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Parallel

Gwen can execute features and scenarios in parallel threads.

Maximum threads

The maximum number of parallel threads can be controlled through the following setting:

  • gwen.parallel.maxThreads
    • By default this is set to auto, meaning that one thread will execute on each available CPU core (for example: 8 threads would execute on an 8 core machine)
    • This can be set to a desired number of threads
      • When less than the number of available cores, the remaining cores will be free
      • When greater than the number of available cores, more than one thread may execute on some or all cores (use judiciously)

Parallel feature execution

Since v1.0.0

Features will run in parallel if you specify:

When maxThreads is auto (default)

  • If you launch Gwen on an 8 core machine with the --parallel option passing in 8 feature files (or a single directory containing 8 feature files), then the 8 features will run in parallel across the cores. If you instead provide 9 features, then 8 of them will execute in parallel and the remaining feature execution will be deferred until one of those completes.

Parallel scenario execution

Since v2.22.1

Scenarios will run in parallel if you specify:

When maxThreads is auto (default)

  • If you launch Gwen on a 8 core machine with the --parallel option passing in many feature files (or a single directory containing many feature files), then at most 8 scenarios will run in parallel across the cores at any one time. If there are a total of 9 scenarios, then 8 of them will execute in parallel and the remaining scenario execution be deferred wait until one of those completes.

Staggering

Since v1.1.0

An optional ramp up interval can be configured to stagger parallel executions.

Example:

A 5 second interval would stagger parallel feature executions like this over 4 cores:

    time  00   05   10   15   seconds
│ │ │ │
core 1 │<── feature 1a ──>|<── feature 1b ──> ..
core 2 │ │<── feature 2a ──>|<── feature 2b ──> ..
core 3 │ │ │<── feature 3a ──>|<── feature 3b ──> ..
core 4 │ │ │ │<── feature 4a ──>|<── feature 4b ──> ..