1 |
NAME |
2 |
AnyEvent - provide framework for multiple event loops |
3 |
|
4 |
EV, Event, Glib, Tk, Perl, Event::Lib, Qt and POE are various supported |
5 |
event loops. |
6 |
|
7 |
SYNOPSIS |
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use AnyEvent; |
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|
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# file descriptor readable |
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my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... }); |
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|
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# one-shot or repeating timers |
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my $w = AnyEvent->timer (after => $seconds, cb => sub { ... }); |
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my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ... |
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|
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print AnyEvent->now; # prints current event loop time |
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print AnyEvent->time; # think Time::HiRes::time or simply CORE::time. |
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|
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# POSIX signal |
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my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... }); |
22 |
|
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# child process exit |
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my $w = AnyEvent->child (pid => $pid, cb => sub { |
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my ($pid, $status) = @_; |
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... |
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}); |
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|
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# called when event loop idle (if applicable) |
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my $w = AnyEvent->idle (cb => sub { ... }); |
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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 $condvar gets ->send |
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# use a condvar in callback mode: |
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$w->cb (sub { $_[0]->recv }); |
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|
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INTRODUCTION/TUTORIAL |
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This manpage is mainly a reference manual. If you are interested in a |
40 |
tutorial or some gentle introduction, have a look at the AnyEvent::Intro |
41 |
manpage. |
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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, |
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only one event loop can be active at the same time in a process. |
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AnyEvent cannot change this, but it can hide the differences between |
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those event loops. |
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|
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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 |
67 |
cannot use anything else, as they are simply incompatible to everything |
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that isn't them. 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 IO::Async, as long as those use |
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one of the supported event loops. It is trivial to add new event loops |
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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, AnyEvent comes with a big (and fully optional!) toolbox of |
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useful functionality, such as an asynchronous DNS resolver, 100% |
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non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms |
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such as Windows) and lots of real-world knowledge and workarounds for |
91 |
platform bugs and differences. |
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|
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Now, if you *do 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 |
131 |
"AnyEvent::Impl::Perl". Like other event modules you can load it |
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explicitly and enjoy the high availability of that event loop :) |
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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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Note that callbacks must not permanently change global variables |
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potentially in use by the event loop (such as $_ or $[) and that |
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callbacks must not "die". The former is good programming practise in |
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Perl and the latter stems from the fact that exception handling differs |
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widely between event loops. |
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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" is the Perl *file handle* (or a naked file descriptor) to watch for |
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events (AnyEvent might or might not keep a reference to this file |
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handle). Note that only file handles pointing to things for which |
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non-blocking operation makes sense are allowed. This includes sockets, |
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most character devices, pipes, fifos and so on, but not for example |
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files or block devices. |
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|
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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. |
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|
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"cb" 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: wait for readability of STDIN, then read a line and disable the |
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watcher. |
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|
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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 callback will normally be invoked once only. If you specify another |
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parameter, "interval", as a strictly positive number (> 0), then the |
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callback will be invoked regularly at that interval (in fractional |
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seconds) after the first invocation. If "interval" is specified with a |
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false value, then it is treated as if it were missing. |
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|
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The callback will be rescheduled before invoking the callback, but no |
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attempt is done to avoid timer drift in most backends, so the interval |
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is only approximate. |
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|
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Example: fire an event after 7.7 seconds. |
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|
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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: fire an event after 0.5 seconds, then roughly every second. |
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|
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my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub { |
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warn "timeout\n"; |
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}; |
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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"). |
248 |
|
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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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AnyEvent has two additional methods that return the "current time": |
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|
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AnyEvent->time |
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This returns the "current wallclock time" as a fractional number of |
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seconds since the Epoch (the same thing as "time" or |
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"Time::HiRes::time" return, and the result is guaranteed to be |
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compatible with those). |
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|
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It progresses independently of any event loop processing, i.e. each |
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call will check the system clock, which usually gets updated |
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frequently. |
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|
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AnyEvent->now |
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This also returns the "current wallclock time", but unlike "time", |
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above, this value might change only once per event loop iteration, |
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depending on the event loop (most return the same time as "time", |
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above). This is the time that AnyEvent's timers get scheduled |
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against. |
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|
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*In almost all cases (in all cases if you don't care), this is the |
