Barriers are always team local only

[fmoessbauer]

Currently it is not possible to use barriers which block all units if a team is split. Each barrier only blocks the units of the current team. See this example

auto & team = dash::Team::All();
auto & myteam = team.locality_split(dash::util::Locality::Scope::Core, 2);                                    if(myteam.dart_id() == 1){                                                       
  {                                                                              
      // Do somethings in team 1  
  }                                                                              
}
// does not work                                         
myteam.parent().barrier();
// does not work too
dash::Team::All().barrier();

  if(myteam.dart_id() == 2){                                                       
    // do something else after team 1 has finished                          
  } 

[fmoessbauer]

This bug is really strange. In branch bug-114-team the new team split unit tests work as expected. However almost the same case in feat-hdf5-team does not work.
And for debugging, keep in mind that the bug does not occur on CI, as there the team is not splitted.

For details see HDF5ArrayTest and TeamTest

[fuchsto]

Hm. Also, the question is what Team::All() should refer to. I think there is some specification missing.
Will get back to this soon.

[fuerlinger]

dash::Team::All() always refers to all units with which the program has been started. dash::Team::All().barrier() is synonymous with dash::barrier() and should work as intended (barrier on all units) regardless of what sub-teams have been created.

[fuerlinger]

I have not tested with locality split, but with the simple regular split things work as expected:

  auto myid = dash::myid();

  auto& team = dash::Team::All();
  auto& myteam = team.split(2);

  if( myteam.position()==1 ) {
    cout << myid << " is member of team 1 (local id:"
     << myteam.myid() << ")"  << endl;
    sleep(1);
  }

  cout << myid << " before barrier"<< endl;
  myteam.parent().barrier();
  cout << myid << " after barrier"<< endl;

Note the usage of position() to distinguish the teams after the split. position might not be the best name, we should probably rename it to either rank() or id() or something.

[fuchsto]

@fuerlinger Okay, that's what one would expect. We will extend unit tests for this then.
@fmoessbauer Does it depend on locality_split perhaps? The underlying mechanism for splitting is the same, though.

I suggest renaming position() to relative_id. The term local is misleading because units in a child
team may be spread among non-local domains.
In the DART locality module, I use id. global_id and relative_id.

[fmoessbauer]

Ok, the team splits work properly. However, for locality_splits it is not guaranteed to get the requested number of teams (Bug #127).
The bug itself is a symptom of #125, #126 and #127

IMO the ticket can be closed.