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

Macro, What is macro expansion

What is macro expansion

Multiprogramming, how response times are reduced by allowing time sharing o...

how response times are reduced by allowing time sharing on top of multiprogramming

Give an overview of unix based file systems, Give an overview of UNIX based...

Give an overview of UNIX based file systems. UNIX and UNIX-like operating systems allocate a device name to each device, other than this isn't how the files on that device are

What is independent process, What is independent process? A process is ...

What is independent process? A process is independent it cannot influence or be affected by the other processes implementing in the system. Any process does not share data with

Define spooling, Define spooling. A spool is a buffer that holds output...

Define spooling. A spool is a buffer that holds output for a device, like printer, that cannot accept interleaved data streams. When a request finishes printing, the spooling s

What are the advantages of using unequal- size partitions, In fixed portion...

In fixed portioning scheme, what are the advantages of using unequal- size partitions? With unequal-size partitions there are two probable ways to assign process to partitions.

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 lru enhanced second chance algorithm, Enhanced Second chance algori...

Enhanced Second chance algorithm In this a modify bit is as well used. Now if the ordered pair of reference and modify is (0,0) neither recently used nor modified - the best

Computer organisation, basic advantage of using interrupt initiated data tr...

basic advantage of using interrupt initiated data transfer over transfer under program control without an interrupt

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