Producer Consumer Problem

This algorithm uses blocking send and receive primitives to solve the producer/consumer (or bounded-buffer) problem. In this solution, the buffer size depends on the capacity of the link.

 1	var nextp, nextc: item;
 2	procedure producer;
 3	begin
 4		while true do begin
 5			(* produce item in nextp *)
 6			send("Consumerprocess", nextp);
 7		end;
 8	end;
 9	procedure consumer;
10	begin
11		while true do begin
12			receive("Producerprocess", nextc);
13			(* consume item in nextc *)
14		end;
15	end;
16	begin
17		parbegin
18			Consumerprocess: consumer;
19			Producerprocess: producer;
20		parend
21	end.

line 1 Here, nextp is the item the consumer produces, and nextc the item that the consumer consumes.

lines 2-8 This procedure simply generates items and sends them to the consumer process (named Consumerprocess). Suppose the capacity of the link is n items. If n items are waiting to be consumed, and the producer tries to send the n+1-st item, the producer will block (suspend) until the consumer has removed one item from the link (i.e., done a receive on the producer process). Note the name of the consumer process is given explicitly, so this is an example of “explicit naming” or “direct communication.” Also, since the send is blocking, it is an example of “synchronous communication.”

lines 9-15 This code simply receives items from the producer process (named Producerprocess) and consumes them. If when the receive statement is executed there are no items in the link, the consumer will block (suspend) until the producer has put an item from the link (i.e., done a send to the consumer process). Note the name of the producer process is given explicitly; again this is an example of “explicit naming” or “direct communication.” Also, since the receive is blocking, it is an example of “synchronous communication.”

lines 17-20 This starts two concurrent processes, the Consumerprocess and the Producerprocess.