Hi there

Delphi 7 & EDB 2.03 build 8.

I have a problem in closing the Engine that lives in a data module of my app. I thought it reasonable to Close the engine in the OnDestroy method of the DataModule, but it gives a resounding AV when I try it. The code is

procedure TDModule.DataModuleDestroy(Sender: TObject);
var i: integer;
begin
for i := 0 to EDBDatabase1.DataSetCount-1 do
 EDBDatabase1.Datasets[i].Close;

for i := 0 to EDBDatabase2.DataSetCount-1 do
 EDBDatabase2.Datasets[i].Close;

for i := 0 to EDBSession1.DatabaseCount - 1 do
 EDBSession1.Databases[i].Close;  // wasn't closing Configuration database

EDBSession1.DropConnections;
EDBSession1.Close; // AV here, or if I rem this line, the AV on next line

EDBEngine1.Close;
end;

I had been simply calling the EDBEngine1.Close, and letting it worry about the other components downstream, but I added the other lines when the AV started. This happens after a long migration & database creation process, so I must be destroying something that the Session expects to find, but I cannot see what.

The call stack shows SetConnected after TEDBSession.Destroy, but I don't have the sorce so I can only assume that that is the way it should be:

Access violation at address 005E414B in module 'Ver8NewData.exe'. Read of address 00000000.

TEDBSession.InternalDisconnect
TEDBSession.SetConnected
TEDBSession.Destroy
TComponent.DestroyComponents
TComponent.Destroy
TDataModule.Destroy
TComponent.DestroyComponents
DoneApplication
DoExitProc
@Halt0
initialization

I tried closing the Engine in the form that calls the DataModule - same AV.

Have you any suggestions as to where I should look? It must be something belonging to the Session, but what?

Regards, Peter

Peter,

<< I have a problem in closing the Engine that lives in a data module of my
app. I thought it reasonable to Close the engine in the OnDestroy method of
the DataModule, but it gives a resounding AV when I try it. >>

How is the application being terminated ?  There's an issue with using Halt
to terminate an application:

http://www.elevatesoft.com/forums?action=view&category=edb&id=edb_general&page=1&msg=7491#7491

If not that, then there is most likely something amiss with the destruction
order of the units.

--
Tim Young
Elevate Software
www.elevatesoft.com

Tim

I don't use Halt anywhere.

<<If not that, then there is most likely something amiss with the destruction
order of the units.>>

It would appear so, but as they are components in a DataModule, how can I control their destruction?

I tried closing the Engine in the form that calls the DataModule, but that caused an AV, then I moved the Engine.Close to the DataModule's OnDestroy method - same sequence of events in the stack.

Is there a way I can control the destruction?

The AV appears to be in TEDBSession.InternalDisconnec, and I agree with your statement in the 'Halt problem' thread, in that "That causes the EDB components to try and shut down when some of the resources of the engine have already been destroyed.", which is what I am experiencing. I just can't see which resources I'm whacking.

Thanks, Peter

Peter


I've had similar (not the same but close) problems before and it came down to components the tables were connected to and events. I had to introduce a global variable AppClosing to detect what was going on and exit some events.

Roy Lambert [Team Elevate]

Peter,

<< It would appear so, but as they are components in a DataModule, how can I
control their destruction? >>

You shouldn't have to.

Can you send me your data module that causes this problem ?  I can pop it
into a test application here and see what the issue is.

I suspect that the issue is the component creation order on the data module,
and that the data module is trying to free the engine component before the
session component, or something similar.

--
Tim Young
Elevate Software
www.elevatesoft.com