pi.c

linux下多线程实现生产者消费者及用并行算法求圆周率等经典算法

/* Parallel C code to demonstrate Linux thread interface */
/* Algorithm appears to be based on the series expansion of arctan(pi/4) */

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

volatile double pi = 0.0;  /* Approximation to pi (shared) */
pthread_mutex_t pi_lock;   /* Lock for above */
volatile double intervals; /* How many intervals? */

void *process(void *arg)
{
	register double width, localsum;
	register int i;
	register int iproc = (*((char *) arg) - '0');

	/* Set width */
	width = 1.0 / intervals;

	/* Do the local computations */
	localsum = 0;
	for (i=iproc; i<intervals; i+=2) 
	{
		register double x = (i + 0.5) * width;
		localsum += 4.0 / (1.0 + x * x);
	}
	localsum *= width;

	/* Lock pi for update, update it, and unlock */
	pthread_mutex_lock(&pi_lock);
	pi += localsum;
	pthread_mutex_unlock(&pi_lock);

	return(NULL);
}

int main(int argc, char **argv)
{
	pthread_t thread0, thread1;
	void * retval;

	/* Get the number of intervals */
	intervals = atoi(argv[1]);

	/* Initialize the lock on pi */
	pthread_mutex_init(&pi_lock, NULL);

	/* Make the two threads */
	pthread_create(&thread0, NULL, process, "0");
	pthread_create(&thread1, NULL, process, "1");


	/* Join (collapse) the two threads */
	pthread_join(thread0, &retval);
	pthread_join(thread1, &retval);

	/* Print the result */
	printf("Estimation of pi is %20.18f\n", pi);

	return 0;
}