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1=> NAME 1NAME
2 AnyEvent - provide framework for multiple event loops 2 AnyEvent - the DBI of event loop programming
3 3
4 EV, Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event 4 EV, Event, Glib, Tk, UV, Perl, Event::Lib, Irssi, rxvt-unicode,
5 loops 5 IO::Async, Qt, FLTK and POE are various supported event
6 loops/environments.
6 7
7SYNOPSIS 8SYNOPSIS
8 use AnyEvent; 9 use AnyEvent;
9 10
11 # if you prefer function calls, look at the AE manpage for
12 # an alternative API.
13
14 # file handle or descriptor readable
10 my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub { 15 my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });
16
17 # one-shot or repeating timers
18 my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
19 my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...);
20
21 print AnyEvent->now; # prints current event loop time
22 print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
23
24 # POSIX signal
25 my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });
26
27 # child process exit
28 my $w = AnyEvent->child (pid => $pid, cb => sub {
29 my ($pid, $status) = @_;
11 ... 30 ...
12 }); 31 });
13 32
14 my $w = AnyEvent->timer (after => $seconds, cb => sub { 33 # called when event loop idle (if applicable)
15 ... 34 my $w = AnyEvent->idle (cb => sub { ... });
16 });
17 35
18 my $w = AnyEvent->condvar; # stores whether a condition was flagged 36 my $w = AnyEvent->condvar; # stores whether a condition was flagged
19 $w->send; # wake up current and all future recv's 37 $w->send; # wake up current and all future recv's
20 $w->recv; # enters "main loop" till $condvar gets ->send 38 $w->recv; # enters "main loop" till $condvar gets ->send
39 # use a condvar in callback mode:
40 $w->cb (sub { $_[0]->recv });
41
42INTRODUCTION/TUTORIAL
43 This manpage is mainly a reference manual. If you are interested in a
44 tutorial or some gentle introduction, have a look at the AnyEvent::Intro
45 manpage.
46
47SUPPORT
48 An FAQ document is available as AnyEvent::FAQ.
49
50 There also is a mailinglist for discussing all things AnyEvent, and an
51 IRC channel, too.
52
53 See the AnyEvent project page at the Schmorpforge Ta-Sa Software
54 Repository, at <http://anyevent.schmorp.de>, for more info.
21 55
22WHY YOU SHOULD USE THIS MODULE (OR NOT) 56WHY YOU SHOULD USE THIS MODULE (OR NOT)
23 Glib, POE, IO::Async, Event... CPAN offers event models by the dozen 57 Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
24 nowadays. So what is different about AnyEvent? 58 nowadays. So what is different about AnyEvent?
25 59
26 Executive Summary: AnyEvent is *compatible*, AnyEvent is *free of 60 Executive Summary: AnyEvent is *compatible*, AnyEvent is *free of
27 policy* and AnyEvent is *small and efficient*. 61 policy* and AnyEvent is *small and efficient*.
28 62
29 First and foremost, *AnyEvent is not an event model* itself, it only 63 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 64 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, 65 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, 66 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. 67 only one event loop can be active at the same time in a process.
34 AnyEvent helps hiding the differences between those event loops. 68 AnyEvent cannot change this, but it can hide the differences between
69 those event loops.
35 70
36 The goal of AnyEvent is to offer module authors the ability to do event 71 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 72 programming (waiting for I/O or timer events) without subscribing to a
38 religion, a way of living, and most importantly: without forcing your 73 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 74 module users into the same thing by forcing them to use the same event
40 model you use. 75 model you use.
41 76
42 For modules like POE or IO::Async (which is a total misnomer as it is 77 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 78 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 79 like joining a cult: After you join, you are dependent on them and you
45 cannot use anything else, as it is simply incompatible to everything 80 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 81 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. 82 are *also* forced to use the same event loop you use.
48 83
49 AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works 84 AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
50 fine. AnyEvent + Tk works fine etc. etc. but none of these work together 85 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 86 with the rest: POE + EV? No go. Tk + Event? No go. Again: if your module
52 module uses one of those, every user of your module has to use it, too. 87 uses one of those, every user of your module has to use it, too. But if
53 But if your module uses AnyEvent, it works transparently with all event 88 your module uses AnyEvent, it works transparently with all event models
54 models it supports (including stuff like POE and IO::Async, as long as 89 it supports (including stuff like IO::Async, as long as those use one of
55 those use one of the supported event loops. It is trivial to add new 90 the supported event loops. It is easy to add new event loops to
56 event loops to AnyEvent, too, so it is future-proof). 91 AnyEvent, too, so it is future-proof).
57 92
58 In addition to being free of having to use *the one and only true event 93 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 94 model*, AnyEvent also is free of bloat and policy: with POE or similar
60 modules, you get an enormous amount of code and strict rules you have to 95 modules, you get an enormous amount of code and strict rules you have to
61 follow. AnyEvent, on the other hand, is lean and up to the point, by 96 follow. AnyEvent, on the other hand, is lean and to the point, by only
62 only offering the functionality that is necessary, in as thin as a 97 offering the functionality that is necessary, in as thin as a wrapper as
63 wrapper as technically possible. 98 technically possible.
64 99
100 Of course, AnyEvent comes with a big (and fully optional!) toolbox of
101 useful functionality, such as an asynchronous DNS resolver, 100%
102 non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
103 such as Windows) and lots of real-world knowledge and workarounds for
104 platform bugs and differences.
105
65 Of course, if you want lots of policy (this can arguably be somewhat 106 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 107 useful) and you want to force your users to use the one and only event
67 model, you should *not* use this module. 108 model, you should *not* use this module.
68 109
69DESCRIPTION 110DESCRIPTION
70 AnyEvent provides an identical interface to multiple event loops. This 111 AnyEvent provides a uniform interface to various event loops. This
71 allows module authors to utilise an event loop without forcing module 112 allows module authors to use event loop functionality without forcing
72 users to use the same event loop (as only a single event loop can 113 module users to use a specific event loop implementation (since more
73 coexist peacefully at any one time). 114 than one event loop cannot coexist peacefully).
74 115
75 The interface itself is vaguely similar, but not identical to the Event 116 The interface itself is vaguely similar, but not identical to the Event
76 module. 117 module.
77 118
78 During the first call of any watcher-creation method, the module tries 119 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 120 to detect the currently loaded event loop by probing whether one of the
80 following modules is already loaded: EV, Event, Glib, 121 following modules is already loaded: EV, AnyEvent::Loop, Event, Glib,
81 AnyEvent::Impl::Perl, Tk, Event::Lib, Qt, POE. The first one found is 122 Tk, Event::Lib, Qt, POE. The first one found is used. If none are
82 used. If none are found, the module tries to load these modules 123 detected, the module tries to load the first four modules in the order
83 (excluding Tk, Event::Lib, Qt and POE as the pure perl adaptor should 124 given; but note that if EV is not available, the pure-perl
84 always succeed) in the order given. The first one that can be 125 AnyEvent::Loop should always work, so the other two are not normally
85 successfully loaded will be used. If, after this, still none could be 126 tried.
86 found, AnyEvent will fall back to a pure-perl event loop, which is not
87 very efficient, but should work everywhere.
88 127
89 Because AnyEvent first checks for modules that are already loaded, 128 Because AnyEvent first checks for modules that are already loaded,
90 loading an event model explicitly before first using AnyEvent will 129 loading an event model explicitly before first using AnyEvent will
91 likely make that model the default. For example: 130 likely make that model the default. For example:
92 131
… …
94 use AnyEvent; 133 use AnyEvent;
95 134
96 # .. AnyEvent will likely default to Tk 135 # .. AnyEvent will likely default to Tk
97 136
98 The *likely* means that, if any module loads another event model and 137 The *likely* means that, if any module loads another event model and
99 starts using it, all bets are off. Maybe you should tell their authors 138 starts using it, all bets are off - this case should be very rare
100 to use AnyEvent so their modules work together with others seamlessly... 139 though, as very few modules hardcode event loops without announcing this
140 very loudly.
101 141
102 The pure-perl implementation of AnyEvent is called 142 The pure-perl implementation of AnyEvent is called "AnyEvent::Loop".
103 "AnyEvent::Impl::Perl". Like other event modules you can load it 143 Like other event modules you can load it explicitly and enjoy the high
104 explicitly. 144 availability of that event loop :)
105 145
106WATCHERS 146WATCHERS
107 AnyEvent has the central concept of a *watcher*, which is an object that 147 AnyEvent has the central concept of a *watcher*, which is an object that
108 stores relevant data for each kind of event you are waiting for, such as 148 stores relevant data for each kind of event you are waiting for, such as
109 the callback to call, the file handle to watch, etc. 149 the callback to call, the file handle to watch, etc.
… …
111 These watchers are normal Perl objects with normal Perl lifetime. After 151 These watchers are normal Perl objects with normal Perl lifetime. After
112 creating a watcher it will immediately "watch" for events and invoke the 152 creating a watcher it will immediately "watch" for events and invoke the
113 callback when the event occurs (of course, only when the event model is 153 callback when the event occurs (of course, only when the event model is
114 in control). 154 in control).
115 155
156 Note that callbacks must not permanently change global variables
157 potentially in use by the event loop (such as $_ or $[) and that
158 callbacks must not "die". The former is good programming practice in
159 Perl and the latter stems from the fact that exception handling differs
160 widely between event loops.
161
116 To disable the watcher you have to destroy it (e.g. by setting the 162 To disable a watcher you have to destroy it (e.g. by setting the
117 variable you store it in to "undef" or otherwise deleting all references 163 variable you store it in to "undef" or otherwise deleting all references
118 to it). 164 to it).
119 165
120 All watchers are created by calling a method on the "AnyEvent" class. 166 All watchers are created by calling a method on the "AnyEvent" class.
121 167
122 Many watchers either are used with "recursion" (repeating timers for 168 Many watchers either are used with "recursion" (repeating timers for
123 example), or need to refer to their watcher object in other ways. 169 example), or need to refer to their watcher object in other ways.
124 170
125 An any way to achieve that is this pattern: 171 One way to achieve that is this pattern:
126 172
127 my $w; $w = AnyEvent->type (arg => value ..., cb => sub { 173 my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
128 # you can use $w here, for example to undef it 174 # you can use $w here, for example to undef it
129 undef $w; 175 undef $w;
130 }); 176 });
131 177
132 Note that "my $w; $w =" combination. This is necessary because in Perl, 178 Note that "my $w; $w =" combination. This is necessary because in Perl,
133 my variables are only visible after the statement in which they are 179 my variables are only visible after the statement in which they are
134 declared. 180 declared.
135 181
136 I/O WATCHERS 182 I/O WATCHERS
183 $w = AnyEvent->io (
184 fh => <filehandle_or_fileno>,
185 poll => <"r" or "w">,
186 cb => <callback>,
187 );
188
137 You can create an I/O watcher by calling the "AnyEvent->io" method with 189 You can create an I/O watcher by calling the "AnyEvent->io" method with
138 the following mandatory key-value pairs as arguments: 190 the following mandatory key-value pairs as arguments:
139 191
140 "fh" the Perl *file handle* (*not* file descriptor) to watch for events. 192 "fh" is the Perl *file handle* (or a naked file descriptor) to watch for
193 events (AnyEvent might or might not keep a reference to this file
194 handle). Note that only file handles pointing to things for which
195 non-blocking operation makes sense are allowed. This includes sockets,
196 most character devices, pipes, fifos and so on, but not for example
197 files or block devices.
198
141 "poll" must be a string that is either "r" or "w", which creates a 199 "poll" must be a string that is either "r" or "w", which creates a
142 watcher waiting for "r"eadable or "w"ritable events, respectively. "cb" 200 watcher waiting for "r"eadable or "w"ritable events, respectively.
201
143 is the callback to invoke each time the file handle becomes ready. 202 "cb" is the callback to invoke each time the file handle becomes ready.
144 203
145 Although the callback might get passed parameters, their value and 204 Although the callback might get passed parameters, their value and
146 presence is undefined and you cannot rely on them. Portable AnyEvent 205 presence is undefined and you cannot rely on them. Portable AnyEvent
147 callbacks cannot use arguments passed to I/O watcher callbacks. 206 callbacks cannot use arguments passed to I/O watcher callbacks.
148 207
149 The I/O watcher might use the underlying file descriptor or a copy of 208 The I/O watcher might use the underlying file descriptor or a copy of
150 it. You must not close a file handle as long as any watcher is active on 209 it. You must not close a file handle as long as any watcher is active on
151 the underlying file descriptor. 210 the underlying file descriptor.
152 211
153 Some event loops issue spurious readyness notifications, so you should 212 Some event loops issue spurious readiness notifications, so you should
154 always use non-blocking calls when reading/writing from/to your file 213 always use non-blocking calls when reading/writing from/to your file
155 handles. 214 handles.
156 215
157 Example:
158
159 # wait for readability of STDIN, then read a line and disable the watcher 216 Example: wait for readability of STDIN, then read a line and disable the
217 watcher.
