mechanism.
399.Sp
400Here are the gory details of what ev_loop does: 713Here are the gory details of what \f(CW\*(C`ev_loop\*(C'\fR does:
401.Sp 714.Sp
402.Vb 15 715.Vb 10
403\& 1. If there are no active watchers (reference count is zero), return. 716\& \- Before the first iteration, call any pending watchers.
717\& * If EVFLAG_FORKCHECK was used, check for a fork.
718\& \- If a fork was detected, queue and call all fork watchers.
404\& 2. Queue and immediately call all prepare watchers. 719\& \- Queue and call all prepare watchers.
405\& 3. If we have been forked, recreate the kernel state. 720\& \- If we have been forked, recreate the kernel state.
406\& 4. Update the kernel state with all outstanding changes. 721\& \- Update the kernel state with all outstanding changes.
407\& 5. Update the "event loop time". 722\& \- Update the "event loop time".
408\& 6. Calculate for how long to block. 723\& \- Calculate for how long to sleep or block, if at all
724\& (active idle watchers, EVLOOP_NONBLOCK or not having
725\& any active watchers at all will result in not sleeping).
726\& \- Sleep if the I/O and timer collect interval say so.
409\& 7. Block the process, waiting for events. 727\& \- Block the process, waiting for any events.
728\& \- Queue all outstanding I/O (fd) events.
410\& 8. Update the "event loop time" and do time jump handling. 729\& \- Update the "event loop time" and do time jump handling.
411\& 9. Queue all outstanding timers. 730\& \- Queue all outstanding timers.
412\& 10. Queue all outstanding periodics. 731\& \- Queue all outstanding periodics.
413\& 11. If no events are pending now, queue all idle watchers. 732\& \- If no events are pending now, queue all idle watchers.
414\& 12. Queue all check watchers. 733\& \- Queue all check watchers.
415\& 13. Call all queued watchers in reverse order (i.e. check watchers first). 734\& \- Call all queued watchers in reverse order (i.e. check watchers first).
735\& Signals and child watchers are implemented as I/O watchers, and will
736\& be handled here by queueing them when their watcher gets executed.
416\& 14. If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK 737\& \- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
417\& was used, return, otherwise continue with step #1. 738\& were used, or there are no active watchers, return, otherwise
739\& continue with step *.
740.Ve
741.Sp
742Example: Queue some jobs and then loop until no events are outstanding
743anymore.
744.Sp
745.Vb 4
746\& ... queue jobs here, make sure they register event watchers as long
747\& ... as they still have work to do (even an idle watcher will do..)
748\& ev_loop (my_loop, 0);
749\& ... jobs done. yeah!
418.Ve 750.Ve
419.IP "ev_unloop (loop, how)" 4 751.IP "ev_unloop (loop, how)" 4
420.IX Item "ev_unloop (loop, how)" 752.IX Item "ev_unloop (loop, how)"
421Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it 753Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it
422has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either 754has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
423\&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or 755\&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or
424\&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return. 756\&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return.
757.Sp
758This \*(L"unloop state\*(R" will be cleared when entering \f(CW\*(C`ev_loop\*(C'\fR again.
425.IP "ev_ref (loop)" 4 759.IP "ev_ref (loop)" 4
426.IX Item "ev_ref (loop)" 760.IX Item "ev_ref (loop)"
427.PD 0 761.PD 0
428.IP "ev_unref (loop)" 4 762.IP "ev_unref (loop)" 4
429.IX Item "ev_unref (loop)" 763.IX Item "ev_unref (loop)"
… …
435returning, \fIev_unref()\fR after starting, and \fIev_ref()\fR before stopping it. For 769returning, \fIev_unref()\fR after starting, and \fIev_ref()\fR before stopping it. For
436example, libev itself uses this for its internal signal pipe: It is not 770example, libev itself uses this for its internal signal pipe: It is not
437visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from exiting if 771visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from exiting if
438no event watchers registered by it are active. It is also an excellent 772no event watchers registered by it are active. It is also an excellent
439way to do this for generic recurring timers or from within third-party 773way to do this for generic recurring timers or from within third-party
440libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR. 774libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR
775(but only if the watcher wasn't active before, or was active before,
776respectively).
777.Sp
778Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_loop\*(C'\fR
779running when nothing else is active.
780.Sp
781.Vb 4
782\& struct ev_signal exitsig;
783\& ev_signal_init (&exitsig, sig_cb, SIGINT);
784\& ev_signal_start (loop, &exitsig);
785\& evf_unref (loop);
786.Ve
787.Sp
788Example: For some weird reason, unregister the above signal handler again.
789.Sp
790.Vb 2
791\& ev_ref (loop);
792\& ev_signal_stop (loop, &exitsig);
793.Ve
794.IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4
795.IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"
796.PD 0
797.IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4
798.IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"
799.PD
800These advanced functions influence the time that libev will spend waiting
801for events. Both are by default \f(CW0\fR, meaning that libev will try to
802invoke timer/periodic callbacks and I/O callbacks with minimum latency.
803.Sp
804Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR)
805allows libev to delay invocation of I/O and timer/periodic callbacks to
806increase efficiency of loop iterations.
807.Sp
808The background is that sometimes your program runs just fast enough to
809handle one (or very few) event(s) per loop iteration. While this makes
810the program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new
811events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high
812overhead for the actual polling but can deliver many events at once.
813.Sp
814By setting a higher \fIio collect interval\fR you allow libev to spend more
815time collecting I/O events, so you can handle more events per iteration,
816at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and
817\&\f(CW\*(C`ev_timer\*(C'\fR) will be not affected. Setting this to a non-null value will
818introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations.
819.Sp
820Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
821to spend more time collecting timeouts, at the expense of increased
822latency (the watcher callback will be called later). \f(CW\*(C`ev_io\*(C'\fR watchers
823will not be affected. Setting this to a non-null value will not introduce
824any overhead in libev.
825.Sp
826Many (busy) programs can usually benefit by setting the io collect
827interval to a value near \f(CW0.1\fR or so, which is often enough for
828interactive servers (of course not for games), likewise for timeouts. It
829usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR,
830as this approsaches the timing granularity of most systems.
441.SH "ANATOMY OF A WATCHER" 831.SH "ANATOMY OF A WATCHER"
442.IX Header "ANATOMY OF A WATCHER" 832.IX Header "ANATOMY OF A WATCHER"
443A watcher is a structure that you create and register to record your 833A watcher is a structure that you create and register to record your
444interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to 834interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to
445become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that: 835become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that:
… …
448\& static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) 838\& static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
449\& { 839\& {
450\& ev_io_stop (w); 840\& ev_io_stop (w);
451\& ev_unloop (loop, EVUNLOOP_ALL); 841\& ev_unloop (loop, EVUNLOOP_ALL);
452\& } 842\& }
453.Ve 843\&
454.PP
455.Vb 6
456\& struct ev_loop *loop = ev_default_loop (0); 844\& struct ev_loop *loop = ev_default_loop (0);
457\& struct ev_io stdin_watcher; 845\& struct ev_io stdin_watcher;
458\& ev_init (&stdin_watcher, my_cb); 846\& ev_init (&stdin_watcher, my_cb);
459\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); 847\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
460\& ev_io_start (loop, &stdin_watcher); 848\& ev_io_start (loop, &stdin_watcher);
… …
481*)\*(C'\fR), and you can stop watching for events at any time by calling the 869*)\*(C'\fR), and you can stop watching for events at any time by calling the
482corresponding stop function (\f(CW\*(C`ev_<type>_stop (loop, watcher *)\*(C'\fR. 870corresponding stop function (\f(CW\*(C`ev_<type>_stop (loop, watcher *)\*(C'\fR.
483.PP 871.PP
484As long as your watcher is active (has been started but not stopped) you 872As long as your watcher is active (has been started but not stopped) you
485must not touch the values stored in it. Most specifically you must never 873must not touch the values stored in it. Most specifically you must never
486reinitialise it or call its set method. 874reinitialise it or call its \f(CW\*(C`set\*(C'\fR macro.
487.PP
488You can check whether an event is active by calling the \f(CW\*(C`ev_is_active
489(watcher *)\*(C'\fR macro. To see whether an event is outstanding (but the
490callback for it has not been called yet) you can use the \f(CW\*(C`ev_is_pending
491(watcher *)\*(C'\fR macro.
492.PP 875.PP
493Each and every callback receives the event loop pointer as first, the 876Each and every callback receives the event loop pointer as first, the
494registered watcher structure as second, and a bitset of received events as 877registered watcher structure as second, and a bitset of received events as
495third argument. 878third argument.
496.PP 879.PP
… …
521The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread. 904The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread.
522.ie n .IP """EV_CHILD""" 4 905.ie n .IP """EV_CHILD""" 4
523.el .IP "\f(CWEV_CHILD\fR" 4 906.el .IP "\f(CWEV_CHILD\fR" 4
524.IX Item "EV_CHILD" 907.IX Item "EV_CHILD"
525The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change. 908The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change.
909.ie n .IP """EV_STAT""" 4
910.el .IP "\f(CWEV_STAT\fR" 4
911.IX Item "EV_STAT"
912The path specified in the \f(CW\*(C`ev_stat\*(C'\fR watcher changed its attributes somehow.
526.ie n .IP """EV_IDLE""" 4 913.ie n .IP """EV_IDLE""" 4
527.el .IP "\f(CWEV_IDLE\fR" 4 914.el .IP "\f(CWEV_IDLE\fR" 4
528.IX Item "EV_IDLE" 915.IX Item "EV_IDLE"
529The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do. 916The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do.
530.ie n .IP """EV_PREPARE""" 4 917.ie n .IP """EV_PREPARE""" 4
… …
540\&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any 927\&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any
541received events. Callbacks of both watcher types can start and stop as 928received events. Callbacks of both watcher types can start and stop as
542many watchers as they want, and all of them will be taken into account 929many watchers as they want, and all of them will be taken into account
543(for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep 930(for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep
544\&\f(CW\*(C`ev_loop\*(C'\fR from blocking). 931\&\f(CW\*(C`ev_loop\*(C'\fR from blocking).
932.ie n .IP """EV_EMBED""" 4
933.el .IP "\f(CWEV_EMBED\fR" 4
934.IX Item "EV_EMBED"
935The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.
936.ie n .IP """EV_FORK""" 4
937.el .IP "\f(CWEV_FORK\fR" 4
938.IX Item "EV_FORK"
939The event loop has been resumed in the child process after fork (see
940\&\f(CW\*(C`ev_fork\*(C'\fR).
941.ie n .IP """EV_ASYNC""" 4
942.el .IP "\f(CWEV_ASYNC\fR" 4
943.IX Item "EV_ASYNC"
944The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR).
545.ie n .IP """EV_ERROR""" 4 945.ie n .IP """EV_ERROR""" 4
546.el .IP "\f(CWEV_ERROR\fR" 4 946.el .IP "\f(CWEV_ERROR\fR" 4
547.IX Item "EV_ERROR" 947.IX Item "EV_ERROR"
548An unspecified error has occured, the watcher has been stopped. This might 948An unspecified error has occured, the watcher has been stopped. This might
549happen because the watcher could not be properly started because libev 949happen because the watcher could not be properly started because libev
… …
554Libev will usually signal a few \*(L"dummy\*(R" events together with an error, 954Libev will usually signal a few \*(L"dummy\*(R" events together with an error,
555for example it might indicate that a fd is readable or writable, and if 955for example it might indicate that a fd is readable or writable, and if
556your callbacks is well-written it can just attempt the operation and cope 956your callbacks is well-written it can just attempt the operation and cope
557with the error from \fIread()\fR or \fIwrite()\fR. This will not work in multithreaded 957with the error from \fIread()\fR or \fIwrite()\fR. This will not work in multithreaded
558programs, though, so beware. 958programs, though, so beware.
959.Sh "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0"
960.IX Subsection "GENERIC WATCHER FUNCTIONS"
961In the following description, \f(CW\*(C`TYPE\*(C'\fR stands for the watcher type,
962e.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.
963.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
964.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
965.IX Item "ev_init (ev_TYPE *watcher, callback)"
966This macro initialises the generic portion of a watcher. The contents
967of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
968the generic parts of the watcher are initialised, you \fIneed\fR to call
969the type-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR macro afterwards to initialise the
970type-specific parts. For each type there is also a \f(CW\*(C`ev_TYPE_init\*(C'\fR macro
971which rolls both calls into one.
972.Sp
973You can reinitialise a watcher at any time as long as it has been stopped
974(or never started) and there are no pending events outstanding.
975.Sp
976The callback is always of type \f(CW\*(C`void (*)(ev_loop *loop, ev_TYPE *watcher,
977int revents)\*(C'\fR.
978.ie n .IP """ev_TYPE_set"" (ev_TYPE *, [args])" 4
979.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *, [args])" 4
980.IX Item "ev_TYPE_set (ev_TYPE *, [args])"
981This macro initialises the type-specific parts of a watcher. You need to
982call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
983call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
984macro on a watcher that is active (it can be pending, however, which is a
985difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
986.Sp
987Although some watcher types do not have type-specific arguments
988(e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
989.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
990.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
991.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
992This convinience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
993calls into a single call. This is the most convinient method to initialise
994a watcher. The same limitations apply, of course.
995.ie n .IP """ev_TYPE_start"" (loop *, ev_TYPE *watcher)" 4
996.el .IP "\f(CWev_TYPE_start\fR (loop *, ev_TYPE *watcher)" 4
997.IX Item "ev_TYPE_start (loop *, ev_TYPE *watcher)"
998Starts (activates) the given watcher. Only active watchers will receive
999events. If the watcher is already active nothing will happen.
1000.ie n .IP """ev_TYPE_stop"" (loop *, ev_TYPE *watcher)" 4
1001.el .IP "\f(CWev_TYPE_stop\fR (loop *, ev_TYPE *watcher)" 4
1002.IX Item "ev_TYPE_stop (loop *, ev_TYPE *watcher)"
1003Stops the given watcher again (if active) and clears the pending
1004status. It is possible that stopped watchers are pending (for example,
1005non-repeating timers are being stopped when they become pending), but
1006\&\f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor pending. If
1007you want to free or reuse the memory used by the watcher it is therefore a
1008good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
1009.IP "bool ev_is_active (ev_TYPE *watcher)" 4
1010.IX Item "bool ev_is_active (ev_TYPE *watcher)"
1011Returns a true value iff the watcher is active (i.e. it has been started
1012and not yet been stopped). As long as a watcher is active you must not modify
1013it.
1014.IP "bool ev_is_pending (ev_TYPE *watcher)" 4
1015.IX Item "bool ev_is_pending (ev_TYPE *watcher)"
1016Returns a true value iff the watcher is pending, (i.e. it has outstanding
1017events but its callback has not yet been invoked). As long as a watcher
1018is pending (but not active) you must not call an init function on it (but
1019\&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe), you must not change its priority, and you must
1020make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR
1021it).
1022.IP "callback ev_cb (ev_TYPE *watcher)" 4
1023.IX Item "callback ev_cb (ev_TYPE *watcher)"
1024Returns the callback currently set on the watcher.
1025.IP "ev_cb_set (ev_TYPE *watcher, callback)" 4
1026.IX Item "ev_cb_set (ev_TYPE *watcher, callback)"
1027Change the callback. You can change the callback at virtually any time
1028(modulo threads).
1029.IP "ev_set_priority (ev_TYPE *watcher, priority)" 4
1030.IX Item "ev_set_priority (ev_TYPE *watcher, priority)"
1031.PD 0
1032.IP "int ev_priority (ev_TYPE *watcher)" 4
1033.IX Item "int ev_priority (ev_TYPE *watcher)"
1034.PD
1035Set and query the priority of the watcher. The priority is a small
1036integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR
1037(default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked
1038before watchers with lower priority, but priority will not keep watchers
1039from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
1040.Sp
1041This means that priorities are \fIonly\fR used for ordering callback
1042invocation after new events have been received. This is useful, for
1043example, to reduce latency after idling, or more often, to bind two
1044watchers on the same event and make sure one is called first.
