Perf: Add cached SqlReferenceCollection find delegate and context objects (#380)

Author: Wraith2

src/Microsoft.Data.SqlClient/netcore/src/Microsoft/Data/SqlClient/SqlInternalConnection.cs

@@ -567,17 +567,6 @@ internal SqlDataReader FindLiveReader(SqlCommand command)
             return reader;
         }
 
-        internal SqlCommand FindLiveCommand(TdsParserStateObject stateObj)
-        {
-            SqlCommand command = null;
-            SqlReferenceCollection referenceCollection = (SqlReferenceCollection)ReferenceCollection;
-            if (null != referenceCollection)
-            {
-                command = referenceCollection.FindLiveCommand(stateObj);
-            }
-            return command;
-        }
-
         abstract protected byte[] GetDTCAddress();
 
         static private byte[] GetTransactionCookie(Transaction transaction, byte[] whereAbouts)

src/Microsoft.Data.SqlClient/netcore/src/Microsoft/Data/SqlClient/SqlReferenceCollection.cs

@@ -2,18 +2,38 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System;
 using System.Diagnostics;
+using System.Threading;
 using Microsoft.Data.ProviderBase;
 
 namespace Microsoft.Data.SqlClient
 {
     sealed internal class SqlReferenceCollection : DbReferenceCollection
     {
+        private sealed class FindLiveReaderContext
+        {
+            public readonly Func<SqlDataReader, bool> Func;
+
+            private SqlCommand _command;
+
+            public FindLiveReaderContext() => Func = Predicate;
+
+            public void Setup(SqlCommand command) => _command = command;
+
+            public void Clear() => _command = null;
+
+            private bool Predicate(SqlDataReader reader) => (!reader.IsClosed) && (_command == reader.Command);
+        }
+
         internal const int DataReaderTag = 1;
         internal const int CommandTag = 2;
         internal const int BulkCopyTag = 3;
 
-        override public void Add(object value, int tag)
+        private readonly static Func<SqlDataReader, bool> s_hasOpenReaderFunc = HasOpenReaderPredicate;
+        private static FindLiveReaderContext s_cachedFindLiveReaderContext;
+
+        public override void Add(object value, int tag)
         {
             Debug.Assert(DataReaderTag == tag || CommandTag == tag || BulkCopyTag == tag, "unexpected tag?");
             Debug.Assert(DataReaderTag != tag || value is SqlDataReader, "tag doesn't match object type: SqlDataReader");
@@ -30,25 +50,24 @@ internal void Deactivate()
 
         internal SqlDataReader FindLiveReader(SqlCommand command)
         {
-            if (command == null)
+            if (command is null)
             {
                 // if null == command, will find first live datareader
-                return FindItem<SqlDataReader>(DataReaderTag, (dataReader) => (!dataReader.IsClosed));
+                return FindItem(DataReaderTag, s_hasOpenReaderFunc);
             }
             else
             {
                 // else will find live datareader associated with the command
-                return FindItem<SqlDataReader>(DataReaderTag, (dataReader) => ((!dataReader.IsClosed) && (command == dataReader.Command)));
+                FindLiveReaderContext context = Interlocked.Exchange(ref s_cachedFindLiveReaderContext, null) ?? new FindLiveReaderContext();
+                context.Setup(command);
+                SqlDataReader retval = FindItem(DataReaderTag, context.Func);
+                context.Clear();
+                Interlocked.CompareExchange(ref s_cachedFindLiveReaderContext, context, null);
+                return retval;
             }
         }
 
-        // Finds a SqlCommand associated with the given StateObject
-        internal SqlCommand FindLiveCommand(TdsParserStateObject stateObj)
-        {
-            return FindItem<SqlCommand>(CommandTag, (command) => (command.StateObject == stateObj));
-        }
-
-        override protected void NotifyItem(int message, int tag, object value)
+        protected override void NotifyItem(int message, int tag, object value)
         {
             Debug.Assert(0 == message, "unexpected message?");
             Debug.Assert(DataReaderTag == tag || CommandTag == tag || BulkCopyTag == tag, "unexpected tag?");
@@ -74,11 +93,13 @@ override protected void NotifyItem(int message, int tag, object value)
             }
         }
 
-        override public void Remove(object value)
+        public override void Remove(object value)
         {
             Debug.Assert(value is SqlDataReader || value is SqlCommand || value is SqlBulkCopy, "SqlReferenceCollection.Remove expected a SqlDataReader or SqlCommand or SqlBulkCopy");
 
             base.RemoveItem(value);
         }
+
+        private static bool HasOpenReaderPredicate(SqlDataReader reader) => !reader.IsClosed;
     }
 }