tfrun

mio.hpp (59393B)

---

 /* Copyright 2017 https://github.com/mandreyel
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy of this
  * software and associated documentation files (the "Software"), to deal in the Software
  * without restriction, including without limitation the rights to use, copy, modify,
  * merge, publish, distribute, sublicense, and/or sell copies of the Software, and to
  * permit persons to whom the Software is furnished to do so, subject to the following
  * conditions:
  *
  * The above copyright notice and this permission notice shall be included in all copies
  * or substantial portions of the Software.
  *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
  * INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
  * PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
  * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
  * CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE
  * OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  */
 
 #ifndef MIO_MMAP_HEADER
 #define MIO_MMAP_HEADER
 
 // #include "mio/page.hpp"
 /* Copyright 2017 https://github.com/mandreyel
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy of this
  * software and associated documentation files (the "Software"), to deal in the Software
  * without restriction, including without limitation the rights to use, copy, modify,
  * merge, publish, distribute, sublicense, and/or sell copies of the Software, and to
  * permit persons to whom the Software is furnished to do so, subject to the following
  * conditions:
  *
  * The above copyright notice and this permission notice shall be included in all copies
  * or substantial portions of the Software.
  *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
  * INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
  * PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
  * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
  * CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE
  * OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  */
 
 #ifndef MIO_PAGE_HEADER
 #define MIO_PAGE_HEADER
 
 #ifdef _WIN32
 # include <windows.h>
 #else
 # include <unistd.h>
 #endif
 
 namespace mio {
 
 /**
  * This is used by `basic_mmap` to determine whether to create a read-only or
  * a read-write memory mapping.
  */
 enum class access_mode
 {
     read,
     write
 };
 
 /**
  * Determines the operating system's page allocation granularity.
  *
  * On the first call to this function, it invokes the operating system specific syscall
  * to determine the page size, caches the value, and returns it. Any subsequent call to
  * this function serves the cached value, so no further syscalls are made.
  */
 inline size_t page_size()
 {
     static const size_t page_size = []
     {
 #ifdef _WIN32
         SYSTEM_INFO SystemInfo;
         GetSystemInfo(&SystemInfo);
         return SystemInfo.dwAllocationGranularity;
 #else
         return sysconf(_SC_PAGE_SIZE);
 #endif
     }();
     return page_size;
 }
 
 /**
  * Alligns `offset` to the operating's system page size such that it subtracts the
  * difference until the nearest page boundary before `offset`, or does nothing if
  * `offset` is already page aligned.
  */
 inline size_t make_offset_page_aligned(size_t offset) noexcept
 {
     const size_t page_size_ = page_size();
     // Use integer division to round down to the nearest page alignment.
     return offset / page_size_ * page_size_;
 }
 
 } // namespace mio
 
 #endif // MIO_PAGE_HEADER
 
 
 #include <iterator>
 #include <string>
 #include <system_error>
 #include <cstdint>
 
 #ifdef _WIN32
 # ifndef WIN32_LEAN_AND_MEAN
 #  define WIN32_LEAN_AND_MEAN
 # endif // WIN32_LEAN_AND_MEAN
 # include <windows.h>
 #else // ifdef _WIN32
 # define INVALID_HANDLE_VALUE -1
 #endif // ifdef _WIN32
 
 namespace mio {
 
 // This value may be provided as the `length` parameter to the constructor or
 // `map`, in which case a memory mapping of the entire file is created.
 enum { map_entire_file = 0 };
 
 #ifdef _WIN32
 using file_handle_type = HANDLE;
 #else
 using file_handle_type = int;
 #endif
 
 // This value represents an invalid file handle type. This can be used to
 // determine whether `basic_mmap::file_handle` is valid, for example.
 const static file_handle_type invalid_handle = INVALID_HANDLE_VALUE;
 
 template<access_mode AccessMode, typename ByteT>
 struct basic_mmap
 {
     using value_type = ByteT;
     using size_type = size_t;
     using reference = value_type&;
     using const_reference = const value_type&;
     using pointer = value_type*;
     using const_pointer = const value_type*;
     using difference_type = std::ptrdiff_t;
     using iterator = pointer;
     using const_iterator = const_pointer;
     using reverse_iterator = std::reverse_iterator<iterator>;
     using const_reverse_iterator = std::reverse_iterator<const_iterator>;
     using iterator_category = std::random_access_iterator_tag;
     using handle_type = file_handle_type;
 
     static_assert(sizeof(ByteT) == sizeof(char), "ByteT must be the same size as char.");
 
 private:
     // Points to the first requested byte, and not to the actual start of the mapping.
     pointer data_ = nullptr;
 
     // Length--in bytes--requested by user (which may not be the length of the
     // full mapping) and the length of the full mapping.
     size_type length_ = 0;
     size_type mapped_length_ = 0;
 
     // Letting user map a file using both an existing file handle and a path
     // introcudes some complexity (see `is_handle_internal_`).
     // On POSIX, we only need a file handle to create a mapping, while on
     // Windows systems the file handle is necessary to retrieve a file mapping
     // handle, but any subsequent operations on the mapped region must be done
     // through the latter.
     handle_type file_handle_ = INVALID_HANDLE_VALUE;
 #ifdef _WIN32
     handle_type file_mapping_handle_ = INVALID_HANDLE_VALUE;
 #endif
 
     // Letting user map a file using both an existing file handle and a path
     // introcudes some complexity in that we must not close the file handle if
     // user provided it, but we must close it if we obtained it using the
     // provided path. For this reason, this flag is used to determine when to
     // close `file_handle_`.
     bool is_handle_internal_;
 
 public:
     /**
      * The default constructed mmap object is in a non-mapped state, that is,
      * any operation that attempts to access nonexistent underlying data will
      * result in undefined behaviour/segmentation faults.
      */
     basic_mmap() = default;
 
 #ifdef __cpp_exceptions
     /**
      * The same as invoking the `map` function, except any error that may occur
      * while establishing the mapping is wrapped in a `std::system_error` and is
      * thrown.
      */
     template<typename String>
     basic_mmap(const String& path, const size_type offset = 0, const size_type length = map_entire_file)
     {
         std::error_code error;
         map(path, offset, length, error);
         if(error) { throw std::system_error(error); }
     }
 
     /**
      * The same as invoking the `map` function, except any error that may occur
      * while establishing the mapping is wrapped in a `std::system_error` and is
      * thrown.
      */
     basic_mmap(const handle_type handle, const size_type offset = 0, const size_type length = map_entire_file)
     {
         std::error_code error;
         map(handle, offset, length, error);
         if(error) { throw std::system_error(error); }
     }
 #endif // __cpp_exceptions
 
     /**
      * `basic_mmap` has single-ownership semantics, so transferring ownership
      * may only be accomplished by moving the object.
      */
     basic_mmap(const basic_mmap&) = delete;
     basic_mmap(basic_mmap&&);
     basic_mmap& operator=(const basic_mmap&) = delete;
     basic_mmap& operator=(basic_mmap&&);
 
