AH1: Initializing async hooks (bindings between c++ and JS contexts)

async_wrap.cc

static void SetupHooks(const FunctionCallbackInfo<Value>& args) {
  Environment* env = Environment::GetCurrent(args);

  CHECK(args[0]->IsObject());

  // All of init, before, after, destroy are supplied by async_hooks
  // internally, so this should every only be called once. At which time all
  // the functions should be set. Detect this by checking if init !IsEmpty().
  CHECK(env->async_hooks_init_function().IsEmpty());

  Local<Object> fn_obj = args[0].As<Object>();

#define SET_HOOK_FN(name)                                                      \
  do {                                                                         \
    Local<Value> v =                                                           \
        fn_obj->Get(env->context(),                                            \
                    FIXED_ONE_BYTE_STRING(env->isolate(), #name))              \
            .ToLocalChecked();                                                 \
    CHECK(v->IsFunction());                                                    \
    env->set_async_hooks_##name##_function(v.As<Function>());                  \
  } while (0)

  SET_HOOK_FN(init);
  SET_HOOK_FN(before);
  SET_HOOK_FN(after);
  SET_HOOK_FN(destroy);
  SET_HOOK_FN(promise_resolve);
#undef SET_HOOK_FN

  {
    Local<FunctionTemplate> ctor =
        FunctionTemplate::New(env->isolate());
    ctor->SetClassName(FIXED_ONE_BYTE_STRING(env->isolate(), "PromiseWrap"));
    Local<ObjectTemplate> promise_wrap_template = ctor->InstanceTemplate();
    promise_wrap_template->SetInternalFieldCount(
        PromiseWrap::kInternalFieldCount);
    promise_wrap_template->SetAccessor(
        FIXED_ONE_BYTE_STRING(env->isolate(), "isChainedPromise"),
        PromiseWrap::getIsChainedPromise);
    env->set_promise_wrap_template(promise_wrap_template);
  }
}