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, Event::Lib, Qt - |
4 | EV, Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event |
5 | various supported 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, Event::Lib, Qt. The first one found is used. If none are |
81 | AnyEvent::Impl::Perl, Tk, Event::Lib, Qt, POE. The first one found is |
82 | found, the module tries to load these modules (excluding Event::Lib and |
82 | used. If none are found, the module tries to load these modules |
83 | Qt) in the order given. The first one that can be successfully loaded |
83 | (excluding Tk, Event::Lib, Qt and POE as the pure perl adaptor should |
84 | will be used. If, after this, still none could be found, AnyEvent will |
84 | always succeed) in the order given. The first one that can be |
85 | fall back to a pure-perl event loop, which is not very efficient, but |
85 | successfully loaded will be used. If, after this, still none could be |
86 | should work everywhere. |
86 | found, AnyEvent will fall back to a pure-perl event loop, which is not |
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87 | very efficient, but should work everywhere. |
87 | |
88 | |
88 | Because AnyEvent first checks for modules that are already loaded, |
89 | Because AnyEvent first checks for modules that are already loaded, |
89 | loading an event model explicitly before first using AnyEvent will |
90 | loading an event model explicitly before first using AnyEvent will |
90 | likely make that model the default. For example: |
91 | likely make that model the default. For example: |
91 | |
92 | |
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103 | explicitly. |
104 | explicitly. |
104 | |
105 | |
105 | WATCHERS |
106 | WATCHERS |
106 | 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 |
107 | 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 |
108 | the callback to call, the filehandle to watch, etc. |
109 | the callback to call, the file handle to watch, etc. |
109 | |
110 | |
110 | These watchers are normal Perl objects with normal Perl lifetime. After |
111 | These watchers are normal Perl objects with normal Perl lifetime. After |
111 | 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 |
112 | 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 |
113 | in control). |
114 | in control). |
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130 | |
131 | |
131 | 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, |
132 | 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 |
133 | declared. |
134 | declared. |
134 | |
135 | |
135 | IO WATCHERS |
136 | I/O WATCHERS |
136 | 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 |
137 | the following mandatory key-value pairs as arguments: |
138 | the following mandatory key-value pairs as arguments: |
138 | |
139 | |
139 | "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. |
140 | "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 |
141 | watcher waiting for "r"eadable or "w"ritable events, respectively. "cb" |
142 | watcher waiting for "r"eadable or "w"ritable events, respectively. "cb" |
142 | 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. |
143 | |
144 | |
144 | As long as the I/O watcher exists it will keep the file descriptor or a |
145 | Although the callback might get passed parameters, their value and |
145 | copy of it alive/open. |
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. |
146 | |
148 | |
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149 | The I/O watcher might use the underlying file descriptor or a copy of |
147 | 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 |
148 | active on the underlying file descriptor. |
151 | the underlying file descriptor. |
149 | |
152 | |
150 | Some event loops issue spurious readyness notifications, so you should |
153 | Some event loops issue spurious readyness notifications, so you should |
151 | 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 |
152 | handles. |
155 | handles. |
153 | |
156 | |
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163 | TIME WATCHERS |
166 | TIME WATCHERS |
164 | 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 |
165 | with the following mandatory arguments: |
168 | with the following mandatory arguments: |
166 | |
169 | |
167 | "after" specifies after how many seconds (fractional values are |
170 | "after" specifies after how many seconds (fractional values are |
168 | supported) should the timer activate. "cb" the callback to invoke in |
171 | supported) the callback should be invoked. "cb" is the callback to |
169 | 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. |
170 | |
177 | |
171 | 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 |
172 | 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 |
173 | and Glib). |
180 | and Glib). |
174 | |
181 | |
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218 | SIGNAL WATCHERS |
225 | SIGNAL WATCHERS |
219 | 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 |
220 | *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 |
221 | whenever a signal occurs. |
228 | whenever a signal occurs. |
222 | |
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 | |
223 | Multiple signal occurances can be clumped together into one callback |
234 | Multiple signal occurrences can be clumped together into one callback |
224 | invocation, and callback invocation will be synchronous. synchronous |
235 | invocation, and callback invocation will be synchronous. Synchronous |
225 | 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 |
226 | process, but it is guarenteed not to interrupt any other callbacks. |
237 | process, but it is guaranteed not to interrupt any other callbacks. |
227 | |
238 | |
228 | 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 |
229 | signal between multiple watchers. |
240 | signal between multiple watchers. |
230 | |
241 | |
231 | 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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240 | |
251 | |
241 | 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 |
242 | 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 |
243 | 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 |
244 | 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 |
245 | 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. |
246 | |
258 | |
247 | 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; |
248 | |
277 | |
249 | my $w = AnyEvent->child ( |
278 | my $w = AnyEvent->child ( |
250 | pid => 1333, |
279 | pid => $pid, |
251 | cb => sub { |
280 | cb => sub { |
252 | my ($pid, $status) = @_; |
281 | my ($pid, $status) = @_; |
253 | warn "pid $pid exited with status $status"; |
282 | warn "pid $pid exited with status $status"; |
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283 | $done->send; |
254 | }, |
284 | }, |
255 | ); |
285 | ); |
256 | |
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 | |
257 | 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 | |
258 | Condition variables can be created by calling the "AnyEvent->condvar" |
301 | Condition variables can be created by calling the "AnyEvent->condvar" |
259 | 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. |
