在fork中调用函数，在函数中是一个while循环，它应该读取输入，但是，scanf()被完全跳过了

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <pthread.h>

pthread_mutex_t input_mutex = PTHREAD_MUTEX_INITIALIZER;

void* child_process(void* arg) {
    pthread_mutex_lock(&input_mutex);
    printf("Child process: Enter a number: ");
    int num;
    scanf("%d", &num);
    printf("Child process: You entered %d\n", num);
    pthread_mutex_unlock(&input_mutex);
    return NULL;
}

int main() {
    pid_t pid = fork();

    if (pid == 0) {
        // Child process
        child_process(NULL);
    } else if (pid > 0) {
        // Parent process
        pthread_mutex_lock(&input_mutex);
        printf("Parent process: Enter a number: ");
        int num;
        scanf("%d", &num);
        printf("Parent process: You entered %d\n", num);
        pthread_mutex_unlock(&input_mutex);
    } else {
        perror("fork");
        exit(EXIT_FAILURE);
    }

    return 0;
}