Question

This question might or might not solve my problem – but I hope to learn how Delphi/Windows can behave in a way which can cause this.

I have an application which uses a 3rd party component to load an Outlook .msg file.

In some cases (specific mails) the application freezes when calling SetLength (inside of the component, I have the source code).
This happens sometimes when setLength is called inside of a procedure which loads the properties from the file (stream). It happens the exact same place on the same mail – and can be reproduced every time.

Obviously the component does a lot of stuff and it is probably a sideeffect of some of this. However, the mails contains confidential data which I cannot send to the developer of the 3rd party component, so I cannot send it to him to debug it.

The program is running under windows XP on a domain.
The curious thing is that it only happens when the user running the program is not set to be administrator on the local machine.

ms := TMemoryStream.Create;
try
  WriteStorageToStream(SubStorage, ms);
  ApplyValue(ms, ms.Size)
finally
  ms.Free;
end;

procedure ApplyValue(Stream: TStream; brLen: Integer);
var
  s: AnsiString;
begin
  SetLength(s, brLen);          // this freezes it all. brLen=3512
  FillChar(s[1], brLen, #0);
  Stream.Read(s[1], brLen);
  Value := s;
end;

What WriteStorageToStream does exactly is unknown to me, but since we are not manipulating the stream and brLen has an integer value, I assume it’s irrelevant.

Answer 1

I’d say it was simple memory overwrite, causing a failure of the memory manager when the SetLength is called which then tries to use the memory management structures. The problem is in WriteStorageToStream(SubStorage, ms);

To find it, use the FastMM debug version with the memory overwrite detection options turned on.