Inter Process Communication in Distributed System

Inter Process Communication:

The process needs frequently to communicate with other processes.
Example: Consider a shell pipeline in UNIX or DOS.

$ process1 | process2

Here the first process must be passed the output to process2. Process1 output is to be input to process2. So, there is a need for communication between processes. This type of communication is said to be ‘Inter Process Communication‘.

Types of Methods for Inter-Process Communication:

Shared Memory:

Shared Memory is the fastest method for inter-process communication. It provides a common block in the main memory. Each process can read the messages from the common block and each process can write the messages in the common block.

Message Passing:

Message Passing system provides a mechanism to allow the process to communicate and synchronize. These actions without sharing the same address space. It is particularly useful in a distributed environment where the communicating processes may reside on different computers collected by the network. This facility or system provides at least two operations – send (message), and receive (message).


A Pipe is a mechanism that allows a stream of data to be passed between reader and writer processes. It is a first-in-first-out queue and it is written by one process and read by another process. When a pipe is created, it is given fixed-size bytes. When a process wants to write something into the pipe, the request will be accepted if that has room for data writing, otherwise, the process is blocked.


A signal is a software mechanism that informs processes of the occurrence of asynchronous events. When a signal is sent the operating system interrupts the target process flow of execution to deliver the signal. Execution can be interrupted during any non-atomic instruction. If the process has previously registered a signal handler that routine is executed and otherwise the default signal handler is executed.
Example: Some predefined signals in Unix:

1. #define SIGHUP   // Hangup (POSIX)
2. #define SIGINT   // Interrupt (ANSI)
3. #define SIGKILL  // Kill, unblocked (POSIX)
4. #define SIGALRM  // Alarm Clock (POSIX)
5. #define SIGQUIT  // Quit (POSIX)


A semaphore is an integer value used for signalling among processes. Only three operations may be performed on a semaphore, all of which are atomic, initialize, decrement and increment. The decrement operation may result in the blocking of a process and the increment operation may result in the unblocking of a process. A semaphore in UNIX allows the process to synchronize execution by doing a set of operations atomically on a set of semaphores.