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MPI provides a ``caching'' facility that allows an application to
attach arbitrary pieces of information, called attributes, to
communicators. More precisely, the caching
facility allows a portable library to do the following:
- pass information between calls by associating it
with an MPI intra- or inter-communicator,
- quickly retrieve that information, and
- be guaranteed that out-of-date information is never retrieved, even if
the communicator is freed and its handle subsequently reused by MPI.
The caching capabilities, in some form, are required by built-in MPI routines
such as collective communication and application topology. Defining an
interface to these capabilities as part of the MPI standard is valuable
because it permits routines like collective communication and application
topologies to be implemented as portable code, and also because it makes MPI
more extensible by allowing user-written routines to use standard MPI calling
sequences.
[] Advice to users.
The communicator MPI_COMM_SELF is a suitable choice for posting
process-local attributes, via this attributing-caching mechanism.
( End of advice to users.)
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