1 |
NAME |
2 |
AnyEvent - the DBI of event loop programming |
3 |
|
4 |
EV, Event, Glib, Tk, Perl, Event::Lib, Irssi, rxvt-unicode, IO::Async, |
5 |
Qt and POE are various supported event loops/environments. |
6 |
|
7 |
SYNOPSIS |
8 |
use AnyEvent; |
9 |
|
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# file descriptor readable |
11 |
my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... }); |
12 |
|
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# one-shot or repeating timers |
14 |
my $w = AnyEvent->timer (after => $seconds, cb => sub { ... }); |
15 |
my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ... |
16 |
|
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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. |
19 |
|
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# POSIX signal |
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my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... }); |
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|
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# child process exit |
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my $w = AnyEvent->child (pid => $pid, cb => sub { |
25 |
my ($pid, $status) = @_; |
26 |
... |
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}); |
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|
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# called when event loop idle (if applicable) |
30 |
my $w = AnyEvent->idle (cb => sub { ... }); |
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|
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my $w = AnyEvent->condvar; # stores whether a condition was flagged |
33 |
$w->send; # wake up current and all future recv's |
34 |
$w->recv; # enters "main loop" till $condvar gets ->send |
35 |
# use a condvar in callback mode: |
36 |
$w->cb (sub { $_[0]->recv }); |
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|
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INTRODUCTION/TUTORIAL |
39 |
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. |
42 |
|
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SUPPORT |
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There is a mailinglist for discussing all things AnyEvent, and an IRC |
45 |
channel, too. |
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|
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See the AnyEvent project page at the Schmorpforge Ta-Sa Software |
48 |
Repository, at <http://anyevent.schmorp.de>, for more info. |
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|
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WHY YOU SHOULD USE THIS MODULE (OR NOT) |
51 |
Glib, POE, IO::Async, Event... CPAN offers event models by the dozen |
52 |
nowadays. So what is different about AnyEvent? |
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|
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Executive Summary: AnyEvent is *compatible*, AnyEvent is *free of |
55 |
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, |
61 |
only one event loop can be active at the same time in a process. |
62 |
AnyEvent cannot change this, but it can hide the differences between |
63 |
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 |
67 |
religion, a way of living, and most importantly: without forcing your |
68 |
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 |
74 |
cannot use anything else, as they are simply incompatible to everything |
75 |
that isn't them. What's worse, all the potential users of your module |
76 |
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 |
79 |
fine. AnyEvent + Tk works fine etc. etc. but none of these work together |
80 |
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). |
86 |
|
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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 |
90 |
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 |
97 |
such as Windows) and lots of real-world knowledge and workarounds for |
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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 |
105 |
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 |
111 |
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 |
121 |
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, |
125 |
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 |
132 |
|
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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 |
138 |
"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 :) |
140 |
|
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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 |
152 |
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 |
154 |
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 |
186 |
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 |
223 |
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. |
231 |
|
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The callback will be rescheduled before invoking the callback, but no |
233 |
attempt is done to avoid timer drift in most backends, so the interval |
234 |
is only approximate. |
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|
236 |
Example: fire an event after 7.7 seconds. |
237 |
|
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my $w = AnyEvent->timer (after => 7.7, cb => sub { |
239 |
warn "timeout\n"; |
240 |
}); |
241 |
|
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# to cancel the timer: |
243 |
undef $w; |
244 |
|
245 |
Example 2: fire an event after 0.5 seconds, then roughly every second. |
246 |
|
247 |
my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub { |
248 |
warn "timeout\n"; |
249 |
}; |
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|
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TIMING ISSUES |
252 |
There are two ways to handle timers: based on real time (relative, "fire |
253 |
in 10 seconds") and based on wallclock time (absolute, "fire at 12 |
254 |
o'clock"). |
255 |
|
256 |
While most event loops expect timers to specified in a relative way, |
257 |
they use absolute time internally. This makes a difference when your |
258 |
clock "jumps", for example, when ntp decides to set your clock backwards |
259 |
from the wrong date of 2014-01-01 to 2008-01-01, a watcher that is |
260 |
supposed to fire "after" a second might actually take six years to |
261 |
finally fire. |
262 |
|
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AnyEvent cannot compensate for this. The only event loop that is |
264 |
conscious about these issues is EV, which offers both relative |
265 |
(ev_timer, based on true relative time) and absolute (ev_periodic, based |
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on wallclock time) timers. |
267 |
|
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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 |
274 |
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 |
276 |
"Time::HiRes::time" return, and the result is guaranteed to be |
277 |
compatible with those). |
278 |
|
279 |
It progresses independently of any event loop processing, i.e. each |
280 |
call will check the system clock, which usually gets updated |
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frequently. |
282 |
|
283 |
AnyEvent->now |
284 |
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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|
290 |
*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.* |
292 |
|
293 |
This function is also often faster then "AnyEvent->time", and thus |
294 |
the preferred method if you want some timestamp (for example, |
295 |
AnyEvent::Handle uses this to update it's activity timeouts). |
296 |
|
297 |
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. |
299 |
|
300 |
For a practical example of when these times differ, consider |
301 |
Event::Lib and EV and the following set-up: |
302 |
|
303 |
The event loop is running and has just invoked one of your callback |
304 |
at time=500 (assume no other callbacks delay processing). In your |
305 |
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 |
307 |
timer that fires after three seconds. |
308 |
|
309 |
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 |
311 |
scheduled to fire at time=504 (501 + 3). |
312 |
|
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With EV, "AnyEvent->time" returns 501 (as that is the current time), |
314 |
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 |
316 |
at time=503 (500 + 3). |
317 |
|
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In one sense, Event::Lib is more exact, as it uses the current time |
319 |
regardless of any delays introduced by event processing. However, |
320 |
most callbacks do not expect large delays in processing, so this |
321 |
causes a higher drift (and a lot more system calls to get the |
322 |
current time). |
323 |
|
324 |
In another sense, EV is more exact, as your timer will be scheduled |
325 |
at the same time, regardless of how long event processing actually |
326 |
took. |
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|
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In either case, if you care (and in most cases, you don't), then you |
329 |
can get whatever behaviour you want with any event loop, by taking |
330 |
the difference between "AnyEvent->time" and "AnyEvent->now" into |
331 |
account. |
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|
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AnyEvent->now_update |
334 |
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). |
337 |
|
338 |
When a callback runs for a long time (or when the process sleeps), |
339 |
then this "current" time will differ substantially from the real |
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time, which might affect timers and time-outs. |
341 |
|
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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". |
