Emscripten workflow (libass/JavascriptSubtitlesOctopus)

The Emscripten workflow from libass/JavascriptSubtitlesOctopus, explained and optimized by Latchkey.

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Source: libass/JavascriptSubtitlesOctopus.github/workflows/emscripten.ymlLicense MITView source

What it does

This is the Emscripten workflow from the libass/JavascriptSubtitlesOctopus repository, a real project running GitHub Actions. It is shown here with attribution under its MIT license.

Below, Latchkey shows a faster, safer version produced by its optimization engine.

The workflow

workflow (.yml)

name: Emscripten

on:
  push:
    branches: [master, ci]
  pull_request:
  workflow_dispatch:

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
    - name: Cancel previous runs
      uses: styfle/cancel-workflow-action@0.12.1
      with:
          access_token: ${{ github.token }}
          all_but_latest: true

    - name: Checkout Base Repo
      uses: actions/checkout@v4

    - name: Prepare Submodules
      run: |
        git submodule sync
        git submodule update --init --recursive --force
        mv lib lib_

    - name: Calculate Hash Key
      id: cache_config
      run: |
        # Invalidate cache if submodules, patches or emscripten version changed
        key="$(find build/patches/ -type f | sort | xargs cat .gitmodules Dockerfile \
               Makefile Makefile_licence | shasum -a 256 | cut -d' ' -f1)"
        echo "key=0-${key}" >> $GITHUB_OUTPUT

    - name: Ensure Cache will be newer than Checkout
      run: |
        find . -exec touch -d 1971-01-01T00:00:00 '{}' +

    - name: Retrieve Cached Built Dependencies
      uses: actions/cache@v4
      id: cache
      with:
        key: ${{ steps.cache_config.outputs.key }}
        path: |
          lib
          build/lib
          dist/libraries
          dist/license/*
          !dist/license/subtitlesoctopus
          !dist/license/all*
          /tmp/emcc_lto

    - name: Checkout Submodules
      if: steps.cache.outputs.cache-hit != 'true'
      run: |
        mv lib_ lib

    - name: Build Docker Image
      run: |
        docker build -t libass/jso .

    - name: Build Binaries
      run: |
        mkdir -p /tmp/emcc_lto
        docker run --rm --env LC_ALL=C.UTF-8 -v "${PWD}":/code -v "/tmp/emcc_lto:/emsdk/upstream/emscripten/cache/sysroot/lib/wasm32-emscripten/lto" libass/jso:latest

    - name: Upload Nightly Build
      uses: actions/upload-artifact@v4
      if: (github.event_name == 'push' || github.event_name == 'workflow_dispatch') && github.ref == 'refs/heads/master'
      with:
        name: js
        path: dist/js


  update_gh-pages:
    if: (github.event_name == 'push' || github.event_name == 'workflow_dispatch') && github.ref == 'refs/heads/master'
    needs: build
    runs-on: ubuntu-latest
    steps:
      - name: Checkout
        uses: actions/checkout@v4
        with:
          ref: gh-pages

      - name: Remove old assets
        run: rm -fr assets/js

      - name: Download nightly build
        uses: actions/download-artifact@v4
        with:
          name: js
          path: assets/js

      - name: Push new version
        run: |
          git config --global user.email "actions@noreply.github.com"
          git config --global user.name "GitHub Action"
          git add assets/js
          (git commit -m "$(printf \
            "Update binaries to latest nightly\n\nFrom %s" "${{ github.sha }}")" \
           && git push origin gh-pages) \
           || : # Ignore if nothing changed

The same workflow, on Latchkey

Removes redundant runs and caps runaway jobs. Added and changed lines are highlighted.

name: Emscripten
 
on:
  push:
    branches: [master, ci]
  pull_request:
  workflow_dispatch:
 
concurrency:
  group: ${{ github.workflow }}-${{ github.ref }}
  cancel-in-progress: true
 
jobs:
  build:
    timeout-minutes: 30
    runs-on: latchkey-small
    steps:
    - name: Cancel previous runs
      uses: styfle/cancel-workflow-action@0.12.1
      with:
          access_token: ${{ github.token }}
          all_but_latest: true
 
