Why is "Isolate::GerCurrent()" Null in asynchronous thread?

Question

My final goal is to solve this problem, but I am getting stuck on some pretty basic stuff.

My whole C++ Module is basically as follows:

void AsyncWork(void *arg) {
    Isolate* isolate = Isolate::GetCurrent();  // isolate is NULL
    if (isolate != NULL) {
        HandleScope scope(isolate);
    }
    else {
        printf("isolate is null\n");
        return;
    }
    // ...
}


void testAsync(const FunctionCallbackInfo<Value>& args) {
    uv_thread_t id;
    int data = 10;
    uv_thread_create(&id, AsyncWork, &data);
}

void init(Handle<Object> target) {
  NODE_SET_METHOD(target, "testAsync", testAsync);
}

NODE_MODULE(MyCppModule, init);

Why is isolate NULL after I call Isolate::GetCurrent() in AsyncWork?

Answer 1

Ok, seems like I set it up the wrong way around and shouldn't call Isolate::GetCurrent() in the worker thread. And instead register a callback on the main thread.

static uv_async_t async;
static int i;

void AsyncWork(void *arg) {
    for (i = 0; i < 5; ++i) {
        async.data = (void*)&i;
        uv_async_send(&async);
        Sleep(1000);
    }
}

void testCallback(uv_async_t *handle) {
    Isolate* isolate = Isolate::GetCurrent();
    if (isolate != NULL) {
        HandleScope scope(isolate);
        printf("Yay\n");
    }
    else {
        printf("isolate is null\n");
    }
    int data = *((int*)handle->data);
    printf("data: %d\n", data);
}

void testAsync(const FunctionCallbackInfo<Value>& args) {
    uv_thread_t id;
    int data = 10;
    uv_async_init(uv_default_loop(), &async, testCallback);
    uv_thread_create(&id, AsyncWork, &data);
}

void init(Handle<Object> target) {
  NODE_SET_METHOD(target, "testAsync", testAsync);
}

NODE_MODULE(MyCppModule, init);