Problem of unbalanced loads, Operating System

Present your own fully documented and tested programming example illustrating the problem of unbalanced loads. Describe the use of OpenMP's scheduler as a means of mitigating this problem.

The below example shows a number of tasks that all update a global counter. Since threads share the same memory space, they indeed see and update the same memory location. The code returns a false result because updating the variable isĀ  much quicker than creating the thread as on a multicore processor the chance of errors will greatly increase. If we artificially increase the time for the update, we will no longer get the right result. All threads read out the value of sum, wait a while (presumably calculating something) and then update.

#include

#include

#include "pthread.h"

int sum=0;

void adder() {

int sum = 0;

int t = sum; sleep(1); sum = t+1;

return;

}

#define NTHREADS 50

int main() {

int i;

pthread_t threads[NTHREADS];

printf("forking\n");

for (i=0; i

if (pthread_create(threads+i,NULL,&adder,NULL)!=0) return i+1;

printf("joining\n");

for (i=0; i

{

if (pthread_join(threads[i],NULL)!=0) return NTHREADS+i+1;

printf("Sum computed: %d\n",sum);

}

return 0;

}

The use of OpenMP is the parallel loop. Here, all iterations can be executed independently and in any order. The pragma CPP directive then conveys this fact to the compiler. A sequential code can be easily parallelized this way.

#include 
#include 
#include "pthread.h"
int sum=0;
void adder() {
int sum = 0;
int t = sum; sleep(1); sum = t+1;
return;
}
#define NTHREADS 50
int main() {
int i;
pthread_t threads[NTHREADS];
printf("forking\n");
#pragma omp for
for (i=0; i
if (pthread_create(threads+i,NULL,&adder,NULL)!=0) return i+1;
}
printf("joining\n");
for (i=0; i
{
if (pthread_join(threads[i],NULL)!=0) return NTHREADS+i+1;
printf("Sum computed: %d\n",sum);
}
return 0;
}
Posted Date: 6/29/2012 2:17:42 AM | Location : United States







Related Discussions:- Problem of unbalanced loads, Assignment Help, Ask Question on Problem of unbalanced loads, Get Answer, Expert's Help, Problem of unbalanced loads Discussions

Write discussion on Problem of unbalanced loads
Your posts are moderated
Related Questions


What is spooling? Spooling overlaps the I/O of single job with the computation of other jobs.

Q. Illustrate the function of Loader? A loader is a routine which loads an object program and prepares it for execution. There are many loading schemes: relocating, absolute an

What are the five major activities of an operating system in regard to file management? The creation and deletion of files The creation and deletion of directories The s

Virtual addresses are made up of two parts: the ?rst part is the page number, and the second part is an offset inside that page. Suppose our pages are 4kb (4096 = 212 bytes) long,

TURNAROUND TIME

linked allocation using i node

Define rotational latency and disk bandwidth. Rotational latency is the additional time waiting for the disk to rotate the wanted sector to the disk head. The disk bandwidth is

Hashed page tables A common approach for handling address spaces larger than 32 bits is to use a hashed page table. Every entry in the hash table having a linked list of elemen