Re: pack-objects: Fix segfault when object count is less than thread count

On Mon, 21 Jan 2008, Sergey Vlasov wrote:

quoted

When partitioning the work amongst threads, dividing the number of
objects by the number of threads may return 0 when there are less
objects than threads; this will cause the subsequent code to segfault
when accessing list[sub_size-1].  Fix this by ensuring that sub_size
is not zero if there is at least one object to process.

No.  Forcing one object in a thread is counter productive since it won't 
have anything to delta against.  Instead, the thread should be allowed 
to have zero objects and let the other threads have more.

This patch would be a proper fix:

diff --git a/builtin-pack-objects.c b/builtin-pack-objects.c
index ec10238..d3efeff 100644
--- a/builtin-pack-objects.c
+++ b/builtin-pack-objects.c

@@ -1672,7 +1672,8 @@ static void ll_find_deltas(struct object_entry **list, unsigned list_size,
 		p[i].data_ready = 0;
 
 		/* try to split chunks on "path" boundaries */
-		while (sub_size < list_size && list[sub_size]->hash &&
+		while (sub_size && sub_size < list_size &&
+		       list[sub_size]->hash &&
 		       list[sub_size]->hash == list[sub_size-1]->hash)
 			sub_size++;