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129.\" ======================================================================== 132.\" ========================================================================
130.\" 133.\"
131.IX Title ""<STANDARD INPUT>" 1" 134.IX Title "LIBEV 3"
132.TH "<STANDARD INPUT>" 1 "2007-11-23" "perl v5.8.8" "User Contributed Perl Documentation" 135.TH LIBEV 3 "2008-05-22" "libev-3.41" "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.
257.SH "ERROR HANDLING"
258.IX Header "ERROR HANDLING"
259Libev knows three classes of errors: operating system errors, usage errors
260and internal errors (bugs).
261.PP
262When libev catches an operating system error it cannot handle (for example
263a syscall indicating a condition libev cannot fix), it calls the callback
264set via \f(CW\*(C`ev_set_syserr_cb\*(C'\fR, which is supposed to fix the problem or
265abort. The default is to print a diagnostic message and to call \f(CW\*(C`abort
266()\*(C'\fR.
267.PP
268When libev detects a usage error such as a negative timer interval, then
269it will print a diagnostic message and abort (via the \f(CW\*(C`assert\*(C'\fR mechanism,
270so \f(CW\*(C`NDEBUG\*(C'\fR will disable this checking): these are programming errors in
271the libev caller and need to be fixed there.
272.PP
273Libev also has a few internal error-checking \f(CW\*(C`assert\*(C'\fRions, and also has
274extensive consistency checking code. These do not trigger under normal
275circumstances, as they indicate either a bug in libev or worse.
179.SH "GLOBAL FUNCTIONS" 276.SH "GLOBAL FUNCTIONS"
180.IX Header "GLOBAL FUNCTIONS" 277.IX Header "GLOBAL FUNCTIONS"
181These functions can be called anytime, even before initialising the 278These functions can be called anytime, even before initialising the
182library in any way. 279library in any way.
183.IP "ev_tstamp ev_time ()" 4 280.IP "ev_tstamp ev_time ()" 4
184.IX Item "ev_tstamp ev_time ()" 281.IX Item "ev_tstamp ev_time ()"
185Returns the current time as libev would use it. Please note that the 282Returns the current time as libev would use it. Please note that the
186\&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp 283\&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp
187you actually want to know. 284you actually want to know.
285.IP "ev_sleep (ev_tstamp interval)" 4
286.IX Item "ev_sleep (ev_tstamp interval)"
287Sleep for the given interval: The current thread will be blocked until
288either it is interrupted or the given time interval has passed. Basically
289this is a subsecond-resolution \f(CW\*(C`sleep ()\*(C'\fR.
188.IP "int ev_version_major ()" 4 290.IP "int ev_version_major ()" 4
189.IX Item "int ev_version_major ()" 291.IX Item "int ev_version_major ()"
190.PD 0 292.PD 0
191.IP "int ev_version_minor ()" 4 293.IP "int ev_version_minor ()" 4
192.IX Item "int ev_version_minor ()" 294.IX Item "int ev_version_minor ()"
193.PD 295.PD
194You can find out the major and minor version numbers of the library 296You can find out the major and minor \s-1ABI\s0 version numbers of the library
195you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and 297you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and
196\&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global 298\&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global
197symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the 299symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the
198version of the library your program was compiled against. 300version of the library your program was compiled against.
199.Sp 301.Sp
302These version numbers refer to the \s-1ABI\s0 version of the library, not the
303release version.
304.Sp
200Usually, it's a good idea to terminate if the major versions mismatch, 305Usually, it's a good idea to terminate if the major versions mismatch,
201as this indicates an incompatible change. Minor versions are usually 306as this indicates an incompatible change. Minor versions are usually
202compatible to older versions, so a larger minor version alone is usually 307compatible to older versions, so a larger minor version alone is usually
203not a problem. 308not a problem.
309.Sp
310Example: Make sure we haven't accidentally been linked against the wrong
311version.
312.Sp
313.Vb 3
314\& assert (("libev version mismatch",
315\& ev_version_major () == EV_VERSION_MAJOR
316\& && ev_version_minor () >= EV_VERSION_MINOR));
317.Ve
318.IP "unsigned int ev_supported_backends ()" 4
319.IX Item "unsigned int ev_supported_backends ()"
320Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR
321value) compiled into this binary of libev (independent of their
322availability on the system you are running on). See \f(CW\*(C`ev_default_loop\*(C'\fR for
323a description of the set values.
324.Sp
325Example: make sure we have the epoll method, because yeah this is cool and
326a must have and can we have a torrent of it please!!!11
327.Sp
328.Vb 2
329\& assert (("sorry, no epoll, no sex",
330\& ev_supported_backends () & EVBACKEND_EPOLL));
331.Ve
332.IP "unsigned int ev_recommended_backends ()" 4
333.IX Item "unsigned int ev_recommended_backends ()"
334Return the set of all backends compiled into this binary of libev and also
335recommended for this platform. This set is often smaller than the one
336returned by \f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on
337most BSDs and will not be autodetected unless you explicitly request it
338(assuming you know what you are doing). This is the set of backends that
339libev will probe for if you specify no backends explicitly.
340.IP "unsigned int ev_embeddable_backends ()" 4
341.IX Item "unsigned int ev_embeddable_backends ()"
342Returns the set of backends that are embeddable in other event loops. This
343is the theoretical, all-platform, value. To find which backends
344might be supported on the current system, you would need to look at
345\&\f(CW\*(C`ev_embeddable_backends () & ev_supported_backends ()\*(C'\fR, likewise for
346recommended ones.
347.Sp
348See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
204.IP "ev_set_allocator (void *(*cb)(void *ptr, long size))" 4 349.IP "ev_set_allocator (void *(*cb)(void *ptr, long size))" 4
205.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))" 350.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))"
206Sets the allocation function to use (the prototype is similar to the 351Sets the allocation function to use (the prototype is similar \- the
207realloc C function, the semantics are identical). It is used to allocate 352semantics are identical to the \f(CW\*(C`realloc\*(C'\fR C89/SuS/POSIX function). It is
208and free memory (no surprises here). If it returns zero when memory 353used to allocate and free memory (no surprises here). If it returns zero
209needs to be allocated, the library might abort or take some potentially 354when memory needs to be allocated (\f(CW\*(C`size != 0\*(C'\fR), the library might abort
210destructive action. The default is your system realloc function. 355or take some potentially destructive action.
356.Sp
357Since some systems (at least OpenBSD and Darwin) fail to implement
358correct \f(CW\*(C`realloc\*(C'\fR semantics, libev will use a wrapper around the system
359\&\f(CW\*(C`realloc\*(C'\fR and \f(CW\*(C`free\*(C'\fR functions by default.
211.Sp 360.Sp
212You could override this function in high-availability programs to, say, 361You could override this function in high-availability programs to, say,
213free some memory if it cannot allocate memory, to use a special allocator, 362free some memory if it cannot allocate memory, to use a special allocator,
214or even to sleep a while and retry until some memory is available. 363or even to sleep a while and retry until some memory is available.
364.Sp
365Example: Replace the libev allocator with one that waits a bit and then
366retries (example requires a standards-compliant \f(CW\*(C`realloc\*(C'\fR).
367.Sp
368.Vb 6
369\& static void *
370\& persistent_realloc (void *ptr, size_t size)
371\& {
372\& for (;;)
373\& {
374\& void *newptr = realloc (ptr, size);
375\&
376\& if (newptr)
377\& return newptr;
378\&
379\& sleep (60);
380\& }
381\& }
382\&
383\& ...
384\& ev_set_allocator (persistent_realloc);
385.Ve
215.IP "ev_set_syserr_cb (void (*cb)(const char *msg));" 4 386.IP "ev_set_syserr_cb (void (*cb)(const char *msg));" 4
216.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg));" 387.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg));"
217Set the callback function to call on a retryable syscall error (such 388Set the callback function to call on a retryable syscall error (such
218as failed select, poll, epoll_wait). The message is a printable string 389as failed select, poll, epoll_wait). The message is a printable string
219indicating the system call or subsystem causing the problem. If this 390indicating the system call or subsystem causing the problem. If this
220callback is set, then libev will expect it to remedy the sitution, no 391callback is set, then libev will expect it to remedy the sitution, no
221matter what, when it returns. That is, libev will generally retry the 392matter what, when it returns. That is, libev will generally retry the
222requested operation, or, if the condition doesn't go away, do bad stuff 393requested operation, or, if the condition doesn't go away, do bad stuff
223(such as abort). 394(such as abort).
395.Sp
396Example: This is basically the same thing that libev does internally, too.
397.Sp
398.Vb 6
399\& static void
400\& fatal_error (const char *msg)
401\& {
402\& perror (msg);
403\& abort ();
404\& }
405\&
406\& ...
407\& ev_set_syserr_cb (fatal_error);
408.Ve
224.SH "FUNCTIONS CONTROLLING THE EVENT LOOP" 409.SH "FUNCTIONS CONTROLLING THE EVENT LOOP"
225.IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP" 410.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 411An 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 412types of such loops, the \fIdefault\fR loop, which supports signals and child
228events, and dynamically created loops which do not. 413events, 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)" 4 414.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
237.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)" 415.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
238This will initialise the default event loop if it hasn't been initialised 416This will initialise the default event loop if it hasn't been initialised
239yet and return it. If the default loop could not be initialised, returns 417yet and return it. If the default loop could not be initialised, returns
240false. If it already was initialised it simply returns it (and ignores the 418false. If it already was initialised it simply returns it (and ignores the
241flags). 419flags. If that is troubling you, check \f(CW\*(C`ev_backend ()\*(C'\fR afterwards).
242.Sp 420.Sp
243If you don't know what event loop to use, use the one returned from this 421If you don't know what event loop to use, use the one returned from this
244function. 422function.
245.Sp 423.Sp
424Note that this function is \fInot\fR thread-safe, so if you want to use it
425from multiple threads, you have to lock (note also that this is unlikely,
426as loops cannot bes hared easily between threads anyway).
427.Sp
428The default loop is the only loop that can handle \f(CW\*(C`ev_signal\*(C'\fR and
429\&\f(CW\*(C`ev_child\*(C'\fR watchers, and to do this, it always registers a handler
430for \f(CW\*(C`SIGCHLD\*(C'\fR. If this is a problem for your app you can either
431create a dynamic loop with \f(CW\*(C`ev_loop_new\*(C'\fR that doesn't do that, or you
432can simply overwrite the \f(CW\*(C`SIGCHLD\*(C'\fR signal handler \fIafter\fR calling
433\&\f(CW\*(C`ev_default_init\*(C'\fR.
434.Sp
246The flags argument can be used to specify special behaviour or specific 435The 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). 436backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).
248.Sp 437.Sp
249It supports the following flags: 438The following flags are supported:
250.RS 4 439.RS 4
251.ie n .IP """EVFLAG_AUTO""" 4 440.ie n .IP """EVFLAG_AUTO""" 4
252.el .IP "\f(CWEVFLAG_AUTO\fR" 4 441.el .IP "\f(CWEVFLAG_AUTO\fR" 4
253.IX Item "EVFLAG_AUTO" 442.IX Item "EVFLAG_AUTO"
254The default flags value. Use this if you have no clue (it's the right 443The default flags value. Use this if you have no clue (it's the right
… …
260or setgid) then libev will \fInot\fR look at the environment variable 449or 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 450\&\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 451override 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 452useful to try out specific backends to test their performance, or to work
264around bugs. 453around bugs.
454.ie n .IP """EVFLAG_FORKCHECK""" 4
455.el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4
456.IX Item "EVFLAG_FORKCHECK"
457Instead of calling \f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR manually after
458a fork, you can also make libev check for a fork in each iteration by
459enabling this flag.
460.Sp
461This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop,
462and thus this might slow down your event loop if you do a lot of loop
463iterations and little real work, but is usually not noticeable (on my
464GNU/Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn sequence
465without a syscall and thus \fIvery\fR fast, but my GNU/Linux system also has
466\&\f(CW\*(C`pthread_atfork\*(C'\fR which is even faster).
467.Sp
468The big advantage of this flag is that you can forget about fork (and
469forget about forgetting to tell libev about forking) when you use this
470flag.
471.Sp
472This flag setting cannot be overriden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR
473environment variable.
265.ie n .IP """EVMETHOD_SELECT"" (value 1, portable select backend)" 4 474.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
266.el .IP "\f(CWEVMETHOD_SELECT\fR (value 1, portable select backend)" 4 475.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
267.IX Item "EVMETHOD_SELECT (value 1, portable select backend)" 476.IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
268This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as 477This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as
269libev tries to roll its own fd_set with no limits on the number of fds, 478libev tries to roll its own fd_set with no limits on the number of fds,
270but if that fails, expect a fairly low limit on the number of fds when 479but if that fails, expect a fairly low limit on the number of fds when
271using this backend. It doesn't scale too well (O(highest_fd)), but its usually 480using this backend. It doesn't scale too well (O(highest_fd)), but its
272the fastest backend for a low number of fds. 481usually the fastest backend for a low number of (low-numbered :) fds.
482.Sp
483To get good performance out of this backend you need a high amount of
484parallelity (most of the file descriptors should be busy). If you are
485writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many
486connections as possible during one iteration. You might also want to have
487a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of
488readiness notifications you get per iteration.
273.ie n .IP """EVMETHOD_POLL"" (value 2, poll backend, available everywhere except on windows)" 4 489.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)" 4 490.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)" 491.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 492And 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 493than select, but handles sparse fds better and has no artificial
278number of fds you can use (except it will slow down considerably with a 494limit 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). 495considerably with a lot of inactive fds). It scales similarly to select,
496i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for
497performance tips.
280.ie n .IP """EVMETHOD_EPOLL"" (value 4, Linux)" 4 498.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
281.el .IP "\f(CWEVMETHOD_EPOLL\fR (value 4, Linux)" 4 499.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
282.IX Item "EVMETHOD_EPOLL (value 4, Linux)" 500.IX Item "EVBACKEND_EPOLL (value 4, Linux)"
283For few fds, this backend is a bit little slower than poll and select, 501For 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 502but 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 503like O(total_fds) where n is the total number of fds (or the highest fd),
286either O(1) or O(active_fds). 504epoll scales either O(1) or O(active_fds). The epoll design has a number
505of shortcomings, such as silently dropping events in some hard-to-detect
506cases and requiring a syscall per fd change, no fork support and bad
507support for dup.
287.Sp 508.Sp
288While stopping and starting an I/O watcher in the same iteration will 509While stopping, setting and starting an I/O watcher in the same iteration
289result in some caching, there is still a syscall per such incident 510will 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 511(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 512best to avoid that. Also, \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors might not work
292well if you register events for both fds. 513very well if you register events for both fds.
514.Sp
515Please note that epoll sometimes generates spurious notifications, so you
516need to use non-blocking I/O or other means to avoid blocking when no data
517(or space) is available.
518.Sp
519Best performance from this backend is achieved by not unregistering all
520watchers for a file descriptor until it has been closed, if possible, i.e.
521keep at least one watcher active per fd at all times.
522.Sp
523While nominally embeddeble in other event loops, this feature is broken in
524all kernel versions tested so far.
293.ie n .IP """EVMETHOD_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4 525.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)" 4 526.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
295.IX Item "EVMETHOD_KQUEUE (value 8, most BSD clones)" 527.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
296Kqueue deserves special mention, as at the time of this writing, it 528Kqueue deserves special mention, as at the time of this writing, it
297was broken on all BSDs except NetBSD (usually it doesn't work with 529was broken on all BSDs except NetBSD (usually it doesn't work reliably
298anything but sockets and pipes, except on Darwin, where of course its 530with anything but sockets and pipes, except on Darwin, where of course
299completely useless). For this reason its not being \*(L"autodetected\*(R" unless 531it'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). 532unless you explicitly specify it explicitly in the flags (i.e. using
533\&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a known-to-be-good (\-enough)
534system like NetBSD.
535.Sp
536You still can embed kqueue into a normal poll or select backend and use it
537only for sockets (after having made sure that sockets work with kqueue on
538the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
301.Sp 539.Sp
302It scales in the same way as the epoll backend, but the interface to the 540It 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 541kernel is more efficient (which says nothing about its actual speed, of
304course). While starting and stopping an I/O watcher does not cause an 542course). 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 543cause an extra syscall as with \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to
306incident, so its best to avoid that. 544two event changes per incident, support for \f(CW\*(C`fork ()\*(C'\fR is very bad and it
545drops fds silently in similarly hard-to-detect cases.
546.Sp
547This backend usually performs well under most conditions.
548.Sp
549While nominally embeddable in other event loops, this doesn't work
550everywhere, so you might need to test for this. And since it is broken
551almost everywhere, you should only use it when you have a lot of sockets
552(for which it usually works), by embedding it into another event loop
553(e.g. \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR) and using it only for
554sockets.
307.ie n .IP """EVMETHOD_DEVPOLL"" (value 16, Solaris 8)" 4 555.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
308.el .IP "\f(CWEVMETHOD_DEVPOLL\fR (value 16, Solaris 8)" 4 556.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
309.IX Item "EVMETHOD_DEVPOLL (value 16, Solaris 8)" 557.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
310This is not implemented yet (and might never be). 558This is not implemented yet (and might never be, unless you send me an
559implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets
560and is not embeddable, which would limit the usefulness of this backend
561immensely.
311.ie n .IP """EVMETHOD_PORT"" (value 32, Solaris 10)" 4 562.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
312.el .IP "\f(CWEVMETHOD_PORT\fR (value 32, Solaris 10)" 4 563.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
313.IX Item "EVMETHOD_PORT (value 32, Solaris 10)" 564.IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
314This uses the Solaris 10 port mechanism. As with everything on Solaris, 565This 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)). 566it's really slow, but it still scales very well (O(active_fds)).
567.Sp
568Please note that solaris event ports can deliver a lot of spurious
569notifications, so you need to use non-blocking I/O or other means to avoid
570blocking when no data (or space) is available.
571.Sp
572While this backend scales well, it requires one system call per active
573file descriptor per loop iteration. For small and medium numbers of file
574descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend
575might perform better.
576.Sp
577On the positive side, ignoring the spurious readiness notifications, this
578backend actually performed to specification in all tests and is fully
579embeddable, which is a rare feat among the OS-specific backends.
316.ie n .IP """EVMETHOD_ALL""" 4 580.ie n .IP """EVBACKEND_ALL""" 4
317.el .IP "\f(CWEVMETHOD_ALL\fR" 4 581.el .IP "\f(CWEVBACKEND_ALL\fR" 4
318.IX Item "EVMETHOD_ALL" 582.IX Item "EVBACKEND_ALL"
319Try all backends (even potentially broken ones that wouldn't be tried 583Try all backends (even potentially broken ones that wouldn't be tried
320with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as 584with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as
321\&\f(CW\*(C`EVMETHOD_ALL & ~EVMETHOD_KQUEUE\*(C'\fR. 585\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR.
586.Sp
587It is definitely not recommended to use this flag.
322.RE 588.RE
323.RS 4 589.RS 4
324.Sp 590.Sp
325If one or more of these are ored into the flags value, then only these 591If one or more of these are ored into the flags value, then only these
326backends will be tried (in the reverse order as given here). If none are 592backends will be tried (in the reverse order as listed here). If none are
327specified, most compiled-in backend will be tried, usually in reverse 593specified, all backends in \f(CW\*(C`ev_recommended_backends ()\*(C'\fR will be tried.
328order of their flag values :) 594.Sp
595The most typical usage is like this:
596.Sp
597.Vb 2
598\& if (!ev_default_loop (0))
599\& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
600.Ve
601.Sp
602Restrict libev to the select and poll backends, and do not allow
603environment settings to be taken into account:
604.Sp
605.Vb 1
606\& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
607.Ve
608.Sp
609Use whatever libev has to offer, but make sure that kqueue is used if
610available (warning, breaks stuff, best use only with your own private
611event loop and only if you know the \s-1OS\s0 supports your types of fds):
612.Sp
613.Vb 1
614\& ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
615.Ve
329.RE 616.RE
330.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4 617.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
331.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)" 618.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
332Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is 619Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is
333always distinct from the default loop. Unlike the default loop, it cannot 620always distinct from the default loop. Unlike the default loop, it cannot
334handle signal and child watchers, and attempts to do so will be greeted by 621handle signal and child watchers, and attempts to do so will be greeted by
335undefined behaviour (or a failed assertion if assertions are enabled). 622undefined behaviour (or a failed assertion if assertions are enabled).
