Add a custom switch to clean up the leaked Dart VM (flutter#30541)

common/settings.h

@@ -207,6 +207,10 @@ struct Settings {
   // shells in the platform (via their embedding APIs) should cooperate to make
   // sure this flag is never set if they want the VM to shutdown and free all
   // associated resources.
+  // It can be customized by application, more detail:
+  // https://github.com/flutter/flutter/issues/95903
+  // TODO(eggfly): Should it be set to false by default?
+  // https://github.com/flutter/flutter/issues/96843
   bool leak_vm = true;
 
   // Engine settings

shell/common/switches.cc

@@ -384,6 +384,10 @@ Settings SettingsFromCommandLine(const fml::CommandLine& command_line) {
   command_line.GetOptionValue(FlagForSwitch(Switch::CacheDirPath),
                               &settings.temp_directory_path);
 
+  bool leak_vm = "true" == command_line.GetOptionValueWithDefault(
+                               FlagForSwitch(Switch::LeakVM), "true");
+  settings.leak_vm = leak_vm;
+
   if (settings.icu_initialization_required) {
     command_line.GetOptionValue(FlagForSwitch(Switch::ICUDataFilePath),
                                 &settings.icu_data_path);

shell/common/switches.h

@@ -215,6 +215,11 @@ DEF_SWITCH(EnableSkParagraph,
            "enable-skparagraph",
            "Selects the SkParagraph implementation of the text layout engine.")
 
+DEF_SWITCH(LeakVM,
+           "leak-vm",
+           "When the last shell shuts down, the shared VM is leaked by default "
+           "(the leak_vm in VM settings is true). To clean up the leak VM, set "
+           "this value to false.")
 DEF_SWITCHES_END
 
 void PrintUsage(const std::string& executable_name);

shell/platform/android/io/flutter/embedding/engine/loader/FlutterLoader.java

@@ -40,6 +40,19 @@ public class FlutterLoader {
   private static final String ENABLE_SKPARAGRAPH_META_DATA_KEY =
       "io.flutter.embedding.android.EnableSkParagraph";
 
+  /**
+   * Set whether leave or clean up the VM after the last shell shuts down. It can be set from app's
+   * meta-data in <application /> in AndroidManifest.xml. Set it to true in to leave the Dart VM,
+   * set it to false to destroy VM.
+   *
+   * <p>If your want to let your app destroy the last shell and re-create shells more quickly, set
+   * it to true, otherwise if you want to clean up the memory of the leak VM, set it to false.
+   *
+   * <p>TODO(eggfly): Should it be set to false by default?
+   * https://github.com/flutter/flutter/issues/96843
+   */
+  private static final String LEAK_VM_META_DATA_KEY = "io.flutter.embedding.android.LeakVM";
+
   // Must match values in flutter::switches
   static final String AOT_SHARED_LIBRARY_NAME = "aot-shared-library-name";
   static final String AOT_VMSERVICE_SHARED_LIBRARY_NAME = "aot-vmservice-shared-library-name";
@@ -299,6 +312,9 @@ public void ensureInitializationComplete(
         shellArgs.add("--enable-skparagraph");
       }
 
+      final String leakVM = isLeakVM(metaData) ? "true" : "false";
+      shellArgs.add("--leak-vm=" + leakVM);
+
       long initTimeMillis = SystemClock.uptimeMillis() - initStartTimestampMillis;
 
       flutterJNI.init(
@@ -318,6 +334,14 @@ public void ensureInitializationComplete(
     }
   }
 
+  private static boolean isLeakVM(@Nullable Bundle metaData) {
+    final boolean leakVMDefaultValue = true;
+    if (metaData == null) {
+      return leakVMDefaultValue;
+    }
+    return metaData.getBoolean(LEAK_VM_META_DATA_KEY, leakVMDefaultValue);
+  }
+
   /**
    * Same as {@link #ensureInitializationComplete(Context, String[])} but waiting on a background
    * thread, then invoking {@code callback} on the {@code callbackHandler}.

shell/platform/android/test/io/flutter/embedding/engine/loader/FlutterLoaderTest.java

@@ -21,6 +21,7 @@
 import android.annotation.TargetApi;
 import android.app.ActivityManager;
 import android.content.Context;
+import android.os.Bundle;
 import io.flutter.embedding.engine.FlutterJNI;
 import java.util.Arrays;
 import java.util.List;
@@ -85,6 +86,58 @@ public void itDefaultsTheOldGenHeapSizeAppropriately() {
     assertTrue(arguments.contains(oldGenHeapArg));
   }
 
