1 | NAME |
1 | => NAME |
2 | AnyEvent - provide framework for multiple event loops |
2 | AnyEvent - provide framework for multiple event loops |
3 | |
3 | |
4 | EV, Event, Coro::EV, Coro::Event, Glib, Tk, Perl - various supported |
4 | EV, Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event |
5 | event loops |
5 | loops |
6 | |
6 | |
7 | SYNOPSIS |
7 | SYNOPSIS |
8 | use AnyEvent; |
8 | use AnyEvent; |
9 | |
9 | |
10 | my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub { |
10 | my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub { |
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14 | my $w = AnyEvent->timer (after => $seconds, cb => sub { |
14 | my $w = AnyEvent->timer (after => $seconds, cb => sub { |
15 | ... |
15 | ... |
16 | }); |
16 | }); |
17 | |
17 | |
18 | my $w = AnyEvent->condvar; # stores whether a condition was flagged |
18 | my $w = AnyEvent->condvar; # stores whether a condition was flagged |
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19 | $w->send; # wake up current and all future recv's |
19 | $w->wait; # enters "main loop" till $condvar gets ->broadcast |
20 | $w->recv; # enters "main loop" till $condvar gets ->send |
20 | $w->broadcast; # wake up current and all future wait's |
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21 | |
21 | |
22 | WHY YOU SHOULD USE THIS MODULE (OR NOT) |
22 | WHY YOU SHOULD USE THIS MODULE (OR NOT) |
23 | Glib, POE, IO::Async, Event... CPAN offers event models by the dozen |
23 | Glib, POE, IO::Async, Event... CPAN offers event models by the dozen |
24 | nowadays. So what is different about AnyEvent? |
24 | nowadays. So what is different about AnyEvent? |
25 | |
25 | |
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55 | those use one of the supported event loops. It is trivial to add new |
55 | those use one of the supported event loops. It is trivial to add new |
56 | event loops to AnyEvent, too, so it is future-proof). |
56 | event loops to AnyEvent, too, so it is future-proof). |
57 | |
57 | |
58 | In addition to being free of having to use *the one and only true event |
58 | 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 |
59 | model*, AnyEvent also is free of bloat and policy: with POE or similar |
60 | modules, you get an enourmous amount of code and strict rules you have |
60 | modules, you get an enormous amount of code and strict rules you have to |
61 | to follow. AnyEvent, on the other hand, is lean and up to the point, by |
61 | follow. AnyEvent, on the other hand, is lean and up to the point, by |
62 | only offering the functionality that is necessary, in as thin as a |
62 | only offering the functionality that is necessary, in as thin as a |
63 | wrapper as technically possible. |
63 | wrapper as technically possible. |
64 | |
64 | |
65 | Of course, if you want lots of policy (this can arguably be somewhat |
65 | Of course, if you 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 |
66 | useful) and you want to force your users to use the one and only event |
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75 | The interface itself is vaguely similar, but not identical to the Event |
75 | The interface itself is vaguely similar, but not identical to the Event |
76 | module. |
76 | module. |
77 | |
77 | |
78 | During the first call of any watcher-creation method, the module tries |
78 | 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 |
79 | to detect the currently loaded event loop by probing whether one of the |
80 | following modules is already loaded: Coro::EV, Coro::Event, EV, Event, |
80 | following modules is already loaded: EV, Event, Glib, |
81 | Glib, Tk. The first one found is used. If none are found, the module |
81 | AnyEvent::Impl::Perl, Tk, Event::Lib, Qt, POE. The first one found is |
82 | tries to load these modules in the stated order. The first one that can |
82 | used. If none are found, the module tries to load these modules |
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83 | (excluding Tk, Event::Lib, Qt and POE as the pure perl adaptor should |
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84 | always succeed) in the order given. The first one that can be |
83 | be successfully loaded will be used. If, after this, still none could be |
85 | successfully loaded will be used. If, after this, still none could be |
84 | found, AnyEvent will fall back to a pure-perl event loop, which is not |
86 | found, AnyEvent will fall back to a pure-perl event loop, which is not |
85 | very efficient, but should work everywhere. |
87 | very efficient, but should work everywhere. |
86 | |
88 | |
87 | Because AnyEvent first checks for modules that are already loaded, |
89 | Because AnyEvent first checks for modules that are already loaded, |
88 | loading an event model explicitly before first using AnyEvent will |
90 | loading an event model explicitly before first using AnyEvent will |
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102 | explicitly. |
104 | explicitly. |
103 | |
105 | |
104 | WATCHERS |
106 | WATCHERS |
105 | AnyEvent has the central concept of a *watcher*, which is an object that |
107 | AnyEvent has the central concept of a *watcher*, which is an object that |
106 | stores relevant data for each kind of event you are waiting for, such as |
108 | stores relevant data for each kind of event you are waiting for, such as |
107 | the callback to call, the filehandle to watch, etc. |
109 | the callback to call, the file handle to watch, etc. |
108 | |
110 | |
109 | These watchers are normal Perl objects with normal Perl lifetime. After |
111 | These watchers are normal Perl objects with normal Perl lifetime. After |
110 | creating a watcher it will immediately "watch" for events and invoke the |
112 | creating a watcher it will immediately "watch" for events and invoke the |
111 | callback when the event occurs (of course, only when the event model is |
113 | callback when the event occurs (of course, only when the event model is |
112 | in control). |
114 | in control). |
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129 | |
131 | |
130 | Note that "my $w; $w =" combination. This is necessary because in Perl, |
132 | Note that "my $w; $w =" combination. This is necessary because in Perl, |
131 | my variables are only visible after the statement in which they are |
133 | my variables are only visible after the statement in which they are |
132 | declared. |
134 | declared. |
133 | |
135 | |
134 | IO WATCHERS |
136 | I/O WATCHERS |
135 | You can create an I/O watcher by calling the "AnyEvent->io" method with |
137 | You can create an I/O watcher by calling the "AnyEvent->io" method with |
136 | the following mandatory key-value pairs as arguments: |
138 | the following mandatory key-value pairs as arguments: |
137 | |
139 | |
138 | "fh" the Perl *file handle* (*not* file descriptor) to watch for events. |
140 | "fh" the Perl *file handle* (*not* file descriptor) to watch for events. |
139 | "poll" must be a string that is either "r" or "w", which creates a |
141 | "poll" must be a string that is either "r" or "w", which creates a |
140 | watcher waiting for "r"eadable or "w"ritable events, respectively. "cb" |
142 | watcher waiting for "r"eadable or "w"ritable events, respectively. "cb" |
141 | is the callback to invoke each time the file handle becomes ready. |
143 | is the callback to invoke each time the file handle becomes ready. |
142 | |
144 | |
143 | File handles will be kept alive, so as long as the watcher exists, the |
145 | Although the callback might get passed parameters, their value and |
144 | file handle exists, too. |
146 | presence is undefined and you cannot rely on them. Portable AnyEvent |
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147 | callbacks cannot use arguments passed to I/O watcher callbacks. |
145 | |
148 | |
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149 | The I/O watcher might use the underlying file descriptor or a copy of |
146 | It is not allowed to close a file handle as long as any watcher is |
150 | it. You must not close a file handle as long as any watcher is active on |
147 | active on the underlying file descriptor. |
151 | the underlying file descriptor. |
148 | |
152 | |
149 | Some event loops issue spurious readyness notifications, so you should |
153 | Some event loops issue spurious readyness notifications, so you should |
150 | always use non-blocking calls when reading/writing from/to your file |
154 | always use non-blocking calls when reading/writing from/to your file |
151 | handles. |
155 | handles. |
152 | |
156 | |
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162 | TIME WATCHERS |
166 | TIME WATCHERS |
163 | You can create a time watcher by calling the "AnyEvent->timer" method |
167 | You can create a time watcher by calling the "AnyEvent->timer" method |
164 | with the following mandatory arguments: |
168 | with the following mandatory arguments: |
165 | |
169 | |
166 | "after" specifies after how many seconds (fractional values are |
170 | "after" specifies after how many seconds (fractional values are |
167 | supported) should the timer activate. "cb" the callback to invoke in |
171 | supported) the callback should be invoked. "cb" is the callback to |
168 | that case. |
172 | invoke in that case. |
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173 | |
