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1NAME 1NAME
2 AnyEvent - provide framework for multiple event loops 2 AnyEvent - the DBI of event loop programming
3 3
4 EV, Event, Coro::EV, Coro::Event, Glib, Tk, Perl - various supported 4 EV, Event, Glib, Tk, Perl, Event::Lib, Irssi, rxvt-unicode, IO::Async,
5 event loops 5 Qt and POE are various supported event loops/environments.
6 6
7SYNOPSIS 7SYNOPSIS
8 use AnyEvent; 8 use AnyEvent;
9 9
10 # file descriptor readable
10 my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub { 11 my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });
12
13 # one-shot or repeating timers
14 my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
15 my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...
16
17 print AnyEvent->now; # prints current event loop time
18 print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
19
20 # POSIX signal
21 my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });
22
23 # child process exit
24 my $w = AnyEvent->child (pid => $pid, cb => sub {
25 my ($pid, $status) = @_;
11 ... 26 ...
12 }); 27 });
13 28
14 my $w = AnyEvent->timer (after => $seconds, cb => sub { 29 # called when event loop idle (if applicable)
15 ... 30 my $w = AnyEvent->idle (cb => sub { ... });
16 });
17 31
18 my $w = AnyEvent->condvar; # stores whether a condition was flagged 32 my $w = AnyEvent->condvar; # stores whether a condition was flagged
33 $w->send; # wake up current and all future recv's
19 $w->wait; # enters "main loop" till $condvar gets ->broadcast 34 $w->recv; # enters "main loop" till $condvar gets ->send
20 $w->broadcast; # wake up current and all future wait's 35 # use a condvar in callback mode:
36 $w->cb (sub { $_[0]->recv });
37
38INTRODUCTION/TUTORIAL
39 This manpage is mainly a reference manual. If you are interested in a
40 tutorial or some gentle introduction, have a look at the AnyEvent::Intro
41 manpage.
42
43SUPPORT
44 There is a mailinglist for discussing all things AnyEvent, and an IRC
45 channel, too.
46
47 See the AnyEvent project page at the Schmorpforge Ta-Sa Software
48 Repository, at <http://anyevent.schmorp.de>, for more info.
21 49
22WHY YOU SHOULD USE THIS MODULE (OR NOT) 50WHY YOU SHOULD USE THIS MODULE (OR NOT)
23 Glib, POE, IO::Async, Event... CPAN offers event models by the dozen 51 Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
24 nowadays. So what is different about AnyEvent? 52 nowadays. So what is different about AnyEvent?
25 53
26 Executive Summary: AnyEvent is *compatible*, AnyEvent is *free of 54 Executive Summary: AnyEvent is *compatible*, AnyEvent is *free of
27 policy* and AnyEvent is *small and efficient*. 55 policy* and AnyEvent is *small and efficient*.
28 56
29 First and foremost, *AnyEvent is not an event model* itself, it only 57 First and foremost, *AnyEvent is not an event model* itself, it only
30 interfaces to whatever event model the main program happens to use in a 58 interfaces to whatever event model the main program happens to use, in a
31 pragmatic way. For event models and certain classes of immortals alike, 59 pragmatic way. For event models and certain classes of immortals alike,
32 the statement "there can only be one" is a bitter reality: In general, 60 the statement "there can only be one" is a bitter reality: In general,
33 only one event loop can be active at the same time in a process. 61 only one event loop can be active at the same time in a process.
34 AnyEvent helps hiding the differences between those event loops. 62 AnyEvent cannot change this, but it can hide the differences between
63 those event loops.
35 64
36 The goal of AnyEvent is to offer module authors the ability to do event 65 The goal of AnyEvent is to offer module authors the ability to do event
37 programming (waiting for I/O or timer events) without subscribing to a 66 programming (waiting for I/O or timer events) without subscribing to a
38 religion, a way of living, and most importantly: without forcing your 67 religion, a way of living, and most importantly: without forcing your
39 module users into the same thing by forcing them to use the same event 68 module users into the same thing by forcing them to use the same event
40 model you use. 69 model you use.
41 70
42 For modules like POE or IO::Async (which is a total misnomer as it is 71 For modules like POE or IO::Async (which is a total misnomer as it is
43 actually doing all I/O *synchronously*...), using them in your module is 72 actually doing all I/O *synchronously*...), using them in your module is
44 like joining a cult: After you joined, you are dependent on them and you 73 like joining a cult: After you joined, you are dependent on them and you
45 cannot use anything else, as it is simply incompatible to everything 74 cannot use anything else, as they are simply incompatible to everything
46 that isn't itself. What's worse, all the potential users of your module 75 that isn't them. What's worse, all the potential users of your module
47 are *also* forced to use the same event loop you use. 76 are *also* forced to use the same event loop you use.
48 77
49 AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works 78 AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
50 fine. AnyEvent + Tk works fine etc. etc. but none of these work together 79 fine. AnyEvent + Tk works fine etc. etc. but none of these work together
51 with the rest: POE + IO::Async? no go. Tk + Event? no go. Again: if your 80 with the rest: POE + IO::Async? No go. Tk + Event? No go. Again: if your
52 module uses one of those, every user of your module has to use it, too. 81 module uses one of those, every user of your module has to use it, too.
53 But if your module uses AnyEvent, it works transparently with all event 82 But if your module uses AnyEvent, it works transparently with all event
54 models it supports (including stuff like POE and IO::Async, as long as 83 models it supports (including stuff like IO::Async, as long as those use
55 those use one of the supported event loops. It is trivial to add new 84 one of the supported event loops. It is trivial to add new event loops
56 event loops to AnyEvent, too, so it is future-proof). 85 to AnyEvent, too, so it is future-proof).
57 86
58 In addition to being free of having to use *the one and only true event 87 In addition to being free of having to use *the one and only true event
59 model*, AnyEvent also is free of bloat and policy: with POE or similar 88 model*, AnyEvent also is free of bloat and policy: with POE or similar
60 modules, you get an enourmous amount of code and strict rules you have 89 modules, you get an enormous amount of code and strict rules you have to
61 to follow. AnyEvent, on the other hand, is lean and up to the point, by 90 follow. AnyEvent, on the other hand, is lean and up to the point, by
62 only offering the functionality that is necessary, in as thin as a 91 only offering the functionality that is necessary, in as thin as a
63 wrapper as technically possible. 92 wrapper as technically possible.
64 93
94 Of course, AnyEvent comes with a big (and fully optional!) toolbox of
95 useful functionality, such as an asynchronous DNS resolver, 100%
96 non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
97 such as Windows) and lots of real-world knowledge and workarounds for
98 platform bugs and differences.
99
65 Of course, if you want lots of policy (this can arguably be somewhat 100 Now, if you *do want* lots of policy (this can arguably be somewhat
66 useful) and you want to force your users to use the one and only event 101 useful) and you want to force your users to use the one and only event
67 model, you should *not* use this module. 102 model, you should *not* use this module.
68 103
69DESCRIPTION 104DESCRIPTION
70 AnyEvent provides an identical interface to multiple event loops. This 105 AnyEvent provides an identical interface to multiple event loops. This
… …
75 The interface itself is vaguely similar, but not identical to the Event 110 The interface itself is vaguely similar, but not identical to the Event
76 module. 111 module.
77 112
78 During the first call of any watcher-creation method, the module tries 113 During the first call of any watcher-creation method, the module tries
79 to detect the currently loaded event loop by probing whether one of the 114 to detect the currently loaded event loop by probing whether one of the
80 following modules is already loaded: Coro::EV, Coro::Event, EV, Event, 115 following modules is already loaded: EV, Event, Glib,
81 Glib, Tk. The first one found is used. If none are found, the module 116 AnyEvent::Impl::Perl, Tk, Event::Lib, Qt, POE. The first one found is
82 tries to load these modules in the stated order. The first one that can 117 used. If none are found, the module tries to load these modules
118 (excluding Tk, Event::Lib, Qt and POE as the pure perl adaptor should
119 always succeed) in the order given. The first one that can be
83 be successfully loaded will be used. If, after this, still none could be 120 successfully loaded will be used. If, after this, still none could be
84 found, AnyEvent will fall back to a pure-perl event loop, which is not 121 found, AnyEvent will fall back to a pure-perl event loop, which is not
85 very efficient, but should work everywhere. 122 very efficient, but should work everywhere.
86 123
87 Because AnyEvent first checks for modules that are already loaded, 124 Because AnyEvent first checks for modules that are already loaded,
88 loading an event model explicitly before first using AnyEvent will 125 loading an event model explicitly before first using AnyEvent will
… …
97 starts using it, all bets are off. Maybe you should tell their authors 134 starts using it, all bets are off. Maybe you should tell their authors
98 to use AnyEvent so their modules work together with others seamlessly... 135 to use AnyEvent so their modules work together with others seamlessly...
99 136
100 The pure-perl implementation of AnyEvent is called 137 The pure-perl implementation of AnyEvent is called
101 "AnyEvent::Impl::Perl". Like other event modules you can load it 138 "AnyEvent::Impl::Perl". Like other event modules you can load it
102 explicitly. 139 explicitly and enjoy the high availability of that event loop :)
103 140
104WATCHERS 141WATCHERS
105 AnyEvent has the central concept of a *watcher*, which is an object that 142 AnyEvent has the central concept of a *watcher*, which is an object that
106 stores relevant data for each kind of event you are waiting for, such as 143 stores relevant data for each kind of event you are waiting for, such as
107 the callback to call, the filehandle to watch, etc. 144 the callback to call, the file handle to watch, etc.
108 145
109 These watchers are normal Perl objects with normal Perl lifetime. After 146 These watchers are normal Perl objects with normal Perl lifetime. After
110 creating a watcher it will immediately "watch" for events and invoke the 147 creating a watcher it will immediately "watch" for events and invoke the
111 callback when the event occurs (of course, only when the event model is 148 callback when the event occurs (of course, only when the event model is
112 in control). 149 in control).
113 150
151 Note that callbacks must not permanently change global variables
152 potentially in use by the event loop (such as $_ or $[) and that
153 callbacks must not "die". The former is good programming practise in
154 Perl and the latter stems from the fact that exception handling differs
155 widely between event loops.
156
114 To disable the watcher you have to destroy it (e.g. by setting the 157 To disable the watcher you have to destroy it (e.g. by setting the
115 variable you store it in to "undef" or otherwise deleting all references 158 variable you store it in to "undef" or otherwise deleting all references
116 to it). 159 to it).
117 160
118 All watchers are created by calling a method on the "AnyEvent" class. 161 All watchers are created by calling a method on the "AnyEvent" class.
… …
120 Many watchers either are used with "recursion" (repeating timers for 163 Many watchers either are used with "recursion" (repeating timers for
121 example), or need to refer to their watcher object in other ways. 164 example), or need to refer to their watcher object in other ways.
