pkgs/jni/lib/src/jreference.dart

// Copyright (c) 2022, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

part of 'types.dart';

/// A class which holds one or more JNI references, and has a `delete` operation
/// which disposes the reference(s).
abstract class JReference implements Finalizable {
  static final _finalizer = NativeFinalizer(_env.ref.DeleteGlobalRef);

  JReference.fromRef(this.reference) {
    _finalizer.attach(this, reference, detach: this);
  }

  bool _deleted = false;

  void _ensureNotDeleted() {
    if (_deleted) throw UseAfterFreeException(this, reference);
  }

  /// Check whether the underlying JNI reference is `null`.
  bool get isNull => reference == nullptr;

  /// Returns whether this object is deleted.
  bool get isDeleted => _deleted;

  void _setAsDeleted() {
    if (_deleted) {
      throw DoubleFreeException(this, reference);
    }
    _deleted = true;
    _finalizer.detach(this);
  }

  /// Deletes the underlying JNI reference. Further uses will throw
  /// [UseAfterFreeException].
  void delete() {
    _setAsDeleted();
    _env.DeleteGlobalRef(reference);
  }

  /// The underlying JNI global object reference.
  final JObjectPtr reference;

  /// Registers this object to be deleted at the end of [arena]'s lifetime.
  void deletedIn(Arena arena) => arena.onReleaseAll(delete);
}

extension JReferenceUseExtension<T extends JReference> on T {
  /// Applies [callback] on [this] object and then delete the underlying JNI
  /// reference, returning the result of [callback].
  R use<R>(R Function(T) callback) {
    _ensureNotDeleted();
    try {
      final result = callback(this);
      delete();
      return result;
    } catch (e) {
      delete();
      rethrow;
    }
  }
}