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1.\" Automatically generated by Pod::Man v1.37, Pod::Parser v1.35 1.\" Automatically generated by Pod::Man 2.22 (Pod::Simple 3.07)
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129.\" ======================================================================== 124.\" ========================================================================
130.\" 125.\"
131.IX Title ""<STANDARD INPUT>" 1" 126.IX Title "LIBEV 3"
132.TH "<STANDARD INPUT>" 1 "2007-11-24" "perl v5.8.8" "User Contributed Perl Documentation" 127.TH LIBEV 3 "2011-01-11" "libev-4.03" "libev - high performance full featured event loop"
128.\" For nroff, turn off justification. Always turn off hyphenation; it makes
129.\" way too many mistakes in technical documents.
130.if n .ad l
131.nh
133.SH "NAME" 132.SH "NAME"
134libev \- a high performance full\-featured event loop written in C 133libev \- a high performance full\-featured event loop written in C
135.SH "SYNOPSIS" 134.SH "SYNOPSIS"
136.IX Header "SYNOPSIS" 135.IX Header "SYNOPSIS"
137.Vb 1 136.Vb 1
138\& #include <ev.h> 137\& #include <ev.h>
139.Ve 138.Ve
140.SH "DESCRIPTION" 139.SS "\s-1EXAMPLE\s0 \s-1PROGRAM\s0"
141.IX Header "DESCRIPTION" 140.IX Subsection "EXAMPLE PROGRAM"
141.Vb 2
142\& // a single header file is required
143\& #include <ev.h>
144\&
145\& #include <stdio.h> // for puts
146\&
147\& // every watcher type has its own typedef\*(Aqd struct
148\& // with the name ev_TYPE
149\& ev_io stdin_watcher;
150\& ev_timer timeout_watcher;
151\&
152\& // all watcher callbacks have a similar signature
153\& // this callback is called when data is readable on stdin
154\& static void
155\& stdin_cb (EV_P_ ev_io *w, int revents)
156\& {
157\& puts ("stdin ready");
158\& // for one\-shot events, one must manually stop the watcher
159\& // with its corresponding stop function.
160\& ev_io_stop (EV_A_ w);
161\&
162\& // this causes all nested ev_run\*(Aqs to stop iterating
163\& ev_break (EV_A_ EVBREAK_ALL);
164\& }
165\&
166\& // another callback, this time for a time\-out
167\& static void
168\& timeout_cb (EV_P_ ev_timer *w, int revents)
169\& {
170\& puts ("timeout");
171\& // this causes the innermost ev_run to stop iterating
172\& ev_break (EV_A_ EVBREAK_ONE);
173\& }
174\&
175\& int
176\& main (void)
177\& {
178\& // use the default event loop unless you have special needs
179\& struct ev_loop *loop = EV_DEFAULT;
180\&
181\& // initialise an io watcher, then start it
182\& // this one will watch for stdin to become readable
183\& ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
184\& ev_io_start (loop, &stdin_watcher);
185\&
186\& // initialise a timer watcher, then start it
187\& // simple non\-repeating 5.5 second timeout
188\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
189\& ev_timer_start (loop, &timeout_watcher);
190\&
191\& // now wait for events to arrive
192\& ev_run (loop, 0);
193\&
194\& // unloop was called, so exit
195\& return 0;
196\& }
197.Ve
198.SH "ABOUT THIS DOCUMENT"
199.IX Header "ABOUT THIS DOCUMENT"
200This document documents the libev software package.
201.PP
202The newest version of this document is also available as an html-formatted
203web page you might find easier to navigate when reading it for the first
204time: <http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
205.PP
206While this document tries to be as complete as possible in documenting
207libev, its usage and the rationale behind its design, it is not a tutorial
208on event-based programming, nor will it introduce event-based programming
209with libev.
210.PP
211Familiarity with event based programming techniques in general is assumed
212throughout this document.
213.SH "WHAT TO READ WHEN IN A HURRY"
214.IX Header "WHAT TO READ WHEN IN A HURRY"
215This manual tries to be very detailed, but unfortunately, this also makes
216it very long. If you just want to know the basics of libev, I suggest
217reading \*(L"\s-1ANATOMY\s0 \s-1OF\s0 A \s-1WATCHER\s0\*(R", then the \*(L"\s-1EXAMPLE\s0 \s-1PROGRAM\s0\*(R" above and
218look up the missing functions in \*(L"\s-1GLOBAL\s0 \s-1FUNCTIONS\s0\*(R" and the \f(CW\*(C`ev_io\*(C'\fR and
219\&\f(CW\*(C`ev_timer\*(C'\fR sections in \*(L"\s-1WATCHER\s0 \s-1TYPES\s0\*(R".
220.SH "ABOUT LIBEV"
221.IX Header "ABOUT LIBEV"
142Libev is an event loop: you register interest in certain events (such as a 222Libev is an event loop: you register interest in certain events (such as a
143file descriptor being readable or a timeout occuring), and it will manage 223file descriptor being readable or a timeout occurring), and it will manage
144these event sources and provide your program with events. 224these event sources and provide your program with events.
145.PP 225.PP
146To do this, it must take more or less complete control over your process 226To do this, it must take more or less complete control over your process
147(or thread) by executing the \fIevent loop\fR handler, and will then 227(or thread) by executing the \fIevent loop\fR handler, and will then
148communicate events via a callback mechanism. 228communicate events via a callback mechanism.
149.PP 229.PP
150You register interest in certain events by registering so-called \fIevent 230You register interest in certain events by registering so-called \fIevent
151watchers\fR, which are relatively small C structures you initialise with the 231watchers\fR, which are relatively small C structures you initialise with the
152details of the event, and then hand it over to libev by \fIstarting\fR the 232details of the event, and then hand it over to libev by \fIstarting\fR the
153watcher. 233watcher.
154.SH "FEATURES" 234.SS "\s-1FEATURES\s0"
155.IX Header "FEATURES" 235.IX Subsection "FEATURES"
156Libev supports select, poll, the linux-specific epoll and the bsd-specific 236Libev supports \f(CW\*(C`select\*(C'\fR, \f(CW\*(C`poll\*(C'\fR, the Linux-specific \f(CW\*(C`epoll\*(C'\fR, the
157kqueue mechanisms for file descriptor events, relative timers, absolute 237BSD-specific \f(CW\*(C`kqueue\*(C'\fR and the Solaris-specific event port mechanisms
158timers with customised rescheduling, signal events, process status change 238for file descriptor events (\f(CW\*(C`ev_io\*(C'\fR), the Linux \f(CW\*(C`inotify\*(C'\fR interface
159events (related to \s-1SIGCHLD\s0), and event watchers dealing with the event 239(for \f(CW\*(C`ev_stat\*(C'\fR), Linux eventfd/signalfd (for faster and cleaner
160loop mechanism itself (idle, prepare and check watchers). It also is quite 240inter-thread wakeup (\f(CW\*(C`ev_async\*(C'\fR)/signal handling (\f(CW\*(C`ev_signal\*(C'\fR)) relative
161fast (see this benchmark comparing 241timers (\f(CW\*(C`ev_timer\*(C'\fR), absolute timers with customised rescheduling
162it to libevent for example). 242(\f(CW\*(C`ev_periodic\*(C'\fR), synchronous signals (\f(CW\*(C`ev_signal\*(C'\fR), process status
243change events (\f(CW\*(C`ev_child\*(C'\fR), and event watchers dealing with the event
244loop mechanism itself (\f(CW\*(C`ev_idle\*(C'\fR, \f(CW\*(C`ev_embed\*(C'\fR, \f(CW\*(C`ev_prepare\*(C'\fR and
245\&\f(CW\*(C`ev_check\*(C'\fR watchers) as well as file watchers (\f(CW\*(C`ev_stat\*(C'\fR) and even
246limited support for fork events (\f(CW\*(C`ev_fork\*(C'\fR).
247.PP
248It also is quite fast (see this
249<benchmark> comparing it to libevent
250for example).
163.SH "CONVENTIONS" 251.SS "\s-1CONVENTIONS\s0"
164.IX Header "CONVENTIONS" 252.IX Subsection "CONVENTIONS"
165Libev is very configurable. In this manual the default configuration 253Libev is very configurable. In this manual the default (and most common)
166will be described, which supports multiple event loops. For more info 254configuration will be described, which supports multiple event loops. For
167about various configuration options please have a look at the file 255more info about various configuration options please have a look at
168\&\fI\s-1README\s0.embed\fR in the libev distribution. If libev was configured without 256\&\fB\s-1EMBED\s0\fR section in this manual. If libev was configured without support
169support for multiple event loops, then all functions taking an initial 257for multiple event loops, then all functions taking an initial argument of
170argument of name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) 258name \f(CW\*(C`loop\*(C'\fR (which is always of type \f(CW\*(C`struct ev_loop *\*(C'\fR) will not have
171will not have this argument. 259this argument.
172.SH "TIME REPRESENTATION" 260.SS "\s-1TIME\s0 \s-1REPRESENTATION\s0"
173.IX Header "TIME REPRESENTATION" 261.IX Subsection "TIME REPRESENTATION"
174Libev represents time as a single floating point number, representing the 262Libev represents time as a single floating point number, representing
175(fractional) number of seconds since the (\s-1POSIX\s0) epoch (somewhere near 263the (fractional) number of seconds since the (\s-1POSIX\s0) epoch (in practice
176the beginning of 1970, details are complicated, don't ask). This type is 264somewhere near the beginning of 1970, details are complicated, don't
177called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use too. It usually aliases 265ask). This type is called \f(CW\*(C`ev_tstamp\*(C'\fR, which is what you should use
178to the \f(CW\*(C`double\*(C'\fR type in C, and when you need to do any calculations on 266too. It usually aliases to the \f(CW\*(C`double\*(C'\fR type in C. When you need to do
179it, you should treat it as such. 267any calculations on it, you should treat it as some floating point value.
268.PP
269Unlike the name component \f(CW\*(C`stamp\*(C'\fR might indicate, it is also used for
270time differences (e.g. delays) throughout libev.
271.SH "ERROR HANDLING"
272.IX Header "ERROR HANDLING"
273Libev knows three classes of errors: operating system errors, usage errors
274and internal errors (bugs).
275.PP
276When libev catches an operating system error it cannot handle (for example
277a system call indicating a condition libev cannot fix), it calls the callback
278set via \f(CW\*(C`ev_set_syserr_cb\*(C'\fR, which is supposed to fix the problem or
279abort. The default is to print a diagnostic message and to call \f(CW\*(C`abort
280()\*(C'\fR.
281.PP
282When libev detects a usage error such as a negative timer interval, then
283it will print a diagnostic message and abort (via the \f(CW\*(C`assert\*(C'\fR mechanism,
284so \f(CW\*(C`NDEBUG\*(C'\fR will disable this checking): these are programming errors in
285the libev caller and need to be fixed there.
286.PP
287Libev also has a few internal error-checking \f(CW\*(C`assert\*(C'\fRions, and also has
288extensive consistency checking code. These do not trigger under normal
289circumstances, as they indicate either a bug in libev or worse.
180.SH "GLOBAL FUNCTIONS" 290.SH "GLOBAL FUNCTIONS"
181.IX Header "GLOBAL FUNCTIONS" 291.IX Header "GLOBAL FUNCTIONS"
182These functions can be called anytime, even before initialising the 292These functions can be called anytime, even before initialising the
183library in any way. 293library in any way.
184.IP "ev_tstamp ev_time ()" 4 294.IP "ev_tstamp ev_time ()" 4
185.IX Item "ev_tstamp ev_time ()" 295.IX Item "ev_tstamp ev_time ()"
186Returns the current time as libev would use it. Please note that the 296Returns the current time as libev would use it. Please note that the
187\&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp 297\&\f(CW\*(C`ev_now\*(C'\fR function is usually faster and also often returns the timestamp
188you actually want to know. 298you actually want to know. Also interesting is the combination of
299\&\f(CW\*(C`ev_update_now\*(C'\fR and \f(CW\*(C`ev_now\*(C'\fR.
300.IP "ev_sleep (ev_tstamp interval)" 4
301.IX Item "ev_sleep (ev_tstamp interval)"
302Sleep for the given interval: The current thread will be blocked until
303either it is interrupted or the given time interval has passed. Basically
304this is a sub-second-resolution \f(CW\*(C`sleep ()\*(C'\fR.
189.IP "int ev_version_major ()" 4 305.IP "int ev_version_major ()" 4
190.IX Item "int ev_version_major ()" 306.IX Item "int ev_version_major ()"
191.PD 0 307.PD 0
192.IP "int ev_version_minor ()" 4 308.IP "int ev_version_minor ()" 4
193.IX Item "int ev_version_minor ()" 309.IX Item "int ev_version_minor ()"
194.PD 310.PD
195You can find out the major and minor version numbers of the library 311You can find out the major and minor \s-1ABI\s0 version numbers of the library
196you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and 312you linked against by calling the functions \f(CW\*(C`ev_version_major\*(C'\fR and
197\&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global 313\&\f(CW\*(C`ev_version_minor\*(C'\fR. If you want, you can compare against the global
198symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the 314symbols \f(CW\*(C`EV_VERSION_MAJOR\*(C'\fR and \f(CW\*(C`EV_VERSION_MINOR\*(C'\fR, which specify the
199version of the library your program was compiled against. 315version of the library your program was compiled against.
200.Sp 316.Sp
317These version numbers refer to the \s-1ABI\s0 version of the library, not the
318release version.
319.Sp
201Usually, it's a good idea to terminate if the major versions mismatch, 320Usually, it's a good idea to terminate if the major versions mismatch,
202as this indicates an incompatible change. Minor versions are usually 321as this indicates an incompatible change. Minor versions are usually
203compatible to older versions, so a larger minor version alone is usually 322compatible to older versions, so a larger minor version alone is usually
204not a problem. 323not a problem.
205.Sp 324.Sp
206Example: make sure we haven't accidentally been linked against the wrong 325Example: Make sure we haven't accidentally been linked against the wrong
207version: 326version (note, however, that this will not detect other \s-1ABI\s0 mismatches,
327such as \s-1LFS\s0 or reentrancy).
208.Sp 328.Sp
209.Vb 3 329.Vb 3
210\& assert (("libev version mismatch", 330\& assert (("libev version mismatch",
211\& ev_version_major () == EV_VERSION_MAJOR 331\& ev_version_major () == EV_VERSION_MAJOR
212\& && ev_version_minor () >= EV_VERSION_MINOR)); 332\& && ev_version_minor () >= EV_VERSION_MINOR));
213.Ve 333.Ve
214.IP "unsigned int ev_supported_backends ()" 4 334.IP "unsigned int ev_supported_backends ()" 4
215.IX Item "unsigned int ev_supported_backends ()" 335.IX Item "unsigned int ev_supported_backends ()"
216Return the set of all backends (i.e. their corresponding \f(CW\*(C`EV_BACKEND_*\*(C'\fR 336Return 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 337value) compiled into this binary of libev (independent of their
… …
220.Sp 340.Sp
221Example: make sure we have the epoll method, because yeah this is cool and 341Example: 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 342a must have and can we have a torrent of it please!!!11
223.Sp 343.Sp
224.Vb 2 344.Vb 2
225\& assert (("sorry, no epoll, no sex", 345\& assert (("sorry, no epoll, no sex",
226\& ev_supported_backends () & EVBACKEND_EPOLL)); 346\& ev_supported_backends () & EVBACKEND_EPOLL));
227.Ve 347.Ve
228.IP "unsigned int ev_recommended_backends ()" 4 348.IP "unsigned int ev_recommended_backends ()" 4
229.IX Item "unsigned int ev_recommended_backends ()" 349.IX Item "unsigned int ev_recommended_backends ()"
230Return the set of all backends compiled into this binary of libev and also 350Return the set of all backends compiled into this binary of libev and
231recommended for this platform. This set is often smaller than the one 351also recommended for this platform, meaning it will work for most file
352descriptor types. This set is often smaller than the one returned by
232returned by \f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on 353\&\f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on most BSDs
233most BSDs and will not be autodetected unless you explicitly request it 354and will not be auto-detected unless you explicitly request it (assuming
234(assuming you know what you are doing). This is the set of backends that 355you know what you are doing). This is the set of backends that libev will
235libev will probe for if you specify no backends explicitly. 356probe for if you specify no backends explicitly.
236.IP "unsigned int ev_embeddable_backends ()" 4 357.IP "unsigned int ev_embeddable_backends ()" 4
237.IX Item "unsigned int ev_embeddable_backends ()" 358.IX Item "unsigned int ev_embeddable_backends ()"
238Returns the set of backends that are embeddable in other event loops. This 359Returns the set of backends that are embeddable in other event loops. This
239is the theoretical, all\-platform, value. To find which backends 360value is platform-specific but can include backends not available on the
240might be supported on the current system, you would need to look at 361current system. To find which embeddable backends might be supported on
241\&\f(CW\*(C`ev_embeddable_backends () & ev_supported_backends ()\*(C'\fR, likewise for 362the current system, you would need to look at \f(CW\*(C`ev_embeddable_backends ()
242recommended ones. 363& ev_supported_backends ()\*(C'\fR, likewise for recommended ones.
243.Sp 364.Sp
244See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info. 365See 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))" 4 366.IP "ev_set_allocator (void *(*cb)(void *ptr, long size))" 4
246.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))" 367.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))"
247Sets the allocation function to use (the prototype is similar to the 368Sets the allocation function to use (the prototype is similar \- the
248realloc C function, the semantics are identical). It is used to allocate 369semantics are identical to the \f(CW\*(C`realloc\*(C'\fR C89/SuS/POSIX function). It is
249and free memory (no surprises here). If it returns zero when memory 370used to allocate and free memory (no surprises here). If it returns zero
250needs to be allocated, the library might abort or take some potentially 371when memory needs to be allocated (\f(CW\*(C`size != 0\*(C'\fR), the library might abort
251destructive action. The default is your system realloc function. 372or take some potentially destructive action.
373.Sp
374Since some systems (at least OpenBSD and Darwin) fail to implement
375correct \f(CW\*(C`realloc\*(C'\fR semantics, libev will use a wrapper around the system
376\&\f(CW\*(C`realloc\*(C'\fR and \f(CW\*(C`free\*(C'\fR functions by default.
252.Sp 377.Sp
253You could override this function in high-availability programs to, say, 378You could override this function in high-availability programs to, say,
254free some memory if it cannot allocate memory, to use a special allocator, 379free some memory if it cannot allocate memory, to use a special allocator,
255or even to sleep a while and retry until some memory is available. 380or even to sleep a while and retry until some memory is available.
256.Sp 381.Sp
257Example: replace the libev allocator with one that waits a bit and then 382Example: Replace the libev allocator with one that waits a bit and then
258retries: better than mine). 383retries (example requires a standards-compliant \f(CW\*(C`realloc\*(C'\fR).
259.Sp 384.Sp
260.Vb 6 385.Vb 6
261\& static void * 386\& static void *
262\& persistent_realloc (void *ptr, long size) 387\& persistent_realloc (void *ptr, size_t size)
263\& { 388\& {
264\& for (;;) 389\& for (;;)
265\& { 390\& {
266\& void *newptr = realloc (ptr, size); 391\& void *newptr = realloc (ptr, size);
267.Ve 392\&
268.Sp
269.Vb 2
270\& if (newptr) 393\& if (newptr)
271\& return newptr; 394\& return newptr;
272.Ve 395\&
273.Sp
274.Vb 3
275\& sleep (60); 396\& sleep (60);
276\& } 397\& }
277\& } 398\& }
278.Ve 399\&
279.Sp
280.Vb 2
281\& ... 400\& ...
282\& ev_set_allocator (persistent_realloc); 401\& ev_set_allocator (persistent_realloc);
283.Ve 402.Ve
284.IP "ev_set_syserr_cb (void (*cb)(const char *msg));" 4 403.IP "ev_set_syserr_cb (void (*cb)(const char *msg))" 4
285.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg));" 404.IX Item "ev_set_syserr_cb (void (*cb)(const char *msg))"
286Set the callback function to call on a retryable syscall error (such 405Set the callback function to call on a retryable system call error (such
287as failed select, poll, epoll_wait). The message is a printable string 406as failed select, poll, epoll_wait). The message is a printable string
288indicating the system call or subsystem causing the problem. If this 407indicating the system call or subsystem causing the problem. If this
289callback is set, then libev will expect it to remedy the sitution, no 408callback is set, then libev will expect it to remedy the situation, no
290matter what, when it returns. That is, libev will generally retry the 409matter what, when it returns. That is, libev will generally retry the
291requested operation, or, if the condition doesn't go away, do bad stuff 410requested operation, or, if the condition doesn't go away, do bad stuff
292(such as abort). 411(such as abort).
293.Sp 412.Sp
294Example: do the same thing as libev does internally: 413Example: This is basically the same thing that libev does internally, too.
295.Sp 414.Sp
296.Vb 6 415.Vb 6
297\& static void 416\& static void
298\& fatal_error (const char *msg) 417\& fatal_error (const char *msg)
299\& { 418\& {
300\& perror (msg); 419\& perror (msg);
301\& abort (); 420\& abort ();
302\& } 421\& }
303.Ve 422\&
304.Sp
305.Vb 2
306\& ... 423\& ...
307\& ev_set_syserr_cb (fatal_error); 424\& ev_set_syserr_cb (fatal_error);
308.Ve 425.Ve
426.IP "ev_feed_signal (int signum)" 4
427.IX Item "ev_feed_signal (int signum)"
428This function can be used to \*(L"simulate\*(R" a signal receive. It is completely
429safe to call this function at any time, from any context, including signal
430handlers or random threads.
431.Sp
432Its main use is to customise signal handling in your process, especially
433in the presence of threads. For example, you could block signals
434by default in all threads (and specifying \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when
435creating any loops), and in one thread, use \f(CW\*(C`sigwait\*(C'\fR or any other
436mechanism to wait for signals, then \*(L"deliver\*(R" them to libev by calling
437\&\f(CW\*(C`ev_feed_signal\*(C'\fR.
309.SH "FUNCTIONS CONTROLLING THE EVENT LOOP" 438.SH "FUNCTIONS CONTROLLING EVENT LOOPS"
310.IX Header "FUNCTIONS CONTROLLING THE EVENT LOOP" 439.IX Header "FUNCTIONS CONTROLLING EVENT LOOPS"
311An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR. The library knows two 440An event loop is described by a \f(CW\*(C`struct ev_loop *\*(C'\fR (the \f(CW\*(C`struct\*(C'\fR is
312types of such loops, the \fIdefault\fR loop, which supports signals and child 441\&\fInot\fR optional in this case unless libev 3 compatibility is disabled, as
313events, and dynamically created loops which do not. 442libev 3 had an \f(CW\*(C`ev_loop\*(C'\fR function colliding with the struct name).
314.PP 443.PP
315If you use threads, a common model is to run the default event loop 444The 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 445supports child process events, and dynamically created event loops which
317create, you also create another event loop. Libev itself does no locking 446do not.
318whatsoever, so if you mix calls to the same event loop in different
319threads, make sure you lock (this is usually a bad idea, though, even if
320done correctly, because it's hideous and inefficient).
321.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4 447.IP "struct ev_loop *ev_default_loop (unsigned int flags)" 4
322.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)" 448.IX Item "struct ev_loop *ev_default_loop (unsigned int flags)"
323This will initialise the default event loop if it hasn't been initialised 449This returns the \*(L"default\*(R" event loop object, which is what you should
324yet and return it. If the default loop could not be initialised, returns 450normally use when you just need \*(L"the event loop\*(R". Event loop objects and
325false. If it already was initialised it simply returns it (and ignores the 451the \f(CW\*(C`flags\*(C'\fR parameter are described in more detail in the entry for
326flags. If that is troubling you, check \f(CW\*(C`ev_backend ()\*(C'\fR afterwards). 452\&\f(CW\*(C`ev_loop_new\*(C'\fR.
453.Sp
454If the default loop is already initialised then this function simply
455returns it (and ignores the flags. If that is troubling you, check
456\&\f(CW\*(C`ev_backend ()\*(C'\fR afterwards). Otherwise it will create it with the given
457flags, which should almost always be \f(CW0\fR, unless the caller is also the
458one calling \f(CW\*(C`ev_run\*(C'\fR or otherwise qualifies as \*(L"the main program\*(R".
327.Sp 459.Sp
328If you don't know what event loop to use, use the one returned from this 460If you don't know what event loop to use, use the one returned from this
329function. 461function (or via the \f(CW\*(C`EV_DEFAULT\*(C'\fR macro).
462.Sp
463Note that this function is \fInot\fR thread-safe, so if you want to use it
464from multiple threads, you have to employ some kind of mutex (note also
465that this case is unlikely, as loops cannot be shared easily between
466threads anyway).
467.Sp
468The default loop is the only loop that can handle \f(CW\*(C`ev_child\*(C'\fR watchers,
469and to do this, it always registers a handler for \f(CW\*(C`SIGCHLD\*(C'\fR. If this is
470a problem for your application you can either create a dynamic loop with
471\&\f(CW\*(C`ev_loop_new\*(C'\fR which doesn't do that, or you can simply overwrite the
472\&\f(CW\*(C`SIGCHLD\*(C'\fR signal handler \fIafter\fR calling \f(CW\*(C`ev_default_init\*(C'\fR.
473.Sp
474Example: This is the most typical usage.
475.Sp
476.Vb 2
477\& if (!ev_default_loop (0))
478\& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
479.Ve
480.Sp
481Example: Restrict libev to the select and poll backends, and do not allow
482environment settings to be taken into account:
483.Sp
484.Vb 1
485\& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
486.Ve
487.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
488.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
489This will create and initialise a new event loop object. If the loop
490could not be initialised, returns false.
491.Sp
492This function is thread-safe, and one common way to use libev with
493threads is indeed to create one loop per thread, and using the default
494loop in the \*(L"main\*(R" or \*(L"initial\*(R" thread.
330.Sp 495.Sp
331The flags argument can be used to specify special behaviour or specific 496The 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). 497backends to use, and is usually specified as \f(CW0\fR (or \f(CW\*(C`EVFLAG_AUTO\*(C'\fR).
333.Sp 498.Sp
334The following flags are supported: 499The following flags are supported:
… …
339The default flags value. Use this if you have no clue (it's the right 504The default flags value. Use this if you have no clue (it's the right
340thing, believe me). 505thing, believe me).
341.ie n .IP """EVFLAG_NOENV""" 4 506.ie n .IP """EVFLAG_NOENV""" 4
342.el .IP "\f(CWEVFLAG_NOENV\fR" 4 507.el .IP "\f(CWEVFLAG_NOENV\fR" 4
343.IX Item "EVFLAG_NOENV" 508.IX Item "EVFLAG_NOENV"
344If this flag bit is ored into the flag value (or the program runs setuid 509If 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 510or 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 511\&\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 512override 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 513useful to try out specific backends to test their performance, or to work
349around bugs. 514around bugs.
515.ie n .IP """EVFLAG_FORKCHECK""" 4
516.el .IP "\f(CWEVFLAG_FORKCHECK\fR" 4
517.IX Item "EVFLAG_FORKCHECK"
518Instead of calling \f(CW\*(C`ev_loop_fork\*(C'\fR manually after a fork, you can also
519make libev check for a fork in each iteration by enabling this flag.
520.Sp
521This works by calling \f(CW\*(C`getpid ()\*(C'\fR on every iteration of the loop,
522and thus this might slow down your event loop if you do a lot of loop
523iterations and little real work, but is usually not noticeable (on my
524GNU/Linux system for example, \f(CW\*(C`getpid\*(C'\fR is actually a simple 5\-insn sequence
525without a system call and thus \fIvery\fR fast, but my GNU/Linux system also has
526\&\f(CW\*(C`pthread_atfork\*(C'\fR which is even faster).
527.Sp
528The big advantage of this flag is that you can forget about fork (and
529forget about forgetting to tell libev about forking) when you use this
530flag.
531.Sp
532This flag setting cannot be overridden or specified in the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR
533environment variable.
534.ie n .IP """EVFLAG_NOINOTIFY""" 4
535.el .IP "\f(CWEVFLAG_NOINOTIFY\fR" 4
536.IX Item "EVFLAG_NOINOTIFY"
537When this flag is specified, then libev will not attempt to use the
538\&\fIinotify\fR \s-1API\s0 for its \f(CW\*(C`ev_stat\*(C'\fR watchers. Apart from debugging and
539testing, this flag can be useful to conserve inotify file descriptors, as
540otherwise each loop using \f(CW\*(C`ev_stat\*(C'\fR watchers consumes one inotify handle.
541.ie n .IP """EVFLAG_SIGNALFD""" 4
542.el .IP "\f(CWEVFLAG_SIGNALFD\fR" 4
543.IX Item "EVFLAG_SIGNALFD"
544When this flag is specified, then libev will attempt to use the
545\&\fIsignalfd\fR \s-1API\s0 for its \f(CW\*(C`ev_signal\*(C'\fR (and \f(CW\*(C`ev_child\*(C'\fR) watchers. This \s-1API\s0
546delivers signals synchronously, which makes it both faster and might make
547it possible to get the queued signal data. It can also simplify signal
548handling with threads, as long as you properly block signals in your
549threads that are not interested in handling them.
550.Sp
551Signalfd will not be used by default as this changes your signal mask, and
552there are a lot of shoddy libraries and programs (glib's threadpool for
553example) that can't properly initialise their signal masks.
554.ie n .IP """EVFLAG_NOSIGMASK""" 4
555.el .IP "\f(CWEVFLAG_NOSIGMASK\fR" 4
556.IX Item "EVFLAG_NOSIGMASK"
557When this flag is specified, then libev will avoid to modify the signal
558mask. Specifically, this means you ahve to make sure signals are unblocked
559when you want to receive them.
560.Sp
561This behaviour is useful when you want to do your own signal handling, or
562want to handle signals only in specific threads and want to avoid libev
563unblocking the signals.
564.Sp
565This flag's behaviour will become the default in future versions of libev.
350.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4 566.ie n .IP """EVBACKEND_SELECT"" (value 1, portable select backend)" 4
351.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4 567.el .IP "\f(CWEVBACKEND_SELECT\fR (value 1, portable select backend)" 4
352.IX Item "EVBACKEND_SELECT (value 1, portable select backend)" 568.IX Item "EVBACKEND_SELECT (value 1, portable select backend)"
353This is your standard \fIselect\fR\|(2) backend. Not \fIcompletely\fR standard, as 569This 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, 570libev 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 571but 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 572using this backend. It doesn't scale too well (O(highest_fd)), but its
357the fastest backend for a low number of fds. 573usually the fastest backend for a low number of (low-numbered :) fds.
574.Sp
575To get good performance out of this backend you need a high amount of
576parallelism (most of the file descriptors should be busy). If you are
577writing a server, you should \f(CW\*(C`accept ()\*(C'\fR in a loop to accept as many
578connections as possible during one iteration. You might also want to have
579a look at \f(CW\*(C`ev_set_io_collect_interval ()\*(C'\fR to increase the amount of
580readiness notifications you get per iteration.
581.Sp
582This 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
583\&\f(CW\*(C`writefds\*(C'\fR set (and to work around Microsoft Windows bugs, also onto the
584\&\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)" 4 585.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)" 4 586.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)" 587.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 588And 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 589than select, but handles sparse fds better and has no artificial
363number of fds you can use (except it will slow down considerably with a 590limit 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). 591considerably with a lot of inactive fds). It scales similarly to select,
592i.e. O(total_fds). See the entry for \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR, above, for
593performance tips.
594.Sp
595This backend maps \f(CW\*(C`EV_READ\*(C'\fR to \f(CW\*(C`POLLIN | POLLERR | POLLHUP\*(C'\fR, and
596\&\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)" 4 597.ie n .IP """EVBACKEND_EPOLL"" (value 4, Linux)" 4
366.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4 598.el .IP "\f(CWEVBACKEND_EPOLL\fR (value 4, Linux)" 4
367.IX Item "EVBACKEND_EPOLL (value 4, Linux)" 599.IX Item "EVBACKEND_EPOLL (value 4, Linux)"
600Use the linux-specific \fIepoll\fR\|(7) interface (for both pre\- and post\-2.6.9
601kernels).
602.Sp
368For few fds, this backend is a bit little slower than poll and select, 603For 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 604but 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 605like O(total_fds) where n is the total number of fds (or the highest fd),
371either O(1) or O(active_fds). 606epoll scales either O(1) or O(active_fds).
372.Sp 607.Sp
608The epoll mechanism deserves honorable mention as the most misdesigned
609of the more advanced event mechanisms: mere annoyances include silently
610dropping file descriptors, requiring a system call per change per file
611descriptor (and unnecessary guessing of parameters), problems with dup,
612returning before the timeout value, resulting in additional iterations
613(and only giving 5ms accuracy while select on the same platform gives
6140.1ms) and so on. The biggest issue is fork races, however \- if a program
615forks then \fIboth\fR parent and child process have to recreate the epoll
616set, which can take considerable time (one syscall per file descriptor)
617and is of course hard to detect.
618.Sp
619Epoll is also notoriously buggy \- embedding epoll fds \fIshould\fR work, but
620of course \fIdoesn't\fR, and epoll just loves to report events for totally
621\&\fIdifferent\fR file descriptors (even already closed ones, so one cannot
622even remove them from the set) than registered in the set (especially
623on \s-1SMP\s0 systems). Libev tries to counter these spurious notifications by
624employing an additional generation counter and comparing that against the
625events to filter out spurious ones, recreating the set when required. Last
626not least, it also refuses to work with some file descriptors which work
627perfectly fine with \f(CW\*(C`select\*(C'\fR (files, many character devices...).
628.Sp
629Epoll is truly the train wreck analog among event poll mechanisms,
630a frankenpoll, cobbled together in a hurry, no thought to design or
631interaction with others.
632.Sp
373While stopping and starting an I/O watcher in the same iteration will 633While stopping, setting and starting an I/O watcher in the same iteration
374result in some caching, there is still a syscall per such incident 634will 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 635incident (because the same \fIfile descriptor\fR could point to a different
376best to avoid that. Also, \fIdup()\fRed file descriptors might not work very 636\&\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. 637file descriptors might not work very well if you register events for both
638file descriptors.
378.Sp 639.Sp
379Please note that epoll sometimes generates spurious notifications, so you 640Best 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 641watchers for a file descriptor until it has been closed, if possible,
381(or space) is available. 642i.e. keep at least one watcher active per fd at all times. Stopping and
643starting a watcher (without re-setting it) also usually doesn't cause
644extra overhead. A fork can both result in spurious notifications as well
645as in libev having to destroy and recreate the epoll object, which can
646take considerable time and thus should be avoided.
647.Sp
648All this means that, in practice, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR can be as fast or
649faster than epoll for maybe up to a hundred file descriptors, depending on
650the usage. So sad.
651.Sp
652While nominally embeddable in other event loops, this feature is broken in
653all kernel versions tested so far.
654.Sp
655This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
656\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
382.ie n .IP """EVBACKEND_KQUEUE"" (value 8, most \s-1BSD\s0 clones)" 4 657.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)" 4 658.el .IP "\f(CWEVBACKEND_KQUEUE\fR (value 8, most \s-1BSD\s0 clones)" 4
384.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)" 659.IX Item "EVBACKEND_KQUEUE (value 8, most BSD clones)"
385Kqueue deserves special mention, as at the time of this writing, it 660Kqueue deserves special mention, as at the time of this writing, it
386was broken on all BSDs except NetBSD (usually it doesn't work with 661was broken on all BSDs except NetBSD (usually it doesn't work reliably
387anything but sockets and pipes, except on Darwin, where of course its 662with anything but sockets and pipes, except on Darwin, where of course
388completely useless). For this reason its not being \*(L"autodetected\*(R" 663it's completely useless). Unlike epoll, however, whose brokenness
664is by design, these kqueue bugs can (and eventually will) be fixed
665without \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 666\&\*(L"auto-detected\*(R" unless you explicitly specify it in the flags (i.e. using
390\&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR). 667\&\f(CW\*(C`EVBACKEND_KQUEUE\*(C'\fR) or libev was compiled on a known-to-be-good (\-enough)
668system like NetBSD.
669.Sp
670You still can embed kqueue into a normal poll or select backend and use it
671only for sockets (after having made sure that sockets work with kqueue on
672the target platform). See \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
391.Sp 673.Sp
392It scales in the same way as the epoll backend, but the interface to the 674It 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 675kernel is more efficient (which says nothing about its actual speed, of
394course). While starting and stopping an I/O watcher does not cause an 676course). 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 677cause 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. 678two event changes per incident. Support for \f(CW\*(C`fork ()\*(C'\fR is very bad (but
679sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
680cases
681.Sp
682This backend usually performs well under most conditions.
683.Sp
684While nominally embeddable in other event loops, this doesn't work
685everywhere, so you might need to test for this. And since it is broken
686almost everywhere, you should only use it when you have a lot of sockets
687(for which it usually works), by embedding it into another event loop
688(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
689also broken on \s-1OS\s0 X)) and, did I mention it, using it only for sockets.
690.Sp
691This backend maps \f(CW\*(C`EV_READ\*(C'\fR into an \f(CW\*(C`EVFILT_READ\*(C'\fR kevent with
692\&\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
693\&\f(CW\*(C`NOTE_EOF\*(C'\fR.
397.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4 694.ie n .IP """EVBACKEND_DEVPOLL"" (value 16, Solaris 8)" 4
398.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4 695.el .IP "\f(CWEVBACKEND_DEVPOLL\fR (value 16, Solaris 8)" 4
399.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)" 696.IX Item "EVBACKEND_DEVPOLL (value 16, Solaris 8)"
400This is not implemented yet (and might never be). 697This is not implemented yet (and might never be, unless you send me an
698implementation). According to reports, \f(CW\*(C`/dev/poll\*(C'\fR only supports sockets
699and is not embeddable, which would limit the usefulness of this backend
700immensely.
401.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4 701.ie n .IP """EVBACKEND_PORT"" (value 32, Solaris 10)" 4
402.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4 702.el .IP "\f(CWEVBACKEND_PORT\fR (value 32, Solaris 10)" 4
403.IX Item "EVBACKEND_PORT (value 32, Solaris 10)" 703.IX Item "EVBACKEND_PORT (value 32, Solaris 10)"
404This uses the Solaris 10 port mechanism. As with everything on Solaris, 704This 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)). 705it's really slow, but it still scales very well (O(active_fds)).
406.Sp 706.Sp
407Please note that solaris ports can result in a lot of spurious 707While this backend scales well, it requires one system call per active
408notifications, so you need to use non-blocking I/O or other means to avoid 708file descriptor per loop iteration. For small and medium numbers of file
409blocking when no data (or space) is available. 709descriptors a \*(L"slow\*(R" \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR backend
710might perform better.
711.Sp
712On the positive side, this backend actually performed fully to
713specification in all tests and is fully embeddable, which is a rare feat
714among the OS-specific backends (I vastly prefer correctness over speed
715hacks).
716.Sp
717On the negative side, the interface is \fIbizarre\fR \- so bizarre that
718even sun itself gets it wrong in their code examples: The event polling
719function sometimes returning events to the caller even though an error
720occurred, but with no indication whether it has done so or not (yes, it's
721even documented that way) \- deadly for edge-triggered interfaces where
722you absolutely have to know whether an event occurred or not because you
723have to re-arm the watcher.
724.Sp
725Fortunately libev seems to be able to work around these idiocies.
726.Sp
727This backend maps \f(CW\*(C`EV_READ\*(C'\fR and \f(CW\*(C`EV_WRITE\*(C'\fR in the same way as
728\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
410.ie n .IP """EVBACKEND_ALL""" 4 729.ie n .IP """EVBACKEND_ALL""" 4
411.el .IP "\f(CWEVBACKEND_ALL\fR" 4 730.el .IP "\f(CWEVBACKEND_ALL\fR" 4
412.IX Item "EVBACKEND_ALL" 731.IX Item "EVBACKEND_ALL"
413Try all backends (even potentially broken ones that wouldn't be tried 732Try 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 733with \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. 734\&\f(CW\*(C`EVBACKEND_ALL & ~EVBACKEND_KQUEUE\*(C'\fR.
735.Sp
736It is definitely not recommended to use this flag, use whatever
737\&\f(CW\*(C`ev_recommended_backends ()\*(C'\fR returns, or simply do not specify a backend
738at all.
739.ie n .IP """EVBACKEND_MASK""" 4
740.el .IP "\f(CWEVBACKEND_MASK\fR" 4
741.IX Item "EVBACKEND_MASK"
742Not a backend at all, but a mask to select all backend bits from a
743\&\f(CW\*(C`flags\*(C'\fR value, in case you want to mask out any backends from a flags
744value (e.g. when modifying the \f(CW\*(C`LIBEV_FLAGS\*(C'\fR environment variable).
416.RE 745.RE
417.RS 4 746.RS 4
418.Sp 747.Sp
419If one or more of these are ored into the flags value, then only these 748If one or more of the backend flags are or'ed into the flags value,
420backends will be tried (in the reverse order as given here). If none are 749then only these backends will be tried (in the reverse order as listed
421specified, most compiled-in backend will be tried, usually in reverse 750here). If none are specified, all backends in \f(CW\*(C`ev_recommended_backends
422order of their flag values :) 751()\*(C'\fR will be tried.
423.Sp 752.Sp
424The most typical usage is like this: 753Example: Try to create a event loop that uses epoll and nothing else.
425.Sp 754.Sp
426.Vb 2 755.Vb 3
427\& if (!ev_default_loop (0)) 756\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
428\& fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?"); 757\& if (!epoller)
758\& fatal ("no epoll found here, maybe it hides under your chair");
429.Ve 759.Ve
430.Sp 760.Sp
431Restrict libev to the select and poll backends, and do not allow 761Example: Use whatever libev has to offer, but make sure that kqueue is
432environment settings to be taken into account: 762used if available.
433.Sp 763.Sp
434.Vb 1 764.Vb 1
435\& ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
436.Ve
437.Sp
438Use whatever libev has to offer, but make sure that kqueue is used if
439available (warning, breaks stuff, best use only with your own private
440event loop and only if you know the \s-1OS\s0 supports your types of fds):
441.Sp
442.Vb 1
443\& ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE); 765\& struct ev_loop *loop = ev_loop_new (ev_recommended_backends () | EVBACKEND_KQUEUE);
444.Ve 766.Ve
445.RE 767.RE
446.IP "struct ev_loop *ev_loop_new (unsigned int flags)" 4
447.IX Item "struct ev_loop *ev_loop_new (unsigned int flags)"
448Similar to \f(CW\*(C`ev_default_loop\*(C'\fR, but always creates a new event loop that is
449always distinct from the default loop. Unlike the default loop, it cannot
450handle signal and child watchers, and attempts to do so will be greeted by
451undefined behaviour (or a failed assertion if assertions are enabled).
