Data races, critical sections, processor loading, Operating System

Research the phenomenon of data races. Give an example of how an unprotected data race can give rise to data inconsistency. How do OpenMP and Cilk resolve this problem?

Data race is that situation or condition in which multiple threads, without intervening synchronization, try to access the same memory location, with at least one thread performing a write operation. For eg. many data races occur on numerical algorithms owing to chaotic relaxation and asynchronous iterative methods. Also, there are systems where synchronized threads or processes maintain probabilities with best-estimate-matrix and may race with one other to provide updates.This is usually described in higher-level language specs by the phrase: "undefined behavior." A data race could legitimately reprogram the BIOS delete data from the disk and may also stop the processor's fan leading to a multi-core meltdown. 

example code:

 

int checker = 0;

int counts = 0;

Lock lock;

 

bool TryEnter() {

    if (checker == /* get thread id */) {

        counts += 1;

        return true;

    }

 

    if (lock.TryEnter()) {

        checker = /* get thread id */;

        return true;

    }

    return false;

}

 

void Exit() {

    if (counts != 0) {

        counts -= 1;

        return;

    }

    checker = 0;

    lock.Exit();

}

 

the compiler or the processor may “optimize” this program as:

 

void Exit() {

    if (counts != 0) {

        counts -= 1;

        return;

    }

    checker = 42;

    checker = 0;

    lock.Exit();

} 

The effect of this is perhaps not observable in the current thread, nor is it observable by other threads in the absence of data races. Here, the unfortunate thread whose ID is 42 might observe this value and take the ignite the mistake. 

OpenMP and Cilk resolve data racing through a technique known as Data parallelism.It focuses on distributing the data across different parallel computing nodes. This is achieved when each processor performs the same task on different pieces of distributed data. In some situations, a single execution thread controls operations on all pieces of data. In others, individual threads control the operation, but they execute the same code.

Posted Date: 6/29/2012 2:09:57 AM | Location : United States







Related Discussions:- Data races, critical sections, processor loading, Assignment Help, Ask Question on Data races, critical sections, processor loading, Get Answer, Expert's Help, Data races, critical sections, processor loading Discussions

Write discussion on Data races, critical sections, processor loading
Your posts are moderated
Related Questions
How can a user program disturb the normal operation of the system? a) Issuing illegal I/O operation. b) By accessing memory locations within the OS itself. c) Refusing to

Introduction of linux

Define where a Program generation activity aims  Program generation activity aims at Automatic generation of program


Problem: (a) (i) Explain what a single system image is and how it is related to the concept of a distributed operating system? (ii) What are the main differences between a

. Nested Macro calls are expanded using the

What do you mean by semaphore?  Semaphore : A synchronization variable that acquires on positive integer values. Invented by the Dijkstra P (semaphore): an atomic proce

how do semaphores help us in eliminating deadlock conditions?

Q. Provide two programming instances in which multithreading provides better performance than a single-threaded solution. Answer: (1) A Web server that services every request

What is the purpose of the command interpreter? Why is it usually separate from the kernel? It reads commands from the user or from a file of commands and executes them, usuall