Fix a race condition when multiple threads do the "first send" to an endpoint simultaneously.

ompi/mca/pml/ob1/pml_ob1_comm.h

@@ -73,10 +73,11 @@ static inline mca_pml_ob1_comm_proc_t *mca_pml_ob1_peer_lookup (struct ompi_comm
     if (OPAL_UNLIKELY(NULL == pml_comm->procs[rank])) {
         OPAL_THREAD_LOCK(&pml_comm->proc_lock);
         if (NULL == pml_comm->procs[rank]) {
-            pml_comm->procs[rank] = OBJ_NEW(mca_pml_ob1_comm_proc_t);
-            pml_comm->procs[rank]->ompi_proc = ompi_comm_peer_lookup (comm, rank);
-            OBJ_RETAIN(pml_comm->procs[rank]->ompi_proc);
+            mca_pml_ob1_comm_proc_t* proc = OBJ_NEW(mca_pml_ob1_comm_proc_t);
+            proc->ompi_proc = ompi_comm_peer_lookup (comm, rank);
+            OBJ_RETAIN(proc->ompi_proc);
             opal_atomic_wmb ();
+            pml_comm->procs[rank] = proc;
         }
         OPAL_THREAD_UNLOCK(&pml_comm->proc_lock);
     }