218
160 my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub { 219 my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
161 chomp (my $input = <STDIN>); 220 chomp (my $input = <STDIN>);
162 warn "read: $input\n"; 221 warn "read: $input\n";
163 undef $w; 222 undef $w;
164 }); 223 });
165 224
166 TIME WATCHERS 225 TIME WATCHERS
226 $w = AnyEvent->timer (after => <seconds>, cb => <callback>);
227
228 $w = AnyEvent->timer (
229 after => <fractional_seconds>,
230 interval => <fractional_seconds>,
231 cb => <callback>,
232 );
233
167 You can create a time watcher by calling the "AnyEvent->timer" method 234 You can create a time watcher by calling the "AnyEvent->timer" method
168 with the following mandatory arguments: 235 with the following mandatory arguments:
169 236
170 "after" specifies after how many seconds (fractional values are 237 "after" specifies after how many seconds (fractional values are
171 supported) the callback should be invoked. "cb" is the callback to 238 supported) the callback should be invoked. "cb" is the callback to
… …
173 240
174 Although the callback might get passed parameters, their value and 241 Although the callback might get passed parameters, their value and
175 presence is undefined and you cannot rely on them. Portable AnyEvent 242 presence is undefined and you cannot rely on them. Portable AnyEvent
176 callbacks cannot use arguments passed to time watcher callbacks. 243 callbacks cannot use arguments passed to time watcher callbacks.
177 244
178 The timer callback will be invoked at most once: if you want a repeating 245 The callback will normally be invoked only once. If you specify another
179 timer you have to create a new watcher (this is a limitation by both Tk 246 parameter, "interval", as a strictly positive number (> 0), then the
180 and Glib). 247 callback will be invoked regularly at that interval (in fractional
248 seconds) after the first invocation. If "interval" is specified with a
249 false value, then it is treated as if it were not specified at all.
181 250
182 Example: 251 The callback will be rescheduled before invoking the callback, but no
252 attempt is made to avoid timer drift in most backends, so the interval
253 is only approximate.
183 254
184 # fire an event after 7.7 seconds 255 Example: fire an event after 7.7 seconds.
256
185 my $w = AnyEvent->timer (after => 7.7, cb => sub { 257 my $w = AnyEvent->timer (after => 7.7, cb => sub {
186 warn "timeout\n"; 258 warn "timeout\n";
187 }); 259 });
188 260
189 # to cancel the timer: 261 # to cancel the timer:
190 undef $w; 262 undef $w;
191 263
192 Example 2:
193
194 # fire an event after 0.5 seconds, then roughly every second 264 Example 2: fire an event after 0.5 seconds, then roughly every second.
195 my $w;
196 265
197 my $cb = sub {
198 # cancel the old timer while creating a new one
199 $w = AnyEvent->timer (after => 1, cb => $cb); 266 my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
267 warn "timeout\n";
200 }; 268 });
201
202 # start the "loop" by creating the first watcher
203 $w = AnyEvent->timer (after => 0.5, cb => $cb);
204 269
205 TIMING ISSUES 270 TIMING ISSUES
206 There are two ways to handle timers: based on real time (relative, "fire 271 There are two ways to handle timers: based on real time (relative, "fire
207 in 10 seconds") and based on wallclock time (absolute, "fire at 12 272 in 10 seconds") and based on wallclock time (absolute, "fire at 12
208 o'clock"). 273 o'clock").
209 274
210 While most event loops expect timers to specified in a relative way, 275 While most event loops expect timers to specified in a relative way,
211 they use absolute time internally. This makes a difference when your 276 they use absolute time internally. This makes a difference when your
212 clock "jumps", for example, when ntp decides to set your clock backwards 277 clock "jumps", for example, when ntp decides to set your clock backwards
213 from the wrong date of 2014-01-01 to 2008-01-01, a watcher that is 278 from the wrong date of 2014-01-01 to 2008-01-01, a watcher that is
214 supposed to fire "after" a second might actually take six years to 279 supposed to fire "after a second" might actually take six years to
215 finally fire. 280 finally fire.
216 281
217 AnyEvent cannot compensate for this. The only event loop that is 282 AnyEvent cannot compensate for this. The only event loop that is
218 conscious about these issues is EV, which offers both relative 283 conscious of these issues is EV, which offers both relative (ev_timer,
219 (ev_timer, based on true relative time) and absolute (ev_periodic, based 284 based on true relative time) and absolute (ev_periodic, based on
220 on wallclock time) timers. 285 wallclock time) timers.
221 286
222 AnyEvent always prefers relative timers, if available, matching the 287 AnyEvent always prefers relative timers, if available, matching the
223 AnyEvent API. 288 AnyEvent API.
224 289
290 AnyEvent has two additional methods that return the "current time":
291
292 AnyEvent->time
293 This returns the "current wallclock time" as a fractional number of
294 seconds since the Epoch (the same thing as "time" or
295 "Time::HiRes::time" return, and the result is guaranteed to be
296 compatible with those).
297
298 It progresses independently of any event loop processing, i.e. each
299 call will check the system clock, which usually gets updated
300 frequently.
301
302 AnyEvent->now
303 This also returns the "current wallclock time", but unlike "time",
304 above, this value might change only once per event loop iteration,
305 depending on the event loop (most return the same time as "time",
306 above). This is the time that AnyEvent's timers get scheduled
307 against.
308
309 *In almost all cases (in all cases if you don't care), this is the
310 function to call when you want to know the current time.*
311
312 This function is also often faster then "AnyEvent->time", and thus
313 the preferred method if you want some timestamp (for example,
314 AnyEvent::Handle uses this to update its activity timeouts).
315
316 The rest of this section is only of relevance if you try to be very
317 exact with your timing; you can skip it without a bad conscience.
318
319 For a practical example of when these times differ, consider
320 Event::Lib and EV and the following set-up:
321
322 The event loop is running and has just invoked one of your callbacks
323 at time=500 (assume no other callbacks delay processing). In your
324 callback, you wait a second by executing "sleep 1" (blocking the
325 process for a second) and then (at time=501) you create a relative
326 timer that fires after three seconds.
327
328 With Event::Lib, "AnyEvent->time" and "AnyEvent->now" will both
329 return 501, because that is the current time, and the timer will be
330 scheduled to fire at time=504 (501 + 3).
331
332 With EV, "AnyEvent->time" returns 501 (as that is the current time),
333 but "AnyEvent->now" returns 500, as that is the time the last event
334 processing phase started. With EV, your timer gets scheduled to run
335 at time=503 (500 + 3).
336
337 In one sense, Event::Lib is more exact, as it uses the current time
338 regardless of any delays introduced by event processing. However,
339 most callbacks do not expect large delays in processing, so this
340 causes a higher drift (and a lot more system calls to get the
341 current time).
342
343 In another sense, EV is more exact, as your timer will be scheduled
344 at the same time, regardless of how long event processing actually
345 took.
346
347 In either case, if you care (and in most cases, you don't), then you
348 can get whatever behaviour you want with any event loop, by taking
349 the difference between "AnyEvent->time" and "AnyEvent->now" into
350 account.
351
352 AnyEvent->now_update
353 Some event loops (such as EV or AnyEvent::Loop) cache the current
354 time for each loop iteration (see the discussion of AnyEvent->now,
355 above).
356
357 When a callback runs for a long time (or when the process sleeps),
358 then this "current" time will differ substantially from the real
359 time, which might affect timers and time-outs.
360
361 When this is the case, you can call this method, which will update
362 the event loop's idea of "current time".
363
364 A typical example would be a script in a web server (e.g.
365 "mod_perl") - when mod_perl executes the script, then the event loop
366 will have the wrong idea about the "current time" (being potentially
367 far in the past, when the script ran the last time). In that case
368 you should arrange a call to "AnyEvent->now_update" each time the
369 web server process wakes up again (e.g. at the start of your script,
370 or in a handler).
371
372 Note that updating the time *might* cause some events to be handled.
373
225 SIGNAL WATCHERS 374 SIGNAL WATCHERS
375 $w = AnyEvent->signal (signal => <uppercase_signal_name>, cb => <callback>);
376
226 You can watch for signals using a signal watcher, "signal" is the signal 377 You can watch for signals using a signal watcher, "signal" is the signal
227 *name* without any "SIG" prefix, "cb" is the Perl callback to be invoked 378 *name* in uppercase and without any "SIG" prefix, "cb" is the Perl
228 whenever a signal occurs. 379 callback to be invoked whenever a signal occurs.
229 380
230 Although the callback might get passed parameters, their value and 381 Although the callback might get passed parameters, their value and
231 presence is undefined and you cannot rely on them. Portable AnyEvent 382 presence is undefined and you cannot rely on them. Portable AnyEvent
232 callbacks cannot use arguments passed to signal watcher callbacks. 383 callbacks cannot use arguments passed to signal watcher callbacks.
233 384
… …
235 invocation, and callback invocation will be synchronous. Synchronous 386 invocation, and callback invocation will be synchronous. Synchronous
236 means that it might take a while until the signal gets handled by the 387 means that it might take a while until the signal gets handled by the
237 process, but it is guaranteed not to interrupt any other callbacks. 388 process, but it is guaranteed not to interrupt any other callbacks.
238 389
239 The main advantage of using these watchers is that you can share a 390 The main advantage of using these watchers is that you can share a
240 signal between multiple watchers. 391 signal between multiple watchers, and AnyEvent will ensure that signals
392 will not interrupt your program at bad times.
241 393
242 This watcher might use %SIG, so programs overwriting those signals 394 This watcher might use %SIG (depending on the event loop used), so
243 directly will likely not work correctly. 395 programs overwriting those signals directly will likely not work
396 correctly.
244 397
245 Example: exit on SIGINT 398 Example: exit on SIGINT
246 399
247 my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 }); 400 my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
248 401
402 Restart Behaviour
403 While restart behaviour is up to the event loop implementation, most
404 will not restart syscalls (that includes Async::Interrupt and AnyEvent's
405 pure perl implementation).
406
407 Safe/Unsafe Signals
408 Perl signals can be either "safe" (synchronous to opcode handling) or
409 "unsafe" (asynchronous) - the former might delay signal delivery
410 indefinitely, the latter might corrupt your memory.
411
412 AnyEvent signal handlers are, in addition, synchronous to the event
413 loop, i.e. they will not interrupt your running perl program but will
414 only be called as part of the normal event handling (just like timer,
415 I/O etc. callbacks, too).
416
417 Signal Races, Delays and Workarounds
418 Many event loops (e.g. Glib, Tk, Qt, IO::Async) do not support attaching
419 callbacks to signals in a generic way, which is a pity, as you cannot do
420 race-free signal handling in perl, requiring C libraries for this.
421 AnyEvent will try to do its best, which means in some cases, signals
422 will be delayed. The maximum time a signal might be delayed is 10
423 seconds by default, but can be overriden via
424 $ENV{PERL_ANYEVENT_MAX_SIGNAL_LATENCY} or $AnyEvent::MAX_SIGNAL_LATENCY
425 - see the "ENVIRONMENT VARIABLES" section for details.
426
427 All these problems can be avoided by installing the optional
428 Async::Interrupt module, which works with most event loops. It will not
429 work with inherently broken event loops such as Event or Event::Lib (and
430 not with POE currently). For those, you just have to suffer the delays.
431
249 CHILD PROCESS WATCHERS 432 CHILD PROCESS WATCHERS
433 $w = AnyEvent->child (pid => <process id>, cb => <callback>);
434
250 You can also watch on a child process exit and catch its exit status. 435 You can also watch for a child process exit and catch its exit status.
251 436
252 The child process is specified by the "pid" argument (if set to 0, it 437 The child process is specified by the "pid" argument (on some backends,
253 watches for any child process exit). The watcher will trigger as often 438 using 0 watches for any child process exit, on others this will croak).
254 as status change for the child are received. This works by installing a 439 The watcher will be triggered only when the child process has finished
255 signal handler for "SIGCHLD". The callback will be called with the pid 440 and an exit status is available, not on any trace events
256 and exit status (as returned by waitpid), so unlike other watcher types, 441 (stopped/continued).
257 you *can* rely on child watcher callback arguments. 442
443 The callback will be called with the pid and exit status (as returned by
444 waitpid), so unlike other watcher types, you *can* rely on child watcher
445 callback arguments.
446
447 This watcher type works by installing a signal handler for "SIGCHLD",
448 and since it cannot be shared, nothing else should use SIGCHLD or reap
449 random child processes (waiting for specific child processes, e.g.
450 inside "system", is just fine).
258 451
259 There is a slight catch to child watchers, however: you usually start 452 There is a slight catch to child watchers, however: you usually start
260 them *after* the child process was created, and this means the process 453 them *after* the child process was created, and this means the process
261 could have exited already (and no SIGCHLD will be sent anymore). 454 could have exited already (and no SIGCHLD will be sent anymore).
262 455
263 Not all event models handle this correctly (POE doesn't), but even for 456 Not all event models handle this correctly (neither POE nor IO::Async
457 do, see their AnyEvent::Impl manpages for details), but even for event
264 event models that *do* handle this correctly, they usually need to be 458 models that *do* handle this correctly, they usually need to be loaded
265 loaded before the process exits (i.e. before you fork in the first 459 before the process exits (i.e. before you fork in the first place).
266 place). 460 AnyEvent's pure perl event loop handles all cases correctly regardless
461 of when you start the watcher.
267 462
268 This means you cannot create a child watcher as the very first thing in 463 This means you cannot create a child watcher as the very first thing in
269 an AnyEvent program, you *have* to create at least one watcher before 464 an AnyEvent program, you *have* to create at least one watcher before
270 you "fork" the child (alternatively, you can call "AnyEvent::detect"). 465 you "fork" the child (alternatively, you can call "AnyEvent::detect").
271 466
467 As most event loops do not support waiting for child events, they will
468 be emulated by AnyEvent in most cases, in which case the latency and
469 race problems mentioned in the description of signal watchers apply.
