Move implementation to DateTimeOffset.Now

src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems

@@ -254,6 +254,8 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\DateTime.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\DateTimeKind.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\DateTimeOffset.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\DateTimeOffset.NonAndroid.cs" Condition="'$(TargetsAndroid)' != 'true'" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\DateTimeOffset.Android.cs" Condition="'$(TargetsAndroid)' == 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\DayOfWeek.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\DBNull.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Decimal.cs" />

src/libraries/System.Private.CoreLib/src/System/DateTimeOffset.Android.cs

@@ -0,0 +1,80 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Threading;
+
+namespace System
+{
+    public readonly partial struct DateTimeOffset
+    {
+        private static bool s_androidTZDataLoaded;
+        private static readonly object s_localUtcOffsetLock = new();
+        private static Thread? s_loadAndroidTZData;
+
+        // TryGetNow is a helper function on Android responsible for:
+        // 1) quickly returning a fast path offset when first called
+        // 2) starting a background thread to pursue the original implementation
+        //
+        // On Android, loading AndroidTZData is expensive for startup performance.
+        // The fast result relies on `System.TimeZoneInfo.LocalDateTimeOffset` being set
+        // in the App Context's properties as the appropriate local date time offset from UTC.
+        // monovm_initialize(_preparsed) can be leveraged to do so.
+        // However, to handle timezone changes during the app lifetime, AndroidTZData needs to be loaded.
+        // So, on first call, we return the fast path and start a background thread to pursue the original
+        // implementation which eventually loads AndroidTZData.
+
+        private static TimeSpan TryGetNow()
+        {
+            if (s_androidTZDataLoaded) // The background thread finished, the cache is loaded.
+                return TimeZoneInfo.GetLocalUtcOffset(DateTime.UtcNow, TimeZoneInfoOptions.NoThrowOnInvalidTime);
+
+            if (!s_androidTZDataLoaded && s_loadAndroidTZData == null) // The cache isn't loaded and no background thread has been created
+            {
+                lock (s_localUtcOffsetLock)
+                {
+                    // GetLocalUtcOffset may be called multiple times before a cache is loaded and a background thread is running,
+                    // once the lock is available, check for a cache and background thread.
+                    if (s_androidTZDataLoaded)
+                        return TimeZoneInfo.GetLocalUtcOffset(DateTime.UtcNow, TimeZoneInfoOptions.NoThrowOnInvalidTime);
+
+                    if (s_loadAndroidTZData == null)
+                    {
+                        s_loadAndroidTZData = new Thread(() => {
+                            Thread.Sleep(1000);
+                            _ = TimeZoneInfo.GetLocalUtcOffset(DateTime.UtcNow, TimeZoneInfoOptions.NoThrowOnInvalidTime);
+                            lock (s_localUtcOffsetLock)
+                            {
+                                s_androidTZDataLoaded = true;
+                                s_loadAndroidTZData = null; // Ensure thread is cleared when cache is loaded
+                            }
+                        });
+                        s_loadAndroidTZData.IsBackground = true;
+                        s_loadAndroidTZData.Start();
+                    }
+                }
+            }
+
+            object? localDateTimeOffset = AppContext.GetData("System.TimeZoneInfo.LocalDateTimeOffset");
+            if (localDateTimeOffset == null)
+                return TimeZoneInfo.GetLocalUtcOffset(DateTime.UtcNow, TimeZoneInfoOptions.NoThrowOnInvalidTime); // If no offset property provided through monovm app context, default
+
+            int localDateTimeOffsetSeconds = Convert.ToInt32(localDateTimeOffset);
+            TimeSpan offset = TimeSpan.FromSeconds(localDateTimeOffsetSeconds);
+            return offset;
+        }
+
+        public static DateTimeOffset Now
+        {
+            get
+            {
+                DateTime utcDateTime = DateTime.UtcNow;
+                TimeSpan offset = TryGetNow();
+                long localTicks = utcDateTime.Ticks + offset.Ticks;
+                if (localTicks < DateTime.MinTicks || localTicks > DateTime.MaxTicks)
+                    throw new ArgumentException(SR.Arg_ArgumentOutOfRangeException);
+
+                return new DateTimeOffset(localTicks, offset);
+            }
+        }
+    }
+}

src/libraries/System.Private.CoreLib/src/System/DateTimeOffset.NonAndroid.cs

@@ -0,0 +1,12 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace System
+{
+        public readonly partial struct DateTimeOffset
+        {
+                // Returns a DateTimeOffset representing the current date and time. The
+                // resolution of the returned value depends on the system timer.
+                public static DateTimeOffset Now => ToLocalTime(DateTime.UtcNow, true);
+        }
+}

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

@@ -34,7 +34,7 @@ namespace System
     [StructLayout(LayoutKind.Auto)]
     [Serializable]
     [TypeForwardedFrom("mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089")]
-    public readonly struct DateTimeOffset
+    public readonly partial struct DateTimeOffset
         : IComparable,
           ISpanFormattable,
           IComparable<DateTimeOffset>,
@@ -321,10 +321,6 @@ public DateTimeOffset(int year, int month, int day, int hour, int minute, int se
             _dateTime = _dateTime.AddMicroseconds(microsecond);
         }
 
-        // Returns a DateTimeOffset representing the current date and time. The
-        // resolution of the returned value depends on the system timer.
-        public static DateTimeOffset Now => ToLocalTime(DateTime.UtcNow, true);
-
         public static DateTimeOffset UtcNow
         {
             get

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

@@ -142,62 +142,6 @@ private static TimeZoneInfo GetLocalTimeZoneCore()
             return Utc;
         }
 
-        private static TimeSpan GetCacheLocalUtcOffset(DateTime dateTime, TimeZoneInfoOptions flags)
-        {
-            CachedData cachedData = s_cachedData;
-            return cachedData.Local.GetUtcOffset(dateTime, flags, cachedData);
-        }
-
-        private static bool s_androidTZDataLoaded;
-        private static object s_localUtcOffsetLock = new();
-        private static Thread? s_loadAndroidTZData;
-        // Shortcut for TimeZoneInfo.Local.GetUtcOffset
-        // On Android, loading AndroidTZData while obtaining cachedData.Local is expensive for startup.
-        // We introduce a fast result for GetLocalUtcOffset that relies on the date time offset being
-        // passed into monovm_initialize(_preparsed) from Java in seconds as LOCAL_DATE_TIME_OFFSET.
-        // However, to handle timezone changes during the app lifetime, AndroidTZData needs to be loaded.
-        // The fast path is initially used, and we start a background thread to get cachedData.Local
-        internal static TimeSpan GetLocalUtcOffset(DateTime dateTime, TimeZoneInfoOptions flags)
-        {
-            if (s_androidTZDataLoaded) // The background thread finished, the cache is loaded.
-                return GetCacheLocalUtcOffset(dateTime, flags);
-
-            if (!s_androidTZDataLoaded && s_loadAndroidTZData == null) // The cache isn't loaded and no background thread has been created
-            {
-                lock (s_localUtcOffsetLock)
-                {
-                    // GetLocalUtcOffset may be called multiple times before a cache is loaded and a background thread is running,
-                    // once the lock is available, check for a cache and background thread.
-                    if (s_androidTZDataLoaded)
-                        return GetCacheLocalUtcOffset(dateTime, flags);
-
-                    if (s_loadAndroidTZData == null)
-                    {
-                        s_loadAndroidTZData = new Thread(() => {
-                            Thread.Sleep(1000);
-                            CachedData cachedData = s_cachedData;
-                            _ = cachedData.Local;
-                            lock (s_localUtcOffsetLock)
-                            {
-                                s_androidTZDataLoaded = true;
-                                s_loadAndroidTZData = null; // Ensure thread is cleared when cache is loaded
-                            }
-                        });
-                        s_loadAndroidTZData.IsBackground = true;
-                        s_loadAndroidTZData.Start();
-                    }
-                }
-            }
-
-            object? localDateTimeOffset = AppContext.GetData("System.TimeZoneInfo.LocalDateTimeOffset");
-            if (localDateTimeOffset == null)
-                return GetCacheLocalUtcOffset(dateTime, flags); // If no offset property provided through monovm app context, default
-
-            int localDateTimeOffsetSeconds = Convert.ToInt32(localDateTimeOffset);
-            TimeSpan offset = TimeSpan.FromSeconds(localDateTimeOffsetSeconds);
-            return offset;
-        }
-
         private static TimeZoneInfoResult TryGetTimeZoneFromLocalMachineCore(string id, out TimeZoneInfo? value, out Exception? e)
         {
 

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

@@ -24,13 +24,6 @@ private static TimeZoneInfo GetLocalTimeZoneCore()
             return GetLocalTimeZoneFromTzFile();
         }
 
-        // Shortcut for TimeZoneInfo.Local.GetUtcOffset
-        internal static TimeSpan GetLocalUtcOffset(DateTime dateTime, TimeZoneInfoOptions flags)
-        {
-            CachedData cachedData = s_cachedData;
-            return cachedData.Local.GetUtcOffset(dateTime, flags, cachedData);
-        }
-
         private static TimeZoneInfoResult TryGetTimeZoneFromLocalMachineCore(string id, out TimeZoneInfo? value, out Exception? e)
         {
             value = null;

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

@@ -76,13 +76,6 @@ public OffsetAndRule(int year, TimeSpan offset, AdjustmentRule? rule)
             }
         }
 
-        // Shortcut for TimeZoneInfo.Local.GetUtcOffset
-        internal static TimeSpan GetLocalUtcOffset(DateTime dateTime, TimeZoneInfoOptions flags)
-        {
-            CachedData cachedData = s_cachedData;
-            return cachedData.Local.GetUtcOffset(dateTime, flags, cachedData);
-        }
-
         /// <summary>
         /// Returns a cloned array of AdjustmentRule objects
         /// </summary>

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

@@ -312,6 +312,13 @@ public TimeSpan GetUtcOffset(DateTimeOffset dateTimeOffset) =>
         public TimeSpan GetUtcOffset(DateTime dateTime) =>
             GetUtcOffset(dateTime, TimeZoneInfoOptions.NoThrowOnInvalidTime, s_cachedData);
 
+        // Shortcut for TimeZoneInfo.Local.GetUtcOffset
+        internal static TimeSpan GetLocalUtcOffset(DateTime dateTime, TimeZoneInfoOptions flags)
+        {
+            CachedData cachedData = s_cachedData;
+            return cachedData.Local.GetUtcOffset(dateTime, flags, cachedData);
+        }
+
         /// <summary>
         /// Returns the Universal Coordinated Time (UTC) Offset for the current TimeZoneInfo instance.
         /// </summary>