sub threadProc1 :threaded { ... }
sub threadProc2 :threaded { ... }


my $result1 = threadProc1( @args );
my $result2 = threadProc2( @otherArgs );

unless( defined $result1 && defined $result2 ) {
    ## continue doing other stuff while we wait
}

## If the threads have completed by the time we reach this statement
## then the statements completes immediately. Otherwise it blocks until
## both results are available. Effectively joining both threads.
my $composite = $result1 + $result2;