     /**
      * If this is a read-write mapping, the destructor invokes sync. Regardless
      * of the access mode, unmap is invoked as a final step.
      */
     ~basic_mmap();
 
     /**
      * On UNIX systems 'file_handle' and 'mapping_handle' are the same. On Windows,
      * however, a mapped region of a file gets its own handle, which is returned by
      * 'mapping_handle'.
      */
     handle_type file_handle() const noexcept { return file_handle_; }
     handle_type mapping_handle() const noexcept;
 
     /** Returns whether a valid memory mapping has been created. */
     bool is_open() const noexcept { return file_handle_ != invalid_handle; }
 
     /**
      * Returns true if no mapping was established, that is, conceptually the
      * same as though the length that was mapped was 0. This function is
      * provided so that this class has Container semantics.
      */
     bool empty() const noexcept { return length() == 0; }
 
     /** Returns true if a mapping was established. */
     bool is_mapped() const noexcept;
 
     /**
      * `size` and `length` both return the logical length, i.e. the number of bytes
      * user requested to be mapped, while `mapped_length` returns the actual number of
      * bytes that were mapped which is a multiple of the underlying operating system's
      * page allocation granularity.
      */
     size_type size() const noexcept { return length(); }
     size_type length() const noexcept { return length_; }
     size_type mapped_length() const noexcept { return mapped_length_; }
 
     /** Returns the offset relative to the start of the mapping. */
     size_type mapping_offset() const noexcept
     {
         return mapped_length_ - length_;
     }
 
     /**
      * Returns a pointer to the first requested byte, or `nullptr` if no memory mapping
      * exists.
      */
     template<
         access_mode A = AccessMode,
         typename = typename std::enable_if<A == access_mode::write>::type
     > pointer data() noexcept { return data_; }
     const_pointer data() const noexcept { return data_; }
 
     /**
      * Returns an iterator to the first requested byte, if a valid memory mapping
      * exists, otherwise this function call is undefined behaviour.
      */
     template<
         access_mode A = AccessMode,
         typename = typename std::enable_if<A == access_mode::write>::type
     > iterator begin() noexcept { return data(); }
     const_iterator begin() const noexcept { return data(); }
     const_iterator cbegin() const noexcept { return data(); }
 
     /**
      * Returns an iterator one past the last requested byte, if a valid memory mapping
      * exists, otherwise this function call is undefined behaviour.
      */
     template<
         access_mode A = AccessMode,
         typename = typename std::enable_if<A == access_mode::write>::type
     > iterator end() noexcept { return data() + length(); }
     const_iterator end() const noexcept { return data() + length(); }
     const_iterator cend() const noexcept { return data() + length(); }
 
     /**
      * Returns a reverse iterator to the last memory mapped byte, if a valid
      * memory mapping exists, otherwise this function call is undefined
      * behaviour.
      */
     template<
         access_mode A = AccessMode,
         typename = typename std::enable_if<A == access_mode::write>::type
     > reverse_iterator rbegin() noexcept { return reverse_iterator(end()); }
     const_reverse_iterator rbegin() const noexcept
     { return const_reverse_iterator(end()); }
     const_reverse_iterator crbegin() const noexcept
     { return const_reverse_iterator(end()); }
 
     /**
      * Returns a reverse iterator past the first mapped byte, if a valid memory
      * mapping exists, otherwise this function call is undefined behaviour.
      */
     template<
         access_mode A = AccessMode,
         typename = typename std::enable_if<A == access_mode::write>::type
     > reverse_iterator rend() noexcept { return reverse_iterator(begin()); }
     const_reverse_iterator rend() const noexcept
     { return const_reverse_iterator(begin()); }
     const_reverse_iterator crend() const noexcept
     { return const_reverse_iterator(begin()); }
 
     /**
      * Returns a reference to the `i`th byte from the first requested byte (as returned
      * by `data`). If this is invoked when no valid memory mapping has been created
      * prior to this call, undefined behaviour ensues.
      */
     reference operator[](const size_type i) noexcept { return data_[i]; }
     const_reference operator[](const size_type i) const noexcept { return data_[i]; }
 
     /**
      * Establishes a memory mapping with AccessMode. If the mapping is unsuccesful, the
      * reason is reported via `error` and the object remains in a state as if this
      * function hadn't been called.
      *
      * `path`, which must be a path to an existing file, is used to retrieve a file
      * handle (which is closed when the object destructs or `unmap` is called), which is
      * then used to memory map the requested region. Upon failure, `error` is set to
      * indicate the reason and the object remains in an unmapped state.
      *
      * `offset` is the number of bytes, relative to the start of the file, where the
      * mapping should begin. When specifying it, there is no need to worry about
      * providing a value that is aligned with the operating system's page allocation
      * granularity. This is adjusted by the implementation such that the first requested
      * byte (as returned by `data` or `begin`), so long as `offset` is valid, will be at
      * `offset` from the start of the file.
      *
      * `length` is the number of bytes to map. It may be `map_entire_file`, in which
      * case a mapping of the entire file is created.
      */
     template<typename String>
     void map(const String& path, const size_type offset,
             const size_type length, std::error_code& error);
 
     /**
      * Establishes a memory mapping with AccessMode. If the mapping is unsuccesful, the
      * reason is reported via `error` and the object remains in a state as if this
      * function hadn't been called.
      *
      * `path`, which must be a path to an existing file, is used to retrieve a file
      * handle (which is closed when the object destructs or `unmap` is called), which is
      * then used to memory map the requested region. Upon failure, `error` is set to
      * indicate the reason and the object remains in an unmapped state.
      *
      * The entire file is mapped.
      */
     template<typename String>
     void map(const String& path, std::error_code& error)
     {
         map(path, 0, map_entire_file, error);
     }
 
     /**
      * Establishes a memory mapping with AccessMode. If the mapping is
      * unsuccesful, the reason is reported via `error` and the object remains in
      * a state as if this function hadn't been called.
      *
      * `handle`, which must be a valid file handle, which is used to memory map the
      * requested region. Upon failure, `error` is set to indicate the reason and the
      * object remains in an unmapped state.
      *
      * `offset` is the number of bytes, relative to the start of the file, where the
      * mapping should begin. When specifying it, there is no need to worry about
      * providing a value that is aligned with the operating system's page allocation
      * granularity. This is adjusted by the implementation such that the first requested
      * byte (as returned by `data` or `begin`), so long as `offset` is valid, will be at
      * `offset` from the start of the file.
      *
      * `length` is the number of bytes to map. It may be `map_entire_file`, in which
      * case a mapping of the entire file is created.
      */
     void map(const handle_type handle, const size_type offset,
             const size_type length, std::error_code& error);
 
     /**
      * Establishes a memory mapping with AccessMode. If the mapping is
      * unsuccesful, the reason is reported via `error` and the object remains in
      * a state as if this function hadn't been called.
      *
      * `handle`, which must be a valid file handle, which is used to memory map the
      * requested region. Upon failure, `error` is set to indicate the reason and the
      * object remains in an unmapped state.
      *
      * The entire file is mapped.
      */
     void map(const handle_type handle, std::error_code& error)
     {
         map(handle, 0, map_entire_file, error);
     }
 
