Task Lifecycle

Task States

State	Description
PENDING	Task is queued, waiting to be claimed
CLAIMED	Worker has claimed the task, preparing to execute
RUNNING	Task is actively executing in a worker process
COMPLETED	Task finished successfully
FAILED	Task failed (error returned or exception)
CANCELLED	Task was cancelled before execution
EXPIRED	Task was never claimed before good_until deadline passed

Terminal states: COMPLETED, FAILED, CANCELLED, EXPIRED.

Status Enum

TaskStatus values:

Enum	Value	Terminal
PENDING	"PENDING"	No
CLAIMED	"CLAIMED"	No
RUNNING	"RUNNING"	No
COMPLETED	"COMPLETED"	Yes
FAILED	"FAILED"	Yes
CANCELLED	"CANCELLED"	Yes
EXPIRED	"EXPIRED"	Yes

Use is_terminal or TASK_TERMINAL_STATES to check terminal status programmatically:

from horsies import TaskStatus, TASK_TERMINAL_STATES

status = TaskStatus.FAILED
status.is_terminal  # True

TaskStatus.RUNNING.is_terminal  # False

# Frozenset for use in queries or filters
TASK_TERMINAL_STATES  # frozenset({TaskStatus.COMPLETED, TaskStatus.FAILED, TaskStatus.CANCELLED, TaskStatus.EXPIRED})

State Transitions

                    ┌──────────────┐
              ┌─────│   PENDING    │─────┐
              │     └──────┬───────┘     │
              │            │ Worker      │ good_until
              │            │ claims      │ passed
              │            ▼             ▼
              │     ┌──────────────┐ ┌──────────┐
    timeout   │     │   CLAIMED    │ │ EXPIRED  │
   (requeue)◄─┼─────┤              │ └──────────┘
              │     └──────┬───────┘
              │            │ Execution starts
              │            ▼
              │     ┌──────────────┐
              │     │   RUNNING    │
              │     └──────┬───────┘
              │            │
              │ ┌──────────┼────────────┐
              │ │          │            │
              │ ▼          ▼            ▼
              │ ┌──────────┐ ┌──────────┐  (retry)
              │ │COMPLETED │ │  FAILED  │────┐
              │ └──────────┘ └──────────┘    │
              │                              │
              └──────────────────────────────┘

Transition Details

PENDING → CLAIMED

• Worker executes claim query with FOR UPDATE SKIP LOCKED
• Sets claimed=TRUE, claimed_at=NOW(), claimed_by_worker_id
• Task is reserved for this worker

CLAIMED → RUNNING

• Task dispatched to worker’s process pool
• Child process sets status=RUNNING, started_at=NOW()
• Heartbeat thread begins sending runner heartbeats

RUNNING → COMPLETED

• Task returns TaskResult(ok=value)
• Worker stores serialized result
• Sets completed_at=NOW()

COMPLETED means the task succeeded (returned TaskResult.ok). Execution that ends with TaskResult.err or an exception is FAILED, not COMPLETED.

RUNNING → FAILED

• Task returns TaskResult(err=TaskError(...)) or
• Task raises unhandled exception or
• Worker process crashes (detected via missing heartbeats)
• Sets failed_at=NOW(), stores error in result

RUNNING → PENDING (retry)

• Only if retry policy configured and retries remaining
• Sets status=PENDING, increments retry_count
• Sets next_retry_at based on retry policy intervals

PENDING → EXPIRED

• Task has good_until set and deadline has passed without being claimed
• Reaper transitions to EXPIRED with TASK_EXPIRED outcome code
• No attempt row is written (task never started)

CLAIMED → PENDING (stale recovery)

• Claimer heartbeat missing for claimed_stale_threshold_ms
• Reaper automatically requeues (safe - user code never ran)
• Sets claimed=FALSE, claimed_at=NULL

Timestamps

Each task records timing information:

Field	Set When
sent_at	Immutable call-site timestamp — when .send() or .schedule() was called. Captured inside the TaskSendResult flow before enqueue.
enqueued_at	When task becomes eligible for claiming (updated on retry)
claimed_at	Worker claims task
started_at	Execution begins in child process
completed_at	Successful completion
failed_at	Failure
next_retry_at	Scheduled retry time

Heartbeats

Two types of heartbeats track task health:

1. Claimer heartbeat: Worker sends for CLAIMED tasks (task not yet running)
2. Runner heartbeat: Child process sends for RUNNING tasks

Missing heartbeats trigger automatic recovery. See Heartbeats & Recovery.

Task Expiry

Tasks can have a good_until deadline:

• If task isn’t claimed before good_until, it becomes unclaimable
• The reaper periodically transitions unclaimed expired tasks to EXPIRED with a TASK_EXPIRED result
• Useful for time-sensitive operations

from datetime import datetime, timedelta, timezone

@app.task("urgent_task")
def urgent_task() -> TaskResult[str, TaskError]:
    ...

# Compute deadline at send time, not module load time
urgent_task.send(good_until=datetime.now(timezone.utc) + timedelta(minutes=5))