Ping control port for unreachable servers

Closes #3339

drift_flutter/CHANGELOG.md

@@ -1,3 +1,8 @@
+## 0.2.2
+
+- Fix infinite loop in isolate server lookups when using `shareAcrossIsolates`
+  across hot restarts.
+
 ## 0.2.1
 
 - Enable serialization between background isolates where necessary.

drift_flutter/lib/src/native.dart

@@ -21,6 +21,10 @@ String portName(String databaseName) {
   return 'drift-db/$databaseName';
 }
 
+String isolateControlPortName(String databaseName) {
+  return 'drift-db/$databaseName/control';
+}
+
 QueryExecutor driftDatabase({
   required String name,
   DriftWebOptions? web,
@@ -63,6 +67,21 @@ QueryExecutor driftDatabase({
             // Isolate has stopped shortly after the register call. It should
             // also remove the port mapping, so we can just try again in another
             // iteration.
+            // However, it's possible for the isolate to become unreachable
+            // without unregistering itself (either due to a fatal error or when
+            // doing a hot restart). Check if the isolate is still reachable,
+            // and remove the mapping if it's not.
+            final controlPort = IsolateNameServer.lookupPortByName(
+                isolateControlPortName(name));
+            if (controlPort == null) {
+              continue;
+            }
+            final supposedIsolate = Isolate(controlPort);
+            if (!await supposedIsolate.pingWithTimeout()) {
+              // Yup, gone!
+              IsolateNameServer.removePortNameMapping(portName(name));
+            }
+            // Otherwise, the isolate is probably paused. Keep trying...
           }
         } else {
           // No port has been registered yet! Spawn an isolate that will try to
@@ -106,20 +125,55 @@ void _isolateEntrypoint(_EntrypointMessage message) {
   final connections = ReceivePort();
   if (IsolateNameServer.registerPortWithName(
       connections.sendPort, portName(message.name))) {
+    final controlPortName = isolateControlPortName(message.name);
     final server = DriftIsolate.inCurrent(
       () => NativeDatabase(File(message.path)),
       port: connections,
       beforeShutdown: () {
         IsolateNameServer.removePortNameMapping(portName(message.name));
+        IsolateNameServer.removePortNameMapping(controlPortName);
       },
       killIsolateWhenDone: true,
       shutdownAfterLastDisconnect: true,
     );
 
     message.sendResponses.send(server.connectPort);
+
+    IsolateNameServer.removePortNameMapping(controlPortName);
+    IsolateNameServer.registerPortWithName(
+        Isolate.current.controlPort, controlPortName);
   } else {
     // Another isolate is responsible for hosting this database, abort.
     connections.close();
     return;
   }
 }
+
+extension PingWithTimeout on Isolate {
+  Future<bool> pingWithTimeout(
+      [Duration timeout = const Duration(milliseconds: 500)]) {
+    final completer = Completer<bool>();
+    final receive = ReceivePort();
+    late StreamSubscription subscription;
+    subscription = receive.listen((_) {
+      subscription.cancel();
+
+      if (!completer.isCompleted) {
+        completer.complete(true); // Isolate reachable!
+        receive.close();
+      }
+    });
+
+    ping(receive.sendPort, priority: Isolate.immediate);
+
+    Timer(timeout, () {
+      if (!completer.isCompleted) {
+        completer.complete(false); // Isolate timed out!
+        subscription.cancel();
+        receive.close();
+      }
+    });
+
+    return completer.future;
+  }
+}

drift_flutter/pubspec.yaml

@@ -1,6 +1,6 @@
 name: drift_flutter
 description: Easily set up drift databases across platforms in Flutter apps.
-version: 0.2.1
+version: 0.2.2
 repository: https://github.com/simolus3/drift
 homepage: https://drift.simonbinder.eu/
 issue_tracker: https://github.com/simolus3/drift/issues

drift_flutter/test/native_test.dart

@@ -11,7 +11,7 @@ import 'package:drift/internal/versioned_schema.dart';
 import 'package:drift/native.dart';
 import 'package:drift_flutter/drift_flutter.dart';
 import 'package:drift_flutter/src/native.dart'
-    show hasConfiguredSqlite, portName;
+    show PingWithTimeout, hasConfiguredSqlite, portName;
 import 'package:flutter/services.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:sqlite3/sqlite3.dart';
@@ -125,6 +125,34 @@ void main() {
       await raw.simpleTable.insertOne(RawValuesInsertable({}));
     });
   });
+
+  group('pingWithTimeout', () {
+    test('works with alive isolates', () async {
+      expect(await Isolate.current.pingWithTimeout(), true);
+    });
+
+    test('works with stopped isolates', () async {
+      final isolate = await Isolate.spawn((_) {}, '');
+      isolate.kill();
+
+      expect(await isolate.pingWithTimeout(), false);
+    });
+
+    test('works with paused isolates', () async {
+      final isolate = await Isolate.spawn((_) async {
+        while (true) {
+          await Future.delayed(const Duration(seconds: 10));
+        }
+      }, '');
+      final resume = isolate.pause();
+      addTearDown(() => isolate.kill());
+
+      await pumpEventQueue(); // Make sure the isolate is actually paused..
+      expect(await isolate.pingWithTimeout(), true); // Still reachable!
+
+      isolate.resume(resume);
+    });
+  });
 }
 
 class SimpleDatabase extends GeneratedDatabase {