Subject: Process ids

From: [email-masked]
Date: Thu, 4 Mar 1993 14:21:56 GMT

recently there has been a discussion on process identifiers, groups,
and dynamic process creation. I would like to add a few comments.

1. It is not so much the dynamic creation of new processes which calls
   for something like opaque process ids, but rather the dynamic
   removal of processes. In the former case process ids can be added
   at the end (n, n+1, ...) without changing the 0,..,n-1 numbering
   of the existing processes. If a process terminates, however, there
   is a gap in the numbering scheme. On the other hand, the same gap
   occurs in the group ranking which also Bill and Rusty want to keep.
   So, I don't see how the opaque process ids resolve the problem.

2. As Bill and Rusty say at the end of their note, inquiries like
   "give me my right neighbor" should be done by using the process
   topology functions, and not on the ranks themselves. Only this
   way an optimization of the process ordering is possible. The
   ranks mainly serve to define the buffer ordering in collective
   communication.

3. At our last meeting we already saw that the MPI time schedule is
   becoming tight. I don't think it would be wise to deal with
   dynamic process creation in MPI-1, and as far as I remember there
   was already some consensus on that. Of course, in the design of the
   static interface we have to keep in mind that dynamic extensions
   will be added later. It should not be seen as a problem if on the
   basis of MPI-1 non-standard extensions will emerge. After all, only
   this kind of experimenting can make a later standardization
   possible.

Rolf Hempel