Retries with exponential backoff for dismissals

chrome/browser/resources/google_now/utility.js

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // 'use strict'; TODO(vadimt): Uncomment once crbug.com/237617 is fixed.
 
 // TODO(vadimt): Remove alerts.
 
 /**
  * @fileoverview Utility objects and functions for Google Now extension.
@@ skipping 203 matching lines @@
   });
 
   return {
     add: add,
     // TODO(vadimt): Replace with instrumenting callbacks.
     debugSetStepName: debugSetStepName,
     instrumentApiFunction: instrumentApiFunction,
     wrapCallback: wrapCallback
   };
 }
+
+var storage = chrome.storage.local;
+
+/**
+ * Builds an object to manage retrying activities with exponential backoff.
+ * @param {string} name Name of this attempt manager.
+ * @param {function()} attempt Activity that the manager retries till it

[skare_, 2013/05/14 02:03:52]

nit: expand till->until

[vadimt, 2013/05/14 18:47:50]

Done.

+ *     calls 'stop' method.
+ * @param {number} initialDelaySeconds Default first delay until first retry.
+ * @param {number} maximumDelaySeconds Maximum delay between retries.
+ * @return {Object} Attempt manager interface.
+ */
+function buildAttemptManager(
+    name, attempt, initialDelaySeconds, maximumDelaySeconds) {
+  var alarmName = name + '-scheduler';
+  var currentDelayStorageKey = name + '-current-delay';
+
+  /**
+   * Creates an alarm for the next attempt. The alarm is repeating for the case
+   * when the next attempt crashes before registering next alarm.
+   * @param {number} delaySeconds Delay until next retry.
+   */
+  function createAlarm(delaySeconds) {
+    var alarmInfo = {
+      delayInMinutes: delaySeconds / 60,
+      periodInMinutes: maximumDelaySeconds / 60
+    };
+    chrome.alarms.create(alarmName, alarmInfo);
+  }
+
+  /**
+   * Schedules next attempt.
+   * @param {number=} opt_previousDelaySeconds Previous delay in a sequence of
+   *     retry attemps, if specified. Not specified for scheduling first retry

[rgustafson, 2013/05/14 01:25:17]

attempts

[vadimt, 2013/05/14 18:47:50]

Done.

+   *     in the exponential sequence.
+   */
+  function scheduleNextAttempt(opt_previousDelaySeconds) {
+    var base = opt_previousDelaySeconds ? opt_previousDelaySeconds * 2 :

[skare_, 2013/05/14 02:03:52]

it's likely this isn't a concern since this isn't exposed publicly and this
class will be the only caller, but just in case -- do you need to differentiate
undefined from 0?

[vadimt, 2013/05/14 18:47:50]

No. Anyways, we'd need to special-case 0, otherwise the calculations would
result in 0 again.

+                                          initialDelaySeconds;
+    var newRetryDelaySeconds =
+        Math.min(base * (1 + 0.2 * Math.random()), maximumDelaySeconds);
+
+    createAlarm(newRetryDelaySeconds);
+
+    var items = {};
+    items[currentDelayStorageKey] = newRetryDelaySeconds;
+    storage.set(items);
+  }
+
+  /**
+   * Starts repeated attempts.
+   * @param {number=} opt_firstDelaySeconds Time until the first attempt, if
+   *     specified. Otherwise, initialDelaySeconds will be used for the first
+   *     attempt.
+   */
+  function start(opt_firstDelaySeconds) {
+    if (opt_firstDelaySeconds) {
+      createAlarm(opt_firstDelaySeconds);
+      storage.remove(currentDelayStorageKey);
+    } else {
+      scheduleNextAttempt();
+    }
+  }
+
+  /**
+   * Stops repeated attempts.
+   */
+  function stop() {
+    chrome.alarms.clear(alarmName);
+    storage.remove(currentDelayStorageKey);
+  }
+
+  /**
+   * Plans for the next attempt.
+   * @param {function()} callback Completion callback.
+   */
+  function planForNext(callback) {

[rgustafson, 2013/05/14 01:25:17]

The wording of this confused me too. At the least, include the fact that the
callback is called after scheduling the next attempt in the function comment.
Just passing a function in looks like that's what you're going to do next time
rather than something to be called now, after the next one is scheduled.

[vadimt, 2013/05/14 18:47:50]

Done.

+    tasks.debugSetStepName('planForNext-get-storage');
+    storage.get(currentDelayStorageKey, function(items) {
+      console.log('planForNext-get-storage ' + JSON.stringify(items));
+      scheduleNextAttempt(items[currentDelayStorageKey]);

[rgustafson, 2013/05/14 01:25:17]

This value isn't going to exist if you call this after start with
opt_firstDelaySeconds, right? It only gets set in scheduleNextAttempt.

[vadimt, 2013/05/14 18:47:50]

Yes, in this case, we start from the default value here.

+      callback();
+    });
+  }
+
+  chrome.alarms.onAlarm.addListener(function(alarm) {
+    if (alarm.name == alarmName)
+      attempt();
+  });
+
+  return {
+    start: start,
+    planForNext: planForNext,
+    stop: stop
+  };
+}