     /**
      * If a valid memory mapping has been created prior to this call, this call
      * instructs the kernel to unmap the memory region and disassociate this object
      * from the file.
      *
      * The file handle associated with the file that is mapped is only closed if the
      * mapping was created using a file path. If, on the other hand, an existing
      * file handle was used to create the mapping, the file handle is not closed.
      */
     void unmap();
 
     void swap(basic_mmap& other);
 
     /** Flushes the memory mapped page to disk. Errors are reported via `error`. */
     template<access_mode A = AccessMode>
     typename std::enable_if<A == access_mode::write, void>::type
     sync(std::error_code& error);
 
     /**
      * All operators compare the address of the first byte and size of the two mapped
      * regions.
      */
 
 private:
     template<
         access_mode A = AccessMode,
         typename = typename std::enable_if<A == access_mode::write>::type
     > pointer get_mapping_start() noexcept
     {
         return !data() ? nullptr : data() - mapping_offset();
     }
 
     const_pointer get_mapping_start() const noexcept
     {
         return !data() ? nullptr : data() - mapping_offset();
     }
 
     /**
      * The destructor syncs changes to disk if `AccessMode` is `write`, but not
      * if it's `read`, but since the destructor cannot be templated, we need to
      * do SFINAE in a dedicated function, where one syncs and the other is a noop.
      */
     template<access_mode A = AccessMode>
     typename std::enable_if<A == access_mode::write, void>::type
     conditional_sync();
     template<access_mode A = AccessMode>
     typename std::enable_if<A == access_mode::read, void>::type conditional_sync();
 };
 
 template<access_mode AccessMode, typename ByteT>
 bool operator==(const basic_mmap<AccessMode, ByteT>& a,
         const basic_mmap<AccessMode, ByteT>& b);
 
 template<access_mode AccessMode, typename ByteT>
 bool operator!=(const basic_mmap<AccessMode, ByteT>& a,
         const basic_mmap<AccessMode, ByteT>& b);
 
 template<access_mode AccessMode, typename ByteT>
 bool operator<(const basic_mmap<AccessMode, ByteT>& a,
         const basic_mmap<AccessMode, ByteT>& b);
 
 template<access_mode AccessMode, typename ByteT>
 bool operator<=(const basic_mmap<AccessMode, ByteT>& a,
         const basic_mmap<AccessMode, ByteT>& b);
 
 template<access_mode AccessMode, typename ByteT>
 bool operator>(const basic_mmap<AccessMode, ByteT>& a,
         const basic_mmap<AccessMode, ByteT>& b);
 
 template<access_mode AccessMode, typename ByteT>
 bool operator>=(const basic_mmap<AccessMode, ByteT>& a,
         const basic_mmap<AccessMode, ByteT>& b);
 
 /**
  * This is the basis for all read-only mmap objects and should be preferred over
  * directly using `basic_mmap`.
  */
 template<typename ByteT>
 using basic_mmap_source = basic_mmap<access_mode::read, ByteT>;
 
 /**
  * This is the basis for all read-write mmap objects and should be preferred over
  * directly using `basic_mmap`.
  */
 template<typename ByteT>
 using basic_mmap_sink = basic_mmap<access_mode::write, ByteT>;
 
 /**
  * These aliases cover the most common use cases, both representing a raw byte stream
  * (either with a char or an unsigned char/uint8_t).
  */
 using mmap_source = basic_mmap_source<char>;
 using ummap_source = basic_mmap_source<unsigned char>;
 
 using mmap_sink = basic_mmap_sink<char>;
 using ummap_sink = basic_mmap_sink<unsigned char>;
 
 /**
  * Convenience factory method that constructs a mapping for any `basic_mmap` or
  * `basic_mmap` type.
  */
 template<
     typename MMap,
     typename MappingToken
 > MMap make_mmap(const MappingToken& token,
         int64_t offset, int64_t length, std::error_code& error)
 {
     MMap mmap;
     mmap.map(token, offset, length, error);
     return mmap;
 }
 
 /**
  * Convenience factory method.
  *
  * MappingToken may be a String (`std::string`, `std::string_view`, `const char*`,
  * `std::filesystem::path`, `std::vector<char>`, or similar), or a
  * `mmap_source::handle_type`.
  */
 template<typename MappingToken>
 mmap_source make_mmap_source(const MappingToken& token, mmap_source::size_type offset,
         mmap_source::size_type length, std::error_code& error)
 {
     return make_mmap<mmap_source>(token, offset, length, error);
 }
 
 template<typename MappingToken>
 mmap_source make_mmap_source(const MappingToken& token, std::error_code& error)
 {
     return make_mmap_source(token, 0, map_entire_file, error);
 }
 
 /**
  * Convenience factory method.
  *
  * MappingToken may be a String (`std::string`, `std::string_view`, `const char*`,
  * `std::filesystem::path`, `std::vector<char>`, or similar), or a
  * `mmap_sink::handle_type`.
  */
 template<typename MappingToken>
 mmap_sink make_mmap_sink(const MappingToken& token, mmap_sink::size_type offset,
         mmap_sink::size_type length, std::error_code& error)
 {
     return make_mmap<mmap_sink>(token, offset, length, error);
 }
 
 template<typename MappingToken>
 mmap_sink make_mmap_sink(const MappingToken& token, std::error_code& error)
 {
     return make_mmap_sink(token, 0, map_entire_file, error);
 }
 
 } // namespace mio
 
 // #include "detail/mmap.ipp"
 /* Copyright 2017 https://github.com/mandreyel
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy of this
  * software and associated documentation files (the "Software"), to deal in the Software
  * without restriction, including without limitation the rights to use, copy, modify,
  * merge, publish, distribute, sublicense, and/or sell copies of the Software, and to
  * permit persons to whom the Software is furnished to do so, subject to the following
  * conditions:
  *
  * The above copyright notice and this permission notice shall be included in all copies
  * or substantial portions of the Software.
  *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
  * INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
  * PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
  * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
  * CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE
  * OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  */
 
 #ifndef MIO_BASIC_MMAP_IMPL
 #define MIO_BASIC_MMAP_IMPL
 
 // #include "mio/mmap.hpp"
 
 // #include "mio/page.hpp"
 
 // #include "mio/detail/string_util.hpp"
 /* Copyright 2017 https://github.com/mandreyel
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy of this
  * software and associated documentation files (the "Software"), to deal in the Software
  * without restriction, including without limitation the rights to use, copy, modify,
  * merge, publish, distribute, sublicense, and/or sell copies of the Software, and to
  * permit persons to whom the Software is furnished to do so, subject to the following
  * conditions:
  *
  * The above copyright notice and this permission notice shall be included in all copies
  * or substantial portions of the Software.
  *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
  * INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
  * PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
  * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
  * CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE
  * OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  */
 
