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Dummy compute backend

The dummy compute backend gives every compute parcel of the Transformation System a successful outcome without running anything. It lets the parcel lifecycle be exercised before the dispatcher and the real compute backends exist.

It walks each parcel through the parcel state machine of DX-ADR-005, standing in for two components of DX-ADR-003:

  • the dispatcher, which claims a parcel: Unassigned → Reserved → Assigned;
  • a compute backend, which reports the outcome: Assigned → Completing → Done.

Reaching Done moves the parcel's inputs from Assigned to Processed in the same transaction.

How it works

Two tasks in diracx.tasks.transformations share the work:

  • DummyComputeBackendMonitorTask runs periodically. It claims a batch of Unassigned compute parcels, oldest first, and moves them to Assigned with Backend = "dummy". After committing, it schedules one DummyComputeBackendTask per parcel, runtime_seconds later.
  • DummyComputeBackendTask moves its parcel from Assigned to Done, holding a mutex on the parcel.

The transitions go through diracx.logic.transformations.set_parcel_status, which checks them against the state machine and applies the outcome to the inputs. In the database they are compare-and-set: only parcels still in the expected status move. Two monitors running at once, or a retried completion task, therefore never move a parcel twice.

The settings are documented with the environment variables, and Run a task manually shows how to run both tasks by hand.

Limitations

  • Nothing creates parcels yet, as there is no packer.
  • Every parcel succeeds and produces no output. PartiallyDone is not supported until the recovery split exists.
  • If the monitor dies after its commit and before it has scheduled every completion task, those parcels stay Assigned. Reconciling them is an open issue of DX-ADR-003 for every backend.
  • When the dispatcher exists, the claim moves there and a backend keeps only its submission and its outcome reporting.