Fix race condition in database opening

extras/integration_tests/flutter_db/pubspec.lock

@@ -159,7 +159,7 @@ packages:
       name: meta
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.1.7"
+    version: "1.1.6"
   mime:
     dependency: transitive
     description:
@@ -173,14 +173,14 @@ packages:
       path: "../../../moor"
       relative: true
     source: path
-    version: "1.6.0"
+    version: "1.7.1"
   moor_flutter:
     dependency: "direct main"
     description:
       path: "../../../moor_flutter"
       relative: true
     source: path
-    version: "1.6.0"
+    version: "1.7.0"
   multi_server_socket:
     dependency: transitive
     description:

moor/lib/src/runtime/executor/helpers/engines.dart

@@ -232,6 +232,8 @@ class DelegatedDatabase extends QueryExecutor with _ExecutorWithQueryDelegate {
   @override
   SqlDialect get dialect => delegate.dialect;
 
+  final Lock _openingLock = Lock();
+
   DelegatedDatabase(this.delegate,
       {this.logStatements, this.isSequential = false}) {
     // not using default value because it's commonly set to null
@@ -240,7 +242,7 @@ class DelegatedDatabase extends QueryExecutor with _ExecutorWithQueryDelegate {
 
   @override
   Future<bool> ensureOpen() {
-    return _synchronized(() async {
+    return _openingLock.synchronized(() async {
       final alreadyOpen = await delegate.isOpen;
       if (alreadyOpen) return true;
 

moor_flutter/lib/moor_flutter.dart

@@ -53,6 +53,7 @@ class _SqfliteDelegate extends DatabaseDelegate with _SqfliteExecutor {
 
   @override
   Future<void> open([GeneratedDatabase db]) async {
+    print('uses fix for the opening problem.');
     assert(
         !_debugIsOpening && !isOpen,
         'Database opened multiple times, this should never happen. '