452.Sp
453Example: try to create a event loop that uses epoll and nothing else.
454.Sp
455.Vb 3
456\& struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
457\& if (!epoller)
458\& fatal ("no epoll found here, maybe it hides under your chair");
459.Ve
460.IP "ev_default_destroy ()" 4 768.IP "ev_loop_destroy (loop)" 4
461.IX Item "ev_default_destroy ()" 769.IX Item "ev_loop_destroy (loop)"
462Destroys the default loop again (frees all memory and kernel state 770Destroys an event loop object (frees all memory and kernel state
463etc.). None of the active event watchers will be stopped in the normal 771etc.). None of the active event watchers will be stopped in the normal
464sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your 772sense, so e.g. \f(CW\*(C`ev_is_active\*(C'\fR might still return true. It is your
465responsibility to either stop all watchers cleanly yoursef \fIbefore\fR 773responsibility to either stop all watchers cleanly yourself \fIbefore\fR
466calling this function, or cope with the fact afterwards (which is usually 774calling this function, or cope with the fact afterwards (which is usually
467the easiest thing, youc na just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them 775the easiest thing, you can just ignore the watchers and/or \f(CW\*(C`free ()\*(C'\fR them
468for example). 776for example).
469.IP "ev_loop_destroy (loop)" 4
470.IX Item "ev_loop_destroy (loop)"
471Like \f(CW\*(C`ev_default_destroy\*(C'\fR, but destroys an event loop created by an
472earlier call to \f(CW\*(C`ev_loop_new\*(C'\fR.
473.IP "ev_default_fork ()" 4
474.IX Item "ev_default_fork ()"
475This function reinitialises the kernel state for backends that have
476one. Despite the name, you can call it anytime, but it makes most sense
477after forking, in either the parent or child process (or both, but that
478again makes little sense).
479.Sp 777.Sp
480You \fImust\fR call this function in the child process after forking if and 778Note that certain global state, such as signal state (and installed signal
481only if you want to use the event library in both processes. If you just 779handlers), will not be freed by this function, and related watchers (such
482fork+exec, you don't have to call it. 780as signal and child watchers) would need to be stopped manually.
483.Sp 781.Sp
484The function itself is quite fast and it's usually not a problem to call 782This function is normally used on loop objects allocated by
485it just in case after a fork. To make this easy, the function will fit in 783\&\f(CW\*(C`ev_loop_new\*(C'\fR, but it can also be used on the default loop returned by
486quite nicely into a call to \f(CW\*(C`pthread_atfork\*(C'\fR: 784\&\f(CW\*(C`ev_default_loop\*(C'\fR, in which case it is not thread-safe.
487.Sp 785.Sp
488.Vb 1 786Note that it is not advisable to call this function on the default loop
489\& pthread_atfork (0, 0, ev_default_fork); 787except in the rare occasion where you really need to free its resources.
490.Ve 788If you need dynamically allocated loops it is better to use \f(CW\*(C`ev_loop_new\*(C'\fR
491.Sp 789and \f(CW\*(C`ev_loop_destroy\*(C'\fR.
492At the moment, \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and \f(CW\*(C`EVBACKEND_POLL\*(C'\fR are safe to use
493without calling this function, so if you force one of those backends you
494do not need to care.
495.IP "ev_loop_fork (loop)" 4 790.IP "ev_loop_fork (loop)" 4
496.IX Item "ev_loop_fork (loop)" 791.IX Item "ev_loop_fork (loop)"
497Like \f(CW\*(C`ev_default_fork\*(C'\fR, but acts on an event loop created by 792This function sets a flag that causes subsequent \f(CW\*(C`ev_run\*(C'\fR iterations to
498\&\f(CW\*(C`ev_loop_new\*(C'\fR. Yes, you have to call this on every allocated event loop 793reinitialise the kernel state for backends that have one. Despite the
499after fork, and how you do this is entirely your own problem. 794name, you can call it anytime, but it makes most sense after forking, in
795the child process. You \fImust\fR call it (or use \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR) in the
796child before resuming or calling \f(CW\*(C`ev_run\*(C'\fR.
797.Sp
798Again, you \fIhave\fR to call it on \fIany\fR loop that you want to re-use after
799a fork, \fIeven if you do not plan to use the loop in the parent\fR. This is
800because some kernel interfaces *cough* \fIkqueue\fR *cough* do funny things
801during fork.
802.Sp
803On the other hand, you only need to call this function in the child
804process if and only if you want to use the event loop in the child. If
805you just fork+exec or create a new loop in the child, you don't have to
806call it at all (in fact, \f(CW\*(C`epoll\*(C'\fR is so badly broken that it makes a
807difference, but libev will usually detect this case on its own and do a
808costly reset of the backend).
809.Sp
810The function itself is quite fast and it's usually not a problem to call
811it just in case after a fork.
812.Sp
813Example: Automate calling \f(CW\*(C`ev_loop_fork\*(C'\fR on the default loop when
814using pthreads.
815.Sp
816.Vb 5
817\& static void
818\& post_fork_child (void)
819\& {
820\& ev_loop_fork (EV_DEFAULT);
821\& }
822\&
823\& ...
824\& pthread_atfork (0, 0, post_fork_child);
825.Ve
826.IP "int ev_is_default_loop (loop)" 4
827.IX Item "int ev_is_default_loop (loop)"
828Returns true when the given loop is, in fact, the default loop, and false
829otherwise.
830.IP "unsigned int ev_iteration (loop)" 4
831.IX Item "unsigned int ev_iteration (loop)"
832Returns the current iteration count for the event loop, which is identical
833to the number of times libev did poll for new events. It starts at \f(CW0\fR
834and happily wraps around with enough iterations.
835.Sp
836This value can sometimes be useful as a generation counter of sorts (it
837\&\*(L"ticks\*(R" the number of loop iterations), as it roughly corresponds with
838\&\f(CW\*(C`ev_prepare\*(C'\fR and \f(CW\*(C`ev_check\*(C'\fR calls \- and is incremented between the
839prepare and check phases.
840.IP "unsigned int ev_depth (loop)" 4
841.IX Item "unsigned int ev_depth (loop)"
842Returns the number of times \f(CW\*(C`ev_run\*(C'\fR was entered minus the number of
843times \f(CW\*(C`ev_run\*(C'\fR was exited normally, in other words, the recursion depth.
844.Sp
845Outside \f(CW\*(C`ev_run\*(C'\fR, this number is zero. In a callback, this number is
846\&\f(CW1\fR, unless \f(CW\*(C`ev_run\*(C'\fR was invoked recursively (or from another thread),
847in which case it is higher.
848.Sp
849Leaving \f(CW\*(C`ev_run\*(C'\fR abnormally (setjmp/longjmp, cancelling the thread,
850throwing an exception etc.), doesn't count as \*(L"exit\*(R" \- consider this
851as a hint to avoid such ungentleman-like behaviour unless it's really
852convenient, in which case it is fully supported.
500.IP "unsigned int ev_backend (loop)" 4 853.IP "unsigned int ev_backend (loop)" 4
501.IX Item "unsigned int ev_backend (loop)" 854.IX Item "unsigned int ev_backend (loop)"
502Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in 855Returns one of the \f(CW\*(C`EVBACKEND_*\*(C'\fR flags indicating the event backend in
503use. 856use.
504.IP "ev_tstamp ev_now (loop)" 4 857.IP "ev_tstamp ev_now (loop)" 4
505.IX Item "ev_tstamp ev_now (loop)" 858.IX Item "ev_tstamp ev_now (loop)"
506Returns the current \*(L"event loop time\*(R", which is the time the event loop 859Returns the current \*(L"event loop time\*(R", which is the time the event loop
507received events and started processing them. This timestamp does not 860received events and started processing them. This timestamp does not
508change as long as callbacks are being processed, and this is also the base 861change as long as callbacks are being processed, and this is also the base
509time used for relative timers. You can treat it as the timestamp of the 862time used for relative timers. You can treat it as the timestamp of the
510event occuring (or more correctly, libev finding out about it). 863event occurring (or more correctly, libev finding out about it).
864.IP "ev_now_update (loop)" 4
865.IX Item "ev_now_update (loop)"
866Establishes the current time by querying the kernel, updating the time
867returned by \f(CW\*(C`ev_now ()\*(C'\fR in the progress. This is a costly operation and
868is usually done automatically within \f(CW\*(C`ev_run ()\*(C'\fR.
869.Sp
870This function is rarely useful, but when some event callback runs for a
871very long time without entering the event loop, updating libev's idea of
872the current time is a good idea.
873.Sp
874See also \*(L"The special problem of time updates\*(R" in the \f(CW\*(C`ev_timer\*(C'\fR section.
875.IP "ev_suspend (loop)" 4
876.IX Item "ev_suspend (loop)"
877.PD 0
878.IP "ev_resume (loop)" 4
879.IX Item "ev_resume (loop)"
880.PD
881These two functions suspend and resume an event loop, for use when the
882loop is not used for a while and timeouts should not be processed.
883.Sp
884A typical use case would be an interactive program such as a game: When
885the user presses \f(CW\*(C`^Z\*(C'\fR to suspend the game and resumes it an hour later it
886would be best to handle timeouts as if no time had actually passed while
887the program was suspended. This can be achieved by calling \f(CW\*(C`ev_suspend\*(C'\fR
888in your \f(CW\*(C`SIGTSTP\*(C'\fR handler, sending yourself a \f(CW\*(C`SIGSTOP\*(C'\fR and calling
889\&\f(CW\*(C`ev_resume\*(C'\fR directly afterwards to resume timer processing.
890.Sp
891Effectively, all \f(CW\*(C`ev_timer\*(C'\fR watchers will be delayed by the time spend
892between \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
893will be rescheduled (that is, they will lose any events that would have
894occurred while suspended).
895.Sp
896After calling \f(CW\*(C`ev_suspend\*(C'\fR you \fBmust not\fR call \fIany\fR function on the
897given loop other than \f(CW\*(C`ev_resume\*(C'\fR, and you \fBmust not\fR call \f(CW\*(C`ev_resume\*(C'\fR
898without a previous call to \f(CW\*(C`ev_suspend\*(C'\fR.
899.Sp
900Calling \f(CW\*(C`ev_suspend\*(C'\fR/\f(CW\*(C`ev_resume\*(C'\fR has the side effect of updating the
901event loop time (see \f(CW\*(C`ev_now_update\*(C'\fR).
511.IP "ev_loop (loop, int flags)" 4 902.IP "ev_run (loop, int flags)" 4
512.IX Item "ev_loop (loop, int flags)" 903.IX Item "ev_run (loop, int flags)"
513Finally, this is it, the event handler. This function usually is called 904Finally, this is it, the event handler. This function usually is called
514after you initialised all your watchers and you want to start handling 905after you have initialised all your watchers and you want to start
515events. 906handling events. It will ask the operating system for any new events, call
907the watcher callbacks, an then repeat the whole process indefinitely: This
908is why event loops are called \fIloops\fR.
516.Sp 909.Sp
517If the flags argument is specified as \f(CW0\fR, it will not return until 910If the flags argument is specified as \f(CW0\fR, it will keep handling events
518either no event watchers are active anymore or \f(CW\*(C`ev_unloop\*(C'\fR was called. 911until either no event watchers are active anymore or \f(CW\*(C`ev_break\*(C'\fR was
912called.
519.Sp 913.Sp
520Please note that an explicit \f(CW\*(C`ev_unloop\*(C'\fR is usually better than 914Please note that an explicit \f(CW\*(C`ev_break\*(C'\fR is usually better than
521relying on all watchers to be stopped when deciding when a program has 915relying on all watchers to be stopped when deciding when a program has
522finished (especially in interactive programs), but having a program that 916finished (especially in interactive programs), but having a program
523automatically loops as long as it has to and no longer by virtue of 917that automatically loops as long as it has to and no longer by virtue
524relying on its watchers stopping correctly is a thing of beauty. 918of relying on its watchers stopping correctly, that is truly a thing of
919beauty.
525.Sp 920.Sp
921This function is also \fImostly\fR exception-safe \- you can break out of
922a \f(CW\*(C`ev_run\*(C'\fR call by calling \f(CW\*(C`longjmp\*(C'\fR in a callback, throwing a \*(C+
923exception and so on. This does not decrement the \f(CW\*(C`ev_depth\*(C'\fR value, nor
924will it clear any outstanding \f(CW\*(C`EVBREAK_ONE\*(C'\fR breaks.
925.Sp
526A flags value of \f(CW\*(C`EVLOOP_NONBLOCK\*(C'\fR will look for new events, will handle 926A flags value of \f(CW\*(C`EVRUN_NOWAIT\*(C'\fR will look for new events, will handle
527those events and any outstanding ones, but will not block your process in 927those events and any already outstanding ones, but will not wait and
528case there are no events and will return after one iteration of the loop. 928block your process in case there are no events and will return after one
929iteration of the loop. This is sometimes useful to poll and handle new
930events while doing lengthy calculations, to keep the program responsive.
529.Sp 931.Sp
530A flags value of \f(CW\*(C`EVLOOP_ONESHOT\*(C'\fR will look for new events (waiting if 932A flags value of \f(CW\*(C`EVRUN_ONCE\*(C'\fR will look for new events (waiting if
531neccessary) and will handle those and any outstanding ones. It will block 933necessary) and will handle those and any already outstanding ones. It
532your process until at least one new event arrives, and will return after 934will block your process until at least one new event arrives (which could
533one iteration of the loop. This is useful if you are waiting for some 935be an event internal to libev itself, so there is no guarantee that a
534external event in conjunction with something not expressible using other 936user-registered callback will be called), and will return after one
937iteration of the loop.
938.Sp
939This is useful if you are waiting for some external event in conjunction
940with something not expressible using other libev watchers (i.e. "roll your
535libev watchers. However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is 941own \f(CW\*(C`ev_run\*(C'\fR"). However, a pair of \f(CW\*(C`ev_prepare\*(C'\fR/\f(CW\*(C`ev_check\*(C'\fR watchers is
536usually a better approach for this kind of thing. 942usually a better approach for this kind of thing.
537.Sp 943.Sp
538Here are the gory details of what \f(CW\*(C`ev_loop\*(C'\fR does: 944Here are the gory details of what \f(CW\*(C`ev_run\*(C'\fR does:
539.Sp 945.Sp
540.Vb 18 946.Vb 10
541\& * If there are no active watchers (reference count is zero), return. 947\& \- Increment loop depth.
542\& - Queue prepare watchers and then call all outstanding watchers. 948\& \- Reset the ev_break status.
949\& \- Before the first iteration, call any pending watchers.
950\& LOOP:
951\& \- If EVFLAG_FORKCHECK was used, check for a fork.
952\& \- If a fork was detected (by any means), queue and call all fork watchers.
953\& \- Queue and call all prepare watchers.
954\& \- If ev_break was called, goto FINISH.
543\& - If we have been forked, recreate the kernel state. 955\& \- If we have been forked, detach and recreate the kernel state
956\& as to not disturb the other process.
544\& - Update the kernel state with all outstanding changes. 957\& \- Update the kernel state with all outstanding changes.
545\& - Update the "event loop time". 958\& \- Update the "event loop time" (ev_now ()).
546\& - Calculate for how long to block. 959\& \- Calculate for how long to sleep or block, if at all
960\& (active idle watchers, EVRUN_NOWAIT or not having
961\& any active watchers at all will result in not sleeping).
962\& \- Sleep if the I/O and timer collect interval say so.
963\& \- Increment loop iteration counter.
547\& - Block the process, waiting for any events. 964\& \- Block the process, waiting for any events.
548\& - Queue all outstanding I/O (fd) events. 965\& \- Queue all outstanding I/O (fd) events.
549\& - Update the "event loop time" and do time jump handling. 966\& \- Update the "event loop time" (ev_now ()), and do time jump adjustments.
550\& - Queue all outstanding timers. 967\& \- Queue all expired timers.
551\& - Queue all outstanding periodics. 968\& \- Queue all expired periodics.
552\& - If no events are pending now, queue all idle watchers. 969\& \- Queue all idle watchers with priority higher than that of pending events.
553\& - Queue all check watchers. 970\& \- Queue all check watchers.
554\& - Call all queued watchers in reverse order (i.e. check watchers first). 971\& \- Call all queued watchers in reverse order (i.e. check watchers first).
555\& Signals and child watchers are implemented as I/O watchers, and will 972\& Signals and child watchers are implemented as I/O watchers, and will
556\& be handled here by queueing them when their watcher gets executed. 973\& be handled here by queueing them when their watcher gets executed.
557\& - If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK 974\& \- If ev_break has been called, or EVRUN_ONCE or EVRUN_NOWAIT
558\& were used, return, otherwise continue with step *. 975\& were used, or there are no active watchers, goto FINISH, otherwise
976\& continue with step LOOP.
977\& FINISH:
978\& \- Reset the ev_break status iff it was EVBREAK_ONE.
979\& \- Decrement the loop depth.
980\& \- Return.
559.Ve 981.Ve
560.Sp 982.Sp
561Example: queue some jobs and then loop until no events are outsanding 983Example: Queue some jobs and then loop until no events are outstanding
562anymore. 984anymore.
563.Sp 985.Sp
564.Vb 4 986.Vb 4
565\& ... queue jobs here, make sure they register event watchers as long 987\& ... queue jobs here, make sure they register event watchers as long
566\& ... as they still have work to do (even an idle watcher will do..) 988\& ... as they still have work to do (even an idle watcher will do..)
567\& ev_loop (my_loop, 0); 989\& ev_run (my_loop, 0);
568\& ... jobs done. yeah! 990\& ... jobs done or somebody called unloop. yeah!
569.Ve 991.Ve
570.IP "ev_unloop (loop, how)" 4 992.IP "ev_break (loop, how)" 4
571.IX Item "ev_unloop (loop, how)" 993.IX Item "ev_break (loop, how)"
572Can be used to make a call to \f(CW\*(C`ev_loop\*(C'\fR return early (but only after it 994Can be used to make a call to \f(CW\*(C`ev_run\*(C'\fR return early (but only after it
573has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either 995has processed all outstanding events). The \f(CW\*(C`how\*(C'\fR argument must be either
574\&\f(CW\*(C`EVUNLOOP_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_loop\*(C'\fR call return, or 996\&\f(CW\*(C`EVBREAK_ONE\*(C'\fR, which will make the innermost \f(CW\*(C`ev_run\*(C'\fR call return, or
575\&\f(CW\*(C`EVUNLOOP_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_loop\*(C'\fR calls return. 997\&\f(CW\*(C`EVBREAK_ALL\*(C'\fR, which will make all nested \f(CW\*(C`ev_run\*(C'\fR calls return.
998.Sp
999This \*(L"break state\*(R" will be cleared on the next call to \f(CW\*(C`ev_run\*(C'\fR.
1000.Sp
1001It is safe to call \f(CW\*(C`ev_break\*(C'\fR from outside any \f(CW\*(C`ev_run\*(C'\fR calls, too, in
1002which case it will have no effect.
576.IP "ev_ref (loop)" 4 1003.IP "ev_ref (loop)" 4
577.IX Item "ev_ref (loop)" 1004.IX Item "ev_ref (loop)"
578.PD 0 1005.PD 0
579.IP "ev_unref (loop)" 4 1006.IP "ev_unref (loop)" 4
580.IX Item "ev_unref (loop)" 1007.IX Item "ev_unref (loop)"
581.PD 1008.PD
582Ref/unref can be used to add or remove a reference count on the event 1009Ref/unref can be used to add or remove a reference count on the event
583loop: Every watcher keeps one reference, and as long as the reference 1010loop: Every watcher keeps one reference, and as long as the reference
584count is nonzero, \f(CW\*(C`ev_loop\*(C'\fR will not return on its own. If you have 1011count is nonzero, \f(CW\*(C`ev_run\*(C'\fR will not return on its own.
585a watcher you never unregister that should not keep \f(CW\*(C`ev_loop\*(C'\fR from 1012.Sp
586returning, \fIev_unref()\fR after starting, and \fIev_ref()\fR before stopping it. For 1013This is useful when you have a watcher that you never intend to
1014unregister, but that nevertheless should not keep \f(CW\*(C`ev_run\*(C'\fR from
1015returning. In such a case, call \f(CW\*(C`ev_unref\*(C'\fR after starting, and \f(CW\*(C`ev_ref\*(C'\fR
1016before stopping it.
1017.Sp
587example, libev itself uses this for its internal signal pipe: It is not 1018As an example, libev itself uses this for its internal signal pipe: It
588visible to the libev user and should not keep \f(CW\*(C`ev_loop\*(C'\fR from exiting if 1019is not visible to the libev user and should not keep \f(CW\*(C`ev_run\*(C'\fR from
589no event watchers registered by it are active. It is also an excellent 1020exiting if no event watchers registered by it are active. It is also an
590way to do this for generic recurring timers or from within third-party 1021excellent way to do this for generic recurring timers or from within
591libraries. Just remember to \fIunref after start\fR and \fIref before stop\fR. 1022third-party libraries. Just remember to \fIunref after start\fR and \fIref
1023before stop\fR (but only if the watcher wasn't active before, or was active
1024before, respectively. Note also that libev might stop watchers itself
1025(e.g. non-repeating timers) in which case you have to \f(CW\*(C`ev_ref\*(C'\fR
1026in the callback).
592.Sp 1027.Sp
593Example: create a signal watcher, but keep it from keeping \f(CW\*(C`ev_loop\*(C'\fR 1028Example: Create a signal watcher, but keep it from keeping \f(CW\*(C`ev_run\*(C'\fR
594running when nothing else is active. 1029running when nothing else is active.
595.Sp 1030.Sp
596.Vb 4 1031.Vb 4
597\& struct dv_signal exitsig; 1032\& ev_signal exitsig;
598\& ev_signal_init (&exitsig, sig_cb, SIGINT); 1033\& ev_signal_init (&exitsig, sig_cb, SIGINT);
599\& ev_signal_start (myloop, &exitsig); 1034\& ev_signal_start (loop, &exitsig);
600\& evf_unref (myloop); 1035\& ev_unref (loop);
601.Ve 1036.Ve
602.Sp 1037.Sp
603Example: for some weird reason, unregister the above signal handler again. 1038Example: For some weird reason, unregister the above signal handler again.
604.Sp 1039.Sp
605.Vb 2 1040.Vb 2
606\& ev_ref (myloop); 1041\& ev_ref (loop);
607\& ev_signal_stop (myloop, &exitsig); 1042\& ev_signal_stop (loop, &exitsig);
608.Ve 1043.Ve
1044.IP "ev_set_io_collect_interval (loop, ev_tstamp interval)" 4
1045.IX Item "ev_set_io_collect_interval (loop, ev_tstamp interval)"
1046.PD 0
1047.IP "ev_set_timeout_collect_interval (loop, ev_tstamp interval)" 4
1048.IX Item "ev_set_timeout_collect_interval (loop, ev_tstamp interval)"
1049.PD
1050These advanced functions influence the time that libev will spend waiting
1051for events. Both time intervals are by default \f(CW0\fR, meaning that libev
1052will try to invoke timer/periodic callbacks and I/O callbacks with minimum
1053latency.
1054.Sp
1055Setting these to a higher value (the \f(CW\*(C`interval\*(C'\fR \fImust\fR be >= \f(CW0\fR)
1056allows libev to delay invocation of I/O and timer/periodic callbacks
1057to increase efficiency of loop iterations (or to increase power-saving
1058opportunities).
1059.Sp
1060The idea is that sometimes your program runs just fast enough to handle
1061one (or very few) event(s) per loop iteration. While this makes the
1062program responsive, it also wastes a lot of \s-1CPU\s0 time to poll for new
1063events, especially with backends like \f(CW\*(C`select ()\*(C'\fR which have a high
1064overhead for the actual polling but can deliver many events at once.
1065.Sp
1066By setting a higher \fIio collect interval\fR you allow libev to spend more
1067time collecting I/O events, so you can handle more events per iteration,
1068at the cost of increasing latency. Timeouts (both \f(CW\*(C`ev_periodic\*(C'\fR and
1069\&\f(CW\*(C`ev_timer\*(C'\fR) will be not affected. Setting this to a non-null value will
1070introduce an additional \f(CW\*(C`ev_sleep ()\*(C'\fR call into most loop iterations. The
1071sleep time ensures that libev will not poll for I/O events more often then
1072once per this interval, on average.
1073.Sp
1074Likewise, by setting a higher \fItimeout collect interval\fR you allow libev
1075to spend more time collecting timeouts, at the expense of increased
1076latency/jitter/inexactness (the watcher callback will be called
1077later). \f(CW\*(C`ev_io\*(C'\fR watchers will not be affected. Setting this to a non-null
1078value will not introduce any overhead in libev.
1079.Sp
1080Many (busy) programs can usually benefit by setting the I/O collect
1081interval to a value near \f(CW0.1\fR or so, which is often enough for
1082interactive servers (of course not for games), likewise for timeouts. It
1083usually doesn't make much sense to set it to a lower value than \f(CW0.01\fR,
1084as this approaches the timing granularity of most systems. Note that if
1085you do transactions with the outside world and you can't increase the
1086parallelity, then this setting will limit your transaction rate (if you
1087need to poll once per transaction and the I/O collect interval is 0.01,
1088then you can't do more than 100 transactions per second).
1089.Sp
1090Setting the \fItimeout collect interval\fR can improve the opportunity for
1091saving power, as the program will \*(L"bundle\*(R" timer callback invocations that
1092are \*(L"near\*(R" in time together, by delaying some, thus reducing the number of
1093times the process sleeps and wakes up again. Another useful technique to
1094reduce iterations/wake\-ups is to use \f(CW\*(C`ev_periodic\*(C'\fR watchers and make sure
1095they fire on, say, one-second boundaries only.
1096.Sp
1097Example: we only need 0.1s timeout granularity, and we wish not to poll
1098more often than 100 times per second:
1099.Sp
1100.Vb 2
1101\& ev_set_timeout_collect_interval (EV_DEFAULT_UC_ 0.1);
1102\& ev_set_io_collect_interval (EV_DEFAULT_UC_ 0.01);
1103.Ve
1104.IP "ev_invoke_pending (loop)" 4
1105.IX Item "ev_invoke_pending (loop)"
1106This call will simply invoke all pending watchers while resetting their
1107pending state. Normally, \f(CW\*(C`ev_run\*(C'\fR does this automatically when required,
1108but when overriding the invoke callback this call comes handy. This
1109function can be invoked from a watcher \- this can be useful for example
1110when you want to do some lengthy calculation and want to pass further
1111event handling to another thread (you still have to make sure only one
1112thread executes within \f(CW\*(C`ev_invoke_pending\*(C'\fR or \f(CW\*(C`ev_run\*(C'\fR of course).
1113.IP "int ev_pending_count (loop)" 4
1114.IX Item "int ev_pending_count (loop)"
1115Returns the number of pending watchers \- zero indicates that no watchers
1116are pending.
1117.IP "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(\s-1EV_P\s0))" 4
1118.IX Item "ev_set_invoke_pending_cb (loop, void (*invoke_pending_cb)(EV_P))"
1119This overrides the invoke pending functionality of the loop: Instead of
1120invoking all pending watchers when there are any, \f(CW\*(C`ev_run\*(C'\fR will call
1121this callback instead. This is useful, for example, when you want to
1122invoke the actual watchers inside another context (another thread etc.).
1123.Sp
1124If you want to reset the callback, use \f(CW\*(C`ev_invoke_pending\*(C'\fR as new
1125callback.
1126.IP "ev_set_loop_release_cb (loop, void (*release)(\s-1EV_P\s0), void (*acquire)(\s-1EV_P\s0))" 4
1127.IX Item "ev_set_loop_release_cb (loop, void (*release)(EV_P), void (*acquire)(EV_P))"
1128Sometimes you want to share the same loop between multiple threads. This
1129can be done relatively simply by putting mutex_lock/unlock calls around
1130each call to a libev function.
1131.Sp
1132However, \f(CW\*(C`ev_run\*(C'\fR can run an indefinite time, so it is not feasible
1133to wait for it to return. One way around this is to wake up the event
1134loop via \f(CW\*(C`ev_break\*(C'\fR and \f(CW\*(C`av_async_send\*(C'\fR, another way is to set these
1135\&\fIrelease\fR and \fIacquire\fR callbacks on the loop.
1136.Sp
1137When set, then \f(CW\*(C`release\*(C'\fR will be called just before the thread is
1138suspended waiting for new events, and \f(CW\*(C`acquire\*(C'\fR is called just
1139afterwards.
1140.Sp
1141Ideally, \f(CW\*(C`release\*(C'\fR will just call your mutex_unlock function, and
1142\&\f(CW\*(C`acquire\*(C'\fR will just call the mutex_lock function again.
1143.Sp
1144While event loop modifications are allowed between invocations of
1145\&\f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR (that's their only purpose after all), no
1146modifications done will affect the event loop, i.e. adding watchers will
1147have no effect on the set of file descriptors being watched, or the time
1148waited. Use an \f(CW\*(C`ev_async\*(C'\fR watcher to wake up \f(CW\*(C`ev_run\*(C'\fR when you want it
1149to take note of any changes you made.
1150.Sp
1151In theory, threads executing \f(CW\*(C`ev_run\*(C'\fR will be async-cancel safe between
1152invocations of \f(CW\*(C`release\*(C'\fR and \f(CW\*(C`acquire\*(C'\fR.
1153.Sp
1154See also the locking example in the \f(CW\*(C`THREADS\*(C'\fR section later in this
1155document.
1156.IP "ev_set_userdata (loop, void *data)" 4
1157.IX Item "ev_set_userdata (loop, void *data)"
1158.PD 0
1159.IP "void *ev_userdata (loop)" 4
1160.IX Item "void *ev_userdata (loop)"
1161.PD
1162Set and retrieve a single \f(CW\*(C`void *\*(C'\fR associated with a loop. When
1163\&\f(CW\*(C`ev_set_userdata\*(C'\fR has never been called, then \f(CW\*(C`ev_userdata\*(C'\fR returns
1164\&\f(CW0\fR.
1165.Sp
1166These two functions can be used to associate arbitrary data with a loop,
1167and are intended solely for the \f(CW\*(C`invoke_pending_cb\*(C'\fR, \f(CW\*(C`release\*(C'\fR and
1168\&\f(CW\*(C`acquire\*(C'\fR callbacks described above, but of course can be (ab\-)used for
1169any other purpose as well.
1170.IP "ev_verify (loop)" 4
1171.IX Item "ev_verify (loop)"
1172This function only does something when \f(CW\*(C`EV_VERIFY\*(C'\fR support has been
1173compiled in, which is the default for non-minimal builds. It tries to go
1174through all internal structures and checks them for validity. If anything
1175is found to be inconsistent, it will print an error message to standard
1176error and call \f(CW\*(C`abort ()\*(C'\fR.
1177.Sp
1178This can be used to catch bugs inside libev itself: under normal
1179circumstances, this function will never abort as of course libev keeps its
1180data structures consistent.
609.SH "ANATOMY OF A WATCHER" 1181.SH "ANATOMY OF A WATCHER"
610.IX Header "ANATOMY OF A WATCHER" 1182.IX Header "ANATOMY OF A WATCHER"
1183In the following description, uppercase \f(CW\*(C`TYPE\*(C'\fR in names stands for the
1184watcher type, e.g. \f(CW\*(C`ev_TYPE_start\*(C'\fR can mean \f(CW\*(C`ev_timer_start\*(C'\fR for timer
1185watchers and \f(CW\*(C`ev_io_start\*(C'\fR for I/O watchers.
1186.PP
611A watcher is a structure that you create and register to record your 1187A watcher is an opaque structure that you allocate and register to record
612interest in some event. For instance, if you want to wait for \s-1STDIN\s0 to 1188your interest in some event. To make a concrete example, imagine you want
613become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher for that: 1189to wait for \s-1STDIN\s0 to become readable, you would create an \f(CW\*(C`ev_io\*(C'\fR watcher
1190for that:
614.PP 1191.PP
615.Vb 5 1192.Vb 5
616\& static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents) 1193\& static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
617\& { 1194\& {
618\& ev_io_stop (w); 1195\& ev_io_stop (w);
619\& ev_unloop (loop, EVUNLOOP_ALL); 1196\& ev_break (loop, EVBREAK_ALL);
620\& } 1197\& }
621.Ve 1198\&
622.PP
623.Vb 6
624\& struct ev_loop *loop = ev_default_loop (0); 1199\& struct ev_loop *loop = ev_default_loop (0);
1200\&
625\& struct ev_io stdin_watcher; 1201\& ev_io stdin_watcher;
1202\&
626\& ev_init (&stdin_watcher, my_cb); 1203\& ev_init (&stdin_watcher, my_cb);
627\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ); 1204\& ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
628\& ev_io_start (loop, &stdin_watcher); 1205\& ev_io_start (loop, &stdin_watcher);
1206\&
629\& ev_loop (loop, 0); 1207\& ev_run (loop, 0);
630.Ve 1208.Ve
631.PP 1209.PP
632As you can see, you are responsible for allocating the memory for your 1210As you can see, you are responsible for allocating the memory for your
633watcher structures (and it is usually a bad idea to do this on the stack, 1211watcher structures (and it is \fIusually\fR a bad idea to do this on the
634although this can sometimes be quite valid). 1212stack).
635.PP 1213.PP
1214Each watcher has an associated watcher structure (called \f(CW\*(C`struct ev_TYPE\*(C'\fR
1215or simply \f(CW\*(C`ev_TYPE\*(C'\fR, as typedefs are provided for all watcher structs).
1216.PP
636Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init 1217Each watcher structure must be initialised by a call to \f(CW\*(C`ev_init (watcher
637(watcher *, callback)\*(C'\fR, which expects a callback to be provided. This 1218*, callback)\*(C'\fR, which expects a callback to be provided. This callback is
638callback gets invoked each time the event occurs (or, in the case of io 1219invoked each time the event occurs (or, in the case of I/O watchers, each
639watchers, each time the event loop detects that the file descriptor given 1220time the event loop detects that the file descriptor given is readable
640is readable and/or writable). 1221and/or writable).
641.PP 1222.PP
642Each watcher type has its own \f(CW\*(C`ev_<type>_set (watcher *, ...)\*(C'\fR macro 1223Each watcher type further has its own \f(CW\*(C`ev_TYPE_set (watcher *, ...)\*(C'\fR
643with arguments specific to this watcher type. There is also a macro 1224macro to configure it, with arguments specific to the watcher type. There
644to combine initialisation and setting in one call: \f(CW\*(C`ev_<type>_init 1225is also a macro to combine initialisation and setting in one call: \f(CW\*(C`ev_TYPE_init (watcher *, callback, ...)\*(C'\fR.
645(watcher *, callback, ...)\*(C'\fR.
646.PP 1226.PP
647To make the watcher actually watch out for events, you have to start it 1227To make the watcher actually watch out for events, you have to start it
648with a watcher-specific start function (\f(CW\*(C`ev_<type>_start (loop, watcher 1228with a watcher-specific start function (\f(CW\*(C`ev_TYPE_start (loop, watcher
649*)\*(C'\fR), and you can stop watching for events at any time by calling the 1229*)\*(C'\fR), and you can stop watching for events at any time by calling the
650corresponding stop function (\f(CW\*(C`ev_<type>_stop (loop, watcher *)\*(C'\fR. 1230corresponding stop function (\f(CW\*(C`ev_TYPE_stop (loop, watcher *)\*(C'\fR.
651.PP 1231.PP
652As long as your watcher is active (has been started but not stopped) you 1232As long as your watcher is active (has been started but not stopped) you
653must not touch the values stored in it. Most specifically you must never 1233must not touch the values stored in it. Most specifically you must never
654reinitialise it or call its \f(CW\*(C`set\*(C'\fR macro. 1234reinitialise it or call its \f(CW\*(C`ev_TYPE_set\*(C'\fR macro.
655.PP 1235.PP
656Each and every callback receives the event loop pointer as first, the 1236Each and every callback receives the event loop pointer as first, the
657registered watcher structure as second, and a bitset of received events as 1237registered watcher structure as second, and a bitset of received events as
658third argument. 1238third argument.
659.PP 1239.PP
… …
668.el .IP "\f(CWEV_WRITE\fR" 4 1248.el .IP "\f(CWEV_WRITE\fR" 4
669.IX Item "EV_WRITE" 1249.IX Item "EV_WRITE"
670.PD 1250.PD
671The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or 1251The file descriptor in the \f(CW\*(C`ev_io\*(C'\fR watcher has become readable and/or
672writable. 1252writable.
673.ie n .IP """EV_TIMEOUT""" 4 1253.ie n .IP """EV_TIMER""" 4
674.el .IP "\f(CWEV_TIMEOUT\fR" 4 1254.el .IP "\f(CWEV_TIMER\fR" 4
675.IX Item "EV_TIMEOUT" 1255.IX Item "EV_TIMER"
676The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out. 1256The \f(CW\*(C`ev_timer\*(C'\fR watcher has timed out.
677.ie n .IP """EV_PERIODIC""" 4 1257.ie n .IP """EV_PERIODIC""" 4
678.el .IP "\f(CWEV_PERIODIC\fR" 4 1258.el .IP "\f(CWEV_PERIODIC\fR" 4
679.IX Item "EV_PERIODIC" 1259.IX Item "EV_PERIODIC"
680The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out. 1260The \f(CW\*(C`ev_periodic\*(C'\fR watcher has timed out.
… …
684The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread. 1264The signal specified in the \f(CW\*(C`ev_signal\*(C'\fR watcher has been received by a thread.
685.ie n .IP """EV_CHILD""" 4 1265.ie n .IP """EV_CHILD""" 4
686.el .IP "\f(CWEV_CHILD\fR" 4 1266.el .IP "\f(CWEV_CHILD\fR" 4
687.IX Item "EV_CHILD" 1267.IX Item "EV_CHILD"
688The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change. 1268The pid specified in the \f(CW\*(C`ev_child\*(C'\fR watcher has received a status change.
1269.ie n .IP """EV_STAT""" 4
1270.el .IP "\f(CWEV_STAT\fR" 4
1271.IX Item "EV_STAT"
1272The path specified in the \f(CW\*(C`ev_stat\*(C'\fR watcher changed its attributes somehow.
689.ie n .IP """EV_IDLE""" 4 1273.ie n .IP """EV_IDLE""" 4
690.el .IP "\f(CWEV_IDLE\fR" 4 1274.el .IP "\f(CWEV_IDLE\fR" 4
691.IX Item "EV_IDLE" 1275.IX Item "EV_IDLE"
692The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do. 1276The \f(CW\*(C`ev_idle\*(C'\fR watcher has determined that you have nothing better to do.
693.ie n .IP """EV_PREPARE""" 4 1277.ie n .IP """EV_PREPARE""" 4
… …
696.PD 0 1280.PD 0
697.ie n .IP """EV_CHECK""" 4 1281.ie n .IP """EV_CHECK""" 4
698.el .IP "\f(CWEV_CHECK\fR" 4 1282.el .IP "\f(CWEV_CHECK\fR" 4
699.IX Item "EV_CHECK" 1283.IX Item "EV_CHECK"
700.PD 1284.PD
701All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_loop\*(C'\fR starts 1285All \f(CW\*(C`ev_prepare\*(C'\fR watchers are invoked just \fIbefore\fR \f(CW\*(C`ev_run\*(C'\fR starts
702to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after 1286to gather new events, and all \f(CW\*(C`ev_check\*(C'\fR watchers are invoked just after
703\&\f(CW\*(C`ev_loop\*(C'\fR has gathered them, but before it invokes any callbacks for any 1287\&\f(CW\*(C`ev_run\*(C'\fR has gathered them, but before it invokes any callbacks for any
704received events. Callbacks of both watcher types can start and stop as 1288received events. Callbacks of both watcher types can start and stop as
705many watchers as they want, and all of them will be taken into account 1289many watchers as they want, and all of them will be taken into account
706(for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep 1290(for example, a \f(CW\*(C`ev_prepare\*(C'\fR watcher might start an idle watcher to keep
707\&\f(CW\*(C`ev_loop\*(C'\fR from blocking). 1291\&\f(CW\*(C`ev_run\*(C'\fR from blocking).
1292.ie n .IP """EV_EMBED""" 4
1293.el .IP "\f(CWEV_EMBED\fR" 4
1294.IX Item "EV_EMBED"
1295The embedded event loop specified in the \f(CW\*(C`ev_embed\*(C'\fR watcher needs attention.
1296.ie n .IP """EV_FORK""" 4
1297.el .IP "\f(CWEV_FORK\fR" 4
1298.IX Item "EV_FORK"
1299The event loop has been resumed in the child process after fork (see
1300\&\f(CW\*(C`ev_fork\*(C'\fR).
1301.ie n .IP """EV_CLEANUP""" 4
1302.el .IP "\f(CWEV_CLEANUP\fR" 4
1303.IX Item "EV_CLEANUP"
1304The event loop is about to be destroyed (see \f(CW\*(C`ev_cleanup\*(C'\fR).
1305.ie n .IP """EV_ASYNC""" 4
1306.el .IP "\f(CWEV_ASYNC\fR" 4
1307.IX Item "EV_ASYNC"
1308The given async watcher has been asynchronously notified (see \f(CW\*(C`ev_async\*(C'\fR).
1309.ie n .IP """EV_CUSTOM""" 4
1310.el .IP "\f(CWEV_CUSTOM\fR" 4
1311.IX Item "EV_CUSTOM"
1312Not ever sent (or otherwise used) by libev itself, but can be freely used
1313by libev users to signal watchers (e.g. via \f(CW\*(C`ev_feed_event\*(C'\fR).
708.ie n .IP """EV_ERROR""" 4 1314.ie n .IP """EV_ERROR""" 4
709.el .IP "\f(CWEV_ERROR\fR" 4 1315.el .IP "\f(CWEV_ERROR\fR" 4
710.IX Item "EV_ERROR" 1316.IX Item "EV_ERROR"
711An unspecified error has occured, the watcher has been stopped. This might 1317An unspecified error has occurred, the watcher has been stopped. This might
712happen because the watcher could not be properly started because libev 1318happen because the watcher could not be properly started because libev
713ran out of memory, a file descriptor was found to be closed or any other 1319ran out of memory, a file descriptor was found to be closed or any other
1320problem. Libev considers these application bugs.
1321.Sp
714problem. You best act on it by reporting the problem and somehow coping 1322You best act on it by reporting the problem and somehow coping with the
715with the watcher being stopped. 1323watcher being stopped. Note that well-written programs should not receive
1324an error ever, so when your watcher receives it, this usually indicates a
1325bug in your program.