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174 | Although the callback might get passed parameters, their value and |
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175 | presence is undefined and you cannot rely on them. Portable AnyEvent |
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176 | callbacks cannot use arguments passed to time watcher callbacks. |
169 | |
177 | |
170 | The timer callback will be invoked at most once: if you want a repeating |
178 | The timer callback will be invoked at most once: if you want a repeating |
171 | timer you have to create a new watcher (this is a limitation by both Tk |
179 | timer you have to create a new watcher (this is a limitation by both Tk |
172 | and Glib). |
180 | and Glib). |
173 | |
181 | |
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200 | o'clock"). |
208 | o'clock"). |
201 | |
209 | |
202 | While most event loops expect timers to specified in a relative way, |
210 | While most event loops expect timers to specified in a relative way, |
203 | they use absolute time internally. This makes a difference when your |
211 | they use absolute time internally. This makes a difference when your |
204 | clock "jumps", for example, when ntp decides to set your clock backwards |
212 | clock "jumps", for example, when ntp decides to set your clock backwards |
205 | from the wrong 2014-01-01 to 2008-01-01, a watcher that you created to |
213 | from the wrong date of 2014-01-01 to 2008-01-01, a watcher that is |
206 | fire "after" a second might actually take six years to finally fire. |
214 | supposed to fire "after" a second might actually take six years to |
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215 | finally fire. |
207 | |
216 | |
208 | AnyEvent cannot compensate for this. The only event loop that is |
217 | AnyEvent cannot compensate for this. The only event loop that is |
209 | conscious about these issues is EV, which offers both relative |
218 | conscious about these issues is EV, which offers both relative |
210 | (ev_timer) and absolute (ev_periodic) timers. |
219 | (ev_timer, based on true relative time) and absolute (ev_periodic, based |
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220 | on wallclock time) timers. |
211 | |
221 | |
212 | AnyEvent always prefers relative timers, if available, matching the |
222 | AnyEvent always prefers relative timers, if available, matching the |
213 | AnyEvent API. |
223 | AnyEvent API. |
214 | |
224 | |
215 | SIGNAL WATCHERS |
225 | SIGNAL WATCHERS |
216 | You can watch for signals using a signal watcher, "signal" is the signal |
226 | You can watch for signals using a signal watcher, "signal" is the signal |
217 | *name* without any "SIG" prefix, "cb" is the Perl callback to be invoked |
227 | *name* without any "SIG" prefix, "cb" is the Perl callback to be invoked |
218 | whenever a signal occurs. |
228 | whenever a signal occurs. |
219 | |
229 | |
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230 | Although the callback might get passed parameters, their value and |
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231 | presence is undefined and you cannot rely on them. Portable AnyEvent |
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232 | callbacks cannot use arguments passed to signal watcher callbacks. |
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233 | |
220 | Multiple signals occurances can be clumped together into one callback |
234 | Multiple signal occurrences can be clumped together into one callback |
221 | invocation, and callback invocation will be synchronous. synchronous |
235 | invocation, and callback invocation will be synchronous. Synchronous |
222 | means that it might take a while until the signal gets handled by the |
236 | means that it might take a while until the signal gets handled by the |
223 | process, but it is guarenteed not to interrupt any other callbacks. |
237 | process, but it is guaranteed not to interrupt any other callbacks. |
224 | |
238 | |
225 | The main advantage of using these watchers is that you can share a |
239 | The main advantage of using these watchers is that you can share a |
226 | signal between multiple watchers. |
240 | signal between multiple watchers. |
227 | |
241 | |
228 | This watcher might use %SIG, so programs overwriting those signals |
242 | This watcher might use %SIG, so programs overwriting those signals |
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237 | |
251 | |
238 | The child process is specified by the "pid" argument (if set to 0, it |
252 | The child process is specified by the "pid" argument (if set to 0, it |
239 | watches for any child process exit). The watcher will trigger as often |
253 | watches for any child process exit). The watcher will trigger as often |
240 | as status change for the child are received. This works by installing a |
254 | as status change for the child are received. This works by installing a |
241 | signal handler for "SIGCHLD". The callback will be called with the pid |
255 | signal handler for "SIGCHLD". The callback will be called with the pid |
242 | and exit status (as returned by waitpid). |
256 | and exit status (as returned by waitpid), so unlike other watcher types, |
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257 | you *can* rely on child watcher callback arguments. |
243 | |
258 | |
244 | Example: wait for pid 1333 |
259 | There is a slight catch to child watchers, however: you usually start |
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260 | them *after* the child process was created, and this means the process |
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261 | could have exited already (and no SIGCHLD will be sent anymore). |
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262 | |
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263 | Not all event models handle this correctly (POE doesn't), but even for |
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264 | event models that *do* handle this correctly, they usually need to be |
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265 | loaded before the process exits (i.e. before you fork in the first |
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266 | place). |
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267 | |
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268 | This means you cannot create a child watcher as the very first thing in |
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269 | an AnyEvent program, you *have* to create at least one watcher before |
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270 | you "fork" the child (alternatively, you can call "AnyEvent::detect"). |
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271 | |
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272 | Example: fork a process and wait for it |
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273 | |
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274 | my $done = AnyEvent->condvar; |
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275 | |
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276 | my $pid = fork or exit 5; |
245 | |
277 | |
246 | my $w = AnyEvent->child ( |
278 | my $w = AnyEvent->child ( |
247 | pid => 1333, |
279 | pid => $pid, |
248 | cb => sub { |
280 | cb => sub { |
249 | my ($pid, $status) = @_; |
281 | my ($pid, $status) = @_; |
250 | warn "pid $pid exited with status $status"; |
282 | warn "pid $pid exited with status $status"; |
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283 | $done->send; |
251 | }, |
284 | }, |
252 | ); |
285 | ); |
253 | |
286 | |
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287 | # do something else, then wait for process exit |
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288 | $done->recv; |
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289 | |
254 | CONDITION VARIABLES |
290 | CONDITION VARIABLES |
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291 | If you are familiar with some event loops you will know that all of them |
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292 | require you to run some blocking "loop", "run" or similar function that |
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293 | will actively watch for new events and call your callbacks. |
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294 | |
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295 | AnyEvent is different, it expects somebody else to run the event loop |
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296 | and will only block when necessary (usually when told by the user). |
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297 | |
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298 | The instrument to do that is called a "condition variable", so called |
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299 | because they represent a condition that must become true. |
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300 | |
255 | Condition variables can be created by calling the "AnyEvent->condvar" |
301 | Condition variables can be created by calling the "AnyEvent->condvar" |
256 | method without any arguments. |
302 | method, usually without arguments. The only argument pair allowed is |
