带 pthread 的线程安全队列

Question

Is this the correct way to implement a thread-safe queue in C++? I have multiple threads constantly enqueuing and dequeuing items until a certain condition happens, during which I "stop" the queue. Thanks

#include <queue>
#include <pthread.h>

template <typename T>
class ThreadSafeQueue {

private:
    std::queue<T> _queue;
    pthread_mutex_t queueMutex;
    pthread_cond_t emptyCondVar;

public:
    ThreadSafeQueue();

    bool volatile Stopped;

    void Enqueue(T data);
    T Dequeue();
    void StopQueue();
    void DestroyQueue();
};

template <typename T>
ThreadSafeQueue<T>::ThreadSafeQueue() {
    pthread_mutex_init(&queueMutex, NULL);
    pthread_cond_init(&emptyCondVar, NULL);
    Stopped = false;
}

template <typename T>
void ThreadSafeQueue<T>::Enqueue(T data) {
    pthread_mutex_lock(&queueMutex);
    _queue.push(data);
    pthread_cond_signal(&emptyCondVar);
    pthread_mutex_unlock(&queueMutex);

}

template <typename T>
T ThreadSafeQueue<T>::Dequeue() {

    pthread_mutex_lock(&queueMutex);
    if (_queue.empty()) {
        pthread_cond_wait(&emptyCondVar, &queueMutex);
    }
    if (Stopped) {
        pthread_mutex_unlock(&queueMutex);
        return NULL;
    }

    T elem = _queue.front();
    _queue.pop();
    pthread_mutex_unlock(&queueMutex);
    return elem;
}

template <typename T>
void ThreadSafeQueue<T>::StopQueue() {  
    pthread_mutex_lock(&queueMutex);
    Stopped = true;
    pthread_cond_broadcast(&emptyCondVar);
    pthread_mutex_unlock(&queueMutex);
}

template <typename T>
void ThreadSafeQueue<T>::DestroyQueue() {   
    pthread_mutex_lock(&queueMutex);
    _queue = std::queue<T>();
    pthread_mutex_unlock(&queueMutex);
}

Answer 1

Your Dequeue needs to loop on the pthread_cond_wait() :

while (_queue.empty() && !Stopped) {
    pthread_cond_wait(&emptyCondVar, &queueMutex);
}