Upstream oodles of Chrome for Android code into Chromium.

chrome/android/java_staging/src/org/chromium/chrome/browser/omaha/ExponentialBackoffScheduler.java

Index: chrome/android/java_staging/src/org/chromium/chrome/browser/omaha/ExponentialBackoffScheduler.java
diff --git a/chrome/android/java_staging/src/org/chromium/chrome/browser/omaha/ExponentialBackoffScheduler.java b/chrome/android/java_staging/src/org/chromium/chrome/browser/omaha/ExponentialBackoffScheduler.java
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+// Copyright 2015 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.
+
+package org.chromium.chrome.browser.omaha;
+
+import android.app.AlarmManager;
+import android.app.PendingIntent;
+import android.content.Context;
+import android.content.Intent;
+import android.content.SharedPreferences;
+import android.util.Log;
+
+import org.chromium.base.VisibleForTesting;
+
+import java.util.Date;
+import java.util.Random;
+
+import javax.annotation.concurrent.NotThreadSafe;
+
+/**
+ * Manages a timer that implements exponential backoff for failed attempts.
+ *
+ * The first timer will fire after BASE_MILLISECONDS.  On a failure, the timer is changed to
+ * (randomInteger[0, 2^failures) + 1) * BASE_MILLISECONDS.  MAX_MILLISECONDS is used to ensure that
+ * you aren't waiting years for a timer to fire.
+ *
+ * The state is stored in shared preferences to ensure that they are kept after the device sleeps.
+ * Because multiple ExponentialBackoffSchedulers can be used by different components,
+ * the owning class must set the preference name.
+ *
+ * Timestamps are recorded in RTC to avoid situations where the phone is rebooted, messing up
+ * any timestamps generated using elapsedRealtime().
+ *
+ * This class is not thread-safe because any two different classes could be accessing the same
+ * SharedPreferences.
+ *
+ * TODO(dfalcantara): Consider making this an AlarmManagerHelper class to manage general alarms.
+ */
+@NotThreadSafe
+public class ExponentialBackoffScheduler {
+    private static final String TAG = "ExponentialBackoffScheduler";
+
+    private static final String PREFERENCE_DELAY = "delay";
+    private static final String PREFERENCE_FAILED_ATTEMPTS = "backoffFailedAttempts";
+
+    private static Random sRandom = new Random();
+
+    private static final int MAX_EXPONENT = 10;
+
+    private final long mBaseMilliseconds;
+    private final long mMaxMilliseconds;
+    private final Context mContext;
+    private final String mPreferencePackage;
+
+    /**
+     * Creates a new scheduler.
+     * @param packageName The name under which to store its state in SharedPreferences.
+     * @param context The application's context.
+     * @param baseMilliseconds Used to calculate random backoff times.
+     * @param maxMilliseconds The absolute maximum delay allowed.
+     */
+    public ExponentialBackoffScheduler(String packageName, Context context, long baseMilliseconds,
+            long maxMilliseconds) {
+        mPreferencePackage = packageName;
+        mContext = context;
+        mBaseMilliseconds = baseMilliseconds;
+        mMaxMilliseconds = maxMilliseconds;
+    }
+
+    /**
+     * Creates an alarm to fire the specified intent after a random delay.
+     * @param intent The intent to fire.
+     * @return the timestamp of the scheduled intent
+     */
+    public long createAlarm(Intent intent) {
+        long delay = generateRandomDelay();
+        long timestamp = delay + getCurrentTime();
+        return createAlarm(intent, timestamp);
+    }
+
+    /**
+     * Creates an alarm to fire the specified intent at the specified time.
+     * @param intent The intent to fire.
+     * @return the timestamp of the scheduled intent
+     */
+    public long createAlarm(Intent intent, long timestamp) {
+        PendingIntent retryPIntent = PendingIntent.getService(mContext, 0, intent, 0);
+        AlarmManager am = (AlarmManager) mContext.getSystemService(Context.ALARM_SERVICE);
+        setAlarm(am, timestamp, retryPIntent);
+        return timestamp;
+    }
+
+    /**
+     * Attempts to cancel any alarms set using the given Intent.
