pinion-queue 0.2.4

Pinion: a tiny pluggable job queue with retries.

Pinion

Pinion is a tiny, pluggable job queue and worker for Python. It provides a simple @task registry, an in-memory queue for quick starts, and a durable SQLite backend for cross-process work, plus a retry policy with exponential backoff.

Features

• In-memory queue with thread-safe Condition coordination
• Durable SQLite storage with atomic job claim (WAL) across processes
• Pluggable Storage protocol (SPI) for custom backends
• Task registry via @task decorator (case-insensitive names)
• Worker loop with polling, retries, timeouts, and graceful stop/join
• Exponential backoff retries with optional jitter and cap
• Dead-letter queue (DLQ) after exhausted retries
• Basic worker metrics (processed/succeeded/failed/retried/dead_lettered/reaped)
• Job lifecycle tracking: PENDING, RUNNING, SUCCESS, FAILED

Requirements

• Python 3.12+

Installation

• From source (local dev): pip install -e .
• CLI entry point installs as pinion

Quick Start

CLI

• pinion prints a concise quickstart, admin command cheatsheet, and exits.
• pinion --demo runs a tiny in-memory demo (adds 1+2).
• SQLite admin commands: status, running, pending, dlq-list, dlq-replay, enqueue, worker.

Examples:

# Show queue summary for a DB
pinion status --db pinion.db

# Run a worker for 5s and import your task module for registration
pinion worker --db pinion.db --max-retries 2 --task-timeout 5 \
  --import your_project.tasks --run-seconds 5

# Enqueue a job by name with JSON args/kwargs
pinion enqueue add --db pinion.db --args '[1,2]'

Library usage (in-memory)

import threading, time
from pinion import task, Job, InMemoryStorage, Worker, RetryPolicy

@task()
def add(a: int, b: int) -> int:
    return a + b

storage = InMemoryStorage()
worker = Worker(storage, retry=RetryPolicy(jitter=False), task_timeout=2.0)
thread = threading.Thread(target=worker.run_forever, daemon=True)
thread.start()

storage.enqueue(Job("add", (1, 2)))   # args tuple
storage.enqueue(Job("BOOM"))           # case-insensitive lookup (if registered)

time.sleep(2.5)
worker.stop()
thread.join()
# Optional: access basic metrics
print(worker.metrics)

Library usage (SQLite)

import threading, time
from pinion import task, Job, Worker, RetryPolicy, SqliteStorage  # durable backend

@task("boom")
def fail() -> None:
    raise ValueError("kaboom")

storage = SqliteStorage("pinion.db")
worker = Worker(storage, retry=RetryPolicy(jitter=False), task_timeout=2.0)
t = threading.Thread(target=worker.run_forever, daemon=True)
t.start()

storage.enqueue(Job("fail"))

time.sleep(4.5)
worker.stop()
t.join()

# Inspect DLQ (SQLite backend) for permanently failed jobs
# rows: (id, func_name, args_json, kwargs_json, attempts, error, failed_at)
print(storage._conn.execute("SELECT * FROM dlq").fetchall())

Core Concepts

• Job: encapsulates function name, args/kwargs, id, status, attempts, timestamps
• Storage: SPI with enqueue, dequeue, mark_done, mark_failed, size, heartbeat, reap_stale, dead_letter
• Task registry: mapping of case-insensitive names to callables via @task
• Worker: pulls jobs, executes callables, applies retry policy and optional per-task timeouts
• Retry policy: max_retries, base_delay, cap, optional jitter
• DLQ: jobs moved to durable dead-letter storage after retries are exhausted
• Metrics: basic counters available via worker.metrics

Extending Storage

Implement the Storage protocol to plug in your own backend (e.g., Redis, DB, file-based):

class MyStorage:
    def enqueue(self, job: Job) -> None: ...
    def dequeue(self, timeout: float | None = None) -> Job | None: ...
    def mark_done(self, job: Job) -> None: ...
    def mark_failed(self, job: Job, exc: Exception) -> None: ...
    def size(self) -> int: ...
    def heartbeat(self, job: Job) -> None: ...
    def reap_stale(self, visibility_timeout: float) -> int: ...
    def dead_letter(self, job: Job, exc: Exception) -> None: ...

dequeue should block until timeout or a job is available, mark the job RUNNING, and increment attempts before returning the job.

Design Notes

• InMemoryStorage uses a Condition for coordinating producers/consumers.
• SqliteStorage uses WAL mode and an atomic claim (BEGIN IMMEDIATE + UPDATE) to safely select a PENDING job across processes. Access is serialized with a lock.
• Worker uses a JobExecution context manager to mark success/failure and provides a thread-based per-task timeout option.
• Retries are scheduled by re-enqueuing the same job after a computed delay.
• Registry keys are normalized to lowercase for case-insensitive task names.
• DLQ persists final failures (SQLite backend has a dlq table).

Limitations

• In-memory storage is ephemeral; jobs are not persisted across restarts.
• SQLite backend is local to a machine; horizontal scaling requires a different backend.
• Thread-based timeouts cannot kill Python threads; long-running tasks should be cooperative or run in separate processes.
• No result storage/return channel; tasks handle their own outputs.
• Minimal inspection/metrics API.

Breaking Changes (since 0.1.x)

• Storage SPI: added dead_letter(job, exc); custom backends must implement it.

Release and Publishing

Pinion targets Python 3.12+ and is published as pinion-queue.

Suggested versioning for this release: bump to 0.2.0.

1. Update version

• Edit pyproject.toml: set version = "0.2.0".
• Edit pinion/__init__.py: set __version__ = "0.2.0".

2. Build distributions

python -m pip install --upgrade pip build twine
python -m build
twine check dist/*

3. Publish to PyPI

# Set PYPI token in environment (from your PyPI account)
export TWINE_USERNAME="__token__"
export TWINE_PASSWORD="pypi-***your-token***"

twine upload dist/*

4. Tag the release

git tag v0.2.0
git push --tags

If pinion-queue is not available on PyPI, choose an alternative name or organization namespace.

Project Layout

• pinion/queue.py — core queue, worker, storages, demo tasks
• pinion/cli.py — simple CLI demo (pinion)

Upgrading

• pip: pip install -U pinion-queue
• pipx: pipx upgrade pinion-queue
• Poetry: poetry update pinion-queue

The CLI performs a lightweight update check (with a short timeout) and prints a hint if a newer version is available. Disable via PINION_NO_UPDATE_CHECK=1 or pinion --no-update-check.

See the Changelog for release notes: CHANGELOG.md.

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Pinion aims to be a tiny, understandable foundation you can extend with a real storage backend and operational features as needed.