344 |
|
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Note that updating the time *might* cause some events to be handled. |
346 |
|
347 |
SIGNAL WATCHERS |
348 |
You can watch for signals using a signal watcher, "signal" is the signal |
349 |
*name* in uppercase and without any "SIG" prefix, "cb" is the Perl |
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callback to be invoked whenever a signal occurs. |
351 |
|
352 |
Although the callback might get passed parameters, their value and |
353 |
presence is undefined and you cannot rely on them. Portable AnyEvent |
354 |
callbacks cannot use arguments passed to signal watcher callbacks. |
355 |
|
356 |
Multiple signal occurrences can be clumped together into one callback |
357 |
invocation, and callback invocation will be synchronous. Synchronous |
358 |
means that it might take a while until the signal gets handled by the |
359 |
process, but it is guaranteed not to interrupt any other callbacks. |
360 |
|
361 |
The main advantage of using these watchers is that you can share a |
362 |
signal between multiple watchers, and AnyEvent will ensure that signals |
363 |
will not interrupt your program at bad times. |
364 |
|
365 |
This watcher might use %SIG (depending on the event loop used), so |
366 |
programs overwriting those signals directly will likely not work |
367 |
correctly. |
368 |
|
369 |
Example: exit on SIGINT |
370 |
|
371 |
my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 }); |
372 |
|
373 |
Signal Races, Delays and Workarounds |
374 |
Many event loops (e.g. Glib, Tk, Qt, IO::Async) do not support attaching |
375 |
callbacks to signals in a generic way, which is a pity, as you cannot do |
376 |
race-free signal handling in perl. AnyEvent will try to do it's best, |
377 |
but in some cases, signals will be delayed. The maximum time a signal |
378 |
might be delayed is specified in $AnyEvent::MAX_SIGNAL_LATENCY (default: |
379 |
10 seconds). This variable can be changed only before the first signal |
380 |
watcher is created, and should be left alone otherwise. Higher values |
381 |
will cause fewer spurious wake-ups, which is better for power and CPU |
382 |
saving. All these problems can be avoided by installing the optional |
383 |
Async::Interrupt module. This will not work with inherently broken event |
384 |
loops such as Event or Event::Lib (and not with POE currently, as POE |
385 |
does it's own workaround with one-second latency). With those, you just |
386 |
have to suffer the delays. |
387 |
|
388 |
CHILD PROCESS WATCHERS |
389 |
You can also watch on a child process exit and catch its exit status. |
390 |
|
391 |
The child process is specified by the "pid" argument (one some backends, |
392 |
using 0 watches for any child process exit, on others this will croak). |
393 |
The watcher will be triggered only when the child process has finished |
394 |
and an exit status is available, not on any trace events |
395 |
(stopped/continued). |
396 |
|
397 |
The callback will be called with the pid and exit status (as returned by |
398 |
waitpid), so unlike other watcher types, you *can* rely on child watcher |
399 |
callback arguments. |
400 |
|
401 |
This watcher type works by installing a signal handler for "SIGCHLD", |
402 |
and since it cannot be shared, nothing else should use SIGCHLD or reap |
403 |
random child processes (waiting for specific child processes, e.g. |
404 |
inside "system", is just fine). |
405 |
|
406 |
There is a slight catch to child watchers, however: you usually start |
407 |
them *after* the child process was created, and this means the process |
408 |
could have exited already (and no SIGCHLD will be sent anymore). |
409 |
|
410 |
Not all event models handle this correctly (neither POE nor IO::Async |
411 |
do, see their AnyEvent::Impl manpages for details), but even for event |
412 |
models that *do* handle this correctly, they usually need to be loaded |
413 |
before the process exits (i.e. before you fork in the first place). |
414 |
AnyEvent's pure perl event loop handles all cases correctly regardless |
415 |
of when you start the watcher. |
416 |
|
417 |
This means you cannot create a child watcher as the very first thing in |
418 |
an AnyEvent program, you *have* to create at least one watcher before |
419 |
you "fork" the child (alternatively, you can call "AnyEvent::detect"). |
420 |
|
421 |
As most event loops do not support waiting for child events, they will |
422 |
be emulated by AnyEvent in most cases, in which the latency and race |
423 |
problems mentioned in the description of signal watchers apply. |
424 |
|
425 |
Example: fork a process and wait for it |
426 |
|
427 |
my $done = AnyEvent->condvar; |
428 |
|
429 |
my $pid = fork or exit 5; |
430 |
|
431 |
my $w = AnyEvent->child ( |
432 |
pid => $pid, |
433 |
cb => sub { |
434 |
my ($pid, $status) = @_; |
435 |
warn "pid $pid exited with status $status"; |
436 |
$done->send; |
437 |
}, |
438 |
); |
439 |
|
440 |
# do something else, then wait for process exit |
441 |
$done->recv; |
442 |
|
443 |
IDLE WATCHERS |
444 |
Sometimes there is a need to do something, but it is not so important to |
445 |
do it instantly, but only when there is nothing better to do. This |
446 |
"nothing better to do" is usually defined to be "no other events need |
447 |
attention by the event loop". |
448 |
|
449 |
Idle watchers ideally get invoked when the event loop has nothing better |
450 |
to do, just before it would block the process to wait for new events. |
451 |
Instead of blocking, the idle watcher is invoked. |
452 |
|
453 |
Most event loops unfortunately do not really support idle watchers (only |
454 |
EV, Event and Glib do it in a usable fashion) - for the rest, AnyEvent |
455 |
will simply call the callback "from time to time". |
456 |
|
457 |
Example: read lines from STDIN, but only process them when the program |
458 |
is otherwise idle: |
459 |
|
460 |
my @lines; # read data |
461 |
my $idle_w; |
462 |
my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub { |
463 |
push @lines, scalar <STDIN>; |
464 |
|
465 |
# start an idle watcher, if not already done |
466 |
$idle_w ||= AnyEvent->idle (cb => sub { |
467 |
# handle only one line, when there are lines left |
468 |
if (my $line = shift @lines) { |
469 |
print "handled when idle: $line"; |
470 |
} else { |
471 |
# otherwise disable the idle watcher again |
472 |
undef $idle_w; |
473 |
} |
474 |
}); |
475 |
}); |
476 |
|
477 |
CONDITION VARIABLES |
478 |
If you are familiar with some event loops you will know that all of them |
479 |
require you to run some blocking "loop", "run" or similar function that |
480 |
will actively watch for new events and call your callbacks. |
481 |
|
482 |
AnyEvent is slightly different: it expects somebody else to run the |
483 |
event loop and will only block when necessary (usually when told by the |
484 |
user). |
485 |
|
486 |
The instrument to do that is called a "condition variable", so called |
487 |
because they represent a condition that must become true. |
488 |
|
489 |
Now is probably a good time to look at the examples further below. |
490 |
|
491 |
Condition variables can be created by calling the "AnyEvent->condvar" |
492 |
method, usually without arguments. The only argument pair allowed is |
493 |
"cb", which specifies a callback to be called when the condition |
494 |
variable becomes true, with the condition variable as the first argument |
495 |
(but not the results). |
496 |
|
497 |
After creation, the condition variable is "false" until it becomes |
498 |
"true" by calling the "send" method (or calling the condition variable |
499 |
as if it were a callback, read about the caveats in the description for |
500 |
the "->send" method). |
501 |
|
502 |
Condition variables are similar to callbacks, except that you can |
503 |
optionally wait for them. They can also be called merge points - points |
504 |
in time where multiple outstanding events have been processed. And yet |
505 |
another way to call them is transactions - each condition variable can |
506 |
be used to represent a transaction, which finishes at some point and |
507 |
delivers a result. And yet some people know them as "futures" - a |
508 |
promise to compute/deliver something that you can wait for. |
509 |
|
510 |
Condition variables are very useful to signal that something has |
511 |
finished, for example, if you write a module that does asynchronous http |
512 |
requests, then a condition variable would be the ideal candidate to |
513 |
signal the availability of results. The user can either act when the |
514 |
callback is called or can synchronously "->recv" for the results. |
515 |
|
516 |
You can also use them to simulate traditional event loops - for example, |
517 |
you can block your main program until an event occurs - for example, you |
518 |
could "->recv" in your main program until the user clicks the Quit |
519 |
button of your app, which would "->send" the "quit" event. |
520 |
|
521 |
Note that condition variables recurse into the event loop - if you have |
522 |
two pieces of code that call "->recv" in a round-robin fashion, you |
523 |
lose. Therefore, condition variables are good to export to your caller, |
524 |
but you should avoid making a blocking wait yourself, at least in |
525 |
callbacks, as this asks for trouble. |
526 |
|
527 |
Condition variables are represented by hash refs in perl, and the keys |
528 |
used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy |
529 |
(it is often useful to build your own transaction class on top of |
530 |
AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call |
531 |
it's "new" method in your own "new" method. |
532 |
|
533 |
There are two "sides" to a condition variable - the "producer side" |
534 |
which eventually calls "-> send", and the "consumer side", which waits |
535 |
for the send to occur. |
