Mpi4py

==========================

* 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.

==========================

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()``.