1045.Sp
1046If you need to suppress invocation when higher priority events are pending
1047you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
1048.Sp
1049You \fImust not\fR change the priority of a watcher as long as it is active or
1050pending.
1051.Sp
1052The default priority used by watchers when no priority has been set is
1053always \f(CW0\fR, which is supposed to not be too high and not be too low :).
1054.Sp
1055Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
1056fine, as long as you do not mind that the priority value you query might
1057or might not have been adjusted to be within valid range.
1058.IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
1059.IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
1060Invoke the \f(CW\*(C`watcher\*(C'\fR with the given \f(CW\*(C`loop\*(C'\fR and \f(CW\*(C`revents\*(C'\fR. Neither
1061\&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback
1062can deal with that fact.
1063.IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
1064.IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
1065If the watcher is pending, this function returns clears its pending status
1066and returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the
1067watcher isn't pending it does nothing and returns \f(CW0\fR.
559.Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0" 1068.Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0"
560.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER" 1069.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
561Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change 1070Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change
562and read at any time, libev will completely ignore it. This can be used 1071and read at any time, libev will completely ignore it. This can be used
563to associate arbitrary data with your watcher. If you need more data and 1072to associate arbitrary data with your watcher. If you need more data and
… …
584\& struct my_io *w = (struct my_io *)w_; 1093\& struct my_io *w = (struct my_io *)w_;
585\& ... 1094\& ...
586\& } 1095\& }
587.Ve 1096.Ve
588.PP 1097.PP
589More interesting and less C\-conformant ways of catsing your callback type 1098More interesting and less C\-conformant ways of casting your callback type
590have been omitted.... 1099instead have been omitted.
1100.PP
1101Another common scenario is having some data structure with multiple
1102watchers:
1103.PP
1104.Vb 6
1105\& struct my_biggy
1106\& {
1107\& int some_data;
1108\& ev_timer t1;
1109\& ev_timer t2;
1110\& }
1111.Ve
1112.PP
1113In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more complicated,
1114you need to use \f(CW\*(C`offsetof\*(C'\fR:
1115.PP
1116.Vb 1
1117\& #include <stddef.h>
1118\&
1119\& static void
1120\& t1_cb (EV_P_ struct ev_timer *w, int revents)
1121\& {
1122\& struct my_biggy big = (struct my_biggy *
1123\& (((char *)w) \- offsetof (struct my_biggy, t1));
1124\& }
1125\&
1126\& static void
1127\& t2_cb (EV_P_ struct ev_timer *w, int revents)
1128\& {
1129\& struct my_biggy big = (struct my_biggy *
1130\& (((char *)w) \- offsetof (struct my_biggy, t2));
1131\& }
1132.Ve
591.SH "WATCHER TYPES" 1133.SH "WATCHER TYPES"
592.IX Header "WATCHER TYPES" 1134.IX Header "WATCHER TYPES"
593This section describes each watcher in detail, but will not repeat 1135This section describes each watcher in detail, but will not repeat
594information given in the last section. 1136information given in the last section. Any initialisation/set macros,
1137functions and members specific to the watcher type are explained.
1138.PP
1139Members are additionally marked with either \fI[read\-only]\fR, meaning that,
1140while the watcher is active, you can look at the member and expect some
1141sensible content, but you must not modify it (you can modify it while the
1142watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
1143means you can expect it to have some sensible content while the watcher
1144is active, but you can also modify it. Modifying it may not do something
1145sensible or take immediate effect (or do anything at all), but libev will
1146not crash or malfunction in any way.
595.ie n .Sh """ev_io"" \- is this file descriptor readable or writable" 1147.ie n .Sh """ev_io"" \- is this file descriptor readable or writable?"
596.el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable" 1148.el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable?"
597.IX Subsection "ev_io - is this file descriptor readable or writable" 1149.IX Subsection "ev_io - is this file descriptor readable or writable?"
598I/O watchers check whether a file descriptor is readable or writable 1150I/O watchers check whether a file descriptor is readable or writable
599in each iteration of the event loop (This behaviour is called 1151in each iteration of the event loop, or, more precisely, when reading
600level-triggering because you keep receiving events as long as the 1152would not block the process and writing would at least be able to write
601condition persists. Remember you can stop the watcher if you don't want to 1153some data. This behaviour is called level-triggering because you keep
602act on the event and neither want to receive future events). 1154receiving events as long as the condition persists. Remember you can stop
1155the watcher if you don't want to act on the event and neither want to
1156receive future events.
603.PP 1157.PP
604In general you can register as many read and/or write event watchers per 1158In general you can register as many read and/or write event watchers per
605fd as you want (as long as you don't confuse yourself). Setting all file 1159fd as you want (as long as you don't confuse yourself). Setting all file
606descriptors to non-blocking mode is also usually a good idea (but not 1160descriptors to non-blocking mode is also usually a good idea (but not
607required if you know what you are doing). 1161required if you know what you are doing).
608.PP 1162.PP
609You have to be careful with dup'ed file descriptors, though. Some backends
610(the linux epoll backend is a notable example) cannot handle dup'ed file
611descriptors correctly if you register interest in two or more fds pointing
612to the same underlying file/socket etc. description (that is, they share
613the same underlying \*(L"file open\*(R").
614.PP
615If you must do this, then force the use of a known-to-be-good backend 1163If you must do this, then force the use of a known-to-be-good backend
616(at the time of this writing, this includes only \s-1EVMETHOD_SELECT\s0 and 1164(at the time of this writing, this includes only \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and
617\&\s-1EVMETHOD_POLL\s0). 1165\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR).
1166.PP
1167Another thing you have to watch out for is that it is quite easy to
1168receive \*(L"spurious\*(R" readyness notifications, that is your callback might
1169be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block
1170because there is no data. Not only are some backends known to create a
1171lot of those (for example solaris ports), it is very easy to get into
1172this situation even with a relatively standard program structure. Thus
1173it is best to always use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning
1174\&\f(CW\*(C`EAGAIN\*(C'\fR is far preferable to a program hanging until some data arrives.
1175.PP
1176If you cannot run the fd in non-blocking mode (for example you should not
1177play around with an Xlib connection), then you have to seperately re-test
1178whether a file descriptor is really ready with a known-to-be good interface
1179such as poll (fortunately in our Xlib example, Xlib already does this on
1180its own, so its quite safe to use).
1181.PP
1182\fIThe special problem of disappearing file descriptors\fR
1183.IX Subsection "The special problem of disappearing file descriptors"
1184.PP
1185Some backends (e.g. kqueue, epoll) need to be told about closing a file
1186descriptor (either by calling \f(CW\*(C`close\*(C'\fR explicitly or by any other means,
1187such as \f(CW\*(C`dup\*(C'\fR). The reason is that you register interest in some file
1188descriptor, but when it goes away, the operating system will silently drop
1189this interest. If another file descriptor with the same number then is
1190registered with libev, there is no efficient way to see that this is, in
1191fact, a different file descriptor.
1192.PP
1193To avoid having to explicitly tell libev about such cases, libev follows
1194the following policy: Each time \f(CW\*(C`ev_io_set\*(C'\fR is being called, libev
1195will assume that this is potentially a new file descriptor, otherwise
1196it is assumed that the file descriptor stays the same. That means that
1197you \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
1198descriptor even if the file descriptor number itself did not change.
1199.PP
1200This is how one would do it normally anyway, the important point is that
1201the libev application should not optimise around libev but should leave
1202optimisations to libev.
1203.PP
1204\fIThe special problem of dup'ed file descriptors\fR
1205.IX Subsection "The special problem of dup'ed file descriptors"
1206.PP
1207Some backends (e.g. epoll), cannot register events for file descriptors,
1208but only events for the underlying file descriptions. That means when you
1209have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register
1210events for them, only one file descriptor might actually receive events.
1211.PP
1212There is no workaround possible except not registering events
1213for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
1214\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1215.PP
1216\fIThe special problem of fork\fR
1217.IX Subsection "The special problem of fork"
1218.PP
1219Some backends (epoll, kqueue) do not support \f(CW\*(C`fork ()\*(C'\fR at all or exhibit
1220useless behaviour. Libev fully supports fork, but needs to be told about
1221it in the child.
1222.PP
1223To support fork in your programs, you either have to call
1224\&\f(CW\*(C`ev_default_fork ()\*(C'\fR or \f(CW\*(C`ev_loop_fork ()\*(C'\fR after a fork in the child,
1225enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or
1226\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1227.PP
1228\fIThe special problem of \s-1SIGPIPE\s0\fR
1229.IX Subsection "The special problem of SIGPIPE"
1230.PP
1231While not really specific to libev, it is easy to forget about \s-1SIGPIPE:\s0
1232when reading from a pipe whose other end has been closed, your program
1233gets send a \s-1SIGPIPE\s0, which, by default, aborts your program. For most
1234programs this is sensible behaviour, for daemons, this is usually
1235undesirable.
1236.PP
1237So when you encounter spurious, unexplained daemon exits, make sure you
1238ignore \s-1SIGPIPE\s0 (and maybe make sure you log the exit status of your daemon
1239somewhere, as that would have given you a big clue).
1240.PP
1241\fIWatcher-Specific Functions\fR
1242.IX Subsection "Watcher-Specific Functions"
618.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4 1243.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
619.IX Item "ev_io_init (ev_io *, callback, int fd, int events)" 1244.IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
620.PD 0 1245.PD 0
621.IP "ev_io_set (ev_io *, int fd, int events)" 4 1246.IP "ev_io_set (ev_io *, int fd, int events)" 4
622.IX Item "ev_io_set (ev_io *, int fd, int events)" 1247.IX Item "ev_io_set (ev_io *, int fd, int events)"
623.PD 1248.PD
624Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The fd is the file descriptor to rceeive 1249Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to
625events 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 | 1250rceeive events for and events is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or
626EV_WRITE\*(C'\fR to receive the given events. 1251\&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR to receive the given events.
1252.IP "int fd [read\-only]" 4
1253.IX Item "int fd [read-only]"
1254The file descriptor being watched.
1255.IP "int events [read\-only]" 4
1256.IX Item "int events [read-only]"
1257The events being watched.
1258.PP
1259\fIExamples\fR
1260.IX Subsection "Examples"
1261.PP
1262Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
1263readable, but only once. Since it is likely line-buffered, you could
1264attempt to read a whole line in the callback.
1265.PP
1266.Vb 6
1267\& static void
1268\& stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
1269\& {
1270\& ev_io_stop (loop, w);
1271\& .. read from stdin here (or from w\->fd) and haqndle any I/O errors
1272\& }
1273\&
1274\& ...
1275\& struct ev_loop *loop = ev_default_init (0);
1276\& struct ev_io stdin_readable;
1277\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1278\& ev_io_start (loop, &stdin_readable);
1279\& ev_loop (loop, 0);
1280.Ve
627.ie n .Sh """ev_timer"" \- relative and optionally recurring timeouts" 1281.ie n .Sh """ev_timer"" \- relative and optionally repeating timeouts"
628.el .Sh "\f(CWev_timer\fP \- relative and optionally recurring timeouts" 1282.el .Sh "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
629.IX Subsection "ev_timer - relative and optionally recurring timeouts" 1283.IX Subsection "ev_timer - relative and optionally repeating timeouts"
630Timer watchers are simple relative timers that generate an event after a 1284Timer watchers are simple relative timers that generate an event after a
631given time, and optionally repeating in regular intervals after that. 1285given time, and optionally repeating in regular intervals after that.
632.PP 1286.PP
633The timers are based on real time, that is, if you register an event that 1287The timers are based on real time, that is, if you register an event that
634times out after an hour and you reset your system clock to last years 1288times out after an hour and you reset your system clock to last years
… …
641of the event triggering whatever timeout you are modifying/starting. If 1295of the event triggering whatever timeout you are modifying/starting. If
642you suspect event processing to be delayed and you \fIneed\fR to base the timeout 1296you suspect event processing to be delayed and you \fIneed\fR to base the timeout
643on the current time, use something like this to adjust for this: 1297on the current time, use something like this to adjust for this:
644.PP 1298.PP
645.Vb 1 1299.Vb 1
646\& ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); 1300\& ev_timer_set (&timer, after + ev_now () \- ev_time (), 0.);
647.Ve 1301.Ve
648.PP 1302.PP
649The callback is guarenteed to be invoked only when its timeout has passed, 1303The callback is guarenteed to be invoked only when its timeout has passed,
650but if multiple timers become ready during the same loop iteration then 1304but if multiple timers become ready during the same loop iteration then
651order of execution is undefined. 1305order of execution is undefined.
1306.PP
1307\fIWatcher-Specific Functions and Data Members\fR
1308.IX Subsection "Watcher-Specific Functions and Data Members"
652.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4 1309.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
653.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 1310.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
654.PD 0 1311.PD 0
655.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4 1312.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
656.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 1313.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
… …
663The timer itself will do a best-effort at avoiding drift, that is, if you 1320The timer itself will do a best-effort at avoiding drift, that is, if you
664configure a timer to trigger every 10 seconds, then it will trigger at 1321configure a timer to trigger every 10 seconds, then it will trigger at
665exactly 10 second intervals. If, however, your program cannot keep up with 1322exactly 10 second intervals. If, however, your program cannot keep up with
666the timer (because it takes longer than those 10 seconds to do stuff) the 1323the timer (because it takes longer than those 10 seconds to do stuff) the
667timer will not fire more than once per event loop iteration. 1324timer will not fire more than once per event loop iteration.
668.IP "ev_timer_again (loop)" 4 1325.IP "ev_timer_again (loop, ev_timer *)" 4
669.IX Item "ev_timer_again (loop)" 1326.IX Item "ev_timer_again (loop, ev_timer *)"
670This will act as if the timer timed out and restart it again if it is 1327This will act as if the timer timed out and restart it again if it is
671repeating. The exact semantics are: 1328repeating. The exact semantics are:
672.Sp 1329.Sp
1330If the timer is pending, its pending status is cleared.
1331.Sp
673If the timer is started but nonrepeating, stop it. 1332If the timer is started but nonrepeating, stop it (as if it timed out).
674.Sp 1333.Sp
675If the timer is repeating, either start it if necessary (with the repeat 1334If the timer is repeating, either start it if necessary (with the
676value), or reset the running timer to the repeat value. 1335\&\f(CW\*(C`repeat\*(C'\fR value), or reset the running timer to the \f(CW\*(C`repeat\*(C'\fR value.
677.Sp 1336.Sp
678This sounds a bit complicated, but here is a useful and typical 1337This sounds a bit complicated, but here is a useful and typical
679example: Imagine you have a tcp connection and you want a so-called idle 1338example: Imagine you have a tcp connection and you want a so-called idle
680timeout, that is, you want to be called when there have been, say, 60 1339timeout, that is, you want to be called when there have been, say, 60
681seconds of inactivity on the socket. The easiest way to do this is to 1340seconds of inactivity on the socket. The easiest way to do this is to
682configure an \f(CW\*(C`ev_timer\*(C'\fR with after=repeat=60 and calling ev_timer_again each 1341configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value of \f(CW60\fR and then call
683time you successfully read or write some data. If you go into an idle 1342\&\f(CW\*(C`ev_timer_again\*(C'\fR each time you successfully read or write some data. If
684state where you do not expect data to travel on the socket, you can stop 1343you go into an idle state where you do not expect data to travel on the
685the timer, and again will automatically restart it if need be. 1344socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will
1345automatically restart it if need be.
1346.Sp
1347That means you can ignore the \f(CW\*(C`after\*(C'\fR value and \f(CW\*(C`ev_timer_start\*(C'\fR
1348altogether and only ever use the \f(CW\*(C`repeat\*(C'\fR value and \f(CW\*(C`ev_timer_again\*(C'\fR:
1349.Sp
1350.Vb 8
1351\& ev_timer_init (timer, callback, 0., 5.);
1352\& ev_timer_again (loop, timer);
1353\& ...
