#! perl -slw
use strict;
use threads qw[ yield ];
use threads::shared;

use constant NUM_THREADS => 2;                         # <--

sub thread {
    my $tid = threads->tid;
    my $refSem = shift;
    while( 1 ) {
        warn( "$tid:locking sem\n" );
        lock( $$refSem );
        warn( "$tid:waiting sem\n" );
        cond_wait( $$refSem );
        print "$tid: got $$refSem";
        warn( "$tid:yielding\n" );
        yield;
        warn( "$tid:looping\n" );
    }
}

my @workers;                                           # <--
for (1..NUM_THREADS) {                                 # <--
   my $sem :shared;                                    # <--
   my $thread = threads->create( \&thread, \$sem );    # <--
   push @workers, [ $thread, \$sem ];                  # <--
}                                                      # <--

while( sleep 1 ) {
    my $value = int( rand 1000 );
    my $thread = int rand( @workers );                 # <--
    my $refSem = $workers[$thread][1];                 # <--
    warn( "0:locking sem for thread $thread\n" );
    lock( $$refSem );
    warn( "0:Setting sem$thread to $value\n" );
    $$refSem = $value;
    warn( "0:signalling sem$thread\n" );
    cond_signal( $refSem );
    warn( "0:Sleeping\n" );
}