allocators.h

// Tencent is pleased to support the open source community by making RapidJSON available.
// 
// Copyright (C) 2015 THL A29 Limited, a Tencent company, and Milo Yip.
//
// Licensed under the MIT License (the "License"); you may not use this file except
// in compliance with the License. You may obtain a copy of the License at
//
// http://opensource.org/licenses/MIT
//
// Unless required by applicable law or agreed to in writing, software distributed 
// under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR 
// CONDITIONS OF ANY KIND, either express or implied. See the License for the 
// specific language governing permissions and limitations under the License.

#ifndef RAPIDJSON_ALLOCATORS_H_
#define RAPIDJSON_ALLOCATORS_H_

#include "rapidjson.h"
#include "internal/meta.h"

#include <memory>

#if RAPIDJSON_HAS_CXX11
#include <type_traits>
#endif

RAPIDJSON_NAMESPACE_BEGIN

// Allocator

#ifndef RAPIDJSON_ALLOCATOR_DEFAULT_CHUNK_CAPACITY
#define RAPIDJSON_ALLOCATOR_DEFAULT_CHUNK_CAPACITY (64 * 1024)
#endif


// CrtAllocator


class CrtAllocator {
public:
    static const bool kNeedFree = true;
    void* Malloc(size_t size) { 
        if (size) //  behavior of malloc(0) is implementation defined.
            return RAPIDJSON_MALLOC(size);
        else
            return NULL; // standardize to returning NULL.
    }
    void* Realloc(void* originalPtr, size_t originalSize, size_t newSize) {
        (void)originalSize;
        if (newSize == 0) {
            RAPIDJSON_FREE(originalPtr);
            return NULL;
        }
        return RAPIDJSON_REALLOC(originalPtr, newSize);
    }
    static void Free(void *ptr) RAPIDJSON_NOEXCEPT { RAPIDJSON_FREE(ptr); }

    bool operator==(const CrtAllocator&) const RAPIDJSON_NOEXCEPT {
        return true;
    }
    bool operator!=(const CrtAllocator&) const RAPIDJSON_NOEXCEPT {
        return false;
    }
};

// MemoryPoolAllocator


template <typename BaseAllocator = CrtAllocator>
class MemoryPoolAllocator {

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

    struct SharedData {
        ChunkHeader *chunkHead;  
        BaseAllocator* ownBaseAllocator; 
        size_t refcount;
        bool ownBuffer;
    };

    static const size_t SIZEOF_SHARED_DATA = RAPIDJSON_ALIGN(sizeof(SharedData));
    static const size_t SIZEOF_CHUNK_HEADER = RAPIDJSON_ALIGN(sizeof(ChunkHeader));

    static inline ChunkHeader *GetChunkHead(SharedData *shared)
    {
        return reinterpret_cast<ChunkHeader*>(reinterpret_cast<uint8_t*>(shared) + SIZEOF_SHARED_DATA);
    }
    static inline uint8_t *GetChunkBuffer(SharedData *shared)
    {
        return reinterpret_cast<uint8_t*>(shared->chunkHead) + SIZEOF_CHUNK_HEADER;
    }

    static const size_t kDefaultChunkCapacity = RAPIDJSON_ALLOCATOR_DEFAULT_CHUNK_CAPACITY; 

public:
    static const bool kNeedFree = false;    
    static const bool kRefCounted = true;   


    explicit
    MemoryPoolAllocator(size_t chunkSize = kDefaultChunkCapacity, BaseAllocator* baseAllocator = 0) : 
        chunk_capacity_(chunkSize),
        baseAllocator_(baseAllocator ? baseAllocator : RAPIDJSON_NEW(BaseAllocator)()),
        shared_(static_cast<SharedData*>(baseAllocator_ ? baseAllocator_->Malloc(SIZEOF_SHARED_DATA + SIZEOF_CHUNK_HEADER) : 0))
    {
        RAPIDJSON_ASSERT(baseAllocator_ != 0);
        RAPIDJSON_ASSERT(shared_ != 0);
        if (baseAllocator) {
            shared_->ownBaseAllocator = 0;
        }
        else {
            shared_->ownBaseAllocator = baseAllocator_;
        }
        shared_->chunkHead = GetChunkHead(shared_);
        shared_->chunkHead->capacity = 0;
        shared_->chunkHead->size = 0;
        shared_->chunkHead->next = 0;
        shared_->ownBuffer = true;
        shared_->refcount = 1;
    }