716.Sp 1326.Sp
717Libev will usually signal a few \*(L"dummy\*(R" events together with an error, 1327Libev will usually signal a few \*(L"dummy\*(R" events together with an error, for
718for example it might indicate that a fd is readable or writable, and if 1328example it might indicate that a fd is readable or writable, and if your
719your callbacks is well-written it can just attempt the operation and cope 1329callbacks is well-written it can just attempt the operation and cope with
720with the error from \fIread()\fR or \fIwrite()\fR. This will not work in multithreaded 1330the error from \fIread()\fR or \fIwrite()\fR. This will not work in multi-threaded
721programs, though, so beware. 1331programs, though, as the fd could already be closed and reused for another
1332thing, so beware.
722.Sh "\s-1SUMMARY\s0 \s-1OF\s0 \s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0" 1333.SS "\s-1GENERIC\s0 \s-1WATCHER\s0 \s-1FUNCTIONS\s0"
723.IX Subsection "SUMMARY OF GENERIC WATCHER FUNCTIONS" 1334.IX Subsection "GENERIC WATCHER FUNCTIONS"
724In the following description, \f(CW\*(C`TYPE\*(C'\fR stands for the watcher type,
725e.g. \f(CW\*(C`timer\*(C'\fR for \f(CW\*(C`ev_timer\*(C'\fR watchers and \f(CW\*(C`io\*(C'\fR for \f(CW\*(C`ev_io\*(C'\fR watchers.
726.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4 1335.ie n .IP """ev_init"" (ev_TYPE *watcher, callback)" 4
727.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4 1336.el .IP "\f(CWev_init\fR (ev_TYPE *watcher, callback)" 4
728.IX Item "ev_init (ev_TYPE *watcher, callback)" 1337.IX Item "ev_init (ev_TYPE *watcher, callback)"
729This macro initialises the generic portion of a watcher. The contents 1338This macro initialises the generic portion of a watcher. The contents
730of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only 1339of the watcher object can be arbitrary (so \f(CW\*(C`malloc\*(C'\fR will do). Only
… …
734which rolls both calls into one. 1343which rolls both calls into one.
735.Sp 1344.Sp
736You can reinitialise a watcher at any time as long as it has been stopped 1345You can reinitialise a watcher at any time as long as it has been stopped
737(or never started) and there are no pending events outstanding. 1346(or never started) and there are no pending events outstanding.
738.Sp 1347.Sp
739The callbakc is always of type \f(CW\*(C`void (*)(ev_loop *loop, ev_TYPE *watcher, 1348The callback is always of type \f(CW\*(C`void (*)(struct ev_loop *loop, ev_TYPE *watcher,
740int revents)\*(C'\fR. 1349int revents)\*(C'\fR.
1350.Sp
1351Example: Initialise an \f(CW\*(C`ev_io\*(C'\fR watcher in two steps.
1352.Sp
1353.Vb 3
1354\& ev_io w;
1355\& ev_init (&w, my_cb);
1356\& ev_io_set (&w, STDIN_FILENO, EV_READ);
1357.Ve
741.ie n .IP """ev_TYPE_set"" (ev_TYPE *, [args])" 4 1358.ie n .IP """ev_TYPE_set"" (ev_TYPE *watcher, [args])" 4
742.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *, [args])" 4 1359.el .IP "\f(CWev_TYPE_set\fR (ev_TYPE *watcher, [args])" 4
743.IX Item "ev_TYPE_set (ev_TYPE *, [args])" 1360.IX Item "ev_TYPE_set (ev_TYPE *watcher, [args])"
744This macro initialises the type-specific parts of a watcher. You need to 1361This macro initialises the type-specific parts of a watcher. You need to
745call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can 1362call \f(CW\*(C`ev_init\*(C'\fR at least once before you call this macro, but you can
746call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this 1363call \f(CW\*(C`ev_TYPE_set\*(C'\fR any number of times. You must not, however, call this
747macro on a watcher that is active (it can be pending, however, which is a 1364macro on a watcher that is active (it can be pending, however, which is a
748difference to the \f(CW\*(C`ev_init\*(C'\fR macro). 1365difference to the \f(CW\*(C`ev_init\*(C'\fR macro).
749.Sp 1366.Sp
750Although some watcher types do not have type-specific arguments 1367Although some watcher types do not have type-specific arguments
751(e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro. 1368(e.g. \f(CW\*(C`ev_prepare\*(C'\fR) you still need to call its \f(CW\*(C`set\*(C'\fR macro.
1369.Sp
1370See \f(CW\*(C`ev_init\*(C'\fR, above, for an example.
752.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4 1371.ie n .IP """ev_TYPE_init"" (ev_TYPE *watcher, callback, [args])" 4
753.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4 1372.el .IP "\f(CWev_TYPE_init\fR (ev_TYPE *watcher, callback, [args])" 4
754.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])" 1373.IX Item "ev_TYPE_init (ev_TYPE *watcher, callback, [args])"
755This convinience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro 1374This convenience macro rolls both \f(CW\*(C`ev_init\*(C'\fR and \f(CW\*(C`ev_TYPE_set\*(C'\fR macro
756calls into a single call. This is the most convinient method to initialise 1375calls into a single call. This is the most convenient method to initialise
757a watcher. The same limitations apply, of course. 1376a watcher. The same limitations apply, of course.
1377.Sp
1378Example: Initialise and set an \f(CW\*(C`ev_io\*(C'\fR watcher in one step.
1379.Sp
1380.Vb 1
1381\& ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
1382.Ve
758.ie n .IP """ev_TYPE_start"" (loop *, ev_TYPE *watcher)" 4 1383.ie n .IP """ev_TYPE_start"" (loop, ev_TYPE *watcher)" 4
759.el .IP "\f(CWev_TYPE_start\fR (loop *, ev_TYPE *watcher)" 4 1384.el .IP "\f(CWev_TYPE_start\fR (loop, ev_TYPE *watcher)" 4
760.IX Item "ev_TYPE_start (loop *, ev_TYPE *watcher)" 1385.IX Item "ev_TYPE_start (loop, ev_TYPE *watcher)"
761Starts (activates) the given watcher. Only active watchers will receive 1386Starts (activates) the given watcher. Only active watchers will receive
762events. If the watcher is already active nothing will happen. 1387events. If the watcher is already active nothing will happen.
1388.Sp
1389Example: Start the \f(CW\*(C`ev_io\*(C'\fR watcher that is being abused as example in this
1390whole section.
1391.Sp
1392.Vb 1
1393\& ev_io_start (EV_DEFAULT_UC, &w);
1394.Ve
763.ie n .IP """ev_TYPE_stop"" (loop *, ev_TYPE *watcher)" 4 1395.ie n .IP """ev_TYPE_stop"" (loop, ev_TYPE *watcher)" 4
764.el .IP "\f(CWev_TYPE_stop\fR (loop *, ev_TYPE *watcher)" 4 1396.el .IP "\f(CWev_TYPE_stop\fR (loop, ev_TYPE *watcher)" 4
765.IX Item "ev_TYPE_stop (loop *, ev_TYPE *watcher)" 1397.IX Item "ev_TYPE_stop (loop, ev_TYPE *watcher)"
766Stops the given watcher again (if active) and clears the pending 1398Stops the given watcher if active, and clears the pending status (whether
1399the watcher was active or not).
1400.Sp
767status. It is possible that stopped watchers are pending (for example, 1401It is possible that stopped watchers are pending \- for example,
768non-repeating timers are being stopped when they become pending), but 1402non-repeating timers are being stopped when they become pending \- but
769\&\f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor pending. If 1403calling \f(CW\*(C`ev_TYPE_stop\*(C'\fR ensures that the watcher is neither active nor
770you want to free or reuse the memory used by the watcher it is therefore a 1404pending. If you want to free or reuse the memory used by the watcher it is
771good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. 1405therefore a good idea to always call its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function.
772.IP "bool ev_is_active (ev_TYPE *watcher)" 4 1406.IP "bool ev_is_active (ev_TYPE *watcher)" 4
773.IX Item "bool ev_is_active (ev_TYPE *watcher)" 1407.IX Item "bool ev_is_active (ev_TYPE *watcher)"
774Returns a true value iff the watcher is active (i.e. it has been started 1408Returns a true value iff the watcher is active (i.e. it has been started
775and not yet been stopped). As long as a watcher is active you must not modify 1409and not yet been stopped). As long as a watcher is active you must not modify
776it. 1410it.
777.IP "bool ev_is_pending (ev_TYPE *watcher)" 4 1411.IP "bool ev_is_pending (ev_TYPE *watcher)" 4
778.IX Item "bool ev_is_pending (ev_TYPE *watcher)" 1412.IX Item "bool ev_is_pending (ev_TYPE *watcher)"
779Returns a true value iff the watcher is pending, (i.e. it has outstanding 1413Returns a true value iff the watcher is pending, (i.e. it has outstanding
780events but its callback has not yet been invoked). As long as a watcher 1414events but its callback has not yet been invoked). As long as a watcher
781is pending (but not active) you must not call an init function on it (but 1415is pending (but not active) you must not call an init function on it (but
782\&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe) and you must make sure the watcher is available to 1416\&\f(CW\*(C`ev_TYPE_set\*(C'\fR is safe), you must not change its priority, and you must
783libev (e.g. you cnanot \f(CW\*(C`free ()\*(C'\fR it). 1417make sure the watcher is available to libev (e.g. you cannot \f(CW\*(C`free ()\*(C'\fR
1418it).
784.IP "callback = ev_cb (ev_TYPE *watcher)" 4 1419.IP "callback ev_cb (ev_TYPE *watcher)" 4
785.IX Item "callback = ev_cb (ev_TYPE *watcher)" 1420.IX Item "callback ev_cb (ev_TYPE *watcher)"
786Returns the callback currently set on the watcher. 1421Returns the callback currently set on the watcher.
787.IP "ev_cb_set (ev_TYPE *watcher, callback)" 4 1422.IP "ev_cb_set (ev_TYPE *watcher, callback)" 4
788.IX Item "ev_cb_set (ev_TYPE *watcher, callback)" 1423.IX Item "ev_cb_set (ev_TYPE *watcher, callback)"
789Change the callback. You can change the callback at virtually any time 1424Change the callback. You can change the callback at virtually any time
790(modulo threads). 1425(modulo threads).
791.Sh "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0" 1426.IP "ev_set_priority (ev_TYPE *watcher, int priority)" 4
792.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER" 1427.IX Item "ev_set_priority (ev_TYPE *watcher, int priority)"
793Each watcher has, by default, a member \f(CW\*(C`void *data\*(C'\fR that you can change 1428.PD 0
794and read at any time, libev will completely ignore it. This can be used 1429.IP "int ev_priority (ev_TYPE *watcher)" 4
795to associate arbitrary data with your watcher. If you need more data and 1430.IX Item "int ev_priority (ev_TYPE *watcher)"
796don't want to allocate memory and store a pointer to it in that data 1431.PD
797member, you can also \*(L"subclass\*(R" the watcher type and provide your own 1432Set and query the priority of the watcher. The priority is a small
798data: 1433integer between \f(CW\*(C`EV_MAXPRI\*(C'\fR (default: \f(CW2\fR) and \f(CW\*(C`EV_MINPRI\*(C'\fR
1434(default: \f(CW\*(C`\-2\*(C'\fR). Pending watchers with higher priority will be invoked
1435before watchers with lower priority, but priority will not keep watchers
1436from being executed (except for \f(CW\*(C`ev_idle\*(C'\fR watchers).
1437.Sp
1438If you need to suppress invocation when higher priority events are pending
1439you need to look at \f(CW\*(C`ev_idle\*(C'\fR watchers, which provide this functionality.
1440.Sp
1441You \fImust not\fR change the priority of a watcher as long as it is active or
1442pending.
1443.Sp
1444Setting a priority outside the range of \f(CW\*(C`EV_MINPRI\*(C'\fR to \f(CW\*(C`EV_MAXPRI\*(C'\fR is
1445fine, as long as you do not mind that the priority value you query might
1446or might not have been clamped to the valid range.
1447.Sp
1448The default priority used by watchers when no priority has been set is
1449always \f(CW0\fR, which is supposed to not be too high and not be too low :).
1450.Sp
1451See \*(L"\s-1WATCHER\s0 \s-1PRIORITY\s0 \s-1MODELS\s0\*(R", below, for a more thorough treatment of
1452priorities.
1453.IP "ev_invoke (loop, ev_TYPE *watcher, int revents)" 4
1454.IX Item "ev_invoke (loop, ev_TYPE *watcher, int revents)"
1455Invoke the \f(CW\*(C`watcher\*(C'\fR with the given \f(CW\*(C`loop\*(C'\fR and \f(CW\*(C`revents\*(C'\fR. Neither
1456\&\f(CW\*(C`loop\*(C'\fR nor \f(CW\*(C`revents\*(C'\fR need to be valid as long as the watcher callback
1457can deal with that fact, as both are simply passed through to the
1458callback.
1459.IP "int ev_clear_pending (loop, ev_TYPE *watcher)" 4
1460.IX Item "int ev_clear_pending (loop, ev_TYPE *watcher)"
1461If the watcher is pending, this function clears its pending status and
1462returns its \f(CW\*(C`revents\*(C'\fR bitset (as if its callback was invoked). If the
1463watcher isn't pending it does nothing and returns \f(CW0\fR.
1464.Sp
1465Sometimes it can be useful to \*(L"poll\*(R" a watcher instead of waiting for its
1466callback to be invoked, which can be accomplished with this function.
1467.IP "ev_feed_event (loop, ev_TYPE *watcher, int revents)" 4
1468.IX Item "ev_feed_event (loop, ev_TYPE *watcher, int revents)"
1469Feeds the given event set into the event loop, as if the specified event
1470had happened for the specified watcher (which must be a pointer to an
1471initialised but not necessarily started event watcher). Obviously you must
1472not free the watcher as long as it has pending events.
1473.Sp
1474Stopping the watcher, letting libev invoke it, or calling
1475\&\f(CW\*(C`ev_clear_pending\*(C'\fR will clear the pending event, even if the watcher was
1476not started in the first place.
1477.Sp
1478See also \f(CW\*(C`ev_feed_fd_event\*(C'\fR and \f(CW\*(C`ev_feed_signal_event\*(C'\fR for related
1479functions that do not need a watcher.
799.PP 1480.PP
1481See also the \*(L"\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0\*(R" and \*(L"\s-1BUILDING\s0 \s-1YOUR\s0
1482\&\s-1OWN\s0 \s-1COMPOSITE\s0 \s-1WATCHERS\s0\*(R" idioms.
1483.SS "\s-1WATCHER\s0 \s-1STATES\s0"
1484.IX Subsection "WATCHER STATES"
1485There are various watcher states mentioned throughout this manual \-
1486active, pending and so on. In this section these states and the rules to
1487transition between them will be described in more detail \- and while these
1488rules might look complicated, they usually do \*(L"the right thing\*(R".
1489.IP "initialiased" 4
1490.IX Item "initialiased"
1491Before a watcher can be registered with the event looop it has to be
1492initialised. This can be done with a call to \f(CW\*(C`ev_TYPE_init\*(C'\fR, or calls to
1493\&\f(CW\*(C`ev_init\*(C'\fR followed by the watcher-specific \f(CW\*(C`ev_TYPE_set\*(C'\fR function.
1494.Sp
1495In this state it is simply some block of memory that is suitable for use
1496in an event loop. It can be moved around, freed, reused etc. at will.
1497.IP "started/running/active" 4
1498.IX Item "started/running/active"
1499Once a watcher has been started with a call to \f(CW\*(C`ev_TYPE_start\*(C'\fR it becomes
1500property of the event loop, and is actively waiting for events. While in
1501this state it cannot be accessed (except in a few documented ways), moved,
1502freed or anything else \- the only legal thing is to keep a pointer to it,
1503and call libev functions on it that are documented to work on active watchers.
1504.IP "pending" 4
1505.IX Item "pending"
1506If a watcher is active and libev determines that an event it is interested
1507in has occurred (such as a timer expiring), it will become pending. It will
1508stay in this pending state until either it is stopped or its callback is
1509about to be invoked, so it is not normally pending inside the watcher
1510callback.
1511.Sp
1512The watcher might or might not be active while it is pending (for example,
1513an expired non-repeating timer can be pending but no longer active). If it
1514is stopped, it can be freely accessed (e.g. by calling \f(CW\*(C`ev_TYPE_set\*(C'\fR),
1515but it is still property of the event loop at this time, so cannot be
1516moved, freed or reused. And if it is active the rules described in the
1517previous item still apply.
1518.Sp
1519It is also possible to feed an event on a watcher that is not active (e.g.
1520via \f(CW\*(C`ev_feed_event\*(C'\fR), in which case it becomes pending without being
1521active.
1522.IP "stopped" 4
1523.IX Item "stopped"
1524A watcher can be stopped implicitly by libev (in which case it might still
1525be pending), or explicitly by calling its \f(CW\*(C`ev_TYPE_stop\*(C'\fR function. The
1526latter will clear any pending state the watcher might be in, regardless
1527of whether it was active or not, so stopping a watcher explicitly before
1528freeing it is often a good idea.
1529.Sp
1530While stopped (and not pending) the watcher is essentially in the
1531initialised state, that is it can be reused, moved, modified in any way
1532you wish.
1533.SS "\s-1WATCHER\s0 \s-1PRIORITY\s0 \s-1MODELS\s0"
1534.IX Subsection "WATCHER PRIORITY MODELS"
1535Many event loops support \fIwatcher priorities\fR, which are usually small
1536integers that influence the ordering of event callback invocation
1537between watchers in some way, all else being equal.
1538.PP
1539In libev, Watcher priorities can be set using \f(CW\*(C`ev_set_priority\*(C'\fR. See its
1540description for the more technical details such as the actual priority
1541range.
1542.PP
1543There are two common ways how these these priorities are being interpreted
1544by event loops:
1545.PP
1546In the more common lock-out model, higher priorities \*(L"lock out\*(R" invocation
1547of lower priority watchers, which means as long as higher priority
1548watchers receive events, lower priority watchers are not being invoked.
1549.PP
1550The less common only-for-ordering model uses priorities solely to order
1551callback invocation within a single event loop iteration: Higher priority
1552watchers are invoked before lower priority ones, but they all get invoked
1553before polling for new events.
1554.PP
1555Libev uses the second (only-for-ordering) model for all its watchers
1556except for idle watchers (which use the lock-out model).
1557.PP
1558The rationale behind this is that implementing the lock-out model for
1559watchers is not well supported by most kernel interfaces, and most event
1560libraries will just poll for the same events again and again as long as
1561their callbacks have not been executed, which is very inefficient in the
1562common case of one high-priority watcher locking out a mass of lower
1563priority ones.
1564.PP
1565Static (ordering) priorities are most useful when you have two or more
1566watchers handling the same resource: a typical usage example is having an
1567\&\f(CW\*(C`ev_io\*(C'\fR watcher to receive data, and an associated \f(CW\*(C`ev_timer\*(C'\fR to handle
1568timeouts. Under load, data might be received while the program handles
1569other jobs, but since timers normally get invoked first, the timeout
1570handler will be executed before checking for data. In that case, giving
1571the timer a lower priority than the I/O watcher ensures that I/O will be
1572handled first even under adverse conditions (which is usually, but not
1573always, what you want).
1574.PP
1575Since idle watchers use the \*(L"lock-out\*(R" model, meaning that idle watchers
1576will only be executed when no same or higher priority watchers have
1577received events, they can be used to implement the \*(L"lock-out\*(R" model when
1578required.
1579.PP
1580For example, to emulate how many other event libraries handle priorities,
1581you can associate an \f(CW\*(C`ev_idle\*(C'\fR watcher to each such watcher, and in
1582the normal watcher callback, you just start the idle watcher. The real
1583processing is done in the idle watcher callback. This causes libev to
1584continuously poll and process kernel event data for the watcher, but when
1585the lock-out case is known to be rare (which in turn is rare :), this is
1586workable.
1587.PP
1588Usually, however, the lock-out model implemented that way will perform
1589miserably under the type of load it was designed to handle. In that case,
1590it might be preferable to stop the real watcher before starting the
1591idle watcher, so the kernel will not have to process the event in case
1592the actual processing will be delayed for considerable time.
1593.PP
1594Here is an example of an I/O watcher that should run at a strictly lower
1595priority than the default, and which should only process data when no
1596other events are pending:
1597.PP
800.Vb 7 1598.Vb 2
801\& struct my_io 1599\& ev_idle idle; // actual processing watcher
1600\& ev_io io; // actual event watcher
1601\&
1602\& static void
1603\& io_cb (EV_P_ ev_io *w, int revents)
802\& { 1604\& {
803\& struct ev_io io; 1605\& // stop the I/O watcher, we received the event, but
804\& int otherfd; 1606\& // are not yet ready to handle it.
805\& void *somedata; 1607\& ev_io_stop (EV_A_ w);
806\& struct whatever *mostinteresting; 1608\&
1609\& // start the idle watcher to handle the actual event.
1610\& // it will not be executed as long as other watchers
1611\& // with the default priority are receiving events.
1612\& ev_idle_start (EV_A_ &idle);
807\& } 1613\& }
808.Ve 1614\&
809.PP 1615\& static void
810And since your callback will be called with a pointer to the watcher, you 1616\& idle_cb (EV_P_ ev_idle *w, int revents)
811can cast it back to your own type:
812.PP
813.Vb 5
814\& static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)
815\& { 1617\& {
816\& struct my_io *w = (struct my_io *)w_; 1618\& // actual processing
817\& ... 1619\& read (STDIN_FILENO, ...);
1620\&
1621\& // have to start the I/O watcher again, as
1622\& // we have handled the event
1623\& ev_io_start (EV_P_ &io);
818\& } 1624\& }
1625\&
1626\& // initialisation
1627\& ev_idle_init (&idle, idle_cb);
1628\& ev_io_init (&io, io_cb, STDIN_FILENO, EV_READ);
1629\& ev_io_start (EV_DEFAULT_ &io);
819.Ve 1630.Ve
820.PP 1631.PP
821More interesting and less C\-conformant ways of catsing your callback type 1632In the \*(L"real\*(R" world, it might also be beneficial to start a timer, so that
822have been omitted.... 1633low-priority connections can not be locked out forever under load. This
1634enables your program to keep a lower latency for important connections
1635during short periods of high load, while not completely locking out less
1636important ones.
823.SH "WATCHER TYPES" 1637.SH "WATCHER TYPES"
824.IX Header "WATCHER TYPES" 1638.IX Header "WATCHER TYPES"
825This section describes each watcher in detail, but will not repeat 1639This section describes each watcher in detail, but will not repeat
826information given in the last section. 1640information given in the last section. Any initialisation/set macros,
1641functions and members specific to the watcher type are explained.
1642.PP
1643Members are additionally marked with either \fI[read\-only]\fR, meaning that,
1644while the watcher is active, you can look at the member and expect some
1645sensible content, but you must not modify it (you can modify it while the
1646watcher is stopped to your hearts content), or \fI[read\-write]\fR, which
1647means you can expect it to have some sensible content while the watcher
1648is active, but you can also modify it. Modifying it may not do something
1649sensible or take immediate effect (or do anything at all), but libev will
1650not crash or malfunction in any way.
827.ie n .Sh """ev_io"" \- is this file descriptor readable or writable" 1651.ie n .SS """ev_io"" \- is this file descriptor readable or writable?"
828.el .Sh "\f(CWev_io\fP \- is this file descriptor readable or writable" 1652.el .SS "\f(CWev_io\fP \- is this file descriptor readable or writable?"
829.IX Subsection "ev_io - is this file descriptor readable or writable" 1653.IX Subsection "ev_io - is this file descriptor readable or writable?"
830I/O watchers check whether a file descriptor is readable or writable 1654I/O watchers check whether a file descriptor is readable or writable
831in each iteration of the event loop (This behaviour is called 1655in each iteration of the event loop, or, more precisely, when reading
832level-triggering because you keep receiving events as long as the 1656would not block the process and writing would at least be able to write
833condition persists. Remember you can stop the watcher if you don't want to 1657some data. This behaviour is called level-triggering because you keep
834act on the event and neither want to receive future events). 1658receiving events as long as the condition persists. Remember you can stop
1659the watcher if you don't want to act on the event and neither want to
1660receive future events.
835.PP 1661.PP
836In general you can register as many read and/or write event watchers per 1662In general you can register as many read and/or write event watchers per
837fd as you want (as long as you don't confuse yourself). Setting all file 1663fd as you want (as long as you don't confuse yourself). Setting all file
838descriptors to non-blocking mode is also usually a good idea (but not 1664descriptors to non-blocking mode is also usually a good idea (but not
839required if you know what you are doing). 1665required if you know what you are doing).
840.PP 1666.PP
841You have to be careful with dup'ed file descriptors, though. Some backends 1667Another thing you have to watch out for is that it is quite easy to
842(the linux epoll backend is a notable example) cannot handle dup'ed file 1668receive \*(L"spurious\*(R" readiness notifications, that is, your callback might
843descriptors correctly if you register interest in two or more fds pointing 1669be called with \f(CW\*(C`EV_READ\*(C'\fR but a subsequent \f(CW\*(C`read\*(C'\fR(2) will actually block
844to the same underlying file/socket etc. description (that is, they share 1670because there is no data. It is very easy to get into this situation even
845the same underlying \*(L"file open\*(R"). 1671with a relatively standard program structure. Thus it is best to always
1672use non-blocking I/O: An extra \f(CW\*(C`read\*(C'\fR(2) returning \f(CW\*(C`EAGAIN\*(C'\fR is far
1673preferable to a program hanging until some data arrives.
846.PP 1674.PP
847If you must do this, then force the use of a known-to-be-good backend 1675If you cannot run the fd in non-blocking mode (for example you should
848(at the time of this writing, this includes only \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR and 1676not play around with an Xlib connection), then you have to separately
849\&\f(CW\*(C`EVBACKEND_POLL\*(C'\fR). 1677re-test whether a file descriptor is really ready with a known-to-be good
1678interface such as poll (fortunately in the case of Xlib, it already does
1679this on its own, so its quite safe to use). Some people additionally
1680use \f(CW\*(C`SIGALRM\*(C'\fR and an interval timer, just to be sure you won't block
1681indefinitely.
1682.PP
1683But really, best use non-blocking mode.
1684.PP
1685\fIThe special problem of disappearing file descriptors\fR
1686.IX Subsection "The special problem of disappearing file descriptors"
1687.PP
1688Some backends (e.g. kqueue, epoll) need to be told about closing a file
1689descriptor (either due to calling \f(CW\*(C`close\*(C'\fR explicitly or any other means,
1690such as \f(CW\*(C`dup2\*(C'\fR). The reason is that you register interest in some file
1691descriptor, but when it goes away, the operating system will silently drop
1692this interest. If another file descriptor with the same number then is
1693registered with libev, there is no efficient way to see that this is, in
1694fact, a different file descriptor.
1695.PP
1696To avoid having to explicitly tell libev about such cases, libev follows
1697the following policy: Each time \f(CW\*(C`ev_io_set\*(C'\fR is being called, libev
1698will assume that this is potentially a new file descriptor, otherwise
1699it is assumed that the file descriptor stays the same. That means that
1700you \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
1701descriptor even if the file descriptor number itself did not change.
1702.PP
1703This is how one would do it normally anyway, the important point is that
1704the libev application should not optimise around libev but should leave
1705optimisations to libev.
1706.PP
1707\fIThe special problem of dup'ed file descriptors\fR
1708.IX Subsection "The special problem of dup'ed file descriptors"
1709.PP
1710Some backends (e.g. epoll), cannot register events for file descriptors,
1711but only events for the underlying file descriptions. That means when you
1712have \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors or weirder constellations, and register
1713events for them, only one file descriptor might actually receive events.
1714.PP
1715There is no workaround possible except not registering events
1716for potentially \f(CW\*(C`dup ()\*(C'\fR'ed file descriptors, or to resort to
1717\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1718.PP
1719\fIThe special problem of files\fR
1720.IX Subsection "The special problem of files"
1721.PP
1722Many people try to use \f(CW\*(C`select\*(C'\fR (or libev) on file descriptors
1723representing files, and expect it to become ready when their program
1724doesn't block on disk accesses (which can take a long time on their own).
1725.PP
1726However, this cannot ever work in the \*(L"expected\*(R" way \- you get a readiness
1727notification as soon as the kernel knows whether and how much data is
1728there, and in the case of open files, that's always the case, so you
1729always get a readiness notification instantly, and your read (or possibly
1730write) will still block on the disk I/O.
1731.PP
1732Another way to view it is that in the case of sockets, pipes, character
1733devices and so on, there is another party (the sender) that delivers data
1734on its own, but in the case of files, there is no such thing: the disk
1735will not send data on its own, simply because it doesn't know what you
1736wish to read \- you would first have to request some data.
1737.PP
1738Since files are typically not-so-well supported by advanced notification
1739mechanism, libev tries hard to emulate \s-1POSIX\s0 behaviour with respect
1740to files, even though you should not use it. The reason for this is
1741convenience: sometimes you want to watch \s-1STDIN\s0 or \s-1STDOUT\s0, which is
1742usually a tty, often a pipe, but also sometimes files or special devices
1743(for example, \f(CW\*(C`epoll\*(C'\fR on Linux works with \fI/dev/random\fR but not with
1744\&\fI/dev/urandom\fR), and even though the file might better be served with
1745asynchronous I/O instead of with non-blocking I/O, it is still useful when
1746it \*(L"just works\*(R" instead of freezing.
1747.PP
1748So avoid file descriptors pointing to files when you know it (e.g. use
1749libeio), but use them when it is convenient, e.g. for \s-1STDIN/STDOUT\s0, or
1750when you rarely read from a file instead of from a socket, and want to
1751reuse the same code path.
1752.PP
1753\fIThe special problem of fork\fR
1754.IX Subsection "The special problem of fork"
1755.PP
1756Some backends (epoll, kqueue) do not support \f(CW\*(C`fork ()\*(C'\fR at all or exhibit
1757useless behaviour. Libev fully supports fork, but needs to be told about
1758it in the child if you want to continue to use it in the child.
1759.PP
1760To support fork in your child processes, you have to call \f(CW\*(C`ev_loop_fork
1761()\*(C'\fR after a fork in the child, enable \f(CW\*(C`EVFLAG_FORKCHECK\*(C'\fR, or resort to
1762\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR.
1763.PP
1764\fIThe special problem of \s-1SIGPIPE\s0\fR
1765.IX Subsection "The special problem of SIGPIPE"
1766.PP
1767While not really specific to libev, it is easy to forget about \f(CW\*(C`SIGPIPE\*(C'\fR:
1768when writing to a pipe whose other end has been closed, your program gets
1769sent a \s-1SIGPIPE\s0, which, by default, aborts your program. For most programs
1770this is sensible behaviour, for daemons, this is usually undesirable.
1771.PP
1772So when you encounter spurious, unexplained daemon exits, make sure you
1773ignore \s-1SIGPIPE\s0 (and maybe make sure you log the exit status of your daemon
1774somewhere, as that would have given you a big clue).
1775.PP
1776\fIThe special problem of \fIaccept()\fIing when you can't\fR
1777.IX Subsection "The special problem of accept()ing when you can't"
1778.PP
1779Many implementations of the \s-1POSIX\s0 \f(CW\*(C`accept\*(C'\fR function (for example,
1780found in post\-2004 Linux) have the peculiar behaviour of not removing a
1781connection from the pending queue in all error cases.
1782.PP
1783For example, larger servers often run out of file descriptors (because
1784of resource limits), causing \f(CW\*(C`accept\*(C'\fR to fail with \f(CW\*(C`ENFILE\*(C'\fR but not
1785rejecting the connection, leading to libev signalling readiness on
1786the next iteration again (the connection still exists after all), and
1787typically causing the program to loop at 100% \s-1CPU\s0 usage.
1788.PP
1789Unfortunately, the set of errors that cause this issue differs between
1790operating systems, there is usually little the app can do to remedy the
1791situation, and no known thread-safe method of removing the connection to
1792cope with overload is known (to me).
1793.PP
1794One of the easiest ways to handle this situation is to just ignore it
1795\&\- when the program encounters an overload, it will just loop until the
1796situation is over. While this is a form of busy waiting, no \s-1OS\s0 offers an
1797event-based way to handle this situation, so it's the best one can do.
1798.PP
1799A better way to handle the situation is to log any errors other than
1800\&\f(CW\*(C`EAGAIN\*(C'\fR and \f(CW\*(C`EWOULDBLOCK\*(C'\fR, making sure not to flood the log with such
1801messages, and continue as usual, which at least gives the user an idea of
1802what could be wrong (\*(L"raise the ulimit!\*(R"). For extra points one could stop
1803the \f(CW\*(C`ev_io\*(C'\fR watcher on the listening fd \*(L"for a while\*(R", which reduces \s-1CPU\s0
1804usage.
1805.PP
1806If your program is single-threaded, then you could also keep a dummy file
1807descriptor for overload situations (e.g. by opening \fI/dev/null\fR), and
1808when you run into \f(CW\*(C`ENFILE\*(C'\fR or \f(CW\*(C`EMFILE\*(C'\fR, close it, run \f(CW\*(C`accept\*(C'\fR,
1809close that fd, and create a new dummy fd. This will gracefully refuse
1810clients under typical overload conditions.
1811.PP
1812The last way to handle it is to simply log the error and \f(CW\*(C`exit\*(C'\fR, as
1813is often done with \f(CW\*(C`malloc\*(C'\fR failures, but this results in an easy
1814opportunity for a DoS attack.
1815.PP
1816\fIWatcher-Specific Functions\fR
1817.IX Subsection "Watcher-Specific Functions"
850.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4 1818.IP "ev_io_init (ev_io *, callback, int fd, int events)" 4
851.IX Item "ev_io_init (ev_io *, callback, int fd, int events)" 1819.IX Item "ev_io_init (ev_io *, callback, int fd, int events)"
852.PD 0 1820.PD 0
853.IP "ev_io_set (ev_io *, int fd, int events)" 4 1821.IP "ev_io_set (ev_io *, int fd, int events)" 4
854.IX Item "ev_io_set (ev_io *, int fd, int events)" 1822.IX Item "ev_io_set (ev_io *, int fd, int events)"
855.PD 1823.PD
856Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The fd is the file descriptor to rceeive 1824Configures an \f(CW\*(C`ev_io\*(C'\fR watcher. The \f(CW\*(C`fd\*(C'\fR is the file descriptor to
857events for and events is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or \f(CW\*(C`EV_READ | 1825receive events for and \f(CW\*(C`events\*(C'\fR is either \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or
858EV_WRITE\*(C'\fR to receive the given events. 1826\&\f(CW\*(C`EV_READ | EV_WRITE\*(C'\fR, to express the desire to receive the given events.
859.Sp 1827.IP "int fd [read\-only]" 4
860Please note that most of the more scalable backend mechanisms (for example 1828.IX Item "int fd [read-only]"
861epoll and solaris ports) can result in spurious readyness notifications 1829The file descriptor being watched.
862for file descriptors, so you practically need to use non-blocking I/O (and 1830.IP "int events [read\-only]" 4
863treat callback invocation as hint only), or retest separately with a safe 1831.IX Item "int events [read-only]"
864interface before doing I/O (XLib can do this), or force the use of either 1832The events being watched.
865\&\f(CW\*(C`EVBACKEND_SELECT\*(C'\fR or \f(CW\*(C`EVBACKEND_POLL\*(C'\fR, which don't suffer from this
866problem. Also note that it is quite easy to have your callback invoked
867when the readyness condition is no longer valid even when employing
868typical ways of handling events, so its a good idea to use non-blocking
869I/O unconditionally.
870.PP 1833.PP
1834\fIExamples\fR
1835.IX Subsection "Examples"
1836.PP
871Example: call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well 1837Example: Call \f(CW\*(C`stdin_readable_cb\*(C'\fR when \s-1STDIN_FILENO\s0 has become, well
872readable, but only once. Since it is likely line\-buffered, you could 1838readable, but only once. Since it is likely line-buffered, you could
873attempt to read a whole line in the callback: 1839attempt to read a whole line in the callback.
874.PP 1840.PP
875.Vb 6 1841.Vb 6
876\& static void 1842\& static void
877\& stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents) 1843\& stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
878\& { 1844\& {
879\& ev_io_stop (loop, w); 1845\& ev_io_stop (loop, w);
880\& .. read from stdin here (or from w->fd) and haqndle any I/O errors 1846\& .. read from stdin here (or from w\->fd) and handle any I/O errors
881\& } 1847\& }
882.Ve 1848\&
883.PP
884.Vb 6
885\& ... 1849\& ...
886\& struct ev_loop *loop = ev_default_init (0); 1850\& struct ev_loop *loop = ev_default_init (0);
887\& struct ev_io stdin_readable; 1851\& ev_io stdin_readable;
888\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ); 1852\& ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
889\& ev_io_start (loop, &stdin_readable); 1853\& ev_io_start (loop, &stdin_readable);
890\& ev_loop (loop, 0); 1854\& ev_run (loop, 0);
891.Ve 1855.Ve
892.ie n .Sh """ev_timer"" \- relative and optionally recurring timeouts" 1856.ie n .SS """ev_timer"" \- relative and optionally repeating timeouts"
893.el .Sh "\f(CWev_timer\fP \- relative and optionally recurring timeouts" 1857.el .SS "\f(CWev_timer\fP \- relative and optionally repeating timeouts"
894.IX Subsection "ev_timer - relative and optionally recurring timeouts" 1858.IX Subsection "ev_timer - relative and optionally repeating timeouts"
895Timer watchers are simple relative timers that generate an event after a 1859Timer watchers are simple relative timers that generate an event after a
896given time, and optionally repeating in regular intervals after that. 1860given time, and optionally repeating in regular intervals after that.
897.PP 1861.PP
898The timers are based on real time, that is, if you register an event that 1862The timers are based on real time, that is, if you register an event that
899times out after an hour and you reset your system clock to last years 1863times out after an hour and you reset your system clock to January last
900time, it will still time out after (roughly) and hour. \*(L"Roughly\*(R" because 1864year, it will still time out after (roughly) one hour. \*(L"Roughly\*(R" because
901detecting time jumps is hard, and some inaccuracies are unavoidable (the 1865detecting time jumps is hard, and some inaccuracies are unavoidable (the
902monotonic clock option helps a lot here). 1866monotonic clock option helps a lot here).
1867.PP
1868The callback is guaranteed to be invoked only \fIafter\fR its timeout has
1869passed (not \fIat\fR, so on systems with very low-resolution clocks this
1870might introduce a small delay). If multiple timers become ready during the
1871same loop iteration then the ones with earlier time-out values are invoked
1872before ones of the same priority with later time-out values (but this is
1873no longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
1874.PP
1875\fIBe smart about timeouts\fR
1876.IX Subsection "Be smart about timeouts"
1877.PP
1878Many real-world problems involve some kind of timeout, usually for error
1879recovery. A typical example is an \s-1HTTP\s0 request \- if the other side hangs,
1880you want to raise some error after a while.
1881.PP
1882What follows are some ways to handle this problem, from obvious and
1883inefficient to smart and efficient.
1884.PP
1885In the following, a 60 second activity timeout is assumed \- a timeout that
1886gets reset to 60 seconds each time there is activity (e.g. each time some
1887data or other life sign was received).
1888.IP "1. Use a timer and stop, reinitialise and start it on activity." 4
1889.IX Item "1. Use a timer and stop, reinitialise and start it on activity."
1890This is the most obvious, but not the most simple way: In the beginning,
1891start the watcher:
1892.Sp
1893.Vb 2
1894\& ev_timer_init (timer, callback, 60., 0.);
1895\& ev_timer_start (loop, timer);
1896.Ve
1897.Sp
1898Then, each time there is some activity, \f(CW\*(C`ev_timer_stop\*(C'\fR it, initialise it
1899and start it again:
1900.Sp
1901.Vb 3
1902\& ev_timer_stop (loop, timer);
1903\& ev_timer_set (timer, 60., 0.);
1904\& ev_timer_start (loop, timer);
1905.Ve
1906.Sp
1907This is relatively simple to implement, but means that each time there is
1908some activity, libev will first have to remove the timer from its internal
1909data structure and then add it again. Libev tries to be fast, but it's
1910still not a constant-time operation.
1911.ie n .IP "2. Use a timer and re-start it with ""ev_timer_again"" inactivity." 4
1912.el .IP "2. Use a timer and re-start it with \f(CWev_timer_again\fR inactivity." 4
1913.IX Item "2. Use a timer and re-start it with ev_timer_again inactivity."
1914This is the easiest way, and involves using \f(CW\*(C`ev_timer_again\*(C'\fR instead of
1915\&\f(CW\*(C`ev_timer_start\*(C'\fR.
1916.Sp
1917To implement this, configure an \f(CW\*(C`ev_timer\*(C'\fR with a \f(CW\*(C`repeat\*(C'\fR value
1918of \f(CW60\fR and then call \f(CW\*(C`ev_timer_again\*(C'\fR at start and each time you
1919successfully read or write some data. If you go into an idle state where
1920you do not expect data to travel on the socket, you can \f(CW\*(C`ev_timer_stop\*(C'\fR
1921the timer, and \f(CW\*(C`ev_timer_again\*(C'\fR will automatically restart it if need be.
1922.Sp
1923That means you can ignore both the \f(CW\*(C`ev_timer_start\*(C'\fR function and the
1924\&\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
1925member and \f(CW\*(C`ev_timer_again\*(C'\fR.
1926.Sp
1927At start:
1928.Sp
1929.Vb 3
1930\& ev_init (timer, callback);
1931\& timer\->repeat = 60.;
1932\& ev_timer_again (loop, timer);
1933.Ve
1934.Sp
1935Each time there is some activity:
1936.Sp
1937.Vb 1
1938\& ev_timer_again (loop, timer);
1939.Ve
1940.Sp
1941It is even possible to change the time-out on the fly, regardless of
1942whether the watcher is active or not:
1943.Sp
1944.Vb 2
1945\& timer\->repeat = 30.;
1946\& ev_timer_again (loop, timer);
1947.Ve
1948.Sp
1949This is slightly more efficient then stopping/starting the timer each time
1950you want to modify its timeout value, as libev does not have to completely
1951remove and re-insert the timer from/into its internal data structure.
1952.Sp
1953It is, however, even simpler than the \*(L"obvious\*(R" way to do it.
1954.IP "3. Let the timer time out, but then re-arm it as required." 4
1955.IX Item "3. Let the timer time out, but then re-arm it as required."
1956This method is more tricky, but usually most efficient: Most timeouts are
1957relatively long compared to the intervals between other activity \- in
1958our example, within 60 seconds, there are usually many I/O events with
1959associated activity resets.