623.Sp
624Note that this function \fIis\fR thread-safe, and the recommended way to use
625libev with threads is indeed to create one loop per thread, and using the
626default loop in the \*(L"main\*(R" or \*(L"initial\*(R" thread.
627.Sp
628Example: Try to create a event loop that uses epoll and nothing else.
629.Sp
630.Vb 3
631\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
632\& if (!epoller)
633\& fatal ("no epoll found here, maybe it hides under your chair");
634.Ve
336.IP "ev_default_destroy ()" 4 635.IP "ev_default_destroy ()" 4
337.IX Item "ev_default_destroy ()" 636.IX Item "ev_default_destroy ()"
338Destroys the default loop again (frees all memory and kernel state 637Destroys the default loop again (frees all memory and kernel state
339etc.). This stops all registered event watchers (by not touching them in 638etc.). None of the active event watchers will be stopped in the normal
340any way whatsoever, although you cannot rely on this :). 639sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your
640responsibility to either stop all watchers cleanly yoursef \fIbefore\fR
641calling this function, or cope with the fact afterwards (which is usually
642the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them
643for example).
644.Sp
645Note that certain global state, such as signal state, will not be freed by
646this function, and related watchers (such as signal and child watchers)
647would need to be stopped manually.
648.Sp
649In general it is not advisable to call this function except in the
650rare occasion where you really need to free e.g. the signal handling
651pipe fds. If you need dynamically allocated loops it is better to use
652\&\f(CW\*(C`ev_loop_new\*(C'\fR and \f(CW\*(C`ev_loop_destroy\*(C'\fR).
341.IP "ev_loop_destroy (loop)" 4 653.IP "ev_loop_destroy (loop)" 4
342.IX Item "ev_loop_destroy (loop)" 654.IX Item "ev_loop_destroy (loop)"
343Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an 655Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an
344earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR. 656earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR.
345.IP "ev_default_fork ()" 4 657.IP "ev_default_fork ()" 4
346.IX Item "ev_default_fork ()" 658.IX Item "ev_default_fork ()"
659This function sets a flag that causes subsequent \f(CW\*(C`ev_loop\*(C'\fR iterations
347This function reinitialises the kernel state for backends that have 660to reinitialise the kernel state for backends that have one. Despite the
348one. Despite the name, you can call it anytime, but it makes most sense 661name, you can call it anytime, but it makes most sense after forking, in
349after forking, in either the parent or child process (or both, but that 662the child process (or both child and parent, but that again makes little
350again makes little sense). 663sense). You \fImust\fR call it in the child before using any of the libev
664functions, and it will only take effect at the next \f(CW\*(C`ev_loop\*(C'\fR iteration.
351.Sp 665.Sp
352You \fImust\fR call this function in the child process after forking if and 666On the other hand, you only need to call this function in the child
353only if you want to use the event library in both processes. If you just 667process if and only if you want to use the event library in the child. If
354fork+exec, you don't have to call it. 668you just fork+exec, you don't have to call it at all.
355.Sp 669.Sp
356The function itself is quite fast and it's usually not a problem to call 670The function itself is quite fast and it's usually not a problem to call
357it just in case after a fork. To make this easy, the function will fit in 671it just in case after a fork. To make this easy, the function will fit in
358quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR: 672quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR:
359.Sp 673.Sp
… …
363.IP "ev_loop_fork (loop)" 4 677.IP "ev_loop_fork (loop)" 4
364.IX Item "ev_loop_fork (loop)" 678.IX Item "ev_loop_fork (loop)"
365Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by 679Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by
366\&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop 680\&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop
367after fork, and how you do this is entirely your own problem. 681after fork, and how you do this is entirely your own problem.
682.IP "int ev_is_default_loop (loop)" 4
683.IX Item "int ev_is_default_loop (loop)"
684Returns true when the given loop actually is the default loop, false otherwise.
685.IP "unsigned int ev_loop_count (loop)" 4
686.IX Item "unsigned int ev_loop_count (loop)"
687Returns the count of loop iterations for the loop, which is identical to
688the number of times libev did poll for new events. It starts at \f(CW0\fR and
689happily wraps around with enough iterations.
690.Sp
691This value can sometimes be useful as a generation counter of sorts (it
692\&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with
693\&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls.
368.IP "unsigned int ev_method (loop)" 4 694.IP "unsigned int ev_backend (loop)" 4
369.IX Item "unsigned int ev_method (loop)" 695.IX Item "unsigned int ev_backend (loop)"
370Returns one of the \f(CW\*(C`EVMETHOD_*\*(C'\fR flags indicating the event backend in 696Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
371use. 697use.
372.IP "ev_tstamp ev_now (loop)" 4 698.IP "ev_tstamp ev_now (loop)" 4
373.IX Item "ev_tstamp ev_now (loop)" 699.IX Item "ev_tstamp ev_now (loop)"
374Returns the current \*(L"event loop time\*(R", which is the time the event loop 700Returns the current \*(L"event loop time\*(R", which is the time the event loop
375got events and started processing them. This timestamp does not change 701received events and started processing them. This timestamp does not
376as long as callbacks are being processed, and this is also the base time 702change as long as callbacks are being processed, and this is also the base
377used for relative timers. You can treat it as the timestamp of the event 703time used for relative timers. You can treat it as the timestamp of the
378occuring (or more correctly, the mainloop finding out about it). 704event occurring (or more correctly, libev finding out about it).
379.IP "ev_loop (loop, int flags)" 4 705.IP "ev_loop (loop, int flags)" 4
380.IX Item "ev_loop (loop, int flags)" 706.IX Item "ev_loop (loop, int flags)"
381Finally, this is it, the event handler. This function usually is called 707Finally, this is it, the event handler. This function usually is called
382after you initialised all your watchers and you want to start handling 708after you initialised all your watchers and you want to start handling
383events. 709events.
384.Sp 710.Sp
385If the flags argument is specified as 0, it will not return until either 711If the flags argument is specified as \f(CW0\fR, it will not return until
386no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called. 712either no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called.
713.Sp
714Please note that an explicit \f(CW\*(C`ev_unloop\*(C'\fR is usually better than
715relying on all watchers to be stopped when deciding when a program has
716finished (especially in interactive programs), but having a program that
717automatically loops as long as it has to and no longer by virtue of
718relying on its watchers stopping correctly is a thing of beauty.
387.Sp 719.Sp
388A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle 720A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle
389those events and any outstanding ones, but will not block your process in 721those events and any outstanding ones, but will not block your process in
390case there are no events and will return after one iteration of the loop. 722case there are no events and will return after one iteration of the loop.
391.Sp 723.Sp
392A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if 724A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if
393neccessary) and will handle those and any outstanding ones. It will block 725neccessary) and will handle those and any outstanding ones. It will block
394your process until at least one new event arrives, and will return after 726your process until at least one new event arrives, and will return after
395one iteration of the loop. 727one iteration of the loop. This is useful if you are waiting for some
728external event in conjunction with something not expressible using other
729libev watchers. However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is
730usually a better approach for this kind of thing.
396.Sp 731.Sp
397This flags value could be used to implement alternative looping
398constructs, but the \f(CW\*(C`prepare\*(C'\fR and \f(CW\*(C`check\*(C'\fR watchers provide a better and
399more generic mechanism.
400.Sp
401Here are the gory details of what ev_loop does: 732Here are the gory details of what \f(CW\*(C`ev_loop\*(C'\fR does:
402.Sp 733.Sp
403.Vb 15 734.Vb 10
404\& 1. If there are no active watchers (reference count is zero), return. 735\& \- Before the first iteration, call any pending watchers.
736\& * If EVFLAG_FORKCHECK was used, check for a fork.
737\& \- If a fork was detected, queue and call all fork watchers.
405\& 2. Queue and immediately call all prepare watchers. 738\& \- Queue and call all prepare watchers.
406\& 3. If we have been forked, recreate the kernel state. 739\& \- If we have been forked, recreate the kernel state.
407\& 4. Update the kernel state with all outstanding changes. 740\& \- Update the kernel state with all outstanding changes.
408\& 5. Update the "event loop time". 741\& \- Update the "event loop time".
409\& 6. Calculate for how long to block. 742\& \- Calculate for how long to sleep or block, if at all
743\& (active idle watchers, EVLOOP_NONBLOCK or not having
744\& any active watchers at all will result in not sleeping).
745\& \- Sleep if the I/O and timer collect interval say so.
410\& 7. Block the process, waiting for events. 746\& \- Block the process, waiting for any events.
747\& \- Queue all outstanding I/O (fd) events.
411\& 8. Update the "event loop time" and do time jump handling. 748\& \- Update the "event loop time" and do time jump handling.
412\& 9. Queue all outstanding timers. 749\& \- Queue all outstanding timers.
413\& 10. Queue all outstanding periodics. 750\& \- Queue all outstanding periodics.
414\& 11. If no events are pending now, queue all idle watchers. 751\& \- If no events are pending now, queue all idle watchers.
415\& 12. Queue all check watchers. 752\& \- Queue all check watchers.
416\& 13. Call all queued watchers in reverse order (i.e. check watchers first). 753\& \- Call all queued watchers in reverse order (i.e. check watchers first).
754\& Signals and child watchers are implemented as I/O watchers, and will
755\& be handled here by queueing them when their watcher gets executed.
417\& 14. If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK 756\& \- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
418\& was used, return, otherwise continue with step #1. 757\& were used, or there are no active watchers, return, otherwise
758\& continue with step *.
759.Ve
760.Sp
761Example: Queue some jobs and then loop until no events are outstanding
762anymore.
763.Sp
764.Vb 4
765\& ... queue jobs here, make sure they register event watchers as long
766\& ... as they still have work to do (even an idle watcher will do..)
767\& ev_loop (my_loop, 0);
768\& ... jobs done. yeah!
419.Ve 769.Ve
420.IP "ev_unloop (loop, how)" 4 770.IP "ev_unloop (loop, how)" 4
421.IX Item "ev_unloop (loop, how)" 771.IX Item "ev_unloop (loop, how)"
422Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it 772Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it
423has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either 773has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
424\&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or 774\&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or
425\&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return. 775\&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return.
776.Sp
777This \*(L"unloop state\*(R" will be cleared when entering \f(CW\*(C`ev_loop\*(C'\fR again.
426.IP "ev_ref (loop)" 4 778.IP "ev_ref (loop)" 4
427.IX Item "ev_ref (loop)" 779.IX Item "ev_ref (loop)"
428.PD 0 780.PD 0
429.IP "ev_unref (loop)" 4 781.IP "ev_unref (loop)" 4
430.IX Item "ev_unref (loop)" 782.IX Item "ev_unref (loop)"
… …
436returning, \fIev_unref()\fR after starting, and \fIev_ref()\fR before stopping it. For 788returning, \fIev_unref()\fR after starting, and \fIev_ref()\fR before stopping it. For
437example, libev itself uses this for its internal signal pipe: It is not 789example, libev itself uses this for its internal signal pipe: It is not
438visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from exiting if 790visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from exiting if
439no event watchers registered by it are active. It is also an excellent 791no event watchers registered by it are active. It is also an excellent
440way to do this for generic recurring timers or from within third-party 792way to do this for generic recurring timers or from within third-party
441libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR. 793libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR
794(but only if the watcher wasn't active before, or was active before,
795respectively).
796.Sp
797Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_loop\*(C'\fR
798running when nothing else is active.
799.Sp
800.Vb 4
801\& struct ev_signal exitsig;
802\& ev_signal_init (&exitsig, sig_cb, SIGINT);
803\& ev_signal_start (loop, &exitsig);
804\& evf_unref (loop);
805.Ve
806.Sp
807Example: For some weird reason, unregister the above signal handler again.
808.Sp
809.Vb 2
810\& ev_ref (loop);
811\& ev_signal_stop (loop, &exitsig);
812.Ve
813.IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4
814.IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"
815.PD 0
816.IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4
817.IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"
818.PD
819These advanced functions influence the time that libev will spend waiting
820for events. Both are by default \f(CW0\fR, meaning that libev will try to
821invoke timer/periodic callbacks and I/O callbacks with minimum latency.
822.Sp
823Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR)
824allows libev to delay invocation of I/O and timer/periodic callbacks to
825increase efficiency of loop iterations.
826.Sp
827The background is that sometimes your program runs just fast enough to
828handle one (or very few) event(s) per loop iteration. While this makes
829the program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new
830events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high
831overhead for the actual polling but can deliver many events at once.
832.Sp
833By setting a higher \fIio collect interval\fR you allow libev to spend more
834time collecting I/O events, so you can handle more events per iteration,
835at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and
836\&\f(CW\*(C`ev_timer\*(C'\fR) will be not affected. Setting this to a non-null value will
837introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations.
838.Sp
839Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
840to spend more time collecting timeouts, at the expense of increased
841latency (the watcher callback will be called later). \f(CW\*(C`ev_io\*(C'\fR watchers
842will not be affected. Setting this to a non-null value will not introduce
843any overhead in libev.
844.Sp
845Many (busy) programs can usually benefit by setting the io collect
846interval to a value near \f(CW0.1\fR or so, which is often enough for
847interactive servers (of course not for games), likewise for timeouts. It
848usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR,
849as this approsaches the timing granularity of most systems.
850.IP "ev_loop_verify (loop)" 4
851.IX Item "ev_loop_verify (loop)"
852This function only does something when \f(CW\*(C`EV_VERIFY\*(C'\fR support has been
853compiled in. It tries to go through all internal structures and checks
854them for validity. If anything is found to be inconsistent, it will print
855an error message to standard error and call \f(CW\*(C`abort ()\*(C'\fR.
856.Sp
857This can be used to catch bugs inside libev itself: under normal
858circumstances, this function will never abort as of course libev keeps its
859data structures consistent.
442.SH "ANATOMY OF A WATCHER" 860.SH "ANATOMY OF A WATCHER"
443.IX Header "ANATOMY OF A WATCHER" 861.IX Header "ANATOMY OF A WATCHER"
444A watcher is a structure that you create and register to record your 862A watcher is a structure that you create and register to record your
445interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to 863interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to
446become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that: 864become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that:
… …
449\& static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) 867\& static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)
450\& { 868\& {
451\& ev_io_stop (w); 869\& ev_io_stop (w);
452\& ev_unloop (loop, EVUNLOOP_ALL); 870\& ev_unloop (loop, EVUNLOOP_ALL);
453\& } 871\& }
454.Ve 872\&
455.PP
456.Vb 6
457\& struct ev_loop *loop = ev_default_loop (0); 873\& struct ev_loop *loop = ev_default_loop (0);
458\& struct ev_io stdin_watcher; 874\& struct ev_io stdin_watcher;
459\& ev_init (&stdin_watcher, my_cb); 875\& ev_init (&stdin_watcher, my_cb);
460\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); 876\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
461\& ev_io_start (loop, &stdin_watcher); 877\& ev_io_start (loop, &stdin_watcher);
… …
482*)\*(C'\fR), and you can stop watching for events at any time by calling the 898*)\*(C'\fR), and you can stop watching for events at any time by calling the
483corresponding stop function (\f(CW\*(C`ev_<type>_stop (loop, watcher *)\*(C'\fR. 899corresponding stop function (\f(CW\*(C`ev_<type>_stop (loop, watcher *)\*(C'\fR.
484.PP 900.PP
485As long as your watcher is active (has been started but not stopped) you 901As long as your watcher is active (has been started but not stopped) you
486must not touch the values stored in it. Most specifically you must never 902must not touch the values stored in it. Most specifically you must never
487reinitialise it or call its set method. 903reinitialise it or call its \f(CW\*(C`set\*(C'\fR macro.
488.PP
489You can check whether an event is active by calling the \f(CW\*(C`ev_is_active
490(watcher *)\*(C'\fR macro. To see whether an event is outstanding (but the
491callback for it has not been called yet) you can use the \f(CW\*(C`ev_is_pending
492(watcher *)\*(C'\fR macro.
493.PP 904.PP
494Each and every callback receives the event loop pointer as first, the 905Each and every callback receives the event loop pointer as first, the
495registered watcher structure as second, and a bitset of received events as 906registered watcher structure as second, and a bitset of received events as
496third argument. 907third argument.
497.PP 908.PP
… …
522The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread. 933The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread.
523.ie n .IP """EV_CHILD""" 4 934.ie n .IP """EV_CHILD""" 4
524.el .IP "\f(CWEV_CHILD\fR" 4 935.el .IP "\f(CWEV_CHILD\fR" 4
525.IX Item "EV_CHILD" 936.IX Item "EV_CHILD"
526The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change. 937The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change.
938.ie n .IP """EV_STAT""" 4
939.el .IP "\f(CWEV_STAT\fR" 4
940.IX Item "EV_STAT"
941The path specified in the \f(CW\*(C`ev_stat\*(C'\fR watcher changed its attributes somehow.
527.ie n .IP """EV_IDLE""" 4 942.ie n .IP """EV_IDLE""" 4
528.el .IP "\f(CWEV_IDLE\fR" 4 943.el .IP "\f(CWEV_IDLE\fR" 4
529.IX Item "EV_IDLE" 944.IX Item "EV_IDLE"
530The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do. 945The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do.
531.ie n .IP """EV_PREPARE""" 4 946.ie n .IP """EV_PREPARE""" 4
… …
541\&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any 956\&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any
542received events. Callbacks of both watcher types can start and stop as 957received events. Callbacks of both watcher types can start and stop as
543many watchers as they want, and all of them will be taken into account 958many watchers as they want, and all of them will be taken into account
544(for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep 959(for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep
545\&\f(CW\*(C`ev_loop\*(C'\fR from blocking). 960\&\f(CW\*(C`ev_loop\*(C'\fR from blocking).
961.ie n .IP """EV_EMBED""" 4
962.el .IP "\f(CWEV_EMBED\fR" 4
963.IX Item "EV_EMBED"
964The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.
965.ie n .IP """EV_FORK""" 4
966.el .IP "\f(CWEV_FORK\fR" 4
967.IX Item "EV_FORK"
968The event loop has been resumed in the child process after fork (see
969\&\f(CW\*(C`ev_fork\*(C'\fR).
970.ie n .IP """EV_ASYNC""" 4
971.el .IP "\f(CWEV_ASYNC\fR" 4
972.IX Item "EV_ASYNC"
973The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR).
546.ie n .IP """EV_ERROR""" 4 974.ie n .IP """EV_ERROR""" 4
547.el .IP "\f(CWEV_ERROR\fR" 4 975.el .IP "\f(CWEV_ERROR\fR" 4
548.IX Item "EV_ERROR" 976.IX Item "EV_ERROR"
549An unspecified error has occured, the watcher has been stopped. This might 977An unspecified error has occured, the watcher has been stopped. This might
550happen because the watcher could not be properly started because libev 978happen because the watcher could not be properly started because libev
… …
555Libev will usually signal a few \*(L"dummy\*(R" events together with an error, 983Libev will usually signal a few \*(L"dummy\*(R" events together with an error,
556for example it might indicate that a fd is readable or writable, and if 984for example it might indicate that a fd is readable or writable, and if
557your callbacks is well-written it can just attempt the operation and cope 985your callbacks is well-written it can just attempt the operation and cope
558with the error from \fIread()\fR or \fIwrite()\fR. This will not work in multithreaded 986with the error from \fIread()\fR or \fIwrite()\fR. This will not work in multithreaded
559programs, though, so beware. 987programs, though, so beware.
988.Sh "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0"
989.IX Subsection "GENERIC WATCHER FUNCTIONS"
990In the following description, \f(CW\*(C`TYPE\*(C'\fR stands for the watcher type,
991e.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.
992.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
993.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
994.IX Item "ev_init (ev_TYPE *watcher, callback)"
995This macro initialises the generic portion of a watcher. The contents
996of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
997the generic parts of the watcher are initialised, you \fIneed\fR to call
998the type-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR macro afterwards to initialise the
999type-specific parts. For each type there is also a \f(CW\*(C`ev_TYPE_init\*(C'\fR macro
1000which rolls both calls into one.