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function to call when you want to know the current time.* |
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|
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This function is also often faster then "AnyEvent->time", and thus |
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the preferred method if you want some timestamp (for example, |
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AnyEvent::Handle uses this to update it's activity timeouts). |
289 |
|
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The rest of this section is only of relevance if you try to be very |
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exact with your timing, you can skip it without bad conscience. |
292 |
|
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For a practical example of when these times differ, consider |
294 |
Event::Lib and EV and the following set-up: |
295 |
|
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The event loop is running and has just invoked one of your callback |
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at time=500 (assume no other callbacks delay processing). In your |
298 |
callback, you wait a second by executing "sleep 1" (blocking the |
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process for a second) and then (at time=501) you create a relative |
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timer that fires after three seconds. |
301 |
|
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With Event::Lib, "AnyEvent->time" and "AnyEvent->now" will both |
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return 501, because that is the current time, and the timer will be |
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scheduled to fire at time=504 (501 + 3). |
305 |
|
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With EV, "AnyEvent->time" returns 501 (as that is the current time), |
307 |
but "AnyEvent->now" returns 500, as that is the time the last event |
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processing phase started. With EV, your timer gets scheduled to run |
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at time=503 (500 + 3). |
310 |
|
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In one sense, Event::Lib is more exact, as it uses the current time |
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regardless of any delays introduced by event processing. However, |
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most callbacks do not expect large delays in processing, so this |
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causes a higher drift (and a lot more system calls to get the |
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current time). |
316 |
|
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In another sense, EV is more exact, as your timer will be scheduled |
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at the same time, regardless of how long event processing actually |
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took. |
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|
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In either case, if you care (and in most cases, you don't), then you |
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can get whatever behaviour you want with any event loop, by taking |
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the difference between "AnyEvent->time" and "AnyEvent->now" into |
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account. |
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|
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AnyEvent->now_update |
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Some event loops (such as EV or AnyEvent::Impl::Perl) cache the |
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current time for each loop iteration (see the discussion of |
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AnyEvent->now, above). |
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|
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When a callback runs for a long time (or when the process sleeps), |
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then this "current" time will differ substantially from the real |
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time, which might affect timers and time-outs. |
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|
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When this is the case, you can call this method, which will update |
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the event loop's idea of "current time". |
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|
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Note that updating the time *might* cause some events to be handled. |
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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* in uppercase and without any "SIG" prefix, "cb" is the Perl |
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callback to be invoked whenever a signal occurs. |
344 |
|
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Although the callback might get passed parameters, their value and |
346 |
presence is undefined and you cannot rely on them. Portable AnyEvent |
347 |
callbacks cannot use arguments passed to signal watcher callbacks. |
348 |
|
349 |
Multiple signal occurrences can be clumped together into one callback |
350 |
invocation, and callback invocation will be synchronous. Synchronous |
351 |
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, and AnyEvent will ensure that signals |
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will not interrupt your program at bad times. |
357 |
|
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This watcher might use %SIG (depending on the event loop used), so |
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programs overwriting those signals directly will likely not work |
360 |
correctly. |
361 |
|
362 |
Also note that many event loops (e.g. Glib, Tk, Qt, IO::Async) do not |
363 |
support attaching callbacks to signals, which is a pity, as you cannot |
364 |
do race-free signal handling in perl. AnyEvent will try to do it's best, |
365 |
but in some cases, signals will be delayed. The maximum time a signal |
366 |
might be delayed is specified in $AnyEvent::MAX_SIGNAL_LATENCY (default: |
367 |
10 seconds). This variable can be changed only before the first signal |
368 |
watcher is created, and should be left alone otherwise. Higher values |
369 |
will cause fewer spurious wake-ups, which is better for power and CPU |
370 |
saving. All these problems can be avoided by installing the optional |
371 |
Async::Interrupt module. |
372 |
|
373 |
Example: exit on SIGINT |
374 |
|
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my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 }); |
376 |
|
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CHILD PROCESS WATCHERS |
378 |
You can also watch on a child process exit and catch its exit status. |
379 |
|
380 |
The child process is specified by the "pid" argument (if set to 0, it |
381 |
watches for any child process exit). The watcher will triggered only |
382 |
when the child process has finished and an exit status is available, not |
383 |
on any trace events (stopped/continued). |
384 |
|
385 |
The callback will be called with the pid and exit status (as returned by |
386 |
waitpid), so unlike other watcher types, you *can* rely on child watcher |
387 |
callback arguments. |
388 |
|
389 |
This watcher type works by installing a signal handler for "SIGCHLD", |
390 |
and since it cannot be shared, nothing else should use SIGCHLD or reap |
391 |
random child processes (waiting for specific child processes, e.g. |
392 |
inside "system", is just fine). |
393 |
|
394 |
There is a slight catch to child watchers, however: you usually start |
395 |
them *after* the child process was created, and this means the process |
396 |
could have exited already (and no SIGCHLD will be sent anymore). |
397 |
|
398 |
Not all event models handle this correctly (neither POE nor IO::Async |
399 |
do, see their AnyEvent::Impl manpages for details), but even for event |
400 |
models that *do* handle this correctly, they usually need to be loaded |
401 |
before the process exits (i.e. before you fork in the first place). |
402 |
AnyEvent's pure perl event loop handles all cases correctly regardless |
403 |
of when you start the watcher. |
404 |
|
405 |
This means you cannot create a child watcher as the very first thing in |
406 |
an AnyEvent program, you *have* to create at least one watcher before |
407 |
you "fork" the child (alternatively, you can call "AnyEvent::detect"). |
408 |
|
409 |
As most event loops do not support waiting for child events, they will |
410 |
be emulated by AnyEvent in most cases, in which the latency and race |
411 |
problems mentioned in the description of signal watchers apply. |
412 |
|
413 |
Example: fork a process and wait for it |
414 |
|
415 |
my $done = AnyEvent->condvar; |
416 |
|
417 |
my $pid = fork or exit 5; |
418 |
|
419 |
my $w = AnyEvent->child ( |
420 |
pid => $pid, |
421 |
cb => sub { |
422 |
my ($pid, $status) = @_; |
423 |
warn "pid $pid exited with status $status"; |
424 |
$done->send; |
425 |
}, |
426 |
); |
427 |
|
428 |
# do something else, then wait for process exit |
429 |
$done->recv; |
430 |
|
431 |
IDLE WATCHERS |
432 |
Sometimes there is a need to do something, but it is not so important to |
433 |
do it instantly, but only when there is nothing better to do. This |
434 |
"nothing better to do" is usually defined to be "no other events need |
435 |
attention by the event loop". |
436 |
|
437 |
Idle watchers ideally get invoked when the event loop has nothing better |
438 |
to do, just before it would block the process to wait for new events. |
439 |
Instead of blocking, the idle watcher is invoked. |
440 |
|
441 |
Most event loops unfortunately do not really support idle watchers (only |
442 |
EV, Event and Glib do it in a usable fashion) - for the rest, AnyEvent |
443 |
will simply call the callback "from time to time". |
444 |
|
445 |
Example: read lines from STDIN, but only process them when the program |
446 |
