Re: [netcdfgroup] How to inquire if a NetCDF file is already open for reading or writing?

• To: Hernan Arango <arango@xxxxxxxxxxxxxxxxxx>, Lucas Villa Real <lucasvr@xxxxxxxxxx>
• Subject: Re: [netcdfgroup] How to inquire if a NetCDF file is already open for reading or writing?
• From: Dennis Heimbigner <dmh@xxxxxxxx>
• Date: Fri, 22 Jan 2021 21:25:37 -0700

looking for a name match. This is probably complicated if mpio is being used
because that list is duplicated on every processor.
As an alternative, you could implement wrapper around nc_create and nc_open

path arguments.

=Dennis Heimbigner
  Unidata

On 1/22/2021 8:35 PM, Hernan Arango wrote:

Hi Lucas,

Thank you for your answer.  However, what I am specifically asking is:  Given ONLY the NetCDF dataset filename, is there a function that can be used in a Fortran code (or a C-binding routine) to inquire if the filename is open (with a logical true or false result).  If true,  return the one or more identifiers (vector) associated with the opening of that specific filename.   Notice that It is possible that such filename has been opened more than once and not closed.

I assume that this is a very difficult question because I don’t have an idea how to code such function.  Maybe the developers of NetCDF can tell us if it is possible or not.

Cheers, Hernan

*From: *Lucas Villa Real <lucasvr@xxxxxxxxxx>
*Date: *Friday, January 22, 2021 at 10:17 PM
*To: *Hernan Arango <arango@xxxxxxxxxxxxxxxxxx>
*Cc: *"netcdfgroup@xxxxxxxxxxxxxxxx" <netcdfgroup@xxxxxxxxxxxxxxxx>

*Subject: *Re: [netcdfgroup] How to inquire if a NetCDF file is already open for reading or writing?

    ----- Original message -----
    From: Hernan Arango <arango@xxxxxxxxxxxxxxxxxx>
    Sent by: "netcdfgroup" <netcdfgroup-bounces@xxxxxxxxxxxxxxxx>
    To: "netcdfgroup@xxxxxxxxxxxxxxxx" <netcdfgroup@xxxxxxxxxxxxxxxx>
    Cc:
    Subject: [EXTERNAL] [netcdfgroup] How to inquire if a NetCDF file
    is already open for reading or writing?
    Date: Fri, Jan 22, 2021 6:01 PM


    Hello,

    I am wondering if there is a function to determine if a NetCDF is
    already open for reading or writing based on the filename?   I am
    trying to avoid open too many files.   I know that there are ways
    in Unix to increase the number of open files, but that’s not what
    I am asking.   In parallel I/O running on lots of processes, there
    is a need to avoid opening too many files.   I am using both the
    standard NetCDF library and the PIO library that is the basis of
    the SCORPIO library (https://e3sm.org/scorpio-parallel-io-library
    
<https://urldefense.proofpoint.com/v2/url?u=https-3A__e3sm.org_scorpio-2Dparallel-2Dio-2Dlibrary&d=DwMGaQ&c=jf_iaSHvJObTbx-siA1ZOg&r=yZCLoPFNF2xM1OIVBISlXxZvERMVKNT1d5PSrOJfnc8&m=QnVlDcV5suiBIhpLT3T5oRt9rSpedaNzD5PPQIaVwoY&s=9fcAm4IjIU6e3FbfD7JzZm28BtCM1zMwV3G7jQ-Bc0A&e=>).
    Therefore, I have integer file ID (ncid) and file descriptors of
    TYPE (file_desc_t).

    I am looking for something like:

    ncid=is_nc_open(‘my_file.nc’)

    or

    fileDesc=is_pio_open(iosystem, my_paralle_file.nc’)

    Thank you, H

Hi Hernan,

If you're on Linux, then one option is to scan the symlinks under /proc/self/fd looking for a target whose name matches the file name you're looking for.

I'm not sure if ncids have a 1:1 correspondence with HDF5 file ids; if they do, then perhaps you could also look into H5Fget_obj_count(ncid, H5F_OBJ_FILE) and/or H5Fget_obj_count(H5F_OBJ_ALL, H5F_OBJ_FILE). See https://support.hdfgroup.org/HDF5/doc/RM/RM_H5F.html#File-GetObjCount <https://support.hdfgroup.org/HDF5/doc/RM/RM_H5F.html#File-GetObjCount> for more details on that API.

Best regards,

Lucas




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    • From: Hernan Arango
  • Re: [netcdfgroup] How to inquire if a NetCDF file is already open for reading or writing?
    • From: Lucas Villa Real
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