c++ - pthreads - 强制线程运行

Question

我有一个从主线程调用的函数:

void create_thread() {    
    pthread_t bg_thread;
    pthread_create(&bg_thread, NULL, run_in_background, NULL);

    //wait here
    pthread_mutex_lock(&MAIN_MUTEX);
    pthread_cond_wait(&wakeUpMainThread, &MAIN_MUTEX);
    pthread_mutex_unlock(&MAIN_MUTEX);

    pthread_cond_signal(wakeUpBgThread);
}

这是在后台线程中运行的函数的简短版本:

void* run_in_background(void* v) {                   
    pthread_mutex_t mutex;
    pthread_cond_t  cond;
    pthread_mutex_init(&mutex, NULL);
    pthread_cond_init(&cond, NULL);

    //NOTE: wakeUpBgThread == cond
    save_condition_and_mutex(&cond, &mutex);

    pthread_mutex_lock(&mutex);
    {
        pthread_cond_signal(&wakeUpMainThread);

        while( run_condition ) {
            pthread_cond_wait(&cond, &mutex);

            do_smth();
        }
    }
    pthread_mutex_unlock(&mutex);

    pthread_mutex_destroy(&mutex);
    pthread_cond_destroy(&cond);

    pthread_exit(NULL);
}

所以目标是:

1. Create a thread in the main one.
2. Make the main thread sleep until the signal from that thread.
3. Make the background thread sleep until the signal from the main thread.
4. Invoke the background thread from the main one.

问题是:有时在

 pthread_cond_signal(&wakeUpMainThread);

调度程序立即切换到主线程并为后台线程触发唤醒信号。在这个调度器切换回后台线程并开始等待已经触发的信号后，它就永远休眠了。

问题:有没有办法强制后台线程执行代码直到

pthread_cond_wait(&cond, &mutex);

Answer 1

您在 create_thread 中对 pthread_mutex_lock 的调用需要发生在之前 pthread_create，而不是之后。否则你会遇到竞争条件。