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129.\" ======================================================================== 132.\" ========================================================================
130.\" 133.\"
131.IX Title ""<STANDARD INPUT>" 1" 134.IX Title "LIBEV 3"
132.TH "<STANDARD INPUT>" 1 "2007-11-24" "perl v5.8.8" "User Contributed Perl Documentation" 135.TH LIBEV 3 "2009-04-25" "libev-3.6" "libev - high performance full featured event loop"
136.\" For nroff, turn off justification. Always turn off hyphenation; it makes
137.\" way too many mistakes in technical documents.
138.if n .ad l
139.nh
133.SH "NAME" 140.SH "NAME"
134libev \- a high performance full\-featured event loop written in C 141libev \- a high performance full\-featured event loop written in C
135.SH "SYNOPSIS" 142.SH "SYNOPSIS"
136.IX Header "SYNOPSIS" 143.IX Header "SYNOPSIS"
137.Vb 1 144.Vb 1
138\& #include <ev.h> 145\& #include <ev.h>
139.Ve 146.Ve
140.SH "DESCRIPTION" 147.Sh "\s-1EXAMPLE\s0 \s-1PROGRAM\s0"
141.IX Header "DESCRIPTION" 148.IX Subsection "EXAMPLE PROGRAM"
149.Vb 2
150\& // a single header file is required
151\& #include <ev.h>
152\&
153\& #include <stdio.h> // for puts
154\&
155\& // every watcher type has its own typedef\*(Aqd struct
156\& // with the name ev_TYPE
157\& ev_io stdin_watcher;
158\& ev_timer timeout_watcher;
159\&
160\& // all watcher callbacks have a similar signature
161\& // this callback is called when data is readable on stdin
162\& static void
163\& stdin_cb (EV_P_ ev_io *w, int revents)
164\& {
165\& puts ("stdin ready");
166\& // for one\-shot events, one must manually stop the watcher
167\& // with its corresponding stop function.
168\& ev_io_stop (EV_A_ w);
169\&
170\& // this causes all nested ev_loop\*(Aqs to stop iterating
171\& ev_unloop (EV_A_ EVUNLOOP_ALL);
172\& }
173\&
174\& // another callback, this time for a time\-out
175\& static void
176\& timeout_cb (EV_P_ ev_timer *w, int revents)
177\& {
178\& puts ("timeout");
179\& // this causes the innermost ev_loop to stop iterating
180\& ev_unloop (EV_A_ EVUNLOOP_ONE);
181\& }
182\&
183\& int
184\& main (void)
185\& {
186\& // use the default event loop unless you have special needs
187\& struct ev_loop *loop = ev_default_loop (0);
188\&
189\& // initialise an io watcher, then start it
190\& // this one will watch for stdin to become readable
191\& ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
192\& ev_io_start (loop, &stdin_watcher);
193\&
194\& // initialise a timer watcher, then start it
195\& // simple non\-repeating 5.5 second timeout
196\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
197\& ev_timer_start (loop, &timeout_watcher);
198\&
199\& // now wait for events to arrive
200\& ev_loop (loop, 0);
201\&
202\& // unloop was called, so exit
203\& return 0;
204\& }
205.Ve
206.SH "ABOUT THIS DOCUMENT"
207.IX Header "ABOUT THIS DOCUMENT"
208This document documents the libev software package.
209.PP
210The newest version of this document is also available as an html-formatted
211web page you might find easier to navigate when reading it for the first
212time: <http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
213.PP
214While this document tries to be as complete as possible in documenting
215libev, its usage and the rationale behind its design, it is not a tutorial
216on event-based programming, nor will it introduce event-based programming
217with libev.
218.PP
219Familarity with event based programming techniques in general is assumed
220throughout this document.
221.SH "ABOUT LIBEV"
222.IX Header "ABOUT LIBEV"
142Libev is an event loop: you register interest in certain events (such as a 223Libev 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 224file descriptor being readable or a timeout occurring), and it will manage
144these event sources and provide your program with events. 225these event sources and provide your program with events.
145.PP 226.PP
146To do this, it must take more or less complete control over your process 227To 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 228(or thread) by executing the \fIevent loop\fR handler, and will then
148communicate events via a callback mechanism. 229communicate events via a callback mechanism.
149.PP 230.PP
150You register interest in certain events by registering so-called \fIevent 231You register interest in certain events by registering so-called \fIevent
151watchers\fR, which are relatively small C structures you initialise with the 232watchers\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 233details of the event, and then hand it over to libev by \fIstarting\fR the
153watcher. 234watcher.
154.SH "FEATURES" 235.Sh "\s-1FEATURES\s0"
155.IX Header "FEATURES" 236.IX Subsection "FEATURES"
156Libev supports select, poll, the linux-specific epoll and the bsd-specific 237Libev 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 238BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port mechanisms
158timers with customised rescheduling, signal events, process status change 239for 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 240(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 241with customised rescheduling (\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals
161fast (see this benchmark comparing 242(\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). 243watchers dealing with the event loop mechanism itself (\f(CW\*(C`ev_idle\*(C'\fR,
244\&\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
245file watchers (\f(CW\*(C`ev_stat\*(C'\fR) and even limited support for fork events
246(\f(CW\*(C`ev_fork\*(C'\fR).
247.PP
248It also is quite fast (see this
249benchmark comparing it to libevent
250for example).
163.SH "CONVENTIONS" 251.Sh "\s-1CONVENTIONS\s0"
164.IX Header "CONVENTIONS" 252.IX Subsection "CONVENTIONS"
165Libev is very configurable. In this manual the default configuration 253Libev is very configurable. In this manual the default (and most common)
166will be described, which supports multiple event loops. For more info 254configuration will be described, which supports multiple event loops. For
167about various configuration options please have a look at the file 255more info about various configuration options please have a look at
168\&\fI\s-1README\s0.embed\fR in the libev distribution. If libev was configured without 256\&\fB\s-1EMBED\s0\fR section in this manual. If libev was configured without support
169support for multiple event loops, then all functions taking an initial 257for multiple event loops, then all functions taking an initial argument of
170argument of name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) 258name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`ev_loop *\*(C'\fR) will not have
171will not have this argument. 259this argument.
172.SH "TIME REPRESENTATION" 260.Sh "\s-1TIME\s0 \s-1REPRESENTATION\s0"
173.IX Header "TIME REPRESENTATION" 261.IX Subsection "TIME REPRESENTATION"
174Libev represents time as a single floating point number, representing the 262Libev represents time as a single floating point number, representing
175(fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere near 263the (fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere
176the beginning of 1970, details are complicated, don't ask). This type is 264near 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 265type 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 266aliases 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. 267on it, you should treat it as some floating point value. Unlike the name
268component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for time differences
269throughout libev.
270.SH "ERROR HANDLING"
271.IX Header "ERROR HANDLING"
272Libev knows three classes of errors: operating system errors, usage errors
273and internal errors (bugs).
274.PP
275When libev catches an operating system error it cannot handle (for example
276a system call indicating a condition libev cannot fix), it calls the callback
277set via \f(CW\*(C`ev_set_syserr_cb\*(C'\fR, which is supposed to fix the problem or
278abort. The default is to print a diagnostic message and to call \f(CW\*(C`abort
279()\*(C'\fR.
280.PP
281When libev detects a usage error such as a negative timer interval, then
282it will print a diagnostic message and abort (via the \f(CW\*(C`assert\*(C'\fR mechanism,
283so \f(CW\*(C`NDEBUG\*(C'\fR will disable this checking): these are programming errors in
284the libev caller and need to be fixed there.
285.PP
286Libev also has a few internal error-checking \f(CW\*(C`assert\*(C'\fRions, and also has
287extensive consistency checking code. These do not trigger under normal
288circumstances, as they indicate either a bug in libev or worse.
180.SH "GLOBAL FUNCTIONS" 289.SH "GLOBAL FUNCTIONS"
181.IX Header "GLOBAL FUNCTIONS" 290.IX Header "GLOBAL FUNCTIONS"
182These functions can be called anytime, even before initialising the 291These functions can be called anytime, even before initialising the
183library in any way. 292library in any way.
184.IP "ev_tstamp ev_time ()" 4 293.IP "ev_tstamp ev_time ()" 4
185.IX Item "ev_tstamp ev_time ()" 294.IX Item "ev_tstamp ev_time ()"
186Returns the current time as libev would use it. Please note that the 295Returns 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 296\&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp
188you actually want to know. 297you actually want to know.
298.IP "ev_sleep (ev_tstamp interval)" 4
299.IX Item "ev_sleep (ev_tstamp interval)"
300Sleep for the given interval: The current thread will be blocked until
301either it is interrupted or the given time interval has passed. Basically
302this is a sub-second-resolution \f(CW\*(C`sleep ()\*(C'\fR.
189.IP "int ev_version_major ()" 4 303.IP "int ev_version_major ()" 4
190.IX Item "int ev_version_major ()" 304.IX Item "int ev_version_major ()"
191.PD 0 305.PD 0
192.IP "int ev_version_minor ()" 4 306.IP "int ev_version_minor ()" 4
193.IX Item "int ev_version_minor ()" 307.IX Item "int ev_version_minor ()"
194.PD 308.PD
195You can find out the major and minor version numbers of the library 309You 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 310you 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 311\&\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 312symbols \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. 313version of the library your program was compiled against.
200.Sp 314.Sp
315These version numbers refer to the \s-1ABI\s0 version of the library, not the
316release version.
317.Sp
201Usually, it's a good idea to terminate if the major versions mismatch, 318Usually, it's a good idea to terminate if the major versions mismatch,
202as this indicates an incompatible change. Minor versions are usually 319as this indicates an incompatible change. Minor versions are usually
203compatible to older versions, so a larger minor version alone is usually 320compatible to older versions, so a larger minor version alone is usually
204not a problem. 321not a problem.
205.Sp 322.Sp
206Example: make sure we haven't accidentally been linked against the wrong 323Example: Make sure we haven't accidentally been linked against the wrong
207version: 324version.
208.Sp 325.Sp
209.Vb 3 326.Vb 3
210\& assert (("libev version mismatch", 327\& assert (("libev version mismatch",
211\& ev_version_major () == EV_VERSION_MAJOR 328\& ev_version_major () == EV_VERSION_MAJOR
212\& && ev_version_minor () >= EV_VERSION_MINOR)); 329\& && ev_version_minor () >= EV_VERSION_MINOR));
213.Ve 330.Ve
214.IP "unsigned int ev_supported_backends ()" 4 331.IP "unsigned int ev_supported_backends ()" 4
215.IX Item "unsigned int ev_supported_backends ()" 332.IX Item "unsigned int ev_supported_backends ()"
216Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR 333Return 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 334value) compiled into this binary of libev (independent of their
… …
220.Sp 337.Sp
221Example: make sure we have the epoll method, because yeah this is cool and 338Example: 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 339a must have and can we have a torrent of it please!!!11
223.Sp 340.Sp
224.Vb 2 341.Vb 2
225\& assert (("sorry, no epoll, no sex", 342\& assert (("sorry, no epoll, no sex",
226\& ev_supported_backends () & EVBACKEND_EPOLL)); 343\& ev_supported_backends () & EVBACKEND_EPOLL));
227.Ve 344.Ve
228.IP "unsigned int ev_recommended_backends ()" 4 345.IP "unsigned int ev_recommended_backends ()" 4
229.IX Item "unsigned int ev_recommended_backends ()" 346.IX Item "unsigned int ev_recommended_backends ()"
230Return the set of all backends compiled into this binary of libev and also 347Return 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 348recommended 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 349returned 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 350most 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 351(assuming you know what you are doing). This is the set of backends that
235libev will probe for if you specify no backends explicitly. 352libev will probe for if you specify no backends explicitly.
236.IP "unsigned int ev_embeddable_backends ()" 4 353.IP "unsigned int ev_embeddable_backends ()" 4
237.IX Item "unsigned int ev_embeddable_backends ()" 354.IX Item "unsigned int ev_embeddable_backends ()"
238Returns the set of backends that are embeddable in other event loops. This 355Returns the set of backends that are embeddable in other event loops. This
239is the theoretical, all\-platform, value. To find which backends 356is the theoretical, all-platform, value. To find which backends
240might be supported on the current system, you would need to look at 357might be supported on the current system, you would need to look at
241\&\f(CW\*(C`ev_embeddable_backends () & ev_supported_backends ()\*(C'\fR, likewise for 358\&\f(CW\*(C`ev_embeddable_backends () & ev_supported_backends ()\*(C'\fR, likewise for
242recommended ones. 359recommended ones.
243.Sp 360.Sp
244See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info. 361See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
245.IP "ev_set_allocator (void *(*cb)(void *ptr, long size))" 4 362.IP "ev_set_allocator (void *(*cb)(void *ptr, long size)) [\s-1NOT\s0 \s-1REENTRANT\s0]" 4
246.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))" 363.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]"
247Sets the allocation function to use (the prototype is similar to the 364Sets the allocation function to use (the prototype is similar \- the
248realloc C function, the semantics are identical). It is used to allocate 365semantics are identical to the \f(CW\*(C`realloc\*(C'\fR C89/SuS/POSIX function). It is
249and free memory (no surprises here). If it returns zero when memory 366used to allocate and free memory (no surprises here). If it returns zero
250needs to be allocated, the library might abort or take some potentially 367when memory needs to be allocated (\f(CW\*(C`size != 0\*(C'\fR), the library might abort
251destructive action. The default is your system realloc function. 368or take some potentially destructive action.
369.Sp
370Since some systems (at least OpenBSD and Darwin) fail to implement
371correct \f(CW\*(C`realloc\*(C'\fR semantics, libev will use a wrapper around the system
372\&\f(CW\*(C`realloc\*(C'\fR and \f(CW\*(C`free\*(C'\fR functions by default.
252.Sp 373.Sp
253You could override this function in high-availability programs to, say, 374You could override this function in high-availability programs to, say,
254free some memory if it cannot allocate memory, to use a special allocator, 375free some memory if it cannot allocate memory, to use a special allocator,
255or even to sleep a while and retry until some memory is available. 376or even to sleep a while and retry until some memory is available.
256.Sp 377.Sp
257Example: replace the libev allocator with one that waits a bit and then 378Example: Replace the libev allocator with one that waits a bit and then
258retries: better than mine). 379retries (example requires a standards-compliant \f(CW\*(C`realloc\*(C'\fR).
259.Sp 380.Sp
260.Vb 6 381.Vb 6
261\& static void * 382\& static void *
262\& persistent_realloc (void *ptr, long size) 383\& persistent_realloc (void *ptr, size_t size)
263\& { 384\& {
264\& for (;;) 385\& for (;;)
265\& { 386\& {
266\& void *newptr = realloc (ptr, size); 387\& void *newptr = realloc (ptr, size);
267.Ve 388\&
268.Sp
269.Vb 2
270\& if (newptr) 389\& if (newptr)
271\& return newptr; 390\& return newptr;
272.Ve 391\&
273.Sp
274.Vb 3
275\& sleep (60); 392\& sleep (60);
276\& } 393\& }
277\& } 394\& }
278.Ve 395\&
279.Sp
280.Vb 2
281\& ... 396\& ...
282\& ev_set_allocator (persistent_realloc); 397\& ev_set_allocator (persistent_realloc);
283.Ve 398.Ve
284.IP "ev_set_syserr_cb (void (*cb)(const char *msg));" 4 399.IP "ev_set_syserr_cb (void (*cb)(const char *msg)); [\s-1NOT\s0 \s-1REENTRANT\s0]" 4
285.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg));" 400.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]"
286Set the callback function to call on a retryable syscall error (such 401Set the callback function to call on a retryable system call error (such
287as failed select, poll, epoll_wait). The message is a printable string 402as failed select, poll, epoll_wait). The message is a printable string
288indicating the system call or subsystem causing the problem. If this 403indicating the system call or subsystem causing the problem. If this
289callback is set, then libev will expect it to remedy the sitution, no 404callback is set, then libev will expect it to remedy the situation, no
290matter what, when it returns. That is, libev will generally retry the 405matter what, when it returns. That is, libev will generally retry the
291requested operation, or, if the condition doesn't go away, do bad stuff 406requested operation, or, if the condition doesn't go away, do bad stuff
292(such as abort). 407(such as abort).
293.Sp 408.Sp
294Example: do the same thing as libev does internally: 409Example: This is basically the same thing that libev does internally, too.
295.Sp 410.Sp
296.Vb 6 411.Vb 6
297\& static void 412\& static void
298\& fatal_error (const char *msg) 413\& fatal_error (const char *msg)
299\& { 414\& {
300\& perror (msg); 415\& perror (msg);
301\& abort (); 416\& abort ();
302\& } 417\& }
303.Ve 418\&
304.Sp
305.Vb 2
306\& ... 419\& ...
307\& ev_set_syserr_cb (fatal_error); 420\& ev_set_syserr_cb (fatal_error);
308.Ve 421.Ve
309.SH "FUNCTIONS CONTROLLING THE EVENT LOOP" 422.SH "FUNCTIONS CONTROLLING THE EVENT LOOP"
310.IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP" 423.IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP"
311An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR. The library knows two 424An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR (the \f(CW\*(C`struct\*(C'\fR
312types of such loops, the \fIdefault\fR loop, which supports signals and child 425is \fInot\fR optional in this case, as there is also an \f(CW\*(C`ev_loop\*(C'\fR
313events, and dynamically created loops which do not. 426\&\fIfunction\fR).
314.PP 427.PP
315If you use threads, a common model is to run the default event loop 428The library knows two types of such loops, the \fIdefault\fR loop, which
316in your main thread (or in a separate thread) and for each thread you 429supports signals and child events, and dynamically created loops which do
317create, you also create another event loop. Libev itself does no locking 430not.
318whatsoever, so if you mix calls to the same event loop in different
319threads, make sure you lock (this is usually a bad idea, though, even if
320done correctly, because it's hideous and inefficient).
321.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4 431.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
322.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)" 432.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
323This will initialise the default event loop if it hasn't been initialised 433This will initialise the default event loop if it hasn't been initialised
324yet and return it. If the default loop could not be initialised, returns 434yet and return it. If the default loop could not be initialised, returns
325false. If it already was initialised it simply returns it (and ignores the 435false. If it already was initialised it simply returns it (and ignores the
326flags. If that is troubling you, check \f(CW\*(C`ev_backend ()\*(C'\fR afterwards). 436flags. If that is troubling you, check \f(CW\*(C`ev_backend ()\*(C'\fR afterwards).
327.Sp 437.Sp
328If you don't know what event loop to use, use the one returned from this 438If you don't know what event loop to use, use the one returned from this
329function. 439function.
440.Sp
441Note that this function is \fInot\fR thread-safe, so if you want to use it
442from multiple threads, you have to lock (note also that this is unlikely,
443as loops cannot be shared easily between threads anyway).
444.Sp
445The default loop is the only loop that can handle \f(CW\*(C`ev_signal\*(C'\fR and
446\&\f(CW\*(C`ev_child\*(C'\fR watchers, and to do this, it always registers a handler
447for \f(CW\*(C`SIGCHLD\*(C'\fR. If this is a problem for your application you can either
448create a dynamic loop with \f(CW\*(C`ev_loop_new\*(C'\fR that doesn't do that, or you
449can simply overwrite the \f(CW\*(C`SIGCHLD\*(C'\fR signal handler \fIafter\fR calling
450\&\f(CW\*(C`ev_default_init\*(C'\fR.
330.Sp 451.Sp
331The flags argument can be used to specify special behaviour or specific 452The flags argument can be used to specify special behaviour or specific
332backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). 453backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).
333.Sp 454.Sp
334The following flags are supported: 455The following flags are supported:
… …
339The default flags value. Use this if you have no clue (it's the right 460The default flags value. Use this if you have no clue (it's the right
340thing, believe me). 461thing, believe me).
341.ie n .IP """EVFLAG_NOENV""" 4 462.ie n .IP """EVFLAG_NOENV""" 4
342.el .IP "\f(CWEVFLAG_NOENV\fR" 4 463.el .IP "\f(CWEVFLAG_NOENV\fR" 4
343.IX Item "EVFLAG_NOENV" 464.IX Item "EVFLAG_NOENV"
344If this flag bit is ored into the flag value (or the program runs setuid 465If this flag bit is or'ed into the flag value (or the program runs setuid
345or setgid) then libev will \fInot\fR look at the environment variable 466or setgid) then libev will \fInot\fR look at the environment variable
346\&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will 467\&\f(CW\*(C`LIBEV_FLAGS\*(C'\fR. Otherwise (the default), this environment variable will
347override the flags completely if it is found in the environment. This is 468override the flags completely if it is found in the environment. This is
348useful to try out specific backends to test their performance, or to work 469useful to try out specific backends to test their performance, or to work
349around bugs. 470around bugs.
471.ie n .IP """EVFLAG_FORKCHECK""" 4
472.el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4
473.IX Item "EVFLAG_FORKCHECK"
474Instead of calling \f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR manually after
475a fork, you can also make libev check for a fork in each iteration by
476enabling this flag.
477.Sp
478This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop,
479and thus this might slow down your event loop if you do a lot of loop
480iterations and little real work, but is usually not noticeable (on my
481GNU/Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn sequence
482without a system call and thus \fIvery\fR fast, but my GNU/Linux system also has
483\&\f(CW\*(C`pthread_atfork\*(C'\fR which is even faster).
484.Sp
485The big advantage of this flag is that you can forget about fork (and
486forget about forgetting to tell libev about forking) when you use this
487flag.
488.Sp
489This flag setting cannot be overridden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR
490environment variable.
350.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4 491.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
351.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4 492.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
352.IX Item "EVBACKEND_SELECT (value 1, portable select backend)" 493.IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
353This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as 494This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as
354libev tries to roll its own fd_set with no limits on the number of fds, 495libev tries to roll its own fd_set with no limits on the number of fds,
355but if that fails, expect a fairly low limit on the number of fds when 496but if that fails, expect a fairly low limit on the number of fds when
356using this backend. It doesn't scale too well (O(highest_fd)), but its usually 497using this backend. It doesn't scale too well (O(highest_fd)), but its
357the fastest backend for a low number of fds. 498usually the fastest backend for a low number of (low-numbered :) fds.
499.Sp
500To get good performance out of this backend you need a high amount of
501parallelism (most of the file descriptors should be busy). If you are
502writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many
503connections as possible during one iteration. You might also want to have
504a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of
505readiness notifications you get per iteration.
506.Sp
507This 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
508\&\f(CW\*(C`writefds\*(C'\fR set (and to work around Microsoft Windows bugs, also onto the
509\&\f(CW\*(C`exceptfds\*(C'\fR set on that platform).
358.ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4 510.ie n .IP """EVBACKEND_POLL"" (value 2, poll backend, available everywhere except on windows)" 4
359.el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4 511.el .IP "\f(CWEVBACKEND_POLL\fR (value 2, poll backend, available everywhere except on windows)" 4
360.IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)" 512.IX Item "EVBACKEND_POLL (value 2, poll backend, available everywhere except on windows)"
361And this is your standard \fIpoll\fR\|(2) backend. It's more complicated than 513And this is your standard \fIpoll\fR\|(2) backend. It's more complicated
362select, but handles sparse fds better and has no artificial limit on the 514than select, but handles sparse fds better and has no artificial
363number of fds you can use (except it will slow down considerably with a 515limit on the number of fds you can use (except it will slow down
364lot of inactive fds). It scales similarly to select, i.e. O(total_fds). 516considerably with a lot of inactive fds). It scales similarly to select,
517i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for
518performance tips.
519.Sp
520This backend maps \f(CW\*(C`EV_READ\*(C'\fR to \f(CW\*(C`POLLIN | POLLERR | POLLHUP\*(C'\fR, and
521\&\f(CW\*(C`EV_WRITE\*(C'\fR to \f(CW\*(C`POLLOUT | POLLERR | POLLHUP\*(C'\fR.
365.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4 522.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
366.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4 523.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
367.IX Item "EVBACKEND_EPOLL (value 4, Linux)" 524.IX Item "EVBACKEND_EPOLL (value 4, Linux)"
368For few fds, this backend is a bit little slower than poll and select, 525For few fds, this backend is a bit little slower than poll and select,
369but it scales phenomenally better. While poll and select usually scale like 526but it scales phenomenally better. While poll and select usually scale
370O(total_fds) where n is the total number of fds (or the highest fd), epoll scales 527like O(total_fds) where n is the total number of fds (or the highest fd),
371either O(1) or O(active_fds). 528epoll scales either O(1) or O(active_fds).
372.Sp 529.Sp
530The epoll mechanism deserves honorable mention as the most misdesigned
531of the more advanced event mechanisms: mere annoyances include silently
532dropping file descriptors, requiring a system call per change per file
533descriptor (and unnecessary guessing of parameters), problems with dup and
534so on. The biggest issue is fork races, however \- if a program forks then
535\&\fIboth\fR parent and child process have to recreate the epoll set, which can
536take considerable time (one syscall per file descriptor) and is of course
537hard to detect.
538.Sp
539Epoll is also notoriously buggy \- embedding epoll fds \fIshould\fR work, but
540of course \fIdoesn't\fR, and epoll just loves to report events for totally
541\&\fIdifferent\fR file descriptors (even already closed ones, so one cannot
542even remove them from the set) than registered in the set (especially
543on \s-1SMP\s0 systems). Libev tries to counter these spurious notifications by
544employing an additional generation counter and comparing that against the
545events to filter out spurious ones, recreating the set when required.
546.Sp
373While stopping and starting an I/O watcher in the same iteration will 547While stopping, setting and starting an I/O watcher in the same iteration
374result in some caching, there is still a syscall per such incident 548will result in some caching, there is still a system call per such
375(because the fd could point to a different file description now), so its 549incident (because the same \fIfile descriptor\fR could point to a different
376best to avoid that. Also, \fIdup()\fRed file descriptors might not work very 550\&\fIfile description\fR now), so its best to avoid that. Also, \f(CW\*(C`dup ()\*(C'\fR'ed
377well if you register events for both fds. 551file descriptors might not work very well if you register events for both
552file descriptors.
378.Sp 553.Sp
379Please note that epoll sometimes generates spurious notifications, so you 554Best performance from this backend is achieved by not unregistering all
380need to use non-blocking I/O or other means to avoid blocking when no data 555watchers for a file descriptor until it has been closed, if possible,
381(or space) is available. 556i.e. keep at least one watcher active per fd at all times. Stopping and
557starting a watcher (without re-setting it) also usually doesn't cause
558extra overhead. A fork can both result in spurious notifications as well
559as in libev having to destroy and recreate the epoll object, which can
560take considerable time and thus should be avoided.
561.Sp
562All this means that, in practice, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR can be as fast or
563faster than epoll for maybe up to a hundred file descriptors, depending on
564the usage. So sad.
565.Sp
566While nominally embeddable in other event loops, this feature is broken in
567all kernel versions tested so far.
568.Sp
569This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
570\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
382.ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4 571.ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4
383.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4 572.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
384.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)" 573.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
385Kqueue deserves special mention, as at the time of this writing, it 574Kqueue deserves special mention, as at the time of this writing, it
386was broken on all BSDs except NetBSD (usually it doesn't work with 575was broken on all BSDs except NetBSD (usually it doesn't work reliably
387anything but sockets and pipes, except on Darwin, where of course its 576with anything but sockets and pipes, except on Darwin, where of course
388completely useless). For this reason its not being \*(L"autodetected\*(R" 577it's completely useless). Unlike epoll, however, whose brokenness
578is by design, these kqueue bugs can (and eventually will) be fixed
579without \s-1API\s0 changes to existing programs. For this reason it's not being
389unless you explicitly specify it explicitly in the flags (i.e. using 580\&\*(L"auto-detected\*(R" unless you explicitly specify it in the flags (i.e. using
390\&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR). 581\&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a known-to-be-good (\-enough)
582system like NetBSD.
583.Sp
584You still can embed kqueue into a normal poll or select backend and use it
585only for sockets (after having made sure that sockets work with kqueue on
586the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
391.Sp 587.Sp
392It scales in the same way as the epoll backend, but the interface to the 588It scales in the same way as the epoll backend, but the interface to the
393kernel is more efficient (which says nothing about its actual speed, of 589kernel is more efficient (which says nothing about its actual speed, of
394course). While starting and stopping an I/O watcher does not cause an 590course). While stopping, setting and starting an I/O watcher does never
395extra syscall as with epoll, it still adds up to four event changes per 591cause an extra system call as with \f(CW\*(C`EVBACKEND_EPOLL\*(C'\fR, it still adds up to
396incident, so its best to avoid that. 592two event changes per incident. Support for \f(CW\*(C`fork ()\*(C'\fR is very bad (but
593sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
594cases
595.Sp
596This backend usually performs well under most conditions.