470
272 Example: fork a process and wait for it 471 Example: fork a process and wait for it
273 472
274 my $done = AnyEvent->condvar; 473 my $done = AnyEvent->condvar;
275 474
475 # this forks and immediately calls exit in the child. this
476 # normally has all sorts of bad consequences for your parent,
477 # so take this as an example only. always fork and exec,
478 # or call POSIX::_exit, in real code.
276 my $pid = fork or exit 5; 479 my $pid = fork or exit 5;
277 480
278 my $w = AnyEvent->child ( 481 my $w = AnyEvent->child (
279 pid => $pid, 482 pid => $pid,
280 cb => sub { 483 cb => sub {
281 my ($pid, $status) = @_; 484 my ($pid, $status) = @_;
282 warn "pid $pid exited with status $status"; 485 warn "pid $pid exited with status $status";
283 $done->send; 486 $done->send;
284 }, 487 },
285 ); 488 );
286 489
287 # do something else, then wait for process exit 490 # do something else, then wait for process exit
288 $done->recv; 491 $done->recv;
492
493 IDLE WATCHERS
494 $w = AnyEvent->idle (cb => <callback>);
495
496 This will repeatedly invoke the callback after the process becomes idle,
497 until either the watcher is destroyed or new events have been detected.
498
499 Idle watchers are useful when there is a need to do something, but it is
500 not so important (or wise) to do it instantly. The callback will be
501 invoked only when there is "nothing better to do", which is usually
502 defined as "all outstanding events have been handled and no new events
503 have been detected". That means that idle watchers ideally get invoked
504 when the event loop has just polled for new events but none have been
505 detected. Instead of blocking to wait for more events, the idle watchers
506 will be invoked.
507
508 Unfortunately, most event loops do not really support idle watchers
509 (only EV, Event and Glib do it in a usable fashion) - for the rest,
510 AnyEvent will simply call the callback "from time to time".
511
512 Example: read lines from STDIN, but only process them when the program
513 is otherwise idle:
514
515 my @lines; # read data
516 my $idle_w;
517 my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
518 push @lines, scalar <STDIN>;
519
520 # start an idle watcher, if not already done
521 $idle_w ||= AnyEvent->idle (cb => sub {
522 # handle only one line, when there are lines left
523 if (my $line = shift @lines) {
524 print "handled when idle: $line";
525 } else {
526 # otherwise disable the idle watcher again
527 undef $idle_w;
528 }
529 });
530 });
289 531
290 CONDITION VARIABLES 532 CONDITION VARIABLES
533 $cv = AnyEvent->condvar;
534
535 $cv->send (<list>);
536 my @res = $cv->recv;
537
291 If you are familiar with some event loops you will know that all of them 538 If you are familiar with some event loops you will know that all of them
292 require you to run some blocking "loop", "run" or similar function that 539 require you to run some blocking "loop", "run" or similar function that
293 will actively watch for new events and call your callbacks. 540 will actively watch for new events and call your callbacks.
294 541
295 AnyEvent is different, it expects somebody else to run the event loop 542 AnyEvent is slightly different: it expects somebody else to run the
296 and will only block when necessary (usually when told by the user). 543 event loop and will only block when necessary (usually when told by the
544 user).
297 545
298 The instrument to do that is called a "condition variable", so called 546 The tool to do that is called a "condition variable", so called because
299 because they represent a condition that must become true. 547 they represent a condition that must become true.
548
549 Now is probably a good time to look at the examples further below.
300 550
301 Condition variables can be created by calling the "AnyEvent->condvar" 551 Condition variables can be created by calling the "AnyEvent->condvar"
302 method, usually without arguments. The only argument pair allowed is 552 method, usually without arguments. The only argument pair allowed is
303 "cb", which specifies a callback to be called when the condition 553 "cb", which specifies a callback to be called when the condition
304 variable becomes true. 554 variable becomes true, with the condition variable as the first argument
555 (but not the results).
305 556
306 After creation, the condition variable is "false" until it becomes 557 After creation, the condition variable is "false" until it becomes
307 "true" by calling the "send" method (or calling the condition variable 558 "true" by calling the "send" method (or calling the condition variable
308 as if it were a callback). 559 as if it were a callback, read about the caveats in the description for
560 the "->send" method).
309 561
310 Condition variables are similar to callbacks, except that you can 562 Since condition variables are the most complex part of the AnyEvent API,
311 optionally wait for them. They can also be called merge points - points 563 here are some different mental models of what they are - pick the ones
312 in time where multiple outstanding events have been processed. And yet 564 you can connect to:
313 another way to call them is transactions - each condition variable can 565
314 be used to represent a transaction, which finishes at some point and 566 * Condition variables are like callbacks - you can call them (and pass
315 delivers a result. 567 them instead of callbacks). Unlike callbacks however, you can also
568 wait for them to be called.
569
570 * Condition variables are signals - one side can emit or send them,
571 the other side can wait for them, or install a handler that is
572 called when the signal fires.
573
574 * Condition variables are like "Merge Points" - points in your program
575 where you merge multiple independent results/control flows into one.
576
577 * Condition variables represent a transaction - functions that start
578 some kind of transaction can return them, leaving the caller the
579 choice between waiting in a blocking fashion, or setting a callback.
580
581 * Condition variables represent future values, or promises to deliver
582 some result, long before the result is available.
316 583
317 Condition variables are very useful to signal that something has 584 Condition variables are very useful to signal that something has
318 finished, for example, if you write a module that does asynchronous http 585 finished, for example, if you write a module that does asynchronous http
319 requests, then a condition variable would be the ideal candidate to 586 requests, then a condition variable would be the ideal candidate to
320 signal the availability of results. The user can either act when the 587 signal the availability of results. The user can either act when the
… …
333 600
334 Condition variables are represented by hash refs in perl, and the keys 601 Condition variables are represented by hash refs in perl, and the keys
335 used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy 602 used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy
336 (it is often useful to build your own transaction class on top of 603 (it is often useful to build your own transaction class on top of
337 AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call 604 AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call
338 it's "new" method in your own "new" method. 605 its "new" method in your own "new" method.
339 606
340 There are two "sides" to a condition variable - the "producer side" 607 There are two "sides" to a condition variable - the "producer side"
341 which eventually calls "-> send", and the "consumer side", which waits 608 which eventually calls "-> send", and the "consumer side", which waits
342 for the send to occur. 609 for the send to occur.
343 610
344 Example: wait for a timer. 611 Example: wait for a timer.
345 612
346 # wait till the result is ready 613 # condition: "wait till the timer is fired"
347 my $result_ready = AnyEvent->condvar; 614 my $timer_fired = AnyEvent->condvar;
348 615
349 # do something such as adding a timer 616 # create the timer - we could wait for, say
350 # or socket watcher the calls $result_ready->send 617 # a handle becomign ready, or even an
351 # when the "result" is ready. 618 # AnyEvent::HTTP request to finish, but
352 # in this case, we simply use a timer: 619 # in this case, we simply use a timer:
353 my $w = AnyEvent->timer ( 620 my $w = AnyEvent->timer (
354 after => 1, 621 after => 1,
355 cb => sub { $result_ready->send }, 622 cb => sub { $timer_fired->send },
356 ); 623 );
357 624
358 # this "blocks" (while handling events) till the callback 625 # this "blocks" (while handling events) till the callback
359 # calls send 626 # calls ->send
360 $result_ready->recv; 627 $timer_fired->recv;
361 628
362 Example: wait for a timer, but take advantage of the fact that condition 629 Example: wait for a timer, but take advantage of the fact that condition
363 variables are also code references. 630 variables are also callable directly.
364 631
365 my $done = AnyEvent->condvar; 632 my $done = AnyEvent->condvar;
366 my $delay = AnyEvent->timer (after => 5, cb => $done); 633 my $delay = AnyEvent->timer (after => 5, cb => $done);
367 $done->recv; 634 $done->recv;
635
636 Example: Imagine an API that returns a condvar and doesn't support
637 callbacks. This is how you make a synchronous call, for example from the
638 main program:
639
640 use AnyEvent::CouchDB;
641
642 ...
643
644 my @info = $couchdb->info->recv;
645
646 And this is how you would just set a callback to be called whenever the
647 results are available:
648
649 $couchdb->info->cb (sub {
650 my @info = $_[0]->recv;
651 });
368 652
369 METHODS FOR PRODUCERS 653 METHODS FOR PRODUCERS
370 These methods should only be used by the producing side, i.e. the 654 These methods should only be used by the producing side, i.e. the
371 code/module that eventually sends the signal. Note that it is also the 655 code/module that eventually sends the signal. Note that it is also the
372 producer side which creates the condvar in most cases, but it isn't 656 producer side which creates the condvar in most cases, but it isn't
… …
382 666
383 Any arguments passed to the "send" call will be returned by all 667 Any arguments passed to the "send" call will be returned by all
384 future "->recv" calls. 668 future "->recv" calls.
385 669
386 Condition variables are overloaded so one can call them directly (as 670 Condition variables are overloaded so one can call them directly (as
387 a code reference). Calling them directly is the same as calling 671 if they were a code reference). Calling them directly is the same as
388 "send". 672 calling "send".
389 673
390 $cv->croak ($error) 674 $cv->croak ($error)
391 Similar to send, but causes all call's to "->recv" to invoke 675 Similar to send, but causes all calls to "->recv" to invoke
392 "Carp::croak" with the given error message/object/scalar. 676 "Carp::croak" with the given error message/object/scalar.
393 677
394 This can be used to signal any errors to the condition variable 678 This can be used to signal any errors to the condition variable
395 user/consumer. 679 user/consumer. Doing it this way instead of calling "croak" directly
680 delays the error detection, but has the overwhelming advantage that
681 it diagnoses the error at the place where the result is expected,
682 and not deep in some event callback with no connection to the actual
683 code causing the problem.
396 684
397 $cv->begin ([group callback]) 685 $cv->begin ([group callback])
398 $cv->end 686 $cv->end
399 These two methods are EXPERIMENTAL and MIGHT CHANGE.
400
401 These two methods can be used to combine many transactions/events 687 These two methods can be used to combine many transactions/events
402 into one. For example, a function that pings many hosts in parallel 688 into one. For example, a function that pings many hosts in parallel
403 might want to use a condition variable for the whole process. 689 might want to use a condition variable for the whole process.
404 690
405 Every call to "->begin" will increment a counter, and every call to 691 Every call to "->begin" will increment a counter, and every call to
406 "->end" will decrement it. If the counter reaches 0 in "->end", the 692 "->end" will decrement it. If the counter reaches 0 in "->end", the
407 (last) callback passed to "begin" will be executed. That callback is 693 (last) callback passed to "begin" will be executed, passing the
408 *supposed* to call "->send", but that is not required. If no 694 condvar as first argument. That callback is *supposed* to call
695 "->send", but that is not required. If no group callback was set,
409 callback was set, "send" will be called without any arguments. 696 "send" will be called without any arguments.
410 697
411 Let's clarify this with the ping example: 698 You can think of "$cv->send" giving you an OR condition (one call
699 sends), while "$cv->begin" and "$cv->end" giving you an AND
700 condition (all "begin" calls must be "end"'ed before the condvar
701 sends).
702
703 Let's start with a simple example: you have two I/O watchers (for
704 example, STDOUT and STDERR for a program), and you want to wait for
705 both streams to close before activating a condvar:
412 706
413 my $cv = AnyEvent->condvar; 707 my $cv = AnyEvent->condvar;
414 708
709 $cv->begin; # first watcher
710 my $w1 = AnyEvent->io (fh => $fh1, cb => sub {
711 defined sysread $fh1, my $buf, 4096
712 or $cv->end;
713 });
714
715 $cv->begin; # second watcher
716 my $w2 = AnyEvent->io (fh => $fh2, cb => sub {
717 defined sysread $fh2, my $buf, 4096
718 or $cv->end;
719 });
720
721 $cv->recv;
722
723 This works because for every event source (EOF on file handle),
724 there is one call to "begin", so the condvar waits for all calls to
725 "end" before sending.
726
727 The ping example mentioned above is slightly more complicated, as
728 the there are results to be passed back, and the number of tasks
729 that are begun can potentially be zero:
730
731 my $cv = AnyEvent->condvar;
732
415 my %result; 733 my %result;
416 $cv->begin (sub { $cv->send (\%result) }); 734 $cv->begin (sub { shift->send (\%result) });
417 735
418 for my $host (@list_of_hosts) { 736 for my $host (@list_of_hosts) {
419 $cv->begin; 737 $cv->begin;
420 ping_host_then_call_callback $host, sub { 738 ping_host_then_call_callback $host, sub {
421 $result{$host} = ...; 739 $result{$host} = ...;
… …
423 }; 741 };
424 } 742 }
425 743
426 $cv->end; 744 $cv->end;
427 745
746 ...
747
748 my $results = $cv->recv;
749
428 This code fragment supposedly pings a number of hosts and calls 750 This code fragment supposedly pings a number of hosts and calls
429 "send" after results for all then have have been gathered - in any 751 "send" after results for all then have have been gathered - in any
430 order. To achieve this, the code issues a call to "begin" when it 752 order. To achieve this, the code issues a call to "begin" when it
431 starts each ping request and calls "end" when it has received some 753 starts each ping request and calls "end" when it has received some
432 result for it. Since "begin" and "end" only maintain a counter, the 754 result for it. Since "begin" and "end" only maintain a counter, the
… …
436 the loop, which serves two important purposes: first, it sets the 758 the loop, which serves two important purposes: first, it sets the
437 callback to be called once the counter reaches 0, and second, it 759 callback to be called once the counter reaches 0, and second, it
438 ensures that "send" is called even when "no" hosts are being pinged 760 ensures that "send" is called even when "no" hosts are being pinged
439 (the loop doesn't execute once). 761 (the loop doesn't execute once).
