Inter-Process Communication

Definition:

Shared memory:

• An area of memory shared among the processes that wish to communicate.
• The communication is under the control of the users processes not OSs
• Other way is have many processes accessing shared memory, Shared memory
• Main issue: Process Synchronization

Message passing

• Processes communicate with each other
  • without resorting to shared variables
  • using communication link
• IPC facility provides two operations:
  • send(P, message): send message to P
  • receive(Q, message): receive message from Q
• The message size is either fixed or variable
• Direct vs Indirect communication:
  • Direct: peer to peer
  • Indirect communication: has a MailBox for each of a group of process to subscribe to
• Synchronous vs asynchronous communication:

	send(P,message)	receive(Q,message)
Synchronous (blocking)	The sender wait until the message is received then continue	The receiver wait until a message is sent	doesnt need much buffer size
Asynchronous (non-blocking)	The senders send message and continue	The receiver checks received message, can be null or a message	buffer needs to be large enough

• Buffering communication:
  • Zero capacity – no messages are queued on a link.
    • synchronous
  • Bounded capacity – finite length of n messages
    • Sender must wait if link full
    • asynchronous
  • Unbounded capacity – infinite length
    • Sender never waits
    • asynchronous