Skip to main content

YAML Exec Concurrency

The settings.functions.exec section controls how many !exec expressions can run at the same time during a document evaluation. Existing stack syntax stays unchanged.

Configuration​

atmos.yaml
settings:
  functions:
    exec:
      max_concurrency: 4
settings.functions.exec.max_concurrency

A positive integer. Defaults to 1, preserving serial execution. Set it above 1 to allow up to that many !exec calls to overlap during one document evaluation. Values below 1 are invalid.

Example​

With a limit of 4, these three expressions can run concurrently:

vars:
  network: !exec ./lookup-network
  cluster: !exec ./lookup-cluster
  registry: !exec ./lookup-registry

Each result is assigned to its original location, regardless of completion order. Existing output decoding still applies, including JSON objects and arrays. No new tag or grouping syntax is needed.

Atmos does not infer dependencies between shell commands. When enabling concurrency, you are responsible for coordinating commands that share files or other external state. Set the limit to 1 when serial execution is required.

Commands inherit Atmos standard input. Concurrent commands share that input stream; input is not broadcast to every command, and which command reads each part is not guaranteed. Coordinate commands that read stdin, or set the limit to 1 when they must read serially.

Cancellation stops outstanding execution. Errors identify the expression's location. Skipping function processing or using --skip=exec continues to prevent the corresponding commands from running.

Related​