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303 | "cb", which specifies a callback to be called when the condition |
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304 | variable becomes true. |
257 | |
305 | |
258 | A condition variable waits for a condition - precisely that the |
306 | After creation, the condition variable is "false" until it becomes |
259 | "->broadcast" method has been called. |
307 | "true" by calling the "send" method (or calling the condition variable |
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308 | as if it were a callback, read about the caveats in the description for |
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309 | the "->send" method). |
260 | |
310 | |
261 | They are very useful to signal that a condition has been fulfilled, for |
311 | Condition variables are similar to callbacks, except that you can |
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312 | optionally wait for them. They can also be called merge points - points |
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313 | in time where multiple outstanding events have been processed. And yet |
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314 | another way to call them is transactions - each condition variable can |
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315 | be used to represent a transaction, which finishes at some point and |
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316 | delivers a result. |
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317 | |
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318 | Condition variables are very useful to signal that something has |
262 | example, if you write a module that does asynchronous http requests, |
319 | finished, for example, if you write a module that does asynchronous http |
263 | then a condition variable would be the ideal candidate to signal the |
320 | requests, then a condition variable would be the ideal candidate to |
264 | availability of results. |
321 | signal the availability of results. The user can either act when the |
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322 | callback is called or can synchronously "->recv" for the results. |
265 | |
323 | |
266 | You can also use condition variables to block your main program until an |
324 | You can also use them to simulate traditional event loops - for example, |
267 | event occurs - for example, you could "->wait" in your main program |
325 | you can block your main program until an event occurs - for example, you |
268 | until the user clicks the Quit button in your app, which would |
326 | could "->recv" in your main program until the user clicks the Quit |
269 | "->broadcast" the "quit" event. |
327 | button of your app, which would "->send" the "quit" event. |
270 | |
328 | |
271 | Note that condition variables recurse into the event loop - if you have |
329 | Note that condition variables recurse into the event loop - if you have |
272 | two pirces of code that call "->wait" in a round-robbin fashion, you |
330 | two pieces of code that call "->recv" in a round-robin fashion, you |
273 | lose. Therefore, condition variables are good to export to your caller, |
331 | lose. Therefore, condition variables are good to export to your caller, |
274 | but you should avoid making a blocking wait yourself, at least in |
332 | but you should avoid making a blocking wait yourself, at least in |
275 | callbacks, as this asks for trouble. |
333 | callbacks, as this asks for trouble. |
276 | |
334 | |
277 | This object has two methods: |
335 | Condition variables are represented by hash refs in perl, and the keys |
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336 | used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy |
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337 | (it is often useful to build your own transaction class on top of |
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338 | AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call |
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339 | it's "new" method in your own "new" method. |
278 | |
340 | |
279 | $cv->wait |
341 | There are two "sides" to a condition variable - the "producer side" |
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342 | which eventually calls "-> send", and the "consumer side", which waits |
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343 | for the send to occur. |
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344 | |
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345 | Example: wait for a timer. |
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346 | |
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347 | # wait till the result is ready |
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348 | my $result_ready = AnyEvent->condvar; |
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349 | |
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350 | # do something such as adding a timer |
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351 | # or socket watcher the calls $result_ready->send |
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352 | # when the "result" is ready. |
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353 | # in this case, we simply use a timer: |
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354 | my $w = AnyEvent->timer ( |
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355 | after => 1, |
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356 | cb => sub { $result_ready->send }, |
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357 | ); |
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358 | |
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359 | # this "blocks" (while handling events) till the callback |
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360 | # calls send |
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361 | $result_ready->recv; |
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362 | |
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363 | Example: wait for a timer, but take advantage of the fact that condition |
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364 | variables are also code references. |
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365 | |
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366 | my $done = AnyEvent->condvar; |
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367 | my $delay = AnyEvent->timer (after => 5, cb => $done); |
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368 | $done->recv; |
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369 | |
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370 | METHODS FOR PRODUCERS |
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371 | These methods should only be used by the producing side, i.e. the |
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372 | code/module that eventually sends the signal. Note that it is also the |
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373 | producer side which creates the condvar in most cases, but it isn't |
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374 | uncommon for the consumer to create it as well. |
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375 | |
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376 | $cv->send (...) |
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377 | Flag the condition as ready - a running "->recv" and all further |
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378 | calls to "recv" will (eventually) return after this method has been |
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379 | called. If nobody is waiting the send will be remembered. |
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380 | |
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381 | If a callback has been set on the condition variable, it is called |
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382 | immediately from within send. |
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383 | |
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384 | Any arguments passed to the "send" call will be returned by all |
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385 | future "->recv" calls. |
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386 | |
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387 | Condition variables are overloaded so one can call them directly (as |
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388 | a code reference). Calling them directly is the same as calling |
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389 | "send". Note, however, that many C-based event loops do not handle |
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390 | overloading, so as tempting as it may be, passing a condition |
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391 | variable instead of a callback does not work. Both the pure perl and |
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392 | EV loops support overloading, however, as well as all functions that |
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393 | use perl to invoke a callback (as in AnyEvent::Socket and |
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394 | AnyEvent::DNS for example). |
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395 | |