1354\& timer\->again = 17.;
1355\& ev_timer_again (loop, timer);
1356\& ...
1357\& timer\->again = 10.;
1358\& ev_timer_again (loop, timer);
1359.Ve
1360.Sp
1361This is more slightly efficient then stopping/starting the timer each time
1362you want to modify its timeout value.
1363.IP "ev_tstamp repeat [read\-write]" 4
1364.IX Item "ev_tstamp repeat [read-write]"
1365The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
1366or \f(CW\*(C`ev_timer_again\*(C'\fR is called and determines the next timeout (if any),
1367which is also when any modifications are taken into account.
1368.PP
1369\fIExamples\fR
1370.IX Subsection "Examples"
1371.PP
1372Example: Create a timer that fires after 60 seconds.
1373.PP
1374.Vb 5
1375\& static void
1376\& one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
1377\& {
1378\& .. one minute over, w is actually stopped right here
1379\& }
1380\&
1381\& struct ev_timer mytimer;
1382\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1383\& ev_timer_start (loop, &mytimer);
1384.Ve
1385.PP
1386Example: Create a timeout timer that times out after 10 seconds of
1387inactivity.
1388.PP
1389.Vb 5
1390\& static void
1391\& timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
1392\& {
1393\& .. ten seconds without any activity
1394\& }
1395\&
1396\& struct ev_timer mytimer;
1397\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1398\& ev_timer_again (&mytimer); /* start timer */
1399\& ev_loop (loop, 0);
1400\&
1401\& // and in some piece of code that gets executed on any "activity":
1402\& // reset the timeout to start ticking again at 10 seconds
1403\& ev_timer_again (&mytimer);
1404.Ve
686.ie n .Sh """ev_periodic"" \- to cron or not to cron" 1405.ie n .Sh """ev_periodic"" \- to cron or not to cron?"
687.el .Sh "\f(CWev_periodic\fP \- to cron or not to cron" 1406.el .Sh "\f(CWev_periodic\fP \- to cron or not to cron?"
688.IX Subsection "ev_periodic - to cron or not to cron" 1407.IX Subsection "ev_periodic - to cron or not to cron?"
689Periodic watchers are also timers of a kind, but they are very versatile 1408Periodic watchers are also timers of a kind, but they are very versatile
690(and unfortunately a bit complex). 1409(and unfortunately a bit complex).
691.PP 1410.PP
692Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time) 1411Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time)
693but on wallclock time (absolute time). You can tell a periodic watcher 1412but on wallclock time (absolute time). You can tell a periodic watcher
694to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a 1413to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a
695periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now () 1414periodic watcher to trigger in 10 seconds (by specifiying e.g. \f(CW\*(C`ev_now ()
696+ 10.>) and then reset your system clock to the last year, then it will 1415+ 10.\*(C'\fR) and then reset your system clock to the last year, then it will
697take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger 1416take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger
698roughly 10 seconds later and of course not if you reset your system time 1417roughly 10 seconds later).
699again).
700.PP 1418.PP
701They can also be used to implement vastly more complex timers, such as 1419They can also be used to implement vastly more complex timers, such as
702triggering an event on eahc midnight, local time. 1420triggering an event on each midnight, local time or other, complicated,
1421rules.
703.PP 1422.PP
704As with timers, the callback is guarenteed to be invoked only when the 1423As with timers, the callback is guarenteed to be invoked only when the
705time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready 1424time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready
706during the same loop iteration then order of execution is undefined. 1425during the same loop iteration then order of execution is undefined.
1426.PP
1427\fIWatcher-Specific Functions and Data Members\fR
1428.IX Subsection "Watcher-Specific Functions and Data Members"
707.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4 1429.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4
708.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 1430.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)"
709.PD 0 1431.PD 0
710.IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4 1432.IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4
711.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 1433.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)"
712.PD 1434.PD
713Lots of arguments, lets sort it out... There are basically three modes of 1435Lots of arguments, lets sort it out... There are basically three modes of
714operation, and we will explain them from simplest to complex: 1436operation, and we will explain them from simplest to complex:
715.RS 4 1437.RS 4
1438.IP "\(bu" 4
716.IP "* absolute timer (interval = reschedule_cb = 0)" 4 1439absolute timer (at = time, interval = reschedule_cb = 0)
717.IX Item "absolute timer (interval = reschedule_cb = 0)" 1440.Sp
718In this configuration the watcher triggers an event at the wallclock time 1441In this configuration the watcher triggers an event at the wallclock time
719\&\f(CW\*(C`at\*(C'\fR and doesn't repeat. It will not adjust when a time jump occurs, 1442\&\f(CW\*(C`at\*(C'\fR and doesn't repeat. It will not adjust when a time jump occurs,
720that is, if it is to be run at January 1st 2011 then it will run when the 1443that is, if it is to be run at January 1st 2011 then it will run when the
721system time reaches or surpasses this time. 1444system time reaches or surpasses this time.
1445.IP "\(bu" 4
722.IP "* non-repeating interval timer (interval > 0, reschedule_cb = 0)" 4 1446repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
723.IX Item "non-repeating interval timer (interval > 0, reschedule_cb = 0)" 1447.Sp
724In this mode the watcher will always be scheduled to time out at the next 1448In this mode the watcher will always be scheduled to time out at the next
725\&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N) and then repeat, regardless 1449\&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N, which can also be negative)
726of any time jumps. 1450and then repeat, regardless of any time jumps.
727.Sp 1451.Sp
728This can be used to create timers that do not drift with respect to system 1452This can be used to create timers that do not drift with respect to system
729time: 1453time:
730.Sp 1454.Sp
731.Vb 1 1455.Vb 1
… …
738by 3600. 1462by 3600.
739.Sp 1463.Sp
740Another way to think about it (for the mathematically inclined) is that 1464Another way to think about it (for the mathematically inclined) is that
741\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible 1465\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
742time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps. 1466time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps.
743.IP "* manual reschedule mode (reschedule_cb = callback)" 4 1467.Sp
744.IX Item "manual reschedule mode (reschedule_cb = callback)" 1468For numerical stability it is preferable that the \f(CW\*(C`at\*(C'\fR value is near
1469\&\f(CW\*(C`ev_now ()\*(C'\fR (the current time), but there is no range requirement for
1470this value.
1471.IP "\(bu" 4
1472manual reschedule mode (at and interval ignored, reschedule_cb = callback)
1473.Sp
745In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being 1474In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being
746ignored. Instead, each time the periodic watcher gets scheduled, the 1475ignored. Instead, each time the periodic watcher gets scheduled, the
747reschedule callback will be called with the watcher as first, and the 1476reschedule callback will be called with the watcher as first, and the
748current time as second argument. 1477current time as second argument.
749.Sp 1478.Sp
750\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, 1479\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher,
751ever, or make any event loop modifications\fR. If you need to stop it, 1480ever, or make any event loop modifications\fR. If you need to stop it,
752return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by 1481return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by
753starting a prepare watcher). 1482starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is legal).
754.Sp 1483.Sp
755Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w, 1484Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w,
756ev_tstamp now)\*(C'\fR, e.g.: 1485ev_tstamp now)\*(C'\fR, e.g.:
757.Sp 1486.Sp
758.Vb 4 1487.Vb 4
… …
782.IX Item "ev_periodic_again (loop, ev_periodic *)" 1511.IX Item "ev_periodic_again (loop, ev_periodic *)"
783Simply stops and restarts the periodic watcher again. This is only useful 1512Simply stops and restarts the periodic watcher again. This is only useful
784when you changed some parameters or the reschedule callback would return 1513when you changed some parameters or the reschedule callback would return
785a different time than the last time it was called (e.g. in a crond like 1514a different time than the last time it was called (e.g. in a crond like
786program when the crontabs have changed). 1515program when the crontabs have changed).
1516.IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4
1517.IX Item "ev_tstamp ev_periodic_at (ev_periodic *)"
1518When active, returns the absolute time that the watcher is supposed to
1519trigger next.
1520.IP "ev_tstamp offset [read\-write]" 4
1521.IX Item "ev_tstamp offset [read-write]"
1522When repeating, this contains the offset value, otherwise this is the
1523absolute point in time (the \f(CW\*(C`at\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR).
1524.Sp
1525Can be modified any time, but changes only take effect when the periodic
1526timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1527.IP "ev_tstamp interval [read\-write]" 4
1528.IX Item "ev_tstamp interval [read-write]"
1529The current interval value. Can be modified any time, but changes only
1530take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
1531called.
1532.IP "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read\-write]" 4
1533.IX Item "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]"
1534The current reschedule callback, or \f(CW0\fR, if this functionality is
1535switched off. Can be changed any time, but changes only take effect when
1536the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1537.PP
1538\fIExamples\fR
1539.IX Subsection "Examples"
1540.PP
1541Example: Call a callback every hour, or, more precisely, whenever the
1542system clock is divisible by 3600. The callback invocation times have
1543potentially a lot of jittering, but good long-term stability.
1544.PP
1545.Vb 5
1546\& static void
1547\& clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
1548\& {
1549\& ... its now a full hour (UTC, or TAI or whatever your clock follows)
1550\& }
1551\&
1552\& struct ev_periodic hourly_tick;
1553\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1554\& ev_periodic_start (loop, &hourly_tick);
1555.Ve
1556.PP
1557Example: The same as above, but use a reschedule callback to do it:
1558.PP
1559.Vb 1
1560\& #include <math.h>
1561\&
1562\& static ev_tstamp
1563\& my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
1564\& {
1565\& return fmod (now, 3600.) + 3600.;
1566\& }
1567\&
1568\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1569.Ve
1570.PP
1571Example: Call a callback every hour, starting now:
1572.PP
1573.Vb 4
1574\& struct ev_periodic hourly_tick;
1575\& ev_periodic_init (&hourly_tick, clock_cb,
1576\& fmod (ev_now (loop), 3600.), 3600., 0);
1577\& ev_periodic_start (loop, &hourly_tick);
1578.Ve
787.ie n .Sh """ev_signal"" \- signal me when a signal gets signalled" 1579.ie n .Sh """ev_signal"" \- signal me when a signal gets signalled!"
788.el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled" 1580.el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
789.IX Subsection "ev_signal - signal me when a signal gets signalled" 1581.IX Subsection "ev_signal - signal me when a signal gets signalled!"
790Signal watchers will trigger an event when the process receives a specific 1582Signal watchers will trigger an event when the process receives a specific
791signal one or more times. Even though signals are very asynchronous, libev 1583signal one or more times. Even though signals are very asynchronous, libev
792will try it's best to deliver signals synchronously, i.e. as part of the 1584will try it's best to deliver signals synchronously, i.e. as part of the
793normal event processing, like any other event. 1585normal event processing, like any other event.
794.PP 1586.PP
… …
796first watcher gets started will libev actually register a signal watcher 1588first watcher gets started will libev actually register a signal watcher
797with the kernel (thus it coexists with your own signal handlers as long 1589with the kernel (thus it coexists with your own signal handlers as long
798as you don't register any with libev). Similarly, when the last signal 1590as you don't register any with libev). Similarly, when the last signal
799watcher for a signal is stopped libev will reset the signal handler to 1591watcher for a signal is stopped libev will reset the signal handler to
800\&\s-1SIG_DFL\s0 (regardless of what it was set to before). 1592\&\s-1SIG_DFL\s0 (regardless of what it was set to before).
1593.PP
1594If possible and supported, libev will install its handlers with
1595\&\f(CW\*(C`SA_RESTART\*(C'\fR behaviour enabled, so syscalls should not be unduly
1596interrupted. If you have a problem with syscalls getting interrupted by
1597signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher and unblock
1598them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher.
1599.PP
1600\fIWatcher-Specific Functions and Data Members\fR
1601.IX Subsection "Watcher-Specific Functions and Data Members"
801.IP "ev_signal_init (ev_signal *, callback, int signum)" 4 1602.IP "ev_signal_init (ev_signal *, callback, int signum)" 4
802.IX Item "ev_signal_init (ev_signal *, callback, int signum)" 1603.IX Item "ev_signal_init (ev_signal *, callback, int signum)"
803.PD 0 1604.PD 0
804.IP "ev_signal_set (ev_signal *, int signum)" 4 1605.IP "ev_signal_set (ev_signal *, int signum)" 4
805.IX Item "ev_signal_set (ev_signal *, int signum)" 1606.IX Item "ev_signal_set (ev_signal *, int signum)"
806.PD 1607.PD
807Configures the watcher to trigger on the given signal number (usually one 1608Configures the watcher to trigger on the given signal number (usually one
808of the \f(CW\*(C`SIGxxx\*(C'\fR constants). 1609of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
1610.IP "int signum [read\-only]" 4
1611.IX Item "int signum [read-only]"
1612The signal the watcher watches out for.
1613.PP
1614\fIExamples\fR
1615.IX Subsection "Examples"
1616.PP
1617Example: Try to exit cleanly on \s-1SIGINT\s0 and \s-1SIGTERM\s0.
1618.PP
1619.Vb 5
1620\& static void
1621\& sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
1622\& {
1623\& ev_unloop (loop, EVUNLOOP_ALL);
1624\& }
1625\&
1626\& struct ev_signal signal_watcher;
1627\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1628\& ev_signal_start (loop, &sigint_cb);
1629.Ve
809.ie n .Sh """ev_child"" \- wait for pid status changes" 1630.ie n .Sh """ev_child"" \- watch out for process status changes"
810.el .Sh "\f(CWev_child\fP \- wait for pid status changes" 1631.el .Sh "\f(CWev_child\fP \- watch out for process status changes"
811.IX Subsection "ev_child - wait for pid status changes" 1632.IX Subsection "ev_child - watch out for process status changes"
812Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to 1633Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
813some child status changes (most typically when a child of yours dies). 1634some child status changes (most typically when a child of yours dies). It
1635is permissible to install a child watcher \fIafter\fR the child has been
1636forked (which implies it might have already exited), as long as the event
1637loop isn't entered (or is continued from a watcher).
1638.PP
1639Only the default event loop is capable of handling signals, and therefore
1640you can only rgeister child watchers in the default event loop.
1641.PP
1642\fIProcess Interaction\fR
1643.IX Subsection "Process Interaction"
1644.PP
1645Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is
1646initialised. This is necessary to guarantee proper behaviour even if
1647the first child watcher is started after the child exits. The occurance
1648of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done
1649synchronously as part of the event loop processing. Libev always reaps all
1650children, even ones not watched.
1651.PP
1652\fIOverriding the Built-In Processing\fR
1653.IX Subsection "Overriding the Built-In Processing"
1654.PP
1655Libev offers no special support for overriding the built-in child
1656processing, but if your application collides with libev's default child
1657handler, you can override it easily by installing your own handler for
1658\&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the
1659default loop never gets destroyed. You are encouraged, however, to use an
1660event-based approach to child reaping and thus use libev's support for
1661that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely.
1662.PP
1663\fIWatcher-Specific Functions and Data Members\fR
1664.IX Subsection "Watcher-Specific Functions and Data Members"
814.IP "ev_child_init (ev_child *, callback, int pid)" 4 1665.IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4
815.IX Item "ev_child_init (ev_child *, callback, int pid)" 1666.IX Item "ev_child_init (ev_child *, callback, int pid, int trace)"
816.PD 0 1667.PD 0
817.IP "ev_child_set (ev_child *, int pid)" 4 1668.IP "ev_child_set (ev_child *, int pid, int trace)" 4
818.IX Item "ev_child_set (ev_child *, int pid)" 1669.IX Item "ev_child_set (ev_child *, int pid, int trace)"
819.PD 1670.PD
820Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or 1671Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
821\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look 1672\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
822at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see 1673at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
823the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems 1674the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
824\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the 1675\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
825process causing the status change. 1676process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only
1677activate the watcher when the process terminates) or \f(CW1\fR (additionally
1678activate the watcher when the process is stopped or continued).
