tryAcquire static method

ProjectLock? tryAcquire(JustProject project)

Takes the lock on project, or returns null when another change holds it. Throws a FileSystemException when the lock can't be made at all (a read-only folder, a path too long).

Implementation

static ProjectLock? tryAcquire(JustProject project) {
  final file = project.file(path);
  file.parent.createSync(recursive: true);
  final token = _newToken();
  for (var attempt = 1; ; attempt++) {
    try {
      file.createSync(exclusive: true);
    } on FileSystemException catch (e) {
      final held = _Holder.read(file);
      if (held == null) {
        // Released in between — or the file can't be made at all.
        if (attempt < 3) continue;
        throw FileSystemException(
          'Could not make the project lock',
          file.path,
          e.osError,
        );
      }
      if (DateTime.now().difference(held.touched) <= stale &&
          !_crashedHere(held)) {
        return null;
      }
      // Left by a crash: out of the way with it, then try again.
      if (attempt >= 3) return null;
      _takeOver(file, held, token);
      continue;
    }
    try {
      file.writeAsStringSync(
        jsonEncode({
          'pid': pid,
          ..._here,
          'token': token,
          'since': DateTime.now().toUtc().toIso8601String(),
        }),
        flush: true,
      );
    } on FileSystemException {
      try {
        file.deleteSync();
      } on FileSystemException {
        // It goes stale on its own.
      }
      rethrow;
    }
    return ProjectLock._(file, token);
  }
}