    MemoryPoolAllocator(void *buffer, size_t size, size_t chunkSize = kDefaultChunkCapacity, BaseAllocator* baseAllocator = 0) :
        chunk_capacity_(chunkSize),
        baseAllocator_(baseAllocator),
        shared_(static_cast<SharedData*>(AlignBuffer(buffer, size)))
    {
        RAPIDJSON_ASSERT(size >= SIZEOF_SHARED_DATA + SIZEOF_CHUNK_HEADER);
        shared_->chunkHead = GetChunkHead(shared_);
        shared_->chunkHead->capacity = size - SIZEOF_SHARED_DATA - SIZEOF_CHUNK_HEADER;
        shared_->chunkHead->size = 0;
        shared_->chunkHead->next = 0;
        shared_->ownBaseAllocator = 0;
        shared_->ownBuffer = false;
        shared_->refcount = 1;
    }

    MemoryPoolAllocator(const MemoryPoolAllocator& rhs) RAPIDJSON_NOEXCEPT :
        chunk_capacity_(rhs.chunk_capacity_),
        baseAllocator_(rhs.baseAllocator_),
        shared_(rhs.shared_)
    {
        RAPIDJSON_NOEXCEPT_ASSERT(shared_->refcount > 0);
        ++shared_->refcount;
    }
    MemoryPoolAllocator& operator=(const MemoryPoolAllocator& rhs) RAPIDJSON_NOEXCEPT
    {
        RAPIDJSON_NOEXCEPT_ASSERT(rhs.shared_->refcount > 0);
        ++rhs.shared_->refcount;
        this->~MemoryPoolAllocator();
        baseAllocator_ = rhs.baseAllocator_;
        chunk_capacity_ = rhs.chunk_capacity_;
        shared_ = rhs.shared_;
        return *this;
    }

#if RAPIDJSON_HAS_CXX11_RVALUE_REFS
    MemoryPoolAllocator(MemoryPoolAllocator&& rhs) RAPIDJSON_NOEXCEPT :
        chunk_capacity_(rhs.chunk_capacity_),
        baseAllocator_(rhs.baseAllocator_),
        shared_(rhs.shared_)
    {
        RAPIDJSON_NOEXCEPT_ASSERT(rhs.shared_->refcount > 0);
        rhs.shared_ = 0;
    }
    MemoryPoolAllocator& operator=(MemoryPoolAllocator&& rhs) RAPIDJSON_NOEXCEPT
    {
        RAPIDJSON_NOEXCEPT_ASSERT(rhs.shared_->refcount > 0);
        this->~MemoryPoolAllocator();
        baseAllocator_ = rhs.baseAllocator_;
        chunk_capacity_ = rhs.chunk_capacity_;
        shared_ = rhs.shared_;
        rhs.shared_ = 0;
        return *this;
    }
#endif


    ~MemoryPoolAllocator() RAPIDJSON_NOEXCEPT {
        if (!shared_) {
            // do nothing if moved
            return;
        }
        if (shared_->refcount > 1) {
            --shared_->refcount;
            return;
        }
        Clear();
        BaseAllocator *a = shared_->ownBaseAllocator;
        if (shared_->ownBuffer) {
            baseAllocator_->Free(shared_);
        }
        RAPIDJSON_DELETE(a);
    }

    void Clear() RAPIDJSON_NOEXCEPT {
        RAPIDJSON_NOEXCEPT_ASSERT(shared_->refcount > 0);
        for (;;) {
            ChunkHeader* c = shared_->chunkHead;
            if (!c->next) {
                break;
            }
            shared_->chunkHead = c->next;
            baseAllocator_->Free(c);
        }
        shared_->chunkHead->size = 0;
    }


