Introducing TimeZoneInfo.GetSystemTimeZones(bool skipSorting)

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

@@ -131,7 +131,7 @@ private static unsafe void GetDisplayName(string timeZoneId, Interop.Globalizati
  // Helper function that builds the value backing the DisplayName field from globalization data.
  private static void GetFullValueForDisplayNameField(string timeZoneId, TimeSpan baseUtcOffset, ref string? displayName)
  {
- // There are a few diffent ways we might show the display name depending on the data.
+ // There are a few different ways we might show the display name depending on the data.
  // The algorithm used below should avoid duplicating the same words while still achieving the
  // goal of providing a unique, discoverable, and intuitive name.
 

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

@@ -131,6 +131,7 @@ public DateTimeKind GetCorrespondingKind(TimeZoneInfo? timeZone)
 
  public Dictionary<string, TimeZoneInfo>? _systemTimeZones;
  public ReadOnlyCollection<TimeZoneInfo>? _readOnlySystemTimeZones;
+ public ReadOnlyCollection<TimeZoneInfo>? _readOnlyUnsortedSystemTimeZones;
  public Dictionary<string, TimeZoneInfo>? _timeZonesUsingAlternativeIds;
  public bool _allSystemTimeZonesRead;
  }
@@ -880,41 +881,62 @@ public static TimeZoneInfo FromSerializedString(string source)
  /// <see cref="DisplayName"/>.
  /// This method does *not* throw TimeZoneNotFoundException or InvalidTimeZoneException.
  /// </summary>
- public static ReadOnlyCollection<TimeZoneInfo> GetSystemTimeZones()
+ public static ReadOnlyCollection<TimeZoneInfo> GetSystemTimeZones() => GetSystemTimeZones(skipSorting: false);
+
+ /// <summary>
+ /// Returns a <see cref="ReadOnlyCollection{TimeZoneInfo}"/> containing all valid TimeZone's from the local machine.
+ /// This method does *not* throw TimeZoneNotFoundException or InvalidTimeZoneException.
+ /// </summary>
+ /// <param name="skipSorting">If true, The collection returned may not necessarily be sorted.</param>
+ /// <remarks>By setting the skipSorting parameter to true, the method will attempt to avoid sorting the returned collection.
+ /// This option can be beneficial when the caller does not require a sorted list and aims to enhance the performance. </remarks>
+ public static ReadOnlyCollection<TimeZoneInfo> GetSystemTimeZones(bool skipSorting)
  {
  CachedData cachedData = s_cachedData;
 
  lock (cachedData)
  {
- if (cachedData._readOnlySystemTimeZones == null)
+ if ((skipSorting ? cachedData._readOnlyUnsortedSystemTimeZones : cachedData._readOnlySystemTimeZones) is null)
  {
- PopulateAllSystemTimeZones(cachedData);
- cachedData._allSystemTimeZonesRead = true;
+ if (!cachedData._allSystemTimeZonesRead)
+ {
+ PopulateAllSystemTimeZones(cachedData);
+ cachedData._allSystemTimeZonesRead = true;
+ }
 
  if (cachedData._systemTimeZones != null)
  {
  // return a collection of the cached system time zones
  TimeZoneInfo[] array = new TimeZoneInfo[cachedData._systemTimeZones.Count];
  cachedData._systemTimeZones.Values.CopyTo(array, 0);
 
- // sort and copy the TimeZoneInfo's into a ReadOnlyCollection for the user
- Array.Sort(array, static (x, y) =>
+ if (!skipSorting)
  {
- // sort by BaseUtcOffset first and by DisplayName second - this is similar to the Windows Date/Time control panel
- int comparison = x.BaseUtcOffset.CompareTo(y.BaseUtcOffset);
- return comparison == 0 ? string.CompareOrdinal(x.DisplayName, y.DisplayName) : comparison;
- });
-
- cachedData._readOnlySystemTimeZones = new ReadOnlyCollection<TimeZoneInfo>(array);
+ // sort and copy the TimeZoneInfo's into a ReadOnlyCollection for the user
+ Array.Sort(array, static (x, y) =>
+ {
+ // sort by BaseUtcOffset first and by DisplayName second - this is similar to the Windows Date/Time control panel
+ int comparison = x.BaseUtcOffset.CompareTo(y.BaseUtcOffset);
+ return comparison == 0 ? string.CompareOrdinal(x.DisplayName, y.DisplayName) : comparison;
+ });
+
+ // Always reset _readOnlyUnsortedSystemTimeZones even if it was initialized before. This prevents the need to maintain two separate cache lists in memory
+ // and guarantees that if _readOnlySystemTimeZones is initialized, _readOnlyUnsortedSystemTimeZones is also initialized.
+ cachedData._readOnlySystemTimeZones = cachedData._readOnlyUnsortedSystemTimeZones = new ReadOnlyCollection<TimeZoneInfo>(array);
+ }
+ else
+ {
+ cachedData._readOnlyUnsortedSystemTimeZones = new ReadOnlyCollection<TimeZoneInfo>(array);
+ }
  }
  else
  {
- cachedData._readOnlySystemTimeZones = ReadOnlyCollection<TimeZoneInfo>.Empty;
+ cachedData._readOnlySystemTimeZones = cachedData._readOnlyUnsortedSystemTimeZones = ReadOnlyCollection<TimeZoneInfo>.Empty;
  }
  }
  }
 
- return cachedData._readOnlySystemTimeZones;
+ return skipSorting ? cachedData._readOnlyUnsortedSystemTimeZones! : cachedData._readOnlySystemTimeZones!;
  }
 
  /// <summary>

src/libraries/System.Runtime/ref/System.Runtime.cs

@@ -5687,6 +5687,7 @@ public static void ClearCachedData() { }
  public System.TimeSpan[] GetAmbiguousTimeOffsets(System.DateTimeOffset dateTimeOffset) { throw null; }
  public override int GetHashCode() { throw null; }
  public static System.Collections.ObjectModel.ReadOnlyCollection<System.TimeZoneInfo> GetSystemTimeZones() { throw null; }
+ public static System.Collections.ObjectModel.ReadOnlyCollection<System.TimeZoneInfo> GetSystemTimeZones(bool skipSorting) { throw null; }
  public System.TimeSpan GetUtcOffset(System.DateTime dateTime) { throw null; }
  public System.TimeSpan GetUtcOffset(System.DateTimeOffset dateTimeOffset) { throw null; }
  public bool HasSameRules(System.TimeZoneInfo other) { throw null; }

src/libraries/System.Runtime/tests/System/TimeZoneInfoTests.cs

@@ -1999,6 +1999,84 @@ public static void GetSystemTimeZones()
  }
  }
 
+ private static void ValidateTimeZonesSorting(ReadOnlyCollection<TimeZoneInfo> zones)
+ {
+ // validate sorting: first by base offset, then by display name
+ for (int i = 1; i < zones.Count; i++)
+ {
+ TimeZoneInfo previous = zones[i - 1];
+ TimeZoneInfo current = zones[i];
+
+ int baseOffsetsCompared = current.BaseUtcOffset.CompareTo(previous.BaseUtcOffset);
+ Assert.True(baseOffsetsCompared >= 0,
+ string.Format($"TimeZoneInfos are out of order. {previous.Id}:{previous.BaseUtcOffset} should be before {current.Id}:{current.BaseUtcOffset}"));
+
+ if (baseOffsetsCompared == 0)
+ {
+ Assert.True(string.CompareOrdinal(current.DisplayName, previous.DisplayName) >= 0,
+ string.Format($"TimeZoneInfos are out of order. {previous.DisplayName} should be before {current.DisplayName}"));
+ }
+ }
+ }
+
+ private static void ValidateDifferentTimeZoneLists(ReadOnlyCollection<TimeZoneInfo> defaultList, ReadOnlyCollection<TimeZoneInfo> nonSortedList, ReadOnlyCollection<TimeZoneInfo> sortedList)
+ {
+ Assert.Equal(defaultList.Count, nonSortedList.Count);
+ Assert.Equal(defaultList.Count, sortedList.Count);
+
+ Assert.Equal(defaultList.Count, nonSortedList.Count);
+ Assert.True(object.ReferenceEquals(defaultList, sortedList));
+ Dictionary<string, TimeZoneInfo> zones1Dict = defaultList.ToDictionary(t => t.Id);
+ foreach (TimeZoneInfo zone in nonSortedList)
+ {
+ Assert.True(zones1Dict.TryGetValue(zone.Id, out TimeZoneInfo zone1));
+ }
+
+ ValidateTimeZonesSorting(defaultList);
+ }
+
+ [ConditionalFact(typeof(RemoteExecutor), nameof(RemoteExecutor.IsSupported))]
+ public static void TestGetSystemTimeZonesCollectionsCallsOrder()
+ {
+ RemoteExecutor.Invoke(() =>
+ {
+ //
+ // Get sorted list first and then the unsorted list
+ //
+ var zones1 = TimeZoneInfo.GetSystemTimeZones();
+ var zones2 = TimeZoneInfo.GetSystemTimeZones(skipSorting: true);
+ var zones3 = TimeZoneInfo.GetSystemTimeZones(skipSorting: false);
+
+ ValidateDifferentTimeZoneLists(zones1, zones2, zones3);
+
+ //
+ // Clear our caches so zone enumeration is forced to re-read the data
+ //
+ TimeZoneInfo.ClearCachedData();
+
+ //
+ // Get unsorted list first and then the sorted list
+ //
+ zones2 = TimeZoneInfo.GetSystemTimeZones(skipSorting: true);
+ zones3 = TimeZoneInfo.GetSystemTimeZones(skipSorting: false);
+ zones1 = TimeZoneInfo.GetSystemTimeZones();
+ ValidateDifferentTimeZoneLists(zones1, zones2, zones3);
+
+ }).Dispose();
+ }
+
+ [Fact]
+ public static void TestGetSystemTimeZonesCollections()
+ {
+ // This test doing similar checks as TestGetSystemTimeZonesCollectionsCallsOrder does except we need to
+ // run this test without the RemoteExecutor to ensure testing on platforms like Android.
+
+ ReadOnlyCollection<TimeZoneInfo> unsortedList = TimeZoneInfo.GetSystemTimeZones(skipSorting: true);
+ ReadOnlyCollection<TimeZoneInfo> sortedList = TimeZoneInfo.GetSystemTimeZones(skipSorting: false);
+ ReadOnlyCollection<TimeZoneInfo> defaultList = TimeZoneInfo.GetSystemTimeZones();
+ ValidateDifferentTimeZoneLists(defaultList, unsortedList, sortedList);
+ }
+
  [Fact]
  public static void DaylightTransitionsExactTime()
  {

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

@@ -131,7 +131,7 @@ private static unsafe void GetDisplayName(string timeZoneId, Interop.Globalizati
  // Helper function that builds the value backing the DisplayName field from globalization data.
  private static void GetFullValueForDisplayNameField(string timeZoneId, TimeSpan baseUtcOffset, ref string? displayName)
  {
- // There are a few diffent ways we might show the display name depending on the data.
+ // There are a few different ways we might show the display name depending on the data.
  // The algorithm used below should avoid duplicating the same words while still achieving the
  // goal of providing a unique, discoverable, and intuitive name.
 

