Avoid SerialPort IOLoop when there's no event handlers (#102829)

Author: MrJul

src/libraries/System.IO.Ports/src/System/IO/Ports/SerialPort.cs

@@ -64,12 +64,14 @@ public partial class SerialPort : Component
         private char[] _singleCharBuffer;
 
         public event SerialErrorReceivedEventHandler ErrorReceived;
-        public event SerialPinChangedEventHandler PinChanged;
 
-        // handler for the underlying stream
+        // handlers for the underlying stream
         private readonly SerialDataReceivedEventHandler _dataReceivedHandler;
+        private readonly SerialPinChangedEventHandler _pinChangedHandler;
 
         private SerialDataReceivedEventHandler _dataReceived;
+        private SerialPinChangedEventHandler _pinChanged;
+
         public event SerialDataReceivedEventHandler DataReceived
         {
             add
@@ -99,6 +101,35 @@ public event SerialDataReceivedEventHandler DataReceived
             }
         }
 
+        public event SerialPinChangedEventHandler PinChanged
+        {
+            add
+            {
+                bool wasNull = _pinChanged == null;
+                _pinChanged += value;
+
+                if (wasNull)
+                {
+                    if (_internalSerialStream != null)
+                    {
+                        _internalSerialStream.PinChanged += _pinChangedHandler;
+                    }
+                }
+            }
+            remove
+            {
+                _pinChanged -= value;
+
+                if (_pinChanged == null)
+                {
+                    if (_internalSerialStream != null)
+                    {
+                        _internalSerialStream.PinChanged -= _pinChangedHandler;
+                    }
+                }
+            }
+        }
+
         //--- component properties---------------*
 
         // ---- SECTION: public properties --------------*
@@ -511,6 +542,7 @@ public int WriteTimeout
         public SerialPort()
         {
             _dataReceivedHandler = new SerialDataReceivedEventHandler(CatchReceivedEvents);
+            _pinChangedHandler = CatchPinChangedEvents;
         }
 
         public SerialPort(IContainer container) : this()
@@ -563,6 +595,7 @@ protected override void Dispose(bool disposing)
                 if (IsOpen)
                 {
                     _internalSerialStream.DataReceived -= _dataReceivedHandler;
+                    _internalSerialStream.PinChanged -= _pinChangedHandler;
                     _internalSerialStream.Flush();
                     _internalSerialStream.Close();
                     _internalSerialStream = null;
@@ -601,7 +634,11 @@ public void Open()
             _internalSerialStream.SetBufferSizes(_readBufferSize, _writeBufferSize);
 
             _internalSerialStream.ErrorReceived += new SerialErrorReceivedEventHandler(CatchErrorEvents);
-            _internalSerialStream.PinChanged += new SerialPinChangedEventHandler(CatchPinChangedEvents);
+
+            if (_pinChanged != null)
+            {
+                _internalSerialStream.PinChanged += _pinChangedHandler;
+            }
 
             if (_dataReceived != null)
             {
@@ -1213,7 +1250,7 @@ private void CatchErrorEvents(object src, SerialErrorReceivedEventArgs e)
 
         private void CatchPinChangedEvents(object src, SerialPinChangedEventArgs e)
         {
-            SerialPinChangedEventHandler eventHandler = PinChanged;
+            SerialPinChangedEventHandler eventHandler = _pinChanged;
             SerialStream stream = _internalSerialStream;
 
             if ((eventHandler != null) && (stream != null))