rtems-docs/c-user/region/directives.rst

.. SPDX-License-Identifier: CC-BY-SA-4.0

.. Copyright (C) 2020, 2021 embedded brains GmbH & Co. KG
.. Copyright (C) 1988, 2008 On-Line Applications Research Corporation (OAR)

.. This file is part of the RTEMS quality process and was automatically
.. generated.  If you find something that needs to be fixed or
.. worded better please post a report or patch to an RTEMS mailing list
.. or raise a bug report:
..
.. https://www.rtems.org/bugs.html
..
.. For information on updating and regenerating please refer to the How-To
.. section in the Software Requirements Engineering chapter of the
.. RTEMS Software Engineering manual.  The manual is provided as a part of
.. a release.  For development sources please refer to the online
.. documentation at:
..
.. https://docs.rtems.org

.. _RegionManagerDirectives:

Directives
==========

This section details the directives of the Region Manager. A subsection is
dedicated to each of this manager's directives and lists the calling sequence,
parameters, description, return values, and notes of the directive.

.. Generated from spec:/rtems/region/if/create

.. raw:: latex

    \clearpage

.. index:: rtems_region_create()
.. index:: create a region

.. _InterfaceRtemsRegionCreate:

rtems_region_create()
---------------------

Creates a region.

.. rubric:: CALLING SEQUENCE:

.. code-block:: c

    rtems_status_code rtems_region_create(
      rtems_name      name,
      void           *starting_address,
      uintptr_t       length,
      uintptr_t       page_size,
      rtems_attribute attribute_set,
      rtems_id       *id
    );

.. rubric:: PARAMETERS:

``name``
    This parameter is the object name of the region.

``starting_address``
    This parameter is the starting address of the memory area managed by the
    region.

``length``
    This parameter is the length in bytes of the memory area managed by the
    region.

``page_size``
    This parameter is the alignment of the starting address and length of each
    allocated segment of the region.

``attribute_set``
    This parameter is the attribute set of the region.

``id``
    This parameter is the pointer to an :ref:`InterfaceRtemsId` object.  When
    the directive call is successful, the identifier of the created region will
    be stored in this object.

.. rubric:: DESCRIPTION:

This directive creates a region which resides on the local node.  The region
has the user-defined object name specified in ``name``.  The assigned object
identifier is returned in ``id``.  This identifier is used to access the region
with other region related directives.

The region manages the **contiguous memory area** which starts at
``starting_address`` and is ``length`` bytes long.  The memory area shall be
large enough to contain some internal region administration data.

The **starting address** and **length of segments** allocated from the region
will be an integral multiple of ``page_size``.  The specified page size will be
aligned to an implementation-dependent minimum alignment if necessary.

The **attribute set** specified in ``attribute_set`` is built through a
*bitwise or* of the attribute constants described below.  Not all combinations
of attributes are allowed.  Some attributes are mutually exclusive.  If
mutually exclusive attributes are combined, the behaviour is undefined.
Attributes not mentioned below are not evaluated by this directive and have no
effect.  Default attributes can be selected by using the
:c:macro:`RTEMS_DEFAULT_ATTRIBUTES` constant.

The **task wait queue discipline** is selected by the mutually exclusive
:c:macro:`RTEMS_FIFO` and :c:macro:`RTEMS_PRIORITY` attributes. The discipline
defines the order in which tasks wait for allocatable segments on a currently
empty region.

* The **FIFO discipline** is the default and can be emphasized through use of
  the :c:macro:`RTEMS_FIFO` attribute.

* The **priority discipline** is selected by the :c:macro:`RTEMS_PRIORITY`
  attribute.

.. rubric:: RETURN VALUES:

:c:macro:`RTEMS_SUCCESSFUL`
    The requested operation was successful.

:c:macro:`RTEMS_INVALID_NAME`
    The ``name`` parameter was invalid.

:c:macro:`RTEMS_INVALID_ADDRESS`
    The ``id`` parameter was `NULL
    <https://en.cppreference.com/w/c/types/NULL>`_.

:c:macro:`RTEMS_INVALID_ADDRESS`
    The ``starting_address`` parameter was `NULL
    <https://en.cppreference.com/w/c/types/NULL>`_.