260 | |
305 | |
261 | A condition variable waits for a condition - precisely that the |
306 | After creation, the condition variable is "false" until it becomes |
262 | "->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). |
263 | |
309 | |
264 | They are very useful to signal that a condition has been fulfilled, for |
310 | Condition variables are similar to callbacks, except that you can |
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311 | optionally wait for them. They can also be called merge points - points |
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312 | in time where multiple outstanding events have been processed. And yet |
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313 | another way to call them is transactions - each condition variable can |
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314 | be used to represent a transaction, which finishes at some point and |
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315 | delivers a result. |
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316 | |
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317 | Condition variables are very useful to signal that something has |
265 | example, if you write a module that does asynchronous http requests, |
318 | finished, for example, if you write a module that does asynchronous http |
266 | then a condition variable would be the ideal candidate to signal the |
319 | requests, then a condition variable would be the ideal candidate to |
267 | availability of results. |
320 | signal the availability of results. The user can either act when the |
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321 | callback is called or can synchronously "->recv" for the results. |
268 | |
322 | |
269 | You can also use condition variables to block your main program until an |
323 | You can also use them to simulate traditional event loops - for example, |
270 | event occurs - for example, you could "->wait" in your main program |
324 | you can block your main program until an event occurs - for example, you |
271 | until the user clicks the Quit button in your app, which would |
325 | could "->recv" in your main program until the user clicks the Quit |
272 | "->broadcast" the "quit" event. |
326 | button of your app, which would "->send" the "quit" event. |
273 | |
327 | |
274 | Note that condition variables recurse into the event loop - if you have |
328 | Note that condition variables recurse into the event loop - if you have |
275 | two pirces of code that call "->wait" in a round-robbin fashion, you |
329 | two pieces of code that call "->recv" in a round-robin fashion, you |
276 | lose. Therefore, condition variables are good to export to your caller, |
330 | lose. Therefore, condition variables are good to export to your caller, |
277 | but you should avoid making a blocking wait yourself, at least in |
331 | but you should avoid making a blocking wait yourself, at least in |
278 | callbacks, as this asks for trouble. |
332 | callbacks, as this asks for trouble. |
279 | |
333 | |
280 | This object has two methods: |
334 | Condition variables are represented by hash refs in perl, and the keys |
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335 | used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy |
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336 | (it is often useful to build your own transaction class on top of |
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337 | AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call |
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338 | it's "new" method in your own "new" method. |
281 | |
339 | |
282 | $cv->wait |
340 | There are two "sides" to a condition variable - the "producer side" |
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341 | which eventually calls "-> send", and the "consumer side", which waits |
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342 | for the send to occur. |
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343 | |
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344 | Example: wait for a timer. |
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345 | |
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346 | # wait till the result is ready |
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347 | my $result_ready = AnyEvent->condvar; |
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348 | |
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349 | # do something such as adding a timer |
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350 | # or socket watcher the calls $result_ready->send |
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351 | # when the "result" is ready. |
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352 | # in this case, we simply use a timer: |
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353 | my $w = AnyEvent->timer ( |
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354 | after => 1, |
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355 | cb => sub { $result_ready->send }, |
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356 | ); |
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357 | |
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358 | # this "blocks" (while handling events) till the callback |
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359 | # calls send |
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360 | $result_ready->recv; |
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361 | |
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362 | Example: wait for a timer, but take advantage of the fact that condition |
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363 | variables are also code references. |
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364 | |
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365 | my $done = AnyEvent->condvar; |
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366 | my $delay = AnyEvent->timer (after => 5, cb => $done); |
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367 | $done->recv; |
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368 | |
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369 | METHODS FOR PRODUCERS |
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370 | These methods should only be used by the producing side, i.e. the |
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371 | code/module that eventually sends the signal. Note that it is also the |
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372 | producer side which creates the condvar in most cases, but it isn't |
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373 | uncommon for the consumer to create it as well. |
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374 | |
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375 | $cv->send (...) |
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376 | Flag the condition as ready - a running "->recv" and all further |
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377 | calls to "recv" will (eventually) return after this method has been |
