Issue 3815 - Fix TabAllocator. Now it returns tab with initialized outerWindowID

lib/crawler.js

 /*
  * This Source Code is subject to the terms of the Mozilla Public License
  * version 2.0 (the "License"). You can obtain a copy of the License at
  * http://mozilla.org/MPL/2.0/.
  */
 
 /**
  * @module crawler
  */
 
 Cu.import("resource://gre/modules/Services.jsm");
 Cu.import("resource://gre/modules/Task.jsm");
 Cu.import("resource://gre/modules/Promise.jsm");
 
 function abprequire(module)
 {
   let result = {};
   result.wrappedJSObject = result;
   Services.obs.notifyObservers(result, "adblockplus-require", module);
   return result.exports;
 }
 
 let {RequestNotifier} = abprequire("requestNotifier");
 let {FilterNotifier} = abprequire("filterNotifier");
 let {FilterStorage} = abprequire("filterStorage");
-
-/**
- * Creates a blank tab in the browser.
- *
- * @param {tabbrowser} browser
- *    The tabbed browser where the tab should be created.
- * @return {Promise.<tab>} promise which resolves once the tab is fully initialized.
- */
-function createTab(browser)
-{
-  let tab = browser.addTab("about:blank");
-  if (tab.linkedBrowser.outerWindowID)
-    return Promise.resolve(tab);
-  return new Promise((resolve, reject) =>
-  {
-    let onBrowserInit = (msg) =>
-    {
-      // https://bugzilla.mozilla.org/show_bug.cgi?id=1256602#c1
-      tab.linkedBrowser.messageManager.removeMessageListener("Browser:Init", onBrowserInit);
-      resolve(tab);
-    };
-    tab.linkedBrowser.messageManager.addMessageListener("Browser:Init", onBrowserInit);
-  });
-}
 
 /**
  * Allocates tabs on request but not more than maxtabs at the same time.
  *
  * @param {tabbrowser} browser
  *    The tabbed browser where tabs should be created
  * @param {int} maxtabs
  *    The maximum number of tabs to be allocated
  * @constructor
  */
 function TabAllocator(browser, maxtabs)
 {
   this._browser = browser;
   this._tabs = 0;
   this._maxtabs = maxtabs;
   // The queue containing resolve functions of promises waiting for a tab.
   this._resolvers = [];
   // Keep at least one tab alive to prevent browser from closing itself.
-  // That tab will be removed when the first tab is requested.
-  browser.removeAllTabsBut(browser.tabs[0])
+  this._tabKeepingWindowAlive = this._browser.tabs[0];
+  this._browser.removeAllTabsBut(this._tabKeepingWindowAlive);
 }
 TabAllocator.prototype = {
+  _removeTabKeepingWindowAlive: function()
+  {
+    if (!this._tabKeepingWindowAlive)
+      return;
+    this._browser.removeTab(this._tabKeepingWindowAlive);
+    delete this._tabKeepingWindowAlive;
+  },
+
+  /**
+   * Creates a blank tab in this._browser.
+   *
+   * @return {Promise.<tab>} promise which resolves once the tab is fully initialized.
+   */
+  _createTab: function()
+  {
+    this._tabs++;
+    let tab = this._browser.addTab("about:blank");
+    if (tab.linkedBrowser.outerWindowID)
+    {
+      this._removeTabKeepingWindowAlive();
+      return Promise.resolve(tab);
+    }
+    return new Promise((resolve, reject) =>
+    {
+      let onBrowserInit = (msg) =>
+      {
+        tab.linkedBrowser.messageManager.removeMessageListener("Browser:Init", onBrowserInit);
+        this._removeTabKeepingWindowAlive();
+        resolve(tab);
+      };
+      // "Browser:Init" message is sent once the browser is ready, see
+      // https://bugzil.la/1256602#c1
+      tab.linkedBrowser.messageManager.addMessageListener("Browser:Init", onBrowserInit);
+    });
+  },
+
   /**
    * Returns a promise that will resolve into a tab once a tab is allocated.
    * The tab cannot be used by other tasks until releaseTab() is called.
    *
    * @result {Promise.<tab>}
    */
   getTab: function()
   {
     if (this._tabs < this._maxtabs)
-    {
-      let tab = createTab(this._browser);
-      // Close initial tab, we don't need it anymore.
-      if (this._tabs == 0)
-        this._browser.removeTab(this._browser.tabs[0]);
-      this._tabs++;
-      return tab;
-    }
-    return new Promise((resolve, reject) =>
-    {
-      this._resolvers.push(resolve);
-    });
+      return this._createTab();
+    return new Promise((resolve, reject) => this._resolvers.push(resolve));
   },
 
   /**
    * Adds a tab back to the pool so that it can be used by other tasks.
    *
    * @param {tab} tab
    */
   releaseTab: function(tab)
   {
-    let browser = tab.parentNode.tabbrowser;
-    browser.removeTab(tab);
-
-    if (this._resolvers.length)
-      this._resolvers.shift()(createTab(this._browser));
+    // If we are about to close last tab don't close it immediately to keep
+    // the window alive. It will be closed when a new tab is created.
+    if (this._tabs > 1)
+      this._browser.removeTab(tab);
     else
-      this._tabs--;
-  }
+    {
+      // navigate away from early opened URL
+      tab.linkedBrowser.loadURI('about:blank', null, null);
+      this._tabKeepingWindowAlive = tab;
+    }
+
+    this._tabs--;
+    if (this._resolvers.length && this._tabs < this._maxtabs)
+    {
+      this._resolvers.shift()(this._createTab());
+    }
+  },
 };
 
 /**
  * Observes page loads in a particular tabbed browser.
  *
  * @param {tabbrowser} browser
  *    The tabbed browser to be observed
  * @param {int} timeout
  *    Load timeout in milliseconds
  * @constructor
@@ skipping 263 matching lines @@
 
 function reportException(e)
 {
   let stack = "";
   if (e && typeof e == "object" && "stack" in e)
     stack = e.stack + "\n";
 
   Cu.reportError(e);
   dump(e + "\n" + stack + "\n");
 }