c++ - 如何确保对象只有一个线程

Question

我有以下代码:

class Service {
public:
    void start(); // creates thread which creates window and goes to message loop
    void stop();  // sends WM_CLOSE message to thread window
private:
    HANDLE hMutex;
    HANDLE hThread;
    HWND   hWindow;
};

我希望我的类(class)执行这样的行为:

Service obj;
obj.start(); // new thread
obj.start(); // do nothing because thread already exists

现在我被困在互斥锁覆盖哪个句柄的问题上:

void Service::start() {
    // check if service is already running
    if (/*!!*/) // what should I check: (hThread != NULL)? or (hWindow != NULL)?
        return; // no need to create another thread
    else
        hThread = CreateThread(...);
}

Answer 1

您可以控制线程句柄hThread 的状态，如果它发出信号则表示线程已终止:

DWORD result = WaitForSingleObject( hThread, 0);

if (result == WAIT_OBJECT_0) {
    // the signal is sent and therefore the thread has been terminated
}
else {
    // the signal is not sent and hThread is alive
}

注意第二个参数是超时时间，非阻塞调用需要设置为0。

详细的可以查看reference