| 1 |
NAME |
| 2 |
AnyEvent - provide framework for multiple event loops |
| 3 |
|
| 4 |
Event, Coro, Glib, Tk, Perl - various supported event loops |
| 5 |
|
| 6 |
SYNOPSIS |
| 7 |
use AnyEvent; |
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|
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my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub { |
| 10 |
... |
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}); |
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|
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my $w = AnyEvent->timer (after => $seconds, cb => sub { |
| 14 |
... |
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}); |
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|
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my $w = AnyEvent->condvar; # stores wether a condition was flagged |
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$w->wait; # enters "main loop" till $condvar gets ->broadcast |
| 19 |
$w->broadcast; # wake up current and all future wait's |
| 20 |
|
| 21 |
WHY YOU SHOULD USE THIS MODULE (OR NOT) |
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Glib, POE, IO::Async, Event... CPAN offers event models by the dozen |
| 23 |
nowadays. So what is different about AnyEvent? |
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|
| 25 |
Executive Summary: AnyEvent is *compatible*, AnyEvent is *free of |
| 26 |
policy* and AnyEvent is *small and efficient*. |
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|
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First and foremost, *AnyEvent is not an event model* itself, it only |
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interfaces to whatever event model the main program happens to use in a |
| 30 |
pragmatic way. For event models and certain classes of immortals alike, |
| 31 |
the statement "there can only be one" is a bitter reality, and AnyEvent |
| 32 |
helps hiding the differences. |
| 33 |
|
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The goal of AnyEvent is to offer module authors the ability to do event |
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programming (waiting for I/O or timer events) without subscribing to a |
| 36 |
religion, a way of living, and most importantly: without forcing your |
| 37 |
module users into the same thing by forcing them to use the same event |
| 38 |
model you use. |
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|
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For modules like POE or IO::Async (which is actually doing all I/O |
| 41 |
*synchronously*...), using them in your module is like joining a cult: |
| 42 |
After you joined, you are dependent on them and you cannot use anything |
| 43 |
else, as it is simply incompatible to everything that isn't itself. |
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|
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AnyEvent + POE works fine. AnyEvent + Glib works fine. AnyEvent + Tk |
| 46 |
works fine etc. etc. but none of these work together with the rest: POE |
| 47 |
+ IO::Async? no go. Tk + Event? no go. If your module uses one of those, |
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every user of your module has to use it, too. If your module uses |
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AnyEvent, it works transparently with all event models it supports |
| 50 |
(including stuff like POE and IO::Async). |
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|
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In addition of being free of having to use *the one and only true event |
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model*, AnyEvent also is free of bloat and policy: with POE or similar |
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modules, you get an enourmous amount of code and strict rules you have |
| 55 |
to follow. AnyEvent, on the other hand, is lean and to the point by only |
| 56 |
offering the functionality that is useful, in as thin as a wrapper as |
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technically possible. |
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|
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Of course, if you want lots of policy (this can arguably be somewhat |
| 60 |
useful) and you want to force your users to use the one and only event |
| 61 |
model, you should *not* use this module. |
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|
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DESCRIPTION |
| 64 |
AnyEvent provides an identical interface to multiple event loops. This |
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allows module authors to utilise an event loop without forcing module |
| 66 |
users to use the same event loop (as only a single event loop can |
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coexist peacefully at any one time). |
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|
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The interface itself is vaguely similar but not identical to the Event |
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module. |
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|
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On the first call of any method, the module tries to detect the |
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currently loaded event loop by probing wether any of the following |
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modules is loaded: Coro::Event, Event, Glib, Tk. The first one found is |
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used. If none is found, the module tries to load these modules in the |
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order given. The first one that could be successfully loaded will be |
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used. If still none could be found, AnyEvent will fall back to a |
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pure-perl event loop, which is also not very efficient. |
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|
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Because AnyEvent first checks for modules that are already loaded, |
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loading an Event model explicitly before first using AnyEvent will |
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likely make that model the default. For example: |
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|
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use Tk; |
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use AnyEvent; |
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|
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# .. AnyEvent will likely default to Tk |