440 762
441 This is the general pattern when you "fan out" into multiple 763 This is the general pattern when you "fan out" into multiple (but
442 subrequests: use an outer "begin"/"end" pair to set the callback and 764 potentially zero) subrequests: use an outer "begin"/"end" pair to
443 ensure "end" is called at least once, and then, for each subrequest 765 set the callback and ensure "end" is called at least once, and then,
444 you start, call "begin" and for each subrequest you finish, call 766 for each subrequest you start, call "begin" and for each subrequest
445 "end". 767 you finish, call "end".
446 768
447 METHODS FOR CONSUMERS 769 METHODS FOR CONSUMERS
448 These methods should only be used by the consuming side, i.e. the code 770 These methods should only be used by the consuming side, i.e. the code
449 awaits the condition. 771 awaits the condition.
450 772
451 $cv->recv 773 $cv->recv
452 Wait (blocking if necessary) until the "->send" or "->croak" methods 774 Wait (blocking if necessary) until the "->send" or "->croak" methods
453 have been called on c<$cv>, while servicing other watchers normally. 775 have been called on $cv, while servicing other watchers normally.
454 776
455 You can only wait once on a condition - additional calls are valid 777 You can only wait once on a condition - additional calls are valid
456 but will return immediately. 778 but will return immediately.
457 779
458 If an error condition has been set by calling "->croak", then this 780 If an error condition has been set by calling "->croak", then this
459 function will call "croak". 781 function will call "croak".
460 782
461 In list context, all parameters passed to "send" will be returned, 783 In list context, all parameters passed to "send" will be returned,
462 in scalar context only the first one will be returned. 784 in scalar context only the first one will be returned.
463 785
786 Note that doing a blocking wait in a callback is not supported by
787 any event loop, that is, recursive invocation of a blocking "->recv"
788 is not allowed and the "recv" call will "croak" if such a condition
789 is detected. This requirement can be dropped by relying on
790 Coro::AnyEvent , which allows you to do a blocking "->recv" from any
791 thread that doesn't run the event loop itself. Coro::AnyEvent is
792 loaded automatically when Coro is used with AnyEvent, so code does
793 not need to do anything special to take advantage of that: any code
794 that would normally block your program because it calls "recv", be
795 executed in an "async" thread instead without blocking other
796 threads.
797
464 Not all event models support a blocking wait - some die in that case 798 Not all event models support a blocking wait - some die in that case
465 (programs might want to do that to stay interactive), so *if you are 799 (programs might want to do that to stay interactive), so *if you are
466 using this from a module, never require a blocking wait*, but let 800 using this from a module, never require a blocking wait*. Instead,
467 the caller decide whether the call will block or not (for example, 801 let the caller decide whether the call will block or not (for
468 by coupling condition variables with some kind of request results 802 example, by coupling condition variables with some kind of request
469 and supporting callbacks so the caller knows that getting the result 803 results and supporting callbacks so the caller knows that getting
470 will not block, while still supporting blocking waits if the caller 804 the result will not block, while still supporting blocking waits if
471 so desires). 805 the caller so desires).
472 806
473 Another reason *never* to "->recv" in a module is that you cannot
474 sensibly have two "->recv"'s in parallel, as that would require
475 multiple interpreters or coroutines/threads, none of which
476 "AnyEvent" can supply.
477
478 The Coro module, however, *can* and *does* supply coroutines and, in
479 fact, Coro::AnyEvent replaces AnyEvent's condvars by coroutine-safe
480 versions and also integrates coroutines into AnyEvent, making
481 blocking "->recv" calls perfectly safe as long as they are done from
482 another coroutine (one that doesn't run the event loop).
483
484 You can ensure that "-recv" never blocks by setting a callback and 807 You can ensure that "->recv" never blocks by setting a callback and
485 only calling "->recv" from within that callback (or at a later 808 only calling "->recv" from within that callback (or at a later
486 time). This will work even when the event loop does not support 809 time). This will work even when the event loop does not support
487 blocking waits otherwise. 810 blocking waits otherwise.
488 811
489 $bool = $cv->ready 812 $bool = $cv->ready
490 Returns true when the condition is "true", i.e. whether "send" or 813 Returns true when the condition is "true", i.e. whether "send" or
491 "croak" have been called. 814 "croak" have been called.
492 815
493 $cb = $cv->cb ([new callback]) 816 $cb = $cv->cb ($cb->($cv))
494 This is a mutator function that returns the callback set and 817 This is a mutator function that returns the callback set and
495 optionally replaces it before doing so. 818 optionally replaces it before doing so.
496 819
497 The callback will be called when the condition becomes "true", i.e. 820 The callback will be called when the condition becomes "true", i.e.
498 when "send" or "croak" are called. Calling "recv" inside the 821 when "send" or "croak" are called, with the only argument being the
822 condition variable itself. If the condition is already true, the
823 callback is called immediately when it is set. Calling "recv" inside
499 callback or at any later time is guaranteed not to block. 824 the callback or at any later time is guaranteed not to block.
825
826SUPPORTED EVENT LOOPS/BACKENDS
827 The available backend classes are (every class has its own manpage):
828
829 Backends that are autoprobed when no other event loop can be found.
830 EV is the preferred backend when no other event loop seems to be in
831 use. If EV is not installed, then AnyEvent will fall back to its own
832 pure-perl implementation, which is available everywhere as it comes
833 with AnyEvent itself.
834
835 AnyEvent::Impl::EV based on EV (interface to libev, best choice).
836 AnyEvent::Impl::Perl pure-perl AnyEvent::Loop, fast and portable.
837
838 Backends that are transparently being picked up when they are used.
839 These will be used if they are already loaded when the first watcher
840 is created, in which case it is assumed that the application is
841 using them. This means that AnyEvent will automatically pick the
842 right backend when the main program loads an event module before
843 anything starts to create watchers. Nothing special needs to be done
844 by the main program.
845
846 AnyEvent::Impl::Event based on Event, very stable, few glitches.
847 AnyEvent::Impl::Glib based on Glib, slow but very stable.
848 AnyEvent::Impl::Tk based on Tk, very broken.
849 AnyEvent::Impl::UV based on UV, innovated square wheels.
850 AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
851 AnyEvent::Impl::POE based on POE, very slow, some limitations.
852 AnyEvent::Impl::Irssi used when running within irssi.
853 AnyEvent::Impl::IOAsync based on IO::Async.
854 AnyEvent::Impl::Cocoa based on Cocoa::EventLoop.
855 AnyEvent::Impl::FLTK based on FLTK (fltk 2 binding).
856
857 Backends with special needs.
858 Qt requires the Qt::Application to be instantiated first, but will
859 otherwise be picked up automatically. As long as the main program
860 instantiates the application before any AnyEvent watchers are
861 created, everything should just work.
862
863 AnyEvent::Impl::Qt based on Qt.
864
865 Event loops that are indirectly supported via other backends.
866 Some event loops can be supported via other modules:
867
868 There is no direct support for WxWidgets (Wx) or Prima.
869
870 WxWidgets has no support for watching file handles. However, you can
871 use WxWidgets through the POE adaptor, as POE has a Wx backend that
872 simply polls 20 times per second, which was considered to be too
873 horrible to even consider for AnyEvent.
874
875 Prima is not supported as nobody seems to be using it, but it has a
876 POE backend, so it can be supported through POE.
877
878 AnyEvent knows about both Prima and Wx, however, and will try to
879 load POE when detecting them, in the hope that POE will pick them
880 up, in which case everything will be automatic.
500 881
501GLOBAL VARIABLES AND FUNCTIONS 882GLOBAL VARIABLES AND FUNCTIONS
883 These are not normally required to use AnyEvent, but can be useful to
884 write AnyEvent extension modules.
885
502 $AnyEvent::MODEL 886 $AnyEvent::MODEL
503 Contains "undef" until the first watcher is being created. Then it 887 Contains "undef" until the first watcher is being created, before
888 the backend has been autodetected.
889
504 contains the event model that is being used, which is the name of 890 Afterwards it contains the event model that is being used, which is
505 the Perl class implementing the model. This class is usually one of 891 the name of the Perl class implementing the model. This class is
506 the "AnyEvent::Impl:xxx" modules, but can be any other class in the 892 usually one of the "AnyEvent::Impl::xxx" modules, but can be any
507 case AnyEvent has been extended at runtime (e.g. in *rxvt-unicode*). 893 other class in the case AnyEvent has been extended at runtime (e.g.
508 894 in *rxvt-unicode* it will be "urxvt::anyevent").
509 The known classes so far are:
510
511 AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
512 AnyEvent::Impl::Event based on Event, second best choice.
513 AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
514 AnyEvent::Impl::Glib based on Glib, third-best choice.
515 AnyEvent::Impl::Tk based on Tk, very bad choice.
516 AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
517 AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
518 AnyEvent::Impl::POE based on POE, not generic enough for full support.
519
520 There is no support for WxWidgets, as WxWidgets has no support for
521 watching file handles. However, you can use WxWidgets through the
522 POE Adaptor, as POE has a Wx backend that simply polls 20 times per
523 second, which was considered to be too horrible to even consider for
524 AnyEvent. Likewise, other POE backends can be used by AnyEvent by
525 using it's adaptor.
526
527 AnyEvent knows about Prima and Wx and will try to use POE when
528 autodetecting them.
529 895
530 AnyEvent::detect 896 AnyEvent::detect
531 Returns $AnyEvent::MODEL, forcing autodetection of the event model 897 Returns $AnyEvent::MODEL, forcing autodetection of the event model
532 if necessary. You should only call this function right before you 898 if necessary. You should only call this function right before you
533 would have created an AnyEvent watcher anyway, that is, as late as 899 would have created an AnyEvent watcher anyway, that is, as late as
534 possible at runtime. 900 possible at runtime, and not e.g. during initialisation of your
901 module.
902
903 The effect of calling this function is as if a watcher had been
904 created (specifically, actions that happen "when the first watcher
905 is created" happen when calling detetc as well).
906
907 If you need to do some initialisation before AnyEvent watchers are
908 created, use "post_detect".
535 909
536 $guard = AnyEvent::post_detect { BLOCK } 910 $guard = AnyEvent::post_detect { BLOCK }
537 Arranges for the code block to be executed as soon as the event 911 Arranges for the code block to be executed as soon as the event
538 model is autodetected (or immediately if this has already happened). 912 model is autodetected (or immediately if that has already happened).
913
914 The block will be executed *after* the actual backend has been
915 detected ($AnyEvent::MODEL is set), but *before* any watchers have
916 been created, so it is possible to e.g. patch @AnyEvent::ISA or do
917 other initialisations - see the sources of AnyEvent::Strict or
918 AnyEvent::AIO to see how this is used.
919
920 The most common usage is to create some global watchers, without
921 forcing event module detection too early, for example, AnyEvent::AIO
922 creates and installs the global IO::AIO watcher in a "post_detect"
923 block to avoid autodetecting the event module at load time.
539 924
540 If called in scalar or list context, then it creates and returns an 925 If called in scalar or list context, then it creates and returns an
541 object that automatically removes the callback again when it is 926 object that automatically removes the callback again when it is
927 destroyed (or "undef" when the hook was immediately executed). See
542 destroyed. See Coro::BDB for a case where this is useful. 928 AnyEvent::AIO for a case where this is useful.
929
930 Example: Create a watcher for the IO::AIO module and store it in
931 $WATCHER, but do so only do so after the event loop is initialised.
932
933 our WATCHER;
934
935 my $guard = AnyEvent::post_detect {
936 $WATCHER = AnyEvent->io (fh => IO::AIO::poll_fileno, poll => 'r', cb => \&IO::AIO::poll_cb);
937 };
938
939 # the ||= is important in case post_detect immediately runs the block,
940 # as to not clobber the newly-created watcher. assigning both watcher and
941 # post_detect guard to the same variable has the advantage of users being
942 # able to just C<undef $WATCHER> if the watcher causes them grief.
943
944 $WATCHER ||= $guard;
543 945
544 @AnyEvent::post_detect 946 @AnyEvent::post_detect
545 If there are any code references in this array (you can "push" to it 947 If there are any code references in this array (you can "push" to it
546 before or after loading AnyEvent), then they will called directly 948 before or after loading AnyEvent), then they will be called directly
547 after the event loop has been chosen. 949 after the event loop has been chosen.
548 950
549 You should check $AnyEvent::MODEL before adding to this array, 951 You should check $AnyEvent::MODEL before adding to this array,
550 though: if it contains a true value then the event loop has already 952 though: if it is defined then the event loop has already been
551 been detected, and the array will be ignored. 953 detected, and the array will be ignored.
552 954
553 Best use "AnyEvent::post_detect { BLOCK }" instead. 955 Best use "AnyEvent::post_detect { BLOCK }" when your application
956 allows it, as it takes care of these details.
957
958 This variable is mainly useful for modules that can do something
959 useful when AnyEvent is used and thus want to know when it is
960 initialised, but do not need to even load it by default. This array
961 provides the means to hook into AnyEvent passively, without loading
962 it.
