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129.\" ======================================================================== 133.\" ========================================================================
130.\" 134.\"
131.IX Title ""<STANDARD INPUT>" 1" 135.IX Title "LIBEV 3"
132.TH "<STANDARD INPUT>" 1 "2007-11-24" "perl v5.8.8" "User Contributed Perl Documentation" 136.TH LIBEV 3 "2015-05-01" "libev-4.19" "libev - high performance full featured event loop"
137.\" For nroff, turn off justification. Always turn off hyphenation; it makes
138.\" way too many mistakes in technical documents.
139.if n .ad l
140.nh
133.SH "NAME" 141.SH "NAME"
134libev \- a high performance full\-featured event loop written in C 142libev \- a high performance full\-featured event loop written in C
135.SH "SYNOPSIS" 143.SH "SYNOPSIS"
136.IX Header "SYNOPSIS" 144.IX Header "SYNOPSIS"
137.Vb 1 145.Vb 1
138\& #include <ev.h> 146\& #include <ev.h>
139.Ve 147.Ve
140.SH "DESCRIPTION" 148.SS "\s-1EXAMPLE PROGRAM\s0"
141.IX Header "DESCRIPTION" 149.IX Subsection "EXAMPLE PROGRAM"
150.Vb 2
151\& // a single header file is required
152\& #include <ev.h>
153\&
154\& #include <stdio.h> // for puts
155\&
156\& // every watcher type has its own typedef\*(Aqd struct
157\& // with the name ev_TYPE
158\& ev_io stdin_watcher;
159\& ev_timer timeout_watcher;
160\&
161\& // all watcher callbacks have a similar signature
162\& // this callback is called when data is readable on stdin
163\& static void
164\& stdin_cb (EV_P_ ev_io *w, int revents)
165\& {
166\& puts ("stdin ready");
167\& // for one\-shot events, one must manually stop the watcher
168\& // with its corresponding stop function.
169\& ev_io_stop (EV_A_ w);
170\&
171\& // this causes all nested ev_run\*(Aqs to stop iterating
172\& ev_break (EV_A_ EVBREAK_ALL);
173\& }
174\&
175\& // another callback, this time for a time\-out
176\& static void
177\& timeout_cb (EV_P_ ev_timer *w, int revents)
178\& {
179\& puts ("timeout");
180\& // this causes the innermost ev_run to stop iterating
181\& ev_break (EV_A_ EVBREAK_ONE);
182\& }
183\&
184\& int
185\& main (void)
186\& {
187\& // use the default event loop unless you have special needs
188\& struct ev_loop *loop = EV_DEFAULT;
189\&
190\& // initialise an io watcher, then start it
191\& // this one will watch for stdin to become readable
192\& ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
193\& ev_io_start (loop, &stdin_watcher);
194\&
195\& // initialise a timer watcher, then start it
196\& // simple non\-repeating 5.5 second timeout
197\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
198\& ev_timer_start (loop, &timeout_watcher);
199\&
200\& // now wait for events to arrive
201\& ev_run (loop, 0);
202\&
203\& // break was called, so exit
204\& return 0;
205\& }
206.Ve
207.SH "ABOUT THIS DOCUMENT"
208.IX Header "ABOUT THIS DOCUMENT"
209This document documents the libev software package.
210.PP
211The newest version of this document is also available as an html-formatted
212web page you might find easier to navigate when reading it for the first
213time: <http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
214.PP
215While this document tries to be as complete as possible in documenting
216libev, its usage and the rationale behind its design, it is not a tutorial
217on event-based programming, nor will it introduce event-based programming
218with libev.
219.PP
220Familiarity with event based programming techniques in general is assumed
221throughout this document.
222.SH "WHAT TO READ WHEN IN A HURRY"
223.IX Header "WHAT TO READ WHEN IN A HURRY"
224This manual tries to be very detailed, but unfortunately, this also makes
225it very long. If you just want to know the basics of libev, I suggest
226reading \*(L"\s-1ANATOMY OF A WATCHER\*(R"\s0, then the \*(L"\s-1EXAMPLE PROGRAM\*(R"\s0 above and
227look up the missing functions in \*(L"\s-1GLOBAL FUNCTIONS\*(R"\s0 and the \f(CW\*(C`ev_io\*(C'\fR and
228\&\f(CW\*(C`ev_timer\*(C'\fR sections in \*(L"\s-1WATCHER TYPES\*(R"\s0.
229.SH "ABOUT LIBEV"
230.IX Header "ABOUT LIBEV"
142Libev is an event loop: you register interest in certain events (such as a 231Libev 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 232file descriptor being readable or a timeout occurring), and it will manage
144these event sources and provide your program with events. 233these event sources and provide your program with events.
145.PP 234.PP
146To do this, it must take more or less complete control over your process 235To 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 236(or thread) by executing the \fIevent loop\fR handler, and will then
148communicate events via a callback mechanism. 237communicate events via a callback mechanism.
149.PP 238.PP
150You register interest in certain events by registering so-called \fIevent 239You register interest in certain events by registering so-called \fIevent
151watchers\fR, which are relatively small C structures you initialise with the 240watchers\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 241details of the event, and then hand it over to libev by \fIstarting\fR the
153watcher. 242watcher.
154.SH "FEATURES" 243.SS "\s-1FEATURES\s0"
155.IX Header "FEATURES" 244.IX Subsection "FEATURES"
156Libev supports select, poll, the linux-specific epoll and the bsd-specific 245Libev 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 246BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port mechanisms
158timers with customised rescheduling, signal events, process status change 247for 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 248(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 249inter-thread wakeup (\f(CW\*(C`ev_async\*(C'\fR)/signal handling (\f(CW\*(C`ev_signal\*(C'\fR)) relative
161fast (see this benchmark comparing 250timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers with customised rescheduling
162it to libevent for example). 251(\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals (\f(CW\*(C`ev_signal\*(C'\fR), process status
252change events (\f(CW\*(C`ev_child\*(C'\fR), and event watchers dealing with the event
253loop mechanism itself (\f(CW\*(C`ev_idle\*(C'\fR, \f(CW\*(C`ev_embed\*(C'\fR, \f(CW\*(C`ev_prepare\*(C'\fR and
254\&\f(CW\*(C`ev_check\*(C'\fR watchers) as well as file watchers (\f(CW\*(C`ev_stat\*(C'\fR) and even
255limited support for fork events (\f(CW\*(C`ev_fork\*(C'\fR).
256.PP
257It also is quite fast (see this
258benchmark <http://libev.schmorp.de/bench.html> comparing it to libevent
259for example).
163.SH "CONVENTIONS" 260.SS "\s-1CONVENTIONS\s0"
164.IX Header "CONVENTIONS" 261.IX Subsection "CONVENTIONS"
165Libev is very configurable. In this manual the default configuration 262Libev is very configurable. In this manual the default (and most common)
166will be described, which supports multiple event loops. For more info 263configuration will be described, which supports multiple event loops. For
167about various configuration options please have a look at the file 264more 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 265\&\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 266for 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) 267name \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. 268this argument.
172.SH "TIME REPRESENTATION" 269.SS "\s-1TIME REPRESENTATION\s0"
173.IX Header "TIME REPRESENTATION" 270.IX Subsection "TIME REPRESENTATION"
174Libev represents time as a single floating point number, representing the 271Libev represents time as a single floating point number, representing
175(fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere near 272the (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 273somewhere 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 274ask). This type is called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use
178to the \f(CW\*(C`double\*(C'\fR type in C, and when you need to do any calculations on 275too. It usually aliases to the \f(CW\*(C`double\*(C'\fR type in C. When you need to do
179it, you should treat it as such. 276any calculations on it, you should treat it as some floating point value.
277.PP
278Unlike the name component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for
279time differences (e.g. delays) throughout libev.
280.SH "ERROR HANDLING"
281.IX Header "ERROR HANDLING"
282Libev knows three classes of errors: operating system errors, usage errors
283and internal errors (bugs).
284.PP
285When libev catches an operating system error it cannot handle (for example
286a system call indicating a condition libev cannot fix), it calls the callback
287set via \f(CW\*(C`ev_set_syserr_cb\*(C'\fR, which is supposed to fix the problem or
288abort. The default is to print a diagnostic message and to call \f(CW\*(C`abort
289()\*(C'\fR.
290.PP
291When libev detects a usage error such as a negative timer interval, then
292it will print a diagnostic message and abort (via the \f(CW\*(C`assert\*(C'\fR mechanism,
293so \f(CW\*(C`NDEBUG\*(C'\fR will disable this checking): these are programming errors in
294the libev caller and need to be fixed there.
295.PP
296Libev also has a few internal error-checking \f(CW\*(C`assert\*(C'\fRions, and also has
297extensive consistency checking code. These do not trigger under normal
298circumstances, as they indicate either a bug in libev or worse.
180.SH "GLOBAL FUNCTIONS" 299.SH "GLOBAL FUNCTIONS"
181.IX Header "GLOBAL FUNCTIONS" 300.IX Header "GLOBAL FUNCTIONS"
182These functions can be called anytime, even before initialising the 301These functions can be called anytime, even before initialising the
183library in any way. 302library in any way.
184.IP "ev_tstamp ev_time ()" 4 303.IP "ev_tstamp ev_time ()" 4
185.IX Item "ev_tstamp ev_time ()" 304.IX Item "ev_tstamp ev_time ()"
186Returns the current time as libev would use it. Please note that the 305Returns the current time as libev would use it. Please note that the
187\&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp 306\&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp
188you actually want to know. 307you actually want to know. Also interesting is the combination of
308\&\f(CW\*(C`ev_now_update\*(C'\fR and \f(CW\*(C`ev_now\*(C'\fR.
309.IP "ev_sleep (ev_tstamp interval)" 4
310.IX Item "ev_sleep (ev_tstamp interval)"
311Sleep for the given interval: The current thread will be blocked
312until either it is interrupted or the given time interval has
313passed (approximately \- it might return a bit earlier even if not
314interrupted). Returns immediately if \f(CW\*(C`interval <= 0\*(C'\fR.
315.Sp
316Basically this is a sub-second-resolution \f(CW\*(C`sleep ()\*(C'\fR.
317.Sp
318The range of the \f(CW\*(C`interval\*(C'\fR is limited \- libev only guarantees to work
319with sleep times of up to one day (\f(CW\*(C`interval <= 86400\*(C'\fR).
189.IP "int ev_version_major ()" 4 320.IP "int ev_version_major ()" 4
190.IX Item "int ev_version_major ()" 321.IX Item "int ev_version_major ()"
191.PD 0 322.PD 0
192.IP "int ev_version_minor ()" 4 323.IP "int ev_version_minor ()" 4
193.IX Item "int ev_version_minor ()" 324.IX Item "int ev_version_minor ()"
194.PD 325.PD
195You can find out the major and minor version numbers of the library 326You can find out the major and minor \s-1ABI\s0 version numbers of the library
196you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and 327you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and
197\&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global 328\&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global
198symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the 329symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the
199version of the library your program was compiled against. 330version of the library your program was compiled against.
200.Sp 331.Sp
332These version numbers refer to the \s-1ABI\s0 version of the library, not the
333release version.
334.Sp
201Usually, it's a good idea to terminate if the major versions mismatch, 335Usually, it's a good idea to terminate if the major versions mismatch,
202as this indicates an incompatible change. Minor versions are usually 336as this indicates an incompatible change. Minor versions are usually
203compatible to older versions, so a larger minor version alone is usually 337compatible to older versions, so a larger minor version alone is usually
204not a problem. 338not a problem.
205.Sp 339.Sp
206Example: make sure we haven't accidentally been linked against the wrong 340Example: Make sure we haven't accidentally been linked against the wrong
207version: 341version (note, however, that this will not detect other \s-1ABI\s0 mismatches,
342such as \s-1LFS\s0 or reentrancy).
208.Sp 343.Sp
209.Vb 3 344.Vb 3
210\& assert (("libev version mismatch", 345\& assert (("libev version mismatch",
211\& ev_version_major () == EV_VERSION_MAJOR 346\& ev_version_major () == EV_VERSION_MAJOR
212\& && ev_version_minor () >= EV_VERSION_MINOR)); 347\& && ev_version_minor () >= EV_VERSION_MINOR));
213.Ve 348.Ve
214.IP "unsigned int ev_supported_backends ()" 4 349.IP "unsigned int ev_supported_backends ()" 4
215.IX Item "unsigned int ev_supported_backends ()" 350.IX Item "unsigned int ev_supported_backends ()"
216Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR 351Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR
217value) compiled into this binary of libev (independent of their 352value) compiled into this binary of libev (independent of their
… …
220.Sp 355.Sp
221Example: make sure we have the epoll method, because yeah this is cool and 356Example: make sure we have the epoll method, because yeah this is cool and
222a must have and can we have a torrent of it please!!!11 357a must have and can we have a torrent of it please!!!11
223.Sp 358.Sp
224.Vb 2 359.Vb 2
225\& assert (("sorry, no epoll, no sex", 360\& assert (("sorry, no epoll, no sex",
226\& ev_supported_backends () & EVBACKEND_EPOLL)); 361\& ev_supported_backends () & EVBACKEND_EPOLL));
227.Ve 362.Ve
228.IP "unsigned int ev_recommended_backends ()" 4 363.IP "unsigned int ev_recommended_backends ()" 4
229.IX Item "unsigned int ev_recommended_backends ()" 364.IX Item "unsigned int ev_recommended_backends ()"
230Return the set of all backends compiled into this binary of libev and also 365Return the set of all backends compiled into this binary of libev and
231recommended for this platform. This set is often smaller than the one 366also recommended for this platform, meaning it will work for most file
367descriptor types. This set is often smaller than the one returned by
232returned by \f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on 368\&\f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on most BSDs
233most BSDs and will not be autodetected unless you explicitly request it 369and will not be auto-detected unless you explicitly request it (assuming
234(assuming you know what you are doing). This is the set of backends that 370you know what you are doing). This is the set of backends that libev will
235libev will probe for if you specify no backends explicitly. 371probe for if you specify no backends explicitly.
236.IP "unsigned int ev_embeddable_backends ()" 4 372.IP "unsigned int ev_embeddable_backends ()" 4
237.IX Item "unsigned int ev_embeddable_backends ()" 373.IX Item "unsigned int ev_embeddable_backends ()"
238Returns the set of backends that are embeddable in other event loops. This 374Returns the set of backends that are embeddable in other event loops. This
239is the theoretical, all\-platform, value. To find which backends 375value is platform-specific but can include backends not available on the
240might be supported on the current system, you would need to look at 376current system. To find which embeddable backends might be supported on
241\&\f(CW\*(C`ev_embeddable_backends () & ev_supported_backends ()\*(C'\fR, likewise for 377the current system, you would need to look at \f(CW\*(C`ev_embeddable_backends ()
242recommended ones. 378& ev_supported_backends ()\*(C'\fR, likewise for recommended ones.
243.Sp 379.Sp
244See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info. 380See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
245.IP "ev_set_allocator (void *(*cb)(void *ptr, long size))" 4 381.IP "ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())" 4
246.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))" 382.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size) throw ())"
247Sets the allocation function to use (the prototype is similar to the 383Sets the allocation function to use (the prototype is similar \- the
248realloc C function, the semantics are identical). It is used to allocate 384semantics are identical to the \f(CW\*(C`realloc\*(C'\fR C89/SuS/POSIX function). It is
249and free memory (no surprises here). If it returns zero when memory 385used to allocate and free memory (no surprises here). If it returns zero
250needs to be allocated, the library might abort or take some potentially 386when memory needs to be allocated (\f(CW\*(C`size != 0\*(C'\fR), the library might abort
251destructive action. The default is your system realloc function. 387or take some potentially destructive action.
388.Sp
389Since some systems (at least OpenBSD and Darwin) fail to implement
390correct \f(CW\*(C`realloc\*(C'\fR semantics, libev will use a wrapper around the system
391\&\f(CW\*(C`realloc\*(C'\fR and \f(CW\*(C`free\*(C'\fR functions by default.
252.Sp 392.Sp
253You could override this function in high-availability programs to, say, 393You could override this function in high-availability programs to, say,
254free some memory if it cannot allocate memory, to use a special allocator, 394free some memory if it cannot allocate memory, to use a special allocator,
255or even to sleep a while and retry until some memory is available. 395or even to sleep a while and retry until some memory is available.
256.Sp 396.Sp
257Example: replace the libev allocator with one that waits a bit and then 397Example: Replace the libev allocator with one that waits a bit and then
258retries: better than mine). 398retries (example requires a standards-compliant \f(CW\*(C`realloc\*(C'\fR).
259.Sp 399.Sp
260.Vb 6 400.Vb 6
261\& static void * 401\& static void *
262\& persistent_realloc (void *ptr, long size) 402\& persistent_realloc (void *ptr, size_t size)
263\& { 403\& {
264\& for (;;) 404\& for (;;)
265\& { 405\& {
266\& void *newptr = realloc (ptr, size); 406\& void *newptr = realloc (ptr, size);
267.Ve 407\&
268.Sp
269.Vb 2
270\& if (newptr) 408\& if (newptr)
271\& return newptr; 409\& return newptr;
272.Ve 410\&
273.Sp
274.Vb 3
275\& sleep (60); 411\& sleep (60);
276\& } 412\& }
277\& } 413\& }
278.Ve 414\&
279.Sp
280.Vb 2
281\& ... 415\& ...
282\& ev_set_allocator (persistent_realloc); 416\& ev_set_allocator (persistent_realloc);
283.Ve 417.Ve
284.IP "ev_set_syserr_cb (void (*cb)(const char *msg));" 4 418.IP "ev_set_syserr_cb (void (*cb)(const char *msg) throw ())" 4
285.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg));" 419.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg) throw ())"
286Set the callback function to call on a retryable syscall error (such 420Set the callback function to call on a retryable system call error (such
287as failed select, poll, epoll_wait). The message is a printable string 421as failed select, poll, epoll_wait). The message is a printable string
288indicating the system call or subsystem causing the problem. If this 422indicating the system call or subsystem causing the problem. If this
289callback is set, then libev will expect it to remedy the sitution, no 423callback is set, then libev will expect it to remedy the situation, no
290matter what, when it returns. That is, libev will generally retry the 424matter what, when it returns. That is, libev will generally retry the
291requested operation, or, if the condition doesn't go away, do bad stuff 425requested operation, or, if the condition doesn't go away, do bad stuff
292(such as abort). 426(such as abort).
293.Sp 427.Sp
294Example: do the same thing as libev does internally: 428Example: This is basically the same thing that libev does internally, too.
295.Sp 429.Sp
296.Vb 6 430.Vb 6
297\& static void 431\& static void
298\& fatal_error (const char *msg) 432\& fatal_error (const char *msg)
299\& { 433\& {
300\& perror (msg); 434\& perror (msg);
301\& abort (); 435\& abort ();
302\& } 436\& }
303.Ve 437\&
304.Sp
305.Vb 2
306\& ... 438\& ...
307\& ev_set_syserr_cb (fatal_error); 439\& ev_set_syserr_cb (fatal_error);
308.Ve 440.Ve
441.IP "ev_feed_signal (int signum)" 4
442.IX Item "ev_feed_signal (int signum)"
443This function can be used to \*(L"simulate\*(R" a signal receive. It is completely
444safe to call this function at any time, from any context, including signal
445handlers or random threads.
446.Sp
447Its main use is to customise signal handling in your process, especially
448in the presence of threads. For example, you could block signals
449by default in all threads (and specifying \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when
450creating any loops), and in one thread, use \f(CW\*(C`sigwait\*(C'\fR or any other
451mechanism to wait for signals, then \*(L"deliver\*(R" them to libev by calling
452\&\f(CW\*(C`ev_feed_signal\*(C'\fR.
309.SH "FUNCTIONS CONTROLLING THE EVENT LOOP" 453.SH "FUNCTIONS CONTROLLING EVENT LOOPS"
310.IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP" 454.IX Header "FUNCTIONS CONTROLLING EVENT LOOPS"
311An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR. The library knows two 455An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR (the \f(CW\*(C`struct\*(C'\fR is
312types of such loops, the \fIdefault\fR loop, which supports signals and child 456\&\fInot\fR optional in this case unless libev 3 compatibility is disabled, as
313events, and dynamically created loops which do not. 457libev 3 had an \f(CW\*(C`ev_loop\*(C'\fR function colliding with the struct name).
314.PP 458.PP
315If you use threads, a common model is to run the default event loop 459The library knows two types of such loops, the \fIdefault\fR loop, which
316in your main thread (or in a separate thread) and for each thread you 460supports child process events, and dynamically created event loops which
317create, you also create another event loop. Libev itself does no locking 461do not.
318whatsoever, so if you mix calls to the same event loop in different
319threads, make sure you lock (this is usually a bad idea, though, even if
320done correctly, because it's hideous and inefficient).
321.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4 462.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
322.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)" 463.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
323This will initialise the default event loop if it hasn't been initialised 464This returns the \*(L"default\*(R" event loop object, which is what you should
324yet and return it. If the default loop could not be initialised, returns 465normally use when you just need \*(L"the event loop\*(R". Event loop objects and
325false. If it already was initialised it simply returns it (and ignores the 466the \f(CW\*(C`flags\*(C'\fR parameter are described in more detail in the entry for
326flags. If that is troubling you, check \f(CW\*(C`ev_backend ()\*(C'\fR afterwards). 467\&\f(CW\*(C`ev_loop_new\*(C'\fR.
468.Sp
469If the default loop is already initialised then this function simply
470returns it (and ignores the flags. If that is troubling you, check
471\&\f(CW\*(C`ev_backend ()\*(C'\fR afterwards). Otherwise it will create it with the given
472flags, which should almost always be \f(CW0\fR, unless the caller is also the
473one calling \f(CW\*(C`ev_run\*(C'\fR or otherwise qualifies as \*(L"the main program\*(R".
327.Sp 474.Sp
328If you don't know what event loop to use, use the one returned from this 475If you don't know what event loop to use, use the one returned from this
329function. 476function (or via the \f(CW\*(C`EV_DEFAULT\*(C'\fR macro).
477.Sp
478Note that this function is \fInot\fR thread-safe, so if you want to use it
479from multiple threads, you have to employ some kind of mutex (note also
480that this case is unlikely, as loops cannot be shared easily between
481threads anyway).
482.Sp
483The default loop is the only loop that can handle \f(CW\*(C`ev_child\*(C'\fR watchers,
484and to do this, it always registers a handler for \f(CW\*(C`SIGCHLD\*(C'\fR. If this is
485a problem for your application you can either create a dynamic loop with
486\&\f(CW\*(C`ev_loop_new\*(C'\fR which doesn't do that, or you can simply overwrite the
487\&\f(CW\*(C`SIGCHLD\*(C'\fR signal handler \fIafter\fR calling \f(CW\*(C`ev_default_init\*(C'\fR.
488.Sp
489Example: This is the most typical usage.
490.Sp
491.Vb 2
492\& if (!ev_default_loop (0))
493\& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
494.Ve
495.Sp
496Example: Restrict libev to the select and poll backends, and do not allow
497environment settings to be taken into account:
498.Sp
499.Vb 1
500\& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
501.Ve
502.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
503.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
504This will create and initialise a new event loop object. If the loop
505could not be initialised, returns false.
506.Sp
507This function is thread-safe, and one common way to use libev with
508threads is indeed to create one loop per thread, and using the default
509loop in the \*(L"main\*(R" or \*(L"initial\*(R" thread.
330.Sp 510.Sp
331The flags argument can be used to specify special behaviour or specific 511The flags argument can be used to specify special behaviour or specific
332backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). 512backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).
333.Sp 513.Sp
334The following flags are supported: 514The following flags are supported:
… …
339The default flags value. Use this if you have no clue (it's the right 519The default flags value. Use this if you have no clue (it's the right
340thing, believe me). 520thing, believe me).
341.ie n .IP """EVFLAG_NOENV""" 4 521.ie n .IP """EVFLAG_NOENV""" 4
342.el .IP "\f(CWEVFLAG_NOENV\fR" 4 522.el .IP "\f(CWEVFLAG_NOENV\fR" 4
343.IX Item "EVFLAG_NOENV" 523.IX Item "EVFLAG_NOENV"
344If this flag bit is ored into the flag value (or the program runs setuid 524If this flag bit is or'ed into the flag value (or the program runs setuid
345or setgid) then libev will \fInot\fR look at the environment variable 525or setgid) then libev will \fInot\fR look at the environment variable
346\&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will 526\&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will
347override the flags completely if it is found in the environment. This is 527override the flags completely if it is found in the environment. This is
348useful to try out specific backends to test their performance, or to work 528useful to try out specific backends to test their performance, to work
349around bugs. 529around bugs, or to make libev threadsafe (accessing environment variables
530cannot be done in a threadsafe way, but usually it works if no other
531thread modifies them).
532.ie n .IP """EVFLAG_FORKCHECK""" 4
533.el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4
534.IX Item "EVFLAG_FORKCHECK"
535Instead of calling \f(CW\*(C`ev_loop_fork\*(C'\fR manually after a fork, you can also
536make libev check for a fork in each iteration by enabling this flag.
537.Sp
538This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop,
539and thus this might slow down your event loop if you do a lot of loop
540iterations and little real work, but is usually not noticeable (on my
541GNU/Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn sequence
542without a system call and thus \fIvery\fR fast, but my GNU/Linux system also has
543\&\f(CW\*(C`pthread_atfork\*(C'\fR which is even faster).
544.Sp
545The big advantage of this flag is that you can forget about fork (and
546forget about forgetting to tell libev about forking) when you use this
547flag.
548.Sp
549This flag setting cannot be overridden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR
550environment variable.
551.ie n .IP """EVFLAG_NOINOTIFY""" 4
552.el .IP "\f(CWEVFLAG_NOINOTIFY\fR" 4
553.IX Item "EVFLAG_NOINOTIFY"
554When this flag is specified, then libev will not attempt to use the
555\&\fIinotify\fR \s-1API\s0 for its \f(CW\*(C`ev_stat\*(C'\fR watchers. Apart from debugging and
556testing, this flag can be useful to conserve inotify file descriptors, as
557otherwise each loop using \f(CW\*(C`ev_stat\*(C'\fR watchers consumes one inotify handle.
558.ie n .IP """EVFLAG_SIGNALFD""" 4
559.el .IP "\f(CWEVFLAG_SIGNALFD\fR" 4
560.IX Item "EVFLAG_SIGNALFD"
561When this flag is specified, then libev will attempt to use the
562\&\fIsignalfd\fR \s-1API\s0 for its \f(CW\*(C`ev_signal\*(C'\fR (and \f(CW\*(C`ev_child\*(C'\fR) watchers. This \s-1API\s0
563delivers signals synchronously, which makes it both faster and might make
564it possible to get the queued signal data. It can also simplify signal
565handling with threads, as long as you properly block signals in your
566threads that are not interested in handling them.
567.Sp
568Signalfd will not be used by default as this changes your signal mask, and
569there are a lot of shoddy libraries and programs (glib's threadpool for
570example) that can't properly initialise their signal masks.
571.ie n .IP """EVFLAG_NOSIGMASK""" 4
572.el .IP "\f(CWEVFLAG_NOSIGMASK\fR" 4
573.IX Item "EVFLAG_NOSIGMASK"
574When this flag is specified, then libev will avoid to modify the signal
575mask. Specifically, this means you have to make sure signals are unblocked
576when you want to receive them.
577.Sp
578This behaviour is useful when you want to do your own signal handling, or
579want to handle signals only in specific threads and want to avoid libev
580unblocking the signals.
581.Sp
582It's also required by \s-1POSIX\s0 in a threaded program, as libev calls
583\&\f(CW\*(C`sigprocmask\*(C'\fR, whose behaviour is officially unspecified.
584.Sp
585This flag's behaviour will become the default in future versions of libev.
350.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4 586.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
351.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4 587.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
352.IX Item "EVBACKEND_SELECT (value 1, portable select backend)" 588.IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
353This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as 589This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as
354libev tries to roll its own fd_set with no limits on the number of fds, 590libev tries to roll its own fd_set with no limits on the number of fds,
355but if that fails, expect a fairly low limit on the number of fds when 591but if that fails, expect a fairly low limit on the number of fds when
356using this backend. It doesn't scale too well (O(highest_fd)), but its usually 592using this backend. It doesn't scale too well (O(highest_fd)), but its
357the fastest backend for a low number of fds. 593usually the fastest backend for a low number of (low-numbered :) fds.
594.Sp
595To get good performance out of this backend you need a high amount of
596parallelism (most of the file descriptors should be busy). If you are
597writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many
598connections as possible during one iteration. You might also want to have
599a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of
600readiness notifications you get per iteration.
601.Sp
602This 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
603\&\f(CW\*(C`writefds\*(C'\fR set (and to work around Microsoft Windows bugs, also onto the
604\&\f(CW\*(C`exceptfds\*(C'\fR set on that platform).
358.ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4 605.ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4
359.el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4 606.el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4
360.IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)" 607.IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)"
361And this is your standard \fIpoll\fR\|(2) backend. It's more complicated than 608And this is your standard \fIpoll\fR\|(2) backend. It's more complicated
362select, but handles sparse fds better and has no artificial limit on the 609than select, but handles sparse fds better and has no artificial
363number of fds you can use (except it will slow down considerably with a 610limit on the number of fds you can use (except it will slow down
364lot of inactive fds). It scales similarly to select, i.e. O(total_fds). 611considerably with a lot of inactive fds). It scales similarly to select,
612i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for
613performance tips.
614.Sp
615This backend maps \f(CW\*(C`EV_READ\*(C'\fR to \f(CW\*(C`POLLIN | POLLERR | POLLHUP\*(C'\fR, and
616\&\f(CW\*(C`EV_WRITE\*(C'\fR to \f(CW\*(C`POLLOUT | POLLERR | POLLHUP\*(C'\fR.
365.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4 617.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
366.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4 618.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
367.IX Item "EVBACKEND_EPOLL (value 4, Linux)" 619.IX Item "EVBACKEND_EPOLL (value 4, Linux)"
620Use the linux-specific \fIepoll\fR\|(7) interface (for both pre\- and post\-2.6.9
621kernels).
622.Sp
368For few fds, this backend is a bit little slower than poll and select, 623For few fds, this backend is a bit little slower than poll and select, but
369but it scales phenomenally better. While poll and select usually scale like 624it scales phenomenally better. While poll and select usually scale like
370O(total_fds) where n is the total number of fds (or the highest fd), epoll scales 625O(total_fds) where total_fds is the total number of fds (or the highest
371either O(1) or O(active_fds). 626fd), epoll scales either O(1) or O(active_fds).
372.Sp 627.Sp
628The epoll mechanism deserves honorable mention as the most misdesigned
629of the more advanced event mechanisms: mere annoyances include silently
630dropping file descriptors, requiring a system call per change per file
631descriptor (and unnecessary guessing of parameters), problems with dup,
632returning before the timeout value, resulting in additional iterations
633(and only giving 5ms accuracy while select on the same platform gives
6340.1ms) and so on. The biggest issue is fork races, however \- if a program
635forks then \fIboth\fR parent and child process have to recreate the epoll
636set, which can take considerable time (one syscall per file descriptor)
637and is of course hard to detect.
638.Sp
639Epoll is also notoriously buggy \- embedding epoll fds \fIshould\fR work,
640but of course \fIdoesn't\fR, and epoll just loves to report events for
641totally \fIdifferent\fR file descriptors (even already closed ones, so
642one cannot even remove them from the set) than registered in the set
643(especially on \s-1SMP\s0 systems). Libev tries to counter these spurious
644notifications by employing an additional generation counter and comparing
645that against the events to filter out spurious ones, recreating the set
646when required. Epoll also erroneously rounds down timeouts, but gives you
647no way to know when and by how much, so sometimes you have to busy-wait
648because epoll returns immediately despite a nonzero timeout. And last
649not least, it also refuses to work with some file descriptors which work
650perfectly fine with \f(CW\*(C`select\*(C'\fR (files, many character devices...).
651.Sp
652Epoll is truly the train wreck among event poll mechanisms, a frankenpoll,
653cobbled together in a hurry, no thought to design or interaction with
654others. Oh, the pain, will it ever stop...
655.Sp
373While stopping and starting an I/O watcher in the same iteration will 656While stopping, setting and starting an I/O watcher in the same iteration
374result in some caching, there is still a syscall per such incident 657will result in some caching, there is still a system call per such
375(because the fd could point to a different file description now), so its 658incident (because the same \fIfile descriptor\fR could point to a different
376best to avoid that. Also, \fIdup()\fRed file descriptors might not work very 659\&\fIfile description\fR now), so its best to avoid that. Also, \f(CW\*(C`dup ()\*(C'\fR'ed
377well if you register events for both fds. 660file descriptors might not work very well if you register events for both
661file descriptors.
378.Sp 662.Sp
379Please note that epoll sometimes generates spurious notifications, so you 663Best performance from this backend is achieved by not unregistering all
380need to use non-blocking I/O or other means to avoid blocking when no data 664watchers for a file descriptor until it has been closed, if possible,
381(or space) is available. 665i.e. keep at least one watcher active per fd at all times. Stopping and
666starting a watcher (without re-setting it) also usually doesn't cause
667extra overhead. A fork can both result in spurious notifications as well
668as in libev having to destroy and recreate the epoll object, which can
669take considerable time and thus should be avoided.
670.Sp
671All this means that, in practice, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR can be as fast or
672faster than epoll for maybe up to a hundred file descriptors, depending on
673the usage. So sad.
674.Sp
675While nominally embeddable in other event loops, this feature is broken in
676all kernel versions tested so far.
677.Sp
678This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
679\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
382.ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4 680.ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4
383.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4 681.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
384.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)" 682.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
385Kqueue deserves special mention, as at the time of this writing, it 683Kqueue deserves special mention, as at the time of this writing, it
386was broken on all BSDs except NetBSD (usually it doesn't work with 684was broken on all BSDs except NetBSD (usually it doesn't work reliably
387anything but sockets and pipes, except on Darwin, where of course its 685with anything but sockets and pipes, except on Darwin, where of course
388completely useless). For this reason its not being \*(L"autodetected\*(R" 686it's completely useless). Unlike epoll, however, whose brokenness
687is by design, these kqueue bugs can (and eventually will) be fixed
688without \s-1API\s0 changes to existing programs. For this reason it's not being
389unless you explicitly specify it explicitly in the flags (i.e. using 689\&\*(L"auto-detected\*(R" unless you explicitly specify it in the flags (i.e. using
390\&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR). 690\&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a known-to-be-good (\-enough)
691system like NetBSD.
692.Sp
693You still can embed kqueue into a normal poll or select backend and use it
694only for sockets (after having made sure that sockets work with kqueue on
695the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
391.Sp 696.Sp
392It scales in the same way as the epoll backend, but the interface to the 697It scales in the same way as the epoll backend, but the interface to the
393kernel is more efficient (which says nothing about its actual speed, of 698kernel is more efficient (which says nothing about its actual speed, of
394course). While starting and stopping an I/O watcher does not cause an 699course). While stopping, setting and starting an I/O watcher does never
395extra syscall as with epoll, it still adds up to four event changes per 700cause an extra system call as with \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to
396incident, so its best to avoid that. 701two event changes per incident. Support for \f(CW\*(C`fork ()\*(C'\fR is very bad (you
702might have to leak fd's on fork, but it's more sane than epoll) and it
703drops fds silently in similarly hard-to-detect cases.
704.Sp
705This backend usually performs well under most conditions.
706.Sp
707While nominally embeddable in other event loops, this doesn't work
708everywhere, so you might need to test for this. And since it is broken
709almost everywhere, you should only use it when you have a lot of sockets
710(for which it usually works), by embedding it into another event loop
711(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
712also broken on \s-1OS X\s0)) and, did I mention it, using it only for sockets.
713.Sp
714This backend maps \f(CW\*(C`EV_READ\*(C'\fR into an \f(CW\*(C`EVFILT_READ\*(C'\fR kevent with
715\&\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
716\&\f(CW\*(C`NOTE_EOF\*(C'\fR.
397.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4 717.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
398.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4 718.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
399.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)" 719.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
400This is not implemented yet (and might never be). 720This is not implemented yet (and might never be, unless you send me an
721implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets
722and is not embeddable, which would limit the usefulness of this backend
723immensely.
401.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4 724.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
402.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4 725.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
403.IX Item "EVBACKEND_PORT (value 32, Solaris 10)" 726.IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
404This uses the Solaris 10 port mechanism. As with everything on Solaris, 727This uses the Solaris 10 event port mechanism. As with everything on Solaris,
405it's really slow, but it still scales very well (O(active_fds)). 728it's really slow, but it still scales very well (O(active_fds)).
406.Sp 729.Sp
407Please note that solaris ports can result in a lot of spurious 730While this backend scales well, it requires one system call per active
408notifications, so you need to use non-blocking I/O or other means to avoid 731file descriptor per loop iteration. For small and medium numbers of file
409blocking when no data (or space) is available. 732descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend
733might perform better.
734.Sp
735On the positive side, this backend actually performed fully to
736specification in all tests and is fully embeddable, which is a rare feat
737among the OS-specific backends (I vastly prefer correctness over speed
738hacks).
739.Sp
740On the negative side, the interface is \fIbizarre\fR \- so bizarre that
741even sun itself gets it wrong in their code examples: The event polling
742function sometimes returns events to the caller even though an error
743occurred, but with no indication whether it has done so or not (yes, it's
744even documented that way) \- deadly for edge-triggered interfaces where you
745absolutely have to know whether an event occurred or not because you have
746to re-arm the watcher.
747.Sp
748Fortunately libev seems to be able to work around these idiocies.
749.Sp
750This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
751\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
410.ie n .IP """EVBACKEND_ALL""" 4 752.ie n .IP """EVBACKEND_ALL""" 4
411.el .IP "\f(CWEVBACKEND_ALL\fR" 4 753.el .IP "\f(CWEVBACKEND_ALL\fR" 4
412.IX Item "EVBACKEND_ALL" 754.IX Item "EVBACKEND_ALL"
413Try all backends (even potentially broken ones that wouldn't be tried 755Try all backends (even potentially broken ones that wouldn't be tried
414with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as 756with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as
415\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR. 757\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR.
758.Sp
759It is definitely not recommended to use this flag, use whatever
760\&\f(CW\*(C`ev_recommended_backends ()\*(C'\fR returns, or simply do not specify a backend
761at all.
762.ie n .IP """EVBACKEND_MASK""" 4
763.el .IP "\f(CWEVBACKEND_MASK\fR" 4
764.IX Item "EVBACKEND_MASK"
765Not a backend at all, but a mask to select all backend bits from a
766\&\f(CW\*(C`flags\*(C'\fR value, in case you want to mask out any backends from a flags
767value (e.g. when modifying the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR environment variable).
416.RE 768.RE
417.RS 4 769.RS 4
418.Sp 770.Sp
419If one or more of these are ored into the flags value, then only these 771If one or more of the backend flags are or'ed into the flags value,
420backends will be tried (in the reverse order as given here). If none are 772then only these backends will be tried (in the reverse order as listed
421specified, most compiled-in backend will be tried, usually in reverse 773here). If none are specified, all backends in \f(CW\*(C`ev_recommended_backends
422order of their flag values :) 774()\*(C'\fR will be tried.
423.Sp 775.Sp
424The most typical usage is like this: 776Example: Try to create a event loop that uses epoll and nothing else.
425.Sp 777.Sp
426.Vb 2 778.Vb 3
427\& if (!ev_default_loop (0)) 779\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
428\& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?"); 780\& if (!epoller)
781\& fatal ("no epoll found here, maybe it hides under your chair");
429.Ve 782.Ve
430.Sp 783.Sp
431Restrict libev to the select and poll backends, and do not allow 784Example: Use whatever libev has to offer, but make sure that kqueue is
432environment settings to be taken into account: 785used if available.
433.Sp 786.Sp
434.Vb 1 787.Vb 1
435\& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
436.Ve
437.Sp
438Use whatever libev has to offer, but make sure that kqueue is used if
439available (warning, breaks stuff, best use only with your own private
440event loop and only if you know the \s-1OS\s0 supports your types of fds):
441.Sp
442.Vb 1
443\& ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE); 788\& struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
444.Ve 789.Ve
445.RE 790.RE
446.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
447.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
448Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is
449always distinct from the default loop. Unlike the default loop, it cannot
450handle signal and child watchers, and attempts to do so will be greeted by
451undefined behaviour (or a failed assertion if assertions are enabled).
