pthread.c

#include <stdio.h>
#include <assert.h>
#include <stdlib.h>
#include <pthread.h>
#include <math.h>
#include <sys/time.h>

typedef struct _thread_param
{
  long start, end;
  double sum;
}ThreadParameter;

const double PI = 3.1415926535897932;
const long STEP_NUM = 1070596096;
const double STEP_LENGTH = 1.0 / 1070596096;
const int THREAD_NUM = 16;

void *calc(void * p)
{
  ThreadParameter * param = (ThreadParameter *)p;

  double x;
  double sum = 0.0;
  for(long i = param->start; i < param->end; i++)
  {
    x = (i + 0.5) * STEP_LENGTH;
    sum += 1.0 / (1.0 + x * x);
  }
  param->sum = sum;

  return NULL;
}

int main()
{
  struct timeval startTime;
  gettimeofday(&startTime, NULL);

  double pi = 0;

  pthread_t *threadHandles = (pthread_t *) malloc(sizeof(pthread_t) * THREAD_NUM);
  ThreadParameter * paramArray[THREAD_NUM];

  printf("\nStart calculating with %d threads...\n", THREAD_NUM);
  for (int i = 0; i < THREAD_NUM; i++)
  {
    ThreadParameter *param = (ThreadParameter *)malloc(sizeof(ThreadParameter));
    param->start = i * STEP_NUM / THREAD_NUM;
    param->end = param->start + STEP_NUM / THREAD_NUM;
    paramArray[i] = param;
    pthread_create(&threadHandles[i], NULL, calc, (void *)param);
  }

  for (int i = 0; i < THREAD_NUM; i++)
    pthread_join(threadHandles[i], NULL);

  for(int i = 0; i < THREAD_NUM; i++)
  {
    pi += paramArray[i]->sum;
    free(paramArray[i]);
  }

  pi = STEP_LENGTH * pi * 4;

  free(threadHandles);

  struct timeval endTime;
  gettimeofday(&endTime, NULL);

  printf("PI = %.16lf with error %.16lf\nTime elapsed : %lf seconds.\n\n", pi, fabs(pi - PI), (endTime.tv_sec - startTime.tv_sec) + ((double)(endTime.tv_usec - startTime.tv_usec) / 10E6 ));
  assert(fabs(pi - PI) <= 0.001);
  return 0;
}