pthreads/sleepbarber.c

   1 #include <stdio.h>
   2 #include <stdlib.h>
   3 #include <pthread.h>
   4 #include <semaphore.h>
   5 #include <unistd.h>
   6
   7 #define NUM_CUSTOMERS 10
   8 #define MAX_FREESEATS 2
   9
  10 sem_t barsem;
  11 sem_t cussem;
  12 sem_t seasem;   /* mutual exclusion for 'freeseats' */
  13
  14 unsigned int freeseats = MAX_FREESEATS;
  15
  16 /* function prototypes  */
  17 void *barthread(void *arg);
  18 void *custhread(void *arg);
  19
  20 int main() {
  21    pthread_t bartid;
  22    pthread_t custid[NUM_CUSTOMERS];
  23    int i;
  24
  25    /* initialize the semaphores */
  26    sem_init(&barsem, 0, 0);
  27    sem_init(&cussem, 0, 0);
  28    sem_init(&seasem, 0, 1);
  29
  30    /* create the barber thread */
  31    if (pthread_create(&bartid, NULL, barthread, NULL)) {
  32       perror("pthread_create() error");
  33       exit(EXIT_FAILURE);
  34    }
  35
  36    /* create the customer threads */
  37    for (i=0; i<NUM_CUSTOMERS; i++) {
  38       if (pthread_create(&custid[i], NULL, custhread, NULL)) {
  39          perror("pthread_create() error");
  40          exit(EXIT_FAILURE);
  41       }
  42    }
  43
  44    pthread_join(bartid, NULL);   /* wait for the barber to retire :) */
  45    return EXIT_SUCCESS;
  46 }
  47
  48 void *barthread(void *arg) {
  49    while (1) {
  50       printf("ZZZzzz\n");
  51       sem_wait(&cussem);
  52       sem_wait(&seasem);
  53       freeseats++;
  54       sem_post(&barsem);
  55       sem_post(&seasem);
  56       printf("The barber is cutting hair\n");
  57    }
  58    pthread_exit(NULL);
  59 }
  60
  61 void *custhread(void *arg) {
  62    printf("Customer has arrived\n");
  63    sem_wait(&seasem);
  64    if (freeseats > 0) {
  65       freeseats--;
  66       sem_post(&cussem);
  67       sem_post(&seasem);
  68       sem_wait(&barsem);
  69    }
  70    else {
  71       printf("No free seats - customer leaving\n");
  72       sem_post(&seasem);
  73    }
  74
  75    pthread_exit(NULL);
  76 }