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1.\" Automatically generated by Pod::Man v1.37, Pod::Parser v1.35 1.\" Automatically generated by Pod::Man 2.22 (Pod::Simple 3.07)
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129.\" ======================================================================== 124.\" ========================================================================
130.\" 125.\"
131.IX Title ""<STANDARD INPUT>" 1" 126.IX Title "LIBEV 3"
132.TH "<STANDARD INPUT>" 1 "2007-11-23" "perl v5.8.8" "User Contributed Perl Documentation" 127.TH LIBEV 3 "2009-07-15" "libev-3.7" "libev - high performance full featured event loop"
128.\" For nroff, turn off justification. Always turn off hyphenation; it makes
129.\" way too many mistakes in technical documents.
130.if n .ad l
131.nh
133.SH "NAME" 132.SH "NAME"
134libev \- a high performance full\-featured event loop written in C 133libev \- a high performance full\-featured event loop written in C
135.SH "SYNOPSIS" 134.SH "SYNOPSIS"
136.IX Header "SYNOPSIS" 135.IX Header "SYNOPSIS"
137.Vb 1 136.Vb 1
138\& #include <ev.h> 137\& #include <ev.h>
139.Ve 138.Ve
140.SH "DESCRIPTION" 139.SS "\s-1EXAMPLE\s0 \s-1PROGRAM\s0"
141.IX Header "DESCRIPTION" 140.IX Subsection "EXAMPLE PROGRAM"
141.Vb 2
142\& // a single header file is required
143\& #include <ev.h>
144\&
145\& #include <stdio.h> // for puts
146\&
147\& // every watcher type has its own typedef\*(Aqd struct
148\& // with the name ev_TYPE
149\& ev_io stdin_watcher;
150\& ev_timer timeout_watcher;
151\&
152\& // all watcher callbacks have a similar signature
153\& // this callback is called when data is readable on stdin
154\& static void
155\& stdin_cb (EV_P_ ev_io *w, int revents)
156\& {
157\& puts ("stdin ready");
158\& // for one\-shot events, one must manually stop the watcher
159\& // with its corresponding stop function.
160\& ev_io_stop (EV_A_ w);
161\&
162\& // this causes all nested ev_loop\*(Aqs to stop iterating
163\& ev_unloop (EV_A_ EVUNLOOP_ALL);
164\& }
165\&
166\& // another callback, this time for a time\-out
167\& static void
168\& timeout_cb (EV_P_ ev_timer *w, int revents)
169\& {
170\& puts ("timeout");
171\& // this causes the innermost ev_loop to stop iterating
172\& ev_unloop (EV_A_ EVUNLOOP_ONE);
173\& }
174\&
175\& int
176\& main (void)
177\& {
178\& // use the default event loop unless you have special needs
179\& struct ev_loop *loop = ev_default_loop (0);
180\&
181\& // initialise an io watcher, then start it
182\& // this one will watch for stdin to become readable
183\& ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
184\& ev_io_start (loop, &stdin_watcher);
185\&
186\& // initialise a timer watcher, then start it
187\& // simple non\-repeating 5.5 second timeout
188\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
189\& ev_timer_start (loop, &timeout_watcher);
190\&
191\& // now wait for events to arrive
192\& ev_loop (loop, 0);
193\&
194\& // unloop was called, so exit
195\& return 0;
196\& }
197.Ve
198.SH "ABOUT THIS DOCUMENT"
199.IX Header "ABOUT THIS DOCUMENT"
200This document documents the libev software package.
201.PP
202The newest version of this document is also available as an html-formatted
203web page you might find easier to navigate when reading it for the first
204time: <http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
205.PP
206While this document tries to be as complete as possible in documenting
207libev, its usage and the rationale behind its design, it is not a tutorial
208on event-based programming, nor will it introduce event-based programming
209with libev.
210.PP
211Familarity with event based programming techniques in general is assumed
212throughout this document.
213.SH "ABOUT LIBEV"
214.IX Header "ABOUT LIBEV"
142Libev is an event loop: you register interest in certain events (such as a 215Libev 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 216file descriptor being readable or a timeout occurring), and it will manage
144these event sources and provide your program with events. 217these event sources and provide your program with events.
145.PP 218.PP
146To do this, it must take more or less complete control over your process 219To 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 220(or thread) by executing the \fIevent loop\fR handler, and will then
148communicate events via a callback mechanism. 221communicate events via a callback mechanism.
149.PP 222.PP
150You register interest in certain events by registering so-called \fIevent 223You register interest in certain events by registering so-called \fIevent
151watchers\fR, which are relatively small C structures you initialise with the 224watchers\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 225details of the event, and then hand it over to libev by \fIstarting\fR the
153watcher. 226watcher.
154.SH "FEATURES" 227.SS "\s-1FEATURES\s0"
155.IX Header "FEATURES" 228.IX Subsection "FEATURES"
156Libev supports select, poll, the linux-specific epoll and the bsd-specific 229Libev 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 230BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port mechanisms
158timers with customised rescheduling, signal events, process status change 231for 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 232(for \f(CW\*(C`ev_stat\*(C'\fR), relative timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers
160loop mechanism itself (idle, prepare and check watchers). It also is quite 233with customised rescheduling (\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals
161fast (see this benchmark comparing 234(\f(CW\*(C`ev_signal\*(C'\fR), process status change events (\f(CW\*(C`ev_child\*(C'\fR), and event
162it to libevent for example). 235watchers dealing with the event loop mechanism itself (\f(CW\*(C`ev_idle\*(C'\fR,
236\&\f(CW\*(C`ev_embed\*(C'\fR, \f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR watchers) as well as
237file watchers (\f(CW\*(C`ev_stat\*(C'\fR) and even limited support for fork events
238(\f(CW\*(C`ev_fork\*(C'\fR).
239.PP
240It also is quite fast (see this
241<benchmark> comparing it to libevent
242for example).
163.SH "CONVENTIONS" 243.SS "\s-1CONVENTIONS\s0"
164.IX Header "CONVENTIONS" 244.IX Subsection "CONVENTIONS"
165Libev is very configurable. In this manual the default configuration 245Libev is very configurable. In this manual the default (and most common)
166will be described, which supports multiple event loops. For more info 246configuration will be described, which supports multiple event loops. For
167about various configuration options please have a look at the file 247more 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 248\&\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 249for 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) 250name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`ev_loop *\*(C'\fR) will not have
171will not have this argument. 251this argument.
172.SH "TIME REPRESENTATION" 252.SS "\s-1TIME\s0 \s-1REPRESENTATION\s0"
173.IX Header "TIME REPRESENTATION" 253.IX Subsection "TIME REPRESENTATION"
174Libev represents time as a single floating point number, representing the 254Libev represents time as a single floating point number, representing
175(fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere near 255the (fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere
176the beginning of 1970, details are complicated, don't ask). This type is 256near the beginning of 1970, details are complicated, don't ask). This
177called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use too. It usually aliases 257type is called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use too. It usually
178to the \f(CW\*(C`double\*(C'\fR type in C, and when you need to do any calculations on 258aliases to the \f(CW\*(C`double\*(C'\fR type in C. When you need to do any calculations
179it, you should treat it as such. 259on it, you should treat it as some floating point value. Unlike the name
260component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for time differences
261throughout libev.
262.SH "ERROR HANDLING"
263.IX Header "ERROR HANDLING"
264Libev knows three classes of errors: operating system errors, usage errors
265and internal errors (bugs).
266.PP
267When libev catches an operating system error it cannot handle (for example
268a system call indicating a condition libev cannot fix), it calls the callback
269set via \f(CW\*(C`ev_set_syserr_cb\*(C'\fR, which is supposed to fix the problem or
270abort. The default is to print a diagnostic message and to call \f(CW\*(C`abort
271()\*(C'\fR.
272.PP
273When libev detects a usage error such as a negative timer interval, then
274it will print a diagnostic message and abort (via the \f(CW\*(C`assert\*(C'\fR mechanism,
275so \f(CW\*(C`NDEBUG\*(C'\fR will disable this checking): these are programming errors in
276the libev caller and need to be fixed there.
277.PP
278Libev also has a few internal error-checking \f(CW\*(C`assert\*(C'\fRions, and also has
279extensive consistency checking code. These do not trigger under normal
280circumstances, as they indicate either a bug in libev or worse.
180.SH "GLOBAL FUNCTIONS" 281.SH "GLOBAL FUNCTIONS"
181.IX Header "GLOBAL FUNCTIONS" 282.IX Header "GLOBAL FUNCTIONS"
182These functions can be called anytime, even before initialising the 283These functions can be called anytime, even before initialising the
183library in any way. 284library in any way.
184.IP "ev_tstamp ev_time ()" 4 285.IP "ev_tstamp ev_time ()" 4
185.IX Item "ev_tstamp ev_time ()" 286.IX Item "ev_tstamp ev_time ()"
186Returns the current time as libev would use it. Please note that the 287Returns 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 288\&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp
188you actually want to know. 289you actually want to know.
290.IP "ev_sleep (ev_tstamp interval)" 4
291.IX Item "ev_sleep (ev_tstamp interval)"
292Sleep for the given interval: The current thread will be blocked until
293either it is interrupted or the given time interval has passed. Basically
294this is a sub-second-resolution \f(CW\*(C`sleep ()\*(C'\fR.
189.IP "int ev_version_major ()" 4 295.IP "int ev_version_major ()" 4
190.IX Item "int ev_version_major ()" 296.IX Item "int ev_version_major ()"
191.PD 0 297.PD 0
192.IP "int ev_version_minor ()" 4 298.IP "int ev_version_minor ()" 4
193.IX Item "int ev_version_minor ()" 299.IX Item "int ev_version_minor ()"
194.PD 300.PD
195You can find out the major and minor version numbers of the library 301You 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 302you 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 303\&\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 304symbols \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. 305version of the library your program was compiled against.
200.Sp 306.Sp
307These version numbers refer to the \s-1ABI\s0 version of the library, not the
308release version.
309.Sp
201Usually, it's a good idea to terminate if the major versions mismatch, 310Usually, it's a good idea to terminate if the major versions mismatch,
202as this indicates an incompatible change. Minor versions are usually 311as this indicates an incompatible change. Minor versions are usually
203compatible to older versions, so a larger minor version alone is usually 312compatible to older versions, so a larger minor version alone is usually
204not a problem. 313not a problem.
205.Sp 314.Sp
206Example: make sure we haven't accidentally been linked against the wrong 315Example: Make sure we haven't accidentally been linked against the wrong
207version: 316version.
208.Sp 317.Sp
209.Vb 3 318.Vb 3
210\& assert (("libev version mismatch", 319\& assert (("libev version mismatch",
211\& ev_version_major () == EV_VERSION_MAJOR 320\& ev_version_major () == EV_VERSION_MAJOR
212\& && ev_version_minor () >= EV_VERSION_MINOR)); 321\& && ev_version_minor () >= EV_VERSION_MINOR));
213.Ve 322.Ve
214.IP "unsigned int ev_supported_backends ()" 4 323.IP "unsigned int ev_supported_backends ()" 4
215.IX Item "unsigned int ev_supported_backends ()" 324.IX Item "unsigned int ev_supported_backends ()"
216Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR 325Return 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 326value) compiled into this binary of libev (independent of their
… …
220.Sp 329.Sp
221Example: make sure we have the epoll method, because yeah this is cool and 330Example: 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 331a must have and can we have a torrent of it please!!!11
223.Sp 332.Sp
224.Vb 2 333.Vb 2
225\& assert (("sorry, no epoll, no sex", 334\& assert (("sorry, no epoll, no sex",
226\& ev_supported_backends () & EVBACKEND_EPOLL)); 335\& ev_supported_backends () & EVBACKEND_EPOLL));
227.Ve 336.Ve
228.IP "unsigned int ev_recommended_backends ()" 4 337.IP "unsigned int ev_recommended_backends ()" 4
229.IX Item "unsigned int ev_recommended_backends ()" 338.IX Item "unsigned int ev_recommended_backends ()"
230Return the set of all backends compiled into this binary of libev and also 339Return the set of all backends compiled into this binary of libev and also
231recommended for this platform. This set is often smaller than the one 340recommended for this platform. This set is often smaller than the one
232returned by \f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on 341returned by \f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on
233most BSDs and will not be autodetected unless you explicitly request it 342most BSDs and will not be auto-detected unless you explicitly request it
234(assuming you know what you are doing). This is the set of backends that 343(assuming you know what you are doing). This is the set of backends that
235libev will probe for if you specify no backends explicitly. 344libev will probe for if you specify no backends explicitly.
345.IP "unsigned int ev_embeddable_backends ()" 4
346.IX Item "unsigned int ev_embeddable_backends ()"
347Returns the set of backends that are embeddable in other event loops. This
348is the theoretical, all-platform, value. To find which backends
349might be supported on the current system, you would need to look at
350\&\f(CW\*(C`ev_embeddable_backends () & ev_supported_backends ()\*(C'\fR, likewise for
351recommended ones.
352.Sp
353See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
236.IP "ev_set_allocator (void *(*cb)(void *ptr, long size))" 4 354.IP "ev_set_allocator (void *(*cb)(void *ptr, long size)) [\s-1NOT\s0 \s-1REENTRANT\s0]" 4
237.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))" 355.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]"
238Sets the allocation function to use (the prototype is similar to the 356Sets the allocation function to use (the prototype is similar \- the
239realloc C function, the semantics are identical). It is used to allocate 357semantics are identical to the \f(CW\*(C`realloc\*(C'\fR C89/SuS/POSIX function). It is
240and free memory (no surprises here). If it returns zero when memory 358used to allocate and free memory (no surprises here). If it returns zero
241needs to be allocated, the library might abort or take some potentially 359when memory needs to be allocated (\f(CW\*(C`size != 0\*(C'\fR), the library might abort
242destructive action. The default is your system realloc function. 360or take some potentially destructive action.
361.Sp
362Since some systems (at least OpenBSD and Darwin) fail to implement
363correct \f(CW\*(C`realloc\*(C'\fR semantics, libev will use a wrapper around the system
364\&\f(CW\*(C`realloc\*(C'\fR and \f(CW\*(C`free\*(C'\fR functions by default.
243.Sp 365.Sp
244You could override this function in high-availability programs to, say, 366You could override this function in high-availability programs to, say,
245free some memory if it cannot allocate memory, to use a special allocator, 367free some memory if it cannot allocate memory, to use a special allocator,
246or even to sleep a while and retry until some memory is available. 368or even to sleep a while and retry until some memory is available.
247.Sp 369.Sp
248Example: replace the libev allocator with one that waits a bit and then 370Example: Replace the libev allocator with one that waits a bit and then
249retries: better than mine). 371retries (example requires a standards-compliant \f(CW\*(C`realloc\*(C'\fR).
250.Sp 372.Sp
251.Vb 6 373.Vb 6
252\& static void * 374\& static void *
253\& persistent_realloc (void *ptr, long size) 375\& persistent_realloc (void *ptr, size_t size)
254\& { 376\& {
255\& for (;;) 377\& for (;;)
256\& { 378\& {
257\& void *newptr = realloc (ptr, size); 379\& void *newptr = realloc (ptr, size);
258.Ve 380\&
259.Sp
260.Vb 2
261\& if (newptr) 381\& if (newptr)
262\& return newptr; 382\& return newptr;
263.Ve 383\&
264.Sp
265.Vb 3
266\& sleep (60); 384\& sleep (60);
267\& } 385\& }
268\& } 386\& }
269.Ve 387\&
270.Sp
271.Vb 2
272\& ... 388\& ...
273\& ev_set_allocator (persistent_realloc); 389\& ev_set_allocator (persistent_realloc);
274.Ve 390.Ve
275.IP "ev_set_syserr_cb (void (*cb)(const char *msg));" 4 391.IP "ev_set_syserr_cb (void (*cb)(const char *msg)); [\s-1NOT\s0 \s-1REENTRANT\s0]" 4
276.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg));" 392.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]"
277Set the callback function to call on a retryable syscall error (such 393Set the callback function to call on a retryable system call error (such
278as failed select, poll, epoll_wait). The message is a printable string 394as failed select, poll, epoll_wait). The message is a printable string
279indicating the system call or subsystem causing the problem. If this 395indicating the system call or subsystem causing the problem. If this
280callback is set, then libev will expect it to remedy the sitution, no 396callback is set, then libev will expect it to remedy the situation, no
281matter what, when it returns. That is, libev will generally retry the 397matter what, when it returns. That is, libev will generally retry the
282requested operation, or, if the condition doesn't go away, do bad stuff 398requested operation, or, if the condition doesn't go away, do bad stuff
283(such as abort). 399(such as abort).
284.Sp 400.Sp
285Example: do the same thing as libev does internally: 401Example: This is basically the same thing that libev does internally, too.
286.Sp 402.Sp
287.Vb 6 403.Vb 6
288\& static void 404\& static void
289\& fatal_error (const char *msg) 405\& fatal_error (const char *msg)
290\& { 406\& {
291\& perror (msg); 407\& perror (msg);
292\& abort (); 408\& abort ();
293\& } 409\& }
294.Ve 410\&
295.Sp
296.Vb 2
297\& ... 411\& ...
298\& ev_set_syserr_cb (fatal_error); 412\& ev_set_syserr_cb (fatal_error);
299.Ve 413.Ve
300.SH "FUNCTIONS CONTROLLING THE EVENT LOOP" 414.SH "FUNCTIONS CONTROLLING THE EVENT LOOP"
301.IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP" 415.IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP"
302An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR. The library knows two 416An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR (the \f(CW\*(C`struct\*(C'\fR
303types of such loops, the \fIdefault\fR loop, which supports signals and child 417is \fInot\fR optional in this case, as there is also an \f(CW\*(C`ev_loop\*(C'\fR
304events, and dynamically created loops which do not. 418\&\fIfunction\fR).
305.PP 419.PP
306If you use threads, a common model is to run the default event loop 420The library knows two types of such loops, the \fIdefault\fR loop, which
307in your main thread (or in a separate thread) and for each thread you 421supports signals and child events, and dynamically created loops which do
308create, you also create another event loop. Libev itself does no locking 422not.
309whatsoever, so if you mix calls to the same event loop in different
310threads, make sure you lock (this is usually a bad idea, though, even if
311done correctly, because it's hideous and inefficient).
312.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4 423.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
313.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)" 424.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
314This will initialise the default event loop if it hasn't been initialised 425This will initialise the default event loop if it hasn't been initialised
315yet and return it. If the default loop could not be initialised, returns 426yet and return it. If the default loop could not be initialised, returns
316false. If it already was initialised it simply returns it (and ignores the 427false. If it already was initialised it simply returns it (and ignores the
317flags. If that is troubling you, check \f(CW\*(C`ev_backend ()\*(C'\fR afterwards). 428flags. If that is troubling you, check \f(CW\*(C`ev_backend ()\*(C'\fR afterwards).
318.Sp 429.Sp
319If you don't know what event loop to use, use the one returned from this 430If you don't know what event loop to use, use the one returned from this
320function. 431function.
432.Sp
433Note that this function is \fInot\fR thread-safe, so if you want to use it
434from multiple threads, you have to lock (note also that this is unlikely,
435as loops cannot be shared easily between threads anyway).
436.Sp
437The default loop is the only loop that can handle \f(CW\*(C`ev_signal\*(C'\fR and
438\&\f(CW\*(C`ev_child\*(C'\fR watchers, and to do this, it always registers a handler
439for \f(CW\*(C`SIGCHLD\*(C'\fR. If this is a problem for your application you can either
440create a dynamic loop with \f(CW\*(C`ev_loop_new\*(C'\fR that doesn't do that, or you
441can simply overwrite the \f(CW\*(C`SIGCHLD\*(C'\fR signal handler \fIafter\fR calling
442\&\f(CW\*(C`ev_default_init\*(C'\fR.
321.Sp 443.Sp
322The flags argument can be used to specify special behaviour or specific 444The flags argument can be used to specify special behaviour or specific
323backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). 445backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).
324.Sp 446.Sp
325The following flags are supported: 447The following flags are supported:
… …
330The default flags value. Use this if you have no clue (it's the right 452The default flags value. Use this if you have no clue (it's the right
331thing, believe me). 453thing, believe me).
332.ie n .IP """EVFLAG_NOENV""" 4 454.ie n .IP """EVFLAG_NOENV""" 4
333.el .IP "\f(CWEVFLAG_NOENV\fR" 4 455.el .IP "\f(CWEVFLAG_NOENV\fR" 4
334.IX Item "EVFLAG_NOENV" 456.IX Item "EVFLAG_NOENV"
335If this flag bit is ored into the flag value (or the program runs setuid 457If this flag bit is or'ed into the flag value (or the program runs setuid
336or setgid) then libev will \fInot\fR look at the environment variable 458or setgid) then libev will \fInot\fR look at the environment variable
337\&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will 459\&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will
338override the flags completely if it is found in the environment. This is 460override the flags completely if it is found in the environment. This is
339useful to try out specific backends to test their performance, or to work 461useful to try out specific backends to test their performance, or to work
340around bugs. 462around bugs.
463.ie n .IP """EVFLAG_FORKCHECK""" 4
464.el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4
465.IX Item "EVFLAG_FORKCHECK"
466Instead of calling \f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR manually after
467a fork, you can also make libev check for a fork in each iteration by
468enabling this flag.
469.Sp
470This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop,
471and thus this might slow down your event loop if you do a lot of loop
472iterations and little real work, but is usually not noticeable (on my
473GNU/Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn sequence
474without a system call and thus \fIvery\fR fast, but my GNU/Linux system also has
475\&\f(CW\*(C`pthread_atfork\*(C'\fR which is even faster).
476.Sp
477The big advantage of this flag is that you can forget about fork (and
478forget about forgetting to tell libev about forking) when you use this
479flag.
480.Sp
481This flag setting cannot be overridden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR
482environment variable.
341.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4 483.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
342.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4 484.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
343.IX Item "EVBACKEND_SELECT (value 1, portable select backend)" 485.IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
344This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as 486This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as
345libev tries to roll its own fd_set with no limits on the number of fds, 487libev tries to roll its own fd_set with no limits on the number of fds,
346but if that fails, expect a fairly low limit on the number of fds when 488but if that fails, expect a fairly low limit on the number of fds when
347using this backend. It doesn't scale too well (O(highest_fd)), but its usually 489using this backend. It doesn't scale too well (O(highest_fd)), but its
348the fastest backend for a low number of fds. 490usually the fastest backend for a low number of (low-numbered :) fds.
491.Sp
492To get good performance out of this backend you need a high amount of
493parallelism (most of the file descriptors should be busy). If you are
494writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many
495connections as possible during one iteration. You might also want to have
496a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of
497readiness notifications you get per iteration.
498.Sp
499This 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
500\&\f(CW\*(C`writefds\*(C'\fR set (and to work around Microsoft Windows bugs, also onto the
501\&\f(CW\*(C`exceptfds\*(C'\fR set on that platform).
349.ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4 502.ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4
350.el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4 503.el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4
351.IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)" 504.IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)"
352And this is your standard \fIpoll\fR\|(2) backend. It's more complicated than 505And this is your standard \fIpoll\fR\|(2) backend. It's more complicated
353select, but handles sparse fds better and has no artificial limit on the 506than select, but handles sparse fds better and has no artificial
354number of fds you can use (except it will slow down considerably with a 507limit on the number of fds you can use (except it will slow down
355lot of inactive fds). It scales similarly to select, i.e. O(total_fds). 508considerably with a lot of inactive fds). It scales similarly to select,
509i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for
510performance tips.
511.Sp
512This backend maps \f(CW\*(C`EV_READ\*(C'\fR to \f(CW\*(C`POLLIN | POLLERR | POLLHUP\*(C'\fR, and
513\&\f(CW\*(C`EV_WRITE\*(C'\fR to \f(CW\*(C`POLLOUT | POLLERR | POLLHUP\*(C'\fR.
356.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4 514.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
357.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4 515.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
358.IX Item "EVBACKEND_EPOLL (value 4, Linux)" 516.IX Item "EVBACKEND_EPOLL (value 4, Linux)"
359For few fds, this backend is a bit little slower than poll and select, 517For few fds, this backend is a bit little slower than poll and select,
360but it scales phenomenally better. While poll and select usually scale like 518but it scales phenomenally better. While poll and select usually scale
361O(total_fds) where n is the total number of fds (or the highest fd), epoll scales 519like O(total_fds) where n is the total number of fds (or the highest fd),
362either O(1) or O(active_fds). 520epoll scales either O(1) or O(active_fds).
363.Sp 521.Sp
522The epoll mechanism deserves honorable mention as the most misdesigned
523of the more advanced event mechanisms: mere annoyances include silently
524dropping file descriptors, requiring a system call per change per file
525descriptor (and unnecessary guessing of parameters), problems with dup and
526so on. The biggest issue is fork races, however \- if a program forks then
527\&\fIboth\fR parent and child process have to recreate the epoll set, which can
528take considerable time (one syscall per file descriptor) and is of course
529hard to detect.
530.Sp
531Epoll is also notoriously buggy \- embedding epoll fds \fIshould\fR work, but
532of course \fIdoesn't\fR, and epoll just loves to report events for totally
533\&\fIdifferent\fR file descriptors (even already closed ones, so one cannot
534even remove them from the set) than registered in the set (especially
535on \s-1SMP\s0 systems). Libev tries to counter these spurious notifications by
536employing an additional generation counter and comparing that against the
537events to filter out spurious ones, recreating the set when required.
538.Sp
364While stopping and starting an I/O watcher in the same iteration will 539While stopping, setting and starting an I/O watcher in the same iteration
365result in some caching, there is still a syscall per such incident 540will result in some caching, there is still a system call per such
366(because the fd could point to a different file description now), so its 541incident (because the same \fIfile descriptor\fR could point to a different
367best to avoid that. Also, \fIdup()\fRed file descriptors might not work very 542\&\fIfile description\fR now), so its best to avoid that. Also, \f(CW\*(C`dup ()\*(C'\fR'ed
368well if you register events for both fds. 543file descriptors might not work very well if you register events for both
544file descriptors.
369.Sp 545.Sp
370Please note that epoll sometimes generates spurious notifications, so you 546Best performance from this backend is achieved by not unregistering all
371need to use non-blocking I/O or other means to avoid blocking when no data 547watchers for a file descriptor until it has been closed, if possible,
372(or space) is available. 548i.e. keep at least one watcher active per fd at all times. Stopping and
549starting a watcher (without re-setting it) also usually doesn't cause
550extra overhead. A fork can both result in spurious notifications as well
551as in libev having to destroy and recreate the epoll object, which can
552take considerable time and thus should be avoided.
553.Sp
554All this means that, in practice, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR can be as fast or
555faster than epoll for maybe up to a hundred file descriptors, depending on
556the usage. So sad.
557.Sp
558While nominally embeddable in other event loops, this feature is broken in
559all kernel versions tested so far.
560.Sp
561This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
562\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
373.ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4 563.ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4
374.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4 564.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
375.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)" 565.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
376Kqueue deserves special mention, as at the time of this writing, it 566Kqueue deserves special mention, as at the time of this writing, it
377was broken on all BSDs except NetBSD (usually it doesn't work with 567was broken on all BSDs except NetBSD (usually it doesn't work reliably
378anything but sockets and pipes, except on Darwin, where of course its 568with anything but sockets and pipes, except on Darwin, where of course
379completely useless). For this reason its not being \*(L"autodetected\*(R" 569it's completely useless). Unlike epoll, however, whose brokenness
570is by design, these kqueue bugs can (and eventually will) be fixed
571without \s-1API\s0 changes to existing programs. For this reason it's not being
380unless you explicitly specify it explicitly in the flags (i.e. using 572\&\*(L"auto-detected\*(R" unless you explicitly specify it in the flags (i.e. using
381\&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR). 573\&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a known-to-be-good (\-enough)
574system like NetBSD.
575.Sp
576You still can embed kqueue into a normal poll or select backend and use it
577only for sockets (after having made sure that sockets work with kqueue on
578the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
382.Sp 579.Sp
383It scales in the same way as the epoll backend, but the interface to the 580It scales in the same way as the epoll backend, but the interface to the
384kernel is more efficient (which says nothing about its actual speed, of 581kernel is more efficient (which says nothing about its actual speed, of
385course). While starting and stopping an I/O watcher does not cause an 582course). While stopping, setting and starting an I/O watcher does never
386extra syscall as with epoll, it still adds up to four event changes per 583cause an extra system call as with \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to
387incident, so its best to avoid that. 584two event changes per incident. Support for \f(CW\*(C`fork ()\*(C'\fR is very bad (but
585sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
586cases
587.Sp
588This backend usually performs well under most conditions.
589.Sp
590While nominally embeddable in other event loops, this doesn't work
591everywhere, so you might need to test for this. And since it is broken
592almost everywhere, you should only use it when you have a lot of sockets
593(for which it usually works), by embedding it into another event loop
594(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
595also broken on \s-1OS\s0 X)) and, did I mention it, using it only for sockets.
596.Sp
597This backend maps \f(CW\*(C`EV_READ\*(C'\fR into an \f(CW\*(C`EVFILT_READ\*(C'\fR kevent with
598\&\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
599\&\f(CW\*(C`NOTE_EOF\*(C'\fR.
388.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4 600.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
389.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4 601.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
390.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)" 602.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
391This is not implemented yet (and might never be). 603This is not implemented yet (and might never be, unless you send me an
604implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets
605and is not embeddable, which would limit the usefulness of this backend
606immensely.
392.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4 607.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
393.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4 608.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
394.IX Item "EVBACKEND_PORT (value 32, Solaris 10)" 609.IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
395This uses the Solaris 10 port mechanism. As with everything on Solaris, 610This uses the Solaris 10 event port mechanism. As with everything on Solaris,
396it's really slow, but it still scales very well (O(active_fds)). 611it's really slow, but it still scales very well (O(active_fds)).