1001.Sp
1002You can reinitialise a watcher at any time as long as it has been stopped
1003(or never started) and there are no pending events outstanding.
1004.Sp
1005The callback is always of type \f(CW\*(C`void (*)(ev_loop *loop, ev_TYPE *watcher,
1006int revents)\*(C'\fR.
1007.ie n .IP """ev_TYPE_set"" (ev_TYPE *, [args])" 4
1008.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *, [args])" 4
1009.IX Item "ev_TYPE_set (ev_TYPE *, [args])"
1010This macro initialises the type-specific parts of a watcher. You need to
1011call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
1012call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
1013macro on a watcher that is active (it can be pending, however, which is a
1014difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
1015.Sp
1016Although some watcher types do not have type-specific arguments
1017(e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
1018.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
1019.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
1020.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
1021This convinience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
1022calls into a single call. This is the most convinient method to initialise
1023a watcher. The same limitations apply, of course.
1024.ie n .IP """ev_TYPE_start"" (loop *, ev_TYPE *watcher)" 4
1025.el .IP "\f(CWev_TYPE_start\fR (loop *, ev_TYPE *watcher)" 4
1026.IX Item "ev_TYPE_start (loop *, ev_TYPE *watcher)"
1027Starts (activates) the given watcher. Only active watchers will receive
1028events. If the watcher is already active nothing will happen.
1029.ie n .IP """ev_TYPE_stop"" (loop *, ev_TYPE *watcher)" 4
1030.el .IP "\f(CWev_TYPE_stop\fR (loop *, ev_TYPE *watcher)" 4
1031.IX Item "ev_TYPE_stop (loop *, ev_TYPE *watcher)"
1032Stops the given watcher again (if active) and clears the pending
1033status. It is possible that stopped watchers are pending (for example,
1034non-repeating timers are being stopped when they become pending), but
1035\&\f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor pending. If
1036you want to free or reuse the memory used by the watcher it is therefore a
1037good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
1038.IP "bool ev_is_active (ev_TYPE *watcher)" 4
1039.IX Item "bool ev_is_active (ev_TYPE *watcher)"
1040Returns a true value iff the watcher is active (i.e. it has been started
1041and not yet been stopped). As long as a watcher is active you must not modify
1042it.
1043.IP "bool ev_is_pending (ev_TYPE *watcher)" 4
1044.IX Item "bool ev_is_pending (ev_TYPE *watcher)"
1045Returns a true value iff the watcher is pending, (i.e. it has outstanding
1046events but its callback has not yet been invoked). As long as a watcher
1047is pending (but not active) you must not call an init function on it (but
1048\&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe), you must not change its priority, and you must
1049make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR
1050it).
1051.IP "callback ev_cb (ev_TYPE *watcher)" 4
1052.IX Item "callback ev_cb (ev_TYPE *watcher)"
1053Returns the callback currently set on the watcher.
1054.IP "ev_cb_set (ev_TYPE *watcher, callback)" 4
1055.IX Item "ev_cb_set (ev_TYPE *watcher, callback)"
1056Change the callback. You can change the callback at virtually any time
1057(modulo threads).
1058.IP "ev_set_priority (ev_TYPE *watcher, priority)" 4
1059.IX Item "ev_set_priority (ev_TYPE *watcher, priority)"
1060.PD 0
1061.IP "int ev_priority (ev_TYPE *watcher)" 4
1062.IX Item "int ev_priority (ev_TYPE *watcher)"
1063.PD
1064Set and query the priority of the watcher. The priority is a small
1065integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR
1066(default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked
1067before watchers with lower priority, but priority will not keep watchers
1068from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
1069.Sp
1070This means that priorities are \fIonly\fR used for ordering callback
1071invocation after new events have been received. This is useful, for
1072example, to reduce latency after idling, or more often, to bind two
1073watchers on the same event and make sure one is called first.
1074.Sp
1075If you need to suppress invocation when higher priority events are pending
1076you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
1077.Sp
1078You \fImust not\fR change the priority of a watcher as long as it is active or
1079pending.
1080.Sp
1081The default priority used by watchers when no priority has been set is
1082always \f(CW0\fR, which is supposed to not be too high and not be too low :).
1083.Sp
1084Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
1085fine, as long as you do not mind that the priority value you query might
1086or might not have been adjusted to be within valid range.
1087.IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
1088.IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
1089Invoke the \f(CW\*(C`watcher\*(C'\fR with the given \f(CW\*(C`loop\*(C'\fR and \f(CW\*(C`revents\*(C'\fR. Neither
1090\&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback
1091can deal with that fact.
1092.IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
1093.IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
1094If the watcher is pending, this function returns clears its pending status
1095and returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the
1096watcher isn't pending it does nothing and returns \f(CW0\fR.
560.Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0" 1097.Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0"
561.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER" 1098.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
562Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change 1099Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change
563and read at any time, libev will completely ignore it. This can be used 1100and read at any time, libev will completely ignore it. This can be used
564to associate arbitrary data with your watcher. If you need more data and 1101to associate arbitrary data with your watcher. If you need more data and
… …
585\& struct my_io *w = (struct my_io *)w_; 1122\& struct my_io *w = (struct my_io *)w_;
586\& ... 1123\& ...
587\& } 1124\& }
588.Ve 1125.Ve
589.PP 1126.PP
590More interesting and less C\-conformant ways of catsing your callback type 1127More interesting and less C\-conformant ways of casting your callback type
591have been omitted.... 1128instead have been omitted.
1129.PP
1130Another common scenario is having some data structure with multiple
1131watchers:
1132.PP
1133.Vb 6
1134\& struct my_biggy
1135\& {
1136\& int some_data;
1137\& ev_timer t1;
1138\& ev_timer t2;
1139\& }
1140.Ve
1141.PP
1142In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more complicated,
1143you need to use \f(CW\*(C`offsetof\*(C'\fR:
1144.PP
1145.Vb 1
1146\& #include <stddef.h>
1147\&
1148\& static void
1149\& t1_cb (EV_P_ struct ev_timer *w, int revents)
1150\& {
1151\& struct my_biggy big = (struct my_biggy *
1152\& (((char *)w) \- offsetof (struct my_biggy, t1));
1153\& }
1154\&
1155\& static void
1156\& t2_cb (EV_P_ struct ev_timer *w, int revents)
1157\& {
1158\& struct my_biggy big = (struct my_biggy *
1159\& (((char *)w) \- offsetof (struct my_biggy, t2));
1160\& }
1161.Ve
592.SH "WATCHER TYPES" 1162.SH "WATCHER TYPES"
593.IX Header "WATCHER TYPES" 1163.IX Header "WATCHER TYPES"
594This section describes each watcher in detail, but will not repeat 1164This section describes each watcher in detail, but will not repeat
595information given in the last section. 1165information given in the last section. Any initialisation/set macros,
1166functions and members specific to the watcher type are explained.
1167.PP
1168Members are additionally marked with either \fI[read\-only]\fR, meaning that,
1169while the watcher is active, you can look at the member and expect some
1170sensible content, but you must not modify it (you can modify it while the
1171watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
1172means you can expect it to have some sensible content while the watcher
1173is active, but you can also modify it. Modifying it may not do something
1174sensible or take immediate effect (or do anything at all), but libev will
1175not crash or malfunction in any way.
596.ie n .Sh """ev_io"" \- is this file descriptor readable or writable" 1176.ie n .Sh """ev_io"" \- is this file descriptor readable or writable?"
597.el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable" 1177.el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable?"
598.IX Subsection "ev_io - is this file descriptor readable or writable" 1178.IX Subsection "ev_io - is this file descriptor readable or writable?"
599I/O watchers check whether a file descriptor is readable or writable 1179I/O watchers check whether a file descriptor is readable or writable
600in each iteration of the event loop (This behaviour is called 1180in each iteration of the event loop, or, more precisely, when reading
601level-triggering because you keep receiving events as long as the 1181would not block the process and writing would at least be able to write
602condition persists. Remember you can stop the watcher if you don't want to 1182some data. This behaviour is called level-triggering because you keep
603act on the event and neither want to receive future events). 1183receiving events as long as the condition persists. Remember you can stop
1184the watcher if you don't want to act on the event and neither want to
1185receive future events.
604.PP 1186.PP
605In general you can register as many read and/or write event watchers per 1187In general you can register as many read and/or write event watchers per
606fd as you want (as long as you don't confuse yourself). Setting all file 1188fd as you want (as long as you don't confuse yourself). Setting all file
607descriptors to non-blocking mode is also usually a good idea (but not 1189descriptors to non-blocking mode is also usually a good idea (but not
608required if you know what you are doing). 1190required if you know what you are doing).
609.PP 1191.PP
610You have to be careful with dup'ed file descriptors, though. Some backends
611(the linux epoll backend is a notable example) cannot handle dup'ed file
612descriptors correctly if you register interest in two or more fds pointing
613to the same underlying file/socket etc. description (that is, they share
614the same underlying \*(L"file open\*(R").
615.PP
616If you must do this, then force the use of a known-to-be-good backend 1192If you must do this, then force the use of a known-to-be-good backend
617(at the time of this writing, this includes only \s-1EVMETHOD_SELECT\s0 and 1193(at the time of this writing, this includes only \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and
618\&\s-1EVMETHOD_POLL\s0). 1194\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR).
1195.PP
1196Another thing you have to watch out for is that it is quite easy to
1197receive \*(L"spurious\*(R" readiness notifications, that is your callback might
1198be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block
1199because there is no data. Not only are some backends known to create a
1200lot of those (for example solaris ports), it is very easy to get into
1201this situation even with a relatively standard program structure. Thus
1202it is best to always use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning
1203\&\f(CW\*(C`EAGAIN\*(C'\fR is far preferable to a program hanging until some data arrives.
1204.PP
1205If you cannot run the fd in non-blocking mode (for example you should not
1206play around with an Xlib connection), then you have to seperately re-test
1207whether a file descriptor is really ready with a known-to-be good interface
1208such as poll (fortunately in our Xlib example, Xlib already does this on
1209its own, so its quite safe to use).
1210.PP
1211\fIThe special problem of disappearing file descriptors\fR
1212.IX Subsection "The special problem of disappearing file descriptors"
1213.PP
1214Some backends (e.g. kqueue, epoll) need to be told about closing a file
1215descriptor (either by calling \f(CW\*(C`close\*(C'\fR explicitly or by any other means,
1216such as \f(CW\*(C`dup\*(C'\fR). The reason is that you register interest in some file
1217descriptor, but when it goes away, the operating system will silently drop
1218this interest. If another file descriptor with the same number then is
1219registered with libev, there is no efficient way to see that this is, in
1220fact, a different file descriptor.
1221.PP
1222To avoid having to explicitly tell libev about such cases, libev follows
1223the following policy: Each time \f(CW\*(C`ev_io_set\*(C'\fR is being called, libev
1224will assume that this is potentially a new file descriptor, otherwise
1225it is assumed that the file descriptor stays the same. That means that
1226you \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
1227descriptor even if the file descriptor number itself did not change.
1228.PP
1229This is how one would do it normally anyway, the important point is that
1230the libev application should not optimise around libev but should leave
1231optimisations to libev.
1232.PP
1233\fIThe special problem of dup'ed file descriptors\fR
1234.IX Subsection "The special problem of dup'ed file descriptors"
1235.PP
1236Some backends (e.g. epoll), cannot register events for file descriptors,
1237but only events for the underlying file descriptions. That means when you
1238have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register
1239events for them, only one file descriptor might actually receive events.
1240.PP
1241There is no workaround possible except not registering events
1242for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
1243\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1244.PP
1245\fIThe special problem of fork\fR
1246.IX Subsection "The special problem of fork"
1247.PP
1248Some backends (epoll, kqueue) do not support \f(CW\*(C`fork ()\*(C'\fR at all or exhibit
1249useless behaviour. Libev fully supports fork, but needs to be told about
1250it in the child.
1251.PP
1252To support fork in your programs, you either have to call
1253\&\f(CW\*(C`ev_default_fork ()\*(C'\fR or \f(CW\*(C`ev_loop_fork ()\*(C'\fR after a fork in the child,
1254enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or
1255\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1256.PP
1257\fIThe special problem of \s-1SIGPIPE\s0\fR
1258.IX Subsection "The special problem of SIGPIPE"
1259.PP
1260While not really specific to libev, it is easy to forget about \s-1SIGPIPE:\s0
1261when reading from a pipe whose other end has been closed, your program
1262gets send a \s-1SIGPIPE\s0, which, by default, aborts your program. For most
1263programs this is sensible behaviour, for daemons, this is usually
1264undesirable.
1265.PP
1266So when you encounter spurious, unexplained daemon exits, make sure you
1267ignore \s-1SIGPIPE\s0 (and maybe make sure you log the exit status of your daemon
1268somewhere, as that would have given you a big clue).
1269.PP
1270\fIWatcher-Specific Functions\fR
1271.IX Subsection "Watcher-Specific Functions"
619.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4 1272.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
620.IX Item "ev_io_init (ev_io *, callback, int fd, int events)" 1273.IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
621.PD 0 1274.PD 0
622.IP "ev_io_set (ev_io *, int fd, int events)" 4 1275.IP "ev_io_set (ev_io *, int fd, int events)" 4
623.IX Item "ev_io_set (ev_io *, int fd, int events)" 1276.IX Item "ev_io_set (ev_io *, int fd, int events)"
624.PD 1277.PD
625Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The fd is the file descriptor to rceeive 1278Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to
626events for and events is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or \f(CW\*(C`EV_READ | 1279rceeive events for and events is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or
627EV_WRITE\*(C'\fR to receive the given events. 1280\&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR to receive the given events.
1281.IP "int fd [read\-only]" 4
1282.IX Item "int fd [read-only]"
1283The file descriptor being watched.
1284.IP "int events [read\-only]" 4
1285.IX Item "int events [read-only]"
1286The events being watched.
1287.PP
1288\fIExamples\fR
1289.IX Subsection "Examples"
1290.PP
1291Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
1292readable, but only once. Since it is likely line-buffered, you could
1293attempt to read a whole line in the callback.
1294.PP
1295.Vb 6
1296\& static void
1297\& stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)
1298\& {
1299\& ev_io_stop (loop, w);
1300\& .. read from stdin here (or from w\->fd) and haqndle any I/O errors
1301\& }
1302\&
1303\& ...
1304\& struct ev_loop *loop = ev_default_init (0);
1305\& struct ev_io stdin_readable;
1306\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1307\& ev_io_start (loop, &stdin_readable);
1308\& ev_loop (loop, 0);
1309.Ve
628.ie n .Sh """ev_timer"" \- relative and optionally recurring timeouts" 1310.ie n .Sh """ev_timer"" \- relative and optionally repeating timeouts"
629.el .Sh "\f(CWev_timer\fP \- relative and optionally recurring timeouts" 1311.el .Sh "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
630.IX Subsection "ev_timer - relative and optionally recurring timeouts" 1312.IX Subsection "ev_timer - relative and optionally repeating timeouts"
631Timer watchers are simple relative timers that generate an event after a 1313Timer watchers are simple relative timers that generate an event after a
632given time, and optionally repeating in regular intervals after that. 1314given time, and optionally repeating in regular intervals after that.
633.PP 1315.PP
634The timers are based on real time, that is, if you register an event that 1316The timers are based on real time, that is, if you register an event that
635times out after an hour and you reset your system clock to last years 1317times out after an hour and you reset your system clock to january last
636time, it will still time out after (roughly) and hour. \*(L"Roughly\*(R" because 1318year, it will still time out after (roughly) and hour. \*(L"Roughly\*(R" because
637detecting time jumps is hard, and some inaccuracies are unavoidable (the 1319detecting time jumps is hard, and some inaccuracies are unavoidable (the
638monotonic clock option helps a lot here). 1320monotonic clock option helps a lot here).
639.PP 1321.PP
640The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR 1322The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
641time. This is usually the right thing as this timestamp refers to the time 1323time. This is usually the right thing as this timestamp refers to the time
642of the event triggering whatever timeout you are modifying/starting. If 1324of the event triggering whatever timeout you are modifying/starting. If
643you suspect event processing to be delayed and you \fIneed\fR to base the timeout 1325you suspect event processing to be delayed and you \fIneed\fR to base the timeout
644on the current time, use something like this to adjust for this: 1326on the current time, use something like this to adjust for this:
645.PP 1327.PP
646.Vb 1 1328.Vb 1
647\& ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); 1329\& ev_timer_set (&timer, after + ev_now () \- ev_time (), 0.);
648.Ve 1330.Ve
649.PP 1331.PP
650The callback is guarenteed to be invoked only when its timeout has passed, 1332The callback is guarenteed to be invoked only after its timeout has passed,
651but if multiple timers become ready during the same loop iteration then 1333but if multiple timers become ready during the same loop iteration then
652order of execution is undefined. 1334order of execution is undefined.
1335.PP
1336\fIWatcher-Specific Functions and Data Members\fR
1337.IX Subsection "Watcher-Specific Functions and Data Members"
653.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4 1338.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
654.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 1339.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
655.PD 0 1340.PD 0
656.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4 1341.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
657.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 1342.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
658.PD 1343.PD
659Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR is 1344Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR
660\&\f(CW0.\fR, then it will automatically be stopped. If it is positive, then the 1345is \f(CW0.\fR, then it will automatically be stopped once the timeout is
661timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds 1346reached. If it is positive, then the timer will automatically be
662later, again, and again, until stopped manually. 1347configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds later, again, and again,
1348until stopped manually.
663.Sp 1349.Sp
664The timer itself will do a best-effort at avoiding drift, that is, if you 1350The timer itself will do a best-effort at avoiding drift, that is, if
665configure a timer to trigger every 10 seconds, then it will trigger at 1351you configure a timer to trigger every 10 seconds, then it will normally
666exactly 10 second intervals. If, however, your program cannot keep up with 1352trigger at exactly 10 second intervals. If, however, your program cannot
667the timer (because it takes longer than those 10 seconds to do stuff) the 1353keep up with the timer (because it takes longer than those 10 seconds to
668timer will not fire more than once per event loop iteration. 1354do stuff) the timer will not fire more than once per event loop iteration.
669.IP "ev_timer_again (loop)" 4 1355.IP "ev_timer_again (loop, ev_timer *)" 4
670.IX Item "ev_timer_again (loop)" 1356.IX Item "ev_timer_again (loop, ev_timer *)"
671This will act as if the timer timed out and restart it again if it is 1357This will act as if the timer timed out and restart it again if it is
672repeating. The exact semantics are: 1358repeating. The exact semantics are:
673.Sp 1359.Sp
1360If the timer is pending, its pending status is cleared.
1361.Sp
674If the timer is started but nonrepeating, stop it. 1362If the timer is started but nonrepeating, stop it (as if it timed out).
675.Sp 1363.Sp
676If the timer is repeating, either start it if necessary (with the repeat 1364If the timer is repeating, either start it if necessary (with the
677value), or reset the running timer to the repeat value. 1365\&\f(CW\*(C`repeat\*(C'\fR value), or reset the running timer to the \f(CW\*(C`repeat\*(C'\fR value.
678.Sp 1366.Sp
679This sounds a bit complicated, but here is a useful and typical 1367This sounds a bit complicated, but here is a useful and typical
680example: Imagine you have a tcp connection and you want a so-called idle 1368example: Imagine you have a tcp connection and you want a so-called idle
681timeout, that is, you want to be called when there have been, say, 60 1369timeout, that is, you want to be called when there have been, say, 60
682seconds of inactivity on the socket. The easiest way to do this is to 1370seconds of inactivity on the socket. The easiest way to do this is to
683configure an \f(CW\*(C`ev_timer\*(C'\fR with after=repeat=60 and calling ev_timer_again each 1371configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value of \f(CW60\fR and then call
684time you successfully read or write some data. If you go into an idle 1372\&\f(CW\*(C`ev_timer_again\*(C'\fR each time you successfully read or write some data. If
685state where you do not expect data to travel on the socket, you can stop 1373you go into an idle state where you do not expect data to travel on the
686the timer, and again will automatically restart it if need be. 1374socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will
1375automatically restart it if need be.
