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