Resolve the limitation of FFI-based plugins

[swift-kim]

FFI-based plugins (path_provider_tizen, shared_preferences_tizen, url_launcher_tizen) currently only work when running in the main isolate and require additional initialization to run in secondary isolates: #122 (review)

[bbrto21]

to solve this limitation, do we need re-implement plugins based on native?

[swift-kim]

No, we need to check how other platforms tackle this problem but I had not enough time to investigate.

[swift-kim]

• I tested path_provider_windows on Windows and it worked without problem on secondary isolates. I'm still not exactly sure how the Dart plugin registry for Windows is different from flutter-tizen's.
• generated_main.dart was not generated by flutter_tools even with Reland the Dart plugin registry flutter/flutter#79669 applied on Windows. I don't know why.
• Still Reland the Dart plugin registry flutter/flutter#79669 will land to the stable branch soon and it would be better to re-implement flutter-tizen's Dart plugin registry based on the official one. In fact its approach is not quite different from ours, but the main difference is that generateMainDartWithPluginRegistrant (equivalent of _createEntrypoint for Tizen) is part of the build graph.
• Consider adding implements: attributes to Tizen plugins' pubspecs. It's not quite necessary tho because the attribute doesn't do very much thing.

[swift-kim]

I'll test swift-kim/flutter-tizen@1ed4ee7 when the next stable Flutter version is released.

Related engine PR: flutter/engine#25496

[swift-kim]

The implementation of the third solution in flutter-tizen/flutter-tizen#177 (comment) can be found at: swift-kim/flutter-tizen@6fd8233

The commit should land after the next Flutter stable release.

cc @HakkyuKim

[HakkyuKim]

@swift-kim That was really fast! Thank you!
I'll have a closer look tomorrow.

[swift-kim]

It seems Dart plugin registrants are not yet fully implemented for secondary isolates in the upstream engine: flutter/flutter#81421

Thus the change in #123 (comment) has no effect.

[swift-kim]

I tried invoking InvokeDartPluginRegistrantIfAvailable (Dart_RootLibrary~Dart_Invoke) after initializing secondary isolates but encountered only some segmentation faults. I'm not sure where I can safely put the code (I tried in DartIsolateInitializeCallback and SpawnIsolateTask:Run).

[swift-kim]

My conclusion is that plugins are generally not expected to work properly inside isolates. This applies to other platforms as well, regardless of the underlying implementation mechanism (platform channel or Dart plugin registrant). (There's even a third-party package called flutter_isolate that allows invoking plugins from isolates.)

The only workaround is to call the register function of a plugin (Dart plugin) before invoking its API from an isolate.

Example (path_provider_tizen):

import 'package:flutter/foundation.dart';
import 'package:path_provider/path_provider.dart';
import 'package:path_provider_tizen/path_provider_tizen.dart';

compute((Object? message) async {
  PathProviderPlugin.register();
  await getApplicationDocumentsDirectory();
}, null);

[swift-kim]

Will be fixed by flutter-tizen/flutter-tizen#516.