[ffi]Is it necessary to manually free the memory?

[xuexin]

class RawImage extends Struct {
  @Int32()
  external int length;
  external Pointer<Uint8> bytes;
}

Pointer<RawImage> mallocRawImage(Uint8List bytes) {
  final bytesPointer = bytes.allocatePointer();
  final refPointer = malloc<RawImage>();
  refPointer.ref
    ..length = bytes.length
    ..bytes = bytesPointer;
  return refPointer;
}
extension Uint8ListBlobConversion on Uint8List {
  Pointer<Uint8> allocatePointer() {
    final blob = malloc<Uint8>(length);
    final blobBytes = blob.asTypedList(length);
    blobBytes.setAll(0, this);
    return blob;
  }
}

I manually malloc memory for Struct to pass it to native, should I manually free the Pointer and the Pointer? And how about the Struct returned from native?

[dcharkes]

Hi @xuexin,

When you malloc/calloc you should malloc.free/calloc.free it.

When a struct gets returned by value it is backed by TypedData instead of Pointer and lives in the Dart heap. So in that case it is garbage collected automatically.

[dcharkes]

I can take a look into #45697, that would enable creating structs backed by TypedData also when passing them as arguments.

Of course it will take a while before that would be available in the stable Dart release, so for now you need to be careful to free your allocated structs.

[xuexin]

@dcharkes
Thanks for your answer