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lock.sh
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lock.sh
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# create a lock using `flock(2)`. A name is required as first argument.
# the lock will be automatically unlocked when the shell process quits.
# Noted due to the fixed FD, a shell process can only create one lock.
# HOMEBREW_PREFIX is set by extend/ENV/super.rb
# shellcheck disable=SC2154
lock() {
local name="$1"
local lock_dir="${HOMEBREW_PREFIX}/var/homebrew/locks"
local lock_file="${lock_dir}/${name}"
[[ -d "${lock_dir}" ]] || mkdir -p "${lock_dir}"
if [[ ! -w "${lock_dir}" ]]
then
odie <<EOS
Can't create ${name} lock in ${lock_dir}!
Fix permissions by running:
sudo chown -R ${USER-\$(whoami)} ${HOMEBREW_PREFIX}/var/homebrew
EOS
fi
# 200 is the file descriptor used in the lock.
# This FD should be used exclusively for lock purpose.
# Any value except 0(stdin), 1(stdout) and 2(stderr) can do the job.
# Noted, FD is unique per process but it will be shared to subprocess.
# It is recommended to choose a large number to avoid conflicting with
# other FD opened by the script.
#
# close FD first, this is required if parent process holds a different lock.
exec 200>&-
# open the lock file to FD, so the shell process can hold the lock.
exec 200>"${lock_file}"
if ! _create_lock 200 "${name}"
then
odie <<EOS
Another active Homebrew ${name} process is already in progress.
Please wait for it to finish or terminate it to continue.
EOS
fi
}
_create_lock() {
local lock_fd="$1"
local name="$2"
local ruby="/usr/bin/ruby"
local python="/usr/bin/python"
[[ -x "${ruby}" ]] || ruby="$(type -P ruby)"
[[ -x "${python}" ]] || python="$(type -P python)"
# Use a bash subprocess to reset setuid, which Ruby can error if != euid.
if [[ -x "${ruby}" ]] && /bin/bash -c "\"${ruby}\" -e \"exit(RUBY_VERSION >= '1.8.7')\""
then
/bin/bash <<-SCRIPT
"${ruby}" -e "File.new(${lock_fd}).flock(File::LOCK_EX | File::LOCK_NB) || exit(1)"
SCRIPT
elif [[ -x "${python}" ]]
then
/bin/bash <<-SCRIPT
"${python}" -c "import fcntl; fcntl.flock(${lock_fd}, fcntl.LOCK_EX | fcntl.LOCK_NB)"
SCRIPT
elif [[ -x "$(type -P flock)" ]]
then
flock -n "${lock_fd}"
else
onoe "Cannot create ${name} lock, please avoid running Homebrew in parallel."
fi
}