963
964 Example: To load Coro::AnyEvent whenever Coro and AnyEvent are used
965 together, you could put this into Coro (this is the actual code used
966 by Coro to accomplish this):
967
968 if (defined $AnyEvent::MODEL) {
969 # AnyEvent already initialised, so load Coro::AnyEvent
970 require Coro::AnyEvent;
971 } else {
972 # AnyEvent not yet initialised, so make sure to load Coro::AnyEvent
973 # as soon as it is
974 push @AnyEvent::post_detect, sub { require Coro::AnyEvent };
975 }
976
977 AnyEvent::postpone { BLOCK }
978 Arranges for the block to be executed as soon as possible, but not
979 before the call itself returns. In practise, the block will be
980 executed just before the event loop polls for new events, or shortly
981 afterwards.
982
983 This function never returns anything (to make the "return postpone {
984 ... }" idiom more useful.
985
986 To understand the usefulness of this function, consider a function
987 that asynchronously does something for you and returns some
988 transaction object or guard to let you cancel the operation. For
989 example, "AnyEvent::Socket::tcp_connect":
990
991 # start a connection attempt unless one is active
992 $self->{connect_guard} ||= AnyEvent::Socket::tcp_connect "www.example.net", 80, sub {
993 delete $self->{connect_guard};
994 ...
995 };
996
997 Imagine that this function could instantly call the callback, for
998 example, because it detects an obvious error such as a negative port
999 number. Invoking the callback before the function returns causes
1000 problems however: the callback will be called and will try to delete
1001 the guard object. But since the function hasn't returned yet, there
1002 is nothing to delete. When the function eventually returns it will
1003 assign the guard object to "$self->{connect_guard}", where it will
1004 likely never be deleted, so the program thinks it is still trying to
1005 connect.
1006
1007 This is where "AnyEvent::postpone" should be used. Instead of
1008 calling the callback directly on error:
1009
1010 $cb->(undef), return # signal error to callback, BAD!
1011 if $some_error_condition;
1012
1013 It should use "postpone":
1014
1015 AnyEvent::postpone { $cb->(undef) }, return # signal error to callback, later
1016 if $some_error_condition;
1017
1018 AnyEvent::log $level, $msg[, @args]
1019 Log the given $msg at the given $level.
1020
1021 If AnyEvent::Log is not loaded then this function makes a simple
1022 test to see whether the message will be logged. If the test succeeds
1023 it will load AnyEvent::Log and call "AnyEvent::Log::log" -
1024 consequently, look at the AnyEvent::Log documentation for details.
1025
1026 If the test fails it will simply return. Right now this happens when
1027 a numerical loglevel is used and it is larger than the level
1028 specified via $ENV{PERL_ANYEVENT_VERBOSE}.
1029
1030 If you want to sprinkle loads of logging calls around your code,
1031 consider creating a logger callback with the "AnyEvent::Log::logger"
1032 function, which can reduce typing, codesize and can reduce the
1033 logging overhead enourmously.
554 1034
555WHAT TO DO IN A MODULE 1035WHAT TO DO IN A MODULE
556 As a module author, you should "use AnyEvent" and call AnyEvent methods 1036 As a module author, you should "use AnyEvent" and call AnyEvent methods
557 freely, but you should not load a specific event module or rely on it. 1037 freely, but you should not load a specific event module or rely on it.
558 1038
… …
566 stall the whole program, and the whole point of using events is to stay 1046 stall the whole program, and the whole point of using events is to stay
567 interactive. 1047 interactive.
568 1048
569 It is fine, however, to call "->recv" when the user of your module 1049 It is fine, however, to call "->recv" when the user of your module
570 requests it (i.e. if you create a http request object ad have a method 1050 requests it (i.e. if you create a http request object ad have a method
571 called "results" that returns the results, it should call "->recv" 1051 called "results" that returns the results, it may call "->recv" freely,
572 freely, as the user of your module knows what she is doing. always). 1052 as the user of your module knows what she is doing. Always).
573 1053
574WHAT TO DO IN THE MAIN PROGRAM 1054WHAT TO DO IN THE MAIN PROGRAM
575 There will always be a single main program - the only place that should 1055 There will always be a single main program - the only place that should
576 dictate which event model to use. 1056 dictate which event model to use.
577 1057
578 If it doesn't care, it can just "use AnyEvent" and use it itself, or not 1058 If the program is not event-based, it need not do anything special, even
579 do anything special (it does not need to be event-based) and let 1059 when it depends on a module that uses an AnyEvent. If the program itself
580 AnyEvent decide which implementation to chose if some module relies on 1060 uses AnyEvent, but does not care which event loop is used, all it needs
581 it. 1061 to do is "use AnyEvent". In either case, AnyEvent will choose the best
1062 available loop implementation.
582 1063
583 If the main program relies on a specific event model. For example, in 1064 If the main program relies on a specific event model - for example, in
584 Gtk2 programs you have to rely on the Glib module. You should load the 1065 Gtk2 programs you have to rely on the Glib module - you should load the
585 event module before loading AnyEvent or any module that uses it: 1066 event module before loading AnyEvent or any module that uses it:
586 generally speaking, you should load it as early as possible. The reason 1067 generally speaking, you should load it as early as possible. The reason
587 is that modules might create watchers when they are loaded, and AnyEvent 1068 is that modules might create watchers when they are loaded, and AnyEvent
588 will decide on the event model to use as soon as it creates watchers, 1069 will decide on the event model to use as soon as it creates watchers,
589 and it might chose the wrong one unless you load the correct one 1070 and it might choose the wrong one unless you load the correct one
590 yourself. 1071 yourself.
591 1072
592 You can chose to use a rather inefficient pure-perl implementation by 1073 You can chose to use a pure-perl implementation by loading the
593 loading the "AnyEvent::Impl::Perl" module, which gives you similar 1074 "AnyEvent::Loop" module, which gives you similar behaviour everywhere,
594 behaviour everywhere, but letting AnyEvent chose is generally better. 1075 but letting AnyEvent chose the model is generally better.
1076
1077 MAINLOOP EMULATION
1078 Sometimes (often for short test scripts, or even standalone programs who
1079 only want to use AnyEvent), you do not want to run a specific event
1080 loop.
1081
1082 In that case, you can use a condition variable like this:
1083
1084 AnyEvent->condvar->recv;
1085
1086 This has the effect of entering the event loop and looping forever.
1087
1088 Note that usually your program has some exit condition, in which case it
1089 is better to use the "traditional" approach of storing a condition
1090 variable somewhere, waiting for it, and sending it when the program
1091 should exit cleanly.
595 1092
596OTHER MODULES 1093OTHER MODULES
597 The following is a non-exhaustive list of additional modules that use 1094 The following is a non-exhaustive list of additional modules that use
598 AnyEvent and can therefore be mixed easily with other AnyEvent modules 1095 AnyEvent as a client and can therefore be mixed easily with other
599 in the same program. Some of the modules come with AnyEvent, some are 1096 AnyEvent modules and other event loops in the same program. Some of the
600 available via CPAN. 1097 modules come as part of AnyEvent, the others are available via CPAN (see
1098 <http://search.cpan.org/search?m=module&q=anyevent%3A%3A*> for a longer
1099 non-exhaustive list), and the list is heavily biased towards modules of
1100 the AnyEvent author himself :)
601 1101
602 AnyEvent::Util 1102 AnyEvent::Util (part of the AnyEvent distribution)
603 Contains various utility functions that replace often-used but 1103 Contains various utility functions that replace often-used blocking
604 blocking functions such as "inet_aton" by event-/callback-based 1104 functions such as "inet_aton" with event/callback-based versions.
605 versions.
606 1105
607 AnyEvent::Handle 1106 AnyEvent::Socket (part of the AnyEvent distribution)
608 Provide read and write buffers and manages watchers for reads and
609 writes.
610
611 AnyEvent::Socket
612 Provides various utility functions for (internet protocol) sockets, 1107 Provides various utility functions for (internet protocol) sockets,
613 addresses and name resolution. Also functions to create non-blocking 1108 addresses and name resolution. Also functions to create non-blocking
614 tcp connections or tcp servers, with IPv6 and SRV record support and 1109 tcp connections or tcp servers, with IPv6 and SRV record support and
615 more. 1110 more.
616 1111
617 AnyEvent::HTTPD 1112 AnyEvent::Handle (part of the AnyEvent distribution)
618 Provides a simple web application server framework. 1113 Provide read and write buffers, manages watchers for reads and
1114 writes, supports raw and formatted I/O, I/O queued and fully
1115 transparent and non-blocking SSL/TLS (via AnyEvent::TLS).
619 1116
620 AnyEvent::DNS 1117 AnyEvent::DNS (part of the AnyEvent distribution)
621 Provides rich asynchronous DNS resolver capabilities. 1118 Provides rich asynchronous DNS resolver capabilities.
1119
1120 AnyEvent::HTTP, AnyEvent::IRC, AnyEvent::XMPP, AnyEvent::GPSD,
1121 AnyEvent::IGS, AnyEvent::FCP
1122 Implement event-based interfaces to the protocols of the same name
1123 (for the curious, IGS is the International Go Server and FCP is the
1124 Freenet Client Protocol).
1125
1126 AnyEvent::AIO (part of the AnyEvent distribution)
1127 Truly asynchronous (as opposed to non-blocking) I/O, should be in
1128 the toolbox of every event programmer. AnyEvent::AIO transparently
1129 fuses IO::AIO and AnyEvent together, giving AnyEvent access to
1130 event-based file I/O, and much more.
1131
1132 AnyEvent::Fork, AnyEvent::Fork::RPC, AnyEvent::Fork::Pool,
1133 AnyEvent::Fork::Remote
1134 These let you safely fork new subprocesses, either locally or
1135 remotely (e.g.v ia ssh), using some RPC protocol or not, without the
1136 limitations normally imposed by fork (AnyEvent works fine for
1137 example). Dynamically-resized worker pools are obviously included as
1138 well.
1139
1140 And they are quite tiny and fast as well - "abusing" AnyEvent::Fork
1141 just to exec external programs can easily beat using "fork" and
1142 "exec" (or even "system") in most programs.
1143
1144 AnyEvent::Filesys::Notify
1145 AnyEvent is good for non-blocking stuff, but it can't detect file or
1146 path changes (e.g. "watch this directory for new files", "watch this
1147 file for changes"). The AnyEvent::Filesys::Notify module promises to
1148 do just that in a portbale fashion, supporting inotify on GNU/Linux
1149 and some weird, without doubt broken, stuff on OS X to monitor
1150 files. It can fall back to blocking scans at regular intervals
1151 transparently on other platforms, so it's about as portable as it
1152 gets.
1153
1154 (I haven't used it myself, but it seems the biggest problem with it
1155 is it quite bad performance).
1156
1157 AnyEvent::DBI
1158 Executes DBI requests asynchronously in a proxy process for you,
1159 notifying you in an event-based way when the operation is finished.
622 1160
623 AnyEvent::FastPing 1161 AnyEvent::FastPing
624 The fastest ping in the west. 1162 The fastest ping in the west.
625 1163
626 Net::IRC3
627 AnyEvent based IRC client module family.
628
629 Net::XMPP2
630 AnyEvent based XMPP (Jabber protocol) module family.
631
632 Net::FCP
633 AnyEvent-based implementation of the Freenet Client Protocol,
634 birthplace of AnyEvent.
635
636 Event::ExecFlow
637 High level API for event-based execution flow control.
638
639 Coro 1164 Coro
640 Has special support for AnyEvent via Coro::AnyEvent. 1165 Has special support for AnyEvent via Coro::AnyEvent, which allows
1166 you to simply invert the flow control - don't call us, we will call
1167 you:
641 1168
642 AnyEvent::AIO, IO::AIO 1169 async {
643 Truly asynchronous I/O, should be in the toolbox of every event 1170 Coro::AnyEvent::sleep 5; # creates a 5s timer and waits for it
644 programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent 1171 print "5 seconds later!\n";
645 together.
646 1172
647 AnyEvent::BDB, BDB 1173 Coro::AnyEvent::readable *STDIN; # uses an I/O watcher
648 Truly asynchronous Berkeley DB access. AnyEvent::AIO transparently 1174 my $line = <STDIN>; # works for ttys
649 fuses IO::AIO and AnyEvent together.
650 1175
651 IO::Lambda 1176 AnyEvent::HTTP::http_get "url", Coro::rouse_cb;
652 The lambda approach to I/O - don't ask, look there. Can use 1177 my ($body, $hdr) = Coro::rouse_wait;
1178 };
1179
1180SIMPLIFIED AE API
1181 Starting with version 5.0, AnyEvent officially supports a second, much
1182 simpler, API that is designed to reduce the calling, typing and memory
1183 overhead by using function call syntax and a fixed number of parameters.
1184
1185 See the AE manpage for details.
1186
1187ERROR AND EXCEPTION HANDLING
1188 In general, AnyEvent does not do any error handling - it relies on the
1189 caller to do that if required. The AnyEvent::Strict module (see also the
1190 "PERL_ANYEVENT_STRICT" environment variable, below) provides strict
1191 checking of all AnyEvent methods, however, which is highly useful during
1192 development.
1193
1194 As for exception handling (i.e. runtime errors and exceptions thrown
1195 while executing a callback), this is not only highly event-loop
1196 specific, but also not in any way wrapped by this module, as this is the
1197 job of the main program.
