C pthread : How to wake it up after some time?

Question

我想从另一个 pthread 中唤醒一个 pthread - 但需要一段时间。我知道 signal 或 pthread_signal 与 pthread_cond_wait 可用于唤醒另一个线程，但我看不到安排此操作的方法。情况大概是这样的:

THREAD 1:
========
while(1)
    recv(low priority msg); 
    dump msg to buffer 


THREAD 2:
========
while(1)
    recv(high priority msg); 
    ..do a little bit of processing with msg .. 
    dump msg to buffer 

    wake(THREAD3, 5-seconds-later);  <-- **HOW TO DO THIS? ** 
    //let some msgs collect for at least a 5 sec window. 
    //i.e.,Don't wake thread3 immediately for every msg rcvd. 


THREAD 3: 
=========
while(1)
    do some stuff .. 
    Process all msgs in buffer 
    sleep(60 seconds). 

任何简单的方法来安排唤醒(除了创建每秒唤醒一次并决定是否有线程 3 唤醒的计划条目的第四个线程)。如果队列中只有低优先级消息，我真的不想频繁唤醒线程 3。另外，由于消息是突发式的(比如一次突发中有 1000 条高优先级消息)，我不想为每条消息唤醒线程 3。它确实减慢了速度(因为每次唤醒时它都会执行许多其他处理工作)。

我使用的是 ubuntu 电脑。

Answer 1

通过 pthread API 使用 pthread_cond_t 对象怎么样？您可以在线程中共享这样的对象，并让它们对其进行适当的操作。
生成的代码应如下所示:

/*
 * I lazily chose to make it global.
 * You could dynamically allocate the memory for it
 * And share the pointer between your threads in
 * A data structure through the argument pointer
 */
pthread_cond_t cond_var;
pthread_mutex_t cond_mutex;
int wake_up = 0;

/* To call before creating your threads: */
int err;
if (0 != (err = pthread_cond_init(&cond_var, NULL))) {
    /* An error occurred, handle it nicely */
}
if (0 != (err = pthread_mutex_init(&cond_mutex, NULL))) {
    /* Error ! */
}
/*****************************************/

/* Within your threads */
void *thread_one(void *arg)
{
    int err = 0;
    /* Remember you can embed the cond_var
     * and the cond_mutex in
     * Whatever you get from arg pointer */

    /* Some work */
    /* Argh ! I want to wake up thread 3 */
    pthread_mutex_lock(&cond_mutex);
    wake_up = 1; // Tell thread 3 a wake_up rq has been done
    pthread_mutex_unlock(&cond_mutex);
    if (0 != (err = pthread_cond_broadcast(&cond_var))) {
        /* Oops ... Error :S */
    } else {
        /* Thread 3 should be alright now ! */
    }
    /* Some work */
    pthread_exit(NULL);
    return NULL;
}

void *thread_three(void *arg)
{
    int err;
    /* Some work */
    /* Oh, I need to sleep for a while ...
     * I'll wait for thread_one to wake me up. */
    pthread_mutex_lock(&cond_mutex);
    while (!wake_up) {
        err = pthread_cond_wait(&cond_var, &cond_mutex);
        pthread_mutex_unlock(&cond_mutex);
        if (!err || ETIMEDOUT == err) {
            /* Woken up or time out */        
        } else {
            /* Oops : error */
            /* We might have to break the loop */
        }
        /* We lock the mutex again before the test */
        pthread_mutex_lock(&cond_mutex);
    }
    /* Since we have acknowledged the wake_up rq
     * We set "wake_up" to 0. */
    wake_up = 0;
    pthread_mutex_unlock(&cond_mutex);
    /* Some work */
    pthread_exit(NULL);
    return NULL;
}

如果您希望线程 3 在超时后退出对 pthread_cond_wait() 的阻塞调用，请考虑使用 pthread_cond_timedwait() (仔细阅读该手册，超时您提供的值是绝对时间，而不是您不想超过的时间。
如果超时，pthread_cond_timedwait() 将返回 ETIMEDOUT 错误。

编辑:我跳过了锁定/解锁调用中的错误检查，不要忘记处理这个潜在的问题!

编辑²:我稍微检查了一下代码