test.php

<?php
/**
 * Test running a console command in threads (PHP pthread extension) vs loop vs &&
 */ 
class WorkerThreads extends Thread
{
    private $workerId;

    public $data;

    public function __construct($id)
    {
        $this->workerId = $id;
    }

    public function run()
    {
        // sleep(1);
        echo "[{$this->workerId}] Running" . PHP_EOL;
        $this->data = shell_exec('phantomjs yslow.js -i basic example.com');
        echo "[{$this->workerId}] Done" . PHP_EOL;
        
    }
}

// Worker pool
$workers = [];

echo "Threads:" . PHP_EOL;
// Initialize and start the threads
foreach (range(0, 5) as $i) {
    $workers[$i] = new WorkerThreads($i);
    $workers[$i]->start();
}

// Let the threads come back
$time = microtime(true);
foreach (range(0, 5) as $i) {
    $workers[$i]->join();
    echo "[{$i}] Data: " . $workers[$i]->data . PHP_EOL;
}
$time = microtime(true) - $time;
echo "time: " . $time . PHP_EOL;

echo "Foreach: " . PHP_EOL;
$time = microtime(true);
foreach (range(0, 5) as $i) {
	echo "[{$i}] ";
    echo shell_exec('phantomjs yslow.js -i basic example.com');
}
$time = microtime(true) - $time;
echo "time: " . $time . PHP_EOL;

echo "&&: " . PHP_EOL;
$cmd = "phantomjs yslow.js -i basic example.com";
$time = microtime(true);
foreach (range(0, 5) as $i) {
	$cmd .= " && phantomjs yslow.js -i basic example.com";
    
}
echo shell_exec($cmd);
$time = microtime(true) - $time;
echo "time: " . $time . PHP_EOL;

echo "ALL DONE" . PHP_EOL;

/*
Result: 

$ php threads.php 
Threads:
[0] Running
[1] Running
[2] Running
[3] Running
[4] Running
[5] Running
[1] Done
[0] Done
[0] Data: {"v":"3.1.8","w":2540,"o":98,"u":"http%3A%2F%2Fexample.com%2F","r":2,"i":"ydefault","lt":333}

[1] Data: {"v":"3.1.8","w":2540,"o":98,"u":"http%3A%2F%2Fexample.com%2F","r":2,"i":"ydefault","lt":324}

[2] Done
[2] Data: {"v":"3.1.8","w":2540,"o":98,"u":"http%3A%2F%2Fexample.com%2F","r":2,"i":"ydefault","lt":327}

[3] Done
[3] Data: {"v":"3.1.8","w":2540,"o":98,"u":"http%3A%2F%2Fexample.com%2F","r":2,"i":"ydefault","lt":321}

[5] Done
[4] Done
[4] Data: {"v":"3.1.8","w":2540,"o":98,"u":"http%3A%2F%2Fexample.com%2F","r":2,"i":"ydefault","lt":305}

[5] Data: {"v":"3.1.8","w":2540,"o":98,"u":"http%3A%2F%2Fexample.com%2F","r":2,"i":"ydefault","lt":317}

time: 5.6576030254364
Foreach: 
[0] {"v":"3.1.8","w":2540,"o":98,"u":"http%3A%2F%2Fexample.com%2F","r":2,"i":"ydefault","lt":285}
[1] {"v":"3.1.8","w":2540,"o":98,"u":"http%3A%2F%2Fexample.com%2F","r":2,"i":"ydefault","lt":291}
[2] {"v":"3.1.8","w":2540,"o":98,"u":"http%3A%2F%2Fexample.com%2F","r":2,"i":"ydefault","lt":300}
[3] {"v":"3.1.8","w":2540,"o":98,"u":"http%3A%2F%2Fexample.com%2F","r":2,"i":"ydefault","lt":300}
[4] {"v":"3.1.8","w":2540,"o":98,"u":"http%3A%2F%2Fexample.com%2F","r":2,"i":"ydefault","lt":286}
[5] {"v":"3.1.8","w":2540,"o":98,"u":"http%3A%2F%2Fexample.com%2F","r":2,"i":"ydefault","lt":290}
time: 17.812369823456
&&: 
{"v":"3.1.8","w":2540,"o":98,"u":"http%3A%2F%2Fexample.com%2F","r":2,"i":"ydefault","lt":306}
{"v":"3.1.8","w":2540,"o":98,"u":"http%3A%2F%2Fexample.com%2F","r":2,"i":"ydefault","lt":303}
{"v":"3.1.8","w":2540,"o":98,"u":"http%3A%2F%2Fexample.com%2F","r":2,"i":"ydefault","lt":289}
{"v":"3.1.8","w":2540,"o":98,"u":"http%3A%2F%2Fexample.com%2F","r":2,"i":"ydefault","lt":286}
{"v":"3.1.8","w":2540,"o":98,"u":"http%3A%2F%2Fexample.com%2F","r":2,"i":"ydefault","lt":311}
{"v":"3.1.8","w":2540,"o":98,"u":"http%3A%2F%2Fexample.com%2F","r":2,"i":"ydefault","lt":291}
{"v":"3.1.8","w":2540,"o":98,"u":"http%3A%2F%2Fexample.com%2F","r":2,"i":"ydefault","lt":293}
time: 20.895822048187
ALL DONE

