1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/layout/base/StackArena.h Wed Dec 31 06:09:35 2014 +0100
1.3 @@ -0,0 +1,98 @@
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 file,
1.6 + * You can obtain one at http://mozilla.org/MPL/2.0/. */
1.7 +
1.8 +#ifndef StackArena_h
1.9 +#define StackArena_h
1.10 +
1.11 +#include "nsError.h"
1.12 +#include "mozilla/Assertions.h"
1.13 +#include "mozilla/MemoryReporting.h"
1.14 +#include "mozilla/NullPtr.h"
1.15 +
1.16 +namespace mozilla {
1.17 +
1.18 +struct StackBlock;
1.19 +struct StackMark;
1.20 +class AutoStackArena;
1.21 +
1.22 +// Private helper class for AutoStackArena.
1.23 +class StackArena {
1.24 +private:
1.25 + friend class AutoStackArena;
1.26 + StackArena();
1.27 + ~StackArena();
1.28 +
1.29 + nsresult Init() { return mBlocks ? NS_OK : NS_ERROR_OUT_OF_MEMORY; }
1.30 +
1.31 + // Memory management functions.
1.32 + void* Allocate(size_t aSize);
1.33 + void Push();
1.34 + void Pop();
1.35 +
1.36 + size_t SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) const;
1.37 +
1.38 + // Our current position in memory.
1.39 + size_t mPos;
1.40 +
1.41 + // A list of memory blocks. Usually there is only one
1.42 + // but if we overrun our stack size we can get more memory.
1.43 + StackBlock* mBlocks;
1.44 +
1.45 + // The current block.
1.46 + StackBlock* mCurBlock;
1.47 +
1.48 + // Our stack of mark where push has been called.
1.49 + StackMark* mMarks;
1.50 +
1.51 + // The current top of the mark list.
1.52 + uint32_t mStackTop;
1.53 +
1.54 + // The size of the mark array.
1.55 + uint32_t mMarkLength;
1.56 +};
1.57 +
1.58 +// Class for stack scoped arena memory allocations.
1.59 +//
1.60 +// Callers who wish to allocate memory whose lifetime corresponds to the
1.61 +// lifetime of a stack-allocated object can use this class. First,
1.62 +// declare an AutoStackArena object on the stack. Then all subsequent
1.63 +// calls to Allocate will allocate memory from an arena pool that will
1.64 +// be freed when that variable goes out of scope. Nesting is allowed.
1.65 +//
1.66 +// Individual allocations cannot exceed StackBlock::MAX_USABLE_SIZE
1.67 +// bytes.
1.68 +//
1.69 +class MOZ_STACK_CLASS AutoStackArena {
1.70 +public:
1.71 + AutoStackArena()
1.72 + : mOwnsStackArena(false)
1.73 + {
1.74 + if (!gStackArena) {
1.75 + gStackArena = new StackArena();
1.76 + mOwnsStackArena = true;
1.77 + gStackArena->Init();
1.78 + }
1.79 + gStackArena->Push();
1.80 + }
1.81 +
1.82 + ~AutoStackArena() {
1.83 + gStackArena->Pop();
1.84 + if (mOwnsStackArena) {
1.85 + delete gStackArena;
1.86 + gStackArena = nullptr;
1.87 + }
1.88 + }
1.89 +
1.90 + static void* Allocate(size_t aSize) {
1.91 + return gStackArena->Allocate(aSize);
1.92 + }
1.93 +
1.94 +private:
1.95 + static StackArena* gStackArena;
1.96 + bool mOwnsStackArena;
1.97 +};
1.98 +
1.99 +} // namespace mozilla
1.100 +
1.101 +#endif
