From 54edaee83fda7090aa0aa6200e65766cda3775a3 Mon Sep 17 00:00:00 2001
From: Ilya <darpa@yandex.ru>
Date: Fri, 1 Nov 2019 23:14:31 +0500
Subject: [PATCH] Improve the caching when creating new `Regex` instances
 (#10657)

---
 .../engine/lang/parserutils.cs                | 43 ++++++++++---------
 .../engine/regex.cs                           |  4 +-
 2 files changed, 24 insertions(+), 23 deletions(-)

diff --git a/src/System.Management.Automation/engine/lang/parserutils.cs b/src/System.Management.Automation/engine/lang/parserutils.cs
index 60d4711da3..e629a427b7 100644
--- a/src/System.Management.Automation/engine/lang/parserutils.cs
+++ b/src/System.Management.Automation/engine/lang/parserutils.cs
@@ -2,6 +2,7 @@
 // Licensed under the MIT License.
 
 using System.Collections;
+using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
@@ -9,10 +10,8 @@ using System.Management.Automation.Internal;
 using System.Management.Automation.Internal.Host;
 using System.Management.Automation.Language;
 using System.Management.Automation.Runspaces;
-using System.Reflection;
 using System.Runtime.CompilerServices;
 using System.Runtime.Serialization;
-using System.Text;
 using System.Text.RegularExpressions;
 
 using Dbg = System.Management.Automation.Diagnostics;
@@ -1347,35 +1346,37 @@ namespace System.Management.Automation
         }
 
         /// <summary>
-        /// Cache regular expressions...
+        /// Cache regular expressions.
         /// </summary>
         /// <param name="patternString">The string to find the pattern for.</param>
-        /// <param name="options">The options used to create the regex...</param>
-        /// <returns>A case-insensitive Regex...</returns>
+        /// <param name="options">The options used to create the regex.</param>
+        /// <returns>New or cached Regex.</returns>
         internal static Regex NewRegex(string patternString, RegexOptions options)
         {
-            if (options != RegexOptions.IgnoreCase)
-                return new Regex(patternString, options);
-
-            lock (s_regexCache)
+            var subordinateRegexCache = s_regexCache.GetOrAdd(options, s_subordinateRegexCacheCreationDelegate);
+            if (subordinateRegexCache.TryGetValue(patternString, out Regex result))
             {
-                Regex result;
-                if (s_regexCache.TryGetValue(patternString, out result))
+                return result;
+            }
+            else
+            {
+                if (subordinateRegexCache.Count > MaxRegexCache)
                 {
-                    return result;
-                }
-                else
-                {
-                    if (s_regexCache.Count > MaxRegexCache)
-                        s_regexCache.Clear();
-                    Regex re = new Regex(patternString, RegexOptions.IgnoreCase);
-                    s_regexCache.Add(patternString, re);
-                    return re;
+                    // TODO: it would be useful to get a notice (in telemetry?) if the cache is full.
+                    subordinateRegexCache.Clear();
                 }
+
+                var regex = new Regex(patternString, options);
+                return subordinateRegexCache.GetOrAdd(patternString, regex);
             }
         }
 
-        private static Dictionary<string, Regex> s_regexCache = new Dictionary<string, Regex>();
+        private static readonly ConcurrentDictionary<RegexOptions, ConcurrentDictionary<string, Regex>> s_regexCache =
+            new ConcurrentDictionary<RegexOptions, ConcurrentDictionary<string, Regex>>();
+
+        private static readonly Func<RegexOptions, ConcurrentDictionary<string, Regex>> s_subordinateRegexCacheCreationDelegate =
+            key => new ConcurrentDictionary<string, Regex>(StringComparer.Ordinal);
+
         private const int MaxRegexCache = 1000;
 
         /// <summary>
diff --git a/src/System.Management.Automation/engine/regex.cs b/src/System.Management.Automation/engine/regex.cs
index 71c6c8bac8..2c4ade7cb5 100644
--- a/src/System.Management.Automation/engine/regex.cs
+++ b/src/System.Management.Automation/engine/regex.cs
@@ -909,7 +909,7 @@ namespace System.Management.Automation
             WildcardPatternParser.Parse(wildcardPattern, parser);
             try
             {
-                return new Regex(parser._regexPattern.ToString(), parser._regexOptions);
+                return ParserOps.NewRegex(parser._regexPattern.ToString(), parser._regexOptions);
             }
             catch (ArgumentException)
             {
@@ -1258,7 +1258,7 @@ namespace System.Management.Automation
             protected override void EndBracketExpression()
             {
                 _bracketExpressionBuilder.Append(']');
-                Regex regex = new Regex(_bracketExpressionBuilder.ToString(), _regexOptions);
+                Regex regex = ParserOps.NewRegex(_bracketExpressionBuilder.ToString(), _regexOptions);
                 _patternElements.Add(new BracketExpressionElement(regex));
             }
         }