[OpenMP] Solution 9 : Random Number Generator

This material is part of the course Practical Introduction to Parallel Programming and meant for educational purposes only.

Task

Write a program that generates random numbers between 0 and 1 and counts how many times the random number is smaller than 0.3. Once the program has found 10 random numbers smaller than 0.3 it should return and print the random numbers found.

Hint

Write a function that generates a single random number and stores it into a global array if the random number is smaller than 0.3. The function should generate a new task if less than 10 random numbers have been found so far.

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Câu hỏi 1: Random Number Generator

#include <stdio.h>
#include <stdlib.h>

#ifdef _OPENMP
#include <omp.h>
#else
#define omp_get_num_threads() 1
#define omp_get_max_threads() 1
#define omp_get_thread_num()  0
#endif

/* ---------------------------------------------------------------------
 * random_nmuber()
 *
 * Returns a uniform random number in the range [0,1].
 * ------------------------------------------------------------------ */

double random_number ()
{
  int  num;

  /* The rand() function is not thread safe. */
  #pragma omp critical
  {
    num = rand ();
  }

  return ((double) num / (double) RAND_MAX);
}

/* ---------------------------------------------------------------------
 * find_next_number()
 *
 * Searches for at most 10 random numbers smaller than 0.3.
 * ------------------------------------------------------------------ */

void find_next_number ( int* count, double* store )
{
  double  x;
  int     n;

  x = random_number ();

  if ( x < 0.3 )
  {
    #pragma omp atomic capture
    n = (*count)++;

    if ( n < 10 )
    {
      store[n] = x;
    }
  }
  else
  {
    #pragma omp atomic read
    n = *count;
  }

  if ( n < 10 )
  {
    #pragma omp task
    {
      find_next_number ( count, store );
    }
  }
}

/* ---------------------------------------------------------------------
 * main()
 * ------------------------------------------------------------------ */

int main ( int argc, char** argv )
{
  int     count = 0;
  double  store[10];
  int     i;

  #pragma omp parallel shared(count,store)
  {
    /* Introduce some parallelism */
    find_next_number ( &count, store );
  }

  printf ( "Numbers:\n" );

  for ( i = 0; i < 10; i++ )
  {
    printf ( "  %g\n", store[i] );
  }

  return 0;
}

Câu hỏi 2: OpenMP environment variables

Specify the OpenMP environment variables that should be used for running your program (export OMP_NUM_THREADS=1 ...). Use semicolons to separate multiple variables

Câu hỏi 3: Command Line Argument

Specify the command line arguments that should be passed to your program when it is run. Arguments must be given in quotes and separated by commas. Leave this filed empty if you do not want to specify command line arguments.

Example: "1","int","arg=2" is interpreted as three arguments 1, int, and arg=2.

Tác giả	Erik-Jan Lingen, Matthias Möller
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