There are two primary forms of data exchange between parallel tasks - accessing a shared data space and exchanging messages. Message passing refers to a means of communication between different threads within a process different processes running on the same node different processes running on different nodes When messages are passed between two different processes we speak of inter-process communication, or IPC. Message passing can be used as a more process-oriented approach to synchronization than the "data-oriented" approaches used in providing mutual exclusion for shared resources. The two main dimensions Synchronous vs. asynchronous Symmetric or asymmetric process/thread naming

2. INTER-PROCESS COMMUNICATION
• When messages are passed between two different processes we
speak of inter-process communication.
• Message is a block of information.
• Communication may be of two types.
1. Message passing.
2. Shared memory.

3. MESSAGE PASSING
• Message passing is a paradiagram of communication where
messages are sent from a sender to one or more recipent.
OR
• Message passing refers to mean of communication between:
1. Different threads within a process.
2. Different processes running on same node.
3. Different processes running on different node.

4. • MESSAGE has a predefined structure.
• Message passing uses two system calls:
1. Send(name of destination process, message);
2. Receive(name of source process , message);

5. MESSAGE PASSING COMMUNICTION
Mesaage passing communication may be of two types.
1. Direct communication: Explicitly name the process you are
communicating with.
2. Indirect comunication: communicate using mailboxes owned by
receiver.

6. DIRECT COMMUNICATION
INDIRECT COMMUNICATION

7. Message passing uses two system calls.
Send(B, message);
Receive(A, message);
A B
DIRECT COMMUNICATION
Symmetric addressing:
Send(B,msg
)
Receive(A,msg)

8. DIRECT COMMUNICATION
Asymmetric addressing:
A B
Message passing uses 2 system call:
Send(B, message)
Receive( message)
Send(B,Msg)
Receive(msg)

9. INDIRECT COMMUNICATION
INDIRECT COMMUNICATION MAIL
BOX

10. 1. Synchronous message passing: requires the sender and receiver
to wait for each other to transfer the message.
• Blocking send.
• Blocking receive.
1. Asynchronous message passing: delivers a message from sender
to receiver, without waiting for a receiver to be ready.
• Non blocking send .
• Non blocking receive.

11. SYNCHRONOUS MESSAGE PASSING
BLOCKING SEND
door
Waiting busy
msg

12. SYNCHRONOUS MESSAGE PASSING
Blocking receive
door
Busy
waiting

13. ASYNCHORON0US MESSAGE PASSING
Non-blocking send
msg
msg
MAIL BOX

14. NON-blocking receive
msg
MAIL BOX
door
Zzzzzz

15. THE FOLLOWING TYPES OF COMMUNICATION
LINK ARE POSSIBLE THROUGH MAILBOX
• One-to-one link
• Many-to-one link
• One-to-many link
• Many-to-many link