async-limit

0.1.0 • Public • Published

async-limit

Create a concurrency-constrained copy of an asynchronous javascript function.

Usage

var request = require('request');
var limit = require('async-limit');
 
var limitedGet = limit(request.get, 2);
limitedGet('http://www.google.com', function(err, res, body) {
 
});
limitedGet('http://www.jezebel.com', function(err, res, body) {
 
});
limitedGet('http://www.pinterest.com', function(err, res, body) {
    // `limitedGet` only permits two pending operations at a time,
    // so this one won't kick off till the first two have returned.
});

This is a relatively low-level primitive. If you're using it as in the simple example above, you're better off with something like mapLimit from async.

Its real use is in controlling behavior of the underlying method when individual calls are abstracted away by higher-level approaches to async control flow. E.g., using the co library to drive ES6 generators:

var fs = require('fs');
var _ = require('lodash');
var co = require('co');
var request = require('request');
var thunkify = require('thunkify');
var limit = require('async-limit');
 
var get = thunkify(limit(request.get, 2));
 
var writeFile = thunkify(fs.writeFile);
 
co(function*() {
    var toGet = [
        {
            site: 'google',
            url: 'http://www.google.com'
        },
        {
            site: 'jezebel',
            url: 'http://www.jezebel.com'
        },
        {
            site: 'pinterest',
            url: 'http://www.pinterest.com'
        },
        {
            site: 'newyorker',
            url: 'http://www.newyorker.com'
        }
    ];
    var urlRequests = _.map(toGet, function(elem) {
        return get(elem.url);
    });
    var bodies = yield urlRequests;
    // `bodies` contains an array of the downloaded bodies
    // of the four URLs above, in the correct order.
 
    var asFiles = _.map(_.zip(toGet, bodies), function(elem) {
        return {
            fileName: ['./downloaded/', elem[0].site, '.html'].join(''),
            body: elem[1]
        };
    });
    var toWrite = _.map(asFiles, function(elem) {
        return writeFile(elem.fileName, elem.body);
    });
    yield toWrite;
})();

Here async-limit provides a way to control concurrency without any changes to the generator passed into co. This allows the generator to cleanly express the operation's control flow (HTTP GET -> fs write) while remaining ignorant of lower-level implementation details.

Installation

npm install async-limit

GitHub

https://github.com/scivey/async-limit

Contact

https://github.com/scivey

scott.ivey@gmail.com

License

MIT License (MIT)

Copyright (c) 2014 Scott Ivey, scott.ivey@gmail.com

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

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npm i async-limit

Weekly Downloads

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Version

0.1.0

License

MIT

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  • scivey