SYNCHRONIZATION BASICS

SYNCHRONIZATION BASICS

Synchronization : The concept of Synchronization is concerned with cooperating

processes that share some resources. Co-operating processes must

synchronize with each other when they use shared resources. Thus we can view

the Synchronization as a set of constraints on the ordering of events.

Semaphores : A Semaphore is a protected variable whose value can be accessed

and altered only by operations P and V.

 

A Semaphore Mechanism basically consists of the two primitive operations

SIGNAL and WAIT.

The Semaphore variable can assume only positive integer value. The integer

value of the Semaphore in the wait and signal operations must be executed

indivisible.

That is, when one process modifies the Semaphore value, no other process can

simultaneously modify that same Semaphore value.

Importance of semaphores :

(i) Semaphores can be used to deal with n process critical section problem.

As the n processes shares the semaphores, mutex (standing for mutual

exclusion), is initialized to 1.

 

(ii) Semaphores can also be used to solve various synchronization problems.

 

Co-operating Processes : The concurrent processes executing in the Operating

System may be either Independent Processes or Co-operating Processes.

A process is Co-operating if it can affect or is affected by the other processes

executing in the System.

That means any process that shares data with other processes is a Co-operating

Process.

 

Inter-Process Communication : Cooperating processes can communicate in a

shared-memory environment. Cooperating processes communicate with each

other via an Inter-Process-Communication (IPC) facility. IPC provides a

mechanism to allow processes to communicate and to synchronize their actions.

Inter-Process Communication is best provided by a Message System. Message

System can be defined in many different ways. An IPC facility provides at least

the two operations - send(message) and receive(message).