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

How many disks can be used effectively by one fast wide bus, Q. More than ...

Q. More than one disk drive is able to be attached to a SCSI bus. Especially a fast wide SCSI-II bus can be connected to at most 15 disk drives. Remember that this bus has a bandw

Safety algorithm and resource request algorithm, Safety algorithm : This is...

Safety algorithm : This is to make sure if the system is in safe state or not. It may need an order of m x n2 operation to determine if the state of the system is safe or not.

Explain the basic method of paging method, Explain the basic method of pagi...

Explain the basic method of paging method. Physical memory is divided into the fixed-sized blocks called frames. Logical memory is as well divided into blocks of the same size

What is process control block, What is process control block? Every pro...

What is process control block? Every process is represented in the OS by a process control block. It has many pieces of information associated with an exact process.

Activities of operating system - memory management, Q. What are the three m...

Q. What are the three main activities of an operating system in regard to memory management? Answer: a. Keep follows of which parts of memory are currently being used and

Paging, Paging full question

Paging full question

Split the hexadecimal format, The following is a dump of a TCP header in h...

The following is a dump of a TCP header in hexadecimal format: 00CD0018 00000EF1 00000D5D 502200D1 01BF0010 We need to first split the above hex as such 00 CD 00 18 00 00

Necessary conditions for deadlock, Here are the conditions necessary for a ...

Here are the conditions necessary for a deadlock to occur; note that all of them are necessary, and none is suf?cient: 1. ?nite resources: the resources are held in a mutually-e

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