Limit of PostMessage message size?

Question

I'm sending a log message to the main form using this:

For send the message:

procedure LogMsg(Msg: string; Kind:TMsgType=msgNormal);
var
  p: pChar;
begin    
  case Kind of
    msgError: Msg := '[Error] ' + Msg;
    msgInformation: Msg := '# ' + Msg;
    msgExternal: Msg := 'Plugin: ' + Msg;
  end;//if

  GetMem(p, (Length(Msg) + 1)*SizeOf(Char));
  Move(Msg[1], p^, (Length(Msg)+ 1)*SizeOf(Char));

  PostMessage(Application.MainForm.Handle, WM_LOG_MESSAGE, 0, integer(p));
end;

And display it:

procedure TfrmMain.WMLog(var Message: TMessage);
var
  p: pChar;
  Lista:TStringList;
begin
  try
    p := pChar(Message.LParam);

    if EditLog.Lines.Count>100 then
    begin
      EditLog.Lines.Clear;
    end;//if

    Lista := TStringList.Create;
    try
      Lista.Delimiter := #10;
      Lista.text := p;
      EditLog.Lines.AddStrings(Lista);
    finally
      Lista.Free;
    end;//try

{$ifndef FPC}
    EditLog.GotoLineAndCenter( EditLog.Lines.Count );
{$endif}

    Freemem(p);
  except
    on E: Exception do
      EditLog.Lines.Add(E.Classname + ': ' + E.Message);
  end;//try
end;

This is for log the output from execute some python scripts.

However look like if the message string is too large, the process hang and is necesary kill the python process.

I was not aware that could exist a limit. PostMessage have a limit in the size of the data or could be something else?

This is with Delphi 2010.

EDIT: Sorry, I forget to show the type of msg. Is a String.

Answer 1

I thought you shouldn't use Move. Are you sure all characters are from the same length ?

UPDATE:

GetMem(p, (Length(Msg) + 1)*SizeOf(Char)); 
Move(Msg[1], p^, (Length(Msg)+ 1)*SizeOf(Char)); 

I never have used pChar's too much, but don't you have to append a #0 character to the Msg string before you do this. Delphi 2010 does not zero out memory when using GetMem.

Answer 2

I'm taking the other route than mghie here (whoes answer just magically completely and utterly non-magically disappeared on me :P), looking at your code I can only deduce you ARE sending data from within the same process.

You are simply passing a pointer through PostMessage, so there is no limit on message size. When you debug your code (you are debugging that piece of code, right?), on what line does it break? The assignment of .text?

Try assigning the pchar to a string first, and writing that string to a file. If that works, you have a direction to look into.

If that doesn't work, verify using the debugger the pointer is indeed pointing towards a string, and if that string is zero-terminated. From the code you posted, it looks like it is.