597.Sp
598While nominally embeddable in other event loops, this doesn't work
599everywhere, so you might need to test for this. And since it is broken
600almost everywhere, you should only use it when you have a lot of sockets
601(for which it usually works), by embedding it into another event loop
602(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
603also broken on \s-1OS\s0 X)) and, did I mention it, using it only for sockets.
604.Sp
605This backend maps \f(CW\*(C`EV_READ\*(C'\fR into an \f(CW\*(C`EVFILT_READ\*(C'\fR kevent with
606\&\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
607\&\f(CW\*(C`NOTE_EOF\*(C'\fR.
397.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4 608.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
398.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4 609.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
399.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)" 610.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
400This is not implemented yet (and might never be). 611This is not implemented yet (and might never be, unless you send me an
612implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets
613and is not embeddable, which would limit the usefulness of this backend
614immensely.
401.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4 615.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
402.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4 616.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
403.IX Item "EVBACKEND_PORT (value 32, Solaris 10)" 617.IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
404This uses the Solaris 10 port mechanism. As with everything on Solaris, 618This uses the Solaris 10 event port mechanism. As with everything on Solaris,
405it's really slow, but it still scales very well (O(active_fds)). 619it's really slow, but it still scales very well (O(active_fds)).
406.Sp 620.Sp
407Please note that solaris ports can result in a lot of spurious 621Please note that Solaris event ports can deliver a lot of spurious
408notifications, so you need to use non-blocking I/O or other means to avoid 622notifications, so you need to use non-blocking I/O or other means to avoid
409blocking when no data (or space) is available. 623blocking when no data (or space) is available.
624.Sp
625While this backend scales well, it requires one system call per active
626file descriptor per loop iteration. For small and medium numbers of file
627descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend
628might perform better.
629.Sp
630On the positive side, with the exception of the spurious readiness
631notifications, this backend actually performed fully to specification
632in all tests and is fully embeddable, which is a rare feat among the
633OS-specific backends (I vastly prefer correctness over speed hacks).
634.Sp
635This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
636\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
410.ie n .IP """EVBACKEND_ALL""" 4 637.ie n .IP """EVBACKEND_ALL""" 4
411.el .IP "\f(CWEVBACKEND_ALL\fR" 4 638.el .IP "\f(CWEVBACKEND_ALL\fR" 4
412.IX Item "EVBACKEND_ALL" 639.IX Item "EVBACKEND_ALL"
413Try all backends (even potentially broken ones that wouldn't be tried 640Try all backends (even potentially broken ones that wouldn't be tried
414with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as 641with \f(CW\*(C`EVFLAG_AUTO\*(C'\fR). Since this is a mask, you can do stuff such as
415\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR. 642\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR.
643.Sp
644It is definitely not recommended to use this flag.
416.RE 645.RE
417.RS 4 646.RS 4
418.Sp 647.Sp
419If one or more of these are ored into the flags value, then only these 648If one or more of these are or'ed into the flags value, then only these
420backends will be tried (in the reverse order as given here). If none are 649backends will be tried (in the reverse order as listed here). If none are
421specified, most compiled-in backend will be tried, usually in reverse 650specified, all backends in \f(CW\*(C`ev_recommended_backends ()\*(C'\fR will be tried.
422order of their flag values :)
423.Sp 651.Sp
424The most typical usage is like this: 652Example: This is the most typical usage.
425.Sp 653.Sp
426.Vb 2 654.Vb 2
427\& if (!ev_default_loop (0)) 655\& if (!ev_default_loop (0))
428\& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?"); 656\& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
429.Ve 657.Ve
430.Sp 658.Sp
431Restrict libev to the select and poll backends, and do not allow 659Example: Restrict libev to the select and poll backends, and do not allow
432environment settings to be taken into account: 660environment settings to be taken into account:
433.Sp 661.Sp
434.Vb 1 662.Vb 1
435\& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV); 663\& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
436.Ve 664.Ve
437.Sp 665.Sp
438Use whatever libev has to offer, but make sure that kqueue is used if 666Example: Use whatever libev has to offer, but make sure that kqueue is
439available (warning, breaks stuff, best use only with your own private 667used if available (warning, breaks stuff, best use only with your own
440event loop and only if you know the \s-1OS\s0 supports your types of fds): 668private event loop and only if you know the \s-1OS\s0 supports your types of
669fds):
441.Sp 670.Sp
442.Vb 1 671.Vb 1
443\& ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE); 672\& ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
444.Ve 673.Ve
445.RE 674.RE
446.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4 675.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
447.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)" 676.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
448Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is 677Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is
449always distinct from the default loop. Unlike the default loop, it cannot 678always distinct from the default loop. Unlike the default loop, it cannot
450handle signal and child watchers, and attempts to do so will be greeted by 679handle signal and child watchers, and attempts to do so will be greeted by
451undefined behaviour (or a failed assertion if assertions are enabled). 680undefined behaviour (or a failed assertion if assertions are enabled).
452.Sp 681.Sp
682Note that this function \fIis\fR thread-safe, and the recommended way to use
683libev with threads is indeed to create one loop per thread, and using the
684default loop in the \*(L"main\*(R" or \*(L"initial\*(R" thread.
685.Sp
453Example: try to create a event loop that uses epoll and nothing else. 686Example: Try to create a event loop that uses epoll and nothing else.
454.Sp 687.Sp
455.Vb 3 688.Vb 3
456\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV); 689\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
457\& if (!epoller) 690\& if (!epoller)
458\& fatal ("no epoll found here, maybe it hides under your chair"); 691\& fatal ("no epoll found here, maybe it hides under your chair");
459.Ve 692.Ve
460.IP "ev_default_destroy ()" 4 693.IP "ev_default_destroy ()" 4
461.IX Item "ev_default_destroy ()" 694.IX Item "ev_default_destroy ()"
462Destroys the default loop again (frees all memory and kernel state 695Destroys the default loop again (frees all memory and kernel state
463etc.). This stops all registered event watchers (by not touching them in 696etc.). None of the active event watchers will be stopped in the normal
464any way whatsoever, although you cannot rely on this :). 697sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your
698responsibility to either stop all watchers cleanly yourself \fIbefore\fR
699calling this function, or cope with the fact afterwards (which is usually
700the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them
701for example).
702.Sp
703Note that certain global state, such as signal state (and installed signal
704handlers), will not be freed by this function, and related watchers (such
705as signal and child watchers) would need to be stopped manually.
706.Sp
707In general it is not advisable to call this function except in the
708rare occasion where you really need to free e.g. the signal handling
709pipe fds. If you need dynamically allocated loops it is better to use
710\&\f(CW\*(C`ev_loop_new\*(C'\fR and \f(CW\*(C`ev_loop_destroy\*(C'\fR).
465.IP "ev_loop_destroy (loop)" 4 711.IP "ev_loop_destroy (loop)" 4
466.IX Item "ev_loop_destroy (loop)" 712.IX Item "ev_loop_destroy (loop)"
467Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an 713Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an
468earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR. 714earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR.
469.IP "ev_default_fork ()" 4 715.IP "ev_default_fork ()" 4
470.IX Item "ev_default_fork ()" 716.IX Item "ev_default_fork ()"
717This function sets a flag that causes subsequent \f(CW\*(C`ev_loop\*(C'\fR iterations
471This function reinitialises the kernel state for backends that have 718to reinitialise the kernel state for backends that have one. Despite the
472one. Despite the name, you can call it anytime, but it makes most sense 719name, you can call it anytime, but it makes most sense after forking, in
473after forking, in either the parent or child process (or both, but that 720the child process (or both child and parent, but that again makes little
474again makes little sense). 721sense). You \fImust\fR call it in the child before using any of the libev
722functions, and it will only take effect at the next \f(CW\*(C`ev_loop\*(C'\fR iteration.
475.Sp 723.Sp
476You \fImust\fR call this function in the child process after forking if and 724On the other hand, you only need to call this function in the child
477only if you want to use the event library in both processes. If you just 725process if and only if you want to use the event library in the child. If
478fork+exec, you don't have to call it. 726you just fork+exec, you don't have to call it at all.
479.Sp 727.Sp
480The function itself is quite fast and it's usually not a problem to call 728The function itself is quite fast and it's usually not a problem to call
481it just in case after a fork. To make this easy, the function will fit in 729it just in case after a fork. To make this easy, the function will fit in
482quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR: 730quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR:
483.Sp 731.Sp
484.Vb 1 732.Vb 1
485\& pthread_atfork (0, 0, ev_default_fork); 733\& pthread_atfork (0, 0, ev_default_fork);
486.Ve 734.Ve
487.Sp
488At the moment, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and \f(CW\*(C`EVBACKEND_POLL\*(C'\fR are safe to use
489without calling this function, so if you force one of those backends you
490do not need to care.
491.IP "ev_loop_fork (loop)" 4 735.IP "ev_loop_fork (loop)" 4
492.IX Item "ev_loop_fork (loop)" 736.IX Item "ev_loop_fork (loop)"
493Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by 737Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by
494\&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop 738\&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop
495after fork, and how you do this is entirely your own problem. 739after fork that you want to re-use in the child, and how you do this is
740entirely your own problem.
741.IP "int ev_is_default_loop (loop)" 4
742.IX Item "int ev_is_default_loop (loop)"
743Returns true when the given loop is, in fact, the default loop, and false
744otherwise.
745.IP "unsigned int ev_loop_count (loop)" 4
746.IX Item "unsigned int ev_loop_count (loop)"
747Returns the count of loop iterations for the loop, which is identical to
748the number of times libev did poll for new events. It starts at \f(CW0\fR and
749happily wraps around with enough iterations.
750.Sp
751This value can sometimes be useful as a generation counter of sorts (it
752\&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with
753\&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls.
496.IP "unsigned int ev_backend (loop)" 4 754.IP "unsigned int ev_backend (loop)" 4
497.IX Item "unsigned int ev_backend (loop)" 755.IX Item "unsigned int ev_backend (loop)"
498Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in 756Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
499use. 757use.
500.IP "ev_tstamp ev_now (loop)" 4 758.IP "ev_tstamp ev_now (loop)" 4
501.IX Item "ev_tstamp ev_now (loop)" 759.IX Item "ev_tstamp ev_now (loop)"
502Returns the current \*(L"event loop time\*(R", which is the time the event loop 760Returns the current \*(L"event loop time\*(R", which is the time the event loop
503received events and started processing them. This timestamp does not 761received events and started processing them. This timestamp does not
504change as long as callbacks are being processed, and this is also the base 762change as long as callbacks are being processed, and this is also the base
505time used for relative timers. You can treat it as the timestamp of the 763time used for relative timers. You can treat it as the timestamp of the
506event occuring (or more correctly, libev finding out about it). 764event occurring (or more correctly, libev finding out about it).
765.IP "ev_now_update (loop)" 4
766.IX Item "ev_now_update (loop)"
767Establishes the current time by querying the kernel, updating the time
768returned by \f(CW\*(C`ev_now ()\*(C'\fR in the progress. This is a costly operation and
769is usually done automatically within \f(CW\*(C`ev_loop ()\*(C'\fR.
770.Sp
771This function is rarely useful, but when some event callback runs for a
772very long time without entering the event loop, updating libev's idea of
773the current time is a good idea.
774.Sp
775See also \*(L"The special problem of time updates\*(R" in the \f(CW\*(C`ev_timer\*(C'\fR section.
776.IP "ev_suspend (loop)" 4
777.IX Item "ev_suspend (loop)"
778.PD 0
779.IP "ev_resume (loop)" 4
780.IX Item "ev_resume (loop)"
781.PD
782These two functions suspend and resume a loop, for use when the loop is
783not used for a while and timeouts should not be processed.
784.Sp
785A typical use case would be an interactive program such as a game: When
786the user presses \f(CW\*(C`^Z\*(C'\fR to suspend the game and resumes it an hour later it
787would be best to handle timeouts as if no time had actually passed while
788the program was suspended. This can be achieved by calling \f(CW\*(C`ev_suspend\*(C'\fR
789in your \f(CW\*(C`SIGTSTP\*(C'\fR handler, sending yourself a \f(CW\*(C`SIGSTOP\*(C'\fR and calling
790\&\f(CW\*(C`ev_resume\*(C'\fR directly afterwards to resume timer processing.
791.Sp
792Effectively, all \f(CW\*(C`ev_timer\*(C'\fR watchers will be delayed by the time spend
793between \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
794will be rescheduled (that is, they will lose any events that would have
795occured while suspended).
796.Sp
797After calling \f(CW\*(C`ev_suspend\*(C'\fR you \fBmust not\fR call \fIany\fR function on the
798given loop other than \f(CW\*(C`ev_resume\*(C'\fR, and you \fBmust not\fR call \f(CW\*(C`ev_resume\*(C'\fR
799without a previous call to \f(CW\*(C`ev_suspend\*(C'\fR.
800.Sp
801Calling \f(CW\*(C`ev_suspend\*(C'\fR/\f(CW\*(C`ev_resume\*(C'\fR has the side effect of updating the
802event loop time (see \f(CW\*(C`ev_now_update\*(C'\fR).
507.IP "ev_loop (loop, int flags)" 4 803.IP "ev_loop (loop, int flags)" 4
508.IX Item "ev_loop (loop, int flags)" 804.IX Item "ev_loop (loop, int flags)"
509Finally, this is it, the event handler. This function usually is called 805Finally, this is it, the event handler. This function usually is called
510after you initialised all your watchers and you want to start handling 806after you initialised all your watchers and you want to start handling
511events. 807events.
… …
513If the flags argument is specified as \f(CW0\fR, it will not return until 809If the flags argument is specified as \f(CW0\fR, it will not return until
514either no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called. 810either no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called.
515.Sp 811.Sp
516Please note that an explicit \f(CW\*(C`ev_unloop\*(C'\fR is usually better than 812Please note that an explicit \f(CW\*(C`ev_unloop\*(C'\fR is usually better than
517relying on all watchers to be stopped when deciding when a program has 813relying on all watchers to be stopped when deciding when a program has
518finished (especially in interactive programs), but having a program that 814finished (especially in interactive programs), but having a program
519automatically loops as long as it has to and no longer by virtue of 815that automatically loops as long as it has to and no longer by virtue
520relying on its watchers stopping correctly is a thing of beauty. 816of relying on its watchers stopping correctly, that is truly a thing of
817beauty.
521.Sp 818.Sp
522A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle 819A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle
523those events and any outstanding ones, but will not block your process in 820those events and any already outstanding ones, but will not block your
524case there are no events and will return after one iteration of the loop. 821process in case there are no events and will return after one iteration of
822the loop.
525.Sp 823.Sp
526A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if 824A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if
527neccessary) and will handle those and any outstanding ones. It will block 825necessary) and will handle those and any already outstanding ones. It
528your process until at least one new event arrives, and will return after 826will block your process until at least one new event arrives (which could
529one iteration of the loop. This is useful if you are waiting for some 827be an event internal to libev itself, so there is no guarantee that a
530external event in conjunction with something not expressible using other 828user-registered callback will be called), and will return after one
829iteration of the loop.
830.Sp
831This is useful if you are waiting for some external event in conjunction
832with something not expressible using other libev watchers (i.e. "roll your
531libev watchers. However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is 833own \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
532usually a better approach for this kind of thing. 834usually a better approach for this kind of thing.
533.Sp 835.Sp
534Here are the gory details of what \f(CW\*(C`ev_loop\*(C'\fR does: 836Here are the gory details of what \f(CW\*(C`ev_loop\*(C'\fR does:
535.Sp 837.Sp
536.Vb 18 838.Vb 10
537\& * If there are no active watchers (reference count is zero), return. 839\& \- Before the first iteration, call any pending watchers.
538\& - Queue prepare watchers and then call all outstanding watchers. 840\& * If EVFLAG_FORKCHECK was used, check for a fork.
841\& \- If a fork was detected (by any means), queue and call all fork watchers.
842\& \- Queue and call all prepare watchers.
539\& - If we have been forked, recreate the kernel state. 843\& \- If we have been forked, detach and recreate the kernel state
844\& as to not disturb the other process.
540\& - Update the kernel state with all outstanding changes. 845\& \- Update the kernel state with all outstanding changes.
541\& - Update the "event loop time". 846\& \- Update the "event loop time" (ev_now ()).
542\& - Calculate for how long to block. 847\& \- Calculate for how long to sleep or block, if at all
848\& (active idle watchers, EVLOOP_NONBLOCK or not having
849\& any active watchers at all will result in not sleeping).
850\& \- Sleep if the I/O and timer collect interval say so.
543\& - Block the process, waiting for any events. 851\& \- Block the process, waiting for any events.
544\& - Queue all outstanding I/O (fd) events. 852\& \- Queue all outstanding I/O (fd) events.
545\& - Update the "event loop time" and do time jump handling. 853\& \- Update the "event loop time" (ev_now ()), and do time jump adjustments.
546\& - Queue all outstanding timers. 854\& \- Queue all expired timers.
547\& - Queue all outstanding periodics. 855\& \- Queue all expired periodics.
548\& - If no events are pending now, queue all idle watchers. 856\& \- Unless any events are pending now, queue all idle watchers.
549\& - Queue all check watchers. 857\& \- Queue all check watchers.
550\& - Call all queued watchers in reverse order (i.e. check watchers first). 858\& \- Call all queued watchers in reverse order (i.e. check watchers first).
551\& Signals and child watchers are implemented as I/O watchers, and will 859\& Signals and child watchers are implemented as I/O watchers, and will
552\& be handled here by queueing them when their watcher gets executed. 860\& be handled here by queueing them when their watcher gets executed.
553\& - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK 861\& \- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
554\& were used, return, otherwise continue with step *. 862\& were used, or there are no active watchers, return, otherwise
863\& continue with step *.
555.Ve 864.Ve
556.Sp 865.Sp
557Example: queue some jobs and then loop until no events are outsanding 866Example: Queue some jobs and then loop until no events are outstanding
558anymore. 867anymore.
559.Sp 868.Sp
560.Vb 4 869.Vb 4
561\& ... queue jobs here, make sure they register event watchers as long 870\& ... queue jobs here, make sure they register event watchers as long
562\& ... as they still have work to do (even an idle watcher will do..) 871\& ... as they still have work to do (even an idle watcher will do..)
563\& ev_loop (my_loop, 0); 872\& ev_loop (my_loop, 0);
564\& ... jobs done. yeah! 873\& ... jobs done or somebody called unloop. yeah!
565.Ve 874.Ve
566.IP "ev_unloop (loop, how)" 4 875.IP "ev_unloop (loop, how)" 4
567.IX Item "ev_unloop (loop, how)" 876.IX Item "ev_unloop (loop, how)"
568Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it 877Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it
569has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either 878has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
570\&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or 879\&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or
571\&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return. 880\&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return.
881.Sp
882This \*(L"unloop state\*(R" will be cleared when entering \f(CW\*(C`ev_loop\*(C'\fR again.
883.Sp
884It is safe to call \f(CW\*(C`ev_unloop\*(C'\fR from otuside any \f(CW\*(C`ev_loop\*(C'\fR calls.
572.IP "ev_ref (loop)" 4 885.IP "ev_ref (loop)" 4
573.IX Item "ev_ref (loop)" 886.IX Item "ev_ref (loop)"
574.PD 0 887.PD 0
575.IP "ev_unref (loop)" 4 888.IP "ev_unref (loop)" 4
576.IX Item "ev_unref (loop)" 889.IX Item "ev_unref (loop)"
577.PD 890.PD
578Ref/unref can be used to add or remove a reference count on the event 891Ref/unref can be used to add or remove a reference count on the event
579loop: Every watcher keeps one reference, and as long as the reference 892loop: Every watcher keeps one reference, and as long as the reference
580count is nonzero, \f(CW\*(C`ev_loop\*(C'\fR will not return on its own. If you have 893count is nonzero, \f(CW\*(C`ev_loop\*(C'\fR will not return on its own.
894.Sp
581a watcher you never unregister that should not keep \f(CW\*(C`ev_loop\*(C'\fR from 895If you have a watcher you never unregister that should not keep \f(CW\*(C`ev_loop\*(C'\fR
582returning, \fIev_unref()\fR after starting, and \fIev_ref()\fR before stopping it. For 896from returning, call \fIev_unref()\fR after starting, and \fIev_ref()\fR before
897stopping it.
898.Sp
583example, libev itself uses this for its internal signal pipe: It is not 899As an example, libev itself uses this for its internal signal pipe: It
584visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from exiting if 900is not visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from
585no event watchers registered by it are active. It is also an excellent 901exiting if no event watchers registered by it are active. It is also an
586way to do this for generic recurring timers or from within third-party 902excellent way to do this for generic recurring timers or from within
587libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR. 903third-party libraries. Just remember to \fIunref after start\fR and \fIref
904before stop\fR (but only if the watcher wasn't active before, or was active
905before, respectively. Note also that libev might stop watchers itself
906(e.g. non-repeating timers) in which case you have to \f(CW\*(C`ev_ref\*(C'\fR
907in the callback).
588.Sp 908.Sp
589Example: create a signal watcher, but keep it from keeping \f(CW\*(C`ev_loop\*(C'\fR 909Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_loop\*(C'\fR
590running when nothing else is active. 910running when nothing else is active.
591.Sp 911.Sp
592.Vb 4 912.Vb 4
593\& struct dv_signal exitsig; 913\& ev_signal exitsig;
594\& ev_signal_init (&exitsig, sig_cb, SIGINT); 914\& ev_signal_init (&exitsig, sig_cb, SIGINT);
595\& ev_signal_start (myloop, &exitsig); 915\& ev_signal_start (loop, &exitsig);
596\& evf_unref (myloop); 916\& evf_unref (loop);
597.Ve 917.Ve
598.Sp 918.Sp
599Example: for some weird reason, unregister the above signal handler again. 919Example: For some weird reason, unregister the above signal handler again.
600.Sp 920.Sp
601.Vb 2 921.Vb 2
602\& ev_ref (myloop); 922\& ev_ref (loop);
603\& ev_signal_stop (myloop, &exitsig); 923\& ev_signal_stop (loop, &exitsig);
604.Ve 924.Ve
925.IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4
926.IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"
927.PD 0
928.IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4
929.IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"
930.PD
931These advanced functions influence the time that libev will spend waiting
932for events. Both time intervals are by default \f(CW0\fR, meaning that libev
933will try to invoke timer/periodic callbacks and I/O callbacks with minimum
934latency.
935.Sp
936Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR)
937allows libev to delay invocation of I/O and timer/periodic callbacks
938to increase efficiency of loop iterations (or to increase power-saving
939opportunities).
940.Sp
941The idea is that sometimes your program runs just fast enough to handle
942one (or very few) event(s) per loop iteration. While this makes the
943program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new
944events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high
945overhead for the actual polling but can deliver many events at once.
946.Sp
947By setting a higher \fIio collect interval\fR you allow libev to spend more
948time collecting I/O events, so you can handle more events per iteration,
949at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and
950\&\f(CW\*(C`ev_timer\*(C'\fR) will be not affected. Setting this to a non-null value will
951introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations.
952.Sp
953Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
954to spend more time collecting timeouts, at the expense of increased
955latency/jitter/inexactness (the watcher callback will be called
956later). \f(CW\*(C`ev_io\*(C'\fR watchers will not be affected. Setting this to a non-null
957value will not introduce any overhead in libev.
958.Sp
959Many (busy) programs can usually benefit by setting the I/O collect
960interval to a value near \f(CW0.1\fR or so, which is often enough for
961interactive servers (of course not for games), likewise for timeouts. It
962usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR,
963as this approaches the timing granularity of most systems.
964.Sp
965Setting the \fItimeout collect interval\fR can improve the opportunity for
966saving power, as the program will \*(L"bundle\*(R" timer callback invocations that
967are \*(L"near\*(R" in time together, by delaying some, thus reducing the number of
968times the process sleeps and wakes up again. Another useful technique to
969reduce iterations/wake\-ups is to use \f(CW\*(C`ev_periodic\*(C'\fR watchers and make sure
970they fire on, say, one-second boundaries only.
971.IP "ev_loop_verify (loop)" 4
972.IX Item "ev_loop_verify (loop)"
973This function only does something when \f(CW\*(C`EV_VERIFY\*(C'\fR support has been
974compiled in, which is the default for non-minimal builds. It tries to go
975through all internal structures and checks them for validity. If anything
976is found to be inconsistent, it will print an error message to standard
977error and call \f(CW\*(C`abort ()\*(C'\fR.
978.Sp
979This can be used to catch bugs inside libev itself: under normal
980circumstances, this function will never abort as of course libev keeps its
981data structures consistent.
605.SH "ANATOMY OF A WATCHER" 982.SH "ANATOMY OF A WATCHER"
606.IX Header "ANATOMY OF A WATCHER" 983.IX Header "ANATOMY OF A WATCHER"
984In the following description, uppercase \f(CW\*(C`TYPE\*(C'\fR in names stands for the
985watcher type, e.g. \f(CW\*(C`ev_TYPE_start\*(C'\fR can mean \f(CW\*(C`ev_timer_start\*(C'\fR for timer
986watchers and \f(CW\*(C`ev_io_start\*(C'\fR for I/O watchers.
987.PP
607A watcher is a structure that you create and register to record your 988A watcher is a structure that you create and register to record your
608interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to 989interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to
609become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that: 990become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that:
610.PP 991.PP
611.Vb 5 992.Vb 5
612\& static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) 993\& static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
613\& { 994\& {
614\& ev_io_stop (w); 995\& ev_io_stop (w);
615\& ev_unloop (loop, EVUNLOOP_ALL); 996\& ev_unloop (loop, EVUNLOOP_ALL);
616\& } 997\& }
617.Ve 998\&
618.PP
619.Vb 6
620\& struct ev_loop *loop = ev_default_loop (0); 999\& struct ev_loop *loop = ev_default_loop (0);
1000\&
621\& struct ev_io stdin_watcher; 1001\& ev_io stdin_watcher;
1002\&
622\& ev_init (&stdin_watcher, my_cb); 1003\& ev_init (&stdin_watcher, my_cb);
623\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); 1004\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
624\& ev_io_start (loop, &stdin_watcher); 1005\& ev_io_start (loop, &stdin_watcher);
1006\&
625\& ev_loop (loop, 0); 1007\& ev_loop (loop, 0);
626.Ve 1008.Ve
627.PP 1009.PP
628As you can see, you are responsible for allocating the memory for your 1010As you can see, you are responsible for allocating the memory for your
629watcher structures (and it is usually a bad idea to do this on the stack, 1011watcher structures (and it is \fIusually\fR a bad idea to do this on the
630although this can sometimes be quite valid). 1012stack).
1013.PP
1014Each watcher has an associated watcher structure (called \f(CW\*(C`struct ev_TYPE\*(C'\fR
1015or simply \f(CW\*(C`ev_TYPE\*(C'\fR, as typedefs are provided for all watcher structs).
631.PP 1016.PP
632Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init 1017Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init
633(watcher *, callback)\*(C'\fR, which expects a callback to be provided. This 1018(watcher *, callback)\*(C'\fR, which expects a callback to be provided. This
634callback gets invoked each time the event occurs (or, in the case of io 1019callback gets invoked each time the event occurs (or, in the case of I/O
635watchers, each time the event loop detects that the file descriptor given 1020watchers, each time the event loop detects that the file descriptor given
636is readable and/or writable). 1021is readable and/or writable).
637.PP 1022.PP
638Each watcher type has its own \f(CW\*(C`ev_<type>_set (watcher *, ...)\*(C'\fR macro 1023Each watcher type further has its own \f(CW\*(C`ev_TYPE_set (watcher *, ...)\*(C'\fR
639with arguments specific to this watcher type. There is also a macro 1024macro to configure it, with arguments specific to the watcher type. There
640to combine initialisation and setting in one call: \f(CW\*(C`ev_<type>_init 1025is also a macro to combine initialisation and setting in one call: \f(CW\*(C`ev_TYPE_init (watcher *, callback, ...)\*(C'\fR.
