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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/. */

 #ifndef StackArena_h

 #define StackArena_h

 #include "nsError.h"

 #include "mozilla/Assertions.h"

 #include "mozilla/MemoryReporting.h"

 #include "mozilla/NullPtr.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(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_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) {

     return gStackArena->Allocate(aSize);

   }

 private:

   static StackArena* gStackArena;

   bool mOwnsStackArena;

 };

 } // namespace mozilla

 #endif