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 witht he consequences.
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. Its advised to directly refer to this variable each time you want to use it, without making a local copy.
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:
Apart from these fatal flaws, there are a number of unpleasent properties that just need some mentioning:
No support for multiple watchers per event In most (all? documentation?) cases you cannot have multiple watchers for the same event (whats the point of having all these fancy notifier classes when you cannot have multiple notifiers for the same event? Thats 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?).
On the positive side, performance with IO::Async is quite good even in my very demanding eyes.
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 AnyEvents rather simple timers on top of IO::Asyncs 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).
Marc Lehmann <email@example.com> http://anyevent.schmorp.de Paul Evans <firstname.lastname@example.org> Rewrote the backend for IO::Async version 0.33.
|perl v5.20.3||ANYEVENT::IMPL::IOASYNC (3)||2013-12-10|