536 |
|
537 |
Example: wait for a timer. |
538 |
|
539 |
# wait till the result is ready |
540 |
my $result_ready = AnyEvent->condvar; |
541 |
|
542 |
# do something such as adding a timer |
543 |
# or socket watcher the calls $result_ready->send |
544 |
# when the "result" is ready. |
545 |
# in this case, we simply use a timer: |
546 |
my $w = AnyEvent->timer ( |
547 |
after => 1, |
548 |
cb => sub { $result_ready->send }, |
549 |
); |
550 |
|
551 |
# this "blocks" (while handling events) till the callback |
552 |
# calls -<send |
553 |
$result_ready->recv; |
554 |
|
555 |
Example: wait for a timer, but take advantage of the fact that condition |
556 |
variables are also callable directly. |
557 |
|
558 |
my $done = AnyEvent->condvar; |
559 |
my $delay = AnyEvent->timer (after => 5, cb => $done); |
560 |
$done->recv; |
561 |
|
562 |
Example: Imagine an API that returns a condvar and doesn't support |
563 |
callbacks. This is how you make a synchronous call, for example from the |
564 |
main program: |
565 |
|
566 |
use AnyEvent::CouchDB; |
567 |
|
568 |
... |
569 |
|
570 |
my @info = $couchdb->info->recv; |
571 |
|
572 |
And this is how you would just set a callback to be called whenever the |
573 |
results are available: |
574 |
|
575 |
$couchdb->info->cb (sub { |
576 |
my @info = $_[0]->recv; |
577 |
}); |
578 |
|
579 |
METHODS FOR PRODUCERS |
580 |
These methods should only be used by the producing side, i.e. the |
581 |
code/module that eventually sends the signal. Note that it is also the |
582 |
producer side which creates the condvar in most cases, but it isn't |
583 |
uncommon for the consumer to create it as well. |
584 |
|
585 |
$cv->send (...) |
586 |
Flag the condition as ready - a running "->recv" and all further |
587 |
calls to "recv" will (eventually) return after this method has been |
588 |
called. If nobody is waiting the send will be remembered. |
589 |
|
590 |
If a callback has been set on the condition variable, it is called |
591 |
immediately from within send. |
592 |
|
593 |
Any arguments passed to the "send" call will be returned by all |
594 |
future "->recv" calls. |
595 |
|
596 |
Condition variables are overloaded so one can call them directly (as |
597 |
if they were a code reference). Calling them directly is the same as |
598 |
calling "send". |
599 |
|
600 |
$cv->croak ($error) |
601 |
Similar to send, but causes all call's to "->recv" to invoke |
602 |
"Carp::croak" with the given error message/object/scalar. |
603 |
|
604 |
This can be used to signal any errors to the condition variable |
605 |
user/consumer. Doing it this way instead of calling "croak" directly |
606 |
delays the error detetcion, but has the overwhelmign advantage that |
607 |
it diagnoses the error at the place where the result is expected, |
608 |
and not deep in some event clalback without connection to the actual |
609 |
code causing the problem. |
610 |
|
611 |
$cv->begin ([group callback]) |
612 |
$cv->end |
613 |
These two methods can be used to combine many transactions/events |
614 |
into one. For example, a function that pings many hosts in parallel |
615 |
might want to use a condition variable for the whole process. |
616 |
|
617 |
Every call to "->begin" will increment a counter, and every call to |
618 |
"->end" will decrement it. If the counter reaches 0 in "->end", the |
619 |
(last) callback passed to "begin" will be executed. That callback is |
620 |
*supposed* to call "->send", but that is not required. If no |
621 |
callback was set, "send" will be called without any arguments. |
622 |
|
623 |
You can think of "$cv->send" giving you an OR condition (one call |
624 |
sends), while "$cv->begin" and "$cv->end" giving you an AND |
625 |
condition (all "begin" calls must be "end"'ed before the condvar |
626 |
sends). |
627 |
|
628 |
Let's start with a simple example: you have two I/O watchers (for |
629 |
example, STDOUT and STDERR for a program), and you want to wait for |
630 |
both streams to close before activating a condvar: |
631 |
|
632 |
my $cv = AnyEvent->condvar; |
633 |
|
634 |
$cv->begin; # first watcher |
635 |
my $w1 = AnyEvent->io (fh => $fh1, cb => sub { |
636 |
defined sysread $fh1, my $buf, 4096 |
637 |
or $cv->end; |
638 |
}); |
639 |
|
640 |
$cv->begin; # second watcher |
641 |
my $w2 = AnyEvent->io (fh => $fh2, cb => sub { |
642 |
defined sysread $fh2, my $buf, 4096 |
643 |
or $cv->end; |
644 |
}); |
645 |
|
646 |
$cv->recv; |
647 |
|
648 |
This works because for every event source (EOF on file handle), |
649 |
there is one call to "begin", so the condvar waits for all calls to |
650 |
"end" before sending. |
651 |
|
652 |
The ping example mentioned above is slightly more complicated, as |
653 |
the there are results to be passwd back, and the number of tasks |
654 |
that are begung can potentially be zero: |
655 |
|
656 |
my $cv = AnyEvent->condvar; |
657 |
|
658 |
my %result; |
659 |
$cv->begin (sub { $cv->send (\%result) }); |
660 |
|
661 |
for my $host (@list_of_hosts) { |
662 |
$cv->begin; |
663 |
ping_host_then_call_callback $host, sub { |
664 |
$result{$host} = ...; |
665 |
$cv->end; |
666 |
}; |
667 |
} |
668 |
|
669 |
$cv->end; |
670 |
|
671 |
This code fragment supposedly pings a number of hosts and calls |
672 |
"send" after results for all then have have been gathered - in any |
673 |
order. To achieve this, the code issues a call to "begin" when it |
674 |
starts each ping request and calls "end" when it has received some |
675 |
result for it. Since "begin" and "end" only maintain a counter, the |
676 |
order in which results arrive is not relevant. |
677 |
|
678 |
There is an additional bracketing call to "begin" and "end" outside |
679 |
the loop, which serves two important purposes: first, it sets the |
680 |
callback to be called once the counter reaches 0, and second, it |
681 |
ensures that "send" is called even when "no" hosts are being pinged |
682 |
(the loop doesn't execute once). |
683 |
|
684 |
This is the general pattern when you "fan out" into multiple (but |
685 |
potentially none) subrequests: use an outer "begin"/"end" pair to |
686 |
set the callback and ensure "end" is called at least once, and then, |
687 |
for each subrequest you start, call "begin" and for each subrequest |
688 |
you finish, call "end". |
689 |
|
690 |
METHODS FOR CONSUMERS |
691 |
These methods should only be used by the consuming side, i.e. the code |
692 |
awaits the condition. |
693 |
|
694 |
$cv->recv |
695 |
Wait (blocking if necessary) until the "->send" or "->croak" methods |
696 |
have been called on c<$cv>, while servicing other watchers normally. |
697 |
|
698 |
You can only wait once on a condition - additional calls are valid |
699 |
but will return immediately. |
700 |
|
701 |
If an error condition has been set by calling "->croak", then this |
702 |
function will call "croak". |
703 |
|
704 |
In list context, all parameters passed to "send" will be returned, |
705 |
in scalar context only the first one will be returned. |
706 |
|
707 |
Note that doing a blocking wait in a callback is not supported by |
708 |
any event loop, that is, recursive invocation of a blocking "->recv" |
709 |
is not allowed, and the "recv" call will "croak" if such a condition |
710 |
is detected. This condition can be slightly loosened by using |
711 |
Coro::AnyEvent, which allows you to do a blocking "->recv" from any |
712 |
thread that doesn't run the event loop itself. |
713 |
|
714 |
Not all event models support a blocking wait - some die in that case |
715 |
(programs might want to do that to stay interactive), so *if you are |
716 |
using this from a module, never require a blocking wait*. Instead, |
717 |
let the caller decide whether the call will block or not (for |
718 |
example, by coupling condition variables with some kind of request |
719 |
results and supporting callbacks so the caller knows that getting |
720 |
the result will not block, while still supporting blocking waits if |
721 |
the caller so desires). |
722 |
|
723 |
You can ensure that "-recv" never blocks by setting a callback and |
724 |
only calling "->recv" from within that callback (or at a later |
725 |
time). This will work even when the event loop does not support |
726 |
blocking waits otherwise. |
727 |
|
728 |
$bool = $cv->ready |
729 |
Returns true when the condition is "true", i.e. whether "send" or |
730 |
"croak" have been called. |
731 |
|
732 |
$cb = $cv->cb ($cb->($cv)) |
733 |
This is a mutator function that returns the callback set and |
734 |
optionally replaces it before doing so. |
735 |
|
736 |
The callback will be called when the condition becomes "true", i.e. |
737 |
when "send" or "croak" are called, with the only argument being the |
738 |
condition variable itself. Calling "recv" inside the callback or at |
739 |
any later time is guaranteed not to block. |
740 |
|
741 |
SUPPORTED EVENT LOOPS/BACKENDS |
742 |
The available backend classes are (every class has its own manpage): |
743 |
|
744 |
Backends that are autoprobed when no other event loop can be found. |
745 |
EV is the preferred backend when no other event loop seems to be in |
746 |
use. If EV is not installed, then AnyEvent will try Event, and, |
747 |
failing that, will fall back to its own pure-perl implementation, |
748 |
which is available everywhere as it comes with AnyEvent itself. |
749 |
|
750 |
AnyEvent::Impl::EV based on EV (interface to libev, best choice). |
751 |
AnyEvent::Impl::Event based on Event, very stable, few glitches. |
752 |
AnyEvent::Impl::Perl pure-perl implementation, fast and portable. |
753 |
|
754 |
Backends that are transparently being picked up when they are used. |
755 |
These will be used when they are currently loaded when the first |
756 |
watcher is created, in which case it is assumed that the application |
757 |
is using them. This means that AnyEvent will automatically pick the |
758 |