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|
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The pure-perl implementation of AnyEvent is called |
| 90 |
"AnyEvent::Impl::Perl". Like other event modules you can load it |
| 91 |
explicitly. |
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|
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WATCHERS |
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AnyEvent has the central concept of a *watcher*, which is an object that |
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stores relevant data for each kind of event you are waiting for, such as |
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the callback to call, the filehandle to watch, etc. |
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|
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These watchers are normal Perl objects with normal Perl lifetime. After |
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creating a watcher it will immediately "watch" for events and invoke the |
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callback. To disable the watcher you have to destroy it (e.g. by setting |
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the variable that stores it to "undef" or otherwise deleting all |
| 102 |
references to it). |
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|
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All watchers are created by calling a method on the "AnyEvent" class. |
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|
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IO WATCHERS |
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You can create I/O watcher by calling the "AnyEvent->io" method with the |
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following mandatory arguments: |
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|
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"fh" the Perl *filehandle* (not filedescriptor) to watch for events. |
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"poll" must be a string that is either "r" or "w", that creates a |
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watcher waiting for "r"eadable or "w"ritable events. "cb" the callback |
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to invoke everytime the filehandle becomes ready. |
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|
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Only one io watcher per "fh" and "poll" combination is allowed (i.e. on |
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a socket you can have one r + one w, not any more (limitation comes from |
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Tk - if you are sure you are not using Tk this limitation is gone). |
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|
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Filehandles will be kept alive, so as long as the watcher exists, the |
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filehandle exists, too. |
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|
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Example: |
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|
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# wait for readability of STDIN, then read a line and disable the watcher |
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my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub { |
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chomp (my $input = <STDIN>); |
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warn "read: $input\n"; |
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undef $w; |
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}); |
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|
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TIME WATCHERS |
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You can create a time watcher by calling the "AnyEvent->timer" method |
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with the following mandatory arguments: |
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|
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"after" after how many seconds (fractions are supported) should the |
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timer activate. "cb" the callback to invoke. |
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|
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The timer callback will be invoked at most once: if you want a repeating |
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timer you have to create a new watcher (this is a limitation by both Tk |
| 140 |
and Glib). |
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|
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Example: |
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|
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# fire an event after 7.7 seconds |
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my $w = AnyEvent->timer (after => 7.7, cb => sub { |
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warn "timeout\n"; |
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}); |
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|
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# to cancel the timer: |
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undef $w; |
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|
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CONDITION WATCHERS |
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Condition watchers can be created by calling the "AnyEvent->condvar" |
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method without any arguments. |
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|
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A condition watcher watches for a condition - precisely that the |
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"->broadcast" method has been called. |
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|
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Note that condition watchers recurse into the event loop - if you have |
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two watchers that call "->wait" in a round-robbin fashion, you lose. |
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Therefore, condition watchers are good to export to your caller, but you |
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should avoid making a blocking wait, at least in callbacks, as this |
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usually asks for trouble. |
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|
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The watcher has only two methods: |
