This macro unlocks a Mutex or RwLock. If the lock is poisoned (i.e. a panic before a MutexGuard / RwLockGuard is dropped) the last value before the panic occurred is used.
Acquire a read lock on a RwLock, silently recovering the lock if it is poisoned
Acquire a write lock on a RwLock, silently recovering the lock if it is poisoned
Recovers a poisoned lock by returning the value before the lock was poisoned