[vtkusers] vtkWin32OutputWindow hangs in multithreaded debugging mode - with fix

[Andrew Dolgert]

Hi - The debug, multi-threaded version of vtkWin32OutputWindow hangs
because slave threads use ::SendMessage() to print debugging messages to
the main thread's window, possibly after the main thread is waiting on a
signal.  It causes deadlock.  A simple solution is to change SendMessage
to SendNotifyMessage, which acts like SendMessage when called from the
same thread but acts more like PostMessage from slave threads.

I saw this problem while stepping through vtkImageMagnify, but it should
be a very common problem for debug, multi-threaded builds on Windows.
How could I submit a bug report?  Thanks,
Drew Dolgert, Cornell Theory Center