Issue 6855 - Release all references to Subscription object once removed

lib/filterStorage.js

Index: lib/filterStorage.js
===================================================================
--- a/lib/filterStorage.js
+++ b/lib/filterStorage.js
@@ -143,16 +143,21 @@
     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);
+
+        // This should be the last remaining reference to the Subscription
+        // object.
+        Subscription.knownSubscriptions.delete(subscription.url);
+
         FilterNotifier.triggerListeners("subscription.removed", subscription);
         return;
       }
     }
   },
 
   /**
    * Moves a subscription in the list to a new position.
@@ -672,19 +677,24 @@
  */
 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()