[PHP] timeout이 있는 shell_exec 만들기

function shell_exec_timeout($cmd, $timeout)
{
 if(!$cmd || !$timeout) return NULL;

 // File descriptors passed to the process.
 $descriptors = array(
  0 => array('pipe', 'r'),  // stdin
  1 => array('pipe', 'w'),  // stdout
  2 => array('pipe', 'w')   // stderr
 );

 // Start the process.
 $process = proc_open($cmd, $descriptors, $pipes);

 if (!is_resource($process))
 {
  throw new Exception('Could not execute process');
 }

 // Set the stdout stream to none-blocking.
 stream_set_blocking($pipes[1], 0);

 // Turn the timeout into microseconds.
 $timeout = $timeout * 1000000;

 // Output buffer.
 $buffer = '';

 // While we have time to wait.
 while ($timeout > 0)
 {
  $start = microtime(true);

  // Wait until we have output or the timer expired.
  $read  = array($pipes[1]);
  $other = array();

  stream_select($read, $other, $other, 0, $timeout);

  // Get the status of the process.
  // Do this before we read from the stream,
  // this way we can't lose the last bit of output if the process dies between these functions.
  $status = proc_get_status($process);

  // Read the contents from the buffer.
  // This function will always return immediately as the stream is none-blocking.
  $buffer .= stream_get_contents($pipes[1]);

  if (!$status['running'])
  {
   // Break from this loop if the process exited before the timeout.
   break;
  }

  // Subtract the number of microseconds that we waited.
  //$timeout -= (microtime(true) - $start) * 1000000;

  $during = (microtime(true) - $start) * 1000000;
  $timeout = $timeout - $during;
 } // while ($timeout > 0)

 proc_terminate($process, 9);

 // Close all streams.
 fclose($pipes[0]);
 fclose($pipes[1]);
 fclose($pipes[2]);

 proc_close($process);

 return $buffer;
} // function shell_exec_timeout($cmd, $timeout)