1679.IP "int pid [read\-only]" 4
1680.IX Item "int pid [read-only]"
1681The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
1682.IP "int rpid [read\-write]" 4
1683.IX Item "int rpid [read-write]"
1684The process id that detected a status change.
1685.IP "int rstatus [read\-write]" 4
1686.IX Item "int rstatus [read-write]"
1687The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
1688\&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
1689.PP
1690\fIExamples\fR
1691.IX Subsection "Examples"
1692.PP
1693Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for
1694its completion.
1695.PP
1696.Vb 1
1697\& ev_child cw;
1698\&
1699\& static void
1700\& child_cb (EV_P_ struct ev_child *w, int revents)
1701\& {
1702\& ev_child_stop (EV_A_ w);
1703\& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus);
1704\& }
1705\&
1706\& pid_t pid = fork ();
1707\&
1708\& if (pid < 0)
1709\& // error
1710\& else if (pid == 0)
1711\& {
1712\& // the forked child executes here
1713\& exit (1);
1714\& }
1715\& else
1716\& {
1717\& ev_child_init (&cw, child_cb, pid, 0);
1718\& ev_child_start (EV_DEFAULT_ &cw);
1719\& }
1720.Ve
1721.ie n .Sh """ev_stat"" \- did the file attributes just change?"
1722.el .Sh "\f(CWev_stat\fP \- did the file attributes just change?"
1723.IX Subsection "ev_stat - did the file attributes just change?"
1724This watches a filesystem path for attribute changes. That is, it calls
1725\&\f(CW\*(C`stat\*(C'\fR regularly (or when the \s-1OS\s0 says it changed) and sees if it changed
1726compared to the last time, invoking the callback if it did.
1727.PP
1728The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does
1729not exist\*(R" is a status change like any other. The condition \*(L"path does
1730not exist\*(R" is signified by the \f(CW\*(C`st_nlink\*(C'\fR field being zero (which is
1731otherwise always forced to be at least one) and all the other fields of
1732the stat buffer having unspecified contents.
1733.PP
1734The path \fIshould\fR be absolute and \fImust not\fR end in a slash. If it is
1735relative and your working directory changes, the behaviour is undefined.
1736.PP
1737Since there is no standard to do this, the portable implementation simply
1738calls \f(CW\*(C`stat (2)\*(C'\fR regularly on the path to see if it changed somehow. You
1739can specify a recommended polling interval for this case. If you specify
1740a polling interval of \f(CW0\fR (highly recommended!) then a \fIsuitable,
1741unspecified default\fR value will be used (which you can expect to be around
1742five seconds, although this might change dynamically). Libev will also
1743impose a minimum interval which is currently around \f(CW0.1\fR, but thats
1744usually overkill.
1745.PP
1746This watcher type is not meant for massive numbers of stat watchers,
1747as even with OS-supported change notifications, this can be
1748resource-intensive.
1749.PP
1750At the time of this writing, only the Linux inotify interface is
1751implemented (implementing kqueue support is left as an exercise for the
1752reader, note, however, that the author sees no way of implementing ev_stat
1753semantics with kqueue). Inotify will be used to give hints only and should
1754not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers, which means that libev
1755sometimes needs to fall back to regular polling again even with inotify,
1756but changes are usually detected immediately, and if the file exists there
1757will be no polling.
1758.PP
1759\fI\s-1ABI\s0 Issues (Largefile Support)\fR
1760.IX Subsection "ABI Issues (Largefile Support)"
1761.PP
1762Libev by default (unless the user overrides this) uses the default
1763compilation environment, which means that on systems with optionally
1764disabled large file support, you get the 32 bit version of the stat
1765structure. When using the library from programs that change the \s-1ABI\s0 to
1766use 64 bit file offsets the programs will fail. In that case you have to
1767compile libev with the same flags to get binary compatibility. This is
1768obviously the case with any flags that change the \s-1ABI\s0, but the problem is
1769most noticably with ev_stat and largefile support.
1770.PP
1771\fIInotify\fR
1772.IX Subsection "Inotify"
1773.PP
1774When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev (generally only
1775available on Linux) and present at runtime, it will be used to speed up
1776change detection where possible. The inotify descriptor will be created lazily
1777when the first \f(CW\*(C`ev_stat\*(C'\fR watcher is being started.
1778.PP
1779Inotify presence does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
1780except that changes might be detected earlier, and in some cases, to avoid
1781making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presence of inotify support
1782there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling.
1783.PP
1784(There is no support for kqueue, as apparently it cannot be used to
1785implement this functionality, due to the requirement of having a file
1786descriptor open on the object at all times).
1787.PP
1788\fIThe special problem of stat time resolution\fR
1789.IX Subsection "The special problem of stat time resolution"
1790.PP
1791The \f(CW\*(C`stat ()\*(C'\fR syscall only supports full-second resolution portably, and
1792even on systems where the resolution is higher, many filesystems still
1793only support whole seconds.
1794.PP
1795That means that, if the time is the only thing that changes, you can
1796easily miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and
1797calls your callback, which does something. When there is another update
1798within the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect it as the stat
1799data does not change.
1800.PP
1801The solution to this is to delay acting on a change for slightly more
1802than second (or till slightly after the next full second boundary), using
1803a roughly one-second-delay \f(CW\*(C`ev_timer\*(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02);
1804ev_timer_again (loop, w)\*(C'\fR).
1805.PP
1806The \f(CW.02\fR offset is added to work around small timing inconsistencies
1807of some operating systems (where the second counter of the current time
1808might be be delayed. One such system is the Linux kernel, where a call to
1809\&\f(CW\*(C`gettimeofday\*(C'\fR might return a timestamp with a full second later than
1810a subsequent \f(CW\*(C`time\*(C'\fR call \- if the equivalent of \f(CW\*(C`time ()\*(C'\fR is used to
1811update file times then there will be a small window where the kernel uses
1812the previous second to update file times but libev might already execute
1813the timer callback).
1814.PP
1815\fIWatcher-Specific Functions and Data Members\fR
1816.IX Subsection "Watcher-Specific Functions and Data Members"
1817.IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
1818.IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
1819.PD 0
1820.IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4
1821.IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)"
1822.PD
1823Configures the watcher to wait for status changes of the given
1824\&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to
1825be detected and should normally be specified as \f(CW0\fR to let libev choose
1826a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same
1827path for as long as the watcher is active.
1828.Sp
1829The callback will receive \f(CW\*(C`EV_STAT\*(C'\fR when a change was detected, relative
1830to the attributes at the time the watcher was started (or the last change
1831was detected).
1832.IP "ev_stat_stat (loop, ev_stat *)" 4
1833.IX Item "ev_stat_stat (loop, ev_stat *)"
1834Updates the stat buffer immediately with new values. If you change the
1835watched path in your callback, you could call this function to avoid
1836detecting this change (while introducing a race condition if you are not
1837the only one changing the path). Can also be useful simply to find out the
1838new values.
1839.IP "ev_statdata attr [read\-only]" 4
1840.IX Item "ev_statdata attr [read-only]"
1841The most-recently detected attributes of the file. Although the type is
1842\&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
1843suitable for your system, but you can only rely on the POSIX-standardised
1844members to be present. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there was
1845some error while \f(CW\*(C`stat\*(C'\fRing the file.
1846.IP "ev_statdata prev [read\-only]" 4
1847.IX Item "ev_statdata prev [read-only]"
1848The previous attributes of the file. The callback gets invoked whenever
1849\&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR, or, more precisely, one or more of these members
1850differ: \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,
1851\&\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.
1852.IP "ev_tstamp interval [read\-only]" 4
1853.IX Item "ev_tstamp interval [read-only]"
1854The specified interval.
1855.IP "const char *path [read\-only]" 4
1856.IX Item "const char *path [read-only]"
1857The filesystem path that is being watched.
1858.PP
1859\fIExamples\fR
1860.IX Subsection "Examples"
1861.PP
1862Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
1863.PP
1864.Vb 10
1865\& static void
1866\& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1867\& {
1868\& /* /etc/passwd changed in some way */
1869\& if (w\->attr.st_nlink)
1870\& {
1871\& printf ("passwd current size %ld\en", (long)w\->attr.st_size);
1872\& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime);
1873\& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime);
1874\& }
1875\& else
1876\& /* you shalt not abuse printf for puts */
1877\& puts ("wow, /etc/passwd is not there, expect problems. "
1878\& "if this is windows, they already arrived\en");
1879\& }
1880\&
1881\& ...
1882\& ev_stat passwd;
1883\&
1884\& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1885\& ev_stat_start (loop, &passwd);
1886.Ve
1887.PP
1888Example: Like above, but additionally use a one-second delay so we do not
1889miss updates (however, frequent updates will delay processing, too, so
1890one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
1891\&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
1892.PP
1893.Vb 2
1894\& static ev_stat passwd;
1895\& static ev_timer timer;
1896\&
1897\& static void
1898\& timer_cb (EV_P_ ev_timer *w, int revents)
1899\& {
1900\& ev_timer_stop (EV_A_ w);
1901\&
1902\& /* now it\*(Aqs one second after the most recent passwd change */
1903\& }
1904\&
1905\& static void
1906\& stat_cb (EV_P_ ev_stat *w, int revents)
1907\& {
1908\& /* reset the one\-second timer */
1909\& ev_timer_again (EV_A_ &timer);
1910\& }
1911\&
1912\& ...
1913\& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1914\& ev_stat_start (loop, &passwd);
1915\& ev_timer_init (&timer, timer_cb, 0., 1.02);
1916.Ve
826.ie n .Sh """ev_idle"" \- when you've got nothing better to do" 1917.ie n .Sh """ev_idle"" \- when you've got nothing better to do..."
827.el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do" 1918.el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do..."
828.IX Subsection "ev_idle - when you've got nothing better to do" 1919.IX Subsection "ev_idle - when you've got nothing better to do..."
829Idle watchers trigger events when there are no other events are pending 1920Idle watchers trigger events when no other events of the same or higher
830(prepare, check and other idle watchers do not count). That is, as long 1921priority are pending (prepare, check and other idle watchers do not
831as your process is busy handling sockets or timeouts (or even signals, 1922count).
832imagine) it will not be triggered. But when your process is idle all idle 1923.PP
833watchers are being called again and again, once per event loop iteration \- 1924That is, as long as your process is busy handling sockets or timeouts
1925(or even signals, imagine) of the same or higher priority it will not be
1926triggered. But when your process is idle (or only lower-priority watchers
1927are pending), the idle watchers are being called once per event loop
834until stopped, that is, or your process receives more events and becomes 1928iteration \- until stopped, that is, or your process receives more events
835busy. 1929and becomes busy again with higher priority stuff.
836.PP 1930.PP
837The most noteworthy effect is that as long as any idle watchers are 1931The most noteworthy effect is that as long as any idle watchers are
838active, the process will not block when waiting for new events. 1932active, the process will not block when waiting for new events.
839.PP 1933.PP
840Apart from keeping your process non-blocking (which is a useful 1934Apart from keeping your process non-blocking (which is a useful
841effect on its own sometimes), idle watchers are a good place to do 1935effect on its own sometimes), idle watchers are a good place to do
842\&\*(L"pseudo\-background processing\*(R", or delay processing stuff to after the 1936\&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the
843event loop has handled all outstanding events. 1937event loop has handled all outstanding events.
1938.PP
1939\fIWatcher-Specific Functions and Data Members\fR
1940.IX Subsection "Watcher-Specific Functions and Data Members"
844.IP "ev_idle_init (ev_signal *, callback)" 4 1941.IP "ev_idle_init (ev_signal *, callback)" 4
845.IX Item "ev_idle_init (ev_signal *, callback)" 1942.IX Item "ev_idle_init (ev_signal *, callback)"
846Initialises and configures the idle watcher \- it has no parameters of any 1943Initialises and configures the idle watcher \- it has no parameters of any
847kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless, 1944kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
848believe me. 1945believe me.
1946.PP
1947\fIExamples\fR
1948.IX Subsection "Examples"
1949.PP
1950Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the
1951callback, free it. Also, use no error checking, as usual.
1952.PP
1953.Vb 7
1954\& static void
1955\& idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
1956\& {
1957\& free (w);
1958\& // now do something you wanted to do when the program has
1959\& // no longer anything immediate to do.
1960\& }
1961\&
1962\& struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
1963\& ev_idle_init (idle_watcher, idle_cb);
1964\& ev_idle_start (loop, idle_cb);
1965.Ve
849.ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop" 1966.ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop!"
850.el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop" 1967.el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
851.IX Subsection "ev_prepare and ev_check - customise your event loop" 1968.IX Subsection "ev_prepare and ev_check - customise your event loop!"
852Prepare and check watchers are usually (but not always) used in tandem: 1969Prepare and check watchers are usually (but not always) used in tandem:
853prepare watchers get invoked before the process blocks and check watchers 1970prepare watchers get invoked before the process blocks and check watchers
854afterwards. 1971afterwards.
855.PP 1972.PP
1973You \fImust not\fR call \f(CW\*(C`ev_loop\*(C'\fR or similar functions that enter
1974the current event loop from either \f(CW\*(C`ev_prepare\*(C'\fR or \f(CW\*(C`ev_check\*(C'\fR
1975watchers. Other loops than the current one are fine, however. The
1976rationale behind this is that you do not need to check for recursion in
1977those watchers, i.e. the sequence will always be \f(CW\*(C`ev_prepare\*(C'\fR, blocking,
1978\&\f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each kind they will always be
1979called in pairs bracketing the blocking call.
1980.PP
856Their main purpose is to integrate other event mechanisms into libev. This 1981Their main purpose is to integrate other event mechanisms into libev and
857could be used, for example, to track variable changes, implement your own 1982their use is somewhat advanced. This could be used, for example, to track
858watchers, integrate net-snmp or a coroutine library and lots more. 1983variable changes, implement your own watchers, integrate net-snmp or a
1984coroutine library and lots more. They are also occasionally useful if
1985you cache some data and want to flush it before blocking (for example,
1986in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
1987watcher).
859.PP 1988.PP
860This is done by examining in each prepare call which file descriptors need 1989This is done by examining in each prepare call which file descriptors need
861to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers for 1990to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers for
862them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many libraries 1991them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many libraries
863provide just this functionality). Then, in the check watcher you check for 1992provide just this functionality). Then, in the check watcher you check for
… …
872are ready to run (it's actually more complicated: it only runs coroutines 2001are ready to run (it's actually more complicated: it only runs coroutines
873with priority higher than or equal to the event loop and one coroutine 2002with priority higher than or equal to the event loop and one coroutine
874of lower priority, but only once, using idle watchers to keep the event 2003of lower priority, but only once, using idle watchers to keep the event
875loop from blocking if lower-priority coroutines are active, thus mapping 2004loop from blocking if lower-priority coroutines are active, thus mapping
876low-priority coroutines to idle/background tasks). 2005low-priority coroutines to idle/background tasks).
2006.PP
2007It is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR)
2008priority, to ensure that they are being run before any other watchers
2009after the poll. Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers,
2010too) should not activate (\*(L"feed\*(R") events into libev. While libev fully
2011supports this, they might get executed before other \f(CW\*(C`ev_check\*(C'\fR watchers
2012did their job. As \f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other
2013(non-libev) event loops those other event loops might be in an unusable
2014state until their \f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to
2015coexist peacefully with others).
