Memory heap usage increases when importing mathjs

[sublayerio]

🐛 Bug Report

Memory heap continues to grow when importing mathjs library.

To Reproduce

Steps to reproduce the behavior:

Create several test files that import the mathjs library.

Expected behavior

Memory heap usage should not increase or at least not as much.

Link to repl or repo (highly encouraged)

Checkout this repo.

https://github.com/keyflight/memory-mathjs-jest

Install the dependencies.

yarn install

Run the following commands to compare

yarn tests-without-mathjs

yarn tests-with-mathjs

Run npx envinfo --preset jest

Paste the results here:

  System:
    OS: macOS 10.14.5
    CPU: (8) x64 Intel(R) Core(TM) i7-4870HQ CPU @ 2.50GHz
  Binaries:
    Node: 10.15.3 - /usr/local/bin/node
    Yarn: 1.15.2 - /usr/local/bin/yarn
    npm: 6.4.1 - /usr/local/bin/npm
  npmPackages:
    jest: ^24.8.0 => 24.8.0 

[SimenB]

Hmm, this is odd. Does mathjs keep references to any globals? Or override any node core modules (we had an issue about a leak with somebody overriding something on http without cleaning up, but I'm unable to find the issue). E.g. const keepMath = global.Math or some such? Quick look at the module showed it was minified, so not the easiest to debug without messing in node_modules

[Mark1626]

Hope this might me useful for anyone who is looking into this. I ran the tests with a custom environment, jest-circus(to use handleTestEvent) and took snapshots with heapdump before the test_start event.

This is the snapshot from the 10th test run, it looks that _moduleRegistry in Runtime seems to be retained. I'll dig into the code to see if I can find anything

@SimenB A second opinion might be good.

[Mark1626]

@SimenB resetModules is by default false as per the documentation

https://jestjs.io/docs/en/configuration#resetmodules-boolean

The memory leak caused by #8282 is only fixed when resetModules is true

https://github.com/facebook/jest/blob/fb7b132b7230dac3fca30d79fcc57c98ecffbc81/packages/jest-runtime/src/index.ts#L539-L543

[SimenB]

@scotthovestadt ^

[terite]

I was able to reproduce this with mathjs 6.6.0 and jest 25.1.0 when running with the following command

jest --detectLeaks --runInBand --no-cache --logHeapUsage

With the following command, jest detects no leaks

node --expose-gc ./node_modules/.bin/jest --detectLeaks --runInBand --no-cache --logHeapUsage

Here is the repository I used for testing - https://github.com/terite/jest-unleak-modules

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