/******************************************************** * An example source module to accompany... * * "Using POSIX Threads: Programming with Pthreads" *     by Brad nichols, Dick Buttlar, Jackie Farrell *     O'Reilly & Associates, Inc. * ******************************************************** * goodlocks.c * * Showing better 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        1pthread_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++) {      temp = sqrt(x);      fd = open(fname,O_CREAT | O_RDWR, 0666);                pthread_mutex_lock(&count_lock);      count++;       pthread_mutex_unlock(&count_lock);      *bufp = (char *)malloc(256);      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;    for (i = start; i < end; i++) {         fd = open(fname,O_CREAT | O_RDWR, 0666);         pthread_mutex_lock(&count_lock);         x = x + count;         temp = sqrt(x);         if (temp == THRESHOLD)            count++;         pthread_mutex_unlock(&count_lock);	 *bufp = (char *)malloc(256);         read(fd, *bufp, 24);         free(*bufp);         close(fd);   }}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 intmain(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;}