lab4 child读完之后还可以继续写入pipe吗，这学期助教验收要求child读完之后再写入pipe，试了用信号量控制先后顺序但是还是不行QAQ

我添加了semaphore的代码如下：

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/sem.h>
#include <sys/types.h>
#include <sys/ipc.h>

// Function to perform P (wait) operation
void P(int semaphoreId) {
    struct sembuf sops;
    sops.sem_num = 0; // Specify semaphore index in the set (0 in this case)
    sops.sem_op = -1; // Wait operation
    sops.sem_flg = 0; // Flags (usually set to 0)

    semop(semaphoreId, &sops, 1); // Perform the semaphore operation
}

// Function to perform V (signal) operation
void V(int semaphoreId) {
    struct sembuf sops;
    sops.sem_num = 0; // Specify semaphore index in the set (0 in this case)
    sops.sem_op = 1; // Signal operation
    sops.sem_flg = 0; // Flags (usually set to 0)

    semop(semaphoreId, &sops, 1); // Perform the semaphore operation
}

int main() {
    int semaphoreId;

    // Generate a unique key for the semaphore set
    key_t key = ftok(".", 'S');

    // Create or get the identifier of the semaphore set
    semaphoreId = semget(key, 1, IPC_CREAT | 0666);
    if (semaphoreId == -1) {
        perror("semget");
        exit(1);
    }

    // Initialize the semaphore to a value of 0
    semctl(semaphoreId, 0, SETVAL, 0);

    // 0 is write and 1 is read
    int fd[2];
    pid_t pid;
    char buffer[20];

    // Create a one-way communication channel (pipe)
    if (pipe(fd) == -1) {
        perror("pipe");
        exit(EXIT_FAILURE);
    }

    pid = fork();
    if (pid < 0) {
        perror("fork");
        exit(EXIT_FAILURE);
    }

    if (pid > 0) {  // Parent process

        printf("Parent: Writing message to child\n");
        char* msg = "Hello from parent";

        // Write message to child
        write(fd[1], msg, strlen(msg));
        close(fd[1]);  // Close the write end of the pipe

        P(semaphoreId);
        printf("**\n");
        printf("Parent: waiting...\n");
        // Read message from child
        read(fd[0], buffer, sizeof(buffer));
        sleep(1);
        printf("Parent: Received: %s, from child!\n", buffer);
        close(fd[0]);

    } else {  // Child process
        close(fd[1]);  // Close the write end of the pipe

        // Read message from parent
        read(fd[0], buffer, sizeof(buffer));
        printf("Child: Received message: %s\n", buffer);

        while (read(fd[0], buffer, sizeof(buffer)) > 0) {
            // 读取并丢弃管道中的数据
        }

        printf("Child: Received message from parent!\n");
        char* msg = "Hello from child";
        write(fd[1], msg, strlen(msg));
        close(fd[0]);
        close(fd[1]);   
        printf("*\n");
        V(semaphoreId);

    }

    return 0;
}

TheR1sing3un / xdu-cs-os-lab

lab4 child读完之后还可以继续写入pipe吗，这学期助教验收要求child读完之后再写入pipe，试了用信号量控制先后顺序但是还是不行QAQ #1