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Re: [ferret_users] Reading NetCDF files while they are being written to



Hi -
I'd say Ryo has it right. When Ferret opens a files it catalogs and stores information about the grid, including the number of time steps. So if what you're doing is to use Ferret to look at the file as your program is getting underway then you're fine. But Ferret will not see any time steps written after that first "use dataset.nc" command is issued.

Ansley

Ryo Furue wrote:
Roman,

I don't know internal workings of Ferret and I speak only from
my experience.

| I have a question about NetCDF files and I apologize if this is
| tangential to the theme of the list.
| | I was wondering if reading data by Ferret from NetCDF files while
| they are being written to by another program (i.e. Fortran) is safe?
| I was told that it should be OK as long as the reading program
| (Ferret in this case) does not lock the file. Do you know if it
| locks the files?

Probably Ferret doesn't lock files on Linux/Unix.
I'm not sure about Windows or Mac.  (On Windows,
you often find applications lock the files they open.)

I often overwrite an existing netCDF file while it's being opened
by Ferret.  Nothing bad happens.  In that sense, it's "safe".

But, probably you have to close the file and open it again
in Ferret after it is modified.  I don't exactly know
what happens if you try to continue to use it without first
closing it.

If I hazard a guess . . . If you add a time slice at the end
of the existing time series, Ferret may not see the new time
slice.

Regards,
Ryo


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