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378 | called. If nobody is waiting the send will be remembered. |
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379 | |
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380 | If a callback has been set on the condition variable, it is called |
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381 | immediately from within send. |
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382 | |
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383 | Any arguments passed to the "send" call will be returned by all |
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384 | future "->recv" calls. |
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385 | |
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386 | Condition variables are overloaded so one can call them directly (as |
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387 | a code reference). Calling them directly is the same as calling |
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388 | "send". |
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389 | |
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390 | $cv->croak ($error) |
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391 | Similar to send, but causes all call's to "->recv" to invoke |
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392 | "Carp::croak" with the given error message/object/scalar. |
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393 | |
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394 | This can be used to signal any errors to the condition variable |
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395 | user/consumer. |
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396 | |
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397 | $cv->begin ([group callback]) |
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398 | $cv->end |
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399 | These two methods are EXPERIMENTAL and MIGHT CHANGE. |
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400 | |
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401 | These two methods can be used to combine many transactions/events |
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402 | into one. For example, a function that pings many hosts in parallel |
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403 | might want to use a condition variable for the whole process. |
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404 | |
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405 | Every call to "->begin" will increment a counter, and every call to |
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406 | "->end" will decrement it. If the counter reaches 0 in "->end", the |
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407 | (last) callback passed to "begin" will be executed. That callback is |
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408 | *supposed* to call "->send", but that is not required. If no |
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409 | callback was set, "send" will be called without any arguments. |
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410 | |
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411 | Let's clarify this with the ping example: |
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412 | |
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413 | my $cv = AnyEvent->condvar; |
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414 | |
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415 | my %result; |
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416 | $cv->begin (sub { $cv->send (\%result) }); |
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417 | |
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418 | for my $host (@list_of_hosts) { |
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419 | $cv->begin; |
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420 | ping_host_then_call_callback $host, sub { |
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421 | $result{$host} = ...; |
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422 | $cv->end; |
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423 | }; |
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424 | } |
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425 | |
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426 | $cv->end; |
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427 | |
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428 | This code fragment supposedly pings a number of hosts and calls |
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429 | "send" after results for all then have have been gathered - in any |
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430 | order. To achieve this, the code issues a call to "begin" when it |
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431 | starts each ping request and calls "end" when it has received some |
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432 | result for it. Since "begin" and "end" only maintain a counter, the |
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433 | order in which results arrive is not relevant. |
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434 | |
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435 | There is an additional bracketing call to "begin" and "end" outside |
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436 | the loop, which serves two important purposes: first, it sets the |
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437 | callback to be called once the counter reaches 0, and second, it |
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438 | ensures that "send" is called even when "no" hosts are being pinged |
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439 | (the loop doesn't execute once). |
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440 | |
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441 | This is the general pattern when you "fan out" into multiple |
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442 | subrequests: use an outer "begin"/"end" pair to set the callback and |
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443 | ensure "end" is called at least once, and then, for each subrequest |
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444 | you start, call "begin" and for each subrequest you finish, call |
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445 | "end". |
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446 | |
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447 | METHODS FOR CONSUMERS |
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448 | These methods should only be used by the consuming side, i.e. the code |
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449 | awaits the condition. |
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450 | |
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451 | $cv->recv |
283 | Wait (blocking if necessary) until the "->broadcast" method has been |
452 | Wait (blocking if necessary) until the "->send" or "->croak" methods |
