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98 lines
2.3 KiB
C++
98 lines
2.3 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 file,
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* You can obtain one at http://mozilla.org/MPL/2.0/. */
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#include "mozilla/Assertions.h"
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#include "mozilla/MemoryReporting.h"
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#include "nsAlgorithm.h"
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#include "nsDebug.h"
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namespace mozilla {
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struct StackBlock;
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struct StackMark;
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class AutoStackArena;
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/**
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* Private helper class for AutoStackArena.
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*/
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class StackArena {
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private:
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friend class AutoStackArena;
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StackArena();
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~StackArena();
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nsresult Init() { return mBlocks ? NS_OK : NS_ERROR_OUT_OF_MEMORY; }
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// Memory management functions
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void* Allocate(size_t aSize);
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void Push();
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void Pop();
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size_t SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) const;
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// our current position in memory
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size_t mPos;
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// a list of memory block. Usually there is only one
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// but if we overrun our stack size we can get more memory.
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StackBlock* mBlocks;
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// the current block of memory we are passing our chucks of
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StackBlock* mCurBlock;
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// our stack of mark where push has been called
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StackMark* mMarks;
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// the current top of the mark list
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uint32_t mStackTop;
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// the size of the mark array
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uint32_t mMarkLength;
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};
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/**
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* Class for stack scoped arena memory allocations.
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*
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* Callers who wish to allocate memory whose lifetime corresponds to
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* the lifetime of a stack-allocated object can use this class.
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* First, declare an AutoStackArena object on the stack.
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* Then all subsequent calls to Allocate will allocate memory from an
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* arena pool that will be freed when that variable goes out of scope.
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* Nesting is allowed.
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*
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* The allocations cannot be for more than 4044 bytes.
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*/
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class MOZ_STACK_CLASS AutoStackArena {
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public:
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AutoStackArena() : mOwnsStackArena(false) {
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if (!gStackArena) {
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gStackArena = new StackArena();
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mOwnsStackArena = true;
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gStackArena->Init();
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}
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gStackArena->Push();
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}
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~AutoStackArena() {
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gStackArena->Pop();
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if (mOwnsStackArena) {
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delete gStackArena;
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gStackArena = nullptr;
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}
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}
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static void* Allocate(size_t aSize) {
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MOZ_ASSERT(aSize <= 4044);
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return gStackArena->Allocate(aSize);
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}
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private:
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static StackArena* gStackArena;
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bool mOwnsStackArena;
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};
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} // namespace mozilla
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