IBX, external SIGSEGV At address 1
lazarus / 16-Databases

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mobilevil · 2018-07-05 13:51

Hello,
Lazarus 1.8.4 64bit on Windows 10 pro 64bit
IBX SVN revision 238, latest. should be the same as 2.3.0 release.

I found that the application may crash when I close it if it is
running lazarus ide. as a standalone EXE it is fine.  I think I first
saw this problem after I updated to IBX 2.3.0. I think I was using IBX
2.2.0

Is there any problem with my code? or anyone seeing this kind of
problem? it feels like a race condition in transaction shut down code.

the crash happens at this line in FormClose event.
  self.IBDatabase1.DefaultTransaction.Active:=false;

procedure TForm1.FormCreate(Sender: TObject);
begin
  DateTimePicker1.Date:=now;
  DateTimePicker1Change(self);
end; 

procedure TForm1.IBDatabase1AfterConnect(Sender: TObject);
begin
  IBEvents1.RegisterEvents;
end;

procedure TForm1.IBEvents1EventAlert(Sender: TObject; EventName:
string;
  EventCount: longint; var CancelAlerts: Boolean);
begin
  DateTimePicker1Change(self);//reload data
end;        

procedure TForm1.DateTimePicker1Change(Sender: TObject);
begin
//simplified, there's a date condition based on a checkbox
  ibquery1.SQL.clear;
  ibquery2.SQL.clear;
  ibquery3.SQL.clear;
  ibquery1.SQL.Add('select something');
  ibquery2.SQL.Add('select something');
  ibquery3.SQL.Add('select something');

  ibquery1.close;
  ibquery1.open;
  ibquery2.close;
  ibquery2.open;
  ibquery3.close;
  ibquery3.open;

end;          
procedure TForm1.FormClose(Sender: TObject; var CloseAction:
TCloseAction);
begin
  ibquery1.close;
  ibquery2.close;
  ibquery3.close;
  ibevents1.UnRegisterEvents;
  self.IBDatabase1.DefaultTransaction.Active:=false;//crashing here
  self.IBDatabase1.Close();
end;

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tonyw · 2018-07-06 12:34

I would suggest removing the line

ibevents1.UnRegisterEvents;

In general, there is no need to explicitly call UnRegisterEvents
before you close a database connection, as this is done automatically.
Queries are also automatically closed and you can remove those lines
as well.

Event handling is also multi-threaded and when you close a transaction
you might see an event trigger if it was held back by transaction
isolation. This is the kind of circumstance where you might see a race
condition  and operating under the IDE will change the dynamics.

It would be interesting to know the exact line of code that the
exception fired on.

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mobilevil · 2018-07-08 11:04

oh I have tested just now, even without any closing of db/query/event,
the crash still happen when I close the application.

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egsuh · 2018-07-20 08:35

I meed SIGSEGV very frequently. Most of them happen when I access "NOT
created" object.
If this is the case, the error should have occurred because
transaction object is not defined. Would you check if you have a
TSQLTransaction within your program, and it is linked to IBDatabase1?

By the way don't we commit or rollback transactions as following?

SQLTransaction1.StartTransaction;
.....
SQLTransaction1.Commit;  or
SQLTransaction1.Rollback; 


I use transactions only in these ways. Please advise me if active :=
true/false is better.

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mobilevil · 2018-08-20 20:25

oh sorry I didn't notice your post.
the exception is a minor issue that only happens during program exit
and under debugger, so I ignored it for now. I should have rolled back
to the previous IBX and test though.

yes I have transaction object assigned, but it's TIBTransaction for
me. without it nothing will work.

I think both .active:=true or .open are fine, it's some funny ancient
decision made in Delphi 1 U think.