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Re^3: AnyEvent: How to protect critical sections?

by Corion (Pope)
on May 17, 2011 at 20:43 UTC ( #905360=note: print w/replies, xml ) Need Help??


in reply to Re^2: AnyEvent: How to protect critical sections?
in thread AnyEvent: How to protect critical sections?

Then I would cancel the timer when starting the HTTP request, and relaunch the timer in the HTTP request on_body callback (and likely in the on_error callback too). You can "immediately" launch a timer by launching it with after => 0 - this will launch the timer callback the next time the event loop is entered.

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Re^4: AnyEvent: How to protect critical sections?
by saintmike (Vicar) on May 17, 2011 at 20:56 UTC
    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(); }

      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,".

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