Write a note on semaphores, Operating System

Assignment Help:

Write a note on semaphores

A semaphore is a tool meant for synchronizing multiple processes trying to access a shared variable. That is a semaphore is used to deal with the critical section problem or in other words to evade the race condition. A semaphore S is in fact an integer variable that apart from initialization is accessed only through two standard atomic operations:

*Wait and signal.

 

The traditional definition of wait in pseudo code is:

    wait (S) {

             while (S<=0)

                ; // no-op

             S--;

    }

The traditional definition of signal in pseudo code is:

    signal (S) {

               S++;

    }

 

For each process P,

    do {

WAIT

           Critical Section

SIGNALS

 

          } while (1);

 

A semaphore is able to be defined as:

typedef struct {

             int value;

             struct process *L;

} semphore;

 

Once more, the wait semaphore operation can be defined as:

void wait (semaphore S) {

                S.value--;

                if (S.value < 0) {

                    add this process to S.L;

                    block();

                }

}

 

As well, the signal semaphore operation is able to be defined as:

void signal( semaphore S) {

                   S.value++;

                   if (S.value <= 0) {

                       remove a process P from S.L;

                       wakeup(P);

                   }

}


Related Discussions:- Write a note on semaphores

Explain the reasons why an organisation fail to plan, Problem 1: (a) Wh...

Problem 1: (a) What are the likely benefits which an organisation may derive from the planning process? (b) Explain the main reasons why an organisation may fail to plan.

Define i/o and cpu bursts, Define I/O and CPU Bursts   Applications typ...

Define I/O and CPU Bursts   Applications typically to through cycle of CPU bursts and Input/output bursts. Since the CPU sits idle during I/O operations, efficiency is improved

Explain the worker model, Explain the Worker Model The Worker Model of ...

Explain the Worker Model The Worker Model of client-server application architecture provides a very good understanding of threads and their power to the developer. This exercis

Explain about error detection method, Q. Explain about Error detection meth...

Q. Explain about Error detection method? Error detection: error can occur in CPU, in I/O devices or in memory hardware. Operating system constantly needs to be aware of possi

Define dynamic linking, Define dynamic linking. Dynamic linking is same...

Define dynamic linking. Dynamic linking is same to dynamic loading, rather that loading being postponed unless execution time, linking is postponed. This feature is usually use

Binary arithmetic, The principle is that of ordinary addition; however reme...

The principle is that of ordinary addition; however remember the highest number is 1.   Calculate the following:                             11001 +                           11

We can view an operating system as a resource allocator, We can view an ope...

We can view an operating system as a resource allocator. Explain. We can outlook an operating system as a resource allocator. A computer system has Many resources (software and

What is busy waiting, What is busy waiting? The repeated implementation...

What is busy waiting? The repeated implementation of a loop of code while waiting for an event to happen is known as busy-waiting. The CPU is not engaged in any actual producti

What are a safe state and an unsafe state, What are a safe state and an uns...

What are a safe state and an unsafe state? Answer:  A state is safe if the system can allocate resources to every process in some order and still avoid a deadlock. A system is

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd