[monodroid, java-runtime] Add local date time offset monovm prop (#7331)

Context: dotnet/runtime#74459
Context: dotnet/runtime#71004
Context: dotnet/runtime#54845

dotnet/runtime#54845 added support TimeZoneInfo support for Android.
This was found to slow down initial use of `DateTimeOffset.Now` by
~277ms (dotnet/runtime#17004).

dotnet/runtime#74459 started reducing this startup overhead by adding
support for a new `System.TimeZoneInfo.LocalDateTimeOffset` property
on `AppContext`: if `System.TimeZoneInfo.LocalDateTimeOffset` is set,
it is used as the initial local DateTime Offset value.

Update `mono.android.MonoPackageManager.LoadApplication()` and
`libmono-android*.so` so that the
`System.TimeZoneInfo.LocalDateTimeOffset` AppContext property is set
during process startup.  This can reduce `DateTimeOffset.Now` startup
overhead from ~277ms to ~50ms.

Note: `System.TimeZoneInfo.LocalDateTimeOffset` is fastest on
API-26+ (Android 8.0+) targets, as it uses
[`java.time.ZoneOffset.getTotalSeconds()`][0].

Note: `$(AndroidJavaRuntimeApiLevel)` is updated to API-26 so that
`ZoneOffset.getTotalSeconds()` can be used.  Care should be taken
within `src/java-runtime` to ensure that Android API use is
appropriately protected behind runtime version checks.

[0]: https://developer.android.com/reference/kotlin/java/time/ZoneOffset#gettotalseconds

Author: mdh1418

Configuration.props

@@ -25,7 +25,7 @@
     <!-- Should correspond to the first value from `$(API_LEVELS)` in `build-tools/api-xml-adjuster/Makefile` -->
     <AndroidFirstFrameworkVersion Condition="'$(AndroidFirstFrameworkVersion)' == ''">v4.4</AndroidFirstFrameworkVersion>
     <AndroidFirstApiLevel Condition="'$(AndroidFirstApiLevel)' == ''">19</AndroidFirstApiLevel>
-    <AndroidJavaRuntimeApiLevel Condition="'$(AndroidJavaRuntimeApiLevel)' == ''">21</AndroidJavaRuntimeApiLevel>
+    <AndroidJavaRuntimeApiLevel Condition="'$(AndroidJavaRuntimeApiLevel)' == ''">26</AndroidJavaRuntimeApiLevel>
     <!-- The min API level supported by Microsoft.Android.Sdk, should refactor/remove when this value is the same as $(AndroidFirstApiLevel) -->
     <AndroidMinimumDotNetApiLevel Condition="'$(AndroidMinimumDotNetApiLevel)' == ''">21</AndroidMinimumDotNetApiLevel>
     <AndroidFirstPlatformId Condition="'$(AndroidFirstPlatformId)' == ''">$(AndroidFirstApiLevel)</AndroidFirstPlatformId>

src/java-runtime/java/mono/android/MonoPackageManager.java

@@ -2,6 +2,9 @@
 
 import java.io.*;
 import java.lang.String;
+import java.time.OffsetDateTime;
+import java.time.ZoneOffset;
+import java.util.Calendar;
 import java.util.Locale;
 import java.util.HashSet;
 import java.util.zip.*;
@@ -42,6 +45,14 @@ public static void LoadApplication (Context context, ApplicationInfo runtimePack
 				String dataDir      = getNativeLibraryPath (context);
 				ClassLoader loader  = context.getClassLoader ();
 				String runtimeDir = getNativeLibraryPath (runtimePackage);
+				int localDateTimeOffset;
+
+				if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.O) {
+					localDateTimeOffset = OffsetDateTime.now().getOffset().getTotalSeconds();
+				}
+				else {
+					localDateTimeOffset = (Calendar.getInstance ().get (Calendar.ZONE_OFFSET) + Calendar.getInstance ().get (Calendar.DST_OFFSET)) / 1000;
+				}
 
 				//
 				// Should the order change here, src/monodroid/jni/SharedConstants.hh must be updated accordingly
@@ -106,6 +117,7 @@ public static void LoadApplication (Context context, ApplicationInfo runtimePack
 						apks,
 						runtimeDir,
 						appDirs,
+						localDateTimeOffset,
 						loader,
 						MonoPackageManager_Resources.Assemblies,
 						Build.VERSION.SDK_INT,

src/java-runtime/java/mono/android/Runtime.java

@@ -20,6 +20,7 @@ public static native void initInternal (
 		String[] runtimeApks,
 		String runtimeDataDir,
 		String[] appDirs,
+		int localDateTimeOffset,
 		ClassLoader loader,
 		String[] assemblies,
 		int apiLevel,

src/monodroid/jni/mono_android_Runtime.h

@@ -174,8 +174,8 @@ namespace xamarin::android::internal
 	public:
 		void Java_mono_android_Runtime_register (JNIEnv *env, jstring managedType, jclass nativeClass, jstring methods);
 		void Java_mono_android_Runtime_initInternal (JNIEnv *env, jclass klass, jstring lang, jobjectArray runtimeApksJava,
-		                                             jstring runtimeNativeLibDir, jobjectArray appDirs, jobject loader,
-		                                             jobjectArray assembliesJava, jint apiLevel, jboolean isEmulator,
+		                                             jstring runtimeNativeLibDir, jobjectArray appDirs, jint localDateTimeOffset,
+		                                             jobject loader, jobjectArray assembliesJava, jint apiLevel, jboolean isEmulator,
 		                                             jboolean haveSplitApks);
 #if !defined (ANDROID)
 		jint Java_mono_android_Runtime_createNewContextWithData (JNIEnv *env, jclass klass, jobjectArray runtimeApksJava, jobjectArray assembliesJava,

src/monodroid/jni/monodroid-glue-internal.hh

@@ -2152,8 +2152,8 @@ MonodroidRuntime::install_logging_handlers ()
 
 inline void
 MonodroidRuntime::Java_mono_android_Runtime_initInternal (JNIEnv *env, jclass klass, jstring lang, jobjectArray runtimeApksJava,
-                                                          jstring runtimeNativeLibDir, jobjectArray appDirs, jobject loader,
-                                                          jobjectArray assembliesJava, jint apiLevel, jboolean isEmulator,
+                                                          jstring runtimeNativeLibDir, jobjectArray appDirs, jint localDateTimeOffset,
+                                                          jobject loader, jobjectArray assembliesJava, jint apiLevel, jboolean isEmulator,
                                                           jboolean haveSplitApks)
 {
 	char *mono_log_mask_raw = nullptr;
@@ -2180,7 +2180,7 @@ MonodroidRuntime::Java_mono_android_Runtime_initInternal (JNIEnv *env, jclass kl
 	mono_opt_aot_lazy_assembly_load = application_config.aot_lazy_load ? TRUE : FALSE;
 
 	{
-		MonoVMProperties monovm_props { home };
+		MonoVMProperties monovm_props { home, localDateTimeOffset };
 
 		// NOTE: the `const_cast` breaks the contract made to MonoVMProperties that the arrays it returns won't be
 		// modified, but it's "ok" since Mono doesn't modify them and by using `const char* const*` in MonoVMProperties
@@ -2455,6 +2455,7 @@ Java_mono_android_Runtime_init (JNIEnv *env, jclass klass, jstring lang, jobject
 		runtimeApksJava,
 		runtimeNativeLibDir,
 		appDirs,
+		0,
 		loader,
 		assembliesJava,
 		apiLevel,
@@ -2465,7 +2466,7 @@ Java_mono_android_Runtime_init (JNIEnv *env, jclass klass, jstring lang, jobject
 
 JNIEXPORT void JNICALL
 Java_mono_android_Runtime_initInternal (JNIEnv *env, jclass klass, jstring lang, jobjectArray runtimeApksJava,
-                                jstring runtimeNativeLibDir, jobjectArray appDirs, jobject loader,
+                                jstring runtimeNativeLibDir, jobjectArray appDirs, jint localDateTimeOffset, jobject loader,
                                 jobjectArray assembliesJava, jint apiLevel, jboolean isEmulator,
                                 jboolean haveSplitApks)
 {
@@ -2476,6 +2477,7 @@ Java_mono_android_Runtime_initInternal (JNIEnv *env, jclass klass, jstring lang,
 		runtimeApksJava,
 		runtimeNativeLibDir,
 		appDirs,
+		localDateTimeOffset,
 		loader,
 		assembliesJava,
 		apiLevel,

src/monodroid/jni/monodroid-glue.cc

@@ -5,9 +5,11 @@ using namespace xamarin::android::internal;
 MonoVMProperties::property_array MonoVMProperties::_property_keys {
 	RUNTIME_IDENTIFIER_KEY,
 	APP_CONTEXT_BASE_DIRECTORY_KEY,
+	LOCAL_DATE_TIME_OFFSET_KEY,
 };
 
 MonoVMProperties::property_array MonoVMProperties::_property_values {
 	SharedConstants::runtime_identifier,
 	nullptr,
+	nullptr,
 };

src/monodroid/jni/monovm-properties.cc

@@ -10,23 +10,30 @@ namespace xamarin::android::internal
 {
 	class MonoVMProperties final
 	{
-		constexpr static size_t PROPERTY_COUNT = 2;
+		constexpr static size_t PROPERTY_COUNT = 3;
 
 		constexpr static char RUNTIME_IDENTIFIER_KEY[] = "RUNTIME_IDENTIFIER";
 		constexpr static size_t RUNTIME_IDENTIFIER_INDEX = 0;
 
 		constexpr static char APP_CONTEXT_BASE_DIRECTORY_KEY[] = "APP_CONTEXT_BASE_DIRECTORY";
 		constexpr static size_t APP_CONTEXT_BASE_DIRECTORY_INDEX = 1;
 
+		constexpr static char LOCAL_DATE_TIME_OFFSET_KEY[] = "System.TimeZoneInfo.LocalDateTimeOffset";
+		constexpr static size_t LOCAL_DATE_TIME_OFFSET_INDEX = 2;
+
 		using property_array = const char*[PROPERTY_COUNT];
 
 	public:
-		explicit MonoVMProperties (jstring_wrapper& filesDir)
+		explicit MonoVMProperties (jstring_wrapper& filesDir, jint localDateTimeOffset)
 		{
 			static_assert (PROPERTY_COUNT == N_PROPERTY_KEYS);
 			static_assert (PROPERTY_COUNT == N_PROPERTY_VALUES);
 
 			_property_values[APP_CONTEXT_BASE_DIRECTORY_INDEX] = strdup (filesDir.get_cstr ());
+
+			static_local_string<32> localDateTimeOffsetBuffer;
+			localDateTimeOffsetBuffer.append (localDateTimeOffset);
+			_property_values[LOCAL_DATE_TIME_OFFSET_INDEX] = strdup (localDateTimeOffsetBuffer.get ());
 		}
 
 		constexpr int property_count () const