diff --git a/app/lib/app_db.dart b/app/lib/app_db.dart
index aeb24340..395c4550 100644
--- a/app/lib/app_db.dart
+++ b/app/lib/app_db.dart
@@ -8,6 +8,7 @@ import 'package:nc_photos/ci_string.dart';
 import 'package:nc_photos/entity/album.dart';
 import 'package:nc_photos/entity/album/upgrader.dart';
 import 'package:nc_photos/entity/file.dart';
+import 'package:nc_photos/k.dart' as k;
 import 'package:nc_photos/mobile/platform.dart'
     if (dart.library.html) 'package:nc_photos/web/platform.dart' as platform;
 import 'package:nc_photos/num_extension.dart';
@@ -33,13 +34,19 @@ class AppDb {
   /// This function guarantees that:
   /// 1) Database is always closed after [fn] exits, even with an error
   /// 2) Only at most 1 database instance being opened at any time
-  Future<T> use<T>(FutureOr<T> Function(Database db) fn) async {
+  Future<T> use<T>(Transaction Function(Database db) transactionBuilder,
+      FutureOr<T> Function(Transaction transaction) fn) async {
     // make sure only one client is opening the db
-    return await _lock.synchronized(() async {
+    return await platform.Lock.synchronized(k.appDbLockId, () async {
       final db = await _open();
+      Transaction? transaction;
       try {
-        return await fn(db);
+        transaction = transactionBuilder(db);
+        return await fn(transaction);
       } finally {
+        if (transaction != null) {
+          await transaction.completed;
+        }
         db.close();
       }
     });
diff --git a/app/lib/entity/album.dart b/app/lib/entity/album.dart
index c5d98755..62ac854e 100644
--- a/app/lib/entity/album.dart
+++ b/app/lib/entity/album.dart
@@ -398,34 +398,36 @@ class AlbumAppDbDataSource implements AlbumDataSource {
   @override
   get(Account account, File albumFile) {
     _log.info("[get] ${albumFile.path}");
-    return appDb.use((db) async {
-      final transaction = db.transaction(AppDb.albumStoreName, idbModeReadOnly);
-      final store = transaction.objectStore(AppDb.albumStoreName);
-      final index = store.index(AppDbAlbumEntry.indexName);
-      final path = AppDbAlbumEntry.toPathFromFile(account, albumFile);
-      final range = KeyRange.bound([path, 0], [path, int_util.int32Max]);
-      final List results = await index.getAll(range);
-      if (results.isNotEmpty == true) {
-        final entries = results.map((e) =>
-            AppDbAlbumEntry.fromJson(e.cast<String, dynamic>(), account));
-        if (entries.length > 1) {
-          final items = entries.map((e) {
-            _log.info("[get] ${e.path}[${e.index}]");
-            return AlbumStaticProvider.of(e.album).items;
-          }).reduce((value, element) => value + element);
-          return entries.first.album.copyWith(
-            lastUpdated: OrNull(null),
-            provider: AlbumStaticProvider.of(entries.first.album).copyWith(
-              items: items,
-            ),
-          );
+    return appDb.use(
+      (db) => db.transaction(AppDb.albumStoreName, idbModeReadOnly),
+      (transaction) async {
+        final store = transaction.objectStore(AppDb.albumStoreName);
+        final index = store.index(AppDbAlbumEntry.indexName);
+        final path = AppDbAlbumEntry.toPathFromFile(account, albumFile);
+        final range = KeyRange.bound([path, 0], [path, int_util.int32Max]);
+        final List results = await index.getAll(range);
+        if (results.isNotEmpty == true) {
+          final entries = results.map((e) =>
+              AppDbAlbumEntry.fromJson(e.cast<String, dynamic>(), account));
+          if (entries.length > 1) {
+            final items = entries.map((e) {
+              _log.info("[get] ${e.path}[${e.index}]");
+              return AlbumStaticProvider.of(e.album).items;
+            }).reduce((value, element) => value + element);
+            return entries.first.album.copyWith(
+              lastUpdated: OrNull(null),
+              provider: AlbumStaticProvider.of(entries.first.album).copyWith(
+                items: items,
+              ),
+            );
+          } else {
+            return entries.first.album;
+          }
         } else {
-          return entries.first.album;
+          throw CacheNotFoundException("No entry: $path");
         }
-      } else {
-        throw CacheNotFoundException("No entry: $path");
-      }
-    });
+      },
+    );
   }
 
   @override
@@ -437,12 +439,13 @@ class AlbumAppDbDataSource implements AlbumDataSource {
   @override
   update(Account account, Album album) {
     _log.info("[update] ${album.albumFile!.path}");
-    return appDb.use((db) async {
-      final transaction =
-          db.transaction(AppDb.albumStoreName, idbModeReadWrite);
-      final store = transaction.objectStore(AppDb.albumStoreName);
-      await _cacheAlbum(store, account, album);
-    });
+    return appDb.use(
+      (db) => db.transaction(AppDb.albumStoreName, idbModeReadWrite),
+      (transaction) async {
+        final store = transaction.objectStore(AppDb.albumStoreName);
+        await _cacheAlbum(store, account, album);
+      },
+    );
   }
 
   @override
@@ -492,43 +495,45 @@ class AlbumCachedDataSource implements AlbumDataSource {
 
   @override
   cleanUp(Account account, String rootDir, List<File> albumFiles) async {
-    appDb.use((db) async {
-      final transaction =
-          db.transaction(AppDb.albumStoreName, idbModeReadWrite);
-      final store = transaction.objectStore(AppDb.albumStoreName);
-      final index = store.index(AppDbAlbumEntry.indexName);
-      final rootPath = AppDbAlbumEntry.toPath(account, rootDir);
-      final range = KeyRange.bound(
-          ["$rootPath/", 0], ["$rootPath/\uffff", int_util.int32Max]);
-      final danglingKeys = await index
-          // get all albums for this account
-          .openKeyCursor(range: range, autoAdvance: true)
-          .map((cursor) => Tuple2((cursor.key as List)[0], cursor.primaryKey))
-          // and pick the dangling ones
-          .where((pair) => !albumFiles.any(
-              (f) => pair.item1 == AppDbAlbumEntry.toPathFromFile(account, f)))
-          // map to primary keys
-          .map((pair) => pair.item2)
-          .toList();
-      for (final k in danglingKeys) {
-        _log.fine("[cleanUp] Removing albumStore entry: $k");
-        try {
-          await store.delete(k);
-        } catch (e, stackTrace) {
-          _log.shout(
-              "[cleanUp] Failed removing albumStore entry", e, stackTrace);
+    appDb.use(
+      (db) => db.transaction(AppDb.albumStoreName, idbModeReadWrite),
+      (transaction) async {
+        final store = transaction.objectStore(AppDb.albumStoreName);
+        final index = store.index(AppDbAlbumEntry.indexName);
+        final rootPath = AppDbAlbumEntry.toPath(account, rootDir);
+        final range = KeyRange.bound(
+            ["$rootPath/", 0], ["$rootPath/\uffff", int_util.int32Max]);
+        final danglingKeys = await index
+            // get all albums for this account
+            .openKeyCursor(range: range, autoAdvance: true)
+            .map((cursor) => Tuple2((cursor.key as List)[0], cursor.primaryKey))
+            // and pick the dangling ones
+            .where((pair) => !albumFiles.any((f) =>
+                pair.item1 == AppDbAlbumEntry.toPathFromFile(account, f)))
+            // map to primary keys
+            .map((pair) => pair.item2)
+            .toList();
+        for (final k in danglingKeys) {
+          _log.fine("[cleanUp] Removing albumStore entry: $k");
+          try {
+            await store.delete(k);
+          } catch (e, stackTrace) {
+            _log.shout(
+                "[cleanUp] Failed removing albumStore entry", e, stackTrace);
+          }
         }
-      }
-    });
+      },
+    );
   }
 
