Charm++ parallel programming system

[Robert Steinke <rsteinke AT uwyo.edu>]

Is there a way in Charm++ to do a barrier without doing a reduction?

I have a situation where I need a chare group to do six barriers through 
a sequence of code.  Having them do a reduction to the main chare and 
then have the main chare send a message to proceed is bloating the 
code.  I don't need to do a reduction to produce a value.  I just need a 
barrier.  It would be nice if I could just put a barrier statement in 
the charm group code.

I suppose one solution would be to call MPI_Barrier directly, but I 
don't like that solution.  First of all, is it safe to do that from 
within my Charm++ code?  Will it always be safe in future versions of 
Charm++?  It seems like a dangerous use of undocumented functionality.  
Also, the code would not be portable to Charm++ installs that were not 
compiled to use MPI.

For anyone who is curious why I need six barriers, this group is using a 
parallel library to write NetCDF files.  Every member must perform 
define actions where they specify what variables are in the file.  Then 
they all perform data actions where they write values to those 
variables.  Then they all must close the file.  The define actions of 
all group members must be done before any group member performs a data 
action, and the data actions of all group members must be done before 
any group member closes the file.  I need two barriers per file and they 
are doing this for three files so I need six barriers.  This is an 
infrequent operation so speed is not much of an issue, just code bloat.

Bob Steinke