我正在研究多线程并编写了基本的生产者/消费者。我在下面写的生产者/消费者有两个问题。 1)即使将消费者的睡眠时间设置为低于生产者的睡眠时间,生产者似乎仍然可以更快地执行。 2)在生产者完成添加到队列的情况下,在使用者中我复制了代码,但是队列中仍然有元素。有什么建议可以更好地构造代码吗?
#include <iostream>
#include <queue>
#include <mutex>
class App {
private:
std::queue<int> m_data;
bool m_bFinished;
std::mutex m_Mutex;
int m_ConsumerSleep;
int m_ProducerSleep;
int m_QueueSize;
public:
App(int &MaxQueue) :m_bFinished(false), m_ConsumerSleep(1), m_ProducerSleep(5), m_QueueSize(MaxQueue){}
void Producer() {
for (int i = 0; i < m_QueueSize; ++i) {
std::lock_guard<std::mutex> guard(m_Mutex);
m_data.push(i);
std::cout << "Producer Thread, queue size: " << m_data.size() << std::endl;
std::this_thread::sleep_for(std::chrono::seconds(m_ProducerSleep));
}
m_bFinished = true;
}
void Consumer() {
while (!m_bFinished) {
if (m_data.size() > 0) {
std::lock_guard<std::mutex> guard(m_Mutex);
std::cout << "Consumer Thread, queue element: " << m_data.front() << " size: " << m_data.size() << std::endl;
m_data.pop();
}
else {
std::cout << "No elements, skipping" << std::endl;
}
std::this_thread::sleep_for(std::chrono::seconds(m_ConsumerSleep));
}
while (m_data.size() > 0) {
std::lock_guard<std::mutex> guard(m_Mutex);
std::cout << "Emptying remaining elements " << m_data.front() << std::endl;
m_data.pop();
std::this_thread::sleep_for(std::chrono::seconds(m_ConsumerSleep));
}
}
};
int main()
{
int QueueElements = 10;
App app(QueueElements);
std::thread consumer_thread(&App::Consumer, &app);
std::thread producer_thread(&App::Producer, &app);
producer_thread.join();
consumer_thread.join();
std::cout << "loop exited" << std::endl;
return 0;
}
首先,您应该使用条件变量,而不是对使用者造成延迟。这样,使用者线程仅在队列不为空且生产者通知时唤醒。
也就是说,您的生产者调用更加频繁的原因是生产者线程上的延迟。它在保持互斥锁的同时执行,因此使用者直到延迟结束后才执行。您应在调用sleep_for
之前释放互斥锁:
for (int i = 0; i < m_QueueSize; ++i) {
/* Introduce a scope to release the mutex before sleeping*/
{
std::lock_guard<std::mutex> guard(m_Mutex);
m_data.push(i);
std::cout << "Producer Thread, queue size: " << m_data.size() << std::endl;
} // Mutex is released here
std::this_thread::sleep_for(std::chrono::seconds(m_ProducerSleep));
}
您应使用condition_variable。不要对线程使用睡眠。