 #ifndef MIO_STRING_UTIL_HEADER
 #define MIO_STRING_UTIL_HEADER
 
 #include <type_traits>
 
 namespace mio {
 namespace detail {
 
 template<
     typename S,
     typename C = typename std::decay<S>::type,
     typename = decltype(std::declval<C>().data()),
     typename = typename std::enable_if<
         std::is_same<typename C::value_type, char>::value
 #ifdef _WIN32
         || std::is_same<typename C::value_type, wchar_t>::value
 #endif
     >::type
 > struct char_type_helper {
     using type = typename C::value_type;
 };
 
 template<class T>
 struct char_type {
     using type = typename char_type_helper<T>::type;
 };
 
 // TODO: can we avoid this brute force approach?
 template<>
 struct char_type<char*> {
     using type = char;
 };
 
 template<>
 struct char_type<const char*> {
     using type = char;
 };
 
 template<size_t N>
 struct char_type<char[N]> {
     using type = char;
 };
 
 template<size_t N>
 struct char_type<const char[N]> {
     using type = char;
 };
 
 #ifdef _WIN32
 template<>
 struct char_type<wchar_t*> {
     using type = wchar_t;
 };
 
 template<>
 struct char_type<const wchar_t*> {
     using type = wchar_t;
 };
 
 template<size_t N>
 struct char_type<wchar_t[N]> {
     using type = wchar_t;
 };
 
 template<size_t N>
 struct char_type<const wchar_t[N]> {
     using type = wchar_t;
 };
 #endif // _WIN32
 
 template<typename CharT, typename S>
 struct is_c_str_helper
 {
     static constexpr bool value = std::is_same<
         CharT*,
         // TODO: I'm so sorry for this... Can this be made cleaner?
         typename std::add_pointer<
             typename std::remove_cv<
                 typename std::remove_pointer<
                     typename std::decay<
                         S
                     >::type
                 >::type
             >::type
         >::type
     >::value;
 };
 
 template<typename S>
 struct is_c_str
 {
     static constexpr bool value = is_c_str_helper<char, S>::value;
 };
 
 #ifdef _WIN32
 template<typename S>
 struct is_c_wstr
 {
     static constexpr bool value = is_c_str_helper<wchar_t, S>::value;
 };
 #endif // _WIN32
 
 template<typename S>
 struct is_c_str_or_c_wstr
 {
     static constexpr bool value = is_c_str<S>::value
 #ifdef _WIN32
         || is_c_wstr<S>::value
 #endif
         ;
 };
 
 template<
     typename String,
     typename = decltype(std::declval<String>().data()),
     typename = typename std::enable_if<!is_c_str_or_c_wstr<String>::value>::type
 > const typename char_type<String>::type* c_str(const String& path)
 {
     return path.data();
 }
 
 template<
     typename String,
     typename = decltype(std::declval<String>().empty()),
     typename = typename std::enable_if<!is_c_str_or_c_wstr<String>::value>::type
 > bool empty(const String& path)
 {
     return path.empty();
 }
 
 template<
     typename String,
     typename = typename std::enable_if<is_c_str_or_c_wstr<String>::value>::type
 > const typename char_type<String>::type* c_str(String path)
 {
     return path;
 }
 
 template<
     typename String,
     typename = typename std::enable_if<is_c_str_or_c_wstr<String>::value>::type
 > bool empty(String path)
 {
     return !path || (*path == 0);
 }
 
 } // namespace detail
 } // namespace mio
 
 #endif // MIO_STRING_UTIL_HEADER
 
 
 #include <algorithm>
 
 #ifndef _WIN32
 # include <unistd.h>
 # include <fcntl.h>
 # include <sys/mman.h>
 # include <sys/stat.h>
 #endif
 
 namespace mio {
 namespace detail {
 
 #ifdef _WIN32
 namespace win {
 
 /** Returns the 4 upper bytes of an 8-byte integer. */
 inline DWORD int64_high(int64_t n) noexcept
 {
     return n >> 32;
 }
 
 /** Returns the 4 lower bytes of an 8-byte integer. */
 inline DWORD int64_low(int64_t n) noexcept
 {
     return n & 0xffffffff;
 }
 
 template<
     typename String,
     typename = typename std::enable_if<
         std::is_same<typename char_type<String>::type, char>::value
     >::type
 > file_handle_type open_file_helper(const String& path, const access_mode mode)
 {
     return ::CreateFileA(c_str(path),
             mode == access_mode::read ? GENERIC_READ : GENERIC_READ | GENERIC_WRITE,
             FILE_SHARE_READ | FILE_SHARE_WRITE,
             0,
             OPEN_EXISTING,
             FILE_ATTRIBUTE_NORMAL,
             0);
 }
 
 template<typename String>
 typename std::enable_if<
     std::is_same<typename char_type<String>::type, wchar_t>::value,
     file_handle_type
 >::type open_file_helper(const String& path, const access_mode mode)
 {
     return ::CreateFileW(c_str(path),
             mode == access_mode::read ? GENERIC_READ : GENERIC_READ | GENERIC_WRITE,
             FILE_SHARE_READ | FILE_SHARE_WRITE,
             0,
             OPEN_EXISTING,
             FILE_ATTRIBUTE_NORMAL,
             0);
 }
 
 } // win
 #endif // _WIN32
 
 /**
  * Returns the last platform specific system error (errno on POSIX and
  * GetLastError on Win) as a `std::error_code`.
  */
 inline std::error_code last_error() noexcept
 {
     std::error_code error;
 #ifdef _WIN32
     error.assign(GetLastError(), std::system_category());
 #else
     error.assign(errno, std::system_category());
 #endif
     return error;
 }
 
 template<typename String>
 file_handle_type open_file(const String& path, const access_mode mode,
         std::error_code& error)
 {
     error.clear();
     if(detail::empty(path))
     {
         error = std::make_error_code(std::errc::invalid_argument);
         return invalid_handle;
     }
 #ifdef _WIN32
     const auto handle = win::open_file_helper(path, mode);
 #else // POSIX
     const auto handle = ::open(c_str(path),
             mode == access_mode::read ? O_RDONLY : O_RDWR);
 #endif
     if(handle == invalid_handle)
     {
         error = detail::last_error();
     }
     return handle;
 }
 
 inline size_t query_file_size(file_handle_type handle, std::error_code& error)
 {
     error.clear();
 #ifdef _WIN32
     LARGE_INTEGER file_size;
     if(::GetFileSizeEx(handle, &file_size) == 0)
     {
         error = detail::last_error();
         return 0;
     }
 	return static_cast<int64_t>(file_size.QuadPart);
 #else // POSIX
     struct stat sbuf;
     if(::fstat(handle, &sbuf) == -1)
     {
         error = detail::last_error();
         return 0;
     }
     return sbuf.st_size;
 #endif
 }
 
 struct mmap_context
 {
     char* data;
     int64_t length;
     int64_t mapped_length;
 #ifdef _WIN32
     file_handle_type file_mapping_handle;
 #endif
 };
 
