Add graphql-subscriptions to list of modules breaking async continuity

[basti1302]

Not sure if this list is still maintained or not, but if it is, the graphql-subscriptions should be on it. It has a custom queueing mechanism.

It works roughly like this: GraphQL subscriptions use an instance of the async iterator. The subscription engine waits for new events by calling next() on it, which internally calls pullValue(), which in turn creates a promise and puts that promise's resolve function into an internal queue called pullQueue (here).

When a new event is published via pushValue, the resolve function is pulled out of that queue and called with the event that is to be published. This is where async continuity is lost, in particular, the execution of the then of that promise is not connected to the async context of the call to pushValue.

My guess is that the reason for this is that the promise has already been created earlier, outside of that context. The different approaches to promises discussed in othiym23/node-continuation-local-storage#64 might be relevant here. As a matter of fact, I stumbled upon this while using https://github.com/jeff-lewis/cls-hooked, which relies on async_hooks internally.

As a user of async_hooks I would expect that everything that is triggered by publishing the event (that is, calling pushValue) happens in that context. The module graphql-subscriptions breaks that expectation.

[gireeshpunathil]

landed as 0d19067