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396 | $cv->croak ($error) |
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397 | Similar to send, but causes all call's to "->recv" to invoke |
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398 | "Carp::croak" with the given error message/object/scalar. |
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399 | |
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400 | This can be used to signal any errors to the condition variable |
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401 | user/consumer. |
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402 | |
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403 | $cv->begin ([group callback]) |
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404 | $cv->end |
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405 | These two methods are EXPERIMENTAL and MIGHT CHANGE. |
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406 | |
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407 | These two methods can be used to combine many transactions/events |
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408 | into one. For example, a function that pings many hosts in parallel |
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409 | might want to use a condition variable for the whole process. |
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410 | |
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411 | Every call to "->begin" will increment a counter, and every call to |
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412 | "->end" will decrement it. If the counter reaches 0 in "->end", the |
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413 | (last) callback passed to "begin" will be executed. That callback is |
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414 | *supposed* to call "->send", but that is not required. If no |
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415 | callback was set, "send" will be called without any arguments. |
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416 | |
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417 | Let's clarify this with the ping example: |
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418 | |
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419 | my $cv = AnyEvent->condvar; |
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420 | |
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421 | my %result; |
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422 | $cv->begin (sub { $cv->send (\%result) }); |
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423 | |
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424 | for my $host (@list_of_hosts) { |
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425 | $cv->begin; |
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426 | ping_host_then_call_callback $host, sub { |
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427 | $result{$host} = ...; |
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428 | $cv->end; |
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429 | }; |
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430 | } |
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431 | |
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432 | $cv->end; |
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433 | |
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434 | This code fragment supposedly pings a number of hosts and calls |
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435 | "send" after results for all then have have been gathered - in any |
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436 | order. To achieve this, the code issues a call to "begin" when it |
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437 | starts each ping request and calls "end" when it has received some |
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438 | result for it. Since "begin" and "end" only maintain a counter, the |
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439 | order in which results arrive is not relevant. |
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440 | |
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441 | There is an additional bracketing call to "begin" and "end" outside |
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442 | the loop, which serves two important purposes: first, it sets the |
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443 | callback to be called once the counter reaches 0, and second, it |
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444 | ensures that "send" is called even when "no" hosts are being pinged |
|
|
445 | (the loop doesn't execute once). |
|
|
446 | |
|
|
447 | This is the general pattern when you "fan out" into multiple |
|
|
448 | subrequests: use an outer "begin"/"end" pair to set the callback and |
|
|
449 | ensure "end" is called at least once, and then, for each subrequest |
|
|
450 | you start, call "begin" and for each subrequest you finish, call |
|
|
451 | "end". |
|
|
452 | |
|
|
453 | METHODS FOR CONSUMERS |
|
|
454 | These methods should only be used by the consuming side, i.e. the code |
|
|
455 | awaits the condition. |
|
|
456 | |
|
|
457 | $cv->recv |
280 | Wait (blocking if necessary) until the "->broadcast" method has been |
458 | Wait (blocking if necessary) until the "->send" or "->croak" methods |
281 | called on c<$cv>, while servicing other watchers normally. |
459 | have been called on c<$cv>, while servicing other watchers normally. |
282 | |
460 | |
283 | You can only wait once on a condition - additional calls will return |
461 | You can only wait once on a condition - additional calls are valid |
284 | immediately. |
462 | but will return immediately. |
|
|
463 | |
|
|
464 | If an error condition has been set by calling "->croak", then this |
|
|
465 | function will call "croak". |
|
|
466 | |
|
|
467 | In list context, all parameters passed to "send" will be returned, |
|
|
468 | in scalar context only the first one will be returned. |
285 | |
469 | |
286 | Not all event models support a blocking wait - some die in that case |
470 | Not all event models support a blocking wait - some die in that case |
287 | (programs might want to do that to stay interactive), so *if you are |
471 | (programs might want to do that to stay interactive), so *if you are |
288 | using this from a module, never require a blocking wait*, but let |
472 | using this from a module, never require a blocking wait*, but let |
289 | the caller decide whether the call will block or not (for example, |
473 | the caller decide whether the call will block or not (for example, |
290 | by coupling condition variables with some kind of request results |
474 | by coupling condition variables with some kind of request results |
291 | and supporting callbacks so the caller knows that getting the result |
475 | and supporting callbacks so the caller knows that getting the result |
292 | will not block, while still suppporting blocking waits if the caller |
476 | will not block, while still supporting blocking waits if the caller |
293 | so desires). |
477 | so desires). |
294 | |
478 | |
295 | Another reason *never* to "->wait" in a module is that you cannot |
479 | Another reason *never* to "->recv" in a module is that you cannot |
296 | sensibly have two "->wait"'s in parallel, as that would require |
480 | sensibly have two "->recv"'s in parallel, as that would require |
297 | multiple interpreters or coroutines/threads, none of which |
481 | multiple interpreters or coroutines/threads, none of which |
298 | "AnyEvent" can supply (the coroutine-aware backends |
482 | "AnyEvent" can supply. |
299 | AnyEvent::Impl::CoroEV and AnyEvent::Impl::CoroEvent explicitly |
|
|
300 | support concurrent "->wait"'s from different coroutines, however). |
|
|
301 | |
483 | |
302 | $cv->broadcast |
484 | The Coro module, however, *can* and *does* supply coroutines and, in |
303 | Flag the condition as ready - a running "->wait" and all further |
485 | fact, Coro::AnyEvent replaces AnyEvent's condvars by coroutine-safe |
304 | calls to "wait" will (eventually) return after this method has been |
486 | versions and also integrates coroutines into AnyEvent, making |
305 | called. If nobody is waiting the broadcast will be remembered.. |
487 | blocking "->recv" calls perfectly safe as long as they are done from |
|
|
488 | another coroutine (one that doesn't run the event loop). |
306 | |
489 | |
307 | Example: |
490 | You can ensure that "-recv" never blocks by setting a callback and |
|
|
491 | only calling "->recv" from within that callback (or at a later |
|
|
492 | time). This will work even when the event loop does not support |
|
|
493 | blocking waits otherwise. |
308 | |
494 | |
309 | # wait till the result is ready |
495 | $bool = $cv->ready |
310 | my $result_ready = AnyEvent->condvar; |
496 | Returns true when the condition is "true", i.e. whether "send" or |
|
|
497 | "croak" have been called. |
311 | |
498 | |
312 | # do something such as adding a timer |
499 | $cb = $cv->cb ([new callback]) |
313 | # or socket watcher the calls $result_ready->broadcast |
500 | This is a mutator function that returns the callback set and |
314 | # when the "result" is ready. |
