线程在执行 SerialPort.Close() 时卡住

我遇到了一个问题，当我想关闭gsm终端的串行端口时，应用程序中的线程遇到死锁。这个问题在这里和这里都是众所周知的，但这些线程中的所有建议都没有帮助我。

/// <summary>
///     Closes the COM port, prevents reading and writing
/// </summary>
public void Stop()
{
    Debug.WriteLine("stop called");
    var block = true;
    var bgw = new BackgroundWorker
    {
        WorkerReportsProgress = false,
        WorkerSupportsCancellation = false,
    };
    bgw.DoWork += (s, e) =>
    {
        if (!CanAccessPort())
            return;
        try
        {
            _serialPort.DataReceived -= Read;
            GC.ReRegisterForFinalize(_serialPort.BaseStream);
            _serialPort.Close();
            _isOpen = false;
        }
        catch (Exception ex)
        {
            throw new Exception(PORTERROR, ex);
        }
    };
    bgw.RunWorkerCompleted += (s, e) =>
    {
        Debug.WriteLine("block is set to false =)");
        block = false;
    };
    bgw.RunWorkerAsync();
    while (block)
        Thread.Sleep(250);
}

上面的代码在执行_serialPort.Close()时永远运行。作为推荐的建议，我阅读了有关在单独线程中运行关闭操作的信息。我尝试了BackgroundWorker和Thread课程，但没有任何效果。按照另一个线程中的建议使用AutoResetEvent也不起作用。在关闭端口之前，我正在向其发送一些命令并收到几个结果，但它不会关闭。当我运行一个简单的命令行程序来启动端口、读取数据并尝试关闭它时，一切正常，甚至没有线程。

什么可能导致僵局？我没有做任何与GUI相关的事情，正如几乎所有其他答案中提到的。

此处为数据接收事件处理程序代码：

/// <summary>
///     Reads input from the COM interface and invokes the corresponding event depending on the input
/// </summary>
private void Read(object sender, SerialDataReceivedEventArgs e)
{
    var buffer = new char[1024];
    var counter = 0;
    _keepRunning = true;
     if (_timeout == null)
     {
        // timeout must be at least 3 seconds because when sending a sms to the terminal the receive notification (+CSDI) can be lost with less timeout 
        _timeout = new Timer(3000);
        _timeout.Elapsed += (s, ev) =>
        {
            _keepRunning = false;
            _timeout.Stop();
        };
    }
    _timeout.Start();
    // cancel condition: no more new data for 3 seconds or "OK"/"ERROR" found within the result
    while (_keepRunning)
    {
        var toRead = _serialPort.BytesToRead;
        if (toRead == 0)
        {
            Thread.Sleep(100);
            continue;
        }
        _timeout.Stop();
        _timeout.Start();
        counter += _serialPort.Read(buffer, counter, toRead);
        // ok or error found in result string
        var tmp = new string(buffer).Replace("'0", "").Trim();
        if (tmp.EndsWith("OK") || tmp.EndsWith("ERROR"))
        {
            _timeout.Stop();
            _keepRunning = false;
        }
    }
    // remove empty array slots from the back
    var nullTerminalCounter = 0;
    for (var i = buffer.Length - 1; i != 0; i--)
    {
        if (buffer[i] == ''0')
        {
            nullTerminalCounter++;
            continue;
        }
        break;
    }
    Array.Resize(ref buffer, buffer.Length - nullTerminalCounter);
    var str = new String(buffer).Trim();
    // result must be something different than incoming messages (+CMTI: '"MT'", 25)
    if (!((str.StartsWith("+CMTI") || str.StartsWith("+CSDI")) && str.Length < 20))
    {
        // when an incoming message is received, it does not belong to the command issued, so result has not yet arrived, hence port is still blocked!
        _isBlocked = false;
        Debug.WriteLine("port is unblocked");
    }

    var args = new CommandReturnValueReceivedEventArgs
    {
        ResultString = str
    };
    OnCommandReturnValueReceived(this, args);
}