Re: [PATCH 1/3] Add read_cache_from() and discard_cache()

> Johannes Schindelin <Johannes.Schindelin@gmx.de> writes:
> 
> > +int discard_cache()
> > +{
> > +	int ret;
> > +	
> > +	if (cache_mmap == NULL)
> > +		return 0;
> > +	ret = munmap(cache_mmap, cache_mmap_size);
> > +	cache_mmap = NULL;
> > +	cache_mmap_size = 0;
> > +	active_nr = active_cache_changed = 0;
> > +	/* no need to throw away allocated active_cache */
> > +	return ret;
> > +}
> > +
> 
> I haven't been following the details of the patches in this
> thread while they are being cooked actively, but two things to
> look out for are:
> 
>  - I am guessing you run discard_cache() because you want to
>    read in a new cache (or start from a clean slate).  I am not
>    sure what you are doing with the old cache tree data
>    structure.  If you are starting from a clean slate
>    (i.e. there is no read_cache_from() after you call
>    discard_cache), you would probably need to discard the old
>    cache tree; otherwise your next write-tree may produce an
>    incorrect index file.  If you keep the old one and later
>    swap it in, the problem might be even more severe.

>  - index_timestamp is left as the old value in this patch when
>    you switch cache using read_cache_from() directly.  I have a
>    suspicion you may be bitten by "Racy Git" problem, especially
>    because the operations are supposed to happen quickly thanks
>    to the effort of you two ;-) increasing the risks that the
>    file timestamp of the working tree file and the cached entry
>    match.