to run script you need first to create lock folder in the same place

gistfile1.txt

#!/usr/bin/env php

<?php
declare(ticks=1);

// setup signal handlers
pcntl_signal(SIGTERM, "sig_handler");
pcntl_signal(SIGHUP, "sig_handler");

$children = array();
$max_count = 5;
for($i=0;$i<10;$i++) {
	
	$amount = count(scandir(dirname(__FILE__).'/lock')) - 2;
	if($amount < $max_count){
		print 'creating new thred '. "\r\n";
		$pid = pcntl_fork();
		exec('touch '.dirname(__FILE__).'/lock/'.$i);
	    if ($pid == -1) {
	        die("could not fork"); 
	    } else if ($pid) {
	        //exit(); // we are the parent 
	        $children[$i] = $pid;
	        continue;
	    } else {
	        // we are the child
	        $sl = rand(15,19);
	        sleep($sl);
	        echo $sl.'blablabla'. $i . "\r\n";
			exec('rm '.dirname(__FILE__).'/lock/'.$i);
			print "closed thread \r\n";
	        exit(0);
	    }
	} else {
		$i--;
	}
}

foreach ($children as $key => $pid) {
    // We are the parent, so we shall wait till all children will die.
    // Otherwise there will be bunch of zombies.
    pcntl_waitpid($pid, $status);
}

exit(0);


function sig_handler($signo) {
     switch ($signo) {
         case SIGTERM:
             // handle shutdown tasks
             exit;
             break;
         case SIGHUP:
             // handle restart tasks
             break;
         default:
             // handle all other signals
     }
}

?>