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					72 lines
				
				1.5 KiB
			
		
		
			
		
	
	
					72 lines
				
				1.5 KiB
			| 
											3 years ago
										 | 'use strict'; | ||
|  | const Queue = require('yocto-queue'); | ||
|  | 
 | ||
|  | const pLimit = concurrency => { | ||
|  | 	if (!((Number.isInteger(concurrency) || concurrency === Infinity) && concurrency > 0)) { | ||
|  | 		throw new TypeError('Expected `concurrency` to be a number from 1 and up'); | ||
|  | 	} | ||
|  | 
 | ||
|  | 	const queue = new Queue(); | ||
|  | 	let activeCount = 0; | ||
|  | 
 | ||
|  | 	const next = () => { | ||
|  | 		activeCount--; | ||
|  | 
 | ||
|  | 		if (queue.size > 0) { | ||
|  | 			queue.dequeue()(); | ||
|  | 		} | ||
|  | 	}; | ||
|  | 
 | ||
|  | 	const run = async (fn, resolve, ...args) => { | ||
|  | 		activeCount++; | ||
|  | 
 | ||
|  | 		const result = (async () => fn(...args))(); | ||
|  | 
 | ||
|  | 		resolve(result); | ||
|  | 
 | ||
|  | 		try { | ||
|  | 			await result; | ||
|  | 		} catch {} | ||
|  | 
 | ||
|  | 		next(); | ||
|  | 	}; | ||
|  | 
 | ||
|  | 	const enqueue = (fn, resolve, ...args) => { | ||
|  | 		queue.enqueue(run.bind(null, fn, resolve, ...args)); | ||
|  | 
 | ||
|  | 		(async () => { | ||
|  | 			// This function needs to wait until the next microtask before comparing
 | ||
|  | 			// `activeCount` to `concurrency`, because `activeCount` is updated asynchronously
 | ||
|  | 			// when the run function is dequeued and called. The comparison in the if-statement
 | ||
|  | 			// needs to happen asynchronously as well to get an up-to-date value for `activeCount`.
 | ||
|  | 			await Promise.resolve(); | ||
|  | 
 | ||
|  | 			if (activeCount < concurrency && queue.size > 0) { | ||
|  | 				queue.dequeue()(); | ||
|  | 			} | ||
|  | 		})(); | ||
|  | 	}; | ||
|  | 
 | ||
|  | 	const generator = (fn, ...args) => new Promise(resolve => { | ||
|  | 		enqueue(fn, resolve, ...args); | ||
|  | 	}); | ||
|  | 
 | ||
|  | 	Object.defineProperties(generator, { | ||
|  | 		activeCount: { | ||
|  | 			get: () => activeCount | ||
|  | 		}, | ||
|  | 		pendingCount: { | ||
|  | 			get: () => queue.size | ||
|  | 		}, | ||
|  | 		clearQueue: { | ||
|  | 			value: () => { | ||
|  | 				queue.clear(); | ||
|  | 			} | ||
|  | 		} | ||
|  | 	}); | ||
|  | 
 | ||
|  | 	return generator; | ||
|  | }; | ||
|  | 
 | ||
|  | module.exports = pLimit; |