Re: Tasking children from a single pipe

Do it the easy way:

#! perl -slw
use strict;
use threads;
use Thread::Queue;

$| = 1;

our $KIDS ||= 10;
our $WORK ||= 1000;
our $SLEEP||= 10;

sub kid {
    my( $Q ) = shift;
    my $tid = threads->tid;
    printf "Kid: %d started\n", $tid;

    ## Pick a work item off the queue and process it
    while( my $work = $Q->dequeue ) {
        printf "Kid: %d processing work item '%s'\n", $tid, $work;

        ## Replace the sleep with the code to process the work items
        sleep rand( $SLEEP );
    }
    printf "kid: %d ending\n", $tid;
}

## A queue for communications
my $Q = new Thread::Queue;

## Start the kids
my @kids = map{ threads->create( \&kid, $Q ) } 1 .. $KIDS;

## Wait till they're all up and running
sleep 1 until @{[ threads->list ]} == $KIDS;

## Feed the queue with work
## The limit just ensures we don't fill lots of memory
for my $workitem ( 1 .. $WORK ) {
    sleep 1 while $Q->pending > $KIDS *2;
    print "Queueing work item $workitem";
    $Q->enqueue( $workitem );
}

## Tell them to stop
$Q->enqueue( (undef) x $KIDS );

## And wait for them to do so.
$_->join for @kids;
[download]

Throw out the comments & demo print statements and it is all of 20 lines of code. It could easily be reduced to 15.

A test run

C:\test>536937 -SLEEP=5 -WORK=20
Kid: 1 started
Kid: 2 started
Kid: 3 started
Kid: 4 started
Kid: 5 started
Kid: 6 started
Kid: 7 started
Kid: 8 started
Kid: 9 started
Kid: 10 started
Queueing work item 1
Kid: 1 processing work item '1'
Queueing work item 2
Kid: 2 processing work item '2'
Queueing work item 3
Kid: 3 processing work item '3'
Queueing work item 4
Kid: 4 processing work item '4'
Queueing work item 5
Kid: 5 processing work item '5'
Queueing work item 6
Kid: 6 processing work item '6'
Queueing work item 7
Kid: 7 processing work item '7'
Queueing work item 8
Kid: 8 processing work item '8'
Queueing work item 9
Kid: 9 processing work item '9'
Queueing work item 10
Kid: 10 processing work item '10'
Queueing work item 11
Kid: 2 processing work item '11'
Queueing work item 12
Kid: 3 processing work item '12'
Queueing work item 13
Kid: 6 processing work item '13'
Queueing work item 14
Kid: 7 processing work item '14'
Queueing work item 15
Kid: 8 processing work item '15'
Queueing work item 16
Kid: 2 processing work item '16'
Queueing work item 17
Kid: 8 processing work item '17'
Queueing work item 18
Queueing work item 19
Queueing work item 20
Kid: 7 processing work item '18'
Kid: 8 processing work item '19'
Kid: 1 processing work item '20'
kid: 1 ending
kid: 5 ending
kid: 9 ending
kid: 2 ending
kid: 7 ending
kid: 4 ending
kid: 6 ending
kid: 10 ending
kid: 3 ending
kid: 8 ending
[download]

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