text: // Copyright (c) 2011 The Chromium Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style license that can be
  // found in the LICENSE file.
  
  // This is the browser side of the cache manager, it tracks the activity of the
  // render processes and allocates available memory cache resources.
  
  #ifndef CHROME_BROWSER_RENDERER_HOST_WEB_CACHE_MANAGER_H_
  #define CHROME_BROWSER_RENDERER_HOST_WEB_CACHE_MANAGER_H_
  
  #include <list>
  #include <map>
  #include <set>
  
  #include "base/basictypes.h"
  #include "base/compiler_specific.h"
  #include "base/gtest_prod_util.h"
  #include "base/memory/weak_ptr.h"
  #include "base/time/time.h"
  #include "content/public/browser/notification_observer.h"
  #include "content/public/browser/notification_registrar.h"
  #include "third_party/WebKit/public/web/WebCache.h"
  
  template<typename Type>
  struct DefaultSingletonTraits;
  class PrefRegistrySimple;
  
  class WebCacheManager : public content::NotificationObserver {
    friend class WebCacheManagerTest;
    FRIEND_TEST_ALL_PREFIXES(WebCacheManagerBrowserTest, CrashOnceOnly);
  
   public:
    static void RegisterPrefs(PrefRegistrySimple* registry);
  
    // Gets the singleton WebCacheManager object.  The first time this method
    // is called, a WebCacheManager object is constructed and returned.
    // Subsequent calls will return the same object.
    static WebCacheManager* GetInstance();
  
    // When a render process is created, it registers itself with the cache
    // manager host, causing the renderer to be allocated cache resources.
    void Add(int renderer_id);
  
    // When a render process ends, it removes itself from the cache manager host,
    // freeing the manager to assign its cache resources to other renderers.
    void Remove(int renderer_id);
  
    // The cache manager assigns more cache resources to active renderer.  When a
    // renderer is active, it should inform the cache manager to receive more
    // cache resources.
    //
    // When a renderer moves from being inactive to being active, the cache
    // manager may decide to adjust its resource allocation, but it will delay
    // the recalculation, allowing ObserveActivity to return quickly.
    void ObserveActivity(int renderer_id);
  
    // Periodically, renderers should inform the cache manager of their current
    // statistics.  The more up-to-date the cache manager's statistics, the
    // better it can allocate cache resources.
    void ObserveStats(
        int renderer_id, const blink::WebCache::UsageStats& stats);
  
    // The global limit on the number of bytes in all the in-memory caches.
    size_t global_size_limit() const { return global_size_limit_; }
  
    // Sets the global size limit, forcing a recalculation of cache allocations.
    void SetGlobalSizeLimit(size_t bytes);
  
    // Clears all in-memory caches.
    void ClearCache();
  
    // Clears all in-memory caches when a tab is reloaded or the user navigates
    // to a different website.
    void ClearCacheOnNavigation();
  
    // content::NotificationObserver implementation:
    virtual void Observe(int type,
                         const content::NotificationSource& source,
                         const content::NotificationDetails& details) OVERRIDE;
  
    // Gets the default global size limit.  This interrogates system metrics to
    // tune the default size to the current system.
    static size_t GetDefaultGlobalSizeLimit();
  
   protected:
    // The amount of idle time before we consider a tab to be "inactive"
    static const int kRendererInactiveThresholdMinutes = 5;
  
    // Keep track of some renderer information.
    struct RendererInfo : blink::WebCache::UsageStats {
      // The access time for this renderer.
      base::Time access;
    };
  
    typedef std::map<int, RendererInfo> StatsMap;
  
    // An allocation is the number of bytes a specific renderer should use for
    // its cache.
    typedef std::pair<int,size_t> Allocation;
  
    // An allocation strategy is a list of allocations specifying the resources
    // each renderer is permitted to consume for its cache.
    typedef std::list<Allocation> AllocationStrategy;
  
    // This class is a singleton.  Do not instantiate directly.
    WebCacheManager();
    friend struct DefaultSingletonTraits<WebCacheManager>;
  
    virtual ~WebCacheManager();
  
    // Recomputes the allocation of cache resources among the renderers.  Also
    // informs the renderers of their new allocation.
    void ReviseAllocationStrategy();
  
