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=> NAME |
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AnyEvent - provide framework for multiple event loops |
3 |
|
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EV, Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event |
5 |
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 $w = AnyEvent->condvar; # stores whether a condition was flagged |
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$w->send; # wake up current and all future recv's |
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$w->recv; # enters "main loop" till $condvar gets ->send |
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|
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WHY YOU SHOULD USE THIS MODULE (OR NOT) |
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Glib, POE, IO::Async, Event... CPAN offers event models by the dozen |
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nowadays. So what is different about AnyEvent? |
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|
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Executive Summary: AnyEvent is *compatible*, AnyEvent is *free of |
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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 |
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pragmatic way. For event models and certain classes of immortals alike, |
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the statement "there can only be one" is a bitter reality: In general, |
33 |
only one event loop can be active at the same time in a process. |
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AnyEvent helps hiding the differences between those event loops. |
35 |
|
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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 |
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religion, a way of living, and most importantly: without forcing your |
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module users into the same thing by forcing them to use the same event |
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model you use. |
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|
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For modules like POE or IO::Async (which is a total misnomer as it is |
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actually doing all I/O *synchronously*...), using them in your module is |
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like joining a cult: After you joined, you are dependent on them and you |
45 |
cannot use anything else, as it is simply incompatible to everything |
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that isn't itself. What's worse, all the potential users of your module |
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are *also* forced to use the same event loop you use. |
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|
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AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works |
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fine. AnyEvent + Tk works fine etc. etc. but none of these work together |
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with the rest: POE + IO::Async? no go. Tk + Event? no go. Again: if your |
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module uses one of those, every user of your module has to use it, too. |
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But if your module uses AnyEvent, it works transparently with all event |
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models it supports (including stuff like POE and IO::Async, as long as |
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those use one of the supported event loops. It is trivial to add new |
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event loops to AnyEvent, too, so it is future-proof). |
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|
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In addition to 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 enormous amount of code and strict rules you have to |
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follow. AnyEvent, on the other hand, is lean and up to the point, by |
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only offering the functionality that is necessary, in as thin as a |
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wrapper as technically possible. |
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|
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Of course, if you want lots of policy (this can arguably be somewhat |
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useful) and you want to force your users to use the one and only event |
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model, you should *not* use this module. |
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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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During the first call of any watcher-creation method, the module tries |
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to detect the currently loaded event loop by probing whether one of the |
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following modules is already loaded: EV, Event, Glib, |
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AnyEvent::Impl::Perl, Tk, Event::Lib, Qt, POE. The first one found is |
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used. If none are found, the module tries to load these modules |
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(excluding Tk, Event::Lib, Qt and POE as the pure perl adaptor should |
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always succeed) in the order given. The first one that can be |
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successfully loaded will be used. If, after this, still none could be |
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found, AnyEvent will fall back to a pure-perl event loop, which is not |
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very efficient, but should work everywhere. |
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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 *likely* means that, if any module loads another event model and |
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starts using it, all bets are off. Maybe you should tell their authors |
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to use AnyEvent so their modules work together with others seamlessly... |
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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 file handle 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 when the event occurs (of course, only when the event model is |
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in control). |
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|
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To disable the watcher you have to destroy it (e.g. by setting the |
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variable you store it in to "undef" or otherwise deleting all references |
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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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Many watchers either are used with "recursion" (repeating timers for |
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example), or need to refer to their watcher object in other ways. |
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|
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An any way to achieve that is this pattern: |
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|
