badlocks.c

linux下多线程程序设计,包括signals,mutex,simple_once

/********************************************************
 * An example source module to accompany...
 *
 * "Using POSIX Threads: Programming with Pthreads"
 *     by Brad nichols, Dick Buttlar, Jackie Farrell
 *     O'Reilly & Associates, Inc.
 *
 ********************************************************
 * badlocks.c
 *
 * Showing bad choice for lock placement
 */


#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <math.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>

#include <pthread.h>

#define THREADS_MAX      5
#define LOCAL_COUNT_MAX  1000
#define THRESHOLD        1


pthread_mutex_t count_lock=PTHREAD_MUTEX_INITIALIZER;
int count=0;

void r1(char *fname, int x, char **bufp)
{
   double temp;
   int local_count=0;
   int fd;

   for (local_count = 0; local_count < LOCAL_COUNT_MAX; local_count++) 
   {
      pthread_mutex_lock(&count_lock);
      temp = sqrt(x);
      fd = open(fname,O_CREAT | O_RDWR, 0666);     
      count++; 
      *bufp = (char *)malloc(256);
      pthread_mutex_unlock(&count_lock);
      sprintf(*bufp, "%e is the square root of %d", temp, x);
      write(fd, *bufp, strlen(*bufp)); 
      close(fd); 
      free(*bufp);
   }
}


void r2(char *fname, int x, char **bufp)
{
	double temp;
	int i, reads;
	int start=0, end=LOCAL_COUNT_MAX;
	int fd;
	
	pthread_mutex_lock(&count_lock);
	for (i = start; i < end; i++) 
	{
		fd = open(fname,O_CREAT | O_RDWR, 0666);
		x = x + count;
		temp = sqrt(x);
		if (temp == THRESHOLD)
			count++;
		*bufp = (char *)malloc(256);
		read(fd, *bufp, 24);
		free(*bufp);
		close(fd);
	}
	pthread_mutex_unlock(&count_lock);
}

void *base(void *not_used)
{
	int x = 10;
	char *buf;
	char fname[22];
	
	sprintf(fname, ".%lX", (long) pthread_self());
	/*
	r1(fname, x, &buf);
	*/
	r2(fname, x, &buf);
	unlink(fname);
	
	return(NULL);  
}
  
extern int	main(void)
{
	pthread_t threads[THREADS_MAX];
	int i;
	
	for (i = 0; i < THREADS_MAX; i++)
		pthread_create(&(threads[i]), NULL, base, NULL);
	
	for (i = 0; i < THREADS_MAX; i++) 
		pthread_join(threads[i], NULL);

	return 0;
}