1 |
=head1 NAME |
2 |
|
3 |
AnyEvent - provide framework for multiple event loops |
4 |
|
5 |
EV, Event, Coro::EV, Coro::Event, Glib, Tk, Perl, Event::Lib - various supported event loops |
6 |
|
7 |
=head1 SYNOPSIS |
8 |
|
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use AnyEvent; |
10 |
|
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my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub { |
12 |
... |
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}); |
14 |
|
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my $w = AnyEvent->timer (after => $seconds, cb => sub { |
16 |
... |
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}); |
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|
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my $w = AnyEvent->condvar; # stores whether a condition was flagged |
20 |
$w->wait; # enters "main loop" till $condvar gets ->broadcast |
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$w->broadcast; # wake up current and all future wait's |
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|
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=head1 WHY YOU SHOULD USE THIS MODULE (OR NOT) |
24 |
|
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Glib, POE, IO::Async, Event... CPAN offers event models by the dozen |
26 |
nowadays. So what is different about AnyEvent? |
27 |
|
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Executive Summary: AnyEvent is I<compatible>, AnyEvent is I<free of |
29 |
policy> and AnyEvent is I<small and efficient>. |
30 |
|
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First and foremost, I<AnyEvent is not an event model> itself, it only |
32 |
interfaces to whatever event model the main program happens to use in a |
33 |
pragmatic way. For event models and certain classes of immortals alike, |
34 |
the statement "there can only be one" is a bitter reality: In general, |
35 |
only one event loop can be active at the same time in a process. AnyEvent |
36 |
helps hiding the differences between those event loops. |
37 |
|
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The goal of AnyEvent is to offer module authors the ability to do event |
39 |
programming (waiting for I/O or timer events) without subscribing to a |
40 |
religion, a way of living, and most importantly: without forcing your |
41 |
module users into the same thing by forcing them to use the same event |
42 |
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 |
45 |
actually doing all I/O I<synchronously>...), using them in your module is |
46 |
like joining a cult: After you joined, you are dependent on them and you |
47 |
cannot use anything else, as it is simply incompatible to everything that |
48 |
isn't itself. What's worse, all the potential users of your module are |
49 |
I<also> forced to use the same event loop you use. |
50 |
|
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AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works |
52 |
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 |
54 |
your module uses one of those, every user of your module has to use it, |
55 |
too. But if your module uses AnyEvent, it works transparently with all |
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event models it supports (including stuff like POE and IO::Async, as long |
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as those use one of the supported event loops. It is trivial to add new |
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event loops to AnyEvent, too, so it is future-proof). |
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|
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In addition to being free of having to use I<the one and only true event |
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model>, AnyEvent also is free of bloat and policy: with POE or similar |
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modules, you get an enourmous amount of code and strict rules you have to |
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follow. AnyEvent, on the other hand, is lean and up to the point, by only |
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offering the functionality that is necessary, in as thin as a wrapper as |
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technically possible. |
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|
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Of course, if you want lots of policy (this can arguably be somewhat |
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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 I<not> use this module. |
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|
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|
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=head1 DESCRIPTION |
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|
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L<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 coexist |
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peacefully at any one time). |
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|
