1// Copyright (c) 2011 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// This is the browser side of the cache manager, it tracks the activity of the
6// render processes and allocates available memory cache resources.
7
8#ifndef CHROME_BROWSER_RENDERER_HOST_WEB_CACHE_MANAGER_H_
9#define CHROME_BROWSER_RENDERER_HOST_WEB_CACHE_MANAGER_H_
10
11#include <list>
12#include <map>
13#include <set>
14
15#include "base/basictypes.h"
16#include "base/compiler_specific.h"
17#include "base/gtest_prod_util.h"
18#include "base/memory/weak_ptr.h"
19#include "base/time/time.h"
20#include "content/public/browser/notification_observer.h"
21#include "content/public/browser/notification_registrar.h"
22#include "third_party/WebKit/public/web/WebCache.h"
23
24template<typename Type>
25struct DefaultSingletonTraits;
26class PrefRegistrySimple;
27
28class WebCacheManager : public content::NotificationObserver {
29  friend class WebCacheManagerTest;
30  FRIEND_TEST_ALL_PREFIXES(WebCacheManagerBrowserTest, CrashOnceOnly);
31
32 public:
33  static void RegisterPrefs(PrefRegistrySimple* registry);
34
35  // Gets the singleton WebCacheManager object.  The first time this method
36  // is called, a WebCacheManager object is constructed and returned.
37  // Subsequent calls will return the same object.
38  static WebCacheManager* GetInstance();
39
40  // When a render process is created, it registers itself with the cache
41  // manager host, causing the renderer to be allocated cache resources.
42  void Add(int renderer_id);
43
44  // When a render process ends, it removes itself from the cache manager host,
45  // freeing the manager to assign its cache resources to other renderers.
46  void Remove(int renderer_id);
47
48  // The cache manager assigns more cache resources to active renderer.  When a
49  // renderer is active, it should inform the cache manager to receive more
50  // cache resources.
51  //
52  // When a renderer moves from being inactive to being active, the cache
53  // manager may decide to adjust its resource allocation, but it will delay
54  // the recalculation, allowing ObserveActivity to return quickly.
55  void ObserveActivity(int renderer_id);
56
57  // Periodically, renderers should inform the cache manager of their current
58  // statistics.  The more up-to-date the cache manager's statistics, the
59  // better it can allocate cache resources.
60  void ObserveStats(
61      int renderer_id, const WebKit::WebCache::UsageStats& stats);
62
63  // The global limit on the number of bytes in all the in-memory caches.
64  size_t global_size_limit() const { return global_size_limit_; }
65
66  // Sets the global size limit, forcing a recalculation of cache allocations.
67  void SetGlobalSizeLimit(size_t bytes);
68
69  // Clears all in-memory caches.
70  void ClearCache();
71
72  // Clears all in-memory caches when a tab is reloaded or the user navigates
73  // to a different website.
74  void ClearCacheOnNavigation();
75
76  // content::NotificationObserver implementation:
77  virtual void Observe(int type,
78                       const content::NotificationSource& source,
79                       const content::NotificationDetails& details) OVERRIDE;
80
81  // Gets the default global size limit.  This interrogates system metrics to
82  // tune the default size to the current system.
83  static size_t GetDefaultGlobalSizeLimit();
84
85 protected:
86  // The amount of idle time before we consider a tab to be "inactive"
87  static const int kRendererInactiveThresholdMinutes = 5;
88
89  // Keep track of some renderer information.
90  struct RendererInfo : WebKit::WebCache::UsageStats {
91    // The access time for this renderer.
92    base::Time access;
93  };
94
95  typedef std::map<int, RendererInfo> StatsMap;
96
97  // An allocation is the number of bytes a specific renderer should use for
98  // its cache.
99  typedef std::pair<int,size_t> Allocation;
100
101  // An allocation strategy is a list of allocations specifying the resources
102  // each renderer is permitted to consume for its cache.
103  typedef std::list<Allocation> AllocationStrategy;
104
105  // This class is a singleton.  Do not instantiate directly.
106  WebCacheManager();
107  friend struct DefaultSingletonTraits<WebCacheManager>;
108
109  virtual ~WebCacheManager();
110
111  // Recomputes the allocation of cache resources among the renderers.  Also
112  // informs the renderers of their new allocation.
113  void ReviseAllocationStrategy();
114
115  // Schedules a call to ReviseAllocationStrategy after a short delay.
