blockingqueue.h

#include <condition_variable>
#include <mutex>
#include <queue>

template <typename T>
class blockingqueue {
public:
	blockingqueue() {}
	void enqueue(const T& item) {
		std::lock_guard<std::mutex> lk(lk_);
		const bool was_empty = queue_.empty();
		queue_.push(item);
		if (was_empty) {
			empty_wait_.notify_all();  // notify_one() may be suitable?
		}
	}

	T dequeue() {
		std::unique_lock<std::mutex> lk(lk_);
		while (queue_.empty()) {
			empty_wait_.wait(lk);
		}
		T result = queue_.front();
		queue_.pop();
		return result;
	}

	size_t size() const {
		boost::mutex::scoped_lock lk(lk_);
		return queue_.size();
	}

private:
	mutable std::mutex lk_;
	mutable std::condition_variable empty_wait_;
	std::queue<T> queue_;
};