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exponential-backoff.js
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/**
* Copyright 2015 The AMP HTML Authors. All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS-IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/**
* @param {number=} opt_base Exponential base. Defaults to 2.
* @return {function(function()): number} Function that when invoked will
* call the passed in function. On every invocation the next
* invocation of the passed in function will be exponentially
* later. Returned function returns timeout id.
*/
export function exponentialBackoff(opt_base) {
const getTimeout = exponentialBackoffClock(opt_base);
return work => {
return setTimeout(work, getTimeout());
};
}
/**
* @param {number=} opt_base Exponential base. Defaults to 2.
* @return {function(): number} Function that when invoked will return
* a number that exponentially grows per invocation.
*/
export function exponentialBackoffClock(opt_base) {
const base = opt_base || 2;
let count = 0;
return () => {
let wait = Math.pow(base, count++);
wait += getJitter(wait);
return wait * 1000;
};
}
/**
* Add jitter to avoid the thundering herd. This can e.g. happen when
* we poll a backend and it fails for everyone at the same time.
* We add up to 30% (default) longer or shorter than the given time.
*
* @param {number} wait the amount if base milliseconds
* @param {number=} opt_perc the min/max percentage to add or sutract
* @return {number}
*/
export function getJitter(wait, opt_perc) {
opt_perc = opt_perc || 0.3;
let jitter = wait * opt_perc * Math.random();
if (Math.random() > 0.5) {
jitter *= -1;
}
return jitter;
}