right backend when the main program loads an event module before |
759 |
anything starts to create watchers. Nothing special needs to be done |
760 |
by the main program. |
761 |
|
762 |
AnyEvent::Impl::Glib based on Glib, slow but very stable. |
763 |
AnyEvent::Impl::Tk based on Tk, very broken. |
764 |
AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse. |
765 |
AnyEvent::Impl::POE based on POE, very slow, some limitations. |
766 |
AnyEvent::Impl::Irssi used when running within irssi. |
767 |
|
768 |
Backends with special needs. |
769 |
Qt requires the Qt::Application to be instantiated first, but will |
770 |
otherwise be picked up automatically. As long as the main program |
771 |
instantiates the application before any AnyEvent watchers are |
772 |
created, everything should just work. |
773 |
|
774 |
AnyEvent::Impl::Qt based on Qt. |
775 |
|
776 |
Support for IO::Async can only be partial, as it is too broken and |
777 |
architecturally limited to even support the AnyEvent API. It also is |
778 |
the only event loop that needs the loop to be set explicitly, so it |
779 |
can only be used by a main program knowing about AnyEvent. See |
780 |
AnyEvent::Impl::Async for the gory details. |
781 |
|
782 |
AnyEvent::Impl::IOAsync based on IO::Async, cannot be autoprobed. |
783 |
|
784 |
Event loops that are indirectly supported via other backends. |
785 |
Some event loops can be supported via other modules: |
786 |
|
787 |
There is no direct support for WxWidgets (Wx) or Prima. |
788 |
|
789 |
WxWidgets has no support for watching file handles. However, you can |
790 |
use WxWidgets through the POE adaptor, as POE has a Wx backend that |
791 |
simply polls 20 times per second, which was considered to be too |
792 |
horrible to even consider for AnyEvent. |
793 |
|
794 |
Prima is not supported as nobody seems to be using it, but it has a |
795 |
POE backend, so it can be supported through POE. |
796 |
|
797 |
AnyEvent knows about both Prima and Wx, however, and will try to |
798 |
load POE when detecting them, in the hope that POE will pick them |
799 |
up, in which case everything will be automatic. |
800 |
|
801 |
GLOBAL VARIABLES AND FUNCTIONS |
802 |
These are not normally required to use AnyEvent, but can be useful to |
803 |
write AnyEvent extension modules. |
804 |
|
805 |
$AnyEvent::MODEL |
806 |
Contains "undef" until the first watcher is being created, before |
807 |
the backend has been autodetected. |
808 |
|
809 |
Afterwards it contains the event model that is being used, which is |
810 |
the name of the Perl class implementing the model. This class is |
811 |
usually one of the "AnyEvent::Impl:xxx" modules, but can be any |
812 |
other class in the case AnyEvent has been extended at runtime (e.g. |
813 |
in *rxvt-unicode* it will be "urxvt::anyevent"). |
814 |
|
815 |
AnyEvent::detect |
816 |
Returns $AnyEvent::MODEL, forcing autodetection of the event model |
817 |
if necessary. You should only call this function right before you |
818 |
would have created an AnyEvent watcher anyway, that is, as late as |
819 |
possible at runtime, and not e.g. while initialising of your module. |
820 |
|
821 |
If you need to do some initialisation before AnyEvent watchers are |
822 |
created, use "post_detect". |
823 |
|
824 |
$guard = AnyEvent::post_detect { BLOCK } |
825 |
Arranges for the code block to be executed as soon as the event |
826 |
model is autodetected (or immediately if this has already happened). |
827 |
|
828 |
The block will be executed *after* the actual backend has been |
829 |
detected ($AnyEvent::MODEL is set), but *before* any watchers have |
830 |
been created, so it is possible to e.g. patch @AnyEvent::ISA or do |
831 |
other initialisations - see the sources of AnyEvent::Strict or |
832 |
AnyEvent::AIO to see how this is used. |
833 |
|
834 |
The most common usage is to create some global watchers, without |
835 |
forcing event module detection too early, for example, AnyEvent::AIO |
836 |
creates and installs the global IO::AIO watcher in a "post_detect" |
837 |
block to avoid autodetecting the event module at load time. |
838 |
|
839 |
If called in scalar or list context, then it creates and returns an |
840 |
object that automatically removes the callback again when it is |
841 |
destroyed (or "undef" when the hook was immediately executed). See |
842 |
AnyEvent::AIO for a case where this is useful. |
843 |
|
844 |
Example: Create a watcher for the IO::AIO module and store it in |
845 |
$WATCHER. Only do so after the event loop is initialised, though. |
846 |
|
847 |
our WATCHER; |
848 |
|
849 |
my $guard = AnyEvent::post_detect { |
850 |
$WATCHER = AnyEvent->io (fh => IO::AIO::poll_fileno, poll => 'r', cb => \&IO::AIO::poll_cb); |
851 |
}; |
852 |
|
853 |
# the ||= is important in case post_detect immediately runs the block, |
854 |
# as to not clobber the newly-created watcher. assigning both watcher and |
855 |
# post_detect guard to the same variable has the advantage of users being |
856 |
# able to just C<undef $WATCHER> if the watcher causes them grief. |
857 |
|
858 |
$WATCHER ||= $guard; |
859 |
|
860 |
@AnyEvent::post_detect |
861 |
If there are any code references in this array (you can "push" to it |
862 |
before or after loading AnyEvent), then they will called directly |
863 |
after the event loop has been chosen. |
864 |
|
865 |
You should check $AnyEvent::MODEL before adding to this array, |
866 |
though: if it is defined then the event loop has already been |
867 |
detected, and the array will be ignored. |
868 |
|
869 |
Best use "AnyEvent::post_detect { BLOCK }" when your application |
870 |
allows it,as it takes care of these details. |
871 |
|
872 |
This variable is mainly useful for modules that can do something |
873 |
useful when AnyEvent is used and thus want to know when it is |
874 |
initialised, but do not need to even load it by default. This array |
875 |
provides the means to hook into AnyEvent passively, without loading |
876 |
it. |
877 |
|
878 |
WHAT TO DO IN A MODULE |
879 |
As a module author, you should "use AnyEvent" and call AnyEvent methods |
880 |
freely, but you should not load a specific event module or rely on it. |
881 |
|
882 |
Be careful when you create watchers in the module body - AnyEvent will |
883 |
decide which event module to use as soon as the first method is called, |
884 |
so by calling AnyEvent in your module body you force the user of your |
885 |
module to load the event module first. |
886 |
|
887 |
Never call "->recv" on a condition variable unless you *know* that the |
888 |
"->send" method has been called on it already. This is because it will |
889 |
stall the whole program, and the whole point of using events is to stay |
890 |
interactive. |
891 |
|
892 |
It is fine, however, to call "->recv" when the user of your module |
893 |
requests it (i.e. if you create a http request object ad have a method |
894 |
called "results" that returns the results, it should call "->recv" |
895 |
freely, as the user of your module knows what she is doing. always). |
896 |
|
897 |
WHAT TO DO IN THE MAIN PROGRAM |
898 |
There will always be a single main program - the only place that should |
899 |
dictate which event model to use. |
900 |
|
901 |
If it doesn't care, it can just "use AnyEvent" and use it itself, or not |
902 |
do anything special (it does not need to be event-based) and let |
903 |
AnyEvent decide which implementation to chose if some module relies on |
904 |
it. |
905 |
|
906 |
If the main program relies on a specific event model - for example, in |
907 |
Gtk2 programs you have to rely on the Glib module - you should load the |
908 |
event module before loading AnyEvent or any module that uses it: |
909 |
generally speaking, you should load it as early as possible. The reason |
910 |
is that modules might create watchers when they are loaded, and AnyEvent |
911 |
will decide on the event model to use as soon as it creates watchers, |
912 |
and it might chose the wrong one unless you load the correct one |
913 |
yourself. |
914 |
|
915 |
You can chose to use a pure-perl implementation by loading the |
916 |
"AnyEvent::Impl::Perl" module, which gives you similar behaviour |
917 |
everywhere, but letting AnyEvent chose the model is generally better. |
918 |
|
919 |
MAINLOOP EMULATION |
920 |
Sometimes (often for short test scripts, or even standalone programs who |
921 |
only want to use AnyEvent), you do not want to run a specific event |
922 |
loop. |
923 |
|
924 |
In that case, you can use a condition variable like this: |
925 |
|
926 |
AnyEvent->condvar->recv; |
927 |
|
928 |
This has the effect of entering the event loop and looping forever. |
929 |
|
930 |
Note that usually your program has some exit condition, in which case it |
931 |
is better to use the "traditional" approach of storing a condition |
932 |
variable somewhere, waiting for it, and sending it when the program |
933 |
should exit cleanly. |
934 |
|
935 |
OTHER MODULES |
936 |
The following is a non-exhaustive list of additional modules that use |
937 |
AnyEvent as a client and can therefore be mixed easily with other |
938 |
AnyEvent modules and other event loops in the same program. Some of the |
939 |
modules come with AnyEvent, most are available via CPAN. |
940 |
|
941 |
AnyEvent::Util |
942 |
Contains various utility functions that replace often-used but |
943 |
blocking functions such as "inet_aton" by event-/callback-based |
944 |
versions. |
945 |
|
946 |
AnyEvent::Socket |
947 |
Provides various utility functions for (internet protocol) sockets, |
948 |
addresses and name resolution. Also functions to create non-blocking |
949 |
tcp connections or tcp servers, with IPv6 and SRV record support and |
950 |
more. |
951 |
|
952 |
AnyEvent::Handle |
953 |
Provide read and write buffers, manages watchers for reads and |
954 |
writes, supports raw and formatted I/O, I/O queued and fully |
955 |