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

@@ -131,6 +131,7 @@ public DateTimeKind GetCorrespondingKind(TimeZoneInfo? timeZone)
 
  public Dictionary<string, TimeZoneInfo>? _systemTimeZones;
  public ReadOnlyCollection<TimeZoneInfo>? _readOnlySystemTimeZones;
+ public ReadOnlyCollection<TimeZoneInfo>? _readOnlyUnsortedSystemTimeZones;
  public Dictionary<string, TimeZoneInfo>? _timeZonesUsingAlternativeIds;
  public bool _allSystemTimeZonesRead;
  }
@@ -880,41 +881,62 @@ public static TimeZoneInfo FromSerializedString(string source)
  /// <see cref="DisplayName"/>.
  /// This method does *not* throw TimeZoneNotFoundException or InvalidTimeZoneException.
  /// </summary>
- public static ReadOnlyCollection<TimeZoneInfo> GetSystemTimeZones()
+ public static ReadOnlyCollection<TimeZoneInfo> GetSystemTimeZones() => GetSystemTimeZones(skipSorting: false);
+
+ /// <summary>
+ /// Returns a <see cref="ReadOnlyCollection{TimeZoneInfo}"/> containing all valid TimeZone's from the local machine.
+ /// This method does *not* throw TimeZoneNotFoundException or InvalidTimeZoneException.
+ /// </summary>
+ /// <param name="skipSorting">If true, The collection returned may not necessarily be sorted.</param>
+ /// <remarks>By setting the skipSorting parameter to true, the method will attempt to avoid sorting the returned collection.
+ /// This option can be beneficial when the caller does not require a sorted list and aims to enhance the performance. </remarks>
+ public static ReadOnlyCollection<TimeZoneInfo> GetSystemTimeZones(bool skipSorting)
  {
  CachedData cachedData = s_cachedData;
 
  lock (cachedData)
  {
- if (cachedData._readOnlySystemTimeZones == null)
+ if ((skipSorting ? cachedData._readOnlyUnsortedSystemTimeZones : cachedData._readOnlySystemTimeZones) is null)
  {
- PopulateAllSystemTimeZones(cachedData);
- cachedData._allSystemTimeZonesRead = true;
+ if (!cachedData._allSystemTimeZonesRead)
+ {
+ PopulateAllSystemTimeZones(cachedData);
+ cachedData._allSystemTimeZonesRead = true;
+ }
 
  if (cachedData._systemTimeZones != null)
  {
  // return a collection of the cached system time zones
  TimeZoneInfo[] array = new TimeZoneInfo[cachedData._systemTimeZones.Count];
  cachedData._systemTimeZones.Values.CopyTo(array, 0);
 
- // sort and copy the TimeZoneInfo's into a ReadOnlyCollection for the user
- Array.Sort(array, static (x, y) =>
+ if (!skipSorting)
  {
- // sort by BaseUtcOffset first and by DisplayName second - this is similar to the Windows Date/Time control panel
- int comparison = x.BaseUtcOffset.CompareTo(y.BaseUtcOffset);
- return comparison == 0 ? string.CompareOrdinal(x.DisplayName, y.DisplayName) : comparison;
- });
-
- cachedData._readOnlySystemTimeZones = new ReadOnlyCollection<TimeZoneInfo>(array);
+ // sort and copy the TimeZoneInfo's into a ReadOnlyCollection for the user
+ Array.Sort(array, static (x, y) =>
+ {
+ // sort by BaseUtcOffset first and by DisplayName second - this is similar to the Windows Date/Time control panel
+ int comparison = x.BaseUtcOffset.CompareTo(y.BaseUtcOffset);
+ return comparison == 0 ? string.CompareOrdinal(x.DisplayName, y.DisplayName) : comparison;
+ });
+
+ // Always reset _readOnlyUnsortedSystemTimeZones even if it was initialized before. This prevents the need to maintain two separate cache lists in memory
+ // and guarantees that if _readOnlySystemTimeZones is initialized, _readOnlyUnsortedSystemTimeZones is also initialized.
+ cachedData._readOnlySystemTimeZones = cachedData._readOnlyUnsortedSystemTimeZones = new ReadOnlyCollection<TimeZoneInfo>(array);
+ }
+ else
+ {
+ cachedData._readOnlyUnsortedSystemTimeZones = new ReadOnlyCollection<TimeZoneInfo>(array);
+ }
  }
  else
  {
- cachedData._readOnlySystemTimeZones = ReadOnlyCollection<TimeZoneInfo>.Empty;
+ cachedData._readOnlySystemTimeZones = cachedData._readOnlyUnsortedSystemTimeZones = ReadOnlyCollection<TimeZoneInfo>.Empty;
  }
  }
  }
 
- return cachedData._readOnlySystemTimeZones;
+ return skipSorting ? cachedData._readOnlyUnsortedSystemTimeZones! : cachedData._readOnlySystemTimeZones!;
  }
 
  /// <summary>

src/libraries/System.Runtime/ref/System.Runtime.cs

@@ -5687,6 +5687,7 @@ public static void ClearCachedData() { }
  public System.TimeSpan[] GetAmbiguousTimeOffsets(System.DateTimeOffset dateTimeOffset) { throw null; }
  public override int GetHashCode() { throw null; }
  public static System.Collections.ObjectModel.ReadOnlyCollection<System.TimeZoneInfo> GetSystemTimeZones() { throw null; }
+ public static System.Collections.ObjectModel.ReadOnlyCollection<System.TimeZoneInfo> GetSystemTimeZones(bool skipSorting) { throw null; }
  public System.TimeSpan GetUtcOffset(System.DateTime dateTime) { throw null; }
  public System.TimeSpan GetUtcOffset(System.DateTimeOffset dateTimeOffset) { throw null; }
  public bool HasSameRules(System.TimeZoneInfo other) { throw null; }

src/libraries/System.Runtime/tests/System/TimeZoneInfoTests.cs

@@ -1999,6 +1999,84 @@ public static void GetSystemTimeZones()
  }
  }
 
+ private static void ValidateTimeZonesSorting(ReadOnlyCollection<TimeZoneInfo> zones)
+ {
+ // validate sorting: first by base offset, then by display name
+ for (int i = 1; i < zones.Count; i++)
+ {
+ TimeZoneInfo previous = zones[i - 1];
+ TimeZoneInfo current = zones[i];
+
+ int baseOffsetsCompared = current.BaseUtcOffset.CompareTo(previous.BaseUtcOffset);
+ Assert.True(baseOffsetsCompared >= 0,
+ string.Format($"TimeZoneInfos are out of order. {previous.Id}:{previous.BaseUtcOffset} should be before {current.Id}:{current.BaseUtcOffset}"));
+
+ if (baseOffsetsCompared == 0)
+ {
+ Assert.True(string.CompareOrdinal(current.DisplayName, previous.DisplayName) >= 0,
+ string.Format($"TimeZoneInfos are out of order. {previous.DisplayName} should be before {current.DisplayName}"));
+ }
+ }
+ }
+
+ private static void ValidateDifferentTimeZoneLists(ReadOnlyCollection<TimeZoneInfo> defaultList, ReadOnlyCollection<TimeZoneInfo> nonSortedList, ReadOnlyCollection<TimeZoneInfo> sortedList)
+ {
+ Assert.Equal(defaultList.Count, nonSortedList.Count);
+ Assert.Equal(defaultList.Count, sortedList.Count);
+
+ Assert.Equal(defaultList.Count, nonSortedList.Count);
+ Assert.True(object.ReferenceEquals(defaultList, sortedList));
+ Dictionary<string, TimeZoneInfo> zones1Dict = defaultList.ToDictionary(t => t.Id);
+ foreach (TimeZoneInfo zone in nonSortedList)
+ {
+ Assert.True(zones1Dict.TryGetValue(zone.Id, out TimeZoneInfo zone1));
+ }
+
+ ValidateTimeZonesSorting(defaultList);
+ }
+
+ [ConditionalFact(typeof(RemoteExecutor), nameof(RemoteExecutor.IsSupported))]
+ public static void TestGetSystemTimeZonesCollectionsCallsOrder()
+ {
+ RemoteExecutor.Invoke(() =>
+ {
+ //
+ // Get sorted list first and then the unsorted list
+ //
+ var zones1 = TimeZoneInfo.GetSystemTimeZones();
+ var zones2 = TimeZoneInfo.GetSystemTimeZones(skipSorting: true);
+ var zones3 = TimeZoneInfo.GetSystemTimeZones(skipSorting: false);
+
+ ValidateDifferentTimeZoneLists(zones1, zones2, zones3);
+
+ //
+ // Clear our caches so zone enumeration is forced to re-read the data
+ //
+ TimeZoneInfo.ClearCachedData();
+
+ //
+ // Get unsorted list first and then the sorted list
+ //
+ zones2 = TimeZoneInfo.GetSystemTimeZones(skipSorting: true);
+ zones3 = TimeZoneInfo.GetSystemTimeZones(skipSorting: false);
+ zones1 = TimeZoneInfo.GetSystemTimeZones();
+ ValidateDifferentTimeZoneLists(zones1, zones2, zones3);
+
+ }).Dispose();
+ }
+
+ [Fact]
+ public static void TestGetSystemTimeZonesCollections()
+ {
+ // This test doing similar checks as TestGetSystemTimeZonesCollectionsCallsOrder does except we need to
+ // run this test without the RemoteExecutor to ensure testing on platforms like Android.
+
+ ReadOnlyCollection<TimeZoneInfo> unsortedList = TimeZoneInfo.GetSystemTimeZones(skipSorting: true);
+ ReadOnlyCollection<TimeZoneInfo> sortedList = TimeZoneInfo.GetSystemTimeZones(skipSorting: false);
+ ReadOnlyCollection<TimeZoneInfo> defaultList = TimeZoneInfo.GetSystemTimeZones();
+ ValidateDifferentTimeZoneLists(defaultList, unsortedList, sortedList);
+ }
+
  [Fact]
  public static void DaylightTransitionsExactTime()
  {

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

@@ -131,7 +131,7 @@ private static unsafe void GetDisplayName(string timeZoneId, Interop.Globalizati
  // Helper function that builds the value backing the DisplayName field from globalization data.
  private static void GetFullValueForDisplayNameField(string timeZoneId, TimeSpan baseUtcOffset, ref string? displayName)
  {
- // There are a few diffent ways we might show the display name depending on the data.
+ // There are a few different ways we might show the display name depending on the data.
  // The algorithm used below should avoid duplicating the same words while still achieving the
  // goal of providing a unique, discoverable, and intuitive name.
 

