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88 lines
1.9 KiB
C++
88 lines
1.9 KiB
C++
#pragma once
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#include <unistd.h>
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#include <errno.h>
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#include <DB/Core/Exception.h>
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#include <DB/Core/ErrorCodes.h>
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#include <DB/IO/WriteBuffer.h>
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#include <DB/IO/WriteHelpers.h>
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#include <DB/IO/BufferWithOwnMemory.h>
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namespace DB
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{
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/** Работает с готовым файловым дескриптором. Не открывает и не закрывает файл.
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*/
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class WriteBufferFromFileDescriptor : public BufferWithOwnMemory<WriteBuffer>
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{
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protected:
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int fd;
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void nextImpl()
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{
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if (!offset())
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return;
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size_t bytes_written = 0;
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while (bytes_written != offset())
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{
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ssize_t res = ::write(fd, working_buffer.begin() + bytes_written, offset() - bytes_written);
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if ((-1 == res || 0 == res) && errno != EINTR)
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throwFromErrno("Cannot write to file " + getFileName(), ErrorCodes::CANNOT_WRITE_TO_FILE_DESCRIPTOR);
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if (res > 0)
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bytes_written += res;
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}
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}
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/// Имя или описание файла
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virtual std::string getFileName()
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{
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return "(fd = " + toString(fd) + ")";
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}
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public:
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WriteBufferFromFileDescriptor(int fd_ = -1, size_t buf_size = DBMS_DEFAULT_BUFFER_SIZE)
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: BufferWithOwnMemory<WriteBuffer>(buf_size), fd(fd_) {}
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/** Можно вызывать для инициализации, если нужный fd не был передан в конструктор.
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* Менять fd во время работы нельзя.
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*/
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void setFD(int fd_)
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{
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fd = fd_;
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}
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~WriteBufferFromFileDescriptor()
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{
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if (!std::uncaught_exception())
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next();
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}
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int getFD()
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{
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return fd;
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}
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off_t seek(off_t offset, int whence = SEEK_SET)
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{
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off_t res = lseek(fd, offset, whence);
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if (-1 == res)
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throwFromErrno("Cannot seek through file " + getFileName(), ErrorCodes::CANNOT_SEEK_THROUGH_FILE);
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return res;
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}
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void truncate(off_t length = 0)
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{
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int res = ftruncate(fd, length);
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if (-1 == res)
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throwFromErrno("Cannot truncate file " + getFileName(), ErrorCodes::CANNOT_TRUNCATE_FILE);
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}
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};
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}
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