1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/memory/mozalloc/VolatileBuffer.h Wed Dec 31 06:09:35 2014 +0100
1.3 @@ -0,0 +1,121 @@
1.4 +/* This Source Code Form is subject to the terms of the Mozilla Public
1.5 + * License, v. 2.0. If a copy of the MPL was not distributed with this
1.6 + * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
1.7 +
1.8 +#ifndef mozalloc_VolatileBuffer_h
1.9 +#define mozalloc_VolatileBuffer_h
1.10 +
1.11 +#include "mozilla/mozalloc.h"
1.12 +#include "mozilla/RefPtr.h"
1.13 +#include "mozilla/MemoryReporting.h"
1.14 +#include "mozilla/NullPtr.h"
1.15 +
1.16 +/* VolatileBuffer
1.17 + *
1.18 + * This class represents a piece of memory that can potentially be reclaimed
1.19 + * by the OS when not in use. As long as there are one or more
1.20 + * VolatileBufferPtrs holding on to a VolatileBuffer, the memory will remain
1.21 + * available. However, when there are no VolatileBufferPtrs holding a
1.22 + * VolatileBuffer, the OS can purge the pages if it wants to. The OS can make
1.23 + * better decisions about what pages to purge than we can.
1.24 + *
1.25 + * VolatileBuffers may not always be volatile - if the allocation is too small,
1.26 + * or if the OS doesn't support the feature, or if the OS doesn't want to,
1.27 + * the buffer will be allocated on heap.
1.28 + *
1.29 + * VolatileBuffer allocations are fallible. They are intended for uses where
1.30 + * one may allocate large buffers for caching data. Init() must be called
1.31 + * exactly once.
1.32 + *
1.33 + * After getting a reference to VolatileBuffer using VolatileBufferPtr,
1.34 + * WasPurged() can be used to check if the OS purged any pages in the buffer.
1.35 + * The OS cannot purge a buffer immediately after a VolatileBuffer is
1.36 + * initialized. At least one VolatileBufferPtr must be created before the
1.37 + * buffer can be purged, so the first use of VolatileBufferPtr does not need
1.38 + * to check WasPurged().
1.39 + *
1.40 + * When a buffer is purged, some or all of the buffer is zeroed out. This
1.41 + * API cannot tell which parts of the buffer were lost.
1.42 + *
1.43 + * VolatileBuffer is not thread safe. Do not use VolatileBufferPtrs on
1.44 + * different threads.
1.45 + */
1.46 +
1.47 +namespace mozilla {
1.48 +
1.49 +class MOZALLOC_EXPORT VolatileBuffer : public RefCounted<VolatileBuffer>
1.50 +{
1.51 + friend class VolatileBufferPtr_base;
1.52 +public:
1.53 + MOZ_DECLARE_REFCOUNTED_TYPENAME(VolatileBuffer)
1.54 + VolatileBuffer();
1.55 + ~VolatileBuffer();
1.56 +
1.57 + /* aAlignment must be a multiple of the pointer size */
1.58 + bool Init(size_t aSize, size_t aAlignment = sizeof(void*));
1.59 +
1.60 + size_t HeapSizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const;
1.61 + size_t NonHeapSizeOfExcludingThis() const;
1.62 + bool OnHeap() const;
1.63 +
1.64 +protected:
1.65 + bool Lock(void** aBuf);
1.66 + void Unlock();
1.67 +
1.68 +private:
1.69 + void* mBuf;
1.70 + size_t mSize;
1.71 + int mLockCount;
1.72 +#if defined(ANDROID)
1.73 + int mFd;
1.74 +#elif defined(XP_DARWIN)
1.75 + bool mHeap;
1.76 +#elif defined(XP_WIN)
1.77 + bool mHeap;
1.78 + bool mFirstLock;
1.79 +#endif
1.80 +};
1.81 +
1.82 +class VolatileBufferPtr_base {
1.83 +public:
1.84 + VolatileBufferPtr_base(VolatileBuffer* vbuf) : mVBuf(vbuf) {
1.85 + if (vbuf) {
1.86 + mPurged = !vbuf->Lock(&mMapping);
1.87 + } else {
1.88 + mMapping = nullptr;
1.89 + mPurged = false;
1.90 + }
1.91 + }
1.92 +
1.93 + ~VolatileBufferPtr_base() {
1.94 + if (mVBuf) {
1.95 + mVBuf->Unlock();
1.96 + }
1.97 + }
1.98 +
1.99 + bool WasBufferPurged() const {
1.100 + return mPurged;
1.101 + }
1.102 +
1.103 +protected:
1.104 + void* mMapping;
1.105 +
1.106 +private:
1.107 + RefPtr<VolatileBuffer> mVBuf;
1.108 + bool mPurged;
1.109 +};
1.110 +
1.111 +template <class T>
1.112 +class VolatileBufferPtr : public VolatileBufferPtr_base
1.113 +{
1.114 +public:
1.115 + VolatileBufferPtr(VolatileBuffer* vbuf) : VolatileBufferPtr_base(vbuf) {}
1.116 +
1.117 + operator T*() const {
1.118 + return (T*) mMapping;
1.119 + }
1.120 +};
1.121 +
1.122 +}; /* namespace mozilla */
1.123 +
1.124 +#endif /* mozalloc_VolatileBuffer_h */
