in reply to Boolean Thread::Semaphore ?

Is there a way of using Thread::Semaphore in this way, or an alternative semaphore module that can be used for this purpose?

You don't want a semaphore.

The simplest mechanism is:

wbile( my $workitem = sourceOfWork() ) {
    sleep 1 while $Q->pending > MAXQ;
    $Q->enqueue( $workitem );
}

[download]

If you are concerned that the queue might empty during that 1 second, use Time::HiRes::usleep().

If you really insist on not polling the queuesize, then use a condition vatiable:

my $cond :shared;

...
wbile( my $workitem = sourceOfWork() ) {
    cond_wait( $cond );
    $Q->enqueue( $workitem );
}


## somewhere else ...
...
cond_signal( $cond ) if $Q->pending < MAXQ;
...

[download]

But really, the latter involves more work and is less effective.

With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.

The start of some sanity?

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Re^2: Boolean Thread::Semaphore ?
by chrestomanci (Priest) on Feb 08, 2012 at 16:10 UTC

    You don't want a semaphore.

    The simplest mechanism is:

    while( my $workitem = sourceOfWork() ) {
    sleep 1 while $Q->pending > MAXQ;
    $Q->enqueue( $workitem );
}

    [download]

    Thanks, that looks to be a much more sensible approach compared with what I was doing with semaphores.

    That should teach me to read algorithoms online that are intened for other languages or problem domains where near realtime responses are required.

[reply]
[d/l]

      The best way (aka not polling) would be that the worker thread will stop itself if the queue is full, and will be restarted by a client thread by a signal.

      take a look at thread signalling chapter in threads documentation

[reply]
        take a look at thread signalling chapter in threads documentation

        That is a truly awful idea.

        Try it for yourself to find out why.

        With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
        Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
        "Science is about questioning the status quo. Questioning authority".
        In the absence of evidence, opinion is indistinguishable from prejudice.

        The start of some sanity?
[reply]

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