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The interface itself is vaguely similar, but not identical to the L<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: L<Coro::EV>, L<Coro::Event>, L<EV>, |
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L<Event>, L<Glib>, L<Tk>. The first one found is used. If none are found, |
86 |
the module tries to load these modules in the stated order. The first one |
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that can be successfully loaded will be used. If, after this, still none |
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could be found, AnyEvent will fall back to a pure-perl event loop, which |
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is not very efficient, but should work everywhere. |
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|
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Because AnyEvent first checks for modules that are already loaded, loading |
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an event model explicitly before first using AnyEvent will likely make |
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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 I<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 to |
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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 |
105 |
C<AnyEvent::Impl::Perl>. Like other event modules you can load it |
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explicitly. |
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|
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=head1 WATCHERS |
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|
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AnyEvent has the central concept of a I<watcher>, which is an object that |
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stores relevant data for each kind of event you are waiting for, such as |
112 |
the callback to call, the filehandle to watch, etc. |
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|
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These watchers are normal Perl objects with normal Perl lifetime. After |
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creating a watcher it will immediately "watch" for events and invoke the |
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callback when the event occurs (of course, only when the event model |
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is in control). |
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|
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To disable the watcher you have to destroy it (e.g. by setting the |
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variable you store it in to C<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 C<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 |
132 |
undef $w; |
133 |
}); |
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|
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Note that C<my $w; $w => combination. This is necessary because in Perl, |
136 |
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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=head2 IO WATCHERS |
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|
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You can create an I/O watcher by calling the C<< AnyEvent->io >> method |
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with the following mandatory key-value pairs as arguments: |
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|
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C<fh> the Perl I<file handle> (I<not> file descriptor) to watch for |
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events. C<poll> must be a string that is either C<r> or C<w>, which |
146 |
creates a watcher waiting for "r"eadable or "w"ritable events, |
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respectively. C<cb> is the callback to invoke each time the file handle |
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becomes ready. |
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|
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File handles will be kept alive, so as long as the watcher exists, the |
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file handle exists, too. |
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|
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It is not allowed to close a file handle as long as any watcher is active |
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on the underlying file descriptor. |
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|
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Some event loops issue spurious readyness notifications, so you should |
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always use non-blocking calls when reading/writing from/to your file |
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handles. |
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|
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Example: |
