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https://github.com/mauriceboe/TREK.git
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Maurice
68504b337f
acquire() made sure a row existed and then raced on a conditional UPDATE, two statements the registrar wrapped in a transaction of its own. lint:tx cannot follow a repository reached through a local variable, so it reported the method. One INSERT ... ON CONFLICT DO UPDATE ... WHERE now takes a free lease, renews the holder's and leaves anyone else's alone, atomically on SQLite and on Postgres, and needs no transaction.
44 lines
2.0 KiB
TypeScript
44 lines
2.0 KiB
TypeScript
import type { SchedulerLeases } from '../entities/SchedulerLeases.entity';
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import { TrekRepository } from './_shared/trek-repository';
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import type { DB } from '../kysely/db';
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/**
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* `scheduler_leases`: which process may run a cron job's tick, and until when
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* (`CronRegistrarService`). A lease is free when no row exists yet, when its
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* `expires_at` has passed, or when the asking process already holds it.
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*/
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export class SchedulerLeasesRepository extends TrekRepository<SchedulerLeases> {
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/**
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* Take (or renew) the lease on `name` for `owner` until `until`, if it is
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* free at `now`. One statement: the insert takes a lease nobody has held
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* yet, and on a conflict the update only applies while the lease has run out
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* or already belongs to `owner`. Of two processes asking at the same moment
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* exactly one gets a row written. True when `owner` holds the lease afterwards.
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*/
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async acquire(name: string, owner: string, now: number, until: number): Promise<boolean> {
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const result = await this.kysely<Pick<DB, 'scheduler_leases'>>()
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.insertInto('scheduler_leases')
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.values({ name, owner, expires_at: until })
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.onConflict((oc) =>
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oc
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.column('name')
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.doUpdateSet({ owner, expires_at: until })
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.where((eb) => eb.or([eb('scheduler_leases.expires_at', '<=', now), eb('scheduler_leases.owner', '=', owner)])),
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)
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.executeTakeFirst();
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return (result.numInsertedOrUpdatedRows ?? 0n) > 0n;
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}
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/** Move the expiry of a lease `owner` still holds; false when somebody else has it now. */
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async extend(name: string, owner: string, until: number): Promise<boolean> {
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const changed = await this.nativeUpdate({ name, owner }, { expires_at: until });
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return changed > 0;
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}
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/** The current holder and expiry, for diagnostics and tests. */
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async holder(name: string): Promise<{ owner: string; expires_at: number } | null> {
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const row = await this.findOne({ name }, { fields: ['owner', 'expires_at'] });
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return row ? { owner: row.owner, expires_at: row.expires_at } : null;
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}
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}
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