// See www.openfst.org for extensive documentation on this weighted
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// finite-state transducer library.
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#ifndef FST_MAPPED_FILE_H_
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#define FST_MAPPED_FILE_H_
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#include <cstddef>
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#include <istream>
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#include <string>
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#include <fst/compat.h>
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#include <fst/flags.h>
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namespace fst {
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// A memory region is a simple abstraction for allocated memory or data from
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// memory-mapped files. If mmap is null, then data represents an owned region
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// of size bytes. Otherwise, mmap and size refer to the mapping and data is a
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// casted pointer to a region contained within [mmap, mmap + size). If size is
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// 0, then mmap and data refer to a block of memory managed externally by some
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// other allocator. The offset is used when allocating memory to providing
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// padding for alignment.
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struct MemoryRegion {
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void *data;
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void *mmap;
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size_t size;
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int offset;
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};
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class MappedFile {
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public:
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~MappedFile();
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void *mutable_data() const { return region_.data; }
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const void *data() const { return region_.data; }
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// Returns a MappedFile object that contains the contents of the input stream
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// strm starting from the current file position with size bytes. The memorymap
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// bool is advisory, and Map will default to allocating and reading. The
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// source argument needs to contain the filename that was used to open the
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// input stream.
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static MappedFile *Map(std::istream *istrm, bool memorymap,
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const string &source, size_t size);
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// Returns a MappedFile object that contains the contents of the file referred
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// to by the file descriptor starting from pos with size bytes. If the
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// memory mapping fails, nullptr is returned. In contrast to Map(), this
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// factory function does not backoff to allocating and reading.
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static MappedFile *MapFromFileDescriptor(int fd, int pos, size_t size);
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// Creates a MappedFile object with a new[]'ed block of memory of size. The
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// align argument can be used to specify a desired block alignment.
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// This is RECOMMENDED FOR INTERNAL USE ONLY as it may change in future
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// releases.
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static MappedFile *Allocate(size_t size, int align = kArchAlignment);
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// Creates a MappedFile object pointing to a borrowed reference to data. This
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// block of memory is not owned by the MappedFile object and will not be
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// freed. This is RECOMMENDED FOR INTERNAL USE ONLY, may change in future
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// releases.
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static MappedFile *Borrow(void *data);
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// Alignment required for mapping structures in bytes. Regions of memory that
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// are not aligned upon a 128-bit boundary are read from the file instead.
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// This is consistent with the alignment boundary set in ConstFst and
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// CompactFst.
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static constexpr int kArchAlignment = 16;
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static constexpr size_t kMaxReadChunk = 256 * 1024 * 1024; // 256 MB.
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private:
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explicit MappedFile(const MemoryRegion ®ion);
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MemoryRegion region_;
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MappedFile(const MappedFile &) = delete;
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MappedFile &operator=(const MappedFile &) = delete;
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};
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} // namespace fst
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#endif // FST_MAPPED_FILE_H_
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