[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: 20050202: netCDF C++ - Why is static valiable used in NcVar::put function?

>To: address@hidden
>From: "Masahiro Miiyaki" <address@hidden>
>Subject: netCDF C++ - Why is static variable used in NcVar::put function?
>Organization: WeatherNews Inc.
>Keywords: 200502021156.j12BuUFh022284 netCDF C++

Hi Masahiro Miiyaki,

> Inquiry: I am trying to be able to work the NetCDF library in multi
> thread environment.
> 
> I have been almost finished the modification that the C library can
> work in multi thread.
> 
> But I found the point which was harmful to multi thread environment in
> the netcdf.cpp file. Line number 807,
> 
>     static long start[5] = {0, 0, 0, 0, 0};
>     for (int j = 0; j < 5; j++) {
>        start[j] = the_cur[j]; 
>     }
> 
> Why is the static variable used in this macro?

There is no good reason, it looks like a mistake.  If you delete the
"static" and the initialization to {0, 0, 0, 0, 0}, I think it will
still work as intended:

    long start[5];                                                            \
    for (int j = 0; j < 5; j++) {                                             \
     start[j] = the_cur[j];                                                   \
    }                                                                         \

Thanks for pointing out the error.  Please let us know if this fix
works.

There may be other problems with trying to make the C library
thread-safe, since there are several global data structures, e.g. the
list of open netCDF files declared in libsrc/nc.c:

  /* list of open netcdf's */
  static NC *NClist = NULL;

Also, you should not expect to be able to do multiple concurrent
writes on the same open file.

I would be interested in whether you have success making it work for
multiple threads.

--Russ

_____________________________________________________________________

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