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

@@ -131,6 +131,7 @@ public DateTimeKind GetCorrespondingKind(TimeZoneInfo? timeZone)
 
  public Dictionary<string, TimeZoneInfo>? _systemTimeZones;
  public ReadOnlyCollection<TimeZoneInfo>? _readOnlySystemTimeZones;
+ public ReadOnlyCollection<TimeZoneInfo>? _readOnlyUnsortedSystemTimeZones;
  public Dictionary<string, TimeZoneInfo>? _timeZonesUsingAlternativeIds;
  public bool _allSystemTimeZonesRead;
  }
@@ -880,41 +881,62 @@ public static TimeZoneInfo FromSerializedString(string source)
  /// <see cref="DisplayName"/>.
  /// This method does *not* throw TimeZoneNotFoundException or InvalidTimeZoneException.
  /// </summary>
- public static ReadOnlyCollection<TimeZoneInfo> GetSystemTimeZones()
+ public static ReadOnlyCollection<TimeZoneInfo> GetSystemTimeZones() => GetSystemTimeZones(skipSorting: false);
+
+ /// <summary>
+ /// Returns a <see cref="ReadOnlyCollection{TimeZoneInfo}"/> containing all valid TimeZone's from the local machine.
+ /// This method does *not* throw TimeZoneNotFoundException or InvalidTimeZoneException.
+ /// </summary>
+ /// <param name="skipSorting">If true, The collection returned may not necessarily be sorted.</param>
+ /// <remarks>By setting the skipSorting parameter to true, the method will attempt to avoid sorting the returned collection.
+ /// This option can be beneficial when the caller does not require a sorted list and aims to enhance the performance. </remarks>
+ public static ReadOnlyCollection<TimeZoneInfo> GetSystemTimeZones(bool skipSorting)
  {
  CachedData cachedData = s_cachedData;
 
  lock (cachedData)
  {
- if (cachedData._readOnlySystemTimeZones == null)
+ if ((skipSorting ? cachedData._readOnlyUnsortedSystemTimeZones : cachedData._readOnlySystemTimeZones) is null)
  {
- PopulateAllSystemTimeZones(cachedData);
- cachedData._allSystemTimeZonesRead = true;
+ if (!cachedData._allSystemTimeZonesRead)
+ {
+ PopulateAllSystemTimeZones(cachedData);
+ cachedData._allSystemTimeZonesRead = true;
+ }
 
  if (cachedData._systemTimeZones != null)
  {
  // return a collection of the cached system time zones
  TimeZoneInfo[] array = new TimeZoneInfo[cachedData._systemTimeZones.Count];
  cachedData._systemTimeZones.Values.CopyTo(array, 0);
 
- // sort and copy the TimeZoneInfo's into a ReadOnlyCollection for the user
- Array.Sort(array, static (x, y) =>
+ if (!skipSorting)
  {
- // sort by BaseUtcOffset first and by DisplayName second - this is similar to the Windows Date/Time control panel
- int comparison = x.BaseUtcOffset.CompareTo(y.BaseUtcOffset);
- return comparison == 0 ? string.CompareOrdinal(x.DisplayName, y.DisplayName) : comparison;
- });
-
- cachedData._readOnlySystemTimeZones = new ReadOnlyCollection<TimeZoneInfo>(array);
+ // sort and copy the TimeZoneInfo's into a ReadOnlyCollection for the user
+ Array.Sort(array, static (x, y) =>
+ {
+ // sort by BaseUtcOffset first and by DisplayName second - this is similar to the Windows Date/Time control panel
+ int comparison = x.BaseUtcOffset.CompareTo(y.BaseUtcOffset);
+ return comparison == 0 ? string.CompareOrdinal(x.DisplayName, y.DisplayName) : comparison;
+ });
+
+ // Always reset _readOnlyUnsortedSystemTimeZones even if it was initialized before. This prevents the need to maintain two separate cache lists in memory
+ // and guarantees that if _readOnlySystemTimeZones is initialized, _readOnlyUnsortedSystemTimeZones is also initialized.
+ cachedData._readOnlySystemTimeZones = cachedData._readOnlyUnsortedSystemTimeZones = new ReadOnlyCollection<TimeZoneInfo>(array);
+ }
+ else
+ {
+ cachedData._readOnlyUnsortedSystemTimeZones = new ReadOnlyCollection<TimeZoneInfo>(array);
+ }
  }
  else
  {
- cachedData._readOnlySystemTimeZones = ReadOnlyCollection<TimeZoneInfo>.Empty;
+ cachedData._readOnlySystemTimeZones = cachedData._readOnlyUnsortedSystemTimeZones = ReadOnlyCollection<TimeZoneInfo>.Empty;
  }
  }
  }
 
- return cachedData._readOnlySystemTimeZones;
+ return skipSorting ? cachedData._readOnlyUnsortedSystemTimeZones! : cachedData._readOnlySystemTimeZones!;
  }
 
  /// <summary>

src/libraries/System.Runtime/ref/System.Runtime.cs

@@ -5687,6 +5687,7 @@ public static void ClearCachedData() { }
  public System.TimeSpan[] GetAmbiguousTimeOffsets(System.DateTimeOffset dateTimeOffset) { throw null; }
  public override int GetHashCode() { throw null; }
  public static System.Collections.ObjectModel.ReadOnlyCollection<System.TimeZoneInfo> GetSystemTimeZones() { throw null; }
+ public static System.Collections.ObjectModel.ReadOnlyCollection<System.TimeZoneInfo> GetSystemTimeZones(bool skipSorting) { throw null; }
  public System.TimeSpan GetUtcOffset(System.DateTime dateTime) { throw null; }
  public System.TimeSpan GetUtcOffset(System.DateTimeOffset dateTimeOffset) { throw null; }
  public bool HasSameRules(System.TimeZoneInfo other) { throw null; }

src/libraries/System.Runtime/tests/System/TimeZoneInfoTests.cs

@@ -1999,6 +1999,84 @@ public static void GetSystemTimeZones()
  }
  }
 
+ private static void ValidateTimeZonesSorting(ReadOnlyCollection<TimeZoneInfo> zones)
+ {
+ // validate sorting: first by base offset, then by display name
+ for (int i = 1; i < zones.Count; i++)
+ {
+ TimeZoneInfo previous = zones[i - 1];
+ TimeZoneInfo current = zones[i];
+
+ int baseOffsetsCompared = current.BaseUtcOffset.CompareTo(previous.BaseUtcOffset);
+ Assert.True(baseOffsetsCompared >= 0,
+ string.Format($"TimeZoneInfos are out of order. {previous.Id}:{previous.BaseUtcOffset} should be before {current.Id}:{current.BaseUtcOffset}"));
+
+ if (baseOffsetsCompared == 0)
+ {
+ Assert.True(string.CompareOrdinal(current.DisplayName, previous.DisplayName) >= 0,
+ string.Format($"TimeZoneInfos are out of order. {previous.DisplayName} should be before {current.DisplayName}"));
+ }
+ }
+ }
+
+ private static void ValidateDifferentTimeZoneLists(ReadOnlyCollection<TimeZoneInfo> defaultList, ReadOnlyCollection<TimeZoneInfo> nonSortedList, ReadOnlyCollection<TimeZoneInfo> sortedList)
+ {
+ Assert.Equal(defaultList.Count, nonSortedList.Count);
+ Assert.Equal(defaultList.Count, sortedList.Count);
+
+ Assert.Equal(defaultList.Count, nonSortedList.Count);
+ Assert.True(object.ReferenceEquals(defaultList, sortedList));
+ Dictionary<string, TimeZoneInfo> zones1Dict = defaultList.ToDictionary(t => t.Id);
+ foreach (TimeZoneInfo zone in nonSortedList)
+ {
+ Assert.True(zones1Dict.TryGetValue(zone.Id, out TimeZoneInfo zone1));
+ }
+
+ ValidateTimeZonesSorting(defaultList);
+ }
+
+ [ConditionalFact(typeof(RemoteExecutor), nameof(RemoteExecutor.IsSupported))]
+ public static void TestGetSystemTimeZonesCollectionsCallsOrder()
+ {
+ RemoteExecutor.Invoke(() =>
+ {
+ //
+ // Get sorted list first and then the unsorted list
+ //
+ var zones1 = TimeZoneInfo.GetSystemTimeZones();
+ var zones2 = TimeZoneInfo.GetSystemTimeZones(skipSorting: true);
+ var zones3 = TimeZoneInfo.GetSystemTimeZones(skipSorting: false);
+
+ ValidateDifferentTimeZoneLists(zones1, zones2, zones3);
+
+ //
+ // Clear our caches so zone enumeration is forced to re-read the data
+ //
+ TimeZoneInfo.ClearCachedData();
+
+ //
+ // Get unsorted list first and then the sorted list
+ //
+ zones2 = TimeZoneInfo.GetSystemTimeZones(skipSorting: true);
+ zones3 = TimeZoneInfo.GetSystemTimeZones(skipSorting: false);
+ zones1 = TimeZoneInfo.GetSystemTimeZones();
+ ValidateDifferentTimeZoneLists(zones1, zones2, zones3);
+
+ }).Dispose();
+ }
+
+ [Fact]
+ public static void TestGetSystemTimeZonesCollections()
+ {
+ // This test doing similar checks as TestGetSystemTimeZonesCollectionsCallsOrder does except we need to
+ // run this test without the RemoteExecutor to ensure testing on platforms like Android.
+
+ ReadOnlyCollection<TimeZoneInfo> unsortedList = TimeZoneInfo.GetSystemTimeZones(skipSorting: true);
+ ReadOnlyCollection<TimeZoneInfo> sortedList = TimeZoneInfo.GetSystemTimeZones(skipSorting: false);
+ ReadOnlyCollection<TimeZoneInfo> defaultList = TimeZoneInfo.GetSystemTimeZones();
+ ValidateDifferentTimeZoneLists(defaultList, unsortedList, sortedList);
+ }
+
  [Fact]
  public static void DaylightTransitionsExactTime()
  {

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

@@ -131,7 +131,7 @@ private static unsafe void GetDisplayName(string timeZoneId, Interop.Globalizati
  // Helper function that builds the value backing the DisplayName field from globalization data.
  private static void GetFullValueForDisplayNameField(string timeZoneId, TimeSpan baseUtcOffset, ref string? displayName)
  {
- // There are a few diffent ways we might show the display name depending on the data.
+ // There are a few different ways we might show the display name depending on the data.
  // The algorithm used below should avoid duplicating the same words while still achieving the
  // goal of providing a unique, discoverable, and intuitive name.
 

