1 May
2019
1 May
'19
9:53 p.m.
Dear Itaru,
Short answer: For experimental purposes, you can remove those try-catch blocks and NEST
will continue to work.
Longer answer:
Handling exceptions in multithreaded code is difficult in C++, since C++ does not support
exception handling across threads, at least not when using OpenMP threads. To handle
potential exceptions safely, we therefore handle exceptions inside each thread-parallel
context, store them and then re-throw them as soon as we reach a single-threaded context.
This allows us to provide proper error messages. If you remove the error-handling code and
an exception is thrown in a parallel context, NEST will crash, because the exception is
never caught.
Typical situations where such exceptions could occur is during parallel connection if
trying to make invalid connections, or when encountering numerical instabilities, e.g. due
to the exponential term in aeif neurons.
To ensure proper error handling in NEST, we need to keep the per-thread error handling in
the master branch, but for experimental purposes it can be removed without changing the
way NEST works.
Best,
Hans Ekkehard
On 1 May 2019, at 07:33, Itaru Kitayama
<itaru.kitayama(a)gmail.com> wrote:
Hans,
Not limited to this part of code, though for example, we have in
nestkernle/simulation_manager.cpp
[...]
#pragma omp target teams distribute parallel for
for(int i=0;i<len;i++)
{
// We update in a parallel region. Therefore, we need to catch
// exceptions here and then handle them after the parallel region.
//try
//{
if ( not( *node )->is_frozen() )
{
( *node )->update( clock_, from_step_, to_step_ );
}
//}
/*catch ( std::exception& e )
{
// so throw the exception after parallel region
exceptions_raised.at( tid ) = lockPTR< WrappedThreadException >(
new WrappedThreadException( e ) );
}*/
++node;
}
OpenMP offload doesn't support exception handling on devices, so any loop that can be
offloadable, but
contains exception handling, can we safely comment out?
Itaru.
On Tue, Apr 30, 2019 at 6:49 AM Hans Ekkehard Plesser
<hans.ekkehard.plesser(a)nmbu.no> wrote:
Dear Itaru,
Could you be more specific about where you would like to remove exception handling code
and why? In general, I would be rather reluctant to remove exception handling code.
Best,
Hans Ekkehard
--
Prof. Dr. Hans Ekkehard Plesser
Head, Data Science Section
Faculty of Science and Technology
Norwegian University of Life Sciences
PO Box 5003, 1432 Aas, Norway
Phone +47 6723 1560
Email hans.ekkehard.plesser(a)nmbu.no
Home http://arken.nmbu.no/~plesser
On 26 Apr 2019, at 13:56, Itaru Kitayama
<itaru.kitayama(a)gmail.com> wrote:
Hi,
Am I able to safely comment out all those exception handling codes provided
they're provided for the defensive purposes? I ask because I am trying to
insert offloading directives into the NEST code base wherever I can.
Thanks,
Itaru.
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--
Prof. Dr. Hans Ekkehard Plesser
Head, Data Science Section
Faculty of Science and Technology
Norwegian University of Life Sciences
PO Box 5003, 1432 Aas, Norway
Phone +47 6723 1560
Email hans.ekkehard.plesser(a)nmbu.no
Home http://arken.nmbu.no/~plesser
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