Re: [boost] [modular boost] non-linked headers

Subject: Re: [boost] [modular boost] non-linked headers
From: Edward Diener (eldiener_at_[hidden])
Date: 2013-12-02 20:01:42

On 12/2/2013 7:08 PM, Bjørn Roald wrote:
> On 12/03/2013 12:39 AM, Edward Diener wrote:
>> On 12/2/2013 5:29 PM, Bjørn Roald wrote:
>>> On 12/02/2013 10:45 PM, Edward Diener wrote:
>>>> On Windows after the .\b2 headers step, there are these directories
>>>> under the modular-boost/boost diectory which are not symbolic links:
>>>>
>>>> detail
>>>
>>> It is because they have more than one source directory, so a symbolic
>>> link will not do what is needed.
>>
>> Symbolic links can be created to individual files also.
>
> yes, but b2 headers create hard links rather than symbolic links
> individual files on platforms supporting hardlinks.  If you have no
> simple way of checking if you got hardlinks, simply try to modify one to
> see if you have a link or a copy.  Windows have had hardlinks since at
> least XP, so if it does not work for you it  is a bug I think.
>
> b2 headers will fall back to copy if that is the only thing supported I
> think, or that is what it should do.
>
>
>>>  I do not think windows is changing
>>> anything unless you are on a version not supporting symbolic links.
>>>
>>> $ find libs -name detail | grep include/boost/detail
>>> libs/optional/include/boost/detail
>>> libs/detail/include/boost/detail
>>> libs/thread/include/boost/detail
>>> libs/config/include/boost/detail
>>> libs/smart_ptr/include/boost/detail
>>> libs/utility/include/boost/detail
>>> libs/conversion/include/boost/detail
>>> libs/graph/include/boost/detail
>>> libs/dynamic_bitset/include/boost/detail
>>
>> Just looking at detail we are evidently creating duplicating files
>> rather than creating symbolic links to files.
>>
>> For instance in libs/detail, which is a submodule, we have
>> allocator_utilities.hpp. In boost/detail we have
>> allocator_utilities.hpp. Let us suppose that the
>> libs/detail/allocator_utilities.hpp gets updated in git. When this
>> happens, how is the boost/detail/allocator_utilities.hpp supposed to be
>> updated if it is an entirely separate file ?
>
> It wan't get updated.  And that is a major pain for any platforms that
> don't support links.  But links should work on any "normal" development
> host computer these days.

I see now that the boost/detail/allocator_utilities.hpp is a hard link. 
Unfortunately Windows doesn't normally indicate hard links either in 
Explorer or via the 'dir' command. One must use a shell extension or the 
'fsutil hardlink list xxx' command to get that information.

I assume then that git never deletes a file and recreates it with the 
same name when the file is updated, else the hardlink would no longer be 
pointing to the same file and the purpose of having a hardlink, as 
opposed to a symbolic link, would be defeated.