397.Sp 612.Sp
398Please note that solaris ports can result in a lot of spurious 613Please note that Solaris event ports can deliver a lot of spurious
399notifications, so you need to use non-blocking I/O or other means to avoid 614notifications, so you need to use non-blocking I/O or other means to avoid
400blocking when no data (or space) is available. 615blocking when no data (or space) is available.
616.Sp
617While this backend scales well, it requires one system call per active
618file descriptor per loop iteration. For small and medium numbers of file
619descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend
620might perform better.
621.Sp
622On the positive side, with the exception of the spurious readiness
623notifications, this backend actually performed fully to specification
624in all tests and is fully embeddable, which is a rare feat among the
625OS-specific backends (I vastly prefer correctness over speed hacks).
626.Sp
627This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
628\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
401.ie n .IP """EVBACKEND_ALL""" 4 629.ie n .IP """EVBACKEND_ALL""" 4
402.el .IP "\f(CWEVBACKEND_ALL\fR" 4 630.el .IP "\f(CWEVBACKEND_ALL\fR" 4
403.IX Item "EVBACKEND_ALL" 631.IX Item "EVBACKEND_ALL"
404Try all backends (even potentially broken ones that wouldn't be tried 632Try all backends (even potentially broken ones that wouldn't be tried
405with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as 633with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as
406\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR. 634\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR.
635.Sp
636It is definitely not recommended to use this flag.
407.RE 637.RE
408.RS 4 638.RS 4
409.Sp 639.Sp
410If one or more of these are ored into the flags value, then only these 640If one or more of these are or'ed into the flags value, then only these
411backends will be tried (in the reverse order as given here). If none are 641backends will be tried (in the reverse order as listed here). If none are
412specified, most compiled-in backend will be tried, usually in reverse 642specified, all backends in \f(CW\*(C`ev_recommended_backends ()\*(C'\fR will be tried.
413order of their flag values :)
414.Sp 643.Sp
415The most typical usage is like this: 644Example: This is the most typical usage.
416.Sp 645.Sp
417.Vb 2 646.Vb 2
418\& if (!ev_default_loop (0)) 647\& if (!ev_default_loop (0))
419\& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?"); 648\& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
420.Ve 649.Ve
421.Sp 650.Sp
422Restrict libev to the select and poll backends, and do not allow 651Example: Restrict libev to the select and poll backends, and do not allow
423environment settings to be taken into account: 652environment settings to be taken into account:
424.Sp 653.Sp
425.Vb 1 654.Vb 1
426\& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV); 655\& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
427.Ve 656.Ve
428.Sp 657.Sp
429Use whatever libev has to offer, but make sure that kqueue is used if 658Example: Use whatever libev has to offer, but make sure that kqueue is
430available (warning, breaks stuff, best use only with your own private 659used if available (warning, breaks stuff, best use only with your own
431event loop and only if you know the \s-1OS\s0 supports your types of fds): 660private event loop and only if you know the \s-1OS\s0 supports your types of
661fds):
432.Sp 662.Sp
433.Vb 1 663.Vb 1
434\& ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE); 664\& ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
435.Ve 665.Ve
436.RE 666.RE
437.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4 667.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
438.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)" 668.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
439Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is 669Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is
440always distinct from the default loop. Unlike the default loop, it cannot 670always distinct from the default loop. Unlike the default loop, it cannot
441handle signal and child watchers, and attempts to do so will be greeted by 671handle signal and child watchers, and attempts to do so will be greeted by
442undefined behaviour (or a failed assertion if assertions are enabled). 672undefined behaviour (or a failed assertion if assertions are enabled).
443.Sp 673.Sp
674Note that this function \fIis\fR thread-safe, and the recommended way to use
675libev with threads is indeed to create one loop per thread, and using the
676default loop in the \*(L"main\*(R" or \*(L"initial\*(R" thread.
677.Sp
444Example: try to create a event loop that uses epoll and nothing else. 678Example: Try to create a event loop that uses epoll and nothing else.
445.Sp 679.Sp
446.Vb 3 680.Vb 3
447\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV); 681\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
448\& if (!epoller) 682\& if (!epoller)
449\& fatal ("no epoll found here, maybe it hides under your chair"); 683\& fatal ("no epoll found here, maybe it hides under your chair");
450.Ve 684.Ve
451.IP "ev_default_destroy ()" 4 685.IP "ev_default_destroy ()" 4
452.IX Item "ev_default_destroy ()" 686.IX Item "ev_default_destroy ()"
453Destroys the default loop again (frees all memory and kernel state 687Destroys the default loop again (frees all memory and kernel state
454etc.). This stops all registered event watchers (by not touching them in 688etc.). None of the active event watchers will be stopped in the normal
455any way whatsoever, although you cannot rely on this :). 689sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your
690responsibility to either stop all watchers cleanly yourself \fIbefore\fR
691calling this function, or cope with the fact afterwards (which is usually
692the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them
693for example).
694.Sp
695Note that certain global state, such as signal state (and installed signal
696handlers), will not be freed by this function, and related watchers (such
697as signal and child watchers) would need to be stopped manually.
698.Sp
699In general it is not advisable to call this function except in the
700rare occasion where you really need to free e.g. the signal handling
701pipe fds. If you need dynamically allocated loops it is better to use
702\&\f(CW\*(C`ev_loop_new\*(C'\fR and \f(CW\*(C`ev_loop_destroy\*(C'\fR).
456.IP "ev_loop_destroy (loop)" 4 703.IP "ev_loop_destroy (loop)" 4
457.IX Item "ev_loop_destroy (loop)" 704.IX Item "ev_loop_destroy (loop)"
458Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an 705Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an
459earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR. 706earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR.
460.IP "ev_default_fork ()" 4 707.IP "ev_default_fork ()" 4
461.IX Item "ev_default_fork ()" 708.IX Item "ev_default_fork ()"
709This function sets a flag that causes subsequent \f(CW\*(C`ev_loop\*(C'\fR iterations
462This function reinitialises the kernel state for backends that have 710to reinitialise the kernel state for backends that have one. Despite the
463one. Despite the name, you can call it anytime, but it makes most sense 711name, you can call it anytime, but it makes most sense after forking, in
464after forking, in either the parent or child process (or both, but that 712the child process (or both child and parent, but that again makes little
465again makes little sense). 713sense). You \fImust\fR call it in the child before using any of the libev
714functions, and it will only take effect at the next \f(CW\*(C`ev_loop\*(C'\fR iteration.
466.Sp 715.Sp
467You \fImust\fR call this function in the child process after forking if and 716On the other hand, you only need to call this function in the child
468only if you want to use the event library in both processes. If you just 717process if and only if you want to use the event library in the child. If
469fork+exec, you don't have to call it. 718you just fork+exec, you don't have to call it at all.
470.Sp 719.Sp
471The function itself is quite fast and it's usually not a problem to call 720The function itself is quite fast and it's usually not a problem to call
472it just in case after a fork. To make this easy, the function will fit in 721it just in case after a fork. To make this easy, the function will fit in
473quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR: 722quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR:
474.Sp 723.Sp
475.Vb 1 724.Vb 1
476\& pthread_atfork (0, 0, ev_default_fork); 725\& pthread_atfork (0, 0, ev_default_fork);
477.Ve 726.Ve
478.Sp
479At the moment, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and \f(CW\*(C`EVBACKEND_POLL\*(C'\fR are safe to use
480without calling this function, so if you force one of those backends you
481do not need to care.
482.IP "ev_loop_fork (loop)" 4 727.IP "ev_loop_fork (loop)" 4
483.IX Item "ev_loop_fork (loop)" 728.IX Item "ev_loop_fork (loop)"
484Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by 729Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by
485\&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop 730\&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop
486after fork, and how you do this is entirely your own problem. 731after fork that you want to re-use in the child, and how you do this is
732entirely your own problem.
733.IP "int ev_is_default_loop (loop)" 4
734.IX Item "int ev_is_default_loop (loop)"
735Returns true when the given loop is, in fact, the default loop, and false
736otherwise.
737.IP "unsigned int ev_loop_count (loop)" 4
738.IX Item "unsigned int ev_loop_count (loop)"
739Returns the count of loop iterations for the loop, which is identical to
740the number of times libev did poll for new events. It starts at \f(CW0\fR and
741happily wraps around with enough iterations.
742.Sp
743This value can sometimes be useful as a generation counter of sorts (it
744\&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with
745\&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls.
746.IP "unsigned int ev_loop_depth (loop)" 4
747.IX Item "unsigned int ev_loop_depth (loop)"
748Returns the number of times \f(CW\*(C`ev_loop\*(C'\fR was entered minus the number of
749times \f(CW\*(C`ev_loop\*(C'\fR was exited, in other words, the recursion depth.
750.Sp
751Outside \f(CW\*(C`ev_loop\*(C'\fR, this number is zero. In a callback, this number is
752\&\f(CW1\fR, unless \f(CW\*(C`ev_loop\*(C'\fR was invoked recursively (or from another thread),
753in which case it is higher.
754.Sp
755Leaving \f(CW\*(C`ev_loop\*(C'\fR abnormally (setjmp/longjmp, cancelling the thread
756etc.), doesn't count as exit.
487.IP "unsigned int ev_backend (loop)" 4 757.IP "unsigned int ev_backend (loop)" 4
488.IX Item "unsigned int ev_backend (loop)" 758.IX Item "unsigned int ev_backend (loop)"
489Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in 759Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
490use. 760use.
491.IP "ev_tstamp ev_now (loop)" 4 761.IP "ev_tstamp ev_now (loop)" 4
492.IX Item "ev_tstamp ev_now (loop)" 762.IX Item "ev_tstamp ev_now (loop)"
493Returns the current \*(L"event loop time\*(R", which is the time the event loop 763Returns the current \*(L"event loop time\*(R", which is the time the event loop
494received events and started processing them. This timestamp does not 764received events and started processing them. This timestamp does not
495change as long as callbacks are being processed, and this is also the base 765change as long as callbacks are being processed, and this is also the base
496time used for relative timers. You can treat it as the timestamp of the 766time used for relative timers. You can treat it as the timestamp of the
497event occuring (or more correctly, libev finding out about it). 767event occurring (or more correctly, libev finding out about it).
768.IP "ev_now_update (loop)" 4
769.IX Item "ev_now_update (loop)"
770Establishes the current time by querying the kernel, updating the time
771returned by \f(CW\*(C`ev_now ()\*(C'\fR in the progress. This is a costly operation and
772is usually done automatically within \f(CW\*(C`ev_loop ()\*(C'\fR.
773.Sp
774This function is rarely useful, but when some event callback runs for a
775very long time without entering the event loop, updating libev's idea of
776the current time is a good idea.
777.Sp
778See also \*(L"The special problem of time updates\*(R" in the \f(CW\*(C`ev_timer\*(C'\fR section.
779.IP "ev_suspend (loop)" 4
780.IX Item "ev_suspend (loop)"
781.PD 0
782.IP "ev_resume (loop)" 4
783.IX Item "ev_resume (loop)"
784.PD
785These two functions suspend and resume a loop, for use when the loop is
786not used for a while and timeouts should not be processed.
787.Sp
788A typical use case would be an interactive program such as a game: When
789the user presses \f(CW\*(C`^Z\*(C'\fR to suspend the game and resumes it an hour later it
790would be best to handle timeouts as if no time had actually passed while
791the program was suspended. This can be achieved by calling \f(CW\*(C`ev_suspend\*(C'\fR
792in your \f(CW\*(C`SIGTSTP\*(C'\fR handler, sending yourself a \f(CW\*(C`SIGSTOP\*(C'\fR and calling
793\&\f(CW\*(C`ev_resume\*(C'\fR directly afterwards to resume timer processing.
794.Sp
795Effectively, all \f(CW\*(C`ev_timer\*(C'\fR watchers will be delayed by the time spend
796between \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
797will be rescheduled (that is, they will lose any events that would have
798occured while suspended).
799.Sp
800After calling \f(CW\*(C`ev_suspend\*(C'\fR you \fBmust not\fR call \fIany\fR function on the
801given loop other than \f(CW\*(C`ev_resume\*(C'\fR, and you \fBmust not\fR call \f(CW\*(C`ev_resume\*(C'\fR
802without a previous call to \f(CW\*(C`ev_suspend\*(C'\fR.
803.Sp
804Calling \f(CW\*(C`ev_suspend\*(C'\fR/\f(CW\*(C`ev_resume\*(C'\fR has the side effect of updating the
805event loop time (see \f(CW\*(C`ev_now_update\*(C'\fR).
498.IP "ev_loop (loop, int flags)" 4 806.IP "ev_loop (loop, int flags)" 4
499.IX Item "ev_loop (loop, int flags)" 807.IX Item "ev_loop (loop, int flags)"
500Finally, this is it, the event handler. This function usually is called 808Finally, this is it, the event handler. This function usually is called
501after you initialised all your watchers and you want to start handling 809after you initialised all your watchers and you want to start handling
502events. 810events.
… …
504If the flags argument is specified as \f(CW0\fR, it will not return until 812If the flags argument is specified as \f(CW0\fR, it will not return until
505either no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called. 813either no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called.
506.Sp 814.Sp
507Please note that an explicit \f(CW\*(C`ev_unloop\*(C'\fR is usually better than 815Please note that an explicit \f(CW\*(C`ev_unloop\*(C'\fR is usually better than
508relying on all watchers to be stopped when deciding when a program has 816relying on all watchers to be stopped when deciding when a program has
509finished (especially in interactive programs), but having a program that 817finished (especially in interactive programs), but having a program
510automatically loops as long as it has to and no longer by virtue of 818that automatically loops as long as it has to and no longer by virtue
511relying on its watchers stopping correctly is a thing of beauty. 819of relying on its watchers stopping correctly, that is truly a thing of
820beauty.
512.Sp 821.Sp
513A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle 822A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle
514those events and any outstanding ones, but will not block your process in 823those events and any already outstanding ones, but will not block your
515case there are no events and will return after one iteration of the loop. 824process in case there are no events and will return after one iteration of
825the loop.
516.Sp 826.Sp
517A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if 827A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if
518neccessary) and will handle those and any outstanding ones. It will block 828necessary) and will handle those and any already outstanding ones. It
519your process until at least one new event arrives, and will return after 829will block your process until at least one new event arrives (which could
520one iteration of the loop. This is useful if you are waiting for some 830be an event internal to libev itself, so there is no guarantee that a
521external event in conjunction with something not expressible using other 831user-registered callback will be called), and will return after one
832iteration of the loop.
833.Sp
834This is useful if you are waiting for some external event in conjunction
835with something not expressible using other libev watchers (i.e. "roll your
522libev watchers. However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is 836own \f(CW\*(C`ev_loop\*(C'\fR"). However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is
523usually a better approach for this kind of thing. 837usually a better approach for this kind of thing.
524.Sp 838.Sp
525Here are the gory details of what \f(CW\*(C`ev_loop\*(C'\fR does: 839Here are the gory details of what \f(CW\*(C`ev_loop\*(C'\fR does:
526.Sp 840.Sp
527.Vb 18 841.Vb 10
528\& * If there are no active watchers (reference count is zero), return. 842\& \- Before the first iteration, call any pending watchers.
529\& - Queue prepare watchers and then call all outstanding watchers. 843\& * If EVFLAG_FORKCHECK was used, check for a fork.
844\& \- If a fork was detected (by any means), queue and call all fork watchers.
845\& \- Queue and call all prepare watchers.
530\& - If we have been forked, recreate the kernel state. 846\& \- If we have been forked, detach and recreate the kernel state
847\& as to not disturb the other process.
531\& - Update the kernel state with all outstanding changes. 848\& \- Update the kernel state with all outstanding changes.
532\& - Update the "event loop time". 849\& \- Update the "event loop time" (ev_now ()).
533\& - Calculate for how long to block. 850\& \- Calculate for how long to sleep or block, if at all
851\& (active idle watchers, EVLOOP_NONBLOCK or not having
852\& any active watchers at all will result in not sleeping).
853\& \- Sleep if the I/O and timer collect interval say so.
534\& - Block the process, waiting for any events. 854\& \- Block the process, waiting for any events.
535\& - Queue all outstanding I/O (fd) events. 855\& \- Queue all outstanding I/O (fd) events.
536\& - Update the "event loop time" and do time jump handling. 856\& \- Update the "event loop time" (ev_now ()), and do time jump adjustments.
537\& - Queue all outstanding timers. 857\& \- Queue all expired timers.
538\& - Queue all outstanding periodics. 858\& \- Queue all expired periodics.
539\& - If no events are pending now, queue all idle watchers. 859\& \- Unless any events are pending now, queue all idle watchers.
540\& - Queue all check watchers. 860\& \- Queue all check watchers.
541\& - Call all queued watchers in reverse order (i.e. check watchers first). 861\& \- Call all queued watchers in reverse order (i.e. check watchers first).
542\& Signals and child watchers are implemented as I/O watchers, and will 862\& Signals and child watchers are implemented as I/O watchers, and will
543\& be handled here by queueing them when their watcher gets executed. 863\& be handled here by queueing them when their watcher gets executed.
544\& - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK 864\& \- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
545\& were used, return, otherwise continue with step *. 865\& were used, or there are no active watchers, return, otherwise
866\& continue with step *.
546.Ve 867.Ve
547.Sp 868.Sp
548Example: queue some jobs and then loop until no events are outsanding 869Example: Queue some jobs and then loop until no events are outstanding
549anymore. 870anymore.
550.Sp 871.Sp
551.Vb 4 872.Vb 4
552\& ... queue jobs here, make sure they register event watchers as long 873\& ... queue jobs here, make sure they register event watchers as long
553\& ... as they still have work to do (even an idle watcher will do..) 874\& ... as they still have work to do (even an idle watcher will do..)
554\& ev_loop (my_loop, 0); 875\& ev_loop (my_loop, 0);
555\& ... jobs done. yeah! 876\& ... jobs done or somebody called unloop. yeah!
556.Ve 877.Ve
557.IP "ev_unloop (loop, how)" 4 878.IP "ev_unloop (loop, how)" 4
558.IX Item "ev_unloop (loop, how)" 879.IX Item "ev_unloop (loop, how)"
559Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it 880Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it
560has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either 881has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
561\&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or 882\&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or
562\&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return. 883\&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return.
884.Sp
885This \*(L"unloop state\*(R" will be cleared when entering \f(CW\*(C`ev_loop\*(C'\fR again.
886.Sp
887It is safe to call \f(CW\*(C`ev_unloop\*(C'\fR from otuside any \f(CW\*(C`ev_loop\*(C'\fR calls.
563.IP "ev_ref (loop)" 4 888.IP "ev_ref (loop)" 4
564.IX Item "ev_ref (loop)" 889.IX Item "ev_ref (loop)"
565.PD 0 890.PD 0
566.IP "ev_unref (loop)" 4 891.IP "ev_unref (loop)" 4
567.IX Item "ev_unref (loop)" 892.IX Item "ev_unref (loop)"
568.PD 893.PD
569Ref/unref can be used to add or remove a reference count on the event 894Ref/unref can be used to add or remove a reference count on the event
570loop: Every watcher keeps one reference, and as long as the reference 895loop: Every watcher keeps one reference, and as long as the reference
571count is nonzero, \f(CW\*(C`ev_loop\*(C'\fR will not return on its own. If you have 896count is nonzero, \f(CW\*(C`ev_loop\*(C'\fR will not return on its own.
897.Sp
572a watcher you never unregister that should not keep \f(CW\*(C`ev_loop\*(C'\fR from 898If you have a watcher you never unregister that should not keep \f(CW\*(C`ev_loop\*(C'\fR
573returning, \fIev_unref()\fR after starting, and \fIev_ref()\fR before stopping it. For 899from returning, call \fIev_unref()\fR after starting, and \fIev_ref()\fR before
900stopping it.
901.Sp
574example, libev itself uses this for its internal signal pipe: It is not 902As an example, libev itself uses this for its internal signal pipe: It
575visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from exiting if 903is not visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from
576no event watchers registered by it are active. It is also an excellent 904exiting if no event watchers registered by it are active. It is also an
577way to do this for generic recurring timers or from within third-party 905excellent way to do this for generic recurring timers or from within
578libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR. 906third-party libraries. Just remember to \fIunref after start\fR and \fIref
907before stop\fR (but only if the watcher wasn't active before, or was active
908before, respectively. Note also that libev might stop watchers itself
909(e.g. non-repeating timers) in which case you have to \f(CW\*(C`ev_ref\*(C'\fR
910in the callback).
579.Sp 911.Sp
580Example: create a signal watcher, but keep it from keeping \f(CW\*(C`ev_loop\*(C'\fR 912Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_loop\*(C'\fR
581running when nothing else is active. 913running when nothing else is active.
582.Sp 914.Sp
583.Vb 4 915.Vb 4
584\& struct dv_signal exitsig; 916\& ev_signal exitsig;
585\& ev_signal_init (&exitsig, sig_cb, SIGINT); 917\& ev_signal_init (&exitsig, sig_cb, SIGINT);
586\& ev_signal_start (myloop, &exitsig); 918\& ev_signal_start (loop, &exitsig);
587\& evf_unref (myloop); 919\& evf_unref (loop);
588.Ve 920.Ve
589.Sp 921.Sp
590Example: for some weird reason, unregister the above signal handler again. 922Example: For some weird reason, unregister the above signal handler again.
591.Sp 923.Sp
592.Vb 2 924.Vb 2
593\& ev_ref (myloop); 925\& ev_ref (loop);
594\& ev_signal_stop (myloop, &exitsig); 926\& ev_signal_stop (loop, &exitsig);
595.Ve 927.Ve
928.IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4
929.IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"
930.PD 0
931.IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4
932.IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"
933.PD
934These advanced functions influence the time that libev will spend waiting
935for events. Both time intervals are by default \f(CW0\fR, meaning that libev
936will try to invoke timer/periodic callbacks and I/O callbacks with minimum
937latency.
938.Sp
939Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR)
940allows libev to delay invocation of I/O and timer/periodic callbacks
941to increase efficiency of loop iterations (or to increase power-saving
942opportunities).
943.Sp
944The idea is that sometimes your program runs just fast enough to handle
945one (or very few) event(s) per loop iteration. While this makes the
946program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new
947events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high
948overhead for the actual polling but can deliver many events at once.
949.Sp
950By setting a higher \fIio collect interval\fR you allow libev to spend more
951time collecting I/O events, so you can handle more events per iteration,
952at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and
953\&\f(CW\*(C`ev_timer\*(C'\fR) will be not affected. Setting this to a non-null value will
954introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations. The
955sleep time ensures that libev will not poll for I/O events more often then
956once per this interval, on average.
957.Sp
958Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
959to spend more time collecting timeouts, at the expense of increased
960latency/jitter/inexactness (the watcher callback will be called
961later). \f(CW\*(C`ev_io\*(C'\fR watchers will not be affected. Setting this to a non-null
962value will not introduce any overhead in libev.
963.Sp
964Many (busy) programs can usually benefit by setting the I/O collect
965interval to a value near \f(CW0.1\fR or so, which is often enough for
966interactive servers (of course not for games), likewise for timeouts. It
967usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR,
968as this approaches the timing granularity of most systems. Note that if
969you do transactions with the outside world and you can't increase the
970parallelity, then this setting will limit your transaction rate (if you
971need to poll once per transaction and the I/O collect interval is 0.01,
972then you can't do more than 100 transations per second).
973.Sp
974Setting the \fItimeout collect interval\fR can improve the opportunity for
975saving power, as the program will \*(L"bundle\*(R" timer callback invocations that
976are \*(L"near\*(R" in time together, by delaying some, thus reducing the number of
977times the process sleeps and wakes up again. Another useful technique to
978reduce iterations/wake\-ups is to use \f(CW\*(C`ev_periodic\*(C'\fR watchers and make sure
979they fire on, say, one-second boundaries only.
980.Sp
981Example: we only need 0.1s timeout granularity, and we wish not to poll
982more often than 100 times per second:
983.Sp
984.Vb 2
985\& ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
986\& ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
987.Ve
988.IP "ev_invoke_pending (loop)" 4
989.IX Item "ev_invoke_pending (loop)"
990This call will simply invoke all pending watchers while resetting their
991pending state. Normally, \f(CW\*(C`ev_loop\*(C'\fR does this automatically when required,
992but when overriding the invoke callback this call comes handy.
993.IP "int ev_pending_count (loop)" 4
994.IX Item "int ev_pending_count (loop)"
995Returns the number of pending watchers \- zero indicates that no watchers
996are pending.
997.IP "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(\s-1EV_P\s0))" 4
998.IX Item "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))"
999This overrides the invoke pending functionality of the loop: Instead of
1000invoking all pending watchers when there are any, \f(CW\*(C`ev_loop\*(C'\fR will call
1001this callback instead. This is useful, for example, when you want to
1002invoke the actual watchers inside another context (another thread etc.).
1003.Sp
1004If you want to reset the callback, use \f(CW\*(C`ev_invoke_pending\*(C'\fR as new
1005callback.
1006.IP "ev_set_loop_release_cb (loop, void (*release)(\s-1EV_P\s0), void (*acquire)(\s-1EV_P\s0))" 4
1007.IX Item "ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))"
1008Sometimes you want to share the same loop between multiple threads. This
1009can be done relatively simply by putting mutex_lock/unlock calls around
1010each call to a libev function.
1011.Sp
1012However, \f(CW\*(C`ev_loop\*(C'\fR can run an indefinite time, so it is not feasible to
1013wait for it to return. One way around this is to wake up the loop via
1014\&\f(CW\*(C`ev_unloop\*(C'\fR and \f(CW\*(C`av_async_send\*(C'\fR, another way is to set these \fIrelease\fR
1015and \fIacquire\fR callbacks on the loop.
1016.Sp
1017When set, then \f(CW\*(C`release\*(C'\fR will be called just before the thread is
1018suspended waiting for new events, and \f(CW\*(C`acquire\*(C'\fR is called just
1019afterwards.
1020.Sp
1021Ideally, \f(CW\*(C`release\*(C'\fR will just call your mutex_unlock function, and
1022\&\f(CW\*(C`acquire\*(C'\fR will just call the mutex_lock function again.
1023.Sp
1024While event loop modifications are allowed between invocations of
1025\&\f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR (that's their only purpose after all), no
1026modifications done will affect the event loop, i.e. adding watchers will
1027have no effect on the set of file descriptors being watched, or the time
1028waited. USe an \f(CW\*(C`ev_async\*(C'\fR watcher to wake up \f(CW\*(C`ev_loop\*(C'\fR when you want it
1029to take note of any changes you made.
1030.Sp
1031In theory, threads executing \f(CW\*(C`ev_loop\*(C'\fR will be async-cancel safe between
1032invocations of \f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR.
1033.Sp
1034See also the locking example in the \f(CW\*(C`THREADS\*(C'\fR section later in this
1035document.
1036.IP "ev_set_userdata (loop, void *data)" 4
1037.IX Item "ev_set_userdata (loop, void *data)"
1038.PD 0
1039.IP "ev_userdata (loop)" 4
1040.IX Item "ev_userdata (loop)"
1041.PD
1042Set and retrieve a single \f(CW\*(C`void *\*(C'\fR associated with a loop. When
1043\&\f(CW\*(C`ev_set_userdata\*(C'\fR has never been called, then \f(CW\*(C`ev_userdata\*(C'\fR returns
1044\&\f(CW0.\fR
1045.Sp
1046These two functions can be used to associate arbitrary data with a loop,
1047and are intended solely for the \f(CW\*(C`invoke_pending_cb\*(C'\fR, \f(CW\*(C`release\*(C'\fR and
1048\&\f(CW\*(C`acquire\*(C'\fR callbacks described above, but of course can be (ab\-)used for
1049any other purpose as well.
1050.IP "ev_loop_verify (loop)" 4
1051.IX Item "ev_loop_verify (loop)"
1052This function only does something when \f(CW\*(C`EV_VERIFY\*(C'\fR support has been
1053compiled in, which is the default for non-minimal builds. It tries to go
1054through all internal structures and checks them for validity. If anything
1055is found to be inconsistent, it will print an error message to standard
1056error and call \f(CW\*(C`abort ()\*(C'\fR.
1057.Sp
1058This can be used to catch bugs inside libev itself: under normal
1059circumstances, this function will never abort as of course libev keeps its
1060data structures consistent.
596.SH "ANATOMY OF A WATCHER" 1061.SH "ANATOMY OF A WATCHER"
597.IX Header "ANATOMY OF A WATCHER" 1062.IX Header "ANATOMY OF A WATCHER"
1063In the following description, uppercase \f(CW\*(C`TYPE\*(C'\fR in names stands for the
1064watcher type, e.g. \f(CW\*(C`ev_TYPE_start\*(C'\fR can mean \f(CW\*(C`ev_timer_start\*(C'\fR for timer
1065watchers and \f(CW\*(C`ev_io_start\*(C'\fR for I/O watchers.
