Message Passing: Difference between revisions

:Process A delivers the message directly to process B. If process B is not ready to receive at the moment of sending, Process A is suspended and queued upon Process B's 'sending' queue, until Process B is receiving. Using this method, you don't need to care for message queues - but you enqueue processes. Note that if process B is waiting to receive a message from process A, and the message fails to be delivered (due to an error, or some failure in the message delivery system, for example) then process B will block indefinitely.

:Process A sends the message to Process B. The message is copied to a dedicated region in kernel space and attached to Process B's message queue (lets call it the Post box). The next time, Process B looks into its postbox, it will retrieve the message. You can have processes block for receiving a message or just stroll by and check whether there is something to fetch. One could call this method "store and forward message passing". The main benefit of asynchronous messaging is that it allows a single thread/process to wait for the results of many unrelated "requests" at the same time. However, any erroneous (or malicious) process can repeatedly spam messages in quick succession to other processes, thus tying up system resources in a denial-of-service attack.