[Sync] Add support for loading, updating and querying delete journals in

sync/syncable/delete_journal.h

+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef SYNC_SYNCABLE_DELETE_JOURNAL_H_
+#define SYNC_SYNCABLE_DELETE_JOURNAL_H_
+
+#include <set>
+
+#include "base/gtest_prod_util.h"
+#include "base/synchronization/lock.h"
+#include "sync/syncable/metahandle_set.h"
+#include "sync/syncable/syncable-inl.h"
+
+namespace syncer {
+namespace syncable {
+
+class BaseTransaction;
+struct EntryKernel;
+
+typedef std::set<const EntryKernel*, LessField<IdField, ID> > JournalIndex;
+
+// DeleteJournal manages deleted entries that are not in sync directory until
+// it's safe to drop them after the deletion is confirmed with native models.
+// DeleteJournal is thread-safe and can be accessed on any thread. Has to hold
+// a valid transaction object when calling methods of DeleteJournal, thus each
+// method requires a non-null |trans| parameter.
+class DeleteJournal {
+ public:
+  FRIEND_TEST_ALL_PREFIXES(SyncableDirectoryTest, ManageDeleteJournals);
+
+  // Initialize |delete_journals_| using |intitial_journal|, whose content is
+  // destroyed during initialization.
+  explicit DeleteJournal(JournalIndex* initial_journal);
+  ~DeleteJournal();
+
+  // For testing only.
+  size_t GetDeleteJournalSize(BaseTransaction* trans) const;
+
+  // Add/remove |entry| to/from |delete_journals_| according to its
+  // SERVER_IS_DEL field and |was_deleted|. Called on sync thread.
+  void UpdateDeleteJournalForServerDelete(BaseTransaction* trans,
+                                          bool was_deleted,
+                                          const EntryKernel& entry);
+
+  // Return entries of specified type in |delete_journals_|. This should be
+  // called ONCE in model association. |deleted_entries| can be used to
+  // detect deleted sync data that's not persisted in native model to
+  // prevent back-from-dead problem. |deleted_entries| are only valid during
+  // lifetime of |trans|. |type| is added to |passive_delete_journal_types_| to
+  // enable periodically saving/clearing of delete journals of |type| because
+  // new journals added later are not needed until next model association.
+  // Can be called on any thread.
+  void GetDeleteJournals(BaseTransaction* trans, ModelType type,
+                         EntryKernelSet* deleted_entries);
+
+  // Purge entries of specified type in |delete_journals_| if their handles are
+  // in |to_purge|. This should be called after model association and
+  // |to_purge| should contain handles of the entries whose deletions are
+  // confirmed in native model. Can be called on any thread.
+  void PurgeDeleteJournals(BaseTransaction* trans,
+                           const MetahandleSet& to_purge);
+
+  // Move entries in |delete_journals_| whose types are in
+  // |passive_delete_journal_types_| to |journal_entries|. Move handles in
+  // |delete_journals_to_purge_| to |journals_to_purge|. Called on sync thread.
+  void TakeSnapshotAndClear(BaseTransaction* trans,
+                            EntryKernelSet* journal_entries,
+                            MetahandleSet* journals_to_purge);
+
+  // Add |entries| to |delete_journals_| regardless of their SERVER_IS_DEL
+  // value. This is used to:
+  // * restore delete journals from snapshot if snapshot failed to save.
+  // * batch add entries of a data type with unrecoverable error to delete
+  //   journal before purging them.
+  // Called on sync thread.
+  void AddJournalBatch(BaseTransaction* trans, const EntryKernelSet& entries);
+
+  // Return true if delete journals of |type| are maintained.
+  static bool IsDeleteJournalEnabled(ModelType type);
+
+ private:
+  // Contains deleted entries that may not be persisted in native models. And
+  // in case of unrecoverable error, all purged entries are moved here for
+  // bookkeeping to prevent back-from-dead entries that are deleted elsewhere
+  // when sync's down.
+  JournalIndex delete_journals_;
+
+  // Contains meta handles of deleted entries that have been persisted or
+  // undeleted, thus can be removed from database.
+  MetahandleSet delete_journals_to_purge_;
+
+  // Delete journals of these types can be cleared from memory after being
+  // saved to database.
+  ModelTypeSet passive_delete_journal_types_;
+
+  DISALLOW_COPY_AND_ASSIGN(DeleteJournal);
+};
+
+}  // namespace syncable
+}  // namespace syncer
+
+#endif  // SYNC_SYNCABLE_DELETE_JOURNAL_H_