зеркало из https://github.com/mozilla/gecko-dev.git
143 строки
3.6 KiB
C++
143 строки
3.6 KiB
C++
/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef mozalloc_VolatileBuffer_h
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#define mozalloc_VolatileBuffer_h
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#include "mozilla/mozalloc.h"
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#include "mozilla/RefPtr.h"
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#include "mozilla/MemoryReporting.h"
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#include "mozilla/NullPtr.h"
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/* VolatileBuffer
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*
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* This class represents a piece of memory that can potentially be reclaimed
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* by the OS when not in use. As long as there are one or more
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* VolatileBufferPtrs holding on to a VolatileBuffer, the memory will remain
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* available. However, when there are no VolatileBufferPtrs holding a
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* VolatileBuffer, the OS can purge the pages if it wants to. The OS can make
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* better decisions about what pages to purge than we can.
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*
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* VolatileBuffers may not always be volatile - if the allocation is too small,
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* or if the OS doesn't support the feature, or if the OS doesn't want to,
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* the buffer will be allocated on heap.
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*
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* VolatileBuffer allocations are fallible. They are intended for uses where
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* one may allocate large buffers for caching data. Init() must be called
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* exactly once.
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*
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* After getting a reference to VolatileBuffer using VolatileBufferPtr,
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* WasPurged() can be used to check if the OS purged any pages in the buffer.
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* The OS cannot purge a buffer immediately after a VolatileBuffer is
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* initialized. At least one VolatileBufferPtr must be created before the
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* buffer can be purged, so the first use of VolatileBufferPtr does not need
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* to check WasPurged().
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*
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* When a buffer is purged, some or all of the buffer is zeroed out. This
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* API cannot tell which parts of the buffer were lost.
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*
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* VolatileBuffer is not thread safe. Do not use VolatileBufferPtrs on
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* different threads.
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*/
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namespace mozilla {
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class MOZALLOC_EXPORT VolatileBuffer : public RefCounted<VolatileBuffer>
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{
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friend class VolatileBufferPtr_base;
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public:
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MOZ_DECLARE_REFCOUNTED_TYPENAME(VolatileBuffer)
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VolatileBuffer();
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~VolatileBuffer();
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/* aAlignment must be a multiple of the pointer size */
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bool Init(size_t aSize, size_t aAlignment = sizeof(void*));
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size_t HeapSizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const;
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size_t NonHeapSizeOfExcludingThis() const;
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protected:
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bool Lock(void** aBuf);
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void Unlock();
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bool OnHeap() const;
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private:
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void* mBuf;
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size_t mSize;
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int mLockCount;
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#if defined(ANDROID)
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int mFd;
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#elif defined(XP_DARWIN)
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bool mHeap;
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#elif defined(XP_WIN)
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bool mHeap;
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bool mFirstLock;
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#endif
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};
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class VolatileBufferPtr_base {
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public:
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explicit VolatileBufferPtr_base(VolatileBuffer* vbuf) : mVBuf(vbuf) {
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Lock();
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}
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~VolatileBufferPtr_base() {
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Unlock();
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}
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bool WasBufferPurged() const {
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return mPurged;
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}
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protected:
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void* mMapping;
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void Set(VolatileBuffer* vbuf) {
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Unlock();
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mVBuf = vbuf;
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Lock();
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}
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private:
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RefPtr<VolatileBuffer> mVBuf;
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bool mPurged;
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void Lock() {
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if (mVBuf) {
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mPurged = !mVBuf->Lock(&mMapping);
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} else {
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mMapping = nullptr;
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mPurged = false;
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}
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}
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void Unlock() {
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if (mVBuf) {
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mVBuf->Unlock();
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}
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}
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};
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template <class T>
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class VolatileBufferPtr : public VolatileBufferPtr_base
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{
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public:
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explicit VolatileBufferPtr(VolatileBuffer* vbuf) : VolatileBufferPtr_base(vbuf) {}
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VolatileBufferPtr() : VolatileBufferPtr_base(nullptr) {}
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operator T*() const {
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return (T*) mMapping;
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}
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void operator =(VolatileBuffer* vbuf) {
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Set(vbuf);
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}
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private:
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VolatileBufferPtr(VolatileBufferPtr const& vbufptr) MOZ_DELETE;
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};
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}; /* namespace mozilla */
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#endif /* mozalloc_VolatileBuffer_h */
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