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

@@ -131,6 +131,7 @@ public DateTimeKind GetCorrespondingKind(TimeZoneInfo? timeZone)
 
  public Dictionary<string, TimeZoneInfo>? _systemTimeZones;
  public ReadOnlyCollection<TimeZoneInfo>? _readOnlySystemTimeZones;
+ public ReadOnlyCollection<TimeZoneInfo>? _readOnlyUnsortedSystemTimeZones;
  public Dictionary<string, TimeZoneInfo>? _timeZonesUsingAlternativeIds;
  public bool _allSystemTimeZonesRead;
  }
@@ -880,41 +881,62 @@ public static TimeZoneInfo FromSerializedString(string source)
  /// <see cref="DisplayName"/>.
  /// This method does *not* throw TimeZoneNotFoundException or InvalidTimeZoneException.
  /// </summary>
- public static ReadOnlyCollection<TimeZoneInfo> GetSystemTimeZones()
+ public static ReadOnlyCollection<TimeZoneInfo> GetSystemTimeZones() => GetSystemTimeZones(skipSorting: false);
+
+ /// <summary>
+ /// Returns a <see cref="ReadOnlyCollection{TimeZoneInfo}"/> containing all valid TimeZone's from the local machine.
+ /// This method does *not* throw TimeZoneNotFoundException or InvalidTimeZoneException.
+ /// </summary>
+ /// <param name="skipSorting">If true, The collection returned may not necessarily be sorted.</param>
+ /// <remarks>By setting the skipSorting parameter to true, the method will attempt to avoid sorting the returned collection.
+ /// This option can be beneficial when the caller does not require a sorted list and aims to enhance the performance. </remarks>
+ public static ReadOnlyCollection<TimeZoneInfo> GetSystemTimeZones(bool skipSorting)
  {
  CachedData cachedData = s_cachedData;
 
  lock (cachedData)
  {
- if (cachedData._readOnlySystemTimeZones == null)
+ if ((skipSorting ? cachedData._readOnlyUnsortedSystemTimeZones : cachedData._readOnlySystemTimeZones) is null)
  {
- PopulateAllSystemTimeZones(cachedData);
- cachedData._allSystemTimeZonesRead = true;
+ if (!cachedData._allSystemTimeZonesRead)
+ {
+ PopulateAllSystemTimeZones(cachedData);
+ cachedData._allSystemTimeZonesRead = true;
+ }
 
  if (cachedData._systemTimeZones != null)
  {
  // return a collection of the cached system time zones
  TimeZoneInfo[] array = new TimeZoneInfo[cachedData._systemTimeZones.Count];
  cachedData._systemTimeZones.Values.CopyTo(array, 0);
 
- // sort and copy the TimeZoneInfo's into a ReadOnlyCollection for the user
- Array.Sort(array, static (x, y) =>
+ if (!skipSorting)
  {
- // sort by BaseUtcOffset first and by DisplayName second - this is similar to the Windows Date/Time control panel
- int comparison = x.BaseUtcOffset.CompareTo(y.BaseUtcOffset);
- return comparison == 0 ? string.CompareOrdinal(x.DisplayName, y.DisplayName) : comparison;
- });
-
- cachedData._readOnlySystemTimeZones = new ReadOnlyCollection<TimeZoneInfo>(array);
+ // sort and copy the TimeZoneInfo's into a ReadOnlyCollection for the user
+ Array.Sort(array, static (x, y) =>
+ {
+ // sort by BaseUtcOffset first and by DisplayName second - this is similar to the Windows Date/Time control panel
+ int comparison = x.BaseUtcOffset.CompareTo(y.BaseUtcOffset);
+ return comparison == 0 ? string.CompareOrdinal(x.DisplayName, y.DisplayName) : comparison;
+ });
+
+ // Always reset _readOnlyUnsortedSystemTimeZones even if it was initialized before. This prevents the need to maintain two separate cache lists in memory
+ // and guarantees that if _readOnlySystemTimeZones is initialized, _readOnlyUnsortedSystemTimeZones is also initialized.
+ cachedData._readOnlySystemTimeZones = cachedData._readOnlyUnsortedSystemTimeZones = new ReadOnlyCollection<TimeZoneInfo>(array);
+ }
+ else
+ {
+ cachedData._readOnlyUnsortedSystemTimeZones = new ReadOnlyCollection<TimeZoneInfo>(array);
+ }
  }
  else
  {
- cachedData._readOnlySystemTimeZones = ReadOnlyCollection<TimeZoneInfo>.Empty;
+ cachedData._readOnlySystemTimeZones = cachedData._readOnlyUnsortedSystemTimeZones = ReadOnlyCollection<TimeZoneInfo>.Empty;
  }
  }
  }
 
- return cachedData._readOnlySystemTimeZones;
+ return skipSorting ? cachedData._readOnlyUnsortedSystemTimeZones! : cachedData._readOnlySystemTimeZones!;
  }
 
  /// <summary>

src/libraries/System.Runtime/ref/System.Runtime.cs

@@ -5687,6 +5687,7 @@ public static void ClearCachedData() { }
  public System.TimeSpan[] GetAmbiguousTimeOffsets(System.DateTimeOffset dateTimeOffset) { throw null; }
  public override int GetHashCode() { throw null; }
  public static System.Collections.ObjectModel.ReadOnlyCollection<System.TimeZoneInfo> GetSystemTimeZones() { throw null; }
+ public static System.Collections.ObjectModel.ReadOnlyCollection<System.TimeZoneInfo> GetSystemTimeZones(bool skipSorting) { throw null; }
  public System.TimeSpan GetUtcOffset(System.DateTime dateTime) { throw null; }
  public System.TimeSpan GetUtcOffset(System.DateTimeOffset dateTimeOffset) { throw null; }
  public bool HasSameRules(System.TimeZoneInfo other) { throw null; }

src/libraries/System.Runtime/tests/System/TimeZoneInfoTests.cs

@@ -1999,6 +1999,84 @@ public static void GetSystemTimeZones()
  }
  }
 
+ private static void ValidateTimeZonesSorting(ReadOnlyCollection<TimeZoneInfo> zones)
+ {
+ // validate sorting: first by base offset, then by display name
+ for (int i = 1; i < zones.Count; i++)
+ {
+ TimeZoneInfo previous = zones[i - 1];
+ TimeZoneInfo current = zones[i];
+
+ int baseOffsetsCompared = current.BaseUtcOffset.CompareTo(previous.BaseUtcOffset);
+ Assert.True(baseOffsetsCompared >= 0,
+ string.Format($"TimeZoneInfos are out of order. {previous.Id}:{previous.BaseUtcOffset} should be before {current.Id}:{current.BaseUtcOffset}"));
+
+ if (baseOffsetsCompared == 0)
+ {
+ Assert.True(string.CompareOrdinal(current.DisplayName, previous.DisplayName) >= 0,
+ string.Format($"TimeZoneInfos are out of order. {previous.DisplayName} should be before {current.DisplayName}"));
+ }
+ }
+ }
+
+ private static void ValidateDifferentTimeZoneLists(ReadOnlyCollection<TimeZoneInfo> defaultList, ReadOnlyCollection<TimeZoneInfo> nonSortedList, ReadOnlyCollection<TimeZoneInfo> sortedList)
+ {
+ Assert.Equal(defaultList.Count, nonSortedList.Count);
+ Assert.Equal(defaultList.Count, sortedList.Count);
+
+ Assert.Equal(defaultList.Count, nonSortedList.Count);
+ Assert.True(object.ReferenceEquals(defaultList, sortedList));
+ Dictionary<string, TimeZoneInfo> zones1Dict = defaultList.ToDictionary(t => t.Id);
+ foreach (TimeZoneInfo zone in nonSortedList)
+ {
+ Assert.True(zones1Dict.TryGetValue(zone.Id, out TimeZoneInfo zone1));
+ }
+
+ ValidateTimeZonesSorting(defaultList);
+ }
+
+ [ConditionalFact(typeof(RemoteExecutor), nameof(RemoteExecutor.IsSupported))]
+ public static void TestGetSystemTimeZonesCollectionsCallsOrder()
+ {
+ RemoteExecutor.Invoke(() =>
+ {
+ //
+ // Get sorted list first and then the unsorted list
+ //
+ var zones1 = TimeZoneInfo.GetSystemTimeZones();
+ var zones2 = TimeZoneInfo.GetSystemTimeZones(skipSorting: true);
+ var zones3 = TimeZoneInfo.GetSystemTimeZones(skipSorting: false);
+
+ ValidateDifferentTimeZoneLists(zones1, zones2, zones3);
+
+ //
+ // Clear our caches so zone enumeration is forced to re-read the data
+ //
+ TimeZoneInfo.ClearCachedData();
+
+ //
+ // Get unsorted list first and then the sorted list
+ //
+ zones2 = TimeZoneInfo.GetSystemTimeZones(skipSorting: true);
+ zones3 = TimeZoneInfo.GetSystemTimeZones(skipSorting: false);
+ zones1 = TimeZoneInfo.GetSystemTimeZones();
+ ValidateDifferentTimeZoneLists(zones1, zones2, zones3);
+
+ }).Dispose();
+ }
+
+ [Fact]
+ public static void TestGetSystemTimeZonesCollections()
+ {
+ // This test doing similar checks as TestGetSystemTimeZonesCollectionsCallsOrder does except we need to
+ // run this test without the RemoteExecutor to ensure testing on platforms like Android.
+
+ ReadOnlyCollection<TimeZoneInfo> unsortedList = TimeZoneInfo.GetSystemTimeZones(skipSorting: true);
+ ReadOnlyCollection<TimeZoneInfo> sortedList = TimeZoneInfo.GetSystemTimeZones(skipSorting: false);
+ ReadOnlyCollection<TimeZoneInfo> defaultList = TimeZoneInfo.GetSystemTimeZones();
+ ValidateDifferentTimeZoneLists(defaultList, unsortedList, sortedList);
+ }
+
  [Fact]
  public static void DaylightTransitionsExactTime()
  {

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

@@ -131,7 +131,7 @@ private static unsafe void GetDisplayName(string timeZoneId, Interop.Globalizati
  // Helper function that builds the value backing the DisplayName field from globalization data.
  private static void GetFullValueForDisplayNameField(string timeZoneId, TimeSpan baseUtcOffset, ref string? displayName)
  {
- // There are a few diffent ways we might show the display name depending on the data.
+ // There are a few different ways we might show the display name depending on the data.
  // The algorithm used below should avoid duplicating the same words while still achieving the
  // goal of providing a unique, discoverable, and intuitive name.
 