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|
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# wait for readability of STDIN, then read a line and disable the watcher |
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my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub { |
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chomp (my $input = <STDIN>); |
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warn "read: $input\n"; |
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undef $w; |
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}); |
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|
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=head2 TIME WATCHERS |
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|
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You can create a time watcher by calling the C<< AnyEvent->timer >> |
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method with the following mandatory arguments: |
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|
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C<after> specifies after how many seconds (fractional values are |
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supported) should the timer activate. C<cb> the callback to invoke in that |
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case. |
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|
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The timer callback will be invoked at most once: if you want a repeating |
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timer you have to create a new watcher (this is a limitation by both Tk |
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and Glib). |
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|
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Example: |
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|
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# fire an event after 7.7 seconds |
185 |
my $w = AnyEvent->timer (after => 7.7, cb => sub { |
186 |
warn "timeout\n"; |
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}); |
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|
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# to cancel the timer: |
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undef $w; |
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|
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Example 2: |
193 |
|
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# fire an event after 0.5 seconds, then roughly every second |
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my $w; |
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|
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my $cb = sub { |
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# cancel the old timer while creating a new one |
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$w = AnyEvent->timer (after => 1, cb => $cb); |
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}; |
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|
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# start the "loop" by creating the first watcher |
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$w = AnyEvent->timer (after => 0.5, cb => $cb); |
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|
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=head3 TIMING ISSUES |
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|
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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"). |
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|
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While most event loops expect timers to specified in a relative way, they use |
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absolute time internally. This makes a difference when your clock "jumps", |
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for example, when ntp decides to set your clock backwards from the wrong 2014-01-01 to |
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2008-01-01, a watcher that you created to fire "after" a second might actually take |
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six years to finally fire. |
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|
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AnyEvent cannot compensate for this. The only event loop that is conscious |
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about these issues is L<EV>, which offers both relative (ev_timer) and |
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absolute (ev_periodic) 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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=head2 SIGNAL WATCHERS |
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|
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You can watch for signals using a signal watcher, C<signal> is the signal |
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I<name> without any C<SIG> prefix, C<cb> is the Perl callback to |