+  @Test
+  public void itSetsLeakVMToTrueByDefault() {
+    FlutterJNI mockFlutterJNI = mock(FlutterJNI.class);
+    FlutterLoader flutterLoader = new FlutterLoader(mockFlutterJNI);
+
+    assertFalse(flutterLoader.initialized());
+    flutterLoader.startInitialization(RuntimeEnvironment.application);
+    flutterLoader.ensureInitializationComplete(RuntimeEnvironment.application, null);
+    shadowOf(getMainLooper()).idle();
+
+    final String leakVMArg = "--leak-vm=true";
+    ArgumentCaptor<String[]> shellArgsCaptor = ArgumentCaptor.forClass(String[].class);
+    verify(mockFlutterJNI, times(1))
+        .init(
+            eq(RuntimeEnvironment.application),
+            shellArgsCaptor.capture(),
+            anyString(),
+            anyString(),
+            anyString(),
+            anyLong());
+    List<String> arguments = Arrays.asList(shellArgsCaptor.getValue());
+    assertTrue(arguments.contains(leakVMArg));
+  }
+
+  @Test
+  public void itSetsTheLeakVMFromMetaData() {
+    FlutterJNI mockFlutterJNI = mock(FlutterJNI.class);
+    FlutterLoader flutterLoader = new FlutterLoader(mockFlutterJNI);
+    Bundle metaData = new Bundle();
+    metaData.putBoolean("io.flutter.embedding.android.LeakVM", false);
+    RuntimeEnvironment.application.getApplicationInfo().metaData = metaData;
+
+    FlutterLoader.Settings settings = new FlutterLoader.Settings();
+    assertFalse(flutterLoader.initialized());
+    flutterLoader.startInitialization(RuntimeEnvironment.application, settings);
+    flutterLoader.ensureInitializationComplete(RuntimeEnvironment.application, null);
+    shadowOf(getMainLooper()).idle();
+
+    final String leakVMArg = "--leak-vm=false";
+    ArgumentCaptor<String[]> shellArgsCaptor = ArgumentCaptor.forClass(String[].class);
+    verify(mockFlutterJNI, times(1))
+        .init(
+            eq(RuntimeEnvironment.application),
+            shellArgsCaptor.capture(),
+            anyString(),
+            anyString(),
+            anyString(),
+            anyLong());
+    List<String> arguments = Arrays.asList(shellArgsCaptor.getValue());
+    assertTrue(arguments.contains(leakVMArg));
+  }
+
   @Test
   public void itUsesCorrectExecutorService() {
     FlutterJNI mockFlutterJNI = mock(FlutterJNI.class);

shell/platform/darwin/ios/framework/Source/FlutterDartProject.mm

@@ -160,6 +160,13 @@
   NSNumber* enableSkParagraph = [mainBundle objectForInfoDictionaryKey:@"FLTEnableSkParagraph"];
   settings.enable_skparagraph = (enableSkParagraph != nil) ? enableSkParagraph.boolValue : false;
 
+  // Leak Dart VM settings, set whether leave or clean up the VM after the last shell shuts down.
+  NSNumber* leakDartVM = [mainBundle objectForInfoDictionaryKey:@"FLTLeakDartVM"];
+  // It will change the default leak_vm value in settings only if the key exists.
+  if (leakDartVM != nil) {
+    settings.leak_vm = leakDartVM.boolValue;
+  }
+
 #if FLUTTER_RUNTIME_MODE == FLUTTER_RUNTIME_MODE_DEBUG
   // There are no ownership concerns here as all mappings are owned by the
   // embedder and not the engine.

shell/platform/darwin/ios/framework/Source/FlutterDartProjectTest.mm

@@ -39,6 +39,17 @@ - (void)testMainBundleSettingsAreCorrectlyParsed {
       [FlutterDartProject domainNetworkPolicy:appTransportSecurity]);
 }
 
+- (void)testLeakDartVMSettingsAreCorrectlyParsed {
+  // The FLTLeakDartVM's value is defined in Info.plist
+  NSBundle* mainBundle = [NSBundle mainBundle];
+  NSNumber* leakDartVM = [mainBundle objectForInfoDictionaryKey:@"FLTLeakDartVM"];
+  XCTAssertEqual(leakDartVM.boolValue, NO);
+
+  auto settings = FLTDefaultSettingsForBundle();
+  // Check settings.leak_vm value is same as the value defined in Info.plist.
+  XCTAssertEqual(settings.leak_vm, NO);
+}
+
 - (void)testEmptySettingsAreCorrect {
   XCTAssertFalse([FlutterDartProject allowsArbitraryLoads:[[NSDictionary alloc] init]]);
   XCTAssertEqualObjects(@"", [FlutterDartProject domainNetworkPolicy:[[NSDictionary alloc] init]]);

testing/ios/IosUnitTests/App/Info.plist

@@ -44,6 +44,8 @@
                         </dict>
 		</dict>
 	</dict>
+	<key>FLTLeakDartVM</key>
+	<false/>
 	<key>UIRequiredDeviceCapabilities</key>
 	<array>
 		<string>armv7</string>