1960.Sp
1961In this case, it would be more efficient to leave the \f(CW\*(C`ev_timer\*(C'\fR alone,
1962but remember the time of last activity, and check for a real timeout only
1963within the callback:
1964.Sp
1965.Vb 1
1966\& ev_tstamp last_activity; // time of last activity
1967\&
1968\& static void
1969\& callback (EV_P_ ev_timer *w, int revents)
1970\& {
1971\& ev_tstamp now = ev_now (EV_A);
1972\& ev_tstamp timeout = last_activity + 60.;
1973\&
1974\& // if last_activity + 60. is older than now, we did time out
1975\& if (timeout < now)
1976\& {
1977\& // timeout occurred, take action
1978\& }
1979\& else
1980\& {
1981\& // callback was invoked, but there was some activity, re\-arm
1982\& // the watcher to fire in last_activity + 60, which is
1983\& // guaranteed to be in the future, so "again" is positive:
1984\& w\->repeat = timeout \- now;
1985\& ev_timer_again (EV_A_ w);
1986\& }
1987\& }
1988.Ve
1989.Sp
1990To summarise the callback: first calculate the real timeout (defined
1991as \*(L"60 seconds after the last activity\*(R"), then check if that time has
1992been reached, which means something \fIdid\fR, in fact, time out. Otherwise
1993the callback was invoked too early (\f(CW\*(C`timeout\*(C'\fR is in the future), so
1994re-schedule the timer to fire at that future time, to see if maybe we have
1995a timeout then.
1996.Sp
1997Note how \f(CW\*(C`ev_timer_again\*(C'\fR is used, taking advantage of the
1998\&\f(CW\*(C`ev_timer_again\*(C'\fR optimisation when the timer is already running.
1999.Sp
2000This scheme causes more callback invocations (about one every 60 seconds
2001minus half the average time between activity), but virtually no calls to
2002libev to change the timeout.
2003.Sp
2004To start the timer, simply initialise the watcher and set \f(CW\*(C`last_activity\*(C'\fR
2005to the current time (meaning we just have some activity :), then call the
2006callback, which will \*(L"do the right thing\*(R" and start the timer:
2007.Sp
2008.Vb 3
2009\& ev_init (timer, callback);
2010\& last_activity = ev_now (loop);
2011\& callback (loop, timer, EV_TIMER);
2012.Ve
2013.Sp
2014And when there is some activity, simply store the current time in
2015\&\f(CW\*(C`last_activity\*(C'\fR, no libev calls at all:
2016.Sp
2017.Vb 1
2018\& last_activity = ev_now (loop);
2019.Ve
2020.Sp
2021This technique is slightly more complex, but in most cases where the
2022time-out is unlikely to be triggered, much more efficient.
2023.Sp
2024Changing the timeout is trivial as well (if it isn't hard-coded in the
2025callback :) \- just change the timeout and invoke the callback, which will
2026fix things for you.
2027.IP "4. Wee, just use a double-linked list for your timeouts." 4
2028.IX Item "4. Wee, just use a double-linked list for your timeouts."
2029If there is not one request, but many thousands (millions...), all
2030employing some kind of timeout with the same timeout value, then one can
2031do even better:
2032.Sp
2033When starting the timeout, calculate the timeout value and put the timeout
2034at the \fIend\fR of the list.
2035.Sp
2036Then use an \f(CW\*(C`ev_timer\*(C'\fR to fire when the timeout at the \fIbeginning\fR of
2037the list is expected to fire (for example, using the technique #3).
2038.Sp
2039When there is some activity, remove the timer from the list, recalculate
2040the timeout, append it to the end of the list again, and make sure to
2041update the \f(CW\*(C`ev_timer\*(C'\fR if it was taken from the beginning of the list.
2042.Sp
2043This way, one can manage an unlimited number of timeouts in O(1) time for
2044starting, stopping and updating the timers, at the expense of a major
2045complication, and having to use a constant timeout. The constant timeout
2046ensures that the list stays sorted.
2047.PP
2048So which method the best?
2049.PP
2050Method #2 is a simple no-brain-required solution that is adequate in most
2051situations. Method #3 requires a bit more thinking, but handles many cases
2052better, and isn't very complicated either. In most case, choosing either
2053one is fine, with #3 being better in typical situations.
2054.PP
2055Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
2056rather complicated, but extremely efficient, something that really pays
2057off after the first million or so of active timers, i.e. it's usually
2058overkill :)
2059.PP
2060\fIThe special problem of time updates\fR
2061.IX Subsection "The special problem of time updates"
2062.PP
2063Establishing the current time is a costly operation (it usually takes at
2064least two system calls): \s-1EV\s0 therefore updates its idea of the current
2065time only before and after \f(CW\*(C`ev_run\*(C'\fR collects new events, which causes a
2066growing difference between \f(CW\*(C`ev_now ()\*(C'\fR and \f(CW\*(C`ev_time ()\*(C'\fR when handling
2067lots of events in one iteration.
903.PP 2068.PP
904The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR 2069The relative timeouts are calculated relative to the \f(CW\*(C`ev_now ()\*(C'\fR
905time. This is usually the right thing as this timestamp refers to the time 2070time. This is usually the right thing as this timestamp refers to the time
906of the event triggering whatever timeout you are modifying/starting. If 2071of the event triggering whatever timeout you are modifying/starting. If
907you suspect event processing to be delayed and you \fIneed\fR to base the timeout 2072you suspect event processing to be delayed and you \fIneed\fR to base the
908on the current time, use something like this to adjust for this: 2073timeout on the current time, use something like this to adjust for this:
909.PP 2074.PP
910.Vb 1 2075.Vb 1
911\& ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); 2076\& ev_timer_set (&timer, after + ev_now () \- ev_time (), 0.);
912.Ve 2077.Ve
913.PP 2078.PP
914The callback is guarenteed to be invoked only when its timeout has passed, 2079If the event loop is suspended for a long time, you can also force an
915but if multiple timers become ready during the same loop iteration then 2080update of the time returned by \f(CW\*(C`ev_now ()\*(C'\fR by calling \f(CW\*(C`ev_now_update
916order of execution is undefined. 2081()\*(C'\fR.
2082.PP
2083\fIThe special problems of suspended animation\fR
2084.IX Subsection "The special problems of suspended animation"
2085.PP
2086When you leave the server world it is quite customary to hit machines that
2087can suspend/hibernate \- what happens to the clocks during such a suspend?
2088.PP
2089Some quick tests made with a Linux 2.6.28 indicate that a suspend freezes
2090all processes, while the clocks (\f(CW\*(C`times\*(C'\fR, \f(CW\*(C`CLOCK_MONOTONIC\*(C'\fR) continue
2091to run until the system is suspended, but they will not advance while the
2092system is suspended. That means, on resume, it will be as if the program
2093was frozen for a few seconds, but the suspend time will not be counted
2094towards \f(CW\*(C`ev_timer\*(C'\fR when a monotonic clock source is used. The real time
2095clock advanced as expected, but if it is used as sole clocksource, then a
2096long suspend would be detected as a time jump by libev, and timers would
2097be adjusted accordingly.
2098.PP
2099I would not be surprised to see different behaviour in different between
2100operating systems, \s-1OS\s0 versions or even different hardware.
2101.PP
2102The other form of suspend (job control, or sending a \s-1SIGSTOP\s0) will see a
2103time jump in the monotonic clocks and the realtime clock. If the program
2104is suspended for a very long time, and monotonic clock sources are in use,
2105then you can expect \f(CW\*(C`ev_timer\*(C'\fRs to expire as the full suspension time
2106will be counted towards the timers. When no monotonic clock source is in
2107use, then libev will again assume a timejump and adjust accordingly.
2108.PP
2109It might be beneficial for this latter case to call \f(CW\*(C`ev_suspend\*(C'\fR
2110and \f(CW\*(C`ev_resume\*(C'\fR in code that handles \f(CW\*(C`SIGTSTP\*(C'\fR, to at least get
2111deterministic behaviour in this case (you can do nothing against
2112\&\f(CW\*(C`SIGSTOP\*(C'\fR).
2113.PP
2114\fIWatcher-Specific Functions and Data Members\fR
2115.IX Subsection "Watcher-Specific Functions and Data Members"
917.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4 2116.IP "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 4
918.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)" 2117.IX Item "ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)"
919.PD 0 2118.PD 0
920.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4 2119.IP "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 4
921.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)" 2120.IX Item "ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)"
922.PD 2121.PD
923Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR is 2122Configure the timer to trigger after \f(CW\*(C`after\*(C'\fR seconds. If \f(CW\*(C`repeat\*(C'\fR
924\&\f(CW0.\fR, then it will automatically be stopped. If it is positive, then the 2123is \f(CW0.\fR, then it will automatically be stopped once the timeout is
925timer will automatically be configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds 2124reached. If it is positive, then the timer will automatically be
926later, again, and again, until stopped manually. 2125configured to trigger again \f(CW\*(C`repeat\*(C'\fR seconds later, again, and again,
2126until stopped manually.
927.Sp 2127.Sp
928The timer itself will do a best-effort at avoiding drift, that is, if you 2128The timer itself will do a best-effort at avoiding drift, that is, if
929configure a timer to trigger every 10 seconds, then it will trigger at 2129you configure a timer to trigger every 10 seconds, then it will normally
930exactly 10 second intervals. If, however, your program cannot keep up with 2130trigger at exactly 10 second intervals. If, however, your program cannot
931the timer (because it takes longer than those 10 seconds to do stuff) the 2131keep up with the timer (because it takes longer than those 10 seconds to
932timer will not fire more than once per event loop iteration. 2132do stuff) the timer will not fire more than once per event loop iteration.
933.IP "ev_timer_again (loop)" 4 2133.IP "ev_timer_again (loop, ev_timer *)" 4
934.IX Item "ev_timer_again (loop)" 2134.IX Item "ev_timer_again (loop, ev_timer *)"
935This will act as if the timer timed out and restart it again if it is 2135This will act as if the timer timed out and restart it again if it is
936repeating. The exact semantics are: 2136repeating. The exact semantics are:
937.Sp 2137.Sp
2138If the timer is pending, its pending status is cleared.
2139.Sp
938If the timer is started but nonrepeating, stop it. 2140If the timer is started but non-repeating, stop it (as if it timed out).
939.Sp 2141.Sp
940If the timer is repeating, either start it if necessary (with the repeat 2142If the timer is repeating, either start it if necessary (with the
941value), or reset the running timer to the repeat value. 2143\&\f(CW\*(C`repeat\*(C'\fR value), or reset the running timer to the \f(CW\*(C`repeat\*(C'\fR value.
942.Sp 2144.Sp
943This sounds a bit complicated, but here is a useful and typical 2145This sounds a bit complicated, see \*(L"Be smart about timeouts\*(R", above, for a
944example: Imagine you have a tcp connection and you want a so-called idle 2146usage example.
945timeout, that is, you want to be called when there have been, say, 60 2147.IP "ev_tstamp ev_timer_remaining (loop, ev_timer *)" 4
946seconds of inactivity on the socket. The easiest way to do this is to 2148.IX Item "ev_tstamp ev_timer_remaining (loop, ev_timer *)"
947configure an \f(CW\*(C`ev_timer\*(C'\fR with after=repeat=60 and calling ev_timer_again each 2149Returns the remaining time until a timer fires. If the timer is active,
948time you successfully read or write some data. If you go into an idle 2150then this time is relative to the current event loop time, otherwise it's
949state where you do not expect data to travel on the socket, you can stop 2151the timeout value currently configured.
950the timer, and again will automatically restart it if need be. 2152.Sp
2153That is, after an \f(CW\*(C`ev_timer_set (w, 5, 7)\*(C'\fR, \f(CW\*(C`ev_timer_remaining\*(C'\fR returns
2154\&\f(CW5\fR. When the timer is started and one second passes, \f(CW\*(C`ev_timer_remaining\*(C'\fR
2155will return \f(CW4\fR. When the timer expires and is restarted, it will return
2156roughly \f(CW7\fR (likely slightly less as callback invocation takes some time,
2157too), and so on.
2158.IP "ev_tstamp repeat [read\-write]" 4
2159.IX Item "ev_tstamp repeat [read-write]"
2160The current \f(CW\*(C`repeat\*(C'\fR value. Will be used each time the watcher times out
2161or \f(CW\*(C`ev_timer_again\*(C'\fR is called, and determines the next timeout (if any),
2162which is also when any modifications are taken into account.
951.PP 2163.PP
2164\fIExamples\fR
2165.IX Subsection "Examples"
2166.PP
952Example: create a timer that fires after 60 seconds. 2167Example: Create a timer that fires after 60 seconds.
953.PP 2168.PP
954.Vb 5 2169.Vb 5
955\& static void 2170\& static void
956\& one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents) 2171\& one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
957\& { 2172\& {
958\& .. one minute over, w is actually stopped right here 2173\& .. one minute over, w is actually stopped right here
959\& } 2174\& }
960.Ve 2175\&
961.PP
962.Vb 3
963\& struct ev_timer mytimer; 2176\& ev_timer mytimer;
964\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.); 2177\& ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
965\& ev_timer_start (loop, &mytimer); 2178\& ev_timer_start (loop, &mytimer);
966.Ve 2179.Ve
967.PP 2180.PP
968Example: create a timeout timer that times out after 10 seconds of 2181Example: Create a timeout timer that times out after 10 seconds of
969inactivity. 2182inactivity.
970.PP 2183.PP
971.Vb 5 2184.Vb 5
972\& static void 2185\& static void
973\& timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents) 2186\& timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
974\& { 2187\& {
975\& .. ten seconds without any activity 2188\& .. ten seconds without any activity
976\& } 2189\& }
977.Ve 2190\&
978.PP
979.Vb 4
980\& struct ev_timer mytimer; 2191\& ev_timer mytimer;
981\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */ 2192\& ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
982\& ev_timer_again (&mytimer); /* start timer */ 2193\& ev_timer_again (&mytimer); /* start timer */
983\& ev_loop (loop, 0); 2194\& ev_run (loop, 0);
984.Ve 2195\&
985.PP
986.Vb 3
987\& // and in some piece of code that gets executed on any "activity": 2196\& // and in some piece of code that gets executed on any "activity":
988\& // reset the timeout to start ticking again at 10 seconds 2197\& // reset the timeout to start ticking again at 10 seconds
989\& ev_timer_again (&mytimer); 2198\& ev_timer_again (&mytimer);
990.Ve 2199.Ve
991.ie n .Sh """ev_periodic"" \- to cron or not to cron" 2200.ie n .SS """ev_periodic"" \- to cron or not to cron?"
992.el .Sh "\f(CWev_periodic\fP \- to cron or not to cron" 2201.el .SS "\f(CWev_periodic\fP \- to cron or not to cron?"
993.IX Subsection "ev_periodic - to cron or not to cron" 2202.IX Subsection "ev_periodic - to cron or not to cron?"
994Periodic watchers are also timers of a kind, but they are very versatile 2203Periodic watchers are also timers of a kind, but they are very versatile
995(and unfortunately a bit complex). 2204(and unfortunately a bit complex).
996.PP 2205.PP
997Unlike \f(CW\*(C`ev_timer\*(C'\fR's, they are not based on real time (or relative time) 2206Unlike \f(CW\*(C`ev_timer\*(C'\fR, periodic watchers are not based on real time (or
998but on wallclock time (absolute time). You can tell a periodic watcher 2207relative time, the physical time that passes) but on wall clock time
999to trigger \*(L"at\*(R" some specific point in time. For example, if you tell a 2208(absolute time, the thing you can read on your calender or clock). The
1000periodic watcher to trigger in 10 seconds (by specifiying e.g. \f(CW\*(C`ev_now () 2209difference is that wall clock time can run faster or slower than real
1001+ 10.\*(C'\fR) and then reset your system clock to the last year, then it will 2210time, and time jumps are not uncommon (e.g. when you adjust your
1002take a year to trigger the event (unlike an \f(CW\*(C`ev_timer\*(C'\fR, which would trigger 2211wrist-watch).
1003roughly 10 seconds later and of course not if you reset your system time
1004again).
1005.PP 2212.PP
1006They can also be used to implement vastly more complex timers, such as 2213You can tell a periodic watcher to trigger after some specific point
1007triggering an event on eahc midnight, local time. 2214in time: for example, if you tell a periodic watcher to trigger \*(L"in 10
2215seconds\*(R" (by specifying e.g. \f(CW\*(C`ev_now () + 10.\*(C'\fR, that is, an absolute time
2216not a delay) and then reset your system clock to January of the previous
2217year, then it will take a year or more to trigger the event (unlike an
2218\&\f(CW\*(C`ev_timer\*(C'\fR, which would still trigger roughly 10 seconds after starting
2219it, as it uses a relative timeout).
1008.PP 2220.PP
2221\&\f(CW\*(C`ev_periodic\*(C'\fR watchers can also be used to implement vastly more complex
2222timers, such as triggering an event on each \*(L"midnight, local time\*(R", or
2223other complicated rules. This cannot be done with \f(CW\*(C`ev_timer\*(C'\fR watchers, as
2224those cannot react to time jumps.
2225.PP
1009As with timers, the callback is guarenteed to be invoked only when the 2226As with timers, the callback is guaranteed to be invoked only when the
1010time (\f(CW\*(C`at\*(C'\fR) has been passed, but if multiple periodic timers become ready 2227point in time where it is supposed to trigger has passed. If multiple
1011during the same loop iteration then order of execution is undefined. 2228timers become ready during the same loop iteration then the ones with
2229earlier time-out values are invoked before ones with later time-out values
2230(but this is no longer true when a callback calls \f(CW\*(C`ev_run\*(C'\fR recursively).
2231.PP
2232\fIWatcher-Specific Functions and Data Members\fR
2233.IX Subsection "Watcher-Specific Functions and Data Members"
1012.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 4 2234.IP "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
1013.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)" 2235.IX Item "ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
1014.PD 0 2236.PD 0
1015.IP "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 4 2237.IP "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)" 4
1016.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)" 2238.IX Item "ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)"
1017.PD 2239.PD
1018Lots of arguments, lets sort it out... There are basically three modes of 2240Lots of arguments, let's sort it out... There are basically three modes of
1019operation, and we will explain them from simplest to complex: 2241operation, and we will explain them from simplest to most complex:
1020.RS 4 2242.RS 4
1021.IP "* absolute timer (interval = reschedule_cb = 0)" 4 2243.IP "\(bu" 4
1022.IX Item "absolute timer (interval = reschedule_cb = 0)" 2244absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
2245.Sp
1023In this configuration the watcher triggers an event at the wallclock time 2246In this configuration the watcher triggers an event after the wall clock
1024\&\f(CW\*(C`at\*(C'\fR and doesn't repeat. It will not adjust when a time jump occurs, 2247time \f(CW\*(C`offset\*(C'\fR has passed. It will not repeat and will not adjust when a
1025that is, if it is to be run at January 1st 2011 then it will run when the 2248time jump occurs, that is, if it is to be run at January 1st 2011 then it
1026system time reaches or surpasses this time. 2249will be stopped and invoked when the system clock reaches or surpasses
1027.IP "* non-repeating interval timer (interval > 0, reschedule_cb = 0)" 4 2250this point in time.
1028.IX Item "non-repeating interval timer (interval > 0, reschedule_cb = 0)" 2251.IP "\(bu" 4
2252repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
2253.Sp
1029In this mode the watcher will always be scheduled to time out at the next 2254In this mode the watcher will always be scheduled to time out at the next
1030\&\f(CW\*(C`at + N * interval\*(C'\fR time (for some integer N) and then repeat, regardless 2255\&\f(CW\*(C`offset + N * interval\*(C'\fR time (for some integer N, which can also be
1031of any time jumps. 2256negative) and then repeat, regardless of any time jumps. The \f(CW\*(C`offset\*(C'\fR
2257argument is merely an offset into the \f(CW\*(C`interval\*(C'\fR periods.
1032.Sp 2258.Sp
1033This can be used to create timers that do not drift with respect to system 2259This can be used to create timers that do not drift with respect to the
1034time: 2260system clock, for example, here is an \f(CW\*(C`ev_periodic\*(C'\fR that triggers each
2261hour, on the hour (with respect to \s-1UTC\s0):
1035.Sp 2262.Sp
1036.Vb 1 2263.Vb 1
1037\& ev_periodic_set (&periodic, 0., 3600., 0); 2264\& ev_periodic_set (&periodic, 0., 3600., 0);
1038.Ve 2265.Ve
1039.Sp 2266.Sp
1040This doesn't mean there will always be 3600 seconds in between triggers, 2267This doesn't mean there will always be 3600 seconds in between triggers,
1041but only that the the callback will be called when the system time shows a 2268but only that the callback will be called when the system time shows a
1042full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible 2269full hour (\s-1UTC\s0), or more correctly, when the system time is evenly divisible
1043by 3600. 2270by 3600.
1044.Sp 2271.Sp
1045Another way to think about it (for the mathematically inclined) is that 2272Another way to think about it (for the mathematically inclined) is that
1046\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible 2273\&\f(CW\*(C`ev_periodic\*(C'\fR will try to run the callback in this mode at the next possible
1047time where \f(CW\*(C`time = at (mod interval)\*(C'\fR, regardless of any time jumps. 2274time where \f(CW\*(C`time = offset (mod interval)\*(C'\fR, regardless of any time jumps.
1048.IP "* manual reschedule mode (reschedule_cb = callback)" 4 2275.Sp
1049.IX Item "manual reschedule mode (reschedule_cb = callback)" 2276For numerical stability it is preferable that the \f(CW\*(C`offset\*(C'\fR value is near
2277\&\f(CW\*(C`ev_now ()\*(C'\fR (the current time), but there is no range requirement for
2278this value, and in fact is often specified as zero.
2279.Sp
2280Note also that there is an upper limit to how often a timer can fire (\s-1CPU\s0
2281speed for example), so if \f(CW\*(C`interval\*(C'\fR is very small then timing stability
2282will of course deteriorate. Libev itself tries to be exact to be about one
2283millisecond (if the \s-1OS\s0 supports it and the machine is fast enough).
2284.IP "\(bu" 4
2285manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
2286.Sp
1050In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`at\*(C'\fR are both being 2287In this mode the values for \f(CW\*(C`interval\*(C'\fR and \f(CW\*(C`offset\*(C'\fR are both being
1051ignored. Instead, each time the periodic watcher gets scheduled, the 2288ignored. Instead, each time the periodic watcher gets scheduled, the
1052reschedule callback will be called with the watcher as first, and the 2289reschedule callback will be called with the watcher as first, and the
1053current time as second argument. 2290current time as second argument.
1054.Sp 2291.Sp
1055\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, 2292\&\s-1NOTE:\s0 \fIThis callback \s-1MUST\s0 \s-1NOT\s0 stop or destroy any periodic watcher, ever,
1056ever, or make any event loop modifications\fR. If you need to stop it, 2293or make \s-1ANY\s0 other event loop modifications whatsoever, unless explicitly
1057return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop it afterwards (e.g. by 2294allowed by documentation here\fR.
1058starting a prepare watcher).
1059.Sp 2295.Sp
2296If you need to stop it, return \f(CW\*(C`now + 1e30\*(C'\fR (or so, fudge fudge) and stop
2297it afterwards (e.g. by starting an \f(CW\*(C`ev_prepare\*(C'\fR watcher, which is the
2298only event loop modification you are allowed to do).
2299.Sp
1060Its prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(struct ev_periodic *w, 2300The callback prototype is \f(CW\*(C`ev_tstamp (*reschedule_cb)(ev_periodic
1061ev_tstamp now)\*(C'\fR, e.g.: 2301*w, ev_tstamp now)\*(C'\fR, e.g.:
1062.Sp 2302.Sp
1063.Vb 4 2303.Vb 5
2304\& static ev_tstamp
1064\& static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now) 2305\& my_rescheduler (ev_periodic *w, ev_tstamp now)
1065\& { 2306\& {
1066\& return now + 60.; 2307\& return now + 60.;
1067\& } 2308\& }
1068.Ve 2309.Ve
1069.Sp 2310.Sp
1070It must return the next time to trigger, based on the passed time value 2311It must return the next time to trigger, based on the passed time value
1071(that is, the lowest time value larger than to the second argument). It 2312(that is, the lowest time value larger than to the second argument). It
1072will usually be called just before the callback will be triggered, but 2313will usually be called just before the callback will be triggered, but
1073might be called at other times, too. 2314might be called at other times, too.
1074.Sp 2315.Sp
1075\&\s-1NOTE:\s0 \fIThis callback must always return a time that is later than the 2316\&\s-1NOTE:\s0 \fIThis callback must always return a time that is higher than or
1076passed \f(CI\*(C`now\*(C'\fI value\fR. Not even \f(CW\*(C`now\*(C'\fR itself will do, it \fImust\fR be larger. 2317equal to the passed \f(CI\*(C`now\*(C'\fI value\fR.
1077.Sp 2318.Sp
1078This can be used to create very complex timers, such as a timer that 2319This can be used to create very complex timers, such as a timer that
1079triggers on each midnight, local time. To do this, you would calculate the 2320triggers on \*(L"next midnight, local time\*(R". To do this, you would calculate the
1080next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How 2321next midnight after \f(CW\*(C`now\*(C'\fR and return the timestamp value for this. How
1081you do this is, again, up to you (but it is not trivial, which is the main 2322you do this is, again, up to you (but it is not trivial, which is the main
1082reason I omitted it as an example). 2323reason I omitted it as an example).
1083.RE 2324.RE
1084.RS 4 2325.RS 4
… …
1087.IX Item "ev_periodic_again (loop, ev_periodic *)" 2328.IX Item "ev_periodic_again (loop, ev_periodic *)"
1088Simply stops and restarts the periodic watcher again. This is only useful 2329Simply stops and restarts the periodic watcher again. This is only useful
1089when you changed some parameters or the reschedule callback would return 2330when you changed some parameters or the reschedule callback would return
1090a different time than the last time it was called (e.g. in a crond like 2331a different time than the last time it was called (e.g. in a crond like
1091program when the crontabs have changed). 2332program when the crontabs have changed).
2333.IP "ev_tstamp ev_periodic_at (ev_periodic *)" 4
2334.IX Item "ev_tstamp ev_periodic_at (ev_periodic *)"
2335When active, returns the absolute time that the watcher is supposed
2336to trigger next. This is not the same as the \f(CW\*(C`offset\*(C'\fR argument to
2337\&\f(CW\*(C`ev_periodic_set\*(C'\fR, but indeed works even in interval and manual
2338rescheduling modes.
2339.IP "ev_tstamp offset [read\-write]" 4
2340.IX Item "ev_tstamp offset [read-write]"
2341When repeating, this contains the offset value, otherwise this is the
2342absolute point in time (the \f(CW\*(C`offset\*(C'\fR value passed to \f(CW\*(C`ev_periodic_set\*(C'\fR,
2343although libev might modify this value for better numerical stability).
2344.Sp
2345Can be modified any time, but changes only take effect when the periodic
2346timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
2347.IP "ev_tstamp interval [read\-write]" 4
2348.IX Item "ev_tstamp interval [read-write]"
2349The current interval value. Can be modified any time, but changes only
2350take effect when the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being
2351called.
2352.IP "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read\-write]" 4
2353.IX Item "ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]"
2354The current reschedule callback, or \f(CW0\fR, if this functionality is
2355switched off. Can be changed any time, but changes only take effect when
2356the periodic timer fires or \f(CW\*(C`ev_periodic_again\*(C'\fR is being called.
1092.PP 2357.PP
2358\fIExamples\fR
2359.IX Subsection "Examples"
2360.PP
1093Example: call a callback every hour, or, more precisely, whenever the 2361Example: Call a callback every hour, or, more precisely, whenever the
1094system clock is divisible by 3600. The callback invocation times have 2362system time is divisible by 3600. The callback invocation times have
1095potentially a lot of jittering, but good long-term stability. 2363potentially a lot of jitter, but good long-term stability.
1096.PP 2364.PP
1097.Vb 5 2365.Vb 5
1098\& static void 2366\& static void
1099\& clock_cb (struct ev_loop *loop, struct ev_io *w, int revents) 2367\& clock_cb (struct ev_loop *loop, ev_periodic *w, int revents)
1100\& { 2368\& {
1101\& ... its now a full hour (UTC, or TAI or whatever your clock follows) 2369\& ... its now a full hour (UTC, or TAI or whatever your clock follows)
1102\& } 2370\& }
1103.Ve 2371\&
1104.PP
1105.Vb 3
1106\& struct ev_periodic hourly_tick; 2372\& ev_periodic hourly_tick;
1107\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0); 2373\& ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1108\& ev_periodic_start (loop, &hourly_tick); 2374\& ev_periodic_start (loop, &hourly_tick);
1109.Ve 2375.Ve
1110.PP 2376.PP
1111Example: the same as above, but use a reschedule callback to do it: 2377Example: The same as above, but use a reschedule callback to do it:
1112.PP 2378.PP
1113.Vb 1 2379.Vb 1
1114\& #include <math.h> 2380\& #include <math.h>
1115.Ve 2381\&
1116.PP
1117.Vb 5
1118\& static ev_tstamp 2382\& static ev_tstamp
1119\& my_scheduler_cb (struct ev_periodic *w, ev_tstamp now) 2383\& my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1120\& { 2384\& {
1121\& return fmod (now, 3600.) + 3600.; 2385\& return now + (3600. \- fmod (now, 3600.));
1122\& } 2386\& }
1123.Ve 2387\&
1124.PP
1125.Vb 1
1126\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb); 2388\& ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1127.Ve 2389.Ve
1128.PP 2390.PP
1129Example: call a callback every hour, starting now: 2391Example: Call a callback every hour, starting now:
1130.PP 2392.PP
1131.Vb 4 2393.Vb 4
1132\& struct ev_periodic hourly_tick; 2394\& ev_periodic hourly_tick;
1133\& ev_periodic_init (&hourly_tick, clock_cb, 2395\& ev_periodic_init (&hourly_tick, clock_cb,
1134\& fmod (ev_now (loop), 3600.), 3600., 0); 2396\& fmod (ev_now (loop), 3600.), 3600., 0);
1135\& ev_periodic_start (loop, &hourly_tick); 2397\& ev_periodic_start (loop, &hourly_tick);
1136.Ve 2398.Ve
1137.ie n .Sh """ev_signal"" \- signal me when a signal gets signalled" 2399.ie n .SS """ev_signal"" \- signal me when a signal gets signalled!"
1138.el .Sh "\f(CWev_signal\fP \- signal me when a signal gets signalled" 2400.el .SS "\f(CWev_signal\fP \- signal me when a signal gets signalled!"
1139.IX Subsection "ev_signal - signal me when a signal gets signalled" 2401.IX Subsection "ev_signal - signal me when a signal gets signalled!"
1140Signal watchers will trigger an event when the process receives a specific 2402Signal watchers will trigger an event when the process receives a specific
1141signal one or more times. Even though signals are very asynchronous, libev 2403signal one or more times. Even though signals are very asynchronous, libev
1142will try it's best to deliver signals synchronously, i.e. as part of the 2404will try its best to deliver signals synchronously, i.e. as part of the
1143normal event processing, like any other event. 2405normal event processing, like any other event.
1144.PP 2406.PP
2407If you want signals to be delivered truly asynchronously, just use
2408\&\f(CW\*(C`sigaction\*(C'\fR as you would do without libev and forget about sharing
2409the signal. You can even use \f(CW\*(C`ev_async\*(C'\fR from a signal handler to
2410synchronously wake up an event loop.
2411.PP
1145You can configure as many watchers as you like per signal. Only when the 2412You can configure as many watchers as you like for the same signal, but
2413only within the same loop, i.e. you can watch for \f(CW\*(C`SIGINT\*(C'\fR in your
2414default loop and for \f(CW\*(C`SIGIO\*(C'\fR in another loop, but you cannot watch for
2415\&\f(CW\*(C`SIGINT\*(C'\fR in both the default loop and another loop at the same time. At
2416the moment, \f(CW\*(C`SIGCHLD\*(C'\fR is permanently tied to the default loop.
2417.PP
1146first watcher gets started will libev actually register a signal watcher 2418When the first watcher gets started will libev actually register something
1147with the kernel (thus it coexists with your own signal handlers as long 2419with the kernel (thus it coexists with your own signal handlers as long as
1148as you don't register any with libev). Similarly, when the last signal 2420you don't register any with libev for the same signal).
1149watcher for a signal is stopped libev will reset the signal handler to 2421.PP
1150\&\s-1SIG_DFL\s0 (regardless of what it was set to before). 2422If possible and supported, libev will install its handlers with
2423\&\f(CW\*(C`SA_RESTART\*(C'\fR (or equivalent) behaviour enabled, so system calls should
2424not be unduly interrupted. If you have a problem with system calls getting
2425interrupted by signals you can block all signals in an \f(CW\*(C`ev_check\*(C'\fR watcher
2426and unblock them in an \f(CW\*(C`ev_prepare\*(C'\fR watcher.
2427.PP
2428\fIThe special problem of inheritance over fork/execve/pthread_create\fR
2429.IX Subsection "The special problem of inheritance over fork/execve/pthread_create"
2430.PP
2431Both the signal mask (\f(CW\*(C`sigprocmask\*(C'\fR) and the signal disposition
2432(\f(CW\*(C`sigaction\*(C'\fR) are unspecified after starting a signal watcher (and after
2433stopping it again), that is, libev might or might not block the signal,
2434and might or might not set or restore the installed signal handler.
2435.PP
2436While this does not matter for the signal disposition (libev never
2437sets signals to \f(CW\*(C`SIG_IGN\*(C'\fR, so handlers will be reset to \f(CW\*(C`SIG_DFL\*(C'\fR on
2438\&\f(CW\*(C`execve\*(C'\fR), this matters for the signal mask: many programs do not expect
2439certain signals to be blocked.
2440.PP
2441This means that before calling \f(CW\*(C`exec\*(C'\fR (from the child) you should reset
2442the signal mask to whatever \*(L"default\*(R" you expect (all clear is a good
2443choice usually).
2444.PP
2445The simplest way to ensure that the signal mask is reset in the child is
2446to install a fork handler with \f(CW\*(C`pthread_atfork\*(C'\fR that resets it. That will
2447catch fork calls done by libraries (such as the libc) as well.
2448.PP
2449In current versions of libev, the signal will not be blocked indefinitely
2450unless you use the \f(CW\*(C`signalfd\*(C'\fR \s-1API\s0 (\f(CW\*(C`EV_SIGNALFD\*(C'\fR). While this reduces
2451the window of opportunity for problems, it will not go away, as libev
2452\&\fIhas\fR to modify the signal mask, at least temporarily.
2453.PP
2454So I can't stress this enough: \fIIf you do not reset your signal mask when
2455you expect it to be empty, you have a race condition in your code\fR. This
2456is not a libev-specific thing, this is true for most event libraries.
2457.PP
2458\fIThe special problem of threads signal handling\fR
2459.IX Subsection "The special problem of threads signal handling"
2460.PP
2461\&\s-1POSIX\s0 threads has problematic signal handling semantics, specifically,
2462a lot of functionality (sigfd, sigwait etc.) only really works if all
2463threads in a process block signals, which is hard to achieve.
2464.PP
2465When you want to use sigwait (or mix libev signal handling with your own
2466for the same signals), you can tackle this problem by globally blocking
2467all signals before creating any threads (or creating them with a fully set
2468sigprocmask) and also specifying the \f(CW\*(C`EVFLAG_NOSIGMASK\*(C'\fR when creating
2469loops. Then designate one thread as \*(L"signal receiver thread\*(R" which handles
2470these signals. You can pass on any signals that libev might be interested
2471in by calling \f(CW\*(C`ev_feed_signal\*(C'\fR.
2472.PP
2473\fIWatcher-Specific Functions and Data Members\fR
2474.IX Subsection "Watcher-Specific Functions and Data Members"
1151.IP "ev_signal_init (ev_signal *, callback, int signum)" 4 2475.IP "ev_signal_init (ev_signal *, callback, int signum)" 4
1152.IX Item "ev_signal_init (ev_signal *, callback, int signum)" 2476.IX Item "ev_signal_init (ev_signal *, callback, int signum)"
1153.PD 0 2477.PD 0
1154.IP "ev_signal_set (ev_signal *, int signum)" 4 2478.IP "ev_signal_set (ev_signal *, int signum)" 4
1155.IX Item "ev_signal_set (ev_signal *, int signum)" 2479.IX Item "ev_signal_set (ev_signal *, int signum)"
1156.PD 2480.PD
1157Configures the watcher to trigger on the given signal number (usually one 2481Configures the watcher to trigger on the given signal number (usually one
1158of the \f(CW\*(C`SIGxxx\*(C'\fR constants). 2482of the \f(CW\*(C`SIGxxx\*(C'\fR constants).
2483.IP "int signum [read\-only]" 4
2484.IX Item "int signum [read-only]"
2485The signal the watcher watches out for.
2486.PP
2487\fIExamples\fR
2488.IX Subsection "Examples"
2489.PP
2490Example: Try to exit cleanly on \s-1SIGINT\s0.
2491.PP
2492.Vb 5
2493\& static void
2494\& sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
2495\& {
2496\& ev_break (loop, EVBREAK_ALL);
2497\& }
2498\&
2499\& ev_signal signal_watcher;
2500\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
2501\& ev_signal_start (loop, &signal_watcher);
2502.Ve
1159.ie n .Sh """ev_child"" \- wait for pid status changes" 2503.ie n .SS """ev_child"" \- watch out for process status changes"
1160.el .Sh "\f(CWev_child\fP \- wait for pid status changes" 2504.el .SS "\f(CWev_child\fP \- watch out for process status changes"
1161.IX Subsection "ev_child - wait for pid status changes" 2505.IX Subsection "ev_child - watch out for process status changes"
1162Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to 2506Child watchers trigger when your process receives a \s-1SIGCHLD\s0 in response to
1163some child status changes (most typically when a child of yours dies). 2507some child status changes (most typically when a child of yours dies or
2508exits). It is permissible to install a child watcher \fIafter\fR the child
2509has been forked (which implies it might have already exited), as long
2510as the event loop isn't entered (or is continued from a watcher), i.e.,
2511forking and then immediately registering a watcher for the child is fine,
2512but forking and registering a watcher a few event loop iterations later or
2513in the next callback invocation is not.
2514.PP
2515Only the default event loop is capable of handling signals, and therefore
2516you can only register child watchers in the default event loop.
2517.PP
2518Due to some design glitches inside libev, child watchers will always be
2519handled at maximum priority (their priority is set to \f(CW\*(C`EV_MAXPRI\*(C'\fR by
2520libev)
2521.PP
2522\fIProcess Interaction\fR
2523.IX Subsection "Process Interaction"
2524.PP
2525Libev grabs \f(CW\*(C`SIGCHLD\*(C'\fR as soon as the default event loop is
2526initialised. This is necessary to guarantee proper behaviour even if the
2527first child watcher is started after the child exits. The occurrence
2528of \f(CW\*(C`SIGCHLD\*(C'\fR is recorded asynchronously, but child reaping is done
2529synchronously as part of the event loop processing. Libev always reaps all
2530children, even ones not watched.
2531.PP
2532\fIOverriding the Built-In Processing\fR
2533.IX Subsection "Overriding the Built-In Processing"
2534.PP
2535Libev offers no special support for overriding the built-in child
2536processing, but if your application collides with libev's default child
2537handler, you can override it easily by installing your own handler for
2538\&\f(CW\*(C`SIGCHLD\*(C'\fR after initialising the default loop, and making sure the
2539default loop never gets destroyed. You are encouraged, however, to use an
2540event-based approach to child reaping and thus use libev's support for
2541that, so other libev users can use \f(CW\*(C`ev_child\*(C'\fR watchers freely.
2542.PP
2543\fIStopping the Child Watcher\fR
2544.IX Subsection "Stopping the Child Watcher"
2545.PP
2546Currently, the child watcher never gets stopped, even when the
2547child terminates, so normally one needs to stop the watcher in the
2548callback. Future versions of libev might stop the watcher automatically
2549when a child exit is detected (calling \f(CW\*(C`ev_child_stop\*(C'\fR twice is not a
2550problem).
2551.PP
2552\fIWatcher-Specific Functions and Data Members\fR
2553.IX Subsection "Watcher-Specific Functions and Data Members"
1164.IP "ev_child_init (ev_child *, callback, int pid)" 4 2554.IP "ev_child_init (ev_child *, callback, int pid, int trace)" 4
1165.IX Item "ev_child_init (ev_child *, callback, int pid)" 2555.IX Item "ev_child_init (ev_child *, callback, int pid, int trace)"
1166.PD 0 2556.PD 0
1167.IP "ev_child_set (ev_child *, int pid)" 4 2557.IP "ev_child_set (ev_child *, int pid, int trace)" 4
1168.IX Item "ev_child_set (ev_child *, int pid)" 2558.IX Item "ev_child_set (ev_child *, int pid, int trace)"
1169.PD 2559.PD
1170Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or 2560Configures the watcher to wait for status changes of process \f(CW\*(C`pid\*(C'\fR (or
1171\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look 2561\&\fIany\fR process if \f(CW\*(C`pid\*(C'\fR is specified as \f(CW0\fR). The callback can look
1172at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see 2562at the \f(CW\*(C`rstatus\*(C'\fR member of the \f(CW\*(C`ev_child\*(C'\fR watcher structure to see
1173the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems 2563the status word (use the macros from \f(CW\*(C`sys/wait.h\*(C'\fR and see your systems
1174\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the 2564\&\f(CW\*(C`waitpid\*(C'\fR documentation). The \f(CW\*(C`rpid\*(C'\fR member contains the pid of the
1175process causing the status change. 2565process causing the status change. \f(CW\*(C`trace\*(C'\fR must be either \f(CW0\fR (only
2566activate the watcher when the process terminates) or \f(CW1\fR (additionally
2567activate the watcher when the process is stopped or continued).
2568.IP "int pid [read\-only]" 4
2569.IX Item "int pid [read-only]"
2570The process id this watcher watches out for, or \f(CW0\fR, meaning any process id.
2571.IP "int rpid [read\-write]" 4
2572.IX Item "int rpid [read-write]"
2573The process id that detected a status change.
2574.IP "int rstatus [read\-write]" 4
2575.IX Item "int rstatus [read-write]"
2576The process exit/trace status caused by \f(CW\*(C`rpid\*(C'\fR (see your systems
2577\&\f(CW\*(C`waitpid\*(C'\fR and \f(CW\*(C`sys/wait.h\*(C'\fR documentation for details).
1176.PP 2578.PP
1177Example: try to exit cleanly on \s-1SIGINT\s0 and \s-1SIGTERM\s0. 2579\fIExamples\fR
2580.IX Subsection "Examples"
1178.PP 2581.PP
2582Example: \f(CW\*(C`fork()\*(C'\fR a new process and install a child handler to wait for
2583its completion.
