RwLock

RwLock is used in critical sections to allow multiple concurrent read operations while ensuring that write operations are exclusive. Dart being single threaded, means it is less common to need a RwLock, but they are still useful e.g. reading and writing to data sources or transactions. RwLock uses a fifo model to prevent starvation.

import 'dart:async';

class DataSource {
  final String name;
  DataSource(this.name);

  Future<String> read() async {
    print('Reading from $name');
    await Future.delayed(Duration(milliseconds: 100)); // Simulate delay
    return 'Data from $name';
  }

  Future<void> write(String data) async {
    print('Writing to $name: $data');
    await Future.delayed(Duration(milliseconds: 100)); // Simulate delay
  }
}

class DataManager {
  final List<DataSource> _dataSources;
  final RwLock _rwLock = RwLock();

  DataManager(this._dataSources);

  Future<List<String>> readFromAll() async {
    return await _rwLock.withReadLock(() async {
      final results = <String>[];
      for (var dataSource in _dataSources) {
        results.add(await dataSource.read());
      }
      return results;
    });
  }

  Future<void> writeToAll(String data) async {
    await _rwLock.withWriteLock(() async {
      for (var dataSource in _dataSources) {
        await dataSource.write(data);
      }
    });
  }
}

void main() async {
  final dataSources = [DataSource('DB1'), DataSource('DB2'), DataSource('DB3')];
  final manager = DataManager(dataSources);

  await Future.wait([
    manager.readFromAll().then((data) => print('Read: $data')),
    manager.readFromAll().then((data) => print('Read: $data')),
    manager.writeToAll('New Data'),
  ]);

  print('All operations completed');
}