disk cache generate failure when load data from disk

[yuelng]

776 
777         # Now, it is time to initialize the File extension

--> 778 self._g_new(filename, mode, **params)
779
780 # Check filters and set PyTables format version for new files.

tables/hdf5extension.pyx in tables.hdf5extension.File._g_new()

HDF5ExtError: HDF5 error back trace

File "H5F.c", line 444, in H5Fcreate
unable to create file
File "H5Fint.c", line 1531, in H5F_open
unable to truncate a file which is already open

End of HDF5 error back trace

Unable to open/create file xxxxx qlib_data/cn_data/dataset_cache/pytables-k9tea7t3.tmp