actions-mutex

A GitHub Action for exclusive control.

FEATURE

• avoid running multiple jobs concurrently across workflows

OFFICIAL CONCURRENCY SUPPORT ON GITHUB ACTIONS

The action is no longer maintained.

On April 19, 2021, GitHub launched support for limiting concurrency in the workflow files. Please consider to use this feature.

• GitHub Actions: Limit workflow run or job concurrency

Using this feature, the example in the SYNOPSIS section may be:

on:
  push:
    branches:
      - main

# The workflow level concurrency
# https://docs.github.com/en/actions/reference/workflow-syntax-for-github-actions#concurrency
concurrency: deploy

jobs:
  build:

    # The job level concurrency
    # https://docs.github.com/en/actions/reference/workflow-syntax-for-github-actions#jobsjob_idconcurrency
    concurrency: deploy

    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - run: ': some jobs that can not run concurrently'

Please read the latest document of Workflow syntax for GitHub Actions.

SYNOPSIS

on:
  push:
    branches:
      - main

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2

      - uses: shogo82148/actions-mutex@v1
        with:
          key: deploy

      - run: ': some jobs that can not run concurrently'

INPUTS

key

The name of the critical section. The default is "lock".

token

A GitHub Token. It must have a write access to the repository. The default is "${{ github.token }}"

repository

A repository for locking. The default is the repository that the workflow runs on.

prefix

Prefix of branch names for locking. The default is "actions-mutex-lock/"

HOW THE ACTION WORKS

As you known, Git rejects non-fast-forward updates. The action uses it for locking.

The action tries to push a commit that contains a random string. If the pushing succeeds, it means that no concurrent jobs run.

$ echo "$RANDOM" > lock.txt
$ git add lock.txt
$ git commit -m 'add lock files'
$ git push origin HEAD:actions-mutex-lock/lock
To https://github.com/shogo82148/actions-mutex
 * [new branch]      HEAD -> actions-mutex-lock/lock

If the pushing fails, it means that a concurrent job is now running. The action will retry to push after some wait.

$ echo "$RANDOM" > lock.txt
$ git add lock.txt
$ git commit -m 'add lock files'
$ git push origin HEAD:actions-mutex-lock/lock
To https://github.com/shogo82148/actions-mutex
 ! [rejected]        HEAD -> actions-mutex-lock/lock (fetch first)
error: failed to push some refs to 'https://github.com/shogo82148/actions-mutex'
hint: Updates were rejected because the remote contains work that you do
hint: not have locally. This is usually caused by another repository pushing
hint: to the same ref. You may want to first integrate the remote changes
hint: (e.g., 'git pull ...') before pushing again.
hint: See the 'Note about fast-forwards' in 'git push --help' for details.