Fix for #844 (#845)

Bug fix to go in immediate patch release

Author: RichardIrons-neo4j

Neo4j.Driver/Neo4j.Driver.Tests/HomeDbCaching/HomeDbCacheTests.cs

@@ -0,0 +1,163 @@
+// Copyright (c) "Neo4j"
+// Neo4j Sweden AB [https://neo4j.com]
+// 
+// Licensed under the Apache License, Version 2.0 (the "License").
+// You may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// 
+//     http://www.apache.org/licenses/LICENSE-2.0
+// 
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+using System;
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using FluentAssertions;
+using Neo4j.Driver.Internal.HomeDbCaching;
+using Xunit;
+
+namespace Neo4j.Driver.Tests.HomeDbCaching;
+
+public class HomeDbCacheTests
+{
+    [Fact]
+    public void ShouldAddAndRetrieveCacheItem()
+    {
+        // Arrange
+        var cache = new HomeDbCache();
+        var key = new HomeDbCacheKey("test-key");
+        var databaseName = "testDatabase";
+
+        // Act
+        cache.AddOrUpdate(key, databaseName);
+        var found = cache.TryGetCached(key, out var retrievedValue);
+
+        // Assert
+        found.Should().BeTrue();
+        retrievedValue.Should().Be(databaseName);
+    }
+
+    [Fact]
+    public void ShouldUpdateCacheItem()
+    {
+        // Arrange
+        var cache = new HomeDbCache();
+        var key = new HomeDbCacheKey("test-key");
+        var initialDatabaseName = "initialDatabase";
+        var updatedDatabaseName = "updatedDatabase";
+
+        // Act
+        cache.AddOrUpdate(key, initialDatabaseName);
+        cache.AddOrUpdate(key, updatedDatabaseName);
+        var found = cache.TryGetCached(key, out var retrievedValue);
+
+        // Assert
+        found.Should().BeTrue();
+        retrievedValue.Should().Be(updatedDatabaseName);
+    }
+
+    [Fact]
+    public void ShouldReturnFalseIfKeyNotFound()
+    {
+        // Arrange
+        var cache = new HomeDbCache();
+        var key = new HomeDbCacheKey("test-key");
+
+        // Act
+        var found = cache.TryGetCached(key, out var retrievedValue);
+
+        // Assert
+        found.Should().BeFalse();
+        retrievedValue.Should().BeNull();
+    }
+
+    [Fact]
+    public void ShouldPurgeOldItemsWhenThresholdExceeded()
+    {
+        // Arrange
+        var cache = new HomeDbCache();
+        for (int i = 0; i < 10_001; i++)
+        {
+            var key = new HomeDbCacheKey($"test-key-{i}");
+            cache.AddOrUpdate(key, $"database-{i}");
+        }
+
+        // Act
+        var oldestKey = new HomeDbCacheKey("test-key-0");
+        var found = cache.TryGetCached(oldestKey, out var retrievedValue);
+
+        // Assert
+        found.Should().BeFalse();
+        retrievedValue.Should().BeNull();
+    }
+
+    [Fact]
+    public void ShouldMoveAccessedItemToFront()
+    {
+        // Arrange
+        var cache = new HomeDbCache();
+        var key1 = new HomeDbCacheKey("test-key-1");
+        var key2 = new HomeDbCacheKey("test-key-2");
+        cache.AddOrUpdate(key1, "database-1");
+        cache.AddOrUpdate(key2, "database-2");
+
+        // Act
+        cache.TryGetCached(key1, out _); // Access key1
+        cache.AddOrUpdate(new HomeDbCacheKey("test-key-3"), "database-3");
+
+        // Assert
+        cache.TryGetCached(key1, out var value1).Should().BeTrue();
+        value1.Should().Be("database-1");
+    }
+
+    [Fact]
+    public async Task ShouldBeThreadSafe()
+    {
+        // Arrange
+        var cache = new HomeDbCache();
+        var tasks = new List<Task>();
+        var random = new Random();
+
+        // Act
+        for (int i = 0; i < 4; i++)
+        {
+            var task = Task.Run(
+                () =>
+                {
+                    for (int j = 0; j < 250; j++)
+                    {
+                        var key = new HomeDbCacheKey($"key-{random.Next(0, 50)}");
+                        var value = $"database-{random.Next(0, 50)}";
+
+                        // Randomly perform one of the operations
+                        switch (random.Next(0, 3))
+                        {
+                            case 0: // Add or update
+                                cache.AddOrUpdate(key, value);
+                                break;
+
+                            case 1: // Try to retrieve
+                                cache.TryGetCached(key, out _);
+                                break;
+
+                            case 2: // Remove and re-add
+                                cache.AddOrUpdate(key, value);
+                                cache.TryGetCached(key, out _);
+                                break;
+                        }
+                    }
+                });
+
+            tasks.Add(task);
+        }
+
+        await Task.WhenAll(tasks);
+
+        // Assert
+        // If no exceptions are thrown, the test passes
+    }
+}

Neo4j.Driver/Neo4j.Driver/Internal/HomeDbCaching/HomeDbCache.cs

@@ -19,54 +19,62 @@ public CacheItem(HomeDbCacheKey key, string databaseName)
         }
     }
 
+    private readonly object _lock = new();
     private readonly LinkedList<CacheItem> _cachedItems = new();
     private readonly Dictionary<HomeDbCacheKey, LinkedListNode<CacheItem>> _cacheLookup = new();
 
     public bool TryGetCached(HomeDbCacheKey key, out string value)
     {
-        value = null;
-        var found = _cacheLookup.TryGetValue(key, out var node);
-        if (!found)
+        lock (_lock)
         {
-            return false;
-        }
-
-        _cachedItems.Remove(node);
-        _cachedItems.AddFirst(node);
-        value = node.Value.DatabaseName;
-        return true;
+            value = null;
+            var found = _cacheLookup.TryGetValue(key, out var node);
+            if (!found)
+            {
+                return false;
+            }
 
+            _cachedItems.Remove(node);
+            _cachedItems.AddFirst(node);
+            value = node.Value.DatabaseName;
+            return true;
+        }
     }
 
     public void AddOrUpdate(HomeDbCacheKey key, string value)
     {
-        LinkedListNode<CacheItem> node;
-        // if we already have an entry
-        if (_cacheLookup.TryGetValue(key, out node))
-        {
-            _cachedItems.Remove(node);
-        }
-        else
+        lock (_lock)
         {
-            node = new LinkedListNode<CacheItem>(new CacheItem(key, value));
-            _cacheLookup[key] = node;
-        }
+            // if we already have an entry
+            if (_cacheLookup.TryGetValue(key, out var node))
+            {
+                _cachedItems.Remove(node);
+            }
+            else
+            {
+                node = new LinkedListNode<CacheItem>(new CacheItem(key, value));
+                _cacheLookup[key] = node;
+            }
 
-        node.Value.DatabaseName = value;
-        _cachedItems.AddFirst(node);
-        PurgeOldItems();
+            node.Value.DatabaseName = value;
+            _cachedItems.AddFirst(node);
+            PurgeOldItems();
+        }
     }
 
     private void PurgeOldItems()
     {
-        if (_cachedItems.Count < PurgeThreshold)
+        lock (_lock)
         {
-            return;
-        }
+            if (_cachedItems.Count < PurgeThreshold)
+            {
+                return;
+            }
 
-        for (var i = 0; i < PurgeAmount; i++)
-        {
-            RemoveLastItem();
+            for (var i = 0; i < PurgeAmount; i++)
+            {
+                RemoveLastItem();
+            }
         }
     }