Parallel execution of PHP - php

Question

I have a php script file test1.php
<?php
echo "hello\n"
?>
When i try to run the php through command line using following code only one php process run and other php process is stopped.
We can see only one hello is printed.
Why other process is stopped ?
[root#home usr]# php -f test1.php & php -f test1.php
[30] 20817
hello
[root#home usr]#
[30]+ Stopped php -f test1.php
PS:
PHP 5.4.16 (cli) (built: Jun 23 2015 21:17:27)
Copyright (c) 1997-2013 The PHP Group
Zend Engine v2.4.0, Copyright (c) 1998-2013 Zend Technologies

Answer 1

The scripts get executed in parallel.
Try this modified version of a test script:
<?php
// Read first command line argument
$delay = (int) $argv[1];
// Wait for $delay seconds
sleep($delay);
// Output some message
echo "Result after $delay seconds\n";
If you invoke this script via php hello.php 3 & php hello.php 1 you will see that the first call will run for 3 seconds and print some output while the second call will only run for 1 second and print some output before the first call sends output:
root#httpserver:/tmp# php hello.php 3 & php hello.php 1
[1] 15991
Result after 1 seconds
root#httpserver:/tmp# Result after 3 seconds
If you are looking for other ways of parallel script execution you should have a look at this article https://d-mueller.de/blog/parallel-processing-in-php/