284 | called on c<$cv>, while servicing other watchers normally. |
453 | have been called on c<$cv>, while servicing other watchers normally. |
285 | |
454 | |
286 | You can only wait once on a condition - additional calls will return |
455 | You can only wait once on a condition - additional calls are valid |
287 | immediately. |
456 | but will return immediately. |
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457 | |
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458 | If an error condition has been set by calling "->croak", then this |
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459 | function will call "croak". |
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460 | |
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461 | In list context, all parameters passed to "send" will be returned, |
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462 | in scalar context only the first one will be returned. |
288 | |
463 | |
289 | Not all event models support a blocking wait - some die in that case |
464 | Not all event models support a blocking wait - some die in that case |
290 | (programs might want to do that to stay interactive), so *if you are |
465 | (programs might want to do that to stay interactive), so *if you are |
291 | using this from a module, never require a blocking wait*, but let |
466 | using this from a module, never require a blocking wait*, but let |
292 | the caller decide whether the call will block or not (for example, |
467 | the caller decide whether the call will block or not (for example, |
293 | by coupling condition variables with some kind of request results |
468 | by coupling condition variables with some kind of request results |
294 | and supporting callbacks so the caller knows that getting the result |
469 | and supporting callbacks so the caller knows that getting the result |
295 | will not block, while still suppporting blocking waits if the caller |
470 | will not block, while still supporting blocking waits if the caller |
296 | so desires). |
471 | so desires). |
297 | |
472 | |
298 | Another reason *never* to "->wait" in a module is that you cannot |
473 | Another reason *never* to "->recv" in a module is that you cannot |
299 | sensibly have two "->wait"'s in parallel, as that would require |
474 | sensibly have two "->recv"'s in parallel, as that would require |
300 | multiple interpreters or coroutines/threads, none of which |
475 | multiple interpreters or coroutines/threads, none of which |
301 | "AnyEvent" can supply (the coroutine-aware backends |
476 | "AnyEvent" can supply. |
302 | AnyEvent::Impl::CoroEV and AnyEvent::Impl::CoroEvent explicitly |
|
|
303 | support concurrent "->wait"'s from different coroutines, however). |
|
|
304 | |
477 | |
305 | $cv->broadcast |
478 | The Coro module, however, *can* and *does* supply coroutines and, in |
306 | Flag the condition as ready - a running "->wait" and all further |
479 | fact, Coro::AnyEvent replaces AnyEvent's condvars by coroutine-safe |
307 | calls to "wait" will (eventually) return after this method has been |
480 | versions and also integrates coroutines into AnyEvent, making |
308 | called. If nobody is waiting the broadcast will be remembered.. |
481 | blocking "->recv" calls perfectly safe as long as they are done from |
|
|
482 | another coroutine (one that doesn't run the event loop). |
309 | |
483 | |
310 | Example: |
484 | You can ensure that "-recv" never blocks by setting a callback and |
|
|
485 | only calling "->recv" from within that callback (or at a later |
|
|
486 | time). This will work even when the event loop does not support |
|
|
487 | blocking waits otherwise. |
311 | |
488 | |
312 | # wait till the result is ready |
489 | $bool = $cv->ready |
313 | my $result_ready = AnyEvent->condvar; |
490 | Returns true when the condition is "true", i.e. whether "send" or |
|
|
491 | "croak" have been called. |
314 | |
492 | |
315 | # do something such as adding a timer |
493 | $cb = $cv->cb ([new callback]) |
316 | # or socket watcher the calls $result_ready->broadcast |
494 | This is a mutator function that returns the callback set and |
317 | # when the "result" is ready. |
495 | optionally replaces it before doing so. |
318 | # in this case, we simply use a timer: |
|
|
319 | my $w = AnyEvent->timer ( |
|
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320 | after => 1, |
|
|
321 | cb => sub { $result_ready->broadcast }, |
|
|
322 | ); |
|
|
323 | |
496 | |
324 | # this "blocks" (while handling events) till the watcher |
497 | The callback will be called when the condition becomes "true", i.e. |
325 | # calls broadcast |
498 | when "send" or "croak" are called. Calling "recv" inside the |
326 | $result_ready->wait; |
499 | callback or at any later time is guaranteed not to block. |
327 | |
500 | |
328 | GLOBAL VARIABLES AND FUNCTIONS |
501 | GLOBAL VARIABLES AND FUNCTIONS |
329 | $AnyEvent::MODEL |
502 | $AnyEvent::MODEL |
330 | Contains "undef" until the first watcher is being created. Then it |
503 | Contains "undef" until the first watcher is being created. Then it |
331 | contains the event model that is being used, which is the name of |
504 | contains the event model that is being used, which is the name of |
… | |
… | |
333 | the "AnyEvent::Impl:xxx" modules, but can be any other class in the |
506 | the "AnyEvent::Impl:xxx" modules, but can be any other class in the |
334 | case AnyEvent has been extended at runtime (e.g. in *rxvt-unicode*). |
507 | case AnyEvent has been extended at runtime (e.g. in *rxvt-unicode*). |
335 | |
508 | |
336 | The known classes so far are: |
509 | The known classes so far are: |
337 | |
510 | |
338 | AnyEvent::Impl::CoroEV based on Coro::EV, best choice. |
|
|
339 | AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice. |
|
|
340 | AnyEvent::Impl::EV based on EV (an interface to libev, best choice). |
511 | AnyEvent::Impl::EV based on EV (an interface to libev, best choice). |
341 | AnyEvent::Impl::Event based on Event, second best choice. |
512 | AnyEvent::Impl::Event based on Event, second best choice. |
|
|
513 | AnyEvent::Impl::Perl pure-perl implementation, fast and portable. |
342 | AnyEvent::Impl::Glib based on Glib, third-best choice. |
514 | AnyEvent::Impl::Glib based on Glib, third-best choice. |
343 | AnyEvent::Impl::Tk based on Tk, very bad choice. |
515 | AnyEvent::Impl::Tk based on Tk, very bad choice. |
344 | AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable. |
|
|
345 | AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs). |
516 | AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs). |
346 | AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse. |
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. |
347 | |
529 | |
348 | AnyEvent::detect |
530 | AnyEvent::detect |
349 | Returns $AnyEvent::MODEL, forcing autodetection of the event model |
531 | Returns $AnyEvent::MODEL, forcing autodetection of the event model |
350 | if necessary. You should only call this function right before you |
532 | if necessary. You should only call this function right before you |
351 | would have created an AnyEvent watcher anyway, that is, as late as |
