use strict;
use warnings;
no warnings 'void';
use threads;

use Thread::Semaphore qw( );
use Time::HiRes       qw( time );

use constant NUM_THREADS => 4;

my $t = time;

my $start_sem = Thread::Semaphore->new( 0 );
my @barrier   = map Thread::Semaphore->new( 0 ), 1 .. NUM_THREADS;

my @t = map async {
    my $id = threads-> tid - 1;

    # Wait for main thread to complete.
    $start_sem->down;

    sin for 1 .. 1e7;
    
    printf "first, %d %.3f\n", $id, time - $t;

    # Wait for all threads to reach here.
    $barrier[ $id ]->up( NUM_THREADS );
    $_->down for @barrier;

    printf "next,  %d %.3f\n", $id, time - $t;
}, 1 .. NUM_THREADS;

sin for 1 .. 1e7;

# Main thread done
$start_sem->up( NUM_THREADS );

$_->join for @t;