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Re: multiple open and close (fwd)

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  • Subject: Re: multiple open and close (fwd)
  • Date: Thu, 03 Apr 2003 16:22:09 -0700
------- Forwarded Message

Date:    Thu, 03 Apr 2003 11:36:06 -0700
From:    Russ Rew <address@hidden>
To:      Youlong Xia <address@hidden>
Subject: Re: multiple open and close 

>To: address@hidden
>From: Youlong Xia <address@hidden>
>Subject: Re: 20030328: multiple open and close
>Organization: Institute for Geophysics, University of Texas
>Keywords: 

Hi Youlong,

> recently I used an optimized algorithm to estimate uncertainty of a
> numerical model. This algorithm will make 100,000 runs using similar
> data. Therefore Netcdf open and close will need the same times
> because these data are netcdf format. When my program makes 100
> wrap_open and wrap_close, program stops and shows the error: too
> many NETCDF opens. Could you please tell me how many open and close
> can be done for single netcdf file? Can you tell me some ideas to
> fix it or give me some information how to solve this problem? Many
> thanks in advance.

If the error is really "too many NETCDF opens", then it's not coming
from the netCDF library but from some program or software that uses
netCDF, such as IDL or MATLAB.  In that case, I can't be of any help.

The only similar error from the netCDF library is "Too many netCDF
files open".  That only occurs when the netCDF library gets a system
error on trying to open a file and cannot open it because the
operating system won't permit more open files.  There is no limit in
the netCDF library on the number of files that can be simultaneously
open, despite the existence of the MAX_NC_OPEN macro in the netcdf.h
header file, which was for a much earlier version of netCDF:

  /*
   * Avoid use of this meaningless macro
   * Use sysconf(_SC_OPEN_MAX).
   */
  #ifndef MAX_NC_OPEN
  #define MAX_NC_OPEN 32
  #endif

The only limit is the number of files that the operating system lets
you open simultaneously (returned by sysconf(_SC_OPEN_MAX) on Unix
systems).  Other operating systems have different limits and
different ways of letting users change these limits.

I suggest that you make sure "wrap_close" (whatever that is) calls
nc_close() on netCDF IDs of files that don't need to be open.  If that
doesn't solve the problem, find out how to increase the number of
simultaneously open files you are permitted in your operating system.

--Russ

_____________________________________________________________________

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

------- End of Forwarded Message