linux查看信号量

ipcs -s

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

#define SEM_KEY 1234

union semun {
    int val;
    struct semid_ds *buf;
    unsigned short *array;
};

int create_semaphore() {
    key_t key = ftok(".", SEM_KEY);
    if (key == -1) {
        perror("ftok");
        exit(1);
    }

    int sem_id = semget(key, 1, IPC_CREAT | 0666);
    if (sem_id == -1) {
        perror("semget");
        exit(1);
    }

    union semun arg;
    arg.val = 1;
    if (semctl(sem_id, 0, SETVAL, arg) == -1) {
        perror("semctl");
        exit(1);
    }

    return sem_id;
}

void semaphore_wait(int sem_id) {
    struct sembuf sb = {0, -1, SEM_UNDO};
    if (semop(sem_id, &sb, 1) == -1) {
        perror("semop");
        exit(1);
    }
}

void semaphore_signal(int sem_id) {
    struct sembuf sb = {0, 1, SEM_UNDO};
    if (semop(sem_id, &sb, 1) == -1) {
        perror("semop");
        exit(1);
    }
}

int main() {
    int sem_id = create_semaphore();

    pid_t pid = fork();
    if (pid == 0) {
        // 子进程
        semaphore_wait(sem_id);
        printf("Child process is running\n");
        sleep(2);
        semaphore_signal(sem_id);
        exit(0);
    } else if (pid > 0) {
        // 父进程
        semaphore_wait(sem_id);
        printf("Parent process is running\n");
        semaphore_signal(sem_id);
    } else {
        perror("fork");
        exit(1);
    }

    return 0;
}