501 | optionally replaces it before doing so. |
315 | # in this case, we simply use a timer: |
|
|
316 | my $w = AnyEvent->timer ( |
|
|
317 | after => 1, |
|
|
318 | cb => sub { $result_ready->broadcast }, |
|
|
319 | ); |
|
|
320 | |
502 | |
321 | # this "blocks" (while handling events) till the watcher |
503 | The callback will be called when the condition becomes "true", i.e. |
322 | # calls broadcast |
504 | when "send" or "croak" are called. Calling "recv" inside the |
323 | $result_ready->wait; |
505 | callback or at any later time is guaranteed not to block. |
324 | |
506 | |
325 | GLOBAL VARIABLES AND FUNCTIONS |
507 | GLOBAL VARIABLES AND FUNCTIONS |
326 | $AnyEvent::MODEL |
508 | $AnyEvent::MODEL |
327 | Contains "undef" until the first watcher is being created. Then it |
509 | Contains "undef" until the first watcher is being created. Then it |
328 | contains the event model that is being used, which is the name of |
510 | contains the event model that is being used, which is the name of |
… | |
… | |
330 | the "AnyEvent::Impl:xxx" modules, but can be any other class in the |
512 | the "AnyEvent::Impl:xxx" modules, but can be any other class in the |
331 | case AnyEvent has been extended at runtime (e.g. in *rxvt-unicode*). |
513 | case AnyEvent has been extended at runtime (e.g. in *rxvt-unicode*). |
332 | |
514 | |
333 | The known classes so far are: |
515 | The known classes so far are: |
334 | |
516 | |
335 | AnyEvent::Impl::CoroEV based on Coro::EV, best choice. |
|
|
336 | AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice. |
|
|
337 | AnyEvent::Impl::EV based on EV (an interface to libev, also best choice). |
517 | AnyEvent::Impl::EV based on EV (an interface to libev, best choice). |
338 | AnyEvent::Impl::Event based on Event, also second best choice :) |
518 | AnyEvent::Impl::Event based on Event, second best choice. |
|
|
519 | AnyEvent::Impl::Perl pure-perl implementation, fast and portable. |
339 | AnyEvent::Impl::Glib based on Glib, third-best choice. |
520 | AnyEvent::Impl::Glib based on Glib, third-best choice. |
340 | AnyEvent::Impl::Tk based on Tk, very bad choice. |
521 | AnyEvent::Impl::Tk based on Tk, very bad choice. |
341 | AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable. |
522 | AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs). |
|
|
523 | AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse. |
|
|
524 | AnyEvent::Impl::POE based on POE, not generic enough for full support. |
|
|
525 | |
|
|
526 | There is no support for WxWidgets, as WxWidgets has no support for |
|
|
527 | watching file handles. However, you can use WxWidgets through the |
|
|
528 | POE Adaptor, as POE has a Wx backend that simply polls 20 times per |
|
|
529 | second, which was considered to be too horrible to even consider for |
|
|
530 | AnyEvent. Likewise, other POE backends can be used by AnyEvent by |
|
|
531 | using it's adaptor. |
|
|
532 | |
|
|
533 | AnyEvent knows about Prima and Wx and will try to use POE when |
|
|
534 | autodetecting them. |
342 | |
535 | |
343 | AnyEvent::detect |
536 | AnyEvent::detect |
344 | Returns $AnyEvent::MODEL, forcing autodetection of the event model |
537 | Returns $AnyEvent::MODEL, forcing autodetection of the event model |
345 | if necessary. You should only call this function right before you |
538 | if necessary. You should only call this function right before you |
346 | would have created an AnyEvent watcher anyway, that is, as late as |
539 | would have created an AnyEvent watcher anyway, that is, as late as |
347 | possible at runtime. |
540 | possible at runtime. |
348 | |
541 | |
|
|
542 | $guard = AnyEvent::post_detect { BLOCK } |
|
|
543 | Arranges for the code block to be executed as soon as the event |
|
|
544 | model is autodetected (or immediately if this has already happened). |
|
|
545 | |
|
|
546 | If called in scalar or list context, then it creates and returns an |
|
|
547 | object that automatically removes the callback again when it is |
|
|
548 | destroyed. See Coro::BDB for a case where this is useful. |
|
|
549 | |
|
|
550 | @AnyEvent::post_detect |
|
|
551 | If there are any code references in this array (you can "push" to it |
|
|
552 | before or after loading AnyEvent), then they will called directly |
|
|
553 | after the event loop has been chosen. |
|
|
554 | |
|
|
555 | You should check $AnyEvent::MODEL before adding to this array, |
|
|
556 | though: if it contains a true value then the event loop has already |
|
|
557 | been detected, and the array will be ignored. |
|
|
558 | |
|
|
559 | Best use "AnyEvent::post_detect { BLOCK }" instead. |
|
|
560 | |
349 | WHAT TO DO IN A MODULE |
561 | WHAT TO DO IN A MODULE |
350 | As a module author, you should "use AnyEvent" and call AnyEvent methods |
562 | As a module author, you should "use AnyEvent" and call AnyEvent methods |
351 | freely, but you should not load a specific event module or rely on it. |
563 | freely, but you should not load a specific event module or rely on it. |
352 | |
564 | |
353 | Be careful when you create watchers in the module body - AnyEvent will |
565 | Be careful when you create watchers in the module body - AnyEvent will |
354 | decide which event module to use as soon as the first method is called, |
566 | decide which event module to use as soon as the first method is called, |
355 | so by calling AnyEvent in your module body you force the user of your |
567 | so by calling AnyEvent in your module body you force the user of your |
356 | module to load the event module first. |
568 | module to load the event module first. |
357 | |
569 | |
358 | Never call "->wait" on a condition variable unless you *know* that the |
570 | Never call "->recv" on a condition variable unless you *know* that the |
359 | "->broadcast" method has been called on it already. This is because it |
571 | "->send" method has been called on it already. This is because it will |
360 | will stall the whole program, and the whole point of using events is to |
572 | stall the whole program, and the whole point of using events is to stay |
361 | stay interactive. |
573 | interactive. |
362 | |
574 | |
363 | It is fine, however, to call "->wait" when the user of your module |
575 | It is fine, however, to call "->recv" when the user of your module |
364 | requests it (i.e. if you create a http request object ad have a method |
576 | requests it (i.e. if you create a http request object ad have a method |
365 | called "results" that returns the results, it should call "->wait" |
577 | called "results" that returns the results, it should call "->recv" |
366 | freely, as the user of your module knows what she is doing. always). |
578 | freely, as the user of your module knows what she is doing. always). |
367 | |
579 | |
368 | WHAT TO DO IN THE MAIN PROGRAM |
580 | WHAT TO DO IN THE MAIN PROGRAM |
369 | There will always be a single main program - the only place that should |
581 | There will always be a single main program - the only place that should |
370 | dictate which event model to use. |
582 | dictate which event model to use. |
… | |
… | |
372 | If it doesn't care, it can just "use AnyEvent" and use it itself, or not |
584 | If it doesn't care, it can just "use AnyEvent" and use it itself, or not |
373 | do anything special (it does not need to be event-based) and let |
585 | do anything special (it does not need to be event-based) and let |
374 | AnyEvent decide which implementation to chose if some module relies on |
586 | AnyEvent decide which implementation to chose if some module relies on |
375 | it. |
587 | it. |
376 | |
588 | |
377 | If the main program relies on a specific event model. For example, in |
589 | If the main program relies on a specific event model - for example, in |
378 | Gtk2 programs you have to rely on the Glib module. You should load the |
590 | Gtk2 programs you have to rely on the Glib module - you should load the |
379 | event module before loading AnyEvent or any module that uses it: |
591 | event module before loading AnyEvent or any module that uses it: |
380 | generally speaking, you should load it as early as possible. The reason |
592 | generally speaking, you should load it as early as possible. The reason |
381 | is that modules might create watchers when they are loaded, and AnyEvent |
593 | is that modules might create watchers when they are loaded, and AnyEvent |
382 | will decide on the event model to use as soon as it creates watchers, |
594 | will decide on the event model to use as soon as it creates watchers, |
383 | and it might chose the wrong one unless you load the correct one |
595 | and it might chose the wrong one unless you load the correct one |
384 | yourself. |
596 | yourself. |
385 | |
597 | |
386 | You can chose to use a rather inefficient pure-perl implementation by |
598 | You can chose to use a pure-perl implementation by loading the |
387 | loading the "AnyEvent::Impl::Perl" module, which gives you similar |
599 | "AnyEvent::Impl::Perl" module, which gives you similar behaviour |
388 | behaviour everywhere, but letting AnyEvent chose is generally better. |
600 | everywhere, but letting AnyEvent chose the model is generally better. |
|
|
601 | |
|
|
602 | MAINLOOP EMULATION |
|
|
603 | Sometimes (often for short test scripts, or even standalone programs who |
|
|
