Comment by quotemstr
13 years ago
Between threads, you rely exclusively on PostMessage anyway. You can't directly call into a routine on a different thread, so SendMessage to a window owned by another thread just posts the message to a special queue that's serviced before the regular message queue, then blocks until the other thread's window procedure processes the message.
In all boils down to message-passing: in Windows, the win32k is the trusted third party that mediates interactions between different window-system clients. In the X11 case, the X server and the window manager work together to do the same job. The architecture are fundamentally similar.
Hmm... yeah, that does sound very similar.
Why does Windows need kernel-to-user callbacks in the first place then? Now I'm thinking it shouldn't even be necessary at all...
You may be interested in http://mista.nu/research/mandt-win32k-slides.pdf
Thanks, I took a look at that... but it doesn't seem to quite explain what I meant. I was thinking more like, there's no need for SendMessage() to go from user->kernel->user, even when it's on the same thread. It could just do a system call to get the wndproc for the given window, then call the wndproc from user-mode directly.
Wouldn't that completely avoid needing to call back into user-mode from kernel mode?
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