code: func ExclusiveKeyLock(lockDir string, key string) (*KeyLock, error) {
  	return createAndLock(lockDir, key, keyLockExclusive)
  }
docs: // ExclusiveLock takes an exclusive lock on a key.
  // lockDir is the directory where the lock file will be created.
  // It will block if an exclusive lock is already held on the key.