c - 即使使用正确，Pthreads 也会泄漏内存

Question

我已经为此奋斗了很长时间。环顾四周，我似乎无法找到答案。我只是创建两个分离的线程，然后对它们都使用 pthread_exit() 但时不时地会出现泄漏。

因为我知道人们会问我:

1. 是的，我已阅读所有其他问题，但没有真正的答案
2. 我将线程标记为分离
3. 我给了足够的时间让线程初始化和终止
4. 我已阅读 pthread_exit 的手册并且正确使用
5. 使用 -Wall 可以正常编译

代码:

int threads_keepalive = 1;

void* thread_do(void *arg){
    while(threads_keepalive)
        sleep(1);
    pthread_exit(NULL);
}

int main(){

    /* Make threads */
    pthread_t* threads;
    threads = malloc(2 * sizeof(pthread_t));
    pthread_create(&threads[0], NULL, thread_do, NULL);
    pthread_create(&threads[1], NULL, thread_do, NULL);
    pthread_detach(threads[0]);
    pthread_detach(threads[1]);
    sleep(1); // MAKING SURE THREADS HAVE INITIALIZED

    /* Kill threads */
    threads_keepalive = 0;
    sleep(5); // MAKING SURE THREADS HAVE UNBLOCKED
    free(threads);

    return 0;
}

运行该代码，尽管它是正确的(至少在我看来)，但我会随机出现内存泄漏。我使用 valgrind 多次运行相同的测试，如下所示

> gcc test.c -pthread -o test && for i in {1..100}; do valgrind --leak-check=full --track-origins=yes ./test 2>&1 | grep frees; done
==4088==   total heap usage: 8 allocs, 4 frees, 2,230 bytes allocated
==4211==   total heap usage: 8 allocs, 4 frees, 2,230 bytes allocated
==4337==   total heap usage: 8 allocs, 4 frees, 2,230 bytes allocated
==4463==   total heap usage: 8 allocs, 4 frees, 2,230 bytes allocated
==4590==   total heap usage: 8 allocs, 8 frees, 2,230 bytes allocated
==4717==   total heap usage: 8 allocs, 8 frees, 2,230 bytes allocated
==4853==   total heap usage: 8 allocs, 4 frees, 2,230 bytes allocated
==4981==   total heap usage: 8 allocs, 8 frees, 2,230 bytes allocated
==5110==   total heap usage: 8 allocs, 8 frees, 2,230 bytes allocated
==5239==   total heap usage: 8 allocs, 8 frees, 2,230 bytes allocated
..

这是怎么回事？

更新:创建一个线程而不是两个线程，不会显示内存泄漏。

Answer 1

你的问题的标题是错误的——你没有正确使用线程。但我不认为你的内存泄漏与任何未定义行为的实例有关。这只是 valgrind 报告的一个虚假的“泄漏”，原因是(假设您使用的是带有 glibc 的 Linux 系统)glibc 内部结构。请参阅这些相关问题:

• why pthread causes a memory leak
• Leaking memory with pthreads