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Hornwitser
c53781d16c
Add suffixes like Ms and Ns to variables whos time unit is not in seconds. This is aligning with a new code style of putting units on variables that are not in SI base units.
80 lines
2.6 KiB
TypeScript
80 lines
2.6 KiB
TypeScript
/**
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* Helper class for implementing the exponential backoff algorithm
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*
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* Provides a convenient interface for implementing an exponential backoff
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* when reconnecting or resending in a distributed network.
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*
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* Once instantiated the delay method will return the next interval to wait
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* for in milliseconds before making another attempt. For each attempt the
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* delay chosen is a random value between 0 and the current maximum delay
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* wwhich starts at a value of 2 * `base` and doubles for ever attempt up to
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* the passed value of `max`. The value for the delay will reset back to
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* `base` if more time than the value for `reset` has passed between two
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* invocations of delay.
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*/
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export default class ExponentialBackoff {
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/**
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* Base delay in seconds. The first delay will on average be this
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* long, but can be anywhere between 0 and 2 times this value.
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*/
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base = 1;
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/**
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* Maximum delay in seconds. A delay will not take more than this
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* value.
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*/
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max = 60;
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/**
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* Time in seconds between two invocations of delay which will cause
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* it to start over with `base` instead of doubling.
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*/
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reset: number;
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private _exp = 0;
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private _lastInvocationTimeMs = Date.now();
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/**
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* Construct ExponentialBackoff helper
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*
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* The options passed may also be modified on the instance at runtime.
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*
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* @param options -
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* Options for this exponential backoff helper
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* @param [options.base=1] -
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* Base delay in seconds. The first delay will on average be this
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* long, but can be anywhere between 0 and 2 times this value.
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* @param [options.max=60] -
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* Maximum delay in seconds. A delay will not take more than this
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* value.
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* @param [options.reset=2*max] -
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* Time in seconds between two invocations of delay which will cause
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* it to start over with `base` instead of doubling.
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*/
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constructor(options: { base?: number, max?: number, reset?: number } = {}) {
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this.base = options.base || 1;
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this.max = options.max || 60;
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this.reset = options.reset || 2 * this.max;
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}
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/**
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* Compute the next delay to wait
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*
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* Returns the next delay to wait according to the exponential backoff
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* algorithm. This is a value between 0 and min(2 * options.base *
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* 2<sup>retries</sup>, optinos.max).
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*
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* @returns time in milliseconds to wait.
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*/
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delay() {
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let invocationTimeMs = Date.now();
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let interval = (invocationTimeMs - this._lastInvocationTimeMs) / 1000;
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this._lastInvocationTimeMs = invocationTimeMs;
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if (interval > this.reset) {
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this._exp = 0;
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}
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this._exp = Math.min(this._exp + 1, Math.log2(this.max));
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return Math.random() * this.base * 2 ** this._exp * 1000;
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}
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}
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