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14 
15 #ifndef RAPIDJSON_ALLOCATORS_H_
16 #define RAPIDJSON_ALLOCATORS_H_
17 
18 #include "rapidjson.h"
19 
20 RAPIDJSON_NAMESPACE_BEGIN
21 
22 ///////////////////////////////////////////////////////////////////////////////
23 // Allocator
24 
25 /*! \class rapidjson::Allocator
26     \brief Concept for allocating, resizing and freeing memory block.
27 
28     Note that Malloc() and Realloc() are non-static but Free() is static.
29 
30     So if an allocator need to support Free(), it needs to put its pointer in
31     the header of memory block.
32 
33 \code
34 concept Allocator {
35     static const bool kNeedFree;    //!< Whether this allocator needs to call Free().
36 
37     // Allocate a memory block.
38     // \param size of the memory block in bytes.
39     // \returns pointer to the memory block.
40     void* Malloc(size_t size);
41 
42     // Resize a memory block.
43     // \param originalPtr The pointer to current memory block. Null pointer is permitted.
44     // \param originalSize The current size in bytes. (Design issue: since some allocator may not book-keep this, explicitly pass to it can save memory.)
45     // \param newSize the new size in bytes.
46     void* Realloc(void* originalPtr, size_t originalSize, size_t newSize);
47 
48     // Free a memory block.
49     // \param pointer to the memory block. Null pointer is permitted.
50     static void Free(void *ptr);
51 };
52 \endcode
53 */
54 
55 ///////////////////////////////////////////////////////////////////////////////
56 // CrtAllocator
57 
58 //! C-runtime library allocator.
59 /*! This class is just wrapper for standard C library memory routines.
60     \note implements Allocator concept
61 */
62 class CrtAllocator {
63 public:
64     static const bool kNeedFree = true;
Malloc(size_t size)65     void* Malloc(size_t size) {
66         if (size) //  behavior of malloc(0) is implementation defined.
67             return std::malloc(size);
68         else
69             return NULL; // standardize to returning NULL.
70     }
Realloc(void * originalPtr,size_t originalSize,size_t newSize)71     void* Realloc(void* originalPtr, size_t originalSize, size_t newSize) {
72         (void)originalSize;
73         if (newSize == 0) {
74             std::free(originalPtr);
75             return NULL;
76         }
77         return std::realloc(originalPtr, newSize);
78     }
Free(void * ptr)79     static void Free(void *ptr) { std::free(ptr); }
80 };
81 
82 ///////////////////////////////////////////////////////////////////////////////
83 // MemoryPoolAllocator
84 
85 //! Default memory allocator used by the parser and DOM.
86 /*! This allocator allocate memory blocks from pre-allocated memory chunks.
87 
88     It does not free memory blocks. And Realloc() only allocate new memory.
89 
90     The memory chunks are allocated by BaseAllocator, which is CrtAllocator by default.
91 
92     User may also supply a buffer as the first chunk.
93 
94     If the user-buffer is full then additional chunks are allocated by BaseAllocator.
95 
96     The user-buffer is not deallocated by this allocator.
97 
98     \tparam BaseAllocator the allocator type for allocating memory chunks. Default is CrtAllocator.
99     \note implements Allocator concept
100 */
101 template <typename BaseAllocator = CrtAllocator>
102 class MemoryPoolAllocator {
103 public:
104     static const bool kNeedFree = false;    //!< Tell users that no need to call Free() with this allocator. (concept Allocator)
105 
106     //! Constructor with chunkSize.
107     /*! \param chunkSize The size of memory chunk. The default is kDefaultChunkSize.
108         \param baseAllocator The allocator for allocating memory chunks.
109     */
110     explicit MemoryPoolAllocator(size_t chunkSize = kDefaultChunkCapacity, BaseAllocator* baseAllocator = 0) :
111         chunkHead_(0), chunk_capacity_(chunkSize), userBuffer_(0), baseAllocator_(baseAllocator), ownBaseAllocator_(0)
112     {
113     }
114 
115     //! Constructor with user-supplied buffer.
116     /*! The user buffer will be used firstly. When it is full, memory pool allocates new chunk with chunk size.
117 
118         The user buffer will not be deallocated when this allocator is destructed.
119 
120         \param buffer User supplied buffer.
121         \param size Size of the buffer in bytes. It must at least larger than sizeof(ChunkHeader).
122         \param chunkSize The size of memory chunk. The default is kDefaultChunkSize.
123         \param baseAllocator The allocator for allocating memory chunks.
124     */
125     MemoryPoolAllocator(void *buffer, size_t size, size_t chunkSize = kDefaultChunkCapacity, BaseAllocator* baseAllocator = 0) :
126         chunkHead_(0), chunk_capacity_(chunkSize), userBuffer_(buffer), baseAllocator_(baseAllocator), ownBaseAllocator_(0)
127     {
128         RAPIDJSON_ASSERT(buffer != 0);
129         RAPIDJSON_ASSERT(size > sizeof(ChunkHeader));
130         chunkHead_ = reinterpret_cast<ChunkHeader*>(buffer);
131         chunkHead_->capacity = size - sizeof(ChunkHeader);
132         chunkHead_->size = 0;
133         chunkHead_->next = 0;
134     }
135 
136     //! Destructor.
137     /*! This deallocates all memory chunks, excluding the user-supplied buffer.
