Message Passing

Message Passing is a way for processes to communicate and synchronize by sending and receiving messages. It works well in distributed systems and multiprocessors.

Key Points:

• Send (destination, message): A process sends a message to another process.
• Receive (source, message): A process gets a message from another process.

The receiver cannot receive a message until it has been sent by another process.

Synchronization

• send primitive extecuted
  • sending process is blocked until the message is received, or it is not.
• receive primitive extecuted
  1. If a message has previously been sent, the message is received and execution continues.
  2. If there is no waiting message, then either
     1. the process is blocked until a message arrives
     2. the process continues to execute, abandoning the attempt to receive.

Types of Message Passing:

1. Blocking: The sender or receiver waits until the message is sent/received.
2. Nonblocking: The sender or receiver continues without waiting.

Common Combinations:

1. Blocking send, blocking receive: Both wait (tight synchronization).
2. Nonblocking send, blocking receive: Sender continues, receiver waits.
3. Nonblocking send, nonblocking receive: Both continue without waiting.

Addressing:

• Direct: The send primitive includes a specific identifier of the destination process.

  receive primitive :

  • One possibility is to require that the process explicitly designate a sending process.
  • it is impossible to specify the anticipated source process. (use of implicit addressing )