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129.\" ======================================================================== 124.\" ========================================================================
130.\" 125.\"
131.IX Title ""<STANDARD INPUT>" 1" 126.IX Title "LIBEV 3"
132.TH "<STANDARD INPUT>" 1 "2007-11-22" "perl v5.8.8" "User Contributed Perl Documentation" 127.TH LIBEV 3 "2010-10-25" "libev-4.00" "libev - high performance full featured event loop"
128.\" For nroff, turn off justification. Always turn off hyphenation; it makes
129.\" way too many mistakes in technical documents.
130.if n .ad l
131.nh
133.SH "NAME" 132.SH "NAME"
134libev \- a high performance full\-featured event loop written in C 133libev \- a high performance full\-featured event loop written in C
135.SH "SYNOPSIS" 134.SH "SYNOPSIS"
136.IX Header "SYNOPSIS" 135.IX Header "SYNOPSIS"
137.Vb 1 136.Vb 1
138\& #include <ev.h> 137\& #include <ev.h>
139.Ve 138.Ve
140.SH "DESCRIPTION" 139.SS "\s-1EXAMPLE\s0 \s-1PROGRAM\s0"
141.IX Header "DESCRIPTION" 140.IX Subsection "EXAMPLE PROGRAM"
141.Vb 2
142\& // a single header file is required
143\& #include <ev.h>
144\&
145\& #include <stdio.h> // for puts
146\&
147\& // every watcher type has its own typedef\*(Aqd struct
148\& // with the name ev_TYPE
149\& ev_io stdin_watcher;
150\& ev_timer timeout_watcher;
151\&
152\& // all watcher callbacks have a similar signature
153\& // this callback is called when data is readable on stdin
154\& static void
155\& stdin_cb (EV_P_ ev_io *w, int revents)
156\& {
157\& puts ("stdin ready");
158\& // for one\-shot events, one must manually stop the watcher
159\& // with its corresponding stop function.
160\& ev_io_stop (EV_A_ w);
161\&
162\& // this causes all nested ev_run\*(Aqs to stop iterating
163\& ev_break (EV_A_ EVBREAK_ALL);
164\& }
165\&
166\& // another callback, this time for a time\-out
167\& static void
168\& timeout_cb (EV_P_ ev_timer *w, int revents)
169\& {
170\& puts ("timeout");
171\& // this causes the innermost ev_run to stop iterating
172\& ev_break (EV_A_ EVBREAK_ONE);
173\& }
174\&
175\& int
176\& main (void)
177\& {
178\& // use the default event loop unless you have special needs
179\& struct ev_loop *loop = EV_DEFAULT;
180\&
181\& // initialise an io watcher, then start it
182\& // this one will watch for stdin to become readable
183\& ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
184\& ev_io_start (loop, &stdin_watcher);
185\&
186\& // initialise a timer watcher, then start it
187\& // simple non\-repeating 5.5 second timeout
188\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
189\& ev_timer_start (loop, &timeout_watcher);
190\&
191\& // now wait for events to arrive
192\& ev_run (loop, 0);
193\&
194\& // unloop was called, so exit
195\& return 0;
196\& }
197.Ve
198.SH "ABOUT THIS DOCUMENT"
199.IX Header "ABOUT THIS DOCUMENT"
200This document documents the libev software package.
201.PP
202The newest version of this document is also available as an html-formatted
203web page you might find easier to navigate when reading it for the first
204time: <http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
205.PP
206While this document tries to be as complete as possible in documenting
207libev, its usage and the rationale behind its design, it is not a tutorial
208on event-based programming, nor will it introduce event-based programming
209with libev.
210.PP
211Familiarity with event based programming techniques in general is assumed
212throughout this document.
213.SH "WHAT TO READ WHEN IN A HURRY"
214.IX Header "WHAT TO READ WHEN IN A HURRY"
215This manual tries to be very detailed, but unfortunately, this also makes
216it very long. If you just want to know the basics of libev, I suggest
217reading \*(L"\s-1ANATOMY\s0 \s-1OF\s0 A \s-1WATCHER\s0\*(R", then the \*(L"\s-1EXAMPLE\s0 \s-1PROGRAM\s0\*(R" above and
218look up the missing functions in \*(L"\s-1GLOBAL\s0 \s-1FUNCTIONS\s0\*(R" and the \f(CW\*(C`ev_io\*(C'\fR and
219\&\f(CW\*(C`ev_timer\*(C'\fR sections in \*(L"\s-1WATCHER\s0 \s-1TYPES\s0\*(R".
220.SH "ABOUT LIBEV"
221.IX Header "ABOUT LIBEV"
142Libev is an event loop: you register interest in certain events (such as a 222Libev is an event loop: you register interest in certain events (such as a
143file descriptor being readable or a timeout occuring), and it will manage 223file descriptor being readable or a timeout occurring), and it will manage
144these event sources and provide your program with events. 224these event sources and provide your program with events.
145.PP 225.PP
146To do this, it must take more or less complete control over your process 226To do this, it must take more or less complete control over your process
147(or thread) by executing the \fIevent loop\fR handler, and will then 227(or thread) by executing the \fIevent loop\fR handler, and will then
148communicate events via a callback mechanism. 228communicate events via a callback mechanism.
149.PP 229.PP
150You register interest in certain events by registering so-called \fIevent 230You register interest in certain events by registering so-called \fIevent
151watchers\fR, which are relatively small C structures you initialise with the 231watchers\fR, which are relatively small C structures you initialise with the
152details of the event, and then hand it over to libev by \fIstarting\fR the 232details of the event, and then hand it over to libev by \fIstarting\fR the
153watcher. 233watcher.
154.SH "FEATURES" 234.SS "\s-1FEATURES\s0"
155.IX Header "FEATURES" 235.IX Subsection "FEATURES"
156Libev supports select, poll, the linux-specific epoll and the bsd-specific 236Libev supports \f(CW\*(C`select\*(C'\fR, \f(CW\*(C`poll\*(C'\fR, the Linux-specific \f(CW\*(C`epoll\*(C'\fR, the
157kqueue mechanisms for file descriptor events, relative timers, absolute 237BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port mechanisms
158timers with customised rescheduling, signal events, process status change 238for file descriptor events (\f(CW\*(C`ev_io\*(C'\fR), the Linux \f(CW\*(C`inotify\*(C'\fR interface
159events (related to \s-1SIGCHLD\s0), and event watchers dealing with the event 239(for \f(CW\*(C`ev_stat\*(C'\fR), Linux eventfd/signalfd (for faster and cleaner
160loop mechanism itself (idle, prepare and check watchers). It also is quite 240inter-thread wakeup (\f(CW\*(C`ev_async\*(C'\fR)/signal handling (\f(CW\*(C`ev_signal\*(C'\fR)) relative
161fast (see this benchmark comparing 241timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers with customised rescheduling
162it to libevent for example). 242(\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals (\f(CW\*(C`ev_signal\*(C'\fR), process status
243change events (\f(CW\*(C`ev_child\*(C'\fR), and event watchers dealing with the event
244loop mechanism itself (\f(CW\*(C`ev_idle\*(C'\fR, \f(CW\*(C`ev_embed\*(C'\fR, \f(CW\*(C`ev_prepare\*(C'\fR and
245\&\f(CW\*(C`ev_check\*(C'\fR watchers) as well as file watchers (\f(CW\*(C`ev_stat\*(C'\fR) and even
246limited support for fork events (\f(CW\*(C`ev_fork\*(C'\fR).
247.PP
248It also is quite fast (see this
249<benchmark> comparing it to libevent
250for example).
163.SH "CONVENTIONS" 251.SS "\s-1CONVENTIONS\s0"
164.IX Header "CONVENTIONS" 252.IX Subsection "CONVENTIONS"
165Libev is very configurable. In this manual the default configuration 253Libev is very configurable. In this manual the default (and most common)
166will be described, which supports multiple event loops. For more info 254configuration will be described, which supports multiple event loops. For
167about various configuration options please have a look at the file 255more info about various configuration options please have a look at
168\&\fI\s-1README\s0.embed\fR in the libev distribution. If libev was configured without 256\&\fB\s-1EMBED\s0\fR section in this manual. If libev was configured without support
169support for multiple event loops, then all functions taking an initial 257for multiple event loops, then all functions taking an initial argument of
170argument of name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) 258name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) will not have
171will not have this argument. 259this argument.
172.SH "TIME REPRESENTATION" 260.SS "\s-1TIME\s0 \s-1REPRESENTATION\s0"
173.IX Header "TIME REPRESENTATION" 261.IX Subsection "TIME REPRESENTATION"
174Libev represents time as a single floating point number, representing the 262Libev represents time as a single floating point number, representing
175(fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere near 263the (fractional) number of seconds since the (\s-1POSIX\s0) epoch (in practice
176the beginning of 1970, details are complicated, don't ask). This type is 264somewhere near the beginning of 1970, details are complicated, don't
177called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use too. It usually aliases 265ask). This type is called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use
178to the double type in C. 266too. It usually aliases to the \f(CW\*(C`double\*(C'\fR type in C. When you need to do
267any calculations on it, you should treat it as some floating point value.
268.PP
269Unlike the name component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for
270time differences (e.g. delays) throughout libev.
271.SH "ERROR HANDLING"
272.IX Header "ERROR HANDLING"
273Libev knows three classes of errors: operating system errors, usage errors
274and internal errors (bugs).
275.PP
276When libev catches an operating system error it cannot handle (for example
277a system call indicating a condition libev cannot fix), it calls the callback
278set via \f(CW\*(C`ev_set_syserr_cb\*(C'\fR, which is supposed to fix the problem or
279abort. The default is to print a diagnostic message and to call \f(CW\*(C`abort
280()\*(C'\fR.
281.PP
282When libev detects a usage error such as a negative timer interval, then
283it will print a diagnostic message and abort (via the \f(CW\*(C`assert\*(C'\fR mechanism,
284so \f(CW\*(C`NDEBUG\*(C'\fR will disable this checking): these are programming errors in
285the libev caller and need to be fixed there.
286.PP
287Libev also has a few internal error-checking \f(CW\*(C`assert\*(C'\fRions, and also has
288extensive consistency checking code. These do not trigger under normal
289circumstances, as they indicate either a bug in libev or worse.
179.SH "GLOBAL FUNCTIONS" 290.SH "GLOBAL FUNCTIONS"
180.IX Header "GLOBAL FUNCTIONS" 291.IX Header "GLOBAL FUNCTIONS"
181These functions can be called anytime, even before initialising the 292These functions can be called anytime, even before initialising the
182library in any way. 293library in any way.
183.IP "ev_tstamp ev_time ()" 4 294.IP "ev_tstamp ev_time ()" 4
184.IX Item "ev_tstamp ev_time ()" 295.IX Item "ev_tstamp ev_time ()"
185Returns the current time as libev would use it. Please note that the 296Returns the current time as libev would use it. Please note that the
186\&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp 297\&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp
187you actually want to know. 298you actually want to know. Also interesting is the combination of
299\&\f(CW\*(C`ev_update_now\*(C'\fR and \f(CW\*(C`ev_now\*(C'\fR.
300.IP "ev_sleep (ev_tstamp interval)" 4
301.IX Item "ev_sleep (ev_tstamp interval)"
302Sleep for the given interval: The current thread will be blocked until
303either it is interrupted or the given time interval has passed. Basically
304this is a sub-second-resolution \f(CW\*(C`sleep ()\*(C'\fR.
188.IP "int ev_version_major ()" 4 305.IP "int ev_version_major ()" 4
189.IX Item "int ev_version_major ()" 306.IX Item "int ev_version_major ()"
190.PD 0 307.PD 0
191.IP "int ev_version_minor ()" 4 308.IP "int ev_version_minor ()" 4
192.IX Item "int ev_version_minor ()" 309.IX Item "int ev_version_minor ()"
193.PD 310.PD
194You can find out the major and minor version numbers of the library 311You 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 312you 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 313\&\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 314symbols \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. 315version of the library your program was compiled against.
199.Sp 316.Sp
317These version numbers refer to the \s-1ABI\s0 version of the library, not the
318release version.
319.Sp
200Usually, it's a good idea to terminate if the major versions mismatch, 320Usually, it's a good idea to terminate if the major versions mismatch,
201as this indicates an incompatible change. Minor versions are usually 321as this indicates an incompatible change. Minor versions are usually
202compatible to older versions, so a larger minor version alone is usually 322compatible to older versions, so a larger minor version alone is usually
203not a problem. 323not a problem.
324.Sp
325Example: Make sure we haven't accidentally been linked against the wrong
326version (note, however, that this will not detect other \s-1ABI\s0 mismatches,
327such as \s-1LFS\s0 or reentrancy).
328.Sp
329.Vb 3
330\& assert (("libev version mismatch",
331\& ev_version_major () == EV_VERSION_MAJOR
332\& && ev_version_minor () >= EV_VERSION_MINOR));
333.Ve
334.IP "unsigned int ev_supported_backends ()" 4
335.IX Item "unsigned int ev_supported_backends ()"
336Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR
337value) compiled into this binary of libev (independent of their
338availability on the system you are running on). See \f(CW\*(C`ev_default_loop\*(C'\fR for
339a description of the set values.
340.Sp
341Example: make sure we have the epoll method, because yeah this is cool and
342a must have and can we have a torrent of it please!!!11
343.Sp
344.Vb 2
345\& assert (("sorry, no epoll, no sex",
346\& ev_supported_backends () & EVBACKEND_EPOLL));
347.Ve
348.IP "unsigned int ev_recommended_backends ()" 4
349.IX Item "unsigned int ev_recommended_backends ()"
350Return the set of all backends compiled into this binary of libev and
351also recommended for this platform, meaning it will work for most file
352descriptor types. This set is often smaller than the one returned by
353\&\f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on most BSDs
354and will not be auto-detected unless you explicitly request it (assuming
355you know what you are doing). This is the set of backends that libev will
356probe for if you specify no backends explicitly.
357.IP "unsigned int ev_embeddable_backends ()" 4
358.IX Item "unsigned int ev_embeddable_backends ()"
359Returns the set of backends that are embeddable in other event loops. This
360value is platform-specific but can include backends not available on the
361current system. To find which embeddable backends might be supported on
362the current system, you would need to look at \f(CW\*(C`ev_embeddable_backends ()
363& ev_supported_backends ()\*(C'\fR, likewise for recommended ones.
364.Sp
365See 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))" 4 366.IP "ev_set_allocator (void *(*cb)(void *ptr, long size)) [\s-1NOT\s0 \s-1REENTRANT\s0]" 4
205.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))" 367.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]"
206Sets the allocation function to use (the prototype is similar to the 368Sets the allocation function to use (the prototype is similar \- the
207realloc C function, the semantics are identical). It is used to allocate 369semantics 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 370used to allocate and free memory (no surprises here). If it returns zero
209needs to be allocated, the library might abort or take some potentially 371when 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. 372or take some potentially destructive action.
373.Sp
374Since some systems (at least OpenBSD and Darwin) fail to implement
375correct \f(CW\*(C`realloc\*(C'\fR semantics, libev will use a wrapper around the system
376\&\f(CW\*(C`realloc\*(C'\fR and \f(CW\*(C`free\*(C'\fR functions by default.
211.Sp 377.Sp
212You could override this function in high-availability programs to, say, 378You could override this function in high-availability programs to, say,
213free some memory if it cannot allocate memory, to use a special allocator, 379free 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. 380or even to sleep a while and retry until some memory is available.
381.Sp
382Example: Replace the libev allocator with one that waits a bit and then
383retries (example requires a standards-compliant \f(CW\*(C`realloc\*(C'\fR).
384.Sp
385.Vb 6
386\& static void *
387\& persistent_realloc (void *ptr, size_t size)
388\& {
389\& for (;;)
390\& {
391\& void *newptr = realloc (ptr, size);
392\&
393\& if (newptr)
394\& return newptr;
395\&
396\& sleep (60);
397\& }
398\& }
399\&
400\& ...
401\& ev_set_allocator (persistent_realloc);
402.Ve
215.IP "ev_set_syserr_cb (void (*cb)(const char *msg));" 4 403.IP "ev_set_syserr_cb (void (*cb)(const char *msg)); [\s-1NOT\s0 \s-1REENTRANT\s0]" 4
216.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg));" 404.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]"
217Set the callback function to call on a retryable syscall error (such 405Set the callback function to call on a retryable system call error (such
218as failed select, poll, epoll_wait). The message is a printable string 406as failed select, poll, epoll_wait). The message is a printable string
219indicating the system call or subsystem causing the problem. If this 407indicating the system call or subsystem causing the problem. If this
220callback is set, then libev will expect it to remedy the sitution, no 408callback is set, then libev will expect it to remedy the situation, no
221matter what, when it returns. That is, libev will generally retry the 409matter what, when it returns. That is, libev will generally retry the
222requested operation, or, if the condition doesn't go away, do bad stuff 410requested operation, or, if the condition doesn't go away, do bad stuff
223(such as abort). 411(such as abort).
412.Sp
413Example: This is basically the same thing that libev does internally, too.
414.Sp
415.Vb 6
416\& static void
417\& fatal_error (const char *msg)
418\& {
419\& perror (msg);
420\& abort ();
421\& }
422\&
423\& ...
424\& ev_set_syserr_cb (fatal_error);
425.Ve
224.SH "FUNCTIONS CONTROLLING THE EVENT LOOP" 426.SH "FUNCTIONS CONTROLLING EVENT LOOPS"
225.IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP" 427.IX Header "FUNCTIONS CONTROLLING EVENT LOOPS"
226An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR. The library knows two 428An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR (the \f(CW\*(C`struct\*(C'\fR is
227types of such loops, the \fIdefault\fR loop, which supports signals and child 429\&\fInot\fR optional in this case unless libev 3 compatibility is disabled, as
228events, and dynamically created loops which do not. 430libev 3 had an \f(CW\*(C`ev_loop\*(C'\fR function colliding with the struct name).
229.PP 431.PP
230If you use threads, a common model is to run the default event loop 432The library knows two types of such loops, the \fIdefault\fR loop, which
231in your main thread (or in a separate thread) and for each thread you 433supports child process events, and dynamically created event loops which
232create, you also create another event loop. Libev itself does no locking 434do not.
233whatsoever, so if you mix calls to the same event loop in different
234threads, make sure you lock (this is usually a bad idea, though, even if
235done correctly, because it's hideous and inefficient).
236.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4 435.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
237.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)" 436.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
238This will initialise the default event loop if it hasn't been initialised 437This returns the \*(L"default\*(R" event loop object, which is what you should
239yet and return it. If the default loop could not be initialised, returns 438normally use when you just need \*(L"the event loop\*(R". Event loop objects and
240false. If it already was initialised it simply returns it (and ignores the 439the \f(CW\*(C`flags\*(C'\fR parameter are described in more detail in the entry for
241flags). 440\&\f(CW\*(C`ev_loop_new\*(C'\fR.
441.Sp
442If the default loop is already initialised then this function simply
443returns it (and ignores the flags. If that is troubling you, check
444\&\f(CW\*(C`ev_backend ()\*(C'\fR afterwards). Otherwise it will create it with the given
445flags, which should almost always be \f(CW0\fR, unless the caller is also the
446one calling \f(CW\*(C`ev_run\*(C'\fR or otherwise qualifies as \*(L"the main program\*(R".
242.Sp 447.Sp
243If you don't know what event loop to use, use the one returned from this 448If you don't know what event loop to use, use the one returned from this
244function. 449function (or via the \f(CW\*(C`EV_DEFAULT\*(C'\fR macro).
450.Sp
451Note that this function is \fInot\fR thread-safe, so if you want to use it
452from multiple threads, you have to employ some kind of mutex (note also
453that this case is unlikely, as loops cannot be shared easily between
454threads anyway).
455.Sp
456The default loop is the only loop that can handle \f(CW\*(C`ev_child\*(C'\fR watchers,
457and to do this, it always registers a handler for \f(CW\*(C`SIGCHLD\*(C'\fR. If this is
458a problem for your application you can either create a dynamic loop with
459\&\f(CW\*(C`ev_loop_new\*(C'\fR which doesn't do that, or you can simply overwrite the
460\&\f(CW\*(C`SIGCHLD\*(C'\fR signal handler \fIafter\fR calling \f(CW\*(C`ev_default_init\*(C'\fR.
461.Sp
462Example: This is the most typical usage.
463.Sp
464.Vb 2
465\& if (!ev_default_loop (0))
466\& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
467.Ve
468.Sp
469Example: Restrict libev to the select and poll backends, and do not allow
470environment settings to be taken into account:
471.Sp
472.Vb 1
473\& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
474.Ve
475.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
476.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
477This will create and initialise a new event loop object. If the loop
478could not be initialised, returns false.
479.Sp
480Note that this function \fIis\fR thread-safe, and one common way to use
481libev with threads is indeed to create one loop per thread, and using the
482default loop in the \*(L"main\*(R" or \*(L"initial\*(R" thread.
245.Sp 483.Sp
246The flags argument can be used to specify special behaviour or specific 484The 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). 485backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).
248.Sp 486.Sp
249It supports the following flags: 487The following flags are supported:
250.RS 4 488.RS 4
251.ie n .IP """EVFLAG_AUTO""" 4 489.ie n .IP """EVFLAG_AUTO""" 4
252.el .IP "\f(CWEVFLAG_AUTO\fR" 4 490.el .IP "\f(CWEVFLAG_AUTO\fR" 4
253.IX Item "EVFLAG_AUTO" 491.IX Item "EVFLAG_AUTO"
254The default flags value. Use this if you have no clue (it's the right 492The default flags value. Use this if you have no clue (it's the right
255thing, believe me). 493thing, believe me).
256.ie n .IP """EVFLAG_NOENV""" 4 494.ie n .IP """EVFLAG_NOENV""" 4
257.el .IP "\f(CWEVFLAG_NOENV\fR" 4 495.el .IP "\f(CWEVFLAG_NOENV\fR" 4
258.IX Item "EVFLAG_NOENV" 496.IX Item "EVFLAG_NOENV"
259If this flag bit is ored into the flag value (or the program runs setuid 497If this flag bit is or'ed into the flag value (or the program runs setuid
260or setgid) then libev will \fInot\fR look at the environment variable 498or 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 499\&\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 500override 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 501useful to try out specific backends to test their performance, or to work
264around bugs. 502around bugs.
503.ie n .IP """EVFLAG_FORKCHECK""" 4
504.el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4
505.IX Item "EVFLAG_FORKCHECK"
506Instead of calling \f(CW\*(C`ev_loop_fork\*(C'\fR manually after a fork, you can also
507make libev check for a fork in each iteration by enabling this flag.
508.Sp
509This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop,
510and thus this might slow down your event loop if you do a lot of loop
511iterations and little real work, but is usually not noticeable (on my
512GNU/Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn sequence
513without a system call and thus \fIvery\fR fast, but my GNU/Linux system also has
514\&\f(CW\*(C`pthread_atfork\*(C'\fR which is even faster).
515.Sp
516The big advantage of this flag is that you can forget about fork (and
517forget about forgetting to tell libev about forking) when you use this
518flag.
519.Sp
520This flag setting cannot be overridden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR
521environment variable.
522.ie n .IP """EVFLAG_NOINOTIFY""" 4
523.el .IP "\f(CWEVFLAG_NOINOTIFY\fR" 4
524.IX Item "EVFLAG_NOINOTIFY"
525When this flag is specified, then libev will not attempt to use the
526\&\fIinotify\fR \s-1API\s0 for it's \f(CW\*(C`ev_stat\*(C'\fR watchers. Apart from debugging and
527testing, this flag can be useful to conserve inotify file descriptors, as
528otherwise each loop using \f(CW\*(C`ev_stat\*(C'\fR watchers consumes one inotify handle.
529.ie n .IP """EVFLAG_SIGNALFD""" 4
530.el .IP "\f(CWEVFLAG_SIGNALFD\fR" 4
531.IX Item "EVFLAG_SIGNALFD"
532When this flag is specified, then libev will attempt to use the
533\&\fIsignalfd\fR \s-1API\s0 for it's \f(CW\*(C`ev_signal\*(C'\fR (and \f(CW\*(C`ev_child\*(C'\fR) watchers. This \s-1API\s0
534delivers signals synchronously, which makes it both faster and might make
535it possible to get the queued signal data. It can also simplify signal
536handling with threads, as long as you properly block signals in your
537threads that are not interested in handling them.
538.Sp
539Signalfd will not be used by default as this changes your signal mask, and
540there are a lot of shoddy libraries and programs (glib's threadpool for
541example) that can't properly initialise their signal masks.
265.ie n .IP """EVMETHOD_SELECT"" (value 1, portable select backend)" 4 542.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
266.el .IP "\f(CWEVMETHOD_SELECT\fR (value 1, portable select backend)" 4 543.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
267.IX Item "EVMETHOD_SELECT (value 1, portable select backend)" 544.IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
268This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as 545This 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, 546libev 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 547but 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 548using this backend. It doesn't scale too well (O(highest_fd)), but its
272the fastest backend for a low number of fds. 549usually the fastest backend for a low number of (low-numbered :) fds.
550.Sp
551To get good performance out of this backend you need a high amount of
552parallelism (most of the file descriptors should be busy). If you are
553writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many
554connections as possible during one iteration. You might also want to have
555a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of
556readiness notifications you get per iteration.
557.Sp
558This backend maps \f(CW\*(C`EV_READ\*(C'\fR to the \f(CW\*(C`readfds\*(C'\fR set and \f(CW\*(C`EV_WRITE\*(C'\fR to the
559\&\f(CW\*(C`writefds\*(C'\fR set (and to work around Microsoft Windows bugs, also onto the
560\&\f(CW\*(C`exceptfds\*(C'\fR set on that platform).
273.ie n .IP """EVMETHOD_POLL"" (value 2, poll backend, available everywhere except on windows)" 4 561.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)" 4 562.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)" 563.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 564And 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 565than select, but handles sparse fds better and has no artificial
278number of fds you can use (except it will slow down considerably with a 566limit 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). 567considerably with a lot of inactive fds). It scales similarly to select,
568i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for
569performance tips.
570.Sp
571This backend maps \f(CW\*(C`EV_READ\*(C'\fR to \f(CW\*(C`POLLIN | POLLERR | POLLHUP\*(C'\fR, and
572\&\f(CW\*(C`EV_WRITE\*(C'\fR to \f(CW\*(C`POLLOUT | POLLERR | POLLHUP\*(C'\fR.
280.ie n .IP """EVMETHOD_EPOLL"" (value 4, Linux)" 4 573.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
281.el .IP "\f(CWEVMETHOD_EPOLL\fR (value 4, Linux)" 4 574.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
282.IX Item "EVMETHOD_EPOLL (value 4, Linux)" 575.IX Item "EVBACKEND_EPOLL (value 4, Linux)"
576Use the linux-specific \fIepoll\fR\|(7) interface (for both pre\- and post\-2.6.9
577kernels).
578.Sp
283For few fds, this backend is a bit little slower than poll and select, 579For 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 580but 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 581like O(total_fds) where n is the total number of fds (or the highest fd),
286either O(1) or O(active_fds). 582epoll scales either O(1) or O(active_fds).
287.Sp 583.Sp
584The epoll mechanism deserves honorable mention as the most misdesigned
585of the more advanced event mechanisms: mere annoyances include silently
586dropping file descriptors, requiring a system call per change per file
587descriptor (and unnecessary guessing of parameters), problems with dup and
588so on. The biggest issue is fork races, however \- if a program forks then
589\&\fIboth\fR parent and child process have to recreate the epoll set, which can
590take considerable time (one syscall per file descriptor) and is of course
591hard to detect.
592.Sp
593Epoll is also notoriously buggy \- embedding epoll fds \fIshould\fR work, but
594of course \fIdoesn't\fR, and epoll just loves to report events for totally
595\&\fIdifferent\fR file descriptors (even already closed ones, so one cannot
596even remove them from the set) than registered in the set (especially
597on \s-1SMP\s0 systems). Libev tries to counter these spurious notifications by
598employing an additional generation counter and comparing that against the
599events to filter out spurious ones, recreating the set when required. Last
600not least, it also refuses to work with some file descriptors which work
601perfectly fine with \f(CW\*(C`select\*(C'\fR (files, many character devices...).
602.Sp
288While stopping and starting an I/O watcher in the same iteration will 603While stopping, setting and starting an I/O watcher in the same iteration
289result in some caching, there is still a syscall per such incident 604will result in some caching, there is still a system call per such
290(because the fd could point to a different file description now), so its 605incident (because the same \fIfile descriptor\fR could point to a different
291best to avoid that. Also, \fIdup()\fRed file descriptors might not work very 606\&\fIfile description\fR now), so its best to avoid that. Also, \f(CW\*(C`dup ()\*(C'\fR'ed
292well if you register events for both fds. 607file descriptors might not work very well if you register events for both
608file descriptors.
609.Sp
610Best performance from this backend is achieved by not unregistering all
611watchers for a file descriptor until it has been closed, if possible,
612i.e. keep at least one watcher active per fd at all times. Stopping and
613starting a watcher (without re-setting it) also usually doesn't cause
614extra overhead. A fork can both result in spurious notifications as well
615as in libev having to destroy and recreate the epoll object, which can
616take considerable time and thus should be avoided.
617.Sp
618All this means that, in practice, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR can be as fast or
619faster than epoll for maybe up to a hundred file descriptors, depending on
620the usage. So sad.
621.Sp
622While nominally embeddable in other event loops, this feature is broken in
623all kernel versions tested so far.
624.Sp
625This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
626\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
293.ie n .IP """EVMETHOD_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4 627.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)" 4 628.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
295.IX Item "EVMETHOD_KQUEUE (value 8, most BSD clones)" 629.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
296Kqueue deserves special mention, as at the time of this writing, it 630Kqueue deserves special mention, as at the time of this writing, it
297was broken on all BSDs except NetBSD (usually it doesn't work with 631was broken on all BSDs except NetBSD (usually it doesn't work reliably
298anything but sockets and pipes, except on Darwin, where of course its 632with anything but sockets and pipes, except on Darwin, where of course
299completely useless). For this reason its not being \*(L"autodetected\*(R" unless 633it's completely useless). Unlike epoll, however, whose brokenness
300you explicitly specify the flags (i.e. you don't use \s-1EVFLAG_AUTO\s0). 634is by design, these kqueue bugs can (and eventually will) be fixed
635without \s-1API\s0 changes to existing programs. For this reason it's not being
636\&\*(L"auto-detected\*(R" unless you explicitly specify it in the flags (i.e. using
637\&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a known-to-be-good (\-enough)
638system like NetBSD.
639.Sp
640You still can embed kqueue into a normal poll or select backend and use it
641only for sockets (after having made sure that sockets work with kqueue on
642the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
301.Sp 643.Sp
302It scales in the same way as the epoll backend, but the interface to the 644It 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 645kernel is more efficient (which says nothing about its actual speed, of
304course). While starting and stopping an I/O watcher does not cause an 646course). 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 647cause an extra system call as with \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to
306incident, so its best to avoid that. 648two event changes per incident. Support for \f(CW\*(C`fork ()\*(C'\fR is very bad (but
649sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
650cases
651.Sp
652This backend usually performs well under most conditions.
653.Sp
654While nominally embeddable in other event loops, this doesn't work
655everywhere, so you might need to test for this. And since it is broken
656almost everywhere, you should only use it when you have a lot of sockets
657(for which it usually works), by embedding it into another event loop
658(e.g. \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR (but \f(CW\*(C`poll\*(C'\fR is of course
659also broken on \s-1OS\s0 X)) and, did I mention it, using it only for sockets.
660.Sp
661This backend maps \f(CW\*(C`EV_READ\*(C'\fR into an \f(CW\*(C`EVFILT_READ\*(C'\fR kevent with
662\&\f(CW\*(C`NOTE_EOF\*(C'\fR, and \f(CW\*(C`EV_WRITE\*(C'\fR into an \f(CW\*(C`EVFILT_WRITE\*(C'\fR kevent with
663\&\f(CW\*(C`NOTE_EOF\*(C'\fR.
307.ie n .IP """EVMETHOD_DEVPOLL"" (value 16, Solaris 8)" 4 664.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
308.el .IP "\f(CWEVMETHOD_DEVPOLL\fR (value 16, Solaris 8)" 4 665.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
309.IX Item "EVMETHOD_DEVPOLL (value 16, Solaris 8)" 666.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
310This is not implemented yet (and might never be). 667This is not implemented yet (and might never be, unless you send me an
668implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets
669and is not embeddable, which would limit the usefulness of this backend
670immensely.
311.ie n .IP """EVMETHOD_PORT"" (value 32, Solaris 10)" 4 671.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
312.el .IP "\f(CWEVMETHOD_PORT\fR (value 32, Solaris 10)" 4 672.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
313.IX Item "EVMETHOD_PORT (value 32, Solaris 10)" 673.IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
314This uses the Solaris 10 port mechanism. As with everything on Solaris, 674This 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)). 675it's really slow, but it still scales very well (O(active_fds)).
