Issue 7046 - Defer caching of domain maps

lib/filterClasses.js

Index: lib/filterClasses.js
===================================================================
--- a/lib/filterClasses.js
+++ b/lib/filterClasses.js
@@ -452,16 +452,21 @@
    * @type {?Map.<string,boolean>}
    */
   get domains()
   {
     let domains = null;
 
     if (this.domainSource)
     {
+      // For some filter types this property is accessed only rarely,
+      // especially when the subscriptions are initially loaded. We defer any
+      // caching for such filters.
+      let cacheValue = this.shouldCacheDomains();
+
       let source = this.domainSource.toLowerCase();
 
       let knownMap = knownDomainMaps.get(source);
       if (knownMap)
       {
         domains = knownMap;
       }
       else
@@ -498,25 +503,41 @@
 
             domains.set(domain, include);
           }
 
           if (domains)
             domains.set("", !hasIncludes);
         }
 
-        if (domains)
+        if (!domains || cacheValue)
           knownDomainMaps.set(source, domains);
       }
 
-      this.domainSource = null;
+      if (!domains || cacheValue)
+      {
+        this.domainSource = null;
+        Object.defineProperty(this, "domains", {value: domains});
+      }
     }
 
-    Object.defineProperty(this, "domains", {value: domains});
-    return this.domains;
+    return domains;
+  },
+
+  /**
+   * Whether the value of {@link ActiveFilter#domains} should be cached. This
+   * is meant to be overridden by subclasses that don't want the value to be
+   * cached (for better memory usage).
+   * @return {boolean} Always <code>true</code>, but may be overriden by
+   *   subclasses.
+   * @protected
+   */
+  shouldCacheDomains()
+  {
+    return true;
   },
 
   /**
    * Array containing public keys of websites that this filter should apply to
    * @type {?string[]}
    */
   sitekeys: null,
 
@@ -1149,16 +1170,45 @@
 function ElemHideBase(text, domains, selector)
 {
   ContentFilter.call(this, text, domains, selector);
 }
 exports.ElemHideBase = ElemHideBase;
 
 ElemHideBase.prototype = extend(ContentFilter, {
   /**
+   * Whether {@link ActiveFilter#domains} has been accessed at least once.
+   * @type {boolean}
+   * @private
+   */
+  _domainsAccessed: false,
+
+  /**
+   * See ActiveFilter.domains
+   * @inheritdoc
+   */
+  get domains()
+  {
+    let {get} = Object.getOwnPropertyDescriptor(ActiveFilter.prototype,
+                                                "domains");
+    let value = get.call(this);
+    this._domainsAccessed = true;
+    return value;
+  },
+
+  /**
+   * See ActiveFilter.shouldCacheDomains()
+   * @inheritdoc
+   */
+  shouldCacheDomains()
+  {
+    return this._domainsAccessed;
+  },
+
+  /**
    * CSS selector for the HTML elements that should be hidden
    * @type {string}
    */
   get selector()
   {
     // Braces are being escaped to prevent CSS rule injection.
     return this.body.replace("{", "\\7B ").replace("}", "\\7D ");
   }