    // Schedules a call to ReviseAllocationStrategy after a short delay.
    void ReviseAllocationStrategyLater();
  
    // The various tactics used as part of an allocation strategy.  To decide
    // how many resources a given renderer should be allocated, we consider its
    // usage statistics.  Each tactic specifies the function that maps usage
    // statistics to resource allocations.
    //
    // Determining a resource allocation strategy amounts to picking a tactic
    // for each renderer and checking that the total memory required fits within
    // our |global_size_limit_|.
    enum AllocationTactic {
      // Ignore cache statistics and divide resources equally among the given
      // set of caches.
      DIVIDE_EVENLY,
  
      // Allow each renderer to keep its current set of cached resources, with
      // some extra allocation to store new objects.
      KEEP_CURRENT_WITH_HEADROOM,
  
      // Allow each renderer to keep its current set of cached resources.
      KEEP_CURRENT,
  
      // Allow each renderer to keep cache resources it believes are currently
      // being used, with some extra allocation to store new objects.
      KEEP_LIVE_WITH_HEADROOM,
  
      // Allow each renderer to keep cache resources it believes are currently
      // being used, but instruct the renderer to discard all other data.
      KEEP_LIVE,
    };
  
    // Helper functions for devising an allocation strategy
  
    // Add up all the stats from the given set of renderers and place the result
    // in |stats|.
    void GatherStats(const std::set<int>& renderers,
                     blink::WebCache::UsageStats* stats);
  
    // Get the amount of memory that would be required to implement |tactic|
    // using the specified allocation tactic.  This function defines the
    // semantics for each of the tactics.
    static size_t GetSize(AllocationTactic tactic,
                          const blink::WebCache::UsageStats& stats);
  
    // Attempt to use the specified tactics to compute an allocation strategy
    // and place the result in |strategy|.  |active_stats| and |inactive_stats|
    // are the aggregate statistics for |active_renderers_| and
    // |inactive_renderers_|, respectively.
    //
    // Returns |true| on success and |false| on failure.  Does not modify
    // |strategy| on failure.
    bool AttemptTactic(AllocationTactic active_tactic,
                       const blink::WebCache::UsageStats& active_stats,
                       AllocationTactic inactive_tactic,
                       const blink::WebCache::UsageStats& inactive_stats,
                       AllocationStrategy* strategy);
  
    // For each renderer in |renderers|, computes its allocation according to
    // |tactic| and add the result to |strategy|.  Any |extra_bytes_to_allocate|
    // is divided evenly among the renderers.
    void AddToStrategy(const std::set<int>& renderers,
                       AllocationTactic tactic,
                       size_t extra_bytes_to_allocate,
                       AllocationStrategy* strategy);
  
    // Enact an allocation strategy by informing the renderers of their
    // allocations according to |strategy|.
    void EnactStrategy(const AllocationStrategy& strategy);
  
    enum ClearCacheOccasion {
      // Instructs to clear the cache instantly.
      INSTANTLY,
      // Instructs to clear the cache when a navigation takes place (this
      // includes reloading a tab).
      ON_NAVIGATION
    };
  
    // Inform all |renderers| to clear their cache.
    void ClearRendererCache(const std::set<int>& renderers,
                            ClearCacheOccasion occation);
  
    // Check to see if any active renderers have fallen inactive.
    void FindInactiveRenderers();
  
    // The global size limit for all in-memory caches.
    size_t global_size_limit_;
  
    // Maps every renderer_id our most recent copy of its statistics.
    StatsMap stats_;
  
    // Every renderer we think is still around is in one of these two sets.
    //
    // Active renderers are those renderers that have been active more recently
    // than they have been inactive.
    std::set<int> active_renderers_;
    // Inactive renderers are those renderers that have been inactive more
    // recently than they have been active.
    std::set<int> inactive_renderers_;
  
    base::WeakPtrFactory<WebCacheManager> weak_factory_;
  
    content::NotificationRegistrar registrar_;
  
    DISALLOW_COPY_AND_ASSIGN(WebCacheManager);
  };
  
  #endif  // CHROME_BROWSER_RENDERER_HOST_WEB_CACHE_MANAGER_H_
  