karma: extras: usePolling

[michaelsbradleyjr]

This issue is a:

• Bug report
• Feature request
• Question / support request
• [ X ] Other

When making use of nwb's npm run test:watch, on macOS Sierra (10.12.4), node v7.9.0, I was getting very high CPU usage even when the node process was idle, i.e. just waiting to be triggered by a change to a source or test file.

I spent several hours trying to figure out what was happening. This helped:

sudo fs_usage -f pathname -w

Thousands of files were getting polled in node_modules, relative to my project's top-level directory. I tried to figure out whether it was karma or webpack, or both, and whether I could tell either or both to exclude node_modules ....... long story short, nothing I changed in the extra: fields for karma and webpack, in nwb.config.js, was having any significant effect.

Later, while digging around in some GitHub issues, I saw where one can set usePolling: false in one's karma config (that options seems not well documented)

So, in nwb.config.js:

module.exports = {
  ...,
  karma: {
    extra: {
      ...,
      usePolling: false
    },
  ...
};

Finally, that worked. Now, the node process for npm run test:watch sits idle at ~0% cpu usage, which is what one would expect, i.e. when it's not busy compiling or running tests.

I'm filing this issue since it may be helpful to others, and perhaps warrants a note in nwb's configuration documentation.

[michaelsbradleyjr]

Okay, so it seems that on macOS, usePolling is getting set to true at runtime:

https://github.com/karma-runner/karma/blob/master/lib/config.js#L318

tracking it back with blame:

karma-runner/karma@66f50d7

That commit was about 3 1/2 years ago, and it seems that non-polling file watching on macOS works fine now, i.e. since I set usePolling to false and the autoWatch facility is picking up changes and w/ low impact on CPU usage, as I noted previously. I'll leave the karma maintainers a note.

[michaelsbradleyjr]

Filed an issue yesterday with karma-runner/karma:

karma-runner/karma#2669

[loklaan]

@michaelsbradleyjr Wow, nice discovery. I hope it becomes default in upstream karma 👍 .

Would you mind updating the docs on the master branch? I'll be sure to merge it in asap.

[michaelsbradleyjr]

What do you think is the best approach? Should I include a note under the extra heading?

[loklaan]

Under the karma intro paragraph with a "Note:" prefix, would be great. Thanks for getting confirmation

[michaelsbradleyjr]

See #298.

[loklaan]

Resolved by #298