Refactor locking mechanism for compatibility with .NET 9.0+ and remove obsolete package reference

Author: alex-jitbit

FastCache/FastCache.cs

@@ -19,7 +19,11 @@ public class FastCache<TKey, TValue> : IEnumerable<KeyValuePair<TKey, TValue>>,
 	{
 		private readonly ConcurrentDictionary<TKey, TtlValue> _dict = new();
 
+#if NET9_0_OR_GREATER
 		private readonly Lock _lock = new();
+#else
+		private readonly object _lock = new();
+#endif
 		private readonly Timer _cleanUpTimer;
 		private readonly EvictionCallback _itemEvicted;
 
@@ -66,7 +70,11 @@ await FastCacheStatics.GlobalStaticLock.WaitAsync()
 		public void EvictExpired()
 		{
 			//Eviction already started by another thread? forget it, lets move on
+#if NET9_0_OR_GREATER
 			if (_lock.TryEnter()) //use the new System.Threading.Lock class for faster locking in .NET9+
+#else
+			if (Monitor.TryEnter(_lock))
+#endif
 			{
 				List<TKey> evictedKeys = null; // Batch eviction callbacks
 				try
@@ -91,7 +99,11 @@ public void EvictExpired()
 				}
 				finally
 				{
-                    _lock.Exit();
+#if NET9_0_OR_GREATER
+					_lock.Exit();
+#else
+					Monitor.Exit(_lock);
+#endif
 				}
 
 				// Trigger batched eviction callbacks outside the loop to prevent flooding the thread pool

FastCache/FastCache.csproj

@@ -28,11 +28,4 @@
     </None>
   </ItemGroup>
 
-  <ItemGroup>
-    <PackageReference Condition="!$([MSBuild]::IsTargetFrameworkCompatible('$(TargetFramework)', 'net9.0'))" Include="Backport.System.Threading.Lock" Version="3.1.5">
-      <PrivateAssets>all</PrivateAssets>
-      <IncludeAssets>analyzers</IncludeAssets>
-    </PackageReference>
-  </ItemGroup>
-
 </Project>