676.Sp
677Please note that Solaris event ports can deliver a lot of spurious
678notifications, so you need to use non-blocking I/O or other means to avoid
679blocking when no data (or space) is available.
680.Sp
681While this backend scales well, it requires one system call per active
682file descriptor per loop iteration. For small and medium numbers of file
683descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend
684might perform better.
685.Sp
686On the positive side, with the exception of the spurious readiness
687notifications, this backend actually performed fully to specification
688in all tests and is fully embeddable, which is a rare feat among the
689OS-specific backends (I vastly prefer correctness over speed hacks).
690.Sp
691This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
692\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
316.ie n .IP """EVMETHOD_ALL""" 4 693.ie n .IP """EVBACKEND_ALL""" 4
317.el .IP "\f(CWEVMETHOD_ALL\fR" 4 694.el .IP "\f(CWEVBACKEND_ALL\fR" 4
318.IX Item "EVMETHOD_ALL" 695.IX Item "EVBACKEND_ALL"
319Try all backends (even potentially broken ones). Since this is a mask, you 696Try all backends (even potentially broken ones that wouldn't be tried
320can do stuff like \f(CW\*(C`EVMETHOD_ALL & ~EVMETHOD_KQUEUE\*(C'\fR. 697with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as
698\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR.
699.Sp
700It is definitely not recommended to use this flag.
321.RE 701.RE
322.RS 4 702.RS 4
323.Sp 703.Sp
324If one or more of these are ored into the flags value, then only these 704If one or more of the backend flags are or'ed into the flags value,
325backends will be tried (in the reverse order as given here). If none are 705then only these backends will be tried (in the reverse order as listed
326specified, most compiled-in backend will be tried, usually in reverse 706here). If none are specified, all backends in \f(CW\*(C`ev_recommended_backends
327order of their flag values :) 707()\*(C'\fR will be tried.
708.Sp
709Example: Try to create a event loop that uses epoll and nothing else.
710.Sp
711.Vb 3
712\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
713\& if (!epoller)
714\& fatal ("no epoll found here, maybe it hides under your chair");
715.Ve
716.Sp
717Example: Use whatever libev has to offer, but make sure that kqueue is
718used if available.
719.Sp
720.Vb 1
721\& struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
722.Ve
328.RE 723.RE
329.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
330.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
331Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is
332always distinct from the default loop. Unlike the default loop, it cannot
333handle signal and child watchers, and attempts to do so will be greeted by
334undefined behaviour (or a failed assertion if assertions are enabled).
335.IP "ev_default_destroy ()" 4
336.IX Item "ev_default_destroy ()"
337Destroys the default loop again (frees all memory and kernel state
338etc.). This stops all registered event watchers (by not touching them in
339any way whatsoever, although you cannot rely on this :).
340.IP "ev_loop_destroy (loop)" 4 724.IP "ev_loop_destroy (loop)" 4
341.IX Item "ev_loop_destroy (loop)" 725.IX Item "ev_loop_destroy (loop)"
342Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an 726Destroys an event loop object (frees all memory and kernel state
343earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR. 727etc.). None of the active event watchers will be stopped in the normal
344.IP "ev_default_fork ()" 4 728sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your
345.IX Item "ev_default_fork ()" 729responsibility to either stop all watchers cleanly yourself \fIbefore\fR
346This function reinitialises the kernel state for backends that have 730calling this function, or cope with the fact afterwards (which is usually
347one. Despite the name, you can call it anytime, but it makes most sense 731the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them
348after forking, in either the parent or child process (or both, but that 732for example).
349again makes little sense).
350.Sp 733.Sp
351You \fImust\fR call this function after forking if and only if you want to 734Note that certain global state, such as signal state (and installed signal
352use the event library in both processes. If you just fork+exec, you don't 735handlers), will not be freed by this function, and related watchers (such
353have to call it. 736as signal and child watchers) would need to be stopped manually.
354.Sp 737.Sp
355The function itself is quite fast and it's usually not a problem to call 738This function is normally used on loop objects allocated by
356it just in case after a fork. To make this easy, the function will fit in 739\&\f(CW\*(C`ev_loop_new\*(C'\fR, but it can also be used on the default loop returned by
357quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR: 740\&\f(CW\*(C`ev_default_loop\*(C'\fR, in which case it is not thread-safe.
358.Sp 741.Sp
359.Vb 1 742Note that it is not advisable to call this function on the default loop
360\& pthread_atfork (0, 0, ev_default_fork); 743except in the rare occasion where you really need to free it's resources.
361.Ve 744If you need dynamically allocated loops it is better to use \f(CW\*(C`ev_loop_new\*(C'\fR
745and \f(CW\*(C`ev_loop_destroy\*(C'\fR.
362.IP "ev_loop_fork (loop)" 4 746.IP "ev_loop_fork (loop)" 4
363.IX Item "ev_loop_fork (loop)" 747.IX Item "ev_loop_fork (loop)"
364Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by 748This function sets a flag that causes subsequent \f(CW\*(C`ev_run\*(C'\fR iterations to
365\&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop 749reinitialise the kernel state for backends that have one. Despite the
366after fork, and how you do this is entirely your own problem. 750name, you can call it anytime, but it makes most sense after forking, in
751the child process. You \fImust\fR call it (or use \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR) in the
752child before resuming or calling \f(CW\*(C`ev_run\*(C'\fR.
753.Sp
754Again, you \fIhave\fR to call it on \fIany\fR loop that you want to re-use after
755a fork, \fIeven if you do not plan to use the loop in the parent\fR. This is
756because some kernel interfaces *cough* \fIkqueue\fR *cough* do funny things
757during fork.
758.Sp
759On the other hand, you only need to call this function in the child
760process if and only if you want to use the event loop in the child. If
761you just fork+exec or create a new loop in the child, you don't have to
762call it at all (in fact, \f(CW\*(C`epoll\*(C'\fR is so badly broken that it makes a
763difference, but libev will usually detect this case on its own and do a
764costly reset of the backend).
765.Sp
766The function itself is quite fast and it's usually not a problem to call
767it just in case after a fork.
768.Sp
769Example: Automate calling \f(CW\*(C`ev_loop_fork\*(C'\fR on the default loop when
770using pthreads.
771.Sp
772.Vb 5
773\& static void
774\& post_fork_child (void)
775\& {
776\& ev_loop_fork (EV_DEFAULT);
777\& }
778\&
779\& ...
780\& pthread_atfork (0, 0, post_fork_child);
781.Ve
782.IP "int ev_is_default_loop (loop)" 4
783.IX Item "int ev_is_default_loop (loop)"
784Returns true when the given loop is, in fact, the default loop, and false
785otherwise.
786.IP "unsigned int ev_iteration (loop)" 4
787.IX Item "unsigned int ev_iteration (loop)"
788Returns the current iteration count for the event loop, which is identical
789to the number of times libev did poll for new events. It starts at \f(CW0\fR
790and happily wraps around with enough iterations.
791.Sp
792This value can sometimes be useful as a generation counter of sorts (it
793\&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with
794\&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls \- and is incremented between the
795prepare and check phases.
367.IP "unsigned int ev_method (loop)" 4 796.IP "unsigned int ev_depth (loop)" 4
368.IX Item "unsigned int ev_method (loop)" 797.IX Item "unsigned int ev_depth (loop)"
798Returns the number of times \f(CW\*(C`ev_run\*(C'\fR was entered minus the number of
799times \f(CW\*(C`ev_run\*(C'\fR was exited, in other words, the recursion depth.
800.Sp
801Outside \f(CW\*(C`ev_run\*(C'\fR, this number is zero. In a callback, this number is
802\&\f(CW1\fR, unless \f(CW\*(C`ev_run\*(C'\fR was invoked recursively (or from another thread),
803in which case it is higher.
804.Sp
805Leaving \f(CW\*(C`ev_run\*(C'\fR abnormally (setjmp/longjmp, cancelling the thread
806etc.), doesn't count as \*(L"exit\*(R" \- consider this as a hint to avoid such
807ungentleman-like behaviour unless it's really convenient.
808.IP "unsigned int ev_backend (loop)" 4
809.IX Item "unsigned int ev_backend (loop)"
369Returns one of the \f(CW\*(C`EVMETHOD_*\*(C'\fR flags indicating the event backend in 810Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
370use. 811use.
371.IP "ev_tstamp ev_now (loop)" 4 812.IP "ev_tstamp ev_now (loop)" 4
372.IX Item "ev_tstamp ev_now (loop)" 813.IX Item "ev_tstamp ev_now (loop)"
373Returns the current \*(L"event loop time\*(R", which is the time the event loop 814Returns the current \*(L"event loop time\*(R", which is the time the event loop
374got events and started processing them. This timestamp does not change 815received events and started processing them. This timestamp does not
375as long as callbacks are being processed, and this is also the base time 816change as long as callbacks are being processed, and this is also the base
376used for relative timers. You can treat it as the timestamp of the event 817time used for relative timers. You can treat it as the timestamp of the
377occuring (or more correctly, the mainloop finding out about it). 818event occurring (or more correctly, libev finding out about it).
819.IP "ev_now_update (loop)" 4
820.IX Item "ev_now_update (loop)"
821Establishes the current time by querying the kernel, updating the time
822returned by \f(CW\*(C`ev_now ()\*(C'\fR in the progress. This is a costly operation and
823is usually done automatically within \f(CW\*(C`ev_run ()\*(C'\fR.
824.Sp
825This function is rarely useful, but when some event callback runs for a
826very long time without entering the event loop, updating libev's idea of
827the current time is a good idea.
828.Sp
829See also \*(L"The special problem of time updates\*(R" in the \f(CW\*(C`ev_timer\*(C'\fR section.
830.IP "ev_suspend (loop)" 4
831.IX Item "ev_suspend (loop)"
832.PD 0
833.IP "ev_resume (loop)" 4
834.IX Item "ev_resume (loop)"
835.PD
836These two functions suspend and resume an event loop, for use when the
837loop is not used for a while and timeouts should not be processed.
838.Sp
839A typical use case would be an interactive program such as a game: When
840the user presses \f(CW\*(C`^Z\*(C'\fR to suspend the game and resumes it an hour later it
841would be best to handle timeouts as if no time had actually passed while
842the program was suspended. This can be achieved by calling \f(CW\*(C`ev_suspend\*(C'\fR
843in your \f(CW\*(C`SIGTSTP\*(C'\fR handler, sending yourself a \f(CW\*(C`SIGSTOP\*(C'\fR and calling
844\&\f(CW\*(C`ev_resume\*(C'\fR directly afterwards to resume timer processing.
845.Sp
846Effectively, all \f(CW\*(C`ev_timer\*(C'\fR watchers will be delayed by the time spend
847between \f(CW\*(C`ev_suspend\*(C'\fR and \f(CW\*(C`ev_resume\*(C'\fR, and all \f(CW\*(C`ev_periodic\*(C'\fR watchers
848will be rescheduled (that is, they will lose any events that would have
849occurred while suspended).
850.Sp
851After calling \f(CW\*(C`ev_suspend\*(C'\fR you \fBmust not\fR call \fIany\fR function on the
852given loop other than \f(CW\*(C`ev_resume\*(C'\fR, and you \fBmust not\fR call \f(CW\*(C`ev_resume\*(C'\fR
853without a previous call to \f(CW\*(C`ev_suspend\*(C'\fR.
854.Sp
855Calling \f(CW\*(C`ev_suspend\*(C'\fR/\f(CW\*(C`ev_resume\*(C'\fR has the side effect of updating the
856event loop time (see \f(CW\*(C`ev_now_update\*(C'\fR).
378.IP "ev_loop (loop, int flags)" 4 857.IP "ev_run (loop, int flags)" 4
379.IX Item "ev_loop (loop, int flags)" 858.IX Item "ev_run (loop, int flags)"
380Finally, this is it, the event handler. This function usually is called 859Finally, this is it, the event handler. This function usually is called
381after you initialised all your watchers and you want to start handling 860after you have initialised all your watchers and you want to start
382events. 861handling events. It will ask the operating system for any new events, call
862the watcher callbacks, an then repeat the whole process indefinitely: This
863is why event loops are called \fIloops\fR.
383.Sp 864.Sp
384If the flags argument is specified as 0, it will not return until either 865If the flags argument is specified as \f(CW0\fR, it will keep handling events
385no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called. 866until either no event watchers are active anymore or \f(CW\*(C`ev_break\*(C'\fR was
867called.
386.Sp 868.Sp
869Please note that an explicit \f(CW\*(C`ev_break\*(C'\fR is usually better than
870relying on all watchers to be stopped when deciding when a program has
871finished (especially in interactive programs), but having a program
872that automatically loops as long as it has to and no longer by virtue
873of relying on its watchers stopping correctly, that is truly a thing of
874beauty.
875.Sp
387A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle 876A flags value of \f(CW\*(C`EVRUN_NOWAIT\*(C'\fR will look for new events, will handle
388those events and any outstanding ones, but will not block your process in 877those events and any already outstanding ones, but will not wait and
389case there are no events and will return after one iteration of the loop. 878block your process in case there are no events and will return after one
879iteration of the loop. This is sometimes useful to poll and handle new
880events while doing lengthy calculations, to keep the program responsive.
390.Sp 881.Sp
391A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if 882A flags value of \f(CW\*(C`EVRUN_ONCE\*(C'\fR will look for new events (waiting if
392neccessary) and will handle those and any outstanding ones. It will block 883necessary) and will handle those and any already outstanding ones. It
393your process until at least one new event arrives, and will return after 884will block your process until at least one new event arrives (which could
885be an event internal to libev itself, so there is no guarantee that a
886user-registered callback will be called), and will return after one
394one iteration of the loop. 887iteration of the loop.
395.Sp 888.Sp
396This flags value could be used to implement alternative looping 889This is useful if you are waiting for some external event in conjunction
397constructs, but the \f(CW\*(C`prepare\*(C'\fR and \f(CW\*(C`check\*(C'\fR watchers provide a better and 890with something not expressible using other libev watchers (i.e. "roll your
398more generic mechanism. 891own \f(CW\*(C`ev_run\*(C'\fR"). However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is
892usually a better approach for this kind of thing.
399.Sp 893.Sp
400Here are the gory details of what ev_loop does: 894Here are the gory details of what \f(CW\*(C`ev_run\*(C'\fR does:
401.Sp 895.Sp
402.Vb 15 896.Vb 10
403\& 1. If there are no active watchers (reference count is zero), return. 897\& \- Increment loop depth.
898\& \- Reset the ev_break status.
899\& \- Before the first iteration, call any pending watchers.
900\& LOOP:
901\& \- If EVFLAG_FORKCHECK was used, check for a fork.
902\& \- If a fork was detected (by any means), queue and call all fork watchers.
404\& 2. Queue and immediately call all prepare watchers. 903\& \- Queue and call all prepare watchers.
904\& \- If ev_break was called, goto FINISH.
405\& 3. If we have been forked, recreate the kernel state. 905\& \- If we have been forked, detach and recreate the kernel state
906\& as to not disturb the other process.
406\& 4. Update the kernel state with all outstanding changes. 907\& \- Update the kernel state with all outstanding changes.
407\& 5. Update the "event loop time". 908\& \- Update the "event loop time" (ev_now ()).
408\& 6. Calculate for how long to block. 909\& \- Calculate for how long to sleep or block, if at all
910\& (active idle watchers, EVRUN_NOWAIT or not having
911\& any active watchers at all will result in not sleeping).
912\& \- Sleep if the I/O and timer collect interval say so.
913\& \- Increment loop iteration counter.
409\& 7. Block the process, waiting for events. 914\& \- Block the process, waiting for any events.
915\& \- Queue all outstanding I/O (fd) events.
410\& 8. Update the "event loop time" and do time jump handling. 916\& \- Update the "event loop time" (ev_now ()), and do time jump adjustments.
411\& 9. Queue all outstanding timers. 917\& \- Queue all expired timers.
412\& 10. Queue all outstanding periodics. 918\& \- Queue all expired periodics.
413\& 11. If no events are pending now, queue all idle watchers. 919\& \- Queue all idle watchers with priority higher than that of pending events.
414\& 12. Queue all check watchers. 920\& \- Queue all check watchers.
415\& 13. Call all queued watchers in reverse order (i.e. check watchers first). 921\& \- Call all queued watchers in reverse order (i.e. check watchers first).
416\& 14. If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK 922\& Signals and child watchers are implemented as I/O watchers, and will
417\& was used, return, otherwise continue with step #1. 923\& be handled here by queueing them when their watcher gets executed.
924\& \- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
925\& were used, or there are no active watchers, goto FINISH, otherwise
926\& continue with step LOOP.
927\& FINISH:
928\& \- Reset the ev_break status iff it was EVBREAK_ONE.
929\& \- Decrement the loop depth.
930\& \- Return.
418.Ve 931.Ve
932.Sp
933Example: Queue some jobs and then loop until no events are outstanding
934anymore.
935.Sp
936.Vb 4
937\& ... queue jobs here, make sure they register event watchers as long
938\& ... as they still have work to do (even an idle watcher will do..)
939\& ev_run (my_loop, 0);
940\& ... jobs done or somebody called unloop. yeah!
941.Ve
419.IP "ev_unloop (loop, how)" 4 942.IP "ev_break (loop, how)" 4
420.IX Item "ev_unloop (loop, how)" 943.IX Item "ev_break (loop, how)"
421Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it 944Can be used to make a call to \f(CW\*(C`ev_run\*(C'\fR return early (but only after it
422has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either 945has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
423\&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or 946\&\f(CW\*(C`EVBREAK_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_run\*(C'\fR call return, or
424\&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return. 947\&\f(CW\*(C`EVBREAK_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_run\*(C'\fR calls return.
948.Sp
949This \*(L"break state\*(R" will be cleared when entering \f(CW\*(C`ev_run\*(C'\fR again.
950.Sp
951It is safe to call \f(CW\*(C`ev_break\*(C'\fR from outside any \f(CW\*(C`ev_run\*(C'\fR calls, too.
425.IP "ev_ref (loop)" 4 952.IP "ev_ref (loop)" 4
426.IX Item "ev_ref (loop)" 953.IX Item "ev_ref (loop)"
427.PD 0 954.PD 0
428.IP "ev_unref (loop)" 4 955.IP "ev_unref (loop)" 4
429.IX Item "ev_unref (loop)" 956.IX Item "ev_unref (loop)"
430.PD 957.PD
431Ref/unref can be used to add or remove a reference count on the event 958Ref/unref can be used to add or remove a reference count on the event
432loop: Every watcher keeps one reference, and as long as the reference 959loop: Every watcher keeps one reference, and as long as the reference
433count is nonzero, \f(CW\*(C`ev_loop\*(C'\fR will not return on its own. If you have 960count is nonzero, \f(CW\*(C`ev_run\*(C'\fR will not return on its own.
434a watcher you never unregister that should not keep \f(CW\*(C`ev_loop\*(C'\fR from 961.Sp
435returning, \fIev_unref()\fR after starting, and \fIev_ref()\fR before stopping it. For 962This is useful when you have a watcher that you never intend to
963unregister, but that nevertheless should not keep \f(CW\*(C`ev_run\*(C'\fR from
964returning. In such a case, call \f(CW\*(C`ev_unref\*(C'\fR after starting, and \f(CW\*(C`ev_ref\*(C'\fR
965before stopping it.
966.Sp
436example, libev itself uses this for its internal signal pipe: It is not 967As an example, libev itself uses this for its internal signal pipe: It
437visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from exiting if 968is not visible to the libev user and should not keep \f(CW\*(C`ev_run\*(C'\fR from
438no event watchers registered by it are active. It is also an excellent 969exiting if no event watchers registered by it are active. It is also an
439way to do this for generic recurring timers or from within third-party 970excellent way to do this for generic recurring timers or from within
440libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR. 971third-party libraries. Just remember to \fIunref after start\fR and \fIref
972before stop\fR (but only if the watcher wasn't active before, or was active
973before, respectively. Note also that libev might stop watchers itself
974(e.g. non-repeating timers) in which case you have to \f(CW\*(C`ev_ref\*(C'\fR
975in the callback).
976.Sp
977Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_run\*(C'\fR
978running when nothing else is active.
979.Sp
980.Vb 4
981\& ev_signal exitsig;
982\& ev_signal_init (&exitsig, sig_cb, SIGINT);
983\& ev_signal_start (loop, &exitsig);
984\& evf_unref (loop);
985.Ve
986.Sp
987Example: For some weird reason, unregister the above signal handler again.
988.Sp
989.Vb 2
990\& ev_ref (loop);
991\& ev_signal_stop (loop, &exitsig);
992.Ve
993.IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4
994.IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"
995.PD 0
996.IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4
997.IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"
998.PD
999These advanced functions influence the time that libev will spend waiting
1000for events. Both time intervals are by default \f(CW0\fR, meaning that libev
1001will try to invoke timer/periodic callbacks and I/O callbacks with minimum
1002latency.
1003.Sp
1004Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR)
1005allows libev to delay invocation of I/O and timer/periodic callbacks
1006to increase efficiency of loop iterations (or to increase power-saving
1007opportunities).
1008.Sp
1009The idea is that sometimes your program runs just fast enough to handle
1010one (or very few) event(s) per loop iteration. While this makes the
1011program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new
1012events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high
1013overhead for the actual polling but can deliver many events at once.
1014.Sp
1015By setting a higher \fIio collect interval\fR you allow libev to spend more
1016time collecting I/O events, so you can handle more events per iteration,
1017at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and
1018\&\f(CW\*(C`ev_timer\*(C'\fR) will be not affected. Setting this to a non-null value will
1019introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations. The
1020sleep time ensures that libev will not poll for I/O events more often then
1021once per this interval, on average.
1022.Sp
1023Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
1024to spend more time collecting timeouts, at the expense of increased
1025latency/jitter/inexactness (the watcher callback will be called
1026later). \f(CW\*(C`ev_io\*(C'\fR watchers will not be affected. Setting this to a non-null
1027value will not introduce any overhead in libev.
1028.Sp
1029Many (busy) programs can usually benefit by setting the I/O collect
1030interval to a value near \f(CW0.1\fR or so, which is often enough for
1031interactive servers (of course not for games), likewise for timeouts. It
1032usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR,
1033as this approaches the timing granularity of most systems. Note that if
1034you do transactions with the outside world and you can't increase the
1035parallelity, then this setting will limit your transaction rate (if you
1036need to poll once per transaction and the I/O collect interval is 0.01,
1037then you can't do more than 100 transactions per second).
1038.Sp
1039Setting the \fItimeout collect interval\fR can improve the opportunity for
1040saving power, as the program will \*(L"bundle\*(R" timer callback invocations that
1041are \*(L"near\*(R" in time together, by delaying some, thus reducing the number of
1042times the process sleeps and wakes up again. Another useful technique to
1043reduce iterations/wake\-ups is to use \f(CW\*(C`ev_periodic\*(C'\fR watchers and make sure
1044they fire on, say, one-second boundaries only.
1045.Sp
1046Example: we only need 0.1s timeout granularity, and we wish not to poll
1047more often than 100 times per second:
1048.Sp
1049.Vb 2
1050\& ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
1051\& ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
1052.Ve
1053.IP "ev_invoke_pending (loop)" 4
1054.IX Item "ev_invoke_pending (loop)"
1055This call will simply invoke all pending watchers while resetting their
1056pending state. Normally, \f(CW\*(C`ev_run\*(C'\fR does this automatically when required,
1057but when overriding the invoke callback this call comes handy. This
1058function can be invoked from a watcher \- this can be useful for example
1059when you want to do some lengthy calculation and want to pass further
1060event handling to another thread (you still have to make sure only one
1061thread executes within \f(CW\*(C`ev_invoke_pending\*(C'\fR or \f(CW\*(C`ev_run\*(C'\fR of course).
1062.IP "int ev_pending_count (loop)" 4
1063.IX Item "int ev_pending_count (loop)"
1064Returns the number of pending watchers \- zero indicates that no watchers
1065are pending.
1066.IP "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(\s-1EV_P\s0))" 4
1067.IX Item "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))"
1068This overrides the invoke pending functionality of the loop: Instead of
1069invoking all pending watchers when there are any, \f(CW\*(C`ev_run\*(C'\fR will call
1070this callback instead. This is useful, for example, when you want to
1071invoke the actual watchers inside another context (another thread etc.).
1072.Sp
1073If you want to reset the callback, use \f(CW\*(C`ev_invoke_pending\*(C'\fR as new
1074callback.
1075.IP "ev_set_loop_release_cb (loop, void (*release)(\s-1EV_P\s0), void (*acquire)(\s-1EV_P\s0))" 4
1076.IX Item "ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))"
1077Sometimes you want to share the same loop between multiple threads. This
1078can be done relatively simply by putting mutex_lock/unlock calls around
1079each call to a libev function.
1080.Sp
1081However, \f(CW\*(C`ev_run\*(C'\fR can run an indefinite time, so it is not feasible
1082to wait for it to return. One way around this is to wake up the event
1083loop via \f(CW\*(C`ev_break\*(C'\fR and \f(CW\*(C`av_async_send\*(C'\fR, another way is to set these
1084\&\fIrelease\fR and \fIacquire\fR callbacks on the loop.
1085.Sp
1086When set, then \f(CW\*(C`release\*(C'\fR will be called just before the thread is
1087suspended waiting for new events, and \f(CW\*(C`acquire\*(C'\fR is called just
1088afterwards.
1089.Sp
1090Ideally, \f(CW\*(C`release\*(C'\fR will just call your mutex_unlock function, and
1091\&\f(CW\*(C`acquire\*(C'\fR will just call the mutex_lock function again.
1092.Sp
1093While event loop modifications are allowed between invocations of
1094\&\f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR (that's their only purpose after all), no
1095modifications done will affect the event loop, i.e. adding watchers will
1096have no effect on the set of file descriptors being watched, or the time
1097waited. Use an \f(CW\*(C`ev_async\*(C'\fR watcher to wake up \f(CW\*(C`ev_run\*(C'\fR when you want it
1098to take note of any changes you made.
1099.Sp
1100In theory, threads executing \f(CW\*(C`ev_run\*(C'\fR will be async-cancel safe between
1101invocations of \f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR.
1102.Sp
1103See also the locking example in the \f(CW\*(C`THREADS\*(C'\fR section later in this
1104document.
1105.IP "ev_set_userdata (loop, void *data)" 4
1106.IX Item "ev_set_userdata (loop, void *data)"
1107.PD 0
1108.IP "ev_userdata (loop)" 4
1109.IX Item "ev_userdata (loop)"
1110.PD
1111Set and retrieve a single \f(CW\*(C`void *\*(C'\fR associated with a loop. When
1112\&\f(CW\*(C`ev_set_userdata\*(C'\fR has never been called, then \f(CW\*(C`ev_userdata\*(C'\fR returns
1113\&\f(CW0.\fR
1114.Sp
1115These two functions can be used to associate arbitrary data with a loop,
1116and are intended solely for the \f(CW\*(C`invoke_pending_cb\*(C'\fR, \f(CW\*(C`release\*(C'\fR and
1117\&\f(CW\*(C`acquire\*(C'\fR callbacks described above, but of course can be (ab\-)used for
1118any other purpose as well.
1119.IP "ev_verify (loop)" 4
1120.IX Item "ev_verify (loop)"
1121This function only does something when \f(CW\*(C`EV_VERIFY\*(C'\fR support has been
1122compiled in, which is the default for non-minimal builds. It tries to go
1123through all internal structures and checks them for validity. If anything
1124is found to be inconsistent, it will print an error message to standard
1125error and call \f(CW\*(C`abort ()\*(C'\fR.
1126.Sp
1127This can be used to catch bugs inside libev itself: under normal
1128circumstances, this function will never abort as of course libev keeps its
1129data structures consistent.
441.SH "ANATOMY OF A WATCHER" 1130.SH "ANATOMY OF A WATCHER"
442.IX Header "ANATOMY OF A WATCHER" 1131.IX Header "ANATOMY OF A WATCHER"
1132In the following description, uppercase \f(CW\*(C`TYPE\*(C'\fR in names stands for the
1133watcher type, e.g. \f(CW\*(C`ev_TYPE_start\*(C'\fR can mean \f(CW\*(C`ev_timer_start\*(C'\fR for timer
1134watchers and \f(CW\*(C`ev_io_start\*(C'\fR for I/O watchers.
1135.PP
443A watcher is a structure that you create and register to record your 1136A watcher is an opaque structure that you allocate and register to record
444interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to 1137your interest in some event. To make a concrete example, imagine you want
445become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that: 1138to wait for \s-1STDIN\s0 to become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher
1139for that:
446.PP 1140.PP
447.Vb 5 1141.Vb 5
448\& static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) 1142\& static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
449\& { 1143\& {
450\& ev_io_stop (w); 1144\& ev_io_stop (w);
451\& ev_unloop (loop, EVUNLOOP_ALL); 1145\& ev_break (loop, EVBREAK_ALL);
452\& } 1146\& }
453.Ve 1147\&
454.PP
455.Vb 6
456\& struct ev_loop *loop = ev_default_loop (0); 1148\& struct ev_loop *loop = ev_default_loop (0);
1149\&
457\& struct ev_io stdin_watcher; 1150\& ev_io stdin_watcher;
1151\&
458\& ev_init (&stdin_watcher, my_cb); 1152\& ev_init (&stdin_watcher, my_cb);
459\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); 1153\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
460\& ev_io_start (loop, &stdin_watcher); 1154\& ev_io_start (loop, &stdin_watcher);
1155\&
461\& ev_loop (loop, 0); 1156\& ev_run (loop, 0);
462.Ve 1157.Ve
463.PP 1158.PP
464As you can see, you are responsible for allocating the memory for your 1159As you can see, you are responsible for allocating the memory for your
465watcher structures (and it is usually a bad idea to do this on the stack, 1160watcher structures (and it is \fIusually\fR a bad idea to do this on the
466although this can sometimes be quite valid). 1161stack).
467.PP 1162.PP
1163Each watcher has an associated watcher structure (called \f(CW\*(C`struct ev_TYPE\*(C'\fR
1164or simply \f(CW\*(C`ev_TYPE\*(C'\fR, as typedefs are provided for all watcher structs).
1165.PP
468Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init 1166Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init (watcher
469(watcher *, callback)\*(C'\fR, which expects a callback to be provided. This 1167*, callback)\*(C'\fR, which expects a callback to be provided. This callback is
470callback gets invoked each time the event occurs (or, in the case of io 1168invoked each time the event occurs (or, in the case of I/O watchers, each
471watchers, each time the event loop detects that the file descriptor given 1169time the event loop detects that the file descriptor given is readable
472is readable and/or writable). 1170and/or writable).
473.PP 1171.PP
474Each watcher type has its own \f(CW\*(C`ev_<type>_set (watcher *, ...)\*(C'\fR macro 1172Each watcher type further has its own \f(CW\*(C`ev_TYPE_set (watcher *, ...)\*(C'\fR
475with arguments specific to this watcher type. There is also a macro 1173macro to configure it, with arguments specific to the watcher type. There
476to combine initialisation and setting in one call: \f(CW\*(C`ev_<type>_init 1174is also a macro to combine initialisation and setting in one call: \f(CW\*(C`ev_TYPE_init (watcher *, callback, ...)\*(C'\fR.
477(watcher *, callback, ...)\*(C'\fR.
478.PP 1175.PP
479To make the watcher actually watch out for events, you have to start it 1176To make the watcher actually watch out for events, you have to start it
480with a watcher-specific start function (\f(CW\*(C`ev_<type>_start (loop, watcher 1177with a watcher-specific start function (\f(CW\*(C`ev_TYPE_start (loop, watcher
481*)\*(C'\fR), and you can stop watching for events at any time by calling the 1178*)\*(C'\fR), and you can stop watching for events at any time by calling the
482corresponding stop function (\f(CW\*(C`ev_<type>_stop (loop, watcher *)\*(C'\fR. 1179corresponding stop function (\f(CW\*(C`ev_TYPE_stop (loop, watcher *)\*(C'\fR.
483.PP 1180.PP
484As long as your watcher is active (has been started but not stopped) you 1181As long as your watcher is active (has been started but not stopped) you
485must not touch the values stored in it. Most specifically you must never 1182must not touch the values stored in it. Most specifically you must never
486reinitialise it or call its set method. 1183reinitialise it or call its \f(CW\*(C`ev_TYPE_set\*(C'\fR macro.
487.PP
488You can check whether an event is active by calling the \f(CW\*(C`ev_is_active
489(watcher *)\*(C'\fR macro. To see whether an event is outstanding (but the
490callback for it has not been called yet) you can use the \f(CW\*(C`ev_is_pending
491(watcher *)\*(C'\fR macro.
492.PP 1184.PP
493Each and every callback receives the event loop pointer as first, the 1185Each and every callback receives the event loop pointer as first, the
494registered watcher structure as second, and a bitset of received events as 1186registered watcher structure as second, and a bitset of received events as
495third argument. 1187third argument.
496.PP 1188.PP
… …
505.el .IP "\f(CWEV_WRITE\fR" 4 1197.el .IP "\f(CWEV_WRITE\fR" 4
506.IX Item "EV_WRITE" 1198.IX Item "EV_WRITE"
507.PD 1199.PD
508The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or 1200The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
509writable. 1201writable.