452.Sp
453Example: try to create a event loop that uses epoll and nothing else.
454.Sp
455.Vb 3
456\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
457\& if (!epoller)
458\& fatal ("no epoll found here, maybe it hides under your chair");
459.Ve
460.IP "ev_default_destroy ()" 4 791.IP "ev_loop_destroy (loop)" 4
461.IX Item "ev_default_destroy ()" 792.IX Item "ev_loop_destroy (loop)"
462Destroys the default loop again (frees all memory and kernel state 793Destroys an event loop object (frees all memory and kernel state
463etc.). None of the active event watchers will be stopped in the normal 794etc.). None of the active event watchers will be stopped in the normal
464sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your 795sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your
465responsibility to either stop all watchers cleanly yoursef \fIbefore\fR 796responsibility to either stop all watchers cleanly yourself \fIbefore\fR
466calling this function, or cope with the fact afterwards (which is usually 797calling this function, or cope with the fact afterwards (which is usually
467the easiest thing, youc na just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them 798the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them
468for example). 799for example).
469.IP "ev_loop_destroy (loop)" 4
470.IX Item "ev_loop_destroy (loop)"
471Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an
472earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR.
473.IP "ev_default_fork ()" 4
474.IX Item "ev_default_fork ()"
475This function reinitialises the kernel state for backends that have
476one. Despite the name, you can call it anytime, but it makes most sense
477after forking, in either the parent or child process (or both, but that
478again makes little sense).
479.Sp 800.Sp
480You \fImust\fR call this function in the child process after forking if and 801Note that certain global state, such as signal state (and installed signal
481only if you want to use the event library in both processes. If you just 802handlers), will not be freed by this function, and related watchers (such
482fork+exec, you don't have to call it. 803as signal and child watchers) would need to be stopped manually.
483.Sp 804.Sp
484The function itself is quite fast and it's usually not a problem to call 805This function is normally used on loop objects allocated by
485it just in case after a fork. To make this easy, the function will fit in 806\&\f(CW\*(C`ev_loop_new\*(C'\fR, but it can also be used on the default loop returned by
486quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR: 807\&\f(CW\*(C`ev_default_loop\*(C'\fR, in which case it is not thread-safe.
487.Sp 808.Sp
488.Vb 1 809Note that it is not advisable to call this function on the default loop
489\& pthread_atfork (0, 0, ev_default_fork); 810except in the rare occasion where you really need to free its resources.
490.Ve 811If you need dynamically allocated loops it is better to use \f(CW\*(C`ev_loop_new\*(C'\fR
491.Sp 812and \f(CW\*(C`ev_loop_destroy\*(C'\fR.
492At the moment, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and \f(CW\*(C`EVBACKEND_POLL\*(C'\fR are safe to use
493without calling this function, so if you force one of those backends you
494do not need to care.
495.IP "ev_loop_fork (loop)" 4 813.IP "ev_loop_fork (loop)" 4
496.IX Item "ev_loop_fork (loop)" 814.IX Item "ev_loop_fork (loop)"
497Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by 815This function sets a flag that causes subsequent \f(CW\*(C`ev_run\*(C'\fR iterations
498\&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop 816to reinitialise the kernel state for backends that have one. Despite
499after fork, and how you do this is entirely your own problem. 817the name, you can call it anytime you are allowed to start or stop
818watchers (except inside an \f(CW\*(C`ev_prepare\*(C'\fR callback), but it makes most
819sense after forking, in the child process. You \fImust\fR call it (or use
820\&\f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR) in the child before resuming or calling \f(CW\*(C`ev_run\*(C'\fR.
821.Sp
822Again, you \fIhave\fR to call it on \fIany\fR loop that you want to re-use after
823a fork, \fIeven if you do not plan to use the loop in the parent\fR. This is
824because some kernel interfaces *cough* \fIkqueue\fR *cough* do funny things
825during fork.
826.Sp
827On the other hand, you only need to call this function in the child
828process if and only if you want to use the event loop in the child. If
829you just fork+exec or create a new loop in the child, you don't have to
830call it at all (in fact, \f(CW\*(C`epoll\*(C'\fR is so badly broken that it makes a
831difference, but libev will usually detect this case on its own and do a
832costly reset of the backend).
833.Sp
834The function itself is quite fast and it's usually not a problem to call
835it just in case after a fork.
836.Sp
837Example: Automate calling \f(CW\*(C`ev_loop_fork\*(C'\fR on the default loop when
838using pthreads.
839.Sp
840.Vb 5
841\& static void
842\& post_fork_child (void)
843\& {
844\& ev_loop_fork (EV_DEFAULT);
845\& }
846\&
847\& ...
848\& pthread_atfork (0, 0, post_fork_child);
849.Ve
850.IP "int ev_is_default_loop (loop)" 4
851.IX Item "int ev_is_default_loop (loop)"
852Returns true when the given loop is, in fact, the default loop, and false
853otherwise.
854.IP "unsigned int ev_iteration (loop)" 4
855.IX Item "unsigned int ev_iteration (loop)"
856Returns the current iteration count for the event loop, which is identical
857to the number of times libev did poll for new events. It starts at \f(CW0\fR
858and happily wraps around with enough iterations.
859.Sp
860This value can sometimes be useful as a generation counter of sorts (it
861\&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with
862\&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls \- and is incremented between the
863prepare and check phases.
864.IP "unsigned int ev_depth (loop)" 4
865.IX Item "unsigned int ev_depth (loop)"
866Returns the number of times \f(CW\*(C`ev_run\*(C'\fR was entered minus the number of
867times \f(CW\*(C`ev_run\*(C'\fR was exited normally, in other words, the recursion depth.
868.Sp
869Outside \f(CW\*(C`ev_run\*(C'\fR, this number is zero. In a callback, this number is
870\&\f(CW1\fR, unless \f(CW\*(C`ev_run\*(C'\fR was invoked recursively (or from another thread),
871in which case it is higher.
872.Sp
873Leaving \f(CW\*(C`ev_run\*(C'\fR abnormally (setjmp/longjmp, cancelling the thread,
874throwing an exception etc.), doesn't count as \*(L"exit\*(R" \- consider this
875as a hint to avoid such ungentleman-like behaviour unless it's really
876convenient, in which case it is fully supported.
500.IP "unsigned int ev_backend (loop)" 4 877.IP "unsigned int ev_backend (loop)" 4
501.IX Item "unsigned int ev_backend (loop)" 878.IX Item "unsigned int ev_backend (loop)"
502Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in 879Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
503use. 880use.
504.IP "ev_tstamp ev_now (loop)" 4 881.IP "ev_tstamp ev_now (loop)" 4
505.IX Item "ev_tstamp ev_now (loop)" 882.IX Item "ev_tstamp ev_now (loop)"
506Returns the current \*(L"event loop time\*(R", which is the time the event loop 883Returns the current \*(L"event loop time\*(R", which is the time the event loop
507received events and started processing them. This timestamp does not 884received events and started processing them. This timestamp does not
508change as long as callbacks are being processed, and this is also the base 885change as long as callbacks are being processed, and this is also the base
509time used for relative timers. You can treat it as the timestamp of the 886time used for relative timers. You can treat it as the timestamp of the
510event occuring (or more correctly, libev finding out about it). 887event occurring (or more correctly, libev finding out about it).
888.IP "ev_now_update (loop)" 4
889.IX Item "ev_now_update (loop)"
890Establishes the current time by querying the kernel, updating the time
891returned by \f(CW\*(C`ev_now ()\*(C'\fR in the progress. This is a costly operation and
892is usually done automatically within \f(CW\*(C`ev_run ()\*(C'\fR.
893.Sp
894This function is rarely useful, but when some event callback runs for a
895very long time without entering the event loop, updating libev's idea of
896the current time is a good idea.
897.Sp
898See also \*(L"The special problem of time updates\*(R" in the \f(CW\*(C`ev_timer\*(C'\fR section.
899.IP "ev_suspend (loop)" 4
900.IX Item "ev_suspend (loop)"
901.PD 0
902.IP "ev_resume (loop)" 4
903.IX Item "ev_resume (loop)"
904.PD
905These two functions suspend and resume an event loop, for use when the
906loop is not used for a while and timeouts should not be processed.
907.Sp
908A typical use case would be an interactive program such as a game: When
909the user presses \f(CW\*(C`^Z\*(C'\fR to suspend the game and resumes it an hour later it
910would be best to handle timeouts as if no time had actually passed while
911the program was suspended. This can be achieved by calling \f(CW\*(C`ev_suspend\*(C'\fR
912in your \f(CW\*(C`SIGTSTP\*(C'\fR handler, sending yourself a \f(CW\*(C`SIGSTOP\*(C'\fR and calling
913\&\f(CW\*(C`ev_resume\*(C'\fR directly afterwards to resume timer processing.
914.Sp
915Effectively, all \f(CW\*(C`ev_timer\*(C'\fR watchers will be delayed by the time spend
916between \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
917will be rescheduled (that is, they will lose any events that would have
918occurred while suspended).
919.Sp
920After calling \f(CW\*(C`ev_suspend\*(C'\fR you \fBmust not\fR call \fIany\fR function on the
921given loop other than \f(CW\*(C`ev_resume\*(C'\fR, and you \fBmust not\fR call \f(CW\*(C`ev_resume\*(C'\fR
922without a previous call to \f(CW\*(C`ev_suspend\*(C'\fR.
923.Sp
924Calling \f(CW\*(C`ev_suspend\*(C'\fR/\f(CW\*(C`ev_resume\*(C'\fR has the side effect of updating the
925event loop time (see \f(CW\*(C`ev_now_update\*(C'\fR).
511.IP "ev_loop (loop, int flags)" 4 926.IP "bool ev_run (loop, int flags)" 4
512.IX Item "ev_loop (loop, int flags)" 927.IX Item "bool ev_run (loop, int flags)"
513Finally, this is it, the event handler. This function usually is called 928Finally, this is it, the event handler. This function usually is called
514after you initialised all your watchers and you want to start handling 929after you have initialised all your watchers and you want to start
515events. 930handling events. It will ask the operating system for any new events, call
931the watcher callbacks, and then repeat the whole process indefinitely: This
932is why event loops are called \fIloops\fR.
516.Sp 933.Sp
517If the flags argument is specified as \f(CW0\fR, it will not return until 934If the flags argument is specified as \f(CW0\fR, it will keep handling events
518either no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called. 935until either no event watchers are active anymore or \f(CW\*(C`ev_break\*(C'\fR was
936called.
519.Sp 937.Sp
938The return value is false if there are no more active watchers (which
939usually means \*(L"all jobs done\*(R" or \*(L"deadlock\*(R"), and true in all other cases
940(which usually means " you should call \f(CW\*(C`ev_run\*(C'\fR again").
941.Sp
520Please note that an explicit \f(CW\*(C`ev_unloop\*(C'\fR is usually better than 942Please note that an explicit \f(CW\*(C`ev_break\*(C'\fR is usually better than
521relying on all watchers to be stopped when deciding when a program has 943relying on all watchers to be stopped when deciding when a program has
522finished (especially in interactive programs), but having a program that 944finished (especially in interactive programs), but having a program
523automatically loops as long as it has to and no longer by virtue of 945that automatically loops as long as it has to and no longer by virtue
524relying on its watchers stopping correctly is a thing of beauty. 946of relying on its watchers stopping correctly, that is truly a thing of
947beauty.
525.Sp 948.Sp
949This function is \fImostly\fR exception-safe \- you can break out of a
950\&\f(CW\*(C`ev_run\*(C'\fR call by calling \f(CW\*(C`longjmp\*(C'\fR in a callback, throwing a \*(C+
951exception and so on. This does not decrement the \f(CW\*(C`ev_depth\*(C'\fR value, nor
952will it clear any outstanding \f(CW\*(C`EVBREAK_ONE\*(C'\fR breaks.
953.Sp
526A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle 954A flags value of \f(CW\*(C`EVRUN_NOWAIT\*(C'\fR will look for new events, will handle
527those events and any outstanding ones, but will not block your process in 955those events and any already outstanding ones, but will not wait and
528case there are no events and will return after one iteration of the loop. 956block your process in case there are no events and will return after one
957iteration of the loop. This is sometimes useful to poll and handle new
958events while doing lengthy calculations, to keep the program responsive.
529.Sp 959.Sp
530A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if 960A flags value of \f(CW\*(C`EVRUN_ONCE\*(C'\fR will look for new events (waiting if
531neccessary) and will handle those and any outstanding ones. It will block 961necessary) and will handle those and any already outstanding ones. It
532your process until at least one new event arrives, and will return after 962will block your process until at least one new event arrives (which could
533one iteration of the loop. This is useful if you are waiting for some 963be an event internal to libev itself, so there is no guarantee that a
534external event in conjunction with something not expressible using other 964user-registered callback will be called), and will return after one
965iteration of the loop.
966.Sp
967This is useful if you are waiting for some external event in conjunction
968with something not expressible using other libev watchers (i.e. "roll your
535libev watchers. However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is 969own \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
536usually a better approach for this kind of thing. 970usually a better approach for this kind of thing.
537.Sp 971.Sp
538Here are the gory details of what \f(CW\*(C`ev_loop\*(C'\fR does: 972Here are the gory details of what \f(CW\*(C`ev_run\*(C'\fR does (this is for your
973understanding, not a guarantee that things will work exactly like this in
974future versions):
539.Sp 975.Sp
540.Vb 18 976.Vb 10
541\& * If there are no active watchers (reference count is zero), return. 977\& \- Increment loop depth.
542\& - Queue prepare watchers and then call all outstanding watchers. 978\& \- Reset the ev_break status.
979\& \- Before the first iteration, call any pending watchers.
980\& LOOP:
981\& \- If EVFLAG_FORKCHECK was used, check for a fork.
982\& \- If a fork was detected (by any means), queue and call all fork watchers.
983\& \- Queue and call all prepare watchers.
984\& \- If ev_break was called, goto FINISH.
543\& - If we have been forked, recreate the kernel state. 985\& \- If we have been forked, detach and recreate the kernel state
986\& as to not disturb the other process.
544\& - Update the kernel state with all outstanding changes. 987\& \- Update the kernel state with all outstanding changes.
545\& - Update the "event loop time". 988\& \- Update the "event loop time" (ev_now ()).
546\& - Calculate for how long to block. 989\& \- Calculate for how long to sleep or block, if at all
990\& (active idle watchers, EVRUN_NOWAIT or not having
991\& any active watchers at all will result in not sleeping).
992\& \- Sleep if the I/O and timer collect interval say so.
993\& \- Increment loop iteration counter.
547\& - Block the process, waiting for any events. 994\& \- Block the process, waiting for any events.
548\& - Queue all outstanding I/O (fd) events. 995\& \- Queue all outstanding I/O (fd) events.
549\& - Update the "event loop time" and do time jump handling. 996\& \- Update the "event loop time" (ev_now ()), and do time jump adjustments.
550\& - Queue all outstanding timers. 997\& \- Queue all expired timers.
551\& - Queue all outstanding periodics. 998\& \- Queue all expired periodics.
552\& - If no events are pending now, queue all idle watchers. 999\& \- Queue all idle watchers with priority higher than that of pending events.
553\& - Queue all check watchers. 1000\& \- Queue all check watchers.
554\& - Call all queued watchers in reverse order (i.e. check watchers first). 1001\& \- Call all queued watchers in reverse order (i.e. check watchers first).
555\& Signals and child watchers are implemented as I/O watchers, and will 1002\& Signals and child watchers are implemented as I/O watchers, and will
556\& be handled here by queueing them when their watcher gets executed. 1003\& be handled here by queueing them when their watcher gets executed.
557\& - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK 1004\& \- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
558\& were used, return, otherwise continue with step *. 1005\& were used, or there are no active watchers, goto FINISH, otherwise
1006\& continue with step LOOP.
1007\& FINISH:
1008\& \- Reset the ev_break status iff it was EVBREAK_ONE.
1009\& \- Decrement the loop depth.
1010\& \- Return.
559.Ve 1011.Ve
560.Sp 1012.Sp
561Example: queue some jobs and then loop until no events are outsanding 1013Example: Queue some jobs and then loop until no events are outstanding
562anymore. 1014anymore.
563.Sp 1015.Sp
564.Vb 4 1016.Vb 4
565\& ... queue jobs here, make sure they register event watchers as long 1017\& ... queue jobs here, make sure they register event watchers as long
566\& ... as they still have work to do (even an idle watcher will do..) 1018\& ... as they still have work to do (even an idle watcher will do..)
567\& ev_loop (my_loop, 0); 1019\& ev_run (my_loop, 0);
568\& ... jobs done. yeah! 1020\& ... jobs done or somebody called break. yeah!
569.Ve 1021.Ve
570.IP "ev_unloop (loop, how)" 4 1022.IP "ev_break (loop, how)" 4
571.IX Item "ev_unloop (loop, how)" 1023.IX Item "ev_break (loop, how)"
572Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it 1024Can be used to make a call to \f(CW\*(C`ev_run\*(C'\fR return early (but only after it
573has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either 1025has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
574\&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or 1026\&\f(CW\*(C`EVBREAK_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_run\*(C'\fR call return, or
575\&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return. 1027\&\f(CW\*(C`EVBREAK_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_run\*(C'\fR calls return.
1028.Sp
1029This \*(L"break state\*(R" will be cleared on the next call to \f(CW\*(C`ev_run\*(C'\fR.
1030.Sp
1031It is safe to call \f(CW\*(C`ev_break\*(C'\fR from outside any \f(CW\*(C`ev_run\*(C'\fR calls, too, in
1032which case it will have no effect.
576.IP "ev_ref (loop)" 4 1033.IP "ev_ref (loop)" 4
577.IX Item "ev_ref (loop)" 1034.IX Item "ev_ref (loop)"
578.PD 0 1035.PD 0
579.IP "ev_unref (loop)" 4 1036.IP "ev_unref (loop)" 4
580.IX Item "ev_unref (loop)" 1037.IX Item "ev_unref (loop)"
581.PD 1038.PD
582Ref/unref can be used to add or remove a reference count on the event 1039Ref/unref can be used to add or remove a reference count on the event
583loop: Every watcher keeps one reference, and as long as the reference 1040loop: Every watcher keeps one reference, and as long as the reference
584count is nonzero, \f(CW\*(C`ev_loop\*(C'\fR will not return on its own. If you have 1041count is nonzero, \f(CW\*(C`ev_run\*(C'\fR will not return on its own.
585a watcher you never unregister that should not keep \f(CW\*(C`ev_loop\*(C'\fR from 1042.Sp
586returning, \fIev_unref()\fR after starting, and \fIev_ref()\fR before stopping it. For 1043This is useful when you have a watcher that you never intend to
1044unregister, but that nevertheless should not keep \f(CW\*(C`ev_run\*(C'\fR from
1045returning. In such a case, call \f(CW\*(C`ev_unref\*(C'\fR after starting, and \f(CW\*(C`ev_ref\*(C'\fR
1046before stopping it.
1047.Sp
587example, libev itself uses this for its internal signal pipe: It is not 1048As an example, libev itself uses this for its internal signal pipe: It
588visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from exiting if 1049is not visible to the libev user and should not keep \f(CW\*(C`ev_run\*(C'\fR from
589no event watchers registered by it are active. It is also an excellent 1050exiting if no event watchers registered by it are active. It is also an
590way to do this for generic recurring timers or from within third-party 1051excellent way to do this for generic recurring timers or from within
591libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR. 1052third-party libraries. Just remember to \fIunref after start\fR and \fIref
1053before stop\fR (but only if the watcher wasn't active before, or was active
1054before, respectively. Note also that libev might stop watchers itself
1055(e.g. non-repeating timers) in which case you have to \f(CW\*(C`ev_ref\*(C'\fR
1056in the callback).
592.Sp 1057.Sp
593Example: create a signal watcher, but keep it from keeping \f(CW\*(C`ev_loop\*(C'\fR 1058Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_run\*(C'\fR
594running when nothing else is active. 1059running when nothing else is active.
595.Sp 1060.Sp
596.Vb 4 1061.Vb 4
597\& struct dv_signal exitsig; 1062\& ev_signal exitsig;
598\& ev_signal_init (&exitsig, sig_cb, SIGINT); 1063\& ev_signal_init (&exitsig, sig_cb, SIGINT);
599\& ev_signal_start (myloop, &exitsig); 1064\& ev_signal_start (loop, &exitsig);
600\& evf_unref (myloop); 1065\& ev_unref (loop);
601.Ve 1066.Ve
602.Sp 1067.Sp
603Example: for some weird reason, unregister the above signal handler again. 1068Example: For some weird reason, unregister the above signal handler again.
604.Sp 1069.Sp
605.Vb 2 1070.Vb 2
606\& ev_ref (myloop); 1071\& ev_ref (loop);
607\& ev_signal_stop (myloop, &exitsig); 1072\& ev_signal_stop (loop, &exitsig);
608.Ve 1073.Ve
1074.IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4
1075.IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"
1076.PD 0
1077.IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4
1078.IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"
1079.PD
1080These advanced functions influence the time that libev will spend waiting
1081for events. Both time intervals are by default \f(CW0\fR, meaning that libev
1082will try to invoke timer/periodic callbacks and I/O callbacks with minimum
1083latency.
1084.Sp
1085Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR)
1086allows libev to delay invocation of I/O and timer/periodic callbacks
1087to increase efficiency of loop iterations (or to increase power-saving
1088opportunities).
1089.Sp
1090The idea is that sometimes your program runs just fast enough to handle
1091one (or very few) event(s) per loop iteration. While this makes the
1092program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new
1093events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high
1094overhead for the actual polling but can deliver many events at once.
1095.Sp
1096By setting a higher \fIio collect interval\fR you allow libev to spend more
1097time collecting I/O events, so you can handle more events per iteration,
1098at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and
1099\&\f(CW\*(C`ev_timer\*(C'\fR) will not be affected. Setting this to a non-null value will
1100introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations. The
1101sleep time ensures that libev will not poll for I/O events more often then
1102once per this interval, on average (as long as the host time resolution is
1103good enough).
1104.Sp
1105Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
1106to spend more time collecting timeouts, at the expense of increased
1107latency/jitter/inexactness (the watcher callback will be called
1108later). \f(CW\*(C`ev_io\*(C'\fR watchers will not be affected. Setting this to a non-null
1109value will not introduce any overhead in libev.
1110.Sp
1111Many (busy) programs can usually benefit by setting the I/O collect
1112interval to a value near \f(CW0.1\fR or so, which is often enough for
1113interactive servers (of course not for games), likewise for timeouts. It
1114usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR,
1115as this approaches the timing granularity of most systems. Note that if
1116you do transactions with the outside world and you can't increase the
1117parallelity, then this setting will limit your transaction rate (if you
1118need to poll once per transaction and the I/O collect interval is 0.01,
1119then you can't do more than 100 transactions per second).
1120.Sp
1121Setting the \fItimeout collect interval\fR can improve the opportunity for
1122saving power, as the program will \*(L"bundle\*(R" timer callback invocations that
1123are \*(L"near\*(R" in time together, by delaying some, thus reducing the number of
1124times the process sleeps and wakes up again. Another useful technique to
1125reduce iterations/wake\-ups is to use \f(CW\*(C`ev_periodic\*(C'\fR watchers and make sure
1126they fire on, say, one-second boundaries only.
1127.Sp
1128Example: we only need 0.1s timeout granularity, and we wish not to poll
1129more often than 100 times per second:
1130.Sp
1131.Vb 2
1132\& ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
1133\& ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
1134.Ve
1135.IP "ev_invoke_pending (loop)" 4
1136.IX Item "ev_invoke_pending (loop)"
1137This call will simply invoke all pending watchers while resetting their
1138pending state. Normally, \f(CW\*(C`ev_run\*(C'\fR does this automatically when required,
1139but when overriding the invoke callback this call comes handy. This
1140function can be invoked from a watcher \- this can be useful for example
1141when you want to do some lengthy calculation and want to pass further
1142event handling to another thread (you still have to make sure only one
1143thread executes within \f(CW\*(C`ev_invoke_pending\*(C'\fR or \f(CW\*(C`ev_run\*(C'\fR of course).
1144.IP "int ev_pending_count (loop)" 4
1145.IX Item "int ev_pending_count (loop)"
1146Returns the number of pending watchers \- zero indicates that no watchers
1147are pending.
1148.IP "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(\s-1EV_P\s0))" 4
1149.IX Item "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))"
1150This overrides the invoke pending functionality of the loop: Instead of
1151invoking all pending watchers when there are any, \f(CW\*(C`ev_run\*(C'\fR will call
1152this callback instead. This is useful, for example, when you want to
1153invoke the actual watchers inside another context (another thread etc.).
1154.Sp
1155If you want to reset the callback, use \f(CW\*(C`ev_invoke_pending\*(C'\fR as new
1156callback.
1157.IP "ev_set_loop_release_cb (loop, void (*release)(\s-1EV_P\s0) throw (), void (*acquire)(\s-1EV_P\s0) throw ())" 4
1158.IX Item "ev_set_loop_release_cb (loop, void (*release)(EV_P) throw (), void (*acquire)(EV_P) throw ())"
1159Sometimes you want to share the same loop between multiple threads. This
1160can be done relatively simply by putting mutex_lock/unlock calls around
1161each call to a libev function.
1162.Sp
1163However, \f(CW\*(C`ev_run\*(C'\fR can run an indefinite time, so it is not feasible
1164to wait for it to return. One way around this is to wake up the event
1165loop via \f(CW\*(C`ev_break\*(C'\fR and \f(CW\*(C`ev_async_send\*(C'\fR, another way is to set these
1166\&\fIrelease\fR and \fIacquire\fR callbacks on the loop.
1167.Sp
1168When set, then \f(CW\*(C`release\*(C'\fR will be called just before the thread is
1169suspended waiting for new events, and \f(CW\*(C`acquire\*(C'\fR is called just
1170afterwards.
1171.Sp
1172Ideally, \f(CW\*(C`release\*(C'\fR will just call your mutex_unlock function, and
1173\&\f(CW\*(C`acquire\*(C'\fR will just call the mutex_lock function again.
1174.Sp
1175While event loop modifications are allowed between invocations of
1176\&\f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR (that's their only purpose after all), no
1177modifications done will affect the event loop, i.e. adding watchers will
1178have no effect on the set of file descriptors being watched, or the time
1179waited. Use an \f(CW\*(C`ev_async\*(C'\fR watcher to wake up \f(CW\*(C`ev_run\*(C'\fR when you want it
1180to take note of any changes you made.
1181.Sp
1182In theory, threads executing \f(CW\*(C`ev_run\*(C'\fR will be async-cancel safe between
1183invocations of \f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR.
1184.Sp
1185See also the locking example in the \f(CW\*(C`THREADS\*(C'\fR section later in this
1186document.
1187.IP "ev_set_userdata (loop, void *data)" 4
1188.IX Item "ev_set_userdata (loop, void *data)"
1189.PD 0
1190.IP "void *ev_userdata (loop)" 4
1191.IX Item "void *ev_userdata (loop)"
1192.PD
1193Set and retrieve a single \f(CW\*(C`void *\*(C'\fR associated with a loop. When
1194\&\f(CW\*(C`ev_set_userdata\*(C'\fR has never been called, then \f(CW\*(C`ev_userdata\*(C'\fR returns
1195\&\f(CW0\fR.
1196.Sp
1197These two functions can be used to associate arbitrary data with a loop,
1198and are intended solely for the \f(CW\*(C`invoke_pending_cb\*(C'\fR, \f(CW\*(C`release\*(C'\fR and
1199\&\f(CW\*(C`acquire\*(C'\fR callbacks described above, but of course can be (ab\-)used for
1200any other purpose as well.
1201.IP "ev_verify (loop)" 4
1202.IX Item "ev_verify (loop)"
1203This function only does something when \f(CW\*(C`EV_VERIFY\*(C'\fR support has been
1204compiled in, which is the default for non-minimal builds. It tries to go
1205through all internal structures and checks them for validity. If anything
1206is found to be inconsistent, it will print an error message to standard
1207error and call \f(CW\*(C`abort ()\*(C'\fR.
1208.Sp
1209This can be used to catch bugs inside libev itself: under normal
1210circumstances, this function will never abort as of course libev keeps its
1211data structures consistent.
609.SH "ANATOMY OF A WATCHER" 1212.SH "ANATOMY OF A WATCHER"
610.IX Header "ANATOMY OF A WATCHER" 1213.IX Header "ANATOMY OF A WATCHER"
1214In the following description, uppercase \f(CW\*(C`TYPE\*(C'\fR in names stands for the
1215watcher type, e.g. \f(CW\*(C`ev_TYPE_start\*(C'\fR can mean \f(CW\*(C`ev_timer_start\*(C'\fR for timer
1216watchers and \f(CW\*(C`ev_io_start\*(C'\fR for I/O watchers.
1217.PP
611A watcher is a structure that you create and register to record your 1218A watcher is an opaque structure that you allocate and register to record
612interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to 1219your interest in some event. To make a concrete example, imagine you want
613become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that: 1220to wait for \s-1STDIN\s0 to become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher
1221for that:
614.PP 1222.PP
615.Vb 5 1223.Vb 5
616\& static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) 1224\& static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
617\& { 1225\& {
618\& ev_io_stop (w); 1226\& ev_io_stop (w);
619\& ev_unloop (loop, EVUNLOOP_ALL); 1227\& ev_break (loop, EVBREAK_ALL);
620\& } 1228\& }
621.Ve 1229\&
622.PP
623.Vb 6
624\& struct ev_loop *loop = ev_default_loop (0); 1230\& struct ev_loop *loop = ev_default_loop (0);
1231\&
625\& struct ev_io stdin_watcher; 1232\& ev_io stdin_watcher;
1233\&
626\& ev_init (&stdin_watcher, my_cb); 1234\& ev_init (&stdin_watcher, my_cb);
627\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); 1235\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
628\& ev_io_start (loop, &stdin_watcher); 1236\& ev_io_start (loop, &stdin_watcher);
1237\&
629\& ev_loop (loop, 0); 1238\& ev_run (loop, 0);
630.Ve 1239.Ve
631.PP 1240.PP
632As you can see, you are responsible for allocating the memory for your 1241As you can see, you are responsible for allocating the memory for your
633watcher structures (and it is usually a bad idea to do this on the stack, 1242watcher structures (and it is \fIusually\fR a bad idea to do this on the
634although this can sometimes be quite valid). 1243stack).
635.PP 1244.PP
1245Each watcher has an associated watcher structure (called \f(CW\*(C`struct ev_TYPE\*(C'\fR
1246or simply \f(CW\*(C`ev_TYPE\*(C'\fR, as typedefs are provided for all watcher structs).
1247.PP
636Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init 1248Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init (watcher
637(watcher *, callback)\*(C'\fR, which expects a callback to be provided. This 1249*, callback)\*(C'\fR, which expects a callback to be provided. This callback is
638callback gets invoked each time the event occurs (or, in the case of io 1250invoked each time the event occurs (or, in the case of I/O watchers, each
639watchers, each time the event loop detects that the file descriptor given 1251time the event loop detects that the file descriptor given is readable
640is readable and/or writable). 1252and/or writable).
641.PP 1253.PP
642Each watcher type has its own \f(CW\*(C`ev_<type>_set (watcher *, ...)\*(C'\fR macro 1254Each watcher type further has its own \f(CW\*(C`ev_TYPE_set (watcher *, ...)\*(C'\fR
643with arguments specific to this watcher type. There is also a macro 1255macro to configure it, with arguments specific to the watcher type. There
644to combine initialisation and setting in one call: \f(CW\*(C`ev_<type>_init 1256is also a macro to combine initialisation and setting in one call: \f(CW\*(C`ev_TYPE_init (watcher *, callback, ...)\*(C'\fR.
645(watcher *, callback, ...)\*(C'\fR.
646.PP 1257.PP
647To make the watcher actually watch out for events, you have to start it 1258To make the watcher actually watch out for events, you have to start it
648with a watcher-specific start function (\f(CW\*(C`ev_<type>_start (loop, watcher 1259with a watcher-specific start function (\f(CW\*(C`ev_TYPE_start (loop, watcher
649*)\*(C'\fR), and you can stop watching for events at any time by calling the 1260*)\*(C'\fR), and you can stop watching for events at any time by calling the
650corresponding stop function (\f(CW\*(C`ev_<type>_stop (loop, watcher *)\*(C'\fR. 1261corresponding stop function (\f(CW\*(C`ev_TYPE_stop (loop, watcher *)\*(C'\fR.
651.PP 1262.PP
652As long as your watcher is active (has been started but not stopped) you 1263As long as your watcher is active (has been started but not stopped) you
653must not touch the values stored in it. Most specifically you must never 1264must not touch the values stored in it. Most specifically you must never
654reinitialise it or call its \f(CW\*(C`set\*(C'\fR macro. 1265reinitialise it or call its \f(CW\*(C`ev_TYPE_set\*(C'\fR macro.
655.PP 1266.PP
656Each and every callback receives the event loop pointer as first, the 1267Each and every callback receives the event loop pointer as first, the
657registered watcher structure as second, and a bitset of received events as 1268registered watcher structure as second, and a bitset of received events as
658third argument. 1269third argument.
659.PP 1270.PP
… …
668.el .IP "\f(CWEV_WRITE\fR" 4 1279.el .IP "\f(CWEV_WRITE\fR" 4
669.IX Item "EV_WRITE" 1280.IX Item "EV_WRITE"
670.PD 1281.PD
671The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or 1282The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
672writable. 1283writable.
673.ie n .IP """EV_TIMEOUT""" 4 1284.ie n .IP """EV_TIMER""" 4
674.el .IP "\f(CWEV_TIMEOUT\fR" 4 1285.el .IP "\f(CWEV_TIMER\fR" 4
675.IX Item "EV_TIMEOUT" 1286.IX Item "EV_TIMER"
676The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out. 1287The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
677.ie n .IP """EV_PERIODIC""" 4 1288.ie n .IP """EV_PERIODIC""" 4
678.el .IP "\f(CWEV_PERIODIC\fR" 4 1289.el .IP "\f(CWEV_PERIODIC\fR" 4
679.IX Item "EV_PERIODIC" 1290.IX Item "EV_PERIODIC"
680The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out. 1291The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
… …
684The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread. 1295The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread.
685.ie n .IP """EV_CHILD""" 4 1296.ie n .IP """EV_CHILD""" 4
686.el .IP "\f(CWEV_CHILD\fR" 4 1297.el .IP "\f(CWEV_CHILD\fR" 4
687.IX Item "EV_CHILD" 1298.IX Item "EV_CHILD"
688The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change. 1299The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change.
1300.ie n .IP """EV_STAT""" 4
1301.el .IP "\f(CWEV_STAT\fR" 4
1302.IX Item "EV_STAT"
1303The path specified in the \f(CW\*(C`ev_stat\*(C'\fR watcher changed its attributes somehow.
689.ie n .IP """EV_IDLE""" 4 1304.ie n .IP """EV_IDLE""" 4
690.el .IP "\f(CWEV_IDLE\fR" 4 1305.el .IP "\f(CWEV_IDLE\fR" 4
691.IX Item "EV_IDLE" 1306.IX Item "EV_IDLE"
692The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do. 1307The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do.
693.ie n .IP """EV_PREPARE""" 4 1308.ie n .IP """EV_PREPARE""" 4
… …
696.PD 0 1311.PD 0
697.ie n .IP """EV_CHECK""" 4 1312.ie n .IP """EV_CHECK""" 4
698.el .IP "\f(CWEV_CHECK\fR" 4 1313.el .IP "\f(CWEV_CHECK\fR" 4
699.IX Item "EV_CHECK" 1314.IX Item "EV_CHECK"
700.PD 1315.PD
701All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_loop\*(C'\fR starts 1316All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_run\*(C'\fR starts to
702to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after 1317gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are queued (not invoked)
703\&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any 1318just after \f(CW\*(C`ev_run\*(C'\fR has gathered them, but before it queues any callbacks
1319for any received events. That means \f(CW\*(C`ev_prepare\*(C'\fR watchers are the last
1320watchers invoked before the event loop sleeps or polls for new events, and
1321\&\f(CW\*(C`ev_check\*(C'\fR watchers will be invoked before any other watchers of the same
1322or lower priority within an event loop iteration.
1323.Sp
704received events. Callbacks of both watcher types can start and stop as 1324Callbacks of both watcher types can start and stop as many watchers as
705many watchers as they want, and all of them will be taken into account 1325they want, and all of them will be taken into account (for example, a
706(for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep 1326\&\f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep \f(CW\*(C`ev_run\*(C'\fR from
707\&\f(CW\*(C`ev_loop\*(C'\fR from blocking). 1327blocking).
1328.ie n .IP """EV_EMBED""" 4
1329.el .IP "\f(CWEV_EMBED\fR" 4
1330.IX Item "EV_EMBED"
1331The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.
1332.ie n .IP """EV_FORK""" 4
1333.el .IP "\f(CWEV_FORK\fR" 4
1334.IX Item "EV_FORK"
1335The event loop has been resumed in the child process after fork (see
1336\&\f(CW\*(C`ev_fork\*(C'\fR).
1337.ie n .IP """EV_CLEANUP""" 4
1338.el .IP "\f(CWEV_CLEANUP\fR" 4
1339.IX Item "EV_CLEANUP"
1340The event loop is about to be destroyed (see \f(CW\*(C`ev_cleanup\*(C'\fR).
1341.ie n .IP """EV_ASYNC""" 4
1342.el .IP "\f(CWEV_ASYNC\fR" 4
1343.IX Item "EV_ASYNC"
1344The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR).
1345.ie n .IP """EV_CUSTOM""" 4
1346.el .IP "\f(CWEV_CUSTOM\fR" 4
1347.IX Item "EV_CUSTOM"
1348Not ever sent (or otherwise used) by libev itself, but can be freely used
1349by libev users to signal watchers (e.g. via \f(CW\*(C`ev_feed_event\*(C'\fR).
708.ie n .IP """EV_ERROR""" 4 1350.ie n .IP """EV_ERROR""" 4
709.el .IP "\f(CWEV_ERROR\fR" 4 1351.el .IP "\f(CWEV_ERROR\fR" 4
710.IX Item "EV_ERROR" 1352.IX Item "EV_ERROR"
711An unspecified error has occured, the watcher has been stopped. This might 1353An unspecified error has occurred, the watcher has been stopped. This might
712happen because the watcher could not be properly started because libev 1354happen because the watcher could not be properly started because libev
713ran out of memory, a file descriptor was found to be closed or any other 1355ran out of memory, a file descriptor was found to be closed or any other
1356problem. Libev considers these application bugs.
1357.Sp
714problem. You best act on it by reporting the problem and somehow coping 1358You best act on it by reporting the problem and somehow coping with the
715with the watcher being stopped. 1359watcher being stopped. Note that well-written programs should not receive
1360an error ever, so when your watcher receives it, this usually indicates a
1361bug in your program.
716.Sp 1362.Sp
717Libev will usually signal a few \*(L"dummy\*(R" events together with an error, 1363Libev will usually signal a few \*(L"dummy\*(R" events together with an error, for
718for example it might indicate that a fd is readable or writable, and if 1364example it might indicate that a fd is readable or writable, and if your
719your callbacks is well-written it can just attempt the operation and cope 1365callbacks is well-written it can just attempt the operation and cope with
720with the error from \fIread()\fR or \fIwrite()\fR. This will not work in multithreaded 1366the error from \fIread()\fR or \fIwrite()\fR. This will not work in multi-threaded
721programs, though, so beware. 1367programs, though, as the fd could already be closed and reused for another
722.Sh "\s-1SUMMARY\s0 \s-1OF\s0 \s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0" 1368thing, so beware.
1369.SS "\s-1GENERIC WATCHER FUNCTIONS\s0"
723.IX Subsection "SUMMARY OF GENERIC WATCHER FUNCTIONS" 1370.IX Subsection "GENERIC WATCHER FUNCTIONS"
724In the following description, \f(CW\*(C`TYPE\*(C'\fR stands for the watcher type,
725e.g. \f(CW\*(C`timer\*(C'\fR for \f(CW\*(C`ev_timer\*(C'\fR watchers and \f(CW\*(C`io\*(C'\fR for \f(CW\*(C`ev_io\*(C'\fR watchers.