*/

/*
Unexpected result in browser (Chrome)

[5] Running
[5] Done
HTTP/1.1 200 OK
Host: localhost:8088
Connection: close
Content-type: text/html

[0] Running
[0] Done
HTTP/1.1 200 OK
Host: localhost:8088
Connection: close
Content-type: text/html

[1] Running
[1] Done
HTTP/1.1 200 OK
Host: localhost:8088
Connection: close
Content-type: text/html

[2] Running
[2] Done
HTTP/1.1 200 OK
Host: localhost:8088
Connection: close
Content-type: text/html

[4] Running
[4] Done
HTTP/1.1 200 OK
Host: localhost:8088
Connection: close
Content-type: text/html

[3] Running
[3] Done
HTTP/1.1 200 OK
Host: localhost:8088
Connection: close
X-Powered-By: PHP/5.5.8
Content-type: text/html

Threads:
[0] Data: {"v":"3.1.8","w":2540,"o":98,"u":"http%3A%2F%2Fexample.com%2F","r":2,"i":"ydefault","lt":314}

[1] Data: {"v":"3.1.8","w":2540,"o":98,"u":"http%3A%2F%2Fexample.com%2F","r":2,"i":"ydefault","lt":361}

[2] Data: {"v":"3.1.8","w":2540,"o":98,"u":"http%3A%2F%2Fexample.com%2F","r":2,"i":"ydefault","lt":373}

[3] Data: {"v":"3.1.8","w":2540,"o":98,"u":"http%3A%2F%2Fexample.com%2F","r":2,"i":"ydefault","lt":358}

[4] Data: {"v":"3.1.8","w":2540,"o":98,"u":"http%3A%2F%2Fexample.com%2F","r":2,"i":"ydefault","lt":298}

[5] Data: {"v":"3.1.8","w":2540,"o":98,"u":"http%3A%2F%2Fexample.com%2F","r":2,"i":"ydefault","lt":312}

time: 5.7645590305328
Foreach: 
[0] {"v":"3.1.8","w":2540,"o":98,"u":"http%3A%2F%2Fexample.com%2F","r":2,"i":"ydefault","lt":304}
[1] {"v":"3.1.8","w":2540,"o":98,"u":"http%3A%2F%2Fexample.com%2F","r":2,"i":"ydefault","lt":294}
[2] {"v":"3.1.8","w":2540,"o":98,"u":"http%3A%2F%2Fexample.com%2F","r":2,"i":"ydefault","lt":916}
[3] {"v":"3.1.8","w":2540,"o":98,"u":"http%3A%2F%2Fexample.com%2F","r":2,"i":"ydefault","lt":295}
[4] {"v":"3.1.8","w":2540,"o":98,"u":"http%3A%2F%2Fexample.com%2F","r":2,"i":"ydefault","lt":332}
[5] {"v":"3.1.8","w":2540,"o":98,"u":"http%3A%2F%2Fexample.com%2F","r":2,"i":"ydefault","lt":297}
time: 19.387635946274
&&: 
{"v":"3.1.8","w":2540,"o":98,"u":"http%3A%2F%2Fexample.com%2F","r":2,"i":"ydefault","lt":292}
{"v":"3.1.8","w":2540,"o":98,"u":"http%3A%2F%2Fexample.com%2F","r":2,"i":"ydefault","lt":308}
{"v":"3.1.8","w":2540,"o":98,"u":"http%3A%2F%2Fexample.com%2F","r":2,"i":"ydefault","lt":291}
{"v":"3.1.8","w":2540,"o":98,"u":"http%3A%2F%2Fexample.com%2F","r":2,"i":"ydefault","lt":290}
{"v":"3.1.8","w":2540,"o":98,"u":"http%3A%2F%2Fexample.com%2F","r":2,"i":"ydefault","lt":286}
{"v":"3.1.8","w":2540,"o":98,"u":"http%3A%2F%2Fexample.com%2F","r":2,"i":"ydefault","lt":283}
{"v":"3.1.8","w":2540,"o":98,"u":"http%3A%2F%2Fexample.com%2F","r":2,"i":"ydefault","lt":475}
time: 21.387857913971
ALL DONE
*/