Hello,

I am having a strange concurrency issue with Thread::Queue. Specifically, in some code that uses threads, the program runs for a time, but eventually all threads are put to sleep. The goal of my program is to read lines from text file A, have each thread perform an operation on a line using another text file B, and then write each result to another text file C. Here is a description of the threads:

• The main perl process is responsible for reading lines from A, and giving work to "worker" threads
• 5 worker threads, each of which has its own input Thread::Queue inQ, work independently and put their results in a Thread::Queue outQ
• 1 "writer" thread reads results from outQ and prints them to C.

My problem is that somehow the 5 workers become blocked, which blocks the main process (since there are no workers to work) and then the writer thread (since there are no results to write). The code for the workers looks as follows:

use threads;
use threads::shared;
use Thread::Queue;
...

my $thr  = threads->create( sub {
    my $threadId = $i;
    
    open my $REFERENCE_FILE, '<', "$refFileName" or 
        die "Can't open $refFileName: $!";
    
    while ( defined( my $item = $inQ->dequeue() ) )
    {
        # get info from the current item
        my $lot          = $item->{ 'lot'   };
        my $batch        = $item->{ 'batch' };
        my $part         = $item->{ 'part'  };
        ...
        
        # perform an operation on the item
        ...
        
        my %result = ( 'lot'        => $lot,
                       'batch'      => $batch,
                       'part'       => $part,
                       'thread'     => $threadId,
                       'extensions' => \@bestSeedExtensions,
                       'num_mm'     => $bestSeedOverallMismatches,
                       'beadid'     => $beadID,
                       'read'       => $readSequence, );
        
        $outQ->enqueue( \%result ); # <------ I AM BROKEN :(
    }
} );# end sub
[download]

Using print statements, I've traced the problem to the outQ->enqueue() statement. The strange part is that everything runs fine for millions of lines and then suddenly all progress stops. Can anyone tell me why this might be happening? I have tried both perl v5.8.5 and v5.10.1.

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