You don't manage the instance, the v8 engine does. When it's no longer referenced in the engine, it's garbage collected which triggers the callback set when the perisstent object is made weak.
You don't need to keep it anywhere, the object returned into the engine has Internal Fields ( SetInternalFieldCount(1) ) which is used to point to your native class instance. So when the callback is called, it knows what to call to destruct it. You have to 'keep it' in the javascript scrpit if you want to keep it, it's not 'kept' in the native code... --- This is some code I've done that uses setweak directly; but it's fairly scattered.... https://github.com/d3x0r/sack.vfs/blob/master/src/jsonParse.cc#L18 You can create an instance of your wrapped object with Local<Function> cons = Local<Function>::New( isolate, constructor ); cons->NewInstance( isolate->GetCurrentContext(), argc, argv ).ToLocalChecked() ; Hmm that's not the best example source... https://github.com/d3x0r/sack.vfs/blob/master/src/vfs_module.cc#L407 This creates a buffer, and makes it weak... https://github.com/d3x0r/sack.vfs/blob/master/src/vfs_module.cc#L438 Local<Object> arrayBuffer = ArrayBuffer::New( isolate, buf, len ); PARRAY_BUFFER_HOLDER holder = GetHolder(); holder->o.Reset( isolate, arrayBuffer ); holder->o.SetWeak<ARRAY_BUFFER_HOLDER>( holder, releaseBuffer, WeakCallbackType::kParameter ); holder->buffer = buf; PARRAY_BUFFER_HOLDER is just a type that holds the thing to be free (or object containing things to be released), and the persistent reference that has been made weak... struct arrayBufferHolder { void *buffer; Persistent<Object> o; }; On Thu, Nov 16, 2017 at 9:56 AM, Jean-Marc Le Roux <jeanmarc.ler...@aerys.in > wrote: > Node offers a C++ Clss extention ObjectWrap > > > Thanks ! > It is related to node. Yet I'm not sure how I'm supposed to use ObjectWrap. > > I understand I have to create my own class that extends ObjectWrap and > implement a proper destructor. > Then I'll instanciate that class to wrap my Local<Object>. But how do I > manage such instance? > If I don't keep it somewhere, it will be destructed. > If I keep it around, then I'm keeping references to potentially > deallocated memory. > > It feels like I end up with the same problem... > > 2017-11-16 18:36 GMT+01:00 J Decker <d3c...@gmail.com>: > >> >> >> On Thu, Nov 16, 2017 at 1:24 AM, Jean-Marc Le Roux < >> jeanmarc.ler...@aerys.in> wrote: >> >>> I assume you're storing references to the objects as Persistent? >>> >>> >>> Nope. You've got the whole code up there. >>> So if I understand correctly: >>> >>> - the objects I need to keep track of the lifecycle should be made >>> Persistent ; >>> - all the other values can be set as Local ; >>> - I should set the weak callback using MakeWeak ; >>> - callback will be called when such object is GCed and I can free my >>> C/C++ memory then. >>> >>> Is that correct ? >>> >> >> Yes. I sthis perhaps related to Node? >> Node offers a C++ Clss extention ObjectWrap >> >> https://nodejs.org/api/addons.html#addons_wrapping_c_objects >> https://github.com/nodejs/node/blob/master/src/node_object_wrap.h >> >> which simplifies that whole process... when the object is GC'd the class >> destructor will get called so you can release values there. >> >> >> >>> >>> 2017-11-15 19:50 GMT+01:00 J Decker <d3c...@gmail.com>: >>> >>>> I assume you're storing references to the objects as Persistent? All >>>> you need to do then is call SetWeak() https://v8docs.nodes >>>> ource.com/node-0.10/d2/d78/classv8_1_1_persistent.html >>>> void MakeWeak (void *parameters, WeakReferenceCallback callback) >>>> >>>> the callback is called when the object is GC'd. >>>> >>>> >>>> On Wed, Nov 15, 2017 at 8:37 AM, Jean-Marc Le Roux < >>>> jeanmarc.ler...