=======================
HISTORY: MPI for Python
=======================

:Author:       Lisandro Dalcin
:Contact:      dalcinl@gmail.com
:Web Site:     http://mpi4py.googlecode.com/
:Organization: CIMEC <http://www.cimec.org.ar>
:Address:      PTLC, 3000 Santa Fe, Argentina


Release 1.1.0
=============

* Fix bug in ``Comm.Iprobe()`` that caused segfaults as Python C-API
  calls were issued with the GIL released (issue #2).

* Add ``Comm.bsend()`` and ``Comm.ssend()`` for buffered and
  synchronous send semantics when communicating general Python
  objects.

* Now the call ``Info.Get(key)`` return a *single* value (i.e, instead
  of a 2-tuple); this value is ``None`` if ``key`` is not in the
  ``Info`` object, or a string otherwise. Previously, the call
  redundantly returned ``(None, False)`` for missing key-value pairs;
  ``None`` is enough to signal a missing entry.

* Add support for parametrized Fortran datatypes.

* Add support for decoding user-defined datatypes.

* Add support for user-defined reduction operations on memory
  buffers. However, at most 16 user-defined reduction operations
  can be created. Ask the author for more room if you need it.


Release 1.0.0
=============

This is the fist release of the all-new, Cython-based, implementation
of *MPI for Python*. Unfortunately, this implementation is not
backward-compatible with the previous one. The list below summarizes
the more important changes that can impact user codes.

* Some communication calls had *overloaded* functionality. Now there
  is a clear distinction between communication of general Python
  object with *pickle*, and (fast, near C-speed) communication of
  buffer-like objects (e.g., NumPy arrays).

  - for communicating general Python objects, you have to use
    all-lowercase methods, like ``send()``, ``recv()``, ``bcast()``,
    etc.

  - for communicating array data, you have to use ``Send()``,
    ``Recv()``, ``Bcast()``, etc. methods. Buffer arguments to these
    calls must be explicitly specified by using a 2/3-list/tuple like
    ``[data, MPI.DOUBLE]``, or ``[data, count, MPI.DOUBLE]`` (the
    former one uses the byte-size of ``data`` and the extent of the
    MPI datatype to define the ``count``).

* Indexing a communicator with an integer returned a special object
  associating the communication with a target rank, alleviating you
  from specifying source/destination/root arguments in point-to-point
  and collective communications. This functionality is no longer
  available, expressions like::

     MPI.COMM_WORLD[0].Send(...)
     MPI.COMM_WORLD[0].Recv(...)
     MPI.COMM_WORLD[0].Bcast(...)

  have to be replaced by::

     MPI.COMM_WORLD.Send(..., dest=0)
     MPI.COMM_WORLD.Recv(..., source=0)
     MPI.COMM_WORLD.Bcast(..., root=0)

* Automatic MPI initialization (i.e., at import time) requests the
  maximum level of MPI thread support (i.e., it is done by calling
  ``MPI_Init_thread()`` and passing ``MPI_THREAD_MULTIPLE``). In case
  you need to change this behavior, you can tweak the contents of the
  ``mpi4py.rc`` module.

* In order to obtain the values of predefined attributes attached to
  the world communicator, now you have to use the ``Get_attr()``
  method on the ``MPI.COMM_WORLD`` instance::

     tag_ub = MPI.COMM_WORLD.Get_attr(MPI.TAG_UB)

* In the previous implementation, ``MPI.COMM_WORLD`` and
  ``MPI.COMM_SELF`` were associated to **duplicates** of the (C-level)
  ``MPI_COMM_WORLD`` and ``MPI_COMM_SELF`` predefined communicator
  handles. Now this is no longer the case, ``MPI.COMM_WORLD`` and
  ``MPI.COMM_SELF`` proxies the **actual** ``MPI_COMM_WORLD`` and
  ``MPI_COMM_SELF`` handles.

* Convenience aliases ``MPI.WORLD`` and ``MPI.SELF`` were removed. Use
  instead ``MPI.COMM_WORLD`` and ``MPI.COMM_SELF``.

* Convenience constants ``MPI.WORLD_SIZE`` and ``MPI.WORLD_RANK`` were
  removed. Use instead ``MPI.COMM_WORLD.Get_size()`` and
  ``MPI.COMM_WORLD.Get_rank()``.