Multithreading 在线程之间使用SendMessageToDescendant

在我的MFC应用程序中，我有一个工作线程监听网络连接，当一些信息到达时，我调用

sendMessageToDescendats

通过lparam参数发送该信息。因此，每个帧窗口将获取消息，并可能通过

WM\u SYNCHRONOTIFICATION

消息的消息处理程序对其进行处理（

WM\u SYNCHRONOTIFICATION

是

WM\u APP+x

消息）

工作线程中的代码：（为简洁起见简化）

主线程中的消息处理程序：

LRESULT CMyFrame::OnSynchroNotification(WPARAM p1, LPARAM p2)
{
  CNotificationMessage *pNotification = (CNotificationMessage*)p2;

  // process message (ommited for brevity)
}

---

代码工作正常，但我不确定从

SendMessageToDescendants

返回时是否调用了所有

OnSynchroNotification

。

最简单的解决方案是使用计数器。在调用

SendMessage

之前，将共享计数器初始化为您希望处理消息的子窗口数。然后，每个消息处理程序负责在完成其工作时递减计数器，并且事件循环可以在生成更多事件之前检查计数器是否为0。在伪C++中：

unsigned int sharedCount; // global/static shared value

while (TRUE)
{
    CNotificationMessage notificationmessage;
    Listen(&notificationmessage);  // blocking until some information arrives

    unsigned int current = InterlockedCompareExchange(&sharedCount, activeWindowCount, 0);
    if (current == 0)
    {   
        m_pMainWnd->SendMessageToDescendants(WM_SYNCHRONOTIFICATION, NULL, (LPARAM)(newnotif));
    }
    else
    {
        // Still processing the last message.
    }

    while (InterlockedCompareExchange(&sharedCount, 0, 0) != 0)
    {
        Sleep(100);
    }
}

LRESULT CMyFrame::OnSynchroNotification(WPARAM p1, LPARAM p2)
{
    // Processing
    InterlockedDecrement(&sharedCount);
}

while (TRUE)
{
    CNotificationMessage notificationmessage;
    Listen(&notificationmessage);  // blocking until some information arrives

    m_pMainWnd->SendMessageToDescendants(WM_SYNCHRONOTIFICATION, NULL, (LPARAM)(newnotif));

    DWORD waitResult = WaitForMultipleObjects(activeWindowCount, FrameEvents, TRUE, INFINITE);
    if (waitResult == WAIT_OBJECT_0)
    {
        // Success
    }
    else if (waitResult == WAIT_FAILED)
    {
        // Failure: Use GetLastError() to figure out why the function call failed.
    }

    // Reset the events
}    

LRESULT CMyFrame::OnSynchroNotification(WPARAM p1, LPARAM p2)
{
    // Processing
    SetEvent(thisFramesEvent);
}

稍微复杂一点的解决方案，但我个人更喜欢，因为您不必在等待完成时消耗CPU，就是为每个消息处理窗口创建一个事件，然后使用（或Ex版本）停止事件循环，直到完成。同样，在伪C++中：

unsigned int sharedCount; // global/static shared value

while (TRUE)
{
    CNotificationMessage notificationmessage;
    Listen(&notificationmessage);  // blocking until some information arrives

    unsigned int current = InterlockedCompareExchange(&sharedCount, activeWindowCount, 0);
    if (current == 0)
    {   
        m_pMainWnd->SendMessageToDescendants(WM_SYNCHRONOTIFICATION, NULL, (LPARAM)(newnotif));
    }
    else
    {
        // Still processing the last message.
    }

    while (InterlockedCompareExchange(&sharedCount, 0, 0) != 0)
    {
        Sleep(100);
    }
}

LRESULT CMyFrame::OnSynchroNotification(WPARAM p1, LPARAM p2)
{
    // Processing
    InterlockedDecrement(&sharedCount);
}

while (TRUE)
{
    CNotificationMessage notificationmessage;
    Listen(&notificationmessage);  // blocking until some information arrives

    m_pMainWnd->SendMessageToDescendants(WM_SYNCHRONOTIFICATION, NULL, (LPARAM)(newnotif));

    DWORD waitResult = WaitForMultipleObjects(activeWindowCount, FrameEvents, TRUE, INFINITE);
    if (waitResult == WAIT_OBJECT_0)
    {
        // Success
    }
    else if (waitResult == WAIT_FAILED)
    {
        // Failure: Use GetLastError() to figure out why the function call failed.
    }

    // Reset the events
}    

LRESULT CMyFrame::OnSynchroNotification(WPARAM p1, LPARAM p2)
{
    // Processing
    SetEvent(thisFramesEvent);
}

本例使用无限超时，但您始终可以设置合理的超时，并检查返回值

WAIT\u timeout

，查看时间是否已过

（必需的免责声明：为了简洁易读，错误检查和变量初始化已从这两个版本中删除。有关如何检查错误的信息，请参阅文档。）

。