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my $w; $w = AnyEvent->type (arg => value ..., cb => sub { |
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# you can use $w here, for example to undef it |
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undef $w; |
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}); |
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|
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Note that "my $w; $w =" combination. This is necessary because in Perl, |
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my variables are only visible after the statement in which they are |
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declared. |
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|
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I/O WATCHERS |
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You can create an I/O watcher by calling the "AnyEvent->io" method with |
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the following mandatory key-value pairs as arguments: |
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|
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"fh" the Perl *file handle* (*not* file descriptor) to watch for events. |
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"poll" must be a string that is either "r" or "w", which creates a |
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watcher waiting for "r"eadable or "w"ritable events, respectively. "cb" |
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is the callback to invoke each time the file handle becomes ready. |
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|
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Although the callback might get passed parameters, their value and |
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presence is undefined and you cannot rely on them. Portable AnyEvent |
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callbacks cannot use arguments passed to I/O watcher callbacks. |
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|
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The I/O watcher might use the underlying file descriptor or a copy of |
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it. You must not close a file handle as long as any watcher is active on |
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the underlying file descriptor. |
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|
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Some event loops issue spurious readyness notifications, so you should |
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always use non-blocking calls when reading/writing from/to your file |
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handles. |
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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" specifies after how many seconds (fractional values are |
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supported) the callback should be invoked. "cb" is the callback to |
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invoke in that case. |
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|
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Although the callback might get passed parameters, their value and |
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presence is undefined and you cannot rely on them. Portable AnyEvent |
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callbacks cannot use arguments passed to time watcher callbacks. |
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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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Example 2: |
193 |
|
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# fire an event after 0.5 seconds, then roughly every second |
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my $w; |
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|
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my $cb = sub { |
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# cancel the old timer while creating a new one |
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$w = AnyEvent->timer (after => 1, cb => $cb); |
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}; |
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|
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# start the "loop" by creating the first watcher |
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$w = AnyEvent->timer (after => 0.5, cb => $cb); |
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|
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TIMING ISSUES |
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There are two ways to handle timers: based on real time (relative, "fire |
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in 10 seconds") and based on wallclock time (absolute, "fire at 12 |
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o'clock"). |
209 |
|
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While most event loops expect timers to specified in a relative way, |
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they use absolute time internally. This makes a difference when your |
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clock "jumps", for example, when ntp decides to set your clock backwards |
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from the wrong date of 2014-01-01 to 2008-01-01, a watcher that is |
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supposed to fire "after" a second might actually take six years to |
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finally fire. |
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|
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AnyEvent cannot compensate for this. The only event loop that is |
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conscious about these issues is EV, which offers both relative |
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(ev_timer, based on true relative time) and absolute (ev_periodic, based |
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on wallclock time) timers. |
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|
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AnyEvent always prefers relative timers, if available, matching the |
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AnyEvent API. |
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|
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SIGNAL WATCHERS |
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You can watch for signals using a signal watcher, "signal" is the signal |
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*name* without any "SIG" prefix, "cb" is the Perl callback to be invoked |
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whenever a signal occurs. |
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|
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Although the callback might get passed parameters, their value and |
231 |
presence is undefined and you cannot rely on them. Portable AnyEvent |
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callbacks cannot use arguments passed to signal watcher callbacks. |
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|
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Multiple signal occurrences can be clumped together into one callback |
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invocation, and callback invocation will be synchronous. Synchronous |
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means that it might take a while until the signal gets handled by the |
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process, but it is guaranteed not to interrupt any other callbacks. |
