Thread::Queue how to spread jobs evenly between the threads - multithreading

Question

Here is the code:
#!/usr/bin/perl
use strict;
use warnings;
use threads;
use Thread::Queue;
my $queue = Thread::Queue->new();
sub run_queries {
my $n = shift;
print "$n\n-------------\n";
# $queue->dequeue_nb() does the same
while (defined(my $text = $queue->dequeue())) {
print "$text\n";
}
}
my #threads;
push(#threads, threads->create(\&run_queries, 1));
push(#threads, threads->create(\&run_queries, 2));
push(#threads, threads->create(\&run_queries, 3));
push(#threads, threads->create(\&run_queries, 4));
for (my $i = 0; $i < 12; $i++)
{
$queue->enqueue($i);
}
$queue->end();
foreach (#threads) {
$_->join();
}
Output:
1
-------------
2
-------------
3
-------------
4
-------------
0
1
2
3
... all the items here
I expected that the output will be spread evenly between the threads and as soon as one thread takes the item from the queue, the second will activate and start processing the next item.
But in reality we see that one thread is processing everything, while the others are idle.
What do I need to do to split the jobs evenly between the threads?

Answer 1

What makes you think it's all one thread?
Change
print "$text\n";
to
print "[$n] $text\n";
or
print "[" . threads->tid . "] $text\n";
Sample output:
1
-------------
2
-------------
3
-------------
4
-------------
[2] 0
[1] 1
[2] 2
[4] 3
[3] 4
[3] 5
[1] 6
[1] 7
[2] 8
[1] 9
[2] 10
[4] 11
You might also want to experiment using
use Time::HiRes qw( sleep );
print "[" . threads->tid . "] START $text\n";
sleep(rand()+1); # [1,2) seconds
print "[" . threads->tid . "] END $text\n";
# After the loop.
print "[" . threads->tid . "] EXIT\n";
Sample output:
[2] START 0 \
[3] START 1 \ All the workers start right off the bat.
[4] START 2 /
[1] START 3 /
[1] END 3 \ As soon as a worker finishes one job,
[1] START 4 / it starts the next available job.
[4] END 2
[4] START 5
[3] END 1
[3] START 6
[2] END 0
[2] START 7
[1] END 4
[1] START 8
[4] END 5
[4] START 9
[1] END 8
[1] START 10
[2] END 7
[2] START 11
[3] END 6 \ There are no jobs left. Because ->end was called, it exits.
[3] EXIT / Otherwise, it would block until ->enqueue or ->end is called.
[4] END 9
[4] EXIT
[2] END 11
[2] EXIT
[1] END 10
[1] EXIT