is otherwise idle: |
447 |
|
448 |
my @lines; # read data |
449 |
my $idle_w; |
450 |
my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub { |
451 |
push @lines, scalar <STDIN>; |
452 |
|
453 |
# start an idle watcher, if not already done |
454 |
$idle_w ||= AnyEvent->idle (cb => sub { |
455 |
# handle only one line, when there are lines left |
456 |
if (my $line = shift @lines) { |
457 |
print "handled when idle: $line"; |
458 |
} else { |
459 |
# otherwise disable the idle watcher again |
460 |
undef $idle_w; |
461 |
} |
462 |
}); |
463 |
}); |
464 |
|
465 |
CONDITION VARIABLES |
466 |
If you are familiar with some event loops you will know that all of them |
467 |
require you to run some blocking "loop", "run" or similar function that |
468 |
will actively watch for new events and call your callbacks. |
469 |
|
470 |
AnyEvent is slightly different: it expects somebody else to run the |
471 |
event loop and will only block when necessary (usually when told by the |
472 |
user). |
473 |
|
474 |
The instrument to do that is called a "condition variable", so called |
475 |
because they represent a condition that must become true. |
476 |
|
477 |
Now is probably a good time to look at the examples further below. |
478 |
|
479 |
Condition variables can be created by calling the "AnyEvent->condvar" |
480 |
method, usually without arguments. The only argument pair allowed is |
481 |
"cb", which specifies a callback to be called when the condition |
482 |
variable becomes true, with the condition variable as the first argument |
483 |
(but not the results). |
484 |
|
485 |
After creation, the condition variable is "false" until it becomes |
486 |
"true" by calling the "send" method (or calling the condition variable |
487 |
as if it were a callback, read about the caveats in the description for |
488 |
the "->send" method). |
489 |
|
490 |
Condition variables are similar to callbacks, except that you can |
491 |
optionally wait for them. They can also be called merge points - points |
492 |
in time where multiple outstanding events have been processed. And yet |
493 |
another way to call them is transactions - each condition variable can |
494 |
be used to represent a transaction, which finishes at some point and |
495 |
delivers a result. |
496 |
|
497 |
Condition variables are very useful to signal that something has |
498 |
finished, for example, if you write a module that does asynchronous http |
499 |
requests, then a condition variable would be the ideal candidate to |
500 |
signal the availability of results. The user can either act when the |
501 |
callback is called or can synchronously "->recv" for the results. |
502 |
|
503 |
You can also use them to simulate traditional event loops - for example, |
504 |
you can block your main program until an event occurs - for example, you |
505 |
could "->recv" in your main program until the user clicks the Quit |
506 |
button of your app, which would "->send" the "quit" event. |
507 |
|
508 |
Note that condition variables recurse into the event loop - if you have |
509 |
two pieces of code that call "->recv" in a round-robin fashion, you |
510 |
lose. Therefore, condition variables are good to export to your caller, |
511 |
but you should avoid making a blocking wait yourself, at least in |
512 |
callbacks, as this asks for trouble. |
513 |
|
514 |
Condition variables are represented by hash refs in perl, and the keys |
515 |
used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy |
516 |
(it is often useful to build your own transaction class on top of |
517 |
AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call |
518 |
it's "new" method in your own "new" method. |
519 |
|
520 |
There are two "sides" to a condition variable - the "producer side" |
521 |
which eventually calls "-> send", and the "consumer side", which waits |
522 |
for the send to occur. |
523 |
|
524 |
Example: wait for a timer. |
525 |
|
526 |
# wait till the result is ready |
527 |
my $result_ready = AnyEvent->condvar; |
528 |
|
529 |
# do something such as adding a timer |
530 |
# or socket watcher the calls $result_ready->send |
531 |
# when the "result" is ready. |
532 |
# in this case, we simply use a timer: |
533 |
my $w = AnyEvent->timer ( |
534 |
after => 1, |
535 |
cb => sub { $result_ready->send }, |
536 |
); |
537 |
|
538 |
# this "blocks" (while handling events) till the callback |
539 |
# calls -<send |
540 |
$result_ready->recv; |
541 |
|
542 |
Example: wait for a timer, but take advantage of the fact that condition |
543 |
variables are also callable directly. |
544 |
|
545 |
my $done = AnyEvent->condvar; |
546 |
my $delay = AnyEvent->timer (after => 5, cb => $done); |
547 |
$done->recv; |
548 |
|
549 |
Example: Imagine an API that returns a condvar and doesn't support |
550 |
callbacks. This is how you make a synchronous call, for example from the |
551 |
main program: |
552 |
|
553 |
use AnyEvent::CouchDB; |
554 |
|
555 |
... |
556 |
|
557 |
my @info = $couchdb->info->recv; |
558 |
|
559 |
And this is how you would just set a callback to be called whenever the |
560 |
results are available: |
561 |
|
562 |
$couchdb->info->cb (sub { |
563 |
my @info = $_[0]->recv; |
564 |
}); |
565 |
|
566 |
METHODS FOR PRODUCERS |
567 |
These methods should only be used by the producing side, i.e. the |
568 |
code/module that eventually sends the signal. Note that it is also the |
569 |
producer side which creates the condvar in most cases, but it isn't |
570 |
uncommon for the consumer to create it as well. |
571 |
|
572 |
$cv->send (...) |
573 |
Flag the condition as ready - a running "->recv" and all further |
574 |
calls to "recv" will (eventually) return after this method has been |
575 |
called. If nobody is waiting the send will be remembered. |
576 |
|
577 |
If a callback has been set on the condition variable, it is called |
578 |
immediately from within send. |
579 |
|
580 |
Any arguments passed to the "send" call will be returned by all |
581 |
future "->recv" calls. |
582 |
|
583 |
Condition variables are overloaded so one can call them directly (as |
584 |
if they were a code reference). Calling them directly is the same as |
585 |
calling "send". |
586 |
|
587 |
$cv->croak ($error) |
588 |
Similar to send, but causes all call's to "->recv" to invoke |
589 |
"Carp::croak" with the given error message/object/scalar. |
590 |
|
591 |
This can be used to signal any errors to the condition variable |
592 |
user/consumer. Doing it this way instead of calling "croak" directly |
593 |
delays the error detetcion, but has the overwhelmign advantage that |
594 |
it diagnoses the error at the place where the result is expected, |
595 |
and not deep in some event clalback without connection to the actual |
596 |
code causing the problem. |
597 |
|
598 |
$cv->begin ([group callback]) |
599 |
$cv->end |
600 |
These two methods can be used to combine many transactions/events |
601 |
into one. For example, a function that pings many hosts in parallel |
602 |
might want to use a condition variable for the whole process. |
603 |
|
604 |
Every call to "->begin" will increment a counter, and every call to |
605 |
"->end" will decrement it. If the counter reaches 0 in "->end", the |
606 |
(last) callback passed to "begin" will be executed. That callback is |
607 |
*supposed* to call "->send", but that is not required. If no |
608 |
callback was set, "send" will be called without any arguments. |
609 |
|
610 |
You can think of "$cv->send" giving you an OR condition (one call |
611 |
sends), while "$cv->begin" and "$cv->end" giving you an AND |
612 |
condition (all "begin" calls must be "end"'ed before the condvar |
613 |
sends). |
614 |
|
615 |
Let's start with a simple example: you have two I/O watchers (for |
616 |
example, STDOUT and STDERR for a program), and you want to wait for |
617 |
both streams to close before activating a condvar: |
618 |
|
619 |
my $cv = AnyEvent->condvar; |
620 |
|
621 |
$cv->begin; # first watcher |
622 |
my $w1 = AnyEvent->io (fh => $fh1, cb => sub { |
623 |
defined sysread $fh1, my $buf, 4096 |
624 |
or $cv->end; |
625 |
}); |
626 |
|
627 |
$cv->begin; # second watcher |
628 |
my $w2 = AnyEvent->io (fh => $fh2, cb => sub { |
629 |
defined sysread $fh2, my $buf, 4096 |
630 |
or $cv->end; |
631 |
}); |
632 |
|
633 |
$cv->recv; |
634 |
|
635 |
This works because for every event source (EOF on file handle), |
636 |
there is one call to "begin", so the condvar waits for all calls to |
637 |
"end" before sending. |
638 |
|
639 |
The ping example mentioned above is slightly more complicated, as |
640 |
the there are results to be passwd back, and the number of tasks |
641 |
that are begung can potentially be zero: |
642 |
|
643 |
my $cv = AnyEvent->condvar; |
644 |
|
645 |
my %result; |
646 |
$cv->begin (sub { $cv->send (\%result) }); |
647 |
|
648 |
for my $host (@list_of_hosts) { |
649 |
$cv->begin; |
650 |
ping_host_then_call_callback $host, sub { |
651 |
$result{$host} = ...; |
652 |
$cv->end; |
653 |
}; |
654 |
} |
655 |
|
656 |
$cv->end; |
657 |
|
658 |
This code fragment supposedly pings a number of hosts and calls |
659 |
"send" after results for all then have have been gathered - in any |
660 |
order. To achieve this, the code issues a call to "begin" when it |
661 |
starts each ping request and calls "end" when it has received some |
662 |
result for it. Since "begin" and "end" only maintain a counter, the |
663 |
order in which results arrive is not relevant. |
664 |
|
665 |
There is an additional bracketing call to "begin" and "end" outside |
666 |
the loop, which serves two important purposes: first, it sets the |
667 |
callback to be called once the counter reaches 0, and second, it |
668 |
ensures that "send" is called even when "no" hosts are being pinged |
669 |
(the loop doesn't execute once). |
670 |
|
671 |
This is the general pattern when you "fan out" into multiple (but |
672 |
potentially none) subrequests: use an outer "begin"/"end" pair to |
673 |
set the callback and ensure "end" is called at least once, and then, |
674 |
for each subrequest you start, call "begin" and for each subrequest |
675 |
you finish, call "end". |
676 |
|
677 |
METHODS FOR CONSUMERS |
678 |
These methods should only be used by the consuming side, i.e. the code |
679 |
awaits the condition. |
680 |
|
681 |
$cv->recv |
682 |
Wait (blocking if necessary) until the "->send" or "->croak" methods |
