Charm++ parallel programming system

[Phil Miller <mille121 AT illinois.edu>]

Hi John,

There's no provided API to get the number of elements in a dynamic array (*). We would have to do exactly the same reduction as user code, which presents some issues:

- It adds overhead for use cases that don't need the runtime system to tell the application the number of elements inserted

- When would that API be safe to call? Would doneInserting have to be a blocking call, or take a callback, to indicate when the value is available?

Given that this is something we expect the application code to have a straightforward time implementing for its specific insertion logic, that seems preferable. I'd be interested to hear about cases where doing it in the application is complicated or hard.

(*) Note that I say "number of elements" and not "length", because the population of the array need not be a dense, contiguous set of indices. It can be arbitrarily sparse. We could nominally distinguish 'chare arrays' (elements named by all indices within a k-dimensional rectangle) from 'chare sets' (elements named by an arbitrary set of indices)

Phil

On Wed, Jun 14, 2017 at 4:04 PM, Mitchell, John A <jamitch AT sandia.gov> wrote:

Hi,

I am using dynamic insertion of a chare array and do not know apriori the array length.

After calling 'doneInserting()' is there a way to get the array length without doing a collective reduction somehow?

Thanks.

John