Forms, multi-threading, Chats

[Mahesh Devjibhai Dhola [MVP]]

We are building Chat like application using Forms and as a result our
programming is becoming complicated to display messages received on
different threads in the chat window (due to STA requirements of Forms). Is
there a way to build Chat like application WITHOUT using FORM, so that one
can use free threading model (The link
http://msdn.microsoft.com/library/d...evelopingmultithreadedwindowsformscontrol.asp
has statement "Outside Windows Forms, classes in the .NET Framework use the
free threading model. For information about threading in the .NET Framework,
see Threading."). IS THERE ANY WAY TO BUILD CHAT-like application without
having to do complicated programming to satisfy STA requirements)?

Thanks in Advance,
Regards,
Mahesh

 

[Jochen Kalmbach [MVP]]

Hi Mahesh!

We are building Chat like application using Forms and as a result our
programming is becoming complicated to display messages received on
different threads in the chat window (due to STA requirements of Forms). Is
there a way to build Chat like application WITHOUT using FORM, so that one
can use free threading model (The link
http://msdn.microsoft.com/library/d...evelopingmultithreadedwindowsformscontrol.asp
has statement "Outside Windows Forms, classes in the .NET Framework use the
free threading model. For information about threading in the .NET Framework,
see Threading."). IS THERE ANY WAY TO BUILD CHAT-like application without
having to do complicated programming to satisfy STA requirements)?

As long as you do not have any GUI, it is very easy.
But if you want to display it in some Windows-GUI, then you are limited
(in most cases) to single-threaded (or to be more specific: (Most)
messages to a window must be sent from the same thread, that created the
window).
Sometimes there are also two different functions (like: ShowWindow and
ShowWindowAsync).

From my point of view: Working with Windows-Forms is very easy (even
with multi-threaded; the approch of "BeginInvoke" and "Invoke" is
streight forward).

See: Multiple Threads in the User Interface
http://msdn.microsoft.com/library/en-us/dndllpro/html/msdn_winthr.asp

--
Greetings
Jochen

My blog about Win32 and .NET
http://blog.kalmbachnet.de/

 

[Jon Skeet [C# MVP]]

We are building Chat like application using Forms and as a result our
programming is becoming complicated to display messages received on
different threads in the chat window (due to STA requirements of Forms).

It's got nothing to do with the STA requirement of Forms - it's a
fundamental Windows GUI programming requirement that you only access a
UI component on the thread which created it.

Howveer, it shouldn't be particularly complicated to update the UI
appropriately.

See http://www.pobox.com/~skeet/csharp/threads/winforms.shtml

 

[Ioannis Vranos]

It's got nothing to do with the STA requirement of Forms - it's a
fundamental Windows GUI programming requirement that you only access a
UI component on the thread which created it.

Howveer, it shouldn't be particularly complicated to update the UI
appropriately.

See http://www.pobox.com/~skeet/csharp/threads/winforms.shtml

I am currently reading .NET networking (and have read .NET multithreading in the past),
and I see no problem updating GUI components from different threads. In addition, STA etc
have nothing to do with pure .NET applications (applications that do not use COM and other
past APIs).

For example we can update a TextBox from different threads upon receiving or sending data
(in the chat client example). In fact this is what I am currently reading about, Chat
client/server applications using connection (TCP/IP stream sockets) and connectionless
(UDP) String exchanges.


Am I missing something?

 

[Willy Denoyette [MVP]]

I am currently reading .NET networking (and have read .NET multithreading
in the past), and I see no problem updating GUI components from different
threads. In addition, STA etc have nothing to do with pure .NET
applications (applications that do not use COM and other past APIs).

For example we can update a TextBox from different threads upon receiving
or sending data (in the chat client example). In fact this is what I am
currently reading about, Chat client/server applications using connection
(TCP/IP stream sockets) and connectionless (UDP) String exchanges.


Am I missing something?

Yes, a fundamental rule in Windows that say's that Windows handles (HWND's)
have thread affinity, that means they should not be used from another thread
than the owning thread. Note that v2.0 contains a debug user probe that
warns you about cross-thread access to window UI elements.
Also note that the UI thread needs to run in a STA because some of the UI
controls might use COM under the covers. Another reason to have the thread
running in a STA is that and Cut/Paste (Clipboard access) is using OLE based
and needs a STA to run.

Willy.

 

[Jon Skeet [C# MVP]]

I am currently reading .NET networking (and have read .NET
multithreading in the past), and I see no problem updating GUI
components from different threads.

Then you haven't read the documentation clearly enough. From
Control.Invoke:

<quote>
Note There are four methods on a control that are safe to call from
any thread: Invoke, BeginInvoke, EndInvoke, and CreateGraphics. For all
other method calls, you should use one of the invoke methods to marshal
the call to the control's thread.

In addition, STA etc have nothing to do with pure .NET applications
(applications that do not use COM and other past APIs).

Many Windows Forms controls use COM components internally.

For example we can update a TextBox from different threads upon
receiving or sending data (in the chat client example).

No you can't - not reliably. It may happen to work for you at the
moment, but you shouldn't do it.