Chirag's Blog: Inter-Processor Communication & Synchronization

Inter-Processor Communication

In a multiprocessing environment processor implies parallelism by concurrent processing. The concurrent processing requires sharing of resources between the processors and inter-processor communication.

Basically, there are two ways by which inter process communication is achieved:

1. Using Shared Variables 2. Using Message Passing

1. IPC Using Shared Variable

In this system shared variable are stored in common memory which is accessible to all processors in the system. While sharing common resources or shared variables conflict problem may arise. It is necessary to prevent conflict use of shared resources by several processors. This task is done by operating system.

Figure : IPC using Shared Variable

Master-slave operating system: In this system, processor that executes the operating system function is called master. The other processors are called slave. When slave needs operating system service it requests it by interrupting the master.

Separate operating system: In each processor has entire copy of operating system can be execute operating system functions. This organization is more suitable for loosely couple system.

Distributed operating system: In this operating system, routines are distributed among the available processors. Such type operating system is also known as floating operating system.

2. Using Message Passing

In multiprocessor system with no shared memory, we use message passing mechanism to perform inter-process communication. When processor wants to communicate with another processor, it uses a special procedure which initiates communication.

Figure : IPC using message passing

It identifies the destination processor and once source and destination processors are identified a communication channel is established. A message is then sent through the communication channel.

Inter-Processer Synchronization

At the higher level of parallelism, the program is partitioned into process that are executed in different processors. This technique is called concurrent processing. During concurrent processing when two or more processors need the same resource at a time, the contention problem arise. Such problem can be solved by synchronization.

To achieve synchronization a set of hardware primitives are used to automatically read and modified a memory location without any interruption between the two operations. Such mechanisms are necessary to protect data from being changed simultaneously by two or more processors. This mechanism is known as mutual exclusion.

A program sequence which accesses the shared resources, one begun, must complete execution before another processor accesses the same shared address. Thus, program sequence which accesses the shared memory is known as critical section of the program. Inter-process communication done by mutual exclusion with semaphore and mutual exclusion using load and store conditional instruction.

To learn more about Interprocessor Communication & Synchronization, watch below video