Merge pull request #1671 from sharwell/weakreference

Author: sharwell

StyleCop.Analyzers/StyleCop.Analyzers/AnalyzerExtensions.cs

@@ -5,7 +5,6 @@ namespace StyleCop.Analyzers
 {
     using System;
     using System.Collections.Concurrent;
-    using System.Runtime.CompilerServices;
     using System.Threading;
     using Microsoft.CodeAnalysis;
     using Microsoft.CodeAnalysis.Diagnostics;
@@ -22,8 +21,8 @@ internal static class AnalyzerExtensions
         /// This allows many analyzers that run on every token in the file to avoid checking
         /// the same state in the document repeatedly.
         /// </remarks>
-        private static readonly ConditionalWeakTable<Compilation, ConcurrentDictionary<SyntaxTree, bool>> GeneratedHeaderCache
-            = new ConditionalWeakTable<Compilation, ConcurrentDictionary<SyntaxTree, bool>>();
+        private static Tuple<WeakReference<Compilation>, ConcurrentDictionary<SyntaxTree, bool>> generatedHeaderCache
+            = Tuple.Create(new WeakReference<Compilation>(null), default(ConcurrentDictionary<SyntaxTree, bool>));
 
         /// <summary>
         /// Register an action to be executed at completion of parsing of a code document. A syntax tree action reports
@@ -35,7 +34,7 @@ private static readonly ConditionalWeakTable<Compilation, ConcurrentDictionary<S
         public static void RegisterSyntaxTreeActionHonorExclusions(this CompilationStartAnalysisContext context, Action<SyntaxTreeAnalysisContext> action)
         {
             Compilation compilation = context.Compilation;
-            ConcurrentDictionary<SyntaxTree, bool> cache = GeneratedHeaderCache.GetOrCreateValue(compilation);
+            ConcurrentDictionary<SyntaxTree, bool> cache = GetOrCreateGeneratedDocumentCache(compilation);
 
             context.RegisterSyntaxTreeAction(
                 c =>
@@ -53,6 +52,40 @@ public static void RegisterSyntaxTreeActionHonorExclusions(this CompilationStart
                 });
         }
 
+        /// <summary>
+        /// Gets or creates a cache which can be used with <see cref="GeneratedCodeAnalysisExtensions"/> methods to
+        /// efficiently determine whether or not a source file is considered generated.
+        /// </summary>
+        /// <param name="compilation">The compilation which the cache applies to.</param>
+        /// <returns>A cache which tracks the syntax trees in a compilation which are considered generated.</returns>
+        public static ConcurrentDictionary<SyntaxTree, bool> GetOrCreateGeneratedDocumentCache(this Compilation compilation)
+        {
+            var headerCache = generatedHeaderCache;
+
+            Compilation cachedCompilation;
+            if (!headerCache.Item1.TryGetTarget(out cachedCompilation) || cachedCompilation != compilation)
+            {
+                var replacementCache = Tuple.Create(new WeakReference<Compilation>(compilation), new ConcurrentDictionary<SyntaxTree, bool>());
+                while (true)
+                {
+                    var prior = Interlocked.CompareExchange(ref generatedHeaderCache, replacementCache, headerCache);
+                    if (prior == headerCache)
+                    {
+                        headerCache = replacementCache;
+                        break;
+                    }
+
+                    headerCache = prior;
+                    if (headerCache.Item1.TryGetTarget(out cachedCompilation) && cachedCompilation == compilation)
+                    {
+                        break;
+                    }
+                }
+            }
+
+            return headerCache.Item2;
+        }
+
         /// <summary>
         /// Register an action to be executed at completion of semantic analysis of a <see cref="SyntaxNode"/> with an
         /// appropriate kind. A syntax node action can report diagnostics about a <see cref="SyntaxNode"/>, and can also
@@ -70,7 +103,7 @@ public static void RegisterSyntaxNodeActionHonorExclusions<TLanguageKindEnum>(th
             where TLanguageKindEnum : struct
         {
             Compilation compilation = context.Compilation;
-            ConcurrentDictionary<SyntaxTree, bool> cache = GeneratedHeaderCache.GetOrCreateValue(compilation);
+            ConcurrentDictionary<SyntaxTree, bool> cache = GetOrCreateGeneratedDocumentCache(compilation);
 
             context.RegisterSyntaxNodeAction(
                 c =>
@@ -88,36 +121,5 @@ public static void RegisterSyntaxNodeActionHonorExclusions<TLanguageKindEnum>(th
                 },
                 syntaxKinds);
         }
-
-        /// <summary>
-        /// Checks whether the given document is auto generated by a tool (based on filename or comment header).
-        /// </summary>
-        /// <remarks>
-        /// <para>The exact conditions used to identify generated code are subject to change in future releases. The
-        /// current algorithm uses the following checks.</para>
-        /// <para>Code is considered generated if it meets any of the following conditions.</para>
-        /// <list type="bullet">
-        /// <item>The code is contained in a file which starts with a comment containing the text
-        /// <c>&lt;auto-generated</c>.</item>
-        /// <item>The code is contained in a file with a name matching certain patterns (case-insensitive):
-        /// <list type="bullet">
-        /// <item>*.designer.cs</item>
-        /// </list>
-        /// </item>
-        /// </list>
-        /// </remarks>
-        /// <param name="tree">The syntax tree to examine.</param>
-        /// <param name="compilation">The <see cref="Compilation"/> containing the specified <paramref name="tree"/>.</param>
-        /// <param name="cancellationToken">The <see cref="CancellationToken"/> that the task will observe.</param>
-        /// <returns>
-        /// <para><see langword="true"/> if <paramref name="tree"/> is located in generated code; otherwise,
-        /// <see langword="false"/>. If <paramref name="tree"/> is <see langword="null"/>, this method returns
-        /// <see langword="false"/>.</para>
-        /// </returns>
-        public static bool IsGeneratedDocument(this SyntaxTree tree, Compilation compilation, CancellationToken cancellationToken)
-        {
-            ConcurrentDictionary<SyntaxTree, bool> cache = GeneratedHeaderCache.GetOrCreateValue(compilation);
-            return tree.IsGeneratedDocument(cache, cancellationToken);
-        }
     }
 }