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|
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The main advantage of using these watchers is that you can share a |
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signal between multiple watchers. |
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|
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This watcher 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 watch on a child process exit and catch its exit status. |
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|
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The child process is specified by the "pid" argument (if set to 0, it |
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watches for any child process exit). The watcher will trigger as often |
254 |
as status change for the child are received. This works by installing a |
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signal handler for "SIGCHLD". The callback will be called with the pid |
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and exit status (as returned by waitpid), so unlike other watcher types, |
257 |
you *can* rely on child watcher callback arguments. |
258 |
|
259 |
There is a slight catch to child watchers, however: you usually start |
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them *after* the child process was created, and this means the process |
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could have exited already (and no SIGCHLD will be sent anymore). |
262 |
|
263 |
Not all event models handle this correctly (POE doesn't), but even for |
264 |
event models that *do* handle this correctly, they usually need to be |
265 |
loaded before the process exits (i.e. before you fork in the first |
266 |
place). |
267 |
|
268 |
This means you cannot create a child watcher as the very first thing in |
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an AnyEvent program, you *have* to create at least one watcher before |
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you "fork" the child (alternatively, you can call "AnyEvent::detect"). |
271 |
|
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Example: fork a process and wait for it |
273 |
|
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my $done = AnyEvent->condvar; |
275 |
|
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my $pid = fork or exit 5; |
277 |
|
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my $w = AnyEvent->child ( |
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pid => $pid, |
280 |
cb => sub { |
281 |
my ($pid, $status) = @_; |
282 |
warn "pid $pid exited with status $status"; |
283 |
$done->send; |
284 |
}, |
285 |
); |
286 |
|
287 |
# do something else, then wait for process exit |
288 |
$done->recv; |
289 |
|
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CONDITION VARIABLES |
291 |
If you are familiar with some event loops you will know that all of them |
292 |
require you to run some blocking "loop", "run" or similar function that |
293 |
will actively watch for new events and call your callbacks. |
294 |
|
295 |
AnyEvent is different, it expects somebody else to run the event loop |
296 |
and will only block when necessary (usually when told by the user). |
297 |
|
298 |
The instrument to do that is called a "condition variable", so called |
299 |
because they represent a condition that must become true. |
300 |
|
301 |
Condition variables can be created by calling the "AnyEvent->condvar" |
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method, usually without arguments. The only argument pair allowed is |
303 |
"cb", which specifies a callback to be called when the condition |
304 |
variable becomes true. |
305 |
|
306 |
After creation, the condition variable is "false" until it becomes |
307 |
"true" by calling the "send" method (or calling the condition variable |
308 |
as if it were a callback, read about the caveats in the description for |
309 |
the "->send" method). |
310 |
|
311 |
Condition variables are similar to callbacks, except that you can |
312 |
optionally wait for them. They can also be called merge points - points |
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in time where multiple outstanding events have been processed. And yet |
314 |
another way to call them is transactions - each condition variable can |
315 |
be used to represent a transaction, which finishes at some point and |
316 |
delivers a result. |
317 |
|
318 |
Condition variables are very useful to signal that something has |
319 |
finished, for example, if you write a module that does asynchronous http |
320 |
requests, then a condition variable would be the ideal candidate to |
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signal the availability of results. The user can either act when the |
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callback is called or can synchronously "->recv" for the results. |
323 |
|
324 |
You can also use them to simulate traditional event loops - for example, |
325 |
you can block your main program until an event occurs - for example, you |
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could "->recv" in your main program until the user clicks the Quit |
327 |
button of your app, which would "->send" the "quit" event. |
328 |
|
329 |
Note that condition variables recurse into the event loop - if you have |
330 |
two pieces of code that call "->recv" in a round-robin fashion, you |
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lose. Therefore, condition variables are good to export to your caller, |
332 |
but you should avoid making a blocking wait yourself, at least in |
333 |
callbacks, as this asks for trouble. |
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|
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Condition variables are represented by hash refs in perl, and the keys |
336 |
used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy |
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(it is often useful to build your own transaction class on top of |
338 |
AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call |
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it's "new" method in your own "new" method. |
340 |
|
341 |
There are two "sides" to a condition variable - the "producer side" |
342 |
which eventually calls "-> send", and the "consumer side", which waits |
343 |
for the send to occur. |
344 |
|
345 |
Example: wait for a timer. |
346 |
|
347 |
# wait till the result is ready |
348 |
my $result_ready = AnyEvent->condvar; |
349 |
|
350 |
# do something such as adding a timer |
351 |
# or socket watcher the calls $result_ready->send |
352 |
# when the "result" is ready. |
353 |
# in this case, we simply use a timer: |
354 |
my $w = AnyEvent->timer ( |
355 |
after => 1, |
356 |
cb => sub { $result_ready->send }, |
357 |
); |
358 |
|
359 |
# this "blocks" (while handling events) till the callback |
360 |
# calls send |
361 |
$result_ready->recv; |
362 |
|
363 |
Example: wait for a timer, but take advantage of the fact that condition |
364 |
variables are also code references. |
365 |
|
366 |
my $done = AnyEvent->condvar; |
367 |
my $delay = AnyEvent->timer (after => 5, cb => $done); |
368 |
$done->recv; |
369 |
|
370 |
METHODS FOR PRODUCERS |
371 |
These methods should only be used by the producing side, i.e. the |
372 |
code/module that eventually sends the signal. Note that it is also the |
373 |
producer side which creates the condvar in most cases, but it isn't |
374 |
uncommon for the consumer to create it as well. |
375 |
|
376 |
$cv->send (...) |
377 |
Flag the condition as ready - a running "->recv" and all further |
378 |
calls to "recv" will (eventually) return after this method has been |
379 |
