CompactionStrategy unusable with IsolatedHive

[mbenabda]

SendPort.send cannot transmit a function reference across isolate boundaries

Steps to Reproduce
use a compaction strategy when opening a box with IsolatedHive

Code sample

await IsolatedHive.openBox<String>('stuff', compactionStrategy: (entries, deletedEntries) => false);

Version

• Flutter version: 3.41.4
• Hive version:
  • hive_ce: "2.19.3"
  • hive_ce_flutter: "2.3.4"

[Rexios80]

I figured this would come up at some point. I'm not sure this is fixable, but I will look into it when I have time.

[mbenabda]

@Rexios80 Hi. thank you for your prompt answer.

May i suggest changing the CompactionStrategy declaration from a typedef Function to an interface declaring a single function ?

that way, instead of having to pass a function across the isolate boundary, it would be an object, which should be valid.
That would however, be a breaking change to the API.

[Rexios80]

You cannot pass custom objects either

[mbenabda]

Seems to work fine:

import 'dart:isolate';

abstract interface class IWork {
  bool printProgress();
}

class ProgressPrinter extends IWork {
  final int progress;

  ProgressPrinter({required this.progress});

  @override
  bool printProgress() {
    print('Progress: $progress%');
    return progress == 100;
  }
}

void _longRunningTask(SendPort sendPort) {
  for (int i = 0; i <= 100; i += 10) {
    sendPort.send(ProgressPrinter(progress: i));
  }
}

main(List<String> args) async {
  final receivePort = ReceivePort();
  await Isolate.spawn(_longRunningTask, receivePort.sendPort);

  receivePort.listen((message) {
    if (message is IWork) {
      final done = message.printProgress();
      if (done) {
        receivePort.close();
      }
    }
  });
}

[Rexios80]

It only works if one library owns both isolates. That is not the case here.

[Rexios80]

Would something like this solve your use-case? #306

Passing a compaction strategy causes a crash currently, correct? If so, this would not count as a breaking change.

[Rexios80]

Although I will say if you are actually disabling compaction I'm not sure that is a good idea. It means deleted entries never get cleaned up, and your database file will grow indefinitely.