transparent and non-blocking SSL/TLS (via AnyEvent::TLS. |
956 |
|
957 |
AnyEvent::DNS |
958 |
Provides rich asynchronous DNS resolver capabilities. |
959 |
|
960 |
AnyEvent::HTTP |
961 |
A simple-to-use HTTP library that is capable of making a lot of |
962 |
concurrent HTTP requests. |
963 |
|
964 |
AnyEvent::HTTPD |
965 |
Provides a simple web application server framework. |
966 |
|
967 |
AnyEvent::FastPing |
968 |
The fastest ping in the west. |
969 |
|
970 |
AnyEvent::DBI |
971 |
Executes DBI requests asynchronously in a proxy process. |
972 |
|
973 |
AnyEvent::AIO |
974 |
Truly asynchronous I/O, should be in the toolbox of every event |
975 |
programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent |
976 |
together. |
977 |
|
978 |
AnyEvent::BDB |
979 |
Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently |
980 |
fuses BDB and AnyEvent together. |
981 |
|
982 |
AnyEvent::GPSD |
983 |
A non-blocking interface to gpsd, a daemon delivering GPS |
984 |
information. |
985 |
|
986 |
AnyEvent::IRC |
987 |
AnyEvent based IRC client module family (replacing the older |
988 |
Net::IRC3). |
989 |
|
990 |
AnyEvent::XMPP |
991 |
AnyEvent based XMPP (Jabber protocol) module family (replacing the |
992 |
older Net::XMPP2>. |
993 |
|
994 |
AnyEvent::IGS |
995 |
A non-blocking interface to the Internet Go Server protocol (used by |
996 |
App::IGS). |
997 |
|
998 |
Net::FCP |
999 |
AnyEvent-based implementation of the Freenet Client Protocol, |
1000 |
birthplace of AnyEvent. |
1001 |
|
1002 |
Event::ExecFlow |
1003 |
High level API for event-based execution flow control. |
1004 |
|
1005 |
Coro |
1006 |
Has special support for AnyEvent via Coro::AnyEvent. |
1007 |
|
1008 |
ERROR AND EXCEPTION HANDLING |
1009 |
In general, AnyEvent does not do any error handling - it relies on the |
1010 |
caller to do that if required. The AnyEvent::Strict module (see also the |
1011 |
"PERL_ANYEVENT_STRICT" environment variable, below) provides strict |
1012 |
checking of all AnyEvent methods, however, which is highly useful during |
1013 |
development. |
1014 |
|
1015 |
As for exception handling (i.e. runtime errors and exceptions thrown |
1016 |
while executing a callback), this is not only highly event-loop |
1017 |
specific, but also not in any way wrapped by this module, as this is the |
1018 |
job of the main program. |
1019 |
|
1020 |
The pure perl event loop simply re-throws the exception (usually within |
1021 |
"condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()", |
1022 |
Glib uses "install_exception_handler" and so on. |
1023 |
|
1024 |
ENVIRONMENT VARIABLES |
1025 |
The following environment variables are used by this module or its |
1026 |
submodules. |
1027 |
|
1028 |
Note that AnyEvent will remove *all* environment variables starting with |
1029 |
"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is |
1030 |
enabled. |
1031 |
|
1032 |
"PERL_ANYEVENT_VERBOSE" |
1033 |
By default, AnyEvent will be completely silent except in fatal |
1034 |
conditions. You can set this environment variable to make AnyEvent |
1035 |
more talkative. |
1036 |
|
1037 |
When set to 1 or higher, causes AnyEvent to warn about unexpected |
1038 |
conditions, such as not being able to load the event model specified |
1039 |
by "PERL_ANYEVENT_MODEL". |
1040 |
|
1041 |
When set to 2 or higher, cause AnyEvent to report to STDERR which |
1042 |
event model it chooses. |
1043 |
|
1044 |
When set to 8 or higher, then AnyEvent will report extra information |
1045 |
on which optional modules it loads and how it implements certain |
1046 |
features. |
1047 |
|
1048 |
"PERL_ANYEVENT_STRICT" |
1049 |
AnyEvent does not do much argument checking by default, as thorough |
1050 |
argument checking is very costly. Setting this variable to a true |
1051 |
value will cause AnyEvent to load "AnyEvent::Strict" and then to |
1052 |
thoroughly check the arguments passed to most method calls. If it |
1053 |
finds any problems, it will croak. |
1054 |
|
1055 |
In other words, enables "strict" mode. |
1056 |
|
1057 |
Unlike "use strict" (or it's modern cousin, "use common::sense", it |
1058 |
is definitely recommended to keep it off in production. Keeping |
1059 |
"PERL_ANYEVENT_STRICT=1" in your environment while developing |
1060 |
programs can be very useful, however. |
1061 |
|
1062 |
"PERL_ANYEVENT_MODEL" |
1063 |
This can be used to specify the event model to be used by AnyEvent, |
1064 |
before auto detection and -probing kicks in. It must be a string |
1065 |
consisting entirely of ASCII letters. The string "AnyEvent::Impl::" |
1066 |
gets prepended and the resulting module name is loaded and if the |
1067 |
load was successful, used as event model. If it fails to load |
1068 |
AnyEvent will proceed with auto detection and -probing. |
1069 |
|
1070 |
This functionality might change in future versions. |
1071 |
|
1072 |
For example, to force the pure perl model (AnyEvent::Impl::Perl) you |
1073 |
could start your program like this: |
1074 |
|
1075 |
PERL_ANYEVENT_MODEL=Perl perl ... |
1076 |
|
1077 |
"PERL_ANYEVENT_PROTOCOLS" |
1078 |
Used by both AnyEvent::DNS and AnyEvent::Socket to determine |
1079 |
preferences for IPv4 or IPv6. The default is unspecified (and might |
1080 |
change, or be the result of auto probing). |
1081 |
|
1082 |
Must be set to a comma-separated list of protocols or address |
1083 |
families, current supported: "ipv4" and "ipv6". Only protocols |
1084 |
mentioned will be used, and preference will be given to protocols |
1085 |
mentioned earlier in the list. |
1086 |
|
1087 |
This variable can effectively be used for denial-of-service attacks |
1088 |
against local programs (e.g. when setuid), although the impact is |
1089 |
likely small, as the program has to handle conenction and other |
1090 |
failures anyways. |
1091 |
|
1092 |
Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over |
1093 |
IPv6, but support both and try to use both. |
1094 |
"PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to |
1095 |
resolve or contact IPv6 addresses. |
1096 |
"PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but |
1097 |
prefer IPv6 over IPv4. |
1098 |
|
1099 |
"PERL_ANYEVENT_EDNS0" |
1100 |
Used by AnyEvent::DNS to decide whether to use the EDNS0 extension |
1101 |
for DNS. This extension is generally useful to reduce DNS traffic, |
1102 |
but some (broken) firewalls drop such DNS packets, which is why it |
1103 |
is off by default. |
1104 |
|
1105 |
Setting this variable to 1 will cause AnyEvent::DNS to announce |
1106 |
EDNS0 in its DNS requests. |
1107 |
|
1108 |
"PERL_ANYEVENT_MAX_FORKS" |
1109 |
The maximum number of child processes that |
1110 |
"AnyEvent::Util::fork_call" will create in parallel. |
1111 |
|
1112 |
"PERL_ANYEVENT_MAX_OUTSTANDING_DNS" |
1113 |
The default value for the "max_outstanding" parameter for the |
1114 |
default DNS resolver - this is the maximum number of parallel DNS |
1115 |
requests that are sent to the DNS server. |
1116 |
|
1117 |
"PERL_ANYEVENT_RESOLV_CONF" |
1118 |
The file to use instead of /etc/resolv.conf (or OS-specific |
1119 |
configuration) in the default resolver. When set to the empty |
1120 |
string, no default config will be used. |
1121 |
|
1122 |
"PERL_ANYEVENT_CA_FILE", "PERL_ANYEVENT_CA_PATH". |
1123 |
When neither "ca_file" nor "ca_path" was specified during |
1124 |
AnyEvent::TLS context creation, and either of these environment |
1125 |
variables exist, they will be used to specify CA certificate |
1126 |
locations instead of a system-dependent default. |
1127 |
|
1128 |
"PERL_ANYEVENT_AVOID_GUARD" and "PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT" |
1129 |
When these are set to 1, then the respective modules are not loaded. |
1130 |
Mostly good for testing AnyEvent itself. |
1131 |
|
1132 |
SUPPLYING YOUR OWN EVENT MODEL INTERFACE |
1133 |
This is an advanced topic that you do not normally need to use AnyEvent |
1134 |
in a module. This section is only of use to event loop authors who want |
1135 |
to provide AnyEvent compatibility. |
1136 |
|
1137 |
If you need to support another event library which isn't directly |
1138 |
supported by AnyEvent, you can supply your own interface to it by |
1139 |
pushing, before the first watcher gets created, the package name of the |
1140 |
event module and the package name of the interface to use onto |
1141 |
@AnyEvent::REGISTRY. You can do that before and even without loading |
1142 |
AnyEvent, so it is reasonably cheap. |
1143 |
|
1144 |
Example: |
1145 |
|
1146 |
push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::]; |
1147 |
|
1148 |
This tells AnyEvent to (literally) use the "urxvt::anyevent::" |
1149 |
package/class when it finds the "urxvt" package/module is already |
1150 |
loaded. |
1151 |
|
1152 |
When AnyEvent is loaded and asked to find a suitable event model, it |
1153 |
will first check for the presence of urxvt by trying to "use" the |
1154 |
"urxvt::anyevent" module. |
1155 |
|
1156 |
The class should provide implementations for all watcher types. See |
1157 |
AnyEvent::Impl::EV (source code), AnyEvent::Impl::Glib (Source code) and |
1158 |
so on for actual examples. Use "perldoc -m AnyEvent::Impl::Glib" to see |
1159 |
the sources. |
1160 |
|
1161 |
If you don't provide "signal" and "child" watchers than AnyEvent will |
1162 |
provide suitable (hopefully) replacements. |
1163 |
|
1164 |
The above example isn't fictitious, the *rxvt-unicode* (a.k.a. urxvt) |
1165 |
terminal emulator uses the above line as-is. An interface isn't included |
1166 |
in AnyEvent because it doesn't make sense outside the embedded |
1167 |
interpreter inside *rxvt-unicode*, and it is updated and maintained as |
1168 |
part of the *rxvt-unicode* distribution. |
1169 |
|
1170 |
*rxvt-unicode* also cheats a bit by not providing blocking access to |
1171 |
condition variables: code blocking while waiting for a condition will |
1172 |
"die". This still works with most modules/usages, and blocking calls |