533 | would have created an AnyEvent watcher anyway, that is, as late as |
352 | possible at runtime. |
534 | possible at runtime. |
353 | |
535 | |
|
|
536 | $guard = AnyEvent::post_detect { BLOCK } |
|
|
537 | Arranges for the code block to be executed as soon as the event |
|
|
538 | model is autodetected (or immediately if this has already happened). |
|
|
539 | |
|
|
540 | If called in scalar or list context, then it creates and returns an |
|
|
541 | object that automatically removes the callback again when it is |
|
|
542 | destroyed. See Coro::BDB for a case where this is useful. |
|
|
543 | |
|
|
544 | @AnyEvent::post_detect |
|
|
545 | 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 |
|
|
547 | after the event loop has been chosen. |
|
|
548 | |
|
|
549 | You should check $AnyEvent::MODEL before adding to this array, |
|
|
550 | though: if it contains a true value then the event loop has already |
|
|
551 | been detected, and the array will be ignored. |
|
|
552 | |
|
|
553 | Best use "AnyEvent::post_detect { BLOCK }" instead. |
|
|
554 | |
354 | WHAT TO DO IN A MODULE |
555 | WHAT TO DO IN A MODULE |
355 | As a module author, you should "use AnyEvent" and call AnyEvent methods |
556 | As a module author, you should "use AnyEvent" and call AnyEvent methods |
356 | freely, but you should not load a specific event module or rely on it. |
557 | freely, but you should not load a specific event module or rely on it. |
357 | |
558 | |
358 | Be careful when you create watchers in the module body - AnyEvent will |
559 | Be careful when you create watchers in the module body - AnyEvent will |
359 | decide which event module to use as soon as the first method is called, |
560 | decide which event module to use as soon as the first method is called, |
360 | so by calling AnyEvent in your module body you force the user of your |
561 | so by calling AnyEvent in your module body you force the user of your |
361 | module to load the event module first. |
562 | module to load the event module first. |
362 | |
563 | |
363 | Never call "->wait" on a condition variable unless you *know* that the |
564 | Never call "->recv" on a condition variable unless you *know* that the |
364 | "->broadcast" method has been called on it already. This is because it |
565 | "->send" method has been called on it already. This is because it will |
365 | will stall the whole program, and the whole point of using events is to |
566 | stall the whole program, and the whole point of using events is to stay |
366 | stay interactive. |
567 | interactive. |
367 | |
568 | |
368 | It is fine, however, to call "->wait" when the user of your module |
569 | It is fine, however, to call "->recv" when the user of your module |
369 | requests it (i.e. if you create a http request object ad have a method |
570 | requests it (i.e. if you create a http request object ad have a method |
370 | called "results" that returns the results, it should call "->wait" |
571 | called "results" that returns the results, it should call "->recv" |
371 | freely, as the user of your module knows what she is doing. always). |
572 | freely, as the user of your module knows what she is doing. always). |
372 | |
573 | |
373 | WHAT TO DO IN THE MAIN PROGRAM |
574 | WHAT TO DO IN THE MAIN PROGRAM |
374 | There will always be a single main program - the only place that should |
575 | There will always be a single main program - the only place that should |
375 | dictate which event model to use. |
576 | dictate which event model to use. |
… | |
… | |
390 | |
591 | |
391 | You can chose to use a rather inefficient pure-perl implementation by |
592 | You can chose to use a rather inefficient pure-perl implementation by |
392 | loading the "AnyEvent::Impl::Perl" module, which gives you similar |
593 | loading the "AnyEvent::Impl::Perl" module, which gives you similar |
393 | behaviour everywhere, but letting AnyEvent chose is generally better. |
594 | behaviour everywhere, but letting AnyEvent chose is generally better. |
394 | |
595 | |
|
|
596 | OTHER MODULES |
|
|
597 | The following is a non-exhaustive list of additional modules that use |
|
|
598 | AnyEvent and can therefore be mixed easily with other AnyEvent modules |
|
|
599 | in the same program. Some of the modules come with AnyEvent, some are |
|
|
600 | available via CPAN. |
|
|
601 | |
|
|
602 | AnyEvent::Util |
|
|
603 | Contains various utility functions that replace often-used but |
|
|
604 | blocking functions such as "inet_aton" by event-/callback-based |
|
|
605 | versions. |
|
|
606 | |
|
|
607 | AnyEvent::Handle |
|
|
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, |
|
|
613 | addresses and name resolution. Also functions to create non-blocking |
|
|
614 | tcp connections or tcp servers, with IPv6 and SRV record support and |
|
|
615 | more. |
|
|
616 | |
|
|
617 | AnyEvent::HTTPD |
|
|
618 | Provides a simple web application server framework. |
|
|
619 | |
|
|
620 | AnyEvent::DNS |
|
|
621 | Provides rich asynchronous DNS resolver capabilities. |
|
|
622 | |
|
|
623 | AnyEvent::FastPing |
|
|
624 | The fastest ping in the west. |
|
|
625 | |
|
|
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 |
|
|
640 | Has special support for AnyEvent via Coro::AnyEvent. |
|
|
641 | |
|
|
642 | AnyEvent::AIO, IO::AIO |
|
|
643 | Truly asynchronous I/O, should be in the toolbox of every event |
|
|
644 | programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent |
|
|
645 | together. |
|
|
646 | |
|
|
647 | AnyEvent::BDB, BDB |
|
|
648 | Truly asynchronous Berkeley DB access. AnyEvent::AIO transparently |
|
|
649 | fuses IO::AIO and AnyEvent together. |
|
|
650 | |
|
|
651 | IO::Lambda |
|
|
652 | The lambda approach to I/O - don't ask, look there. Can use |
|
|
653 | AnyEvent. |
|
|
654 | |
395 | SUPPLYING YOUR OWN EVENT MODEL INTERFACE |
655 | SUPPLYING YOUR OWN EVENT MODEL INTERFACE |
396 | This is an advanced topic that you do not normally need to use AnyEvent |
656 | This is an advanced topic that you do not normally need to use AnyEvent |
397 | in a module. This section is only of use to event loop authors who want |
657 | in a module. This section is only of use to event loop authors who want |
398 | to provide AnyEvent compatibility. |
658 | to provide AnyEvent compatibility. |
399 | |
659 | |
… | |
… | |
437 | |
697 | |
438 | ENVIRONMENT VARIABLES |
698 | ENVIRONMENT VARIABLES |
439 | The following environment variables are used by this module: |
699 | The following environment variables are used by this module: |
440 | |
700 | |
441 | "PERL_ANYEVENT_VERBOSE" |
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 | |
442 | When set to 2 or higher, cause AnyEvent to report to STDERR which |
710 | When set to 2 or higher, cause AnyEvent to report to STDERR which |
443 | event model it chooses. |
711 | event model it chooses. |
444 | |
712 | |
445 | "PERL_ANYEVENT_MODEL" |
713 | "PERL_ANYEVENT_MODEL" |
446 | This can be used to specify the event model to be used by AnyEvent, |
714 | This can be used to specify the event model to be used by AnyEvent, |
447 | before autodetection and -probing kicks in. It must be a string |