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be invoked whenever a signal occurs. |
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|
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Multiple signals occurances can be clumped together into one callback |
231 |
invocation, and callback invocation will be synchronous. synchronous means |
232 |
that it might take a while until the signal gets handled by the process, |
233 |
but it is guarenteed not to interrupt any other callbacks. |
234 |
|
235 |
The main advantage of using these watchers is that you can share a signal |
236 |
between multiple watchers. |
237 |
|
238 |
This watcher might use C<%SIG>, so programs overwriting those signals |
239 |
directly will likely not work correctly. |
240 |
|
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Example: exit on SIGINT |
242 |
|
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my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 }); |
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|
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=head2 CHILD PROCESS WATCHERS |
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|
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You can also watch on a child process exit and catch its exit status. |
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|
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The child process is specified by the C<pid> argument (if set to C<0>, it |
250 |
watches for any child process exit). The watcher will trigger as often |
251 |
as status change for the child are received. This works by installing a |
252 |
signal handler for C<SIGCHLD>. The callback will be called with the pid |
253 |
and exit status (as returned by waitpid). |
254 |
|
255 |
Example: wait for pid 1333 |
256 |
|
257 |
my $w = AnyEvent->child ( |
258 |
pid => 1333, |
259 |
cb => sub { |
260 |
my ($pid, $status) = @_; |
261 |
warn "pid $pid exited with status $status"; |
262 |
}, |
263 |
); |
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|
265 |
=head2 CONDITION VARIABLES |
266 |
|
267 |
Condition variables can be created by calling the C<< AnyEvent->condvar >> |
268 |
method without any arguments. |
269 |
|
270 |
A condition variable waits for a condition - precisely that the C<< |
271 |
->broadcast >> method has been called. |
272 |
|
273 |
They are very useful to signal that a condition has been fulfilled, for |
274 |
example, if you write a module that does asynchronous http requests, |
275 |
then a condition variable would be the ideal candidate to signal the |
276 |
availability of results. |
277 |
|
278 |
You can also use condition variables to block your main program until |
279 |
an event occurs - for example, you could C<< ->wait >> in your main |
280 |
program until the user clicks the Quit button in your app, which would C<< |
281 |
->broadcast >> the "quit" event. |
282 |
|
283 |
Note that condition variables recurse into the event loop - if you have |
284 |
two pirces of code that call C<< ->wait >> in a round-robbin fashion, you |
285 |
lose. Therefore, condition variables are good to export to your caller, but |
286 |
you should avoid making a blocking wait yourself, at least in callbacks, |
287 |
as this asks for trouble. |
288 |
|
289 |
This object has two methods: |
290 |
|
291 |
=over 4 |
292 |
|
293 |
=item $cv->wait |
294 |
|
295 |
Wait (blocking if necessary) until the C<< ->broadcast >> method has been |
296 |
called on c<$cv>, while servicing other watchers normally. |
297 |
|
298 |
You can only wait once on a condition - additional calls will return |
299 |
immediately. |
300 |
|
301 |
Not all event models support a blocking wait - some die in that case |
302 |
(programs might want to do that to stay interactive), so I<if you are |
303 |
using this from a module, never require a blocking wait>, but let the |
304 |
caller decide whether the call will block or not (for example, by coupling |
305 |
condition variables with some kind of request results and supporting |
306 |
callbacks so the caller knows that getting the result will not block, |
307 |
while still suppporting blocking waits if the caller so desires). |
308 |
|
309 |
Another reason I<never> to C<< ->wait >> in a module is that you cannot |
310 |
sensibly have two C<< ->wait >>'s in parallel, as that would require |
311 |
multiple interpreters or coroutines/threads, none of which C<AnyEvent> |
312 |
can supply (the coroutine-aware backends L<AnyEvent::Impl::CoroEV> and |
313 |
L<AnyEvent::Impl::CoroEvent> explicitly support concurrent C<< ->wait >>'s |
314 |
from different coroutines, however). |
315 |
|
316 |
=item $cv->broadcast |
317 |
|
318 |
Flag the condition as ready - a running C<< ->wait >> and all further |
319 |
calls to C<wait> will (eventually) return after this method has been |
320 |
called. If nobody is waiting the broadcast will be remembered.. |
321 |
|
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=back |
323 |
|
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Example: |
325 |
|
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# wait till the result is ready |
327 |
