fixes #134 IndexOutOfRangeException in LogLog.LogReceived (#135)

src/log4net.Tests/Util/LogLogTest.cs

@@ -19,8 +19,11 @@
  *
 */
 
+using System;
+using System.Collections;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Threading.Tasks;
 using log4net.Util;
 using NUnit.Framework;
 
@@ -73,33 +76,54 @@ public void LogReceivedAdapter()
     {
       var messages = new List<LogLog>();
 
-      using (new LogLog.LogReceivedAdapter(messages))
-      {
-        LogLog.Debug(GetType(), "Won't be recorded");
-        LogLog.Error(GetType(), "This will be recorded.");
-        LogLog.Error(GetType(), "This will be recorded.");
-      }
+      using var _ = new LogLog.LogReceivedAdapter(messages);
+      LogLog.Debug(GetType(), "Won't be recorded");
+      LogLog.Error(GetType(), "This will be recorded.");
+      LogLog.Error(GetType(), "This will be recorded.");
 
       Assert.AreEqual(2, messages.Count);
     }
-  }
-
-  public class TraceListenerCounter : TraceListener
-  {
-    public override void Write(string? message)
+
+    /// <summary>
+    /// Tests multi threaded calls to <see cref="LogLog.OnLogReceived"/>
+    /// </summary>
+    [Test]
+    public void LogReceivedAdapterThreading()
     {
-      Count++;
+      for (int i = 0; i < 1000; i++)
+      {
+        LogReceivedAdapterThreadingCore(i);
+      }
     }
 
-    public override void WriteLine(string? message)
+    private void LogReceivedAdapterThreadingCore(int seed)
     {
-      Write(message);
+      var messages = new List<LogLog>(1);
+      var syncRoot = ((ICollection)messages).SyncRoot;
+      var random = new Random(seed);
+      using var _ = new LogLog.LogReceivedAdapter(messages);
+      Parallel.For(0, 10, i =>
+      {
+        if (random.Next(10) > 8)
+        {
+          lock (syncRoot)
+          {
+            messages.Clear();
+            messages.Capacity = 1;
+          }
+        }
+        LogLog.Warn(GetType(), messages.Capacity.ToString() + ' ' + messages.Count);
+      });
     }
+  }
 
-    public void Reset()
-    {
-      Count = 0;
-    }
+  internal sealed class TraceListenerCounter : TraceListener
+  {
+    public override void Write(string? message) => Count++;
+
+    public override void WriteLine(string? message) => Write(message);
+
+    public void Reset() => Count = 0;
 
     public int Count { get; private set; }
   }

src/log4net/Util/LogLog.cs

@@ -98,10 +98,7 @@ public sealed class LogLog
     /// sent to Console.Out and Trace.Write.
     /// </summary>
     /// <returns></returns>
-    public override string ToString()
-    {
-      return Prefix + Source.Name + ": " + Message;
-    }
+    public override string ToString() => $"{Prefix}{Source.Name}: {Message}";
 
     /// <summary>
     /// Initializes a new instance of the <see cref="LogLog" /> class. 
@@ -522,7 +519,10 @@ public LogReceivedAdapter(List<LogLog> items)
 
       void LogLog_LogReceived(object? source, LogReceivedEventArgs e)
       {
-        Items.Add(e.LogLog);
+        lock (((ICollection)Items).SyncRoot)
+        {
+          Items.Add(e.LogLog);
+        }
       }
 
       /// <summary>