Basic implementation

Author: franzpoeschel

include/openPMD/auxiliary/JSON.hpp

@@ -21,6 +21,12 @@
 
 #pragma once
 
+#include "openPMD/config.hpp"
+
+#if openPMD_HAVE_MPI
+#include <mpi.h>
+#endif
+
 #include <string>
 
 namespace openPMD
@@ -61,5 +67,12 @@ namespace json
      */
     std::string
     merge(std::string const &defaultValue, std::string const &overwrite);
+
+#if openPMD_HAVE_MPI
+    std::string merge(
+        std::string const &defaultValue,
+        std::string const &overwrite,
+        MPI_Comm);
+#endif
 } // namespace json
 } // namespace openPMD

src/auxiliary/JSON.cpp

@@ -597,11 +597,22 @@ merge(nlohmann::json &defaultVal, nlohmann::json const &overwrite)
     return defaultVal;
 }
 
-std::string merge(std::string const &defaultValue, std::string const &overwrite)
+template <typename... MPI_Comm_t>
+std::string merge_impl(
+    std::string const &defaultValue,
+    std::string const &overwrite,
+    MPI_Comm_t &&...comm)
 {
-    auto [res, returnFormat] =
-        parseOptions(defaultValue, /* considerFiles = */ false);
-    merge(res, parseOptions(overwrite, /* considerFiles = */ false).config);
+    auto res = parseOptions(
+                   defaultValue,
+                   std::forward<MPI_Comm_t>(comm)...,
+                   /* considerFiles = */ true)
+                   .config;
+    auto [second, returnFormat] = parseOptions(
+        overwrite,
+        std::forward<MPI_Comm_t>(comm)...,
+        /* considerFiles = */ true);
+    merge(res, second);
     switch (returnFormat)
     {
     case SupportedLanguages::JSON:
@@ -617,6 +628,21 @@ std::string merge(std::string const &defaultValue, std::string const &overwrite)
     throw std::runtime_error("Unreachable!");
 }
 
+std::string merge(std::string const &defaultValue, std::string const &overwrite)
+{
+    return merge_impl(defaultValue, overwrite);
+}
+
+#if openPMD_HAVE_MPI
+std::string merge(
+    std::string const &defaultValue,
+    std::string const &overwrite,
+    MPI_Comm comm)
+{
+    return merge_impl(defaultValue, overwrite, comm);
+}
+#endif
+
 nlohmann::json &
 filterByTemplate(nlohmann::json &defaultVal, nlohmann::json const &positiveMask)
 {

src/binding/python/Series.cpp

@@ -408,12 +408,7 @@ Look for the WriteIterations class for further documentation.
             return series;
         });
 
-    m.def(
-        "merge_json",
-        &json::merge,
-        py::arg("default_value") = "{}",
-        py::arg("overwrite") = "{}",
-        R"END(
+    constexpr char const *docs_merge_json = &R"END(
 Merge two JSON/TOML datasets into one.
 
 Merging rules:
@@ -445,5 +440,37 @@ users to overwrite default options, while keeping any other ones.
 * returns:       The merged dataset, according to the above rules.
                  If `defaultValue` was a JSON dataset, then as a JSON string,
                  otherwise as a TOML string.
-        )END");
+        )END"[1];
+
+    m.def(
+         "merge_json",
+         py::overload_cast<std::string const &, std::string const &>(
+             &json::merge),
+         py::arg("default_value") = "{}",
+         py::arg("overwrite") = "{}",
+         docs_merge_json)
+#if openPMD_HAVE_MPI
+        .def(
+            "merge_json",
+            [](std::string const &default_value,
+               std::string const &overwrite,
+               py::object &comm) {
+                auto variant = pythonObjectAsMpiComm(comm);
+                if (auto errorMsg = std::get_if<std::string>(&variant))
+                {
+                    throw std::runtime_error("[merge_json] " + *errorMsg);
+                }
+                else
+                {
+                    py::gil_scoped_release release;
+                    return json::merge(
+                        default_value, overwrite, std::get<MPI_Comm>(variant));
+                }
+            },
+            py::arg("default_value") = "{}",
+            py::arg("overwrite") = "{}",
+            py::arg("comm"),
+            docs_merge_json)
+#endif
+        ;
 }