Semaphores-R.D.Sivakumar

1. Video Lecture and E-Content Created by
R.D.SIVAKUMAR,M.Sc.,M.Phil.,M.Tech.,
Assistant Professor of Computer Science &
Assistant Professor and Head, Department of M.Com.(CA),
Ayya Nadar Janaki Ammal College,
Sivakasi – 626 124.
Mobile: 099440-42243
e-mail : sivamsccsit@gmail.com website: www.rdsivakumar.blogspot.in
SEMAPHORES

2. It is a synchronization tool.
It deal with n-process critical section problem
It was proposed by Dijkstra.
It is an integer value used for signaling among processes.
SEMAPHORES

3. Wait ( ) – To use a resource.
Signal ( ) – To release a resource.
 To transmit a signal via semaphore S, a process executes the primitive
semsignal (s).
To receive a signal via semaphore S, a process executes the primitive semwait (s).
Semaphores can be used to control access to a given resource.
SEMAPHORES FUNCTIONS

4. Semaphore is initialized to the number of resources available.
Each process that wishes to use a resource performs a wait ( )
operation.
wait (s)
{
while (s<=0)
// no operation
s--;
WAIT ( )

5. When a process releases a resource, if performs a signal ( )
operation.
Signal (s)
{
s++;
}
When the count for the semaphores goes to 0, resources
are being used.
After that, processes that with to use a resource will block
until the count becomes > 0.
SIGNAL ( )