android_webview/browser/global_tile_manager.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 ANDROID_WEBVIEW_BROWSER_GLOBAL_TILE_MANAGER_H_
   6 #define ANDROID_WEBVIEW_BROWSER_GLOBAL_TILE_MANAGER_H_
   7
   8 #include <list>
   9 #include "base/basictypes.h"
  10 #include "base/lazy_instance.h"
  11 #include "base/sequence_checker.h"
  12 #include "base/synchronization/lock.h"
  13
  14 namespace android_webview {
  15
  16 class GlobalTileManagerClient;
  17
  18 // A global tile manager that keeps track of the number of tile resources. Each
  19 // tile needs file descriptors (typically 2) and there is a soft limit of 1024
  20 // file descriptors per Android process. The GlobalTileManager does not keep
  21 // track of how many tiles each individual view is actually using. The purpose
  22 // of GlobalTileManager is to behave gracefully (as in not crashing) when the
  23 // embedder of webview creates a lot of webviews and draw them at the same time.
  24 class GlobalTileManager {
  25  private:
  26   typedef std::list<GlobalTileManagerClient*> ListType;
  27
  28  public:
  29   typedef ListType::iterator Key;
  30   static GlobalTileManager* GetInstance();
  31
  32   void SetTileLimit(size_t num_tiles_limit);
  33
  34   // Requests the |num_of_tiles| from the available global pool. Calls
  35   // GlobalTileManagerClient.SetNumTiles after the manager determines how many
  36   // tiles are available for the client. If the number of tiles left is not
  37   // enough to satisfy the request, the manager will evict tiles allocated to
  38   // other clients.
  39   void RequestTiles(size_t new_num_of_tiles, Key key);
  40
  41   Key PushBack(GlobalTileManagerClient* client);
  42
  43   // |key| must be already in manager. Move the tile manager client
  44   // corresponding to |key| to most recent. This function should be called after
  45   // RequestTiles.
  46   void DidUse(Key key);
  47
  48   void Remove(Key key);
  49
  50  private:
  51   friend struct base::DefaultLazyInstanceTraits<GlobalTileManager>;
  52   GlobalTileManager();
  53   ~GlobalTileManager();
  54
  55   // Continues evicting the inactive views until freeing up at least amount of
  56   // tiles specified by |desired_num_tiles| to draw a view specified by |key|,
  57   // or until all inactive views have been evicted. Returns the amount of
  58   // memory that was actually evicted. This function is called when a
  59   // request cannot be satisfied.
  60   size_t Evict(size_t desired_num_tiles, Key key);
  61
  62   // Check that the sum of all client's tiles is equal to
  63   // total_allocated_tiles_.
  64   bool IsConsistent() const;
  65
  66   size_t num_tiles_limit_;
  67
  68   size_t total_allocated_tiles_;
  69   ListType mru_list_;
  70   base::SequenceChecker sequence_checker_;
  71
  72   DISALLOW_COPY_AND_ASSIGN(GlobalTileManager);
  73 };
  74
  75 }  // namespace android_webview
  76
  77 #endif  // ANDROID_WEBVIEW_BROWSER_GLOBAL_TILE_MANAGER_H_