[netcdfgroup] NetCdf + OpenMP in Fortran90

• To: netcdfgroup@xxxxxxxxxxxxxxxx
• Subject: [netcdfgroup] NetCdf + OpenMP in Fortran90
• From: "Andrea Storto" <andrea.storto@xxxxxxx>
• Date: Thu, 20 Jan 2011 13:25:59 +0100

Hi all,

  I am experiencing a problem
in using NetCdf Fortran90 interface with OpenMP.

Imagine I read as many different files
as the number of threads:

!$OMP PARALLEL
DEFAULT(SHARED),PRIVATE(JF,ISTARTX,ISTARTY,IENDX,IENDY,ILX,ILY,&
!$OMP & STAT,IDVAR,NCD)
!$OMP DO SCHEDULE(STATIC,1)
DO JF=1,NICEFILES
! [...]
!... Define indexes (ISTARTX,ISTARTY,IENDX,IENDY,ILX,IL) for each thread
!...
    STAT = NF90_OPEN(CICEFILES(JF), NF90_NOWRITE, NCD)
    IF (STAT /= NF90_NOERR) CALL HANDLE_ERR(STAT)
    STAT = NF90_INQ_VARID (NCD, CVARNAME, IDVAR)
    IF (STAT /= NF90_NOERR) CALL HANDLE_ERR(STAT)
    STAT = NF90_GET_VAR (NCD,IDVAR,F3T(ISTARTX:IENDX,ISTARTY:IENDY),&
    & START=(/1,1,1/),COUNT=(/ILX,ILY,1/))
    IF (STAT /= NF90_NOERR) CALL HANDLE_ERR(STAT)
    STAT = NF90_CLOSE(NCD)
    IF (STAT /= NF90_NOERR) CALL HANDLE_ERR(STAT)
ENDDO
!$OMP END DO
!$OMP END PARALLEL

Note that each thread reads a different file,
no overlapping of data occurs,
but sometimes, randomly (one every 50 times), this code
crashes because of "ERROR: Not a netCDF id",
which, I guess, depends on the fact that
being NetCdf "thread-unsafe" as I found on docs,
NetCdf ids might overlap
between different threads.

Do you figure out any solution to safely use OpenMP
for reading different NetCdf files?

If this is crucial, note that this code
runs on a NEC SX-9 vectorial machine (sxf90)
with netcdf-3.6.1p1 (build: dwdW-multi-64).
Or would you suggest to recompile
NetCdf in a different thread-safe way (which i don't know)

Thanks a lot in advance

Regards
Andrea


====================
Andrea Storto, Ph.D.
Dept. of Numerical Applications and Scenarios (ANS)
Euro-Mediterranean Centre for Climate Change (CMCC) - www.cmcc.it
viale Aldo Moro, 44, 7th Floor - 40127 BOLOGNA - Italy
Phone: +39 (0)51 3782605 (int. 205) Mobile: +39 339 8176646
Fax: +39 (0)51 3782655  Email: andrea.storto@xxxxxxx
====================