A thread of execution is the smallest sequence of programmed instructions that can be managed independently by a scheduler, which is typically a part of the operating system. In the PHP, you can divide and conquer your planned process efficiently by Thread.

The below is the simple example of thread:

<?php

class workerThread extends Thread
{
	public function __construct($i)
	{
		  $this->i=$i;
	}

	public function run()
	{
		while(true)
		{
			echo $this->i;
			sleep(1);
		}
	}
}

for($i=0;$i<50;$i++)
{
	$workers[$i]=new workerThread($i);
	$workers[$i]->start();
}

?>


To understand of the concept for Thread, below example will be super helpful:

<?php
class STD extends Thread{
    public function put()
	{
        $this->synchronized(function()
		{
           	for($i=0;$i<7;$i++)
			{
			    printf("%d\n",$i);
			    $this->notify();
			    if($i < 6)
				    $this->wait();
			    else
			        exit();
			    sleep(1);
			}
        });

    }

	public function flush()
	{
		$this->synchronized(function()
		{
            for($i=0;$i<7;$i++)
			{
			    flush();
			    $this->notify();
			    if($i < 6)
				    $this->wait();
			    else
			        exit();
		    }
		});
	}
}

class A extends Thread
{
    private $std;
    public function __construct($std)
	{
        $this->std = $std;
    }
    public function run()
	{
        $this->std->put();
    }
}

class B extends Thread
{
    private $std;
    public function __construct($std)
	{
        $this->std = $std;
    }
    public function run()
	{
        $this->std->flush();
    }
}

ob_end_clean();
echo str_repeat(" ", 1024);
$std = new STD();
$ta = new A($std);
$tb = new B($std);
$ta->start();
$tb->start();