122 165
123 An any way to achieve that is this pattern: 166 An any way to achieve that is this pattern:
124 167
125 my $w; $w = AnyEvent->type (arg => value ..., cb => sub { 168 my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
126 # you can use $w here, for example to undef it 169 # you can use $w here, for example to undef it
127 undef $w; 170 undef $w;
128 }); 171 });
129 172
130 Note that "my $w; $w =" combination. This is necessary because in Perl, 173 Note that "my $w; $w =" combination. This is necessary because in Perl,
131 my variables are only visible after the statement in which they are 174 my variables are only visible after the statement in which they are
132 declared. 175 declared.
133 176
134 IO WATCHERS 177 I/O WATCHERS
178 $w = AnyEvent->io (
179 fh => <filehandle_or_fileno>,
180 poll => <"r" or "w">,
181 cb => <callback>,
182 );
183
135 You can create an I/O watcher by calling the "AnyEvent->io" method with 184 You can create an I/O watcher by calling the "AnyEvent->io" method with
136 the following mandatory key-value pairs as arguments: 185 the following mandatory key-value pairs as arguments:
137 186
138 "fh" the Perl *file handle* (*not* file descriptor) to watch for events. 187 "fh" is the Perl *file handle* (or a naked file descriptor) to watch for
188 events (AnyEvent might or might not keep a reference to this file
189 handle). Note that only file handles pointing to things for which
190 non-blocking operation makes sense are allowed. This includes sockets,
191 most character devices, pipes, fifos and so on, but not for example
192 files or block devices.
193
139 "poll" must be a string that is either "r" or "w", which creates a 194 "poll" must be a string that is either "r" or "w", which creates a
140 watcher waiting for "r"eadable or "w"ritable events, respectively. "cb" 195 watcher waiting for "r"eadable or "w"ritable events, respectively.
196
141 is the callback to invoke each time the file handle becomes ready. 197 "cb" is the callback to invoke each time the file handle becomes ready.
142 198
143 File handles will be kept alive, so as long as the watcher exists, the 199 Although the callback might get passed parameters, their value and
144 file handle exists, too. 200 presence is undefined and you cannot rely on them. Portable AnyEvent
201 callbacks cannot use arguments passed to I/O watcher callbacks.
145 202
203 The I/O watcher might use the underlying file descriptor or a copy of
146 It is not allowed to close a file handle as long as any watcher is 204 it. You must not close a file handle as long as any watcher is active on
147 active on the underlying file descriptor. 205 the underlying file descriptor.
148 206
149 Some event loops issue spurious readyness notifications, so you should 207 Some event loops issue spurious readyness notifications, so you should
150 always use non-blocking calls when reading/writing from/to your file 208 always use non-blocking calls when reading/writing from/to your file
151 handles. 209 handles.
152 210
153 Example:
154
155 # wait for readability of STDIN, then read a line and disable the watcher 211 Example: wait for readability of STDIN, then read a line and disable the
212 watcher.
213
156 my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub { 214 my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
157 chomp (my $input = <STDIN>); 215 chomp (my $input = <STDIN>);
158 warn "read: $input\n"; 216 warn "read: $input\n";
159 undef $w; 217 undef $w;
160 }); 218 });
161 219
162 TIME WATCHERS 220 TIME WATCHERS
221 $w = AnyEvent->timer (after => <seconds>, cb => <callback>);
222
223 $w = AnyEvent->timer (
224 after => <fractional_seconds>,
225 interval => <fractional_seconds>,
226 cb => <callback>,
227 );
228
163 You can create a time watcher by calling the "AnyEvent->timer" method 229 You can create a time watcher by calling the "AnyEvent->timer" method
164 with the following mandatory arguments: 230 with the following mandatory arguments:
165 231
166 "after" specifies after how many seconds (fractional values are 232 "after" specifies after how many seconds (fractional values are
167 supported) should the timer activate. "cb" the callback to invoke in 233 supported) the callback should be invoked. "cb" is the callback to
168 that case. 234 invoke in that case.
169 235
170 The timer callback will be invoked at most once: if you want a repeating 236 Although the callback might get passed parameters, their value and
171 timer you have to create a new watcher (this is a limitation by both Tk 237 presence is undefined and you cannot rely on them. Portable AnyEvent
172 and Glib). 238 callbacks cannot use arguments passed to time watcher callbacks.
173 239
174 Example: 240 The callback will normally be invoked once only. If you specify another
241 parameter, "interval", as a strictly positive number (> 0), then the
242 callback will be invoked regularly at that interval (in fractional
243 seconds) after the first invocation. If "interval" is specified with a
244 false value, then it is treated as if it were missing.
175 245
246 The callback will be rescheduled before invoking the callback, but no
247 attempt is done to avoid timer drift in most backends, so the interval
248 is only approximate.
249
176 # fire an event after 7.7 seconds 250 Example: fire an event after 7.7 seconds.
251
177 my $w = AnyEvent->timer (after => 7.7, cb => sub { 252 my $w = AnyEvent->timer (after => 7.7, cb => sub {
178 warn "timeout\n"; 253 warn "timeout\n";
179 }); 254 });
180 255
181 # to cancel the timer: 256 # to cancel the timer:
182 undef $w; 257 undef $w;
183 258
184 Example 2:
185
186 # fire an event after 0.5 seconds, then roughly every second 259 Example 2: fire an event after 0.5 seconds, then roughly every second.
187 my $w;
188 260
189 my $cb = sub {
190 # cancel the old timer while creating a new one
191 $w = AnyEvent->timer (after => 1, cb => $cb); 261 my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
262 warn "timeout\n";
192 }; 263 };
193
194 # start the "loop" by creating the first watcher
195 $w = AnyEvent->timer (after => 0.5, cb => $cb);
196 264
197 TIMING ISSUES 265 TIMING ISSUES
198 There are two ways to handle timers: based on real time (relative, "fire 266 There are two ways to handle timers: based on real time (relative, "fire
199 in 10 seconds") and based on wallclock time (absolute, "fire at 12 267 in 10 seconds") and based on wallclock time (absolute, "fire at 12
200 o'clock"). 268 o'clock").
201 269
202 While most event loops expect timers to specified in a relative way, 270 While most event loops expect timers to specified in a relative way,
203 they use absolute time internally. This makes a difference when your 271 they use absolute time internally. This makes a difference when your
204 clock "jumps", for example, when ntp decides to set your clock backwards 272 clock "jumps", for example, when ntp decides to set your clock backwards
205 from the wrong 2014-01-01 to 2008-01-01, a watcher that you created to 273 from the wrong date of 2014-01-01 to 2008-01-01, a watcher that is
206 fire "after" a second might actually take six years to finally fire. 274 supposed to fire "after" a second might actually take six years to
275 finally fire.
207 276
208 AnyEvent cannot compensate for this. The only event loop that is 277 AnyEvent cannot compensate for this. The only event loop that is
209 conscious about these issues is EV, which offers both relative 278 conscious about these issues is EV, which offers both relative
210 (ev_timer) and absolute (ev_periodic) timers. 279 (ev_timer, based on true relative time) and absolute (ev_periodic, based
280 on wallclock time) timers.
211 281
212 AnyEvent always prefers relative timers, if available, matching the 282 AnyEvent always prefers relative timers, if available, matching the
213 AnyEvent API. 283 AnyEvent API.
214 284
285 AnyEvent has two additional methods that return the "current time":
286
287 AnyEvent->time
288 This returns the "current wallclock time" as a fractional number of
289 seconds since the Epoch (the same thing as "time" or
290 "Time::HiRes::time" return, and the result is guaranteed to be
291 compatible with those).
292
293 It progresses independently of any event loop processing, i.e. each
294 call will check the system clock, which usually gets updated
295 frequently.
296
297 AnyEvent->now
298 This also returns the "current wallclock time", but unlike "time",
299 above, this value might change only once per event loop iteration,
300 depending on the event loop (most return the same time as "time",
301 above). This is the time that AnyEvent's timers get scheduled
302 against.
303
304 *In almost all cases (in all cases if you don't care), this is the
305 function to call when you want to know the current time.*
306
307 This function is also often faster then "AnyEvent->time", and thus
308 the preferred method if you want some timestamp (for example,
309 AnyEvent::Handle uses this to update it's activity timeouts).
310
311 The rest of this section is only of relevance if you try to be very
312 exact with your timing, you can skip it without bad conscience.
313
314 For a practical example of when these times differ, consider
315 Event::Lib and EV and the following set-up:
316
317 The event loop is running and has just invoked one of your callback
318 at time=500 (assume no other callbacks delay processing). In your
319 callback, you wait a second by executing "sleep 1" (blocking the
320 process for a second) and then (at time=501) you create a relative
321 timer that fires after three seconds.
322
323 With Event::Lib, "AnyEvent->time" and "AnyEvent->now" will both
324 return 501, because that is the current time, and the timer will be
325 scheduled to fire at time=504 (501 + 3).
326
327 With EV, "AnyEvent->time" returns 501 (as that is the current time),
328 but "AnyEvent->now" returns 500, as that is the time the last event
329 processing phase started. With EV, your timer gets scheduled to run
330 at time=503 (500 + 3).
331
332 In one sense, Event::Lib is more exact, as it uses the current time
333 regardless of any delays introduced by event processing. However,
334 most callbacks do not expect large delays in processing, so this
335 causes a higher drift (and a lot more system calls to get the
336 current time).
337
338 In another sense, EV is more exact, as your timer will be scheduled
339 at the same time, regardless of how long event processing actually
340 took.
341
342 In either case, if you care (and in most cases, you don't), then you
343 can get whatever behaviour you want with any event loop, by taking
344 the difference between "AnyEvent->time" and "AnyEvent->now" into
345 account.
346
347 AnyEvent->now_update
348 Some event loops (such as EV or AnyEvent::Impl::Perl) cache the
349 current time for each loop iteration (see the discussion of
350 AnyEvent->now, above).
351
352 When a callback runs for a long time (or when the process sleeps),
353 then this "current" time will differ substantially from the real
354 time, which might affect timers and time-outs.
355
356 When this is the case, you can call this method, which will update
357 the event loop's idea of "current time".
358
359 A typical example would be a script in a web server (e.g.
360 "mod_perl") - when mod_perl executes the script, then the event loop
361 will have the wrong idea about the "current time" (being potentially
362 far in the past, when the script ran the last time). In that case
363 you should arrange a call to "AnyEvent->now_update" each time the
364 web server process wakes up again (e.g. at the start of your script,
365 or in a handler).
366
367 Note that updating the time *might* cause some events to be handled.
368
215 SIGNAL WATCHERS 369 SIGNAL WATCHERS
370 $w = AnyEvent->signal (signal => <uppercase_signal_name>, cb => <callback>);
371
216 You can watch for signals using a signal watcher, "signal" is the signal 372 You can watch for signals using a signal watcher, "signal" is the signal
217 *name* without any "SIG" prefix, "cb" is the Perl callback to be invoked 373 *name* in uppercase and without any "SIG" prefix, "cb" is the Perl
218 whenever a signal occurs. 374 callback to be invoked whenever a signal occurs.
