ENVS 1800 Lecture Notes - Lecture 19: Message Passing
14 May 2018
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ENVS 1800 Tutorial 19 Notes – Synchronization
Introduction
• In others, there may be a complex message passing arrangement, with mailboxes set up
for each process.
• Inter process communication has increased in importance over the past few years
• Due to the desire to move data and program execution more easily from one application
to another
• One form of communication that is sometimes very important is the ability to
synchronize processes with each other.
• Two or more processes may be cooperating on the solution of a complex problem, and
one may be dependent on the solution provided by another.
• Furthermore, both may be required to access the same data, the order and timing in
which access takes place can be critical, and these conditions can affect the overall
results.
• This requires a solution to the problem of process synchronization.
• As a simple example, consider an address card file shared by you and your roommate or
partner.
• A friend calls to tell you that she has moved and to give you her new phone number.
• You place a new card with this information in the card file box.
• Meanwhile, your roommate has taken the old card from the box and has used it to write
a letter.
• He returns to the box, sees the new card, figures that it must be obsolete, and so throws
it away and replaces it with the original.
• The new data is now lost.
• Similar situations can occur with data being shared by more than one process.
• As another simple example, consider two processes, with the goal to produce the result
c, where process 1 solves the program statement a = a + b with initial values a = 2 and b
= 3.
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