510.ie n .IP """EV_TIMEOUT""" 4 1202.ie n .IP """EV_TIMER""" 4
511.el .IP "\f(CWEV_TIMEOUT\fR" 4 1203.el .IP "\f(CWEV_TIMER\fR" 4
512.IX Item "EV_TIMEOUT" 1204.IX Item "EV_TIMER"
513The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out. 1205The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
514.ie n .IP """EV_PERIODIC""" 4 1206.ie n .IP """EV_PERIODIC""" 4
515.el .IP "\f(CWEV_PERIODIC\fR" 4 1207.el .IP "\f(CWEV_PERIODIC\fR" 4
516.IX Item "EV_PERIODIC" 1208.IX Item "EV_PERIODIC"
517The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out. 1209The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
… …
521The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread. 1213The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread.
522.ie n .IP """EV_CHILD""" 4 1214.ie n .IP """EV_CHILD""" 4
523.el .IP "\f(CWEV_CHILD\fR" 4 1215.el .IP "\f(CWEV_CHILD\fR" 4
524.IX Item "EV_CHILD" 1216.IX Item "EV_CHILD"
525The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change. 1217The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change.
1218.ie n .IP """EV_STAT""" 4
1219.el .IP "\f(CWEV_STAT\fR" 4
1220.IX Item "EV_STAT"
1221The path specified in the \f(CW\*(C`ev_stat\*(C'\fR watcher changed its attributes somehow.
526.ie n .IP """EV_IDLE""" 4 1222.ie n .IP """EV_IDLE""" 4
527.el .IP "\f(CWEV_IDLE\fR" 4 1223.el .IP "\f(CWEV_IDLE\fR" 4
528.IX Item "EV_IDLE" 1224.IX Item "EV_IDLE"
529The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do. 1225The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do.
530.ie n .IP """EV_PREPARE""" 4 1226.ie n .IP """EV_PREPARE""" 4
… …
533.PD 0 1229.PD 0
534.ie n .IP """EV_CHECK""" 4 1230.ie n .IP """EV_CHECK""" 4
535.el .IP "\f(CWEV_CHECK\fR" 4 1231.el .IP "\f(CWEV_CHECK\fR" 4
536.IX Item "EV_CHECK" 1232.IX Item "EV_CHECK"
537.PD 1233.PD
538All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_loop\*(C'\fR starts 1234All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_run\*(C'\fR starts
539to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after 1235to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after
540\&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any 1236\&\f(CW\*(C`ev_run\*(C'\fR has gathered them, but before it invokes any callbacks for any
541received events. Callbacks of both watcher types can start and stop as 1237received events. Callbacks of both watcher types can start and stop as
542many watchers as they want, and all of them will be taken into account 1238many watchers as they want, and all of them will be taken into account
543(for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep 1239(for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep
544\&\f(CW\*(C`ev_loop\*(C'\fR from blocking). 1240\&\f(CW\*(C`ev_run\*(C'\fR from blocking).
1241.ie n .IP """EV_EMBED""" 4
1242.el .IP "\f(CWEV_EMBED\fR" 4
1243.IX Item "EV_EMBED"
1244The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.
1245.ie n .IP """EV_FORK""" 4
1246.el .IP "\f(CWEV_FORK\fR" 4
1247.IX Item "EV_FORK"
1248The event loop has been resumed in the child process after fork (see
1249\&\f(CW\*(C`ev_fork\*(C'\fR).
1250.ie n .IP """EV_CLEANUP""" 4
1251.el .IP "\f(CWEV_CLEANUP\fR" 4
1252.IX Item "EV_CLEANUP"
1253The event loop is about to be destroyed (see \f(CW\*(C`ev_cleanup\*(C'\fR).
1254.ie n .IP """EV_ASYNC""" 4
1255.el .IP "\f(CWEV_ASYNC\fR" 4
1256.IX Item "EV_ASYNC"
1257The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR).
1258.ie n .IP """EV_CUSTOM""" 4
1259.el .IP "\f(CWEV_CUSTOM\fR" 4
1260.IX Item "EV_CUSTOM"
1261Not ever sent (or otherwise used) by libev itself, but can be freely used
1262by libev users to signal watchers (e.g. via \f(CW\*(C`ev_feed_event\*(C'\fR).
545.ie n .IP """EV_ERROR""" 4 1263.ie n .IP """EV_ERROR""" 4
546.el .IP "\f(CWEV_ERROR\fR" 4 1264.el .IP "\f(CWEV_ERROR\fR" 4
547.IX Item "EV_ERROR" 1265.IX Item "EV_ERROR"
548An unspecified error has occured, the watcher has been stopped. This might 1266An unspecified error has occurred, the watcher has been stopped. This might
549happen because the watcher could not be properly started because libev 1267happen because the watcher could not be properly started because libev
550ran out of memory, a file descriptor was found to be closed or any other 1268ran out of memory, a file descriptor was found to be closed or any other
1269problem. Libev considers these application bugs.
1270.Sp
551problem. You best act on it by reporting the problem and somehow coping 1271You best act on it by reporting the problem and somehow coping with the
552with the watcher being stopped. 1272watcher being stopped. Note that well-written programs should not receive
1273an error ever, so when your watcher receives it, this usually indicates a
1274bug in your program.
553.Sp 1275.Sp
554Libev will usually signal a few \*(L"dummy\*(R" events together with an error, 1276Libev will usually signal a few \*(L"dummy\*(R" events together with an error, for
555for example it might indicate that a fd is readable or writable, and if 1277example it might indicate that a fd is readable or writable, and if your
556your callbacks is well-written it can just attempt the operation and cope 1278callbacks is well-written it can just attempt the operation and cope with
557with the error from \fIread()\fR or \fIwrite()\fR. This will not work in multithreaded 1279the error from \fIread()\fR or \fIwrite()\fR. This will not work in multi-threaded
558programs, though, so beware. 1280programs, though, as the fd could already be closed and reused for another
1281thing, so beware.
1282.SS "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0"
1283.IX Subsection "GENERIC WATCHER FUNCTIONS"
1284.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
1285.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
1286.IX Item "ev_init (ev_TYPE *watcher, callback)"
1287This macro initialises the generic portion of a watcher. The contents
1288of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
1289the generic parts of the watcher are initialised, you \fIneed\fR to call
1290the type-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR macro afterwards to initialise the
1291type-specific parts. For each type there is also a \f(CW\*(C`ev_TYPE_init\*(C'\fR macro
1292which rolls both calls into one.
1293.Sp
1294You can reinitialise a watcher at any time as long as it has been stopped
1295(or never started) and there are no pending events outstanding.
1296.Sp
1297The callback is always of type \f(CW\*(C`void (*)(struct ev_loop *loop, ev_TYPE *watcher,
1298int revents)\*(C'\fR.
1299.Sp
1300Example: Initialise an \f(CW\*(C`ev_io\*(C'\fR watcher in two steps.
1301.Sp
1302.Vb 3
1303\& ev_io w;
1304\& ev_init (&w, my_cb);
1305\& ev_io_set (&w, STDIN_FILENO, EV_READ);
1306.Ve
1307.ie n .IP """ev_TYPE_set"" (ev_TYPE *watcher, [args])" 4
1308.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *watcher, [args])" 4
1309.IX Item "ev_TYPE_set (ev_TYPE *watcher, [args])"
1310This macro initialises the type-specific parts of a watcher. You need to
1311call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
1312call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
1313macro on a watcher that is active (it can be pending, however, which is a
1314difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
1315.Sp
1316Although some watcher types do not have type-specific arguments
1317(e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
1318.Sp
1319See \f(CW\*(C`ev_init\*(C'\fR, above, for an example.
1320.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
1321.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
1322.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
1323This convenience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
1324calls into a single call. This is the most convenient method to initialise
1325a watcher. The same limitations apply, of course.
1326.Sp
1327Example: Initialise and set an \f(CW\*(C`ev_io\*(C'\fR watcher in one step.
1328.Sp
1329.Vb 1
1330\& ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1331.Ve
1332.ie n .IP """ev_TYPE_start"" (loop, ev_TYPE *watcher)" 4
1333.el .IP "\f(CWev_TYPE_start\fR (loop, ev_TYPE *watcher)" 4
1334.IX Item "ev_TYPE_start (loop, ev_TYPE *watcher)"
1335Starts (activates) the given watcher. Only active watchers will receive
1336events. If the watcher is already active nothing will happen.
1337.Sp
1338Example: Start the \f(CW\*(C`ev_io\*(C'\fR watcher that is being abused as example in this
1339whole section.
1340.Sp
1341.Vb 1
1342\& ev_io_start (EV_DEFAULT_UC, &w);
1343.Ve
1344.ie n .IP """ev_TYPE_stop"" (loop, ev_TYPE *watcher)" 4
1345.el .IP "\f(CWev_TYPE_stop\fR (loop, ev_TYPE *watcher)" 4
1346.IX Item "ev_TYPE_stop (loop, ev_TYPE *watcher)"
1347Stops the given watcher if active, and clears the pending status (whether
1348the watcher was active or not).
1349.Sp
1350It is possible that stopped watchers are pending \- for example,
1351non-repeating timers are being stopped when they become pending \- but
1352calling \f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor
1353pending. If you want to free or reuse the memory used by the watcher it is
1354therefore a good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
1355.IP "bool ev_is_active (ev_TYPE *watcher)" 4
1356.IX Item "bool ev_is_active (ev_TYPE *watcher)"
1357Returns a true value iff the watcher is active (i.e. it has been started
1358and not yet been stopped). As long as a watcher is active you must not modify
1359it.
1360.IP "bool ev_is_pending (ev_TYPE *watcher)" 4
1361.IX Item "bool ev_is_pending (ev_TYPE *watcher)"
1362Returns a true value iff the watcher is pending, (i.e. it has outstanding
1363events but its callback has not yet been invoked). As long as a watcher
1364is pending (but not active) you must not call an init function on it (but
1365\&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe), you must not change its priority, and you must
1366make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR
1367it).
1368.IP "callback ev_cb (ev_TYPE *watcher)" 4
1369.IX Item "callback ev_cb (ev_TYPE *watcher)"
1370Returns the callback currently set on the watcher.
1371.IP "ev_cb_set (ev_TYPE *watcher, callback)" 4
1372.IX Item "ev_cb_set (ev_TYPE *watcher, callback)"
1373Change the callback. You can change the callback at virtually any time
1374(modulo threads).
1375.IP "ev_set_priority (ev_TYPE *watcher, int priority)" 4
1376.IX Item "ev_set_priority (ev_TYPE *watcher, int priority)"
1377.PD 0
1378.IP "int ev_priority (ev_TYPE *watcher)" 4
1379.IX Item "int ev_priority (ev_TYPE *watcher)"
1380.PD
1381Set and query the priority of the watcher. The priority is a small
1382integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR
1383(default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked
1384before watchers with lower priority, but priority will not keep watchers
1385from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
1386.Sp
1387If you need to suppress invocation when higher priority events are pending
1388you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
1389.Sp
1390You \fImust not\fR change the priority of a watcher as long as it is active or
1391pending.
1392.Sp
1393Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
1394fine, as long as you do not mind that the priority value you query might
1395or might not have been clamped to the valid range.
1396.Sp
1397The default priority used by watchers when no priority has been set is
1398always \f(CW0\fR, which is supposed to not be too high and not be too low :).
1399.Sp
1400See \*(L"\s-1WATCHER\s0 \s-1PRIORITY\s0 \s-1MODELS\s0\*(R", below, for a more thorough treatment of
1401priorities.
1402.IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
1403.IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
1404Invoke the \f(CW\*(C`watcher\*(C'\fR with the given \f(CW\*(C`loop\*(C'\fR and \f(CW\*(C`revents\*(C'\fR. Neither
1405\&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback
1406can deal with that fact, as both are simply passed through to the
1407callback.
1408.IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
1409.IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
1410If the watcher is pending, this function clears its pending status and
1411returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the
1412watcher isn't pending it does nothing and returns \f(CW0\fR.
1413.Sp
1414Sometimes it can be useful to \*(L"poll\*(R" a watcher instead of waiting for its
1415callback to be invoked, which can be accomplished with this function.
1416.IP "ev_feed_event (loop, ev_TYPE *watcher, int revents)" 4
1417.IX Item "ev_feed_event (loop, ev_TYPE *watcher, int revents)"
1418Feeds the given event set into the event loop, as if the specified event
1419had happened for the specified watcher (which must be a pointer to an
1420initialised but not necessarily started event watcher). Obviously you must
1421not free the watcher as long as it has pending events.
1422.Sp
1423Stopping the watcher, letting libev invoke it, or calling
1424\&\f(CW\*(C`ev_clear_pending\*(C'\fR will clear the pending event, even if the watcher was
1425not started in the first place.
1426.Sp
1427See also \f(CW\*(C`ev_feed_fd_event\*(C'\fR and \f(CW\*(C`ev_feed_signal_event\*(C'\fR for related
1428functions that do not need a watcher.
559.Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0" 1429.SS "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0"
560.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER" 1430.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
561Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change 1431Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change
562and read at any time, libev will completely ignore it. This can be used 1432and read at any time: libev will completely ignore it. This can be used
563to associate arbitrary data with your watcher. If you need more data and 1433to associate arbitrary data with your watcher. If you need more data and
564don't want to allocate memory and store a pointer to it in that data 1434don't want to allocate memory and store a pointer to it in that data
565member, you can also \*(L"subclass\*(R" the watcher type and provide your own 1435member, you can also \*(L"subclass\*(R" the watcher type and provide your own
566data: 1436data:
567.PP 1437.PP
568.Vb 7 1438.Vb 7
569\& struct my_io 1439\& struct my_io
570\& { 1440\& {
571\& struct ev_io io; 1441\& ev_io io;
572\& int otherfd; 1442\& int otherfd;
573\& void *somedata; 1443\& void *somedata;
574\& struct whatever *mostinteresting; 1444\& struct whatever *mostinteresting;
575\& } 1445\& };
1446\&
1447\& ...
1448\& struct my_io w;
1449\& ev_io_init (&w.io, my_cb, fd, EV_READ);
576.Ve 1450.Ve
577.PP 1451.PP
578And since your callback will be called with a pointer to the watcher, you 1452And since your callback will be called with a pointer to the watcher, you
579can cast it back to your own type: 1453can cast it back to your own type:
580.PP 1454.PP
581.Vb 5 1455.Vb 5
582\& static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents) 1456\& static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
583\& { 1457\& {
584\& struct my_io *w = (struct my_io *)w_; 1458\& struct my_io *w = (struct my_io *)w_;
585\& ... 1459\& ...
586\& } 1460\& }
587.Ve 1461.Ve
588.PP 1462.PP
589More interesting and less C\-conformant ways of catsing your callback type 1463More interesting and less C\-conformant ways of casting your callback type
590have been omitted.... 1464instead have been omitted.
1465.PP
1466Another common scenario is to use some data structure with multiple
1467embedded watchers:
1468.PP
1469.Vb 6
1470\& struct my_biggy
1471\& {
1472\& int some_data;
1473\& ev_timer t1;
1474\& ev_timer t2;
1475\& }
1476.Ve
1477.PP
1478In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more
1479complicated: Either you store the address of your \f(CW\*(C`my_biggy\*(C'\fR struct
1480in the \f(CW\*(C`data\*(C'\fR member of the watcher (for woozies), or you need to use
1481some pointer arithmetic using \f(CW\*(C`offsetof\*(C'\fR inside your watchers (for real
1482programmers):
1483.PP
1484.Vb 1
1485\& #include <stddef.h>
1486\&
1487\& static void
1488\& t1_cb (EV_P_ ev_timer *w, int revents)
1489\& {
1490\& struct my_biggy big = (struct my_biggy *)
1491\& (((char *)w) \- offsetof (struct my_biggy, t1));
1492\& }
1493\&
1494\& static void
1495\& t2_cb (EV_P_ ev_timer *w, int revents)
1496\& {
1497\& struct my_biggy big = (struct my_biggy *)
1498\& (((char *)w) \- offsetof (struct my_biggy, t2));
1499\& }
1500.Ve
1501.SS "\s-1WATCHER\s0 \s-1STATES\s0"
1502.IX Subsection "WATCHER STATES"
1503There are various watcher states mentioned throughout this manual \-
1504active, pending and so on. In this section these states and the rules to
1505transition between them will be described in more detail \- and while these
1506rules might look complicated, they usually do \*(L"the right thing\*(R".
1507.IP "initialiased" 4
1508.IX Item "initialiased"
1509Before a watcher can be registered with the event looop it has to be
1510initialised. This can be done with a call to \f(CW\*(C`ev_TYPE_init\*(C'\fR, or calls to
1511\&\f(CW\*(C`ev_init\*(C'\fR followed by the watcher-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR function.
1512.Sp
1513In this state it is simply some block of memory that is suitable for use
1514in an event loop. It can be moved around, freed, reused etc. at will.
1515.IP "started/running/active" 4
1516.IX Item "started/running/active"
1517Once a watcher has been started with a call to \f(CW\*(C`ev_TYPE_start\*(C'\fR it becomes
1518property of the event loop, and is actively waiting for events. While in
1519this state it cannot be accessed (except in a few documented ways), moved,
1520freed or anything else \- the only legal thing is to keep a pointer to it,
1521and call libev functions on it that are documented to work on active watchers.
1522.IP "pending" 4
1523.IX Item "pending"
1524If a watcher is active and libev determines that an event it is interested
1525in has occurred (such as a timer expiring), it will become pending. It will
1526stay in this pending state until either it is stopped or its callback is
1527about to be invoked, so it is not normally pending inside the watcher
1528callback.
1529.Sp
1530The watcher might or might not be active while it is pending (for example,
1531an expired non-repeating timer can be pending but no longer active). If it
1532is stopped, it can be freely accessed (e.g. by calling \f(CW\*(C`ev_TYPE_set\*(C'\fR),
1533but it is still property of the event loop at this time, so cannot be
1534moved, freed or reused. And if it is active the rules described in the
1535previous item still apply.
1536.Sp
1537It is also possible to feed an event on a watcher that is not active (e.g.
1538via \f(CW\*(C`ev_feed_event\*(C'\fR), in which case it becomes pending without being
1539active.
1540.IP "stopped" 4
1541.IX Item "stopped"
1542A watcher can be stopped implicitly by libev (in which case it might still
1543be pending), or explicitly by calling its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. The
1544latter will clear any pending state the watcher might be in, regardless
1545of whether it was active or not, so stopping a watcher explicitly before
1546freeing it is often a good idea.
1547.Sp
1548While stopped (and not pending) the watcher is essentially in the
1549initialised state, that is it can be reused, moved, modified in any way
1550you wish.
1551.SS "\s-1WATCHER\s0 \s-1PRIORITY\s0 \s-1MODELS\s0"
1552.IX Subsection "WATCHER PRIORITY MODELS"
1553Many event loops support \fIwatcher priorities\fR, which are usually small
1554integers that influence the ordering of event callback invocation
1555between watchers in some way, all else being equal.
1556.PP
1557In libev, Watcher priorities can be set using \f(CW\*(C`ev_set_priority\*(C'\fR. See its
1558description for the more technical details such as the actual priority
1559range.
1560.PP
1561There are two common ways how these these priorities are being interpreted
1562by event loops:
1563.PP
1564In the more common lock-out model, higher priorities \*(L"lock out\*(R" invocation
1565of lower priority watchers, which means as long as higher priority
1566watchers receive events, lower priority watchers are not being invoked.
1567.PP
1568The less common only-for-ordering model uses priorities solely to order
1569callback invocation within a single event loop iteration: Higher priority
1570watchers are invoked before lower priority ones, but they all get invoked
1571before polling for new events.
1572.PP
1573Libev uses the second (only-for-ordering) model for all its watchers
1574except for idle watchers (which use the lock-out model).
1575.PP
1576The rationale behind this is that implementing the lock-out model for
1577watchers is not well supported by most kernel interfaces, and most event
1578libraries will just poll for the same events again and again as long as
1579their callbacks have not been executed, which is very inefficient in the
1580common case of one high-priority watcher locking out a mass of lower
1581priority ones.
1582.PP
1583Static (ordering) priorities are most useful when you have two or more
1584watchers handling the same resource: a typical usage example is having an
1585\&\f(CW\*(C`ev_io\*(C'\fR watcher to receive data, and an associated \f(CW\*(C`ev_timer\*(C'\fR to handle
1586timeouts. Under load, data might be received while the program handles
1587other jobs, but since timers normally get invoked first, the timeout
1588handler will be executed before checking for data. In that case, giving
1589the timer a lower priority than the I/O watcher ensures that I/O will be
1590handled first even under adverse conditions (which is usually, but not
1591always, what you want).
1592.PP
1593Since idle watchers use the \*(L"lock-out\*(R" model, meaning that idle watchers
1594will only be executed when no same or higher priority watchers have
1595received events, they can be used to implement the \*(L"lock-out\*(R" model when
1596required.
1597.PP
1598For example, to emulate how many other event libraries handle priorities,
1599you can associate an \f(CW\*(C`ev_idle\*(C'\fR watcher to each such watcher, and in
1600the normal watcher callback, you just start the idle watcher. The real
1601processing is done in the idle watcher callback. This causes libev to
1602continuously poll and process kernel event data for the watcher, but when
1603the lock-out case is known to be rare (which in turn is rare :), this is
1604workable.
1605.PP
1606Usually, however, the lock-out model implemented that way will perform
1607miserably under the type of load it was designed to handle. In that case,
1608it might be preferable to stop the real watcher before starting the
1609idle watcher, so the kernel will not have to process the event in case
1610the actual processing will be delayed for considerable time.
1611.PP
1612Here is an example of an I/O watcher that should run at a strictly lower
1613priority than the default, and which should only process data when no
1614other events are pending:
1615.PP
1616.Vb 2
1617\& ev_idle idle; // actual processing watcher
1618\& ev_io io; // actual event watcher
1619\&
1620\& static void
1621\& io_cb (EV_P_ ev_io *w, int revents)
1622\& {
1623\& // stop the I/O watcher, we received the event, but
1624\& // are not yet ready to handle it.
1625\& ev_io_stop (EV_A_ w);
1626\&
1627\& // start the idle watcher to handle the actual event.
1628\& // it will not be executed as long as other watchers
1629\& // with the default priority are receiving events.
1630\& ev_idle_start (EV_A_ &idle);
1631\& }
1632\&
1633\& static void
1634\& idle_cb (EV_P_ ev_idle *w, int revents)
1635\& {
1636\& // actual processing
1637\& read (STDIN_FILENO, ...);
1638\&
1639\& // have to start the I/O watcher again, as
1640\& // we have handled the event
1641\& ev_io_start (EV_P_ &io);
1642\& }
1643\&
1644\& // initialisation
1645\& ev_idle_init (&idle, idle_cb);
1646\& ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
1647\& ev_io_start (EV_DEFAULT_ &io);
1648.Ve
1649.PP
1650In the \*(L"real\*(R" world, it might also be beneficial to start a timer, so that
1651low-priority connections can not be locked out forever under load. This
1652enables your program to keep a lower latency for important connections
1653during short periods of high load, while not completely locking out less
1654important ones.
591.SH "WATCHER TYPES" 1655.SH "WATCHER TYPES"
592.IX Header "WATCHER TYPES" 1656.IX Header "WATCHER TYPES"
593This section describes each watcher in detail, but will not repeat 1657This section describes each watcher in detail, but will not repeat
594information given in the last section. 1658information given in the last section. Any initialisation/set macros,
1659functions and members specific to the watcher type are explained.
1660.PP
1661Members are additionally marked with either \fI[read\-only]\fR, meaning that,
1662while the watcher is active, you can look at the member and expect some
1663sensible content, but you must not modify it (you can modify it while the
1664watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
1665means you can expect it to have some sensible content while the watcher
1666is active, but you can also modify it. Modifying it may not do something
1667sensible or take immediate effect (or do anything at all), but libev will
1668not crash or malfunction in any way.
595.ie n .Sh """ev_io"" \- is this file descriptor readable or writable" 1669.ie n .SS """ev_io"" \- is this file descriptor readable or writable?"
596.el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable" 1670.el .SS "\f(CWev_io\fP \- is this file descriptor readable or writable?"
597.IX Subsection "ev_io - is this file descriptor readable or writable" 1671.IX Subsection "ev_io - is this file descriptor readable or writable?"
598I/O watchers check whether a file descriptor is readable or writable 1672I/O watchers check whether a file descriptor is readable or writable
599in each iteration of the event loop (This behaviour is called 1673in each iteration of the event loop, or, more precisely, when reading
600level-triggering because you keep receiving events as long as the 1674would not block the process and writing would at least be able to write
601condition persists. Remember you can stop the watcher if you don't want to 1675some data. This behaviour is called level-triggering because you keep
602act on the event and neither want to receive future events). 1676receiving events as long as the condition persists. Remember you can stop
1677the watcher if you don't want to act on the event and neither want to
1678receive future events.
603.PP 1679.PP
604In general you can register as many read and/or write event watchers per 1680In general you can register as many read and/or write event watchers per
605fd as you want (as long as you don't confuse yourself). Setting all file 1681fd as you want (as long as you don't confuse yourself). Setting all file
606descriptors to non-blocking mode is also usually a good idea (but not 1682descriptors to non-blocking mode is also usually a good idea (but not
607required if you know what you are doing). 1683required if you know what you are doing).
608.PP 1684.PP
609You have to be careful with dup'ed file descriptors, though. Some backends 1685If you cannot use non-blocking mode, then force the use of a
610(the linux epoll backend is a notable example) cannot handle dup'ed file 1686known-to-be-good backend (at the time of this writing, this includes only
611descriptors correctly if you register interest in two or more fds pointing 1687\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and \f(CW\*(C`EVBACKEND_POLL\*(C'\fR). The same applies to file
612to the same underlying file/socket etc. description (that is, they share 1688descriptors for which non-blocking operation makes no sense (such as
613the same underlying \*(L"file open\*(R"). 1689files) \- libev doesn't guarantee any specific behaviour in that case.
614.PP 1690.PP
615If you must do this, then force the use of a known-to-be-good backend 1691Another thing you have to watch out for is that it is quite easy to
616(at the time of this writing, this includes only \s-1EVMETHOD_SELECT\s0 and 1692receive \*(L"spurious\*(R" readiness notifications, that is your callback might
617\&\s-1EVMETHOD_POLL\s0). 1693be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block
1694because there is no data. Not only are some backends known to create a
1695lot of those (for example Solaris ports), it is very easy to get into
1696this situation even with a relatively standard program structure. Thus
1697it is best to always use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning
1698\&\f(CW\*(C`EAGAIN\*(C'\fR is far preferable to a program hanging until some data arrives.
1699.PP
1700If you cannot run the fd in non-blocking mode (for example you should
1701not play around with an Xlib connection), then you have to separately
1702re-test whether a file descriptor is really ready with a known-to-be good
1703interface such as poll (fortunately in our Xlib example, Xlib already
1704does this on its own, so its quite safe to use). Some people additionally
1705use \f(CW\*(C`SIGALRM\*(C'\fR and an interval timer, just to be sure you won't block
1706indefinitely.
1707.PP
1708But really, best use non-blocking mode.
1709.PP
1710\fIThe special problem of disappearing file descriptors\fR
1711.IX Subsection "The special problem of disappearing file descriptors"
1712.PP
1713Some backends (e.g. kqueue, epoll) need to be told about closing a file
1714descriptor (either due to calling \f(CW\*(C`close\*(C'\fR explicitly or any other means,
1715such as \f(CW\*(C`dup2\*(C'\fR). The reason is that you register interest in some file
1716descriptor, but when it goes away, the operating system will silently drop
1717this interest. If another file descriptor with the same number then is
1718registered with libev, there is no efficient way to see that this is, in
1719fact, a different file descriptor.
1720.PP
1721To avoid having to explicitly tell libev about such cases, libev follows
1722the following policy: Each time \f(CW\*(C`ev_io_set\*(C'\fR is being called, libev
1723will assume that this is potentially a new file descriptor, otherwise
1724it is assumed that the file descriptor stays the same. That means that
1725you \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
1726descriptor even if the file descriptor number itself did not change.
1727.PP
1728This is how one would do it normally anyway, the important point is that
1729the libev application should not optimise around libev but should leave
1730optimisations to libev.
1731.PP
1732\fIThe special problem of dup'ed file descriptors\fR
1733.IX Subsection "The special problem of dup'ed file descriptors"
1734.PP
1735Some backends (e.g. epoll), cannot register events for file descriptors,
1736but only events for the underlying file descriptions. That means when you
1737have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register
1738events for them, only one file descriptor might actually receive events.
1739.PP
1740There is no workaround possible except not registering events
1741for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
1742\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1743.PP
1744\fIThe special problem of fork\fR
1745.IX Subsection "The special problem of fork"
1746.PP
1747Some backends (epoll, kqueue) do not support \f(CW\*(C`fork ()\*(C'\fR at all or exhibit
1748useless behaviour. Libev fully supports fork, but needs to be told about
1749it in the child.
1750.PP
1751To support fork in your programs, you either have to call
1752\&\f(CW\*(C`ev_default_fork ()\*(C'\fR or \f(CW\*(C`ev_loop_fork ()\*(C'\fR after a fork in the child,
1753enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or
1754\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1755.PP
1756\fIThe special problem of \s-1SIGPIPE\s0\fR
1757.IX Subsection "The special problem of SIGPIPE"
1758.PP
1759While not really specific to libev, it is easy to forget about \f(CW\*(C`SIGPIPE\*(C'\fR:
1760when writing to a pipe whose other end has been closed, your program gets
1761sent a \s-1SIGPIPE\s0, which, by default, aborts your program. For most programs
1762this is sensible behaviour, for daemons, this is usually undesirable.
1763.PP
1764So when you encounter spurious, unexplained daemon exits, make sure you
1765ignore \s-1SIGPIPE\s0 (and maybe make sure you log the exit status of your daemon
1766somewhere, as that would have given you a big clue).
1767.PP
1768\fIThe special problem of \fIaccept()\fIing when you can't\fR
1769.IX Subsection "The special problem of accept()ing when you can't"
1770.PP
1771Many implementations of the \s-1POSIX\s0 \f(CW\*(C`accept\*(C'\fR function (for example,
1772found in post\-2004 Linux) have the peculiar behaviour of not removing a
1773connection from the pending queue in all error cases.
1774.PP
1775For example, larger servers often run out of file descriptors (because
1776of resource limits), causing \f(CW\*(C`accept\*(C'\fR to fail with \f(CW\*(C`ENFILE\*(C'\fR but not
1777rejecting the connection, leading to libev signalling readiness on
1778the next iteration again (the connection still exists after all), and
1779typically causing the program to loop at 100% \s-1CPU\s0 usage.
1780.PP
1781Unfortunately, the set of errors that cause this issue differs between
1782operating systems, there is usually little the app can do to remedy the
1783situation, and no known thread-safe method of removing the connection to
1784cope with overload is known (to me).
1785.PP
1786One of the easiest ways to handle this situation is to just ignore it
1787\&\- when the program encounters an overload, it will just loop until the
1788situation is over. While this is a form of busy waiting, no \s-1OS\s0 offers an
1789event-based way to handle this situation, so it's the best one can do.
1790.PP
1791A better way to handle the situation is to log any errors other than
1792\&\f(CW\*(C`EAGAIN\*(C'\fR and \f(CW\*(C`EWOULDBLOCK\*(C'\fR, making sure not to flood the log with such
1793messages, and continue as usual, which at least gives the user an idea of
1794what could be wrong (\*(L"raise the ulimit!\*(R"). For extra points one could stop
1795the \f(CW\*(C`ev_io\*(C'\fR watcher on the listening fd \*(L"for a while\*(R", which reduces \s-1CPU\s0
1796usage.
1797.PP
1798If your program is single-threaded, then you could also keep a dummy file
1799descriptor for overload situations (e.g. by opening \fI/dev/null\fR), and
1800when you run into \f(CW\*(C`ENFILE\*(C'\fR or \f(CW\*(C`EMFILE\*(C'\fR, close it, run \f(CW\*(C`accept\*(C'\fR,
1801close that fd, and create a new dummy fd. This will gracefully refuse
1802clients under typical overload conditions.
1803.PP
1804The last way to handle it is to simply log the error and \f(CW\*(C`exit\*(C'\fR, as
1805is often done with \f(CW\*(C`malloc\*(C'\fR failures, but this results in an easy
1806opportunity for a DoS attack.
1807.PP
1808\fIWatcher-Specific Functions\fR
1809.IX Subsection "Watcher-Specific Functions"
618.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4 1810.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
619.IX Item "ev_io_init (ev_io *, callback, int fd, int events)" 1811.IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
620.PD 0 1812.PD 0
621.IP "ev_io_set (ev_io *, int fd, int events)" 4 1813.IP "ev_io_set (ev_io *, int fd, int events)" 4
622.IX Item "ev_io_set (ev_io *, int fd, int events)" 1814.IX Item "ev_io_set (ev_io *, int fd, int events)"
623.PD 1815.PD
624Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The fd is the file descriptor to rceeive 1816Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to
625events for and events is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or \f(CW\*(C`EV_READ | 1817receive events for and \f(CW\*(C`events\*(C'\fR is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or
626EV_WRITE\*(C'\fR to receive the given events. 1818\&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR, to express the desire to receive the given events.
