Thanks. That clears up the cond_signal thing, but regarding the caveat and your update.

With the following code, which I think incorporates all your changes,if I leave the sleep in, or as show, replace it by yield, any number of threads appear to run reliably.

But if I comment out the yields, it locks up almost straight away. Do you get a different result?

I'm running this on a single processor. Are you using a multi? 

use strict;
use warnings;
use Time::HiRes 'sleep';
use threads 'yield';
use threads::shared;

my $baton:shared = 0;

sub sprinter {
    my ($no_of_threads,$sleep) = @_;
    my $id = threads->self->tid;
    warn ("Thread $id started\n");
    while (1) {
        lock ($baton);
        cond_wait ($baton) until $baton == $id;
        warn ("Thread $id has the baton\n");
#        yield;
        $baton = int (rand ($no_of_threads)) until $baton != $id;
        warn ("Thread $id passing the baton to thread $baton\n");
        cond_broadcast ($baton);
    }
}

my ($no_of_sprinters) = @ARGV;
$no_of_sprinters ||= 3;

my @threads;
push @threads,threads->new (\&sprinter,$no_of_sprinters)
    for 1..$no_of_sprinters;

sleep 1;
while(1){
    lock ($baton);
    cond_wait ($baton) until $baton == 0;
    warn ("Thread 0 has the baton\n");
#    yield;
    $baton = int (rand ($no_of_sprinters))+1 until $baton != 0;
    warn ("Thread 0 passing the baton to thread $baton\n");
    cond_broadcast ($baton);
}

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In reply to Re^2: baton passing threads and cond_signal by Anonymous Monk
in thread baton passing threads and cond_signal by Anonymous Monk

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