教土豆学计算机
Safety property: Mutual exclusion. At any given moment, only one client can hold a lock.
Liveness property A: Deadlock free. Eventually it is always possible to acquire a lock, even if the client that locked a resource crashed or gets partitioned.
SETNX can be used as a locking primitive. For example, to acquire the lock of key foo, the client could try the following
SETNX lock.foo <current Unix timestamp + lock timeout + 1>
In order to making this locking mechanism more robust, a client holding the lock should always check the timeout did not expire before unlocking the key with DEL because client failures can be complex, not just crashing but also blocking a lot of time against some operations and trying to issue DEL after a lot of time (when the LOCK is already held by another client)
What happens if a client fails, crashes, or is otherwise not able to release the lock?
Another property added here
Liveness property B: Fault tolerance. As long as the majority of Redis nodes are up, clients are able to acquire and release locks.Refers to