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睡觉理发师 - 共享内存队列不起作用？

分类：编程问答

如何解决睡觉理发师 - 共享内存队列不起作用？

几天前我开始研究 sleeping barber problem，遇到了一些分段错误 But they have been solved here 即使我修复了缺失的部分，我仍然有问题。我需要使用 FIFO 队列，并为其创建共享内存。创建它时我没有收到任何错误。运行客户端应该让我将 clientAmount 个客户端放入队列，理发师应该从中获取它们。每个客户端都由他的进程 ID 描述。但是当我尝试这样做时，客户端程序显示客户端已添加到队列中：

2101 entered the queue
2099 entered the queue
2104 entered the queue
2097 entered the queue
2103 entered the queue
2095 entered the queue
2102 entered the queue
2098 entered the queue
2096 entered the queue

但是当我运行理发师代码时，我得到的是：

Queue empty,I fall asleep
I'm waking up
Queue empty,I fall asleep
I'm waking up

我真的不知道在这里做什么。

客户端代码：

#include <stdio.h>
#include <stdlib.h>
#include <semaphore.h>
#include <sys/stat.h>
#include <fcntl.h>
#include "functions.h"
#include <sys/mman.h>
#include <unistd.h>
#include <signal.h>
int numberOfCuts;
int isCut;
int isDone;
void status(int f);
int main(int argc,char* argv[])
{

     if(argc < 3){
        printf("Error while executing program,invalid amount of arguments");
        return 0;
    }
    sem_t *barber;
    sem_t *queue;
    sem_t *client;
    sem_t *pillow;
    int clientsAmount;

    int sharedmem,waitRoomSize;
    struct Queue* waitroom;
    void *space;
    int i;
    signal(SIGUSR1,status);


    clientsAmount = atoi(argv[1]);
    numberOfCuts = atoi(argv[4]);

    barber = sem_open("/B",O_RDWR);
     if((barber == SEM_Failed)){
        perror("Error while getting semaphore for barber");
        exit(1);
        }

    queue = sem_open("/Q",O_RDWR);
    if((queue  == SEM_Failed)) {
        perror("Error while creating semaphore for queue");
        exit(1);
      }

    client = sem_open("/C",O_RDWR);
    if(client == SEM_Failed){
        perror("Error while creating semaphore for pillow");
        exit(0);
      }

    sharedmem = shm_open("QueueMem",O_RDWR,0666);
   if(sharedmem==-1){
       perror("Error while getting shared memory");
       exit(1);
    }
    space = mmap(NULL,sizeof(waitroom),PROT_READ | PROT_WRITE,MAP_SHARED,sharedmem,0);
   if((space == MAP_Failed)){
       perror("Error while mapping memory");
       exit(1);
       }
    waitroom = (struct Queue*) space;


    for(i = 0; i< clientsAmount; i++){
        if(fork() == 0){
            int isCut = 0;

                 int id = getpid();
                 printf("%d entered the queue \n",id);
                    sem_wait(queue);

                    sem_post(queue);
                    if( push(waitroom,id)==-1){
                        printf("Queue is full,leaving...");
                        exit(0);
                    }else {
                    push(waitroom,id);
                    sem_wait(pillow);
                    printf("%d: Barber is sleeping,he needs to wake up",id);
                    int x;
                    sem_getvalue(barber,&x);
                    if(x==0){
                        sem_post(barber);
                        while(x!= 0){
                        sem_post(barber);
                        printf("Barber is waking up to cut %d",id);
                        }
                    }
                    sem_post(pillow);

                    _exit(0);
                    }

                }
            }






sem_close(barber);
    sem_unlink("/B");
    sem_close(queue);
    sem_unlink("/Q");
    sem_close(client);
    sem_unlink("/C");


}

void status(int f){
numberOfCuts--;
printf("Remaining cuts: %d",numberOfCuts);
isCut = 1;
while(!numberOfCuts)
{
    printf("Leaving the barber");
    isDone =1;
}
}

理发师代码：

#include <stdio.h>
#include <stdlib.h>
#include <semaphore.h>
#include <sys/stat.h>
#include <fcntl.h>
#include "functions.h"
#include <sys/mman.h>
#include <unistd.h>
#include <signal.h>
#define BARBER "Barber"
int main(int argc,char* argv[])
{
    if(argc < 2){
        printf("Error while executing program,invalid amount of arguments");
        return 0;
    }
    sem_t *barber;
    sem_t *queue;

    sem_t *client;
    int seats;
    int sharedmem,waitRoomSize;
    struct Queue* waitroom;


    queue = sem_open("/Q",O_CREAT | O_RDWR,0666,1);
     if((queue  == SEM_Failed)) {
        printf("Error while creating semaphore for queue");
        exit(1);
      }
      barber= sem_open("/B",1);
     if((barber == SEM_Failed)){
        printf("Error while creating semaphore for barber");
        exit(1);
        }
     client = sem_open("/C",0);
      if(client == SEM_Failed){
        printf("Error while creating semaphore for pillow");
        exit(0);
      }




