Issue 4057 - Further speedup ElemHide.getSelectorsforDomain

lib/elemHide.js

Index: lib/elemHide.js
diff --git a/lib/elemHide.js b/lib/elemHide.js
index 574ef91dff6340a1e9408571fef1b31726cec78c..c7ba87f7645603bc14242f79ae60c9cdb54948a0 100644
--- a/lib/elemHide.js
+++ b/lib/elemHide.js
@@ -40,17 +40,31 @@ var filterByKey = [];
 var keyByFilter = Object.create(null);
 
 /**
- * Nested lookup table, filter (or false if inactive) by filter text by domain
+ * Indicates whether we are using the getSelectorsForDomain function and
+ * therefore mainting the required filtersByDomain, filtersBySelector and
+ * unconditionalSelectors lookups. (Will be false for Firefox)
+ * @type Boolean
+ */
+var usingGetSelectorsForDomain = !("nsIStyleSheetService" in Ci);
+
+/**
+ * Nested lookup table, filter (or false if inactive) by filter key by domain.
+ * (Only contains filters that aren't unconditionally matched for all domains.)
  * @type Object
  */
 var filtersByDomain = Object.create(null);
 
 /**
- * Indicates whether we are using (and maintaining) the filtersByDomain lookup.
- * (Will be false for Firefox)
- * @type Boolean
+ * Lookup table, filters by selector. (Only contains filters that have a
+ * selector that is unconditionally matched for all domains.)
  */
-var usingFiltersByDomain = !("nsIStyleSheetService" in Ci);
+var filtersBySelector = Object.create(null);
+
+/**
+ * Array of selectors which unconditionally apply to all domains, or null if
+ * the array needs to be regenerated.

[Wladimir Palant, 2016/05/25 10:43:03]

Maybe change the description to better indicate what function this array has
now, something like:

  This array caches the keys of filtersBySelector table (selectors which
unconditionally apply on all domains). It will be null if the cache needs to be
rebuilt.

[kzar, 2016/05/25 10:51:28]

Done.

+ */
+var unconditionalSelectors = [];

[Wladimir Palant, 2016/05/25 10:43:03]

Nit: Please initialize with null here and in clear(), this is now purely a cache
which is built on demand. While technically initializing with an empty array is
correct, in 99.9999% of the cases we will immediately throw away that array
again.

[kzar, 2016/05/25 10:51:28]

Done.

 
 /**
  * Object to be used instead when a filter has a blank domains property.
@@ -119,12 +133,31 @@ var ElemHide = exports.ElemHide =
     filterByKey = [];
     keyByFilter = Object.create(null);
     filtersByDomain = Object.create(null);
+    filtersBySelector = Object.create(null);
+    unconditionalSelectors = [];
     knownExceptions = Object.create(null);
     exceptions = Object.create(null);
     ElemHide.isDirty = false;
     ElemHide.unapply();
   },
 
+  _addToFiltersByDomain: function(filter)
+  {
+    let key = keyByFilter[filter.text];
+    let domains = filter.domains || defaultDomains;
+    for (let domain in domains)
+    {
+      let filters = filtersByDomain[domain];
+      if (!filters)
+        filters = filtersByDomain[domain] = Object.create(null);
+
+      if (domains[domain])
+        filters[key] = filter;
+      else
+        filters[key] = false;
+    }
+  },
+
   /**
    * Add a new element hiding filter
    * @param {ElemHideFilter} filter
@@ -140,6 +173,22 @@ var ElemHide = exports.ElemHide =
       if (!(selector in exceptions))
         exceptions[selector] = [];
       exceptions[selector].push(filter);
+
+      if (usingGetSelectorsForDomain)
+      {
+        // If this is the first exception for a previously unconditionally
+        // applied element hiding selector we need to take care to update the
+        // lookups.
+        let unconditionalFilters = filtersBySelector[selector];
+        if (unconditionalFilters)
+        {
+          for (let f of unconditionalFilters)
+            this._addToFiltersByDomain(f);
+          delete filtersBySelector[selector];
+          unconditionalSelectors = null;
+        }
+      }
+
       knownExceptions[filter.text] = true;
     }
     else
@@ -150,19 +199,26 @@ var ElemHide = exports.ElemHide =
       let key = filterByKey.push(filter) - 1;
       keyByFilter[filter.text] = key;
 
