forked from zhurui/management
43 lines
633 B
JavaScript
43 lines
633 B
JavaScript
'use strict';
|
|
const pTry = require('p-try');
|
|
|
|
module.exports = concurrency => {
|
|
if (concurrency < 1) {
|
|
throw new TypeError('Expected `concurrency` to be a number from 1 and up');
|
|
}
|
|
|
|
const queue = [];
|
|
let activeCount = 0;
|
|
|
|
const next = () => {
|
|
activeCount--;
|
|
|
|
if (queue.length > 0) {
|
|
queue.shift()();
|
|
}
|
|
};
|
|
|
|
return fn => new Promise((resolve, reject) => {
|
|
const run = () => {
|
|
activeCount++;
|
|
|
|
pTry(fn).then(
|
|
val => {
|
|
resolve(val);
|
|
next();
|
|
},
|
|
err => {
|
|
reject(err);
|
|
next();
|
|
}
|
|
);
|
|
};
|
|
|
|
if (activeCount < concurrency) {
|
|
run();
|
|
} else {
|
|
queue.push(run);
|
|
}
|
|
});
|
|
};
|