2016.PP
2017\fIWatcher-Specific Functions and Data Members\fR
2018.IX Subsection "Watcher-Specific Functions and Data Members"
877.IP "ev_prepare_init (ev_prepare *, callback)" 4 2019.IP "ev_prepare_init (ev_prepare *, callback)" 4
878.IX Item "ev_prepare_init (ev_prepare *, callback)" 2020.IX Item "ev_prepare_init (ev_prepare *, callback)"
879.PD 0 2021.PD 0
880.IP "ev_check_init (ev_check *, callback)" 4 2022.IP "ev_check_init (ev_check *, callback)" 4
881.IX Item "ev_check_init (ev_check *, callback)" 2023.IX Item "ev_check_init (ev_check *, callback)"
882.PD 2024.PD
883Initialises and configures the prepare or check watcher \- they have no 2025Initialises and configures the prepare or check watcher \- they have no
884parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR 2026parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
885macros, but using them is utterly, utterly and completely pointless. 2027macros, but using them is utterly, utterly and completely pointless.
2028.PP
2029\fIExamples\fR
2030.IX Subsection "Examples"
2031.PP
2032There are a number of principal ways to embed other event loops or modules
2033into libev. Here are some ideas on how to include libadns into libev
2034(there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could
2035use as a working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR embeds a
2036Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 into the
2037Glib event loop).
2038.PP
2039Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
2040and in a check watcher, destroy them and call into libadns. What follows
2041is pseudo-code only of course. This requires you to either use a low
2042priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as
2043the callbacks for the IO/timeout watchers might not have been called yet.
2044.PP
2045.Vb 2
2046\& static ev_io iow [nfd];
2047\& static ev_timer tw;
2048\&
2049\& static void
2050\& io_cb (ev_loop *loop, ev_io *w, int revents)
2051\& {
2052\& }
2053\&
2054\& // create io watchers for each fd and a timer before blocking
2055\& static void
2056\& adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
2057\& {
2058\& int timeout = 3600000;
2059\& struct pollfd fds [nfd];
2060\& // actual code will need to loop here and realloc etc.
2061\& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2062\&
2063\& /* the callback is illegal, but won\*(Aqt be called as we stop during check */
2064\& ev_timer_init (&tw, 0, timeout * 1e\-3);
2065\& ev_timer_start (loop, &tw);
2066\&
2067\& // create one ev_io per pollfd
2068\& for (int i = 0; i < nfd; ++i)
2069\& {
2070\& ev_io_init (iow + i, io_cb, fds [i].fd,
2071\& ((fds [i].events & POLLIN ? EV_READ : 0)
2072\& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
2073\&
2074\& fds [i].revents = 0;
2075\& ev_io_start (loop, iow + i);
2076\& }
2077\& }
2078\&
2079\& // stop all watchers after blocking
2080\& static void
2081\& adns_check_cb (ev_loop *loop, ev_check *w, int revents)
2082\& {
2083\& ev_timer_stop (loop, &tw);
2084\&
2085\& for (int i = 0; i < nfd; ++i)
2086\& {
2087\& // set the relevant poll flags
2088\& // could also call adns_processreadable etc. here
2089\& struct pollfd *fd = fds + i;
2090\& int revents = ev_clear_pending (iow + i);
2091\& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN;
2092\& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT;
2093\&
2094\& // now stop the watcher
2095\& ev_io_stop (loop, iow + i);
2096\& }
2097\&
2098\& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
2099\& }
2100.Ve
2101.PP
2102Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR
2103in the prepare watcher and would dispose of the check watcher.
2104.PP
2105Method 3: If the module to be embedded supports explicit event
2106notification (adns does), you can also make use of the actual watcher
2107callbacks, and only destroy/create the watchers in the prepare watcher.
2108.PP
2109.Vb 5
2110\& static void
2111\& timer_cb (EV_P_ ev_timer *w, int revents)
2112\& {
2113\& adns_state ads = (adns_state)w\->data;
2114\& update_now (EV_A);
2115\&
2116\& adns_processtimeouts (ads, &tv_now);
2117\& }
2118\&
2119\& static void
2120\& io_cb (EV_P_ ev_io *w, int revents)
2121\& {
2122\& adns_state ads = (adns_state)w\->data;
2123\& update_now (EV_A);
2124\&
2125\& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now);
2126\& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now);
2127\& }
2128\&
2129\& // do not ever call adns_afterpoll
2130.Ve
2131.PP
2132Method 4: Do not use a prepare or check watcher because the module you
2133want to embed is too inflexible to support it. Instead, youc na override
2134their poll function. The drawback with this solution is that the main
2135loop is now no longer controllable by \s-1EV\s0. The \f(CW\*(C`Glib::EV\*(C'\fR module does
2136this.
2137.PP
2138.Vb 4
2139\& static gint
2140\& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
2141\& {
2142\& int got_events = 0;
2143\&
2144\& for (n = 0; n < nfds; ++n)
2145\& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
2146\&
2147\& if (timeout >= 0)
2148\& // create/start timer
2149\&
2150\& // poll
2151\& ev_loop (EV_A_ 0);
2152\&
2153\& // stop timer again
2154\& if (timeout >= 0)
2155\& ev_timer_stop (EV_A_ &to);
2156\&
2157\& // stop io watchers again \- their callbacks should have set
2158\& for (n = 0; n < nfds; ++n)
2159\& ev_io_stop (EV_A_ iow [n]);
2160\&
2161\& return got_events;
2162\& }
2163.Ve
2164.ie n .Sh """ev_embed"" \- when one backend isn't enough..."
2165.el .Sh "\f(CWev_embed\fP \- when one backend isn't enough..."
2166.IX Subsection "ev_embed - when one backend isn't enough..."
2167This is a rather advanced watcher type that lets you embed one event loop
2168into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
2169loop, other types of watchers might be handled in a delayed or incorrect
2170fashion and must not be used).
2171.PP
2172There are primarily two reasons you would want that: work around bugs and
2173prioritise I/O.
2174.PP
2175As an example for a bug workaround, the kqueue backend might only support
2176sockets on some platform, so it is unusable as generic backend, but you
2177still want to make use of it because you have many sockets and it scales
2178so nicely. In this case, you would create a kqueue-based loop and embed it
2179into your default loop (which might use e.g. poll). Overall operation will
2180be a bit slower because first libev has to poll and then call kevent, but
2181at least you can use both at what they are best.
2182.PP
2183As for prioritising I/O: rarely you have the case where some fds have
2184to be watched and handled very quickly (with low latency), and even
2185priorities and idle watchers might have too much overhead. In this case
2186you would put all the high priority stuff in one loop and all the rest in
2187a second one, and embed the second one in the first.
2188.PP
2189As long as the watcher is active, the callback will be invoked every time
2190there might be events pending in the embedded loop. The callback must then
2191call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single sweep and invoke
2192their callbacks (you could also start an idle watcher to give the embedded
2193loop strictly lower priority for example). You can also set the callback
2194to \f(CW0\fR, in which case the embed watcher will automatically execute the
2195embedded loop sweep.
2196.PP
2197As long as the watcher is started it will automatically handle events. The
2198callback will be invoked whenever some events have been handled. You can
2199set the callback to \f(CW0\fR to avoid having to specify one if you are not
2200interested in that.
2201.PP
2202Also, there have not currently been made special provisions for forking:
2203when you fork, you not only have to call \f(CW\*(C`ev_loop_fork\*(C'\fR on both loops,
2204but you will also have to stop and restart any \f(CW\*(C`ev_embed\*(C'\fR watchers
2205yourself.
2206.PP
2207Unfortunately, not all backends are embeddable, only the ones returned by
2208\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
2209portable one.
2210.PP
2211So when you want to use this feature you will always have to be prepared
2212that you cannot get an embeddable loop. The recommended way to get around
2213this is to have a separate variables for your embeddable loop, try to
2214create it, and if that fails, use the normal loop for everything.
2215.PP
2216\fIWatcher-Specific Functions and Data Members\fR
2217.IX Subsection "Watcher-Specific Functions and Data Members"
2218.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
2219.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
2220.PD 0
2221.IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
2222.IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)"
2223.PD
2224Configures the watcher to embed the given loop, which must be
2225embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
2226invoked automatically, otherwise it is the responsibility of the callback
2227to invoke it (it will continue to be called until the sweep has been done,
2228if you do not want thta, you need to temporarily stop the embed watcher).
2229.IP "ev_embed_sweep (loop, ev_embed *)" 4
2230.IX Item "ev_embed_sweep (loop, ev_embed *)"
2231Make a single, non-blocking sweep over the embedded loop. This works
2232similarly to \f(CW\*(C`ev_loop (embedded_loop, EVLOOP_NONBLOCK)\*(C'\fR, but in the most
2233apropriate way for embedded loops.
2234.IP "struct ev_loop *other [read\-only]" 4
2235.IX Item "struct ev_loop *other [read-only]"
2236The embedded event loop.
2237.PP
2238\fIExamples\fR
2239.IX Subsection "Examples"
2240.PP
2241Example: Try to get an embeddable event loop and embed it into the default
2242event loop. If that is not possible, use the default loop. The default
2243loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the mebeddable loop is stored in
2244\&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the acse no embeddable loop can be
2245used).
2246.PP
2247.Vb 3
2248\& struct ev_loop *loop_hi = ev_default_init (0);
2249\& struct ev_loop *loop_lo = 0;
2250\& struct ev_embed embed;
2251\&
2252\& // see if there is a chance of getting one that works
2253\& // (remember that a flags value of 0 means autodetection)
2254\& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2255\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
2256\& : 0;
2257\&
2258\& // if we got one, then embed it, otherwise default to loop_hi
2259\& if (loop_lo)
2260\& {
2261\& ev_embed_init (&embed, 0, loop_lo);
2262\& ev_embed_start (loop_hi, &embed);
2263\& }
2264\& else
2265\& loop_lo = loop_hi;
2266.Ve
2267.PP
2268Example: Check if kqueue is available but not recommended and create
2269a kqueue backend for use with sockets (which usually work with any
2270kqueue implementation). Store the kqueue/socket\-only event loop in
2271\&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too).
2272.PP
2273.Vb 3
2274\& struct ev_loop *loop = ev_default_init (0);
2275\& struct ev_loop *loop_socket = 0;
2276\& struct ev_embed embed;
2277\&
2278\& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2279\& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2280\& {
2281\& ev_embed_init (&embed, 0, loop_socket);
2282\& ev_embed_start (loop, &embed);
2283\& }
2284\&
2285\& if (!loop_socket)
2286\& loop_socket = loop;
2287\&
2288\& // now use loop_socket for all sockets, and loop for everything else
2289.Ve
2290.ie n .Sh """ev_fork"" \- the audacity to resume the event loop after a fork"
2291.el .Sh "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
2292.IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
2293Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
2294whoever is a good citizen cared to tell libev about it by calling
2295\&\f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the
2296event loop blocks next and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called,
2297and only in the child after the fork. If whoever good citizen calling
2298\&\f(CW\*(C`ev_default_fork\*(C'\fR cheats and calls it in the wrong process, the fork
2299handlers will be invoked, too, of course.
2300.PP
2301\fIWatcher-Specific Functions and Data Members\fR
2302.IX Subsection "Watcher-Specific Functions and Data Members"
2303.IP "ev_fork_init (ev_signal *, callback)" 4
2304.IX Item "ev_fork_init (ev_signal *, callback)"
2305Initialises and configures the fork watcher \- it has no parameters of any
2306kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
2307believe me.
2308.ie n .Sh """ev_async"" \- how to wake up another event loop"
2309.el .Sh "\f(CWev_async\fP \- how to wake up another event loop"
2310.IX Subsection "ev_async - how to wake up another event loop"
2311In general, you cannot use an \f(CW\*(C`ev_loop\*(C'\fR from multiple threads or other
2312asynchronous sources such as signal handlers (as opposed to multiple event
2313loops \- those are of course safe to use in different threads).
2314.PP
2315Sometimes, however, you need to wake up another event loop you do not
2316control, for example because it belongs to another thread. This is what
2317\&\f(CW\*(C`ev_async\*(C'\fR watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you
2318can signal it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal
2319safe.
2320.PP
2321This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals,
2322too, are asynchronous in nature, and signals, too, will be compressed
2323(i.e. the number of callback invocations may be less than the number of
2324\&\f(CW\*(C`ev_async_sent\*(C'\fR calls).
2325.PP
2326Unlike \f(CW\*(C`ev_signal\*(C'\fR watchers, \f(CW\*(C`ev_async\*(C'\fR works with any event loop, not
2327just the default loop.
2328.PP
2329\fIQueueing\fR
2330.IX Subsection "Queueing"
2331.PP
2332\&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason
2333is that the author does not know of a simple (or any) algorithm for a
2334multiple-writer-single-reader queue that works in all cases and doesn't
2335need elaborate support such as pthreads.
2336.PP
2337That means that if you want to queue data, you have to provide your own
2338queue. But at least I can tell you would implement locking around your
2339queue:
2340.IP "queueing from a signal handler context" 4
2341.IX Item "queueing from a signal handler context"
2342To implement race-free queueing, you simply add to the queue in the signal
2343handler but you block the signal handler in the watcher callback. Here is an example that does that for
2344some fictitiuous \s-1SIGUSR1\s0 handler:
2345.Sp
2346.Vb 1
2347\& static ev_async mysig;
2348\&
2349\& static void
2350\& sigusr1_handler (void)
2351\& {
2352\& sometype data;
2353\&
2354\& // no locking etc.
2355\& queue_put (data);
2356\& ev_async_send (EV_DEFAULT_ &mysig);
2357\& }
2358\&
2359\& static void
2360\& mysig_cb (EV_P_ ev_async *w, int revents)
2361\& {
2362\& sometype data;
2363\& sigset_t block, prev;
2364\&
2365\& sigemptyset (&block);
2366\& sigaddset (&block, SIGUSR1);
2367\& sigprocmask (SIG_BLOCK, &block, &prev);
2368\&
2369\& while (queue_get (&data))
2370\& process (data);
2371\&
2372\& if (sigismember (&prev, SIGUSR1)
2373\& sigprocmask (SIG_UNBLOCK, &block, 0);
2374\& }
2375.Ve
2376.Sp
2377(Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR
2378instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it
2379either...).
2380.IP "queueing from a thread context" 4
2381.IX Item "queueing from a thread context"
2382The strategy for threads is different, as you cannot (easily) block
2383threads but you can easily preempt them, so to queue safely you need to
2384employ a traditional mutex lock, such as in this pthread example:
2385.Sp
2386.Vb 2
2387\& static ev_async mysig;
2388\& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
2389\&
2390\& static void
2391\& otherthread (void)
2392\& {
2393\& // only need to lock the actual queueing operation
2394\& pthread_mutex_lock (&mymutex);
2395\& queue_put (data);
2396\& pthread_mutex_unlock (&mymutex);
2397\&
2398\& ev_async_send (EV_DEFAULT_ &mysig);
2399\& }
2400\&
2401\& static void
2402\& mysig_cb (EV_P_ ev_async *w, int revents)
2403\& {
2404\& pthread_mutex_lock (&mymutex);
2405\&
2406\& while (queue_get (&data))
2407\& process (data);
2408\&
2409\& pthread_mutex_unlock (&mymutex);
2410\& }
2411.Ve
2412.PP
2413\fIWatcher-Specific Functions and Data Members\fR
2414.IX Subsection "Watcher-Specific Functions and Data Members"
2415.IP "ev_async_init (ev_async *, callback)" 4
2416.IX Item "ev_async_init (ev_async *, callback)"
2417Initialises and configures the async watcher \- it has no parameters of any
2418kind. There is a \f(CW\*(C`ev_asynd_set\*(C'\fR macro, but using it is utterly pointless,
2419believe me.
2420.IP "ev_async_send (loop, ev_async *)" 4
2421.IX Item "ev_async_send (loop, ev_async *)"
2422Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds
2423an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop. Unlike
2424\&\f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do in other threads, signal or
2425similar contexts (see the dicusssion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the embedding
2426section below on what exactly this means).
2427.Sp
2428This call incurs the overhead of a syscall only once per loop iteration,
2429so while the overhead might be noticable, it doesn't apply to repeated
2430calls to \f(CW\*(C`ev_async_send\*(C'\fR.