   Future<void> _cacheResult(Account account, Album result) {
-    return appDb.use((db) async {
-      final transaction =
-          db.transaction(AppDb.albumStoreName, idbModeReadWrite);
-      final store = transaction.objectStore(AppDb.albumStoreName);
-      await _cacheAlbum(store, account, result);
-    });
+    return appDb.use(
+      (db) => db.transaction(AppDb.albumStoreName, idbModeReadWrite),
+      (transaction) async {
+        final store = transaction.objectStore(AppDb.albumStoreName);
+        await _cacheAlbum(store, account, result);
+      },
+    );
   }
 
   final AppDb appDb;
diff --git a/app/lib/entity/file/data_source.dart b/app/lib/entity/file/data_source.dart
index 37d23f88..4ac5a6fc 100644
--- a/app/lib/entity/file/data_source.dart
+++ b/app/lib/entity/file/data_source.dart
@@ -269,31 +269,34 @@ class FileAppDbDataSource implements FileDataSource {
   @override
   list(Account account, File dir) {
     _log.info("[list] ${dir.path}");
-    return appDb.use((db) async {
-      final transaction = db.transaction(
-          [AppDb.dirStoreName, AppDb.file2StoreName], idbModeReadOnly);
-      final fileStore = transaction.objectStore(AppDb.file2StoreName);
-      final dirStore = transaction.objectStore(AppDb.dirStoreName);
-      final dirItem = await dirStore
-          .getObject(AppDbDirEntry.toPrimaryKeyForDir(account, dir)) as Map?;
-      if (dirItem == null) {
-        throw CacheNotFoundException("No entry: ${dir.path}");
-      }
-      final dirEntry = AppDbDirEntry.fromJson(dirItem.cast<String, dynamic>());
-      final entries = await Future.wait(dirEntry.children.map((c) async {
-        final fileItem = await fileStore
-            .getObject(AppDbFile2Entry.toPrimaryKey(account, c)) as Map?;
-        if (fileItem == null) {
-          _log.warning(
-              "[list] Missing file ($c) in db for dir: ${logFilename(dir.path)}");
-          throw CacheNotFoundException("No entry for dir child: $c");
+    return appDb.use(
+      (db) => db.transaction(
+          [AppDb.dirStoreName, AppDb.file2StoreName], idbModeReadOnly),
+      (transaction) async {
+        final fileStore = transaction.objectStore(AppDb.file2StoreName);
+        final dirStore = transaction.objectStore(AppDb.dirStoreName);
+        final dirItem = await dirStore
+            .getObject(AppDbDirEntry.toPrimaryKeyForDir(account, dir)) as Map?;
+        if (dirItem == null) {
+          throw CacheNotFoundException("No entry: ${dir.path}");
         }
-        return AppDbFile2Entry.fromJson(fileItem.cast<String, dynamic>());
-      }));
-      // we need to add dir to match the remote query
-      return [dirEntry.dir] +
-          entries.map((e) => e.file).where((f) => _validateFile(f)).toList();
-    });
+        final dirEntry =
+            AppDbDirEntry.fromJson(dirItem.cast<String, dynamic>());
+        final entries = await Future.wait(dirEntry.children.map((c) async {
+          final fileItem = await fileStore
+              .getObject(AppDbFile2Entry.toPrimaryKey(account, c)) as Map?;
+          if (fileItem == null) {
+            _log.warning(
+                "[list] Missing file ($c) in db for dir: ${logFilename(dir.path)}");
+            throw CacheNotFoundException("No entry for dir child: $c");
+          }
+          return AppDbFile2Entry.fromJson(fileItem.cast<String, dynamic>());
+        }));
+        // we need to add dir to match the remote query
+        return [dirEntry.dir] +
+            entries.map((e) => e.file).where((f) => _validateFile(f)).toList();
+      },
+    );
   }
 
   @override
@@ -307,19 +310,21 @@ class FileAppDbDataSource implements FileDataSource {
   Future<List<File>> listByDate(
       Account account, int fromEpochMs, int toEpochMs) async {
     _log.info("[listByDate] [$fromEpochMs, $toEpochMs]");
-    final items = await appDb.use((db) async {
-      final transaction = db.transaction(AppDb.file2StoreName, idbModeReadOnly);
-      final fileStore = transaction.objectStore(AppDb.file2StoreName);
-      final dateTimeEpochMsIndex =
-          fileStore.index(AppDbFile2Entry.dateTimeEpochMsIndexName);
-      final range = KeyRange.bound(
-        AppDbFile2Entry.toDateTimeEpochMsIndexKey(account, fromEpochMs),
-        AppDbFile2Entry.toDateTimeEpochMsIndexKey(account, toEpochMs),
-        false,
-        true,
-      );
-      return await dateTimeEpochMsIndex.getAll(range);
-    });
+    final items = await appDb.use(
+      (db) => db.transaction(AppDb.file2StoreName, idbModeReadOnly),
+      (transaction) async {
+        final fileStore = transaction.objectStore(AppDb.file2StoreName);
+        final dateTimeEpochMsIndex =
+            fileStore.index(AppDbFile2Entry.dateTimeEpochMsIndexName);
+        final range = KeyRange.bound(
+          AppDbFile2Entry.toDateTimeEpochMsIndexKey(account, fromEpochMs),
+          AppDbFile2Entry.toDateTimeEpochMsIndexKey(account, toEpochMs),
+          false,
+          true,
+        );
+        return await dateTimeEpochMsIndex.getAll(range);
+      },
+    );
     return items
         .cast<Map>()
         .map((i) => AppDbFile2Entry.fromJson(i.cast<String, dynamic>()))
@@ -357,21 +362,21 @@ class FileAppDbDataSource implements FileDataSource {
     bool? favorite,
   }) {
     _log.info("[updateProperty] ${f.path}");
-    return appDb.use((db) async {
-      final transaction =
-          db.transaction(AppDb.file2StoreName, idbModeReadWrite);
-
-      // update file store
-      final newFile = f.copyWith(
-        metadata: metadata,
-        isArchived: isArchived,
-        overrideDateTime: overrideDateTime,
-        isFavorite: favorite,
-      );
-      final fileStore = transaction.objectStore(AppDb.file2StoreName);
-      await fileStore.put(AppDbFile2Entry.fromFile(account, newFile).toJson(),
-          AppDbFile2Entry.toPrimaryKeyForFile(account, newFile));
-    });
+    return appDb.use(
+      (db) => db.transaction(AppDb.file2StoreName, idbModeReadWrite),
+      (transaction) async {
+        // update file store
+        final newFile = f.copyWith(
+          metadata: metadata,
+          isArchived: isArchived,
+          overrideDateTime: overrideDateTime,
+          isFavorite: favorite,
+        );
+        final fileStore = transaction.objectStore(AppDb.file2StoreName);
+        await fileStore.put(AppDbFile2Entry.fromFile(account, newFile).toJson(),
+            AppDbFile2Entry.toPrimaryKeyForFile(account, newFile));
+      },
+    );
   }
 
   @override
@@ -577,20 +582,22 @@ class FileForwardCacheManager {
   }
 
   Future<void> _cacheDir(Account account, File dir) async {
-    final dirItems = await appDb.use((db) async {
-      final transaction = db.transaction(AppDb.dirStoreName, idbModeReadOnly);
-      final store = transaction.objectStore(AppDb.dirStoreName);
-      final dirItem = await store
-          .getObject(AppDbDirEntry.toPrimaryKeyForDir(account, dir)) as Map?;
-      if (dirItem == null) {
-        return null;
-      }
-      final range = KeyRange.bound(
-        AppDbDirEntry.toPrimaryLowerKeyForSubDirs(account, dir),
-        AppDbDirEntry.toPrimaryUpperKeyForSubDirs(account, dir),
-      );
-      return [dirItem] + (await store.getAll(range)).cast<Map>();
-    });
+    final dirItems = await appDb.use(
+      (db) => db.transaction(AppDb.dirStoreName, idbModeReadOnly),
+      (transaction) async {
+        final store = transaction.objectStore(AppDb.dirStoreName);
+        final dirItem = await store
+            .getObject(AppDbDirEntry.toPrimaryKeyForDir(account, dir)) as Map?;
+        if (dirItem == null) {
+          return null;
+        }
+        final range = KeyRange.bound(
+          AppDbDirEntry.toPrimaryLowerKeyForSubDirs(account, dir),
+          AppDbDirEntry.toPrimaryUpperKeyForSubDirs(account, dir),
+        );
+        return [dirItem] + (await store.getAll(range)).cast<Map>();
+      },
+    );
     if (dirItems == null) {
       // no cache
       return;
@@ -606,12 +613,14 @@ class FileForwardCacheManager {
     // cache files
     final fileIds = dirs.map((e) => e.children).fold<List<int>>(
         [], (previousValue, element) => previousValue + element);
-    final fileItems = await appDb.use((db) async {
-      final transaction = db.transaction(AppDb.file2StoreName, idbModeReadOnly);
-      final store = transaction.objectStore(AppDb.file2StoreName);
-      return await Future.wait(fileIds.map(
-          (id) => store.getObject(AppDbFile2Entry.toPrimaryKey(account, id))));
-    });
+    final fileItems = await appDb.use(
+      (db) => db.transaction(AppDb.file2StoreName, idbModeReadOnly),
+      (transaction) async {
+        final store = transaction.objectStore(AppDb.file2StoreName);
+        return await Future.wait(fileIds.map((id) =>
+            store.getObject(AppDbFile2Entry.toPrimaryKey(account, id))));
+      },
+    );
     final files = fileItems
         .cast<Map?>()
         .whereType<Map>()
diff --git a/app/lib/entity/file/file_cache_manager.dart b/app/lib/entity/file/file_cache_manager.dart
index 0f15f6b0..8a8b14d2 100644
--- a/app/lib/entity/file/file_cache_manager.dart
+++ b/app/lib/entity/file/file_cache_manager.dart
@@ -124,27 +124,30 @@ class FileCacheUpdater {
   }
 
