communicator that we created has a lower CID than the parent comm. This can
happen when using the hierarch collective communication module or for
inter-communicators (since we make a duplicate of the original communicator).
This is not a problem as long as the user calls MPI_Comm_free on the parent
communicator. However, if the communicators are not freed by the user but
released by Open MPI in MPI_Finalize, we walk through the list of still
available communicators and free them one by one. Thus, local_comm is freed
before the actual inter-communicator. However, the local_comm pointer in the
inter communicator will still contain the 'previous' address of the local_comm
and thus this will lead to a segmentation violation. In order to prevent that
from happening, we increase the reference counter local_comm by one if its CID
is lower than the parent. We cannot increase however its reference counter if
the CID of local_comm is larger than the CID of the inter communicators, since
a regular MPI_Comm_free would leave in that the case the local_comm hanging
around and thus we would not recycle CID's properly, which was the reason and
the cause for this trouble.
This commit fixes tickets 2094 and 2166. Note however, that I want to close
them manually, since a slightly different patch is required for the 1.4
series. This commit will have to be applied for the 1.5 series. And I will
need a volunteer to review it.
This commit was SVN r22671.
61dee816db