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 on the next tick.
// 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) {});
}
t.onDone(function() {
console.timeEnd('deflate');
});npm install async-limiter
npm test
Constructor. opts may contain inital values for:
t.concurrency
fn will be called once and only once, when the queue is empty.
If the queue is empty on the next tick, onDone() will be called.
Mozilla has docs on how these methods work here.
On the next tick, job processing will start.
Max number of jobs the queue should process concurrently, defaults to Infinity.
Jobs pending jobs to process (readonly).