Question

Objective:
My script will download a remote file upon form submission, since the file might be big, I would like to fork off a process and let the user go on with his/her life.

Example of a command:

wget -q –limit-rate=1k –tries=10 “http://helios.gsfc.nasa.gov/image_euv_press.jpg” -O /web/assets/content/image/image_euv_press.jpg

Method tried:

1. pcntl forking,

       $pid = pcntl_fork();
   
       if ( $pid == -1 ) {
           exit;
       } else if ( $pid ) {
           //We are the parent process, the pid is child pid right?
   
           return $pid;
       } else {
           // We are the child process
   
           exec($command.' > /dev/null');
           // > /dev/null &
   
           posix_kill(getmypid(),9);
           return;
       }
   

I do get the PID but then there is a risk that the forked process becomes a zombie and since I am using nginx -> php-fpm (tested and confirmed, upon running several times alot of defunct php-fpm processes), I would have to restart the server just to eliminate the zombies, this would leave me to PID exhaustion attack? ( I am guessing)

2. Background process:

           exec($command . ' > /dev/null &');//background process
       $proc = passthru ("ps aux | grep '$command'");//search for the command
       echo var_dump($proc);
       $pid = (int)(next(explode(' ',$proc)));//parse the pid (not implemented)
   

Question:
the background process method works but it’s not clean, is there a better way to fork off a process to download and get that wget command PID so I can kill it later?.

I have tried echoing $! after doing the exec just to get the PID but exec(‘echo $!’) doesnt return anything, i think it’s because every exec is a different “space”

I added ‘> /dev/null 2>/dev/null &’ to the end of the command on my terminal it would return something like: [3] 30751, but through php exec, there is no way to capture that returned PID.

Thank you.

Answer 1

Try the following command:

exec("ps -C $command -o pid=", $pids);

But I recommend you to use Zend Server Job Queue, which exists for these objectives.