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

Why is it complicated to protect a system, Q. Why is it complicated to prot...

Q. Why is it complicated to protect a system in which users are allowed to do their own I/O? Answer: In earlier chapters we identified a distinction among kernel and user mod

Define an imperative statement, Determine an imperative statement Imper...

Determine an imperative statement Imperative statement points out an action to be carried out during execution of assembled program

Paging, Paging full question

Paging full question

Define the tlsfree(tlsindex) function, Define the TlsFree(TLSIndex) Functio...

Define the TlsFree(TLSIndex) Function This function should be called to free a TLSindex allocated by TlsAlloc. It would be executed when there are no more threads in a process

Explain general graph directory structure, General Graph Directory A s...

General Graph Directory A serious trouble with using an acyclic graph structure is making sure that there are no cycles. When links are further added to an existing tree struc

Medium term scheduler, Medium term scheduling is form of the swapping ope...

Medium term scheduling is form of the swapping operation. This attaches to processes that are in a suspended or blocked state. They are swapped out of real-memory storage until t

Distinguish between long and short term scheduler, Question 1: a) Disti...

Question 1: a) Distinguish between "Long-Term Scheduler" and "Short-Term Scheduler". b) Describe the benefits of "Threads". c) Name three types of CPU Scheduling. Que

Is it essential to bind a real-time thread to an lwp, Q. Presume an operati...

Q. Presume an operating system maps user-level threads to the kernel using the many-to-many model and the mapping is done through LWPs. Additionally the system allows developers to

Model, list trhe various classification of model and types?

list trhe various classification of model and types?

What is a resource-allocation graph, What is a resource-allocation graph? ...

What is a resource-allocation graph? Deadlocks can be explained more precisely in terms of a directed graph called a system resource allocation graph. This graph having of a se

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