如何：使用带有 Windows 消息循环的任务队列

示例

任务队列可以与 Windows 消息循环集成。 通常，您希望在运行消息循环的线程上运行在完成端口排队的回调。

下列示例使用线程池来执行工作，但将完成端口回调集成到 Win32 窗口进程中。 此示例还演示了在将某一任务队列与其他线程模型集成时如何正确终止任务队列。

  
// Example of using a task queue and Window proc together.  
  
XTaskQueueHandle g_queue; 
XTaskQueueRegistrationToken g_monitorToken;  
  
// Posted when there's a completion callback.  
#define WM_QUEUE_COMPLETION (WM_USER + 1)  
  
struct WorkData  
{  
    HWND hwnd;  
    WCHAR text[80];  
};  
  
void CALLBACK WorkCompletion(void* context, bool cancel)  
{  
    WorkData* data = (WorkData*)context;  
  
    if (!cancel)  
    {  
        SetWindowText(data->hwnd, data->text);  
    }  
  
    delete data;  
}  
  
void CALLBACK BackgroundWork(void* context, bool cancel)  
{  
    if (!cancel)  
    {  
        WorkData* data = new WorkData;  
        data->hwnd = (HWND)context;  
  
        if (GetTimeFormatEx(  
            LOCALE_NAME_USER_DEFAULT, 0, nullptr,  
            nullptr, data->text, 80) == 0)  
        {  
            swprintf_s(data->text, L"Error : %d", GetLastError());  
        }  
  
        // Now, take our formatted string and submit it as a completion callback. 
        XTaskQueueSubmitCallback(  
            g_queue,  
            XTaskQueuePort::Completion,  
            data,  
            WorkCompletion);  
    }  
}  
  
LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)  
{  
    HRESULT hr;  
  
    switch (msg)  
    {  
    case WM_CREATE:  
  
        // We'll do work on the thread pool, but completion  
        // callbacks should be manual so that we can integrate them with  
        // the message loop.  
  
        hr = XTaskQueueCreate(  
            XTaskQueueDispatchMode::ThreadPool,  
            XTaskQueueDispatchMode::Manual,  
            &g_queue);  
  
        if (SUCCEEDED(hr))  
        {  
            hr = XTaskQueueRegisterMonitor(g_queue, hwnd,  
                [](void* context, XTaskQueueHandle, XTaskQueuePort port)  
            {  
                // If a new callback was submitted to the completion  
                // port, post a message so that we dispatch it in our message loop.  
                if (port == XTaskQueuePort::Completion)  
                {  
                    HWND hwnd = static_cast<HWND>(context);  
                    PostMessage(hwnd, WM_QUEUE_COMPLETION, 0, 0);  
                }  
            }, &g_monitorToken);  
        }  
  
        if (FAILED(hr))  
        {  
            PostQuitMessage(1);  
            return 0;  
        }  
        break;  
  
    case WM_LBUTTONDOWN:  
        hr = XTaskQueueSubmitCallback(  
            g_queue,  
            XTaskQueuePort::Completion,  
            hwnd,  
            BackgroundWork);  
  
        if (FAILED(hr))  
        {  
            MessageBox(hwnd, L"Failed to submit callback.", L"Error", MB_OK);  
        }  
        break;  
  
    case WM_QUEUE_COMPLETION:  
        XTaskQueueDispatch(g_queue, XTaskQueuePort::Completion, 0);  
        break;  
  
    case WM_CLOSE:  
  
        // Terminate the task queue. When this is done, destroy our window.  
        // The termination callback is queued to the completion  
        // port, so it will already be on the UI thread.  
  
        hr = XTaskQueueTerminate(g_queue, false, hwnd, [](void* context)  
        {  
            HWND hwnd = static_cast<HWND>(context);  
            DestroyWindow(hwnd);  
            XTaskQueueUnregisterMonitor(g_queue, g_monitorToken);  
            XTaskQueueCloseHandle(g_queue);  
        });  
  
        if (SUCCEEDED(hr))  
        {  
            // Prevent DefWndProc from destroying our window because  
            // the termination callback will do it.  
            return 0;  
        }  
        break;  
  
    case WM_DESTROY:  
        PostQuitMessage(0);  
        break;  
  
    }  
  
    return DefWindowProc(hwnd, msg, wParam, lParam);  
}  
  
void TestWndProc()  
{  
    WNDCLASS wndClass;  
    ZeroMemory(&wndClass, sizeof(wndClass));  
    wndClass.lpfnWndProc = WndProc;  
    wndClass.lpszClassName = L"TestClass";  
    wndClass.hInstance = GetModuleHandle(nullptr);  
    wndClass.hbrBackground = GetSysColorBrush(COLOR_WINDOW);  
  
    ATOM c = RegisterClass(&wndClass);  
  
    HWND h = CreateWindow(L"TestClass", L"Window",  
        WS_OVERLAPPEDWINDOW | WS_VISIBLE,  
        10, 10, 300, 100, nullptr, nullptr,  
        GetModuleHandle(nullptr), 0);  
  
    if (!h)  
    {  
        return;  
    }  
  
    MSG m;  
  
    while (GetMessage(&m, nullptr, 0, 0))  
    {  
        TranslateMessage(&m);  
        DispatchMessage(&m);  
    }  
}  

另请参阅

设计任务队列