called. If nobody is waiting the send will be remembered. |
380 |
|
381 |
If a callback has been set on the condition variable, it is called |
382 |
immediately from within send. |
383 |
|
384 |
Any arguments passed to the "send" call will be returned by all |
385 |
future "->recv" calls. |
386 |
|
387 |
Condition variables are overloaded so one can call them directly (as |
388 |
a code reference). Calling them directly is the same as calling |
389 |
"send". Note, however, that many C-based event loops do not handle |
390 |
overloading, so as tempting as it may be, passing a condition |
391 |
variable instead of a callback does not work. Both the pure perl and |
392 |
EV loops support overloading, however, as well as all functions that |
393 |
use perl to invoke a callback (as in AnyEvent::Socket and |
394 |
AnyEvent::DNS for example). |
395 |
|
396 |
$cv->croak ($error) |
397 |
Similar to send, but causes all call's to "->recv" to invoke |
398 |
"Carp::croak" with the given error message/object/scalar. |
399 |
|
400 |
This can be used to signal any errors to the condition variable |
401 |
user/consumer. |
402 |
|
403 |
$cv->begin ([group callback]) |
404 |
$cv->end |
405 |
These two methods are EXPERIMENTAL and MIGHT CHANGE. |
406 |
|
407 |
These two methods can be used to combine many transactions/events |
408 |
into one. For example, a function that pings many hosts in parallel |
409 |
might want to use a condition variable for the whole process. |
410 |
|
411 |
Every call to "->begin" will increment a counter, and every call to |
412 |
"->end" will decrement it. If the counter reaches 0 in "->end", the |
413 |
(last) callback passed to "begin" will be executed. That callback is |
414 |
*supposed* to call "->send", but that is not required. If no |
415 |
callback was set, "send" will be called without any arguments. |
416 |
|
417 |
Let's clarify this with the ping example: |
418 |
|
419 |
my $cv = AnyEvent->condvar; |
420 |
|
421 |
my %result; |
422 |
$cv->begin (sub { $cv->send (\%result) }); |
423 |
|
424 |
for my $host (@list_of_hosts) { |
425 |
$cv->begin; |
426 |
ping_host_then_call_callback $host, sub { |
427 |
$result{$host} = ...; |
428 |
$cv->end; |
429 |
}; |
430 |
} |
431 |
|
432 |
$cv->end; |
433 |
|
434 |
This code fragment supposedly pings a number of hosts and calls |
435 |
"send" after results for all then have have been gathered - in any |
436 |
order. To achieve this, the code issues a call to "begin" when it |
437 |
starts each ping request and calls "end" when it has received some |
438 |
result for it. Since "begin" and "end" only maintain a counter, the |
439 |
order in which results arrive is not relevant. |
440 |
|
441 |
There is an additional bracketing call to "begin" and "end" outside |
442 |
the loop, which serves two important purposes: first, it sets the |
443 |
callback to be called once the counter reaches 0, and second, it |
444 |
ensures that "send" is called even when "no" hosts are being pinged |
445 |
(the loop doesn't execute once). |
446 |
|
447 |
This is the general pattern when you "fan out" into multiple |
448 |
subrequests: use an outer "begin"/"end" pair to set the callback and |
449 |
ensure "end" is called at least once, and then, for each subrequest |
450 |
you start, call "begin" and for each subrequest you finish, call |
451 |
"end". |
452 |
|
453 |
METHODS FOR CONSUMERS |
454 |
These methods should only be used by the consuming side, i.e. the code |
455 |
awaits the condition. |
456 |
|
457 |
$cv->recv |
458 |
Wait (blocking if necessary) until the "->send" or "->croak" methods |
459 |
have been called on c<$cv>, while servicing other watchers normally. |
460 |
|
461 |
You can only wait once on a condition - additional calls are valid |
462 |
but will return immediately. |
463 |
|
464 |
If an error condition has been set by calling "->croak", then this |
465 |
function will call "croak". |
466 |
|
467 |
In list context, all parameters passed to "send" will be returned, |
468 |
in scalar context only the first one will be returned. |
469 |
|
470 |
Not all event models support a blocking wait - some die in that case |
471 |
(programs might want to do that to stay interactive), so *if you are |
472 |
using this from a module, never require a blocking wait*, but let |
473 |
the caller decide whether the call will block or not (for example, |
474 |
by coupling condition variables with some kind of request results |
475 |
and supporting callbacks so the caller knows that getting the result |
476 |
will not block, while still supporting blocking waits if the caller |
477 |
so desires). |
478 |
|
479 |
Another reason *never* to "->recv" in a module is that you cannot |
480 |
sensibly have two "->recv"'s in parallel, as that would require |
481 |
multiple interpreters or coroutines/threads, none of which |
482 |
"AnyEvent" can supply. |
483 |
|
484 |
The Coro module, however, *can* and *does* supply coroutines and, in |
485 |
fact, Coro::AnyEvent replaces AnyEvent's condvars by coroutine-safe |
486 |
versions and also integrates coroutines into AnyEvent, making |
487 |
blocking "->recv" calls perfectly safe as long as they are done from |
488 |
another coroutine (one that doesn't run the event loop). |
489 |
|
490 |
You can ensure that "-recv" never blocks by setting a callback and |
491 |
only calling "->recv" from within that callback (or at a later |
492 |
time). This will work even when the event loop does not support |
493 |
blocking waits otherwise. |
494 |
|
495 |
$bool = $cv->ready |
496 |
Returns true when the condition is "true", i.e. whether "send" or |
497 |
"croak" have been called. |
498 |
|
499 |
$cb = $cv->cb ([new callback]) |
500 |
This is a mutator function that returns the callback set and |
501 |
optionally replaces it before doing so. |
502 |
|
503 |
The callback will be called when the condition becomes "true", i.e. |
504 |
when "send" or "croak" are called. Calling "recv" inside the |
505 |
callback or at any later time is guaranteed not to block. |
506 |
|
507 |
GLOBAL VARIABLES AND FUNCTIONS |
508 |
$AnyEvent::MODEL |
509 |
Contains "undef" until the first watcher is being created. Then it |
510 |
contains the event model that is being used, which is the name of |
511 |
the Perl class implementing the model. This class is usually one of |
512 |
the "AnyEvent::Impl:xxx" modules, but can be any other class in the |
513 |
case AnyEvent has been extended at runtime (e.g. in *rxvt-unicode*). |
514 |
|
515 |
The known classes so far are: |
516 |
|
517 |
AnyEvent::Impl::EV based on EV (an interface to libev, best choice). |
518 |
AnyEvent::Impl::Event based on Event, second best choice. |
519 |
AnyEvent::Impl::Perl pure-perl implementation, fast and portable. |
520 |
AnyEvent::Impl::Glib based on Glib, third-best choice. |
521 |
AnyEvent::Impl::Tk based on Tk, very bad choice. |
522 |
AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs). |
523 |
AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse. |
524 |
AnyEvent::Impl::POE based on POE, not generic enough for full support. |
525 |
|
526 |
There is no support for WxWidgets, as WxWidgets has no support for |
527 |
watching file handles. However, you can use WxWidgets through the |
528 |
POE Adaptor, as POE has a Wx backend that simply polls 20 times per |
529 |
second, which was considered to be too horrible to even consider for |
530 |
AnyEvent. Likewise, other POE backends can be used by AnyEvent by |
531 |
using it's adaptor. |
532 |
|
533 |
AnyEvent knows about Prima and Wx and will try to use POE when |
534 |
autodetecting them. |
535 |
|
536 |
AnyEvent::detect |
537 |
Returns $AnyEvent::MODEL, forcing autodetection of the event model |
538 |
if necessary. You should only call this function right before you |
539 |
would have created an AnyEvent watcher anyway, that is, as late as |
540 |