715 | before auto detection and -probing kicks in. It must be a string |
448 | consisting entirely of ASCII letters. The string "AnyEvent::Impl::" |
716 | consisting entirely of ASCII letters. The string "AnyEvent::Impl::" |
449 | gets prepended and the resulting module name is loaded and if the |
717 | gets prepended and the resulting module name is loaded and if the |
450 | load was successful, used as event model. If it fails to load |
718 | load was successful, used as event model. If it fails to load |
451 | AnyEvent will proceed with autodetection and -probing. |
719 | AnyEvent will proceed with auto detection and -probing. |
452 | |
720 | |
453 | This functionality might change in future versions. |
721 | This functionality might change in future versions. |
454 | |
722 | |
455 | For example, to force the pure perl model (AnyEvent::Impl::Perl) you |
723 | For example, to force the pure perl model (AnyEvent::Impl::Perl) you |
456 | could start your program like this: |
724 | could start your program like this: |
457 | |
725 | |
458 | PERL_ANYEVENT_MODEL=Perl perl ... |
726 | PERL_ANYEVENT_MODEL=Perl perl ... |
459 | |
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 | |
460 | EXAMPLE PROGRAM |
759 | EXAMPLE PROGRAM |
461 | The following program uses an IO watcher to read data from STDIN, a |
760 | The following program uses an I/O watcher to read data from STDIN, a |
462 | timer to display a message once per second, and a condition variable to |
761 | timer to display a message once per second, and a condition variable to |
463 | quit the program when the user enters quit: |
762 | quit the program when the user enters quit: |
464 | |
763 | |
465 | use AnyEvent; |
764 | use AnyEvent; |
466 | |
765 | |
… | |
… | |
471 | poll => 'r', |
770 | poll => 'r', |
472 | cb => sub { |
771 | cb => sub { |
473 | warn "io event <$_[0]>\n"; # will always output <r> |
772 | warn "io event <$_[0]>\n"; # will always output <r> |
474 | chomp (my $input = <STDIN>); # read a line |
773 | chomp (my $input = <STDIN>); # read a line |
475 | warn "read: $input\n"; # output what has been read |
774 | warn "read: $input\n"; # output what has been read |
476 | $cv->broadcast if $input =~ /^q/i; # quit program if /^q/i |
775 | $cv->send if $input =~ /^q/i; # quit program if /^q/i |
477 | }, |
776 | }, |
478 | ); |
777 | ); |
479 | |
778 | |
480 | my $time_watcher; # can only be used once |
779 | my $time_watcher; # can only be used once |
481 | |
780 | |
… | |
… | |
486 | }); |
785 | }); |
487 | } |
786 | } |
488 | |
787 | |
489 | new_timer; # create first timer |
788 | new_timer; # create first timer |
490 | |
789 | |
491 | $cv->wait; # wait until user enters /^q/i |
790 | $cv->recv; # wait until user enters /^q/i |
492 | |
791 | |
493 | REAL-WORLD EXAMPLE |
792 | REAL-WORLD EXAMPLE |
494 | Consider the Net::FCP module. It features (among others) the following |
793 | Consider the Net::FCP module. It features (among others) the following |
495 | API calls, which are to freenet what HTTP GET requests are to http: |
794 | API calls, which are to freenet what HTTP GET requests are to http: |
496 | |
795 | |
… | |
… | |
545 | syswrite $txn->{fh}, $txn->{request} |
844 | syswrite $txn->{fh}, $txn->{request} |
546 | or die "connection or write error"; |
845 | or die "connection or write error"; |
547 | $txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r }); |
846 | $txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r }); |
548 | |
847 | |
549 | Again, "fh_ready_r" waits till all data has arrived, and then stores the |
848 | Again, "fh_ready_r" waits till all data has arrived, and then stores the |
550 | result and signals any possible waiters that the request ahs finished: |
849 | result and signals any possible waiters that the request has finished: |
551 | |
850 | |
552 | sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf}; |
851 | sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf}; |
553 | |
852 | |
554 | if (end-of-file or data complete) { |
853 | if (end-of-file or data complete) { |
555 | $txn->{result} = $txn->{buf}; |
854 | $txn->{result} = $txn->{buf}; |
556 | $txn->{finished}->broadcast; |
855 | $txn->{finished}->send; |
557 | $txb->{cb}->($txn) of $txn->{cb}; # also call callback |
856 | $txb->{cb}->($txn) of $txn->{cb}; # also call callback |
558 | } |
857 | } |
559 | |
858 | |
560 | The "result" method, finally, just waits for the finished signal (if the |
859 | The "result" method, finally, just waits for the finished signal (if the |
561 | request was already finished, it doesn't wait, of course, and returns |
860 | request was already finished, it doesn't wait, of course, and returns |
562 | the data: |
861 | the data: |
563 | |
862 | |
564 | $txn->{finished}->wait; |
863 | $txn->{finished}->recv; |
565 | return $txn->{result}; |
864 | return $txn->{result}; |
566 | |
865 | |
567 | The actual code goes further and collects all errors ("die"s, |
866 | The actual code goes further and collects all errors ("die"s, |
568 | exceptions) that occured during request processing. The "result" method |
867 | exceptions) that occurred during request processing. The "result" method |
569 | detects whether an exception as thrown (it is stored inside the $txn |
868 | detects whether an exception as thrown (it is stored inside the $txn |
570 | object) and just throws the exception, which means connection errors and |
869 | object) and just throws the exception, which means connection errors and |
571 | other problems get reported tot he code that tries to use the result, |
870 | other problems get reported tot he code that tries to use the result, |
572 | not in a random callback. |
871 | not in a random callback. |
573 | |
872 | |
… | |
… | |
604 | |
903 | |
605 | my $quit = AnyEvent->condvar; |
904 | my $quit = AnyEvent->condvar; |
606 | |
905 | |
607 | $fcp->txn_client_get ($url)->cb (sub { |
906 | $fcp->txn_client_get ($url)->cb (sub { |
608 | ... |
907 | ... |
609 | $quit->broadcast; |
908 | $quit->send; |
610 | }); |
909 | }); |
611 | |
910 | |
612 | $quit->wait; |
911 | $quit->recv; |
|
|
912 | |
|
|
913 | BENCHMARKS |
|
|
914 | To give you an idea of the performance and overheads that AnyEvent adds |
|
|
915 | over the event loops themselves and to give you an impression of the |
|
|
916 | speed of various event loops I prepared some benchmarks. |
|
|
917 | |
|
|
918 | BENCHMARKING ANYEVENT OVERHEAD |
|
|
919 | Here is a benchmark of various supported event models used natively and |
|
|
920 | 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, |
|
|
922 | which it is), lets them fire exactly once and destroys them again. |
|
|
923 | |
|
|
924 | Source code for this benchmark is found as eg/bench in the AnyEvent |
|
|
925 | distribution. |
|
|
926 | |
|
|
927 | Explanation of the columns |
|
|
928 | *watcher* is the number of event watchers created/destroyed. Since |
|
|
929 | different event models feature vastly different performances, each event |
|
|
930 | loop was given a number of watchers so that overall runtime is |
|
|
931 | acceptable and similar between tested event loop (and keep them from |
|
|
932 | crashing): Glib would probably take thousands of years if asked to |