1819.IP "int fd [read\-only]" 4
1820.IX Item "int fd [read-only]"
1821The file descriptor being watched.
1822.IP "int events [read\-only]" 4
1823.IX Item "int events [read-only]"
1824The events being watched.
1825.PP
1826\fIExamples\fR
1827.IX Subsection "Examples"
1828.PP
1829Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
1830readable, but only once. Since it is likely line-buffered, you could
1831attempt to read a whole line in the callback.
1832.PP
1833.Vb 6
1834\& static void
1835\& stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1836\& {
1837\& ev_io_stop (loop, w);
1838\& .. read from stdin here (or from w\->fd) and handle any I/O errors
1839\& }
1840\&
1841\& ...
1842\& struct ev_loop *loop = ev_default_init (0);
1843\& ev_io stdin_readable;
1844\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1845\& ev_io_start (loop, &stdin_readable);
1846\& ev_run (loop, 0);
1847.Ve
627.ie n .Sh """ev_timer"" \- relative and optionally recurring timeouts" 1848.ie n .SS """ev_timer"" \- relative and optionally repeating timeouts"
628.el .Sh "\f(CWev_timer\fP \- relative and optionally recurring timeouts" 1849.el .SS "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
629.IX Subsection "ev_timer - relative and optionally recurring timeouts" 1850.IX Subsection "ev_timer - relative and optionally repeating timeouts"
630Timer watchers are simple relative timers that generate an event after a 1851Timer watchers are simple relative timers that generate an event after a
631given time, and optionally repeating in regular intervals after that. 1852given time, and optionally repeating in regular intervals after that.
632.PP 1853.PP
633The timers are based on real time, that is, if you register an event that 1854The timers are based on real time, that is, if you register an event that
634times out after an hour and you reset your system clock to last years 1855times out after an hour and you reset your system clock to January last
635time, it will still time out after (roughly) and hour. \*(L"Roughly\*(R" because 1856year, it will still time out after (roughly) one hour. \*(L"Roughly\*(R" because
636detecting time jumps is hard, and some inaccuracies are unavoidable (the 1857detecting time jumps is hard, and some inaccuracies are unavoidable (the
637monotonic clock option helps a lot here). 1858monotonic clock option helps a lot here).
1859.PP
1860The callback is guaranteed to be invoked only \fIafter\fR its timeout has
1861passed (not \fIat\fR, so on systems with very low-resolution clocks this
1862might introduce a small delay). If multiple timers become ready during the
1863same loop iteration then the ones with earlier time-out values are invoked
1864before ones of the same priority with later time-out values (but this is
1865no longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
1866.PP
1867\fIBe smart about timeouts\fR
1868.IX Subsection "Be smart about timeouts"
1869.PP
1870Many real-world problems involve some kind of timeout, usually for error
1871recovery. A typical example is an \s-1HTTP\s0 request \- if the other side hangs,
1872you want to raise some error after a while.
1873.PP
1874What follows are some ways to handle this problem, from obvious and
1875inefficient to smart and efficient.
1876.PP
1877In the following, a 60 second activity timeout is assumed \- a timeout that
1878gets reset to 60 seconds each time there is activity (e.g. each time some
1879data or other life sign was received).
1880.IP "1. Use a timer and stop, reinitialise and start it on activity." 4
1881.IX Item "1. Use a timer and stop, reinitialise and start it on activity."
1882This is the most obvious, but not the most simple way: In the beginning,
1883start the watcher:
1884.Sp
1885.Vb 2
1886\& ev_timer_init (timer, callback, 60., 0.);
1887\& ev_timer_start (loop, timer);
1888.Ve
1889.Sp
1890Then, each time there is some activity, \f(CW\*(C`ev_timer_stop\*(C'\fR it, initialise it
1891and start it again:
1892.Sp
1893.Vb 3
1894\& ev_timer_stop (loop, timer);
1895\& ev_timer_set (timer, 60., 0.);
1896\& ev_timer_start (loop, timer);
1897.Ve
1898.Sp
1899This is relatively simple to implement, but means that each time there is
1900some activity, libev will first have to remove the timer from its internal
1901data structure and then add it again. Libev tries to be fast, but it's
1902still not a constant-time operation.
1903.ie n .IP "2. Use a timer and re-start it with ""ev_timer_again"" inactivity." 4
1904.el .IP "2. Use a timer and re-start it with \f(CWev_timer_again\fR inactivity." 4
1905.IX Item "2. Use a timer and re-start it with ev_timer_again inactivity."
1906This is the easiest way, and involves using \f(CW\*(C`ev_timer_again\*(C'\fR instead of
1907\&\f(CW\*(C`ev_timer_start\*(C'\fR.
1908.Sp
1909To implement this, configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value
1910of \f(CW60\fR and then call \f(CW\*(C`ev_timer_again\*(C'\fR at start and each time you
1911successfully read or write some data. If you go into an idle state where
1912you do not expect data to travel on the socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR
1913the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will automatically restart it if need be.
1914.Sp
1915That means you can ignore both the \f(CW\*(C`ev_timer_start\*(C'\fR function and the
1916\&\f(CW\*(C`after\*(C'\fR argument to \f(CW\*(C`ev_timer_set\*(C'\fR, and only ever use the \f(CW\*(C`repeat\*(C'\fR
1917member and \f(CW\*(C`ev_timer_again\*(C'\fR.
1918.Sp
1919At start:
1920.Sp
1921.Vb 3
1922\& ev_init (timer, callback);
1923\& timer\->repeat = 60.;
1924\& ev_timer_again (loop, timer);
1925.Ve
1926.Sp
1927Each time there is some activity:
1928.Sp
1929.Vb 1
1930\& ev_timer_again (loop, timer);
1931.Ve
1932.Sp
1933It is even possible to change the time-out on the fly, regardless of
1934whether the watcher is active or not:
1935.Sp
1936.Vb 2
1937\& timer\->repeat = 30.;
1938\& ev_timer_again (loop, timer);
1939.Ve
1940.Sp
1941This is slightly more efficient then stopping/starting the timer each time
1942you want to modify its timeout value, as libev does not have to completely
1943remove and re-insert the timer from/into its internal data structure.
1944.Sp
1945It is, however, even simpler than the \*(L"obvious\*(R" way to do it.
1946.IP "3. Let the timer time out, but then re-arm it as required." 4
1947.IX Item "3. Let the timer time out, but then re-arm it as required."
1948This method is more tricky, but usually most efficient: Most timeouts are
1949relatively long compared to the intervals between other activity \- in
1950our example, within 60 seconds, there are usually many I/O events with
1951associated activity resets.
1952.Sp
1953In this case, it would be more efficient to leave the \f(CW\*(C`ev_timer\*(C'\fR alone,
1954but remember the time of last activity, and check for a real timeout only
1955within the callback:
1956.Sp
1957.Vb 1
1958\& ev_tstamp last_activity; // time of last activity
1959\&
1960\& static void
1961\& callback (EV_P_ ev_timer *w, int revents)
1962\& {
1963\& ev_tstamp now = ev_now (EV_A);
1964\& ev_tstamp timeout = last_activity + 60.;
1965\&
1966\& // if last_activity + 60. is older than now, we did time out
1967\& if (timeout < now)
1968\& {
1969\& // timeout occurred, take action
1970\& }
1971\& else
1972\& {
1973\& // callback was invoked, but there was some activity, re\-arm
1974\& // the watcher to fire in last_activity + 60, which is
1975\& // guaranteed to be in the future, so "again" is positive:
1976\& w\->repeat = timeout \- now;
1977\& ev_timer_again (EV_A_ w);
1978\& }
1979\& }
1980.Ve
1981.Sp
1982To summarise the callback: first calculate the real timeout (defined
1983as \*(L"60 seconds after the last activity\*(R"), then check if that time has
1984been reached, which means something \fIdid\fR, in fact, time out. Otherwise
1985the callback was invoked too early (\f(CW\*(C`timeout\*(C'\fR is in the future), so
1986re-schedule the timer to fire at that future time, to see if maybe we have
1987a timeout then.
1988.Sp
1989Note how \f(CW\*(C`ev_timer_again\*(C'\fR is used, taking advantage of the
1990\&\f(CW\*(C`ev_timer_again\*(C'\fR optimisation when the timer is already running.
1991.Sp
1992This scheme causes more callback invocations (about one every 60 seconds
1993minus half the average time between activity), but virtually no calls to
1994libev to change the timeout.
1995.Sp
1996To start the timer, simply initialise the watcher and set \f(CW\*(C`last_activity\*(C'\fR
1997to the current time (meaning we just have some activity :), then call the
1998callback, which will \*(L"do the right thing\*(R" and start the timer:
1999.Sp
2000.Vb 3
2001\& ev_init (timer, callback);
2002\& last_activity = ev_now (loop);
2003\& callback (loop, timer, EV_TIMER);
2004.Ve
2005.Sp
2006And when there is some activity, simply store the current time in
2007\&\f(CW\*(C`last_activity\*(C'\fR, no libev calls at all:
2008.Sp
2009.Vb 1
2010\& last_activity = ev_now (loop);
2011.Ve
2012.Sp
2013This technique is slightly more complex, but in most cases where the
2014time-out is unlikely to be triggered, much more efficient.
2015.Sp
2016Changing the timeout is trivial as well (if it isn't hard-coded in the
2017callback :) \- just change the timeout and invoke the callback, which will
2018fix things for you.
2019.IP "4. Wee, just use a double-linked list for your timeouts." 4
2020.IX Item "4. Wee, just use a double-linked list for your timeouts."
2021If there is not one request, but many thousands (millions...), all
2022employing some kind of timeout with the same timeout value, then one can
2023do even better:
2024.Sp
2025When starting the timeout, calculate the timeout value and put the timeout
2026at the \fIend\fR of the list.
2027.Sp
2028Then use an \f(CW\*(C`ev_timer\*(C'\fR to fire when the timeout at the \fIbeginning\fR of
2029the list is expected to fire (for example, using the technique #3).
2030.Sp
2031When there is some activity, remove the timer from the list, recalculate
2032the timeout, append it to the end of the list again, and make sure to
2033update the \f(CW\*(C`ev_timer\*(C'\fR if it was taken from the beginning of the list.
2034.Sp
2035This way, one can manage an unlimited number of timeouts in O(1) time for
2036starting, stopping and updating the timers, at the expense of a major
2037complication, and having to use a constant timeout. The constant timeout
2038ensures that the list stays sorted.
2039.PP
2040So which method the best?
2041.PP
2042Method #2 is a simple no-brain-required solution that is adequate in most
2043situations. Method #3 requires a bit more thinking, but handles many cases
2044better, and isn't very complicated either. In most case, choosing either
2045one is fine, with #3 being better in typical situations.
2046.PP
2047Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
2048rather complicated, but extremely efficient, something that really pays
2049off after the first million or so of active timers, i.e. it's usually
2050overkill :)
2051.PP
2052\fIThe special problem of time updates\fR
2053.IX Subsection "The special problem of time updates"
2054.PP
2055Establishing the current time is a costly operation (it usually takes at
2056least two system calls): \s-1EV\s0 therefore updates its idea of the current
2057time only before and after \f(CW\*(C`ev_run\*(C'\fR collects new events, which causes a
2058growing difference between \f(CW\*(C`ev_now ()\*(C'\fR and \f(CW\*(C`ev_time ()\*(C'\fR when handling
2059lots of events in one iteration.
638.PP 2060.PP
639The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR 2061The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
640time. This is usually the right thing as this timestamp refers to the time 2062time. This is usually the right thing as this timestamp refers to the time
641of the event triggering whatever timeout you are modifying/starting. If 2063of the event triggering whatever timeout you are modifying/starting. If
642you suspect event processing to be delayed and you \fIneed\fR to base the timeout 2064you suspect event processing to be delayed and you \fIneed\fR to base the
643on the current time, use something like this to adjust for this: 2065timeout on the current time, use something like this to adjust for this:
644.PP 2066.PP
645.Vb 1 2067.Vb 1
646\& ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); 2068\& ev_timer_set (&timer, after + ev_now () \- ev_time (), 0.);
647.Ve 2069.Ve
648.PP 2070.PP
649The callback is guarenteed to be invoked only when its timeout has passed, 2071If the event loop is suspended for a long time, you can also force an
650but if multiple timers become ready during the same loop iteration then 2072update of the time returned by \f(CW\*(C`ev_now ()\*(C'\fR by calling \f(CW\*(C`ev_now_update
651order of execution is undefined. 2073()\*(C'\fR.
2074.PP
2075\fIThe special problems of suspended animation\fR
2076.IX Subsection "The special problems of suspended animation"
2077.PP
2078When you leave the server world it is quite customary to hit machines that
2079can suspend/hibernate \- what happens to the clocks during such a suspend?
2080.PP
2081Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
2082all processes, while the clocks (\f(CW\*(C`times\*(C'\fR, \f(CW\*(C`CLOCK_MONOTONIC\*(C'\fR) continue
2083to run until the system is suspended, but they will not advance while the
2084system is suspended. That means, on resume, it will be as if the program
2085was frozen for a few seconds, but the suspend time will not be counted
2086towards \f(CW\*(C`ev_timer\*(C'\fR when a monotonic clock source is used. The real time
2087clock advanced as expected, but if it is used as sole clocksource, then a
2088long suspend would be detected as a time jump by libev, and timers would
2089be adjusted accordingly.
2090.PP
2091I would not be surprised to see different behaviour in different between
2092operating systems, \s-1OS\s0 versions or even different hardware.
2093.PP
2094The other form of suspend (job control, or sending a \s-1SIGSTOP\s0) will see a
2095time jump in the monotonic clocks and the realtime clock. If the program
2096is suspended for a very long time, and monotonic clock sources are in use,
2097then you can expect \f(CW\*(C`ev_timer\*(C'\fRs to expire as the full suspension time
2098will be counted towards the timers. When no monotonic clock source is in
2099use, then libev will again assume a timejump and adjust accordingly.
2100.PP
2101It might be beneficial for this latter case to call \f(CW\*(C`ev_suspend\*(C'\fR
2102and \f(CW\*(C`ev_resume\*(C'\fR in code that handles \f(CW\*(C`SIGTSTP\*(C'\fR, to at least get
2103deterministic behaviour in this case (you can do nothing against
2104\&\f(CW\*(C`SIGSTOP\*(C'\fR).
2105.PP
2106\fIWatcher-Specific Functions and Data Members\fR
2107.IX Subsection "Watcher-Specific Functions and Data Members"
652.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4 2108.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
653.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 2109.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
654.PD 0 2110.PD 0
655.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4 2111.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
656.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 2112.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
657.PD 2113.PD
658Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR is 2114Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR
659\&\f(CW0.\fR, then it will automatically be stopped. If it is positive, then the 2115is \f(CW0.\fR, then it will automatically be stopped once the timeout is
660timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds 2116reached. If it is positive, then the timer will automatically be
661later, again, and again, until stopped manually. 2117configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds later, again, and again,
2118until stopped manually.
662.Sp 2119.Sp
663The timer itself will do a best-effort at avoiding drift, that is, if you 2120The timer itself will do a best-effort at avoiding drift, that is, if
664configure a timer to trigger every 10 seconds, then it will trigger at 2121you configure a timer to trigger every 10 seconds, then it will normally
665exactly 10 second intervals. If, however, your program cannot keep up with 2122trigger at exactly 10 second intervals. If, however, your program cannot
666the timer (because it takes longer than those 10 seconds to do stuff) the 2123keep up with the timer (because it takes longer than those 10 seconds to
667timer will not fire more than once per event loop iteration. 2124do stuff) the timer will not fire more than once per event loop iteration.
668.IP "ev_timer_again (loop)" 4 2125.IP "ev_timer_again (loop, ev_timer *)" 4
669.IX Item "ev_timer_again (loop)" 2126.IX Item "ev_timer_again (loop, ev_timer *)"
670This will act as if the timer timed out and restart it again if it is 2127This will act as if the timer timed out and restart it again if it is
671repeating. The exact semantics are: 2128repeating. The exact semantics are:
672.Sp 2129.Sp
2130If the timer is pending, its pending status is cleared.
2131.Sp
673If the timer is started but nonrepeating, stop it. 2132If the timer is started but non-repeating, stop it (as if it timed out).
674.Sp 2133.Sp
675If the timer is repeating, either start it if necessary (with the repeat 2134If the timer is repeating, either start it if necessary (with the
676value), or reset the running timer to the repeat value. 2135\&\f(CW\*(C`repeat\*(C'\fR value), or reset the running timer to the \f(CW\*(C`repeat\*(C'\fR value.
677.Sp 2136.Sp
678This sounds a bit complicated, but here is a useful and typical 2137This sounds a bit complicated, see \*(L"Be smart about timeouts\*(R", above, for a
679example: Imagine you have a tcp connection and you want a so-called idle 2138usage example.
680timeout, that is, you want to be called when there have been, say, 60 2139.IP "ev_tstamp ev_timer_remaining (loop, ev_timer *)" 4
681seconds of inactivity on the socket. The easiest way to do this is to 2140.IX Item "ev_tstamp ev_timer_remaining (loop, ev_timer *)"
682configure an \f(CW\*(C`ev_timer\*(C'\fR with after=repeat=60 and calling ev_timer_again each 2141Returns the remaining time until a timer fires. If the timer is active,
683time you successfully read or write some data. If you go into an idle 2142then this time is relative to the current event loop time, otherwise it's
684state where you do not expect data to travel on the socket, you can stop 2143the timeout value currently configured.
685the timer, and again will automatically restart it if need be. 2144.Sp
2145That is, after an \f(CW\*(C`ev_timer_set (w, 5, 7)\*(C'\fR, \f(CW\*(C`ev_timer_remaining\*(C'\fR returns
2146\&\f(CW5\fR. When the timer is started and one second passes, \f(CW\*(C`ev_timer_remaining\*(C'\fR
2147will return \f(CW4\fR. When the timer expires and is restarted, it will return
2148roughly \f(CW7\fR (likely slightly less as callback invocation takes some time,
2149too), and so on.
2150.IP "ev_tstamp repeat [read\-write]" 4
2151.IX Item "ev_tstamp repeat [read-write]"
2152The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
2153or \f(CW\*(C`ev_timer_again\*(C'\fR is called, and determines the next timeout (if any),
2154which is also when any modifications are taken into account.
2155.PP
2156\fIExamples\fR
2157.IX Subsection "Examples"
2158.PP
2159Example: Create a timer that fires after 60 seconds.
2160.PP
2161.Vb 5
2162\& static void
2163\& one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
2164\& {
2165\& .. one minute over, w is actually stopped right here
2166\& }
2167\&
2168\& ev_timer mytimer;
2169\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
2170\& ev_timer_start (loop, &mytimer);
2171.Ve
2172.PP
2173Example: Create a timeout timer that times out after 10 seconds of
2174inactivity.
2175.PP
2176.Vb 5
2177\& static void
2178\& timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
2179\& {
2180\& .. ten seconds without any activity
2181\& }
2182\&
2183\& ev_timer mytimer;
2184\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
2185\& ev_timer_again (&mytimer); /* start timer */
2186\& ev_run (loop, 0);
2187\&
2188\& // and in some piece of code that gets executed on any "activity":
2189\& // reset the timeout to start ticking again at 10 seconds
2190\& ev_timer_again (&mytimer);
2191.Ve
686.ie n .Sh """ev_periodic"" \- to cron or not to cron" 2192.ie n .SS """ev_periodic"" \- to cron or not to cron?"
687.el .Sh "\f(CWev_periodic\fP \- to cron or not to cron" 2193.el .SS "\f(CWev_periodic\fP \- to cron or not to cron?"
688.IX Subsection "ev_periodic - to cron or not to cron" 2194.IX Subsection "ev_periodic - to cron or not to cron?"
689Periodic watchers are also timers of a kind, but they are very versatile 2195Periodic watchers are also timers of a kind, but they are very versatile
690(and unfortunately a bit complex). 2196(and unfortunately a bit complex).
691.PP 2197.PP
692Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time) 2198Unlike \f(CW\*(C`ev_timer\*(C'\fR, periodic watchers are not based on real time (or
693but on wallclock time (absolute time). You can tell a periodic watcher 2199relative time, the physical time that passes) but on wall clock time
694to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a 2200(absolute time, the thing you can read on your calender or clock). The
695periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now () 2201difference is that wall clock time can run faster or slower than real
696+ 10.>) and then reset your system clock to the last year, then it will 2202time, and time jumps are not uncommon (e.g. when you adjust your
697take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger 2203wrist-watch).
698roughly 10 seconds later and of course not if you reset your system time
699again).
700.PP 2204.PP
701They can also be used to implement vastly more complex timers, such as 2205You can tell a periodic watcher to trigger after some specific point
702triggering an event on eahc midnight, local time. 2206in time: for example, if you tell a periodic watcher to trigger \*(L"in 10
2207seconds\*(R" (by specifying e.g. \f(CW\*(C`ev_now () + 10.\*(C'\fR, that is, an absolute time
2208not a delay) and then reset your system clock to January of the previous
2209year, then it will take a year or more to trigger the event (unlike an
2210\&\f(CW\*(C`ev_timer\*(C'\fR, which would still trigger roughly 10 seconds after starting
2211it, as it uses a relative timeout).
703.PP 2212.PP
2213\&\f(CW\*(C`ev_periodic\*(C'\fR watchers can also be used to implement vastly more complex
2214timers, such as triggering an event on each \*(L"midnight, local time\*(R", or
2215other complicated rules. This cannot be done with \f(CW\*(C`ev_timer\*(C'\fR watchers, as
2216those cannot react to time jumps.
2217.PP
704As with timers, the callback is guarenteed to be invoked only when the 2218As with timers, the callback is guaranteed to be invoked only when the
705time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready 2219point in time where it is supposed to trigger has passed. If multiple
706during the same loop iteration then order of execution is undefined. 2220timers become ready during the same loop iteration then the ones with
2221earlier time-out values are invoked before ones with later time-out values
2222(but this is no longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
2223.PP
2224\fIWatcher-Specific Functions and Data Members\fR
2225.IX Subsection "Watcher-Specific Functions and Data Members"
707.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4 2226.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
708.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 2227.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
709.PD 0 2228.PD 0
710.IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4 2229.IP "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
711.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 2230.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
712.PD 2231.PD
713Lots of arguments, lets sort it out... There are basically three modes of 2232Lots of arguments, let's sort it out... There are basically three modes of
714operation, and we will explain them from simplest to complex: 2233operation, and we will explain them from simplest to most complex:
715.RS 4 2234.RS 4
716.IP "* absolute timer (interval = reschedule_cb = 0)" 4 2235.IP "\(bu" 4
717.IX Item "absolute timer (interval = reschedule_cb = 0)" 2236absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
2237.Sp
718In this configuration the watcher triggers an event at the wallclock time 2238In this configuration the watcher triggers an event after the wall clock
719\&\f(CW\*(C`at\*(C'\fR and doesn't repeat. It will not adjust when a time jump occurs, 2239time \f(CW\*(C`offset\*(C'\fR has passed. It will not repeat and will not adjust when a
720that is, if it is to be run at January 1st 2011 then it will run when the 2240time jump occurs, that is, if it is to be run at January 1st 2011 then it
721system time reaches or surpasses this time. 2241will be stopped and invoked when the system clock reaches or surpasses
722.IP "* non-repeating interval timer (interval > 0, reschedule_cb = 0)" 4 2242this point in time.
723.IX Item "non-repeating interval timer (interval > 0, reschedule_cb = 0)" 2243.IP "\(bu" 4
2244repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
2245.Sp
724In this mode the watcher will always be scheduled to time out at the next 2246In this mode the watcher will always be scheduled to time out at the next
725\&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N) and then repeat, regardless 2247\&\f(CW\*(C`offset + N * interval\*(C'\fR time (for some integer N, which can also be
726of any time jumps. 2248negative) and then repeat, regardless of any time jumps. The \f(CW\*(C`offset\*(C'\fR
2249argument is merely an offset into the \f(CW\*(C`interval\*(C'\fR periods.
727.Sp 2250.Sp
728This can be used to create timers that do not drift with respect to system 2251This can be used to create timers that do not drift with respect to the
729time: 2252system clock, for example, here is an \f(CW\*(C`ev_periodic\*(C'\fR that triggers each
2253hour, on the hour (with respect to \s-1UTC\s0):
730.Sp 2254.Sp
731.Vb 1 2255.Vb 1
732\& ev_periodic_set (&periodic, 0., 3600., 0); 2256\& ev_periodic_set (&periodic, 0., 3600., 0);
733.Ve 2257.Ve
734.Sp 2258.Sp
735This doesn't mean there will always be 3600 seconds in between triggers, 2259This doesn't mean there will always be 3600 seconds in between triggers,
736but only that the the callback will be called when the system time shows a 2260but only that the callback will be called when the system time shows a
737full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible 2261full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
738by 3600. 2262by 3600.
739.Sp 2263.Sp
740Another way to think about it (for the mathematically inclined) is that 2264Another way to think about it (for the mathematically inclined) is that
741\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible 2265\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
742time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps. 2266time where \f(CW\*(C`time = offset (mod interval)\*(C'\fR, regardless of any time jumps.
743.IP "* manual reschedule mode (reschedule_cb = callback)" 4 2267.Sp
744.IX Item "manual reschedule mode (reschedule_cb = callback)" 2268For numerical stability it is preferable that the \f(CW\*(C`offset\*(C'\fR value is near
2269\&\f(CW\*(C`ev_now ()\*(C'\fR (the current time), but there is no range requirement for
2270this value, and in fact is often specified as zero.
2271.Sp
2272Note also that there is an upper limit to how often a timer can fire (\s-1CPU\s0
2273speed for example), so if \f(CW\*(C`interval\*(C'\fR is very small then timing stability
2274will of course deteriorate. Libev itself tries to be exact to be about one
2275millisecond (if the \s-1OS\s0 supports it and the machine is fast enough).
2276.IP "\(bu" 4
2277manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
2278.Sp
745In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being 2279In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`offset\*(C'\fR are both being
746ignored. Instead, each time the periodic watcher gets scheduled, the 2280ignored. Instead, each time the periodic watcher gets scheduled, the
747reschedule callback will be called with the watcher as first, and the 2281reschedule callback will be called with the watcher as first, and the
748current time as second argument. 2282current time as second argument.
749.Sp 2283.Sp
750\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, 2284\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, ever,
751ever, or make any event loop modifications\fR. If you need to stop it, 2285or make \s-1ANY\s0 other event loop modifications whatsoever, unless explicitly
752return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by 2286allowed by documentation here\fR.
753starting a prepare watcher).
754.Sp 2287.Sp
2288If you need to stop it, return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop
2289it afterwards (e.g. by starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is the
2290only event loop modification you are allowed to do).
2291.Sp
755Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w, 2292The callback prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(ev_periodic
756ev_tstamp now)\*(C'\fR, e.g.: 2293*w, ev_tstamp now)\*(C'\fR, e.g.:
757.Sp 2294.Sp
758.Vb 4 2295.Vb 5
2296\& static ev_tstamp
759\& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) 2297\& my_rescheduler (ev_periodic *w, ev_tstamp now)
760\& { 2298\& {
761\& return now + 60.; 2299\& return now + 60.;
762\& } 2300\& }
763.Ve 2301.Ve
764.Sp 2302.Sp
765It must return the next time to trigger, based on the passed time value 2303It must return the next time to trigger, based on the passed time value
766(that is, the lowest time value larger than to the second argument). It 2304(that is, the lowest time value larger than to the second argument). It
767will usually be called just before the callback will be triggered, but 2305will usually be called just before the callback will be triggered, but
768might be called at other times, too. 2306might be called at other times, too.
769.Sp 2307.Sp
770\&\s-1NOTE:\s0 \fIThis callback must always return a time that is later than the 2308\&\s-1NOTE:\s0 \fIThis callback must always return a time that is higher than or
771passed \f(CI\*(C`now\*(C'\fI value\fR. Not even \f(CW\*(C`now\*(C'\fR itself will do, it \fImust\fR be larger. 2309equal to the passed \f(CI\*(C`now\*(C'\fI value\fR.
772.Sp 2310.Sp
773This can be used to create very complex timers, such as a timer that 2311This can be used to create very complex timers, such as a timer that
774triggers on each midnight, local time. To do this, you would calculate the 2312triggers on \*(L"next midnight, local time\*(R". To do this, you would calculate the
775next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How 2313next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How
776you do this is, again, up to you (but it is not trivial, which is the main 2314you do this is, again, up to you (but it is not trivial, which is the main
777reason I omitted it as an example). 2315reason I omitted it as an example).
778.RE 2316.RE
779.RS 4 2317.RS 4
… …
782.IX Item "ev_periodic_again (loop, ev_periodic *)" 2320.IX Item "ev_periodic_again (loop, ev_periodic *)"
783Simply stops and restarts the periodic watcher again. This is only useful 2321Simply stops and restarts the periodic watcher again. This is only useful
784when you changed some parameters or the reschedule callback would return 2322when you changed some parameters or the reschedule callback would return
785a different time than the last time it was called (e.g. in a crond like 2323a different time than the last time it was called (e.g. in a crond like
786program when the crontabs have changed). 2324program when the crontabs have changed).
2325.IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4
2326.IX Item "ev_tstamp ev_periodic_at (ev_periodic *)"
2327When active, returns the absolute time that the watcher is supposed
2328to trigger next. This is not the same as the \f(CW\*(C`offset\*(C'\fR argument to
2329\&\f(CW\*(C`ev_periodic_set\*(C'\fR, but indeed works even in interval and manual
2330rescheduling modes.
2331.IP "ev_tstamp offset [read\-write]" 4
2332.IX Item "ev_tstamp offset [read-write]"
2333When repeating, this contains the offset value, otherwise this is the
2334absolute point in time (the \f(CW\*(C`offset\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR,
2335although libev might modify this value for better numerical stability).
2336.Sp
2337Can be modified any time, but changes only take effect when the periodic
2338timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
2339.IP "ev_tstamp interval [read\-write]" 4
2340.IX Item "ev_tstamp interval [read-write]"
2341The current interval value. Can be modified any time, but changes only
2342take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
2343called.
2344.IP "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read\-write]" 4
2345.IX Item "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]"
2346The current reschedule callback, or \f(CW0\fR, if this functionality is
2347switched off. Can be changed any time, but changes only take effect when
2348the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
2349.PP
2350\fIExamples\fR
2351.IX Subsection "Examples"
2352.PP
2353Example: Call a callback every hour, or, more precisely, whenever the
2354system time is divisible by 3600. The callback invocation times have
2355potentially a lot of jitter, but good long-term stability.
2356.PP
2357.Vb 5
2358\& static void
2359\& clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
2360\& {
2361\& ... its now a full hour (UTC, or TAI or whatever your clock follows)
2362\& }
2363\&
2364\& ev_periodic hourly_tick;
2365\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
2366\& ev_periodic_start (loop, &hourly_tick);
2367.Ve
2368.PP
2369Example: The same as above, but use a reschedule callback to do it:
2370.PP
2371.Vb 1
2372\& #include <math.h>
2373\&
2374\& static ev_tstamp
2375\& my_scheduler_cb (ev_periodic *w, ev_tstamp now)
2376\& {
2377\& return now + (3600. \- fmod (now, 3600.));
2378\& }
2379\&
2380\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
2381.Ve
2382.PP
2383Example: Call a callback every hour, starting now:
2384.PP
2385.Vb 4
2386\& ev_periodic hourly_tick;
2387\& ev_periodic_init (&hourly_tick, clock_cb,
2388\& fmod (ev_now (loop), 3600.), 3600., 0);
2389\& ev_periodic_start (loop, &hourly_tick);
2390.Ve
787.ie n .Sh """ev_signal"" \- signal me when a signal gets signalled" 2391.ie n .SS """ev_signal"" \- signal me when a signal gets signalled!"
788.el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled" 2392.el .SS "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
789.IX Subsection "ev_signal - signal me when a signal gets signalled" 2393.IX Subsection "ev_signal - signal me when a signal gets signalled!"
790Signal watchers will trigger an event when the process receives a specific 2394Signal watchers will trigger an event when the process receives a specific
791signal one or more times. Even though signals are very asynchronous, libev 2395signal one or more times. Even though signals are very asynchronous, libev
792will try it's best to deliver signals synchronously, i.e. as part of the 2396will try it's best to deliver signals synchronously, i.e. as part of the
793normal event processing, like any other event. 2397normal event processing, like any other event.
794.PP 2398.PP
2399If you want signals to be delivered truly asynchronously, just use
2400\&\f(CW\*(C`sigaction\*(C'\fR as you would do without libev and forget about sharing
2401the signal. You can even use \f(CW\*(C`ev_async\*(C'\fR from a signal handler to
2402synchronously wake up an event loop.