1066.PP
598A watcher is a structure that you create and register to record your 1067A watcher is a structure that you create and register to record your
599interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to 1068interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to
600become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that: 1069become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that:
601.PP 1070.PP
602.Vb 5 1071.Vb 5
603\& static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) 1072\& static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
604\& { 1073\& {
605\& ev_io_stop (w); 1074\& ev_io_stop (w);
606\& ev_unloop (loop, EVUNLOOP_ALL); 1075\& ev_unloop (loop, EVUNLOOP_ALL);
607\& } 1076\& }
608.Ve 1077\&
609.PP
610.Vb 6
611\& struct ev_loop *loop = ev_default_loop (0); 1078\& struct ev_loop *loop = ev_default_loop (0);
1079\&
612\& struct ev_io stdin_watcher; 1080\& ev_io stdin_watcher;
1081\&
613\& ev_init (&stdin_watcher, my_cb); 1082\& ev_init (&stdin_watcher, my_cb);
614\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); 1083\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
615\& ev_io_start (loop, &stdin_watcher); 1084\& ev_io_start (loop, &stdin_watcher);
1085\&
616\& ev_loop (loop, 0); 1086\& ev_loop (loop, 0);
617.Ve 1087.Ve
618.PP 1088.PP
619As you can see, you are responsible for allocating the memory for your 1089As you can see, you are responsible for allocating the memory for your
620watcher structures (and it is usually a bad idea to do this on the stack, 1090watcher structures (and it is \fIusually\fR a bad idea to do this on the
621although this can sometimes be quite valid). 1091stack).
1092.PP
1093Each watcher has an associated watcher structure (called \f(CW\*(C`struct ev_TYPE\*(C'\fR
1094or simply \f(CW\*(C`ev_TYPE\*(C'\fR, as typedefs are provided for all watcher structs).
622.PP 1095.PP
623Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init 1096Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init
624(watcher *, callback)\*(C'\fR, which expects a callback to be provided. This 1097(watcher *, callback)\*(C'\fR, which expects a callback to be provided. This
625callback gets invoked each time the event occurs (or, in the case of io 1098callback gets invoked each time the event occurs (or, in the case of I/O
626watchers, each time the event loop detects that the file descriptor given 1099watchers, each time the event loop detects that the file descriptor given
627is readable and/or writable). 1100is readable and/or writable).
628.PP 1101.PP
629Each watcher type has its own \f(CW\*(C`ev_<type>_set (watcher *, ...)\*(C'\fR macro 1102Each watcher type further has its own \f(CW\*(C`ev_TYPE_set (watcher *, ...)\*(C'\fR
630with arguments specific to this watcher type. There is also a macro 1103macro to configure it, with arguments specific to the watcher type. There
631to combine initialisation and setting in one call: \f(CW\*(C`ev_<type>_init 1104is also a macro to combine initialisation and setting in one call: \f(CW\*(C`ev_TYPE_init (watcher *, callback, ...)\*(C'\fR.
632(watcher *, callback, ...)\*(C'\fR.
633.PP 1105.PP
634To make the watcher actually watch out for events, you have to start it 1106To make the watcher actually watch out for events, you have to start it
635with a watcher-specific start function (\f(CW\*(C`ev_<type>_start (loop, watcher 1107with a watcher-specific start function (\f(CW\*(C`ev_TYPE_start (loop, watcher
636*)\*(C'\fR), and you can stop watching for events at any time by calling the 1108*)\*(C'\fR), and you can stop watching for events at any time by calling the
637corresponding stop function (\f(CW\*(C`ev_<type>_stop (loop, watcher *)\*(C'\fR. 1109corresponding stop function (\f(CW\*(C`ev_TYPE_stop (loop, watcher *)\*(C'\fR.
638.PP 1110.PP
639As long as your watcher is active (has been started but not stopped) you 1111As long as your watcher is active (has been started but not stopped) you
640must not touch the values stored in it. Most specifically you must never 1112must not touch the values stored in it. Most specifically you must never
641reinitialise it or call its set macro. 1113reinitialise it or call its \f(CW\*(C`ev_TYPE_set\*(C'\fR macro.
642.PP
643You can check whether an event is active by calling the \f(CW\*(C`ev_is_active
644(watcher *)\*(C'\fR macro. To see whether an event is outstanding (but the
645callback for it has not been called yet) you can use the \f(CW\*(C`ev_is_pending
646(watcher *)\*(C'\fR macro.
647.PP 1114.PP
648Each and every callback receives the event loop pointer as first, the 1115Each and every callback receives the event loop pointer as first, the
649registered watcher structure as second, and a bitset of received events as 1116registered watcher structure as second, and a bitset of received events as
650third argument. 1117third argument.
651.PP 1118.PP
… …
676The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread. 1143The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread.
677.ie n .IP """EV_CHILD""" 4 1144.ie n .IP """EV_CHILD""" 4
678.el .IP "\f(CWEV_CHILD\fR" 4 1145.el .IP "\f(CWEV_CHILD\fR" 4
679.IX Item "EV_CHILD" 1146.IX Item "EV_CHILD"
680The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change. 1147The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change.
1148.ie n .IP """EV_STAT""" 4
1149.el .IP "\f(CWEV_STAT\fR" 4
1150.IX Item "EV_STAT"
1151The path specified in the \f(CW\*(C`ev_stat\*(C'\fR watcher changed its attributes somehow.
681.ie n .IP """EV_IDLE""" 4 1152.ie n .IP """EV_IDLE""" 4
682.el .IP "\f(CWEV_IDLE\fR" 4 1153.el .IP "\f(CWEV_IDLE\fR" 4
683.IX Item "EV_IDLE" 1154.IX Item "EV_IDLE"
684The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do. 1155The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do.
685.ie n .IP """EV_PREPARE""" 4 1156.ie n .IP """EV_PREPARE""" 4
… …
695\&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any 1166\&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any
696received events. Callbacks of both watcher types can start and stop as 1167received events. Callbacks of both watcher types can start and stop as
697many watchers as they want, and all of them will be taken into account 1168many watchers as they want, and all of them will be taken into account
698(for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep 1169(for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep
699\&\f(CW\*(C`ev_loop\*(C'\fR from blocking). 1170\&\f(CW\*(C`ev_loop\*(C'\fR from blocking).
1171.ie n .IP """EV_EMBED""" 4
1172.el .IP "\f(CWEV_EMBED\fR" 4
1173.IX Item "EV_EMBED"
1174The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.
1175.ie n .IP """EV_FORK""" 4
1176.el .IP "\f(CWEV_FORK\fR" 4
1177.IX Item "EV_FORK"
1178The event loop has been resumed in the child process after fork (see
1179\&\f(CW\*(C`ev_fork\*(C'\fR).
1180.ie n .IP """EV_ASYNC""" 4
1181.el .IP "\f(CWEV_ASYNC\fR" 4
1182.IX Item "EV_ASYNC"
1183The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR).
1184.ie n .IP """EV_CUSTOM""" 4
1185.el .IP "\f(CWEV_CUSTOM\fR" 4
1186.IX Item "EV_CUSTOM"
1187Not ever sent (or otherwise used) by libev itself, but can be freely used
1188by libev users to signal watchers (e.g. via \f(CW\*(C`ev_feed_event\*(C'\fR).
700.ie n .IP """EV_ERROR""" 4 1189.ie n .IP """EV_ERROR""" 4
701.el .IP "\f(CWEV_ERROR\fR" 4 1190.el .IP "\f(CWEV_ERROR\fR" 4
702.IX Item "EV_ERROR" 1191.IX Item "EV_ERROR"
703An unspecified error has occured, the watcher has been stopped. This might 1192An unspecified error has occurred, the watcher has been stopped. This might
704happen because the watcher could not be properly started because libev 1193happen because the watcher could not be properly started because libev
705ran out of memory, a file descriptor was found to be closed or any other 1194ran out of memory, a file descriptor was found to be closed or any other
1195problem. Libev considers these application bugs.
1196.Sp
706problem. You best act on it by reporting the problem and somehow coping 1197You best act on it by reporting the problem and somehow coping with the
707with the watcher being stopped. 1198watcher being stopped. Note that well-written programs should not receive
1199an error ever, so when your watcher receives it, this usually indicates a
1200bug in your program.
708.Sp 1201.Sp
709Libev will usually signal a few \*(L"dummy\*(R" events together with an error, 1202Libev will usually signal a few \*(L"dummy\*(R" events together with an error, for
710for example it might indicate that a fd is readable or writable, and if 1203example it might indicate that a fd is readable or writable, and if your
711your callbacks is well-written it can just attempt the operation and cope 1204callbacks is well-written it can just attempt the operation and cope with
712with the error from \fIread()\fR or \fIwrite()\fR. This will not work in multithreaded 1205the error from \fIread()\fR or \fIwrite()\fR. This will not work in multi-threaded
713programs, though, so beware. 1206programs, though, as the fd could already be closed and reused for another
1207thing, so beware.
1208.SS "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0"
1209.IX Subsection "GENERIC WATCHER FUNCTIONS"
1210.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
1211.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
1212.IX Item "ev_init (ev_TYPE *watcher, callback)"
1213This macro initialises the generic portion of a watcher. The contents
1214of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
1215the generic parts of the watcher are initialised, you \fIneed\fR to call
1216the type-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR macro afterwards to initialise the
1217type-specific parts. For each type there is also a \f(CW\*(C`ev_TYPE_init\*(C'\fR macro
1218which rolls both calls into one.
1219.Sp
1220You can reinitialise a watcher at any time as long as it has been stopped
1221(or never started) and there are no pending events outstanding.
1222.Sp
1223The callback is always of type \f(CW\*(C`void (*)(struct ev_loop *loop, ev_TYPE *watcher,
1224int revents)\*(C'\fR.
1225.Sp
1226Example: Initialise an \f(CW\*(C`ev_io\*(C'\fR watcher in two steps.
1227.Sp
1228.Vb 3
1229\& ev_io w;
1230\& ev_init (&w, my_cb);
1231\& ev_io_set (&w, STDIN_FILENO, EV_READ);
1232.Ve
1233.ie n .IP """ev_TYPE_set"" (ev_TYPE *, [args])" 4
1234.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *, [args])" 4
1235.IX Item "ev_TYPE_set (ev_TYPE *, [args])"
1236This macro initialises the type-specific parts of a watcher. You need to
1237call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
1238call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
1239macro on a watcher that is active (it can be pending, however, which is a
1240difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
1241.Sp
1242Although some watcher types do not have type-specific arguments
1243(e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
1244.Sp
1245See \f(CW\*(C`ev_init\*(C'\fR, above, for an example.
1246.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
1247.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
1248.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
1249This convenience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
1250calls into a single call. This is the most convenient method to initialise
1251a watcher. The same limitations apply, of course.
1252.Sp
1253Example: Initialise and set an \f(CW\*(C`ev_io\*(C'\fR watcher in one step.
1254.Sp
1255.Vb 1
1256\& ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1257.Ve
1258.ie n .IP """ev_TYPE_start"" (loop *, ev_TYPE *watcher)" 4
1259.el .IP "\f(CWev_TYPE_start\fR (loop *, ev_TYPE *watcher)" 4
1260.IX Item "ev_TYPE_start (loop *, ev_TYPE *watcher)"
1261Starts (activates) the given watcher. Only active watchers will receive
1262events. If the watcher is already active nothing will happen.
1263.Sp
1264Example: Start the \f(CW\*(C`ev_io\*(C'\fR watcher that is being abused as example in this
1265whole section.
1266.Sp
1267.Vb 1
1268\& ev_io_start (EV_DEFAULT_UC, &w);
1269.Ve
1270.ie n .IP """ev_TYPE_stop"" (loop *, ev_TYPE *watcher)" 4
1271.el .IP "\f(CWev_TYPE_stop\fR (loop *, ev_TYPE *watcher)" 4
1272.IX Item "ev_TYPE_stop (loop *, ev_TYPE *watcher)"
1273Stops the given watcher if active, and clears the pending status (whether
1274the watcher was active or not).
1275.Sp
1276It is possible that stopped watchers are pending \- for example,
1277non-repeating timers are being stopped when they become pending \- but
1278calling \f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor
1279pending. If you want to free or reuse the memory used by the watcher it is
1280therefore a good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
1281.IP "bool ev_is_active (ev_TYPE *watcher)" 4
1282.IX Item "bool ev_is_active (ev_TYPE *watcher)"
1283Returns a true value iff the watcher is active (i.e. it has been started
1284and not yet been stopped). As long as a watcher is active you must not modify
1285it.
1286.IP "bool ev_is_pending (ev_TYPE *watcher)" 4
1287.IX Item "bool ev_is_pending (ev_TYPE *watcher)"
1288Returns a true value iff the watcher is pending, (i.e. it has outstanding
1289events but its callback has not yet been invoked). As long as a watcher
1290is pending (but not active) you must not call an init function on it (but
1291\&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe), you must not change its priority, and you must
1292make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR
1293it).
1294.IP "callback ev_cb (ev_TYPE *watcher)" 4
1295.IX Item "callback ev_cb (ev_TYPE *watcher)"
1296Returns the callback currently set on the watcher.
1297.IP "ev_cb_set (ev_TYPE *watcher, callback)" 4
1298.IX Item "ev_cb_set (ev_TYPE *watcher, callback)"
1299Change the callback. You can change the callback at virtually any time
1300(modulo threads).
1301.IP "ev_set_priority (ev_TYPE *watcher, priority)" 4
1302.IX Item "ev_set_priority (ev_TYPE *watcher, priority)"
1303.PD 0
1304.IP "int ev_priority (ev_TYPE *watcher)" 4
1305.IX Item "int ev_priority (ev_TYPE *watcher)"
1306.PD
1307Set and query the priority of the watcher. The priority is a small
1308integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR
1309(default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked
1310before watchers with lower priority, but priority will not keep watchers
1311from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
1312.Sp
1313If you need to suppress invocation when higher priority events are pending
1314you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
1315.Sp
1316You \fImust not\fR change the priority of a watcher as long as it is active or
1317pending.
1318.Sp
1319Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
1320fine, as long as you do not mind that the priority value you query might
1321or might not have been clamped to the valid range.
1322.Sp
1323The default priority used by watchers when no priority has been set is
1324always \f(CW0\fR, which is supposed to not be too high and not be too low :).
1325.Sp
1326See \*(L"\s-1WATCHER\s0 \s-1PRIORITY\s0 \s-1MODELS\s0\*(R", below, for a more thorough treatment of
1327priorities.
1328.IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
1329.IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
1330Invoke the \f(CW\*(C`watcher\*(C'\fR with the given \f(CW\*(C`loop\*(C'\fR and \f(CW\*(C`revents\*(C'\fR. Neither
1331\&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback
1332can deal with that fact, as both are simply passed through to the
1333callback.
1334.IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
1335.IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
1336If the watcher is pending, this function clears its pending status and
1337returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the
1338watcher isn't pending it does nothing and returns \f(CW0\fR.
1339.Sp
1340Sometimes it can be useful to \*(L"poll\*(R" a watcher instead of waiting for its
1341callback to be invoked, which can be accomplished with this function.
714.Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0" 1342.SS "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0"
715.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER" 1343.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
716Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change 1344Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change
717and read at any time, libev will completely ignore it. This can be used 1345and read at any time: libev will completely ignore it. This can be used
718to associate arbitrary data with your watcher. If you need more data and 1346to associate arbitrary data with your watcher. If you need more data and
719don't want to allocate memory and store a pointer to it in that data 1347don't want to allocate memory and store a pointer to it in that data
720member, you can also \*(L"subclass\*(R" the watcher type and provide your own 1348member, you can also \*(L"subclass\*(R" the watcher type and provide your own
721data: 1349data:
722.PP 1350.PP
723.Vb 7 1351.Vb 7
724\& struct my_io 1352\& struct my_io
725\& { 1353\& {
726\& struct ev_io io; 1354\& ev_io io;
727\& int otherfd; 1355\& int otherfd;
728\& void *somedata; 1356\& void *somedata;
729\& struct whatever *mostinteresting; 1357\& struct whatever *mostinteresting;
730\& } 1358\& };
1359\&
1360\& ...
1361\& struct my_io w;
1362\& ev_io_init (&w.io, my_cb, fd, EV_READ);
731.Ve 1363.Ve
732.PP 1364.PP
733And since your callback will be called with a pointer to the watcher, you 1365And since your callback will be called with a pointer to the watcher, you
734can cast it back to your own type: 1366can cast it back to your own type:
735.PP 1367.PP
736.Vb 5 1368.Vb 5
737\& static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents) 1369\& static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
738\& { 1370\& {
739\& struct my_io *w = (struct my_io *)w_; 1371\& struct my_io *w = (struct my_io *)w_;
740\& ... 1372\& ...
741\& } 1373\& }
742.Ve 1374.Ve
743.PP 1375.PP
744More interesting and less C\-conformant ways of catsing your callback type 1376More interesting and less C\-conformant ways of casting your callback type
745have been omitted.... 1377instead have been omitted.
1378.PP
1379Another common scenario is to use some data structure with multiple
1380embedded watchers:
1381.PP
1382.Vb 6
1383\& struct my_biggy
1384\& {
1385\& int some_data;
1386\& ev_timer t1;
1387\& ev_timer t2;
1388\& }
1389.Ve
1390.PP
1391In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more
1392complicated: Either you store the address of your \f(CW\*(C`my_biggy\*(C'\fR struct
1393in the \f(CW\*(C`data\*(C'\fR member of the watcher (for woozies), or you need to use
1394some pointer arithmetic using \f(CW\*(C`offsetof\*(C'\fR inside your watchers (for real
1395programmers):
1396.PP
1397.Vb 1
1398\& #include <stddef.h>
1399\&
1400\& static void
1401\& t1_cb (EV_P_ ev_timer *w, int revents)
1402\& {
1403\& struct my_biggy big = (struct my_biggy *)
1404\& (((char *)w) \- offsetof (struct my_biggy, t1));
1405\& }
1406\&
1407\& static void
1408\& t2_cb (EV_P_ ev_timer *w, int revents)
1409\& {
1410\& struct my_biggy big = (struct my_biggy *)
1411\& (((char *)w) \- offsetof (struct my_biggy, t2));
1412\& }
1413.Ve
1414.SS "\s-1WATCHER\s0 \s-1PRIORITY\s0 \s-1MODELS\s0"
1415.IX Subsection "WATCHER PRIORITY MODELS"
1416Many event loops support \fIwatcher priorities\fR, which are usually small
1417integers that influence the ordering of event callback invocation
1418between watchers in some way, all else being equal.
1419.PP
1420In libev, Watcher priorities can be set using \f(CW\*(C`ev_set_priority\*(C'\fR. See its
1421description for the more technical details such as the actual priority
1422range.
1423.PP
1424There are two common ways how these these priorities are being interpreted
1425by event loops:
1426.PP
1427In the more common lock-out model, higher priorities \*(L"lock out\*(R" invocation
1428of lower priority watchers, which means as long as higher priority
1429watchers receive events, lower priority watchers are not being invoked.
1430.PP
1431The less common only-for-ordering model uses priorities solely to order
1432callback invocation within a single event loop iteration: Higher priority
1433watchers are invoked before lower priority ones, but they all get invoked
1434before polling for new events.
1435.PP
1436Libev uses the second (only-for-ordering) model for all its watchers
1437except for idle watchers (which use the lock-out model).
1438.PP
1439The rationale behind this is that implementing the lock-out model for
1440watchers is not well supported by most kernel interfaces, and most event
1441libraries will just poll for the same events again and again as long as
1442their callbacks have not been executed, which is very inefficient in the
1443common case of one high-priority watcher locking out a mass of lower
1444priority ones.
1445.PP
1446Static (ordering) priorities are most useful when you have two or more
1447watchers handling the same resource: a typical usage example is having an
1448\&\f(CW\*(C`ev_io\*(C'\fR watcher to receive data, and an associated \f(CW\*(C`ev_timer\*(C'\fR to handle
1449timeouts. Under load, data might be received while the program handles
1450other jobs, but since timers normally get invoked first, the timeout
1451handler will be executed before checking for data. In that case, giving
1452the timer a lower priority than the I/O watcher ensures that I/O will be
1453handled first even under adverse conditions (which is usually, but not
1454always, what you want).
1455.PP
1456Since idle watchers use the \*(L"lock-out\*(R" model, meaning that idle watchers
1457will only be executed when no same or higher priority watchers have
1458received events, they can be used to implement the \*(L"lock-out\*(R" model when
1459required.
1460.PP
1461For example, to emulate how many other event libraries handle priorities,
1462you can associate an \f(CW\*(C`ev_idle\*(C'\fR watcher to each such watcher, and in
1463the normal watcher callback, you just start the idle watcher. The real
1464processing is done in the idle watcher callback. This causes libev to
1465continously poll and process kernel event data for the watcher, but when
1466the lock-out case is known to be rare (which in turn is rare :), this is
1467workable.
1468.PP
1469Usually, however, the lock-out model implemented that way will perform
1470miserably under the type of load it was designed to handle. In that case,
1471it might be preferable to stop the real watcher before starting the
1472idle watcher, so the kernel will not have to process the event in case
1473the actual processing will be delayed for considerable time.
1474.PP
1475Here is an example of an I/O watcher that should run at a strictly lower
1476priority than the default, and which should only process data when no
1477other events are pending:
1478.PP
1479.Vb 2
1480\& ev_idle idle; // actual processing watcher
1481\& ev_io io; // actual event watcher
1482\&
1483\& static void
1484\& io_cb (EV_P_ ev_io *w, int revents)
1485\& {
1486\& // stop the I/O watcher, we received the event, but
1487\& // are not yet ready to handle it.
1488\& ev_io_stop (EV_A_ w);
1489\&
1490\& // start the idle watcher to ahndle the actual event.
1491\& // it will not be executed as long as other watchers
1492\& // with the default priority are receiving events.
1493\& ev_idle_start (EV_A_ &idle);
1494\& }
1495\&
1496\& static void
1497\& idle_cb (EV_P_ ev_idle *w, int revents)
1498\& {
1499\& // actual processing
1500\& read (STDIN_FILENO, ...);
1501\&
1502\& // have to start the I/O watcher again, as
1503\& // we have handled the event
1504\& ev_io_start (EV_P_ &io);
1505\& }
1506\&
1507\& // initialisation
1508\& ev_idle_init (&idle, idle_cb);
1509\& ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
1510\& ev_io_start (EV_DEFAULT_ &io);
1511.Ve
1512.PP
1513In the \*(L"real\*(R" world, it might also be beneficial to start a timer, so that
1514low-priority connections can not be locked out forever under load. This
1515enables your program to keep a lower latency for important connections
1516during short periods of high load, while not completely locking out less
1517important ones.
746.SH "WATCHER TYPES" 1518.SH "WATCHER TYPES"
747.IX Header "WATCHER TYPES" 1519.IX Header "WATCHER TYPES"
748This section describes each watcher in detail, but will not repeat 1520This section describes each watcher in detail, but will not repeat
749information given in the last section. 1521information given in the last section. Any initialisation/set macros,
1522functions and members specific to the watcher type are explained.
1523.PP
1524Members are additionally marked with either \fI[read\-only]\fR, meaning that,
1525while the watcher is active, you can look at the member and expect some
1526sensible content, but you must not modify it (you can modify it while the
1527watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
1528means you can expect it to have some sensible content while the watcher
1529is active, but you can also modify it. Modifying it may not do something
1530sensible or take immediate effect (or do anything at all), but libev will
1531not crash or malfunction in any way.
750.ie n .Sh """ev_io"" \- is this file descriptor readable or writable" 1532.ie n .SS """ev_io"" \- is this file descriptor readable or writable?"
751.el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable" 1533.el .SS "\f(CWev_io\fP \- is this file descriptor readable or writable?"
752.IX Subsection "ev_io - is this file descriptor readable or writable" 1534.IX Subsection "ev_io - is this file descriptor readable or writable?"
753I/O watchers check whether a file descriptor is readable or writable 1535I/O watchers check whether a file descriptor is readable or writable
754in each iteration of the event loop (This behaviour is called 1536in each iteration of the event loop, or, more precisely, when reading
755level-triggering because you keep receiving events as long as the 1537would not block the process and writing would at least be able to write
756condition persists. Remember you can stop the watcher if you don't want to 1538some data. This behaviour is called level-triggering because you keep
757act on the event and neither want to receive future events). 1539receiving events as long as the condition persists. Remember you can stop
1540the watcher if you don't want to act on the event and neither want to
1541receive future events.
758.PP 1542.PP
759In general you can register as many read and/or write event watchers per 1543In general you can register as many read and/or write event watchers per
760fd as you want (as long as you don't confuse yourself). Setting all file 1544fd as you want (as long as you don't confuse yourself). Setting all file
761descriptors to non-blocking mode is also usually a good idea (but not 1545descriptors to non-blocking mode is also usually a good idea (but not
762required if you know what you are doing). 1546required if you know what you are doing).
763.PP 1547.PP
764You have to be careful with dup'ed file descriptors, though. Some backends 1548If you cannot use non-blocking mode, then force the use of a
765(the linux epoll backend is a notable example) cannot handle dup'ed file 1549known-to-be-good backend (at the time of this writing, this includes only
766descriptors correctly if you register interest in two or more fds pointing 1550\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and \f(CW\*(C`EVBACKEND_POLL\*(C'\fR). The same applies to file
767to the same underlying file/socket etc. description (that is, they share 1551descriptors for which non-blocking operation makes no sense (such as
768the same underlying \*(L"file open\*(R"). 1552files) \- libev doesn't guarentee any specific behaviour in that case.
769.PP 1553.PP
770If you must do this, then force the use of a known-to-be-good backend 1554Another thing you have to watch out for is that it is quite easy to
771(at the time of this writing, this includes only \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and 1555receive \*(L"spurious\*(R" readiness notifications, that is your callback might
1556be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block
1557because there is no data. Not only are some backends known to create a
1558lot of those (for example Solaris ports), it is very easy to get into
1559this situation even with a relatively standard program structure. Thus
1560it is best to always use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning
1561\&\f(CW\*(C`EAGAIN\*(C'\fR is far preferable to a program hanging until some data arrives.
1562.PP
1563If you cannot run the fd in non-blocking mode (for example you should
1564not play around with an Xlib connection), then you have to separately
1565re-test whether a file descriptor is really ready with a known-to-be good
1566interface such as poll (fortunately in our Xlib example, Xlib already
1567does this on its own, so its quite safe to use). Some people additionally
1568use \f(CW\*(C`SIGALRM\*(C'\fR and an interval timer, just to be sure you won't block
1569indefinitely.
1570.PP
1571But really, best use non-blocking mode.
1572.PP
1573\fIThe special problem of disappearing file descriptors\fR
1574.IX Subsection "The special problem of disappearing file descriptors"
1575.PP
1576Some backends (e.g. kqueue, epoll) need to be told about closing a file
1577descriptor (either due to calling \f(CW\*(C`close\*(C'\fR explicitly or any other means,
1578such as \f(CW\*(C`dup2\*(C'\fR). The reason is that you register interest in some file
1579descriptor, but when it goes away, the operating system will silently drop
1580this interest. If another file descriptor with the same number then is
1581registered with libev, there is no efficient way to see that this is, in
1582fact, a different file descriptor.
1583.PP
1584To avoid having to explicitly tell libev about such cases, libev follows
1585the following policy: Each time \f(CW\*(C`ev_io_set\*(C'\fR is being called, libev
1586will assume that this is potentially a new file descriptor, otherwise
1587it is assumed that the file descriptor stays the same. That means that
1588you \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
1589descriptor even if the file descriptor number itself did not change.
1590.PP
1591This is how one would do it normally anyway, the important point is that
1592the libev application should not optimise around libev but should leave
1593optimisations to libev.
1594.PP
1595\fIThe special problem of dup'ed file descriptors\fR
1596.IX Subsection "The special problem of dup'ed file descriptors"
1597.PP
1598Some backends (e.g. epoll), cannot register events for file descriptors,
1599but only events for the underlying file descriptions. That means when you
1600have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register
1601events for them, only one file descriptor might actually receive events.
1602.PP
1603There is no workaround possible except not registering events
1604for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
1605\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1606.PP
1607\fIThe special problem of fork\fR
1608.IX Subsection "The special problem of fork"
1609.PP
1610Some backends (epoll, kqueue) do not support \f(CW\*(C`fork ()\*(C'\fR at all or exhibit
1611useless behaviour. Libev fully supports fork, but needs to be told about
1612it in the child.
1613.PP
1614To support fork in your programs, you either have to call
1615\&\f(CW\*(C`ev_default_fork ()\*(C'\fR or \f(CW\*(C`ev_loop_fork ()\*(C'\fR after a fork in the child,
1616enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or
772\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR). 1617\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1618.PP
1619\fIThe special problem of \s-1SIGPIPE\s0\fR
1620.IX Subsection "The special problem of SIGPIPE"
1621.PP
1622While not really specific to libev, it is easy to forget about \f(CW\*(C`SIGPIPE\*(C'\fR:
1623when writing to a pipe whose other end has been closed, your program gets
1624sent a \s-1SIGPIPE\s0, which, by default, aborts your program. For most programs
1625this is sensible behaviour, for daemons, this is usually undesirable.
1626.PP
1627So when you encounter spurious, unexplained daemon exits, make sure you
1628ignore \s-1SIGPIPE\s0 (and maybe make sure you log the exit status of your daemon
1629somewhere, as that would have given you a big clue).
1630.PP
1631\fIWatcher-Specific Functions\fR
1632.IX Subsection "Watcher-Specific Functions"
773.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4 1633.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
774.IX Item "ev_io_init (ev_io *, callback, int fd, int events)" 1634.IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
775.PD 0 1635.PD 0
776.IP "ev_io_set (ev_io *, int fd, int events)" 4 1636.IP "ev_io_set (ev_io *, int fd, int events)" 4
777.IX Item "ev_io_set (ev_io *, int fd, int events)" 1637.IX Item "ev_io_set (ev_io *, int fd, int events)"
778.PD 1638.PD
779Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The fd is the file descriptor to rceeive 1639Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to
780events 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 | 1640receive 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
781EV_WRITE\*(C'\fR to receive the given events. 1641\&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR, to express the desire to receive the given events.
