使用信號量的理髮師

Question

我在線程同步時遇到問題。我試圖以不同的方式實施睡眠理髮師問題。 當我運行代碼時，線程以完全模糊的方式運行。 當我加入到線程的進程一個接一個地運行，這是不需要的。 我知道睡覺理髮師問題的解決方案，但任何人都可以告訴我這個代碼有什麼問題。

謝謝

#include<stdio.h> 
#include<pthread.h> 
#include<time.h> 
#include <unistd.h> 
#include<semaphore.h> 
#define n 1 
#define n1 50 
int status[n]; 
int b=0; 
sem_t mutex; 
sem_t barber; 
void *barb() 
{ 
printf("Barber Sleeping\n"); 
b=1; 
sem_wait(&barber); 
printf("Barber woke up\n"); 
sleep(1); 
b=0; 
} 
void *handler(void *ptr) 
{ 
int x; 
    x = *((int *) ptr); 
int flag=0; 
int i=0; 
int cnt=0; 
for(i=0;i<n;i++) 
{ 
    if(status[i]==1) 
    { 
    flag=1; 
    cnt++;  
    } 
} 
printf("Count=%d",cnt); 
if(cnt==n) 
{ 
    printf("%d Customer Returned\n",x); 
    return 0; 
} 
if(flag==1) 
{ 
    status[x]=1; 
    printf("%d Customer waiting\n",x); 
    sem_wait(&mutex); 
} 
if(b==1) 
{ 
    printf("Customer %d woke up barber",x); 
    sem_post(&barber); 
} 
printf("Cutting Hair of customer %d\n",x); 
status[x]=1; 
sleep(5); 
flag=0; 
for(i=0;i<n;i++) 
{ 
    if(status[i]==1) 
    { 
     flag=1;  
    } 
} 
status[x]=0; 
printf("Finished cutting Hair of customer %d\n",x); 
if(flag==1) 
sem_post(&mutex); 
} 
int main() 
{ 
sem_init(&mutex, 0, n); 
sem_init(&barber, 0, 1); 
pthread_t thread[n1]; 
pthread_t barber; 
int i=0; 
for(i=0;i<n;i++) 
{ 
    status[i]=0; 
} 

pthread_create(&barber,NULL,barb,NULL); 
pthread_join(barber,NULL); 
for(i=0;i<n1;i++) 
{ 
    sleep(1); 
    printf("Customer entered %d\n",i); 
    pthread_create(&thread[i], NULL, handler, (void *)&i); 
    //pthread_join(thread[i],NULL); 
} 
for(i=0;i<n1;i++) 
{ 
    //pthread_join(thread[i],NULL); 
} 
//sem_post(&barber); 

}

Answer 1

我的代碼，以幫助您

#define _REENTRANT 

#include <stdio.h> 
#include <unistd.h> 
#include <stdlib.h> 

#include <pthread.h> 
#include <semaphore.h> 

// The maximum number of customer threads. 
#define MAX_CUSTOMERS 25 

// Function prototypes... 
void *customer(void *num); 
void *barber(void *); 

void randwait(int secs); 

// 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; 

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);  
} 

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); 
} 

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"); 
    } 
    } 
} 

void randwait(int secs) { 
    int len; 

    // Generate a random number... 
    len = (int) ((drand48() * secs) + 1); 
    sleep(len); 
}