cdm/src/main/java/ucar/nc2/util/cache/FileCacheARC.java
@Override
  public FileCacheable acquire(FileFactory factory, DatasetUrl location) throws IOException {
    return acquire(factory, location.trueurl, location, -1, null, null);
  }
@Override
  public FileCacheable acquire(FileFactory factory, DatasetUrl location) throws IOException {
    return acquire(factory, location.trueurl, location, -1, null, null);
  }
Acquire a FileCacheable, and lock it so no one else can use it.
call FileCacheable.close() when done.

@param factory    use this factory to open the file; may not be null
@param location   file location, also used as the cache name, will be passed to the NetcdfFileFactory
@return NetcdfFile corresponding to location.
@throws IOException on error