Aug 14 2008

OpenMP in Visual C++

Category: OpenMP,Paralell/Concurrentsemihozmen @ 07:31

Here is a sample code given by MSDN and commented by me to remember the milestones of OpenMP which is one of the simplest ways of parallelizing a program.

// The OpenMP DLLs are in the Visual C++ redistributable directory and
// need to be distributed with applications that use OpenMP.
#include "stdafx.h"
#include <iostream>
#include <math .h>
#include <omp .h> 
// If _DEBUG is defined in a compilation and if #include omp.h is in source code,
// VCOMPD.LIB will be the default lib. Otherwise, VCOMP.LIB will be used.
#define NUM_THREADS 4
#define NUM_START 1
#define NUM_END 10
int main() {
int i, nRet = 0, nSum = 0, nStart = NUM_START, nEnd = NUM_END;
int nThreads = 0, nTmp = nStart + nEnd;
unsigned uTmp = (unsigned((abs(nStart - nEnd) + 1)) *
unsigned(abs(nTmp))) / 2;
int nSumCalc = uTmp;
if (nTmp < 0)
nSumCalc = -nSumCalc;
// Sets the number of threads in subsequent parallel regions,
// unless overridden by a num_threads clause.
// parallel:: Defines a parallel region, which is code that will be executed by multiple threads in parallel.
// default::: shared, which is in effect if the default clause is not specified, means that any variable
// in a parallel region will be treated as if it were specified with the shared (OpenMP) clause.
// none means that any variables used in a parallel region that are not scoped with
// the private (OpenMP), shared (OpenMP), reduction, firstprivate, or lastprivate clause will
// cause a compiler error.
// private::: Specifies that each thread should have its own instance of a variable.
// shared::: Specifies that one or more variables should be shared among all threads.
#pragma omp parallel default(none) private(i) shared(nSum, nThreads, nStart, nEnd)
#pragma omp master 
// only master thread will run following statement
nThreads = omp_get_num_threads();
#pragma omp for 
// Causes the work done in a for loop inside a parallel region to be divided among threads.
for (i=nStart; i<=nEnd; ++i) {
#pragma omp atomic 
// The statement containing the lvalue whose
// memory location you want to protect against multiple writes.
nSum += i;
if (nThreads == NUM_THREADS) {
printf_s("%d OpenMP threads were used.\n", NUM_THREADS);
nRet = 0;
else {
printf_s("Expected %d OpenMP threads, but %d were used.\n",
NUM_THREADS, nThreads);
nRet = 1;
if (nSum != nSumCalc) {
printf_s("The sum of %d through %d should be %d, "
"but %d was reported!\n",
NUM_START, NUM_END, nSumCalc, nSum);
nRet = 1;
printf_s("The sum of %d through %d is %d\n",

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Aug 14 2008

About the Future Of Software Development

Category: Papers and Journalssemihozmen @ 07:17

A statement by Grace Hopper, pioneer computer scientist and U.S Navy admiral.

“In pioneer days they used oxen for heavy pulling, and when one ox could not budge a log, they did not try to grow a larger ox but used more oxen, we should not be trying for bigger computers, but for more systems of computers.”

Here, there are interesting set of links about the future of software development:

1-) Free Lunch is Over

2-) The Future of Windows Is Manycore/Multicore

3-) A Fundamental Turn Toward Concurrency in Software

4-) Sharing Is the Root of All Contention


6-) Multicore and Parallelism: Catching Up

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