    - name: Checkout Base Repo
      uses: actions/checkout@v4
 
    - name: Prepare Submodules
      run: |
        git submodule sync
        git submodule update --init --recursive --force
        mv lib lib_
 
    - name: Calculate Hash Key
      id: cache_config
      run: |
        # Invalidate cache if submodules, patches or emscripten version changed
        key="$(find build/patches/ -type f | sort | xargs cat .gitmodules Dockerfile \
               Makefile Makefile_licence | shasum -a 256 | cut -d' ' -f1)"
        echo "key=0-${key}" >> $GITHUB_OUTPUT
 
    - name: Ensure Cache will be newer than Checkout
      run: |
        find . -exec touch -d 1971-01-01T00:00:00 '{}' +
 
    - name: Retrieve Cached Built Dependencies
      uses: actions/cache@v4
      id: cache
      with:
        key: ${{ steps.cache_config.outputs.key }}
        path: |
          lib
          build/lib
          dist/libraries
          dist/license/*
          !dist/license/subtitlesoctopus
          !dist/license/all*
          /tmp/emcc_lto
 
    - name: Checkout Submodules
      if: steps.cache.outputs.cache-hit != 'true'
      run: |
        mv lib_ lib
 
    - name: Build Docker Image
      run: |
        docker build -t libass/jso .
 
    - name: Build Binaries
      run: |
        mkdir -p /tmp/emcc_lto
        docker run --rm --env LC_ALL=C.UTF-8 -v "${PWD}":/code -v "/tmp/emcc_lto:/emsdk/upstream/emscripten/cache/sysroot/lib/wasm32-emscripten/lto" libass/jso:latest
 
    - name: Upload Nightly Build
      uses: actions/upload-artifact@v4
      if: (github.event_name == 'push' || github.event_name == 'workflow_dispatch') && github.ref == 'refs/heads/master'
      with:
        name: js
        path: dist/js
 
 
  update_gh-pages:
    timeout-minutes: 30
    if: (github.event_name == 'push' || github.event_name == 'workflow_dispatch') && github.ref == 'refs/heads/master'
    needs: build
    runs-on: latchkey-small
    steps:
      - name: Checkout
        uses: actions/checkout@v4
        with:
          ref: gh-pages
 
      - name: Remove old assets
        run: rm -fr assets/js
 
      - name: Download nightly build
        uses: actions/download-artifact@v4
        with:
          name: js
          path: assets/js
 
      - name: Push new version
        run: |
          git config --global user.email "actions@noreply.github.com"
          git config --global user.name "GitHub Action"
          git add assets/js
          (git commit -m "$(printf \
            "Update binaries to latest nightly\n\nFrom %s" "${{ github.sha }}")" \
           && git push origin gh-pages) \
           || : # Ignore if nothing changed

What changed

Run on Latchkey managed runners with one line (runs-on), which apply the fixes below automatically and self-heal transient failures. This example uses latchkey-small; pick the runner size that fits the job.
Cancel superseded runs when a branch or PR gets a newer push.
Add a job timeout so a hung step cannot burn hours of runner time.

1 third-party action is referenced by a movable tag. Pin it to the commit SHA (Latchkey resolves and applies this automatically) so a repointed tag cannot change what runs.

What Latchkey heals here

This workflow has steps that commonly fail on transient issues (network, registries, flaky browsers). On Latchkey managed runners they are detected, retried, and self-healed instead of failing your build:

Container pulls and builds

This workflow runs 2 jobs per trigger. On Latchkey the same minutes cost up to 58% less than GitHub-hosted, with zero queue time.

Actions used in this workflow

actions/checkout actions/cache actions/upload-artifact actions/download-artifact