How does PostQuitMessage know which thread to post the quit message to?
Commenter bav016 asks
how functions like PostQuitMessage
and SetTimer(NULL) know which thread the messages should
go to.
Unlike some functions such as InvalidateRect which have a window
handle parameter that lets you say which window you want to operate on,
PostQuitMessage and SetTimer(NULL)
don't say which thread the WM_QUIT
or WM_TIMER message should go to.
How do they decide?
The messages go to the current thread;
that is, they are delivered to the thread that called the function
in the first place.
There are many functions which operate on an implicit message queue,
and those cases, they operate on the message queue associated
with the thread making the call.
If you call GetKeyState
you retrieve the calling thread's keyboard state.
If you call GetMessage
you retrieve messages from the calling thread's message queue.
If you call InSendMessage,
you are told about the calling thread's message processing state.
If you call GetQueueStatus
you retrieve information about the calling thread's msesage queue.
You get the idea.
If you want these functions to operate on a thread different
from the one that is executing,
you'll have to ask that thread to make the call for you.
