frees C memory from Dart

Author: craiglabenz

packages/mediapipe-core/lib/src/containers.dart

@@ -1,4 +1,5 @@
 import 'dart:ffi';
+import 'package:ffi/ffi.dart';
 import 'package:mediapipe_core/mediapipe_core.dart';
 import 'mediapipe_common_bindings.dart' as bindings;
 
@@ -34,6 +35,17 @@ class Category {
     );
   }
 
+  static void freeStructs(Pointer<bindings.Category> structs, int count) {
+    int index = 0;
+    while (index < count) {
+      bindings.Category obj = structs[index];
+      calloc.free(obj.category_name);
+      calloc.free(obj.display_name);
+      index++;
+    }
+    calloc.free(structs);
+  }
+
   @override
   String toString() => 'Category(index=$index, score=$score, '
       'categoryName=$categoryName, displayName=$displayName)';
@@ -71,6 +83,20 @@ class Classifications {
     );
   }
 
+  static void freeStructs(
+    Pointer<bindings.Classifications> structs,
+    int count,
+  ) {
+    int index = 0;
+    while (index < count) {
+      bindings.Classifications obj = structs[index];
+      Category.freeStructs(obj.categories, obj.categories_count);
+      calloc.free(obj.head_name);
+      index++;
+    }
+    calloc.free(structs);
+  }
+
   Category? get firstCategory =>
       categories.isNotEmpty ? categories.first : null;
 

packages/mediapipe-task-text/lib/src/tasks/text_classification/containers/text_classifier_result.dart

@@ -1,3 +1,5 @@
+import 'dart:ffi';
+import 'package:ffi/ffi.dart';
 import 'package:mediapipe_core/mediapipe_core.dart';
 import 'package:mediapipe_text/src/mediapipe_text_bindings.dart' as bindings;
 
@@ -32,6 +34,14 @@ class TextClassifierResult {
     );
   }
 
+  static void freeStruct(Pointer<bindings.TextClassifierResult> struct) {
+    Classifications.freeStructs(
+      struct.ref.classifications,
+      struct.ref.classifications_count,
+    );
+    calloc.free(struct);
+  }
+
   Classifications? get firstClassification =>
       classifications.isNotEmpty ? classifications.first : null;
 

packages/mediapipe-task-text/lib/src/tasks/text_classification/ffi_text_classifier.dart

@@ -40,7 +40,7 @@ class TextClassifier extends BaseTextClassifier {
     final result = TextClassifierResult.fromStruct(resultsPtr.ref);
     _log.fine('Text classification result: $result');
     _bindings.text_classifier_close(classifierPtr);
-    calloc.free(resultsPtr);
+    TextClassifierResult.freeStruct(resultsPtr);
     return result;
   }
 }