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[3.11] Docs: Align multiprocessing.shared_memory docs with Sphinx rec…
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…ommendations (python#114103) (python#114114)

(cherry picked from commit af85274)

- add :class: and :mod: markups where needed
- fix incorrect escaping of a star in ShareableList arg spec
- mark up parameters with stars: *val*
- mark up list of built-in types using list markup
- remove unneeded parentheses from :meth: markups
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erlend-aasland authored Jan 16, 2024
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104 changes: 56 additions & 48 deletions Doc/library/multiprocessing.shared_memory.rst
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Expand Up @@ -20,8 +20,8 @@ and management of shared memory to be accessed by one or more processes
on a multicore or symmetric multiprocessor (SMP) machine. To assist with
the life-cycle management of shared memory especially across distinct
processes, a :class:`~multiprocessing.managers.BaseManager` subclass,
:class:`SharedMemoryManager`, is also provided in the
``multiprocessing.managers`` module.
:class:`~multiprocessing.managers.SharedMemoryManager`, is also provided in the
:mod:`multiprocessing.managers` module.

In this module, shared memory refers to "System V style" shared memory blocks
(though is not necessarily implemented explicitly as such) and does not refer
Expand All @@ -47,9 +47,9 @@ copying of data.
As a resource for sharing data across processes, shared memory blocks
may outlive the original process that created them. When one process
no longer needs access to a shared memory block that might still be
needed by other processes, the :meth:`close()` method should be called.
needed by other processes, the :meth:`close` method should be called.
When a shared memory block is no longer needed by any process, the
:meth:`unlink()` method should be called to ensure proper cleanup.
:meth:`unlink` method should be called to ensure proper cleanup.

*name* is the unique name for the requested shared memory, specified as
a string. When creating a new shared memory block, if ``None`` (the
Expand All @@ -62,28 +62,28 @@ copying of data.
memory block. Because some platforms choose to allocate chunks of memory
based upon that platform's memory page size, the exact size of the shared
memory block may be larger or equal to the size requested. When attaching
to an existing shared memory block, the ``size`` parameter is ignored.
to an existing shared memory block, the *size* parameter is ignored.

.. method:: close()

Closes access to the shared memory from this instance. In order to
ensure proper cleanup of resources, all instances should call
``close()`` once the instance is no longer needed. Note that calling
``close()`` does not cause the shared memory block itself to be
:meth:`close` once the instance is no longer needed. Note that calling
:meth:`!close` does not cause the shared memory block itself to be
destroyed.

.. method:: unlink()

Requests that the underlying shared memory block be destroyed. In
order to ensure proper cleanup of resources, ``unlink()`` should be
order to ensure proper cleanup of resources, :meth:`unlink` should be
called once (and only once) across all processes which have need
for the shared memory block. After requesting its destruction, a
shared memory block may or may not be immediately destroyed and
this behavior may differ across platforms. Attempts to access data
inside the shared memory block after ``unlink()`` has been called may
inside the shared memory block after :meth:`!unlink` has been called may
result in memory access errors. Note: the last process relinquishing
its hold on a shared memory block may call ``unlink()`` and
:meth:`close()` in either order.
its hold on a shared memory block may call :meth:`!unlink` and
:meth:`close` in either order.

.. attribute:: buf

Expand Down Expand Up @@ -126,7 +126,7 @@ instances::

The following example demonstrates a practical use of the :class:`SharedMemory`
class with `NumPy arrays <https://numpy.org/>`_, accessing the
same ``numpy.ndarray`` from two distinct Python shells:
same :class:`!numpy.ndarray` from two distinct Python shells:

.. doctest::
:options: +SKIP
Expand Down Expand Up @@ -178,43 +178,43 @@ same ``numpy.ndarray`` from two distinct Python shells:
.. class:: SharedMemoryManager([address[, authkey]])
:module: multiprocessing.managers

A subclass of :class:`~multiprocessing.managers.BaseManager` which can be
A subclass of :class:`multiprocessing.managers.BaseManager` which can be
used for the management of shared memory blocks across processes.

A call to :meth:`~multiprocessing.managers.BaseManager.start` on a
:class:`SharedMemoryManager` instance causes a new process to be started.
:class:`!SharedMemoryManager` instance causes a new process to be started.
This new process's sole purpose is to manage the life cycle
of all shared memory blocks created through it. To trigger the release
of all shared memory blocks managed by that process, call
:meth:`~multiprocessing.managers.BaseManager.shutdown()` on the instance.
This triggers a :meth:`SharedMemory.unlink()` call on all of the
:class:`SharedMemory` objects managed by that process and then
stops the process itself. By creating ``SharedMemory`` instances
through a ``SharedMemoryManager``, we avoid the need to manually track
:meth:`~multiprocessing.managers.BaseManager.shutdown` on the instance.
This triggers a :meth:`~multiprocessing.shared_memory.SharedMemory.unlink` call
on all of the :class:`SharedMemory` objects managed by that process and then
stops the process itself. By creating :class:`!SharedMemory` instances
through a :class:`!SharedMemoryManager`, we avoid the need to manually track
and trigger the freeing of shared memory resources.

This class provides methods for creating and returning :class:`SharedMemory`
instances and for creating a list-like object (:class:`ShareableList`)
backed by shared memory.