683 |
have been called on c<$cv>, while servicing other watchers normally. |
684 |
|
685 |
You can only wait once on a condition - additional calls are valid |
686 |
but will return immediately. |
687 |
|
688 |
If an error condition has been set by calling "->croak", then this |
689 |
function will call "croak". |
690 |
|
691 |
In list context, all parameters passed to "send" will be returned, |
692 |
in scalar context only the first one will be returned. |
693 |
|
694 |
Note that doing a blocking wait in a callback is not supported by |
695 |
any event loop, that is, recursive invocation of a blocking "->recv" |
696 |
is not allowed, and the "recv" call will "croak" if such a condition |
697 |
is detected. This condition can be slightly loosened by using |
698 |
Coro::AnyEvent, which allows you to do a blocking "->recv" from any |
699 |
thread that doesn't run the event loop itself. |
700 |
|
701 |
Not all event models support a blocking wait - some die in that case |
702 |
(programs might want to do that to stay interactive), so *if you are |
703 |
using this from a module, never require a blocking wait*. Instead, |
704 |
let the caller decide whether the call will block or not (for |
705 |
example, by coupling condition variables with some kind of request |
706 |
results and supporting callbacks so the caller knows that getting |
707 |
the result will not block, while still supporting blocking waits if |
708 |
the caller so desires). |
709 |
|
710 |
You can ensure that "-recv" never blocks by setting a callback and |
711 |
only calling "->recv" from within that callback (or at a later |
712 |
time). This will work even when the event loop does not support |
713 |
blocking waits otherwise. |
714 |
|
715 |
$bool = $cv->ready |
716 |
Returns true when the condition is "true", i.e. whether "send" or |
717 |
"croak" have been called. |
718 |
|
719 |
$cb = $cv->cb ($cb->($cv)) |
720 |
This is a mutator function that returns the callback set and |
721 |
optionally replaces it before doing so. |
722 |
|
723 |
The callback will be called when the condition becomes "true", i.e. |
724 |
when "send" or "croak" are called, with the only argument being the |
725 |
condition variable itself. Calling "recv" inside the callback or at |
726 |
any later time is guaranteed not to block. |
727 |
|
728 |
SUPPORTED EVENT LOOPS/BACKENDS |
729 |
The available backend classes are (every class has its own manpage): |
730 |
|
731 |
Backends that are autoprobed when no other event loop can be found. |
732 |
EV is the preferred backend when no other event loop seems to be in |
733 |
use. If EV is not installed, then AnyEvent will try Event, and, |
734 |
failing that, will fall back to its own pure-perl implementation, |
735 |
which is available everywhere as it comes with AnyEvent itself. |
736 |
|
737 |
AnyEvent::Impl::EV based on EV (interface to libev, best choice). |
738 |
AnyEvent::Impl::Event based on Event, very stable, few glitches. |
739 |
AnyEvent::Impl::Perl pure-perl implementation, fast and portable. |
740 |
|
741 |
Backends that are transparently being picked up when they are used. |
742 |
These will be used when they are currently loaded when the first |
743 |
watcher is created, in which case it is assumed that the application |
744 |
is using them. This means that AnyEvent will automatically pick the |
745 |
right backend when the main program loads an event module before |
746 |
anything starts to create watchers. Nothing special needs to be done |
747 |
by the main program. |
748 |
|
749 |
AnyEvent::Impl::Glib based on Glib, slow but very stable. |
750 |
AnyEvent::Impl::Tk based on Tk, very broken. |
751 |
AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse. |
752 |
AnyEvent::Impl::POE based on POE, very slow, some limitations. |
753 |
|
754 |
Backends with special needs. |
755 |
Qt requires the Qt::Application to be instantiated first, but will |
756 |
otherwise be picked up automatically. As long as the main program |
757 |
instantiates the application before any AnyEvent watchers are |
758 |
created, everything should just work. |
759 |
|
760 |
AnyEvent::Impl::Qt based on Qt. |
761 |
|
762 |
Support for IO::Async can only be partial, as it is too broken and |
763 |
architecturally limited to even support the AnyEvent API. It also is |
764 |
the only event loop that needs the loop to be set explicitly, so it |
765 |
can only be used by a main program knowing about AnyEvent. See |
766 |
AnyEvent::Impl::Async for the gory details. |
767 |
|
768 |
AnyEvent::Impl::IOAsync based on IO::Async, cannot be autoprobed. |
769 |
|
770 |
Event loops that are indirectly supported via other backends. |
771 |
Some event loops can be supported via other modules: |
772 |
|
773 |
There is no direct support for WxWidgets (Wx) or Prima. |
774 |
|
775 |
WxWidgets has no support for watching file handles. However, you can |
776 |
use WxWidgets through the POE adaptor, as POE has a Wx backend that |
777 |
simply polls 20 times per second, which was considered to be too |
778 |
horrible to even consider for AnyEvent. |
779 |
|
780 |
Prima is not supported as nobody seems to be using it, but it has a |
781 |
POE backend, so it can be supported through POE. |
782 |
|
783 |
AnyEvent knows about both Prima and Wx, however, and will try to |
784 |
load POE when detecting them, in the hope that POE will pick them |
785 |
up, in which case everything will be automatic. |
786 |
|
787 |
GLOBAL VARIABLES AND FUNCTIONS |
788 |
These are not normally required to use AnyEvent, but can be useful to |
789 |
write AnyEvent extension modules. |
790 |
|
791 |
$AnyEvent::MODEL |
792 |
Contains "undef" until the first watcher is being created, before |
793 |
the backend has been autodetected. |
794 |
|
795 |
Afterwards it contains the event model that is being used, which is |
796 |
the name of the Perl class implementing the model. This class is |
797 |
usually one of the "AnyEvent::Impl:xxx" modules, but can be any |
798 |
other class in the case AnyEvent has been extended at runtime (e.g. |
799 |
in *rxvt-unicode* it will be "urxvt::anyevent"). |
800 |
|
801 |
AnyEvent::detect |
802 |
Returns $AnyEvent::MODEL, forcing autodetection of the event model |
803 |
if necessary. You should only call this function right before you |
804 |
would have created an AnyEvent watcher anyway, that is, as late as |
805 |
possible at runtime, and not e.g. while initialising of your module. |
806 |
|
807 |
If you need to do some initialisation before AnyEvent watchers are |
808 |
created, use "post_detect". |
809 |
|
810 |
$guard = AnyEvent::post_detect { BLOCK } |
811 |
Arranges for the code block to be executed as soon as the event |
812 |
model is autodetected (or immediately if this has already happened). |
813 |
|
814 |
The block will be executed *after* the actual backend has been |
815 |
detected ($AnyEvent::MODEL is set), but *before* any watchers have |
816 |
been created, so it is possible to e.g. patch @AnyEvent::ISA or do |
817 |
other initialisations - see the sources of AnyEvent::Strict or |
818 |
AnyEvent::AIO to see how this is used. |
819 |
|
820 |
The most common usage is to create some global watchers, without |
821 |
forcing event module detection too early, for example, AnyEvent::AIO |
822 |
creates and installs the global IO::AIO watcher in a "post_detect" |
823 |
block to avoid autodetecting the event module at load time. |
824 |
|
825 |
If called in scalar or list context, then it creates and returns an |
826 |
object that automatically removes the callback again when it is |
827 |
destroyed. See Coro::BDB for a case where this is useful. |
828 |
|
829 |
@AnyEvent::post_detect |
830 |
If there are any code references in this array (you can "push" to it |
831 |
before or after loading AnyEvent), then they will called directly |
832 |
after the event loop has been chosen. |
833 |
|
834 |
You should check $AnyEvent::MODEL before adding to this array, |
835 |
though: if it is defined then the event loop has already been |
836 |
detected, and the array will be ignored. |
837 |
|
838 |
Best use "AnyEvent::post_detect { BLOCK }" when your application |
839 |
allows it,as it takes care of these details. |
840 |
|
841 |
This variable is mainly useful for modules that can do something |
842 |
useful when AnyEvent is used and thus want to know when it is |
843 |
initialised, but do not need to even load it by default. This array |
844 |
provides the means to hook into AnyEvent passively, without loading |
845 |
it. |
846 |
|
847 |
WHAT TO DO IN A MODULE |
848 |
As a module author, you should "use AnyEvent" and call AnyEvent methods |
849 |
freely, but you should not load a specific event module or rely on it. |
850 |
|
851 |
Be careful when you create watchers in the module body - AnyEvent will |
852 |
decide which event module to use as soon as the first method is called, |
853 |
so by calling AnyEvent in your module body you force the user of your |
854 |
module to load the event module first. |
855 |
|
856 |
Never call "->recv" on a condition variable unless you *know* that the |
857 |
"->send" method has been called on it already. This is because it will |
858 |
stall the whole program, and the whole point of using events is to stay |
859 |
interactive. |
860 |
|
861 |
It is fine, however, to call "->recv" when the user of your module |
862 |
requests it (i.e. if you create a http request object ad have a method |
863 |
called "results" that returns the results, it should call "->recv" |
864 |
freely, as the user of your module knows what she is doing. always). |
865 |
|
866 |
WHAT TO DO IN THE MAIN PROGRAM |
867 |
There will always be a single main program - the only place that should |
868 |
dictate which event model to use. |
869 |
|
870 |
If it doesn't care, it can just "use AnyEvent" and use it itself, or not |
871 |
do anything special (it does not need to be event-based) and let |
872 |
AnyEvent decide which implementation to chose if some module relies on |
873 |
it. |
874 |
|
875 |
If the main program relies on a specific event model - for example, in |
876 |
Gtk2 programs you have to rely on the Glib module - you should load the |
877 |
event module before loading AnyEvent or any module that uses it: |
878 |
generally speaking, you should load it as early as possible. The reason |
879 |
