Retry opening database if locked.

Author: rkistner

packages/powersync/lib/src/open_factory.dart

@@ -2,6 +2,7 @@ import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 import 'dart:isolate';
+import 'dart:math';
 
 import 'package:sqlite_async/sqlite3.dart' as sqlite;
 import 'package:sqlite_async/sqlite_async.dart';
@@ -39,12 +40,41 @@ class PowerSyncOpenFactory extends DefaultSqliteOpenFactory {
   sqlite.Database open(SqliteOpenOptions options) {
     // ignore: deprecated_member_use_from_same_package
     _sqliteSetup?.setup();
-    final db = super.open(options);
+    final db = _retriedOpen(options);
     db.execute('PRAGMA recursive_triggers = TRUE');
     setupFunctions(db);
     return db;
   }
 
+  /// When opening the powersync connection and the standard write connection
+  /// at the same time, one could fail with this error:
+  ///
+  ///     SqliteException(5): while opening the database, automatic extension loading failed: , database is locked (code 5)
+  ///
+  /// It happens before we have a chance to set the busy timeout, so we just
+  /// retry opening the database.
+  ///
+  /// Usually a delay of 1-2ms is sufficient for the next try to succeed, but
+  /// we increase the retry delay up to 16ms per retry, and a maximum of 500ms
+  /// in total.
+  sqlite.Database _retriedOpen(SqliteOpenOptions options) {
+    final stopwatch = Stopwatch()..start();
+    var retryDelay = 2;
+    while (stopwatch.elapsedMilliseconds < 500) {
+      try {
+        return super.open(options);
+      } catch (e) {
+        if (e is sqlite.SqliteException && e.resultCode == 5) {
+          sleep(Duration(milliseconds: retryDelay));
+          retryDelay = min(retryDelay * 2, 16);
+          continue;
+        }
+        rethrow;
+      }
+    }
+    throw AssertionError('Cannot reach this point');
+  }
+
   void setupFunctions(sqlite.Database db) {
     db.createFunction(
       functionName: 'uuid',