Re: [PATCH 10/17] get_revision_internal(): make check less mysterious
- From
Michael Haggerty <mhagger@alum.mit.edu>
- Date
- May 23, 2013, 06:39 UTC
- Message-ID
- <519DB985.5040103@alum.mit.edu>
- In-Reply-To
- <7vsj1gnsgn.fsf@alter.siamese.dyndns.org>
On 05/21/2013 07:38 PM, Junio C Hamano wrote:
Show 31 quoted lines
> Michael Haggerty <mhagger@alum.mit.edu> writes: > >> The condition under which gc_boundary() is called was previously >> >> if (alloc <= nr) >> >> . But by construction, nr can never exceed alloc, so the check looks >> unnecessarily mysterious. In fact, the purpose of the check is to try >> to avoid a realloc() call by shrinking the array if possible if it is >> at its allocation limit when a new element is about to be added. So >> change the check to >> >> if (nr == alloc) >> >> and add a comment to explain what's going on. >> >> Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu> >> --- >> Please check that I have properly described the purpose of this check. >> >> The way the code is written, it looks like a bad pattern of growth and >> shrinkage of the array (namely, just under the resize limit) could >> cause gc_boundary() to be called over and over again with (most of) >> the same data. I hope that the author had some reason to believe that >> such a pattern is unlikely. > > That is about comparing with "alloc", not having high and low > watermarks, right? > > I do not see "alloc <= nr" is mysterious at all; it is merely being > defensive.
If nr would ever exceed alloc, then the code would be broken and would probably have already performed an illegal memory access. Pretending to support nr > alloc here is not defensive but misleading, because by that time the ship is going down anyway.
On a more practical level, when I saw this code I thought to myself "that's strange, I'd better look into it because it suggests that I don't understand the meaning of nr and alloc". I think that the suggested change will help prevent the next reader from repeating the same pointless investigation.
Michael
-- Michael Haggerty mhagger@alum.mit.edu http://softwareswirl.blogspot.com/