24 lines
1.3 KiB
TypeScript
24 lines
1.3 KiB
TypeScript
import { ClockError } from './clock';
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export interface LockBackend {
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create(employee:string):Promise<{id:string}>;
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find(employee:string):Promise<{id:string;created:string}|null>;
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remove(id:string):Promise<unknown>;
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}
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/** Record ID is the ownership token. Never release a lock by employee filter. */
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export async function acquireEmployeeLock(backend:LockBackend,employee:string,now=Date.now()) {
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try{return (await backend.create(employee)).id;}
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catch(error) {
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if(![400,409].includes((error as {status:number}).status))throw error;
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const previous=await backend.find(employee);
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if(!previous)throw error;
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const age=now-Date.parse(previous.created);
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if(Number.isFinite(age) && age>120_000) {
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// Concurrent recoverers can only delete this exact expired record. The
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// unique employee lock and unique event predecessor also fence old writers.
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try{await backend.remove(previous.id);}catch(e){if((e as {status:number}).status!==404)throw e;}
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try{return (await backend.create(employee)).id;}
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catch(e){if(![400,409].includes((e as {status:number}).status))throw e;}
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}
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throw new ClockError('Another scan is being saved for this worker. Retry this confirmation; an interrupted scan lock clears after two minutes.',423);
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}
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}
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