1173 |
must not be done in an interactive application, so it makes sense. |
1174 |
|
1175 |
EXAMPLE PROGRAM |
1176 |
The following program uses an I/O watcher to read data from STDIN, a |
1177 |
timer to display a message once per second, and a condition variable to |
1178 |
quit the program when the user enters quit: |
1179 |
|
1180 |
use AnyEvent; |
1181 |
|
1182 |
my $cv = AnyEvent->condvar; |
1183 |
|
1184 |
my $io_watcher = AnyEvent->io ( |
1185 |
fh => \*STDIN, |
1186 |
poll => 'r', |
1187 |
cb => sub { |
1188 |
warn "io event <$_[0]>\n"; # will always output <r> |
1189 |
chomp (my $input = <STDIN>); # read a line |
1190 |
warn "read: $input\n"; # output what has been read |
1191 |
$cv->send if $input =~ /^q/i; # quit program if /^q/i |
1192 |
}, |
1193 |
); |
1194 |
|
1195 |
my $time_watcher; # can only be used once |
1196 |
|
1197 |
sub new_timer { |
1198 |
$timer = AnyEvent->timer (after => 1, cb => sub { |
1199 |
warn "timeout\n"; # print 'timeout' about every second |
1200 |
&new_timer; # and restart the time |
1201 |
}); |
1202 |
} |
1203 |
|
1204 |
new_timer; # create first timer |
1205 |
|
1206 |
$cv->recv; # wait until user enters /^q/i |
1207 |
|
1208 |
REAL-WORLD EXAMPLE |
1209 |
Consider the Net::FCP module. It features (among others) the following |
1210 |
API calls, which are to freenet what HTTP GET requests are to http: |
1211 |
|
1212 |
my $data = $fcp->client_get ($url); # blocks |
1213 |
|
1214 |
my $transaction = $fcp->txn_client_get ($url); # does not block |
1215 |
$transaction->cb ( sub { ... } ); # set optional result callback |
1216 |
my $data = $transaction->result; # possibly blocks |
1217 |
|
1218 |
The "client_get" method works like "LWP::Simple::get": it requests the |
1219 |
given URL and waits till the data has arrived. It is defined to be: |
1220 |
|
1221 |
sub client_get { $_[0]->txn_client_get ($_[1])->result } |
1222 |
|
1223 |
And in fact is automatically generated. This is the blocking API of |
1224 |
Net::FCP, and it works as simple as in any other, similar, module. |
1225 |
|
1226 |
More complicated is "txn_client_get": It only creates a transaction |
1227 |
(completion, result, ...) object and initiates the transaction. |
1228 |
|
1229 |
my $txn = bless { }, Net::FCP::Txn::; |
1230 |
|
1231 |
It also creates a condition variable that is used to signal the |
1232 |
completion of the request: |
1233 |
|
1234 |
$txn->{finished} = AnyAvent->condvar; |
1235 |
|
1236 |
It then creates a socket in non-blocking mode. |
1237 |
|
1238 |
socket $txn->{fh}, ...; |
1239 |
fcntl $txn->{fh}, F_SETFL, O_NONBLOCK; |
1240 |
connect $txn->{fh}, ... |
1241 |
and !$!{EWOULDBLOCK} |
1242 |
and !$!{EINPROGRESS} |
1243 |
and Carp::croak "unable to connect: $!\n"; |
1244 |
|
1245 |
Then it creates a write-watcher which gets called whenever an error |
1246 |
occurs or the connection succeeds: |
1247 |
|
1248 |
$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'w', cb => sub { $txn->fh_ready_w }); |
1249 |
|
1250 |
And returns this transaction object. The "fh_ready_w" callback gets |
1251 |
called as soon as the event loop detects that the socket is ready for |
1252 |
writing. |
1253 |
|
1254 |
The "fh_ready_w" method makes the socket blocking again, writes the |
1255 |
request data and replaces the watcher by a read watcher (waiting for |
1256 |
reply data). The actual code is more complicated, but that doesn't |
1257 |
matter for this example: |
1258 |
|
1259 |
fcntl $txn->{fh}, F_SETFL, 0; |
1260 |
syswrite $txn->{fh}, $txn->{request} |
1261 |
or die "connection or write error"; |
1262 |
$txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r }); |
1263 |
|
1264 |
Again, "fh_ready_r" waits till all data has arrived, and then stores the |
1265 |
result and signals any possible waiters that the request has finished: |
1266 |
|
1267 |
sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf}; |
1268 |
|
1269 |
if (end-of-file or data complete) { |
1270 |
$txn->{result} = $txn->{buf}; |
1271 |
$txn->{finished}->send; |
1272 |
$txb->{cb}->($txn) of $txn->{cb}; # also call callback |
1273 |
} |
1274 |
|
1275 |
The "result" method, finally, just waits for the finished signal (if the |
1276 |
request was already finished, it doesn't wait, of course, and returns |
1277 |
the data: |
1278 |
|
1279 |
$txn->{finished}->recv; |
1280 |
return $txn->{result}; |
1281 |
|
1282 |
The actual code goes further and collects all errors ("die"s, |
1283 |
exceptions) that occurred during request processing. The "result" method |
1284 |
detects whether an exception as thrown (it is stored inside the $txn |
1285 |
object) and just throws the exception, which means connection errors and |
1286 |
other problems get reported tot he code that tries to use the result, |
1287 |
not in a random callback. |
1288 |
|
1289 |
All of this enables the following usage styles: |
1290 |
|
1291 |
1. Blocking: |
1292 |
|
1293 |
my $data = $fcp->client_get ($url); |
1294 |
|
1295 |
2. Blocking, but running in parallel: |
1296 |
|
1297 |
my @datas = map $_->result, |
1298 |
map $fcp->txn_client_get ($_), |
1299 |
@urls; |
1300 |
|
1301 |
Both blocking examples work without the module user having to know |
1302 |
anything about events. |
1303 |
|
1304 |
3a. Event-based in a main program, using any supported event module: |
1305 |
|
1306 |
use EV; |
1307 |
|
1308 |
$fcp->txn_client_get ($url)->cb (sub { |
1309 |
my $txn = shift; |
1310 |
my $data = $txn->result; |
1311 |
... |
1312 |
}); |
1313 |
|
1314 |
EV::loop; |
1315 |
|
1316 |
3b. The module user could use AnyEvent, too: |
1317 |
|
1318 |
use AnyEvent; |
1319 |
|
1320 |
my $quit = AnyEvent->condvar; |
1321 |
|
1322 |
$fcp->txn_client_get ($url)->cb (sub { |
1323 |
... |
1324 |
$quit->send; |
1325 |
}); |
1326 |
|
1327 |
$quit->recv; |
1328 |
|
1329 |
BENCHMARKS |
1330 |
To give you an idea of the performance and overheads that AnyEvent adds |
1331 |
over the event loops themselves and to give you an impression of the |
1332 |
speed of various event loops I prepared some benchmarks. |
1333 |
|
1334 |
BENCHMARKING ANYEVENT OVERHEAD |
1335 |
Here is a benchmark of various supported event models used natively and |
1336 |
through AnyEvent. The benchmark creates a lot of timers (with a zero |
1337 |
timeout) and I/O watchers (watching STDOUT, a pty, to become writable, |
1338 |
which it is), lets them fire exactly once and destroys them again. |
1339 |
|
1340 |
Source code for this benchmark is found as eg/bench in the AnyEvent |
1341 |
distribution. |
1342 |
|
1343 |
Explanation of the columns |
1344 |
*watcher* is the number of event watchers created/destroyed. Since |
1345 |
different event models feature vastly different performances, each event |
1346 |
loop was given a number of watchers so that overall runtime is |
1347 |
acceptable and similar between tested event loop (and keep them from |
1348 |
crashing): Glib would probably take thousands of years if asked to |
1349 |
process the same number of watchers as EV in this benchmark. |
1350 |
|
1351 |
*bytes* is the number of bytes (as measured by the resident set size, |
1352 |
RSS) consumed by each watcher. This method of measuring captures both C |
1353 |
and Perl-based overheads. |
1354 |
|
1355 |
*create* is the time, in microseconds (millionths of seconds), that it |
1356 |
takes to create a single watcher. The callback is a closure shared |
1357 |
between all watchers, to avoid adding memory overhead. That means |
1358 |
closure creation and memory usage is not included in the figures. |
1359 |
|
1360 |
*invoke* is the time, in microseconds, used to invoke a simple callback. |
1361 |
The callback simply counts down a Perl variable and after it was invoked |
1362 |
"watcher" times, it would "->send" a condvar once to signal the end of |
1363 |
this phase. |
1364 |
|
1365 |
*destroy* is the time, in microseconds, that it takes to destroy a |
1366 |
single watcher. |
1367 |
|
1368 |
Results |
1369 |
name watchers bytes create invoke destroy comment |
1370 |
EV/EV 400000 224 0.47 0.35 0.27 EV native interface |
1371 |
EV/Any 100000 224 2.88 0.34 0.27 EV + AnyEvent watchers |
1372 |
CoroEV/Any 100000 224 2.85 0.35 0.28 coroutines + Coro::Signal |
1373 |
Perl/Any 100000 452 4.13 0.73 0.95 pure perl implementation |
1374 |
Event/Event 16000 517 32.20 31.80 0.81 Event native interface |
1375 |
Event/Any 16000 590 35.85 31.55 1.06 Event + AnyEvent watchers |
1376 |
IOAsync/Any 16000 989 38.10 32.77 11.13 via IO::Async::Loop::IO_Poll |
1377 |
IOAsync/Any 16000 990 37.59 29.50 10.61 via IO::Async::Loop::Epoll |
1378 |
Glib/Any 16000 1357 102.33 12.31 51.00 quadratic behaviour |
1379 |
Tk/Any 2000 1860 27.20 66.31 14.00 SEGV with >> 2000 watchers |
1380 |
POE/Event 2000 6328 109.99 751.67 14.02 via POE::Loop::Event |
1381 |
POE/Select 2000 6027 94.54 809.13 579.80 via POE::Loop::Select |
1382 |
|
1383 |
Discussion |
1384 |
The benchmark does *not* measure scalability of the event loop very |
1385 |
well. For example, a select-based event loop (such as the pure perl one) |
1386 |
can never compete with an event loop that uses epoll when the number of |
1387 |
file descriptors grows high. In this benchmark, all events become ready |
1388 |
at the same time, so select/poll-based implementations get an unnatural |
1389 |
speed boost. |
1390 |
|
1391 |
Also, note that the number of watchers usually has a nonlinear effect on |
1392 |
overall speed, that is, creating twice as many watchers doesn't take |
1393 |
twice the time - usually it takes longer. This puts event loops tested |
1394 |
with a higher number of watchers at a disadvantage. |
1395 |
|
1396 |
To put the range of results into perspective, consider that on the |
1397 |
benchmark machine, handling an event takes roughly 1600 CPU cycles with |
1398 |
EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 |
1399 |
CPU cycles with POE. |
1400 |
|
1401 |
"EV" is the sole leader regarding speed and memory use, which are both |
