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[netCDF #TLB-677315]: FW: Net CDF-4 Issues

Hi Coy,

> I am using NetCDF-4. 

Yes, I understood that.  When I referenced netCDF-3, I was referring
to the netCDF-3 library embedded in the netCDF-4 library that is still
used to handle netCDF-3 files.  But even if you are only using
netCDF-4/HDF5 files, there is still a similar global linked list of
open files, so if you have different threads opening and closing files
that list can become corrupted unless you have a semaphore or lock
that prevents use of the netCDF library by more than one thread at a
time.

>                     ... How would one make a call from the Windows C
> interface to determine if another thread is currently using the NetCDF
> dll?

I don't know of an easy way to do that (maybe there's something in the
Microsoft documentation that deals with that), but you could just make
sure no two thredds are making calls to the library at the same time
with your own lock/semaphore shared among your threads.  It's not
enough to make sure different threads are accessing distinct files,
you must guarantee that they can't be making netCDF library calls at
the same time.

> I just need a simply way to make sure only one of my threads is using
> the NetCDF dll at a time.

Right.  There's no netCDF call that can help with that.  It should be
done at the application level, unless there is a Microsoft-specific
way that the OS provides for DLLs.

Note that the underlying HDF5 library is also not thread-safe by
default, but if you build it with the --enable-threadsafe
configuration option, it prevents any concurrent calls to HDF5
functions from different threads.  We eventually plan to provide a
similar capability for netCDF, but it's not there yet.

--Russ

Russ Rew                                         UCAR Unidata Program
address@hidden                     http://www.unidata.ucar.edu



Ticket Details
===================
Ticket ID: TLB-677315
Department: Support netCDF
Priority: Normal
Status: Closed