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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     /**
     47      * Returns the total allocated size of the GrMemoryPool minus any preallocated amount
     48      */
     49     size_t size() const { return fSize; }
     50 
     51 private:
     52     struct BlockHeader;
     53 
     54     static BlockHeader* CreateBlock(size_t size);
     55 
     56     static void DeleteBlock(BlockHeader* block);
     57 
     58     void validate();
     59 
     60     struct BlockHeader {
     61 #ifdef SK_DEBUG
     62         uint32_t     fBlockSentinal;  ///< known value to check for bad back pointers to blocks
     63 #endif
     64         BlockHeader* fNext;      ///< doubly-linked list of blocks.
     65         BlockHeader* fPrev;
     66         int          fLiveCount; ///< number of outstanding allocations in the
     67                                  ///< block.
     68         intptr_t     fCurrPtr;   ///< ptr to the start of blocks free space.
     69         intptr_t     fPrevPtr;   ///< ptr to the last allocation made
     70         size_t       fFreeSize;  ///< amount of free space left in the block.
     71         size_t       fSize;      ///< total allocated size of the block
     72     };
     73 
     74     static const uint32_t kAssignedMarker = 0xCDCDCDCD;
     75     static const uint32_t kFreedMarker    = 0xEFEFEFEF;
     76 
     77     struct AllocHeader {
     78 #ifdef SK_DEBUG
     79         uint32_t fSentinal;      ///< known value to check for memory stomping (e.g., (CD)*)
     80 #endif
     81         BlockHeader* fHeader;    ///< pointer back to the block header in which an alloc resides
     82     };
     83 
     84     enum {
     85         // We assume this alignment is good enough for everybody.
     86         kAlignment    = 8,
     87         kHeaderSize   = GR_CT_ALIGN_UP(sizeof(BlockHeader), kAlignment),
     88         kPerAllocPad  = GR_CT_ALIGN_UP(sizeof(AllocHeader), kAlignment),
     89     };
     90     size_t                            fSize;
     91     size_t                            fPreallocSize;
     92     size_t                            fMinAllocSize;
     93     BlockHeader*                      fHead;
     94     BlockHeader*                      fTail;
     95 #ifdef SK_DEBUG
     96     int                               fAllocationCnt;
     97     int                               fAllocBlockCnt;
     98 #endif
     99 };
    100 
    101 #endif
    102