2431.IP "bool = ev_async_pending (ev_async *)" 4
2432.IX Item "bool = ev_async_pending (ev_async *)"
2433Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the
2434watcher but the event has not yet been processed (or even noted) by the
2435event loop.
2436.Sp
2437\&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When
2438the loop iterates next and checks for the watcher to have become active,
2439it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very
2440quickly check wether invoking the loop might be a good idea.
2441.Sp
2442Not that this does \fInot\fR check wether the watcher itself is pending, only
2443wether it has been requested to make this watcher pending.
886.SH "OTHER FUNCTIONS" 2444.SH "OTHER FUNCTIONS"
887.IX Header "OTHER FUNCTIONS" 2445.IX Header "OTHER FUNCTIONS"
888There are some other functions of possible interest. Described. Here. Now. 2446There are some other functions of possible interest. Described. Here. Now.
889.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4 2447.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
890.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 2448.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"
… …
914\& if (revents & EV_TIMEOUT) 2472\& if (revents & EV_TIMEOUT)
915\& /* doh, nothing entered */; 2473\& /* doh, nothing entered */;
916\& else if (revents & EV_READ) 2474\& else if (revents & EV_READ)
917\& /* stdin might have data for us, joy! */; 2475\& /* stdin might have data for us, joy! */;
918\& } 2476\& }
919.Ve 2477\&
920.Sp
921.Vb 1
922\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); 2478\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
923.Ve 2479.Ve
924.IP "ev_feed_event (loop, watcher, int events)" 4 2480.IP "ev_feed_event (ev_loop *, watcher *, int revents)" 4
925.IX Item "ev_feed_event (loop, watcher, int events)" 2481.IX Item "ev_feed_event (ev_loop *, watcher *, int revents)"
926Feeds the given event set into the event loop, as if the specified event 2482Feeds the given event set into the event loop, as if the specified event
927had happened for the specified watcher (which must be a pointer to an 2483had happened for the specified watcher (which must be a pointer to an
928initialised but not necessarily started event watcher). 2484initialised but not necessarily started event watcher).
929.IP "ev_feed_fd_event (loop, int fd, int revents)" 4 2485.IP "ev_feed_fd_event (ev_loop *, int fd, int revents)" 4
930.IX Item "ev_feed_fd_event (loop, int fd, int revents)" 2486.IX Item "ev_feed_fd_event (ev_loop *, int fd, int revents)"
931Feed an event on the given fd, as if a file descriptor backend detected 2487Feed an event on the given fd, as if a file descriptor backend detected
932the given events it. 2488the given events it.
933.IP "ev_feed_signal_event (loop, int signum)" 4 2489.IP "ev_feed_signal_event (ev_loop *loop, int signum)" 4
934.IX Item "ev_feed_signal_event (loop, int signum)" 2490.IX Item "ev_feed_signal_event (ev_loop *loop, int signum)"
935Feed an event as if the given signal occured (loop must be the default loop!). 2491Feed an event as if the given signal occured (\f(CW\*(C`loop\*(C'\fR must be the default
2492loop!).
936.SH "LIBEVENT EMULATION" 2493.SH "LIBEVENT EMULATION"
937.IX Header "LIBEVENT EMULATION" 2494.IX Header "LIBEVENT EMULATION"
938Libev offers a compatibility emulation layer for libevent. It cannot 2495Libev offers a compatibility emulation layer for libevent. It cannot
939emulate the internals of libevent, so here are some usage hints: 2496emulate the internals of libevent, so here are some usage hints:
2497.IP "\(bu" 4
940.IP "* Use it by including <event.h>, as usual." 4 2498Use it by including <event.h>, as usual.
941.IX Item "Use it by including <event.h>, as usual." 2499.IP "\(bu" 4
942.PD 0 2500The following members are fully supported: ev_base, ev_callback,
943.IP "* The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4 2501ev_arg, ev_fd, ev_res, ev_events.
944.IX Item "The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 2502.IP "\(bu" 4
945.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 2503Avoid using ev_flags and the EVLIST_*\-macros, while it is
946.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)." 2504maintained by libev, it does not work exactly the same way as in libevent (consider
947.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 2505it a private \s-1API\s0).
948.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." 2506.IP "\(bu" 4
2507Priorities are not currently supported. Initialising priorities
2508will fail and all watchers will have the same priority, even though there
2509is an ev_pri field.
2510.IP "\(bu" 4
2511In libevent, the last base created gets the signals, in libev, the
2512first base created (== the default loop) gets the signals.
2513.IP "\(bu" 4
949.IP "* Other members are not supported." 4 2514Other members are not supported.
950.IX Item "Other members are not supported." 2515.IP "\(bu" 4
951.IP "* The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need to use the libev header file and library." 4 2516The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need
952.IX Item "The libev emulation is not ABI compatible to libevent, you need to use the libev header file and library." 2517to use the libev header file and library.
953.PD
954.SH "\*(C+ SUPPORT" 2518.SH "\*(C+ SUPPORT"
955.IX Header " SUPPORT" 2519.IX Header " SUPPORT"
956\&\s-1TBD\s0. 2520Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
2521you to use some convinience methods to start/stop watchers and also change
2522the callback model to a model using method callbacks on objects.
2523.PP
2524To use it,
2525.PP
2526.Vb 1
2527\& #include <ev++.h>
2528.Ve
2529.PP
2530This automatically includes \fIev.h\fR and puts all of its definitions (many
2531of them macros) into the global namespace. All \*(C+ specific things are
2532put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding
2533options as \fIev.h\fR, most notably \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR.
2534.PP
2535Care has been taken to keep the overhead low. The only data member the \*(C+
2536classes add (compared to plain C\-style watchers) is the event loop pointer
2537that the watcher is associated with (or no additional members at all if
2538you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
2539.PP
2540Currently, functions, and static and non-static member functions can be
2541used as callbacks. Other types should be easy to add as long as they only
2542need one additional pointer for context. If you need support for other
2543types of functors please contact the author (preferably after implementing
2544it).
2545.PP
2546Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
2547.ie n .IP """ev::READ""\fR, \f(CW""ev::WRITE"" etc." 4
2548.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
2549.IX Item "ev::READ, ev::WRITE etc."
2550These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
2551macros from \fIev.h\fR.
2552.ie n .IP """ev::tstamp""\fR, \f(CW""ev::now""" 4
2553.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
2554.IX Item "ev::tstamp, ev::now"
2555Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
2556.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
2557.el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
2558.IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
2559For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
2560the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
2561which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
2562defines by many implementations.
2563.Sp
2564All of those classes have these methods:
2565.RS 4
2566.IP "ev::TYPE::TYPE ()" 4
2567.IX Item "ev::TYPE::TYPE ()"
2568.PD 0
2569.IP "ev::TYPE::TYPE (struct ev_loop *)" 4
2570.IX Item "ev::TYPE::TYPE (struct ev_loop *)"
2571.IP "ev::TYPE::~TYPE" 4
2572.IX Item "ev::TYPE::~TYPE"
2573.PD
2574The constructor (optionally) takes an event loop to associate the watcher
2575with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR.
2576.Sp
2577The constructor calls \f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the
2578\&\f(CW\*(C`set\*(C'\fR method before starting it.
2579.Sp
2580It will not set a callback, however: You have to call the templated \f(CW\*(C`set\*(C'\fR
2581method to set a callback before you can start the watcher.
2582.Sp
2583(The reason why you have to use a method is a limitation in \*(C+ which does
2584not allow explicit template arguments for constructors).
2585.Sp
2586The destructor automatically stops the watcher if it is active.
2587.IP "w\->set<class, &class::method> (object *)" 4
2588.IX Item "w->set<class, &class::method> (object *)"
2589This method sets the callback method to call. The method has to have a
2590signature of \f(CW\*(C`void (*)(ev_TYPE &, int)\*(C'\fR, it receives the watcher as
2591first argument and the \f(CW\*(C`revents\*(C'\fR as second. The object must be given as
2592parameter and is stored in the \f(CW\*(C`data\*(C'\fR member of the watcher.
2593.Sp
2594This method synthesizes efficient thunking code to call your method from
2595the C callback that libev requires. If your compiler can inline your
2596callback (i.e. it is visible to it at the place of the \f(CW\*(C`set\*(C'\fR call and
2597your compiler is good :), then the method will be fully inlined into the
2598thunking function, making it as fast as a direct C callback.
2599.Sp
2600Example: simple class declaration and watcher initialisation
2601.Sp
2602.Vb 4
2603\& struct myclass
2604\& {
2605\& void io_cb (ev::io &w, int revents) { }
2606\& }
2607\&
2608\& myclass obj;
2609\& ev::io iow;
2610\& iow.set <myclass, &myclass::io_cb> (&obj);
2611.Ve
2612.IP "w\->set<function> (void *data = 0)" 4
2613.IX Item "w->set<function> (void *data = 0)"
2614Also sets a callback, but uses a static method or plain function as
2615callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
2616\&\f(CW\*(C`data\*(C'\fR member and is free for you to use.
2617.Sp
2618The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
2619.Sp
2620See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
2621.Sp
2622Example:
2623.Sp
2624.Vb 2
2625\& static void io_cb (ev::io &w, int revents) { }
2626\& iow.set <io_cb> ();
2627.Ve
2628.IP "w\->set (struct ev_loop *)" 4
2629.IX Item "w->set (struct ev_loop *)"
2630Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
2631do this when the watcher is inactive (and not pending either).
2632.IP "w\->set ([args])" 4
2633.IX Item "w->set ([args])"
2634Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same args. Must be
2635called at least once. Unlike the C counterpart, an active watcher gets
2636automatically stopped and restarted when reconfiguring it with this
2637method.
2638.IP "w\->start ()" 4
2639.IX Item "w->start ()"
2640Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
2641constructor already stores the event loop.
2642.IP "w\->stop ()" 4
2643.IX Item "w->stop ()"
2644Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
2645.ie n .IP "w\->again () (""ev::timer""\fR, \f(CW""ev::periodic"" only)" 4
2646.el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
2647.IX Item "w->again () (ev::timer, ev::periodic only)"
2648For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
2649\&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
2650.ie n .IP "w\->sweep () (""ev::embed"" only)" 4
2651.el .IP "w\->sweep () (\f(CWev::embed\fR only)" 4
2652.IX Item "w->sweep () (ev::embed only)"
2653Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR.
2654.ie n .IP "w\->update () (""ev::stat"" only)" 4
2655.el .IP "w\->update () (\f(CWev::stat\fR only)" 4
2656.IX Item "w->update () (ev::stat only)"
2657Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
2658.RE
2659.RS 4
2660.RE
2661.PP
2662Example: Define a class with an \s-1IO\s0 and idle watcher, start one of them in
2663the constructor.
2664.PP
2665.Vb 4
2666\& class myclass
2667\& {
2668\& ev::io io; void io_cb (ev::io &w, int revents);
2669\& ev:idle idle void idle_cb (ev::idle &w, int revents);
2670\&
2671\& myclass (int fd)
2672\& {
2673\& io .set <myclass, &myclass::io_cb > (this);
2674\& idle.set <myclass, &myclass::idle_cb> (this);
2675\&
2676\& io.start (fd, ev::READ);
2677\& }
2678\& };
2679.Ve
2680.SH "OTHER LANGUAGE BINDINGS"
2681.IX Header "OTHER LANGUAGE BINDINGS"
2682Libev does not offer other language bindings itself, but bindings for a
2683numbe rof languages exist in the form of third-party packages. If you know
2684any interesting language binding in addition to the ones listed here, drop
2685me a note.
2686.IP "Perl" 4
2687.IX Item "Perl"
2688The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test
2689libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module,
2690there are additional modules that implement libev-compatible interfaces
2691to \f(CW\*(C`libadns\*(C'\fR (\f(CW\*(C`EV::ADNS\*(C'\fR), \f(CW\*(C`Net::SNMP\*(C'\fR (\f(CW\*(C`Net::SNMP::EV\*(C'\fR) and the
2692\&\f(CW\*(C`libglib\*(C'\fR event core (\f(CW\*(C`Glib::EV\*(C'\fR and \f(CW\*(C`EV::Glib\*(C'\fR).
2693.Sp
2694It can be found and installed via \s-1CPAN\s0, its homepage is found at
2695<http://software.schmorp.de/pkg/EV>.
2696.IP "Ruby" 4
2697.IX Item "Ruby"
2698Tony Arcieri has written a ruby extension that offers access to a subset
2699of the libev \s-1API\s0 and adds filehandle abstractions, asynchronous \s-1DNS\s0 and
2700more on top of it. It can be found via gem servers. Its homepage is at
2701<http://rev.rubyforge.org/>.
2702.IP "D" 4
2703.IX Item "D"
2704Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
2705be found at <http://git.llucax.com.ar/?p=software/ev.d.git;a=summary>.
2706.SH "MACRO MAGIC"
2707.IX Header "MACRO MAGIC"
2708Libev can be compiled with a variety of options, the most fundamantal
2709of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most)
2710functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
2711.PP
2712To make it easier to write programs that cope with either variant, the
2713following macros are defined:
2714.ie n .IP """EV_A""\fR, \f(CW""EV_A_""" 4
2715.el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
2716.IX Item "EV_A, EV_A_"
2717This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
2718loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
2719\&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
2720.Sp
2721.Vb 3
2722\& ev_unref (EV_A);
2723\& ev_timer_add (EV_A_ watcher);
2724\& ev_loop (EV_A_ 0);
2725.Ve
2726.Sp
2727It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
2728which is often provided by the following macro.
2729.ie n .IP """EV_P""\fR, \f(CW""EV_P_""" 4
2730.el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
2731.IX Item "EV_P, EV_P_"
2732This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
2733loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
2734\&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
2735.Sp
2736.Vb 2
2737\& // this is how ev_unref is being declared
2738\& static void ev_unref (EV_P);
2739\&
2740\& // this is how you can declare your typical callback
2741\& static void cb (EV_P_ ev_timer *w, int revents)
2742.Ve
2743.Sp
2744It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
2745suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
2746.ie n .IP """EV_DEFAULT""\fR, \f(CW""EV_DEFAULT_""" 4
2747.el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
2748.IX Item "EV_DEFAULT, EV_DEFAULT_"
2749Similar to the other two macros, this gives you the value of the default
2750loop, if multiple loops are supported (\*(L"ev loop default\*(R").
2751.ie n .IP """EV_DEFAULT_UC""\fR, \f(CW""EV_DEFAULT_UC_""" 4
2752.el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
2753.IX Item "EV_DEFAULT_UC, EV_DEFAULT_UC_"
2754Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the
2755default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour
2756is undefined when the default loop has not been initialised by a previous
2757execution of \f(CW\*(C`EV_DEFAULT\*(C'\fR, \f(CW\*(C`EV_DEFAULT_\*(C'\fR or \f(CW\*(C`ev_default_init (...)\*(C'\fR.
2758.Sp
2759It is often prudent to use \f(CW\*(C`EV_DEFAULT\*(C'\fR when initialising the first
2760watcher in a function but use \f(CW\*(C`EV_DEFAULT_UC\*(C'\fR afterwards.
2761.PP
2762Example: Declare and initialise a check watcher, utilising the above
2763macros so it will work regardless of whether multiple loops are supported
2764or not.
2765.PP
2766.Vb 5
2767\& static void
2768\& check_cb (EV_P_ ev_timer *w, int revents)
2769\& {
2770\& ev_check_stop (EV_A_ w);
2771\& }
2772\&
2773\& ev_check check;
2774\& ev_check_init (&check, check_cb);
2775\& ev_check_start (EV_DEFAULT_ &check);
2776\& ev_loop (EV_DEFAULT_ 0);
2777.Ve
2778.SH "EMBEDDING"
2779.IX Header "EMBEDDING"
2780Libev can (and often is) directly embedded into host
2781applications. Examples of applications that embed it include the Deliantra
2782Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
2783and rxvt-unicode.
