ClickHouse/src/Common/ArenaAllocator.h

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#pragma once
#include <Common/Arena.h>
#include <Common/Allocator.h>
namespace DB
{
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/// Allocator which proxies all allocations to Arena. Used in aggregate functions.
class ArenaAllocator
{
public:
static void * alloc(size_t size, Arena * arena)
{
return arena->alloc(size);
}
static void * realloc(void * buf, size_t old_size, size_t new_size, Arena * arena)
{
char const * data = reinterpret_cast<char *>(buf);
// Invariant should be maintained: new_size > old_size
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if (data + old_size == arena->head.pos)
{
// Consecutive optimization
arena->allocContinue(new_size - old_size, data);
return reinterpret_cast<void *>(const_cast<char *>(data));
}
else
{
return arena->realloc(data, old_size, new_size);
}
}
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static void free(void * /*buf*/, size_t /*size*/)
{
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// Do nothing, trash in arena remains.
}
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protected:
static constexpr size_t getStackThreshold()
{
return 0;
}
};
/// Allocates in Arena with proper alignment.
template <size_t alignment>
class AlignedArenaAllocator
{
public:
static void * alloc(size_t size, Arena * arena)
{
return arena->alignedAlloc(size, alignment);
}
static void * realloc(void * buf, size_t old_size, size_t new_size, Arena * arena)
{
char const * data = reinterpret_cast<char *>(buf);
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if (data + old_size == arena->head.pos)
{
arena->allocContinue(new_size - old_size, data, alignment);
return reinterpret_cast<void *>(const_cast<char *>(data));
}
else
{
return arena->alignedRealloc(data, old_size, new_size, alignment);
}
}
static void free(void * /*buf*/, size_t /*size*/)
{
}
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protected:
static constexpr size_t getStackThreshold()
{
return 0;
}
};
/// Switches to ordinary Allocator after REAL_ALLOCATION_TRESHOLD bytes to avoid fragmentation and trash in Arena.
template <size_t REAL_ALLOCATION_TRESHOLD = 4096, typename TRealAllocator = Allocator<false>, typename TArenaAllocator = ArenaAllocator, size_t alignment = 0>
class MixedArenaAllocator : private TRealAllocator
{
public:
void * alloc(size_t size, Arena * arena)
{
return (size < REAL_ALLOCATION_TRESHOLD) ? TArenaAllocator::alloc(size, arena) : TRealAllocator::alloc(size, alignment);
}
void * realloc(void * buf, size_t old_size, size_t new_size, Arena * arena)
{
// Invariant should be maintained: new_size > old_size
if (new_size < REAL_ALLOCATION_TRESHOLD)
return TArenaAllocator::realloc(buf, old_size, new_size, arena);
if (old_size >= REAL_ALLOCATION_TRESHOLD)
return TRealAllocator::realloc(buf, old_size, new_size, alignment);
void * new_buf = TRealAllocator::alloc(new_size, alignment);
memcpy(new_buf, buf, old_size);
return new_buf;
}
void free(void * buf, size_t size)
{
if (size >= REAL_ALLOCATION_TRESHOLD)
TRealAllocator::free(buf, size);
}
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protected:
static constexpr size_t getStackThreshold()
{
return 0;
}
};
template <size_t alignment, size_t REAL_ALLOCATION_TRESHOLD = 4096>
using MixedAlignedArenaAllocator = MixedArenaAllocator<REAL_ALLOCATION_TRESHOLD, Allocator<false>, AlignedArenaAllocator<alignment>, alignment>;
template <size_t N = 64, typename Base = ArenaAllocator>
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class ArenaAllocatorWithStackMemory : public Base
{
char stack_memory[N];
public:
void * alloc(size_t size, Arena * arena)
{
return (size > N) ? Base::alloc(size, arena) : stack_memory;
}
void * realloc(void * buf, size_t old_size, size_t new_size, Arena * arena)
{
/// Was in stack_memory, will remain there.
if (new_size <= N)
return buf;
/// Already was big enough to not fit in stack_memory.
if (old_size > N)
return Base::realloc(buf, old_size, new_size, arena);
/// Was in stack memory, but now will not fit there.
void * new_buf = Base::alloc(new_size, arena);
memcpy(new_buf, buf, old_size);
return new_buf;
}
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void free(void * /*buf*/, size_t /*size*/) {}
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protected:
static constexpr size_t getStackThreshold()
{
return N;
}
};
}