726.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4 1371.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
727.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4 1372.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
728.IX Item "ev_init (ev_TYPE *watcher, callback)" 1373.IX Item "ev_init (ev_TYPE *watcher, callback)"
729This macro initialises the generic portion of a watcher. The contents 1374This macro initialises the generic portion of a watcher. The contents
730of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only 1375of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
… …
734which rolls both calls into one. 1379which rolls both calls into one.
735.Sp 1380.Sp
736You can reinitialise a watcher at any time as long as it has been stopped 1381You can reinitialise a watcher at any time as long as it has been stopped
737(or never started) and there are no pending events outstanding. 1382(or never started) and there are no pending events outstanding.
738.Sp 1383.Sp
739The callbakc is always of type \f(CW\*(C`void (*)(ev_loop *loop, ev_TYPE *watcher, 1384The callback is always of type \f(CW\*(C`void (*)(struct ev_loop *loop, ev_TYPE *watcher,
740int revents)\*(C'\fR. 1385int revents)\*(C'\fR.
1386.Sp
1387Example: Initialise an \f(CW\*(C`ev_io\*(C'\fR watcher in two steps.
1388.Sp
1389.Vb 3
1390\& ev_io w;
1391\& ev_init (&w, my_cb);
1392\& ev_io_set (&w, STDIN_FILENO, EV_READ);
1393.Ve
741.ie n .IP """ev_TYPE_set"" (ev_TYPE *, [args])" 4 1394.ie n .IP """ev_TYPE_set"" (ev_TYPE *watcher, [args])" 4
742.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *, [args])" 4 1395.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *watcher, [args])" 4
743.IX Item "ev_TYPE_set (ev_TYPE *, [args])" 1396.IX Item "ev_TYPE_set (ev_TYPE *watcher, [args])"
744This macro initialises the type-specific parts of a watcher. You need to 1397This macro initialises the type-specific parts of a watcher. You need to
745call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can 1398call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
746call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this 1399call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
747macro on a watcher that is active (it can be pending, however, which is a 1400macro on a watcher that is active (it can be pending, however, which is a
748difference to the \f(CW\*(C`ev_init\*(C'\fR macro). 1401difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
749.Sp 1402.Sp
750Although some watcher types do not have type-specific arguments 1403Although some watcher types do not have type-specific arguments
751(e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro. 1404(e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
1405.Sp
1406See \f(CW\*(C`ev_init\*(C'\fR, above, for an example.
752.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4 1407.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
753.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4 1408.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
754.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])" 1409.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
755This convinience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro 1410This convenience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
756calls into a single call. This is the most convinient method to initialise 1411calls into a single call. This is the most convenient method to initialise
757a watcher. The same limitations apply, of course. 1412a watcher. The same limitations apply, of course.
1413.Sp
1414Example: Initialise and set an \f(CW\*(C`ev_io\*(C'\fR watcher in one step.
1415.Sp
1416.Vb 1
1417\& ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1418.Ve
758.ie n .IP """ev_TYPE_start"" (loop *, ev_TYPE *watcher)" 4 1419.ie n .IP """ev_TYPE_start"" (loop, ev_TYPE *watcher)" 4
759.el .IP "\f(CWev_TYPE_start\fR (loop *, ev_TYPE *watcher)" 4 1420.el .IP "\f(CWev_TYPE_start\fR (loop, ev_TYPE *watcher)" 4
760.IX Item "ev_TYPE_start (loop *, ev_TYPE *watcher)" 1421.IX Item "ev_TYPE_start (loop, ev_TYPE *watcher)"
761Starts (activates) the given watcher. Only active watchers will receive 1422Starts (activates) the given watcher. Only active watchers will receive
762events. If the watcher is already active nothing will happen. 1423events. If the watcher is already active nothing will happen.
1424.Sp
1425Example: Start the \f(CW\*(C`ev_io\*(C'\fR watcher that is being abused as example in this
1426whole section.
1427.Sp
1428.Vb 1
1429\& ev_io_start (EV_DEFAULT_UC, &w);
1430.Ve
763.ie n .IP """ev_TYPE_stop"" (loop *, ev_TYPE *watcher)" 4 1431.ie n .IP """ev_TYPE_stop"" (loop, ev_TYPE *watcher)" 4
764.el .IP "\f(CWev_TYPE_stop\fR (loop *, ev_TYPE *watcher)" 4 1432.el .IP "\f(CWev_TYPE_stop\fR (loop, ev_TYPE *watcher)" 4
765.IX Item "ev_TYPE_stop (loop *, ev_TYPE *watcher)" 1433.IX Item "ev_TYPE_stop (loop, ev_TYPE *watcher)"
766Stops the given watcher again (if active) and clears the pending 1434Stops the given watcher if active, and clears the pending status (whether
1435the watcher was active or not).
1436.Sp
767status. It is possible that stopped watchers are pending (for example, 1437It is possible that stopped watchers are pending \- for example,
768non-repeating timers are being stopped when they become pending), but 1438non-repeating timers are being stopped when they become pending \- but
769\&\f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor pending. If 1439calling \f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor
770you want to free or reuse the memory used by the watcher it is therefore a 1440pending. If you want to free or reuse the memory used by the watcher it is
771good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. 1441therefore a good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
772.IP "bool ev_is_active (ev_TYPE *watcher)" 4 1442.IP "bool ev_is_active (ev_TYPE *watcher)" 4
773.IX Item "bool ev_is_active (ev_TYPE *watcher)" 1443.IX Item "bool ev_is_active (ev_TYPE *watcher)"
774Returns a true value iff the watcher is active (i.e. it has been started 1444Returns a true value iff the watcher is active (i.e. it has been started
775and not yet been stopped). As long as a watcher is active you must not modify 1445and not yet been stopped). As long as a watcher is active you must not modify
776it. 1446it.
777.IP "bool ev_is_pending (ev_TYPE *watcher)" 4 1447.IP "bool ev_is_pending (ev_TYPE *watcher)" 4
778.IX Item "bool ev_is_pending (ev_TYPE *watcher)" 1448.IX Item "bool ev_is_pending (ev_TYPE *watcher)"
779Returns a true value iff the watcher is pending, (i.e. it has outstanding 1449Returns a true value iff the watcher is pending, (i.e. it has outstanding
780events but its callback has not yet been invoked). As long as a watcher 1450events but its callback has not yet been invoked). As long as a watcher
781is pending (but not active) you must not call an init function on it (but 1451is pending (but not active) you must not call an init function on it (but
782\&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe) and you must make sure the watcher is available to 1452\&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe), you must not change its priority, and you must
783libev (e.g. you cnanot \f(CW\*(C`free ()\*(C'\fR it). 1453make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR
1454it).
784.IP "callback = ev_cb (ev_TYPE *watcher)" 4 1455.IP "callback ev_cb (ev_TYPE *watcher)" 4
785.IX Item "callback = ev_cb (ev_TYPE *watcher)" 1456.IX Item "callback ev_cb (ev_TYPE *watcher)"
786Returns the callback currently set on the watcher. 1457Returns the callback currently set on the watcher.
787.IP "ev_cb_set (ev_TYPE *watcher, callback)" 4 1458.IP "ev_set_cb (ev_TYPE *watcher, callback)" 4
788.IX Item "ev_cb_set (ev_TYPE *watcher, callback)" 1459.IX Item "ev_set_cb (ev_TYPE *watcher, callback)"
789Change the callback. You can change the callback at virtually any time 1460Change the callback. You can change the callback at virtually any time
790(modulo threads). 1461(modulo threads).
791.Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0" 1462.IP "ev_set_priority (ev_TYPE *watcher, int priority)" 4
792.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER" 1463.IX Item "ev_set_priority (ev_TYPE *watcher, int priority)"
793Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change 1464.PD 0
794and read at any time, libev will completely ignore it. This can be used 1465.IP "int ev_priority (ev_TYPE *watcher)" 4
795to associate arbitrary data with your watcher. If you need more data and 1466.IX Item "int ev_priority (ev_TYPE *watcher)"
796don't want to allocate memory and store a pointer to it in that data 1467.PD
797member, you can also \*(L"subclass\*(R" the watcher type and provide your own 1468Set and query the priority of the watcher. The priority is a small
798data: 1469integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR
1470(default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked
1471before watchers with lower priority, but priority will not keep watchers
1472from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
1473.Sp
1474If you need to suppress invocation when higher priority events are pending
1475you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
1476.Sp
1477You \fImust not\fR change the priority of a watcher as long as it is active or
1478pending.
1479.Sp
1480Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
1481fine, as long as you do not mind that the priority value you query might
1482or might not have been clamped to the valid range.
1483.Sp
1484The default priority used by watchers when no priority has been set is
1485always \f(CW0\fR, which is supposed to not be too high and not be too low :).
1486.Sp
1487See \*(L"\s-1WATCHER PRIORITY MODELS\*(R"\s0, below, for a more thorough treatment of
1488priorities.
1489.IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
1490.IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
1491Invoke the \f(CW\*(C`watcher\*(C'\fR with the given \f(CW\*(C`loop\*(C'\fR and \f(CW\*(C`revents\*(C'\fR. Neither
1492\&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback
1493can deal with that fact, as both are simply passed through to the
1494callback.
1495.IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
1496.IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
1497If the watcher is pending, this function clears its pending status and
1498returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the
1499watcher isn't pending it does nothing and returns \f(CW0\fR.
1500.Sp
1501Sometimes it can be useful to \*(L"poll\*(R" a watcher instead of waiting for its
1502callback to be invoked, which can be accomplished with this function.
1503.IP "ev_feed_event (loop, ev_TYPE *watcher, int revents)" 4
1504.IX Item "ev_feed_event (loop, ev_TYPE *watcher, int revents)"
1505Feeds the given event set into the event loop, as if the specified event
1506had happened for the specified watcher (which must be a pointer to an
1507initialised but not necessarily started event watcher). Obviously you must
1508not free the watcher as long as it has pending events.
1509.Sp
1510Stopping the watcher, letting libev invoke it, or calling
1511\&\f(CW\*(C`ev_clear_pending\*(C'\fR will clear the pending event, even if the watcher was
1512not started in the first place.
1513.Sp
1514See also \f(CW\*(C`ev_feed_fd_event\*(C'\fR and \f(CW\*(C`ev_feed_signal_event\*(C'\fR for related
1515functions that do not need a watcher.
799.PP 1516.PP
1517See also the \*(L"\s-1ASSOCIATING CUSTOM DATA WITH A WATCHER\*(R"\s0 and \*(L"\s-1BUILDING YOUR
1518OWN COMPOSITE WATCHERS\*(R"\s0 idioms.
1519.SS "\s-1WATCHER STATES\s0"
1520.IX Subsection "WATCHER STATES"
1521There are various watcher states mentioned throughout this manual \-
1522active, pending and so on. In this section these states and the rules to
1523transition between them will be described in more detail \- and while these
1524rules might look complicated, they usually do \*(L"the right thing\*(R".
1525.IP "initialised" 4
1526.IX Item "initialised"
1527Before a watcher can be registered with the event loop it has to be
1528initialised. This can be done with a call to \f(CW\*(C`ev_TYPE_init\*(C'\fR, or calls to
1529\&\f(CW\*(C`ev_init\*(C'\fR followed by the watcher-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR function.
1530.Sp
1531In this state it is simply some block of memory that is suitable for
1532use in an event loop. It can be moved around, freed, reused etc. at
1533will \- as long as you either keep the memory contents intact, or call
1534\&\f(CW\*(C`ev_TYPE_init\*(C'\fR again.
1535.IP "started/running/active" 4
1536.IX Item "started/running/active"
1537Once a watcher has been started with a call to \f(CW\*(C`ev_TYPE_start\*(C'\fR it becomes
1538property of the event loop, and is actively waiting for events. While in
1539this state it cannot be accessed (except in a few documented ways), moved,
1540freed or anything else \- the only legal thing is to keep a pointer to it,
1541and call libev functions on it that are documented to work on active watchers.
1542.IP "pending" 4
1543.IX Item "pending"
1544If a watcher is active and libev determines that an event it is interested
1545in has occurred (such as a timer expiring), it will become pending. It will
1546stay in this pending state until either it is stopped or its callback is
1547about to be invoked, so it is not normally pending inside the watcher
1548callback.
1549.Sp
1550The watcher might or might not be active while it is pending (for example,
1551an expired non-repeating timer can be pending but no longer active). If it
1552is stopped, it can be freely accessed (e.g. by calling \f(CW\*(C`ev_TYPE_set\*(C'\fR),
1553but it is still property of the event loop at this time, so cannot be
1554moved, freed or reused. And if it is active the rules described in the
1555previous item still apply.
1556.Sp
1557It is also possible to feed an event on a watcher that is not active (e.g.
1558via \f(CW\*(C`ev_feed_event\*(C'\fR), in which case it becomes pending without being
1559active.
1560.IP "stopped" 4
1561.IX Item "stopped"
1562A watcher can be stopped implicitly by libev (in which case it might still
1563be pending), or explicitly by calling its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. The
1564latter will clear any pending state the watcher might be in, regardless
1565of whether it was active or not, so stopping a watcher explicitly before
1566freeing it is often a good idea.
1567.Sp
1568While stopped (and not pending) the watcher is essentially in the
1569initialised state, that is, it can be reused, moved, modified in any way
1570you wish (but when you trash the memory block, you need to \f(CW\*(C`ev_TYPE_init\*(C'\fR
1571it again).
1572.SS "\s-1WATCHER PRIORITY MODELS\s0"
1573.IX Subsection "WATCHER PRIORITY MODELS"
1574Many event loops support \fIwatcher priorities\fR, which are usually small
1575integers that influence the ordering of event callback invocation
1576between watchers in some way, all else being equal.
1577.PP
1578In libev, Watcher priorities can be set using \f(CW\*(C`ev_set_priority\*(C'\fR. See its
1579description for the more technical details such as the actual priority
1580range.
1581.PP
1582There are two common ways how these these priorities are being interpreted
1583by event loops:
1584.PP
1585In the more common lock-out model, higher priorities \*(L"lock out\*(R" invocation
1586of lower priority watchers, which means as long as higher priority
1587watchers receive events, lower priority watchers are not being invoked.
1588.PP
1589The less common only-for-ordering model uses priorities solely to order
1590callback invocation within a single event loop iteration: Higher priority
1591watchers are invoked before lower priority ones, but they all get invoked
1592before polling for new events.
1593.PP
1594Libev uses the second (only-for-ordering) model for all its watchers
1595except for idle watchers (which use the lock-out model).
1596.PP
1597The rationale behind this is that implementing the lock-out model for
1598watchers is not well supported by most kernel interfaces, and most event
1599libraries will just poll for the same events again and again as long as
1600their callbacks have not been executed, which is very inefficient in the
1601common case of one high-priority watcher locking out a mass of lower
1602priority ones.
1603.PP
1604Static (ordering) priorities are most useful when you have two or more
1605watchers handling the same resource: a typical usage example is having an
1606\&\f(CW\*(C`ev_io\*(C'\fR watcher to receive data, and an associated \f(CW\*(C`ev_timer\*(C'\fR to handle
1607timeouts. Under load, data might be received while the program handles
1608other jobs, but since timers normally get invoked first, the timeout
1609handler will be executed before checking for data. In that case, giving
1610the timer a lower priority than the I/O watcher ensures that I/O will be
1611handled first even under adverse conditions (which is usually, but not
1612always, what you want).
1613.PP
1614Since idle watchers use the \*(L"lock-out\*(R" model, meaning that idle watchers
1615will only be executed when no same or higher priority watchers have
1616received events, they can be used to implement the \*(L"lock-out\*(R" model when
1617required.
1618.PP
1619For example, to emulate how many other event libraries handle priorities,
1620you can associate an \f(CW\*(C`ev_idle\*(C'\fR watcher to each such watcher, and in
1621the normal watcher callback, you just start the idle watcher. The real
1622processing is done in the idle watcher callback. This causes libev to
1623continuously poll and process kernel event data for the watcher, but when
1624the lock-out case is known to be rare (which in turn is rare :), this is
1625workable.
1626.PP
1627Usually, however, the lock-out model implemented that way will perform
1628miserably under the type of load it was designed to handle. In that case,
1629it might be preferable to stop the real watcher before starting the
1630idle watcher, so the kernel will not have to process the event in case
1631the actual processing will be delayed for considerable time.
1632.PP
1633Here is an example of an I/O watcher that should run at a strictly lower
1634priority than the default, and which should only process data when no
1635other events are pending:
1636.PP
800.Vb 7 1637.Vb 2
801\& struct my_io 1638\& ev_idle idle; // actual processing watcher
1639\& ev_io io; // actual event watcher
1640\&
1641\& static void
1642\& io_cb (EV_P_ ev_io *w, int revents)
802\& { 1643\& {
803\& struct ev_io io; 1644\& // stop the I/O watcher, we received the event, but
804\& int otherfd; 1645\& // are not yet ready to handle it.
805\& void *somedata; 1646\& ev_io_stop (EV_A_ w);
806\& struct whatever *mostinteresting; 1647\&
1648\& // start the idle watcher to handle the actual event.
1649\& // it will not be executed as long as other watchers
1650\& // with the default priority are receiving events.
1651\& ev_idle_start (EV_A_ &idle);
807\& } 1652\& }
808.Ve 1653\&
809.PP 1654\& static void
810And since your callback will be called with a pointer to the watcher, you 1655\& idle_cb (EV_P_ ev_idle *w, int revents)
811can cast it back to your own type:
812.PP
813.Vb 5
814\& static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
815\& { 1656\& {
816\& struct my_io *w = (struct my_io *)w_; 1657\& // actual processing
817\& ... 1658\& read (STDIN_FILENO, ...);
1659\&
1660\& // have to start the I/O watcher again, as
1661\& // we have handled the event
1662\& ev_io_start (EV_P_ &io);
818\& } 1663\& }
1664\&
1665\& // initialisation
1666\& ev_idle_init (&idle, idle_cb);
1667\& ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
1668\& ev_io_start (EV_DEFAULT_ &io);
819.Ve 1669.Ve
820.PP 1670.PP
821More interesting and less C\-conformant ways of catsing your callback type 1671In the \*(L"real\*(R" world, it might also be beneficial to start a timer, so that
822have been omitted.... 1672low-priority connections can not be locked out forever under load. This
1673enables your program to keep a lower latency for important connections
1674during short periods of high load, while not completely locking out less
1675important ones.
823.SH "WATCHER TYPES" 1676.SH "WATCHER TYPES"
824.IX Header "WATCHER TYPES" 1677.IX Header "WATCHER TYPES"
825This section describes each watcher in detail, but will not repeat 1678This section describes each watcher in detail, but will not repeat
826information given in the last section. 1679information given in the last section. Any initialisation/set macros,
1680functions and members specific to the watcher type are explained.
1681.PP
1682Members are additionally marked with either \fI[read\-only]\fR, meaning that,
1683while the watcher is active, you can look at the member and expect some
1684sensible content, but you must not modify it (you can modify it while the
1685watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
1686means you can expect it to have some sensible content while the watcher
1687is active, but you can also modify it. Modifying it may not do something
1688sensible or take immediate effect (or do anything at all), but libev will
1689not crash or malfunction in any way.
827.ie n .Sh """ev_io"" \- is this file descriptor readable or writable" 1690.ie n .SS """ev_io"" \- is this file descriptor readable or writable?"
828.el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable" 1691.el .SS "\f(CWev_io\fP \- is this file descriptor readable or writable?"
829.IX Subsection "ev_io - is this file descriptor readable or writable" 1692.IX Subsection "ev_io - is this file descriptor readable or writable?"
830I/O watchers check whether a file descriptor is readable or writable 1693I/O watchers check whether a file descriptor is readable or writable
831in each iteration of the event loop (This behaviour is called 1694in each iteration of the event loop, or, more precisely, when reading
832level-triggering because you keep receiving events as long as the 1695would not block the process and writing would at least be able to write
833condition persists. Remember you can stop the watcher if you don't want to 1696some data. This behaviour is called level-triggering because you keep
834act on the event and neither want to receive future events). 1697receiving events as long as the condition persists. Remember you can stop
1698the watcher if you don't want to act on the event and neither want to
1699receive future events.
835.PP 1700.PP
836In general you can register as many read and/or write event watchers per 1701In general you can register as many read and/or write event watchers per
837fd as you want (as long as you don't confuse yourself). Setting all file 1702fd as you want (as long as you don't confuse yourself). Setting all file
838descriptors to non-blocking mode is also usually a good idea (but not 1703descriptors to non-blocking mode is also usually a good idea (but not
839required if you know what you are doing). 1704required if you know what you are doing).
840.PP 1705.PP
841You have to be careful with dup'ed file descriptors, though. Some backends 1706Another thing you have to watch out for is that it is quite easy to
842(the linux epoll backend is a notable example) cannot handle dup'ed file 1707receive \*(L"spurious\*(R" readiness notifications, that is, your callback might
843descriptors correctly if you register interest in two or more fds pointing 1708be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block
844to the same underlying file/socket etc. description (that is, they share 1709because there is no data. It is very easy to get into this situation even
845the same underlying \*(L"file open\*(R"). 1710with a relatively standard program structure. Thus it is best to always
1711use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning \f(CW\*(C`EAGAIN\*(C'\fR is far
1712preferable to a program hanging until some data arrives.
846.PP 1713.PP
847If you must do this, then force the use of a known-to-be-good backend 1714If you cannot run the fd in non-blocking mode (for example you should
848(at the time of this writing, this includes only \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and 1715not play around with an Xlib connection), then you have to separately
849\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR). 1716re-test whether a file descriptor is really ready with a known-to-be good
1717interface such as poll (fortunately in the case of Xlib, it already does
1718this on its own, so its quite safe to use). Some people additionally
1719use \f(CW\*(C`SIGALRM\*(C'\fR and an interval timer, just to be sure you won't block
1720indefinitely.
1721.PP
1722But really, best use non-blocking mode.
1723.PP
1724\fIThe special problem of disappearing file descriptors\fR
1725.IX Subsection "The special problem of disappearing file descriptors"
1726.PP
1727Some backends (e.g. kqueue, epoll) need to be told about closing a file
1728descriptor (either due to calling \f(CW\*(C`close\*(C'\fR explicitly or any other means,
1729such as \f(CW\*(C`dup2\*(C'\fR). The reason is that you register interest in some file
1730descriptor, but when it goes away, the operating system will silently drop
1731this interest. If another file descriptor with the same number then is
1732registered with libev, there is no efficient way to see that this is, in
1733fact, a different file descriptor.
1734.PP
1735To avoid having to explicitly tell libev about such cases, libev follows
1736the following policy: Each time \f(CW\*(C`ev_io_set\*(C'\fR is being called, libev
1737will assume that this is potentially a new file descriptor, otherwise
1738it is assumed that the file descriptor stays the same. That means that
1739you \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
1740descriptor even if the file descriptor number itself did not change.
1741.PP
1742This is how one would do it normally anyway, the important point is that
1743the libev application should not optimise around libev but should leave
1744optimisations to libev.
1745.PP
1746\fIThe special problem of dup'ed file descriptors\fR
1747.IX Subsection "The special problem of dup'ed file descriptors"
1748.PP
1749Some backends (e.g. epoll), cannot register events for file descriptors,
1750but only events for the underlying file descriptions. That means when you
1751have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register
1752events for them, only one file descriptor might actually receive events.
1753.PP
1754There is no workaround possible except not registering events
1755for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
1756\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1757.PP
1758\fIThe special problem of files\fR
1759.IX Subsection "The special problem of files"
1760.PP
1761Many people try to use \f(CW\*(C`select\*(C'\fR (or libev) on file descriptors
1762representing files, and expect it to become ready when their program
1763doesn't block on disk accesses (which can take a long time on their own).
1764.PP
1765However, this cannot ever work in the \*(L"expected\*(R" way \- you get a readiness
1766notification as soon as the kernel knows whether and how much data is
1767there, and in the case of open files, that's always the case, so you
1768always get a readiness notification instantly, and your read (or possibly
1769write) will still block on the disk I/O.
1770.PP
1771Another way to view it is that in the case of sockets, pipes, character
1772devices and so on, there is another party (the sender) that delivers data
1773on its own, but in the case of files, there is no such thing: the disk
1774will not send data on its own, simply because it doesn't know what you
1775wish to read \- you would first have to request some data.
1776.PP
1777Since files are typically not-so-well supported by advanced notification
1778mechanism, libev tries hard to emulate \s-1POSIX\s0 behaviour with respect
1779to files, even though you should not use it. The reason for this is
1780convenience: sometimes you want to watch \s-1STDIN\s0 or \s-1STDOUT,\s0 which is
1781usually a tty, often a pipe, but also sometimes files or special devices
1782(for example, \f(CW\*(C`epoll\*(C'\fR on Linux works with \fI/dev/random\fR but not with
1783\&\fI/dev/urandom\fR), and even though the file might better be served with
1784asynchronous I/O instead of with non-blocking I/O, it is still useful when
1785it \*(L"just works\*(R" instead of freezing.
1786.PP
1787So avoid file descriptors pointing to files when you know it (e.g. use
1788libeio), but use them when it is convenient, e.g. for \s-1STDIN/STDOUT,\s0 or
1789when you rarely read from a file instead of from a socket, and want to
1790reuse the same code path.
1791.PP
1792\fIThe special problem of fork\fR
1793.IX Subsection "The special problem of fork"
1794.PP
1795Some backends (epoll, kqueue) do not support \f(CW\*(C`fork ()\*(C'\fR at all or exhibit
1796useless behaviour. Libev fully supports fork, but needs to be told about
1797it in the child if you want to continue to use it in the child.
1798.PP
1799To support fork in your child processes, you have to call \f(CW\*(C`ev_loop_fork
1800()\*(C'\fR after a fork in the child, enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to
1801\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1802.PP
1803\fIThe special problem of \s-1SIGPIPE\s0\fR
1804.IX Subsection "The special problem of SIGPIPE"
1805.PP
1806While not really specific to libev, it is easy to forget about \f(CW\*(C`SIGPIPE\*(C'\fR:
1807when writing to a pipe whose other end has been closed, your program gets
1808sent a \s-1SIGPIPE,\s0 which, by default, aborts your program. For most programs
1809this is sensible behaviour, for daemons, this is usually undesirable.
1810.PP
1811So when you encounter spurious, unexplained daemon exits, make sure you
1812ignore \s-1SIGPIPE \s0(and maybe make sure you log the exit status of your daemon
1813somewhere, as that would have given you a big clue).
1814.PP
1815\fIThe special problem of \fIaccept()\fIing when you can't\fR
1816.IX Subsection "The special problem of accept()ing when you can't"
1817.PP
1818Many implementations of the \s-1POSIX \s0\f(CW\*(C`accept\*(C'\fR function (for example,
1819found in post\-2004 Linux) have the peculiar behaviour of not removing a
1820connection from the pending queue in all error cases.
1821.PP
1822For example, larger servers often run out of file descriptors (because
1823of resource limits), causing \f(CW\*(C`accept\*(C'\fR to fail with \f(CW\*(C`ENFILE\*(C'\fR but not
1824rejecting the connection, leading to libev signalling readiness on
1825the next iteration again (the connection still exists after all), and
1826typically causing the program to loop at 100% \s-1CPU\s0 usage.
1827.PP
1828Unfortunately, the set of errors that cause this issue differs between
1829operating systems, there is usually little the app can do to remedy the
1830situation, and no known thread-safe method of removing the connection to
1831cope with overload is known (to me).
1832.PP
1833One of the easiest ways to handle this situation is to just ignore it
1834\&\- when the program encounters an overload, it will just loop until the
1835situation is over. While this is a form of busy waiting, no \s-1OS\s0 offers an
1836event-based way to handle this situation, so it's the best one can do.
1837.PP
1838A better way to handle the situation is to log any errors other than
1839\&\f(CW\*(C`EAGAIN\*(C'\fR and \f(CW\*(C`EWOULDBLOCK\*(C'\fR, making sure not to flood the log with such
1840messages, and continue as usual, which at least gives the user an idea of
1841what could be wrong (\*(L"raise the ulimit!\*(R"). For extra points one could stop
1842the \f(CW\*(C`ev_io\*(C'\fR watcher on the listening fd \*(L"for a while\*(R", which reduces \s-1CPU\s0
1843usage.
1844.PP
1845If your program is single-threaded, then you could also keep a dummy file
1846descriptor for overload situations (e.g. by opening \fI/dev/null\fR), and
1847when 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,
1848close that fd, and create a new dummy fd. This will gracefully refuse
1849clients under typical overload conditions.
1850.PP
1851The last way to handle it is to simply log the error and \f(CW\*(C`exit\*(C'\fR, as
1852is often done with \f(CW\*(C`malloc\*(C'\fR failures, but this results in an easy
1853opportunity for a DoS attack.
1854.PP
1855\fIWatcher-Specific Functions\fR
1856.IX Subsection "Watcher-Specific Functions"
850.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4 1857.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
851.IX Item "ev_io_init (ev_io *, callback, int fd, int events)" 1858.IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
852.PD 0 1859.PD 0
853.IP "ev_io_set (ev_io *, int fd, int events)" 4 1860.IP "ev_io_set (ev_io *, int fd, int events)" 4
854.IX Item "ev_io_set (ev_io *, int fd, int events)" 1861.IX Item "ev_io_set (ev_io *, int fd, int events)"
855.PD 1862.PD
856Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The fd is the file descriptor to rceeive 1863Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to
857events 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 | 1864receive 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
858EV_WRITE\*(C'\fR to receive the given events. 1865\&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR, to express the desire to receive the given events.
859.Sp 1866.IP "int fd [read\-only]" 4
860Please note that most of the more scalable backend mechanisms (for example 1867.IX Item "int fd [read-only]"
861epoll and solaris ports) can result in spurious readyness notifications 1868The file descriptor being watched.
862for file descriptors, so you practically need to use non-blocking I/O (and 1869.IP "int events [read\-only]" 4
863treat callback invocation as hint only), or retest separately with a safe 1870.IX Item "int events [read-only]"
864interface before doing I/O (XLib can do this), or force the use of either 1871The events being watched.
865\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR, which don't suffer from this
866problem. Also note that it is quite easy to have your callback invoked
867when the readyness condition is no longer valid even when employing
868typical ways of handling events, so its a good idea to use non-blocking
869I/O unconditionally.
870.PP 1872.PP
1873\fIExamples\fR
1874.IX Subsection "Examples"
1875.PP
871Example: call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well 1876Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
872readable, but only once. Since it is likely line\-buffered, you could 1877readable, but only once. Since it is likely line-buffered, you could
873attempt to read a whole line in the callback: 1878attempt to read a whole line in the callback.
874.PP 1879.PP
875.Vb 6 1880.Vb 6
876\& static void 1881\& static void
877\& stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents) 1882\& stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
878\& { 1883\& {
879\& ev_io_stop (loop, w); 1884\& ev_io_stop (loop, w);
880\& .. read from stdin here (or from w->fd) and haqndle any I/O errors 1885\& .. read from stdin here (or from w\->fd) and handle any I/O errors
881\& } 1886\& }
882.Ve 1887\&
883.PP
884.Vb 6
885\& ... 1888\& ...
886\& struct ev_loop *loop = ev_default_init (0); 1889\& struct ev_loop *loop = ev_default_init (0);
887\& struct ev_io stdin_readable; 1890\& ev_io stdin_readable;
888\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ); 1891\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
889\& ev_io_start (loop, &stdin_readable); 1892\& ev_io_start (loop, &stdin_readable);
890\& ev_loop (loop, 0); 1893\& ev_run (loop, 0);
891.Ve 1894.Ve
892.ie n .Sh """ev_timer"" \- relative and optionally recurring timeouts" 1895.ie n .SS """ev_timer"" \- relative and optionally repeating timeouts"
893.el .Sh "\f(CWev_timer\fP \- relative and optionally recurring timeouts" 1896.el .SS "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
894.IX Subsection "ev_timer - relative and optionally recurring timeouts" 1897.IX Subsection "ev_timer - relative and optionally repeating timeouts"
895Timer watchers are simple relative timers that generate an event after a 1898Timer watchers are simple relative timers that generate an event after a
896given time, and optionally repeating in regular intervals after that. 1899given time, and optionally repeating in regular intervals after that.
897.PP 1900.PP
898The timers are based on real time, that is, if you register an event that 1901The timers are based on real time, that is, if you register an event that
899times out after an hour and you reset your system clock to last years 1902times out after an hour and you reset your system clock to January last
900time, it will still time out after (roughly) and hour. \*(L"Roughly\*(R" because 1903year, it will still time out after (roughly) one hour. \*(L"Roughly\*(R" because
901detecting time jumps is hard, and some inaccuracies are unavoidable (the 1904detecting time jumps is hard, and some inaccuracies are unavoidable (the
902monotonic clock option helps a lot here). 1905monotonic clock option helps a lot here).
1906.PP
1907The callback is guaranteed to be invoked only \fIafter\fR its timeout has
1908passed (not \fIat\fR, so on systems with very low-resolution clocks this
1909might introduce a small delay, see \*(L"the special problem of being too
1910early\*(R", below). If multiple timers become ready during the same loop
1911iteration then the ones with earlier time-out values are invoked before
1912ones of the same priority with later time-out values (but this is no
1913longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
1914.PP
1915\fIBe smart about timeouts\fR
1916.IX Subsection "Be smart about timeouts"
1917.PP
1918Many real-world problems involve some kind of timeout, usually for error
1919recovery. A typical example is an \s-1HTTP\s0 request \- if the other side hangs,
1920you want to raise some error after a while.
1921.PP
1922What follows are some ways to handle this problem, from obvious and
1923inefficient to smart and efficient.
1924.PP
1925In the following, a 60 second activity timeout is assumed \- a timeout that
1926gets reset to 60 seconds each time there is activity (e.g. each time some
1927data or other life sign was received).
1928.IP "1. Use a timer and stop, reinitialise and start it on activity." 4
1929.IX Item "1. Use a timer and stop, reinitialise and start it on activity."
1930This is the most obvious, but not the most simple way: In the beginning,
1931start the watcher:
1932.Sp
1933.Vb 2
1934\& ev_timer_init (timer, callback, 60., 0.);
1935\& ev_timer_start (loop, timer);
1936.Ve
1937.Sp
1938Then, each time there is some activity, \f(CW\*(C`ev_timer_stop\*(C'\fR it, initialise it
1939and start it again:
1940.Sp
1941.Vb 3
1942\& ev_timer_stop (loop, timer);
1943\& ev_timer_set (timer, 60., 0.);
1944\& ev_timer_start (loop, timer);
1945.Ve
1946.Sp
1947This is relatively simple to implement, but means that each time there is
1948some activity, libev will first have to remove the timer from its internal
1949data structure and then add it again. Libev tries to be fast, but it's
1950still not a constant-time operation.
1951.ie n .IP "2. Use a timer and re-start it with ""ev_timer_again"" inactivity." 4
1952.el .IP "2. Use a timer and re-start it with \f(CWev_timer_again\fR inactivity." 4
1953.IX Item "2. Use a timer and re-start it with ev_timer_again inactivity."
1954This is the easiest way, and involves using \f(CW\*(C`ev_timer_again\*(C'\fR instead of
1955\&\f(CW\*(C`ev_timer_start\*(C'\fR.
1956.Sp
1957To implement this, configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value
1958of \f(CW60\fR and then call \f(CW\*(C`ev_timer_again\*(C'\fR at start and each time you
1959successfully read or write some data. If you go into an idle state where
1960you do not expect data to travel on the socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR
1961the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will automatically restart it if need be.
1962.Sp
1963That means you can ignore both the \f(CW\*(C`ev_timer_start\*(C'\fR function and the
1964\&\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
1965member and \f(CW\*(C`ev_timer_again\*(C'\fR.
1966.Sp
1967At start:
1968.Sp
1969.Vb 3
1970\& ev_init (timer, callback);
1971\& timer\->repeat = 60.;
1972\& ev_timer_again (loop, timer);
1973.Ve
1974.Sp
1975Each time there is some activity:
1976.Sp
1977.Vb 1
1978\& ev_timer_again (loop, timer);
1979.Ve
1980.Sp
1981It is even possible to change the time-out on the fly, regardless of
1982whether the watcher is active or not:
1983.Sp
1984.Vb 2
1985\& timer\->repeat = 30.;
1986\& ev_timer_again (loop, timer);
1987.Ve
1988.Sp
1989This is slightly more efficient then stopping/starting the timer each time
1990you want to modify its timeout value, as libev does not have to completely
1991remove and re-insert the timer from/into its internal data structure.
1992.Sp
1993It is, however, even simpler than the \*(L"obvious\*(R" way to do it.
1994.IP "3. Let the timer time out, but then re-arm it as required." 4
1995.IX Item "3. Let the timer time out, but then re-arm it as required."
1996This method is more tricky, but usually most efficient: Most timeouts are
1997relatively long compared to the intervals between other activity \- in
1998our example, within 60 seconds, there are usually many I/O events with
1999associated activity resets.
2000.Sp
2001In this case, it would be more efficient to leave the \f(CW\*(C`ev_timer\*(C'\fR alone,
2002but remember the time of last activity, and check for a real timeout only
2003within the callback:
2004.Sp
2005.Vb 3
2006\& ev_tstamp timeout = 60.;
2007\& ev_tstamp last_activity; // time of last activity
2008\& ev_timer timer;
2009\&
2010\& static void
2011\& callback (EV_P_ ev_timer *w, int revents)
2012\& {
2013\& // calculate when the timeout would happen
2014\& ev_tstamp after = last_activity \- ev_now (EV_A) + timeout;
2015\&
2016\& // if negative, it means we the timeout already occurred
2017\& if (after < 0.)
2018\& {
2019\& // timeout occurred, take action
2020\& }
2021\& else
2022\& {
2023\& // callback was invoked, but there was some recent
2024\& // activity. simply restart the timer to time out
2025\& // after "after" seconds, which is the earliest time
2026\& // the timeout can occur.
2027\& ev_timer_set (w, after, 0.);
2028\& ev_timer_start (EV_A_ w);
2029\& }
2030\& }
2031.Ve
2032.Sp
2033To summarise the callback: first calculate in how many seconds the
2034timeout will occur (by calculating the absolute time when it would occur,
2035\&\f(CW\*(C`last_activity + timeout\*(C'\fR, and subtracting the current time, \f(CW\*(C`ev_now
2036(EV_A)\*(C'\fR from that).
2037.Sp
2038If this value is negative, then we are already past the timeout, i.e. we
2039timed out, and need to do whatever is needed in this case.
2040.Sp
2041Otherwise, we now the earliest time at which the timeout would trigger,
2042and simply start the timer with this timeout value.
2043.Sp
2044In other words, each time the callback is invoked it will check whether
2045the timeout occurred. If not, it will simply reschedule itself to check
2046again at the earliest time it could time out. Rinse. Repeat.
2047.Sp
2048This scheme causes more callback invocations (about one every 60 seconds
2049minus half the average time between activity), but virtually no calls to
2050libev to change the timeout.
2051.Sp
2052To start the machinery, simply initialise the watcher and set
2053\&\f(CW\*(C`last_activity\*(C'\fR to the current time (meaning there was some activity just
2054now), then call the callback, which will \*(L"do the right thing\*(R" and start
2055the timer:
2056.Sp
2057.Vb 3
2058\& last_activity = ev_now (EV_A);
2059\& ev_init (&timer, callback);
2060\& callback (EV_A_ &timer, 0);
2061.Ve
2062.Sp
2063When there is some activity, simply store the current time in
2064\&\f(CW\*(C`last_activity\*(C'\fR, no libev calls at all:
2065.Sp
2066.Vb 2
2067\& if (activity detected)
2068\& last_activity = ev_now (EV_A);
2069.Ve
2070.Sp
2071When your timeout value changes, then the timeout can be changed by simply
2072providing a new value, stopping the timer and calling the callback, which
2073will again do the right thing (for example, time out immediately :).
2074.Sp
2075.Vb 3
2076\& timeout = new_value;
2077\& ev_timer_stop (EV_A_ &timer);
2078\& callback (EV_A_ &timer, 0);
2079.Ve
2080.Sp
2081This technique is slightly more complex, but in most cases where the
2082time-out is unlikely to be triggered, much more efficient.
2083.IP "4. Wee, just use a double-linked list for your timeouts." 4
2084.IX Item "4. Wee, just use a double-linked list for your timeouts."
