ClickHouse/dbms/IO/BufferWithOwnMemory.h

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#pragma once
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#include <boost/noncopyable.hpp>
#include <Common/ProfileEvents.h>
#include <Common/Allocator.h>
#include <Common/Exception.h>
#include <Core/Defines.h>
namespace ProfileEvents
{
extern const Event IOBufferAllocs;
extern const Event IOBufferAllocBytes;
}
namespace DB
{
/** Replacement for std::vector<char> to use in buffers.
* Differs in that is doesn't do unneeded memset. (And also tries to do as little as possible.)
* Also allows to allocate aligned piece of memory (to use with O_DIRECT, for example).
*/
template <typename Allocator = Allocator<false>>
struct Memory : boost::noncopyable, Allocator
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{
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/// Padding is needed to allow usage of 'memcpySmallAllowReadWriteOverflow15' function with this buffer.
static constexpr size_t pad_right = 15;
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size_t m_capacity = 0; /// With padding.
size_t m_size = 0;
char * m_data = nullptr;
size_t alignment = 0;
Memory() {}
/// If alignment != 0, then allocate memory aligned to specified value.
Memory(size_t size_, size_t alignment_ = 0) : m_capacity(size_), m_size(m_capacity), alignment(alignment_)
{
alloc();
}
~Memory()
{
dealloc();
}
Memory(Memory && rhs) noexcept
{
*this = std::move(rhs);
}
Memory & operator=(Memory && rhs) noexcept
{
std::swap(m_capacity, rhs.m_capacity);
std::swap(m_size, rhs.m_size);
std::swap(m_data, rhs.m_data);
std::swap(alignment, rhs.alignment);
return *this;
}
size_t size() const { return m_size; }
const char & operator[](size_t i) const { return m_data[i]; }
char & operator[](size_t i) { return m_data[i]; }
const char * data() const { return m_data; }
char * data() { return m_data; }
void resize(size_t new_size)
{
if (0 == m_capacity)
{
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m_size = new_size;
m_capacity = new_size;
alloc();
}
else if (new_size <= m_capacity - pad_right)
{
m_size = new_size;
return;
}
else
{
size_t new_capacity = align(new_size + pad_right, alignment);
m_data = static_cast<char *>(Allocator::realloc(m_data, m_capacity, new_capacity, alignment));
m_capacity = new_capacity;
m_size = m_capacity - pad_right;
}
}
private:
static size_t align(const size_t value, const size_t alignment)
{
if (!alignment)
return value;
return (value + alignment - 1) / alignment * alignment;
}
void alloc()
{
if (!m_capacity)
{
m_data = nullptr;
return;
}
size_t padded_capacity = m_capacity + pad_right;
ProfileEvents::increment(ProfileEvents::IOBufferAllocs);
ProfileEvents::increment(ProfileEvents::IOBufferAllocBytes, padded_capacity);
size_t new_capacity = align(padded_capacity, alignment);
m_data = static_cast<char *>(Allocator::alloc(new_capacity, alignment));
m_capacity = new_capacity;
m_size = m_capacity - pad_right;
}
void dealloc()
{
if (!m_data)
return;
Allocator::free(m_data, m_capacity);
m_data = nullptr; /// To avoid double free if next alloc will throw an exception.
}
};
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/** Buffer that could own its working memory.
* Template parameter: ReadBuffer or WriteBuffer
*/
template <typename Base>
class BufferWithOwnMemory : public Base
{
protected:
Memory<> memory;
public:
/// If non-nullptr 'existing_memory' is passed, then buffer will not create its own memory and will use existing_memory without ownership.
BufferWithOwnMemory(size_t size = DBMS_DEFAULT_BUFFER_SIZE, char * existing_memory = nullptr, size_t alignment = 0)
: Base(nullptr, 0), memory(existing_memory ? 0 : size, alignment)
{
Base::set(existing_memory ? existing_memory : memory.data(), size);
Base::padded = !existing_memory;
}
};
}