Leak Detection & Prevention

Memory management is a critical aspect of mobile development. Fasq Riverpod is designed to be “leak-proof” by default, leveraging Riverpod’s built-in disposal mechanisms.

Automatic Disposal

The standard queryProvider uses Riverpod’s AutoDisposeAsyncNotifier. This means that as soon as the last widget unmounts (or the last listener is removed), the provider is marked for disposal.

How it Works

When a provider is disposed:

Riverpod calls the notifier’s _cleanup method.
fasq_riverpod cancels all internal stream subscriptions.
fasq_riverpod calls query.removeListener().
If no other providers are using that query, the core Query enters a “stale” state and is eventually removed from memory after its cacheTime expires.

Manual Disposal in Custom Providers

If you are creating custom providers that interact with the QueryClient directly (via fasqClientProvider), it is your responsibility to ensure resources are cleaned up.

Always use ref.onDispose to remove listeners:


final customProvider = Provider((ref) {
  final client = ref.watch(fasqClientProvider);
  final query = client.getQuery(...);
 
  query.addListener();
 
  // CRITICAL: Ensure the listener is removed when the provider is disposed
  ref.onDispose(() {
    query.removeListener();
  });
 
  return query;
});

Testing for Leaks

Fasq includes a LeakDetector utility specifically for identifying memory leaks in your unit and widget tests.

Integration with Riverpod Tests

When testing providers, you should verify that no queries are left active after the ProviderContainer is disposed.


import 'package:fasq/testing.dart';
import 'package:fasq_riverpod/fasq_riverpod.dart';
import 'package:flutter_test/flutter_test.dart';
 
void main() {
  late LeakDetector detector;
 
  setUp(() {
    detector = LeakDetector();
  });
 
  test('provider should not leak queries', () async {
    final container = ProviderContainer();
    final client = container.read(fasqClientProvider);
 
    // Use a query provider
    final result = await container.read(myQueryProvider.future);
 
    // Dispose the container (this should trigger provider disposal)
    container.dispose();
 
    // Verify no queries are leaked
    detector.expectNoLeakedQueries(client);
  });
}

Debug Instrumentation

In debug mode only, you can inspect the reference holders of any query to see exactly what is keeping it alive. This is useful for identifying “zombie” providers or widgets.


final client = ref.read(fasqClientProvider);
final debugInfo = client.activeQueryDebugInfoMap;
 
for (final entry in debugInfo.entries) {
  print('Query ${entry.key} is held by: ${entry.value.referenceHolders.keys}');
}

Best Practices

Use AutoDispose: Always prefer AutoDispose providers unless you have a specific reason to keep data in memory indefinitely.
Check Tests: Run your tests with LeakDetector to catch leaks early in the development cycle.
Avoid Global Clients: Avoid creating QueryClient instances outside of fasqClientProvider, as they won’t benefit from Riverpod’s lifecycle management.