2085If there is not one request, but many thousands (millions...), all
2086employing some kind of timeout with the same timeout value, then one can
2087do even better:
2088.Sp
2089When starting the timeout, calculate the timeout value and put the timeout
2090at the \fIend\fR of the list.
2091.Sp
2092Then use an \f(CW\*(C`ev_timer\*(C'\fR to fire when the timeout at the \fIbeginning\fR of
2093the list is expected to fire (for example, using the technique #3).
2094.Sp
2095When there is some activity, remove the timer from the list, recalculate
2096the timeout, append it to the end of the list again, and make sure to
2097update the \f(CW\*(C`ev_timer\*(C'\fR if it was taken from the beginning of the list.
2098.Sp
2099This way, one can manage an unlimited number of timeouts in O(1) time for
2100starting, stopping and updating the timers, at the expense of a major
2101complication, and having to use a constant timeout. The constant timeout
2102ensures that the list stays sorted.
2103.PP
2104So which method the best?
2105.PP
2106Method #2 is a simple no-brain-required solution that is adequate in most
2107situations. Method #3 requires a bit more thinking, but handles many cases
2108better, and isn't very complicated either. In most case, choosing either
2109one is fine, with #3 being better in typical situations.
2110.PP
2111Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
2112rather complicated, but extremely efficient, something that really pays
2113off after the first million or so of active timers, i.e. it's usually
2114overkill :)
2115.PP
2116\fIThe special problem of being too early\fR
2117.IX Subsection "The special problem of being too early"
2118.PP
2119If you ask a timer to call your callback after three seconds, then
2120you expect it to be invoked after three seconds \- but of course, this
2121cannot be guaranteed to infinite precision. Less obviously, it cannot be
2122guaranteed to any precision by libev \- imagine somebody suspending the
2123process with a \s-1STOP\s0 signal for a few hours for example.
2124.PP
2125So, libev tries to invoke your callback as soon as possible \fIafter\fR the
2126delay has occurred, but cannot guarantee this.
2127.PP
2128A less obvious failure mode is calling your callback too early: many event
2129loops compare timestamps with a \*(L"elapsed delay >= requested delay\*(R", but
2130this can cause your callback to be invoked much earlier than you would
2131expect.
2132.PP
2133To see why, imagine a system with a clock that only offers full second
2134resolution (think windows if you can't come up with a broken enough \s-1OS\s0
2135yourself). If you schedule a one-second timer at the time 500.9, then the
2136event loop will schedule your timeout to elapse at a system time of 500
2137(500.9 truncated to the resolution) + 1, or 501.
2138.PP
2139If an event library looks at the timeout 0.1s later, it will see \*(L"501 >=
2140501\*(R" and invoke the callback 0.1s after it was started, even though a
2141one-second delay was requested \- this is being \*(L"too early\*(R", despite best
2142intentions.
2143.PP
2144This is the reason why libev will never invoke the callback if the elapsed
2145delay equals the requested delay, but only when the elapsed delay is
2146larger than the requested delay. In the example above, libev would only invoke
2147the callback at system time 502, or 1.1s after the timer was started.
2148.PP
2149So, while libev cannot guarantee that your callback will be invoked
2150exactly when requested, it \fIcan\fR and \fIdoes\fR guarantee that the requested
2151delay has actually elapsed, or in other words, it always errs on the \*(L"too
2152late\*(R" side of things.
2153.PP
2154\fIThe special problem of time updates\fR
2155.IX Subsection "The special problem of time updates"
2156.PP
2157Establishing the current time is a costly operation (it usually takes
2158at least one system call): \s-1EV\s0 therefore updates its idea of the current
2159time only before and after \f(CW\*(C`ev_run\*(C'\fR collects new events, which causes a
2160growing difference between \f(CW\*(C`ev_now ()\*(C'\fR and \f(CW\*(C`ev_time ()\*(C'\fR when handling
2161lots of events in one iteration.
903.PP 2162.PP
904The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR 2163The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
905time. This is usually the right thing as this timestamp refers to the time 2164time. This is usually the right thing as this timestamp refers to the time
906of the event triggering whatever timeout you are modifying/starting. If 2165of the event triggering whatever timeout you are modifying/starting. If
907you suspect event processing to be delayed and you \fIneed\fR to base the timeout 2166you suspect event processing to be delayed and you \fIneed\fR to base the
908on the current time, use something like this to adjust for this: 2167timeout on the current time, use something like the following to adjust
2168for it:
909.PP 2169.PP
910.Vb 1 2170.Vb 1
911\& ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); 2171\& ev_timer_set (&timer, after + (ev_time () \- ev_now ()), 0.);
912.Ve 2172.Ve
913.PP 2173.PP
914The callback is guarenteed to be invoked only when its timeout has passed, 2174If the event loop is suspended for a long time, you can also force an
915but if multiple timers become ready during the same loop iteration then 2175update of the time returned by \f(CW\*(C`ev_now ()\*(C'\fR by calling \f(CW\*(C`ev_now_update
916order of execution is undefined. 2176()\*(C'\fR, although that will push the event time of all outstanding events
2177further into the future.
2178.PP
2179\fIThe special problem of unsynchronised clocks\fR
2180.IX Subsection "The special problem of unsynchronised clocks"
2181.PP
2182Modern systems have a variety of clocks \- libev itself uses the normal
2183\&\*(L"wall clock\*(R" clock and, if available, the monotonic clock (to avoid time
2184jumps).
2185.PP
2186Neither of these clocks is synchronised with each other or any other clock
2187on the system, so \f(CW\*(C`ev_time ()\*(C'\fR might return a considerably different time
2188than \f(CW\*(C`gettimeofday ()\*(C'\fR or \f(CW\*(C`time ()\*(C'\fR. On a GNU/Linux system, for example,
2189a call to \f(CW\*(C`gettimeofday\*(C'\fR might return a second count that is one higher
2190than a directly following call to \f(CW\*(C`time\*(C'\fR.
2191.PP
2192The moral of this is to only compare libev-related timestamps with
2193\&\f(CW\*(C`ev_time ()\*(C'\fR and \f(CW\*(C`ev_now ()\*(C'\fR, at least if you want better precision than
2194a second or so.
2195.PP
2196One more problem arises due to this lack of synchronisation: if libev uses
2197the system monotonic clock and you compare timestamps from \f(CW\*(C`ev_time\*(C'\fR
2198or \f(CW\*(C`ev_now\*(C'\fR from when you started your timer and when your callback is
2199invoked, you will find that sometimes the callback is a bit \*(L"early\*(R".
2200.PP
2201This is because \f(CW\*(C`ev_timer\*(C'\fRs work in real time, not wall clock time, so
2202libev makes sure your callback is not invoked before the delay happened,
2203\&\fImeasured according to the real time\fR, not the system clock.
2204.PP
2205If your timeouts are based on a physical timescale (e.g. \*(L"time out this
2206connection after 100 seconds\*(R") then this shouldn't bother you as it is
2207exactly the right behaviour.
2208.PP
2209If you want to compare wall clock/system timestamps to your timers, then
2210you need to use \f(CW\*(C`ev_periodic\*(C'\fRs, as these are based on the wall clock
2211time, where your comparisons will always generate correct results.
2212.PP
2213\fIThe special problems of suspended animation\fR
2214.IX Subsection "The special problems of suspended animation"
2215.PP
2216When you leave the server world it is quite customary to hit machines that
2217can suspend/hibernate \- what happens to the clocks during such a suspend?
2218.PP
2219Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
2220all processes, while the clocks (\f(CW\*(C`times\*(C'\fR, \f(CW\*(C`CLOCK_MONOTONIC\*(C'\fR) continue
2221to run until the system is suspended, but they will not advance while the
2222system is suspended. That means, on resume, it will be as if the program
2223was frozen for a few seconds, but the suspend time will not be counted
2224towards \f(CW\*(C`ev_timer\*(C'\fR when a monotonic clock source is used. The real time
2225clock advanced as expected, but if it is used as sole clocksource, then a
2226long suspend would be detected as a time jump by libev, and timers would
2227be adjusted accordingly.
2228.PP
2229I would not be surprised to see different behaviour in different between
2230operating systems, \s-1OS\s0 versions or even different hardware.
2231.PP
2232The other form of suspend (job control, or sending a \s-1SIGSTOP\s0) will see a
2233time jump in the monotonic clocks and the realtime clock. If the program
2234is suspended for a very long time, and monotonic clock sources are in use,
2235then you can expect \f(CW\*(C`ev_timer\*(C'\fRs to expire as the full suspension time
2236will be counted towards the timers. When no monotonic clock source is in
2237use, then libev will again assume a timejump and adjust accordingly.
2238.PP
2239It might be beneficial for this latter case to call \f(CW\*(C`ev_suspend\*(C'\fR
2240and \f(CW\*(C`ev_resume\*(C'\fR in code that handles \f(CW\*(C`SIGTSTP\*(C'\fR, to at least get
2241deterministic behaviour in this case (you can do nothing against
2242\&\f(CW\*(C`SIGSTOP\*(C'\fR).
2243.PP
2244\fIWatcher-Specific Functions and Data Members\fR
2245.IX Subsection "Watcher-Specific Functions and Data Members"
917.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4 2246.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
918.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 2247.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
919.PD 0 2248.PD 0
920.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4 2249.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
921.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 2250.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
922.PD 2251.PD
923Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR is 2252Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR
924\&\f(CW0.\fR, then it will automatically be stopped. If it is positive, then the 2253is \f(CW0.\fR, then it will automatically be stopped once the timeout is
925timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds 2254reached. If it is positive, then the timer will automatically be
926later, again, and again, until stopped manually. 2255configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds later, again, and again,
2256until stopped manually.
927.Sp 2257.Sp
928The timer itself will do a best-effort at avoiding drift, that is, if you 2258The timer itself will do a best-effort at avoiding drift, that is, if
929configure a timer to trigger every 10 seconds, then it will trigger at 2259you configure a timer to trigger every 10 seconds, then it will normally
930exactly 10 second intervals. If, however, your program cannot keep up with 2260trigger at exactly 10 second intervals. If, however, your program cannot
931the timer (because it takes longer than those 10 seconds to do stuff) the 2261keep up with the timer (because it takes longer than those 10 seconds to
932timer will not fire more than once per event loop iteration. 2262do stuff) the timer will not fire more than once per event loop iteration.
933.IP "ev_timer_again (loop)" 4 2263.IP "ev_timer_again (loop, ev_timer *)" 4
934.IX Item "ev_timer_again (loop)" 2264.IX Item "ev_timer_again (loop, ev_timer *)"
935This will act as if the timer timed out and restart it again if it is 2265This will act as if the timer timed out, and restarts it again if it is
936repeating. The exact semantics are: 2266repeating. It basically works like calling \f(CW\*(C`ev_timer_stop\*(C'\fR, updating the
2267timeout to the \f(CW\*(C`repeat\*(C'\fR value and calling \f(CW\*(C`ev_timer_start\*(C'\fR.
937.Sp 2268.Sp
938If the timer is started but nonrepeating, stop it. 2269The exact semantics are as in the following rules, all of which will be
2270applied to the watcher:
2271.RS 4
2272.IP "If the timer is pending, the pending status is always cleared." 4
2273.IX Item "If the timer is pending, the pending status is always cleared."
2274.PD 0
2275.IP "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)." 4
2276.IX Item "If the timer is started but non-repeating, stop it (as if it timed out, without invoking it)."
2277.ie n .IP "If the timer is repeating, make the ""repeat"" value the new timeout and start the timer, if necessary." 4
2278.el .IP "If the timer is repeating, make the \f(CWrepeat\fR value the new timeout and start the timer, if necessary." 4
2279.IX Item "If the timer is repeating, make the repeat value the new timeout and start the timer, if necessary."
2280.RE
2281.RS 4
2282.PD
939.Sp 2283.Sp
940If the timer is repeating, either start it if necessary (with the repeat 2284This sounds a bit complicated, see \*(L"Be smart about timeouts\*(R", above, for a
941value), or reset the running timer to the repeat value. 2285usage example.
2286.RE
2287.IP "ev_tstamp ev_timer_remaining (loop, ev_timer *)" 4
2288.IX Item "ev_tstamp ev_timer_remaining (loop, ev_timer *)"
2289Returns the remaining time until a timer fires. If the timer is active,
2290then this time is relative to the current event loop time, otherwise it's
2291the timeout value currently configured.
942.Sp 2292.Sp
943This sounds a bit complicated, but here is a useful and typical 2293That is, after an \f(CW\*(C`ev_timer_set (w, 5, 7)\*(C'\fR, \f(CW\*(C`ev_timer_remaining\*(C'\fR returns
944example: Imagine you have a tcp connection and you want a so-called idle 2294\&\f(CW5\fR. When the timer is started and one second passes, \f(CW\*(C`ev_timer_remaining\*(C'\fR
945timeout, that is, you want to be called when there have been, say, 60 2295will return \f(CW4\fR. When the timer expires and is restarted, it will return
946seconds of inactivity on the socket. The easiest way to do this is to 2296roughly \f(CW7\fR (likely slightly less as callback invocation takes some time,
947configure an \f(CW\*(C`ev_timer\*(C'\fR with after=repeat=60 and calling ev_timer_again each 2297too), and so on.
948time you successfully read or write some data. If you go into an idle 2298.IP "ev_tstamp repeat [read\-write]" 4
949state where you do not expect data to travel on the socket, you can stop 2299.IX Item "ev_tstamp repeat [read-write]"
950the timer, and again will automatically restart it if need be. 2300The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
2301or \f(CW\*(C`ev_timer_again\*(C'\fR is called, and determines the next timeout (if any),
2302which is also when any modifications are taken into account.
951.PP 2303.PP
2304\fIExamples\fR
2305.IX Subsection "Examples"
2306.PP
952Example: create a timer that fires after 60 seconds. 2307Example: Create a timer that fires after 60 seconds.
953.PP 2308.PP
954.Vb 5 2309.Vb 5
955\& static void 2310\& static void
956\& one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents) 2311\& one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
957\& { 2312\& {
958\& .. one minute over, w is actually stopped right here 2313\& .. one minute over, w is actually stopped right here
959\& } 2314\& }
960.Ve 2315\&
961.PP
962.Vb 3
963\& struct ev_timer mytimer; 2316\& ev_timer mytimer;
964\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.); 2317\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
965\& ev_timer_start (loop, &mytimer); 2318\& ev_timer_start (loop, &mytimer);
966.Ve 2319.Ve
967.PP 2320.PP
968Example: create a timeout timer that times out after 10 seconds of 2321Example: Create a timeout timer that times out after 10 seconds of
969inactivity. 2322inactivity.
970.PP 2323.PP
971.Vb 5 2324.Vb 5
972\& static void 2325\& static void
973\& timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents) 2326\& timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
974\& { 2327\& {
975\& .. ten seconds without any activity 2328\& .. ten seconds without any activity
976\& } 2329\& }
977.Ve 2330\&
978.PP
979.Vb 4
980\& struct ev_timer mytimer; 2331\& ev_timer mytimer;
981\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */ 2332\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
982\& ev_timer_again (&mytimer); /* start timer */ 2333\& ev_timer_again (&mytimer); /* start timer */
983\& ev_loop (loop, 0); 2334\& ev_run (loop, 0);
984.Ve 2335\&
985.PP
986.Vb 3
987\& // and in some piece of code that gets executed on any "activity": 2336\& // and in some piece of code that gets executed on any "activity":
988\& // reset the timeout to start ticking again at 10 seconds 2337\& // reset the timeout to start ticking again at 10 seconds
989\& ev_timer_again (&mytimer); 2338\& ev_timer_again (&mytimer);
990.Ve 2339.Ve
991.ie n .Sh """ev_periodic"" \- to cron or not to cron" 2340.ie n .SS """ev_periodic"" \- to cron or not to cron?"
992.el .Sh "\f(CWev_periodic\fP \- to cron or not to cron" 2341.el .SS "\f(CWev_periodic\fP \- to cron or not to cron?"
993.IX Subsection "ev_periodic - to cron or not to cron" 2342.IX Subsection "ev_periodic - to cron or not to cron?"
994Periodic watchers are also timers of a kind, but they are very versatile 2343Periodic watchers are also timers of a kind, but they are very versatile
995(and unfortunately a bit complex). 2344(and unfortunately a bit complex).
996.PP 2345.PP
997Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time) 2346Unlike \f(CW\*(C`ev_timer\*(C'\fR, periodic watchers are not based on real time (or
998but on wallclock time (absolute time). You can tell a periodic watcher 2347relative time, the physical time that passes) but on wall clock time
999to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a 2348(absolute time, the thing you can read on your calender or clock). The
1000periodic watcher to trigger in 10 seconds (by specifiying e.g. \f(CW\*(C`ev_now () 2349difference is that wall clock time can run faster or slower than real
1001+ 10.\*(C'\fR) and then reset your system clock to the last year, then it will 2350time, and time jumps are not uncommon (e.g. when you adjust your
1002take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger 2351wrist-watch).
1003roughly 10 seconds later and of course not if you reset your system time
1004again).
1005.PP 2352.PP
1006They can also be used to implement vastly more complex timers, such as 2353You can tell a periodic watcher to trigger after some specific point
1007triggering an event on eahc midnight, local time. 2354in time: for example, if you tell a periodic watcher to trigger \*(L"in 10
2355seconds\*(R" (by specifying e.g. \f(CW\*(C`ev_now () + 10.\*(C'\fR, that is, an absolute time
2356not a delay) and then reset your system clock to January of the previous
2357year, then it will take a year or more to trigger the event (unlike an
2358\&\f(CW\*(C`ev_timer\*(C'\fR, which would still trigger roughly 10 seconds after starting
2359it, as it uses a relative timeout).
1008.PP 2360.PP
2361\&\f(CW\*(C`ev_periodic\*(C'\fR watchers can also be used to implement vastly more complex
2362timers, such as triggering an event on each \*(L"midnight, local time\*(R", or
2363other complicated rules. This cannot be done with \f(CW\*(C`ev_timer\*(C'\fR watchers, as
2364those cannot react to time jumps.
2365.PP
1009As with timers, the callback is guarenteed to be invoked only when the 2366As with timers, the callback is guaranteed to be invoked only when the
1010time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready 2367point in time where it is supposed to trigger has passed. If multiple
1011during the same loop iteration then order of execution is undefined. 2368timers become ready during the same loop iteration then the ones with
2369earlier time-out values are invoked before ones with later time-out values
2370(but this is no longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
2371.PP
2372\fIWatcher-Specific Functions and Data Members\fR
2373.IX Subsection "Watcher-Specific Functions and Data Members"
1012.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4 2374.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
1013.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 2375.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
1014.PD 0 2376.PD 0
1015.IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4 2377.IP "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
1016.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 2378.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
1017.PD 2379.PD
1018Lots of arguments, lets sort it out... There are basically three modes of 2380Lots of arguments, let's sort it out... There are basically three modes of
1019operation, and we will explain them from simplest to complex: 2381operation, and we will explain them from simplest to most complex:
1020.RS 4 2382.RS 4
1021.IP "* absolute timer (interval = reschedule_cb = 0)" 4 2383.IP "\(bu" 4
1022.IX Item "absolute timer (interval = reschedule_cb = 0)" 2384absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
2385.Sp
1023In this configuration the watcher triggers an event at the wallclock time 2386In this configuration the watcher triggers an event after the wall clock
1024\&\f(CW\*(C`at\*(C'\fR and doesn't repeat. It will not adjust when a time jump occurs, 2387time \f(CW\*(C`offset\*(C'\fR has passed. It will not repeat and will not adjust when a
1025that is, if it is to be run at January 1st 2011 then it will run when the 2388time jump occurs, that is, if it is to be run at January 1st 2011 then it
1026system time reaches or surpasses this time. 2389will be stopped and invoked when the system clock reaches or surpasses
1027.IP "* non-repeating interval timer (interval > 0, reschedule_cb = 0)" 4 2390this point in time.
1028.IX Item "non-repeating interval timer (interval > 0, reschedule_cb = 0)" 2391.IP "\(bu" 4
2392repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
2393.Sp
1029In this mode the watcher will always be scheduled to time out at the next 2394In this mode the watcher will always be scheduled to time out at the next
1030\&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N) and then repeat, regardless 2395\&\f(CW\*(C`offset + N * interval\*(C'\fR time (for some integer N, which can also be
1031of any time jumps. 2396negative) and then repeat, regardless of any time jumps. The \f(CW\*(C`offset\*(C'\fR
2397argument is merely an offset into the \f(CW\*(C`interval\*(C'\fR periods.
1032.Sp 2398.Sp
1033This can be used to create timers that do not drift with respect to system 2399This can be used to create timers that do not drift with respect to the
1034time: 2400system clock, for example, here is an \f(CW\*(C`ev_periodic\*(C'\fR that triggers each
2401hour, on the hour (with respect to \s-1UTC\s0):
1035.Sp 2402.Sp
1036.Vb 1 2403.Vb 1
1037\& ev_periodic_set (&periodic, 0., 3600., 0); 2404\& ev_periodic_set (&periodic, 0., 3600., 0);
1038.Ve 2405.Ve
1039.Sp 2406.Sp
1040This doesn't mean there will always be 3600 seconds in between triggers, 2407This doesn't mean there will always be 3600 seconds in between triggers,
1041but only that the the callback will be called when the system time shows a 2408but only that the callback will be called when the system time shows a
1042full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible 2409full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
1043by 3600. 2410by 3600.
1044.Sp 2411.Sp
1045Another way to think about it (for the mathematically inclined) is that 2412Another way to think about it (for the mathematically inclined) is that
1046\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible 2413\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
1047time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps. 2414time where \f(CW\*(C`time = offset (mod interval)\*(C'\fR, regardless of any time jumps.
1048.IP "* manual reschedule mode (reschedule_cb = callback)" 4 2415.Sp
1049.IX Item "manual reschedule mode (reschedule_cb = callback)" 2416The \f(CW\*(C`interval\*(C'\fR \fI\s-1MUST\s0\fR be positive, and for numerical stability, the
2417interval value should be higher than \f(CW\*(C`1/8192\*(C'\fR (which is around 100
2418microseconds) and \f(CW\*(C`offset\*(C'\fR should be higher than \f(CW0\fR and should have
2419at most a similar magnitude as the current time (say, within a factor of
2420ten). Typical values for offset are, in fact, \f(CW0\fR or something between
2421\&\f(CW0\fR and \f(CW\*(C`interval\*(C'\fR, which is also the recommended range.
2422.Sp
2423Note also that there is an upper limit to how often a timer can fire (\s-1CPU\s0
2424speed for example), so if \f(CW\*(C`interval\*(C'\fR is very small then timing stability
2425will of course deteriorate. Libev itself tries to be exact to be about one
2426millisecond (if the \s-1OS\s0 supports it and the machine is fast enough).
2427.IP "\(bu" 4
2428manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
2429.Sp
1050In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being 2430In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`offset\*(C'\fR are both being
1051ignored. Instead, each time the periodic watcher gets scheduled, the 2431ignored. Instead, each time the periodic watcher gets scheduled, the
1052reschedule callback will be called with the watcher as first, and the 2432reschedule callback will be called with the watcher as first, and the
1053current time as second argument. 2433current time as second argument.
1054.Sp 2434.Sp
1055\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, 2435\&\s-1NOTE: \s0\fIThis callback \s-1MUST NOT\s0 stop or destroy any periodic watcher, ever,
1056ever, or make any event loop modifications\fR. If you need to stop it, 2436or make \s-1ANY\s0 other event loop modifications whatsoever, unless explicitly
1057return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by 2437allowed by documentation here\fR.
1058starting a prepare watcher).
1059.Sp 2438.Sp
2439If you need to stop it, return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop
2440it afterwards (e.g. by starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is the
2441only event loop modification you are allowed to do).
2442.Sp
1060Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w, 2443The callback prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(ev_periodic
1061ev_tstamp now)\*(C'\fR, e.g.: 2444*w, ev_tstamp now)\*(C'\fR, e.g.:
1062.Sp 2445.Sp
1063.Vb 4 2446.Vb 5
2447\& static ev_tstamp
1064\& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) 2448\& my_rescheduler (ev_periodic *w, ev_tstamp now)
1065\& { 2449\& {
1066\& return now + 60.; 2450\& return now + 60.;
1067\& } 2451\& }
1068.Ve 2452.Ve
1069.Sp 2453.Sp
1070It must return the next time to trigger, based on the passed time value 2454It must return the next time to trigger, based on the passed time value
1071(that is, the lowest time value larger than to the second argument). It 2455(that is, the lowest time value larger than to the second argument). It
1072will usually be called just before the callback will be triggered, but 2456will usually be called just before the callback will be triggered, but
1073might be called at other times, too. 2457might be called at other times, too.
1074.Sp 2458.Sp
1075\&\s-1NOTE:\s0 \fIThis callback must always return a time that is later than the 2459\&\s-1NOTE: \s0\fIThis callback must always return a time that is higher than or
1076passed \f(CI\*(C`now\*(C'\fI value\fR. Not even \f(CW\*(C`now\*(C'\fR itself will do, it \fImust\fR be larger. 2460equal to the passed \f(CI\*(C`now\*(C'\fI value\fR.
1077.Sp 2461.Sp
1078This can be used to create very complex timers, such as a timer that 2462This can be used to create very complex timers, such as a timer that
1079triggers on each midnight, local time. To do this, you would calculate the 2463triggers on \*(L"next midnight, local time\*(R". To do this, you would calculate the
1080next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How 2464next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How
1081you do this is, again, up to you (but it is not trivial, which is the main 2465you do this is, again, up to you (but it is not trivial, which is the main
1082reason I omitted it as an example). 2466reason I omitted it as an example).
1083.RE 2467.RE
1084.RS 4 2468.RS 4
… …
1087.IX Item "ev_periodic_again (loop, ev_periodic *)" 2471.IX Item "ev_periodic_again (loop, ev_periodic *)"
1088Simply stops and restarts the periodic watcher again. This is only useful 2472Simply stops and restarts the periodic watcher again. This is only useful
1089when you changed some parameters or the reschedule callback would return 2473when you changed some parameters or the reschedule callback would return
1090a different time than the last time it was called (e.g. in a crond like 2474a different time than the last time it was called (e.g. in a crond like
1091program when the crontabs have changed). 2475program when the crontabs have changed).
2476.IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4
2477.IX Item "ev_tstamp ev_periodic_at (ev_periodic *)"
2478When active, returns the absolute time that the watcher is supposed
2479to trigger next. This is not the same as the \f(CW\*(C`offset\*(C'\fR argument to
2480\&\f(CW\*(C`ev_periodic_set\*(C'\fR, but indeed works even in interval and manual
2481rescheduling modes.
2482.IP "ev_tstamp offset [read\-write]" 4
2483.IX Item "ev_tstamp offset [read-write]"
2484When repeating, this contains the offset value, otherwise this is the
2485absolute point in time (the \f(CW\*(C`offset\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR,
2486although libev might modify this value for better numerical stability).
2487.Sp
2488Can be modified any time, but changes only take effect when the periodic
2489timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
2490.IP "ev_tstamp interval [read\-write]" 4
2491.IX Item "ev_tstamp interval [read-write]"
2492The current interval value. Can be modified any time, but changes only
2493take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
2494called.
2495.IP "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read\-write]" 4
2496.IX Item "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]"
2497The current reschedule callback, or \f(CW0\fR, if this functionality is
2498switched off. Can be changed any time, but changes only take effect when
2499the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1092.PP 2500.PP
2501\fIExamples\fR
2502.IX Subsection "Examples"
2503.PP
1093Example: call a callback every hour, or, more precisely, whenever the 2504Example: Call a callback every hour, or, more precisely, whenever the
1094system clock is divisible by 3600. The callback invocation times have 2505system time is divisible by 3600. The callback invocation times have
1095potentially a lot of jittering, but good long-term stability. 2506potentially a lot of jitter, but good long-term stability.
1096.PP 2507.PP
1097.Vb 5 2508.Vb 5
1098\& static void 2509\& static void
1099\& clock_cb (struct ev_loop *loop, struct ev_io *w, int revents) 2510\& clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1100\& { 2511\& {
1101\& ... its now a full hour (UTC, or TAI or whatever your clock follows) 2512\& ... its now a full hour (UTC, or TAI or whatever your clock follows)
1102\& } 2513\& }
1103.Ve 2514\&
1104.PP
1105.Vb 3
1106\& struct ev_periodic hourly_tick; 2515\& ev_periodic hourly_tick;
1107\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0); 2516\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1108\& ev_periodic_start (loop, &hourly_tick); 2517\& ev_periodic_start (loop, &hourly_tick);
1109.Ve 2518.Ve
1110.PP 2519.PP
1111Example: the same as above, but use a reschedule callback to do it: 2520Example: The same as above, but use a reschedule callback to do it:
1112.PP 2521.PP
1113.Vb 1 2522.Vb 1
1114\& #include <math.h> 2523\& #include <math.h>
1115.Ve 2524\&
1116.PP
1117.Vb 5
1118\& static ev_tstamp 2525\& static ev_tstamp
1119\& my_scheduler_cb (struct ev_periodic *w, ev_tstamp now) 2526\& my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1120\& { 2527\& {
1121\& return fmod (now, 3600.) + 3600.; 2528\& return now + (3600. \- fmod (now, 3600.));
1122\& } 2529\& }
1123.Ve 2530\&
1124.PP
1125.Vb 1
1126\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb); 2531\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1127.Ve 2532.Ve
1128.PP 2533.PP
1129Example: call a callback every hour, starting now: 2534Example: Call a callback every hour, starting now:
1130.PP 2535.PP
1131.Vb 4 2536.Vb 4
1132\& struct ev_periodic hourly_tick; 2537\& ev_periodic hourly_tick;
1133\& ev_periodic_init (&hourly_tick, clock_cb, 2538\& ev_periodic_init (&hourly_tick, clock_cb,
1134\& fmod (ev_now (loop), 3600.), 3600., 0); 2539\& fmod (ev_now (loop), 3600.), 3600., 0);
1135\& ev_periodic_start (loop, &hourly_tick); 2540\& ev_periodic_start (loop, &hourly_tick);
1136.Ve 2541.Ve
1137.ie n .Sh """ev_signal"" \- signal me when a signal gets signalled" 2542.ie n .SS """ev_signal"" \- signal me when a signal gets signalled!"
1138.el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled" 2543.el .SS "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
1139.IX Subsection "ev_signal - signal me when a signal gets signalled" 2544.IX Subsection "ev_signal - signal me when a signal gets signalled!"
1140Signal watchers will trigger an event when the process receives a specific 2545Signal watchers will trigger an event when the process receives a specific
1141signal one or more times. Even though signals are very asynchronous, libev 2546signal one or more times. Even though signals are very asynchronous, libev
1142will try it's best to deliver signals synchronously, i.e. as part of the 2547will try its best to deliver signals synchronously, i.e. as part of the
1143normal event processing, like any other event. 2548normal event processing, like any other event.
1144.PP 2549.PP
2550If you want signals to be delivered truly asynchronously, just use
2551\&\f(CW\*(C`sigaction\*(C'\fR as you would do without libev and forget about sharing
2552the signal. You can even use \f(CW\*(C`ev_async\*(C'\fR from a signal handler to
2553synchronously wake up an event loop.
2554.PP
1145You can configure as many watchers as you like per signal. Only when the 2555You can configure as many watchers as you like for the same signal, but
1146first watcher gets started will libev actually register a signal watcher 2556only within the same loop, i.e. you can watch for \f(CW\*(C`SIGINT\*(C'\fR in your
1147with the kernel (thus it coexists with your own signal handlers as long 2557default loop and for \f(CW\*(C`SIGIO\*(C'\fR in another loop, but you cannot watch for
1148as you don't register any with libev). Similarly, when the last signal 2558\&\f(CW\*(C`SIGINT\*(C'\fR in both the default loop and another loop at the same time. At
1149watcher for a signal is stopped libev will reset the signal handler to 2559the moment, \f(CW\*(C`SIGCHLD\*(C'\fR is permanently tied to the default loop.
1150\&\s-1SIG_DFL\s0 (regardless of what it was set to before). 2560.PP
2561Only after the first watcher for a signal is started will libev actually
2562register something with the kernel. It thus coexists with your own signal
2563handlers as long as you don't register any with libev for the same signal.
2564.PP
2565If possible and supported, libev will install its handlers with
2566\&\f(CW\*(C`SA_RESTART\*(C'\fR (or equivalent) behaviour enabled, so system calls should
2567not be unduly interrupted. If you have a problem with system calls getting
2568interrupted by signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher
2569and unblock them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher.
2570.PP
2571\fIThe special problem of inheritance over fork/execve/pthread_create\fR
2572.IX Subsection "The special problem of inheritance over fork/execve/pthread_create"
2573.PP
2574Both the signal mask (\f(CW\*(C`sigprocmask\*(C'\fR) and the signal disposition
2575(\f(CW\*(C`sigaction\*(C'\fR) are unspecified after starting a signal watcher (and after
2576stopping it again), that is, libev might or might not block the signal,
2577and might or might not set or restore the installed signal handler (but
2578see \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR).
2579.PP
2580While this does not matter for the signal disposition (libev never
2581sets signals to \f(CW\*(C`SIG_IGN\*(C'\fR, so handlers will be reset to \f(CW\*(C`SIG_DFL\*(C'\fR on
2582\&\f(CW\*(C`execve\*(C'\fR), this matters for the signal mask: many programs do not expect
2583certain signals to be blocked.
2584.PP
2585This means that before calling \f(CW\*(C`exec\*(C'\fR (from the child) you should reset
2586the signal mask to whatever \*(L"default\*(R" you expect (all clear is a good
2587choice usually).
2588.PP
2589The simplest way to ensure that the signal mask is reset in the child is
2590to install a fork handler with \f(CW\*(C`pthread_atfork\*(C'\fR that resets it. That will
2591catch fork calls done by libraries (such as the libc) as well.
2592.PP
2593In current versions of libev, the signal will not be blocked indefinitely
2594unless you use the \f(CW\*(C`signalfd\*(C'\fR \s-1API \s0(\f(CW\*(C`EV_SIGNALFD\*(C'\fR). While this reduces
2595the window of opportunity for problems, it will not go away, as libev
2596\&\fIhas\fR to modify the signal mask, at least temporarily.
2597.PP
2598So I can't stress this enough: \fIIf you do not reset your signal mask when
2599you expect it to be empty, you have a race condition in your code\fR. This
2600is not a libev-specific thing, this is true for most event libraries.
2601.PP
2602\fIThe special problem of threads signal handling\fR
2603.IX Subsection "The special problem of threads signal handling"
2604.PP
2605\&\s-1POSIX\s0 threads has problematic signal handling semantics, specifically,
2606a lot of functionality (sigfd, sigwait etc.) only really works if all
2607threads in a process block signals, which is hard to achieve.
2608.PP
2609When you want to use sigwait (or mix libev signal handling with your own
2610for the same signals), you can tackle this problem by globally blocking
2611all signals before creating any threads (or creating them with a fully set
2612sigprocmask) and also specifying the \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when creating
2613loops. Then designate one thread as \*(L"signal receiver thread\*(R" which handles
2614these signals. You can pass on any signals that libev might be interested
2615in by calling \f(CW\*(C`ev_feed_signal\*(C'\fR.
2616.PP
2617\fIWatcher-Specific Functions and Data Members\fR
2618.IX Subsection "Watcher-Specific Functions and Data Members"
1151.IP "ev_signal_init (ev_signal *, callback, int signum)" 4 2619.IP "ev_signal_init (ev_signal *, callback, int signum)" 4
1152.IX Item "ev_signal_init (ev_signal *, callback, int signum)" 2620.IX Item "ev_signal_init (ev_signal *, callback, int signum)"
1153.PD 0 2621.PD 0
1154.IP "ev_signal_set (ev_signal *, int signum)" 4 2622.IP "ev_signal_set (ev_signal *, int signum)" 4
1155.IX Item "ev_signal_set (ev_signal *, int signum)" 2623.IX Item "ev_signal_set (ev_signal *, int signum)"
1156.PD 2624.PD
1157Configures the watcher to trigger on the given signal number (usually one 2625Configures the watcher to trigger on the given signal number (usually one
1158of the \f(CW\*(C`SIGxxx\*(C'\fR constants). 2626of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
2627.IP "int signum [read\-only]" 4
2628.IX Item "int signum [read-only]"
2629The signal the watcher watches out for.
2630.PP
2631\fIExamples\fR
2632.IX Subsection "Examples"
2633.PP
2634Example: Try to exit cleanly on \s-1SIGINT.\s0
2635.PP
2636.Vb 5
2637\& static void
2638\& sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
2639\& {
2640\& ev_break (loop, EVBREAK_ALL);
2641\& }
2642\&
2643\& ev_signal signal_watcher;
2644\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
2645\& ev_signal_start (loop, &signal_watcher);
2646.Ve
1159.ie n .Sh """ev_child"" \- wait for pid status changes" 2647.ie n .SS """ev_child"" \- watch out for process status changes"
1160.el .Sh "\f(CWev_child\fP \- wait for pid status changes" 2648.el .SS "\f(CWev_child\fP \- watch out for process status changes"
1161.IX Subsection "ev_child - wait for pid status changes" 2649.IX Subsection "ev_child - watch out for process status changes"
1162Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to 2650Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
1163some child status changes (most typically when a child of yours dies). 2651some child status changes (most typically when a child of yours dies or
2652exits). It is permissible to install a child watcher \fIafter\fR the child
2653has been forked (which implies it might have already exited), as long
2654as the event loop isn't entered (or is continued from a watcher), i.e.,
2655forking and then immediately registering a watcher for the child is fine,
2656but forking and registering a watcher a few event loop iterations later or
2657in the next callback invocation is not.
2658.PP
2659Only the default event loop is capable of handling signals, and therefore
2660you can only register child watchers in the default event loop.
2661.PP
2662Due to some design glitches inside libev, child watchers will always be
2663handled at maximum priority (their priority is set to \f(CW\*(C`EV_MAXPRI\*(C'\fR by
2664libev)
2665.PP
2666\fIProcess Interaction\fR
2667.IX Subsection "Process Interaction"
2668.PP
2669Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is
2670initialised. This is necessary to guarantee proper behaviour even if the
2671first child watcher is started after the child exits. The occurrence
2672of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done
2673synchronously as part of the event loop processing. Libev always reaps all
2674children, even ones not watched.
2675.PP
2676\fIOverriding the Built-In Processing\fR
2677.IX Subsection "Overriding the Built-In Processing"
2678.PP
2679Libev offers no special support for overriding the built-in child
2680processing, but if your application collides with libev's default child
2681handler, you can override it easily by installing your own handler for
2682\&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the
2683default loop never gets destroyed. You are encouraged, however, to use an
2684event-based approach to child reaping and thus use libev's support for
2685that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely.
2686.PP
2687\fIStopping the Child Watcher\fR
2688.IX Subsection "Stopping the Child Watcher"
2689.PP
2690Currently, the child watcher never gets stopped, even when the
2691child terminates, so normally one needs to stop the watcher in the
2692callback. Future versions of libev might stop the watcher automatically
2693when a child exit is detected (calling \f(CW\*(C`ev_child_stop\*(C'\fR twice is not a
2694problem).
2695.PP
2696\fIWatcher-Specific Functions and Data Members\fR
2697.IX Subsection "Watcher-Specific Functions and Data Members"
1164.IP "ev_child_init (ev_child *, callback, int pid)" 4 2698.IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4
1165.IX Item "ev_child_init (ev_child *, callback, int pid)" 2699.IX Item "ev_child_init (ev_child *, callback, int pid, int trace)"
1166.PD 0 2700.PD 0
1167.IP "ev_child_set (ev_child *, int pid)" 4 2701.IP "ev_child_set (ev_child *, int pid, int trace)" 4
1168.IX Item "ev_child_set (ev_child *, int pid)" 2702.IX Item "ev_child_set (ev_child *, int pid, int trace)"
1169.PD 2703.PD
1170Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or 2704Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
1171\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look 2705\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
1172at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see 2706at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
1173the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems 2707the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
1174\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the 2708\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
1175process causing the status change. 2709process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only
2710activate the watcher when the process terminates) or \f(CW1\fR (additionally
2711activate the watcher when the process is stopped or continued).