219 375
376 Although the callback might get passed parameters, their value and
377 presence is undefined and you cannot rely on them. Portable AnyEvent
378 callbacks cannot use arguments passed to signal watcher callbacks.
379
220 Multiple signals occurances can be clumped together into one callback 380 Multiple signal occurrences can be clumped together into one callback
221 invocation, and callback invocation will be synchronous. synchronous 381 invocation, and callback invocation will be synchronous. Synchronous
222 means that it might take a while until the signal gets handled by the 382 means that it might take a while until the signal gets handled by the
223 process, but it is guarenteed not to interrupt any other callbacks. 383 process, but it is guaranteed not to interrupt any other callbacks.
224 384
225 The main advantage of using these watchers is that you can share a 385 The main advantage of using these watchers is that you can share a
226 signal between multiple watchers. 386 signal between multiple watchers, and AnyEvent will ensure that signals
387 will not interrupt your program at bad times.
227 388
228 This watcher might use %SIG, so programs overwriting those signals 389 This watcher might use %SIG (depending on the event loop used), so
229 directly will likely not work correctly. 390 programs overwriting those signals directly will likely not work
391 correctly.
230 392
231 Example: exit on SIGINT 393 Example: exit on SIGINT
232 394
233 my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 }); 395 my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
234 396
397 Signal Races, Delays and Workarounds
398 Many event loops (e.g. Glib, Tk, Qt, IO::Async) do not support attaching
399 callbacks to signals in a generic way, which is a pity, as you cannot do
400 race-free signal handling in perl, requiring C libraries for this.
401 AnyEvent will try to do it's best, which means in some cases, signals
402 will be delayed. The maximum time a signal might be delayed is specified
403 in $AnyEvent::MAX_SIGNAL_LATENCY (default: 10 seconds). This variable
404 can be changed only before the first signal watcher is created, and
405 should be left alone otherwise. This variable determines how often
406 AnyEvent polls for signals (in case a wake-up was missed). Higher values
407 will cause fewer spurious wake-ups, which is better for power and CPU
408 saving.
409
410 All these problems can be avoided by installing the optional
411 Async::Interrupt module, which works with most event loops. It will not
412 work with inherently broken event loops such as Event or Event::Lib (and
413 not with POE currently, as POE does it's own workaround with one-second
414 latency). For those, you just have to suffer the delays.
415
235 CHILD PROCESS WATCHERS 416 CHILD PROCESS WATCHERS
417 $w = AnyEvent->child (pid => <process id>, cb => <callback>);
418
236 You can also watch on a child process exit and catch its exit status. 419 You can also watch on a child process exit and catch its exit status.
237 420
238 The child process is specified by the "pid" argument (if set to 0, it 421 The child process is specified by the "pid" argument (one some backends,
239 watches for any child process exit). The watcher will trigger as often 422 using 0 watches for any child process exit, on others this will croak).
240 as status change for the child are received. This works by installing a 423 The watcher will be triggered only when the child process has finished
241 signal handler for "SIGCHLD". The callback will be called with the pid 424 and an exit status is available, not on any trace events
242 and exit status (as returned by waitpid). 425 (stopped/continued).
243 426
244 Example: wait for pid 1333 427 The callback will be called with the pid and exit status (as returned by
428 waitpid), so unlike other watcher types, you *can* rely on child watcher
429 callback arguments.
245 430
431 This watcher type works by installing a signal handler for "SIGCHLD",
432 and since it cannot be shared, nothing else should use SIGCHLD or reap
433 random child processes (waiting for specific child processes, e.g.
434 inside "system", is just fine).
435
436 There is a slight catch to child watchers, however: you usually start
437 them *after* the child process was created, and this means the process
438 could have exited already (and no SIGCHLD will be sent anymore).
439
440 Not all event models handle this correctly (neither POE nor IO::Async
441 do, see their AnyEvent::Impl manpages for details), but even for event
442 models that *do* handle this correctly, they usually need to be loaded
443 before the process exits (i.e. before you fork in the first place).
444 AnyEvent's pure perl event loop handles all cases correctly regardless
445 of when you start the watcher.
446
447 This means you cannot create a child watcher as the very first thing in
448 an AnyEvent program, you *have* to create at least one watcher before
449 you "fork" the child (alternatively, you can call "AnyEvent::detect").
450
451 As most event loops do not support waiting for child events, they will
452 be emulated by AnyEvent in most cases, in which the latency and race
453 problems mentioned in the description of signal watchers apply.
454
455 Example: fork a process and wait for it
456
457 my $done = AnyEvent->condvar;
458
459 my $pid = fork or exit 5;
460
246 my $w = AnyEvent->child ( 461 my $w = AnyEvent->child (
247 pid => 1333, 462 pid => $pid,
248 cb => sub { 463 cb => sub {
249 my ($pid, $status) = @_; 464 my ($pid, $status) = @_;
250 warn "pid $pid exited with status $status"; 465 warn "pid $pid exited with status $status";
466 $done->send;
251 }, 467 },
252 ); 468 );
469
470 # do something else, then wait for process exit
471 $done->recv;
472
473 IDLE WATCHERS
474 $w = AnyEvent->idle (cb => <callback>);
475
476 Sometimes there is a need to do something, but it is not so important to
477 do it instantly, but only when there is nothing better to do. This
478 "nothing better to do" is usually defined to be "no other events need
479 attention by the event loop".
480
481 Idle watchers ideally get invoked when the event loop has nothing better
482 to do, just before it would block the process to wait for new events.
483 Instead of blocking, the idle watcher is invoked.
484
485 Most event loops unfortunately do not really support idle watchers (only
486 EV, Event and Glib do it in a usable fashion) - for the rest, AnyEvent
487 will simply call the callback "from time to time".
488
489 Example: read lines from STDIN, but only process them when the program
490 is otherwise idle:
491
492 my @lines; # read data
493 my $idle_w;
494 my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
495 push @lines, scalar <STDIN>;
496
497 # start an idle watcher, if not already done
498 $idle_w ||= AnyEvent->idle (cb => sub {
499 # handle only one line, when there are lines left
500 if (my $line = shift @lines) {
501 print "handled when idle: $line";
502 } else {
503 # otherwise disable the idle watcher again
504 undef $idle_w;
505 }
506 });
507 });
253 508
254 CONDITION VARIABLES 509 CONDITION VARIABLES
510 $cv = AnyEvent->condvar;
511
512 $cv->send (<list>);
513 my @res = $cv->recv;
514
515 If you are familiar with some event loops you will know that all of them
516 require you to run some blocking "loop", "run" or similar function that
517 will actively watch for new events and call your callbacks.
518
519 AnyEvent is slightly different: it expects somebody else to run the
520 event loop and will only block when necessary (usually when told by the
521 user).
522
523 The instrument to do that is called a "condition variable", so called
524 because they represent a condition that must become true.
525
526 Now is probably a good time to look at the examples further below.
527
255 Condition variables can be created by calling the "AnyEvent->condvar" 528 Condition variables can be created by calling the "AnyEvent->condvar"
256 method without any arguments. 529 method, usually without arguments. The only argument pair allowed is
530 "cb", which specifies a callback to be called when the condition
531 variable becomes true, with the condition variable as the first argument
532 (but not the results).
257 533
258 A condition variable waits for a condition - precisely that the 534 After creation, the condition variable is "false" until it becomes
259 "->broadcast" method has been called. 535 "true" by calling the "send" method (or calling the condition variable
536 as if it were a callback, read about the caveats in the description for
537 the "->send" method).
260 538
261 They are very useful to signal that a condition has been fulfilled, for 539 Condition variables are similar to callbacks, except that you can
540 optionally wait for them. They can also be called merge points - points
541 in time where multiple outstanding events have been processed. And yet
542 another way to call them is transactions - each condition variable can
543 be used to represent a transaction, which finishes at some point and
544 delivers a result. And yet some people know them as "futures" - a
545 promise to compute/deliver something that you can wait for.
546
547 Condition variables are very useful to signal that something has
262 example, if you write a module that does asynchronous http requests, 548 finished, for example, if you write a module that does asynchronous http
263 then a condition variable would be the ideal candidate to signal the 549 requests, then a condition variable would be the ideal candidate to
264 availability of results. 550 signal the availability of results. The user can either act when the
551 callback is called or can synchronously "->recv" for the results.
265 552
266 You can also use condition variables to block your main program until an 553 You can also use them to simulate traditional event loops - for example,
267 event occurs - for example, you could "->wait" in your main program 554 you can block your main program until an event occurs - for example, you
268 until the user clicks the Quit button in your app, which would 555 could "->recv" in your main program until the user clicks the Quit
269 "->broadcast" the "quit" event. 556 button of your app, which would "->send" the "quit" event.
270 557
271 Note that condition variables recurse into the event loop - if you have 558 Note that condition variables recurse into the event loop - if you have
272 two pirces of code that call "->wait" in a round-robbin fashion, you 559 two pieces of code that call "->recv" in a round-robin fashion, you
273 lose. Therefore, condition variables are good to export to your caller, 560 lose. Therefore, condition variables are good to export to your caller,
274 but you should avoid making a blocking wait yourself, at least in 561 but you should avoid making a blocking wait yourself, at least in
275 callbacks, as this asks for trouble. 562 callbacks, as this asks for trouble.
276 563
277 This object has two methods: 564 Condition variables are represented by hash refs in perl, and the keys
565 used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy
566 (it is often useful to build your own transaction class on top of
567 AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call
568 it's "new" method in your own "new" method.
278 569
279 $cv->wait 570 There are two "sides" to a condition variable - the "producer side"
280 Wait (blocking if necessary) until the "->broadcast" method has been 571 which eventually calls "-> send", and the "consumer side", which waits
281 called on c<$cv>, while servicing other watchers normally. 572 for the send to occur.
282 573
283 You can only wait once on a condition - additional calls will return 574 Example: wait for a timer.
284 immediately.
285
286 Not all event models support a blocking wait - some die in that case
287 (programs might want to do that to stay interactive), so *if you are
288 using this from a module, never require a blocking wait*, but let
289 the caller decide whether the call will block or not (for example,
290 by coupling condition variables with some kind of request results
291 and supporting callbacks so the caller knows that getting the result
292 will not block, while still suppporting blocking waits if the caller
293 so desires).
294
295 Another reason *never* to "->wait" in a module is that you cannot
296 sensibly have two "->wait"'s in parallel, as that would require
297 multiple interpreters or coroutines/threads, none of which
298 "AnyEvent" can supply (the coroutine-aware backends
299 AnyEvent::Impl::CoroEV and AnyEvent::Impl::CoroEvent explicitly
300 support concurrent "->wait"'s from different coroutines, however).