my $result_ready = AnyEvent->condvar; |
328 |
|
329 |
# do something such as adding a timer |
330 |
# or socket watcher the calls $result_ready->broadcast |
331 |
# when the "result" is ready. |
332 |
# in this case, we simply use a timer: |
333 |
my $w = AnyEvent->timer ( |
334 |
after => 1, |
335 |
cb => sub { $result_ready->broadcast }, |
336 |
); |
337 |
|
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# this "blocks" (while handling events) till the watcher |
339 |
# calls broadcast |
340 |
$result_ready->wait; |
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|
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=head1 GLOBAL VARIABLES AND FUNCTIONS |
343 |
|
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=over 4 |
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|
346 |
=item $AnyEvent::MODEL |
347 |
|
348 |
Contains C<undef> until the first watcher is being created. Then it |
349 |
contains the event model that is being used, which is the name of the |
350 |
Perl class implementing the model. This class is usually one of the |
351 |
C<AnyEvent::Impl:xxx> modules, but can be any other class in the case |
352 |
AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>). |
353 |
|
354 |
The known classes so far are: |
355 |
|
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AnyEvent::Impl::CoroEV based on Coro::EV, best choice. |
357 |
AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice. |
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AnyEvent::Impl::EV based on EV (an interface to libev, also best choice). |
359 |
AnyEvent::Impl::Event based on Event, also second best choice :) |
360 |
AnyEvent::Impl::Glib based on Glib, third-best choice. |
361 |
AnyEvent::Impl::Tk based on Tk, very bad choice. |
362 |
AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable. |
363 |
AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse. |
364 |
|
365 |
=item AnyEvent::detect |
366 |
|
367 |
Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model |
368 |
if necessary. You should only call this function right before you would |
369 |
have created an AnyEvent watcher anyway, that is, as late as possible at |
370 |
runtime. |
371 |
|
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=back |
373 |
|
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=head1 WHAT TO DO IN A MODULE |
375 |
|
376 |
As a module author, you should C<use AnyEvent> and call AnyEvent methods |
377 |
freely, but you should not load a specific event module or rely on it. |
378 |
|
379 |
Be careful when you create watchers in the module body - AnyEvent will |
380 |
decide which event module to use as soon as the first method is called, so |
381 |
by calling AnyEvent in your module body you force the user of your module |
382 |
to load the event module first. |
383 |
|
384 |
Never call C<< ->wait >> on a condition variable unless you I<know> that |
385 |
the C<< ->broadcast >> method has been called on it already. This is |
386 |
because it will stall the whole program, and the whole point of using |
387 |
events is to stay interactive. |
388 |
|
389 |
It is fine, however, to call C<< ->wait >> when the user of your module |
390 |
requests it (i.e. if you create a http request object ad have a method |
391 |
called C<results> that returns the results, it should call C<< ->wait >> |
392 |
freely, as the user of your module knows what she is doing. always). |
393 |
|
394 |
=head1 WHAT TO DO IN THE MAIN PROGRAM |
395 |
|
396 |
There will always be a single main program - the only place that should |
397 |
dictate which event model to use. |
398 |
|
399 |
If it doesn't care, it can just "use AnyEvent" and use it itself, or not |
400 |
do anything special (it does not need to be event-based) and let AnyEvent |
401 |
decide which implementation to chose if some module relies on it. |
402 |
|
403 |
If the main program relies on a specific event model. For example, in |
404 |
Gtk2 programs you have to rely on the Glib module. You should load the |
405 |
event module before loading AnyEvent or any module that uses it: generally |
406 |
speaking, you should load it as early as possible. The reason is that |
407 |
modules might create watchers when they are loaded, and AnyEvent will |
408 |
decide on the event model to use as soon as it creates watchers, and it |
409 |
might chose the wrong one unless you load the correct one yourself. |
410 |
|
411 |
You can chose to use a rather inefficient pure-perl implementation by |
412 |
loading the C<AnyEvent::Impl::Perl> module, which gives you similar |
413 |
behaviour everywhere, but letting AnyEvent chose is generally better. |
414 |
|
415 |
=cut |
416 |
|
417 |
package AnyEvent; |
418 |
|
419 |
no warnings; |
420 |
use strict; |
421 |
|
422 |
use Carp; |
423 |
|
424 |
our $VERSION = '3.12'; |
425 |
our $MODEL; |
426 |
|
427 |
our $AUTOLOAD; |
428 |
our @ISA; |
429 |
|
430 |
our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1; |
431 |
|
432 |
our @REGISTRY; |
433 |
|
434 |
my @models = ( |
435 |
[Coro::EV:: => AnyEvent::Impl::CoroEV::], |
436 |
[Coro::Event:: => AnyEvent::Impl::CoroEvent::], |
437 |
