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 void diep(const char *s);
  23
  24 int main(void)
  25 {
  26     pthread_t bartid;
  27     pthread_t custid[NUM_CUSTOMERS];
  28     int i;
  29
  30     /* Initialize the semaphores */
  31     sem_init(&barsem, 0, 0);
  32     sem_init(&cussem, 0, 0);
  33     sem_init(&seasem, 0, 1);
  34
  35     /* Create the barber thread */
  36     if (pthread_create(&bartid, NULL, barthread, NULL))
  37         diep("pthread_create");
  38
  39     /* Create the customer threads */
  40     for (i = 0; i < NUM_CUSTOMERS; i++)
  41         if (pthread_create(&custid[i], NULL, custhread, NULL))
  42             diep("pthread_create");
  43
  44     if (pthread_join(bartid, NULL))    /* wait for the barber to retire :) */
  45         diep("pthread_join");
  46
  47     return EXIT_SUCCESS;
  48 }
  49
  50 void *barthread(void *arg)
  51 {
  52     for (;;) {
  53         printf("ZZZzzz\n");
  54         sem_wait(&cussem);
  55         sem_wait(&seasem);
  56         freeseats++;
  57         sem_post(&barsem);
  58         sem_post(&seasem);
  59         printf("The barber is cutting hair\n");
  60     }
  61
  62     pthread_exit(NULL);
  63 }
  64
  65 void *custhread(void *arg)
  66 {
  67     printf("Customer has arrived\n");
  68     sem_wait(&seasem);
  69     if (freeseats > 0) {
  70         freeseats--;
  71         sem_post(&cussem);
  72         sem_post(&seasem);
  73         sem_wait(&barsem);
  74     }
  75     else {
  76         printf("No free seats - customer leaving\n");
  77         sem_post(&seasem);
  78     }
  79
  80     pthread_exit(NULL);
  81 }
  82
  83 void diep(const char *s)
  84 {
  85     perror(s);
  86     exit(EXIT_FAILURE);
  87 }