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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>
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
45 class PODArena : public RefCounted<PODArena> {
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> {
51 virtual void* allocate(size_t size) = 0;
52 virtual void free(void* ptr) = 0;
54 virtual ~Allocator() { }
55 friend class WTF::RefCounted<Allocator>;
58 // The Arena's default allocator, which uses fastMalloc and
59 // fastFree to allocate chunks of storage.
60 class FastMallocAllocator : public Allocator {
62 static PassRefPtr<FastMallocAllocator> create()
64 return adoptRef(new FastMallocAllocator);
67 virtual void* allocate(size_t size) { return fastMalloc(size); }
68 virtual void free(void* ptr) { fastFree(ptr); }
71 FastMallocAllocator() { }
74 // Creates a new PODArena configured with a FastMallocAllocator.
75 static PassRefPtr<PODArena> create()
77 return adoptRef(new PODArena);
80 // Creates a new PODArena configured with the given Allocator.
81 static PassRefPtr<PODArena> create(PassRefPtr<Allocator> allocator)
83 return adoptRef(new PODArena(allocator));
86 // Allocates an object from the arena.
87 template<class T> T* allocateObject()
89 void* ptr = allocateBase<T>();
91 // Use placement operator new to allocate a T at this location.
94 return static_cast<T*>(ptr);
97 // Allocates an object from the arena, calling a single-argument constructor.
98 template<class T, class Argument1Type> T* allocateObject(const Argument1Type& argument1)
100 void* ptr = allocateBase<T>();
102 // Use placement operator new to allocate a T at this location.
103 new(ptr) T(argument1);
105 return static_cast<T*>(ptr);
108 // The initial size of allocated chunks; increases as necessary to
109 // satisfy large allocations. Mainly public for unit tests.
111 DefaultChunkSize = 16384
116 friend class WTF::RefCounted<PODArena>;
120 : m_allocator(FastMallocAllocator::create())
122 , m_currentChunkSize(DefaultChunkSize) { }
124 explicit PODArena(PassRefPtr<Allocator> allocator)
125 : m_allocator(allocator)
127 , m_currentChunkSize(DefaultChunkSize) { }
129 // Returns the alignment requirement for classes and structs on the
131 template <class T> static size_t minAlignment()
133 return WTF_ALIGN_OF(T);
136 template<class T> void* allocateBase()
139 size_t roundedSize = roundUp(sizeof(T), minAlignment<T>());
141 ptr = m_current->allocate(roundedSize);
144 if (roundedSize > m_currentChunkSize)
145 m_currentChunkSize = roundedSize;
146 m_chunks.append(adoptPtr(new Chunk(m_allocator.get(), m_currentChunkSize)));
147 m_current = m_chunks.last().get();
148 ptr = m_current->allocate(roundedSize);
153 // Rounds up the given allocation size to the specified alignment.
154 size_t roundUp(size_t size, size_t alignment)
156 ASSERT(!(alignment % 2));
157 return (size + alignment - 1) & ~(alignment - 1);
160 // Manages a chunk of memory and individual allocations out of it.
162 WTF_MAKE_NONCOPYABLE(Chunk);
164 // Allocates a block of memory of the given size from the passed
166 Chunk(Allocator* allocator, size_t size)
167 : m_allocator(allocator)
171 m_base = static_cast<uint8_t*>(m_allocator->allocate(size));
174 // Frees the memory allocated from the Allocator in the
178 m_allocator->free(m_base);
181 // Returns a pointer to "size" bytes of storage, or 0 if this
182 // Chunk could not satisfy the allocation.
183 void* allocate(size_t size)
185 // Check for overflow
186 if (m_currentOffset + size < m_currentOffset)
189 if (m_currentOffset + size > m_size)
192 void* result = m_base + m_currentOffset;
193 m_currentOffset += size;
198 Allocator* m_allocator;
201 size_t m_currentOffset;
204 RefPtr<Allocator> m_allocator;
206 size_t m_currentChunkSize;
207 Vector<OwnPtr<Chunk> > m_chunks;
210 } // namespace WebCore