1 files changed, 76 insertions, 0 deletions
diff --git a/browser/modules/TabUnloader.jsm b/browser/modules/TabUnloader.jsm
new file mode 100644
index 0000000000..772c7eac94
--- /dev/null
+++ b/browser/modules/TabUnloader.jsm
@@ -0,0 +1,76 @@
+/* -*- mode: js; indent-tabs-mode: nil; js-indent-level: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+var EXPORTED_SYMBOLS = ["TabUnloader"];
+
+const { Services } = ChromeUtils.import("resource://gre/modules/Services.jsm");
+
+/**
+ * This module is responsible for detecting low-memory scenarios and unloading
+ * tabs in response to them.
+ */
+
+var TabUnloader = {
+  /**
+   * Initialize low-memory detection and tab auto-unloading.
+   */
+  init() {
+    if (Services.prefs.getBoolPref("browser.tabs.unloadOnLowMemory", true)) {
+      Services.obs.addObserver(this, "memory-pressure", /* ownsWeak */ true);
+    }
+  },
+
+  observe(subject, topic, data) {
+    if (topic == "memory-pressure" && data != "heap-minimize") {
+      unloadLeastRecentlyUsedTab();
+    }
+  },
+
+  QueryInterface: ChromeUtils.generateQI([
+    "nsIObserver",
+    "nsISupportsWeakReference",
+  ]),
+};
+
+function unloadLeastRecentlyUsedTab() {
+  let bgTabBrowsers = getSortedBackgroundTabBrowsers();
+
+  for (let tb of bgTabBrowsers) {
+    if (tb.browser.discardBrowser(tb.tab)) {
+      return;
+    }
+  }
+}
+
+/* Sort tabs in the order we use for unloading, first non-pinned, non-audible
+ * tabs in LRU order, then non-audible tabs in LRU order, then non-pinned
+ * audible tabs in LRU order and finally pinned, audible tabs in LRU order. */
+function sortTabs(a, b) {
+  if (a.tab.soundPlaying != b.tab.soundPlaying) {
+    return a.tab.soundPlaying - b.tab.soundPlaying;
+  }
+
+  if (a.tab.pinned != b.tab.pinned) {
+    return a.tab.pinned - b.tab.pinned;
+  }
+
+  return a.tab.lastAccessed - b.tab.lastAccessed;
+}
+
+function getSortedBackgroundTabBrowsers() {
+  let bgTabBrowsers = [];
+
+  for (let win of Services.wm.getEnumerator("navigator:browser")) {
+    for (let tab of win.gBrowser.tabs) {
+      if (!tab.selected && tab.linkedBrowser.isConnected) {
+        bgTabBrowsers.push({ tab, browser: win.gBrowser });
+      }
+    }
+  }
+
+  return bgTabBrowsers.sort(sortTabs);
+}