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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.
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 \$(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="$(which ruby 2>/dev/null)"
[[ -x "$python" ]] || python="$(which python 2>/dev/null)"
if [[ -x "$ruby" ]] && "$ruby" -e "exit(RUBY_VERSION >= '1.8.7')"
then
"$ruby" -e "File.new($lock_fd).flock(File::LOCK_EX | File::LOCK_NB) || exit(1)"
elif [[ -x "$(which flock 2>/dev/null)" ]]
then
flock -n "$lock_fd"
elif [[ -x "$python" ]]
then
"$python" -c "import fcntl; fcntl.flock($lock_fd, fcntl.LOCK_EX | fcntl.LOCK_NB)"
else
onoe "Cannot create $name lock, please avoid running Homebrew in parallel."
fi
}
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