301
302 $cv->broadcast
303 Flag the condition as ready - a running "->wait" and all further
304 calls to "wait" will (eventually) return after this method has been
305 called. If nobody is waiting the broadcast will be remembered..
306
307 Example:
308 575
309 # wait till the result is ready 576 # wait till the result is ready
310 my $result_ready = AnyEvent->condvar; 577 my $result_ready = AnyEvent->condvar;
311 578
312 # do something such as adding a timer 579 # do something such as adding a timer
313 # or socket watcher the calls $result_ready->broadcast 580 # or socket watcher the calls $result_ready->send
314 # when the "result" is ready. 581 # when the "result" is ready.
315 # in this case, we simply use a timer: 582 # in this case, we simply use a timer:
316 my $w = AnyEvent->timer ( 583 my $w = AnyEvent->timer (
317 after => 1, 584 after => 1,
318 cb => sub { $result_ready->broadcast }, 585 cb => sub { $result_ready->send },
319 ); 586 );
320 587
321 # this "blocks" (while handling events) till the watcher 588 # this "blocks" (while handling events) till the callback
322 # calls broadcast 589 # calls ->send
323 $result_ready->wait; 590 $result_ready->recv;
591
592 Example: wait for a timer, but take advantage of the fact that condition
593 variables are also callable directly.
594
595 my $done = AnyEvent->condvar;
596 my $delay = AnyEvent->timer (after => 5, cb => $done);
597 $done->recv;
598
599 Example: Imagine an API that returns a condvar and doesn't support
600 callbacks. This is how you make a synchronous call, for example from the
601 main program:
602
603 use AnyEvent::CouchDB;
604
605 ...
606
607 my @info = $couchdb->info->recv;
608
609 And this is how you would just set a callback to be called whenever the
610 results are available:
611
612 $couchdb->info->cb (sub {
613 my @info = $_[0]->recv;
614 });
615
616 METHODS FOR PRODUCERS
617 These methods should only be used by the producing side, i.e. the
618 code/module that eventually sends the signal. Note that it is also the
619 producer side which creates the condvar in most cases, but it isn't
620 uncommon for the consumer to create it as well.
621
622 $cv->send (...)
623 Flag the condition as ready - a running "->recv" and all further
624 calls to "recv" will (eventually) return after this method has been
625 called. If nobody is waiting the send will be remembered.
626
627 If a callback has been set on the condition variable, it is called
628 immediately from within send.
629
630 Any arguments passed to the "send" call will be returned by all
631 future "->recv" calls.
632
633 Condition variables are overloaded so one can call them directly (as
634 if they were a code reference). Calling them directly is the same as
635 calling "send".
636
637 $cv->croak ($error)
638 Similar to send, but causes all call's to "->recv" to invoke
639 "Carp::croak" with the given error message/object/scalar.
640
641 This can be used to signal any errors to the condition variable
642 user/consumer. Doing it this way instead of calling "croak" directly
643 delays the error detetcion, but has the overwhelmign advantage that
644 it diagnoses the error at the place where the result is expected,
645 and not deep in some event clalback without connection to the actual
646 code causing the problem.
647
648 $cv->begin ([group callback])
649 $cv->end
650 These two methods can be used to combine many transactions/events
651 into one. For example, a function that pings many hosts in parallel
652 might want to use a condition variable for the whole process.
653
654 Every call to "->begin" will increment a counter, and every call to
655 "->end" will decrement it. If the counter reaches 0 in "->end", the
656 (last) callback passed to "begin" will be executed, passing the
657 condvar as first argument. That callback is *supposed* to call
658 "->send", but that is not required. If no group callback was set,
659 "send" will be called without any arguments.
660
661 You can think of "$cv->send" giving you an OR condition (one call
662 sends), while "$cv->begin" and "$cv->end" giving you an AND
663 condition (all "begin" calls must be "end"'ed before the condvar
664 sends).
665
666 Let's start with a simple example: you have two I/O watchers (for
667 example, STDOUT and STDERR for a program), and you want to wait for
668 both streams to close before activating a condvar:
669
670 my $cv = AnyEvent->condvar;
671
672 $cv->begin; # first watcher
673 my $w1 = AnyEvent->io (fh => $fh1, cb => sub {
674 defined sysread $fh1, my $buf, 4096
675 or $cv->end;
676 });
677
678 $cv->begin; # second watcher
679 my $w2 = AnyEvent->io (fh => $fh2, cb => sub {
680 defined sysread $fh2, my $buf, 4096
681 or $cv->end;
682 });
683
684 $cv->recv;
685
686 This works because for every event source (EOF on file handle),
687 there is one call to "begin", so the condvar waits for all calls to
688 "end" before sending.
689
690 The ping example mentioned above is slightly more complicated, as
691 the there are results to be passwd back, and the number of tasks
692 that are begung can potentially be zero:
693
694 my $cv = AnyEvent->condvar;
695
696 my %result;
697 $cv->begin (sub { shift->send (\%result) });
698
699 for my $host (@list_of_hosts) {
700 $cv->begin;
701 ping_host_then_call_callback $host, sub {
702 $result{$host} = ...;
703 $cv->end;
704 };
705 }
706
707 $cv->end;
708
709 This code fragment supposedly pings a number of hosts and calls
710 "send" after results for all then have have been gathered - in any
711 order. To achieve this, the code issues a call to "begin" when it
712 starts each ping request and calls "end" when it has received some
713 result for it. Since "begin" and "end" only maintain a counter, the
714 order in which results arrive is not relevant.
715
716 There is an additional bracketing call to "begin" and "end" outside
717 the loop, which serves two important purposes: first, it sets the
718 callback to be called once the counter reaches 0, and second, it
719 ensures that "send" is called even when "no" hosts are being pinged
720 (the loop doesn't execute once).
721
722 This is the general pattern when you "fan out" into multiple (but
723 potentially none) subrequests: use an outer "begin"/"end" pair to
724 set the callback and ensure "end" is called at least once, and then,
725 for each subrequest you start, call "begin" and for each subrequest
726 you finish, call "end".
727
728 METHODS FOR CONSUMERS
729 These methods should only be used by the consuming side, i.e. the code
730 awaits the condition.
731
732 $cv->recv
733 Wait (blocking if necessary) until the "->send" or "->croak" methods
734 have been called on c<$cv>, while servicing other watchers normally.
735
736 You can only wait once on a condition - additional calls are valid
737 but will return immediately.
738
739 If an error condition has been set by calling "->croak", then this
740 function will call "croak".
741
742 In list context, all parameters passed to "send" will be returned,
743 in scalar context only the first one will be returned.
744
745 Note that doing a blocking wait in a callback is not supported by
746 any event loop, that is, recursive invocation of a blocking "->recv"
747 is not allowed, and the "recv" call will "croak" if such a condition
748 is detected. This condition can be slightly loosened by using
749 Coro::AnyEvent, which allows you to do a blocking "->recv" from any
750 thread that doesn't run the event loop itself.
751
752 Not all event models support a blocking wait - some die in that case
753 (programs might want to do that to stay interactive), so *if you are
754 using this from a module, never require a blocking wait*. Instead,
755 let the caller decide whether the call will block or not (for
756 example, by coupling condition variables with some kind of request
757 results and supporting callbacks so the caller knows that getting
758 the result will not block, while still supporting blocking waits if
759 the caller so desires).
760
761 You can ensure that "-recv" never blocks by setting a callback and
762 only calling "->recv" from within that callback (or at a later
763 time). This will work even when the event loop does not support
764 blocking waits otherwise.
765
766 $bool = $cv->ready
767 Returns true when the condition is "true", i.e. whether "send" or
768 "croak" have been called.
769
770 $cb = $cv->cb ($cb->($cv))
771 This is a mutator function that returns the callback set and
772 optionally replaces it before doing so.
773
774 The callback will be called when the condition becomes (or already
775 was) "true", i.e. when "send" or "croak" are called (or were
776 called), with the only argument being the condition variable itself.
777 Calling "recv" inside the callback or at any later time is
778 guaranteed not to block.
779
780SUPPORTED EVENT LOOPS/BACKENDS
781 The available backend classes are (every class has its own manpage):
782
783 Backends that are autoprobed when no other event loop can be found.
784 EV is the preferred backend when no other event loop seems to be in
785 use. If EV is not installed, then AnyEvent will fall back to its own
786 pure-perl implementation, which is available everywhere as it comes
787 with AnyEvent itself.
788
789 AnyEvent::Impl::EV based on EV (interface to libev, best choice).
790 AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
791
792 Backends that are transparently being picked up when they are used.
793 These will be used when they are currently loaded when the first
794 watcher is created, in which case it is assumed that the application
795 is using them. This means that AnyEvent will automatically pick the
796 right backend when the main program loads an event module before
797 anything starts to create watchers. Nothing special needs to be done
798 by the main program.
799
800 AnyEvent::Impl::Event based on Event, very stable, few glitches.
801 AnyEvent::Impl::Glib based on Glib, slow but very stable.
802 AnyEvent::Impl::Tk based on Tk, very broken.
803 AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
804 AnyEvent::Impl::POE based on POE, very slow, some limitations.
805 AnyEvent::Impl::Irssi used when running within irssi.
806
807 Backends with special needs.
808 Qt requires the Qt::Application to be instantiated first, but will
809 otherwise be picked up automatically. As long as the main program
810 instantiates the application before any AnyEvent watchers are
811 created, everything should just work.
812
813 AnyEvent::Impl::Qt based on Qt.
814
815 Support for IO::Async can only be partial, as it is too broken and
816 architecturally limited to even support the AnyEvent API. It also is
817 the only event loop that needs the loop to be set explicitly, so it
818 can only be used by a main program knowing about AnyEvent. See
819 AnyEvent::Impl::Async for the gory details.
820
821 AnyEvent::Impl::IOAsync based on IO::Async, cannot be autoprobed.
822
823 Event loops that are indirectly supported via other backends.
824 Some event loops can be supported via other modules:
825
826 There is no direct support for WxWidgets (Wx) or Prima.
827
828 WxWidgets has no support for watching file handles. However, you can
829 use WxWidgets through the POE adaptor, as POE has a Wx backend that
830 simply polls 20 times per second, which was considered to be too
831 horrible to even consider for AnyEvent.
832
833 Prima is not supported as nobody seems to be using it, but it has a
834 POE backend, so it can be supported through POE.
835
836 AnyEvent knows about both Prima and Wx, however, and will try to
837 load POE when detecting them, in the hope that POE will pick them
838 up, in which case everything will be automatic.
324 839
325GLOBAL VARIABLES AND FUNCTIONS 840GLOBAL VARIABLES AND FUNCTIONS
841 These are not normally required to use AnyEvent, but can be useful to
842 write AnyEvent extension modules.