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

@@ -131,6 +131,7 @@ public DateTimeKind GetCorrespondingKind(TimeZoneInfo? timeZone)
 
  public Dictionary<string, TimeZoneInfo>? _systemTimeZones;
  public ReadOnlyCollection<TimeZoneInfo>? _readOnlySystemTimeZones;
+ public ReadOnlyCollection<TimeZoneInfo>? _readOnlyUnsortedSystemTimeZones;
  public Dictionary<string, TimeZoneInfo>? _timeZonesUsingAlternativeIds;
  public bool _allSystemTimeZonesRead;
  }
@@ -880,41 +881,62 @@ public static TimeZoneInfo FromSerializedString(string source)
  /// <see cref="DisplayName"/>.
  /// This method does *not* throw TimeZoneNotFoundException or InvalidTimeZoneException.
  /// </summary>
- public static ReadOnlyCollection<TimeZoneInfo> GetSystemTimeZones()
+ public static ReadOnlyCollection<TimeZoneInfo> GetSystemTimeZones() => GetSystemTimeZones(skipSorting: false);
+
+ /// <summary>
+ /// Returns a <see cref="ReadOnlyCollection{TimeZoneInfo}"/> containing all valid TimeZone's from the local machine.
+ /// This method does *not* throw TimeZoneNotFoundException or InvalidTimeZoneException.
+ /// </summary>
+ /// <param name="skipSorting">If true, The collection returned may not necessarily be sorted.</param>
+ /// <remarks>By setting the skipSorting parameter to true, the method will attempt to avoid sorting the returned collection.
+ /// This option can be beneficial when the caller does not require a sorted list and aims to enhance the performance. </remarks>
+ public static ReadOnlyCollection<TimeZoneInfo> GetSystemTimeZones(bool skipSorting)
  {
  CachedData cachedData = s_cachedData;
 
  lock (cachedData)
  {
- if (cachedData._readOnlySystemTimeZones == null)
+ if ((skipSorting ? cachedData._readOnlyUnsortedSystemTimeZones : cachedData._readOnlySystemTimeZones) is null)
  {
- PopulateAllSystemTimeZones(cachedData);
- cachedData._allSystemTimeZonesRead = true;
+ if (!cachedData._allSystemTimeZonesRead)
+ {
+ PopulateAllSystemTimeZones(cachedData);
+ cachedData._allSystemTimeZonesRead = true;
+ }
 
  if (cachedData._systemTimeZones != null)
  {
  // return a collection of the cached system time zones
  TimeZoneInfo[] array = new TimeZoneInfo[cachedData._systemTimeZones.Count];
  cachedData._systemTimeZones.Values.CopyTo(array, 0);
 
- // sort and copy the TimeZoneInfo's into a ReadOnlyCollection for the user
- Array.Sort(array, static (x, y) =>
+ if (!skipSorting)
  {
- // sort by BaseUtcOffset first and by DisplayName second - this is similar to the Windows Date/Time control panel
- int comparison = x.BaseUtcOffset.CompareTo(y.BaseUtcOffset);
- return comparison == 0 ? string.CompareOrdinal(x.DisplayName, y.DisplayName) : comparison;
- });
-
- cachedData._readOnlySystemTimeZones = new ReadOnlyCollection<TimeZoneInfo>(array);
+ // sort and copy the TimeZoneInfo's into a ReadOnlyCollection for the user
+ Array.Sort(array, static (x, y) =>
+ {
+ // sort by BaseUtcOffset first and by DisplayName second - this is similar to the Windows Date/Time control panel
+ int comparison = x.BaseUtcOffset.CompareTo(y.BaseUtcOffset);
+ return comparison == 0 ? string.CompareOrdinal(x.DisplayName, y.DisplayName) : comparison;
+ });
+
+ // Always reset _readOnlyUnsortedSystemTimeZones even if it was initialized before. This prevents the need to maintain two separate cache lists in memory
+ // and guarantees that if _readOnlySystemTimeZones is initialized, _readOnlyUnsortedSystemTimeZones is also initialized.
+ cachedData._readOnlySystemTimeZones = cachedData._readOnlyUnsortedSystemTimeZones = new ReadOnlyCollection<TimeZoneInfo>(array);
+ }
+ else
+ {
+ cachedData._readOnlyUnsortedSystemTimeZones = new ReadOnlyCollection<TimeZoneInfo>(array);
+ }
  }
  else
  {
- cachedData._readOnlySystemTimeZones = ReadOnlyCollection<TimeZoneInfo>.Empty;
+ cachedData._readOnlySystemTimeZones = cachedData._readOnlyUnsortedSystemTimeZones = ReadOnlyCollection<TimeZoneInfo>.Empty;
  }
  }
  }
 
- return cachedData._readOnlySystemTimeZones;
+ return skipSorting ? cachedData._readOnlyUnsortedSystemTimeZones! : cachedData._readOnlySystemTimeZones!;
  }
 
  /// <summary>

src/libraries/System.Runtime/ref/System.Runtime.cs

@@ -5687,6 +5687,7 @@ public static void ClearCachedData() { }
  public System.TimeSpan[] GetAmbiguousTimeOffsets(System.DateTimeOffset dateTimeOffset) { throw null; }
  public override int GetHashCode() { throw null; }
  public static System.Collections.ObjectModel.ReadOnlyCollection<System.TimeZoneInfo> GetSystemTimeZones() { throw null; }
+ public static System.Collections.ObjectModel.ReadOnlyCollection<System.TimeZoneInfo> GetSystemTimeZones(bool skipSorting) { throw null; }
  public System.TimeSpan GetUtcOffset(System.DateTime dateTime) { throw null; }
  public System.TimeSpan GetUtcOffset(System.DateTimeOffset dateTimeOffset) { throw null; }
  public bool HasSameRules(System.TimeZoneInfo other) { throw null; }

src/libraries/System.Runtime/tests/System/TimeZoneInfoTests.cs

@@ -1999,6 +1999,84 @@ public static void GetSystemTimeZones()
  }
  }
 
+ private static void ValidateTimeZonesSorting(ReadOnlyCollection<TimeZoneInfo> zones)
+ {
+ // validate sorting: first by base offset, then by display name
+ for (int i = 1; i < zones.Count; i++)
+ {
+ TimeZoneInfo previous = zones[i - 1];
+ TimeZoneInfo current = zones[i];
+
+ int baseOffsetsCompared = current.BaseUtcOffset.CompareTo(previous.BaseUtcOffset);
+ Assert.True(baseOffsetsCompared >= 0,
+ string.Format($"TimeZoneInfos are out of order. {previous.Id}:{previous.BaseUtcOffset} should be before {current.Id}:{current.BaseUtcOffset}"));
+
+ if (baseOffsetsCompared == 0)
+ {
+ Assert.True(string.CompareOrdinal(current.DisplayName, previous.DisplayName) >= 0,
+ string.Format($"TimeZoneInfos are out of order. {previous.DisplayName} should be before {current.DisplayName}"));
+ }
+ }
+ }
+
+ private static void ValidateDifferentTimeZoneLists(ReadOnlyCollection<TimeZoneInfo> defaultList, ReadOnlyCollection<TimeZoneInfo> nonSortedList, ReadOnlyCollection<TimeZoneInfo> sortedList)
+ {
+ Assert.Equal(defaultList.Count, nonSortedList.Count);
+ Assert.Equal(defaultList.Count, sortedList.Count);
+
+ Assert.Equal(defaultList.Count, nonSortedList.Count);
+ Assert.True(object.ReferenceEquals(defaultList, sortedList));
+ Dictionary<string, TimeZoneInfo> zones1Dict = defaultList.ToDictionary(t => t.Id);
+ foreach (TimeZoneInfo zone in nonSortedList)
+ {
+ Assert.True(zones1Dict.TryGetValue(zone.Id, out TimeZoneInfo zone1));
+ }
+
+ ValidateTimeZonesSorting(defaultList);
+ }
+
+ [ConditionalFact(typeof(RemoteExecutor), nameof(RemoteExecutor.IsSupported))]
+ public static void TestGetSystemTimeZonesCollectionsCallsOrder()
+ {
+ RemoteExecutor.Invoke(() =>
+ {
+ //
+ // Get sorted list first and then the unsorted list
+ //
+ var zones1 = TimeZoneInfo.GetSystemTimeZones();
+ var zones2 = TimeZoneInfo.GetSystemTimeZones(skipSorting: true);
+ var zones3 = TimeZoneInfo.GetSystemTimeZones(skipSorting: false);
+
+ ValidateDifferentTimeZoneLists(zones1, zones2, zones3);
+
+ //
+ // Clear our caches so zone enumeration is forced to re-read the data
+ //
+ TimeZoneInfo.ClearCachedData();
+
+ //
+ // Get unsorted list first and then the sorted list
+ //
+ zones2 = TimeZoneInfo.GetSystemTimeZones(skipSorting: true);
+ zones3 = TimeZoneInfo.GetSystemTimeZones(skipSorting: false);
+ zones1 = TimeZoneInfo.GetSystemTimeZones();
+ ValidateDifferentTimeZoneLists(zones1, zones2, zones3);
+
+ }).Dispose();
+ }
+
+ [Fact]
+ public static void TestGetSystemTimeZonesCollections()
+ {
+ // This test doing similar checks as TestGetSystemTimeZonesCollectionsCallsOrder does except we need to
+ // run this test without the RemoteExecutor to ensure testing on platforms like Android.
+
+ ReadOnlyCollection<TimeZoneInfo> unsortedList = TimeZoneInfo.GetSystemTimeZones(skipSorting: true);
+ ReadOnlyCollection<TimeZoneInfo> sortedList = TimeZoneInfo.GetSystemTimeZones(skipSorting: false);
+ ReadOnlyCollection<TimeZoneInfo> defaultList = TimeZoneInfo.GetSystemTimeZones();
+ ValidateDifferentTimeZoneLists(defaultList, unsortedList, sortedList);
+ }
+
  [Fact]
  public static void DaylightTransitionsExactTime()
  {

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

@@ -131,7 +131,7 @@ private static unsafe void GetDisplayName(string timeZoneId, Interop.Globalizati
  // Helper function that builds the value backing the DisplayName field from globalization data.
  private static void GetFullValueForDisplayNameField(string timeZoneId, TimeSpan baseUtcOffset, ref string? displayName)
  {
- // There are a few diffent ways we might show the display name depending on the data.
+ // There are a few different ways we might show the display name depending on the data.
  // The algorithm used below should avoid duplicating the same words while still achieving the
  // goal of providing a unique, discoverable, and intuitive name.
 

