One of the two techniques for communicating between parallel
A common use of message passing is for communication in a
send a message to a process running on the same processor or
another. The actual transmission of the message is usually
generally used in computers with relatively few processors.
This is because the total communications
bandwidth usually
increases with the number of processors.
A message passing system provides primitives for sending and
receiving messages. These primitives may by either
will not complete (will not allow the sender to proceed) until
the receiving process has received the message. This allows
the sender to know whether the message was received
successfully or not (like when you speak to someone on the
telephone). An asynchronous send simply queues the message
for transmission without waiting for it to be received (like
posting a letter). A synchronous receive primitive will wait
until there is a message to read whereas an asynchronous
receive will return immediately, either with a message or to
say that no message has arrived.
Messages may be sent to a named process or to a named
mailbox which may be readable by one or many processes.
Transmission involves determining the location of the
recipient and then choosing a route to reach that location.
The message may be transmitted in one go or may be split into
packets which are transmitted independently (e.g. using
message passing system must ensure that sufficient memory is
available to buffer the message at its destination and at
intermediate nodes.
Messages may be typed or untyped at the programming language
level. They may have a priority, allowing the receiver to
read the highest priority messages first.
objects as a metaphor for procedure call.
(1994-11-11)