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 */
20class GrMemoryPool {
21public:
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
46private:
47    struct BlockHeader;
48
49    static BlockHeader* CreateBlock(size_t size);
50
51    static 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#ifdef SK_DEBUG
76    int                               fAllocationCnt;
77#endif
78};
79
80#endif
81