:c:macro:`RTEMS_TOO_MANY`
    There was no inactive object available to create a region.  The number of
    regions available to the application is configured through the
    :ref:`CONFIGURE_MAXIMUM_REGIONS` application configuration option.

:c:macro:`RTEMS_INVALID_SIZE`
    The ``page_size`` parameter was invalid.

:c:macro:`RTEMS_INVALID_SIZE`
    The memory area specified in ``starting_address`` and ``length`` was too
    small.

.. rubric:: NOTES:

For control and maintenance of the region, RTEMS allocates a :term:`RNCB` from
the local RNCB free pool and initializes it.

.. rubric:: CONSTRAINTS:

The following constraints apply to this directive:

* The directive may be called from within device driver initialization context.

* The directive may be called from within task context.

* The directive may obtain and release the object allocator mutex.  This may
  cause the calling task to be preempted.

* The number of regions available to the application is configured through the
  :ref:`CONFIGURE_MAXIMUM_REGIONS` application configuration option.

* Where the object class corresponding to the directive is configured to use
  unlimited objects, the directive may allocate memory from the RTEMS
  Workspace.

.. Generated from spec:/rtems/region/if/ident

.. raw:: latex

    \clearpage

.. index:: rtems_region_ident()

.. _InterfaceRtemsRegionIdent:

rtems_region_ident()
--------------------

Identifies a region by the object name.

.. rubric:: CALLING SEQUENCE:

.. code-block:: c

    rtems_status_code rtems_region_ident( rtems_name name, rtems_id *id );

.. rubric:: PARAMETERS:

``name``
    This parameter is the object name to look up.

``id``
    This parameter is the pointer to an :ref:`InterfaceRtemsId` object.  When
    the directive call is successful, the object identifier of an object with
    the specified name will be stored in this object.

.. rubric:: DESCRIPTION:

This directive obtains a region identifier associated with the region name
specified in ``name``.

.. rubric:: RETURN VALUES:

:c:macro:`RTEMS_SUCCESSFUL`
    The requested operation was successful.

:c:macro:`RTEMS_INVALID_ADDRESS`
    The ``id`` parameter was `NULL
    <https://en.cppreference.com/w/c/types/NULL>`_.

:c:macro:`RTEMS_INVALID_NAME`
    The ``name`` parameter was 0.

:c:macro:`RTEMS_INVALID_NAME`
    There was no object with the specified name on the local node.

.. rubric:: NOTES:

If the region name is not unique, then the region identifier will match the
first region with that name in the search order.  However, this region
identifier is not guaranteed to correspond to the desired region.

The objects are searched from lowest to the highest index.  Only the local node
is searched.

The region identifier is used with other region related directives to access
the region.

.. rubric:: CONSTRAINTS:

The following constraints apply to this directive:

* The directive may be called from within any runtime context.

* The directive will not cause the calling task to be preempted.

.. Generated from spec:/rtems/region/if/delete

.. raw:: latex

    \clearpage

.. index:: rtems_region_delete()
.. index:: delete a region

.. _InterfaceRtemsRegionDelete:

rtems_region_delete()
---------------------

Deletes the region.

.. rubric:: CALLING SEQUENCE:

.. code-block:: c

    rtems_status_code rtems_region_delete( rtems_id id );

.. rubric:: PARAMETERS:

``id``
    This parameter is the region identifier.

.. rubric:: DESCRIPTION:

This directive deletes the region specified by ``id``.

.. rubric:: RETURN VALUES:

:c:macro:`RTEMS_SUCCESSFUL`
    The requested operation was successful.

:c:macro:`RTEMS_INVALID_ID`
    There was no region associated with the identifier specified by ``id``.

:c:macro:`RTEMS_RESOURCE_IN_USE`
    There were segments of the region still in use.

.. rubric:: NOTES:

The region cannot be deleted if any of its segments are still allocated.

The :term:`RNCB` for the deleted region is reclaimed by RTEMS.

.. rubric:: CONSTRAINTS:

The following constraints apply to this directive:

* The directive may be called from within device driver initialization context.

* The directive may be called from within task context.

* The directive may obtain and release the object allocator mutex.  This may
  cause the calling task to be preempted.

* The calling task does not have to be the task that created the object.  Any
  local task that knows the object identifier can delete the object.

* Where the object class corresponding to the directive is configured to use
  unlimited objects, the directive may free memory to the RTEMS Workspace.

