Add option to enable serial GC (flutter#30975)

* Roll Dart SDK from e256855 to a3b62f3 (4 revisions) (flutter#21809)

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* Trigger an engine build to re-open the tree (flutter#26056)

This commit is empty and simply triggers a new build to open the tree.

Commit 106963e was re-built after a
succesful build; upload to the cloud storage bin failed.

* Roll Skia from d9a7c5953df3 to 827bb729a84d (2 revisions) (flutter#26096)

* Roll Dart SDK from d616108 to a527411 (0 revision) (flutter#26156)

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* Roll buildroot to 275038b (flutter#26945)

* [test] empty commit (flutter#27599)

https://flutter-review.googlesource.com/c/infra/+/15660

* Roll Dart SDK from e141400 to 6860708 (1 revision) (flutter#27620)

* Empty commit to apply latest LUCI config (flutter#27767)

* Roll Dart SDK from 3b11f88 to 976f160 (3 revisions) (flutter#29436)

* Empty commit to fix main tree status (flutter#29760)

* Add option to enable serial GC
This option can be used to avoid thread contention issues for the UI thread when running on low power devices with limited number of cores.

* Fix format.

* Added test.

* Add build rule.

* Address review comments.

Co-authored-by: skia-flutter-autoroll <[email protected]>
Co-authored-by: Chris Bracken <[email protected]>
Co-authored-by: Casey Hillers <[email protected]>

common/settings.cc

@@ -45,6 +45,7 @@ std::string Settings::ToString() const {
   stream << "endless_trace_buffer: " << endless_trace_buffer << std::endl;
   stream << "enable_dart_profiling: " << enable_dart_profiling << std::endl;
   stream << "disable_dart_asserts: " << disable_dart_asserts << std::endl;
+  stream << "enable_serial_gc: " << enable_serial_gc << std::endl;
   stream << "enable_observatory: " << enable_observatory << std::endl;
   stream << "enable_observatory_publication: " << enable_observatory_publication
          << std::endl;

common/settings.h

@@ -140,6 +140,7 @@ struct Settings {
   bool endless_trace_buffer = false;
   bool enable_dart_profiling = false;
   bool disable_dart_asserts = false;
+  bool enable_serial_gc = false;
 
   // Whether embedder only allows secure connections.
   bool may_insecurely_connect_to_all_domains = true;

runtime/dart_vm.cc

@@ -59,6 +59,16 @@ static const char* kDartLanguageArgs[] = {
 
 static const char* kDartPrecompilationArgs[] = {"--precompilation"};
 
+static const char* kSerialGCArgs[] = {
+    // clang-format off
+    "--concurrent_mark=false",
+    "--concurrent_sweep=false",
+    "--compactor_tasks=1",
+    "--scavenger_tasks=0",
+    "--marker_tasks=0",
+    // clang-format on
+};
+
 FML_ALLOW_UNUSED_TYPE
 static const char* kDartWriteProtectCodeArgs[] = {
     "--no_write_protect_code",
@@ -358,6 +368,13 @@ DartVM::DartVM(std::shared_ptr<const DartVMData> vm_data,
     PushBackAll(&args, kDartAssertArgs, fml::size(kDartAssertArgs));
   }
 
+  // On low power devices with lesser number of cores, using concurrent
+  // marking or sweeping causes contention for the UI thread leading to
+  // Jank, this option can be used to turn off all concurrent GC activities.
+  if (settings_.enable_serial_gc) {
+    PushBackAll(&args, kSerialGCArgs, fml::size(kSerialGCArgs));
+  }
+
   if (settings_.start_paused) {
     PushBackAll(&args, kDartStartPausedArgs, fml::size(kDartStartPausedArgs));
   }

shell/common/switches.cc

@@ -300,6 +300,9 @@ Settings SettingsFromCommandLine(const fml::CommandLine& command_line) {
   settings.trace_startup =
       command_line.HasOption(FlagForSwitch(Switch::TraceStartup));
 
+  settings.enable_serial_gc =
+      command_line.HasOption(FlagForSwitch(Switch::EnableSerialGC));
+
 #if !FLUTTER_RELEASE
   settings.trace_skia = true;
 

shell/common/switches.h

@@ -193,6 +193,12 @@ DEF_SWITCH(DisableDartAsserts,
            "disabled. This flag may be specified if the user wishes to run "
            "with assertions disabled in the debug product mode (i.e. with JIT "
            "or DBC).")
+DEF_SWITCH(EnableSerialGC,
+           "enable-serial-gc",
+           "On low power devices with low core counts, running concurrent "
+           "GC tasks on threads can cause them to contend with the UI thread "
+           "which could potentially lead to jank. This option turns off all "
+           "concurrent GC activities")
 DEF_SWITCH(DisallowInsecureConnections,
            "disallow-insecure-connections",
            "By default, dart:io allows all socket connections. If this switch "

testing/dart/BUILD.gn

@@ -34,6 +34,7 @@ tests = [
   "platform_view_test.dart",
   "plugin_utilities_test.dart",
   "semantics_test.dart",
+  "serial_gc_test.dart",
   "spirv_exception_test.dart",
   "task_order_test.dart",
   "text_test.dart",

testing/dart/serial_gc_test.dart

@@ -0,0 +1,17 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// FlutterTesterOptions=--enable-serial-gc
+
+import 'package:litetest/litetest.dart';
+
+void main() {
+  test('Serial GC option test ', () async {
+    bool threw = false;
+    for (int i = 0; i < 100; i++) {
+      var a = <int>[100];
+    }
+    expect(threw, false);
+  });
+}