2584.PP
1179.Vb 5 2585.Vb 1
2586\& ev_child cw;
2587\&
1180\& static void 2588\& static void
1181\& sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents) 2589\& child_cb (EV_P_ ev_child *w, int revents)
1182\& { 2590\& {
1183\& ev_unloop (loop, EVUNLOOP_ALL); 2591\& ev_child_stop (EV_A_ w);
2592\& printf ("process %d exited with status %x\en", w\->rpid, w\->rstatus);
1184\& } 2593\& }
2594\&
2595\& pid_t pid = fork ();
2596\&
2597\& if (pid < 0)
2598\& // error
2599\& else if (pid == 0)
2600\& {
2601\& // the forked child executes here
2602\& exit (1);
2603\& }
2604\& else
2605\& {
2606\& ev_child_init (&cw, child_cb, pid, 0);
2607\& ev_child_start (EV_DEFAULT_ &cw);
2608\& }
1185.Ve 2609.Ve
2610.ie n .SS """ev_stat"" \- did the file attributes just change?"
2611.el .SS "\f(CWev_stat\fP \- did the file attributes just change?"
2612.IX Subsection "ev_stat - did the file attributes just change?"
2613This watches a file system path for attribute changes. That is, it calls
2614\&\f(CW\*(C`stat\*(C'\fR on that path in regular intervals (or when the \s-1OS\s0 says it changed)
2615and sees if it changed compared to the last time, invoking the callback if
2616it did.
1186.PP 2617.PP
2618The path does not need to exist: changing from \*(L"path exists\*(R" to \*(L"path does
2619not exist\*(R" is a status change like any other. The condition \*(L"path does not
2620exist\*(R" (or more correctly \*(L"path cannot be stat'ed\*(R") is signified by the
2621\&\f(CW\*(C`st_nlink\*(C'\fR field being zero (which is otherwise always forced to be at
2622least one) and all the other fields of the stat buffer having unspecified
2623contents.
2624.PP
2625The path \fImust not\fR end in a slash or contain special components such as
2626\&\f(CW\*(C`.\*(C'\fR or \f(CW\*(C`..\*(C'\fR. The path \fIshould\fR be absolute: If it is relative and
2627your working directory changes, then the behaviour is undefined.
2628.PP
2629Since there is no portable change notification interface available, the
2630portable implementation simply calls \f(CWstat(2)\fR regularly on the path
2631to see if it changed somehow. You can specify a recommended polling
2632interval for this case. If you specify a polling interval of \f(CW0\fR (highly
2633recommended!) then a \fIsuitable, unspecified default\fR value will be used
2634(which you can expect to be around five seconds, although this might
2635change dynamically). Libev will also impose a minimum interval which is
2636currently around \f(CW0.1\fR, but that's usually overkill.
2637.PP
2638This watcher type is not meant for massive numbers of stat watchers,
2639as even with OS-supported change notifications, this can be
2640resource-intensive.
2641.PP
2642At the time of this writing, the only OS-specific interface implemented
2643is the Linux inotify interface (implementing kqueue support is left as an
2644exercise for the reader. Note, however, that the author sees no way of
2645implementing \f(CW\*(C`ev_stat\*(C'\fR semantics with kqueue, except as a hint).
2646.PP
2647\fI\s-1ABI\s0 Issues (Largefile Support)\fR
2648.IX Subsection "ABI Issues (Largefile Support)"
2649.PP
2650Libev by default (unless the user overrides this) uses the default
2651compilation environment, which means that on systems with large file
2652support disabled by default, you get the 32 bit version of the stat
2653structure. When using the library from programs that change the \s-1ABI\s0 to
2654use 64 bit file offsets the programs will fail. In that case you have to
2655compile libev with the same flags to get binary compatibility. This is
2656obviously the case with any flags that change the \s-1ABI\s0, but the problem is
2657most noticeably displayed with ev_stat and large file support.
2658.PP
2659The solution for this is to lobby your distribution maker to make large
2660file interfaces available by default (as e.g. FreeBSD does) and not
2661optional. Libev cannot simply switch on large file support because it has
2662to exchange stat structures with application programs compiled using the
2663default compilation environment.
2664.PP
2665\fIInotify and Kqueue\fR
2666.IX Subsection "Inotify and Kqueue"
2667.PP
2668When \f(CW\*(C`inotify (7)\*(C'\fR support has been compiled into libev and present at
2669runtime, it will be used to speed up change detection where possible. The
2670inotify descriptor will be created lazily when the first \f(CW\*(C`ev_stat\*(C'\fR
2671watcher is being started.
2672.PP
2673Inotify presence does not change the semantics of \f(CW\*(C`ev_stat\*(C'\fR watchers
2674except that changes might be detected earlier, and in some cases, to avoid
2675making regular \f(CW\*(C`stat\*(C'\fR calls. Even in the presence of inotify support
2676there are many cases where libev has to resort to regular \f(CW\*(C`stat\*(C'\fR polling,
2677but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
2678many bugs), the path exists (i.e. stat succeeds), and the path resides on
2679a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
2680xfs are fully working) libev usually gets away without polling.
2681.PP
2682There is no support for kqueue, as apparently it cannot be used to
2683implement this functionality, due to the requirement of having a file
2684descriptor open on the object at all times, and detecting renames, unlinks
2685etc. is difficult.
2686.PP
2687\fI\f(CI\*(C`stat ()\*(C'\fI is a synchronous operation\fR
2688.IX Subsection "stat () is a synchronous operation"
2689.PP
2690Libev doesn't normally do any kind of I/O itself, and so is not blocking
2691the process. The exception are \f(CW\*(C`ev_stat\*(C'\fR watchers \- those call \f(CW\*(C`stat
2692()\*(C'\fR, which is a synchronous operation.
2693.PP
2694For local paths, this usually doesn't matter: unless the system is very
2695busy or the intervals between stat's are large, a stat call will be fast,
2696as the path data is usually in memory already (except when starting the
2697watcher).
2698.PP
2699For networked file systems, calling \f(CW\*(C`stat ()\*(C'\fR can block an indefinite
2700time due to network issues, and even under good conditions, a stat call
2701often takes multiple milliseconds.
2702.PP
2703Therefore, it is best to avoid using \f(CW\*(C`ev_stat\*(C'\fR watchers on networked
2704paths, although this is fully supported by libev.
2705.PP
2706\fIThe special problem of stat time resolution\fR
2707.IX Subsection "The special problem of stat time resolution"
2708.PP
2709The \f(CW\*(C`stat ()\*(C'\fR system call only supports full-second resolution portably,
2710and even on systems where the resolution is higher, most file systems
2711still only support whole seconds.
2712.PP
2713That means that, if the time is the only thing that changes, you can
2714easily miss updates: on the first update, \f(CW\*(C`ev_stat\*(C'\fR detects a change and
2715calls your callback, which does something. When there is another update
2716within the same second, \f(CW\*(C`ev_stat\*(C'\fR will be unable to detect unless the
2717stat data does change in other ways (e.g. file size).
2718.PP
2719The solution to this is to delay acting on a change for slightly more
2720than a second (or till slightly after the next full second boundary), using
2721a roughly one-second-delay \f(CW\*(C`ev_timer\*(C'\fR (e.g. \f(CW\*(C`ev_timer_set (w, 0., 1.02);
2722ev_timer_again (loop, w)\*(C'\fR).
2723.PP
2724The \f(CW.02\fR offset is added to work around small timing inconsistencies
2725of some operating systems (where the second counter of the current time
2726might be be delayed. One such system is the Linux kernel, where a call to
2727\&\f(CW\*(C`gettimeofday\*(C'\fR might return a timestamp with a full second later than
2728a subsequent \f(CW\*(C`time\*(C'\fR call \- if the equivalent of \f(CW\*(C`time ()\*(C'\fR is used to
2729update file times then there will be a small window where the kernel uses
2730the previous second to update file times but libev might already execute
2731the timer callback).
2732.PP
2733\fIWatcher-Specific Functions and Data Members\fR
2734.IX Subsection "Watcher-Specific Functions and Data Members"
2735.IP "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)" 4
2736.IX Item "ev_stat_init (ev_stat *, callback, const char *path, ev_tstamp interval)"
2737.PD 0
2738.IP "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)" 4
2739.IX Item "ev_stat_set (ev_stat *, const char *path, ev_tstamp interval)"
2740.PD
2741Configures the watcher to wait for status changes of the given
2742\&\f(CW\*(C`path\*(C'\fR. The \f(CW\*(C`interval\*(C'\fR is a hint on how quickly a change is expected to
2743be detected and should normally be specified as \f(CW0\fR to let libev choose
2744a suitable value. The memory pointed to by \f(CW\*(C`path\*(C'\fR must point to the same
2745path for as long as the watcher is active.
2746.Sp
2747The callback will receive an \f(CW\*(C`EV_STAT\*(C'\fR event when a change was detected,
2748relative to the attributes at the time the watcher was started (or the
2749last change was detected).
2750.IP "ev_stat_stat (loop, ev_stat *)" 4
2751.IX Item "ev_stat_stat (loop, ev_stat *)"
2752Updates the stat buffer immediately with new values. If you change the
2753watched path in your callback, you could call this function to avoid
2754detecting this change (while introducing a race condition if you are not
2755the only one changing the path). Can also be useful simply to find out the
2756new values.
2757.IP "ev_statdata attr [read\-only]" 4
2758.IX Item "ev_statdata attr [read-only]"
2759The most-recently detected attributes of the file. Although the type is
2760\&\f(CW\*(C`ev_statdata\*(C'\fR, this is usually the (or one of the) \f(CW\*(C`struct stat\*(C'\fR types
2761suitable for your system, but you can only rely on the POSIX-standardised
2762members to be present. If the \f(CW\*(C`st_nlink\*(C'\fR member is \f(CW0\fR, then there was
2763some error while \f(CW\*(C`stat\*(C'\fRing the file.
2764.IP "ev_statdata prev [read\-only]" 4
2765.IX Item "ev_statdata prev [read-only]"
2766The previous attributes of the file. The callback gets invoked whenever
2767\&\f(CW\*(C`prev\*(C'\fR != \f(CW\*(C`attr\*(C'\fR, or, more precisely, one or more of these members
2768differ: \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,
2769\&\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.
2770.IP "ev_tstamp interval [read\-only]" 4
2771.IX Item "ev_tstamp interval [read-only]"
2772The specified interval.
2773.IP "const char *path [read\-only]" 4
2774.IX Item "const char *path [read-only]"
2775The file system path that is being watched.
2776.PP
2777\fIExamples\fR
2778.IX Subsection "Examples"
2779.PP
2780Example: Watch \f(CW\*(C`/etc/passwd\*(C'\fR for attribute changes.
2781.PP
2782.Vb 10
2783\& static void
2784\& passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
2785\& {
2786\& /* /etc/passwd changed in some way */
2787\& if (w\->attr.st_nlink)
2788\& {
2789\& printf ("passwd current size %ld\en", (long)w\->attr.st_size);
2790\& printf ("passwd current atime %ld\en", (long)w\->attr.st_mtime);
2791\& printf ("passwd current mtime %ld\en", (long)w\->attr.st_mtime);
2792\& }
2793\& else
2794\& /* you shalt not abuse printf for puts */
2795\& puts ("wow, /etc/passwd is not there, expect problems. "
2796\& "if this is windows, they already arrived\en");
2797\& }
2798\&
2799\& ...
2800\& ev_stat passwd;
2801\&
2802\& ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
2803\& ev_stat_start (loop, &passwd);
2804.Ve
2805.PP
2806Example: Like above, but additionally use a one-second delay so we do not
2807miss updates (however, frequent updates will delay processing, too, so
2808one might do the work both on \f(CW\*(C`ev_stat\*(C'\fR callback invocation \fIand\fR on
2809\&\f(CW\*(C`ev_timer\*(C'\fR callback invocation).
2810.PP
1187.Vb 3 2811.Vb 2
1188\& struct ev_signal signal_watcher; 2812\& static ev_stat passwd;
1189\& ev_signal_init (&signal_watcher, sigint_cb, SIGINT); 2813\& static ev_timer timer;
1190\& ev_signal_start (loop, &sigint_cb); 2814\&
2815\& static void
2816\& timer_cb (EV_P_ ev_timer *w, int revents)
2817\& {
2818\& ev_timer_stop (EV_A_ w);
2819\&
2820\& /* now it\*(Aqs one second after the most recent passwd change */
2821\& }
2822\&
2823\& static void
2824\& stat_cb (EV_P_ ev_stat *w, int revents)
2825\& {
2826\& /* reset the one\-second timer */
2827\& ev_timer_again (EV_A_ &timer);
2828\& }
2829\&
2830\& ...
2831\& ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
2832\& ev_stat_start (loop, &passwd);
2833\& ev_timer_init (&timer, timer_cb, 0., 1.02);
1191.Ve 2834.Ve
1192.ie n .Sh """ev_idle"" \- when you've got nothing better to do" 2835.ie n .SS """ev_idle"" \- when you've got nothing better to do..."
1193.el .Sh "\f(CWev_idle\fP \- when you've got nothing better to do" 2836.el .SS "\f(CWev_idle\fP \- when you've got nothing better to do..."
1194.IX Subsection "ev_idle - when you've got nothing better to do" 2837.IX Subsection "ev_idle - when you've got nothing better to do..."
1195Idle watchers trigger events when there are no other events are pending 2838Idle watchers trigger events when no other events of the same or higher
1196(prepare, check and other idle watchers do not count). That is, as long 2839priority are pending (prepare, check and other idle watchers do not count
1197as your process is busy handling sockets or timeouts (or even signals, 2840as receiving \*(L"events\*(R").
1198imagine) it will not be triggered. But when your process is idle all idle 2841.PP
1199watchers are being called again and again, once per event loop iteration \- 2842That is, as long as your process is busy handling sockets or timeouts
2843(or even signals, imagine) of the same or higher priority it will not be
2844triggered. But when your process is idle (or only lower-priority watchers
2845are pending), the idle watchers are being called once per event loop
1200until stopped, that is, or your process receives more events and becomes 2846iteration \- until stopped, that is, or your process receives more events
1201busy. 2847and becomes busy again with higher priority stuff.
1202.PP 2848.PP
1203The most noteworthy effect is that as long as any idle watchers are 2849The most noteworthy effect is that as long as any idle watchers are
1204active, the process will not block when waiting for new events. 2850active, the process will not block when waiting for new events.
1205.PP 2851.PP
1206Apart from keeping your process non-blocking (which is a useful 2852Apart from keeping your process non-blocking (which is a useful
1207effect on its own sometimes), idle watchers are a good place to do 2853effect on its own sometimes), idle watchers are a good place to do
1208\&\*(L"pseudo\-background processing\*(R", or delay processing stuff to after the 2854\&\*(L"pseudo-background processing\*(R", or delay processing stuff to after the
1209event loop has handled all outstanding events. 2855event loop has handled all outstanding events.
2856.PP
2857\fIWatcher-Specific Functions and Data Members\fR
2858.IX Subsection "Watcher-Specific Functions and Data Members"
1210.IP "ev_idle_init (ev_signal *, callback)" 4 2859.IP "ev_idle_init (ev_idle *, callback)" 4
1211.IX Item "ev_idle_init (ev_signal *, callback)" 2860.IX Item "ev_idle_init (ev_idle *, callback)"
1212Initialises and configures the idle watcher \- it has no parameters of any 2861Initialises and configures the idle watcher \- it has no parameters of any
1213kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless, 2862kind. There is a \f(CW\*(C`ev_idle_set\*(C'\fR macro, but using it is utterly pointless,
1214believe me. 2863believe me.
1215.PP 2864.PP
2865\fIExamples\fR
2866.IX Subsection "Examples"
2867.PP
1216Example: dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR, start it, and in the 2868Example: Dynamically allocate an \f(CW\*(C`ev_idle\*(C'\fR watcher, start it, and in the
1217callback, free it. Alos, use no error checking, as usual. 2869callback, free it. Also, use no error checking, as usual.
1218.PP 2870.PP
1219.Vb 7 2871.Vb 7
1220\& static void 2872\& static void
1221\& idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents) 2873\& idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1222\& { 2874\& {
1223\& free (w); 2875\& free (w);
1224\& // now do something you wanted to do when the program has 2876\& // now do something you wanted to do when the program has
1225\& // no longer asnything immediate to do. 2877\& // no longer anything immediate to do.
1226\& } 2878\& }
1227.Ve 2879\&
1228.PP
1229.Vb 3
1230\& struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle)); 2880\& ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1231\& ev_idle_init (idle_watcher, idle_cb); 2881\& ev_idle_init (idle_watcher, idle_cb);
1232\& ev_idle_start (loop, idle_cb); 2882\& ev_idle_start (loop, idle_watcher);
1233.Ve 2883.Ve
1234.ie n .Sh """ev_prepare""\fP and \f(CW""ev_check"" \- customise your event loop" 2884.ie n .SS """ev_prepare"" and ""ev_check"" \- customise your event loop!"
1235.el .Sh "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop" 2885.el .SS "\f(CWev_prepare\fP and \f(CWev_check\fP \- customise your event loop!"
1236.IX Subsection "ev_prepare and ev_check - customise your event loop" 2886.IX Subsection "ev_prepare and ev_check - customise your event loop!"
1237Prepare and check watchers are usually (but not always) used in tandem: 2887Prepare and check watchers are usually (but not always) used in pairs:
1238prepare watchers get invoked before the process blocks and check watchers 2888prepare watchers get invoked before the process blocks and check watchers
1239afterwards. 2889afterwards.
1240.PP 2890.PP
2891You \fImust not\fR call \f(CW\*(C`ev_run\*(C'\fR or similar functions that enter
2892the current event loop from either \f(CW\*(C`ev_prepare\*(C'\fR or \f(CW\*(C`ev_check\*(C'\fR
2893watchers. Other loops than the current one are fine, however. The
2894rationale behind this is that you do not need to check for recursion in
2895those watchers, i.e. the sequence will always be \f(CW\*(C`ev_prepare\*(C'\fR, blocking,
2896\&\f(CW\*(C`ev_check\*(C'\fR so if you have one watcher of each kind they will always be
2897called in pairs bracketing the blocking call.
2898.PP
1241Their main purpose is to integrate other event mechanisms into libev and 2899Their main purpose is to integrate other event mechanisms into libev and
1242their use is somewhat advanced. This could be used, for example, to track 2900their use is somewhat advanced. They could be used, for example, to track
1243variable changes, implement your own watchers, integrate net-snmp or a 2901variable changes, implement your own watchers, integrate net-snmp or a
1244coroutine library and lots more. 2902coroutine library and lots more. They are also occasionally useful if
2903you cache some data and want to flush it before blocking (for example,
2904in X programs you might want to do an \f(CW\*(C`XFlush ()\*(C'\fR in an \f(CW\*(C`ev_prepare\*(C'\fR
2905watcher).
1245.PP 2906.PP
1246This is done by examining in each prepare call which file descriptors need 2907This is done by examining in each prepare call which file descriptors
1247to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers for 2908need to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers
1248them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many libraries 2909for them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many
1249provide just this functionality). Then, in the check watcher you check for 2910libraries provide exactly this functionality). Then, in the check watcher,
1250any events that occured (by checking the pending status of all watchers 2911you check for any events that occurred (by checking the pending status
1251and stopping them) and call back into the library. The I/O and timer 2912of all watchers and stopping them) and call back into the library. The
1252callbacks will never actually be called (but must be valid nevertheless, 2913I/O and timer callbacks will never actually be called (but must be valid
1253because you never know, you know?). 2914nevertheless, because you never know, you know?).
1254.PP 2915.PP
1255As another example, the Perl Coro module uses these hooks to integrate 2916As another example, the Perl Coro module uses these hooks to integrate
1256coroutines into libev programs, by yielding to other active coroutines 2917coroutines into libev programs, by yielding to other active coroutines
1257during each prepare and only letting the process block if no coroutines 2918during each prepare and only letting the process block if no coroutines
1258are ready to run (it's actually more complicated: it only runs coroutines 2919are ready to run (it's actually more complicated: it only runs coroutines
1259with priority higher than or equal to the event loop and one coroutine 2920with priority higher than or equal to the event loop and one coroutine
1260of lower priority, but only once, using idle watchers to keep the event 2921of lower priority, but only once, using idle watchers to keep the event
1261loop from blocking if lower-priority coroutines are active, thus mapping 2922loop from blocking if lower-priority coroutines are active, thus mapping
1262low-priority coroutines to idle/background tasks). 2923low-priority coroutines to idle/background tasks).
2924.PP
2925It is recommended to give \f(CW\*(C`ev_check\*(C'\fR watchers highest (\f(CW\*(C`EV_MAXPRI\*(C'\fR)
2926priority, to ensure that they are being run before any other watchers
2927after the poll (this doesn't matter for \f(CW\*(C`ev_prepare\*(C'\fR watchers).
2928.PP
2929Also, \f(CW\*(C`ev_check\*(C'\fR watchers (and \f(CW\*(C`ev_prepare\*(C'\fR watchers, too) should not
2930activate (\*(L"feed\*(R") events into libev. While libev fully supports this, they
2931might get executed before other \f(CW\*(C`ev_check\*(C'\fR watchers did their job. As
2932\&\f(CW\*(C`ev_check\*(C'\fR watchers are often used to embed other (non-libev) event
2933loops those other event loops might be in an unusable state until their
2934\&\f(CW\*(C`ev_check\*(C'\fR watcher ran (always remind yourself to coexist peacefully with
2935others).
2936.PP
2937\fIWatcher-Specific Functions and Data Members\fR
2938.IX Subsection "Watcher-Specific Functions and Data Members"
1263.IP "ev_prepare_init (ev_prepare *, callback)" 4 2939.IP "ev_prepare_init (ev_prepare *, callback)" 4
1264.IX Item "ev_prepare_init (ev_prepare *, callback)" 2940.IX Item "ev_prepare_init (ev_prepare *, callback)"
1265.PD 0 2941.PD 0
1266.IP "ev_check_init (ev_check *, callback)" 4 2942.IP "ev_check_init (ev_check *, callback)" 4
1267.IX Item "ev_check_init (ev_check *, callback)" 2943.IX Item "ev_check_init (ev_check *, callback)"
1268.PD 2944.PD
1269Initialises and configures the prepare or check watcher \- they have no 2945Initialises and configures the prepare or check watcher \- they have no
1270parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR 2946parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
1271macros, but using them is utterly, utterly and completely pointless. 2947macros, but using them is utterly, utterly, utterly and completely
2948pointless.
1272.PP 2949.PP
1273Example: *TODO*. 2950\fIExamples\fR
2951.IX Subsection "Examples"
2952.PP
2953There are a number of principal ways to embed other event loops or modules
2954into libev. Here are some ideas on how to include libadns into libev
2955(there is a Perl module named \f(CW\*(C`EV::ADNS\*(C'\fR that does this, which you could
2956use as a working example. Another Perl module named \f(CW\*(C`EV::Glib\*(C'\fR embeds a
2957Glib main context into libev, and finally, \f(CW\*(C`Glib::EV\*(C'\fR embeds \s-1EV\s0 into the
2958Glib event loop).
2959.PP
2960Method 1: Add \s-1IO\s0 watchers and a timeout watcher in a prepare handler,
2961and in a check watcher, destroy them and call into libadns. What follows
2962is pseudo-code only of course. This requires you to either use a low
2963priority for the check watcher or use \f(CW\*(C`ev_clear_pending\*(C'\fR explicitly, as
2964the callbacks for the IO/timeout watchers might not have been called yet.
2965.PP
2966.Vb 2
2967\& static ev_io iow [nfd];
2968\& static ev_timer tw;
2969\&
2970\& static void
2971\& io_cb (struct ev_loop *loop, ev_io *w, int revents)
2972\& {
2973\& }
2974\&
2975\& // create io watchers for each fd and a timer before blocking
2976\& static void
2977\& adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
2978\& {
2979\& int timeout = 3600000;
2980\& struct pollfd fds [nfd];
2981\& // actual code will need to loop here and realloc etc.
2982\& adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
2983\&
2984\& /* the callback is illegal, but won\*(Aqt be called as we stop during check */
2985\& ev_timer_init (&tw, 0, timeout * 1e\-3, 0.);
2986\& ev_timer_start (loop, &tw);
2987\&
2988\& // create one ev_io per pollfd
2989\& for (int i = 0; i < nfd; ++i)
2990\& {
2991\& ev_io_init (iow + i, io_cb, fds [i].fd,
2992\& ((fds [i].events & POLLIN ? EV_READ : 0)
2993\& | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
2994\&
2995\& fds [i].revents = 0;
2996\& ev_io_start (loop, iow + i);
2997\& }
2998\& }
2999\&
3000\& // stop all watchers after blocking
3001\& static void
3002\& adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
3003\& {
3004\& ev_timer_stop (loop, &tw);
3005\&
3006\& for (int i = 0; i < nfd; ++i)
3007\& {
3008\& // set the relevant poll flags
3009\& // could also call adns_processreadable etc. here
3010\& struct pollfd *fd = fds + i;
3011\& int revents = ev_clear_pending (iow + i);
3012\& if (revents & EV_READ ) fd\->revents |= fd\->events & POLLIN;
3013\& if (revents & EV_WRITE) fd\->revents |= fd\->events & POLLOUT;
3014\&
3015\& // now stop the watcher
3016\& ev_io_stop (loop, iow + i);
3017\& }
3018\&
3019\& adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
3020\& }
3021.Ve
3022.PP
3023Method 2: This would be just like method 1, but you run \f(CW\*(C`adns_afterpoll\*(C'\fR
3024in the prepare watcher and would dispose of the check watcher.
3025.PP
3026Method 3: If the module to be embedded supports explicit event
3027notification (libadns does), you can also make use of the actual watcher
3028callbacks, and only destroy/create the watchers in the prepare watcher.
3029.PP
3030.Vb 5
3031\& static void
3032\& timer_cb (EV_P_ ev_timer *w, int revents)
3033\& {
3034\& adns_state ads = (adns_state)w\->data;
3035\& update_now (EV_A);
3036\&
3037\& adns_processtimeouts (ads, &tv_now);
3038\& }
3039\&
3040\& static void
3041\& io_cb (EV_P_ ev_io *w, int revents)
3042\& {
3043\& adns_state ads = (adns_state)w\->data;
3044\& update_now (EV_A);
3045\&
3046\& if (revents & EV_READ ) adns_processreadable (ads, w\->fd, &tv_now);
3047\& if (revents & EV_WRITE) adns_processwriteable (ads, w\->fd, &tv_now);
3048\& }
3049\&
3050\& // do not ever call adns_afterpoll
3051.Ve
3052.PP
3053Method 4: Do not use a prepare or check watcher because the module you
3054want to embed is not flexible enough to support it. Instead, you can
3055override their poll function. The drawback with this solution is that the
3056main loop is now no longer controllable by \s-1EV\s0. The \f(CW\*(C`Glib::EV\*(C'\fR module uses
3057this approach, effectively embedding \s-1EV\s0 as a client into the horrible
3058libglib event loop.
3059.PP
3060.Vb 4
3061\& static gint
3062\& event_poll_func (GPollFD *fds, guint nfds, gint timeout)
3063\& {
3064\& int got_events = 0;
3065\&
3066\& for (n = 0; n < nfds; ++n)
3067\& // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
3068\&
3069\& if (timeout >= 0)
3070\& // create/start timer
3071\&
3072\& // poll
3073\& ev_run (EV_A_ 0);
3074\&
3075\& // stop timer again
3076\& if (timeout >= 0)
3077\& ev_timer_stop (EV_A_ &to);
3078\&
3079\& // stop io watchers again \- their callbacks should have set
3080\& for (n = 0; n < nfds; ++n)
3081\& ev_io_stop (EV_A_ iow [n]);
3082\&
3083\& return got_events;
3084\& }
3085.Ve
1274.ie n .Sh """ev_embed"" \- when one backend isn't enough" 3086.ie n .SS """ev_embed"" \- when one backend isn't enough..."
1275.el .Sh "\f(CWev_embed\fP \- when one backend isn't enough" 3087.el .SS "\f(CWev_embed\fP \- when one backend isn't enough..."
1276.IX Subsection "ev_embed - when one backend isn't enough" 3088.IX Subsection "ev_embed - when one backend isn't enough..."
1277This is a rather advanced watcher type that lets you embed one event loop 3089This is a rather advanced watcher type that lets you embed one event loop
1278into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded 3090into another (currently only \f(CW\*(C`ev_io\*(C'\fR events are supported in the embedded
1279loop, other types of watchers might be handled in a delayed or incorrect 3091loop, other types of watchers might be handled in a delayed or incorrect
1280fashion and must not be used). 3092fashion and must not be used).
1281.PP 3093.PP
… …
1283prioritise I/O. 3095prioritise I/O.
1284.PP 3096.PP
1285As an example for a bug workaround, the kqueue backend might only support 3097As an example for a bug workaround, the kqueue backend might only support
1286sockets on some platform, so it is unusable as generic backend, but you 3098sockets on some platform, so it is unusable as generic backend, but you
1287still want to make use of it because you have many sockets and it scales 3099still want to make use of it because you have many sockets and it scales
1288so nicely. In this case, you would create a kqueue-based loop and embed it 3100so nicely. In this case, you would create a kqueue-based loop and embed
1289into your default loop (which might use e.g. poll). Overall operation will 3101it into your default loop (which might use e.g. poll). Overall operation
1290be a bit slower because first libev has to poll and then call kevent, but 3102will be a bit slower because first libev has to call \f(CW\*(C`poll\*(C'\fR and then
1291at least you can use both at what they are best. 3103\&\f(CW\*(C`kevent\*(C'\fR, but at least you can use both mechanisms for what they are
3104best: \f(CW\*(C`kqueue\*(C'\fR for scalable sockets and \f(CW\*(C`poll\*(C'\fR if you want it to work :)
1292.PP 3105.PP
1293As for prioritising I/O: rarely you have the case where some fds have 3106As for prioritising I/O: under rare circumstances you have the case where
1294to be watched and handled very quickly (with low latency), and even 3107some fds have to be watched and handled very quickly (with low latency),
1295priorities and idle watchers might have too much overhead. In this case 3108and even priorities and idle watchers might have too much overhead. In
1296you would put all the high priority stuff in one loop and all the rest in 3109this case you would put all the high priority stuff in one loop and all
1297a second one, and embed the second one in the first. 3110the rest in a second one, and embed the second one in the first.
1298.PP 3111.PP
1299As long as the watcher is active, the callback will be invoked every time 3112As long as the watcher is active, the callback will be invoked every
1300there might be events pending in the embedded loop. The callback must then 3113time there might be events pending in the embedded loop. The callback
1301call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single sweep and invoke 3114must then call \f(CW\*(C`ev_embed_sweep (mainloop, watcher)\*(C'\fR to make a single
1302their callbacks (you could also start an idle watcher to give the embedded 3115sweep and invoke their callbacks (the callback doesn't need to invoke the
1303loop strictly lower priority for example). You can also set the callback 3116\&\f(CW\*(C`ev_embed_sweep\*(C'\fR function directly, it could also start an idle watcher
1304to \f(CW0\fR, in which case the embed watcher will automatically execute the 3117to give the embedded loop strictly lower priority for example).
1305embedded loop sweep.
1306.PP 3118.PP
1307As long as the watcher is started it will automatically handle events. The 3119You can also set the callback to \f(CW0\fR, in which case the embed watcher
1308callback will be invoked whenever some events have been handled. You can 3120will automatically execute the embedded loop sweep whenever necessary.
1309set the callback to \f(CW0\fR to avoid having to specify one if you are not
1310interested in that.
1311.PP 3121.PP
1312Also, there have not currently been made special provisions for forking: 3122Fork detection will be handled transparently while the \f(CW\*(C`ev_embed\*(C'\fR watcher
1313when you fork, you not only have to call \f(CW\*(C`ev_loop_fork\*(C'\fR on both loops, 3123is active, i.e., the embedded loop will automatically be forked when the
1314but you will also have to stop and restart any \f(CW\*(C`ev_embed\*(C'\fR watchers 3124embedding loop forks. In other cases, the user is responsible for calling
1315yourself. 3125\&\f(CW\*(C`ev_loop_fork\*(C'\fR on the embedded loop.
1316.PP 3126.PP
1317Unfortunately, not all backends are embeddable, only the ones returned by 3127Unfortunately, not all backends are embeddable: only the ones returned by
1318\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any 3128\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
1319portable one. 3129portable one.
1320.PP 3130.PP
1321So when you want to use this feature you will always have to be prepared 3131So when you want to use this feature you will always have to be prepared
1322that you cannot get an embeddable loop. The recommended way to get around 3132that you cannot get an embeddable loop. The recommended way to get around
1323this is to have a separate variables for your embeddable loop, try to 3133this is to have a separate variables for your embeddable loop, try to
1324create it, and if that fails, use the normal loop for everything: 3134create it, and if that fails, use the normal loop for everything.
1325.PP 3135.PP
1326.Vb 3 3136\fI\f(CI\*(C`ev_embed\*(C'\fI and fork\fR
1327\& struct ev_loop *loop_hi = ev_default_init (0); 3137.IX Subsection "ev_embed and fork"
1328\& struct ev_loop *loop_lo = 0;
1329\& struct ev_embed embed;
1330.Ve
1331.PP 3138.PP
1332.Vb 5 3139While the \f(CW\*(C`ev_embed\*(C'\fR watcher is running, forks in the embedding loop will
1333\& // see if there is a chance of getting one that works 3140automatically be applied to the embedded loop as well, so no special
1334\& // (remember that a flags value of 0 means autodetection) 3141fork handling is required in that case. When the watcher is not running,
1335\& loop_lo = ev_embeddable_backends () & ev_recommended_backends () 3142however, it is still the task of the libev user to call \f(CW\*(C`ev_loop_fork ()\*(C'\fR
1336\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ()) 3143as applicable.
1337\& : 0;
1338.Ve
1339.PP 3144.PP
1340.Vb 8 3145\fIWatcher-Specific Functions and Data Members\fR
1341\& // if we got one, then embed it, otherwise default to loop_hi 3146.IX Subsection "Watcher-Specific Functions and Data Members"
1342\& if (loop_lo)
1343\& {
1344\& ev_embed_init (&embed, 0, loop_lo);
1345\& ev_embed_start (loop_hi, &embed);
1346\& }
1347\& else
1348\& loop_lo = loop_hi;
1349.Ve
1350.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4 3147.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
1351.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)" 3148.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *embedded_loop)"
1352.PD 0 3149.PD 0
1353.IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4 3150.IP "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 4
1354.IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)" 3151.IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *embedded_loop)"
1355.PD 3152.PD
1356Configures the watcher to embed the given loop, which must be 3153Configures the watcher to embed the given loop, which must be
1357embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be 3154embeddable. If the callback is \f(CW0\fR, then \f(CW\*(C`ev_embed_sweep\*(C'\fR will be
1358invoked automatically, otherwise it is the responsibility of the callback 3155invoked automatically, otherwise it is the responsibility of the callback
1359to invoke it (it will continue to be called until the sweep has been done, 3156to invoke it (it will continue to be called until the sweep has been done,
1360if you do not want thta, you need to temporarily stop the embed watcher). 3157if you do not want that, you need to temporarily stop the embed watcher).
1361.IP "ev_embed_sweep (loop, ev_embed *)" 4 3158.IP "ev_embed_sweep (loop, ev_embed *)" 4
1362.IX Item "ev_embed_sweep (loop, ev_embed *)" 3159.IX Item "ev_embed_sweep (loop, ev_embed *)"
1363Make a single, non-blocking sweep over the embedded loop. This works 3160Make a single, non-blocking sweep over the embedded loop. This works
1364similarly to \f(CW\*(C`ev_loop (embedded_loop, EVLOOP_NONBLOCK)\*(C'\fR, but in the most 3161similarly to \f(CW\*(C`ev_run (embedded_loop, EVRUN_NOWAIT)\*(C'\fR, but in the most
1365apropriate way for embedded loops. 3162appropriate way for embedded loops.
3163.IP "struct ev_loop *other [read\-only]" 4
3164.IX Item "struct ev_loop *other [read-only]"
3165The embedded event loop.
3166.PP
3167\fIExamples\fR
3168.IX Subsection "Examples"
3169.PP
3170Example: Try to get an embeddable event loop and embed it into the default
3171event loop. If that is not possible, use the default loop. The default
3172loop is stored in \f(CW\*(C`loop_hi\*(C'\fR, while the embeddable loop is stored in
3173\&\f(CW\*(C`loop_lo\*(C'\fR (which is \f(CW\*(C`loop_hi\*(C'\fR in the case no embeddable loop can be
3174used).
3175.PP
3176.Vb 3
3177\& struct ev_loop *loop_hi = ev_default_init (0);
3178\& struct ev_loop *loop_lo = 0;
3179\& ev_embed embed;
3180\&
3181\& // see if there is a chance of getting one that works
3182\& // (remember that a flags value of 0 means autodetection)
3183\& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
3184\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
3185\& : 0;
3186\&
3187\& // if we got one, then embed it, otherwise default to loop_hi
3188\& if (loop_lo)
3189\& {
3190\& ev_embed_init (&embed, 0, loop_lo);
3191\& ev_embed_start (loop_hi, &embed);
3192\& }
3193\& else
3194\& loop_lo = loop_hi;
3195.Ve
3196.PP
3197Example: Check if kqueue is available but not recommended and create
3198a kqueue backend for use with sockets (which usually work with any
3199kqueue implementation). Store the kqueue/socket\-only event loop in
3200\&\f(CW\*(C`loop_socket\*(C'\fR. (One might optionally use \f(CW\*(C`EVFLAG_NOENV\*(C'\fR, too).
3201.PP
3202.Vb 3
3203\& struct ev_loop *loop = ev_default_init (0);
3204\& struct ev_loop *loop_socket = 0;
3205\& ev_embed embed;
3206\&
3207\& if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
3208\& if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
3209\& {
3210\& ev_embed_init (&embed, 0, loop_socket);
3211\& ev_embed_start (loop, &embed);
3212\& }
3213\&
3214\& if (!loop_socket)
3215\& loop_socket = loop;
3216\&
3217\& // now use loop_socket for all sockets, and loop for everything else
3218.Ve
3219.ie n .SS """ev_fork"" \- the audacity to resume the event loop after a fork"
3220.el .SS "\f(CWev_fork\fP \- the audacity to resume the event loop after a fork"
3221.IX Subsection "ev_fork - the audacity to resume the event loop after a fork"
3222Fork watchers are called when a \f(CW\*(C`fork ()\*(C'\fR was detected (usually because
3223whoever is a good citizen cared to tell libev about it by calling
3224\&\f(CW\*(C`ev_default_fork\*(C'\fR or \f(CW\*(C`ev_loop_fork\*(C'\fR). The invocation is done before the
3225event loop blocks next and before \f(CW\*(C`ev_check\*(C'\fR watchers are being called,
3226and only in the child after the fork. If whoever good citizen calling
3227\&\f(CW\*(C`ev_default_fork\*(C'\fR cheats and calls it in the wrong process, the fork
3228handlers will be invoked, too, of course.
3229.PP
3230\fIThe special problem of life after fork \- how is it possible?\fR
3231.IX Subsection "The special problem of life after fork - how is it possible?"
3232.PP
3233Most uses of \f(CW\*(C`fork()\*(C'\fR consist of forking, then some simple calls to set
3234up/change the process environment, followed by a call to \f(CW\*(C`exec()\*(C'\fR. This
3235sequence should be handled by libev without any problems.
3236.PP
3237This changes when the application actually wants to do event handling
3238in the child, or both parent in child, in effect \*(L"continuing\*(R" after the
3239fork.
3240.PP
3241The default mode of operation (for libev, with application help to detect
3242forks) is to duplicate all the state in the child, as would be expected
3243when \fIeither\fR the parent \fIor\fR the child process continues.
3244.PP
3245When both processes want to continue using libev, then this is usually the
3246wrong result. In that case, usually one process (typically the parent) is
3247supposed to continue with all watchers in place as before, while the other
3248process typically wants to start fresh, i.e. without any active watchers.
3249.PP
3250The cleanest and most efficient way to achieve that with libev is to
3251simply create a new event loop, which of course will be \*(L"empty\*(R", and
3252use that for new watchers. This has the advantage of not touching more
3253memory than necessary, and thus avoiding the copy-on-write, and the
3254disadvantage of having to use multiple event loops (which do not support
3255signal watchers).
3256.PP
3257When this is not possible, or you want to use the default loop for
3258other reasons, then in the process that wants to start \*(L"fresh\*(R", call
3259\&\f(CW\*(C`ev_loop_destroy (EV_DEFAULT)\*(C'\fR followed by \f(CW\*(C`ev_default_loop (...)\*(C'\fR.
3260Destroying the default loop will \*(L"orphan\*(R" (not stop) all registered
3261watchers, so you have to be careful not to execute code that modifies
3262those watchers. Note also that in that case, you have to re-register any
3263signal watchers.
3264.PP
3265\fIWatcher-Specific Functions and Data Members\fR
3266.IX Subsection "Watcher-Specific Functions and Data Members"
3267.IP "ev_fork_init (ev_fork *, callback)" 4
3268.IX Item "ev_fork_init (ev_fork *, callback)"
3269Initialises and configures the fork watcher \- it has no parameters of any
3270kind. There is a \f(CW\*(C`ev_fork_set\*(C'\fR macro, but using it is utterly pointless,
3271really.
3272.ie n .SS """ev_cleanup"" \- even the best things end"
3273.el .SS "\f(CWev_cleanup\fP \- even the best things end"
3274.IX Subsection "ev_cleanup - even the best things end"
3275Cleanup watchers are called just before the event loop is being destroyed
3276by a call to \f(CW\*(C`ev_loop_destroy\*(C'\fR.
3277.PP
3278While there is no guarantee that the event loop gets destroyed, cleanup
3279watchers provide a convenient method to install cleanup hooks for your
3280program, worker threads and so on \- you just to make sure to destroy the
3281loop when you want them to be invoked.
3282.PP
3283Cleanup watchers are invoked in the same way as any other watcher. Unlike
3284all other watchers, they do not keep a reference to the event loop (which
3285makes a lot of sense if you think about it). Like all other watchers, you
3286can call libev functions in the callback, except \f(CW\*(C`ev_cleanup_start\*(C'\fR.
3287.PP
3288\fIWatcher-Specific Functions and Data Members\fR
3289.IX Subsection "Watcher-Specific Functions and Data Members"
3290.IP "ev_cleanup_init (ev_cleanup *, callback)" 4
3291.IX Item "ev_cleanup_init (ev_cleanup *, callback)"
3292Initialises and configures the cleanup watcher \- it has no parameters of
3293any kind. There is a \f(CW\*(C`ev_cleanup_set\*(C'\fR macro, but using it is utterly
3294pointless, I assure you.
