Issue 6855 - Release all references to Subscription object once removed

lib/filterStorage.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 131 matching lines @@
   {
     for (let i = 0; i < FilterStorage.subscriptions.length; i++)
     {
       if (FilterStorage.subscriptions[i].url == subscription.url)
       {
         removeSubscriptionFilters(subscription);
 
         FilterStorage.subscriptions.splice(i--, 1);
         FilterStorage.knownSubscriptions.delete(subscription.url);
         FilterNotifier.triggerListeners("subscription.removed", subscription);
+
+        // This should be the last remaining reference to the Subscription
+        // object.
+        Subscription.knownSubscriptions.delete(subscription.url);
         return;
       }
     }
   },
 
   /**
    * Moves a subscription in the list to a new position.
    * @param {Subscription} subscription filter subscription to be moved
    * @param {Subscription} [insertBefore] filter subscription to insert before
    *        (if omitted the subscription will be put at the end of the list)
@@ skipping 508 matching lines @@
  * notifications.
  * @param {Subscription} subscription filter subscription to be removed
  */
 function removeSubscriptionFilters(subscription)
 {
   if (!FilterStorage.knownSubscriptions.has(subscription.url))
     return;
 
   for (let filter of subscription.filters)
   {
-    let i = filter.subscriptions.indexOf(subscription);
-    if (i >= 0)
-      filter.subscriptions.splice(i, 1);
+    let index = 0;
+
+    // The same filter can occur more than once in a subscription. We could
+    // avoid making duplicate subscription entries in a Filter object in
+    // INIParser, but we don't do this in order to avoid slowing down the
+    // loading of the initial subscriptions from disk.
+    while ((index = filter.subscriptions.indexOf(subscription), index) != -1)
+      filter.subscriptions.splice(index, 1);
   }
 }
 
 /**
  * Listener returned by FilterStorage.importData(), parses filter data.
  * @constructor
  */
 function INIParser()
 {
   this.fileProperties = this.curObj = {};
@@ skipping 80 matching lines @@
       else if (this.wantObj === false && val)
         this.curObj.push(val.replace(/\\\[/g, "["));
     }
     finally
     {
       Filter.knownFilters = origKnownFilters;
       Subscription.knownSubscriptions = origKnownSubscriptions;
     }
   }
 };