questions on Producer Consumer

flethuseo · March 6th, 2014, 02:42 AM

Hi all,

1. In the code for the producer/consumer without any synchronization, why is there a 'while true' in the add and remove methods? I have removed it and it seems to work better:

Code:

		private void add(int num) {
			if (index < buffer.length) {
				buffer[index++] = num;
				return;
			}
		}

		private int remove() {
			if (index > 0) {
				return buffer[--index];
			}
			return -1;
		}

2. After synchronizing access to the buffer for the producer and consumer. What would be the best way to make the consumer stop when the producer stops producing and the queue is empty?

John Mongan · July 11th, 2017, 03:18 PM

Without the while loops, add will silently fail to add the value to the buffer if it is full, and remove will fail to retrieve a valid value from the queue if it is empty.

There are a variety of means that can be used to stop the consumer. One way to do it is called "poison pill": when the producer is ready to shut down it puts a special value on the queue just before it shuts down; when the consumer sees that value it shuts down. To make this work, you have to be sure that the special "poison pill" value is one that would never be placed on the queue in any other context, or you'll have the consumer shutting down when you don't want it to.

John