Infrequent Segfault on Node.js/Nan Callback in C++ Addon

I'm making a NodeJS addon using the Nan library, and I'm running into an issue where calling a callback (created on the javascript side and passed to the addon to be executed asyncronously) will cause a segfault - but only about once every 10 thousand or so runs.

There's quite a bit of complexity involved in how everything operates, but I'm hoping that someone will see something I missed or be able to figure out what's going on.

The C++ callback function is created from the javascript callback like this:

   auto nodeFunc = val.As<v8::Function>();
   auto nodeCb   = std::make_shared<Nan::Callback>(nodeFunc);

   auto callback = [nodeCb] (std::string err, std::string val) -> void {
        Nan::HandleScope     scope;
        v8::Local<v8::Value> argv[2];

       if (err.length() == 0) {
            auto isolate = v8::Isolate::GetCurrent();
            auto json    = v8::JSON::Parse(isolate, Nan::New(val).ToLocalChecked());
            auto object  = json.ToLocalChecked();
            argv[0] = Nan::Null();
            argv[1] = object;
        } else {
            argv[0] = Nan::Error(err.c_str());
            argv[1] = Nan::Null();
        }

        try {
            nodeCb->Call(2, argv);
        } catch (std::exception& ex) {
            std::cout << ex.what() << std::endl;
            Nan::ThrowReferenceError(ex.what());
        }
    };

After creation, it is passed to a separate thread which eventually sends the callback to the main libuv thread using uv_async_send() and executes it. This works fine the vast majority of the time, but will very rarely segfault on the nodeCb->Call(2, argv) line.

If anyone has any insight into what's happening here, I'd really appreciate it.

Also, here's the call stack from gdb in case that's any help:

#0  0x00000000009870e0 in v8::Function::Call(v8::Local<v8::Value>, int, v8::Local<v8::Value>*) ()
#1  0x00000000010a562c in node::MakeCallback(node::Environment*, v8::Local<v8::Value>, v8::Local<v8::Function>, int, v8::Local<v8::Value>*) ()
#2  0x00000000010a5a98 in node::MakeCallback(v8::Isolate*, v8::Local<v8::Object>, v8::Local<v8::Function>, int, v8::Local<v8::Value>*) ()
#3  0x00007ffff47b4b30 in Nan::Callback::Call_ (this=0x20c3500, isolate=0x1ded750, target=..., argc=2,
    argv=0x7fffffffa430) at ../node_modules/nan/nan.h:1477
#4  0x00007ffff47b4a93 in Nan::Callback::Call (this=0x20c3500, argc=2, argv=0x7fffffffa430)
    at ../node_modules/nan/nan.h:1443
#5  0x00007ffff47b194b in detail::info::__lambda1::operator() (__closure=0x1e40710, err="",
    val="{\"index\":1,\"status\":1}") at ../node/utils.hpp:125
#6  0x00007ffff47b37f2 in std::_Function_handler<void(std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::basic_string<char, std::char_traits<char>, std::allocator<char> >), detail::info::setElementValue(T&, v8::Local<v8::Value>, size_t) [with T = std::function<void(std::basic_string<char>, std::basic_string<char>)>; size_t = long unsigned int]::__lambda1>::_M_invoke(const std::_Any_data &, std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::basic_string<char, std::char_traits<char>, std::allocator<char> >) (__functor=..., __args#0="", __args#1="")
    at /usr/include/c++/4.8.2/functional:2071
#7  0x00007ffff44cd339 in std::function<void (std::string, std::string)>::operator()(std::string, std::string) const (this=0x1e29c80, __args#0="", __args#1="")
    at /opt/rh/devtoolset-4/root/usr/include/c++/5.2.1/functional:2271
#8  0x00007ffff44e172c in std::_Bind<std::function<void (std::string, std::string)> (char const*, std::string)>::__call<void, , 0ul, 1ul>(std::tuple<>&&, std::_Index_tuple<0ul, 1ul>) (this=0x1e29c80,
    __args=<unknown type in /usr/local/lib/libSCPlay.so, CU 0x0, DIE 0x83e21>)
    at /opt/rh/devtoolset-4/root/usr/include/c++/5.2.1/functional:1074
#9  0x00007ffff44daec8 in std::_Bind<std::function<void (std::string, std::string)> (char const*, std::string)>::operator()<, void>() (this=0x1e29c80)
    at /opt/rh/devtoolset-4/root/usr/include/c++/5.2.1/functional:1133
#10 0x00007ffff44d3b58 in std::_Function_handler<void (), std::_Bind<std::function<void (std::string, std::string)> (char const*, std::string)> >::_M_invoke(std::_Any_data const&) (__functor=...)
    at /opt/rh/devtoolset-4/root/usr/include/c++/5.2.1/functional:1871
#11 0x00007ffff44fab0a in std::function<void ()>::operator()() const (this=0x7fffffffa650)
    at /opt/rh/devtoolset-4/root/usr/include/c++/5.2.1/functional:2271
#12 0x00007ffff44f890c in DeviceThread::asyncListener (handle=0x1efb9f0)
    at /home/scl37510/Projects/SCPlay2/lib/device_thread.cpp:124
#13 0x0000000001316b0b in uv__async_event (loop=0x1de7fe0 <default_loop_struct>, w=<optimized out>,
    nevents=<optimized out>) at ../deps/uv/src/unix/async.c:98
#14 0x0000000001316be3 in uv__async_io (loop=0x1de7fe0 <default_loop_struct>,
    w=0x1de81a8 <default_loop_struct+456>, events=<optimized out>) at ../deps/uv/src/unix/async.c:138
#15 0x00000000013271b0 in uv__io_poll (loop=loop@entry=0x1de7fe0 <default_loop_struct>, timeout=0)
    at ../deps/uv/src/unix/linux-core.c:380
#16 0x00000000013176c6 in uv_run (loop=0x1de7fe0 <default_loop_struct>, mode=UV_RUN_ONCE)
    at ../deps/uv/src/unix/core.c:354
#17 0x00000000010aabe0 in node::Start(int, char**) ()
#18 0x00007ffff6bf5b35 in __libc_start_main () from /lib64/libc.so.6
#19 0x00000000007b1f1d in _start ()

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