Execution State Machine

In Julep, an Execution represents an instance of a Task that has been started with some input. The Execution follows a specific state machine model, ensuring consistent and predictable behavior throughout its lifecycle.

Execution States

An Execution can be in one of the following states:

1. queued: The execution is waiting to start

2. starting: The execution is in the process of starting

3. running: The execution is actively running

4. awaiting_input: The execution is suspended and waiting for input to resume

5. succeeded: The execution has completed successfully

6. failed: The execution has failed

7. cancelled: The execution has been cancelled by the user

State Transitions

The valid transitions between execution states are as follows:

• queued → starting

• starting → running, awaiting_input, cancelled, succeeded, failed

• running → running, awaiting_input, cancelled, succeeded, failed

• awaiting_input → running, cancelled

• cancelled, succeeded, failed → (terminal states, no further transitions)

Transition Types

Executions can go through various transition types:

• init: Initializes the execution

• init_branch: Starts a new branch in the execution

• finish: Completes the execution successfully

• finish_branch: Completes a branch in the execution

• wait: Pauses the execution, waiting for input

• resume: Resumes a paused execution

• error: Indicates an error occurred

• step: Represents a step in the execution process

• cancelled: Indicates the execution was cancelled

State Machine Diagram

stateDiagram-v2
    [*] --> queued
    queued --> starting
    queued --> cancelled
    starting --> cancelled
    starting --> failed
    starting --> running
    running --> running
    running --> awaiting_input
    running --> cancelled
    running --> failed
    running --> succeeded
    awaiting_input --> running
    awaiting_input --> cancelled
    
    %% Added transitions for branching
    running --> init_branch : init_branch
    init_branch --> waiting : wait
    init_branch --> cancelled : cancelled
    init_branch --> finish_branch : finish_branch
    finish_branch --> running : resume
    
    %% Updated terminal states
    cancelled --> [*]
    succeeded --> [*]
    failed --> [*]
    finish_branch --> [*]

This state machine ensures that executions in Julep follow a consistent and predictable flow, allowing for complex workflows while maintaining clear status tracking. It provides a robust framework for managing long-running tasks, handling interruptions, and recovering from failures.