604 | only want to use AnyEvent), you do not want to run a specific event |
|
|
605 | loop. |
|
|
606 | |
|
|
607 | In that case, you can use a condition variable like this: |
|
|
608 | |
|
|
609 | AnyEvent->condvar->recv; |
|
|
610 | |
|
|
611 | This has the effect of entering the event loop and looping forever. |
|
|
612 | |
|
|
613 | Note that usually your program has some exit condition, in which case it |
|
|
614 | is better to use the "traditional" approach of storing a condition |
|
|
615 | variable somewhere, waiting for it, and sending it when the program |
|
|
616 | should exit cleanly. |
|
|
617 | |
|
|
618 | OTHER MODULES |
|
|
619 | The following is a non-exhaustive list of additional modules that use |
|
|
620 | AnyEvent and can therefore be mixed easily with other AnyEvent modules |
|
|
621 | in the same program. Some of the modules come with AnyEvent, some are |
|
|
622 | available via CPAN. |
|
|
623 | |
|
|
624 | AnyEvent::Util |
|
|
625 | Contains various utility functions that replace often-used but |
|
|
626 | blocking functions such as "inet_aton" by event-/callback-based |
|
|
627 | versions. |
|
|
628 | |
|
|
629 | AnyEvent::Handle |
|
|
630 | Provide read and write buffers and manages watchers for reads and |
|
|
631 | writes. |
|
|
632 | |
|
|
633 | AnyEvent::Socket |
|
|
634 | Provides various utility functions for (internet protocol) sockets, |
|
|
635 | addresses and name resolution. Also functions to create non-blocking |
|
|
636 | tcp connections or tcp servers, with IPv6 and SRV record support and |
|
|
637 | more. |
|
|
638 | |
|
|
639 | AnyEvent::DNS |
|
|
640 | Provides rich asynchronous DNS resolver capabilities. |
|
|
641 | |
|
|
642 | AnyEvent::HTTPD |
|
|
643 | Provides a simple web application server framework. |
|
|
644 | |
|
|
645 | AnyEvent::FastPing |
|
|
646 | The fastest ping in the west. |
|
|
647 | |
|
|
648 | Net::IRC3 |
|
|
649 | AnyEvent based IRC client module family. |
|
|
650 | |
|
|
651 | Net::XMPP2 |
|
|
652 | AnyEvent based XMPP (Jabber protocol) module family. |
|
|
653 | |
|
|
654 | Net::FCP |
|
|
655 | AnyEvent-based implementation of the Freenet Client Protocol, |
|
|
656 | birthplace of AnyEvent. |
|
|
657 | |
|
|
658 | Event::ExecFlow |
|
|
659 | High level API for event-based execution flow control. |
|
|
660 | |
|
|
661 | Coro |
|
|
662 | Has special support for AnyEvent via Coro::AnyEvent. |
|
|
663 | |
|
|
664 | AnyEvent::AIO, IO::AIO |
|
|
665 | Truly asynchronous I/O, should be in the toolbox of every event |
|
|
666 | programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent |
|
|
667 | together. |
|
|
668 | |
|
|
669 | AnyEvent::BDB, BDB |
|
|
670 | Truly asynchronous Berkeley DB access. AnyEvent::AIO transparently |
|
|
671 | fuses IO::AIO and AnyEvent together. |
|
|
672 | |
|
|
673 | IO::Lambda |
|
|
674 | The lambda approach to I/O - don't ask, look there. Can use |
|
|
675 | AnyEvent. |
389 | |
676 | |
390 | SUPPLYING YOUR OWN EVENT MODEL INTERFACE |
677 | SUPPLYING YOUR OWN EVENT MODEL INTERFACE |
391 | This is an advanced topic that you do not normally need to use AnyEvent |
678 | This is an advanced topic that you do not normally need to use AnyEvent |
392 | in a module. This section is only of use to event loop authors who want |
679 | in a module. This section is only of use to event loop authors who want |
393 | to provide AnyEvent compatibility. |
680 | to provide AnyEvent compatibility. |
… | |
… | |
431 | must not be done in an interactive application, so it makes sense. |
718 | must not be done in an interactive application, so it makes sense. |
432 | |
719 | |
433 | ENVIRONMENT VARIABLES |
720 | ENVIRONMENT VARIABLES |
434 | The following environment variables are used by this module: |
721 | The following environment variables are used by this module: |
435 | |
722 | |
436 | "PERL_ANYEVENT_VERBOSE" when set to 2 or higher, cause AnyEvent to |
723 | "PERL_ANYEVENT_VERBOSE" |
437 | report to STDERR which event model it chooses. |
724 | By default, AnyEvent will be completely silent except in fatal |
|
|
725 | conditions. You can set this environment variable to make AnyEvent |
|
|
726 | more talkative. |
|
|
727 | |
|
|
728 | When set to 1 or higher, causes AnyEvent to warn about unexpected |
|
|
729 | conditions, such as not being able to load the event model specified |
|
|
730 | by "PERL_ANYEVENT_MODEL". |
|
|
731 | |
|
|
732 | When set to 2 or higher, cause AnyEvent to report to STDERR which |
|
|
733 | event model it chooses. |
|
|
734 | |
|
|
735 | "PERL_ANYEVENT_MODEL" |
|
|
736 | This can be used to specify the event model to be used by AnyEvent, |
|
|
737 | before auto detection and -probing kicks in. It must be a string |
|
|
738 | consisting entirely of ASCII letters. The string "AnyEvent::Impl::" |
|
|
739 | gets prepended and the resulting module name is loaded and if the |
|
|
740 | load was successful, used as event model. If it fails to load |
|
|
741 | AnyEvent will proceed with auto detection and -probing. |
|
|
742 | |
|
|
743 | This functionality might change in future versions. |
|
|
744 | |
|
|
745 | For example, to force the pure perl model (AnyEvent::Impl::Perl) you |
|
|
746 | could start your program like this: |
|
|
747 | |
|
|
748 | PERL_ANYEVENT_MODEL=Perl perl ... |
|
|
749 | |
|
|
750 | "PERL_ANYEVENT_PROTOCOLS" |
|
|
751 | Used by both AnyEvent::DNS and AnyEvent::Socket to determine |
|
|
752 | preferences for IPv4 or IPv6. The default is unspecified (and might |
|
|
753 | change, or be the result of auto probing). |
|
|
754 | |
|
|
755 | Must be set to a comma-separated list of protocols or address |
|
|
756 | families, current supported: "ipv4" and "ipv6". Only protocols |
|
|
757 | mentioned will be used, and preference will be given to protocols |
|
|
758 | mentioned earlier in the list. |
|
|
759 | |
|
|
760 | This variable can effectively be used for denial-of-service attacks |
|
|
761 | against local programs (e.g. when setuid), although the impact is |
|
|
762 | likely small, as the program has to handle connection errors |
|
|
763 | already- |
|
|
764 | |
|
|
765 | Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over |
|
|
766 | IPv6, but support both and try to use both. |
|
|
767 | "PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to |
|
|
768 | resolve or contact IPv6 addresses. |
|
|
769 | "PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but |
|
|
770 | prefer IPv6 over IPv4. |
|
|
771 | |
|
|
772 | "PERL_ANYEVENT_EDNS0" |
|
|
773 | Used by AnyEvent::DNS to decide whether to use the EDNS0 extension |
|
|
774 | for DNS. This extension is generally useful to reduce DNS traffic, |
|
|
775 | but some (broken) firewalls drop such DNS packets, which is why it |
|
|
776 | is off by default. |
|
|
777 | |
|
|
778 | Setting this variable to 1 will cause AnyEvent::DNS to announce |
|
|
779 | EDNS0 in its DNS requests. |
438 | |
780 | |
439 | EXAMPLE PROGRAM |
781 | EXAMPLE PROGRAM |
440 | The following program uses an IO watcher to read data from STDIN, a |
782 | The following program uses an I/O watcher to read data from STDIN, a |
441 | timer to display a message once per second, and a condition variable to |
783 | timer to display a message once per second, and a condition variable to |
442 | quit the program when the user enters quit: |
784 | quit the program when the user enters quit: |
443 | |
785 | |
444 | use AnyEvent; |
786 | use AnyEvent; |
445 | |
787 | |
… | |
… | |
450 | poll => 'r', |
792 | poll => 'r', |
451 | cb => sub { |
793 | cb => sub { |
452 | warn "io event <$_[0]>\n"; # will always output <r> |
794 | warn "io event <$_[0]>\n"; # will always output <r> |
453 | chomp (my $input = <STDIN>); # read a line |
795 | chomp (my $input = <STDIN>); # read a line |
454 | warn "read: $input\n"; # output what has been read |
796 | warn "read: $input\n"; # output what has been read |
455 | $cv->broadcast if $input =~ /^q/i; # quit program if /^q/i |
797 | $cv->send if $input =~ /^q/i; # quit program if /^q/i |
456 | }, |
798 | }, |
457 | ); |
799 | ); |
458 | |
800 | |
459 | my $time_watcher; # can only be used once |
801 | my $time_watcher; # can only be used once |
460 | |
802 | |
… | |
… | |
465 | }); |
807 | }); |
466 | } |
808 | } |
467 | |
809 | |
468 | new_timer; # create first timer |
810 | new_timer; # create first timer |
469 | |
811 | |
470 | $cv->wait; # wait until user enters /^q/i |
812 | $cv->recv; # wait until user enters /^q/i |
471 | |
813 | |
472 | REAL-WORLD EXAMPLE |
814 | REAL-WORLD EXAMPLE |
473 | Consider the Net::FCP module. It features (among others) the following |
815 | Consider the Net::FCP module. It features (among others) the following |
474 | API calls, which are to freenet what HTTP GET requests are to http: |
816 | API calls, which are to freenet what HTTP GET requests are to http: |
475 | |
817 | |
… | |
… | |
524 | syswrite $txn->{fh}, $txn->{request} |
866 | syswrite $txn->{fh}, $txn->{request} |
525 | or die "connection or write error"; |
867 | or die "connection or write error"; |
526 | $txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r }); |
868 | $txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r }); |
527 | |
869 | |
528 | Again, "fh_ready_r" waits till all data has arrived, and then stores the |
870 | Again, "fh_ready_r" waits till all data has arrived, and then stores the |