@aerys.in> wrote: >>>> >>>>> So I've found a solution to make things lazy: I set an accessor >>>>> instead of decoding/setting the actual value. >>>>> >>>>> void >>>>> getter(Local<Name> property, const PropertyCallbackInfo<Value>& info) >>>>> { >>>>> Isolate* isolate = info.GetIsolate(); >>>>> >>>>> const bson_t* document = reinterpret_cast<bson_t*>( >>>>> info.This() >>>>> ->Get(String::NewFromUtf8(isolate, "__bson_document_ptr")) >>>>> ->ToInt32()->Value() >>>>> ); >>>>> >>>>> char key[255]; >>>>> property->ToString(isolate)->WriteUtf8(key, 255); >>>>> >>>>> bson_iter_t iter; >>>>> bson_iter_init(&iter, document); >>>>> // FIXME: index the property so we don't have to find it >>>>> bson_iter_find(&iter, key); >>>>> >>>>> // FIXME: replace the accessor with the deserialized value >>>>> >>>>> info.GetReturnValue().Set(iterator_to_value(isolate, &iter)); >>>>> } >>>>> >>>>> Local<Value> >>>>> fill_object(Isolate* isolate, Local<Object>& obj, const bson_t* >>>>> document) >>>>> { >>>>> obj->Set( >>>>> String::NewFromUtf8(isolate, "__bson_document_ptr"), >>>>> Int32::New(isolate, reinterpret_cast<intptr_t>(document)) >>>>> ); >>>>> >>>>> bson_iter_t iter; >>>>> if (bson_iter_init(&iter, document)) >>>>> { >>>>> while (bson_iter_next(&iter)) >>>>> { >>>>> const char* key = bson_iter_key(&iter); >>>>> >>>>> if (!obj->Has(String::NewFromUtf8(isolate, >>>>> key))) >>>>> { >>>>> obj->SetAccessor( >>>>> isolate->GetCurrentContext(), >>>>> String::NewFromUtf8(isolate, key), >>>>> &getter >>>>> ); >>>>> } >>>>> } >>>>> } >>>>> } >>>>> >>>>> The secret sauce is to : >>>>> >>>>> - keep the original data (the bson_t) allocated >>>>> - store the corresponding pointer in a v8::Object >>>>> >>>>> But now I have a memory leak because those pointers will never be >>>>> freed. >>>>> How can I know when the Object will be disposed by the GC? >>>>> >>>>> Thanks, >>>>> >>>>> -- >>>>> -- >>>>> v8-users mailing list >>>>> v8-users@googlegroups.com >>>>> http://groups.google.com/group/v8-users >>>>> --- >>>>> You received this message because you are subscribed to the Google >>>>> Groups "v8-users" group. >>>>> To unsubscribe from this group and stop receiving emails from it, send >>>>> an email to v8-users+unsubscr...@googlegroups.com. >>>>> For more options, visit https://groups.google.com/d/optout. >>>>> >>>> >>>> -- >>>> -- >>>> v8-users mailing list >>>> v8-users@googlegroups.com >>>> http://groups.google.com/group/v8-users >>>> --- >>>> You received this message because you are subscribed to a topic in the >>>> Google Groups "v8-users" group. >>>> To unsubscribe from this topic, visit https://groups.google.com/d/to >>>> pic/v8-users/aVeevQcHJ2c/unsubscribe. >>>> To unsubscribe from this group and all its topics, send an email to >>>> v8-users+unsubscr...@googlegroups.com. >>>> For more options, visit https://groups.google.com/d/optout. >>>> >>> >>> >>> >>> -- >>> *Jean-Marc Le Roux* >>> >>> >>> Founder and CEO of Aerys (http://aerys.in) >>> >>> Blog: http://blogs.aerys.in/jeanmarc-leroux >>> Cell: (+33)6 20 56 45 78 <+33%206%2020%2056%2045%2078> >>> Phone: (+33)9 72 40 17 58 <+33%209%2072%2040%2017%2058> >>> >>> -- >>> -- >>> v8-users mailing list >>> v8-users@googlegroups.com >>> http://groups.google.com/group/v8-users >>> --- >>> You received this message because you are subscribed to the Google >>> Groups "v8-users" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to v8-users+unsubscr...@googlegroups.com. >>> For more options, visit https://groups.google.com/d/optout. >>> >> >> -- >> -- >> v8-users mailing list >> v8-users@googlegroups.com >> http://groups.google.com/group/v8-users >> --- >> You received this message because you are subscribed to a topic in the >> Google Groups "v8-users" group. >> To unsubscribe from this topic, visit https://groups.google.com/d/to >> pic/v8-users/aVeevQcHJ2c/unsubscribe. >> To unsubscribe from this group and all its topics, send an email to >> v8-users+unsubscr...@googlegroups.com. >> For more options, visit https://groups.google.com/d/optout. >> > > > > -- > *Jean-Marc Le Roux* > > > Founder and CEO of Aerys (http://aerys.in) > > Blog: http://blogs.aerys.in/jeanmarc-leroux > Cell: (+33)6 20 56 45 78 <+33%206%2020%2056%2045%2078> > Phone: (+33)9 72 40 17 58 <+33%209%2072%2040%2017%2058> > > -- > -- > v8-users mailing list > v8-users@googlegroups.com > http://groups.google.com/group/v8-users > --- > You received this message because you are subscribed to the Google Groups > "v8-users" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to v8-users+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. > -- -- v8-users mailing list v8-users@googlegroups.com http://groups.google.com/group/v8-users --- You received this message because you are subscribed to the Google Groups "v8-users" group. 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