 inline mmap_context memory_map(const file_handle_type file_handle, const int64_t offset,
     const int64_t length, const access_mode mode, std::error_code& error)
 {
     const int64_t aligned_offset = make_offset_page_aligned(offset);
     const int64_t length_to_map = offset - aligned_offset + length;
 #ifdef _WIN32
     const int64_t max_file_size = offset + length;
     const auto file_mapping_handle = ::CreateFileMapping(
             file_handle,
             0,
             mode == access_mode::read ? PAGE_READONLY : PAGE_READWRITE,
             win::int64_high(max_file_size),
             win::int64_low(max_file_size),
             0);
     if(file_mapping_handle == invalid_handle)
     {
         error = detail::last_error();
         return {};
     }
     char* mapping_start = static_cast<char*>(::MapViewOfFile(
             file_mapping_handle,
             mode == access_mode::read ? FILE_MAP_READ : FILE_MAP_WRITE,
             win::int64_high(aligned_offset),
             win::int64_low(aligned_offset),
             length_to_map));
     if(mapping_start == nullptr)
     {
         error = detail::last_error();
         return {};
     }
 #else // POSIX
     char* mapping_start = static_cast<char*>(::mmap(
             0, // Don't give hint as to where to map.
             length_to_map,
             mode == access_mode::read ? PROT_READ : PROT_WRITE,
             MAP_SHARED,
             file_handle,
             aligned_offset));
     if(mapping_start == MAP_FAILED)
     {
         error = detail::last_error();
         return {};
     }
 #endif
     mmap_context ctx;
     ctx.data = mapping_start + offset - aligned_offset;
     ctx.length = length;
     ctx.mapped_length = length_to_map;
 #ifdef _WIN32
     ctx.file_mapping_handle = file_mapping_handle;
 #endif
     return ctx;
 }
 
 } // namespace detail
 
 // -- basic_mmap --
 
 template<access_mode AccessMode, typename ByteT>
 basic_mmap<AccessMode, ByteT>::~basic_mmap()
 {
     conditional_sync();
     unmap();
 }
 
 template<access_mode AccessMode, typename ByteT>
 basic_mmap<AccessMode, ByteT>::basic_mmap(basic_mmap&& other)
     : data_(std::move(other.data_))
     , length_(std::move(other.length_))
     , mapped_length_(std::move(other.mapped_length_))
     , file_handle_(std::move(other.file_handle_))
 #ifdef _WIN32
     , file_mapping_handle_(std::move(other.file_mapping_handle_))
 #endif
     , is_handle_internal_(std::move(other.is_handle_internal_))
 {
     other.data_ = nullptr;
     other.length_ = other.mapped_length_ = 0;
     other.file_handle_ = invalid_handle;
 #ifdef _WIN32
     other.file_mapping_handle_ = invalid_handle;
 #endif
 }
 
 template<access_mode AccessMode, typename ByteT>
 basic_mmap<AccessMode, ByteT>&
 basic_mmap<AccessMode, ByteT>::operator=(basic_mmap&& other)
 {
     if(this != &other)
     {
         // First the existing mapping needs to be removed.
         unmap();
         data_ = std::move(other.data_);
         length_ = std::move(other.length_);
         mapped_length_ = std::move(other.mapped_length_);
         file_handle_ = std::move(other.file_handle_);
 #ifdef _WIN32
         file_mapping_handle_ = std::move(other.file_mapping_handle_);
 #endif
         is_handle_internal_ = std::move(other.is_handle_internal_);
 
         // The moved from basic_mmap's fields need to be reset, because
         // otherwise other's destructor will unmap the same mapping that was
         // just moved into this.
         other.data_ = nullptr;
         other.length_ = other.mapped_length_ = 0;
         other.file_handle_ = invalid_handle;
 #ifdef _WIN32
         other.file_mapping_handle_ = invalid_handle;
 #endif
         other.is_handle_internal_ = false;
     }
     return *this;
 }
 
 template<access_mode AccessMode, typename ByteT>
 typename basic_mmap<AccessMode, ByteT>::handle_type
 basic_mmap<AccessMode, ByteT>::mapping_handle() const noexcept
 {
 #ifdef _WIN32
     return file_mapping_handle_;
 #else
     return file_handle_;
 #endif
 }
 
 template<access_mode AccessMode, typename ByteT>
 template<typename String>
 void basic_mmap<AccessMode, ByteT>::map(const String& path, const size_type offset,
         const size_type length, std::error_code& error)
 {
     error.clear();
     if(detail::empty(path))
     {
         error = std::make_error_code(std::errc::invalid_argument);
         return;
     }
     const auto handle = detail::open_file(path, AccessMode, error);
     if(error)
     {
         return;
     }
 
     map(handle, offset, length, error);
     // This MUST be after the call to map, as that sets this to true.
     if(!error)
     {
         is_handle_internal_ = true;
     }
 }
 
 template<access_mode AccessMode, typename ByteT>
 void basic_mmap<AccessMode, ByteT>::map(const handle_type handle,
         const size_type offset, const size_type length, std::error_code& error)
 {
     error.clear();
     if(handle == invalid_handle)
     {
         error = std::make_error_code(std::errc::bad_file_descriptor);
         return;
     }
 
     const auto file_size = detail::query_file_size(handle, error);
     if(error)
     {
         return;
     }
 
     if(offset + length > file_size)
     {
         error = std::make_error_code(std::errc::invalid_argument);
         return;
     }
 
     const auto ctx = detail::memory_map(handle, offset,
             length == map_entire_file ? (file_size - offset) : length,
             AccessMode, error);
     if(!error)
     {
         // We must unmap the previous mapping that may have existed prior to this call.
         // Note that this must only be invoked after a new mapping has been created in
         // order to provide the strong guarantee that, should the new mapping fail, the
         // `map` function leaves this instance in a state as though the function had
         // never been invoked.
         unmap();
         file_handle_ = handle;
         is_handle_internal_ = false;
         data_ = reinterpret_cast<pointer>(ctx.data);
         length_ = ctx.length;
         mapped_length_ = ctx.mapped_length;
 #ifdef _WIN32
         file_mapping_handle_ = ctx.file_mapping_handle;
 #endif
     }
 }
 
 template<access_mode AccessMode, typename ByteT>
 template<access_mode A>
 typename std::enable_if<A == access_mode::write, void>::type
 basic_mmap<AccessMode, ByteT>::sync(std::error_code& error)
 {
     error.clear();
     if(!is_open())
     {
         error = std::make_error_code(std::errc::bad_file_descriptor);
         return;
     }
 
     if(data())
     {
 #ifdef _WIN32
         if(::FlushViewOfFile(get_mapping_start(), mapped_length_) == 0
            || ::FlushFileBuffers(file_handle_) == 0)
 #else // POSIX
         if(::msync(get_mapping_start(), mapped_length_, MS_SYNC) != 0)
 #endif
         {
             error = detail::last_error();
             return;
         }
     }
 #ifdef _WIN32
     if(::FlushFileBuffers(file_handle_) == 0)
     {
         error = detail::last_error();
     }
 #endif
 }
 
 template<access_mode AccessMode, typename ByteT>
 void basic_mmap<AccessMode, ByteT>::unmap()
 {
     if(!is_open()) { return; }
     // TODO do we care about errors here?
 #ifdef _WIN32
     if(is_mapped())
     {
         ::UnmapViewOfFile(get_mapping_start());
         ::CloseHandle(file_mapping_handle_);
     }
 #else // POSIX
     if(data_) { ::munmap(const_cast<pointer>(get_mapping_start()), mapped_length_); }
 #endif
 
