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#pragma once
#include <IO/ReadBufferFromFileBase.h>
#include <IO/AsynchronousReader.h>
#include <Interpreters/Context.h>
#include <Common/Throttler_fwd.h>
#include <Common/Priority.h>
#include <optional>
#include <unistd.h>
namespace DB
{
/** Use ready file descriptor. Does not open or close a file.
*/
class AsynchronousReadBufferFromFileDescriptor : public ReadBufferFromFileBase
{
protected:
IAsynchronousReader & reader;
Priority base_priority;
Memory<> prefetch_buffer;
std::future<IAsynchronousReader::Result> prefetch_future;
const size_t required_alignment = 0; /// For O_DIRECT both file offsets and memory addresses have to be aligned.
size_t file_offset_of_buffer_end = 0; /// What offset in file corresponds to working_buffer.end().
size_t bytes_to_ignore = 0; /// How many bytes should we ignore upon a new read request.
int fd;
ThrottlerPtr throttler;
bool nextImpl() override;
/// Name or some description of file.
std::string getFileName() const override;
void finalize();
public:
AsynchronousReadBufferFromFileDescriptor(
IAsynchronousReader & reader_,
Priority priority_,
int fd_,
size_t buf_size = DBMS_DEFAULT_BUFFER_SIZE,
char * existing_memory = nullptr,
size_t alignment = 0,
std::optional<size_t> file_size_ = std::nullopt,
ThrottlerPtr throttler_ = {});
~AsynchronousReadBufferFromFileDescriptor() override;
void prefetch(Priority priority) override;
int getFD() const
{
return fd;
}
off_t getPosition() override
{
return file_offset_of_buffer_end - (working_buffer.end() - pos);
}
/// If 'offset' is small enough to stay in buffer after seek, then true seek in file does not happen.
off_t seek(off_t off, int whence) override;
/// Seek to the beginning, discarding already read data if any. Useful to reread file that changes on every read.
void rewind();
size_t getFileSize() override;
private:
std::future<IAsynchronousReader::Result> asyncReadInto(char * data, size_t size, Priority priority);
};
}
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