1376.Sp
1377That means you can ignore the \f(CW\*(C`after\*(C'\fR value and \f(CW\*(C`ev_timer_start\*(C'\fR
1378altogether and only ever use the \f(CW\*(C`repeat\*(C'\fR value and \f(CW\*(C`ev_timer_again\*(C'\fR:
1379.Sp
1380.Vb 8
1381\& ev_timer_init (timer, callback, 0., 5.);
1382\& ev_timer_again (loop, timer);
1383\& ...
1384\& timer\->again = 17.;
1385\& ev_timer_again (loop, timer);
1386\& ...
1387\& timer\->again = 10.;
1388\& ev_timer_again (loop, timer);
1389.Ve
1390.Sp
1391This is more slightly efficient then stopping/starting the timer each time
1392you want to modify its timeout value.
1393.IP "ev_tstamp repeat [read\-write]" 4
1394.IX Item "ev_tstamp repeat [read-write]"
1395The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
1396or \f(CW\*(C`ev_timer_again\*(C'\fR is called and determines the next timeout (if any),
1397which is also when any modifications are taken into account.
1398.PP
1399\fIExamples\fR
1400.IX Subsection "Examples"
1401.PP
1402Example: Create a timer that fires after 60 seconds.
1403.PP
1404.Vb 5
1405\& static void
1406\& one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
1407\& {
1408\& .. one minute over, w is actually stopped right here
1409\& }
1410\&
1411\& struct ev_timer mytimer;
1412\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1413\& ev_timer_start (loop, &mytimer);
1414.Ve
1415.PP
1416Example: Create a timeout timer that times out after 10 seconds of
1417inactivity.
1418.PP
1419.Vb 5
1420\& static void
1421\& timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)
1422\& {
1423\& .. ten seconds without any activity
1424\& }
1425\&
1426\& struct ev_timer mytimer;
1427\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1428\& ev_timer_again (&mytimer); /* start timer */
1429\& ev_loop (loop, 0);
1430\&
1431\& // and in some piece of code that gets executed on any "activity":
1432\& // reset the timeout to start ticking again at 10 seconds
1433\& ev_timer_again (&mytimer);
1434.Ve
687.ie n .Sh """ev_periodic"" \- to cron or not to cron" 1435.ie n .Sh """ev_periodic"" \- to cron or not to cron?"
688.el .Sh "\f(CWev_periodic\fP \- to cron or not to cron" 1436.el .Sh "\f(CWev_periodic\fP \- to cron or not to cron?"
689.IX Subsection "ev_periodic - to cron or not to cron" 1437.IX Subsection "ev_periodic - to cron or not to cron?"
690Periodic watchers are also timers of a kind, but they are very versatile 1438Periodic watchers are also timers of a kind, but they are very versatile
691(and unfortunately a bit complex). 1439(and unfortunately a bit complex).
692.PP 1440.PP
693Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time) 1441Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time)
694but on wallclock time (absolute time). You can tell a periodic watcher 1442but on wallclock time (absolute time). You can tell a periodic watcher
695to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a 1443to trigger after some specific point in time. For example, if you tell a
696periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now () 1444periodic watcher to trigger in 10 seconds (by specifiying e.g. \f(CW\*(C`ev_now ()
697+ 10.>) and then reset your system clock to the last year, then it will 1445+ 10.\*(C'\fR, that is, an absolute time not a delay) and then reset your system
1446clock to january of the previous year, then it will take more than year
698take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger 1447to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would still trigger
699roughly 10 seconds later and of course not if you reset your system time 1448roughly 10 seconds later as it uses a relative timeout).
700again).
701.PP 1449.PP
702They can also be used to implement vastly more complex timers, such as 1450\&\f(CW\*(C`ev_periodic\*(C'\fRs can also be used to implement vastly more complex timers,
703triggering an event on eahc midnight, local time. 1451such as triggering an event on each \*(L"midnight, local time\*(R", or other
1452complicated, rules.
704.PP 1453.PP
705As with timers, the callback is guarenteed to be invoked only when the 1454As with timers, the callback is guarenteed to be invoked only when the
706time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready 1455time (\f(CW\*(C`at\*(C'\fR) has passed, but if multiple periodic timers become ready
707during the same loop iteration then order of execution is undefined. 1456during the same loop iteration then order of execution is undefined.
1457.PP
1458\fIWatcher-Specific Functions and Data Members\fR
1459.IX Subsection "Watcher-Specific Functions and Data Members"
708.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4 1460.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4
709.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 1461.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)"
710.PD 0 1462.PD 0
711.IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4 1463.IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4
712.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 1464.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)"
713.PD 1465.PD
714Lots of arguments, lets sort it out... There are basically three modes of 1466Lots of arguments, lets sort it out... There are basically three modes of
715operation, and we will explain them from simplest to complex: 1467operation, and we will explain them from simplest to complex:
716.RS 4 1468.RS 4
1469.IP "\(bu" 4
717.IP "* absolute timer (interval = reschedule_cb = 0)" 4 1470absolute timer (at = time, interval = reschedule_cb = 0)
718.IX Item "absolute timer (interval = reschedule_cb = 0)" 1471.Sp
719In this configuration the watcher triggers an event at the wallclock time 1472In this configuration the watcher triggers an event after the wallclock
720\&\f(CW\*(C`at\*(C'\fR and doesn't repeat. It will not adjust when a time jump occurs, 1473time \f(CW\*(C`at\*(C'\fR has passed and doesn't repeat. It will not adjust when a time
721that is, if it is to be run at January 1st 2011 then it will run when the 1474jump occurs, that is, if it is to be run at January 1st 2011 then it will
722system time reaches or surpasses this time. 1475run when the system time reaches or surpasses this time.
1476.IP "\(bu" 4
723.IP "* non-repeating interval timer (interval > 0, reschedule_cb = 0)" 4 1477repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)
724.IX Item "non-repeating interval timer (interval > 0, reschedule_cb = 0)" 1478.Sp
725In this mode the watcher will always be scheduled to time out at the next 1479In this mode the watcher will always be scheduled to time out at the next
726\&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N) and then repeat, regardless 1480\&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N, which can also be negative)
727of any time jumps. 1481and then repeat, regardless of any time jumps.
728.Sp 1482.Sp
729This can be used to create timers that do not drift with respect to system 1483This can be used to create timers that do not drift with respect to system
730time: 1484time, for example, here is a \f(CW\*(C`ev_periodic\*(C'\fR that triggers each hour, on
1485the hour:
731.Sp 1486.Sp
732.Vb 1 1487.Vb 1
733\& ev_periodic_set (&periodic, 0., 3600., 0); 1488\& ev_periodic_set (&periodic, 0., 3600., 0);
734.Ve 1489.Ve
735.Sp 1490.Sp
… …
739by 3600. 1494by 3600.
740.Sp 1495.Sp
741Another way to think about it (for the mathematically inclined) is that 1496Another way to think about it (for the mathematically inclined) is that
742\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible 1497\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
743time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps. 1498time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps.
744.IP "* manual reschedule mode (reschedule_cb = callback)" 4 1499.Sp
745.IX Item "manual reschedule mode (reschedule_cb = callback)" 1500For numerical stability it is preferable that the \f(CW\*(C`at\*(C'\fR value is near
1501\&\f(CW\*(C`ev_now ()\*(C'\fR (the current time), but there is no range requirement for
1502this value, and in fact is often specified as zero.
1503.Sp
1504Note also that there is an upper limit to how often a timer can fire (cpu
1505speed for example), so if \f(CW\*(C`interval\*(C'\fR is very small then timing stability
1506will of course detoriate. Libev itself tries to be exact to be about one
1507millisecond (if the \s-1OS\s0 supports it and the machine is fast enough).
1508.IP "\(bu" 4
1509manual reschedule mode (at and interval ignored, reschedule_cb = callback)
1510.Sp
746In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being 1511In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being
747ignored. Instead, each time the periodic watcher gets scheduled, the 1512ignored. Instead, each time the periodic watcher gets scheduled, the
748reschedule callback will be called with the watcher as first, and the 1513reschedule callback will be called with the watcher as first, and the
749current time as second argument. 1514current time as second argument.
750.Sp 1515.Sp
751\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, 1516\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher,
752ever, or make any event loop modifications\fR. If you need to stop it, 1517ever, or make \s-1ANY\s0 event loop modifications whatsoever\fR.
753return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by
754starting a prepare watcher).
755.Sp 1518.Sp
1519If you need to stop it, return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop
1520it afterwards (e.g. by starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is the
1521only event loop modification you are allowed to do).
1522.Sp
756Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w, 1523The callback prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic
757ev_tstamp now)\*(C'\fR, e.g.: 1524*w, ev_tstamp now)\*(C'\fR, e.g.:
758.Sp 1525.Sp
759.Vb 4 1526.Vb 4
760\& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) 1527\& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)
761\& { 1528\& {
762\& return now + 60.; 1529\& return now + 60.;
… …
766It must return the next time to trigger, based on the passed time value 1533It must return the next time to trigger, based on the passed time value
767(that is, the lowest time value larger than to the second argument). It 1534(that is, the lowest time value larger than to the second argument). It
768will usually be called just before the callback will be triggered, but 1535will usually be called just before the callback will be triggered, but
769might be called at other times, too. 1536might be called at other times, too.
770.Sp 1537.Sp
771\&\s-1NOTE:\s0 \fIThis callback must always return a time that is later than the 1538\&\s-1NOTE:\s0 \fIThis callback must always return a time that is higher than or
772passed \f(CI\*(C`now\*(C'\fI value\fR. Not even \f(CW\*(C`now\*(C'\fR itself will do, it \fImust\fR be larger. 1539equal to the passed \f(CI\*(C`now\*(C'\fI value\fR.
773.Sp 1540.Sp
774This can be used to create very complex timers, such as a timer that 1541This can be used to create very complex timers, such as a timer that
775triggers on each midnight, local time. To do this, you would calculate the 1542triggers on \*(L"next midnight, local time\*(R". To do this, you would calculate the
776next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How 1543next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How
777you do this is, again, up to you (but it is not trivial, which is the main 1544you do this is, again, up to you (but it is not trivial, which is the main
778reason I omitted it as an example). 1545reason I omitted it as an example).
779.RE 1546.RE
780.RS 4 1547.RS 4
… …
783.IX Item "ev_periodic_again (loop, ev_periodic *)" 1550.IX Item "ev_periodic_again (loop, ev_periodic *)"
784Simply stops and restarts the periodic watcher again. This is only useful 1551Simply stops and restarts the periodic watcher again. This is only useful
785when you changed some parameters or the reschedule callback would return 1552when you changed some parameters or the reschedule callback would return
786a different time than the last time it was called (e.g. in a crond like 1553a different time than the last time it was called (e.g. in a crond like
787program when the crontabs have changed). 1554program when the crontabs have changed).
1555.IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4
1556.IX Item "ev_tstamp ev_periodic_at (ev_periodic *)"
1557When active, returns the absolute time that the watcher is supposed to
1558trigger next.
1559.IP "ev_tstamp offset [read\-write]" 4
1560.IX Item "ev_tstamp offset [read-write]"
1561When repeating, this contains the offset value, otherwise this is the
1562absolute point in time (the \f(CW\*(C`at\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR).
1563.Sp
1564Can be modified any time, but changes only take effect when the periodic
1565timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1566.IP "ev_tstamp interval [read\-write]" 4
1567.IX Item "ev_tstamp interval [read-write]"
1568The current interval value. Can be modified any time, but changes only
1569take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
1570called.
1571.IP "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read\-write]" 4
1572.IX Item "ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]"
1573The current reschedule callback, or \f(CW0\fR, if this functionality is
1574switched off. Can be changed any time, but changes only take effect when
1575the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1576.PP
1577\fIExamples\fR
1578.IX Subsection "Examples"
1579.PP
1580Example: Call a callback every hour, or, more precisely, whenever the
1581system clock is divisible by 3600. The callback invocation times have
1582potentially a lot of jittering, but good long-term stability.
1583.PP
1584.Vb 5
1585\& static void
1586\& clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)
1587\& {
1588\& ... its now a full hour (UTC, or TAI or whatever your clock follows)
1589\& }
1590\&
1591\& struct ev_periodic hourly_tick;
1592\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1593\& ev_periodic_start (loop, &hourly_tick);
1594.Ve
1595.PP
1596Example: The same as above, but use a reschedule callback to do it:
1597.PP
1598.Vb 1
1599\& #include <math.h>
1600\&
1601\& static ev_tstamp
1602\& my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)
1603\& {
1604\& return fmod (now, 3600.) + 3600.;
1605\& }
1606\&
1607\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1608.Ve
1609.PP
1610Example: Call a callback every hour, starting now:
1611.PP
1612.Vb 4
1613\& struct ev_periodic hourly_tick;
1614\& ev_periodic_init (&hourly_tick, clock_cb,
1615\& fmod (ev_now (loop), 3600.), 3600., 0);
1616\& ev_periodic_start (loop, &hourly_tick);
1617.Ve
788.ie n .Sh """ev_signal"" \- signal me when a signal gets signalled" 1618.ie n .Sh """ev_signal"" \- signal me when a signal gets signalled!"
789.el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled" 1619.el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
790.IX Subsection "ev_signal - signal me when a signal gets signalled" 1620.IX Subsection "ev_signal - signal me when a signal gets signalled!"
791Signal watchers will trigger an event when the process receives a specific 1621Signal watchers will trigger an event when the process receives a specific
792signal one or more times. Even though signals are very asynchronous, libev 1622signal one or more times. Even though signals are very asynchronous, libev
793will try it's best to deliver signals synchronously, i.e. as part of the 1623will try it's best to deliver signals synchronously, i.e. as part of the
794normal event processing, like any other event. 1624normal event processing, like any other event.
795.PP 1625.PP
… …
797first watcher gets started will libev actually register a signal watcher 1627first watcher gets started will libev actually register a signal watcher
798with the kernel (thus it coexists with your own signal handlers as long 1628with the kernel (thus it coexists with your own signal handlers as long
799as you don't register any with libev). Similarly, when the last signal 1629as you don't register any with libev). Similarly, when the last signal
800watcher for a signal is stopped libev will reset the signal handler to 1630watcher for a signal is stopped libev will reset the signal handler to
801\&\s-1SIG_DFL\s0 (regardless of what it was set to before). 1631\&\s-1SIG_DFL\s0 (regardless of what it was set to before).
1632.PP
1633If possible and supported, libev will install its handlers with
1634\&\f(CW\*(C`SA_RESTART\*(C'\fR behaviour enabled, so syscalls should not be unduly
1635interrupted. If you have a problem with syscalls getting interrupted by
1636signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher and unblock
1637them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher.
1638.PP
1639\fIWatcher-Specific Functions and Data Members\fR
1640.IX Subsection "Watcher-Specific Functions and Data Members"
802.IP "ev_signal_init (ev_signal *, callback, int signum)" 4 1641.IP "ev_signal_init (ev_signal *, callback, int signum)" 4
803.IX Item "ev_signal_init (ev_signal *, callback, int signum)" 1642.IX Item "ev_signal_init (ev_signal *, callback, int signum)"
804.PD 0 1643.PD 0
805.IP "ev_signal_set (ev_signal *, int signum)" 4 1644.IP "ev_signal_set (ev_signal *, int signum)" 4
806.IX Item "ev_signal_set (ev_signal *, int signum)" 1645.IX Item "ev_signal_set (ev_signal *, int signum)"
807.PD 1646.PD
808Configures the watcher to trigger on the given signal number (usually one 1647Configures the watcher to trigger on the given signal number (usually one
809of the \f(CW\*(C`SIGxxx\*(C'\fR constants). 1648of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
1649.IP "int signum [read\-only]" 4
1650.IX Item "int signum [read-only]"
1651The signal the watcher watches out for.
1652.PP
1653\fIExamples\fR
1654.IX Subsection "Examples"
1655.PP
1656Example: Try to exit cleanly on \s-1SIGINT\s0 and \s-1SIGTERM\s0.
1657.PP
1658.Vb 5
1659\& static void
1660\& sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)
1661\& {
1662\& ev_unloop (loop, EVUNLOOP_ALL);
1663\& }
1664\&
1665\& struct ev_signal signal_watcher;
1666\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
1667\& ev_signal_start (loop, &sigint_cb);
1668.Ve
810.ie n .Sh """ev_child"" \- wait for pid status changes" 1669.ie n .Sh """ev_child"" \- watch out for process status changes"
811.el .Sh "\f(CWev_child\fP \- wait for pid status changes" 1670.el .Sh "\f(CWev_child\fP \- watch out for process status changes"
812.IX Subsection "ev_child - wait for pid status changes" 1671.IX Subsection "ev_child - watch out for process status changes"
813Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to 1672Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
814some child status changes (most typically when a child of yours dies). 1673some child status changes (most typically when a child of yours dies). It
1674is permissible to install a child watcher \fIafter\fR the child has been
1675forked (which implies it might have already exited), as long as the event
1676loop isn't entered (or is continued from a watcher).
1677.PP
1678Only the default event loop is capable of handling signals, and therefore
1679you can only rgeister child watchers in the default event loop.
1680.PP
1681\fIProcess Interaction\fR
1682.IX Subsection "Process Interaction"
1683.PP
1684Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is
1685initialised. This is necessary to guarantee proper behaviour even if
1686the first child watcher is started after the child exits. The occurance
1687of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done
1688synchronously as part of the event loop processing. Libev always reaps all
1689children, even ones not watched.
1690.PP
1691\fIOverriding the Built-In Processing\fR
1692.IX Subsection "Overriding the Built-In Processing"
1693.PP
1694Libev offers no special support for overriding the built-in child
1695processing, but if your application collides with libev's default child
1696handler, you can override it easily by installing your own handler for
1697\&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the
1698default loop never gets destroyed. You are encouraged, however, to use an
1699event-based approach to child reaping and thus use libev's support for
1700that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely.
1701.PP
1702\fIWatcher-Specific Functions and Data Members\fR
1703.IX Subsection "Watcher-Specific Functions and Data Members"
815.IP "ev_child_init (ev_child *, callback, int pid)" 4 1704.IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4
816.IX Item "ev_child_init (ev_child *, callback, int pid)" 1705.IX Item "ev_child_init (ev_child *, callback, int pid, int trace)"
817.PD 0 1706.PD 0
818.IP "ev_child_set (ev_child *, int pid)" 4 1707.IP "ev_child_set (ev_child *, int pid, int trace)" 4
819.IX Item "ev_child_set (ev_child *, int pid)" 1708.IX Item "ev_child_set (ev_child *, int pid, int trace)"
820.PD 1709.PD
821Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or 1710Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
822\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look 1711\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
823at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see 1712at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
824the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems 1713the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
825\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the 1714\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
826process causing the status change. 1715process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only
1716activate the watcher when the process terminates) or \f(CW1\fR (additionally
1717activate the watcher when the process is stopped or continued).
1718.IP "int pid [read\-only]" 4
1719.IX Item "int pid [read-only]"
1720The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
1721.IP "int rpid [read\-write]" 4
1722.IX Item "int rpid [read-write]"
1723The process id that detected a status change.
1724.IP "int rstatus [read\-write]" 4
1725.IX Item "int rstatus [read-write]"
1726The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
1727\&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
1728.PP
1729\fIExamples\fR
1730.IX Subsection "Examples"
1731.PP
1732Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for
1733its completion.
1734.PP
1735.Vb 1
1736\& ev_child cw;
1737\&
1738\& static void
1739\& child_cb (EV_P_ struct ev_child *w, int revents)
1740\& {
1741\& ev_child_stop (EV_A_ w);
1742\& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus);
1743\& }
1744\&
1745\& pid_t pid = fork ();
1746\&
1747\& if (pid < 0)
1748\& // error
1749\& else if (pid == 0)
1750\& {
1751\& // the forked child executes here
1752\& exit (1);
1753\& }
1754\& else
1755\& {
1756\& ev_child_init (&cw, child_cb, pid, 0);
1757\& ev_child_start (EV_DEFAULT_ &cw);
1758\& }
1759.Ve
1760.ie n .Sh """ev_stat"" \- did the file attributes just change?"
1761.el .Sh "\f(CWev_stat\fP \- did the file attributes just change?"
1762.IX Subsection "ev_stat - did the file attributes just change?"
1763This watches a filesystem path for attribute changes. That is, it calls
1764\&\f(CW\*(C`stat\*(C'\fR regularly (or when the \s-1OS\s0 says it changed) and sees if it changed
1765compared to the last time, invoking the callback if it did.
