delphiaccess-violationjvcl

Sporadic Access Violation in TJvMemoryData.InternalSetFieldData

I am trying to resolve an access violation in a Delphi XE7 application which is occurs in this code, which is part of the Jedi VCL JvMemoryDataset component (current source at Github):

begin
  Data^ := Ord(Buffer <> nil);
  Inc(Data);
  if Buffer <> nil then
    Move(Buffer^, Data^, CalcFieldLen(Field.DataType, Field.Size)) <---------- AV here
  else
    FillChar(Data^, CalcFieldLen(Field.DataType, Field.Size), 0);
end;

The code sporadically causes a read access violation at address 04020111. Is there an obvious problem in this code? (CalcFieldLen might return 0, not sure if this is relevant here).

I have checked the current development version of JVCL and the Move call is the same as in my (older) local version.

It might be related to the issue https://issuetracker.delphi-jedi.org/view.php?id=6276

Related (with debugging suggestions): Sporadic Access Violation after porting from D2006 to XE5, doesn't happen in XP compatibility mode

Solution

  • The access violation disappeared after switching the FetchOptions.Unidirectional property of the FireDAC query to True. (The property default value is False)

    I guess this access violation was caused by memory corruption in low-memory situations. The FireDAC query was closed and re-opened (paging through a large dataset) so it happened when the amount of loaded data was high.