116  void ReviseAllocationStrategyLater();
117
118  // The various tactics used as part of an allocation strategy.  To decide
119  // how many resources a given renderer should be allocated, we consider its
120  // usage statistics.  Each tactic specifies the function that maps usage
121  // statistics to resource allocations.
122  //
123  // Determining a resource allocation strategy amounts to picking a tactic
124  // for each renderer and checking that the total memory required fits within
125  // our |global_size_limit_|.
126  enum AllocationTactic {
127    // Ignore cache statistics and divide resources equally among the given
128    // set of caches.
129    DIVIDE_EVENLY,
130
131    // Allow each renderer to keep its current set of cached resources, with
132    // some extra allocation to store new objects.
133    KEEP_CURRENT_WITH_HEADROOM,
134
135    // Allow each renderer to keep its current set of cached resources.
136    KEEP_CURRENT,
137
138    // Allow each renderer to keep cache resources it believes are currently
139    // being used, with some extra allocation to store new objects.
140    KEEP_LIVE_WITH_HEADROOM,
141
142    // Allow each renderer to keep cache resources it believes are currently
143    // being used, but instruct the renderer to discard all other data.
144    KEEP_LIVE,
145  };
146
147  // Helper functions for devising an allocation strategy
148
149  // Add up all the stats from the given set of renderers and place the result
150  // in |stats|.
151  void GatherStats(const std::set<int>& renderers,
152                   WebKit::WebCache::UsageStats* stats);
153
154  // Get the amount of memory that would be required to implement |tactic|
155  // using the specified allocation tactic.  This function defines the
156  // semantics for each of the tactics.
157  static size_t GetSize(AllocationTactic tactic,
158                        const WebKit::WebCache::UsageStats& stats);
159
160  // Attempt to use the specified tactics to compute an allocation strategy
161  // and place the result in |strategy|.  |active_stats| and |inactive_stats|
162  // are the aggregate statistics for |active_renderers_| and
163  // |inactive_renderers_|, respectively.
164  //
165  // Returns |true| on success and |false| on failure.  Does not modify
166  // |strategy| on failure.
167  bool AttemptTactic(AllocationTactic active_tactic,
168                     const WebKit::WebCache::UsageStats& active_stats,
169                     AllocationTactic inactive_tactic,
170                     const WebKit::WebCache::UsageStats& inactive_stats,
171                     AllocationStrategy* strategy);
172
173  // For each renderer in |renderers|, computes its allocation according to
174  // |tactic| and add the result to |strategy|.  Any |extra_bytes_to_allocate|
175  // is divided evenly among the renderers.
176  void AddToStrategy(const std::set<int>& renderers,
177                     AllocationTactic tactic,
178                     size_t extra_bytes_to_allocate,
179                     AllocationStrategy* strategy);
180
181  // Enact an allocation strategy by informing the renderers of their
182  // allocations according to |strategy|.
183  void EnactStrategy(const AllocationStrategy& strategy);
184
185  enum ClearCacheOccasion {
186    // Instructs to clear the cache instantly.
187    INSTANTLY,
188    // Instructs to clear the cache when a navigation takes place (this
189    // includes reloading a tab).
190    ON_NAVIGATION
191  };
192
193  // Inform all |renderers| to clear their cache.
194  void ClearRendererCache(const std::set<int>& renderers,
195                          ClearCacheOccasion occation);
196
197  // Check to see if any active renderers have fallen inactive.
198  void FindInactiveRenderers();
199
200  // The global size limit for all in-memory caches.
201  size_t global_size_limit_;
202
203  // Maps every renderer_id our most recent copy of its statistics.
204  StatsMap stats_;
205
206  // Every renderer we think is still around is in one of these two sets.
207  //
208  // Active renderers are those renderers that have been active more recently
209  // than they have been inactive.
210  std::set<int> active_renderers_;
211  // Inactive renderers are those renderers that have been inactive more
212  // recently than they have been active.
213  std::set<int> inactive_renderers_;
214
215  base::WeakPtrFactory<WebCacheManager> weak_factory_;
216
217  content::NotificationRegistrar registrar_;
218
219  DISALLOW_COPY_AND_ASSIGN(WebCacheManager);
220};
221
222#endif  // CHROME_BROWSER_RENDERER_HOST_WEB_CACHE_MANAGER_H_
223