mutex.dart

import 'dart:async';

class Mutex {
  Completer<void>? _completer;

  Future<void> lock() async {
    while (_completer != null) {
      await _completer!.future;
    }
    _completer = Completer<void>();
  }

  /// Notice: must be call [unlock] after [lock] method called to prevent the deadlock.
  /// ```dart
  /// final mutex = Mutex();
  /// // ...
  /// Future<void> doSth() async {
  ///   try {
  ///     await mutex.lock();
  ///     // do something...
  ///   } finally {
  ///     mutex.unlock();
  ///   }
  /// }
  /// ```
  void unlock() {
    final completer = _completer;
    _completer = null;
    completer?.complete();
  }

  Future<T> withLock<T>(FutureOr<T> Function() block) async {
    try {
      await lock();
      return await block();
    } finally {
      unlock();
    }
  }
}