[mpich-commits] [mpich] MPICH primary repository branch, master, updated. v3.2-341-g702baee

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http://git.mpich.org/mpich.git/commitdiff/702baeed4b46166aea2b292ac556f0b2589cc8f3

commit 702baeed4b46166aea2b292ac556f0b2589cc8f3
Author: Lena Oden <loden at anl.gov>
Date:   Mon Apr 25 18:02:36 2016 -0500

    Fixes intercom_merge temporal context_id usage
    
    This patch fixes a problem in the intecom_merge routine. Intercom_merge
    needs a temporaly communicator to find the context_id for the merged
    communicator. However, this communicator also needs a context_id,
    which is unique on every process and the same on all processes.
    
    The problem with the previous routine is that the context_id  of an
    inter-communicator may be used by another communicator – which can be
    an intra-communicator with a sub-internode communicator. In this case,
    the context id is not longer unique. A subcommunicator with ID 3 normally
    is not allowed - so it is  allways unique. But we have to make sure that
    for this communicator, no sub-communicators are created, so we avoid
    the creation of sub communicators, if the sub communicator flag is set.
    
    Signed-off-by: Yanfei Guo <yguo at anl.gov>

diff --git a/src/mpi/comm/commutil.c b/src/mpi/comm/commutil.c
index ded0bb4..305fb9c 100644
--- a/src/mpi/comm/commutil.c
+++ b/src/mpi/comm/commutil.c
@@ -549,7 +549,8 @@ int MPIR_Comm_commit(MPIR_Comm * comm)
 
     MPIR_Comm_map_free(comm);
 
-    if (comm->comm_kind == MPIR_COMM_KIND__INTRACOMM) {
+    if (comm->comm_kind == MPIR_COMM_KIND__INTRACOMM &&
+            !MPIR_CONTEXT_READ_FIELD(SUBCOMM,comm->context_id)) {  /*make sure this is not a subcomm*/
 
         mpi_errno = MPIR_Find_local_and_external(comm,
                                                  &num_local, &local_rank, &local_procs,
diff --git a/src/mpi/comm/intercomm_merge.c b/src/mpi/comm/intercomm_merge.c
index 5d01edb..c7283f3 100644
--- a/src/mpi/comm/intercomm_merge.c
+++ b/src/mpi/comm/intercomm_merge.c
@@ -141,14 +141,20 @@ int MPIR_Intercomm_merge_impl(MPIR_Comm *comm_ptr, int high, MPIR_Comm **new_int
     
     new_size = comm_ptr->local_size + comm_ptr->remote_size;
 
-    /* FIXME: For the intracomm, we need a consistent context id.
+    /* For the intracomm, we need a consistent context id.
        That means that one of the two groups needs to use
-       the recvcontext_id and the other must use the context_id */
+       the recvcontext_id and the other must use the context_id
+       The recvcontext_id is unique on each process, but another
+       communicator may use the context_id. Therefore, we do a small hack.
+       We set both flags indicating a sub-communicator (intra-node and
+       inter-node) to one. This is normally not possible (a communicator
+       is either intra- or inter-node) - which makes this context_id unique.  */
+
     if (local_high) {
-        (*new_intracomm_ptr)->context_id = comm_ptr->recvcontext_id + 2; /* See below */
+        (*new_intracomm_ptr)->context_id = MPIR_CONTEXT_SET_FIELD(SUBCOMM,comm_ptr->recvcontext_id, 3);
     }
     else {
-        (*new_intracomm_ptr)->context_id = comm_ptr->context_id + 2; /* See below */
+        (*new_intracomm_ptr)->context_id = MPIR_CONTEXT_SET_FIELD(SUBCOMM, comm_ptr->context_id, 3);
     }
     (*new_intracomm_ptr)->recvcontext_id = (*new_intracomm_ptr)->context_id;
     (*new_intracomm_ptr)->remote_size    = (*new_intracomm_ptr)->local_size   = new_size;

-----------------------------------------------------------------------

Summary of changes:
 src/mpi/comm/commutil.c        |    3 ++-
 src/mpi/comm/intercomm_merge.c |   14 ++++++++++----
 2 files changed, 12 insertions(+), 5 deletions(-)


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