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110 lines
3.0 KiB
C++
110 lines
3.0 KiB
C++
#pragma once
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#include <unistd.h>
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#include <errno.h>
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#include <DB/Common/ProfileEvents.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/ReadBufferFromFileBase.h>
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#include <DB/IO/ReadBuffer.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 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; /// Какому сдвигу в файле соответствует working_buffer.end().
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bool nextImpl()
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{
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size_t bytes_read = 0;
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while (!bytes_read)
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{
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ProfileEvents::increment(ProfileEvents::ReadBufferFromFileDescriptorRead);
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ssize_t res = ::read(fd, internal_buffer.begin(), internal_buffer.size());
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if (!res)
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break;
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if (-1 == res && errno != EINTR)
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throwFromErrno("Cannot read from file " + getFileName(), ErrorCodes::CANNOT_READ_FROM_FILE_DESCRIPTOR);
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if (res > 0)
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bytes_read += res;
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}
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pos_in_file += bytes_read;
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if (bytes_read)
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working_buffer.resize(bytes_read);
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else
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return false;
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return true;
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}
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/// Имя или описание файла
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virtual std::string getFileName() const noexcept override
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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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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 noexcept override
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{
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return fd;
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}
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/// Если offset такой маленький, что мы не выйдем за пределы буфера, настоящий seek по файлу не делается.
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off_t seek(off_t offset, int whence = SEEK_CUR) override
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{
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off_t new_pos = offset;
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if (whence == SEEK_CUR)
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new_pos = pos_in_file - (working_buffer.end() - pos) + offset;
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else if (whence != SEEK_SET)
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throw Exception("ReadBufferFromFileDescriptor::seek expects SEEK_SET or SEEK_CUR as whence", ErrorCodes::ARGUMENT_OUT_OF_BOUND);
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/// Никуда не сдвинулись.
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if (new_pos + (working_buffer.end() - pos) == pos_in_file)
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return new_pos;
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if (hasPendingData() && new_pos <= pos_in_file && new_pos >= pos_in_file - static_cast<off_t>(working_buffer.size()))
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{
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/// Остались в пределах буфера.
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pos = working_buffer.begin() + (new_pos - (pos_in_file - working_buffer.size()));
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return new_pos;
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}
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else
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{
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ProfileEvents::increment(ProfileEvents::Seek);
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pos = working_buffer.end();
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off_t res = lseek(fd, new_pos, SEEK_SET);
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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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pos_in_file = new_pos;
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return res;
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}
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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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};
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}
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