Avoid MPI mocking, use ifdefs

Also use parallel logical or for file existence check

Author: franzpoeschel

include/openPMD/IO/ADIOS/ADIOS2IOHandler.hpp

@@ -232,7 +232,9 @@ class ADIOS2IOHandlerImpl
 
 private:
     adios2::ADIOS m_ADIOS;
-    std::optional<auxiliary::Mock_MPI_Comm> m_communicator;
+#if openPMD_HAVE_MPI
+    std::optional<MPI_Comm> m_communicator;
+#endif
     /*
      * If the iteration encoding is variableBased, we default to using the
      * 2021_02_09 schema since it allows mutable attributes.

include/openPMD/IO/HDF5/HDF5IOHandlerImpl.hpp

@@ -95,7 +95,13 @@ class HDF5IOHandlerImpl : public AbstractIOHandlerImpl
     hid_t m_H5T_CLONG_DOUBLE;
 
 protected:
-    std::optional<auxiliary::Mock_MPI_Comm> m_mockedMpiComm;
+#if openPMD_HAVE_MPI
+    /*
+     * Not defined in ParallelHDF5IOHandlerImpl, so we don't have to write
+     * some methods twice.
+     */
+    std::optional<MPI_Comm> m_communicator;
+#endif
 
 private:
     json::TracingJSON m_config;

include/openPMD/auxiliary/Mpi.hpp

@@ -79,67 +79,5 @@ namespace
     [[maybe_unused]] MPI_Datatype const MPI_Types<char>::value = MPI_CHAR;
 } // namespace
 
-template <typename Functor>
-void runOnRankZero(Mock_MPI_Comm comm, Functor &&functor)
-{
-    int rank;
-    int status = MPI_Comm_rank(comm, &rank);
-    if (status != 0)
-    {
-        throw std::runtime_error("Can't inquire MPI rank!");
-    }
-    if (rank == 0)
-    {
-        functor();
-    }
-}
-
-template <typename T>
-void MPI_Bcast_fromRankZero(Mock_MPI_Comm comm, T *value)
-{
-    int status = MPI_Bcast(value, 1, MPI_Types<T>::value, 0, comm);
-    if (status != 0)
-    {
-        throw std::runtime_error("MPI_Bcast failed!");
-    }
-}
-
-#else
-
-struct Mock_MPI_Comm
-{};
-
-template <typename Functor>
-void runOnRankZero(Mock_MPI_Comm, Functor &&functor)
-{
-    functor();
-}
-
-template <typename T>
-void MPI_Bcast_fromRankZero(Mock_MPI_Comm, T *)
-{}
-
 #endif
-
-template <typename Functor>
-void runOnRankZero(std::optional<Mock_MPI_Comm> comm, Functor &&functor)
-{
-    if (comm.has_value())
-    {
-        runOnRankZero(comm.value(), std::forward<Functor>(functor));
-    }
-    else
-    {
-        functor();
-    }
-}
-
-template <typename T>
-void MPI_Bcast_fromRankZero(std::optional<Mock_MPI_Comm> comm, T *value)
-{
-    if (comm.has_value())
-    {
-        MPI_Bcast_fromRankZero(comm.value(), value);
-    }
-}
 } // namespace openPMD::auxiliary

src/IO/ADIOS/ADIOS2IOHandler.cpp

@@ -531,12 +531,26 @@ bool ADIOS2IOHandlerImpl::checkFile(std::string fullFilePath) const
          */
         fullFilePath += ".sst";
     }
-    char fileExists = false;
-    auxiliary::runOnRankZero(m_communicator, [&fileExists, &fullFilePath]() {
-        fileExists = auxiliary::file_exists(fullFilePath) ||
-            auxiliary::directory_exists(fullFilePath);
-    });
-    auxiliary::MPI_Bcast_fromRankZero(m_communicator, &fileExists);
+    bool fileExists = auxiliary::directory_exists(fullFilePath) ||
+        auxiliary::file_exists(fullFilePath);
+
+#if openPMD_HAVE_MPI
+    if (m_communicator.has_value())
+    {
+        int status = MPI_Allreduce(
+            &fileExists,
+            &fileExists,
+            1,
+            MPI_C_BOOL,
+            MPI_LOR, // logical or
+            m_communicator.value());
+        if (status != 0)
+        {
+            throw std::runtime_error("MPI Reduction failed!");
+        }
+    }
+#endif
+
     return fileExists;
 }
 

src/IO/HDF5/HDF5IOHandler.cpp

@@ -293,12 +293,26 @@ void HDF5IOHandlerImpl::checkFile(
     {
         name += ".h5";
     }
-    char fileExists = false;
-    auxiliary::runOnRankZero(m_mockedMpiComm, [&fileExists, &name]() {
-        fileExists =
-            auxiliary::file_exists(name) || auxiliary::directory_exists(name);
-    });
-    auxiliary::MPI_Bcast_fromRankZero(m_mockedMpiComm, &fileExists);
+    bool fileExists =
+        auxiliary::file_exists(name) || auxiliary::directory_exists(name);
+
+#if openPMD_HAVE_MPI
+    if (m_communicator.has_value())
+    {
+        int status = MPI_Allreduce(
+            &fileExists,
+            &fileExists,
+            1,
+            MPI_C_BOOL,
+            MPI_LOR, // logical or
+            m_communicator.value());
+        if (status != 0)
+        {
+            throw std::runtime_error("MPI Reduction failed!");
+        }
+    }
+#endif
+
     using FileExists = Parameter<Operation::CHECK_FILE>::FileExists;
     *parameters.fileExists = fileExists ? FileExists::Yes : FileExists::No;
 }

src/IO/HDF5/ParallelHDF5IOHandler.cpp

@@ -67,7 +67,7 @@ ParallelHDF5IOHandlerImpl::ParallelHDF5IOHandlerImpl(
 {
     // Set this so the parent class can use the MPI communicator in functions
     // that are written with special implemenations for MPI-enabled HDF5.
-    m_mockedMpiComm = m_mpiComm;
+    m_communicator = m_mpiComm;
     m_datasetTransferProperty = H5Pcreate(H5P_DATASET_XFER);
     m_fileAccessProperty = H5Pcreate(H5P_FILE_ACCESS);
     m_fileCreateProperty = H5Pcreate(H5P_FILE_CREATE);