Running a php script via ajax, but only if it is not already running

Question

My intention is this.

My client.html calls a php script check.php via ajax. I want check.php to check if another script task.php is already being run. If it is, I do not

Answer 1

Lets make the whole process from B to D simple

Step B-D:

$rslt =array(); // output from first exec
$output = array(); // output of task.php execution

//Check if any process by the name 'task.php' is running
exec("ps -auxf | grep 'task.php' | grep -v 'grep'",$rslt);

if(count($rslt)==0) // if none,
  exec('php task.php',$output); // run the task,

Explanation:

ps -auxf        --> gets all running processes with details 
grep 'task.php' --> filter the process by 'task.php' keyword
grep -v 'grep'  --> filters the grep process out

NB:

1. Its also advisable to put the same check in task.php file.

2. If task.php is executed directly via httpd (webserver), it will only be displayed as a httpd process and cannot be identified by 'ps' command

3. It wouldn't work under load-balanced environment. [Edited: 17Jul17]