1766.PP
1767The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does
1768not exist\*(R" is a status change like any other. The condition \*(L"path does
1769not exist\*(R" is signified by the \f(CW\*(C`st_nlink\*(C'\fR field being zero (which is
1770otherwise always forced to be at least one) and all the other fields of
1771the stat buffer having unspecified contents.
1772.PP
1773The path \fIshould\fR be absolute and \fImust not\fR end in a slash. If it is
1774relative and your working directory changes, the behaviour is undefined.
1775.PP
1776Since there is no standard to do this, the portable implementation simply
1777calls \f(CW\*(C`stat (2)\*(C'\fR regularly on the path to see if it changed somehow. You
1778can specify a recommended polling interval for this case. If you specify
1779a polling interval of \f(CW0\fR (highly recommended!) then a \fIsuitable,
1780unspecified default\fR value will be used (which you can expect to be around
1781five seconds, although this might change dynamically). Libev will also
1782impose a minimum interval which is currently around \f(CW0.1\fR, but thats
1783usually overkill.
1784.PP
1785This watcher type is not meant for massive numbers of stat watchers,
1786as even with OS-supported change notifications, this can be
1787resource-intensive.
1788.PP
1789At the time of this writing, only the Linux inotify interface is
1790implemented (implementing kqueue support is left as an exercise for the
1791reader, note, however, that the author sees no way of implementing ev_stat
1792semantics with kqueue). Inotify will be used to give hints only and should
1793not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers, which means that libev
1794sometimes needs to fall back to regular polling again even with inotify,
1795but changes are usually detected immediately, and if the file exists there
1796will be no polling.
1797.PP
1798\fI\s-1ABI\s0 Issues (Largefile Support)\fR
1799.IX Subsection "ABI Issues (Largefile Support)"
1800.PP
1801Libev by default (unless the user overrides this) uses the default
1802compilation environment, which means that on systems with optionally
1803disabled large file support, you get the 32 bit version of the stat
1804structure. When using the library from programs that change the \s-1ABI\s0 to
1805use 64 bit file offsets the programs will fail. In that case you have to
1806compile libev with the same flags to get binary compatibility. This is
1807obviously the case with any flags that change the \s-1ABI\s0, but the problem is
1808most noticably with ev_stat and largefile support.
1809.PP
1810\fIInotify\fR
1811.IX Subsection "Inotify"
1812.PP
1813When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev (generally only
1814available on Linux) and present at runtime, it will be used to speed up
1815change detection where possible. The inotify descriptor will be created lazily
1816when the first \f(CW\*(C`ev_stat\*(C'\fR watcher is being started.
1817.PP
1818Inotify presence does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
1819except that changes might be detected earlier, and in some cases, to avoid
1820making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presence of inotify support
1821there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling.
1822.PP
1823(There is no support for kqueue, as apparently it cannot be used to
1824implement this functionality, due to the requirement of having a file
1825descriptor open on the object at all times).
1826.PP
1827\fIThe special problem of stat time resolution\fR
1828.IX Subsection "The special problem of stat time resolution"
1829.PP
1830The \f(CW\*(C`stat ()\*(C'\fR syscall only supports full-second resolution portably, and
1831even on systems where the resolution is higher, many filesystems still
1832only support whole seconds.
1833.PP
1834That means that, if the time is the only thing that changes, you can
1835easily miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and
1836calls your callback, which does something. When there is another update
1837within the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect it as the stat
1838data does not change.
1839.PP
1840The solution to this is to delay acting on a change for slightly more
1841than a second (or till slightly after the next full second boundary), using
1842a roughly one-second-delay \f(CW\*(C`ev_timer\*(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02);
1843ev_timer_again (loop, w)\*(C'\fR).
1844.PP
1845The \f(CW.02\fR offset is added to work around small timing inconsistencies
1846of some operating systems (where the second counter of the current time
1847might be be delayed. One such system is the Linux kernel, where a call to
1848\&\f(CW\*(C`gettimeofday\*(C'\fR might return a timestamp with a full second later than
1849a subsequent \f(CW\*(C`time\*(C'\fR call \- if the equivalent of \f(CW\*(C`time ()\*(C'\fR is used to
1850update file times then there will be a small window where the kernel uses
1851the previous second to update file times but libev might already execute
1852the timer callback).
1853.PP
1854\fIWatcher-Specific Functions and Data Members\fR
1855.IX Subsection "Watcher-Specific Functions and Data Members"
1856.IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
1857.IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
1858.PD 0
1859.IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4
1860.IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)"
1861.PD
1862Configures the watcher to wait for status changes of the given
1863\&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to
1864be detected and should normally be specified as \f(CW0\fR to let libev choose
1865a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same
1866path for as long as the watcher is active.
1867.Sp
1868The callback will receive \f(CW\*(C`EV_STAT\*(C'\fR when a change was detected, relative
1869to the attributes at the time the watcher was started (or the last change
1870was detected).
1871.IP "ev_stat_stat (loop, ev_stat *)" 4
1872.IX Item "ev_stat_stat (loop, ev_stat *)"
1873Updates the stat buffer immediately with new values. If you change the
1874watched path in your callback, you could call this function to avoid
1875detecting this change (while introducing a race condition if you are not
1876the only one changing the path). Can also be useful simply to find out the
1877new values.
1878.IP "ev_statdata attr [read\-only]" 4
1879.IX Item "ev_statdata attr [read-only]"
1880The most-recently detected attributes of the file. Although the type is
1881\&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
1882suitable for your system, but you can only rely on the POSIX-standardised
1883members to be present. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there was
1884some error while \f(CW\*(C`stat\*(C'\fRing the file.
1885.IP "ev_statdata prev [read\-only]" 4
1886.IX Item "ev_statdata prev [read-only]"
1887The previous attributes of the file. The callback gets invoked whenever
1888\&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR, or, more precisely, one or more of these members
1889differ: \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,
1890\&\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.
1891.IP "ev_tstamp interval [read\-only]" 4
1892.IX Item "ev_tstamp interval [read-only]"
1893The specified interval.
1894.IP "const char *path [read\-only]" 4
1895.IX Item "const char *path [read-only]"
1896The filesystem path that is being watched.
1897.PP
1898\fIExamples\fR
1899.IX Subsection "Examples"
1900.PP
1901Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
1902.PP
1903.Vb 10
1904\& static void
1905\& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1906\& {
1907\& /* /etc/passwd changed in some way */
1908\& if (w\->attr.st_nlink)
1909\& {
1910\& printf ("passwd current size %ld\en", (long)w\->attr.st_size);
1911\& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime);
1912\& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime);
1913\& }
1914\& else
1915\& /* you shalt not abuse printf for puts */
1916\& puts ("wow, /etc/passwd is not there, expect problems. "
1917\& "if this is windows, they already arrived\en");
1918\& }
1919\&
1920\& ...
1921\& ev_stat passwd;
1922\&
1923\& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1924\& ev_stat_start (loop, &passwd);
1925.Ve
1926.PP
1927Example: Like above, but additionally use a one-second delay so we do not
1928miss updates (however, frequent updates will delay processing, too, so
1929one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
1930\&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
1931.PP
1932.Vb 2
1933\& static ev_stat passwd;
1934\& static ev_timer timer;
1935\&
1936\& static void
1937\& timer_cb (EV_P_ ev_timer *w, int revents)
1938\& {
1939\& ev_timer_stop (EV_A_ w);
1940\&
1941\& /* now it\*(Aqs one second after the most recent passwd change */
1942\& }
1943\&
1944\& static void
1945\& stat_cb (EV_P_ ev_stat *w, int revents)
1946\& {
1947\& /* reset the one\-second timer */
1948\& ev_timer_again (EV_A_ &timer);
1949\& }
1950\&
1951\& ...
1952\& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
1953\& ev_stat_start (loop, &passwd);
1954\& ev_timer_init (&timer, timer_cb, 0., 1.02);
1955.Ve
827.ie n .Sh """ev_idle"" \- when you've got nothing better to do" 1956.ie n .Sh """ev_idle"" \- when you've got nothing better to do..."
828.el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do" 1957.el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do..."
829.IX Subsection "ev_idle - when you've got nothing better to do" 1958.IX Subsection "ev_idle - when you've got nothing better to do..."
830Idle watchers trigger events when there are no other events are pending 1959Idle watchers trigger events when no other events of the same or higher
831(prepare, check and other idle watchers do not count). That is, as long 1960priority are pending (prepare, check and other idle watchers do not
832as your process is busy handling sockets or timeouts (or even signals, 1961count).
833imagine) it will not be triggered. But when your process is idle all idle 1962.PP
834watchers are being called again and again, once per event loop iteration \- 1963That is, as long as your process is busy handling sockets or timeouts
1964(or even signals, imagine) of the same or higher priority it will not be
1965triggered. But when your process is idle (or only lower-priority watchers
1966are pending), the idle watchers are being called once per event loop
835until stopped, that is, or your process receives more events and becomes 1967iteration \- until stopped, that is, or your process receives more events
836busy. 1968and becomes busy again with higher priority stuff.
837.PP 1969.PP
838The most noteworthy effect is that as long as any idle watchers are 1970The most noteworthy effect is that as long as any idle watchers are
839active, the process will not block when waiting for new events. 1971active, the process will not block when waiting for new events.
840.PP 1972.PP
841Apart from keeping your process non-blocking (which is a useful 1973Apart from keeping your process non-blocking (which is a useful
842effect on its own sometimes), idle watchers are a good place to do 1974effect on its own sometimes), idle watchers are a good place to do
843\&\*(L"pseudo\-background processing\*(R", or delay processing stuff to after the 1975\&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the
844event loop has handled all outstanding events. 1976event loop has handled all outstanding events.
1977.PP
1978\fIWatcher-Specific Functions and Data Members\fR
1979.IX Subsection "Watcher-Specific Functions and Data Members"
845.IP "ev_idle_init (ev_signal *, callback)" 4 1980.IP "ev_idle_init (ev_signal *, callback)" 4
846.IX Item "ev_idle_init (ev_signal *, callback)" 1981.IX Item "ev_idle_init (ev_signal *, callback)"
847Initialises and configures the idle watcher \- it has no parameters of any 1982Initialises and configures the idle watcher \- it has no parameters of any
848kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless, 1983kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
849believe me. 1984believe me.
1985.PP
1986\fIExamples\fR
1987.IX Subsection "Examples"
1988.PP
1989Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the
1990callback, free it. Also, use no error checking, as usual.
1991.PP
1992.Vb 7
1993\& static void
1994\& idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)
1995\& {
1996\& free (w);
1997\& // now do something you wanted to do when the program has
1998\& // no longer anything immediate to do.
1999\& }
2000\&
2001\& struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));
2002\& ev_idle_init (idle_watcher, idle_cb);
2003\& ev_idle_start (loop, idle_cb);
2004.Ve
850.ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop" 2005.ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop!"
851.el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop" 2006.el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
852.IX Subsection "ev_prepare and ev_check - customise your event loop" 2007.IX Subsection "ev_prepare and ev_check - customise your event loop!"
853Prepare and check watchers are usually (but not always) used in tandem: 2008Prepare and check watchers are usually (but not always) used in tandem:
854prepare watchers get invoked before the process blocks and check watchers 2009prepare watchers get invoked before the process blocks and check watchers
855afterwards. 2010afterwards.
856.PP 2011.PP
2012You \fImust not\fR call \f(CW\*(C`ev_loop\*(C'\fR or similar functions that enter
2013the current event loop from either \f(CW\*(C`ev_prepare\*(C'\fR or \f(CW\*(C`ev_check\*(C'\fR
2014watchers. Other loops than the current one are fine, however. The
2015rationale behind this is that you do not need to check for recursion in
2016those watchers, i.e. the sequence will always be \f(CW\*(C`ev_prepare\*(C'\fR, blocking,
2017\&\f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each kind they will always be
2018called in pairs bracketing the blocking call.
2019.PP
857Their main purpose is to integrate other event mechanisms into libev. This 2020Their main purpose is to integrate other event mechanisms into libev and
858could be used, for example, to track variable changes, implement your own 2021their use is somewhat advanced. This could be used, for example, to track
859watchers, integrate net-snmp or a coroutine library and lots more. 2022variable changes, implement your own watchers, integrate net-snmp or a
2023coroutine library and lots more. They are also occasionally useful if
2024you cache some data and want to flush it before blocking (for example,
2025in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
2026watcher).
860.PP 2027.PP
861This is done by examining in each prepare call which file descriptors need 2028This is done by examining in each prepare call which file descriptors need
862to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers for 2029to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers for
863them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many libraries 2030them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many libraries
864provide just this functionality). Then, in the check watcher you check for 2031provide just this functionality). Then, in the check watcher you check for
… …
873are ready to run (it's actually more complicated: it only runs coroutines 2040are ready to run (it's actually more complicated: it only runs coroutines
874with priority higher than or equal to the event loop and one coroutine 2041with priority higher than or equal to the event loop and one coroutine
875of lower priority, but only once, using idle watchers to keep the event 2042of lower priority, but only once, using idle watchers to keep the event
876loop from blocking if lower-priority coroutines are active, thus mapping 2043loop from blocking if lower-priority coroutines are active, thus mapping
877low-priority coroutines to idle/background tasks). 2044low-priority coroutines to idle/background tasks).
2045.PP
2046It is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR)
2047priority, to ensure that they are being run before any other watchers
2048after the poll. Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers,
2049too) should not activate (\*(L"feed\*(R") events into libev. While libev fully
2050supports this, they might get executed before other \f(CW\*(C`ev_check\*(C'\fR watchers
2051did their job. As \f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other
2052(non-libev) event loops those other event loops might be in an unusable
2053state until their \f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to
2054coexist peacefully with others).
2055.PP
2056\fIWatcher-Specific Functions and Data Members\fR
2057.IX Subsection "Watcher-Specific Functions and Data Members"
878.IP "ev_prepare_init (ev_prepare *, callback)" 4 2058.IP "ev_prepare_init (ev_prepare *, callback)" 4
879.IX Item "ev_prepare_init (ev_prepare *, callback)" 2059.IX Item "ev_prepare_init (ev_prepare *, callback)"
880.PD 0 2060.PD 0
881.IP "ev_check_init (ev_check *, callback)" 4 2061.IP "ev_check_init (ev_check *, callback)" 4
882.IX Item "ev_check_init (ev_check *, callback)" 2062.IX Item "ev_check_init (ev_check *, callback)"
883.PD 2063.PD
884Initialises and configures the prepare or check watcher \- they have no 2064Initialises and configures the prepare or check watcher \- they have no
885parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR 2065parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
886macros, but using them is utterly, utterly and completely pointless. 2066macros, but using them is utterly, utterly and completely pointless.
2067.PP
2068\fIExamples\fR
2069.IX Subsection "Examples"
2070.PP
2071There are a number of principal ways to embed other event loops or modules
2072into libev. Here are some ideas on how to include libadns into libev
2073(there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could
2074use as a working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR embeds a
2075Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 into the
2076Glib event loop).
2077.PP
2078Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
2079and in a check watcher, destroy them and call into libadns. What follows
2080is pseudo-code only of course. This requires you to either use a low
2081priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as
2082the callbacks for the IO/timeout watchers might not have been called yet.
2083.PP
2084.Vb 2
2085\& static ev_io iow [nfd];
2086\& static ev_timer tw;
2087\&
2088\& static void
2089\& io_cb (ev_loop *loop, ev_io *w, int revents)
2090\& {
2091\& }
2092\&
2093\& // create io watchers for each fd and a timer before blocking
2094\& static void
2095\& adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
2096\& {
2097\& int timeout = 3600000;
2098\& struct pollfd fds [nfd];
2099\& // actual code will need to loop here and realloc etc.
2100\& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2101\&
2102\& /* the callback is illegal, but won\*(Aqt be called as we stop during check */
2103\& ev_timer_init (&tw, 0, timeout * 1e\-3);
2104\& ev_timer_start (loop, &tw);
2105\&
2106\& // create one ev_io per pollfd
2107\& for (int i = 0; i < nfd; ++i)
2108\& {
2109\& ev_io_init (iow + i, io_cb, fds [i].fd,
2110\& ((fds [i].events & POLLIN ? EV_READ : 0)
2111\& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
2112\&
2113\& fds [i].revents = 0;
2114\& ev_io_start (loop, iow + i);
2115\& }
2116\& }
2117\&
2118\& // stop all watchers after blocking
2119\& static void
2120\& adns_check_cb (ev_loop *loop, ev_check *w, int revents)
2121\& {
2122\& ev_timer_stop (loop, &tw);
2123\&
2124\& for (int i = 0; i < nfd; ++i)
2125\& {
2126\& // set the relevant poll flags
2127\& // could also call adns_processreadable etc. here
2128\& struct pollfd *fd = fds + i;
2129\& int revents = ev_clear_pending (iow + i);
2130\& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN;
2131\& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT;
2132\&
2133\& // now stop the watcher
2134\& ev_io_stop (loop, iow + i);
2135\& }
2136\&
2137\& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
2138\& }
2139.Ve
2140.PP
2141Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR
2142in the prepare watcher and would dispose of the check watcher.
2143.PP
2144Method 3: If the module to be embedded supports explicit event
2145notification (adns does), you can also make use of the actual watcher
2146callbacks, and only destroy/create the watchers in the prepare watcher.
2147.PP
2148.Vb 5
2149\& static void
2150\& timer_cb (EV_P_ ev_timer *w, int revents)
2151\& {
2152\& adns_state ads = (adns_state)w\->data;
2153\& update_now (EV_A);
2154\&
2155\& adns_processtimeouts (ads, &tv_now);
2156\& }
2157\&
2158\& static void
2159\& io_cb (EV_P_ ev_io *w, int revents)
2160\& {
2161\& adns_state ads = (adns_state)w\->data;
2162\& update_now (EV_A);
2163\&
2164\& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now);
2165\& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now);
2166\& }
2167\&
2168\& // do not ever call adns_afterpoll
2169.Ve
2170.PP
2171Method 4: Do not use a prepare or check watcher because the module you
2172want to embed is too inflexible to support it. Instead, youc na override
2173their poll function. The drawback with this solution is that the main
2174loop is now no longer controllable by \s-1EV\s0. The \f(CW\*(C`Glib::EV\*(C'\fR module does
2175this.
2176.PP
2177.Vb 4
2178\& static gint
2179\& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
2180\& {
2181\& int got_events = 0;
2182\&
2183\& for (n = 0; n < nfds; ++n)
2184\& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
2185\&
2186\& if (timeout >= 0)
2187\& // create/start timer
2188\&
2189\& // poll
2190\& ev_loop (EV_A_ 0);
2191\&
2192\& // stop timer again
2193\& if (timeout >= 0)
2194\& ev_timer_stop (EV_A_ &to);
2195\&
2196\& // stop io watchers again \- their callbacks should have set
2197\& for (n = 0; n < nfds; ++n)
2198\& ev_io_stop (EV_A_ iow [n]);
2199\&
2200\& return got_events;
2201\& }
2202.Ve
2203.ie n .Sh """ev_embed"" \- when one backend isn't enough..."
2204.el .Sh "\f(CWev_embed\fP \- when one backend isn't enough..."
2205.IX Subsection "ev_embed - when one backend isn't enough..."
2206This is a rather advanced watcher type that lets you embed one event loop
2207into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
2208loop, other types of watchers might be handled in a delayed or incorrect
2209fashion and must not be used).
2210.PP
2211There are primarily two reasons you would want that: work around bugs and
2212prioritise I/O.
2213.PP
2214As an example for a bug workaround, the kqueue backend might only support
2215sockets on some platform, so it is unusable as generic backend, but you
2216still want to make use of it because you have many sockets and it scales
2217so nicely. In this case, you would create a kqueue-based loop and embed it
2218into your default loop (which might use e.g. poll). Overall operation will
2219be a bit slower because first libev has to poll and then call kevent, but
2220at least you can use both at what they are best.
2221.PP
2222As for prioritising I/O: rarely you have the case where some fds have
2223to be watched and handled very quickly (with low latency), and even
2224priorities and idle watchers might have too much overhead. In this case
2225you would put all the high priority stuff in one loop and all the rest in
2226a second one, and embed the second one in the first.
