query and property query - add a reachabilityFence() after each use of a native pointer with a finalizer attached to prevent premature finalization. (#243)

Author: vaind

objectbox/lib/src/native/bindings/bindings.dart

@@ -122,3 +122,13 @@ late final native_query_close =
     _lib!.lookup<NativeFunction<_native_close>>('obx_query_close');
 late final native_query_prop_close =
     _lib!.lookup<NativeFunction<_native_close>>('obx_query_prop_close');
+
+/// Keeps `this` alive until this call, preventing finalizers to run.
+/// Necessary for objects with a finalizer attached because the optimizer may
+/// mark the object as unused (-> GCed -> finalized) even before it's method
+/// finished executing.
+/// See https://github.com/dart-lang/sdk/issues/35770#issuecomment-840398463
+@pragma('vm:never-inline')
+Object reachabilityFence(Object obj) {
+  return obj;
+}

objectbox/lib/src/native/query/property.dart

@@ -9,10 +9,8 @@ class PropertyQuery<T> {
   bool _distinct = false;
   bool _caseSensitive = false;
 
-  PropertyQuery._(Pointer<OBX_query> cQuery, ModelProperty property)
-      : _type = property.type,
-        _cProp = checkObxPtr(
-            C.query_prop(cQuery, property.id.id), 'property query') {
+  PropertyQuery._(this._cProp, this._type) {
+    checkObxPtr(_cProp, 'property query');
     _cFinalizer = C.dartc_attach_finalizer(
         this, native_query_prop_close, _cProp.cast(), 64);
     if (_cFinalizer == nullptr) {
@@ -38,6 +36,7 @@ class PropertyQuery<T> {
     final ptr = malloc<Uint64>();
     try {
       checkObx(C.query_prop_count(_cProp, ptr));
+      reachabilityFence(this);
       return ptr.value;
     } finally {
       malloc.free(ptr);
@@ -53,6 +52,7 @@ class PropertyQuery<T> {
     try {
       cItems = checkObxPtr(
           findFn(_cProp, cDefault ?? nullptr), 'Property query failed');
+      reachabilityFence(this);
       return listReadFn(cItems);
     } finally {
       if (cDefault != null) malloc.free(cDefault);
@@ -64,6 +64,7 @@ class PropertyQuery<T> {
     final ptr = malloc<Double>();
     try {
       checkObx(C.query_prop_avg(_cProp, ptr, nullptr));
+      reachabilityFence(this);
       return ptr.value;
     } finally {
       malloc.free(ptr);
@@ -79,6 +80,7 @@ extension IntegerPropertyQuery on PropertyQuery<int> {
     final ptr = malloc<Int64>();
     try {
       checkObx(fn(_cProp, ptr, nullptr));
+      reachabilityFence(this);
       return ptr.value;
     } finally {
       malloc.free(ptr);
@@ -101,6 +103,7 @@ extension IntegerPropertyQuery on PropertyQuery<int> {
   set distinct(bool d) {
     _distinct = d;
     checkObx(C.query_prop_distinct(_cProp, d));
+    reachabilityFence(this);
   }
 
   /// Minimum value of the property over all objects matching the query.
@@ -175,6 +178,7 @@ extension DoublePropertyQuery on PropertyQuery<double> {
     final ptr = malloc<Double>();
     try {
       checkObx(fn(_cProp, ptr, nullptr));
+      reachabilityFence(this);
       return ptr.value;
     } finally {
       malloc.free(ptr);
@@ -197,6 +201,7 @@ extension DoublePropertyQuery on PropertyQuery<double> {
   set distinct(bool d) {
     _distinct = d;
     checkObx(C.query_prop_distinct(_cProp, d));
+    reachabilityFence(this);
   }
 
   /// Minimum value of the property over all objects matching the query.
@@ -248,6 +253,7 @@ extension StringPropertyQuery on PropertyQuery<String> {
   set caseSensitive(bool caseSensitive) {
     _caseSensitive = caseSensitive;
     checkObx(C.query_prop_distinct_case(_cProp, _distinct, _caseSensitive));
+    reachabilityFence(this);
   }
 
