IPC in Message-Passing Systems

IPC provides a way to communicate without sharing a file/vars:

• send(location, message)

• receive(location, message)

size of message can be fixed or variable

How to do it:

1. Create a link

2. send messages

Implementation:

Direct Communication

Properties of direct communication links:

• 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

Indirect Communication

Messages are sent to and received via ports (mailboxes)

Each port:

• has a unique ID

• can only communicate if each process shares the port

Properties of Indirect Communication link:

• Link established only if processes share a common mailbox

• A link may be associated with many processes

• Each pair of processes may share several communication links

• Link may be unidirectional or bi-directional

How indirect is done:

1. create a new port

2. send and receive messages via that port

3. destroy port

Synchronization

Blocking (synchronous)

Blocking send - sender is blocked until message is received

Blocking receive - receiver is blocked until message is available (i think it means sent)

rendezvous - when both send and receive are blocked

Non-blocking (asynchronous)

Non-Blocking send - can send

Non-Blocking receive - can receive either a NULL value or a message

Buffering

Queue of messages attached to a link

LINK = port

Implementation:

• Zero capacity - no messages are queued on a link. Sender must wait for receiver (rendezvous)

• Bounded capacity - finite length of n messages, sender must wait if link is full

• Unbounded capacity - infinate length, sender never waits

Pipes

Allows two processes to communicate

Ordinary Pipes

Ordinary pipes – cannot be accessed from outside the process that created it.
Typically, a parent process creates a pipe and uses it to communicate with a child
process that it created.

• Ordinary Pipes allow communication in standard producer-consumer style

• Producer writes to one end (the write-end of the pipe)

• Consumer reads from the other end (the read-end of the pipe)

• Ordinary pipes are therefore unidirectional

• Require parent-child relationship between communicating processes

Named Pipes

Named pipes – can be accessed without a parent-child relationship.

• Named Pipes are more powerful than ordinary pipes

• Communication is bidirectional

• No parent-child relationship is necessary between the communicating processes

• Several processes can use the named pipe for communication

• Provided on both UNIX and Windows systems