|
|
933 | process the same number of watchers as EV in this benchmark. |
|
|
934 | |
|
|
935 | *bytes* is the number of bytes (as measured by the resident set size, |
|
|
936 | RSS) consumed by each watcher. This method of measuring captures both C |
|
|
937 | and Perl-based overheads. |
|
|
938 | |
|
|
939 | *create* is the time, in microseconds (millionths of seconds), that it |
|
|
940 | takes to create a single watcher. The callback is a closure shared |
|
|
941 | between all watchers, to avoid adding memory overhead. That means |
|
|
942 | closure creation and memory usage is not included in the figures. |
|
|
943 | |
|
|
944 | *invoke* is the time, in microseconds, used to invoke a simple callback. |
|
|
945 | The callback simply counts down a Perl variable and after it was invoked |
|
|
946 | "watcher" times, it would "->send" a condvar once to signal the end of |
|
|
947 | this phase. |
|
|
948 | |
|
|
949 | *destroy* is the time, in microseconds, that it takes to destroy a |
|
|
950 | single watcher. |
|
|
951 | |
|
|
952 | Results |
|
|
953 | name watchers bytes create invoke destroy comment |
|
|
954 | EV/EV 400000 244 0.56 0.46 0.31 EV native interface |
|
|
955 | EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers |
|
|
956 | CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal |
|
|
957 | Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation |
|
|
958 | Event/Event 16000 516 31.88 31.30 0.85 Event native interface |
|
|
959 | Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers |
|
|
960 | Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour |
|
|
961 | Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers |
|
|
962 | POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event |
|
|
963 | POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select |
|
|
964 | |
|
|
965 | Discussion |
|
|
966 | 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) |
|
|
968 | can never compete with an event loop that uses epoll when the number of |
|
|
969 | file descriptors grows high. In this benchmark, all events become ready |
|
|
970 | at the same time, so select/poll-based implementations get an unnatural |
|
|
971 | speed boost. |
|
|
972 | |
|
|
973 | Also, note that the number of watchers usually has a nonlinear effect on |
|
|
974 | overall speed, that is, creating twice as many watchers doesn't take |
|
|
975 | twice the time - usually it takes longer. This puts event loops tested |
|
|
976 | with a higher number of watchers at a disadvantage. |
|
|
977 | |
|
|
978 | To put the range of results into perspective, consider that on the |
|
|
979 | 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 |
|
|
981 | CPU cycles with POE. |
|
|
982 | |
|
|
983 | "EV" is the sole leader regarding speed and memory use, which are both |
|
|
984 | maximal/minimal, respectively. Even when going through AnyEvent, it uses |
|
|
985 | far less memory than any other event loop and is still faster than Event |
|
|
986 | natively. |
|
|
987 | |
|
|
988 | 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 |
|
|
990 | perl interpreter and the backend itself). Nevertheless this shows that |
|
|
991 | it adds very little overhead in itself. Like any select-based backend |
|
|
992 | its performance becomes really bad with lots of file descriptors (and |
|
|
993 | few of them active), of course, but this was not subject of this |
|
|
994 | benchmark. |
|
|
995 | |
|
|
996 | The "Event" module has a relatively high setup and callback invocation |
|
|
997 | cost, but overall scores in on the third place. |
|
|
998 | |
|
|
999 | "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". |
|
|
1001 | However, Glib scales extremely badly, doubling the number of watchers |
|
|
1002 | increases the processing time by more than a factor of four, making it |
|
|
1003 | completely unusable when using larger numbers of watchers (note that |
|
|
1004 | only a single file descriptor was used in the benchmark, so |
|
|
1005 | inefficiencies of "poll" do not account for this). |
|
|
1006 | |
|
|
1007 | The "Tk" adaptor works relatively well. The fact that it crashes with |
|
|
1008 | more than 2000 watchers is a big setback, however, as correctness takes |
|
|
1009 | precedence over speed. Nevertheless, its performance is surprising, as |
|
|
1010 | the file descriptor is dup()ed for each watcher. This shows that the |
|
|
1011 | dup() employed by some adaptors is not a big performance issue (it does |
|
|
1012 | incur a hidden memory cost inside the kernel which is not reflected in |
|
|
1013 | the figures above). |
|
|
1014 | |
|
|
1015 | "POE", regardless of underlying event loop (whether using its pure perl |
|
|
1016 | select-based backend or the Event module, the POE-EV backend couldn't be |
|
|
1017 | tested because it wasn't working) shows abysmal performance and memory |
|
|
1018 | usage with AnyEvent: Watchers use almost 30 times as much memory as EV |
|
|
1019 | watchers, and 10 times as much memory as Event (the high memory |
|
|
1020 | requirements are caused by requiring a session for each watcher). |
|
|
1021 | Watcher invocation speed is almost 900 times slower than with AnyEvent's |
|
|
1022 | pure perl implementation. |
|
|
1023 | |
|
|
1024 | The design of the POE adaptor class in AnyEvent can not really account |
|
|
1025 | for the performance issues, though, as session creation overhead is |
|
|
1026 | small compared to execution of the state machine, which is coded pretty |
|
|
1027 | optimally within AnyEvent::Impl::POE (and while everybody agrees that |
|
|
1028 | using multiple sessions is not a good approach, especially regarding |
|
|
1029 | memory usage, even the author of POE could not come up with a faster |
|
|
1030 | design). |
|
|
1031 | |
|
|
1032 | Summary |
|
|
1033 | * Using EV through AnyEvent is faster than any other event loop (even |
|
|
1034 | when used without AnyEvent), but most event loops have acceptable |
|
|
1035 | performance with or without AnyEvent. |
|
|
1036 | |
|
|
1037 | * The overhead AnyEvent adds is usually much smaller than the overhead |
|
|
1038 | of the actual event loop, only with extremely fast event loops such |
|
|
1039 | as EV adds AnyEvent significant overhead. |
|
|
1040 | |
|
|
1041 | * You should avoid POE like the plague if you want performance or |
|
|
1042 | reasonable memory usage. |
|
|
1043 | |
|
|
1044 | BENCHMARKING THE LARGE SERVER CASE |
|
|
1045 | This benchmark actually benchmarks the event loop itself. It works by |
|
|
1046 | creating a number of "servers": each server consists of a socket pair, a |
|
|
1047 | timeout watcher that gets reset on activity (but never fires), and an |
|
|
1048 | I/O watcher waiting for input on one side of the socket. Each time the |
|
|
1049 | socket watcher reads a byte it will write that byte to a random other |
|
|
1050 | "server". |
|
|
1051 | |
|
|
1052 | The effect is that there will be a lot of I/O watchers, only part of |
|
|
1053 | which are active at any one point (so there is a constant number of |
|
|
1054 | active fds for each loop iteration, but which fds these are is random). |
|
|
1055 | The timeout is reset each time something is read because that reflects |
