bluebird 2.9.14 hangs

[ben-page]

Description

One of my applications started hanging after upgrading to 2.9.14 (on node v0.12.0). I've narrowed the issue to the change from setImmediate to nextTick.

Example

This is the simplest example I could come up with that reliably demonstrates the problem:

1. git clone https://github.com/ben-page/bluebird-issue.git
2. cd bluebird-issue
3. npm install
4. node index.js

If you run the code as is, it will hang. If you uncomment line 7 (to change the scheduler to setImmediate) or install bluebird 2.9.13, it will complete as expected.

Background

Honestly, I don't fully understand the problem, but I have found found several discussions that may be helpful. Apparently there are issues with race conditions or IO starvation related to nextTick.

nodejs/node-v0.x-archive#7996
http://blog.nodejs.org/2013/03/11/node-v0-10-0-stable/
nodejs/node-v0.x-archive#3335
https://groups.google.com/forum/#!topic/nodejs-dev/DvENgK8Nubw

[petkaantonov]

2.9.14 doesn't do anything but specifically change to using anything but nextTick, so I guess you could use 2.9.13?

[ben-page]

Yes, I can use 2.9.13.

[benjamingr]

@petkaantonov loves nextTick in node and how it's implemented :D

@ben-page you can use 2.9.14 and setScheduler if you'd like. The hanging is really odd though.

[ben-page]

@benjamingr That's what I'm currently doing.

I'm not trying to say that bluebird shouldn't use nextTick, just that I've found an issue with its current usage. I don't understand the bluebird internals well enough to say whether the issue can be fixed in bluebird or if its fundamental to nextTick.