From e61fde1fbd88fe7288bbb60dfc7093220c461199 Mon Sep 17 00:00:00 2001
From: Manish Goregaokar <manishsmail@gmail.com>
Date: Thu, 29 Aug 2013 09:09:51 +0200
Subject: [PATCH] Bug 506975 - Write sessionstore.js less often when on
 battery; r=ttaubert

---
 browser/app/profile/firefox.js                |  2 +
 .../sessionstore/src/SessionSaver.jsm         | 43 ++++++++++++++++---
 2 files changed, 40 insertions(+), 5 deletions(-)

diff --git a/browser/app/profile/firefox.js b/browser/app/profile/firefox.js
index 801ccf845f7..719661b84f9 100644
--- a/browser/app/profile/firefox.js
+++ b/browser/app/profile/firefox.js
@@ -820,6 +820,8 @@ pref("browser.sessionstore.resume_session_once", false);
 
 // minimal interval between two save operations in milliseconds
 pref("browser.sessionstore.interval", 15000);
+// interval when device is unplugged
+pref("browser.sessionstore.interval_battery", 60000);
 // maximum amount of POSTDATA to be saved in bytes per history entry (-1 = all of it)
 // (NB: POSTDATA will be saved either entirely or not at all)
 pref("browser.sessionstore.postdata", 0);
diff --git a/browser/components/sessionstore/src/SessionSaver.jsm b/browser/components/sessionstore/src/SessionSaver.jsm
index b1977d9727c..06fbb312e02 100644
--- a/browser/components/sessionstore/src/SessionSaver.jsm
+++ b/browser/components/sessionstore/src/SessionSaver.jsm
@@ -29,15 +29,48 @@ XPCOMUtils.defineLazyGetter(this, "gInterval", function () {
   Services.prefs.addObserver(PREF, () => {
     this.gInterval = Services.prefs.getIntPref(PREF);
 
-    // Cancel any pending runs and call runDelayed() with
-    // zero to apply the newly configured interval.
-    SessionSaverInternal.cancel();
-    SessionSaverInternal.runDelayed(0);
+    if (isBatteryCharging()) {
+      // Cancel any pending runs and call runDelayed()
+      // to apply the newly configured interval.
+      SessionSaverInternal.cancel();
+      SessionSaverInternal.runDelayed(0);
+    }
   }, false);
 
   return Services.prefs.getIntPref(PREF);
 });
 
+XPCOMUtils.defineLazyGetter(this, "gIntervalBattery", function () {
+  const PREF = "browser.sessionstore.interval_battery";
+
+  // Observer that updates the cached value when the preference changes.
+  Services.prefs.addObserver(PREF, () => {
+    this.gIntervalBattery = Services.prefs.getIntPref(PREF);
+
+    if (!isBatteryCharging()) {
+      // Cancel any pending runs and call runDelayed()
+      // to apply the newly configured interval.
+      SessionSaverInternal.cancel();
+      SessionSaverInternal.runDelayed(0);
+    }
+  }, false);
+
+  return Services.prefs.getIntPref(PREF);
+});
+
+// Check if battery is charging
+function isBatteryCharging() {
+   return Services.appShell.hiddenDOMWindow.navigator.battery.charging;
+}
+
+// Get the current session store interval based on battery status
+function getInterval() {
+  if (isBatteryCharging()) {
+    return gInterval;
+  }
+  return gIntervalBattery;
+}
+
 // Wrap a string as a nsISupports.
 function createSupportsString(data) {
   let string = Cc["@mozilla.org/supports-string;1"]
@@ -148,7 +181,7 @@ let SessionSaverInternal = {
     }
 
     // Interval until the next disk operation is allowed.
-    delay = Math.max(this._lastSaveTime + gInterval - Date.now(), delay, 0);
+    delay = Math.max(this._lastSaveTime + getInterval() - Date.now(), delay, 0);
 
     // Schedule a state save.
     this._timeoutID = setTimeout(() => this._saveState(), delay);