State Model and Commands¶

Workflows can (not required) follow a practical ISA-88 model with cooperative commands. There is some guidance as part of the library and some details can be found below.

States¶

• IDLE
• STARTING
• RUNNING
• HOLDING
• HELD
• RESUMING
• STOPPING
• STOPPED
• COMPLETE
• ERROR

Commands¶

• HOLD
• RESUME
• STOP
• RESET

Priority is fixed:

• STOP > HOLD > RESUME > RESET

Allowed command policy¶

State diagram¶

stateDiagram
    [*] --> IDLE: Initial state
    IDLE --> STARTING: Cmd-Start
    STARTING --> EXECUTE: SC
    EXECUTE --> PAUSING: Cmd-Pause
    PAUSING --> PAUSED: SC  
    PAUSED --> RESUMING: Cmd-Resume
    RESUMING --> EXECUTE: SC
    EXECUTE --> COMPLETING: SC
    COMPLETING --> COMPLETED: SC
    COMPLETED --> RESETTING: Cmd-Reset
    EXECUTE --> STOPPING: Cmd-Stop
    STOPPING --> STOPPED: SC
    STOPPED --> RESETTING: Cmd-Reset
    RESETTING --> IDLE: SC

Command arbitration¶

recvCommand() drains a bounded set of mailbox messages and uses exchange.workflows.is88.models.pickHighestPriority(...).

flowchart TD
  A[recv first message] --> B[drain up to maxMessages]
  B --> C[normalize command names]
  C --> D[filter by allowed state]
  D --> E[pick highest priority]
  E --> F[return chosen command or None]

Workflow example¶

@workflow(name="demo.commands_60s")
def commands_60s():
    rt = getWorkflows()

    while True: # (1)!
        rt.checkCancelled()
        cmd_info = rt.recvCommand(currentState="RUNNING", topic="cmd", timeoutSeconds=0.2)

        if cmd_info:
            cmd = str(cmd_info.get("cmd", "")).upper()
            if cmd == "HOLD":
                while True:
                    rt.checkCancelled()
                    held_cmd = rt.recvCommand(currentState="HELD", topic="cmd", timeoutSeconds=0.2)
                    if held_cmd and str(held_cmd.get("cmd", "")).upper() == "RESUME":
                        break
            elif cmd == "STOP":
                raise Exception("Stopped by operator")

        sleep_chunked(total_ms=500, chunk_ms=250)

1. You can actually do a while True as much as it is not recommended. The workflow decorator has default timeouts that will timeout the workflow and cancel (IF you have your workflow actually check if a cancel has been issued). A better way might be to have while not rt.checkCancelled() however.