Page 63 - DCAP403_Operating System

Operating System

Notes Computation Speedup

A task can often be run faster if it is broken into subtasks and distributed among different
processes. For example, the matrix multiplication code you saw in class. This depends upon the
processes sharing data. (Of course, real speedup also required having multiple CPUs that can be
shared as well.) For another example, consider a web server which may be serving many clients.
Each client can have their own process or thread helping them. This allows the server to use the
operating system to distribute the computer’s resources, including CPU time, among the many
clients.

Modularity

It may be easier to organize a complex task into separate subtasks, and then have different
processes or threads running each subtask.

Example: A single server process dedicated to a single client may have multiple threads
running – each performing a different task for the client.
Convenience

An individual user can run several programs at the same time, to perform some task.

Example: A network browser is open, while the user has a remote terminal program
running (such as telnet), and a word processing program editing data.

Cooperation between processes requires mechanisms that allow processes to communicate data
between each other and synchronize their actions so they do not harmfully interfere with each
other. The purpose of this note is to consider ways that processes can communicate data with
each other, called Inter-process Communcation (IPC).

Note Another note will discuss process synchronization, and in particular, the most
important means of synchronizing activity, the use of semaphores.

4.5 Inter-process Communication

Inter-process Communication (IPC) is a set of techniques for the exchange of data among two
or more threads in one or more processes. It involves sending information from one process
to another. Processes may be running on one or more computers connected by a network. IPC
techniques are divided into methods for message passing, synchronization, shared memory, and
Remote Procedure Calls (RPC). The method of IPC used may vary based on the bandwidth and
latency of communication between the threads, and the type of data being communicated.
Two processes might want to co-operate in performing a particular task. For example a process
might want to print to document in response to a user request, so it starts another process to
handle the printing and sends a message to it to start printing. Once the process handling the

printing request finishes, it sends a message back to the original process, which reads the message
and uses this to pop up a dialog box informing the user that the document has been printed.
There are other ways in which processes can communicate with each other, such as using a
shared memory space.

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