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'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);
}
});
};
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