Re: Need help solving a threading issue
"Joseph M. Newcomer" <newcomer@flounder.com> wrote in message
news:ccpra3d5g8ci87f9ubm5q2ure7bh8e7jhe@4ax.com...
If the HWND is not a top-level owned window, you end up in trouble,
because the
complexities of interthread interaction are going to be a source of
potential problems.
For example, the way CAsyncSocket gets its callbacks is to create a
top-level invisible
window (hence it has no parent to have to send notifications to), and when
a callback
(represented by a SendMessage to the window) is received, the SOCKET value
passed in is
looked up in the thread's handle map, and the CAsyncSocket class object is
retrieved. The
virtual methods (such as OnReceive, OnSend, etc.) are called, which causes
the virtual
method of your derived class to be called.
But having a thread create a child HWND, or a CDialog, or something like
that, opens up
opportunities for deadlock and similar nasty behavior, which are best
avoided.
I would say these issues are the same regardless of whether they are
performed on the primary UI thread or a secondary UI thread. The fact that
CAsyncSocket creates it's own hidden window confirms that it is fine to
create HWND's on a secondary thread.
I agree a child HWND whose parent was created in another thread is an issue,
but again it is an issue regardless of whether the child is part of a
secondary UI thread or not. A CDialog can be a top-level, owned window, so
I don't see an issue with creating one on the secondary UI thread either
(but I agree a CDialog is not the right choice for a hidden window).
-- David