Add a means to check for hangs in MPIAlState, enabled with AL_DEBUG_H…

…ANG_CHECK.

src/Al.hpp

@@ -37,6 +37,7 @@
 #include "Al_config.hpp"
 #include "base.hpp"
 #include "tuning_params.hpp"
+#include "utils.hpp"
 
 namespace Al {
 

src/CMakeLists.txt

@@ -6,6 +6,7 @@ set_full_path(THIS_DIR_HEADERS
   mempool.hpp
   mpi_impl.hpp
   tuning_params.hpp
+  utils.hpp
   )
 set_full_path(THIS_DIR_CXX_SOURCES
   Al.cpp

src/mpi_impl.hpp

@@ -497,18 +497,36 @@ class MPIAlState : public AlState {
   int tag;
   /** Requests for send_recv. */
   MPI_Request send_recv_reqs[2] = {MPI_REQUEST_NULL, MPI_REQUEST_NULL};
+#ifdef AL_DEBUG_HANG_CHECK
+  bool hang_reported = false;
+  double send_recv_start = std::numeric_limits<double>::max();
+#endif
 
   /** Start a send/recv. */
   void start_send_recv(
     const void* send, int send_count, int dest,
     void* recv, int recv_count, int source) {
     MPI_Irecv(recv, recv_count, type, source, tag, comm, &(send_recv_reqs[0]));
     MPI_Isend(send, send_count, type, dest, tag, comm, &(send_recv_reqs[1]));
+#ifdef AL_DEBUG_HANG_CHECK
+    send_recv_start = get_time();
+#endif
   }
   /** Return true if the outstanding send/recv has completed. */
   bool test_send_recv() {
     int flag;
     MPI_Testall(2, send_recv_reqs, &flag, MPI_STATUSES_IGNORE);
+#ifdef AL_DEBUG_HANG_CHECK
+    if (!flag && !hang_reported) {
+      double t = get_time();
+      // Choice of 10 + rank is arbitrary, but seems reasonable.
+      // The + rank part helps ensure printing from ranks isn't interleaved.
+      if (t - sr_start > 10.0 + rank) {
+        std::cout << rank << ": Possible send/recv hang detected, tag=" << tag << std::endl;
+        hang_reported = true;
+      }
+    }
+#endif
     return flag;
   }
 };

src/utils.hpp

@@ -0,0 +1,41 @@
+////////////////////////////////////////////////////////////////////////////////
+// Copyright (c) 2018, Lawrence Livermore National Security, LLC.  Produced at the
+// Lawrence Livermore National Laboratory in collaboration with University of
+// Illinois Urbana-Champaign.
+//
+// Written by the LBANN Research Team (N. Dryden, N. Maruyama, et al.) listed in
+// the CONTRIBUTORS file. <[email protected]>
+//
+// LLNL-CODE-756777.
+// All rights reserved.
+//
+// This file is part of Aluminum GPU-aware Communication Library. For details, see
+// http://software.llnl.gov/Aluminum or https://github.com/LLNL/Aluminum.
+//
+// Licensed under the Apache License, Version 2.0 (the "Licensee"); you
+// may not use this file except in compliance with the License.  You may
+// obtain a copy of the License at:
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+// implied. See the License for the specific language governing
+// permissions and limitations under the license.
+////////////////////////////////////////////////////////////////////////////////
+
+#pragma once
+
+#include <chrono>
+
+namespace Al {
+
+/** Return time, in seconds (with decimal), since a fixed epoch. */
+inline double get_time() {                                                      
+  using namespace std::chrono;                                                  
+  return duration_cast<duration<double>>(                                       
+    steady_clock::now().time_since_epoch()).count();                            
+}
+
+}  // namespace Al