FastAPI pattern

Create the manager during application startup and stop it during shutdown.

import time
from contextlib import asynccontextmanager
from typing import AsyncIterator

from fastapi import FastAPI

from leasepool import LeasedExecutorManager


def blocking_vendor_call(device_id: str) -> dict[str, str]:
    time.sleep(0.2)
    return {"device_id": device_id, "status": "ok"}


@asynccontextmanager
async def lifespan(app: FastAPI) -> AsyncIterator[None]:
    manager = LeasedExecutorManager(
        backend="thread",
        max_pools=4,
        min_pools=1,
        workers_per_pool=4,
    )

    await manager.start()
    app.state.executor_manager = manager

    try:
        yield
    finally:
        await manager.stop()


app = FastAPI(lifespan=lifespan)


@app.get("/devices/{device_id}/status")
async def get_device_status(device_id: str) -> dict[str, str]:
    manager: LeasedExecutorManager = app.state.executor_manager

    async with await manager.acquire(owner=f"device:{device_id}") as lease:
        return await lease.run(blocking_vendor_call, device_id)