782.Sp 1642.IP "int fd [read\-only]" 4
783Please note that most of the more scalable backend mechanisms (for example 1643.IX Item "int fd [read-only]"
784epoll and solaris ports) can result in spurious readyness notifications 1644The file descriptor being watched.
785for file descriptors, so you practically need to use non-blocking I/O (and 1645.IP "int events [read\-only]" 4
786treat callback invocation as hint only), or retest separately with a safe 1646.IX Item "int events [read-only]"
787interface before doing I/O (XLib can do this), or force the use of either 1647The events being watched.
788\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR, which don't suffer from this
789problem. Also note that it is quite easy to have your callback invoked
790when the readyness condition is no longer valid even when employing
791typical ways of handling events, so its a good idea to use non-blocking
792I/O unconditionally.
793.PP 1648.PP
1649\fIExamples\fR
1650.IX Subsection "Examples"
1651.PP
794Example: call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well 1652Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
795readable, but only once. Since it is likely line\-buffered, you could 1653readable, but only once. Since it is likely line-buffered, you could
796attempt to read a whole line in the callback: 1654attempt to read a whole line in the callback.
797.PP 1655.PP
798.Vb 6 1656.Vb 6
799\& static void 1657\& static void
800\& stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents) 1658\& stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
801\& { 1659\& {
802\& ev_io_stop (loop, w); 1660\& ev_io_stop (loop, w);
803\& .. read from stdin here (or from w->fd) and haqndle any I/O errors 1661\& .. read from stdin here (or from w\->fd) and handle any I/O errors
804\& } 1662\& }
805.Ve 1663\&
806.PP
807.Vb 6
808\& ... 1664\& ...
809\& struct ev_loop *loop = ev_default_init (0); 1665\& struct ev_loop *loop = ev_default_init (0);
810\& struct ev_io stdin_readable; 1666\& ev_io stdin_readable;
811\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ); 1667\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
812\& ev_io_start (loop, &stdin_readable); 1668\& ev_io_start (loop, &stdin_readable);
813\& ev_loop (loop, 0); 1669\& ev_loop (loop, 0);
814.Ve 1670.Ve
815.ie n .Sh """ev_timer"" \- relative and optionally recurring timeouts" 1671.ie n .SS """ev_timer"" \- relative and optionally repeating timeouts"
816.el .Sh "\f(CWev_timer\fP \- relative and optionally recurring timeouts" 1672.el .SS "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
817.IX Subsection "ev_timer - relative and optionally recurring timeouts" 1673.IX Subsection "ev_timer - relative and optionally repeating timeouts"
818Timer watchers are simple relative timers that generate an event after a 1674Timer watchers are simple relative timers that generate an event after a
819given time, and optionally repeating in regular intervals after that. 1675given time, and optionally repeating in regular intervals after that.
820.PP 1676.PP
821The timers are based on real time, that is, if you register an event that 1677The timers are based on real time, that is, if you register an event that
822times out after an hour and you reset your system clock to last years 1678times out after an hour and you reset your system clock to January last
823time, it will still time out after (roughly) and hour. \*(L"Roughly\*(R" because 1679year, it will still time out after (roughly) one hour. \*(L"Roughly\*(R" because
824detecting time jumps is hard, and some inaccuracies are unavoidable (the 1680detecting time jumps is hard, and some inaccuracies are unavoidable (the
825monotonic clock option helps a lot here). 1681monotonic clock option helps a lot here).
1682.PP
1683The callback is guaranteed to be invoked only \fIafter\fR its timeout has
1684passed (not \fIat\fR, so on systems with very low-resolution clocks this
1685might introduce a small delay). If multiple timers become ready during the
1686same loop iteration then the ones with earlier time-out values are invoked
1687before ones of the same priority with later time-out values (but this is
1688no longer true when a callback calls \f(CW\*(C`ev_loop\*(C'\fR recursively).
1689.PP
1690\fIBe smart about timeouts\fR
1691.IX Subsection "Be smart about timeouts"
1692.PP
1693Many real-world problems involve some kind of timeout, usually for error
1694recovery. A typical example is an \s-1HTTP\s0 request \- if the other side hangs,
1695you want to raise some error after a while.
1696.PP
1697What follows are some ways to handle this problem, from obvious and
1698inefficient to smart and efficient.
1699.PP
1700In the following, a 60 second activity timeout is assumed \- a timeout that
1701gets reset to 60 seconds each time there is activity (e.g. each time some
1702data or other life sign was received).
1703.IP "1. Use a timer and stop, reinitialise and start it on activity." 4
1704.IX Item "1. Use a timer and stop, reinitialise and start it on activity."
1705This is the most obvious, but not the most simple way: In the beginning,
1706start the watcher:
1707.Sp
1708.Vb 2
1709\& ev_timer_init (timer, callback, 60., 0.);
1710\& ev_timer_start (loop, timer);
1711.Ve
1712.Sp
1713Then, each time there is some activity, \f(CW\*(C`ev_timer_stop\*(C'\fR it, initialise it
1714and start it again:
1715.Sp
1716.Vb 3
1717\& ev_timer_stop (loop, timer);
1718\& ev_timer_set (timer, 60., 0.);
1719\& ev_timer_start (loop, timer);
1720.Ve
1721.Sp
1722This is relatively simple to implement, but means that each time there is
1723some activity, libev will first have to remove the timer from its internal
1724data structure and then add it again. Libev tries to be fast, but it's
1725still not a constant-time operation.
1726.ie n .IP "2. Use a timer and re-start it with ""ev_timer_again"" inactivity." 4
1727.el .IP "2. Use a timer and re-start it with \f(CWev_timer_again\fR inactivity." 4
1728.IX Item "2. Use a timer and re-start it with ev_timer_again inactivity."
1729This is the easiest way, and involves using \f(CW\*(C`ev_timer_again\*(C'\fR instead of
1730\&\f(CW\*(C`ev_timer_start\*(C'\fR.
1731.Sp
1732To implement this, configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value
1733of \f(CW60\fR and then call \f(CW\*(C`ev_timer_again\*(C'\fR at start and each time you
1734successfully read or write some data. If you go into an idle state where
1735you do not expect data to travel on the socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR
1736the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will automatically restart it if need be.
1737.Sp
1738That means you can ignore both the \f(CW\*(C`ev_timer_start\*(C'\fR function and the
1739\&\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
1740member and \f(CW\*(C`ev_timer_again\*(C'\fR.
1741.Sp
1742At start:
1743.Sp
1744.Vb 3
1745\& ev_init (timer, callback);
1746\& timer\->repeat = 60.;
1747\& ev_timer_again (loop, timer);
1748.Ve
1749.Sp
1750Each time there is some activity:
1751.Sp
1752.Vb 1
1753\& ev_timer_again (loop, timer);
1754.Ve
1755.Sp
1756It is even possible to change the time-out on the fly, regardless of
1757whether the watcher is active or not:
1758.Sp
1759.Vb 2
1760\& timer\->repeat = 30.;
1761\& ev_timer_again (loop, timer);
1762.Ve
1763.Sp
1764This is slightly more efficient then stopping/starting the timer each time
1765you want to modify its timeout value, as libev does not have to completely
1766remove and re-insert the timer from/into its internal data structure.
1767.Sp
1768It is, however, even simpler than the \*(L"obvious\*(R" way to do it.
1769.IP "3. Let the timer time out, but then re-arm it as required." 4
1770.IX Item "3. Let the timer time out, but then re-arm it as required."
1771This method is more tricky, but usually most efficient: Most timeouts are
1772relatively long compared to the intervals between other activity \- in
1773our example, within 60 seconds, there are usually many I/O events with
1774associated activity resets.
1775.Sp
1776In this case, it would be more efficient to leave the \f(CW\*(C`ev_timer\*(C'\fR alone,
1777but remember the time of last activity, and check for a real timeout only
1778within the callback:
1779.Sp
1780.Vb 1
1781\& ev_tstamp last_activity; // time of last activity
1782\&
1783\& static void
1784\& callback (EV_P_ ev_timer *w, int revents)
1785\& {
1786\& ev_tstamp now = ev_now (EV_A);
1787\& ev_tstamp timeout = last_activity + 60.;
1788\&
1789\& // if last_activity + 60. is older than now, we did time out
1790\& if (timeout < now)
1791\& {
1792\& // timeout occured, take action
1793\& }
1794\& else
1795\& {
1796\& // callback was invoked, but there was some activity, re\-arm
1797\& // the watcher to fire in last_activity + 60, which is
1798\& // guaranteed to be in the future, so "again" is positive:
1799\& w\->repeat = timeout \- now;
1800\& ev_timer_again (EV_A_ w);
1801\& }
1802\& }
1803.Ve
1804.Sp
1805To summarise the callback: first calculate the real timeout (defined
1806as \*(L"60 seconds after the last activity\*(R"), then check if that time has
1807been reached, which means something \fIdid\fR, in fact, time out. Otherwise
1808the callback was invoked too early (\f(CW\*(C`timeout\*(C'\fR is in the future), so
1809re-schedule the timer to fire at that future time, to see if maybe we have
1810a timeout then.
1811.Sp
1812Note how \f(CW\*(C`ev_timer_again\*(C'\fR is used, taking advantage of the
1813\&\f(CW\*(C`ev_timer_again\*(C'\fR optimisation when the timer is already running.
1814.Sp
1815This scheme causes more callback invocations (about one every 60 seconds
1816minus half the average time between activity), but virtually no calls to
1817libev to change the timeout.
1818.Sp
1819To start the timer, simply initialise the watcher and set \f(CW\*(C`last_activity\*(C'\fR
1820to the current time (meaning we just have some activity :), then call the
1821callback, which will \*(L"do the right thing\*(R" and start the timer:
1822.Sp
1823.Vb 3
1824\& ev_init (timer, callback);
1825\& last_activity = ev_now (loop);
1826\& callback (loop, timer, EV_TIMEOUT);
1827.Ve
1828.Sp
1829And when there is some activity, simply store the current time in
1830\&\f(CW\*(C`last_activity\*(C'\fR, no libev calls at all:
1831.Sp
1832.Vb 1
1833\& last_actiivty = ev_now (loop);
1834.Ve
1835.Sp
1836This technique is slightly more complex, but in most cases where the
1837time-out is unlikely to be triggered, much more efficient.
1838.Sp
1839Changing the timeout is trivial as well (if it isn't hard-coded in the
1840callback :) \- just change the timeout and invoke the callback, which will
1841fix things for you.
1842.IP "4. Wee, just use a double-linked list for your timeouts." 4
1843.IX Item "4. Wee, just use a double-linked list for your timeouts."
1844If there is not one request, but many thousands (millions...), all
1845employing some kind of timeout with the same timeout value, then one can
1846do even better:
1847.Sp
1848When starting the timeout, calculate the timeout value and put the timeout
1849at the \fIend\fR of the list.
1850.Sp
1851Then use an \f(CW\*(C`ev_timer\*(C'\fR to fire when the timeout at the \fIbeginning\fR of
1852the list is expected to fire (for example, using the technique #3).
1853.Sp
1854When there is some activity, remove the timer from the list, recalculate
1855the timeout, append it to the end of the list again, and make sure to
1856update the \f(CW\*(C`ev_timer\*(C'\fR if it was taken from the beginning of the list.
1857.Sp
1858This way, one can manage an unlimited number of timeouts in O(1) time for
1859starting, stopping and updating the timers, at the expense of a major
1860complication, and having to use a constant timeout. The constant timeout
1861ensures that the list stays sorted.
1862.PP
1863So which method the best?
1864.PP
1865Method #2 is a simple no-brain-required solution that is adequate in most
1866situations. Method #3 requires a bit more thinking, but handles many cases
1867better, and isn't very complicated either. In most case, choosing either
1868one is fine, with #3 being better in typical situations.
1869.PP
1870Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
1871rather complicated, but extremely efficient, something that really pays
1872off after the first million or so of active timers, i.e. it's usually
1873overkill :)
1874.PP
1875\fIThe special problem of time updates\fR
1876.IX Subsection "The special problem of time updates"
1877.PP
1878Establishing the current time is a costly operation (it usually takes at
1879least two system calls): \s-1EV\s0 therefore updates its idea of the current
1880time only before and after \f(CW\*(C`ev_loop\*(C'\fR collects new events, which causes a
1881growing difference between \f(CW\*(C`ev_now ()\*(C'\fR and \f(CW\*(C`ev_time ()\*(C'\fR when handling
1882lots of events in one iteration.
826.PP 1883.PP
827The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR 1884The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
828time. This is usually the right thing as this timestamp refers to the time 1885time. This is usually the right thing as this timestamp refers to the time
829of the event triggering whatever timeout you are modifying/starting. If 1886of the event triggering whatever timeout you are modifying/starting. If
830you suspect event processing to be delayed and you \fIneed\fR to base the timeout 1887you suspect event processing to be delayed and you \fIneed\fR to base the
831on the current time, use something like this to adjust for this: 1888timeout on the current time, use something like this to adjust for this:
832.PP 1889.PP
833.Vb 1 1890.Vb 1
834\& ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); 1891\& ev_timer_set (&timer, after + ev_now () \- ev_time (), 0.);
835.Ve 1892.Ve
836.PP 1893.PP
837The callback is guarenteed to be invoked only when its timeout has passed, 1894If the event loop is suspended for a long time, you can also force an
838but if multiple timers become ready during the same loop iteration then 1895update of the time returned by \f(CW\*(C`ev_now ()\*(C'\fR by calling \f(CW\*(C`ev_now_update
839order of execution is undefined. 1896()\*(C'\fR.
1897.PP
1898\fIThe special problems of suspended animation\fR
1899.IX Subsection "The special problems of suspended animation"
1900.PP
1901When you leave the server world it is quite customary to hit machines that
1902can suspend/hibernate \- what happens to the clocks during such a suspend?
1903.PP
1904Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
1905all processes, while the clocks (\f(CW\*(C`times\*(C'\fR, \f(CW\*(C`CLOCK_MONOTONIC\*(C'\fR) continue
1906to run until the system is suspended, but they will not advance while the
1907system is suspended. That means, on resume, it will be as if the program
1908was frozen for a few seconds, but the suspend time will not be counted
1909towards \f(CW\*(C`ev_timer\*(C'\fR when a monotonic clock source is used. The real time
1910clock advanced as expected, but if it is used as sole clocksource, then a
1911long suspend would be detected as a time jump by libev, and timers would
1912be adjusted accordingly.
1913.PP
1914I would not be surprised to see different behaviour in different between
1915operating systems, \s-1OS\s0 versions or even different hardware.
1916.PP
1917The other form of suspend (job control, or sending a \s-1SIGSTOP\s0) will see a
1918time jump in the monotonic clocks and the realtime clock. If the program
1919is suspended for a very long time, and monotonic clock sources are in use,
1920then you can expect \f(CW\*(C`ev_timer\*(C'\fRs to expire as the full suspension time
1921will be counted towards the timers. When no monotonic clock source is in
1922use, then libev will again assume a timejump and adjust accordingly.
1923.PP
1924It might be beneficial for this latter case to call \f(CW\*(C`ev_suspend\*(C'\fR
1925and \f(CW\*(C`ev_resume\*(C'\fR in code that handles \f(CW\*(C`SIGTSTP\*(C'\fR, to at least get
1926deterministic behaviour in this case (you can do nothing against
1927\&\f(CW\*(C`SIGSTOP\*(C'\fR).
1928.PP
1929\fIWatcher-Specific Functions and Data Members\fR
1930.IX Subsection "Watcher-Specific Functions and Data Members"
840.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4 1931.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
841.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 1932.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
842.PD 0 1933.PD 0
843.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4 1934.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
844.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 1935.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
845.PD 1936.PD
846Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR is 1937Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR
847\&\f(CW0.\fR, then it will automatically be stopped. If it is positive, then the 1938is \f(CW0.\fR, then it will automatically be stopped once the timeout is
848timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds 1939reached. If it is positive, then the timer will automatically be
849later, again, and again, until stopped manually. 1940configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds later, again, and again,
1941until stopped manually.
850.Sp 1942.Sp
851The timer itself will do a best-effort at avoiding drift, that is, if you 1943The timer itself will do a best-effort at avoiding drift, that is, if
852configure a timer to trigger every 10 seconds, then it will trigger at 1944you configure a timer to trigger every 10 seconds, then it will normally
853exactly 10 second intervals. If, however, your program cannot keep up with 1945trigger at exactly 10 second intervals. If, however, your program cannot
854the timer (because it takes longer than those 10 seconds to do stuff) the 1946keep up with the timer (because it takes longer than those 10 seconds to
855timer will not fire more than once per event loop iteration. 1947do stuff) the timer will not fire more than once per event loop iteration.
856.IP "ev_timer_again (loop)" 4 1948.IP "ev_timer_again (loop, ev_timer *)" 4
857.IX Item "ev_timer_again (loop)" 1949.IX Item "ev_timer_again (loop, ev_timer *)"
858This will act as if the timer timed out and restart it again if it is 1950This will act as if the timer timed out and restart it again if it is
859repeating. The exact semantics are: 1951repeating. The exact semantics are:
860.Sp 1952.Sp
1953If the timer is pending, its pending status is cleared.
1954.Sp
861If the timer is started but nonrepeating, stop it. 1955If the timer is started but non-repeating, stop it (as if it timed out).
862.Sp 1956.Sp
863If the timer is repeating, either start it if necessary (with the repeat 1957If the timer is repeating, either start it if necessary (with the
864value), or reset the running timer to the repeat value. 1958\&\f(CW\*(C`repeat\*(C'\fR value), or reset the running timer to the \f(CW\*(C`repeat\*(C'\fR value.
865.Sp 1959.Sp
866This sounds a bit complicated, but here is a useful and typical 1960This sounds a bit complicated, see \*(L"Be smart about timeouts\*(R", above, for a
867example: Imagine you have a tcp connection and you want a so-called idle 1961usage example.
868timeout, that is, you want to be called when there have been, say, 60 1962.IP "ev_timer_remaining (loop, ev_timer *)" 4
869seconds of inactivity on the socket. The easiest way to do this is to 1963.IX Item "ev_timer_remaining (loop, ev_timer *)"
870configure an \f(CW\*(C`ev_timer\*(C'\fR with after=repeat=60 and calling ev_timer_again each 1964Returns the remaining time until a timer fires. If the timer is active,
871time you successfully read or write some data. If you go into an idle 1965then this time is relative to the current event loop time, otherwise it's
872state where you do not expect data to travel on the socket, you can stop 1966the timeout value currently configured.
873the timer, and again will automatically restart it if need be. 1967.Sp
1968That is, after an \f(CW\*(C`ev_timer_set (w, 5, 7)\*(C'\fR, \f(CW\*(C`ev_timer_remaining\*(C'\fR returns
1969\&\f(CW5\fR. When the timer is started and one second passes, \f(CW\*(C`ev_timer_remain\*(C'\fR
1970will return \f(CW4\fR. When the timer expires and is restarted, it will return
1971roughly \f(CW7\fR (likely slightly less as callback invocation takes some time,
1972too), and so on.
1973.IP "ev_tstamp repeat [read\-write]" 4
1974.IX Item "ev_tstamp repeat [read-write]"
1975The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
1976or \f(CW\*(C`ev_timer_again\*(C'\fR is called, and determines the next timeout (if any),
1977which is also when any modifications are taken into account.
874.PP 1978.PP
1979\fIExamples\fR
1980.IX Subsection "Examples"
1981.PP
875Example: create a timer that fires after 60 seconds. 1982Example: Create a timer that fires after 60 seconds.
876.PP 1983.PP
877.Vb 5 1984.Vb 5
878\& static void 1985\& static void
879\& one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents) 1986\& one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
880\& { 1987\& {
881\& .. one minute over, w is actually stopped right here 1988\& .. one minute over, w is actually stopped right here
882\& } 1989\& }
883.Ve 1990\&
884.PP
885.Vb 3
886\& struct ev_timer mytimer; 1991\& ev_timer mytimer;
887\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.); 1992\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
888\& ev_timer_start (loop, &mytimer); 1993\& ev_timer_start (loop, &mytimer);
889.Ve 1994.Ve
890.PP 1995.PP
891Example: create a timeout timer that times out after 10 seconds of 1996Example: Create a timeout timer that times out after 10 seconds of
892inactivity. 1997inactivity.
893.PP 1998.PP
894.Vb 5 1999.Vb 5
895\& static void 2000\& static void
896\& timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents) 2001\& timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
897\& { 2002\& {
898\& .. ten seconds without any activity 2003\& .. ten seconds without any activity
899\& } 2004\& }
900.Ve 2005\&
901.PP
902.Vb 4
903\& struct ev_timer mytimer; 2006\& ev_timer mytimer;
904\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */ 2007\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
905\& ev_timer_again (&mytimer); /* start timer */ 2008\& ev_timer_again (&mytimer); /* start timer */
906\& ev_loop (loop, 0); 2009\& ev_loop (loop, 0);
907.Ve 2010\&
908.PP
909.Vb 3
910\& // and in some piece of code that gets executed on any "activity": 2011\& // and in some piece of code that gets executed on any "activity":
911\& // reset the timeout to start ticking again at 10 seconds 2012\& // reset the timeout to start ticking again at 10 seconds
912\& ev_timer_again (&mytimer); 2013\& ev_timer_again (&mytimer);
913.Ve 2014.Ve
914.ie n .Sh """ev_periodic"" \- to cron or not to cron" 2015.ie n .SS """ev_periodic"" \- to cron or not to cron?"
915.el .Sh "\f(CWev_periodic\fP \- to cron or not to cron" 2016.el .SS "\f(CWev_periodic\fP \- to cron or not to cron?"
916.IX Subsection "ev_periodic - to cron or not to cron" 2017.IX Subsection "ev_periodic - to cron or not to cron?"
917Periodic watchers are also timers of a kind, but they are very versatile 2018Periodic watchers are also timers of a kind, but they are very versatile
918(and unfortunately a bit complex). 2019(and unfortunately a bit complex).
919.PP 2020.PP
920Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time) 2021Unlike \f(CW\*(C`ev_timer\*(C'\fR, periodic watchers are not based on real time (or
921but on wallclock time (absolute time). You can tell a periodic watcher 2022relative time, the physical time that passes) but on wall clock time
922to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a 2023(absolute time, the thing you can read on your calender or clock). The
923periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now () 2024difference is that wall clock time can run faster or slower than real
924+ 10.>) and then reset your system clock to the last year, then it will 2025time, and time jumps are not uncommon (e.g. when you adjust your
925take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger 2026wrist-watch).
926roughly 10 seconds later and of course not if you reset your system time
927again).
928.PP 2027.PP
929They can also be used to implement vastly more complex timers, such as 2028You can tell a periodic watcher to trigger after some specific point
930triggering an event on eahc midnight, local time. 2029in time: for example, if you tell a periodic watcher to trigger \*(L"in 10
2030seconds\*(R" (by specifying e.g. \f(CW\*(C`ev_now () + 10.\*(C'\fR, that is, an absolute time
2031not a delay) and then reset your system clock to January of the previous
2032year, then it will take a year or more to trigger the event (unlike an
2033\&\f(CW\*(C`ev_timer\*(C'\fR, which would still trigger roughly 10 seconds after starting
2034it, as it uses a relative timeout).
931.PP 2035.PP
2036\&\f(CW\*(C`ev_periodic\*(C'\fR watchers can also be used to implement vastly more complex
2037timers, such as triggering an event on each \*(L"midnight, local time\*(R", or
2038other complicated rules. This cannot be done with \f(CW\*(C`ev_timer\*(C'\fR watchers, as
2039those cannot react to time jumps.
2040.PP
932As with timers, the callback is guarenteed to be invoked only when the 2041As with timers, the callback is guaranteed to be invoked only when the
933time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready 2042point in time where it is supposed to trigger has passed. If multiple
934during the same loop iteration then order of execution is undefined. 2043timers become ready during the same loop iteration then the ones with
2044earlier time-out values are invoked before ones with later time-out values
2045(but this is no longer true when a callback calls \f(CW\*(C`ev_loop\*(C'\fR recursively).
2046.PP
2047\fIWatcher-Specific Functions and Data Members\fR
2048.IX Subsection "Watcher-Specific Functions and Data Members"
935.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4 2049.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
936.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 2050.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
937.PD 0 2051.PD 0
938.IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4 2052.IP "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
939.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 2053.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
940.PD 2054.PD
941Lots of arguments, lets sort it out... There are basically three modes of 2055Lots of arguments, let's sort it out... There are basically three modes of
942operation, and we will explain them from simplest to complex: 2056operation, and we will explain them from simplest to most complex:
943.RS 4 2057.RS 4
944.IP "* absolute timer (interval = reschedule_cb = 0)" 4 2058.IP "\(bu" 4
945.IX Item "absolute timer (interval = reschedule_cb = 0)" 2059absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
2060.Sp
946In this configuration the watcher triggers an event at the wallclock time 2061In this configuration the watcher triggers an event after the wall clock
947\&\f(CW\*(C`at\*(C'\fR and doesn't repeat. It will not adjust when a time jump occurs, 2062time \f(CW\*(C`offset\*(C'\fR has passed. It will not repeat and will not adjust when a
948that is, if it is to be run at January 1st 2011 then it will run when the 2063time jump occurs, that is, if it is to be run at January 1st 2011 then it
949system time reaches or surpasses this time. 2064will be stopped and invoked when the system clock reaches or surpasses
950.IP "* non-repeating interval timer (interval > 0, reschedule_cb = 0)" 4 2065this point in time.
951.IX Item "non-repeating interval timer (interval > 0, reschedule_cb = 0)" 2066.IP "\(bu" 4
2067repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
2068.Sp
952In this mode the watcher will always be scheduled to time out at the next 2069In this mode the watcher will always be scheduled to time out at the next
953\&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N) and then repeat, regardless 2070\&\f(CW\*(C`offset + N * interval\*(C'\fR time (for some integer N, which can also be
954of any time jumps. 2071negative) and then repeat, regardless of any time jumps. The \f(CW\*(C`offset\*(C'\fR
2072argument is merely an offset into the \f(CW\*(C`interval\*(C'\fR periods.
955.Sp 2073.Sp
956This can be used to create timers that do not drift with respect to system 2074This can be used to create timers that do not drift with respect to the
957time: 2075system clock, for example, here is an \f(CW\*(C`ev_periodic\*(C'\fR that triggers each
2076hour, on the hour (with respect to \s-1UTC\s0):
958.Sp 2077.Sp
959.Vb 1 2078.Vb 1
960\& ev_periodic_set (&periodic, 0., 3600., 0); 2079\& ev_periodic_set (&periodic, 0., 3600., 0);
961.Ve 2080.Ve
962.Sp 2081.Sp
963This doesn't mean there will always be 3600 seconds in between triggers, 2082This doesn't mean there will always be 3600 seconds in between triggers,
964but only that the the callback will be called when the system time shows a 2083but only that the callback will be called when the system time shows a
965full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible 2084full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
966by 3600. 2085by 3600.
967.Sp 2086.Sp
968Another way to think about it (for the mathematically inclined) is that 2087Another way to think about it (for the mathematically inclined) is that
969\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible 2088\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
970time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps. 2089time where \f(CW\*(C`time = offset (mod interval)\*(C'\fR, regardless of any time jumps.
971.IP "* manual reschedule mode (reschedule_cb = callback)" 4 2090.Sp
972.IX Item "manual reschedule mode (reschedule_cb = callback)" 2091For numerical stability it is preferable that the \f(CW\*(C`offset\*(C'\fR value is near
2092\&\f(CW\*(C`ev_now ()\*(C'\fR (the current time), but there is no range requirement for
2093this value, and in fact is often specified as zero.
2094.Sp
2095Note also that there is an upper limit to how often a timer can fire (\s-1CPU\s0
2096speed for example), so if \f(CW\*(C`interval\*(C'\fR is very small then timing stability
2097will of course deteriorate. Libev itself tries to be exact to be about one
2098millisecond (if the \s-1OS\s0 supports it and the machine is fast enough).
2099.IP "\(bu" 4
2100manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
2101.Sp
973In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being 2102In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`offset\*(C'\fR are both being
974ignored. Instead, each time the periodic watcher gets scheduled, the 2103ignored. Instead, each time the periodic watcher gets scheduled, the
975reschedule callback will be called with the watcher as first, and the 2104reschedule callback will be called with the watcher as first, and the
976current time as second argument. 2105current time as second argument.
977.Sp 2106.Sp
978\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, 2107\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, ever,
979ever, or make any event loop modifications\fR. If you need to stop it, 2108or make \s-1ANY\s0 other event loop modifications whatsoever, unless explicitly
980return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by 2109allowed by documentation here\fR.
981starting a prepare watcher).
982.Sp 2110.Sp
2111If you need to stop it, return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop
2112it afterwards (e.g. by starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is the
2113only event loop modification you are allowed to do).
2114.Sp
983Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w, 2115The callback prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(ev_periodic
984ev_tstamp now)\*(C'\fR, e.g.: 2116*w, ev_tstamp now)\*(C'\fR, e.g.:
985.Sp 2117.Sp
986.Vb 4 2118.Vb 5
2119\& static ev_tstamp
987\& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) 2120\& my_rescheduler (ev_periodic *w, ev_tstamp now)
988\& { 2121\& {
989\& return now + 60.; 2122\& return now + 60.;
990\& } 2123\& }
991.Ve 2124.Ve
992.Sp 2125.Sp
993It must return the next time to trigger, based on the passed time value 2126It must return the next time to trigger, based on the passed time value
994(that is, the lowest time value larger than to the second argument). It 2127(that is, the lowest time value larger than to the second argument). It
995will usually be called just before the callback will be triggered, but 2128will usually be called just before the callback will be triggered, but
996might be called at other times, too. 2129might be called at other times, too.
