Let SyncBackupManager keep backup data in memory until shutdown. Only persist

sync/syncable/deferred_on_disk_directory_backing_store.cc

Index: sync/syncable/deferred_on_disk_directory_backing_store.cc
diff --git a/sync/syncable/deferred_on_disk_directory_backing_store.cc b/sync/syncable/deferred_on_disk_directory_backing_store.cc
new file mode 100644
index 0000000000000000000000000000000000000000..04540803f1bd199bf4ef77a2c3f6b0a0ea14d45c
--- /dev/null
+++ b/sync/syncable/deferred_on_disk_directory_backing_store.cc
@@ -0,0 +1,73 @@
+// Copyright (c) 2014 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.
+
+#include "sync/syncable/deferred_on_disk_directory_backing_store.h"
+
+#include "base/logging.h"
+#include "base/metrics/histogram.h"
+#include "base/stl_util.h"
+#include "sync/syncable/syncable-inl.h"
+
+namespace syncer {
+namespace syncable {
+
+DeferredOnDiskDirectoryBackingStore::DeferredOnDiskDirectoryBackingStore(
+    const std::string& dir_name, const base::FilePath& backing_filepath)
+    : DirectoryBackingStore(dir_name),
+      backing_filepath_(backing_filepath),
+      db_is_on_disk_(false) {
+}
+
+DeferredOnDiskDirectoryBackingStore::~DeferredOnDiskDirectoryBackingStore() {}
+
+bool DeferredOnDiskDirectoryBackingStore::SaveChanges(
+    const Directory::SaveChangesSnapshot& snapshot) {
+  DCHECK(CalledOnValidThread());
+
+  // Back out early if there is nothing to save.
+  if (snapshot.dirty_metas.empty() && snapshot.metahandles_to_purge.empty() &&
+      snapshot.delete_journals.empty() &&
+      snapshot.delete_journals_to_purge.empty()) {
+    return true;
+  }
+
+  if (!db_is_on_disk_) {
+    if (!base::DeleteFile(backing_filepath_, false))
+      return false;
+
+    // Reopen DB on disk.
+    db_.reset(new sql::Connection);
+    db_->set_exclusive_locking();
+    db_->set_page_size(4096);
+    if (!db_->Open(backing_filepath_) || !InitializeTables())
+      return false;
+
+    db_is_on_disk_ = true;
+  }
+
+  return DirectoryBackingStore::SaveChanges(snapshot);
+}
+
+DirOpenResult DeferredOnDiskDirectoryBackingStore::Load(
+    Directory::MetahandlesMap* handles_map,
+    JournalIndex* delete_journals,
+    Directory::KernelLoadInfo* kernel_load_info) {
+  // Open an in-memory database at first to create initial sync data needed by
+  // Directory.
+  CHECK(!db_->is_open());
+  if (!db_->OpenInMemory())
+    return FAILED_OPEN_DATABASE;
+
+  if (!InitializeTables())
+    return FAILED_OPEN_DATABASE;
+  if (!LoadEntries(handles_map))
+    return FAILED_DATABASE_CORRUPT;
+  if (!LoadInfo(kernel_load_info))
+    return FAILED_DATABASE_CORRUPT;
+
+  return OPENED;
+}
+
+}  // namespace syncable
+}  // namespace syncer