OpenMPI 4.x TMPDIR race vader unlink error workaround

CMakeLists.txt

# this is a dummy exmaple project. The actual workaround is in openmpi.cmake.
cmake_minimum_required(VERSION 3.14)

project(Workaround LANGUAGES C)

enable_testing()

include(openmpi.cmake)

set(MPI_DETERMINE_LIBRARY_VERSION true)
find_package(MPI COMPONENTS C REQUIRED)
message(STATUS "MPI Library Version: ${MPI_C_LIBRARY_VERSION_STRING}")

add_executable(my_mpi main.c)

add_test(NAME MyMPI
COMMAND ${MPIEXEC_EXECUTABLE} ${MPIEXEC_NUMPROC_FLAG} ${MPIEXEC_MAX_NUMPROCS} my_mpi)

get_property(tests DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR} PROPERTY TESTS)
if(DEFINED mpi_tmpdir)
  # enact the workaround
  set_property(TEST ${tests} PROPERTY ENVIRONMENT TMPDIR=${mpi_tmpdir})
endif()

openmpi.cmake

# https://github.com/open-mpi/ompi/issues/7393
# https://github.com/gerlero/openfoam-app/pull/112
# https://apple.stackexchange.com/a/287710
# *** OpenMPI workaround
if(UNIX AND MPI_C_LIBRARY_VERSION_STRING MATCHES "Open[ ]?MPI"))
  if(NOT DEFINED mpi_tmpdir)
    execute_process(COMMAND mktemp -d /tmp/mpi-XXXXXXXX
    RESULT_VARIABLE ret
    OUTPUT_VARIABLE mpi_tmpdir
    OUTPUT_STRIP_TRAILING_WHITESPACE
    )
    if(NOT ret EQUAL 0)
      message(FATAL_ERROR "could not create MPI working dir via mktemp -d: ${ret}")
    endif()
    set(mpi_tmpdir ${mpi_tmpdir} CACHE PATH "MPI working dir")
    message(STATUS "${ret}: Created MPI working dir ${mpi_tmpdir}")
  endif()
endif()
# *** END OpenMPI workaround