# One (of several) things missing from the API as it stands
# is any way to determine if the thread has finished 
# without blocking.

I think that's pretty easy to do with Thread::Exit.

use threads ();
use threads::shared ();

my %exited : shared;
use Thread::Exit end => sub { $exited{threads->tid} = 1 };

my $thread = threads->new( sub { whatever } );
my $tid = $thread->tid;

while (!$exited{$tid}) {
# do your stuff
}
[download]

Liz

Update:
I worked a little on it ;-)

The uploaded file

    Thread-Running-0.01.tar.gz

has entered CPAN as

  file: $CPAN/authors/id/E/EL/ELIZABETH/Thread-Running-0.01.tar.gz
  size: 3963 bytes
   md5: 847d0175b6f5f355c97d20c73dce7311

NAME
       Thread::Running - provide non-blocking check whether threads are running

SYNOPSIS
           use Thread::Running;      # exports running(), exited() and tojoin()
           use Thread::Running qw(running);   # only exports running()
           use Thread::Running ();   # threads class methods only

           my $thread = threads->new( sub { whatever } );
           while (threads->running( $thread )) {
           # do your stuff
           }

           $_->join foreach threads->tojoin;

           until (threads->exited( $tid )) {
           # do your stuff
           }

DESCRIPTION

       This module adds three features to threads that are sorely
       missed by some: you can check whether a thread is running,
       whether it can be joined or whether it has exited without
       waiting for that thread to be finished (non-blocking).