Re: [boost] Re: Any interest in cross platform memory mapped file management class?

From: Malte Starostik (malte_at_[hidden])
Date: 2002-10-12 12:12:22

On Thursday 10 October 2002 10:03, Craig Henderson wrote:
> > >         typedef enum { readonly, readwrite } open_access;
> >
> > In some cases, writeonly access makes sense as well (e.g. shared memory)
>
> This would need to be a POSIX only option as Win32 does not provide
> write-only access AFAIK. It would also complicate the interface as the
> pointer returned from get() would be write-only. I guess attempting to read
> this pointer could be documented as an undefined behaviour, as we couldn't
> actually prevent the user from doing it.
I thought I used writeonly on Win32, maybe misremembered. If it's POSIX only 
and since C++ doesn't provide for it (duh, I should really have thought of 
this) it's probably not worth it.

> > Maybe add these?:
> > bool map_writeonly(memory_mapped_file::memmap_file &handle); // see above
> > memorory_mapped_file(const std::string& file_name, open_access access);
> > bool map_readonly(const std::string& file_name);
> > bool map_readwrite(const std::string& file_name);
> > bool map_writeonly(const std::string& file_name); // see above
>
> I deliberately stayed away from these in the initial design, but just knew
> someone would request them :-)  I wanted to keep the class as clean as
> possible, and therefore decided to restrict it to managing the memory
> mapping to an open file. IMO, adding the file open/close handling muddies
> the interface for little gain. The interface changes to support file handle
> management would be quite large, because of the number of flags and options
> for the Win32 CreateFile(). Perhaps a file management class would be a good
> addition to Boost, and then this class could use that:
>
> // warning: partial interface pseudo code follows
> namespace boost {
>     template<...>
>     class file   // bad name !
>     {
>       public:
>         bool close(void);
>         bool create(...);
>         bool is_open(void) const;
>         bool open_readonly(...);
>         bool open_readwrite(...);
>
>         bool create_temporary(...);     // no file path required
>     };
>
>     template <typename T>
>     class memory_mapped_file
>     {
>         ...
>         bool map_readonly(const ::boost::file &);
>         bool map_readwrite(const ::boost::file &);
>         ...
>     };
> } // namespace boost
Fully agreed.

Regards,
-Malte

-- 
#!/usr/bin/perl
$t='char|short|int|long|void';%m=qw(U "unsigned\040$3" W "w$3_t");while(<>)
{/#define UNICODE/and$m{T}=$m{W};s/\b(LP)?([UWT])?($t)\b/lc(eval$m{$2}||$3)
.($1?'*':'')/gei;print;}print"/* Cleaned by Malte's WinAPI sanitizer */\n";