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

@@ -131,6 +131,7 @@ public DateTimeKind GetCorrespondingKind(TimeZoneInfo? timeZone)
 
  public Dictionary<string, TimeZoneInfo>? _systemTimeZones;
  public ReadOnlyCollection<TimeZoneInfo>? _readOnlySystemTimeZones;
+ public ReadOnlyCollection<TimeZoneInfo>? _readOnlyUnsortedSystemTimeZones;
  public Dictionary<string, TimeZoneInfo>? _timeZonesUsingAlternativeIds;
  public bool _allSystemTimeZonesRead;
  }
@@ -880,41 +881,62 @@ public static TimeZoneInfo FromSerializedString(string source)
  /// <see cref="DisplayName"/>.
  /// This method does *not* throw TimeZoneNotFoundException or InvalidTimeZoneException.
  /// </summary>
- public static ReadOnlyCollection<TimeZoneInfo> GetSystemTimeZones()
+ public static ReadOnlyCollection<TimeZoneInfo> GetSystemTimeZones() => GetSystemTimeZones(skipSorting: false);
+
+ /// <summary>
+ /// Returns a <see cref="ReadOnlyCollection{TimeZoneInfo}"/> containing all valid TimeZone's from the local machine.
+ /// This method does *not* throw TimeZoneNotFoundException or InvalidTimeZoneException.
+ /// </summary>
+ /// <param name="skipSorting">If true, The collection returned may not necessarily be sorted.</param>
+ /// <remarks>By setting the skipSorting parameter to true, the method will attempt to avoid sorting the returned collection.
+ /// This option can be beneficial when the caller does not require a sorted list and aims to enhance the performance. </remarks>
+ public static ReadOnlyCollection<TimeZoneInfo> GetSystemTimeZones(bool skipSorting)
  {
  CachedData cachedData = s_cachedData;
 
  lock (cachedData)
  {
- if (cachedData._readOnlySystemTimeZones == null)
+ if ((skipSorting ? cachedData._readOnlyUnsortedSystemTimeZones : cachedData._readOnlySystemTimeZones) is null)
  {
- PopulateAllSystemTimeZones(cachedData);
- cachedData._allSystemTimeZonesRead = true;
+ if (!cachedData._allSystemTimeZonesRead)
+ {
+ PopulateAllSystemTimeZones(cachedData);
+ cachedData._allSystemTimeZonesRead = true;
+ }
 
  if (cachedData._systemTimeZones != null)
  {
  // return a collection of the cached system time zones
  TimeZoneInfo[] array = new TimeZoneInfo[cachedData._systemTimeZones.Count];
  cachedData._systemTimeZones.Values.CopyTo(array, 0);
 
- // sort and copy the TimeZoneInfo's into a ReadOnlyCollection for the user
- Array.Sort(array, static (x, y) =>
+ if (!skipSorting)
  {
- // sort by BaseUtcOffset first and by DisplayName second - this is similar to the Windows Date/Time control panel
- int comparison = x.BaseUtcOffset.CompareTo(y.BaseUtcOffset);
- return comparison == 0 ? string.CompareOrdinal(x.DisplayName, y.DisplayName) : comparison;
- });
-
- cachedData._readOnlySystemTimeZones = new ReadOnlyCollection<TimeZoneInfo>(array);
+ // sort and copy the TimeZoneInfo's into a ReadOnlyCollection for the user
+ Array.Sort(array, static (x, y) =>
+ {
+ // sort by BaseUtcOffset first and by DisplayName second - this is similar to the Windows Date/Time control panel
+ int comparison = x.BaseUtcOffset.CompareTo(y.BaseUtcOffset);
+ return comparison == 0 ? string.CompareOrdinal(x.DisplayName, y.DisplayName) : comparison;
+ });
+
+ // Always reset _readOnlyUnsortedSystemTimeZones even if it was initialized before. This prevents the need to maintain two separate cache lists in memory
+ // and guarantees that if _readOnlySystemTimeZones is initialized, _readOnlyUnsortedSystemTimeZones is also initialized.
+ cachedData._readOnlySystemTimeZones = cachedData._readOnlyUnsortedSystemTimeZones = new ReadOnlyCollection<TimeZoneInfo>(array);
+ }
+ else
+ {
+ cachedData._readOnlyUnsortedSystemTimeZones = new ReadOnlyCollection<TimeZoneInfo>(array);
+ }
  }
  else
  {
- cachedData._readOnlySystemTimeZones = ReadOnlyCollection<TimeZoneInfo>.Empty;
+ cachedData._readOnlySystemTimeZones = cachedData._readOnlyUnsortedSystemTimeZones = ReadOnlyCollection<TimeZoneInfo>.Empty;
  }
  }
  }
 
- return cachedData._readOnlySystemTimeZones;
+ return skipSorting ? cachedData._readOnlyUnsortedSystemTimeZones! : cachedData._readOnlySystemTimeZones!;
  }
 
  /// <summary>

src/libraries/System.Runtime/ref/System.Runtime.cs

@@ -5687,6 +5687,7 @@ public static void ClearCachedData() { }
  public System.TimeSpan[] GetAmbiguousTimeOffsets(System.DateTimeOffset dateTimeOffset) { throw null; }
  public override int GetHashCode() { throw null; }
  public static System.Collections.ObjectModel.ReadOnlyCollection<System.TimeZoneInfo> GetSystemTimeZones() { throw null; }
+ public static System.Collections.ObjectModel.ReadOnlyCollection<System.TimeZoneInfo> GetSystemTimeZones(bool skipSorting) { throw null; }
  public System.TimeSpan GetUtcOffset(System.DateTime dateTime) { throw null; }
  public System.TimeSpan GetUtcOffset(System.DateTimeOffset dateTimeOffset) { throw null; }
  public bool HasSameRules(System.TimeZoneInfo other) { throw null; }

src/libraries/System.Runtime/tests/System/TimeZoneInfoTests.cs

@@ -1999,6 +1999,84 @@ public static void GetSystemTimeZones()
  }
  }
 
+ private static void ValidateTimeZonesSorting(ReadOnlyCollection<TimeZoneInfo> zones)
+ {
+ // validate sorting: first by base offset, then by display name
+ for (int i = 1; i < zones.Count; i++)
+ {
+ TimeZoneInfo previous = zones[i - 1];
+ TimeZoneInfo current = zones[i];
+
+ int baseOffsetsCompared = current.BaseUtcOffset.CompareTo(previous.BaseUtcOffset);
+ Assert.True(baseOffsetsCompared >= 0,
+ string.Format($"TimeZoneInfos are out of order. {previous.Id}:{previous.BaseUtcOffset} should be before {current.Id}:{current.BaseUtcOffset}"));
+
+ if (baseOffsetsCompared == 0)
+ {
+ Assert.True(string.CompareOrdinal(current.DisplayName, previous.DisplayName) >= 0,
+ string.Format($"TimeZoneInfos are out of order. {previous.DisplayName} should be before {current.DisplayName}"));
+ }
+ }
+ }
+
+ private static void ValidateDifferentTimeZoneLists(ReadOnlyCollection<TimeZoneInfo> defaultList, ReadOnlyCollection<TimeZoneInfo> nonSortedList, ReadOnlyCollection<TimeZoneInfo> sortedList)
+ {
+ Assert.Equal(defaultList.Count, nonSortedList.Count);
+ Assert.Equal(defaultList.Count, sortedList.Count);
+
+ Assert.Equal(defaultList.Count, nonSortedList.Count);
+ Assert.True(object.ReferenceEquals(defaultList, sortedList));
+ Dictionary<string, TimeZoneInfo> zones1Dict = defaultList.ToDictionary(t => t.Id);
+ foreach (TimeZoneInfo zone in nonSortedList)
+ {
+ Assert.True(zones1Dict.TryGetValue(zone.Id, out TimeZoneInfo zone1));
+ }
+
+ ValidateTimeZonesSorting(defaultList);
+ }
+
+ [ConditionalFact(typeof(RemoteExecutor), nameof(RemoteExecutor.IsSupported))]
+ public static void TestGetSystemTimeZonesCollectionsCallsOrder()
+ {
+ RemoteExecutor.Invoke(() =>
+ {
+ //
+ // Get sorted list first and then the unsorted list
+ //
+ var zones1 = TimeZoneInfo.GetSystemTimeZones();
+ var zones2 = TimeZoneInfo.GetSystemTimeZones(skipSorting: true);
+ var zones3 = TimeZoneInfo.GetSystemTimeZones(skipSorting: false);
+
+ ValidateDifferentTimeZoneLists(zones1, zones2, zones3);
+
+ //
+ // Clear our caches so zone enumeration is forced to re-read the data
+ //
+ TimeZoneInfo.ClearCachedData();
+
+ //
+ // Get unsorted list first and then the sorted list
+ //
+ zones2 = TimeZoneInfo.GetSystemTimeZones(skipSorting: true);
+ zones3 = TimeZoneInfo.GetSystemTimeZones(skipSorting: false);
+ zones1 = TimeZoneInfo.GetSystemTimeZones();
+ ValidateDifferentTimeZoneLists(zones1, zones2, zones3);
+
+ }).Dispose();
+ }
+
+ [Fact]
+ public static void TestGetSystemTimeZonesCollections()
+ {
+ // This test doing similar checks as TestGetSystemTimeZonesCollectionsCallsOrder does except we need to
+ // run this test without the RemoteExecutor to ensure testing on platforms like Android.
+
+ ReadOnlyCollection<TimeZoneInfo> unsortedList = TimeZoneInfo.GetSystemTimeZones(skipSorting: true);
+ ReadOnlyCollection<TimeZoneInfo> sortedList = TimeZoneInfo.GetSystemTimeZones(skipSorting: false);
+ ReadOnlyCollection<TimeZoneInfo> defaultList = TimeZoneInfo.GetSystemTimeZones();
+ ValidateDifferentTimeZoneLists(defaultList, unsortedList, sortedList);
+ }
+
  [Fact]
  public static void DaylightTransitionsExactTime()
  {

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

@@ -131,7 +131,7 @@ private static unsafe void GetDisplayName(string timeZoneId, Interop.Globalizati
  // Helper function that builds the value backing the DisplayName field from globalization data.
  private static void GetFullValueForDisplayNameField(string timeZoneId, TimeSpan baseUtcOffset, ref string? displayName)
  {
- // There are a few diffent ways we might show the display name depending on the data.
+ // There are a few different ways we might show the display name depending on the data.
  // The algorithm used below should avoid duplicating the same words while still achieving the
  // goal of providing a unique, discoverable, and intuitive name.
 

