3.1.1. Open MPI v6.1.x series

This file contains all the NEWS updates for the Open MPI v6.1.x series, in reverse chronological order.

3.1.1.1. Open MPI version v6.1.0

Date:

…fill me in…

  • Nonblocking file I/O no longer loses data when the operating system’s asynchronous I/O queue fills, which on macOS it readily does: the posix fbtl component sized its batch of concurrent aio_write calls from sysconf(_SC_AIO_MAX), which there reports the machine-wide kern.aiomax (90 by default) rather than the kern.aioprocmax a single process is held to (16). The component now bounds the batch by the per-process limit, defers requests the queue will not accept instead of discarding them, and reaps the operations it has posted before releasing their control blocks – an unreaped operation used to cost the process a queue slot permanently, so one refusal disabled nonblocking file I/O for the rest of its life. The new fbtl_posix_max_aio_reqs MCA parameter overrides the limit. A nonblocking operation the fbtl cannot post is now reported as MPI_ERR_IO; previously MPI_File_iwrite_all and MPI_Wait both returned MPI_SUCCESS for a write that never reached the file.

  • Reporting an error for a failed nonblocking file operation no longer crashes the process. MPI_Wait and MPI_Test reach a file’s error handler through the request, and a nonblocking file request did not record which file it came from, so invoking the error handler dereferenced a null pointer.

  • MPI_Info_set now accepts a zero-length (empty) value string. It previously raised MPI_ERR_INFO_VALUE for an empty value, but MPI-5.0 chapter 10 only limits the maximum length of an info value, and gives the empty string a defined meaning for the mpi_memory_alloc_kinds info key. Empty keys remain invalid.

  • Partitioned communication fixes:

    • MPI_Parrived now returns flag = true for a null request (MPI_REQUEST_NULL) and for an inactive request, as required by MPI-5.0 section 4.2.2. It previously raised MPI_ERR_REQUEST for a null request and returned flag = false for a partitioned receive request that had never been started.

    • MPI_Psend_init and MPI_Precv_init now accept MPI_PROC_NULL as the peer rank, per MPI-5.0 section 3.10. Such a request completes as soon as it is started, MPI_Pready on it has no effect, and MPI_Parrived reports every partition as arrived. Previously, MPI_PROC_NULL was passed down as if it were a real peer rank, reading outside the communicator’s process array.

    • Freeing a partitioned communication request that was never started no longer leaves its internal setup receive posted. Such a stale receive could consume the setup message of the next partitioned operation using the same communicator, peer, and tag, which then never completed.

  • Renamed the --enable-weak-symbols configure option to --enable-weak-aliases, which more accurately reflects the linker feature (weak symbol aliases) that Open MPI actually tests for and uses. --enable-weak-symbols is retained as a deprecated synonym.

  • The documentation now publishes machine-readable, LLM-friendly artifacts for the public MPI APIs alongside the human-facing HTML and man pages: a JSONL API catalog, aggregate and per-interface Markdown corpora, per-symbol Markdown pages, curated examples, an interface guide, an ompi_info runtime-introspection guide (how to query an installed Open MPI for its version, configuration, components, and run-time MCA parameters), and a manifest, all indexed from llms.txt. See the “LLM-friendly documentation artifacts” page in the developer documentation.