2403.PP
795You can configure as many watchers as you like per signal. Only when the 2404You can configure as many watchers as you like for the same signal, but
2405only within the same loop, i.e. you can watch for \f(CW\*(C`SIGINT\*(C'\fR in your
2406default loop and for \f(CW\*(C`SIGIO\*(C'\fR in another loop, but you cannot watch for
2407\&\f(CW\*(C`SIGINT\*(C'\fR in both the default loop and another loop at the same time. At
2408the moment, \f(CW\*(C`SIGCHLD\*(C'\fR is permanently tied to the default loop.
2409.PP
796first watcher gets started will libev actually register a signal watcher 2410When the first watcher gets started will libev actually register something
797with the kernel (thus it coexists with your own signal handlers as long 2411with the kernel (thus it coexists with your own signal handlers as long as
798as you don't register any with libev). Similarly, when the last signal 2412you don't register any with libev for the same signal).
799watcher for a signal is stopped libev will reset the signal handler to 2413.PP
800\&\s-1SIG_DFL\s0 (regardless of what it was set to before). 2414If possible and supported, libev will install its handlers with
2415\&\f(CW\*(C`SA_RESTART\*(C'\fR (or equivalent) behaviour enabled, so system calls should
2416not be unduly interrupted. If you have a problem with system calls getting
2417interrupted by signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher
2418and unblock them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher.
2419.PP
2420\fIThe special problem of inheritance over fork/execve/pthread_create\fR
2421.IX Subsection "The special problem of inheritance over fork/execve/pthread_create"
2422.PP
2423Both the signal mask (\f(CW\*(C`sigprocmask\*(C'\fR) and the signal disposition
2424(\f(CW\*(C`sigaction\*(C'\fR) are unspecified after starting a signal watcher (and after
2425stopping it again), that is, libev might or might not block the signal,
2426and might or might not set or restore the installed signal handler.
2427.PP
2428While this does not matter for the signal disposition (libev never
2429sets signals to \f(CW\*(C`SIG_IGN\*(C'\fR, so handlers will be reset to \f(CW\*(C`SIG_DFL\*(C'\fR on
2430\&\f(CW\*(C`execve\*(C'\fR), this matters for the signal mask: many programs do not expect
2431certain signals to be blocked.
2432.PP
2433This means that before calling \f(CW\*(C`exec\*(C'\fR (from the child) you should reset
2434the signal mask to whatever \*(L"default\*(R" you expect (all clear is a good
2435choice usually).
2436.PP
2437The simplest way to ensure that the signal mask is reset in the child is
2438to install a fork handler with \f(CW\*(C`pthread_atfork\*(C'\fR that resets it. That will
2439catch fork calls done by libraries (such as the libc) as well.
2440.PP
2441In current versions of libev, the signal will not be blocked indefinitely
2442unless you use the \f(CW\*(C`signalfd\*(C'\fR \s-1API\s0 (\f(CW\*(C`EV_SIGNALFD\*(C'\fR). While this reduces
2443the window of opportunity for problems, it will not go away, as libev
2444\&\fIhas\fR to modify the signal mask, at least temporarily.
2445.PP
2446So I can't stress this enough: \fIIf you do not reset your signal mask when
2447you expect it to be empty, you have a race condition in your code\fR. This
2448is not a libev-specific thing, this is true for most event libraries.
2449.PP
2450\fIWatcher-Specific Functions and Data Members\fR
2451.IX Subsection "Watcher-Specific Functions and Data Members"
801.IP "ev_signal_init (ev_signal *, callback, int signum)" 4 2452.IP "ev_signal_init (ev_signal *, callback, int signum)" 4
802.IX Item "ev_signal_init (ev_signal *, callback, int signum)" 2453.IX Item "ev_signal_init (ev_signal *, callback, int signum)"
803.PD 0 2454.PD 0
804.IP "ev_signal_set (ev_signal *, int signum)" 4 2455.IP "ev_signal_set (ev_signal *, int signum)" 4
805.IX Item "ev_signal_set (ev_signal *, int signum)" 2456.IX Item "ev_signal_set (ev_signal *, int signum)"
806.PD 2457.PD
807Configures the watcher to trigger on the given signal number (usually one 2458Configures the watcher to trigger on the given signal number (usually one
808of the \f(CW\*(C`SIGxxx\*(C'\fR constants). 2459of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
2460.IP "int signum [read\-only]" 4
2461.IX Item "int signum [read-only]"
2462The signal the watcher watches out for.
2463.PP
2464\fIExamples\fR
2465.IX Subsection "Examples"
2466.PP
2467Example: Try to exit cleanly on \s-1SIGINT\s0.
2468.PP
2469.Vb 5
2470\& static void
2471\& sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
2472\& {
2473\& ev_break (loop, EVBREAK_ALL);
2474\& }
2475\&
2476\& ev_signal signal_watcher;
2477\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
2478\& ev_signal_start (loop, &signal_watcher);
2479.Ve
809.ie n .Sh """ev_child"" \- wait for pid status changes" 2480.ie n .SS """ev_child"" \- watch out for process status changes"
810.el .Sh "\f(CWev_child\fP \- wait for pid status changes" 2481.el .SS "\f(CWev_child\fP \- watch out for process status changes"
811.IX Subsection "ev_child - wait for pid status changes" 2482.IX Subsection "ev_child - watch out for process status changes"
812Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to 2483Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
813some child status changes (most typically when a child of yours dies). 2484some child status changes (most typically when a child of yours dies or
2485exits). It is permissible to install a child watcher \fIafter\fR the child
2486has been forked (which implies it might have already exited), as long
2487as the event loop isn't entered (or is continued from a watcher), i.e.,
2488forking and then immediately registering a watcher for the child is fine,
2489but forking and registering a watcher a few event loop iterations later or
2490in the next callback invocation is not.
2491.PP
2492Only the default event loop is capable of handling signals, and therefore
2493you can only register child watchers in the default event loop.
2494.PP
2495Due to some design glitches inside libev, child watchers will always be
2496handled at maximum priority (their priority is set to \f(CW\*(C`EV_MAXPRI\*(C'\fR by
2497libev)
2498.PP
2499\fIProcess Interaction\fR
2500.IX Subsection "Process Interaction"
2501.PP
2502Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is
2503initialised. This is necessary to guarantee proper behaviour even if the
2504first child watcher is started after the child exits. The occurrence
2505of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done
2506synchronously as part of the event loop processing. Libev always reaps all
2507children, even ones not watched.
2508.PP
2509\fIOverriding the Built-In Processing\fR
2510.IX Subsection "Overriding the Built-In Processing"
2511.PP
2512Libev offers no special support for overriding the built-in child
2513processing, but if your application collides with libev's default child
2514handler, you can override it easily by installing your own handler for
2515\&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the
2516default loop never gets destroyed. You are encouraged, however, to use an
2517event-based approach to child reaping and thus use libev's support for
2518that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely.
2519.PP
2520\fIStopping the Child Watcher\fR
2521.IX Subsection "Stopping the Child Watcher"
2522.PP
2523Currently, the child watcher never gets stopped, even when the
2524child terminates, so normally one needs to stop the watcher in the
2525callback. Future versions of libev might stop the watcher automatically
2526when a child exit is detected (calling \f(CW\*(C`ev_child_stop\*(C'\fR twice is not a
2527problem).
2528.PP
2529\fIWatcher-Specific Functions and Data Members\fR
2530.IX Subsection "Watcher-Specific Functions and Data Members"
814.IP "ev_child_init (ev_child *, callback, int pid)" 4 2531.IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4
815.IX Item "ev_child_init (ev_child *, callback, int pid)" 2532.IX Item "ev_child_init (ev_child *, callback, int pid, int trace)"
816.PD 0 2533.PD 0
817.IP "ev_child_set (ev_child *, int pid)" 4 2534.IP "ev_child_set (ev_child *, int pid, int trace)" 4
818.IX Item "ev_child_set (ev_child *, int pid)" 2535.IX Item "ev_child_set (ev_child *, int pid, int trace)"
819.PD 2536.PD
820Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or 2537Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
821\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look 2538\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
822at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see 2539at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
823the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems 2540the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
824\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the 2541\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
825process causing the status change. 2542process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only
2543activate the watcher when the process terminates) or \f(CW1\fR (additionally
2544activate the watcher when the process is stopped or continued).
2545.IP "int pid [read\-only]" 4
2546.IX Item "int pid [read-only]"
2547The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
2548.IP "int rpid [read\-write]" 4
2549.IX Item "int rpid [read-write]"
2550The process id that detected a status change.
2551.IP "int rstatus [read\-write]" 4
2552.IX Item "int rstatus [read-write]"
2553The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
2554\&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
2555.PP
2556\fIExamples\fR
2557.IX Subsection "Examples"
2558.PP
2559Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for
2560its completion.
2561.PP
2562.Vb 1
2563\& ev_child cw;
2564\&
2565\& static void
2566\& child_cb (EV_P_ ev_child *w, int revents)
2567\& {
2568\& ev_child_stop (EV_A_ w);
2569\& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus);
2570\& }
2571\&
2572\& pid_t pid = fork ();
2573\&
2574\& if (pid < 0)
2575\& // error
2576\& else if (pid == 0)
2577\& {
2578\& // the forked child executes here
2579\& exit (1);
2580\& }
2581\& else
2582\& {
2583\& ev_child_init (&cw, child_cb, pid, 0);
2584\& ev_child_start (EV_DEFAULT_ &cw);
2585\& }
2586.Ve
2587.ie n .SS """ev_stat"" \- did the file attributes just change?"
2588.el .SS "\f(CWev_stat\fP \- did the file attributes just change?"
2589.IX Subsection "ev_stat - did the file attributes just change?"
2590This watches a file system path for attribute changes. That is, it calls
2591\&\f(CW\*(C`stat\*(C'\fR on that path in regular intervals (or when the \s-1OS\s0 says it changed)
2592and sees if it changed compared to the last time, invoking the callback if
2593it did.
2594.PP
2595The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does
2596not exist\*(R" is a status change like any other. The condition \*(L"path does not
2597exist\*(R" (or more correctly \*(L"path cannot be stat'ed\*(R") is signified by the
2598\&\f(CW\*(C`st_nlink\*(C'\fR field being zero (which is otherwise always forced to be at
2599least one) and all the other fields of the stat buffer having unspecified
2600contents.
2601.PP
2602The path \fImust not\fR end in a slash or contain special components such as
2603\&\f(CW\*(C`.\*(C'\fR or \f(CW\*(C`..\*(C'\fR. The path \fIshould\fR be absolute: If it is relative and
2604your working directory changes, then the behaviour is undefined.
2605.PP
2606Since there is no portable change notification interface available, the
2607portable implementation simply calls \f(CWstat(2)\fR regularly on the path
2608to see if it changed somehow. You can specify a recommended polling
2609interval for this case. If you specify a polling interval of \f(CW0\fR (highly
2610recommended!) then a \fIsuitable, unspecified default\fR value will be used
2611(which you can expect to be around five seconds, although this might
2612change dynamically). Libev will also impose a minimum interval which is
2613currently around \f(CW0.1\fR, but that's usually overkill.
2614.PP
2615This watcher type is not meant for massive numbers of stat watchers,
2616as even with OS-supported change notifications, this can be
2617resource-intensive.
2618.PP
2619At the time of this writing, the only OS-specific interface implemented
2620is the Linux inotify interface (implementing kqueue support is left as an
2621exercise for the reader. Note, however, that the author sees no way of
2622implementing \f(CW\*(C`ev_stat\*(C'\fR semantics with kqueue, except as a hint).
2623.PP
2624\fI\s-1ABI\s0 Issues (Largefile Support)\fR
2625.IX Subsection "ABI Issues (Largefile Support)"
2626.PP
2627Libev by default (unless the user overrides this) uses the default
2628compilation environment, which means that on systems with large file
2629support disabled by default, you get the 32 bit version of the stat
2630structure. When using the library from programs that change the \s-1ABI\s0 to
2631use 64 bit file offsets the programs will fail. In that case you have to
2632compile libev with the same flags to get binary compatibility. This is
2633obviously the case with any flags that change the \s-1ABI\s0, but the problem is
2634most noticeably displayed with ev_stat and large file support.
2635.PP
2636The solution for this is to lobby your distribution maker to make large
2637file interfaces available by default (as e.g. FreeBSD does) and not
2638optional. Libev cannot simply switch on large file support because it has
2639to exchange stat structures with application programs compiled using the
2640default compilation environment.
2641.PP
2642\fIInotify and Kqueue\fR
2643.IX Subsection "Inotify and Kqueue"
2644.PP
2645When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev and present at
2646runtime, it will be used to speed up change detection where possible. The
2647inotify descriptor will be created lazily when the first \f(CW\*(C`ev_stat\*(C'\fR
2648watcher is being started.
2649.PP
2650Inotify presence does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
2651except that changes might be detected earlier, and in some cases, to avoid
2652making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presence of inotify support
2653there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling,
2654but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
2655many bugs), the path exists (i.e. stat succeeds), and the path resides on
2656a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
2657xfs are fully working) libev usually gets away without polling.
2658.PP
2659There is no support for kqueue, as apparently it cannot be used to
2660implement this functionality, due to the requirement of having a file
2661descriptor open on the object at all times, and detecting renames, unlinks
2662etc. is difficult.
2663.PP
2664\fI\f(CI\*(C`stat ()\*(C'\fI is a synchronous operation\fR
2665.IX Subsection "stat () is a synchronous operation"
2666.PP
2667Libev doesn't normally do any kind of I/O itself, and so is not blocking
2668the process. The exception are \f(CW\*(C`ev_stat\*(C'\fR watchers \- those call \f(CW\*(C`stat
2669()\*(C'\fR, which is a synchronous operation.
2670.PP
2671For local paths, this usually doesn't matter: unless the system is very
2672busy or the intervals between stat's are large, a stat call will be fast,
2673as the path data is usually in memory already (except when starting the
2674watcher).
2675.PP
2676For networked file systems, calling \f(CW\*(C`stat ()\*(C'\fR can block an indefinite
2677time due to network issues, and even under good conditions, a stat call
2678often takes multiple milliseconds.
2679.PP
2680Therefore, it is best to avoid using \f(CW\*(C`ev_stat\*(C'\fR watchers on networked
2681paths, although this is fully supported by libev.
2682.PP
2683\fIThe special problem of stat time resolution\fR
2684.IX Subsection "The special problem of stat time resolution"
2685.PP
2686The \f(CW\*(C`stat ()\*(C'\fR system call only supports full-second resolution portably,
2687and even on systems where the resolution is higher, most file systems
2688still only support whole seconds.
2689.PP
2690That means that, if the time is the only thing that changes, you can
2691easily miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and
2692calls your callback, which does something. When there is another update
2693within the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect unless the
2694stat data does change in other ways (e.g. file size).
2695.PP
2696The solution to this is to delay acting on a change for slightly more
2697than a second (or till slightly after the next full second boundary), using
2698a roughly one-second-delay \f(CW\*(C`ev_timer\*(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02);
2699ev_timer_again (loop, w)\*(C'\fR).
2700.PP
2701The \f(CW.02\fR offset is added to work around small timing inconsistencies
2702of some operating systems (where the second counter of the current time
2703might be be delayed. One such system is the Linux kernel, where a call to
2704\&\f(CW\*(C`gettimeofday\*(C'\fR might return a timestamp with a full second later than
2705a subsequent \f(CW\*(C`time\*(C'\fR call \- if the equivalent of \f(CW\*(C`time ()\*(C'\fR is used to
2706update file times then there will be a small window where the kernel uses
2707the previous second to update file times but libev might already execute
2708the timer callback).
2709.PP
2710\fIWatcher-Specific Functions and Data Members\fR
2711.IX Subsection "Watcher-Specific Functions and Data Members"
2712.IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
2713.IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
2714.PD 0
2715.IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4
2716.IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)"
2717.PD
2718Configures the watcher to wait for status changes of the given
2719\&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to
2720be detected and should normally be specified as \f(CW0\fR to let libev choose
2721a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same
2722path for as long as the watcher is active.
2723.Sp
2724The callback will receive an \f(CW\*(C`EV_STAT\*(C'\fR event when a change was detected,
2725relative to the attributes at the time the watcher was started (or the
2726last change was detected).
2727.IP "ev_stat_stat (loop, ev_stat *)" 4
2728.IX Item "ev_stat_stat (loop, ev_stat *)"
2729Updates the stat buffer immediately with new values. If you change the
2730watched path in your callback, you could call this function to avoid
2731detecting this change (while introducing a race condition if you are not
2732the only one changing the path). Can also be useful simply to find out the
2733new values.
2734.IP "ev_statdata attr [read\-only]" 4
2735.IX Item "ev_statdata attr [read-only]"
2736The most-recently detected attributes of the file. Although the type is
2737\&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
2738suitable for your system, but you can only rely on the POSIX-standardised
2739members to be present. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there was
2740some error while \f(CW\*(C`stat\*(C'\fRing the file.
2741.IP "ev_statdata prev [read\-only]" 4
2742.IX Item "ev_statdata prev [read-only]"
2743The previous attributes of the file. The callback gets invoked whenever
2744\&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR, or, more precisely, one or more of these members
2745differ: \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,
2746\&\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.
2747.IP "ev_tstamp interval [read\-only]" 4
2748.IX Item "ev_tstamp interval [read-only]"
2749The specified interval.
2750.IP "const char *path [read\-only]" 4
2751.IX Item "const char *path [read-only]"
2752The file system path that is being watched.
2753.PP
2754\fIExamples\fR
2755.IX Subsection "Examples"
2756.PP
2757Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
2758.PP
2759.Vb 10
2760\& static void
2761\& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
2762\& {
2763\& /* /etc/passwd changed in some way */
2764\& if (w\->attr.st_nlink)
2765\& {
2766\& printf ("passwd current size %ld\en", (long)w\->attr.st_size);
2767\& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime);
2768\& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime);
2769\& }
2770\& else
2771\& /* you shalt not abuse printf for puts */
2772\& puts ("wow, /etc/passwd is not there, expect problems. "
2773\& "if this is windows, they already arrived\en");
2774\& }
2775\&
2776\& ...
2777\& ev_stat passwd;
2778\&
2779\& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
2780\& ev_stat_start (loop, &passwd);
2781.Ve
2782.PP
2783Example: Like above, but additionally use a one-second delay so we do not
2784miss updates (however, frequent updates will delay processing, too, so
2785one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
2786\&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
2787.PP
2788.Vb 2
2789\& static ev_stat passwd;
2790\& static ev_timer timer;
2791\&
2792\& static void
2793\& timer_cb (EV_P_ ev_timer *w, int revents)
2794\& {
2795\& ev_timer_stop (EV_A_ w);
2796\&
2797\& /* now it\*(Aqs one second after the most recent passwd change */
2798\& }
2799\&
2800\& static void
2801\& stat_cb (EV_P_ ev_stat *w, int revents)
2802\& {
2803\& /* reset the one\-second timer */
2804\& ev_timer_again (EV_A_ &timer);
2805\& }
2806\&
2807\& ...
2808\& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
2809\& ev_stat_start (loop, &passwd);
2810\& ev_timer_init (&timer, timer_cb, 0., 1.02);
2811.Ve
826.ie n .Sh """ev_idle"" \- when you've got nothing better to do" 2812.ie n .SS """ev_idle"" \- when you've got nothing better to do..."
827.el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do" 2813.el .SS "\f(CWev_idle\fP \- when you've got nothing better to do..."
828.IX Subsection "ev_idle - when you've got nothing better to do" 2814.IX Subsection "ev_idle - when you've got nothing better to do..."
829Idle watchers trigger events when there are no other events are pending 2815Idle watchers trigger events when no other events of the same or higher
830(prepare, check and other idle watchers do not count). That is, as long 2816priority are pending (prepare, check and other idle watchers do not count
831as your process is busy handling sockets or timeouts (or even signals, 2817as receiving \*(L"events\*(R").
832imagine) it will not be triggered. But when your process is idle all idle 2818.PP
833watchers are being called again and again, once per event loop iteration \- 2819That is, as long as your process is busy handling sockets or timeouts
2820(or even signals, imagine) of the same or higher priority it will not be
2821triggered. But when your process is idle (or only lower-priority watchers
2822are pending), the idle watchers are being called once per event loop
834until stopped, that is, or your process receives more events and becomes 2823iteration \- until stopped, that is, or your process receives more events
835busy. 2824and becomes busy again with higher priority stuff.
836.PP 2825.PP
837The most noteworthy effect is that as long as any idle watchers are 2826The most noteworthy effect is that as long as any idle watchers are
838active, the process will not block when waiting for new events. 2827active, the process will not block when waiting for new events.
839.PP 2828.PP
840Apart from keeping your process non-blocking (which is a useful 2829Apart from keeping your process non-blocking (which is a useful
841effect on its own sometimes), idle watchers are a good place to do 2830effect on its own sometimes), idle watchers are a good place to do
842\&\*(L"pseudo\-background processing\*(R", or delay processing stuff to after the 2831\&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the
843event loop has handled all outstanding events. 2832event loop has handled all outstanding events.
2833.PP
2834\fIWatcher-Specific Functions and Data Members\fR
2835.IX Subsection "Watcher-Specific Functions and Data Members"
844.IP "ev_idle_init (ev_signal *, callback)" 4 2836.IP "ev_idle_init (ev_idle *, callback)" 4
845.IX Item "ev_idle_init (ev_signal *, callback)" 2837.IX Item "ev_idle_init (ev_idle *, callback)"
846Initialises and configures the idle watcher \- it has no parameters of any 2838Initialises and configures the idle watcher \- it has no parameters of any
847kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless, 2839kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
848believe me. 2840believe me.
2841.PP
2842\fIExamples\fR
2843.IX Subsection "Examples"
2844.PP
2845Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the
2846callback, free it. Also, use no error checking, as usual.
2847.PP
2848.Vb 7
2849\& static void
2850\& idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
2851\& {
2852\& free (w);
2853\& // now do something you wanted to do when the program has
2854\& // no longer anything immediate to do.
2855\& }
2856\&
2857\& ev_idle *idle_watcher = malloc (sizeof (ev_idle));
2858\& ev_idle_init (idle_watcher, idle_cb);
2859\& ev_idle_start (loop, idle_watcher);
2860.Ve
849.ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop" 2861.ie n .SS """ev_prepare"" and ""ev_check"" \- customise your event loop!"
850.el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop" 2862.el .SS "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
851.IX Subsection "ev_prepare and ev_check - customise your event loop" 2863.IX Subsection "ev_prepare and ev_check - customise your event loop!"
852Prepare and check watchers are usually (but not always) used in tandem: 2864Prepare and check watchers are usually (but not always) used in pairs:
853prepare watchers get invoked before the process blocks and check watchers 2865prepare watchers get invoked before the process blocks and check watchers
854afterwards. 2866afterwards.
855.PP 2867.PP
2868You \fImust not\fR call \f(CW\*(C`ev_run\*(C'\fR or similar functions that enter
2869the current event loop from either \f(CW\*(C`ev_prepare\*(C'\fR or \f(CW\*(C`ev_check\*(C'\fR
2870watchers. Other loops than the current one are fine, however. The
2871rationale behind this is that you do not need to check for recursion in
2872those watchers, i.e. the sequence will always be \f(CW\*(C`ev_prepare\*(C'\fR, blocking,
2873\&\f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each kind they will always be
2874called in pairs bracketing the blocking call.
2875.PP
856Their main purpose is to integrate other event mechanisms into libev. This 2876Their main purpose is to integrate other event mechanisms into libev and
857could be used, for example, to track variable changes, implement your own 2877their use is somewhat advanced. They could be used, for example, to track
858watchers, integrate net-snmp or a coroutine library and lots more. 2878variable changes, implement your own watchers, integrate net-snmp or a
2879coroutine library and lots more. They are also occasionally useful if
2880you cache some data and want to flush it before blocking (for example,
2881in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
2882watcher).
859.PP 2883.PP
860This is done by examining in each prepare call which file descriptors need 2884This is done by examining in each prepare call which file descriptors
861to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers for 2885need to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers
862them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many libraries 2886for them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many
863provide just this functionality). Then, in the check watcher you check for 2887libraries provide exactly this functionality). Then, in the check watcher,
864any events that occured (by checking the pending status of all watchers 2888you check for any events that occurred (by checking the pending status
865and stopping them) and call back into the library. The I/O and timer 2889of all watchers and stopping them) and call back into the library. The
866callbacks will never actually be called (but must be valid nevertheless, 2890I/O and timer callbacks will never actually be called (but must be valid
867because you never know, you know?). 2891nevertheless, because you never know, you know?).
868.PP 2892.PP
869As another example, the Perl Coro module uses these hooks to integrate 2893As another example, the Perl Coro module uses these hooks to integrate
870coroutines into libev programs, by yielding to other active coroutines 2894coroutines into libev programs, by yielding to other active coroutines
871during each prepare and only letting the process block if no coroutines 2895during each prepare and only letting the process block if no coroutines
872are ready to run (it's actually more complicated: it only runs coroutines 2896are ready to run (it's actually more complicated: it only runs coroutines
873with priority higher than or equal to the event loop and one coroutine 2897with priority higher than or equal to the event loop and one coroutine
874of lower priority, but only once, using idle watchers to keep the event 2898of lower priority, but only once, using idle watchers to keep the event
875loop from blocking if lower-priority coroutines are active, thus mapping 2899loop from blocking if lower-priority coroutines are active, thus mapping
876low-priority coroutines to idle/background tasks). 2900low-priority coroutines to idle/background tasks).
2901.PP
2902It is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR)
2903priority, to ensure that they are being run before any other watchers
2904after the poll (this doesn't matter for \f(CW\*(C`ev_prepare\*(C'\fR watchers).
2905.PP
2906Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, too) should not
2907activate (\*(L"feed\*(R") events into libev. While libev fully supports this, they
2908might get executed before other \f(CW\*(C`ev_check\*(C'\fR watchers did their job. As
2909\&\f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other (non-libev) event
2910loops those other event loops might be in an unusable state until their
2911\&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with
2912others).
2913.PP
2914\fIWatcher-Specific Functions and Data Members\fR
2915.IX Subsection "Watcher-Specific Functions and Data Members"
877.IP "ev_prepare_init (ev_prepare *, callback)" 4 2916.IP "ev_prepare_init (ev_prepare *, callback)" 4
878.IX Item "ev_prepare_init (ev_prepare *, callback)" 2917.IX Item "ev_prepare_init (ev_prepare *, callback)"
879.PD 0 2918.PD 0
880.IP "ev_check_init (ev_check *, callback)" 4 2919.IP "ev_check_init (ev_check *, callback)" 4
881.IX Item "ev_check_init (ev_check *, callback)" 2920.IX Item "ev_check_init (ev_check *, callback)"
882.PD 2921.PD
883Initialises and configures the prepare or check watcher \- they have no 2922Initialises and configures the prepare or check watcher \- they have no
884parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR 2923parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
885macros, but using them is utterly, utterly and completely pointless. 2924macros, but using them is utterly, utterly, utterly and completely
2925pointless.
2926.PP
2927\fIExamples\fR
2928.IX Subsection "Examples"
2929.PP
2930There are a number of principal ways to embed other event loops or modules
2931into libev. Here are some ideas on how to include libadns into libev
2932(there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could
2933use as a working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR embeds a
2934Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 into the
2935Glib event loop).
2936.PP
2937Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
2938and in a check watcher, destroy them and call into libadns. What follows
2939is pseudo-code only of course. This requires you to either use a low
2940priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as
2941the callbacks for the IO/timeout watchers might not have been called yet.
2942.PP
2943.Vb 2
2944\& static ev_io iow [nfd];
2945\& static ev_timer tw;
2946\&
2947\& static void
2948\& io_cb (struct ev_loop *loop, ev_io *w, int revents)
2949\& {
2950\& }
2951\&
2952\& // create io watchers for each fd and a timer before blocking
2953\& static void
2954\& adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
2955\& {
2956\& int timeout = 3600000;
2957\& struct pollfd fds [nfd];
2958\& // actual code will need to loop here and realloc etc.
2959\& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2960\&
2961\& /* the callback is illegal, but won\*(Aqt be called as we stop during check */
2962\& ev_timer_init (&tw, 0, timeout * 1e\-3, 0.);
2963\& ev_timer_start (loop, &tw);
2964\&
2965\& // create one ev_io per pollfd
2966\& for (int i = 0; i < nfd; ++i)
2967\& {
2968\& ev_io_init (iow + i, io_cb, fds [i].fd,
2969\& ((fds [i].events & POLLIN ? EV_READ : 0)
2970\& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
2971\&
2972\& fds [i].revents = 0;
2973\& ev_io_start (loop, iow + i);
2974\& }
2975\& }
2976\&
2977\& // stop all watchers after blocking
2978\& static void
2979\& adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
2980\& {
2981\& ev_timer_stop (loop, &tw);
2982\&
2983\& for (int i = 0; i < nfd; ++i)
2984\& {
2985\& // set the relevant poll flags
2986\& // could also call adns_processreadable etc. here
2987\& struct pollfd *fd = fds + i;
2988\& int revents = ev_clear_pending (iow + i);
2989\& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN;
2990\& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT;
2991\&
2992\& // now stop the watcher
2993\& ev_io_stop (loop, iow + i);
2994\& }
2995\&
2996\& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
2997\& }
2998.Ve
2999.PP
3000Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR
3001in the prepare watcher and would dispose of the check watcher.
3002.PP
3003Method 3: If the module to be embedded supports explicit event
3004notification (libadns does), you can also make use of the actual watcher
3005callbacks, and only destroy/create the watchers in the prepare watcher.
3006.PP
3007.Vb 5
3008\& static void
3009\& timer_cb (EV_P_ ev_timer *w, int revents)
3010\& {
3011\& adns_state ads = (adns_state)w\->data;
3012\& update_now (EV_A);
3013\&
3014\& adns_processtimeouts (ads, &tv_now);
3015\& }
3016\&
3017\& static void
3018\& io_cb (EV_P_ ev_io *w, int revents)
3019\& {
3020\& adns_state ads = (adns_state)w\->data;
3021\& update_now (EV_A);
3022\&
3023\& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now);
3024\& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now);
3025\& }
3026\&
3027\& // do not ever call adns_afterpoll
3028.Ve
3029.PP
3030Method 4: Do not use a prepare or check watcher because the module you
3031want to embed is not flexible enough to support it. Instead, you can
3032override their poll function. The drawback with this solution is that the
3033main loop is now no longer controllable by \s-1EV\s0. The \f(CW\*(C`Glib::EV\*(C'\fR module uses
3034this approach, effectively embedding \s-1EV\s0 as a client into the horrible
3035libglib event loop.
3036.PP
3037.Vb 4
3038\& static gint
3039\& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
3040\& {
3041\& int got_events = 0;
3042\&
3043\& for (n = 0; n < nfds; ++n)
3044\& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
3045\&
3046\& if (timeout >= 0)
3047\& // create/start timer
3048\&
3049\& // poll
3050\& ev_run (EV_A_ 0);
3051\&
3052\& // stop timer again
3053\& if (timeout >= 0)
3054\& ev_timer_stop (EV_A_ &to);
3055\&
3056\& // stop io watchers again \- their callbacks should have set
3057\& for (n = 0; n < nfds; ++n)
3058\& ev_io_stop (EV_A_ iow [n]);
3059\&
3060\& return got_events;
3061\& }
3062.Ve
3063.ie n .SS """ev_embed"" \- when one backend isn't enough..."
3064.el .SS "\f(CWev_embed\fP \- when one backend isn't enough..."
3065.IX Subsection "ev_embed - when one backend isn't enough..."
3066This is a rather advanced watcher type that lets you embed one event loop
3067into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
3068loop, other types of watchers might be handled in a delayed or incorrect
3069fashion and must not be used).
3070.PP
3071There are primarily two reasons you would want that: work around bugs and
3072prioritise I/O.
3073.PP
3074As an example for a bug workaround, the kqueue backend might only support
3075sockets on some platform, so it is unusable as generic backend, but you
3076still want to make use of it because you have many sockets and it scales
3077so nicely. In this case, you would create a kqueue-based loop and embed
3078it into your default loop (which might use e.g. poll). Overall operation
3079will be a bit slower because first libev has to call \f(CW\*(C`poll\*(C'\fR and then
3080\&\f(CW\*(C`kevent\*(C'\fR, but at least you can use both mechanisms for what they are
3081best: \f(CW\*(C`kqueue\*(C'\fR for scalable sockets and \f(CW\*(C`poll\*(C'\fR if you want it to work :)
3082.PP
3083As for prioritising I/O: under rare circumstances you have the case where
3084some fds have to be watched and handled very quickly (with low latency),
3085and even priorities and idle watchers might have too much overhead. In
3086this case you would put all the high priority stuff in one loop and all
3087the rest in a second one, and embed the second one in the first.
