MPL is a message passing library written in C++17 based on the Message Passing Interface (MPI) standard. Since the C++ API has been dropped from the MPI standard in version 3.1, it is the aim of MPL to provide a modern C++ message passing library for high performance computing.
MPL will neither bring all functions of the C language MPI-API to C++ nor provide a direct mapping of the C API to some C++ functions and classes. The library's focus lies on the MPI core message passing functions, ease of use, type safety, and elegance. The aim of MPL is to provide an idiomatic C++ message passing library without introducing a significant overhead compared to utilizing MPI via its plain C-API. This library is most useful for developers who have at least some basic knowledge of the Message Passing Interface standard and would like to utilize it via a more user-friendly interface in modern C++. Unlike (Boost.MPI)[https://www.boost.org/doc/libs/1_77_0/doc/html/mpi.html], MPL does not rely on an external serialization library and has a negligible run-time overhead.
MPL assumes that the underlying MPI implementation supports the version 3.1 of the Message Passing Interface standard. Future versions of MPL may also employ features of the new version 4.0 or later MPI versions.
MPL gives currently access via a convenient C++ interface to the following features of the Message Passing Interface standard:
- environmental management (implicit initialization and finalization, timers, but no error handling).
- point-to-point communication (blocking and non-blocking),
- collective communication (blocking and non-blocking),
- derived data types (happens automatically for many custom data types or via the
base_struct_builderhelper class and the layout classes of MPL), - communicator- and group-management and
- process topologies (cartesian and graph topologies),
Currently, the following MPI features are not yet supported by MPL:
- inter-communicators (planed for v0.2)
- error handling,
- process creation and management,
- one-sided communication and
- I/O.
Although MPL covers a subset of the MPI functionality only, it has probably the largest MPI-feature coverage among all alternative C++ interfaces to MPI.
MPL is built on MPI. An MPI implementation needs to be installed as a
prerequisite, e.g., Open MPI or
MPICH. As MPL is a header-only library,
it suffices to download the source
and copy the mpl directory, which contains all header files to a place,
where the compiler will find it, e.g., /usr/local/include on a typical
Unix/Linux system.
For convenience and better integration into various IDEs, MPL also comes
with CMake support. To install MPL via CMake get the sources and create
a new build folder in the MPL source directory, e.g.,
user@host:~/mpl$ mkdir build
user@host:~/mpl$ cd buildThen, call the CMake tool to detect all dependencies and to generate the project configuration for your build system or IDE, e.g.
user@host:~/mpl/build$ cmake -DCMAKE_INSTALL_PREFIX:PATH=/usr/local ..The option -DCMAKE_INSTALL_PREFIX:PATH specifies the installation path.
Cmake can also be utilized to install the MPL header files. Just call
CMake a second time and specify the --install option now, e.g.,
user@host:~/mpl/build$ cmake --install .A set of unit tests and a collection of examples that illustrate the
usage of MPL can be complied via CMake, too, if required. To build the
MPL unit tests add the option -DBUILD_TESTING=ON to the initial CMake
call. Similarly, -DMPL_BUILD_EXAMPLES=ON enables building example
codes. Thus,
user@host:~/mpl/build$ cmake -DCMAKE_INSTALL_PREFIX:PATH=/usr/local -DBUILD_TESTING=ON -DMPL_BUILD_EXAMPLES=ON ..enables both, building unit tests and examples. MPL unit tests utilize the Boost.Test framework. Finally, build the unit tests and/or the example code via
user@host:~/mpl/build$ cmake --build .After the unit test have been build successfully, they can be run conveniently by utilizing the CTest tool, i.e., via
user@host:~/mpl/build$ ctest
Test project /home/user/mpl/build
Start 1: test_communicator
1/27 Test #1: test_communicator ........................ Passed 0.19 sec
Start 2: test_cartesian_communicator
2/27 Test #2: test_cartesian_communicator .............. Passed 0.11 sec
Start 3: test_graph_communicator
3/27 Test #3: test_graph_communicator .................. Passed 0.07 sec
Start 4: test_dist_graph_communicator
4/27 Test #4: test_dist_graph_communicator ............. Passed 0.11 sec
Start 5: test_communicator_send_recv
5/27 Test #5: test_communicator_send_recv .............. Passed 0.11 sec
Start 6: test_communicator_isend_irecv
6/27 Test #6: test_communicator_isend_irecv ............ Passed 0.12 sec
Start 7: test_communicator_init_send_init_recv
7/27 Test #7: test_communicator_init_send_init_recv .... Passed 0.11 sec