2227.PP
2228As long as the watcher is active, the callback will be invoked every time
2229there might be events pending in the embedded loop. The callback must then
2230call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single sweep and invoke
2231their callbacks (you could also start an idle watcher to give the embedded
2232loop strictly lower priority for example). You can also set the callback
2233to \f(CW0\fR, in which case the embed watcher will automatically execute the
2234embedded loop sweep.
2235.PP
2236As long as the watcher is started it will automatically handle events. The
2237callback will be invoked whenever some events have been handled. You can
2238set the callback to \f(CW0\fR to avoid having to specify one if you are not
2239interested in that.
2240.PP
2241Also, there have not currently been made special provisions for forking:
2242when you fork, you not only have to call \f(CW\*(C`ev_loop_fork\*(C'\fR on both loops,
2243but you will also have to stop and restart any \f(CW\*(C`ev_embed\*(C'\fR watchers
2244yourself.
2245.PP
2246Unfortunately, not all backends are embeddable, only the ones returned by
2247\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
2248portable one.
2249.PP
2250So when you want to use this feature you will always have to be prepared
2251that you cannot get an embeddable loop. The recommended way to get around
2252this is to have a separate variables for your embeddable loop, try to
2253create it, and if that fails, use the normal loop for everything.
2254.PP
2255\fIWatcher-Specific Functions and Data Members\fR
2256.IX Subsection "Watcher-Specific Functions and Data Members"
2257.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
2258.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
2259.PD 0
2260.IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
2261.IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)"
2262.PD
2263Configures the watcher to embed the given loop, which must be
2264embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
2265invoked automatically, otherwise it is the responsibility of the callback
2266to invoke it (it will continue to be called until the sweep has been done,
2267if you do not want thta, you need to temporarily stop the embed watcher).
2268.IP "ev_embed_sweep (loop, ev_embed *)" 4
2269.IX Item "ev_embed_sweep (loop, ev_embed *)"
2270Make a single, non-blocking sweep over the embedded loop. This works
2271similarly to \f(CW\*(C`ev_loop (embedded_loop, EVLOOP_NONBLOCK)\*(C'\fR, but in the most
2272apropriate way for embedded loops.
2273.IP "struct ev_loop *other [read\-only]" 4
2274.IX Item "struct ev_loop *other [read-only]"
2275The embedded event loop.
2276.PP
2277\fIExamples\fR
2278.IX Subsection "Examples"
2279.PP
2280Example: Try to get an embeddable event loop and embed it into the default
2281event loop. If that is not possible, use the default loop. The default
2282loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the mebeddable loop is stored in
2283\&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the acse no embeddable loop can be
2284used).
2285.PP
2286.Vb 3
2287\& struct ev_loop *loop_hi = ev_default_init (0);
2288\& struct ev_loop *loop_lo = 0;
2289\& struct ev_embed embed;
2290\&
2291\& // see if there is a chance of getting one that works
2292\& // (remember that a flags value of 0 means autodetection)
2293\& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2294\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
2295\& : 0;
2296\&
2297\& // if we got one, then embed it, otherwise default to loop_hi
2298\& if (loop_lo)
2299\& {
2300\& ev_embed_init (&embed, 0, loop_lo);
2301\& ev_embed_start (loop_hi, &embed);
2302\& }
2303\& else
2304\& loop_lo = loop_hi;
2305.Ve
2306.PP
2307Example: Check if kqueue is available but not recommended and create
2308a kqueue backend for use with sockets (which usually work with any
2309kqueue implementation). Store the kqueue/socket\-only event loop in
2310\&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too).
2311.PP
2312.Vb 3
2313\& struct ev_loop *loop = ev_default_init (0);
2314\& struct ev_loop *loop_socket = 0;
2315\& struct ev_embed embed;
2316\&
2317\& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2318\& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2319\& {
2320\& ev_embed_init (&embed, 0, loop_socket);
2321\& ev_embed_start (loop, &embed);
2322\& }
2323\&
2324\& if (!loop_socket)
2325\& loop_socket = loop;
2326\&
2327\& // now use loop_socket for all sockets, and loop for everything else
2328.Ve
2329.ie n .Sh """ev_fork"" \- the audacity to resume the event loop after a fork"
2330.el .Sh "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
2331.IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
2332Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
2333whoever is a good citizen cared to tell libev about it by calling
2334\&\f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the
2335event loop blocks next and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called,
2336and only in the child after the fork. If whoever good citizen calling
2337\&\f(CW\*(C`ev_default_fork\*(C'\fR cheats and calls it in the wrong process, the fork
2338handlers will be invoked, too, of course.
2339.PP
2340\fIWatcher-Specific Functions and Data Members\fR
2341.IX Subsection "Watcher-Specific Functions and Data Members"
2342.IP "ev_fork_init (ev_signal *, callback)" 4
2343.IX Item "ev_fork_init (ev_signal *, callback)"
2344Initialises and configures the fork watcher \- it has no parameters of any
2345kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
2346believe me.
2347.ie n .Sh """ev_async"" \- how to wake up another event loop"
2348.el .Sh "\f(CWev_async\fP \- how to wake up another event loop"
2349.IX Subsection "ev_async - how to wake up another event loop"
2350In general, you cannot use an \f(CW\*(C`ev_loop\*(C'\fR from multiple threads or other
2351asynchronous sources such as signal handlers (as opposed to multiple event
2352loops \- those are of course safe to use in different threads).
2353.PP
2354Sometimes, however, you need to wake up another event loop you do not
2355control, for example because it belongs to another thread. This is what
2356\&\f(CW\*(C`ev_async\*(C'\fR watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you
2357can signal it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal
2358safe.
2359.PP
2360This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals,
2361too, are asynchronous in nature, and signals, too, will be compressed
2362(i.e. the number of callback invocations may be less than the number of
2363\&\f(CW\*(C`ev_async_sent\*(C'\fR calls).
2364.PP
2365Unlike \f(CW\*(C`ev_signal\*(C'\fR watchers, \f(CW\*(C`ev_async\*(C'\fR works with any event loop, not
2366just the default loop.
2367.PP
2368\fIQueueing\fR
2369.IX Subsection "Queueing"
2370.PP
2371\&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason
2372is that the author does not know of a simple (or any) algorithm for a
2373multiple-writer-single-reader queue that works in all cases and doesn't
2374need elaborate support such as pthreads.
2375.PP
2376That means that if you want to queue data, you have to provide your own
2377queue. But at least I can tell you would implement locking around your
2378queue:
2379.IP "queueing from a signal handler context" 4
2380.IX Item "queueing from a signal handler context"
2381To implement race-free queueing, you simply add to the queue in the signal
2382handler but you block the signal handler in the watcher callback. Here is an example that does that for
2383some fictitiuous \s-1SIGUSR1\s0 handler:
2384.Sp
2385.Vb 1
2386\& static ev_async mysig;
2387\&
2388\& static void
2389\& sigusr1_handler (void)
2390\& {
2391\& sometype data;
2392\&
2393\& // no locking etc.
2394\& queue_put (data);
2395\& ev_async_send (EV_DEFAULT_ &mysig);
2396\& }
2397\&
2398\& static void
2399\& mysig_cb (EV_P_ ev_async *w, int revents)
2400\& {
2401\& sometype data;
2402\& sigset_t block, prev;
2403\&
2404\& sigemptyset (&block);
2405\& sigaddset (&block, SIGUSR1);
2406\& sigprocmask (SIG_BLOCK, &block, &prev);
2407\&
2408\& while (queue_get (&data))
2409\& process (data);
2410\&
2411\& if (sigismember (&prev, SIGUSR1)
2412\& sigprocmask (SIG_UNBLOCK, &block, 0);
2413\& }
2414.Ve
2415.Sp
2416(Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR
2417instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it
2418either...).
2419.IP "queueing from a thread context" 4
2420.IX Item "queueing from a thread context"
2421The strategy for threads is different, as you cannot (easily) block
2422threads but you can easily preempt them, so to queue safely you need to
2423employ a traditional mutex lock, such as in this pthread example:
2424.Sp
2425.Vb 2
2426\& static ev_async mysig;
2427\& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
2428\&
2429\& static void
2430\& otherthread (void)
2431\& {
2432\& // only need to lock the actual queueing operation
2433\& pthread_mutex_lock (&mymutex);
2434\& queue_put (data);
2435\& pthread_mutex_unlock (&mymutex);
2436\&
2437\& ev_async_send (EV_DEFAULT_ &mysig);
2438\& }
2439\&
2440\& static void
2441\& mysig_cb (EV_P_ ev_async *w, int revents)
2442\& {
2443\& pthread_mutex_lock (&mymutex);
2444\&
2445\& while (queue_get (&data))
2446\& process (data);
2447\&
2448\& pthread_mutex_unlock (&mymutex);
2449\& }
2450.Ve
2451.PP
2452\fIWatcher-Specific Functions and Data Members\fR
2453.IX Subsection "Watcher-Specific Functions and Data Members"
2454.IP "ev_async_init (ev_async *, callback)" 4
2455.IX Item "ev_async_init (ev_async *, callback)"
2456Initialises and configures the async watcher \- it has no parameters of any
2457kind. There is a \f(CW\*(C`ev_asynd_set\*(C'\fR macro, but using it is utterly pointless,
2458believe me.
2459.IP "ev_async_send (loop, ev_async *)" 4
2460.IX Item "ev_async_send (loop, ev_async *)"
2461Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds
2462an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop. Unlike
2463\&\f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do in other threads, signal or
2464similar contexts (see the dicusssion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the embedding
2465section below on what exactly this means).
2466.Sp
2467This call incurs the overhead of a syscall only once per loop iteration,
2468so while the overhead might be noticable, it doesn't apply to repeated
2469calls to \f(CW\*(C`ev_async_send\*(C'\fR.
2470.IP "bool = ev_async_pending (ev_async *)" 4
2471.IX Item "bool = ev_async_pending (ev_async *)"
2472Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the
2473watcher but the event has not yet been processed (or even noted) by the
2474event loop.
2475.Sp
2476\&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When
2477the loop iterates next and checks for the watcher to have become active,
2478it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very
2479quickly check wether invoking the loop might be a good idea.
2480.Sp
2481Not that this does \fInot\fR check wether the watcher itself is pending, only
2482wether it has been requested to make this watcher pending.
887.SH "OTHER FUNCTIONS" 2483.SH "OTHER FUNCTIONS"
888.IX Header "OTHER FUNCTIONS" 2484.IX Header "OTHER FUNCTIONS"
889There are some other functions of possible interest. Described. Here. Now. 2485There are some other functions of possible interest. Described. Here. Now.
890.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4 2486.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
891.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 2487.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"
… …
915\& if (revents & EV_TIMEOUT) 2511\& if (revents & EV_TIMEOUT)
916\& /* doh, nothing entered */; 2512\& /* doh, nothing entered */;
917\& else if (revents & EV_READ) 2513\& else if (revents & EV_READ)
918\& /* stdin might have data for us, joy! */; 2514\& /* stdin might have data for us, joy! */;
919\& } 2515\& }
920.Ve 2516\&
921.Sp
922.Vb 1
923\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); 2517\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
924.Ve 2518.Ve
925.IP "ev_feed_event (loop, watcher, int events)" 4 2519.IP "ev_feed_event (ev_loop *, watcher *, int revents)" 4
926.IX Item "ev_feed_event (loop, watcher, int events)" 2520.IX Item "ev_feed_event (ev_loop *, watcher *, int revents)"
927Feeds the given event set into the event loop, as if the specified event 2521Feeds the given event set into the event loop, as if the specified event
928had happened for the specified watcher (which must be a pointer to an 2522had happened for the specified watcher (which must be a pointer to an
929initialised but not necessarily started event watcher). 2523initialised but not necessarily started event watcher).
930.IP "ev_feed_fd_event (loop, int fd, int revents)" 4 2524.IP "ev_feed_fd_event (ev_loop *, int fd, int revents)" 4
931.IX Item "ev_feed_fd_event (loop, int fd, int revents)" 2525.IX Item "ev_feed_fd_event (ev_loop *, int fd, int revents)"
932Feed an event on the given fd, as if a file descriptor backend detected 2526Feed an event on the given fd, as if a file descriptor backend detected
933the given events it. 2527the given events it.
934.IP "ev_feed_signal_event (loop, int signum)" 4 2528.IP "ev_feed_signal_event (ev_loop *loop, int signum)" 4
935.IX Item "ev_feed_signal_event (loop, int signum)" 2529.IX Item "ev_feed_signal_event (ev_loop *loop, int signum)"
936Feed an event as if the given signal occured (loop must be the default loop!). 2530Feed an event as if the given signal occured (\f(CW\*(C`loop\*(C'\fR must be the default
2531loop!).
937.SH "LIBEVENT EMULATION" 2532.SH "LIBEVENT EMULATION"
938.IX Header "LIBEVENT EMULATION" 2533.IX Header "LIBEVENT EMULATION"
939Libev offers a compatibility emulation layer for libevent. It cannot 2534Libev offers a compatibility emulation layer for libevent. It cannot
940emulate the internals of libevent, so here are some usage hints: 2535emulate the internals of libevent, so here are some usage hints:
2536.IP "\(bu" 4
941.IP "* Use it by including <event.h>, as usual." 4 2537Use it by including <event.h>, as usual.
942.IX Item "Use it by including <event.h>, as usual." 2538.IP "\(bu" 4
943.PD 0 2539The following members are fully supported: ev_base, ev_callback,
944.IP "* The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4 2540ev_arg, ev_fd, ev_res, ev_events.
945.IX Item "The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 2541.IP "\(bu" 4
946.IP "* Avoid using ev_flags and the EVLIST_*\-macros, while it is maintained by libev, it does not work exactly the same way as in libevent (consider it a private \s-1API\s0)." 4 2542Avoid using ev_flags and the EVLIST_*\-macros, while it is
947.IX Item "Avoid using ev_flags and the EVLIST_*-macros, while it is maintained by libev, it does not work exactly the same way as in libevent (consider it a private API)." 2543maintained by libev, it does not work exactly the same way as in libevent (consider
948.IP "* Priorities are not currently supported. Initialising priorities will fail and all watchers will have the same priority, even though there is an ev_pri field." 4 2544it a private \s-1API\s0).
949.IX Item "Priorities are not currently supported. Initialising priorities will fail and all watchers will have the same priority, even though there is an ev_pri field." 2545.IP "\(bu" 4
2546Priorities are not currently supported. Initialising priorities
2547will fail and all watchers will have the same priority, even though there
2548is an ev_pri field.
2549.IP "\(bu" 4
2550In libevent, the last base created gets the signals, in libev, the
2551first base created (== the default loop) gets the signals.
2552.IP "\(bu" 4
950.IP "* Other members are not supported." 4 2553Other members are not supported.
951.IX Item "Other members are not supported." 2554.IP "\(bu" 4
952.IP "* The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need to use the libev header file and library." 4 2555The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need
953.IX Item "The libev emulation is not ABI compatible to libevent, you need to use the libev header file and library." 2556to use the libev header file and library.
954.PD
955.SH "\*(C+ SUPPORT" 2557.SH "\*(C+ SUPPORT"
956.IX Header " SUPPORT" 2558.IX Header " SUPPORT"
957\&\s-1TBD\s0. 2559Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
2560you to use some convinience methods to start/stop watchers and also change
2561the callback model to a model using method callbacks on objects.
2562.PP
2563To use it,
2564.PP
2565.Vb 1
2566\& #include <ev++.h>
2567.Ve
2568.PP
2569This automatically includes \fIev.h\fR and puts all of its definitions (many
2570of them macros) into the global namespace. All \*(C+ specific things are
2571put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding
2572options as \fIev.h\fR, most notably \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR.
2573.PP
2574Care has been taken to keep the overhead low. The only data member the \*(C+
2575classes add (compared to plain C\-style watchers) is the event loop pointer
2576that the watcher is associated with (or no additional members at all if
2577you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
2578.PP
2579Currently, functions, and static and non-static member functions can be
2580used as callbacks. Other types should be easy to add as long as they only
2581need one additional pointer for context. If you need support for other
2582types of functors please contact the author (preferably after implementing
2583it).
2584.PP
2585Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
2586.ie n .IP """ev::READ""\fR, \f(CW""ev::WRITE"" etc." 4
2587.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
2588.IX Item "ev::READ, ev::WRITE etc."
2589These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
2590macros from \fIev.h\fR.
2591.ie n .IP """ev::tstamp""\fR, \f(CW""ev::now""" 4
2592.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
2593.IX Item "ev::tstamp, ev::now"
2594Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
2595.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
2596.el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
2597.IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
2598For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
2599the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
2600which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
2601defines by many implementations.
2602.Sp
2603All of those classes have these methods:
2604.RS 4
2605.IP "ev::TYPE::TYPE ()" 4
2606.IX Item "ev::TYPE::TYPE ()"
2607.PD 0
2608.IP "ev::TYPE::TYPE (struct ev_loop *)" 4
2609.IX Item "ev::TYPE::TYPE (struct ev_loop *)"
2610.IP "ev::TYPE::~TYPE" 4
2611.IX Item "ev::TYPE::~TYPE"
2612.PD
2613The constructor (optionally) takes an event loop to associate the watcher
2614with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR.
2615.Sp
2616The constructor calls \f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the
2617\&\f(CW\*(C`set\*(C'\fR method before starting it.
2618.Sp
2619It will not set a callback, however: You have to call the templated \f(CW\*(C`set\*(C'\fR
2620method to set a callback before you can start the watcher.
2621.Sp
2622(The reason why you have to use a method is a limitation in \*(C+ which does
2623not allow explicit template arguments for constructors).
2624.Sp
2625The destructor automatically stops the watcher if it is active.
2626.IP "w\->set<class, &class::method> (object *)" 4
2627.IX Item "w->set<class, &class::method> (object *)"
2628This method sets the callback method to call. The method has to have a
2629signature of \f(CW\*(C`void (*)(ev_TYPE &, int)\*(C'\fR, it receives the watcher as
2630first argument and the \f(CW\*(C`revents\*(C'\fR as second. The object must be given as
2631parameter and is stored in the \f(CW\*(C`data\*(C'\fR member of the watcher.
2632.Sp
2633This method synthesizes efficient thunking code to call your method from
2634the C callback that libev requires. If your compiler can inline your
2635callback (i.e. it is visible to it at the place of the \f(CW\*(C`set\*(C'\fR call and
2636your compiler is good :), then the method will be fully inlined into the
2637thunking function, making it as fast as a direct C callback.
2638.Sp
2639Example: simple class declaration and watcher initialisation
2640.Sp
2641.Vb 4
2642\& struct myclass
2643\& {
2644\& void io_cb (ev::io &w, int revents) { }
2645\& }
2646\&
2647\& myclass obj;
2648\& ev::io iow;
2649\& iow.set <myclass, &myclass::io_cb> (&obj);
2650.Ve
2651.IP "w\->set<function> (void *data = 0)" 4
2652.IX Item "w->set<function> (void *data = 0)"
2653Also sets a callback, but uses a static method or plain function as
2654callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
2655\&\f(CW\*(C`data\*(C'\fR member and is free for you to use.
2656.Sp
2657The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
2658.Sp
2659See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
2660.Sp
2661Example:
2662.Sp
2663.Vb 2
2664\& static void io_cb (ev::io &w, int revents) { }
2665\& iow.set <io_cb> ();
2666.Ve
2667.IP "w\->set (struct ev_loop *)" 4
2668.IX Item "w->set (struct ev_loop *)"
2669Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
2670do this when the watcher is inactive (and not pending either).
2671.IP "w\->set ([args])" 4
2672.IX Item "w->set ([args])"
2673Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same args. Must be
2674called at least once. Unlike the C counterpart, an active watcher gets
2675automatically stopped and restarted when reconfiguring it with this
2676method.
2677.IP "w\->start ()" 4
2678.IX Item "w->start ()"
2679Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
2680constructor already stores the event loop.
