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

Execution without entering a deadlock state, Q. Presume that a system is in...

Q. Presume that a system is in an unsafe state. Illustrate that it is possible for the processes to complete their execution without entering a deadlock state. Answer: An unsaf

Life of a page, Suppose your process starts up, and allocates some memory w...

Suppose your process starts up, and allocates some memory with malloc(). The allocator will then give part of a memory page to your process. The OS then updates the corresponding p

Operating systems structures, with the aid of diagrams describe the followi...

with the aid of diagrams describe the following OS structure monolithic,layered and client server.

Define i/o and cpu bursts, Define I/O and CPU Bursts   Applications typ...

Define I/O and CPU Bursts   Applications typically to through cycle of CPU bursts and Input/output bursts. Since the CPU sits idle during I/O operations, efficiency is improved

Define busy waiting and spinlock, Define busy waiting and spinlock. Whe...

Define busy waiting and spinlock. When a process is in its significant section, any other process that tries to enter its critical section must loop continuously in the entry c

Explain about time sharing systems, Q. Explain about Time Sharing Systems? ...

Q. Explain about Time Sharing Systems? Time Sharing Systems Multi-programmed batched systems provide an environment where various system resources (for illustration CP

What is preallocation, What is preallocation? Why do it? Allocating spa...

What is preallocation? Why do it? Allocating space for a file before making the file to allow for expansion. This reserves space for a certain file so that other files can't gr

Replacement algorithm for tlb, Consider the following C program where M, N,...

Consider the following C program where M, N, K are predefined constants. Assume int is 4 bytes. Suppose this program is run on a machine with 4KB page size and 32 TLB entries. Init

Advantages and disadvantages of thread, OPERATING SYSTEM 1. Describe th...

OPERATING SYSTEM 1. Describe the term operating system. Write down the functions of operating system. 2. Explain Thread? Write down the advantages and disadvantages of threa

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