type
  TSignatureVerificationThread2 = class(TThread)
  private
    FCS: TCriticalSection;
    FEvent: TEvent;
    FWorkList: TObjectList;
    function GetItem: TObject;
  protected
    procedure Execute; override;
    {$IFDEF USE_TERMINATEDSET}
    procedure TerminatedSet; override;
    {$ENDIF USE_TERMINATEDSET}
  public
    constructor Create;
    destructor Destroy; override;
    procedure WorkOnItem(const AItem: TObject);
  end;

implementation

{ TSignatureVerificationThread2 }

constructor TSignatureVerificationThread2.Create;
begin
// FreeOnTerminate:= True;
    FCS:= TCriticalSection.Create;
    FEvent:= TEvent.Create(nil, False, False, '');
    FWorkList:= TObjectList.Create(True);
    inherited Create(False);
end;

destructor TSignatureVerificationThread2.Destroy;
begin
{$IFDEF USE_TERMINATEDSET}
{$ELSE}
    Terminate;
    FEvent.SetEvent;
{$ENDIF USE_TERMINATEDSET}
    inherited;
    FWorkList.Free;
    FEvent.Free;
    FCS.Free;
end;

{$IFDEF USE_TERMINATEDSET}
procedure TSignatureVerificationThread2.TerminatedSet;
begin
    inherited;
    FEvent.SetEvent;
end;
{$ENDIF USE_TERMINATEDSET}

function TSignatureVerificationThread2.GetItem: TObject;
begin
    FCS.Enter;
    try
        Result:= FWorkList.Extract(FWorkList.First);
        if (FWorkList.Count > 0) then
            FEvent.SetEvent;
    finally
        FCS.Leave;
    end;
end;

procedure TSignatureVerificationThread2.Execute;
begin
    while NOT Terminated do begin
        FEvent.WaitFor(INFINITE);
        if NOT Terminated then begin
        end;
    end;
end;

procedure TSignatureVerificationThread2.WorkOnItem(const AItem: TObject);
begin
   FCS.Enter;
   try
       FWorkList.Add(AItem);
       FEvent.SetEvent;
   finally
       FCS.Leave;
   end;
end;

library FooBar;

{$IFDEF VERIFY_IN_BACKGROUND_THREAD}
var Glob_SigThread: TSignatureVerificationThread2;
    {$ENDIF VERIFY_IN_BACKGROUND_THREAD}

[...]

procedure DllEntryPoint(dwReason: DWORD);
begin
[...]
DLL_PROCESS_DETACH:
            begin
              {$IFDEF VERIFY_IN_BACKGROUND_THREAD}
              if Assigned(Glob_SigThread) then begin
                  Glob_SigThread.Terminate;
// Glob_SigThread.WaitFor;
              end;
              FreeAndNil(Glob_SigThread);
              {$ENDIF VERIFY_IN_BACKGROUND_THREAD}
           end;
[...]
end;