997.Sp 2130.Sp
998\&\s-1NOTE:\s0 \fIThis callback must always return a time that is later than the 2131\&\s-1NOTE:\s0 \fIThis callback must always return a time that is higher than or
999passed \f(CI\*(C`now\*(C'\fI value\fR. Not even \f(CW\*(C`now\*(C'\fR itself will do, it \fImust\fR be larger. 2132equal to the passed \f(CI\*(C`now\*(C'\fI value\fR.
1000.Sp 2133.Sp
1001This can be used to create very complex timers, such as a timer that 2134This can be used to create very complex timers, such as a timer that
1002triggers on each midnight, local time. To do this, you would calculate the 2135triggers on \*(L"next midnight, local time\*(R". To do this, you would calculate the
1003next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How 2136next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How
1004you do this is, again, up to you (but it is not trivial, which is the main 2137you do this is, again, up to you (but it is not trivial, which is the main
1005reason I omitted it as an example). 2138reason I omitted it as an example).
1006.RE 2139.RE
1007.RS 4 2140.RS 4
… …
1010.IX Item "ev_periodic_again (loop, ev_periodic *)" 2143.IX Item "ev_periodic_again (loop, ev_periodic *)"
1011Simply stops and restarts the periodic watcher again. This is only useful 2144Simply stops and restarts the periodic watcher again. This is only useful
1012when you changed some parameters or the reschedule callback would return 2145when you changed some parameters or the reschedule callback would return
1013a different time than the last time it was called (e.g. in a crond like 2146a different time than the last time it was called (e.g. in a crond like
1014program when the crontabs have changed). 2147program when the crontabs have changed).
2148.IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4
2149.IX Item "ev_tstamp ev_periodic_at (ev_periodic *)"
2150When active, returns the absolute time that the watcher is supposed
2151to trigger next. This is not the same as the \f(CW\*(C`offset\*(C'\fR argument to
2152\&\f(CW\*(C`ev_periodic_set\*(C'\fR, but indeed works even in interval and manual
2153rescheduling modes.
2154.IP "ev_tstamp offset [read\-write]" 4
2155.IX Item "ev_tstamp offset [read-write]"
2156When repeating, this contains the offset value, otherwise this is the
2157absolute point in time (the \f(CW\*(C`offset\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR,
2158although libev might modify this value for better numerical stability).
2159.Sp
2160Can be modified any time, but changes only take effect when the periodic
2161timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
2162.IP "ev_tstamp interval [read\-write]" 4
2163.IX Item "ev_tstamp interval [read-write]"
2164The current interval value. Can be modified any time, but changes only
2165take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
2166called.
2167.IP "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read\-write]" 4
2168.IX Item "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]"
2169The current reschedule callback, or \f(CW0\fR, if this functionality is
2170switched off. Can be changed any time, but changes only take effect when
2171the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1015.PP 2172.PP
2173\fIExamples\fR
2174.IX Subsection "Examples"
2175.PP
1016Example: call a callback every hour, or, more precisely, whenever the 2176Example: Call a callback every hour, or, more precisely, whenever the
1017system clock is divisible by 3600. The callback invocation times have 2177system time is divisible by 3600. The callback invocation times have
1018potentially a lot of jittering, but good long-term stability. 2178potentially a lot of jitter, but good long-term stability.
1019.PP 2179.PP
1020.Vb 5 2180.Vb 5
1021\& static void 2181\& static void
1022\& clock_cb (struct ev_loop *loop, struct ev_io *w, int revents) 2182\& clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1023\& { 2183\& {
1024\& ... its now a full hour (UTC, or TAI or whatever your clock follows) 2184\& ... its now a full hour (UTC, or TAI or whatever your clock follows)
1025\& } 2185\& }
1026.Ve 2186\&
1027.PP
1028.Vb 3
1029\& struct ev_periodic hourly_tick; 2187\& ev_periodic hourly_tick;
1030\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0); 2188\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1031\& ev_periodic_start (loop, &hourly_tick); 2189\& ev_periodic_start (loop, &hourly_tick);
1032.Ve 2190.Ve
1033.PP 2191.PP
1034Example: the same as above, but use a reschedule callback to do it: 2192Example: The same as above, but use a reschedule callback to do it:
1035.PP 2193.PP
1036.Vb 1 2194.Vb 1
1037\& #include <math.h> 2195\& #include <math.h>
1038.Ve 2196\&
1039.PP
1040.Vb 5
1041\& static ev_tstamp 2197\& static ev_tstamp
1042\& my_scheduler_cb (struct ev_periodic *w, ev_tstamp now) 2198\& my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1043\& { 2199\& {
1044\& return fmod (now, 3600.) + 3600.; 2200\& return now + (3600. \- fmod (now, 3600.));
1045\& } 2201\& }
1046.Ve 2202\&
1047.PP
1048.Vb 1
1049\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb); 2203\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1050.Ve 2204.Ve
1051.PP 2205.PP
1052Example: call a callback every hour, starting now: 2206Example: Call a callback every hour, starting now:
1053.PP 2207.PP
1054.Vb 4 2208.Vb 4
1055\& struct ev_periodic hourly_tick; 2209\& ev_periodic hourly_tick;
1056\& ev_periodic_init (&hourly_tick, clock_cb, 2210\& ev_periodic_init (&hourly_tick, clock_cb,
1057\& fmod (ev_now (loop), 3600.), 3600., 0); 2211\& fmod (ev_now (loop), 3600.), 3600., 0);
1058\& ev_periodic_start (loop, &hourly_tick); 2212\& ev_periodic_start (loop, &hourly_tick);
1059.Ve 2213.Ve
1060.ie n .Sh """ev_signal"" \- signal me when a signal gets signalled" 2214.ie n .SS """ev_signal"" \- signal me when a signal gets signalled!"
1061.el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled" 2215.el .SS "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
1062.IX Subsection "ev_signal - signal me when a signal gets signalled" 2216.IX Subsection "ev_signal - signal me when a signal gets signalled!"
1063Signal watchers will trigger an event when the process receives a specific 2217Signal watchers will trigger an event when the process receives a specific
1064signal one or more times. Even though signals are very asynchronous, libev 2218signal one or more times. Even though signals are very asynchronous, libev
1065will try it's best to deliver signals synchronously, i.e. as part of the 2219will try it's best to deliver signals synchronously, i.e. as part of the
1066normal event processing, like any other event. 2220normal event processing, like any other event.
1067.PP 2221.PP
2222If you want signals asynchronously, just use \f(CW\*(C`sigaction\*(C'\fR as you would
2223do without libev and forget about sharing the signal. You can even use
2224\&\f(CW\*(C`ev_async\*(C'\fR from a signal handler to synchronously wake up an event loop.
2225.PP
1068You can configure as many watchers as you like per signal. Only when the 2226You can configure as many watchers as you like per signal. Only when the
1069first watcher gets started will libev actually register a signal watcher 2227first watcher gets started will libev actually register a signal handler
1070with the kernel (thus it coexists with your own signal handlers as long 2228with the kernel (thus it coexists with your own signal handlers as long as
1071as you don't register any with libev). Similarly, when the last signal 2229you don't register any with libev for the same signal). Similarly, when
1072watcher for a signal is stopped libev will reset the signal handler to 2230the last signal watcher for a signal is stopped, libev will reset the
1073\&\s-1SIG_DFL\s0 (regardless of what it was set to before). 2231signal handler to \s-1SIG_DFL\s0 (regardless of what it was set to before).
2232.PP
2233If possible and supported, libev will install its handlers with
2234\&\f(CW\*(C`SA_RESTART\*(C'\fR behaviour enabled, so system calls should not be unduly
2235interrupted. If you have a problem with system calls getting interrupted by
2236signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher and unblock
2237them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher.
2238.PP
2239\fIWatcher-Specific Functions and Data Members\fR
2240.IX Subsection "Watcher-Specific Functions and Data Members"
1074.IP "ev_signal_init (ev_signal *, callback, int signum)" 4 2241.IP "ev_signal_init (ev_signal *, callback, int signum)" 4
1075.IX Item "ev_signal_init (ev_signal *, callback, int signum)" 2242.IX Item "ev_signal_init (ev_signal *, callback, int signum)"
1076.PD 0 2243.PD 0
1077.IP "ev_signal_set (ev_signal *, int signum)" 4 2244.IP "ev_signal_set (ev_signal *, int signum)" 4
1078.IX Item "ev_signal_set (ev_signal *, int signum)" 2245.IX Item "ev_signal_set (ev_signal *, int signum)"
1079.PD 2246.PD
1080Configures the watcher to trigger on the given signal number (usually one 2247Configures the watcher to trigger on the given signal number (usually one
1081of the \f(CW\*(C`SIGxxx\*(C'\fR constants). 2248of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
2249.IP "int signum [read\-only]" 4
2250.IX Item "int signum [read-only]"
2251The signal the watcher watches out for.
2252.PP
2253\fIExamples\fR
2254.IX Subsection "Examples"
2255.PP
2256Example: Try to exit cleanly on \s-1SIGINT\s0.
2257.PP
2258.Vb 5
2259\& static void
2260\& sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
2261\& {
2262\& ev_unloop (loop, EVUNLOOP_ALL);
2263\& }
2264\&
2265\& ev_signal signal_watcher;
2266\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
2267\& ev_signal_start (loop, &signal_watcher);
2268.Ve
1082.ie n .Sh """ev_child"" \- wait for pid status changes" 2269.ie n .SS """ev_child"" \- watch out for process status changes"
1083.el .Sh "\f(CWev_child\fP \- wait for pid status changes" 2270.el .SS "\f(CWev_child\fP \- watch out for process status changes"
1084.IX Subsection "ev_child - wait for pid status changes" 2271.IX Subsection "ev_child - watch out for process status changes"
1085Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to 2272Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
1086some child status changes (most typically when a child of yours dies). 2273some child status changes (most typically when a child of yours dies or
2274exits). It is permissible to install a child watcher \fIafter\fR the child
2275has been forked (which implies it might have already exited), as long
2276as the event loop isn't entered (or is continued from a watcher), i.e.,
2277forking and then immediately registering a watcher for the child is fine,
2278but forking and registering a watcher a few event loop iterations later or
2279in the next callback invocation is not.
2280.PP
2281Only the default event loop is capable of handling signals, and therefore
2282you can only register child watchers in the default event loop.
2283.PP
2284Due to some design glitches inside libev, child watchers will always be
2285handled at maximum priority (their priority is set to \f(CW\*(C`EV_MAXPRI\*(C'\fR by
2286libev)
2287.PP
2288\fIProcess Interaction\fR
2289.IX Subsection "Process Interaction"
2290.PP
2291Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is
2292initialised. This is necessary to guarantee proper behaviour even if
2293the first child watcher is started after the child exits. The occurrence
2294of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done
2295synchronously as part of the event loop processing. Libev always reaps all
2296children, even ones not watched.
2297.PP
2298\fIOverriding the Built-In Processing\fR
2299.IX Subsection "Overriding the Built-In Processing"
2300.PP
2301Libev offers no special support for overriding the built-in child
2302processing, but if your application collides with libev's default child
2303handler, you can override it easily by installing your own handler for
2304\&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the
2305default loop never gets destroyed. You are encouraged, however, to use an
2306event-based approach to child reaping and thus use libev's support for
2307that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely.
2308.PP
2309\fIStopping the Child Watcher\fR
2310.IX Subsection "Stopping the Child Watcher"
2311.PP
2312Currently, the child watcher never gets stopped, even when the
2313child terminates, so normally one needs to stop the watcher in the
2314callback. Future versions of libev might stop the watcher automatically
2315when a child exit is detected.
2316.PP
2317\fIWatcher-Specific Functions and Data Members\fR
2318.IX Subsection "Watcher-Specific Functions and Data Members"
1087.IP "ev_child_init (ev_child *, callback, int pid)" 4 2319.IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4
1088.IX Item "ev_child_init (ev_child *, callback, int pid)" 2320.IX Item "ev_child_init (ev_child *, callback, int pid, int trace)"
1089.PD 0 2321.PD 0
1090.IP "ev_child_set (ev_child *, int pid)" 4 2322.IP "ev_child_set (ev_child *, int pid, int trace)" 4
1091.IX Item "ev_child_set (ev_child *, int pid)" 2323.IX Item "ev_child_set (ev_child *, int pid, int trace)"
1092.PD 2324.PD
1093Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or 2325Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
1094\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look 2326\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
1095at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see 2327at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
1096the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems 2328the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
1097\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the 2329\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
1098process causing the status change. 2330process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only
2331activate the watcher when the process terminates) or \f(CW1\fR (additionally
2332activate the watcher when the process is stopped or continued).
2333.IP "int pid [read\-only]" 4
2334.IX Item "int pid [read-only]"
2335The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
2336.IP "int rpid [read\-write]" 4
2337.IX Item "int rpid [read-write]"
2338The process id that detected a status change.
2339.IP "int rstatus [read\-write]" 4
2340.IX Item "int rstatus [read-write]"
2341The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
2342\&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
1099.PP 2343.PP
1100Example: try to exit cleanly on \s-1SIGINT\s0 and \s-1SIGTERM\s0. 2344\fIExamples\fR
2345.IX Subsection "Examples"
1101.PP 2346.PP
2347Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for
2348its completion.
2349.PP
1102.Vb 5 2350.Vb 1
2351\& ev_child cw;
2352\&
1103\& static void 2353\& static void
1104\& sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents) 2354\& child_cb (EV_P_ ev_child *w, int revents)
1105\& { 2355\& {
1106\& ev_unloop (loop, EVUNLOOP_ALL); 2356\& ev_child_stop (EV_A_ w);
2357\& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus);
1107\& } 2358\& }
2359\&
2360\& pid_t pid = fork ();
2361\&
2362\& if (pid < 0)
2363\& // error
2364\& else if (pid == 0)
2365\& {
2366\& // the forked child executes here
2367\& exit (1);
2368\& }
2369\& else
2370\& {
2371\& ev_child_init (&cw, child_cb, pid, 0);
2372\& ev_child_start (EV_DEFAULT_ &cw);
2373\& }
1108.Ve 2374.Ve
2375.ie n .SS """ev_stat"" \- did the file attributes just change?"
2376.el .SS "\f(CWev_stat\fP \- did the file attributes just change?"
2377.IX Subsection "ev_stat - did the file attributes just change?"
2378This watches a file system path for attribute changes. That is, it calls
2379\&\f(CW\*(C`stat\*(C'\fR on that path in regular intervals (or when the \s-1OS\s0 says it changed)
2380and sees if it changed compared to the last time, invoking the callback if
2381it did.
1109.PP 2382.PP
2383The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does
2384not exist\*(R" is a status change like any other. The condition \*(L"path does not
2385exist\*(R" (or more correctly \*(L"path cannot be stat'ed\*(R") is signified by the
2386\&\f(CW\*(C`st_nlink\*(C'\fR field being zero (which is otherwise always forced to be at
2387least one) and all the other fields of the stat buffer having unspecified
2388contents.
2389.PP
2390The path \fImust not\fR end in a slash or contain special components such as
2391\&\f(CW\*(C`.\*(C'\fR or \f(CW\*(C`..\*(C'\fR. The path \fIshould\fR be absolute: If it is relative and
2392your working directory changes, then the behaviour is undefined.
2393.PP
2394Since there is no portable change notification interface available, the
2395portable implementation simply calls \f(CWstat(2)\fR regularly on the path
2396to see if it changed somehow. You can specify a recommended polling
2397interval for this case. If you specify a polling interval of \f(CW0\fR (highly
2398recommended!) then a \fIsuitable, unspecified default\fR value will be used
2399(which you can expect to be around five seconds, although this might
2400change dynamically). Libev will also impose a minimum interval which is
2401currently around \f(CW0.1\fR, but that's usually overkill.
2402.PP
2403This watcher type is not meant for massive numbers of stat watchers,
2404as even with OS-supported change notifications, this can be
2405resource-intensive.
2406.PP
2407At the time of this writing, the only OS-specific interface implemented
2408is the Linux inotify interface (implementing kqueue support is left as an
2409exercise for the reader. Note, however, that the author sees no way of
2410implementing \f(CW\*(C`ev_stat\*(C'\fR semantics with kqueue, except as a hint).
2411.PP
2412\fI\s-1ABI\s0 Issues (Largefile Support)\fR
2413.IX Subsection "ABI Issues (Largefile Support)"
2414.PP
2415Libev by default (unless the user overrides this) uses the default
2416compilation environment, which means that on systems with large file
2417support disabled by default, you get the 32 bit version of the stat
2418structure. When using the library from programs that change the \s-1ABI\s0 to
2419use 64 bit file offsets the programs will fail. In that case you have to
2420compile libev with the same flags to get binary compatibility. This is
2421obviously the case with any flags that change the \s-1ABI\s0, but the problem is
2422most noticeably displayed with ev_stat and large file support.
2423.PP
2424The solution for this is to lobby your distribution maker to make large
2425file interfaces available by default (as e.g. FreeBSD does) and not
2426optional. Libev cannot simply switch on large file support because it has
2427to exchange stat structures with application programs compiled using the
2428default compilation environment.
2429.PP
2430\fIInotify and Kqueue\fR
2431.IX Subsection "Inotify and Kqueue"
2432.PP
2433When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev and present at
2434runtime, it will be used to speed up change detection where possible. The
2435inotify descriptor will be created lazily when the first \f(CW\*(C`ev_stat\*(C'\fR
2436watcher is being started.
2437.PP
2438Inotify presence does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
2439except that changes might be detected earlier, and in some cases, to avoid
2440making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presence of inotify support
2441there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling,
2442but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
2443many bugs), the path exists (i.e. stat succeeds), and the path resides on
2444a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
2445xfs are fully working) libev usually gets away without polling.
2446.PP
2447There is no support for kqueue, as apparently it cannot be used to
2448implement this functionality, due to the requirement of having a file
2449descriptor open on the object at all times, and detecting renames, unlinks
2450etc. is difficult.
2451.PP
2452\fI\f(CI\*(C`stat ()\*(C'\fI is a synchronous operation\fR
2453.IX Subsection "stat () is a synchronous operation"
2454.PP
2455Libev doesn't normally do any kind of I/O itself, and so is not blocking
2456the process. The exception are \f(CW\*(C`ev_stat\*(C'\fR watchers \- those call \f(CW\*(C`stat
2457()\*(C'\fR, which is a synchronous operation.
2458.PP
2459For local paths, this usually doesn't matter: unless the system is very
2460busy or the intervals between stat's are large, a stat call will be fast,
2461as the path data is usually in memory already (except when starting the
2462watcher).
2463.PP
2464For networked file systems, calling \f(CW\*(C`stat ()\*(C'\fR can block an indefinite
2465time due to network issues, and even under good conditions, a stat call
2466often takes multiple milliseconds.
2467.PP
2468Therefore, it is best to avoid using \f(CW\*(C`ev_stat\*(C'\fR watchers on networked
2469paths, although this is fully supported by libev.
2470.PP
2471\fIThe special problem of stat time resolution\fR
2472.IX Subsection "The special problem of stat time resolution"
2473.PP
2474The \f(CW\*(C`stat ()\*(C'\fR system call only supports full-second resolution portably,
2475and even on systems where the resolution is higher, most file systems
2476still only support whole seconds.
2477.PP
2478That means that, if the time is the only thing that changes, you can
2479easily miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and
2480calls your callback, which does something. When there is another update
2481within the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect unless the
2482stat data does change in other ways (e.g. file size).
2483.PP
2484The solution to this is to delay acting on a change for slightly more
2485than a second (or till slightly after the next full second boundary), using
2486a roughly one-second-delay \f(CW\*(C`ev_timer\*(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02);
2487ev_timer_again (loop, w)\*(C'\fR).
2488.PP
2489The \f(CW.02\fR offset is added to work around small timing inconsistencies
2490of some operating systems (where the second counter of the current time
2491might be be delayed. One such system is the Linux kernel, where a call to
2492\&\f(CW\*(C`gettimeofday\*(C'\fR might return a timestamp with a full second later than
2493a subsequent \f(CW\*(C`time\*(C'\fR call \- if the equivalent of \f(CW\*(C`time ()\*(C'\fR is used to
2494update file times then there will be a small window where the kernel uses
2495the previous second to update file times but libev might already execute
2496the timer callback).
2497.PP
2498\fIWatcher-Specific Functions and Data Members\fR
2499.IX Subsection "Watcher-Specific Functions and Data Members"
2500.IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
2501.IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
2502.PD 0
2503.IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4
2504.IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)"
2505.PD
2506Configures the watcher to wait for status changes of the given
2507\&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to
2508be detected and should normally be specified as \f(CW0\fR to let libev choose
2509a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same
2510path for as long as the watcher is active.
2511.Sp
2512The callback will receive an \f(CW\*(C`EV_STAT\*(C'\fR event when a change was detected,
2513relative to the attributes at the time the watcher was started (or the
2514last change was detected).
2515.IP "ev_stat_stat (loop, ev_stat *)" 4
2516.IX Item "ev_stat_stat (loop, ev_stat *)"
2517Updates the stat buffer immediately with new values. If you change the
2518watched path in your callback, you could call this function to avoid
2519detecting this change (while introducing a race condition if you are not
2520the only one changing the path). Can also be useful simply to find out the
2521new values.
2522.IP "ev_statdata attr [read\-only]" 4
2523.IX Item "ev_statdata attr [read-only]"
2524The most-recently detected attributes of the file. Although the type is
2525\&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
2526suitable for your system, but you can only rely on the POSIX-standardised
2527members to be present. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there was
2528some error while \f(CW\*(C`stat\*(C'\fRing the file.
2529.IP "ev_statdata prev [read\-only]" 4
2530.IX Item "ev_statdata prev [read-only]"
2531The previous attributes of the file. The callback gets invoked whenever
2532\&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR, or, more precisely, one or more of these members
2533differ: \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,
2534\&\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.
2535.IP "ev_tstamp interval [read\-only]" 4
2536.IX Item "ev_tstamp interval [read-only]"
2537The specified interval.
2538.IP "const char *path [read\-only]" 4
2539.IX Item "const char *path [read-only]"
2540The file system path that is being watched.
2541.PP
2542\fIExamples\fR
2543.IX Subsection "Examples"
2544.PP
2545Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
2546.PP
2547.Vb 10
2548\& static void
2549\& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
2550\& {
2551\& /* /etc/passwd changed in some way */
2552\& if (w\->attr.st_nlink)
2553\& {
2554\& printf ("passwd current size %ld\en", (long)w\->attr.st_size);
2555\& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime);
2556\& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime);
2557\& }
2558\& else
2559\& /* you shalt not abuse printf for puts */
2560\& puts ("wow, /etc/passwd is not there, expect problems. "
2561\& "if this is windows, they already arrived\en");
2562\& }
2563\&
2564\& ...
2565\& ev_stat passwd;
2566\&
2567\& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
2568\& ev_stat_start (loop, &passwd);
2569.Ve
2570.PP
2571Example: Like above, but additionally use a one-second delay so we do not
2572miss updates (however, frequent updates will delay processing, too, so
2573one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
2574\&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
2575.PP
1110.Vb 3 2576.Vb 2
1111\& struct ev_signal signal_watcher; 2577\& static ev_stat passwd;
1112\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT); 2578\& static ev_timer timer;
1113\& ev_signal_start (loop, &sigint_cb); 2579\&
2580\& static void
2581\& timer_cb (EV_P_ ev_timer *w, int revents)
2582\& {
2583\& ev_timer_stop (EV_A_ w);
2584\&
2585\& /* now it\*(Aqs one second after the most recent passwd change */
2586\& }
2587\&
2588\& static void
2589\& stat_cb (EV_P_ ev_stat *w, int revents)
2590\& {
2591\& /* reset the one\-second timer */
2592\& ev_timer_again (EV_A_ &timer);
2593\& }
2594\&
2595\& ...
2596\& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
2597\& ev_stat_start (loop, &passwd);
2598\& ev_timer_init (&timer, timer_cb, 0., 1.02);
1114.Ve 2599.Ve
1115.ie n .Sh """ev_idle"" \- when you've got nothing better to do" 2600.ie n .SS """ev_idle"" \- when you've got nothing better to do..."
1116.el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do" 2601.el .SS "\f(CWev_idle\fP \- when you've got nothing better to do..."
1117.IX Subsection "ev_idle - when you've got nothing better to do" 2602.IX Subsection "ev_idle - when you've got nothing better to do..."
1118Idle watchers trigger events when there are no other events are pending 2603Idle watchers trigger events when no other events of the same or higher
1119(prepare, check and other idle watchers do not count). That is, as long 2604priority are pending (prepare, check and other idle watchers do not count
1120as your process is busy handling sockets or timeouts (or even signals, 2605as receiving \*(L"events\*(R").
1121imagine) it will not be triggered. But when your process is idle all idle 2606.PP
1122watchers are being called again and again, once per event loop iteration \- 2607That is, as long as your process is busy handling sockets or timeouts
2608(or even signals, imagine) of the same or higher priority it will not be
2609triggered. But when your process is idle (or only lower-priority watchers
2610are pending), the idle watchers are being called once per event loop
1123until stopped, that is, or your process receives more events and becomes 2611iteration \- until stopped, that is, or your process receives more events
1124busy. 2612and becomes busy again with higher priority stuff.
1125.PP 2613.PP
1126The most noteworthy effect is that as long as any idle watchers are 2614The most noteworthy effect is that as long as any idle watchers are
1127active, the process will not block when waiting for new events. 2615active, the process will not block when waiting for new events.
1128.PP 2616.PP
1129Apart from keeping your process non-blocking (which is a useful 2617Apart from keeping your process non-blocking (which is a useful
1130effect on its own sometimes), idle watchers are a good place to do 2618effect on its own sometimes), idle watchers are a good place to do
1131\&\*(L"pseudo\-background processing\*(R", or delay processing stuff to after the 2619\&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the
1132event loop has handled all outstanding events. 2620event loop has handled all outstanding events.
2621.PP
2622\fIWatcher-Specific Functions and Data Members\fR
2623.IX Subsection "Watcher-Specific Functions and Data Members"
1133.IP "ev_idle_init (ev_signal *, callback)" 4 2624.IP "ev_idle_init (ev_idle *, callback)" 4
1134.IX Item "ev_idle_init (ev_signal *, callback)" 2625.IX Item "ev_idle_init (ev_idle *, callback)"
1135Initialises and configures the idle watcher \- it has no parameters of any 2626Initialises and configures the idle watcher \- it has no parameters of any
1136kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless, 2627kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
1137believe me. 2628believe me.
1138.PP 2629.PP
2630\fIExamples\fR
2631.IX Subsection "Examples"
2632.PP
1139Example: dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR, start it, and in the 2633Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the
1140callback, free it. Alos, use no error checking, as usual. 2634callback, free it. Also, use no error checking, as usual.
1141.PP 2635.PP
1142.Vb 7 2636.Vb 7
1143\& static void 2637\& static void
1144\& idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents) 2638\& idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1145\& { 2639\& {
1146\& free (w); 2640\& free (w);
1147\& // now do something you wanted to do when the program has 2641\& // now do something you wanted to do when the program has
1148\& // no longer asnything immediate to do. 2642\& // no longer anything immediate to do.
1149\& } 2643\& }
1150.Ve 2644\&
1151.PP
1152.Vb 3
1153\& struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle)); 2645\& ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1154\& ev_idle_init (idle_watcher, idle_cb); 2646\& ev_idle_init (idle_watcher, idle_cb);
1155\& ev_idle_start (loop, idle_cb); 2647\& ev_idle_start (loop, idle_watcher);
1156.Ve 2648.Ve
1157.ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop" 2649.ie n .SS """ev_prepare"" and ""ev_check"" \- customise your event loop!"
1158.el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop" 2650.el .SS "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
1159.IX Subsection "ev_prepare and ev_check - customise your event loop" 2651.IX Subsection "ev_prepare and ev_check - customise your event loop!"
1160Prepare and check watchers are usually (but not always) used in tandem: 2652Prepare and check watchers are usually (but not always) used in pairs:
1161prepare watchers get invoked before the process blocks and check watchers 2653prepare watchers get invoked before the process blocks and check watchers
1162afterwards. 2654afterwards.
1163.PP 2655.PP
2656You \fImust not\fR call \f(CW\*(C`ev_loop\*(C'\fR or similar functions that enter
2657the current event loop from either \f(CW\*(C`ev_prepare\*(C'\fR or \f(CW\*(C`ev_check\*(C'\fR
2658watchers. Other loops than the current one are fine, however. The
2659rationale behind this is that you do not need to check for recursion in
2660those watchers, i.e. the sequence will always be \f(CW\*(C`ev_prepare\*(C'\fR, blocking,
2661\&\f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each kind they will always be
2662called in pairs bracketing the blocking call.
2663.PP
1164Their main purpose is to integrate other event mechanisms into libev. This 2664Their main purpose is to integrate other event mechanisms into libev and
1165could be used, for example, to track variable changes, implement your own 2665their use is somewhat advanced. They could be used, for example, to track
1166watchers, integrate net-snmp or a coroutine library and lots more. 2666variable changes, implement your own watchers, integrate net-snmp or a
2667coroutine library and lots more. They are also occasionally useful if
2668you cache some data and want to flush it before blocking (for example,
2669in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
2670watcher).
1167.PP 2671.PP
1168This is done by examining in each prepare call which file descriptors need 2672This is done by examining in each prepare call which file descriptors
1169to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers for 2673need to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers
1170them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many libraries 2674for them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many
1171provide just this functionality). Then, in the check watcher you check for 2675libraries provide exactly this functionality). Then, in the check watcher,
1172any events that occured (by checking the pending status of all watchers 2676you check for any events that occurred (by checking the pending status
1173and stopping them) and call back into the library. The I/O and timer 2677of all watchers and stopping them) and call back into the library. The
1174callbacks will never actually be called (but must be valid nevertheless, 2678I/O and timer callbacks will never actually be called (but must be valid
1175because you never know, you know?). 2679nevertheless, because you never know, you know?).
