memory/mozalloc/VolatileBuffer.h@b8a032363ba2 (annotated)
memory/mozalloc/VolatileBuffer.h
Thu, 22 Jan 2015 13:21:57 +0100
- author
- Michael Schloh von Bennewitz <michael@schloh.com>
- date
- Thu, 22 Jan 2015 13:21:57 +0100
- branch
- TOR_BUG_9701
- changeset 15
- b8a032363ba2
- permissions
- -rw-r--r--
Incorporate requested changes from Mozilla in review:
https://bugzilla.mozilla.org/show_bug.cgi?id=1123480#c6
| michael@0 | 1 | /* This Source Code Form is subject to the terms of the Mozilla Public |
| michael@0 | 2 | * License, v. 2.0. If a copy of the MPL was not distributed with this |
| michael@0 | 3 | * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ |
| michael@0 | 4 | |
| michael@0 | 5 | #ifndef mozalloc_VolatileBuffer_h |
| michael@0 | 6 | #define mozalloc_VolatileBuffer_h |
| michael@0 | 7 | |
| michael@0 | 8 | #include "mozilla/mozalloc.h" |
| michael@0 | 9 | #include "mozilla/RefPtr.h" |
| michael@0 | 10 | #include "mozilla/MemoryReporting.h" |
| michael@0 | 11 | #include "mozilla/NullPtr.h" |
| michael@0 | 12 | |
| michael@0 | 13 | /* VolatileBuffer |
| michael@0 | 14 | * |
| michael@0 | 15 | * This class represents a piece of memory that can potentially be reclaimed |
| michael@0 | 16 | * by the OS when not in use. As long as there are one or more |
| michael@0 | 17 | * VolatileBufferPtrs holding on to a VolatileBuffer, the memory will remain |
| michael@0 | 18 | * available. However, when there are no VolatileBufferPtrs holding a |
| michael@0 | 19 | * VolatileBuffer, the OS can purge the pages if it wants to. The OS can make |
| michael@0 | 20 | * better decisions about what pages to purge than we can. |
| michael@0 | 21 | * |
| michael@0 | 22 | * VolatileBuffers may not always be volatile - if the allocation is too small, |
| michael@0 | 23 | * or if the OS doesn't support the feature, or if the OS doesn't want to, |
| michael@0 | 24 | * the buffer will be allocated on heap. |
| michael@0 | 25 | * |
| michael@0 | 26 | * VolatileBuffer allocations are fallible. They are intended for uses where |
| michael@0 | 27 | * one may allocate large buffers for caching data. Init() must be called |
| michael@0 | 28 | * exactly once. |
| michael@0 | 29 | * |
| michael@0 | 30 | * After getting a reference to VolatileBuffer using VolatileBufferPtr, |
| michael@0 | 31 | * WasPurged() can be used to check if the OS purged any pages in the buffer. |
| michael@0 | 32 | * The OS cannot purge a buffer immediately after a VolatileBuffer is |
| michael@0 | 33 | * initialized. At least one VolatileBufferPtr must be created before the |
| michael@0 | 34 | * buffer can be purged, so the first use of VolatileBufferPtr does not need |
| michael@0 | 35 | * to check WasPurged(). |
| michael@0 | 36 | * |
| michael@0 | 37 | * When a buffer is purged, some or all of the buffer is zeroed out. This |
| michael@0 | 38 | * API cannot tell which parts of the buffer were lost. |
| michael@0 | 39 | * |
| michael@0 | 40 | * VolatileBuffer is not thread safe. Do not use VolatileBufferPtrs on |
| michael@0 | 41 | * different threads. |
