Avoid lazy initialization where internal display name fields are set to null

Author: mdh1418

src/libraries/System.Private.CoreLib/src/System/TimeZoneInfo.Win32.cs

@@ -154,8 +154,11 @@ private TimeZoneInfo(in TIME_ZONE_INFORMATION zone, bool dstDisabled)
 
             ValidateTimeZoneInfo(_id, _baseUtcOffset, _adjustmentRules, out _supportsDaylightSavingTime);
             _displayName = standardName;
+            _displayNameSet = true;
             _standardDisplayName = standardName;
+            _standardDisplayNameSet = true;
             _daylightDisplayName = zone.GetDaylightName();
+            _daylightDisplayNameSet = true;
         }
 
         /// <summary>

src/libraries/System.Private.CoreLib/src/System/TimeZoneInfo.cs

@@ -44,8 +44,11 @@ private enum TimeZoneInfoResult
         private const int MaxKeyLength = 255;
 
         private readonly string _id;
+        private bool _displayNameSet;
         private string? _displayName;
+        private bool _standardDisplayNameSet;
         private string? _standardDisplayName;
+        private bool _daylightDisplayNameSet;
         private string? _daylightDisplayName;
         private readonly TimeSpan _baseUtcOffset;
         private readonly bool _supportsDaylightSavingTime;
@@ -150,8 +153,11 @@ public string DisplayName
         {
             get
             {
-                if (_displayName == null)
+                if (_displayName == null && !_displayNameSet)
+                {
                     Interlocked.CompareExchange(ref _displayName, PopulateDisplayName(), null);
+                    _displayNameSet = true;
+                }
 
                 return _displayName ?? string.Empty;
             }
@@ -161,8 +167,11 @@ public string StandardName
         {
             get
             {
-                if (_standardDisplayName == null)
+                if (_standardDisplayName == null && !_standardDisplayNameSet)
+                {
                     Interlocked.CompareExchange(ref _standardDisplayName, PopulateStandardDisplayName(), null);
+                    _standardDisplayNameSet = true;
+                }
 
                 return _standardDisplayName ?? string.Empty;
             }
@@ -172,8 +181,11 @@ public string DaylightName
         {
             get
             {
-                if (_daylightDisplayName == null)
+                if (_daylightDisplayName == null && !_daylightDisplayNameSet)
+                {
                     Interlocked.CompareExchange(ref _daylightDisplayName, PopulateDaylightDisplayName(), null);
+                    _daylightDisplayNameSet = true;
+                }
 
                 return _daylightDisplayName ?? string.Empty;
             }
@@ -990,8 +1002,11 @@ private TimeZoneInfo(
             _id = id;
             _baseUtcOffset = baseUtcOffset;
             _displayName = displayName;
+            _displayNameSet = true;
             _standardDisplayName = standardDisplayName;
+            _standardDisplayNameSet = true;
             _daylightDisplayName = disableDaylightSavingTime ? null : daylightDisplayName;
+            _daylightDisplayNameSet = true;
             _supportsDaylightSavingTime = adjustmentRulesSupportDst && !disableDaylightSavingTime;
             _adjustmentRules = adjustmentRules;
 
@@ -1136,8 +1151,11 @@ private TimeZoneInfo(SerializationInfo info, StreamingContext context)
 
             _id = (string)info.GetValue("Id", typeof(string))!; // Do not rename (binary serialization)
             _displayName = (string?)info.GetValue("DisplayName", typeof(string)); // Do not rename (binary serialization)
+            _displayNameSet = true;
             _standardDisplayName = (string?)info.GetValue("StandardName", typeof(string)); // Do not rename (binary serialization)
+            _standardDisplayNameSet = true;
             _daylightDisplayName = (string?)info.GetValue("DaylightName", typeof(string)); // Do not rename (binary serialization)
+            _daylightDisplayNameSet = true;
             _baseUtcOffset = (TimeSpan)info.GetValue("BaseUtcOffset", typeof(TimeSpan))!; // Do not rename (binary serialization)
             _adjustmentRules = (AdjustmentRule[]?)info.GetValue("AdjustmentRules", typeof(AdjustmentRule[])); // Do not rename (binary serialization)
             _supportsDaylightSavingTime = (bool)info.GetValue("SupportsDaylightSavingTime", typeof(bool))!; // Do not rename (binary serialization)