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      1 /*
      2  * Copyright (C) 2010 Google Inc. All rights reserved.
      3  *
      4  * Redistribution and use in source and binary forms, with or without
      5  * modification, are permitted provided that the following conditions
      6  * are met:
      7  *
      8  * 1.  Redistributions of source code must retain the above copyright
      9  *     notice, this list of conditions and the following disclaimer.
     10  * 2.  Redistributions in binary form must reproduce the above copyright
     11  *     notice, this list of conditions and the following disclaimer in the
     12  *     documentation and/or other materials provided with the distribution.
     13  *
     14  * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
     15  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
     16  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
     17  * DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
     18  * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
     19  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
     20  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
     21  * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
     22  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
     23  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     24  */
     25 
     26 #ifndef PODArena_h
     27 #define PODArena_h
     28 
     29 #include <stdint.h>
     30 #include "wtf/Assertions.h"
     31 #include "wtf/FastMalloc.h"
     32 #include "wtf/Noncopyable.h"
     33 #include "wtf/OwnPtr.h"
     34 #include "wtf/PassOwnPtr.h"
     35 #include "wtf/RefCounted.h"
     36 #include "wtf/Vector.h"
     37 
     38 namespace WebCore {
     39 
     40 // An arena which allocates only Plain Old Data (POD), or classes and
     41 // structs bottoming out in Plain Old Data. NOTE: the constructors of
     42 // the objects allocated in this arena are called, but _not_ their
     43 // destructors.
     44 
     45 class PODArena FINAL : public RefCounted<PODArena> {
     46 public:
     47     // The arena is configured with an allocator, which is responsible
     48     // for allocating and freeing chunks of memory at a time.
     49     class Allocator : public RefCounted<Allocator> {
     50     public:
     51         virtual void* allocate(size_t size) = 0;
     52         virtual void free(void* ptr) = 0;
     53     protected:
     54         virtual ~Allocator() { }
     55         friend class WTF::RefCounted<Allocator>;
     56     };
     57 
     58     // The Arena's default allocator, which uses fastMalloc and
     59     // fastFree to allocate chunks of storage.
     60     class FastMallocAllocator : public Allocator {
     61     public:
     62         static PassRefPtr<FastMallocAllocator> create()
     63         {
     64             return adoptRef(new FastMallocAllocator);
     65         }
     66 
     67         virtual void* allocate(size_t size) OVERRIDE { return fastMalloc(size); }
     68         virtual void free(void* ptr) OVERRIDE { fastFree(ptr); }
     69 
     70     protected:
     71         FastMallocAllocator() { }
     72     };
     73 
     74     // Creates a new PODArena configured with a FastMallocAllocator.
     75     static PassRefPtr<PODArena> create()
     76     {
     77         return adoptRef(new PODArena);
     78     }
     79 
     80     // Creates a new PODArena configured with the given Allocator.
     81     static PassRefPtr<PODArena> create(PassRefPtr<Allocator> allocator)
     82     {
     83         return adoptRef(new PODArena(allocator));
     84     }
     85 
     86     // Allocates an object from the arena.
     87     template<class T> T* allocateObject()
     88     {
     89         return new (allocateBase<T>()) T();
     90     }
     91 
     92     // Allocates an object from the arena, calling a single-argument constructor.
     93     template<class T, class Argument1Type> T* allocateObject(const Argument1Type& argument1)
     94     {
     95         return new (allocateBase<T>()) T(argument1);
     96     }
     97 
     98     // The initial size of allocated chunks; increases as necessary to
     99     // satisfy large allocations. Mainly public for unit tests.
    100     enum {
    101         DefaultChunkSize = 16384
    102     };
    103 
    104 protected:
    105     friend class WTF::RefCounted<PODArena>;
    106 
    107     PODArena()
    108         : m_allocator(FastMallocAllocator::create())
    109         , m_current(0)
    110         , m_currentChunkSize(DefaultChunkSize) { }
    111 
    112     explicit PODArena(PassRefPtr<Allocator> allocator)
    113         : m_allocator(allocator)
    114         , m_current(0)
    115         , m_currentChunkSize(DefaultChunkSize) { }
    116 
    117     // Returns the alignment requirement for classes and structs on the
    118     // current platform.
    119     template <class T> static size_t minAlignment()
    120     {
    121         return WTF_ALIGN_OF(T);
    122     }
    123 
    124     template<class T> void* allocateBase()
    125     {
    126         void* ptr = 0;
    127         size_t roundedSize = roundUp(sizeof(T), minAlignment<T>());
    128         if (m_current)
    129             ptr = m_current->allocate(roundedSize);
    130 
    131         if (!ptr) {
    132             if (roundedSize > m_currentChunkSize)
    133                 m_currentChunkSize = roundedSize;
    134             m_chunks.append(adoptPtr(new Chunk(m_allocator.get(), m_currentChunkSize)));
    135             m_current = m_chunks.last().get();
    136             ptr = m_current->allocate(roundedSize);
    137         }
    138         return ptr;
    139     }
    140 
    141     // Rounds up the given allocation size to the specified alignment.
    142     size_t roundUp(size_t size, size_t alignment)
    143     {
    144         ASSERT(!(alignment % 2));
    145         return (size + alignment - 1) & ~(alignment - 1);
    146     }
    147 
    148     // Manages a chunk of memory and individual allocations out of it.
    149     class Chunk FINAL {
    150         WTF_MAKE_NONCOPYABLE(Chunk);
    151     public:
    152         // Allocates a block of memory of the given size from the passed
    153         // Allocator.
    154         Chunk(Allocator* allocator, size_t size)
    155             : m_allocator(allocator)
    156             , m_size(size)
    157             , m_currentOffset(0)
    158         {
    159             m_base = static_cast<uint8_t*>(m_allocator->allocate(size));
    160         }
    161 
    162         // Frees the memory allocated from the Allocator in the
    163         // constructor.
    164         ~Chunk()
    165         {
    166             m_allocator->free(m_base);
    167         }
    168 
    169         // Returns a pointer to "size" bytes of storage, or 0 if this
    170         // Chunk could not satisfy the allocation.
    171         void* allocate(size_t size)
    172         {
    173             // Check for overflow
    174             if (m_currentOffset + size < m_currentOffset)
    175                 return 0;
    176 
    177             if (m_currentOffset + size > m_size)
    178                 return 0;
    179 
    180             void* result = m_base + m_currentOffset;
    181             m_currentOffset += size;
    182             return result;
    183         }
    184 
    185     protected:
    186         Allocator* m_allocator;
    187         uint8_t* m_base;
    188         size_t m_size;
    189         size_t m_currentOffset;
    190     };
    191 
    192     RefPtr<Allocator> m_allocator;
    193     Chunk* m_current;
    194     size_t m_currentChunkSize;
    195     Vector<OwnPtr<Chunk> > m_chunks;
    196 };
    197 
    198 } // namespace WebCore
    199 
    200 #endif // PODArena_h
    201