perl : Thread::Semaphore 多线程

#!/usr/bin/perl
use threads;
use threads::shared;
use Thread::Semaphore;
my $max_process_num = 3;
my $sem = Thread::Semaphore->new($max_process_num);
my $arr = [ 4, 1, 2, 3, 5, 6 ];
my $work_func = sub {
    my ($i) = @_;
    my $s = $arr->[$i] * $arr->[$i];
    $sem->up;
    return [ $i, $s ];
};
my @threads = map {
    $sem->down;
    threads->create( $work_func, $_ );
} 0 .. $#$arr;
my @res;
for (@threads) {
    my $r = $_->join;
    $res[ $r->[0] ] = $r->[1];
}
print $_, "\n" for @res;