Memory leak in `_contexts`

[holm]

We upgraded to Node 8 yesterday, and are now seeing memory leaks. Taking some heap snapshots I can see the _contexts map growing all the time. We run 4.2.2, so it shouldn't be the memory leak fixed recently.

It's hard to follow the code, but I would guess this is related to how the promises are handled. At least it seems the contexts are not always removed from the map.

[holm]

I looked into this further, and it seems destroy is just never called for some asyncIds. Reading other issues from Node it seems this is caused by the promises not being destroyed until GC. However for some reason they seem to never be gc'ed, and I am not sure how to debug that.

[Jeff-Lewis]

I'm looking into something we can do with the context's enter() and exit() and remove items from _context on exit(). Not sure yet if that's the answer.

[holm]

There is a similar looking issue in Node, see nodejs/node#14446 (comment). This looks from a quick glance to be the same issue.

[clakech]

Hi, any news about this issue, what should be done in the code of cls-hooked to solve this one ?

[clakech]

Hum, seems like, it is a normal behavior in this issue nodejs/node#14446 (comment)

so maybe this issue here is OK too.

[holm]

We eventually worked out what was causing this. Turned out to actually be the NewRelic that was the main culprit, albeit we also had some of our own.

The fact that the contexts are only destroyed when the promise is garbage collected, requires you to be very careful that you do not in some indirect way reference the promises from the data you store in the cls.