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

Plot a function for value of heights, The performance of a file system depe...

The performance of a file system depends upon the cache hit rate (fraction of blocks found in the cache). If it takes 1 msec to satisfy a request from the cache, but 40 msec to sat

Processes- making the system more responsive and useful, Processes- Making ...

Processes- Making the System More Responsive and Useful A method by definition build up of a code execution and resource ownership. A process has two main characteristics, code

Explain the steps in deadlock recovery, Explain the steps in deadlock recov...

Explain the steps in deadlock recovery. a)      Exterminate off all processes involved - drastic. b)      Exterminate off one at a time till deadlock gone - select a victim.

What is preemptive and nonpreemptive scheduling, What is preemptive and non...

What is preemptive and nonpreemptive scheduling? Under nonpreemptive scheduling once the CPU has been allocated to a process, the process keeps the CPU unless it releases the C

Estimate the continued transfer rate of drive, Q. The term "fast wide SCSI...

Q. The term "fast wide SCSI-II" signifies a SCSI bus that operates at a data rate of 20 megabytes per second when it moves a packet of bytes among the host and a device. Presume t

Multilevel queue scheduling, Explain multilevel queue scheduling and multil...

Explain multilevel queue scheduling and multilevel feedback queue scheduling #Minimum 100 words accepted#

Batch oriented and interactive operating system., properies of Batch orient...

properies of Batch oriented and interactive operating system.

Synchronization, As we already know, threadsmust ensure consistency; otherw...

As we already know, threadsmust ensure consistency; otherwise, race conditions (non-deterministic results) might happen. Now consider the "too much milk problem": two people share

Locks - mutexes, Locks (also known as mutexes, short for mutual exclusion l...

Locks (also known as mutexes, short for mutual exclusion locks) provide mutual exclusion to shared data inside a critical session. They are implemented by means of two atomic routi

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