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Re^4: What is the correct way to finish multithreaded program?

by Gangabass (Vicar)
on May 05, 2014 at 12:18 UTC ( [id://1085053]=note: print w/replies, xml ) Need Help??


in reply to Re^3: What is the correct way to finish multithreaded program?
in thread What is the correct way to finish multithreaded program?

I'm pushing undef into the queue with
foreach ( 1 .. $config->{number_of_threads} ) { $q->enqueue(undef); }
and I think this will cause thread to return:
while ( my $org = $q->dequeue() ) { parse_org( $org, $mech ); $pq->enqueue($org); } say "Finishing worker [$thread_id]"; return;
Also I have Finishing worker [SOME_ID] in the output...

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Re^5: What is the correct way to finish multithreaded program?
by BrowserUk (Patriarch) on May 05, 2014 at 15:49 UTC
    I'm pushing undef into the queue with ... and I think this will cause thread to return:

    It will. Eventually. But there is no guarantee -- indeed it is most unlikely -- that all of the threads will: a) get a timeslice; b) receive the undef from the queue; c) act upon it and exit; before your main thread tries to join them.

    The whole point of join is that it waits for the threads to finish, thus ensuring that your main thread doesn't exit before your child threads are finished.

    It rarely makes any sense to turn it into a non-blocking operation by calling is_joinable before calling join.

    The are a few specialist uses for that, but in the case of your code it only guarantees that any thread that is slow to finish will not get joined before you terminate the main thread; hence the error message.


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Re^5: What is the correct way to finish multithreaded program?
by Anonymous Monk on May 05, 2014 at 13:08 UTC
    Here you go ... just because queue is empty, doesn't mean threads are joinable

    This reliably exits with 6 running and unjoined on my old machine, YMMV

      Thank you for nice explanation! Now I got it.
Re^5: What is the correct way to finish multithreaded program?
by Anonymous Monk on May 05, 2014 at 12:24 UTC
    If you can make the code run .. and reproduce the problem, you can see the only real way to wait is to join everything not merely the immediately joinable :)

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