INTERPROCESS COMMUNICATION

INTER PROCESS COMMUNICATION:

• Interprocess communication (IPC) is a set of programming interfaces that allow a programmer to coordinate activities among different program processes that can run concurrently in an operating system.
• This allows a program to handle many user requests at the same time.

PURPOSE FOR IPC:

• DATA TRANSFER
• SHARING DATA
• EVENT NOTIFICATION
• RESOURCE SHARING AND SYNCHRONIZATION
• PROCESS CONTROL

IPC MACHANISMS:

• MESSAGE PASSING:
• SHARED MEMORY

MESSAGE PASSING:

1. In massage passing there are no shared variables.
2. IPC provides two operations for fixed and variable sized message:

• send(message)
• receive(message)

3.If process P and Q wish to communicate ,they need to establish

• a communication link
• exchange message via send and receive

4.Implementation of physical link

• physical(e,g shared memory,hardware bus)
• logical(e.g syntax and semantics,abstractions)

5. Methods for communication link:

• Direct or Indirect(Naming)
• Symmetric or Asymmetric communications
• Automatic or Explicit buffering
• send-by-copy or send-by-reference
• fixed or variable sized messages

6.Direct communication:

1. Process must name each other explicitly

-symmetric addressing

• send(P,message)-sends message to process P
• receive(q,message)-receive from Q

-Asymmetric Addressing

• Send(A,message)-sends message to mail box A
• receive(A,message)-receive message from mail box A

2.Properties of communication link:

• Links established automatically between pairs
• process must know each others ID
• Exactly one link per pair of communicating processes

3.Disadvantage:

A process must know the name or ID of process(es) it wish to communicate with

7.Indirect communication:

• Messages are sent or received from mailboxes

-Each mail box has unique ID

-Process can communicate only if they share a mail box

• properties of communication link

1. links established only if they share common mail box
2. a link may be associated with more than two processes
3. Each pair of processes may share several communication link

• ownership:

-process owns:only owner may receive messages through this mailbox. other processes may only send. When process terminates any “owned” mailboxes are destroyed.

-System owns: mechanisms provided to create, delete, send and receive through mailboxes. Process that creates mailbox owns it but may transfer ownership to another process

8.SYNCHRINIZING MESSAGE FLOW:

Message passing may be either blocking or non-blocking

blocking send -sender blocked until message received by mailbox or process

non-blocking send -sender resumes operation immediately after sending

blocking receive- receiver blocks until a message is available

non-blocking receive-receiver returns immediately with either a valid or null message.