Am 26.07.2012 19:15, schrieb Simon:
On 26/07/2012 09:16, Russel Winder wrote:
On Wed, 2012-07-25 at 23:17 +0200, Kagamin wrote:
On Wednesday, 25 July 2012 at 18:50:51 UTC, Simon wrote:
You have to be very, very careful with trying to do multi
threading w/ windoze windows. Try doing a google search on it,
and the advice is invariably: don't do multi threaded windows.
Everybody including people famous for their in-depth window
knowledge recommends a single thread UI with non-UI worker
threads.
So if Windows is really doing multi-threaded widget management, this
would be very interesting. Where is the material that I can look at
that leads you to say that Windows is a multi-threaded UI.
On 'doze every thread can have it's own message pump and therefore it's
own UI, but if you have an ancestor/descent relation between 2 windows
they must belong to the same thread.
Otherwise you are pretty much guaranteed a deadlock, unless you only
ever use MsgWaitForMultipleObjectsEx to synchronise. But that's kinda of
unachievable unless you have written every single line of code yourself.
So you can have threads with separate UIs as long as you don't make the
windows of one thread the child of another.
Every thread that creates a window will get a message queue created and
assigned (It's then called a GUI thread).
Under normal circumstances your thread will enter an event loop where
you call the GetMessage/DispatchMessage function pair. GetMessage gets
only messages from the threads message queue and DispatchMessage
dispatches only to the windows owned by the thread.
You can get into troubles when you send a message via SendMessage from
thread A to a window owned by thread B and the event loop of thread B
does not handle this message (e.g. by having a modal dialog opened in
thread B). In this case thread A is blocked until the message is
processed by B's event loop.
SendMessage is often used in code dealing with Parent/Child window
relations, so the warning above is justified. But as long as your child
window event loop is not blocked (or some other access to a shared
resource creates a deadlock) it works.
There is a technical article about multithreaded GUI and Win32 on MSDN. See
http://msdn.microsoft.com/en-us/library/ms810439.aspx
