Lucene.Net.Util.Automaton: Fixed State class to initialize and trim m…

…ore efficiently (#295, #261). Fixes the performance of Lucene.Net.Util.Automaton.TestBasicOperations::TestEmptyLanguageConcatenate().
apache · Jun 30, 2020 · 867834b · 867834b
1 parent b66279b
commit 867834b
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Showing 2 changed files with 20 additions and 8 deletions.
diff --git a/Directory.Build.targets b/Directory.Build.targets
@@ -19,8 +19,10 @@
 
 -->
 <Project>
+  <!-- Features in .NET Standard and .NET Core only (no .NET Framework support) -->
   <PropertyGroup Condition=" $(TargetFramework.StartsWith('netstandard')) Or $(TargetFramework.StartsWith('netcoreapp')) ">
     <DefineConstants>$(DefineConstants);NETSTANDARD</DefineConstants>
+    <DefineConstants>$(DefineConstants);FEATURE_ARRAYEMPTY</DefineConstants>
     <DebugType>portable</DebugType>
   </PropertyGroup>
 
@@ -66,7 +68,11 @@
 
   </PropertyGroup>
 
-  <!-- Features in .NET Framework 4.5+ only -->
+  <!-- Features in .NET Framework 4.6+ only -->
+  <PropertyGroup Condition="$(TargetFramework.StartsWith('net46')) Or $(TargetFramework.StartsWith('net47')) Or $(TargetFramework.StartsWith('net48'))">
+    <DefineConstants>$(DefineConstants);FEATURE_ARRAYEMPTY</DefineConstants>
+  </PropertyGroup>
+
   <PropertyGroup Condition="$(TargetFramework.StartsWith('net4'))">
 
     <DefineConstants>$(DefineConstants);FEATURE_SERIALIZABLE_EXCEPTIONS</DefineConstants>

diff --git a/src/Lucene.Net/Util/Automaton/State.cs b/src/Lucene.Net/Util/Automaton/State.cs
@@ -48,11 +48,15 @@ public class State : IComparable<State>, IEquatable<State> // LUCENENET specific
         [SuppressMessage("Microsoft.Performance", "CA1819", Justification = "Lucene's design requires some writable array properties")]
         public Transition[] TransitionsArray
         {
-            get { return transitionsArray; }
+            get => transitionsArray;
             // LUCENENET NOTE: Setter removed because it is apparently not in use outside of this class
         }
-        private Transition[] transitionsArray;
-        internal int numTransitions; // LUCENENET NOTE: Made internal because we already have a public property for access
+#if FEATURE_ARRAYEMPTY
+        private Transition[] transitionsArray = Array.Empty<Transition>();
+#else
+        private Transition[] transitionsArray = new Transition[0];
+#endif
+        internal int numTransitions = 0;// LUCENENET NOTE: Made internal because we already have a public property for access
 
         internal int number;
 
@@ -64,7 +68,7 @@ public Transition[] TransitionsArray
         /// </summary>
         public State()
         {
-            ResetTransitions();
+            //ResetTransitions(); // LUCENENET: Let class initializer set these
             id = next_id++;
         }
 
@@ -73,7 +77,11 @@ public State()
         /// </summary>
         internal void ResetTransitions()
         {
+#if FEATURE_ARRAYEMPTY
+            transitionsArray = Array.Empty<Transition>();
+#else
             transitionsArray = new Transition[0];
+#endif
             numTransitions = 0;
         }
 
@@ -242,9 +250,7 @@ public virtual void TrimTransitionsArray()
         {
             if (numTransitions < transitionsArray.Length)
             {
-                Transition[] newArray = new Transition[numTransitions];
-                Array.Copy(transitionsArray, 0, newArray, 0, numTransitions);
-                transitionsArray = newArray;
+                Array.Resize(ref transitionsArray, numTransitions); // LUCENENET: Resize rather than copy
             }
         }