2784.PP
2785The goal is to enable you to just copy the necessary files into your
2786source directory without having to change even a single line in them, so
2787you can easily upgrade by simply copying (or having a checked-out copy of
2788libev somewhere in your source tree).
2789.Sh "\s-1FILESETS\s0"
2790.IX Subsection "FILESETS"
2791Depending on what features you need you need to include one or more sets of files
2792in your app.
2793.PP
2794\fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR
2795.IX Subsection "CORE EVENT LOOP"
2796.PP
2797To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
2798configuration (no autoconf):
2799.PP
2800.Vb 2
2801\& #define EV_STANDALONE 1
2802\& #include "ev.c"
2803.Ve
2804.PP
2805This will automatically include \fIev.h\fR, too, and should be done in a
2806single C source file only to provide the function implementations. To use
2807it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best
2808done by writing a wrapper around \fIev.h\fR that you can include instead and
2809where you can put other configuration options):
2810.PP
2811.Vb 2
2812\& #define EV_STANDALONE 1
2813\& #include "ev.h"
2814.Ve
2815.PP
2816Both header files and implementation files can be compiled with a \*(C+
2817compiler (at least, thats a stated goal, and breakage will be treated
2818as a bug).
2819.PP
2820You need the following files in your source tree, or in a directory
2821in your include path (e.g. in libev/ when using \-Ilibev):
2822.PP
2823.Vb 4
2824\& ev.h
2825\& ev.c
2826\& ev_vars.h
2827\& ev_wrap.h
2828\&
2829\& ev_win32.c required on win32 platforms only
2830\&
2831\& ev_select.c only when select backend is enabled (which is enabled by default)
2832\& ev_poll.c only when poll backend is enabled (disabled by default)
2833\& ev_epoll.c only when the epoll backend is enabled (disabled by default)
2834\& ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2835\& ev_port.c only when the solaris port backend is enabled (disabled by default)
2836.Ve
2837.PP
2838\&\fIev.c\fR includes the backend files directly when enabled, so you only need
2839to compile this single file.
2840.PP
2841\fI\s-1LIBEVENT\s0 \s-1COMPATIBILITY\s0 \s-1API\s0\fR
2842.IX Subsection "LIBEVENT COMPATIBILITY API"
2843.PP
2844To include the libevent compatibility \s-1API\s0, also include:
2845.PP
2846.Vb 1
2847\& #include "event.c"
2848.Ve
2849.PP
2850in the file including \fIev.c\fR, and:
2851.PP
2852.Vb 1
2853\& #include "event.h"
2854.Ve
2855.PP
2856in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR.
2857.PP
2858You need the following additional files for this:
2859.PP
2860.Vb 2
2861\& event.h
2862\& event.c
2863.Ve
2864.PP
2865\fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR
2866.IX Subsection "AUTOCONF SUPPORT"
2867.PP
2868Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your config in
2869whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
2870\&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then
2871include \fIconfig.h\fR and configure itself accordingly.
2872.PP
2873For this of course you need the m4 file:
2874.PP
2875.Vb 1
2876\& libev.m4
2877.Ve
2878.Sh "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0"
2879.IX Subsection "PREPROCESSOR SYMBOLS/MACROS"
2880Libev can be configured via a variety of preprocessor symbols you have to
2881define before including any of its files. The default in the absense of
2882autoconf is noted for every option.
2883.IP "\s-1EV_STANDALONE\s0" 4
2884.IX Item "EV_STANDALONE"
2885Must always be \f(CW1\fR if you do not use autoconf configuration, which
2886keeps libev from including \fIconfig.h\fR, and it also defines dummy
2887implementations for some libevent functions (such as logging, which is not
2888supported). It will also not define any of the structs usually found in
2889\&\fIevent.h\fR that are not directly supported by the libev core alone.
2890.IP "\s-1EV_USE_MONOTONIC\s0" 4
2891.IX Item "EV_USE_MONOTONIC"
2892If defined to be \f(CW1\fR, libev will try to detect the availability of the
2893monotonic clock option at both compiletime and runtime. Otherwise no use
2894of the monotonic clock option will be attempted. If you enable this, you
2895usually have to link against librt or something similar. Enabling it when
2896the functionality isn't available is safe, though, although you have
2897to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
2898function is hiding in (often \fI\-lrt\fR).
2899.IP "\s-1EV_USE_REALTIME\s0" 4
2900.IX Item "EV_USE_REALTIME"
2901If defined to be \f(CW1\fR, libev will try to detect the availability of the
2902realtime clock option at compiletime (and assume its availability at
2903runtime if successful). Otherwise no use of the realtime clock option will
2904be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR by \f(CW\*(C`clock_get
2905(CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect correctness. See the
2906note about libraries in the description of \f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though.
2907.IP "\s-1EV_USE_NANOSLEEP\s0" 4
2908.IX Item "EV_USE_NANOSLEEP"
2909If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available
2910and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR.
2911.IP "\s-1EV_USE_EVENTFD\s0" 4
2912.IX Item "EV_USE_EVENTFD"
2913If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
2914available and will probe for kernel support at runtime. This will improve
2915\&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
2916If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
29172.7 or newer, otherwise disabled.
2918.IP "\s-1EV_USE_SELECT\s0" 4
2919.IX Item "EV_USE_SELECT"
2920If undefined or defined to be \f(CW1\fR, libev will compile in support for the
2921\&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at autodetection will be done: if no
2922other method takes over, select will be it. Otherwise the select backend
2923will not be compiled in.
2924.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
2925.IX Item "EV_SELECT_USE_FD_SET"
2926If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR
2927structure. This is useful if libev doesn't compile due to a missing
2928\&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it misguesses the bitset layout on
2929exotic systems. This usually limits the range of file descriptors to some
2930low limit such as 1024 or might have other limitations (winsocket only
2931allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation, might
2932influence the size of the \f(CW\*(C`fd_set\*(C'\fR used.
2933.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
2934.IX Item "EV_SELECT_IS_WINSOCKET"
2935When defined to \f(CW1\fR, the select backend will assume that
2936select/socket/connect etc. don't understand file descriptors but
2937wants osf handles on win32 (this is the case when the select to
2938be used is the winsock select). This means that it will call
2939\&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
2940it is assumed that all these functions actually work on fds, even
2941on win32. Should not be defined on non\-win32 platforms.
2942.IP "\s-1EV_FD_TO_WIN32_HANDLE\s0" 4
2943.IX Item "EV_FD_TO_WIN32_HANDLE"
2944If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map
2945file descriptors to socket handles. When not defining this symbol (the
2946default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually
2947correct. In some cases, programs use their own file descriptor management,
2948in which case they can provide this function to map fds to socket handles.
2949.IP "\s-1EV_USE_POLL\s0" 4
2950.IX Item "EV_USE_POLL"
2951If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2)
2952backend. Otherwise it will be enabled on non\-win32 platforms. It
2953takes precedence over select.
2954.IP "\s-1EV_USE_EPOLL\s0" 4
2955.IX Item "EV_USE_EPOLL"
2956If defined to be \f(CW1\fR, libev will compile in support for the Linux
2957\&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime,
2958otherwise another method will be used as fallback. This is the preferred
2959backend for GNU/Linux systems. If undefined, it will be enabled if the
2960headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2961.IP "\s-1EV_USE_KQUEUE\s0" 4
2962.IX Item "EV_USE_KQUEUE"
2963If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
2964\&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime,
2965otherwise another method will be used as fallback. This is the preferred
2966backend for \s-1BSD\s0 and BSD-like systems, although on most BSDs kqueue only
2967supports some types of fds correctly (the only platform we found that
2968supports ptys for example was NetBSD), so kqueue might be compiled in, but
2969not be used unless explicitly requested. The best way to use it is to find
2970out whether kqueue supports your type of fd properly and use an embedded
2971kqueue loop.
2972.IP "\s-1EV_USE_PORT\s0" 4
2973.IX Item "EV_USE_PORT"
2974If defined to be \f(CW1\fR, libev will compile in support for the Solaris
297510 port style backend. Its availability will be detected at runtime,
2976otherwise another method will be used as fallback. This is the preferred
2977backend for Solaris 10 systems.
2978.IP "\s-1EV_USE_DEVPOLL\s0" 4
2979.IX Item "EV_USE_DEVPOLL"
2980reserved for future expansion, works like the \s-1USE\s0 symbols above.
2981.IP "\s-1EV_USE_INOTIFY\s0" 4
2982.IX Item "EV_USE_INOTIFY"
2983If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
2984interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
2985be detected at runtime. If undefined, it will be enabled if the headers
2986indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2987.IP "\s-1EV_ATOMIC_T\s0" 4
2988.IX Item "EV_ATOMIC_T"
2989Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
2990access is atomic with respect to other threads or signal contexts. No such
2991type is easily found in the C language, so you can provide your own type
2992that you know is safe for your purposes. It is used both for signal handler \*(L"locking\*(R"
2993as well as for signal and thread safety in \f(CW\*(C`ev_async\*(C'\fR watchers.
2994.Sp
2995In the absense of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR
2996(from \fIsignal.h\fR), which is usually good enough on most platforms.
2997.IP "\s-1EV_H\s0" 4
2998.IX Item "EV_H"
2999The name of the \fIev.h\fR header file used to include it. The default if
3000undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be
3001used to virtually rename the \fIev.h\fR header file in case of conflicts.
3002.IP "\s-1EV_CONFIG_H\s0" 4
3003.IX Item "EV_CONFIG_H"
3004If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
3005\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
3006\&\f(CW\*(C`EV_H\*(C'\fR, above.
3007.IP "\s-1EV_EVENT_H\s0" 4
3008.IX Item "EV_EVENT_H"
3009Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea
3010of how the \fIevent.h\fR header can be found, the default is \f(CW"event.h"\fR.
3011.IP "\s-1EV_PROTOTYPES\s0" 4
3012.IX Item "EV_PROTOTYPES"
3013If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
3014prototypes, but still define all the structs and other symbols. This is
3015occasionally useful if you want to provide your own wrapper functions
3016around libev functions.
3017.IP "\s-1EV_MULTIPLICITY\s0" 4
3018.IX Item "EV_MULTIPLICITY"
3019If undefined or defined to \f(CW1\fR, then all event-loop-specific functions
3020will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create
3021additional independent event loops. Otherwise there will be no support
3022for multiple event loops and there is no first event loop pointer
3023argument. Instead, all functions act on the single default loop.
3024.IP "\s-1EV_MINPRI\s0" 4
3025.IX Item "EV_MINPRI"
3026.PD 0
3027.IP "\s-1EV_MAXPRI\s0" 4
3028.IX Item "EV_MAXPRI"
3029.PD
3030The range of allowed priorities. \f(CW\*(C`EV_MINPRI\*(C'\fR must be smaller or equal to
3031\&\f(CW\*(C`EV_MAXPRI\*(C'\fR, but otherwise there are no non-obvious limitations. You can
3032provide for more priorities by overriding those symbols (usually defined
3033to be \f(CW\*(C`\-2\*(C'\fR and \f(CW2\fR, respectively).
3034.Sp
3035When doing priority-based operations, libev usually has to linearly search
3036all the priorities, so having many of them (hundreds) uses a lot of space
3037and time, so using the defaults of five priorities (\-2 .. +2) is usually
3038fine.
3039.Sp
3040If your embedding app does not need any priorities, defining these both to
3041\&\f(CW0\fR will save some memory and cpu.
3042.IP "\s-1EV_PERIODIC_ENABLE\s0" 4
3043.IX Item "EV_PERIODIC_ENABLE"
3044If undefined or defined to be \f(CW1\fR, then periodic timers are supported. If
3045defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of
3046code.
3047.IP "\s-1EV_IDLE_ENABLE\s0" 4
3048.IX Item "EV_IDLE_ENABLE"
3049If undefined or defined to be \f(CW1\fR, then idle watchers are supported. If
3050defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of
3051code.
3052.IP "\s-1EV_EMBED_ENABLE\s0" 4
3053.IX Item "EV_EMBED_ENABLE"
3054If undefined or defined to be \f(CW1\fR, then embed watchers are supported. If
3055defined to be \f(CW0\fR, then they are not.
3056.IP "\s-1EV_STAT_ENABLE\s0" 4
3057.IX Item "EV_STAT_ENABLE"
3058If undefined or defined to be \f(CW1\fR, then stat watchers are supported. If
3059defined to be \f(CW0\fR, then they are not.
3060.IP "\s-1EV_FORK_ENABLE\s0" 4
3061.IX Item "EV_FORK_ENABLE"
3062If undefined or defined to be \f(CW1\fR, then fork watchers are supported. If
3063defined to be \f(CW0\fR, then they are not.
3064.IP "\s-1EV_ASYNC_ENABLE\s0" 4
3065.IX Item "EV_ASYNC_ENABLE"
3066If undefined or defined to be \f(CW1\fR, then async watchers are supported. If
3067defined to be \f(CW0\fR, then they are not.
3068.IP "\s-1EV_MINIMAL\s0" 4
3069.IX Item "EV_MINIMAL"
3070If you need to shave off some kilobytes of code at the expense of some
3071speed, define this symbol to \f(CW1\fR. Currently this is used to override some
3072inlining decisions, saves roughly 30% codesize of amd64. It also selects a
3073much smaller 2\-heap for timer management over the default 4\-heap.
3074.IP "\s-1EV_PID_HASHSIZE\s0" 4
3075.IX Item "EV_PID_HASHSIZE"
3076\&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by
3077pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR), usually more
3078than enough. If you need to manage thousands of children you might want to
3079increase this value (\fImust\fR be a power of two).
3080.IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4
3081.IX Item "EV_INOTIFY_HASHSIZE"
3082\&\f(CW\*(C`ev_stat\*(C'\fR watchers use a small hash table to distribute workload by
3083inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR),
3084usually more than enough. If you need to manage thousands of \f(CW\*(C`ev_stat\*(C'\fR
3085watchers you might want to increase this value (\fImust\fR be a power of
3086two).
3087.IP "\s-1EV_USE_4HEAP\s0" 4
3088.IX Item "EV_USE_4HEAP"
3089Heaps are not very cache-efficient. To improve the cache-efficiency of the
3090timer and periodics heap, libev uses a 4\-heap when this symbol is defined
3091to \f(CW1\fR. The 4\-heap uses more complicated (longer) code but has a
3092noticable after performance with many (thousands) of watchers.
3093.Sp
3094The default is \f(CW1\fR unless \f(CW\*(C`EV_MINIMAL\*(C'\fR is set in which case it is \f(CW0\fR
3095(disabled).
3096.IP "\s-1EV_HEAP_CACHE_AT\s0" 4
3097.IX Item "EV_HEAP_CACHE_AT"
3098Heaps are not very cache-efficient. To improve the cache-efficiency of the
3099timer and periodics heap, libev can cache the timestamp (\fIat\fR) within
3100the heap structure (selected by defining \f(CW\*(C`EV_HEAP_CACHE_AT\*(C'\fR to \f(CW1\fR),
3101which uses 8\-12 bytes more per watcher and a few hundred bytes more code,
3102but avoids random read accesses on heap changes. This noticably improves
3103performance noticably with with many (hundreds) of watchers.
3104.Sp
3105The default is \f(CW1\fR unless \f(CW\*(C`EV_MINIMAL\*(C'\fR is set in which case it is \f(CW0\fR
3106(disabled).
3107.IP "\s-1EV_COMMON\s0" 4
3108.IX Item "EV_COMMON"
3109By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining
3110this macro to a something else you can include more and other types of
3111members. You have to define it each time you include one of the files,
3112though, and it must be identical each time.
