如何保证对象只有一个线程

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;
};

我希望我的班级执行这样的行为：

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

现在我陷入了互斥锁处理的问题：

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(...);
}

可以控制线程句柄的状态hThread，如果收到信号则意味着线程已终止：

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
}

请注意，第二个参数是超时，需要将其设置为零以进行非阻塞调用。

您可以查看详细信息参考 https://msdn.microsoft.com/en-us/library/windows/desktop/ms687032(v=vs.85).aspx