Interprocess Communication

Direct Communication
Processes must name each other explicitly:

• send (P, message) – send a message to process P
• receive(Q, message) – receive a message from process Q
  

Properties of communication link

• Links are established automatically
• A link is associated with exactly one pair of communicating
  processes.
• Between each pair there exists exactly one link.
• The link may be unidirectional, but is usually bi-directional.
  Asymmetric variant
• receive(id, message) – receive a message from any
  process, pid stored in id

Indirect Communication

Operations

• create a new mailbox
• send and receive messages through mailbox
  destroy a mailbox

Primitives are defined as:

• send(A, message) – send a message to mailbox A
• receive(A, message) – receive a message from mailbox A

Synchronization

• Message passing may be either blocking or non-blocking
• Blocking is considered synchronous
• Non-blocking is considered asynchronous
• send and receive primitives may be either blocking or
  non-blocking.

Buffering

• Queue of messages attached to the link; implemented in
  one of three ways.
  1. Zero capacity – 0 messages
  Sender must wait for receiver (rendezvous).
  2. Bounded capacity – finite length of n messages
  Sender must wait if link full.
  3. Unbounded capacity – infinite length
  Sender never waits.
  

Producer - Consumer Example

• Producer generates an integer between 0 and 9 (inclusive), then stores it in a CubbyHole object. To make the synchronization problem more interesting, the Producer sleeps for a random amount of time between 0 and 100 milliseconds before repeating the number-generating cycle.
• Producer generates an integer between 0 and 9 (inclusive), then stores it in a CubbyHole object. To make the synchronization problem more interesting, the Producer sleeps for a random amount of time between 0 and 100 milliseconds before repeating the number-generating cycle.