2681.IP "w\->stop ()" 4
2682.IX Item "w->stop ()"
2683Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
2684.ie n .IP "w\->again () (""ev::timer""\fR, \f(CW""ev::periodic"" only)" 4
2685.el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
2686.IX Item "w->again () (ev::timer, ev::periodic only)"
2687For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
2688\&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
2689.ie n .IP "w\->sweep () (""ev::embed"" only)" 4
2690.el .IP "w\->sweep () (\f(CWev::embed\fR only)" 4
2691.IX Item "w->sweep () (ev::embed only)"
2692Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR.
2693.ie n .IP "w\->update () (""ev::stat"" only)" 4
2694.el .IP "w\->update () (\f(CWev::stat\fR only)" 4
2695.IX Item "w->update () (ev::stat only)"
2696Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
2697.RE
2698.RS 4
2699.RE
2700.PP
2701Example: Define a class with an \s-1IO\s0 and idle watcher, start one of them in
2702the constructor.
2703.PP
2704.Vb 4
2705\& class myclass
2706\& {
2707\& ev::io io; void io_cb (ev::io &w, int revents);
2708\& ev:idle idle void idle_cb (ev::idle &w, int revents);
2709\&
2710\& myclass (int fd)
2711\& {
2712\& io .set <myclass, &myclass::io_cb > (this);
2713\& idle.set <myclass, &myclass::idle_cb> (this);
2714\&
2715\& io.start (fd, ev::READ);
2716\& }
2717\& };
2718.Ve
2719.SH "OTHER LANGUAGE BINDINGS"
2720.IX Header "OTHER LANGUAGE BINDINGS"
2721Libev does not offer other language bindings itself, but bindings for a
2722numbe rof languages exist in the form of third-party packages. If you know
2723any interesting language binding in addition to the ones listed here, drop
2724me a note.
2725.IP "Perl" 4
2726.IX Item "Perl"
2727The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test
2728libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module,
2729there are additional modules that implement libev-compatible interfaces
2730to \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
2731\&\f(CW\*(C`libglib\*(C'\fR event core (\f(CW\*(C`Glib::EV\*(C'\fR and \f(CW\*(C`EV::Glib\*(C'\fR).
2732.Sp
2733It can be found and installed via \s-1CPAN\s0, its homepage is found at
2734<http://software.schmorp.de/pkg/EV>.
2735.IP "Ruby" 4
2736.IX Item "Ruby"
2737Tony Arcieri has written a ruby extension that offers access to a subset
2738of the libev \s-1API\s0 and adds filehandle abstractions, asynchronous \s-1DNS\s0 and
2739more on top of it. It can be found via gem servers. Its homepage is at
2740<http://rev.rubyforge.org/>.
2741.IP "D" 4
2742.IX Item "D"
2743Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
2744be found at <http://git.llucax.com.ar/?p=software/ev.d.git;a=summary>.
2745.SH "MACRO MAGIC"
2746.IX Header "MACRO MAGIC"
2747Libev can be compiled with a variety of options, the most fundamantal
2748of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most)
2749functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
2750.PP
2751To make it easier to write programs that cope with either variant, the
2752following macros are defined:
2753.ie n .IP """EV_A""\fR, \f(CW""EV_A_""" 4
2754.el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
2755.IX Item "EV_A, EV_A_"
2756This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
2757loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
2758\&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
2759.Sp
2760.Vb 3
2761\& ev_unref (EV_A);
2762\& ev_timer_add (EV_A_ watcher);
2763\& ev_loop (EV_A_ 0);
2764.Ve
2765.Sp
2766It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
2767which is often provided by the following macro.
2768.ie n .IP """EV_P""\fR, \f(CW""EV_P_""" 4
2769.el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
2770.IX Item "EV_P, EV_P_"
2771This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
2772loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
2773\&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
2774.Sp
2775.Vb 2
2776\& // this is how ev_unref is being declared
2777\& static void ev_unref (EV_P);
2778\&
2779\& // this is how you can declare your typical callback
2780\& static void cb (EV_P_ ev_timer *w, int revents)
2781.Ve
2782.Sp
2783It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
2784suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
2785.ie n .IP """EV_DEFAULT""\fR, \f(CW""EV_DEFAULT_""" 4
2786.el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
2787.IX Item "EV_DEFAULT, EV_DEFAULT_"
2788Similar to the other two macros, this gives you the value of the default
2789loop, if multiple loops are supported (\*(L"ev loop default\*(R").
2790.ie n .IP """EV_DEFAULT_UC""\fR, \f(CW""EV_DEFAULT_UC_""" 4
2791.el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
2792.IX Item "EV_DEFAULT_UC, EV_DEFAULT_UC_"
2793Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the
2794default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour
2795is undefined when the default loop has not been initialised by a previous
2796execution of \f(CW\*(C`EV_DEFAULT\*(C'\fR, \f(CW\*(C`EV_DEFAULT_\*(C'\fR or \f(CW\*(C`ev_default_init (...)\*(C'\fR.
2797.Sp
2798It is often prudent to use \f(CW\*(C`EV_DEFAULT\*(C'\fR when initialising the first
2799watcher in a function but use \f(CW\*(C`EV_DEFAULT_UC\*(C'\fR afterwards.
2800.PP
2801Example: Declare and initialise a check watcher, utilising the above
2802macros so it will work regardless of whether multiple loops are supported
2803or not.
2804.PP
2805.Vb 5
2806\& static void
2807\& check_cb (EV_P_ ev_timer *w, int revents)
2808\& {
2809\& ev_check_stop (EV_A_ w);
2810\& }
2811\&
2812\& ev_check check;
2813\& ev_check_init (&check, check_cb);
2814\& ev_check_start (EV_DEFAULT_ &check);
2815\& ev_loop (EV_DEFAULT_ 0);
2816.Ve
2817.SH "EMBEDDING"
2818.IX Header "EMBEDDING"
2819Libev can (and often is) directly embedded into host
2820applications. Examples of applications that embed it include the Deliantra
2821Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
2822and rxvt-unicode.
2823.PP
2824The goal is to enable you to just copy the necessary files into your
2825source directory without having to change even a single line in them, so
2826you can easily upgrade by simply copying (or having a checked-out copy of
2827libev somewhere in your source tree).
2828.Sh "\s-1FILESETS\s0"
2829.IX Subsection "FILESETS"
2830Depending on what features you need you need to include one or more sets of files
2831in your app.
2832.PP
2833\fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR
2834.IX Subsection "CORE EVENT LOOP"
2835.PP
2836To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
2837configuration (no autoconf):
2838.PP
2839.Vb 2
2840\& #define EV_STANDALONE 1
2841\& #include "ev.c"
2842.Ve
2843.PP
2844This will automatically include \fIev.h\fR, too, and should be done in a
2845single C source file only to provide the function implementations. To use
2846it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best
2847done by writing a wrapper around \fIev.h\fR that you can include instead and
2848where you can put other configuration options):
2849.PP
2850.Vb 2
2851\& #define EV_STANDALONE 1
2852\& #include "ev.h"
2853.Ve
2854.PP
2855Both header files and implementation files can be compiled with a \*(C+
2856compiler (at least, thats a stated goal, and breakage will be treated
2857as a bug).
2858.PP
2859You need the following files in your source tree, or in a directory
2860in your include path (e.g. in libev/ when using \-Ilibev):
2861.PP
2862.Vb 4
2863\& ev.h
2864\& ev.c
2865\& ev_vars.h
2866\& ev_wrap.h
2867\&
2868\& ev_win32.c required on win32 platforms only
2869\&
2870\& ev_select.c only when select backend is enabled (which is enabled by default)
2871\& ev_poll.c only when poll backend is enabled (disabled by default)
2872\& ev_epoll.c only when the epoll backend is enabled (disabled by default)
2873\& ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2874\& ev_port.c only when the solaris port backend is enabled (disabled by default)
2875.Ve
2876.PP
2877\&\fIev.c\fR includes the backend files directly when enabled, so you only need
2878to compile this single file.
2879.PP
2880\fI\s-1LIBEVENT\s0 \s-1COMPATIBILITY\s0 \s-1API\s0\fR
2881.IX Subsection "LIBEVENT COMPATIBILITY API"
2882.PP
2883To include the libevent compatibility \s-1API\s0, also include:
2884.PP
2885.Vb 1
2886\& #include "event.c"
2887.Ve
2888.PP
2889in the file including \fIev.c\fR, and:
2890.PP
2891.Vb 1
2892\& #include "event.h"
2893.Ve
2894.PP
2895in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR.
2896.PP
2897You need the following additional files for this:
2898.PP
2899.Vb 2
2900\& event.h
2901\& event.c
2902.Ve
2903.PP
2904\fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR
2905.IX Subsection "AUTOCONF SUPPORT"
2906.PP
2907Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your config in
2908whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
2909\&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then
2910include \fIconfig.h\fR and configure itself accordingly.
2911.PP
2912For this of course you need the m4 file:
2913.PP
2914.Vb 1
2915\& libev.m4
2916.Ve
2917.Sh "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0"
2918.IX Subsection "PREPROCESSOR SYMBOLS/MACROS"
2919Libev can be configured via a variety of preprocessor symbols you have to
2920define before including any of its files. The default in the absense of
2921autoconf is noted for every option.
2922.IP "\s-1EV_STANDALONE\s0" 4
2923.IX Item "EV_STANDALONE"
2924Must always be \f(CW1\fR if you do not use autoconf configuration, which
2925keeps libev from including \fIconfig.h\fR, and it also defines dummy
2926implementations for some libevent functions (such as logging, which is not
2927supported). It will also not define any of the structs usually found in
2928\&\fIevent.h\fR that are not directly supported by the libev core alone.
2929.IP "\s-1EV_USE_MONOTONIC\s0" 4
2930.IX Item "EV_USE_MONOTONIC"
2931If defined to be \f(CW1\fR, libev will try to detect the availability of the
2932monotonic clock option at both compiletime and runtime. Otherwise no use
2933of the monotonic clock option will be attempted. If you enable this, you
2934usually have to link against librt or something similar. Enabling it when
2935the functionality isn't available is safe, though, although you have
2936to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
2937function is hiding in (often \fI\-lrt\fR).
2938.IP "\s-1EV_USE_REALTIME\s0" 4
2939.IX Item "EV_USE_REALTIME"
2940If defined to be \f(CW1\fR, libev will try to detect the availability of the
2941realtime clock option at compiletime (and assume its availability at
2942runtime if successful). Otherwise no use of the realtime clock option will
2943be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR by \f(CW\*(C`clock_get
2944(CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect correctness. See the
2945note about libraries in the description of \f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though.
2946.IP "\s-1EV_USE_NANOSLEEP\s0" 4
2947.IX Item "EV_USE_NANOSLEEP"
2948If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available
2949and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR.
2950.IP "\s-1EV_USE_EVENTFD\s0" 4
2951.IX Item "EV_USE_EVENTFD"
2952If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
2953available and will probe for kernel support at runtime. This will improve
2954\&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
2955If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
29562.7 or newer, otherwise disabled.
2957.IP "\s-1EV_USE_SELECT\s0" 4
2958.IX Item "EV_USE_SELECT"
2959If undefined or defined to be \f(CW1\fR, libev will compile in support for the
2960\&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at autodetection will be done: if no
2961other method takes over, select will be it. Otherwise the select backend
2962will not be compiled in.
2963.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
2964.IX Item "EV_SELECT_USE_FD_SET"
2965If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR
2966structure. This is useful if libev doesn't compile due to a missing
2967\&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it misguesses the bitset layout on
2968exotic systems. This usually limits the range of file descriptors to some
2969low limit such as 1024 or might have other limitations (winsocket only
2970allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation, might
2971influence the size of the \f(CW\*(C`fd_set\*(C'\fR used.
2972.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
2973.IX Item "EV_SELECT_IS_WINSOCKET"
2974When defined to \f(CW1\fR, the select backend will assume that
2975select/socket/connect etc. don't understand file descriptors but
2976wants osf handles on win32 (this is the case when the select to
2977be used is the winsock select). This means that it will call
2978\&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
2979it is assumed that all these functions actually work on fds, even
2980on win32. Should not be defined on non\-win32 platforms.
2981.IP "\s-1EV_FD_TO_WIN32_HANDLE\s0" 4
2982.IX Item "EV_FD_TO_WIN32_HANDLE"
2983If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map
2984file descriptors to socket handles. When not defining this symbol (the
2985default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually
2986correct. In some cases, programs use their own file descriptor management,
2987in which case they can provide this function to map fds to socket handles.
2988.IP "\s-1EV_USE_POLL\s0" 4
2989.IX Item "EV_USE_POLL"
2990If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2)
2991backend. Otherwise it will be enabled on non\-win32 platforms. It
2992takes precedence over select.
2993.IP "\s-1EV_USE_EPOLL\s0" 4
2994.IX Item "EV_USE_EPOLL"
2995If defined to be \f(CW1\fR, libev will compile in support for the Linux
2996\&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime,
2997otherwise another method will be used as fallback. This is the preferred
2998backend for GNU/Linux systems. If undefined, it will be enabled if the
2999headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3000.IP "\s-1EV_USE_KQUEUE\s0" 4
3001.IX Item "EV_USE_KQUEUE"
3002If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
3003\&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime,
3004otherwise another method will be used as fallback. This is the preferred
3005backend for \s-1BSD\s0 and BSD-like systems, although on most BSDs kqueue only
3006supports some types of fds correctly (the only platform we found that
3007supports ptys for example was NetBSD), so kqueue might be compiled in, but
3008not be used unless explicitly requested. The best way to use it is to find
3009out whether kqueue supports your type of fd properly and use an embedded
3010kqueue loop.
3011.IP "\s-1EV_USE_PORT\s0" 4
3012.IX Item "EV_USE_PORT"
3013If defined to be \f(CW1\fR, libev will compile in support for the Solaris
301410 port style backend. Its availability will be detected at runtime,
3015otherwise another method will be used as fallback. This is the preferred
3016backend for Solaris 10 systems.
3017.IP "\s-1EV_USE_DEVPOLL\s0" 4
3018.IX Item "EV_USE_DEVPOLL"
3019reserved for future expansion, works like the \s-1USE\s0 symbols above.
3020.IP "\s-1EV_USE_INOTIFY\s0" 4
3021.IX Item "EV_USE_INOTIFY"
3022If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
3023interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
3024be detected at runtime. If undefined, it will be enabled if the headers
3025indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3026.IP "\s-1EV_ATOMIC_T\s0" 4
3027.IX Item "EV_ATOMIC_T"
3028Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
3029access is atomic with respect to other threads or signal contexts. No such
3030type is easily found in the C language, so you can provide your own type
3031that you know is safe for your purposes. It is used both for signal handler \*(L"locking\*(R"
3032as well as for signal and thread safety in \f(CW\*(C`ev_async\*(C'\fR watchers.
3033.Sp
3034In the absense of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR
3035(from \fIsignal.h\fR), which is usually good enough on most platforms.
3036.IP "\s-1EV_H\s0" 4
3037.IX Item "EV_H"
3038The name of the \fIev.h\fR header file used to include it. The default if
3039undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be
3040used to virtually rename the \fIev.h\fR header file in case of conflicts.
3041.IP "\s-1EV_CONFIG_H\s0" 4
3042.IX Item "EV_CONFIG_H"
3043If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
3044\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
3045\&\f(CW\*(C`EV_H\*(C'\fR, above.
3046.IP "\s-1EV_EVENT_H\s0" 4
3047.IX Item "EV_EVENT_H"
3048Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea
3049of how the \fIevent.h\fR header can be found, the default is \f(CW"event.h"\fR.
3050.IP "\s-1EV_PROTOTYPES\s0" 4
3051.IX Item "EV_PROTOTYPES"
3052If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
3053prototypes, but still define all the structs and other symbols. This is
3054occasionally useful if you want to provide your own wrapper functions
3055around libev functions.
3056.IP "\s-1EV_MULTIPLICITY\s0" 4
3057.IX Item "EV_MULTIPLICITY"
3058If undefined or defined to \f(CW1\fR, then all event-loop-specific functions
3059will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create
3060additional independent event loops. Otherwise there will be no support
3061for multiple event loops and there is no first event loop pointer
3062argument. Instead, all functions act on the single default loop.
3063.IP "\s-1EV_MINPRI\s0" 4
3064.IX Item "EV_MINPRI"
3065.PD 0
3066.IP "\s-1EV_MAXPRI\s0" 4
3067.IX Item "EV_MAXPRI"
3068.PD
3069The range of allowed priorities. \f(CW\*(C`EV_MINPRI\*(C'\fR must be smaller or equal to
3070\&\f(CW\*(C`EV_MAXPRI\*(C'\fR, but otherwise there are no non-obvious limitations. You can
3071provide for more priorities by overriding those symbols (usually defined
3072to be \f(CW\*(C`\-2\*(C'\fR and \f(CW2\fR, respectively).
3073.Sp
3074When doing priority-based operations, libev usually has to linearly search
3075all the priorities, so having many of them (hundreds) uses a lot of space
3076and time, so using the defaults of five priorities (\-2 .. +2) is usually
3077fine.
3078.Sp
3079If your embedding app does not need any priorities, defining these both to
3080\&\f(CW0\fR will save some memory and cpu.
3081.IP "\s-1EV_PERIODIC_ENABLE\s0" 4
3082.IX Item "EV_PERIODIC_ENABLE"
3083If undefined or defined to be \f(CW1\fR, then periodic timers are supported. If
3084defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of
3085code.
3086.IP "\s-1EV_IDLE_ENABLE\s0" 4
3087.IX Item "EV_IDLE_ENABLE"
3088If undefined or defined to be \f(CW1\fR, then idle watchers are supported. If
3089defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of
3090code.
3091.IP "\s-1EV_EMBED_ENABLE\s0" 4
3092.IX Item "EV_EMBED_ENABLE"
3093If undefined or defined to be \f(CW1\fR, then embed watchers are supported. If
3094defined to be \f(CW0\fR, then they are not.
3095.IP "\s-1EV_STAT_ENABLE\s0" 4
3096.IX Item "EV_STAT_ENABLE"
3097If undefined or defined to be \f(CW1\fR, then stat watchers are supported. If
3098defined to be \f(CW0\fR, then they are not.
3099.IP "\s-1EV_FORK_ENABLE\s0" 4
3100.IX Item "EV_FORK_ENABLE"
3101If undefined or defined to be \f(CW1\fR, then fork watchers are supported. If
3102defined to be \f(CW0\fR, then they are not.
3103.IP "\s-1EV_ASYNC_ENABLE\s0" 4
3104.IX Item "EV_ASYNC_ENABLE"
3105If undefined or defined to be \f(CW1\fR, then async watchers are supported. If
3106defined to be \f(CW0\fR, then they are not.
3107.IP "\s-1EV_MINIMAL\s0" 4
3108.IX Item "EV_MINIMAL"
3109If you need to shave off some kilobytes of code at the expense of some
3110speed, define this symbol to \f(CW1\fR. Currently this is used to override some
3111inlining decisions, saves roughly 30% codesize of amd64. It also selects a
3112much smaller 2\-heap for timer management over the default 4\-heap.
3113.IP "\s-1EV_PID_HASHSIZE\s0" 4
3114.IX Item "EV_PID_HASHSIZE"
3115\&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by
3116pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR), usually more
3117than enough. If you need to manage thousands of children you might want to
3118increase this value (\fImust\fR be a power of two).
3119.IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4
3120.IX Item "EV_INOTIFY_HASHSIZE"
3121\&\f(CW\*(C`ev_stat\*(C'\fR watchers use a small hash table to distribute workload by
3122inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR),
3123usually more than enough. If you need to manage thousands of \f(CW\*(C`ev_stat\*(C'\fR
3124watchers you might want to increase this value (\fImust\fR be a power of
3125two).
3126.IP "\s-1EV_USE_4HEAP\s0" 4
3127.IX Item "EV_USE_4HEAP"
3128Heaps are not very cache-efficient. To improve the cache-efficiency of the
3129timer and periodics heap, libev uses a 4\-heap when this symbol is defined
3130to \f(CW1\fR. The 4\-heap uses more complicated (longer) code but has
3131noticably faster performance with many (thousands) of watchers.
3132.Sp
3133The default is \f(CW1\fR unless \f(CW\*(C`EV_MINIMAL\*(C'\fR is set in which case it is \f(CW0\fR
3134(disabled).
