Вы можете сделать асинхронное поведение синхронным, выполнив что-то вроде этого и вызывая WaitForData() перед каждым чтением:
static SerialPort port;
static AutoResetEvent dataArrived = new AutoResetEvent(false);
static void Main(string[] args) {
port = new SerialPort(...);
port.DataReceived += new SerialDataReceivedEventHandler(port_DataReceived);
port.Open();
WaitForData(1000);
int data = port.ReadByte();
Console.WriteLine(data);
Console.ReadKey();
}
static void WaitForData(int millisecondsTimeout) {
dataArrived.WaitOne(millisecondsTimeout);
}
static void port_DataReceived(object sender, SerialDataReceivedEventArgs e) {
dataArrived.Set();
}
Этот ответ не такой «правильный», как поиск и решение основной проблемы, но может стать основой обходного пути.
Я видел некоторые странные вещи с классом SerialPort, включая поведение, которое вы описали. Помните, что событие DataReceived вызывается во вторичном потоке (см. MSDN ). Вы можете немного повысить производительность, используя семантику lock () с Monitor.Wait () и .Pulse (), как описано здесь
Если вы ленивый, вы также можете попробовать вставить строку Thread.Sleep () (например, 200 мс) прямо перед вызовом ReadByte, чтобы увидеть, если это что-то изменит. Кроме того, я мог бы поклясться, что однажды увидел случай, когда SerialPort, который блокировал ReadByte () в консольном приложении, был портирован в приложение WinForms без значительных изменений кода, и проблема исчезла. У меня не было возможности провести тщательное расследование, но вы могли убедиться, что вам больше повезло в WinForms, а затем устранить неполадки.
Этот ответ немного запаздывает, но я решил, что я перезвоню следующему человеку, который озадачен этим вопросом.
РЕДАКТИРОВАТЬ: Вот удобный WaitForBytes(count, timeout) метод расширения, который хорошо отфильтровывает описанное вами поведение "бесконечной блокировки".
Использование: port.WaitForBytes(1) для ожидания поступления 1 байта данных. Или для меньших накладных расходов используйте SerialPortWatcher.WaitForBytes(n).
using System;
using System.Diagnostics;
using System.IO.Ports;
using System.Threading;
public static class SerialPortExtensions {
/// <summary>
/// Wait for a specified number of bytes to arrive on the serial port, or until a timeout occurs.
/// </summary>
/// <param name="port">Serial port on which bytes are expected to arrive.</param>
/// <param name="count">Number of bytes expected.</param>
/// <param name="millisecondsTimeout">Maximum amount of time to wait.</param>
/// <exception cref="TimeoutException">Thrown if <paramref name="count"/> bytes are not received
/// within <paramref name="millisecondsTimeout"/> milliseconds.</exception>
/// <exception cref="ArgumentNullException">Thrown if <paramref name="port"/> is null.</exception>
/// <exception cref="ArgumentOutOfRangeException">Thrown if either <paramref name="count"/> or
/// <paramref name="millisecondsTimeout"/> is less than zero.</exception>
/// <exception cref="InvalidOperationException">Thrown if the serial port is closed.</exception>
/// <remarks>This extension method is intended only as an ad-hoc aid. If you're using it a lot,
/// then it's recommended for performance reasons to instead instantiate a
/// <see cref="SerialPortWatcher"/> instance for the lifetime of your SerialPort.</remarks>
public static void WaitForBytes(this SerialPort port, int count, int millisecondsTimeout) {
if (port == null) throw new ArgumentNullException("port");
if (port.BytesToRead >= count) return;
using (var watcher = new SerialPortWatcher(port)) {
watcher.WaitForBytes(count, millisecondsTimeout);
}
}
/// <summary>
/// Wait for a specified number of bytes to arrive on the serial port, or until a timeout occurs.
/// </summary>
/// <param name="port">Serial port on which bytes are expected to arrive.</param>
/// <param name="count">Number of bytes expected.</param>
/// <exception cref="ArgumentNullException">Thrown if <paramref name="port"/> is null.</exception>
/// <exception cref="ArgumentOutOfRangeException">Thrown if either <paramref name="count"/> or
/// <paramref name="millisecondsTimeout"/> is less than zero.</exception>
/// <exception cref="InvalidOperationException">Thrown if the serial port is closed.</exception>
/// <exception cref="TimeoutException">Thrown if <paramref name="count"/> bytes are not received
/// within the number of milliseconds specified in the <see cref="SerialPort.ReadTimeout"/> property
/// of <paramref name="port"/>.</exception>
/// <remarks>This extension method is intended only as an ad-hoc aid. If you're using it a lot,
/// then it's recommended for performance reasons to instead instantiate a
/// <see cref="SerialPortWatcher"/> instance for the lifetime of your SerialPort.</remarks>
public static void WaitForBytes(this SerialPort port, int count) {
if (port == null) throw new ArgumentNullException("port");
WaitForBytes(port, count, port.ReadTimeout);
}
}
/// <summary>
/// Watches for incoming bytes on a serial port and provides a reliable method to wait for a given
/// number of bytes in a synchronous communications algorithm.