2712.IP "int pid [read\-only]" 4
2713.IX Item "int pid [read-only]"
2714The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
2715.IP "int rpid [read\-write]" 4
2716.IX Item "int rpid [read-write]"
2717The process id that detected a status change.
2718.IP "int rstatus [read\-write]" 4
2719.IX Item "int rstatus [read-write]"
2720The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
2721\&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
1176.PP 2722.PP
1177Example: try to exit cleanly on \s-1SIGINT\s0 and \s-1SIGTERM\s0. 2723\fIExamples\fR
2724.IX Subsection "Examples"
1178.PP 2725.PP
2726Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for
2727its completion.
2728.PP
1179.Vb 5 2729.Vb 1
2730\& ev_child cw;
2731\&
1180\& static void 2732\& static void
1181\& sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents) 2733\& child_cb (EV_P_ ev_child *w, int revents)
1182\& { 2734\& {
1183\& ev_unloop (loop, EVUNLOOP_ALL); 2735\& ev_child_stop (EV_A_ w);
2736\& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus);
1184\& } 2737\& }
2738\&
2739\& pid_t pid = fork ();
2740\&
2741\& if (pid < 0)
2742\& // error
2743\& else if (pid == 0)
2744\& {
2745\& // the forked child executes here
2746\& exit (1);
2747\& }
2748\& else
2749\& {
2750\& ev_child_init (&cw, child_cb, pid, 0);
2751\& ev_child_start (EV_DEFAULT_ &cw);
2752\& }
1185.Ve 2753.Ve
2754.ie n .SS """ev_stat"" \- did the file attributes just change?"
2755.el .SS "\f(CWev_stat\fP \- did the file attributes just change?"
2756.IX Subsection "ev_stat - did the file attributes just change?"
2757This watches a file system path for attribute changes. That is, it calls
2758\&\f(CW\*(C`stat\*(C'\fR on that path in regular intervals (or when the \s-1OS\s0 says it changed)
2759and sees if it changed compared to the last time, invoking the callback
2760if it did. Starting the watcher \f(CW\*(C`stat\*(C'\fR's the file, so only changes that
2761happen after the watcher has been started will be reported.
1186.PP 2762.PP
2763The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does
2764not exist\*(R" is a status change like any other. The condition \*(L"path does not
2765exist\*(R" (or more correctly \*(L"path cannot be stat'ed\*(R") is signified by the
2766\&\f(CW\*(C`st_nlink\*(C'\fR field being zero (which is otherwise always forced to be at
2767least one) and all the other fields of the stat buffer having unspecified
2768contents.
2769.PP
2770The path \fImust not\fR end in a slash or contain special components such as
2771\&\f(CW\*(C`.\*(C'\fR or \f(CW\*(C`..\*(C'\fR. The path \fIshould\fR be absolute: If it is relative and
2772your working directory changes, then the behaviour is undefined.
2773.PP
2774Since there is no portable change notification interface available, the
2775portable implementation simply calls \f(CWstat(2)\fR regularly on the path
2776to see if it changed somehow. You can specify a recommended polling
2777interval for this case. If you specify a polling interval of \f(CW0\fR (highly
2778recommended!) then a \fIsuitable, unspecified default\fR value will be used
2779(which you can expect to be around five seconds, although this might
2780change dynamically). Libev will also impose a minimum interval which is
2781currently around \f(CW0.1\fR, but that's usually overkill.
2782.PP
2783This watcher type is not meant for massive numbers of stat watchers,
2784as even with OS-supported change notifications, this can be
2785resource-intensive.
2786.PP
2787At the time of this writing, the only OS-specific interface implemented
2788is the Linux inotify interface (implementing kqueue support is left as an
2789exercise for the reader. Note, however, that the author sees no way of
2790implementing \f(CW\*(C`ev_stat\*(C'\fR semantics with kqueue, except as a hint).
2791.PP
2792\fI\s-1ABI\s0 Issues (Largefile Support)\fR
2793.IX Subsection "ABI Issues (Largefile Support)"
2794.PP
2795Libev by default (unless the user overrides this) uses the default
2796compilation environment, which means that on systems with large file
2797support disabled by default, you get the 32 bit version of the stat
2798structure. When using the library from programs that change the \s-1ABI\s0 to
2799use 64 bit file offsets the programs will fail. In that case you have to
2800compile libev with the same flags to get binary compatibility. This is
2801obviously the case with any flags that change the \s-1ABI,\s0 but the problem is
2802most noticeably displayed with ev_stat and large file support.
2803.PP
2804The solution for this is to lobby your distribution maker to make large
2805file interfaces available by default (as e.g. FreeBSD does) and not
2806optional. Libev cannot simply switch on large file support because it has
2807to exchange stat structures with application programs compiled using the
2808default compilation environment.
2809.PP
2810\fIInotify and Kqueue\fR
2811.IX Subsection "Inotify and Kqueue"
2812.PP
2813When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev and present at
2814runtime, it will be used to speed up change detection where possible. The
2815inotify descriptor will be created lazily when the first \f(CW\*(C`ev_stat\*(C'\fR
2816watcher is being started.
2817.PP
2818Inotify presence does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
2819except that changes might be detected earlier, and in some cases, to avoid
2820making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presence of inotify support
2821there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling,
2822but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
2823many bugs), the path exists (i.e. stat succeeds), and the path resides on
2824a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
2825xfs are fully working) libev usually gets away without polling.
2826.PP
2827There is no support for kqueue, as apparently it cannot be used to
2828implement this functionality, due to the requirement of having a file
2829descriptor open on the object at all times, and detecting renames, unlinks
2830etc. is difficult.
2831.PP
2832\fI\f(CI\*(C`stat ()\*(C'\fI is a synchronous operation\fR
2833.IX Subsection "stat () is a synchronous operation"
2834.PP
2835Libev doesn't normally do any kind of I/O itself, and so is not blocking
2836the process. The exception are \f(CW\*(C`ev_stat\*(C'\fR watchers \- those call \f(CW\*(C`stat
2837()\*(C'\fR, which is a synchronous operation.
2838.PP
2839For local paths, this usually doesn't matter: unless the system is very
2840busy or the intervals between stat's are large, a stat call will be fast,
2841as the path data is usually in memory already (except when starting the
2842watcher).
2843.PP
2844For networked file systems, calling \f(CW\*(C`stat ()\*(C'\fR can block an indefinite
2845time due to network issues, and even under good conditions, a stat call
2846often takes multiple milliseconds.
2847.PP
2848Therefore, it is best to avoid using \f(CW\*(C`ev_stat\*(C'\fR watchers on networked
2849paths, although this is fully supported by libev.
2850.PP
2851\fIThe special problem of stat time resolution\fR
2852.IX Subsection "The special problem of stat time resolution"
2853.PP
2854The \f(CW\*(C`stat ()\*(C'\fR system call only supports full-second resolution portably,
2855and even on systems where the resolution is higher, most file systems
2856still only support whole seconds.
2857.PP
2858That means that, if the time is the only thing that changes, you can
2859easily miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and
2860calls your callback, which does something. When there is another update
2861within the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect unless the
2862stat data does change in other ways (e.g. file size).
2863.PP
2864The solution to this is to delay acting on a change for slightly more
2865than a second (or till slightly after the next full second boundary), using
2866a roughly one-second-delay \f(CW\*(C`ev_timer\*(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02);
2867ev_timer_again (loop, w)\*(C'\fR).
2868.PP
2869The \f(CW.02\fR offset is added to work around small timing inconsistencies
2870of some operating systems (where the second counter of the current time
2871might be be delayed. One such system is the Linux kernel, where a call to
2872\&\f(CW\*(C`gettimeofday\*(C'\fR might return a timestamp with a full second later than
2873a subsequent \f(CW\*(C`time\*(C'\fR call \- if the equivalent of \f(CW\*(C`time ()\*(C'\fR is used to
2874update file times then there will be a small window where the kernel uses
2875the previous second to update file times but libev might already execute
2876the timer callback).
2877.PP
2878\fIWatcher-Specific Functions and Data Members\fR
2879.IX Subsection "Watcher-Specific Functions and Data Members"
2880.IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
2881.IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
2882.PD 0
2883.IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4
2884.IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)"
2885.PD
2886Configures the watcher to wait for status changes of the given
2887\&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to
2888be detected and should normally be specified as \f(CW0\fR to let libev choose
2889a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same
2890path for as long as the watcher is active.
2891.Sp
2892The callback will receive an \f(CW\*(C`EV_STAT\*(C'\fR event when a change was detected,
2893relative to the attributes at the time the watcher was started (or the
2894last change was detected).
2895.IP "ev_stat_stat (loop, ev_stat *)" 4
2896.IX Item "ev_stat_stat (loop, ev_stat *)"
2897Updates the stat buffer immediately with new values. If you change the
2898watched path in your callback, you could call this function to avoid
2899detecting this change (while introducing a race condition if you are not
2900the only one changing the path). Can also be useful simply to find out the
2901new values.
2902.IP "ev_statdata attr [read\-only]" 4
2903.IX Item "ev_statdata attr [read-only]"
2904The most-recently detected attributes of the file. Although the type is
2905\&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
2906suitable for your system, but you can only rely on the POSIX-standardised
2907members to be present. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there was
2908some error while \f(CW\*(C`stat\*(C'\fRing the file.
2909.IP "ev_statdata prev [read\-only]" 4
2910.IX Item "ev_statdata prev [read-only]"
2911The previous attributes of the file. The callback gets invoked whenever
2912\&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR, or, more precisely, one or more of these members
2913differ: \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,
2914\&\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.
2915.IP "ev_tstamp interval [read\-only]" 4
2916.IX Item "ev_tstamp interval [read-only]"
2917The specified interval.
2918.IP "const char *path [read\-only]" 4
2919.IX Item "const char *path [read-only]"
2920The file system path that is being watched.
2921.PP
2922\fIExamples\fR
2923.IX Subsection "Examples"
2924.PP
2925Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
2926.PP
2927.Vb 10
2928\& static void
2929\& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
2930\& {
2931\& /* /etc/passwd changed in some way */
2932\& if (w\->attr.st_nlink)
2933\& {
2934\& printf ("passwd current size %ld\en", (long)w\->attr.st_size);
2935\& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime);
2936\& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime);
2937\& }
2938\& else
2939\& /* you shalt not abuse printf for puts */
2940\& puts ("wow, /etc/passwd is not there, expect problems. "
2941\& "if this is windows, they already arrived\en");
2942\& }
2943\&
2944\& ...
2945\& ev_stat passwd;
2946\&
2947\& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
2948\& ev_stat_start (loop, &passwd);
2949.Ve
2950.PP
2951Example: Like above, but additionally use a one-second delay so we do not
2952miss updates (however, frequent updates will delay processing, too, so
2953one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
2954\&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
2955.PP
1187.Vb 3 2956.Vb 2
1188\& struct ev_signal signal_watcher; 2957\& static ev_stat passwd;
1189\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT); 2958\& static ev_timer timer;
1190\& ev_signal_start (loop, &sigint_cb); 2959\&
2960\& static void
2961\& timer_cb (EV_P_ ev_timer *w, int revents)
2962\& {
2963\& ev_timer_stop (EV_A_ w);
2964\&
2965\& /* now it\*(Aqs one second after the most recent passwd change */
2966\& }
2967\&
2968\& static void
2969\& stat_cb (EV_P_ ev_stat *w, int revents)
2970\& {
2971\& /* reset the one\-second timer */
2972\& ev_timer_again (EV_A_ &timer);
2973\& }
2974\&
2975\& ...
2976\& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
2977\& ev_stat_start (loop, &passwd);
2978\& ev_timer_init (&timer, timer_cb, 0., 1.02);
1191.Ve 2979.Ve
1192.ie n .Sh """ev_idle"" \- when you've got nothing better to do" 2980.ie n .SS """ev_idle"" \- when you've got nothing better to do..."
1193.el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do" 2981.el .SS "\f(CWev_idle\fP \- when you've got nothing better to do..."
1194.IX Subsection "ev_idle - when you've got nothing better to do" 2982.IX Subsection "ev_idle - when you've got nothing better to do..."
1195Idle watchers trigger events when there are no other events are pending 2983Idle watchers trigger events when no other events of the same or higher
1196(prepare, check and other idle watchers do not count). That is, as long 2984priority are pending (prepare, check and other idle watchers do not count
1197as your process is busy handling sockets or timeouts (or even signals, 2985as receiving \*(L"events\*(R").
1198imagine) it will not be triggered. But when your process is idle all idle 2986.PP
1199watchers are being called again and again, once per event loop iteration \- 2987That is, as long as your process is busy handling sockets or timeouts
2988(or even signals, imagine) of the same or higher priority it will not be
2989triggered. But when your process is idle (or only lower-priority watchers
2990are pending), the idle watchers are being called once per event loop
1200until stopped, that is, or your process receives more events and becomes 2991iteration \- until stopped, that is, or your process receives more events
1201busy. 2992and becomes busy again with higher priority stuff.
1202.PP 2993.PP
1203The most noteworthy effect is that as long as any idle watchers are 2994The most noteworthy effect is that as long as any idle watchers are
1204active, the process will not block when waiting for new events. 2995active, the process will not block when waiting for new events.
1205.PP 2996.PP
1206Apart from keeping your process non-blocking (which is a useful 2997Apart from keeping your process non-blocking (which is a useful
1207effect on its own sometimes), idle watchers are a good place to do 2998effect on its own sometimes), idle watchers are a good place to do
1208\&\*(L"pseudo\-background processing\*(R", or delay processing stuff to after the 2999\&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the
1209event loop has handled all outstanding events. 3000event loop has handled all outstanding events.
3001.PP
3002\fIAbusing an \f(CI\*(C`ev_idle\*(C'\fI watcher for its side-effect\fR
3003.IX Subsection "Abusing an ev_idle watcher for its side-effect"
3004.PP
3005As long as there is at least one active idle watcher, libev will never
3006sleep unnecessarily. Or in other words, it will loop as fast as possible.
3007For this to work, the idle watcher doesn't need to be invoked at all \- the
3008lowest priority will do.
3009.PP
3010This mode of operation can be useful together with an \f(CW\*(C`ev_check\*(C'\fR watcher,
3011to do something on each event loop iteration \- for example to balance load
3012between different connections.
3013.PP
3014See \*(L"Abusing an ev_check watcher for its side-effect\*(R" for a longer
3015example.
3016.PP
3017\fIWatcher-Specific Functions and Data Members\fR
3018.IX Subsection "Watcher-Specific Functions and Data Members"
1210.IP "ev_idle_init (ev_signal *, callback)" 4 3019.IP "ev_idle_init (ev_idle *, callback)" 4
1211.IX Item "ev_idle_init (ev_signal *, callback)" 3020.IX Item "ev_idle_init (ev_idle *, callback)"
1212Initialises and configures the idle watcher \- it has no parameters of any 3021Initialises and configures the idle watcher \- it has no parameters of any
1213kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless, 3022kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
1214believe me. 3023believe me.
1215.PP 3024.PP
3025\fIExamples\fR
3026.IX Subsection "Examples"
3027.PP
1216Example: dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR, start it, and in the 3028Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the
1217callback, free it. Alos, use no error checking, as usual. 3029callback, free it. Also, use no error checking, as usual.
1218.PP 3030.PP
1219.Vb 7 3031.Vb 5
1220\& static void 3032\& static void
1221\& idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents) 3033\& idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1222\& { 3034\& {
3035\& // stop the watcher
3036\& ev_idle_stop (loop, w);
3037\&
3038\& // now we can free it
1223\& free (w); 3039\& free (w);
3040\&
1224\& // now do something you wanted to do when the program has 3041\& // now do something you wanted to do when the program has
1225\& // no longer asnything immediate to do. 3042\& // no longer anything immediate to do.
1226\& } 3043\& }
1227.Ve 3044\&
1228.PP
1229.Vb 3
1230\& struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle)); 3045\& ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1231\& ev_idle_init (idle_watcher, idle_cb); 3046\& ev_idle_init (idle_watcher, idle_cb);
1232\& ev_idle_start (loop, idle_cb); 3047\& ev_idle_start (loop, idle_watcher);
1233.Ve 3048.Ve
1234.ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop" 3049.ie n .SS """ev_prepare"" and ""ev_check"" \- customise your event loop!"
1235.el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop" 3050.el .SS "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
1236.IX Subsection "ev_prepare and ev_check - customise your event loop" 3051.IX Subsection "ev_prepare and ev_check - customise your event loop!"
1237Prepare and check watchers are usually (but not always) used in tandem: 3052Prepare and check watchers are often (but not always) used in pairs:
1238prepare watchers get invoked before the process blocks and check watchers 3053prepare watchers get invoked before the process blocks and check watchers
1239afterwards. 3054afterwards.
1240.PP 3055.PP
3056You \fImust not\fR call \f(CW\*(C`ev_run\*(C'\fR (or similar functions that enter the
3057current event loop) or \f(CW\*(C`ev_loop_fork\*(C'\fR from either \f(CW\*(C`ev_prepare\*(C'\fR or
3058\&\f(CW\*(C`ev_check\*(C'\fR watchers. Other loops than the current one are fine,
3059however. The rationale behind this is that you do not need to check
3060for recursion in those watchers, i.e. the sequence will always be
3061\&\f(CW\*(C`ev_prepare\*(C'\fR, blocking, \f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each
3062kind they will always be called in pairs bracketing the blocking call.
3063.PP
1241Their main purpose is to integrate other event mechanisms into libev and 3064Their main purpose is to integrate other event mechanisms into libev and
1242their use is somewhat advanced. This could be used, for example, to track 3065their use is somewhat advanced. They could be used, for example, to track
1243variable changes, implement your own watchers, integrate net-snmp or a 3066variable changes, implement your own watchers, integrate net-snmp or a
1244coroutine library and lots more. 3067coroutine library and lots more. They are also occasionally useful if
3068you cache some data and want to flush it before blocking (for example,
3069in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
3070watcher).
1245.PP 3071.PP
1246This is done by examining in each prepare call which file descriptors need 3072This is done by examining in each prepare call which file descriptors
1247to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers for 3073need to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers
1248them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many libraries 3074for them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many
1249provide just this functionality). Then, in the check watcher you check for 3075libraries provide exactly this functionality). Then, in the check watcher,
1250any events that occured (by checking the pending status of all watchers 3076you check for any events that occurred (by checking the pending status
1251and stopping them) and call back into the library. The I/O and timer 3077of all watchers and stopping them) and call back into the library. The
1252callbacks will never actually be called (but must be valid nevertheless, 3078I/O and timer callbacks will never actually be called (but must be valid
1253because you never know, you know?). 3079nevertheless, because you never know, you know?).
1254.PP 3080.PP
1255As another example, the Perl Coro module uses these hooks to integrate 3081As another example, the Perl Coro module uses these hooks to integrate
1256coroutines into libev programs, by yielding to other active coroutines 3082coroutines into libev programs, by yielding to other active coroutines
1257during each prepare and only letting the process block if no coroutines 3083during each prepare and only letting the process block if no coroutines
1258are ready to run (it's actually more complicated: it only runs coroutines 3084are ready to run (it's actually more complicated: it only runs coroutines
1259with priority higher than or equal to the event loop and one coroutine 3085with priority higher than or equal to the event loop and one coroutine
1260of lower priority, but only once, using idle watchers to keep the event 3086of lower priority, but only once, using idle watchers to keep the event
1261loop from blocking if lower-priority coroutines are active, thus mapping 3087loop from blocking if lower-priority coroutines are active, thus mapping
1262low-priority coroutines to idle/background tasks). 3088low-priority coroutines to idle/background tasks).
3089.PP
3090When used for this purpose, it is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers
3091highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR) priority, to ensure that they are being run before
3092any other watchers after the poll (this doesn't matter for \f(CW\*(C`ev_prepare\*(C'\fR
3093watchers).
3094.PP
3095Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, too) should not
3096activate (\*(L"feed\*(R") events into libev. While libev fully supports this, they
3097might get executed before other \f(CW\*(C`ev_check\*(C'\fR watchers did their job. As
3098\&\f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other (non-libev) event
3099loops those other event loops might be in an unusable state until their
3100\&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with
3101others).
3102.PP
3103\fIAbusing an \f(CI\*(C`ev_check\*(C'\fI watcher for its side-effect\fR
3104.IX Subsection "Abusing an ev_check watcher for its side-effect"
3105.PP
3106\&\f(CW\*(C`ev_check\*(C'\fR (and less often also \f(CW\*(C`ev_prepare\*(C'\fR) watchers can also be
3107useful because they are called once per event loop iteration. For
3108example, if you want to handle a large number of connections fairly, you
3109normally only do a bit of work for each active connection, and if there
3110is more work to do, you wait for the next event loop iteration, so other
3111connections have a chance of making progress.
3112.PP
3113Using an \f(CW\*(C`ev_check\*(C'\fR watcher is almost enough: it will be called on the
3114next event loop iteration. However, that isn't as soon as possible \-
3115without external events, your \f(CW\*(C`ev_check\*(C'\fR watcher will not be invoked.
3116.PP
3117This is where \f(CW\*(C`ev_idle\*(C'\fR watchers come in handy \- all you need is a
3118single global idle watcher that is active as long as you have one active
3119\&\f(CW\*(C`ev_check\*(C'\fR watcher. The \f(CW\*(C`ev_idle\*(C'\fR watcher makes sure the event loop
3120will not sleep, and the \f(CW\*(C`ev_check\*(C'\fR watcher makes sure a callback gets
3121invoked. Neither watcher alone can do that.
3122.PP
3123\fIWatcher-Specific Functions and Data Members\fR
3124.IX Subsection "Watcher-Specific Functions and Data Members"
1263.IP "ev_prepare_init (ev_prepare *, callback)" 4 3125.IP "ev_prepare_init (ev_prepare *, callback)" 4
1264.IX Item "ev_prepare_init (ev_prepare *, callback)" 3126.IX Item "ev_prepare_init (ev_prepare *, callback)"
1265.PD 0 3127.PD 0
1266.IP "ev_check_init (ev_check *, callback)" 4 3128.IP "ev_check_init (ev_check *, callback)" 4
1267.IX Item "ev_check_init (ev_check *, callback)" 3129.IX Item "ev_check_init (ev_check *, callback)"
1268.PD 3130.PD
1269Initialises and configures the prepare or check watcher \- they have no 3131Initialises and configures the prepare or check watcher \- they have no
1270parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR 3132parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
1271macros, but using them is utterly, utterly and completely pointless. 3133macros, but using them is utterly, utterly, utterly and completely
3134pointless.
1272.PP 3135.PP
1273Example: *TODO*. 3136\fIExamples\fR
3137.IX Subsection "Examples"
3138.PP
3139There are a number of principal ways to embed other event loops or modules
3140into libev. Here are some ideas on how to include libadns into libev
3141(there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could
3142use as a working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR embeds a
3143Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 into the
3144Glib event loop).
3145.PP
3146Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
3147and in a check watcher, destroy them and call into libadns. What follows
3148is pseudo-code only of course. This requires you to either use a low
3149priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as
3150the callbacks for the IO/timeout watchers might not have been called yet.
3151.PP
3152.Vb 2
3153\& static ev_io iow [nfd];
3154\& static ev_timer tw;
3155\&
3156\& static void
3157\& io_cb (struct ev_loop *loop, ev_io *w, int revents)
3158\& {
3159\& }
3160\&
3161\& // create io watchers for each fd and a timer before blocking
3162\& static void
3163\& adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
3164\& {
3165\& int timeout = 3600000;
3166\& struct pollfd fds [nfd];
3167\& // actual code will need to loop here and realloc etc.
3168\& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
3169\&
3170\& /* the callback is illegal, but won\*(Aqt be called as we stop during check */
3171\& ev_timer_init (&tw, 0, timeout * 1e\-3, 0.);
3172\& ev_timer_start (loop, &tw);
3173\&
3174\& // create one ev_io per pollfd
3175\& for (int i = 0; i < nfd; ++i)
3176\& {
3177\& ev_io_init (iow + i, io_cb, fds [i].fd,
3178\& ((fds [i].events & POLLIN ? EV_READ : 0)
3179\& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
3180\&
3181\& fds [i].revents = 0;
3182\& ev_io_start (loop, iow + i);
3183\& }
3184\& }
3185\&
3186\& // stop all watchers after blocking
3187\& static void
3188\& adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
3189\& {
3190\& ev_timer_stop (loop, &tw);
3191\&
3192\& for (int i = 0; i < nfd; ++i)
3193\& {
3194\& // set the relevant poll flags
3195\& // could also call adns_processreadable etc. here
3196\& struct pollfd *fd = fds + i;
3197\& int revents = ev_clear_pending (iow + i);
3198\& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN;
3199\& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT;
3200\&
3201\& // now stop the watcher
3202\& ev_io_stop (loop, iow + i);
3203\& }
3204\&
3205\& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
3206\& }
3207.Ve
3208.PP
3209Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR
3210in the prepare watcher and would dispose of the check watcher.
3211.PP
3212Method 3: If the module to be embedded supports explicit event
3213notification (libadns does), you can also make use of the actual watcher
3214callbacks, and only destroy/create the watchers in the prepare watcher.
3215.PP
3216.Vb 5
3217\& static void
3218\& timer_cb (EV_P_ ev_timer *w, int revents)
3219\& {
3220\& adns_state ads = (adns_state)w\->data;
3221\& update_now (EV_A);
3222\&
3223\& adns_processtimeouts (ads, &tv_now);
3224\& }
3225\&
3226\& static void
3227\& io_cb (EV_P_ ev_io *w, int revents)
3228\& {
3229\& adns_state ads = (adns_state)w\->data;
3230\& update_now (EV_A);
3231\&
3232\& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now);
3233\& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now);
3234\& }
3235\&
3236\& // do not ever call adns_afterpoll
3237.Ve
3238.PP
3239Method 4: Do not use a prepare or check watcher because the module you
3240want to embed is not flexible enough to support it. Instead, you can
3241override their poll function. The drawback with this solution is that the
3242main loop is now no longer controllable by \s-1EV.\s0 The \f(CW\*(C`Glib::EV\*(C'\fR module uses
3243this approach, effectively embedding \s-1EV\s0 as a client into the horrible
3244libglib event loop.
3245.PP
3246.Vb 4
3247\& static gint
3248\& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
3249\& {
3250\& int got_events = 0;
3251\&
3252\& for (n = 0; n < nfds; ++n)
3253\& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
3254\&
3255\& if (timeout >= 0)
3256\& // create/start timer
3257\&
3258\& // poll
3259\& ev_run (EV_A_ 0);
3260\&
3261\& // stop timer again
3262\& if (timeout >= 0)
3263\& ev_timer_stop (EV_A_ &to);
3264\&
3265\& // stop io watchers again \- their callbacks should have set
3266\& for (n = 0; n < nfds; ++n)
3267\& ev_io_stop (EV_A_ iow [n]);
3268\&
3269\& return got_events;
3270\& }
3271.Ve
1274.ie n .Sh """ev_embed"" \- when one backend isn't enough" 3272.ie n .SS """ev_embed"" \- when one backend isn't enough..."
1275.el .Sh "\f(CWev_embed\fP \- when one backend isn't enough" 3273.el .SS "\f(CWev_embed\fP \- when one backend isn't enough..."
1276.IX Subsection "ev_embed - when one backend isn't enough" 3274.IX Subsection "ev_embed - when one backend isn't enough..."
1277This is a rather advanced watcher type that lets you embed one event loop 3275This is a rather advanced watcher type that lets you embed one event loop
1278into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded 3276into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
1279loop, other types of watchers might be handled in a delayed or incorrect 3277loop, other types of watchers might be handled in a delayed or incorrect
1280fashion and must not be used). 3278fashion and must not be used).
1281.PP 3279.PP
… …
1283prioritise I/O. 3281prioritise I/O.
1284.PP 3282.PP
1285As an example for a bug workaround, the kqueue backend might only support 3283As an example for a bug workaround, the kqueue backend might only support
1286sockets on some platform, so it is unusable as generic backend, but you 3284sockets on some platform, so it is unusable as generic backend, but you
1287still want to make use of it because you have many sockets and it scales 3285still want to make use of it because you have many sockets and it scales
1288so nicely. In this case, you would create a kqueue-based loop and embed it 3286so nicely. In this case, you would create a kqueue-based loop and embed
1289into your default loop (which might use e.g. poll). Overall operation will 3287it into your default loop (which might use e.g. poll). Overall operation
1290be a bit slower because first libev has to poll and then call kevent, but 3288will be a bit slower because first libev has to call \f(CW\*(C`poll\*(C'\fR and then
1291at least you can use both at what they are best. 3289\&\f(CW\*(C`kevent\*(C'\fR, but at least you can use both mechanisms for what they are
3290best: \f(CW\*(C`kqueue\*(C'\fR for scalable sockets and \f(CW\*(C`poll\*(C'\fR if you want it to work :)
1292.PP 3291.PP
1293As for prioritising I/O: rarely you have the case where some fds have 3292As for prioritising I/O: under rare circumstances you have the case where
1294to be watched and handled very quickly (with low latency), and even 3293some fds have to be watched and handled very quickly (with low latency),
1295priorities and idle watchers might have too much overhead. In this case 3294and even priorities and idle watchers might have too much overhead. In
1296you would put all the high priority stuff in one loop and all the rest in 3295this case you would put all the high priority stuff in one loop and all
1297a second one, and embed the second one in the first. 3296the rest in a second one, and embed the second one in the first.
1298.PP 3297.PP
1299As long as the watcher is active, the callback will be invoked every time 3298As long as the watcher is active, the callback will be invoked every
1300there might be events pending in the embedded loop. The callback must then 3299time there might be events pending in the embedded loop. The callback
1301call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single sweep and invoke 3300must then call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single
1302their callbacks (you could also start an idle watcher to give the embedded 3301sweep and invoke their callbacks (the callback doesn't need to invoke the
1303loop strictly lower priority for example). You can also set the callback 3302\&\f(CW\*(C`ev_embed_sweep\*(C'\fR function directly, it could also start an idle watcher
1304to \f(CW0\fR, in which case the embed watcher will automatically execute the 3303to give the embedded loop strictly lower priority for example).
1305embedded loop sweep.
1306.PP 3304.PP
1307As long as the watcher is started it will automatically handle events. The 3305You can also set the callback to \f(CW0\fR, in which case the embed watcher
1308callback will be invoked whenever some events have been handled. You can 3306will automatically execute the embedded loop sweep whenever necessary.
1309set the callback to \f(CW0\fR to avoid having to specify one if you are not
1310interested in that.
1311.PP 3307.PP
1312Also, there have not currently been made special provisions for forking: 3308Fork detection will be handled transparently while the \f(CW\*(C`ev_embed\*(C'\fR watcher
1313when you fork, you not only have to call \f(CW\*(C`ev_loop_fork\*(C'\fR on both loops, 3309is active, i.e., the embedded loop will automatically be forked when the
1314but you will also have to stop and restart any \f(CW\*(C`ev_embed\*(C'\fR watchers 3310embedding loop forks. In other cases, the user is responsible for calling
1315yourself. 3311\&\f(CW\*(C`ev_loop_fork\*(C'\fR on the embedded loop.
1316.PP 3312.PP
1317Unfortunately, not all backends are embeddable, only the ones returned by 3313Unfortunately, not all backends are embeddable: only the ones returned by
1318\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any 3314\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
1319portable one. 3315portable one.
1320.PP 3316.PP
1321So when you want to use this feature you will always have to be prepared 3317So when you want to use this feature you will always have to be prepared
1322that you cannot get an embeddable loop. The recommended way to get around 3318that you cannot get an embeddable loop. The recommended way to get around
1323this is to have a separate variables for your embeddable loop, try to 3319this is to have a separate variables for your embeddable loop, try to
1324create it, and if that fails, use the normal loop for everything: 3320create it, and if that fails, use the normal loop for everything.
1325.PP 3321.PP
1326.Vb 3 3322\fI\f(CI\*(C`ev_embed\*(C'\fI and fork\fR
1327\& struct ev_loop *loop_hi = ev_default_init (0); 3323.IX Subsection "ev_embed and fork"
1328\& struct ev_loop *loop_lo = 0;
1329\& struct ev_embed embed;
1330.Ve
1331.PP 3324.PP
1332.Vb 5 3325While the \f(CW\*(C`ev_embed\*(C'\fR watcher is running, forks in the embedding loop will
1333\& // see if there is a chance of getting one that works 3326automatically be applied to the embedded loop as well, so no special
1334\& // (remember that a flags value of 0 means autodetection) 3327fork handling is required in that case. When the watcher is not running,
1335\& loop_lo = ev_embeddable_backends () & ev_recommended_backends () 3328however, it is still the task of the libev user to call \f(CW\*(C`ev_loop_fork ()\*(C'\fR
1336\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ()) 3329as applicable.
1337\& : 0;
1338.Ve
1339.PP 3330.PP
1340.Vb 8 3331\fIWatcher-Specific Functions and Data Members\fR
1341\& // if we got one, then embed it, otherwise default to loop_hi 3332.IX Subsection "Watcher-Specific Functions and Data Members"
1342\& if (loop_lo)
1343\& {
1344\& ev_embed_init (&embed, 0, loop_lo);
1345\& ev_embed_start (loop_hi, &embed);
1346\& }
1347\& else
1348\& loop_lo = loop_hi;
1349.Ve
1350.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4 3333.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
1351.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 3334.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
1352.PD 0 3335.PD 0
1353.IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4 3336.IP "ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)" 4
1354.IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 3337.IX Item "ev_embed_set (ev_embed *, struct ev_loop *embedded_loop)"
1355.PD 3338.PD
1356Configures the watcher to embed the given loop, which must be 3339Configures the watcher to embed the given loop, which must be
1357embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be 3340embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
1358invoked automatically, otherwise it is the responsibility of the callback 3341invoked automatically, otherwise it is the responsibility of the callback
1359to invoke it (it will continue to be called until the sweep has been done, 3342to invoke it (it will continue to be called until the sweep has been done,
1360if you do not want thta, you need to temporarily stop the embed watcher). 3343if you do not want that, you need to temporarily stop the embed watcher).
1361.IP "ev_embed_sweep (loop, ev_embed *)" 4 3344.IP "ev_embed_sweep (loop, ev_embed *)" 4
1362.IX Item "ev_embed_sweep (loop, ev_embed *)" 3345.IX Item "ev_embed_sweep (loop, ev_embed *)"
1363Make a single, non-blocking sweep over the embedded loop. This works 3346Make a single, non-blocking sweep over the embedded loop. This works
1364similarly to \f(CW\*(C`ev_loop (embedded_loop, EVLOOP_NONBLOCK)\*(C'\fR, but in the most 3347similarly to \f(CW\*(C`ev_run (embedded_loop, EVRUN_NOWAIT)\*(C'\fR, but in the most
1365apropriate way for embedded loops. 3348appropriate way for embedded loops.
3349.IP "struct ev_loop *other [read\-only]" 4
3350.IX Item "struct ev_loop *other [read-only]"
3351The embedded event loop.
3352.PP
3353\fIExamples\fR
3354.IX Subsection "Examples"
3355.PP
3356Example: Try to get an embeddable event loop and embed it into the default
3357event loop. If that is not possible, use the default loop. The default
3358loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the embeddable loop is stored in
3359\&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the case no embeddable loop can be
3360used).
3361.PP
3362.Vb 3
3363\& struct ev_loop *loop_hi = ev_default_init (0);
3364\& struct ev_loop *loop_lo = 0;
3365\& ev_embed embed;
3366\&
3367\& // see if there is a chance of getting one that works
3368\& // (remember that a flags value of 0 means autodetection)
3369\& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3370\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3371\& : 0;
3372\&
3373\& // if we got one, then embed it, otherwise default to loop_hi
3374\& if (loop_lo)
3375\& {
3376\& ev_embed_init (&embed, 0, loop_lo);
3377\& ev_embed_start (loop_hi, &embed);
3378\& }
3379\& else
3380\& loop_lo = loop_hi;
3381.Ve
3382.PP
3383Example: Check if kqueue is available but not recommended and create
3384a kqueue backend for use with sockets (which usually work with any
3385kqueue implementation). Store the kqueue/socket\-only event loop in
3386\&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too).
3387.PP
3388.Vb 3
3389\& struct ev_loop *loop = ev_default_init (0);
3390\& struct ev_loop *loop_socket = 0;
3391\& ev_embed embed;
3392\&
3393\& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3394\& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3395\& {
3396\& ev_embed_init (&embed, 0, loop_socket);
3397\& ev_embed_start (loop, &embed);
3398\& }
3399\&
3400\& if (!loop_socket)
3401\& loop_socket = loop;
3402\&
3403\& // now use loop_socket for all sockets, and loop for everything else
3404.Ve
3405.ie n .SS """ev_fork"" \- the audacity to resume the event loop after a fork"
3406.el .SS "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
3407.IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
3408Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
3409whoever is a good citizen cared to tell libev about it by calling
3410\&\f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the event loop blocks next
3411and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called, and only in the child
3412after the fork. If whoever good citizen calling \f(CW\*(C`ev_default_fork\*(C'\fR cheats
3413and calls it in the wrong process, the fork handlers will be invoked, too,
3414of course.
3415.PP
3416\fIThe special problem of life after fork \- how is it possible?\fR
3417.IX Subsection "The special problem of life after fork - how is it possible?"
3418.PP
3419Most uses of \f(CW\*(C`fork ()\*(C'\fR consist of forking, then some simple calls to set
3420up/change the process environment, followed by a call to \f(CW\*(C`exec()\*(C'\fR. This
3421sequence should be handled by libev without any problems.
3422.PP
3423This changes when the application actually wants to do event handling
3424in the child, or both parent in child, in effect \*(L"continuing\*(R" after the
3425fork.
3426.PP
3427The default mode of operation (for libev, with application help to detect
3428forks) is to duplicate all the state in the child, as would be expected
3429when \fIeither\fR the parent \fIor\fR the child process continues.
3430.PP
3431When both processes want to continue using libev, then this is usually the
3432wrong result. In that case, usually one process (typically the parent) is
3433supposed to continue with all watchers in place as before, while the other
3434process typically wants to start fresh, i.e. without any active watchers.
3435.PP
3436The cleanest and most efficient way to achieve that with libev is to
3437simply create a new event loop, which of course will be \*(L"empty\*(R", and
3438use that for new watchers. This has the advantage of not touching more
3439memory than necessary, and thus avoiding the copy-on-write, and the
3440disadvantage of having to use multiple event loops (which do not support
3441signal watchers).
3442.PP
3443When this is not possible, or you want to use the default loop for
3444other reasons, then in the process that wants to start \*(L"fresh\*(R", call
3445\&\f(CW\*(C`ev_loop_destroy (EV_DEFAULT)\*(C'\fR followed by \f(CW\*(C`ev_default_loop (...)\*(C'\fR.
3446Destroying the default loop will \*(L"orphan\*(R" (not stop) all registered
3447watchers, so you have to be careful not to execute code that modifies
3448those watchers. Note also that in that case, you have to re-register any
3449signal watchers.
3450.PP
3451\fIWatcher-Specific Functions and Data Members\fR
3452.IX Subsection "Watcher-Specific Functions and Data Members"
3453.IP "ev_fork_init (ev_fork *, callback)" 4
3454.IX Item "ev_fork_init (ev_fork *, callback)"
3455Initialises and configures the fork watcher \- it has no parameters of any
3456kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
3457really.
3458.ie n .SS """ev_cleanup"" \- even the best things end"
3459.el .SS "\f(CWev_cleanup\fP \- even the best things end"
3460.IX Subsection "ev_cleanup - even the best things end"
3461Cleanup watchers are called just before the event loop is being destroyed
3462by a call to \f(CW\*(C`ev_loop_destroy\*(C'\fR.
3463.PP
3464While there is no guarantee that the event loop gets destroyed, cleanup
3465watchers provide a convenient method to install cleanup hooks for your
3466program, worker threads and so on \- you just to make sure to destroy the
3467loop when you want them to be invoked.
3468.PP
3469Cleanup watchers are invoked in the same way as any other watcher. Unlike
3470all other watchers, they do not keep a reference to the event loop (which
3471makes a lot of sense if you think about it). Like all other watchers, you
3472can call libev functions in the callback, except \f(CW\*(C`ev_cleanup_start\*(C'\fR.
