Go library for creating finer-grained locking

 Locker provides a mechanism for creating finer-grained locking to help free up
 more global locks to handle other tasks.
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 The implementation looks close to a sync.Mutex, however, the user must provide
 a reference to use to refer to the underlying lock when locking and unlocking,
 and unlock may generate an error.
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 If a lock with a given name does not exist when Lock is called, one is
 created. Lock references are automatically cleaned up on Unlock if nothing
 else is waiting for the lock.