1402 |
maximal/minimal, respectively. Even when going through AnyEvent, it uses |
1403 |
far less memory than any other event loop and is still faster than Event |
1404 |
natively. |
1405 |
|
1406 |
The pure perl implementation is hit in a few sweet spots (both the |
1407 |
constant timeout and the use of a single fd hit optimisations in the |
1408 |
perl interpreter and the backend itself). Nevertheless this shows that |
1409 |
it adds very little overhead in itself. Like any select-based backend |
1410 |
its performance becomes really bad with lots of file descriptors (and |
1411 |
few of them active), of course, but this was not subject of this |
1412 |
benchmark. |
1413 |
|
1414 |
The "Event" module has a relatively high setup and callback invocation |
1415 |
cost, but overall scores in on the third place. |
1416 |
|
1417 |
"IO::Async" performs admirably well, about on par with "Event", even |
1418 |
when using its pure perl backend. |
1419 |
|
1420 |
"Glib"'s memory usage is quite a bit higher, but it features a faster |
1421 |
callback invocation and overall ends up in the same class as "Event". |
1422 |
However, Glib scales extremely badly, doubling the number of watchers |
1423 |
increases the processing time by more than a factor of four, making it |
1424 |
completely unusable when using larger numbers of watchers (note that |
1425 |
only a single file descriptor was used in the benchmark, so |
1426 |
inefficiencies of "poll" do not account for this). |
1427 |
|
1428 |
The "Tk" adaptor works relatively well. The fact that it crashes with |
1429 |
more than 2000 watchers is a big setback, however, as correctness takes |
1430 |
precedence over speed. Nevertheless, its performance is surprising, as |
1431 |
the file descriptor is dup()ed for each watcher. This shows that the |
1432 |
dup() employed by some adaptors is not a big performance issue (it does |
1433 |
incur a hidden memory cost inside the kernel which is not reflected in |
1434 |
the figures above). |
1435 |
|
1436 |
"POE", regardless of underlying event loop (whether using its pure perl |
1437 |
select-based backend or the Event module, the POE-EV backend couldn't be |
1438 |
tested because it wasn't working) shows abysmal performance and memory |
1439 |
usage with AnyEvent: Watchers use almost 30 times as much memory as EV |
1440 |
watchers, and 10 times as much memory as Event (the high memory |
1441 |
requirements are caused by requiring a session for each watcher). |
1442 |
Watcher invocation speed is almost 900 times slower than with AnyEvent's |
1443 |
pure perl implementation. |
1444 |
|
1445 |
The design of the POE adaptor class in AnyEvent can not really account |
1446 |
for the performance issues, though, as session creation overhead is |
1447 |
small compared to execution of the state machine, which is coded pretty |
1448 |
optimally within AnyEvent::Impl::POE (and while everybody agrees that |
1449 |
using multiple sessions is not a good approach, especially regarding |
1450 |
memory usage, even the author of POE could not come up with a faster |
1451 |
design). |
1452 |
|
1453 |
Summary |
1454 |
* Using EV through AnyEvent is faster than any other event loop (even |
1455 |
when used without AnyEvent), but most event loops have acceptable |
1456 |
performance with or without AnyEvent. |
1457 |
|
1458 |
* The overhead AnyEvent adds is usually much smaller than the overhead |
1459 |
of the actual event loop, only with extremely fast event loops such |
1460 |
as EV adds AnyEvent significant overhead. |
1461 |
|
1462 |
* You should avoid POE like the plague if you want performance or |
1463 |
reasonable memory usage. |
1464 |
|
1465 |
BENCHMARKING THE LARGE SERVER CASE |
1466 |
This benchmark actually benchmarks the event loop itself. It works by |
1467 |
creating a number of "servers": each server consists of a socket pair, a |
1468 |
timeout watcher that gets reset on activity (but never fires), and an |
1469 |
I/O watcher waiting for input on one side of the socket. Each time the |
1470 |
socket watcher reads a byte it will write that byte to a random other |
1471 |
"server". |
1472 |
|
1473 |
The effect is that there will be a lot of I/O watchers, only part of |
1474 |
which are active at any one point (so there is a constant number of |
1475 |
active fds for each loop iteration, but which fds these are is random). |
1476 |
The timeout is reset each time something is read because that reflects |
1477 |
how most timeouts work (and puts extra pressure on the event loops). |
1478 |
|
1479 |
In this benchmark, we use 10000 socket pairs (20000 sockets), of which |
1480 |
100 (1%) are active. This mirrors the activity of large servers with |
1481 |
many connections, most of which are idle at any one point in time. |
1482 |
|
1483 |
Source code for this benchmark is found as eg/bench2 in the AnyEvent |
1484 |
distribution. |
1485 |
|
1486 |
Explanation of the columns |
1487 |
*sockets* is the number of sockets, and twice the number of "servers" |
1488 |
(as each server has a read and write socket end). |
1489 |
|
1490 |
*create* is the time it takes to create a socket pair (which is |
1491 |
nontrivial) and two watchers: an I/O watcher and a timeout watcher. |
1492 |
|
1493 |
*request*, the most important value, is the time it takes to handle a |
1494 |
single "request", that is, reading the token from the pipe and |
1495 |
forwarding it to another server. This includes deleting the old timeout |
1496 |
and creating a new one that moves the timeout into the future. |
1497 |
|
1498 |
Results |
1499 |
name sockets create request |
1500 |
EV 20000 69.01 11.16 |
1501 |
Perl 20000 73.32 35.87 |
1502 |
IOAsync 20000 157.00 98.14 epoll |
1503 |
IOAsync 20000 159.31 616.06 poll |
1504 |
Event 20000 212.62 257.32 |
1505 |
Glib 20000 651.16 1896.30 |
1506 |
POE 20000 349.67 12317.24 uses POE::Loop::Event |
1507 |
|
1508 |
Discussion |
1509 |
This benchmark *does* measure scalability and overall performance of the |
1510 |
particular event loop. |
1511 |
|
1512 |
EV is again fastest. Since it is using epoll on my system, the setup |
1513 |
time is relatively high, though. |
1514 |
|
1515 |
Perl surprisingly comes second. It is much faster than the C-based event |
1516 |
loops Event and Glib. |
1517 |
|
1518 |
IO::Async performs very well when using its epoll backend, and still |
1519 |
quite good compared to Glib when using its pure perl backend. |
1520 |
|
1521 |
Event suffers from high setup time as well (look at its code and you |
1522 |
will understand why). Callback invocation also has a high overhead |
1523 |
compared to the "$_->() for .."-style loop that the Perl event loop |
1524 |
uses. Event uses select or poll in basically all documented |
1525 |
configurations. |
1526 |
|
1527 |
Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It |
1528 |
clearly fails to perform with many filehandles or in busy servers. |
1529 |
|
1530 |
POE is still completely out of the picture, taking over 1000 times as |
1531 |
long as EV, and over 100 times as long as the Perl implementation, even |
1532 |
though it uses a C-based event loop in this case. |
1533 |
|
1534 |
Summary |
1535 |
* The pure perl implementation performs extremely well. |
1536 |
|
1537 |
* Avoid Glib or POE in large projects where performance matters. |
1538 |
|
1539 |
BENCHMARKING SMALL SERVERS |
1540 |
While event loops should scale (and select-based ones do not...) even to |
1541 |
large servers, most programs we (or I :) actually write have only a few |
1542 |
I/O watchers. |
1543 |
|
1544 |
In this benchmark, I use the same benchmark program as in the large |
1545 |
server case, but it uses only eight "servers", of which three are active |
1546 |
at any one time. This should reflect performance for a small server |
1547 |
relatively well. |
1548 |
|
1549 |
The columns are identical to the previous table. |
1550 |
|
1551 |
Results |
1552 |
name sockets create request |
1553 |
EV 16 20.00 6.54 |
1554 |
Perl 16 25.75 12.62 |
1555 |
Event 16 81.27 35.86 |
1556 |
Glib 16 32.63 15.48 |
1557 |
POE 16 261.87 276.28 uses POE::Loop::Event |
1558 |
|
1559 |
Discussion |
1560 |
The benchmark tries to test the performance of a typical small server. |
1561 |
While knowing how various event loops perform is interesting, keep in |
1562 |
mind that their overhead in this case is usually not as important, due |
1563 |
to the small absolute number of watchers (that is, you need efficiency |
1564 |
and speed most when you have lots of watchers, not when you only have a |
1565 |
few of them). |
1566 |
|
1567 |
EV is again fastest. |
1568 |
|
1569 |
Perl again comes second. It is noticeably faster than the C-based event |
1570 |
loops Event and Glib, although the difference is too small to really |
1571 |
matter. |
1572 |
|
1573 |
POE also performs much better in this case, but is is still far behind |
1574 |
the others. |
1575 |
|
1576 |
Summary |
1577 |
* C-based event loops perform very well with small number of watchers, |
1578 |
as the management overhead dominates. |
1579 |
|
1580 |
THE IO::Lambda BENCHMARK |
1581 |
Recently I was told about the benchmark in the IO::Lambda manpage, which |
1582 |
could be misinterpreted to make AnyEvent look bad. In fact, the |
1583 |
benchmark simply compares IO::Lambda with POE, and IO::Lambda looks |
1584 |
better (which shouldn't come as a surprise to anybody). As such, the |
1585 |
benchmark is fine, and mostly shows that the AnyEvent backend from |
1586 |
IO::Lambda isn't very optimal. But how would AnyEvent compare when used |
1587 |
without the extra baggage? To explore this, I wrote the equivalent |
1588 |
benchmark for AnyEvent. |
1589 |
|
1590 |
The benchmark itself creates an echo-server, and then, for 500 times, |
1591 |
connects to the echo server, sends a line, waits for the reply, and then |
1592 |
creates the next connection. This is a rather bad benchmark, as it |
