MPI_barrier()

johndeas · November 1, 2009, 09:45

Hi,

I need my master processor to carry out some operations on some files. I would like all the other processors to pause while this is going on, as their behaviour might be affected by the non completion of the task on the master proc.

I have read about MPI_barrier() which seems to be what I need:

Code:

if not on the masterProc:
    MPI_barrier()
else:
    carry out operation
    MPI_barrier()

Is it possible to do this directly using OpenFOAM commands and if not, is it possible to use the vanilla MPI_barrier() ?

In that case what arguments should be put in:

Code:

int MPI_Barrier ( MPI_Comm comm )

?

Thanks !

fra76 · November 3, 2009, 14:29

When I need this, I usually do a reduction, as MPI_barrier is not exposed by Pstream, as far as I know.

I.e.:

Code:

if (Pstream.master())
{
   carry out operation
}
{
    label tmp = Pstream.myProcNo();
    reduce(tmp,sumOp<label>());
}

At the reduce statement, all the processors must pass together, so the effect is like MPI_barrier even if with a very low unnecessary traffic.

Hope this helps,
Francesco

johndeas · November 23, 2009, 12:59

Since I am putting a lot of commands, a proper MPI_barrier might have helped, but, thank you for you advice, will use it !

November 1, 2009, 09:45	MPI_barrier()	#1
johndeas Senior Member John Deas Join Date: Mar 2009 Posts: 160 Rep Power: 17	Hi, I need my master processor to carry out some operations on some files. I would like all the other processors to pause while this is going on, as their behaviour might be affected by the non completion of the task on the master proc. I have read about MPI_barrier() which seems to be what I need: Code: if not on the masterProc: MPI_barrier() else: carry out operation MPI_barrier() Is it possible to do this directly using OpenFOAM commands and if not, is it possible to use the vanilla MPI_barrier() ? In that case what arguments should be put in: Code: int MPI_Barrier ( MPI_Comm comm ) ? Thanks !

November 3, 2009, 14:29		#2
fra76 Senior Member Francesco Del Citto Join Date: Mar 2009 Location: Zürich Area, Switzerland Posts: 237 Rep Power: 18	When I need this, I usually do a reduction, as MPI_barrier is not exposed by Pstream, as far as I know. I.e.: Code: if (Pstream.master()) { carry out operation } { label tmp = Pstream.myProcNo(); reduce(tmp,sumOp<label>()); } At the reduce statement, all the processors must pass together, so the effect is like MPI_barrier even if with a very low unnecessary traffic. Hope this helps, Francesco pm11dt and scleakey like this.

November 23, 2009, 12:59		#3
johndeas Senior Member John Deas Join Date: Mar 2009 Posts: 160 Rep Power: 17	Since I am putting a lot of commands, a proper MPI_barrier might have helped, but, thank you for you advice, will use it !