843
326 $AnyEvent::MODEL 844 $AnyEvent::MODEL
327 Contains "undef" until the first watcher is being created. Then it 845 Contains "undef" until the first watcher is being created, before
846 the backend has been autodetected.
847
328 contains the event model that is being used, which is the name of 848 Afterwards it contains the event model that is being used, which is
329 the Perl class implementing the model. This class is usually one of 849 the name of the Perl class implementing the model. This class is
330 the "AnyEvent::Impl:xxx" modules, but can be any other class in the 850 usually one of the "AnyEvent::Impl:xxx" modules, but can be any
331 case AnyEvent has been extended at runtime (e.g. in *rxvt-unicode*). 851 other class in the case AnyEvent has been extended at runtime (e.g.
332 852 in *rxvt-unicode* it will be "urxvt::anyevent").
333 The known classes so far are:
334
335 AnyEvent::Impl::CoroEV based on Coro::EV, best choice.
336 AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
337 AnyEvent::Impl::EV based on EV (an interface to libev, also best choice).
338 AnyEvent::Impl::Event based on Event, also second best choice :)
339 AnyEvent::Impl::Glib based on Glib, third-best choice.
340 AnyEvent::Impl::Tk based on Tk, very bad choice.
341 AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable.
342 853
343 AnyEvent::detect 854 AnyEvent::detect
344 Returns $AnyEvent::MODEL, forcing autodetection of the event model 855 Returns $AnyEvent::MODEL, forcing autodetection of the event model
345 if necessary. You should only call this function right before you 856 if necessary. You should only call this function right before you
346 would have created an AnyEvent watcher anyway, that is, as late as 857 would have created an AnyEvent watcher anyway, that is, as late as
347 possible at runtime. 858 possible at runtime, and not e.g. while initialising of your module.
859
860 If you need to do some initialisation before AnyEvent watchers are
861 created, use "post_detect".
862
863 $guard = AnyEvent::post_detect { BLOCK }
864 Arranges for the code block to be executed as soon as the event
865 model is autodetected (or immediately if this has already happened).
866
867 The block will be executed *after* the actual backend has been
868 detected ($AnyEvent::MODEL is set), but *before* any watchers have
869 been created, so it is possible to e.g. patch @AnyEvent::ISA or do
870 other initialisations - see the sources of AnyEvent::Strict or
871 AnyEvent::AIO to see how this is used.
872
873 The most common usage is to create some global watchers, without
874 forcing event module detection too early, for example, AnyEvent::AIO
875 creates and installs the global IO::AIO watcher in a "post_detect"
876 block to avoid autodetecting the event module at load time.
877
878 If called in scalar or list context, then it creates and returns an
879 object that automatically removes the callback again when it is
880 destroyed (or "undef" when the hook was immediately executed). See
881 AnyEvent::AIO for a case where this is useful.
882
883 Example: Create a watcher for the IO::AIO module and store it in
884 $WATCHER. Only do so after the event loop is initialised, though.
885
886 our WATCHER;
887
888 my $guard = AnyEvent::post_detect {
889 $WATCHER = AnyEvent->io (fh => IO::AIO::poll_fileno, poll => 'r', cb => \&IO::AIO::poll_cb);
890 };
891
892 # the ||= is important in case post_detect immediately runs the block,
893 # as to not clobber the newly-created watcher. assigning both watcher and
894 # post_detect guard to the same variable has the advantage of users being
895 # able to just C<undef $WATCHER> if the watcher causes them grief.
896
897 $WATCHER ||= $guard;
898
899 @AnyEvent::post_detect
900 If there are any code references in this array (you can "push" to it
901 before or after loading AnyEvent), then they will called directly
902 after the event loop has been chosen.
903
904 You should check $AnyEvent::MODEL before adding to this array,
905 though: if it is defined then the event loop has already been
906 detected, and the array will be ignored.
907
908 Best use "AnyEvent::post_detect { BLOCK }" when your application
909 allows it,as it takes care of these details.
910
911 This variable is mainly useful for modules that can do something
912 useful when AnyEvent is used and thus want to know when it is
913 initialised, but do not need to even load it by default. This array
914 provides the means to hook into AnyEvent passively, without loading
915 it.
348 916
349WHAT TO DO IN A MODULE 917WHAT TO DO IN A MODULE
350 As a module author, you should "use AnyEvent" and call AnyEvent methods 918 As a module author, you should "use AnyEvent" and call AnyEvent methods
351 freely, but you should not load a specific event module or rely on it. 919 freely, but you should not load a specific event module or rely on it.
352 920
353 Be careful when you create watchers in the module body - AnyEvent will 921 Be careful when you create watchers in the module body - AnyEvent will
354 decide which event module to use as soon as the first method is called, 922 decide which event module to use as soon as the first method is called,
355 so by calling AnyEvent in your module body you force the user of your 923 so by calling AnyEvent in your module body you force the user of your
356 module to load the event module first. 924 module to load the event module first.
357 925
358 Never call "->wait" on a condition variable unless you *know* that the 926 Never call "->recv" on a condition variable unless you *know* that the
359 "->broadcast" method has been called on it already. This is because it 927 "->send" method has been called on it already. This is because it will
360 will stall the whole program, and the whole point of using events is to 928 stall the whole program, and the whole point of using events is to stay
361 stay interactive. 929 interactive.
362 930
363 It is fine, however, to call "->wait" when the user of your module 931 It is fine, however, to call "->recv" when the user of your module
364 requests it (i.e. if you create a http request object ad have a method 932 requests it (i.e. if you create a http request object ad have a method
365 called "results" that returns the results, it should call "->wait" 933 called "results" that returns the results, it should call "->recv"
366 freely, as the user of your module knows what she is doing. always). 934 freely, as the user of your module knows what she is doing. always).
367 935
368WHAT TO DO IN THE MAIN PROGRAM 936WHAT TO DO IN THE MAIN PROGRAM
369 There will always be a single main program - the only place that should 937 There will always be a single main program - the only place that should
370 dictate which event model to use. 938 dictate which event model to use.
… …
372 If it doesn't care, it can just "use AnyEvent" and use it itself, or not 940 If it doesn't care, it can just "use AnyEvent" and use it itself, or not
373 do anything special (it does not need to be event-based) and let 941 do anything special (it does not need to be event-based) and let
374 AnyEvent decide which implementation to chose if some module relies on 942 AnyEvent decide which implementation to chose if some module relies on
375 it. 943 it.
376 944
377 If the main program relies on a specific event model. For example, in 945 If the main program relies on a specific event model - for example, in
378 Gtk2 programs you have to rely on the Glib module. You should load the 946 Gtk2 programs you have to rely on the Glib module - you should load the
379 event module before loading AnyEvent or any module that uses it: 947 event module before loading AnyEvent or any module that uses it:
380 generally speaking, you should load it as early as possible. The reason 948 generally speaking, you should load it as early as possible. The reason
381 is that modules might create watchers when they are loaded, and AnyEvent 949 is that modules might create watchers when they are loaded, and AnyEvent
382 will decide on the event model to use as soon as it creates watchers, 950 will decide on the event model to use as soon as it creates watchers,
383 and it might chose the wrong one unless you load the correct one 951 and it might chose the wrong one unless you load the correct one
384 yourself. 952 yourself.
385 953
386 You can chose to use a rather inefficient pure-perl implementation by 954 You can chose to use a pure-perl implementation by loading the
387 loading the "AnyEvent::Impl::Perl" module, which gives you similar 955 "AnyEvent::Impl::Perl" module, which gives you similar behaviour
388 behaviour everywhere, but letting AnyEvent chose is generally better. 956 everywhere, but letting AnyEvent chose the model is generally better.
957
958 MAINLOOP EMULATION
959 Sometimes (often for short test scripts, or even standalone programs who
960 only want to use AnyEvent), you do not want to run a specific event
961 loop.
962
963 In that case, you can use a condition variable like this:
964
965 AnyEvent->condvar->recv;
966
967 This has the effect of entering the event loop and looping forever.
968
969 Note that usually your program has some exit condition, in which case it
970 is better to use the "traditional" approach of storing a condition
971 variable somewhere, waiting for it, and sending it when the program
972 should exit cleanly.
973
974OTHER MODULES
975 The following is a non-exhaustive list of additional modules that use
976 AnyEvent as a client and can therefore be mixed easily with other
977 AnyEvent modules and other event loops in the same program. Some of the
978 modules come with AnyEvent, most are available via CPAN.
979
980 AnyEvent::Util
981 Contains various utility functions that replace often-used but
982 blocking functions such as "inet_aton" by event-/callback-based
983 versions.
984
985 AnyEvent::Socket
986 Provides various utility functions for (internet protocol) sockets,
987 addresses and name resolution. Also functions to create non-blocking
988 tcp connections or tcp servers, with IPv6 and SRV record support and
989 more.
990
991 AnyEvent::Handle
992 Provide read and write buffers, manages watchers for reads and
993 writes, supports raw and formatted I/O, I/O queued and fully
994 transparent and non-blocking SSL/TLS (via AnyEvent::TLS.
995
996 AnyEvent::DNS
997 Provides rich asynchronous DNS resolver capabilities.
998
999 AnyEvent::HTTP
1000 A simple-to-use HTTP library that is capable of making a lot of
1001 concurrent HTTP requests.
1002
1003 AnyEvent::HTTPD
1004 Provides a simple web application server framework.
1005
1006 AnyEvent::FastPing
1007 The fastest ping in the west.
1008
1009 AnyEvent::DBI
1010 Executes DBI requests asynchronously in a proxy process.
1011
1012 AnyEvent::AIO
1013 Truly asynchronous I/O, should be in the toolbox of every event
1014 programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
1015 together.
1016
1017 AnyEvent::BDB
1018 Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently
1019 fuses BDB and AnyEvent together.
1020
1021 AnyEvent::GPSD
1022 A non-blocking interface to gpsd, a daemon delivering GPS
1023 information.
1024
1025 AnyEvent::IRC
1026 AnyEvent based IRC client module family (replacing the older
1027 Net::IRC3).
1028
1029 AnyEvent::XMPP
1030 AnyEvent based XMPP (Jabber protocol) module family (replacing the
1031 older Net::XMPP2>.
1032
1033 AnyEvent::IGS
1034 A non-blocking interface to the Internet Go Server protocol (used by
1035 App::IGS).
1036
1037 Net::FCP
1038 AnyEvent-based implementation of the Freenet Client Protocol,
1039 birthplace of AnyEvent.
1040
1041 Event::ExecFlow
1042 High level API for event-based execution flow control.
1043
1044 Coro
1045 Has special support for AnyEvent via Coro::AnyEvent.
1046
1047SIMPLIFIED AE API
1048 Starting with version 5.0, AnyEvent officially supports a second, much
1049 simpler, API that is designed to reduce the calling, typing and memory
1050 overhead.
