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Simple KV backoff with Deno
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| // const voidFn = (...args: unknown[]) => void args | |
| const log = console.log /* voidFn */; | |
| export async function expensive() { | |
| const kv = await Deno.openKv(); | |
| const now = `[${performance.now()}]`; | |
| const key = ["namespace", "expensive"]; | |
| const cache = await kv.get(key); | |
| log(`${now} kv.get(${key}) = ${cache.value}`); | |
| if (cache.value) { | |
| log(`${now} 💶 found!`); | |
| return cache.value; | |
| } | |
| if (!(await acquireLock(key))) { | |
| log(`${now} 😔 backing off!`); | |
| return backoff(kv, key); | |
| } | |
| log(`${now} 🥵 working!`); | |
| await sleep(1000); | |
| const data = Math.random(); | |
| await kv.set(key, data, { expireIn: 1000 * 5}); | |
| log(`${now} 😎 done!`); | |
| await releaseLock(key); | |
| log(`${now} 🔓 released lock!`); | |
| return data; | |
| } | |
| async function acquireLock(key: Deno.KvKey) { | |
| const kv = await Deno.openKv("locks"); | |
| const lock = await kv.get(key); | |
| if (lock.value) return false; | |
| return ( | |
| await kv.atomic() | |
| .check(lock) | |
| .set(key, "🔒", { expireIn: 1000 * 60 }) | |
| .commit() | |
| ).ok; | |
| } | |
| async function releaseLock(key: Deno.KvKey) { | |
| const kv = await Deno.openKv("locks"); | |
| await kv.delete(key); | |
| } | |
| async function backoff<T>(kv: Deno.Kv, key: Deno.KvKey) { | |
| for (let i = 0; i < 5; i++) { | |
| const item = await kv.get<T>(key); | |
| if (item.value) { | |
| log(`😔✅ got it after ${i} tries`); | |
| return item.value; | |
| } | |
| await sleep(100 + i * 100); | |
| } | |
| throw new Error("Could not backoff"); | |
| } | |
| function sleep(ms: number) { | |
| return new Promise((resolve) => { | |
| setTimeout(resolve, ms); | |
| }); | |
| } |
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