3295.PP
3296Example: Register an atexit handler to destroy the default loop, so any
3297cleanup functions are called.
3298.PP
3299.Vb 5
3300\& static void
3301\& program_exits (void)
3302\& {
3303\& ev_loop_destroy (EV_DEFAULT_UC);
3304\& }
3305\&
3306\& ...
3307\& atexit (program_exits);
3308.Ve
3309.ie n .SS """ev_async"" \- how to wake up an event loop"
3310.el .SS "\f(CWev_async\fP \- how to wake up an event loop"
3311.IX Subsection "ev_async - how to wake up an event loop"
3312In general, you cannot use an \f(CW\*(C`ev_run\*(C'\fR from multiple threads or other
3313asynchronous sources such as signal handlers (as opposed to multiple event
3314loops \- those are of course safe to use in different threads).
3315.PP
3316Sometimes, however, you need to wake up an event loop you do not control,
3317for example because it belongs to another thread. This is what \f(CW\*(C`ev_async\*(C'\fR
3318watchers do: as long as the \f(CW\*(C`ev_async\*(C'\fR watcher is active, you can signal
3319it by calling \f(CW\*(C`ev_async_send\*(C'\fR, which is thread\- and signal safe.
3320.PP
3321This functionality is very similar to \f(CW\*(C`ev_signal\*(C'\fR watchers, as signals,
3322too, are asynchronous in nature, and signals, too, will be compressed
3323(i.e. the number of callback invocations may be less than the number of
3324\&\f(CW\*(C`ev_async_sent\*(C'\fR calls). In fact, you could use signal watchers as a kind
3325of \*(L"global async watchers\*(R" by using a watcher on an otherwise unused
3326signal, and \f(CW\*(C`ev_feed_signal\*(C'\fR to signal this watcher from another thread,
3327even without knowing which loop owns the signal.
3328.PP
3329Unlike \f(CW\*(C`ev_signal\*(C'\fR watchers, \f(CW\*(C`ev_async\*(C'\fR works with any event loop, not
3330just the default loop.
3331.PP
3332\fIQueueing\fR
3333.IX Subsection "Queueing"
3334.PP
3335\&\f(CW\*(C`ev_async\*(C'\fR does not support queueing of data in any way. The reason
3336is that the author does not know of a simple (or any) algorithm for a
3337multiple-writer-single-reader queue that works in all cases and doesn't
3338need elaborate support such as pthreads or unportable memory access
3339semantics.
3340.PP
3341That means that if you want to queue data, you have to provide your own
3342queue. But at least I can tell you how to implement locking around your
3343queue:
3344.IP "queueing from a signal handler context" 4
3345.IX Item "queueing from a signal handler context"
3346To implement race-free queueing, you simply add to the queue in the signal
3347handler but you block the signal handler in the watcher callback. Here is
3348an example that does that for some fictitious \s-1SIGUSR1\s0 handler:
3349.Sp
3350.Vb 1
3351\& static ev_async mysig;
3352\&
3353\& static void
3354\& sigusr1_handler (void)
3355\& {
3356\& sometype data;
3357\&
3358\& // no locking etc.
3359\& queue_put (data);
3360\& ev_async_send (EV_DEFAULT_ &mysig);
3361\& }
3362\&
3363\& static void
3364\& mysig_cb (EV_P_ ev_async *w, int revents)
3365\& {
3366\& sometype data;
3367\& sigset_t block, prev;
3368\&
3369\& sigemptyset (&block);
3370\& sigaddset (&block, SIGUSR1);
3371\& sigprocmask (SIG_BLOCK, &block, &prev);
3372\&
3373\& while (queue_get (&data))
3374\& process (data);
3375\&
3376\& if (sigismember (&prev, SIGUSR1)
3377\& sigprocmask (SIG_UNBLOCK, &block, 0);
3378\& }
3379.Ve
3380.Sp
3381(Note: pthreads in theory requires you to use \f(CW\*(C`pthread_setmask\*(C'\fR
3382instead of \f(CW\*(C`sigprocmask\*(C'\fR when you use threads, but libev doesn't do it
3383either...).
3384.IP "queueing from a thread context" 4
3385.IX Item "queueing from a thread context"
3386The strategy for threads is different, as you cannot (easily) block
3387threads but you can easily preempt them, so to queue safely you need to
3388employ a traditional mutex lock, such as in this pthread example:
3389.Sp
3390.Vb 2
3391\& static ev_async mysig;
3392\& static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
3393\&
3394\& static void
3395\& otherthread (void)
3396\& {
3397\& // only need to lock the actual queueing operation
3398\& pthread_mutex_lock (&mymutex);
3399\& queue_put (data);
3400\& pthread_mutex_unlock (&mymutex);
3401\&
3402\& ev_async_send (EV_DEFAULT_ &mysig);
3403\& }
3404\&
3405\& static void
3406\& mysig_cb (EV_P_ ev_async *w, int revents)
3407\& {
3408\& pthread_mutex_lock (&mymutex);
3409\&
3410\& while (queue_get (&data))
3411\& process (data);
3412\&
3413\& pthread_mutex_unlock (&mymutex);
3414\& }
3415.Ve
3416.PP
3417\fIWatcher-Specific Functions and Data Members\fR
3418.IX Subsection "Watcher-Specific Functions and Data Members"
3419.IP "ev_async_init (ev_async *, callback)" 4
3420.IX Item "ev_async_init (ev_async *, callback)"
3421Initialises and configures the async watcher \- it has no parameters of any
3422kind. There is a \f(CW\*(C`ev_async_set\*(C'\fR macro, but using it is utterly pointless,
3423trust me.
3424.IP "ev_async_send (loop, ev_async *)" 4
3425.IX Item "ev_async_send (loop, ev_async *)"
3426Sends/signals/activates the given \f(CW\*(C`ev_async\*(C'\fR watcher, that is, feeds
3427an \f(CW\*(C`EV_ASYNC\*(C'\fR event on the watcher into the event loop. Unlike
3428\&\f(CW\*(C`ev_feed_event\*(C'\fR, this call is safe to do from other threads, signal or
3429similar contexts (see the discussion of \f(CW\*(C`EV_ATOMIC_T\*(C'\fR in the embedding
3430section below on what exactly this means).
3431.Sp
3432Note that, as with other watchers in libev, multiple events might get
3433compressed into a single callback invocation (another way to look at this
3434is that \f(CW\*(C`ev_async\*(C'\fR watchers are level-triggered, set on \f(CW\*(C`ev_async_send\*(C'\fR,
3435reset when the event loop detects that).
3436.Sp
3437This call incurs the overhead of a system call only once per event loop
3438iteration, so while the overhead might be noticeable, it doesn't apply to
3439repeated calls to \f(CW\*(C`ev_async_send\*(C'\fR for the same event loop.
3440.IP "bool = ev_async_pending (ev_async *)" 4
3441.IX Item "bool = ev_async_pending (ev_async *)"
3442Returns a non-zero value when \f(CW\*(C`ev_async_send\*(C'\fR has been called on the
3443watcher but the event has not yet been processed (or even noted) by the
3444event loop.
3445.Sp
3446\&\f(CW\*(C`ev_async_send\*(C'\fR sets a flag in the watcher and wakes up the loop. When
3447the loop iterates next and checks for the watcher to have become active,
3448it will reset the flag again. \f(CW\*(C`ev_async_pending\*(C'\fR can be used to very
3449quickly check whether invoking the loop might be a good idea.
3450.Sp
3451Not that this does \fInot\fR check whether the watcher itself is pending,
3452only whether it has been requested to make this watcher pending: there
3453is a time window between the event loop checking and resetting the async
3454notification, and the callback being invoked.
1366.SH "OTHER FUNCTIONS" 3455.SH "OTHER FUNCTIONS"
1367.IX Header "OTHER FUNCTIONS" 3456.IX Header "OTHER FUNCTIONS"
1368There are some other functions of possible interest. Described. Here. Now. 3457There are some other functions of possible interest. Described. Here. Now.
1369.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4 3458.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
1370.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 3459.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"
1371This function combines a simple timer and an I/O watcher, calls your 3460This function combines a simple timer and an I/O watcher, calls your
1372callback on whichever event happens first and automatically stop both 3461callback on whichever event happens first and automatically stops both
1373watchers. This is useful if you want to wait for a single event on an fd 3462watchers. This is useful if you want to wait for a single event on an fd
1374or timeout without having to allocate/configure/start/stop/free one or 3463or timeout without having to allocate/configure/start/stop/free one or
1375more watchers yourself. 3464more watchers yourself.
1376.Sp 3465.Sp
1377If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and events 3466If \f(CW\*(C`fd\*(C'\fR is less than 0, then no I/O watcher will be started and the
1378is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for the given \f(CW\*(C`fd\*(C'\fR and 3467\&\f(CW\*(C`events\*(C'\fR argument is being ignored. Otherwise, an \f(CW\*(C`ev_io\*(C'\fR watcher for
1379\&\f(CW\*(C`events\*(C'\fR set will be craeted and started. 3468the given \f(CW\*(C`fd\*(C'\fR and \f(CW\*(C`events\*(C'\fR set will be created and started.
1380.Sp 3469.Sp
1381If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be 3470If \f(CW\*(C`timeout\*(C'\fR is less than 0, then no timeout watcher will be
1382started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and 3471started. Otherwise an \f(CW\*(C`ev_timer\*(C'\fR watcher with after = \f(CW\*(C`timeout\*(C'\fR (and
1383repeat = 0) will be started. While \f(CW0\fR is a valid timeout, it is of 3472repeat = 0) will be started. \f(CW0\fR is a valid timeout.
1384dubious value.
1385.Sp 3473.Sp
1386The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and gets 3474The callback has the type \f(CW\*(C`void (*cb)(int revents, void *arg)\*(C'\fR and is
1387passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of 3475passed an \f(CW\*(C`revents\*(C'\fR set like normal event callbacks (a combination of
1388\&\f(CW\*(C`EV_ERROR\*(C'\fR, \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or \f(CW\*(C`EV_TIMEOUT\*(C'\fR) and the \f(CW\*(C`arg\*(C'\fR 3476\&\f(CW\*(C`EV_ERROR\*(C'\fR, \f(CW\*(C`EV_READ\*(C'\fR, \f(CW\*(C`EV_WRITE\*(C'\fR or \f(CW\*(C`EV_TIMER\*(C'\fR) and the \f(CW\*(C`arg\*(C'\fR
1389value passed to \f(CW\*(C`ev_once\*(C'\fR: 3477value passed to \f(CW\*(C`ev_once\*(C'\fR. Note that it is possible to receive \fIboth\fR
3478a timeout and an io event at the same time \- you probably should give io
3479events precedence.
3480.Sp
3481Example: wait up to ten seconds for data to appear on \s-1STDIN_FILENO\s0.
1390.Sp 3482.Sp
1391.Vb 7 3483.Vb 7
1392\& static void stdin_ready (int revents, void *arg) 3484\& static void stdin_ready (int revents, void *arg)
1393\& { 3485\& {
1394\& if (revents & EV_TIMEOUT)
1395\& /* doh, nothing entered */;
1396\& else if (revents & EV_READ) 3486\& if (revents & EV_READ)
1397\& /* stdin might have data for us, joy! */; 3487\& /* stdin might have data for us, joy! */;
3488\& else if (revents & EV_TIMER)
3489\& /* doh, nothing entered */;
1398\& } 3490\& }
1399.Ve 3491\&
1400.Sp
1401.Vb 1
1402\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0); 3492\& ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1403.Ve 3493.Ve
1404.IP "ev_feed_event (ev_loop *, watcher *, int revents)" 4
1405.IX Item "ev_feed_event (ev_loop *, watcher *, int revents)"
1406Feeds the given event set into the event loop, as if the specified event
1407had happened for the specified watcher (which must be a pointer to an
1408initialised but not necessarily started event watcher).
1409.IP "ev_feed_fd_event (ev_loop *, int fd, int revents)" 4 3494.IP "ev_feed_fd_event (loop, int fd, int revents)" 4
1410.IX Item "ev_feed_fd_event (ev_loop *, int fd, int revents)" 3495.IX Item "ev_feed_fd_event (loop, int fd, int revents)"
1411Feed an event on the given fd, as if a file descriptor backend detected 3496Feed an event on the given fd, as if a file descriptor backend detected
1412the given events it. 3497the given events it.
1413.IP "ev_feed_signal_event (ev_loop *loop, int signum)" 4 3498.IP "ev_feed_signal_event (loop, int signum)" 4
1414.IX Item "ev_feed_signal_event (ev_loop *loop, int signum)" 3499.IX Item "ev_feed_signal_event (loop, int signum)"
1415Feed an event as if the given signal occured (\f(CW\*(C`loop\*(C'\fR must be the default 3500Feed an event as if the given signal occurred. See also \f(CW\*(C`ev_feed_signal\*(C'\fR,
1416loop!). 3501which is async-safe.
3502.SH "COMMON OR USEFUL IDIOMS (OR BOTH)"
3503.IX Header "COMMON OR USEFUL IDIOMS (OR BOTH)"
3504This section explains some common idioms that are not immediately
3505obvious. Note that examples are sprinkled over the whole manual, and this
3506section only contains stuff that wouldn't fit anywhere else.
3507.SS "\s-1ASSOCIATING\s0 \s-1CUSTOM\s0 \s-1DATA\s0 \s-1WITH\s0 A \s-1WATCHER\s0"
3508.IX Subsection "ASSOCIATING CUSTOM DATA WITH A WATCHER"
3509Each watcher has, by default, a \f(CW\*(C`void *data\*(C'\fR member that you can read
3510or modify at any time: libev will completely ignore it. This can be used
3511to associate arbitrary data with your watcher. If you need more data and
3512don't want to allocate memory separately and store a pointer to it in that
3513data member, you can also \*(L"subclass\*(R" the watcher type and provide your own
3514data:
3515.PP
3516.Vb 7
3517\& struct my_io
3518\& {
3519\& ev_io io;
3520\& int otherfd;
3521\& void *somedata;
3522\& struct whatever *mostinteresting;
3523\& };
3524\&
3525\& ...
3526\& struct my_io w;
3527\& ev_io_init (&w.io, my_cb, fd, EV_READ);
3528.Ve
3529.PP
3530And since your callback will be called with a pointer to the watcher, you
3531can cast it back to your own type:
3532.PP
3533.Vb 5
3534\& static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
3535\& {
3536\& struct my_io *w = (struct my_io *)w_;
3537\& ...
3538\& }
3539.Ve
3540.PP
3541More interesting and less C\-conformant ways of casting your callback
3542function type instead have been omitted.
3543.SS "\s-1BUILDING\s0 \s-1YOUR\s0 \s-1OWN\s0 \s-1COMPOSITE\s0 \s-1WATCHERS\s0"
3544.IX Subsection "BUILDING YOUR OWN COMPOSITE WATCHERS"
3545Another common scenario is to use some data structure with multiple
3546embedded watchers, in effect creating your own watcher that combines
3547multiple libev event sources into one \*(L"super-watcher\*(R":
3548.PP
3549.Vb 6
3550\& struct my_biggy
3551\& {
3552\& int some_data;
3553\& ev_timer t1;
3554\& ev_timer t2;
3555\& }
3556.Ve
3557.PP
3558In this case getting the pointer to \f(CW\*(C`my_biggy\*(C'\fR is a bit more
3559complicated: Either you store the address of your \f(CW\*(C`my_biggy\*(C'\fR struct in
3560the \f(CW\*(C`data\*(C'\fR member of the watcher (for woozies or \*(C+ coders), or you need
3561to use some pointer arithmetic using \f(CW\*(C`offsetof\*(C'\fR inside your watchers (for
3562real programmers):
3563.PP
3564.Vb 1
3565\& #include <stddef.h>
3566\&
3567\& static void
3568\& t1_cb (EV_P_ ev_timer *w, int revents)
3569\& {
3570\& struct my_biggy big = (struct my_biggy *)
3571\& (((char *)w) \- offsetof (struct my_biggy, t1));
3572\& }
3573\&
3574\& static void
3575\& t2_cb (EV_P_ ev_timer *w, int revents)
3576\& {
3577\& struct my_biggy big = (struct my_biggy *)
3578\& (((char *)w) \- offsetof (struct my_biggy, t2));
3579\& }
3580.Ve
3581.SS "\s-1MODEL/NESTED\s0 \s-1EVENT\s0 \s-1LOOP\s0 \s-1INVOCATIONS\s0 \s-1AND\s0 \s-1EXIT\s0 \s-1CONDITIONS\s0"
3582.IX Subsection "MODEL/NESTED EVENT LOOP INVOCATIONS AND EXIT CONDITIONS"
3583Often (especially in \s-1GUI\s0 toolkits) there are places where you have
3584\&\fImodal\fR interaction, which is most easily implemented by recursively
3585invoking \f(CW\*(C`ev_run\*(C'\fR.
3586.PP
3587This brings the problem of exiting \- a callback might want to finish the
3588main \f(CW\*(C`ev_run\*(C'\fR call, but not the nested one (e.g. user clicked \*(L"Quit\*(R", but
3589a modal \*(L"Are you sure?\*(R" dialog is still waiting), or just the nested one
3590and not the main one (e.g. user clocked \*(L"Ok\*(R" in a modal dialog), or some
3591other combination: In these cases, \f(CW\*(C`ev_break\*(C'\fR will not work alone.
3592.PP
3593The solution is to maintain \*(L"break this loop\*(R" variable for each \f(CW\*(C`ev_run\*(C'\fR
3594invocation, and use a loop around \f(CW\*(C`ev_run\*(C'\fR until the condition is
3595triggered, using \f(CW\*(C`EVRUN_ONCE\*(C'\fR:
3596.PP
3597.Vb 2
3598\& // main loop
3599\& int exit_main_loop = 0;
3600\&
3601\& while (!exit_main_loop)
3602\& ev_run (EV_DEFAULT_ EVRUN_ONCE);
3603\&
3604\& // in a model watcher
3605\& int exit_nested_loop = 0;
3606\&
3607\& while (!exit_nested_loop)
3608\& ev_run (EV_A_ EVRUN_ONCE);
3609.Ve
3610.PP
3611To exit from any of these loops, just set the corresponding exit variable:
3612.PP
3613.Vb 2
3614\& // exit modal loop
3615\& exit_nested_loop = 1;
3616\&
3617\& // exit main program, after modal loop is finished
3618\& exit_main_loop = 1;
3619\&
3620\& // exit both
3621\& exit_main_loop = exit_nested_loop = 1;
3622.Ve
3623.SS "\s-1THREAD\s0 \s-1LOCKING\s0 \s-1EXAMPLE\s0"
3624.IX Subsection "THREAD LOCKING EXAMPLE"
3625Here is a fictitious example of how to run an event loop in a different
3626thread from where callbacks are being invoked and watchers are
3627created/added/removed.
3628.PP
3629For a real-world example, see the \f(CW\*(C`EV::Loop::Async\*(C'\fR perl module,
3630which uses exactly this technique (which is suited for many high-level
3631languages).
3632.PP
3633The example uses a pthread mutex to protect the loop data, a condition
3634variable to wait for callback invocations, an async watcher to notify the
3635event loop thread and an unspecified mechanism to wake up the main thread.
3636.PP
3637First, you need to associate some data with the event loop:
3638.PP
3639.Vb 6
3640\& typedef struct {
3641\& mutex_t lock; /* global loop lock */
3642\& ev_async async_w;
3643\& thread_t tid;
3644\& cond_t invoke_cv;
3645\& } userdata;
3646\&
3647\& void prepare_loop (EV_P)
3648\& {
3649\& // for simplicity, we use a static userdata struct.
3650\& static userdata u;
3651\&
3652\& ev_async_init (&u\->async_w, async_cb);
3653\& ev_async_start (EV_A_ &u\->async_w);
3654\&
3655\& pthread_mutex_init (&u\->lock, 0);
3656\& pthread_cond_init (&u\->invoke_cv, 0);
3657\&
3658\& // now associate this with the loop
3659\& ev_set_userdata (EV_A_ u);
3660\& ev_set_invoke_pending_cb (EV_A_ l_invoke);
3661\& ev_set_loop_release_cb (EV_A_ l_release, l_acquire);
3662\&
3663\& // then create the thread running ev_loop
3664\& pthread_create (&u\->tid, 0, l_run, EV_A);
3665\& }
3666.Ve
3667.PP
3668The callback for the \f(CW\*(C`ev_async\*(C'\fR watcher does nothing: the watcher is used
3669solely to wake up the event loop so it takes notice of any new watchers
3670that might have been added:
3671.PP
3672.Vb 5
3673\& static void
3674\& async_cb (EV_P_ ev_async *w, int revents)
3675\& {
3676\& // just used for the side effects
3677\& }
3678.Ve
3679.PP
3680The \f(CW\*(C`l_release\*(C'\fR and \f(CW\*(C`l_acquire\*(C'\fR callbacks simply unlock/lock the mutex
3681protecting the loop data, respectively.
3682.PP
3683.Vb 6
3684\& static void
3685\& l_release (EV_P)
3686\& {
3687\& userdata *u = ev_userdata (EV_A);
3688\& pthread_mutex_unlock (&u\->lock);
3689\& }
3690\&
3691\& static void
3692\& l_acquire (EV_P)
3693\& {
3694\& userdata *u = ev_userdata (EV_A);
3695\& pthread_mutex_lock (&u\->lock);
3696\& }
3697.Ve
3698.PP
3699The event loop thread first acquires the mutex, and then jumps straight
3700into \f(CW\*(C`ev_run\*(C'\fR:
3701.PP
3702.Vb 4
3703\& void *
3704\& l_run (void *thr_arg)
3705\& {
3706\& struct ev_loop *loop = (struct ev_loop *)thr_arg;
3707\&
3708\& l_acquire (EV_A);
3709\& pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
3710\& ev_run (EV_A_ 0);
3711\& l_release (EV_A);
3712\&
3713\& return 0;
3714\& }
3715.Ve
3716.PP
3717Instead of invoking all pending watchers, the \f(CW\*(C`l_invoke\*(C'\fR callback will
3718signal the main thread via some unspecified mechanism (signals? pipe
3719writes? \f(CW\*(C`Async::Interrupt\*(C'\fR?) and then waits until all pending watchers
3720have been called (in a while loop because a) spurious wakeups are possible
3721and b) skipping inter-thread-communication when there are no pending
3722watchers is very beneficial):
3723.PP
3724.Vb 4
3725\& static void
3726\& l_invoke (EV_P)
3727\& {
3728\& userdata *u = ev_userdata (EV_A);
3729\&
3730\& while (ev_pending_count (EV_A))
3731\& {
3732\& wake_up_other_thread_in_some_magic_or_not_so_magic_way ();
3733\& pthread_cond_wait (&u\->invoke_cv, &u\->lock);
3734\& }
3735\& }
3736.Ve
3737.PP
3738Now, whenever the main thread gets told to invoke pending watchers, it
3739will grab the lock, call \f(CW\*(C`ev_invoke_pending\*(C'\fR and then signal the loop
3740thread to continue:
3741.PP
3742.Vb 4
3743\& static void
3744\& real_invoke_pending (EV_P)
3745\& {
3746\& userdata *u = ev_userdata (EV_A);
3747\&
3748\& pthread_mutex_lock (&u\->lock);
3749\& ev_invoke_pending (EV_A);
3750\& pthread_cond_signal (&u\->invoke_cv);
3751\& pthread_mutex_unlock (&u\->lock);
3752\& }
3753.Ve
3754.PP
3755Whenever you want to start/stop a watcher or do other modifications to an
3756event loop, you will now have to lock:
3757.PP
3758.Vb 2
3759\& ev_timer timeout_watcher;
3760\& userdata *u = ev_userdata (EV_A);
3761\&
3762\& ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
3763\&
3764\& pthread_mutex_lock (&u\->lock);
3765\& ev_timer_start (EV_A_ &timeout_watcher);
3766\& ev_async_send (EV_A_ &u\->async_w);
3767\& pthread_mutex_unlock (&u\->lock);
3768.Ve
3769.PP
3770Note that sending the \f(CW\*(C`ev_async\*(C'\fR watcher is required because otherwise
3771an event loop currently blocking in the kernel will have no knowledge
3772about the newly added timer. By waking up the loop it will pick up any new
3773watchers in the next event loop iteration.
3774.SS "\s-1THREADS\s0, \s-1COROUTINES\s0, \s-1CONTINUATIONS\s0, \s-1QUEUES\s0... \s-1INSTEAD\s0 \s-1OF\s0 \s-1CALLBACKS\s0"
3775.IX Subsection "THREADS, COROUTINES, CONTINUATIONS, QUEUES... INSTEAD OF CALLBACKS"
3776While the overhead of a callback that e.g. schedules a thread is small, it
3777is still an overhead. If you embed libev, and your main usage is with some
3778kind of threads or coroutines, you might want to customise libev so that
3779doesn't need callbacks anymore.
3780.PP
3781Imagine you have coroutines that you can switch to using a function
3782\&\f(CW\*(C`switch_to (coro)\*(C'\fR, that libev runs in a coroutine called \f(CW\*(C`libev_coro\*(C'\fR
3783and that due to some magic, the currently active coroutine is stored in a
3784global called \f(CW\*(C`current_coro\*(C'\fR. Then you can build your own \*(L"wait for libev
3785event\*(R" primitive by changing \f(CW\*(C`EV_CB_DECLARE\*(C'\fR and \f(CW\*(C`EV_CB_INVOKE\*(C'\fR (note
3786the differing \f(CW\*(C`;\*(C'\fR conventions):
3787.PP
3788.Vb 2
3789\& #define EV_CB_DECLARE(type) struct my_coro *cb;
3790\& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb)
3791.Ve
3792.PP
3793That means instead of having a C callback function, you store the
3794coroutine to switch to in each watcher, and instead of having libev call
3795your callback, you instead have it switch to that coroutine.
3796.PP
3797A coroutine might now wait for an event with a function called
3798\&\f(CW\*(C`wait_for_event\*(C'\fR. (the watcher needs to be started, as always, but it doesn't
3799matter when, or whether the watcher is active or not when this function is
3800called):
3801.PP
3802.Vb 6
3803\& void
3804\& wait_for_event (ev_watcher *w)
3805\& {
3806\& ev_cb_set (w) = current_coro;
3807\& switch_to (libev_coro);
3808\& }
3809.Ve
3810.PP
3811That basically suspends the coroutine inside \f(CW\*(C`wait_for_event\*(C'\fR and
3812continues the libev coroutine, which, when appropriate, switches back to
3813this or any other coroutine. I am sure if you sue this your own :)
3814.PP
3815You can do similar tricks if you have, say, threads with an event queue \-
3816instead of storing a coroutine, you store the queue object and instead of
3817switching to a coroutine, you push the watcher onto the queue and notify
3818any waiters.
3819.PP
3820To embed libev, see \s-1EMBEDDING\s0, but in short, it's easiest to create two
3821files, \fImy_ev.h\fR and \fImy_ev.c\fR that include the respective libev files:
3822.PP
3823.Vb 4
3824\& // my_ev.h
3825\& #define EV_CB_DECLARE(type) struct my_coro *cb;
3826\& #define EV_CB_INVOKE(watcher) switch_to ((watcher)\->cb);
3827\& #include "../libev/ev.h"
3828\&
3829\& // my_ev.c
3830\& #define EV_H "my_ev.h"
3831\& #include "../libev/ev.c"
3832.Ve
3833.PP
3834And then use \fImy_ev.h\fR when you would normally use \fIev.h\fR, and compile
3835\&\fImy_ev.c\fR into your project. When properly specifying include paths, you
3836can even use \fIev.h\fR as header file name directly.
1417.SH "LIBEVENT EMULATION" 3837.SH "LIBEVENT EMULATION"
1418.IX Header "LIBEVENT EMULATION" 3838.IX Header "LIBEVENT EMULATION"
1419Libev offers a compatibility emulation layer for libevent. It cannot 3839Libev offers a compatibility emulation layer for libevent. It cannot
1420emulate the internals of libevent, so here are some usage hints: 3840emulate the internals of libevent, so here are some usage hints:
3841.IP "\(bu" 4
3842Only the libevent\-1.4.1\-beta \s-1API\s0 is being emulated.
3843.Sp
3844This was the newest libevent version available when libev was implemented,
3845and is still mostly unchanged in 2010.
3846.IP "\(bu" 4
1421.IP "* Use it by including <event.h>, as usual." 4 3847Use it by including <event.h>, as usual.
1422.IX Item "Use it by including <event.h>, as usual." 3848.IP "\(bu" 4
1423.PD 0 3849The following members are fully supported: ev_base, ev_callback,
1424.IP "* The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 4 3850ev_arg, ev_fd, ev_res, ev_events.
1425.IX Item "The following members are fully supported: ev_base, ev_callback, ev_arg, ev_fd, ev_res, ev_events." 3851.IP "\(bu" 4
1426.IP "* Avoid using ev_flags and the EVLIST_*\-macros, while it is maintained by libev, it does not work exactly the same way as in libevent (consider it a private \s-1API\s0)." 4 3852Avoid using ev_flags and the EVLIST_*\-macros, while it is
1427.IX Item "Avoid using ev_flags and the EVLIST_*-macros, while it is maintained by libev, it does not work exactly the same way as in libevent (consider it a private API)." 3853maintained by libev, it does not work exactly the same way as in libevent (consider
1428.IP "* Priorities are not currently supported. Initialising priorities will fail and all watchers will have the same priority, even though there is an ev_pri field." 4 3854it a private \s-1API\s0).
1429.IX Item "Priorities are not currently supported. Initialising priorities will fail and all watchers will have the same priority, even though there is an ev_pri field." 3855.IP "\(bu" 4
3856Priorities are not currently supported. Initialising priorities
3857will fail and all watchers will have the same priority, even though there
3858is an ev_pri field.
3859.IP "\(bu" 4
3860In libevent, the last base created gets the signals, in libev, the
3861base that registered the signal gets the signals.
3862.IP "\(bu" 4
1430.IP "* Other members are not supported." 4 3863Other members are not supported.
1431.IX Item "Other members are not supported." 3864.IP "\(bu" 4
1432.IP "* The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need to use the libev header file and library." 4 3865The libev emulation is \fInot\fR \s-1ABI\s0 compatible to libevent, you need
1433.IX Item "The libev emulation is not ABI compatible to libevent, you need to use the libev header file and library." 3866to use the libev header file and library.
1434.PD
1435.SH "\*(C+ SUPPORT" 3867.SH "\*(C+ SUPPORT"
1436.IX Header " SUPPORT" 3868.IX Header " SUPPORT"
1437Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow 3869Libev comes with some simplistic wrapper classes for \*(C+ that mainly allow
1438you to use some convinience methods to start/stop watchers and also change 3870you to use some convenience methods to start/stop watchers and also change
1439the callback model to a model using method callbacks on objects. 3871the callback model to a model using method callbacks on objects.
1440.PP 3872.PP
1441To use it, 3873To use it,
1442.PP 3874.PP
1443.Vb 1 3875.Vb 1
1444\& #include <ev++.h> 3876\& #include <ev++.h>
1445.Ve 3877.Ve
1446.PP 3878.PP
1447(it is not installed by default). This automatically includes \fIev.h\fR 3879This automatically includes \fIev.h\fR and puts all of its definitions (many
1448and puts all of its definitions (many of them macros) into the global 3880of them macros) into the global namespace. All \*(C+ specific things are
1449namespace. All \*(C+ specific things are put into the \f(CW\*(C`ev\*(C'\fR namespace. 3881put into the \f(CW\*(C`ev\*(C'\fR namespace. It should support all the same embedding
3882options as \fIev.h\fR, most notably \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR.
1450.PP 3883.PP
1451It should support all the same embedding options as \fIev.h\fR, most notably 3884Care has been taken to keep the overhead low. The only data member the \*(C+
1452\&\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. 3885classes add (compared to plain C\-style watchers) is the event loop pointer
3886that the watcher is associated with (or no additional members at all if
3887you disable \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR when embedding libev).
3888.PP
3889Currently, functions, static and non-static member functions and classes
3890with \f(CW\*(C`operator ()\*(C'\fR can be used as callbacks. Other types should be easy
3891to add as long as they only need one additional pointer for context. If
3892you need support for other types of functors please contact the author
3893(preferably after implementing it).
1453.PP 3894.PP
1454Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace: 3895Here is a list of things available in the \f(CW\*(C`ev\*(C'\fR namespace:
1455.ie n .IP """ev::READ""\fR, \f(CW""ev::WRITE"" etc." 4 3896.ie n .IP """ev::READ"", ""ev::WRITE"" etc." 4
1456.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4 3897.el .IP "\f(CWev::READ\fR, \f(CWev::WRITE\fR etc." 4
1457.IX Item "ev::READ, ev::WRITE etc." 3898.IX Item "ev::READ, ev::WRITE etc."
1458These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc. 3899These are just enum values with the same values as the \f(CW\*(C`EV_READ\*(C'\fR etc.
1459macros from \fIev.h\fR. 3900macros from \fIev.h\fR.
1460.ie n .IP """ev::tstamp""\fR, \f(CW""ev::now""" 4 3901.ie n .IP """ev::tstamp"", ""ev::now""" 4
1461.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4 3902.el .IP "\f(CWev::tstamp\fR, \f(CWev::now\fR" 4
1462.IX Item "ev::tstamp, ev::now" 3903.IX Item "ev::tstamp, ev::now"
1463Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix. 3904Aliases to the same types/functions as with the \f(CW\*(C`ev_\*(C'\fR prefix.
1464.ie n .IP """ev::io""\fR, \f(CW""ev::timer""\fR, \f(CW""ev::periodic""\fR, \f(CW""ev::idle""\fR, \f(CW""ev::sig"" etc." 4 3905.ie n .IP """ev::io"", ""ev::timer"", ""ev::periodic"", ""ev::idle"", ""ev::sig"" etc." 4
1465.el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4 3906.el .IP "\f(CWev::io\fR, \f(CWev::timer\fR, \f(CWev::periodic\fR, \f(CWev::idle\fR, \f(CWev::sig\fR etc." 4
1466.IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc." 3907.IX Item "ev::io, ev::timer, ev::periodic, ev::idle, ev::sig etc."
1467For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of 3908For each \f(CW\*(C`ev_TYPE\*(C'\fR watcher in \fIev.h\fR there is a corresponding class of
1468the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR 3909the same name in the \f(CW\*(C`ev\*(C'\fR namespace, with the exception of \f(CW\*(C`ev_signal\*(C'\fR
1469which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro 3910which is called \f(CW\*(C`ev::sig\*(C'\fR to avoid clashes with the \f(CW\*(C`signal\*(C'\fR macro
1470defines by many implementations. 3911defines by many implementations.
1471.Sp 3912.Sp
1472All of those classes have these methods: 3913All of those classes have these methods:
1473.RS 4 3914.RS 4
1474.IP "ev::TYPE::TYPE (object *, object::method *)" 4 3915.IP "ev::TYPE::TYPE ()" 4
1475.IX Item "ev::TYPE::TYPE (object *, object::method *)" 3916.IX Item "ev::TYPE::TYPE ()"
1476.PD 0 3917.PD 0
1477.IP "ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)" 4 3918.IP "ev::TYPE::TYPE (loop)" 4
1478.IX Item "ev::TYPE::TYPE (object *, object::method *, struct ev_loop *)" 3919.IX Item "ev::TYPE::TYPE (loop)"
1479.IP "ev::TYPE::~TYPE" 4 3920.IP "ev::TYPE::~TYPE" 4
1480.IX Item "ev::TYPE::~TYPE" 3921.IX Item "ev::TYPE::~TYPE"
1481.PD 3922.PD
1482The constructor takes a pointer to an object and a method pointer to 3923The constructor (optionally) takes an event loop to associate the watcher
1483the event handler callback to call in this class. The constructor calls 3924with. If it is omitted, it will use \f(CW\*(C`EV_DEFAULT\*(C'\fR.
1484\&\f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the \f(CW\*(C`set\*(C'\fR method 3925.Sp
1485before starting it. If you do not specify a loop then the constructor 3926The constructor calls \f(CW\*(C`ev_init\*(C'\fR for you, which means you have to call the
1486automatically associates the default loop with this watcher. 3927\&\f(CW\*(C`set\*(C'\fR method before starting it.
3928.Sp
3929It will not set a callback, however: You have to call the templated \f(CW\*(C`set\*(C'\fR
3930method to set a callback before you can start the watcher.
3931.Sp
3932(The reason why you have to use a method is a limitation in \*(C+ which does
3933not allow explicit template arguments for constructors).
1487.Sp 3934.Sp
1488The destructor automatically stops the watcher if it is active. 3935The destructor automatically stops the watcher if it is active.
3936.IP "w\->set<class, &class::method> (object *)" 4
3937.IX Item "w->set<class, &class::method> (object *)"
3938This method sets the callback method to call. The method has to have a
3939signature of \f(CW\*(C`void (*)(ev_TYPE &, int)\*(C'\fR, it receives the watcher as
3940first argument and the \f(CW\*(C`revents\*(C'\fR as second. The object must be given as
3941parameter and is stored in the \f(CW\*(C`data\*(C'\fR member of the watcher.
3942.Sp
3943This method synthesizes efficient thunking code to call your method from
3944the C callback that libev requires. If your compiler can inline your
3945callback (i.e. it is visible to it at the place of the \f(CW\*(C`set\*(C'\fR call and
3946your compiler is good :), then the method will be fully inlined into the
3947thunking function, making it as fast as a direct C callback.
3948.Sp
3949Example: simple class declaration and watcher initialisation
3950.Sp
3951.Vb 4
3952\& struct myclass
3953\& {
3954\& void io_cb (ev::io &w, int revents) { }
3955\& }
3956\&
3957\& myclass obj;
3958\& ev::io iow;
3959\& iow.set <myclass, &myclass::io_cb> (&obj);
3960.Ve
3961.IP "w\->set (object *)" 4
3962.IX Item "w->set (object *)"
3963This is a variation of a method callback \- leaving out the method to call
3964will default the method to \f(CW\*(C`operator ()\*(C'\fR, which makes it possible to use
3965functor objects without having to manually specify the \f(CW\*(C`operator ()\*(C'\fR all
3966the time. Incidentally, you can then also leave out the template argument
3967list.
3968.Sp
3969The \f(CW\*(C`operator ()\*(C'\fR method prototype must be \f(CW\*(C`void operator ()(watcher &w,
3970int revents)\*(C'\fR.
3971.Sp
3972See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
3973.Sp
3974Example: use a functor object as callback.
3975.Sp
3976.Vb 7
3977\& struct myfunctor
3978\& {
3979\& void operator() (ev::io &w, int revents)
3980\& {
3981\& ...
3982\& }
3983\& }
3984\&
3985\& myfunctor f;
3986\&
3987\& ev::io w;
3988\& w.set (&f);
3989.Ve
3990.IP "w\->set<function> (void *data = 0)" 4
3991.IX Item "w->set<function> (void *data = 0)"
3992Also sets a callback, but uses a static method or plain function as
3993callback. The optional \f(CW\*(C`data\*(C'\fR argument will be stored in the watcher's
3994\&\f(CW\*(C`data\*(C'\fR member and is free for you to use.
3995.Sp
3996The prototype of the \f(CW\*(C`function\*(C'\fR must be \f(CW\*(C`void (*)(ev::TYPE &w, int)\*(C'\fR.
3997.Sp
3998See the method\-\f(CW\*(C`set\*(C'\fR above for more details.
3999.Sp
4000Example: Use a plain function as callback.
4001.Sp
4002.Vb 2
4003\& static void io_cb (ev::io &w, int revents) { }
4004\& iow.set <io_cb> ();
4005.Ve
1489.IP "w\->set (struct ev_loop *)" 4 4006.IP "w\->set (loop)" 4
1490.IX Item "w->set (struct ev_loop *)" 4007.IX Item "w->set (loop)"
1491Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only 4008Associates a different \f(CW\*(C`struct ev_loop\*(C'\fR with this watcher. You can only
1492do this when the watcher is inactive (and not pending either). 4009do this when the watcher is inactive (and not pending either).
1493.IP "w\->set ([args])" 4 4010.IP "w\->set ([arguments])" 4
1494.IX Item "w->set ([args])" 4011.IX Item "w->set ([arguments])"
1495Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same args. Must be 4012Basically the same as \f(CW\*(C`ev_TYPE_set\*(C'\fR, with the same arguments. Either this
1496called at least once. Unlike the C counterpart, an active watcher gets 4013method or a suitable start method must be called at least once. Unlike the
1497automatically stopped and restarted. 4014C counterpart, an active watcher gets automatically stopped and restarted
4015when reconfiguring it with this method.
1498.IP "w\->start ()" 4 4016.IP "w\->start ()" 4
1499.IX Item "w->start ()" 4017.IX Item "w->start ()"
1500Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument as the 4018Starts the watcher. Note that there is no \f(CW\*(C`loop\*(C'\fR argument, as the
1501constructor already takes the loop. 4019constructor already stores the event loop.
4020.IP "w\->start ([arguments])" 4
4021.IX Item "w->start ([arguments])"
4022Instead of calling \f(CW\*(C`set\*(C'\fR and \f(CW\*(C`start\*(C'\fR methods separately, it is often
4023convenient to wrap them in one call. Uses the same type of arguments as
4024the configure \f(CW\*(C`set\*(C'\fR method of the watcher.
1502.IP "w\->stop ()" 4 4025.IP "w\->stop ()" 4
1503.IX Item "w->stop ()" 4026.IX Item "w->stop ()"
1504Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument. 4027Stops the watcher if it is active. Again, no \f(CW\*(C`loop\*(C'\fR argument.
1505.ie n .IP "w\->again () ""ev::timer""\fR, \f(CW""ev::periodic"" only" 4 4028.ie n .IP "w\->again () (""ev::timer"", ""ev::periodic"" only)" 4
1506.el .IP "w\->again () \f(CWev::timer\fR, \f(CWev::periodic\fR only" 4 4029.el .IP "w\->again () (\f(CWev::timer\fR, \f(CWev::periodic\fR only)" 4
1507.IX Item "w->again () ev::timer, ev::periodic only" 4030.IX Item "w->again () (ev::timer, ev::periodic only)"
1508For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding 4031For \f(CW\*(C`ev::timer\*(C'\fR and \f(CW\*(C`ev::periodic\*(C'\fR, this invokes the corresponding
1509\&\f(CW\*(C`ev_TYPE_again\*(C'\fR function. 4032\&\f(CW\*(C`ev_TYPE_again\*(C'\fR function.
