Re: Boolean Thread::Semaphore ?

[BrowserUk]

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 );
}

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;
...

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

[chrestomanci]

You don't want a semaphore.

The simplest mechanism is:

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

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.

[mellon85]

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

[BrowserUk]

take a look at thread signalling chapter in threads documentation

That is a truly awful idea.

Try it for yourself to find out why.