Problem of unbalanced loads, Operating System

Assignment Help:

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 is  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;
}

Related Discussions:- Problem of unbalanced loads

Batch system, what is a batch system give me answer in simple words so that...

what is a batch system give me answer in simple words so that i can understand

Explain the spawnlp functions used in the netware, Explain the Spawnlp Func...

Explain the Spawnlp Functions Used in the NetWare Spawnlp(flags, execName, arg0,...)  The Spawnlp function is used to load  a NetWare executable file (NLM) specified by exec

Explain the request/response interface, Explain the Request/Response Interf...

Explain the Request/Response Interface   Many issues are involved in providing a procedural interface for client functions to interact with server components. First off, since

Define deadlock, Define deadlock. A process requests resources; if the ...

Define deadlock. A process requests resources; if the resources are not available at that time, the process enters a wait state. Waiting processes might be never again change s

Request or response interface - interaction using message, Explain the Requ...

Explain the Request or Response interface The Request/Response interface is ideal for a message based client-server interaction. By modeling components to interact via a reque

What is a thread, What is a thread? A thread or else called a lightweig...

What is a thread? A thread or else called a lightweight process (LWP) is a basic unit of CPU utilization, it comprises of a thread id, a program counter, a register set and a s

What is page fault, Problem: a) The CPU can access 2 storage devices di...

Problem: a) The CPU can access 2 storage devices directly. What are these 2 storage devices? b) Define 2 key issues involved in memory management. c) How do processes sha

What is the hardware support required to implement paging, What is the hard...

What is the hardware support required to implement paging? Each operating system has its own techniques for storing page tables. The majority allocates a page table for each pr

Explain segmentation and paging, Why are segmentation and paging sometimes ...

Why are segmentation and paging sometimes combined into one scheme? Segmentation and paging are often combined in order to improve upon each other. Segmented paging is helpful

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