641(watcher *, callback, ...)\*(C'\fR.
642.PP 1026.PP
643To make the watcher actually watch out for events, you have to start it 1027To make the watcher actually watch out for events, you have to start it
644with a watcher-specific start function (\f(CW\*(C`ev_<type>_start (loop, watcher 1028with a watcher-specific start function (\f(CW\*(C`ev_TYPE_start (loop, watcher
645*)\*(C'\fR), and you can stop watching for events at any time by calling the 1029*)\*(C'\fR), and you can stop watching for events at any time by calling the
646corresponding stop function (\f(CW\*(C`ev_<type>_stop (loop, watcher *)\*(C'\fR. 1030corresponding stop function (\f(CW\*(C`ev_TYPE_stop (loop, watcher *)\*(C'\fR.
647.PP 1031.PP
648As long as your watcher is active (has been started but not stopped) you 1032As long as your watcher is active (has been started but not stopped) you
649must not touch the values stored in it. Most specifically you must never 1033must not touch the values stored in it. Most specifically you must never
650reinitialise it or call its set macro. 1034reinitialise it or call its \f(CW\*(C`ev_TYPE_set\*(C'\fR macro.
651.PP
652You can check whether an event is active by calling the \f(CW\*(C`ev_is_active
653(watcher *)\*(C'\fR macro. To see whether an event is outstanding (but the
654callback for it has not been called yet) you can use the \f(CW\*(C`ev_is_pending
655(watcher *)\*(C'\fR macro.
656.PP 1035.PP
657Each and every callback receives the event loop pointer as first, the 1036Each and every callback receives the event loop pointer as first, the
658registered watcher structure as second, and a bitset of received events as 1037registered watcher structure as second, and a bitset of received events as
659third argument. 1038third argument.
660.PP 1039.PP
… …
685The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread. 1064The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread.
686.ie n .IP """EV_CHILD""" 4 1065.ie n .IP """EV_CHILD""" 4
687.el .IP "\f(CWEV_CHILD\fR" 4 1066.el .IP "\f(CWEV_CHILD\fR" 4
688.IX Item "EV_CHILD" 1067.IX Item "EV_CHILD"
689The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change. 1068The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change.
1069.ie n .IP """EV_STAT""" 4
1070.el .IP "\f(CWEV_STAT\fR" 4
1071.IX Item "EV_STAT"
1072The path specified in the \f(CW\*(C`ev_stat\*(C'\fR watcher changed its attributes somehow.
690.ie n .IP """EV_IDLE""" 4 1073.ie n .IP """EV_IDLE""" 4
691.el .IP "\f(CWEV_IDLE\fR" 4 1074.el .IP "\f(CWEV_IDLE\fR" 4
692.IX Item "EV_IDLE" 1075.IX Item "EV_IDLE"
693The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do. 1076The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do.
694.ie n .IP """EV_PREPARE""" 4 1077.ie n .IP """EV_PREPARE""" 4
… …
704\&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any 1087\&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any
705received events. Callbacks of both watcher types can start and stop as 1088received events. Callbacks of both watcher types can start and stop as
706many watchers as they want, and all of them will be taken into account 1089many watchers as they want, and all of them will be taken into account
707(for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep 1090(for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep
708\&\f(CW\*(C`ev_loop\*(C'\fR from blocking). 1091\&\f(CW\*(C`ev_loop\*(C'\fR from blocking).
1092.ie n .IP """EV_EMBED""" 4
1093.el .IP "\f(CWEV_EMBED\fR" 4
1094.IX Item "EV_EMBED"
1095The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.
1096.ie n .IP """EV_FORK""" 4
1097.el .IP "\f(CWEV_FORK\fR" 4
1098.IX Item "EV_FORK"
1099The event loop has been resumed in the child process after fork (see
1100\&\f(CW\*(C`ev_fork\*(C'\fR).
1101.ie n .IP """EV_ASYNC""" 4
1102.el .IP "\f(CWEV_ASYNC\fR" 4
1103.IX Item "EV_ASYNC"
1104The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR).
1105.ie n .IP """EV_CUSTOM""" 4
1106.el .IP "\f(CWEV_CUSTOM\fR" 4
1107.IX Item "EV_CUSTOM"
1108Not ever sent (or otherwise used) by libev itself, but can be freely used
1109by libev users to signal watchers (e.g. via \f(CW\*(C`ev_feed_event\*(C'\fR).
709.ie n .IP """EV_ERROR""" 4 1110.ie n .IP """EV_ERROR""" 4
710.el .IP "\f(CWEV_ERROR\fR" 4 1111.el .IP "\f(CWEV_ERROR\fR" 4
711.IX Item "EV_ERROR" 1112.IX Item "EV_ERROR"
712An unspecified error has occured, the watcher has been stopped. This might 1113An unspecified error has occurred, the watcher has been stopped. This might
713happen because the watcher could not be properly started because libev 1114happen because the watcher could not be properly started because libev
714ran out of memory, a file descriptor was found to be closed or any other 1115ran out of memory, a file descriptor was found to be closed or any other
1116problem. Libev considers these application bugs.
1117.Sp
715problem. You best act on it by reporting the problem and somehow coping 1118You best act on it by reporting the problem and somehow coping with the
716with the watcher being stopped. 1119watcher being stopped. Note that well-written programs should not receive
1120an error ever, so when your watcher receives it, this usually indicates a
1121bug in your program.
717.Sp 1122.Sp
718Libev will usually signal a few \*(L"dummy\*(R" events together with an error, 1123Libev will usually signal a few \*(L"dummy\*(R" events together with an error, for
719for example it might indicate that a fd is readable or writable, and if 1124example it might indicate that a fd is readable or writable, and if your
720your callbacks is well-written it can just attempt the operation and cope 1125callbacks is well-written it can just attempt the operation and cope with
721with the error from \fIread()\fR or \fIwrite()\fR. This will not work in multithreaded 1126the error from \fIread()\fR or \fIwrite()\fR. This will not work in multi-threaded
722programs, though, so beware. 1127programs, though, as the fd could already be closed and reused for another
1128thing, so beware.
1129.Sh "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0"
1130.IX Subsection "GENERIC WATCHER FUNCTIONS"
1131.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
1132.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
1133.IX Item "ev_init (ev_TYPE *watcher, callback)"
1134This macro initialises the generic portion of a watcher. The contents
1135of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
1136the generic parts of the watcher are initialised, you \fIneed\fR to call
1137the type-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR macro afterwards to initialise the
1138type-specific parts. For each type there is also a \f(CW\*(C`ev_TYPE_init\*(C'\fR macro
1139which rolls both calls into one.
1140.Sp
1141You can reinitialise a watcher at any time as long as it has been stopped
1142(or never started) and there are no pending events outstanding.
1143.Sp
1144The callback is always of type \f(CW\*(C`void (*)(struct ev_loop *loop, ev_TYPE *watcher,
1145int revents)\*(C'\fR.
1146.Sp
1147Example: Initialise an \f(CW\*(C`ev_io\*(C'\fR watcher in two steps.
1148.Sp
1149.Vb 3
1150\& ev_io w;
1151\& ev_init (&w, my_cb);
1152\& ev_io_set (&w, STDIN_FILENO, EV_READ);
1153.Ve
1154.ie n .IP """ev_TYPE_set"" (ev_TYPE *, [args])" 4
1155.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *, [args])" 4
1156.IX Item "ev_TYPE_set (ev_TYPE *, [args])"
1157This macro initialises the type-specific parts of a watcher. You need to
1158call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
1159call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
1160macro on a watcher that is active (it can be pending, however, which is a
1161difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
1162.Sp
1163Although some watcher types do not have type-specific arguments
1164(e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
1165.Sp
1166See \f(CW\*(C`ev_init\*(C'\fR, above, for an example.
1167.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
1168.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
1169.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
1170This convenience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
1171calls into a single call. This is the most convenient method to initialise
1172a watcher. The same limitations apply, of course.
1173.Sp
1174Example: Initialise and set an \f(CW\*(C`ev_io\*(C'\fR watcher in one step.
1175.Sp
1176.Vb 1
1177\& ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1178.Ve
1179.ie n .IP """ev_TYPE_start"" (loop *, ev_TYPE *watcher)" 4
1180.el .IP "\f(CWev_TYPE_start\fR (loop *, ev_TYPE *watcher)" 4
1181.IX Item "ev_TYPE_start (loop *, ev_TYPE *watcher)"
1182Starts (activates) the given watcher. Only active watchers will receive
1183events. If the watcher is already active nothing will happen.
1184.Sp
1185Example: Start the \f(CW\*(C`ev_io\*(C'\fR watcher that is being abused as example in this
1186whole section.
1187.Sp
1188.Vb 1
1189\& ev_io_start (EV_DEFAULT_UC, &w);
1190.Ve
1191.ie n .IP """ev_TYPE_stop"" (loop *, ev_TYPE *watcher)" 4
1192.el .IP "\f(CWev_TYPE_stop\fR (loop *, ev_TYPE *watcher)" 4
1193.IX Item "ev_TYPE_stop (loop *, ev_TYPE *watcher)"
1194Stops the given watcher if active, and clears the pending status (whether
1195the watcher was active or not).
1196.Sp
1197It is possible that stopped watchers are pending \- for example,
1198non-repeating timers are being stopped when they become pending \- but
1199calling \f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor
1200pending. If you want to free or reuse the memory used by the watcher it is
1201therefore a good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
1202.IP "bool ev_is_active (ev_TYPE *watcher)" 4
1203.IX Item "bool ev_is_active (ev_TYPE *watcher)"
1204Returns a true value iff the watcher is active (i.e. it has been started
1205and not yet been stopped). As long as a watcher is active you must not modify
1206it.
1207.IP "bool ev_is_pending (ev_TYPE *watcher)" 4
1208.IX Item "bool ev_is_pending (ev_TYPE *watcher)"
1209Returns a true value iff the watcher is pending, (i.e. it has outstanding
1210events but its callback has not yet been invoked). As long as a watcher
1211is pending (but not active) you must not call an init function on it (but
1212\&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe), you must not change its priority, and you must
1213make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR
1214it).
1215.IP "callback ev_cb (ev_TYPE *watcher)" 4
1216.IX Item "callback ev_cb (ev_TYPE *watcher)"
1217Returns the callback currently set on the watcher.
1218.IP "ev_cb_set (ev_TYPE *watcher, callback)" 4
1219.IX Item "ev_cb_set (ev_TYPE *watcher, callback)"
1220Change the callback. You can change the callback at virtually any time
1221(modulo threads).
1222.IP "ev_set_priority (ev_TYPE *watcher, priority)" 4
1223.IX Item "ev_set_priority (ev_TYPE *watcher, priority)"
1224.PD 0
1225.IP "int ev_priority (ev_TYPE *watcher)" 4
1226.IX Item "int ev_priority (ev_TYPE *watcher)"
1227.PD
1228Set and query the priority of the watcher. The priority is a small
1229integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR
1230(default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked
1231before watchers with lower priority, but priority will not keep watchers
1232from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
1233.Sp
1234If you need to suppress invocation when higher priority events are pending
1235you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
1236.Sp
1237You \fImust not\fR change the priority of a watcher as long as it is active or
1238pending.
1239.Sp
1240Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
1241fine, as long as you do not mind that the priority value you query might
1242or might not have been clamped to the valid range.
1243.Sp
1244The default priority used by watchers when no priority has been set is
1245always \f(CW0\fR, which is supposed to not be too high and not be too low :).
1246.Sp
1247See \*(L"\s-1WATCHER\s0 \s-1PRIORITY\s0 \s-1MODELS\s0\*(R", below, for a more thorough treatment of
1248priorities.
1249.IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
1250.IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
1251Invoke the \f(CW\*(C`watcher\*(C'\fR with the given \f(CW\*(C`loop\*(C'\fR and \f(CW\*(C`revents\*(C'\fR. Neither
1252\&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback
1253can deal with that fact, as both are simply passed through to the
1254callback.
1255.IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
1256.IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
1257If the watcher is pending, this function clears its pending status and
1258returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the
1259watcher isn't pending it does nothing and returns \f(CW0\fR.
1260.Sp
1261Sometimes it can be useful to \*(L"poll\*(R" a watcher instead of waiting for its
1262callback to be invoked, which can be accomplished with this function.
723.Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0" 1263.Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0"
724.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER" 1264.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
725Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change 1265Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change
726and read at any time, libev will completely ignore it. This can be used 1266and read at any time: libev will completely ignore it. This can be used
727to associate arbitrary data with your watcher. If you need more data and 1267to associate arbitrary data with your watcher. If you need more data and
728don't want to allocate memory and store a pointer to it in that data 1268don't want to allocate memory and store a pointer to it in that data
729member, you can also \*(L"subclass\*(R" the watcher type and provide your own 1269member, you can also \*(L"subclass\*(R" the watcher type and provide your own
730data: 1270data:
731.PP 1271.PP
732.Vb 7 1272.Vb 7
733\& struct my_io 1273\& struct my_io
734\& { 1274\& {
735\& struct ev_io io; 1275\& ev_io io;
736\& int otherfd; 1276\& int otherfd;
737\& void *somedata; 1277\& void *somedata;
738\& struct whatever *mostinteresting; 1278\& struct whatever *mostinteresting;
739\& } 1279\& };
1280\&
1281\& ...
1282\& struct my_io w;
1283\& ev_io_init (&w.io, my_cb, fd, EV_READ);
740.Ve 1284.Ve
741.PP 1285.PP
742And since your callback will be called with a pointer to the watcher, you 1286And since your callback will be called with a pointer to the watcher, you
743can cast it back to your own type: 1287can cast it back to your own type:
744.PP 1288.PP
745.Vb 5 1289.Vb 5
746\& static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents) 1290\& static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
747\& { 1291\& {
748\& struct my_io *w = (struct my_io *)w_; 1292\& struct my_io *w = (struct my_io *)w_;
749\& ... 1293\& ...
750\& } 1294\& }
751.Ve 1295.Ve
752.PP 1296.PP
753More interesting and less C\-conformant ways of catsing your callback type 1297More interesting and less C\-conformant ways of casting your callback type
754have been omitted.... 1298instead have been omitted.
1299.PP
1300Another common scenario is to use some data structure with multiple
1301embedded watchers:
1302.PP
1303.Vb 6
1304\& struct my_biggy
1305\& {
1306\& int some_data;
1307\& ev_timer t1;
1308\& ev_timer t2;
1309\& }
1310.Ve
1311.PP
1312In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more
1313complicated: Either you store the address of your \f(CW\*(C`my_biggy\*(C'\fR struct
1314in the \f(CW\*(C`data\*(C'\fR member of the watcher (for woozies), or you need to use
1315some pointer arithmetic using \f(CW\*(C`offsetof\*(C'\fR inside your watchers (for real
1316programmers):
1317.PP
1318.Vb 1
1319\& #include <stddef.h>
1320\&
1321\& static void
1322\& t1_cb (EV_P_ ev_timer *w, int revents)
1323\& {
1324\& struct my_biggy big = (struct my_biggy *
1325\& (((char *)w) \- offsetof (struct my_biggy, t1));
1326\& }
1327\&
1328\& static void
1329\& t2_cb (EV_P_ ev_timer *w, int revents)
1330\& {
1331\& struct my_biggy big = (struct my_biggy *
1332\& (((char *)w) \- offsetof (struct my_biggy, t2));
1333\& }
1334.Ve
1335.Sh "\s-1WATCHER\s0 \s-1PRIORITY\s0 \s-1MODELS\s0"
1336.IX Subsection "WATCHER PRIORITY MODELS"
1337Many event loops support \fIwatcher priorities\fR, which are usually small
1338integers that influence the ordering of event callback invocation
1339between watchers in some way, all else being equal.
1340.PP
1341In libev, Watcher priorities can be set using \f(CW\*(C`ev_set_priority\*(C'\fR. See its
1342description for the more technical details such as the actual priority
1343range.
1344.PP
1345There are two common ways how these these priorities are being interpreted
1346by event loops:
1347.PP
1348In the more common lock-out model, higher priorities \*(L"lock out\*(R" invocation
1349of lower priority watchers, which means as long as higher priority
1350watchers receive events, lower priority watchers are not being invoked.
1351.PP
1352The less common only-for-ordering model uses priorities solely to order
1353callback invocation within a single event loop iteration: Higher priority
1354watchers are invoked before lower priority ones, but they all get invoked
1355before polling for new events.
1356.PP
1357Libev uses the second (only-for-ordering) model for all its watchers
1358except for idle watchers (which use the lock-out model).
1359.PP
1360The rationale behind this is that implementing the lock-out model for
1361watchers is not well supported by most kernel interfaces, and most event
1362libraries will just poll for the same events again and again as long as
1363their callbacks have not been executed, which is very inefficient in the
1364common case of one high-priority watcher locking out a mass of lower
1365priority ones.
1366.PP
1367Static (ordering) priorities are most useful when you have two or more
1368watchers handling the same resource: a typical usage example is having an
1369\&\f(CW\*(C`ev_io\*(C'\fR watcher to receive data, and an associated \f(CW\*(C`ev_timer\*(C'\fR to handle
1370timeouts. Under load, data might be received while the program handles
1371other jobs, but since timers normally get invoked first, the timeout
1372handler will be executed before checking for data. In that case, giving
1373the timer a lower priority than the I/O watcher ensures that I/O will be
1374handled first even under adverse conditions (which is usually, but not
1375always, what you want).
1376.PP
1377Since idle watchers use the \*(L"lock-out\*(R" model, meaning that idle watchers
1378will only be executed when no same or higher priority watchers have
1379received events, they can be used to implement the \*(L"lock-out\*(R" model when
1380required.
1381.PP
1382For example, to emulate how many other event libraries handle priorities,
1383you can associate an \f(CW\*(C`ev_idle\*(C'\fR watcher to each such watcher, and in
1384the normal watcher callback, you just start the idle watcher. The real
1385processing is done in the idle watcher callback. This causes libev to
1386continously poll and process kernel event data for the watcher, but when
1387the lock-out case is known to be rare (which in turn is rare :), this is
1388workable.
1389.PP
1390Usually, however, the lock-out model implemented that way will perform
1391miserably under the type of load it was designed to handle. In that case,
1392it might be preferable to stop the real watcher before starting the
1393idle watcher, so the kernel will not have to process the event in case
1394the actual processing will be delayed for considerable time.
1395.PP
1396Here is an example of an I/O watcher that should run at a strictly lower
1397priority than the default, and which should only process data when no
1398other events are pending:
1399.PP
1400.Vb 2
1401\& ev_idle idle; // actual processing watcher
1402\& ev_io io; // actual event watcher
1403\&
1404\& static void
1405\& io_cb (EV_P_ ev_io *w, int revents)
1406\& {
1407\& // stop the I/O watcher, we received the event, but
1408\& // are not yet ready to handle it.
1409\& ev_io_stop (EV_A_ w);
1410\&
1411\& // start the idle watcher to ahndle the actual event.
1412\& // it will not be executed as long as other watchers
1413\& // with the default priority are receiving events.
1414\& ev_idle_start (EV_A_ &idle);
1415\& }
1416\&
1417\& static void
1418\& idle\-cb (EV_P_ ev_idle *w, int revents)
1419\& {
1420\& // actual processing
1421\& read (STDIN_FILENO, ...);
1422\&
1423\& // have to start the I/O watcher again, as
1424\& // we have handled the event
1425\& ev_io_start (EV_P_ &io);
1426\& }
1427\&
1428\& // initialisation
1429\& ev_idle_init (&idle, idle_cb);
1430\& ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
1431\& ev_io_start (EV_DEFAULT_ &io);
1432.Ve
1433.PP
1434In the \*(L"real\*(R" world, it might also be beneficial to start a timer, so that
1435low-priority connections can not be locked out forever under load. This
1436enables your program to keep a lower latency for important connections
1437during short periods of high load, while not completely locking out less
1438important ones.
755.SH "WATCHER TYPES" 1439.SH "WATCHER TYPES"
756.IX Header "WATCHER TYPES" 1440.IX Header "WATCHER TYPES"
757This section describes each watcher in detail, but will not repeat 1441This section describes each watcher in detail, but will not repeat
758information given in the last section. 1442information given in the last section. Any initialisation/set macros,
1443functions and members specific to the watcher type are explained.
1444.PP
1445Members are additionally marked with either \fI[read\-only]\fR, meaning that,
1446while the watcher is active, you can look at the member and expect some
1447sensible content, but you must not modify it (you can modify it while the
1448watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
1449means you can expect it to have some sensible content while the watcher
1450is active, but you can also modify it. Modifying it may not do something
1451sensible or take immediate effect (or do anything at all), but libev will
1452not crash or malfunction in any way.
759.ie n .Sh """ev_io"" \- is this file descriptor readable or writable" 1453.ie n .Sh """ev_io"" \- is this file descriptor readable or writable?"
760.el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable" 1454.el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable?"
761.IX Subsection "ev_io - is this file descriptor readable or writable" 1455.IX Subsection "ev_io - is this file descriptor readable or writable?"
762I/O watchers check whether a file descriptor is readable or writable 1456I/O watchers check whether a file descriptor is readable or writable
763in each iteration of the event loop (This behaviour is called 1457in each iteration of the event loop, or, more precisely, when reading
764level-triggering because you keep receiving events as long as the 1458would not block the process and writing would at least be able to write
765condition persists. Remember you can stop the watcher if you don't want to 1459some data. This behaviour is called level-triggering because you keep
766act on the event and neither want to receive future events). 1460receiving events as long as the condition persists. Remember you can stop
1461the watcher if you don't want to act on the event and neither want to
1462receive future events.
767.PP 1463.PP
768In general you can register as many read and/or write event watchers per 1464In general you can register as many read and/or write event watchers per
769fd as you want (as long as you don't confuse yourself). Setting all file 1465fd as you want (as long as you don't confuse yourself). Setting all file
770descriptors to non-blocking mode is also usually a good idea (but not 1466descriptors to non-blocking mode is also usually a good idea (but not
771required if you know what you are doing). 1467required if you know what you are doing).
772.PP 1468.PP
773You have to be careful with dup'ed file descriptors, though. Some backends 1469If you cannot use non-blocking mode, then force the use of a
774(the linux epoll backend is a notable example) cannot handle dup'ed file 1470known-to-be-good backend (at the time of this writing, this includes only
775descriptors correctly if you register interest in two or more fds pointing 1471\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and \f(CW\*(C`EVBACKEND_POLL\*(C'\fR). The same applies to file
776to the same underlying file/socket etc. description (that is, they share 1472descriptors for which non-blocking operation makes no sense (such as
777the same underlying \*(L"file open\*(R"). 1473files) \- libev doesn't guarentee any specific behaviour in that case.
778.PP 1474.PP
779If you must do this, then force the use of a known-to-be-good backend 1475Another thing you have to watch out for is that it is quite easy to
780(at the time of this writing, this includes only \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and 1476receive \*(L"spurious\*(R" readiness notifications, that is your callback might
1477be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block
1478because there is no data. Not only are some backends known to create a
1479lot of those (for example Solaris ports), it is very easy to get into
1480this situation even with a relatively standard program structure. Thus
1481it is best to always use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning
1482\&\f(CW\*(C`EAGAIN\*(C'\fR is far preferable to a program hanging until some data arrives.
1483.PP
1484If you cannot run the fd in non-blocking mode (for example you should
1485not play around with an Xlib connection), then you have to separately
1486re-test whether a file descriptor is really ready with a known-to-be good
1487interface such as poll (fortunately in our Xlib example, Xlib already
1488does this on its own, so its quite safe to use). Some people additionally
1489use \f(CW\*(C`SIGALRM\*(C'\fR and an interval timer, just to be sure you won't block
1490indefinitely.
1491.PP
1492But really, best use non-blocking mode.
1493.PP
1494\fIThe special problem of disappearing file descriptors\fR
1495.IX Subsection "The special problem of disappearing file descriptors"
1496.PP
1497Some backends (e.g. kqueue, epoll) need to be told about closing a file
1498descriptor (either due to calling \f(CW\*(C`close\*(C'\fR explicitly or any other means,
1499such as \f(CW\*(C`dup2\*(C'\fR). The reason is that you register interest in some file
1500descriptor, but when it goes away, the operating system will silently drop
1501this interest. If another file descriptor with the same number then is
1502registered with libev, there is no efficient way to see that this is, in
1503fact, a different file descriptor.
1504.PP
1505To avoid having to explicitly tell libev about such cases, libev follows
1506the following policy: Each time \f(CW\*(C`ev_io_set\*(C'\fR is being called, libev
1507will assume that this is potentially a new file descriptor, otherwise
1508it is assumed that the file descriptor stays the same. That means that
1509you \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
1510descriptor even if the file descriptor number itself did not change.
1511.PP
1512This is how one would do it normally anyway, the important point is that
1513the libev application should not optimise around libev but should leave
1514optimisations to libev.
1515.PP
1516\fIThe special problem of dup'ed file descriptors\fR
1517.IX Subsection "The special problem of dup'ed file descriptors"
1518.PP
1519Some backends (e.g. epoll), cannot register events for file descriptors,
1520but only events for the underlying file descriptions. That means when you
1521have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register
1522events for them, only one file descriptor might actually receive events.
1523.PP
1524There is no workaround possible except not registering events
1525for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
1526\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1527.PP
1528\fIThe special problem of fork\fR
1529.IX Subsection "The special problem of fork"
1530.PP
1531Some backends (epoll, kqueue) do not support \f(CW\*(C`fork ()\*(C'\fR at all or exhibit
1532useless behaviour. Libev fully supports fork, but needs to be told about
1533it in the child.
1534.PP
1535To support fork in your programs, you either have to call
1536\&\f(CW\*(C`ev_default_fork ()\*(C'\fR or \f(CW\*(C`ev_loop_fork ()\*(C'\fR after a fork in the child,
1537enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or
781\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR). 1538\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1539.PP
1540\fIThe special problem of \s-1SIGPIPE\s0\fR
1541.IX Subsection "The special problem of SIGPIPE"
1542.PP
1543While not really specific to libev, it is easy to forget about \f(CW\*(C`SIGPIPE\*(C'\fR:
1544when writing to a pipe whose other end has been closed, your program gets
1545sent a \s-1SIGPIPE\s0, which, by default, aborts your program. For most programs
1546this is sensible behaviour, for daemons, this is usually undesirable.
1547.PP
1548So when you encounter spurious, unexplained daemon exits, make sure you
1549ignore \s-1SIGPIPE\s0 (and maybe make sure you log the exit status of your daemon
1550somewhere, as that would have given you a big clue).
1551.PP
1552\fIWatcher-Specific Functions\fR
1553.IX Subsection "Watcher-Specific Functions"
782.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4 1554.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
783.IX Item "ev_io_init (ev_io *, callback, int fd, int events)" 1555.IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
784.PD 0 1556.PD 0
785.IP "ev_io_set (ev_io *, int fd, int events)" 4 1557.IP "ev_io_set (ev_io *, int fd, int events)" 4
786.IX Item "ev_io_set (ev_io *, int fd, int events)" 1558.IX Item "ev_io_set (ev_io *, int fd, int events)"
787.PD 1559.PD
788Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The fd is the file descriptor to rceeive 1560Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to
789events 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 | 1561receive 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
790EV_WRITE\*(C'\fR to receive the given events. 1562\&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR, to express the desire to receive the given events.
791.Sp 1563.IP "int fd [read\-only]" 4
792Please note that most of the more scalable backend mechanisms (for example 1564.IX Item "int fd [read-only]"
793epoll and solaris ports) can result in spurious readyness notifications 1565The file descriptor being watched.
794for file descriptors, so you practically need to use non-blocking I/O (and 1566.IP "int events [read\-only]" 4
795treat callback invocation as hint only), or retest separately with a safe 1567.IX Item "int events [read-only]"
796interface before doing I/O (XLib can do this), or force the use of either 1568The events being watched.
797\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR, which don't suffer from this
798problem. Also note that it is quite easy to have your callback invoked
799when the readyness condition is no longer valid even when employing
800typical ways of handling events, so its a good idea to use non-blocking
801I/O unconditionally.
802.PP 1569.PP
1570\fIExamples\fR
1571.IX Subsection "Examples"
1572.PP
803Example: call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well 1573Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
804readable, but only once. Since it is likely line\-buffered, you could 1574readable, but only once. Since it is likely line-buffered, you could
805attempt to read a whole line in the callback: 1575attempt to read a whole line in the callback.
