/******************************************************** * An example source module to accompany... * * "Using POSIX Threads: Programming with Pthreads" *     by Brad nichols, Dick Buttlar, Jackie Farrell *     O'Reilly & Associates, Inc. * ******************************************************** * simple_mutex.c * * Simple multi-threaded example with a mutex lock. */#include <stdlib.h>#include <stdio.h>#include <errno.h>#include <pthread.h>void *do_one_thing(void *);void *do_another_thing(void *);void do_wrap_up(int, int);int r1 = 0, r2 = 0, r3 = 0;pthread_mutex_t r3_mutex=PTHREAD_MUTEX_INITIALIZER;extern intmain(int argc, char **argv){  pthread_t       thread1, thread2;  if (argc > 1)   	r3 = atoi(argv[1]);  if (pthread_create(&thread1, 		 NULL,		 do_one_thing,		 (void *) &r1) != 0)	perror("pthread_create"),exit(1);   if (pthread_create(&thread2, 		 NULL, 		 do_another_thing,		 (void *) &r2) != 0)	perror("pthread_create"),exit(1);     if (pthread_join(thread1, NULL) != 0)	perror("pthread_join"), exit(1);  if (pthread_join(thread2, NULL) != 0)	perror("pthread_join"), exit(1);  do_wrap_up(r1, r2);  return 0; }void *do_one_thing(void *pnum_times){  int i, j, x;    pthread_mutex_lock(&r3_mutex);  if(r3 > 0) {	x = r3;	r3--;  } else {	x = 1;  }   pthread_mutex_unlock(&r3_mutex);   for (i = 0;  i < 4; i++) {    printf("doing one thing\n");     for (j = 0; j < 10000; j++) x = x + i;    (*(int *)pnum_times)++;  }  return(NULL);}void *do_another_thing(void *pnum_times){  int i, j, x;    pthread_mutex_lock(&r3_mutex);  if(r3 > 0) {        x = r3;        r3--;  } else {        x = 1;  }  pthread_mutex_unlock(&r3_mutex);  for (i = 0;  i < 4; i++) {    printf("doing another \n");     for (j = 0; j < 10000; j++) x = x + i;    (*(int *)pnum_times)++;  }  return(NULL);}void do_wrap_up(int one_times, int another_times){  int total;  total = one_times + another_times;  printf("All done, one thing %d, another %d for a total of %d\n",	one_times, another_times, total);}