Message Passing Interface: Difference between revisions

Revision as of 02:02, 19 October 2024

Revision as of 09:51, 21 October 2024

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''MPI-2'' is mostly a superset of MPI-1, although some functions have been deprecated. MPI-1.3 programs still work under MPI implementations compliant with the MPI-2 standard.

''MPI-3.0'' introduces significant updates to the MPI standard, including nonblocking versions of collective operations, enhancements to one-sided operations, and a Fortran 2008 binding. It removes deprecated C++ bindings and various obsolete routines and objects. Importantly, any valid MPI-2.2 program that avoids the removed elements is also valid in MPI-3.0.

''MPI-3'' includes new Fortran 2008 bindings, while it removes deprecated C++ bindings as well as many deprecated routines and MPI objects.

''MPI-3.1'' is a minor update focused on corrections and clarifications, particularly for Fortran bindings. It introduces new functions for manipulating MPI_Aint values, nonblocking collective I/O routines, and methods for retrieving index values by name for MPI_T performance variables. Additionally, a general index was added. All valid MPI-3.0 programs are also valid in MPI-3.1.

''MPI-4.0'' is a major update that introduces large-count versions of many routines, persistent collective operations, partitioned communications, and a new MPI initialization method. It also adds application info assertions and improves error handling definitions, along with various smaller enhancements. Any valid MPI-3.1 program is compatible with MPI-4.0.

MPI-4.1 is a minor update focused on corrections and clarifications to the MPI-4.0 standard. It deprecates several routines, the MPI_HOST attribute key, and the mpif.h Fortran include file. A new routine has been added to inquire about the hardware running the MPI program. Any valid MPI-4.0 program remains valid in MPI-4.1.

MPI is often compared with [[Parallel Virtual Machine]] (PVM), which is a popular distributed environment and message passing system developed in 1989, and which was one of the systems that motivated the need for standard parallel message passing. Threaded shared memory programming models (such as [[Pthreads]] and [[OpenMP]]) and message passing programming (MPI/PVM) can be considered complementary and have been used together on occasion in, for example, servers with multiple large shared-memory nodes.

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==Future==

Some aspects of the MPI's future appear solid; others less so. The [[MPI Forum]] reconvened in 2007 to clarify some MPI-2 issues and explore developments for a possible MPI-3, which resulted in versions MPI-3.0 (September 2012)<ref>https://www.mpi-forum.org/docs/mpi-3.0/mpi30-report.pdf</ref> and MPI-3.1 (June 2015)<ref>https://www.mpi-forum.org/docs/mpi-3.1/mpi31-report.pdf</ref>.The development continued with the approval of MPI-4.0 on June 9, 2021<ref>https://www.mpi-forum.org/docs/mpi-4.0/mpi40-report.pdf</ref>, and most recently, MPI-4.1 was approved on November 2, 2023.<ref>https://www.mpi-forum.org/docs/mpi-4.1/mpi41-report.pdf</ref>

Architectures are changing, with greater internal concurrency ([[Multi-core processor|multi-core]]), better fine-grained concurrency control (threading, affinity), and more levels of [[memory hierarchy]]. [[Multithreading (computer architecture)|Multithreaded]] programs can take advantage of these developments more easily than single-threaded applications. This has already yielded separate, complementary standards for [[symmetric multiprocessing]], namely [[OpenMP]]. MPI-2 defines how standard-conforming implementations should deal with multithreaded issues, but does not require that implementations be multithreaded, or even thread-safe. MPI-3 adds the ability to use shared-memory parallelism within a node. Implementations of MPI such as Adaptive MPI, Hybrid MPI, Fine-Grained MPI, MPC and others offer extensions to the MPI standard that address different challenges in MPI.