+     * @param scheduledIntent Intent that may have been previously scheduled.
+     * @return whether or not an alarm was canceled.
+     */
+    public boolean cancelAlarm(Intent scheduledIntent) {
+        PendingIntent pendingIntent = PendingIntent.getService(mContext, 0, scheduledIntent,
+                PendingIntent.FLAG_NO_CREATE);
+        if (pendingIntent != null) {
+            AlarmManager am = (AlarmManager) mContext.getSystemService(Context.ALARM_SERVICE);
+            am.cancel(pendingIntent);
+            pendingIntent.cancel();
+            return true;
+        } else {
+            return false;
+        }
+    }
+
+    public int getNumFailedAttempts() {
+        SharedPreferences preferences = getSharedPreferences();
+        return preferences.getInt(PREFERENCE_FAILED_ATTEMPTS, 0);
+    }
+
+    public void increaseFailedAttempts() {
+        SharedPreferences preferences = getSharedPreferences();
+        int numFailedAttempts = getNumFailedAttempts() + 1;
+        preferences.edit()
+            .putInt(PREFERENCE_FAILED_ATTEMPTS, numFailedAttempts)
+            .apply();
+    }
+
+    public void resetFailedAttempts() {
+        SharedPreferences preferences = getSharedPreferences();
+        preferences.edit()
+            .putInt(PREFERENCE_FAILED_ATTEMPTS, 0)
+            .apply();
+    }
+
+    /**
+     * Returns a timestamp representing now, according to the backoff scheduler.
+     */
+    public long getCurrentTime() {
+        return System.currentTimeMillis();
+    }
+
+    /**
+     * Returns the delay used to generate the last alarm.  If no previous alarm was generated,
+     * return the base delay.
+     */
+    public long getGeneratedDelay() {
+        SharedPreferences preferences = getSharedPreferences();
+        return preferences.getLong(PREFERENCE_DELAY, mBaseMilliseconds);
+    }
+
+    /**
+     * Sets an alarm in the alarm manager.
+     */
+    @VisibleForTesting
+    protected void setAlarm(AlarmManager am, long timestamp, PendingIntent retryPIntent) {
+        Log.v(TAG, "now(" + new Date(getCurrentTime()) + ") refiringAt("
+                + new Date(timestamp) + ")");
+        am.set(AlarmManager.RTC, timestamp, retryPIntent);
+    }
+
+    /**
+     * Determines the amount of time to wait for the current delay, then saves it.
+     * @return the number of milliseconds to wait.
+     */
+    private long generateRandomDelay() {
+        long delay;
+        int numFailedAttempts = getNumFailedAttempts();
+        if (numFailedAttempts == 0) {
+            delay = Math.min(mBaseMilliseconds, mMaxMilliseconds);
+        } else {
+            int backoffCoefficient = computeConstrainedBackoffCoefficient(numFailedAttempts);
+            delay = Math.min(backoffCoefficient * mBaseMilliseconds, mMaxMilliseconds);
+        }
+
+        // Save the delay for sanity checks.
+        SharedPreferences preferences = getSharedPreferences();
+        preferences.edit()
+            .putLong(PREFERENCE_DELAY, delay)
+            .apply();
+        return delay;
+    }
+
+    /**
+     * Calculates a random coefficient based on the number of cumulative failed attempts.
+     * @param numFailedAttempts Number of cumulative failed attempts
+     * @return A random number between 1 and 2^N, where N is the smallest value of MAX_EXPONENT and
+     *         numFailedAttempts
+     */
+    private int computeConstrainedBackoffCoefficient(int numFailedAttempts) {
+        int n = Math.min(MAX_EXPONENT, numFailedAttempts);
+        int twoToThePowerOfN = 1 << n;
+        return sRandom.nextInt(twoToThePowerOfN) + 1;
+    }
+
+    private SharedPreferences getSharedPreferences() {
+        SharedPreferences preferences =
+                mContext.getSharedPreferences(mPreferencePackage, Context.MODE_PRIVATE);
+        return preferences;
+    }
+}