    size_t Capacity() const RAPIDJSON_NOEXCEPT {
        RAPIDJSON_NOEXCEPT_ASSERT(shared_->refcount > 0);
        size_t capacity = 0;
        for (ChunkHeader* c = shared_->chunkHead; c != 0; c = c->next)
            capacity += c->capacity;
        return capacity;
    }


    size_t Size() const RAPIDJSON_NOEXCEPT {
        RAPIDJSON_NOEXCEPT_ASSERT(shared_->refcount > 0);
        size_t size = 0;
        for (ChunkHeader* c = shared_->chunkHead; c != 0; c = c->next)
            size += c->size;
        return size;
    }


    bool Shared() const RAPIDJSON_NOEXCEPT {
        RAPIDJSON_NOEXCEPT_ASSERT(shared_->refcount > 0);
        return shared_->refcount > 1;
    }

    void* Malloc(size_t size) {
        RAPIDJSON_NOEXCEPT_ASSERT(shared_->refcount > 0);
        if (!size)
            return NULL;

        size = RAPIDJSON_ALIGN(size);
        if (RAPIDJSON_UNLIKELY(shared_->chunkHead->size + size > shared_->chunkHead->capacity))
            if (!AddChunk(chunk_capacity_ > size ? chunk_capacity_ : size))
                return NULL;

        void *buffer = GetChunkBuffer(shared_) + shared_->chunkHead->size;
        shared_->chunkHead->size += size;
        return buffer;
    }

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

        RAPIDJSON_NOEXCEPT_ASSERT(shared_->refcount > 0);
        if (newSize == 0)
            return NULL;

        originalSize = RAPIDJSON_ALIGN(originalSize);
        newSize = RAPIDJSON_ALIGN(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 == GetChunkBuffer(shared_) + shared_->chunkHead->size - originalSize) {
            size_t increment = static_cast<size_t>(newSize - originalSize);
            if (shared_->chunkHead->size + increment <= shared_->chunkHead->capacity) {
                shared_->chunkHead->size += increment;
                return originalPtr;
            }
        }

        // Realloc process: allocate and copy memory, do not free original buffer.
        if (void* newBuffer = Malloc(newSize)) {
            if (originalSize)
                std::memcpy(newBuffer, originalPtr, originalSize);
            return newBuffer;
        }
        else
            return NULL;
    }

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

    bool operator==(const MemoryPoolAllocator& rhs) const RAPIDJSON_NOEXCEPT {
        RAPIDJSON_NOEXCEPT_ASSERT(shared_->refcount > 0);
        RAPIDJSON_NOEXCEPT_ASSERT(rhs.shared_->refcount > 0);
        return shared_ == rhs.shared_;
    }
    bool operator!=(const MemoryPoolAllocator& rhs) const RAPIDJSON_NOEXCEPT {
        return !operator==(rhs);
    }

private:

    bool AddChunk(size_t capacity) {
        if (!baseAllocator_)
            shared_->ownBaseAllocator = baseAllocator_ = RAPIDJSON_NEW(BaseAllocator)();
        if (ChunkHeader* chunk = static_cast<ChunkHeader*>(baseAllocator_->Malloc(SIZEOF_CHUNK_HEADER + capacity))) {
            chunk->capacity = capacity;
            chunk->size = 0;
            chunk->next = shared_->chunkHead;
            shared_->chunkHead = chunk;
            return true;
        }
        else
            return false;
    }

    static inline void* AlignBuffer(void* buf, size_t &size)
    {
        RAPIDJSON_NOEXCEPT_ASSERT(buf != 0);
        const uintptr_t mask = sizeof(void*) - 1;
        const uintptr_t ubuf = reinterpret_cast<uintptr_t>(buf);
        if (RAPIDJSON_UNLIKELY(ubuf & mask)) {
            const uintptr_t abuf = (ubuf + mask) & ~mask;
            RAPIDJSON_ASSERT(size >= abuf - ubuf);
            buf = reinterpret_cast<void*>(abuf);
            size -= abuf - ubuf;
        }
        return buf;
    }

    size_t chunk_capacity_;     
    BaseAllocator* baseAllocator_;  
    SharedData *shared_;        
};