Start 8: test_communicator_sendrecv
8/27 Test #8: test_communicator_sendrecv ............... Passed 0.11 sec
Start 9: test_communicator_probe
9/27 Test #9: test_communicator_probe .................. Passed 0.11 sec
Start 10: test_communicator_mprobe_mrecv
10/27 Test #10: test_communicator_mprobe_mrecv ........... Passed 0.11 sec
Start 11: test_communicator_barrier
11/27 Test #11: test_communicator_barrier ................ Passed 0.11 sec
Start 12: test_communicator_bcast
12/27 Test #12: test_communicator_bcast .................. Passed 0.10 sec
Start 13: test_communicator_gather
13/27 Test #13: test_communicator_gather ................. Passed 0.10 sec
Start 14: test_communicator_gatherv
14/27 Test #14: test_communicator_gatherv ................ Passed 0.06 sec
Start 15: test_communicator_allgather
15/27 Test #15: test_communicator_allgather .............. Passed 0.11 sec
Start 16: test_communicator_allgatherv
16/27 Test #16: test_communicator_allgatherv ............. Passed 0.14 sec
Start 17: test_communicator_scatter
17/27 Test #17: test_communicator_scatter ................ Passed 0.12 sec
Start 18: test_communicator_scatterv
18/27 Test #18: test_communicator_scatterv ............... Passed 0.12 sec
Start 19: test_communicator_alltoall
19/27 Test #19: test_communicator_alltoall ............... Passed 0.11 sec
Start 20: test_communicator_alltoallv
20/27 Test #20: test_communicator_alltoallv .............. Passed 0.15 sec
Start 21: test_communicator_reduce
21/27 Test #21: test_communicator_reduce ................. Passed 0.13 sec
Start 22: test_communicator_allreduce
22/27 Test #22: test_communicator_allreduce .............. Passed 0.13 sec
Start 23: test_communicator_reduce_scatter_block
23/27 Test #23: test_communicator_reduce_scatter_block ... Passed 0.12 sec
Start 24: test_communicator_reduce_scatter
24/27 Test #24: test_communicator_reduce_scatter ......... Passed 0.08 sec
Start 25: test_communicator_scan
25/27 Test #25: test_communicator_scan ................... Passed 0.05 sec
Start 26: test_communicator_exscan
26/27 Test #26: test_communicator_exscan ................. Passed 0.05 sec
Start 27: test_displacements
27/27 Test #27: test_displacements ....................... Passed 0.02 sec
100% tests passed, 0 tests failed out of 27
Total Test time (real) = 2.86 secor via your IDE if it features support for CTest.
Alternatively, MPL may be installed via the Spack package manager. This will install the library headers ony but not compile the unit tests and the examples.
Usually, CMake will find the required MPI installation as well as the Boost Test library automatically. Depending on the local setup, however, CMake may need some hints to find these dependencies. See the CMake documentation on FindMPI and FindBoost for further details.
MPL is built on top of the Message Passing Interface (MPI) standard. Therefore, MPL shares many concepts known from the MPI standard, e.g., the concept of a communicator. Communicators manage the message exchange between different processes, i.e., messages are sent and received with the help of a communicator.
The MPL environment provides a global default communicator comm_world, which will
be used in the following Hello-World program. The program prints out some information
about each process:
- its rank,
- the total number of processes and
- the computer's name the process is running on.
If there are two or more processes, a message is sent from process 0 to process 1, which is also printed.
#include <cstdlib>
#include <iostream>
// include MPL header file
#include <mpl/mpl.hpp>
int main() {
// get a reference to communicator "world"
const mpl::communicator &comm_world{mpl::environment::comm_world()};
// each process prints a message containing the processor name, the rank
// in communicator world and the size of communicator world
// output may depend on the underlying MPI implementation
std::cout << "Hello world! I am running on \"" << mpl::environment::processor_name()
<< "\". My rank is " << comm_world.rank() << " out of " << comm_world.size()
<< " processes.\n";
// if there are two or more processes send a message from process 0 to process 1
if (comm_world.size() >= 2) {
if (comm_world.rank() == 0) {
std::string message{"Hello world!"};
comm_world.send(message, 1); // send message to rank 1
} else if (comm_world.rank() == 1) {
std::string message;
comm_world.recv(message, 0); // receive message from rank 0
std::cout << "got: \"" << message << "\"\n";
}
}
return EXIT_SUCCESS;
}For further documentation see the Doxygen-generated documentation, the blog posts
the presentation
- Message Passing mit modernem C++ (German only),
the book
- Parallel Programming for Science and Engineering by Victor Eijkhout
and the files in the examples directory of the source package.