[EV:: => AnyEvent::Impl::EV::], |
438 |
[Event:: => AnyEvent::Impl::Event::], |
439 |
[Glib:: => AnyEvent::Impl::Glib::], |
440 |
[Tk:: => AnyEvent::Impl::Tk::], |
441 |
[AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::], |
442 |
[Event::Lib:: => AnyEvent::Impl::EventLib::], |
443 |
); |
444 |
|
445 |
our %method = map +($_ => 1), qw(io timer condvar broadcast wait signal one_event DESTROY); |
446 |
|
447 |
sub detect() { |
448 |
unless ($MODEL) { |
449 |
no strict 'refs'; |
450 |
|
451 |
if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) { |
452 |
my $model = "AnyEvent::Impl::$1"; |
453 |
if (eval "require $model") { |
454 |
$MODEL = $model; |
455 |
warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1; |
456 |
} |
457 |
} |
458 |
|
459 |
# check for already loaded models |
460 |
unless ($MODEL) { |
461 |
for (@REGISTRY, @models) { |
462 |
my ($package, $model) = @$_; |
463 |
if (${"$package\::VERSION"} > 0) { |
464 |
if (eval "require $model") { |
465 |
$MODEL = $model; |
466 |
warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1; |
467 |
last; |
468 |
} |
469 |
} |
470 |
} |
471 |
|
472 |
unless ($MODEL) { |
473 |
# try to load a model |
474 |
|
475 |
for (@REGISTRY, @models) { |
476 |
my ($package, $model) = @$_; |
477 |
if (eval "require $package" |
478 |
and ${"$package\::VERSION"} > 0 |
479 |
and eval "require $model") { |
480 |
$MODEL = $model; |
481 |
warn "AnyEvent: autoprobed model '$model', using it.\n" if $verbose > 1; |
482 |
last; |
483 |
} |
484 |
} |
485 |
|
486 |
$MODEL |
487 |
or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV (or Coro+EV), Event (or Coro+Event) or Glib."; |
488 |
} |
489 |
} |
490 |
|
491 |
unshift @ISA, $MODEL; |
492 |
push @{"$MODEL\::ISA"}, "AnyEvent::Base"; |
493 |
} |
494 |
|
495 |
$MODEL |
496 |
} |
497 |
|
498 |
sub AUTOLOAD { |
499 |
(my $func = $AUTOLOAD) =~ s/.*://; |
500 |
|
501 |
$method{$func} |
502 |
or croak "$func: not a valid method for AnyEvent objects"; |
503 |
|
504 |
detect unless $MODEL; |
505 |
|
506 |
my $class = shift; |
507 |
$class->$func (@_); |
508 |
} |
509 |
|
510 |
package AnyEvent::Base; |
511 |
|
512 |
# default implementation for ->condvar, ->wait, ->broadcast |
513 |
|
514 |
sub condvar { |
515 |
bless \my $flag, "AnyEvent::Base::CondVar" |
516 |
} |
517 |
|
518 |
sub AnyEvent::Base::CondVar::broadcast { |
519 |
${$_[0]}++; |
520 |
} |
521 |
|
522 |
sub AnyEvent::Base::CondVar::wait { |
523 |
AnyEvent->one_event while !${$_[0]}; |
524 |
} |
525 |
|
526 |
# default implementation for ->signal |
527 |
|
528 |
our %SIG_CB; |
529 |
|
530 |
sub signal { |
531 |
my (undef, %arg) = @_; |
532 |
|
533 |
my $signal = uc $arg{signal} |
534 |
or Carp::croak "required option 'signal' is missing"; |
535 |
|
536 |
$SIG_CB{$signal}{$arg{cb}} = $arg{cb}; |
537 |
$SIG{$signal} ||= sub { |
538 |
$_->() for values %{ $SIG_CB{$signal} || {} }; |
539 |
}; |
540 |
|
541 |
bless [$signal, $arg{cb}], "AnyEvent::Base::Signal" |
542 |
} |
543 |
|
544 |
sub AnyEvent::Base::Signal::DESTROY { |
545 |
my ($signal, $cb) = @{$_[0]}; |
546 |
|
547 |
delete $SIG_CB{$signal}{$cb}; |
548 |
|
549 |
$SIG{$signal} = 'DEFAULT' unless keys %{ $SIG_CB{$signal} }; |
550 |
} |
551 |
|
552 |
# default implementation for ->child |
553 |
|
554 |
our %PID_CB; |
555 |
our $CHLD_W; |
556 |
our $CHLD_DELAY_W; |
557 |
our $PID_IDLE; |
558 |
our $WNOHANG; |
559 |
|
560 |
sub _child_wait { |
561 |
while (0 < (my $pid = waitpid -1, $WNOHANG)) { |
562 |
$_->($pid, $?) for (values %{ $PID_CB{$pid} || {} }), |
563 |
(values %{ $PID_CB{0} || {} }); |
564 |
} |
565 |
|
566 |
undef $PID_IDLE; |
567 |
} |
568 |
|
569 |
sub _sigchld { |
570 |
# make sure we deliver these changes "synchronous" with the event loop. |
571 |
$CHLD_DELAY_W ||= AnyEvent->timer (after => 0, cb => sub { |
572 |
undef $CHLD_DELAY_W; |
573 |
&_child_wait; |
574 |
}); |
575 |
} |
576 |
|
577 |
sub child { |
578 |
my (undef, %arg) = @_; |
579 |
|
580 |
defined (my $pid = $arg{pid} + 0) |
581 |
or Carp::croak "required option 'pid' is missing"; |
582 |
|
583 |
$PID_CB{$pid}{$arg{cb}} = $arg{cb}; |
584 |
|
585 |
unless ($WNOHANG) { |
586 |
$WNOHANG = eval { require POSIX; &POSIX::WNOHANG } || 1; |
587 |
} |
588 |
|
589 |
unless ($CHLD_W) { |
590 |
$CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld); |
591 |
# child could be a zombie already, so make at least one round |
592 |
&_sigchld; |
593 |
} |
594 |
|
595 |
bless [$pid, $arg{cb}], "AnyEvent::Base::Child" |
596 |
} |
597 |
|
598 |
sub AnyEvent::Base::Child::DESTROY { |
599 |
my ($pid, $cb) = @{$_[0]}; |
600 |
|
601 |
delete $PID_CB{$pid}{$cb}; |
602 |
delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} }; |
603 |
|
604 |
undef $CHLD_W unless keys %PID_CB; |
605 |
} |
606 |
|
607 |
=head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE |
608 |
|
609 |
This is an advanced topic that you do not normally need to use AnyEvent in |
610 |
a module. This section is only of use to event loop authors who want to |
611 |
provide AnyEvent compatibility. |
612 |
|
613 |
If you need to support another event library which isn't directly |
614 |
supported by AnyEvent, you can supply your own interface to it by |
