CODEWITHSUNDEEP
windowsdelphiwinapi
yankee
yankee

Reputation: 509

Guest Process with a reparented window hangs on Dialog invocation if Host process blocked on a WaitFor<...>

I'm developing a multi-process framework for a complex application. A Host process acts as a container, and one or more guest processes can be spawn from it. A Window of such guest processes is reparented to a Hosts's window (such as a notebook tabSheet). (InterProcess Communication is not an issue here - it works) Imagine something similar to Google Chrome. I've read many answers about reparenting windows across processes, but I can't figure out what's happening in this case:

Doesn't the guest process run on a separate message queue? What am I missing?

I think I followed the best guidelines about SetParent when I embedded the Guest Form:

SetWindowLong(GuestHWnd, GWL_STYLE, GetWindowLong(GuestHWND, GWL_STYLE) and WS_EX_NOPARENTNOTIFY and (not WS_POPUP) or WS_CHILD);
SetParent(GuestHWnd, HostHWnd);
PostMessage(GuestHWnd, WM_UPDATEUISTATE, UIS_INITIALIZE, 0);
SendMessage(HostHWnd, WM_UPDATEUISTATE, UIS_INITIALIZE, 0);
SetWindowPos(GuestHWnd, 0, 0, 0, 0, 0, SWP_NOMOVE or SWP_NOSIZE or SWP_NOZORDER or SWP_FRAMECHANGED);

Notice also that I haven't called any sort of AttachThreadInput. The problem doesn't arise if the Host is not blocked, or if the Guest window is not a child of a host's (obviously).

Thank you.

Upvotes: 1

Views: 180

Answers (1)

Daniel
Daniel

Reputation: 1051

I can only recommend Raymond chen's explanation to this: http://blogs.msdn.com/b/oldnewthing/archive/2013/04/12/10410454.aspx

Long story short:

Creating a cross-thread parent/child or owner/owned window relationship implicitly attaches the input queues of the threads which those windows belong to.

The problem is in this statement:

Notice also that I haven't called any sort of AttachThreadInput. The problem doesn't arise if the Host is not blocked, or if the Guest window is not a child of a host's (obviously).

Since it's a child/parent relationship, there IS an implicit AttachThreadInput.

Upvotes: 1

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