ASynch delegate / Invoke is freezing application after windows is locked. : freeze, invoke, delegate

May 17, 2008 08:47am pdt

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09.14.2007 at 08:32AM PDT, ID: 22829178

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8.0

ASynch delegate / Invoke is freezing application after windows is locked.

Zones: C# Programming Language, Microsoft Visual Basic.Net, .NET Framework 2.0

Tags: freeze, invoke, delegate

I'm firing off 4 asynch delegates, each with the same callback. Inside the callback I'm keeping track of a simple integer counter. When the counter reaches 4, it reaches up into the main GUI, and makes the appropriate panel visible, using Invoke. Everything works GREAT.

Now, if I lock windows, and then unlock it, my entire application is completely frozen - I can't click anything, and if I drag another window in front, then move it, the application will not re-paint, but instead becomes distorted.

This even happens if I go through the asynch routine, and then do some other stuff with the program, then lock windows.

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Question Stats

Zone: Programming

Question Asked By: ARACK04

Solution Provided By: AlexFM

Participating Experts: 2

Solution Grade: A

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09.14.2007 at 08:50AM PDT, ID: 19892627

Rank: Sage

AlexFM:

Try to replace Invoke with BeginInvoke for GUI update from the delegate callback.

09.14.2007 at 08:58AM PDT, ID: 19892714

ARACK04:

no change

09.14.2007 at 09:03AM PDT, ID: 19892760

Rank: Guru

AkisC:

What AlexFM wrote is something you must do.
Invoke waits for the method to complete, so if an event is being handled by the user interface thread currently, Invoke will waitfor that handler to finish. Here is a potential for deadlock;
BeginInvoke is sometimes a better choice because it doesnt wait for the invoked method to finish runningit just adds the request to run the method to the frameworks internal event queue and then returns immediately.

Just an idea, that might help
It seems that when you lock windows the main thread or other threads "die" somehow!
If you can test the status of the treads, and discover if they are "alive" or "dead" it might give you and idea how to work it around.
Some more expirience expert can help more.

Assisted Solution

09.14.2007 at 09:18AM PDT, ID: 19892869

Rank: Sage

AlexFM:

Remove Invoke/BeginInvoke call from asynchronous callback. Does the program freeze now?
Add a lot of Trace.WriteLine calls to all suspicious functions, specifically, all functions working with asynchronous delegate, Invoke/BeginInvoke call and UI callback function. It can look like this:

void DoSomething()
{
Trace.WriteLine("DoSomething started");

Trace.WriteLine("Call BeginInvoke");
form.BeginInvoke(...);
Trace.WriteLine("BeginInvoke returned");

...
Trace.WriteLine("DoSomething started");
}
...

Run DebugView and your program, reproduce the bug and see what call doesn't return in the DebugView. This should happen in some function running in the main application thread which is responsible for GUI update. Having this information, you can detect deadlock reason.

09.14.2007 at 09:35AM PDT, ID: 19893026

ARACK04:

I completely got rid of the callback function - now I just have 4 delegate.begininvokes (and no form.Invoke or form.BeginInvoke). I put traces before and after each one.

Everything run 100% as expected, as it did before. The same problem stil exists though, which is that after locking windows, and unlocking it (logging back in), my application is now completely frozed, won't accept any input, can't re-paint, etc.

09.14.2007 at 09:38AM PDT, ID: 19893057

ARACK04:

This is what the delegates getting called looks like, in case it will help at all.

lc = New LoadCustomerDelegate(AddressOf HighLightsPanelClass.GetInstance().LoadCustomer)
Trace.WriteLine("start 1")
lc.BeginInvoke(oCust, Nothing, Nothing)
Trace.WriteLine("end 1")

lc = New LoadCustomerDelegate(AddressOf AccountsPanelClass.GetInstance().LoadCustomer)
Trace.WriteLine("start 2")
lc.BeginInvoke(oCust, Nothing, Nothing)
Trace.WriteLine("end 2")

lc = New LoadCustomerDelegate(AddressOf CreditDocumentsPanelClass.GetInstance().LoadCustomer)
Trace.WriteLine("start 3")
lc.BeginInvoke(oCust, Nothing, Nothing)
Trace.WriteLine("end 3")

lc = New LoadCustomerDelegate(AddressOf NotesPanelClass.GetInstance().LoadCustomer)
Trace.WriteLine("start 4")
lc.BeginInvoke(oCust, Nothing, Nothing)
Trace.WriteLine("end 4")

09.14.2007 at 09:39AM PDT, ID: 19893061

Rank: Sage

AlexFM:

So, the reason is in the delegate.begininvoke stuff. Please show your code which causes this behavior.
You can continue this investigation commenting off different code lines until you detect exact action which causes program freezing.

09.14.2007 at 09:42AM PDT, ID: 19893087

ARACK04:

I don't see how this can be a regular code exception - the code does what it's supposed to. This problem only occurs when I lock my OS. Has anyone seen this behavior before?

09.14.2007 at 09:43AM PDT, ID: 19893104

Rank: Sage

AlexFM:

What is oCust?

09.14.2007 at 09:46AM PDT, ID: 19893128

ARACK04:

Just a business layer object. Again, this method works perfectly until I like windows. Nothing is null, or anything like that.

09.14.2007 at 01:40PM PDT, ID: 19895010

ARACK04:

Screw it, I moved the code to a regular thread, hit start, and it works fine now. If anyone else can think of why this was happening I'd be happy dole out the points, if not I'll split them between you two.

09.15.2007 at 04:21AM PDT, ID: 19897205

Rank: Sage

AlexFM:

The only thing which looks suspicious here is using BeginInvoke without EndInvoke, which causes small memory leak, however, this is obviously not enough.
Trying to recall some .NET internals that I know, I can say that using BeginInvoke without EndInvoke causes leaking IAsyncResult instance and one native Windows event. Possibly it is internally implemented using thread from the thread pool, which is released only when EndInvoke is called. I don't know whether this is enough to get this strange behavior.

Accepted Solution

09.15.2007 at 01:43PM PDT, ID: 19898563

ARACK04:

Thanks, I'll give this a try on Monday.

20080236-EE-VQP-29 / EE_QW_1_20070628