.. Generated from spec:/rtems/region/if/extend

.. raw:: latex

    \clearpage

.. index:: rtems_region_extend()
.. index:: add memory to a region
.. index:: region, add memory

.. _InterfaceRtemsRegionExtend:

rtems_region_extend()
---------------------

Extends the region.

.. rubric:: CALLING SEQUENCE:

.. code-block:: c

    rtems_status_code rtems_region_extend(
      rtems_id  id,
      void     *starting_address,
      uintptr_t length
    );

.. rubric:: PARAMETERS:

``id``
    This parameter is the region identifier.

``starting_address``
    This parameter is the starting address of the memory area to extend the
    region.

``length``
    This parameter is the length in bytes of the memory area to extend the
    region.

.. rubric:: DESCRIPTION:

This directive adds the memory area which starts at ``starting_address`` for
``length`` bytes to the region specified by ``id``.

.. rubric:: RETURN VALUES:

:c:macro:`RTEMS_SUCCESSFUL`
    The requested operation was successful.

:c:macro:`RTEMS_INVALID_ADDRESS`
    The ``starting_address`` parameter was `NULL
    <https://en.cppreference.com/w/c/types/NULL>`_.

:c:macro:`RTEMS_INVALID_ID`
    There was no region associated with the identifier specified by ``id``.

:c:macro:`RTEMS_INVALID_ADDRESS`
    The memory area specified by ``starting_address`` and ``length`` was
    insufficient to extend the heap.

.. rubric:: NOTES:

There are no alignment requirements for the memory area.  The memory area must
be big enough to contain some maintenance blocks.  It must not overlap parts of
the current heap memory areas.  Disconnected memory areas added to the heap
will lead to used blocks which cover the gaps.  Extending with an inappropriate
memory area will corrupt the heap resulting in undefined behaviour.

.. rubric:: CONSTRAINTS:

The following constraints apply to this directive:

* The directive may be called from within device driver initialization context.

* The directive may be called from within task context.

* The directive may obtain and release the object allocator mutex.  This may
  cause the calling task to be preempted.

.. Generated from spec:/rtems/region/if/get-segment

.. raw:: latex

    \clearpage

.. index:: rtems_region_get_segment()
.. index:: get segment from region

.. _InterfaceRtemsRegionGetSegment:

rtems_region_get_segment()
--------------------------

Gets a segment from the region.

.. rubric:: CALLING SEQUENCE:

.. code-block:: c

    rtems_status_code rtems_region_get_segment(
      rtems_id       id,
      uintptr_t      size,
      rtems_option   option_set,
      rtems_interval timeout,
      void         **segment
    );

.. rubric:: PARAMETERS:

``id``
    This parameter is the region identifier.

``size``
    This parameter is the size in bytes of the segment to allocate.

``option_set``
    This parameter is the option set.

``timeout``
    This parameter is the timeout in :term:`clock ticks <clock tick>` if the
    :c:macro:`RTEMS_WAIT` option is set.  Use :c:macro:`RTEMS_NO_TIMEOUT` to
    wait potentially forever.

``segment``
    This parameter is the pointer to a ``void`` pointer object.  When the
    directive call is successful, the begin address of the allocated segment
    will be stored in this object.

.. rubric:: DESCRIPTION:

This directive gets a segment from the region specified by ``id``.

The **option set** specified in ``option_set`` is built through a *bitwise or*
of the option constants described below.  Not all combinations of options are
allowed.  Some options are mutually exclusive.  If mutually exclusive options
are combined, the behaviour is undefined.  Options not mentioned below are not
evaluated by this directive and have no effect. Default options can be selected
by using the :c:macro:`RTEMS_DEFAULT_OPTIONS` constant.

The calling task can **wait** or **try to get** a segment from the region
according to the mutually exclusive :c:macro:`RTEMS_WAIT` and
:c:macro:`RTEMS_NO_WAIT` options.

* **Waiting to get** a segment from the region is the default and can be
  emphasized through the use of the :c:macro:`RTEMS_WAIT` option. The
  ``timeout`` parameter defines how long the calling task is willing to wait.
  Use :c:macro:`RTEMS_NO_TIMEOUT` to wait potentially forever, otherwise set a
  timeout interval in clock ticks.

