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Re^4: AnyEvent: How to protect critical sections?

by saintmike (Vicar)
on May 17, 2011 at 20:56 UTC ( #905364=note: print w/replies, xml ) Need Help??


in reply to Re^3: AnyEvent: How to protect critical sections?
in thread AnyEvent: How to protect critical sections?

Nice idea, that could actually work, I'll try that in a minute.

I was just hoping that there was some kind of $condvar->send/recv mechanism that supported lock()/unlock() so that I could write something like

$condvar->lock(); http_get "http://blah", sub { $condvar->unlock(); print $_[1] };

sub timer_callback { $condvar->lock(); # ... $condvar->unlock(); }

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Re^5: AnyEvent: How to protect critical sections?
by Corion (Pope) on May 17, 2011 at 21:03 UTC

    This cannot work - if you expect ->lock() to block until the semaphore is released, how can it continue to execute the remaining code elsewhere?

    I would either use a plain boolean variable, like you did in your first case, and keep the timer running:

    my $critical; sub on_timer { if (! $critical) { ... }; };

    ... or manually restart the timer when it's allowed to restart again. The guard values returned from creating a timer allow you to conveniently stop a timer.

      This cannot work - if you expect ->lock() to block until the semaphore is released, how can it continue to execute the remaining code elsewhere?
      The same way that $condvar->recv() blocks and lets code run elsewhere.

      Only problem: $condvar->recv() cannot be called from within a callback, according to the AnyEvent docs:

      "Note that doing a blocking wait in a callback is not supported by any event loop, that is, recursive invocation of a blocking "->recv" is not allowed,".

        Indeed, if you would need to do that, you need to use real threads (e.g. Coro) - the limitation of condvars is partially lifted under Coro.

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