Remove async.waterfall

[pksunkara]

Using async.waterfall is blocking the event loop.

/cc @zdne @honzajavorek @Almad

[Almad]

@pksunkara @zdne I'd be interested in measurement behind this.

async.waterfall is no different from any other function call (that, yes, is blocking by default). But if anything, and if you want to do cooperative multitasking, it should IMHO be easier to wrap waterfall in process.nextTick that allows other things in queue to be executed.

I am not disputing results of your investigation, but I am personally really curious to see how this change affected performance and whether async is really performance hog.

[zdne]

@Almad interesting – with our limited knowledge of this I guess we haven't realized wrapping it in nextTick is the way to go. /cc @smizell

[smizell]

@Almad @zdne In playing around with this last night, something was really strange. I've used async.waterfall a lot and have never seen it.

This would not block the event loop.

return callback()

But if replaced with this exact code, it would block until all calls were finished.

async.waterfall [
  (next) -> next()
], -> callback()

If you did not use this but introduced another async.waterfall in the callback chain, it would block until almost all had been completed.

[smizell]

@Almad @zdne Additionally, in the above example that blocked, if I changed to async.series, it worked.

[honzajavorek]

Could this be related? caolan/async#696 Just browsed through their issues, I did not look into its internals.