EV::Loop::Async - run an EV event loop asynchronously

      use EV::Loop::Async;
      my $loop = EV::Loop::Async::default;
      my $timer;
      my $flag;
      # create a watcher, but make sure the loop is locked
         $loop->scope_lock; # lock the loop structures
         $timer = $loop->timer (5, 1, sub { $flag = 1 });
         $loop->notify; # tell loop to take note of the timer
      1 while $flag; # $flag will be set asynchronously
      # implement a critical section, uninterrupted by any callbacks
         # critical section, no watcher callback interruptions
      # stop the timer watcher again - locking is required once more
         $loop->scope_lock; # lock the loop structures
         # no need to notify

    This module implements a rather specialised event loop - it takes a
    normal EV event loop and runs it in a separate thread. That means it
    will poll for events even while your foreground Perl interpreter is busy
    (you don't need to have perls pseudo-threads enabled for this either).

    Whenever the event loop detecs new events, it will interrupt perl and
    ask it to invoke all the pending watcher callbacks. This invocation will
    be "synchronous" (in the perl thread), but it can happen at any time.

    See the documentation for Async::Interrupt for details on when and how
    your perl program can be interrupted (and how to avoid it), and how to
    integrate background event loops into foreground ones.

    Why on earth...???
        Sometimes you need lower latency for specific events, but it's too
        heavy to continuously poll for events. And perl already does this
        for you anyways, so this module only uses this existing mechanism.

    When do I have to lock?
        When in doubt, lock. Do not start or stop a watcher, do not create a
        watcher (unless with the "_ns" methods) and do not DESTROY an active
        watcher without locking either.

        Any other event loop modifications need to be done while locked as
        well. So when in doubt, lock (best using "scope_lock").

    Why explicit locking?
        Because I was too lazy to wrap everything and there are probably
        only a few people on this world using this module.

    $loop = EV::Loop::Async::default
        Return the default loop, usable by all programs. The default loop
        will be created on the first call to "default" by calling , and
        should be used by all programs unless they have special

        The associated Async::Interrupt object is stored in
        $EV::Loop::Async::AI, and can be used to lock critical sections etc.

        The default async loop, available after the first call to

        The default loop's Async::Interrupt object, for easy access.

        Example: create a section of code where no callback invocations will

              # no default loop callbacks will be executed here.
              # the loop will not be locked, however.

        Example: embed the default EV::Async::Loop loop into the default EV
        loop (note that it could be any other event loop as well).

           my $async_w = EV::io
                            sub { };

    $loop = new EV::Loop::Async $flags, [Async-Interrupt-Arguments...]
        This constructor:

        1. creates a new "EV::Loop" (similar "new EV::Loop").
        2. creates a new Async::Interrupt object and attaches itself to it.
        3. creates a new background thread.
        4. runs "$loop->run" in that thread.

        The resulting loop will be running and unlocked when it is returned.

        Example: create a new loop, block it's interrupt object and embed it
        into the foreground AnyEvent event loop. This basically runs the
        "EV::Loop::Async" loop in a synchronous way inside another loop.

           my $loop  = new EV::Loop::Async 0;
           my $async = $loop->interrupt;


           my $async_w = AnyEvent->io (
              fh => $async->pipe_fileno,
              poll => "r",
              cb => sub {
                 # temporarily unblock to handle events

        Wake up the asynchronous loop. This is useful after registering a
        new watcher, to ensure that the background event loop integrates the
        new watcher(s) (which only happens when it iterates, which you can
        force by calling this method).

        Without calling this method, the event loop *eventually* takes
        notice of new watchers, bit when this happens is not well-defined
        (can be instantaneous, or take a few hours).

        No locking is required.

        Example: lock the loop, create a timer, nudge the loop so it takes
        notice of the new timer, then evily busy-wait till the timer fires.

           my $timer;
           my $flag;

              $timer = $loop->timer (1, 0, sub { $flag = 1 });

           1 until $flag;

        Lock/unlock the loop data structures. Since the event loop runs in a
        separate thread, you have to lock the loop data structures before
        accessing them in any way. Since I was lazy, you have to do this

        You must lock under the same conditions as you would have to lock
        the underlying C library, e.g. when starting or stopping watchers
        (but not when creating or destroying them, but note that create and
        destroy often starts and stops for you, in which case you have to

        When in doubt, lock.

        See also the next method, "$loop->scope_lock" for a more failsafe
        way to lock parts of your code.

        Note that there must be exactly one call of "unblock" for every
        previous call to "block" (i.e. calls can nest).

        Calls "lock" immediately, and "unlock" automatically whent he
        current scope is left.

    $loop->set_max_foreground_loops ($max_loops)
        The background loop will immediately stop polling for new events
        after it has collected at least one new event, regardless of how
        long it then takes to actually handle them.

        When Perl finally handles the events, there could be many more ready
        file descriptors. To improve latency and performance, you can ask
        "EV::Loop::Async" to loop an additional number of times in the
        foreground after invoking the callbacks, effectively doing the
        polling in the foreground.

        The default is 0, meaning that no foreground polling will be done. A
        value of 1 means that, after handling the pending events, it will
        call "$loop->loop (EV::LOOP_NONBLOCK)" and handle the resulting
        events, if any. A value of 2 means that this will be iterated twice.

        When a foreground event poll does not yield any new events, then no
        further iterations will be made, so this is only a *maximum* value
        of additional loop runs.

        Take also note of the standard EV "set_io_collect_interval"
        functionality, which can achieve a similar, but different, effect -

    EV, Async::Interrupt.

     Marc Lehmann <>