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132 lines
3.3 KiB
Markdown
132 lines
3.3 KiB
Markdown
# Async-Limiter
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A module for limiting concurrent asynchronous actions in flight. Forked from [queue](https://github.com/jessetane/queue).
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[](http://www.npmjs.org/async-limiter)
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[](https://travis-ci.org/STRML/async-limiter)
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[](https://coveralls.io/r/STRML/async-limiter)
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This module exports a class `Limiter` that implements some of the `Array` API.
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Pass async functions (ones that accept a callback or return a promise) to an instance's additive array methods.
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## Motivation
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Certain functions, like `zlib`, have [undesirable behavior](https://github.com/nodejs/node/issues/8871#issuecomment-250915913) when
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run at infinite concurrency.
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In this case, it is actually faster, and takes far less memory, to limit concurrency.
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This module should do the absolute minimum work necessary to queue up functions. PRs are welcome that would
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make this module faster or lighter, but new functionality is not desired.
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Style should confirm to nodejs/node style.
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## Example
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``` javascript
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var Limiter = require('async-limiter')
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var t = new Limiter({concurrency: 2});
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var results = []
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// add jobs using the familiar Array API
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t.push(function (cb) {
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results.push('two')
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cb()
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})
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t.push(
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function (cb) {
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results.push('four')
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cb()
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},
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function (cb) {
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results.push('five')
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cb()
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}
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)
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t.unshift(function (cb) {
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results.push('one')
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cb()
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})
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t.splice(2, 0, function (cb) {
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results.push('three')
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cb()
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})
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// Jobs run automatically. If you want a callback when all are done,
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// call 'onDone()'.
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t.onDone(function () {
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console.log('all done:', results)
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})
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```
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## Zlib Example
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```js
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const zlib = require('zlib');
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const Limiter = require('async-limiter');
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const message = {some: "data"};
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const payload = new Buffer(JSON.stringify(message));
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// Try with different concurrency values to see how this actually
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// slows significantly with higher concurrency!
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//
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// 5: 1398.607ms
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// 10: 1375.668ms
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// Infinity: 4423.300ms
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//
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const t = new Limiter({concurrency: 5});
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function deflate(payload, cb) {
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t.push(function(done) {
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zlib.deflate(payload, function(err, buffer) {
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done();
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cb(err, buffer);
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});
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});
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}
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console.time('deflate');
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for(let i = 0; i < 30000; ++i) {
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deflate(payload, function (err, buffer) {});
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}
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q.onDone(function() {
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console.timeEnd('deflate');
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});
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```
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## Install
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`npm install async-limiter`
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## Test
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`npm test`
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## API
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### `var t = new Limiter([opts])`
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Constructor. `opts` may contain inital values for:
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* `q.concurrency`
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## Instance methods
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### `q.onDone(fn)`
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`fn` will be called once and only once, when the queue is empty.
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## Instance methods mixed in from `Array`
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Mozilla has docs on how these methods work [here](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array).
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### `q.push(element1, ..., elementN)`
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### `q.unshift(element1, ..., elementN)`
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### `q.splice(index , howMany[, element1[, ...[, elementN]]])`
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## Properties
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### `q.concurrency`
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Max number of jobs the queue should process concurrently, defaults to `Infinity`.
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### `q.length`
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Jobs pending + jobs to process (readonly).
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