如何使我自己的malloc线程安全，以及在哪里锁定和解锁？

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

// 定义一个互斥锁
pthread_mutex_t malloc_lock = PTHREAD_MUTEX_INITIALIZER;

void* my_malloc(size_t size) {
    // 加锁
    pthread_mutex_lock(&malloc_lock);

    void* ptr = malloc(size);

    // 解锁
    pthread_mutex_unlock(&malloc_lock);

    return ptr;
}

void my_free(void* ptr) {
    // 加锁
    pthread_mutex_lock(&malloc_lock);

    free(ptr);

    // 解锁
    pthread_mutex_unlock(&malloc_lock);
}

// 测试函数
void* thread_func(void* arg) {
    int* data = (int*)my_malloc(sizeof(int));
    if (data == NULL) {
        perror("Failed to allocate memory");
        return NULL;
    }
    *data = 42;
    printf("Thread %ld: Allocated memory with value %d\n", pthread_self(), *data);
    my_free(data);
    return NULL;
}

int main() {
    pthread_t threads[5];

    for (int i = 0; i < 5; ++i) {
        if (pthread_create(&threads[i], NULL, thread_func, NULL) != 0) {
            perror("Failed to create thread");
            return 1;
        }
    }

    for (int i = 0; i < 5; ++i) {
        pthread_join(threads[i], NULL);
    }

    return 0;
}