     // If `file_handle_` was obtained by our opening it (when map is called with
     // a path, rather than an existing file handle), we need to close it,
     // otherwise it must not be closed as it may still be used outside this
     // instance.
     if(is_handle_internal_)
     {
 #ifdef _WIN32
         ::CloseHandle(file_handle_);
 #else // POSIX
         ::close(file_handle_);
 #endif
     }
 
     // Reset fields to their default values.
     data_ = nullptr;
     length_ = mapped_length_ = 0;
     file_handle_ = invalid_handle;
 #ifdef _WIN32
     file_mapping_handle_ = invalid_handle;
 #endif
 }
 
 template<access_mode AccessMode, typename ByteT>
 bool basic_mmap<AccessMode, ByteT>::is_mapped() const noexcept
 {
 #ifdef _WIN32
     return file_mapping_handle_ != invalid_handle;
 #else // POSIX
     return is_open();
 #endif
 }
 
 template<access_mode AccessMode, typename ByteT>
 void basic_mmap<AccessMode, ByteT>::swap(basic_mmap& other)
 {
     if(this != &other)
     {
         using std::swap;
         swap(data_, other.data_);
         swap(file_handle_, other.file_handle_);
 #ifdef _WIN32
         swap(file_mapping_handle_, other.file_mapping_handle_);
 #endif
         swap(length_, other.length_);
         swap(mapped_length_, other.mapped_length_);
         swap(is_handle_internal_, other.is_handle_internal_);
     }
 }
 
 template<access_mode AccessMode, typename ByteT>
 template<access_mode A>
 typename std::enable_if<A == access_mode::write, void>::type
 basic_mmap<AccessMode, ByteT>::conditional_sync()
 {
     // This is invoked from the destructor, so not much we can do about
     // failures here.
     std::error_code ec;
     sync(ec);
 }
 
 template<access_mode AccessMode, typename ByteT>
 template<access_mode A>
 typename std::enable_if<A == access_mode::read, void>::type
 basic_mmap<AccessMode, ByteT>::conditional_sync()
 {
     // noop
 }
 
 template<access_mode AccessMode, typename ByteT>
 bool operator==(const basic_mmap<AccessMode, ByteT>& a,
         const basic_mmap<AccessMode, ByteT>& b)
 {
     return a.data() == b.data()
         && a.size() == b.size();
 }
 
 template<access_mode AccessMode, typename ByteT>
 bool operator!=(const basic_mmap<AccessMode, ByteT>& a,
         const basic_mmap<AccessMode, ByteT>& b)
 {
     return !(a == b);
 }
 
 template<access_mode AccessMode, typename ByteT>
 bool operator<(const basic_mmap<AccessMode, ByteT>& a,
         const basic_mmap<AccessMode, ByteT>& b)
 {
     if(a.data() == b.data()) { return a.size() < b.size(); }
     return a.data() < b.data();
 }
 
 template<access_mode AccessMode, typename ByteT>
 bool operator<=(const basic_mmap<AccessMode, ByteT>& a,
         const basic_mmap<AccessMode, ByteT>& b)
 {
     return !(a > b);
 }
 
 template<access_mode AccessMode, typename ByteT>
 bool operator>(const basic_mmap<AccessMode, ByteT>& a,
         const basic_mmap<AccessMode, ByteT>& b)
 {
     if(a.data() == b.data()) { return a.size() > b.size(); }
     return a.data() > b.data();
 }
 
 template<access_mode AccessMode, typename ByteT>
 bool operator>=(const basic_mmap<AccessMode, ByteT>& a,
         const basic_mmap<AccessMode, ByteT>& b)
 {
     return !(a < b);
 }
 
 } // namespace mio
 
 #endif // MIO_BASIC_MMAP_IMPL
 
 
 #endif // MIO_MMAP_HEADER
 /* Copyright 2017 https://github.com/mandreyel
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy of this
  * software and associated documentation files (the "Software"), to deal in the Software
  * without restriction, including without limitation the rights to use, copy, modify,
  * merge, publish, distribute, sublicense, and/or sell copies of the Software, and to
  * permit persons to whom the Software is furnished to do so, subject to the following
  * conditions:
  *
  * The above copyright notice and this permission notice shall be included in all copies
  * or substantial portions of the Software.
  *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
  * INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
  * PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
  * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
  * CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE
  * OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  */
 
 #ifndef MIO_PAGE_HEADER
 #define MIO_PAGE_HEADER
 
 #ifdef _WIN32
 # include <windows.h>
 #else
 # include <unistd.h>
 #endif
 
 namespace mio {
 
 /**
  * This is used by `basic_mmap` to determine whether to create a read-only or
  * a read-write memory mapping.
  */
 enum class access_mode
 {
     read,
     write
 };
 
 /**
  * Determines the operating system's page allocation granularity.
  *
  * On the first call to this function, it invokes the operating system specific syscall
  * to determine the page size, caches the value, and returns it. Any subsequent call to
  * this function serves the cached value, so no further syscalls are made.
  */
 inline size_t page_size()
 {
     static const size_t page_size = []
     {
 #ifdef _WIN32
         SYSTEM_INFO SystemInfo;
         GetSystemInfo(&SystemInfo);
         return SystemInfo.dwAllocationGranularity;
 #else
         return sysconf(_SC_PAGE_SIZE);
 #endif
     }();
     return page_size;
 }
 
 /**
  * Alligns `offset` to the operating's system page size such that it subtracts the
  * difference until the nearest page boundary before `offset`, or does nothing if
  * `offset` is already page aligned.
  */
 inline size_t make_offset_page_aligned(size_t offset) noexcept
 {
     const size_t page_size_ = page_size();
     // Use integer division to round down to the nearest page alignment.
     return offset / page_size_ * page_size_;
 }
 
 } // namespace mio
 
 #endif // MIO_PAGE_HEADER
 /* Copyright 2017 https://github.com/mandreyel
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy of this
  * software and associated documentation files (the "Software"), to deal in the Software
  * without restriction, including without limitation the rights to use, copy, modify,
  * merge, publish, distribute, sublicense, and/or sell copies of the Software, and to
  * permit persons to whom the Software is furnished to do so, subject to the following
  * conditions:
  *
  * The above copyright notice and this permission notice shall be included in all copies
  * or substantial portions of the Software.
  *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
  * INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
  * PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
  * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
  * CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE
  * OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  */
 
 #ifndef MIO_SHARED_MMAP_HEADER
 #define MIO_SHARED_MMAP_HEADER
 
 // #include "mio/mmap.hpp"
 