1593 |
doesn't test the efficiency of the framework or much non-blocking I/O, |
1594 |
but it is a benchmark nevertheless. |
1595 |
|
1596 |
name runtime |
1597 |
Lambda/select 0.330 sec |
1598 |
+ optimized 0.122 sec |
1599 |
Lambda/AnyEvent 0.327 sec |
1600 |
+ optimized 0.138 sec |
1601 |
Raw sockets/select 0.077 sec |
1602 |
POE/select, components 0.662 sec |
1603 |
POE/select, raw sockets 0.226 sec |
1604 |
POE/select, optimized 0.404 sec |
1605 |
|
1606 |
AnyEvent/select/nb 0.085 sec |
1607 |
AnyEvent/EV/nb 0.068 sec |
1608 |
+state machine 0.134 sec |
1609 |
|
1610 |
The benchmark is also a bit unfair (my fault): the IO::Lambda/POE |
1611 |
benchmarks actually make blocking connects and use 100% blocking I/O, |
1612 |
defeating the purpose of an event-based solution. All of the newly |
1613 |
written AnyEvent benchmarks use 100% non-blocking connects (using |
1614 |
AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS |
1615 |
resolver), so AnyEvent is at a disadvantage here, as non-blocking |
1616 |
connects generally require a lot more bookkeeping and event handling |
1617 |
than blocking connects (which involve a single syscall only). |
1618 |
|
1619 |
The last AnyEvent benchmark additionally uses AnyEvent::Handle, which |
1620 |
offers similar expressive power as POE and IO::Lambda, using |
1621 |
conventional Perl syntax. This means that both the echo server and the |
1622 |
client are 100% non-blocking, further placing it at a disadvantage. |
1623 |
|
1624 |
As you can see, the AnyEvent + EV combination even beats the |
1625 |
hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl |
1626 |
backend easily beats IO::Lambda and POE. |
1627 |
|
1628 |
And even the 100% non-blocking version written using the high-level (and |
1629 |
slow :) AnyEvent::Handle abstraction beats both POE and IO::Lambda by a |
1630 |
large margin, even though it does all of DNS, tcp-connect and socket I/O |
1631 |
in a non-blocking way. |
1632 |
|
1633 |
The two AnyEvent benchmarks programs can be found as eg/ae0.pl and |
1634 |
eg/ae2.pl in the AnyEvent distribution, the remaining benchmarks are |
1635 |
part of the IO::lambda distribution and were used without any changes. |
1636 |
|
1637 |
SIGNALS |
1638 |
AnyEvent currently installs handlers for these signals: |
1639 |
|
1640 |
SIGCHLD |
1641 |
A handler for "SIGCHLD" is installed by AnyEvent's child watcher |
1642 |
emulation for event loops that do not support them natively. Also, |
1643 |
some event loops install a similar handler. |
1644 |
|
1645 |
Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE, |
1646 |
then AnyEvent will reset it to default, to avoid losing child exit |
1647 |
statuses. |
1648 |
|
1649 |
SIGPIPE |
1650 |
A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is |
1651 |
"undef" when AnyEvent gets loaded. |
1652 |
|
1653 |
The rationale for this is that AnyEvent users usually do not really |
1654 |
depend on SIGPIPE delivery (which is purely an optimisation for |
1655 |
shell use, or badly-written programs), but "SIGPIPE" can cause |
1656 |
spurious and rare program exits as a lot of people do not expect |
1657 |
"SIGPIPE" when writing to some random socket. |
1658 |
|
1659 |
The rationale for installing a no-op handler as opposed to ignoring |
1660 |
it is that this way, the handler will be restored to defaults on |
1661 |
exec. |
1662 |
|
1663 |
Feel free to install your own handler, or reset it to defaults. |
1664 |
|
1665 |
RECOMMENDED/OPTIONAL MODULES |
1666 |
One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and |
1667 |
it's built-in modules) are required to use it. |
1668 |
|
1669 |
That does not mean that AnyEvent won't take advantage of some additional |
1670 |
modules if they are installed. |
1671 |
|
1672 |
This section epxlains which additional modules will be used, and how |
1673 |
they affect AnyEvent's operetion. |
1674 |
|
1675 |
Async::Interrupt |
1676 |
This slightly arcane module is used to implement fast signal |
1677 |
handling: To my knowledge, there is no way to do completely |
1678 |
race-free and quick signal handling in pure perl. To ensure that |
1679 |
signals still get delivered, AnyEvent will start an interval timer |
1680 |
to wake up perl (and catch the signals) with some delay (default is |
1681 |
10 seconds, look for $AnyEvent::MAX_SIGNAL_LATENCY). |
1682 |
|
1683 |
If this module is available, then it will be used to implement |
1684 |
signal catching, which means that signals will not be delayed, and |
1685 |
the event loop will not be interrupted regularly, which is more |
1686 |
efficient (And good for battery life on laptops). |
1687 |
|
1688 |
This affects not just the pure-perl event loop, but also other event |
1689 |
loops that have no signal handling on their own (e.g. Glib, Tk, Qt). |
1690 |
|
1691 |
Some event loops (POE, Event, Event::Lib) offer signal watchers |
1692 |
natively, and either employ their own workarounds (POE) or use |
1693 |
AnyEvent's workaround (using $AnyEvent::MAX_SIGNAL_LATENCY). |
1694 |
Installing Async::Interrupt does nothing for those backends. |
1695 |
|
1696 |
EV This module isn't really "optional", as it is simply one of the |
1697 |
backend event loops that AnyEvent can use. However, it is simply the |
1698 |
best event loop available in terms of features, speed and stability: |
1699 |
It supports the AnyEvent API optimally, implements all the watcher |
1700 |
types in XS, does automatic timer adjustments even when no monotonic |
1701 |
clock is available, can take avdantage of advanced kernel interfaces |
1702 |
such as "epoll" and "kqueue", and is the fastest backend *by far*. |
1703 |
You can even embed Glib/Gtk2 in it (or vice versa, see EV::Glib and |
1704 |
Glib::EV). |
1705 |
|
1706 |
Guard |
1707 |
The guard module, when used, will be used to implement |
1708 |
"AnyEvent::Util::guard". This speeds up guards considerably (and |
1709 |
uses a lot less memory), but otherwise doesn't affect guard |
1710 |
operation much. It is purely used for performance. |
1711 |
|
1712 |
JSON and JSON::XS |
1713 |
This module is required when you want to read or write JSON data via |
1714 |
AnyEvent::Handle. It is also written in pure-perl, but can take |
1715 |
advantage of the ultra-high-speed JSON::XS module when it is |
1716 |
installed. |
1717 |
|
1718 |
In fact, AnyEvent::Handle will use JSON::XS by default if it is |
1719 |
installed. |
1720 |
|
1721 |
Net::SSLeay |
1722 |
Implementing TLS/SSL in Perl is certainly interesting, but not very |
1723 |
worthwhile: If this module is installed, then AnyEvent::Handle (with |
1724 |
the help of AnyEvent::TLS), gains the ability to do TLS/SSL. |
1725 |
|
1726 |
Time::HiRes |
1727 |
This module is part of perl since release 5.008. It will be used |
1728 |
when the chosen event library does not come with a timing source on |
1729 |
it's own. The pure-perl event loop (AnyEvent::Impl::Perl) will |
1730 |
additionally use it to try to use a monotonic clock for timing |
1731 |
stability. |
1732 |
|
1733 |
FORK |
1734 |
Most event libraries are not fork-safe. The ones who are usually are |
1735 |
because they rely on inefficient but fork-safe "select" or "poll" calls. |
1736 |
Only EV is fully fork-aware. |
1737 |
|
1738 |
If you have to fork, you must either do so *before* creating your first |
1739 |
watcher OR you must not use AnyEvent at all in the child OR you must do |
1740 |
something completely out of the scope of AnyEvent. |
1741 |
|
1742 |
SECURITY CONSIDERATIONS |
1743 |
AnyEvent can be forced to load any event model via |
1744 |
$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used |
1745 |
to execute arbitrary code or directly gain access, it can easily be used |
1746 |
to make the program hang or malfunction in subtle ways, as AnyEvent |
1747 |
watchers will not be active when the program uses a different event |
1748 |
model than specified in the variable. |
1749 |
|
1750 |
You can make AnyEvent completely ignore this variable by deleting it |
1751 |
before the first watcher gets created, e.g. with a "BEGIN" block: |
1752 |
|
1753 |
BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} } |
1754 |
|
1755 |
use AnyEvent; |
1756 |
|
1757 |
Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can |
1758 |
be used to probe what backend is used and gain other information (which |
1759 |
is probably even less useful to an attacker than PERL_ANYEVENT_MODEL), |
1760 |
and $ENV{PERL_ANYEVENT_STRICT}. |
1761 |
|
1762 |
Note that AnyEvent will remove *all* environment variables starting with |
1763 |
"PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is |
1764 |
enabled. |
1765 |
|
1766 |
BUGS |
1767 |
Perl 5.8 has numerous memleaks that sometimes hit this module and are |
1768 |
hard to work around. If you suffer from memleaks, first upgrade to Perl |
1769 |
5.10 and check wether the leaks still show up. (Perl 5.10.0 has other |
1770 |
annoying memleaks, such as leaking on "map" and "grep" but it is usually |
1771 |
not as pronounced). |
1772 |
|
1773 |
SEE ALSO |
1774 |
Utility functions: AnyEvent::Util. |
1775 |
|
1776 |
Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk, |
1777 |
Event::Lib, Qt, POE. |
1778 |
|
1779 |
Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event, |
1780 |
AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl, |
1781 |
AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE, |
1782 |
AnyEvent::Impl::IOAsync, Anyevent::Impl::Irssi. |
1783 |
|
1784 |
Non-blocking file handles, sockets, TCP clients and servers: |
1785 |
AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS. |
1786 |
|
1787 |
Asynchronous DNS: AnyEvent::DNS. |
1788 |
|
1789 |
Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event, |
1790 |
|
1791 |
Nontrivial usage examples: AnyEvent::GPSD, AnyEvent::XMPP, |
1792 |
AnyEvent::HTTP. |
1793 |
|
1794 |
AUTHOR |
1795 |
Marc Lehmann <schmorp@schmorp.de> |
1796 |
http://home.schmorp.de/ |
1797 |
|