--- /dev/null
+#ifdef _REENTRANT
+#undef _REENTRANT
+#endif
+#define _REENTRANT
+
+#include <pthread.h>
+#include <semaphore.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+// The maximum number of customer threads.
+#define MAX_CUSTOMERS 25
+
+// Define the semaphores.
+
+// waitingRoom Limits the # of customers allowed
+// to enter the waiting room at one time.
+sem_t waitingRoom;
+
+// barberChair ensures mutually exclusive access to
+// the barber chair.
+sem_t barberChair;
+
+// barberPillow is used to allow the barber to sleep
+// until a customer arrives.
+sem_t barberPillow;
+
+// seatBelt is used to make the customer to wait until
+// the barber is done cutting his/her hair.
+sem_t seatBelt;
+
+// Flag to stop the barber thread when all customers
+// have been serviced.
+int allDone = 0;
+
+static void randwait(int secs)
+{
+ int len;
+
+ // Generate a random number...
+ len = (int)((drand48() * secs) + 1);
+ sleep(len);
+}
+
+static void* customer(void* number)
+{
+ int num = *(int*)number;
+
+ // Leave for the shop and take some random amount of
+ // time to arrive.
+ printf("Customer %d leaving for barber shop.\n", num);
+ randwait(5);
+ printf("Customer %d arrived at barber shop.\n", num);
+
+ // Wait for space to open up in the waiting room...
+ sem_wait(&waitingRoom);
+ printf("Customer %d entering waiting room.\n", num);
+
+ // Wait for the barber chair to become free.
+ sem_wait(&barberChair);
+
+ // The chair is free so give up your spot in the
+ // waiting room.
+ sem_post(&waitingRoom);
+
+ // Wake up the barber...
+ printf("Customer %d waking the barber.\n", num);
+ sem_post(&barberPillow);
+
+ // Wait for the barber to finish cutting your hair.
+ sem_wait(&seatBelt);
+
+ // Give up the chair.
+ sem_post(&barberChair);
+ printf("Customer %d leaving barber shop.\n", num);
+ return NULL;
+}
+
+static void* barber(void* junk)
+{
+ // While there are still customers to be serviced...
+ // Our barber is omnicient and can tell if there are
+ // customers still on the way to his shop.
+ while (!allDone) {
+
+ // Sleep until someone arrives and wakes you..
+ printf("The barber is sleeping\n");
+ sem_wait(&barberPillow);
+
+ // Skip this stuff at the end...
+ if (!allDone) {
+
+ // Take a random amount of time to cut the
+ // customer's hair.
+ printf("The barber is cutting hair\n");
+ randwait(3);
+ printf("The barber has finished cutting hair.\n");
+
+ // Release the customer when done cutting...
+ sem_post(&seatBelt);
+ } else {
+ printf("The barber is going home for the day.\n");
+ }
+ }
+ return NULL;
+}
+
+int main(int argc, char* argv[])
+{
+ pthread_t btid;
+ pthread_t tid[MAX_CUSTOMERS];
+ long RandSeed;
+ int i, numCustomers, numChairs;
+ int Number[MAX_CUSTOMERS];
+
+ // Check to make sure there are the right number of
+ // command line arguments.
+ if (argc != 4) {
+ printf("Use: SleepBarber <Num Customers> <Num Chairs> <rand seed>\n");
+ exit(-1);
+ }
+
+ // Get the command line arguments and convert them
+ // into integers.
+ numCustomers = atoi(argv[1]);
+ numChairs = atoi(argv[2]);
+ RandSeed = atol(argv[3]);
+
+ // Make sure the number of threads is less than the number of
+ // customers we can support.
+ if (numCustomers > MAX_CUSTOMERS) {
+ printf("The maximum number of Customers is %d.\n", MAX_CUSTOMERS);
+ exit(-1);
+ }
+
+ printf("\nSleepBarber.c\n\n");
+ printf("A solution to the sleeping barber problem using semaphores.\n");
+
+ // Initialize the random number generator with a new seed.
+ srand48(RandSeed);
+
+ // Initialize the numbers array.
+ for (i = 0; i < MAX_CUSTOMERS; i++) {
+ Number[i] = i;
+ }
+
+ // Initialize the semaphores with initial values...
+ sem_init(&waitingRoom, 0, numChairs);
+ sem_init(&barberChair, 0, 1);
+ sem_init(&barberPillow, 0, 0);
+ sem_init(&seatBelt, 0, 0);
+
+ // Create the barber.
+ pthread_create(&btid, NULL, barber, NULL);
+
+ // Create the customers.
+ for (i = 0; i < numCustomers; i++) {
+ pthread_create(&tid[i], NULL, customer, (void*)&Number[i]);
+ }
+
+ // Join each of the threads to wait for them to finish.
+ for (i = 0; i < numCustomers; i++) {
+ pthread_join(tid[i], NULL);
+ }
+
+ // When all of the customers are finished, kill the
+ // barber thread.
+ allDone = 1;
+ sem_post(&barberPillow); // Wake the barber so he will exit.
+ pthread_join(btid, NULL);
+}