3088.PP
3089As long as the watcher is active, the callback will be invoked every
3090time there might be events pending in the embedded loop. The callback
3091must then call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single
3092sweep and invoke their callbacks (the callback doesn't need to invoke the
3093\&\f(CW\*(C`ev_embed_sweep\*(C'\fR function directly, it could also start an idle watcher
3094to give the embedded loop strictly lower priority for example).
3095.PP
3096You can also set the callback to \f(CW0\fR, in which case the embed watcher
3097will automatically execute the embedded loop sweep whenever necessary.
3098.PP
3099Fork detection will be handled transparently while the \f(CW\*(C`ev_embed\*(C'\fR watcher
3100is active, i.e., the embedded loop will automatically be forked when the
3101embedding loop forks. In other cases, the user is responsible for calling
3102\&\f(CW\*(C`ev_loop_fork\*(C'\fR on the embedded loop.
3103.PP
3104Unfortunately, not all backends are embeddable: only the ones returned by
3105\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
3106portable one.
3107.PP
3108So when you want to use this feature you will always have to be prepared
3109that you cannot get an embeddable loop. The recommended way to get around
3110this is to have a separate variables for your embeddable loop, try to
3111create it, and if that fails, use the normal loop for everything.
3112.PP
3113\fI\f(CI\*(C`ev_embed\*(C'\fI and fork\fR
3114.IX Subsection "ev_embed and fork"
3115.PP
3116While the \f(CW\*(C`ev_embed\*(C'\fR watcher is running, forks in the embedding loop will
3117automatically be applied to the embedded loop as well, so no special
3118fork handling is required in that case. When the watcher is not running,
3119however, it is still the task of the libev user to call \f(CW\*(C`ev_loop_fork ()\*(C'\fR
3120as applicable.
3121.PP
3122\fIWatcher-Specific Functions and Data Members\fR
3123.IX Subsection "Watcher-Specific Functions and Data Members"
3124.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
3125.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
3126.PD 0
3127.IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
3128.IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)"
3129.PD
3130Configures the watcher to embed the given loop, which must be
3131embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
3132invoked automatically, otherwise it is the responsibility of the callback
3133to invoke it (it will continue to be called until the sweep has been done,
3134if you do not want that, you need to temporarily stop the embed watcher).
3135.IP "ev_embed_sweep (loop, ev_embed *)" 4
3136.IX Item "ev_embed_sweep (loop, ev_embed *)"
3137Make a single, non-blocking sweep over the embedded loop. This works
3138similarly to \f(CW\*(C`ev_run (embedded_loop, EVRUN_NOWAIT)\*(C'\fR, but in the most
3139appropriate way for embedded loops.
3140.IP "struct ev_loop *other [read\-only]" 4
3141.IX Item "struct ev_loop *other [read-only]"
3142The embedded event loop.
3143.PP
3144\fIExamples\fR
3145.IX Subsection "Examples"
3146.PP
3147Example: Try to get an embeddable event loop and embed it into the default
3148event loop. If that is not possible, use the default loop. The default
3149loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the embeddable loop is stored in
3150\&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the case no embeddable loop can be
3151used).
3152.PP
3153.Vb 3
3154\& struct ev_loop *loop_hi = ev_default_init (0);
3155\& struct ev_loop *loop_lo = 0;
3156\& ev_embed embed;
3157\&
3158\& // see if there is a chance of getting one that works
3159\& // (remember that a flags value of 0 means autodetection)
3160\& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3161\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3162\& : 0;
3163\&
3164\& // if we got one, then embed it, otherwise default to loop_hi
3165\& if (loop_lo)
3166\& {
3167\& ev_embed_init (&embed, 0, loop_lo);
3168\& ev_embed_start (loop_hi, &embed);
3169\& }
3170\& else
3171\& loop_lo = loop_hi;
3172.Ve
3173.PP
3174Example: Check if kqueue is available but not recommended and create
3175a kqueue backend for use with sockets (which usually work with any
3176kqueue implementation). Store the kqueue/socket\-only event loop in
3177\&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too).
3178.PP
3179.Vb 3
3180\& struct ev_loop *loop = ev_default_init (0);
3181\& struct ev_loop *loop_socket = 0;
3182\& ev_embed embed;
3183\&
3184\& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3185\& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3186\& {
3187\& ev_embed_init (&embed, 0, loop_socket);
3188\& ev_embed_start (loop, &embed);
3189\& }
3190\&
3191\& if (!loop_socket)
3192\& loop_socket = loop;
3193\&
3194\& // now use loop_socket for all sockets, and loop for everything else
3195.Ve
3196.ie n .SS """ev_fork"" \- the audacity to resume the event loop after a fork"
3197.el .SS "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
3198.IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
3199Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
3200whoever is a good citizen cared to tell libev about it by calling
3201\&\f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the
3202event loop blocks next and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called,
3203and only in the child after the fork. If whoever good citizen calling
3204\&\f(CW\*(C`ev_default_fork\*(C'\fR cheats and calls it in the wrong process, the fork
3205handlers will be invoked, too, of course.
3206.PP
3207\fIThe special problem of life after fork \- how is it possible?\fR
3208.IX Subsection "The special problem of life after fork - how is it possible?"
3209.PP
3210Most uses of \f(CW\*(C`fork()\*(C'\fR consist of forking, then some simple calls to set
3211up/change the process environment, followed by a call to \f(CW\*(C`exec()\*(C'\fR. This
3212sequence should be handled by libev without any problems.
3213.PP
3214This changes when the application actually wants to do event handling
3215in the child, or both parent in child, in effect \*(L"continuing\*(R" after the
3216fork.
3217.PP
3218The default mode of operation (for libev, with application help to detect
3219forks) is to duplicate all the state in the child, as would be expected
3220when \fIeither\fR the parent \fIor\fR the child process continues.
3221.PP
3222When both processes want to continue using libev, then this is usually the
3223wrong result. In that case, usually one process (typically the parent) is
3224supposed to continue with all watchers in place as before, while the other
3225process typically wants to start fresh, i.e. without any active watchers.
3226.PP
3227The cleanest and most efficient way to achieve that with libev is to
3228simply create a new event loop, which of course will be \*(L"empty\*(R", and
3229use that for new watchers. This has the advantage of not touching more
3230memory than necessary, and thus avoiding the copy-on-write, and the
3231disadvantage of having to use multiple event loops (which do not support
3232signal watchers).
3233.PP
3234When this is not possible, or you want to use the default loop for
3235other reasons, then in the process that wants to start \*(L"fresh\*(R", call
3236\&\f(CW\*(C`ev_loop_destroy (EV_DEFAULT)\*(C'\fR followed by \f(CW\*(C`ev_default_loop (...)\*(C'\fR.
3237Destroying the default loop will \*(L"orphan\*(R" (not stop) all registered
3238watchers, so you have to be careful not to execute code that modifies
3239those watchers. Note also that in that case, you have to re-register any
3240signal watchers.
3241.PP
3242\fIWatcher-Specific Functions and Data Members\fR
3243.IX Subsection "Watcher-Specific Functions and Data Members"
3244.IP "ev_fork_init (ev_fork *, callback)" 4
3245.IX Item "ev_fork_init (ev_fork *, callback)"
3246Initialises and configures the fork watcher \- it has no parameters of any
3247kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
3248really.
3249.ie n .SS """ev_cleanup"" \- even the best things end"
3250.el .SS "\f(CWev_cleanup\fP \- even the best things end"
3251.IX Subsection "ev_cleanup - even the best things end"
3252Cleanup watchers are called just before the event loop is being destroyed
3253by a call to \f(CW\*(C`ev_loop_destroy\*(C'\fR.
3254.PP
3255While there is no guarantee that the event loop gets destroyed, cleanup
3256watchers provide a convenient method to install cleanup hooks for your
3257program, worker threads and so on \- you just to make sure to destroy the
3258loop when you want them to be invoked.
3259.PP
3260Cleanup watchers are invoked in the same way as any other watcher. Unlike
3261all other watchers, they do not keep a reference to the event loop (which
3262makes a lot of sense if you think about it). Like all other watchers, you
3263can call libev functions in the callback, except \f(CW\*(C`ev_cleanup_start\*(C'\fR.
3264.PP
3265\fIWatcher-Specific Functions and Data Members\fR
3266.IX Subsection "Watcher-Specific Functions and Data Members"
3267.IP "ev_cleanup_init (ev_cleanup *, callback)" 4
3268.IX Item "ev_cleanup_init (ev_cleanup *, callback)"
3269Initialises and configures the cleanup watcher \- it has no parameters of
3270any kind. There is a \f(CW\*(C`ev_cleanup_set\*(C'\fR macro, but using it is utterly
3271pointless, I assure you.
3272.PP
3273Example: Register an atexit handler to destroy the default loop, so any
3274cleanup functions are called.
3275.PP
3276.Vb 5
3277\& static void
3278\& program_exits (void)
3279\& {
3280\& ev_loop_destroy (EV_DEFAULT_UC);
3281\& }
3282\&
3283\& ...
3284\& atexit (program_exits);
3285.Ve
3286.ie n .SS """ev_async"" \- how to wake up an event loop"
3287.el .SS "\f(CWev_async\fP \- how to wake up an event loop"
3288.IX Subsection "ev_async - how to wake up an event loop"
3289In general, you cannot use an \f(CW\*(C`ev_run\*(C'\fR from multiple threads or other
3290asynchronous sources such as signal handlers (as opposed to multiple event
3291loops \- those are of course safe to use in different threads).
3292.PP
3293Sometimes, however, you need to wake up an event loop you do not control,
3294for example because it belongs to another thread. This is what \f(CW\*(C`ev_async\*(C'\fR
3295watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you can signal
3296it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal safe.
3297.PP
3298This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals,
3299too, are asynchronous in nature, and signals, too, will be compressed
3300(i.e. the number of callback invocations may be less than the number of
3301\&\f(CW\*(C`ev_async_sent\*(C'\fR calls).
3302.PP
3303Unlike \f(CW\*(C`ev_signal\*(C'\fR watchers, \f(CW\*(C`ev_async\*(C'\fR works with any event loop, not
3304just the default loop.
3305.PP
3306\fIQueueing\fR
3307.IX Subsection "Queueing"
3308.PP
3309\&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason
3310is that the author does not know of a simple (or any) algorithm for a
3311multiple-writer-single-reader queue that works in all cases and doesn't
3312need elaborate support such as pthreads or unportable memory access
3313semantics.
3314.PP
3315That means that if you want to queue data, you have to provide your own
3316queue. But at least I can tell you how to implement locking around your
3317queue:
3318.IP "queueing from a signal handler context" 4
3319.IX Item "queueing from a signal handler context"
3320To implement race-free queueing, you simply add to the queue in the signal
3321handler but you block the signal handler in the watcher callback. Here is
3322an example that does that for some fictitious \s-1SIGUSR1\s0 handler:
3323.Sp
3324.Vb 1
3325\& static ev_async mysig;
3326\&
3327\& static void
3328\& sigusr1_handler (void)
3329\& {
3330\& sometype data;
3331\&
3332\& // no locking etc.
3333\& queue_put (data);
3334\& ev_async_send (EV_DEFAULT_ &mysig);
3335\& }
3336\&
3337\& static void
3338\& mysig_cb (EV_P_ ev_async *w, int revents)
3339\& {
3340\& sometype data;
3341\& sigset_t block, prev;
3342\&
3343\& sigemptyset (&block);
3344\& sigaddset (&block, SIGUSR1);
3345\& sigprocmask (SIG_BLOCK, &block, &prev);
3346\&
3347\& while (queue_get (&data))
3348\& process (data);
3349\&
3350\& if (sigismember (&prev, SIGUSR1)
3351\& sigprocmask (SIG_UNBLOCK, &block, 0);
3352\& }
3353.Ve
3354.Sp
3355(Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR
3356instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it
3357either...).
3358.IP "queueing from a thread context" 4
3359.IX Item "queueing from a thread context"
3360The strategy for threads is different, as you cannot (easily) block
3361threads but you can easily preempt them, so to queue safely you need to
3362employ a traditional mutex lock, such as in this pthread example:
3363.Sp
3364.Vb 2
3365\& static ev_async mysig;
3366\& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
3367\&
3368\& static void
3369\& otherthread (void)
3370\& {
3371\& // only need to lock the actual queueing operation
3372\& pthread_mutex_lock (&mymutex);
3373\& queue_put (data);
3374\& pthread_mutex_unlock (&mymutex);
3375\&
3376\& ev_async_send (EV_DEFAULT_ &mysig);
3377\& }
3378\&
3379\& static void
3380\& mysig_cb (EV_P_ ev_async *w, int revents)
3381\& {
3382\& pthread_mutex_lock (&mymutex);
3383\&
3384\& while (queue_get (&data))
3385\& process (data);
3386\&
3387\& pthread_mutex_unlock (&mymutex);
3388\& }
3389.Ve
3390.PP
3391\fIWatcher-Specific Functions and Data Members\fR
3392.IX Subsection "Watcher-Specific Functions and Data Members"
3393.IP "ev_async_init (ev_async *, callback)" 4
3394.IX Item "ev_async_init (ev_async *, callback)"
3395Initialises and configures the async watcher \- it has no parameters of any
3396kind. There is a \f(CW\*(C`ev_async_set\*(C'\fR macro, but using it is utterly pointless,
3397trust me.
3398.IP "ev_async_send (loop, ev_async *)" 4
3399.IX Item "ev_async_send (loop, ev_async *)"
3400Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds
3401an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop. Unlike
3402\&\f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do from other threads, signal or
3403similar contexts (see the discussion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the embedding
3404section below on what exactly this means).
3405.Sp
3406Note that, as with other watchers in libev, multiple events might get
3407compressed into a single callback invocation (another way to look at this
3408is that \f(CW\*(C`ev_async\*(C'\fR watchers are level-triggered, set on \f(CW\*(C`ev_async_send\*(C'\fR,
3409reset when the event loop detects that).
3410.Sp
3411This call incurs the overhead of a system call only once per event loop
3412iteration, so while the overhead might be noticeable, it doesn't apply to
3413repeated calls to \f(CW\*(C`ev_async_send\*(C'\fR for the same event loop.
3414.IP "bool = ev_async_pending (ev_async *)" 4
3415.IX Item "bool = ev_async_pending (ev_async *)"
3416Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the
3417watcher but the event has not yet been processed (or even noted) by the
3418event loop.
3419.Sp
3420\&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When
3421the loop iterates next and checks for the watcher to have become active,
3422it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very
3423quickly check whether invoking the loop might be a good idea.
3424.Sp
3425Not that this does \fInot\fR check whether the watcher itself is pending,
3426only whether it has been requested to make this watcher pending: there
3427is a time window between the event loop checking and resetting the async
3428notification, and the callback being invoked.
886.SH "OTHER FUNCTIONS" 3429.SH "OTHER FUNCTIONS"
887.IX Header "OTHER FUNCTIONS" 3430.IX Header "OTHER FUNCTIONS"
888There are some other functions of possible interest. Described. Here. Now. 3431There are some other functions of possible interest. Described. Here. Now.
889.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4 3432.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
890.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 3433.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"
891This function combines a simple timer and an I/O watcher, calls your 3434This function combines a simple timer and an I/O watcher, calls your
892callback on whichever event happens first and automatically stop both 3435callback on whichever event happens first and automatically stops both
893watchers. This is useful if you want to wait for a single event on an fd 3436watchers. This is useful if you want to wait for a single event on an fd
894or timeout without having to allocate/configure/start/stop/free one or 3437or timeout without having to allocate/configure/start/stop/free one or
895more watchers yourself. 3438more watchers yourself.
896.Sp 3439.Sp
897If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and events 3440If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and the
898is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for the given \f(CW\*(C`fd\*(C'\fR and 3441\&\f(CW\*(C`events\*(C'\fR argument is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for
899\&\f(CW\*(C`events\*(C'\fR set will be craeted and started. 3442the given \f(CW\*(C`fd\*(C'\fR and \f(CW\*(C`events\*(C'\fR set will be created and started.
900.Sp 3443.Sp
901If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be 3444If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
902started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and 3445started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
903repeat = 0) will be started. While \f(CW0\fR is a valid timeout, it is of 3446repeat = 0) will be started. \f(CW0\fR is a valid timeout.
904dubious value.
905.Sp 3447.Sp
906The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets 3448The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and is
907passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of 3449passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
908\&\f(CW\*(C`EV_ERROR\*(C'\fR, \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or \f(CW\*(C`EV_TIMEOUT\*(C'\fR) and the \f(CW\*(C`arg\*(C'\fR 3450\&\f(CW\*(C`EV_ERROR\*(C'\fR, \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or \f(CW\*(C`EV_TIMER\*(C'\fR) and the \f(CW\*(C`arg\*(C'\fR
909value passed to \f(CW\*(C`ev_once\*(C'\fR: 3451value passed to \f(CW\*(C`ev_once\*(C'\fR. Note that it is possible to receive \fIboth\fR
3452a timeout and an io event at the same time \- you probably should give io
3453events precedence.
3454.Sp
3455Example: wait up to ten seconds for data to appear on \s-1STDIN_FILENO\s0.
910.Sp 3456.Sp
911.Vb 7 3457.Vb 7
912\& static void stdin_ready (int revents, void *arg) 3458\& static void stdin_ready (int revents, void *arg)
913\& { 3459\& {
914\& if (revents & EV_TIMEOUT)
915\& /* doh, nothing entered */;
916\& else if (revents & EV_READ) 3460\& if (revents & EV_READ)
917\& /* stdin might have data for us, joy! */; 3461\& /* stdin might have data for us, joy! */;
3462\& else if (revents & EV_TIMER)
3463\& /* doh, nothing entered */;
918\& } 3464\& }
919.Ve 3465\&
920.Sp
921.Vb 1
922\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); 3466\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
923.Ve 3467.Ve
924.IP "ev_feed_event (loop, watcher, int events)" 4
925.IX Item "ev_feed_event (loop, watcher, int events)"
926Feeds the given event set into the event loop, as if the specified event
927had happened for the specified watcher (which must be a pointer to an
928initialised but not necessarily started event watcher).
929.IP "ev_feed_fd_event (loop, int fd, int revents)" 4 3468.IP "ev_feed_fd_event (loop, int fd, int revents)" 4
930.IX Item "ev_feed_fd_event (loop, int fd, int revents)" 3469.IX Item "ev_feed_fd_event (loop, int fd, int revents)"
931Feed an event on the given fd, as if a file descriptor backend detected 3470Feed an event on the given fd, as if a file descriptor backend detected
932the given events it. 3471the given events it.
933.IP "ev_feed_signal_event (loop, int signum)" 4 3472.IP "ev_feed_signal_event (loop, int signum)" 4
934.IX Item "ev_feed_signal_event (loop, int signum)" 3473.IX Item "ev_feed_signal_event (loop, int signum)"
935Feed an event as if the given signal occured (loop must be the default loop!). 3474Feed an event as if the given signal occurred (\f(CW\*(C`loop\*(C'\fR must be the default
3475loop!).
936.SH "LIBEVENT EMULATION" 3476.SH "LIBEVENT EMULATION"
937.IX Header "LIBEVENT EMULATION" 3477.IX Header "LIBEVENT EMULATION"
938Libev offers a compatibility emulation layer for libevent. It cannot 3478Libev offers a compatibility emulation layer for libevent. It cannot
939emulate the internals of libevent, so here are some usage hints: 3479emulate the internals of libevent, so here are some usage hints:
3480.IP "\(bu" 4
940.IP "* Use it by including <event.h>, as usual." 4 3481Use it by including <event.h>, as usual.
941.IX Item "Use it by including <event.h>, as usual." 3482.IP "\(bu" 4
942.PD 0 3483The following members are fully supported: ev_base, ev_callback,
943.IP "* The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4 3484ev_arg, ev_fd, ev_res, ev_events.
944.IX Item "The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 3485.IP "\(bu" 4
945.IP "* Avoid using ev_flags and the EVLIST_*\-macros, while it is maintained by libev, it does not work exactly the same way as in libevent (consider it a private \s-1API\s0)." 4 3486Avoid using ev_flags and the EVLIST_*\-macros, while it is
946.IX Item "Avoid using ev_flags and the EVLIST_*-macros, while it is maintained by libev, it does not work exactly the same way as in libevent (consider it a private API)." 3487maintained by libev, it does not work exactly the same way as in libevent (consider
947.IP "* Priorities are not currently supported. Initialising priorities will fail and all watchers will have the same priority, even though there is an ev_pri field." 4 3488it a private \s-1API\s0).
948.IX Item "Priorities are not currently supported. Initialising priorities will fail and all watchers will have the same priority, even though there is an ev_pri field." 3489.IP "\(bu" 4
3490Priorities are not currently supported. Initialising priorities
3491will fail and all watchers will have the same priority, even though there
3492is an ev_pri field.
3493.IP "\(bu" 4
3494In libevent, the last base created gets the signals, in libev, the
3495first base created (== the default loop) gets the signals.
3496.IP "\(bu" 4
949.IP "* Other members are not supported." 4 3497Other members are not supported.
950.IX Item "Other members are not supported." 3498.IP "\(bu" 4
951.IP "* The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need to use the libev header file and library." 4 3499The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need
952.IX Item "The libev emulation is not ABI compatible to libevent, you need to use the libev header file and library." 3500to use the libev header file and library.
953.PD
954.SH "\*(C+ SUPPORT" 3501.SH "\*(C+ SUPPORT"
955.IX Header " SUPPORT" 3502.IX Header " SUPPORT"
956\&\s-1TBD\s0. 3503Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
3504you to use some convenience methods to start/stop watchers and also change
3505the callback model to a model using method callbacks on objects.
3506.PP
3507To use it,
3508.PP
3509.Vb 1
3510\& #include <ev++.h>
3511.Ve
3512.PP
3513This automatically includes \fIev.h\fR and puts all of its definitions (many
3514of them macros) into the global namespace. All \*(C+ specific things are
3515put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding
3516options as \fIev.h\fR, most notably \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR.
3517.PP
3518Care has been taken to keep the overhead low. The only data member the \*(C+
3519classes add (compared to plain C\-style watchers) is the event loop pointer
3520that the watcher is associated with (or no additional members at all if
3521you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
3522.PP
3523Currently, functions, and static and non-static member functions can be
3524used as callbacks. Other types should be easy to add as long as they only
3525need one additional pointer for context. If you need support for other
3526types of functors please contact the author (preferably after implementing
3527it).
3528.PP
3529Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
3530.ie n .IP """ev::READ"", ""ev::WRITE"" etc." 4
3531.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
3532.IX Item "ev::READ, ev::WRITE etc."
3533These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
3534macros from \fIev.h\fR.
3535.ie n .IP """ev::tstamp"", ""ev::now""" 4
3536.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
3537.IX Item "ev::tstamp, ev::now"
3538Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
3539.ie n .IP """ev::io"", ""ev::timer"", ""ev::periodic"", ""ev::idle"", ""ev::sig"" etc." 4
3540.el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
3541.IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
3542For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
3543the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
3544which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
3545defines by many implementations.
3546.Sp
3547All of those classes have these methods:
3548.RS 4
3549.IP "ev::TYPE::TYPE ()" 4
3550.IX Item "ev::TYPE::TYPE ()"
3551.PD 0
3552.IP "ev::TYPE::TYPE (loop)" 4
3553.IX Item "ev::TYPE::TYPE (loop)"
3554.IP "ev::TYPE::~TYPE" 4
3555.IX Item "ev::TYPE::~TYPE"
3556.PD
3557The constructor (optionally) takes an event loop to associate the watcher
3558with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR.
3559.Sp
3560The constructor calls \f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the
3561\&\f(CW\*(C`set\*(C'\fR method before starting it.
3562.Sp
3563It will not set a callback, however: You have to call the templated \f(CW\*(C`set\*(C'\fR
3564method to set a callback before you can start the watcher.
3565.Sp
3566(The reason why you have to use a method is a limitation in \*(C+ which does
3567not allow explicit template arguments for constructors).
3568.Sp
3569The destructor automatically stops the watcher if it is active.
3570.IP "w\->set<class, &class::method> (object *)" 4
3571.IX Item "w->set<class, &class::method> (object *)"
3572This method sets the callback method to call. The method has to have a
3573signature of \f(CW\*(C`void (*)(ev_TYPE &, int)\*(C'\fR, it receives the watcher as
3574first argument and the \f(CW\*(C`revents\*(C'\fR as second. The object must be given as
3575parameter and is stored in the \f(CW\*(C`data\*(C'\fR member of the watcher.
3576.Sp
3577This method synthesizes efficient thunking code to call your method from
3578the C callback that libev requires. If your compiler can inline your
3579callback (i.e. it is visible to it at the place of the \f(CW\*(C`set\*(C'\fR call and
3580your compiler is good :), then the method will be fully inlined into the
3581thunking function, making it as fast as a direct C callback.
3582.Sp
3583Example: simple class declaration and watcher initialisation
3584.Sp
3585.Vb 4
3586\& struct myclass
3587\& {
3588\& void io_cb (ev::io &w, int revents) { }
3589\& }
3590\&
3591\& myclass obj;
3592\& ev::io iow;
3593\& iow.set <myclass, &myclass::io_cb> (&obj);
3594.Ve
3595.IP "w\->set (object *)" 4
3596.IX Item "w->set (object *)"
3597This is a variation of a method callback \- leaving out the method to call
3598will default the method to \f(CW\*(C`operator ()\*(C'\fR, which makes it possible to use
3599functor objects without having to manually specify the \f(CW\*(C`operator ()\*(C'\fR all
3600the time. Incidentally, you can then also leave out the template argument
3601list.
3602.Sp
3603The \f(CW\*(C`operator ()\*(C'\fR method prototype must be \f(CW\*(C`void operator ()(watcher &w,
3604int revents)\*(C'\fR.
3605.Sp
3606See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
3607.Sp
3608Example: use a functor object as callback.
3609.Sp
3610.Vb 7
3611\& struct myfunctor
3612\& {
3613\& void operator() (ev::io &w, int revents)
3614\& {
3615\& ...
3616\& }
3617\& }
3618\&
3619\& myfunctor f;
3620\&
3621\& ev::io w;
3622\& w.set (&f);
3623.Ve
3624.IP "w\->set<function> (void *data = 0)" 4
3625.IX Item "w->set<function> (void *data = 0)"
3626Also sets a callback, but uses a static method or plain function as
3627callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
3628\&\f(CW\*(C`data\*(C'\fR member and is free for you to use.
3629.Sp
3630The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
3631.Sp
3632See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
3633.Sp
3634Example: Use a plain function as callback.
3635.Sp
3636.Vb 2
3637\& static void io_cb (ev::io &w, int revents) { }
3638\& iow.set <io_cb> ();
3639.Ve
3640.IP "w\->set (loop)" 4
3641.IX Item "w->set (loop)"
3642Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
3643do this when the watcher is inactive (and not pending either).
3644.IP "w\->set ([arguments])" 4
3645.IX Item "w->set ([arguments])"
3646Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same arguments. Either this
3647method or a suitable start method must be called at least once. Unlike the
3648C counterpart, an active watcher gets automatically stopped and restarted
3649when reconfiguring it with this method.
3650.IP "w\->start ()" 4
3651.IX Item "w->start ()"
3652Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
3653constructor already stores the event loop.
3654.IP "w\->start ([arguments])" 4
3655.IX Item "w->start ([arguments])"
3656Instead of calling \f(CW\*(C`set\*(C'\fR and \f(CW\*(C`start\*(C'\fR methods separately, it is often
3657convenient to wrap them in one call. Uses the same type of arguments as
3658the configure \f(CW\*(C`set\*(C'\fR method of the watcher.
3659.IP "w\->stop ()" 4
3660.IX Item "w->stop ()"
3661Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
3662.ie n .IP "w\->again () (""ev::timer"", ""ev::periodic"" only)" 4
3663.el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
3664.IX Item "w->again () (ev::timer, ev::periodic only)"
3665For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
3666\&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
3667.ie n .IP "w\->sweep () (""ev::embed"" only)" 4
3668.el .IP "w\->sweep () (\f(CWev::embed\fR only)" 4
3669.IX Item "w->sweep () (ev::embed only)"
3670Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR.
3671.ie n .IP "w\->update () (""ev::stat"" only)" 4
3672.el .IP "w\->update () (\f(CWev::stat\fR only)" 4
3673.IX Item "w->update () (ev::stat only)"
3674Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
3675.RE
3676.RS 4
3677.RE
3678.PP
3679Example: Define a class with two I/O and idle watchers, start the I/O
3680watchers in the constructor.
3681.PP
3682.Vb 5
3683\& class myclass
3684\& {
3685\& ev::io io ; void io_cb (ev::io &w, int revents);
3686\& ev::io2 io2 ; void io2_cb (ev::io &w, int revents);
3687\& ev::idle idle; void idle_cb (ev::idle &w, int revents);
3688\&
3689\& myclass (int fd)
3690\& {
3691\& io .set <myclass, &myclass::io_cb > (this);
3692\& io2 .set <myclass, &myclass::io2_cb > (this);
3693\& idle.set <myclass, &myclass::idle_cb> (this);
3694\&
3695\& io.set (fd, ev::WRITE); // configure the watcher
3696\& io.start (); // start it whenever convenient
3697\&
3698\& io2.start (fd, ev::READ); // set + start in one call
3699\& }
3700\& };
3701.Ve
3702.SH "OTHER LANGUAGE BINDINGS"
3703.IX Header "OTHER LANGUAGE BINDINGS"
3704Libev does not offer other language bindings itself, but bindings for a
3705number of languages exist in the form of third-party packages. If you know
3706any interesting language binding in addition to the ones listed here, drop
3707me a note.
3708.IP "Perl" 4
3709.IX Item "Perl"
3710The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test
3711libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module,
3712there are additional modules that implement libev-compatible interfaces
3713to \f(CW\*(C`libadns\*(C'\fR (\f(CW\*(C`EV::ADNS\*(C'\fR, but \f(CW\*(C`AnyEvent::DNS\*(C'\fR is preferred nowadays),
3714\&\f(CW\*(C`Net::SNMP\*(C'\fR (\f(CW\*(C`Net::SNMP::EV\*(C'\fR) and the \f(CW\*(C`libglib\*(C'\fR event core (\f(CW\*(C`Glib::EV\*(C'\fR
3715and \f(CW\*(C`EV::Glib\*(C'\fR).
3716.Sp
3717It can be found and installed via \s-1CPAN\s0, its homepage is at
3718<http://software.schmorp.de/pkg/EV>.
3719.IP "Python" 4
3720.IX Item "Python"
3721Python bindings can be found at <http://code.google.com/p/pyev/>. It
3722seems to be quite complete and well-documented.
3723.IP "Ruby" 4
3724.IX Item "Ruby"
3725Tony Arcieri has written a ruby extension that offers access to a subset
3726of the libev \s-1API\s0 and adds file handle abstractions, asynchronous \s-1DNS\s0 and
3727more on top of it. It can be found via gem servers. Its homepage is at
3728<http://rev.rubyforge.org/>.
3729.Sp
3730Roger Pack reports that using the link order \f(CW\*(C`\-lws2_32 \-lmsvcrt\-ruby\-190\*(C'\fR
3731makes rev work even on mingw.
3732.IP "Haskell" 4
3733.IX Item "Haskell"
3734A haskell binding to libev is available at
3735<http://hackage.haskell.org/cgi\-bin/hackage\-scripts/package/hlibev>.
3736.IP "D" 4
3737.IX Item "D"
3738Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
3739be found at <http://proj.llucax.com.ar/wiki/evd>.
3740.IP "Ocaml" 4
3741.IX Item "Ocaml"
3742Erkki Seppala has written Ocaml bindings for libev, to be found at
3743<http://modeemi.cs.tut.fi/~flux/software/ocaml\-ev/>.
3744.IP "Lua" 4
3745.IX Item "Lua"
3746Brian Maher has written a partial interface to libev for lua (at the
3747time of this writing, only \f(CW\*(C`ev_io\*(C'\fR and \f(CW\*(C`ev_timer\*(C'\fR), to be found at
3748<http://github.com/brimworks/lua\-ev>.
3749.SH "MACRO MAGIC"
3750.IX Header "MACRO MAGIC"
3751Libev can be compiled with a variety of options, the most fundamental
3752of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most)
3753functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
3754.PP
3755To make it easier to write programs that cope with either variant, the
3756following macros are defined:
3757.ie n .IP """EV_A"", ""EV_A_""" 4
3758.el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
3759.IX Item "EV_A, EV_A_"
3760This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
3761loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
3762\&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
3763.Sp
3764.Vb 3
3765\& ev_unref (EV_A);
3766\& ev_timer_add (EV_A_ watcher);
3767\& ev_run (EV_A_ 0);
3768.Ve
3769.Sp
3770It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
3771which is often provided by the following macro.
