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

Control the access of the three global variables, Give a brief introduction...

Give a brief introduction about the operation of your program and show that you understand the idea behind threads and mutual exclusion variable. Why do we need to use mutual exclu

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.

Explain about deadlock prevention, Explain about deadlock prevention? I...

Explain about deadlock prevention? In order for the occurrence of deadlock, the four conditions like mutual exclusion, hold and wait, no pre-emption and  circular wait must hap

Linux operation system, wat are the commands used for creating the file hie...

wat are the commands used for creating the file hierarchy

Explain page-replacement algorithms, Q. Consider the following page-replac...

Q. Consider the following page-replacement algorithms. Rank the algorithms on a five-point scale from "bad" to "perfect" according to their page-fault rate. Detach those algorithm

Os installation, Question: OS Installation / File system a) Why is NTFS...

Question: OS Installation / File system a) Why is NTFS portioning preferred over FAT16 or FAT32 when security is of primary concern? b) State a situation or an application w

Virtual memory, How a virtual memory can be implemented? What are the benef...

How a virtual memory can be implemented? What are the benefits of using virtual memory?

Explain the file-system manipulation, Q. Explain the File-system manipulati...

Q. Explain the File-system manipulation? File-system manipulation there is several details in file allocation, creation, deletion and naming that users should not have to perfo

Structures for a file''s data, Q. Likewise some systems support many types ...

Q. Likewise some systems support many types of structures for a file's data while others simply support a stream of bytes. What are the merits in addition to demerits? Answer:

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