third_party/WebKit/Source/platform/PODArena.h

   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 blink {
  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         void* allocate(size_t size) override { return fastMalloc(size); }
  68         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 blink
 199
 200 #endif // PODArena_h