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#!/bin/bash
# Copyright (C) 2022 The Android Open Source Project
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
usage() { # exit code
cat <<-EOF
NAME
git-gc-preserve - Run git gc and preserve old packs to avoid races for JGit
SYNOPSIS
git gc-preserve
DESCRIPTION
Runs git gc and can preserve old packs to avoid races with concurrently
executed commands in JGit.
This command uses custom git config options to configure if preserved packs
from the last run of git gc should be pruned and if packs should be preserved.
This is similar to the implementation in JGit [1] which is used by
JGit to avoid errors [2] in such situations.
The command prevents concurrent runs of the command on the same repository
by acquiring an exclusive file lock on the file
"\$repopath/gc-preserve.pid"
If it cannot acquire the lock it fails immediately with exit code 3.
Failure Exit Codes
1: General failure
2: Couldn't determine repository path. If the current working directory
is outside of the working tree of the git repository use git option
--git-dir to pass the root path of the repository.
E.g.
$ git --git-dir ~/git/foo gc-preserve
3: Another process already runs $0 on the same repository
[1] https://git.eclipse.org/r/c/jgit/jgit/+/87969
[2] https://git.eclipse.org/r/c/jgit/jgit/+/122288
CONFIGURATION
"pack.prunepreserved": if set to "true" preserved packs from the last gc run
are pruned before current packs are preserved.
"pack.preserveoldpacks": if set to "true" current packs will be hard linked
to objects/pack/preserved before git gc is executed. JGit will
fallback to the preserved packs in this directory in case it comes
across missing objects which might be caused by a concurrent run of
git gc.
EOF
exit "$1"
}
# acquire file lock, unlock when the script exits
lock() { # repo
readonly LOCKFILE="$1/gc-preserve.pid"
test -f "$LOCKFILE" || touch "$LOCKFILE"
exec 9> "$LOCKFILE"
if flock -nx 9; then
echo -n "$$ $USERNAME@$HOSTNAME" >&9
trap unlock EXIT
else
echo "$0 is already running"
exit 3
fi
}
unlock() {
# only delete if the file descriptor 9 is open
if { : >&9 ; } &> /dev/null; then
rm -f "$LOCKFILE"
fi
# close the file handle to release file lock
exec 9>&-
}
# prune preserved packs if pack.prunepreserved == true
prune_preserved() { # repo
configured=$(git --git-dir="$1" config --get pack.prunepreserved)
if [ "$configured" != "true" ]; then
return 0
fi
local preserved=$1/objects/pack/preserved
if [ -d "$preserved" ]; then
printf "Pruning old preserved packs: "
count=$(find "$preserved" -name "*.old-pack" | wc -l)
rm -rf "$preserved"
echo "$count, done."
fi
}
# preserve packs if pack.preserveoldpacks == true
preserve_packs() { # repo
configured=$(git --git-dir="$1" config --get pack.preserveoldpacks)
if [ "$configured" != "true" ]; then
return 0
fi
local packdir=$1/objects/pack
pushd "$packdir" >/dev/null || exit 1
mkdir -p preserved
printf "Preserving packs: "
count=0
for file in pack-*{.pack,.idx} ; do
ln -f "$file" preserved/"$(get_preserved_packfile_name "$file")"
if [[ "$file" == pack-*.pack ]]; then
((count++))
fi
done
echo "$count, done."
popd >/dev/null || exit 1
}
# pack-0...2.pack to pack-0...2.old-pack
# pack-0...2.idx to pack-0...2.old-idx
get_preserved_packfile_name() { # packfile > preserved_packfile
local old=${1/%\.pack/.old-pack}
old=${old/%\.idx/.old-idx}
echo "$old"
}
# main
while [ $# -gt 0 ] ; do
case "$1" in
-u|-h) usage 0 ;;
esac
shift
done
args=$(git rev-parse --sq-quote "$@")
repopath=$(git rev-parse --git-dir)
if [ -z "$repopath" ]; then
usage 2
fi
lock "$repopath"
prune_preserved "$repopath"
preserve_packs "$repopath"
git gc ${args:+"$args"} || { echo "git gc failed"; exit "$?"; }