mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-11-18 13:42:02 +00:00
48 lines
1.1 KiB
C++
48 lines
1.1 KiB
C++
#pragma once
|
|
|
|
#include <unistd.h>
|
|
|
|
#include <DB/IO/ReadBufferFromFileBase.h>
|
|
#include <DB/IO/ReadBuffer.h>
|
|
|
|
|
|
namespace DB
|
|
{
|
|
|
|
/** Use ready file descriptor. Does not open or close a file.
|
|
*/
|
|
class ReadBufferFromFileDescriptor : public ReadBufferFromFileBase
|
|
{
|
|
protected:
|
|
int fd;
|
|
off_t pos_in_file; /// What offset in file corresponds to working_buffer.end().
|
|
|
|
bool nextImpl() override;
|
|
|
|
/// Name or some description of file.
|
|
std::string getFileName() const override;
|
|
|
|
public:
|
|
ReadBufferFromFileDescriptor(int fd_, size_t buf_size = DBMS_DEFAULT_BUFFER_SIZE, char * existing_memory = nullptr, size_t alignment = 0)
|
|
: ReadBufferFromFileBase(buf_size, existing_memory, alignment), fd(fd_), pos_in_file(0) {}
|
|
|
|
int getFD() const override
|
|
{
|
|
return fd;
|
|
}
|
|
|
|
off_t getPositionInFile() override
|
|
{
|
|
return pos_in_file - (working_buffer.end() - pos);
|
|
}
|
|
|
|
private:
|
|
/// If 'offset' is small enough to stay in buffer after seek, then true seek in file does not happen.
|
|
off_t doSeek(off_t offset, int whence) override;
|
|
|
|
/// Assuming file descriptor supports 'select', check that we have data to read or wait until timeout.
|
|
bool poll(size_t timeout_microseconds);
|
|
};
|
|
|
|
}
|