possible at runtime. |
541 |
|
542 |
$guard = AnyEvent::post_detect { BLOCK } |
543 |
Arranges for the code block to be executed as soon as the event |
544 |
model is autodetected (or immediately if this has already happened). |
545 |
|
546 |
If called in scalar or list context, then it creates and returns an |
547 |
object that automatically removes the callback again when it is |
548 |
destroyed. See Coro::BDB for a case where this is useful. |
549 |
|
550 |
@AnyEvent::post_detect |
551 |
If there are any code references in this array (you can "push" to it |
552 |
before or after loading AnyEvent), then they will called directly |
553 |
after the event loop has been chosen. |
554 |
|
555 |
You should check $AnyEvent::MODEL before adding to this array, |
556 |
though: if it contains a true value then the event loop has already |
557 |
been detected, and the array will be ignored. |
558 |
|
559 |
Best use "AnyEvent::post_detect { BLOCK }" instead. |
560 |
|
561 |
WHAT TO DO IN A MODULE |
562 |
As a module author, you should "use AnyEvent" and call AnyEvent methods |
563 |
freely, but you should not load a specific event module or rely on it. |
564 |
|
565 |
Be careful when you create watchers in the module body - AnyEvent will |
566 |
decide which event module to use as soon as the first method is called, |
567 |
so by calling AnyEvent in your module body you force the user of your |
568 |
module to load the event module first. |
569 |
|
570 |
Never call "->recv" on a condition variable unless you *know* that the |
571 |
"->send" method has been called on it already. This is because it will |
572 |
stall the whole program, and the whole point of using events is to stay |
573 |
interactive. |
574 |
|
575 |
It is fine, however, to call "->recv" when the user of your module |
576 |
requests it (i.e. if you create a http request object ad have a method |
577 |
called "results" that returns the results, it should call "->recv" |
578 |
freely, as the user of your module knows what she is doing. always). |
579 |
|
580 |
WHAT TO DO IN THE MAIN PROGRAM |
581 |
There will always be a single main program - the only place that should |
582 |
dictate which event model to use. |
583 |
|
584 |
If it doesn't care, it can just "use AnyEvent" and use it itself, or not |
585 |
do anything special (it does not need to be event-based) and let |
586 |
AnyEvent decide which implementation to chose if some module relies on |
587 |
it. |
588 |
|
589 |
If the main program relies on a specific event model - for example, in |
590 |
Gtk2 programs you have to rely on the Glib module - you should load the |
591 |
event module before loading AnyEvent or any module that uses it: |
592 |
generally speaking, you should load it as early as possible. The reason |
593 |
is that modules might create watchers when they are loaded, and AnyEvent |
594 |
will decide on the event model to use as soon as it creates watchers, |
595 |
and it might chose the wrong one unless you load the correct one |
596 |
yourself. |
597 |
|
598 |
You can chose to use a pure-perl implementation by loading the |
599 |
"AnyEvent::Impl::Perl" module, which gives you similar behaviour |
600 |
everywhere, but letting AnyEvent chose the model is generally better. |
601 |
|
602 |
MAINLOOP EMULATION |
603 |
Sometimes (often for short test scripts, or even standalone programs who |
604 |
only want to use AnyEvent), you do not want to run a specific event |
605 |
loop. |
606 |
|
607 |
In that case, you can use a condition variable like this: |
608 |
|
609 |
AnyEvent->condvar->recv; |
610 |
|
611 |
This has the effect of entering the event loop and looping forever. |
612 |
|
613 |
Note that usually your program has some exit condition, in which case it |
614 |
is better to use the "traditional" approach of storing a condition |
615 |
variable somewhere, waiting for it, and sending it when the program |
616 |
should exit cleanly. |
617 |
|
618 |
OTHER MODULES |
619 |
The following is a non-exhaustive list of additional modules that use |
620 |
AnyEvent and can therefore be mixed easily with other AnyEvent modules |
621 |
in the same program. Some of the modules come with AnyEvent, some are |
622 |
available via CPAN. |
623 |
|
624 |
AnyEvent::Util |
625 |
Contains various utility functions that replace often-used but |
626 |
blocking functions such as "inet_aton" by event-/callback-based |
627 |
versions. |
628 |
|
629 |
AnyEvent::Handle |
630 |
Provide read and write buffers and manages watchers for reads and |
631 |
writes. |
632 |
|
633 |
AnyEvent::Socket |
634 |
Provides various utility functions for (internet protocol) sockets, |
635 |
addresses and name resolution. Also functions to create non-blocking |
636 |
tcp connections or tcp servers, with IPv6 and SRV record support and |
637 |
more. |
638 |
|
639 |
AnyEvent::DNS |
640 |
Provides rich asynchronous DNS resolver capabilities. |
641 |
|
642 |
AnyEvent::HTTPD |
643 |
Provides a simple web application server framework. |
644 |
|
645 |
AnyEvent::FastPing |
646 |
The fastest ping in the west. |
647 |
|
648 |
Net::IRC3 |
649 |
AnyEvent based IRC client module family. |
650 |
|
651 |
Net::XMPP2 |
652 |
AnyEvent based XMPP (Jabber protocol) module family. |
653 |
|
654 |
Net::FCP |
655 |
AnyEvent-based implementation of the Freenet Client Protocol, |
656 |
birthplace of AnyEvent. |
657 |
|
658 |
Event::ExecFlow |
659 |
High level API for event-based execution flow control. |
660 |
|
661 |
Coro |
662 |
Has special support for AnyEvent via Coro::AnyEvent. |
663 |
|
664 |
AnyEvent::AIO, IO::AIO |
665 |
Truly asynchronous I/O, should be in the toolbox of every event |
666 |
programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent |
667 |
together. |
668 |
|
669 |
AnyEvent::BDB, BDB |
670 |
Truly asynchronous Berkeley DB access. AnyEvent::AIO transparently |
671 |
fuses IO::AIO and AnyEvent together. |
672 |
|
673 |
IO::Lambda |
674 |
The lambda approach to I/O - don't ask, look there. Can use |
675 |
AnyEvent. |
676 |
|
677 |
SUPPLYING YOUR OWN EVENT MODEL INTERFACE |
678 |
This is an advanced topic that you do not normally need to use AnyEvent |
679 |
in a module. This section is only of use to event loop authors who want |
680 |
to provide AnyEvent compatibility. |
681 |
|
682 |
If you need to support another event library which isn't directly |
683 |
supported by AnyEvent, you can supply your own interface to it by |
684 |
pushing, before the first watcher gets created, the package name of the |
685 |
event module and the package name of the interface to use onto |
686 |
@AnyEvent::REGISTRY. You can do that before and even without loading |
687 |
AnyEvent, so it is reasonably cheap. |
688 |
|
689 |
Example: |
690 |
|
691 |
push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::]; |
692 |
|
693 |
This tells AnyEvent to (literally) use the "urxvt::anyevent::" |
694 |
package/class when it finds the "urxvt" package/module is already |
695 |
loaded. |
696 |
|
697 |
When AnyEvent is loaded and asked to find a suitable event model, it |
698 |
will first check for the presence of urxvt by trying to "use" the |
699 |
"urxvt::anyevent" module. |
700 |
|
701 |
The class should provide implementations for all watcher types. See |
702 |
AnyEvent::Impl::EV (source code), AnyEvent::Impl::Glib (Source code) and |
703 |
so on for actual examples. Use "perldoc -m AnyEvent::Impl::Glib" to see |
704 |
the sources. |
705 |
|
706 |
If you don't provide "signal" and "child" watchers than AnyEvent will |
707 |
provide suitable (hopefully) replacements. |
708 |
|
709 |
The above example isn't fictitious, the *rxvt-unicode* (a.k.a. urxvt) |
710 |
terminal emulator uses the above line as-is. An interface isn't included |
711 |
in AnyEvent because it doesn't make sense outside the embedded |
712 |
interpreter inside *rxvt-unicode*, and it is updated and maintained as |
