allocators.h

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// Copyright (C) 2011 Milo Yip
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

#ifndef RAPIDJSON_ALLOCATORS_H_
#define RAPIDJSON_ALLOCATORS_H_

#include "rapidjson.h"

RAPIDJSON_NAMESPACE_BEGIN

// Allocator

// CrtAllocator


class CrtAllocator {
public:
    static const bool kNeedFree = true;
    void* Malloc(size_t size) { return std::malloc(size); }
    void* Realloc(void* originalPtr, size_t originalSize, size_t newSize) { (void)originalSize; return std::realloc(originalPtr, newSize); }
    static void Free(void *ptr) { std::free(ptr); }
};

// MemoryPoolAllocator


template <typename BaseAllocator = CrtAllocator>
class MemoryPoolAllocator {
public:
    static const bool kNeedFree = false;    


    MemoryPoolAllocator(size_t chunkSize = kDefaultChunkCapacity, BaseAllocator* baseAllocator = 0) : 
        chunkHead_(0), chunk_capacity_(chunkSize), userBuffer_(0), baseAllocator_(baseAllocator), ownBaseAllocator_(0)
    {
    }


    MemoryPoolAllocator(void *buffer, size_t size, size_t chunkSize = kDefaultChunkCapacity, BaseAllocator* baseAllocator = 0) :
        chunkHead_(0), chunk_capacity_(chunkSize), userBuffer_(buffer), baseAllocator_(baseAllocator), ownBaseAllocator_(0)
    {
        RAPIDJSON_ASSERT(buffer != 0);
        RAPIDJSON_ASSERT(size > sizeof(ChunkHeader));
        chunkHead_ = reinterpret_cast<ChunkHeader*>(buffer);
        chunkHead_->capacity = size - sizeof(ChunkHeader);
        chunkHead_->size = 0;
        chunkHead_->next = 0;
    }


    ~MemoryPoolAllocator() {
        Clear();
        RAPIDJSON_DELETE(ownBaseAllocator_);
    }

    void Clear() {
        while(chunkHead_ != 0 && chunkHead_ != userBuffer_) {
            ChunkHeader* next = chunkHead_->next;
            baseAllocator_->Free(chunkHead_);
            chunkHead_ = next;
        }
    }


    size_t Capacity() const {
        size_t capacity = 0;
        for (ChunkHeader* c = chunkHead_; c != 0; c = c->next)
            capacity += c->capacity;
        return capacity;
    }


    size_t Size() const {
        size_t size = 0;
        for (ChunkHeader* c = chunkHead_; c != 0; c = c->next)
            size += c->size;
        return size;
    }

    void* Malloc(size_t size) {
        size = RAPIDJSON_ALIGN(size);
        if (chunkHead_ == 0 || chunkHead_->size + size > chunkHead_->capacity)
            AddChunk(chunk_capacity_ > size ? chunk_capacity_ : size);

        void *buffer = reinterpret_cast<char *>(chunkHead_ + 1) + chunkHead_->size;
        chunkHead_->size += size;
        return buffer;
    }

    void* Realloc(void* originalPtr, size_t originalSize, size_t newSize) {
        if (originalPtr == 0)
            return Malloc(newSize);

        // Do not shrink if new size is smaller than original
        if (originalSize >= newSize)
            return originalPtr;

        // Simply expand it if it is the last allocation and there is sufficient space
        if (originalPtr == (char *)(chunkHead_ + 1) + chunkHead_->size - originalSize) {
            size_t increment = static_cast<size_t>(newSize - originalSize);
            increment = RAPIDJSON_ALIGN(increment);
            if (chunkHead_->size + increment <= chunkHead_->capacity) {
                chunkHead_->size += increment;
                return originalPtr;
            }
        }

        // Realloc process: allocate and copy memory, do not free original buffer.
        void* newBuffer = Malloc(newSize);
        RAPIDJSON_ASSERT(newBuffer != 0);   // Do not handle out-of-memory explicitly.
        return std::memcpy(newBuffer, originalPtr, originalSize);
    }

    static void Free(void *ptr) { (void)ptr; } // Do nothing

private:
    MemoryPoolAllocator(const MemoryPoolAllocator& rhs) /* = delete */;
    MemoryPoolAllocator& operator=(const MemoryPoolAllocator& rhs) /* = delete */;


    void AddChunk(size_t capacity) {
        if (!baseAllocator_)
            ownBaseAllocator_ = baseAllocator_ = RAPIDJSON_NEW(BaseAllocator());
        ChunkHeader* chunk = reinterpret_cast<ChunkHeader*>(baseAllocator_->Malloc(sizeof(ChunkHeader) + capacity));
        chunk->capacity = capacity;
        chunk->size = 0;
        chunk->next = chunkHead_;
        chunkHead_ =  chunk;
    }

    static const int kDefaultChunkCapacity = 64 * 1024; 


    struct ChunkHeader {
        size_t capacity;    
        size_t size;        
        ChunkHeader *next;  
    };

    ChunkHeader *chunkHead_;    
    size_t chunk_capacity_;     
    void *userBuffer_;          
    BaseAllocator* baseAllocator_;  
    BaseAllocator* ownBaseAllocator_;   
};

RAPIDJSON_NAMESPACE_END

#endif // RAPIDJSON_ENCODINGS_H_