1198
1199 The pure perl event loop simply re-throws the exception (usually within
1200 "condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",
1201 Glib uses "install_exception_handler" and so on.
1202
1203ENVIRONMENT VARIABLES
1204 AnyEvent supports a number of environment variables that tune the
1205 runtime behaviour. They are usually evaluated when AnyEvent is loaded,
1206 initialised, or a submodule that uses them is loaded. Many of them also
1207 cause AnyEvent to load additional modules - for example,
1208 "PERL_ANYEVENT_DEBUG_WRAP" causes the AnyEvent::Debug module to be
1209 loaded.
1210
1211 All the environment variables documented here start with
1212 "PERL_ANYEVENT_", which is what AnyEvent considers its own namespace.
1213 Other modules are encouraged (but by no means required) to use
1214 "PERL_ANYEVENT_SUBMODULE" if they have registered the
1215 AnyEvent::Submodule namespace on CPAN, for any submodule. For example,
1216 AnyEvent::HTTP could be expected to use "PERL_ANYEVENT_HTTP_PROXY" (it
1217 should not access env variables starting with "AE_", see below).
1218
1219 All variables can also be set via the "AE_" prefix, that is, instead of
1220 setting "PERL_ANYEVENT_VERBOSE" you can also set "AE_VERBOSE". In case
1221 there is a clash btween anyevent and another program that uses
1222 "AE_something" you can set the corresponding "PERL_ANYEVENT_something"
1223 variable to the empty string, as those variables take precedence.
1224
1225 When AnyEvent is first loaded, it copies all "AE_xxx" env variables to
1226 their "PERL_ANYEVENT_xxx" counterpart unless that variable already
1227 exists. If taint mode is on, then AnyEvent will remove *all* environment
1228 variables starting with "PERL_ANYEVENT_" from %ENV (or replace them with
1229 "undef" or the empty string, if the corresaponding "AE_" variable is
1230 set).
1231
1232 The exact algorithm is currently:
1233
1234 1. if taint mode enabled, delete all PERL_ANYEVENT_xyz variables from %ENV
1235 2. copy over AE_xyz to PERL_ANYEVENT_xyz unless the latter alraedy exists
1236 3. if taint mode enabled, set all PERL_ANYEVENT_xyz variables to undef.
1237
1238 This ensures that child processes will not see the "AE_" variables.
1239
1240 The following environment variables are currently known to AnyEvent:
1241
1242 "PERL_ANYEVENT_VERBOSE"
1243 By default, AnyEvent will log messages with loglevel 4 ("error") or
1244 higher (see AnyEvent::Log). You can set this environment variable to
1245 a numerical loglevel to make AnyEvent more (or less) talkative.
1246
1247 If you want to do more than just set the global logging level you
1248 should have a look at "PERL_ANYEVENT_LOG", which allows much more
1249 complex specifications.
1250
1251 When set to 0 ("off"), then no messages whatsoever will be logged
1252 with everything else at defaults.
1253
1254 When set to 5 or higher ("warn"), AnyEvent warns about unexpected
1255 conditions, such as not being able to load the event model specified
1256 by "PERL_ANYEVENT_MODEL", or a guard callback throwing an exception
1257 - this is the minimum recommended level for use during development.
1258
1259 When set to 7 or higher (info), AnyEvent reports which event model
1260 it chooses.
1261
1262 When set to 8 or higher (debug), then AnyEvent will report extra
1263 information on which optional modules it loads and how it implements
1264 certain features.
1265
1266 "PERL_ANYEVENT_LOG"
1267 Accepts rather complex logging specifications. For example, you
1268 could log all "debug" messages of some module to stderr, warnings
1269 and above to stderr, and errors and above to syslog, with:
1270
1271 PERL_ANYEVENT_LOG=Some::Module=debug,+log:filter=warn,+%syslog:%syslog=error,syslog
1272
1273 For the rather extensive details, see AnyEvent::Log.
1274
1275 This variable is evaluated when AnyEvent (or AnyEvent::Log) is
1276 loaded, so will take effect even before AnyEvent has initialised
1277 itself.
1278
1279 Note that specifying this environment variable causes the
1280 AnyEvent::Log module to be loaded, while "PERL_ANYEVENT_VERBOSE"
1281 does not, so only using the latter saves a few hundred kB of memory
1282 unless a module explicitly needs the extra features of
653 AnyEvent. 1283 AnyEvent::Log.
1284
1285 "PERL_ANYEVENT_STRICT"
1286 AnyEvent does not do much argument checking by default, as thorough
1287 argument checking is very costly. Setting this variable to a true
1288 value will cause AnyEvent to load "AnyEvent::Strict" and then to
1289 thoroughly check the arguments passed to most method calls. If it
1290 finds any problems, it will croak.
1291
1292 In other words, enables "strict" mode.
1293
1294 Unlike "use strict" (or its modern cousin, "use common::sense", it
1295 is definitely recommended to keep it off in production. Keeping
1296 "PERL_ANYEVENT_STRICT=1" in your environment while developing
1297 programs can be very useful, however.
1298
1299 "PERL_ANYEVENT_DEBUG_SHELL"
1300 If this env variable is nonempty, then its contents will be
1301 interpreted by "AnyEvent::Socket::parse_hostport" and
1302 "AnyEvent::Debug::shell" (after replacing every occurance of $$ by
1303 the process pid). The shell object is saved in
1304 $AnyEvent::Debug::SHELL.
1305
1306 This happens when the first watcher is created.
1307
1308 For example, to bind a debug shell on a unix domain socket in
1309 /tmp/debug<pid>.sock, you could use this:
1310
1311 PERL_ANYEVENT_DEBUG_SHELL=/tmp/debug\$\$.sock perlprog
1312 # connect with e.g.: socat readline /tmp/debug123.sock
1313
1314 Or to bind to tcp port 4545 on localhost:
1315
1316 PERL_ANYEVENT_DEBUG_SHELL=127.0.0.1:4545 perlprog
1317 # connect with e.g.: telnet localhost 4545
1318
1319 Note that creating sockets in /tmp or on localhost is very unsafe on
1320 multiuser systems.
1321
1322 "PERL_ANYEVENT_DEBUG_WRAP"
1323 Can be set to 0, 1 or 2 and enables wrapping of all watchers for
1324 debugging purposes. See "AnyEvent::Debug::wrap" for details.
1325
1326 "PERL_ANYEVENT_MODEL"
1327 This can be used to specify the event model to be used by AnyEvent,
1328 before auto detection and -probing kicks in.
1329
1330 It normally is a string consisting entirely of ASCII letters (e.g.
1331 "EV" or "IOAsync"). The string "AnyEvent::Impl::" gets prepended and
1332 the resulting module name is loaded and - if the load was successful
1333 - used as event model backend. If it fails to load then AnyEvent
1334 will proceed with auto detection and -probing.
1335
1336 If the string ends with "::" instead (e.g. "AnyEvent::Impl::EV::")
1337 then nothing gets prepended and the module name is used as-is (hint:
1338 "::" at the end of a string designates a module name and quotes it
1339 appropriately).
1340
1341 For example, to force the pure perl model (AnyEvent::Loop::Perl) you
1342 could start your program like this:
1343
1344 PERL_ANYEVENT_MODEL=Perl perl ...
1345
1346 "PERL_ANYEVENT_IO_MODEL"
1347 The current file I/O model - see AnyEvent::IO for more info.
1348
1349 At the moment, only "Perl" (small, pure-perl, synchronous) and
1350 "IOAIO" (truly asynchronous) are supported. The default is "IOAIO"
1351 if AnyEvent::AIO can be loaded, otherwise it is "Perl".
1352
1353 "PERL_ANYEVENT_PROTOCOLS"
1354 Used by both AnyEvent::DNS and AnyEvent::Socket to determine
1355 preferences for IPv4 or IPv6. The default is unspecified (and might
1356 change, or be the result of auto probing).
1357
1358 Must be set to a comma-separated list of protocols or address
1359 families, current supported: "ipv4" and "ipv6". Only protocols
1360 mentioned will be used, and preference will be given to protocols
1361 mentioned earlier in the list.
1362
1363 This variable can effectively be used for denial-of-service attacks
1364 against local programs (e.g. when setuid), although the impact is
1365 likely small, as the program has to handle connection and other
1366 failures anyways.
1367
1368 Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
1369 IPv6, but support both and try to use both.
1370 "PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
1371 resolve or contact IPv6 addresses.
1372 "PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but
1373 prefer IPv6 over IPv4.
1374
1375 "PERL_ANYEVENT_HOSTS"
1376 This variable, if specified, overrides the /etc/hosts file used by
1377 AnyEvent::Socket"::resolve_sockaddr", i.e. hosts aliases will be
1378 read from that file instead.
1379
1380 "PERL_ANYEVENT_EDNS0"
1381 Used by AnyEvent::DNS to decide whether to use the EDNS0 extension
1382 for DNS. This extension is generally useful to reduce DNS traffic,
1383 especially when DNSSEC is involved, but some (broken) firewalls drop
1384 such DNS packets, which is why it is off by default.
1385
1386 Setting this variable to 1 will cause AnyEvent::DNS to announce
1387 EDNS0 in its DNS requests.
1388
1389 "PERL_ANYEVENT_MAX_FORKS"
1390 The maximum number of child processes that
1391 "AnyEvent::Util::fork_call" will create in parallel.
1392
1393 "PERL_ANYEVENT_MAX_OUTSTANDING_DNS"
1394 The default value for the "max_outstanding" parameter for the
1395 default DNS resolver - this is the maximum number of parallel DNS
1396 requests that are sent to the DNS server.
1397
1398 "PERL_ANYEVENT_MAX_SIGNAL_LATENCY"
1399 Perl has inherently racy signal handling (you can basically choose
1400 between losing signals and memory corruption) - pure perl event
1401 loops (including "AnyEvent::Loop", when "Async::Interrupt" isn't
1402 available) therefore have to poll regularly to avoid losing signals.
1403
1404 Some event loops are racy, but don't poll regularly, and some event
1405 loops are written in C but are still racy. For those event loops,
1406 AnyEvent installs a timer that regularly wakes up the event loop.
1407
1408 By default, the interval for this timer is 10 seconds, but you can
1409 override this delay with this environment variable (or by setting
1410 the $AnyEvent::MAX_SIGNAL_LATENCY variable before creating signal
1411 watchers).
1412
1413 Lower values increase CPU (and energy) usage, higher values can
1414 introduce long delays when reaping children or waiting for signals.
1415
1416 The AnyEvent::Async module, if available, will be used to avoid this
1417 polling (with most event loops).
1418
1419 "PERL_ANYEVENT_RESOLV_CONF"
1420 The absolute path to a resolv.conf-style file to use instead of
1421 /etc/resolv.conf (or the OS-specific configuration) in the default
1422 resolver, or the empty string to select the default configuration.
1423
1424 "PERL_ANYEVENT_CA_FILE", "PERL_ANYEVENT_CA_PATH".
1425 When neither "ca_file" nor "ca_path" was specified during
1426 AnyEvent::TLS context creation, and either of these environment
1427 variables are nonempty, they will be used to specify CA certificate
1428 locations instead of a system-dependent default.
1429
1430 "PERL_ANYEVENT_AVOID_GUARD" and "PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT"
1431 When these are set to 1, then the respective modules are not loaded.
1432 Mostly good for testing AnyEvent itself.
654 1433
655SUPPLYING YOUR OWN EVENT MODEL INTERFACE 1434SUPPLYING YOUR OWN EVENT MODEL INTERFACE
656 This is an advanced topic that you do not normally need to use AnyEvent 1435 This is an advanced topic that you do not normally need to use AnyEvent
657 in a module. This section is only of use to event loop authors who want 1436 in a module. This section is only of use to event loop authors who want
658 to provide AnyEvent compatibility. 1437 to provide AnyEvent compatibility.
… …
692 1471
693 *rxvt-unicode* also cheats a bit by not providing blocking access to 1472 *rxvt-unicode* also cheats a bit by not providing blocking access to
694 condition variables: code blocking while waiting for a condition will 1473 condition variables: code blocking while waiting for a condition will
695 "die". This still works with most modules/usages, and blocking calls 1474 "die". This still works with most modules/usages, and blocking calls
696 must not be done in an interactive application, so it makes sense. 1475 must not be done in an interactive application, so it makes sense.
697
698ENVIRONMENT VARIABLES
699 The following environment variables are used by this module:
700
701 "PERL_ANYEVENT_VERBOSE"
702 By default, AnyEvent will be completely silent except in fatal
703 conditions. You can set this environment variable to make AnyEvent
704 more talkative.
705
706 When set to 1 or higher, causes AnyEvent to warn about unexpected
707 conditions, such as not being able to load the event model specified
708 by "PERL_ANYEVENT_MODEL".
709
710 When set to 2 or higher, cause AnyEvent to report to STDERR which
711 event model it chooses.
712
713 "PERL_ANYEVENT_MODEL"
714 This can be used to specify the event model to be used by AnyEvent,
715 before auto detection and -probing kicks in. It must be a string
716 consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
717 gets prepended and the resulting module name is loaded and if the
718 load was successful, used as event model. If it fails to load
719 AnyEvent will proceed with auto detection and -probing.
720
721 This functionality might change in future versions.
722
723 For example, to force the pure perl model (AnyEvent::Impl::Perl) you
724 could start your program like this:
725
726 PERL_ANYEVENT_MODEL=Perl perl ...
727
728 "PERL_ANYEVENT_PROTOCOLS"
729 Used by both AnyEvent::DNS and AnyEvent::Socket to determine
730 preferences for IPv4 or IPv6. The default is unspecified (and might
731 change, or be the result of auto probing).