   Future<void> _cacheRemote(Account account, File dir, List<File> remote) {
-    return appDb.use((db) async {
-      final transaction = db.transaction(
-          [AppDb.dirStoreName, AppDb.file2StoreName], idbModeReadWrite);
-      final dirStore = transaction.objectStore(AppDb.dirStoreName);
-      final fileStore = transaction.objectStore(AppDb.file2StoreName);
+    return appDb.use(
+      (db) => db.transaction(
+          [AppDb.dirStoreName, AppDb.file2StoreName], idbModeReadWrite),
+      (transaction) async {
+        final dirStore = transaction.objectStore(AppDb.dirStoreName);
+        final fileStore = transaction.objectStore(AppDb.file2StoreName);
 
-      // add files to db
-      await Future.wait(remote.map((f) => fileStore.put(
-          AppDbFile2Entry.fromFile(account, f).toJson(),
-          AppDbFile2Entry.toPrimaryKeyForFile(account, f))));
+        // add files to db
+        await Future.wait(remote.map((f) => fileStore.put(
+            AppDbFile2Entry.fromFile(account, f).toJson(),
+            AppDbFile2Entry.toPrimaryKeyForFile(account, f))));
 
-      // results from remote also contain the dir itself
-      final resultGroup =
-          remote.groupListsBy((f) => f.compareServerIdentity(dir));
-      final remoteDir = resultGroup[true]!.first;
-      final remoteChildren = resultGroup[false] ?? [];
-      // add dir to db
-      await dirStore.put(
-          AppDbDirEntry.fromFiles(account, remoteDir, remoteChildren).toJson(),
-          AppDbDirEntry.toPrimaryKeyForDir(account, remoteDir));
-    });
+        // results from remote also contain the dir itself
+        final resultGroup =
+            remote.groupListsBy((f) => f.compareServerIdentity(dir));
+        final remoteDir = resultGroup[true]!.first;
+        final remoteChildren = resultGroup[false] ?? [];
+        // add dir to db
+        await dirStore.put(
+            AppDbDirEntry.fromFiles(account, remoteDir, remoteChildren)
+                .toJson(),
+            AppDbDirEntry.toPrimaryKeyForDir(account, remoteDir));
+      },
+    );
   }
 
   /// Remove extra entries from local cache based on remote contents
@@ -159,27 +162,29 @@ class FileCacheUpdater {
     _log.info(
         "[_cleanUpCache] Removed: ${removed.map((f) => f.path).toReadableString()}");
 
-    await appDb.use((db) async {
-      final transaction = db.transaction(
-          [AppDb.dirStoreName, AppDb.file2StoreName], idbModeReadWrite);
-      final dirStore = transaction.objectStore(AppDb.dirStoreName);
-      final fileStore = transaction.objectStore(AppDb.file2StoreName);
-      for (final f in removed) {
-        try {
-          if (f.isCollection == true) {
-            await _removeDirFromAppDb(account, f,
-                dirStore: dirStore, fileStore: fileStore);
-          } else {
-            await _removeFileFromAppDb(account, f, fileStore: fileStore);
+    await appDb.use(
+      (db) => db.transaction(
+          [AppDb.dirStoreName, AppDb.file2StoreName], idbModeReadWrite),
+      (transaction) async {
+        final dirStore = transaction.objectStore(AppDb.dirStoreName);
+        final fileStore = transaction.objectStore(AppDb.file2StoreName);
+        for (final f in removed) {
+          try {
+            if (f.isCollection == true) {
+              await _removeDirFromAppDb(account, f,
+                  dirStore: dirStore, fileStore: fileStore);
+            } else {
+              await _removeFileFromAppDb(account, f, fileStore: fileStore);
+            }
+          } catch (e, stackTrace) {
+            _log.shout(
+                "[_cleanUpCache] Failed while removing file: ${logFilename(f.path)}",
+                e,
+                stackTrace);
           }
-        } catch (e, stackTrace) {
-          _log.shout(
-              "[_cleanUpCache] Failed while removing file: ${logFilename(f.path)}",
-              e,
-              stackTrace);
         }
-      }
-    });
+      },
+    );
   }
 
   final AppDb appDb;
@@ -198,23 +203,28 @@ class FileCacheRemover {
   /// If [f] is a file, the file will be removed from file2Store, but no changes
   /// to dirStore.
   Future<void> call(Account account, File f) async {
-    await appDb.use((db) async {
-      if (f.isCollection != false) {
-        // removing dir is basically a superset of removing file, so we'll treat
-        // unspecified file as dir
-        final transaction = db.transaction(
-            [AppDb.dirStoreName, AppDb.file2StoreName], idbModeReadWrite);
-        final dirStore = transaction.objectStore(AppDb.dirStoreName);
-        final fileStore = transaction.objectStore(AppDb.file2StoreName);
-        await _removeDirFromAppDb(account, f,
-            dirStore: dirStore, fileStore: fileStore);
-      } else {
-        final transaction =
-            db.transaction(AppDb.file2StoreName, idbModeReadWrite);
-        final fileStore = transaction.objectStore(AppDb.file2StoreName);
-        await _removeFileFromAppDb(account, f, fileStore: fileStore);
-      }
-    });
+    if (f.isCollection != false) {
+      // removing dir is basically a superset of removing file, so we'll treat
+      // unspecified file as dir
+      await appDb.use(
+        (db) => db.transaction(
+            [AppDb.dirStoreName, AppDb.file2StoreName], idbModeReadWrite),
+        (transaction) async {
+          final dirStore = transaction.objectStore(AppDb.dirStoreName);
+          final fileStore = transaction.objectStore(AppDb.file2StoreName);
+          await _removeDirFromAppDb(account, f,
+              dirStore: dirStore, fileStore: fileStore);
+        },
+      );
+    } else {
+      await appDb.use(
+        (db) => db.transaction(AppDb.file2StoreName, idbModeReadWrite),
+        (transaction) async {
+          final fileStore = transaction.objectStore(AppDb.file2StoreName);
+          await _removeFileFromAppDb(account, f, fileStore: fileStore);
+        },
+      );
+    }
   }
 
   final AppDb appDb;
diff --git a/app/lib/k.dart b/app/lib/k.dart
index a1a5f964..a92ed075 100644
--- a/app/lib/k.dart
+++ b/app/lib/k.dart
@@ -33,3 +33,7 @@ const photoLargeSize = 1080;
 