1051
1052 See the AE manpage for details.
1053
1054ERROR AND EXCEPTION HANDLING
1055 In general, AnyEvent does not do any error handling - it relies on the
1056 caller to do that if required. The AnyEvent::Strict module (see also the
1057 "PERL_ANYEVENT_STRICT" environment variable, below) provides strict
1058 checking of all AnyEvent methods, however, which is highly useful during
1059 development.
1060
1061 As for exception handling (i.e. runtime errors and exceptions thrown
1062 while executing a callback), this is not only highly event-loop
1063 specific, but also not in any way wrapped by this module, as this is the
1064 job of the main program.
1065
1066 The pure perl event loop simply re-throws the exception (usually within
1067 "condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",
1068 Glib uses "install_exception_handler" and so on.
1069
1070ENVIRONMENT VARIABLES
1071 The following environment variables are used by this module or its
1072 submodules.
1073
1074 Note that AnyEvent will remove *all* environment variables starting with
1075 "PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
1076 enabled.
1077
1078 "PERL_ANYEVENT_VERBOSE"
1079 By default, AnyEvent will be completely silent except in fatal
1080 conditions. You can set this environment variable to make AnyEvent
1081 more talkative.
1082
1083 When set to 1 or higher, causes AnyEvent to warn about unexpected
1084 conditions, such as not being able to load the event model specified
1085 by "PERL_ANYEVENT_MODEL".
1086
1087 When set to 2 or higher, cause AnyEvent to report to STDERR which
1088 event model it chooses.
1089
1090 When set to 8 or higher, then AnyEvent will report extra information
1091 on which optional modules it loads and how it implements certain
1092 features.
1093
1094 "PERL_ANYEVENT_STRICT"
1095 AnyEvent does not do much argument checking by default, as thorough
1096 argument checking is very costly. Setting this variable to a true
1097 value will cause AnyEvent to load "AnyEvent::Strict" and then to
1098 thoroughly check the arguments passed to most method calls. If it
1099 finds any problems, it will croak.
1100
1101 In other words, enables "strict" mode.
1102
1103 Unlike "use strict" (or it's modern cousin, "use common::sense", it
1104 is definitely recommended to keep it off in production. Keeping
1105 "PERL_ANYEVENT_STRICT=1" in your environment while developing
1106 programs can be very useful, however.
1107
1108 "PERL_ANYEVENT_MODEL"
1109 This can be used to specify the event model to be used by AnyEvent,
1110 before auto detection and -probing kicks in. It must be a string
1111 consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
1112 gets prepended and the resulting module name is loaded and if the
1113 load was successful, used as event model. If it fails to load
1114 AnyEvent will proceed with auto detection and -probing.
1115
1116 This functionality might change in future versions.
1117
1118 For example, to force the pure perl model (AnyEvent::Impl::Perl) you
1119 could start your program like this:
1120
1121 PERL_ANYEVENT_MODEL=Perl perl ...
1122
1123 "PERL_ANYEVENT_PROTOCOLS"
1124 Used by both AnyEvent::DNS and AnyEvent::Socket to determine
1125 preferences for IPv4 or IPv6. The default is unspecified (and might
1126 change, or be the result of auto probing).
1127
1128 Must be set to a comma-separated list of protocols or address
1129 families, current supported: "ipv4" and "ipv6". Only protocols
1130 mentioned will be used, and preference will be given to protocols
1131 mentioned earlier in the list.
1132
1133 This variable can effectively be used for denial-of-service attacks
1134 against local programs (e.g. when setuid), although the impact is
1135 likely small, as the program has to handle conenction and other
1136 failures anyways.
1137
1138 Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
1139 IPv6, but support both and try to use both.
1140 "PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
1141 resolve or contact IPv6 addresses.
1142 "PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but
1143 prefer IPv6 over IPv4.
1144
1145 "PERL_ANYEVENT_EDNS0"
1146 Used by AnyEvent::DNS to decide whether to use the EDNS0 extension
1147 for DNS. This extension is generally useful to reduce DNS traffic,
1148 but some (broken) firewalls drop such DNS packets, which is why it
1149 is off by default.
1150
1151 Setting this variable to 1 will cause AnyEvent::DNS to announce
1152 EDNS0 in its DNS requests.
1153
1154 "PERL_ANYEVENT_MAX_FORKS"
1155 The maximum number of child processes that
1156 "AnyEvent::Util::fork_call" will create in parallel.
1157
1158 "PERL_ANYEVENT_MAX_OUTSTANDING_DNS"
1159 The default value for the "max_outstanding" parameter for the
1160 default DNS resolver - this is the maximum number of parallel DNS
1161 requests that are sent to the DNS server.
1162
1163 "PERL_ANYEVENT_RESOLV_CONF"
1164 The file to use instead of /etc/resolv.conf (or OS-specific
1165 configuration) in the default resolver. When set to the empty
1166 string, no default config will be used.
1167
1168 "PERL_ANYEVENT_CA_FILE", "PERL_ANYEVENT_CA_PATH".
1169 When neither "ca_file" nor "ca_path" was specified during
1170 AnyEvent::TLS context creation, and either of these environment
1171 variables exist, they will be used to specify CA certificate
1172 locations instead of a system-dependent default.
1173
1174 "PERL_ANYEVENT_AVOID_GUARD" and "PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT"
1175 When these are set to 1, then the respective modules are not loaded.
1176 Mostly good for testing AnyEvent itself.
389 1177
390SUPPLYING YOUR OWN EVENT MODEL INTERFACE 1178SUPPLYING YOUR OWN EVENT MODEL INTERFACE
391 This is an advanced topic that you do not normally need to use AnyEvent 1179 This is an advanced topic that you do not normally need to use AnyEvent
392 in a module. This section is only of use to event loop authors who want 1180 in a module. This section is only of use to event loop authors who want
393 to provide AnyEvent compatibility. 1181 to provide AnyEvent compatibility.
… …
428 *rxvt-unicode* also cheats a bit by not providing blocking access to 1216 *rxvt-unicode* also cheats a bit by not providing blocking access to
429 condition variables: code blocking while waiting for a condition will 1217 condition variables: code blocking while waiting for a condition will
430 "die". This still works with most modules/usages, and blocking calls 1218 "die". This still works with most modules/usages, and blocking calls
431 must not be done in an interactive application, so it makes sense. 1219 must not be done in an interactive application, so it makes sense.
432 1220
433ENVIRONMENT VARIABLES
434 The following environment variables are used by this module:
435
436 "PERL_ANYEVENT_VERBOSE" when set to 2 or higher, cause AnyEvent to
437 report to STDERR which event model it chooses.
438
439EXAMPLE PROGRAM 1221EXAMPLE PROGRAM
440 The following program uses an IO watcher to read data from STDIN, a 1222 The following program uses an I/O watcher to read data from STDIN, a
441 timer to display a message once per second, and a condition variable to 1223 timer to display a message once per second, and a condition variable to
442 quit the program when the user enters quit: 1224 quit the program when the user enters quit:
443 1225
444 use AnyEvent; 1226 use AnyEvent;
445 1227
… …
450 poll => 'r', 1232 poll => 'r',
451 cb => sub { 1233 cb => sub {
452 warn "io event <$_[0]>\n"; # will always output <r> 1234 warn "io event <$_[0]>\n"; # will always output <r>
453 chomp (my $input = <STDIN>); # read a line 1235 chomp (my $input = <STDIN>); # read a line
454 warn "read: $input\n"; # output what has been read 1236 warn "read: $input\n"; # output what has been read
455 $cv->broadcast if $input =~ /^q/i; # quit program if /^q/i 1237 $cv->send if $input =~ /^q/i; # quit program if /^q/i
456 }, 1238 },
457 ); 1239 );
458 1240
459 my $time_watcher; # can only be used once
460
461 sub new_timer {
462 $timer = AnyEvent->timer (after => 1, cb => sub { 1241 my $time_watcher = AnyEvent->timer (after => 1, interval => 1, cb => sub {
463 warn "timeout\n"; # print 'timeout' about every second 1242 warn "timeout\n"; # print 'timeout' at most every second
464 &new_timer; # and restart the time
465 });
466 } 1243 });
467 1244
468 new_timer; # create first timer
469
470 $cv->wait; # wait until user enters /^q/i 1245 $cv->recv; # wait until user enters /^q/i
471 1246
472REAL-WORLD EXAMPLE 1247REAL-WORLD EXAMPLE
473 Consider the Net::FCP module. It features (among others) the following 1248 Consider the Net::FCP module. It features (among others) the following
474 API calls, which are to freenet what HTTP GET requests are to http: 1249 API calls, which are to freenet what HTTP GET requests are to http:
475 1250
… …
524 syswrite $txn->{fh}, $txn->{request} 1299 syswrite $txn->{fh}, $txn->{request}
525 or die "connection or write error"; 1300 or die "connection or write error";
526 $txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r }); 1301 $txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
527 1302
528 Again, "fh_ready_r" waits till all data has arrived, and then stores the 1303 Again, "fh_ready_r" waits till all data has arrived, and then stores the
529 result and signals any possible waiters that the request ahs finished: 1304 result and signals any possible waiters that the request has finished:
530 1305
531 sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf}; 1306 sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
532 1307
533 if (end-of-file or data complete) { 1308 if (end-of-file or data complete) {
534 $txn->{result} = $txn->{buf}; 1309 $txn->{result} = $txn->{buf};
535 $txn->{finished}->broadcast; 1310 $txn->{finished}->send;
536 $txb->{cb}->($txn) of $txn->{cb}; # also call callback 1311 $txb->{cb}->($txn) of $txn->{cb}; # also call callback
537 } 1312 }
538 1313
539 The "result" method, finally, just waits for the finished signal (if the 1314 The "result" method, finally, just waits for the finished signal (if the
540 request was already finished, it doesn't wait, of course, and returns 1315 request was already finished, it doesn't wait, of course, and returns
541 the data: 1316 the data:
542 1317
543 $txn->{finished}->wait; 1318 $txn->{finished}->recv;
544 return $txn->{result}; 1319 return $txn->{result};
545 1320
546 The actual code goes further and collects all errors ("die"s, 1321 The actual code goes further and collects all errors ("die"s,
547 exceptions) that occured during request processing. The "result" method 1322 exceptions) that occurred during request processing. The "result" method
548 detects whether an exception as thrown (it is stored inside the $txn 1323 detects whether an exception as thrown (it is stored inside the $txn
549 object) and just throws the exception, which means connection errors and 1324 object) and just throws the exception, which means connection errors and
550 other problems get reported tot he code that tries to use the result, 1325 other problems get reported tot he code that tries to use the result,
551 not in a random callback. 1326 not in a random callback.
552 1327
… …
583 1358
584 my $quit = AnyEvent->condvar; 1359 my $quit = AnyEvent->condvar;
585 1360
586 $fcp->txn_client_get ($url)->cb (sub { 1361 $fcp->txn_client_get ($url)->cb (sub {
587 ... 1362 ...
