SafeQueue类继承与信号量mutex（用于加锁），nonocopyable
定义如下：
template <typename T>
struct SafeQueue : private std::mutex, private noncopyable {
static const int wait_infinite = std::numeric_limits<int>::max(); SafeQueue(size_t capacity = ) : capacity_(capacity), exit_(false) {}
bool push(T&& v)
T pop_wait(int waitMs = wait_infinite);
bool pop_wait(T* v, int waitMs = wait_infinite); size_t size();
void exit();
bool exited() { return exit_; } private:
std::list<T> items_;
std::condition_variable ready_;
size_t capacity_;
std::atomic<bool> exit_;
void wait_ready(std::unique_lock<std::mutex>& lk, int waitMs);
};
该类可以安全的添加和删除任务，类内部使用容器list来存储具体的任务，具有退出状态：exit_，取出任务时可以设定超时时间。
其中Task的定义为：typedef std::function<void()> Task; Task为返回值为空的函数对象
SafeQueue的具体实现如下：
template <typename T>
size_t SafeQueue<T>::size() {
std::lock_guard(std::mutex) lk(*this);
return items_.size();
} template <typename T>
void SafeQueue<T>::exit() {
exit_ = true;
std::lock_guard<std::mutex> lk(*this);
ready_.notify_all();
} template <typename T>
bool SafeQueue<T>::push(T&& v) {
std::lock_guard<std::mutex> lk(*this);
if (exit_ || (capacity_ && items_.size() >= capacity_)) {
return false;
} items_.push_back(std::move(v));
ready_.notify_one();
return true;
} template <typename T>
void SafeQueue<T>::wait_ready(std::unique_lock<std::mutex>& lk, int waitMs) {
if (exit_ || !items_.empty()) {
return;
}
if (waitMs == wait_infinite) {
ready_.wait(lk, [this] { return exit_ || !items_.empty(); });
} else if (waitMs > ) {
auto tp = std::chrono::steady_clock::now() + std::chrono::milliseconds(waitMs);
while (ready_.wait_until(lk, tp) != std::cv_status::timeout && items_.empty() && !exit_) {
}
}
} template <typename T>
bool SafeQueue<T>::pop_wait(T* v, int waitMs) {
std::unique_lock<std::mutex> lk(*this);
wait_ready(lk, waitMs);
if (items_.empty()) {
return false;
} *v = std::move(items_.front());
items_.pop_front();
return true;
} template <typename T>
T SafeQueue<T>::pop_wait(int waitMs) {
std::unique_lock<std::mutex> lk(*this);
wait_ready(lk, waitMs);
if (items_.empty()) {
return T();
}
T r = std::move(items_.front());
items_.pop_front();
return r;
}