806.PP 1576.PP
807.Vb 6 1577.Vb 6
808\& static void 1578\& static void
809\& stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents) 1579\& stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
810\& { 1580\& {
811\& ev_io_stop (loop, w); 1581\& ev_io_stop (loop, w);
812\& .. read from stdin here (or from w->fd) and haqndle any I/O errors 1582\& .. read from stdin here (or from w\->fd) and handle any I/O errors
813\& } 1583\& }
814.Ve 1584\&
815.PP
816.Vb 6
817\& ... 1585\& ...
818\& struct ev_loop *loop = ev_default_init (0); 1586\& struct ev_loop *loop = ev_default_init (0);
819\& struct ev_io stdin_readable; 1587\& ev_io stdin_readable;
820\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ); 1588\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
821\& ev_io_start (loop, &stdin_readable); 1589\& ev_io_start (loop, &stdin_readable);
822\& ev_loop (loop, 0); 1590\& ev_loop (loop, 0);
823.Ve 1591.Ve
824.ie n .Sh """ev_timer"" \- relative and optionally recurring timeouts" 1592.ie n .Sh """ev_timer"" \- relative and optionally repeating timeouts"
825.el .Sh "\f(CWev_timer\fP \- relative and optionally recurring timeouts" 1593.el .Sh "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
826.IX Subsection "ev_timer - relative and optionally recurring timeouts" 1594.IX Subsection "ev_timer - relative and optionally repeating timeouts"
827Timer watchers are simple relative timers that generate an event after a 1595Timer watchers are simple relative timers that generate an event after a
828given time, and optionally repeating in regular intervals after that. 1596given time, and optionally repeating in regular intervals after that.
829.PP 1597.PP
830The timers are based on real time, that is, if you register an event that 1598The timers are based on real time, that is, if you register an event that
831times out after an hour and you reset your system clock to last years 1599times out after an hour and you reset your system clock to January last
832time, it will still time out after (roughly) and hour. \*(L"Roughly\*(R" because 1600year, it will still time out after (roughly) one hour. \*(L"Roughly\*(R" because
833detecting time jumps is hard, and some inaccuracies are unavoidable (the 1601detecting time jumps is hard, and some inaccuracies are unavoidable (the
834monotonic clock option helps a lot here). 1602monotonic clock option helps a lot here).
1603.PP
1604The callback is guaranteed to be invoked only \fIafter\fR its timeout has
1605passed (not \fIat\fR, so on systems with very low-resolution clocks this
1606might introduce a small delay). If multiple timers become ready during the
1607same loop iteration then the ones with earlier time-out values are invoked
1608before ones with later time-out values (but this is no longer true when a
1609callback calls \f(CW\*(C`ev_loop\*(C'\fR recursively).
1610.PP
1611\fIBe smart about timeouts\fR
1612.IX Subsection "Be smart about timeouts"
1613.PP
1614Many real-world problems involve some kind of timeout, usually for error
1615recovery. A typical example is an \s-1HTTP\s0 request \- if the other side hangs,
1616you want to raise some error after a while.
1617.PP
1618What follows are some ways to handle this problem, from obvious and
1619inefficient to smart and efficient.
1620.PP
1621In the following, a 60 second activity timeout is assumed \- a timeout that
1622gets reset to 60 seconds each time there is activity (e.g. each time some
1623data or other life sign was received).
1624.IP "1. Use a timer and stop, reinitialise and start it on activity." 4
1625.IX Item "1. Use a timer and stop, reinitialise and start it on activity."
1626This is the most obvious, but not the most simple way: In the beginning,
1627start the watcher:
1628.Sp
1629.Vb 2
1630\& ev_timer_init (timer, callback, 60., 0.);
1631\& ev_timer_start (loop, timer);
1632.Ve
1633.Sp
1634Then, each time there is some activity, \f(CW\*(C`ev_timer_stop\*(C'\fR it, initialise it
1635and start it again:
1636.Sp
1637.Vb 3
1638\& ev_timer_stop (loop, timer);
1639\& ev_timer_set (timer, 60., 0.);
1640\& ev_timer_start (loop, timer);
1641.Ve
1642.Sp
1643This is relatively simple to implement, but means that each time there is
1644some activity, libev will first have to remove the timer from its internal
1645data structure and then add it again. Libev tries to be fast, but it's
1646still not a constant-time operation.
1647.ie n .IP "2. Use a timer and re-start it with ""ev_timer_again"" inactivity." 4
1648.el .IP "2. Use a timer and re-start it with \f(CWev_timer_again\fR inactivity." 4
1649.IX Item "2. Use a timer and re-start it with ev_timer_again inactivity."
1650This is the easiest way, and involves using \f(CW\*(C`ev_timer_again\*(C'\fR instead of
1651\&\f(CW\*(C`ev_timer_start\*(C'\fR.
1652.Sp
1653To implement this, configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value
1654of \f(CW60\fR and then call \f(CW\*(C`ev_timer_again\*(C'\fR at start and each time you
1655successfully read or write some data. If you go into an idle state where
1656you do not expect data to travel on the socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR
1657the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will automatically restart it if need be.
1658.Sp
1659That means you can ignore both the \f(CW\*(C`ev_timer_start\*(C'\fR function and the
1660\&\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
1661member and \f(CW\*(C`ev_timer_again\*(C'\fR.
1662.Sp
1663At start:
1664.Sp
1665.Vb 3
1666\& ev_timer_init (timer, callback);
1667\& timer\->repeat = 60.;
1668\& ev_timer_again (loop, timer);
1669.Ve
1670.Sp
1671Each time there is some activity:
1672.Sp
1673.Vb 1
1674\& ev_timer_again (loop, timer);
1675.Ve
1676.Sp
1677It is even possible to change the time-out on the fly, regardless of
1678whether the watcher is active or not:
1679.Sp
1680.Vb 2
1681\& timer\->repeat = 30.;
1682\& ev_timer_again (loop, timer);
1683.Ve
1684.Sp
1685This is slightly more efficient then stopping/starting the timer each time
1686you want to modify its timeout value, as libev does not have to completely
1687remove and re-insert the timer from/into its internal data structure.
1688.Sp
1689It is, however, even simpler than the \*(L"obvious\*(R" way to do it.
1690.IP "3. Let the timer time out, but then re-arm it as required." 4
1691.IX Item "3. Let the timer time out, but then re-arm it as required."
1692This method is more tricky, but usually most efficient: Most timeouts are
1693relatively long compared to the intervals between other activity \- in
1694our example, within 60 seconds, there are usually many I/O events with
1695associated activity resets.
1696.Sp
1697In this case, it would be more efficient to leave the \f(CW\*(C`ev_timer\*(C'\fR alone,
1698but remember the time of last activity, and check for a real timeout only
1699within the callback:
1700.Sp
1701.Vb 1
1702\& ev_tstamp last_activity; // time of last activity
1703\&
1704\& static void
1705\& callback (EV_P_ ev_timer *w, int revents)
1706\& {
1707\& ev_tstamp now = ev_now (EV_A);
1708\& ev_tstamp timeout = last_activity + 60.;
1709\&
1710\& // if last_activity + 60. is older than now, we did time out
1711\& if (timeout < now)
1712\& {
1713\& // timeout occured, take action
1714\& }
1715\& else
1716\& {
1717\& // callback was invoked, but there was some activity, re\-arm
1718\& // the watcher to fire in last_activity + 60, which is
1719\& // guaranteed to be in the future, so "again" is positive:
1720\& w\->repeat = timeout \- now;
1721\& ev_timer_again (EV_A_ w);
1722\& }
1723\& }
1724.Ve
1725.Sp
1726To summarise the callback: first calculate the real timeout (defined
1727as \*(L"60 seconds after the last activity\*(R"), then check if that time has
1728been reached, which means something \fIdid\fR, in fact, time out. Otherwise
1729the callback was invoked too early (\f(CW\*(C`timeout\*(C'\fR is in the future), so
1730re-schedule the timer to fire at that future time, to see if maybe we have
1731a timeout then.
1732.Sp
1733Note how \f(CW\*(C`ev_timer_again\*(C'\fR is used, taking advantage of the
1734\&\f(CW\*(C`ev_timer_again\*(C'\fR optimisation when the timer is already running.
1735.Sp
1736This scheme causes more callback invocations (about one every 60 seconds
1737minus half the average time between activity), but virtually no calls to
1738libev to change the timeout.
1739.Sp
1740To start the timer, simply initialise the watcher and set \f(CW\*(C`last_activity\*(C'\fR
1741to the current time (meaning we just have some activity :), then call the
1742callback, which will \*(L"do the right thing\*(R" and start the timer:
1743.Sp
1744.Vb 3
1745\& ev_timer_init (timer, callback);
1746\& last_activity = ev_now (loop);
1747\& callback (loop, timer, EV_TIMEOUT);
1748.Ve
1749.Sp
1750And when there is some activity, simply store the current time in
1751\&\f(CW\*(C`last_activity\*(C'\fR, no libev calls at all:
1752.Sp
1753.Vb 1
1754\& last_actiivty = ev_now (loop);
1755.Ve
1756.Sp
1757This technique is slightly more complex, but in most cases where the
1758time-out is unlikely to be triggered, much more efficient.
1759.Sp
1760Changing the timeout is trivial as well (if it isn't hard-coded in the
1761callback :) \- just change the timeout and invoke the callback, which will
1762fix things for you.
1763.IP "4. Wee, just use a double-linked list for your timeouts." 4
1764.IX Item "4. Wee, just use a double-linked list for your timeouts."
1765If there is not one request, but many thousands (millions...), all
1766employing some kind of timeout with the same timeout value, then one can
1767do even better:
1768.Sp
1769When starting the timeout, calculate the timeout value and put the timeout
1770at the \fIend\fR of the list.
1771.Sp
1772Then use an \f(CW\*(C`ev_timer\*(C'\fR to fire when the timeout at the \fIbeginning\fR of
1773the list is expected to fire (for example, using the technique #3).
1774.Sp
1775When there is some activity, remove the timer from the list, recalculate
1776the timeout, append it to the end of the list again, and make sure to
1777update the \f(CW\*(C`ev_timer\*(C'\fR if it was taken from the beginning of the list.
1778.Sp
1779This way, one can manage an unlimited number of timeouts in O(1) time for
1780starting, stopping and updating the timers, at the expense of a major
1781complication, and having to use a constant timeout. The constant timeout
1782ensures that the list stays sorted.
1783.PP
1784So which method the best?
1785.PP
1786Method #2 is a simple no-brain-required solution that is adequate in most
1787situations. Method #3 requires a bit more thinking, but handles many cases
1788better, and isn't very complicated either. In most case, choosing either
1789one is fine, with #3 being better in typical situations.
1790.PP
1791Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
1792rather complicated, but extremely efficient, something that really pays
1793off after the first million or so of active timers, i.e. it's usually
1794overkill :)
1795.PP
1796\fIThe special problem of time updates\fR
1797.IX Subsection "The special problem of time updates"
1798.PP
1799Establishing the current time is a costly operation (it usually takes at
1800least two system calls): \s-1EV\s0 therefore updates its idea of the current
1801time only before and after \f(CW\*(C`ev_loop\*(C'\fR collects new events, which causes a
1802growing difference between \f(CW\*(C`ev_now ()\*(C'\fR and \f(CW\*(C`ev_time ()\*(C'\fR when handling
1803lots of events in one iteration.
835.PP 1804.PP
836The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR 1805The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
837time. This is usually the right thing as this timestamp refers to the time 1806time. This is usually the right thing as this timestamp refers to the time
838of the event triggering whatever timeout you are modifying/starting. If 1807of the event triggering whatever timeout you are modifying/starting. If
839you suspect event processing to be delayed and you \fIneed\fR to base the timeout 1808you suspect event processing to be delayed and you \fIneed\fR to base the
840on the current time, use something like this to adjust for this: 1809timeout on the current time, use something like this to adjust for this:
841.PP 1810.PP
842.Vb 1 1811.Vb 1
843\& ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); 1812\& ev_timer_set (&timer, after + ev_now () \- ev_time (), 0.);
844.Ve 1813.Ve
845.PP 1814.PP
846The callback is guarenteed to be invoked only when its timeout has passed, 1815If the event loop is suspended for a long time, you can also force an
847but if multiple timers become ready during the same loop iteration then 1816update of the time returned by \f(CW\*(C`ev_now ()\*(C'\fR by calling \f(CW\*(C`ev_now_update
848order of execution is undefined. 1817()\*(C'\fR.
1818.PP
1819\fIWatcher-Specific Functions and Data Members\fR
1820.IX Subsection "Watcher-Specific Functions and Data Members"
849.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4 1821.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
850.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 1822.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
851.PD 0 1823.PD 0
852.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4 1824.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
853.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 1825.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
854.PD 1826.PD
855Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR is 1827Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR
856\&\f(CW0.\fR, then it will automatically be stopped. If it is positive, then the 1828is \f(CW0.\fR, then it will automatically be stopped once the timeout is
857timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds 1829reached. If it is positive, then the timer will automatically be
858later, again, and again, until stopped manually. 1830configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds later, again, and again,
1831until stopped manually.
859.Sp 1832.Sp
860The timer itself will do a best-effort at avoiding drift, that is, if you 1833The timer itself will do a best-effort at avoiding drift, that is, if
861configure a timer to trigger every 10 seconds, then it will trigger at 1834you configure a timer to trigger every 10 seconds, then it will normally
862exactly 10 second intervals. If, however, your program cannot keep up with 1835trigger at exactly 10 second intervals. If, however, your program cannot
863the timer (because it takes longer than those 10 seconds to do stuff) the 1836keep up with the timer (because it takes longer than those 10 seconds to
864timer will not fire more than once per event loop iteration. 1837do stuff) the timer will not fire more than once per event loop iteration.
865.IP "ev_timer_again (loop)" 4 1838.IP "ev_timer_again (loop, ev_timer *)" 4
866.IX Item "ev_timer_again (loop)" 1839.IX Item "ev_timer_again (loop, ev_timer *)"
867This will act as if the timer timed out and restart it again if it is 1840This will act as if the timer timed out and restart it again if it is
868repeating. The exact semantics are: 1841repeating. The exact semantics are:
869.Sp 1842.Sp
1843If the timer is pending, its pending status is cleared.
1844.Sp
870If the timer is started but nonrepeating, stop it. 1845If the timer is started but non-repeating, stop it (as if it timed out).
871.Sp 1846.Sp
872If the timer is repeating, either start it if necessary (with the repeat 1847If the timer is repeating, either start it if necessary (with the
873value), or reset the running timer to the repeat value. 1848\&\f(CW\*(C`repeat\*(C'\fR value), or reset the running timer to the \f(CW\*(C`repeat\*(C'\fR value.
874.Sp 1849.Sp
875This sounds a bit complicated, but here is a useful and typical 1850This sounds a bit complicated, see \*(L"Be smart about timeouts\*(R", above, for a
876example: Imagine you have a tcp connection and you want a so-called idle 1851usage example.
877timeout, that is, you want to be called when there have been, say, 60 1852.IP "ev_tstamp repeat [read\-write]" 4
878seconds of inactivity on the socket. The easiest way to do this is to 1853.IX Item "ev_tstamp repeat [read-write]"
879configure an \f(CW\*(C`ev_timer\*(C'\fR with after=repeat=60 and calling ev_timer_again each 1854The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
880time you successfully read or write some data. If you go into an idle 1855or \f(CW\*(C`ev_timer_again\*(C'\fR is called, and determines the next timeout (if any),
881state where you do not expect data to travel on the socket, you can stop 1856which is also when any modifications are taken into account.
882the timer, and again will automatically restart it if need be.
883.PP 1857.PP
1858\fIExamples\fR
1859.IX Subsection "Examples"
1860.PP
884Example: create a timer that fires after 60 seconds. 1861Example: Create a timer that fires after 60 seconds.
885.PP 1862.PP
886.Vb 5 1863.Vb 5
887\& static void 1864\& static void
888\& one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents) 1865\& one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
889\& { 1866\& {
890\& .. one minute over, w is actually stopped right here 1867\& .. one minute over, w is actually stopped right here
891\& } 1868\& }
892.Ve 1869\&
893.PP
894.Vb 3
895\& struct ev_timer mytimer; 1870\& ev_timer mytimer;
896\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.); 1871\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
897\& ev_timer_start (loop, &mytimer); 1872\& ev_timer_start (loop, &mytimer);
898.Ve 1873.Ve
899.PP 1874.PP
900Example: create a timeout timer that times out after 10 seconds of 1875Example: Create a timeout timer that times out after 10 seconds of
901inactivity. 1876inactivity.
902.PP 1877.PP
903.Vb 5 1878.Vb 5
904\& static void 1879\& static void
905\& timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents) 1880\& timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
906\& { 1881\& {
907\& .. ten seconds without any activity 1882\& .. ten seconds without any activity
908\& } 1883\& }
909.Ve 1884\&
910.PP
911.Vb 4
912\& struct ev_timer mytimer; 1885\& ev_timer mytimer;
913\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */ 1886\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
914\& ev_timer_again (&mytimer); /* start timer */ 1887\& ev_timer_again (&mytimer); /* start timer */
915\& ev_loop (loop, 0); 1888\& ev_loop (loop, 0);
916.Ve 1889\&
917.PP
918.Vb 3
919\& // and in some piece of code that gets executed on any "activity": 1890\& // and in some piece of code that gets executed on any "activity":
920\& // reset the timeout to start ticking again at 10 seconds 1891\& // reset the timeout to start ticking again at 10 seconds
921\& ev_timer_again (&mytimer); 1892\& ev_timer_again (&mytimer);
922.Ve 1893.Ve
923.ie n .Sh """ev_periodic"" \- to cron or not to cron" 1894.ie n .Sh """ev_periodic"" \- to cron or not to cron?"
924.el .Sh "\f(CWev_periodic\fP \- to cron or not to cron" 1895.el .Sh "\f(CWev_periodic\fP \- to cron or not to cron?"
925.IX Subsection "ev_periodic - to cron or not to cron" 1896.IX Subsection "ev_periodic - to cron or not to cron?"
926Periodic watchers are also timers of a kind, but they are very versatile 1897Periodic watchers are also timers of a kind, but they are very versatile
927(and unfortunately a bit complex). 1898(and unfortunately a bit complex).
928.PP 1899.PP
929Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time) 1900Unlike \f(CW\*(C`ev_timer\*(C'\fR, periodic watchers are not based on real time (or
930but on wallclock time (absolute time). You can tell a periodic watcher 1901relative time, the physical time that passes) but on wall clock time
931to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a 1902(absolute time, the thing you can read on your calender or clock). The
932periodic watcher to trigger in 10 seconds (by specifiying e.g. c<ev_now () 1903difference is that wall clock time can run faster or slower than real
933+ 10.>) and then reset your system clock to the last year, then it will 1904time, and time jumps are not uncommon (e.g. when you adjust your
934take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger 1905wrist-watch).
935roughly 10 seconds later and of course not if you reset your system time
936again).
937.PP 1906.PP
938They can also be used to implement vastly more complex timers, such as 1907You can tell a periodic watcher to trigger after some specific point
939triggering an event on eahc midnight, local time. 1908in time: for example, if you tell a periodic watcher to trigger \*(L"in 10
1909seconds\*(R" (by specifying e.g. \f(CW\*(C`ev_now () + 10.\*(C'\fR, that is, an absolute time
1910not a delay) and then reset your system clock to January of the previous
1911year, then it will take a year or more to trigger the event (unlike an
1912\&\f(CW\*(C`ev_timer\*(C'\fR, which would still trigger roughly 10 seconds after starting
1913it, as it uses a relative timeout).
940.PP 1914.PP
1915\&\f(CW\*(C`ev_periodic\*(C'\fR watchers can also be used to implement vastly more complex
1916timers, such as triggering an event on each \*(L"midnight, local time\*(R", or
1917other complicated rules. This cannot be done with \f(CW\*(C`ev_timer\*(C'\fR watchers, as
1918those cannot react to time jumps.
1919.PP
941As with timers, the callback is guarenteed to be invoked only when the 1920As with timers, the callback is guaranteed to be invoked only when the
942time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready 1921point in time where it is supposed to trigger has passed. If multiple
943during the same loop iteration then order of execution is undefined. 1922timers become ready during the same loop iteration then the ones with
1923earlier time-out values are invoked before ones with later time-out values
1924(but this is no longer true when a callback calls \f(CW\*(C`ev_loop\*(C'\fR recursively).
1925.PP
1926\fIWatcher-Specific Functions and Data Members\fR
1927.IX Subsection "Watcher-Specific Functions and Data Members"
944.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4 1928.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
945.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 1929.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
946.PD 0 1930.PD 0
947.IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4 1931.IP "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
948.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 1932.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
949.PD 1933.PD
950Lots of arguments, lets sort it out... There are basically three modes of 1934Lots of arguments, let's sort it out... There are basically three modes of
951operation, and we will explain them from simplest to complex: 1935operation, and we will explain them from simplest to most complex:
952.RS 4 1936.RS 4
953.IP "* absolute timer (interval = reschedule_cb = 0)" 4 1937.IP "\(bu" 4
954.IX Item "absolute timer (interval = reschedule_cb = 0)" 1938absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1939.Sp
955In this configuration the watcher triggers an event at the wallclock time 1940In this configuration the watcher triggers an event after the wall clock
956\&\f(CW\*(C`at\*(C'\fR and doesn't repeat. It will not adjust when a time jump occurs, 1941time \f(CW\*(C`offset\*(C'\fR has passed. It will not repeat and will not adjust when a
957that is, if it is to be run at January 1st 2011 then it will run when the 1942time jump occurs, that is, if it is to be run at January 1st 2011 then it
958system time reaches or surpasses this time. 1943will be stopped and invoked when the system clock reaches or surpasses
959.IP "* non-repeating interval timer (interval > 0, reschedule_cb = 0)" 4 1944this point in time.
960.IX Item "non-repeating interval timer (interval > 0, reschedule_cb = 0)" 1945.IP "\(bu" 4
1946repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1947.Sp
961In this mode the watcher will always be scheduled to time out at the next 1948In this mode the watcher will always be scheduled to time out at the next
962\&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N) and then repeat, regardless 1949\&\f(CW\*(C`offset + N * interval\*(C'\fR time (for some integer N, which can also be
963of any time jumps. 1950negative) and then repeat, regardless of any time jumps. The \f(CW\*(C`offset\*(C'\fR
1951argument is merely an offset into the \f(CW\*(C`interval\*(C'\fR periods.
964.Sp 1952.Sp
965This can be used to create timers that do not drift with respect to system 1953This can be used to create timers that do not drift with respect to the
966time: 1954system clock, for example, here is an \f(CW\*(C`ev_periodic\*(C'\fR that triggers each
1955hour, on the hour (with respect to \s-1UTC\s0):
967.Sp 1956.Sp
968.Vb 1 1957.Vb 1
969\& ev_periodic_set (&periodic, 0., 3600., 0); 1958\& ev_periodic_set (&periodic, 0., 3600., 0);
970.Ve 1959.Ve
971.Sp 1960.Sp
972This doesn't mean there will always be 3600 seconds in between triggers, 1961This doesn't mean there will always be 3600 seconds in between triggers,
973but only that the the callback will be called when the system time shows a 1962but only that the callback will be called when the system time shows a
974full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible 1963full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
975by 3600. 1964by 3600.
976.Sp 1965.Sp
977Another way to think about it (for the mathematically inclined) is that 1966Another way to think about it (for the mathematically inclined) is that
978\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible 1967\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
979time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps. 1968time where \f(CW\*(C`time = offset (mod interval)\*(C'\fR, regardless of any time jumps.
980.IP "* manual reschedule mode (reschedule_cb = callback)" 4 1969.Sp
981.IX Item "manual reschedule mode (reschedule_cb = callback)" 1970For numerical stability it is preferable that the \f(CW\*(C`offset\*(C'\fR value is near
1971\&\f(CW\*(C`ev_now ()\*(C'\fR (the current time), but there is no range requirement for
1972this value, and in fact is often specified as zero.
1973.Sp
1974Note also that there is an upper limit to how often a timer can fire (\s-1CPU\s0
1975speed for example), so if \f(CW\*(C`interval\*(C'\fR is very small then timing stability
1976will of course deteriorate. Libev itself tries to be exact to be about one
1977millisecond (if the \s-1OS\s0 supports it and the machine is fast enough).
1978.IP "\(bu" 4
1979manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1980.Sp
982In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being 1981In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`offset\*(C'\fR are both being
983ignored. Instead, each time the periodic watcher gets scheduled, the 1982ignored. Instead, each time the periodic watcher gets scheduled, the
984reschedule callback will be called with the watcher as first, and the 1983reschedule callback will be called with the watcher as first, and the
985current time as second argument. 1984current time as second argument.
986.Sp 1985.Sp
987\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, 1986\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, ever,
988ever, or make any event loop modifications\fR. If you need to stop it, 1987or make \s-1ANY\s0 other event loop modifications whatsoever, unless explicitly
989return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by 1988allowed by documentation here\fR.
990starting a prepare watcher).
991.Sp 1989.Sp
1990If you need to stop it, return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop
1991it afterwards (e.g. by starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is the
1992only event loop modification you are allowed to do).
1993.Sp
992Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w, 1994The callback prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(ev_periodic
993ev_tstamp now)\*(C'\fR, e.g.: 1995*w, ev_tstamp now)\*(C'\fR, e.g.:
994.Sp 1996.Sp
995.Vb 4 1997.Vb 5
1998\& static ev_tstamp
996\& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) 1999\& my_rescheduler (ev_periodic *w, ev_tstamp now)
997\& { 2000\& {
998\& return now + 60.; 2001\& return now + 60.;
999\& } 2002\& }
1000.Ve 2003.Ve
1001.Sp 2004.Sp
1002It must return the next time to trigger, based on the passed time value 2005It must return the next time to trigger, based on the passed time value
1003(that is, the lowest time value larger than to the second argument). It 2006(that is, the lowest time value larger than to the second argument). It
1004will usually be called just before the callback will be triggered, but 2007will usually be called just before the callback will be triggered, but
1005might be called at other times, too. 2008might be called at other times, too.
1006.Sp 2009.Sp
1007\&\s-1NOTE:\s0 \fIThis callback must always return a time that is later than the 2010\&\s-1NOTE:\s0 \fIThis callback must always return a time that is higher than or
1008passed \f(CI\*(C`now\*(C'\fI value\fR. Not even \f(CW\*(C`now\*(C'\fR itself will do, it \fImust\fR be larger. 2011equal to the passed \f(CI\*(C`now\*(C'\fI value\fR.
1009.Sp 2012.Sp
1010This can be used to create very complex timers, such as a timer that 2013This can be used to create very complex timers, such as a timer that
1011triggers on each midnight, local time. To do this, you would calculate the 2014triggers on \*(L"next midnight, local time\*(R". To do this, you would calculate the
1012next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How 2015next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How
1013you do this is, again, up to you (but it is not trivial, which is the main 2016you do this is, again, up to you (but it is not trivial, which is the main
1014reason I omitted it as an example). 2017reason I omitted it as an example).
1015.RE 2018.RE
1016.RS 4 2019.RS 4
… …
1019.IX Item "ev_periodic_again (loop, ev_periodic *)" 2022.IX Item "ev_periodic_again (loop, ev_periodic *)"
1020Simply stops and restarts the periodic watcher again. This is only useful 2023Simply stops and restarts the periodic watcher again. This is only useful
1021when you changed some parameters or the reschedule callback would return 2024when you changed some parameters or the reschedule callback would return
1022a different time than the last time it was called (e.g. in a crond like 2025a different time than the last time it was called (e.g. in a crond like
1023program when the crontabs have changed). 2026program when the crontabs have changed).
2027.IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4
2028.IX Item "ev_tstamp ev_periodic_at (ev_periodic *)"
2029When active, returns the absolute time that the watcher is supposed
2030to trigger next. This is not the same as the \f(CW\*(C`offset\*(C'\fR argument to
2031\&\f(CW\*(C`ev_periodic_set\*(C'\fR, but indeed works even in interval and manual
2032rescheduling modes.
