ClickHouse/dbms/include/DB/IO/BufferWithOwnMemory.h
2015-11-15 06:09:40 +03:00

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#pragma once
#include <boost/noncopyable.hpp>
#include <DB/Common/ProfileEvents.h>
#include <DB/Common/Allocator.h>
#include <DB/Common/Exception.h>
#include <DB/Core/ErrorCodes.h>
#include <DB/Core/Defines.h>
namespace DB
{
/** Замена std::vector<char> для использования в буферах.
* Отличается тем, что не делает лишний memset. (И почти ничего не делает.)
* Также можно попросить выделять выровненный кусок памяти.
*/
struct Memory : boost::noncopyable, Allocator<false>
{
size_t m_capacity = 0;
size_t m_size = 0;
char * m_data = nullptr;
size_t alignment = 0;
Memory() {}
/// Если alignment != 0, то будет выделяться память, выровненная на alignment.
Memory(size_t size_, size_t alignment_ = 0) : m_capacity(size_), m_size(m_capacity), alignment(alignment_)
{
alloc();
}
~Memory()
{
dealloc();
}
Memory(Memory && rhs)
{
*this = std::move(rhs);
}
Memory & operator=(Memory && rhs)
{
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]; }
void resize(size_t new_size)
{
if (0 == m_capacity)
{
m_size = m_capacity = new_size;
alloc();
}
else if (new_size < m_capacity)
{
m_size = new_size;
return;
}
else
{
new_size = align(new_size, alignment);
/// @todo pointer to void can be converted to pointer to any type with static_cast by ISO C++, reinterpret_cast has no advantages
m_data = reinterpret_cast<char *>(Allocator::realloc(m_data, m_capacity, new_size, alignment));
m_capacity = new_size;
m_size = m_capacity;
}
}
static size_t align(const size_t value, const size_t alignment)
{
if (!alignment)
return value;
return (value + alignment - 1) / alignment * alignment;
}
private:
void alloc()
{
if (!m_capacity)
{
m_data = nullptr;
return;
}
ProfileEvents::increment(ProfileEvents::IOBufferAllocs);
ProfileEvents::increment(ProfileEvents::IOBufferAllocBytes, m_capacity);
size_t new_capacity = align(m_capacity, alignment);
/// @todo pointer to void can be converted to pointer to any type with static_cast by ISO C++, reinterpret_cast has no advantages
m_data = reinterpret_cast<char *>(Allocator::alloc(new_capacity, alignment));
m_capacity = new_capacity;
m_size = m_capacity;
}
void dealloc()
{
if (!m_data)
return;
/// @todo pointer to any type can be implicitly converted to pointer to void, no cast required
Allocator::free(reinterpret_cast<void *>(m_data), m_capacity);
m_data = nullptr; /// Чтобы избежать double free, если последующий вызов alloc кинет исключение.
}
};
/** Буфер, который может сам владеть своим куском памяти для работы.
* Аргумент шаблона - ReadBuffer или WriteBuffer
*/
template <typename Base>
class BufferWithOwnMemory : public Base
{
protected:
Memory memory;
public:
/// Если передать не-NULL existing_memory, то буфер не будет создавать свой кусок памяти, а будет использовать существующий (и не будет им владеть).
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[0], size);
}
};
}