在C ++中的UI线程中需要帮助

Question

I'm using UI threads and I built one thread with message map and it works fine, the problem is when I'm tring to create another thread from the first one.

When I'm getting to this line:

this->PostThreadMessage(WM_MYTHREADMESSAGE,0,0);

I'm getting the next message:

"No symbols are loaded for any call stack frame. The source code cannot be displayed"

I dont know if its could be the reason for the problem but I have built two message maps, one for each thread, I don't know if its ok to do so.

Answer 1

The question is difficult to understand. I'm assuming that you're stepping through your program in the debugger, and you get to that PostThreadMessage line.

If you choose Step Into, the debugger will try to step into the PostThreadMessage call (or the framework wrapper, depending on the type of this ). Since PostThreadMessage is a system call, it's likely you don't have symbols for that code. The debugger will just show you disassembly. You can try to use the Microsoft symbol server, but I don't see much point in trying to trace into PostThreadMessage . If the parameters are right, it's going to post the message to the specified thread's queue. Not much to see there.

Posting message to other threads is tricky business. Most Windows programs, even multithreaded ones, typically keep all the UI work to a single thread. It can be done, but there are a lot of caveats and it's usually not worth the pain.

Answer 2

So there are couple of things:

1. if you want to notify the UI thread from the worker thread, then you should not use PostThreadMessage , here is why .
2. When this->PostThreadMessage(...) called in a member function of thread A, the message will be sent to thread A, because this points to CWinThread of A. You have to get a pointer to the other thread to post a message to it.
3. Finally if you want to notify your UI thread, use PostMessage to send a message to the window created by that thread. Add a corresponding handler to the window message map.

Hope this helps