Line data    Source code

       1             : /* This Source Code Form is subject to the terms of the Mozilla Public
       2             :  * License, v. 2.0. If a copy of the MPL was not distributed with this file,
       3             :  * You can obtain one at http://mozilla.org/MPL/2.0/. */
       4             : 
       5             : #ifndef StackArena_h
       6             : #define StackArena_h
       7             : 
       8             : #include "nsError.h"
       9             : #include "mozilla/Assertions.h"
      10             : #include "mozilla/MemoryReporting.h"
      11             : 
      12             : namespace mozilla {
      13             : 
      14             : struct StackBlock;
      15             : struct StackMark;
      16             : class AutoStackArena;
      17             : 
      18             : // Private helper class for AutoStackArena.
      19             : class StackArena {
      20             : private:
      21             :   friend class AutoStackArena;
      22             :   StackArena();
      23             :   ~StackArena();
      24             : 
      25             :   // Memory management functions.
      26             :   void* Allocate(size_t aSize);
      27             :   void Push();
      28             :   void Pop();
      29             : 
      30             :   size_t SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) const;
      31             : 
      32             :   // Our current position in memory.
      33             :   size_t mPos;
      34             : 
      35             :   // A list of memory blocks. Usually there is only one
      36             :   // but if we overrun our stack size we can get more memory.
      37             :   StackBlock* mBlocks;
      38             : 
      39             :   // The current block.
      40             :   StackBlock* mCurBlock;
      41             : 
      42             :   // Our stack of mark where push has been called.
      43             :   StackMark* mMarks;
      44             : 
      45             :   // The current top of the mark list.
      46             :   uint32_t mStackTop;
      47             : 
      48             :   // The size of the mark array.
      49             :   uint32_t mMarkLength;
      50             : };
      51             : 
      52             : // Class for stack scoped arena memory allocations.
      53             : //
      54             : // Callers who wish to allocate memory whose lifetime corresponds to the
      55             : // lifetime of a stack-allocated object can use this class.  First,
      56             : // declare an AutoStackArena object on the stack.  Then all subsequent
      57             : // calls to Allocate will allocate memory from an arena pool that will
      58             : // be freed when that variable goes out of scope.  Nesting is allowed.
      59             : //
      60             : // Individual allocations cannot exceed StackBlock::MAX_USABLE_SIZE
      61             : // bytes.
      62             : //
      63             : class MOZ_RAII AutoStackArena {
      64             : public:
      65         438 :   AutoStackArena()
      66         438 :     : mOwnsStackArena(false)
      67             :   {
      68         438 :     if (!gStackArena) {
      69          41 :       gStackArena = new StackArena();
      70          41 :       mOwnsStackArena = true;
      71             :     }
      72         438 :     gStackArena->Push();
      73         438 :   }
      74             : 
      75         876 :   ~AutoStackArena() {
      76         438 :     gStackArena->Pop();
      77         438 :     if (mOwnsStackArena) {
      78          41 :       delete gStackArena;
      79          41 :       gStackArena = nullptr;
      80             :     }
      81         438 :   }
      82             : 
      83        2371 :   static void* Allocate(size_t aSize) {
      84        2371 :     return gStackArena->Allocate(aSize);
      85             :   }
      86             : 
      87             : private:
      88             :   static StackArena* gStackArena;
      89             :   bool mOwnsStackArena;
      90             : };
      91             : 
      92             : } // namespace mozilla
      93             : 
      94             : #endif