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 internal file structure, Internal file structure All disk I/O i...

Internal file structure All disk I/O is performed in units of single block, and all blocks are the similar size. It is unlikely that the physical record size will exactly match

Producer-consumer using condition variables, Now let us present an implemen...

Now let us present an implementation of a producer-consumer system using condition variables. This implementation works. dequeue() lock(A) while (queue empty) { wait(A, C)

Write a note on threads, Question 1 Explain (a) tightly coupled systems   ...

Question 1 Explain (a) tightly coupled systems                               (b) Loosely coupled system Question 2 Describe the RPC model Question 3 Write a note o

Explain operating systems for mainframe computers, What are the main differ...

What are the main differences between operating systems for mainframe computers and personal computers? The design goals of operating systems for those machines are quite diffe

Explain the protection problems, Q. In some systems a subdirectory is able...

Q. In some systems a subdirectory is able to be read and written by an authorized user just as ordinary files can be. a. Explain the protection problems that could arise. b.

Banker''s algorithm, Consider the following snapshot of a system, answer th...

Consider the following snapshot of a system, answer the following questions using the banker's algorithm: 1. What is the content of the matrix Need? Is the system in a safe stat

Describe services of operating systems, (a) Describe services of operating ...

(a) Describe services of operating systems. (b) Differentiate among the short term, medium term and long term scheduling that are given by multi-tasking operating systems.

Financial objective of corporation, The primary financial objective of corp...

The primary financial objective of corporation is usually taken to be the maximization of shareholder wealth. Discuss:- i. Ways in which the shareholder of a company can encour

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