/// </summary>
class SerialPortWatcher : IDisposable {
// This class works primarilly by watching for the SerialPort.DataReceived event. However, since
// that event is not guaranteed to fire, it is neccessary to also periodically poll for new data.
// The polling interval can be fine-tuned here. A higher number means less wasted CPU time, while
// a lower number decreases the maximum possible latency.
private const int POLL_MS = 30;
private AutoResetEvent dataArrived = new AutoResetEvent(false);
private SerialPort port;
public SerialPortWatcher(SerialPort port) {
if (port == null) throw new ArgumentNullException("port");
this.port = port;
this.port.DataReceived += new SerialDataReceivedEventHandler(port_DataReceived);
}
public void Dispose() {
if (port != null) {
port.DataReceived -= port_DataReceived;
port = null;
}
if (dataArrived != null) {
dataArrived.Dispose();
dataArrived = null;
}
}
void port_DataReceived(object sender, SerialDataReceivedEventArgs e) {
// This event will occur on a secondary thread. Signal the waiting thread (if any).
// Note: This handler could fire even after we are disposed.
// MSDN documentation describing DataReceived event:
// http://msdn.microsoft.com/en-us/library/system.io.ports.serialport.datareceived.aspx
// Links discussing thread safety and event handlers:
// /537689/sobytiya-c-i-bezopasnost-potokov
// http://www.codeproject.com/Articles/37474/Threadsafe-Events.aspx
// Note that we do not actually check the SerialPort.BytesToRead property here as it
// is not documented to be thread-safe.
if (dataArrived != null) dataArrived.Set();
}
/// <summary>
/// Blocks the current thread until the specified number of bytes have been received from the
/// serial port, or until a timeout occurs.
/// </summary>
/// <param name="count">Number of bytes expected.</param>
/// <param name="millisecondsTimeout">Maximum amount of time to wait.</param>
/// <exception cref="ArgumentOutOfRangeException">Thrown if either <paramref name="count"/> or
/// <paramref name="millisecondsTimeout"/> is less than zero.</exception>
/// <exception cref="InvalidOperationException">Thrown if the serial port is closed, or if this
/// <see cref="SerialPortWatcher"/> instance has been disposed.</exception>
/// <exception cref="TimeoutException">Thrown if <paramref name="count"/> bytes are not received
/// within the number of milliseconds specified in the <see cref="SerialPort.ReadTimeout"/> property
/// of <paramref name="port"/>.</exception>
public void WaitForBytes(int count, int millisecondsTimeout) {
if (count < 0) throw new ArgumentOutOfRangeException("count");
if (millisecondsTimeout < 0) throw new ArgumentOutOfRangeException("millisecondsTimeout");
if (port == null) throw new InvalidOperationException("SerialPortWatcher has been disposed.");
if (!port.IsOpen) throw new InvalidOperationException("Port is closed");
if (port.BytesToRead >= count) return;
DateTime expire = DateTime.Now.AddMilliseconds(millisecondsTimeout);
// Wait for the specified number of bytes to become available. This is done primarily by
// waiting for a signal from the thread which handles the DataReceived event. However, since
// that event isn't guaranteed to fire, we also poll for new data every POLL_MS milliseconds.
while (port.BytesToRead < count) {
if (DateTime.Now >= expire) {
throw new TimeoutException(String.Format(
"Timed out waiting for data from port {0}", port.PortName));
}
WaitForSignal();
}
}
// Timeout exceptions are expected to be thrown in this block of code, and are perfectly normal.
// A separate method is used so it can be marked with DebuggerNonUserCode, which will cause the
// debugger to ignore these exceptions (even if Thrown is checkmarked under Debug | Exceptions).
[DebuggerNonUserCode]
private void WaitForSignal() {
try {
dataArrived.WaitOne(POLL_MS);
} catch (TimeoutException) { }
}
}