-      if (usingFiltersByDomain)
+      if (usingGetSelectorsForDomain)
       {
-        let domains = filter.domains || defaultDomains;
-        for (let domain in domains)
+        if (!(filter.domains || filter.selector in exceptions))
         {
-          let filters = filtersByDomain[domain];
-          if (!filters)
-            filters = filtersByDomain[domain] = Object.create(null);
-
-          if (domains[domain])
-            filters[filter.text] = filter;
+          // The new filter's selector is unconditionally applied to all domains
+          let filters = filtersBySelector[filter.selector];
+          if (filters)
+          {
+            filters.push(filter);
+          }
           else
-            filters[filter.text] = false;
+          {
+            filtersBySelector[filter.selector] = [filter];
+            unconditionalSelectors = null;
+          }
+        }
+        else
+        {
+          // The new filter's selector only applies to some domains
+          this._addToFiltersByDomain(filter);
         }
       }
 
@@ -197,14 +253,31 @@ var ElemHide = exports.ElemHide =
       delete keyByFilter[filter.text];
       ElemHide.isDirty = true;
 
-      if (usingFiltersByDomain)
+      if (usingGetSelectorsForDomain)
       {
-        let domains = filter.domains || defaultDomains;
-        for (let domain in domains)
+        let filters = filtersBySelector[filter.selector];
+        if (filters)
         {
-          let filters = filtersByDomain[domain];
-          if (filters)
-            delete filters[filter.text];
+          if (filters.length > 1)
+          {
+            let index = filters.indexOf(filter);
+            filters.splice(index, 1);
+          }
+          else
+          {
+            delete filtersBySelector[filter.selector];
+            unconditionalSelectors = null;
+          }
+        }
+        else
+        {
+          let domains = filter.domains || defaultDomains;
+          for (let domain in domains)
+          {
+            let filters = filtersByDomain[domain];
+            if (filters)
+              delete filters[key];
+          }
         }
       }
     }
@@ -416,14 +489,16 @@ var ElemHide = exports.ElemHide =
 
   /**
    * Returns a list of all selectors active on a particular domain, must not be
-   * used in Firefox (when usingFiltersByDomain is false).
+   * used in Firefox (when usingGetSelectorsForDomain is false).
    */
   getSelectorsForDomain: function(/**String*/ domain, /**Boolean*/ specificOnly)
   {
-    if (!usingFiltersByDomain)
+    if (!usingGetSelectorsForDomain)
       throw new Error("getSelectorsForDomain can not be used in Firefox!");
 
-    let selectors = [];
+    if (!unconditionalSelectors)
+      unconditionalSelectors = Object.keys(filtersBySelector);
+    let selectors = specificOnly ? [] : unconditionalSelectors.slice();
 
     let seenFilters = Object.create(null);
     let currentDomain = domain ? domain.toUpperCase() : "";
@@ -435,13 +510,13 @@ var ElemHide = exports.ElemHide =
       let filters = filtersByDomain[currentDomain];
       if (filters)
       {
-        for (let filterText in filters)
+        for (let filterKey in filters)
         {
-          if (filterText in seenFilters)
+          if (filterKey in seenFilters)
             continue;
-          seenFilters[filterText] = true;
+          seenFilters[filterKey] = true;
 
-          let filter = filters[filterText];
+          let filter = filters[filterKey];
           if (filter && !this.getException(filter, domain))
             selectors.push(filter.selector);
         }