is that modules might create watchers when they are loaded, and AnyEvent |
880 |
will decide on the event model to use as soon as it creates watchers, |
881 |
and it might chose the wrong one unless you load the correct one |
882 |
yourself. |
883 |
|
884 |
You can chose to use a pure-perl implementation by loading the |
885 |
"AnyEvent::Impl::Perl" module, which gives you similar behaviour |
886 |
everywhere, but letting AnyEvent chose the model is generally better. |
887 |
|
888 |
MAINLOOP EMULATION |
889 |
Sometimes (often for short test scripts, or even standalone programs who |
890 |
only want to use AnyEvent), you do not want to run a specific event |
891 |
loop. |
892 |
|
893 |
In that case, you can use a condition variable like this: |
894 |
|
895 |
AnyEvent->condvar->recv; |
896 |
|
897 |
This has the effect of entering the event loop and looping forever. |
898 |
|
899 |
Note that usually your program has some exit condition, in which case it |
900 |
is better to use the "traditional" approach of storing a condition |
901 |
variable somewhere, waiting for it, and sending it when the program |
902 |
should exit cleanly. |
903 |
|
904 |
OTHER MODULES |
905 |
The following is a non-exhaustive list of additional modules that use |
906 |
AnyEvent as a client and can therefore be mixed easily with other |
907 |
AnyEvent modules and other event loops in the same program. Some of the |
908 |
modules come with AnyEvent, most are available via CPAN. |
909 |
|
910 |
AnyEvent::Util |
911 |
Contains various utility functions that replace often-used but |
912 |
blocking functions such as "inet_aton" by event-/callback-based |
913 |
versions. |
914 |
|
915 |
AnyEvent::Socket |
916 |
Provides various utility functions for (internet protocol) sockets, |
917 |
addresses and name resolution. Also functions to create non-blocking |
918 |
tcp connections or tcp servers, with IPv6 and SRV record support and |
919 |
more. |
920 |
|
921 |
AnyEvent::Handle |
922 |
Provide read and write buffers, manages watchers for reads and |
923 |
writes, supports raw and formatted I/O, I/O queued and fully |
924 |
transparent and non-blocking SSL/TLS (via AnyEvent::TLS. |
925 |
|
926 |
AnyEvent::DNS |
927 |
Provides rich asynchronous DNS resolver capabilities. |
928 |
|
929 |
AnyEvent::HTTP |
930 |
A simple-to-use HTTP library that is capable of making a lot of |
931 |
concurrent HTTP requests. |
932 |
|
933 |
AnyEvent::HTTPD |
934 |
Provides a simple web application server framework. |
935 |
|
936 |
AnyEvent::FastPing |
937 |
The fastest ping in the west. |
938 |
|
939 |
AnyEvent::DBI |
940 |
Executes DBI requests asynchronously in a proxy process. |
941 |
|
942 |
AnyEvent::AIO |
943 |
Truly asynchronous I/O, should be in the toolbox of every event |
944 |
programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent |
945 |
together. |
946 |
|
947 |
AnyEvent::BDB |
948 |
Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently |
949 |
fuses BDB and AnyEvent together. |
950 |
|
951 |
AnyEvent::GPSD |
952 |
A non-blocking interface to gpsd, a daemon delivering GPS |
953 |
information. |
954 |
|
955 |
AnyEvent::IRC |
956 |
AnyEvent based IRC client module family (replacing the older |
957 |
Net::IRC3). |
958 |
|
959 |
AnyEvent::XMPP |
960 |
AnyEvent based XMPP (Jabber protocol) module family (replacing the |
961 |
older Net::XMPP2>. |
962 |
|
963 |
AnyEvent::IGS |
964 |
A non-blocking interface to the Internet Go Server protocol (used by |
965 |
App::IGS). |
966 |
|
967 |
Net::FCP |
968 |
AnyEvent-based implementation of the Freenet Client Protocol, |
969 |
birthplace of AnyEvent. |
970 |
|
971 |
Event::ExecFlow |
972 |
High level API for event-based execution flow control. |
973 |
|
974 |
Coro |
975 |
Has special support for AnyEvent via Coro::AnyEvent. |
976 |
|
977 |
ERROR AND EXCEPTION HANDLING |
978 |
In general, AnyEvent does not do any error handling - it relies on the |
979 |
caller to do that if required. The AnyEvent::Strict module (see also the |
980 |
"PERL_ANYEVENT_STRICT" environment variable, below) provides strict |
981 |
checking of all AnyEvent methods, however, which is highly useful during |
982 |
development. |
983 |
|
984 |
As for exception handling (i.e. runtime errors and exceptions thrown |
985 |
while executing a callback), this is not only highly event-loop |
986 |
specific, but also not in any way wrapped by this module, as this is the |
987 |
job of the main program. |
988 |
|
989 |
The pure perl event loop simply re-throws the exception (usually within |
990 |
"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()", |
991 |
Glib uses "install_exception_handler" and so on. |
992 |
|
993 |
ENVIRONMENT VARIABLES |
994 |
The following environment variables are used by this module or its |
995 |
submodules. |
996 |
|
997 |
Note that AnyEvent will remove *all* environment variables starting with |
998 |
"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is |
999 |
enabled. |
1000 |
|
1001 |
"PERL_ANYEVENT_VERBOSE" |
1002 |
By default, AnyEvent will be completely silent except in fatal |
1003 |
conditions. You can set this environment variable to make AnyEvent |
1004 |
more talkative. |
1005 |
|
1006 |
When set to 1 or higher, causes AnyEvent to warn about unexpected |
1007 |
conditions, such as not being able to load the event model specified |
1008 |
by "PERL_ANYEVENT_MODEL". |
1009 |
|
1010 |
When set to 2 or higher, cause AnyEvent to report to STDERR which |
1011 |
event model it chooses. |
1012 |
|
1013 |
When set to 8 or higher, then AnyEvent will report extra information |
1014 |
on which optional modules it loads and how it implements certain |
1015 |
features. |
1016 |
|
1017 |
"PERL_ANYEVENT_STRICT" |
1018 |
AnyEvent does not do much argument checking by default, as thorough |
1019 |
argument checking is very costly. Setting this variable to a true |
1020 |
value will cause AnyEvent to load "AnyEvent::Strict" and then to |
1021 |
thoroughly check the arguments passed to most method calls. If it |
1022 |
finds any problems, it will croak. |
1023 |
|
1024 |
In other words, enables "strict" mode. |
1025 |
|
1026 |
Unlike "use strict" (or it's modern cousin, "use common::sense", it |
1027 |
is definitely recommended to keep it off in production. Keeping |
1028 |
"PERL_ANYEVENT_STRICT=1" in your environment while developing |
1029 |
programs can be very useful, however. |
1030 |
|
1031 |
"PERL_ANYEVENT_MODEL" |
1032 |
This can be used to specify the event model to be used by AnyEvent, |
1033 |
before auto detection and -probing kicks in. It must be a string |
1034 |
consisting entirely of ASCII letters. The string "AnyEvent::Impl::" |
1035 |
gets prepended and the resulting module name is loaded and if the |
1036 |
load was successful, used as event model. If it fails to load |
1037 |
AnyEvent will proceed with auto detection and -probing. |
1038 |
|
1039 |
This functionality might change in future versions. |
1040 |
|
1041 |
For example, to force the pure perl model (AnyEvent::Impl::Perl) you |
1042 |
could start your program like this: |
1043 |
|
1044 |
PERL_ANYEVENT_MODEL=Perl perl ... |
1045 |
|
1046 |
"PERL_ANYEVENT_PROTOCOLS" |
1047 |
Used by both AnyEvent::DNS and AnyEvent::Socket to determine |
1048 |
preferences for IPv4 or IPv6. The default is unspecified (and might |
1049 |
change, or be the result of auto probing). |
1050 |
|
1051 |
Must be set to a comma-separated list of protocols or address |
1052 |
families, current supported: "ipv4" and "ipv6". Only protocols |
1053 |
mentioned will be used, and preference will be given to protocols |
1054 |
mentioned earlier in the list. |
1055 |
|
1056 |
This variable can effectively be used for denial-of-service attacks |
1057 |
against local programs (e.g. when setuid), although the impact is |
1058 |
likely small, as the program has to handle conenction and other |
1059 |
failures anyways. |
1060 |
|
1061 |
Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over |
1062 |
IPv6, but support both and try to use both. |
1063 |
"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to |
1064 |
resolve or contact IPv6 addresses. |
1065 |
"PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but |
1066 |
prefer IPv6 over IPv4. |
1067 |
|
1068 |
"PERL_ANYEVENT_EDNS0" |
1069 |
Used by AnyEvent::DNS to decide whether to use the EDNS0 extension |
1070 |
for DNS. This extension is generally useful to reduce DNS traffic, |
1071 |
but some (broken) firewalls drop such DNS packets, which is why it |
1072 |
is off by default. |
1073 |
|
1074 |
Setting this variable to 1 will cause AnyEvent::DNS to announce |
1075 |
EDNS0 in its DNS requests. |
1076 |
|
1077 |
"PERL_ANYEVENT_MAX_FORKS" |
1078 |
The maximum number of child processes that |
1079 |
"AnyEvent::Util::fork_call" will create in parallel. |
1080 |
|
1081 |
"PERL_ANYEVENT_MAX_OUTSTANDING_DNS" |
1082 |
The default value for the "max_outstanding" parameter for the |
1083 |
default DNS resolver - this is the maximum number of parallel DNS |
1084 |
requests that are sent to the DNS server. |
1085 |
|
1086 |
"PERL_ANYEVENT_RESOLV_CONF" |
1087 |
The file to use instead of /etc/resolv.conf (or OS-specific |
1088 |
configuration) in the default resolver. When set to the empty |
1089 |
string, no default config will be used. |
1090 |
|
1091 |
"PERL_ANYEVENT_CA_FILE", "PERL_ANYEVENT_CA_PATH". |
1092 |
When neither "ca_file" nor "ca_path" was specified during |
1093 |
AnyEvent::TLS context creation, and either of these environment |
1094 |
variables exist, they will be used to specify CA certificate |
1095 |
locations instead of a system-dependent default. |
1096 |
|
1097 |
"PERL_ANYEVENT_AVOID_GUARD" and "PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT" |
1098 |
When these are set to 1, then the respective modules are not loaded. |
1099 |
Mostly good for testing AnyEvent itself. |
1100 |
|
1101 |
SUPPLYING YOUR OWN EVENT MODEL INTERFACE |
1102 |
This is an advanced topic that you do not normally need to use AnyEvent |
1103 |
in a module. This section is only of use to event loop authors who want |
1104 |
to provide AnyEvent compatibility. |
1105 |
|
1106 |
If you need to support another event library which isn't directly |
1107 |
supported by AnyEvent, you can supply your own interface to it by |
1108 |
pushing, before the first watcher gets created, the package name of the |
1109 |