615 |
pushing, before the first watcher gets created, the package name of |
616 |
the event module and the package name of the interface to use onto |
617 |
C<@AnyEvent::REGISTRY>. You can do that before and even without loading |
618 |
AnyEvent, so it is reasonably cheap. |
619 |
|
620 |
Example: |
621 |
|
622 |
push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::]; |
623 |
|
624 |
This tells AnyEvent to (literally) use the C<urxvt::anyevent::> |
625 |
package/class when it finds the C<urxvt> package/module is already loaded. |
626 |
|
627 |
When AnyEvent is loaded and asked to find a suitable event model, it |
628 |
will first check for the presence of urxvt by trying to C<use> the |
629 |
C<urxvt::anyevent> module. |
630 |
|
631 |
The class should provide implementations for all watcher types. See |
632 |
L<AnyEvent::Impl::EV> (source code), L<AnyEvent::Impl::Glib> (Source code) |
633 |
and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to |
634 |
see the sources. |
635 |
|
636 |
If you don't provide C<signal> and C<child> watchers than AnyEvent will |
637 |
provide suitable (hopefully) replacements. |
638 |
|
639 |
The above example isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt) |
640 |
terminal emulator uses the above line as-is. An interface isn't included |
641 |
in AnyEvent because it doesn't make sense outside the embedded interpreter |
642 |
inside I<rxvt-unicode>, and it is updated and maintained as part of the |
643 |
I<rxvt-unicode> distribution. |
644 |
|
645 |
I<rxvt-unicode> also cheats a bit by not providing blocking access to |
646 |
condition variables: code blocking while waiting for a condition will |
647 |
C<die>. This still works with most modules/usages, and blocking calls must |
648 |
not be done in an interactive application, so it makes sense. |
649 |
|
650 |
=head1 ENVIRONMENT VARIABLES |
651 |
|
652 |
The following environment variables are used by this module: |
653 |
|
654 |
=over 4 |
655 |
|
656 |
=item C<PERL_ANYEVENT_VERBOSE> |
657 |
|
658 |
When set to C<2> or higher, cause AnyEvent to report to STDERR which event |
659 |
model it chooses. |
660 |
|
661 |
=item C<PERL_ANYEVENT_MODEL> |
662 |
|
663 |
This can be used to specify the event model to be used by AnyEvent, before |
664 |
autodetection and -probing kicks in. It must be a string consisting |
665 |
entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended |
666 |
and the resulting module name is loaded and if the load was successful, |
667 |
used as event model. If it fails to load AnyEvent will proceed with |
668 |
autodetection and -probing. |
669 |
|
670 |
This functionality might change in future versions. |
671 |
|
672 |
For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you |
673 |
could start your program like this: |
674 |
|
675 |
PERL_ANYEVENT_MODEL=Perl perl ... |
676 |
|
677 |
=back |
678 |
|
679 |
=head1 EXAMPLE PROGRAM |
680 |
|
681 |
The following program uses an IO watcher to read data from STDIN, a timer |
682 |
to display a message once per second, and a condition variable to quit the |
683 |
program when the user enters quit: |
684 |
|
685 |
use AnyEvent; |
686 |
|
687 |
my $cv = AnyEvent->condvar; |
688 |
|
689 |
my $io_watcher = AnyEvent->io ( |
690 |
fh => \*STDIN, |
691 |
poll => 'r', |
692 |
cb => sub { |
693 |
warn "io event <$_[0]>\n"; # will always output <r> |
694 |
chomp (my $input = <STDIN>); # read a line |
695 |
warn "read: $input\n"; # output what has been read |
696 |
$cv->broadcast if $input =~ /^q/i; # quit program if /^q/i |
697 |
}, |
698 |
); |
699 |
|
700 |
my $time_watcher; # can only be used once |
701 |
|
702 |
sub new_timer { |
703 |
$timer = AnyEvent->timer (after => 1, cb => sub { |
704 |
warn "timeout\n"; # print 'timeout' about every second |
705 |
&new_timer; # and restart the time |
706 |
}); |
707 |
} |
708 |
|
709 |
new_timer; # create first timer |
710 |
|
711 |
$cv->wait; # wait until user enters /^q/i |
712 |
|
713 |
=head1 REAL-WORLD EXAMPLE |
714 |
|
715 |
Consider the L<Net::FCP> module. It features (among others) the following |
716 |
API calls, which are to freenet what HTTP GET requests are to http: |
717 |
|
718 |
my $data = $fcp->client_get ($url); # blocks |
719 |
|
720 |
my $transaction = $fcp->txn_client_get ($url); # does not block |
721 |
$transaction->cb ( sub { ... } ); # set optional result callback |
722 |
my $data = $transaction->result; # possibly blocks |
723 |
|
724 |
The C<client_get> method works like C<LWP::Simple::get>: it requests the |
725 |
given URL and waits till the data has arrived. It is defined to be: |
726 |
|
727 |
sub client_get { $_[0]->txn_client_get ($_[1])->result } |
728 |
|
729 |
And in fact is automatically generated. This is the blocking API of |
730 |
L<Net::FCP>, and it works as simple as in any other, similar, module. |
731 |
|
732 |
More complicated is C<txn_client_get>: It only creates a transaction |
733 |
(completion, result, ...) object and initiates the transaction. |
734 |
|
735 |
my $txn = bless { }, Net::FCP::Txn::; |
736 |
|
737 |
It also creates a condition variable that is used to signal the completion |