 
 #include <system_error> // std::error_code
 #include <memory> // std::shared_ptr
 
 namespace mio {
 
 /**
  * Exposes (nearly) the same interface as `basic_mmap`, but endowes it with
  * `std::shared_ptr` semantics.
  *
  * This is not the default behaviour of `basic_mmap` to avoid allocating on the heap if
  * shared semantics are not required.
  */
 template<
     access_mode AccessMode,
     typename ByteT
 > class basic_shared_mmap
 {
     using impl_type = basic_mmap<AccessMode, ByteT>;
     std::shared_ptr<impl_type> pimpl_;
 
 public:
     using value_type = typename impl_type::value_type;
     using size_type = typename impl_type::size_type;
     using reference = typename impl_type::reference;
     using const_reference = typename impl_type::const_reference;
     using pointer = typename impl_type::pointer;
     using const_pointer = typename impl_type::const_pointer;
     using difference_type = typename impl_type::difference_type;
     using iterator = typename impl_type::iterator;
     using const_iterator = typename impl_type::const_iterator;
     using reverse_iterator = typename impl_type::reverse_iterator;
     using const_reverse_iterator = typename impl_type::const_reverse_iterator;
     using iterator_category = typename impl_type::iterator_category;
     using handle_type = typename impl_type::handle_type;
     using mmap_type = impl_type;
 
     basic_shared_mmap() = default;
     basic_shared_mmap(const basic_shared_mmap&) = default;
     basic_shared_mmap& operator=(const basic_shared_mmap&) = default;
     basic_shared_mmap(basic_shared_mmap&&) = default;
     basic_shared_mmap& operator=(basic_shared_mmap&&) = default;
 
     /** Takes ownership of an existing mmap object. */
     basic_shared_mmap(mmap_type&& mmap)
         : pimpl_(std::make_shared<mmap_type>(std::move(mmap)))
     {}
 
     /** Takes ownership of an existing mmap object. */
     basic_shared_mmap& operator=(mmap_type&& mmap)
     {
         pimpl_ = std::make_shared<mmap_type>(std::move(mmap));
         return *this;
     }
 
     /** Initializes this object with an already established shared mmap. */
     basic_shared_mmap(std::shared_ptr<mmap_type> mmap) : pimpl_(std::move(mmap)) {}
 
     /** Initializes this object with an already established shared mmap. */
     basic_shared_mmap& operator=(std::shared_ptr<mmap_type> mmap)
     {
         pimpl_ = std::move(mmap);
         return *this;
     }
 
 #ifdef __cpp_exceptions
     /**
      * The same as invoking the `map` function, except any error that may occur
      * while establishing the mapping is wrapped in a `std::system_error` and is
      * thrown.
      */
     template<typename String>
     basic_shared_mmap(const String& path, const size_type offset = 0, const size_type length = map_entire_file)
     {
         std::error_code error;
         map(path, offset, length, error);
         if(error) { throw std::system_error(error); }
     }
 
     /**
      * The same as invoking the `map` function, except any error that may occur
      * while establishing the mapping is wrapped in a `std::system_error` and is
      * thrown.
      */
     basic_shared_mmap(const handle_type handle, const size_type offset = 0, const size_type length = map_entire_file)
     {
         std::error_code error;
         map(handle, offset, length, error);
         if(error) { throw std::system_error(error); }
     }
 #endif // __cpp_exceptions
 
     /**
      * If this is a read-write mapping and the last reference to the mapping,
      * the destructor invokes sync. Regardless of the access mode, unmap is
      * invoked as a final step.
      */
     ~basic_shared_mmap() = default;
 
     /** Returns the underlying `std::shared_ptr` instance that holds the mmap. */
     std::shared_ptr<mmap_type> get_shared_ptr() { return pimpl_; }
 
     /**
      * On UNIX systems 'file_handle' and 'mapping_handle' are the same. On Windows,
      * however, a mapped region of a file gets its own handle, which is returned by
      * 'mapping_handle'.
      */
     handle_type file_handle() const noexcept
     {
         return pimpl_ ? pimpl_->file_handle() : invalid_handle;
     }
 
     handle_type mapping_handle() const noexcept
     {
         return pimpl_ ? pimpl_->mapping_handle() : invalid_handle;
     }
 
     /** Returns whether a valid memory mapping has been created. */
     bool is_open() const noexcept { return pimpl_ && pimpl_->is_open(); }
 
     /**
      * Returns true if no mapping was established, that is, conceptually the
      * same as though the length that was mapped was 0. This function is
      * provided so that this class has Container semantics.
      */
     bool empty() const noexcept { return !pimpl_ || pimpl_->empty(); }
 
     /**
      * `size` and `length` both return the logical length, i.e. the number of bytes
      * user requested to be mapped, while `mapped_length` returns the actual number of
      * bytes that were mapped which is a multiple of the underlying operating system's
      * page allocation granularity.
      */
     size_type size() const noexcept { return pimpl_ ? pimpl_->length() : 0; }
     size_type length() const noexcept { return pimpl_ ? pimpl_->length() : 0; }
     size_type mapped_length() const noexcept
     {
         return pimpl_ ? pimpl_->mapped_length() : 0;
     }
 
     /**
      * Returns a pointer to the first requested byte, or `nullptr` if no memory mapping
      * exists.
      */
     template<
         access_mode A = AccessMode,
         typename = typename std::enable_if<A == access_mode::write>::type
     > pointer data() noexcept { return pimpl_->data(); }
     const_pointer data() const noexcept { return pimpl_ ? pimpl_->data() : nullptr; }
 
     /**
      * Returns an iterator to the first requested byte, if a valid memory mapping
      * exists, otherwise this function call is undefined behaviour.
      */
     iterator begin() noexcept { return pimpl_->begin(); }
     const_iterator begin() const noexcept { return pimpl_->begin(); }
     const_iterator cbegin() const noexcept { return pimpl_->cbegin(); }
 
     /**
      * Returns an iterator one past the last requested byte, if a valid memory mapping
      * exists, otherwise this function call is undefined behaviour.
      */
     template<
         access_mode A = AccessMode,
         typename = typename std::enable_if<A == access_mode::write>::type
     > iterator end() noexcept { return pimpl_->end(); }
     const_iterator end() const noexcept { return pimpl_->end(); }
     const_iterator cend() const noexcept { return pimpl_->cend(); }
 
     /**
      * Returns a reverse iterator to the last memory mapped byte, if a valid
      * memory mapping exists, otherwise this function call is undefined
      * behaviour.
      */
     template<
         access_mode A = AccessMode,
         typename = typename std::enable_if<A == access_mode::write>::type
     > reverse_iterator rbegin() noexcept { return pimpl_->rbegin(); }
     const_reverse_iterator rbegin() const noexcept { return pimpl_->rbegin(); }
     const_reverse_iterator crbegin() const noexcept { return pimpl_->crbegin(); }
 
     /**
      * Returns a reverse iterator past the first mapped byte, if a valid memory
      * mapping exists, otherwise this function call is undefined behaviour.
      */
     template<
         access_mode A = AccessMode,
         typename = typename std::enable_if<A == access_mode::write>::type
     > reverse_iterator rend() noexcept { return pimpl_->rend(); }
     const_reverse_iterator rend() const noexcept { return pimpl_->rend(); }
     const_reverse_iterator crend() const noexcept { return pimpl_->crend(); }
 