* **Trying to get** a segment from the region is selected by the
  :c:macro:`RTEMS_NO_WAIT` option.  If this option is defined, then the
  ``timeout`` parameter is ignored.  When a segment from the region cannot be
  immediately allocated, then the :c:macro:`RTEMS_UNSATISFIED` status is
  returned.

With either :c:macro:`RTEMS_WAIT` or :c:macro:`RTEMS_NO_WAIT` if there is a
segment of the requested size is available, then it is returned in ``segment``
and this directive returns immediately with the :c:macro:`RTEMS_SUCCESSFUL`
status code.

If the calling task chooses to return immediately and the region has no segment
of the requested size available, then the directive returns immediately with
the :c:macro:`RTEMS_UNSATISFIED` status code.  If the calling task chooses to
wait for a segment, then the calling task is placed on the region wait queue
and blocked.  If the region was created with the :c:macro:`RTEMS_PRIORITY`
option specified, then the calling task is inserted into the wait queue
according to its priority.  But, if the region was created with the
:c:macro:`RTEMS_FIFO` option specified, then the calling task is placed at the
rear of the wait queue.

.. rubric:: RETURN VALUES:

:c:macro:`RTEMS_SUCCESSFUL`
    The requested operation was successful.

:c:macro:`RTEMS_INVALID_ADDRESS`
    The ``segment`` parameter was `NULL
    <https://en.cppreference.com/w/c/types/NULL>`_.

:c:macro:`RTEMS_INVALID_SIZE`
    The ``size`` parameter was zero.

:c:macro:`RTEMS_INVALID_ID`
    There was no region associated with the identifier specified by ``id``.

:c:macro:`RTEMS_INVALID_SIZE`
    The ``size`` parameter exceeded the maximum segment size which is possible
    for the region.

:c:macro:`RTEMS_UNSATISFIED`
    The region had no segment of the requested size immediately available.

:c:macro:`RTEMS_TIMEOUT`
    The timeout happened while the calling task was waiting to get a segment
    from the region.

.. rubric:: NOTES:

The actual length of the allocated segment may be larger than the requested
size because a segment size is always a multiple of the region's page size.

.. rubric:: CONSTRAINTS:

The following constraints apply to this directive:

* The directive may be called from within device driver initialization context.

* The directive may be called from within task context.

* The directive may obtain and release the object allocator mutex.  This may
  cause the calling task to be preempted.

* When the request cannot be immediately satisfied and the
  :c:macro:`RTEMS_WAIT` option is set, the calling task blocks at some point
  during the directive call.

* The timeout functionality of the directive requires a :term:`clock tick`.

.. Generated from spec:/rtems/region/if/return-segment

.. raw:: latex

    \clearpage

.. index:: rtems_region_return_segment()
.. index:: return segment to region

.. _InterfaceRtemsRegionReturnSegment:

rtems_region_return_segment()
-----------------------------

Returns the segment to the region.

.. rubric:: CALLING SEQUENCE:

.. code-block:: c

    rtems_status_code rtems_region_return_segment( rtems_id id, void *segment );

.. rubric:: PARAMETERS:

``id``
    This parameter is the region identifier.

``segment``
    This parameter is the begin address of the segment to return.

.. rubric:: DESCRIPTION:

This directive returns the segment specified by ``segment`` to the region
specified by ``id``.  The returned segment is merged with its neighbors to form
the largest possible segment.  The first task on the wait queue is examined to
determine if its segment request can now be satisfied.  If so, it is given a
segment and unblocked.  This process is repeated until the first task's segment
request cannot be satisfied.

.. rubric:: RETURN VALUES:

:c:macro:`RTEMS_SUCCESSFUL`
    The requested operation was successful.

:c:macro:`RTEMS_INVALID_ID`
    There was no region associated with the identifier specified by ``id``.

:c:macro:`RTEMS_INVALID_ADDRESS`
    The segment was not within the region.

.. rubric:: NOTES:

This directive will cause the calling task to be preempted if one or more local
tasks are waiting for a segment and the following conditions exist:

* A waiting task has a higher priority than the calling task.

* The size of the segment required by the waiting task is less than or equal to
  the size of the segment returned.

.. rubric:: CONSTRAINTS:

The following constraints apply to this directive:

* The directive may be called from within device driver initialization context.

* The directive may be called from within task context.

* The directive may unblock a task.  This may cause the calling task to be
  preempted.

