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