1510.ie n .IP "w\->sweep () ""ev::embed"" only" 4 4033.ie n .IP "w\->sweep () (""ev::embed"" only)" 4
1511.el .IP "w\->sweep () \f(CWev::embed\fR only" 4 4034.el .IP "w\->sweep () (\f(CWev::embed\fR only)" 4
1512.IX Item "w->sweep () ev::embed only" 4035.IX Item "w->sweep () (ev::embed only)"
1513Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR. 4036Invokes \f(CW\*(C`ev_embed_sweep\*(C'\fR.
4037.ie n .IP "w\->update () (""ev::stat"" only)" 4
4038.el .IP "w\->update () (\f(CWev::stat\fR only)" 4
4039.IX Item "w->update () (ev::stat only)"
4040Invokes \f(CW\*(C`ev_stat_stat\*(C'\fR.
1514.RE 4041.RE
1515.RS 4 4042.RS 4
1516.RE 4043.RE
1517.PP 4044.PP
1518Example: Define a class with an \s-1IO\s0 and idle watcher, start one of them in 4045Example: Define a class with two I/O and idle watchers, start the I/O
1519the constructor. 4046watchers in the constructor.
1520.PP 4047.PP
1521.Vb 4 4048.Vb 5
1522\& class myclass 4049\& class myclass
1523\& { 4050\& {
1524\& ev_io io; void io_cb (ev::io &w, int revents); 4051\& ev::io io ; void io_cb (ev::io &w, int revents);
4052\& ev::io2 io2 ; void io2_cb (ev::io &w, int revents);
1525\& ev_idle idle void idle_cb (ev::idle &w, int revents); 4053\& ev::idle idle; void idle_cb (ev::idle &w, int revents);
4054\&
4055\& myclass (int fd)
4056\& {
4057\& io .set <myclass, &myclass::io_cb > (this);
4058\& io2 .set <myclass, &myclass::io2_cb > (this);
4059\& idle.set <myclass, &myclass::idle_cb> (this);
4060\&
4061\& io.set (fd, ev::WRITE); // configure the watcher
4062\& io.start (); // start it whenever convenient
4063\&
4064\& io2.start (fd, ev::READ); // set + start in one call
4065\& }
4066\& };
1526.Ve 4067.Ve
4068.SH "OTHER LANGUAGE BINDINGS"
4069.IX Header "OTHER LANGUAGE BINDINGS"
4070Libev does not offer other language bindings itself, but bindings for a
4071number of languages exist in the form of third-party packages. If you know
4072any interesting language binding in addition to the ones listed here, drop
4073me a note.
4074.IP "Perl" 4
4075.IX Item "Perl"
4076The \s-1EV\s0 module implements the full libev \s-1API\s0 and is actually used to test
4077libev. \s-1EV\s0 is developed together with libev. Apart from the \s-1EV\s0 core module,
4078there are additional modules that implement libev-compatible interfaces
4079to \f(CW\*(C`libadns\*(C'\fR (\f(CW\*(C`EV::ADNS\*(C'\fR, but \f(CW\*(C`AnyEvent::DNS\*(C'\fR is preferred nowadays),
4080\&\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
4081and \f(CW\*(C`EV::Glib\*(C'\fR).
4082.Sp
4083It can be found and installed via \s-1CPAN\s0, its homepage is at
4084<http://software.schmorp.de/pkg/EV>.
4085.IP "Python" 4
4086.IX Item "Python"
4087Python bindings can be found at <http://code.google.com/p/pyev/>. It
4088seems to be quite complete and well-documented.
4089.IP "Ruby" 4
4090.IX Item "Ruby"
4091Tony Arcieri has written a ruby extension that offers access to a subset
4092of the libev \s-1API\s0 and adds file handle abstractions, asynchronous \s-1DNS\s0 and
4093more on top of it. It can be found via gem servers. Its homepage is at
4094<http://rev.rubyforge.org/>.
4095.Sp
4096Roger Pack reports that using the link order \f(CW\*(C`\-lws2_32 \-lmsvcrt\-ruby\-190\*(C'\fR
4097makes rev work even on mingw.
4098.IP "Haskell" 4
4099.IX Item "Haskell"
4100A haskell binding to libev is available at
4101<http://hackage.haskell.org/cgi\-bin/hackage\-scripts/package/hlibev>.
4102.IP "D" 4
4103.IX Item "D"
4104Leandro Lucarella has written a D language binding (\fIev.d\fR) for libev, to
4105be found at <http://proj.llucax.com.ar/wiki/evd>.
4106.IP "Ocaml" 4
4107.IX Item "Ocaml"
4108Erkki Seppala has written Ocaml bindings for libev, to be found at
4109<http://modeemi.cs.tut.fi/~flux/software/ocaml\-ev/>.
4110.IP "Lua" 4
4111.IX Item "Lua"
4112Brian Maher has written a partial interface to libev for lua (at the
4113time of this writing, only \f(CW\*(C`ev_io\*(C'\fR and \f(CW\*(C`ev_timer\*(C'\fR), to be found at
4114<http://github.com/brimworks/lua\-ev>.
4115.SH "MACRO MAGIC"
4116.IX Header "MACRO MAGIC"
4117Libev can be compiled with a variety of options, the most fundamental
4118of which is \f(CW\*(C`EV_MULTIPLICITY\*(C'\fR. This option determines whether (most)
4119functions and callbacks have an initial \f(CW\*(C`struct ev_loop *\*(C'\fR argument.
1527.PP 4120.PP
4121To make it easier to write programs that cope with either variant, the
4122following macros are defined:
4123.ie n .IP """EV_A"", ""EV_A_""" 4
4124.el .IP "\f(CWEV_A\fR, \f(CWEV_A_\fR" 4
4125.IX Item "EV_A, EV_A_"
4126This provides the loop \fIargument\fR for functions, if one is required (\*(L"ev
4127loop argument\*(R"). The \f(CW\*(C`EV_A\*(C'\fR form is used when this is the sole argument,
4128\&\f(CW\*(C`EV_A_\*(C'\fR is used when other arguments are following. Example:
4129.Sp
4130.Vb 3
4131\& ev_unref (EV_A);
4132\& ev_timer_add (EV_A_ watcher);
4133\& ev_run (EV_A_ 0);
4134.Ve
4135.Sp
4136It assumes the variable \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR is in scope,
4137which is often provided by the following macro.
4138.ie n .IP """EV_P"", ""EV_P_""" 4
4139.el .IP "\f(CWEV_P\fR, \f(CWEV_P_\fR" 4
4140.IX Item "EV_P, EV_P_"
4141This provides the loop \fIparameter\fR for functions, if one is required (\*(L"ev
4142loop parameter\*(R"). The \f(CW\*(C`EV_P\*(C'\fR form is used when this is the sole parameter,
4143\&\f(CW\*(C`EV_P_\*(C'\fR is used when other parameters are following. Example:
4144.Sp
1528.Vb 2 4145.Vb 2
1529\& myclass (); 4146\& // this is how ev_unref is being declared
1530\& } 4147\& static void ev_unref (EV_P);
4148\&
4149\& // this is how you can declare your typical callback
4150\& static void cb (EV_P_ ev_timer *w, int revents)
1531.Ve 4151.Ve
4152.Sp
4153It declares a parameter \f(CW\*(C`loop\*(C'\fR of type \f(CW\*(C`struct ev_loop *\*(C'\fR, quite
4154suitable for use with \f(CW\*(C`EV_A\*(C'\fR.
4155.ie n .IP """EV_DEFAULT"", ""EV_DEFAULT_""" 4
4156.el .IP "\f(CWEV_DEFAULT\fR, \f(CWEV_DEFAULT_\fR" 4
4157.IX Item "EV_DEFAULT, EV_DEFAULT_"
4158Similar to the other two macros, this gives you the value of the default
4159loop, if multiple loops are supported (\*(L"ev loop default\*(R").
4160.ie n .IP """EV_DEFAULT_UC"", ""EV_DEFAULT_UC_""" 4
4161.el .IP "\f(CWEV_DEFAULT_UC\fR, \f(CWEV_DEFAULT_UC_\fR" 4
4162.IX Item "EV_DEFAULT_UC, EV_DEFAULT_UC_"
4163Usage identical to \f(CW\*(C`EV_DEFAULT\*(C'\fR and \f(CW\*(C`EV_DEFAULT_\*(C'\fR, but requires that the
4164default loop has been initialised (\f(CW\*(C`UC\*(C'\fR == unchecked). Their behaviour
4165is undefined when the default loop has not been initialised by a previous
4166execution of \f(CW\*(C`EV_DEFAULT\*(C'\fR, \f(CW\*(C`EV_DEFAULT_\*(C'\fR or \f(CW\*(C`ev_default_init (...)\*(C'\fR.
4167.Sp
4168It is often prudent to use \f(CW\*(C`EV_DEFAULT\*(C'\fR when initialising the first
4169watcher in a function but use \f(CW\*(C`EV_DEFAULT_UC\*(C'\fR afterwards.
1532.PP 4170.PP
4171Example: Declare and initialise a check watcher, utilising the above
4172macros so it will work regardless of whether multiple loops are supported
4173or not.
4174.PP
1533.Vb 6 4175.Vb 5
1534\& myclass::myclass (int fd) 4176\& static void
1535\& : io (this, &myclass::io_cb), 4177\& check_cb (EV_P_ ev_timer *w, int revents)
1536\& idle (this, &myclass::idle_cb)
1537\& { 4178\& {
1538\& io.start (fd, ev::READ); 4179\& ev_check_stop (EV_A_ w);
1539\& } 4180\& }
4181\&
4182\& ev_check check;
4183\& ev_check_init (&check, check_cb);
4184\& ev_check_start (EV_DEFAULT_ &check);
4185\& ev_run (EV_DEFAULT_ 0);
1540.Ve 4186.Ve
1541.SH "EMBEDDING" 4187.SH "EMBEDDING"
1542.IX Header "EMBEDDING" 4188.IX Header "EMBEDDING"
1543Libev can (and often is) directly embedded into host 4189Libev can (and often is) directly embedded into host
1544applications. Examples of applications that embed it include the Deliantra 4190applications. Examples of applications that embed it include the Deliantra
1545Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe) 4191Game Server, the \s-1EV\s0 perl module, the \s-1GNU\s0 Virtual Private Ethernet (gvpe)
1546and rxvt\-unicode. 4192and rxvt-unicode.
1547.PP 4193.PP
1548The goal is to enable you to just copy the neecssary files into your 4194The goal is to enable you to just copy the necessary files into your
1549source directory without having to change even a single line in them, so 4195source directory without having to change even a single line in them, so
1550you can easily upgrade by simply copying (or having a checked-out copy of 4196you can easily upgrade by simply copying (or having a checked-out copy of
1551libev somewhere in your source tree). 4197libev somewhere in your source tree).
1552.Sh "\s-1FILESETS\s0" 4198.SS "\s-1FILESETS\s0"
1553.IX Subsection "FILESETS" 4199.IX Subsection "FILESETS"
1554Depending on what features you need you need to include one or more sets of files 4200Depending on what features you need you need to include one or more sets of files
1555in your app. 4201in your application.
1556.PP 4202.PP
1557\fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR 4203\fI\s-1CORE\s0 \s-1EVENT\s0 \s-1LOOP\s0\fR
1558.IX Subsection "CORE EVENT LOOP" 4204.IX Subsection "CORE EVENT LOOP"
1559.PP 4205.PP
1560To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual 4206To include only the libev core (all the \f(CW\*(C`ev_*\*(C'\fR functions), with manual
1561configuration (no autoconf): 4207configuration (no autoconf):
1562.PP 4208.PP
1563.Vb 2 4209.Vb 2
1564\& #define EV_STANDALONE 1 4210\& #define EV_STANDALONE 1
1565\& #include "ev.c" 4211\& #include "ev.c"
1566.Ve 4212.Ve
1567.PP 4213.PP
1568This will automatically include \fIev.h\fR, too, and should be done in a 4214This will automatically include \fIev.h\fR, too, and should be done in a
1569single C source file only to provide the function implementations. To use 4215single C source file only to provide the function implementations. To use
1570it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best 4216it, do the same for \fIev.h\fR in all files wishing to use this \s-1API\s0 (best
1571done by writing a wrapper around \fIev.h\fR that you can include instead and 4217done by writing a wrapper around \fIev.h\fR that you can include instead and
1572where you can put other configuration options): 4218where you can put other configuration options):
1573.PP 4219.PP
1574.Vb 2 4220.Vb 2
1575\& #define EV_STANDALONE 1 4221\& #define EV_STANDALONE 1
1576\& #include "ev.h" 4222\& #include "ev.h"
1577.Ve 4223.Ve
1578.PP 4224.PP
1579Both header files and implementation files can be compiled with a \*(C+ 4225Both header files and implementation files can be compiled with a \*(C+
1580compiler (at least, thats a stated goal, and breakage will be treated 4226compiler (at least, that's a stated goal, and breakage will be treated
1581as a bug). 4227as a bug).
1582.PP 4228.PP
1583You need the following files in your source tree, or in a directory 4229You need the following files in your source tree, or in a directory
1584in your include path (e.g. in libev/ when using \-Ilibev): 4230in your include path (e.g. in libev/ when using \-Ilibev):
1585.PP 4231.PP
1586.Vb 4 4232.Vb 4
1587\& ev.h 4233\& ev.h
1588\& ev.c 4234\& ev.c
1589\& ev_vars.h 4235\& ev_vars.h
1590\& ev_wrap.h 4236\& ev_wrap.h
1591.Ve 4237\&
1592.PP
1593.Vb 1
1594\& ev_win32.c required on win32 platforms only 4238\& ev_win32.c required on win32 platforms only
1595.Ve 4239\&
1596.PP
1597.Vb 5
1598\& ev_select.c only when select backend is enabled (which is is by default) 4240\& ev_select.c only when select backend is enabled (which is enabled by default)
1599\& ev_poll.c only when poll backend is enabled (disabled by default) 4241\& ev_poll.c only when poll backend is enabled (disabled by default)
1600\& ev_epoll.c only when the epoll backend is enabled (disabled by default) 4242\& ev_epoll.c only when the epoll backend is enabled (disabled by default)
1601\& ev_kqueue.c only when the kqueue backend is enabled (disabled by default) 4243\& ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
1602\& ev_port.c only when the solaris port backend is enabled (disabled by default) 4244\& ev_port.c only when the solaris port backend is enabled (disabled by default)
1603.Ve 4245.Ve
1604.PP 4246.PP
1605\&\fIev.c\fR includes the backend files directly when enabled, so you only need 4247\&\fIev.c\fR includes the backend files directly when enabled, so you only need
1606to compile a single file. 4248to compile this single file.
1607.PP 4249.PP
1608\fI\s-1LIBEVENT\s0 \s-1COMPATIBILITY\s0 \s-1API\s0\fR 4250\fI\s-1LIBEVENT\s0 \s-1COMPATIBILITY\s0 \s-1API\s0\fR
1609.IX Subsection "LIBEVENT COMPATIBILITY API" 4251.IX Subsection "LIBEVENT COMPATIBILITY API"
1610.PP 4252.PP
1611To include the libevent compatibility \s-1API\s0, also include: 4253To include the libevent compatibility \s-1API\s0, also include:
1612.PP 4254.PP
1613.Vb 1 4255.Vb 1
1614\& #include "event.c" 4256\& #include "event.c"
1615.Ve 4257.Ve
1616.PP 4258.PP
1617in the file including \fIev.c\fR, and: 4259in the file including \fIev.c\fR, and:
1618.PP 4260.PP
1619.Vb 1 4261.Vb 1
1620\& #include "event.h" 4262\& #include "event.h"
1621.Ve 4263.Ve
1622.PP 4264.PP
1623in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR. 4265in the files that want to use the libevent \s-1API\s0. This also includes \fIev.h\fR.
1624.PP 4266.PP
1625You need the following additional files for this: 4267You need the following additional files for this:
1626.PP 4268.PP
1627.Vb 2 4269.Vb 2
1628\& event.h 4270\& event.h
1629\& event.c 4271\& event.c
1630.Ve 4272.Ve
1631.PP 4273.PP
1632\fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR 4274\fI\s-1AUTOCONF\s0 \s-1SUPPORT\s0\fR
1633.IX Subsection "AUTOCONF SUPPORT" 4275.IX Subsection "AUTOCONF SUPPORT"
1634.PP 4276.PP
1635Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your config in 4277Instead of using \f(CW\*(C`EV_STANDALONE=1\*(C'\fR and providing your configuration in
1636whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your 4278whatever way you want, you can also \f(CW\*(C`m4_include([libev.m4])\*(C'\fR in your
1637\&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR off. \fIev.c\fR will then include 4279\&\fIconfigure.ac\fR and leave \f(CW\*(C`EV_STANDALONE\*(C'\fR undefined. \fIev.c\fR will then
1638\&\fIconfig.h\fR and configure itself accordingly. 4280include \fIconfig.h\fR and configure itself accordingly.
1639.PP 4281.PP
1640For this of course you need the m4 file: 4282For this of course you need the m4 file:
1641.PP 4283.PP
1642.Vb 1 4284.Vb 1
1643\& libev.m4 4285\& libev.m4
1644.Ve 4286.Ve
1645.Sh "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0" 4287.SS "\s-1PREPROCESSOR\s0 \s-1SYMBOLS/MACROS\s0"
1646.IX Subsection "PREPROCESSOR SYMBOLS/MACROS" 4288.IX Subsection "PREPROCESSOR SYMBOLS/MACROS"
1647Libev can be configured via a variety of preprocessor symbols you have to define 4289Libev can be configured via a variety of preprocessor symbols you have to
1648before including any of its files. The default is not to build for multiplicity 4290define before including (or compiling) any of its files. The default in
1649and only include the select backend. 4291the absence of autoconf is documented for every option.
4292.PP
4293Symbols marked with \*(L"(h)\*(R" do not change the \s-1ABI\s0, and can have different
4294values when compiling libev vs. including \fIev.h\fR, so it is permissible
4295to redefine them before including \fIev.h\fR without breaking compatibility
4296to a compiled library. All other symbols change the \s-1ABI\s0, which means all
4297users of libev and the libev code itself must be compiled with compatible
4298settings.
4299.IP "\s-1EV_COMPAT3\s0 (h)" 4
4300.IX Item "EV_COMPAT3 (h)"
4301Backwards compatibility is a major concern for libev. This is why this
4302release of libev comes with wrappers for the functions and symbols that
4303have been renamed between libev version 3 and 4.
4304.Sp
4305You can disable these wrappers (to test compatibility with future
4306versions) by defining \f(CW\*(C`EV_COMPAT3\*(C'\fR to \f(CW0\fR when compiling your
4307sources. This has the additional advantage that you can drop the \f(CW\*(C`struct\*(C'\fR
4308from \f(CW\*(C`struct ev_loop\*(C'\fR declarations, as libev will provide an \f(CW\*(C`ev_loop\*(C'\fR
4309typedef in that case.
4310.Sp
4311In some future version, the default for \f(CW\*(C`EV_COMPAT3\*(C'\fR will become \f(CW0\fR,
4312and in some even more future version the compatibility code will be
4313removed completely.
1650.IP "\s-1EV_STANDALONE\s0" 4 4314.IP "\s-1EV_STANDALONE\s0 (h)" 4
1651.IX Item "EV_STANDALONE" 4315.IX Item "EV_STANDALONE (h)"
1652Must always be \f(CW1\fR if you do not use autoconf configuration, which 4316Must always be \f(CW1\fR if you do not use autoconf configuration, which
1653keeps libev from including \fIconfig.h\fR, and it also defines dummy 4317keeps libev from including \fIconfig.h\fR, and it also defines dummy
1654implementations for some libevent functions (such as logging, which is not 4318implementations for some libevent functions (such as logging, which is not
1655supported). It will also not define any of the structs usually found in 4319supported). It will also not define any of the structs usually found in
1656\&\fIevent.h\fR that are not directly supported by the libev core alone. 4320\&\fIevent.h\fR that are not directly supported by the libev core alone.
4321.Sp
4322In standalone mode, libev will still try to automatically deduce the
4323configuration, but has to be more conservative.
1657.IP "\s-1EV_USE_MONOTONIC\s0" 4 4324.IP "\s-1EV_USE_MONOTONIC\s0" 4
1658.IX Item "EV_USE_MONOTONIC" 4325.IX Item "EV_USE_MONOTONIC"
1659If defined to be \f(CW1\fR, libev will try to detect the availability of the 4326If defined to be \f(CW1\fR, libev will try to detect the availability of the
1660monotonic clock option at both compiletime and runtime. Otherwise no use 4327monotonic clock option at both compile time and runtime. Otherwise no
1661of the monotonic clock option will be attempted. If you enable this, you 4328use of the monotonic clock option will be attempted. If you enable this,
1662usually have to link against librt or something similar. Enabling it when 4329you usually have to link against librt or something similar. Enabling it
1663the functionality isn't available is safe, though, althoguh you have 4330when the functionality isn't available is safe, though, although you have
1664to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR 4331to make sure you link against any libraries where the \f(CW\*(C`clock_gettime\*(C'\fR
1665function is hiding in (often \fI\-lrt\fR). 4332function is hiding in (often \fI\-lrt\fR). See also \f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
1666.IP "\s-1EV_USE_REALTIME\s0" 4 4333.IP "\s-1EV_USE_REALTIME\s0" 4
1667.IX Item "EV_USE_REALTIME" 4334.IX Item "EV_USE_REALTIME"
1668If defined to be \f(CW1\fR, libev will try to detect the availability of the 4335If defined to be \f(CW1\fR, libev will try to detect the availability of the
1669realtime clock option at compiletime (and assume its availability at 4336real-time clock option at compile time (and assume its availability
1670runtime if successful). Otherwise no use of the realtime clock option will 4337at runtime if successful). Otherwise no use of the real-time clock
1671be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR by \f(CW\*(C`clock_get 4338option will be attempted. This effectively replaces \f(CW\*(C`gettimeofday\*(C'\fR
1672(CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect correctness. See tzhe note about libraries 4339by \f(CW\*(C`clock_get (CLOCK_REALTIME, ...)\*(C'\fR and will not normally affect
1673in the description of \f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. 4340correctness. See the note about libraries in the description of
4341\&\f(CW\*(C`EV_USE_MONOTONIC\*(C'\fR, though. Defaults to the opposite value of
4342\&\f(CW\*(C`EV_USE_CLOCK_SYSCALL\*(C'\fR.
4343.IP "\s-1EV_USE_CLOCK_SYSCALL\s0" 4
4344.IX Item "EV_USE_CLOCK_SYSCALL"
4345If defined to be \f(CW1\fR, libev will try to use a direct syscall instead
4346of calling the system-provided \f(CW\*(C`clock_gettime\*(C'\fR function. This option
4347exists 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
4348unconditionally pulls in \f(CW\*(C`libpthread\*(C'\fR, slowing down single-threaded
4349programs needlessly. Using a direct syscall is slightly slower (in
4350theory), because no optimised vdso implementation can be used, but avoids
4351the pthread dependency. Defaults to \f(CW1\fR on GNU/Linux with glibc 2.x or
4352higher, as it simplifies linking (no need for \f(CW\*(C`\-lrt\*(C'\fR).
4353.IP "\s-1EV_USE_NANOSLEEP\s0" 4
4354.IX Item "EV_USE_NANOSLEEP"
4355If defined to be \f(CW1\fR, libev will assume that \f(CW\*(C`nanosleep ()\*(C'\fR is available
4356and will use it for delays. Otherwise it will use \f(CW\*(C`select ()\*(C'\fR.
4357.IP "\s-1EV_USE_EVENTFD\s0" 4
4358.IX Item "EV_USE_EVENTFD"
4359If defined to be \f(CW1\fR, then libev will assume that \f(CW\*(C`eventfd ()\*(C'\fR is
4360available and will probe for kernel support at runtime. This will improve
4361\&\f(CW\*(C`ev_signal\*(C'\fR and \f(CW\*(C`ev_async\*(C'\fR performance and reduce resource consumption.
4362If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
43632.7 or newer, otherwise disabled.
1674.IP "\s-1EV_USE_SELECT\s0" 4 4364.IP "\s-1EV_USE_SELECT\s0" 4
1675.IX Item "EV_USE_SELECT" 4365.IX Item "EV_USE_SELECT"
1676If undefined or defined to be \f(CW1\fR, libev will compile in support for the 4366If undefined or defined to be \f(CW1\fR, libev will compile in support for the
1677\&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at autodetection will be done: if no 4367\&\f(CW\*(C`select\*(C'\fR(2) backend. No attempt at auto-detection will be done: if no
1678other method takes over, select will be it. Otherwise the select backend 4368other method takes over, select will be it. Otherwise the select backend
1679will not be compiled in. 4369will not be compiled in.
1680.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4 4370.IP "\s-1EV_SELECT_USE_FD_SET\s0" 4
1681.IX Item "EV_SELECT_USE_FD_SET" 4371.IX Item "EV_SELECT_USE_FD_SET"
1682If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR 4372If defined to \f(CW1\fR, then the select backend will use the system \f(CW\*(C`fd_set\*(C'\fR
1683structure. This is useful if libev doesn't compile due to a missing 4373structure. This is useful if libev doesn't compile due to a missing
1684\&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it misguesses the bitset layout on 4374\&\f(CW\*(C`NFDBITS\*(C'\fR or \f(CW\*(C`fd_mask\*(C'\fR definition or it mis-guesses the bitset layout
1685exotic systems. This usually limits the range of file descriptors to some 4375on exotic systems. This usually limits the range of file descriptors to
1686low limit such as 1024 or might have other limitations (winsocket only 4376some low limit such as 1024 or might have other limitations (winsocket
1687allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation, might 4377only allows 64 sockets). The \f(CW\*(C`FD_SETSIZE\*(C'\fR macro, set before compilation,
1688influence the size of the \f(CW\*(C`fd_set\*(C'\fR used. 4378configures the maximum size of the \f(CW\*(C`fd_set\*(C'\fR.
1689.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4 4379.IP "\s-1EV_SELECT_IS_WINSOCKET\s0" 4
1690.IX Item "EV_SELECT_IS_WINSOCKET" 4380.IX Item "EV_SELECT_IS_WINSOCKET"
1691When defined to \f(CW1\fR, the select backend will assume that 4381When defined to \f(CW1\fR, the select backend will assume that
1692select/socket/connect etc. don't understand file descriptors but 4382select/socket/connect etc. don't understand file descriptors but
1693wants osf handles on win32 (this is the case when the select to 4383wants osf handles on win32 (this is the case when the select to
1694be used is the winsock select). This means that it will call 4384be used is the winsock select). This means that it will call
1695\&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise, 4385\&\f(CW\*(C`_get_osfhandle\*(C'\fR on the fd to convert it to an \s-1OS\s0 handle. Otherwise,
1696it is assumed that all these functions actually work on fds, even 4386it is assumed that all these functions actually work on fds, even
1697on win32. Should not be defined on non\-win32 platforms. 4387on win32. Should not be defined on non\-win32 platforms.
4388.IP "\s-1EV_FD_TO_WIN32_HANDLE\s0(fd)" 4
4389.IX Item "EV_FD_TO_WIN32_HANDLE(fd)"
4390If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR is enabled, then libev needs a way to map
4391file descriptors to socket handles. When not defining this symbol (the
4392default), then libev will call \f(CW\*(C`_get_osfhandle\*(C'\fR, which is usually
4393correct. In some cases, programs use their own file descriptor management,
4394in which case they can provide this function to map fds to socket handles.
4395.IP "\s-1EV_WIN32_HANDLE_TO_FD\s0(handle)" 4
4396.IX Item "EV_WIN32_HANDLE_TO_FD(handle)"
4397If \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR then libev maps handles to file descriptors
4398using the standard \f(CW\*(C`_open_osfhandle\*(C'\fR function. For programs implementing
4399their own fd to handle mapping, overwriting this function makes it easier
4400to do so. This can be done by defining this macro to an appropriate value.
4401.IP "\s-1EV_WIN32_CLOSE_FD\s0(fd)" 4
4402.IX Item "EV_WIN32_CLOSE_FD(fd)"
4403If programs implement their own fd to handle mapping on win32, then this
4404macro can be used to override the \f(CW\*(C`close\*(C'\fR function, useful to unregister
4405file descriptors again. Note that the replacement function has to close
4406the underlying \s-1OS\s0 handle.
1698.IP "\s-1EV_USE_POLL\s0" 4 4407.IP "\s-1EV_USE_POLL\s0" 4
1699.IX Item "EV_USE_POLL" 4408.IX Item "EV_USE_POLL"
1700If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2) 4409If defined to be \f(CW1\fR, libev will compile in support for the \f(CW\*(C`poll\*(C'\fR(2)
1701backend. Otherwise it will be enabled on non\-win32 platforms. It 4410backend. Otherwise it will be enabled on non\-win32 platforms. It
1702takes precedence over select. 4411takes precedence over select.
1703.IP "\s-1EV_USE_EPOLL\s0" 4 4412.IP "\s-1EV_USE_EPOLL\s0" 4
1704.IX Item "EV_USE_EPOLL" 4413.IX Item "EV_USE_EPOLL"
1705If defined to be \f(CW1\fR, libev will compile in support for the Linux 4414If defined to be \f(CW1\fR, libev will compile in support for the Linux
1706\&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime, 4415\&\f(CW\*(C`epoll\*(C'\fR(7) backend. Its availability will be detected at runtime,
1707otherwise another method will be used as fallback. This is the 4416otherwise another method will be used as fallback. This is the preferred
1708preferred backend for GNU/Linux systems. 4417backend for GNU/Linux systems. If undefined, it will be enabled if the
4418headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
1709.IP "\s-1EV_USE_KQUEUE\s0" 4 4419.IP "\s-1EV_USE_KQUEUE\s0" 4
1710.IX Item "EV_USE_KQUEUE" 4420.IX Item "EV_USE_KQUEUE"
1711If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style 4421If defined to be \f(CW1\fR, libev will compile in support for the \s-1BSD\s0 style
1712\&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime, 4422\&\f(CW\*(C`kqueue\*(C'\fR(2) backend. Its actual availability will be detected at runtime,
1713otherwise another method will be used as fallback. This is the preferred 4423otherwise another method will be used as fallback. This is the preferred
1714backend for \s-1BSD\s0 and BSD-like systems, although on most BSDs kqueue only 4424backend for \s-1BSD\s0 and BSD-like systems, although on most BSDs kqueue only
1715supports some types of fds correctly (the only platform we found that 4425supports some types of fds correctly (the only platform we found that
1716supports ptys for example was NetBSD), so kqueue might be compiled in, but 4426supports ptys for example was NetBSD), so kqueue might be compiled in, but
1717not be used unless explicitly requested. The best way to use it is to find 4427not be used unless explicitly requested. The best way to use it is to find
1718out wether kqueue supports your type of fd properly and use an embedded 4428out whether kqueue supports your type of fd properly and use an embedded
1719kqueue loop. 4429kqueue loop.
1720.IP "\s-1EV_USE_PORT\s0" 4 4430.IP "\s-1EV_USE_PORT\s0" 4
1721.IX Item "EV_USE_PORT" 4431.IX Item "EV_USE_PORT"
1722If defined to be \f(CW1\fR, libev will compile in support for the Solaris 4432If defined to be \f(CW1\fR, libev will compile in support for the Solaris
172310 port style backend. Its availability will be detected at runtime, 443310 port style backend. Its availability will be detected at runtime,
1724otherwise another method will be used as fallback. This is the preferred 4434otherwise another method will be used as fallback. This is the preferred
1725backend for Solaris 10 systems. 4435backend for Solaris 10 systems.
1726.IP "\s-1EV_USE_DEVPOLL\s0" 4 4436.IP "\s-1EV_USE_DEVPOLL\s0" 4
1727.IX Item "EV_USE_DEVPOLL" 4437.IX Item "EV_USE_DEVPOLL"
1728reserved for future expansion, works like the \s-1USE\s0 symbols above. 4438Reserved for future expansion, works like the \s-1USE\s0 symbols above.
4439.IP "\s-1EV_USE_INOTIFY\s0" 4
4440.IX Item "EV_USE_INOTIFY"
4441If defined to be \f(CW1\fR, libev will compile in support for the Linux inotify
4442interface to speed up \f(CW\*(C`ev_stat\*(C'\fR watchers. Its actual availability will
4443be detected at runtime. If undefined, it will be enabled if the headers
4444indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
4445.IP "\s-1EV_ATOMIC_T\s0" 4
4446.IX Item "EV_ATOMIC_T"
4447Libev requires an integer type (suitable for storing \f(CW0\fR or \f(CW1\fR) whose
4448access is atomic with respect to other threads or signal contexts. No such
4449type is easily found in the C language, so you can provide your own type
4450that you know is safe for your purposes. It is used both for signal handler \*(L"locking\*(R"
4451as well as for signal and thread safety in \f(CW\*(C`ev_async\*(C'\fR watchers.
4452.Sp
4453In the absence of this define, libev will use \f(CW\*(C`sig_atomic_t volatile\*(C'\fR
4454(from \fIsignal.h\fR), which is usually good enough on most platforms.
1729.IP "\s-1EV_H\s0" 4 4455.IP "\s-1EV_H\s0 (h)" 4
1730.IX Item "EV_H" 4456.IX Item "EV_H (h)"
1731The name of the \fIev.h\fR header file used to include it. The default if 4457The name of the \fIev.h\fR header file used to include it. The default if
1732undefined is \f(CW\*(C`<ev.h>\*(C'\fR in \fIevent.h\fR and \f(CW"ev.h"\fR in \fIev.c\fR. This 4458undefined is \f(CW"ev.h"\fR in \fIevent.h\fR, \fIev.c\fR and \fIev++.h\fR. This can be
1733can be used to virtually rename the \fIev.h\fR header file in case of conflicts. 4459used to virtually rename the \fIev.h\fR header file in case of conflicts.
1734.IP "\s-1EV_CONFIG_H\s0" 4 4460.IP "\s-1EV_CONFIG_H\s0 (h)" 4
1735.IX Item "EV_CONFIG_H" 4461.IX Item "EV_CONFIG_H (h)"
1736If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override 4462If \f(CW\*(C`EV_STANDALONE\*(C'\fR isn't \f(CW1\fR, this variable can be used to override
1737\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to 4463\&\fIev.c\fR's idea of where to find the \fIconfig.h\fR file, similarly to
1738\&\f(CW\*(C`EV_H\*(C'\fR, above. 4464\&\f(CW\*(C`EV_H\*(C'\fR, above.
1739.IP "\s-1EV_EVENT_H\s0" 4 4465.IP "\s-1EV_EVENT_H\s0 (h)" 4
1740.IX Item "EV_EVENT_H" 4466.IX Item "EV_EVENT_H (h)"
1741Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea 4467Similarly to \f(CW\*(C`EV_H\*(C'\fR, this macro can be used to override \fIevent.c\fR's idea
1742of how the \fIevent.h\fR header can be found. 4468of how the \fIevent.h\fR header can be found, the default is \f(CW"event.h"\fR.
1743.IP "\s-1EV_PROTOTYPES\s0" 4 4469.IP "\s-1EV_PROTOTYPES\s0 (h)" 4
1744.IX Item "EV_PROTOTYPES" 4470.IX Item "EV_PROTOTYPES (h)"
1745If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function 4471If defined to be \f(CW0\fR, then \fIev.h\fR will not define any function
1746prototypes, but still define all the structs and other symbols. This is 4472prototypes, but still define all the structs and other symbols. This is
1747occasionally useful if you want to provide your own wrapper functions 4473occasionally useful if you want to provide your own wrapper functions
1748around libev functions. 4474around libev functions.
1749.IP "\s-1EV_MULTIPLICITY\s0" 4 4475.IP "\s-1EV_MULTIPLICITY\s0" 4
… …
1751If undefined or defined to \f(CW1\fR, then all event-loop-specific functions 4477If undefined or defined to \f(CW1\fR, then all event-loop-specific functions
1752will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create 4478will have the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument, and you can create
1753additional independent event loops. Otherwise there will be no support 4479additional independent event loops. Otherwise there will be no support
1754for multiple event loops and there is no first event loop pointer 4480for multiple event loops and there is no first event loop pointer
1755argument. Instead, all functions act on the single default loop. 4481argument. Instead, all functions act on the single default loop.
1756.IP "\s-1EV_PERIODICS\s0" 4 4482.IP "\s-1EV_MINPRI\s0" 4
1757.IX Item "EV_PERIODICS" 4483.IX Item "EV_MINPRI"
1758If undefined or defined to be \f(CW1\fR, then periodic timers are supported, 4484.PD 0
1759otherwise not. This saves a few kb of code. 4485.IP "\s-1EV_MAXPRI\s0" 4
4486.IX Item "EV_MAXPRI"
4487.PD
4488The range of allowed priorities. \f(CW\*(C`EV_MINPRI\*(C'\fR must be smaller or equal to
4489\&\f(CW\*(C`EV_MAXPRI\*(C'\fR, but otherwise there are no non-obvious limitations. You can
4490provide for more priorities by overriding those symbols (usually defined
4491to be \f(CW\*(C`\-2\*(C'\fR and \f(CW2\fR, respectively).
4492.Sp
4493When doing priority-based operations, libev usually has to linearly search
4494all the priorities, so having many of them (hundreds) uses a lot of space
4495and time, so using the defaults of five priorities (\-2 .. +2) is usually
4496fine.
4497.Sp
4498If your embedding application does not need any priorities, defining these
4499both to \f(CW0\fR will save some memory and \s-1CPU\s0.
4500.IP "\s-1EV_PERIODIC_ENABLE\s0, \s-1EV_IDLE_ENABLE\s0, \s-1EV_EMBED_ENABLE\s0, \s-1EV_STAT_ENABLE\s0, \s-1EV_PREPARE_ENABLE\s0, \s-1EV_CHECK_ENABLE\s0, \s-1EV_FORK_ENABLE\s0, \s-1EV_SIGNAL_ENABLE\s0, \s-1EV_ASYNC_ENABLE\s0, \s-1EV_CHILD_ENABLE\s0." 4
4501.IX Item "EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE, EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE, EV_ASYNC_ENABLE, EV_CHILD_ENABLE."
4502If undefined or defined to be \f(CW1\fR (and the platform supports it), then
4503the respective watcher type is supported. If defined to be \f(CW0\fR, then it
4504is not. Disabling watcher types mainly saves code size.
4505.IP "\s-1EV_FEATURES\s0" 4
4506.IX Item "EV_FEATURES"
4507If you need to shave off some kilobytes of code at the expense of some
4508speed (but with the full \s-1API\s0), you can define this symbol to request
4509certain subsets of functionality. The default is to enable all features
4510that can be enabled on the platform.
4511.Sp
4512A typical way to use this symbol is to define it to \f(CW0\fR (or to a bitset
4513with some broad features you want) and then selectively re-enable
4514additional parts you want, for example if you want everything minimal,
4515but multiple event loop support, async and child watchers and the poll
4516backend, use this:
4517.Sp
4518.Vb 5
4519\& #define EV_FEATURES 0
4520\& #define EV_MULTIPLICITY 1
4521\& #define EV_USE_POLL 1
4522\& #define EV_CHILD_ENABLE 1
4523\& #define EV_ASYNC_ENABLE 1
4524.Ve
4525.Sp
4526The actual value is a bitset, it can be a combination of the following
4527values:
4528.RS 4
4529.ie n .IP "1 \- faster/larger code" 4
4530.el .IP "\f(CW1\fR \- faster/larger code" 4
4531.IX Item "1 - faster/larger code"
4532Use larger code to speed up some operations.
4533.Sp
4534Currently this is used to override some inlining decisions (enlarging the
4535code size by roughly 30% on amd64).
4536.Sp
4537When optimising for size, use of compiler flags such as \f(CW\*(C`\-Os\*(C'\fR with
4538gcc is recommended, as well as \f(CW\*(C`\-DNDEBUG\*(C'\fR, as libev contains a number of
4539assertions.
4540.ie n .IP "2 \- faster/larger data structures" 4
4541.el .IP "\f(CW2\fR \- faster/larger data structures" 4
4542.IX Item "2 - faster/larger data structures"
4543Replaces the small 2\-heap for timer management by a faster 4\-heap, larger
4544hash table sizes and so on. This will usually further increase code size
4545and can additionally have an effect on the size of data structures at
4546runtime.
4547.ie n .IP "4 \- full \s-1API\s0 configuration" 4
4548.el .IP "\f(CW4\fR \- full \s-1API\s0 configuration" 4
4549.IX Item "4 - full API configuration"
4550This enables priorities (sets \f(CW\*(C`EV_MAXPRI\*(C'\fR=2 and \f(CW\*(C`EV_MINPRI\*(C'\fR=\-2), and
4551enables multiplicity (\f(CW\*(C`EV_MULTIPLICITY\*(C'\fR=1).
4552.ie n .IP "8 \- full \s-1API\s0" 4
4553.el .IP "\f(CW8\fR \- full \s-1API\s0" 4
4554.IX Item "8 - full API"
4555This enables a lot of the \*(L"lesser used\*(R" \s-1API\s0 functions. See \f(CW\*(C`ev.h\*(C'\fR for
4556details on which parts of the \s-1API\s0 are still available without this
4557feature, and do not complain if this subset changes over time.
4558.ie n .IP "16 \- enable all optional watcher types" 4
4559.el .IP "\f(CW16\fR \- enable all optional watcher types" 4
4560.IX Item "16 - enable all optional watcher types"
4561Enables all optional watcher types. If you want to selectively enable
4562only some watcher types other than I/O and timers (e.g. prepare,
4563embed, async, child...) you can enable them manually by defining
4564\&\f(CW\*(C`EV_watchertype_ENABLE\*(C'\fR to \f(CW1\fR instead.
4565.ie n .IP "32 \- enable all backends" 4
4566.el .IP "\f(CW32\fR \- enable all backends" 4
4567.IX Item "32 - enable all backends"
4568This enables all backends \- without this feature, you need to enable at
4569least one backend manually (\f(CW\*(C`EV_USE_SELECT\*(C'\fR is a good choice).
4570.ie n .IP "64 \- enable OS-specific ""helper"" APIs" 4
4571.el .IP "\f(CW64\fR \- enable OS-specific ``helper'' APIs" 4
4572.IX Item "64 - enable OS-specific helper APIs"
4573Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by
4574default.
4575.RE
4576.RS 4
4577.Sp
4578Compiling with \f(CW\*(C`gcc \-Os \-DEV_STANDALONE \-DEV_USE_EPOLL=1 \-DEV_FEATURES=0\*(C'\fR
4579reduces the compiled size of libev from 24.7Kb code/2.8Kb data to 6.5Kb
4580code/0.3Kb data on my GNU/Linux amd64 system, while still giving you I/O
4581watchers, timers and monotonic clock support.
