chrome/browser/font_family_cache.h

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef CHROME_BROWSER_FONT_FAMILY_CACHE_H_
   6 #define CHROME_BROWSER_FONT_FAMILY_CACHE_H_
   7
   8 #include "base/containers/hash_tables.h"
   9 #include "base/gtest_prod_util.h"
  10 #include "base/prefs/pref_change_registrar.h"
  11 #include "base/strings/string16.h"
  12 #include "base/supports_user_data.h"
  13 #include "content/public/browser/notification_observer.h"
  14 #include "content/public/browser/notification_registrar.h"
  15 #include "content/public/common/web_preferences.h"
  16
  17 class PrefService;
  18 class Profile;
  19
  20 FORWARD_DECLARE_TEST(FontFamilyCacheTest, Caching);
  21
  22 // Caches font family preferences associated with a PrefService. This class
  23 // relies on the assumption that each concatenation of map_name + '.' + script
  24 // is a unique string. It also relies on the assumption that the (const char*)
  25 // keys used in both inner and outer hash_maps are compile time constants.
  26 class FontFamilyCache : public base::SupportsUserData::Data,
  27                         public content::NotificationObserver {
  28  public:
  29   explicit FontFamilyCache(Profile* profile);
  30   ~FontFamilyCache() override;
  31
  32   // Gets or creates the relevant FontFamilyCache, and then fills |map|.
  33   static void FillFontFamilyMap(Profile* profile,
  34                                 const char* map_name,
  35                                 content::ScriptFontFamilyMap* map);
  36
  37   // Fills |map| with font family preferences.
  38   void FillFontFamilyMap(const char* map_name,
  39                          content::ScriptFontFamilyMap* map);
  40
  41  protected:
  42   // Exposed and virtual for testing.
  43   // Fetches the font without checking the cache.
  44   virtual base::string16 FetchFont(const char* script, const char* map_name);
  45
  46  private:
  47   FRIEND_TEST_ALL_PREFIXES(::FontFamilyCacheTest, Caching);
  48
  49   // Map from script to font.
  50   // Key comparison uses pointer equality.
  51   typedef base::hash_map<const char*, base::string16> ScriptFontMap;
  52
  53   // Map from font family to ScriptFontMap.
  54   // Key comparison uses pointer equality.
  55   typedef base::hash_map<const char*, ScriptFontMap> FontFamilyMap;
  56
  57   // Checks the cache for the font. If not present, fetches the font and stores
  58   // the result in the cache.
  59   // This method needs to be very fast, because it's called ~20,000 times on a
  60   // fresh launch with an empty profile. It's important to avoid unnecessary
  61   // object construction, hence the heavy use of const char* and the minimal use
  62   // of std::string.
  63   // |script| and |map_name| must be compile time constants. Two behaviors rely
  64   // on this: key comparison uses pointer equality, and keys must outlive the
  65   // hash_maps.
  66   base::string16 FetchAndCacheFont(const char* script, const char* map_name);
  67
  68   // Called when font family preferences changed.
  69   // Invalidates the cached entry, and removes the relevant observer.
  70   // Note: It is safe to remove the observer from the pref change callback.
  71   void OnPrefsChanged(const std::string& pref_name);
  72
  73   // content::NotificationObserver override.
  74   // Called when the profile is being destructed.
  75   void Observe(int type,
  76                const content::NotificationSource& source,
  77                const content::NotificationDetails& details) override;
  78
  79   // Cache of font family preferences.
  80   FontFamilyMap font_family_map_;
  81
  82   // Weak reference.
  83   // Note: The lifetime of this object is tied to the lifetime of the
  84   // PrefService, so there is no worry about an invalid pointer.
  85   const PrefService* prefs_;
  86
  87   // Reacts to profile changes.
  88   PrefChangeRegistrar profile_pref_registrar_;
  89
  90   // Listens for profile destruction.
  91   content::NotificationRegistrar notification_registrar_;
  92
  93   DISALLOW_COPY_AND_ASSIGN(FontFamilyCache);
  94 };
  95
  96 #endif  // CHROME_BROWSER_FONT_FAMILY_CACHE_H_