Posted on 2006-07-21 09:50
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Win32
SendMessageTimeout并不是簡單在SendMessage加上Timeout的功能。
MSDN上面有一段文字是這樣說的
If the specified window was created by the calling thread, the window procedure is called immediately as a subroutine. If the specified window was created by a different thread, the system switches to that thread and calls the appropriate window procedure. Messages sent between threads are processed only when the receiving thread executes message retrieval code. The sending thread is blocked until the receiving thread processes the message. However, the sending thread will process incoming nonqueued messages while waiting for its message to be processed. To prevent this, use SendMessageTimeout with SMTO_BLOCK set. For more information on nonqueued messages, see Nonqueued Messages.
翻譯一下：
SendMessage : 如果指定窗口由調用線程創建，那么窗口過程會被當成一個子程序立即調用。如果指定窗口由另外一個線程創建，那么系統會切換到那個線程，并且調用合適的窗口過程。在線程之間傳遞的消息僅僅當接收線程執行message retrieval code才會被處理。發送線程會被堵塞直到接收線程處理完消息。但是，發送線程在等待的同時會處理收到的nonqueued messages 。為了阻止這一點，使用帶有SMTO_BLOCK參數 的SendMessageTimeout .
=================================華麗的分割線===========================
我曾經遇到這個問題，我調用SendMessage向另外一個線程窗口發message，本來以為他會一直block住，但是他卻調用了另外一個消息的處理程序，導致了行為不正確。所以一定要小心使用SendMessage發給其他線程的窗口。
我修改了一下，把
pWnd->SendMessage(MSG_LOG_MESSAGE, nMsgType, (LPARAM)(LPCTSTR)m_cstrMessage);
改成了
HWND hWnd = pWnd->GetSafeHwnd();
::SendMessageTimeout(hWnd,MSG_LOG_MESSAGE, nMsgType, (LPARAM)(LPCTSTR)m_cstrMessage,SMTO_BLOCK,15000,0);
解決了這個bug.
Feedback
# re: SendMessage 和 SendMessageTimeout 回復 更多評論
2006-12-27 15:02 by
好!!!雖然我看不懂寫些什么
# re: SendMessage 和 SendMessageTimeout 回復 更多評論
2009-02-12 14:50 by
沒看明白啊。。。可能是我水平不夠。。。
# re: SendMessage 和 SendMessageTimeout 回復 更多評論
2011-11-17 10:56 by
哥也沒看懂呀！！！
# re: SendMessage 和 SendMessageTimeout 回復 更多評論
2012-02-20 15:59 by
首先英文翻譯的的比較準確、專業！
正在研究SendMessage和SendMessageTImeOut區別，其中一個例子是，啟動應用程序新實例前，向已存在的實例發送copydata消息做一些處理，原先用的是sendmessage，現在覺得用sendmessagetimeout應該更穩妥一些
# re: SendMessage 和 SendMessageTimeout 回復 更多評論
2012-02-20 16:21 by
LRESULT SendMessageTimeout(
HWND hWnd, // handle to window
UINT Msg, // message
WPARAM wParam, // first message parameter
LPARAM lParam, // second message parameter
UINT fuFlags, // send options
UINT uTimeout, // time-out duration
PDWORD_PTR lpdwResult // return value for synchronous call
);
fuFlags
[in] Specifies how to send the message. This parameter can be one or more of the following values
SMTO_ABORTIFHUNG
Returns without waiting for the time-out period to elapse if the receiving process appears to be in a "hung" state.
順便翻譯一下最后一句
“如果接收進程處于掛起狀態，不再等待（超時）直接返回”