 /// Size of the cover photos
 const coverSize = 512;
+
+/// AppDb lock ID
+const appDbLockId = 1;
+
diff --git a/app/lib/mobile/lock.dart b/app/lib/mobile/lock.dart
new file mode 100644
index 00000000..e8352e59
--- /dev/null
+++ b/app/lib/mobile/lock.dart
@@ -0,0 +1,24 @@
+import 'package:nc_photos/platform/k.dart' as platform_k;
+import 'package:nc_photos_plugin/nc_photos_plugin.dart' as plugin;
+
+class Lock {
+  static Future<T> synchronized<T>(int lockId, Future<T> Function() fn) async {
+    if (platform_k.isAndroid) {
+      return _synchronizedAndroid(lockId, fn);
+    } else {
+      throw UnimplementedError();
+    }
+  }
+
+  static Future<T> _synchronizedAndroid<T>(
+      int lockId, Future<T> Function() fn) async {
+    while (!await plugin.Lock.tryLock(lockId)) {
+      await Future.delayed(const Duration(milliseconds: 50));
+    }
+    try {
+      return await fn();
+    } finally {
+      await plugin.Lock.unlock(lockId);
+    }
+  }
+}
diff --git a/app/lib/mobile/platform.dart b/app/lib/mobile/platform.dart
index 29cf634f..d102f48f 100644
--- a/app/lib/mobile/platform.dart
+++ b/app/lib/mobile/platform.dart
@@ -2,4 +2,5 @@ export 'db_util.dart';
 export 'download.dart';
 export 'file_saver.dart';
 export 'google_gps_map.dart';
+export 'lock.dart';
 export 'universal_storage.dart';
diff --git a/app/lib/use_case/cache_favorite.dart b/app/lib/use_case/cache_favorite.dart
index 377ab9ff..bf84419a 100644
--- a/app/lib/use_case/cache_favorite.dart
+++ b/app/lib/use_case/cache_favorite.dart
@@ -37,35 +37,36 @@ class CacheFavorite {
     if (newFavorites.isEmpty && removedFavorites.isEmpty) {
       return;
     }
-    await _c.appDb.use((db) async {
-      final transaction =
-          db.transaction(AppDb.file2StoreName, idbModeReadWrite);
-      final fileStore = transaction.objectStore(AppDb.file2StoreName);
-      await Future.wait(newFavorites.map((f) async {
-        _log.info("[call] New favorite: ${f.path}");
-        try {
-          await fileStore.put(AppDbFile2Entry.fromFile(account, f).toJson(),
-              AppDbFile2Entry.toPrimaryKeyForFile(account, f));
-        } catch (e, stackTrace) {
-          _log.shout(
-              "[call] Failed while writing new favorite to AppDb: ${logFilename(f.path)}",
-              e,
-              stackTrace);
-        }
-      }));
-      await Future.wait(removedFavorites.map((f) async {
-        _log.info("[call] Remove favorite: ${f.path}");
-        try {
-          await fileStore.put(AppDbFile2Entry.fromFile(account, f).toJson(),
-              AppDbFile2Entry.toPrimaryKeyForFile(account, f));
-        } catch (e, stackTrace) {
-          _log.shout(
-              "[call] Failed while writing removed favorite to AppDb: ${logFilename(f.path)}",
-              e,
-              stackTrace);
-        }
-      }));
-    });
+    await _c.appDb.use(
+      (db) => db.transaction(AppDb.file2StoreName, idbModeReadWrite),
+      (transaction) async {
+        final fileStore = transaction.objectStore(AppDb.file2StoreName);
+        await Future.wait(newFavorites.map((f) async {
+          _log.info("[call] New favorite: ${f.path}");
+          try {
+            await fileStore.put(AppDbFile2Entry.fromFile(account, f).toJson(),
+                AppDbFile2Entry.toPrimaryKeyForFile(account, f));
+          } catch (e, stackTrace) {
+            _log.shout(
+                "[call] Failed while writing new favorite to AppDb: ${logFilename(f.path)}",
+                e,
+                stackTrace);
+          }
+        }));
+        await Future.wait(removedFavorites.map((f) async {
+          _log.info("[call] Remove favorite: ${f.path}");
+          try {
+            await fileStore.put(AppDbFile2Entry.fromFile(account, f).toJson(),
+                AppDbFile2Entry.toPrimaryKeyForFile(account, f));
+          } catch (e, stackTrace) {
+            _log.shout(
+                "[call] Failed while writing removed favorite to AppDb: ${logFilename(f.path)}",
+                e,
+                stackTrace);
+          }
+        }));
+      },
+    );
 
     KiwiContainer()
         .resolve<EventBus>()
diff --git a/app/lib/use_case/compat/v37.dart b/app/lib/use_case/compat/v37.dart
index d35bd926..64cc58cf 100644
--- a/app/lib/use_case/compat/v37.dart
+++ b/app/lib/use_case/compat/v37.dart
@@ -12,14 +12,15 @@ class CompatV37 {
   static Future<void> setAppDbMigrationFlag(AppDb appDb) async {
     _log.info("[setAppDbMigrationFlag] Set db flag");
     try {
-      await appDb.use((db) async {
-        final transaction =
-            db.transaction(AppDb.metaStoreName, idbModeReadWrite);
-        final metaStore = transaction.objectStore(AppDb.metaStoreName);
-        await metaStore
-            .put(const AppDbMetaEntryCompatV37(false).toEntry().toJson());
-        await transaction.completed;
-      });
+      await appDb.use(
+        (db) => db.transaction(AppDb.metaStoreName, idbModeReadWrite),
+        (transaction) async {
+          final metaStore = transaction.objectStore(AppDb.metaStoreName);
+          await metaStore
+              .put(const AppDbMetaEntryCompatV37(false).toEntry().toJson());
+          await transaction.completed;
+        },
+      );
     } catch (e, stackTrace) {
       _log.shout(
           "[setAppDbMigrationFlag] Failed while setting db flag, drop db instead",
@@ -30,11 +31,13 @@ class CompatV37 {
   }
 
   static Future<bool> isAppDbNeedMigration(AppDb appDb) async {
-    final dbItem = await appDb.use((db) async {
-      final transaction = db.transaction(AppDb.metaStoreName, idbModeReadOnly);
-      final metaStore = transaction.objectStore(AppDb.metaStoreName);
-      return await metaStore.getObject(AppDbMetaEntryCompatV37.key) as Map?;
-    });
+    final dbItem = await appDb.use(
+      (db) => db.transaction(AppDb.metaStoreName, idbModeReadOnly),
+      (transaction) async {
+        final metaStore = transaction.objectStore(AppDb.metaStoreName);
+        return await metaStore.getObject(AppDbMetaEntryCompatV37.key) as Map?;
+      },
+    );
     if (dbItem == null) {
       return false;
     }
@@ -51,51 +54,53 @@ class CompatV37 {
   static Future<void> migrateAppDb(AppDb appDb) async {
     _log.info("[migrateAppDb] Migrate AppDb");
     try {
-      await appDb.use((db) async {
-        final transaction = db.transaction(
+      await appDb.use(
+        (db) => db.transaction(
             [AppDb.file2StoreName, AppDb.dirStoreName, AppDb.metaStoreName],
-            idbModeReadWrite);
-        final noMediaFiles = <_NoMediaFile>[];
-        try {
-          final fileStore = transaction.objectStore(AppDb.file2StoreName);
-          final dirStore = transaction.objectStore(AppDb.dirStoreName);
-          // scan the db to see which dirs contain a no media marker
-          await for (final c in fileStore.openCursor()) {
-            final item = c.value as Map;
-            final strippedPath = item["strippedPath"] as String;
-            if (file_util.isNoMediaMarkerPath(strippedPath)) {
-              noMediaFiles.add(_NoMediaFile(
-                item["server"],
-                item["userId"],
-                path_lib
-                    .dirname(item["strippedPath"])
-                    .run((p) => p == "." ? "" : p),
-                item["file"]["fileId"],
-              ));
+            idbModeReadWrite),
+        (transaction) async {
+          final noMediaFiles = <_NoMediaFile>[];
+          try {
+            final fileStore = transaction.objectStore(AppDb.file2StoreName);
+            final dirStore = transaction.objectStore(AppDb.dirStoreName);
+            // scan the db to see which dirs contain a no media marker
+            await for (final c in fileStore.openCursor()) {
+              final item = c.value as Map;
+              final strippedPath = item["strippedPath"] as String;
+              if (file_util.isNoMediaMarkerPath(strippedPath)) {
+                noMediaFiles.add(_NoMediaFile(
+                  item["server"],
+                  item["userId"],
+                  path_lib
+                      .dirname(item["strippedPath"])
+                      .run((p) => p == "." ? "" : p),
+                  item["file"]["fileId"],
+                ));
+              }
+              c.next();
             }
-            c.next();
-          }
-          // sort to make sure parent dirs are always in front of sub dirs
-          noMediaFiles
-              .sort((a, b) => a.strippedDirPath.compareTo(b.strippedDirPath));
-          _log.info(
-              "[migrateAppDb] nomedia dirs: ${noMediaFiles.toReadableString()}");
+            // sort to make sure parent dirs are always in front of sub dirs
+            noMediaFiles
+                .sort((a, b) => a.strippedDirPath.compareTo(b.strippedDirPath));
+            _log.info(
+                "[migrateAppDb] nomedia dirs: ${noMediaFiles.toReadableString()}");
 
-          if (noMediaFiles.isNotEmpty) {
-            await _migrateAppDbFileStore(appDb, noMediaFiles,
-                fileStore: fileStore);
-            await _migrateAppDbDirStore(appDb, noMediaFiles,
-                dirStore: dirStore);
-          }
+            if (noMediaFiles.isNotEmpty) {
+              await _migrateAppDbFileStore(appDb, noMediaFiles,
+                  fileStore: fileStore);
+              await _migrateAppDbDirStore(appDb, noMediaFiles,
+                  dirStore: dirStore);
+            }
 
