backoff.js

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backoff.js

 Copyright (c) 2012 Mathieu Turcotte
 Licensed under the MIT license.

var events = require('events');
var precond = require('precond');
var util = require('util');

A class to hold the state of a backoff operation. Accepts a backoff strategy to generate the backoff delays.

function Backoff(backoffStrategy) {
    events.EventEmitter.call(this);

    this.backoffStrategy_ = backoffStrategy;
    this.maxNumberOfRetry_ = -1;
    this.backoffNumber_ = 0;
    this.backoffDelay_ = 0;
    this.timeoutID_ = -1;

    this.handlers = {
        backoff: this.onBackoff_.bind(this)
    };
}
util.inherits(Backoff, events.EventEmitter);

Sets a limit, greater than 0, on the maximum number of backoffs. A 'fail' event will be emitted when the limit is reached.

Backoff.prototype.failAfter = function(maxNumberOfRetry) {
    precond.checkArgument(maxNumberOfRetry > 0,
        'Expected a maximum number of retry greater than 0 but got %s.',
        maxNumberOfRetry);

    this.maxNumberOfRetry_ = maxNumberOfRetry;
};

Starts a backoff operation. Accepts an optional parameter to let the listeners know why the backoff operation was started.

Backoff.prototype.backoff = function(err) {
    precond.checkState(this.timeoutID_ === -1, 'Backoff in progress.');

    if (this.backoffNumber_ === this.maxNumberOfRetry_) {
        this.emit('fail', err);
        this.reset();
    } else {
        this.backoffDelay_ = this.backoffStrategy_.next();
        this.timeoutID_ = setTimeout(this.handlers.backoff, this.backoffDelay_);
        this.emit('backoff', this.backoffNumber_, this.backoffDelay_, err);
    }
};

Handles the backoff timeout completion.

Backoff.prototype.onBackoff_ = function() {
    this.timeoutID_ = -1;
    this.emit('ready', this.backoffNumber_, this.backoffDelay_);
    this.backoffNumber_++;
};

Stops any backoff operation and resets the backoff delay to its inital value.

Backoff.prototype.reset = function() {
    this.backoffNumber_ = 0;
    this.backoffStrategy_.reset();
    clearTimeout(this.timeoutID_);
    this.timeoutID_ = -1;
};

module.exports = Backoff;