Using concurrency

Overview

By default, GitHub Actions allows multiple jobs within the same workflow, multiple workflow runs within the same repository, and multiple workflow runs across a repository owner's account to run concurrently. This means that multiple workflow runs, jobs, or steps can run at the same time.

GitHub Actions also allows you to control the concurrency of workflow runs, so that you can ensure that only one run, one job, or one step runs at a time in a specific context. This can be useful for controlling your account's or organization's resources in situations where running multiple workflows, jobs, or steps at the same time could cause conflicts or consume more Actions minutes and storage than expected.

For example, the ability to run workflows concurrently means that if multiple commits are pushed to a repository in quick succession, each push could trigger a separate workflow run, and these runs will execute concurrently.

Using concurrency in different scenarios

You can use jobs.<job_id>.concurrency to ensure that only a single job or workflow using the same concurrency group will run at a time. A concurrency group can be any string or expression. Allowed expression contexts: github, inputs, vars, needs, strategy, and matrix. For more information about expressions, see "Expressions."

You can also specify concurrency at the workflow level. For more information, see concurrency.

When a concurrent job or workflow is queued, if another job or workflow using the same concurrency group in the repository is in progress, the queued job or workflow will be pending. Any previously pending job or workflow in the concurrency group will be canceled. To also cancel any currently running job or workflow in the same concurrency group, specify cancel-in-progress: true.

Example: Using concurrency and the default behavior

The default behavior of GitHub Actions is to allow multiple jobs or workflow runs to run concurrently. The concurrency keyword allows you to control the concurrency of workflow runs.

For example, you can use the concurrency keyword immediately after where trigger conditions are defined to limit the concurrency of entire workflow runs for a specific branch:

on:
  push:
    branches:
      - main

concurrency:
  group: ${{ github.workflow }}-${{ github.ref }}
  cancel-in-progress: true

You can also limit the concurrency of jobs within a workflow by using the concurrency keyword at the job level:

on:
  push:
    branches:
      - main

jobs:
  job-1:
    runs-on: ubuntu-latest
    concurrency:
      group: example-group
      cancel-in-progress: true

Example: Concurrency groups

Concurrency groups provide a way to manage and limit the execution of workflow runs or jobs that share the same concurrency key.

The concurrency key is used to group workflows or jobs together into a concurrency group. When you define a concurrency key, GitHub Actions ensures that only one workflow or job with that key runs at any given time. If a new workflow run or job starts with the same concurrency key, GitHub Actions will cancel any workflow or job already running with that key. The concurrency key can be a hard-coded string, or it can be a dynamic expression that includes context variables.

It is possible to define concurrency conditions in your workflow so that the workflow or job is part of a concurrency group.

This means that when a workflow run or job starts, GitHub will cancel any workflow runs or jobs that are already in progress in the same concurrency group. This is useful in scenarios where you want to prevent parallel runs for a certain set of a workflows or jobs, such as the ones used for deployments to a staging environment, in order to prevent actions that could cause conflicts or consume more resources than necessary.

In this example, job-1 is part of a concurrency group named staging_environment. This means that if a new run of job-1 is triggered, any runs of the same job in the staging_environment concurrency group that are already in progress will be cancelled.

jobs:
  job-1:
    runs-on: ubuntu-latest
    concurrency:
      group: staging_environment
      cancel-in-progress: true

Alternatively, using a dynamic expression such as concurrency: ci-${{ github.ref }} in your workflow means that the workflow or job would be part of a concurrency group named ci- followed by the reference of the branch or tag that triggered the workflow. In this example, if a new commit is pushed to the main branch while a previous run is still in progress, the previous run will be cancelled and the new one will start:

on:
  push:
    branches:
      - main

concurrency:
  group: ci-${{ github.ref }}
  cancel-in-progress: true

Example: Using concurrency to cancel any in-progress job or run

To use concurrency to cancel any in-progress job or run in GitHub Actions, you can use the concurrency key with the cancel-in-progress option set to true:

concurrency:
  group: ${{ github.ref }}
  cancel-in-progress: true

Note that in this example, without defining a particular concurrency group, GitHub Actions will cancel any in-progress run of the job or workflow.

Example: Using a fallback value

If you build the group name with a property that is only defined for specific events, you can use a fallback value. For example, github.head_ref is only defined on pull_request events. If your workflow responds to other events in addition to pull_request events, you will need to provide a fallback to avoid a syntax error. The following concurrency group cancels in-progress jobs or runs on pull_request events only; if github.head_ref is undefined, the concurrency group will fallback to the run ID, which is guaranteed to be both unique and defined for the run.

concurrency:
  group: ${{ github.head_ref || github.run_id }}
  cancel-in-progress: true

Example: Only cancel in-progress jobs or runs for the current workflow

If you have multiple workflows in the same repository, concurrency group names must be unique across workflows to avoid canceling in-progress jobs or runs from other workflows. Otherwise, any previously in-progress or pending job will be canceled, regardless of the workflow.

To only cancel in-progress runs of the same workflow, you can use the github.workflow property to build the concurrency group:

concurrency:
  group: ${{ github.workflow }}-${{ github.ref }}
  cancel-in-progress: true