-          final metaStore = transaction.objectStore(AppDb.metaStoreName);
-          await metaStore
-              .put(const AppDbMetaEntryCompatV37(true).toEntry().toJson());
-        } catch (_) {
-          transaction.abort();
-          rethrow;
-        }
-      });
+            final metaStore = transaction.objectStore(AppDb.metaStoreName);
+            await metaStore
+                .put(const AppDbMetaEntryCompatV37(true).toEntry().toJson());
+          } catch (_) {
+            transaction.abort();
+            rethrow;
+          }
+        },
+      );
     } catch (e, stackTrace) {
       _log.shout("[migrateAppDb] Failed while migrating, drop db instead", e,
           stackTrace);
diff --git a/app/lib/use_case/db_compat/v5.dart b/app/lib/use_case/db_compat/v5.dart
index 7c9d1d22..d0434c2b 100644
--- a/app/lib/use_case/db_compat/v5.dart
+++ b/app/lib/use_case/db_compat/v5.dart
@@ -7,11 +7,13 @@ import 'package:nc_photos/object_extension.dart';
 
 class DbCompatV5 {
   static Future<bool> isNeedMigration(AppDb appDb) async {
-    final dbItem = await appDb.use((db) async {
-      final transaction = db.transaction(AppDb.metaStoreName, idbModeReadOnly);
-      final metaStore = transaction.objectStore(AppDb.metaStoreName);
-      return await metaStore.getObject(AppDbMetaEntryDbCompatV5.key) as Map?;
-    });
+    final dbItem = await appDb.use(
+      (db) => db.transaction(AppDb.metaStoreName, idbModeReadOnly),
+      (transaction) async {
+        final metaStore = transaction.objectStore(AppDb.metaStoreName);
+        return await metaStore.getObject(AppDbMetaEntryDbCompatV5.key) as Map?;
+      },
+    );
     if (dbItem == null) {
       return false;
     }
@@ -28,36 +30,38 @@ class DbCompatV5 {
   static Future<void> migrate(AppDb appDb) async {
     _log.info("[migrate] Migrate AppDb");
     try {
-      await appDb.use((db) async {
-        final transaction = db.transaction(
-            [AppDb.file2StoreName, AppDb.metaStoreName], idbModeReadWrite);
-        try {
-          final fileStore = transaction.objectStore(AppDb.file2StoreName);
-          await for (final c in fileStore.openCursor()) {
-            final item = c.value as Map;
-            // migrate file entry: add bestDateTime
-            final fileEntry = item.cast<String, dynamic>().run((json) {
-              final f = File.fromJson(json["file"].cast<String, dynamic>());
-              return AppDbFile2Entry(
-                json["server"],
-                (json["userId"] as String).toCi(),
-                json["strippedPath"],
-                f.bestDateTime.millisecondsSinceEpoch,
-                File.fromJson(json["file"].cast<String, dynamic>()),
-              );
-            });
-            await c.update(fileEntry.toJson());
+      await appDb.use(
+        (db) => db.transaction(
+            [AppDb.file2StoreName, AppDb.metaStoreName], idbModeReadWrite),
+        (transaction) async {
+          try {
+            final fileStore = transaction.objectStore(AppDb.file2StoreName);
+            await for (final c in fileStore.openCursor()) {
+              final item = c.value as Map;
+              // migrate file entry: add bestDateTime
+              final fileEntry = item.cast<String, dynamic>().run((json) {
+                final f = File.fromJson(json["file"].cast<String, dynamic>());
+                return AppDbFile2Entry(
+                  json["server"],
+                  (json["userId"] as String).toCi(),
+                  json["strippedPath"],
+                  f.bestDateTime.millisecondsSinceEpoch,
+                  File.fromJson(json["file"].cast<String, dynamic>()),
+                );
+              });
+              await c.update(fileEntry.toJson());
 
-            c.next();
+              c.next();
+            }
+            final metaStore = transaction.objectStore(AppDb.metaStoreName);
+            await metaStore
+                .put(const AppDbMetaEntryDbCompatV5(true).toEntry().toJson());
+          } catch (_) {
+            transaction.abort();
+            rethrow;
           }
-          final metaStore = transaction.objectStore(AppDb.metaStoreName);
-          await metaStore
-              .put(const AppDbMetaEntryDbCompatV5(true).toEntry().toJson());
-        } catch (_) {
-          transaction.abort();
-          rethrow;
-        }
-      });
+        },
+      );
     } catch (e, stackTrace) {
       _log.shout(
           "[migrate] Failed while migrating, drop db instead", e, stackTrace);
diff --git a/app/lib/use_case/find_file.dart b/app/lib/use_case/find_file.dart
index 1d842635..43dc743a 100644
--- a/app/lib/use_case/find_file.dart
+++ b/app/lib/use_case/find_file.dart
@@ -19,12 +19,14 @@ class FindFile {
     List<int> fileIds, {
     void Function(int fileId)? onFileNotFound,
   }) async {
-    final dbItems = await _c.appDb.use((db) async {
-      final transaction = db.transaction(AppDb.file2StoreName, idbModeReadOnly);
-      final fileStore = transaction.objectStore(AppDb.file2StoreName);
-      return await Future.wait(fileIds.map((id) =>
-          fileStore.getObject(AppDbFile2Entry.toPrimaryKey(account, id))));
-    });
+    final dbItems = await _c.appDb.use(
+      (db) => db.transaction(AppDb.file2StoreName, idbModeReadOnly),
+      (transaction) async {
+        final fileStore = transaction.objectStore(AppDb.file2StoreName);
+        return await Future.wait(fileIds.map((id) =>
+            fileStore.getObject(AppDbFile2Entry.toPrimaryKey(account, id))));
+      },
+    );
     final files = <File>[];
     for (final pair in zip([fileIds, dbItems])) {
       final dbItem = pair[1] as Map?;
diff --git a/app/lib/use_case/list_favorite_offline.dart b/app/lib/use_case/list_favorite_offline.dart
index 7843579d..f5a0b8da 100644
--- a/app/lib/use_case/list_favorite_offline.dart
+++ b/app/lib/use_case/list_favorite_offline.dart
@@ -18,24 +18,26 @@ class ListFavoriteOffline {
     final rootDirs = account.roots
         .map((r) => File(path: file_util.unstripPath(account, r)))
         .toList();
-    return _c.appDb.use((db) async {
-      final transaction = db.transaction(AppDb.file2StoreName, idbModeReadOnly);
-      final fileStore = transaction.objectStore(AppDb.file2StoreName);
-      final fileIsFavoriteIndex =
-          fileStore.index(AppDbFile2Entry.fileIsFavoriteIndexName);
-      return await fileIsFavoriteIndex
-          .openCursor(
-            key: AppDbFile2Entry.toFileIsFavoriteIndexKey(account, true),
-            autoAdvance: true,
-          )
-          .map((c) => AppDbFile2Entry.fromJson(
-              (c.value as Map).cast<String, dynamic>()))
-          .map((e) => e.file)
-          .where((f) =>
-              file_util.isSupportedFormat(f) &&
-              rootDirs.any((r) => file_util.isOrUnderDir(f, r)))
-          .toList();
-    });
+    return _c.appDb.use(
+      (db) => db.transaction(AppDb.file2StoreName, idbModeReadOnly),
+      (transaction) async {
+        final fileStore = transaction.objectStore(AppDb.file2StoreName);
+        final fileIsFavoriteIndex =
+            fileStore.index(AppDbFile2Entry.fileIsFavoriteIndexName);
+        return await fileIsFavoriteIndex
+            .openCursor(
+              key: AppDbFile2Entry.toFileIsFavoriteIndexKey(account, true),
+              autoAdvance: true,
+            )
+            .map((c) => AppDbFile2Entry.fromJson(
+                (c.value as Map).cast<String, dynamic>()))
+            .map((e) => e.file)
+            .where((f) =>
+                file_util.isSupportedFormat(f) &&
+                rootDirs.any((r) => file_util.isOrUnderDir(f, r)))
+            .toList();
+      },
+    );
   }
 
   final DiContainer _c;
diff --git a/app/lib/use_case/populate_person.dart b/app/lib/use_case/populate_person.dart
index 3eccb38b..fb02589f 100644
--- a/app/lib/use_case/populate_person.dart
+++ b/app/lib/use_case/populate_person.dart
@@ -11,20 +11,22 @@ class PopulatePerson {
 
   /// Return a list of files of the faces
   Future<List<File>> call(Account account, List<Face> faces) async {
-    return await appDb.use((db) async {
-      final transaction = db.transaction(AppDb.file2StoreName, idbModeReadOnly);
-      final store = transaction.objectStore(AppDb.file2StoreName);
-      final products = <File>[];
-      for (final f in faces) {
-        try {
-          products.add(await _populateOne(account, f, fileStore: store));
-        } catch (e, stackTrace) {
-          _log.severe("[call] Failed populating file of face: ${f.fileId}", e,
-              stackTrace);
+    return await appDb.use(
+      (db) => db.transaction(AppDb.file2StoreName, idbModeReadOnly),
+      (transaction) async {
+        final store = transaction.objectStore(AppDb.file2StoreName);
+        final products = <File>[];
+        for (final f in faces) {
+          try {
+            products.add(await _populateOne(account, f, fileStore: store));
+          } catch (e, stackTrace) {
+            _log.severe("[call] Failed populating file of face: ${f.fileId}", e,
+                stackTrace);
+          }
         }
-      }
-      return products;
-    });
+        return products;
+      },
+    );
   }
 
