ClickHouse/dbms/src/Common/Arena.h

196 lines
5.1 KiB
C++

#pragma once
#include <string.h>
#include <memory>
#include <vector>
#include <boost/noncopyable.hpp>
#include <common/likely.h>
#include <Core/Defines.h>
#include <Common/ProfileEvents.h>
#include <Common/Allocator.h>
namespace ProfileEvents
{
extern const Event ArenaAllocChunks;
extern const Event ArenaAllocBytes;
}
namespace DB
{
/** Memory pool to append something. For example, short strings.
* Usage scenario:
* - put lot of strings inside pool, keep their addresses;
* - addresses remain valid during lifetime of pool;
* - at destruction of pool, all memory is freed;
* - memory is allocated and freed by large chunks;
* - freeing parts of data is not possible (but look at ArenaWithFreeLists if you need);
*/
class Arena : private boost::noncopyable
{
private:
/// Contiguous chunk of memory and pointer to free space inside it. Member of single-linked list.
struct Chunk : private Allocator<false> /// empty base optimization
{
char * begin;
char * pos;
char * end;
Chunk * prev;
Chunk(size_t size_, Chunk * prev_)
{
ProfileEvents::increment(ProfileEvents::ArenaAllocChunks);
ProfileEvents::increment(ProfileEvents::ArenaAllocBytes, size_);
begin = reinterpret_cast<char *>(Allocator::alloc(size_));
pos = begin;
end = begin + size_;
prev = prev_;
}
~Chunk()
{
Allocator::free(begin, size());
if (prev)
delete prev;
}
size_t size() const { return end - begin; }
size_t remaining() const { return end - pos; }
};
size_t growth_factor;
size_t linear_growth_threshold;
/// Last contiguous chunk of memory.
Chunk * head;
size_t size_in_bytes;
static size_t roundUpToPageSize(size_t s)
{
return (s + 4096 - 1) / 4096 * 4096;
}
/// If chunks size is less than 'linear_growth_threshold', then use exponential growth, otherwise - linear growth
/// (to not allocate too much excessive memory).
size_t nextSize(size_t min_next_size) const
{
size_t size_after_grow = 0;
if (head->size() < linear_growth_threshold)
size_after_grow = head->size() * growth_factor;
else
size_after_grow = linear_growth_threshold;
if (size_after_grow < min_next_size)
size_after_grow = min_next_size;
return roundUpToPageSize(size_after_grow);
}
/// Add next contiguous chunk of memory with size not less than specified.
void NO_INLINE addChunk(size_t min_size)
{
head = new Chunk(nextSize(min_size), head);
size_in_bytes += head->size();
}
friend class ArenaAllocator;
public:
Arena(size_t initial_size_ = 4096, size_t growth_factor_ = 2, size_t linear_growth_threshold_ = 128 * 1024 * 1024)
: growth_factor(growth_factor_), linear_growth_threshold(linear_growth_threshold_),
head(new Chunk(initial_size_, nullptr)), size_in_bytes(head->size())
{
}
~Arena()
{
delete head;
}
/// Get piece of memory, without alignment.
char * alloc(size_t size)
{
if (unlikely(head->pos + size > head->end))
addChunk(size);
char * res = head->pos;
head->pos += size;
return res;
}
/** Rollback just performed allocation.
* Must pass size not more that was just allocated.
*/
void rollback(size_t size)
{
head->pos -= size;
}
/** Begin or expand allocation of contiguous piece of memory.
* 'begin' - current begin of piece of memory, if it need to be expanded, or nullptr, if it need to be started.
* If there is no space in chunk to expand current piece of memory - then copy all piece to new chunk and change value of 'begin'.
* NOTE This method is usable only for latest allocation. For earlier allocations, see 'realloc' method.
*/
char * allocContinue(size_t size, char const *& begin)
{
while (unlikely(head->pos + size > head->end))
{
char * prev_end = head->pos;
addChunk(size);
if (begin)
begin = insert(begin, prev_end - begin);
else
break;
}
char * res = head->pos;
head->pos += size;
if (!begin)
begin = res;
return res;
}
/// NOTE Old memory region is wasted.
char * realloc(const char * old_data, size_t old_size, size_t new_size)
{
char * res = alloc(new_size);
if (old_data)
memcpy(res, old_data, old_size);
return res;
}
/// Insert string without alignment.
const char * insert(const char * data, size_t size)
{
char * res = alloc(size);
memcpy(res, data, size);
return res;
}
/// Size of chunks in bytes.
size_t size() const
{
return size_in_bytes;
}
size_t remainingSpaceInCurrentChunk() const
{
return head->remaining();
}
};
using ArenaPtr = std::shared_ptr<Arena>;
using Arenas = std::vector<ArenaPtr>;
}