Calling callback from node.js native code

Question

I'm writing an add-on for node.js using c++.

here some snippets:

class Client : public node::ObjectWrap, public someObjectObserver {
public:
  void onAsyncMethodEnds() {
    Local<Value> argv[] = { Local<Value>::New(String::New("TheString")) };
    this->callback->Call(Context::GetCurrent()->Global(), 1, argv);
  }
....
private:
  static v8::Handle<v8::Value> BeInitiator(const v8::Arguments& args) {
    HandleScope scope;
    Client* client = ObjectWrap::Unwrap<Client>(args.This());

    client->someObject->asyncMethod(client, NULL);

    return scope.Close(Boolean::New(true));        
  }      

  static v8::Handle<v8::Value> SetCallback(const v8::Arguments& args) {
    HandleScope scope;
    Client* client = ObjectWrap::Unwrap<Client>(args.This());
    client->callback = Persistent<Function>::New(Handle<Function>::Cast(args[0]));

    return scope.Close(Boolean::New(true));
  }

I need to save a javascript function as callback to call it later. The Client class is an observer for another object and the javascript callback should be called from onAsyncMethodEnds. Unfortunately when I call the function "BeInitiator" I receive "Bus error: 10" error just before the callback Call()

thanks in advice

No.. The "asyncmethod" starts a new thread. This method is part of a lib that I've linked that uses talk_base/thread in order to run asynchronous operations. — helloIAmPau
– helloIAmPau, Commented Jun 13, 2013 at 5:40

loganfsmyth · Accepted Answer · 2013-06-13 15:40:47Z

3

You cannot ->Call from another thread. JavaScript and Node are single threaded and attempting to call a function from another thread amounts to trying to run two threads of JS at once.

You should either re-work your code to not do that, or you should read up on libuv's threading library. It provides uv_async_send which can be used to trigger callback in the main JS loop from a separate thread.

There are docs here: http://nikhilm.github.io/uvbook/threads.html

answered Jun 13, 2013 at 15:40

loganfsmyth

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5 Comments

helloIAmPau Over a year ago

I suppose that this resolves the problem. Unfortunately I can't use libuv.. I will try to do the same thing using the Send method of talk_base/thread. Thanks a lot!

loganfsmyth Over a year ago

Why can't you use libuv?

loganfsmyth Over a year ago

I ask only because you should have access to it automatically if you are compiling for Node.

helloIAmPau Over a year ago

Because the thread was run by an external library that I have linked in to the project. However I have found that uv_send and uv_init work also within "not libuv thread". So thank you.

stanleyxu2005 Over a year ago

Here is a full example blog.scottfrees.com/…

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