nodejs / nodejs/node

100% CPU usage for a long time after execution of the last statement

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#48,581 2 comments 1 reaction 0 assignees View on GitHub

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confirmed-bug v8 engine
Dominant language
JavaScript
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Avg merge
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Merged PRs (30d)
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Description

Version

v12.x-v20.x - severe, v8.x - v10.x - less severe but still visible

Platform

Darwin Andreys-MacBook-Pro.local 22.2.0 Darwin Kernel Version 22.2.0: Fri Nov 11 02:03:51 PST 2022; root:xnu-8792.61.2~4/RELEASE_ARM64_T6000 arm64

Subsystem

suspect GC

What steps will reproduce the bug?

run first script in the gist: https://gist.github.com/sidorares/128160e6b3dea1da3ad45cd672651d2d#file-repro1-js

After last line console.log("done"); is executed CPU spikes to 100% and stays like that for about 5 minutes.
In case of node v8 and v10 cpu spike is much shorter, 5-7 seconds.
Bun.js executes the script almost instantly

How often does it reproduce? Is there a required condition?

Consistently reproduceable

What is the expected behavior? Why is that the expected behavior?

the script is expected to finish in sub second time

What do you see instead?

CPU spikes for 300-400 seconds which is unexpected for the workload

Additional information

The profiler only reports the code before the CPU spike, no high GC usage, the time after cpu spike is "unaccounted".

 [Shared libraries]:
   ticks  total  nonlib   name
     98    0.0%          /Users/laplace/.nvm/versions/node/v20.3.0/bin/node

 [JavaScript]:
   ticks  total  nonlib   name
      2    0.0%    0.0%  JS: *parseLengthCodedInt /Users/laplace/tmp/2090/repro3.js:2014:24

 [C++]:
   ticks  total  nonlib   name

 [Summary]:
   ticks  total  nonlib   name
      2    0.0%    0.0%  JavaScript
      0    0.0%    0.0%  C++
     66    0.0%    0.0%  GC
     98    0.0%          Shared libraries
  291682  100.0%          Unaccounted

 [C++ entry points]:
   ticks    cpp   total   name

 [Bottom up (heavy) profile]:
  Note: percentage shows a share of a particular caller in the total
  amount of its parent calls.
  Callers occupying less than 1.0% are not shown.

   ticks parent  name
  291682  100.0%  UNKNOWN

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by running the first script in the linked gist on the affected Node.js versions and compare its behavior with Node.js v8-v10 and Bun.js. Use the reported profiler output and reproduction timing to investigate the post-console.log CPU spike; done means the script exits in under a second without the sustained CPU usage.

Written by the indexing model from the issue text.

Assessment

Tech stack
node.js
Domain
backend
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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