Issue 7096 - Make it possible to lazy initialize a filter's subscriptions

lib/filterListener.js

Index: lib/filterListener.js
===================================================================
--- a/lib/filterListener.js
+++ b/lib/filterListener.js
@@ -135,16 +135,19 @@
  * if necessary.
  * @param {Filter} filter filter that has been added
  */
 function addFilter(filter)
 {
   if (!(filter instanceof ActiveFilter) || filter.disabled)
     return;
 
+  if (!filter.subscriptionsAdded)

[Manish Jethani, 2018/11/03 21:31:25]

The subscriptions will already be added when the subscriptions are initially
loaded, but when we move to ephemeral filter objects, newly created filter
objects won't have their subscriptions added by default.

This code runs when the subscriptions are initially loaded and then again when a
new version of a subscription is downloaded. For the latter case, the
performance will be worse than it currently is, but this happens once a day per
subscription on average, it should not be a problem. In comparison, having
ephemeral filter objects that don't have their subscriptions already added would
allow us to save several megabytes of memory (the savings come from the objects
not being added to the `Filter.knownFilters` map as well as not being held on to
in other places). It's a good tradeoff.

+    filterStorage.addSubscriptionsToFilter(filter);
+
   let hasEnabled = false;
   let allowSnippets = false;
   for (let subscription of filter.subscriptions())
   {
     if (!subscription.disabled)
     {
       hasEnabled = true;
 
@@ -184,16 +187,19 @@
  */
 function removeFilter(filter)
 {
   if (!(filter instanceof ActiveFilter))
     return;
 
   if (!filter.disabled)
   {
+    if (!filter.subscriptionsAdded)
+      filterStorage.addSubscriptionsToFilter(filter);
+
     let hasEnabled = false;
     for (let subscription of filter.subscriptions())
     {
       if (!subscription.disabled)
       {
         hasEnabled = true;
         break;
       }