   /// Get status of the case-sensitive configuration.
@@ -263,6 +269,7 @@ extension StringPropertyQuery on PropertyQuery<String> {
   set distinct(bool d) {
     _distinct = d;
     checkObx(C.query_prop_distinct_case(_cProp, d, _caseSensitive));
+    reachabilityFence(this);
   }
 
   /// Returns the count of non-null values.

objectbox/lib/src/native/query/query.dart

@@ -538,7 +538,7 @@ class _ByteVectorCondition<EntityT>
               func) =>
       withNativeBytes(
           _value,
-              (Pointer<Uint8> ptr, int size) =>
+          (Pointer<Uint8> ptr, int size) =>
               func(builder._cBuilder, _property._model.id.id, ptr, size));
 
   @override
@@ -652,7 +652,11 @@ class Query<T> {
   /// the whole result, e.g. for "result paging".
   ///
   /// Set offset=0 to reset to the default - starting from the first element.
-  set offset(int offset) => checkObx(C.query_offset(_ptr, offset));
+  set offset(int offset) {
+    final result = checkObx(C.query_offset(_ptr, offset));
+    reachabilityFence(this);
+    return result;
+  }
 
   /// Configure a [limit] for this query.
   ///
@@ -661,13 +665,18 @@ class Query<T> {
   /// the whole result, e.g. for "result paging".
   ///
   /// Set limit=0 to reset to the default behavior - no limit applied.
-  set limit(int limit) => checkObx(C.query_limit(_ptr, limit));
+  set limit(int limit) {
+    final result = checkObx(C.query_limit(_ptr, limit));
+    reachabilityFence(this);
+    return result;
+  }
 
   /// Returns the number of matching Objects.
   int count() {
     final ptr = malloc<Uint64>();
     try {
       checkObx(C.query_count(_ptr, ptr));
+      reachabilityFence(this);
       return ptr.value;
     } finally {
       malloc.free(ptr);
@@ -710,12 +719,14 @@ class Query<T> {
     _store.runInTransaction(TxMode.read, () {
       checkObx(C.query_visit(_ptr, visitor, nullptr));
     });
+    reachabilityFence(this);
     return result;
   }
 
   /// Finds Objects matching the query and returns their IDs.
   List<int> findIds() {
     final idArrayPtr = checkObxPtr(C.query_find_ids(_ptr), 'find ids');
+    reachabilityFence(this);
     try {
       final idArray = idArrayPtr.ref;
       return idArray.count == 0
@@ -732,6 +743,7 @@ class Query<T> {
     final collector = objectCollector(result, _store, _entity);
     _store.runInTransaction(
         TxMode.read, () => checkObx(C.query_visit(_ptr, collector, nullptr)));
+    reachabilityFence(this);
     return result;
   }
 
@@ -754,6 +766,7 @@ class Query<T> {
       closed = true;
       C.dartc_stream_close(cStream);
       port.close();
+      reachabilityFence(this);
     };
 
     try {
@@ -838,10 +851,18 @@ class Query<T> {
   // }
 
   /// For internal testing purposes.
-  String describe() => dartStringFromC(C.query_describe(_ptr));
+  String describe() {
+    final result = dartStringFromC(C.query_describe(_ptr));
+    reachabilityFence(this);
+    return result;
+  }
 
   /// For internal testing purposes.
-  String describeParameters() => dartStringFromC(C.query_describe_params(_ptr));
+  String describeParameters() {
+    final result = dartStringFromC(C.query_describe_params(_ptr));
+    reachabilityFence(this);
+    return result;
+  }
 
   /// Use the same query conditions but only return a single property (field).
   ///
@@ -852,7 +873,9 @@ class Query<T> {
   /// var results = query.property(tInteger).find();
   /// ```
   PropertyQuery<DartType> property<DartType>(QueryProperty<T, DartType> prop) {
-    final result = PropertyQuery<DartType>._(_ptr, prop._model);
+    final result = PropertyQuery<DartType>._(
+        C.query_prop(_ptr, prop._model.id.id), prop._model.type);
+    reachabilityFence(this);
     if (prop._model.type == OBXPropertyType.String) {
       result._caseSensitive = InternalStoreAccess.queryCS(_store);
     }