713 |
part of the *rxvt-unicode* distribution. |
714 |
|
715 |
*rxvt-unicode* also cheats a bit by not providing blocking access to |
716 |
condition variables: code blocking while waiting for a condition will |
717 |
"die". This still works with most modules/usages, and blocking calls |
718 |
must not be done in an interactive application, so it makes sense. |
719 |
|
720 |
ENVIRONMENT VARIABLES |
721 |
The following environment variables are used by this module: |
722 |
|
723 |
"PERL_ANYEVENT_VERBOSE" |
724 |
By default, AnyEvent will be completely silent except in fatal |
725 |
conditions. You can set this environment variable to make AnyEvent |
726 |
more talkative. |
727 |
|
728 |
When set to 1 or higher, causes AnyEvent to warn about unexpected |
729 |
conditions, such as not being able to load the event model specified |
730 |
by "PERL_ANYEVENT_MODEL". |
731 |
|
732 |
When set to 2 or higher, cause AnyEvent to report to STDERR which |
733 |
event model it chooses. |
734 |
|
735 |
"PERL_ANYEVENT_MODEL" |
736 |
This can be used to specify the event model to be used by AnyEvent, |
737 |
before auto detection and -probing kicks in. It must be a string |
738 |
consisting entirely of ASCII letters. The string "AnyEvent::Impl::" |
739 |
gets prepended and the resulting module name is loaded and if the |
740 |
load was successful, used as event model. If it fails to load |
741 |
AnyEvent will proceed with auto detection and -probing. |
742 |
|
743 |
This functionality might change in future versions. |
744 |
|
745 |
For example, to force the pure perl model (AnyEvent::Impl::Perl) you |
746 |
could start your program like this: |
747 |
|
748 |
PERL_ANYEVENT_MODEL=Perl perl ... |
749 |
|
750 |
"PERL_ANYEVENT_PROTOCOLS" |
751 |
Used by both AnyEvent::DNS and AnyEvent::Socket to determine |
752 |
preferences for IPv4 or IPv6. The default is unspecified (and might |
753 |
change, or be the result of auto probing). |
754 |
|
755 |
Must be set to a comma-separated list of protocols or address |
756 |
families, current supported: "ipv4" and "ipv6". Only protocols |
757 |
mentioned will be used, and preference will be given to protocols |
758 |
mentioned earlier in the list. |
759 |
|
760 |
This variable can effectively be used for denial-of-service attacks |
761 |
against local programs (e.g. when setuid), although the impact is |
762 |
likely small, as the program has to handle connection errors |
763 |
already- |
764 |
|
765 |
Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over |
766 |
IPv6, but support both and try to use both. |
767 |
"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to |
768 |
resolve or contact IPv6 addresses. |
769 |
"PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but |
770 |
prefer IPv6 over IPv4. |
771 |
|
772 |
"PERL_ANYEVENT_EDNS0" |
773 |
Used by AnyEvent::DNS to decide whether to use the EDNS0 extension |
774 |
for DNS. This extension is generally useful to reduce DNS traffic, |
775 |
but some (broken) firewalls drop such DNS packets, which is why it |
776 |
is off by default. |
777 |
|
778 |
Setting this variable to 1 will cause AnyEvent::DNS to announce |
779 |
EDNS0 in its DNS requests. |
780 |
|
781 |
EXAMPLE PROGRAM |
782 |
The following program uses an I/O watcher to read data from STDIN, a |
783 |
timer to display a message once per second, and a condition variable to |
784 |
quit the program when the user enters quit: |
785 |
|
786 |
use AnyEvent; |
787 |
|
788 |
my $cv = AnyEvent->condvar; |
789 |
|
790 |
my $io_watcher = AnyEvent->io ( |
791 |
fh => \*STDIN, |
792 |
poll => 'r', |
793 |
cb => sub { |
794 |
warn "io event <$_[0]>\n"; # will always output <r> |
795 |
chomp (my $input = <STDIN>); # read a line |
796 |
warn "read: $input\n"; # output what has been read |
797 |
$cv->send if $input =~ /^q/i; # quit program if /^q/i |
798 |
}, |
799 |
); |
800 |
|
801 |
my $time_watcher; # can only be used once |
802 |
|
803 |
sub new_timer { |
804 |
$timer = AnyEvent->timer (after => 1, cb => sub { |
805 |
warn "timeout\n"; # print 'timeout' about every second |
806 |
&new_timer; # and restart the time |
807 |
}); |
808 |
} |
809 |
|
810 |
new_timer; # create first timer |
811 |
|
812 |
$cv->recv; # wait until user enters /^q/i |
813 |
|
814 |
REAL-WORLD EXAMPLE |
815 |
Consider the Net::FCP module. It features (among others) the following |
816 |
API calls, which are to freenet what HTTP GET requests are to http: |
817 |
|
818 |
my $data = $fcp->client_get ($url); # blocks |
819 |
|
820 |
my $transaction = $fcp->txn_client_get ($url); # does not block |
821 |
$transaction->cb ( sub { ... } ); # set optional result callback |
822 |
my $data = $transaction->result; # possibly blocks |
823 |
|
824 |
The "client_get" method works like "LWP::Simple::get": it requests the |
825 |
given URL and waits till the data has arrived. It is defined to be: |
826 |
|
827 |
sub client_get { $_[0]->txn_client_get ($_[1])->result } |
828 |
|
829 |
And in fact is automatically generated. This is the blocking API of |
830 |
Net::FCP, and it works as simple as in any other, similar, module. |
831 |
|
832 |
More complicated is "txn_client_get": It only creates a transaction |
833 |
(completion, result, ...) object and initiates the transaction. |
834 |
|
835 |
my $txn = bless { }, Net::FCP::Txn::; |
836 |
|
837 |
It also creates a condition variable that is used to signal the |
838 |
completion of the request: |
839 |
|
840 |
$txn->{finished} = AnyAvent->condvar; |
841 |
|
842 |
It then creates a socket in non-blocking mode. |
843 |
|
844 |
socket $txn->{fh}, ...; |
845 |
fcntl $txn->{fh}, F_SETFL, O_NONBLOCK; |
846 |
connect $txn->{fh}, ... |
847 |
and !$!{EWOULDBLOCK} |
848 |
and !$!{EINPROGRESS} |
849 |
and Carp::croak "unable to connect: $!\n"; |
850 |
|
851 |
Then it creates a write-watcher which gets called whenever an error |
852 |
occurs or the connection succeeds: |
853 |
|
854 |
$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'w', cb => sub { $txn->fh_ready_w }); |
855 |
|
856 |
And returns this transaction object. The "fh_ready_w" callback gets |
857 |
called as soon as the event loop detects that the socket is ready for |
858 |
writing. |
859 |
|
860 |
The "fh_ready_w" method makes the socket blocking again, writes the |
861 |
request data and replaces the watcher by a read watcher (waiting for |
862 |
reply data). The actual code is more complicated, but that doesn't |
863 |
matter for this example: |
864 |
|
865 |
fcntl $txn->{fh}, F_SETFL, 0; |
866 |
syswrite $txn->{fh}, $txn->{request} |
867 |
or die "connection or write error"; |
868 |
$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r }); |
869 |
|
870 |
Again, "fh_ready_r" waits till all data has arrived, and then stores the |
871 |
result and signals any possible waiters that the request has finished: |
872 |
|
873 |
sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf}; |
874 |
|
875 |
if (end-of-file or data complete) { |
876 |
$txn->{result} = $txn->{buf}; |
877 |
$txn->{finished}->send; |
878 |
$txb->{cb}->($txn) of $txn->{cb}; # also call callback |
879 |
} |
880 |
|
881 |
The "result" method, finally, just waits for the finished signal (if the |
882 |
request was already finished, it doesn't wait, of course, and returns |
883 |
the data: |
884 |
|
885 |
$txn->{finished}->recv; |
886 |
return $txn->{result}; |
887 |
|
888 |
The actual code goes further and collects all errors ("die"s, |
889 |
exceptions) that occurred during request processing. The "result" method |
890 |
detects whether an exception as thrown (it is stored inside the $txn |
891 |
object) and just throws the exception, which means connection errors and |
892 |
other problems get reported tot he code that tries to use the result, |
893 |
not in a random callback. |
894 |
|
895 |
