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      1 /*
      2  * Copyright 2012 Google Inc.
      3  *
      4  * Use of this source code is governed by a BSD-style license that can be
      5  * found in the LICENSE file.
      6  */
      7 
      8 #ifndef GrMemoryPool_DEFINED
      9 #define GrMemoryPool_DEFINED
     10 
     11 #include "GrTypes.h"
     12 
     13 /**
     14  * Allocates memory in blocks and parcels out space in the blocks for allocation
     15  * requests. It is optimized for allocate / release speed over memory
     16  * effeciency. The interface is designed to be used to implement operator new
     17  * and delete overrides. All allocations are expected to be released before the
     18  * pool's destructor is called. Allocations will be 8-byte aligned.
     19  */
     20 class GrMemoryPool {
     21 public:
     22     /**
     23      * Prealloc size is the amount of space to make available at pool creation
     24      * time and keep around until pool destruction. The min alloc size is the
     25      * smallest allowed size of additional allocations.
     26      */
     27     GrMemoryPool(size_t preallocSize, size_t minAllocSize);
     28 
     29     ~GrMemoryPool();
     30 
     31     /**
     32      * Allocates memory. The memory must be freed with release().
     33      */
     34     void* allocate(size_t size);
     35 
     36     /**
     37      * p must have been returned by allocate()
     38      */
     39     void release(void* p);
     40 
     41     /**
     42      * Returns true if there are no unreleased allocations.
     43      */
     44     bool isEmpty() const { return fTail == fHead && !fHead->fLiveCount; }
     45 
     46 private:
     47     struct BlockHeader;
     48 
     49     BlockHeader* CreateBlock(size_t size);
     50 
     51     void DeleteBlock(BlockHeader* block);
     52 
     53     void validate();
     54 
     55     struct BlockHeader {
     56         BlockHeader* fNext;      ///< doubly-linked list of blocks.
     57         BlockHeader* fPrev;
     58         int          fLiveCount; ///< number of outstanding allocations in the
     59                                  ///< block.
     60         intptr_t     fCurrPtr;   ///< ptr to the start of blocks free space.
     61         intptr_t     fPrevPtr;   ///< ptr to the last allocation made
     62         size_t       fFreeSize;  ///< amount of free space left in the block.
     63     };
     64 
     65     enum {
     66         // We assume this alignment is good enough for everybody.
     67         kAlignment    = 8,
     68         kHeaderSize   = GR_CT_ALIGN_UP(sizeof(BlockHeader), kAlignment),
     69         kPerAllocPad  = GR_CT_ALIGN_UP(sizeof(BlockHeader*), kAlignment),
     70     };
     71     size_t                            fPreallocSize;
     72     size_t                            fMinAllocSize;
     73     BlockHeader*                      fHead;
     74     BlockHeader*                      fTail;
     75 #if GR_DEBUG
     76     int                               fAllocationCnt;
     77 #endif
     78 };
     79 
     80 #endif
     81