fix(nextjs): Fix memory leak

[lforst]

I honestly don't know why this fixes the memory leak.

I tried using

await new Promise(resolve => setTimeout(() => { resolve() }), 50))

and

await new Promise(resolve => { setTimeout(() => { resolve() }) }, 50))

but they both also leak.

Since this was just a nice to have, the best path moving forward is just to remove the artificial delay.

Probably fixes #12317

[AbhiPrasad]

Approve to unblock, but feels weird to me.

Could you share the memory profile? What was not getting GC'd? The request?

[AbhiPrasad]

Can we instead call process.nextTick()? I guess that's not isomorphic though.

[lforst]

Could you share the memory profile? What was not getting GC'd? The request?

Sure thing!

I always profiled with 3 snapshots. (In the beginning, I used more to verify but got the same results):

• Snapshot 1: Right after the next server starts listening
• Snapshot 2: After bombarding a slow page with server components with ~7k requests
• Snapshot 3: After bombarding the same page with another ~7k requests

This is what it looked like with the setTimeout call:

This was after removing it:

The important part is a) heap just growing b) Timeout constructor instances just increasing. I also manually GC'd after the 3rd snapshot and it didn't free the timeouts.

At first, I thought we were spreading globals into the timeout or promise but looking into the profile it seems like knownTimersById just keeps growing / isn't getting cleaned up? (https://github.com/nodejs/node/blob/d1f18b0bf16efbc1e54ba04a54735ce4683cb936/lib/timers.js#L87)

I can DM you the profile but I won't share it here cause I don't know what is contained in the profile since I have auth tokens hard-coded in the app.