Running 2 karma instances with karma-webpack v5 does not seem to be supported

[nicojs]

• Operating System: Both Windows and Ubuntu
• Node Version: 14
• NPM Version: 6.14
• webpack Version: 4.41
• karma-webpack Version: 4.0.2
• karma: 6.0.0

Expected Behavior

I should be able to run multiple karma instances with karma-webpack in parallel.

Actual Behavior

Karma-webpack v5.alpha-5 doesn't seem to support running multiple builds in parallel, at least not using the alternative usage from the readme.

See KarmaWebpackController, the output path is hardcoded to be path.join(os.tmpdir(), '_karma_webpack_'). Which would interfere with other instances of karma-webpack v5.

https://github.com/ryanclark/karma-webpack/blob/4fe1f6093fc6ff25503f1422123b2b3944a4145a/lib/KarmaWebpackController.js#L41-L43

I think the easy solution would be to postfix a random number at the end of the directory as karma does.

How Do We Reproduce?

Run 2 instances of karma in 2 different karma-webpack projects.

[nicojs]

I've noticed this when I saw an error for 'directory already exists' when I ran 2 instances of karma-webpack in parallel. I think that had to do with these lines of code:

https://github.com/ryanclark/karma-webpack/blob/8d7366f3cb747a9493c9f5542b9cb0317ac32d9e/lib/karma-webpack.js#L17-L19

The race condition would be that the 2 instances ran into the if statement simultaneously, which causes this error in 1 of the 2.

[codymikol]

I'll be able to take a look at this on Monday

[sprilukin]

I temporarily workarounded this by adding this code to my karma config file:

const fs = require("fs");
const os = require('os')

const patchedTempDir = path.join(os.tmpdir(), Math.floor(Math.random() * 1000000));
if (!fs.existsSync(patchedTempDir)){
    fs.mkdirSync(patchedTempDir);
}
// different env vars for different OS
process.env.TMPDIR = patchedTempDir;
process.env.TMP = patchedTempDir;
process.env.TEMP = patchedTempDir;

[codymikol]

I was able to reproduce this in a test, it looks like one test suite works and the others just return nothing. It also like chrome is signaled to shut down.

Process ChromeHeadless exited with code null and signal SIGTERM

[codymikol]

I'll see if we can cut another version soon, I believe this should be fixed now with your suggestion to postfix a number.

[codymikol]

This should now work in the alpha.6 version

[sprilukintibco]

Just tested - work well in my env (9 parallel processes)