|
|
1056 | how most timeouts work (and puts extra pressure on the event loops). |
|
|
1057 | |
|
|
1058 | 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 |
|
|
1060 | many connections, most of which are idle at any one point in time. |
|
|
1061 | |
|
|
1062 | Source code for this benchmark is found as eg/bench2 in the AnyEvent |
|
|
1063 | distribution. |
|
|
1064 | |
|
|
1065 | Explanation of the columns |
|
|
1066 | *sockets* is the number of sockets, and twice the number of "servers" |
|
|
1067 | (as each server has a read and write socket end). |
|
|
1068 | |
|
|
1069 | *create* is the time it takes to create a socket pair (which is |
|
|
1070 | nontrivial) and two watchers: an I/O watcher and a timeout watcher. |
|
|
1071 | |
|
|
1072 | *request*, the most important value, is the time it takes to handle a |
|
|
1073 | single "request", that is, reading the token from the pipe and |
|
|
1074 | forwarding it to another server. This includes deleting the old timeout |
|
|
1075 | and creating a new one that moves the timeout into the future. |
|
|
1076 | |
|
|
1077 | Results |
|
|
1078 | name sockets create request |
|
|
1079 | EV 20000 69.01 11.16 |
|
|
1080 | Perl 20000 73.32 35.87 |
|
|
1081 | Event 20000 212.62 257.32 |
|
|
1082 | Glib 20000 651.16 1896.30 |
|
|
1083 | POE 20000 349.67 12317.24 uses POE::Loop::Event |
|
|
1084 | |
|
|
1085 | Discussion |
|
|
1086 | This benchmark *does* measure scalability and overall performance of the |
|
|
1087 | particular event loop. |
|
|
1088 | |
|
|
1089 | EV is again fastest. Since it is using epoll on my system, the setup |
|
|
1090 | time is relatively high, though. |
|
|
1091 | |
|
|
1092 | Perl surprisingly comes second. It is much faster than the C-based event |
|
|
1093 | loops Event and Glib. |
|
|
1094 | |
|
|
1095 | 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 |
|
|
1097 | compared to the "$_->() for .."-style loop that the Perl event loop |
|
|
1098 | uses. Event uses select or poll in basically all documented |
|
|
1099 | configurations. |
|
|
1100 | |
|
|
1101 | Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It |
|
|
1102 | clearly fails to perform with many filehandles or in busy servers. |
|
|
1103 | |
|
|
1104 | POE is still completely out of the picture, taking over 1000 times as |
|
|
1105 | long as EV, and over 100 times as long as the Perl implementation, even |
|
|
1106 | though it uses a C-based event loop in this case. |
|
|
1107 | |
|
|
1108 | Summary |
|
|
1109 | * The pure perl implementation performs extremely well. |
|
|
1110 | |
|
|
1111 | * Avoid Glib or POE in large projects where performance matters. |
|
|
1112 | |
|
|
1113 | BENCHMARKING SMALL SERVERS |
|
|
1114 | While event loops should scale (and select-based ones do not...) even to |
|
|
1115 | large servers, most programs we (or I :) actually write have only a few |
|
|
1116 | I/O watchers. |
|
|
1117 | |
|
|
1118 | In this benchmark, I use the same benchmark program as in the large |
|
|
1119 | server case, but it uses only eight "servers", of which three are active |
|
|
1120 | at any one time. This should reflect performance for a small server |
|
|
1121 | relatively well. |
|
|
1122 | |
|
|
1123 | The columns are identical to the previous table. |
|
|
1124 | |
|
|
1125 | Results |
|
|
1126 | name sockets create request |
|
|
1127 | EV 16 20.00 6.54 |
|
|
1128 | Perl 16 25.75 12.62 |
|
|
1129 | Event 16 81.27 35.86 |
|
|
1130 | Glib 16 32.63 15.48 |
|
|
1131 | POE 16 261.87 276.28 uses POE::Loop::Event |
|
|
1132 | |
|
|
1133 | Discussion |
|
|
1134 | The benchmark tries to test the performance of a typical small server. |
|
|
1135 | While knowing how various event loops perform is interesting, keep in |
|
|
1136 | mind that their overhead in this case is usually not as important, due |
|
|
1137 | to the small absolute number of watchers (that is, you need efficiency |
|
|
1138 | and speed most when you have lots of watchers, not when you only have a |
|
|
1139 | few of them). |
|
|
1140 | |
|
|
1141 | EV is again fastest. |
|
|
1142 | |
|
|
1143 | Perl again comes second. It is noticeably faster than the C-based event |
|
|
1144 | loops Event and Glib, although the difference is too small to really |
|
|
1145 | matter. |
|
|
1146 | |
|
|
1147 | POE also performs much better in this case, but is is still far behind |
|
|
1148 | the others. |
|
|
1149 | |
|
|
1150 | Summary |
|
|
1151 | * C-based event loops perform very well with small number of watchers, |
|
|
1152 | as the management overhead dominates. |
613 | |
1153 | |
614 | FORK |
1154 | FORK |
615 | Most event libraries are not fork-safe. The ones who are usually are |
1155 | Most event libraries are not fork-safe. The ones who are usually are |
616 | because they are so inefficient. Only EV is fully fork-aware. |
1156 | because they rely on inefficient but fork-safe "select" or "poll" calls. |
|
|
1157 | Only EV is fully fork-aware. |
617 | |
1158 | |
618 | If you have to fork, you must either do so *before* creating your first |
1159 | If you have to fork, you must either do so *before* creating your first |
619 | watcher OR you must not use AnyEvent at all in the child. |
1160 | watcher OR you must not use AnyEvent at all in the child. |
620 | |
1161 | |
621 | SECURITY CONSIDERATIONS |
1162 | SECURITY CONSIDERATIONS |
… | |
… | |
631 | |
1172 | |
632 | BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} } |
1173 | BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} } |
633 | |
1174 | |
634 | use AnyEvent; |
1175 | use AnyEvent; |
635 | |
1176 | |
|
|
1177 | 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 |
|
|
1179 | is probably even less useful to an attacker than PERL_ANYEVENT_MODEL). |
|
|
1180 | |
636 | SEE ALSO |
1181 | SEE ALSO |
637 | Event modules: Coro::EV, EV, EV::Glib, Glib::EV, Coro::Event, Event, |
1182 | Utility functions: AnyEvent::Util. |
638 | Glib::Event, Glib, Coro, Tk, Event::Lib, Qt. |
|
|
639 | |
1183 | |
640 | Implementations: AnyEvent::Impl::CoroEV, AnyEvent::Impl::EV, |
1184 | Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk, |
641 | AnyEvent::Impl::CoroEvent, AnyEvent::Impl::Event, AnyEvent::Impl::Glib, |
1185 | Event::Lib, Qt, POE. |
642 | AnyEvent::Impl::Tk, AnyEvent::Impl::Perl, AnyEvent::Impl::EventLib, |
|
|
643 | AnyEvent::Impl::Qt. |
|
|
644 | |
1186 | |
|
|
1187 | Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event, |
|
|
1188 | AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl, |
|
|
1189 | AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE. |
|
|
1190 | |
|
|
1191 | Non-blocking file handles, sockets, TCP clients and servers: |
|
|
1192 | AnyEvent::Handle, AnyEvent::Socket. |
|
|
1193 | |
|
|
1194 | Asynchronous DNS: AnyEvent::DNS. |
|
|
1195 | |
|
|
1196 | Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event, |
|
|
1197 | |
645 | Nontrivial usage examples: Net::FCP, Net::XMPP2. |
1198 | Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS. |
646 | |
1199 | |
647 | AUTHOR |
1200 | AUTHOR |
648 | Marc Lehmann <schmorp@schmorp.de> |
1201 | Marc Lehmann <schmorp@schmorp.de> |
649 | http://home.schmorp.de/ |
1202 | http://home.schmorp.de/ |
650 | |
1203 | |