1176.PP 2680.PP
1177As another example, the Perl Coro module uses these hooks to integrate 2681As another example, the Perl Coro module uses these hooks to integrate
1178coroutines into libev programs, by yielding to other active coroutines 2682coroutines into libev programs, by yielding to other active coroutines
1179during each prepare and only letting the process block if no coroutines 2683during each prepare and only letting the process block if no coroutines
1180are ready to run (it's actually more complicated: it only runs coroutines 2684are ready to run (it's actually more complicated: it only runs coroutines
1181with priority higher than or equal to the event loop and one coroutine 2685with priority higher than or equal to the event loop and one coroutine
1182of lower priority, but only once, using idle watchers to keep the event 2686of lower priority, but only once, using idle watchers to keep the event
1183loop from blocking if lower-priority coroutines are active, thus mapping 2687loop from blocking if lower-priority coroutines are active, thus mapping
1184low-priority coroutines to idle/background tasks). 2688low-priority coroutines to idle/background tasks).
2689.PP
2690It is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR)
2691priority, to ensure that they are being run before any other watchers
2692after the poll (this doesn't matter for \f(CW\*(C`ev_prepare\*(C'\fR watchers).
2693.PP
2694Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, too) should not
2695activate (\*(L"feed\*(R") events into libev. While libev fully supports this, they
2696might get executed before other \f(CW\*(C`ev_check\*(C'\fR watchers did their job. As
2697\&\f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other (non-libev) event
2698loops those other event loops might be in an unusable state until their
2699\&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with
2700others).
2701.PP
2702\fIWatcher-Specific Functions and Data Members\fR
2703.IX Subsection "Watcher-Specific Functions and Data Members"
1185.IP "ev_prepare_init (ev_prepare *, callback)" 4 2704.IP "ev_prepare_init (ev_prepare *, callback)" 4
1186.IX Item "ev_prepare_init (ev_prepare *, callback)" 2705.IX Item "ev_prepare_init (ev_prepare *, callback)"
1187.PD 0 2706.PD 0
1188.IP "ev_check_init (ev_check *, callback)" 4 2707.IP "ev_check_init (ev_check *, callback)" 4
1189.IX Item "ev_check_init (ev_check *, callback)" 2708.IX Item "ev_check_init (ev_check *, callback)"
1190.PD 2709.PD
1191Initialises and configures the prepare or check watcher \- they have no 2710Initialises and configures the prepare or check watcher \- they have no
1192parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR 2711parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
1193macros, but using them is utterly, utterly and completely pointless. 2712macros, but using them is utterly, utterly, utterly and completely
2713pointless.
1194.PP 2714.PP
1195Example: *TODO*. 2715\fIExamples\fR
2716.IX Subsection "Examples"
2717.PP
2718There are a number of principal ways to embed other event loops or modules
2719into libev. Here are some ideas on how to include libadns into libev
2720(there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could
2721use as a working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR embeds a
2722Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 into the
2723Glib event loop).
2724.PP
2725Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
2726and in a check watcher, destroy them and call into libadns. What follows
2727is pseudo-code only of course. This requires you to either use a low
2728priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as
2729the callbacks for the IO/timeout watchers might not have been called yet.
2730.PP
2731.Vb 2
2732\& static ev_io iow [nfd];
2733\& static ev_timer tw;
2734\&
2735\& static void
2736\& io_cb (struct ev_loop *loop, ev_io *w, int revents)
2737\& {
2738\& }
2739\&
2740\& // create io watchers for each fd and a timer before blocking
2741\& static void
2742\& adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
2743\& {
2744\& int timeout = 3600000;
2745\& struct pollfd fds [nfd];
2746\& // actual code will need to loop here and realloc etc.
2747\& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2748\&
2749\& /* the callback is illegal, but won\*(Aqt be called as we stop during check */
2750\& ev_timer_init (&tw, 0, timeout * 1e\-3, 0.);
2751\& ev_timer_start (loop, &tw);
2752\&
2753\& // create one ev_io per pollfd
2754\& for (int i = 0; i < nfd; ++i)
2755\& {
2756\& ev_io_init (iow + i, io_cb, fds [i].fd,
2757\& ((fds [i].events & POLLIN ? EV_READ : 0)
2758\& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
2759\&
2760\& fds [i].revents = 0;
2761\& ev_io_start (loop, iow + i);
2762\& }
2763\& }
2764\&
2765\& // stop all watchers after blocking
2766\& static void
2767\& adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
2768\& {
2769\& ev_timer_stop (loop, &tw);
2770\&
2771\& for (int i = 0; i < nfd; ++i)
2772\& {
2773\& // set the relevant poll flags
2774\& // could also call adns_processreadable etc. here
2775\& struct pollfd *fd = fds + i;
2776\& int revents = ev_clear_pending (iow + i);
2777\& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN;
2778\& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT;
2779\&
2780\& // now stop the watcher
2781\& ev_io_stop (loop, iow + i);
2782\& }
2783\&
2784\& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
2785\& }
2786.Ve
2787.PP
2788Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR
2789in the prepare watcher and would dispose of the check watcher.
2790.PP
2791Method 3: If the module to be embedded supports explicit event
2792notification (libadns does), you can also make use of the actual watcher
2793callbacks, and only destroy/create the watchers in the prepare watcher.
2794.PP
2795.Vb 5
2796\& static void
2797\& timer_cb (EV_P_ ev_timer *w, int revents)
2798\& {
2799\& adns_state ads = (adns_state)w\->data;
2800\& update_now (EV_A);
2801\&
2802\& adns_processtimeouts (ads, &tv_now);
2803\& }
2804\&
2805\& static void
2806\& io_cb (EV_P_ ev_io *w, int revents)
2807\& {
2808\& adns_state ads = (adns_state)w\->data;
2809\& update_now (EV_A);
2810\&
2811\& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now);
2812\& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now);
2813\& }
2814\&
2815\& // do not ever call adns_afterpoll
2816.Ve
2817.PP
2818Method 4: Do not use a prepare or check watcher because the module you
2819want to embed is not flexible enough to support it. Instead, you can
2820override their poll function. The drawback with this solution is that the
2821main loop is now no longer controllable by \s-1EV\s0. The \f(CW\*(C`Glib::EV\*(C'\fR module uses
2822this approach, effectively embedding \s-1EV\s0 as a client into the horrible
2823libglib event loop.
2824.PP
2825.Vb 4
2826\& static gint
2827\& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
2828\& {
2829\& int got_events = 0;
2830\&
2831\& for (n = 0; n < nfds; ++n)
2832\& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
2833\&
2834\& if (timeout >= 0)
2835\& // create/start timer
2836\&
2837\& // poll
2838\& ev_loop (EV_A_ 0);
2839\&
2840\& // stop timer again
2841\& if (timeout >= 0)
2842\& ev_timer_stop (EV_A_ &to);
2843\&
2844\& // stop io watchers again \- their callbacks should have set
2845\& for (n = 0; n < nfds; ++n)
2846\& ev_io_stop (EV_A_ iow [n]);
2847\&
2848\& return got_events;
2849\& }
2850.Ve
2851.ie n .SS """ev_embed"" \- when one backend isn't enough..."
2852.el .SS "\f(CWev_embed\fP \- when one backend isn't enough..."
2853.IX Subsection "ev_embed - when one backend isn't enough..."
2854This is a rather advanced watcher type that lets you embed one event loop
2855into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
2856loop, other types of watchers might be handled in a delayed or incorrect
2857fashion and must not be used).
2858.PP
2859There are primarily two reasons you would want that: work around bugs and
2860prioritise I/O.
2861.PP
2862As an example for a bug workaround, the kqueue backend might only support
2863sockets on some platform, so it is unusable as generic backend, but you
2864still want to make use of it because you have many sockets and it scales
2865so nicely. In this case, you would create a kqueue-based loop and embed
2866it into your default loop (which might use e.g. poll). Overall operation
2867will be a bit slower because first libev has to call \f(CW\*(C`poll\*(C'\fR and then
2868\&\f(CW\*(C`kevent\*(C'\fR, but at least you can use both mechanisms for what they are
2869best: \f(CW\*(C`kqueue\*(C'\fR for scalable sockets and \f(CW\*(C`poll\*(C'\fR if you want it to work :)
2870.PP
2871As for prioritising I/O: under rare circumstances you have the case where
2872some fds have to be watched and handled very quickly (with low latency),
2873and even priorities and idle watchers might have too much overhead. In
2874this case you would put all the high priority stuff in one loop and all
2875the rest in a second one, and embed the second one in the first.
2876.PP
2877As long as the watcher is active, the callback will be invoked every
2878time there might be events pending in the embedded loop. The callback
2879must then call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single
2880sweep and invoke their callbacks (the callback doesn't need to invoke the
2881\&\f(CW\*(C`ev_embed_sweep\*(C'\fR function directly, it could also start an idle watcher
2882to give the embedded loop strictly lower priority for example).
2883.PP
2884You can also set the callback to \f(CW0\fR, in which case the embed watcher
2885will automatically execute the embedded loop sweep whenever necessary.
2886.PP
2887Fork detection will be handled transparently while the \f(CW\*(C`ev_embed\*(C'\fR watcher
2888is active, i.e., the embedded loop will automatically be forked when the
2889embedding loop forks. In other cases, the user is responsible for calling
2890\&\f(CW\*(C`ev_loop_fork\*(C'\fR on the embedded loop.
2891.PP
2892Unfortunately, not all backends are embeddable: only the ones returned by
2893\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
2894portable one.
2895.PP
2896So when you want to use this feature you will always have to be prepared
2897that you cannot get an embeddable loop. The recommended way to get around
2898this is to have a separate variables for your embeddable loop, try to
2899create it, and if that fails, use the normal loop for everything.
2900.PP
2901\fI\f(CI\*(C`ev_embed\*(C'\fI and fork\fR
2902.IX Subsection "ev_embed and fork"
2903.PP
2904While the \f(CW\*(C`ev_embed\*(C'\fR watcher is running, forks in the embedding loop will
2905automatically be applied to the embedded loop as well, so no special
2906fork handling is required in that case. When the watcher is not running,
2907however, it is still the task of the libev user to call \f(CW\*(C`ev_loop_fork ()\*(C'\fR
2908as applicable.
2909.PP
2910\fIWatcher-Specific Functions and Data Members\fR
2911.IX Subsection "Watcher-Specific Functions and Data Members"
2912.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
2913.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
2914.PD 0
2915.IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
2916.IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)"
2917.PD
2918Configures the watcher to embed the given loop, which must be
2919embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
2920invoked automatically, otherwise it is the responsibility of the callback
2921to invoke it (it will continue to be called until the sweep has been done,
2922if you do not want that, you need to temporarily stop the embed watcher).
2923.IP "ev_embed_sweep (loop, ev_embed *)" 4
2924.IX Item "ev_embed_sweep (loop, ev_embed *)"
2925Make a single, non-blocking sweep over the embedded loop. This works
2926similarly to \f(CW\*(C`ev_loop (embedded_loop, EVLOOP_NONBLOCK)\*(C'\fR, but in the most
2927appropriate way for embedded loops.
2928.IP "struct ev_loop *other [read\-only]" 4
2929.IX Item "struct ev_loop *other [read-only]"
2930The embedded event loop.
2931.PP
2932\fIExamples\fR
2933.IX Subsection "Examples"
2934.PP
2935Example: Try to get an embeddable event loop and embed it into the default
2936event loop. If that is not possible, use the default loop. The default
2937loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the embeddable loop is stored in
2938\&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the case no embeddable loop can be
2939used).
2940.PP
2941.Vb 3
2942\& struct ev_loop *loop_hi = ev_default_init (0);
2943\& struct ev_loop *loop_lo = 0;
2944\& ev_embed embed;
2945\&
2946\& // see if there is a chance of getting one that works
2947\& // (remember that a flags value of 0 means autodetection)
2948\& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
2949\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
2950\& : 0;
2951\&
2952\& // if we got one, then embed it, otherwise default to loop_hi
2953\& if (loop_lo)
2954\& {
2955\& ev_embed_init (&embed, 0, loop_lo);
2956\& ev_embed_start (loop_hi, &embed);
2957\& }
2958\& else
2959\& loop_lo = loop_hi;
2960.Ve
2961.PP
2962Example: Check if kqueue is available but not recommended and create
2963a kqueue backend for use with sockets (which usually work with any
2964kqueue implementation). Store the kqueue/socket\-only event loop in
2965\&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too).
2966.PP
2967.Vb 3
2968\& struct ev_loop *loop = ev_default_init (0);
2969\& struct ev_loop *loop_socket = 0;
2970\& ev_embed embed;
2971\&
2972\& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2973\& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2974\& {
2975\& ev_embed_init (&embed, 0, loop_socket);
2976\& ev_embed_start (loop, &embed);
2977\& }
2978\&
2979\& if (!loop_socket)
2980\& loop_socket = loop;
2981\&
2982\& // now use loop_socket for all sockets, and loop for everything else
2983.Ve
2984.ie n .SS """ev_fork"" \- the audacity to resume the event loop after a fork"
2985.el .SS "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
2986.IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
2987Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
2988whoever is a good citizen cared to tell libev about it by calling
2989\&\f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the
2990event loop blocks next and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called,
2991and only in the child after the fork. If whoever good citizen calling
2992\&\f(CW\*(C`ev_default_fork\*(C'\fR cheats and calls it in the wrong process, the fork
2993handlers will be invoked, too, of course.
2994.PP
2995\fIThe special problem of life after fork \- how is it possible?\fR
2996.IX Subsection "The special problem of life after fork - how is it possible?"
2997.PP
2998Most uses of \f(CW\*(C`fork()\*(C'\fR consist of forking, then some simple calls to ste
2999up/change the process environment, followed by a call to \f(CW\*(C`exec()\*(C'\fR. This
3000sequence should be handled by libev without any problems.
3001.PP
3002This changes when the application actually wants to do event handling
3003in the child, or both parent in child, in effect \*(L"continuing\*(R" after the
3004fork.
3005.PP
3006The default mode of operation (for libev, with application help to detect
3007forks) is to duplicate all the state in the child, as would be expected
3008when \fIeither\fR the parent \fIor\fR the child process continues.
3009.PP
3010When both processes want to continue using libev, then this is usually the
3011wrong result. In that case, usually one process (typically the parent) is
3012supposed to continue with all watchers in place as before, while the other
3013process typically wants to start fresh, i.e. without any active watchers.
3014.PP
3015The cleanest and most efficient way to achieve that with libev is to
3016simply create a new event loop, which of course will be \*(L"empty\*(R", and
3017use that for new watchers. This has the advantage of not touching more
3018memory than necessary, and thus avoiding the copy-on-write, and the
3019disadvantage of having to use multiple event loops (which do not support
3020signal watchers).
3021.PP
3022When this is not possible, or you want to use the default loop for
3023other reasons, then in the process that wants to start \*(L"fresh\*(R", call
3024\&\f(CW\*(C`ev_default_destroy ()\*(C'\fR followed by \f(CW\*(C`ev_default_loop (...)\*(C'\fR. Destroying
3025the default loop will \*(L"orphan\*(R" (not stop) all registered watchers, so you
3026have to be careful not to execute code that modifies those watchers. Note
3027also that in that case, you have to re-register any signal watchers.
3028.PP
3029\fIWatcher-Specific Functions and Data Members\fR
3030.IX Subsection "Watcher-Specific Functions and Data Members"
3031.IP "ev_fork_init (ev_signal *, callback)" 4
3032.IX Item "ev_fork_init (ev_signal *, callback)"
3033Initialises and configures the fork watcher \- it has no parameters of any
3034kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
3035believe me.
3036.ie n .SS """ev_async"" \- how to wake up another event loop"
3037.el .SS "\f(CWev_async\fP \- how to wake up another event loop"
3038.IX Subsection "ev_async - how to wake up another event loop"
3039In general, you cannot use an \f(CW\*(C`ev_loop\*(C'\fR from multiple threads or other
3040asynchronous sources such as signal handlers (as opposed to multiple event
3041loops \- those are of course safe to use in different threads).
3042.PP
3043Sometimes, however, you need to wake up another event loop you do not
3044control, for example because it belongs to another thread. This is what
3045\&\f(CW\*(C`ev_async\*(C'\fR watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you
3046can signal it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal
3047safe.
3048.PP
3049This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals,
3050too, are asynchronous in nature, and signals, too, will be compressed
3051(i.e. the number of callback invocations may be less than the number of
3052\&\f(CW\*(C`ev_async_sent\*(C'\fR calls).
3053.PP
3054Unlike \f(CW\*(C`ev_signal\*(C'\fR watchers, \f(CW\*(C`ev_async\*(C'\fR works with any event loop, not
3055just the default loop.
3056.PP
3057\fIQueueing\fR
3058.IX Subsection "Queueing"
3059.PP
3060\&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason
3061is that the author does not know of a simple (or any) algorithm for a
3062multiple-writer-single-reader queue that works in all cases and doesn't
3063need elaborate support such as pthreads.
3064.PP
3065That means that if you want to queue data, you have to provide your own
3066queue. But at least I can tell you how to implement locking around your
3067queue:
3068.IP "queueing from a signal handler context" 4
3069.IX Item "queueing from a signal handler context"
3070To implement race-free queueing, you simply add to the queue in the signal
3071handler but you block the signal handler in the watcher callback. Here is
3072an example that does that for some fictitious \s-1SIGUSR1\s0 handler:
3073.Sp
3074.Vb 1
3075\& static ev_async mysig;
3076\&
3077\& static void
3078\& sigusr1_handler (void)
3079\& {
3080\& sometype data;
3081\&
3082\& // no locking etc.
3083\& queue_put (data);
3084\& ev_async_send (EV_DEFAULT_ &mysig);
3085\& }
3086\&
3087\& static void
3088\& mysig_cb (EV_P_ ev_async *w, int revents)
3089\& {
3090\& sometype data;
3091\& sigset_t block, prev;
3092\&
3093\& sigemptyset (&block);
3094\& sigaddset (&block, SIGUSR1);
3095\& sigprocmask (SIG_BLOCK, &block, &prev);
3096\&
3097\& while (queue_get (&data))
3098\& process (data);
3099\&
3100\& if (sigismember (&prev, SIGUSR1)
3101\& sigprocmask (SIG_UNBLOCK, &block, 0);
3102\& }
3103.Ve
3104.Sp
3105(Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR
3106instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it
3107either...).
3108.IP "queueing from a thread context" 4
3109.IX Item "queueing from a thread context"
3110The strategy for threads is different, as you cannot (easily) block
3111threads but you can easily preempt them, so to queue safely you need to
3112employ a traditional mutex lock, such as in this pthread example:
3113.Sp
3114.Vb 2
3115\& static ev_async mysig;
3116\& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
3117\&
3118\& static void
3119\& otherthread (void)
3120\& {
3121\& // only need to lock the actual queueing operation
3122\& pthread_mutex_lock (&mymutex);
3123\& queue_put (data);
3124\& pthread_mutex_unlock (&mymutex);
3125\&
3126\& ev_async_send (EV_DEFAULT_ &mysig);
3127\& }
3128\&
3129\& static void
3130\& mysig_cb (EV_P_ ev_async *w, int revents)
3131\& {
3132\& pthread_mutex_lock (&mymutex);
3133\&
3134\& while (queue_get (&data))
3135\& process (data);
3136\&
3137\& pthread_mutex_unlock (&mymutex);
3138\& }
3139.Ve
3140.PP
3141\fIWatcher-Specific Functions and Data Members\fR
3142.IX Subsection "Watcher-Specific Functions and Data Members"
3143.IP "ev_async_init (ev_async *, callback)" 4
3144.IX Item "ev_async_init (ev_async *, callback)"
3145Initialises and configures the async watcher \- it has no parameters of any
3146kind. There is a \f(CW\*(C`ev_async_set\*(C'\fR macro, but using it is utterly pointless,
3147trust me.
3148.IP "ev_async_send (loop, ev_async *)" 4
3149.IX Item "ev_async_send (loop, ev_async *)"
3150Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds
3151an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop. Unlike
3152\&\f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do from other threads, signal or
3153similar contexts (see the discussion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the embedding
3154section below on what exactly this means).
3155.Sp
3156Note that, as with other watchers in libev, multiple events might get
3157compressed into a single callback invocation (another way to look at this
3158is that \f(CW\*(C`ev_async\*(C'\fR watchers are level-triggered, set on \f(CW\*(C`ev_async_send\*(C'\fR,
3159reset when the event loop detects that).
3160.Sp
3161This call incurs the overhead of a system call only once per event loop
3162iteration, so while the overhead might be noticeable, it doesn't apply to
3163repeated calls to \f(CW\*(C`ev_async_send\*(C'\fR for the same event loop.
3164.IP "bool = ev_async_pending (ev_async *)" 4
3165.IX Item "bool = ev_async_pending (ev_async *)"
3166Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the
3167watcher but the event has not yet been processed (or even noted) by the
3168event loop.
3169.Sp
3170\&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When
3171the loop iterates next and checks for the watcher to have become active,
3172it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very
3173quickly check whether invoking the loop might be a good idea.
3174.Sp
3175Not that this does \fInot\fR check whether the watcher itself is pending,
3176only whether it has been requested to make this watcher pending: there
3177is a time window between the event loop checking and resetting the async
3178notification, and the callback being invoked.
1196.SH "OTHER FUNCTIONS" 3179.SH "OTHER FUNCTIONS"
1197.IX Header "OTHER FUNCTIONS" 3180.IX Header "OTHER FUNCTIONS"
1198There are some other functions of possible interest. Described. Here. Now. 3181There are some other functions of possible interest. Described. Here. Now.
1199.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4 3182.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
1200.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 3183.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"
1201This function combines a simple timer and an I/O watcher, calls your 3184This function combines a simple timer and an I/O watcher, calls your
1202callback on whichever event happens first and automatically stop both 3185callback on whichever event happens first and automatically stops both
1203watchers. This is useful if you want to wait for a single event on an fd 3186watchers. This is useful if you want to wait for a single event on an fd
1204or timeout without having to allocate/configure/start/stop/free one or 3187or timeout without having to allocate/configure/start/stop/free one or
1205more watchers yourself. 3188more watchers yourself.
1206.Sp 3189.Sp
1207If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and events 3190If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and the
1208is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for the given \f(CW\*(C`fd\*(C'\fR and 3191\&\f(CW\*(C`events\*(C'\fR argument is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for
1209\&\f(CW\*(C`events\*(C'\fR set will be craeted and started. 3192the given \f(CW\*(C`fd\*(C'\fR and \f(CW\*(C`events\*(C'\fR set will be created and started.
1210.Sp 3193.Sp
1211If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be 3194If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
1212started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and 3195started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
1213repeat = 0) will be started. While \f(CW0\fR is a valid timeout, it is of 3196repeat = 0) will be started. \f(CW0\fR is a valid timeout.
1214dubious value.
1215.Sp 3197.Sp
1216The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets 3198The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets
1217passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of 3199passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
1218\&\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 3200\&\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
1219value passed to \f(CW\*(C`ev_once\*(C'\fR: 3201value passed to \f(CW\*(C`ev_once\*(C'\fR. Note that it is possible to receive \fIboth\fR
3202a timeout and an io event at the same time \- you probably should give io
3203events precedence.
3204.Sp
3205Example: wait up to ten seconds for data to appear on \s-1STDIN_FILENO\s0.
1220.Sp 3206.Sp
1221.Vb 7 3207.Vb 7
1222\& static void stdin_ready (int revents, void *arg) 3208\& static void stdin_ready (int revents, void *arg)
1223\& { 3209\& {
1224\& if (revents & EV_TIMEOUT)
1225\& /* doh, nothing entered */;
1226\& else if (revents & EV_READ) 3210\& if (revents & EV_READ)
1227\& /* stdin might have data for us, joy! */; 3211\& /* stdin might have data for us, joy! */;
3212\& else if (revents & EV_TIMEOUT)
3213\& /* doh, nothing entered */;
1228\& } 3214\& }
1229.Ve 3215\&
1230.Sp
1231.Vb 1
1232\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); 3216\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1233.Ve 3217.Ve
1234.IP "ev_feed_event (loop, watcher, int events)" 4 3218.IP "ev_feed_event (struct ev_loop *, watcher *, int revents)" 4
1235.IX Item "ev_feed_event (loop, watcher, int events)" 3219.IX Item "ev_feed_event (struct ev_loop *, watcher *, int revents)"
1236Feeds the given event set into the event loop, as if the specified event 3220Feeds the given event set into the event loop, as if the specified event
1237had happened for the specified watcher (which must be a pointer to an 3221had happened for the specified watcher (which must be a pointer to an
1238initialised but not necessarily started event watcher). 3222initialised but not necessarily started event watcher).
1239.IP "ev_feed_fd_event (loop, int fd, int revents)" 4 3223.IP "ev_feed_fd_event (struct ev_loop *, int fd, int revents)" 4
1240.IX Item "ev_feed_fd_event (loop, int fd, int revents)" 3224.IX Item "ev_feed_fd_event (struct ev_loop *, int fd, int revents)"
1241Feed an event on the given fd, as if a file descriptor backend detected 3225Feed an event on the given fd, as if a file descriptor backend detected
1242the given events it. 3226the given events it.
1243.IP "ev_feed_signal_event (loop, int signum)" 4 3227.IP "ev_feed_signal_event (struct ev_loop *loop, int signum)" 4
1244.IX Item "ev_feed_signal_event (loop, int signum)" 3228.IX Item "ev_feed_signal_event (struct ev_loop *loop, int signum)"
1245Feed an event as if the given signal occured (loop must be the default loop!). 3229Feed an event as if the given signal occurred (\f(CW\*(C`loop\*(C'\fR must be the default
3230loop!).
1246.SH "LIBEVENT EMULATION" 3231.SH "LIBEVENT EMULATION"
1247.IX Header "LIBEVENT EMULATION" 3232.IX Header "LIBEVENT EMULATION"
1248Libev offers a compatibility emulation layer for libevent. It cannot 3233Libev offers a compatibility emulation layer for libevent. It cannot
1249emulate the internals of libevent, so here are some usage hints: 3234emulate the internals of libevent, so here are some usage hints:
3235.IP "\(bu" 4
1250.IP "* Use it by including <event.h>, as usual." 4 3236Use it by including <event.h>, as usual.
1251.IX Item "Use it by including <event.h>, as usual." 3237.IP "\(bu" 4
1252.PD 0 3238The following members are fully supported: ev_base, ev_callback,
1253.IP "* The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4 3239ev_arg, ev_fd, ev_res, ev_events.
1254.IX Item "The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 3240.IP "\(bu" 4
1255.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 3241Avoid using ev_flags and the EVLIST_*\-macros, while it is
1256.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)." 3242maintained by libev, it does not work exactly the same way as in libevent (consider
1257.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 3243it a private \s-1API\s0).
1258.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." 3244.IP "\(bu" 4
3245Priorities are not currently supported. Initialising priorities
3246will fail and all watchers will have the same priority, even though there
3247is an ev_pri field.
3248.IP "\(bu" 4
3249In libevent, the last base created gets the signals, in libev, the
3250first base created (== the default loop) gets the signals.
3251.IP "\(bu" 4
1259.IP "* Other members are not supported." 4 3252Other members are not supported.
1260.IX Item "Other members are not supported." 3253.IP "\(bu" 4
1261.IP "* The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need to use the libev header file and library." 4 3254The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need
1262.IX Item "The libev emulation is not ABI compatible to libevent, you need to use the libev header file and library." 3255to use the libev header file and library.
1263.PD
1264.SH "\*(C+ SUPPORT" 3256.SH "\*(C+ SUPPORT"
1265.IX Header " SUPPORT" 3257.IX Header " SUPPORT"
1266\&\s-1TBD\s0. 3258Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
3259you to use some convenience methods to start/stop watchers and also change
3260the callback model to a model using method callbacks on objects.
3261.PP
3262To use it,
3263.PP
3264.Vb 1
3265\& #include <ev++.h>
3266.Ve
3267.PP
3268This automatically includes \fIev.h\fR and puts all of its definitions (many
3269of them macros) into the global namespace. All \*(C+ specific things are
3270put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding
3271options as \fIev.h\fR, most notably \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR.
3272.PP
3273Care has been taken to keep the overhead low. The only data member the \*(C+
3274classes add (compared to plain C\-style watchers) is the event loop pointer
3275that the watcher is associated with (or no additional members at all if
3276you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
3277.PP
3278Currently, functions, and static and non-static member functions can be
3279used as callbacks. Other types should be easy to add as long as they only
3280need one additional pointer for context. If you need support for other
3281types of functors please contact the author (preferably after implementing
3282it).
3283.PP
3284Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
3285.ie n .IP """ev::READ"", ""ev::WRITE"" etc." 4
3286.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
3287.IX Item "ev::READ, ev::WRITE etc."
3288These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
3289macros from \fIev.h\fR.
3290.ie n .IP """ev::tstamp"", ""ev::now""" 4
3291.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
3292.IX Item "ev::tstamp, ev::now"
3293Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
3294.ie n .IP """ev::io"", ""ev::timer"", ""ev::periodic"", ""ev::idle"", ""ev::sig"" etc." 4
3295.el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
3296.IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
3297For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
3298the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
3299which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
3300defines by many implementations.
