tlmddock TLMDockPanelCloseAction: FastMM has detected an error during a free block scan operation.

Achim Herrmann

Compile the Docking demo in 64 bit with FASTMM4 option:

program pDockingDemo;
{$I LmdCmps.inc}

uses
  FastMM4,
  Forms,
  d_MainFormUnit in 'd_MainFormUnit.pas' {frmMain};

{$R *.res}

begin
  Application.Initialize;
  Application.MainFormOnTaskbar := True;
  Application.CreateForm(TfrmMain, frmMain);
  Application.Run;
end.

Start the demo and click File->NewTextFile. Close the "TextFile1.txt" panel by clicking on the close button of the panel.

Now close the application.

FastMM will now report an error:

FastMM has detected an error during a free block scan operation. FastMM detected that a block has been modified after being freed. (error is attached).

The error is caused by the DocClose procedure. When procedure is called then CloseAction is caHide. Whenever modifying the CloseAction then FastMM reports the error.

procedure TfrmMain.DocClose(Sender: TObject; var CloseAction: TLMDockPanelCloseAction);

begin
  CloseAction := caFree;
end;

Eugene Balabuev (LMD)

I've checked with FastMM5 and see no issues.

Achim Herrmann

Dear Eugene,

you are right. I can confirm: When using FastMM5, then no errors are reported using FullDebugMode.

Seems to be an artefact of FastMM4.

You can close this issue.

Many thanks for your help.