All of this enables the following usage styles: |
896 |
|
897 |
1. Blocking: |
898 |
|
899 |
my $data = $fcp->client_get ($url); |
900 |
|
901 |
2. Blocking, but running in parallel: |
902 |
|
903 |
my @datas = map $_->result, |
904 |
map $fcp->txn_client_get ($_), |
905 |
@urls; |
906 |
|
907 |
Both blocking examples work without the module user having to know |
908 |
anything about events. |
909 |
|
910 |
3a. Event-based in a main program, using any supported event module: |
911 |
|
912 |
use EV; |
913 |
|
914 |
$fcp->txn_client_get ($url)->cb (sub { |
915 |
my $txn = shift; |
916 |
my $data = $txn->result; |
917 |
... |
918 |
}); |
919 |
|
920 |
EV::loop; |
921 |
|
922 |
3b. The module user could use AnyEvent, too: |
923 |
|
924 |
use AnyEvent; |
925 |
|
926 |
my $quit = AnyEvent->condvar; |
927 |
|
928 |
$fcp->txn_client_get ($url)->cb (sub { |
929 |
... |
930 |
$quit->send; |
931 |
}); |
932 |
|
933 |
$quit->recv; |
934 |
|
935 |
BENCHMARKS |
936 |
To give you an idea of the performance and overheads that AnyEvent adds |
937 |
over the event loops themselves and to give you an impression of the |
938 |
speed of various event loops I prepared some benchmarks. |
939 |
|
940 |
BENCHMARKING ANYEVENT OVERHEAD |
941 |
Here is a benchmark of various supported event models used natively and |
942 |
through AnyEvent. The benchmark creates a lot of timers (with a zero |
943 |
timeout) and I/O watchers (watching STDOUT, a pty, to become writable, |
944 |
which it is), lets them fire exactly once and destroys them again. |
945 |
|
946 |
Source code for this benchmark is found as eg/bench in the AnyEvent |
947 |
distribution. |
948 |
|
949 |
Explanation of the columns |
950 |
*watcher* is the number of event watchers created/destroyed. Since |
951 |
different event models feature vastly different performances, each event |
952 |
loop was given a number of watchers so that overall runtime is |
953 |
acceptable and similar between tested event loop (and keep them from |
954 |
crashing): Glib would probably take thousands of years if asked to |
955 |
process the same number of watchers as EV in this benchmark. |
956 |
|
957 |
*bytes* is the number of bytes (as measured by the resident set size, |
958 |
RSS) consumed by each watcher. This method of measuring captures both C |
959 |
and Perl-based overheads. |
960 |
|
961 |
*create* is the time, in microseconds (millionths of seconds), that it |
962 |
takes to create a single watcher. The callback is a closure shared |
963 |
between all watchers, to avoid adding memory overhead. That means |
964 |
closure creation and memory usage is not included in the figures. |
965 |
|
966 |
*invoke* is the time, in microseconds, used to invoke a simple callback. |
967 |
The callback simply counts down a Perl variable and after it was invoked |
968 |
"watcher" times, it would "->send" a condvar once to signal the end of |
969 |
this phase. |
970 |
|
971 |
*destroy* is the time, in microseconds, that it takes to destroy a |
972 |
single watcher. |
973 |
|
974 |
Results |
975 |
name watchers bytes create invoke destroy comment |
976 |
EV/EV 400000 244 0.56 0.46 0.31 EV native interface |
977 |
EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers |
978 |
CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal |
979 |
Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation |
980 |
Event/Event 16000 516 31.88 31.30 0.85 Event native interface |
981 |
Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers |
982 |
Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour |
983 |
Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers |
984 |
POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event |
985 |
POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select |
986 |
|
987 |
Discussion |
988 |
The benchmark does *not* measure scalability of the event loop very |
989 |
well. For example, a select-based event loop (such as the pure perl one) |
990 |
can never compete with an event loop that uses epoll when the number of |
991 |
file descriptors grows high. In this benchmark, all events become ready |
992 |
at the same time, so select/poll-based implementations get an unnatural |
993 |
speed boost. |
994 |
|
995 |
Also, note that the number of watchers usually has a nonlinear effect on |
996 |
overall speed, that is, creating twice as many watchers doesn't take |
997 |
twice the time - usually it takes longer. This puts event loops tested |
998 |
with a higher number of watchers at a disadvantage. |
999 |
|
1000 |
To put the range of results into perspective, consider that on the |
1001 |
benchmark machine, handling an event takes roughly 1600 CPU cycles with |
1002 |
EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 |
1003 |
CPU cycles with POE. |
1004 |
|
1005 |
"EV" is the sole leader regarding speed and memory use, which are both |
1006 |
maximal/minimal, respectively. Even when going through AnyEvent, it uses |
1007 |
far less memory than any other event loop and is still faster than Event |
1008 |
natively. |
1009 |
|
1010 |
The pure perl implementation is hit in a few sweet spots (both the |
1011 |
constant timeout and the use of a single fd hit optimisations in the |
1012 |
perl interpreter and the backend itself). Nevertheless this shows that |
1013 |
it adds very little overhead in itself. Like any select-based backend |
1014 |
its performance becomes really bad with lots of file descriptors (and |
1015 |
few of them active), of course, but this was not subject of this |
1016 |
benchmark. |
1017 |
|
1018 |
The "Event" module has a relatively high setup and callback invocation |
1019 |
cost, but overall scores in on the third place. |
1020 |
|
1021 |
"Glib"'s memory usage is quite a bit higher, but it features a faster |
1022 |
callback invocation and overall ends up in the same class as "Event". |
1023 |
However, Glib scales extremely badly, doubling the number of watchers |
1024 |
increases the processing time by more than a factor of four, making it |
1025 |
completely unusable when using larger numbers of watchers (note that |
1026 |
only a single file descriptor was used in the benchmark, so |
1027 |
inefficiencies of "poll" do not account for this). |
1028 |
|
1029 |
The "Tk" adaptor works relatively well. The fact that it crashes with |
1030 |
more than 2000 watchers is a big setback, however, as correctness takes |
1031 |
precedence over speed. Nevertheless, its performance is surprising, as |
1032 |
the file descriptor is dup()ed for each watcher. This shows that the |
1033 |
dup() employed by some adaptors is not a big performance issue (it does |
1034 |
incur a hidden memory cost inside the kernel which is not reflected in |
1035 |
the figures above). |
1036 |
|
1037 |
"POE", regardless of underlying event loop (whether using its pure perl |
1038 |
select-based backend or the Event module, the POE-EV backend couldn't be |
1039 |
tested because it wasn't working) shows abysmal performance and memory |
1040 |
usage with AnyEvent: Watchers use almost 30 times as much memory as EV |
1041 |
watchers, and 10 times as much memory as Event (the high memory |
1042 |
requirements are caused by requiring a session for each watcher). |
1043 |
Watcher invocation speed is almost 900 times slower than with AnyEvent's |
1044 |
pure perl implementation. |
1045 |
|
1046 |
The design of the POE adaptor class in AnyEvent can not really account |
1047 |
for the performance issues, though, as session creation overhead is |
1048 |
small compared to execution of the state machine, which is coded pretty |
1049 |
optimally within AnyEvent::Impl::POE (and while everybody agrees that |
1050 |
using multiple sessions is not a good approach, especially regarding |
1051 |
memory usage, even the author of POE could not come up with a faster |
1052 |
design). |
1053 |
|
1054 |
Summary |
