The MPI Environment

The Environment Object

The environment object is responsible for the initialization and finalization of MPI environment. It must be defined at the beginning of the main() function and get destroyed at the end. The constructor and destructor of the environment object call standard MPI subroutines to perform actual environment management.

Hence, we require that a MPI program using HIPP must be organized like the following:

int main(int argc, char *argv[]) {
    mpi::Env env;

    // use HIPP MPI module

    return 0;
}

The Env object can be default-constructed. But the most-portable way is to pass the references of argc and argv to construct it:

mpi::Env env(argc, argv);

In multi-thread applications, you may pass two additional arguments required and provided to ensure thread safety:

int required = mpi::Env::THREAD_MULTIPLE,
    provided;
mpi::Env env(argc, argv, required, provided);

The required thread safety hints the MPI implementation and the out-argument provided returns the actual thread safety supported by the library.

After the initialization of MPI environment, it is safe to get the “WORLD” communicator through the static method Env::world and perform communications on it:

auto comm = mpi::Env::world();

Inquiry the Library Information

To get a quick look about your MPI library, stream the environment object directly like:

pout << env;

The output is:

HIPP::MPI::Env instance [loc=0x7ffd806a2d34, size=4, align=4]
----------
Standard: 3.1
Runtime Environment (TAG UB=268435455, HOST=None, IO RANK=Any, WTIME GLOBAL=No)
Processor name: local-HP

To get the MPI standard version supported by the library, use either the preprocessor macro HIPPMPI_STD_VERSION and HIPPMPI_STD_SUBVERSION, or the static method Env::version():

pout << "version = ", HIPPMPI_STD_VERSION, ".", HIPPMPI_STD_SUBVERSION, endl;

int ver, sub_ver;
mpi::Env::version(ver, sub_ver);
pout << "version = ", ver, ".", sub_ver, endl;

The output is (with a MPI-3.1 compliant implementation):

version = 3.1
version = 3.1

Another method, Env::library_version(), returns a string that describes the version information of the library:

pout << mpi::Env::library_version(), endl;

The output is (with a MPICH implementation):

MPICH Version:  3.3.2
MPICH Release date:     Tue Nov 12 21:23:16 CST 2019
MPICH ABI:      13:8:1
MPICH Device:   ch3:nemesis
...

Other methods of Env are defined to inquire different piecees of information about the library:

pout << "Tag upper bound: ",     env.tag_ub(),           '\n',
        "Host rank: ",           env.host(),             '\n',
        "Rank of IO process: ",  env.io(),               '\n',
        "Wtime is global: ",     env.wtime_is_global(),  '\n',
        "Host machine: ",        env.processor_name(),   '\n';

The output on my compute is:

Tag upper bound: 268435455
Host rank: -1
Rank of IO process: -2
Wtime is global: 0
Host machine: local-HP

HIPP 0.0.1 documentation

The MPI Environment

Contents

The MPI Environment

The Environment Object

Inquiry the Library Information