issue_comments: 205133433

Thanks @mrocklin! This has been really helpful and was what I needed to get going.

A prelim design I'm seeing is to modify the NetCDF4DataStore class https://github.com/pydata/xarray/blob/master/xarray/backends/netCDF4_.py#L170 to meet these requirements: 1. At __init__, try to open file via the LRU cache. I think the LRU dict has to be a global because because the file restriction is an attribute of the system, correct? 2. For each read from a file, ensure it hasn't been closed via a @ds.getter property method. If so, reopen it via the LRU cache. This is ok because for a read the file is essentially read-only. The LRU closes out stale entries to prevent the too many open file errors. Checking this should be fast. 3. sync is only for a write but seems like it should following the above approach.

A clean way to do this is just to make sure that each time self.ds is called, it is re-validated via the LRU cache. This should be able to be implemented via property getter methods https://docs.python.org/2/library/functions.html#property.

Unless I'm missing something big, I don't think this change will require at large refactor but it is quite possible I overlooked something important. @shoyer and @mrocklin, do you see any obvious pitfalls in this scope? If not, it shouldn't be too hard to implement.