1055 |
* Using EV through AnyEvent is faster than any other event loop (even |
1056 |
when used without AnyEvent), but most event loops have acceptable |
1057 |
performance with or without AnyEvent. |
1058 |
|
1059 |
* The overhead AnyEvent adds is usually much smaller than the overhead |
1060 |
of the actual event loop, only with extremely fast event loops such |
1061 |
as EV adds AnyEvent significant overhead. |
1062 |
|
1063 |
* You should avoid POE like the plague if you want performance or |
1064 |
reasonable memory usage. |
1065 |
|
1066 |
BENCHMARKING THE LARGE SERVER CASE |
1067 |
This benchmark actually benchmarks the event loop itself. It works by |
1068 |
creating a number of "servers": each server consists of a socket pair, a |
1069 |
timeout watcher that gets reset on activity (but never fires), and an |
1070 |
I/O watcher waiting for input on one side of the socket. Each time the |
1071 |
socket watcher reads a byte it will write that byte to a random other |
1072 |
"server". |
1073 |
|
1074 |
The effect is that there will be a lot of I/O watchers, only part of |
1075 |
which are active at any one point (so there is a constant number of |
1076 |
active fds for each loop iteration, but which fds these are is random). |
1077 |
The timeout is reset each time something is read because that reflects |
1078 |
how most timeouts work (and puts extra pressure on the event loops). |
1079 |
|
1080 |
In this benchmark, we use 10000 socket pairs (20000 sockets), of which |
1081 |
100 (1%) are active. This mirrors the activity of large servers with |
1082 |
many connections, most of which are idle at any one point in time. |
1083 |
|
1084 |
Source code for this benchmark is found as eg/bench2 in the AnyEvent |
1085 |
distribution. |
1086 |
|
1087 |
Explanation of the columns |
1088 |
*sockets* is the number of sockets, and twice the number of "servers" |
1089 |
(as each server has a read and write socket end). |
1090 |
|
1091 |
*create* is the time it takes to create a socket pair (which is |
1092 |
nontrivial) and two watchers: an I/O watcher and a timeout watcher. |
1093 |
|
1094 |
*request*, the most important value, is the time it takes to handle a |
1095 |
single "request", that is, reading the token from the pipe and |
1096 |
forwarding it to another server. This includes deleting the old timeout |
1097 |
and creating a new one that moves the timeout into the future. |
1098 |
|
1099 |
Results |
1100 |
name sockets create request |
1101 |
EV 20000 69.01 11.16 |
1102 |
Perl 20000 73.32 35.87 |
1103 |
Event 20000 212.62 257.32 |
1104 |
Glib 20000 651.16 1896.30 |
1105 |
POE 20000 349.67 12317.24 uses POE::Loop::Event |
1106 |
|
1107 |
Discussion |
1108 |
This benchmark *does* measure scalability and overall performance of the |
1109 |
particular event loop. |
1110 |
|
1111 |
EV is again fastest. Since it is using epoll on my system, the setup |
1112 |
time is relatively high, though. |
1113 |
|
1114 |
Perl surprisingly comes second. It is much faster than the C-based event |
1115 |
loops Event and Glib. |
1116 |
|
1117 |
Event suffers from high setup time as well (look at its code and you |
1118 |
will understand why). Callback invocation also has a high overhead |
1119 |
compared to the "$_->() for .."-style loop that the Perl event loop |
1120 |
uses. Event uses select or poll in basically all documented |
1121 |
configurations. |
1122 |
|
1123 |
Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It |
1124 |
clearly fails to perform with many filehandles or in busy servers. |
1125 |
|
1126 |
POE is still completely out of the picture, taking over 1000 times as |
1127 |
long as EV, and over 100 times as long as the Perl implementation, even |
1128 |
though it uses a C-based event loop in this case. |
1129 |
|
1130 |
Summary |
1131 |
* The pure perl implementation performs extremely well. |
1132 |
|
1133 |
* Avoid Glib or POE in large projects where performance matters. |
1134 |
|
1135 |
BENCHMARKING SMALL SERVERS |
1136 |
While event loops should scale (and select-based ones do not...) even to |
1137 |
large servers, most programs we (or I :) actually write have only a few |
1138 |
I/O watchers. |
1139 |
|
1140 |
In this benchmark, I use the same benchmark program as in the large |
1141 |
server case, but it uses only eight "servers", of which three are active |
1142 |
at any one time. This should reflect performance for a small server |
1143 |
relatively well. |
1144 |
|
1145 |
The columns are identical to the previous table. |
1146 |
|
1147 |
Results |
1148 |
name sockets create request |
1149 |
EV 16 20.00 6.54 |
1150 |
Perl 16 25.75 12.62 |
1151 |
Event 16 81.27 35.86 |
1152 |
Glib 16 32.63 15.48 |
1153 |
POE 16 261.87 276.28 uses POE::Loop::Event |
1154 |
|
1155 |
Discussion |
1156 |
The benchmark tries to test the performance of a typical small server. |
1157 |
While knowing how various event loops perform is interesting, keep in |
1158 |
mind that their overhead in this case is usually not as important, due |
1159 |
to the small absolute number of watchers (that is, you need efficiency |
1160 |
and speed most when you have lots of watchers, not when you only have a |
1161 |
few of them). |
1162 |
|
1163 |
EV is again fastest. |
1164 |
|
1165 |
Perl again comes second. It is noticeably faster than the C-based event |
1166 |
loops Event and Glib, although the difference is too small to really |
1167 |
matter. |
1168 |
|
1169 |
POE also performs much better in this case, but is is still far behind |
1170 |
the others. |
1171 |
|
1172 |
Summary |
1173 |
* C-based event loops perform very well with small number of watchers, |
1174 |
as the management overhead dominates. |
1175 |
|
1176 |
FORK |
1177 |
Most event libraries are not fork-safe. The ones who are usually are |
1178 |
because they rely on inefficient but fork-safe "select" or "poll" calls. |
1179 |
Only EV is fully fork-aware. |
1180 |
|
1181 |
If you have to fork, you must either do so *before* creating your first |
1182 |
watcher OR you must not use AnyEvent at all in the child. |
1183 |
|
1184 |
SECURITY CONSIDERATIONS |
1185 |
AnyEvent can be forced to load any event model via |
1186 |
$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used |
1187 |
to execute arbitrary code or directly gain access, it can easily be used |
1188 |
to make the program hang or malfunction in subtle ways, as AnyEvent |
1189 |
watchers will not be active when the program uses a different event |
1190 |
model than specified in the variable. |
1191 |
|
1192 |
You can make AnyEvent completely ignore this variable by deleting it |
1193 |
before the first watcher gets created, e.g. with a "BEGIN" block: |
1194 |
|
1195 |
BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} } |
1196 |
|
1197 |
use AnyEvent; |
1198 |
|
1199 |
Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can |
1200 |
be used to probe what backend is used and gain other information (which |
1201 |
is probably even less useful to an attacker than PERL_ANYEVENT_MODEL). |
1202 |
|
1203 |
SEE ALSO |
1204 |
Utility functions: AnyEvent::Util. |
1205 |
|
1206 |
Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk, |
1207 |
Event::Lib, Qt, POE. |
1208 |
|
1209 |
Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event, |
1210 |
AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl, |
1211 |
AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE. |
1212 |
|
1213 |
Non-blocking file handles, sockets, TCP clients and servers: |
1214 |
AnyEvent::Handle, AnyEvent::Socket. |
1215 |
|
1216 |
Asynchronous DNS: AnyEvent::DNS. |
1217 |
|
1218 |
Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event, |
1219 |
|
1220 |
Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS. |
1221 |
|
1222 |
AUTHOR |
1223 |
Marc Lehmann <schmorp@schmorp.de> |
1224 |
http://home.schmorp.de/ |
1225 |
|