event module and the package name of the interface to use onto |
1110 |
@AnyEvent::REGISTRY. You can do that before and even without loading |
1111 |
AnyEvent, so it is reasonably cheap. |
1112 |
|
1113 |
Example: |
1114 |
|
1115 |
push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::]; |
1116 |
|
1117 |
This tells AnyEvent to (literally) use the "urxvt::anyevent::" |
1118 |
package/class when it finds the "urxvt" package/module is already |
1119 |
loaded. |
1120 |
|
1121 |
When AnyEvent is loaded and asked to find a suitable event model, it |
1122 |
will first check for the presence of urxvt by trying to "use" the |
1123 |
"urxvt::anyevent" module. |
1124 |
|
1125 |
The class should provide implementations for all watcher types. See |
1126 |
AnyEvent::Impl::EV (source code), AnyEvent::Impl::Glib (Source code) and |
1127 |
so on for actual examples. Use "perldoc -m AnyEvent::Impl::Glib" to see |
1128 |
the sources. |
1129 |
|
1130 |
If you don't provide "signal" and "child" watchers than AnyEvent will |
1131 |
provide suitable (hopefully) replacements. |
1132 |
|
1133 |
The above example isn't fictitious, the *rxvt-unicode* (a.k.a. urxvt) |
1134 |
terminal emulator uses the above line as-is. An interface isn't included |
1135 |
in AnyEvent because it doesn't make sense outside the embedded |
1136 |
interpreter inside *rxvt-unicode*, and it is updated and maintained as |
1137 |
part of the *rxvt-unicode* distribution. |
1138 |
|
1139 |
*rxvt-unicode* also cheats a bit by not providing blocking access to |
1140 |
condition variables: code blocking while waiting for a condition will |
1141 |
"die". This still works with most modules/usages, and blocking calls |
1142 |
must not be done in an interactive application, so it makes sense. |
1143 |
|
1144 |
EXAMPLE PROGRAM |
1145 |
The following program uses an I/O watcher to read data from STDIN, a |
1146 |
timer to display a message once per second, and a condition variable to |
1147 |
quit the program when the user enters quit: |
1148 |
|
1149 |
use AnyEvent; |
1150 |
|
1151 |
my $cv = AnyEvent->condvar; |
1152 |
|
1153 |
my $io_watcher = AnyEvent->io ( |
1154 |
fh => \*STDIN, |
1155 |
poll => 'r', |
1156 |
cb => sub { |
1157 |
warn "io event <$_[0]>\n"; # will always output <r> |
1158 |
chomp (my $input = <STDIN>); # read a line |
1159 |
warn "read: $input\n"; # output what has been read |
1160 |
$cv->send if $input =~ /^q/i; # quit program if /^q/i |
1161 |
}, |
1162 |
); |
1163 |
|
1164 |
my $time_watcher; # can only be used once |
1165 |
|
1166 |
sub new_timer { |
1167 |
$timer = AnyEvent->timer (after => 1, cb => sub { |
1168 |
warn "timeout\n"; # print 'timeout' about every second |
1169 |
&new_timer; # and restart the time |
1170 |
}); |
1171 |
} |
1172 |
|
1173 |
new_timer; # create first timer |
1174 |
|
1175 |
$cv->recv; # wait until user enters /^q/i |
1176 |
|
1177 |
REAL-WORLD EXAMPLE |
1178 |
Consider the Net::FCP module. It features (among others) the following |
1179 |
API calls, which are to freenet what HTTP GET requests are to http: |
1180 |
|
1181 |
my $data = $fcp->client_get ($url); # blocks |
1182 |
|
1183 |
my $transaction = $fcp->txn_client_get ($url); # does not block |
1184 |
$transaction->cb ( sub { ... } ); # set optional result callback |
1185 |
my $data = $transaction->result; # possibly blocks |
1186 |
|
1187 |
The "client_get" method works like "LWP::Simple::get": it requests the |
1188 |
given URL and waits till the data has arrived. It is defined to be: |
1189 |
|
1190 |
sub client_get { $_[0]->txn_client_get ($_[1])->result } |
1191 |
|
1192 |
And in fact is automatically generated. This is the blocking API of |
1193 |
Net::FCP, and it works as simple as in any other, similar, module. |
1194 |
|
1195 |
More complicated is "txn_client_get": It only creates a transaction |
1196 |
(completion, result, ...) object and initiates the transaction. |
1197 |
|
1198 |
my $txn = bless { }, Net::FCP::Txn::; |
1199 |
|
1200 |
It also creates a condition variable that is used to signal the |
1201 |
completion of the request: |
1202 |
|
1203 |
$txn->{finished} = AnyAvent->condvar; |
1204 |
|
1205 |
It then creates a socket in non-blocking mode. |
1206 |
|
1207 |
socket $txn->{fh}, ...; |
1208 |
fcntl $txn->{fh}, F_SETFL, O_NONBLOCK; |
1209 |
connect $txn->{fh}, ... |
1210 |
and !$!{EWOULDBLOCK} |
1211 |
and !$!{EINPROGRESS} |
1212 |
and Carp::croak "unable to connect: $!\n"; |
1213 |
|
1214 |
Then it creates a write-watcher which gets called whenever an error |
1215 |
occurs or the connection succeeds: |
1216 |
|
1217 |
$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'w', cb => sub { $txn->fh_ready_w }); |
1218 |
|
1219 |
And returns this transaction object. The "fh_ready_w" callback gets |
1220 |
called as soon as the event loop detects that the socket is ready for |
1221 |
writing. |
1222 |
|
1223 |
The "fh_ready_w" method makes the socket blocking again, writes the |
1224 |
request data and replaces the watcher by a read watcher (waiting for |
1225 |
reply data). The actual code is more complicated, but that doesn't |
1226 |
matter for this example: |
1227 |
|
1228 |
fcntl $txn->{fh}, F_SETFL, 0; |
1229 |
syswrite $txn->{fh}, $txn->{request} |
1230 |
or die "connection or write error"; |
1231 |
$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r }); |
1232 |
|
1233 |
Again, "fh_ready_r" waits till all data has arrived, and then stores the |
1234 |
result and signals any possible waiters that the request has finished: |
1235 |
|
1236 |
sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf}; |
1237 |
|
1238 |
if (end-of-file or data complete) { |
1239 |
$txn->{result} = $txn->{buf}; |
1240 |
$txn->{finished}->send; |
1241 |
$txb->{cb}->($txn) of $txn->{cb}; # also call callback |
1242 |
} |
1243 |
|
1244 |
The "result" method, finally, just waits for the finished signal (if the |
1245 |
request was already finished, it doesn't wait, of course, and returns |
1246 |
the data: |
1247 |
|
1248 |
$txn->{finished}->recv; |
1249 |
return $txn->{result}; |
1250 |
|
1251 |
The actual code goes further and collects all errors ("die"s, |
1252 |
exceptions) that occurred during request processing. The "result" method |
1253 |
detects whether an exception as thrown (it is stored inside the $txn |
1254 |
object) and just throws the exception, which means connection errors and |
1255 |
other problems get reported tot he code that tries to use the result, |
1256 |
not in a random callback. |
1257 |
|
1258 |
All of this enables the following usage styles: |
1259 |
|
1260 |
1. Blocking: |
1261 |
|
1262 |
my $data = $fcp->client_get ($url); |
1263 |
|
1264 |
2. Blocking, but running in parallel: |
1265 |
|
1266 |
my @datas = map $_->result, |
1267 |
map $fcp->txn_client_get ($_), |
1268 |
@urls; |
1269 |
|
1270 |
Both blocking examples work without the module user having to know |
1271 |
anything about events. |
1272 |
|
1273 |
3a. Event-based in a main program, using any supported event module: |
1274 |
|
1275 |
use EV; |
1276 |
|
1277 |
$fcp->txn_client_get ($url)->cb (sub { |
1278 |
my $txn = shift; |
1279 |
my $data = $txn->result; |
1280 |
... |
1281 |
}); |
1282 |
|
1283 |
EV::loop; |
1284 |
|
1285 |
3b. The module user could use AnyEvent, too: |
1286 |
|
1287 |
use AnyEvent; |
1288 |
|
1289 |
my $quit = AnyEvent->condvar; |
1290 |
|
1291 |
$fcp->txn_client_get ($url)->cb (sub { |
1292 |
... |
1293 |
$quit->send; |
1294 |
}); |
1295 |
|
1296 |
$quit->recv; |
1297 |
|
1298 |
BENCHMARKS |
1299 |
To give you an idea of the performance and overheads that AnyEvent adds |
1300 |
over the event loops themselves and to give you an impression of the |
1301 |
speed of various event loops I prepared some benchmarks. |
1302 |
|
1303 |
BENCHMARKING ANYEVENT OVERHEAD |
1304 |
Here is a benchmark of various supported event models used natively and |
1305 |
through AnyEvent. The benchmark creates a lot of timers (with a zero |
1306 |
timeout) and I/O watchers (watching STDOUT, a pty, to become writable, |
1307 |
which it is), lets them fire exactly once and destroys them again. |
1308 |
|
1309 |
Source code for this benchmark is found as eg/bench in the AnyEvent |
1310 |
distribution. |
1311 |
|
1312 |
Explanation of the columns |
1313 |
*watcher* is the number of event watchers created/destroyed. Since |
1314 |
different event models feature vastly different performances, each event |
1315 |
loop was given a number of watchers so that overall runtime is |
1316 |
acceptable and similar between tested event loop (and keep them from |
1317 |
crashing): Glib would probably take thousands of years if asked to |
1318 |
process the same number of watchers as EV in this benchmark. |
1319 |
|
1320 |
*bytes* is the number of bytes (as measured by the resident set size, |
1321 |
RSS) consumed by each watcher. This method of measuring captures both C |
1322 |
and Perl-based overheads. |
1323 |
|
1324 |
*create* is the time, in microseconds (millionths of seconds), that it |
1325 |
takes to create a single watcher. The callback is a closure shared |
1326 |
between all watchers, to avoid adding memory overhead. That means |
1327 |
closure creation and memory usage is not included in the figures. |
1328 |
|
1329 |
*invoke* is the time, in microseconds, used to invoke a simple callback. |
1330 |
The callback simply counts down a Perl variable and after it was invoked |
1331 |
"watcher" times, it would "->send" a condvar once to signal the end of |
1332 |
this phase. |
1333 |
|
1334 |
*destroy* is the time, in microseconds, that it takes to destroy a |
1335 |
single watcher. |
1336 |
|
1337 |
Results |
1338 |
name watchers bytes create invoke destroy comment |
1339 |
EV/EV 400000 224 0.47 0.35 0.27 EV native interface |
1340 |
EV/Any 100000 224 2.88 0.34 0.27 EV + AnyEvent watchers |
1341 |
CoroEV/Any 100000 224 2.85 0.35 0.28 coroutines + Coro::Signal |
1342 |
Perl/Any 100000 452 4.13 0.73 0.95 pure perl implementation |
1343 |
Event/Event 16000 517 32.20 31.80 0.81 Event native interface |
1344 |
Event/Any 16000 590 35.85 31.55 1.06 Event + AnyEvent watchers |
1345 |
IOAsync/Any 16000 989 38.10 32.77 11.13 via IO::Async::Loop::IO_Poll |
1346 |
IOAsync/Any 16000 990 37.59 29.50 10.61 via IO::Async::Loop::Epoll |
1347 |
Glib/Any 16000 1357 102.33 12.31 51.00 quadratic behaviour |
1348 |
Tk/Any 2000 1860 27.20 66.31 14.00 SEGV with >> 2000 watchers |
1349 |