3113.Sp
3114For example, the perl \s-1EV\s0 module uses something like this:
3115.Sp
3116.Vb 3
3117\& #define EV_COMMON \e
3118\& SV *self; /* contains this struct */ \e
3119\& SV *cb_sv, *fh /* note no trailing ";" */
3120.Ve
3121.IP "\s-1EV_CB_DECLARE\s0 (type)" 4
3122.IX Item "EV_CB_DECLARE (type)"
3123.PD 0
3124.IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4
3125.IX Item "EV_CB_INVOKE (watcher, revents)"
3126.IP "ev_set_cb (ev, cb)" 4
3127.IX Item "ev_set_cb (ev, cb)"
3128.PD
3129Can be used to change the callback member declaration in each watcher,
3130and the way callbacks are invoked and set. Must expand to a struct member
3131definition and a statement, respectively. See the \fIev.h\fR header file for
3132their default definitions. One possible use for overriding these is to
3133avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use
3134method calls instead of plain function calls in \*(C+.
3135.Sh "\s-1EXPORTED\s0 \s-1API\s0 \s-1SYMBOLS\s0"
3136.IX Subsection "EXPORTED API SYMBOLS"
3137If you need to re-export the \s-1API\s0 (e.g. via a dll) and you need a list of
3138exported symbols, you can use the provided \fISymbol.*\fR files which list
3139all public symbols, one per line:
3140.PP
3141.Vb 2
3142\& Symbols.ev for libev proper
3143\& Symbols.event for the libevent emulation
3144.Ve
3145.PP
3146This can also be used to rename all public symbols to avoid clashes with
3147multiple versions of libev linked together (which is obviously bad in
3148itself, but sometimes it is inconvinient to avoid this).
3149.PP
3150A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to
3151include before including \fIev.h\fR:
3152.PP
3153.Vb 1
3154\& <Symbols.ev sed \-e "s/.*/#define & myprefix_&/" >wrap.h
3155.Ve
3156.PP
3157This would create a file \fIwrap.h\fR which essentially looks like this:
3158.PP
3159.Vb 4
3160\& #define ev_backend myprefix_ev_backend
3161\& #define ev_check_start myprefix_ev_check_start
3162\& #define ev_check_stop myprefix_ev_check_stop
3163\& ...
3164.Ve
3165.Sh "\s-1EXAMPLES\s0"
3166.IX Subsection "EXAMPLES"
3167For a real-world example of a program the includes libev
3168verbatim, you can have a look at the \s-1EV\s0 perl module
3169(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
3170the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public
3171interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file
3172will be compiled. It is pretty complex because it provides its own header
3173file.
3174.PP
3175The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file
3176that everybody includes and which overrides some configure choices:
3177.PP
3178.Vb 9
3179\& #define EV_MINIMAL 1
3180\& #define EV_USE_POLL 0
3181\& #define EV_MULTIPLICITY 0
3182\& #define EV_PERIODIC_ENABLE 0
3183\& #define EV_STAT_ENABLE 0
3184\& #define EV_FORK_ENABLE 0
3185\& #define EV_CONFIG_H <config.h>
3186\& #define EV_MINPRI 0
3187\& #define EV_MAXPRI 0
3188\&
3189\& #include "ev++.h"
3190.Ve
3191.PP
3192And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled:
3193.PP
3194.Vb 2
3195\& #include "ev_cpp.h"
3196\& #include "ev.c"
3197.Ve
3198.SH "THREADS AND COROUTINES"
3199.IX Header "THREADS AND COROUTINES"
3200.Sh "\s-1THREADS\s0"
3201.IX Subsection "THREADS"
3202Libev itself is completely threadsafe, but it uses no locking. This
3203means that you can use as many loops as you want in parallel, as long as
3204only one thread ever calls into one libev function with the same loop
3205parameter.
3206.PP
3207Or put differently: calls with different loop parameters can be done in
3208parallel from multiple threads, calls with the same loop parameter must be
3209done serially (but can be done from different threads, as long as only one
3210thread ever is inside a call at any point in time, e.g. by using a mutex
3211per loop).
3212.PP
3213If you want to know which design is best for your problem, then I cannot
3214help you but by giving some generic advice:
3215.IP "\(bu" 4
3216most applications have a main thread: use the default libev loop
3217in that thread, or create a seperate thread running only the default loop.
3218.Sp
3219This helps integrating other libraries or software modules that use libev
3220themselves and don't care/know about threading.
3221.IP "\(bu" 4
3222one loop per thread is usually a good model.
3223.Sp
3224Doing this is almost never wrong, sometimes a better-performance model
3225exists, but it is always a good start.
3226.IP "\(bu" 4
3227other models exist, such as the leader/follower pattern, where one
3228loop is handed through multiple threads in a kind of round-robbin fashion.
3229.Sp
3230Chosing a model is hard \- look around, learn, know that usually you cna do
3231better than you currently do :\-)
3232.IP "\(bu" 4
3233often you need to talk to some other thread which blocks in the
3234event loop \- \f(CW\*(C`ev_async\*(C'\fR watchers can be used to wake them up from other
3235threads safely (or from signal contexts...).
3236.Sh "\s-1COROUTINES\s0"
3237.IX Subsection "COROUTINES"
3238Libev is much more accomodating to coroutines (\*(L"cooperative threads\*(R"):
3239libev fully supports nesting calls to it's functions from different
3240coroutines (e.g. you can call \f(CW\*(C`ev_loop\*(C'\fR on the same loop from two
3241different coroutines and switch freely between both coroutines running the
3242loop, as long as you don't confuse yourself). The only exception is that
3243you must not do this from \f(CW\*(C`ev_periodic\*(C'\fR reschedule callbacks.
3244.PP
3245Care has been invested into making sure that libev does not keep local
3246state inside \f(CW\*(C`ev_loop\*(C'\fR, and other calls do not usually allow coroutine
3247switches.
3248.SH "COMPLEXITIES"
3249.IX Header "COMPLEXITIES"
3250In this section the complexities of (many of) the algorithms used inside
3251libev will be explained. For complexity discussions about backends see the
3252documentation for \f(CW\*(C`ev_default_init\*(C'\fR.
3253.PP
3254All of the following are about amortised time: If an array needs to be
3255extended, libev needs to realloc and move the whole array, but this
3256happens asymptotically never with higher number of elements, so O(1) might
3257mean it might do a lengthy realloc operation in rare cases, but on average
3258it is much faster and asymptotically approaches constant time.
3259.IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4
3260.IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)"
3261This means that, when you have a watcher that triggers in one hour and
3262there are 100 watchers that would trigger before that then inserting will
3263have to skip roughly seven (\f(CW\*(C`ld 100\*(C'\fR) of these watchers.
3264.IP "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 4
3265.IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)"
3266That means that changing a timer costs less than removing/adding them
3267as only the relative motion in the event queue has to be paid for.
3268.IP "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)" 4
3269.IX Item "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)"
3270These just add the watcher into an array or at the head of a list.
3271.IP "Stopping check/prepare/idle/fork/async watchers: O(1)" 4
3272.IX Item "Stopping check/prepare/idle/fork/async watchers: O(1)"
3273.PD 0
3274.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4
3275.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))"
3276.PD
3277These watchers are stored in lists then need to be walked to find the
3278correct watcher to remove. The lists are usually short (you don't usually
3279have many watchers waiting for the same fd or signal).
3280.IP "Finding the next timer in each loop iteration: O(1)" 4
3281.IX Item "Finding the next timer in each loop iteration: O(1)"
3282By virtue of using a binary or 4\-heap, the next timer is always found at a
3283fixed position in the storage array.
3284.IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4
3285.IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)"
3286A change means an I/O watcher gets started or stopped, which requires
3287libev to recalculate its status (and possibly tell the kernel, depending
3288on backend and wether \f(CW\*(C`ev_io_set\*(C'\fR was used).
3289.IP "Activating one watcher (putting it into the pending state): O(1)" 4
3290.IX Item "Activating one watcher (putting it into the pending state): O(1)"
3291.PD 0
3292.IP "Priority handling: O(number_of_priorities)" 4
3293.IX Item "Priority handling: O(number_of_priorities)"
3294.PD
3295Priorities are implemented by allocating some space for each
3296priority. When doing priority-based operations, libev usually has to
3297linearly search all the priorities, but starting/stopping and activating
3298watchers becomes O(1) w.r.t. priority handling.
3299.IP "Sending an ev_async: O(1)" 4
3300.IX Item "Sending an ev_async: O(1)"
3301.PD 0
3302.IP "Processing ev_async_send: O(number_of_async_watchers)" 4
3303.IX Item "Processing ev_async_send: O(number_of_async_watchers)"
3304.IP "Processing signals: O(max_signal_number)" 4
3305.IX Item "Processing signals: O(max_signal_number)"
3306.PD
3307Sending involves a syscall \fIiff\fR there were no other \f(CW\*(C`ev_async_send\*(C'\fR
3308calls in the current loop iteration. Checking for async and signal events
3309involves iterating over all running async watchers or all signal numbers.
3310.SH "Win32 platform limitations and workarounds"
3311.IX Header "Win32 platform limitations and workarounds"
3312Win32 doesn't support any of the standards (e.g. \s-1POSIX\s0) that libev
3313requires, and its I/O model is fundamentally incompatible with the \s-1POSIX\s0
3314model. Libev still offers limited functionality on this platform in
3315the form of the \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR backend, and only supports socket
3316descriptors. This only applies when using Win32 natively, not when using
3317e.g. cygwin.
3318.PP
3319Lifting these limitations would basically require the full
3320re-implementation of the I/O system. If you are into these kinds of
3321things, then note that glib does exactly that for you in a very portable
3322way (note also that glib is the slowest event library known to man).
3323.PP
3324There is no supported compilation method available on windows except
3325embedding it into other applications.
3326.PP
3327Due to the many, low, and arbitrary limits on the win32 platform and
3328the abysmal performance of winsockets, using a large number of sockets
3329is not recommended (and not reasonable). If your program needs to use
3330more than a hundred or so sockets, then likely it needs to use a totally
3331different implementation for windows, as libev offers the \s-1POSIX\s0 readyness
3332notification model, which cannot be implemented efficiently on windows
3333(microsoft monopoly games).
3334.IP "The winsocket select function" 4
3335.IX Item "The winsocket select function"
3336The winsocket \f(CW\*(C`select\*(C'\fR function doesn't follow \s-1POSIX\s0 in that it requires
3337socket \fIhandles\fR and not socket \fIfile descriptors\fR. This makes select
3338very inefficient, and also requires a mapping from file descriptors
3339to socket handles. See the discussion of the \f(CW\*(C`EV_SELECT_USE_FD_SET\*(C'\fR,
3340\&\f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR and \f(CW\*(C`EV_FD_TO_WIN32_HANDLE\*(C'\fR preprocessor
3341symbols for more info.
3342.Sp
3343The configuration for a \*(L"naked\*(R" win32 using the microsoft runtime
3344libraries and raw winsocket select is:
3345.Sp
3346.Vb 2
3347\& #define EV_USE_SELECT 1
3348\& #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
3349.Ve
3350.Sp
3351Note that winsockets handling of fd sets is O(n), so you can easily get a
3352complexity in the O(nA\*^X) range when using win32.
3353.IP "Limited number of file descriptors" 4
3354.IX Item "Limited number of file descriptors"
3355Windows has numerous arbitrary (and low) limits on things.
3356.Sp
3357Early versions of winsocket's select only supported waiting for a maximum
3358of \f(CW64\fR handles (probably owning to the fact that all windows kernels
3359can only wait for \f(CW64\fR things at the same time internally; microsoft
3360recommends spawning a chain of threads and wait for 63 handles and the
3361previous thread in each. Great).
3362.Sp
3363Newer versions support more handles, but you need to define \f(CW\*(C`FD_SETSIZE\*(C'\fR
3364to some high number (e.g. \f(CW2048\fR) before compiling the winsocket select
3365call (which might be in libev or elsewhere, for example, perl does its own
3366select emulation on windows).
3367.Sp
3368Another limit is the number of file descriptors in the microsoft runtime
3369libraries, which by default is \f(CW64\fR (there must be a hidden \fI64\fR fetish
3370or something like this inside microsoft). You can increase this by calling
3371\&\f(CW\*(C`_setmaxstdio\*(C'\fR, which can increase this limit to \f(CW2048\fR (another
3372arbitrary limit), but is broken in many versions of the microsoft runtime
3373libraries.
3374.Sp
3375This might get you to about \f(CW512\fR or \f(CW2048\fR sockets (depending on
3376windows version and/or the phase of the moon). To get more, you need to
3377wrap all I/O functions and provide your own fd management, but the cost of
3378calling select (O(nA\*^X)) will likely make this unworkable.
3379.SH "PORTABILITY REQUIREMENTS"
3380.IX Header "PORTABILITY REQUIREMENTS"
3381In addition to a working ISO-C implementation, libev relies on a few
3382additional extensions:
3383.ie n .IP """sig_atomic_t volatile"" must be thread-atomic as well" 4
3384.el .IP "\f(CWsig_atomic_t volatile\fR must be thread-atomic as well" 4
3385.IX Item "sig_atomic_t volatile must be thread-atomic as well"
3386The type \f(CW\*(C`sig_atomic_t volatile\*(C'\fR (or whatever is defined as
3387\&\f(CW\*(C`EV_ATOMIC_T\*(C'\fR) must be atomic w.r.t. accesses from different
3388threads. This is not part of the specification for \f(CW\*(C`sig_atomic_t\*(C'\fR, but is
3389believed to be sufficiently portable.
3390.ie n .IP """sigprocmask"" must work in a threaded environment" 4
3391.el .IP "\f(CWsigprocmask\fR must work in a threaded environment" 4
3392.IX Item "sigprocmask must work in a threaded environment"
3393Libev uses \f(CW\*(C`sigprocmask\*(C'\fR to temporarily block signals. This is not
3394allowed in a threaded program (\f(CW\*(C`pthread_sigmask\*(C'\fR has to be used). Typical
3395pthread implementations will either allow \f(CW\*(C`sigprocmask\*(C'\fR in the \*(L"main
3396thread\*(R" or will block signals process-wide, both behaviours would
3397be compatible with libev. Interaction between \f(CW\*(C`sigprocmask\*(C'\fR and
3398\&\f(CW\*(C`pthread_sigmask\*(C'\fR could complicate things, however.
3399.Sp
3400The most portable way to handle signals is to block signals in all threads
3401except the initial one, and run the default loop in the initial thread as
3402well.
3403.ie n .IP """long"" must be large enough for common memory allocation sizes" 4
3404.el .IP "\f(CWlong\fR must be large enough for common memory allocation sizes" 4
3405.IX Item "long must be large enough for common memory allocation sizes"
3406To improve portability and simplify using libev, libev uses \f(CW\*(C`long\*(C'\fR
3407internally instead of \f(CW\*(C`size_t\*(C'\fR when allocating its data structures. On
3408non-POSIX systems (Microsoft...) this might be unexpectedly low, but
3409is still at least 31 bits everywhere, which is enough for hundreds of
3410millions of watchers.
3411.ie n .IP """double"" must hold a time value in seconds with enough accuracy" 4
3412.el .IP "\f(CWdouble\fR must hold a time value in seconds with enough accuracy" 4
3413.IX Item "double must hold a time value in seconds with enough accuracy"
3414The type \f(CW\*(C`double\*(C'\fR is used to represent timestamps. It is required to
3415have at least 51 bits of mantissa (and 9 bits of exponent), which is good
3416enough for at least into the year 4000. This requirement is fulfilled by
3417implementations implementing \s-1IEEE\s0 754 (basically all existing ones).
3418.PP
3419If you know of other additional requirements drop me a note.
957.SH "AUTHOR" 3420.SH "AUTHOR"
958.IX Header "AUTHOR" 3421.IX Header "AUTHOR"
959Marc Lehmann <libev@schmorp.de>. 3422Marc Lehmann <libev@schmorp.de>.
3423.SH "POD ERRORS"
3424.IX Header "POD ERRORS"
3425Hey! \fBThe above document had some coding errors, which are explained below:\fR
3426.IP "Around line 3052:" 4
3427.IX Item "Around line 3052:"
3428You forgot a '=back' before '=head2'

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