code: public void checkUnderWritableMountPoint(AlluxioURI alluxioUri)
        throws InvalidPathException, AccessControlException {
      try (LockResource r = new LockResource(mReadLock)) {
        // This will re-acquire the read lock, but that is allowed.
        String mountPoint = getMountPoint(alluxioUri);
        MountInfo mountInfo = mState.getMountTable().get(mountPoint);
        if (mountInfo.getOptions().getReadOnly()) {
          throw new AccessControlException(ExceptionMessage.MOUNT_READONLY, alluxioUri, mountPoint);
        }
      }
    }
docs: Checks to see if a write operation is allowed for the specified Alluxio path, by determining
  if it is under a readonly mount point.
  
  @param alluxioUri an Alluxio path URI
  @throws InvalidPathException if the Alluxio path is invalid
  @throws AccessControlException if the Alluxio path is under a readonly mount point