Pattern for Parallel Sub-Workflow Execution Followed by Wait-for-All Loop

## What this workflow does This set of workflows shows how to start multiple sub-workflows, asynchronously, in parallel, and then wait for all of them to complete. Normally, sub-workflows would need to be run synchronously, in series, or, if they are executed asynchronously (to run concurrently, in parallel), there is no easy way to merge/wait for an arbitrary number of them to complete. This is a design pattern template to show one approach for running multiple, data-driven instances of a sub-workflow asynchronously, in parallel (instead of running them one at a time in series), but still prevent the later steps in the workflow from continuing until all of the sub-workflows have reported back that they are finished, via callback URL. There are other techniques involving messaging services, database tables, or other external flow manager helpers, but this technique accomplishes the goal fully within n8n. ## Setup To implement this pattern, examine the nodes in the template and modify the incoming data leading to: 1. A split-out loop to asynchronously execute a sub-workflow multiple times, in parallel. For instance, each sub-workflow might process one of a list of incoming documents. The resumeUrl for the main/parent workflow is provided to all of the sub-workflow executions, along with a unique identifier that can be counted later (e.g., a document file name). 2. A wait-for-all loop that checks whether all sub-workflows have reported back (`if` node) and builds a unique list of identifiers from the callbacks received from each execution of the sub-workflow. The sub-workflow should be designed to respond immediately (async) and later send a callback request when it has finished processing. The callback request should include the unique identifier value received when the sub-workflow was started. This is meant to be a possible answer to questions like [this one about running things in parallel](https://community.n8n.io/t/is-it-possible-to-run-a-part-of-the-workflow-in-parallel/60221), maybe [this one about waiting for things to finish](https://community.n8n.io/t/node-does-not-wait-for-predecessor-node-always-need-a-merge-node/60773), [this one about managing sub-batches of things by waiting for each batch](https://community.n8n.io/t/maximum-parallel-subworkflows/60052), or [this one about running things in parallel](https://community.n8n.io/t/parallel-execution-of-bat-files/49493). The topic of how to do this comes up a lot, and this is one of the only techniques that (so far) seems to work.

Platform

n8n

Category

Business Operations & ERPs

Price

Free

Creator

Hubschrauber

• if
• set
• code
• noOp
• wait
• webhook
• stickyNote
• httpRequest
• manualTrigger
• splitInBatches