namespace internal {
    template<typename, typename = void>
    struct IsRefCounted :
        public FalseType
    { };
    template<typename T>
    struct IsRefCounted<T, typename internal::EnableIfCond<T::kRefCounted>::Type> :
        public TrueType
    { };
}

template<typename T, typename A>
inline T* Realloc(A& a, T* old_p, size_t old_n, size_t new_n)
{
    RAPIDJSON_NOEXCEPT_ASSERT(old_n <= SIZE_MAX / sizeof(T) && new_n <= SIZE_MAX / sizeof(T));
    return static_cast<T*>(a.Realloc(old_p, old_n * sizeof(T), new_n * sizeof(T)));
}

template<typename T, typename A>
inline T *Malloc(A& a, size_t n = 1)
{
    return Realloc<T, A>(a, NULL, 0, n);
}

template<typename T, typename A>
inline void Free(A& a, T *p, size_t n = 1)
{
    static_cast<void>(Realloc<T, A>(a, p, n, 0));
}

#ifdef __GNUC__
RAPIDJSON_DIAG_PUSH
RAPIDJSON_DIAG_OFF(effc++) // std::allocator can safely be inherited
#endif

template <typename T, typename BaseAllocator = CrtAllocator>
class StdAllocator :
    public std::allocator<T>
{
    typedef std::allocator<T> allocator_type;
#if RAPIDJSON_HAS_CXX11
    typedef std::allocator_traits<allocator_type> traits_type;
#else
    typedef allocator_type traits_type;
#endif

public:
    typedef BaseAllocator BaseAllocatorType;

    StdAllocator() RAPIDJSON_NOEXCEPT :
        allocator_type(),
        baseAllocator_()
    { }

    StdAllocator(const StdAllocator& rhs) RAPIDJSON_NOEXCEPT :
        allocator_type(rhs),
        baseAllocator_(rhs.baseAllocator_)
    { }

    template<typename U>
    StdAllocator(const StdAllocator<U, BaseAllocator>& rhs) RAPIDJSON_NOEXCEPT :
        allocator_type(rhs),
        baseAllocator_(rhs.baseAllocator_)
    { }

#if RAPIDJSON_HAS_CXX11_RVALUE_REFS
    StdAllocator(StdAllocator&& rhs) RAPIDJSON_NOEXCEPT :
        allocator_type(std::move(rhs)),
        baseAllocator_(std::move(rhs.baseAllocator_))
    { }
#endif
#if RAPIDJSON_HAS_CXX11
    using propagate_on_container_move_assignment = std::true_type;
    using propagate_on_container_swap = std::true_type;
#endif

    /* implicit */
    StdAllocator(const BaseAllocator& allocator) RAPIDJSON_NOEXCEPT :
        allocator_type(),
        baseAllocator_(allocator)
    { }

    ~StdAllocator() RAPIDJSON_NOEXCEPT
    { }

    template<typename U>
    struct rebind {
        typedef StdAllocator<U, BaseAllocator> other;
    };

    typedef typename traits_type::size_type         size_type;
    typedef typename traits_type::difference_type   difference_type;

    typedef typename traits_type::value_type        value_type;
    typedef typename traits_type::pointer           pointer;
    typedef typename traits_type::const_pointer     const_pointer;

#if RAPIDJSON_HAS_CXX11

    typedef typename std::add_lvalue_reference<value_type>::type &reference;
    typedef typename std::add_lvalue_reference<typename std::add_const<value_type>::type>::type &const_reference;

    pointer address(reference r) const RAPIDJSON_NOEXCEPT
    {
        return std::addressof(r);
    }
    const_pointer address(const_reference r) const RAPIDJSON_NOEXCEPT
    {
        return std::addressof(r);
    }

    size_type max_size() const RAPIDJSON_NOEXCEPT
    {
        return traits_type::max_size(*this);
    }

    template <typename ...Args>
    void construct(pointer p, Args&&... args)
    {
        traits_type::construct(*this, p, std::forward<Args>(args)...);
    }
    void destroy(pointer p)
    {
        traits_type::destroy(*this, p);
    }