| michael@0 | 42 | */ |
| michael@0 | 43 | |
| michael@0 | 44 | namespace mozilla { |
| michael@0 | 45 | |
| michael@0 | 46 | class MOZALLOC_EXPORT VolatileBuffer : public RefCounted<VolatileBuffer> |
| michael@0 | 47 | { |
| michael@0 | 48 | friend class VolatileBufferPtr_base; |
| michael@0 | 49 | public: |
| michael@0 | 50 | MOZ_DECLARE_REFCOUNTED_TYPENAME(VolatileBuffer) |
| michael@0 | 51 | VolatileBuffer(); |
| michael@0 | 52 | ~VolatileBuffer(); |
| michael@0 | 53 | |
| michael@0 | 54 | /* aAlignment must be a multiple of the pointer size */ |
| michael@0 | 55 | bool Init(size_t aSize, size_t aAlignment = sizeof(void*)); |
| michael@0 | 56 | |
| michael@0 | 57 | size_t HeapSizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const; |
| michael@0 | 58 | size_t NonHeapSizeOfExcludingThis() const; |
| michael@0 | 59 | bool OnHeap() const; |
| michael@0 | 60 | |
| michael@0 | 61 | protected: |
| michael@0 | 62 | bool Lock(void** aBuf); |
| michael@0 | 63 | void Unlock(); |
| michael@0 | 64 | |
| michael@0 | 65 | private: |
| michael@0 | 66 | void* mBuf; |
| michael@0 | 67 | size_t mSize; |
| michael@0 | 68 | int mLockCount; |
| michael@0 | 69 | #if defined(ANDROID) |
| michael@0 | 70 | int mFd; |
| michael@0 | 71 | #elif defined(XP_DARWIN) |
| michael@0 | 72 | bool mHeap; |
| michael@0 | 73 | #elif defined(XP_WIN) |
| michael@0 | 74 | bool mHeap; |
| michael@0 | 75 | bool mFirstLock; |
| michael@0 | 76 | #endif |
| michael@0 | 77 | }; |
| michael@0 | 78 | |
| michael@0 | 79 | class VolatileBufferPtr_base { |
| michael@0 | 80 | public: |
| michael@0 | 81 | VolatileBufferPtr_base(VolatileBuffer* vbuf) : mVBuf(vbuf) { |
| michael@0 | 82 | if (vbuf) { |
| michael@0 | 83 | mPurged = !vbuf->Lock(&mMapping); |
| michael@0 | 84 | } else { |
| michael@0 | 85 | mMapping = nullptr; |
| michael@0 | 86 | mPurged = false; |
| michael@0 | 87 | } |
| michael@0 | 88 | } |
| michael@0 | 89 | |
| michael@0 | 90 | ~VolatileBufferPtr_base() { |
| michael@0 | 91 | if (mVBuf) { |
| michael@0 | 92 | mVBuf->Unlock(); |
| michael@0 | 93 | } |
| michael@0 | 94 | } |
| michael@0 | 95 | |
| michael@0 | 96 | bool WasBufferPurged() const { |
| michael@0 | 97 | return mPurged; |
| michael@0 | 98 | } |
| michael@0 | 99 | |
| michael@0 | 100 | protected: |
| michael@0 | 101 | void* mMapping; |
| michael@0 | 102 | |
| michael@0 | 103 | private: |
| michael@0 | 104 | RefPtr<VolatileBuffer> mVBuf; |
| michael@0 | 105 | bool mPurged; |
| michael@0 | 106 | }; |
| michael@0 | 107 | |
| michael@0 | 108 | template <class T> |
| michael@0 | 109 | class VolatileBufferPtr : public VolatileBufferPtr_base |
| michael@0 | 110 | { |
| michael@0 | 111 | public: |
| michael@0 | 112 | VolatileBufferPtr(VolatileBuffer* vbuf) : VolatileBufferPtr_base(vbuf) {} |
| michael@0 | 113 | |
| michael@0 | 114 | operator T*() const { |
| michael@0 | 115 | return (T*) mMapping; |
| michael@0 | 116 | } |
| michael@0 | 117 | }; |
| michael@0 | 118 | |
| michael@0 | 119 | }; /* namespace mozilla */ |
| michael@0 | 120 | |
| michael@0 | 121 | #endif /* mozalloc_VolatileBuffer_h */ |
