Mutual exclusion variable, Operating System

Assignment Help:

Since each thread has its own processing space therefore communication between threads will need to be done through a common global variable. Since multiple threads can access the same global variable this can leads to race condition. Therefore what we want is to protect the variable so that only one thread can access the variable at any time. In POSIX this is done via the mutual-exclusion variable, mutex. A mutex variable allow us to perform the lock/unlock action so that the critical section of the code can be protected.

A mutual exclusion variable is lock using the function call pthread_mutex_lock(&mutex_variable) and unlock using the function call pthread_mutex_unlock(&mutex_variable). When a mutex variable is locked any other thread attempt to lock it will be blocked and have to wait until the variable is being unlocked. A mutex variable is declared using the following syntax:

pthread_mutex_t mutex_variable=PTHREAD_MUTEX_INITIALIZER;

One problem of mutex is the possibility of deadlock if more than one resource is required for processing. Assume there are two mutexes in total being accessed by two separate threads. If each thread is allowed to lock only one of the two mutex that is required by each thread, then everything will be at a standstill while each thread wait for the other mutex to be unlocked. To see the effect of deadlock compile and run the program intro_mutex_deadlock.c. Does the thread terminate? The answer is no. It is because PrintProcess1 always lock mutex_lock_1 first then mutex_lock_2 while PrintProcess2 always does it in the reverse order. This is known as circular wait, which is one of the four necessary condition required for deadlock. Therefore when multiple mutex are involved the order of the mutex lock is very important. Modify the program so that PrintProcess2 lock the mutex in the same order as PrintProcess1. The deadlock should now be resolved and both threads can complete to termination.

(Note that this is one of the four conditions required for deadlock to occur: circular wait. As an exercise, list the other three necessary conditions for deadlock and identify which part of the intro_mutex_deadlock.c source code satisfies the condition. See if you can modify the program such that the deadlock can be avoided by eliminating each of the required condition.)


Related Discussions:- Mutual exclusion variable

Producer-consumer, The general idea of a producer-consumer architecture is ...

The general idea of a producer-consumer architecture is related to building a pipeline of threads, similar to the web spider from Project 2. Each step of the processing will now be

Financial objective of corporation, The primary financial objective of corp...

The primary financial objective of corporation is usually taken to be the maximization of shareholder wealth. Discuss:- i. Ways in which the shareholder of a company can encour

Semaphores, Synchronization can be achieved by means other than locks and c...

Synchronization can be achieved by means other than locks and condition variables. One alternative is semaphores. A semaphore is used to regulate traf?c in a critical section. A se

Can page tables be set up to replicate base registers, Q. We have an OS (o...

Q. We have an OS (operating system) for a machine that uses base and limit registers however we have modified the machine to provide a page table. Can the page tables be set up to

Describe the purpose of the open and close operations, Q. Describe the pur...

Q. Describe the purpose of the open() and close() operations. Answer: The open() operation notifies the system that the named file is about to become active. The c

Define tii stands for, TII stands for The abbreviation of TII is Table o...

TII stands for The abbreviation of TII is Table of incomplete instructions.

Define memory management, Define memory management In multiprogramming ...

Define memory management In multiprogramming system the user part of memory should be further subdivided to accommodate multiple processes. The task of subdivision is carried o

Define computer system environment, Q. List three instances of deadlocks th...

Q. List three instances of deadlocks that aren't related to a computer system environment. Answer: Two cars passage a single-lane bridge from opposite directions.

Semaphore examples, Ok so i think i got this right by not 100% on this. wha...

Ok so i think i got this right by not 100% on this. what I want to figure out is if there are x visitors that can line up for a ride but only 1 passenger can get on the ride at a t

PSEUDO CODE FOR PROGRAM, THE PROGRAM WILL CHOOSE TWO RANDOM NUMBERS,THEN PR...

THE PROGRAM WILL CHOOSE TWO RANDOM NUMBERS,THEN PRINT THEM OUT AS AN ADDITION PROBLEM.THE PROGRAM WILL THEN ASK THE USERTO ENTER THE CORRECT ANSWER.IF THE ANSWER IS CORRECT,THE PRO

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