#else // !RAPIDJSON_HAS_CXX11

    typedef typename allocator_type::reference       reference;
    typedef typename allocator_type::const_reference const_reference;

    pointer address(reference r) const RAPIDJSON_NOEXCEPT
    {
        return allocator_type::address(r);
    }
    const_pointer address(const_reference r) const RAPIDJSON_NOEXCEPT
    {
        return allocator_type::address(r);
    }

    size_type max_size() const RAPIDJSON_NOEXCEPT
    {
        return allocator_type::max_size();
    }

    void construct(pointer p, const_reference r)
    {
        allocator_type::construct(p, r);
    }
    void destroy(pointer p)
    {
        allocator_type::destroy(p);
    }

#endif // !RAPIDJSON_HAS_CXX11

    template <typename U>
    U* allocate(size_type n = 1, const void* = 0)
    {
        return RAPIDJSON_NAMESPACE::Malloc<U>(baseAllocator_, n);
    }
    template <typename U>
    void deallocate(U* p, size_type n = 1)
    {
        RAPIDJSON_NAMESPACE::Free<U>(baseAllocator_, p, n);
    }

    pointer allocate(size_type n = 1, const void* = 0)
    {
        return allocate<value_type>(n);
    }
    void deallocate(pointer p, size_type n = 1)
    {
        deallocate<value_type>(p, n);
    }

#if RAPIDJSON_HAS_CXX11
    using is_always_equal = std::is_empty<BaseAllocator>;
#endif

    template<typename U>
    bool operator==(const StdAllocator<U, BaseAllocator>& rhs) const RAPIDJSON_NOEXCEPT
    {
        return baseAllocator_ == rhs.baseAllocator_;
    }
    template<typename U>
    bool operator!=(const StdAllocator<U, BaseAllocator>& rhs) const RAPIDJSON_NOEXCEPT
    {
        return !operator==(rhs);
    }

    static const bool kNeedFree = BaseAllocator::kNeedFree;
    static const bool kRefCounted = internal::IsRefCounted<BaseAllocator>::Value;
    void* Malloc(size_t size)
    {
        return baseAllocator_.Malloc(size);
    }
    void* Realloc(void* originalPtr, size_t originalSize, size_t newSize)
    {
        return baseAllocator_.Realloc(originalPtr, originalSize, newSize);
    }
    static void Free(void *ptr) RAPIDJSON_NOEXCEPT
    {
        BaseAllocator::Free(ptr);
    }

private:
    template <typename, typename>
    friend class StdAllocator; // access to StdAllocator<!T>.*

    BaseAllocator baseAllocator_;
};

#if !RAPIDJSON_HAS_CXX17 // std::allocator<void> deprecated in C++17
template <typename BaseAllocator>
class StdAllocator<void, BaseAllocator> :
    public std::allocator<void>
{
    typedef std::allocator<void> allocator_type;

public:
    typedef BaseAllocator BaseAllocatorType;

    StdAllocator() RAPIDJSON_NOEXCEPT :
        allocator_type(),
        baseAllocator_()
    { }

    StdAllocator(const StdAllocator& rhs) RAPIDJSON_NOEXCEPT :
        allocator_type(rhs),
        baseAllocator_(rhs.baseAllocator_)
    { }

    template<typename U>
    StdAllocator(const StdAllocator<U, BaseAllocator>& rhs) RAPIDJSON_NOEXCEPT :
        allocator_type(rhs),
        baseAllocator_(rhs.baseAllocator_)
    { }

    /* implicit */
    StdAllocator(const BaseAllocator& baseAllocator) RAPIDJSON_NOEXCEPT :
        allocator_type(),
        baseAllocator_(baseAllocator)
    { }

    ~StdAllocator() RAPIDJSON_NOEXCEPT
    { }

    template<typename U>
    struct rebind {
        typedef StdAllocator<U, BaseAllocator> other;
    };

    typedef typename allocator_type::value_type value_type;

private:
    template <typename, typename>
    friend class StdAllocator; // access to StdAllocator<!T>.*

    BaseAllocator baseAllocator_;
};
#endif

#ifdef __GNUC__
RAPIDJSON_DIAG_POP
#endif

RAPIDJSON_NAMESPACE_END

#endif // RAPIDJSON_ENCODINGS_H_