   Future<File> _populateOne(
diff --git a/app/lib/use_case/resync_album.dart b/app/lib/use_case/resync_album.dart
index b90ba39f..52b16149 100644
--- a/app/lib/use_case/resync_album.dart
+++ b/app/lib/use_case/resync_album.dart
@@ -20,17 +20,19 @@ class ResyncAlbum {
     final items = AlbumStaticProvider.of(album).items;
     final fileIds =
         items.whereType<AlbumFileItem>().map((i) => i.file.fileId!).toList();
-    final dbItems = Map.fromEntries(await appDb.use((db) async {
-      final transaction = db.transaction(AppDb.file2StoreName, idbModeReadOnly);
-      final store = transaction.objectStore(AppDb.file2StoreName);
-      return await Future.wait(fileIds.map(
-        (id) async => MapEntry(
-          id,
-          await store.getObject(AppDbFile2Entry.toPrimaryKey(account, id))
-              as Map?,
-        ),
-      ));
-    }));
+    final dbItems = Map.fromEntries(await appDb.use(
+      (db) => db.transaction(AppDb.file2StoreName, idbModeReadOnly),
+      (transaction) async {
+        final store = transaction.objectStore(AppDb.file2StoreName);
+        return await Future.wait(fileIds.map(
+          (id) async => MapEntry(
+            id,
+            await store.getObject(AppDbFile2Entry.toPrimaryKey(account, id))
+                as Map?,
+          ),
+        ));
+      },
+    ));
     return items.map((i) {
       if (i is AlbumFileItem) {
         try {
diff --git a/app/lib/use_case/scan_dir_offline.dart b/app/lib/use_case/scan_dir_offline.dart
index f94e11a2..1b289a30 100644
--- a/app/lib/use_case/scan_dir_offline.dart
+++ b/app/lib/use_case/scan_dir_offline.dart
@@ -12,22 +12,25 @@ class ScanDirOffline {
 
   /// List all files under a dir recursively from the local DB
   Future<List<File>> call(Account account, File root) async {
-    return await _c.appDb.use((db) async {
-      final transaction = db.transaction(AppDb.file2StoreName, idbModeReadOnly);
-      final store = transaction.objectStore(AppDb.file2StoreName);
-      final index = store.index(AppDbFile2Entry.strippedPathIndexName);
-      final range = KeyRange.bound(
-        AppDbFile2Entry.toStrippedPathIndexLowerKeyForDir(account, root),
-        AppDbFile2Entry.toStrippedPathIndexUpperKeyForDir(account, root),
-      );
-      return await index
-          .openCursor(range: range, autoAdvance: true)
-          .map((c) => c.value)
-          .cast<Map>()
-          .map((e) => AppDbFile2Entry.fromJson(e.cast<String, dynamic>()).file)
-          .where((f) => file_util.isSupportedFormat(f))
-          .toList();
-    });
+    return await _c.appDb.use(
+      (db) => db.transaction(AppDb.file2StoreName, idbModeReadOnly),
+      (transaction) async {
+        final store = transaction.objectStore(AppDb.file2StoreName);
+        final index = store.index(AppDbFile2Entry.strippedPathIndexName);
+        final range = KeyRange.bound(
+          AppDbFile2Entry.toStrippedPathIndexLowerKeyForDir(account, root),
+          AppDbFile2Entry.toStrippedPathIndexUpperKeyForDir(account, root),
+        );
+        return await index
+            .openCursor(range: range, autoAdvance: true)
+            .map((c) => c.value)
+            .cast<Map>()
+            .map(
+                (e) => AppDbFile2Entry.fromJson(e.cast<String, dynamic>()).file)
+            .where((f) => file_util.isSupportedFormat(f))
+            .toList();
+      },
+    );
   }
 
   final DiContainer _c;
diff --git a/app/lib/web/lock.dart b/app/lib/web/lock.dart
new file mode 100644
index 00000000..450c7f43
--- /dev/null
+++ b/app/lib/web/lock.dart
@@ -0,0 +1,9 @@
+import 'package:synchronized/synchronized.dart' as dart;
+
+// Isolates are not supported on web
+class Lock {
+  static Future<T> synchronized<T>(int lockId, Future<T> Function() fn) =>
+      (_locks[lockId] ??= dart.Lock(reentrant: true)).synchronized(fn);
+
+  static final _locks = <int, dart.Lock>{};
+}
diff --git a/app/lib/web/platform.dart b/app/lib/web/platform.dart
index 29cf634f..d102f48f 100644
--- a/app/lib/web/platform.dart
+++ b/app/lib/web/platform.dart
@@ -2,4 +2,5 @@ export 'db_util.dart';
 export 'download.dart';
 export 'file_saver.dart';
 export 'google_gps_map.dart';
+export 'lock.dart';
 export 'universal_storage.dart';
diff --git a/app/test/mock_type.dart b/app/test/mock_type.dart
index 11b1ddad..cec8bfe0 100644
--- a/app/test/mock_type.dart
+++ b/app/test/mock_type.dart
@@ -100,7 +100,8 @@ class MockAppDb implements AppDb {
   }
 
   @override
-  Future<T> use<T>(FutureOr<T> Function(Database db) fn) async {
+  Future<T> use<T>(Transaction Function(Database db) transactionBuilder,
+      FutureOr<T> Function(Transaction transaction) fn) async {
     final db = await _dbFactory.open(
       "test.db",
       version: 1,
@@ -110,9 +111,14 @@ class MockAppDb implements AppDb {
       },
     );
 
+    Transaction? transaction;
     try {
-      return await fn(db);
+      transaction = transactionBuilder(db);
+      return await fn(transaction);
     } finally {
+      if (transaction != null) {
+        await transaction.completed;
+      }
       db.close();
     }
   }
diff --git a/app/test/test_util.dart b/app/test/test_util.dart
index 6079d1fe..e43afcc8 100644
--- a/app/test/test_util.dart
+++ b/app/test/test_util.dart
@@ -341,36 +341,43 @@ Sharee buildSharee({
 
 Future<void> fillAppDb(
     AppDb appDb, Account account, Iterable<File> files) async {
-  await appDb.use((db) async {
-    final transaction = db.transaction(AppDb.file2StoreName, idbModeReadWrite);
-    final file2Store = transaction.objectStore(AppDb.file2StoreName);
-    for (final f in files) {
-      await file2Store.put(AppDbFile2Entry.fromFile(account, f).toJson(),
-          AppDbFile2Entry.toPrimaryKeyForFile(account, f));
-    }
-  });
+  await appDb.use(
+    (db) => db.transaction(AppDb.file2StoreName, idbModeReadWrite),
+    (transaction) async {
+      final file2Store = transaction.objectStore(AppDb.file2StoreName);
+      for (final f in files) {
+        await file2Store.put(AppDbFile2Entry.fromFile(account, f).toJson(),
+            AppDbFile2Entry.toPrimaryKeyForFile(account, f));
+      }
+    },
+  );
 }
 
 Future<void> fillAppDbDir(
     AppDb appDb, Account account, File dir, List<File> children) async {
-  await appDb.use((db) async {
-    final transaction = db.transaction(AppDb.dirStoreName, idbModeReadWrite);
-    final dirStore = transaction.objectStore(AppDb.dirStoreName);
-    await dirStore.put(AppDbDirEntry.fromFiles(account, dir, children).toJson(),
-        AppDbDirEntry.toPrimaryKeyForDir(account, dir));
-  });
+  await appDb.use(
+    (db) => db.transaction(AppDb.dirStoreName, idbModeReadWrite),
+    (transaction) async {
+      final dirStore = transaction.objectStore(AppDb.dirStoreName);
+      await dirStore.put(
+          AppDbDirEntry.fromFiles(account, dir, children).toJson(),
+          AppDbDirEntry.toPrimaryKeyForDir(account, dir));
+    },
+  );
 }
 
