pthreads/sleepbarber.c

   1 /* compile with:
   2    gcc sleepbarber.c -o sleepbarber -lpthread -Wall -W -Wextra -ansi -pedantic */
   3
   4 #include <stdio.h>
   5 #include <stdlib.h>
   6 #include <pthread.h>
   7 #include <semaphore.h>
   8 #include <unistd.h>
   9
  10 #define NUM_CUSTOMERS 10
  11 #define MAX_FREESEATS 2
  12
  13 sem_t barsem;
  14 sem_t cussem;
  15 sem_t seasem;   /* mutual exclusion for 'freeseats' */
  16
  17 unsigned int freeseats = MAX_FREESEATS;
  18
  19 /* function prototypes  */
  20 void *barthread(void *arg);
  21 void *custhread(void *arg);
  22
  23 int main(void)
  24 {
  25    pthread_t bartid;
  26    pthread_t custid[NUM_CUSTOMERS];
  27    int i;
  28
  29    /* initialize the semaphores */
  30    sem_init(&barsem, 0, 0);
  31    sem_init(&cussem, 0, 0);
  32    sem_init(&seasem, 0, 1);
  33
  34    /* create the barber thread */
  35    if (pthread_create(&bartid, NULL, barthread, NULL)) {
  36       perror("pthread_create() error");
  37       exit(EXIT_FAILURE);
  38    }
  39
  40    /* create the customer threads */
  41    for (i=0; i<NUM_CUSTOMERS; i++) {
  42       if (pthread_create(&custid[i], NULL, custhread, NULL)) {
  43          perror("pthread_create() error");
  44          exit(EXIT_FAILURE);
  45       }
  46    }
  47
  48    pthread_join(bartid, NULL);   /* wait for the barber to retire :) */
  49    return EXIT_SUCCESS;
  50 }
  51
  52 void *barthread(void *arg)
  53 {
  54    while (1) {
  55       printf("ZZZzzz\n");
  56       sem_wait(&cussem);
  57       sem_wait(&seasem);
  58       freeseats++;
  59       sem_post(&barsem);
  60       sem_post(&seasem);
  61       printf("The barber is cutting hair\n");
  62    }
  63    pthread_exit(NULL);
  64 }
  65
  66 void *custhread(void *arg)
  67 {
  68    printf("Customer has arrived\n");
  69    sem_wait(&seasem);
  70    if (freeseats > 0) {
  71       freeseats--;
  72       sem_post(&cussem);
  73       sem_post(&seasem);
  74       sem_wait(&barsem);
  75    }
  76    else {
  77       printf("No free seats - customer leaving\n");
  78       sem_post(&seasem);
  79    }
  80
  81    pthread_exit(NULL);
  82 }