2033.IP "ev_tstamp offset [read\-write]" 4
2034.IX Item "ev_tstamp offset [read-write]"
2035When repeating, this contains the offset value, otherwise this is the
2036absolute point in time (the \f(CW\*(C`offset\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR,
2037although libev might modify this value for better numerical stability).
2038.Sp
2039Can be modified any time, but changes only take effect when the periodic
2040timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
2041.IP "ev_tstamp interval [read\-write]" 4
2042.IX Item "ev_tstamp interval [read-write]"
2043The current interval value. Can be modified any time, but changes only
2044take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
2045called.
2046.IP "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read\-write]" 4
2047.IX Item "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]"
2048The current reschedule callback, or \f(CW0\fR, if this functionality is
2049switched off. Can be changed any time, but changes only take effect when
2050the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1024.PP 2051.PP
2052\fIExamples\fR
2053.IX Subsection "Examples"
2054.PP
1025Example: call a callback every hour, or, more precisely, whenever the 2055Example: Call a callback every hour, or, more precisely, whenever the
1026system clock is divisible by 3600. The callback invocation times have 2056system time is divisible by 3600. The callback invocation times have
1027potentially a lot of jittering, but good long-term stability. 2057potentially a lot of jitter, but good long-term stability.
1028.PP 2058.PP
1029.Vb 5 2059.Vb 5
1030\& static void 2060\& static void
1031\& clock_cb (struct ev_loop *loop, struct ev_io *w, int revents) 2061\& clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1032\& { 2062\& {
1033\& ... its now a full hour (UTC, or TAI or whatever your clock follows) 2063\& ... its now a full hour (UTC, or TAI or whatever your clock follows)
1034\& } 2064\& }
1035.Ve 2065\&
1036.PP
1037.Vb 3
1038\& struct ev_periodic hourly_tick; 2066\& ev_periodic hourly_tick;
1039\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0); 2067\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1040\& ev_periodic_start (loop, &hourly_tick); 2068\& ev_periodic_start (loop, &hourly_tick);
1041.Ve 2069.Ve
1042.PP 2070.PP
1043Example: the same as above, but use a reschedule callback to do it: 2071Example: The same as above, but use a reschedule callback to do it:
1044.PP 2072.PP
1045.Vb 1 2073.Vb 1
1046\& #include <math.h> 2074\& #include <math.h>
1047.Ve 2075\&
1048.PP
1049.Vb 5
1050\& static ev_tstamp 2076\& static ev_tstamp
1051\& my_scheduler_cb (struct ev_periodic *w, ev_tstamp now) 2077\& my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1052\& { 2078\& {
1053\& return fmod (now, 3600.) + 3600.; 2079\& return now + (3600. \- fmod (now, 3600.));
1054\& } 2080\& }
1055.Ve 2081\&
1056.PP
1057.Vb 1
1058\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb); 2082\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1059.Ve 2083.Ve
1060.PP 2084.PP
1061Example: call a callback every hour, starting now: 2085Example: Call a callback every hour, starting now:
1062.PP 2086.PP
1063.Vb 4 2087.Vb 4
1064\& struct ev_periodic hourly_tick; 2088\& ev_periodic hourly_tick;
1065\& ev_periodic_init (&hourly_tick, clock_cb, 2089\& ev_periodic_init (&hourly_tick, clock_cb,
1066\& fmod (ev_now (loop), 3600.), 3600., 0); 2090\& fmod (ev_now (loop), 3600.), 3600., 0);
1067\& ev_periodic_start (loop, &hourly_tick); 2091\& ev_periodic_start (loop, &hourly_tick);
1068.Ve 2092.Ve
1069.ie n .Sh """ev_signal"" \- signal me when a signal gets signalled" 2093.ie n .Sh """ev_signal"" \- signal me when a signal gets signalled!"
1070.el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled" 2094.el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
1071.IX Subsection "ev_signal - signal me when a signal gets signalled" 2095.IX Subsection "ev_signal - signal me when a signal gets signalled!"
1072Signal watchers will trigger an event when the process receives a specific 2096Signal watchers will trigger an event when the process receives a specific
1073signal one or more times. Even though signals are very asynchronous, libev 2097signal one or more times. Even though signals are very asynchronous, libev
1074will try it's best to deliver signals synchronously, i.e. as part of the 2098will try it's best to deliver signals synchronously, i.e. as part of the
1075normal event processing, like any other event. 2099normal event processing, like any other event.
1076.PP 2100.PP
2101If you want signals asynchronously, just use \f(CW\*(C`sigaction\*(C'\fR as you would
2102do without libev and forget about sharing the signal. You can even use
2103\&\f(CW\*(C`ev_async\*(C'\fR from a signal handler to synchronously wake up an event loop.
2104.PP
1077You can configure as many watchers as you like per signal. Only when the 2105You can configure as many watchers as you like per signal. Only when the
1078first watcher gets started will libev actually register a signal watcher 2106first watcher gets started will libev actually register a signal handler
1079with the kernel (thus it coexists with your own signal handlers as long 2107with the kernel (thus it coexists with your own signal handlers as long as
1080as you don't register any with libev). Similarly, when the last signal 2108you don't register any with libev for the same signal). Similarly, when
1081watcher for a signal is stopped libev will reset the signal handler to 2109the last signal watcher for a signal is stopped, libev will reset the
1082\&\s-1SIG_DFL\s0 (regardless of what it was set to before). 2110signal handler to \s-1SIG_DFL\s0 (regardless of what it was set to before).
2111.PP
2112If possible and supported, libev will install its handlers with
2113\&\f(CW\*(C`SA_RESTART\*(C'\fR behaviour enabled, so system calls should not be unduly
2114interrupted. If you have a problem with system calls getting interrupted by
2115signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher and unblock
2116them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher.
2117.PP
2118\fIWatcher-Specific Functions and Data Members\fR
2119.IX Subsection "Watcher-Specific Functions and Data Members"
1083.IP "ev_signal_init (ev_signal *, callback, int signum)" 4 2120.IP "ev_signal_init (ev_signal *, callback, int signum)" 4
1084.IX Item "ev_signal_init (ev_signal *, callback, int signum)" 2121.IX Item "ev_signal_init (ev_signal *, callback, int signum)"
1085.PD 0 2122.PD 0
1086.IP "ev_signal_set (ev_signal *, int signum)" 4 2123.IP "ev_signal_set (ev_signal *, int signum)" 4
1087.IX Item "ev_signal_set (ev_signal *, int signum)" 2124.IX Item "ev_signal_set (ev_signal *, int signum)"
1088.PD 2125.PD
1089Configures the watcher to trigger on the given signal number (usually one 2126Configures the watcher to trigger on the given signal number (usually one
1090of the \f(CW\*(C`SIGxxx\*(C'\fR constants). 2127of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
2128.IP "int signum [read\-only]" 4
2129.IX Item "int signum [read-only]"
2130The signal the watcher watches out for.
2131.PP
2132\fIExamples\fR
2133.IX Subsection "Examples"
2134.PP
2135Example: Try to exit cleanly on \s-1SIGINT\s0.
2136.PP
2137.Vb 5
2138\& static void
2139\& sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
2140\& {
2141\& ev_unloop (loop, EVUNLOOP_ALL);
2142\& }
2143\&
2144\& ev_signal signal_watcher;
2145\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
2146\& ev_signal_start (loop, &signal_watcher);
2147.Ve
1091.ie n .Sh """ev_child"" \- wait for pid status changes" 2148.ie n .Sh """ev_child"" \- watch out for process status changes"
1092.el .Sh "\f(CWev_child\fP \- wait for pid status changes" 2149.el .Sh "\f(CWev_child\fP \- watch out for process status changes"
1093.IX Subsection "ev_child - wait for pid status changes" 2150.IX Subsection "ev_child - watch out for process status changes"
1094Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to 2151Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
1095some child status changes (most typically when a child of yours dies). 2152some child status changes (most typically when a child of yours dies or
2153exits). It is permissible to install a child watcher \fIafter\fR the child
2154has been forked (which implies it might have already exited), as long
2155as the event loop isn't entered (or is continued from a watcher), i.e.,
2156forking and then immediately registering a watcher for the child is fine,
2157but forking and registering a watcher a few event loop iterations later is
2158not.
2159.PP
2160Only the default event loop is capable of handling signals, and therefore
2161you can only register child watchers in the default event loop.
2162.PP
2163\fIProcess Interaction\fR
2164.IX Subsection "Process Interaction"
2165.PP
2166Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is
2167initialised. This is necessary to guarantee proper behaviour even if
2168the first child watcher is started after the child exits. The occurrence
2169of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done
2170synchronously as part of the event loop processing. Libev always reaps all
2171children, even ones not watched.
2172.PP
2173\fIOverriding the Built-In Processing\fR
2174.IX Subsection "Overriding the Built-In Processing"
2175.PP
2176Libev offers no special support for overriding the built-in child
2177processing, but if your application collides with libev's default child
2178handler, you can override it easily by installing your own handler for
2179\&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the
2180default loop never gets destroyed. You are encouraged, however, to use an
2181event-based approach to child reaping and thus use libev's support for
2182that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely.
2183.PP
2184\fIStopping the Child Watcher\fR
2185.IX Subsection "Stopping the Child Watcher"
2186.PP
2187Currently, the child watcher never gets stopped, even when the
2188child terminates, so normally one needs to stop the watcher in the
2189callback. Future versions of libev might stop the watcher automatically
2190when a child exit is detected.
2191.PP
2192\fIWatcher-Specific Functions and Data Members\fR
2193.IX Subsection "Watcher-Specific Functions and Data Members"
1096.IP "ev_child_init (ev_child *, callback, int pid)" 4 2194.IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4
1097.IX Item "ev_child_init (ev_child *, callback, int pid)" 2195.IX Item "ev_child_init (ev_child *, callback, int pid, int trace)"
1098.PD 0 2196.PD 0
1099.IP "ev_child_set (ev_child *, int pid)" 4 2197.IP "ev_child_set (ev_child *, int pid, int trace)" 4
1100.IX Item "ev_child_set (ev_child *, int pid)" 2198.IX Item "ev_child_set (ev_child *, int pid, int trace)"
1101.PD 2199.PD
1102Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or 2200Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
1103\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look 2201\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
1104at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see 2202at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
1105the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems 2203the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
1106\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the 2204\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
1107process causing the status change. 2205process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only
2206activate the watcher when the process terminates) or \f(CW1\fR (additionally
2207activate the watcher when the process is stopped or continued).
2208.IP "int pid [read\-only]" 4
2209.IX Item "int pid [read-only]"
2210The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
2211.IP "int rpid [read\-write]" 4
2212.IX Item "int rpid [read-write]"
2213The process id that detected a status change.
2214.IP "int rstatus [read\-write]" 4
2215.IX Item "int rstatus [read-write]"
2216The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
2217\&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
1108.PP 2218.PP
1109Example: try to exit cleanly on \s-1SIGINT\s0 and \s-1SIGTERM\s0. 2219\fIExamples\fR
2220.IX Subsection "Examples"
1110.PP 2221.PP
2222Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for
2223its completion.
2224.PP
1111.Vb 5 2225.Vb 1
2226\& ev_child cw;
2227\&
1112\& static void 2228\& static void
1113\& sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents) 2229\& child_cb (EV_P_ ev_child *w, int revents)
1114\& { 2230\& {
1115\& ev_unloop (loop, EVUNLOOP_ALL); 2231\& ev_child_stop (EV_A_ w);
2232\& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus);
1116\& } 2233\& }
2234\&
2235\& pid_t pid = fork ();
2236\&
2237\& if (pid < 0)
2238\& // error
2239\& else if (pid == 0)
2240\& {
2241\& // the forked child executes here
2242\& exit (1);
2243\& }
2244\& else
2245\& {
2246\& ev_child_init (&cw, child_cb, pid, 0);
2247\& ev_child_start (EV_DEFAULT_ &cw);
2248\& }
1117.Ve 2249.Ve
2250.ie n .Sh """ev_stat"" \- did the file attributes just change?"
2251.el .Sh "\f(CWev_stat\fP \- did the file attributes just change?"
2252.IX Subsection "ev_stat - did the file attributes just change?"
2253This watches a file system path for attribute changes. That is, it calls
2254\&\f(CW\*(C`stat\*(C'\fR on that path in regular intervals (or when the \s-1OS\s0 says it changed)
2255and sees if it changed compared to the last time, invoking the callback if
2256it did.
1118.PP 2257.PP
2258The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does
2259not exist\*(R" is a status change like any other. The condition \*(L"path does not
2260exist\*(R" (or more correctly \*(L"path cannot be stat'ed\*(R") is signified by the
2261\&\f(CW\*(C`st_nlink\*(C'\fR field being zero (which is otherwise always forced to be at
2262least one) and all the other fields of the stat buffer having unspecified
2263contents.
2264.PP
2265The path \fImust not\fR end in a slash or contain special components such as
2266\&\f(CW\*(C`.\*(C'\fR or \f(CW\*(C`..\*(C'\fR. The path \fIshould\fR be absolute: If it is relative and
2267your working directory changes, then the behaviour is undefined.
2268.PP
2269Since there is no portable change notification interface available, the
2270portable implementation simply calls \f(CWstat(2)\fR regularly on the path
2271to see if it changed somehow. You can specify a recommended polling
2272interval for this case. If you specify a polling interval of \f(CW0\fR (highly
2273recommended!) then a \fIsuitable, unspecified default\fR value will be used
2274(which you can expect to be around five seconds, although this might
2275change dynamically). Libev will also impose a minimum interval which is
2276currently around \f(CW0.1\fR, but that's usually overkill.
2277.PP
2278This watcher type is not meant for massive numbers of stat watchers,
2279as even with OS-supported change notifications, this can be
2280resource-intensive.
2281.PP
2282At the time of this writing, the only OS-specific interface implemented
2283is the Linux inotify interface (implementing kqueue support is left as an
2284exercise for the reader. Note, however, that the author sees no way of
2285implementing \f(CW\*(C`ev_stat\*(C'\fR semantics with kqueue, except as a hint).
2286.PP
2287\fI\s-1ABI\s0 Issues (Largefile Support)\fR
2288.IX Subsection "ABI Issues (Largefile Support)"
2289.PP
2290Libev by default (unless the user overrides this) uses the default
2291compilation environment, which means that on systems with large file
2292support disabled by default, you get the 32 bit version of the stat
2293structure. When using the library from programs that change the \s-1ABI\s0 to
2294use 64 bit file offsets the programs will fail. In that case you have to
2295compile libev with the same flags to get binary compatibility. This is
2296obviously the case with any flags that change the \s-1ABI\s0, but the problem is
2297most noticeably displayed with ev_stat and large file support.
2298.PP
2299The solution for this is to lobby your distribution maker to make large
2300file interfaces available by default (as e.g. FreeBSD does) and not
2301optional. Libev cannot simply switch on large file support because it has
2302to exchange stat structures with application programs compiled using the
2303default compilation environment.
2304.PP
2305\fIInotify and Kqueue\fR
2306.IX Subsection "Inotify and Kqueue"
2307.PP
2308When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev and present at
2309runtime, it will be used to speed up change detection where possible. The
2310inotify descriptor will be created lazily when the first \f(CW\*(C`ev_stat\*(C'\fR
2311watcher is being started.
2312.PP
2313Inotify presence does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
2314except that changes might be detected earlier, and in some cases, to avoid
2315making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presence of inotify support
2316there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling,
2317but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
2318many bugs), the path exists (i.e. stat succeeds), and the path resides on
2319a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
2320xfs are fully working) libev usually gets away without polling.
2321.PP
2322There is no support for kqueue, as apparently it cannot be used to
2323implement this functionality, due to the requirement of having a file
2324descriptor open on the object at all times, and detecting renames, unlinks
2325etc. is difficult.
2326.PP
2327\fI\f(CI\*(C`stat ()\*(C'\fI is a synchronous operation\fR
2328.IX Subsection "stat () is a synchronous operation"
2329.PP
2330Libev doesn't normally do any kind of I/O itself, and so is not blocking
2331the process. The exception are \f(CW\*(C`ev_stat\*(C'\fR watchers \- those call \f(CW\*(C`stat
2332()\*(C'\fR, which is a synchronous operation.
2333.PP
2334For local paths, this usually doesn't matter: unless the system is very
2335busy or the intervals between stat's are large, a stat call will be fast,
2336as the path data is usually in memory already (except when starting the
2337watcher).
2338.PP
2339For networked file systems, calling \f(CW\*(C`stat ()\*(C'\fR can block an indefinite
2340time due to network issues, and even under good conditions, a stat call
2341often takes multiple milliseconds.
2342.PP
2343Therefore, it is best to avoid using \f(CW\*(C`ev_stat\*(C'\fR watchers on networked
2344paths, although this is fully supported by libev.
2345.PP
2346\fIThe special problem of stat time resolution\fR
2347.IX Subsection "The special problem of stat time resolution"
2348.PP
2349The \f(CW\*(C`stat ()\*(C'\fR system call only supports full-second resolution portably,
2350and even on systems where the resolution is higher, most file systems
2351still only support whole seconds.
2352.PP
2353That means that, if the time is the only thing that changes, you can
2354easily miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and
2355calls your callback, which does something. When there is another update
2356within the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect unless the
2357stat data does change in other ways (e.g. file size).
2358.PP
2359The solution to this is to delay acting on a change for slightly more
2360than a second (or till slightly after the next full second boundary), using
2361a roughly one-second-delay \f(CW\*(C`ev_timer\*(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02);
2362ev_timer_again (loop, w)\*(C'\fR).
2363.PP
2364The \f(CW.02\fR offset is added to work around small timing inconsistencies
2365of some operating systems (where the second counter of the current time
2366might be be delayed. One such system is the Linux kernel, where a call to
2367\&\f(CW\*(C`gettimeofday\*(C'\fR might return a timestamp with a full second later than
2368a subsequent \f(CW\*(C`time\*(C'\fR call \- if the equivalent of \f(CW\*(C`time ()\*(C'\fR is used to
2369update file times then there will be a small window where the kernel uses
2370the previous second to update file times but libev might already execute
2371the timer callback).
2372.PP
2373\fIWatcher-Specific Functions and Data Members\fR
2374.IX Subsection "Watcher-Specific Functions and Data Members"
2375.IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
2376.IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
2377.PD 0
2378.IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4
2379.IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)"
2380.PD
2381Configures the watcher to wait for status changes of the given
2382\&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to
2383be detected and should normally be specified as \f(CW0\fR to let libev choose
2384a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same
2385path for as long as the watcher is active.
2386.Sp
2387The callback will receive an \f(CW\*(C`EV_STAT\*(C'\fR event when a change was detected,
2388relative to the attributes at the time the watcher was started (or the
2389last change was detected).
2390.IP "ev_stat_stat (loop, ev_stat *)" 4
2391.IX Item "ev_stat_stat (loop, ev_stat *)"
2392Updates the stat buffer immediately with new values. If you change the
2393watched path in your callback, you could call this function to avoid
2394detecting this change (while introducing a race condition if you are not
2395the only one changing the path). Can also be useful simply to find out the
2396new values.
2397.IP "ev_statdata attr [read\-only]" 4
2398.IX Item "ev_statdata attr [read-only]"
2399The most-recently detected attributes of the file. Although the type is
2400\&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
2401suitable for your system, but you can only rely on the POSIX-standardised
2402members to be present. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there was
2403some error while \f(CW\*(C`stat\*(C'\fRing the file.
2404.IP "ev_statdata prev [read\-only]" 4
2405.IX Item "ev_statdata prev [read-only]"
2406The previous attributes of the file. The callback gets invoked whenever
2407\&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR, or, more precisely, one or more of these members
2408differ: \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,
2409\&\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.
2410.IP "ev_tstamp interval [read\-only]" 4
2411.IX Item "ev_tstamp interval [read-only]"
2412The specified interval.
2413.IP "const char *path [read\-only]" 4
2414.IX Item "const char *path [read-only]"
2415The file system path that is being watched.
2416.PP
2417\fIExamples\fR
2418.IX Subsection "Examples"
2419.PP
2420Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
2421.PP
2422.Vb 10
2423\& static void
2424\& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
2425\& {
2426\& /* /etc/passwd changed in some way */
2427\& if (w\->attr.st_nlink)
2428\& {
2429\& printf ("passwd current size %ld\en", (long)w\->attr.st_size);
2430\& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime);
2431\& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime);
2432\& }
2433\& else
2434\& /* you shalt not abuse printf for puts */
2435\& puts ("wow, /etc/passwd is not there, expect problems. "
2436\& "if this is windows, they already arrived\en");
2437\& }
2438\&
2439\& ...
2440\& ev_stat passwd;
2441\&
2442\& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
2443\& ev_stat_start (loop, &passwd);
2444.Ve
2445.PP
2446Example: Like above, but additionally use a one-second delay so we do not
2447miss updates (however, frequent updates will delay processing, too, so
2448one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
2449\&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
2450.PP
1119.Vb 3 2451.Vb 2
1120\& struct ev_signal signal_watcher; 2452\& static ev_stat passwd;
1121\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT); 2453\& static ev_timer timer;
1122\& ev_signal_start (loop, &sigint_cb); 2454\&
2455\& static void
2456\& timer_cb (EV_P_ ev_timer *w, int revents)
2457\& {
2458\& ev_timer_stop (EV_A_ w);
2459\&
2460\& /* now it\*(Aqs one second after the most recent passwd change */
2461\& }
2462\&
2463\& static void
2464\& stat_cb (EV_P_ ev_stat *w, int revents)
2465\& {
2466\& /* reset the one\-second timer */
2467\& ev_timer_again (EV_A_ &timer);
2468\& }
2469\&
2470\& ...
2471\& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
2472\& ev_stat_start (loop, &passwd);
2473\& ev_timer_init (&timer, timer_cb, 0., 1.02);
1123.Ve 2474.Ve
1124.ie n .Sh """ev_idle"" \- when you've got nothing better to do" 2475.ie n .Sh """ev_idle"" \- when you've got nothing better to do..."
1125.el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do" 2476.el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do..."
1126.IX Subsection "ev_idle - when you've got nothing better to do" 2477.IX Subsection "ev_idle - when you've got nothing better to do..."
1127Idle watchers trigger events when there are no other events are pending 2478Idle watchers trigger events when no other events of the same or higher
1128(prepare, check and other idle watchers do not count). That is, as long 2479priority are pending (prepare, check and other idle watchers do not count
1129as your process is busy handling sockets or timeouts (or even signals, 2480as receiving \*(L"events\*(R").
1130imagine) it will not be triggered. But when your process is idle all idle 2481.PP
1131watchers are being called again and again, once per event loop iteration \- 2482That is, as long as your process is busy handling sockets or timeouts
2483(or even signals, imagine) of the same or higher priority it will not be
2484triggered. But when your process is idle (or only lower-priority watchers
2485are pending), the idle watchers are being called once per event loop
1132until stopped, that is, or your process receives more events and becomes 2486iteration \- until stopped, that is, or your process receives more events
1133busy. 2487and becomes busy again with higher priority stuff.
1134.PP 2488.PP
1135The most noteworthy effect is that as long as any idle watchers are 2489The most noteworthy effect is that as long as any idle watchers are
1136active, the process will not block when waiting for new events. 2490active, the process will not block when waiting for new events.
1137.PP 2491.PP
1138Apart from keeping your process non-blocking (which is a useful 2492Apart from keeping your process non-blocking (which is a useful
1139effect on its own sometimes), idle watchers are a good place to do 2493effect on its own sometimes), idle watchers are a good place to do
1140\&\*(L"pseudo\-background processing\*(R", or delay processing stuff to after the 2494\&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the
1141event loop has handled all outstanding events. 2495event loop has handled all outstanding events.
2496.PP
2497\fIWatcher-Specific Functions and Data Members\fR
2498.IX Subsection "Watcher-Specific Functions and Data Members"
1142.IP "ev_idle_init (ev_signal *, callback)" 4 2499.IP "ev_idle_init (ev_idle *, callback)" 4
1143.IX Item "ev_idle_init (ev_signal *, callback)" 2500.IX Item "ev_idle_init (ev_idle *, callback)"
1144Initialises and configures the idle watcher \- it has no parameters of any 2501Initialises and configures the idle watcher \- it has no parameters of any
1145kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless, 2502kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
1146believe me. 2503believe me.
1147.PP 2504.PP
2505\fIExamples\fR
2506.IX Subsection "Examples"
2507.PP
1148Example: dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR, start it, and in the 2508Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the
1149callback, free it. Alos, use no error checking, as usual. 2509callback, free it. Also, use no error checking, as usual.
1150.PP 2510.PP
1151.Vb 7 2511.Vb 7
1152\& static void 2512\& static void
1153\& idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents) 2513\& idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1154\& { 2514\& {
1155\& free (w); 2515\& free (w);
1156\& // now do something you wanted to do when the program has 2516\& // now do something you wanted to do when the program has
1157\& // no longer asnything immediate to do. 2517\& // no longer anything immediate to do.
1158\& } 2518\& }
1159.Ve 2519\&
1160.PP
1161.Vb 3
1162\& struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle)); 2520\& ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1163\& ev_idle_init (idle_watcher, idle_cb); 2521\& ev_idle_init (idle_watcher, idle_cb);
1164\& ev_idle_start (loop, idle_cb); 2522\& ev_idle_start (loop, idle_cb);
1165.Ve 2523.Ve
1166.ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop" 2524.ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop!"
1167.el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop" 2525.el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
1168.IX Subsection "ev_prepare and ev_check - customise your event loop" 2526.IX Subsection "ev_prepare and ev_check - customise your event loop!"
1169Prepare and check watchers are usually (but not always) used in tandem: 2527Prepare and check watchers are usually (but not always) used in pairs:
1170prepare watchers get invoked before the process blocks and check watchers 2528prepare watchers get invoked before the process blocks and check watchers
1171afterwards. 2529afterwards.
1172.PP 2530.PP
2531You \fImust not\fR call \f(CW\*(C`ev_loop\*(C'\fR or similar functions that enter
2532the current event loop from either \f(CW\*(C`ev_prepare\*(C'\fR or \f(CW\*(C`ev_check\*(C'\fR
2533watchers. Other loops than the current one are fine, however. The
2534rationale behind this is that you do not need to check for recursion in
2535those watchers, i.e. the sequence will always be \f(CW\*(C`ev_prepare\*(C'\fR, blocking,
2536\&\f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each kind they will always be
2537called in pairs bracketing the blocking call.
2538.PP
1173Their main purpose is to integrate other event mechanisms into libev and 2539Their main purpose is to integrate other event mechanisms into libev and
1174their use is somewhat advanced. This could be used, for example, to track 2540their use is somewhat advanced. They could be used, for example, to track
1175variable changes, implement your own watchers, integrate net-snmp or a 2541variable changes, implement your own watchers, integrate net-snmp or a
1176coroutine library and lots more. 2542coroutine library and lots more. They are also occasionally useful if
2543you cache some data and want to flush it before blocking (for example,
2544in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
2545watcher).
1177.PP 2546.PP
1178This is done by examining in each prepare call which file descriptors need 2547This is done by examining in each prepare call which file descriptors
1179to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers for 2548need to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers
1180them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many libraries 2549for them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many
1181provide just this functionality). Then, in the check watcher you check for 2550libraries provide exactly this functionality). Then, in the check watcher,
1182any events that occured (by checking the pending status of all watchers 2551you check for any events that occurred (by checking the pending status
1183and stopping them) and call back into the library. The I/O and timer 2552of all watchers and stopping them) and call back into the library. The
1184callbacks will never actually be called (but must be valid nevertheless, 2553I/O and timer callbacks will never actually be called (but must be valid
1185because you never know, you know?). 2554nevertheless, because you never know, you know?).
1186.PP 2555.PP
1187As another example, the Perl Coro module uses these hooks to integrate 2556As another example, the Perl Coro module uses these hooks to integrate
1188coroutines into libev programs, by yielding to other active coroutines 2557coroutines into libev programs, by yielding to other active coroutines
1189during each prepare and only letting the process block if no coroutines 2558during each prepare and only letting the process block if no coroutines
1190are ready to run (it's actually more complicated: it only runs coroutines 2559are ready to run (it's actually more complicated: it only runs coroutines
1191with priority higher than or equal to the event loop and one coroutine 2560with priority higher than or equal to the event loop and one coroutine
1192of lower priority, but only once, using idle watchers to keep the event 2561of lower priority, but only once, using idle watchers to keep the event
1193loop from blocking if lower-priority coroutines are active, thus mapping 2562loop from blocking if lower-priority coroutines are active, thus mapping
1194low-priority coroutines to idle/background tasks). 2563low-priority coroutines to idle/background tasks).
