node::MakeCallback is dangerous, can you detect misuse and warn?

[metamatt]

This issue springs from TooTallNate/node-weak#35, but the root cause is that node::MakeCallback is dangerous if misused, and it would be nice to prevent its misuse.

By "misuse", I mean: if you have a Handle<Function> in a node addon and you want to call it, you have the choice of calling it directly (Handle<Function>::Call()) or via node::MakeCallback. You should do the former if your addon code was invoked from JS code; you should do the latter if your addon code was invoked directly from libuv as an event callback. This difference, while crucial, is not plainly obvious, and if you get it wrong, the results are really bad (preemption of Javascript code, that breaks Node's entire threadless/concurrency/consistency model).

Note comment TooTallNate/node-weak#36 (comment) from @trevnorris (and the surrounding discussion) saying that MakeCallback should be benign if called unnecessarily, but in my observation, that's not true. So I'm following up on this old discussion with an issue report and demo/repro case (for NodeJS 0.12.0) that shows it's actually (and still) dangerous if called this way.

The repro case is at https://gist.github.com/metamatt/4ce96adbf14de9a97d41.

[trevnorris]

@metamatt Thanks. There's a simple fix, but going to investigate to make sure it's also the best.

[trevnorris]

So, a conceptually simple fix. Working out the details.

[kkoopa]

I hope the solution will make MakeCallback always work, as intended. Having to correctly decide between two different ways of calling javascript from C++ dependent on context is really not acceptable, as it will lead to much confusion and headache.

[trevnorris]

@kkoopa That's the plan. :)

[misterdjules]

Adding to the 0.12.1 milestone, as discussed during the last core team meeting.

[johnhaley81]

Will this be back-ported to 0.10?

[kkoopa]

NAN will most likely reimplement and backport all of it, as I don't imagine 0.8 getting updated, so 0.10 will at least be covered that way.

[misterdjules]

@trevnorris Any update on this?