3135.IP "\s-1EV_HEAP_CACHE_AT\s0" 4
3136.IX Item "EV_HEAP_CACHE_AT"
3137Heaps are not very cache-efficient. To improve the cache-efficiency of the
3138timer and periodics heap, libev can cache the timestamp (\fIat\fR) within
3139the heap structure (selected by defining \f(CW\*(C`EV_HEAP_CACHE_AT\*(C'\fR to \f(CW1\fR),
3140which uses 8\-12 bytes more per watcher and a few hundred bytes more code,
3141but avoids random read accesses on heap changes. This improves performance
3142noticably with with many (hundreds) of watchers.
3143.Sp
3144The default is \f(CW1\fR unless \f(CW\*(C`EV_MINIMAL\*(C'\fR is set in which case it is \f(CW0\fR
3145(disabled).
3146.IP "\s-1EV_VERIFY\s0" 4
3147.IX Item "EV_VERIFY"
3148Controls how much internal verification (see \f(CW\*(C`ev_loop_verify ()\*(C'\fR) will
3149be done: If set to \f(CW0\fR, no internal verification code will be compiled
3150in. If set to \f(CW1\fR, then verification code will be compiled in, but not
3151called. If set to \f(CW2\fR, then the internal verification code will be
3152called once per loop, which can slow down libev. If set to \f(CW3\fR, then the
3153verification code will be called very frequently, which will slow down
3154libev considerably.
3155.Sp
3156The default is \f(CW1\fR, unless \f(CW\*(C`EV_MINIMAL\*(C'\fR is set, in which case it will be
3157\&\f(CW0.\fR
3158.IP "\s-1EV_COMMON\s0" 4
3159.IX Item "EV_COMMON"
3160By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining
3161this macro to a something else you can include more and other types of
3162members. You have to define it each time you include one of the files,
3163though, and it must be identical each time.
3164.Sp
3165For example, the perl \s-1EV\s0 module uses something like this:
3166.Sp
3167.Vb 3
3168\& #define EV_COMMON \e
3169\& SV *self; /* contains this struct */ \e
3170\& SV *cb_sv, *fh /* note no trailing ";" */
3171.Ve
3172.IP "\s-1EV_CB_DECLARE\s0 (type)" 4
3173.IX Item "EV_CB_DECLARE (type)"
3174.PD 0
3175.IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4
3176.IX Item "EV_CB_INVOKE (watcher, revents)"
3177.IP "ev_set_cb (ev, cb)" 4
3178.IX Item "ev_set_cb (ev, cb)"
3179.PD
3180Can be used to change the callback member declaration in each watcher,
3181and the way callbacks are invoked and set. Must expand to a struct member
3182definition and a statement, respectively. See the \fIev.h\fR header file for
3183their default definitions. One possible use for overriding these is to
3184avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use
3185method calls instead of plain function calls in \*(C+.
3186.Sh "\s-1EXPORTED\s0 \s-1API\s0 \s-1SYMBOLS\s0"
3187.IX Subsection "EXPORTED API SYMBOLS"
3188If you need to re-export the \s-1API\s0 (e.g. via a dll) and you need a list of
3189exported symbols, you can use the provided \fISymbol.*\fR files which list
3190all public symbols, one per line:
3191.PP
3192.Vb 2
3193\& Symbols.ev for libev proper
3194\& Symbols.event for the libevent emulation
3195.Ve
3196.PP
3197This can also be used to rename all public symbols to avoid clashes with
3198multiple versions of libev linked together (which is obviously bad in
3199itself, but sometimes it is inconvinient to avoid this).
3200.PP
3201A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to
3202include before including \fIev.h\fR:
3203.PP
3204.Vb 1
3205\& <Symbols.ev sed \-e "s/.*/#define & myprefix_&/" >wrap.h
3206.Ve
3207.PP
3208This would create a file \fIwrap.h\fR which essentially looks like this:
3209.PP
3210.Vb 4
3211\& #define ev_backend myprefix_ev_backend
3212\& #define ev_check_start myprefix_ev_check_start
3213\& #define ev_check_stop myprefix_ev_check_stop
3214\& ...
3215.Ve
3216.Sh "\s-1EXAMPLES\s0"
3217.IX Subsection "EXAMPLES"
3218For a real-world example of a program the includes libev
3219verbatim, you can have a look at the \s-1EV\s0 perl module
3220(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
3221the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public
3222interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file
3223will be compiled. It is pretty complex because it provides its own header
3224file.
3225.PP
3226The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file
3227that everybody includes and which overrides some configure choices:
3228.PP
3229.Vb 9
3230\& #define EV_MINIMAL 1
3231\& #define EV_USE_POLL 0
3232\& #define EV_MULTIPLICITY 0
3233\& #define EV_PERIODIC_ENABLE 0
3234\& #define EV_STAT_ENABLE 0
3235\& #define EV_FORK_ENABLE 0
3236\& #define EV_CONFIG_H <config.h>
3237\& #define EV_MINPRI 0
3238\& #define EV_MAXPRI 0
3239\&
3240\& #include "ev++.h"
3241.Ve
3242.PP
3243And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled:
3244.PP
3245.Vb 2
3246\& #include "ev_cpp.h"
3247\& #include "ev.c"
3248.Ve
3249.SH "THREADS AND COROUTINES"
3250.IX Header "THREADS AND COROUTINES"
3251.Sh "\s-1THREADS\s0"
3252.IX Subsection "THREADS"
3253Libev itself is completely threadsafe, but it uses no locking. This
3254means that you can use as many loops as you want in parallel, as long as
3255only one thread ever calls into one libev function with the same loop
3256parameter.
3257.PP
3258Or put differently: calls with different loop parameters can be done in
3259parallel from multiple threads, calls with the same loop parameter must be
3260done serially (but can be done from different threads, as long as only one
3261thread ever is inside a call at any point in time, e.g. by using a mutex
3262per loop).
3263.PP
3264If you want to know which design is best for your problem, then I cannot
3265help you but by giving some generic advice:
3266.IP "\(bu" 4
3267most applications have a main thread: use the default libev loop
3268in that thread, or create a seperate thread running only the default loop.
3269.Sp
3270This helps integrating other libraries or software modules that use libev
3271themselves and don't care/know about threading.
3272.IP "\(bu" 4
3273one loop per thread is usually a good model.
3274.Sp
3275Doing this is almost never wrong, sometimes a better-performance model
3276exists, but it is always a good start.
3277.IP "\(bu" 4
3278other models exist, such as the leader/follower pattern, where one
3279loop is handed through multiple threads in a kind of round-robbin fashion.
3280.Sp
3281Chosing a model is hard \- look around, learn, know that usually you cna do
3282better than you currently do :\-)
3283.IP "\(bu" 4
3284often you need to talk to some other thread which blocks in the
3285event loop \- \f(CW\*(C`ev_async\*(C'\fR watchers can be used to wake them up from other
3286threads safely (or from signal contexts...).
3287.Sh "\s-1COROUTINES\s0"
3288.IX Subsection "COROUTINES"
3289Libev is much more accomodating to coroutines (\*(L"cooperative threads\*(R"):
3290libev fully supports nesting calls to it's functions from different
3291coroutines (e.g. you can call \f(CW\*(C`ev_loop\*(C'\fR on the same loop from two
3292different coroutines and switch freely between both coroutines running the
3293loop, as long as you don't confuse yourself). The only exception is that
3294you must not do this from \f(CW\*(C`ev_periodic\*(C'\fR reschedule callbacks.
3295.PP
3296Care has been invested into making sure that libev does not keep local
3297state inside \f(CW\*(C`ev_loop\*(C'\fR, and other calls do not usually allow coroutine
3298switches.
3299.SH "COMPLEXITIES"
3300.IX Header "COMPLEXITIES"
3301In this section the complexities of (many of) the algorithms used inside
3302libev will be explained. For complexity discussions about backends see the
3303documentation for \f(CW\*(C`ev_default_init\*(C'\fR.
3304.PP
3305All of the following are about amortised time: If an array needs to be
3306extended, libev needs to realloc and move the whole array, but this
3307happens asymptotically never with higher number of elements, so O(1) might
3308mean it might do a lengthy realloc operation in rare cases, but on average
3309it is much faster and asymptotically approaches constant time.
3310.IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4
3311.IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)"
3312This means that, when you have a watcher that triggers in one hour and
3313there are 100 watchers that would trigger before that then inserting will
3314have to skip roughly seven (\f(CW\*(C`ld 100\*(C'\fR) of these watchers.
3315.IP "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 4
3316.IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)"
3317That means that changing a timer costs less than removing/adding them
3318as only the relative motion in the event queue has to be paid for.
3319.IP "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)" 4
3320.IX Item "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)"
3321These just add the watcher into an array or at the head of a list.
3322.IP "Stopping check/prepare/idle/fork/async watchers: O(1)" 4
3323.IX Item "Stopping check/prepare/idle/fork/async watchers: O(1)"
3324.PD 0
3325.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4
3326.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))"
3327.PD
3328These watchers are stored in lists then need to be walked to find the
3329correct watcher to remove. The lists are usually short (you don't usually
3330have many watchers waiting for the same fd or signal).
3331.IP "Finding the next timer in each loop iteration: O(1)" 4
3332.IX Item "Finding the next timer in each loop iteration: O(1)"
3333By virtue of using a binary or 4\-heap, the next timer is always found at a
3334fixed position in the storage array.
3335.IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4
3336.IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)"
3337A change means an I/O watcher gets started or stopped, which requires
3338libev to recalculate its status (and possibly tell the kernel, depending
3339on backend and wether \f(CW\*(C`ev_io_set\*(C'\fR was used).
3340.IP "Activating one watcher (putting it into the pending state): O(1)" 4
3341.IX Item "Activating one watcher (putting it into the pending state): O(1)"
3342.PD 0
3343.IP "Priority handling: O(number_of_priorities)" 4
3344.IX Item "Priority handling: O(number_of_priorities)"
3345.PD
3346Priorities are implemented by allocating some space for each
3347priority. When doing priority-based operations, libev usually has to
3348linearly search all the priorities, but starting/stopping and activating
3349watchers becomes O(1) w.r.t. priority handling.
3350.IP "Sending an ev_async: O(1)" 4
3351.IX Item "Sending an ev_async: O(1)"
3352.PD 0
3353.IP "Processing ev_async_send: O(number_of_async_watchers)" 4
3354.IX Item "Processing ev_async_send: O(number_of_async_watchers)"
3355.IP "Processing signals: O(max_signal_number)" 4
3356.IX Item "Processing signals: O(max_signal_number)"
3357.PD
3358Sending involves a syscall \fIiff\fR there were no other \f(CW\*(C`ev_async_send\*(C'\fR
3359calls in the current loop iteration. Checking for async and signal events
3360involves iterating over all running async watchers or all signal numbers.
3361.SH "Win32 platform limitations and workarounds"
3362.IX Header "Win32 platform limitations and workarounds"
3363Win32 doesn't support any of the standards (e.g. \s-1POSIX\s0) that libev
3364requires, and its I/O model is fundamentally incompatible with the \s-1POSIX\s0
3365model. Libev still offers limited functionality on this platform in
3366the form of the \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR backend, and only supports socket
3367descriptors. This only applies when using Win32 natively, not when using
3368e.g. cygwin.
3369.PP
3370Lifting these limitations would basically require the full
3371re-implementation of the I/O system. If you are into these kinds of
3372things, then note that glib does exactly that for you in a very portable
3373way (note also that glib is the slowest event library known to man).
3374.PP
3375There is no supported compilation method available on windows except
3376embedding it into other applications.
3377.PP
3378Due to the many, low, and arbitrary limits on the win32 platform and
3379the abysmal performance of winsockets, using a large number of sockets
3380is not recommended (and not reasonable). If your program needs to use
3381more than a hundred or so sockets, then likely it needs to use a totally
3382different implementation for windows, as libev offers the \s-1POSIX\s0 readiness
3383notification model, which cannot be implemented efficiently on windows
3384(microsoft monopoly games).
3385.IP "The winsocket select function" 4
3386.IX Item "The winsocket select function"
3387The winsocket \f(CW\*(C`select\*(C'\fR function doesn't follow \s-1POSIX\s0 in that it
3388requires socket \fIhandles\fR and not socket \fIfile descriptors\fR (it is
3389also extremely buggy). This makes select very inefficient, and also
3390requires a mapping from file descriptors to socket handles. See the
3391discussion of the \f(CW\*(C`EV_SELECT_USE_FD_SET\*(C'\fR, \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR and
3392\&\f(CW\*(C`EV_FD_TO_WIN32_HANDLE\*(C'\fR preprocessor symbols for more info.
3393.Sp
3394The configuration for a \*(L"naked\*(R" win32 using the microsoft runtime
3395libraries and raw winsocket select is:
3396.Sp
3397.Vb 2
3398\& #define EV_USE_SELECT 1
3399\& #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
3400.Ve
3401.Sp
3402Note that winsockets handling of fd sets is O(n), so you can easily get a
3403complexity in the O(nA\*^X) range when using win32.
3404.IP "Limited number of file descriptors" 4
3405.IX Item "Limited number of file descriptors"
3406Windows has numerous arbitrary (and low) limits on things.
3407.Sp
3408Early versions of winsocket's select only supported waiting for a maximum
3409of \f(CW64\fR handles (probably owning to the fact that all windows kernels
3410can only wait for \f(CW64\fR things at the same time internally; microsoft
3411recommends spawning a chain of threads and wait for 63 handles and the
3412previous thread in each. Great).
3413.Sp
3414Newer versions support more handles, but you need to define \f(CW\*(C`FD_SETSIZE\*(C'\fR
3415to some high number (e.g. \f(CW2048\fR) before compiling the winsocket select
3416call (which might be in libev or elsewhere, for example, perl does its own
3417select emulation on windows).
3418.Sp
3419Another limit is the number of file descriptors in the microsoft runtime
3420libraries, which by default is \f(CW64\fR (there must be a hidden \fI64\fR fetish
3421or something like this inside microsoft). You can increase this by calling
3422\&\f(CW\*(C`_setmaxstdio\*(C'\fR, which can increase this limit to \f(CW2048\fR (another
3423arbitrary limit), but is broken in many versions of the microsoft runtime
3424libraries.
3425.Sp
3426This might get you to about \f(CW512\fR or \f(CW2048\fR sockets (depending on
3427windows version and/or the phase of the moon). To get more, you need to
3428wrap all I/O functions and provide your own fd management, but the cost of
3429calling select (O(nA\*^X)) will likely make this unworkable.
3430.SH "PORTABILITY REQUIREMENTS"
3431.IX Header "PORTABILITY REQUIREMENTS"
3432In addition to a working ISO-C implementation, libev relies on a few
3433additional extensions:
3434.ie n .IP """sig_atomic_t volatile"" must be thread-atomic as well" 4
3435.el .IP "\f(CWsig_atomic_t volatile\fR must be thread-atomic as well" 4
3436.IX Item "sig_atomic_t volatile must be thread-atomic as well"
3437The type \f(CW\*(C`sig_atomic_t volatile\*(C'\fR (or whatever is defined as
3438\&\f(CW\*(C`EV_ATOMIC_T\*(C'\fR) must be atomic w.r.t. accesses from different
3439threads. This is not part of the specification for \f(CW\*(C`sig_atomic_t\*(C'\fR, but is
3440believed to be sufficiently portable.
3441.ie n .IP """sigprocmask"" must work in a threaded environment" 4
3442.el .IP "\f(CWsigprocmask\fR must work in a threaded environment" 4
3443.IX Item "sigprocmask must work in a threaded environment"
3444Libev uses \f(CW\*(C`sigprocmask\*(C'\fR to temporarily block signals. This is not
3445allowed in a threaded program (\f(CW\*(C`pthread_sigmask\*(C'\fR has to be used). Typical
3446pthread implementations will either allow \f(CW\*(C`sigprocmask\*(C'\fR in the \*(L"main
3447thread\*(R" or will block signals process-wide, both behaviours would
3448be compatible with libev. Interaction between \f(CW\*(C`sigprocmask\*(C'\fR and
3449\&\f(CW\*(C`pthread_sigmask\*(C'\fR could complicate things, however.
3450.Sp
3451The most portable way to handle signals is to block signals in all threads
3452except the initial one, and run the default loop in the initial thread as
3453well.
3454.ie n .IP """long"" must be large enough for common memory allocation sizes" 4
3455.el .IP "\f(CWlong\fR must be large enough for common memory allocation sizes" 4
3456.IX Item "long must be large enough for common memory allocation sizes"
3457To improve portability and simplify using libev, libev uses \f(CW\*(C`long\*(C'\fR
3458internally instead of \f(CW\*(C`size_t\*(C'\fR when allocating its data structures. On
3459non-POSIX systems (Microsoft...) this might be unexpectedly low, but
3460is still at least 31 bits everywhere, which is enough for hundreds of
3461millions of watchers.
3462.ie n .IP """double"" must hold a time value in seconds with enough accuracy" 4
3463.el .IP "\f(CWdouble\fR must hold a time value in seconds with enough accuracy" 4
3464.IX Item "double must hold a time value in seconds with enough accuracy"
3465The type \f(CW\*(C`double\*(C'\fR is used to represent timestamps. It is required to
3466have at least 51 bits of mantissa (and 9 bits of exponent), which is good
3467enough for at least into the year 4000. This requirement is fulfilled by
3468implementations implementing \s-1IEEE\s0 754 (basically all existing ones).
3469.PP
3470If you know of other additional requirements drop me a note.
3471.SH "COMPILER WARNINGS"
3472.IX Header "COMPILER WARNINGS"
3473Depending on your compiler and compiler settings, you might get no or a
3474lot of warnings when compiling libev code. Some people are apparently
3475scared by this.
3476.PP
3477However, these are unavoidable for many reasons. For one, each compiler
3478has different warnings, and each user has different tastes regarding
3479warning options. \*(L"Warn-free\*(R" code therefore cannot be a goal except when
3480targetting a specific compiler and compiler-version.
3481.PP
3482Another reason is that some compiler warnings require elaborate
3483workarounds, or other changes to the code that make it less clear and less
3484maintainable.
3485.PP
3486And of course, some compiler warnings are just plain stupid, or simply
3487wrong (because they don't actually warn about the cindition their message
3488seems to warn about).
3489.PP
3490While libev is written to generate as few warnings as possible,
3491\&\*(L"warn-free\*(R" code is not a goal, and it is recommended not to build libev
3492with any compiler warnings enabled unless you are prepared to cope with
3493them (e.g. by ignoring them). Remember that warnings are just that:
3494warnings, not errors, or proof of bugs.
3495.SH "VALGRIND"
3496.IX Header "VALGRIND"
3497Valgrind has a special section here because it is a popular tool that is
3498highly useful, but valgrind reports are very hard to interpret.
3499.PP
3500If you think you found a bug (memory leak, uninitialised data access etc.)
3501in libev, then check twice: If valgrind reports something like:
3502.PP
3503.Vb 3
3504\& ==2274== definitely lost: 0 bytes in 0 blocks.
3505\& ==2274== possibly lost: 0 bytes in 0 blocks.
3506\& ==2274== still reachable: 256 bytes in 1 blocks.
3507.Ve
3508.PP
3509then there is no memory leak. Similarly, under some circumstances,
3510valgrind might report kernel bugs as if it were a bug in libev, or it
3511might be confused (it is a very good tool, but only a tool).
3512.PP
3513If you are unsure about something, feel free to contact the mailing list
3514with the full valgrind report and an explanation on why you think this is
3515a bug in libev. However, don't be annoyed when you get a brisk \*(L"this is
3516no bug\*(R" answer and take the chance of learning how to interpret valgrind
3517properly.
3518.PP
3519If you need, for some reason, empty reports from valgrind for your project
3520I suggest using suppression lists.
958.SH "AUTHOR" 3521.SH "AUTHOR"
959.IX Header "AUTHOR" 3522.IX Header "AUTHOR"
960Marc Lehmann <libev@schmorp.de>. 3523Marc Lehmann <libev@schmorp.de>.
3524.SH "POD ERRORS"
3525.IX Header "POD ERRORS"
3526Hey! \fBThe above document had some coding errors, which are explained below:\fR
3527.IP "Around line 3107:" 4
3528.IX Item "Around line 3107:"
3529You forgot a '=back' before '=head2'

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