2564.PP
2565It is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR)
2566priority, to ensure that they are being run before any other watchers
2567after the poll (this doesn't matter for \f(CW\*(C`ev_prepare\*(C'\fR watchers).
2568.PP
2569Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, too) should not
2570activate (\*(L"feed\*(R") events into libev. While libev fully supports this, they
2571might get executed before other \f(CW\*(C`ev_check\*(C'\fR watchers did their job. As
2572\&\f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other (non-libev) event
2573loops those other event loops might be in an unusable state until their
2574\&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with
2575others).
2576.PP
2577\fIWatcher-Specific Functions and Data Members\fR
2578.IX Subsection "Watcher-Specific Functions and Data Members"
1195.IP "ev_prepare_init (ev_prepare *, callback)" 4 2579.IP "ev_prepare_init (ev_prepare *, callback)" 4
1196.IX Item "ev_prepare_init (ev_prepare *, callback)" 2580.IX Item "ev_prepare_init (ev_prepare *, callback)"
1197.PD 0 2581.PD 0
1198.IP "ev_check_init (ev_check *, callback)" 4 2582.IP "ev_check_init (ev_check *, callback)" 4
1199.IX Item "ev_check_init (ev_check *, callback)" 2583.IX Item "ev_check_init (ev_check *, callback)"
1200.PD 2584.PD
1201Initialises and configures the prepare or check watcher \- they have no 2585Initialises and configures the prepare or check watcher \- they have no
1202parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR 2586parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
1203macros, but using them is utterly, utterly and completely pointless. 2587macros, but using them is utterly, utterly, utterly and completely
2588pointless.
1204.PP 2589.PP
1205Example: *TODO*. 2590\fIExamples\fR
2591.IX Subsection "Examples"
2592.PP
2593There are a number of principal ways to embed other event loops or modules
2594into libev. Here are some ideas on how to include libadns into libev
2595(there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could
2596use as a working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR embeds a
2597Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 into the
2598Glib event loop).
2599.PP
2600Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
2601and in a check watcher, destroy them and call into libadns. What follows
2602is pseudo-code only of course. This requires you to either use a low
2603priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as
2604the callbacks for the IO/timeout watchers might not have been called yet.
2605.PP
2606.Vb 2
2607\& static ev_io iow [nfd];
2608\& static ev_timer tw;
2609\&
2610\& static void
2611\& io_cb (struct ev_loop *loop, ev_io *w, int revents)
2612\& {
2613\& }
2614\&
2615\& // create io watchers for each fd and a timer before blocking
2616\& static void
2617\& adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
2618\& {
2619\& int timeout = 3600000;
2620\& struct pollfd fds [nfd];
2621\& // actual code will need to loop here and realloc etc.
2622\& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2623\&
2624\& /* the callback is illegal, but won\*(Aqt be called as we stop during check */
2625\& ev_timer_init (&tw, 0, timeout * 1e\-3);
2626\& ev_timer_start (loop, &tw);
2627\&
2628\& // create one ev_io per pollfd
2629\& for (int i = 0; i < nfd; ++i)
2630\& {
2631\& ev_io_init (iow + i, io_cb, fds [i].fd,
2632\& ((fds [i].events & POLLIN ? EV_READ : 0)
2633\& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
2634\&
2635\& fds [i].revents = 0;
2636\& ev_io_start (loop, iow + i);
2637\& }
2638\& }
2639\&
2640\& // stop all watchers after blocking
2641\& static void
2642\& adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
2643\& {
2644\& ev_timer_stop (loop, &tw);
2645\&
2646\& for (int i = 0; i < nfd; ++i)
2647\& {
2648\& // set the relevant poll flags
2649\& // could also call adns_processreadable etc. here
2650\& struct pollfd *fd = fds + i;
2651\& int revents = ev_clear_pending (iow + i);
2652\& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN;
2653\& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT;
2654\&
2655\& // now stop the watcher
2656\& ev_io_stop (loop, iow + i);
2657\& }
2658\&
2659\& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
2660\& }
2661.Ve
2662.PP
2663Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR
2664in the prepare watcher and would dispose of the check watcher.
2665.PP
2666Method 3: If the module to be embedded supports explicit event
2667notification (libadns does), you can also make use of the actual watcher
2668callbacks, and only destroy/create the watchers in the prepare watcher.
2669.PP
2670.Vb 5
2671\& static void
2672\& timer_cb (EV_P_ ev_timer *w, int revents)
2673\& {
2674\& adns_state ads = (adns_state)w\->data;
2675\& update_now (EV_A);
2676\&
2677\& adns_processtimeouts (ads, &tv_now);
2678\& }
2679\&
2680\& static void
2681\& io_cb (EV_P_ ev_io *w, int revents)
2682\& {
2683\& adns_state ads = (adns_state)w\->data;
2684\& update_now (EV_A);
2685\&
2686\& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now);
2687\& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now);
2688\& }
2689\&
2690\& // do not ever call adns_afterpoll
2691.Ve
2692.PP
2693Method 4: Do not use a prepare or check watcher because the module you
2694want to embed is not flexible enough to support it. Instead, you can
2695override their poll function. The drawback with this solution is that the
2696main loop is now no longer controllable by \s-1EV\s0. The \f(CW\*(C`Glib::EV\*(C'\fR module uses
2697this approach, effectively embedding \s-1EV\s0 as a client into the horrible
2698libglib event loop.
2699.PP
2700.Vb 4
2701\& static gint
2702\& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
2703\& {
2704\& int got_events = 0;
2705\&
2706\& for (n = 0; n < nfds; ++n)
2707\& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
2708\&
2709\& if (timeout >= 0)
2710\& // create/start timer
2711\&
2712\& // poll
2713\& ev_loop (EV_A_ 0);
2714\&
2715\& // stop timer again
2716\& if (timeout >= 0)
2717\& ev_timer_stop (EV_A_ &to);
2718\&
2719\& // stop io watchers again \- their callbacks should have set
2720\& for (n = 0; n < nfds; ++n)
2721\& ev_io_stop (EV_A_ iow [n]);
2722\&
2723\& return got_events;
2724\& }
2725.Ve
1206.ie n .Sh """ev_embed"" \- when one backend isn't enough" 2726.ie n .Sh """ev_embed"" \- when one backend isn't enough..."
1207.el .Sh "\f(CWev_embed\fP \- when one backend isn't enough" 2727.el .Sh "\f(CWev_embed\fP \- when one backend isn't enough..."
1208.IX Subsection "ev_embed - when one backend isn't enough" 2728.IX Subsection "ev_embed - when one backend isn't enough..."
1209This is a rather advanced watcher type that lets you embed one event loop 2729This is a rather advanced watcher type that lets you embed one event loop
1210into another. 2730into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
2731loop, other types of watchers might be handled in a delayed or incorrect
2732fashion and must not be used).
1211.PP 2733.PP
1212There are primarily two reasons you would want that: work around bugs and 2734There are primarily two reasons you would want that: work around bugs and
1213prioritise I/O. 2735prioritise I/O.
1214.PP 2736.PP
1215As an example for a bug workaround, the kqueue backend might only support 2737As an example for a bug workaround, the kqueue backend might only support
1216sockets on some platform, so it is unusable as generic backend, but you 2738sockets on some platform, so it is unusable as generic backend, but you
1217still want to make use of it because you have many sockets and it scales 2739still want to make use of it because you have many sockets and it scales
1218so nicely. In this case, you would create a kqueue-based loop and embed it 2740so nicely. In this case, you would create a kqueue-based loop and embed
1219into your default loop (which might use e.g. poll). Overall operation will 2741it into your default loop (which might use e.g. poll). Overall operation
1220be a bit slower because first libev has to poll and then call kevent, but 2742will be a bit slower because first libev has to call \f(CW\*(C`poll\*(C'\fR and then
1221at least you can use both at what they are best. 2743\&\f(CW\*(C`kevent\*(C'\fR, but at least you can use both mechanisms for what they are
2744best: \f(CW\*(C`kqueue\*(C'\fR for scalable sockets and \f(CW\*(C`poll\*(C'\fR if you want it to work :)
1222.PP 2745.PP
1223As for prioritising I/O: rarely you have the case where some fds have 2746As for prioritising I/O: under rare circumstances you have the case where
1224to be watched and handled very quickly (with low latency), and even 2747some fds have to be watched and handled very quickly (with low latency),
1225priorities and idle watchers might have too much overhead. In this case 2748and even priorities and idle watchers might have too much overhead. In
1226you would put all the high priority stuff in one loop and all the rest in 2749this case you would put all the high priority stuff in one loop and all
1227a second one, and embed the second one in the first. 2750the rest in a second one, and embed the second one in the first.
1228.PP 2751.PP
1229As long as the watcher is started it will automatically handle events. The 2752As long as the watcher is active, the callback will be invoked every
1230callback will be invoked whenever some events have been handled. You can 2753time there might be events pending in the embedded loop. The callback
1231set the callback to \f(CW0\fR to avoid having to specify one if you are not 2754must then call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single
1232interested in that. 2755sweep and invoke their callbacks (the callback doesn't need to invoke the
2756\&\f(CW\*(C`ev_embed_sweep\*(C'\fR function directly, it could also start an idle watcher
2757to give the embedded loop strictly lower priority for example).
1233.PP 2758.PP
1234Also, there have not currently been made special provisions for forking: 2759You can also set the callback to \f(CW0\fR, in which case the embed watcher
1235when you fork, you not only have to call \f(CW\*(C`ev_loop_fork\*(C'\fR on both loops, 2760will automatically execute the embedded loop sweep whenever necessary.
1236but you will also have to stop and restart any \f(CW\*(C`ev_embed\*(C'\fR watchers
1237yourself.
1238.PP 2761.PP
2762Fork detection will be handled transparently while the \f(CW\*(C`ev_embed\*(C'\fR watcher
2763is active, i.e., the embedded loop will automatically be forked when the
2764embedding loop forks. In other cases, the user is responsible for calling
2765\&\f(CW\*(C`ev_loop_fork\*(C'\fR on the embedded loop.
2766.PP
1239Unfortunately, not all backends are embeddable, only the ones returned by 2767Unfortunately, not all backends are embeddable: only the ones returned by
1240\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any 2768\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
1241portable one. 2769portable one.
1242.PP 2770.PP
1243So when you want to use this feature you will always have to be prepared 2771So when you want to use this feature you will always have to be prepared
1244that you cannot get an embeddable loop. The recommended way to get around 2772that you cannot get an embeddable loop. The recommended way to get around
1245this is to have a separate variables for your embeddable loop, try to 2773this is to have a separate variables for your embeddable loop, try to
1246create it, and if that fails, use the normal loop for everything: 2774create it, and if that fails, use the normal loop for everything.
2775.PP
2776\fI\f(CI\*(C`ev_embed\*(C'\fI and fork\fR
2777.IX Subsection "ev_embed and fork"
2778.PP
2779While the \f(CW\*(C`ev_embed\*(C'\fR watcher is running, forks in the embedding loop will
2780automatically be applied to the embedded loop as well, so no special
2781fork handling is required in that case. When the watcher is not running,
2782however, it is still the task of the libev user to call \f(CW\*(C`ev_loop_fork ()\*(C'\fR
2783as applicable.
2784.PP
2785\fIWatcher-Specific Functions and Data Members\fR
2786.IX Subsection "Watcher-Specific Functions and Data Members"
2787.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
2788.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
2789.PD 0
2790.IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
2791.IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)"
2792.PD
2793Configures the watcher to embed the given loop, which must be
2794embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
2795invoked automatically, otherwise it is the responsibility of the callback
2796to invoke it (it will continue to be called until the sweep has been done,
2797if you do not want that, you need to temporarily stop the embed watcher).
2798.IP "ev_embed_sweep (loop, ev_embed *)" 4
2799.IX Item "ev_embed_sweep (loop, ev_embed *)"
2800Make a single, non-blocking sweep over the embedded loop. This works
2801similarly to \f(CW\*(C`ev_loop (embedded_loop, EVLOOP_NONBLOCK)\*(C'\fR, but in the most
2802appropriate way for embedded loops.
2803.IP "struct ev_loop *other [read\-only]" 4
2804.IX Item "struct ev_loop *other [read-only]"
2805The embedded event loop.
2806.PP
2807\fIExamples\fR
2808.IX Subsection "Examples"
2809.PP
2810Example: Try to get an embeddable event loop and embed it into the default
2811event loop. If that is not possible, use the default loop. The default
2812loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the embeddable loop is stored in
2813\&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the case no embeddable loop can be
2814used).
1247.PP 2815.PP
1248.Vb 3 2816.Vb 3
1249\& struct ev_loop *loop_hi = ev_default_init (0); 2817\& struct ev_loop *loop_hi = ev_default_init (0);
1250\& struct ev_loop *loop_lo = 0; 2818\& struct ev_loop *loop_lo = 0;
1251\& struct ev_embed embed; 2819\& ev_embed embed;
1252.Ve 2820\&
1253.PP
1254.Vb 5
1255\& // see if there is a chance of getting one that works 2821\& // see if there is a chance of getting one that works
1256\& // (remember that a flags value of 0 means autodetection) 2822\& // (remember that a flags value of 0 means autodetection)
1257\& loop_lo = ev_embeddable_backends () & ev_recommended_backends () 2823\& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1258\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ()) 2824\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1259\& : 0; 2825\& : 0;
1260.Ve 2826\&
1261.PP
1262.Vb 8
1263\& // if we got one, then embed it, otherwise default to loop_hi 2827\& // if we got one, then embed it, otherwise default to loop_hi
1264\& if (loop_lo) 2828\& if (loop_lo)
1265\& { 2829\& {
1266\& ev_embed_init (&embed, 0, loop_lo); 2830\& ev_embed_init (&embed, 0, loop_lo);
1267\& ev_embed_start (loop_hi, &embed); 2831\& ev_embed_start (loop_hi, &embed);
1268\& } 2832\& }
1269\& else 2833\& else
1270\& loop_lo = loop_hi; 2834\& loop_lo = loop_hi;
1271.Ve 2835.Ve
1272.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *loop)" 4 2836.PP
1273.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *loop)" 2837Example: Check if kqueue is available but not recommended and create
1274.PD 0 2838a kqueue backend for use with sockets (which usually work with any
1275.IP "ev_embed_set (ev_embed *, callback, struct ev_loop *loop)" 4 2839kqueue implementation). Store the kqueue/socket\-only event loop in
1276.IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *loop)" 2840\&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too).
1277.PD 2841.PP
1278Configures the watcher to embed the given loop, which must be embeddable. 2842.Vb 3
2843\& struct ev_loop *loop = ev_default_init (0);
2844\& struct ev_loop *loop_socket = 0;
2845\& ev_embed embed;
2846\&
2847\& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
2848\& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
2849\& {
2850\& ev_embed_init (&embed, 0, loop_socket);
2851\& ev_embed_start (loop, &embed);
2852\& }
2853\&
2854\& if (!loop_socket)
2855\& loop_socket = loop;
2856\&
2857\& // now use loop_socket for all sockets, and loop for everything else
2858.Ve
2859.ie n .Sh """ev_fork"" \- the audacity to resume the event loop after a fork"
2860.el .Sh "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
2861.IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
2862Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
2863whoever is a good citizen cared to tell libev about it by calling
2864\&\f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the
2865event loop blocks next and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called,
2866and only in the child after the fork. If whoever good citizen calling
2867\&\f(CW\*(C`ev_default_fork\*(C'\fR cheats and calls it in the wrong process, the fork
2868handlers will be invoked, too, of course.
2869.PP
2870\fIThe special problem of life after fork \- how is it possible?\fR
2871.IX Subsection "The special problem of life after fork - how is it possible?"
2872.PP
2873Most uses of \f(CW\*(C`fork()\*(C'\fR consist of forking, then some simple calls to ste
2874up/change the process environment, followed by a call to \f(CW\*(C`exec()\*(C'\fR. This
2875sequence should be handled by libev without any problems.
2876.PP
2877This changes when the application actually wants to do event handling
2878in the child, or both parent in child, in effect \*(L"continuing\*(R" after the
2879fork.
2880.PP
2881The default mode of operation (for libev, with application help to detect
2882forks) is to duplicate all the state in the child, as would be expected
2883when \fIeither\fR the parent \fIor\fR the child process continues.
2884.PP
2885When both processes want to continue using libev, then this is usually the
2886wrong result. In that case, usually one process (typically the parent) is
2887supposed to continue with all watchers in place as before, while the other
2888process typically wants to start fresh, i.e. without any active watchers.
2889.PP
2890The cleanest and most efficient way to achieve that with libev is to
2891simply create a new event loop, which of course will be \*(L"empty\*(R", and
2892use that for new watchers. This has the advantage of not touching more
2893memory than necessary, and thus avoiding the copy-on-write, and the
2894disadvantage of having to use multiple event loops (which do not support
2895signal watchers).
2896.PP
2897When this is not possible, or you want to use the default loop for
2898other reasons, then in the process that wants to start \*(L"fresh\*(R", call
2899\&\f(CW\*(C`ev_default_destroy ()\*(C'\fR followed by \f(CW\*(C`ev_default_loop (...)\*(C'\fR. Destroying
2900the default loop will \*(L"orphan\*(R" (not stop) all registered watchers, so you
2901have to be careful not to execute code that modifies those watchers. Note
2902also that in that case, you have to re-register any signal watchers.
2903.PP
2904\fIWatcher-Specific Functions and Data Members\fR
2905.IX Subsection "Watcher-Specific Functions and Data Members"
2906.IP "ev_fork_init (ev_signal *, callback)" 4
2907.IX Item "ev_fork_init (ev_signal *, callback)"
2908Initialises and configures the fork watcher \- it has no parameters of any
2909kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
2910believe me.
2911.ie n .Sh """ev_async"" \- how to wake up another event loop"
2912.el .Sh "\f(CWev_async\fP \- how to wake up another event loop"
2913.IX Subsection "ev_async - how to wake up another event loop"
2914In general, you cannot use an \f(CW\*(C`ev_loop\*(C'\fR from multiple threads or other
2915asynchronous sources such as signal handlers (as opposed to multiple event
2916loops \- those are of course safe to use in different threads).
2917.PP
2918Sometimes, however, you need to wake up another event loop you do not
2919control, for example because it belongs to another thread. This is what
2920\&\f(CW\*(C`ev_async\*(C'\fR watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you
2921can signal it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal
2922safe.
2923.PP
2924This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals,
2925too, are asynchronous in nature, and signals, too, will be compressed
2926(i.e. the number of callback invocations may be less than the number of
2927\&\f(CW\*(C`ev_async_sent\*(C'\fR calls).
2928.PP
2929Unlike \f(CW\*(C`ev_signal\*(C'\fR watchers, \f(CW\*(C`ev_async\*(C'\fR works with any event loop, not
2930just the default loop.
2931.PP
2932\fIQueueing\fR
2933.IX Subsection "Queueing"
2934.PP
2935\&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason
2936is that the author does not know of a simple (or any) algorithm for a
2937multiple-writer-single-reader queue that works in all cases and doesn't
2938need elaborate support such as pthreads.
2939.PP
2940That means that if you want to queue data, you have to provide your own
2941queue. But at least I can tell you how to implement locking around your
2942queue:
2943.IP "queueing from a signal handler context" 4
2944.IX Item "queueing from a signal handler context"
2945To implement race-free queueing, you simply add to the queue in the signal
2946handler but you block the signal handler in the watcher callback. Here is
2947an example that does that for some fictitious \s-1SIGUSR1\s0 handler:
2948.Sp
2949.Vb 1
2950\& static ev_async mysig;
2951\&
2952\& static void
2953\& sigusr1_handler (void)
2954\& {
2955\& sometype data;
2956\&
2957\& // no locking etc.
2958\& queue_put (data);
2959\& ev_async_send (EV_DEFAULT_ &mysig);
2960\& }
2961\&
2962\& static void
2963\& mysig_cb (EV_P_ ev_async *w, int revents)
2964\& {
2965\& sometype data;
2966\& sigset_t block, prev;
2967\&
2968\& sigemptyset (&block);
2969\& sigaddset (&block, SIGUSR1);
2970\& sigprocmask (SIG_BLOCK, &block, &prev);
2971\&
2972\& while (queue_get (&data))
2973\& process (data);
2974\&
2975\& if (sigismember (&prev, SIGUSR1)
2976\& sigprocmask (SIG_UNBLOCK, &block, 0);
2977\& }
2978.Ve
2979.Sp
2980(Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR
2981instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it
2982either...).
2983.IP "queueing from a thread context" 4
2984.IX Item "queueing from a thread context"
2985The strategy for threads is different, as you cannot (easily) block
2986threads but you can easily preempt them, so to queue safely you need to
2987employ a traditional mutex lock, such as in this pthread example:
2988.Sp
2989.Vb 2
2990\& static ev_async mysig;
2991\& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
2992\&
2993\& static void
2994\& otherthread (void)
2995\& {
2996\& // only need to lock the actual queueing operation
2997\& pthread_mutex_lock (&mymutex);
2998\& queue_put (data);
2999\& pthread_mutex_unlock (&mymutex);
3000\&
3001\& ev_async_send (EV_DEFAULT_ &mysig);
3002\& }
3003\&
3004\& static void
3005\& mysig_cb (EV_P_ ev_async *w, int revents)
3006\& {
3007\& pthread_mutex_lock (&mymutex);
3008\&
3009\& while (queue_get (&data))
3010\& process (data);
3011\&
3012\& pthread_mutex_unlock (&mymutex);
3013\& }
3014.Ve
3015.PP
3016\fIWatcher-Specific Functions and Data Members\fR
3017.IX Subsection "Watcher-Specific Functions and Data Members"
3018.IP "ev_async_init (ev_async *, callback)" 4
3019.IX Item "ev_async_init (ev_async *, callback)"
3020Initialises and configures the async watcher \- it has no parameters of any
3021kind. There is a \f(CW\*(C`ev_async_set\*(C'\fR macro, but using it is utterly pointless,
3022trust me.
3023.IP "ev_async_send (loop, ev_async *)" 4
3024.IX Item "ev_async_send (loop, ev_async *)"
3025Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds
3026an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop. Unlike
3027\&\f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do from other threads, signal or
3028similar contexts (see the discussion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the embedding
3029section below on what exactly this means).
3030.Sp
3031Note that, as with other watchers in libev, multiple events might get
3032compressed into a single callback invocation (another way to look at this
3033is that \f(CW\*(C`ev_async\*(C'\fR watchers are level-triggered, set on \f(CW\*(C`ev_async_send\*(C'\fR,
3034reset when the event loop detects that).
3035.Sp
3036This call incurs the overhead of a system call only once per event loop
3037iteration, so while the overhead might be noticeable, it doesn't apply to
3038repeated calls to \f(CW\*(C`ev_async_send\*(C'\fR for the same event loop.
3039.IP "bool = ev_async_pending (ev_async *)" 4
3040.IX Item "bool = ev_async_pending (ev_async *)"
3041Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the
3042watcher but the event has not yet been processed (or even noted) by the
3043event loop.
3044.Sp
3045\&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When
3046the loop iterates next and checks for the watcher to have become active,
3047it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very
3048quickly check whether invoking the loop might be a good idea.
3049.Sp
3050Not that this does \fInot\fR check whether the watcher itself is pending,
3051only whether it has been requested to make this watcher pending: there
3052is a time window between the event loop checking and resetting the async
3053notification, and the callback being invoked.
1279.SH "OTHER FUNCTIONS" 3054.SH "OTHER FUNCTIONS"
1280.IX Header "OTHER FUNCTIONS" 3055.IX Header "OTHER FUNCTIONS"
1281There are some other functions of possible interest. Described. Here. Now. 3056There are some other functions of possible interest. Described. Here. Now.
1282.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4 3057.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
1283.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 3058.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"
1284This function combines a simple timer and an I/O watcher, calls your 3059This function combines a simple timer and an I/O watcher, calls your
1285callback on whichever event happens first and automatically stop both 3060callback on whichever event happens first and automatically stops both
1286watchers. This is useful if you want to wait for a single event on an fd 3061watchers. This is useful if you want to wait for a single event on an fd
1287or timeout without having to allocate/configure/start/stop/free one or 3062or timeout without having to allocate/configure/start/stop/free one or
1288more watchers yourself. 3063more watchers yourself.
1289.Sp 3064.Sp
1290If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and events 3065If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and the
1291is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for the given \f(CW\*(C`fd\*(C'\fR and 3066\&\f(CW\*(C`events\*(C'\fR argument is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for
1292\&\f(CW\*(C`events\*(C'\fR set will be craeted and started. 3067the given \f(CW\*(C`fd\*(C'\fR and \f(CW\*(C`events\*(C'\fR set will be created and started.
1293.Sp 3068.Sp
1294If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be 3069If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
1295started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and 3070started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
1296repeat = 0) will be started. While \f(CW0\fR is a valid timeout, it is of 3071repeat = 0) will be started. \f(CW0\fR is a valid timeout.
1297dubious value.
1298.Sp 3072.Sp
1299The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets 3073The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets
1300passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of 3074passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
1301\&\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 3075\&\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
1302value passed to \f(CW\*(C`ev_once\*(C'\fR: 3076value passed to \f(CW\*(C`ev_once\*(C'\fR. Note that it is possible to receive \fIboth\fR
3077a timeout and an io event at the same time \- you probably should give io
3078events precedence.
3079.Sp
3080Example: wait up to ten seconds for data to appear on \s-1STDIN_FILENO\s0.
1303.Sp 3081.Sp
1304.Vb 7 3082.Vb 7
1305\& static void stdin_ready (int revents, void *arg) 3083\& static void stdin_ready (int revents, void *arg)
1306\& { 3084\& {
1307\& if (revents & EV_TIMEOUT)
1308\& /* doh, nothing entered */;
1309\& else if (revents & EV_READ) 3085\& if (revents & EV_READ)
1310\& /* stdin might have data for us, joy! */; 3086\& /* stdin might have data for us, joy! */;
3087\& else if (revents & EV_TIMEOUT)
3088\& /* doh, nothing entered */;
1311\& } 3089\& }
1312.Ve 3090\&
1313.Sp
1314.Vb 1
1315\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); 3091\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1316.Ve 3092.Ve
1317.IP "ev_feed_event (loop, watcher, int events)" 4 3093.IP "ev_feed_event (struct ev_loop *, watcher *, int revents)" 4
1318.IX Item "ev_feed_event (loop, watcher, int events)" 3094.IX Item "ev_feed_event (struct ev_loop *, watcher *, int revents)"
1319Feeds the given event set into the event loop, as if the specified event 3095Feeds the given event set into the event loop, as if the specified event
1320had happened for the specified watcher (which must be a pointer to an 3096had happened for the specified watcher (which must be a pointer to an
1321initialised but not necessarily started event watcher). 3097initialised but not necessarily started event watcher).
1322.IP "ev_feed_fd_event (loop, int fd, int revents)" 4 3098.IP "ev_feed_fd_event (struct ev_loop *, int fd, int revents)" 4
1323.IX Item "ev_feed_fd_event (loop, int fd, int revents)" 3099.IX Item "ev_feed_fd_event (struct ev_loop *, int fd, int revents)"
1324Feed an event on the given fd, as if a file descriptor backend detected 3100Feed an event on the given fd, as if a file descriptor backend detected
1325the given events it. 3101the given events it.
1326.IP "ev_feed_signal_event (loop, int signum)" 4 3102.IP "ev_feed_signal_event (struct ev_loop *loop, int signum)" 4
1327.IX Item "ev_feed_signal_event (loop, int signum)" 3103.IX Item "ev_feed_signal_event (struct ev_loop *loop, int signum)"
1328Feed an event as if the given signal occured (loop must be the default loop!). 3104Feed an event as if the given signal occurred (\f(CW\*(C`loop\*(C'\fR must be the default
3105loop!).
