问串行端口和重叠I/O操作期间的错误处理

EN

function TSerialPort.Read(var pBuffer; const lBufferSize: Cardinal): Cardinal;
var
  lOverlapped: OVERLAPPED;
  lLastError: Cardinal;
  lEvent: TEvent;
begin
  lEvent := TEvent.Create(nil, True, False, '');
  try
    FillChar(lOverlapped, SizeOf(lOverlapped), 0);
    lOverlapped.hEvent := lEvent.Handle;

    if not ReadFile(FSerialPortHandle, pBuffer, lBufferSize, Result, @lOverlapped) then
    begin
      lLastError := GetLastError;
      if (lLastError <> ERROR_IO_PENDING) and (lLastError <> ERROR_SUCCESS) then
        raise Exception.Create(SysErrorMessage(lLastError));

      case lEvent.WaitFor(INFINITE) of
        wrSignaled:
          if not GetOverlappedResult(FSerialPortHandle, lOverlapped, Result, False) then
            raise Exception.Create(SysErrorMessage(GetLastError));

        wrError:
          begin
            lLastError := lEvent.LastError;
            //this is a call to Windows.CancelIo(FSerialPortHandle);
            if Self.CancelIO() then
              lEvent.WaitFor(INFINITE);
            raise Exception.Create(SysErrorMessage(lLastError));
          end;
      end;
    end;
  finally
    FreeAndNil(lEvent);
  end;
end;