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authorLibravatar Thomas Rast <trast@student.ethz.ch>2013-03-25 19:07:39 +0100
committerLibravatar Junio C Hamano <gitster@pobox.com>2013-03-25 15:48:18 -0700
commit790d96c02344eeff41344731d85fb7b22af1d947 (patch)
tree4d154688781b171c18736601fc028f7feda854d3 /t/t9800-git-p4-basic.sh
parentGit 1.8.2 (diff)
downloadtgif-790d96c02344eeff41344731d85fb7b22af1d947.tar.xz
sha1_file: remove recursion in packed_object_info
packed_object_info() and packed_delta_info() were mutually recursive. The former would handle ordinary types and defer deltas to the latter; the latter would use the former to resolve the delta base. This arrangement, however, leads to trouble with threaded index-pack and long delta chains on platforms where thread stacks are small, as happened on OS X (512kB thread stacks by default) with the chromium repo. The task of the two functions is not all that hard to describe without any recursion, however. It proceeds in three steps: - determine the representation type and size, based on the outermost object (delta or not) - follow through the delta chain, if any - determine the object type from what is found at the end of the delta chain The only complication stems from the error recovery. If parsing fails at any step, we want to mark that object (within the pack) as bad and try getting the corresponding SHA1 from elsewhere. If that also fails, we want to repeat this process back up the delta chain until we find a reasonable solution or conclude that there is no way to reconstruct the object. (This is conveniently checked by t5303.) To achieve that within the pack, we keep track of the entire delta chain in a stack. When things go sour, we process that stack from the top, marking entries as bad and attempting to re-resolve by sha1. To avoid excessive malloc(), the stack starts out with a small stack-allocated array. The choice of 64 is based on the default of pack.depth, which is 50, in the hope that it covers "most" delta chains without any need for malloc(). It's much harder to make the actual re-resolving by sha1 nonrecursive, so we skip that. If you can't afford *that* recursion, your corruption problems are more serious than your stack size problems. Reported-by: Stefan Zager <szager@google.com> Signed-off-by: Thomas Rast <trast@student.ethz.ch> Signed-off-by: Junio C Hamano <gitster@pobox.com>
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