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

use threads;
use Thread::Semaphore ;
use Time::HiRes 'time';

my $t = time;

my @s = map Thread::Semaphore-> new( 0 ), 1 .. 4;

my @t = map async {
    my $id = threads-> tid - 1;
    $s[ $id ]-> down;
    
    sin for 1 .. 1e7;   # work per thread
    
    printf "first, %d %.3f\n", $id, time - $t;
    $s[ $id ]-> up( 4 );
    $_-> down for @s;
    printf "next,  %d %.3f\n", $id, time - $t;
}, 1 .. 4;

sin for 1 .. 1e7;       # initial work

$_-> up for @s;
$_-> join for @t;

__END__

first, 2 1.824
first, 3 1.824
first, 1 1.824
first, 0 1.832
next,  1 1.826
next,  3 1.828
next,  2 1.832
next,  0 1.832