Charm++ parallel programming system

[Jozsef Bakosi <jbakosi AT lanl.gov>]

Hello Charm++ developers,

I wonder if I could request a feature.

As far as I understand, there can be no more than one simultaneous reductions 
in
flight originating from some chare array targeting the some single chare (but
different reduction targets). Also multiple reductions in such fashion are 
okay
as long as the reductions are always guaranteed to be invoked in the same 
order.
As I understand, this a limitation on purpose for performance reasons.

However, I find myself running into the above runtime error (which I believe I
get due to this issue) more than I would like to and this is because (I 
believe)
I initiate such multiple reductions based on SDAG constructs becoming ready at
different times, so I cannot always guarantee the same order.

So far I have been able to work around this and my solution is almost always
having to put in some synchronization (usually global reductions), which is of
course far from ideal. Also, even if such solutions appear correct, this is
pretty hard to do on a complex SDAG, and (2) it is almost impossible to test 
its
correctness as the behavior is pretty stochastic. I believe I have run into 
such
problems every once in a few months in the past couple of years.

To remedy this I would like an option to be able to create reductions for 
which
this is not a problem. Of course, I am willing to trade performance for
correctness for such cases.

Is such a special reduction feasible? Would that be a lot of work for you guys
to implement and maintain?

Thanks,
Jozsef