3772.ie n .IP """EV_P"", ""EV_P_""" 4
3773.el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
3774.IX Item "EV_P, EV_P_"
3775This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
3776loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
3777\&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
3778.Sp
3779.Vb 2
3780\& // this is how ev_unref is being declared
3781\& static void ev_unref (EV_P);
3782\&
3783\& // this is how you can declare your typical callback
3784\& static void cb (EV_P_ ev_timer *w, int revents)
3785.Ve
3786.Sp
3787It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
3788suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
3789.ie n .IP """EV_DEFAULT"", ""EV_DEFAULT_""" 4
3790.el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
3791.IX Item "EV_DEFAULT, EV_DEFAULT_"
3792Similar to the other two macros, this gives you the value of the default
3793loop, if multiple loops are supported (\*(L"ev loop default\*(R").
3794.ie n .IP """EV_DEFAULT_UC"", ""EV_DEFAULT_UC_""" 4
3795.el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
3796.IX Item "EV_DEFAULT_UC, EV_DEFAULT_UC_"
3797Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the
3798default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour
3799is undefined when the default loop has not been initialised by a previous
3800execution of \f(CW\*(C`EV_DEFAULT\*(C'\fR, \f(CW\*(C`EV_DEFAULT_\*(C'\fR or \f(CW\*(C`ev_default_init (...)\*(C'\fR.
3801.Sp
3802It is often prudent to use \f(CW\*(C`EV_DEFAULT\*(C'\fR when initialising the first
3803watcher in a function but use \f(CW\*(C`EV_DEFAULT_UC\*(C'\fR afterwards.
3804.PP
3805Example: Declare and initialise a check watcher, utilising the above
3806macros so it will work regardless of whether multiple loops are supported
3807or not.
3808.PP
3809.Vb 5
3810\& static void
3811\& check_cb (EV_P_ ev_timer *w, int revents)
3812\& {
3813\& ev_check_stop (EV_A_ w);
3814\& }
3815\&
3816\& ev_check check;
3817\& ev_check_init (&check, check_cb);
3818\& ev_check_start (EV_DEFAULT_ &check);
3819\& ev_run (EV_DEFAULT_ 0);
3820.Ve
3821.SH "EMBEDDING"
3822.IX Header "EMBEDDING"
3823Libev can (and often is) directly embedded into host
3824applications. Examples of applications that embed it include the Deliantra
3825Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
3826and rxvt-unicode.
3827.PP
3828The goal is to enable you to just copy the necessary files into your
3829source directory without having to change even a single line in them, so
3830you can easily upgrade by simply copying (or having a checked-out copy of
3831libev somewhere in your source tree).
3832.SS "\s-1FILESETS\s0"
3833.IX Subsection "FILESETS"
3834Depending on what features you need you need to include one or more sets of files
3835in your application.
3836.PP
3837\fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR
3838.IX Subsection "CORE EVENT LOOP"
3839.PP
3840To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
3841configuration (no autoconf):
3842.PP
3843.Vb 2
3844\& #define EV_STANDALONE 1
3845\& #include "ev.c"
3846.Ve
3847.PP
3848This will automatically include \fIev.h\fR, too, and should be done in a
3849single C source file only to provide the function implementations. To use
3850it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best
3851done by writing a wrapper around \fIev.h\fR that you can include instead and
3852where you can put other configuration options):
3853.PP
3854.Vb 2
3855\& #define EV_STANDALONE 1
3856\& #include "ev.h"
3857.Ve
3858.PP
3859Both header files and implementation files can be compiled with a \*(C+
3860compiler (at least, that's a stated goal, and breakage will be treated
3861as a bug).
3862.PP
3863You need the following files in your source tree, or in a directory
3864in your include path (e.g. in libev/ when using \-Ilibev):
3865.PP
3866.Vb 4
3867\& ev.h
3868\& ev.c
3869\& ev_vars.h
3870\& ev_wrap.h
3871\&
3872\& ev_win32.c required on win32 platforms only
3873\&
3874\& ev_select.c only when select backend is enabled (which is enabled by default)
3875\& ev_poll.c only when poll backend is enabled (disabled by default)
3876\& ev_epoll.c only when the epoll backend is enabled (disabled by default)
3877\& ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
3878\& ev_port.c only when the solaris port backend is enabled (disabled by default)
3879.Ve
3880.PP
3881\&\fIev.c\fR includes the backend files directly when enabled, so you only need
3882to compile this single file.
3883.PP
3884\fI\s-1LIBEVENT\s0 \s-1COMPATIBILITY\s0 \s-1API\s0\fR
3885.IX Subsection "LIBEVENT COMPATIBILITY API"
3886.PP
3887To include the libevent compatibility \s-1API\s0, also include:
3888.PP
3889.Vb 1
3890\& #include "event.c"
3891.Ve
3892.PP
3893in the file including \fIev.c\fR, and:
3894.PP
3895.Vb 1
3896\& #include "event.h"
3897.Ve
3898.PP
3899in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR.
3900.PP
3901You need the following additional files for this:
3902.PP
3903.Vb 2
3904\& event.h
3905\& event.c
3906.Ve
3907.PP
3908\fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR
3909.IX Subsection "AUTOCONF SUPPORT"
3910.PP
3911Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your configuration in
3912whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
3913\&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then
3914include \fIconfig.h\fR and configure itself accordingly.
3915.PP
3916For this of course you need the m4 file:
3917.PP
3918.Vb 1
3919\& libev.m4
3920.Ve
3921.SS "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0"
3922.IX Subsection "PREPROCESSOR SYMBOLS/MACROS"
3923Libev can be configured via a variety of preprocessor symbols you have to
3924define before including (or compiling) any of its files. The default in
3925the absence of autoconf is documented for every option.
3926.PP
3927Symbols marked with \*(L"(h)\*(R" do not change the \s-1ABI\s0, and can have different
3928values when compiling libev vs. including \fIev.h\fR, so it is permissible
3929to redefine them before including \fIev.h\fR without breaking compatibility
3930to a compiled library. All other symbols change the \s-1ABI\s0, which means all
3931users of libev and the libev code itself must be compiled with compatible
3932settings.
3933.IP "\s-1EV_COMPAT3\s0 (h)" 4
3934.IX Item "EV_COMPAT3 (h)"
3935Backwards compatibility is a major concern for libev. This is why this
3936release of libev comes with wrappers for the functions and symbols that
3937have been renamed between libev version 3 and 4.
3938.Sp
3939You can disable these wrappers (to test compatibility with future
3940versions) by defining \f(CW\*(C`EV_COMPAT3\*(C'\fR to \f(CW0\fR when compiling your
3941sources. This has the additional advantage that you can drop the \f(CW\*(C`struct\*(C'\fR
3942from \f(CW\*(C`struct ev_loop\*(C'\fR declarations, as libev will provide an \f(CW\*(C`ev_loop\*(C'\fR
3943typedef in that case.
3944.Sp
3945In some future version, the default for \f(CW\*(C`EV_COMPAT3\*(C'\fR will become \f(CW0\fR,
3946and in some even more future version the compatibility code will be
3947removed completely.
3948.IP "\s-1EV_STANDALONE\s0 (h)" 4
3949.IX Item "EV_STANDALONE (h)"
3950Must always be \f(CW1\fR if you do not use autoconf configuration, which
3951keeps libev from including \fIconfig.h\fR, and it also defines dummy
3952implementations for some libevent functions (such as logging, which is not
3953supported). It will also not define any of the structs usually found in
3954\&\fIevent.h\fR that are not directly supported by the libev core alone.
3955.Sp
3956In standalone mode, libev will still try to automatically deduce the
3957configuration, but has to be more conservative.
3958.IP "\s-1EV_USE_MONOTONIC\s0" 4
3959.IX Item "EV_USE_MONOTONIC"
3960If defined to be \f(CW1\fR, libev will try to detect the availability of the
3961monotonic clock option at both compile time and runtime. Otherwise no
3962use of the monotonic clock option will be attempted. If you enable this,
3963you usually have to link against librt or something similar. Enabling it
3964when the functionality isn't available is safe, though, although you have
3965to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
3966function is hiding in (often \fI\-lrt\fR). See also \f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
3967.IP "\s-1EV_USE_REALTIME\s0" 4
3968.IX Item "EV_USE_REALTIME"
3969If defined to be \f(CW1\fR, libev will try to detect the availability of the
3970real-time clock option at compile time (and assume its availability
3971at runtime if successful). Otherwise no use of the real-time clock
3972option will be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR
3973by \f(CW\*(C`clock_get (CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect
3974correctness. See the note about libraries in the description of
3975\&\f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. Defaults to the opposite value of
3976\&\f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
3977.IP "\s-1EV_USE_CLOCK_SYSCALL\s0" 4
3978.IX Item "EV_USE_CLOCK_SYSCALL"
3979If defined to be \f(CW1\fR, libev will try to use a direct syscall instead
3980of calling the system-provided \f(CW\*(C`clock_gettime\*(C'\fR function. This option
3981exists because on GNU/Linux, \f(CW\*(C`clock_gettime\*(C'\fR is in \f(CW\*(C`librt\*(C'\fR, but \f(CW\*(C`librt\*(C'\fR
3982unconditionally pulls in \f(CW\*(C`libpthread\*(C'\fR, slowing down single-threaded
3983programs needlessly. Using a direct syscall is slightly slower (in
3984theory), because no optimised vdso implementation can be used, but avoids
3985the pthread dependency. Defaults to \f(CW1\fR on GNU/Linux with glibc 2.x or
3986higher, as it simplifies linking (no need for \f(CW\*(C`\-lrt\*(C'\fR).
3987.IP "\s-1EV_USE_NANOSLEEP\s0" 4
3988.IX Item "EV_USE_NANOSLEEP"
3989If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available
3990and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR.
3991.IP "\s-1EV_USE_EVENTFD\s0" 4
3992.IX Item "EV_USE_EVENTFD"
3993If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
3994available and will probe for kernel support at runtime. This will improve
3995\&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
3996If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
39972.7 or newer, otherwise disabled.
3998.IP "\s-1EV_USE_SELECT\s0" 4
3999.IX Item "EV_USE_SELECT"
4000If undefined or defined to be \f(CW1\fR, libev will compile in support for the
4001\&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at auto-detection will be done: if no
4002other method takes over, select will be it. Otherwise the select backend
4003will not be compiled in.
4004.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
4005.IX Item "EV_SELECT_USE_FD_SET"
4006If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR
4007structure. This is useful if libev doesn't compile due to a missing
4008\&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it mis-guesses the bitset layout
4009on exotic systems. This usually limits the range of file descriptors to
4010some low limit such as 1024 or might have other limitations (winsocket
4011only allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation,
4012configures the maximum size of the \f(CW\*(C`fd_set\*(C'\fR.
4013.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
4014.IX Item "EV_SELECT_IS_WINSOCKET"
4015When defined to \f(CW1\fR, the select backend will assume that
4016select/socket/connect etc. don't understand file descriptors but
4017wants osf handles on win32 (this is the case when the select to
4018be used is the winsock select). This means that it will call
4019\&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
4020it is assumed that all these functions actually work on fds, even
4021on win32. Should not be defined on non\-win32 platforms.
4022.IP "\s-1EV_FD_TO_WIN32_HANDLE\s0(fd)" 4
4023.IX Item "EV_FD_TO_WIN32_HANDLE(fd)"
4024If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map
4025file descriptors to socket handles. When not defining this symbol (the
4026default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually
4027correct. In some cases, programs use their own file descriptor management,
4028in which case they can provide this function to map fds to socket handles.
4029.IP "\s-1EV_WIN32_HANDLE_TO_FD\s0(handle)" 4
4030.IX Item "EV_WIN32_HANDLE_TO_FD(handle)"
4031If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR then libev maps handles to file descriptors
4032using the standard \f(CW\*(C`_open_osfhandle\*(C'\fR function. For programs implementing
4033their own fd to handle mapping, overwriting this function makes it easier
4034to do so. This can be done by defining this macro to an appropriate value.
4035.IP "\s-1EV_WIN32_CLOSE_FD\s0(fd)" 4
4036.IX Item "EV_WIN32_CLOSE_FD(fd)"
4037If programs implement their own fd to handle mapping on win32, then this
4038macro can be used to override the \f(CW\*(C`close\*(C'\fR function, useful to unregister
4039file descriptors again. Note that the replacement function has to close
4040the underlying \s-1OS\s0 handle.
4041.IP "\s-1EV_USE_POLL\s0" 4
4042.IX Item "EV_USE_POLL"
4043If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2)
4044backend. Otherwise it will be enabled on non\-win32 platforms. It
4045takes precedence over select.
4046.IP "\s-1EV_USE_EPOLL\s0" 4
4047.IX Item "EV_USE_EPOLL"
4048If defined to be \f(CW1\fR, libev will compile in support for the Linux
4049\&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime,
4050otherwise another method will be used as fallback. This is the preferred
4051backend for GNU/Linux systems. If undefined, it will be enabled if the
4052headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4053.IP "\s-1EV_USE_KQUEUE\s0" 4
4054.IX Item "EV_USE_KQUEUE"
4055If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
4056\&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime,
4057otherwise another method will be used as fallback. This is the preferred
4058backend for \s-1BSD\s0 and BSD-like systems, although on most BSDs kqueue only
4059supports some types of fds correctly (the only platform we found that
4060supports ptys for example was NetBSD), so kqueue might be compiled in, but
4061not be used unless explicitly requested. The best way to use it is to find
4062out whether kqueue supports your type of fd properly and use an embedded
4063kqueue loop.
4064.IP "\s-1EV_USE_PORT\s0" 4
4065.IX Item "EV_USE_PORT"
4066If defined to be \f(CW1\fR, libev will compile in support for the Solaris
406710 port style backend. Its availability will be detected at runtime,
4068otherwise another method will be used as fallback. This is the preferred
4069backend for Solaris 10 systems.
4070.IP "\s-1EV_USE_DEVPOLL\s0" 4
4071.IX Item "EV_USE_DEVPOLL"
4072Reserved for future expansion, works like the \s-1USE\s0 symbols above.
4073.IP "\s-1EV_USE_INOTIFY\s0" 4
4074.IX Item "EV_USE_INOTIFY"
4075If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
4076interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
4077be detected at runtime. If undefined, it will be enabled if the headers
4078indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4079.IP "\s-1EV_ATOMIC_T\s0" 4
4080.IX Item "EV_ATOMIC_T"
4081Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
4082access is atomic with respect to other threads or signal contexts. No such
4083type is easily found in the C language, so you can provide your own type
4084that you know is safe for your purposes. It is used both for signal handler \*(L"locking\*(R"
4085as well as for signal and thread safety in \f(CW\*(C`ev_async\*(C'\fR watchers.
4086.Sp
4087In the absence of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR
4088(from \fIsignal.h\fR), which is usually good enough on most platforms.
4089.IP "\s-1EV_H\s0 (h)" 4
4090.IX Item "EV_H (h)"
4091The name of the \fIev.h\fR header file used to include it. The default if
4092undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be
4093used to virtually rename the \fIev.h\fR header file in case of conflicts.
4094.IP "\s-1EV_CONFIG_H\s0 (h)" 4
4095.IX Item "EV_CONFIG_H (h)"
4096If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
4097\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
4098\&\f(CW\*(C`EV_H\*(C'\fR, above.
4099.IP "\s-1EV_EVENT_H\s0 (h)" 4
4100.IX Item "EV_EVENT_H (h)"
4101Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea
4102of how the \fIevent.h\fR header can be found, the default is \f(CW"event.h"\fR.
4103.IP "\s-1EV_PROTOTYPES\s0 (h)" 4
4104.IX Item "EV_PROTOTYPES (h)"
4105If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
4106prototypes, but still define all the structs and other symbols. This is
4107occasionally useful if you want to provide your own wrapper functions
4108around libev functions.
4109.IP "\s-1EV_MULTIPLICITY\s0" 4
4110.IX Item "EV_MULTIPLICITY"
4111If undefined or defined to \f(CW1\fR, then all event-loop-specific functions
4112will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create
4113additional independent event loops. Otherwise there will be no support
4114for multiple event loops and there is no first event loop pointer
4115argument. Instead, all functions act on the single default loop.
4116.IP "\s-1EV_MINPRI\s0" 4
4117.IX Item "EV_MINPRI"
4118.PD 0
4119.IP "\s-1EV_MAXPRI\s0" 4
4120.IX Item "EV_MAXPRI"
4121.PD
4122The range of allowed priorities. \f(CW\*(C`EV_MINPRI\*(C'\fR must be smaller or equal to
4123\&\f(CW\*(C`EV_MAXPRI\*(C'\fR, but otherwise there are no non-obvious limitations. You can
4124provide for more priorities by overriding those symbols (usually defined
4125to be \f(CW\*(C`\-2\*(C'\fR and \f(CW2\fR, respectively).
4126.Sp
4127When doing priority-based operations, libev usually has to linearly search
4128all the priorities, so having many of them (hundreds) uses a lot of space
4129and time, so using the defaults of five priorities (\-2 .. +2) is usually
4130fine.
4131.Sp
4132If your embedding application does not need any priorities, defining these
4133both to \f(CW0\fR will save some memory and \s-1CPU\s0.
4134.IP "\s-1EV_PERIODIC_ENABLE\s0, \s-1EV_IDLE_ENABLE\s0, \s-1EV_EMBED_ENABLE\s0, \s-1EV_STAT_ENABLE\s0, \s-1EV_PREPARE_ENABLE\s0, \s-1EV_CHECK_ENABLE\s0, \s-1EV_FORK_ENABLE\s0, \s-1EV_SIGNAL_ENABLE\s0, \s-1EV_ASYNC_ENABLE\s0, \s-1EV_CHILD_ENABLE\s0." 4
4135.IX Item "EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE, EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE, EV_ASYNC_ENABLE, EV_CHILD_ENABLE."
4136If undefined or defined to be \f(CW1\fR (and the platform supports it), then
4137the respective watcher type is supported. If defined to be \f(CW0\fR, then it
4138is not. Disabling watcher types mainly saves code size.
4139.IP "\s-1EV_FEATURES\s0" 4
4140.IX Item "EV_FEATURES"
4141If you need to shave off some kilobytes of code at the expense of some
4142speed (but with the full \s-1API\s0), you can define this symbol to request
4143certain subsets of functionality. The default is to enable all features
4144that can be enabled on the platform.
4145.Sp
4146A typical way to use this symbol is to define it to \f(CW0\fR (or to a bitset
4147with some broad features you want) and then selectively re-enable
4148additional parts you want, for example if you want everything minimal,
4149but multiple event loop support, async and child watchers and the poll
4150backend, use this:
4151.Sp
4152.Vb 5
4153\& #define EV_FEATURES 0
4154\& #define EV_MULTIPLICITY 1
4155\& #define EV_USE_POLL 1
4156\& #define EV_CHILD_ENABLE 1
4157\& #define EV_ASYNC_ENABLE 1
4158.Ve
4159.Sp
4160The actual value is a bitset, it can be a combination of the following
4161values:
4162.RS 4
4163.ie n .IP "1 \- faster/larger code" 4
4164.el .IP "\f(CW1\fR \- faster/larger code" 4
4165.IX Item "1 - faster/larger code"
4166Use larger code to speed up some operations.
4167.Sp
4168Currently this is used to override some inlining decisions (enlarging the
4169code size by roughly 30% on amd64).
4170.Sp
4171When optimising for size, use of compiler flags such as \f(CW\*(C`\-Os\*(C'\fR with
4172gcc is recommended, as well as \f(CW\*(C`\-DNDEBUG\*(C'\fR, as libev contains a number of
4173assertions.
4174.ie n .IP "2 \- faster/larger data structures" 4
4175.el .IP "\f(CW2\fR \- faster/larger data structures" 4
4176.IX Item "2 - faster/larger data structures"
4177Replaces the small 2\-heap for timer management by a faster 4\-heap, larger
4178hash table sizes and so on. This will usually further increase code size
4179and can additionally have an effect on the size of data structures at
4180runtime.
4181.ie n .IP "4 \- full \s-1API\s0 configuration" 4
4182.el .IP "\f(CW4\fR \- full \s-1API\s0 configuration" 4
4183.IX Item "4 - full API configuration"
4184This enables priorities (sets \f(CW\*(C`EV_MAXPRI\*(C'\fR=2 and \f(CW\*(C`EV_MINPRI\*(C'\fR=\-2), and
4185enables multiplicity (\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR=1).
4186.ie n .IP "8 \- full \s-1API\s0" 4
4187.el .IP "\f(CW8\fR \- full \s-1API\s0" 4
4188.IX Item "8 - full API"
4189This enables a lot of the \*(L"lesser used\*(R" \s-1API\s0 functions. See \f(CW\*(C`ev.h\*(C'\fR for
4190details on which parts of the \s-1API\s0 are still available without this
4191feature, and do not complain if this subset changes over time.
4192.ie n .IP "16 \- enable all optional watcher types" 4
4193.el .IP "\f(CW16\fR \- enable all optional watcher types" 4
4194.IX Item "16 - enable all optional watcher types"
4195Enables all optional watcher types. If you want to selectively enable
4196only some watcher types other than I/O and timers (e.g. prepare,
4197embed, async, child...) you can enable them manually by defining
4198\&\f(CW\*(C`EV_watchertype_ENABLE\*(C'\fR to \f(CW1\fR instead.
4199.ie n .IP "32 \- enable all backends" 4
4200.el .IP "\f(CW32\fR \- enable all backends" 4
4201.IX Item "32 - enable all backends"
4202This enables all backends \- without this feature, you need to enable at
4203least one backend manually (\f(CW\*(C`EV_USE_SELECT\*(C'\fR is a good choice).
4204.ie n .IP "64 \- enable OS-specific ""helper"" APIs" 4
4205.el .IP "\f(CW64\fR \- enable OS-specific ``helper'' APIs" 4
4206.IX Item "64 - enable OS-specific helper APIs"
4207Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
4208default.
4209.RE
4210.RS 4
4211.Sp
4212Compiling with \f(CW\*(C`gcc \-Os \-DEV_STANDALONE \-DEV_USE_EPOLL=1 \-DEV_FEATURES=0\*(C'\fR
4213reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
4214code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
4215watchers, timers and monotonic clock support.
4216.Sp
4217With an intelligent-enough linker (gcc+binutils are intelligent enough
4218when you use \f(CW\*(C`\-Wl,\-\-gc\-sections \-ffunction\-sections\*(C'\fR) functions unused by
4219your program might be left out as well \- a binary starting a timer and an
4220I/O watcher then might come out at only 5Kb.
4221.RE
4222.IP "\s-1EV_AVOID_STDIO\s0" 4
4223.IX Item "EV_AVOID_STDIO"
4224If this is set to \f(CW1\fR at compiletime, then libev will avoid using stdio
4225functions (printf, scanf, perror etc.). This will increase the code size
4226somewhat, but if your program doesn't otherwise depend on stdio and your
4227libc allows it, this avoids linking in the stdio library which is quite
4228big.
4229.Sp
4230Note that error messages might become less precise when this option is
4231enabled.
4232.IP "\s-1EV_NSIG\s0" 4
4233.IX Item "EV_NSIG"
4234The highest supported signal number, +1 (or, the number of
4235signals): Normally, libev tries to deduce the maximum number of signals
4236automatically, but sometimes this fails, in which case it can be
4237specified. Also, using a lower number than detected (\f(CW32\fR should be
4238good for about any system in existence) can save some memory, as libev
4239statically allocates some 12\-24 bytes per signal number.
4240.IP "\s-1EV_PID_HASHSIZE\s0" 4
4241.IX Item "EV_PID_HASHSIZE"
4242\&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by
4243pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR disabled),
4244usually more than enough. If you need to manage thousands of children you
4245might want to increase this value (\fImust\fR be a power of two).
4246.IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4
4247.IX Item "EV_INOTIFY_HASHSIZE"
4248\&\f(CW\*(C`ev_stat\*(C'\fR watchers use a small hash table to distribute workload by
4249inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR
4250disabled), usually more than enough. If you need to manage thousands of
4251\&\f(CW\*(C`ev_stat\*(C'\fR watchers you might want to increase this value (\fImust\fR be a
4252power of two).
4253.IP "\s-1EV_USE_4HEAP\s0" 4
4254.IX Item "EV_USE_4HEAP"
4255Heaps are not very cache-efficient. To improve the cache-efficiency of the
4256timer and periodics heaps, libev uses a 4\-heap when this symbol is defined
4257to \f(CW1\fR. The 4\-heap uses more complicated (longer) code but has noticeably
4258faster performance with many (thousands) of watchers.
4259.Sp
4260The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4261will be \f(CW0\fR.
4262.IP "\s-1EV_HEAP_CACHE_AT\s0" 4
4263.IX Item "EV_HEAP_CACHE_AT"
4264Heaps are not very cache-efficient. To improve the cache-efficiency of the
4265timer and periodics heaps, libev can cache the timestamp (\fIat\fR) within
4266the heap structure (selected by defining \f(CW\*(C`EV_HEAP_CACHE_AT\*(C'\fR to \f(CW1\fR),
4267which uses 8\-12 bytes more per watcher and a few hundred bytes more code,
4268but avoids random read accesses on heap changes. This improves performance
4269noticeably with many (hundreds) of watchers.
4270.Sp
4271The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4272will be \f(CW0\fR.
4273.IP "\s-1EV_VERIFY\s0" 4
4274.IX Item "EV_VERIFY"
4275Controls how much internal verification (see \f(CW\*(C`ev_verify ()\*(C'\fR) will
4276be done: If set to \f(CW0\fR, no internal verification code will be compiled
4277in. If set to \f(CW1\fR, then verification code will be compiled in, but not
4278called. If set to \f(CW2\fR, then the internal verification code will be
4279called once per loop, which can slow down libev. If set to \f(CW3\fR, then the
4280verification code will be called very frequently, which will slow down
4281libev considerably.
4282.Sp
4283The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4284will be \f(CW0\fR.
4285.IP "\s-1EV_COMMON\s0" 4
4286.IX Item "EV_COMMON"
4287By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining
4288this macro to something else you can include more and other types of
4289members. You have to define it each time you include one of the files,
4290though, and it must be identical each time.
4291.Sp
4292For example, the perl \s-1EV\s0 module uses something like this:
4293.Sp
4294.Vb 3
4295\& #define EV_COMMON \e
4296\& SV *self; /* contains this struct */ \e
4297\& SV *cb_sv, *fh /* note no trailing ";" */
4298.Ve
4299.IP "\s-1EV_CB_DECLARE\s0 (type)" 4
4300.IX Item "EV_CB_DECLARE (type)"
4301.PD 0
4302.IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4
4303.IX Item "EV_CB_INVOKE (watcher, revents)"
4304.IP "ev_set_cb (ev, cb)" 4
4305.IX Item "ev_set_cb (ev, cb)"
4306.PD
4307Can be used to change the callback member declaration in each watcher,
4308and the way callbacks are invoked and set. Must expand to a struct member
4309definition and a statement, respectively. See the \fIev.h\fR header file for
4310their default definitions. One possible use for overriding these is to
4311avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use
4312method calls instead of plain function calls in \*(C+.
4313.SS "\s-1EXPORTED\s0 \s-1API\s0 \s-1SYMBOLS\s0"
4314.IX Subsection "EXPORTED API SYMBOLS"
4315If you need to re-export the \s-1API\s0 (e.g. via a \s-1DLL\s0) and you need a list of
4316exported symbols, you can use the provided \fISymbol.*\fR files which list
4317all public symbols, one per line:
4318.PP
4319.Vb 2
4320\& Symbols.ev for libev proper
4321\& Symbols.event for the libevent emulation
4322.Ve
4323.PP
4324This can also be used to rename all public symbols to avoid clashes with
4325multiple versions of libev linked together (which is obviously bad in
4326itself, but sometimes it is inconvenient to avoid this).
4327.PP
4328A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to
4329include before including \fIev.h\fR:
4330.PP
4331.Vb 1
4332\& <Symbols.ev sed \-e "s/.*/#define & myprefix_&/" >wrap.h
4333.Ve
4334.PP
4335This would create a file \fIwrap.h\fR which essentially looks like this:
4336.PP
4337.Vb 4
4338\& #define ev_backend myprefix_ev_backend
4339\& #define ev_check_start myprefix_ev_check_start
4340\& #define ev_check_stop myprefix_ev_check_stop
4341\& ...
4342.Ve
4343.SS "\s-1EXAMPLES\s0"
4344.IX Subsection "EXAMPLES"
4345For a real-world example of a program the includes libev
4346verbatim, you can have a look at the \s-1EV\s0 perl module
4347(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
4348the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public
4349interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file
4350will be compiled. It is pretty complex because it provides its own header
4351file.
4352.PP
4353The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file
4354that everybody includes and which overrides some configure choices:
4355.PP
4356.Vb 8
4357\& #define EV_FEATURES 8
4358\& #define EV_USE_SELECT 1
4359\& #define EV_PREPARE_ENABLE 1
4360\& #define EV_IDLE_ENABLE 1
4361\& #define EV_SIGNAL_ENABLE 1
4362\& #define EV_CHILD_ENABLE 1
4363\& #define EV_USE_STDEXCEPT 0
4364\& #define EV_CONFIG_H <config.h>
4365\&
4366\& #include "ev++.h"
4367.Ve
4368.PP
4369And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled:
4370.PP
4371.Vb 2
4372\& #include "ev_cpp.h"
4373\& #include "ev.c"
4374.Ve
4375.SH "INTERACTION WITH OTHER PROGRAMS OR LIBRARIES"
4376.IX Header "INTERACTION WITH OTHER PROGRAMS OR LIBRARIES"
4377.SS "\s-1THREADS\s0 \s-1AND\s0 \s-1COROUTINES\s0"
4378.IX Subsection "THREADS AND COROUTINES"
4379\fI\s-1THREADS\s0\fR
4380.IX Subsection "THREADS"
4381.PP
4382All libev functions are reentrant and thread-safe unless explicitly
4383documented otherwise, but libev implements no locking itself. This means
4384that you can use as many loops as you want in parallel, as long as there
4385are no concurrent calls into any libev function with the same loop
4386parameter (\f(CW\*(C`ev_default_*\*(C'\fR calls have an implicit default loop parameter,
4387of course): libev guarantees that different event loops share no data
4388structures that need any locking.
4389.PP
4390Or to put it differently: calls with different loop parameters can be done
4391concurrently from multiple threads, calls with the same loop parameter
4392must be done serially (but can be done from different threads, as long as
4393only one thread ever is inside a call at any point in time, e.g. by using
4394a mutex per loop).
4395.PP
4396Specifically to support threads (and signal handlers), libev implements
4397so-called \f(CW\*(C`ev_async\*(C'\fR watchers, which allow some limited form of
4398concurrency on the same event loop, namely waking it up \*(L"from the
4399outside\*(R".
4400.PP
4401If you want to know which design (one loop, locking, or multiple loops
4402without or something else still) is best for your problem, then I cannot
4403help you, but here is some generic advice:
4404.IP "\(bu" 4
4405most applications have a main thread: use the default libev loop
4406in that thread, or create a separate thread running only the default loop.
4407.Sp
4408This helps integrating other libraries or software modules that use libev
4409themselves and don't care/know about threading.
4410.IP "\(bu" 4
4411one loop per thread is usually a good model.
4412.Sp
4413Doing this is almost never wrong, sometimes a better-performance model
4414exists, but it is always a good start.
4415.IP "\(bu" 4
4416other models exist, such as the leader/follower pattern, where one
4417loop is handed through multiple threads in a kind of round-robin fashion.
4418.Sp
4419Choosing a model is hard \- look around, learn, know that usually you can do
4420better than you currently do :\-)
4421.IP "\(bu" 4
4422often you need to talk to some other thread which blocks in the
4423event loop.
4424.Sp
4425\&\f(CW\*(C`ev_async\*(C'\fR watchers can be used to wake them up from other threads safely
4426(or from signal contexts...).
4427.Sp
4428An example use would be to communicate signals or other events that only
4429work in the default loop by registering the signal watcher with the
4430default loop and triggering an \f(CW\*(C`ev_async\*(C'\fR watcher from the default loop
4431watcher callback into the event loop interested in the signal.
4432.PP
4433\s-1THREAD\s0 \s-1LOCKING\s0 \s-1EXAMPLE\s0
4434.IX Subsection "THREAD LOCKING EXAMPLE"
4435.PP
4436Here is a fictitious example of how to run an event loop in a different
4437thread than where callbacks are being invoked and watchers are
4438created/added/removed.
4439.PP
4440For a real-world example, see the \f(CW\*(C`EV::Loop::Async\*(C'\fR perl module,
4441which uses exactly this technique (which is suited for many high-level
4442languages).
4443.PP
4444The example uses a pthread mutex to protect the loop data, a condition
4445variable to wait for callback invocations, an async watcher to notify the
4446event loop thread and an unspecified mechanism to wake up the main thread.
4447.PP
4448First, you need to associate some data with the event loop:
4449.PP
4450.Vb 6
4451\& typedef struct {
4452\& mutex_t lock; /* global loop lock */
4453\& ev_async async_w;
4454\& thread_t tid;
4455\& cond_t invoke_cv;
4456\& } userdata;
4457\&
4458\& void prepare_loop (EV_P)
4459\& {
4460\& // for simplicity, we use a static userdata struct.