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|
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$cv->wait |
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Wait (blocking if necessary) until the "->broadcast" method has been |
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called on c<$cv>, while servicing other watchers normally. |
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|
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Not all event models support a blocking wait - some die in that |
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case, so if you are using this from a module, never require a |
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blocking wait, but let the caller decide wether the call will block |
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or not (for example, by coupling condition variables with some kind |
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of request results and supporting callbacks so the caller knows that |
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getting the result will not block, while still suppporting blockign |
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waits if the caller so desires). |
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|
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You can only wait once on a condition - additional calls will return |
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immediately. |
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|
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$cv->broadcast |
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Flag the condition as ready - a running "->wait" and all further |
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calls to "wait" will return after this method has been called. If |
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nobody is waiting the broadcast will be remembered.. |
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|
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Example: |
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|
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# wait till the result is ready |
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my $result_ready = AnyEvent->condvar; |
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|
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# do something such as adding a timer |
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# or socket watcher the calls $result_ready->broadcast |
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# when the "result" is ready. |
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|
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$result_ready->wait; |
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|
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SIGNAL WATCHERS |
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You can listen for signals using a signal watcher, "signal" is the |
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signal *name* without any "SIG" prefix. Multiple signals events can be |
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clumped together into one callback invocation, and callback invocation |
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might or might not be asynchronous. |
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|
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These watchers might use %SIG, so programs overwriting those signals |
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directly will likely not work correctly. |
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|
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Example: exit on SIGINT |
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|
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my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 }); |
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|
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CHILD PROCESS WATCHERS |
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You can also listen for the status of a child process specified by the |
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"pid" argument (or any child if the pid argument is 0). The watcher will |
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trigger as often as status change for the child are received. This works |
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by installing a signal handler for "SIGCHLD". The callback will be |
| 216 |
called with the pid and exit status (as returned by waitpid). |
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|
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Example: wait for pid 1333 |
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|
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my $w = AnyEvent->child (pid => 1333, cb => sub { warn "exit status $?" }); |
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|
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GLOBALS |
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$AnyEvent::MODEL |
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Contains "undef" until the first watcher is being created. Then it |
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contains the event model that is being used, which is the name of |
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the Perl class implementing the model. This class is usually one of |
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the "AnyEvent::Impl:xxx" modules, but can be any other class in the |
| 228 |
case AnyEvent has been extended at runtime (e.g. in *rxvt-unicode*). |
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|
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The known classes so far are: |
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|
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AnyEvent::Impl::CoroEV based on Coro::EV, best choice. |
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AnyEvent::Impl::EV based on EV (an interface to libev, also best choice). |
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AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice. |
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AnyEvent::Impl::Event based on Event, also second best choice :) |
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AnyEvent::Impl::Glib based on Glib, second-best choice. |
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AnyEvent::Impl::Tk based on Tk, very bad choice. |
| 238 |
AnyEvent::Impl::Perl pure-perl implementation, inefficient. |
| 239 |
|
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AnyEvent::detect |
