How to create a PHP Daemon

Mike Peters, 04-14-2010

A daemon is a Linux program that runs in the background.

Most daemons are written in C. While C is faster and more robust than PHP, looking at development time and cost, PHP generally scores a lot better than C.

Converting your C daemons to PHP where applicable, makes the code more accessible to a wider percentage of your development force and allows better re-use and connecting of existing code.

To Facebook, keeping all code accessible to all developers was so important, that they've decided to come up with a way to compile PHP to C in real time. So you get PHP speed of development with C speed. The HipHop toolkit is available on an open source license.

The simple PHP4 functions included here, will let you easily create PHP daemons.

Features:
* Daemon will not start if another instance is already running
* Daemon PID saved to /var/run/
* Daemon log messages saved to /var/log/
* Run in foreground mode with the "-f" flag

Sample daemon:

require_once("common_daemon.php");

// Get parameters from command line
foreach ($argv as $parameter)
{
$run_in_foreground = Strcasecmp($parameter,"-f")==0;
}

// Start our daemon
if (!PHPDaemonStart("mydaemon", $run_in_foreground))
{
// Already running
return;
}

// Do something useful
while (1)
{
PHPDaemonLog("Hello, the time is ".date("h:i:s", time()));
sleep(1);
}

// Never here

The common_daemon.php functions:

// Give us eternity to execute the script.
ini_set("max_execution_time", "0");
ini_set("max_input_time", "0");
set_time_limit(0);

function PHPDaemonStart($name, $run_in_foreground=0)
{
// This must be global so that the handle is kept alive
// after this function exits
global $handle_lockfile;

// Remember the daemon name
global $phpdaemon_name;
$phpdaemon_name = $name;

// Remember if we're running in foreground mode
global $phpdaemon_run_in_foreground;
$phpdaemon_run_in_foreground = $run_in_foreground;

// Open PID file
$tmpfilename = "/var/run/$name.pid";
if (!($handle_lockfile = @fopen($tmpfilename,"a+")))
{
// Script already running - abort
return 0;
}

// Obtain an exlcusive lock on file
// (If script is running this will fail)
if (!@flock( $handle_lockfile, LOCK_EX | LOCK_NB, &$wouldblock) || $wouldblock)
{
// Script already running - abort
@fclose($handle_lockfile);
return 0;
}

// Write our PID
@ftruncate($handle_lockfile,0);
@fseek($handle_lockfile, 0, 0);
@fwrite($handle_lockfile, getmypid());
@fflush($handle_lockfile);

// If we need to run in foreground, we're done
if ($run_in_foreground)
{
return 1;
}

// If we're up to here we need to fork our process
$pid = pcntl_fork();
if ($pid==-1)
{
// Can't fork
return 0;
}

// If we are the parent
if ($pid)
{
// Sleep for 2 seconds, letting the forked process wake up
// and attempt to grab our lock
sleep(2);

// Release the lock
@flock($handle_lockfile, LOCK_UN);

// Close file
fclose($handle_lockfile);

// Kill parent process
// By now the child has the lock
die;
}
// (Else - we are the child)
else
{
// Open file
while (!($handle_lockfile = @fopen($tmpfilename, "a+")))
{
// Try again
usleep(100);
}

// Re-establish lock on file
while (!@flock($handle_lockfile, LOCK_EX, &$wouldblock))
{
// Try again
usleep(100);
}

// Write pid into file
@ftruncate($handle_lockfile,0);
@fseek($handle_lockfile, 0, 0);
@fwrite($handle_lockfile, getmypid());
@fflush($handle_lockfile);
}

// We have a lock - all good
return 1;
}

function PHPDaemonLog($str)
{
// This is the daemon name
global $phpdaemon_name;

// This indicates whether or not we are running in foreground mode
global $phpdaemon_run_in_foreground ;

// Open log file
$handle = @fopen("/var/log/$phpdaemon_name.log", "a");

// Obtain an exclusive lock (so that this is thread safe)
flock($handle, LOCK_EX, &$wouldblock);

// Write
$output = date("Y-m-d h:i:s", time())." $str\r\n";
@fwrite($handle, $output);

// If we are running in foreground mode, output to screen as well
if ($phpdaemon_run_in_foreground) echo $output;

// Release lock
flock($handle, LOCK_UN);

// Close file
fclose($handle);
}

function IsPHPDaemonRunning($name)
{
// Open PID file
$tmpfilename = "/var/run/$name.pid";
if (!($tmpfile = @fopen($tmpfilename,"r")))
{
// Script not running
return 0;
}

// Obtain an exlcusive lock on file
// (If script is running this will fail)
$not_running = flock( $tmpfile, LOCK_EX | LOCK_NB, &$wouldblock);

// Release lock if successful
if ($not_running) flock($tmpfile, LOCK_UN);

// Close file
@fclose($tmpfile);

// Return result
return !$not_running || $wouldblock;
}

Szyszeja Leonidas, 08-02-2010

Hi, how can i stop the deaemon?
Thanks!

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