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
  25 int main(void)
  26 {
  27    pthread_t bartid;
  28    pthread_t custid[NUM_CUSTOMERS];
  29    int i;
  30
  31    /* initialize the semaphores */
  32    sem_init(&barsem, 0, 0);
  33    sem_init(&cussem, 0, 0);
  34    sem_init(&seasem, 0, 1);
  35
  36    /* create the barber thread */
  37    if (pthread_create(&bartid, NULL, barthread, NULL))
  38        diep("pthread_create");
  39
  40    /* create the customer threads */
  41    for (i = 0; i < NUM_CUSTOMERS; i++)
  42       if (pthread_create(&custid[i], NULL, custhread, NULL))
  43           diep("pthread_create");
  44
  45    if (pthread_join(bartid, NULL))    /* wait for the barber to retire :) */
  46        diep("pthread_join");
  47
  48    return EXIT_SUCCESS;
  49 }
  50
  51 void *barthread(void *arg)
  52 {
  53    while (1) {
  54       printf("ZZZzzz\n");
  55       sem_wait(&cussem);
  56       sem_wait(&seasem);
  57       freeseats++;
  58       sem_post(&barsem);
  59       sem_post(&seasem);
  60       printf("The barber is cutting hair\n");
  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 }