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comparison: memory/mozalloc/VolatileBuffer.h
memory/mozalloc/VolatileBuffer.h
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| 1 /* This Source Code Form is subject to the terms of the Mozilla Public | |
| 2 * License, v. 2.0. If a copy of the MPL was not distributed with this | |
| 3 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ | |
| 4 | |
| 5 #ifndef mozalloc_VolatileBuffer_h | |
| 6 #define mozalloc_VolatileBuffer_h | |
| 7 | |
| 8 #include "mozilla/mozalloc.h" | |
| 9 #include "mozilla/RefPtr.h" | |
| 10 #include "mozilla/MemoryReporting.h" | |
| 11 #include "mozilla/NullPtr.h" | |
| 12 | |
| 13 /* VolatileBuffer | |
| 14 * | |
| 15 * This class represents a piece of memory that can potentially be reclaimed | |
| 16 * by the OS when not in use. As long as there are one or more | |
| 17 * VolatileBufferPtrs holding on to a VolatileBuffer, the memory will remain | |
| 18 * available. However, when there are no VolatileBufferPtrs holding a | |
| 19 * VolatileBuffer, the OS can purge the pages if it wants to. The OS can make | |
| 20 * better decisions about what pages to purge than we can. | |
| 21 * | |
| 22 * VolatileBuffers may not always be volatile - if the allocation is too small, | |
| 23 * or if the OS doesn't support the feature, or if the OS doesn't want to, | |
| 24 * the buffer will be allocated on heap. | |
| 25 * | |
| 26 * VolatileBuffer allocations are fallible. They are intended for uses where | |
| 27 * one may allocate large buffers for caching data. Init() must be called | |
| 28 * exactly once. | |
| 29 * | |
| 30 * After getting a reference to VolatileBuffer using VolatileBufferPtr, | |
| 31 * WasPurged() can be used to check if the OS purged any pages in the buffer. | |
| 32 * The OS cannot purge a buffer immediately after a VolatileBuffer is | |
| 33 * initialized. At least one VolatileBufferPtr must be created before the | |
| 34 * buffer can be purged, so the first use of VolatileBufferPtr does not need | |
| 35 * to check WasPurged(). | |
| 36 * | |
| 37 * When a buffer is purged, some or all of the buffer is zeroed out. This | |
| 38 * API cannot tell which parts of the buffer were lost. | |
| 39 * | |
| 40 * VolatileBuffer is not thread safe. Do not use VolatileBufferPtrs on | |
| 41 * different threads. | |
| 42 */ | |
| 43 | |
| 44 namespace mozilla { | |
| 45 | |
| 46 class MOZALLOC_EXPORT VolatileBuffer : public RefCounted<VolatileBuffer> | |
| 47 { | |
| 48 friend class VolatileBufferPtr_base; | |
| 49 public: | |
| 50 MOZ_DECLARE_REFCOUNTED_TYPENAME(VolatileBuffer) | |
| 51 VolatileBuffer(); | |
| 52 ~VolatileBuffer(); | |
| 53 | |
| 54 /* aAlignment must be a multiple of the pointer size */ | |
| 55 bool Init(size_t aSize, size_t aAlignment = sizeof(void*)); | |
| 56 | |
| 57 size_t HeapSizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const; | |
| 58 size_t NonHeapSizeOfExcludingThis() const; | |
| 59 bool OnHeap() const; | |
| 60 | |
| 61 protected: | |
| 62 bool Lock(void** aBuf); | |
| 63 void Unlock(); | |
| 64 | |
| 65 private: | |
| 66 void* mBuf; | |
| 67 size_t mSize; | |
| 68 int mLockCount; | |
| 69 #if defined(ANDROID) | |
| 70 int mFd; | |
| 71 #elif defined(XP_DARWIN) | |
| 72 bool mHeap; | |
| 73 #elif defined(XP_WIN) | |
| 74 bool mHeap; | |
| 75 bool mFirstLock; | |
| 76 #endif | |
| 77 }; | |
| 78 | |
| 79 class VolatileBufferPtr_base { | |
| 80 public: | |
| 81 VolatileBufferPtr_base(VolatileBuffer* vbuf) : mVBuf(vbuf) { | |
| 82 if (vbuf) { | |
| 83 mPurged = !vbuf->Lock(&mMapping); | |
| 84 } else { | |
| 85 mMapping = nullptr; | |
| 86 mPurged = false; | |
| 87 } | |
| 88 } | |
| 89 | |
| 90 ~VolatileBufferPtr_base() { | |
| 91 if (mVBuf) { | |
| 92 mVBuf->Unlock(); | |
| 93 } | |
| 94 } | |
| 95 | |
| 96 bool WasBufferPurged() const { | |
| 97 return mPurged; | |
| 98 } | |
| 99 | |
| 100 protected: | |
| 101 void* mMapping; | |
| 102 | |
| 103 private: | |
| 104 RefPtr<VolatileBuffer> mVBuf; | |
| 105 bool mPurged; | |
| 106 }; | |
| 107 | |
| 108 template <class T> | |
| 109 class VolatileBufferPtr : public VolatileBufferPtr_base | |
| 110 { | |
| 111 public: | |
| 112 VolatileBufferPtr(VolatileBuffer* vbuf) : VolatileBufferPtr_base(vbuf) {} | |
| 113 | |
| 114 operator T*() const { | |
| 115 return (T*) mMapping; | |
| 116 } | |
| 117 }; | |
| 118 | |
| 119 }; /* namespace mozilla */ | |
| 120 | |
| 121 #endif /* mozalloc_VolatileBuffer_h */ |
