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