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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 #ifdef SK_DEBUG
     13 #include "SkTHash.h"
     14 #endif
     15 
     16 /**
     17  * Allocates memory in blocks and parcels out space in the blocks for allocation
     18  * requests. It is optimized for allocate / release speed over memory
     19  * efficiency. The interface is designed to be used to implement operator new
     20  * and delete overrides. All allocations are expected to be released before the
     21  * pool's destructor is called. Allocations will be 8-byte aligned.
     22  */
     23 class GrMemoryPool {
     24 public:
     25     /**
     26      * Prealloc size is the amount of space to allocate at pool creation
     27      * time and keep around until pool destruction. The min alloc size is
     28      * the smallest allowed size of additional allocations. Both sizes are
     29      * adjusted to ensure that:
     30      *   1. they are are 8-byte aligned
     31      *   2. minAllocSize >= kSmallestMinAllocSize
     32      *   3. preallocSize >= minAllocSize
     33      *
     34      * Both sizes is what the pool will end up allocating from the system, and
     35      * portions of the allocated memory is used for internal bookkeeping.
     36      */
     37     GrMemoryPool(size_t preallocSize, size_t minAllocSize);
     38 
     39     ~GrMemoryPool();
     40 
     41     /**
     42      * Allocates memory. The memory must be freed with release().
     43      */
     44     void* allocate(size_t size);
     45 
     46     /**
     47      * p must have been returned by allocate()
     48      */
     49     void release(void* p);
     50 
     51     /**
     52      * Returns true if there are no unreleased allocations.
     53      */
     54     bool isEmpty() const { return fTail == fHead && !fHead->fLiveCount; }
     55 
     56     /**
     57      * Returns the total allocated size of the GrMemoryPool minus any preallocated amount
     58      */
     59     size_t size() const { return fSize; }
     60 
     61     /**
     62      * Returns the preallocated size of the GrMemoryPool
     63      */
     64     size_t preallocSize() const { return fHead->fSize; }
     65 
     66     /**
     67      * Minimum value of minAllocSize constructor argument.
     68      */
     69     constexpr static size_t kSmallestMinAllocSize = 1 << 10;
     70 
     71 private:
     72     struct BlockHeader;
     73 
     74     static BlockHeader* CreateBlock(size_t size);
     75 
     76     static void DeleteBlock(BlockHeader* block);
     77 
     78     void validate();
     79 
     80     struct BlockHeader {
     81 #ifdef SK_DEBUG
     82         uint32_t     fBlockSentinal;  ///< known value to check for bad back pointers to blocks
     83 #endif
     84         BlockHeader* fNext;      ///< doubly-linked list of blocks.
     85         BlockHeader* fPrev;
     86         int          fLiveCount; ///< number of outstanding allocations in the
     87                                  ///< block.
     88         intptr_t     fCurrPtr;   ///< ptr to the start of blocks free space.
     89         intptr_t     fPrevPtr;   ///< ptr to the last allocation made
     90         size_t       fFreeSize;  ///< amount of free space left in the block.
     91         size_t       fSize;      ///< total allocated size of the block
     92     };
     93 
     94     static const uint32_t kAssignedMarker = 0xCDCDCDCD;
     95     static const uint32_t kFreedMarker    = 0xEFEFEFEF;
     96 
     97     struct AllocHeader {
     98 #ifdef SK_DEBUG
     99         uint32_t fSentinal;      ///< known value to check for memory stomping (e.g., (CD)*)
    100         int32_t fID;             ///< ID that can be used to track down leaks by clients.
    101 #endif
    102         BlockHeader* fHeader;    ///< pointer back to the block header in which an alloc resides
    103     };
    104 
    105     size_t                            fSize;
    106     size_t                            fMinAllocSize;
    107     BlockHeader*                      fHead;
    108     BlockHeader*                      fTail;
    109 #ifdef SK_DEBUG
    110     int                               fAllocationCnt;
    111     int                               fAllocBlockCnt;
    112     SkTHashSet<int32_t>               fAllocatedIDs;
    113 #endif
    114 
    115 protected:
    116     enum {
    117         // We assume this alignment is good enough for everybody.
    118         kAlignment    = 8,
    119         kHeaderSize   = GR_CT_ALIGN_UP(sizeof(BlockHeader), kAlignment),
    120         kPerAllocPad  = GR_CT_ALIGN_UP(sizeof(AllocHeader), kAlignment),
    121     };
    122 };
    123 
    124 /**
    125  * Variant of GrMemoryPool that can only allocate objects of a single type. It is
    126  * not as flexible as GrMemoryPool, but it has more convenient allocate() method,
    127  * and more importantly, it guarantees number of objects that are preallocated at
    128  * construction or when adding a new memory block. I.e.
    129  *
    130  * GrMemoryPool pool(3 * sizeof(T), 1000 * sizeof(T));
    131  * pool.allocate(sizeof(T));
    132  * pool.allocate(sizeof(T));
    133  * pool.allocate(sizeof(T));
    134  *
    135  * will preallocate 3 * sizeof(T) bytes and use some of those bytes for internal
    136  * structures. Because of that, last allocate() call will end up allocating a new
    137  * block of 1000 * sizeof(T) bytes. In contrast,
    138  *
    139  * GrObjectMemoryPool<T> pool(3, 1000);
    140  * pool.allocate();
    141  * pool.allocate();
    142  * pool.allocate();
    143  *
    144  * guarantees to preallocate enough memory for 3 objects of sizeof(T), so last
    145  * allocate() will use preallocated memory and won't cause allocation of a new block.
    146  *
    147  * Same thing is true for the second (minAlloc) ctor argument: this class guarantees
    148  * that a newly added block will have enough space for 1000 objects of sizeof(T), while
    149  * GrMemoryPool does not.
    150  */
    151 template <class T>
    152 class GrObjectMemoryPool: public GrMemoryPool {
    153 public:
    154     /**
    155      * Preallocates memory for preallocCount objects, and sets new block size to be
    156      * enough to hold minAllocCount objects.
    157      */
    158     GrObjectMemoryPool(size_t preallocCount, size_t minAllocCount)
    159         : GrMemoryPool(CountToSize(preallocCount),
    160                        CountToSize(SkTMax(minAllocCount, kSmallestMinAllocCount))) {
    161     }
    162 
    163     /**
    164      * Allocates memory for an object, but doesn't construct or otherwise initialize it.
    165      * The memory must be freed with release().
    166      */
    167     T* allocate() { return static_cast<T*>(GrMemoryPool::allocate(sizeof(T))); }
    168 
    169 private:
    170     constexpr static size_t kTotalObjectSize =
    171         kPerAllocPad + GR_CT_ALIGN_UP(sizeof(T), kAlignment);
    172 
    173     constexpr static size_t CountToSize(size_t count) {
    174         return kHeaderSize + count * kTotalObjectSize;
    175     }
    176 
    177 public:
    178     /**
    179      * Minimum value of minAllocCount constructor argument.
    180      */
    181     constexpr static size_t kSmallestMinAllocCount =
    182         (GrMemoryPool::kSmallestMinAllocSize - kHeaderSize + kTotalObjectSize - 1) /
    183             kTotalObjectSize;
    184 };
    185 
    186 template <class T>
    187 constexpr size_t GrObjectMemoryPool<T>::kSmallestMinAllocCount;
    188 
    189 #endif
    190