Configure Open MPI shmem defaults on macOS

Open MPI 5 can warn while probing mmap backing files under macOS TMPDIR paths, so default to the POSIX shmem component before MPI_Init unless the user already configured it

Author: aobolensk

modules/runners/src/runners.cpp

@@ -1,7 +1,6 @@
 #include "runners/include/runners.hpp"
 
 #include <gtest/gtest.h>
-#include <mpi.h>
 
 #include <chrono>
 #include <cstdint>
@@ -10,6 +9,7 @@
 #include <format>
 #include <iostream>
 #include <memory>
+#include <mpi.h>
 #include <random>
 #include <stdexcept>
 #include <string>
@@ -140,6 +140,7 @@ int RunAllTestsSafely() {
 }  // namespace
 
 int Init(int argc, char **argv) {
+  ppc::util::ConfigureMpiEnvironment();
   const int init_res = MPI_Init(&argc, &argv);
   if (init_res != MPI_SUCCESS) {
     std::cerr << std::format("[  ERROR  ] MPI_Init failed with code {}", init_res) << '\n';

modules/util/include/util.hpp

@@ -95,6 +95,7 @@ double GetTaskMaxTime();
 double GetPerfMaxTime();
 double GetTimeMPI();
 int GetMPIRank();
+void ConfigureMpiEnvironment();
 void SynchronizeMpiRanks();
 
 template <typename T>

modules/util/src/util.cpp

@@ -1,11 +1,10 @@
 #include "util/include/util.hpp"
 
-#include <mpi.h>
-
 #include <algorithm>
 #include <array>
 #include <filesystem>
 #include <libenvpp/detail/get.hpp>
+#include <mpi.h>
 #include <string>
 
 namespace {
@@ -68,6 +67,15 @@ bool ppc::util::IsUnderMpirun() {
   });
 }
 
+void ppc::util::ConfigureMpiEnvironment() {
+#ifdef __APPLE__
+  // Open MPI 5 can emit mmap backing-file probe warnings for macOS TMPDIR paths.
+  if (!env::get<std::string>("OMPI_MCA_shmem").has_value()) {
+    env::detail::set_environment_variable("OMPI_MCA_shmem", "posix");
+  }
+#endif
+}
+
 void ppc::util::SynchronizeMpiRanks() {
   int initialized = 0;
   if (MPI_Initialized(&initialized) != MPI_SUCCESS || initialized == 0) {

tasks/common/runners/performance.cpp

@@ -177,6 +177,7 @@ int SynchronizeStatus(int local_status, std::string_view stage) {
 }
 
 int RunPerformanceMain(int argc, char **argv) {
+  ppc::util::ConfigureMpiEnvironment();
   const int init_res = MPI_Init(&argc, &argv);
   if (init_res != MPI_SUCCESS) {
     std::cerr << "[  ERROR  ] MPI_Init failed with code " << init_res << '\n';