     /**
      * Returns a reference to the `i`th byte from the first requested byte (as returned
      * by `data`). If this is invoked when no valid memory mapping has been created
      * prior to this call, undefined behaviour ensues.
      */
     reference operator[](const size_type i) noexcept { return (*pimpl_)[i]; }
     const_reference operator[](const size_type i) const noexcept { return (*pimpl_)[i]; }
 
     /**
      * Establishes a memory mapping with AccessMode. If the mapping is unsuccesful, the
      * reason is reported via `error` and the object remains in a state as if this
      * function hadn't been called.
      *
      * `path`, which must be a path to an existing file, is used to retrieve a file
      * handle (which is closed when the object destructs or `unmap` is called), which is
      * then used to memory map the requested region. Upon failure, `error` is set to
      * indicate the reason and the object remains in an unmapped state.
      *
      * `offset` is the number of bytes, relative to the start of the file, where the
      * mapping should begin. When specifying it, there is no need to worry about
      * providing a value that is aligned with the operating system's page allocation
      * granularity. This is adjusted by the implementation such that the first requested
      * byte (as returned by `data` or `begin`), so long as `offset` is valid, will be at
      * `offset` from the start of the file.
      *
      * `length` is the number of bytes to map. It may be `map_entire_file`, in which
      * case a mapping of the entire file is created.
      */
     template<typename String>
     void map(const String& path, const size_type offset,
         const size_type length, std::error_code& error)
     {
         map_impl(path, offset, length, error);
     }
 
     /**
      * Establishes a memory mapping with AccessMode. If the mapping is unsuccesful, the
      * reason is reported via `error` and the object remains in a state as if this
      * function hadn't been called.
      *
      * `path`, which must be a path to an existing file, is used to retrieve a file
      * handle (which is closed when the object destructs or `unmap` is called), which is
      * then used to memory map the requested region. Upon failure, `error` is set to
      * indicate the reason and the object remains in an unmapped state.
      *
      * The entire file is mapped.
      */
     template<typename String>
     void map(const String& path, std::error_code& error)
     {
         map_impl(path, 0, map_entire_file, error);
     }
 
     /**
      * Establishes a memory mapping with AccessMode. If the mapping is unsuccesful, the
      * reason is reported via `error` and the object remains in a state as if this
      * function hadn't been called.
      *
      * `handle`, which must be a valid file handle, which is used to memory map the
      * requested region. Upon failure, `error` is set to indicate the reason and the
      * object remains in an unmapped state.
      *
      * `offset` is the number of bytes, relative to the start of the file, where the
      * mapping should begin. When specifying it, there is no need to worry about
      * providing a value that is aligned with the operating system's page allocation
      * granularity. This is adjusted by the implementation such that the first requested
      * byte (as returned by `data` or `begin`), so long as `offset` is valid, will be at
      * `offset` from the start of the file.
      *
      * `length` is the number of bytes to map. It may be `map_entire_file`, in which
      * case a mapping of the entire file is created.
      */
     void map(const handle_type handle, const size_type offset,
         const size_type length, std::error_code& error)
     {
         map_impl(handle, offset, length, error);
     }
 
     /**
      * Establishes a memory mapping with AccessMode. If the mapping is unsuccesful, the
      * reason is reported via `error` and the object remains in a state as if this
      * function hadn't been called.
      *
      * `handle`, which must be a valid file handle, which is used to memory map the
      * requested region. Upon failure, `error` is set to indicate the reason and the
      * object remains in an unmapped state.
      *
      * The entire file is mapped.
      */
     void map(const handle_type handle, std::error_code& error)
     {
         map_impl(handle, 0, map_entire_file, error);
     }
 
     /**
      * If a valid memory mapping has been created prior to this call, this call
      * instructs the kernel to unmap the memory region and disassociate this object
      * from the file.
      *
      * The file handle associated with the file that is mapped is only closed if the
      * mapping was created using a file path. If, on the other hand, an existing
      * file handle was used to create the mapping, the file handle is not closed.
      */
     void unmap() { if(pimpl_) pimpl_->unmap(); }
 
     void swap(basic_shared_mmap& other) { pimpl_.swap(other.pimpl_); }
 
     /** Flushes the memory mapped page to disk. Errors are reported via `error`. */
     template<
         access_mode A = AccessMode,
         typename = typename std::enable_if<A == access_mode::write>::type
     > void sync(std::error_code& error) { if(pimpl_) pimpl_->sync(error); }
 
     /** All operators compare the underlying `basic_mmap`'s addresses. */
 
     friend bool operator==(const basic_shared_mmap& a, const basic_shared_mmap& b)
     {
         return a.pimpl_ == b.pimpl_;
     }
 
     friend bool operator!=(const basic_shared_mmap& a, const basic_shared_mmap& b)
     {
         return !(a == b);
     }
 
     friend bool operator<(const basic_shared_mmap& a, const basic_shared_mmap& b)
     {
         return a.pimpl_ < b.pimpl_;
     }
 
     friend bool operator<=(const basic_shared_mmap& a, const basic_shared_mmap& b)
     {
         return a.pimpl_ <= b.pimpl_;
     }
 
     friend bool operator>(const basic_shared_mmap& a, const basic_shared_mmap& b)
     {
         return a.pimpl_ > b.pimpl_;
     }
 
     friend bool operator>=(const basic_shared_mmap& a, const basic_shared_mmap& b)
     {
         return a.pimpl_ >= b.pimpl_;
     }
 
 private:
     template<typename MappingToken>
     void map_impl(const MappingToken& token, const size_type offset,
         const size_type length, std::error_code& error)
     {
         if(!pimpl_)
         {
             mmap_type mmap = make_mmap<mmap_type>(token, offset, length, error);
             if(error) { return; }
             pimpl_ = std::make_shared<mmap_type>(std::move(mmap));
         }
         else
         {
             pimpl_->map(token, offset, length, error);
         }
     }
 };
 
 /**
  * This is the basis for all read-only mmap objects and should be preferred over
  * directly using basic_shared_mmap.
  */
 template<typename ByteT>
 using basic_shared_mmap_source = basic_shared_mmap<access_mode::read, ByteT>;
 
 /**
  * This is the basis for all read-write mmap objects and should be preferred over
  * directly using basic_shared_mmap.
  */
 template<typename ByteT>
 using basic_shared_mmap_sink = basic_shared_mmap<access_mode::write, ByteT>;
 
 /**
  * These aliases cover the most common use cases, both representing a raw byte stream
  * (either with a char or an unsigned char/uint8_t).
  */
 using shared_mmap_source = basic_shared_mmap_source<char>;
 using shared_ummap_source = basic_shared_mmap_source<unsigned char>;
 
 using shared_mmap_sink = basic_shared_mmap_sink<char>;
 using shared_ummap_sink = basic_shared_mmap_sink<unsigned char>;
 
 } // namespace mio
 
 #endif // MIO_SHARED_MMAP_HEADER