POE/Event 2000 6328 109.99 751.67 14.02 via POE::Loop::Event |
1350 |
POE/Select 2000 6027 94.54 809.13 579.80 via POE::Loop::Select |
1351 |
|
1352 |
Discussion |
1353 |
The benchmark does *not* measure scalability of the event loop very |
1354 |
well. For example, a select-based event loop (such as the pure perl one) |
1355 |
can never compete with an event loop that uses epoll when the number of |
1356 |
file descriptors grows high. In this benchmark, all events become ready |
1357 |
at the same time, so select/poll-based implementations get an unnatural |
1358 |
speed boost. |
1359 |
|
1360 |
Also, note that the number of watchers usually has a nonlinear effect on |
1361 |
overall speed, that is, creating twice as many watchers doesn't take |
1362 |
twice the time - usually it takes longer. This puts event loops tested |
1363 |
with a higher number of watchers at a disadvantage. |
1364 |
|
1365 |
To put the range of results into perspective, consider that on the |
1366 |
benchmark machine, handling an event takes roughly 1600 CPU cycles with |
1367 |
EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 |
1368 |
CPU cycles with POE. |
1369 |
|
1370 |
"EV" is the sole leader regarding speed and memory use, which are both |
1371 |
maximal/minimal, respectively. Even when going through AnyEvent, it uses |
1372 |
far less memory than any other event loop and is still faster than Event |
1373 |
natively. |
1374 |
|
1375 |
The pure perl implementation is hit in a few sweet spots (both the |
1376 |
constant timeout and the use of a single fd hit optimisations in the |
1377 |
perl interpreter and the backend itself). Nevertheless this shows that |
1378 |
it adds very little overhead in itself. Like any select-based backend |
1379 |
its performance becomes really bad with lots of file descriptors (and |
1380 |
few of them active), of course, but this was not subject of this |
1381 |
benchmark. |
1382 |
|
1383 |
The "Event" module has a relatively high setup and callback invocation |
1384 |
cost, but overall scores in on the third place. |
1385 |
|
1386 |
"IO::Async" performs admirably well, about on par with "Event", even |
1387 |
when using its pure perl backend. |
1388 |
|
1389 |
"Glib"'s memory usage is quite a bit higher, but it features a faster |
1390 |
callback invocation and overall ends up in the same class as "Event". |
1391 |
However, Glib scales extremely badly, doubling the number of watchers |
1392 |
increases the processing time by more than a factor of four, making it |
1393 |
completely unusable when using larger numbers of watchers (note that |
1394 |
only a single file descriptor was used in the benchmark, so |
1395 |
inefficiencies of "poll" do not account for this). |
1396 |
|
1397 |
The "Tk" adaptor works relatively well. The fact that it crashes with |
1398 |
more than 2000 watchers is a big setback, however, as correctness takes |
1399 |
precedence over speed. Nevertheless, its performance is surprising, as |
1400 |
the file descriptor is dup()ed for each watcher. This shows that the |
1401 |
dup() employed by some adaptors is not a big performance issue (it does |
1402 |
incur a hidden memory cost inside the kernel which is not reflected in |
1403 |
the figures above). |
1404 |
|
1405 |
"POE", regardless of underlying event loop (whether using its pure perl |
1406 |
select-based backend or the Event module, the POE-EV backend couldn't be |
1407 |
tested because it wasn't working) shows abysmal performance and memory |
1408 |
usage with AnyEvent: Watchers use almost 30 times as much memory as EV |
1409 |
watchers, and 10 times as much memory as Event (the high memory |
1410 |
requirements are caused by requiring a session for each watcher). |
1411 |
Watcher invocation speed is almost 900 times slower than with AnyEvent's |
1412 |
pure perl implementation. |
1413 |
|
1414 |
The design of the POE adaptor class in AnyEvent can not really account |
1415 |
for the performance issues, though, as session creation overhead is |
1416 |
small compared to execution of the state machine, which is coded pretty |
1417 |
optimally within AnyEvent::Impl::POE (and while everybody agrees that |
1418 |
using multiple sessions is not a good approach, especially regarding |
1419 |
memory usage, even the author of POE could not come up with a faster |
1420 |
design). |
1421 |
|
1422 |
Summary |
1423 |
* Using EV through AnyEvent is faster than any other event loop (even |
1424 |
when used without AnyEvent), but most event loops have acceptable |
1425 |
performance with or without AnyEvent. |
1426 |
|
1427 |
* The overhead AnyEvent adds is usually much smaller than the overhead |
1428 |
of the actual event loop, only with extremely fast event loops such |
1429 |
as EV adds AnyEvent significant overhead. |
1430 |
|
1431 |
* You should avoid POE like the plague if you want performance or |
1432 |
reasonable memory usage. |
1433 |
|
1434 |
BENCHMARKING THE LARGE SERVER CASE |
1435 |
This benchmark actually benchmarks the event loop itself. It works by |
1436 |
creating a number of "servers": each server consists of a socket pair, a |
1437 |
timeout watcher that gets reset on activity (but never fires), and an |
1438 |
I/O watcher waiting for input on one side of the socket. Each time the |
1439 |
socket watcher reads a byte it will write that byte to a random other |
1440 |
"server". |
1441 |
|
1442 |
The effect is that there will be a lot of I/O watchers, only part of |
1443 |
which are active at any one point (so there is a constant number of |
1444 |
active fds for each loop iteration, but which fds these are is random). |
1445 |
The timeout is reset each time something is read because that reflects |
1446 |
how most timeouts work (and puts extra pressure on the event loops). |
1447 |
|
1448 |
In this benchmark, we use 10000 socket pairs (20000 sockets), of which |
1449 |
100 (1%) are active. This mirrors the activity of large servers with |
1450 |
many connections, most of which are idle at any one point in time. |
1451 |
|
1452 |
Source code for this benchmark is found as eg/bench2 in the AnyEvent |
1453 |
distribution. |
1454 |
|
1455 |
Explanation of the columns |
1456 |
*sockets* is the number of sockets, and twice the number of "servers" |
1457 |
(as each server has a read and write socket end). |
1458 |
|
1459 |
*create* is the time it takes to create a socket pair (which is |
1460 |
nontrivial) and two watchers: an I/O watcher and a timeout watcher. |
1461 |
|
1462 |
*request*, the most important value, is the time it takes to handle a |
1463 |
single "request", that is, reading the token from the pipe and |
1464 |
forwarding it to another server. This includes deleting the old timeout |
1465 |
and creating a new one that moves the timeout into the future. |
1466 |
|
1467 |
Results |
1468 |
name sockets create request |
1469 |
EV 20000 69.01 11.16 |
1470 |
Perl 20000 73.32 35.87 |
1471 |
IOAsync 20000 157.00 98.14 epoll |
1472 |
IOAsync 20000 159.31 616.06 poll |
1473 |
Event 20000 212.62 257.32 |
1474 |
Glib 20000 651.16 1896.30 |
1475 |
POE 20000 349.67 12317.24 uses POE::Loop::Event |
1476 |
|
1477 |
Discussion |
1478 |
This benchmark *does* measure scalability and overall performance of the |
1479 |
particular event loop. |
1480 |
|
1481 |
EV is again fastest. Since it is using epoll on my system, the setup |
1482 |
time is relatively high, though. |
1483 |
|
1484 |
Perl surprisingly comes second. It is much faster than the C-based event |
1485 |
loops Event and Glib. |
1486 |
|
1487 |
IO::Async performs very well when using its epoll backend, and still |
1488 |
quite good compared to Glib when using its pure perl backend. |
1489 |
|
1490 |
Event suffers from high setup time as well (look at its code and you |
1491 |
will understand why). Callback invocation also has a high overhead |
1492 |
compared to the "$_->() for .."-style loop that the Perl event loop |
1493 |
uses. Event uses select or poll in basically all documented |
1494 |
configurations. |
1495 |
|
1496 |
Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It |
1497 |
clearly fails to perform with many filehandles or in busy servers. |
1498 |
|
1499 |
POE is still completely out of the picture, taking over 1000 times as |
1500 |
long as EV, and over 100 times as long as the Perl implementation, even |
1501 |
though it uses a C-based event loop in this case. |
1502 |
|
1503 |
Summary |
1504 |
* The pure perl implementation performs extremely well. |
1505 |
|
1506 |
* Avoid Glib or POE in large projects where performance matters. |
1507 |
|
1508 |
BENCHMARKING SMALL SERVERS |
1509 |
While event loops should scale (and select-based ones do not...) even to |
1510 |
large servers, most programs we (or I :) actually write have only a few |
1511 |
I/O watchers. |
1512 |
|
1513 |
In this benchmark, I use the same benchmark program as in the large |
1514 |
server case, but it uses only eight "servers", of which three are active |
1515 |
at any one time. This should reflect performance for a small server |
1516 |
relatively well. |
1517 |
|
1518 |
The columns are identical to the previous table. |
1519 |
|
1520 |
Results |
1521 |
name sockets create request |
1522 |
EV 16 20.00 6.54 |
1523 |
Perl 16 25.75 12.62 |
1524 |
Event 16 81.27 35.86 |
1525 |
Glib 16 32.63 15.48 |
1526 |
POE 16 261.87 276.28 uses POE::Loop::Event |
1527 |
|
1528 |
Discussion |
1529 |
The benchmark tries to test the performance of a typical small server. |
1530 |
While knowing how various event loops perform is interesting, keep in |
1531 |
mind that their overhead in this case is usually not as important, due |
1532 |
to the small absolute number of watchers (that is, you need efficiency |
1533 |
and speed most when you have lots of watchers, not when you only have a |
1534 |
few of them). |
1535 |
|
1536 |
EV is again fastest. |
1537 |
|
1538 |
Perl again comes second. It is noticeably faster than the C-based event |
1539 |
loops Event and Glib, although the difference is too small to really |
1540 |
matter. |
1541 |
|
1542 |
POE also performs much better in this case, but is is still far behind |
1543 |
the others. |
1544 |
|
1545 |
Summary |
1546 |
* C-based event loops perform very well with small number of watchers, |
1547 |
as the management overhead dominates. |
1548 |
|
1549 |
THE IO::Lambda BENCHMARK |
1550 |
Recently I was told about the benchmark in the IO::Lambda manpage, which |
