Will another CWinThread object get from main thread's messages
in [MFC]
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From: lizhi on 13 May 2008 02:39 Hi all, My case is like this: I have two threads, which are both CWinThread object, one of them is main thread. When that non-main thread starts, it will enter the thread work function--_AfxThreadEntry, which is one private method MFC provides. During this method is called, m_pMainWnd, the member of this thread, will be attached to the main window of my application. My question is: If the two message loops are both running, which thread will get the message sent to the main window? If the message loop of one thread is ahead of another, what is the result again? Thanks a lot. Robert
From: Scott McPhillips [MVP] on 13 May 2008 08:49 Each message goes to one thread only. If a window is created in a thread, all messages for that window go to the thread in which the window was created. "lizhi" <zhi_lee(a)163.com> wrote in message news:etACbOMtIHA.4528(a)TK2MSFTNGP03.phx.gbl... > Hi all, > My case is like this: > I have two threads, which are both CWinThread object, one of them is main > thread. > When that non-main thread starts, it will enter the thread work > function--_AfxThreadEntry, which is one private method MFC provides. > During this method is called, m_pMainWnd, the member of this thread, will > be attached to the main window of my application. > My question is: > If the two message loops are both running, which thread will get the > message sent to the main window? > If the message loop of one thread is ahead of another, what is the result > again? > > Thanks a lot. > > Robert > > -- Scott McPhillips [VC++ MVP]
From: Joseph M. Newcomer on 13 May 2008 10:43 First, there is a crucial question: why do you think a message should go to a secondary thread? Does this thread have windows of its own? Are they user-visible? A secondary thread should not own or attempt to use any user-visible window at any time. If you have a secondary thread creating user-visible windows, you probably have so many things wrong in your code that you are going to get into serious trouble not very far down the road. If you have done this, rethink your design before it is too late. Messages to a window are handled by the thread that owns the window. There is no possible concept of a message loop of one thread being "ahead" of another; the message loops are unrelated. The thread that owns the window works in total ignorance of any other possible message loop that exists, and consequently the existence of multiple message pumps is irrelevant to your main GUI thread's message pump. It neither knows nor cares about them. A secondary thread may or may not have a message pump. Secondary threads with message pumps are good for lots of things, but owning user-visible windows is not among them. Note, by the way, that the ONLY thing that determines what message pump receives a message is what windows that thread owns. If, for example, you were to assign the m_pMainWnd window to a secondary thread, this would have absolutely no effect on which thread received messages; think of the m_pMainWnd as being a convenient annotation. The window referenced does not affect how message routing is done in the kernel, because Windows itself has no idea that MFC exists, and details like m_pMainWnd are irrelevant to it. It sends themessage to the thread that owns the window, and does not care about random variables that the application might be using to track those windows. Thus assigning m_pMainWnd to another thread will have no effect on the kernel, but MFC itself will start taking assertion failures (and perhaps crashing on access faults or something else seriously unpleasant) because you would have violated fundamental assumptions about its behavior. joe On Tue, 13 May 2008 14:39:28 +0800, "lizhi" <zhi_lee(a)163.com> wrote: >Hi all, >My case is like this: >I have two threads, which are both CWinThread object, one of them is main >thread. >When that non-main thread starts, it will enter the thread work >function--_AfxThreadEntry, which is one private method MFC provides. During >this method is called, m_pMainWnd, the member of this thread, will be >attached to the main window of my application. >My question is: >If the two message loops are both running, which thread will get the message >sent to the main window? >If the message loop of one thread is ahead of another, what is the result >again? > >Thanks a lot. > >Robert > Joseph M. Newcomer [MVP] email: newcomer(a)flounder.com Web: http://www.flounder.com MVP Tips: http://www.flounder.com/mvp_tips.htm
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