ClickHouse/dbms/src/IO/MMapReadBufferFromFileDescriptor.h
2018-08-10 07:02:56 +03:00

40 lines
940 B
C++

#pragma once
#include <IO/ReadBuffer.h>
namespace DB
{
/** MMap range in a file and represent it as a ReadBuffer.
* Please note that mmap is not always the optimal way to read file.
* Also you cannot control whether and how long actual IO take place,
* so this method is not manageable and not recommended for anything except benchmarks.
*/
class MMapReadBufferFromFileDescriptor : public ReadBuffer
{
protected:
MMapReadBufferFromFileDescriptor() : ReadBuffer(nullptr, 0) {}
void init(int fd_, size_t offset, size_t length_);
void init(int fd_, size_t offset);
public:
MMapReadBufferFromFileDescriptor(int fd, size_t offset, size_t length);
/// Map till end of file.
MMapReadBufferFromFileDescriptor(int fd, size_t offset);
~MMapReadBufferFromFileDescriptor() override;
/// unmap memory before call to destructor
void finish();
private:
size_t length = 0;
int fd = -1;
};
}