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EXC_BAD_ACCESS in node::EmitAsyncDestroy

Hi,

I'm occasionally hitting an error in the destructor for AsyncResource. Sorry I don't have a minimal reproduction example yet. I've just started hitting this since migrating js-platform/node-webrtc to AsyncResource. I've got a graph of objects, some of them just ObjectWrap instances and some of the ObjectWrap + AsyncResource instances. The AsyncResource instances wrap libuv's uv_default_loop(). I call Ref when constructing these and Unref in the uv_close_cb. The graph looks like this:

RTCPeerConnection (ObjectWrap, AsyncResource)
  |
  |
  +--> RTCRtpReceiver (ObjectWrap)
         |
         |
         |    MediaStream (ObjectWrap)
         |      |
         |      v
         +--> MediaStreamTrack (ObjectWrap, AsyncResource)

In my tests, I'm only seeing the issues in ~MediaStreamTrack, and then, only occasionally. I'm also not seeing the destructor fire twice or anything like that. Interestingly, if I comment out the node::EmitAsyncDestroy call, I don't see crashes. I'm using Node v9.8.0.

* thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x0)
    frame #0: 0x0000000100009322 node`node::EmitAsyncDestroy(v8::Isolate*, node::async_context) + 18
node`node::EmitAsyncDestroy:
->  0x100009322 <+18>: movq   (%rax), %rax
    0x100009325 <+21>: movq   0x37(%rax), %rax
    0x100009329 <+25>: movq   0x10f(%rax), %rdi
    0x100009330 <+32>: movsd  -0x8(%rbp), %xmm0         ; xmm0 = mem[0],zero
Target 0: (node) stopped.
(lldb) bt
* thread #1, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0x0)
  * frame #0: 0x0000000100009322 node`node::EmitAsyncDestroy(v8::Isolate*, node::async_context) + 18
    frame #1: 0x000000010491cbe0 wrtc.node`Nan::AsyncResource::~AsyncResource(this=0x0000000102a02e88) at nan.h:514
    frame #2: 0x00000001049536f6 wrtc.node`node_webrtc::MediaStreamTrack::~MediaStreamTrack(this=0x0000000102a02e70) at mediastreamtrack.cc:44
    frame #3: 0x00000001049539c5 wrtc.node`node_webrtc::MediaStreamTrack::~MediaStreamTrack(this=0x0000000102a02e70) at mediastreamtrack.cc:40
    frame #4: 0x0000000104953a39 wrtc.node`node_webrtc::MediaStreamTrack::~MediaStreamTrack(this=0x0000000102a02e70) at mediastreamtrack.cc:40
    frame #5: 0x0000000104923fbb wrtc.node`Nan::ObjectWrap::WeakCallback(info=0x00007fff5fbf5b48) at nan_object_wrap.h:126
    frame #6: 0x00000001004f3384 node`v8::internal::GlobalHandles::DispatchPendingPhantomCallbacks(bool) + 180
    frame #7: 0x00000001004f36b1 node`v8::internal::GlobalHandles::PostGarbageCollectionProcessing(v8::internal::GarbageCollector, v8::GCCallbackFlags) + 49
    frame #8: 0x0000000100509085 node`v8::internal::Heap::PerformGarbageCollection(v8::internal::GarbageCollector, v8::GCCallbackFlags) + 2533
    frame #9: 0x000000010050800d node`v8::internal::Heap::CollectGarbage(v8::internal::AllocationSpace, v8::internal::GarbageCollectionReason, v8::GCCallbackFlags) + 733
    frame #10: 0x00000001004c9c92 node`v8::internal::Factory::NewFillerObject(int, bool, v8::internal::AllocationSpace) + 82
    frame #11: 0x0000000100774125 node`v8::internal::Runtime_AllocateInNewSpace(int, v8::internal::Object**, v8::internal::Isolate*) + 101
    frame #12: 0x00000c0326b842fd
    frame #13: 0x00000c0326c842ab
    frame #14: 0x00000c0326c3d196
    frame #15: 0x00000c0326c09cfc
    frame #16: 0x00000c0326b84239
    frame #17: 0x00000c0326b84101
    frame #18: 0x00000001004bf669 node`v8::internal::(anonymous namespace)::Invoke(v8::internal::Isolate*, bool, v8::internal::Handle<v8::internal::Object>, v8::internal::Handle<v8::internal::Object>, int, v8::internal::Handle<v8::internal::Object>*, v8::internal::Handle<v8::internal::Object>, v8::internal::Execution::MessageHandling) + 633
    frame #19: 0x00000001004bf893 node`v8::internal::Execution::TryCall(v8::internal::Isolate*, v8::internal::Handle<v8::internal::Object>, v8::internal::Handle<v8::internal::Object>, int, v8::internal::Handle<v8::internal::Object>*, v8::internal::Execution::MessageHandling, v8::internal::MaybeHandle<v8::internal::Object>*) + 227
    frame #20: 0x00000001005e1c9e node`v8::internal::Isolate::PromiseReactionJob(v8::internal::Handle<v8::internal::PromiseReactionJobInfo>, v8::internal::MaybeHandle<v8::internal::Object>*, v8::internal::MaybeHandle<v8::internal::Object>*) + 654
    frame #21: 0x00000001005e273c node`v8::internal::Isolate::RunMicrotasksInternal() + 1180
    frame #22: 0x00000001005e15e8 node`v8::internal::Isolate::RunMicrotasks() + 56
    frame #23: 0x000000010497d872 wrtc.node`node_webrtc::PromiseFulfillingEventLoop<node_webrtc::PeerConnection>::Run(this=0x0000000101ff7700) at promisefulfillingeventloop.h:34
    frame #24: 0x00000001049822c0 wrtc.node`node_webrtc::EventLoop<node_webrtc::PeerConnection>::EventLoop(this=0x0000000104982270, handle=0x0000000101ff77a0)::'lambda'(uv_async_s*)::operator()(uv_async_s*) const at eventloop.h:49
    frame #25: 0x0000000104982288 wrtc.node`node_webrtc::EventLoop<node_webrtc::PeerConnection>::EventLoop(handle=0x0000000101ff77a0)::'lambda'(uv_async_s*)::__invoke(uv_async_s*) at eventloop.h:47
    frame #26: 0x00000001019e77cb libuv.1.dylib`uv__async_io + 331
    frame #27: 0x00000001019fa41d libuv.1.dylib`uv__io_poll + 2061
    frame #28: 0x00000001019e7d43 libuv.1.dylib`uv_run + 371
    frame #29: 0x0000000100034b75 node`node::Start(v8::Isolate*, node::IsolateData*, int, char const* const*, int, char const* const*) + 661
    frame #30: 0x0000000100031e83 node`node::Start(uv_loop_s*, int, char const* const*, int, char const* const*) + 435
    frame #31: 0x0000000100031988 node`node::Start(int, char**) + 536
    frame #32: 0x00000001000012c4 node`start + 52

I'm opening this in case there's something obvious here I'm missing. The async hooks functionality is very new to me. If it's not obvious, I'll try to create a minimal repro.

Thanks,
Mark