    seats = atoi(argv[1]);
    void *space;



    sharedmem = shm_open("Queue",0666);
    if(sharedmem==-1){
       printf("Error while getting shared memory");
       exit(1);
    }
    waitRoomSize = ftruncate(sharedmem,sizeof(waitroom));
    if((waitRoomSize ==-1)){
       printf("Error while getting size");
       exit(1);
       }
    space = mmap(NULL,sizeof(struct Queue),0);
    if((space == MAP_Failed)){
       printf("Bład podczas mapowania pamiêci");
       exit(1);
       }
    waitroom = (struct Queue*) space;

    queueinit(waitroom,seats);
    printf("semaphores created\n");




    while(1)
    {

     sem_post(queue);
     int x = isEmpty(waitroom);
     sem_wait(queue);
     if(x==1){
        printf("Queue empty,I fall asleep\n");
        sem_post(barber);
        sem_wait(barber);
        printf("I'm waking up\n");
     } else {
     sem_post(queue);

     int id = get(waitroom);
     sem_wait(queue);

     printf("%d,please sit on the chair\n",id);
     printf("Started cutting hair for %d\n",id);
     sleep(2);
     printf("Cutting done for :%d \n",id);

     kill(id,SIGUSR1);

     }
    }


    sem_close(barber);
    sem_unlink("/B");
    sem_close(queue);
    sem_unlink("/Q");
    sem_close(client);
    sem_unlink("/C");

    printf("senaphores unlinked");
    }

队列代码：

#ifndef FUNCTIONS_H_INCLUDED
#define FUNCTIONS_H_INCLUDED
#include <stdio.h>
#include <stdlib.h>
#include <semaphore.h>
#include <sys/stat.h>
#include <fcntl.h>
#include "functions.h"
#include <sys/mman.h>
#include <unistd.h>
#include <signal.h>

struct Queue{
    int elems[500];
    int size;
    int queueIn;
    int queueOut;
    int isAsleep;
    int mainPID;
    int countCurrent;
};
void queueinit(struct Queue* q,int size){
    q->size = size;
    q->queueIn = q->queueOut = 0;
    q->isAsleep = 0;
    q->countCurrent = 0;

}

int push(struct Queue* q,int e){
    if(q->queueIn == ((q->queueOut -1 + q->size) % q->size)){
        return -1; //Queue full
    }

    q->elems[q->queueIn] = e;
    q->queueIn = (q->queueIn + 1) % q->size;
    return 0;
}

int get(struct Queue* q){
    int e = q->elems[q->queueOut];
    q->queueOut = (q->queueOut + 1) % q->size;
    return e;
}

int isEmpty(struct Queue* q){
    if(q->queueIn == q->queueOut)
        return 1;
    return 0;
}


void lock(sem_t* sem){
if(sem_wait(sem) == -1){
    printf("Error while lockin semaphore");
    exit(1);
}

}

void free_sem(sem_t* sem){
if(sem_post(sem) == -1){
    printf("Error while releasing semaphore");
    exit(1);
}

}

#endif // FUNCTIONS_H_INCLUDED

任何建议将不胜感激

编辑 截至目前，已添加少量更改：

  1. 检查 sem_wait 和 sem_post 的返回值
  2. 删除了客户端中对 push(waitroom,id) 的第二个调用
  3. 负责锁定和解锁信号量，主要是将 sem_wait 与 sem_post 交换，反之亦然
  4. 摆脱了枕头信号量

现在该程序几乎可以正常工作，但是在其所有子进程完成工作后，客户端代码并没有退出。按 [ENTER] 有效。所以我接受了给定的建议并创建了一个新的信号量 - p，我锁定它而不是在客户端代码中使用 pause()，并在信号处理程序 status() 中解锁它。我还修改了初始化 barber 信号量的值 - 不再双重锁定或释放信号量。 我也尝试使用 abort() 函数而不是退出，但它没有用。

现在发生了什么：

  1. Barber 代码确实启动了，但没有任何反应。
  2. 客户端代码启动并向队列添加一些值，然后立即退出。

理发师的更新代码：

#include <stdlib.h>
#include <semaphore.h>
#include <sys/stat.h>
#include <fcntl.h>
#include "functions.h"
#include <sys/mman.h>
#include <unistd.h>
#include <signal.h>
#define BARBER "Barber"
int main(int argc,invalid amount of arguments");
        return 0;
    }
    sem_t *barber;
    sem_t *queue;
    sem_t *p;
    int seats;
    int sharedmem,0);
     if((barber == SEM_Failed)){
        printf("Error while creating semaphore for barber");
        exit(1);
        }
    p= sem_open("/P",0);
     if((p == SEM_Failed)){
        printf("Error while creating semaphore for barber");
        exit(1);
        }



    seats = atoi(argv[1]);
    void *space;
    sharedmem = shm_open("QueueMem",0666);

    if(sharedmem==-1){
       printf("Error while getting shared memory");
       exit(1);
    }
    waitRoomSize = ftruncate(sharedmem,0);
    if((space == MAP_Failed)){
       printf("Error while mapping memory");
       exit(1);
       }
    waitroom = (struct Queue*) space;

    queueinit(waitroom,seats);





    while(1)
    {

        lock(queue);
        if(isEmpty(waitroom)==1){
                printf("Queue empty,I fall asleep\n");
                waitroom->isAsleep = 1;
                free_sem(queue);
                lock(barber);

                printf("I'm waking up\n");

