/**

bool empty() const {

std::lock_guard lock(guard);

return queue.empty();

}

/**

void put(const T& item) {

{

std::lock_guard lock(guard);

queue.push(item);

}

signal.notify_one();

}

/**

T take() {

std::unique_lock<std::mutex> lock(guard);

while (queue.empty())

signal.wait(lock);

T item = queue.front();

queue.pop();

return item;

}

std::queue<T> queue;

mutable std::mutex guard;

std::condition_variable signal;