529 | result and signals any possible waiters that the request ahs finished: |
871 | result and signals any possible waiters that the request has finished: |
530 | |
872 | |
531 | sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf}; |
873 | sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf}; |
532 | |
874 | |
533 | if (end-of-file or data complete) { |
875 | if (end-of-file or data complete) { |
534 | $txn->{result} = $txn->{buf}; |
876 | $txn->{result} = $txn->{buf}; |
535 | $txn->{finished}->broadcast; |
877 | $txn->{finished}->send; |
536 | $txb->{cb}->($txn) of $txn->{cb}; # also call callback |
878 | $txb->{cb}->($txn) of $txn->{cb}; # also call callback |
537 | } |
879 | } |
538 | |
880 | |
539 | The "result" method, finally, just waits for the finished signal (if the |
881 | The "result" method, finally, just waits for the finished signal (if the |
540 | request was already finished, it doesn't wait, of course, and returns |
882 | request was already finished, it doesn't wait, of course, and returns |
541 | the data: |
883 | the data: |
542 | |
884 | |
543 | $txn->{finished}->wait; |
885 | $txn->{finished}->recv; |
544 | return $txn->{result}; |
886 | return $txn->{result}; |
545 | |
887 | |
546 | The actual code goes further and collects all errors ("die"s, |
888 | The actual code goes further and collects all errors ("die"s, |
547 | exceptions) that occured during request processing. The "result" method |
889 | exceptions) that occurred during request processing. The "result" method |
548 | detects whether an exception as thrown (it is stored inside the $txn |
890 | detects whether an exception as thrown (it is stored inside the $txn |
549 | object) and just throws the exception, which means connection errors and |
891 | object) and just throws the exception, which means connection errors and |
550 | other problems get reported tot he code that tries to use the result, |
892 | other problems get reported tot he code that tries to use the result, |
551 | not in a random callback. |
893 | not in a random callback. |
552 | |
894 | |
… | |
… | |
583 | |
925 | |
584 | my $quit = AnyEvent->condvar; |
926 | my $quit = AnyEvent->condvar; |
585 | |
927 | |
586 | $fcp->txn_client_get ($url)->cb (sub { |
928 | $fcp->txn_client_get ($url)->cb (sub { |
587 | ... |
929 | ... |
588 | $quit->broadcast; |
930 | $quit->send; |
589 | }); |
931 | }); |
590 | |
932 | |
591 | $quit->wait; |
933 | $quit->recv; |
|
|
934 | |
|
|
935 | BENCHMARKS |
|
|
936 | To give you an idea of the performance and overheads that AnyEvent adds |
|
|
937 | over the event loops themselves and to give you an impression of the |
|
|
938 | speed of various event loops I prepared some benchmarks. |
|
|
939 | |
|
|
940 | BENCHMARKING ANYEVENT OVERHEAD |
|
|
941 | Here is a benchmark of various supported event models used natively and |
|
|
942 | through AnyEvent. The benchmark creates a lot of timers (with a zero |
|
|
943 | timeout) and I/O watchers (watching STDOUT, a pty, to become writable, |
|
|
944 | which it is), lets them fire exactly once and destroys them again. |
|
|
945 | |
|
|
946 | Source code for this benchmark is found as eg/bench in the AnyEvent |
|
|
947 | distribution. |
|
|
948 | |
|
|
949 | Explanation of the columns |
|
|
950 | *watcher* is the number of event watchers created/destroyed. Since |
|
|
951 | different event models feature vastly different performances, each event |
|
|
952 | loop was given a number of watchers so that overall runtime is |
|
|
953 | acceptable and similar between tested event loop (and keep them from |
|
|
954 | crashing): Glib would probably take thousands of years if asked to |
|
|
955 | process the same number of watchers as EV in this benchmark. |
|
|
956 | |
|
|
957 | *bytes* is the number of bytes (as measured by the resident set size, |
|
|
958 | RSS) consumed by each watcher. This method of measuring captures both C |
|
|
959 | and Perl-based overheads. |
|
|
960 | |
|
|
961 | *create* is the time, in microseconds (millionths of seconds), that it |
|
|
962 | takes to create a single watcher. The callback is a closure shared |
|
|
963 | between all watchers, to avoid adding memory overhead. That means |
|
|
964 | closure creation and memory usage is not included in the figures. |
|
|
965 | |
|
|
966 | *invoke* is the time, in microseconds, used to invoke a simple callback. |
|
|
967 | The callback simply counts down a Perl variable and after it was invoked |
|
|
968 | "watcher" times, it would "->send" a condvar once to signal the end of |
|
|
969 | this phase. |
|
|
970 | |
|
|
971 | *destroy* is the time, in microseconds, that it takes to destroy a |
|
|
972 | single watcher. |
|
|
973 | |
|
|
974 | Results |
|
|
975 | name watchers bytes create invoke destroy comment |
|
|
976 | EV/EV 400000 244 0.56 0.46 0.31 EV native interface |
|
|
977 | EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers |
|
|
978 | CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal |
|
|
979 | Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation |
|
|
980 | Event/Event 16000 516 31.88 31.30 0.85 Event native interface |
|
|
981 | Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers |
|
|
982 | Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour |
|
|
983 | Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers |
|
|
984 | POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event |
|
|
985 | POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select |
|
|
986 | |
|
|
987 | Discussion |
|
|
988 | The benchmark does *not* measure scalability of the event loop very |
|
|
989 | well. For example, a select-based event loop (such as the pure perl one) |
|
|
990 | can never compete with an event loop that uses epoll when the number of |
|
|
991 | file descriptors grows high. In this benchmark, all events become ready |
|
|
992 | at the same time, so select/poll-based implementations get an unnatural |
|
|
993 | speed boost. |
|
|
994 | |
|
|
995 | Also, note that the number of watchers usually has a nonlinear effect on |
|
|
996 | overall speed, that is, creating twice as many watchers doesn't take |
|
|
997 | twice the time - usually it takes longer. This puts event loops tested |
|
|
998 | with a higher number of watchers at a disadvantage. |
|
|
999 | |
|
|
1000 | To put the range of results into perspective, consider that on the |
|
|
1001 | benchmark machine, handling an event takes roughly 1600 CPU cycles with |
|
|
1002 | EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 |
|
|
1003 | CPU cycles with POE. |
|
|
1004 | |
|
|
1005 | "EV" is the sole leader regarding speed and memory use, which are both |
|
|
1006 | maximal/minimal, respectively. Even when going through AnyEvent, it uses |
|
|
1007 | far less memory than any other event loop and is still faster than Event |
|
|
1008 | natively. |
|
|
1009 | |
|
|
1010 | The pure perl implementation is hit in a few sweet spots (both the |
|
|
1011 | constant timeout and the use of a single fd hit optimisations in the |
|
|
1012 | perl interpreter and the backend itself). Nevertheless this shows that |
|
|
1013 | it adds very little overhead in itself. Like any select-based backend |
|
|
1014 | its performance becomes really bad with lots of file descriptors (and |
|
|
1015 | few of them active), of course, but this was not subject of this |
|
|
1016 | benchmark. |
|
|
1017 | |
|
|
1018 | The "Event" module has a relatively high setup and callback invocation |
|
|
1019 | cost, but overall scores in on the third place. |
|
|
1020 | |
|
|
1021 | "Glib"'s memory usage is quite a bit higher, but it features a faster |
|
|
1022 | callback invocation and overall ends up in the same class as "Event". |
|
|
1023 | However, Glib scales extremely badly, doubling the number of watchers |
|
|
1024 | increases the processing time by more than a factor of four, making it |
|
|
1025 | completely unusable when using larger numbers of watchers (note that |
|
|
1026 | only a single file descriptor was used in the benchmark, so |
|
|
1027 | inefficiencies of "poll" do not account for this). |
|
|
1028 | |
|
|
1029 | The "Tk" adaptor works relatively well. The fact that it crashes with |
|
|
1030 | more than 2000 watchers is a big setback, however, as correctness takes |
|
|
1031 | precedence over speed. Nevertheless, its performance is surprising, as |
|
|
1032 | the file descriptor is dup()ed for each watcher. This shows that the |
|
|
1033 | dup() employed by some adaptors is not a big performance issue (it does |
|
|
1034 | incur a hidden memory cost inside the kernel which is not reflected in |
|
|
1035 | the figures above). |
|
|
1036 | |
|
|
1037 | "POE", regardless of underlying event loop (whether using its pure perl |
|
|
1038 | select-based backend or the Event module, the POE-EV backend couldn't be |
|
|
1039 | tested because it wasn't working) shows abysmal performance and memory |
|
|
1040 | usage with AnyEvent: Watchers use almost 30 times as much memory as EV |
|
|
1041 | watchers, and 10 times as much memory as Event (the high memory |
|
|
1042 | requirements are caused by requiring a session for each watcher). |
|
|
1043 | Watcher invocation speed is almost 900 times slower than with AnyEvent's |
|
|
1044 | pure perl implementation. |
|
|
1045 | |
|
|
1046 | The design of the POE adaptor class in AnyEvent can not really account |
|
|