138     */
~MemoryPoolAllocator()139     ~MemoryPoolAllocator() {
140         Clear();
141         RAPIDJSON_DELETE(ownBaseAllocator_);
142     }
143 
144     //! Deallocates all memory chunks, excluding the user-supplied buffer.
Clear()145     void Clear() {
146         while (chunkHead_ && chunkHead_ != userBuffer_) {
147             ChunkHeader* next = chunkHead_->next;
148             baseAllocator_->Free(chunkHead_);
149             chunkHead_ = next;
150         }
151         if (chunkHead_ && chunkHead_ == userBuffer_)
152             chunkHead_->size = 0; // Clear user buffer
153     }
154 
155     //! Computes the total capacity of allocated memory chunks.
156     /*! \return total capacity in bytes.
157     */
Capacity()158     size_t Capacity() const {
159         size_t capacity = 0;
160         for (ChunkHeader* c = chunkHead_; c != 0; c = c->next)
161             capacity += c->capacity;
162         return capacity;
163     }
164 
165     //! Computes the memory blocks allocated.
166     /*! \return total used bytes.
167     */
Size()168     size_t Size() const {
169         size_t size = 0;
170         for (ChunkHeader* c = chunkHead_; c != 0; c = c->next)
171             size += c->size;
172         return size;
173     }
174 
175     //! Allocates a memory block. (concept Allocator)
Malloc(size_t size)176     void* Malloc(size_t size) {
177         if (!size)
178             return NULL;
179 
180         size = RAPIDJSON_ALIGN(size);
181         if (chunkHead_ == 0 || chunkHead_->size + size > chunkHead_->capacity)
182             AddChunk(chunk_capacity_ > size ? chunk_capacity_ : size);
183 
184         void *buffer = reinterpret_cast<char *>(chunkHead_) + RAPIDJSON_ALIGN(sizeof(ChunkHeader)) + chunkHead_->size;
185         chunkHead_->size += size;
186         return buffer;
187     }
188 
189     //! Resizes a memory block (concept Allocator)
Realloc(void * originalPtr,size_t originalSize,size_t newSize)190     void* Realloc(void* originalPtr, size_t originalSize, size_t newSize) {
191         if (originalPtr == 0)
192             return Malloc(newSize);
193 
194         if (newSize == 0)
195             return NULL;
196 
197         // Do not shrink if new size is smaller than original
198         if (originalSize >= newSize)
199             return originalPtr;
200 
201         // Simply expand it if it is the last allocation and there is sufficient space
202         if (originalPtr == (char *)(chunkHead_) + RAPIDJSON_ALIGN(sizeof(ChunkHeader)) + chunkHead_->size - originalSize) {
203             size_t increment = static_cast<size_t>(newSize - originalSize);
204             increment = RAPIDJSON_ALIGN(increment);
205             if (chunkHead_->size + increment <= chunkHead_->capacity) {
206                 chunkHead_->size += increment;
207                 return originalPtr;
208             }
209         }
210 
211         // Realloc process: allocate and copy memory, do not free original buffer.
212         void* newBuffer = Malloc(newSize);
213         RAPIDJSON_ASSERT(newBuffer != 0);   // Do not handle out-of-memory explicitly.
214         if (originalSize)
215             std::memcpy(newBuffer, originalPtr, originalSize);
216         return newBuffer;
217     }
218 
219     //! Frees a memory block (concept Allocator)
Free(void * ptr)220     static void Free(void *ptr) { (void)ptr; } // Do nothing
221 
222 private:
223     //! Copy constructor is not permitted.
224     MemoryPoolAllocator(const MemoryPoolAllocator& rhs) /* = delete */;
225     //! Copy assignment operator is not permitted.
226     MemoryPoolAllocator& operator=(const MemoryPoolAllocator& rhs) /* = delete */;
227 
228     //! Creates a new chunk.
229     /*! \param capacity Capacity of the chunk in bytes.
230     */
AddChunk(size_t capacity)231     void AddChunk(size_t capacity) {
232         if (!baseAllocator_)
233             ownBaseAllocator_ = baseAllocator_ = RAPIDJSON_NEW(BaseAllocator());
234         ChunkHeader* chunk = reinterpret_cast<ChunkHeader*>(baseAllocator_->Malloc(RAPIDJSON_ALIGN(sizeof(ChunkHeader)) + capacity));
235         chunk->capacity = capacity;
236         chunk->size = 0;
237         chunk->next = chunkHead_;
238         chunkHead_ =  chunk;
239     }
240 
241     static const int kDefaultChunkCapacity = 64 * 1024; //!< Default chunk capacity.
242 
243     //! Chunk header for perpending to each chunk.
244     /*! Chunks are stored as a singly linked list.
245     */
246     struct ChunkHeader {
247         size_t capacity;    //!< Capacity of the chunk in bytes (excluding the header itself).
248         size_t size;        //!< Current size of allocated memory in bytes.
249         ChunkHeader *next;  //!< Next chunk in the linked list.
250     };
251 
252     ChunkHeader *chunkHead_;    //!< Head of the chunk linked-list. Only the head chunk serves allocation.
253     size_t chunk_capacity_;     //!< The minimum capacity of chunk when they are allocated.
254     void *userBuffer_;          //!< User supplied buffer.
255     BaseAllocator* baseAllocator_;  //!< base allocator for allocating memory chunks.
256     BaseAllocator* ownBaseAllocator_;   //!< base allocator created by this object.
257 };
258 
259 RAPIDJSON_NAMESPACE_END
260 
261 #endif // RAPIDJSON_ENCODINGS_H_
262