C管道:糟糕的文件描述符

Question

我在C中有一个简单的生产者消费者程序，试着用叉子来解决它，当生产者试图在管道上写东西的时候，我得到了一个错误:我已经用同样的逻辑编写了另一个程序，但是这个程序没有给我任何线索来知道为什么？

生产者未能在管道上写入项:糟糕的文件描述符

有人知道我为什么会犯这个错误吗？谢谢

#define READ 0
#define WRITE 1
int mutex = 1, full = 0, empty = BUFFER_SIZE, x = 0;

void consumer();

void producer();

int wait_(int);

int signal_(int);

int pipefd[2];

int main() {
    printf("Starting producer-consumer problem!\n");
    //We intend to run the producer in parent process and the consumer in the child process
    if (pipe(pipefd) == -1) {       /* An error has occurred. */
        fprintf(stderr, "%s", "The call to pipe() has failed.\n");
        exit(EXIT_FAILURE);
    }
    for (int j = 0; j < sizeof(pipefd); j++) {
        if (pipe(&pipefd[j]) < 0) { //Initialize each pipe appropriately
            perror("Error in making pipe...");
        }
    }
    pid_t pid = fork();
    if (pid < 0) {
        perror("**********Error in creating fork()!**************\n");
        exit(STDERR_FILENO);
    } else if (pid == 0) {
        consumer();//We intend to run the consumer in child
    } else {
        producer();//We intend to run the producer in parent
    }
    return 0;
}

int wait_(int s) {
    return (--s);
}

int signal_(int s) {
    return (++s);
}

void producer() {
    printf("Starting Producer\n");
    //while (1) {
    //sleep(1);
    if (close(pipefd[READ]) != 0) {
        perror("Error in closing reading pipe");
    }
    if (write(pipefd[WRITE], &full, 1) < 0) {
        perror("Producer failed to write item on pipe");
    }
    if ((mutex == 1) && (empty != 0)) {
        mutex = wait_(mutex);
        full = signal_(full);
        empty = wait_(empty);
        x++;
        printf("Producer produces the item %d\n", x);
        mutex = signal_(mutex);
    }
    if (close(pipefd[WRITE]) != 0) {
        perror("Error in closing writing pipe");
    }
    //}
}

void consumer() {
    printf("Starting Consumer\n");
    //while (1) {
    //sleep(1);
    int status = 0;
    wait(&status);              /* wait for all children to return back the result */
    if (close(pipefd[WRITE]) != 0) {
        perror("Error in closing reading pipe");
    }
    if (read(pipefd[READ], &full, 1) > 0) {
        printf("Consumer\t%d\n", full);
    }
    if ((mutex == 1) && (full != 0)) {
        mutex = wait_(mutex);
        full = wait_(full);
        empty = signal_(empty);
        printf("Consumer consumes item %d\n", x);
        x--;
        mutex = signal_(mutex);
    }
    if (close(pipefd[READ]) != 0) {
        perror("Error in closing reading pipe");
    }
    //}
}

Answer 1

sizeof运算符返回大小(以字节为单位)。因此，在一个典型的int为四个字节的系统中，sizeof(pipefd)将产生值8。这不是循环中正确的元素数。

而且，pipe(&pipefd[j])也不正确。pipefd中的两个管道已经被初始化为“适当”。不需要再初始化了。特别是在这种情况下和上一种情况下，您将拥有https://en.wikipedia.org/wiki/Undefined_behavior。