pthreads/pthread_mutex.c

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