4461\& static userdata u;
4462\&
4463\& ev_async_init (&u\->async_w, async_cb);
4464\& ev_async_start (EV_A_ &u\->async_w);
4465\&
4466\& pthread_mutex_init (&u\->lock, 0);
4467\& pthread_cond_init (&u\->invoke_cv, 0);
4468\&
4469\& // now associate this with the loop
4470\& ev_set_userdata (EV_A_ u);
4471\& ev_set_invoke_pending_cb (EV_A_ l_invoke);
4472\& ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4473\&
4474\& // then create the thread running ev_loop
4475\& pthread_create (&u\->tid, 0, l_run, EV_A);
4476\& }
4477.Ve
4478.PP
4479The callback for the \f(CW\*(C`ev_async\*(C'\fR watcher does nothing: the watcher is used
4480solely to wake up the event loop so it takes notice of any new watchers
4481that might have been added:
4482.PP
4483.Vb 5
4484\& static void
4485\& async_cb (EV_P_ ev_async *w, int revents)
4486\& {
4487\& // just used for the side effects
4488\& }
4489.Ve
4490.PP
4491The \f(CW\*(C`l_release\*(C'\fR and \f(CW\*(C`l_acquire\*(C'\fR callbacks simply unlock/lock the mutex
4492protecting the loop data, respectively.
4493.PP
4494.Vb 6
4495\& static void
4496\& l_release (EV_P)
4497\& {
4498\& userdata *u = ev_userdata (EV_A);
4499\& pthread_mutex_unlock (&u\->lock);
4500\& }
4501\&
4502\& static void
4503\& l_acquire (EV_P)
4504\& {
4505\& userdata *u = ev_userdata (EV_A);
4506\& pthread_mutex_lock (&u\->lock);
4507\& }
4508.Ve
4509.PP
4510The event loop thread first acquires the mutex, and then jumps straight
4511into \f(CW\*(C`ev_run\*(C'\fR:
4512.PP
4513.Vb 4
4514\& void *
4515\& l_run (void *thr_arg)
4516\& {
4517\& struct ev_loop *loop = (struct ev_loop *)thr_arg;
4518\&
4519\& l_acquire (EV_A);
4520\& pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4521\& ev_run (EV_A_ 0);
4522\& l_release (EV_A);
4523\&
4524\& return 0;
4525\& }
4526.Ve
4527.PP
4528Instead of invoking all pending watchers, the \f(CW\*(C`l_invoke\*(C'\fR callback will
4529signal the main thread via some unspecified mechanism (signals? pipe
4530writes? \f(CW\*(C`Async::Interrupt\*(C'\fR?) and then waits until all pending watchers
4531have been called (in a while loop because a) spurious wakeups are possible
4532and b) skipping inter-thread-communication when there are no pending
4533watchers is very beneficial):
4534.PP
4535.Vb 4
4536\& static void
4537\& l_invoke (EV_P)
4538\& {
4539\& userdata *u = ev_userdata (EV_A);
4540\&
4541\& while (ev_pending_count (EV_A))
4542\& {
4543\& wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4544\& pthread_cond_wait (&u\->invoke_cv, &u\->lock);
4545\& }
4546\& }
4547.Ve
4548.PP
4549Now, whenever the main thread gets told to invoke pending watchers, it
4550will grab the lock, call \f(CW\*(C`ev_invoke_pending\*(C'\fR and then signal the loop
4551thread to continue:
4552.PP
4553.Vb 4
4554\& static void
4555\& real_invoke_pending (EV_P)
4556\& {
4557\& userdata *u = ev_userdata (EV_A);
4558\&
4559\& pthread_mutex_lock (&u\->lock);
4560\& ev_invoke_pending (EV_A);
4561\& pthread_cond_signal (&u\->invoke_cv);
4562\& pthread_mutex_unlock (&u\->lock);
4563\& }
4564.Ve
4565.PP
4566Whenever you want to start/stop a watcher or do other modifications to an
4567event loop, you will now have to lock:
4568.PP
4569.Vb 2
4570\& ev_timer timeout_watcher;
4571\& userdata *u = ev_userdata (EV_A);
4572\&
4573\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4574\&
4575\& pthread_mutex_lock (&u\->lock);
4576\& ev_timer_start (EV_A_ &timeout_watcher);
4577\& ev_async_send (EV_A_ &u\->async_w);
4578\& pthread_mutex_unlock (&u\->lock);
4579.Ve
4580.PP
4581Note that sending the \f(CW\*(C`ev_async\*(C'\fR watcher is required because otherwise
4582an event loop currently blocking in the kernel will have no knowledge
4583about the newly added timer. By waking up the loop it will pick up any new
4584watchers in the next event loop iteration.
4585.PP
4586\fI\s-1COROUTINES\s0\fR
4587.IX Subsection "COROUTINES"
4588.PP
4589Libev is very accommodating to coroutines (\*(L"cooperative threads\*(R"):
4590libev fully supports nesting calls to its functions from different
4591coroutines (e.g. you can call \f(CW\*(C`ev_run\*(C'\fR on the same loop from two
4592different coroutines, and switch freely between both coroutines running
4593the loop, as long as you don't confuse yourself). The only exception is
4594that you must not do this from \f(CW\*(C`ev_periodic\*(C'\fR reschedule callbacks.
4595.PP
4596Care has been taken to ensure that libev does not keep local state inside
4597\&\f(CW\*(C`ev_run\*(C'\fR, and other calls do not usually allow for coroutine switches as
4598they do not call any callbacks.
4599.SS "\s-1COMPILER\s0 \s-1WARNINGS\s0"
4600.IX Subsection "COMPILER WARNINGS"
4601Depending on your compiler and compiler settings, you might get no or a
4602lot of warnings when compiling libev code. Some people are apparently
4603scared by this.
4604.PP
4605However, these are unavoidable for many reasons. For one, each compiler
4606has different warnings, and each user has different tastes regarding
4607warning options. \*(L"Warn-free\*(R" code therefore cannot be a goal except when
4608targeting a specific compiler and compiler-version.
4609.PP
4610Another reason is that some compiler warnings require elaborate
4611workarounds, or other changes to the code that make it less clear and less
4612maintainable.
4613.PP
4614And of course, some compiler warnings are just plain stupid, or simply
4615wrong (because they don't actually warn about the condition their message
4616seems to warn about). For example, certain older gcc versions had some
4617warnings that resulted in an extreme number of false positives. These have
4618been fixed, but some people still insist on making code warn-free with
4619such buggy versions.
4620.PP
4621While libev is written to generate as few warnings as possible,
4622\&\*(L"warn-free\*(R" code is not a goal, and it is recommended not to build libev
4623with any compiler warnings enabled unless you are prepared to cope with
4624them (e.g. by ignoring them). Remember that warnings are just that:
4625warnings, not errors, or proof of bugs.
4626.SS "\s-1VALGRIND\s0"
4627.IX Subsection "VALGRIND"
4628Valgrind has a special section here because it is a popular tool that is
4629highly useful. Unfortunately, valgrind reports are very hard to interpret.
4630.PP
4631If you think you found a bug (memory leak, uninitialised data access etc.)
4632in libev, then check twice: If valgrind reports something like:
4633.PP
4634.Vb 3
4635\& ==2274== definitely lost: 0 bytes in 0 blocks.
4636\& ==2274== possibly lost: 0 bytes in 0 blocks.
4637\& ==2274== still reachable: 256 bytes in 1 blocks.
4638.Ve
4639.PP
4640Then there is no memory leak, just as memory accounted to global variables
4641is not a memleak \- the memory is still being referenced, and didn't leak.
4642.PP
4643Similarly, under some circumstances, valgrind might report kernel bugs
4644as if it were a bug in libev (e.g. in realloc or in the poll backend,
4645although an acceptable workaround has been found here), or it might be
4646confused.
4647.PP
4648Keep in mind that valgrind is a very good tool, but only a tool. Don't
4649make it into some kind of religion.
4650.PP
4651If you are unsure about something, feel free to contact the mailing list
4652with the full valgrind report and an explanation on why you think this
4653is a bug in libev (best check the archives, too :). However, don't be
4654annoyed when you get a brisk \*(L"this is no bug\*(R" answer and take the chance
4655of learning how to interpret valgrind properly.
4656.PP
4657If you need, for some reason, empty reports from valgrind for your project
4658I suggest using suppression lists.
4659.SH "PORTABILITY NOTES"
4660.IX Header "PORTABILITY NOTES"
4661.SS "\s-1GNU/LINUX\s0 32 \s-1BIT\s0 \s-1LIMITATIONS\s0"
4662.IX Subsection "GNU/LINUX 32 BIT LIMITATIONS"
4663GNU/Linux is the only common platform that supports 64 bit file/large file
4664interfaces but \fIdisables\fR them by default.
4665.PP
4666That means that libev compiled in the default environment doesn't support
4667files larger than 2GiB or so, which mainly affects \f(CW\*(C`ev_stat\*(C'\fR watchers.
4668.PP
4669Unfortunately, many programs try to work around this GNU/Linux issue
4670by enabling the large file \s-1API\s0, which makes them incompatible with the
4671standard libev compiled for their system.
4672.PP
4673Likewise, libev cannot enable the large file \s-1API\s0 itself as this would
4674suddenly make it incompatible to the default compile time environment,
4675i.e. all programs not using special compile switches.
4676.SS "\s-1OS/X\s0 \s-1AND\s0 \s-1DARWIN\s0 \s-1BUGS\s0"
4677.IX Subsection "OS/X AND DARWIN BUGS"
4678The whole thing is a bug if you ask me \- basically any system interface
4679you touch is broken, whether it is locales, poll, kqueue or even the
4680OpenGL drivers.
4681.PP
4682\fI\f(CI\*(C`kqueue\*(C'\fI is buggy\fR
4683.IX Subsection "kqueue is buggy"
4684.PP
4685The kqueue syscall is broken in all known versions \- most versions support
4686only sockets, many support pipes.
4687.PP
4688Libev tries to work around this by not using \f(CW\*(C`kqueue\*(C'\fR by default on this
4689rotten platform, but of course you can still ask for it when creating a
4690loop \- embedding a socket-only kqueue loop into a select-based one is
4691probably going to work well.
4692.PP
4693\fI\f(CI\*(C`poll\*(C'\fI is buggy\fR
4694.IX Subsection "poll is buggy"
4695.PP
4696Instead of fixing \f(CW\*(C`kqueue\*(C'\fR, Apple replaced their (working) \f(CW\*(C`poll\*(C'\fR
4697implementation by something calling \f(CW\*(C`kqueue\*(C'\fR internally around the 10.5.6
4698release, so now \f(CW\*(C`kqueue\*(C'\fR \fIand\fR \f(CW\*(C`poll\*(C'\fR are broken.
4699.PP
4700Libev tries to work around this by not using \f(CW\*(C`poll\*(C'\fR by default on
4701this rotten platform, but of course you can still ask for it when creating
4702a loop.
4703.PP
4704\fI\f(CI\*(C`select\*(C'\fI is buggy\fR
4705.IX Subsection "select is buggy"
4706.PP
4707All that's left is \f(CW\*(C`select\*(C'\fR, and of course Apple found a way to fuck this
4708one up as well: On \s-1OS/X\s0, \f(CW\*(C`select\*(C'\fR actively limits the number of file
4709descriptors you can pass in to 1024 \- your program suddenly crashes when
4710you use more.
4711.PP
4712There is an undocumented \*(L"workaround\*(R" for this \- defining
4713\&\f(CW\*(C`_DARWIN_UNLIMITED_SELECT\*(C'\fR, which libev tries to use, so select \fIshould\fR
4714work on \s-1OS/X\s0.
4715.SS "\s-1SOLARIS\s0 \s-1PROBLEMS\s0 \s-1AND\s0 \s-1WORKAROUNDS\s0"
4716.IX Subsection "SOLARIS PROBLEMS AND WORKAROUNDS"
4717\fI\f(CI\*(C`errno\*(C'\fI reentrancy\fR
4718.IX Subsection "errno reentrancy"
4719.PP
4720The default compile environment on Solaris is unfortunately so
4721thread-unsafe that you can't even use components/libraries compiled
4722without \f(CW\*(C`\-D_REENTRANT\*(C'\fR in a threaded program, which, of course, isn't
4723defined by default. A valid, if stupid, implementation choice.
4724.PP
4725If you want to use libev in threaded environments you have to make sure
4726it's compiled with \f(CW\*(C`_REENTRANT\*(C'\fR defined.
4727.PP
4728\fIEvent port backend\fR
4729.IX Subsection "Event port backend"
4730.PP
4731The scalable event interface for Solaris is called \*(L"event
4732ports\*(R". Unfortunately, this mechanism is very buggy in all major
4733releases. If you run into high \s-1CPU\s0 usage, your program freezes or you get
4734a large number of spurious wakeups, make sure you have all the relevant
4735and latest kernel patches applied. No, I don't know which ones, but there
4736are multiple ones to apply, and afterwards, event ports actually work
4737great.
4738.PP
4739If you can't get it to work, you can try running the program by setting
4740the environment variable \f(CW\*(C`LIBEV_FLAGS=3\*(C'\fR to only allow \f(CW\*(C`poll\*(C'\fR and
4741\&\f(CW\*(C`select\*(C'\fR backends.
4742.SS "\s-1AIX\s0 \s-1POLL\s0 \s-1BUG\s0"
4743.IX Subsection "AIX POLL BUG"
4744\&\s-1AIX\s0 unfortunately has a broken \f(CW\*(C`poll.h\*(C'\fR header. Libev works around
4745this by trying to avoid the poll backend altogether (i.e. it's not even
4746compiled in), which normally isn't a big problem as \f(CW\*(C`select\*(C'\fR works fine
4747with large bitsets on \s-1AIX\s0, and \s-1AIX\s0 is dead anyway.
4748.SS "\s-1WIN32\s0 \s-1PLATFORM\s0 \s-1LIMITATIONS\s0 \s-1AND\s0 \s-1WORKAROUNDS\s0"
4749.IX Subsection "WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS"
4750\fIGeneral issues\fR
4751.IX Subsection "General issues"
4752.PP
4753Win32 doesn't support any of the standards (e.g. \s-1POSIX\s0) that libev
4754requires, and its I/O model is fundamentally incompatible with the \s-1POSIX\s0
4755model. Libev still offers limited functionality on this platform in
4756the form of the \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR backend, and only supports socket
4757descriptors. This only applies when using Win32 natively, not when using
4758e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4759as every compielr comes with a slightly differently broken/incompatible
4760environment.
4761.PP
4762Lifting these limitations would basically require the full
4763re-implementation of the I/O system. If you are into this kind of thing,
4764then note that glib does exactly that for you in a very portable way (note
4765also that glib is the slowest event library known to man).
4766.PP
4767There is no supported compilation method available on windows except
4768embedding it into other applications.
4769.PP
4770Sensible signal handling is officially unsupported by Microsoft \- libev
4771tries its best, but under most conditions, signals will simply not work.
4772.PP
4773Not a libev limitation but worth mentioning: windows apparently doesn't
4774accept large writes: instead of resulting in a partial write, windows will
4775either accept everything or return \f(CW\*(C`ENOBUFS\*(C'\fR if the buffer is too large,
4776so make sure you only write small amounts into your sockets (less than a
4777megabyte seems safe, but this apparently depends on the amount of memory
4778available).
4779.PP
4780Due to the many, low, and arbitrary limits on the win32 platform and
4781the abysmal performance of winsockets, using a large number of sockets
4782is not recommended (and not reasonable). If your program needs to use
4783more than a hundred or so sockets, then likely it needs to use a totally
4784different implementation for windows, as libev offers the \s-1POSIX\s0 readiness
4785notification model, which cannot be implemented efficiently on windows
4786(due to Microsoft monopoly games).
4787.PP
4788A typical way to use libev under windows is to embed it (see the embedding
4789section for details) and use the following \fIevwrap.h\fR header file instead
4790of \fIev.h\fR:
4791.PP
4792.Vb 2
4793\& #define EV_STANDALONE /* keeps ev from requiring config.h */
4794\& #define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
4795\&
4796\& #include "ev.h"
4797.Ve
4798.PP
4799And compile the following \fIevwrap.c\fR file into your project (make sure
4800you do \fInot\fR compile the \fIev.c\fR or any other embedded source files!):
4801.PP
4802.Vb 2
4803\& #include "evwrap.h"
4804\& #include "ev.c"
4805.Ve
4806.PP
4807\fIThe winsocket \f(CI\*(C`select\*(C'\fI function\fR
4808.IX Subsection "The winsocket select function"
4809.PP
4810The winsocket \f(CW\*(C`select\*(C'\fR function doesn't follow \s-1POSIX\s0 in that it
4811requires socket \fIhandles\fR and not socket \fIfile descriptors\fR (it is
4812also extremely buggy). This makes select very inefficient, and also
4813requires a mapping from file descriptors to socket handles (the Microsoft
4814C runtime provides the function \f(CW\*(C`_open_osfhandle\*(C'\fR for this). See the
4815discussion of the \f(CW\*(C`EV_SELECT_USE_FD_SET\*(C'\fR, \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR and
4816\&\f(CW\*(C`EV_FD_TO_WIN32_HANDLE\*(C'\fR preprocessor symbols for more info.
4817.PP
4818The configuration for a \*(L"naked\*(R" win32 using the Microsoft runtime
4819libraries and raw winsocket select is:
4820.PP
4821.Vb 2
4822\& #define EV_USE_SELECT 1
4823\& #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
4824.Ve
4825.PP
4826Note that winsockets handling of fd sets is O(n), so you can easily get a
4827complexity in the O(nA\*^X) range when using win32.
4828.PP
4829\fILimited number of file descriptors\fR
4830.IX Subsection "Limited number of file descriptors"
4831.PP
4832Windows has numerous arbitrary (and low) limits on things.
4833.PP
4834Early versions of winsocket's select only supported waiting for a maximum
4835of \f(CW64\fR handles (probably owning to the fact that all windows kernels
4836can only wait for \f(CW64\fR things at the same time internally; Microsoft
4837recommends spawning a chain of threads and wait for 63 handles and the
4838previous thread in each. Sounds great!).
4839.PP
4840Newer versions support more handles, but you need to define \f(CW\*(C`FD_SETSIZE\*(C'\fR
4841to some high number (e.g. \f(CW2048\fR) before compiling the winsocket select
4842call (which might be in libev or elsewhere, for example, perl and many
4843other interpreters do their own select emulation on windows).
4844.PP
4845Another limit is the number of file descriptors in the Microsoft runtime
4846libraries, which by default is \f(CW64\fR (there must be a hidden \fI64\fR
4847fetish or something like this inside Microsoft). You can increase this
4848by calling \f(CW\*(C`_setmaxstdio\*(C'\fR, which can increase this limit to \f(CW2048\fR
4849(another arbitrary limit), but is broken in many versions of the Microsoft
4850runtime libraries. This might get you to about \f(CW512\fR or \f(CW2048\fR sockets
4851(depending on windows version and/or the phase of the moon). To get more,
4852you need to wrap all I/O functions and provide your own fd management, but
4853the cost of calling select (O(nA\*^X)) will likely make this unworkable.
4854.SS "\s-1PORTABILITY\s0 \s-1REQUIREMENTS\s0"
4855.IX Subsection "PORTABILITY REQUIREMENTS"
4856In addition to a working ISO-C implementation and of course the
4857backend-specific APIs, libev relies on a few additional extensions:
4858.ie n .IP """void (*)(ev_watcher_type *, int revents)"" must have compatible calling conventions regardless of ""ev_watcher_type *""." 4
4859.el .IP "\f(CWvoid (*)(ev_watcher_type *, int revents)\fR must have compatible calling conventions regardless of \f(CWev_watcher_type *\fR." 4
4860.IX Item "void (*)(ev_watcher_type *, int revents) must have compatible calling conventions regardless of ev_watcher_type *."
4861Libev assumes not only that all watcher pointers have the same internal
4862structure (guaranteed by \s-1POSIX\s0 but not by \s-1ISO\s0 C for example), but it also
4863assumes that the same (machine) code can be used to call any watcher
4864callback: The watcher callbacks have different type signatures, but libev
4865calls them using an \f(CW\*(C`ev_watcher *\*(C'\fR internally.
4866.IP "pointer accesses must be thread-atomic" 4
4867.IX Item "pointer accesses must be thread-atomic"
4868Accessing a pointer value must be atomic, it must both be readable and
4869writable in one piece \- this is the case on all current architectures.
4870.ie n .IP """sig_atomic_t volatile"" must be thread-atomic as well" 4
4871.el .IP "\f(CWsig_atomic_t volatile\fR must be thread-atomic as well" 4
4872.IX Item "sig_atomic_t volatile must be thread-atomic as well"
4873The type \f(CW\*(C`sig_atomic_t volatile\*(C'\fR (or whatever is defined as
4874\&\f(CW\*(C`EV_ATOMIC_T\*(C'\fR) must be atomic with respect to accesses from different
4875threads. This is not part of the specification for \f(CW\*(C`sig_atomic_t\*(C'\fR, but is
4876believed to be sufficiently portable.
4877.ie n .IP """sigprocmask"" must work in a threaded environment" 4
4878.el .IP "\f(CWsigprocmask\fR must work in a threaded environment" 4
4879.IX Item "sigprocmask must work in a threaded environment"
4880Libev uses \f(CW\*(C`sigprocmask\*(C'\fR to temporarily block signals. This is not
4881allowed in a threaded program (\f(CW\*(C`pthread_sigmask\*(C'\fR has to be used). Typical
4882pthread implementations will either allow \f(CW\*(C`sigprocmask\*(C'\fR in the \*(L"main
4883thread\*(R" or will block signals process-wide, both behaviours would
4884be compatible with libev. Interaction between \f(CW\*(C`sigprocmask\*(C'\fR and
4885\&\f(CW\*(C`pthread_sigmask\*(C'\fR could complicate things, however.
4886.Sp
4887The most portable way to handle signals is to block signals in all threads
4888except the initial one, and run the default loop in the initial thread as
4889well.
4890.ie n .IP """long"" must be large enough for common memory allocation sizes" 4
4891.el .IP "\f(CWlong\fR must be large enough for common memory allocation sizes" 4
4892.IX Item "long must be large enough for common memory allocation sizes"
4893To improve portability and simplify its \s-1API\s0, libev uses \f(CW\*(C`long\*(C'\fR internally
4894instead of \f(CW\*(C`size_t\*(C'\fR when allocating its data structures. On non-POSIX
4895systems (Microsoft...) this might be unexpectedly low, but is still at
4896least 31 bits everywhere, which is enough for hundreds of millions of
4897watchers.
4898.ie n .IP """double"" must hold a time value in seconds with enough accuracy" 4
4899.el .IP "\f(CWdouble\fR must hold a time value in seconds with enough accuracy" 4
4900.IX Item "double must hold a time value in seconds with enough accuracy"
4901The type \f(CW\*(C`double\*(C'\fR is used to represent timestamps. It is required to
4902have at least 51 bits of mantissa (and 9 bits of exponent), which is
4903good enough for at least into the year 4000 with millisecond accuracy
4904(the design goal for libev). This requirement is overfulfilled by
4905implementations using \s-1IEEE\s0 754, which is basically all existing ones. With
4906\&\s-1IEEE\s0 754 doubles, you get microsecond accuracy until at least 2200.
4907.PP
4908If you know of other additional requirements drop me a note.
4909.SH "ALGORITHMIC COMPLEXITIES"
4910.IX Header "ALGORITHMIC COMPLEXITIES"
4911In this section the complexities of (many of) the algorithms used inside
4912libev will be documented. For complexity discussions about backends see
4913the documentation for \f(CW\*(C`ev_default_init\*(C'\fR.
4914.PP
4915All of the following are about amortised time: If an array needs to be
4916extended, libev needs to realloc and move the whole array, but this
4917happens asymptotically rarer with higher number of elements, so O(1) might
4918mean that libev does a lengthy realloc operation in rare cases, but on
4919average it is much faster and asymptotically approaches constant time.
4920.IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4
4921.IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)"
4922This means that, when you have a watcher that triggers in one hour and
4923there are 100 watchers that would trigger before that, then inserting will
4924have to skip roughly seven (\f(CW\*(C`ld 100\*(C'\fR) of these watchers.
4925.IP "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 4
4926.IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)"
4927That means that changing a timer costs less than removing/adding them,
4928as only the relative motion in the event queue has to be paid for.
4929.IP "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)" 4
4930.IX Item "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)"
4931These just add the watcher into an array or at the head of a list.
4932.IP "Stopping check/prepare/idle/fork/async watchers: O(1)" 4
4933.IX Item "Stopping check/prepare/idle/fork/async watchers: O(1)"
4934.PD 0
4935.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4
4936.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))"
4937.PD
4938These watchers are stored in lists, so they need to be walked to find the
4939correct watcher to remove. The lists are usually short (you don't usually
4940have many watchers waiting for the same fd or signal: one is typical, two
4941is rare).
4942.IP "Finding the next timer in each loop iteration: O(1)" 4
4943.IX Item "Finding the next timer in each loop iteration: O(1)"
4944By virtue of using a binary or 4\-heap, the next timer is always found at a
4945fixed position in the storage array.
4946.IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4
4947.IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)"
4948A change means an I/O watcher gets started or stopped, which requires
4949libev to recalculate its status (and possibly tell the kernel, depending
4950on backend and whether \f(CW\*(C`ev_io_set\*(C'\fR was used).
4951.IP "Activating one watcher (putting it into the pending state): O(1)" 4
4952.IX Item "Activating one watcher (putting it into the pending state): O(1)"
4953.PD 0
4954.IP "Priority handling: O(number_of_priorities)" 4
4955.IX Item "Priority handling: O(number_of_priorities)"
4956.PD
4957Priorities are implemented by allocating some space for each
4958priority. When doing priority-based operations, libev usually has to
4959linearly search all the priorities, but starting/stopping and activating
4960watchers becomes O(1) with respect to priority handling.
4961.IP "Sending an ev_async: O(1)" 4
4962.IX Item "Sending an ev_async: O(1)"
4963.PD 0
4964.IP "Processing ev_async_send: O(number_of_async_watchers)" 4
4965.IX Item "Processing ev_async_send: O(number_of_async_watchers)"
4966.IP "Processing signals: O(max_signal_number)" 4
4967.IX Item "Processing signals: O(max_signal_number)"
4968.PD
4969Sending involves a system call \fIiff\fR there were no other \f(CW\*(C`ev_async_send\*(C'\fR
4970calls in the current loop iteration. Checking for async and signal events
4971involves iterating over all running async watchers or all signal numbers.
4972.SH "PORTING FROM LIBEV 3.X TO 4.X"
4973.IX Header "PORTING FROM LIBEV 3.X TO 4.X"
4974The major version 4 introduced some incompatible changes to the \s-1API\s0.
4975.PP
4976At the moment, the \f(CW\*(C`ev.h\*(C'\fR header file provides compatibility definitions
4977for all changes, so most programs should still compile. The compatibility
4978layer might be removed in later versions of libev, so better update to the
4979new \s-1API\s0 early than late.
4980.ie n .IP """EV_COMPAT3"" backwards compatibility mechanism" 4
4981.el .IP "\f(CWEV_COMPAT3\fR backwards compatibility mechanism" 4
4982.IX Item "EV_COMPAT3 backwards compatibility mechanism"
4983The backward compatibility mechanism can be controlled by
4984\&\f(CW\*(C`EV_COMPAT3\*(C'\fR. See \*(L"\s-1MACROS\s0\*(R" in \s-1PREPROCESSOR\s0 \s-1SYMBOLS\s0 in the \s-1EMBEDDING\s0
4985section.
4986.ie n .IP """ev_default_destroy"" and ""ev_default_fork"" have been removed" 4
4987.el .IP "\f(CWev_default_destroy\fR and \f(CWev_default_fork\fR have been removed" 4
4988.IX Item "ev_default_destroy and ev_default_fork have been removed"
4989These calls can be replaced easily by their \f(CW\*(C`ev_loop_xxx\*(C'\fR counterparts:
4990.Sp
4991.Vb 2
4992\& ev_loop_destroy (EV_DEFAULT_UC);
4993\& ev_loop_fork (EV_DEFAULT);
4994.Ve
4995.IP "function/symbol renames" 4
4996.IX Item "function/symbol renames"
4997A number of functions and symbols have been renamed:
4998.Sp
4999.Vb 3
5000\& ev_loop => ev_run
5001\& EVLOOP_NONBLOCK => EVRUN_NOWAIT
5002\& EVLOOP_ONESHOT => EVRUN_ONCE
5003\&
5004\& ev_unloop => ev_break
5005\& EVUNLOOP_CANCEL => EVBREAK_CANCEL
5006\& EVUNLOOP_ONE => EVBREAK_ONE
5007\& EVUNLOOP_ALL => EVBREAK_ALL
5008\&
5009\& EV_TIMEOUT => EV_TIMER
5010\&
5011\& ev_loop_count => ev_iteration
5012\& ev_loop_depth => ev_depth
5013\& ev_loop_verify => ev_verify
5014.Ve
5015.Sp
5016Most functions working on \f(CW\*(C`struct ev_loop\*(C'\fR objects don't have an
5017\&\f(CW\*(C`ev_loop_\*(C'\fR prefix, so it was removed; \f(CW\*(C`ev_loop\*(C'\fR, \f(CW\*(C`ev_unloop\*(C'\fR and
5018associated constants have been renamed to not collide with the \f(CW\*(C`struct
5019ev_loop\*(C'\fR anymore and \f(CW\*(C`EV_TIMER\*(C'\fR now follows the same naming scheme
5020as all other watcher types. Note that \f(CW\*(C`ev_loop_fork\*(C'\fR is still called
5021\&\f(CW\*(C`ev_loop_fork\*(C'\fR because it would otherwise clash with the \f(CW\*(C`ev_fork\*(C'\fR
5022typedef.
5023.ie n .IP """EV_MINIMAL"" mechanism replaced by ""EV_FEATURES""" 4
5024.el .IP "\f(CWEV_MINIMAL\fR mechanism replaced by \f(CWEV_FEATURES\fR" 4
5025.IX Item "EV_MINIMAL mechanism replaced by EV_FEATURES"
5026The preprocessor symbol \f(CW\*(C`EV_MINIMAL\*(C'\fR has been replaced by a different
5027mechanism, \f(CW\*(C`EV_FEATURES\*(C'\fR. Programs using \f(CW\*(C`EV_MINIMAL\*(C'\fR usually compile
5028and work, but the library code will of course be larger.
5029.SH "GLOSSARY"
5030.IX Header "GLOSSARY"
5031.IP "active" 4
5032.IX Item "active"
5033A watcher is active as long as it has been started and not yet stopped.
5034See \*(L"\s-1WATCHER\s0 \s-1STATES\s0\*(R" for details.
5035.IP "application" 4
5036.IX Item "application"
5037In this document, an application is whatever is using libev.
5038.IP "backend" 4
5039.IX Item "backend"
5040The part of the code dealing with the operating system interfaces.
5041.IP "callback" 4
5042.IX Item "callback"
5043The address of a function that is called when some event has been
5044detected. Callbacks are being passed the event loop, the watcher that
5045received the event, and the actual event bitset.
5046.IP "callback/watcher invocation" 4
5047.IX Item "callback/watcher invocation"
5048The act of calling the callback associated with a watcher.
5049.IP "event" 4
5050.IX Item "event"
5051A change of state of some external event, such as data now being available
5052for reading on a file descriptor, time having passed or simply not having
5053any other events happening anymore.
5054.Sp
5055In libev, events are represented as single bits (such as \f(CW\*(C`EV_READ\*(C'\fR or
5056\&\f(CW\*(C`EV_TIMER\*(C'\fR).
5057.IP "event library" 4
5058.IX Item "event library"
5059A software package implementing an event model and loop.
5060.IP "event loop" 4
5061.IX Item "event loop"
5062An entity that handles and processes external events and converts them
5063into callback invocations.
5064.IP "event model" 4
5065.IX Item "event model"
5066The model used to describe how an event loop handles and processes
5067watchers and events.
5068.IP "pending" 4
5069.IX Item "pending"
5070A watcher is pending as soon as the corresponding event has been
5071detected. See \*(L"\s-1WATCHER\s0 \s-1STATES\s0\*(R" for details.
5072.IP "real time" 4
5073.IX Item "real time"
5074The physical time that is observed. It is apparently strictly monotonic :)
5075.IP "wall-clock time" 4
5076.IX Item "wall-clock time"
5077The time and date as shown on clocks. Unlike real time, it can actually
5078be wrong and jump forwards and backwards, e.g. when the you adjust your
5079clock.
5080.IP "watcher" 4
5081.IX Item "watcher"
5082A data structure that describes interest in certain events. Watchers need
5083to be started (attached to an event loop) before they can receive events.
957.SH "AUTHOR" 5084.SH "AUTHOR"
958.IX Header "AUTHOR" 5085.IX Header "AUTHOR"
959Marc Lehmann <libev@schmorp.de>. 5086Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5087Magnusson and Emanuele Giaquinta.

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