588 $quit->broadcast; 1363 $quit->send;
589 }); 1364 });
590 1365
591 $quit->wait; 1366 $quit->recv;
1367
1368BENCHMARKS
1369 To give you an idea of the performance and overheads that AnyEvent adds
1370 over the event loops themselves and to give you an impression of the
1371 speed of various event loops I prepared some benchmarks.
1372
1373 BENCHMARKING ANYEVENT OVERHEAD
1374 Here is a benchmark of various supported event models used natively and
1375 through AnyEvent. The benchmark creates a lot of timers (with a zero
1376 timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
1377 which it is), lets them fire exactly once and destroys them again.
1378
1379 Source code for this benchmark is found as eg/bench in the AnyEvent
1380 distribution. It uses the AE interface, which makes a real difference
1381 for the EV and Perl backends only.
1382
1383 Explanation of the columns
1384 *watcher* is the number of event watchers created/destroyed. Since
1385 different event models feature vastly different performances, each event
1386 loop was given a number of watchers so that overall runtime is
1387 acceptable and similar between tested event loop (and keep them from
1388 crashing): Glib would probably take thousands of years if asked to
1389 process the same number of watchers as EV in this benchmark.
1390
1391 *bytes* is the number of bytes (as measured by the resident set size,
1392 RSS) consumed by each watcher. This method of measuring captures both C
1393 and Perl-based overheads.
1394
1395 *create* is the time, in microseconds (millionths of seconds), that it
1396 takes to create a single watcher. The callback is a closure shared
1397 between all watchers, to avoid adding memory overhead. That means
1398 closure creation and memory usage is not included in the figures.
1399
1400 *invoke* is the time, in microseconds, used to invoke a simple callback.
1401 The callback simply counts down a Perl variable and after it was invoked
1402 "watcher" times, it would "->send" a condvar once to signal the end of
1403 this phase.
1404
1405 *destroy* is the time, in microseconds, that it takes to destroy a
1406 single watcher.
1407
1408 Results
1409 name watchers bytes create invoke destroy comment
1410 EV/EV 100000 223 0.47 0.43 0.27 EV native interface
1411 EV/Any 100000 223 0.48 0.42 0.26 EV + AnyEvent watchers
1412 Coro::EV/Any 100000 223 0.47 0.42 0.26 coroutines + Coro::Signal
1413 Perl/Any 100000 431 2.70 0.74 0.92 pure perl implementation
1414 Event/Event 16000 516 31.16 31.84 0.82 Event native interface
1415 Event/Any 16000 1203 42.61 34.79 1.80 Event + AnyEvent watchers
1416 IOAsync/Any 16000 1911 41.92 27.45 16.81 via IO::Async::Loop::IO_Poll
1417 IOAsync/Any 16000 1726 40.69 26.37 15.25 via IO::Async::Loop::Epoll
1418 Glib/Any 16000 1118 89.00 12.57 51.17 quadratic behaviour
1419 Tk/Any 2000 1346 20.96 10.75 8.00 SEGV with >> 2000 watchers
1420 POE/Any 2000 6951 108.97 795.32 14.24 via POE::Loop::Event
1421 POE/Any 2000 6648 94.79 774.40 575.51 via POE::Loop::Select
1422
1423 Discussion
1424 The benchmark does *not* measure scalability of the event loop very
1425 well. For example, a select-based event loop (such as the pure perl one)
1426 can never compete with an event loop that uses epoll when the number of
1427 file descriptors grows high. In this benchmark, all events become ready
1428 at the same time, so select/poll-based implementations get an unnatural
1429 speed boost.
1430
1431 Also, note that the number of watchers usually has a nonlinear effect on
1432 overall speed, that is, creating twice as many watchers doesn't take
1433 twice the time - usually it takes longer. This puts event loops tested
1434 with a higher number of watchers at a disadvantage.
1435
1436 To put the range of results into perspective, consider that on the
1437 benchmark machine, handling an event takes roughly 1600 CPU cycles with
1438 EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000
1439 CPU cycles with POE.
1440
1441 "EV" is the sole leader regarding speed and memory use, which are both
1442 maximal/minimal, respectively. When using the AE API there is zero
1443 overhead (when going through the AnyEvent API create is about 5-6 times
1444 slower, with other times being equal, so still uses far less memory than
1445 any other event loop and is still faster than Event natively).
1446
1447 The pure perl implementation is hit in a few sweet spots (both the
1448 constant timeout and the use of a single fd hit optimisations in the
1449 perl interpreter and the backend itself). Nevertheless this shows that
1450 it adds very little overhead in itself. Like any select-based backend
1451 its performance becomes really bad with lots of file descriptors (and
1452 few of them active), of course, but this was not subject of this
1453 benchmark.
1454
1455 The "Event" module has a relatively high setup and callback invocation
1456 cost, but overall scores in on the third place.
1457
1458 "IO::Async" performs admirably well, about on par with "Event", even
1459 when using its pure perl backend.
1460
1461 "Glib"'s memory usage is quite a bit higher, but it features a faster
1462 callback invocation and overall ends up in the same class as "Event".
1463 However, Glib scales extremely badly, doubling the number of watchers
1464 increases the processing time by more than a factor of four, making it
1465 completely unusable when using larger numbers of watchers (note that
1466 only a single file descriptor was used in the benchmark, so
1467 inefficiencies of "poll" do not account for this).
1468
1469 The "Tk" adaptor works relatively well. The fact that it crashes with
1470 more than 2000 watchers is a big setback, however, as correctness takes
1471 precedence over speed. Nevertheless, its performance is surprising, as
1472 the file descriptor is dup()ed for each watcher. This shows that the
1473 dup() employed by some adaptors is not a big performance issue (it does
1474 incur a hidden memory cost inside the kernel which is not reflected in
1475 the figures above).
1476
1477 "POE", regardless of underlying event loop (whether using its pure perl
1478 select-based backend or the Event module, the POE-EV backend couldn't be
1479 tested because it wasn't working) shows abysmal performance and memory
1480 usage with AnyEvent: Watchers use almost 30 times as much memory as EV
1481 watchers, and 10 times as much memory as Event (the high memory
1482 requirements are caused by requiring a session for each watcher).
1483 Watcher invocation speed is almost 900 times slower than with AnyEvent's
1484 pure perl implementation.
1485
1486 The design of the POE adaptor class in AnyEvent can not really account
1487 for the performance issues, though, as session creation overhead is
1488 small compared to execution of the state machine, which is coded pretty
1489 optimally within AnyEvent::Impl::POE (and while everybody agrees that
1490 using multiple sessions is not a good approach, especially regarding
1491 memory usage, even the author of POE could not come up with a faster
1492 design).
1493
1494 Summary
1495 * Using EV through AnyEvent is faster than any other event loop (even
1496 when used without AnyEvent), but most event loops have acceptable
1497 performance with or without AnyEvent.
1498
1499 * The overhead AnyEvent adds is usually much smaller than the overhead
1500 of the actual event loop, only with extremely fast event loops such
1501 as EV adds AnyEvent significant overhead.
1502
1503 * You should avoid POE like the plague if you want performance or
1504 reasonable memory usage.
1505
1506 BENCHMARKING THE LARGE SERVER CASE
1507 This benchmark actually benchmarks the event loop itself. It works by
1508 creating a number of "servers": each server consists of a socket pair, a
1509 timeout watcher that gets reset on activity (but never fires), and an
1510 I/O watcher waiting for input on one side of the socket. Each time the
1511 socket watcher reads a byte it will write that byte to a random other
1512 "server".
1513
1514 The effect is that there will be a lot of I/O watchers, only part of
1515 which are active at any one point (so there is a constant number of
1516 active fds for each loop iteration, but which fds these are is random).
1517 The timeout is reset each time something is read because that reflects
1518 how most timeouts work (and puts extra pressure on the event loops).
1519
1520 In this benchmark, we use 10000 socket pairs (20000 sockets), of which
1521 100 (1%) are active. This mirrors the activity of large servers with
1522 many connections, most of which are idle at any one point in time.
1523
1524 Source code for this benchmark is found as eg/bench2 in the AnyEvent
1525 distribution. It uses the AE interface, which makes a real difference
1526 for the EV and Perl backends only.
1527
1528 Explanation of the columns
1529 *sockets* is the number of sockets, and twice the number of "servers"
1530 (as each server has a read and write socket end).
1531
1532 *create* is the time it takes to create a socket pair (which is
1533 nontrivial) and two watchers: an I/O watcher and a timeout watcher.
1534
1535 *request*, the most important value, is the time it takes to handle a
1536 single "request", that is, reading the token from the pipe and
1537 forwarding it to another server. This includes deleting the old timeout
1538 and creating a new one that moves the timeout into the future.
1539
1540 Results
1541 name sockets create request
1542 EV 20000 62.66 7.99
1543 Perl 20000 68.32 32.64
1544 IOAsync 20000 174.06 101.15 epoll
1545 IOAsync 20000 174.67 610.84 poll
1546 Event 20000 202.69 242.91
1547 Glib 20000 557.01 1689.52
1548 POE 20000 341.54 12086.32 uses POE::Loop::Event
1549
1550 Discussion
1551 This benchmark *does* measure scalability and overall performance of the
1552 particular event loop.
1553
1554 EV is again fastest. Since it is using epoll on my system, the setup
1555 time is relatively high, though.
1556
1557 Perl surprisingly comes second. It is much faster than the C-based event
1558 loops Event and Glib.
1559
1560 IO::Async performs very well when using its epoll backend, and still
1561 quite good compared to Glib when using its pure perl backend.
1562
1563 Event suffers from high setup time as well (look at its code and you
1564 will understand why). Callback invocation also has a high overhead
1565 compared to the "$_->() for .."-style loop that the Perl event loop
1566 uses. Event uses select or poll in basically all documented
1567 configurations.
1568
1569 Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
1570 clearly fails to perform with many filehandles or in busy servers.
1571
1572 POE is still completely out of the picture, taking over 1000 times as
1573 long as EV, and over 100 times as long as the Perl implementation, even
1574 though it uses a C-based event loop in this case.
1575
1576 Summary
1577 * The pure perl implementation performs extremely well.
1578
1579 * Avoid Glib or POE in large projects where performance matters.
1580
1581 BENCHMARKING SMALL SERVERS
1582 While event loops should scale (and select-based ones do not...) even to
1583 large servers, most programs we (or I :) actually write have only a few
1584 I/O watchers.
1585
1586 In this benchmark, I use the same benchmark program as in the large
1587 server case, but it uses only eight "servers", of which three are active
1588 at any one time. This should reflect performance for a small server
1589 relatively well.