3301.Sp
3302All of those classes have these methods:
3303.RS 4
3304.IP "ev::TYPE::TYPE ()" 4
3305.IX Item "ev::TYPE::TYPE ()"
3306.PD 0
3307.IP "ev::TYPE::TYPE (struct ev_loop *)" 4
3308.IX Item "ev::TYPE::TYPE (struct ev_loop *)"
3309.IP "ev::TYPE::~TYPE" 4
3310.IX Item "ev::TYPE::~TYPE"
3311.PD
3312The constructor (optionally) takes an event loop to associate the watcher
3313with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR.
3314.Sp
3315The constructor calls \f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the
3316\&\f(CW\*(C`set\*(C'\fR method before starting it.
3317.Sp
3318It will not set a callback, however: You have to call the templated \f(CW\*(C`set\*(C'\fR
3319method to set a callback before you can start the watcher.
3320.Sp
3321(The reason why you have to use a method is a limitation in \*(C+ which does
3322not allow explicit template arguments for constructors).
3323.Sp
3324The destructor automatically stops the watcher if it is active.
3325.IP "w\->set<class, &class::method> (object *)" 4
3326.IX Item "w->set<class, &class::method> (object *)"
3327This method sets the callback method to call. The method has to have a
3328signature of \f(CW\*(C`void (*)(ev_TYPE &, int)\*(C'\fR, it receives the watcher as
3329first argument and the \f(CW\*(C`revents\*(C'\fR as second. The object must be given as
3330parameter and is stored in the \f(CW\*(C`data\*(C'\fR member of the watcher.
3331.Sp
3332This method synthesizes efficient thunking code to call your method from
3333the C callback that libev requires. If your compiler can inline your
3334callback (i.e. it is visible to it at the place of the \f(CW\*(C`set\*(C'\fR call and
3335your compiler is good :), then the method will be fully inlined into the
3336thunking function, making it as fast as a direct C callback.
3337.Sp
3338Example: simple class declaration and watcher initialisation
3339.Sp
3340.Vb 4
3341\& struct myclass
3342\& {
3343\& void io_cb (ev::io &w, int revents) { }
3344\& }
3345\&
3346\& myclass obj;
3347\& ev::io iow;
3348\& iow.set <myclass, &myclass::io_cb> (&obj);
3349.Ve
3350.IP "w\->set (object *)" 4
3351.IX Item "w->set (object *)"
3352This is an \fBexperimental\fR feature that might go away in a future version.
3353.Sp
3354This is a variation of a method callback \- leaving out the method to call
3355will default the method to \f(CW\*(C`operator ()\*(C'\fR, which makes it possible to use
3356functor objects without having to manually specify the \f(CW\*(C`operator ()\*(C'\fR all
3357the time. Incidentally, you can then also leave out the template argument
3358list.
3359.Sp
3360The \f(CW\*(C`operator ()\*(C'\fR method prototype must be \f(CW\*(C`void operator ()(watcher &w,
3361int revents)\*(C'\fR.
3362.Sp
3363See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
3364.Sp
3365Example: use a functor object as callback.
3366.Sp
3367.Vb 7
3368\& struct myfunctor
3369\& {
3370\& void operator() (ev::io &w, int revents)
3371\& {
3372\& ...
3373\& }
3374\& }
3375\&
3376\& myfunctor f;
3377\&
3378\& ev::io w;
3379\& w.set (&f);
3380.Ve
3381.IP "w\->set<function> (void *data = 0)" 4
3382.IX Item "w->set<function> (void *data = 0)"
3383Also sets a callback, but uses a static method or plain function as
3384callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
3385\&\f(CW\*(C`data\*(C'\fR member and is free for you to use.
3386.Sp
3387The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
3388.Sp
3389See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
3390.Sp
3391Example: Use a plain function as callback.
3392.Sp
3393.Vb 2
3394\& static void io_cb (ev::io &w, int revents) { }
3395\& iow.set <io_cb> ();
3396.Ve
3397.IP "w\->set (struct ev_loop *)" 4
3398.IX Item "w->set (struct ev_loop *)"
3399Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
3400do this when the watcher is inactive (and not pending either).
3401.IP "w\->set ([arguments])" 4
3402.IX Item "w->set ([arguments])"
3403Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same arguments. Must be
3404called at least once. Unlike the C counterpart, an active watcher gets
3405automatically stopped and restarted when reconfiguring it with this
3406method.
3407.IP "w\->start ()" 4
3408.IX Item "w->start ()"
3409Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
3410constructor already stores the event loop.
3411.IP "w\->stop ()" 4
3412.IX Item "w->stop ()"
3413Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
3414.ie n .IP "w\->again () (""ev::timer"", ""ev::periodic"" only)" 4
3415.el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
3416.IX Item "w->again () (ev::timer, ev::periodic only)"
3417For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
3418\&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
3419.ie n .IP "w\->sweep () (""ev::embed"" only)" 4
3420.el .IP "w\->sweep () (\f(CWev::embed\fR only)" 4
3421.IX Item "w->sweep () (ev::embed only)"
3422Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR.
3423.ie n .IP "w\->update () (""ev::stat"" only)" 4
3424.el .IP "w\->update () (\f(CWev::stat\fR only)" 4
3425.IX Item "w->update () (ev::stat only)"
3426Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
3427.RE
3428.RS 4
3429.RE
3430.PP
3431Example: Define a class with an \s-1IO\s0 and idle watcher, start one of them in
3432the constructor.
3433.PP
3434.Vb 4
3435\& class myclass
3436\& {
3437\& ev::io io ; void io_cb (ev::io &w, int revents);
3438\& ev::idle idle; void idle_cb (ev::idle &w, int revents);
3439\&
3440\& myclass (int fd)
3441\& {
3442\& io .set <myclass, &myclass::io_cb > (this);
3443\& idle.set <myclass, &myclass::idle_cb> (this);
3444\&
3445\& io.start (fd, ev::READ);
3446\& }
3447\& };
3448.Ve
3449.SH "OTHER LANGUAGE BINDINGS"
3450.IX Header "OTHER LANGUAGE BINDINGS"
3451Libev does not offer other language bindings itself, but bindings for a
3452number of languages exist in the form of third-party packages. If you know
3453any interesting language binding in addition to the ones listed here, drop
3454me a note.
3455.IP "Perl" 4
3456.IX Item "Perl"
3457The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test
3458libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module,
3459there are additional modules that implement libev-compatible interfaces
3460to \f(CW\*(C`libadns\*(C'\fR (\f(CW\*(C`EV::ADNS\*(C'\fR, but \f(CW\*(C`AnyEvent::DNS\*(C'\fR is preferred nowadays),
3461\&\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
3462and \f(CW\*(C`EV::Glib\*(C'\fR).
3463.Sp
3464It can be found and installed via \s-1CPAN\s0, its homepage is at
3465<http://software.schmorp.de/pkg/EV>.
3466.IP "Python" 4
3467.IX Item "Python"
3468Python bindings can be found at <http://code.google.com/p/pyev/>. It
3469seems to be quite complete and well-documented.
3470.IP "Ruby" 4
3471.IX Item "Ruby"
3472Tony Arcieri has written a ruby extension that offers access to a subset
3473of the libev \s-1API\s0 and adds file handle abstractions, asynchronous \s-1DNS\s0 and
3474more on top of it. It can be found via gem servers. Its homepage is at
3475<http://rev.rubyforge.org/>.
3476.Sp
3477Roger Pack reports that using the link order \f(CW\*(C`\-lws2_32 \-lmsvcrt\-ruby\-190\*(C'\fR
3478makes rev work even on mingw.
3479.IP "Haskell" 4
3480.IX Item "Haskell"
3481A haskell binding to libev is available at
3482<http://hackage.haskell.org/cgi\-bin/hackage\-scripts/package/hlibev>.
3483.IP "D" 4
3484.IX Item "D"
3485Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
3486be found at <http://proj.llucax.com.ar/wiki/evd>.
3487.IP "Ocaml" 4
3488.IX Item "Ocaml"
3489Erkki Seppala has written Ocaml bindings for libev, to be found at
3490<http://modeemi.cs.tut.fi/~flux/software/ocaml\-ev/>.
3491.SH "MACRO MAGIC"
3492.IX Header "MACRO MAGIC"
3493Libev can be compiled with a variety of options, the most fundamental
3494of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most)
3495functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
3496.PP
3497To make it easier to write programs that cope with either variant, the
3498following macros are defined:
3499.ie n .IP """EV_A"", ""EV_A_""" 4
3500.el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
3501.IX Item "EV_A, EV_A_"
3502This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
3503loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
3504\&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
3505.Sp
3506.Vb 3
3507\& ev_unref (EV_A);
3508\& ev_timer_add (EV_A_ watcher);
3509\& ev_loop (EV_A_ 0);
3510.Ve
3511.Sp
3512It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
3513which is often provided by the following macro.
3514.ie n .IP """EV_P"", ""EV_P_""" 4
3515.el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
3516.IX Item "EV_P, EV_P_"
3517This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
3518loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
3519\&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
3520.Sp
3521.Vb 2
3522\& // this is how ev_unref is being declared
3523\& static void ev_unref (EV_P);
3524\&
3525\& // this is how you can declare your typical callback
3526\& static void cb (EV_P_ ev_timer *w, int revents)
3527.Ve
3528.Sp
3529It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
3530suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
3531.ie n .IP """EV_DEFAULT"", ""EV_DEFAULT_""" 4
3532.el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
3533.IX Item "EV_DEFAULT, EV_DEFAULT_"
3534Similar to the other two macros, this gives you the value of the default
3535loop, if multiple loops are supported (\*(L"ev loop default\*(R").
3536.ie n .IP """EV_DEFAULT_UC"", ""EV_DEFAULT_UC_""" 4
3537.el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
3538.IX Item "EV_DEFAULT_UC, EV_DEFAULT_UC_"
3539Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the
3540default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour
3541is undefined when the default loop has not been initialised by a previous
3542execution of \f(CW\*(C`EV_DEFAULT\*(C'\fR, \f(CW\*(C`EV_DEFAULT_\*(C'\fR or \f(CW\*(C`ev_default_init (...)\*(C'\fR.
3543.Sp
3544It is often prudent to use \f(CW\*(C`EV_DEFAULT\*(C'\fR when initialising the first
3545watcher in a function but use \f(CW\*(C`EV_DEFAULT_UC\*(C'\fR afterwards.
3546.PP
3547Example: Declare and initialise a check watcher, utilising the above
3548macros so it will work regardless of whether multiple loops are supported
3549or not.
3550.PP
3551.Vb 5
3552\& static void
3553\& check_cb (EV_P_ ev_timer *w, int revents)
3554\& {
3555\& ev_check_stop (EV_A_ w);
3556\& }
3557\&
3558\& ev_check check;
3559\& ev_check_init (&check, check_cb);
3560\& ev_check_start (EV_DEFAULT_ &check);
3561\& ev_loop (EV_DEFAULT_ 0);
3562.Ve
3563.SH "EMBEDDING"
3564.IX Header "EMBEDDING"
3565Libev can (and often is) directly embedded into host
3566applications. Examples of applications that embed it include the Deliantra
3567Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
3568and rxvt-unicode.
3569.PP
3570The goal is to enable you to just copy the necessary files into your
3571source directory without having to change even a single line in them, so
3572you can easily upgrade by simply copying (or having a checked-out copy of
3573libev somewhere in your source tree).
3574.SS "\s-1FILESETS\s0"
3575.IX Subsection "FILESETS"
3576Depending on what features you need you need to include one or more sets of files
3577in your application.
3578.PP
3579\fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR
3580.IX Subsection "CORE EVENT LOOP"
3581.PP
3582To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
3583configuration (no autoconf):
3584.PP
3585.Vb 2
3586\& #define EV_STANDALONE 1
3587\& #include "ev.c"
3588.Ve
3589.PP
3590This will automatically include \fIev.h\fR, too, and should be done in a
3591single C source file only to provide the function implementations. To use
3592it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best
3593done by writing a wrapper around \fIev.h\fR that you can include instead and
3594where you can put other configuration options):
3595.PP
3596.Vb 2
3597\& #define EV_STANDALONE 1
3598\& #include "ev.h"
3599.Ve
3600.PP
3601Both header files and implementation files can be compiled with a \*(C+
3602compiler (at least, that's a stated goal, and breakage will be treated
3603as a bug).
3604.PP
3605You need the following files in your source tree, or in a directory
3606in your include path (e.g. in libev/ when using \-Ilibev):
3607.PP
3608.Vb 4
3609\& ev.h
3610\& ev.c
3611\& ev_vars.h
3612\& ev_wrap.h
3613\&
3614\& ev_win32.c required on win32 platforms only
3615\&
3616\& ev_select.c only when select backend is enabled (which is enabled by default)
3617\& ev_poll.c only when poll backend is enabled (disabled by default)
3618\& ev_epoll.c only when the epoll backend is enabled (disabled by default)
3619\& ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
3620\& ev_port.c only when the solaris port backend is enabled (disabled by default)
3621.Ve
3622.PP
3623\&\fIev.c\fR includes the backend files directly when enabled, so you only need
3624to compile this single file.
3625.PP
3626\fI\s-1LIBEVENT\s0 \s-1COMPATIBILITY\s0 \s-1API\s0\fR
3627.IX Subsection "LIBEVENT COMPATIBILITY API"
3628.PP
3629To include the libevent compatibility \s-1API\s0, also include:
3630.PP
3631.Vb 1
3632\& #include "event.c"
3633.Ve
3634.PP
3635in the file including \fIev.c\fR, and:
3636.PP
3637.Vb 1
3638\& #include "event.h"
3639.Ve
3640.PP
3641in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR.
3642.PP
3643You need the following additional files for this:
3644.PP
3645.Vb 2
3646\& event.h
3647\& event.c
3648.Ve
3649.PP
3650\fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR
3651.IX Subsection "AUTOCONF SUPPORT"
3652.PP
3653Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your configuration in
3654whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
3655\&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then
3656include \fIconfig.h\fR and configure itself accordingly.
3657.PP
3658For this of course you need the m4 file:
3659.PP
3660.Vb 1
3661\& libev.m4
3662.Ve
3663.SS "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0"
3664.IX Subsection "PREPROCESSOR SYMBOLS/MACROS"
3665Libev can be configured via a variety of preprocessor symbols you have to
3666define before including any of its files. The default in the absence of
3667autoconf is documented for every option.
3668.IP "\s-1EV_STANDALONE\s0" 4
3669.IX Item "EV_STANDALONE"
3670Must always be \f(CW1\fR if you do not use autoconf configuration, which
3671keeps libev from including \fIconfig.h\fR, and it also defines dummy
3672implementations for some libevent functions (such as logging, which is not
3673supported). It will also not define any of the structs usually found in
3674\&\fIevent.h\fR that are not directly supported by the libev core alone.
3675.Sp
3676In stanbdalone mode, libev will still try to automatically deduce the
3677configuration, but has to be more conservative.
3678.IP "\s-1EV_USE_MONOTONIC\s0" 4
3679.IX Item "EV_USE_MONOTONIC"
3680If defined to be \f(CW1\fR, libev will try to detect the availability of the
3681monotonic clock option at both compile time and runtime. Otherwise no
3682use of the monotonic clock option will be attempted. If you enable this,
3683you usually have to link against librt or something similar. Enabling it
3684when the functionality isn't available is safe, though, although you have
3685to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
3686function is hiding in (often \fI\-lrt\fR). See also \f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
3687.IP "\s-1EV_USE_REALTIME\s0" 4
3688.IX Item "EV_USE_REALTIME"
3689If defined to be \f(CW1\fR, libev will try to detect the availability of the
3690real-time clock option at compile time (and assume its availability
3691at runtime if successful). Otherwise no use of the real-time clock
3692option will be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR
3693by \f(CW\*(C`clock_get (CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect
3694correctness. See the note about libraries in the description of
3695\&\f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. Defaults to the opposite value of
3696\&\f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
3697.IP "\s-1EV_USE_CLOCK_SYSCALL\s0" 4
3698.IX Item "EV_USE_CLOCK_SYSCALL"
3699If defined to be \f(CW1\fR, libev will try to use a direct syscall instead
3700of calling the system-provided \f(CW\*(C`clock_gettime\*(C'\fR function. This option
3701exists 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
3702unconditionally pulls in \f(CW\*(C`libpthread\*(C'\fR, slowing down single-threaded
3703programs needlessly. Using a direct syscall is slightly slower (in
3704theory), because no optimised vdso implementation can be used, but avoids
3705the pthread dependency. Defaults to \f(CW1\fR on GNU/Linux with glibc 2.x or
3706higher, as it simplifies linking (no need for \f(CW\*(C`\-lrt\*(C'\fR).
3707.IP "\s-1EV_USE_NANOSLEEP\s0" 4
3708.IX Item "EV_USE_NANOSLEEP"
3709If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available
3710and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR.
3711.IP "\s-1EV_USE_EVENTFD\s0" 4
3712.IX Item "EV_USE_EVENTFD"
3713If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
3714available and will probe for kernel support at runtime. This will improve
3715\&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
3716If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
37172.7 or newer, otherwise disabled.
3718.IP "\s-1EV_USE_SELECT\s0" 4
3719.IX Item "EV_USE_SELECT"
3720If undefined or defined to be \f(CW1\fR, libev will compile in support for the
3721\&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at auto-detection will be done: if no
3722other method takes over, select will be it. Otherwise the select backend
3723will not be compiled in.
3724.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
3725.IX Item "EV_SELECT_USE_FD_SET"
3726If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR
3727structure. This is useful if libev doesn't compile due to a missing
3728\&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it mis-guesses the bitset layout
3729on exotic systems. This usually limits the range of file descriptors to
3730some low limit such as 1024 or might have other limitations (winsocket
3731only allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation,
3732configures the maximum size of the \f(CW\*(C`fd_set\*(C'\fR.
3733.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
3734.IX Item "EV_SELECT_IS_WINSOCKET"
3735When defined to \f(CW1\fR, the select backend will assume that
3736select/socket/connect etc. don't understand file descriptors but
3737wants osf handles on win32 (this is the case when the select to
3738be used is the winsock select). This means that it will call
3739\&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
3740it is assumed that all these functions actually work on fds, even
3741on win32. Should not be defined on non\-win32 platforms.
3742.IP "\s-1EV_FD_TO_WIN32_HANDLE\s0" 4
3743.IX Item "EV_FD_TO_WIN32_HANDLE"
3744If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map
3745file descriptors to socket handles. When not defining this symbol (the
3746default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually
3747correct. In some cases, programs use their own file descriptor management,
3748in which case they can provide this function to map fds to socket handles.
3749.IP "\s-1EV_USE_POLL\s0" 4
3750.IX Item "EV_USE_POLL"
3751If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2)
3752backend. Otherwise it will be enabled on non\-win32 platforms. It
3753takes precedence over select.
3754.IP "\s-1EV_USE_EPOLL\s0" 4
3755.IX Item "EV_USE_EPOLL"
3756If defined to be \f(CW1\fR, libev will compile in support for the Linux
3757\&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime,
3758otherwise another method will be used as fallback. This is the preferred
3759backend for GNU/Linux systems. If undefined, it will be enabled if the
3760headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3761.IP "\s-1EV_USE_KQUEUE\s0" 4
3762.IX Item "EV_USE_KQUEUE"
3763If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
3764\&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime,
3765otherwise another method will be used as fallback. This is the preferred
3766backend for \s-1BSD\s0 and BSD-like systems, although on most BSDs kqueue only
3767supports some types of fds correctly (the only platform we found that
3768supports ptys for example was NetBSD), so kqueue might be compiled in, but
3769not be used unless explicitly requested. The best way to use it is to find
3770out whether kqueue supports your type of fd properly and use an embedded
3771kqueue loop.
3772.IP "\s-1EV_USE_PORT\s0" 4
3773.IX Item "EV_USE_PORT"
3774If defined to be \f(CW1\fR, libev will compile in support for the Solaris
377510 port style backend. Its availability will be detected at runtime,
3776otherwise another method will be used as fallback. This is the preferred
3777backend for Solaris 10 systems.
3778.IP "\s-1EV_USE_DEVPOLL\s0" 4
3779.IX Item "EV_USE_DEVPOLL"
3780Reserved for future expansion, works like the \s-1USE\s0 symbols above.
3781.IP "\s-1EV_USE_INOTIFY\s0" 4
3782.IX Item "EV_USE_INOTIFY"
3783If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
3784interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
3785be detected at runtime. If undefined, it will be enabled if the headers
3786indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3787.IP "\s-1EV_ATOMIC_T\s0" 4
3788.IX Item "EV_ATOMIC_T"
3789Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
3790access is atomic with respect to other threads or signal contexts. No such
3791type is easily found in the C language, so you can provide your own type
3792that you know is safe for your purposes. It is used both for signal handler \*(L"locking\*(R"
3793as well as for signal and thread safety in \f(CW\*(C`ev_async\*(C'\fR watchers.
3794.Sp
3795In the absence of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR
3796(from \fIsignal.h\fR), which is usually good enough on most platforms.
3797.IP "\s-1EV_H\s0" 4
3798.IX Item "EV_H"
3799The name of the \fIev.h\fR header file used to include it. The default if
3800undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be
3801used to virtually rename the \fIev.h\fR header file in case of conflicts.
3802.IP "\s-1EV_CONFIG_H\s0" 4
3803.IX Item "EV_CONFIG_H"
3804If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
3805\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
3806\&\f(CW\*(C`EV_H\*(C'\fR, above.
3807.IP "\s-1EV_EVENT_H\s0" 4
3808.IX Item "EV_EVENT_H"
3809Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea
3810of how the \fIevent.h\fR header can be found, the default is \f(CW"event.h"\fR.
3811.IP "\s-1EV_PROTOTYPES\s0" 4
3812.IX Item "EV_PROTOTYPES"
3813If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
3814prototypes, but still define all the structs and other symbols. This is
3815occasionally useful if you want to provide your own wrapper functions
3816around libev functions.
3817.IP "\s-1EV_MULTIPLICITY\s0" 4
3818.IX Item "EV_MULTIPLICITY"
3819If undefined or defined to \f(CW1\fR, then all event-loop-specific functions
3820will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create
3821additional independent event loops. Otherwise there will be no support
3822for multiple event loops and there is no first event loop pointer
3823argument. Instead, all functions act on the single default loop.
3824.IP "\s-1EV_MINPRI\s0" 4
3825.IX Item "EV_MINPRI"
3826.PD 0
3827.IP "\s-1EV_MAXPRI\s0" 4
3828.IX Item "EV_MAXPRI"
3829.PD
3830The range of allowed priorities. \f(CW\*(C`EV_MINPRI\*(C'\fR must be smaller or equal to
3831\&\f(CW\*(C`EV_MAXPRI\*(C'\fR, but otherwise there are no non-obvious limitations. You can
3832provide for more priorities by overriding those symbols (usually defined
3833to be \f(CW\*(C`\-2\*(C'\fR and \f(CW2\fR, respectively).
3834.Sp
3835When doing priority-based operations, libev usually has to linearly search
3836all the priorities, so having many of them (hundreds) uses a lot of space
3837and time, so using the defaults of five priorities (\-2 .. +2) is usually
3838fine.
3839.Sp
3840If your embedding application does not need any priorities, defining these
3841both to \f(CW0\fR will save some memory and \s-1CPU\s0.
3842.IP "\s-1EV_PERIODIC_ENABLE\s0" 4
3843.IX Item "EV_PERIODIC_ENABLE"
3844If undefined or defined to be \f(CW1\fR, then periodic timers are supported. If
3845defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of
3846code.
3847.IP "\s-1EV_IDLE_ENABLE\s0" 4
3848.IX Item "EV_IDLE_ENABLE"
3849If undefined or defined to be \f(CW1\fR, then idle watchers are supported. If
3850defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of
3851code.
3852.IP "\s-1EV_EMBED_ENABLE\s0" 4
3853.IX Item "EV_EMBED_ENABLE"
3854If undefined or defined to be \f(CW1\fR, then embed watchers are supported. If
3855defined to be \f(CW0\fR, then they are not. Embed watchers rely on most other
3856watcher types, which therefore must not be disabled.
3857.IP "\s-1EV_STAT_ENABLE\s0" 4
3858.IX Item "EV_STAT_ENABLE"
3859If undefined or defined to be \f(CW1\fR, then stat watchers are supported. If
3860defined to be \f(CW0\fR, then they are not.
3861.IP "\s-1EV_FORK_ENABLE\s0" 4
3862.IX Item "EV_FORK_ENABLE"
3863If undefined or defined to be \f(CW1\fR, then fork watchers are supported. If
3864defined to be \f(CW0\fR, then they are not.
3865.IP "\s-1EV_ASYNC_ENABLE\s0" 4
3866.IX Item "EV_ASYNC_ENABLE"
3867If undefined or defined to be \f(CW1\fR, then async watchers are supported. If
3868defined to be \f(CW0\fR, then they are not.
3869.IP "\s-1EV_MINIMAL\s0" 4
3870.IX Item "EV_MINIMAL"
3871If you need to shave off some kilobytes of code at the expense of some
3872speed (but with the full \s-1API\s0), define this symbol to \f(CW1\fR. Currently this
3873is used to override some inlining decisions, saves roughly 30% code size
3874on amd64. It also selects a much smaller 2\-heap for timer management over
3875the default 4\-heap.
3876.Sp
3877You can save even more by disabling watcher types you do not need
3878and setting \f(CW\*(C`EV_MAXPRI\*(C'\fR == \f(CW\*(C`EV_MINPRI\*(C'\fR. Also, disabling \f(CW\*(C`assert\*(C'\fR
3879(\f(CW\*(C`\-DNDEBUG\*(C'\fR) will usually reduce code size a lot.
3880.Sp
3881Defining \f(CW\*(C`EV_MINIMAL\*(C'\fR to \f(CW2\fR will additionally reduce the core \s-1API\s0 to
3882provide a bare-bones event library. See \f(CW\*(C`ev.h\*(C'\fR for details on what parts
3883of the \s-1API\s0 are still available, and do not complain if this subset changes
3884over time.
3885.IP "\s-1EV_PID_HASHSIZE\s0" 4
3886.IX Item "EV_PID_HASHSIZE"
3887\&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by
3888pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR), usually more
3889than enough. If you need to manage thousands of children you might want to
3890increase this value (\fImust\fR be a power of two).
3891.IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4
3892.IX Item "EV_INOTIFY_HASHSIZE"
3893\&\f(CW\*(C`ev_stat\*(C'\fR watchers use a small hash table to distribute workload by
3894inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR),
3895usually more than enough. If you need to manage thousands of \f(CW\*(C`ev_stat\*(C'\fR
3896watchers you might want to increase this value (\fImust\fR be a power of
3897two).
3898.IP "\s-1EV_USE_4HEAP\s0" 4
3899.IX Item "EV_USE_4HEAP"
3900Heaps are not very cache-efficient. To improve the cache-efficiency of the
3901timer and periodics heaps, libev uses a 4\-heap when this symbol is defined
3902to \f(CW1\fR. The 4\-heap uses more complicated (longer) code but has noticeably
3903faster performance with many (thousands) of watchers.
3904.Sp
3905The default is \f(CW1\fR unless \f(CW\*(C`EV_MINIMAL\*(C'\fR is set in which case it is \f(CW0\fR
3906(disabled).
3907.IP "\s-1EV_HEAP_CACHE_AT\s0" 4
3908.IX Item "EV_HEAP_CACHE_AT"
3909Heaps are not very cache-efficient. To improve the cache-efficiency of the
3910timer and periodics heaps, libev can cache the timestamp (\fIat\fR) within
3911the heap structure (selected by defining \f(CW\*(C`EV_HEAP_CACHE_AT\*(C'\fR to \f(CW1\fR),
3912which uses 8\-12 bytes more per watcher and a few hundred bytes more code,
3913but avoids random read accesses on heap changes. This improves performance
3914noticeably with many (hundreds) of watchers.
3915.Sp
3916The default is \f(CW1\fR unless \f(CW\*(C`EV_MINIMAL\*(C'\fR is set in which case it is \f(CW0\fR
3917(disabled).
3918.IP "\s-1EV_VERIFY\s0" 4
3919.IX Item "EV_VERIFY"
3920Controls how much internal verification (see \f(CW\*(C`ev_loop_verify ()\*(C'\fR) will
3921be done: If set to \f(CW0\fR, no internal verification code will be compiled
3922in. If set to \f(CW1\fR, then verification code will be compiled in, but not
3923called. If set to \f(CW2\fR, then the internal verification code will be
3924called once per loop, which can slow down libev. If set to \f(CW3\fR, then the
3925verification code will be called very frequently, which will slow down
3926libev considerably.
3927.Sp
3928The default is \f(CW1\fR, unless \f(CW\*(C`EV_MINIMAL\*(C'\fR is set, in which case it will be
3929\&\f(CW0\fR.
3930.IP "\s-1EV_COMMON\s0" 4
3931.IX Item "EV_COMMON"
3932By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining
3933this macro to a something else you can include more and other types of
3934members. You have to define it each time you include one of the files,
3935though, and it must be identical each time.
3936.Sp
3937For example, the perl \s-1EV\s0 module uses something like this:
3938.Sp
3939.Vb 3
3940\& #define EV_COMMON \e
3941\& SV *self; /* contains this struct */ \e
3942\& SV *cb_sv, *fh /* note no trailing ";" */
3943.Ve
3944.IP "\s-1EV_CB_DECLARE\s0 (type)" 4
3945.IX Item "EV_CB_DECLARE (type)"
3946.PD 0
3947.IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4
3948.IX Item "EV_CB_INVOKE (watcher, revents)"
3949.IP "ev_set_cb (ev, cb)" 4
3950.IX Item "ev_set_cb (ev, cb)"
3951.PD
3952Can be used to change the callback member declaration in each watcher,
3953and the way callbacks are invoked and set. Must expand to a struct member
3954definition and a statement, respectively. See the \fIev.h\fR header file for
3955their default definitions. One possible use for overriding these is to
3956avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use
3957method calls instead of plain function calls in \*(C+.
