81 lines
2.7 KiB
JavaScript
81 lines
2.7 KiB
JavaScript
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// Copyright (c) 2012 Mathieu Turcotte
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// Licensed under the MIT license.
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var events = require('events');
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var util = require('util');
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function isDef(value) {
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return value !== undefined && value !== null;
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}
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// Abstract class defining the skeleton for the backoff strategies. Accepts an
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// object holding the options for the backoff strategy:
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//
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// * `randomisationFactor`: The randomisation factor which must be between 0
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// and 1 where 1 equates to a randomization factor of 100% and 0 to no
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// randomization.
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// * `initialDelay`: The backoff initial delay in milliseconds.
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// * `maxDelay`: The backoff maximal delay in milliseconds.
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function BackoffStrategy(options) {
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options = options || {};
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if (isDef(options.initialDelay) && options.initialDelay < 1) {
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throw new Error('The initial timeout must be greater than 0.');
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} else if (isDef(options.maxDelay) && options.maxDelay < 1) {
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throw new Error('The maximal timeout must be greater than 0.');
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}
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this.initialDelay_ = options.initialDelay || 100;
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this.maxDelay_ = options.maxDelay || 10000;
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if (this.maxDelay_ <= this.initialDelay_) {
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throw new Error('The maximal backoff delay must be ' +
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'greater than the initial backoff delay.');
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}
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if (isDef(options.randomisationFactor) &&
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(options.randomisationFactor < 0 || options.randomisationFactor > 1)) {
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throw new Error('The randomisation factor must be between 0 and 1.');
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}
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this.randomisationFactor_ = options.randomisationFactor || 0;
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}
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// Gets the maximal backoff delay.
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BackoffStrategy.prototype.getMaxDelay = function() {
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return this.maxDelay_;
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};
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// Gets the initial backoff delay.
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BackoffStrategy.prototype.getInitialDelay = function() {
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return this.initialDelay_;
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};
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// Template method that computes and returns the next backoff delay in
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// milliseconds.
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BackoffStrategy.prototype.next = function() {
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var backoffDelay = this.next_();
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var randomisationMultiple = 1 + Math.random() * this.randomisationFactor_;
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var randomizedDelay = Math.round(backoffDelay * randomisationMultiple);
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return randomizedDelay;
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};
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// Computes and returns the next backoff delay. Intended to be overridden by
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// subclasses.
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BackoffStrategy.prototype.next_ = function() {
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throw new Error('BackoffStrategy.next_() unimplemented.');
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};
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// Template method that resets the backoff delay to its initial value.
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BackoffStrategy.prototype.reset = function() {
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this.reset_();
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};
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// Resets the backoff delay to its initial value. Intended to be overridden by
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// subclasses.
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BackoffStrategy.prototype.reset_ = function() {
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throw new Error('BackoffStrategy.reset_() unimplemented.');
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};
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module.exports = BackoffStrategy;
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