fix: concurrency conflict in HeaderCache.Count

Author: nan01ab

src/Neo/Ledger/HeaderCache.cs

@@ -55,12 +55,26 @@ public Header this[uint index]
         /// <summary>
         /// Gets the number of elements in the cache.
         /// </summary>
-        public int Count => headers.Count;
+        public int Count
+        {
+            get
+            {
+                readerWriterLock.EnterReadLock();
+                try
+                {
+                    return headers.Count;
+                }
+                finally
+                {
+                    readerWriterLock.ExitReadLock();
+                }
+            }
+        }
 
         /// <summary>
         /// Indicates whether the cache is full.
         /// </summary>
-        public bool Full => headers.Count >= 10000;
+        public bool Full => Count >= 10000;
 
         /// <summary>
         /// Gets the last <see cref="Header"/> in the cache. Or <see langword="null"/> if the cache is empty.

tests/Neo.UnitTests/Ledger/UT_HeaderCache.cs

@@ -0,0 +1,72 @@
+// Copyright (C) 2015-2024 The Neo Project.
+//
+// UT_HeaderCache.cs file belongs to the neo project and is free
+// software distributed under the MIT software license, see the
+// accompanying file LICENSE in the main directory of the
+// repository or http://www.opensource.org/licenses/mit-license.php
+// for more details.
+//
+// Redistribution and use in source and binary forms with or without
+// modifications are permitted.
+
+using FluentAssertions;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using Neo.Ledger;
+using Neo.Network.P2P.Payloads;
+using System;
+
+
+namespace Neo.UnitTests.Ledger
+{
+    [TestClass]
+    public class UT_HeaderCache
+    {
+
+        [TestMethod]
+        public void TestHeaderCache()
+        {
+            var cache = new HeaderCache();
+            var header = new Header();
+            header.Index = 1;
+            cache.Add(header);
+
+            var got = cache[1];
+            got.Should().NotBeNull();
+            got.Index.Should().Be(1);
+
+            var count = cache.Count;
+            count.Should().Be(1);
+
+            var full = cache.Full;
+            full.Should().BeFalse();
+
+            var last = cache.Last;
+            last.Should().NotBeNull();
+            last.Index.Should().Be(1);
+
+            got = cache[2];
+            got.Should().BeNull();
+
+            // enumerate
+            var enumerator = cache.GetEnumerator();
+            enumerator.MoveNext().Should().BeTrue();
+            enumerator.Current.Index.Should().Be(1);
+            enumerator.MoveNext().Should().BeFalse();
+
+            var removed = cache.TryRemoveFirst(out header);
+            removed.Should().BeTrue();
+
+            count = cache.Count;
+            count.Should().Be(0);
+
+            full = cache.Full;
+            full.Should().BeFalse();
+
+            last = cache.Last;
+            last.Should().BeNull();
+
+            got = cache[1];
+            got.Should().BeNull();
+        }
+    }
+}