3958.SS "\s-1EXPORTED\s0 \s-1API\s0 \s-1SYMBOLS\s0"
3959.IX Subsection "EXPORTED API SYMBOLS"
3960If you need to re-export the \s-1API\s0 (e.g. via a \s-1DLL\s0) and you need a list of
3961exported symbols, you can use the provided \fISymbol.*\fR files which list
3962all public symbols, one per line:
3963.PP
3964.Vb 2
3965\& Symbols.ev for libev proper
3966\& Symbols.event for the libevent emulation
3967.Ve
3968.PP
3969This can also be used to rename all public symbols to avoid clashes with
3970multiple versions of libev linked together (which is obviously bad in
3971itself, but sometimes it is inconvenient to avoid this).
3972.PP
3973A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to
3974include before including \fIev.h\fR:
3975.PP
3976.Vb 1
3977\& <Symbols.ev sed \-e "s/.*/#define & myprefix_&/" >wrap.h
3978.Ve
3979.PP
3980This would create a file \fIwrap.h\fR which essentially looks like this:
3981.PP
3982.Vb 4
3983\& #define ev_backend myprefix_ev_backend
3984\& #define ev_check_start myprefix_ev_check_start
3985\& #define ev_check_stop myprefix_ev_check_stop
3986\& ...
3987.Ve
3988.SS "\s-1EXAMPLES\s0"
3989.IX Subsection "EXAMPLES"
3990For a real-world example of a program the includes libev
3991verbatim, you can have a look at the \s-1EV\s0 perl module
3992(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
3993the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public
3994interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file
3995will be compiled. It is pretty complex because it provides its own header
3996file.
3997.PP
3998The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file
3999that everybody includes and which overrides some configure choices:
4000.PP
4001.Vb 9
4002\& #define EV_MINIMAL 1
4003\& #define EV_USE_POLL 0
4004\& #define EV_MULTIPLICITY 0
4005\& #define EV_PERIODIC_ENABLE 0
4006\& #define EV_STAT_ENABLE 0
4007\& #define EV_FORK_ENABLE 0
4008\& #define EV_CONFIG_H <config.h>
4009\& #define EV_MINPRI 0
4010\& #define EV_MAXPRI 0
4011\&
4012\& #include "ev++.h"
4013.Ve
4014.PP
4015And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled:
4016.PP
4017.Vb 2
4018\& #include "ev_cpp.h"
4019\& #include "ev.c"
4020.Ve
4021.SH "INTERACTION WITH OTHER PROGRAMS OR LIBRARIES"
4022.IX Header "INTERACTION WITH OTHER PROGRAMS OR LIBRARIES"
4023.SS "\s-1THREADS\s0 \s-1AND\s0 \s-1COROUTINES\s0"
4024.IX Subsection "THREADS AND COROUTINES"
4025\fI\s-1THREADS\s0\fR
4026.IX Subsection "THREADS"
4027.PP
4028All libev functions are reentrant and thread-safe unless explicitly
4029documented otherwise, but libev implements no locking itself. This means
4030that you can use as many loops as you want in parallel, as long as there
4031are no concurrent calls into any libev function with the same loop
4032parameter (\f(CW\*(C`ev_default_*\*(C'\fR calls have an implicit default loop parameter,
4033of course): libev guarantees that different event loops share no data
4034structures that need any locking.
4035.PP
4036Or to put it differently: calls with different loop parameters can be done
4037concurrently from multiple threads, calls with the same loop parameter
4038must be done serially (but can be done from different threads, as long as
4039only one thread ever is inside a call at any point in time, e.g. by using
4040a mutex per loop).
4041.PP
4042Specifically to support threads (and signal handlers), libev implements
4043so-called \f(CW\*(C`ev_async\*(C'\fR watchers, which allow some limited form of
4044concurrency on the same event loop, namely waking it up \*(L"from the
4045outside\*(R".
4046.PP
4047If you want to know which design (one loop, locking, or multiple loops
4048without or something else still) is best for your problem, then I cannot
4049help you, but here is some generic advice:
4050.IP "\(bu" 4
4051most applications have a main thread: use the default libev loop
4052in that thread, or create a separate thread running only the default loop.
4053.Sp
4054This helps integrating other libraries or software modules that use libev
4055themselves and don't care/know about threading.
4056.IP "\(bu" 4
4057one loop per thread is usually a good model.
4058.Sp
4059Doing this is almost never wrong, sometimes a better-performance model
4060exists, but it is always a good start.
4061.IP "\(bu" 4
4062other models exist, such as the leader/follower pattern, where one
4063loop is handed through multiple threads in a kind of round-robin fashion.
4064.Sp
4065Choosing a model is hard \- look around, learn, know that usually you can do
4066better than you currently do :\-)
4067.IP "\(bu" 4
4068often you need to talk to some other thread which blocks in the
4069event loop.
4070.Sp
4071\&\f(CW\*(C`ev_async\*(C'\fR watchers can be used to wake them up from other threads safely
4072(or from signal contexts...).
4073.Sp
4074An example use would be to communicate signals or other events that only
4075work in the default loop by registering the signal watcher with the
4076default loop and triggering an \f(CW\*(C`ev_async\*(C'\fR watcher from the default loop
4077watcher callback into the event loop interested in the signal.
4078.PP
4079\s-1THREAD\s0 \s-1LOCKING\s0 \s-1EXAMPLE\s0
4080.IX Subsection "THREAD LOCKING EXAMPLE"
4081.PP
4082Here is a fictitious example of how to run an event loop in a different
4083thread than where callbacks are being invoked and watchers are
4084created/added/removed.
4085.PP
4086For a real-world example, see the \f(CW\*(C`EV::Loop::Async\*(C'\fR perl module,
4087which uses exactly this technique (which is suited for many high-level
4088languages).
4089.PP
4090The example uses a pthread mutex to protect the loop data, a condition
4091variable to wait for callback invocations, an async watcher to notify the
4092event loop thread and an unspecified mechanism to wake up the main thread.
4093.PP
4094First, you need to associate some data with the event loop:
4095.PP
4096.Vb 6
4097\& typedef struct {
4098\& mutex_t lock; /* global loop lock */
4099\& ev_async async_w;
4100\& thread_t tid;
4101\& cond_t invoke_cv;
4102\& } userdata;
4103\&
4104\& void prepare_loop (EV_P)
4105\& {
4106\& // for simplicity, we use a static userdata struct.
4107\& static userdata u;
4108\&
4109\& ev_async_init (&u\->async_w, async_cb);
4110\& ev_async_start (EV_A_ &u\->async_w);
4111\&
4112\& pthread_mutex_init (&u\->lock, 0);
4113\& pthread_cond_init (&u\->invoke_cv, 0);
4114\&
4115\& // now associate this with the loop
4116\& ev_set_userdata (EV_A_ u);
4117\& ev_set_invoke_pending_cb (EV_A_ l_invoke);
4118\& ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
4119\&
4120\& // then create the thread running ev_loop
4121\& pthread_create (&u\->tid, 0, l_run, EV_A);
4122\& }
4123.Ve
4124.PP
4125The callback for the \f(CW\*(C`ev_async\*(C'\fR watcher does nothing: the watcher is used
4126solely to wake up the event loop so it takes notice of any new watchers
4127that might have been added:
4128.PP
4129.Vb 5
4130\& static void
4131\& async_cb (EV_P_ ev_async *w, int revents)
4132\& {
4133\& // just used for the side effects
4134\& }
4135.Ve
4136.PP
4137The \f(CW\*(C`l_release\*(C'\fR and \f(CW\*(C`l_acquire\*(C'\fR callbacks simply unlock/lock the mutex
4138protecting the loop data, respectively.
4139.PP
4140.Vb 6
4141\& static void
4142\& l_release (EV_P)
4143\& {
4144\& userdata *u = ev_userdata (EV_A);
4145\& pthread_mutex_unlock (&u\->lock);
4146\& }
4147\&
4148\& static void
4149\& l_acquire (EV_P)
4150\& {
4151\& userdata *u = ev_userdata (EV_A);
4152\& pthread_mutex_lock (&u\->lock);
4153\& }
4154.Ve
4155.PP
4156The event loop thread first acquires the mutex, and then jumps straight
4157into \f(CW\*(C`ev_loop\*(C'\fR:
4158.PP
4159.Vb 4
4160\& void *
4161\& l_run (void *thr_arg)
4162\& {
4163\& struct ev_loop *loop = (struct ev_loop *)thr_arg;
4164\&
4165\& l_acquire (EV_A);
4166\& pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
4167\& ev_loop (EV_A_ 0);
4168\& l_release (EV_A);
4169\&
4170\& return 0;
4171\& }
4172.Ve
4173.PP
4174Instead of invoking all pending watchers, the \f(CW\*(C`l_invoke\*(C'\fR callback will
4175signal the main thread via some unspecified mechanism (signals? pipe
4176writes? \f(CW\*(C`Async::Interrupt\*(C'\fR?) and then waits until all pending watchers
4177have been called (in a while loop because a) spurious wakeups are possible
4178and b) skipping inter-thread-communication when there are no pending
4179watchers is very beneficial):
4180.PP
4181.Vb 4
4182\& static void
4183\& l_invoke (EV_P)
4184\& {
4185\& userdata *u = ev_userdata (EV_A);
4186\&
4187\& while (ev_pending_count (EV_A))
4188\& {
4189\& wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
4190\& pthread_cond_wait (&u\->invoke_cv, &u\->lock);
4191\& }
4192\& }
4193.Ve
4194.PP
4195Now, whenever the main thread gets told to invoke pending watchers, it
4196will grab the lock, call \f(CW\*(C`ev_invoke_pending\*(C'\fR and then signal the loop
4197thread to continue:
4198.PP
4199.Vb 4
4200\& static void
4201\& real_invoke_pending (EV_P)
4202\& {
4203\& userdata *u = ev_userdata (EV_A);
4204\&
4205\& pthread_mutex_lock (&u\->lock);
4206\& ev_invoke_pending (EV_A);
4207\& pthread_cond_signal (&u\->invoke_cv);
4208\& pthread_mutex_unlock (&u\->lock);
4209\& }
4210.Ve
4211.PP
4212Whenever you want to start/stop a watcher or do other modifications to an
4213event loop, you will now have to lock:
4214.PP
4215.Vb 2
4216\& ev_timer timeout_watcher;
4217\& userdata *u = ev_userdata (EV_A);
4218\&
4219\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
4220\&
4221\& pthread_mutex_lock (&u\->lock);
4222\& ev_timer_start (EV_A_ &timeout_watcher);
4223\& ev_async_send (EV_A_ &u\->async_w);
4224\& pthread_mutex_unlock (&u\->lock);
4225.Ve
4226.PP
4227Note that sending the \f(CW\*(C`ev_async\*(C'\fR watcher is required because otherwise
4228an event loop currently blocking in the kernel will have no knowledge
4229about the newly added timer. By waking up the loop it will pick up any new
4230watchers in the next event loop iteration.
4231.PP
4232\fI\s-1COROUTINES\s0\fR
4233.IX Subsection "COROUTINES"
4234.PP
4235Libev is very accommodating to coroutines (\*(L"cooperative threads\*(R"):
4236libev fully supports nesting calls to its functions from different
4237coroutines (e.g. you can call \f(CW\*(C`ev_loop\*(C'\fR on the same loop from two
4238different coroutines, and switch freely between both coroutines running
4239the loop, as long as you don't confuse yourself). The only exception is
4240that you must not do this from \f(CW\*(C`ev_periodic\*(C'\fR reschedule callbacks.
4241.PP
4242Care has been taken to ensure that libev does not keep local state inside
4243\&\f(CW\*(C`ev_loop\*(C'\fR, and other calls do not usually allow for coroutine switches as
4244they do not call any callbacks.
4245.SS "\s-1COMPILER\s0 \s-1WARNINGS\s0"
4246.IX Subsection "COMPILER WARNINGS"
4247Depending on your compiler and compiler settings, you might get no or a
4248lot of warnings when compiling libev code. Some people are apparently
4249scared by this.
4250.PP
4251However, these are unavoidable for many reasons. For one, each compiler
4252has different warnings, and each user has different tastes regarding
4253warning options. \*(L"Warn-free\*(R" code therefore cannot be a goal except when
4254targeting a specific compiler and compiler-version.
4255.PP
4256Another reason is that some compiler warnings require elaborate
4257workarounds, or other changes to the code that make it less clear and less
4258maintainable.
4259.PP
4260And of course, some compiler warnings are just plain stupid, or simply
4261wrong (because they don't actually warn about the condition their message
4262seems to warn about). For example, certain older gcc versions had some
4263warnings that resulted an extreme number of false positives. These have
4264been fixed, but some people still insist on making code warn-free with
4265such buggy versions.
4266.PP
4267While libev is written to generate as few warnings as possible,
4268\&\*(L"warn-free\*(R" code is not a goal, and it is recommended not to build libev
4269with any compiler warnings enabled unless you are prepared to cope with
4270them (e.g. by ignoring them). Remember that warnings are just that:
4271warnings, not errors, or proof of bugs.
4272.SS "\s-1VALGRIND\s0"
4273.IX Subsection "VALGRIND"
4274Valgrind has a special section here because it is a popular tool that is
4275highly useful. Unfortunately, valgrind reports are very hard to interpret.
4276.PP
4277If you think you found a bug (memory leak, uninitialised data access etc.)
4278in libev, then check twice: If valgrind reports something like:
4279.PP
4280.Vb 3
4281\& ==2274== definitely lost: 0 bytes in 0 blocks.
4282\& ==2274== possibly lost: 0 bytes in 0 blocks.
4283\& ==2274== still reachable: 256 bytes in 1 blocks.
4284.Ve
4285.PP
4286Then there is no memory leak, just as memory accounted to global variables
4287is not a memleak \- the memory is still being referenced, and didn't leak.
4288.PP
4289Similarly, under some circumstances, valgrind might report kernel bugs
4290as if it were a bug in libev (e.g. in realloc or in the poll backend,
4291although an acceptable workaround has been found here), or it might be
4292confused.
4293.PP
4294Keep in mind that valgrind is a very good tool, but only a tool. Don't
4295make it into some kind of religion.
4296.PP
4297If you are unsure about something, feel free to contact the mailing list
4298with the full valgrind report and an explanation on why you think this
4299is a bug in libev (best check the archives, too :). However, don't be
4300annoyed when you get a brisk \*(L"this is no bug\*(R" answer and take the chance
4301of learning how to interpret valgrind properly.
4302.PP
4303If you need, for some reason, empty reports from valgrind for your project
4304I suggest using suppression lists.
4305.SH "PORTABILITY NOTES"
4306.IX Header "PORTABILITY NOTES"
4307.SS "\s-1WIN32\s0 \s-1PLATFORM\s0 \s-1LIMITATIONS\s0 \s-1AND\s0 \s-1WORKAROUNDS\s0"
4308.IX Subsection "WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS"
4309Win32 doesn't support any of the standards (e.g. \s-1POSIX\s0) that libev
4310requires, and its I/O model is fundamentally incompatible with the \s-1POSIX\s0
4311model. Libev still offers limited functionality on this platform in
4312the form of the \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR backend, and only supports socket
4313descriptors. This only applies when using Win32 natively, not when using
4314e.g. cygwin.
4315.PP
4316Lifting these limitations would basically require the full
4317re-implementation of the I/O system. If you are into these kinds of
4318things, then note that glib does exactly that for you in a very portable
4319way (note also that glib is the slowest event library known to man).
4320.PP
4321There is no supported compilation method available on windows except
4322embedding it into other applications.
4323.PP
4324Sensible signal handling is officially unsupported by Microsoft \- libev
4325tries its best, but under most conditions, signals will simply not work.
4326.PP
4327Not a libev limitation but worth mentioning: windows apparently doesn't
4328accept large writes: instead of resulting in a partial write, windows will
4329either accept everything or return \f(CW\*(C`ENOBUFS\*(C'\fR if the buffer is too large,
4330so make sure you only write small amounts into your sockets (less than a
4331megabyte seems safe, but this apparently depends on the amount of memory
4332available).
4333.PP
4334Due to the many, low, and arbitrary limits on the win32 platform and
4335the abysmal performance of winsockets, using a large number of sockets
4336is not recommended (and not reasonable). If your program needs to use
4337more than a hundred or so sockets, then likely it needs to use a totally
4338different implementation for windows, as libev offers the \s-1POSIX\s0 readiness
4339notification model, which cannot be implemented efficiently on windows
4340(due to Microsoft monopoly games).
4341.PP
4342A typical way to use libev under windows is to embed it (see the embedding
4343section for details) and use the following \fIevwrap.h\fR header file instead
4344of \fIev.h\fR:
4345.PP
4346.Vb 2
4347\& #define EV_STANDALONE /* keeps ev from requiring config.h */
4348\& #define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
4349\&
4350\& #include "ev.h"
4351.Ve
4352.PP
4353And compile the following \fIevwrap.c\fR file into your project (make sure
4354you do \fInot\fR compile the \fIev.c\fR or any other embedded source files!):
4355.PP
4356.Vb 2
4357\& #include "evwrap.h"
4358\& #include "ev.c"
4359.Ve
4360.IP "The winsocket select function" 4
4361.IX Item "The winsocket select function"
4362The winsocket \f(CW\*(C`select\*(C'\fR function doesn't follow \s-1POSIX\s0 in that it
4363requires socket \fIhandles\fR and not socket \fIfile descriptors\fR (it is
4364also extremely buggy). This makes select very inefficient, and also
4365requires a mapping from file descriptors to socket handles (the Microsoft
4366C runtime provides the function \f(CW\*(C`_open_osfhandle\*(C'\fR for this). See the
4367discussion of the \f(CW\*(C`EV_SELECT_USE_FD_SET\*(C'\fR, \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR and
4368\&\f(CW\*(C`EV_FD_TO_WIN32_HANDLE\*(C'\fR preprocessor symbols for more info.
4369.Sp
4370The configuration for a \*(L"naked\*(R" win32 using the Microsoft runtime
4371libraries and raw winsocket select is:
4372.Sp
4373.Vb 2
4374\& #define EV_USE_SELECT 1
4375\& #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
4376.Ve
4377.Sp
4378Note that winsockets handling of fd sets is O(n), so you can easily get a
4379complexity in the O(nA\*^X) range when using win32.
4380.IP "Limited number of file descriptors" 4
4381.IX Item "Limited number of file descriptors"
4382Windows has numerous arbitrary (and low) limits on things.
4383.Sp
4384Early versions of winsocket's select only supported waiting for a maximum
4385of \f(CW64\fR handles (probably owning to the fact that all windows kernels
4386can only wait for \f(CW64\fR things at the same time internally; Microsoft
4387recommends spawning a chain of threads and wait for 63 handles and the
4388previous thread in each. Sounds great!).
4389.Sp
4390Newer versions support more handles, but you need to define \f(CW\*(C`FD_SETSIZE\*(C'\fR
4391to some high number (e.g. \f(CW2048\fR) before compiling the winsocket select
4392call (which might be in libev or elsewhere, for example, perl and many
4393other interpreters do their own select emulation on windows).
4394.Sp
4395Another limit is the number of file descriptors in the Microsoft runtime
4396libraries, which by default is \f(CW64\fR (there must be a hidden \fI64\fR
4397fetish or something like this inside Microsoft). You can increase this
4398by calling \f(CW\*(C`_setmaxstdio\*(C'\fR, which can increase this limit to \f(CW2048\fR
4399(another arbitrary limit), but is broken in many versions of the Microsoft
4400runtime libraries. This might get you to about \f(CW512\fR or \f(CW2048\fR sockets
4401(depending on windows version and/or the phase of the moon). To get more,
4402you need to wrap all I/O functions and provide your own fd management, but
4403the cost of calling select (O(nA\*^X)) will likely make this unworkable.
4404.SS "\s-1PORTABILITY\s0 \s-1REQUIREMENTS\s0"
4405.IX Subsection "PORTABILITY REQUIREMENTS"
4406In addition to a working ISO-C implementation and of course the
4407backend-specific APIs, libev relies on a few additional extensions:
4408.ie n .IP """void (*)(ev_watcher_type *, int revents)"" must have compatible calling conventions regardless of ""ev_watcher_type *""." 4
4409.el .IP "\f(CWvoid (*)(ev_watcher_type *, int revents)\fR must have compatible calling conventions regardless of \f(CWev_watcher_type *\fR." 4
4410.IX Item "void (*)(ev_watcher_type *, int revents) must have compatible calling conventions regardless of ev_watcher_type *."
4411Libev assumes not only that all watcher pointers have the same internal
4412structure (guaranteed by \s-1POSIX\s0 but not by \s-1ISO\s0 C for example), but it also
4413assumes that the same (machine) code can be used to call any watcher
4414callback: The watcher callbacks have different type signatures, but libev
4415calls them using an \f(CW\*(C`ev_watcher *\*(C'\fR internally.
4416.ie n .IP """sig_atomic_t volatile"" must be thread-atomic as well" 4
4417.el .IP "\f(CWsig_atomic_t volatile\fR must be thread-atomic as well" 4
4418.IX Item "sig_atomic_t volatile must be thread-atomic as well"
4419The type \f(CW\*(C`sig_atomic_t volatile\*(C'\fR (or whatever is defined as
4420\&\f(CW\*(C`EV_ATOMIC_T\*(C'\fR) must be atomic with respect to accesses from different
4421threads. This is not part of the specification for \f(CW\*(C`sig_atomic_t\*(C'\fR, but is
4422believed to be sufficiently portable.
4423.ie n .IP """sigprocmask"" must work in a threaded environment" 4
4424.el .IP "\f(CWsigprocmask\fR must work in a threaded environment" 4
4425.IX Item "sigprocmask must work in a threaded environment"
4426Libev uses \f(CW\*(C`sigprocmask\*(C'\fR to temporarily block signals. This is not
4427allowed in a threaded program (\f(CW\*(C`pthread_sigmask\*(C'\fR has to be used). Typical
4428pthread implementations will either allow \f(CW\*(C`sigprocmask\*(C'\fR in the \*(L"main
4429thread\*(R" or will block signals process-wide, both behaviours would
4430be compatible with libev. Interaction between \f(CW\*(C`sigprocmask\*(C'\fR and
4431\&\f(CW\*(C`pthread_sigmask\*(C'\fR could complicate things, however.
4432.Sp
4433The most portable way to handle signals is to block signals in all threads
4434except the initial one, and run the default loop in the initial thread as
4435well.
4436.ie n .IP """long"" must be large enough for common memory allocation sizes" 4
4437.el .IP "\f(CWlong\fR must be large enough for common memory allocation sizes" 4
4438.IX Item "long must be large enough for common memory allocation sizes"
4439To improve portability and simplify its \s-1API\s0, libev uses \f(CW\*(C`long\*(C'\fR internally
4440instead of \f(CW\*(C`size_t\*(C'\fR when allocating its data structures. On non-POSIX
4441systems (Microsoft...) this might be unexpectedly low, but is still at
4442least 31 bits everywhere, which is enough for hundreds of millions of
4443watchers.
4444.ie n .IP """double"" must hold a time value in seconds with enough accuracy" 4
4445.el .IP "\f(CWdouble\fR must hold a time value in seconds with enough accuracy" 4
4446.IX Item "double must hold a time value in seconds with enough accuracy"
4447The type \f(CW\*(C`double\*(C'\fR is used to represent timestamps. It is required to
4448have at least 51 bits of mantissa (and 9 bits of exponent), which is good
4449enough for at least into the year 4000. This requirement is fulfilled by
4450implementations implementing \s-1IEEE\s0 754, which is basically all existing
4451ones. With \s-1IEEE\s0 754 doubles, you get microsecond accuracy until at least
44522200.
4453.PP
4454If you know of other additional requirements drop me a note.
4455.SH "ALGORITHMIC COMPLEXITIES"
4456.IX Header "ALGORITHMIC COMPLEXITIES"
4457In this section the complexities of (many of) the algorithms used inside
4458libev will be documented. For complexity discussions about backends see
4459the documentation for \f(CW\*(C`ev_default_init\*(C'\fR.
4460.PP
4461All of the following are about amortised time: If an array needs to be
4462extended, libev needs to realloc and move the whole array, but this
4463happens asymptotically rarer with higher number of elements, so O(1) might
4464mean that libev does a lengthy realloc operation in rare cases, but on
4465average it is much faster and asymptotically approaches constant time.
4466.IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4
4467.IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)"
4468This means that, when you have a watcher that triggers in one hour and
4469there are 100 watchers that would trigger before that, then inserting will
4470have to skip roughly seven (\f(CW\*(C`ld 100\*(C'\fR) of these watchers.
4471.IP "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 4
4472.IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)"
4473That means that changing a timer costs less than removing/adding them,
4474as only the relative motion in the event queue has to be paid for.
4475.IP "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)" 4
4476.IX Item "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)"
4477These just add the watcher into an array or at the head of a list.
4478.IP "Stopping check/prepare/idle/fork/async watchers: O(1)" 4
4479.IX Item "Stopping check/prepare/idle/fork/async watchers: O(1)"
4480.PD 0
4481.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4
4482.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))"
4483.PD
4484These watchers are stored in lists, so they need to be walked to find the
4485correct watcher to remove. The lists are usually short (you don't usually
4486have many watchers waiting for the same fd or signal: one is typical, two
4487is rare).
4488.IP "Finding the next timer in each loop iteration: O(1)" 4
4489.IX Item "Finding the next timer in each loop iteration: O(1)"
4490By virtue of using a binary or 4\-heap, the next timer is always found at a
4491fixed position in the storage array.
4492.IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4
4493.IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)"
4494A change means an I/O watcher gets started or stopped, which requires
4495libev to recalculate its status (and possibly tell the kernel, depending
4496on backend and whether \f(CW\*(C`ev_io_set\*(C'\fR was used).
4497.IP "Activating one watcher (putting it into the pending state): O(1)" 4
4498.IX Item "Activating one watcher (putting it into the pending state): O(1)"
4499.PD 0
4500.IP "Priority handling: O(number_of_priorities)" 4
4501.IX Item "Priority handling: O(number_of_priorities)"
4502.PD
4503Priorities are implemented by allocating some space for each
4504priority. When doing priority-based operations, libev usually has to
4505linearly search all the priorities, but starting/stopping and activating
4506watchers becomes O(1) with respect to priority handling.
4507.IP "Sending an ev_async: O(1)" 4
4508.IX Item "Sending an ev_async: O(1)"
4509.PD 0
4510.IP "Processing ev_async_send: O(number_of_async_watchers)" 4
4511.IX Item "Processing ev_async_send: O(number_of_async_watchers)"
4512.IP "Processing signals: O(max_signal_number)" 4
4513.IX Item "Processing signals: O(max_signal_number)"
4514.PD
4515Sending involves a system call \fIiff\fR there were no other \f(CW\*(C`ev_async_send\*(C'\fR
4516calls in the current loop iteration. Checking for async and signal events
4517involves iterating over all running async watchers or all signal numbers.
4518.SH "GLOSSARY"
4519.IX Header "GLOSSARY"
4520.IP "active" 4
4521.IX Item "active"
4522A watcher is active as long as it has been started (has been attached to
4523an event loop) but not yet stopped (disassociated from the event loop).
4524.IP "application" 4
4525.IX Item "application"
4526In this document, an application is whatever is using libev.
4527.IP "callback" 4
4528.IX Item "callback"
4529The address of a function that is called when some event has been
4530detected. Callbacks are being passed the event loop, the watcher that
4531received the event, and the actual event bitset.
4532.IP "callback invocation" 4
4533.IX Item "callback invocation"
4534The act of calling the callback associated with a watcher.
4535.IP "event" 4
4536.IX Item "event"
4537A change of state of some external event, such as data now being available
4538for reading on a file descriptor, time having passed or simply not having
4539any other events happening anymore.
4540.Sp
4541In libev, events are represented as single bits (such as \f(CW\*(C`EV_READ\*(C'\fR or
4542\&\f(CW\*(C`EV_TIMEOUT\*(C'\fR).
4543.IP "event library" 4
4544.IX Item "event library"
4545A software package implementing an event model and loop.
4546.IP "event loop" 4
4547.IX Item "event loop"
4548An entity that handles and processes external events and converts them
4549into callback invocations.
4550.IP "event model" 4
4551.IX Item "event model"
4552The model used to describe how an event loop handles and processes
4553watchers and events.
4554.IP "pending" 4
4555.IX Item "pending"
4556A watcher is pending as soon as the corresponding event has been detected,
4557and stops being pending as soon as the watcher will be invoked or its
4558pending status is explicitly cleared by the application.
4559.Sp
4560A watcher can be pending, but not active. Stopping a watcher also clears
4561its pending status.
4562.IP "real time" 4
4563.IX Item "real time"
4564The physical time that is observed. It is apparently strictly monotonic :)
4565.IP "wall-clock time" 4
4566.IX Item "wall-clock time"
4567The time and date as shown on clocks. Unlike real time, it can actually
4568be wrong and jump forwards and backwards, e.g. when the you adjust your
4569clock.
4570.IP "watcher" 4
4571.IX Item "watcher"
4572A data structure that describes interest in certain events. Watchers need
4573to be started (attached to an event loop) before they can receive events.
4574.IP "watcher invocation" 4
4575.IX Item "watcher invocation"
4576The act of calling the callback associated with a watcher.
1267.SH "AUTHOR" 4577.SH "AUTHOR"
1268.IX Header "AUTHOR" 4578.IX Header "AUTHOR"
1269Marc Lehmann <libev@schmorp.de>. 4579Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.

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