cdm/src/main/java/ucar/nc2/util/cache/FileCache.java
public FileCacheable acquire(FileFactory factory, DatasetUrl durl, ucar.nc2.util.CancelTask cancelTask) throws IOException {
    return acquire(factory, durl.trueurl, durl, -1, cancelTask, null);
  }
public FileCacheable acquire(FileFactory factory, DatasetUrl durl, ucar.nc2.util.CancelTask cancelTask) throws IOException {
    return acquire(factory, durl.trueurl, durl, -1, cancelTask, 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 durl   file location, also used as the cache name, will be passed to the NetcdfFileFactory
@param cancelTask user can cancel, ok to be null.
@return NetcdfFile corresponding to location.
@throws IOException on error