Refer to :class:`multiprocessing.managers.BaseManager` for a description
Refer to :class:`~multiprocessing.managers.BaseManager` for a description
of the inherited *address* and *authkey* optional input arguments and how
they may be used to connect to an existing ``SharedMemoryManager`` service
they may be used to connect to an existing :class:`!SharedMemoryManager` service
from other processes.

.. method:: SharedMemory(size)

Create and return a new :class:`SharedMemory` object with the
specified ``size`` in bytes.
specified *size* in bytes.

.. method:: ShareableList(sequence)

Create and return a new :class:`ShareableList` object, initialized
by the values from the input ``sequence``.
by the values from the input *sequence*.


The following example demonstrates the basic mechanisms of a
:class:`SharedMemoryManager`:
:class:`~multiprocessing.managers.SharedMemoryManager`:

.. doctest::
:options: +SKIP
Expand All @@ -232,9 +232,9 @@ The following example demonstrates the basic mechanisms of a
>>> smm.shutdown() # Calls unlink() on sl, raw_shm, and another_sl

The following example depicts a potentially more convenient pattern for using
:class:`SharedMemoryManager` objects via the :keyword:`with` statement to
ensure that all shared memory blocks are released after they are no longer
needed:
:class:`~multiprocessing.managers.SharedMemoryManager` objects via the
:keyword:`with` statement to ensure that all shared memory blocks are released
after they are no longer needed:

.. doctest::
:options: +SKIP
Expand All @@ -250,38 +250,46 @@ needed:
... p2.join() # Wait for all work to complete in both processes
... total_result = sum(sl) # Consolidate the partial results now in sl

When using a :class:`SharedMemoryManager` in a :keyword:`with` statement, the
shared memory blocks created using that manager are all released when the
:keyword:`with` statement's code block finishes execution.
When using a :class:`~multiprocessing.managers.SharedMemoryManager`
in a :keyword:`with` statement, the shared memory blocks created using that
manager are all released when the :keyword:`!with` statement's code block
finishes execution.


.. class:: ShareableList(sequence=None, \*, name=None)
.. class:: ShareableList(sequence=None, *, name=None)

Provides a mutable list-like object where all values stored within are
stored in a shared memory block. This constrains storable values to
only the ``int`` (signed 64-bit), ``float``, ``bool``, ``str`` (less
than 10M bytes each when encoded as utf-8), ``bytes`` (less than 10M
bytes each), and ``None`` built-in data types. It also notably
differs from the built-in ``list`` type in that these lists can not
change their overall length (i.e. no append, insert, etc.) and do not
support the dynamic creation of new :class:`ShareableList` instances
stored in a shared memory block.
This constrains storable values to the following built-in data types:

* :class:`int` (signed 64-bit)
* :class:`float`
* :class:`bool`
* :class:`str` (less than 10M bytes each when encoded as UTF-8)
* :class:`bytes` (less than 10M bytes each)
* ``None``

It also notably differs from the built-in :class:`list` type
in that these lists can not change their overall length
(i.e. no :meth:`!append`, :meth:`!insert`, etc.) and do not
support the dynamic creation of new :class:`!ShareableList` instances
via slicing.

*sequence* is used in populating a new ``ShareableList`` full of values.
*sequence* is used in populating a new :class:`!ShareableList` full of values.
Set to ``None`` to instead attach to an already existing
``ShareableList`` by its unique shared memory name.
:class:`!ShareableList` by its unique shared memory name.

*name* is the unique name for the requested shared memory, as described
in the definition for :class:`SharedMemory`. When attaching to an
existing ``ShareableList``, specify its shared memory block's unique
name while leaving ``sequence`` set to ``None``.
existing :class:`!ShareableList`, specify its shared memory block's unique
name while leaving *sequence* set to ``None``.

.. note::

A known issue exists for :class:`bytes` and :class:`str` values.
If they end with ``\x00`` nul bytes or characters, those may be
*silently stripped* when fetching them by index from the
:class:`ShareableList`. This ``.rstrip(b'\x00')`` behavior is
:class:`!ShareableList`. This ``.rstrip(b'\x00')`` behavior is
considered a bug and may go away in the future. See :gh:`106939`.

For applications where rstripping of trailing nulls is a problem,
Expand All @@ -307,12 +315,12 @@ shared memory blocks created using that manager are all released when the

.. method:: count(value)

Returns the number of occurrences of ``value``.
Returns the number of occurrences of *value*.

.. method:: index(value)

Returns first index position of ``value``. Raises :exc:`ValueError` if
``value`` is not present.
Returns first index position of *value*. Raises :exc:`ValueError` if
*value* is not present.

.. attribute:: format

Expand Down Expand Up @@ -372,8 +380,8 @@ behind it:
>>> c.shm.close()
>>> c.shm.unlink()

The following examples demonstrates that ``ShareableList``
(and underlying ``SharedMemory``) objects
The following examples demonstrates that :class:`ShareableList`
(and underlying :class:`SharedMemory`) objects
can be pickled and unpickled if needed.
Note, that it will still be the same shared object.
This happens, because the deserialized object has
Expand Down
1 change: 0 additions & 1 deletion Doc/tools/.nitignore
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Expand Up @@ -60,7 +60,6 @@ Doc/library/logging.handlers.rst
Doc/library/lzma.rst
Doc/library/mmap.rst
Doc/library/multiprocessing.rst
Doc/library/multiprocessing.shared_memory.rst
Doc/library/optparse.rst
Doc/library/os.rst
Doc/library/pickle.rst
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