C++11中完善了信號量與條件變量(參見:C++11中線程及信號量與條件變量),但是condition_variable
的一些實現是存在問題的,特別是在Windows下會很容易出現假喚醒的情形(VS2015的實現,在Win10下非常容易出現,而Win7下偶爾出現)。
爲避免此種假喚醒情形,需要使用帶Predicate
參數的重載接口,以下是Event接口的模擬實現:
class XuEvent{ // No signal when init
public:
void wait(){
std::unique_lock<std::mutex> lker(m_mtx);
m_bNotified = false;
m_cv.wait(lker, [this] {return this->m_bNotified; });
}
bool wait(int nSec, int nMillSec=0){
std::unique_lock<std::mutex> lker(m_mtx);
m_bNotified = false;
std::chrono::seconds secs(nSec);
std::chrono::milliseconds mills(nMillSec);
auto ret = m_cv.wait_for(lker, secs + mills, [this] {return this->m_bNotified; });
//return (ret != std::cv_status::timeout);
return ret;
}
void notifyOne(){
m_bNotified = true;
m_cv.notify_one();
}
void notifyAll(){
m_bNotified = true;
m_cv.notify_all();
}
private:
bool m_bNotified = false;
std::mutex m_mtx;
std::condition_variable m_cv;
};