Re: [boost] [Review] Shmem Library

From: Dave Moore (jdmoore99_at_[hidden])
Date: 2006-02-09 05:27:30

 This seems like a good seperation of the concepts (file vs. region) to me.
Most of the higher level functionality in shmem could be built against the
mmapped_region class.

I definitely feel that this is a step in the right direction.

Dave Moore

When I first thought about it, the approach that I considered was to use
> two classes.  mmaped_file represents a file which has zero or more mmaped
> regions, and mmaped_region which represents a single region.  Off the top
> of my head, something like this might be appropriate:
>
>    class mmapped_file : private boost::noncopyable
>    {
>    public:
>        /* A slightly richer set of access modes.  If the operating system
> does
>           not support some mode, the library should pick a mode that at
> least
>           allows the required mode.  (e.g. if the OS doesn't support
> write-only
>           mode, read-write mode is an appropriate substitute since it
> allows
>           writing. */
>        typedef enum {
>                  none_mode = 0x00, ro_mode = 0x01, wo_mode = 0x02, rw_mode
> =
> 0x03, access_mode_mask = 0xff
>        }    accessmode;
>
>        /* Open a file, RAII style.  Throws an exception on failure. */
>        mmapped_file(const char* filename, accessmode mode);
>
>        /* Closes the file.  Does not throw. */
>        ~mmapped_file();
>
>        /* XXX Support for iterating through the mapped regions? */
>    };
>
>    class mmaped_region : private boost::noncopyable
>    {
>    public:
>        /* Map a region from an mmaped_file.  Throws an exception on
> failure. */
>        mmaped_region(shared_ptr<mmaped_file>& file, fileoff_t offset,
>                      size_t size, mmaped_file::accessmode mode);
>
>        /* Unmap the region.  Does not throw. */
>        ~mmapped_region();
>
>        /* Get the size of the mapped region.  Does not throw. */
>        std::size_t get_size() const;
>
>        /* Get a pointer to the base of the mapped region.  Does not throw.
> */
>        void* get_base() const;
>
>        /* Get the file offset of the beginning of the mapped region.  Does
> not
> throw. */
>        fileoff_t get_file_offset() const;
>
>        /* Flush an area of the mapped region.  Does not throw. */
>        bool flush(size_t mapping_offset = 0, size_t numbytes = 0);
>    };
>