3473.PP
3474\fIWatcher-Specific Functions and Data Members\fR
3475.IX Subsection "Watcher-Specific Functions and Data Members"
3476.IP "ev_cleanup_init (ev_cleanup *, callback)" 4
3477.IX Item "ev_cleanup_init (ev_cleanup *, callback)"
3478Initialises and configures the cleanup watcher \- it has no parameters of
3479any kind. There is a \f(CW\*(C`ev_cleanup_set\*(C'\fR macro, but using it is utterly
3480pointless, I assure you.
3481.PP
3482Example: Register an atexit handler to destroy the default loop, so any
3483cleanup functions are called.
3484.PP
3485.Vb 5
3486\& static void
3487\& program_exits (void)
3488\& {
3489\& ev_loop_destroy (EV_DEFAULT_UC);
3490\& }
3491\&
3492\& ...
3493\& atexit (program_exits);
3494.Ve
3495.ie n .SS """ev_async"" \- how to wake up an event loop"
3496.el .SS "\f(CWev_async\fP \- how to wake up an event loop"
3497.IX Subsection "ev_async - how to wake up an event loop"
3498In general, you cannot use an \f(CW\*(C`ev_loop\*(C'\fR from multiple threads or other
3499asynchronous sources such as signal handlers (as opposed to multiple event
3500loops \- those are of course safe to use in different threads).
3501.PP
3502Sometimes, however, you need to wake up an event loop you do not control,
3503for example because it belongs to another thread. This is what \f(CW\*(C`ev_async\*(C'\fR
3504watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you can signal
3505it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal safe.
3506.PP
3507This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals,
3508too, are asynchronous in nature, and signals, too, will be compressed
3509(i.e. the number of callback invocations may be less than the number of
3510\&\f(CW\*(C`ev_async_send\*(C'\fR calls). In fact, you could use signal watchers as a kind
3511of \*(L"global async watchers\*(R" by using a watcher on an otherwise unused
3512signal, and \f(CW\*(C`ev_feed_signal\*(C'\fR to signal this watcher from another thread,
3513even without knowing which loop owns the signal.
3514.PP
3515\fIQueueing\fR
3516.IX Subsection "Queueing"
3517.PP
3518\&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason
3519is that the author does not know of a simple (or any) algorithm for a
3520multiple-writer-single-reader queue that works in all cases and doesn't
3521need elaborate support such as pthreads or unportable memory access
3522semantics.
3523.PP
3524That means that if you want to queue data, you have to provide your own
3525queue. But at least I can tell you how to implement locking around your
3526queue:
3527.IP "queueing from a signal handler context" 4
3528.IX Item "queueing from a signal handler context"
3529To implement race-free queueing, you simply add to the queue in the signal
3530handler but you block the signal handler in the watcher callback. Here is
3531an example that does that for some fictitious \s-1SIGUSR1\s0 handler:
3532.Sp
3533.Vb 1
3534\& static ev_async mysig;
3535\&
3536\& static void
3537\& sigusr1_handler (void)
3538\& {
3539\& sometype data;
3540\&
3541\& // no locking etc.
3542\& queue_put (data);
3543\& ev_async_send (EV_DEFAULT_ &mysig);
3544\& }
3545\&
3546\& static void
3547\& mysig_cb (EV_P_ ev_async *w, int revents)
3548\& {
3549\& sometype data;
3550\& sigset_t block, prev;
3551\&
3552\& sigemptyset (&block);
3553\& sigaddset (&block, SIGUSR1);
3554\& sigprocmask (SIG_BLOCK, &block, &prev);
3555\&
3556\& while (queue_get (&data))
3557\& process (data);
3558\&
3559\& if (sigismember (&prev, SIGUSR1)
3560\& sigprocmask (SIG_UNBLOCK, &block, 0);
3561\& }
3562.Ve
3563.Sp
3564(Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR
3565instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it
3566either...).
3567.IP "queueing from a thread context" 4
3568.IX Item "queueing from a thread context"
3569The strategy for threads is different, as you cannot (easily) block
3570threads but you can easily preempt them, so to queue safely you need to
3571employ a traditional mutex lock, such as in this pthread example:
3572.Sp
3573.Vb 2
3574\& static ev_async mysig;
3575\& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
3576\&
3577\& static void
3578\& otherthread (void)
3579\& {
3580\& // only need to lock the actual queueing operation
3581\& pthread_mutex_lock (&mymutex);
3582\& queue_put (data);
3583\& pthread_mutex_unlock (&mymutex);
3584\&
3585\& ev_async_send (EV_DEFAULT_ &mysig);
3586\& }
3587\&
3588\& static void
3589\& mysig_cb (EV_P_ ev_async *w, int revents)
3590\& {
3591\& pthread_mutex_lock (&mymutex);
3592\&
3593\& while (queue_get (&data))
3594\& process (data);
3595\&
3596\& pthread_mutex_unlock (&mymutex);
3597\& }
3598.Ve
3599.PP
3600\fIWatcher-Specific Functions and Data Members\fR
3601.IX Subsection "Watcher-Specific Functions and Data Members"
3602.IP "ev_async_init (ev_async *, callback)" 4
3603.IX Item "ev_async_init (ev_async *, callback)"
3604Initialises and configures the async watcher \- it has no parameters of any
3605kind. There is a \f(CW\*(C`ev_async_set\*(C'\fR macro, but using it is utterly pointless,
3606trust me.
3607.IP "ev_async_send (loop, ev_async *)" 4
3608.IX Item "ev_async_send (loop, ev_async *)"
3609Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds
3610an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop, and instantly
3611returns.
3612.Sp
3613Unlike \f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do from other threads,
3614signal or similar contexts (see the discussion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the
3615embedding section below on what exactly this means).
3616.Sp
3617Note that, as with other watchers in libev, multiple events might get
3618compressed into a single callback invocation (another way to look at
3619this is that \f(CW\*(C`ev_async\*(C'\fR watchers are level-triggered: they are set on
3620\&\f(CW\*(C`ev_async_send\*(C'\fR, reset when the event loop detects that).
3621.Sp
3622This call incurs the overhead of at most one extra system call per event
3623loop iteration, if the event loop is blocked, and no syscall at all if
3624the event loop (or your program) is processing events. That means that
3625repeated calls are basically free (there is no need to avoid calls for
3626performance reasons) and that the overhead becomes smaller (typically
3627zero) under load.
3628.IP "bool = ev_async_pending (ev_async *)" 4
3629.IX Item "bool = ev_async_pending (ev_async *)"
3630Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the
3631watcher but the event has not yet been processed (or even noted) by the
3632event loop.
3633.Sp
3634\&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When
3635the loop iterates next and checks for the watcher to have become active,
3636it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very
3637quickly check whether invoking the loop might be a good idea.
3638.Sp
3639Not that this does \fInot\fR check whether the watcher itself is pending,
3640only whether it has been requested to make this watcher pending: there
3641is a time window between the event loop checking and resetting the async
3642notification, and the callback being invoked.
1366.SH "OTHER FUNCTIONS" 3643.SH "OTHER FUNCTIONS"
1367.IX Header "OTHER FUNCTIONS" 3644.IX Header "OTHER FUNCTIONS"
1368There are some other functions of possible interest. Described. Here. Now. 3645There are some other functions of possible interest. Described. Here. Now.
1369.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4 3646.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
1370.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 3647.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"
1371This function combines a simple timer and an I/O watcher, calls your 3648This function combines a simple timer and an I/O watcher, calls your
1372callback on whichever event happens first and automatically stop both 3649callback on whichever event happens first and automatically stops both
1373watchers. This is useful if you want to wait for a single event on an fd 3650watchers. This is useful if you want to wait for a single event on an fd
1374or timeout without having to allocate/configure/start/stop/free one or 3651or timeout without having to allocate/configure/start/stop/free one or
1375more watchers yourself. 3652more watchers yourself.
1376.Sp 3653.Sp
1377If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and events 3654If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and the
1378is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for the given \f(CW\*(C`fd\*(C'\fR and 3655\&\f(CW\*(C`events\*(C'\fR argument is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for
1379\&\f(CW\*(C`events\*(C'\fR set will be craeted and started. 3656the given \f(CW\*(C`fd\*(C'\fR and \f(CW\*(C`events\*(C'\fR set will be created and started.
1380.Sp 3657.Sp
1381If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be 3658If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
1382started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and 3659started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
1383repeat = 0) will be started. While \f(CW0\fR is a valid timeout, it is of 3660repeat = 0) will be started. \f(CW0\fR is a valid timeout.
1384dubious value.
1385.Sp 3661.Sp
1386The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets 3662The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and is
1387passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of 3663passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
1388\&\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 3664\&\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
1389value passed to \f(CW\*(C`ev_once\*(C'\fR: 3665value passed to \f(CW\*(C`ev_once\*(C'\fR. Note that it is possible to receive \fIboth\fR
3666a timeout and an io event at the same time \- you probably should give io
3667events precedence.
3668.Sp
3669Example: wait up to ten seconds for data to appear on \s-1STDIN_FILENO.\s0
1390.Sp 3670.Sp
1391.Vb 7 3671.Vb 7
1392\& static void stdin_ready (int revents, void *arg) 3672\& static void stdin_ready (int revents, void *arg)
3673\& {
3674\& if (revents & EV_READ)
3675\& /* stdin might have data for us, joy! */;
3676\& else if (revents & EV_TIMER)
3677\& /* doh, nothing entered */;
3678\& }
3679\&
3680\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
3681.Ve
3682.IP "ev_feed_fd_event (loop, int fd, int revents)" 4
3683.IX Item "ev_feed_fd_event (loop, int fd, int revents)"
3684Feed an event on the given fd, as if a file descriptor backend detected
3685the given events.
3686.IP "ev_feed_signal_event (loop, int signum)" 4
3687.IX Item "ev_feed_signal_event (loop, int signum)"
3688Feed an event as if the given signal occurred. See also \f(CW\*(C`ev_feed_signal\*(C'\fR,
3689which is async-safe.
3690.SH "COMMON OR USEFUL IDIOMS (OR BOTH)"
3691.IX Header "COMMON OR USEFUL IDIOMS (OR BOTH)"
3692This section explains some common idioms that are not immediately
3693obvious. Note that examples are sprinkled over the whole manual, and this
3694section only contains stuff that wouldn't fit anywhere else.
3695.SS "\s-1ASSOCIATING CUSTOM DATA WITH A WATCHER\s0"
3696.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
3697Each watcher has, by default, a \f(CW\*(C`void *data\*(C'\fR member that you can read
3698or modify at any time: libev will completely ignore it. This can be used
3699to associate arbitrary data with your watcher. If you need more data and
3700don't want to allocate memory separately and store a pointer to it in that
3701data member, you can also \*(L"subclass\*(R" the watcher type and provide your own
3702data:
3703.PP
3704.Vb 7
3705\& struct my_io
3706\& {
3707\& ev_io io;
3708\& int otherfd;
3709\& void *somedata;
3710\& struct whatever *mostinteresting;
3711\& };
3712\&
3713\& ...
3714\& struct my_io w;
3715\& ev_io_init (&w.io, my_cb, fd, EV_READ);
3716.Ve
3717.PP
3718And since your callback will be called with a pointer to the watcher, you
3719can cast it back to your own type:
3720.PP
3721.Vb 5
3722\& static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
3723\& {
3724\& struct my_io *w = (struct my_io *)w_;
3725\& ...
3726\& }
3727.Ve
3728.PP
3729More interesting and less C\-conformant ways of casting your callback
3730function type instead have been omitted.
3731.SS "\s-1BUILDING YOUR OWN COMPOSITE WATCHERS\s0"
3732.IX Subsection "BUILDING YOUR OWN COMPOSITE WATCHERS"
3733Another common scenario is to use some data structure with multiple
3734embedded watchers, in effect creating your own watcher that combines
3735multiple libev event sources into one \*(L"super-watcher\*(R":
3736.PP
3737.Vb 6
3738\& struct my_biggy
3739\& {
3740\& int some_data;
3741\& ev_timer t1;
3742\& ev_timer t2;
3743\& }
3744.Ve
3745.PP
3746In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more
3747complicated: Either you store the address of your \f(CW\*(C`my_biggy\*(C'\fR struct in
3748the \f(CW\*(C`data\*(C'\fR member of the watcher (for woozies or \*(C+ coders), or you need
3749to use some pointer arithmetic using \f(CW\*(C`offsetof\*(C'\fR inside your watchers (for
3750real programmers):
3751.PP
3752.Vb 1
3753\& #include <stddef.h>
3754\&
3755\& static void
3756\& t1_cb (EV_P_ ev_timer *w, int revents)
3757\& {
3758\& struct my_biggy big = (struct my_biggy *)
3759\& (((char *)w) \- offsetof (struct my_biggy, t1));
3760\& }
3761\&
3762\& static void
3763\& t2_cb (EV_P_ ev_timer *w, int revents)
3764\& {
3765\& struct my_biggy big = (struct my_biggy *)
3766\& (((char *)w) \- offsetof (struct my_biggy, t2));
3767\& }
3768.Ve
3769.SS "\s-1AVOIDING FINISHING BEFORE RETURNING\s0"
3770.IX Subsection "AVOIDING FINISHING BEFORE RETURNING"
3771Often you have structures like this in event-based programs:
3772.PP
3773.Vb 4
3774\& callback ()
1393\& { 3775\& {
1394\& if (revents & EV_TIMEOUT) 3776\& free (request);
1395\& /* doh, nothing entered */;
1396\& else if (revents & EV_READ)
1397\& /* stdin might have data for us, joy! */;
1398\& } 3777\& }
3778\&
3779\& request = start_new_request (..., callback);
1399.Ve 3780.Ve
1400.Sp 3781.PP
3782The intent is to start some \*(L"lengthy\*(R" operation. The \f(CW\*(C`request\*(C'\fR could be
3783used to cancel the operation, or do other things with it.
3784.PP
3785It's not uncommon to have code paths in \f(CW\*(C`start_new_request\*(C'\fR that
3786immediately invoke the callback, for example, to report errors. Or you add
3787some caching layer that finds that it can skip the lengthy aspects of the
3788operation and simply invoke the callback with the result.
3789.PP
3790The problem here is that this will happen \fIbefore\fR \f(CW\*(C`start_new_request\*(C'\fR
3791has returned, so \f(CW\*(C`request\*(C'\fR is not set.
3792.PP
3793Even if you pass the request by some safer means to the callback, you
3794might want to do something to the request after starting it, such as
3795canceling it, which probably isn't working so well when the callback has
3796already been invoked.
3797.PP
3798A common way around all these issues is to make sure that
3799\&\f(CW\*(C`start_new_request\*(C'\fR \fIalways\fR returns before the callback is invoked. If
3800\&\f(CW\*(C`start_new_request\*(C'\fR immediately knows the result, it can artificially
3801delay invoking the callback by using a \f(CW\*(C`prepare\*(C'\fR or \f(CW\*(C`idle\*(C'\fR watcher for
3802example, or more sneakily, by reusing an existing (stopped) watcher and
3803pushing it into the pending queue:
3804.PP
1401.Vb 1 3805.Vb 2
1402\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); 3806\& ev_set_cb (watcher, callback);
3807\& ev_feed_event (EV_A_ watcher, 0);
1403.Ve 3808.Ve
1404.IP "ev_feed_event (ev_loop *, watcher *, int revents)" 4 3809.PP
1405.IX Item "ev_feed_event (ev_loop *, watcher *, int revents)" 3810This way, \f(CW\*(C`start_new_request\*(C'\fR can safely return before the callback is
1406Feeds the given event set into the event loop, as if the specified event 3811invoked, while not delaying callback invocation too much.
1407had happened for the specified watcher (which must be a pointer to an 3812.SS "\s-1MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS\s0"
1408initialised but not necessarily started event watcher). 3813.IX Subsection "MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS"
1409.IP "ev_feed_fd_event (ev_loop *, int fd, int revents)" 4 3814Often (especially in \s-1GUI\s0 toolkits) there are places where you have
1410.IX Item "ev_feed_fd_event (ev_loop *, int fd, int revents)" 3815\&\fImodal\fR interaction, which is most easily implemented by recursively
1411Feed an event on the given fd, as if a file descriptor backend detected 3816invoking \f(CW\*(C`ev_run\*(C'\fR.
1412the given events it. 3817.PP
1413.IP "ev_feed_signal_event (ev_loop *loop, int signum)" 4 3818This brings the problem of exiting \- a callback might want to finish the
1414.IX Item "ev_feed_signal_event (ev_loop *loop, int signum)" 3819main \f(CW\*(C`ev_run\*(C'\fR call, but not the nested one (e.g. user clicked \*(L"Quit\*(R", but
1415Feed an event as if the given signal occured (\f(CW\*(C`loop\*(C'\fR must be the default 3820a modal \*(L"Are you sure?\*(R" dialog is still waiting), or just the nested one
1416loop!). 3821and not the main one (e.g. user clocked \*(L"Ok\*(R" in a modal dialog), or some
3822other combination: In these cases, a simple \f(CW\*(C`ev_break\*(C'\fR will not work.
3823.PP
3824The solution is to maintain \*(L"break this loop\*(R" variable for each \f(CW\*(C`ev_run\*(C'\fR
3825invocation, and use a loop around \f(CW\*(C`ev_run\*(C'\fR until the condition is
3826triggered, using \f(CW\*(C`EVRUN_ONCE\*(C'\fR:
3827.PP
3828.Vb 2
3829\& // main loop
3830\& int exit_main_loop = 0;
3831\&
3832\& while (!exit_main_loop)
3833\& ev_run (EV_DEFAULT_ EVRUN_ONCE);
3834\&
3835\& // in a modal watcher
3836\& int exit_nested_loop = 0;
3837\&
3838\& while (!exit_nested_loop)
3839\& ev_run (EV_A_ EVRUN_ONCE);
3840.Ve
3841.PP
3842To exit from any of these loops, just set the corresponding exit variable:
3843.PP
3844.Vb 2
3845\& // exit modal loop
3846\& exit_nested_loop = 1;
3847\&
3848\& // exit main program, after modal loop is finished
3849\& exit_main_loop = 1;
3850\&
3851\& // exit both
3852\& exit_main_loop = exit_nested_loop = 1;
3853.Ve
3854.SS "\s-1THREAD LOCKING EXAMPLE\s0"
3855.IX Subsection "THREAD LOCKING EXAMPLE"
3856Here is a fictitious example of how to run an event loop in a different
3857thread from where callbacks are being invoked and watchers are
3858created/added/removed.
3859.PP
3860For a real-world example, see the \f(CW\*(C`EV::Loop::Async\*(C'\fR perl module,
3861which uses exactly this technique (which is suited for many high-level
3862languages).
3863.PP
3864The example uses a pthread mutex to protect the loop data, a condition
3865variable to wait for callback invocations, an async watcher to notify the
3866event loop thread and an unspecified mechanism to wake up the main thread.
3867.PP
3868First, you need to associate some data with the event loop:
3869.PP
3870.Vb 6
3871\& typedef struct {
3872\& mutex_t lock; /* global loop lock */
3873\& ev_async async_w;
3874\& thread_t tid;
3875\& cond_t invoke_cv;
3876\& } userdata;
3877\&
3878\& void prepare_loop (EV_P)
3879\& {
3880\& // for simplicity, we use a static userdata struct.
3881\& static userdata u;
3882\&
3883\& ev_async_init (&u\->async_w, async_cb);
3884\& ev_async_start (EV_A_ &u\->async_w);
3885\&
3886\& pthread_mutex_init (&u\->lock, 0);
3887\& pthread_cond_init (&u\->invoke_cv, 0);
3888\&
3889\& // now associate this with the loop
3890\& ev_set_userdata (EV_A_ u);
3891\& ev_set_invoke_pending_cb (EV_A_ l_invoke);
3892\& ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
3893\&
3894\& // then create the thread running ev_run
3895\& pthread_create (&u\->tid, 0, l_run, EV_A);
3896\& }
3897.Ve
3898.PP
3899The callback for the \f(CW\*(C`ev_async\*(C'\fR watcher does nothing: the watcher is used
3900solely to wake up the event loop so it takes notice of any new watchers
3901that might have been added:
3902.PP
3903.Vb 5
3904\& static void
3905\& async_cb (EV_P_ ev_async *w, int revents)
3906\& {
3907\& // just used for the side effects
3908\& }
3909.Ve
3910.PP
3911The \f(CW\*(C`l_release\*(C'\fR and \f(CW\*(C`l_acquire\*(C'\fR callbacks simply unlock/lock the mutex
3912protecting the loop data, respectively.
3913.PP
3914.Vb 6
3915\& static void
3916\& l_release (EV_P)
3917\& {
3918\& userdata *u = ev_userdata (EV_A);
3919\& pthread_mutex_unlock (&u\->lock);
3920\& }
3921\&
3922\& static void
3923\& l_acquire (EV_P)
3924\& {
3925\& userdata *u = ev_userdata (EV_A);
3926\& pthread_mutex_lock (&u\->lock);
3927\& }
3928.Ve
3929.PP
3930The event loop thread first acquires the mutex, and then jumps straight
3931into \f(CW\*(C`ev_run\*(C'\fR:
3932.PP
3933.Vb 4
3934\& void *
3935\& l_run (void *thr_arg)
3936\& {
3937\& struct ev_loop *loop = (struct ev_loop *)thr_arg;
3938\&
3939\& l_acquire (EV_A);
3940\& pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
3941\& ev_run (EV_A_ 0);
3942\& l_release (EV_A);
3943\&
3944\& return 0;
3945\& }
3946.Ve
3947.PP
3948Instead of invoking all pending watchers, the \f(CW\*(C`l_invoke\*(C'\fR callback will
3949signal the main thread via some unspecified mechanism (signals? pipe
3950writes? \f(CW\*(C`Async::Interrupt\*(C'\fR?) and then waits until all pending watchers
3951have been called (in a while loop because a) spurious wakeups are possible
3952and b) skipping inter-thread-communication when there are no pending
3953watchers is very beneficial):
3954.PP
3955.Vb 4
3956\& static void
3957\& l_invoke (EV_P)
3958\& {
3959\& userdata *u = ev_userdata (EV_A);
3960\&
3961\& while (ev_pending_count (EV_A))
3962\& {
3963\& wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
3964\& pthread_cond_wait (&u\->invoke_cv, &u\->lock);
3965\& }
3966\& }
3967.Ve
3968.PP
3969Now, whenever the main thread gets told to invoke pending watchers, it
3970will grab the lock, call \f(CW\*(C`ev_invoke_pending\*(C'\fR and then signal the loop
3971thread to continue:
3972.PP
3973.Vb 4
3974\& static void
3975\& real_invoke_pending (EV_P)
3976\& {
3977\& userdata *u = ev_userdata (EV_A);
3978\&
3979\& pthread_mutex_lock (&u\->lock);
3980\& ev_invoke_pending (EV_A);
3981\& pthread_cond_signal (&u\->invoke_cv);
3982\& pthread_mutex_unlock (&u\->lock);
3983\& }
3984.Ve
3985.PP
3986Whenever you want to start/stop a watcher or do other modifications to an
3987event loop, you will now have to lock:
3988.PP
3989.Vb 2
3990\& ev_timer timeout_watcher;
3991\& userdata *u = ev_userdata (EV_A);
3992\&
3993\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
3994\&
3995\& pthread_mutex_lock (&u\->lock);
3996\& ev_timer_start (EV_A_ &timeout_watcher);
3997\& ev_async_send (EV_A_ &u\->async_w);
3998\& pthread_mutex_unlock (&u\->lock);
3999.Ve
4000.PP
4001Note that sending the \f(CW\*(C`ev_async\*(C'\fR watcher is required because otherwise
4002an event loop currently blocking in the kernel will have no knowledge
4003about the newly added timer. By waking up the loop it will pick up any new
4004watchers in the next event loop iteration.
4005.SS "\s-1THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS\s0"
4006.IX Subsection "THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS"
4007While the overhead of a callback that e.g. schedules a thread is small, it
4008is still an overhead. If you embed libev, and your main usage is with some
4009kind of threads or coroutines, you might want to customise libev so that
4010doesn't need callbacks anymore.
4011.PP
4012Imagine you have coroutines that you can switch to using a function
4013\&\f(CW\*(C`switch_to (coro)\*(C'\fR, that libev runs in a coroutine called \f(CW\*(C`libev_coro\*(C'\fR
4014and that due to some magic, the currently active coroutine is stored in a
4015global called \f(CW\*(C`current_coro\*(C'\fR. Then you can build your own \*(L"wait for libev
4016event\*(R" primitive by changing \f(CW\*(C`EV_CB_DECLARE\*(C'\fR and \f(CW\*(C`EV_CB_INVOKE\*(C'\fR (note
4017the differing \f(CW\*(C`;\*(C'\fR conventions):
4018.PP
4019.Vb 2
4020\& #define EV_CB_DECLARE(type) struct my_coro *cb;
4021\& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb)
4022.Ve
4023.PP
4024That means instead of having a C callback function, you store the
4025coroutine to switch to in each watcher, and instead of having libev call
4026your callback, you instead have it switch to that coroutine.
4027.PP
4028A coroutine might now wait for an event with a function called
4029\&\f(CW\*(C`wait_for_event\*(C'\fR. (the watcher needs to be started, as always, but it doesn't
4030matter when, or whether the watcher is active or not when this function is
4031called):
4032.PP
4033.Vb 6
4034\& void
4035\& wait_for_event (ev_watcher *w)
4036\& {
4037\& ev_set_cb (w, current_coro);
4038\& switch_to (libev_coro);
4039\& }
4040.Ve
4041.PP
4042That basically suspends the coroutine inside \f(CW\*(C`wait_for_event\*(C'\fR and
4043continues the libev coroutine, which, when appropriate, switches back to
4044this or any other coroutine.
4045.PP
4046You can do similar tricks if you have, say, threads with an event queue \-
4047instead of storing a coroutine, you store the queue object and instead of
4048switching to a coroutine, you push the watcher onto the queue and notify
4049any waiters.
4050.PP
4051To embed libev, see \*(L"\s-1EMBEDDING\*(R"\s0, but in short, it's easiest to create two
4052files, \fImy_ev.h\fR and \fImy_ev.c\fR that include the respective libev files:
4053.PP
4054.Vb 4
4055\& // my_ev.h
4056\& #define EV_CB_DECLARE(type) struct my_coro *cb;
4057\& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb)
4058\& #include "../libev/ev.h"
4059\&
4060\& // my_ev.c
4061\& #define EV_H "my_ev.h"
4062\& #include "../libev/ev.c"
4063.Ve
4064.PP
4065And then use \fImy_ev.h\fR when you would normally use \fIev.h\fR, and compile
4066\&\fImy_ev.c\fR into your project. When properly specifying include paths, you
4067can even use \fIev.h\fR as header file name directly.
1417.SH "LIBEVENT EMULATION" 4068.SH "LIBEVENT EMULATION"
1418.IX Header "LIBEVENT EMULATION" 4069.IX Header "LIBEVENT EMULATION"
1419Libev offers a compatibility emulation layer for libevent. It cannot 4070Libev offers a compatibility emulation layer for libevent. It cannot
1420emulate the internals of libevent, so here are some usage hints: 4071emulate the internals of libevent, so here are some usage hints:
4072.IP "\(bu" 4
4073Only the libevent\-1.4.1\-beta \s-1API\s0 is being emulated.
4074.Sp
4075This was the newest libevent version available when libev was implemented,
4076and is still mostly unchanged in 2010.
4077.IP "\(bu" 4
1421.IP "* Use it by including <event.h>, as usual." 4 4078Use it by including <event.h>, as usual.
1422.IX Item "Use it by including <event.h>, as usual." 4079.IP "\(bu" 4
1423.PD 0 4080The following members are fully supported: ev_base, ev_callback,
1424.IP "* The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4 4081ev_arg, ev_fd, ev_res, ev_events.
1425.IX Item "The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4082.IP "\(bu" 4
1426.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 4083Avoid using ev_flags and the EVLIST_*\-macros, while it is
1427.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)." 4084maintained by libev, it does not work exactly the same way as in libevent (consider
1428.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 4085it a private \s-1API\s0).
1429.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." 4086.IP "\(bu" 4
4087Priorities are not currently supported. Initialising priorities
4088will fail and all watchers will have the same priority, even though there
4089is an ev_pri field.
4090.IP "\(bu" 4
4091In libevent, the last base created gets the signals, in libev, the
4092base that registered the signal gets the signals.
4093.IP "\(bu" 4
1430.IP "* Other members are not supported." 4 4094Other members are not supported.
1431.IX Item "Other members are not supported." 4095.IP "\(bu" 4
1432.IP "* The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need to use the libev header file and library." 4 4096The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need
1433.IX Item "The libev emulation is not ABI compatible to libevent, you need to use the libev header file and library." 4097to use the libev header file and library.
1434.PD
1435.SH "\*(C+ SUPPORT" 4098.SH "\*(C+ SUPPORT"
1436.IX Header " SUPPORT" 4099.IX Header " SUPPORT"
4100.SS "C \s-1API\s0"
4101.IX Subsection "C API"
4102The normal C \s-1API\s0 should work fine when used from \*(C+: both ev.h and the
4103libev sources can be compiled as \*(C+. Therefore, code that uses the C \s-1API\s0
4104will work fine.
4105.PP
4106Proper exception specifications might have to be added to callbacks passed
4107to libev: exceptions may be thrown only from watcher callbacks, all
4108other callbacks (allocator, syserr, loop acquire/release and periodic
4109reschedule callbacks) must not throw exceptions, and might need a \f(CW\*(C`throw
4110()\*(C'\fR specification. If you have code that needs to be compiled as both C
4111and \*(C+ you can use the \f(CW\*(C`EV_THROW\*(C'\fR macro for this:
4112.PP
4113.Vb 6
4114\& static void
4115\& fatal_error (const char *msg) EV_THROW
4116\& {
4117\& perror (msg);
4118\& abort ();
4119\& }
4120\&
4121\& ...
4122\& ev_set_syserr_cb (fatal_error);
4123.Ve
4124.PP
4125The only \s-1API\s0 functions that can currently throw exceptions are \f(CW\*(C`ev_run\*(C'\fR,
4126\&\f(CW\*(C`ev_invoke\*(C'\fR, \f(CW\*(C`ev_invoke_pending\*(C'\fR and \f(CW\*(C`ev_loop_destroy\*(C'\fR (the latter
4127because it runs cleanup watchers).
4128.PP
4129Throwing exceptions in watcher callbacks is only supported if libev itself
4130is compiled with a \*(C+ compiler or your C and \*(C+ environments allow
4131throwing exceptions through C libraries (most do).
4132.SS "\*(C+ \s-1API\s0"
4133.IX Subsection " API"
1437Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow 4134Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
1438you to use some convinience methods to start/stop watchers and also change 4135you to use some convenience methods to start/stop watchers and also change
1439the callback model to a model using method callbacks on objects. 4136the callback model to a model using method callbacks on objects.
1440.PP 4137.PP
1441To use it, 4138To use it,
1442.PP 4139.PP
1443.Vb 1 4140.Vb 1
1444\& #include <ev++.h> 4141\& #include <ev++.h>
1445.Ve 4142.Ve
1446.PP 4143.PP
1447(it is not installed by default). This automatically includes \fIev.h\fR 4144This automatically includes \fIev.h\fR and puts all of its definitions (many
1448and puts all of its definitions (many of them macros) into the global 4145of them macros) into the global namespace. All \*(C+ specific things are
1449namespace. All \*(C+ specific things are put into the \f(CW\*(C`ev\*(C'\fR namespace. 4146put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding
4147options as \fIev.h\fR, most notably \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR.
1450.PP 4148.PP
1451It should support all the same embedding options as \fIev.h\fR, most notably 4149Care has been taken to keep the overhead low. The only data member the \*(C+
1452\&\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. 4150classes add (compared to plain C\-style watchers) is the event loop pointer
4151that the watcher is associated with (or no additional members at all if
4152you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
4153.PP
4154Currently, functions, static and non-static member functions and classes
4155with \f(CW\*(C`operator ()\*(C'\fR can be used as callbacks. Other types should be easy
4156to add as long as they only need one additional pointer for context. If
4157you need support for other types of functors please contact the author
4158(preferably after implementing it).
4159.PP
4160For all this to work, your \*(C+ compiler either has to use the same calling
4161conventions as your C compiler (for static member functions), or you have
4162to embed libev and compile libev itself as \*(C+.
1453.PP 4163.PP
1454Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace: 4164Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
1455.ie n .IP """ev::READ""\fR, \f(CW""ev::WRITE"" etc." 4 4165.ie n .IP """ev::READ"", ""ev::WRITE"" etc." 4
1456.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4 4166.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
1457.IX Item "ev::READ, ev::WRITE etc." 4167.IX Item "ev::READ, ev::WRITE etc."
1458These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc. 4168These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
1459macros from \fIev.h\fR. 4169macros from \fIev.h\fR.
1460.ie n .IP """ev::tstamp""\fR, \f(CW""ev::now""" 4 4170.ie n .IP """ev::tstamp"", ""ev::now""" 4
1461.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4 4171.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
1462.IX Item "ev::tstamp, ev::now" 4172.IX Item "ev::tstamp, ev::now"
1463Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix. 4173Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
1464.ie n .IP """ev::io""\fR, \f(CW""ev::timer""\fR, \f(CW""ev::periodic""\fR, \f(CW""ev::idle""\fR, \f(CW""ev::sig"" etc." 4 4174.ie n .IP """ev::io"", ""ev::timer"", ""ev::periodic"", ""ev::idle"", ""ev::sig"" etc." 4
1465.el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4 4175.el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
1466.IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc." 4176.IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
1467For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of 4177For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
1468the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR 4178the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
1469which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro 4179which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
1470defines by many implementations. 4180defined by many implementations.
1471.Sp 4181.Sp
1472All of those classes have these methods: 4182All of those classes have these methods:
1473.RS 4 4183.RS 4
1474.IP "ev::TYPE::TYPE (object *, object::method *)" 4 4184.IP "ev::TYPE::TYPE ()" 4
1475.IX Item "ev::TYPE::TYPE (object *, object::method *)" 4185.IX Item "ev::TYPE::TYPE ()"
1476.PD 0 4186.PD 0
1477.IP "ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)" 4 4187.IP "ev::TYPE::TYPE (loop)" 4
1478.IX Item "ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)" 4188.IX Item "ev::TYPE::TYPE (loop)"
1479.IP "ev::TYPE::~TYPE" 4 4189.IP "ev::TYPE::~TYPE" 4
1480.IX Item "ev::TYPE::~TYPE" 4190.IX Item "ev::TYPE::~TYPE"
1481.PD 4191.PD
1482The constructor takes a pointer to an object and a method pointer to 4192The constructor (optionally) takes an event loop to associate the watcher
1483the event handler callback to call in this class. The constructor calls 4193with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR.
1484\&\f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the \f(CW\*(C`set\*(C'\fR method 4194.Sp
1485before starting it. If you do not specify a loop then the constructor 4195The constructor calls \f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the
1486automatically associates the default loop with this watcher. 4196\&\f(CW\*(C`set\*(C'\fR method before starting it.
4197.Sp
4198It will not set a callback, however: You have to call the templated \f(CW\*(C`set\*(C'\fR
4199method to set a callback before you can start the watcher.
4200.Sp
4201(The reason why you have to use a method is a limitation in \*(C+ which does
4202not allow explicit template arguments for constructors).
1487.Sp 4203.Sp
1488The destructor automatically stops the watcher if it is active. 4204The destructor automatically stops the watcher if it is active.
4205.IP "w\->set<class, &class::method> (object *)" 4
4206.IX Item "w->set<class, &class::method> (object *)"
4207This method sets the callback method to call. The method has to have a
4208signature of \f(CW\*(C`void (*)(ev_TYPE &, int)\*(C'\fR, it receives the watcher as
4209first argument and the \f(CW\*(C`revents\*(C'\fR as second. The object must be given as
4210parameter and is stored in the \f(CW\*(C`data\*(C'\fR member of the watcher.
4211.Sp
4212This method synthesizes efficient thunking code to call your method from
4213the C callback that libev requires. If your compiler can inline your
4214callback (i.e. it is visible to it at the place of the \f(CW\*(C`set\*(C'\fR call and
4215your compiler is good :), then the method will be fully inlined into the
4216thunking function, making it as fast as a direct C callback.
4217.Sp
4218Example: simple class declaration and watcher initialisation
4219.Sp
4220.Vb 4
4221\& struct myclass
4222\& {
4223\& void io_cb (ev::io &w, int revents) { }
4224\& }
4225\&
4226\& myclass obj;
4227\& ev::io iow;
4228\& iow.set <myclass, &myclass::io_cb> (&obj);
4229.Ve
4230.IP "w\->set (object *)" 4
4231.IX Item "w->set (object *)"
4232This is a variation of a method callback \- leaving out the method to call
4233will default the method to \f(CW\*(C`operator ()\*(C'\fR, which makes it possible to use
4234functor objects without having to manually specify the \f(CW\*(C`operator ()\*(C'\fR all
4235the time. Incidentally, you can then also leave out the template argument
4236list.
4237.Sp
4238The \f(CW\*(C`operator ()\*(C'\fR method prototype must be \f(CW\*(C`void operator ()(watcher &w,
4239int revents)\*(C'\fR.
4240.Sp
4241See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
4242.Sp
4243Example: use a functor object as callback.
4244.Sp
4245.Vb 7
4246\& struct myfunctor
4247\& {
4248\& void operator() (ev::io &w, int revents)
4249\& {
4250\& ...
4251\& }
4252\& }
4253\&
4254\& myfunctor f;
4255\&
4256\& ev::io w;
4257\& w.set (&f);
4258.Ve
4259.IP "w\->set<function> (void *data = 0)" 4
4260.IX Item "w->set<function> (void *data = 0)"
4261Also sets a callback, but uses a static method or plain function as
4262callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
4263\&\f(CW\*(C`data\*(C'\fR member and is free for you to use.
4264.Sp
4265The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
4266.Sp
4267See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
4268.Sp
4269Example: Use a plain function as callback.
4270.Sp
4271.Vb 2
4272\& static void io_cb (ev::io &w, int revents) { }
4273\& iow.set <io_cb> ();
4274.Ve
1489.IP "w\->set (struct ev_loop *)" 4 4275.IP "w\->set (loop)" 4
1490.IX Item "w->set (struct ev_loop *)" 4276.IX Item "w->set (loop)"
1491Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only 4277Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
1492do this when the watcher is inactive (and not pending either). 4278do this when the watcher is inactive (and not pending either).
1493.IP "w\->set ([args])" 4 4279.IP "w\->set ([arguments])" 4
1494.IX Item "w->set ([args])" 4280.IX Item "w->set ([arguments])"
1495Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same args. Must be 4281Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR (except for \f(CW\*(C`ev::embed\*(C'\fR watchers>),
4282with the same arguments. Either this method or a suitable start method
1496called at least once. Unlike the C counterpart, an active watcher gets 4283must be called at least once. Unlike the C counterpart, an active watcher
1497automatically stopped and restarted. 4284gets automatically stopped and restarted when reconfiguring it with this
4285method.
4286.Sp
4287For \f(CW\*(C`ev::embed\*(C'\fR watchers this method is called \f(CW\*(C`set_embed\*(C'\fR, to avoid
4288clashing with the \f(CW\*(C`set (loop)\*(C'\fR method.
1498.IP "w\->start ()" 4 4289.IP "w\->start ()" 4
1499.IX Item "w->start ()" 4290.IX Item "w->start ()"
1500Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument as the 4291Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
1501constructor already takes the loop. 4292constructor already stores the event loop.
4293.IP "w\->start ([arguments])" 4
4294.IX Item "w->start ([arguments])"
4295Instead of calling \f(CW\*(C`set\*(C'\fR and \f(CW\*(C`start\*(C'\fR methods separately, it is often
4296convenient to wrap them in one call. Uses the same type of arguments as
4297the configure \f(CW\*(C`set\*(C'\fR method of the watcher.
