edit method

Future<Editor?> edit(String key, [ int? expectedSequenceNumber ])

Returns an editor for the entry named key, or null if another edit is in progress.

Implementation

Future<Editor?> edit(String key, [int? expectedSequenceNumber]) =>
    _lock.synchronized(() async {
      await _initialize();

      _checkNotClosed();
      _validateKey(key);
      var entry = _lruEntries[key];
      if (expectedSequenceNumber != null &&
          (entry == null || entry.sequenceNumber != expectedSequenceNumber)) {
        return null; // Snapshot is stale.
      }

      if (entry?.currentEditor != null) {
        return null; // Another edit is in progress.
      }

      if (entry != null && entry.lockingSourceCount != 0) {
        return null; // We can't write this file because a reader is still reading it.
      }

      if (_mostRecentTrimFailed || _mostRecentRebuildFailed) {
        // The OS has become our enemy! If the trim job failed, it means we are storing more data than
        // requested by the user. Do not allow edits so we do not go over that limit any further. If
        // the journal rebuild failed, the journal writer will not be active, meaning we will not be
        // able to record the edit, causing file leaks. In both cases, we want to retry the clean up
        // so we can get out of this state!
        _cleanup();
        return null;
      }

      // Flush the journal before creating files to prevent file leaks.
      await _journalWriter!.writeLine('$_kDirty $key');
      await _journalWriter!.flush();

      if (_hasJournalErrors) {
        return null; // Don't edit; the journal can't be written.
      }

      entry = _lruEntries.putIfAbsent(key, () => Entry(key, this));
      final editor = Editor._(this, entry);
      entry.currentEditor = editor;
      return editor;
    });