pre-lock — 路径锁定尝试的通知。
The pre-lock hook runs whenever
someone attempts to lock a path. It can be used to prevent
locks altogether or to create a more complex policy
specifying exactly which users are allowed to lock
particular paths. If the hook notices a pre-existing lock,
then it can also decide whether a user is allowed
to “steal” the existing lock.
If the pre-lock hook program returns
a nonzero exit value, the lock action is aborted and
anything printed to stderr is marshalled back to the
client.