scope_profiler.mpi_launch

Detection of whether the process was launched by an MPI launcher.

Importing mpi4py.MPI calls MPI_Init, and any collective (bcast, Barrier, …) issued afterwards costs something even on a single process. A plain python script.py run should therefore never touch MPI at all, even when mpi4py happens to be installed. This module answers the only question that decides it: was this process started by mpirun/mpiexec/srun (or an equivalent launcher)?

The answer is read from the environment the launcher sets up, so it is available before mpi4py is imported.

Attributes

Name	Description
LAUNCHER_ENV_VARS	No description.

Functions

Name	Description
get_comm	Return MPI.COMM_WORLD, or None when MPI must not be used.
launched_under_mpi	Whether this process was started by an MPI launcher.

LAUNCHER_ENV_VARSattributemodule attribute#

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LAUNCHER_ENV_VARS = (
  'OMPI_COMM_WORLD_RANK',
  'PMI_RANK',
  'PMIX_RANK',
  'MV2_COMM_WORLD_RANK',
  'MPI_LOCALRANKID',
  'ALPS_APP_PE',
  'PALS_RANKID'
)

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get_commfunction#

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def get_comm()

Return MPI.COMM_WORLD, or None when MPI must not be used.

The decision is made entirely by :func:launched_under_mpi, so a plain python script.py run never touches MPI. Override it with the SCOPE_PROFILER_MPI environment variable when a launcher this module does not recognize is in play.

Returns

mpi4py.MPI.Intracomm or None The world communicator, or None if this is not an MPI run or mpi4py is unavailable.

launched_under_mpifunction#

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def launched_under_mpi() -> bool

Whether this process was started by an MPI launcher.

Returns

bool True if a launcher’s per-rank environment variable is present, or if the application itself already initialized MPI (in which case using the communicator is free). SCOPE_PROFILER_MPI=0/1 overrides the detection.