parcel:watch (version 1.12.4) freezes on "Building index.js..."

[triketora]

🐛 bug report

Running npm run parcel:watch hangs indefinitely on "Building index.js...." (this is our entry point; sometimes other file names show, I've mostly noticed js/jsx, not sure if any scss yet) and never finishes.

🎛 Configuration (.babelrc, package.json, cli command)

package.json:

{
  "name": "web",
  "version": "1.0.0",
  "engines": {
    "node": "10.8.0",
    "npm": "6.8.0"
  },
  "description": "",
  "main": "static/src/index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1",
    "parcel:watch": "./node_modules/.bin/parcel watch static/src/index.js --public-url /static/dist --out-dir static/dist --out-file static_assets",
    "parcel:build": "./node_modules/.bin/parcel build static/src/index.js --public-url /static/dist --out-dir static/dist --out-file static_assets",
    "storybook": "start-storybook -p 6006",
    "build-storybook": "build-storybook"
  },
  "sass": {
    "includePaths": [
      "node_modules"
    ]
  },
  "husky": {
    "hooks": {
      "pre-commit": "lint-staged"
    }
  },
  "lint-staged": {
    "static/src/**/*.{js,jsx}": [
      "pretty-quick --staged --pattern \"**/*.*(js|jsx)\"",
      "eslint --fix",
      "git add"
    ]
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "plugins": [
    "transform-react-jsx"
  ],
  "devDependencies": {
    "@babel/core": "^7.6.3",
    "@babel/parser": "^7.3.4",
    "@babel/plugin-proposal-class-properties": "^7.5.5",
    "@babel/plugin-transform-runtime": "^7.6.2",
    "@dump247/storybook-state": "^1.6.1",
    "@storybook/addon-actions": "^5.2.3",
    "@storybook/addon-links": "^5.2.3",
    "@storybook/addons": "^5.2.3",
    "@storybook/react": "^5.2.3",
    "babel-eslint": "^10.0.3",
    "babel-loader": "^8.0.6",
    "eslint": "^4.19.1",
    "eslint-config-airbnb": "^17.1.1",
    "eslint-config-prettier": "^6.4.0",
    "eslint-plugin-import": "^2.18.2",
    "eslint-plugin-jsx-a11y": "^6.2.3",
    "eslint-plugin-react": "^7.16.0",
    "eslint-plugin-react-hooks": "^2.1.1",
    "husky": "^2.7.0",
    "lint-staged": "^8.2.1",
    "node-sass": "^4.12.0",
    "npm-run-all": "^4.1.5",
    "parcel-bundler": "^1.12.4",
    "prettier": "^1.18.2",
    "pretty-quick": "^1.11.1",
    "sass": "^1.23.0",
    "sass-loader": "^7.3.1",
    "snazzy": "^8.0.0"
  },
  "dependencies": {
    "@babel/runtime": "^7.6.3",
    "@babel/runtime-corejs3": "^7.6.3",
    "@sentry/browser": "^5.9.0",
    "apollo-boost": "^0.1.28",
    "apollo-client": "^2.6.4",
    "apollo-link-context": "^1.0.19",
    "axios": "^0.19.1",
    "bootstrap": "^4.3.1",
    "file-type": "^12.3.0",
    "formsy-react": "^2.0.0",
    "graphql": "^14.5.8",
    "graphql-tag": "^2.10.1",
    "immutability-helper": "^3.0.1",
    "jquery": "^3.4.1",
    "libphonenumber-js": "^1.7.30",
    "lodash": "^4.17.15",
    "popper.js": "^1.15.0",
    "prop-types": "^15.7.2",
    "react": "^16.11.0",
    "react-apollo": "^2.5.8",
    "react-calendar": "^2.19.2",
    "react-copy-to-clipboard": "^5.0.2",
    "react-dnd": "^9.4.0",
    "react-dnd-html5-backend": "^9.4.0",
    "react-dom": "^16.11.0",
    "react-habitat": "^1.0.1",
    "react-habitat-redux": "^2.0.4",
    "react-modal": "^3.11.1",
    "react-phone-number-input": "^3.0.13",
    "react-redux": "^7.1.1",
    "react-switch": "^5.0.1",
    "react-toastify": "^5.4.1",
    "react-tooltip": "^3.11.1",
    "react-twitter-embed": "^2.0.8",
    "redux": "^4.0.4",
    "redux-actions": "^2.6.5",
    "redux-thunk": "^2.3.0"
  }
}

🤔 Expected Behavior

npm run parcel:watch should successfully build static assets and put them in the specified output folder.

😯 Current Behavior

npm run parcel:watch hangs indefinitely (I've watched it for 1.5 hours before killing) and never finishes the static assets build.

💁 Possible Solution

Sometimes if I nuke .cache and run npm run parcel:build and then try again on npm run parcel:watch it fixes it. Not a real solution but a workaround.

🔦 Context

💻 Code Sample

🌍 Your Environment

Software	Version(s)
Parcel	1.12.4
Node	10.15.3
npm	6.13.6
Operating System	macOS Catalina 10.15.3

[Banou26]

The same still happen on Parcel v2 if i'm not mistaken

[triketora]

On @jefigo's recommendation, I tried UV_THREADPOOL_SIZE=64 npm run parcel:watch which seems to work. Probably related: #2452

[github-actions]

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