1502.IP "w\->stop ()" 4 4298.IP "w\->stop ()" 4
1503.IX Item "w->stop ()" 4299.IX Item "w->stop ()"
1504Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument. 4300Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
1505.ie n .IP "w\->again () ""ev::timer""\fR, \f(CW""ev::periodic"" only" 4 4301.ie n .IP "w\->again () (""ev::timer"", ""ev::periodic"" only)" 4
1506.el .IP "w\->again () \f(CWev::timer\fR, \f(CWev::periodic\fR only" 4 4302.el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
1507.IX Item "w->again () ev::timer, ev::periodic only" 4303.IX Item "w->again () (ev::timer, ev::periodic only)"
1508For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding 4304For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
1509\&\f(CW\*(C`ev_TYPE_again\*(C'\fR function. 4305\&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
1510.ie n .IP "w\->sweep () ""ev::embed"" only" 4 4306.ie n .IP "w\->sweep () (""ev::embed"" only)" 4
1511.el .IP "w\->sweep () \f(CWev::embed\fR only" 4 4307.el .IP "w\->sweep () (\f(CWev::embed\fR only)" 4
1512.IX Item "w->sweep () ev::embed only" 4308.IX Item "w->sweep () (ev::embed only)"
1513Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR. 4309Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR.
4310.ie n .IP "w\->update () (""ev::stat"" only)" 4
4311.el .IP "w\->update () (\f(CWev::stat\fR only)" 4
4312.IX Item "w->update () (ev::stat only)"
4313Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
1514.RE 4314.RE
1515.RS 4 4315.RS 4
1516.RE 4316.RE
1517.PP 4317.PP
1518Example: Define a class with an \s-1IO\s0 and idle watcher, start one of them in 4318Example: Define a class with two I/O and idle watchers, start the I/O
1519the constructor. 4319watchers in the constructor.
1520.PP 4320.PP
1521.Vb 4 4321.Vb 5
1522\& class myclass 4322\& class myclass
1523\& { 4323\& {
1524\& ev_io io; void io_cb (ev::io &w, int revents); 4324\& ev::io io ; void io_cb (ev::io &w, int revents);
4325\& ev::io io2 ; void io2_cb (ev::io &w, int revents);
1525\& ev_idle idle void idle_cb (ev::idle &w, int revents); 4326\& ev::idle idle; void idle_cb (ev::idle &w, int revents);
4327\&
4328\& myclass (int fd)
4329\& {
4330\& io .set <myclass, &myclass::io_cb > (this);
4331\& io2 .set <myclass, &myclass::io2_cb > (this);
4332\& idle.set <myclass, &myclass::idle_cb> (this);
4333\&
4334\& io.set (fd, ev::WRITE); // configure the watcher
4335\& io.start (); // start it whenever convenient
4336\&
4337\& io2.start (fd, ev::READ); // set + start in one call
4338\& }
4339\& };
1526.Ve 4340.Ve
4341.SH "OTHER LANGUAGE BINDINGS"
4342.IX Header "OTHER LANGUAGE BINDINGS"
4343Libev does not offer other language bindings itself, but bindings for a
4344number of languages exist in the form of third-party packages. If you know
4345any interesting language binding in addition to the ones listed here, drop
4346me a note.
4347.IP "Perl" 4
4348.IX Item "Perl"
4349The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test
4350libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module,
4351there are additional modules that implement libev-compatible interfaces
4352to \f(CW\*(C`libadns\*(C'\fR (\f(CW\*(C`EV::ADNS\*(C'\fR, but \f(CW\*(C`AnyEvent::DNS\*(C'\fR is preferred nowadays),
4353\&\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
4354and \f(CW\*(C`EV::Glib\*(C'\fR).
4355.Sp
4356It can be found and installed via \s-1CPAN,\s0 its homepage is at
4357<http://software.schmorp.de/pkg/EV>.
4358.IP "Python" 4
4359.IX Item "Python"
4360Python bindings can be found at <http://code.google.com/p/pyev/>. It
4361seems to be quite complete and well-documented.
4362.IP "Ruby" 4
4363.IX Item "Ruby"
4364Tony Arcieri has written a ruby extension that offers access to a subset
4365of the libev \s-1API\s0 and adds file handle abstractions, asynchronous \s-1DNS\s0 and
4366more on top of it. It can be found via gem servers. Its homepage is at
4367<http://rev.rubyforge.org/>.
4368.Sp
4369Roger Pack reports that using the link order \f(CW\*(C`\-lws2_32 \-lmsvcrt\-ruby\-190\*(C'\fR
4370makes rev work even on mingw.
4371.IP "Haskell" 4
4372.IX Item "Haskell"
4373A haskell binding to libev is available at
4374<http://hackage.haskell.org/cgi\-bin/hackage\-scripts/package/hlibev>.
4375.IP "D" 4
4376.IX Item "D"
4377Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
4378be found at <http://www.llucax.com.ar/proj/ev.d/index.html>.
4379.IP "Ocaml" 4
4380.IX Item "Ocaml"
4381Erkki Seppala has written Ocaml bindings for libev, to be found at
4382<http://modeemi.cs.tut.fi/~flux/software/ocaml\-ev/>.
4383.IP "Lua" 4
4384.IX Item "Lua"
4385Brian Maher has written a partial interface to libev for lua (at the
4386time of this writing, only \f(CW\*(C`ev_io\*(C'\fR and \f(CW\*(C`ev_timer\*(C'\fR), to be found at
4387<http://github.com/brimworks/lua\-ev>.
4388.IP "Javascript" 4
4389.IX Item "Javascript"
4390Node.js (<http://nodejs.org>) uses libev as the underlying event library.
4391.IP "Others" 4
4392.IX Item "Others"
4393There are others, and I stopped counting.
4394.SH "MACRO MAGIC"
4395.IX Header "MACRO MAGIC"
4396Libev can be compiled with a variety of options, the most fundamental
4397of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most)
4398functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
1527.PP 4399.PP
4400To make it easier to write programs that cope with either variant, the
4401following macros are defined:
4402.ie n .IP """EV_A"", ""EV_A_""" 4
4403.el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
4404.IX Item "EV_A, EV_A_"
4405This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
4406loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
4407\&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
4408.Sp
4409.Vb 3
4410\& ev_unref (EV_A);
4411\& ev_timer_add (EV_A_ watcher);
4412\& ev_run (EV_A_ 0);
4413.Ve
4414.Sp
4415It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
4416which is often provided by the following macro.
4417.ie n .IP """EV_P"", ""EV_P_""" 4
4418.el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
4419.IX Item "EV_P, EV_P_"
4420This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
4421loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
4422\&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
4423.Sp
1528.Vb 2 4424.Vb 2
1529\& myclass (); 4425\& // this is how ev_unref is being declared
1530\& } 4426\& static void ev_unref (EV_P);
4427\&
4428\& // this is how you can declare your typical callback
4429\& static void cb (EV_P_ ev_timer *w, int revents)
1531.Ve 4430.Ve
4431.Sp
4432It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
4433suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
4434.ie n .IP """EV_DEFAULT"", ""EV_DEFAULT_""" 4
4435.el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
4436.IX Item "EV_DEFAULT, EV_DEFAULT_"
4437Similar to the other two macros, this gives you the value of the default
4438loop, if multiple loops are supported (\*(L"ev loop default\*(R"). The default loop
4439will be initialised if it isn't already initialised.
4440.Sp
4441For non-multiplicity builds, these macros do nothing, so you always have
4442to initialise the loop somewhere.
4443.ie n .IP """EV_DEFAULT_UC"", ""EV_DEFAULT_UC_""" 4
4444.el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
4445.IX Item "EV_DEFAULT_UC, EV_DEFAULT_UC_"
4446Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the
4447default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour
4448is undefined when the default loop has not been initialised by a previous
4449execution of \f(CW\*(C`EV_DEFAULT\*(C'\fR, \f(CW\*(C`EV_DEFAULT_\*(C'\fR or \f(CW\*(C`ev_default_init (...)\*(C'\fR.
4450.Sp
4451It is often prudent to use \f(CW\*(C`EV_DEFAULT\*(C'\fR when initialising the first
4452watcher in a function but use \f(CW\*(C`EV_DEFAULT_UC\*(C'\fR afterwards.
1532.PP 4453.PP
4454Example: Declare and initialise a check watcher, utilising the above
4455macros so it will work regardless of whether multiple loops are supported
4456or not.
4457.PP
1533.Vb 6 4458.Vb 5
1534\& myclass::myclass (int fd) 4459\& static void
1535\& : io (this, &myclass::io_cb), 4460\& check_cb (EV_P_ ev_timer *w, int revents)
1536\& idle (this, &myclass::idle_cb)
1537\& { 4461\& {
1538\& io.start (fd, ev::READ); 4462\& ev_check_stop (EV_A_ w);
1539\& } 4463\& }
4464\&
4465\& ev_check check;
4466\& ev_check_init (&check, check_cb);
4467\& ev_check_start (EV_DEFAULT_ &check);
4468\& ev_run (EV_DEFAULT_ 0);
1540.Ve 4469.Ve
1541.SH "EMBEDDING" 4470.SH "EMBEDDING"
1542.IX Header "EMBEDDING" 4471.IX Header "EMBEDDING"
1543Libev can (and often is) directly embedded into host 4472Libev can (and often is) directly embedded into host
1544applications. Examples of applications that embed it include the Deliantra 4473applications. Examples of applications that embed it include the Deliantra
1545Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe) 4474Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
1546and rxvt\-unicode. 4475and rxvt-unicode.
1547.PP 4476.PP
1548The goal is to enable you to just copy the neecssary files into your 4477The goal is to enable you to just copy the necessary files into your
1549source directory without having to change even a single line in them, so 4478source directory without having to change even a single line in them, so
1550you can easily upgrade by simply copying (or having a checked-out copy of 4479you can easily upgrade by simply copying (or having a checked-out copy of
1551libev somewhere in your source tree). 4480libev somewhere in your source tree).
1552.Sh "\s-1FILESETS\s0" 4481.SS "\s-1FILESETS\s0"
1553.IX Subsection "FILESETS" 4482.IX Subsection "FILESETS"
1554Depending on what features you need you need to include one or more sets of files 4483Depending on what features you need you need to include one or more sets of files
1555in your app. 4484in your application.
1556.PP 4485.PP
1557\fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR 4486\fI\s-1CORE EVENT LOOP\s0\fR
1558.IX Subsection "CORE EVENT LOOP" 4487.IX Subsection "CORE EVENT LOOP"
1559.PP 4488.PP
1560To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual 4489To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
1561configuration (no autoconf): 4490configuration (no autoconf):
1562.PP 4491.PP
1563.Vb 2 4492.Vb 2
1564\& #define EV_STANDALONE 1 4493\& #define EV_STANDALONE 1
1565\& #include "ev.c" 4494\& #include "ev.c"
1566.Ve 4495.Ve
1567.PP 4496.PP
1568This will automatically include \fIev.h\fR, too, and should be done in a 4497This will automatically include \fIev.h\fR, too, and should be done in a
1569single C source file only to provide the function implementations. To use 4498single C source file only to provide the function implementations. To use
1570it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best 4499it, do the same for \fIev.h\fR in all files wishing to use this \s-1API \s0(best
1571done by writing a wrapper around \fIev.h\fR that you can include instead and 4500done by writing a wrapper around \fIev.h\fR that you can include instead and
1572where you can put other configuration options): 4501where you can put other configuration options):
1573.PP 4502.PP
1574.Vb 2 4503.Vb 2
1575\& #define EV_STANDALONE 1 4504\& #define EV_STANDALONE 1
1576\& #include "ev.h" 4505\& #include "ev.h"
1577.Ve 4506.Ve
1578.PP 4507.PP
1579Both header files and implementation files can be compiled with a \*(C+ 4508Both header files and implementation files can be compiled with a \*(C+
1580compiler (at least, thats a stated goal, and breakage will be treated 4509compiler (at least, that's a stated goal, and breakage will be treated
1581as a bug). 4510as a bug).
1582.PP 4511.PP
1583You need the following files in your source tree, or in a directory 4512You need the following files in your source tree, or in a directory
1584in your include path (e.g. in libev/ when using \-Ilibev): 4513in your include path (e.g. in libev/ when using \-Ilibev):
1585.PP 4514.PP
1586.Vb 4 4515.Vb 4
1587\& ev.h 4516\& ev.h
1588\& ev.c 4517\& ev.c
1589\& ev_vars.h 4518\& ev_vars.h
1590\& ev_wrap.h 4519\& ev_wrap.h
4520\&
4521\& ev_win32.c required on win32 platforms only
4522\&
4523\& ev_select.c only when select backend is enabled (which is enabled by default)
4524\& ev_poll.c only when poll backend is enabled (disabled by default)
4525\& ev_epoll.c only when the epoll backend is enabled (disabled by default)
4526\& ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
4527\& ev_port.c only when the solaris port backend is enabled (disabled by default)
1591.Ve 4528.Ve
4529.PP
4530\&\fIev.c\fR includes the backend files directly when enabled, so you only need
4531to compile this single file.
4532.PP
4533\fI\s-1LIBEVENT COMPATIBILITY API\s0\fR
4534.IX Subsection "LIBEVENT COMPATIBILITY API"
4535.PP
4536To include the libevent compatibility \s-1API,\s0 also include:
1592.PP 4537.PP
1593.Vb 1 4538.Vb 1
1594\& ev_win32.c required on win32 platforms only 4539\& #include "event.c"
1595.Ve 4540.Ve
1596.PP 4541.PP
1597.Vb 5 4542in the file including \fIev.c\fR, and:
1598\& ev_select.c only when select backend is enabled (which is is by default)
1599\& ev_poll.c only when poll backend is enabled (disabled by default)
1600\& ev_epoll.c only when the epoll backend is enabled (disabled by default)
1601\& ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
1602\& ev_port.c only when the solaris port backend is enabled (disabled by default)
1603.Ve
1604.PP
1605\&\fIev.c\fR includes the backend files directly when enabled, so you only need
1606to compile a single file.
1607.PP
1608\fI\s-1LIBEVENT\s0 \s-1COMPATIBILITY\s0 \s-1API\s0\fR
1609.IX Subsection "LIBEVENT COMPATIBILITY API"
1610.PP
1611To include the libevent compatibility \s-1API\s0, also include:
1612.PP 4543.PP
1613.Vb 1 4544.Vb 1
1614\& #include "event.c" 4545\& #include "event.h"
1615.Ve 4546.Ve
1616.PP 4547.PP
1617in the file including \fIev.c\fR, and: 4548in the files that want to use the libevent \s-1API.\s0 This also includes \fIev.h\fR.
4549.PP
4550You need the following additional files for this:
4551.PP
4552.Vb 2
4553\& event.h
4554\& event.c
4555.Ve
4556.PP
4557\fI\s-1AUTOCONF SUPPORT\s0\fR
4558.IX Subsection "AUTOCONF SUPPORT"
4559.PP
4560Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your configuration in
4561whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
4562\&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then
4563include \fIconfig.h\fR and configure itself accordingly.
4564.PP
4565For this of course you need the m4 file:
1618.PP 4566.PP
1619.Vb 1 4567.Vb 1
1620\& #include "event.h"
1621.Ve
1622.PP
1623in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR.
1624.PP
1625You need the following additional files for this:
1626.PP
1627.Vb 2
1628\& event.h
1629\& event.c
1630.Ve
1631.PP
1632\fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR
1633.IX Subsection "AUTOCONF SUPPORT"
1634.PP
1635Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your config in
1636whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
1637\&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR off. \fIev.c\fR will then include
1638\&\fIconfig.h\fR and configure itself accordingly.
1639.PP
1640For this of course you need the m4 file:
1641.PP
1642.Vb 1
1643\& libev.m4 4568\& libev.m4
1644.Ve 4569.Ve
1645.Sh "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0" 4570.SS "\s-1PREPROCESSOR SYMBOLS/MACROS\s0"
1646.IX Subsection "PREPROCESSOR SYMBOLS/MACROS" 4571.IX Subsection "PREPROCESSOR SYMBOLS/MACROS"
1647Libev can be configured via a variety of preprocessor symbols you have to define 4572Libev can be configured via a variety of preprocessor symbols you have to
1648before including any of its files. The default is not to build for multiplicity 4573define before including (or compiling) any of its files. The default in
1649and only include the select backend. 4574the absence of autoconf is documented for every option.
4575.PP
4576Symbols marked with \*(L"(h)\*(R" do not change the \s-1ABI,\s0 and can have different
4577values when compiling libev vs. including \fIev.h\fR, so it is permissible
4578to redefine them before including \fIev.h\fR without breaking compatibility
4579to a compiled library. All other symbols change the \s-1ABI,\s0 which means all
4580users of libev and the libev code itself must be compiled with compatible
4581settings.
4582.IP "\s-1EV_COMPAT3 \s0(h)" 4
4583.IX Item "EV_COMPAT3 (h)"
4584Backwards compatibility is a major concern for libev. This is why this
4585release of libev comes with wrappers for the functions and symbols that
4586have been renamed between libev version 3 and 4.
4587.Sp
4588You can disable these wrappers (to test compatibility with future
4589versions) by defining \f(CW\*(C`EV_COMPAT3\*(C'\fR to \f(CW0\fR when compiling your
4590sources. This has the additional advantage that you can drop the \f(CW\*(C`struct\*(C'\fR
4591from \f(CW\*(C`struct ev_loop\*(C'\fR declarations, as libev will provide an \f(CW\*(C`ev_loop\*(C'\fR
4592typedef in that case.
4593.Sp
4594In some future version, the default for \f(CW\*(C`EV_COMPAT3\*(C'\fR will become \f(CW0\fR,
4595and in some even more future version the compatibility code will be
4596removed completely.
1650.IP "\s-1EV_STANDALONE\s0" 4 4597.IP "\s-1EV_STANDALONE \s0(h)" 4
1651.IX Item "EV_STANDALONE" 4598.IX Item "EV_STANDALONE (h)"
1652Must always be \f(CW1\fR if you do not use autoconf configuration, which 4599Must always be \f(CW1\fR if you do not use autoconf configuration, which
1653keeps libev from including \fIconfig.h\fR, and it also defines dummy 4600keeps libev from including \fIconfig.h\fR, and it also defines dummy
1654implementations for some libevent functions (such as logging, which is not 4601implementations for some libevent functions (such as logging, which is not
1655supported). It will also not define any of the structs usually found in 4602supported). It will also not define any of the structs usually found in
1656\&\fIevent.h\fR that are not directly supported by the libev core alone. 4603\&\fIevent.h\fR that are not directly supported by the libev core alone.
4604.Sp
4605In standalone mode, libev will still try to automatically deduce the
4606configuration, but has to be more conservative.
4607.IP "\s-1EV_USE_FLOOR\s0" 4
4608.IX Item "EV_USE_FLOOR"
4609If defined to be \f(CW1\fR, libev will use the \f(CW\*(C`floor ()\*(C'\fR function for its
4610periodic reschedule calculations, otherwise libev will fall back on a
4611portable (slower) implementation. If you enable this, you usually have to
4612link against libm or something equivalent. Enabling this when the \f(CW\*(C`floor\*(C'\fR
4613function is not available will fail, so the safe default is to not enable
4614this.
1657.IP "\s-1EV_USE_MONOTONIC\s0" 4 4615.IP "\s-1EV_USE_MONOTONIC\s0" 4
1658.IX Item "EV_USE_MONOTONIC" 4616.IX Item "EV_USE_MONOTONIC"
1659If defined to be \f(CW1\fR, libev will try to detect the availability of the 4617If defined to be \f(CW1\fR, libev will try to detect the availability of the
1660monotonic clock option at both compiletime and runtime. Otherwise no use 4618monotonic clock option at both compile time and runtime. Otherwise no
1661of the monotonic clock option will be attempted. If you enable this, you 4619use of the monotonic clock option will be attempted. If you enable this,
1662usually have to link against librt or something similar. Enabling it when 4620you usually have to link against librt or something similar. Enabling it
1663the functionality isn't available is safe, though, althoguh you have 4621when the functionality isn't available is safe, though, although you have
1664to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR 4622to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
1665function is hiding in (often \fI\-lrt\fR). 4623function is hiding in (often \fI\-lrt\fR). See also \f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
1666.IP "\s-1EV_USE_REALTIME\s0" 4 4624.IP "\s-1EV_USE_REALTIME\s0" 4
1667.IX Item "EV_USE_REALTIME" 4625.IX Item "EV_USE_REALTIME"
1668If defined to be \f(CW1\fR, libev will try to detect the availability of the 4626If defined to be \f(CW1\fR, libev will try to detect the availability of the
1669realtime clock option at compiletime (and assume its availability at 4627real-time clock option at compile time (and assume its availability
1670runtime if successful). Otherwise no use of the realtime clock option will 4628at runtime if successful). Otherwise no use of the real-time clock
1671be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR by \f(CW\*(C`clock_get 4629option will be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR
1672(CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect correctness. See tzhe note about libraries 4630by \f(CW\*(C`clock_get (CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect
1673in the description of \f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. 4631correctness. See the note about libraries in the description of
4632\&\f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. Defaults to the opposite value of
4633\&\f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
4634.IP "\s-1EV_USE_CLOCK_SYSCALL\s0" 4
4635.IX Item "EV_USE_CLOCK_SYSCALL"
4636If defined to be \f(CW1\fR, libev will try to use a direct syscall instead
4637of calling the system-provided \f(CW\*(C`clock_gettime\*(C'\fR function. This option
4638exists 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
4639unconditionally pulls in \f(CW\*(C`libpthread\*(C'\fR, slowing down single-threaded
4640programs needlessly. Using a direct syscall is slightly slower (in
4641theory), because no optimised vdso implementation can be used, but avoids
4642the pthread dependency. Defaults to \f(CW1\fR on GNU/Linux with glibc 2.x or
4643higher, as it simplifies linking (no need for \f(CW\*(C`\-lrt\*(C'\fR).
4644.IP "\s-1EV_USE_NANOSLEEP\s0" 4
4645.IX Item "EV_USE_NANOSLEEP"
4646If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available
4647and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR.
4648.IP "\s-1EV_USE_EVENTFD\s0" 4
4649.IX Item "EV_USE_EVENTFD"
4650If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
4651available and will probe for kernel support at runtime. This will improve
4652\&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
4653If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
46542.7 or newer, otherwise disabled.
1674.IP "\s-1EV_USE_SELECT\s0" 4 4655.IP "\s-1EV_USE_SELECT\s0" 4
1675.IX Item "EV_USE_SELECT" 4656.IX Item "EV_USE_SELECT"
1676If undefined or defined to be \f(CW1\fR, libev will compile in support for the 4657If undefined or defined to be \f(CW1\fR, libev will compile in support for the
1677\&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at autodetection will be done: if no 4658\&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at auto-detection will be done: if no
1678other method takes over, select will be it. Otherwise the select backend 4659other method takes over, select will be it. Otherwise the select backend
1679will not be compiled in. 4660will not be compiled in.
1680.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4 4661.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
1681.IX Item "EV_SELECT_USE_FD_SET" 4662.IX Item "EV_SELECT_USE_FD_SET"
1682If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR 4663If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR
1683structure. This is useful if libev doesn't compile due to a missing 4664structure. This is useful if libev doesn't compile due to a missing
1684\&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it misguesses the bitset layout on 4665\&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it mis-guesses the bitset layout
1685exotic systems. This usually limits the range of file descriptors to some 4666on exotic systems. This usually limits the range of file descriptors to
1686low limit such as 1024 or might have other limitations (winsocket only 4667some low limit such as 1024 or might have other limitations (winsocket
1687allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation, might 4668only allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation,
1688influence the size of the \f(CW\*(C`fd_set\*(C'\fR used. 4669configures the maximum size of the \f(CW\*(C`fd_set\*(C'\fR.
1689.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4 4670.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
1690.IX Item "EV_SELECT_IS_WINSOCKET" 4671.IX Item "EV_SELECT_IS_WINSOCKET"
1691When defined to \f(CW1\fR, the select backend will assume that 4672When defined to \f(CW1\fR, the select backend will assume that
1692select/socket/connect etc. don't understand file descriptors but 4673select/socket/connect etc. don't understand file descriptors but
1693wants osf handles on win32 (this is the case when the select to 4674wants osf handles on win32 (this is the case when the select to
1694be used is the winsock select). This means that it will call 4675be used is the winsock select). This means that it will call
1695\&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise, 4676\&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
1696it is assumed that all these functions actually work on fds, even 4677it is assumed that all these functions actually work on fds, even
1697on win32. Should not be defined on non\-win32 platforms. 4678on win32. Should not be defined on non\-win32 platforms.
4679.IP "\s-1EV_FD_TO_WIN32_HANDLE\s0(fd)" 4
4680.IX Item "EV_FD_TO_WIN32_HANDLE(fd)"
4681If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map
4682file descriptors to socket handles. When not defining this symbol (the
4683default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually
4684correct. In some cases, programs use their own file descriptor management,
4685in which case they can provide this function to map fds to socket handles.
4686.IP "\s-1EV_WIN32_HANDLE_TO_FD\s0(handle)" 4
4687.IX Item "EV_WIN32_HANDLE_TO_FD(handle)"
4688If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR then libev maps handles to file descriptors
4689using the standard \f(CW\*(C`_open_osfhandle\*(C'\fR function. For programs implementing
4690their own fd to handle mapping, overwriting this function makes it easier
4691to do so. This can be done by defining this macro to an appropriate value.
4692.IP "\s-1EV_WIN32_CLOSE_FD\s0(fd)" 4
4693.IX Item "EV_WIN32_CLOSE_FD(fd)"
4694If programs implement their own fd to handle mapping on win32, then this
4695macro can be used to override the \f(CW\*(C`close\*(C'\fR function, useful to unregister
4696file descriptors again. Note that the replacement function has to close
4697the underlying \s-1OS\s0 handle.
4698.IP "\s-1EV_USE_WSASOCKET\s0" 4
4699.IX Item "EV_USE_WSASOCKET"
4700If defined to be \f(CW1\fR, libev will use \f(CW\*(C`WSASocket\*(C'\fR to create its internal
4701communication socket, which works better in some environments. Otherwise,
4702the normal \f(CW\*(C`socket\*(C'\fR function will be used, which works better in other
4703environments.
1698.IP "\s-1EV_USE_POLL\s0" 4 4704.IP "\s-1EV_USE_POLL\s0" 4
1699.IX Item "EV_USE_POLL" 4705.IX Item "EV_USE_POLL"
1700If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2) 4706If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2)
1701backend. Otherwise it will be enabled on non\-win32 platforms. It 4707backend. Otherwise it will be enabled on non\-win32 platforms. It
1702takes precedence over select. 4708takes precedence over select.
1703.IP "\s-1EV_USE_EPOLL\s0" 4 4709.IP "\s-1EV_USE_EPOLL\s0" 4
1704.IX Item "EV_USE_EPOLL" 4710.IX Item "EV_USE_EPOLL"
1705If defined to be \f(CW1\fR, libev will compile in support for the Linux 4711If defined to be \f(CW1\fR, libev will compile in support for the Linux
1706\&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime, 4712\&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime,
1707otherwise another method will be used as fallback. This is the 4713otherwise another method will be used as fallback. This is the preferred
1708preferred backend for GNU/Linux systems. 4714backend for GNU/Linux systems. If undefined, it will be enabled if the
4715headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
1709.IP "\s-1EV_USE_KQUEUE\s0" 4 4716.IP "\s-1EV_USE_KQUEUE\s0" 4
1710.IX Item "EV_USE_KQUEUE" 4717.IX Item "EV_USE_KQUEUE"
1711If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style 4718If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
1712\&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime, 4719\&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime,
1713otherwise another method will be used as fallback. This is the preferred 4720otherwise another method will be used as fallback. This is the preferred
1714backend for \s-1BSD\s0 and BSD-like systems, although on most BSDs kqueue only 4721backend for \s-1BSD\s0 and BSD-like systems, although on most BSDs kqueue only
1715supports some types of fds correctly (the only platform we found that 4722supports some types of fds correctly (the only platform we found that
1716supports ptys for example was NetBSD), so kqueue might be compiled in, but 4723supports ptys for example was NetBSD), so kqueue might be compiled in, but
1717not be used unless explicitly requested. The best way to use it is to find 4724not be used unless explicitly requested. The best way to use it is to find
1718out wether kqueue supports your type of fd properly and use an embedded 4725out whether kqueue supports your type of fd properly and use an embedded
1719kqueue loop. 4726kqueue loop.
1720.IP "\s-1EV_USE_PORT\s0" 4 4727.IP "\s-1EV_USE_PORT\s0" 4
1721.IX Item "EV_USE_PORT" 4728.IX Item "EV_USE_PORT"
1722If defined to be \f(CW1\fR, libev will compile in support for the Solaris 4729If defined to be \f(CW1\fR, libev will compile in support for the Solaris
172310 port style backend. Its availability will be detected at runtime, 473010 port style backend. Its availability will be detected at runtime,
1724otherwise another method will be used as fallback. This is the preferred 4731otherwise another method will be used as fallback. This is the preferred
1725backend for Solaris 10 systems. 4732backend for Solaris 10 systems.
1726.IP "\s-1EV_USE_DEVPOLL\s0" 4 4733.IP "\s-1EV_USE_DEVPOLL\s0" 4
1727.IX Item "EV_USE_DEVPOLL" 4734.IX Item "EV_USE_DEVPOLL"
1728reserved for future expansion, works like the \s-1USE\s0 symbols above. 4735Reserved for future expansion, works like the \s-1USE\s0 symbols above.
4736.IP "\s-1EV_USE_INOTIFY\s0" 4
4737.IX Item "EV_USE_INOTIFY"
4738If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
4739interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
4740be detected at runtime. If undefined, it will be enabled if the headers
4741indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4742.IP "\s-1EV_NO_SMP\s0" 4
4743.IX Item "EV_NO_SMP"
4744If defined to be \f(CW1\fR, libev will assume that memory is always coherent
4745between threads, that is, threads can be used, but threads never run on
4746different cpus (or different cpu cores). This reduces dependencies
4747and makes libev faster.
4748.IP "\s-1EV_NO_THREADS\s0" 4
4749.IX Item "EV_NO_THREADS"
4750If defined to be \f(CW1\fR, libev will assume that it will never be called from
4751different threads (that includes signal handlers), which is a stronger
4752assumption than \f(CW\*(C`EV_NO_SMP\*(C'\fR, above. This reduces dependencies and makes
4753libev faster.
4754.IP "\s-1EV_ATOMIC_T\s0" 4
4755.IX Item "EV_ATOMIC_T"
4756Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
4757access is atomic with respect to other threads or signal contexts. No
4758such type is easily found in the C language, so you can provide your own
4759type that you know is safe for your purposes. It is used both for signal
4760handler \*(L"locking\*(R" as well as for signal and thread safety in \f(CW\*(C`ev_async\*(C'\fR
4761watchers.
4762.Sp
4763In the absence of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR
4764(from \fIsignal.h\fR), which is usually good enough on most platforms.
1729.IP "\s-1EV_H\s0" 4 4765.IP "\s-1EV_H \s0(h)" 4
1730.IX Item "EV_H" 4766.IX Item "EV_H (h)"
1731The name of the \fIev.h\fR header file used to include it. The default if 4767The name of the \fIev.h\fR header file used to include it. The default if
1732undefined is \f(CW\*(C`<ev.h>\*(C'\fR in \fIevent.h\fR and \f(CW"ev.h"\fR in \fIev.c\fR. This 4768undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be
1733can be used to virtually rename the \fIev.h\fR header file in case of conflicts. 4769used to virtually rename the \fIev.h\fR header file in case of conflicts.
1734.IP "\s-1EV_CONFIG_H\s0" 4 4770.IP "\s-1EV_CONFIG_H \s0(h)" 4
1735.IX Item "EV_CONFIG_H" 4771.IX Item "EV_CONFIG_H (h)"
1736If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override 4772If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
1737\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to 4773\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
1738\&\f(CW\*(C`EV_H\*(C'\fR, above. 4774\&\f(CW\*(C`EV_H\*(C'\fR, above.
1739.IP "\s-1EV_EVENT_H\s0" 4 4775.IP "\s-1EV_EVENT_H \s0(h)" 4
1740.IX Item "EV_EVENT_H" 4776.IX Item "EV_EVENT_H (h)"
1741Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea 4777Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea
1742of how the \fIevent.h\fR header can be found. 4778of how the \fIevent.h\fR header can be found, the default is \f(CW"event.h"\fR.
1743.IP "\s-1EV_PROTOTYPES\s0" 4 4779.IP "\s-1EV_PROTOTYPES \s0(h)" 4
1744.IX Item "EV_PROTOTYPES" 4780.IX Item "EV_PROTOTYPES (h)"
1745If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function 4781If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
1746prototypes, but still define all the structs and other symbols. This is 4782prototypes, but still define all the structs and other symbols. This is
1747occasionally useful if you want to provide your own wrapper functions 4783occasionally useful if you want to provide your own wrapper functions
1748around libev functions. 4784around libev functions.
1749.IP "\s-1EV_MULTIPLICITY\s0" 4 4785.IP "\s-1EV_MULTIPLICITY\s0" 4
… …
1751If undefined or defined to \f(CW1\fR, then all event-loop-specific functions 4787If undefined or defined to \f(CW1\fR, then all event-loop-specific functions
1752will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create 4788will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create
1753additional independent event loops. Otherwise there will be no support 4789additional independent event loops. Otherwise there will be no support
1754for multiple event loops and there is no first event loop pointer 4790for multiple event loops and there is no first event loop pointer
1755argument. Instead, all functions act on the single default loop. 4791argument. Instead, all functions act on the single default loop.
4792.Sp
4793Note that \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR will no longer provide a
4794default loop when multiplicity is switched off \- you always have to
4795initialise the loop manually in this case.
1756.IP "\s-1EV_PERIODICS\s0" 4 4796.IP "\s-1EV_MINPRI\s0" 4
1757.IX Item "EV_PERIODICS" 4797.IX Item "EV_MINPRI"
1758If undefined or defined to be \f(CW1\fR, then periodic timers are supported, 4798.PD 0
1759otherwise not. This saves a few kb of code. 4799.IP "\s-1EV_MAXPRI\s0" 4
4800.IX Item "EV_MAXPRI"
4801.PD
4802The range of allowed priorities. \f(CW\*(C`EV_MINPRI\*(C'\fR must be smaller or equal to
4803\&\f(CW\*(C`EV_MAXPRI\*(C'\fR, but otherwise there are no non-obvious limitations. You can
4804provide for more priorities by overriding those symbols (usually defined
4805to be \f(CW\*(C`\-2\*(C'\fR and \f(CW2\fR, respectively).
4806.Sp
4807When doing priority-based operations, libev usually has to linearly search
4808all the priorities, so having many of them (hundreds) uses a lot of space
4809and time, so using the defaults of five priorities (\-2 .. +2) is usually
4810fine.
4811.Sp
4812If your embedding application does not need any priorities, defining these
4813both to \f(CW0\fR will save some memory and \s-1CPU.\s0
4814.IP "\s-1EV_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.\s0" 4
4815.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."
4816If undefined or defined to be \f(CW1\fR (and the platform supports it), then
4817the respective watcher type is supported. If defined to be \f(CW0\fR, then it
4818is not. Disabling watcher types mainly saves code size.
4819.IP "\s-1EV_FEATURES\s0" 4
4820.IX Item "EV_FEATURES"
4821If you need to shave off some kilobytes of code at the expense of some
4822speed (but with the full \s-1API\s0), you can define this symbol to request
4823certain subsets of functionality. The default is to enable all features
4824that can be enabled on the platform.
4825.Sp
4826A typical way to use this symbol is to define it to \f(CW0\fR (or to a bitset
4827with some broad features you want) and then selectively re-enable
4828additional parts you want, for example if you want everything minimal,
4829but multiple event loop support, async and child watchers and the poll
4830backend, use this:
4831.Sp
4832.Vb 5
4833\& #define EV_FEATURES 0
4834\& #define EV_MULTIPLICITY 1
4835\& #define EV_USE_POLL 1
4836\& #define EV_CHILD_ENABLE 1
4837\& #define EV_ASYNC_ENABLE 1
4838.Ve
4839.Sp
4840The actual value is a bitset, it can be a combination of the following
4841values (by default, all of these are enabled):
4842.RS 4
4843.ie n .IP "1 \- faster/larger code" 4
4844.el .IP "\f(CW1\fR \- faster/larger code" 4
4845.IX Item "1 - faster/larger code"
4846Use larger code to speed up some operations.
4847.Sp
4848Currently this is used to override some inlining decisions (enlarging the
4849code size by roughly 30% on amd64).
4850.Sp
4851When optimising for size, use of compiler flags such as \f(CW\*(C`\-Os\*(C'\fR with
4852gcc is recommended, as well as \f(CW\*(C`\-DNDEBUG\*(C'\fR, as libev contains a number of
4853assertions.
4854.Sp
4855The default is off when \f(CW\*(C`_\|_OPTIMIZE_SIZE_\|_\*(C'\fR is defined by your compiler
4856(e.g. gcc with \f(CW\*(C`\-Os\*(C'\fR).
4857.ie n .IP "2 \- faster/larger data structures" 4
4858.el .IP "\f(CW2\fR \- faster/larger data structures" 4
4859.IX Item "2 - faster/larger data structures"
4860Replaces the small 2\-heap for timer management by a faster 4\-heap, larger
4861hash table sizes and so on. This will usually further increase code size
4862and can additionally have an effect on the size of data structures at
4863runtime.
4864.Sp
4865The default is off when \f(CW\*(C`_\|_OPTIMIZE_SIZE_\|_\*(C'\fR is defined by your compiler
4866(e.g. gcc with \f(CW\*(C`\-Os\*(C'\fR).
4867.ie n .IP "4 \- full \s-1API\s0 configuration" 4
4868.el .IP "\f(CW4\fR \- full \s-1API\s0 configuration" 4
4869.IX Item "4 - full API configuration"
4870This enables priorities (sets \f(CW\*(C`EV_MAXPRI\*(C'\fR=2 and \f(CW\*(C`EV_MINPRI\*(C'\fR=\-2), and
4871enables multiplicity (\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR=1).
4872.ie n .IP "8 \- full \s-1API\s0" 4
4873.el .IP "\f(CW8\fR \- full \s-1API\s0" 4
4874.IX Item "8 - full API"
4875This enables a lot of the \*(L"lesser used\*(R" \s-1API\s0 functions. See \f(CW\*(C`ev.h\*(C'\fR for
4876details on which parts of the \s-1API\s0 are still available without this
4877feature, and do not complain if this subset changes over time.
4878.ie n .IP "16 \- enable all optional watcher types" 4
4879.el .IP "\f(CW16\fR \- enable all optional watcher types" 4
4880.IX Item "16 - enable all optional watcher types"
4881Enables all optional watcher types. If you want to selectively enable
4882only some watcher types other than I/O and timers (e.g. prepare,
4883embed, async, child...) you can enable them manually by defining
4884\&\f(CW\*(C`EV_watchertype_ENABLE\*(C'\fR to \f(CW1\fR instead.
4885.ie n .IP "32 \- enable all backends" 4
4886.el .IP "\f(CW32\fR \- enable all backends" 4
4887.IX Item "32 - enable all backends"
4888This enables all backends \- without this feature, you need to enable at
4889least one backend manually (\f(CW\*(C`EV_USE_SELECT\*(C'\fR is a good choice).
4890.ie n .IP "64 \- enable OS-specific ""helper"" APIs" 4
4891.el .IP "\f(CW64\fR \- enable OS-specific ``helper'' APIs" 4
4892.IX Item "64 - enable OS-specific helper APIs"
4893Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
4894default.
4895.RE
4896.RS 4
4897.Sp
4898Compiling with \f(CW\*(C`gcc \-Os \-DEV_STANDALONE \-DEV_USE_EPOLL=1 \-DEV_FEATURES=0\*(C'\fR
4899reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
4900code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
4901watchers, timers and monotonic clock support.
4902.Sp
4903With an intelligent-enough linker (gcc+binutils are intelligent enough
4904when you use \f(CW\*(C`\-Wl,\-\-gc\-sections \-ffunction\-sections\*(C'\fR) functions unused by
4905your program might be left out as well \- a binary starting a timer and an
4906I/O watcher then might come out at only 5Kb.
4907.RE
4908.IP "\s-1EV_API_STATIC\s0" 4
4909.IX Item "EV_API_STATIC"
4910If this symbol is defined (by default it is not), then all identifiers
4911will have static linkage. This means that libev will not export any
4912identifiers, and you cannot link against libev anymore. This can be useful
4913when you embed libev, only want to use libev functions in a single file,
4914and do not want its identifiers to be visible.