1590
1591 The columns are identical to the previous table.
1592
1593 Results
1594 name sockets create request
1595 EV 16 20.00 6.54
1596 Perl 16 25.75 12.62
1597 Event 16 81.27 35.86
1598 Glib 16 32.63 15.48
1599 POE 16 261.87 276.28 uses POE::Loop::Event
1600
1601 Discussion
1602 The benchmark tries to test the performance of a typical small server.
1603 While knowing how various event loops perform is interesting, keep in
1604 mind that their overhead in this case is usually not as important, due
1605 to the small absolute number of watchers (that is, you need efficiency
1606 and speed most when you have lots of watchers, not when you only have a
1607 few of them).
1608
1609 EV is again fastest.
1610
1611 Perl again comes second. It is noticeably faster than the C-based event
1612 loops Event and Glib, although the difference is too small to really
1613 matter.
1614
1615 POE also performs much better in this case, but is is still far behind
1616 the others.
1617
1618 Summary
1619 * C-based event loops perform very well with small number of watchers,
1620 as the management overhead dominates.
1621
1622 THE IO::Lambda BENCHMARK
1623 Recently I was told about the benchmark in the IO::Lambda manpage, which
1624 could be misinterpreted to make AnyEvent look bad. In fact, the
1625 benchmark simply compares IO::Lambda with POE, and IO::Lambda looks
1626 better (which shouldn't come as a surprise to anybody). As such, the
1627 benchmark is fine, and mostly shows that the AnyEvent backend from
1628 IO::Lambda isn't very optimal. But how would AnyEvent compare when used
1629 without the extra baggage? To explore this, I wrote the equivalent
1630 benchmark for AnyEvent.
1631
1632 The benchmark itself creates an echo-server, and then, for 500 times,
1633 connects to the echo server, sends a line, waits for the reply, and then
1634 creates the next connection. This is a rather bad benchmark, as it
1635 doesn't test the efficiency of the framework or much non-blocking I/O,
1636 but it is a benchmark nevertheless.
1637
1638 name runtime
1639 Lambda/select 0.330 sec
1640 + optimized 0.122 sec
1641 Lambda/AnyEvent 0.327 sec
1642 + optimized 0.138 sec
1643 Raw sockets/select 0.077 sec
1644 POE/select, components 0.662 sec
1645 POE/select, raw sockets 0.226 sec
1646 POE/select, optimized 0.404 sec
1647
1648 AnyEvent/select/nb 0.085 sec
1649 AnyEvent/EV/nb 0.068 sec
1650 +state machine 0.134 sec
1651
1652 The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
1653 benchmarks actually make blocking connects and use 100% blocking I/O,
1654 defeating the purpose of an event-based solution. All of the newly
1655 written AnyEvent benchmarks use 100% non-blocking connects (using
1656 AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
1657 resolver), so AnyEvent is at a disadvantage here, as non-blocking
1658 connects generally require a lot more bookkeeping and event handling
1659 than blocking connects (which involve a single syscall only).
1660
1661 The last AnyEvent benchmark additionally uses AnyEvent::Handle, which
1662 offers similar expressive power as POE and IO::Lambda, using
1663 conventional Perl syntax. This means that both the echo server and the
1664 client are 100% non-blocking, further placing it at a disadvantage.
1665
1666 As you can see, the AnyEvent + EV combination even beats the
1667 hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
1668 backend easily beats IO::Lambda and POE.
1669
1670 And even the 100% non-blocking version written using the high-level (and
1671 slow :) AnyEvent::Handle abstraction beats both POE and IO::Lambda
1672 higher level ("unoptimised") abstractions by a large margin, even though
1673 it does all of DNS, tcp-connect and socket I/O in a non-blocking way.
1674
1675 The two AnyEvent benchmarks programs can be found as eg/ae0.pl and
1676 eg/ae2.pl in the AnyEvent distribution, the remaining benchmarks are
1677 part of the IO::Lambda distribution and were used without any changes.
1678
1679SIGNALS
1680 AnyEvent currently installs handlers for these signals:
1681
1682 SIGCHLD
1683 A handler for "SIGCHLD" is installed by AnyEvent's child watcher
1684 emulation for event loops that do not support them natively. Also,
1685 some event loops install a similar handler.
1686
1687 Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE,
1688 then AnyEvent will reset it to default, to avoid losing child exit
1689 statuses.
1690
1691 SIGPIPE
1692 A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is
1693 "undef" when AnyEvent gets loaded.
1694
1695 The rationale for this is that AnyEvent users usually do not really
1696 depend on SIGPIPE delivery (which is purely an optimisation for
1697 shell use, or badly-written programs), but "SIGPIPE" can cause
1698 spurious and rare program exits as a lot of people do not expect
1699 "SIGPIPE" when writing to some random socket.
1700
1701 The rationale for installing a no-op handler as opposed to ignoring
1702 it is that this way, the handler will be restored to defaults on
1703 exec.
1704
1705 Feel free to install your own handler, or reset it to defaults.
1706
1707RECOMMENDED/OPTIONAL MODULES
1708 One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
1709 it's built-in modules) are required to use it.
1710
1711 That does not mean that AnyEvent won't take advantage of some additional
1712 modules if they are installed.
1713
1714 This section epxlains which additional modules will be used, and how
1715 they affect AnyEvent's operetion.
1716
1717 Async::Interrupt
1718 This slightly arcane module is used to implement fast signal
1719 handling: To my knowledge, there is no way to do completely
1720 race-free and quick signal handling in pure perl. To ensure that
1721 signals still get delivered, AnyEvent will start an interval timer
1722 to wake up perl (and catch the signals) with some delay (default is
1723 10 seconds, look for $AnyEvent::MAX_SIGNAL_LATENCY).
1724
1725 If this module is available, then it will be used to implement
1726 signal catching, which means that signals will not be delayed, and
1727 the event loop will not be interrupted regularly, which is more
1728 efficient (And good for battery life on laptops).
1729
1730 This affects not just the pure-perl event loop, but also other event
1731 loops that have no signal handling on their own (e.g. Glib, Tk, Qt).
1732
1733 Some event loops (POE, Event, Event::Lib) offer signal watchers
1734 natively, and either employ their own workarounds (POE) or use
1735 AnyEvent's workaround (using $AnyEvent::MAX_SIGNAL_LATENCY).
1736 Installing Async::Interrupt does nothing for those backends.
1737
1738 EV This module isn't really "optional", as it is simply one of the
1739 backend event loops that AnyEvent can use. However, it is simply the
1740 best event loop available in terms of features, speed and stability:
1741 It supports the AnyEvent API optimally, implements all the watcher
1742 types in XS, does automatic timer adjustments even when no monotonic
1743 clock is available, can take avdantage of advanced kernel interfaces
1744 such as "epoll" and "kqueue", and is the fastest backend *by far*.
1745 You can even embed Glib/Gtk2 in it (or vice versa, see EV::Glib and
1746 Glib::EV).
1747
1748 Guard
1749 The guard module, when used, will be used to implement
1750 "AnyEvent::Util::guard". This speeds up guards considerably (and
1751 uses a lot less memory), but otherwise doesn't affect guard
1752 operation much. It is purely used for performance.
1753
1754 JSON and JSON::XS
1755 One of these modules is required when you want to read or write JSON
1756 data via AnyEvent::Handle. It is also written in pure-perl, but can
1757 take advantage of the ultra-high-speed JSON::XS module when it is
1758 installed.
1759
1760 In fact, AnyEvent::Handle will use JSON::XS by default if it is
1761 installed.
1762
1763 Net::SSLeay
1764 Implementing TLS/SSL in Perl is certainly interesting, but not very
1765 worthwhile: If this module is installed, then AnyEvent::Handle (with
1766 the help of AnyEvent::TLS), gains the ability to do TLS/SSL.
1767
1768 Time::HiRes
1769 This module is part of perl since release 5.008. It will be used
1770 when the chosen event library does not come with a timing source on
1771 it's own. The pure-perl event loop (AnyEvent::Impl::Perl) will
1772 additionally use it to try to use a monotonic clock for timing
1773 stability.
1774
1775FORK
1776 Most event libraries are not fork-safe. The ones who are usually are
1777 because they rely on inefficient but fork-safe "select" or "poll" calls.
1778 Only EV is fully fork-aware.
1779
1780 If you have to fork, you must either do so *before* creating your first
1781 watcher OR you must not use AnyEvent at all in the child OR you must do
1782 something completely out of the scope of AnyEvent.
1783
1784SECURITY CONSIDERATIONS
1785 AnyEvent can be forced to load any event model via
1786 $ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used
1787 to execute arbitrary code or directly gain access, it can easily be used
1788 to make the program hang or malfunction in subtle ways, as AnyEvent
1789 watchers will not be active when the program uses a different event
1790 model than specified in the variable.
1791
1792 You can make AnyEvent completely ignore this variable by deleting it
1793 before the first watcher gets created, e.g. with a "BEGIN" block:
1794
1795 BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
1796
1797 use AnyEvent;
1798
1799 Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
1800 be used to probe what backend is used and gain other information (which
1801 is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),
1802 and $ENV{PERL_ANYEVENT_STRICT}.
1803
1804 Note that AnyEvent will remove *all* environment variables starting with
1805 "PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
1806 enabled.
1807
1808BUGS
1809 Perl 5.8 has numerous memleaks that sometimes hit this module and are
1810 hard to work around. If you suffer from memleaks, first upgrade to Perl
1811 5.10 and check wether the leaks still show up. (Perl 5.10.0 has other
1812 annoying memleaks, such as leaking on "map" and "grep" but it is usually
1813 not as pronounced).
592 1814
593SEE ALSO 1815SEE ALSO
594 Event modules: Coro::EV, EV, EV::Glib, Glib::EV, Coro::Event, Event, 1816 Utility functions: AnyEvent::Util.
595 Glib::Event, Glib, Coro, Tk.
596 1817
597 Implementations: AnyEvent::Impl::CoroEV, AnyEvent::Impl::EV, 1818 Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,
598 AnyEvent::Impl::CoroEvent, AnyEvent::Impl::Event, AnyEvent::Impl::Glib, 1819 Event::Lib, Qt, POE.
1820
1821 Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
1822 AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
1823 AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE,
599 AnyEvent::Impl::Tk, AnyEvent::Impl::Perl. 1824 AnyEvent::Impl::IOAsync, Anyevent::Impl::Irssi.
600 1825
1826 Non-blocking file handles, sockets, TCP clients and servers:
1827 AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS.
1828
1829 Asynchronous DNS: AnyEvent::DNS.
1830
1831 Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,
1832
601 Nontrivial usage examples: Net::FCP, Net::XMPP2. 1833 Nontrivial usage examples: AnyEvent::GPSD, AnyEvent::XMPP,
1834 AnyEvent::HTTP.
602 1835
603AUTHOR 1836AUTHOR
604 Marc Lehmann <schmorp@schmorp.de> 1837 Marc Lehmann <schmorp@schmorp.de>
605 http://home.schmorp.de/ 1838 http://home.schmorp.de/
606 1839

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