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Parallel Job Runner
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| /** | |
| * Creates a function that performs any promisable task in parallel. | |
| * @param {number} [concurrency] - The maximum number of concurrent jobs that are able to run simultaneously. | |
| * @return {Promise} | |
| */ | |
| const createJobRunner = (concurrency = 3) => { | |
| const EMPTY_SLOT = false; | |
| const BUSY_SLOT = true; | |
| const workersQueue = []; | |
| const workingSlots = new Array(concurrency).fill(EMPTY_SLOT); | |
| const next = (availableSlot = workingSlots.indexOf(EMPTY_SLOT)) => { | |
| if (workersQueue.length === 0 || availableSlot < 0) return; | |
| workingSlots[availableSlot] = BUSY_SLOT; | |
| const worker = workersQueue.shift(); | |
| worker(() => { | |
| workingSlots[availableSlot] = EMPTY_SLOT; | |
| next(availableSlot) | |
| }); | |
| } | |
| return (worker) => new Promise( (resolve, reject) => { | |
| workersQueue.push((onFinish) => { | |
| const job = worker(); | |
| if (job instanceof Promise) { | |
| job.then(resolve).catch(reject).finally(onFinish); | |
| } else { | |
| try { | |
| resolve(job); | |
| } catch (e) { | |
| reject(e); | |
| } finally { | |
| onFinish(); | |
| } | |
| } | |
| }); | |
| next(); | |
| }); | |
| } |
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| const doWork = createJobRunner(5); | |
| for (let i=0; i<10; i++) { | |
| doWork(() => new Promise((resolve) => { | |
| console.log(`Job ${i} started`); | |
| setTimeout(() => { | |
| console.log(`Job ${i} done`); | |
| resolve(); | |
| }, Math.random() * 1000) | |
| })); | |
| } | |
| //// Possible output: | |
| // Job 0 started | |
| // Job 1 started | |
| // Job 2 started | |
| // Job 3 started | |
| // Job 4 started | |
| // Job 1 done | |
| // Job 5 started | |
| // Job 5 done | |
| // Job 6 started | |
| // Job 2 done | |
| // Job 7 started | |
| // Job 7 done | |
| // Job 8 started | |
| // Job 4 done | |
| // Job 9 started | |
| // Job 3 done | |
| // Job 0 done | |
| // Job 8 done | |
| // Job 6 done | |
| // Job 9 done |
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