wicket 0.2.0

Which waiting job may start now?

Fair admission of work to shared capacity, for asyncio Python:
priority, fairness between tenants, and limits that hold across every process.

Quick start · PostgreSQL · Decisions · Changelog

Why wicket

One tenant submits a thousand jobs, another submits one. A plain queue makes the second wait behind the first thousand. wicket sits beside the queue you already have and tells your workers what to take next.

• Fair from the first grant. Tenants get their turns by Start-time Fair Queuing; one who comes back after a break gets no burst of turns.
• Priority you can read. A weighted sum of factors: whose turn it is, a trait such as the plan tier, how long the job has waited.
• Limits across processes. Concurrency and rate hold for any number of workers: every grant is a compare-and-swap on the pool's version.
• Safe when a worker dies. Its lease ends and the job is delivered again; a fencing token rejects the old worker's late write.
• Small. One dependency, msgspec. An in-memory store, and a PostgreSQL one that commits a job in your own transaction.

wicket does not run the work, retry it or keep its status. It decides what starts.

Quick start

pip install wicket

import asyncio
from datetime import timedelta

from wicket import (
    Concurrency,
    FairShare,
    MemoryBacklog,
    MemoryLedger,
    MemoryState,
    Pool,
    Priority,
    Ticket,
)


async def main() -> None:
    state = MemoryState()
    backlog, ledger = MemoryBacklog(state), MemoryLedger(state)

    # alice floods the queue first, bob asks once
    for n in range(3):
        await backlog.submit("reports", Ticket(id=f"alice-{n}", tenant="alice"))
    await backlog.submit("reports", Ticket(id="bob-0", tenant="bob"))

    pool = Pool(
        ledger,
        "reports",
        priority=Priority((FairShare(), 1)),
        limits=(Concurrency(2),),
        lease=timedelta(seconds=30),
        poll=timedelta(milliseconds=50),
    )

    async def worker() -> None:
        async with pool.permit() as permit:  # waits for its turn, keeps the lease while it runs
            print("started", permit.waiting.ticket.id)
            await asyncio.sleep(0.1)  # the work

    await asyncio.gather(*(worker() for _ in range(4)))


asyncio.run(main())

started alice-0
started bob-0
started alice-1
started alice-2

Bob submitted last and starts second. Only a block that ends normally releases its ticket; after an error the ticket comes back once its lease ends.

Priority and limits

Factors score tickets in 0..1 and are weighted; limits hold together:

from wicket import Age, Rate, Trait, TraitFactor

pool = Pool(
    ledger,
    "materials",
    priority=Priority(
        (FairShare(), 4),
        (TraitFactor("tier"), 2),
        (Age(full_after=timedelta(minutes=30)), 1),
    ),
    limits=(Concurrency(4), Rate(10, per=timedelta(minutes=1))),
    lease=timedelta(minutes=2),
    poll=timedelta(seconds=1),
)

ticket = Ticket("task-1", "alice", traits=(Trait("tier", 1.0), Trait("urgent", 0.5)))

Trait(name, value) is an immutable number in 0..1 on a ticket. TraitFactor(name) scores tickets by that named value, or 0 when absent. A ticket takes a tuple of traits with unique names; neither the tuple nor its traits can change. Tickets encode and decode with msgspec without hooks.

PostgreSQL

The extra brings SQLAlchemy; bring your driver, asyncpg or psycopg.

pip install "wicket[postgres]"

from wicket.postgres import PostgresBacklog, PostgresLedger, metadata

# in your Alembic env.py: target_metadata = [your_metadata, metadata]

async with session.begin():  # your transaction: the row and its ticket commit together
    session.add(row)
    await session.flush()  # the row gets its id
    await PostgresBacklog(session).submit("materials", Ticket(id=str(row.id), tenant=str(user_id)))

ledger = PostgresLedger(engine, retention=timedelta(hours=1))  # the same retention in every process

Upgrading from 0.1.0 to 0.2.0

This release changes ticket traits and the Ledger contract. Upgrade all producers, workers and custom adapters sharing a pool together. Existing databases need the submission ID migration before using the updated adapters; follow its stop, migrate and upgrade instructions before resuming work.

Status

wicket is pre-alpha: the API may change before 1.0, and every change is in the changelog.

Documentation

• Architecture: how the code is laid out and the rules it keeps.
• Decisions: why it is shaped this way.

Contributing

Issues and pull requests are welcome. Read CONTRIBUTING.md first, and follow the Code of Conduct. Report vulnerabilities privately, as the security policy says.

License

MIT