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

@@ -131,6 +131,7 @@ public DateTimeKind GetCorrespondingKind(TimeZoneInfo? timeZone)
 
  public Dictionary<string, TimeZoneInfo>? _systemTimeZones;
  public ReadOnlyCollection<TimeZoneInfo>? _readOnlySystemTimeZones;
+ public ReadOnlyCollection<TimeZoneInfo>? _readOnlyUnsortedSystemTimeZones;
  public Dictionary<string, TimeZoneInfo>? _timeZonesUsingAlternativeIds;
  public bool _allSystemTimeZonesRead;
  }
@@ -880,41 +881,62 @@ public static TimeZoneInfo FromSerializedString(string source)
  /// <see cref="DisplayName"/>.
  /// This method does *not* throw TimeZoneNotFoundException or InvalidTimeZoneException.
  /// </summary>
- public static ReadOnlyCollection<TimeZoneInfo> GetSystemTimeZones()
+ public static ReadOnlyCollection<TimeZoneInfo> GetSystemTimeZones() => GetSystemTimeZones(skipSorting: false);
+
+ /// <summary>
+ /// Returns a <see cref="ReadOnlyCollection{TimeZoneInfo}"/> containing all valid TimeZone's from the local machine.
+ /// This method does *not* throw TimeZoneNotFoundException or InvalidTimeZoneException.
+ /// </summary>
+ /// <param name="skipSorting">If true, The collection returned may not necessarily be sorted.</param>
+ /// <remarks>By setting the skipSorting parameter to true, the method will attempt to avoid sorting the returned collection.
+ /// This option can be beneficial when the caller does not require a sorted list and aims to enhance the performance. </remarks>
+ public static ReadOnlyCollection<TimeZoneInfo> GetSystemTimeZones(bool skipSorting)
  {
  CachedData cachedData = s_cachedData;
 
  lock (cachedData)
  {
- if (cachedData._readOnlySystemTimeZones == null)
+ if ((skipSorting ? cachedData._readOnlyUnsortedSystemTimeZones : cachedData._readOnlySystemTimeZones) is null)
  {
- PopulateAllSystemTimeZones(cachedData);
- cachedData._allSystemTimeZonesRead = true;
+ if (!cachedData._allSystemTimeZonesRead)
+ {
+ PopulateAllSystemTimeZones(cachedData);
+ cachedData._allSystemTimeZonesRead = true;
+ }
 
  if (cachedData._systemTimeZones != null)
  {
  // return a collection of the cached system time zones
  TimeZoneInfo[] array = new TimeZoneInfo[cachedData._systemTimeZones.Count];
  cachedData._systemTimeZones.Values.CopyTo(array, 0);
 
- // sort and copy the TimeZoneInfo's into a ReadOnlyCollection for the user
- Array.Sort(array, static (x, y) =>
+ if (!skipSorting)
  {
- // sort by BaseUtcOffset first and by DisplayName second - this is similar to the Windows Date/Time control panel
- int comparison = x.BaseUtcOffset.CompareTo(y.BaseUtcOffset);
- return comparison == 0 ? string.CompareOrdinal(x.DisplayName, y.DisplayName) : comparison;
- });
-
- cachedData._readOnlySystemTimeZones = new ReadOnlyCollection<TimeZoneInfo>(array);
+ // sort and copy the TimeZoneInfo's into a ReadOnlyCollection for the user
+ Array.Sort(array, static (x, y) =>
+ {
+ // sort by BaseUtcOffset first and by DisplayName second - this is similar to the Windows Date/Time control panel
+ int comparison = x.BaseUtcOffset.CompareTo(y.BaseUtcOffset);
+ return comparison == 0 ? string.CompareOrdinal(x.DisplayName, y.DisplayName) : comparison;
+ });
+
+ // Always reset _readOnlyUnsortedSystemTimeZones even if it was initialized before. This prevents the need to maintain two separate cache lists in memory
+ // and guarantees that if _readOnlySystemTimeZones is initialized, _readOnlyUnsortedSystemTimeZones is also initialized.
+ cachedData._readOnlySystemTimeZones = cachedData._readOnlyUnsortedSystemTimeZones = new ReadOnlyCollection<TimeZoneInfo>(array);
+ }
+ else
+ {
+ cachedData._readOnlyUnsortedSystemTimeZones = new ReadOnlyCollection<TimeZoneInfo>(array);
+ }
  }
  else
  {
- cachedData._readOnlySystemTimeZones = ReadOnlyCollection<TimeZoneInfo>.Empty;
+ cachedData._readOnlySystemTimeZones = cachedData._readOnlyUnsortedSystemTimeZones = ReadOnlyCollection<TimeZoneInfo>.Empty;
  }
  }
  }
 
- return cachedData._readOnlySystemTimeZones;
+ return skipSorting ? cachedData._readOnlyUnsortedSystemTimeZones! : cachedData._readOnlySystemTimeZones!;
  }
 
  /// <summary>

src/libraries/System.Runtime/ref/System.Runtime.cs

@@ -5687,6 +5687,7 @@ public static void ClearCachedData() { }
  public System.TimeSpan[] GetAmbiguousTimeOffsets(System.DateTimeOffset dateTimeOffset) { throw null; }
  public override int GetHashCode() { throw null; }
  public static System.Collections.ObjectModel.ReadOnlyCollection<System.TimeZoneInfo> GetSystemTimeZones() { throw null; }
+ public static System.Collections.ObjectModel.ReadOnlyCollection<System.TimeZoneInfo> GetSystemTimeZones(bool skipSorting) { throw null; }
  public System.TimeSpan GetUtcOffset(System.DateTime dateTime) { throw null; }
  public System.TimeSpan GetUtcOffset(System.DateTimeOffset dateTimeOffset) { throw null; }
  public bool HasSameRules(System.TimeZoneInfo other) { throw null; }

src/libraries/System.Runtime/tests/System/TimeZoneInfoTests.cs

@@ -1999,6 +1999,84 @@ public static void GetSystemTimeZones()
  }
  }
 
+ private static void ValidateTimeZonesSorting(ReadOnlyCollection<TimeZoneInfo> zones)
+ {
+ // validate sorting: first by base offset, then by display name
+ for (int i = 1; i < zones.Count; i++)
+ {
+ TimeZoneInfo previous = zones[i - 1];
+ TimeZoneInfo current = zones[i];
+
+ int baseOffsetsCompared = current.BaseUtcOffset.CompareTo(previous.BaseUtcOffset);
+ Assert.True(baseOffsetsCompared >= 0,
+ string.Format($"TimeZoneInfos are out of order. {previous.Id}:{previous.BaseUtcOffset} should be before {current.Id}:{current.BaseUtcOffset}"));
+
+ if (baseOffsetsCompared == 0)
+ {
+ Assert.True(string.CompareOrdinal(current.DisplayName, previous.DisplayName) >= 0,
+ string.Format($"TimeZoneInfos are out of order. {previous.DisplayName} should be before {current.DisplayName}"));
+ }
+ }
+ }
+
+ private static void ValidateDifferentTimeZoneLists(ReadOnlyCollection<TimeZoneInfo> defaultList, ReadOnlyCollection<TimeZoneInfo> nonSortedList, ReadOnlyCollection<TimeZoneInfo> sortedList)
+ {
+ Assert.Equal(defaultList.Count, nonSortedList.Count);
+ Assert.Equal(defaultList.Count, sortedList.Count);
+
+ Assert.Equal(defaultList.Count, nonSortedList.Count);
+ Assert.True(object.ReferenceEquals(defaultList, sortedList));
+ Dictionary<string, TimeZoneInfo> zones1Dict = defaultList.ToDictionary(t => t.Id);
+ foreach (TimeZoneInfo zone in nonSortedList)
+ {
+ Assert.True(zones1Dict.TryGetValue(zone.Id, out TimeZoneInfo zone1));
+ }
+
+ ValidateTimeZonesSorting(defaultList);
+ }
+
+ [ConditionalFact(typeof(RemoteExecutor), nameof(RemoteExecutor.IsSupported))]
+ public static void TestGetSystemTimeZonesCollectionsCallsOrder()
+ {
+ RemoteExecutor.Invoke(() =>
+ {
+ //
+ // Get sorted list first and then the unsorted list
+ //
+ var zones1 = TimeZoneInfo.GetSystemTimeZones();
+ var zones2 = TimeZoneInfo.GetSystemTimeZones(skipSorting: true);
+ var zones3 = TimeZoneInfo.GetSystemTimeZones(skipSorting: false);
+
+ ValidateDifferentTimeZoneLists(zones1, zones2, zones3);
+
+ //
+ // Clear our caches so zone enumeration is forced to re-read the data
+ //
+ TimeZoneInfo.ClearCachedData();
+
+ //
+ // Get unsorted list first and then the sorted list
+ //
+ zones2 = TimeZoneInfo.GetSystemTimeZones(skipSorting: true);
+ zones3 = TimeZoneInfo.GetSystemTimeZones(skipSorting: false);
+ zones1 = TimeZoneInfo.GetSystemTimeZones();
+ ValidateDifferentTimeZoneLists(zones1, zones2, zones3);
+
+ }).Dispose();
+ }
+
+ [Fact]
+ public static void TestGetSystemTimeZonesCollections()
+ {
+ // This test doing similar checks as TestGetSystemTimeZonesCollectionsCallsOrder does except we need to
+ // run this test without the RemoteExecutor to ensure testing on platforms like Android.
+
+ ReadOnlyCollection<TimeZoneInfo> unsortedList = TimeZoneInfo.GetSystemTimeZones(skipSorting: true);
+ ReadOnlyCollection<TimeZoneInfo> sortedList = TimeZoneInfo.GetSystemTimeZones(skipSorting: false);
+ ReadOnlyCollection<TimeZoneInfo> defaultList = TimeZoneInfo.GetSystemTimeZones();
+ ValidateDifferentTimeZoneLists(defaultList, unsortedList, sortedList);
+ }
+
  [Fact]
  public static void DaylightTransitionsExactTime()
  {

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

@@ -131,7 +131,7 @@ private static unsafe void GetDisplayName(string timeZoneId, Interop.Globalizati
  // Helper function that builds the value backing the DisplayName field from globalization data.
  private static void GetFullValueForDisplayNameField(string timeZoneId, TimeSpan baseUtcOffset, ref string? displayName)
  {
- // There are a few diffent ways we might show the display name depending on the data.
+ // There are a few different ways we might show the display name depending on the data.
  // The algorithm used below should avoid duplicating the same words while still achieving the
  // goal of providing a unique, discoverable, and intuitive name.
 

