base/memory/discardable_memory_provider.h

   1 // Copyright 2013 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 BASE_MEMORY_DISCARDABLE_MEMORY_PROVIDER_H_
   6 #define BASE_MEMORY_DISCARDABLE_MEMORY_PROVIDER_H_
   7
   8 #include "base/base_export.h"
   9 #include "base/containers/hash_tables.h"
  10 #include "base/containers/mru_cache.h"
  11 #include "base/memory/memory_pressure_listener.h"
  12 #include "base/synchronization/lock.h"
  13
  14 namespace base {
  15 class DiscardableMemory;
  16 }  // namespace base
  17
  18 #if defined(COMPILER_GCC)
  19 namespace BASE_HASH_NAMESPACE {
  20 template <>
  21 struct hash<const base::DiscardableMemory*> {
  22   size_t operator()(const base::DiscardableMemory* ptr) const {
  23     return hash<size_t>()(reinterpret_cast<size_t>(ptr));
  24   }
  25 };
  26 }  // namespace BASE_HASH_NAMESPACE
  27 #endif  // COMPILER
  28
  29 namespace base {
  30 namespace internal {
  31
  32 // The DiscardableMemoryProvider manages a collection of emulated
  33 // DiscardableMemory instances. It is used on platforms that do not support
  34 // discardable memory natively. It keeps track of all DiscardableMemory
  35 // instances (in case they need to be purged), and the total amount of
  36 // allocated memory (in case this forces a purge).
  37 //
  38 // When notified of memory pressure, the provider either purges the LRU
  39 // memory -- if the pressure is moderate -- or all discardable memory
  40 // if the pressure is critical.
  41 //
  42 // NB - this class is an implementation detail. It has been exposed for testing
  43 // purposes. You should not need to use this class directly.
  44 class BASE_EXPORT_PRIVATE DiscardableMemoryProvider {
  45  public:
  46   DiscardableMemoryProvider();
  47   ~DiscardableMemoryProvider();
  48
  49   // Call this to register memory pressure listener. Must be called on a
  50   // thread with a MessageLoop current.
  51   void RegisterMemoryPressureListener();
  52
  53   // Call this to unregister memory pressure listener.
  54   void UnregisterMemoryPressureListener();
  55
  56   // The maximum number of bytes of discardable memory that may be allocated
  57   // before we force a purge. If this amount is zero, it is interpreted as
  58   // having no limit at all.
  59   void SetDiscardableMemoryLimit(size_t bytes);
  60
  61   // Sets the amount of memory to reclaim when we're under moderate pressure.
  62   void SetBytesToReclaimUnderModeratePressure(size_t bytes);
  63
  64   // Adds the given discardable memory to the provider's collection.
  65   void Register(const DiscardableMemory* discardable, size_t bytes);
  66
  67   // Removes the given discardable memory from the provider's collection.
  68   void Unregister(const DiscardableMemory* discardable);
  69
  70   // Returns NULL if an error occurred. Otherwise, returns the backing buffer
  71   // and sets |purged| to indicate whether or not the backing buffer has been
  72   // purged since last use.
  73   scoped_ptr<uint8, FreeDeleter> Acquire(
  74       const DiscardableMemory* discardable, bool* purged);
  75
  76   // Release a previously acquired backing buffer. This gives the buffer back
  77   // to the provider where it can be purged if necessary.
  78   void Release(const DiscardableMemory* discardable,
  79                scoped_ptr<uint8, FreeDeleter> memory);
  80
  81   // Purges all discardable memory.
  82   void PurgeAll();
  83
  84   // Returns true if discardable memory has been added to the provider's
  85   // collection. This should only be used by tests.
  86   bool IsRegisteredForTest(const DiscardableMemory* discardable) const;
  87
  88   // Returns true if discardable memory can be purged. This should only
  89   // be used by tests.
  90   bool CanBePurgedForTest(const DiscardableMemory* discardable) const;
  91
  92   // Returns total amount of allocated discardable memory. This should only
  93   // be used by tests.
  94   size_t GetBytesAllocatedForTest() const;
  95
  96  private:
  97   struct Allocation {
  98    explicit Allocation(size_t bytes)
  99        : bytes(bytes),
 100          memory(NULL) {
 101    }
 102
 103     size_t bytes;
 104     uint8* memory;
 105   };
 106   typedef HashingMRUCache<const DiscardableMemory*, Allocation> AllocationMap;
 107
 108   // This can be called as a hint that the system is under memory pressure.
 109   void OnMemoryPressure(
 110       MemoryPressureListener::MemoryPressureLevel pressure_level);
 111
 112   // Purges |bytes_to_reclaim_under_moderate_pressure_| bytes of
 113   // discardable memory.
 114   void Purge();
 115
 116   // Purges least recently used memory until usage is less or equal to |limit|.
 117   // Caller must acquire |lock_| prior to calling this function.
 118   void PurgeLRUWithLockAcquiredUntilUsageIsWithin(size_t limit);
 119
 120   // Ensures that we don't allocate beyond our memory limit.
 121   // Caller must acquire |lock_| prior to calling this function.
 122   void EnforcePolicyWithLockAcquired();
 123
 124   // Needs to be held when accessing members.
 125   mutable Lock lock_;
 126
 127   // A MRU cache of all allocated bits of discardable memory. Used for purging.
 128   AllocationMap allocations_;
 129
 130   // The total amount of allocated discardable memory.
 131   size_t bytes_allocated_;
 132
 133   // The maximum number of bytes of discardable memory that may be allocated
 134   // before we assume moderate memory pressure.
 135   size_t discardable_memory_limit_;
 136
 137   // Under moderate memory pressure, we will purge this amount of memory.
 138   size_t bytes_to_reclaim_under_moderate_pressure_;
 139
 140   // Allows us to be respond when the system reports that it is under memory
 141   // pressure.
 142   scoped_ptr<MemoryPressureListener> memory_pressure_listener_;
 143
 144   DISALLOW_COPY_AND_ASSIGN(DiscardableMemoryProvider);
 145 };
 146
 147 }  // namespace internal
 148 }  // namespace base
 149
 150 #endif  // BASE_MEMORY_DISCARDABLE_MEMORY_PROVIDER_H_