Question

I have simple queue worker based on standard AMQP Class from PHP. It works with RabbitMQ as a server. I have Queue Class for initialize AMQP connection wirh RabbitMQ. Everything works fine with code below:

$queue = new Queue('myQueue');

 while($envelope = $queue->getEnvelope()) {
   $command = unserialize($envelope->getBody());

   if ($command instanceof QueueCommand) {
     try {
       if ($command->execute()) {
         $queue->ack($envelope->getDeliveryTag());
       }
     } catch (Exception $exc) {
       // an error occurred so do some processing to deal with it
     }
   }
 }

However I wanted to fork queue command execution, but in this case queue goes endless with the first command over and over again. I can’t acknowledge RabbitMQ that message was recieved with $queue->ack(); My forked version (simplified with only one child for testing sake) looks like this :

$queue = new Queue('myQueue');

while($envelope = $queue->getEnvelope()) {
  $command = unserialize($envelope->getBody());

  if ($command instanceof QueueCommand) {
    $pid = pcntl_fork();

    if ($pid) {
      //parent proces
      //wait for child
      pcntl_waitpid($pid, $status, WUNTRACED);

      if($status > 0) {
        // an error occurred so do some processing to deal with it
      } else {
        //remove Command from queue
        $queue->ack($envelope->getDeliveryTag());
      }
    } else {
      //child process
      try {
        if ($command->execute()) {
          exit(0);
        }
      } catch (Exception $exc) {
        exit(1);
      }
    }
  }
}

any help will be appreciated…

Answer 1

I finally solved the problem! I had to run ack command from child process, it works this way!
This is correct code:

$queue = new Queue('myQueue');

while($envelope = $queue->getEnvelope()) {
  $command = unserialize($envelope->getBody());

  if ($command instanceof QueueCommand) {
    $pid = pcntl_fork();

    if ($pid) {
      //parent proces
      //wit for child
      pcntl_waitpid($pid, $status, WUNTRACED);

      if($status > 0) {
        // an error occurred so do some processing to deal with it
      } else {
        // sucess
      }
    } else {
      //child process
      try {
        if ($command->execute()) {
          $queue->ack($envelope->getDeliveryTag());
          exit(0);
        }
      } catch (Exception $exc) {
        exit(1);
      }
    }
  }
}