Can a PHP script be scheduled to run at a specific time or after a specific amount of time has expired?

Question

I am writing a social cloud game for Android and using PHP on the server. Almost all aspects of the game will be user or user-device driven, so most of the time the device will send a request to the server and the server will, in turn, send a response to the device. Sometimes the server will also send out push messages to the devices, but generally in response to one user's device contacting the server.

There is one special case, however, where a user can set a "timer" and, after the given time has elapsed, the server needs to send the push messages to all of the devices. One way to do this would be to keep the timer local to the user's device and, once it goes off, send the signal to the server to send the push messages. However, there were several reasons why I did not want to do it this way. For instance, if the user decides not to play anymore or loses the game, the timer should technically remain in play.

I looked around for a method in PHP that would allow me to do something like this, but all I came up with were alarms, which are not what I need. I also thought of cron jobs and, indeed, they have been recommended for similar situations on this and other forums, but since this is not a recurring event but, rather, a one time event to take place at an arbitrary point in time, I did not know that a cron job is what I want either.

My current best solution involves a cron job that runs once a second and checks to see if one of these events is to occur in the next second and, if so, sends out the push messages. Is this the proper way to handle this situation, or is there a better tool out there that I just haven't found yet?

Answer 1

cron is great for scripts run on a regular basis, but if you want a one-off (or two-off) script to run at a particular time you would use the unix 'at' command, and you can do it directly from php using code like this:

/****
 * Schedule a command using the AT command
 *
 * To do this you need to ensure that the www-data user is allowed to
 * use the 'at' command - check this in /etc/at.deny
 *
 *
 * EXAMPLE USAGE ::
 *
 * scriptat( '/usr/bin/command-to-execute', 'time-to-run');
 * The time-to-run shoud be in this format: strftime("%Y%m%d%H%M", $unixtime)
 *
 **/

function scriptat( $cmd = null, $time = null ) {
    // Both parameters are required
    if (!$cmd) {
        error_log("******* ScriptAt: cmd not specified");
        return false;
    }
    if (!$time) {
        error_log("******* ScriptAt: time not specified");
        return false;
    }

    // We need to locate php (executable)
    if (!file_exists("/usr/bin/php")) {
        error_log("~ ScriptAt: Could not locate /usr/bin/php");
        return false;
    }

    $fullcmd = "/usr/bin/php -f $cmd";

    $r = popen("/usr/bin/at $time", "w");
    if (!$r) {
        error_log("~ ScriptAt: unable to open pipe for AT command");
        return false;
    }
    fwrite($r, $fullcmd);
    pclose($r);

    error_log("~ ScriptAt: cmd=${cmd} time=${time}");

    return true;
}

Answer 2

soloution 1 : your php file can include a ultimate loop

$con = true;
 while($con)
   {
   //do sample operation
   if($end)
      $con = false;
   else
   sleep(5); // 5 seconds for example
   }

soloution 2 : use cron jobs -- Depend on yout CP you can follow the instruction and call your php program at the specific times
limit : in cron job the minimum time between two calling is 1 minute
soloution 3 : use a shell script and call your php program when ever you want

Answer 3

You can make PHP sleep for a certain amount of time - it will then resume the code afterwards but this is seriously not recommended because when a script sleeps it still uses up processor resources, and if you had multiple scripts sleeping for long periods of time it would put impossible load on your server.

The only other option that I know of is Cron. As @Pete says, you can manage Cron jobs from within PHP, e.g.:
http://net.tutsplus.com/tutorials/php/managing-cron-jobs-with-php-2/

This is going to involve a fair bit of coding, but I think it is your best options.

Another option is to have your user's browser call a PHP function using an Ajax request and JavaScript's setTimeout as suggested by the accepted answer in this question:
how to call a function in PHP after 10 seconds of the page load (Not using HTML)