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Returns $AnyEvent::MODEL, forcing autodetection of the event model |
| 242 |
if necessary. You should only call this function right before you |
| 243 |
would have created an AnyEvent watcher anyway, that is, very late at |
| 244 |
runtime. |
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|
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WHAT TO DO IN A MODULE |
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As a module author, you should "use AnyEvent" and call AnyEvent methods |
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freely, but you should not load a specific event module or rely on it. |
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|
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Be careful when you create watchers in the module body - Anyevent will |
| 251 |
decide which event module to use as soon as the first method is called, |
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so by calling AnyEvent in your module body you force the user of your |
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module to load the event module first. |
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|
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WHAT TO DO IN THE MAIN PROGRAM |
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There will always be a single main program - the only place that should |
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dictate which event model to use. |
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|
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If it doesn't care, it can just "use AnyEvent" and use it itself, or not |
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do anything special and let AnyEvent decide which implementation to |
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chose. |
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|
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If the main program relies on a specific event model (for example, in |
| 264 |
Gtk2 programs you have to rely on either Glib or Glib::Event), you |
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should load it before loading AnyEvent or any module that uses it, |
| 266 |
generally, as early as possible. The reason is that modules might create |
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watchers when they are loaded, and AnyEvent will decide on the event |
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model to use as soon as it creates watchers, and it might chose the |
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wrong one unless you load the correct one yourself. |
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|
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You can chose to use a rather inefficient pure-perl implementation by |
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loading the "AnyEvent::Impl::Perl" module, but letting AnyEvent chose is |
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generally better. |
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|
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SUPPLYING YOUR OWN EVENT MODEL INTERFACE |
| 276 |
If you need to support another event library which isn't directly |
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supported by AnyEvent, you can supply your own interface to it by |
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pushing, before the first watcher gets created, the package name of the |
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event module and the package name of the interface to use onto |
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@AnyEvent::REGISTRY. You can do that before and even without loading |
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AnyEvent. |
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|
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Example: |
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|
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push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::]; |
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|
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This tells AnyEvent to (literally) use the "urxvt::anyevent::" |
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package/class when it finds the "urxvt" package/module is loaded. When |
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AnyEvent is loaded and asked to find a suitable event model, it will |
| 290 |
first check for the presence of urxvt. |
| 291 |
|
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The class should provide implementations for all watcher types (see |
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AnyEvent::Impl::Event (source code), AnyEvent::Impl::Glib (Source code) |
| 294 |
and so on for actual examples, use "perldoc -m AnyEvent::Impl::Glib" to |
| 295 |
see the sources). |
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|
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The above isn't fictitious, the *rxvt-unicode* (a.k.a. urxvt) uses the |
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above line as-is. An interface isn't included in AnyEvent because it |
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doesn't make sense outside the embedded interpreter inside |
| 300 |
*rxvt-unicode*, and it is updated and maintained as part of the |
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*rxvt-unicode* distribution. |
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|
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*rxvt-unicode* also cheats a bit by not providing blocking access to |
| 304 |
condition variables: code blocking while waiting for a condition will |
| 305 |
"die". This still works with most modules/usages, and blocking calls |
| 306 |
must not be in an interactive application, so it makes sense. |
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|
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ENVIRONMENT VARIABLES |
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The following environment variables are used by this module: |
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|
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"PERL_ANYEVENT_VERBOSE" when set to 2 or higher, reports which event |
| 312 |
model gets used. |
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|
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EXAMPLE |
| 315 |
The following program uses an io watcher to read data from stdin, a |
| 316 |
timer to display a message once per second, and a condvar to exit the |
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program when the user enters quit: |
