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|
mpi4py.util.pkl5
-----------------
.. module:: mpi4py.util.pkl5
:synopsis: Pickle-based communication using protocol 5.
.. versionadded:: 3.1.0
:mod:`pickle` protocol 5 (see :pep:`574`) introduced support for out-of-band
buffers, allowing for more efficient handling of certain object types with
large memory footprints.
MPI for Python uses the traditional in-band handling of buffers. This approach
is appropriate for communicating non-buffer Python objects, or buffer-like
objects with small memory footprints. For point-to-point communication, in-band
buffer handling allows for the communication of a pickled stream with a single
MPI message, at the expense of additional CPU and memory overhead in the
pickling and unpickling steps.
The :mod:`mpi4py.util.pkl5` module provides communicator wrapper classes
reimplementing pickle-based point-to-point communication methods using pickle
protocol 5. Handling out-of-band buffers necessarily involve multiple MPI
messages, thus increasing latency and hurting performance in case of small size
data. However, in case of large size data, the zero-copy savings of out-of-band
buffer handling more than offset the extra latency costs. Additionally, these
wrapper methods overcome the infamous 2 GiB message count limit (MPI-1 to
MPI-3).
.. note::
Support for pickle protocol 5 is available in the :mod:`pickle` module
within the Python standard library since Python 3.8. Previous Python 3
releases can use the :mod:`pickle5` backport, which is available on `PyPI
<pickle5-pypi_>`_ and can be installed with::
python -m pip install pickle5
.. _pickle5-pypi: https://pypi.org/project/pickle5/
.. autoclass:: Request
Custom request class for nonblocking communications.
.. note:: :class:`Request` is not a subclass of :class:`mpi4py.MPI.Request`
.. automethod:: Free
.. automethod:: cancel
.. automethod:: get_status
.. automethod:: test
.. automethod:: wait
.. automethod:: testall
:classmethod:
.. automethod:: waitall
:classmethod:
.. autoclass:: Message
Custom message class for matching probes.
.. note:: :class:`Message` is not a subclass of :class:`mpi4py.MPI.Message`
.. automethod:: recv
.. automethod:: irecv
.. automethod:: probe
:classmethod:
.. automethod:: iprobe
:classmethod:
.. autoclass:: Comm
Base communicator wrapper class.
.. automethod:: send
.. automethod:: bsend
.. automethod:: ssend
.. automethod:: isend
.. automethod:: ibsend
.. automethod:: issend
.. automethod:: recv
.. automethod:: irecv
.. warning:: This method cannot be supported reliably
and raises :exc:`RuntimeError`.
.. automethod:: sendrecv
.. automethod:: mprobe
.. automethod:: improbe
.. automethod:: bcast
.. autoclass:: Intracomm
Intracommunicator wrapper class.
.. autoclass:: Intercomm
Intercommunicator wrapper class.
Examples
++++++++
.. code-block:: python
:name: test-pkl5-1
:caption: :file:`test-pkl5-1.py`
:emphasize-lines: 3,5,11
:linenos:
import numpy as np
from mpi4py import MPI
from mpi4py.util import pkl5
comm = pkl5.Intracomm(MPI.COMM_WORLD) # comm wrapper
size = comm.Get_size()
rank = comm.Get_rank()
dst = (rank + 1) % size
src = (rank - 1) % size
sobj = np.full(1024**3, rank, dtype='i4') # > 4 GiB
sreq = comm.isend(sobj, dst, tag=42)
robj = comm.recv (None, src, tag=42)
sreq.Free()
assert np.min(robj) == src
assert np.max(robj) == src
.. code-block:: python
:name: test-pkl5-2
:caption: :file:`test-pkl5-2.py`
:emphasize-lines: 3,5,11
:linenos:
import numpy as np
from mpi4py import MPI
from mpi4py.util import pkl5
comm = pkl5.Intracomm(MPI.COMM_WORLD) # comm wrapper
size = comm.Get_size()
rank = comm.Get_rank()
dst = (rank + 1) % size
src = (rank - 1) % size
sobj = np.full(1024**3, rank, dtype='i4') # > 4 GiB
sreq = comm.isend(sobj, dst, tag=42)
status = MPI.Status()
rmsg = comm.mprobe(status=status)
assert status.Get_source() == src
assert status.Get_tag() == 42
rreq = rmsg.irecv()
robj = rreq.wait()
sreq.Free()
assert np.max(robj) == src
assert np.min(robj) == src
.. Local variables:
.. fill-column: 79
.. End:
|
