Fix bad isolate being retrieved when callback are called from unity-scopes-js

[Alexandre Abreu]

When callbacks are called from unity-scopes api to js, the isolate that are tied to the various js callbacks are not accessible (GetCurrent() is TLS based),

[Marcus Tomlinson (marcustomlinson)]

Unfortunately thats not the extent of the issue. If you want the correct isolate available you can simply create the binding class (E.g. ScopeBase) with the isolate as a constructor parameter from addon.cc. However, having a valid isolate is still not good enough. You can't call a V8 function from a non-V8 thread.

What we need to do is enter a "scopes.listen()" function of sorts as the last executed call of the scope's script. This function needs to take the V8 mainloop into a state where we listen for events. Events such as search, preview, etc. then we can react to these events by executing the callbacks from within V8.

This seems to be the norm in the V8 world. I think a good example of this is the node http lib.

E.g.

var http = require('http');

var s = http.createServer(function(req, res)
{
  res.writeHead(200, { 'content-type': 'text/plain' });
  res.end('Hello there\n');
});

s.listen(1000);

[Alexandre Abreu (abreu-alexandre)]

Agree (about isolate not being enough), that's what I was saying when talking about v8's heavy use of TLS,