c++ - 经典的生产者消费者线程

Question

在 Classical producer consumer problem 。当 itemCount == BUFFER_SIZE 时，生产者会休眠，而当它宕机时，生产者会再次醒来。但是一旦 itemCount 增大，生产者线程就会进入休眠状态。它如何知道 itemCount 已下降并且需要唤醒？

Answer 1

在伪代码中，生产者类似于:

void producer_thread()
{
    while(true)
        queue.push( produce() );
}

所以考虑队列推送方法(我在这里使用了pthreads，但相同的逻辑也适用于其他库)

void SynchronizedQueue::push(Item const &i)
{
    pthread_mutex_lock(&mutex);

    // queue is full, so wait for consumer
    while (queue.size() == BUFFER_SIZE)
        pthread_cond_wait(&condition, &mutex);

    // when we get here, the queue has space
    this->queue.push_back(i);

    // make sure we wake a sleeping consumer
    if (queue.size() == 1)
        pthread_cond_signal(&condition);

    pthread_mutex_unlock(&mutex);
}

以及消费者使用的pop方法:

Item SynchronizedQueue::pop()
{
    pthread_mutex_lock(&mutex);

    // wait for something to do
    while (queue.size() == 0)
        pthread_cond_wait(&condition, &mutex);

    // if we get here, we have some work
    Item tmp = queue.front();

    // make sure we wake a sleeping producer
    if (queue.size() == BUFFER_SIZE)
        pthread_cond_signal(&condition)

    queue.pop_front();
    pthread_mutex_unlock(&mutex);
    return tmp;
}