Internals : Windows messages, implicit child process wait

Author: kipod
Subject: Windows messages, implicit child process wait
Posted: 06 January 2014 at 4:18pm

Hello,

I have an application consisting of a window and a child window, each belonging to a different process. A curious issue appears where a hang in the child-window's process leads to a hang of the parent window's process. So, whenever child window's process stops processing messages, the parent process gets hanged.

I found this post, which talks about a similar issue:
http://blog.chromium.org/2008/10/responsiveness-for-plugins-and-renderer.html
In it they say:
"A problem arises for some types of Windows messages. The system will synchronously send them to all windows in a hierarchy, waiting for each window to process the message before sending it to parent or child windows. This introduces an implicit wait"

Any idea what exactly are the messages for which the wait apply?
For a quick look, it seems like when the child window hangs the parent is only issued with WM_TIMER and WM_SYSTIMER messages. All other (reserved and custom) are not issued.
Does anyone have some more detailed explanation about this and how to handle it?

Thanks in advance!