windows - Does the application GetMessage even during MessageBox?

Question

While handling WM_TIMER, I called MessageBox. As a result, a message box popped up with the frequency of the timer. So I believe that the application was trying to continue to process queued/non-queued messages even during MessageBox.

Am I right?

I know that according to MSDN, while an application is sending a message to a different thread from the sending thread, the sending thread will try to process non-queued messages it receives before SendMessage returns --- i.e. before the target thread replies.

Are there any other functions that could try to continue to process queued/non-queued messages before they return, besides MessageBox and SendMessage? I need to know about that to determine whether any functions called in the Window procedure should be reentrant.

Another two relevant questions are 1) Does DispatchMessage not return until the window procedure has returned? 2) Will GetMessage not be called again if the current DispatchMessage hasn't returned yet?

Answer 1

A modal dialog runs its own message loop internally, using the calling thread's message queue. You are calling MessageBox() inside your WM_TIMER handler, so the message loop inside of MessageBox() is receiving and dispatching subsequent WM_TIMER messages while the message box is running.