[英]Sample serial port comms code using Async API in .net 4.5?
有人能指出我使用.net 4.5異步API(異步,等待,任務<>,ReadAsync等)進行串行通信的工作示例嗎?
我試圖調整現有的事件驅動的串行樣本,並且得到各種可怕的行為 - “其他應用程序使用的端口”錯誤,VS2013調試器拋出異常和鎖定 - 這通常需要PC重啟才能從中恢復。
編輯
我從頭開始編寫自己的樣本。 這是一個簡單的Winforms項目,它寫入Output窗口。 表單上的三個按鈕 - 打開端口,關閉端口和讀取數據。 ReadDataAsync方法調用SerialPort.BaseStream.ReadAsync。
截至目前,它將從端口讀取數據,但我遇到了使其變得強大的問題。
例如,如果我拔下串行電纜,打開端口,然后單擊Read Data兩次,我將得到一個System.IO.IOException(我有點期待),但我的應用程序停止響應。
更糟糕的是,當我嘗試停止我的程序時,VS2013會拋出一個“正在進行停止調試”對話框,該對話框永遠不會完成,我甚至無法從任務管理器中刪除VS. 每次發生這種情況都必須重啟我的電腦。
不好。
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.IO.Ports;
namespace WindowsFormsApplication1
{
public partial class Form1 : Form
{
private SerialPort _serialPort;
public Form1()
{
InitializeComponent();
}
private void openPortbutton_Click(object sender, EventArgs e)
{
try
{
if (_serialPort == null )
_serialPort = new SerialPort("COM3", 9600, Parity.None, 8, StopBits.One);
if (!_serialPort.IsOpen)
_serialPort.Open();
Console.Write("Open...");
}
catch(Exception ex)
{
ClosePort();
MessageBox.Show(ex.ToString());
}
}
private void closePortButton_Click(object sender, EventArgs e)
{
ClosePort();
}
private async void ReadDataButton_Click(object sender, EventArgs e)
{
try
{
await ReadDataAsync();
}
catch (Exception ex)
{
ClosePort();
MessageBox.Show(ex.ToString(), "ReadDataButton_Click");
}
}
private async Task ReadDataAsync()
{
byte[] buffer = new byte[4096];
Task<int> readStringTask = _serialPort.BaseStream.ReadAsync(buffer, 0, 100);
if (!readStringTask.IsCompleted)
Console.WriteLine("Waiting...");
int bytesRead = await readStringTask;
string data = Encoding.ASCII.GetString(buffer, 0, bytesRead);
Console.WriteLine(data);
}
private void ClosePort()
{
if (_serialPort == null) return;
if (_serialPort.IsOpen)
_serialPort.Close();
_serialPort.Dispose();
_serialPort = null;
Console.WriteLine("Close");
}
private void Form1_FormClosed(object sender, FormClosedEventArgs e)
{
ClosePort();
}
}
}
我使用TaskCompletionSource<>
來包裝SerialDataReceivedEvent
,類似這樣(未經測試):
using System;
using System.IO.Ports;
using System.Threading;
using System.Threading.Tasks;
class PortDataReceived
{
public static async Task ReadPort(SerialPort port, CancellationToken token)
{
while (true)
{
token.ThrowIfCancellationRequested();
await TaskExt.FromEvent<SerialDataReceivedEventHandler, SerialDataReceivedEventArgs>(
(complete, cancel, reject) => // get handler
(sender, args) => complete(args),
handler => // subscribe
port.DataReceived += handler,
handler => // unsubscribe
port.DataReceived -= handler,
(complete, cancel, reject) => // start the operation
{ if (port.BytesToRead != 0) complete(null); },
token);
Console.WriteLine("Received: " + port.ReadExisting());
}
}
public static void Main()
{
SerialPort port = new SerialPort("COM1");
port.BaudRate = 9600;
port.Parity = Parity.None;
port.StopBits = StopBits.One;
port.DataBits = 8;
port.Handshake = Handshake.None;
port.Open();
Console.WriteLine("Press Enter to stop...");
Console.WriteLine();
var cts = new CancellationTokenSource();
var task = ReadPort(port, cts.Token);
Console.ReadLine();
cts.Cancel();
try
{
task.Wait();
}
catch (AggregateException ex)
{
Console.WriteLine(ex.InnerException.Message);
}
port.Close();
}
// FromEvent<>, based on http://stackoverflow.com/a/22798789/1768303
public static class TaskExt
{
public static async Task<TEventArgs> FromEvent<TEventHandler, TEventArgs>(
Func<Action<TEventArgs>, Action, Action<Exception>, TEventHandler> getHandler,
Action<TEventHandler> subscribe,
Action<TEventHandler> unsubscribe,
Action<Action<TEventArgs>, Action, Action<Exception>> initiate,
CancellationToken token) where TEventHandler : class
{
var tcs = new TaskCompletionSource<TEventArgs>();
Action<TEventArgs> complete = (args) => tcs.TrySetResult(args);
Action cancel = () => tcs.TrySetCanceled();
Action<Exception> reject = (ex) => tcs.TrySetException(ex);
TEventHandler handler = getHandler(complete, cancel, reject);
subscribe(handler);
try
{
using (token.Register(() => tcs.TrySetCanceled()))
{
initiate(complete, cancel, reject);
return await tcs.Task;
}
}
finally
{
unsubscribe(handler);
}
}
}
}
從UI線程關閉SerialPort我遇到了類似的問題。 以下MSDN博客表明,這是由於UI線程和執行關閉的本機線程之間的死鎖。 http://blogs.msdn.com/b/bclteam/archive/2006/10/10/top-5-serialport-tips-_5b00_kim-hamilton_5d00_.aspx
把關閉放到一個單獨的任務中為我修復它。 (該方法在我的項目中的Protocol容器類中實現,並在單擊UI按鈕時調用,調用IDispose接口或關閉主窗口。)
public Task Close()
{
// Close the serial port in a new thread
Task closeTask = new Task(() =>
{
try
{
serialPort.Close();
}
catch (IOException e)
{
// Port was not open
throw e;
}
});
closeTask.Start();
return closeTask;
}
...然后在我的UI命令中......
// The serial stream is stopped in a different thread so that the UI does
// not get deadlocked with the stream waiting for events to complete.
await serialStream.Close();
我認為你的問題很多就是讓用戶觸發ReadDataAsync
,並允許在仍有讀取過程中觸發它(來自你的描述)。
正確的方法是在打開串口時啟動讀取,並在讀取的完成處理程序中啟動另一個(好吧,檢查完成是否不是由端口關閉引起的)。
無論如何,從串口同時讀取都是無用的,因為您無法控制傳入數據以完成例程的順序。
聲明:本站的技術帖子網頁,遵循CC BY-SA 4.0協議,如果您需要轉載,請注明本站網址或者原文地址。任何問題請咨詢:yoyou2525@163.com.