* The directive may obtain and release the object allocator mutex.  This may
  cause the calling task to be preempted.

.. Generated from spec:/rtems/region/if/resize-segment

.. raw:: latex

    \clearpage

.. index:: rtems_region_resize_segment()
.. index:: resize segment

.. _InterfaceRtemsRegionResizeSegment:

rtems_region_resize_segment()
-----------------------------

Changes the size of the segment.

.. rubric:: CALLING SEQUENCE:

.. code-block:: c

    rtems_status_code rtems_region_resize_segment(
      rtems_id   id,
      void      *segment,
      uintptr_t  size,
      uintptr_t *old_size
    );

.. rubric:: PARAMETERS:

``id``
    This parameter is the region identifier.

``segment``
    This parameter is the begin address of the segment to resize.

``size``
    This parameter is the requested new size of the segment.

``old_size``
    This parameter is the pointer to an `uintptr_t
    <https://en.cppreference.com/w/c/types/integer>`_ object.  When the
    directive call is successful, the old size of the segment will be stored in
    this object.

.. rubric:: DESCRIPTION:

This directive is used to increase or decrease the size of the ``segment`` of
the region specified by ``id``.  When increasing the size of a segment, it is
possible that there is no memory available contiguous to the segment.  In this
case, the request is unsatisfied.

.. rubric:: RETURN VALUES:

:c:macro:`RTEMS_SUCCESSFUL`
    The requested operation was successful.

:c:macro:`RTEMS_INVALID_ADDRESS`
    The ``old_size`` parameter was `NULL
    <https://en.cppreference.com/w/c/types/NULL>`_.

:c:macro:`RTEMS_INVALID_ID`
    There was no region associated with the identifier specified by ``id``.

:c:macro:`RTEMS_INVALID_ADDRESS`
    The segment was not within the region.

:c:macro:`RTEMS_UNSATISFIED`
    The region was unable to resize the segment.

.. rubric:: NOTES:

If an attempt to increase the size of a segment fails, then the application may
want to allocate a new segment of the desired size, copy the contents of the
original segment to the new, larger segment and then return the original
segment.

.. rubric:: CONSTRAINTS:

The following constraints apply to this directive:

* The directive may be called from within device driver initialization context.

* The directive may be called from within task context.

* The directive may obtain and release the object allocator mutex.  This may
  cause the calling task to be preempted.

.. Generated from spec:/rtems/region/if/get-information

.. raw:: latex

    \clearpage

.. index:: rtems_region_get_information()
.. index:: obtain region information

.. _InterfaceRtemsRegionGetInformation:

rtems_region_get_information()
------------------------------

Gets the region information.

.. rubric:: CALLING SEQUENCE:

.. code-block:: c

    rtems_status_code rtems_region_get_information(
      rtems_id                id,
      Heap_Information_block *the_info
    );

.. rubric:: PARAMETERS:

``id``
    This parameter is the region identifier.

``the_info``
    This parameter is the pointer to a :c:type:`Heap_Information_block` object.
    When the directive call is successful, the information of the region will
    be stored in this object.

.. rubric:: DESCRIPTION:

This directive is used to obtain information about the used and free memory in
the region specified by ``id``. This is a snapshot at the time of the call. The
information will be returned in the structure pointed to by ``the_info``.

.. rubric:: RETURN VALUES:

:c:macro:`RTEMS_SUCCESSFUL`
    The requested operation was successful.

:c:macro:`RTEMS_INVALID_ADDRESS`
    The ``the_info`` parameter was `NULL
    <https://en.cppreference.com/w/c/types/NULL>`_.

:c:macro:`RTEMS_INVALID_ID`
    There was no region associated with the identifier specified by ``id``.

.. rubric:: NOTES:

This is primarily intended as a mechanism to obtain a diagnostic information.
This method forms am O(n) scan of the free and an O(n) scan of the used blocks
in the region to calculate the information provided. Given that the execution
time is driven by the number of used and free blocks, it can take a
non-deterministic time to execute.

To get only the free information of the region use
:ref:`InterfaceRtemsRegionGetFreeInformation`.

.. rubric:: CONSTRAINTS:

The following constraints apply to this directive:

* The directive may be called from within device driver initialization context.

* The directive may be called from within task context.

* The directive may obtain and release the object allocator mutex.  This may
  cause the calling task to be preempted.

