关闭USB串行端口会使该端口不可用
关闭USB串行端口会使该端口不可用
提问于 2020-03-05 18:21:37
我的应用程序使用基于USB的串行端口来连接物理硬件设备。我可以打开任何有效的USB端口并与外部设备通信。但是，当我关闭连接时，USB端口在一段时间内处于某种不确定状态，在这段时间内，进一步尝试重新连接会导致"Access to port "COM--“is denied”错误。但是，几秒钟后，尝试重新连接成功。如何确定USB端口何时将再次支持新连接？
代码如下所示：
private void Setup(string Port)
{
bool ValidPort = false;
int CloseSleep = 10;
_PortName = Port;
_PortType = this;
string[] AvailablePorts = SerialPort.GetPortNames();
foreach(string aPort in AvailablePorts)
{
if (aPort == _PortName)
{
// The required port is listed in the list of available ports)
ValidPort = true;
break;
}
}
if (ValidPort)
{
try
{
if (_ThePort != null)
{
_ThePort.Close();
_ThePort.DataReceived -= ReceivedDataEventHandler;
while(CloseSleep-- > 0)
System.Threading.Thread.Sleep(100);
_ThePort.Dispose();
_ThePort = null;
}
}
catch (Exception ex)
{
EMS_Config_Tool.ModalDialog md = new EMS_Config_Tool.ModalDialog("Closing Port: " + ex.Message, "System Exception");
md.ShowDialog();
}
System.IO.Ports.SerialPort TheNewPort = new System.IO.Ports.SerialPort(Port, 38400);
// Setup the event handlers from Tx and Rx
Handler.DataOutEvent += CommsSender;
TheNewPort.DataReceived += ReceivedDataEventHandler;
TheNewPort.DataBits = 8;
TheNewPort.Parity = Parity.None;
TheNewPort.Handshake = System.IO.Ports.Handshake.None;
TheNewPort.StopBits = System.IO.Ports.StopBits.One;
// We will try 3 times to open the port, and report an error if we fail to open the port
try
{
TheNewPort.Open();
}
catch (Exception)
{
System.Threading.Thread.Sleep(1000);
try
{
TheNewPort.Open();
}
catch (Exception)
{
System.Threading.Thread.Sleep(1000);
try
{
TheNewPort.Open();
}
catch (Exception ex)
{
EMS_Config_Tool.ModalDialog md = new EMS_Config_Tool.ModalDialog("Opening Port: " + ex.Message, "System Exception");
return;
}
}
}最后一条catch语句是发出有关访问被拒绝的错误的地方。注意:我尝试重新打开端口3次并没有真正的帮助。如果我将端口放在原处大约5到10秒，然后重试调用Setup方法，它会立即成功。
回答 2
Stack Overflow用户
发布于 2020-03-05 22:51:52
正如@Neil所说，有很多问题。在我看来，最好的做法是把搜索放在一个循环中，一旦端口可以打开，它就会被打开。
我以前是这样做的：
public Task WaitingPort()
{
while (port is null)
{
port = CheckPort();
}
}
private SerialPort CheckPort()
{
string[] listPort = SerialPort.GetPortNames();
foreach(string namePort in listPort)
{
SerialPort port = new SerialPort(namePort, 9600);
if (!port.IsOpen)
{
try
{
port.Open();
port.ReadTimeout = 1500;
string data = port.Readline();
// I programmed my device to send an "A" until it receives
// "777" to be able to recognize it once opened
if (data.Substring(0, 1) == "A")
{
port.ReadTimeout = 200;
port.Write("777"); // to make it stop sending "A"
return port;
}
else
{
port.Close();
}
}
catch (Exception e1)
{
port.Close();
}
}
}
return null;
}当然，这只是一种模板，您必须对其进行整形才能使用
Stack Overflow用户
发布于 2020-03-06 19:48:12
我已经修改了我的代码，使用一个受约束的循环，让它有更好的工作机会，这是它通常会做的。我希望有一种更好的方法来做这件事，因为我倾向于有相当不耐烦的用户，如果他们必须等待5到10秒才能建立连接，他们就会发布缺陷报告……
// We will try several times to open the port, upto 10 times over 5 seconds, and report an error if we finally fail to open the port
try
{
TheNewPort.Open();
}
catch (Exception ex)
{
RetryOpenTimer.Interval = 500;
RetryCount = 10;
RetryOpenTimer.Elapsed += new System.Timers.ElapsedEventHandler(RetryOpenTimer_Elapsed);
WaitForOpen = true;
RetryOpenTimer.Start();
while (WaitForOpen && RetryCount > 0)
{
System.Threading.Thread.Sleep(500);
}
if (WaitForOpen)
{
EMS_Config_Tool.ModalDialog md = new EMS_Config_Tool.ModalDialog("Opening Port: " + ex.Message, "System Exception");
return;
}
}..。
void RetryOpenTimer_Elapsed(object sender, System.Timers.ElapsedEventArgs e)
{
RetryOpenTimer.Stop();
RetryOpenTimer.Elapsed -= RetryOpenTimer_Elapsed;
try
{
if (RetryCount-- > 0)
{
TheNewPort.Open();
WaitForOpen = false;
}
else
return;
}
catch (Exception)
{
RetryOpenTimer.Start();
RetryOpenTimer.Elapsed += RetryOpenTimer_Elapsed;
}
}页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/60543091
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