4582.Sp
4583With an intelligent-enough linker (gcc+binutils are intelligent enough
4584when you use \f(CW\*(C`\-Wl,\-\-gc\-sections \-ffunction\-sections\*(C'\fR) functions unused by
4585your program might be left out as well \- a binary starting a timer and an
4586I/O watcher then might come out at only 5Kb.
4587.RE
4588.IP "\s-1EV_AVOID_STDIO\s0" 4
4589.IX Item "EV_AVOID_STDIO"
4590If this is set to \f(CW1\fR at compiletime, then libev will avoid using stdio
4591functions (printf, scanf, perror etc.). This will increase the code size
4592somewhat, but if your program doesn't otherwise depend on stdio and your
4593libc allows it, this avoids linking in the stdio library which is quite
4594big.
4595.Sp
4596Note that error messages might become less precise when this option is
4597enabled.
4598.IP "\s-1EV_NSIG\s0" 4
4599.IX Item "EV_NSIG"
4600The highest supported signal number, +1 (or, the number of
4601signals): Normally, libev tries to deduce the maximum number of signals
4602automatically, but sometimes this fails, in which case it can be
4603specified. Also, using a lower number than detected (\f(CW32\fR should be
4604good for about any system in existence) can save some memory, as libev
4605statically allocates some 12\-24 bytes per signal number.
4606.IP "\s-1EV_PID_HASHSIZE\s0" 4
4607.IX Item "EV_PID_HASHSIZE"
4608\&\f(CW\*(C`ev_child\*(C'\fR watchers use a small hash table to distribute workload by
4609pid. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR disabled),
4610usually more than enough. If you need to manage thousands of children you
4611might want to increase this value (\fImust\fR be a power of two).
4612.IP "\s-1EV_INOTIFY_HASHSIZE\s0" 4
4613.IX Item "EV_INOTIFY_HASHSIZE"
4614\&\f(CW\*(C`ev_stat\*(C'\fR watchers use a small hash table to distribute workload by
4615inotify watch id. The default size is \f(CW16\fR (or \f(CW1\fR with \f(CW\*(C`EV_FEATURES\*(C'\fR
4616disabled), usually more than enough. If you need to manage thousands of
4617\&\f(CW\*(C`ev_stat\*(C'\fR watchers you might want to increase this value (\fImust\fR be a
4618power of two).
4619.IP "\s-1EV_USE_4HEAP\s0" 4
4620.IX Item "EV_USE_4HEAP"
4621Heaps are not very cache-efficient. To improve the cache-efficiency of the
4622timer and periodics heaps, libev uses a 4\-heap when this symbol is defined
4623to \f(CW1\fR. The 4\-heap uses more complicated (longer) code but has noticeably
4624faster performance with many (thousands) of watchers.
4625.Sp
4626The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4627will be \f(CW0\fR.
4628.IP "\s-1EV_HEAP_CACHE_AT\s0" 4
4629.IX Item "EV_HEAP_CACHE_AT"
4630Heaps are not very cache-efficient. To improve the cache-efficiency of the
4631timer and periodics heaps, libev can cache the timestamp (\fIat\fR) within
4632the heap structure (selected by defining \f(CW\*(C`EV_HEAP_CACHE_AT\*(C'\fR to \f(CW1\fR),
4633which uses 8\-12 bytes more per watcher and a few hundred bytes more code,
4634but avoids random read accesses on heap changes. This improves performance
4635noticeably with many (hundreds) of watchers.
4636.Sp
4637The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4638will be \f(CW0\fR.
4639.IP "\s-1EV_VERIFY\s0" 4
4640.IX Item "EV_VERIFY"
4641Controls how much internal verification (see \f(CW\*(C`ev_verify ()\*(C'\fR) will
4642be done: If set to \f(CW0\fR, no internal verification code will be compiled
4643in. If set to \f(CW1\fR, then verification code will be compiled in, but not
4644called. If set to \f(CW2\fR, then the internal verification code will be
4645called once per loop, which can slow down libev. If set to \f(CW3\fR, then the
4646verification code will be called very frequently, which will slow down
4647libev considerably.
4648.Sp
4649The default is \f(CW1\fR, unless \f(CW\*(C`EV_FEATURES\*(C'\fR overrides it, in which case it
4650will be \f(CW0\fR.
1760.IP "\s-1EV_COMMON\s0" 4 4651.IP "\s-1EV_COMMON\s0" 4
1761.IX Item "EV_COMMON" 4652.IX Item "EV_COMMON"
1762By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining 4653By default, all watchers have a \f(CW\*(C`void *data\*(C'\fR member. By redefining
1763this macro to a something else you can include more and other types of 4654this macro to something else you can include more and other types of
1764members. You have to define it each time you include one of the files, 4655members. You have to define it each time you include one of the files,
1765though, and it must be identical each time. 4656though, and it must be identical each time.
1766.Sp 4657.Sp
1767For example, the perl \s-1EV\s0 module uses something like this: 4658For example, the perl \s-1EV\s0 module uses something like this:
1768.Sp 4659.Sp
1769.Vb 3 4660.Vb 3
1770\& #define EV_COMMON \e 4661\& #define EV_COMMON \e
1771\& SV *self; /* contains this struct */ \e 4662\& SV *self; /* contains this struct */ \e
1772\& SV *cb_sv, *fh /* note no trailing ";" */ 4663\& SV *cb_sv, *fh /* note no trailing ";" */
1773.Ve 4664.Ve
1774.IP "\s-1EV_CB_DECLARE\s0(type)" 4 4665.IP "\s-1EV_CB_DECLARE\s0 (type)" 4
1775.IX Item "EV_CB_DECLARE(type)" 4666.IX Item "EV_CB_DECLARE (type)"
1776.PD 0 4667.PD 0
1777.IP "\s-1EV_CB_INVOKE\s0(watcher,revents)" 4 4668.IP "\s-1EV_CB_INVOKE\s0 (watcher, revents)" 4
1778.IX Item "EV_CB_INVOKE(watcher,revents)" 4669.IX Item "EV_CB_INVOKE (watcher, revents)"
1779.IP "ev_set_cb(ev,cb)" 4 4670.IP "ev_set_cb (ev, cb)" 4
1780.IX Item "ev_set_cb(ev,cb)" 4671.IX Item "ev_set_cb (ev, cb)"
1781.PD 4672.PD
1782Can be used to change the callback member declaration in each watcher, 4673Can be used to change the callback member declaration in each watcher,
1783and the way callbacks are invoked and set. Must expand to a struct member 4674and the way callbacks are invoked and set. Must expand to a struct member
1784definition and a statement, respectively. See the \fIev.v\fR header file for 4675definition and a statement, respectively. See the \fIev.h\fR header file for
1785their default definitions. One possible use for overriding these is to 4676their default definitions. One possible use for overriding these is to
1786avoid the ev_loop pointer as first argument in all cases, or to use method 4677avoid the \f(CW\*(C`struct ev_loop *\*(C'\fR as first argument in all cases, or to use
1787calls instead of plain function calls in \*(C+. 4678method calls instead of plain function calls in \*(C+.
4679.SS "\s-1EXPORTED\s0 \s-1API\s0 \s-1SYMBOLS\s0"
4680.IX Subsection "EXPORTED API SYMBOLS"
4681If you need to re-export the \s-1API\s0 (e.g. via a \s-1DLL\s0) and you need a list of
4682exported symbols, you can use the provided \fISymbol.*\fR files which list
4683all public symbols, one per line:
4684.PP
4685.Vb 2
4686\& Symbols.ev for libev proper
4687\& Symbols.event for the libevent emulation
4688.Ve
4689.PP
4690This can also be used to rename all public symbols to avoid clashes with
4691multiple versions of libev linked together (which is obviously bad in
4692itself, but sometimes it is inconvenient to avoid this).
4693.PP
4694A sed command like this will create wrapper \f(CW\*(C`#define\*(C'\fR's that you need to
4695include before including \fIev.h\fR:
4696.PP
4697.Vb 1
4698\& <Symbols.ev sed \-e "s/.*/#define & myprefix_&/" >wrap.h
4699.Ve
4700.PP
4701This would create a file \fIwrap.h\fR which essentially looks like this:
4702.PP
4703.Vb 4
4704\& #define ev_backend myprefix_ev_backend
4705\& #define ev_check_start myprefix_ev_check_start
4706\& #define ev_check_stop myprefix_ev_check_stop
4707\& ...
4708.Ve
1788.Sh "\s-1EXAMPLES\s0" 4709.SS "\s-1EXAMPLES\s0"
1789.IX Subsection "EXAMPLES" 4710.IX Subsection "EXAMPLES"
1790For a real-world example of a program the includes libev 4711For a real-world example of a program the includes libev
1791verbatim, you can have a look at the \s-1EV\s0 perl module 4712verbatim, you can have a look at the \s-1EV\s0 perl module
1792(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in 4713(<http://software.schmorp.de/pkg/EV.html>). It has the libev files in
1793the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public 4714the \fIlibev/\fR subdirectory and includes them in the \fI\s-1EV/EVAPI\s0.h\fR (public
1794interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file 4715interface) and \fI\s-1EV\s0.xs\fR (implementation) files. Only the \fI\s-1EV\s0.xs\fR file
1795will be compiled. It is pretty complex because it provides its own header 4716will be compiled. It is pretty complex because it provides its own header
1796file. 4717file.
1797.Sp 4718.PP
1798The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file 4719The usage in rxvt-unicode is simpler. It has a \fIev_cpp.h\fR header file
1799that everybody includes and which overrides some autoconf choices: 4720that everybody includes and which overrides some configure choices:
1800.Sp 4721.PP
1801.Vb 4 4722.Vb 8
4723\& #define EV_FEATURES 8
4724\& #define EV_USE_SELECT 1
4725\& #define EV_PREPARE_ENABLE 1
4726\& #define EV_IDLE_ENABLE 1
4727\& #define EV_SIGNAL_ENABLE 1
4728\& #define EV_CHILD_ENABLE 1
1802\& #define EV_USE_POLL 0 4729\& #define EV_USE_STDEXCEPT 0
1803\& #define EV_MULTIPLICITY 0
1804\& #define EV_PERIODICS 0
1805\& #define EV_CONFIG_H <config.h> 4730\& #define EV_CONFIG_H <config.h>
1806.Ve 4731\&
1807.Sp
1808.Vb 1
1809\& #include "ev++.h" 4732\& #include "ev++.h"
1810.Ve 4733.Ve
1811.Sp 4734.PP
1812And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled: 4735And a \fIev_cpp.C\fR implementation file that contains libev proper and is compiled:
1813.Sp 4736.PP
1814.Vb 1
1815\& #include "rxvttoolkit.h"
1816.Ve
1817.Sp
1818.Vb 2 4737.Vb 2
1819\& /* darwin has problems with its header files in C++, requiring this namespace juggling */ 4738\& #include "ev_cpp.h"
1820\& using namespace ev;
1821.Ve
1822.Sp
1823.Vb 1
1824\& #include "ev.c" 4739\& #include "ev.c"
1825.Ve 4740.Ve
4741.SH "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT"
4742.IX Header "INTERACTION WITH OTHER PROGRAMS, LIBRARIES OR THE ENVIRONMENT"
4743.SS "\s-1THREADS\s0 \s-1AND\s0 \s-1COROUTINES\s0"
4744.IX Subsection "THREADS AND COROUTINES"
4745\fI\s-1THREADS\s0\fR
4746.IX Subsection "THREADS"
4747.PP
4748All libev functions are reentrant and thread-safe unless explicitly
4749documented otherwise, but libev implements no locking itself. This means
4750that you can use as many loops as you want in parallel, as long as there
4751are no concurrent calls into any libev function with the same loop
4752parameter (\f(CW\*(C`ev_default_*\*(C'\fR calls have an implicit default loop parameter,
4753of course): libev guarantees that different event loops share no data
4754structures that need any locking.
4755.PP
4756Or to put it differently: calls with different loop parameters can be done
4757concurrently from multiple threads, calls with the same loop parameter
4758must be done serially (but can be done from different threads, as long as
4759only one thread ever is inside a call at any point in time, e.g. by using
4760a mutex per loop).
4761.PP
4762Specifically to support threads (and signal handlers), libev implements
4763so-called \f(CW\*(C`ev_async\*(C'\fR watchers, which allow some limited form of
4764concurrency on the same event loop, namely waking it up \*(L"from the
4765outside\*(R".
4766.PP
4767If you want to know which design (one loop, locking, or multiple loops
4768without or something else still) is best for your problem, then I cannot
4769help you, but here is some generic advice:
4770.IP "\(bu" 4
4771most applications have a main thread: use the default libev loop
4772in that thread, or create a separate thread running only the default loop.
4773.Sp
4774This helps integrating other libraries or software modules that use libev
4775themselves and don't care/know about threading.
4776.IP "\(bu" 4
4777one loop per thread is usually a good model.
4778.Sp
4779Doing this is almost never wrong, sometimes a better-performance model
4780exists, but it is always a good start.
4781.IP "\(bu" 4
4782other models exist, such as the leader/follower pattern, where one
4783loop is handed through multiple threads in a kind of round-robin fashion.
4784.Sp
4785Choosing a model is hard \- look around, learn, know that usually you can do
4786better than you currently do :\-)
4787.IP "\(bu" 4
4788often you need to talk to some other thread which blocks in the
4789event loop.
4790.Sp
4791\&\f(CW\*(C`ev_async\*(C'\fR watchers can be used to wake them up from other threads safely
4792(or from signal contexts...).
4793.Sp
4794An example use would be to communicate signals or other events that only
4795work in the default loop by registering the signal watcher with the
4796default loop and triggering an \f(CW\*(C`ev_async\*(C'\fR watcher from the default loop
4797watcher callback into the event loop interested in the signal.
4798.PP
4799See also \*(L"\s-1THREAD\s0 \s-1LOCKING\s0 \s-1EXAMPLE\s0\*(R".
4800.PP
4801\fI\s-1COROUTINES\s0\fR
4802.IX Subsection "COROUTINES"
4803.PP
4804Libev is very accommodating to coroutines (\*(L"cooperative threads\*(R"):
4805libev fully supports nesting calls to its functions from different
4806coroutines (e.g. you can call \f(CW\*(C`ev_run\*(C'\fR on the same loop from two
4807different coroutines, and switch freely between both coroutines running
4808the loop, as long as you don't confuse yourself). The only exception is
4809that you must not do this from \f(CW\*(C`ev_periodic\*(C'\fR reschedule callbacks.
4810.PP
4811Care has been taken to ensure that libev does not keep local state inside
4812\&\f(CW\*(C`ev_run\*(C'\fR, and other calls do not usually allow for coroutine switches as
4813they do not call any callbacks.
4814.SS "\s-1COMPILER\s0 \s-1WARNINGS\s0"
4815.IX Subsection "COMPILER WARNINGS"
4816Depending on your compiler and compiler settings, you might get no or a
4817lot of warnings when compiling libev code. Some people are apparently
4818scared by this.
4819.PP
4820However, these are unavoidable for many reasons. For one, each compiler
4821has different warnings, and each user has different tastes regarding
4822warning options. \*(L"Warn-free\*(R" code therefore cannot be a goal except when
4823targeting a specific compiler and compiler-version.
4824.PP
4825Another reason is that some compiler warnings require elaborate
4826workarounds, or other changes to the code that make it less clear and less
4827maintainable.
4828.PP
4829And of course, some compiler warnings are just plain stupid, or simply
4830wrong (because they don't actually warn about the condition their message
4831seems to warn about). For example, certain older gcc versions had some
4832warnings that resulted in an extreme number of false positives. These have
4833been fixed, but some people still insist on making code warn-free with
4834such buggy versions.
4835.PP
4836While libev is written to generate as few warnings as possible,
4837\&\*(L"warn-free\*(R" code is not a goal, and it is recommended not to build libev
4838with any compiler warnings enabled unless you are prepared to cope with
4839them (e.g. by ignoring them). Remember that warnings are just that:
4840warnings, not errors, or proof of bugs.
4841.SS "\s-1VALGRIND\s0"
4842.IX Subsection "VALGRIND"
4843Valgrind has a special section here because it is a popular tool that is
4844highly useful. Unfortunately, valgrind reports are very hard to interpret.
4845.PP
4846If you think you found a bug (memory leak, uninitialised data access etc.)
4847in libev, then check twice: If valgrind reports something like:
4848.PP
4849.Vb 3
4850\& ==2274== definitely lost: 0 bytes in 0 blocks.
4851\& ==2274== possibly lost: 0 bytes in 0 blocks.
4852\& ==2274== still reachable: 256 bytes in 1 blocks.
4853.Ve
4854.PP
4855Then there is no memory leak, just as memory accounted to global variables
4856is not a memleak \- the memory is still being referenced, and didn't leak.
4857.PP
4858Similarly, under some circumstances, valgrind might report kernel bugs
4859as if it were a bug in libev (e.g. in realloc or in the poll backend,
4860although an acceptable workaround has been found here), or it might be
4861confused.
4862.PP
4863Keep in mind that valgrind is a very good tool, but only a tool. Don't
4864make it into some kind of religion.
4865.PP
4866If you are unsure about something, feel free to contact the mailing list
4867with the full valgrind report and an explanation on why you think this
4868is a bug in libev (best check the archives, too :). However, don't be
4869annoyed when you get a brisk \*(L"this is no bug\*(R" answer and take the chance
4870of learning how to interpret valgrind properly.
4871.PP
4872If you need, for some reason, empty reports from valgrind for your project
4873I suggest using suppression lists.
4874.SH "PORTABILITY NOTES"
4875.IX Header "PORTABILITY NOTES"
4876.SS "\s-1GNU/LINUX\s0 32 \s-1BIT\s0 \s-1LIMITATIONS\s0"
4877.IX Subsection "GNU/LINUX 32 BIT LIMITATIONS"
4878GNU/Linux is the only common platform that supports 64 bit file/large file
4879interfaces but \fIdisables\fR them by default.
4880.PP
4881That means that libev compiled in the default environment doesn't support
4882files larger than 2GiB or so, which mainly affects \f(CW\*(C`ev_stat\*(C'\fR watchers.
4883.PP
4884Unfortunately, many programs try to work around this GNU/Linux issue
4885by enabling the large file \s-1API\s0, which makes them incompatible with the
4886standard libev compiled for their system.
4887.PP
4888Likewise, libev cannot enable the large file \s-1API\s0 itself as this would
4889suddenly make it incompatible to the default compile time environment,
4890i.e. all programs not using special compile switches.
4891.SS "\s-1OS/X\s0 \s-1AND\s0 \s-1DARWIN\s0 \s-1BUGS\s0"
4892.IX Subsection "OS/X AND DARWIN BUGS"
4893The whole thing is a bug if you ask me \- basically any system interface
4894you touch is broken, whether it is locales, poll, kqueue or even the
4895OpenGL drivers.
4896.PP
4897\fI\f(CI\*(C`kqueue\*(C'\fI is buggy\fR
4898.IX Subsection "kqueue is buggy"
4899.PP
4900The kqueue syscall is broken in all known versions \- most versions support
4901only sockets, many support pipes.
4902.PP
4903Libev tries to work around this by not using \f(CW\*(C`kqueue\*(C'\fR by default on this
4904rotten platform, but of course you can still ask for it when creating a
4905loop \- embedding a socket-only kqueue loop into a select-based one is
4906probably going to work well.
4907.PP
4908\fI\f(CI\*(C`poll\*(C'\fI is buggy\fR
4909.IX Subsection "poll is buggy"
4910.PP
4911Instead of fixing \f(CW\*(C`kqueue\*(C'\fR, Apple replaced their (working) \f(CW\*(C`poll\*(C'\fR
4912implementation by something calling \f(CW\*(C`kqueue\*(C'\fR internally around the 10.5.6
4913release, so now \f(CW\*(C`kqueue\*(C'\fR \fIand\fR \f(CW\*(C`poll\*(C'\fR are broken.
4914.PP
4915Libev tries to work around this by not using \f(CW\*(C`poll\*(C'\fR by default on
4916this rotten platform, but of course you can still ask for it when creating
4917a loop.
4918.PP
4919\fI\f(CI\*(C`select\*(C'\fI is buggy\fR
4920.IX Subsection "select is buggy"
4921.PP
4922All that's left is \f(CW\*(C`select\*(C'\fR, and of course Apple found a way to fuck this
4923one up as well: On \s-1OS/X\s0, \f(CW\*(C`select\*(C'\fR actively limits the number of file
4924descriptors you can pass in to 1024 \- your program suddenly crashes when
4925you use more.
4926.PP
4927There is an undocumented \*(L"workaround\*(R" for this \- defining
4928\&\f(CW\*(C`_DARWIN_UNLIMITED_SELECT\*(C'\fR, which libev tries to use, so select \fIshould\fR
4929work on \s-1OS/X\s0.
4930.SS "\s-1SOLARIS\s0 \s-1PROBLEMS\s0 \s-1AND\s0 \s-1WORKAROUNDS\s0"
4931.IX Subsection "SOLARIS PROBLEMS AND WORKAROUNDS"
4932\fI\f(CI\*(C`errno\*(C'\fI reentrancy\fR
4933.IX Subsection "errno reentrancy"
4934.PP
4935The default compile environment on Solaris is unfortunately so
4936thread-unsafe that you can't even use components/libraries compiled
4937without \f(CW\*(C`\-D_REENTRANT\*(C'\fR in a threaded program, which, of course, isn't
4938defined by default. A valid, if stupid, implementation choice.
4939.PP
4940If you want to use libev in threaded environments you have to make sure
4941it's compiled with \f(CW\*(C`_REENTRANT\*(C'\fR defined.
4942.PP
4943\fIEvent port backend\fR
4944.IX Subsection "Event port backend"
4945.PP
4946The scalable event interface for Solaris is called \*(L"event
4947ports\*(R". Unfortunately, this mechanism is very buggy in all major
4948releases. If you run into high \s-1CPU\s0 usage, your program freezes or you get
4949a large number of spurious wakeups, make sure you have all the relevant
4950and latest kernel patches applied. No, I don't know which ones, but there
4951are multiple ones to apply, and afterwards, event ports actually work
4952great.
4953.PP
4954If you can't get it to work, you can try running the program by setting
4955the environment variable \f(CW\*(C`LIBEV_FLAGS=3\*(C'\fR to only allow \f(CW\*(C`poll\*(C'\fR and
4956\&\f(CW\*(C`select\*(C'\fR backends.
4957.SS "\s-1AIX\s0 \s-1POLL\s0 \s-1BUG\s0"
4958.IX Subsection "AIX POLL BUG"
4959\&\s-1AIX\s0 unfortunately has a broken \f(CW\*(C`poll.h\*(C'\fR header. Libev works around
4960this by trying to avoid the poll backend altogether (i.e. it's not even
4961compiled in), which normally isn't a big problem as \f(CW\*(C`select\*(C'\fR works fine
4962with large bitsets on \s-1AIX\s0, and \s-1AIX\s0 is dead anyway.
4963.SS "\s-1WIN32\s0 \s-1PLATFORM\s0 \s-1LIMITATIONS\s0 \s-1AND\s0 \s-1WORKAROUNDS\s0"
4964.IX Subsection "WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS"
4965\fIGeneral issues\fR
4966.IX Subsection "General issues"
4967.PP
4968Win32 doesn't support any of the standards (e.g. \s-1POSIX\s0) that libev
4969requires, and its I/O model is fundamentally incompatible with the \s-1POSIX\s0
4970model. Libev still offers limited functionality on this platform in
4971the form of the \f(CW\*(C`EVBACKEND_SELECT\*(C'\fR backend, and only supports socket
4972descriptors. This only applies when using Win32 natively, not when using
4973e.g. cygwin. Actually, it only applies to the microsofts own compilers,
4974as every compielr comes with a slightly differently broken/incompatible
4975environment.
4976.PP
4977Lifting these limitations would basically require the full
4978re-implementation of the I/O system. If you are into this kind of thing,
4979then note that glib does exactly that for you in a very portable way (note
4980also that glib is the slowest event library known to man).
4981.PP
4982There is no supported compilation method available on windows except
4983embedding it into other applications.
4984.PP
4985Sensible signal handling is officially unsupported by Microsoft \- libev
4986tries its best, but under most conditions, signals will simply not work.
4987.PP
4988Not a libev limitation but worth mentioning: windows apparently doesn't
4989accept large writes: instead of resulting in a partial write, windows will
4990either accept everything or return \f(CW\*(C`ENOBUFS\*(C'\fR if the buffer is too large,
4991so make sure you only write small amounts into your sockets (less than a
4992megabyte seems safe, but this apparently depends on the amount of memory
4993available).
4994.PP
4995Due to the many, low, and arbitrary limits on the win32 platform and
4996the abysmal performance of winsockets, using a large number of sockets
4997is not recommended (and not reasonable). If your program needs to use
4998more than a hundred or so sockets, then likely it needs to use a totally
4999different implementation for windows, as libev offers the \s-1POSIX\s0 readiness
5000notification model, which cannot be implemented efficiently on windows
5001(due to Microsoft monopoly games).
5002.PP
5003A typical way to use libev under windows is to embed it (see the embedding
5004section for details) and use the following \fIevwrap.h\fR header file instead
5005of \fIev.h\fR:
5006.PP
5007.Vb 2
5008\& #define EV_STANDALONE /* keeps ev from requiring config.h */
5009\& #define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
5010\&
5011\& #include "ev.h"
5012.Ve
5013.PP
5014And compile the following \fIevwrap.c\fR file into your project (make sure
5015you do \fInot\fR compile the \fIev.c\fR or any other embedded source files!):
5016.PP
5017.Vb 2
5018\& #include "evwrap.h"
5019\& #include "ev.c"
5020.Ve
5021.PP
5022\fIThe winsocket \f(CI\*(C`select\*(C'\fI function\fR
5023.IX Subsection "The winsocket select function"
5024.PP
5025The winsocket \f(CW\*(C`select\*(C'\fR function doesn't follow \s-1POSIX\s0 in that it
5026requires socket \fIhandles\fR and not socket \fIfile descriptors\fR (it is
5027also extremely buggy). This makes select very inefficient, and also
5028requires a mapping from file descriptors to socket handles (the Microsoft
5029C runtime provides the function \f(CW\*(C`_open_osfhandle\*(C'\fR for this). See the
5030discussion of the \f(CW\*(C`EV_SELECT_USE_FD_SET\*(C'\fR, \f(CW\*(C`EV_SELECT_IS_WINSOCKET\*(C'\fR and
5031\&\f(CW\*(C`EV_FD_TO_WIN32_HANDLE\*(C'\fR preprocessor symbols for more info.
5032.PP
5033The configuration for a \*(L"naked\*(R" win32 using the Microsoft runtime
5034libraries and raw winsocket select is:
5035.PP
5036.Vb 2
5037\& #define EV_USE_SELECT 1
5038\& #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
5039.Ve
5040.PP
5041Note that winsockets handling of fd sets is O(n), so you can easily get a
5042complexity in the O(nA\*^X) range when using win32.
5043.PP
5044\fILimited number of file descriptors\fR
5045.IX Subsection "Limited number of file descriptors"
5046.PP
5047Windows has numerous arbitrary (and low) limits on things.
5048.PP
5049Early versions of winsocket's select only supported waiting for a maximum
5050of \f(CW64\fR handles (probably owning to the fact that all windows kernels
5051can only wait for \f(CW64\fR things at the same time internally; Microsoft
5052recommends spawning a chain of threads and wait for 63 handles and the
5053previous thread in each. Sounds great!).
5054.PP
5055Newer versions support more handles, but you need to define \f(CW\*(C`FD_SETSIZE\*(C'\fR
5056to some high number (e.g. \f(CW2048\fR) before compiling the winsocket select
5057call (which might be in libev or elsewhere, for example, perl and many
5058other interpreters do their own select emulation on windows).
5059.PP
5060Another limit is the number of file descriptors in the Microsoft runtime
5061libraries, which by default is \f(CW64\fR (there must be a hidden \fI64\fR
5062fetish or something like this inside Microsoft). You can increase this
5063by calling \f(CW\*(C`_setmaxstdio\*(C'\fR, which can increase this limit to \f(CW2048\fR
5064(another arbitrary limit), but is broken in many versions of the Microsoft
5065runtime libraries. This might get you to about \f(CW512\fR or \f(CW2048\fR sockets
5066(depending on windows version and/or the phase of the moon). To get more,
5067you need to wrap all I/O functions and provide your own fd management, but
5068the cost of calling select (O(nA\*^X)) will likely make this unworkable.
5069.SS "\s-1PORTABILITY\s0 \s-1REQUIREMENTS\s0"
5070.IX Subsection "PORTABILITY REQUIREMENTS"
5071In addition to a working ISO-C implementation and of course the
5072backend-specific APIs, libev relies on a few additional extensions:
5073.ie n .IP """void (*)(ev_watcher_type *, int revents)"" must have compatible calling conventions regardless of ""ev_watcher_type *""." 4
5074.el .IP "\f(CWvoid (*)(ev_watcher_type *, int revents)\fR must have compatible calling conventions regardless of \f(CWev_watcher_type *\fR." 4
5075.IX Item "void (*)(ev_watcher_type *, int revents) must have compatible calling conventions regardless of ev_watcher_type *."
5076Libev assumes not only that all watcher pointers have the same internal
5077structure (guaranteed by \s-1POSIX\s0 but not by \s-1ISO\s0 C for example), but it also
5078assumes that the same (machine) code can be used to call any watcher
5079callback: The watcher callbacks have different type signatures, but libev
5080calls them using an \f(CW\*(C`ev_watcher *\*(C'\fR internally.
5081.IP "pointer accesses must be thread-atomic" 4
5082.IX Item "pointer accesses must be thread-atomic"
5083Accessing a pointer value must be atomic, it must both be readable and
5084writable in one piece \- this is the case on all current architectures.
5085.ie n .IP """sig_atomic_t volatile"" must be thread-atomic as well" 4
5086.el .IP "\f(CWsig_atomic_t volatile\fR must be thread-atomic as well" 4
5087.IX Item "sig_atomic_t volatile must be thread-atomic as well"
5088The type \f(CW\*(C`sig_atomic_t volatile\*(C'\fR (or whatever is defined as
5089\&\f(CW\*(C`EV_ATOMIC_T\*(C'\fR) must be atomic with respect to accesses from different
5090threads. This is not part of the specification for \f(CW\*(C`sig_atomic_t\*(C'\fR, but is
5091believed to be sufficiently portable.
5092.ie n .IP """sigprocmask"" must work in a threaded environment" 4
5093.el .IP "\f(CWsigprocmask\fR must work in a threaded environment" 4
5094.IX Item "sigprocmask must work in a threaded environment"
5095Libev uses \f(CW\*(C`sigprocmask\*(C'\fR to temporarily block signals. This is not
5096allowed in a threaded program (\f(CW\*(C`pthread_sigmask\*(C'\fR has to be used). Typical
5097pthread implementations will either allow \f(CW\*(C`sigprocmask\*(C'\fR in the \*(L"main
5098thread\*(R" or will block signals process-wide, both behaviours would
5099be compatible with libev. Interaction between \f(CW\*(C`sigprocmask\*(C'\fR and
5100\&\f(CW\*(C`pthread_sigmask\*(C'\fR could complicate things, however.
5101.Sp
5102The most portable way to handle signals is to block signals in all threads
5103except the initial one, and run the default loop in the initial thread as
5104well.
5105.ie n .IP """long"" must be large enough for common memory allocation sizes" 4
5106.el .IP "\f(CWlong\fR must be large enough for common memory allocation sizes" 4
5107.IX Item "long must be large enough for common memory allocation sizes"
5108To improve portability and simplify its \s-1API\s0, libev uses \f(CW\*(C`long\*(C'\fR internally
5109instead of \f(CW\*(C`size_t\*(C'\fR when allocating its data structures. On non-POSIX
5110systems (Microsoft...) this might be unexpectedly low, but is still at
5111least 31 bits everywhere, which is enough for hundreds of millions of
5112watchers.
5113.ie n .IP """double"" must hold a time value in seconds with enough accuracy" 4
5114.el .IP "\f(CWdouble\fR must hold a time value in seconds with enough accuracy" 4
5115.IX Item "double must hold a time value in seconds with enough accuracy"
5116The type \f(CW\*(C`double\*(C'\fR is used to represent timestamps. It is required to
5117have at least 51 bits of mantissa (and 9 bits of exponent), which is
5118good enough for at least into the year 4000 with millisecond accuracy
5119(the design goal for libev). This requirement is overfulfilled by
5120implementations using \s-1IEEE\s0 754, which is basically all existing ones. With
5121\&\s-1IEEE\s0 754 doubles, you get microsecond accuracy until at least 2200.
5122.PP
5123If you know of other additional requirements drop me a note.
5124.SH "ALGORITHMIC COMPLEXITIES"
5125.IX Header "ALGORITHMIC COMPLEXITIES"
5126In this section the complexities of (many of) the algorithms used inside
5127libev will be documented. For complexity discussions about backends see
5128the documentation for \f(CW\*(C`ev_default_init\*(C'\fR.
5129.PP
5130All of the following are about amortised time: If an array needs to be
5131extended, libev needs to realloc and move the whole array, but this
5132happens asymptotically rarer with higher number of elements, so O(1) might
5133mean that libev does a lengthy realloc operation in rare cases, but on
5134average it is much faster and asymptotically approaches constant time.
5135.IP "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)" 4
5136.IX Item "Starting and stopping timer/periodic watchers: O(log skipped_other_timers)"
5137This means that, when you have a watcher that triggers in one hour and
5138there are 100 watchers that would trigger before that, then inserting will
5139have to skip roughly seven (\f(CW\*(C`ld 100\*(C'\fR) of these watchers.
5140.IP "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)" 4
5141.IX Item "Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)"
5142That means that changing a timer costs less than removing/adding them,
5143as only the relative motion in the event queue has to be paid for.
5144.IP "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)" 4
5145.IX Item "Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)"
5146These just add the watcher into an array or at the head of a list.
5147.IP "Stopping check/prepare/idle/fork/async watchers: O(1)" 4
5148.IX Item "Stopping check/prepare/idle/fork/async watchers: O(1)"
5149.PD 0
5150.IP "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % \s-1EV_PID_HASHSIZE\s0))" 4
5151.IX Item "Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))"
5152.PD
5153These watchers are stored in lists, so they need to be walked to find the
5154correct watcher to remove. The lists are usually short (you don't usually
5155have many watchers waiting for the same fd or signal: one is typical, two
5156is rare).
5157.IP "Finding the next timer in each loop iteration: O(1)" 4
5158.IX Item "Finding the next timer in each loop iteration: O(1)"
5159By virtue of using a binary or 4\-heap, the next timer is always found at a
5160fixed position in the storage array.
5161.IP "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)" 4
5162.IX Item "Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)"
5163A change means an I/O watcher gets started or stopped, which requires
5164libev to recalculate its status (and possibly tell the kernel, depending
5165on backend and whether \f(CW\*(C`ev_io_set\*(C'\fR was used).
5166.IP "Activating one watcher (putting it into the pending state): O(1)" 4
5167.IX Item "Activating one watcher (putting it into the pending state): O(1)"
5168.PD 0
5169.IP "Priority handling: O(number_of_priorities)" 4
5170.IX Item "Priority handling: O(number_of_priorities)"
5171.PD
5172Priorities are implemented by allocating some space for each
5173priority. When doing priority-based operations, libev usually has to
5174linearly search all the priorities, but starting/stopping and activating
5175watchers becomes O(1) with respect to priority handling.
5176.IP "Sending an ev_async: O(1)" 4
5177.IX Item "Sending an ev_async: O(1)"
5178.PD 0
5179.IP "Processing ev_async_send: O(number_of_async_watchers)" 4
5180.IX Item "Processing ev_async_send: O(number_of_async_watchers)"
5181.IP "Processing signals: O(max_signal_number)" 4
5182.IX Item "Processing signals: O(max_signal_number)"
5183.PD
5184Sending involves a system call \fIiff\fR there were no other \f(CW\*(C`ev_async_send\*(C'\fR
5185calls in the current loop iteration. Checking for async and signal events
5186involves iterating over all running async watchers or all signal numbers.
5187.SH "PORTING FROM LIBEV 3.X TO 4.X"
5188.IX Header "PORTING FROM LIBEV 3.X TO 4.X"
5189The major version 4 introduced some incompatible changes to the \s-1API\s0.
5190.PP
5191At the moment, the \f(CW\*(C`ev.h\*(C'\fR header file provides compatibility definitions
5192for all changes, so most programs should still compile. The compatibility
5193layer might be removed in later versions of libev, so better update to the
5194new \s-1API\s0 early than late.
5195.ie n .IP """EV_COMPAT3"" backwards compatibility mechanism" 4
5196.el .IP "\f(CWEV_COMPAT3\fR backwards compatibility mechanism" 4
5197.IX Item "EV_COMPAT3 backwards compatibility mechanism"
5198The backward compatibility mechanism can be controlled by
5199\&\f(CW\*(C`EV_COMPAT3\*(C'\fR. See \*(L"\s-1MACROS\s0\*(R" in \s-1PREPROCESSOR\s0 \s-1SYMBOLS\s0 in the \s-1EMBEDDING\s0
5200section.
5201.ie n .IP """ev_default_destroy"" and ""ev_default_fork"" have been removed" 4
5202.el .IP "\f(CWev_default_destroy\fR and \f(CWev_default_fork\fR have been removed" 4
5203.IX Item "ev_default_destroy and ev_default_fork have been removed"
5204These calls can be replaced easily by their \f(CW\*(C`ev_loop_xxx\*(C'\fR counterparts:
5205.Sp
5206.Vb 2
5207\& ev_loop_destroy (EV_DEFAULT_UC);
5208\& ev_loop_fork (EV_DEFAULT);
5209.Ve
5210.IP "function/symbol renames" 4
5211.IX Item "function/symbol renames"
5212A number of functions and symbols have been renamed:
5213.Sp
5214.Vb 3
5215\& ev_loop => ev_run
5216\& EVLOOP_NONBLOCK => EVRUN_NOWAIT
5217\& EVLOOP_ONESHOT => EVRUN_ONCE
5218\&
5219\& ev_unloop => ev_break
5220\& EVUNLOOP_CANCEL => EVBREAK_CANCEL
5221\& EVUNLOOP_ONE => EVBREAK_ONE
5222\& EVUNLOOP_ALL => EVBREAK_ALL
5223\&
5224\& EV_TIMEOUT => EV_TIMER
5225\&
5226\& ev_loop_count => ev_iteration
5227\& ev_loop_depth => ev_depth
5228\& ev_loop_verify => ev_verify
5229.Ve
5230.Sp
5231Most functions working on \f(CW\*(C`struct ev_loop\*(C'\fR objects don't have an
5232\&\f(CW\*(C`ev_loop_\*(C'\fR prefix, so it was removed; \f(CW\*(C`ev_loop\*(C'\fR, \f(CW\*(C`ev_unloop\*(C'\fR and
5233associated constants have been renamed to not collide with the \f(CW\*(C`struct
5234ev_loop\*(C'\fR anymore and \f(CW\*(C`EV_TIMER\*(C'\fR now follows the same naming scheme
5235as all other watcher types. Note that \f(CW\*(C`ev_loop_fork\*(C'\fR is still called
5236\&\f(CW\*(C`ev_loop_fork\*(C'\fR because it would otherwise clash with the \f(CW\*(C`ev_fork\*(C'\fR
5237typedef.
5238.ie n .IP """EV_MINIMAL"" mechanism replaced by ""EV_FEATURES""" 4
5239.el .IP "\f(CWEV_MINIMAL\fR mechanism replaced by \f(CWEV_FEATURES\fR" 4
5240.IX Item "EV_MINIMAL mechanism replaced by EV_FEATURES"
5241The preprocessor symbol \f(CW\*(C`EV_MINIMAL\*(C'\fR has been replaced by a different
5242mechanism, \f(CW\*(C`EV_FEATURES\*(C'\fR. Programs using \f(CW\*(C`EV_MINIMAL\*(C'\fR usually compile
5243and work, but the library code will of course be larger.
5244.SH "GLOSSARY"
5245.IX Header "GLOSSARY"
5246.IP "active" 4
5247.IX Item "active"
5248A watcher is active as long as it has been started and not yet stopped.
5249See \*(L"\s-1WATCHER\s0 \s-1STATES\s0\*(R" for details.
5250.IP "application" 4
5251.IX Item "application"
5252In this document, an application is whatever is using libev.
5253.IP "backend" 4
5254.IX Item "backend"
5255The part of the code dealing with the operating system interfaces.
5256.IP "callback" 4
5257.IX Item "callback"
5258The address of a function that is called when some event has been
5259detected. Callbacks are being passed the event loop, the watcher that
5260received the event, and the actual event bitset.
5261.IP "callback/watcher invocation" 4
5262.IX Item "callback/watcher invocation"
5263The act of calling the callback associated with a watcher.
5264.IP "event" 4
5265.IX Item "event"
5266A change of state of some external event, such as data now being available
5267for reading on a file descriptor, time having passed or simply not having
5268any other events happening anymore.
5269.Sp
5270In libev, events are represented as single bits (such as \f(CW\*(C`EV_READ\*(C'\fR or
5271\&\f(CW\*(C`EV_TIMER\*(C'\fR).
5272.IP "event library" 4
5273.IX Item "event library"
5274A software package implementing an event model and loop.
5275.IP "event loop" 4
5276.IX Item "event loop"
5277An entity that handles and processes external events and converts them
5278into callback invocations.
5279.IP "event model" 4
5280.IX Item "event model"
5281The model used to describe how an event loop handles and processes
5282watchers and events.
5283.IP "pending" 4
5284.IX Item "pending"
5285A watcher is pending as soon as the corresponding event has been
5286detected. See \*(L"\s-1WATCHER\s0 \s-1STATES\s0\*(R" for details.
5287.IP "real time" 4
5288.IX Item "real time"
5289The physical time that is observed. It is apparently strictly monotonic :)
5290.IP "wall-clock time" 4
5291.IX Item "wall-clock time"
5292The time and date as shown on clocks. Unlike real time, it can actually
5293be wrong and jump forwards and backwards, e.g. when the you adjust your
5294clock.
5295.IP "watcher" 4
5296.IX Item "watcher"
5297A data structure that describes interest in certain events. Watchers need
5298to be started (attached to an event loop) before they can receive events.
1826.SH "AUTHOR" 5299.SH "AUTHOR"
1827.IX Header "AUTHOR" 5300.IX Header "AUTHOR"
1828Marc Lehmann <libev@schmorp.de>. 5301Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael
5302Magnusson and Emanuele Giaquinta.

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