pthreads/pthread_mutex.c

   1 /*
   2  * Compile with:
   3  * gcc pthread_mutex.c -o pthread_mutex -lpthread -Wall -W -Wextra -ansi -pedantic
   4 */
   5
   6 #include <stdio.h>
   7 #include <stdlib.h>
   8 #include <pthread.h>
   9 #include  <unistd.h>
  10
  11 #define NUM_THREADS 5
  12
  13 int myglobal = 0;               /* global shared variable */
  14 pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
  15
  16 /* Function prototypes */
  17 void *threadfun(void *arg);
  18 void diep(const char *s);
  19
  20 int main(void)
  21 {
  22     pthread_t tid[NUM_THREADS];
  23     int i;
  24
  25     /* Create the threads */
  26     for (i = 0; i < NUM_THREADS; i++) {
  27         if (pthread_create(&tid[i], NULL, threadfun, NULL))
  28             diep("pthread_create");
  29     }
  30
  31     /* Make sure all threads are done */
  32     for (i = 0; i < NUM_THREADS; i++) {
  33         if (pthread_join(tid[i], NULL))
  34             diep("pthread_join");
  35     }
  36
  37     printf("myglobal = %d\n", myglobal);
  38
  39     return EXIT_SUCCESS;
  40 }
  41
  42 void *threadfun(void *arg)
  43 {
  44     int i, j;
  45
  46     for (i = 0; i < 5; i++) {
  47         pthread_mutex_lock(&mymutex);    /* Begin of critical region */
  48         j = myglobal;
  49         j++;
  50         sleep(1);
  51         myglobal = j;
  52         pthread_mutex_unlock(&mymutex);    /* End of critical region */
  53     }
  54     pthread_exit(NULL);
  55 }
  56
  57 void diep(const char *s)
  58 {
  59     perror(s);
  60     exit(EXIT_FAILURE);
  61 }