738 |
of the request: |
739 |
|
740 |
$txn->{finished} = AnyAvent->condvar; |
741 |
|
742 |
It then creates a socket in non-blocking mode. |
743 |
|
744 |
socket $txn->{fh}, ...; |
745 |
fcntl $txn->{fh}, F_SETFL, O_NONBLOCK; |
746 |
connect $txn->{fh}, ... |
747 |
and !$!{EWOULDBLOCK} |
748 |
and !$!{EINPROGRESS} |
749 |
and Carp::croak "unable to connect: $!\n"; |
750 |
|
751 |
Then it creates a write-watcher which gets called whenever an error occurs |
752 |
or the connection succeeds: |
753 |
|
754 |
$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'w', cb => sub { $txn->fh_ready_w }); |
755 |
|
756 |
And returns this transaction object. The C<fh_ready_w> callback gets |
757 |
called as soon as the event loop detects that the socket is ready for |
758 |
writing. |
759 |
|
760 |
The C<fh_ready_w> method makes the socket blocking again, writes the |
761 |
request data and replaces the watcher by a read watcher (waiting for reply |
762 |
data). The actual code is more complicated, but that doesn't matter for |
763 |
this example: |
764 |
|
765 |
fcntl $txn->{fh}, F_SETFL, 0; |
766 |
syswrite $txn->{fh}, $txn->{request} |
767 |
or die "connection or write error"; |
768 |
$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r }); |
769 |
|
770 |
Again, C<fh_ready_r> waits till all data has arrived, and then stores the |
771 |
result and signals any possible waiters that the request ahs finished: |
772 |
|
773 |
sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf}; |
774 |
|
775 |
if (end-of-file or data complete) { |
776 |
$txn->{result} = $txn->{buf}; |
777 |
$txn->{finished}->broadcast; |
778 |
$txb->{cb}->($txn) of $txn->{cb}; # also call callback |
779 |
} |
780 |
|
781 |
The C<result> method, finally, just waits for the finished signal (if the |
782 |
request was already finished, it doesn't wait, of course, and returns the |
783 |
data: |
784 |
|
785 |
$txn->{finished}->wait; |
786 |
return $txn->{result}; |
787 |
|
788 |
The actual code goes further and collects all errors (C<die>s, exceptions) |
789 |
that occured during request processing. The C<result> method detects |
790 |
whether an exception as thrown (it is stored inside the $txn object) |
791 |
and just throws the exception, which means connection errors and other |
792 |
problems get reported tot he code that tries to use the result, not in a |
793 |
random callback. |
794 |
|
795 |
All of this enables the following usage styles: |
796 |
|
797 |
1. Blocking: |
798 |
|
799 |
my $data = $fcp->client_get ($url); |
800 |
|
801 |
2. Blocking, but running in parallel: |
802 |
|
803 |
my @datas = map $_->result, |
804 |
map $fcp->txn_client_get ($_), |
805 |
@urls; |
806 |
|
807 |
Both blocking examples work without the module user having to know |
808 |
anything about events. |
809 |
|
810 |
3a. Event-based in a main program, using any supported event module: |
811 |
|
812 |
use EV; |
813 |
|
814 |
$fcp->txn_client_get ($url)->cb (sub { |
815 |
my $txn = shift; |
816 |
my $data = $txn->result; |
817 |
... |
818 |
}); |
819 |
|
820 |
EV::loop; |
821 |
|
822 |
3b. The module user could use AnyEvent, too: |
823 |
|
824 |
use AnyEvent; |
825 |
|
826 |
my $quit = AnyEvent->condvar; |
827 |
|
828 |
$fcp->txn_client_get ($url)->cb (sub { |
829 |
... |
830 |
$quit->broadcast; |
831 |
}); |
832 |
|
833 |
$quit->wait; |
834 |
|
835 |
=head1 FORK |
836 |
|
837 |
Most event libraries are not fork-safe. The ones who are usually are |
838 |
because they are so inefficient. Only L<EV> is fully fork-aware. |
839 |
|
840 |
If you have to fork, you must either do so I<before> creating your first |
841 |
watcher OR you must not use AnyEvent at all in the child. |
842 |
|
843 |
=head1 SECURITY CONSIDERATIONS |
844 |
|
845 |
AnyEvent can be forced to load any event model via |
846 |
$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to |
847 |
execute arbitrary code or directly gain access, it can easily be used to |
848 |
make the program hang or malfunction in subtle ways, as AnyEvent watchers |
849 |
will not be active when the program uses a different event model than |
850 |
specified in the variable. |
851 |
|
852 |
You can make AnyEvent completely ignore this variable by deleting it |
853 |
before the first watcher gets created, e.g. with a C<BEGIN> block: |
854 |
|
855 |
BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} } |
856 |
|
857 |
use AnyEvent; |
858 |
|
859 |
=head1 SEE ALSO |
860 |
|
861 |
Event modules: L<Coro::EV>, L<EV>, L<EV::Glib>, L<Glib::EV>, |
862 |
L<Coro::Event>, L<Event>, L<Glib::Event>, L<Glib>, L<Coro>, L<Tk>, |
863 |
L<Event::Lib>. |
864 |
|
865 |
Implementations: L<AnyEvent::Impl::CoroEV>, L<AnyEvent::Impl::EV>, |
866 |
L<AnyEvent::Impl::CoroEvent>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>, |
867 |
L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>, L<AnyEvent::Impl::EventLib>. |
868 |
|
869 |
Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>. |
870 |
|
871 |
=head1 AUTHOR |
872 |
|
873 |
Marc Lehmann <schmorp@schmorp.de> |
874 |
http://home.schmorp.de/ |
875 |
|
876 |
=cut |
877 |
|
878 |
1 |
879 |
|