 Future<List<T>> listAppDb<T>(
     AppDb appDb, String storeName, T Function(JsonObj) transform) {
-  return appDb.use((db) async {
-    final transaction = db.transaction(storeName, idbModeReadOnly);
-    final store = transaction.objectStore(storeName);
-    return await store
-        .openCursor(autoAdvance: true)
-        .map((c) => c.value)
-        .cast<Map>()
-        .map((e) => transform(e.cast<String, dynamic>()))
-        .toList();
-  });
+  return appDb.use(
+    (db) => db.transaction(storeName, idbModeReadOnly),
+    (transaction) async {
+      final store = transaction.objectStore(storeName);
+      return await store
+          .openCursor(autoAdvance: true)
+          .map((c) => c.value)
+          .cast<Map>()
+          .map((e) => transform(e.cast<String, dynamic>()))
+          .toList();
+    },
+  );
 }
diff --git a/app/test/use_case/compat/v37_test.dart b/app/test/use_case/compat/v37_test.dart
index 4691d4b9..fa5b1dd7 100644
--- a/app/test/use_case/compat/v37_test.dart
+++ b/app/test/use_case/compat/v37_test.dart
@@ -29,12 +29,14 @@ void main() {
 /// Expect: true
 Future<void> _isAppDbNeedMigrationEntryFalse() async {
   final appDb = MockAppDb();
-  await appDb.use((db) async {
-    final transaction = db.transaction(AppDb.metaStoreName, idbModeReadWrite);
-    final metaStore = transaction.objectStore(AppDb.metaStoreName);
-    const entry = AppDbMetaEntryCompatV37(false);
-    await metaStore.put(entry.toEntry().toJson());
-  });
+  await appDb.use(
+    (db) => db.transaction(AppDb.metaStoreName, idbModeReadWrite),
+    (transaction) async {
+      final metaStore = transaction.objectStore(AppDb.metaStoreName);
+      const entry = AppDbMetaEntryCompatV37(false);
+      await metaStore.put(entry.toEntry().toJson());
+    },
+  );
 
   expect(await CompatV37.isAppDbNeedMigration(appDb), true);
 }
@@ -44,12 +46,14 @@ Future<void> _isAppDbNeedMigrationEntryFalse() async {
 /// Expect: false
 Future<void> _isAppDbNeedMigrationEntryTrue() async {
   final appDb = MockAppDb();
-  await appDb.use((db) async {
-    final transaction = db.transaction(AppDb.metaStoreName, idbModeReadWrite);
-    final metaStore = transaction.objectStore(AppDb.metaStoreName);
-    const entry = AppDbMetaEntryCompatV37(true);
-    await metaStore.put(entry.toEntry().toJson());
-  });
+  await appDb.use(
+    (db) => db.transaction(AppDb.metaStoreName, idbModeReadWrite),
+    (transaction) async {
+      final metaStore = transaction.objectStore(AppDb.metaStoreName);
+      const entry = AppDbMetaEntryCompatV37(true);
+      await metaStore.put(entry.toEntry().toJson());
+    },
+  );
 
   expect(await CompatV37.isAppDbNeedMigration(appDb), false);
 }
@@ -59,12 +63,14 @@ Future<void> _isAppDbNeedMigrationEntryTrue() async {
 /// Expect: false
 Future<void> _isAppDbNeedMigrationWithoutEntry() async {
   final appDb = MockAppDb();
-  await appDb.use((db) async {
-    final transaction = db.transaction(AppDb.metaStoreName, idbModeReadWrite);
-    final metaStore = transaction.objectStore(AppDb.metaStoreName);
-    const entry = AppDbMetaEntryCompatV37(true);
-    await metaStore.put(entry.toEntry().toJson());
-  });
+  await appDb.use(
+    (db) => db.transaction(AppDb.metaStoreName, idbModeReadWrite),
+    (transaction) async {
+      final metaStore = transaction.objectStore(AppDb.metaStoreName);
+      const entry = AppDbMetaEntryCompatV37(true);
+      await metaStore.put(entry.toEntry().toJson());
+    },
+  );
 
   expect(await CompatV37.isAppDbNeedMigration(appDb), false);
 }
@@ -81,11 +87,9 @@ Future<void> _migrateAppDbWithoutNomedia() async {
         ..addJpeg("admin/dir1/test2.jpg"))
       .build();
   final appDb = MockAppDb();
-  await appDb.use((db) async {
-    await util.fillAppDb(appDb, account, files);
-    await util.fillAppDbDir(appDb, account, files[0], files.slice(1, 3));
-    await util.fillAppDbDir(appDb, account, files[2], [files[3]]);
-  });
+  await util.fillAppDb(appDb, account, files);
+  await util.fillAppDbDir(appDb, account, files[0], files.slice(1, 3));
+  await util.fillAppDbDir(appDb, account, files[2], [files[3]]);
   await CompatV37.migrateAppDb(appDb);
 
   final fileObjs = await util.listAppDb(
@@ -113,11 +117,9 @@ Future<void> _migrateAppDb() async {
         ..addJpeg("admin/dir1/test2.jpg"))
       .build();
   final appDb = MockAppDb();
-  await appDb.use((db) async {
-    await util.fillAppDb(appDb, account, files);
-    await util.fillAppDbDir(appDb, account, files[0], files.slice(1, 3));
-    await util.fillAppDbDir(appDb, account, files[2], files.slice(3, 5));
-  });
+  await util.fillAppDb(appDb, account, files);
+  await util.fillAppDbDir(appDb, account, files[0], files.slice(1, 3));
+  await util.fillAppDbDir(appDb, account, files[2], files.slice(3, 5));
   await CompatV37.migrateAppDb(appDb);
 
   final fileObjs = await util.listAppDb(
@@ -147,12 +149,10 @@ Future<void> _migrateAppDbNestedDir() async {
         ..addJpeg("admin/dir1/dir1-1/test3.jpg"))
       .build();
   final appDb = MockAppDb();
-  await appDb.use((db) async {
-    await util.fillAppDb(appDb, account, files);
-    await util.fillAppDbDir(appDb, account, files[0], files.slice(1, 3));
-    await util.fillAppDbDir(appDb, account, files[2], files.slice(3, 6));
-    await util.fillAppDbDir(appDb, account, files[5], [files[6]]);
-  });
+  await util.fillAppDb(appDb, account, files);
+  await util.fillAppDbDir(appDb, account, files[0], files.slice(1, 3));
+  await util.fillAppDbDir(appDb, account, files[2], files.slice(3, 6));
+  await util.fillAppDbDir(appDb, account, files[5], [files[6]]);
   await CompatV37.migrateAppDb(appDb);
 
   final fileObjs = await util.listAppDb(
@@ -183,12 +183,10 @@ Future<void> _migrateAppDbNestedMarker() async {
         ..addJpeg("admin/dir1/dir1-1/test3.jpg"))
       .build();
   final appDb = MockAppDb();
-  await appDb.use((db) async {
-    await util.fillAppDb(appDb, account, files);
-    await util.fillAppDbDir(appDb, account, files[0], files.slice(1, 3));
-    await util.fillAppDbDir(appDb, account, files[2], files.slice(3, 6));
-    await util.fillAppDbDir(appDb, account, files[5], files.slice(6, 8));
-  });
+  await util.fillAppDb(appDb, account, files);
+  await util.fillAppDbDir(appDb, account, files[0], files.slice(1, 3));
+  await util.fillAppDbDir(appDb, account, files[2], files.slice(3, 6));
+  await util.fillAppDbDir(appDb, account, files[5], files.slice(6, 8));
   await CompatV37.migrateAppDb(appDb);
 
   final fileObjs = await util.listAppDb(
@@ -216,11 +214,9 @@ Future<void> _migrateAppDbRoot() async {
         ..addJpeg("admin/dir1/test2.jpg"))
       .build();
   final appDb = MockAppDb();
-  await appDb.use((db) async {
-    await util.fillAppDb(appDb, account, files);
-    await util.fillAppDbDir(appDb, account, files[0], files.slice(1, 4));
-    await util.fillAppDbDir(appDb, account, files[3], [files[4]]);
-  });
+  await util.fillAppDb(appDb, account, files);
+  await util.fillAppDbDir(appDb, account, files[0], files.slice(1, 4));
+  await util.fillAppDbDir(appDb, account, files[3], [files[4]]);
   await CompatV37.migrateAppDb(appDb);
 
   final objs = await util.listAppDb(
diff --git a/app/test/use_case/db_compat/v5_test.dart b/app/test/use_case/db_compat/v5_test.dart
index 5dbb9b33..9d30a77d 100644
--- a/app/test/use_case/db_compat/v5_test.dart
+++ b/app/test/use_case/db_compat/v5_test.dart
@@ -13,39 +13,42 @@ void main() {
     group("isNeedMigration", () {
       test("w/ meta entry == false", () async {
         final appDb = MockAppDb();
-        await appDb.use((db) async {
-          final transaction =
-              db.transaction(AppDb.metaStoreName, idbModeReadWrite);
-          final metaStore = transaction.objectStore(AppDb.metaStoreName);
-          const entry = AppDbMetaEntryDbCompatV5(false);
-          await metaStore.put(entry.toEntry().toJson());
-        });
+        await appDb.use(
+          (db) => db.transaction(AppDb.metaStoreName, idbModeReadWrite),
+          (transaction) async {
+            final metaStore = transaction.objectStore(AppDb.metaStoreName);
+            const entry = AppDbMetaEntryDbCompatV5(false);
+            await metaStore.put(entry.toEntry().toJson());
+          },
+        );
 