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

@@ -131,6 +131,7 @@ public DateTimeKind GetCorrespondingKind(TimeZoneInfo? timeZone)
 
  public Dictionary<string, TimeZoneInfo>? _systemTimeZones;
  public ReadOnlyCollection<TimeZoneInfo>? _readOnlySystemTimeZones;
+ public ReadOnlyCollection<TimeZoneInfo>? _readOnlyUnsortedSystemTimeZones;
  public Dictionary<string, TimeZoneInfo>? _timeZonesUsingAlternativeIds;
  public bool _allSystemTimeZonesRead;
  }
@@ -880,41 +881,62 @@ public static TimeZoneInfo FromSerializedString(string source)
  /// <see cref="DisplayName"/>.
  /// This method does *not* throw TimeZoneNotFoundException or InvalidTimeZoneException.
  /// </summary>
- public static ReadOnlyCollection<TimeZoneInfo> GetSystemTimeZones()
+ public static ReadOnlyCollection<TimeZoneInfo> GetSystemTimeZones() => GetSystemTimeZones(skipSorting: false);
+
+ /// <summary>
+ /// Returns a <see cref="ReadOnlyCollection{TimeZoneInfo}"/> containing all valid TimeZone's from the local machine.
+ /// This method does *not* throw TimeZoneNotFoundException or InvalidTimeZoneException.
+ /// </summary>
+ /// <param name="skipSorting">If true, The collection returned may not necessarily be sorted.</param>
+ /// <remarks>By setting the skipSorting parameter to true, the method will attempt to avoid sorting the returned collection.
+ /// This option can be beneficial when the caller does not require a sorted list and aims to enhance the performance. </remarks>
+ public static ReadOnlyCollection<TimeZoneInfo> GetSystemTimeZones(bool skipSorting)
  {
  CachedData cachedData = s_cachedData;
 
  lock (cachedData)
  {
- if (cachedData._readOnlySystemTimeZones == null)
+ if ((skipSorting ? cachedData._readOnlyUnsortedSystemTimeZones : cachedData._readOnlySystemTimeZones) is null)
  {
- PopulateAllSystemTimeZones(cachedData);
- cachedData._allSystemTimeZonesRead = true;
+ if (!cachedData._allSystemTimeZonesRead)
+ {
+ PopulateAllSystemTimeZones(cachedData);
+ cachedData._allSystemTimeZonesRead = true;
+ }
 
  if (cachedData._systemTimeZones != null)
  {
  // return a collection of the cached system time zones
  TimeZoneInfo[] array = new TimeZoneInfo[cachedData._systemTimeZones.Count];
  cachedData._systemTimeZones.Values.CopyTo(array, 0);
 
- // sort and copy the TimeZoneInfo's into a ReadOnlyCollection for the user
- Array.Sort(array, static (x, y) =>
+ if (!skipSorting)
  {
- // sort by BaseUtcOffset first and by DisplayName second - this is similar to the Windows Date/Time control panel
- int comparison = x.BaseUtcOffset.CompareTo(y.BaseUtcOffset);
- return comparison == 0 ? string.CompareOrdinal(x.DisplayName, y.DisplayName) : comparison;
- });
-
- cachedData._readOnlySystemTimeZones = new ReadOnlyCollection<TimeZoneInfo>(array);
+ // sort and copy the TimeZoneInfo's into a ReadOnlyCollection for the user
+ Array.Sort(array, static (x, y) =>
+ {
+ // sort by BaseUtcOffset first and by DisplayName second - this is similar to the Windows Date/Time control panel
+ int comparison = x.BaseUtcOffset.CompareTo(y.BaseUtcOffset);
+ return comparison == 0 ? string.CompareOrdinal(x.DisplayName, y.DisplayName) : comparison;
+ });
+
+ // Always reset _readOnlyUnsortedSystemTimeZones even if it was initialized before. This prevents the need to maintain two separate cache lists in memory
+ // and guarantees that if _readOnlySystemTimeZones is initialized, _readOnlyUnsortedSystemTimeZones is also initialized.
+ cachedData._readOnlySystemTimeZones = cachedData._readOnlyUnsortedSystemTimeZones = new ReadOnlyCollection<TimeZoneInfo>(array);
+ }
+ else
+ {
+ cachedData._readOnlyUnsortedSystemTimeZones = new ReadOnlyCollection<TimeZoneInfo>(array);
+ }
  }
  else
  {
- cachedData._readOnlySystemTimeZones = ReadOnlyCollection<TimeZoneInfo>.Empty;
+ cachedData._readOnlySystemTimeZones = cachedData._readOnlyUnsortedSystemTimeZones = ReadOnlyCollection<TimeZoneInfo>.Empty;
  }
  }
  }
 
- return cachedData._readOnlySystemTimeZones;
+ return skipSorting ? cachedData._readOnlyUnsortedSystemTimeZones! : cachedData._readOnlySystemTimeZones!;
  }
 
  /// <summary>

src/libraries/System.Runtime/ref/System.Runtime.cs

@@ -5687,6 +5687,7 @@ public static void ClearCachedData() { }
  public System.TimeSpan[] GetAmbiguousTimeOffsets(System.DateTimeOffset dateTimeOffset) { throw null; }
  public override int GetHashCode() { throw null; }
  public static System.Collections.ObjectModel.ReadOnlyCollection<System.TimeZoneInfo> GetSystemTimeZones() { throw null; }
+ public static System.Collections.ObjectModel.ReadOnlyCollection<System.TimeZoneInfo> GetSystemTimeZones(bool skipSorting) { throw null; }
  public System.TimeSpan GetUtcOffset(System.DateTime dateTime) { throw null; }
  public System.TimeSpan GetUtcOffset(System.DateTimeOffset dateTimeOffset) { throw null; }
  public bool HasSameRules(System.TimeZoneInfo other) { throw null; }

src/libraries/System.Runtime/tests/System/TimeZoneInfoTests.cs

@@ -1999,6 +1999,84 @@ public static void GetSystemTimeZones()
  }
  }
 
+ private static void ValidateTimeZonesSorting(ReadOnlyCollection<TimeZoneInfo> zones)
+ {
+ // validate sorting: first by base offset, then by display name
+ for (int i = 1; i < zones.Count; i++)
+ {
+ TimeZoneInfo previous = zones[i - 1];
+ TimeZoneInfo current = zones[i];
+
+ int baseOffsetsCompared = current.BaseUtcOffset.CompareTo(previous.BaseUtcOffset);
+ Assert.True(baseOffsetsCompared >= 0,
+ string.Format($"TimeZoneInfos are out of order. {previous.Id}:{previous.BaseUtcOffset} should be before {current.Id}:{current.BaseUtcOffset}"));
+
+ if (baseOffsetsCompared == 0)
+ {
+ Assert.True(string.CompareOrdinal(current.DisplayName, previous.DisplayName) >= 0,
+ string.Format($"TimeZoneInfos are out of order. {previous.DisplayName} should be before {current.DisplayName}"));
+ }
+ }
+ }
+
+ private static void ValidateDifferentTimeZoneLists(ReadOnlyCollection<TimeZoneInfo> defaultList, ReadOnlyCollection<TimeZoneInfo> nonSortedList, ReadOnlyCollection<TimeZoneInfo> sortedList)
+ {
+ Assert.Equal(defaultList.Count, nonSortedList.Count);
+ Assert.Equal(defaultList.Count, sortedList.Count);
+
+ Assert.Equal(defaultList.Count, nonSortedList.Count);
+ Assert.True(object.ReferenceEquals(defaultList, sortedList));
+ Dictionary<string, TimeZoneInfo> zones1Dict = defaultList.ToDictionary(t => t.Id);
+ foreach (TimeZoneInfo zone in nonSortedList)
+ {
+ Assert.True(zones1Dict.TryGetValue(zone.Id, out TimeZoneInfo zone1));
+ }
+
+ ValidateTimeZonesSorting(defaultList);
+ }
+
+ [ConditionalFact(typeof(RemoteExecutor), nameof(RemoteExecutor.IsSupported))]
+ public static void TestGetSystemTimeZonesCollectionsCallsOrder()
+ {
+ RemoteExecutor.Invoke(() =>
+ {
+ //
+ // Get sorted list first and then the unsorted list
+ //
+ var zones1 = TimeZoneInfo.GetSystemTimeZones();
+ var zones2 = TimeZoneInfo.GetSystemTimeZones(skipSorting: true);
+ var zones3 = TimeZoneInfo.GetSystemTimeZones(skipSorting: false);
+
+ ValidateDifferentTimeZoneLists(zones1, zones2, zones3);
+
+ //
+ // Clear our caches so zone enumeration is forced to re-read the data
+ //
+ TimeZoneInfo.ClearCachedData();
+
+ //
+ // Get unsorted list first and then the sorted list
+ //
+ zones2 = TimeZoneInfo.GetSystemTimeZones(skipSorting: true);
+ zones3 = TimeZoneInfo.GetSystemTimeZones(skipSorting: false);
+ zones1 = TimeZoneInfo.GetSystemTimeZones();
+ ValidateDifferentTimeZoneLists(zones1, zones2, zones3);
+
+ }).Dispose();
+ }
+
+ [Fact]
+ public static void TestGetSystemTimeZonesCollections()
+ {
+ // This test doing similar checks as TestGetSystemTimeZonesCollectionsCallsOrder does except we need to
+ // run this test without the RemoteExecutor to ensure testing on platforms like Android.
+
+ ReadOnlyCollection<TimeZoneInfo> unsortedList = TimeZoneInfo.GetSystemTimeZones(skipSorting: true);
+ ReadOnlyCollection<TimeZoneInfo> sortedList = TimeZoneInfo.GetSystemTimeZones(skipSorting: false);
+ ReadOnlyCollection<TimeZoneInfo> defaultList = TimeZoneInfo.GetSystemTimeZones();
+ ValidateDifferentTimeZoneLists(defaultList, unsortedList, sortedList);
+ }
+
  [Fact]
  public static void DaylightTransitionsExactTime()
  {