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Parallel Tasks

Run two branches concurrently where the first to finish wins.

What you will learn​

  • How to run workflow branches in parallel using fork
  • How compete: true returns only the first branch to finish
  • How to collect results from all branches using compete: false The slower branch is cancelled.

Workflow​

workflow.yaml
document:
  dsl: 1.0.0
  namespace: zigflow
  name: competing-tasks
  version: 0.0.1
timeout:
  after:
    minutes: 1
do:
  - state:
      export:
        as:
          data: ${ . }
      set:
        id: ${ uuid }
  - race:
      fork:
        compete: true
        branches:
          - task1:
              do:
                - getUser:
                    call: http
                    with:
                      method: get
                      endpoint: >-
                        https://jsonplaceholder.typicode.com/users/2
                - wait:
                    wait:
                      seconds: 2
          - task2:
              do:
                - getUser:
                    call: http
                    with:
                      method: get
                      endpoint: >-
                        https://jsonplaceholder.typicode.com/users/1
                - wait:
                    wait:
                      seconds: 50

Explanation​

PartPurpose
fork.compete: trueFirst branch to finish cancels the others
fork.branchesEach branch runs as a child workflow
state taskGenerates a UUID before the race starts

task1 finishes in roughly 2 seconds. task2 would take 50 seconds. Because compete: true is set, task2 is cancelled as soon as task1 completes.

Cancelled branches are not rolled back. Any HTTP calls or side effects performed before cancellation are not undone. Only the winner's output is returned.

Non-competing fork​

To run all branches and collect every result, use compete: false (the default):

- parallel:
    fork:
      compete: false
      branches:
        - branch1:
            call: http
            with:
              method: get
              endpoint: https://jsonplaceholder.typicode.com/users/1
        - branch2:
            call: http
            with:
              method: get
              endpoint: https://jsonplaceholder.typicode.com/users/2

The output is an object containing each branch's result, keyed by branch name.

How to run​

  1. Start a Temporal development server:

    temporal server start-dev

  2. Start the worker:

    zigflow run -f workflow.yaml

  3. Trigger the workflow:

    temporal workflow start \
      --type competing-tasks \
      --task-queue zigflow \
      --workflow-id race-1

  4. View the result:

    temporal workflow show --workflow-id race-1

Common mistakes​

Expecting the cancelled branch output to be available. With compete: true only the winner's output is returned. Cancelled branch data is discarded.