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

Operating System, my Operating System is windows trust but when the windows...

my Operating System is windows trust but when the windows start say its windows xp. help pleaes

What are batch systems?, What are batch systems? Early computers were p...

What are batch systems? Early computers were physically huge machines run from a console. The general input devices were card readers and tape drivers. The common output device

What is paging? name the different paging techniques, What is paging? Name ...

What is paging? Name the different paging techniques. Paging is a memory management method that permits the physical-address space of a process to be noncontiguous. Paging evad

Distinguish among pcs and scs scheduling, Q. Distinguish among PCS and SCS ...

Q. Distinguish among PCS and SCS scheduling. Answer: PCS scheduling is completed local to the process. It is how a thread library schedules threads onto available LWPs. SCS sch

Explain process state with diagram, Question 1 Explain single Partition Al...

Question 1 Explain single Partition Allocation and Multiple Partition Question 2 What is PCB? What useful information is available in PCB? Question 3 Explain Preemptive and No

Explain advantages and inconveniences of ult, ADVANTAGES AND INCONVENIENCES...

ADVANTAGES AND INCONVENIENCES OF ULT Advantages: Thread switching doesn't involve the kernel - no mode switching Scheduling is able to be application specific -

How many disk operations are needed to fetch the i-node, How many disk oper...

How many disk operations are needed to fetch the i-node for the file /usr/ast/courses/os/handout.t? Assume that the i-node for the root directory is in memory, but nothing else alo

Main advantages of the microkernel approach to system design, What are the ...

What are the main advantages of the microkernel approach to system design? Benefits typically contain the following  (a) Adding a new service does not require modifying the

Operating system as user interface, Q. Operating System as User Interface? ...

Q. Operating System as User Interface? • Every general purpose computer comprises the operating system, hardware, system programs and application programs. The hardware compris

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