[gnuastro-devel] [task #13986] Determine the number of threads at runtime

[Mosè Giordano]

URL:
  <http://savannah.gnu.org/task/?13986>

                 Summary: Determine the number of threads at runtime
                 Project: GNU Astronomy Utilities
            Submitted by: giordano
            Submitted on: lun 02 mag 2016 01:50:05 CEST
         Should Start On: lun 02 mag 2016 00:00:00 CEST
   Should be Finished on: lun 02 mag 2016 00:00:00 CEST
                Category: Development
                Priority: 5 - Normal
              Item Group: None
                  Status: None
                 Privacy: Public
        Percent Complete: 0%
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
                  Effort: 0.00

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Details:

I don't see the point of having the --with-numthreads configure option.  What
happens if the program is built on computer X with N threads and then shipped
on another system Y with M threads?  I guess that on Y it'll use N threads by
default.  This is what happens with running programs provided by distro
repository in most GNU/Linux systems.  What happens if configure script is run
while the system is experiencing a heavy load (so nprocs returns a number
lower than the number of processors actually installed)?  I guess that all
programs will use by default a low number of threads because of an initial
"misconfiguration".

Instead, I think that it's much safer to determine runtime (rather than at
configuration time) the number of threads with `sysconf(_SC_NPROCESSORS_ONLN)'
(or `get_nprocs()', but `_SC_NPROCESSORS_ONLN' should be more portable).  This
is better also because this function returns the number of processors actually
available, so that the programs won't overload the system if already under
stress.




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