/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */

/* vim: set ts=8 sts=2 et sw=2 tw=80: */

/* 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/. */

#ifndef StackArena_h

#define StackArena_h

#include "nsError.h"

#include "mozilla/Assertions.h"

#include "mozilla/MemoryReporting.h"

namespace mozilla {

struct StackBlock;

struct StackMark;

class AutoStackArena;

// Private helper class for AutoStackArena.

class StackArena {

private:

  friend class AutoStackArena;

  StackArena();

  ~StackArena();

  // Memory management functions.

  void* Allocate(size_t aSize);

  void Push();

  void Pop();

  size_t SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) const;

  // Our current position in memory.

  size_t mPos;

  // A list of memory blocks. Usually there is only one

  // but if we overrun our stack size we can get more memory.

  StackBlock* mBlocks;

  // The current block.

  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.

//

// Individual allocations cannot exceed StackBlock::MAX_USABLE_SIZE

// bytes.

//

class MOZ_RAII AutoStackArena {

public:

  AutoStackArena()

    : mOwnsStackArena(false)

  {

    if (!gStackArena) {

      gStackArena = new StackArena();

      mOwnsStackArena = true;

    }

    gStackArena->Push();

  }

  ~AutoStackArena() {

    gStackArena->Pop();

    if (mOwnsStackArena) {

      delete gStackArena;

      gStackArena = nullptr;

    }

  }

  static void* Allocate(size_t aSize) {

    return gStackArena->Allocate(aSize);

  }

private:

  static StackArena* gStackArena;

  bool mOwnsStackArena;

};

} // namespace mozilla

#endif