732
733 Must be set to a comma-separated list of protocols or address
734 families, current supported: "ipv4" and "ipv6". Only protocols
735 mentioned will be used, and preference will be given to protocols
736 mentioned earlier in the list.
737
738 This variable can effectively be used for denial-of-service attacks
739 against local programs (e.g. when setuid), although the impact is
740 likely small, as the program has to handle connection errors
741 already-
742
743 Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
744 IPv6, but support both and try to use both.
745 "PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
746 resolve or contact IPv6 addresses.
747 "PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but
748 prefer IPv6 over IPv4.
749
750 "PERL_ANYEVENT_EDNS0"
751 Used by AnyEvent::DNS to decide whether to use the EDNS0 extension
752 for DNS. This extension is generally useful to reduce DNS traffic,
753 but some (broken) firewalls drop such DNS packets, which is why it
754 is off by default.
755
756 Setting this variable to 1 will cause AnyEvent::DNS to announce
757 EDNS0 in its DNS requests.
758 1476
759EXAMPLE PROGRAM 1477EXAMPLE PROGRAM
760 The following program uses an I/O watcher to read data from STDIN, a 1478 The following program uses an I/O watcher to read data from STDIN, a
761 timer to display a message once per second, and a condition variable to 1479 timer to display a message once per second, and a condition variable to
762 quit the program when the user enters quit: 1480 quit the program when the user enters quit:
… …
774 warn "read: $input\n"; # output what has been read 1492 warn "read: $input\n"; # output what has been read
775 $cv->send if $input =~ /^q/i; # quit program if /^q/i 1493 $cv->send if $input =~ /^q/i; # quit program if /^q/i
776 }, 1494 },
777 ); 1495 );
778 1496
779 my $time_watcher; # can only be used once
780
781 sub new_timer {
782 $timer = AnyEvent->timer (after => 1, cb => sub { 1497 my $time_watcher = AnyEvent->timer (after => 1, interval => 1, cb => sub {
783 warn "timeout\n"; # print 'timeout' about every second 1498 warn "timeout\n"; # print 'timeout' at most every second
784 &new_timer; # and restart the time
785 });
786 } 1499 });
787
788 new_timer; # create first timer
789 1500
790 $cv->recv; # wait until user enters /^q/i 1501 $cv->recv; # wait until user enters /^q/i
791 1502
792REAL-WORLD EXAMPLE 1503REAL-WORLD EXAMPLE
793 Consider the Net::FCP module. It features (among others) the following 1504 Consider the Net::FCP module. It features (among others) the following
… …
865 1576
866 The actual code goes further and collects all errors ("die"s, 1577 The actual code goes further and collects all errors ("die"s,
867 exceptions) that occurred during request processing. The "result" method 1578 exceptions) that occurred during request processing. The "result" method
868 detects whether an exception as thrown (it is stored inside the $txn 1579 detects whether an exception as thrown (it is stored inside the $txn
869 object) and just throws the exception, which means connection errors and 1580 object) and just throws the exception, which means connection errors and
870 other problems get reported tot he code that tries to use the result, 1581 other problems get reported to the code that tries to use the result,
871 not in a random callback. 1582 not in a random callback.
872 1583
873 All of this enables the following usage styles: 1584 All of this enables the following usage styles:
874 1585
875 1. Blocking: 1586 1. Blocking:
… …
920 through AnyEvent. The benchmark creates a lot of timers (with a zero 1631 through AnyEvent. The benchmark creates a lot of timers (with a zero
921 timeout) and I/O watchers (watching STDOUT, a pty, to become writable, 1632 timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
922 which it is), lets them fire exactly once and destroys them again. 1633 which it is), lets them fire exactly once and destroys them again.
923 1634
924 Source code for this benchmark is found as eg/bench in the AnyEvent 1635 Source code for this benchmark is found as eg/bench in the AnyEvent
925 distribution. 1636 distribution. It uses the AE interface, which makes a real difference
1637 for the EV and Perl backends only.
926 1638
927 Explanation of the columns 1639 Explanation of the columns
928 *watcher* is the number of event watchers created/destroyed. Since 1640 *watcher* is the number of event watchers created/destroyed. Since
929 different event models feature vastly different performances, each event 1641 different event models feature vastly different performances, each event
930 loop was given a number of watchers so that overall runtime is 1642 loop was given a number of watchers so that overall runtime is
… …
949 *destroy* is the time, in microseconds, that it takes to destroy a 1661 *destroy* is the time, in microseconds, that it takes to destroy a
950 single watcher. 1662 single watcher.
951 1663
952 Results 1664 Results
953 name watchers bytes create invoke destroy comment 1665 name watchers bytes create invoke destroy comment
954 EV/EV 400000 244 0.56 0.46 0.31 EV native interface 1666 EV/EV 100000 223 0.47 0.43 0.27 EV native interface
955 EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers 1667 EV/Any 100000 223 0.48 0.42 0.26 EV + AnyEvent watchers
956 CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal 1668 Coro::EV/Any 100000 223 0.47 0.42 0.26 coroutines + Coro::Signal
957 Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation 1669 Perl/Any 100000 431 2.70 0.74 0.92 pure perl implementation
958 Event/Event 16000 516 31.88 31.30 0.85 Event native interface 1670 Event/Event 16000 516 31.16 31.84 0.82 Event native interface
959 Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers 1671 Event/Any 16000 1203 42.61 34.79 1.80 Event + AnyEvent watchers
1672 IOAsync/Any 16000 1911 41.92 27.45 16.81 via IO::Async::Loop::IO_Poll
1673 IOAsync/Any 16000 1726 40.69 26.37 15.25 via IO::Async::Loop::Epoll
960 Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour 1674 Glib/Any 16000 1118 89.00 12.57 51.17 quadratic behaviour
961 Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers 1675 Tk/Any 2000 1346 20.96 10.75 8.00 SEGV with >> 2000 watchers
962 POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event 1676 POE/Any 2000 6951 108.97 795.32 14.24 via POE::Loop::Event
963 POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select 1677 POE/Any 2000 6648 94.79 774.40 575.51 via POE::Loop::Select
964 1678
965 Discussion 1679 Discussion
966 The benchmark does *not* measure scalability of the event loop very 1680 The benchmark does *not* measure scalability of the event loop very
967 well. For example, a select-based event loop (such as the pure perl one) 1681 well. For example, a select-based event loop (such as the pure perl one)
968 can never compete with an event loop that uses epoll when the number of 1682 can never compete with an event loop that uses epoll when the number of
… …
979 benchmark machine, handling an event takes roughly 1600 CPU cycles with 1693 benchmark machine, handling an event takes roughly 1600 CPU cycles with
980 EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 1694 EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000
981 CPU cycles with POE. 1695 CPU cycles with POE.
982 1696
983 "EV" is the sole leader regarding speed and memory use, which are both 1697 "EV" is the sole leader regarding speed and memory use, which are both
984 maximal/minimal, respectively. Even when going through AnyEvent, it uses 1698 maximal/minimal, respectively. When using the AE API there is zero
1699 overhead (when going through the AnyEvent API create is about 5-6 times
1700 slower, with other times being equal, so still uses far less memory than
985 far less memory than any other event loop and is still faster than Event 1701 any other event loop and is still faster than Event natively).
986 natively.
987 1702
988 The pure perl implementation is hit in a few sweet spots (both the 1703 The pure perl implementation is hit in a few sweet spots (both the
989 constant timeout and the use of a single fd hit optimisations in the 1704 constant timeout and the use of a single fd hit optimisations in the
990 perl interpreter and the backend itself). Nevertheless this shows that 1705 perl interpreter and the backend itself). Nevertheless this shows that
991 it adds very little overhead in itself. Like any select-based backend 1706 it adds very little overhead in itself. Like any select-based backend
… …
993 few of them active), of course, but this was not subject of this 1708 few of them active), of course, but this was not subject of this
994 benchmark. 1709 benchmark.
995 1710
996 The "Event" module has a relatively high setup and callback invocation 1711 The "Event" module has a relatively high setup and callback invocation
997 cost, but overall scores in on the third place. 1712 cost, but overall scores in on the third place.
1713
1714 "IO::Async" performs admirably well, about on par with "Event", even
1715 when using its pure perl backend.
998 1716
999 "Glib"'s memory usage is quite a bit higher, but it features a faster 1717 "Glib"'s memory usage is quite a bit higher, but it features a faster
1000 callback invocation and overall ends up in the same class as "Event". 1718 callback invocation and overall ends up in the same class as "Event".
1001 However, Glib scales extremely badly, doubling the number of watchers 1719 However, Glib scales extremely badly, doubling the number of watchers
1002 increases the processing time by more than a factor of four, making it 1720 increases the processing time by more than a factor of four, making it
… …
1034 when used without AnyEvent), but most event loops have acceptable 1752 when used without AnyEvent), but most event loops have acceptable
1035 performance with or without AnyEvent. 1753 performance with or without AnyEvent.
1036 1754
1037 * The overhead AnyEvent adds is usually much smaller than the overhead 1755 * The overhead AnyEvent adds is usually much smaller than the overhead
1038 of the actual event loop, only with extremely fast event loops such 1756 of the actual event loop, only with extremely fast event loops such
1039 as EV adds AnyEvent significant overhead. 1757 as EV does AnyEvent add significant overhead.
1040 1758
1041 * You should avoid POE like the plague if you want performance or 1759 * You should avoid POE like the plague if you want performance or
1042 reasonable memory usage. 1760 reasonable memory usage.
1043 1761
1044 BENCHMARKING THE LARGE SERVER CASE 1762 BENCHMARKING THE LARGE SERVER CASE
… …
1058 In this benchmark, we use 10000 socket pairs (20000 sockets), of which 1776 In this benchmark, we use 10000 socket pairs (20000 sockets), of which
1059 100 (1%) are active. This mirrors the activity of large servers with 1777 100 (1%) are active. This mirrors the activity of large servers with
1060 many connections, most of which are idle at any one point in time. 1778 many connections, most of which are idle at any one point in time.
1061 1779
1062 Source code for this benchmark is found as eg/bench2 in the AnyEvent 1780 Source code for this benchmark is found as eg/bench2 in the AnyEvent
1063 distribution. 1781 distribution. It uses the AE interface, which makes a real difference
1782 for the EV and Perl backends only.
1064 1783
1065 Explanation of the columns 1784 Explanation of the columns
1066 *sockets* is the number of sockets, and twice the number of "servers" 1785 *sockets* is the number of sockets, and twice the number of "servers"
1067 (as each server has a read and write socket end). 1786 (as each server has a read and write socket end).
1068 1787
… …
1073 single "request", that is, reading the token from the pipe and 1792 single "request", that is, reading the token from the pipe and
1074 forwarding it to another server. This includes deleting the old timeout 1793 forwarding it to another server. This includes deleting the old timeout
1075 and creating a new one that moves the timeout into the future. 1794 and creating a new one that moves the timeout into the future.
1076 1795
1077 Results 1796 Results
1078 name sockets create request 1797 name sockets create request
1079 EV 20000 69.01 11.16 1798 EV 20000 62.66 7.99
1080 Perl 20000 73.32 35.87 1799 Perl 20000 68.32 32.64
1081 Event 20000 212.62 257.32 1800 IOAsync 20000 174.06 101.15 epoll
1082 Glib 20000 651.16 1896.30 1801 IOAsync 20000 174.67 610.84 poll
1802 Event 20000 202.69 242.91
1803 Glib 20000 557.01 1689.52
1083 POE 20000 349.67 12317.24 uses POE::Loop::Event 1804 POE 20000 341.54 12086.32 uses POE::Loop::Event
1084 1805
1085 Discussion 1806 Discussion
1086 This benchmark *does* measure scalability and overall performance of the 1807 This benchmark *does* measure scalability and overall performance of the
1087 particular event loop. 1808 particular event loop.
1088 1809
1089 EV is again fastest. Since it is using epoll on my system, the setup 1810 EV is again fastest. Since it is using epoll on my system, the setup
1090 time is relatively high, though. 1811 time is relatively high, though.
1091 1812
1092 Perl surprisingly comes second. It is much faster than the C-based event 1813 Perl surprisingly comes second. It is much faster than the C-based event
1093 loops Event and Glib. 1814 loops Event and Glib.
1815
1816 IO::Async performs very well when using its epoll backend, and still
1817 quite good compared to Glib when using its pure perl backend.
1094 1818
1095 Event suffers from high setup time as well (look at its code and you 1819 Event suffers from high setup time as well (look at its code and you
1096 will understand why). Callback invocation also has a high overhead 1820 will understand why). Callback invocation also has a high overhead
1097 compared to the "$_->() for .."-style loop that the Perl event loop 1821 compared to the "$_->() for .."-style loop that the Perl event loop
1098 uses. Event uses select or poll in basically all documented 1822 uses. Event uses select or poll in basically all documented
… …
1149 1873
1150 Summary 1874 Summary
1151 * C-based event loops perform very well with small number of watchers, 1875 * C-based event loops perform very well with small number of watchers,
1152 as the management overhead dominates. 1876 as the management overhead dominates.
