External SIGFPE from TSQLQuery
lazarus / 16-Databases

----------------------------------------------------------------------
cov · 2013-07-23 06:12

Hi,

This may, or may not be related to this thread, but I'm getting an
external SIGFPE on my program when I do a SQLQuery.Close;

Code: [Select]  ID: string;
  b: TStream;
begin
  ID:=Form_DB.Datasource1.DataSet.FieldByName('ID').Value;
  SQLQuery1.Close;
  SQLQuery1.SQL.Text:='SELECT * FROM PREVIEWS WHERE ID='+ID;
  SQLQuery1.Open;
  if SQLQuery1.IsEmpty then
  begin
    getODDrawing(ID);
    SQLQuery1.Close; //<--- SIGFPE Here
  end;
end;

procedure TForm_DB.getODDrawing(ID: String);
var
  BlkHandle: String;
  R: TRect;
  strm: Tstream;
begin
  if BlobList=nil then BlobList:= TStringList.Create;//<---- BlobList
is global TStringList
  currentRecord:=ID;
  SQLQuery1.Close;
  SQLQuery1.SQL.Text:='SELECT PATHID,HANDLE FROM DWGMAP WHERE
FIELDID='+ID;
  SQLQuery1.Open;
  ID:=SQLQuery1.FieldByName('PATHID').AsString;
  BlkHandle:=SQLQuery1.FieldByName('HANDLE').AsString;
  SQLQuery1.Close;
  SQLQuery1.SQL.Text:='SELECT ACCESSED FROM PATHS WHERE ID='+ID;
  SQLQuery1.Open;
  ID:=SQLQuery1.FieldByName('ACCESSED').AsString;
  SQLQuery1.Close;
  SQLQuery1.SQL.Text:='SELECT ODDRAWING FROM USERSACCESS WHERE
ID='+ID;
  SQLQuery1.Open;
  strm:=SQLQuery1.CreateBlobStream(SQLQuery1.Fields[0],bmRead);
  BlobList.LoadFromStream(strm);
  unit_display.showOD(BlkHandle);
  R:=Rect(0,0,ImageWidth,ImageHeight);
  Image1.Canvas.CopyRect(R,ImageBuffer.Canvas,R);
  Screen.Cursor:=crDefault;
  strm.Free;
end;                                       

If it's the first record then it works fine. But if it's the second
record (ie, another record has already been processed) then the SIGFPE
occurs. Possible problem with the BlobList?

The SIGFPE opens an Assembler window which contains the following
snippet:

Code: [Select]5AD7258E 3bc7                     cmp    %edi,%eax
5AD72590 897df8                   mov    %edi,-0x8(%ebp)
5AD72593 7409                     je     0x5ad7259e
5AD72595 844838                   test   %cl,0x38(%eax)
5AD72598 0f851bd60100             jne    0x5ad8fbb9
<UxTheme!GetThemeTextMetrics+8319>
5AD7259E 8b4508                   mov    0x8(%ebp),%eax
5AD725A1 d9e8                     fld1   <- Exception raised at
5AD725A1

The showOD() procedure steps through the blob list and draws on my
ImageBuffer canvas. There is quite a lot of calculation done as each
line in the BlobList contains a series of comma-separated points which
must be split into Doubles and then scaled to fit and then truncated
to integers before being rendered on the Imagebuffer canvas.

I realise that my coding is not all that elegant and my SQL is a
little clunky, but any suggestions would be welcome.

~ Dave

----------------------------------------------------------------------
exdatis · 2013-07-23 06:25

Try:
--
ID:=Form_DB.Datasource1.DataSet.FieldByName('ID').AsInteger;//also set
ID : Integer--var
---
SQLQuery1.Close;
//clear text
SQLQuery1.SQL.Clear;//clear current query

    SQLQuery1.SQL.Text:='SELECT * FROM PREVIEWS WHERE ID='+ID;
//For string fields: QuotedStr(value)

----------------------------------------------------------------------
cov · 2013-07-23 06:39

Thanks for the reply.

ID field is integer, so that is okay. The ID variable is a string, so
that should be alright too.

The SQLQuery1.SQL.Clear; doesn't really have any impact and the
Exception is raised at the same point.

----------------------------------------------------------------------
exdatis · 2013-07-23 06:43

ID : String
I still think it's a mistake, try to change(ID : Integer).
Regards
p.s. Clear query is just a good practice

----------------------------------------------------------------------
ludob · 2013-07-23 12:02

First, SIGFPE exceptions are raised on the next FPU instruction. So
the pointer you get is not the place were it went wrong. It went wrong
in the previous FPU instruction.  Second, UxTheme!GetThemeTextMetrics
is in an external dll. Delphi, and thus Freepascal, have a non
standard FPEMask. A lot of C libraries don't use exceptions to check
FPU problems but inspect the FPU status. Try changing the mask with
SetExceptionMask (http://www.freepascal.org/docs-
html/rtl/math/setexceptionmask.html) as early as possible in your
program.

----------------------------------------------------------------------
cov · 2013-07-23 13:05

Hi, ludob,

Can you point me to how to do that?

I'm sure you're right, there isn't really much to cause an exception
in the SQLQuery.

The drawing record is a List of points which is rendered onto an
imagebuffer. This is rendered on a TImage canvas and also placed into
the database as a bitmap.

This particular drawing record is rendered and the bitmap inserted
without error if it is selected first. If, however, it is selected
after another record has been rendered and inserted, then the
exception is generated.

----------------------------------------------------------------------
ludob · 2013-07-23 13:18

Code: [Select]uses  math;
...
 SetExceptionMask([exInvalidOp, exDenormalized, exZeroDivide,
exOverflow, exUnderflow, exPrecision])
That will turn off all FPU exceptions.

If you think there is something wrong in the FPC code, you can use the
$SAFEFPUEXCEPTIONS (http://www.freepascal.org/docs-
html/prog/progsu69.html ) directive. This will add a FWAIT after every
store of a FPU value to memory. Most FPC float and double operations
end with storing the result somewhere in memory so the outcome is that
the debugger stops on the correct FPC line. FWAIT is a nop for the FPU
but will cause an exception to be raised immediately instead of
somewhere down your code.  It is not done per default because it slows
down floating point operations a lot.

----------------------------------------------------------------------
BigChimp · 2013-07-24 05:55

Added info to
http://wiki.lazarus.freepascal.org/GDB_Debugger_Tips#SIGFPE
... couldn't find a better spot to put it...