1329.SH "LIBEVENT EMULATION" 3106.SH "LIBEVENT EMULATION"
1330.IX Header "LIBEVENT EMULATION" 3107.IX Header "LIBEVENT EMULATION"
1331Libev offers a compatibility emulation layer for libevent. It cannot 3108Libev offers a compatibility emulation layer for libevent. It cannot
1332emulate the internals of libevent, so here are some usage hints: 3109emulate the internals of libevent, so here are some usage hints:
3110.IP "\(bu" 4
1333.IP "* Use it by including <event.h>, as usual." 4 3111Use it by including <event.h>, as usual.
1334.IX Item "Use it by including <event.h>, as usual." 3112.IP "\(bu" 4
1335.PD 0 3113The following members are fully supported: ev_base, ev_callback,
1336.IP "* The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4 3114ev_arg, ev_fd, ev_res, ev_events.
1337.IX Item "The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 3115.IP "\(bu" 4
1338.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 3116Avoid using ev_flags and the EVLIST_*\-macros, while it is
1339.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)." 3117maintained by libev, it does not work exactly the same way as in libevent (consider
1340.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 3118it a private \s-1API\s0).
1341.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." 3119.IP "\(bu" 4
3120Priorities are not currently supported. Initialising priorities
3121will fail and all watchers will have the same priority, even though there
3122is an ev_pri field.
3123.IP "\(bu" 4
3124In libevent, the last base created gets the signals, in libev, the
3125first base created (== the default loop) gets the signals.
3126.IP "\(bu" 4
1342.IP "* Other members are not supported." 4 3127Other members are not supported.
1343.IX Item "Other members are not supported." 3128.IP "\(bu" 4
1344.IP "* The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need to use the libev header file and library." 4 3129The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need
1345.IX Item "The libev emulation is not ABI compatible to libevent, you need to use the libev header file and library." 3130to use the libev header file and library.
1346.PD
1347.SH "\*(C+ SUPPORT" 3131.SH "\*(C+ SUPPORT"
1348.IX Header " SUPPORT" 3132.IX Header " SUPPORT"
1349\&\s-1TBD\s0. 3133Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
3134you to use some convenience methods to start/stop watchers and also change
3135the callback model to a model using method callbacks on objects.
3136.PP
3137To use it,
3138.PP
3139.Vb 1
3140\& #include <ev++.h>
3141.Ve
3142.PP
3143This automatically includes \fIev.h\fR and puts all of its definitions (many
3144of them macros) into the global namespace. All \*(C+ specific things are
3145put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding
3146options as \fIev.h\fR, most notably \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR.
3147.PP
3148Care has been taken to keep the overhead low. The only data member the \*(C+
3149classes add (compared to plain C\-style watchers) is the event loop pointer
3150that the watcher is associated with (or no additional members at all if
3151you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
3152.PP
3153Currently, functions, and static and non-static member functions can be
3154used as callbacks. Other types should be easy to add as long as they only
3155need one additional pointer for context. If you need support for other
3156types of functors please contact the author (preferably after implementing
3157it).
3158.PP
3159Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
3160.ie n .IP """ev::READ""\fR, \f(CW""ev::WRITE"" etc." 4
3161.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
3162.IX Item "ev::READ, ev::WRITE etc."
3163These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
3164macros from \fIev.h\fR.
3165.ie n .IP """ev::tstamp""\fR, \f(CW""ev::now""" 4
3166.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
3167.IX Item "ev::tstamp, ev::now"
3168Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
3169.ie n .IP """ev::io""\fR, \f(CW""ev::timer""\fR, \f(CW""ev::periodic""\fR, \f(CW""ev::idle""\fR, \f(CW""ev::sig"" etc." 4
3170.el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
3171.IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
3172For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
3173the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
3174which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
3175defines by many implementations.
3176.Sp
3177All of those classes have these methods:
3178.RS 4
3179.IP "ev::TYPE::TYPE ()" 4
3180.IX Item "ev::TYPE::TYPE ()"
3181.PD 0
3182.IP "ev::TYPE::TYPE (struct ev_loop *)" 4
3183.IX Item "ev::TYPE::TYPE (struct ev_loop *)"
3184.IP "ev::TYPE::~TYPE" 4
3185.IX Item "ev::TYPE::~TYPE"
3186.PD
3187The constructor (optionally) takes an event loop to associate the watcher
3188with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR.
3189.Sp
3190The constructor calls \f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the
3191\&\f(CW\*(C`set\*(C'\fR method before starting it.
3192.Sp
3193It will not set a callback, however: You have to call the templated \f(CW\*(C`set\*(C'\fR
3194method to set a callback before you can start the watcher.
3195.Sp
3196(The reason why you have to use a method is a limitation in \*(C+ which does
3197not allow explicit template arguments for constructors).
3198.Sp
3199The destructor automatically stops the watcher if it is active.
3200.IP "w\->set<class, &class::method> (object *)" 4
3201.IX Item "w->set<class, &class::method> (object *)"
3202This method sets the callback method to call. The method has to have a
3203signature of \f(CW\*(C`void (*)(ev_TYPE &, int)\*(C'\fR, it receives the watcher as
3204first argument and the \f(CW\*(C`revents\*(C'\fR as second. The object must be given as
3205parameter and is stored in the \f(CW\*(C`data\*(C'\fR member of the watcher.
3206.Sp
3207This method synthesizes efficient thunking code to call your method from
3208the C callback that libev requires. If your compiler can inline your
3209callback (i.e. it is visible to it at the place of the \f(CW\*(C`set\*(C'\fR call and
3210your compiler is good :), then the method will be fully inlined into the
3211thunking function, making it as fast as a direct C callback.
3212.Sp
3213Example: simple class declaration and watcher initialisation
3214.Sp
3215.Vb 4
3216\& struct myclass
3217\& {
3218\& void io_cb (ev::io &w, int revents) { }
3219\& }
3220\&
3221\& myclass obj;
3222\& ev::io iow;
3223\& iow.set <myclass, &myclass::io_cb> (&obj);
3224.Ve
3225.IP "w\->set (object *)" 4
3226.IX Item "w->set (object *)"
3227This is an \fBexperimental\fR feature that might go away in a future version.
3228.Sp
3229This is a variation of a method callback \- leaving out the method to call
3230will default the method to \f(CW\*(C`operator ()\*(C'\fR, which makes it possible to use
3231functor objects without having to manually specify the \f(CW\*(C`operator ()\*(C'\fR all
3232the time. Incidentally, you can then also leave out the template argument
3233list.
3234.Sp
3235The \f(CW\*(C`operator ()\*(C'\fR method prototype must be \f(CW\*(C`void operator ()(watcher &w,
3236int revents)\*(C'\fR.
3237.Sp
3238See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
3239.Sp
3240Example: use a functor object as callback.
3241.Sp
3242.Vb 7
3243\& struct myfunctor
3244\& {
3245\& void operator() (ev::io &w, int revents)
3246\& {
3247\& ...
3248\& }
3249\& }
3250\&
3251\& myfunctor f;
3252\&
3253\& ev::io w;
3254\& w.set (&f);
3255.Ve
3256.IP "w\->set<function> (void *data = 0)" 4
3257.IX Item "w->set<function> (void *data = 0)"
3258Also sets a callback, but uses a static method or plain function as
3259callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
3260\&\f(CW\*(C`data\*(C'\fR member and is free for you to use.
3261.Sp
3262The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
3263.Sp
3264See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
3265.Sp
3266Example: Use a plain function as callback.
3267.Sp
3268.Vb 2
3269\& static void io_cb (ev::io &w, int revents) { }
3270\& iow.set <io_cb> ();
3271.Ve
3272.IP "w\->set (struct ev_loop *)" 4
3273.IX Item "w->set (struct ev_loop *)"
3274Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
3275do this when the watcher is inactive (and not pending either).
3276.IP "w\->set ([arguments])" 4
3277.IX Item "w->set ([arguments])"
3278Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same arguments. Must be
3279called at least once. Unlike the C counterpart, an active watcher gets
3280automatically stopped and restarted when reconfiguring it with this
3281method.
3282.IP "w\->start ()" 4
3283.IX Item "w->start ()"
3284Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
3285constructor already stores the event loop.
3286.IP "w\->stop ()" 4
3287.IX Item "w->stop ()"
3288Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
3289.ie n .IP "w\->again () (""ev::timer""\fR, \f(CW""ev::periodic"" only)" 4
3290.el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
3291.IX Item "w->again () (ev::timer, ev::periodic only)"
3292For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
3293\&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
3294.ie n .IP "w\->sweep () (""ev::embed"" only)" 4
3295.el .IP "w\->sweep () (\f(CWev::embed\fR only)" 4
3296.IX Item "w->sweep () (ev::embed only)"
3297Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR.
3298.ie n .IP "w\->update () (""ev::stat"" only)" 4
3299.el .IP "w\->update () (\f(CWev::stat\fR only)" 4
3300.IX Item "w->update () (ev::stat only)"
3301Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
3302.RE
3303.RS 4
3304.RE
3305.PP
3306Example: Define a class with an \s-1IO\s0 and idle watcher, start one of them in
3307the constructor.
3308.PP
3309.Vb 4
3310\& class myclass
3311\& {
3312\& ev::io io ; void io_cb (ev::io &w, int revents);
3313\& ev::idle idle; void idle_cb (ev::idle &w, int revents);
3314\&
3315\& myclass (int fd)
3316\& {
3317\& io .set <myclass, &myclass::io_cb > (this);
3318\& idle.set <myclass, &myclass::idle_cb> (this);
3319\&
3320\& io.start (fd, ev::READ);
3321\& }
3322\& };
3323.Ve
3324.SH "OTHER LANGUAGE BINDINGS"
3325.IX Header "OTHER LANGUAGE BINDINGS"
3326Libev does not offer other language bindings itself, but bindings for a
3327number of languages exist in the form of third-party packages. If you know
3328any interesting language binding in addition to the ones listed here, drop
3329me a note.
3330.IP "Perl" 4
3331.IX Item "Perl"
3332The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test
3333libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module,
3334there are additional modules that implement libev-compatible interfaces
3335to \f(CW\*(C`libadns\*(C'\fR (\f(CW\*(C`EV::ADNS\*(C'\fR, but \f(CW\*(C`AnyEvent::DNS\*(C'\fR is preferred nowadays),
3336\&\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
3337and \f(CW\*(C`EV::Glib\*(C'\fR).
3338.Sp
3339It can be found and installed via \s-1CPAN\s0, its homepage is at
3340<http://software.schmorp.de/pkg/EV>.
3341.IP "Python" 4
3342.IX Item "Python"
3343Python bindings can be found at <http://code.google.com/p/pyev/>. It
3344seems to be quite complete and well-documented.
3345.IP "Ruby" 4
3346.IX Item "Ruby"
3347Tony Arcieri has written a ruby extension that offers access to a subset
3348of the libev \s-1API\s0 and adds file handle abstractions, asynchronous \s-1DNS\s0 and
3349more on top of it. It can be found via gem servers. Its homepage is at
3350<http://rev.rubyforge.org/>.
3351.Sp
3352Roger Pack reports that using the link order \f(CW\*(C`\-lws2_32 \-lmsvcrt\-ruby\-190\*(C'\fR
3353makes rev work even on mingw.
3354.IP "Haskell" 4
3355.IX Item "Haskell"
3356A haskell binding to libev is available at
3357<http://hackage.haskell.org/cgi\-bin/hackage\-scripts/package/hlibev>.
3358.IP "D" 4
3359.IX Item "D"
3360Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
3361be found at <http://proj.llucax.com.ar/wiki/evd>.
3362.IP "Ocaml" 4
3363.IX Item "Ocaml"
3364Erkki Seppala has written Ocaml bindings for libev, to be found at
3365<http://modeemi.cs.tut.fi/~flux/software/ocaml\-ev/>.
3366.SH "MACRO MAGIC"
3367.IX Header "MACRO MAGIC"
3368Libev can be compiled with a variety of options, the most fundamental
3369of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most)
3370functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
3371.PP
3372To make it easier to write programs that cope with either variant, the
3373following macros are defined:
3374.ie n .IP """EV_A""\fR, \f(CW""EV_A_""" 4
3375.el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
3376.IX Item "EV_A, EV_A_"
3377This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
3378loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
3379\&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
3380.Sp
3381.Vb 3
3382\& ev_unref (EV_A);
3383\& ev_timer_add (EV_A_ watcher);
3384\& ev_loop (EV_A_ 0);
3385.Ve
3386.Sp
3387It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
3388which is often provided by the following macro.
3389.ie n .IP """EV_P""\fR, \f(CW""EV_P_""" 4
3390.el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
3391.IX Item "EV_P, EV_P_"
3392This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
3393loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
3394\&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
3395.Sp
3396.Vb 2
3397\& // this is how ev_unref is being declared
3398\& static void ev_unref (EV_P);
3399\&
3400\& // this is how you can declare your typical callback
3401\& static void cb (EV_P_ ev_timer *w, int revents)
3402.Ve
3403.Sp
3404It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
3405suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
3406.ie n .IP """EV_DEFAULT""\fR, \f(CW""EV_DEFAULT_""" 4
3407.el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
3408.IX Item "EV_DEFAULT, EV_DEFAULT_"
3409Similar to the other two macros, this gives you the value of the default
3410loop, if multiple loops are supported (\*(L"ev loop default\*(R").
3411.ie n .IP """EV_DEFAULT_UC""\fR, \f(CW""EV_DEFAULT_UC_""" 4
3412.el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
3413.IX Item "EV_DEFAULT_UC, EV_DEFAULT_UC_"
3414Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the
3415default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour
3416is undefined when the default loop has not been initialised by a previous
3417execution of \f(CW\*(C`EV_DEFAULT\*(C'\fR, \f(CW\*(C`EV_DEFAULT_\*(C'\fR or \f(CW\*(C`ev_default_init (...)\*(C'\fR.
3418.Sp
3419It is often prudent to use \f(CW\*(C`EV_DEFAULT\*(C'\fR when initialising the first
3420watcher in a function but use \f(CW\*(C`EV_DEFAULT_UC\*(C'\fR afterwards.
3421.PP
3422Example: Declare and initialise a check watcher, utilising the above
3423macros so it will work regardless of whether multiple loops are supported
3424or not.
3425.PP
3426.Vb 5
3427\& static void
3428\& check_cb (EV_P_ ev_timer *w, int revents)
3429\& {
3430\& ev_check_stop (EV_A_ w);
3431\& }
3432\&
3433\& ev_check check;
3434\& ev_check_init (&check, check_cb);
3435\& ev_check_start (EV_DEFAULT_ &check);
3436\& ev_loop (EV_DEFAULT_ 0);
3437.Ve
3438.SH "EMBEDDING"
3439.IX Header "EMBEDDING"
3440Libev can (and often is) directly embedded into host
3441applications. Examples of applications that embed it include the Deliantra
3442Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
3443and rxvt-unicode.
3444.PP
3445The goal is to enable you to just copy the necessary files into your
3446source directory without having to change even a single line in them, so
3447you can easily upgrade by simply copying (or having a checked-out copy of
3448libev somewhere in your source tree).
3449.Sh "\s-1FILESETS\s0"
3450.IX Subsection "FILESETS"
3451Depending on what features you need you need to include one or more sets of files
3452in your application.
3453.PP
3454\fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR
3455.IX Subsection "CORE EVENT LOOP"
3456.PP
3457To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
3458configuration (no autoconf):
3459.PP
3460.Vb 2
3461\& #define EV_STANDALONE 1
3462\& #include "ev.c"
3463.Ve
3464.PP
3465This will automatically include \fIev.h\fR, too, and should be done in a
3466single C source file only to provide the function implementations. To use
3467it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best
3468done by writing a wrapper around \fIev.h\fR that you can include instead and
3469where you can put other configuration options):
3470.PP
3471.Vb 2
3472\& #define EV_STANDALONE 1
3473\& #include "ev.h"
3474.Ve
3475.PP
3476Both header files and implementation files can be compiled with a \*(C+
3477compiler (at least, that's a stated goal, and breakage will be treated
3478as a bug).
3479.PP
3480You need the following files in your source tree, or in a directory
3481in your include path (e.g. in libev/ when using \-Ilibev):
3482.PP
3483.Vb 4
3484\& ev.h
3485\& ev.c
3486\& ev_vars.h
3487\& ev_wrap.h
3488\&
3489\& ev_win32.c required on win32 platforms only
3490\&
3491\& ev_select.c only when select backend is enabled (which is enabled by default)
3492\& ev_poll.c only when poll backend is enabled (disabled by default)
3493\& ev_epoll.c only when the epoll backend is enabled (disabled by default)
3494\& ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
3495\& ev_port.c only when the solaris port backend is enabled (disabled by default)
3496.Ve
3497.PP
3498\&\fIev.c\fR includes the backend files directly when enabled, so you only need
3499to compile this single file.
3500.PP
3501\fI\s-1LIBEVENT\s0 \s-1COMPATIBILITY\s0 \s-1API\s0\fR
3502.IX Subsection "LIBEVENT COMPATIBILITY API"
3503.PP
3504To include the libevent compatibility \s-1API\s0, also include:
3505.PP
3506.Vb 1
3507\& #include "event.c"
3508.Ve
3509.PP
3510in the file including \fIev.c\fR, and:
3511.PP
3512.Vb 1
3513\& #include "event.h"
3514.Ve
3515.PP
3516in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR.
3517.PP
3518You need the following additional files for this:
3519.PP
3520.Vb 2
3521\& event.h
3522\& event.c
3523.Ve
3524.PP
3525\fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR
3526.IX Subsection "AUTOCONF SUPPORT"
3527.PP
3528Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your configuration in
3529whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
3530\&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then
3531include \fIconfig.h\fR and configure itself accordingly.
3532.PP
3533For this of course you need the m4 file:
3534.PP
3535.Vb 1
3536\& libev.m4
3537.Ve
3538.Sh "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0"
3539.IX Subsection "PREPROCESSOR SYMBOLS/MACROS"
3540Libev can be configured via a variety of preprocessor symbols you have to
3541define before including any of its files. The default in the absence of
3542autoconf is documented for every option.
3543.IP "\s-1EV_STANDALONE\s0" 4
3544.IX Item "EV_STANDALONE"
3545Must always be \f(CW1\fR if you do not use autoconf configuration, which
3546keeps libev from including \fIconfig.h\fR, and it also defines dummy
3547implementations for some libevent functions (such as logging, which is not
3548supported). It will also not define any of the structs usually found in
3549\&\fIevent.h\fR that are not directly supported by the libev core alone.
3550.Sp
3551In stanbdalone mode, libev will still try to automatically deduce the
3552configuration, but has to be more conservative.
3553.IP "\s-1EV_USE_MONOTONIC\s0" 4
3554.IX Item "EV_USE_MONOTONIC"
3555If defined to be \f(CW1\fR, libev will try to detect the availability of the
3556monotonic clock option at both compile time and runtime. Otherwise no
3557use of the monotonic clock option will be attempted. If you enable this,
3558you usually have to link against librt or something similar. Enabling it
3559when the functionality isn't available is safe, though, although you have
3560to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
3561function is hiding in (often \fI\-lrt\fR). See also \f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
3562.IP "\s-1EV_USE_REALTIME\s0" 4
3563.IX Item "EV_USE_REALTIME"
3564If defined to be \f(CW1\fR, libev will try to detect the availability of the
3565real-time clock option at compile time (and assume its availability
3566at runtime if successful). Otherwise no use of the real-time clock
3567option will be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR
3568by \f(CW\*(C`clock_get (CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect
3569correctness. See the note about libraries in the description of
3570\&\f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. Defaults to the opposite value of
3571\&\f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
3572.IP "\s-1EV_USE_CLOCK_SYSCALL\s0" 4
3573.IX Item "EV_USE_CLOCK_SYSCALL"
3574If defined to be \f(CW1\fR, libev will try to use a direct syscall instead
3575of calling the system-provided \f(CW\*(C`clock_gettime\*(C'\fR function. This option
3576exists 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
3577unconditionally pulls in \f(CW\*(C`libpthread\*(C'\fR, slowing down single-threaded
3578programs needlessly. Using a direct syscall is slightly slower (in
3579theory), because no optimised vdso implementation can be used, but avoids
3580the pthread dependency. Defaults to \f(CW1\fR on GNU/Linux with glibc 2.x or
3581higher, as it simplifies linking (no need for \f(CW\*(C`\-lrt\*(C'\fR).
3582.IP "\s-1EV_USE_NANOSLEEP\s0" 4
3583.IX Item "EV_USE_NANOSLEEP"
3584If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available
3585and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR.
3586.IP "\s-1EV_USE_EVENTFD\s0" 4
3587.IX Item "EV_USE_EVENTFD"
3588If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
3589available and will probe for kernel support at runtime. This will improve
3590\&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
3591If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
35922.7 or newer, otherwise disabled.
3593.IP "\s-1EV_USE_SELECT\s0" 4
3594.IX Item "EV_USE_SELECT"
3595If undefined or defined to be \f(CW1\fR, libev will compile in support for the
3596\&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at auto-detection will be done: if no
3597other method takes over, select will be it. Otherwise the select backend
3598will not be compiled in.
3599.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
3600.IX Item "EV_SELECT_USE_FD_SET"
3601If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR
3602structure. This is useful if libev doesn't compile due to a missing
3603\&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it mis-guesses the bitset layout
3604on exotic systems. This usually limits the range of file descriptors to
3605some low limit such as 1024 or might have other limitations (winsocket
3606only allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation,
3607configures the maximum size of the \f(CW\*(C`fd_set\*(C'\fR.
3608.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
3609.IX Item "EV_SELECT_IS_WINSOCKET"
3610When defined to \f(CW1\fR, the select backend will assume that
3611select/socket/connect etc. don't understand file descriptors but
3612wants osf handles on win32 (this is the case when the select to
3613be used is the winsock select). This means that it will call
3614\&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
3615it is assumed that all these functions actually work on fds, even
3616on win32. Should not be defined on non\-win32 platforms.
3617.IP "\s-1EV_FD_TO_WIN32_HANDLE\s0" 4
3618.IX Item "EV_FD_TO_WIN32_HANDLE"
3619If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map
3620file descriptors to socket handles. When not defining this symbol (the
3621default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually
3622correct. In some cases, programs use their own file descriptor management,
3623in which case they can provide this function to map fds to socket handles.
3624.IP "\s-1EV_USE_POLL\s0" 4
3625.IX Item "EV_USE_POLL"
3626If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2)
3627backend. Otherwise it will be enabled on non\-win32 platforms. It
3628takes precedence over select.
3629.IP "\s-1EV_USE_EPOLL\s0" 4
3630.IX Item "EV_USE_EPOLL"
3631If defined to be \f(CW1\fR, libev will compile in support for the Linux
3632\&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime,
3633otherwise another method will be used as fallback. This is the preferred
3634backend for GNU/Linux systems. If undefined, it will be enabled if the
3635headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3636.IP "\s-1EV_USE_KQUEUE\s0" 4
3637.IX Item "EV_USE_KQUEUE"
3638If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
3639\&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime,
3640otherwise another method will be used as fallback. This is the preferred
3641backend for \s-1BSD\s0 and BSD-like systems, although on most BSDs kqueue only
3642supports some types of fds correctly (the only platform we found that
3643supports ptys for example was NetBSD), so kqueue might be compiled in, but
3644not be used unless explicitly requested. The best way to use it is to find
3645out whether kqueue supports your type of fd properly and use an embedded
3646kqueue loop.
3647.IP "\s-1EV_USE_PORT\s0" 4
3648.IX Item "EV_USE_PORT"
3649If defined to be \f(CW1\fR, libev will compile in support for the Solaris
365010 port style backend. Its availability will be detected at runtime,
3651otherwise another method will be used as fallback. This is the preferred
3652backend for Solaris 10 systems.
3653.IP "\s-1EV_USE_DEVPOLL\s0" 4
3654.IX Item "EV_USE_DEVPOLL"
3655Reserved for future expansion, works like the \s-1USE\s0 symbols above.
3656.IP "\s-1EV_USE_INOTIFY\s0" 4
3657.IX Item "EV_USE_INOTIFY"
3658If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
3659interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
3660be detected at runtime. If undefined, it will be enabled if the headers
3661indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
3662.IP "\s-1EV_ATOMIC_T\s0" 4
3663.IX Item "EV_ATOMIC_T"
3664Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
3665access is atomic with respect to other threads or signal contexts. No such
3666type is easily found in the C language, so you can provide your own type
3667that you know is safe for your purposes. It is used both for signal handler \*(L"locking\*(R"
3668as well as for signal and thread safety in \f(CW\*(C`ev_async\*(C'\fR watchers.
3669.Sp
3670In the absence of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR
3671(from \fIsignal.h\fR), which is usually good enough on most platforms.
3672.IP "\s-1EV_H\s0" 4
3673.IX Item "EV_H"
3674The name of the \fIev.h\fR header file used to include it. The default if
3675undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be
3676used to virtually rename the \fIev.h\fR header file in case of conflicts.
3677.IP "\s-1EV_CONFIG_H\s0" 4
3678.IX Item "EV_CONFIG_H"
3679If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
3680\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
3681\&\f(CW\*(C`EV_H\*(C'\fR, above.
3682.IP "\s-1EV_EVENT_H\s0" 4
3683.IX Item "EV_EVENT_H"
3684Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea
3685of how the \fIevent.h\fR header can be found, the default is \f(CW"event.h"\fR.
3686.IP "\s-1EV_PROTOTYPES\s0" 4
3687.IX Item "EV_PROTOTYPES"
3688If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
3689prototypes, but still define all the structs and other symbols. This is
3690occasionally useful if you want to provide your own wrapper functions
3691around libev functions.
3692.IP "\s-1EV_MULTIPLICITY\s0" 4
3693.IX Item "EV_MULTIPLICITY"
3694If undefined or defined to \f(CW1\fR, then all event-loop-specific functions
3695will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create
3696additional independent event loops. Otherwise there will be no support
3697for multiple event loops and there is no first event loop pointer
3698argument. Instead, all functions act on the single default loop.
3699.IP "\s-1EV_MINPRI\s0" 4
3700.IX Item "EV_MINPRI"
3701.PD 0
3702.IP "\s-1EV_MAXPRI\s0" 4
3703.IX Item "EV_MAXPRI"
3704.PD
3705The range of allowed priorities. \f(CW\*(C`EV_MINPRI\*(C'\fR must be smaller or equal to
3706\&\f(CW\*(C`EV_MAXPRI\*(C'\fR, but otherwise there are no non-obvious limitations. You can
3707provide for more priorities by overriding those symbols (usually defined
3708to be \f(CW\*(C`\-2\*(C'\fR and \f(CW2\fR, respectively).
3709.Sp
3710When doing priority-based operations, libev usually has to linearly search
3711all the priorities, so having many of them (hundreds) uses a lot of space
3712and time, so using the defaults of five priorities (\-2 .. +2) is usually
3713fine.
3714.Sp
3715If your embedding application does not need any priorities, defining these
3716both to \f(CW0\fR will save some memory and \s-1CPU\s0.
3717.IP "\s-1EV_PERIODIC_ENABLE\s0" 4
3718.IX Item "EV_PERIODIC_ENABLE"
3719If undefined or defined to be \f(CW1\fR, then periodic timers are supported. If
3720defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of
3721code.
3722.IP "\s-1EV_IDLE_ENABLE\s0" 4
3723.IX Item "EV_IDLE_ENABLE"
3724If undefined or defined to be \f(CW1\fR, then idle watchers are supported. If
3725defined to be \f(CW0\fR, then they are not. Disabling them saves a few kB of
3726code.
3727.IP "\s-1EV_EMBED_ENABLE\s0" 4
3728.IX Item "EV_EMBED_ENABLE"
3729If undefined or defined to be \f(CW1\fR, then embed watchers are supported. If
3730defined to be \f(CW0\fR, then they are not. Embed watchers rely on most other
3731watcher types, which therefore must not be disabled.
3732.IP "\s-1EV_STAT_ENABLE\s0" 4
3733.IX Item "EV_STAT_ENABLE"
3734If undefined or defined to be \f(CW1\fR, then stat watchers are supported. If
3735defined to be \f(CW0\fR, then they are not.
3736.IP "\s-1EV_FORK_ENABLE\s0" 4
3737.IX Item "EV_FORK_ENABLE"
3738If undefined or defined to be \f(CW1\fR, then fork watchers are supported. If
3739defined to be \f(CW0\fR, then they are not.
