PARTITION

PARTITION
(RxO == NO ; Mutable == YES)
[ Publisher, Subscriber ]

The default value is a sequence of one empty string.

This policy allows the creation of logical partitions within a domain.
This means that DataReaders and DataWriters will not be associated if
they do not share any partition strings.  While the establishment
of an association depends on matching partition strings on the
publication and subscription ends, the failure to match partitions
is not considered a failure and does not trigger any callbacks or
set any status values.  This is why this policy is not considered
part of the request/offer protocol establishing associations.

Not having this policy set at all will cause the entity to participate
in the default partition, which is considered to have the string "".
The value of this policy may be changed at any time.  Changes to
this policy may cause associations to be removed or created.

Implementing this policy requires that the values for this policy be
made available within the repository so that they can be used when
determining whether to create or remove associations.  The repository
will then make association changes triggered by policy value changes
that are pushed from the individual publishers and subscribers.
All publications and subscriptions held by a Publisher or Subscriber
should have the policy value changed to ensure that associations
are updated correctly.

Implementation notes:

  This is intended to be used as a filter in the Publisher and
  Subscriber to allow data samples to be associated.  Implementation
  is entirely within the repository.

  DCPSInfo

    Creation of associations take into account the QoS.PARTITION
    values of the endpoints.  This is done by matching all
    possible associations, then checking the many to many strings
    with wildcards for a match for each potential association.
    Only associations that pass this matching are actually
    created.

    This is currently done within the DCPS_Utils compatibleQOS method.
    The stanza that checks this should use the standard regcmp/regex
    facility and return a value of not compatible without incrementing
    a mismatched Qos (incompatible_qos) counter on either side of the
    (non) association.

    Note that the fnmatch() call can be used to determine if a value
    string is a pattern to be expanded or not (since the spec requires
    that 2 patterns _not_ be matched):

      #include "ace/os_include/os_fnmatch.h"

      if( 0 == ::fnmatch( value.c_str(), "[[*?]")) {
        // value _is_ a wildcard pattern.
      } else {
        // value is _not_ a wildcard pattern.
      }

    I would highly recommend that we push this entire utility file into
    a DCPS::Utilities namespace at the time this is implemented as well.

    When the value is changed, existing associations that are
    affected are checked to ensure that they continue to match.
    All possible connections should be checked as well, since more
    associations may be created, as well as existing associations
    removed when a policy value is changed.

    If the effort to implement the modified value feature is too great,
    the initial implementation does not need to deal with changed values.
    We can declare that modification of values is not supported initially.