Prevent Access Violation inside PacketHandler (#344)

Author: kayoub5

SharpPcap/LibPcap/PcapDevice.cs

@@ -21,6 +21,7 @@ You should have received a copy of the GNU Lesser General Public License
 using System;
 using System.Collections.Generic;
 using System.ComponentModel;
+using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 
 namespace SharpPcap.LibPcap
@@ -279,12 +280,35 @@ public int GetNextPacketPointers(ref IntPtr header, ref IntPtr data)
         /// </summary>
         protected virtual void PacketHandler(IntPtr param, IntPtr /* pcap_pkthdr* */ header, IntPtr data)
         {
-            unsafe
+            var handle = Handle;
+            var gotRef = false;
+            try
             {
-                var pcapHeader = PcapHeader.FromPointer(header);
-                var dataSpan = new Span<byte>(data.ToPointer(), (int)pcapHeader.CaptureLength);
-
-                SendPacketArrivalEvent(pcapHeader, dataSpan);
+                // Make sure that handle does not get closed until this function is done
+                // See https://github.com/chmorgan/sharppcap/issues/343
+                handle.DangerousAddRef(ref gotRef);
+                if (!gotRef)
+                {
+                    return;
+                }
+                unsafe
+                {
+                    var pcapHeader = PcapHeader.FromPointer(header);
+                    var dataSpan = new Span<byte>(data.ToPointer(), (int)pcapHeader.CaptureLength);
+                    SendPacketArrivalEvent(pcapHeader, dataSpan);
+                }
+            }
+            catch (ObjectDisposedException)
+            {
+                // If Dispose was called in another thread, DangerousAddRef will throw this
+                // Ignore
+            }
+            finally
+            {
+                if (gotRef)
+                {
+                    handle.DangerousRelease();
+                }
             }
         }