1153 1877
1878 THE IO::Lambda BENCHMARK
1879 Recently I was told about the benchmark in the IO::Lambda manpage, which
1880 could be misinterpreted to make AnyEvent look bad. In fact, the
1881 benchmark simply compares IO::Lambda with POE, and IO::Lambda looks
1882 better (which shouldn't come as a surprise to anybody). As such, the
1883 benchmark is fine, and mostly shows that the AnyEvent backend from
1884 IO::Lambda isn't very optimal. But how would AnyEvent compare when used
1885 without the extra baggage? To explore this, I wrote the equivalent
1886 benchmark for AnyEvent.
1887
1888 The benchmark itself creates an echo-server, and then, for 500 times,
1889 connects to the echo server, sends a line, waits for the reply, and then
1890 creates the next connection. This is a rather bad benchmark, as it
1891 doesn't test the efficiency of the framework or much non-blocking I/O,
1892 but it is a benchmark nevertheless.
1893
1894 name runtime
1895 Lambda/select 0.330 sec
1896 + optimized 0.122 sec
1897 Lambda/AnyEvent 0.327 sec
1898 + optimized 0.138 sec
1899 Raw sockets/select 0.077 sec
1900 POE/select, components 0.662 sec
1901 POE/select, raw sockets 0.226 sec
1902 POE/select, optimized 0.404 sec
1903
1904 AnyEvent/select/nb 0.085 sec
1905 AnyEvent/EV/nb 0.068 sec
1906 +state machine 0.134 sec
1907
1908 The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
1909 benchmarks actually make blocking connects and use 100% blocking I/O,
1910 defeating the purpose of an event-based solution. All of the newly
1911 written AnyEvent benchmarks use 100% non-blocking connects (using
1912 AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
1913 resolver), so AnyEvent is at a disadvantage here, as non-blocking
1914 connects generally require a lot more bookkeeping and event handling
1915 than blocking connects (which involve a single syscall only).
1916
1917 The last AnyEvent benchmark additionally uses AnyEvent::Handle, which
1918 offers similar expressive power as POE and IO::Lambda, using
1919 conventional Perl syntax. This means that both the echo server and the
1920 client are 100% non-blocking, further placing it at a disadvantage.
1921
1922 As you can see, the AnyEvent + EV combination even beats the
1923 hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
1924 backend easily beats IO::Lambda and POE.
1925
1926 And even the 100% non-blocking version written using the high-level (and
1927 slow :) AnyEvent::Handle abstraction beats both POE and IO::Lambda
1928 higher level ("unoptimised") abstractions by a large margin, even though
1929 it does all of DNS, tcp-connect and socket I/O in a non-blocking way.
1930
1931 The two AnyEvent benchmarks programs can be found as eg/ae0.pl and
1932 eg/ae2.pl in the AnyEvent distribution, the remaining benchmarks are
1933 part of the IO::Lambda distribution and were used without any changes.
1934
1935SIGNALS
1936 AnyEvent currently installs handlers for these signals:
1937
1938 SIGCHLD
1939 A handler for "SIGCHLD" is installed by AnyEvent's child watcher
1940 emulation for event loops that do not support them natively. Also,
1941 some event loops install a similar handler.
1942
1943 Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE,
1944 then AnyEvent will reset it to default, to avoid losing child exit
1945 statuses.
1946
1947 SIGPIPE
1948 A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is
1949 "undef" when AnyEvent gets loaded.
1950
1951 The rationale for this is that AnyEvent users usually do not really
1952 depend on SIGPIPE delivery (which is purely an optimisation for
1953 shell use, or badly-written programs), but "SIGPIPE" can cause
1954 spurious and rare program exits as a lot of people do not expect
1955 "SIGPIPE" when writing to some random socket.
1956
1957 The rationale for installing a no-op handler as opposed to ignoring
1958 it is that this way, the handler will be restored to defaults on
1959 exec.
1960
1961 Feel free to install your own handler, or reset it to defaults.
1962
1963RECOMMENDED/OPTIONAL MODULES
1964 One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
1965 its built-in modules) are required to use it.
1966
1967 That does not mean that AnyEvent won't take advantage of some additional
1968 modules if they are installed.
1969
1970 This section explains which additional modules will be used, and how
1971 they affect AnyEvent's operation.
1972
1973 Async::Interrupt
1974 This slightly arcane module is used to implement fast signal
1975 handling: To my knowledge, there is no way to do completely
1976 race-free and quick signal handling in pure perl. To ensure that
1977 signals still get delivered, AnyEvent will start an interval timer
1978 to wake up perl (and catch the signals) with some delay (default is
1979 10 seconds, look for $AnyEvent::MAX_SIGNAL_LATENCY).
1980
1981 If this module is available, then it will be used to implement
1982 signal catching, which means that signals will not be delayed, and
1983 the event loop will not be interrupted regularly, which is more
1984 efficient (and good for battery life on laptops).
1985
1986 This affects not just the pure-perl event loop, but also other event
1987 loops that have no signal handling on their own (e.g. Glib, Tk, Qt).
1988
1989 Some event loops (POE, Event, Event::Lib) offer signal watchers
1990 natively, and either employ their own workarounds (POE) or use
1991 AnyEvent's workaround (using $AnyEvent::MAX_SIGNAL_LATENCY).
1992 Installing Async::Interrupt does nothing for those backends.
1993
1994 EV This module isn't really "optional", as it is simply one of the
1995 backend event loops that AnyEvent can use. However, it is simply the
1996 best event loop available in terms of features, speed and stability:
1997 It supports the AnyEvent API optimally, implements all the watcher
1998 types in XS, does automatic timer adjustments even when no monotonic
1999 clock is available, can take avdantage of advanced kernel interfaces
2000 such as "epoll" and "kqueue", and is the fastest backend *by far*.
2001 You can even embed Glib/Gtk2 in it (or vice versa, see EV::Glib and
2002 Glib::EV).
2003
2004 If you only use backends that rely on another event loop (e.g.
2005 "Tk"), then this module will do nothing for you.
2006
2007 Guard
2008 The guard module, when used, will be used to implement
2009 "AnyEvent::Util::guard". This speeds up guards considerably (and
2010 uses a lot less memory), but otherwise doesn't affect guard
2011 operation much. It is purely used for performance.
2012
2013 JSON and JSON::XS
2014 One of these modules is required when you want to read or write JSON
2015 data via AnyEvent::Handle. JSON is also written in pure-perl, but
2016 can take advantage of the ultra-high-speed JSON::XS module when it
2017 is installed.
2018
2019 Net::SSLeay
2020 Implementing TLS/SSL in Perl is certainly interesting, but not very
2021 worthwhile: If this module is installed, then AnyEvent::Handle (with
2022 the help of AnyEvent::TLS), gains the ability to do TLS/SSL.
2023
2024 Time::HiRes
2025 This module is part of perl since release 5.008. It will be used
2026 when the chosen event library does not come with a timing source of
2027 its own. The pure-perl event loop (AnyEvent::Loop) will additionally
2028 load it to try to use a monotonic clock for timing stability.
2029
2030 AnyEvent::AIO (and IO::AIO)
2031 The default implementation of AnyEvent::IO is to do I/O
2032 synchronously, stopping programs while they access the disk, which
2033 is fine for a lot of programs.
2034
2035 Installing AnyEvent::AIO (and its IO::AIO dependency) makes it
2036 switch to a true asynchronous implementation, so event processing
2037 can continue even while waiting for disk I/O.
2038
1154FORK 2039FORK
1155 Most event libraries are not fork-safe. The ones who are usually are 2040 Most event libraries are not fork-safe. The ones who are usually are
1156 because they rely on inefficient but fork-safe "select" or "poll" calls. 2041 because they rely on inefficient but fork-safe "select" or "poll" calls
1157 Only EV is fully fork-aware. 2042 - higher performance APIs such as BSD's kqueue or the dreaded Linux
2043 epoll are usually badly thought-out hacks that are incompatible with
2044 fork in one way or another. Only EV is fully fork-aware and ensures that
2045 you continue event-processing in both parent and child (or both, if you
2046 know what you are doing).
2047
2048 This means that, in general, you cannot fork and do event processing in
2049 the child if the event library was initialised before the fork (which
2050 usually happens when the first AnyEvent watcher is created, or the
2051 library is loaded).
1158 2052
1159 If you have to fork, you must either do so *before* creating your first 2053 If you have to fork, you must either do so *before* creating your first
1160 watcher OR you must not use AnyEvent at all in the child. 2054 watcher OR you must not use AnyEvent at all in the child OR you must do
2055 something completely out of the scope of AnyEvent (see below).
2056
2057 The problem of doing event processing in the parent *and* the child is
2058 much more complicated: even for backends that *are* fork-aware or
2059 fork-safe, their behaviour is not usually what you want: fork clones all
2060 watchers, that means all timers, I/O watchers etc. are active in both
2061 parent and child, which is almost never what you want. Using "exec" to
2062 start worker children from some kind of manage prrocess is usually
2063 preferred, because it is much easier and cleaner, at the expense of
2064 having to have another binary.
2065
2066 In addition to logical problems with fork, there are also implementation
2067 problems. For example, on POSIX systems, you cannot fork at all in Perl
2068 code if a thread (I am talking of pthreads here) was ever created in the
2069 process, and this is just the tip of the iceberg. In general, using fork
2070 from Perl is difficult, and attempting to use fork without an exec to
2071 implement some kind of parallel processing is almost certainly doomed.
2072
2073 To safely fork and exec, you should use a module such as Proc::FastSpawn
2074 that let's you safely fork and exec new processes.
2075
2076 If you want to do multiprocessing using processes, you can look at the
2077 AnyEvent::Fork module (and some related modules such as
2078 AnyEvent::Fork::RPC, AnyEvent::Fork::Pool and AnyEvent::Fork::Remote).
2079 This module allows you to safely create subprocesses without any
2080 limitations - you can use X11 toolkits or AnyEvent in the children
2081 created by AnyEvent::Fork safely and without any special precautions.
1161 2082
1162SECURITY CONSIDERATIONS 2083SECURITY CONSIDERATIONS
1163 AnyEvent can be forced to load any event model via 2084 AnyEvent can be forced to load any event model via
1164 $ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used 2085 $ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used
1165 to execute arbitrary code or directly gain access, it can easily be used 2086 to execute arbitrary code or directly gain access, it can easily be used
… …
1168 model than specified in the variable. 2089 model than specified in the variable.
1169 2090
1170 You can make AnyEvent completely ignore this variable by deleting it 2091 You can make AnyEvent completely ignore this variable by deleting it
1171 before the first watcher gets created, e.g. with a "BEGIN" block: 2092 before the first watcher gets created, e.g. with a "BEGIN" block:
1172 2093
1173 BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} } 2094 BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
1174 2095
1175 use AnyEvent; 2096 use AnyEvent;
1176 2097
1177 Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can 2098 Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
1178 be used to probe what backend is used and gain other information (which 2099 be used to probe what backend is used and gain other information (which
1179 is probably even less useful to an attacker than PERL_ANYEVENT_MODEL). 2100 is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),
2101 and $ENV{PERL_ANYEVENT_STRICT}.
2102
2103 Note that AnyEvent will remove *all* environment variables starting with
2104 "PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
2105 enabled.
2106
2107BUGS
2108 Perl 5.8 has numerous memleaks that sometimes hit this module and are
2109 hard to work around. If you suffer from memleaks, first upgrade to Perl
2110 5.10 and check wether the leaks still show up. (Perl 5.10.0 has other
2111 annoying memleaks, such as leaking on "map" and "grep" but it is usually
2112 not as pronounced).
1180 2113
1181SEE ALSO 2114SEE ALSO
1182 Utility functions: AnyEvent::Util. 2115 Tutorial/Introduction: AnyEvent::Intro.
1183 2116
1184 Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk, 2117 FAQ: AnyEvent::FAQ.
1185 Event::Lib, Qt, POE. 2118
2119 Utility functions: AnyEvent::Util (misc. grab-bag), AnyEvent::Log
2120 (simply logging).
2121
2122 Development/Debugging: AnyEvent::Strict (stricter checking),
2123 AnyEvent::Debug (interactive shell, watcher tracing).
2124
2125 Supported event modules: AnyEvent::Loop, EV, EV::Glib, Glib::EV, Event,
2126 Glib::Event, Glib, Tk, Event::Lib, Qt, POE, FLTK.
1186 2127
1187 Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event, 2128 Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
1188 AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl, 2129 AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
1189 AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE. 2130 AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE,
2131 AnyEvent::Impl::IOAsync, Anyevent::Impl::Irssi, AnyEvent::Impl::FLTK.
1190 2132
1191 Non-blocking file handles, sockets, TCP clients and servers: 2133 Non-blocking handles, pipes, stream sockets, TCP clients and servers:
1192 AnyEvent::Handle, AnyEvent::Socket. 2134 AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS.
2135
2136 Asynchronous File I/O: AnyEvent::IO.
1193 2137
1194 Asynchronous DNS: AnyEvent::DNS. 2138 Asynchronous DNS: AnyEvent::DNS.
1195 2139
1196 Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event, 2140 Thread support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event.
1197 2141
1198 Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS. 2142 Nontrivial usage examples: AnyEvent::GPSD, AnyEvent::IRC,
2143 AnyEvent::HTTP.
1199 2144
1200AUTHOR 2145AUTHOR
1201 Marc Lehmann <schmorp@schmorp.de> 2146 Marc Lehmann <schmorp@schmorp.de>
1202 http://home.schmorp.de/ 2147 http://anyevent.schmorp.de
1203 2148

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