3740.IP "\s-1EV_ASYNC_ENABLE\s0" 4
3741.IX Item "EV_ASYNC_ENABLE"
3742If undefined or defined to be \f(CW1\fR, then async watchers are supported. If
3743defined to be \f(CW0\fR, then they are not.
3744.IP "\s-1EV_MINIMAL\s0" 4
3745.IX Item "EV_MINIMAL"
3746If you need to shave off some kilobytes of code at the expense of some
3747speed, define this symbol to \f(CW1\fR. Currently this is used to override some
3748inlining decisions, saves roughly 30% code size on amd64. It also selects a
3749much smaller 2\-heap for timer management over the default 4\-heap.
3750.IP "\s-1EV_PID_HASHSIZE\s0" 4
3751.IX Item "EV_PID_HASHSIZE"
3752\&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by
3753pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR), usually more
3754than enough. If you need to manage thousands of children you might want to
3755increase this value (\fImust\fR be a power of two).
3756.IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4
3757.IX Item "EV_INOTIFY_HASHSIZE"
3758\&\f(CW\*(C`ev_stat\*(C'\fR watchers use a small hash table to distribute workload by
3759inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_MINIMAL\*(C'\fR),
3760usually more than enough. If you need to manage thousands of \f(CW\*(C`ev_stat\*(C'\fR
3761watchers you might want to increase this value (\fImust\fR be a power of
3762two).
3763.IP "\s-1EV_USE_4HEAP\s0" 4
3764.IX Item "EV_USE_4HEAP"
3765Heaps are not very cache-efficient. To improve the cache-efficiency of the
3766timer and periodics heaps, libev uses a 4\-heap when this symbol is defined
3767to \f(CW1\fR. The 4\-heap uses more complicated (longer) code but has noticeably
3768faster performance with many (thousands) of watchers.
3769.Sp
3770The default is \f(CW1\fR unless \f(CW\*(C`EV_MINIMAL\*(C'\fR is set in which case it is \f(CW0\fR
3771(disabled).
3772.IP "\s-1EV_HEAP_CACHE_AT\s0" 4
3773.IX Item "EV_HEAP_CACHE_AT"
3774Heaps are not very cache-efficient. To improve the cache-efficiency of the
3775timer and periodics heaps, libev can cache the timestamp (\fIat\fR) within
3776the heap structure (selected by defining \f(CW\*(C`EV_HEAP_CACHE_AT\*(C'\fR to \f(CW1\fR),
3777which uses 8\-12 bytes more per watcher and a few hundred bytes more code,
3778but avoids random read accesses on heap changes. This improves performance
3779noticeably with many (hundreds) of watchers.
3780.Sp
3781The default is \f(CW1\fR unless \f(CW\*(C`EV_MINIMAL\*(C'\fR is set in which case it is \f(CW0\fR
3782(disabled).
3783.IP "\s-1EV_VERIFY\s0" 4
3784.IX Item "EV_VERIFY"
3785Controls how much internal verification (see \f(CW\*(C`ev_loop_verify ()\*(C'\fR) will
3786be done: If set to \f(CW0\fR, no internal verification code will be compiled
3787in. If set to \f(CW1\fR, then verification code will be compiled in, but not
3788called. If set to \f(CW2\fR, then the internal verification code will be
3789called once per loop, which can slow down libev. If set to \f(CW3\fR, then the
3790verification code will be called very frequently, which will slow down
3791libev considerably.
3792.Sp
3793The default is \f(CW1\fR, unless \f(CW\*(C`EV_MINIMAL\*(C'\fR is set, in which case it will be
3794\&\f(CW0\fR.
3795.IP "\s-1EV_COMMON\s0" 4
3796.IX Item "EV_COMMON"
3797By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining
3798this macro to a something else you can include more and other types of
3799members. You have to define it each time you include one of the files,
3800though, and it must be identical each time.
3801.Sp
3802For example, the perl \s-1EV\s0 module uses something like this:
3803.Sp
3804.Vb 3
3805\& #define EV_COMMON \e
3806\& SV *self; /* contains this struct */ \e
3807\& SV *cb_sv, *fh /* note no trailing ";" */
3808.Ve
3809.IP "\s-1EV_CB_DECLARE\s0 (type)" 4
3810.IX Item "EV_CB_DECLARE (type)"
3811.PD 0
3812.IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4
3813.IX Item "EV_CB_INVOKE (watcher, revents)"
3814.IP "ev_set_cb (ev, cb)" 4
3815.IX Item "ev_set_cb (ev, cb)"
3816.PD
3817Can be used to change the callback member declaration in each watcher,
3818and the way callbacks are invoked and set. Must expand to a struct member
3819definition and a statement, respectively. See the \fIev.h\fR header file for
3820their default definitions. One possible use for overriding these is to
3821avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use
3822method calls instead of plain function calls in \*(C+.
3823.Sh "\s-1EXPORTED\s0 \s-1API\s0 \s-1SYMBOLS\s0"
3824.IX Subsection "EXPORTED API SYMBOLS"
3825If you need to re-export the \s-1API\s0 (e.g. via a \s-1DLL\s0) and you need a list of
3826exported symbols, you can use the provided \fISymbol.*\fR files which list
3827all public symbols, one per line:
3828.PP
3829.Vb 2
3830\& Symbols.ev for libev proper
3831\& Symbols.event for the libevent emulation
3832.Ve
3833.PP
3834This can also be used to rename all public symbols to avoid clashes with
3835multiple versions of libev linked together (which is obviously bad in
3836itself, but sometimes it is inconvenient to avoid this).
3837.PP
3838A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to
3839include before including \fIev.h\fR:
3840.PP
3841.Vb 1
3842\& <Symbols.ev sed \-e "s/.*/#define & myprefix_&/" >wrap.h
3843.Ve
3844.PP
3845This would create a file \fIwrap.h\fR which essentially looks like this:
3846.PP
3847.Vb 4
3848\& #define ev_backend myprefix_ev_backend
3849\& #define ev_check_start myprefix_ev_check_start
3850\& #define ev_check_stop myprefix_ev_check_stop
3851\& ...
3852.Ve
3853.Sh "\s-1EXAMPLES\s0"
3854.IX Subsection "EXAMPLES"
3855For a real-world example of a program the includes libev
3856verbatim, you can have a look at the \s-1EV\s0 perl module
3857(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
3858the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public
3859interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file
3860will be compiled. It is pretty complex because it provides its own header
3861file.
3862.PP
3863The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file
3864that everybody includes and which overrides some configure choices:
3865.PP
3866.Vb 9
3867\& #define EV_MINIMAL 1
3868\& #define EV_USE_POLL 0
3869\& #define EV_MULTIPLICITY 0
3870\& #define EV_PERIODIC_ENABLE 0
3871\& #define EV_STAT_ENABLE 0
3872\& #define EV_FORK_ENABLE 0
3873\& #define EV_CONFIG_H <config.h>
3874\& #define EV_MINPRI 0
3875\& #define EV_MAXPRI 0
3876\&
3877\& #include "ev++.h"
3878.Ve
3879.PP
3880And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled:
3881.PP
3882.Vb 2
3883\& #include "ev_cpp.h"
3884\& #include "ev.c"
3885.Ve
3886.SH "INTERACTION WITH OTHER PROGRAMS OR LIBRARIES"
3887.IX Header "INTERACTION WITH OTHER PROGRAMS OR LIBRARIES"
3888.Sh "\s-1THREADS\s0 \s-1AND\s0 \s-1COROUTINES\s0"
3889.IX Subsection "THREADS AND COROUTINES"
3890\fI\s-1THREADS\s0\fR
3891.IX Subsection "THREADS"
3892.PP
3893All libev functions are reentrant and thread-safe unless explicitly
3894documented otherwise, but libev implements no locking itself. This means
3895that you can use as many loops as you want in parallel, as long as there
3896are no concurrent calls into any libev function with the same loop
3897parameter (\f(CW\*(C`ev_default_*\*(C'\fR calls have an implicit default loop parameter,
3898of course): libev guarantees that different event loops share no data
3899structures that need any locking.
3900.PP
3901Or to put it differently: calls with different loop parameters can be done
3902concurrently from multiple threads, calls with the same loop parameter
3903must be done serially (but can be done from different threads, as long as
3904only one thread ever is inside a call at any point in time, e.g. by using
3905a mutex per loop).
3906.PP
3907Specifically to support threads (and signal handlers), libev implements
3908so-called \f(CW\*(C`ev_async\*(C'\fR watchers, which allow some limited form of
3909concurrency on the same event loop, namely waking it up \*(L"from the
3910outside\*(R".
3911.PP
3912If you want to know which design (one loop, locking, or multiple loops
3913without or something else still) is best for your problem, then I cannot
3914help you, but here is some generic advice:
3915.IP "\(bu" 4
3916most applications have a main thread: use the default libev loop
3917in that thread, or create a separate thread running only the default loop.
3918.Sp
3919This helps integrating other libraries or software modules that use libev
3920themselves and don't care/know about threading.
3921.IP "\(bu" 4
3922one loop per thread is usually a good model.
3923.Sp
3924Doing this is almost never wrong, sometimes a better-performance model
3925exists, but it is always a good start.
3926.IP "\(bu" 4
3927other models exist, such as the leader/follower pattern, where one
3928loop is handed through multiple threads in a kind of round-robin fashion.
3929.Sp
3930Choosing a model is hard \- look around, learn, know that usually you can do
3931better than you currently do :\-)
3932.IP "\(bu" 4
3933often you need to talk to some other thread which blocks in the
3934event loop.
3935.Sp
3936\&\f(CW\*(C`ev_async\*(C'\fR watchers can be used to wake them up from other threads safely
3937(or from signal contexts...).
3938.Sp
3939An example use would be to communicate signals or other events that only
3940work in the default loop by registering the signal watcher with the
3941default loop and triggering an \f(CW\*(C`ev_async\*(C'\fR watcher from the default loop
3942watcher callback into the event loop interested in the signal.
3943.PP
3944\fI\s-1COROUTINES\s0\fR
3945.IX Subsection "COROUTINES"
3946.PP
3947Libev is very accommodating to coroutines (\*(L"cooperative threads\*(R"):
3948libev fully supports nesting calls to its functions from different
3949coroutines (e.g. you can call \f(CW\*(C`ev_loop\*(C'\fR on the same loop from two
3950different coroutines, and switch freely between both coroutines running the
3951loop, as long as you don't confuse yourself). The only exception is that
3952you must not do this from \f(CW\*(C`ev_periodic\*(C'\fR reschedule callbacks.
3953.PP
3954Care has been taken to ensure that libev does not keep local state inside
3955\&\f(CW\*(C`ev_loop\*(C'\fR, and other calls do not usually allow for coroutine switches as
3956they do not call any callbacks.
3957.Sh "\s-1COMPILER\s0 \s-1WARNINGS\s0"
3958.IX Subsection "COMPILER WARNINGS"
3959Depending on your compiler and compiler settings, you might get no or a
3960lot of warnings when compiling libev code. Some people are apparently
3961scared by this.
3962.PP
3963However, these are unavoidable for many reasons. For one, each compiler
3964has different warnings, and each user has different tastes regarding
3965warning options. \*(L"Warn-free\*(R" code therefore cannot be a goal except when
3966targeting a specific compiler and compiler-version.
3967.PP
3968Another reason is that some compiler warnings require elaborate
3969workarounds, or other changes to the code that make it less clear and less
3970maintainable.
3971.PP
3972And of course, some compiler warnings are just plain stupid, or simply
3973wrong (because they don't actually warn about the condition their message
3974seems to warn about). For example, certain older gcc versions had some
3975warnings that resulted an extreme number of false positives. These have
3976been fixed, but some people still insist on making code warn-free with
3977such buggy versions.
3978.PP
3979While libev is written to generate as few warnings as possible,
3980\&\*(L"warn-free\*(R" code is not a goal, and it is recommended not to build libev
3981with any compiler warnings enabled unless you are prepared to cope with
3982them (e.g. by ignoring them). Remember that warnings are just that:
3983warnings, not errors, or proof of bugs.
3984.Sh "\s-1VALGRIND\s0"
3985.IX Subsection "VALGRIND"
3986Valgrind has a special section here because it is a popular tool that is
3987highly useful. Unfortunately, valgrind reports are very hard to interpret.
3988.PP
3989If you think you found a bug (memory leak, uninitialised data access etc.)
3990in libev, then check twice: If valgrind reports something like:
3991.PP
3992.Vb 3
3993\& ==2274== definitely lost: 0 bytes in 0 blocks.
3994\& ==2274== possibly lost: 0 bytes in 0 blocks.
3995\& ==2274== still reachable: 256 bytes in 1 blocks.
3996.Ve
3997.PP
3998Then there is no memory leak, just as memory accounted to global variables
3999is not a memleak \- the memory is still being referenced, and didn't leak.
4000.PP
4001Similarly, under some circumstances, valgrind might report kernel bugs
4002as if it were a bug in libev (e.g. in realloc or in the poll backend,
4003although an acceptable workaround has been found here), or it might be
4004confused.
4005.PP
4006Keep in mind that valgrind is a very good tool, but only a tool. Don't
4007make it into some kind of religion.
4008.PP
4009If you are unsure about something, feel free to contact the mailing list
4010with the full valgrind report and an explanation on why you think this
4011is a bug in libev (best check the archives, too :). However, don't be
4012annoyed when you get a brisk \*(L"this is no bug\*(R" answer and take the chance
4013of learning how to interpret valgrind properly.
4014.PP
4015If you need, for some reason, empty reports from valgrind for your project
4016I suggest using suppression lists.
4017.SH "PORTABILITY NOTES"
4018.IX Header "PORTABILITY NOTES"
4019.Sh "\s-1WIN32\s0 \s-1PLATFORM\s0 \s-1LIMITATIONS\s0 \s-1AND\s0 \s-1WORKAROUNDS\s0"
4020.IX Subsection "WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS"
4021Win32 doesn't support any of the standards (e.g. \s-1POSIX\s0) that libev
4022requires, and its I/O model is fundamentally incompatible with the \s-1POSIX\s0
4023model. Libev still offers limited functionality on this platform in
4024the form of the \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR backend, and only supports socket
4025descriptors. This only applies when using Win32 natively, not when using
4026e.g. cygwin.
4027.PP
4028Lifting these limitations would basically require the full
4029re-implementation of the I/O system. If you are into these kinds of
4030things, then note that glib does exactly that for you in a very portable
4031way (note also that glib is the slowest event library known to man).
4032.PP
4033There is no supported compilation method available on windows except
4034embedding it into other applications.
4035.PP
4036Sensible signal handling is officially unsupported by Microsoft \- libev
4037tries its best, but under most conditions, signals will simply not work.
4038.PP
4039Not a libev limitation but worth mentioning: windows apparently doesn't
4040accept large writes: instead of resulting in a partial write, windows will
4041either accept everything or return \f(CW\*(C`ENOBUFS\*(C'\fR if the buffer is too large,
4042so make sure you only write small amounts into your sockets (less than a
4043megabyte seems safe, but this apparently depends on the amount of memory
4044available).
4045.PP
4046Due to the many, low, and arbitrary limits on the win32 platform and
4047the abysmal performance of winsockets, using a large number of sockets
4048is not recommended (and not reasonable). If your program needs to use
4049more than a hundred or so sockets, then likely it needs to use a totally
4050different implementation for windows, as libev offers the \s-1POSIX\s0 readiness
4051notification model, which cannot be implemented efficiently on windows
4052(due to Microsoft monopoly games).
4053.PP
4054A typical way to use libev under windows is to embed it (see the embedding
4055section for details) and use the following \fIevwrap.h\fR header file instead
4056of \fIev.h\fR:
4057.PP
4058.Vb 2
4059\& #define EV_STANDALONE /* keeps ev from requiring config.h */
4060\& #define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
4061\&
4062\& #include "ev.h"
4063.Ve
4064.PP
4065And compile the following \fIevwrap.c\fR file into your project (make sure
4066you do \fInot\fR compile the \fIev.c\fR or any other embedded source files!):
4067.PP
4068.Vb 2
4069\& #include "evwrap.h"
4070\& #include "ev.c"
4071.Ve
4072.IP "The winsocket select function" 4
4073.IX Item "The winsocket select function"
4074The winsocket \f(CW\*(C`select\*(C'\fR function doesn't follow \s-1POSIX\s0 in that it
4075requires socket \fIhandles\fR and not socket \fIfile descriptors\fR (it is
4076also extremely buggy). This makes select very inefficient, and also
4077requires a mapping from file descriptors to socket handles (the Microsoft
4078C runtime provides the function \f(CW\*(C`_open_osfhandle\*(C'\fR for this). See the
4079discussion of the \f(CW\*(C`EV_SELECT_USE_FD_SET\*(C'\fR, \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR and
4080\&\f(CW\*(C`EV_FD_TO_WIN32_HANDLE\*(C'\fR preprocessor symbols for more info.
4081.Sp
4082The configuration for a \*(L"naked\*(R" win32 using the Microsoft runtime
4083libraries and raw winsocket select is:
4084.Sp
4085.Vb 2
4086\& #define EV_USE_SELECT 1
4087\& #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
4088.Ve
4089.Sp
4090Note that winsockets handling of fd sets is O(n), so you can easily get a
4091complexity in the O(nA\*^X) range when using win32.
4092.IP "Limited number of file descriptors" 4
4093.IX Item "Limited number of file descriptors"
4094Windows has numerous arbitrary (and low) limits on things.
4095.Sp
4096Early versions of winsocket's select only supported waiting for a maximum
4097of \f(CW64\fR handles (probably owning to the fact that all windows kernels
4098can only wait for \f(CW64\fR things at the same time internally; Microsoft
4099recommends spawning a chain of threads and wait for 63 handles and the
4100previous thread in each. Sounds great!).
4101.Sp
4102Newer versions support more handles, but you need to define \f(CW\*(C`FD_SETSIZE\*(C'\fR
4103to some high number (e.g. \f(CW2048\fR) before compiling the winsocket select
4104call (which might be in libev or elsewhere, for example, perl and many
4105other interpreters do their own select emulation on windows).
4106.Sp
4107Another limit is the number of file descriptors in the Microsoft runtime
4108libraries, which by default is \f(CW64\fR (there must be a hidden \fI64\fR
4109fetish or something like this inside Microsoft). You can increase this
4110by calling \f(CW\*(C`_setmaxstdio\*(C'\fR, which can increase this limit to \f(CW2048\fR
4111(another arbitrary limit), but is broken in many versions of the Microsoft
4112runtime libraries. This might get you to about \f(CW512\fR or \f(CW2048\fR sockets
4113(depending on windows version and/or the phase of the moon). To get more,
4114you need to wrap all I/O functions and provide your own fd management, but
4115the cost of calling select (O(nA\*^X)) will likely make this unworkable.
4116.Sh "\s-1PORTABILITY\s0 \s-1REQUIREMENTS\s0"
4117.IX Subsection "PORTABILITY REQUIREMENTS"
4118In addition to a working ISO-C implementation and of course the
4119backend-specific APIs, libev relies on a few additional extensions:
4120.ie n .IP """void (*)(ev_watcher_type *, int revents)""\fR must have compatible calling conventions regardless of \f(CW""ev_watcher_type *""." 4
4121.el .IP "\f(CWvoid (*)(ev_watcher_type *, int revents)\fR must have compatible calling conventions regardless of \f(CWev_watcher_type *\fR." 4
4122.IX Item "void (*)(ev_watcher_type *, int revents) must have compatible calling conventions regardless of ev_watcher_type *."
4123Libev assumes not only that all watcher pointers have the same internal
4124structure (guaranteed by \s-1POSIX\s0 but not by \s-1ISO\s0 C for example), but it also
4125assumes that the same (machine) code can be used to call any watcher
4126callback: The watcher callbacks have different type signatures, but libev
4127calls them using an \f(CW\*(C`ev_watcher *\*(C'\fR internally.
4128.ie n .IP """sig_atomic_t volatile"" must be thread-atomic as well" 4
4129.el .IP "\f(CWsig_atomic_t volatile\fR must be thread-atomic as well" 4
4130.IX Item "sig_atomic_t volatile must be thread-atomic as well"
4131The type \f(CW\*(C`sig_atomic_t volatile\*(C'\fR (or whatever is defined as
4132\&\f(CW\*(C`EV_ATOMIC_T\*(C'\fR) must be atomic with respect to accesses from different
4133threads. This is not part of the specification for \f(CW\*(C`sig_atomic_t\*(C'\fR, but is
4134believed to be sufficiently portable.
4135.ie n .IP """sigprocmask"" must work in a threaded environment" 4
4136.el .IP "\f(CWsigprocmask\fR must work in a threaded environment" 4
4137.IX Item "sigprocmask must work in a threaded environment"
4138Libev uses \f(CW\*(C`sigprocmask\*(C'\fR to temporarily block signals. This is not
4139allowed in a threaded program (\f(CW\*(C`pthread_sigmask\*(C'\fR has to be used). Typical
4140pthread implementations will either allow \f(CW\*(C`sigprocmask\*(C'\fR in the \*(L"main
4141thread\*(R" or will block signals process-wide, both behaviours would
4142be compatible with libev. Interaction between \f(CW\*(C`sigprocmask\*(C'\fR and
4143\&\f(CW\*(C`pthread_sigmask\*(C'\fR could complicate things, however.
4144.Sp
4145The most portable way to handle signals is to block signals in all threads
4146except the initial one, and run the default loop in the initial thread as
4147well.
4148.ie n .IP """long"" must be large enough for common memory allocation sizes" 4
4149.el .IP "\f(CWlong\fR must be large enough for common memory allocation sizes" 4
4150.IX Item "long must be large enough for common memory allocation sizes"
4151To improve portability and simplify its \s-1API\s0, libev uses \f(CW\*(C`long\*(C'\fR internally
4152instead of \f(CW\*(C`size_t\*(C'\fR when allocating its data structures. On non-POSIX
4153systems (Microsoft...) this might be unexpectedly low, but is still at
4154least 31 bits everywhere, which is enough for hundreds of millions of
4155watchers.
4156.ie n .IP """double"" must hold a time value in seconds with enough accuracy" 4
4157.el .IP "\f(CWdouble\fR must hold a time value in seconds with enough accuracy" 4
4158.IX Item "double must hold a time value in seconds with enough accuracy"
4159The type \f(CW\*(C`double\*(C'\fR is used to represent timestamps. It is required to
4160have at least 51 bits of mantissa (and 9 bits of exponent), which is good
4161enough for at least into the year 4000. This requirement is fulfilled by
4162implementations implementing \s-1IEEE\s0 754 (basically all existing ones).
4163.PP
4164If you know of other additional requirements drop me a note.
4165.SH "ALGORITHMIC COMPLEXITIES"
4166.IX Header "ALGORITHMIC COMPLEXITIES"
4167In this section the complexities of (many of) the algorithms used inside
4168libev will be documented. For complexity discussions about backends see
4169the documentation for \f(CW\*(C`ev_default_init\*(C'\fR.
4170.PP
4171All of the following are about amortised time: If an array needs to be
4172extended, libev needs to realloc and move the whole array, but this
4173happens asymptotically rarer with higher number of elements, so O(1) might
4174mean that libev does a lengthy realloc operation in rare cases, but on
4175average it is much faster and asymptotically approaches constant time.
4176.IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4
4177.IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)"
4178This means that, when you have a watcher that triggers in one hour and
4179there are 100 watchers that would trigger before that, then inserting will
4180have to skip roughly seven (\f(CW\*(C`ld 100\*(C'\fR) of these watchers.
4181.IP "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 4
4182.IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)"
4183That means that changing a timer costs less than removing/adding them,
4184as only the relative motion in the event queue has to be paid for.
4185.IP "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)" 4
4186.IX Item "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)"
4187These just add the watcher into an array or at the head of a list.
4188.IP "Stopping check/prepare/idle/fork/async watchers: O(1)" 4
4189.IX Item "Stopping check/prepare/idle/fork/async watchers: O(1)"
4190.PD 0
4191.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4
4192.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))"
4193.PD
4194These watchers are stored in lists, so they need to be walked to find the
4195correct watcher to remove. The lists are usually short (you don't usually
4196have many watchers waiting for the same fd or signal: one is typical, two
4197is rare).
4198.IP "Finding the next timer in each loop iteration: O(1)" 4
4199.IX Item "Finding the next timer in each loop iteration: O(1)"
4200By virtue of using a binary or 4\-heap, the next timer is always found at a
4201fixed position in the storage array.
4202.IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4
4203.IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)"
4204A change means an I/O watcher gets started or stopped, which requires
4205libev to recalculate its status (and possibly tell the kernel, depending
4206on backend and whether \f(CW\*(C`ev_io_set\*(C'\fR was used).
4207.IP "Activating one watcher (putting it into the pending state): O(1)" 4
4208.IX Item "Activating one watcher (putting it into the pending state): O(1)"
4209.PD 0
4210.IP "Priority handling: O(number_of_priorities)" 4
4211.IX Item "Priority handling: O(number_of_priorities)"
4212.PD
4213Priorities are implemented by allocating some space for each
4214priority. When doing priority-based operations, libev usually has to
4215linearly search all the priorities, but starting/stopping and activating
4216watchers becomes O(1) with respect to priority handling.
4217.IP "Sending an ev_async: O(1)" 4
4218.IX Item "Sending an ev_async: O(1)"
4219.PD 0
4220.IP "Processing ev_async_send: O(number_of_async_watchers)" 4
4221.IX Item "Processing ev_async_send: O(number_of_async_watchers)"
4222.IP "Processing signals: O(max_signal_number)" 4
4223.IX Item "Processing signals: O(max_signal_number)"
4224.PD
4225Sending involves a system call \fIiff\fR there were no other \f(CW\*(C`ev_async_send\*(C'\fR
4226calls in the current loop iteration. Checking for async and signal events
4227involves iterating over all running async watchers or all signal numbers.
4228.SH "GLOSSARY"
4229.IX Header "GLOSSARY"
4230.IP "active" 4
4231.IX Item "active"
4232A watcher is active as long as it has been started (has been attached to
4233an event loop) but not yet stopped (disassociated from the event loop).
4234.IP "application" 4
4235.IX Item "application"
4236In this document, an application is whatever is using libev.
4237.IP "callback" 4
4238.IX Item "callback"
4239The address of a function that is called when some event has been
4240detected. Callbacks are being passed the event loop, the watcher that
4241received the event, and the actual event bitset.
4242.IP "callback invocation" 4
4243.IX Item "callback invocation"
4244The act of calling the callback associated with a watcher.
4245.IP "event" 4
4246.IX Item "event"
4247A change of state of some external event, such as data now being available
4248for reading on a file descriptor, time having passed or simply not having
4249any other events happening anymore.
4250.Sp
4251In libev, events are represented as single bits (such as \f(CW\*(C`EV_READ\*(C'\fR or
4252\&\f(CW\*(C`EV_TIMEOUT\*(C'\fR).
4253.IP "event library" 4
4254.IX Item "event library"
4255A software package implementing an event model and loop.
4256.IP "event loop" 4
4257.IX Item "event loop"
4258An entity that handles and processes external events and converts them
4259into callback invocations.
4260.IP "event model" 4
4261.IX Item "event model"
4262The model used to describe how an event loop handles and processes
4263watchers and events.
4264.IP "pending" 4
4265.IX Item "pending"
4266A watcher is pending as soon as the corresponding event has been detected,
4267and stops being pending as soon as the watcher will be invoked or its
4268pending status is explicitly cleared by the application.
4269.Sp
4270A watcher can be pending, but not active. Stopping a watcher also clears
4271its pending status.
4272.IP "real time" 4
4273.IX Item "real time"
4274The physical time that is observed. It is apparently strictly monotonic :)
4275.IP "wall-clock time" 4
4276.IX Item "wall-clock time"
4277The time and date as shown on clocks. Unlike real time, it can actually
4278be wrong and jump forwards and backwards, e.g. when the you adjust your
4279clock.
4280.IP "watcher" 4
4281.IX Item "watcher"
4282A data structure that describes interest in certain events. Watchers need
4283to be started (attached to an event loop) before they can receive events.
4284.IP "watcher invocation" 4
4285.IX Item "watcher invocation"
4286The act of calling the callback associated with a watcher.
1350.SH "AUTHOR" 4287.SH "AUTHOR"
1351.IX Header "AUTHOR" 4288.IX Header "AUTHOR"
1352Marc Lehmann <libev@schmorp.de>. 4289Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.

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