1551 |
could be misinterpreted to make AnyEvent look bad. In fact, the |
1552 |
benchmark simply compares IO::Lambda with POE, and IO::Lambda looks |
1553 |
better (which shouldn't come as a surprise to anybody). As such, the |
1554 |
benchmark is fine, and mostly shows that the AnyEvent backend from |
1555 |
IO::Lambda isn't very optimal. But how would AnyEvent compare when used |
1556 |
without the extra baggage? To explore this, I wrote the equivalent |
1557 |
benchmark for AnyEvent. |
1558 |
|
1559 |
The benchmark itself creates an echo-server, and then, for 500 times, |
1560 |
connects to the echo server, sends a line, waits for the reply, and then |
1561 |
creates the next connection. This is a rather bad benchmark, as it |
1562 |
doesn't test the efficiency of the framework or much non-blocking I/O, |
1563 |
but it is a benchmark nevertheless. |
1564 |
|
1565 |
name runtime |
1566 |
Lambda/select 0.330 sec |
1567 |
+ optimized 0.122 sec |
1568 |
Lambda/AnyEvent 0.327 sec |
1569 |
+ optimized 0.138 sec |
1570 |
Raw sockets/select 0.077 sec |
1571 |
POE/select, components 0.662 sec |
1572 |
POE/select, raw sockets 0.226 sec |
1573 |
POE/select, optimized 0.404 sec |
1574 |
|
1575 |
AnyEvent/select/nb 0.085 sec |
1576 |
AnyEvent/EV/nb 0.068 sec |
1577 |
+state machine 0.134 sec |
1578 |
|
1579 |
The benchmark is also a bit unfair (my fault): the IO::Lambda/POE |
1580 |
benchmarks actually make blocking connects and use 100% blocking I/O, |
1581 |
defeating the purpose of an event-based solution. All of the newly |
1582 |
written AnyEvent benchmarks use 100% non-blocking connects (using |
1583 |
AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS |
1584 |
resolver), so AnyEvent is at a disadvantage here, as non-blocking |
1585 |
connects generally require a lot more bookkeeping and event handling |
1586 |
than blocking connects (which involve a single syscall only). |
1587 |
|
1588 |
The last AnyEvent benchmark additionally uses AnyEvent::Handle, which |
1589 |
offers similar expressive power as POE and IO::Lambda, using |
1590 |
conventional Perl syntax. This means that both the echo server and the |
1591 |
client are 100% non-blocking, further placing it at a disadvantage. |
1592 |
|
1593 |
As you can see, the AnyEvent + EV combination even beats the |
1594 |
hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl |
1595 |
backend easily beats IO::Lambda and POE. |
1596 |
|
1597 |
And even the 100% non-blocking version written using the high-level (and |
1598 |
slow :) AnyEvent::Handle abstraction beats both POE and IO::Lambda by a |
1599 |
large margin, even though it does all of DNS, tcp-connect and socket I/O |
1600 |
in a non-blocking way. |
1601 |
|
1602 |
The two AnyEvent benchmarks programs can be found as eg/ae0.pl and |
1603 |
eg/ae2.pl in the AnyEvent distribution, the remaining benchmarks are |
1604 |
part of the IO::lambda distribution and were used without any changes. |
1605 |
|
1606 |
SIGNALS |
1607 |
AnyEvent currently installs handlers for these signals: |
1608 |
|
1609 |
SIGCHLD |
1610 |
A handler for "SIGCHLD" is installed by AnyEvent's child watcher |
1611 |
emulation for event loops that do not support them natively. Also, |
1612 |
some event loops install a similar handler. |
1613 |
|
1614 |
Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE, |
1615 |
then AnyEvent will reset it to default, to avoid losing child exit |
1616 |
statuses. |
1617 |
|
1618 |
SIGPIPE |
1619 |
A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is |
1620 |
"undef" when AnyEvent gets loaded. |
1621 |
|
1622 |
The rationale for this is that AnyEvent users usually do not really |
1623 |
depend on SIGPIPE delivery (which is purely an optimisation for |
1624 |
shell use, or badly-written programs), but "SIGPIPE" can cause |
1625 |
spurious and rare program exits as a lot of people do not expect |
1626 |
"SIGPIPE" when writing to some random socket. |
1627 |
|
1628 |
The rationale for installing a no-op handler as opposed to ignoring |
1629 |
it is that this way, the handler will be restored to defaults on |
1630 |
exec. |
1631 |
|
1632 |
Feel free to install your own handler, or reset it to defaults. |
1633 |
|
1634 |
RECOMMENDED/OPTIONAL MODULES |
1635 |
One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and |
1636 |
it's built-in modules) are required to use it. |
1637 |
|
1638 |
That does not mean that AnyEvent won't take advantage of some additional |
1639 |
modules if they are installed. |
1640 |
|
1641 |
This section epxlains which additional modules will be used, and how |
1642 |
they affect AnyEvent's operetion. |
1643 |
|
1644 |
Async::Interrupt |
1645 |
This slightly arcane module is used to implement fast signal |
1646 |
handling: To my knowledge, there is no way to do completely |
1647 |
race-free and quick signal handling in pure perl. To ensure that |
1648 |
signals still get delivered, AnyEvent will start an interval timer |
1649 |
to wake up perl (and catch the signals) with soemd elay (default is |
1650 |
10 seconds, look for $AnyEvent::MAX_SIGNAL_LATENCY). |
1651 |
|
1652 |
If this module is available, then it will be used to implement |
1653 |
signal catching, which means that signals will not be delayed, and |
1654 |
the event loop will not be interrupted regularly, which is more |
1655 |
efficient (And good for battery life on laptops). |
1656 |
|
1657 |
This affects not just the pure-perl event loop, but also other event |
1658 |
loops that have no signal handling on their own (e.g. Glib, Tk, Qt). |
1659 |
|
1660 |
EV This module isn't really "optional", as it is simply one of the |
1661 |
backend event loops that AnyEvent can use. However, it is simply the |
1662 |
best event loop available in terms of features, speed and stability: |
1663 |
It supports the AnyEvent API optimally, implements all the watcher |
1664 |
types in XS, does automatic timer adjustments even when no monotonic |
1665 |
clock is available, can take avdantage of advanced kernel interfaces |
1666 |
such as "epoll" and "kqueue", and is the fastest backend *by far*. |
1667 |
You can even embed Glib/Gtk2 in it (or vice versa, see EV::Glib and |
1668 |
Glib::EV). |
1669 |
|
1670 |
Guard |
1671 |
The guard module, when used, will be used to implement |
1672 |
"AnyEvent::Util::guard". This speeds up guards considerably (and |
1673 |
uses a lot less memory), but otherwise doesn't affect guard |
1674 |
operation much. It is purely used for performance. |
1675 |
|
1676 |
JSON and JSON::XS |
1677 |
This module is required when you want to read or write JSON data via |
1678 |
AnyEvent::Handle. It is also written in pure-perl, but can take |
1679 |
advantage of the ulta-high-speed JSON::XS module when it is |
1680 |
installed. |
1681 |
|
1682 |
In fact, AnyEvent::Handle will use JSON::XS by default if it is |
1683 |
installed. |
1684 |
|
1685 |
Net::SSLeay |
1686 |
Implementing TLS/SSL in Perl is certainly interesting, but not very |
1687 |
worthwhile: If this module is installed, then AnyEvent::Handle (with |
1688 |
the help of AnyEvent::TLS), gains the ability to do TLS/SSL. |
1689 |
|
1690 |
Time::HiRes |
1691 |
This module is part of perl since release 5.008. It will be used |
1692 |
when the chosen event library does not come with a timing source on |
1693 |
it's own. The pure-perl event loop (AnyEvent::Impl::Perl) will |
1694 |
additionally use it to try to use a monotonic clock for timing |
1695 |
stability. |
1696 |
|
1697 |
FORK |
1698 |
Most event libraries are not fork-safe. The ones who are usually are |
1699 |
because they rely on inefficient but fork-safe "select" or "poll" calls. |
1700 |
Only EV is fully fork-aware. |
1701 |
|
1702 |
If you have to fork, you must either do so *before* creating your first |
1703 |
watcher OR you must not use AnyEvent at all in the child OR you must do |
1704 |
something completely out of the scope of AnyEvent. |
1705 |
|
1706 |
SECURITY CONSIDERATIONS |
1707 |
AnyEvent can be forced to load any event model via |
1708 |
$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used |
1709 |
to execute arbitrary code or directly gain access, it can easily be used |
1710 |
to make the program hang or malfunction in subtle ways, as AnyEvent |
1711 |
watchers will not be active when the program uses a different event |
1712 |
model than specified in the variable. |
1713 |
|
1714 |
You can make AnyEvent completely ignore this variable by deleting it |
1715 |
before the first watcher gets created, e.g. with a "BEGIN" block: |
1716 |
|
1717 |
BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} } |
1718 |
|
1719 |
use AnyEvent; |
1720 |
|
1721 |
Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can |
1722 |
be used to probe what backend is used and gain other information (which |
1723 |
is probably even less useful to an attacker than PERL_ANYEVENT_MODEL), |
1724 |
and $ENV{PERL_ANYEVENT_STRICT}. |
1725 |
|
1726 |
Note that AnyEvent will remove *all* environment variables starting with |
1727 |
"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is |
1728 |
enabled. |
1729 |
|
1730 |
BUGS |
1731 |
Perl 5.8 has numerous memleaks that sometimes hit this module and are |
1732 |
hard to work around. If you suffer from memleaks, first upgrade to Perl |
1733 |
5.10 and check wether the leaks still show up. (Perl 5.10.0 has other |
1734 |
annoying memleaks, such as leaking on "map" and "grep" but it is usually |
1735 |
not as pronounced). |
1736 |
|
1737 |
SEE ALSO |
1738 |
Utility functions: AnyEvent::Util. |
1739 |
|
1740 |
Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk, |
1741 |
Event::Lib, Qt, POE. |
1742 |
|
1743 |
Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event, |
1744 |
AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl, |
1745 |
AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE, |
1746 |
AnyEvent::Impl::IOAsync. |
1747 |
|
1748 |
Non-blocking file handles, sockets, TCP clients and servers: |
1749 |
AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS. |
1750 |
|
1751 |
Asynchronous DNS: AnyEvent::DNS. |
1752 |
|
1753 |
Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event, |
1754 |
|
1755 |
Nontrivial usage examples: AnyEvent::GPSD, AnyEvent::XMPP, |
1756 |
AnyEvent::HTTP. |
1757 |
|
1758 |
AUTHOR |
1759 |
Marc Lehmann <schmorp@schmorp.de> |
1760 |
http://home.schmorp.de/ |
1761 |
|