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If you have a PHP script that takes a while to execute (for example, long database operations or file format conversions), you might want to run it in the background so that the rest of your page still loads fast. In this post I’ll describe two ways to do this.

Launching a background process

One approach is to launch a new instance of the PHP interpreter as a background process. On a UNIX-based system this can be done with a single line of code :

exec ("/usr/bin/php path/to/script.php >/dev/null &");

To launch a background process in an OS-independent fashion you’d can use the function below (snatched from this post) -

function launchBackgroundProcess($call) {
     // Windows
    if(is_windows()){
        pclose(popen('start /b '.$call, 'r'));
    }
     // Some sort of UNIX
    else {
        pclose(popen($call.' > /dev/null &', 'r'));
    }
    return true;
}

function is_windows(){
    if(PHP_OS == 'WINNT' || PHP_OS == 'WIN32'){
        return true;
    }
    return false;
}

If you use one of these methods you can pass data to the PHP script using command line arguments.

The main disadvantage of this approach is that the command to execute ($call) is still platform-dependent. Also, the path to the PHP executable may be different on various servers.

Using an asynchronous HTTP request

If the PHP script that needs to be executed is available on the Web, you can easily run it in the background by requesting the URL and dropping the connection right away, so you don’t need to wait until it’s done processing. You can also pass information to the script in the usual way – as URL parameters.

Here’s a function that will submit an asynchronous POST query to the specified URL (this works similar to how a web form is submitted) -

function backgroundPost($url){
  $parts=parse_url($url);

  $fp = fsockopen($parts['host'],
          isset($parts['port'])?$parts['port']:80,
          $errno, $errstr, 30);

  if (!$fp) {
      return false;
  } else {
      $out = "POST ".$parts['path']." HTTP/1.1\r\n";
      $out.= "Host: ".$parts['host']."\r\n";
      $out.= "Content-Type: application/x-www-form-urlencoded\r\n";
      $out.= "Content-Length: ".strlen($parts['query'])."\r\n";
      $out.= "Connection: Close\r\n\r\n";
      if (isset($parts['query'])) $out.= $parts['query'];

      fwrite($fp, $out);
      fclose($fp);
      return true;
  }
}

//Example of use
backgroundPost('http://example.com/slow.php?file='.
                       urlencode('some file.dat'));

Assuming that the target script is located on the same server as the calling script, this function is fast, plus it should work on any operating system.

By the way, I recommend to put a call to ignore_user_abort(true) right at the top of the backgroud script to make sure it’s not terminated when the connection is closed. Disabling the time limit with set_time_limit(0) can also be useful.

Need more?

If for some strange reason you can’t use the aforementioned tricks, you could also launch the script from the client side by using AJAX. This is what I do in my link checker plugin for WordPress. Another possibility is to store the tasks that need to be done in a database and periodically run the script using cron.