From: Eric Erhardt <eric.erhardt@microsoft.com>
Date: Thu, 13 Apr 2017 20:21:58 +0000 (-0500)
Subject: Fix perf of DateTime.Now on Unix
X-Git-Tag: submit/tizen/20210909.063632~11030^2~7215^2~2
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=4cfbfdc580521753ec31b444317fba59ebbee0ae;p=platform%2Fupstream%2Fdotnet%2Fruntime.git

Fix perf of DateTime.Now on Unix

Profiling DateTime.Now on Unix shows that a lot of time is spent in GetPreviousAdjustmentRule and AdjustmentRule::Equals. Instead, it is safe to use ReferenceEquals, which increases the performance of DateTime.Now and other time zone operations on Unix.


Commit migrated from https://github.com/dotnet/coreclr/commit/3aec163d4a1431b89f6e1ec22d9b88c13b399a66
---

diff --git a/src/coreclr/src/mscorlib/src/System/TimeZoneInfo.cs b/src/coreclr/src/mscorlib/src/System/TimeZoneInfo.cs
index 29ea33a..0176c75 100644
--- a/src/coreclr/src/mscorlib/src/System/TimeZoneInfo.cs
+++ b/src/coreclr/src/mscorlib/src/System/TimeZoneInfo.cs
@@ -284,10 +284,16 @@ namespace System
         /// </summary>
         private AdjustmentRule GetPreviousAdjustmentRule(AdjustmentRule rule)
         {
+            Debug.Assert(rule.NoDaylightTransitions, "GetPreviousAdjustmentRule should only be used with NoDaylightTransitions rules.");
+
             AdjustmentRule result = rule;
             for (int i = 1; i < _adjustmentRules.Length; i++)
             {
-                if (rule.Equals(_adjustmentRules[i]))
+                // use ReferenceEquals here instead of AdjustmentRule.Equals because 
+                // ReferenceEquals is much faster. This is safe because all the callers
+                // of GetPreviousAdjustmentRule pass in a rule that was retrieved from
+                // _adjustmentRules.  A different approach will be needed if this ever changes.
+                if (ReferenceEquals(rule, _adjustmentRules[i]))
                 {
                     result = _adjustmentRules[i - 1];
                     break;