# 4498 TDBISAMEngine Can Experience AV During Shutdown

---

I'm seeing an AV error when destroying a session during shutdown of a web application.

The AV error came up here:

procedure TDBISAMEngineInstance.PutSessionNumber(Value: Integer);
begin
if (Value > -1) then
begin
OSEnterCriticalSection(FSessionSection);
try
FSessionNumbers[Value]:=False;
finally
OSLeaveCriticalSection(FSessionSection);
end;
end;
end;

Here is the call stack:

"   dbisamtb.TDBISAMEngineInstance.PutSessionNumber(3)
"   dbisamtb.TDBISAMEngine.PutSessionNumber(???)
"   dbisamtb.TDBISAMSession.Destroy
"   System.TObject.Free
"   GoCircDatabase.TGoCircDatabase.Destroy
"   System.TObject.Free
"   GoCircRequest.TGoCircRequest.Destroy
"   System.TObject.Free
"   WebModule.TWebModule1.Cleanup
"   WebModule.TWebModule1.WebModuleDestroy($4DC3150)
"   System.Classes.TDataModule.DoDestroy
"   System.Classes.TDataModule.BeforeDestruction
"   System._BeforeDestruction(???,???)
"   :004d3186 TDataModule.BeforeDestruction + $2A
"   Web.WebReq.TWebRequestHandler.Destroy
"   IdHTTPWebBrokerBridge.TIdHTTPWebBrokerBridgeRequestHandler.Destroy
"   System.TObject.Free
"   IdHTTPWebBrokerBridge.TIdHTTPWebBrokerBridgeRequestHandler.Destroy@
"   System.FinalizeUnits
"   System._Halt0
"   :0040ab05 @Halt0 + $AD