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61 lines
1.4 KiB
C++
61 lines
1.4 KiB
C++
#pragma once
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#include <cstddef>
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#include <Common/CurrentMetrics.h>
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namespace CurrentMetrics
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{
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extern const Metric MMappedFiles;
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extern const Metric MMappedFileBytes;
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}
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namespace DB
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{
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/// MMaps a region in file (or a whole file) into memory. Unmaps in destructor.
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/// Does not open or close file.
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class MMappedFileDescriptor
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{
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public:
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MMappedFileDescriptor(int fd_, size_t offset_, size_t length_);
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MMappedFileDescriptor(int fd_, size_t offset_);
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/// Makes empty object that can be initialized with `set`.
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MMappedFileDescriptor() = default;
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virtual ~MMappedFileDescriptor();
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char * getData() { return data; }
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const char * getData() const { return data; }
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int getFD() const { return fd; }
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size_t getOffset() const { return offset; }
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size_t getLength() const { return length; }
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/// Unmap memory before call to destructor
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void finish();
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/// Initialize or reset to another fd.
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void set(int fd_, size_t offset_, size_t length_);
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void set(int fd_, size_t offset_);
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MMappedFileDescriptor(const MMappedFileDescriptor &) = delete;
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MMappedFileDescriptor(MMappedFileDescriptor &&) = delete;
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protected:
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void init();
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int fd = -1;
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size_t offset = 0;
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size_t length = 0;
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char * data = nullptr;
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CurrentMetrics::Increment files_metric_increment{CurrentMetrics::MMappedFiles, 0};
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CurrentMetrics::Increment bytes_metric_increment{CurrentMetrics::MMappedFileBytes, 0};
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};
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}
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