c - 命名信号量只是不工作

Question

我们今天有考试，我们的任务是实现“火车处理程序”。

有 7 个序列，每个序列代表一个进程。每列火车在几秒钟后到达，检查我们的 3 条火车轨道中是否有一条可用。如果没有，请等待...如果轨道空闲，则输入并锁定。在火车站停留几秒钟，离开并解锁。

我和几个 friend 试图让我们的程序运行起来，但我们就是做不到。看来是我们的共享内存没有正确同步(信号量)的问题。使用 mac，所以我必须使用命名信号量。

编译为:“gcc -Wall -Werror -std=gnu99 -lpthread process_trains.c -o test”

代码:

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <signal.h>
#include <sys/types.h>
#include <time.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <semaphore.h>
#include <sys/wait.h>
#include <errno.h>


sem_t *sem;
int *shm_ptr;



int *initShm (int size) {
    int shm_fd = 0;

    if((shm_fd = shm_open("/shm", O_CREAT | O_RDWR, 0777)) == -1) {
        perror("Error creating shared memory segment!");
    }

    if ((ftruncate(shm_fd, size)) == -1) {
        perror("Error sizing shared memory segment!");
    }

    return (int*) mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, shm_fd, 0);
}


int trainAboutToArrive(int arrive, int stay, int Y){

    int Z=0;

    //Zug kommt in "arrive" Sekunden an
    sleep(arrive);

    while (shm_ptr[Z]!=0) {
        Z++;
        if(Z==3){
            Z=0;
        }
    }

    sem_wait(sem);
    shm_ptr[Z]=1;
    sem_post(sem);

    printf("Zug %d ist auf Gleis %d eingefahren\n", Y, 1+Z);

    //Zug hat einen Aufenthalt von "stay" Sekunden 
    sleep(stay);

    sem_wait(sem);
    shm_ptr[Z]=0;
    sem_post(sem);

    sem_close(sem);

    printf("Zug %d verlässt Gleis %d\n", Y, 1+Z);

    return EXIT_SUCCESS;
}

int main(int argc, char const *argv[]) {

    shm_unlink("shm");

    int i=0, tracks=3, trains=7, status;
    int arrival[]={0,0,3,2,5,4,2};
    int stay[]={2,3,7,2,1,4,3};

    off_t size = sizeof(int)*tracks;
    shm_ptr = initShm(size);

    if((sem = sem_open("/semap",O_CREAT,0644,1)) == SEM_FAILED) {
        perror("client sem_open");
    }

    for (i=0; i < tracks; i++) {
        shm_ptr[i]= 0;
    }

    pid_t pids[trains];

    for (i = 0; i < trains; i++) {
        pids[i] = fork();
        if(pids[i] == -1) {
            perror("Error creating train-process!!");
        } else if (pids[i] == 0) {
            trainAboutToArrive(arrival[i], stay[i], 1+i);
            exit(0);
        }else if (pids[i] > 0) {

        }
    }

    for(i=0; i < trains; i++){
        waitpid(pids[i], &status, 0);
    }
    shm_unlink("shm");

    return EXIT_SUCCESS;
}

Answer 1

用 -pthread 链接!!!!所有使用的信号量函数的手册页告诉我们 >.<

感谢大家的帮助!!

对于所有感兴趣的人，这是我现在的代码。我改进了很多我在考试中没有时间做的事情。这运行完美，在我的“初学者眼中”，使用给定的功能(信号量，共享内存......)无法改进。如果是，我将不胜感激提示和技巧；)

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <semaphore.h>
#include <sys/wait.h>
#include <errno.h>

int *shm_ptr;

int *initShm (off_t size) {

    int shm_fd = 0;

    if((shm_fd = shm_open("/shm", O_CREAT | O_RDWR, 0777)) == -1) {
        perror("Error creating shared memory segment!");
    }

    if ((ftruncate(shm_fd, size)) == -1) {
        perror("Error sizing shared memory segment!");
    }

    return (int*) mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, shm_fd, 0);
}

void initSem(sem_t **plats) {

    if((plats[0] = sem_open("/one",O_CREAT,0644,1)) == SEM_FAILED) {
        perror("client sem_open");
    }
    if((plats[1] = sem_open("/two",O_CREAT,0644,1)) == SEM_FAILED) {
        perror("client sem_open");
    }
    if((plats[2] = sem_open("/three",O_CREAT,0644,1)) == SEM_FAILED) {
        perror("client sem_open");
    }
}


int trainAboutToArrive(int arrive, int stay, int train, sem_t **plats){

    srand(getpid());
    int platform = rand()%3;

    sleep(arrive);

    while (3) {
        sem_wait(plats[platform]);
        if(shm_ptr[platform]==0){
            shm_ptr[platform]=1;
            break;
        }
        sem_post(plats[platform]);

        platform = rand() % 3;
    }

    printf("Train %d enters platform %d\n", train, 1+platform);

    sleep(stay);

    shm_ptr[platform]=0;

    printf("Train %d leaves platform %d\n", train, 1+platform);

    sem_post(plats[platform]);
    sem_close(plats[platform]);

    return EXIT_SUCCESS;

}

int main(int argc, char const *argv[]) {

    shm_unlink("/shm");
    sem_unlink("/one");
    sem_unlink("/two");
    sem_unlink("/three");

    int i=0, tracks=3, trains=7, status;
    int arrival[]={0,0,3,2,5,4,2};
    int stay[]={2,3,7,2,1,4,3};
    sem_t *plats[3];

    off_t size = sizeof(int)*tracks;
    shm_ptr = initShm(size);
    initSem(plats);

    for (i=0; i < tracks; i++) {
        shm_ptr[i]= 0;
    }

    pid_t pids[trains];

    for (i = 0; i < trains; i++) {
        pids[i] = fork();
        if(pids[i] == -1) {
            perror("Error creating train-process!!");
        } else if (pids[i] == 0) {
            trainAboutToArrive(arrival[i], stay[i], 1+i, plats);
            exit(0);
        }else if (pids[i] > 0) {

        }
    }

    for(i=0; i < trains; i++){
        waitpid(pids[i], &status, 0);
    }

    shm_unlink("/shm");
    sem_unlink("/one");
    sem_unlink("/two");
    sem_unlink("/three");

    return EXIT_SUCCESS;
}