         expect(await DbCompatV5.isNeedMigration(appDb), true);
       });
 
       test("w/ meta entry == true", () async {
         final appDb = MockAppDb();
-        await appDb.use((db) async {
-          final transaction =
-              db.transaction(AppDb.metaStoreName, idbModeReadWrite);
-          final metaStore = transaction.objectStore(AppDb.metaStoreName);
-          const entry = AppDbMetaEntryDbCompatV5(true);
-          await metaStore.put(entry.toEntry().toJson());
-        });
+        await appDb.use(
+          (db) => db.transaction(AppDb.metaStoreName, idbModeReadWrite),
+          (transaction) async {
+            final metaStore = transaction.objectStore(AppDb.metaStoreName);
+            const entry = AppDbMetaEntryDbCompatV5(true);
+            await metaStore.put(entry.toEntry().toJson());
+          },
+        );
 
         expect(await DbCompatV5.isNeedMigration(appDb), false);
       });
 
       test("w/o meta entry", () async {
         final appDb = MockAppDb();
-        await appDb.use((db) async {
-          final transaction =
-              db.transaction(AppDb.metaStoreName, idbModeReadWrite);
-          final metaStore = transaction.objectStore(AppDb.metaStoreName);
-          const entry = AppDbMetaEntryDbCompatV5(true);
-          await metaStore.put(entry.toEntry().toJson());
-        });
+        await appDb.use(
+          (db) => db.transaction(AppDb.metaStoreName, idbModeReadWrite),
+          (transaction) async {
+            final metaStore = transaction.objectStore(AppDb.metaStoreName);
+            const entry = AppDbMetaEntryDbCompatV5(true);
+            await metaStore.put(entry.toEntry().toJson());
+          },
+        );
 
         expect(await DbCompatV5.isNeedMigration(appDb), false);
       });
@@ -60,17 +63,18 @@ void main() {
             ))
           .build();
       final appDb = MockAppDb();
-      await appDb.use((db) async {
-        final transaction =
-            db.transaction(AppDb.file2StoreName, idbModeReadWrite);
-        final fileStore = transaction.objectStore(AppDb.file2StoreName);
-        await fileStore.put({
-          "server": account.url,
-          "userId": account.username.toCaseInsensitiveString(),
-          "strippedPath": files[0].strippedPathWithEmpty,
-          "file": files[0].toJson(),
-        }, "${account.url}/${account.username.toCaseInsensitiveString()}/${files[0].fileId}");
-      });
+      await appDb.use(
+        (db) => db.transaction(AppDb.file2StoreName, idbModeReadWrite),
+        (transaction) async {
+          final fileStore = transaction.objectStore(AppDb.file2StoreName);
+          await fileStore.put({
+            "server": account.url,
+            "userId": account.username.toCaseInsensitiveString(),
+            "strippedPath": files[0].strippedPathWithEmpty,
+            "file": files[0].toJson(),
+          }, "${account.url}/${account.username.toCaseInsensitiveString()}/${files[0].fileId}");
+        },
+      );
       await DbCompatV5.migrate(appDb);
 
       final objs =
diff --git a/plugin/android/src/main/kotlin/com/nkming/nc_photos/plugin/LockChannelHandler.kt b/plugin/android/src/main/kotlin/com/nkming/nc_photos/plugin/LockChannelHandler.kt
new file mode 100644
index 00000000..d5fb4d40
--- /dev/null
+++ b/plugin/android/src/main/kotlin/com/nkming/nc_photos/plugin/LockChannelHandler.kt
@@ -0,0 +1,69 @@
+package com.nkming.nc_photos.plugin
+
+import io.flutter.plugin.common.MethodCall
+import io.flutter.plugin.common.MethodChannel
+
+/*
+ * Platform-side lock mechanism
+ *
+ * Method channel always run on the main thread, so this is safe even when
+ * called from different isolates
+ *
+ * Methods:
+ * Try acquiring an lock. Return true if successful, false if acquired by others.
+ * fun tryLock(lockId: Int): Boolean
+ *
+ * Unlock a previously acquired lock. Unlocking twice is an error.
+ * fun unlock(lockId: Int): Unit
+ */
+class LockChannelHandler : MethodChannel.MethodCallHandler {
+	companion object {
+		const val CHANNEL = "${K.LIB_ID}/lock"
+
+		private val locks = mutableMapOf<Int, Boolean>()
+	}
+
+	override fun onMethodCall(call: MethodCall, result: MethodChannel.Result) {
+		when (call.method) {
+			"tryLock" -> {
+				try {
+					tryLock(call.argument("lockId")!!, result)
+				} catch (e: Throwable) {
+					result.error("systemException", e.toString(), null)
+				}
+			}
+			"unlock" -> {
+				try {
+					unlock(call.argument("lockId")!!, result)
+				} catch (e: Throwable) {
+					result.error("systemException", e.toString(), null)
+				}
+			}
+			else -> {
+				result.notImplemented()
+			}
+		}
+	}
+
+	private fun tryLock(lockId: Int, result: MethodChannel.Result) {
+		if (locks[lockId] != true) {
+			locks[lockId] = true
+			result.success(true)
+		} else {
+			result.success(false)
+		}
+	}
+
+	private fun unlock(lockId: Int, result: MethodChannel.Result) {
+		if (locks[lockId] == true) {
+			locks[lockId] = false
+			result.success(null)
+		} else {
+			result.error(
+				"notLockedException",
+				"Cannot unlock without first locking",
+				null
+			)
+		}
+	}
+}
diff --git a/plugin/android/src/main/kotlin/com/nkming/nc_photos/plugin/NcPhotosPlugin.kt b/plugin/android/src/main/kotlin/com/nkming/nc_photos/plugin/NcPhotosPlugin.kt
index f573bd27..500256dd 100644
--- a/plugin/android/src/main/kotlin/com/nkming/nc_photos/plugin/NcPhotosPlugin.kt
+++ b/plugin/android/src/main/kotlin/com/nkming/nc_photos/plugin/NcPhotosPlugin.kt
@@ -8,6 +8,11 @@ class NcPhotosPlugin : FlutterPlugin {
 	override fun onAttachedToEngine(
 		@NonNull flutterPluginBinding: FlutterPlugin.FlutterPluginBinding
 	) {
+		lockChannel = MethodChannel(
+			flutterPluginBinding.binaryMessenger, LockChannelHandler.CHANNEL
+		)
+		lockChannel.setMethodCallHandler(LockChannelHandler())
+
 		notificationChannel = MethodChannel(
 			flutterPluginBinding.binaryMessenger,
 			NotificationChannelHandler.CHANNEL
@@ -22,8 +27,10 @@ class NcPhotosPlugin : FlutterPlugin {
 	override fun onDetachedFromEngine(
 		@NonNull binding: FlutterPlugin.FlutterPluginBinding
 	) {
+		lockChannel.setMethodCallHandler(null)
 		notificationChannel.setMethodCallHandler(null)
 	}
 
+	private lateinit var lockChannel: MethodChannel
 	private lateinit var notificationChannel: MethodChannel
 }
diff --git a/plugin/lib/nc_photos_plugin.dart b/plugin/lib/nc_photos_plugin.dart
index a023cf4c..8a4c6862 100644
--- a/plugin/lib/nc_photos_plugin.dart
+++ b/plugin/lib/nc_photos_plugin.dart
@@ -2,6 +2,21 @@ import 'dart:async';
 
 import 'package:flutter/services.dart';
 
+class Lock {
+  static Future<bool> tryLock(int lockId) async {
+    return (await _channel.invokeMethod<bool>("tryLock", <String, dynamic>{
+      "lockId": lockId,
+    }))!;
+  }
+
+  static Future<void> unlock(int lockId) =>
+      _channel.invokeMethod("unlock", <String, dynamic>{
+        "lockId": lockId,
+      });
+
+  static const _channel = MethodChannel("com.nkming.nc_photos.plugin/lock");
+}
+
 class Notification {
   static Future<int?> notifyDownloadSuccessful(List<String> fileUris,
           List<String?> mimeTypes, int? notificationId) =>