From 7bb3dba3101e047f8e637257154a2e9965d128dd Mon Sep 17 00:00:00 2001
From: Joakim Hove <joakim.hove@gmail.com>
Date: Tue, 31 Aug 2021 17:31:45 +0200
Subject: [PATCH] Special case wells with no open connections in
 ParallelWellInfo

---
 opm/simulators/wells/ParallelWellInfo.cpp |  3 ++-
 opm/simulators/wells/ParallelWellInfo.hpp | 20 +++++++++++++-------
 tests/test_parallelwellinfo.cpp           | 11 +++++++++++
 3 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/opm/simulators/wells/ParallelWellInfo.cpp b/opm/simulators/wells/ParallelWellInfo.cpp
index 0f08924a0..5ae05b9f4 100644
--- a/opm/simulators/wells/ParallelWellInfo.cpp
+++ b/opm/simulators/wells/ParallelWellInfo.cpp
@@ -381,7 +381,8 @@ void ParallelWellInfo::communicateFirstPerforation(bool hasFirst)
     comm_->allgather(&first, 1, firstVec.data());
     auto found = std::find_if(firstVec.begin(), firstVec.end(),
                               [](int i) -> bool{ return i;});
-    rankWithFirstPerf_ = found - firstVec.begin();
+    if (found != firstVec.end())
+        rankWithFirstPerf_ = found - firstVec.begin();
 }
 
 void ParallelWellInfo::pushBackEclIndex(int above, int current)
diff --git a/opm/simulators/wells/ParallelWellInfo.hpp b/opm/simulators/wells/ParallelWellInfo.hpp
index 6ffc7dd56..c8767f5bd 100644
--- a/opm/simulators/wells/ParallelWellInfo.hpp
+++ b/opm/simulators/wells/ParallelWellInfo.hpp
@@ -279,20 +279,26 @@ public:
     /// \brief Collectively decide which rank has first perforation.
     void communicateFirstPerforation(bool hasFirst);
 
+
+    /// If the well does not have any open connections the member rankWithFirstPerf
+    /// is not initialized, and no broadcast is performed. In this case the argument
+    /// is returned unmodified.
     template<class T>
     T broadcastFirstPerforationValue(const T& t) const
     {
         T res = t;
+        if (rankWithFirstPerf_ >= 0) {
 #ifndef NDEBUG
-        assert(rankWithFirstPerf_ >= 0 && rankWithFirstPerf_ < comm_->size());
-        // At least on some OpenMPI version this might broadcast might interfere
-        // with other communication if there are bugs
-        comm_->barrier();
+            assert(rankWithFirstPerf_ < comm_->size());
+            // At least on some OpenMPI version this might broadcast might interfere
+            // with other communication if there are bugs
+            comm_->barrier();
 #endif
-        comm_->broadcast(&res, 1, rankWithFirstPerf_);
+            comm_->broadcast(&res, 1, rankWithFirstPerf_);
 #ifndef NDEBUG
-        comm_->barrier();
+            comm_->barrier();
 #endif
+        }
         return res;
     }
 
@@ -406,7 +412,7 @@ private:
     bool hasLocalCells_;
     /// \brief Whether we own the well and should do reports etc.
     bool isOwner_;
-    /// \brief Rank with the first perforation on it.
+    /// \brief Rank with the first perforation on it, -1 for wells with no open connections.
     int rankWithFirstPerf_;
     /// \brief Communication object for the well
     ///
diff --git a/tests/test_parallelwellinfo.cpp b/tests/test_parallelwellinfo.cpp
index 660fa4eaf..2fb75f5b7 100644
--- a/tests/test_parallelwellinfo.cpp
+++ b/tests/test_parallelwellinfo.cpp
@@ -468,3 +468,14 @@ BOOST_AUTO_TEST_CASE(GlobalPerfFactoryParallel1)
     testGlobalPerfFactoryParallel(1);
     testGlobalPerfFactoryParallel(3);
 }
+
+
+BOOST_AUTO_TEST_CASE(EmptyWell) {
+    auto comm = Communication(Dune::MPIHelper::getCommunicator());
+    Opm::ParallelWellInfo pw({"WELL1", true}, comm);
+    pw.communicateFirstPerforation(false);
+    double local_p = 1;
+    auto global_p = pw.broadcastFirstPerforationValue(local_p);
+
+    BOOST_CHECK_EQUAL(local_p, global_p);
+}