content/common/discardable_shared_memory_heap.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 CONTENT_COMMON_DISCARDABLE_SHARED_MEMORY_HEAP_H_
   6 #define CONTENT_COMMON_DISCARDABLE_SHARED_MEMORY_HEAP_H_
   7
   8 #include "base/callback.h"
   9 #include "base/containers/hash_tables.h"
  10 #include "base/containers/linked_list.h"
  11 #include "base/memory/scoped_ptr.h"
  12 #include "base/memory/scoped_vector.h"
  13 #include "content/common/content_export.h"
  14
  15 namespace base {
  16 class DiscardableSharedMemory;
  17 }
  18
  19 namespace content {
  20
  21 // Implements a heap of discardable shared memory. An array of free lists
  22 // is used to keep track of free blocks.
  23 class CONTENT_EXPORT DiscardableSharedMemoryHeap {
  24  public:
  25   class CONTENT_EXPORT Span : public base::LinkNode<Span> {
  26    public:
  27     ~Span();
  28
  29     base::DiscardableSharedMemory* shared_memory() { return shared_memory_; }
  30     size_t start() const { return start_; }
  31     size_t length() const { return length_; }
  32
  33    private:
  34     friend class DiscardableSharedMemoryHeap;
  35
  36     Span(base::DiscardableSharedMemory* shared_memory,
  37          size_t start,
  38          size_t length);
  39
  40     base::DiscardableSharedMemory* shared_memory_;
  41     size_t start_;
  42     size_t length_;
  43
  44     DISALLOW_COPY_AND_ASSIGN(Span);
  45   };
  46
  47   explicit DiscardableSharedMemoryHeap(size_t block_size);
  48   ~DiscardableSharedMemoryHeap();
  49
  50   // Grow heap using |shared_memory| and return a span for this new memory.
  51   // |shared_memory| must be aligned to the block size and |size| must be a
  52   // multiple of the block size. |deleted_callback| is called when
  53   // |shared_memory| has been deleted.
  54   scoped_ptr<Span> Grow(scoped_ptr<base::DiscardableSharedMemory> shared_memory,
  55                         size_t size,
  56                         const base::Closure& deleted_callback);
  57
  58   // Merge |span| into the free lists. This will coalesce |span| with
  59   // neighboring free spans when possible.
  60   void MergeIntoFreeLists(scoped_ptr<Span> span);
  61
  62   // Split an allocated span into two spans, one of length |blocks| followed
  63   // by another span of length "span->length - blocks" blocks. Modifies |span|
  64   // to point to the first span of length |blocks|. Return second span.
  65   scoped_ptr<Span> Split(Span* span, size_t blocks);
  66
  67   // Search free lists for span that satisfies the request for |blocks| of
  68   // memory. If found, the span is removed from the free list and returned.
  69   // |slack| determines the fitness requirement. Only spans that are less
  70   // or equal to |blocks| + |slack| are considered, worse fitting spans are
  71   // ignored.
  72   scoped_ptr<Span> SearchFreeLists(size_t blocks, size_t slack);
  73
  74   // Release free shared memory segments.
  75   void ReleaseFreeMemory();
  76
  77   // Release shared memory segments that have been purged.
  78   void ReleasePurgedMemory();
  79
  80   // Returns total bytes of memory in heap.
  81   size_t GetSize() const;
  82
  83   // Returns bytes of memory currently in the free lists.
  84   size_t GetSizeOfFreeLists() const;
  85
  86  private:
  87   class ScopedMemorySegment {
  88    public:
  89     ScopedMemorySegment(DiscardableSharedMemoryHeap* heap,
  90                         scoped_ptr<base::DiscardableSharedMemory> shared_memory,
  91                         size_t size,
  92                         const base::Closure& deleted_callback);
  93     ~ScopedMemorySegment();
  94
  95     bool IsUsed() const;
  96     bool IsResident() const;
  97
  98    private:
  99     DiscardableSharedMemoryHeap* const heap_;
 100     scoped_ptr<base::DiscardableSharedMemory> shared_memory_;
 101     const size_t size_;
 102     const base::Closure deleted_callback_;
 103
 104     DISALLOW_COPY_AND_ASSIGN(ScopedMemorySegment);
 105   };
 106
 107   void InsertIntoFreeList(scoped_ptr<Span> span);
 108   scoped_ptr<Span> RemoveFromFreeList(Span* span);
 109   scoped_ptr<Span> Carve(Span* span, size_t blocks);
 110   void RegisterSpan(Span* span);
 111   void UnregisterSpan(Span* span);
 112   bool IsMemoryUsed(const base::DiscardableSharedMemory* shared_memory,
 113                     size_t size);
 114   bool IsMemoryResident(const base::DiscardableSharedMemory* shared_memory);
 115   void ReleaseMemory(const base::DiscardableSharedMemory* shared_memory,
 116                      size_t size);
 117
 118   size_t block_size_;
 119   size_t num_blocks_;
 120   size_t num_free_blocks_;
 121
 122   // Vector of memory segments.
 123   ScopedVector<ScopedMemorySegment> memory_segments_;
 124
 125   // Mapping from first/last block of span to Span instance.
 126   typedef base::hash_map<size_t, Span*> SpanMap;
 127   SpanMap spans_;
 128
 129   // Array of linked-lists with free discardable memory regions. For i < 256,
 130   // where the 1st entry is located at index 0 of the array, the kth entry
 131   // is a free list of runs that consist of k blocks. The 256th entry is a
 132   // free list of runs that have length >= 256 blocks.
 133   base::LinkedList<Span> free_spans_[256];
 134
 135   DISALLOW_COPY_AND_ASSIGN(DiscardableSharedMemoryHeap);
 136 };
 137
 138 }  // namespace content
 139
 140 #endif  // CONTENT_COMMON_DISCARDABLE_SHARED_MEMORY_HEAP_H_