4915.Sp
4916To use this, define \f(CW\*(C`EV_API_STATIC\*(C'\fR and include \fIev.c\fR in the file that
4917wants to use libev.
4918.Sp
4919This option only works when libev is compiled with a C compiler, as \*(C+
4920doesn't support the required declaration syntax.
4921.IP "\s-1EV_AVOID_STDIO\s0" 4
4922.IX Item "EV_AVOID_STDIO"
4923If this is set to \f(CW1\fR at compiletime, then libev will avoid using stdio
4924functions (printf, scanf, perror etc.). This will increase the code size
4925somewhat, but if your program doesn't otherwise depend on stdio and your
4926libc allows it, this avoids linking in the stdio library which is quite
4927big.
4928.Sp
4929Note that error messages might become less precise when this option is
4930enabled.
4931.IP "\s-1EV_NSIG\s0" 4
4932.IX Item "EV_NSIG"
4933The highest supported signal number, +1 (or, the number of
4934signals): Normally, libev tries to deduce the maximum number of signals
4935automatically, but sometimes this fails, in which case it can be
4936specified. Also, using a lower number than detected (\f(CW32\fR should be
4937good for about any system in existence) can save some memory, as libev
4938statically allocates some 12\-24 bytes per signal number.
4939.IP "\s-1EV_PID_HASHSIZE\s0" 4
4940.IX Item "EV_PID_HASHSIZE"
4941\&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by
4942pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR disabled),
4943usually more than enough. If you need to manage thousands of children you
4944might want to increase this value (\fImust\fR be a power of two).
4945.IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4
4946.IX Item "EV_INOTIFY_HASHSIZE"
4947\&\f(CW\*(C`ev_stat\*(C'\fR watchers use a small hash table to distribute workload by
4948inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR
4949disabled), usually more than enough. If you need to manage thousands of
4950\&\f(CW\*(C`ev_stat\*(C'\fR watchers you might want to increase this value (\fImust\fR be a
4951power of two).
4952.IP "\s-1EV_USE_4HEAP\s0" 4
4953.IX Item "EV_USE_4HEAP"
4954Heaps are not very cache-efficient. To improve the cache-efficiency of the
4955timer and periodics heaps, libev uses a 4\-heap when this symbol is defined
4956to \f(CW1\fR. The 4\-heap uses more complicated (longer) code but has noticeably
4957faster performance with many (thousands) of watchers.
4958.Sp
4959The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4960will be \f(CW0\fR.
4961.IP "\s-1EV_HEAP_CACHE_AT\s0" 4
4962.IX Item "EV_HEAP_CACHE_AT"
4963Heaps are not very cache-efficient. To improve the cache-efficiency of the
4964timer and periodics heaps, libev can cache the timestamp (\fIat\fR) within
4965the heap structure (selected by defining \f(CW\*(C`EV_HEAP_CACHE_AT\*(C'\fR to \f(CW1\fR),
4966which uses 8\-12 bytes more per watcher and a few hundred bytes more code,
4967but avoids random read accesses on heap changes. This improves performance
4968noticeably with many (hundreds) of watchers.
4969.Sp
4970The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4971will be \f(CW0\fR.
4972.IP "\s-1EV_VERIFY\s0" 4
4973.IX Item "EV_VERIFY"
4974Controls how much internal verification (see \f(CW\*(C`ev_verify ()\*(C'\fR) will
4975be done: If set to \f(CW0\fR, no internal verification code will be compiled
4976in. If set to \f(CW1\fR, then verification code will be compiled in, but not
4977called. If set to \f(CW2\fR, then the internal verification code will be
4978called once per loop, which can slow down libev. If set to \f(CW3\fR, then the
4979verification code will be called very frequently, which will slow down
4980libev considerably.
4981.Sp
4982The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4983will be \f(CW0\fR.
1760.IP "\s-1EV_COMMON\s0" 4 4984.IP "\s-1EV_COMMON\s0" 4
1761.IX Item "EV_COMMON" 4985.IX Item "EV_COMMON"
1762By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining 4986By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining
1763this macro to a something else you can include more and other types of 4987this macro to something else you can include more and other types of
1764members. You have to define it each time you include one of the files, 4988members. You have to define it each time you include one of the files,
1765though, and it must be identical each time. 4989though, and it must be identical each time.
1766.Sp 4990.Sp
1767For example, the perl \s-1EV\s0 module uses something like this: 4991For example, the perl \s-1EV\s0 module uses something like this:
1768.Sp 4992.Sp
1769.Vb 3 4993.Vb 3
1770\& #define EV_COMMON \e 4994\& #define EV_COMMON \e
1771\& SV *self; /* contains this struct */ \e 4995\& SV *self; /* contains this struct */ \e
1772\& SV *cb_sv, *fh /* note no trailing ";" */ 4996\& SV *cb_sv, *fh /* note no trailing ";" */
1773.Ve 4997.Ve
1774.IP "\s-1EV_CB_DECLARE\s0(type)" 4 4998.IP "\s-1EV_CB_DECLARE \s0(type)" 4
1775.IX Item "EV_CB_DECLARE(type)" 4999.IX Item "EV_CB_DECLARE (type)"
1776.PD 0 5000.PD 0
1777.IP "\s-1EV_CB_INVOKE\s0(watcher,revents)" 4 5001.IP "\s-1EV_CB_INVOKE \s0(watcher, revents)" 4
1778.IX Item "EV_CB_INVOKE(watcher,revents)" 5002.IX Item "EV_CB_INVOKE (watcher, revents)"
1779.IP "ev_set_cb(ev,cb)" 4 5003.IP "ev_set_cb (ev, cb)" 4
1780.IX Item "ev_set_cb(ev,cb)" 5004.IX Item "ev_set_cb (ev, cb)"
1781.PD 5005.PD
1782Can be used to change the callback member declaration in each watcher, 5006Can be used to change the callback member declaration in each watcher,
1783and the way callbacks are invoked and set. Must expand to a struct member 5007and the way callbacks are invoked and set. Must expand to a struct member
1784definition and a statement, respectively. See the \fIev.v\fR header file for 5008definition and a statement, respectively. See the \fIev.h\fR header file for
1785their default definitions. One possible use for overriding these is to 5009their default definitions. One possible use for overriding these is to
1786avoid the ev_loop pointer as first argument in all cases, or to use method 5010avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use
1787calls instead of plain function calls in \*(C+. 5011method calls instead of plain function calls in \*(C+.
5012.SS "\s-1EXPORTED API SYMBOLS\s0"
5013.IX Subsection "EXPORTED API SYMBOLS"
5014If you need to re-export the \s-1API \s0(e.g. via a \s-1DLL\s0) and you need a list of
5015exported symbols, you can use the provided \fISymbol.*\fR files which list
5016all public symbols, one per line:
5017.PP
5018.Vb 2
5019\& Symbols.ev for libev proper
5020\& Symbols.event for the libevent emulation
5021.Ve
5022.PP
5023This can also be used to rename all public symbols to avoid clashes with
5024multiple versions of libev linked together (which is obviously bad in
5025itself, but sometimes it is inconvenient to avoid this).
5026.PP
5027A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to
5028include before including \fIev.h\fR:
5029.PP
5030.Vb 1
5031\& <Symbols.ev sed \-e "s/.*/#define & myprefix_&/" >wrap.h
5032.Ve
5033.PP
5034This would create a file \fIwrap.h\fR which essentially looks like this:
5035.PP
5036.Vb 4
5037\& #define ev_backend myprefix_ev_backend
5038\& #define ev_check_start myprefix_ev_check_start
5039\& #define ev_check_stop myprefix_ev_check_stop
5040\& ...
5041.Ve
1788.Sh "\s-1EXAMPLES\s0" 5042.SS "\s-1EXAMPLES\s0"
1789.IX Subsection "EXAMPLES" 5043.IX Subsection "EXAMPLES"
1790For a real-world example of a program the includes libev 5044For a real-world example of a program the includes libev
1791verbatim, you can have a look at the \s-1EV\s0 perl module 5045verbatim, you can have a look at the \s-1EV\s0 perl module
1792(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in 5046(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
1793the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public 5047the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public
1794interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file 5048interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file
1795will be compiled. It is pretty complex because it provides its own header 5049will be compiled. It is pretty complex because it provides its own header
1796file. 5050file.
1797.Sp 5051.PP
1798The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file 5052The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file
1799that everybody includes and which overrides some autoconf choices: 5053that everybody includes and which overrides some configure choices:
1800.Sp 5054.PP
1801.Vb 4 5055.Vb 8
5056\& #define EV_FEATURES 8
5057\& #define EV_USE_SELECT 1
5058\& #define EV_PREPARE_ENABLE 1
5059\& #define EV_IDLE_ENABLE 1
5060\& #define EV_SIGNAL_ENABLE 1
5061\& #define EV_CHILD_ENABLE 1
1802\& #define EV_USE_POLL 0 5062\& #define EV_USE_STDEXCEPT 0
1803\& #define EV_MULTIPLICITY 0
1804\& #define EV_PERIODICS 0
1805\& #define EV_CONFIG_H <config.h> 5063\& #define EV_CONFIG_H <config.h>
1806.Ve 5064\&
1807.Sp
1808.Vb 1
1809\& #include "ev++.h" 5065\& #include "ev++.h"
1810.Ve 5066.Ve
1811.Sp 5067.PP
1812And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled: 5068And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled:
1813.Sp 5069.PP
1814.Vb 2 5070.Vb 2
1815\& #include "ev_cpp.h" 5071\& #include "ev_cpp.h"
1816\& #include "ev.c" 5072\& #include "ev.c"
1817.Ve 5073.Ve
5074.SH "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT"
5075.IX Header "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT"
5076.SS "\s-1THREADS AND COROUTINES\s0"
5077.IX Subsection "THREADS AND COROUTINES"
5078\fI\s-1THREADS\s0\fR
5079.IX Subsection "THREADS"
5080.PP
5081All libev functions are reentrant and thread-safe unless explicitly
5082documented otherwise, but libev implements no locking itself. This means
5083that you can use as many loops as you want in parallel, as long as there
5084are no concurrent calls into any libev function with the same loop
5085parameter (\f(CW\*(C`ev_default_*\*(C'\fR calls have an implicit default loop parameter,
5086of course): libev guarantees that different event loops share no data
5087structures that need any locking.
5088.PP
5089Or to put it differently: calls with different loop parameters can be done
5090concurrently from multiple threads, calls with the same loop parameter
5091must be done serially (but can be done from different threads, as long as
5092only one thread ever is inside a call at any point in time, e.g. by using
5093a mutex per loop).
5094.PP
5095Specifically to support threads (and signal handlers), libev implements
5096so-called \f(CW\*(C`ev_async\*(C'\fR watchers, which allow some limited form of
5097concurrency on the same event loop, namely waking it up \*(L"from the
5098outside\*(R".
5099.PP
5100If you want to know which design (one loop, locking, or multiple loops
5101without or something else still) is best for your problem, then I cannot
5102help you, but here is some generic advice:
5103.IP "\(bu" 4
5104most applications have a main thread: use the default libev loop
5105in that thread, or create a separate thread running only the default loop.
5106.Sp
5107This helps integrating other libraries or software modules that use libev
5108themselves and don't care/know about threading.
5109.IP "\(bu" 4
5110one loop per thread is usually a good model.
5111.Sp
5112Doing this is almost never wrong, sometimes a better-performance model
5113exists, but it is always a good start.
5114.IP "\(bu" 4
5115other models exist, such as the leader/follower pattern, where one
5116loop is handed through multiple threads in a kind of round-robin fashion.
5117.Sp
5118Choosing a model is hard \- look around, learn, know that usually you can do
5119better than you currently do :\-)
5120.IP "\(bu" 4
5121often you need to talk to some other thread which blocks in the
5122event loop.
5123.Sp
5124\&\f(CW\*(C`ev_async\*(C'\fR watchers can be used to wake them up from other threads safely
5125(or from signal contexts...).
5126.Sp
5127An example use would be to communicate signals or other events that only
5128work in the default loop by registering the signal watcher with the
5129default loop and triggering an \f(CW\*(C`ev_async\*(C'\fR watcher from the default loop
5130watcher callback into the event loop interested in the signal.
5131.PP
5132See also \*(L"\s-1THREAD LOCKING EXAMPLE\*(R"\s0.
5133.PP
5134\fI\s-1COROUTINES\s0\fR
5135.IX Subsection "COROUTINES"
5136.PP
5137Libev is very accommodating to coroutines (\*(L"cooperative threads\*(R"):
5138libev fully supports nesting calls to its functions from different
5139coroutines (e.g. you can call \f(CW\*(C`ev_run\*(C'\fR on the same loop from two
5140different coroutines, and switch freely between both coroutines running
5141the loop, as long as you don't confuse yourself). The only exception is
5142that you must not do this from \f(CW\*(C`ev_periodic\*(C'\fR reschedule callbacks.
5143.PP
5144Care has been taken to ensure that libev does not keep local state inside
5145\&\f(CW\*(C`ev_run\*(C'\fR, and other calls do not usually allow for coroutine switches as
5146they do not call any callbacks.
5147.SS "\s-1COMPILER WARNINGS\s0"
5148.IX Subsection "COMPILER WARNINGS"
5149Depending on your compiler and compiler settings, you might get no or a
5150lot of warnings when compiling libev code. Some people are apparently
5151scared by this.
5152.PP
5153However, these are unavoidable for many reasons. For one, each compiler
5154has different warnings, and each user has different tastes regarding
5155warning options. \*(L"Warn-free\*(R" code therefore cannot be a goal except when
5156targeting a specific compiler and compiler-version.
5157.PP
5158Another reason is that some compiler warnings require elaborate
5159workarounds, or other changes to the code that make it less clear and less
5160maintainable.
5161.PP
5162And of course, some compiler warnings are just plain stupid, or simply
5163wrong (because they don't actually warn about the condition their message
5164seems to warn about). For example, certain older gcc versions had some
5165warnings that resulted in an extreme number of false positives. These have
5166been fixed, but some people still insist on making code warn-free with
5167such buggy versions.
5168.PP
5169While libev is written to generate as few warnings as possible,
5170\&\*(L"warn-free\*(R" code is not a goal, and it is recommended not to build libev
5171with any compiler warnings enabled unless you are prepared to cope with
5172them (e.g. by ignoring them). Remember that warnings are just that:
5173warnings, not errors, or proof of bugs.
5174.SS "\s-1VALGRIND\s0"
5175.IX Subsection "VALGRIND"
5176Valgrind has a special section here because it is a popular tool that is
5177highly useful. Unfortunately, valgrind reports are very hard to interpret.
5178.PP
5179If you think you found a bug (memory leak, uninitialised data access etc.)
5180in libev, then check twice: If valgrind reports something like:
5181.PP
5182.Vb 3
5183\& ==2274== definitely lost: 0 bytes in 0 blocks.
5184\& ==2274== possibly lost: 0 bytes in 0 blocks.
5185\& ==2274== still reachable: 256 bytes in 1 blocks.
5186.Ve
5187.PP
5188Then there is no memory leak, just as memory accounted to global variables
5189is not a memleak \- the memory is still being referenced, and didn't leak.
5190.PP
5191Similarly, under some circumstances, valgrind might report kernel bugs
5192as if it were a bug in libev (e.g. in realloc or in the poll backend,
5193although an acceptable workaround has been found here), or it might be
5194confused.
5195.PP
5196Keep in mind that valgrind is a very good tool, but only a tool. Don't
5197make it into some kind of religion.
5198.PP
5199If you are unsure about something, feel free to contact the mailing list
5200with the full valgrind report and an explanation on why you think this
5201is a bug in libev (best check the archives, too :). However, don't be
5202annoyed when you get a brisk \*(L"this is no bug\*(R" answer and take the chance
5203of learning how to interpret valgrind properly.
5204.PP
5205If you need, for some reason, empty reports from valgrind for your project
5206I suggest using suppression lists.
5207.SH "PORTABILITY NOTES"
5208.IX Header "PORTABILITY NOTES"
5209.SS "\s-1GNU/LINUX 32 BIT LIMITATIONS\s0"
5210.IX Subsection "GNU/LINUX 32 BIT LIMITATIONS"
5211GNU/Linux is the only common platform that supports 64 bit file/large file
5212interfaces but \fIdisables\fR them by default.
5213.PP
5214That means that libev compiled in the default environment doesn't support
5215files larger than 2GiB or so, which mainly affects \f(CW\*(C`ev_stat\*(C'\fR watchers.
5216.PP
5217Unfortunately, many programs try to work around this GNU/Linux issue
5218by enabling the large file \s-1API,\s0 which makes them incompatible with the
5219standard libev compiled for their system.
5220.PP
5221Likewise, libev cannot enable the large file \s-1API\s0 itself as this would
5222suddenly make it incompatible to the default compile time environment,
5223i.e. all programs not using special compile switches.
5224.SS "\s-1OS/X AND DARWIN BUGS\s0"
5225.IX Subsection "OS/X AND DARWIN BUGS"
5226The whole thing is a bug if you ask me \- basically any system interface
5227you touch is broken, whether it is locales, poll, kqueue or even the
5228OpenGL drivers.
5229.PP
5230\fI\f(CI\*(C`kqueue\*(C'\fI is buggy\fR
5231.IX Subsection "kqueue is buggy"
5232.PP
5233The kqueue syscall is broken in all known versions \- most versions support
5234only sockets, many support pipes.
5235.PP
5236Libev tries to work around this by not using \f(CW\*(C`kqueue\*(C'\fR by default on this
5237rotten platform, but of course you can still ask for it when creating a
5238loop \- embedding a socket-only kqueue loop into a select-based one is
5239probably going to work well.
5240.PP
5241\fI\f(CI\*(C`poll\*(C'\fI is buggy\fR
5242.IX Subsection "poll is buggy"
5243.PP
5244Instead of fixing \f(CW\*(C`kqueue\*(C'\fR, Apple replaced their (working) \f(CW\*(C`poll\*(C'\fR
5245implementation by something calling \f(CW\*(C`kqueue\*(C'\fR internally around the 10.5.6
5246release, so now \f(CW\*(C`kqueue\*(C'\fR \fIand\fR \f(CW\*(C`poll\*(C'\fR are broken.
5247.PP
5248Libev tries to work around this by not using \f(CW\*(C`poll\*(C'\fR by default on
5249this rotten platform, but of course you can still ask for it when creating
5250a loop.
5251.PP
5252\fI\f(CI\*(C`select\*(C'\fI is buggy\fR
5253.IX Subsection "select is buggy"
5254.PP
5255All that's left is \f(CW\*(C`select\*(C'\fR, and of course Apple found a way to fuck this
5256one up as well: On \s-1OS/X, \s0\f(CW\*(C`select\*(C'\fR actively limits the number of file
5257descriptors you can pass in to 1024 \- your program suddenly crashes when
5258you use more.
5259.PP
5260There is an undocumented \*(L"workaround\*(R" for this \- defining
5261\&\f(CW\*(C`_DARWIN_UNLIMITED_SELECT\*(C'\fR, which libev tries to use, so select \fIshould\fR
5262work on \s-1OS/X.\s0
5263.SS "\s-1SOLARIS PROBLEMS AND WORKAROUNDS\s0"
5264.IX Subsection "SOLARIS PROBLEMS AND WORKAROUNDS"
5265\fI\f(CI\*(C`errno\*(C'\fI reentrancy\fR
5266.IX Subsection "errno reentrancy"
5267.PP
5268The default compile environment on Solaris is unfortunately so
5269thread-unsafe that you can't even use components/libraries compiled
5270without \f(CW\*(C`\-D_REENTRANT\*(C'\fR in a threaded program, which, of course, isn't
5271defined by default. A valid, if stupid, implementation choice.
5272.PP
5273If you want to use libev in threaded environments you have to make sure
5274it's compiled with \f(CW\*(C`_REENTRANT\*(C'\fR defined.
5275.PP
5276\fIEvent port backend\fR
5277.IX Subsection "Event port backend"
5278.PP
5279The scalable event interface for Solaris is called \*(L"event
5280ports\*(R". Unfortunately, this mechanism is very buggy in all major
5281releases. If you run into high \s-1CPU\s0 usage, your program freezes or you get
5282a large number of spurious wakeups, make sure you have all the relevant
5283and latest kernel patches applied. No, I don't know which ones, but there
5284are multiple ones to apply, and afterwards, event ports actually work
5285great.
5286.PP
5287If you can't get it to work, you can try running the program by setting
5288the environment variable \f(CW\*(C`LIBEV_FLAGS=3\*(C'\fR to only allow \f(CW\*(C`poll\*(C'\fR and
5289\&\f(CW\*(C`select\*(C'\fR backends.
5290.SS "\s-1AIX POLL BUG\s0"
5291.IX Subsection "AIX POLL BUG"
5292\&\s-1AIX\s0 unfortunately has a broken \f(CW\*(C`poll.h\*(C'\fR header. Libev works around
5293this by trying to avoid the poll backend altogether (i.e. it's not even
5294compiled in), which normally isn't a big problem as \f(CW\*(C`select\*(C'\fR works fine
5295with large bitsets on \s-1AIX,\s0 and \s-1AIX\s0 is dead anyway.
5296.SS "\s-1WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS\s0"
5297.IX Subsection "WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS"
5298\fIGeneral issues\fR
5299.IX Subsection "General issues"
5300.PP
5301Win32 doesn't support any of the standards (e.g. \s-1POSIX\s0) that libev
5302requires, and its I/O model is fundamentally incompatible with the \s-1POSIX\s0
5303model. Libev still offers limited functionality on this platform in
5304the form of the \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR backend, and only supports socket
5305descriptors. This only applies when using Win32 natively, not when using
5306e.g. cygwin. Actually, it only applies to the microsofts own compilers,
5307as every compiler comes with a slightly differently broken/incompatible
5308environment.
5309.PP
5310Lifting these limitations would basically require the full
5311re-implementation of the I/O system. If you are into this kind of thing,
5312then note that glib does exactly that for you in a very portable way (note
5313also that glib is the slowest event library known to man).
5314.PP
5315There is no supported compilation method available on windows except
5316embedding it into other applications.
5317.PP
5318Sensible signal handling is officially unsupported by Microsoft \- libev
5319tries its best, but under most conditions, signals will simply not work.
5320.PP
5321Not a libev limitation but worth mentioning: windows apparently doesn't
5322accept large writes: instead of resulting in a partial write, windows will
5323either accept everything or return \f(CW\*(C`ENOBUFS\*(C'\fR if the buffer is too large,
5324so make sure you only write small amounts into your sockets (less than a
5325megabyte seems safe, but this apparently depends on the amount of memory
5326available).
5327.PP
5328Due to the many, low, and arbitrary limits on the win32 platform and
5329the abysmal performance of winsockets, using a large number of sockets
5330is not recommended (and not reasonable). If your program needs to use
5331more than a hundred or so sockets, then likely it needs to use a totally
5332different implementation for windows, as libev offers the \s-1POSIX\s0 readiness
5333notification model, which cannot be implemented efficiently on windows
5334(due to Microsoft monopoly games).
5335.PP
5336A typical way to use libev under windows is to embed it (see the embedding
5337section for details) and use the following \fIevwrap.h\fR header file instead
5338of \fIev.h\fR:
5339.PP
5340.Vb 2
5341\& #define EV_STANDALONE /* keeps ev from requiring config.h */
5342\& #define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
5343\&
5344\& #include "ev.h"
5345.Ve
5346.PP
5347And compile the following \fIevwrap.c\fR file into your project (make sure
5348you do \fInot\fR compile the \fIev.c\fR or any other embedded source files!):
5349.PP
5350.Vb 2
5351\& #include "evwrap.h"
5352\& #include "ev.c"
5353.Ve
5354.PP
5355\fIThe winsocket \f(CI\*(C`select\*(C'\fI function\fR
5356.IX Subsection "The winsocket select function"
5357.PP
5358The winsocket \f(CW\*(C`select\*(C'\fR function doesn't follow \s-1POSIX\s0 in that it
5359requires socket \fIhandles\fR and not socket \fIfile descriptors\fR (it is
5360also extremely buggy). This makes select very inefficient, and also
5361requires a mapping from file descriptors to socket handles (the Microsoft
5362C runtime provides the function \f(CW\*(C`_open_osfhandle\*(C'\fR for this). See the
5363discussion of the \f(CW\*(C`EV_SELECT_USE_FD_SET\*(C'\fR, \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR and
5364\&\f(CW\*(C`EV_FD_TO_WIN32_HANDLE\*(C'\fR preprocessor symbols for more info.
5365.PP
5366The configuration for a \*(L"naked\*(R" win32 using the Microsoft runtime
5367libraries and raw winsocket select is:
5368.PP
5369.Vb 2
5370\& #define EV_USE_SELECT 1
5371\& #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
5372.Ve
5373.PP
5374Note that winsockets handling of fd sets is O(n), so you can easily get a
5375complexity in the O(nX) range when using win32.
5376.PP
5377\fILimited number of file descriptors\fR
5378.IX Subsection "Limited number of file descriptors"
5379.PP
5380Windows has numerous arbitrary (and low) limits on things.
5381.PP
5382Early versions of winsocket's select only supported waiting for a maximum
5383of \f(CW64\fR handles (probably owning to the fact that all windows kernels
5384can only wait for \f(CW64\fR things at the same time internally; Microsoft
5385recommends spawning a chain of threads and wait for 63 handles and the
5386previous thread in each. Sounds great!).
5387.PP
5388Newer versions support more handles, but you need to define \f(CW\*(C`FD_SETSIZE\*(C'\fR
5389to some high number (e.g. \f(CW2048\fR) before compiling the winsocket select
5390call (which might be in libev or elsewhere, for example, perl and many
5391other interpreters do their own select emulation on windows).
5392.PP
5393Another limit is the number of file descriptors in the Microsoft runtime
5394libraries, which by default is \f(CW64\fR (there must be a hidden \fI64\fR
5395fetish or something like this inside Microsoft). You can increase this
5396by calling \f(CW\*(C`_setmaxstdio\*(C'\fR, which can increase this limit to \f(CW2048\fR
5397(another arbitrary limit), but is broken in many versions of the Microsoft
5398runtime libraries. This might get you to about \f(CW512\fR or \f(CW2048\fR sockets
5399(depending on windows version and/or the phase of the moon). To get more,
5400you need to wrap all I/O functions and provide your own fd management, but
5401the cost of calling select (O(nX)) will likely make this unworkable.
5402.SS "\s-1PORTABILITY REQUIREMENTS\s0"
5403.IX Subsection "PORTABILITY REQUIREMENTS"
5404In addition to a working ISO-C implementation and of course the
5405backend-specific APIs, libev relies on a few additional extensions:
5406.ie n .IP """void (*)(ev_watcher_type *, int revents)"" must have compatible calling conventions regardless of ""ev_watcher_type *""." 4
5407.el .IP "\f(CWvoid (*)(ev_watcher_type *, int revents)\fR must have compatible calling conventions regardless of \f(CWev_watcher_type *\fR." 4
5408.IX Item "void (*)(ev_watcher_type *, int revents) must have compatible calling conventions regardless of ev_watcher_type *."
5409Libev assumes not only that all watcher pointers have the same internal
5410structure (guaranteed by \s-1POSIX\s0 but not by \s-1ISO C\s0 for example), but it also
5411assumes that the same (machine) code can be used to call any watcher
5412callback: The watcher callbacks have different type signatures, but libev
5413calls them using an \f(CW\*(C`ev_watcher *\*(C'\fR internally.
5414.IP "pointer accesses must be thread-atomic" 4
5415.IX Item "pointer accesses must be thread-atomic"
5416Accessing a pointer value must be atomic, it must both be readable and
5417writable in one piece \- this is the case on all current architectures.
5418.ie n .IP """sig_atomic_t volatile"" must be thread-atomic as well" 4
5419.el .IP "\f(CWsig_atomic_t volatile\fR must be thread-atomic as well" 4
5420.IX Item "sig_atomic_t volatile must be thread-atomic as well"
5421The type \f(CW\*(C`sig_atomic_t volatile\*(C'\fR (or whatever is defined as
5422\&\f(CW\*(C`EV_ATOMIC_T\*(C'\fR) must be atomic with respect to accesses from different
5423threads. This is not part of the specification for \f(CW\*(C`sig_atomic_t\*(C'\fR, but is
5424believed to be sufficiently portable.
5425.ie n .IP """sigprocmask"" must work in a threaded environment" 4
5426.el .IP "\f(CWsigprocmask\fR must work in a threaded environment" 4
5427.IX Item "sigprocmask must work in a threaded environment"
5428Libev uses \f(CW\*(C`sigprocmask\*(C'\fR to temporarily block signals. This is not
5429allowed in a threaded program (\f(CW\*(C`pthread_sigmask\*(C'\fR has to be used). Typical
5430pthread implementations will either allow \f(CW\*(C`sigprocmask\*(C'\fR in the \*(L"main
5431thread\*(R" or will block signals process-wide, both behaviours would
5432be compatible with libev. Interaction between \f(CW\*(C`sigprocmask\*(C'\fR and
5433\&\f(CW\*(C`pthread_sigmask\*(C'\fR could complicate things, however.
5434.Sp
5435The most portable way to handle signals is to block signals in all threads
5436except the initial one, and run the signal handling loop in the initial
5437thread as well.
5438.ie n .IP """long"" must be large enough for common memory allocation sizes" 4
5439.el .IP "\f(CWlong\fR must be large enough for common memory allocation sizes" 4
5440.IX Item "long must be large enough for common memory allocation sizes"
5441To improve portability and simplify its \s-1API,\s0 libev uses \f(CW\*(C`long\*(C'\fR internally
5442instead of \f(CW\*(C`size_t\*(C'\fR when allocating its data structures. On non-POSIX
5443systems (Microsoft...) this might be unexpectedly low, but is still at
5444least 31 bits everywhere, which is enough for hundreds of millions of
5445watchers.
5446.ie n .IP """double"" must hold a time value in seconds with enough accuracy" 4
5447.el .IP "\f(CWdouble\fR must hold a time value in seconds with enough accuracy" 4
5448.IX Item "double must hold a time value in seconds with enough accuracy"
5449The type \f(CW\*(C`double\*(C'\fR is used to represent timestamps. It is required to
5450have at least 51 bits of mantissa (and 9 bits of exponent), which is
5451good enough for at least into the year 4000 with millisecond accuracy
5452(the design goal for libev). This requirement is overfulfilled by
5453implementations using \s-1IEEE 754,\s0 which is basically all existing ones.
5454.Sp
5455With \s-1IEEE 754\s0 doubles, you get microsecond accuracy until at least the
5456year 2255 (and millisecond accuracy till the year 287396 \- by then, libev
5457is either obsolete or somebody patched it to use \f(CW\*(C`long double\*(C'\fR or
5458something like that, just kidding).
5459.PP
5460If you know of other additional requirements drop me a note.
5461.SH "ALGORITHMIC COMPLEXITIES"
5462.IX Header "ALGORITHMIC COMPLEXITIES"
5463In this section the complexities of (many of) the algorithms used inside
5464libev will be documented. For complexity discussions about backends see
5465the documentation for \f(CW\*(C`ev_default_init\*(C'\fR.
5466.PP
5467All of the following are about amortised time: If an array needs to be
5468extended, libev needs to realloc and move the whole array, but this
5469happens asymptotically rarer with higher number of elements, so O(1) might
5470mean that libev does a lengthy realloc operation in rare cases, but on
5471average it is much faster and asymptotically approaches constant time.
5472.IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4
5473.IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)"
5474This means that, when you have a watcher that triggers in one hour and
5475there are 100 watchers that would trigger before that, then inserting will
5476have to skip roughly seven (\f(CW\*(C`ld 100\*(C'\fR) of these watchers.
5477.IP "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 4
5478.IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)"
5479That means that changing a timer costs less than removing/adding them,
5480as only the relative motion in the event queue has to be paid for.
5481.IP "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)" 4
5482.IX Item "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)"
5483These just add the watcher into an array or at the head of a list.
5484.IP "Stopping check/prepare/idle/fork/async watchers: O(1)" 4
5485.IX Item "Stopping check/prepare/idle/fork/async watchers: O(1)"
5486.PD 0
5487.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4
5488.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))"
5489.PD
5490These watchers are stored in lists, so they need to be walked to find the
5491correct watcher to remove. The lists are usually short (you don't usually
5492have many watchers waiting for the same fd or signal: one is typical, two
5493is rare).
5494.IP "Finding the next timer in each loop iteration: O(1)" 4
5495.IX Item "Finding the next timer in each loop iteration: O(1)"
5496By virtue of using a binary or 4\-heap, the next timer is always found at a
5497fixed position in the storage array.
5498.IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4
5499.IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)"
5500A change means an I/O watcher gets started or stopped, which requires
5501libev to recalculate its status (and possibly tell the kernel, depending
5502on backend and whether \f(CW\*(C`ev_io_set\*(C'\fR was used).
5503.IP "Activating one watcher (putting it into the pending state): O(1)" 4
5504.IX Item "Activating one watcher (putting it into the pending state): O(1)"
5505.PD 0
5506.IP "Priority handling: O(number_of_priorities)" 4
5507.IX Item "Priority handling: O(number_of_priorities)"
5508.PD
5509Priorities are implemented by allocating some space for each
5510priority. When doing priority-based operations, libev usually has to
5511linearly search all the priorities, but starting/stopping and activating
5512watchers becomes O(1) with respect to priority handling.
5513.IP "Sending an ev_async: O(1)" 4
5514.IX Item "Sending an ev_async: O(1)"
5515.PD 0
5516.IP "Processing ev_async_send: O(number_of_async_watchers)" 4
5517.IX Item "Processing ev_async_send: O(number_of_async_watchers)"
5518.IP "Processing signals: O(max_signal_number)" 4
5519.IX Item "Processing signals: O(max_signal_number)"
5520.PD
5521Sending involves a system call \fIiff\fR there were no other \f(CW\*(C`ev_async_send\*(C'\fR
5522calls in the current loop iteration and the loop is currently
5523blocked. Checking for async and signal events involves iterating over all
5524running async watchers or all signal numbers.
5525.SH "PORTING FROM LIBEV 3.X TO 4.X"
5526.IX Header "PORTING FROM LIBEV 3.X TO 4.X"
5527The major version 4 introduced some incompatible changes to the \s-1API.\s0
5528.PP
5529At the moment, the \f(CW\*(C`ev.h\*(C'\fR header file provides compatibility definitions
5530for all changes, so most programs should still compile. The compatibility
5531layer might be removed in later versions of libev, so better update to the
5532new \s-1API\s0 early than late.
5533.ie n .IP """EV_COMPAT3"" backwards compatibility mechanism" 4
5534.el .IP "\f(CWEV_COMPAT3\fR backwards compatibility mechanism" 4
5535.IX Item "EV_COMPAT3 backwards compatibility mechanism"
5536The backward compatibility mechanism can be controlled by
5537\&\f(CW\*(C`EV_COMPAT3\*(C'\fR. See \*(L"\s-1PREPROCESSOR SYMBOLS/MACROS\*(R"\s0 in the \*(L"\s-1EMBEDDING\*(R"\s0
5538section.
5539.ie n .IP """ev_default_destroy"" and ""ev_default_fork"" have been removed" 4
5540.el .IP "\f(CWev_default_destroy\fR and \f(CWev_default_fork\fR have been removed" 4
5541.IX Item "ev_default_destroy and ev_default_fork have been removed"
5542These calls can be replaced easily by their \f(CW\*(C`ev_loop_xxx\*(C'\fR counterparts:
5543.Sp
5544.Vb 2
5545\& ev_loop_destroy (EV_DEFAULT_UC);
5546\& ev_loop_fork (EV_DEFAULT);
5547.Ve
5548.IP "function/symbol renames" 4
5549.IX Item "function/symbol renames"
5550A number of functions and symbols have been renamed:
5551.Sp
5552.Vb 3
5553\& ev_loop => ev_run
5554\& EVLOOP_NONBLOCK => EVRUN_NOWAIT
5555\& EVLOOP_ONESHOT => EVRUN_ONCE
5556\&
5557\& ev_unloop => ev_break
5558\& EVUNLOOP_CANCEL => EVBREAK_CANCEL
5559\& EVUNLOOP_ONE => EVBREAK_ONE
5560\& EVUNLOOP_ALL => EVBREAK_ALL
5561\&
5562\& EV_TIMEOUT => EV_TIMER
5563\&
5564\& ev_loop_count => ev_iteration
5565\& ev_loop_depth => ev_depth
5566\& ev_loop_verify => ev_verify
5567.Ve
5568.Sp
5569Most functions working on \f(CW\*(C`struct ev_loop\*(C'\fR objects don't have an
5570\&\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
5571associated constants have been renamed to not collide with the \f(CW\*(C`struct
5572ev_loop\*(C'\fR anymore and \f(CW\*(C`EV_TIMER\*(C'\fR now follows the same naming scheme
5573as all other watcher types. Note that \f(CW\*(C`ev_loop_fork\*(C'\fR is still called
5574\&\f(CW\*(C`ev_loop_fork\*(C'\fR because it would otherwise clash with the \f(CW\*(C`ev_fork\*(C'\fR
5575typedef.
5576.ie n .IP """EV_MINIMAL"" mechanism replaced by ""EV_FEATURES""" 4
5577.el .IP "\f(CWEV_MINIMAL\fR mechanism replaced by \f(CWEV_FEATURES\fR" 4
5578.IX Item "EV_MINIMAL mechanism replaced by EV_FEATURES"
5579The preprocessor symbol \f(CW\*(C`EV_MINIMAL\*(C'\fR has been replaced by a different
5580mechanism, \f(CW\*(C`EV_FEATURES\*(C'\fR. Programs using \f(CW\*(C`EV_MINIMAL\*(C'\fR usually compile
5581and work, but the library code will of course be larger.
5582.SH "GLOSSARY"
5583.IX Header "GLOSSARY"
5584.IP "active" 4
5585.IX Item "active"
5586A watcher is active as long as it has been started and not yet stopped.
5587See \*(L"\s-1WATCHER STATES\*(R"\s0 for details.
5588.IP "application" 4
5589.IX Item "application"
5590In this document, an application is whatever is using libev.
5591.IP "backend" 4
5592.IX Item "backend"
5593The part of the code dealing with the operating system interfaces.
5594.IP "callback" 4
5595.IX Item "callback"
5596The address of a function that is called when some event has been
5597detected. Callbacks are being passed the event loop, the watcher that
5598received the event, and the actual event bitset.
5599.IP "callback/watcher invocation" 4
5600.IX Item "callback/watcher invocation"
5601The act of calling the callback associated with a watcher.
5602.IP "event" 4
5603.IX Item "event"
5604A change of state of some external event, such as data now being available
5605for reading on a file descriptor, time having passed or simply not having
5606any other events happening anymore.
5607.Sp
5608In libev, events are represented as single bits (such as \f(CW\*(C`EV_READ\*(C'\fR or
5609\&\f(CW\*(C`EV_TIMER\*(C'\fR).
5610.IP "event library" 4
5611.IX Item "event library"
5612A software package implementing an event model and loop.
5613.IP "event loop" 4
5614.IX Item "event loop"
5615An entity that handles and processes external events and converts them
5616into callback invocations.
5617.IP "event model" 4
5618.IX Item "event model"
5619The model used to describe how an event loop handles and processes
5620watchers and events.
5621.IP "pending" 4
5622.IX Item "pending"
5623A watcher is pending as soon as the corresponding event has been
5624detected. See \*(L"\s-1WATCHER STATES\*(R"\s0 for details.
5625.IP "real time" 4
5626.IX Item "real time"
5627The physical time that is observed. It is apparently strictly monotonic :)
5628.IP "wall-clock time" 4
5629.IX Item "wall-clock time"
5630The time and date as shown on clocks. Unlike real time, it can actually
5631be wrong and jump forwards and backwards, e.g. when you adjust your
5632clock.
5633.IP "watcher" 4
5634.IX Item "watcher"
5635A data structure that describes interest in certain events. Watchers need
5636to be started (attached to an event loop) before they can receive events.
1818.SH "AUTHOR" 5637.SH "AUTHOR"
1819.IX Header "AUTHOR" 5638.IX Header "AUTHOR"
1820Marc Lehmann <libev@schmorp.de>. 5639Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5640Magnusson and Emanuele Giaquinta, and minor corrections by many others.

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