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|
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use AnyEvent; |
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|
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my $cv = AnyEvent->condvar; |
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|
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my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub { |
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warn "io event <$_[0]>\n"; # will always output <r> |
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chomp (my $input = <STDIN>); # read a line |
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warn "read: $input\n"; # output what has been read |
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$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i |
| 328 |
}); |
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|
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my $time_watcher; # can only be used once |
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|
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sub new_timer { |
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$timer = AnyEvent->timer (after => 1, cb => sub { |
| 334 |
warn "timeout\n"; # print 'timeout' about every second |
| 335 |
&new_timer; # and restart the time |
| 336 |
}); |
| 337 |
} |
| 338 |
|
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new_timer; # create first timer |
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|
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$cv->wait; # wait until user enters /^q/i |
| 342 |
|
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REAL-WORLD EXAMPLE |
| 344 |
Consider the Net::FCP module. It features (among others) the following |
| 345 |
API calls, which are to freenet what HTTP GET requests are to http: |
| 346 |
|
| 347 |
my $data = $fcp->client_get ($url); # blocks |
| 348 |
|
| 349 |
my $transaction = $fcp->txn_client_get ($url); # does not block |
| 350 |
$transaction->cb ( sub { ... } ); # set optional result callback |
| 351 |
my $data = $transaction->result; # possibly blocks |
| 352 |
|
| 353 |
The "client_get" method works like "LWP::Simple::get": it requests the |
| 354 |
given URL and waits till the data has arrived. It is defined to be: |
| 355 |
|
| 356 |
sub client_get { $_[0]->txn_client_get ($_[1])->result } |
| 357 |
|
| 358 |
And in fact is automatically generated. This is the blocking API of |
| 359 |
Net::FCP, and it works as simple as in any other, similar, module. |
| 360 |
|
| 361 |
More complicated is "txn_client_get": It only creates a transaction |
| 362 |
(completion, result, ...) object and initiates the transaction. |
| 363 |
|
| 364 |
my $txn = bless { }, Net::FCP::Txn::; |
| 365 |
|
| 366 |
It also creates a condition variable that is used to signal the |
| 367 |
completion of the request: |
| 368 |
|
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$txn->{finished} = AnyAvent->condvar; |
| 370 |
|
| 371 |
It then creates a socket in non-blocking mode. |
| 372 |
|
| 373 |
socket $txn->{fh}, ...; |
| 374 |
fcntl $txn->{fh}, F_SETFL, O_NONBLOCK; |
| 375 |
connect $txn->{fh}, ... |
| 376 |
and !$!{EWOULDBLOCK} |
| 377 |
and !$!{EINPROGRESS} |
| 378 |
and Carp::croak "unable to connect: $!\n"; |
| 379 |
|
| 380 |
Then it creates a write-watcher which gets called whenever an error |
| 381 |
occurs or the connection succeeds: |
| 382 |
|
| 383 |
$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'w', cb => sub { $txn->fh_ready_w }); |
| 384 |
|
| 385 |
And returns this transaction object. The "fh_ready_w" callback gets |
| 386 |
called as soon as the event loop detects that the socket is ready for |
| 387 |
writing. |
| 388 |
|
| 389 |
The "fh_ready_w" method makes the socket blocking again, writes the |
| 390 |
request data and replaces the watcher by a read watcher (waiting for |
| 391 |
reply data). The actual code is more complicated, but that doesn't |
| 392 |
matter for this example: |
| 393 |
|
| 394 |
fcntl $txn->{fh}, F_SETFL, 0; |
| 395 |
syswrite $txn->{fh}, $txn->{request} |
| 396 |
or die "connection or write error"; |
| 397 |
$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r }); |
| 398 |
|
| 399 |
Again, "fh_ready_r" waits till all data has arrived, and then stores the |
| 400 |
result and signals any possible waiters that the request ahs finished: |
| 401 |
|
| 402 |
sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf}; |
| 403 |
|
| 404 |
if (end-of-file or data complete) { |
| 405 |
$txn->{result} = $txn->{buf}; |
| 406 |
$txn->{finished}->broadcast; |
| 407 |
$txb->{cb}->($txn) of $txn->{cb}; # also call callback |
| 408 |
} |
| 409 |
|
| 410 |
The "result" method, finally, just waits for the finished signal (if the |
| 411 |
request was already finished, it doesn't wait, of course, and returns |
| 412 |
the data: |
| 413 |
|
| 414 |
$txn->{finished}->wait; |
| 415 |
return $txn->{result}; |
| 416 |
|
| 417 |
The actual code goes further and collects all errors ("die"s, |
| 418 |
exceptions) that occured during request processing. The "result" method |
| 419 |
detects wether an exception as thrown (it is stored inside the $txn |
| 420 |
object) and just throws the exception, which means connection errors and |
| 421 |
other problems get reported tot he code that tries to use the result, |
| 422 |
not in a random callback. |
| 423 |
|
| 424 |
All of this enables the following usage styles: |
| 425 |
|
| 426 |
1. Blocking: |
| 427 |
|
| 428 |
my $data = $fcp->client_get ($url); |
| 429 |
|
| 430 |
2. Blocking, but parallelizing: |
| 431 |
|
| 432 |
my @datas = map $_->result, |
| 433 |
map $fcp->txn_client_get ($_), |
| 434 |
@urls; |
| 435 |
|
| 436 |
Both blocking examples work without the module user having to know |
| 437 |
anything about events. |
| 438 |
|
| 439 |
3a. Event-based in a main program, using any support Event module: |
| 440 |
|
| 441 |
use Event; |
| 442 |
|
| 443 |
$fcp->txn_client_get ($url)->cb (sub { |
| 444 |
my $txn = shift; |
| 445 |
my $data = $txn->result; |
| 446 |
... |
| 447 |
}); |
| 448 |
|
| 449 |
Event::loop; |
| 450 |
|
| 451 |
3b. The module user could use AnyEvent, too: |
| 452 |
|
| 453 |
use AnyEvent; |
| 454 |
|
| 455 |
my $quit = AnyEvent->condvar; |
| 456 |
|
| 457 |
$fcp->txn_client_get ($url)->cb (sub { |
| 458 |
... |
| 459 |
$quit->broadcast; |
| 460 |
}); |
| 461 |
|
| 462 |
$quit->wait; |
| 463 |
|
| 464 |
SEE ALSO |
| 465 |
Event modules: Coro::Event, Coro, Event, Glib::Event, Glib. |
| 466 |
|
| 467 |
Implementations: AnyEvent::Impl::Coro, AnyEvent::Impl::Event, |
| 468 |
AnyEvent::Impl::Glib, AnyEvent::Impl::Tk. |
| 469 |
|
| 470 |
Nontrivial usage example: Net::FCP. |
| 471 |
|
| 472 |
|
