type
  TIOPort = class(TObject)
  private
    FPort: THandle;
  public
    constructor Create();
    destructor Destroy(); override;
    procedure PushBack(const AValue: Integer); inline;
    function PopFront(out AValue: Integer): Boolean; inline;
  end;
{ TIOPort }

constructor TIOPort.Create;
begin
  inherited Create;
  FPort := CreateIoCompletionPort(INVALID_HANDLE_VALUE, 0, 0, 0);
  if (FPort = 0) then
    RaiseLastOSError();
end;

destructor TIOPort.Destroy;
begin
  if FPort <> 0 then begin
    CloseHandle(FPort);
    FPort := 0;
  end;
  inherited Destroy;
end;

function TIOPort.PopFront(out AValue: Integer): Boolean;
var
  TmpBytes: DWORD;
  TmpOverlapped: POverlapped;
begin
  Result := GetQueuedCompletionStatus(FPort, TmpBytes, ULONG_PTR(AValue), TmpOverlapped, INFINITE);
end;

procedure TIOPort.PushBack(const AValue: Integer);
begin
  if (not PostQueuedCompletionStatus(FPort, 0, UIntPtr(AValue), nil)) then
    RaiseLastOSError();
end;