AnyEvent::Impl::IOAsynUsermContributed Perl DocumeAnyEvent::Impl::IOAsync(3pm)
NAME
AnyEvent::Impl::IOAsync - AnyEvent adaptor for IO::Async
SYNOPSIS
use AnyEvent;
use IO::Async::Loop;
# optionally set another event loop
use AnyEvent::Impl::IOAsync;
my $loop = new IO::Async::Loop;
AnyEvent::Impl::IOAsync::set_loop $loop;
DESCRIPTION
This module provides support for IO::Async as AnyEvent backend. It
supports I/O, timers, signals and child process watchers. Idle watchers
are emulated. I/O watchers need to dup their fh because IO::Async only
supports IO handles, not plain file descriptors.
FUNCTIONS AND VARIABLES
The only user-servicible part in this module is the "set_loop" function
and $LOOP variable:
AnyEvent::Impl::IOAsync::set_loop $new_loop
Unfortunately, IO::Async has no concept of a default loop. Modules
using IO::Async must be told by their caller which loop to use,
which makes it impossible to transparently use IO::Async from a
module.
This module is no exception. It creates a new IO::Async::Loop
object when it is loaded. This might not be the right loop object,
though, and thus you can replace it by a call to this function with
the loop object of your choice.
Note that switching loops while watchers are already initialised
can have unexpected effects, and is not supported unless you can
live with the consequences.
$AnyEvent::Impl::IOAsync::LOOP
This variable always contains the IO::Async::Loop object used by
this AnyEvent backend. See above for more info.
Storing the "default" loop makes this module a possible arbiter for
other modules that want to use IO::Async transparently. It's
advised to directly refer to this variable each time you want to
use it, without making a local copy.
PROBLEMS WITH IO::Async
This section had a long list of problems and shortcomings that made it
almost impossible to support IO::Async. With version 0.33 of IO::Async,
however, most of these have been fixed, so IO::Async can now be used as
easily as many other loops.
There are a few remaining problems that require emulation or
workarounds:
No support for multiple watchers per event
In most (all? documentation?) cases you cannot have multiple
watchers for the same event (what's the point of having all these
fancy notifier classes when you cannot have multiple notifiers for
the same event? That's like only allowing one timer per second or
so...).
For I/O watchers, AnyEvent has to dup() every file handle, as
IO::Async fails to support the same or different file handles
pointing to the same fd (the good thing is that it is documented,
but why not fix it instead?).
Apart from these fatal flaws, there are a number of unpleasent
properties that just need some mentioning:
Confusing and misleading names
Another rather negative point about this module family is its name,
which is deeply confusing: Despite the "async" in the name,
IO::Async only does synchronous I/O, there is nothing
"asynchronous" about it whatsoever (when I first heard about it, I
thought, "wow, a second async I/O module, what does it do compared
to IO::AIO", and was somehow set back when I learned that the only
"async" aspect of it is the name).
Inconsistent, incomplete and convoluted API
Implementing AnyEvent's rather simple timers on top of IO::Async's
timers was a nightmare (try implementing a timer with configurable
interval and delay value...).
The method naming is chaotic: "watch_child" creates a child
watcher, but "watch_io" is an internal method; "detach_signal"
removes a signal watcher, but "detach_child" forks a subprocess and
so on).
Unpleasant surprises on GNU/Linux
When you develop your program on FreeBSD and run it on GNU/Linux,
you might have unpleasant surprises, as IO::Async::Loop will by
default use IO::Async::Loop::Epoll, which is incompatible with
"fork", so your network server will run into spurious and very hard
to debug problems under heavy load, as IO::Async forks a lot of
processes, e.g. for DNS resolution. It would be better if IO::Async
would only load "safe" backends by default (or fix the epoll
backend to work in the presence of fork, which admittedly is hard -
EV does it for you, and also does not use unsafe backends by
default).
On the positive side, performance with IO::Async is quite good even in
my very demanding eyes.
SEE ALSO
AnyEvent, IO::Async.
AUTHOR
Marc Lehmann <schmorp@schmorp.de>
http://anyevent.schmorp.de
Paul Evans <leonerd@leonerd.org.uk>
Rewrote the backend for IO::Async version 0.33.
perl v5.36.0 2022-10-20 AnyEvent::Impl::IOAsync(3pm)
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