        } else {
            int id = get(waitroom);
            free_sem(queue);

            printf("%d,id);
            printf("Started cutting hair for %d\n",id);
            sleep(2);
            printf("Cutting done for :%d \n",id);

            kill(id,SIGUSR1);

     }
    }


    sem_close(barber);
    sem_unlink("/B");
    sem_close(queue);
    sem_unlink("/Q");
    sem_close(p);
    sem_unlink("/P");
    //exit(0);
    //printf("senaphores unlinked");
    }

客户端的更新代码：

#include <stdio.h>
#include <stdlib.h>
#include <semaphore.h>
#include <sys/stat.h>
#include <fcntl.h>
#include "functions.h"
#include <sys/mman.h>
#include <unistd.h>
#include <signal.h>
int numberOfCuts;

#include "functions.h"
int id;
sem_t *barber;
sem_t *queue;
sem_t *p;
int clientsAmount;

int sharedmem,waitRoomSize;
struct Queue* waitroom;
void *space;
void status(int f);
void handler(int f);



int main(int argc,invalid amount of arguments");
        return 0;
    }

    int i;
    signal(SIGUSR1,status);
    signal(SIGINT,handler);
    int pid = getpid();
    clientsAmount = atoi(argv[1]);
    numberOfCuts = atoi(argv[2]);

    barber = sem_open("/B",O_RDWR);
    if((queue  == SEM_Failed)) {
        perror("Error while creating semaphore for queue");
        exit(1);
      }
    p = sem_open("/P",O_RDWR);
    if((p  == SEM_Failed)) {
        perror("Error while creating semaphore for queue");
        exit(1);
      }


    sharedmem = shm_open("QueueMem",0);
   if((space == MAP_Failed)){
       perror("Error while mapping memory");
       exit(1);
       }
    waitroom = (struct Queue*) space;


    for(i = 0; i< clientsAmount; i++) {
        if(fork() == 0) {
            id = getpid();
            printf("%d entered the barbershop \n",id);
            while(1) {

                lock(queue);
                if( push(waitroom,id)==-1 ) {
                   free_sem(queue);
                    printf("Queue is full,%d leaving...\n",id);
                    exit(0);
                } else {
                    free_sem(queue);
                    printf("%d has entered the queue \n",id);
                    lock(queue);
                    int x;
                    x = waitroom->isAsleep;
                    if(x==1){
                        printf("%d: Barber is sleeping,he needs to wake up\n",id);
                        waitroom->isAsleep = 0;
                        free_sem(queue);
                        free_sem(barber);
                        printf("Barber is waking up to cut %d\n",id);
                    } else {
                        printf("Barber is cutting someone else,%d waiting for its turn",id);
                        free_sem(queue);

                    }

                }
                lock(p);
            }

            break;
        }
    }


    //exit(0);
    sem_close(barber);
    sem_close(queue);
    sem_close(p);
    munmap(space,waitRoomSize);

    exit(0);

}


void handler(int f) {
    printf("Closing");
    sem_close(barber);
    sem_close(queue);

    munmap(space,waitRoomSize);

    exit(0);
}

void status(int f) {

    numberOfCuts--;
    free_sem(p);
    printf("Remaining cuts for %d: %d\n",id,numberOfCuts);

    if(!numberOfCuts) {

        printf("%d is done cutting \n",id);

        exit(0);
    }

}

解决方法

你的程序有几个错误：

  1. 在客户端代码中，您正在调用 sem_wait(pillow) 和 sem_post(pillow);，尽管变量 pillow 尚未初始化。这会导致未定义的行为。为了初始化信号量，您可以使用函数 sem_init 或 sem_open。
  2. 在客户端代码中，您在获取互斥锁 queue 后立即释放它。相反，您应该只在完成队列操作后释放它。
  3. 在客户端代码中，您调用 push(waitroom,id) 两次，第二次调用紧接在第一次调用之后。这没有意义。
  4. 在理发师的主循环中，您释放互斥体 queue 和 barber 而不事先获取它们，然后再获取它们。互斥锁通常应该首先被获取，然后被释放，而不是相反。使用 sem_wait 获取互斥锁，使用 sem_post 释放它。编辑：同时，我相信您将信号量 barber 用于信号目的，而不是用作互斥锁。在这种情况下，在没有事先调用 sem_post 的情况下调用 sem_wait 是正确的。
  5. 您没有检查 sem_wait 的返回值。例如，该函数可能由于被信号处理程序中断而失败。
  6. 在信号处理程序中使用函数 printf 是不安全的。有关详细信息，请参阅 this link。
  7. 在终止父进程之前，您不是在等待子进程完成。

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