[release,bugfix] Use correct number of expected recvRequests

Since 0c697d8d messages of size zero
are no longer sent. This can reduce the number of requests we have to
wait for.

(cherry picked from commit f35437e9)
Signed-off-by: Carsten Gräser <graeser@dune-project.org>

dune/common/parallel/communicator.hh

@@ -1420,6 +1420,8 @@ namespace Dune
 
     MPI_Request* sendRequests = new MPI_Request[messageInformation_.size()];
     MPI_Request* recvRequests = new MPI_Request[messageInformation_.size()];
+    /* Number of recvRequests that are not MPI_REQUEST_NULL */
+    size_t numberOfRealRecvRequests = 0;
 
     // Setup receive first
     typedef typename InformationMap::const_iterator const_iterator;
@@ -1433,23 +1435,27 @@ namespace Dune
       if(FORWARD) {
         assert(info->second.second.start_*sizeof(typename CommPolicy<Data>::IndexedType)+info->second.second.size_ <= recvBufferSize );
         Dune::dvverb<<rank<<": receiving "<<info->second.second.size_<<" from "<<info->first<<std::endl;
-        if(info->second.second.size_)
+        if(info->second.second.size_) {
           MPI_Irecv(recvBuffer+info->second.second.start_, info->second.second.size_,
                     MPI_BYTE, info->first, commTag_, communicator_,
                     recvRequests+i);
-        else
+          numberOfRealRecvRequests += 1;
+        } else {
           // Nothing to receive -> set request to inactive
           recvRequests[i]=MPI_REQUEST_NULL;
+        }
       }else{
         assert(info->second.first.start_*sizeof(typename CommPolicy<Data>::IndexedType)+info->second.first.size_ <= recvBufferSize );
         Dune::dvverb<<rank<<": receiving "<<info->second.first.size_<<" to "<<info->first<<std::endl;
-        if(info->second.first.size_)
+        if(info->second.first.size_) {
           MPI_Irecv(recvBuffer+info->second.first.start_, info->second.first.size_,
                     MPI_BYTE, info->first, commTag_, communicator_,
                     recvRequests+i);
-        else
+          numberOfRealRecvRequests += 1;
+        } else {
           // Nothing to receive -> set request to inactive
           recvRequests[i]=MPI_REQUEST_NULL;
+        }
       }
     }
 
@@ -1486,7 +1492,7 @@ namespace Dune
     MPI_Status status; //[messageInformation_.size()];
     //MPI_Waitall(messageInformation_.size(), recvRequests, status);
 
-    for(i=0; i< messageInformation_.size(); i++) {
+    for(i=0; i< numberOfRealRecvRequests; i++) {
       status.MPI_ERROR=MPI_SUCCESS;
       MPI_Waitany(messageInformation_.size(), recvRequests, &finished, &status);
       assert(finished != MPI_UNDEFINED);