tryAcquireSchedulerLock function

Future<bool> tryAcquireSchedulerLock({ SchedulerLockOptions? opts, String? sessionId, })

Try to acquire the scheduler lock for the current session. Returns true on success, false if another live session holds it.

Uses exclusive create for atomic test-and-set. If the file exists:

• Already ours -> true (idempotent re-acquire)
• Another live PID -> false
• Stale (PID dead / corrupt) -> unlink and retry once

Implementation

Future<bool> tryAcquireSchedulerLock({
  SchedulerLockOptions? opts,
  String? sessionId,
}) async {
  final dir = opts?.dir;
  final identity = opts?.lockIdentity ?? sessionId ?? 'unknown';
  final lock = SchedulerLock(
    sessionId: identity,
    pid: pid,
    acquiredAt: DateTime.now().millisecondsSinceEpoch,
  );

  if (await _tryCreateExclusive(lock, dir: dir)) {
    _lastBlockedBy = null;
    return true;
  }

  final existing = await _readLock(dir: dir);

  // Already ours (idempotent).
  if (existing?.sessionId == identity) {
    if (existing!.pid != pid) {
      await File(
        _getLockPath(dir: dir),
      ).writeAsString(jsonEncode(lock.toJson()));
    }
    return true;
  }

  // Another live session -- blocked.
  if (existing != null && _isProcessRunning(existing.pid)) {
    if (_lastBlockedBy != existing.sessionId) {
      _lastBlockedBy = existing.sessionId;
    }
    return false;
  }

  // Stale -- unlink and retry once.
  try {
    await File(_getLockPath(dir: dir)).delete();
  } catch (_) {}
  if (await _tryCreateExclusive(lock, dir: dir)) {
    _lastBlockedBy = null;
    return true;
  }
  // Another session won the recovery race.
  return false;
}