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NAME |
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AnyEvent - provide framework for multiple event loops |
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|
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Event, Coro, Glib, Tk, Perl - various supported event loops |
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|
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SYNOPSIS |
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use AnyEvent; |
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|
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my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub { |
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... |
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}); |
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|
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my $w = AnyEvent->timer (after => $seconds, cb => sub { |
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... |
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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 $condvar gets ->broadcast |
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$w->broadcast; # wake up current and all future wait's |
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|
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DESCRIPTION |
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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 |
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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 |
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"AnyEvent::Impl::Perl". Like other event modules you can load it |
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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 |
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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" teh 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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TIMER WATCHERS |
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You can create a timer 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 |
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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 $w |
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|
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CONDITION WATCHERS |
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Condition watchers can be created by calling the "AnyEvent->condvar" |
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method without any arguments. |
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|
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A condition watcher watches for a condition - precisely that the |
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"->broadcast" method has been called. |
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|
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The watcher has only two methods: |
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|
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$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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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 |
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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::Coro based on Coro::Event, best choise. |
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AnyEvent::Impl::Event based on Event, also 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. |
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AnyEvent::Impl::Perl pure-perl implementation, inefficient. |
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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 |
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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 |
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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, |
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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 |
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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 |
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first check for the presence of urxvt. |
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|
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The class should prove implementations for all watcher types (see |
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AnyEvent::Impl::Event (source code), AnyEvent::Impl::Glib (Source code) |
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and so on for actual examples, use "perldoc -m AnyEvent::Impl::Glib" to |
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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 |
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*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 |
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condition variables: code blocking while waiting for a condition will |
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"die". This still works with most modules/usages, and blocking calls |
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must not be in an interactive appliation, 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 |
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model gets used. |
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|
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EXAMPLE |
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The following program uses an io watcher to read data from stdin, a |
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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 |
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}); |
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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 { |
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warn "timeout\n"; # print 'timeout' about every second |
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&new_timer; # and restart the time |
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}); |
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} |
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|
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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 |
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|
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REAL-WORLD EXAMPLE |
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Consider the Net::FCP module. It features (among others) the following |
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API calls, which are to freenet what HTTP GET requests are to http: |
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|
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my $data = $fcp->client_get ($url); # blocks |
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|
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my $transaction = $fcp->txn_client_get ($url); # does not block |
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$transaction->cb ( sub { ... } ); # set optional result callback |
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my $data = $transaction->result; # possibly blocks |
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|
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The "client_get" method works like "LWP::Simple::get": it requests the |
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given URL and waits till the data has arrived. It is defined to be: |
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|
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sub client_get { $_[0]->txn_client_get ($_[1])->result } |
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|
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And in fact is automatically generated. This is the blocking API of |
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Net::FCP, and it works as simple as in any other, similar, module. |
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|
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More complicated is "txn_client_get": It only creates a transaction |
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(completion, result, ...) object and initiates the transaction. |
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|
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my $txn = bless { }, Net::FCP::Txn::; |
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|
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It also creates a condition variable that is used to signal the |
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completion of the request: |
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|
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$txn->{finished} = AnyAvent->condvar; |
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|
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It then creates a socket in non-blocking mode. |
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|
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socket $txn->{fh}, ...; |
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fcntl $txn->{fh}, F_SETFL, O_NONBLOCK; |
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connect $txn->{fh}, ... |
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and !$!{EWOULDBLOCK} |
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and !$!{EINPROGRESS} |
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and Carp::croak "unable to connect: $!\n"; |
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|
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Then it creates a write-watcher which gets called whenever an error |
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occurs or the connection succeeds: |
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|
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$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'w', cb => sub { $txn->fh_ready_w }); |
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|
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And returns this transaction object. The "fh_ready_w" callback gets |
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called as soon as the event loop detects that the socket is ready for |
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writing. |
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|
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The "fh_ready_w" method makes the socket blocking again, writes the |
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request data and replaces the watcher by a read watcher (waiting for |
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reply data). The actual code is more complicated, but that doesn't |
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matter for this example: |
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|
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fcntl $txn->{fh}, F_SETFL, 0; |
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syswrite $txn->{fh}, $txn->{request} |
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or die "connection or write error"; |
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$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r }); |
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|
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Again, "fh_ready_r" waits till all data has arrived, and then stores the |
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result and signals any possible waiters that the request ahs finished: |
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|
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sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf}; |
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|
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if (end-of-file or data complete) { |
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$txn->{result} = $txn->{buf}; |
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$txn->{finished}->broadcast; |
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$txb->{cb}->($txn) of $txn->{cb}; # also call callback |
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} |
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|
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The "result" method, finally, just waits for the finished signal (if the |
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request was already finished, it doesn't wait, of course, and returns |
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the data: |
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|
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$txn->{finished}->wait; |
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return $txn->{result}; |
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|
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The actual code goes further and collects all errors ("die"s, |
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exceptions) that occured during request processing. The "result" method |
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detects wether an exception as thrown (it is stored inside the $txn |
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object) and just throws the exception, which means connection errors and |
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other problems get reported tot he code that tries to use the result, |
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not in a random callback. |
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|
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All of this enables the following usage styles: |
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|
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1. Blocking: |
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|
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my $data = $fcp->client_get ($url); |
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|
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2. Blocking, but parallelizing: |
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|
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my @datas = map $_->result, |
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map $fcp->txn_client_get ($_), |
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@urls; |
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|
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Both blocking examples work without the module user having to know |
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anything about events. |
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|
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3a. Event-based in a main program, using any support Event module: |
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|
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use Event; |
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|
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$fcp->txn_client_get ($url)->cb (sub { |
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my $txn = shift; |
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my $data = $txn->result; |
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... |
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}); |
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|
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Event::loop; |
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|
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3b. The module user could use AnyEvent, too: |
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|
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use AnyEvent; |
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|
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my $quit = AnyEvent->condvar; |
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|
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$fcp->txn_client_get ($url)->cb (sub { |
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... |
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$quit->broadcast; |
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}); |
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|
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$quit->wait; |
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|
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SEE ALSO |
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Event modules: Coro::Event, Coro, Event, Glib::Event, Glib. |
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|
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Implementations: AnyEvent::Impl::Coro, AnyEvent::Impl::Event, |
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AnyEvent::Impl::Glib, AnyEvent::Impl::Tk. |
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|
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Nontrivial usage example: Net::FCP. |
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|
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|