.. Generated from spec:/rtems/region/if/get-free-information

.. raw:: latex

    \clearpage

.. index:: rtems_region_get_free_information()
.. index:: obtain region information on free blocks

.. _InterfaceRtemsRegionGetFreeInformation:

rtems_region_get_free_information()
-----------------------------------

Gets the region free information.

.. rubric:: CALLING SEQUENCE:

.. code-block:: c

    rtems_status_code rtems_region_get_free_information(
      rtems_id                id,
      Heap_Information_block *the_info
    );

.. rubric:: PARAMETERS:

``id``
    This parameter is the region identifier.

``the_info``
    This parameter is the pointer to a :c:type:`Heap_Information_block` object.
    When the directive call is successful, the free information of the region
    will be stored in this object.

.. rubric:: DESCRIPTION:

This directive is used to obtain information about the free memory in the
region specified by ``id``. This is a snapshot at the time of the call. The
information will be returned in the structure pointed to by ``the_info``.

.. rubric:: RETURN VALUES:

:c:macro:`RTEMS_SUCCESSFUL`
    The requested operation was successful.

:c:macro:`RTEMS_INVALID_ADDRESS`
    The ``the_info`` parameter was `NULL
    <https://en.cppreference.com/w/c/types/NULL>`_.

:c:macro:`RTEMS_INVALID_ID`
    There was no region associated with the identifier specified by ``id``.

.. rubric:: NOTES:

This directive uses the same structure to return information as the
:ref:`InterfaceRtemsRegionGetInformation` directive but does not fill in the
used information.

This is primarily intended as a mechanism to obtain a diagnostic information.
This method forms am O(n) scan of the free in the region to calculate the
information provided. Given that the execution time is driven by the number of
used and free blocks, it can take a non-deterministic time to execute.
Typically, there are many used blocks and a much smaller number of used blocks
making a call to this directive less expensive than a call to
:ref:`InterfaceRtemsRegionGetInformation`.

.. rubric:: CONSTRAINTS:

The following constraints apply to this directive:

* The directive may be called from within device driver initialization context.

* The directive may be called from within task context.

* The directive may obtain and release the object allocator mutex.  This may
  cause the calling task to be preempted.

.. Generated from spec:/rtems/region/if/get-segment-size

.. raw:: latex

    \clearpage

.. index:: rtems_region_get_segment_size()
.. index:: get size of segment

.. _InterfaceRtemsRegionGetSegmentSize:

rtems_region_get_segment_size()
-------------------------------

Gets the size of the region segment.

.. rubric:: CALLING SEQUENCE:

.. code-block:: c

    rtems_status_code rtems_region_get_segment_size(
      rtems_id   id,
      void      *segment,
      uintptr_t *size
    );

.. rubric:: PARAMETERS:

``id``
    This parameter is the region identifier.

``segment``
    This parameter is the begin address of the segment.

``size``
    This parameter is the pointer to a `uintptr_t
    <https://en.cppreference.com/w/c/types/integer>`_ object.  When the
    directive call is successful, the size of the segment in bytes will be
    stored in this object.

.. rubric:: DESCRIPTION:

This directive obtains the size in bytes of the segment specified by
``segment`` of the region specified by ``id`` in ``size``.

.. rubric:: RETURN VALUES:

:c:macro:`RTEMS_SUCCESSFUL`
    The requested operation was successful.

:c:macro:`RTEMS_INVALID_ADDRESS`
    The ``segment`` parameter was `NULL
    <https://en.cppreference.com/w/c/types/NULL>`_.

:c:macro:`RTEMS_INVALID_ADDRESS`
    The ``size`` parameter was `NULL
    <https://en.cppreference.com/w/c/types/NULL>`_.

:c:macro:`RTEMS_INVALID_ID`
    There was no region associated with the identifier specified by ``id``.

:c:macro:`RTEMS_INVALID_ADDRESS`
    The segment was not within the region.

.. rubric:: NOTES:

The actual length of the allocated segment may be larger than the requested
size because a segment size is always a multiple of the region's page size.

.. rubric:: CONSTRAINTS:

The following constraints apply to this directive:

* The directive may be called from within device driver initialization context.

* The directive may be called from within task context.

* The directive may obtain and release the object allocator mutex.  This may
  cause the calling task to be preempted.