1047 | for the performance issues, though, as session creation overhead is |
|
|
1048 | small compared to execution of the state machine, which is coded pretty |
|
|
1049 | optimally within AnyEvent::Impl::POE (and while everybody agrees that |
|
|
1050 | using multiple sessions is not a good approach, especially regarding |
|
|
1051 | memory usage, even the author of POE could not come up with a faster |
|
|
1052 | design). |
|
|
1053 | |
|
|
1054 | Summary |
|
|
1055 | * Using EV through AnyEvent is faster than any other event loop (even |
|
|
1056 | when used without AnyEvent), but most event loops have acceptable |
|
|
1057 | performance with or without AnyEvent. |
|
|
1058 | |
|
|
1059 | * The overhead AnyEvent adds is usually much smaller than the overhead |
|
|
1060 | of the actual event loop, only with extremely fast event loops such |
|
|
1061 | as EV adds AnyEvent significant overhead. |
|
|
1062 | |
|
|
1063 | * You should avoid POE like the plague if you want performance or |
|
|
1064 | reasonable memory usage. |
|
|
1065 | |
|
|
1066 | BENCHMARKING THE LARGE SERVER CASE |
|
|
1067 | This benchmark actually benchmarks the event loop itself. It works by |
|
|
1068 | creating a number of "servers": each server consists of a socket pair, a |
|
|
1069 | timeout watcher that gets reset on activity (but never fires), and an |
|
|
1070 | I/O watcher waiting for input on one side of the socket. Each time the |
|
|
1071 | socket watcher reads a byte it will write that byte to a random other |
|
|
1072 | "server". |
|
|
1073 | |
|
|
1074 | The effect is that there will be a lot of I/O watchers, only part of |
|
|
1075 | which are active at any one point (so there is a constant number of |
|
|
1076 | active fds for each loop iteration, but which fds these are is random). |
|
|
1077 | The timeout is reset each time something is read because that reflects |
|
|
1078 | how most timeouts work (and puts extra pressure on the event loops). |
|
|
1079 | |
|
|
1080 | In this benchmark, we use 10000 socket pairs (20000 sockets), of which |
|
|
1081 | 100 (1%) are active. This mirrors the activity of large servers with |
|
|
1082 | many connections, most of which are idle at any one point in time. |
|
|
1083 | |
|
|
1084 | Source code for this benchmark is found as eg/bench2 in the AnyEvent |
|
|
1085 | distribution. |
|
|
1086 | |
|
|
1087 | Explanation of the columns |
|
|
1088 | *sockets* is the number of sockets, and twice the number of "servers" |
|
|
1089 | (as each server has a read and write socket end). |
|
|
1090 | |
|
|
1091 | *create* is the time it takes to create a socket pair (which is |
|
|
1092 | nontrivial) and two watchers: an I/O watcher and a timeout watcher. |
|
|
1093 | |
|
|
1094 | *request*, the most important value, is the time it takes to handle a |
|
|
1095 | single "request", that is, reading the token from the pipe and |
|
|
1096 | forwarding it to another server. This includes deleting the old timeout |
|
|
1097 | and creating a new one that moves the timeout into the future. |
|
|
1098 | |
|
|
1099 | Results |
|
|
1100 | name sockets create request |
|
|
1101 | EV 20000 69.01 11.16 |
|
|
1102 | Perl 20000 73.32 35.87 |
|
|
1103 | Event 20000 212.62 257.32 |
|
|
1104 | Glib 20000 651.16 1896.30 |
|
|
1105 | POE 20000 349.67 12317.24 uses POE::Loop::Event |
|
|
1106 | |
|
|
1107 | Discussion |
|
|
1108 | This benchmark *does* measure scalability and overall performance of the |
|
|
1109 | particular event loop. |
|
|
1110 | |
|
|
1111 | EV is again fastest. Since it is using epoll on my system, the setup |
|
|
1112 | time is relatively high, though. |
|
|
1113 | |
|
|
1114 | Perl surprisingly comes second. It is much faster than the C-based event |
|
|
1115 | loops Event and Glib. |
|
|
1116 | |
|
|
1117 | Event suffers from high setup time as well (look at its code and you |
|
|
1118 | will understand why). Callback invocation also has a high overhead |
|
|
1119 | compared to the "$_->() for .."-style loop that the Perl event loop |
|
|
1120 | uses. Event uses select or poll in basically all documented |
|
|
1121 | configurations. |
|
|
1122 | |
|
|
1123 | Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It |
|
|
1124 | clearly fails to perform with many filehandles or in busy servers. |
|
|
1125 | |
|
|
1126 | POE is still completely out of the picture, taking over 1000 times as |
|
|
1127 | long as EV, and over 100 times as long as the Perl implementation, even |
|
|
1128 | though it uses a C-based event loop in this case. |
|
|
1129 | |
|
|
1130 | Summary |
|
|
1131 | * The pure perl implementation performs extremely well. |
|
|
1132 | |
|
|
1133 | * Avoid Glib or POE in large projects where performance matters. |
|
|
1134 | |
|
|
1135 | BENCHMARKING SMALL SERVERS |
|
|
1136 | While event loops should scale (and select-based ones do not...) even to |
|
|
1137 | large servers, most programs we (or I :) actually write have only a few |
|
|
1138 | I/O watchers. |
|
|
1139 | |
|
|
1140 | In this benchmark, I use the same benchmark program as in the large |
|
|
1141 | server case, but it uses only eight "servers", of which three are active |
|
|
1142 | at any one time. This should reflect performance for a small server |
|
|
1143 | relatively well. |
|
|
1144 | |
|
|
1145 | The columns are identical to the previous table. |
|
|
1146 | |
|
|
1147 | Results |
|
|
1148 | name sockets create request |
|
|
1149 | EV 16 20.00 6.54 |
|
|
1150 | Perl 16 25.75 12.62 |
|
|
1151 | Event 16 81.27 35.86 |
|
|
1152 | Glib 16 32.63 15.48 |
|
|
1153 | POE 16 261.87 276.28 uses POE::Loop::Event |
|
|
1154 | |
|
|
1155 | Discussion |
|
|
1156 | The benchmark tries to test the performance of a typical small server. |
|
|
1157 | While knowing how various event loops perform is interesting, keep in |
|
|
1158 | mind that their overhead in this case is usually not as important, due |
|
|
1159 | to the small absolute number of watchers (that is, you need efficiency |
|
|
1160 | and speed most when you have lots of watchers, not when you only have a |
|
|
1161 | few of them). |
|
|
1162 | |
|
|
1163 | EV is again fastest. |
|
|
1164 | |
|
|
1165 | Perl again comes second. It is noticeably faster than the C-based event |
|
|
1166 | loops Event and Glib, although the difference is too small to really |
|
|
1167 | matter. |
|
|
1168 | |
|
|
1169 | POE also performs much better in this case, but is is still far behind |
|
|
1170 | the others. |
|
|
1171 | |
|
|
1172 | Summary |
|
|
1173 | * C-based event loops perform very well with small number of watchers, |
|
|
1174 | as the management overhead dominates. |
|
|
1175 | |
|
|
1176 | FORK |
|
|
1177 | Most event libraries are not fork-safe. The ones who are usually are |
|
|
1178 | because they rely on inefficient but fork-safe "select" or "poll" calls. |
|
|
1179 | Only EV is fully fork-aware. |
|
|
1180 | |
|
|
1181 | If you have to fork, you must either do so *before* creating your first |
|
|
1182 | watcher OR you must not use AnyEvent at all in the child. |
|
|
1183 | |
|
|
1184 | SECURITY CONSIDERATIONS |
|
|
1185 | AnyEvent can be forced to load any event model via |
|
|
1186 | $ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used |
|
|
1187 | to execute arbitrary code or directly gain access, it can easily be used |
|
|
1188 | to make the program hang or malfunction in subtle ways, as AnyEvent |
|
|
1189 | watchers will not be active when the program uses a different event |
|
|
1190 | model than specified in the variable. |
|
|
1191 | |
|
|
1192 | You can make AnyEvent completely ignore this variable by deleting it |
|
|
1193 | before the first watcher gets created, e.g. with a "BEGIN" block: |
|
|
1194 | |
|
|
1195 | BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} } |
|
|
1196 | |
|
|
1197 | use AnyEvent; |
|
|
1198 | |
|
|
1199 | Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can |
|
|
1200 | be used to probe what backend is used and gain other information (which |
|
|
1201 | is probably even less useful to an attacker than PERL_ANYEVENT_MODEL). |
592 | |
1202 | |
593 | SEE ALSO |
1203 | SEE ALSO |
594 | Event modules: Coro::EV, EV, EV::Glib, Glib::EV, Coro::Event, Event, |
1204 | Utility functions: AnyEvent::Util. |
595 | Glib::Event, Glib, Coro, Tk. |
|
|
596 | |
1205 | |
597 | Implementations: AnyEvent::Impl::CoroEV, AnyEvent::Impl::EV, |
1206 | Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk, |
598 | AnyEvent::Impl::CoroEvent, AnyEvent::Impl::Event, AnyEvent::Impl::Glib, |
1207 | Event::Lib, Qt, POE. |
|
|
1208 | |
|
|
1209 | Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event, |
599 | AnyEvent::Impl::Tk, AnyEvent::Impl::Perl. |
1210 | AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl, |
|
|
1211 | AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE. |
600 | |
1212 | |
|
|
1213 | Non-blocking file handles, sockets, TCP clients and servers: |
|
|
1214 | AnyEvent::Handle, AnyEvent::Socket. |
|
|
1215 | |
|
|
1216 | Asynchronous DNS: AnyEvent::DNS. |
|
|
1217 | |
|
|
1218 | Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event, |
|
|
1219 | |
601 | Nontrivial usage examples: Net::FCP, Net::XMPP2. |
1220 | Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS. |
602 | |
1221 | |
|
|
1222 | AUTHOR |
|
|
1223 | Marc Lehmann <schmorp@schmorp.de> |
|
|
1224 | http://home.schmorp.de/ |
603 | |
1225 | |