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c-user: Document task life states

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Update #4679.
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Sebastian Huber 2022-07-27 11:18:13 +02:00
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c-user/task/background.rst
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.. SPDX-License-Identifier: CC-BY-SA-4.0
.. Copyright (C) 2020 embedded brains GmbH (http://www.embedded-brains.de)
.. Copyright (C) 2020, 2022 embedded brains GmbH (http://www.embedded-brains.de)
.. Copyright (C) 1988, 2008 On-Line Applications Research Corporation (OAR)
Background
@ -233,6 +233,58 @@ the task will execute at interrupt level n.
The set of default modes may be selected by specifying the
``RTEMS_DEFAULT_MODES`` constant.
.. index:: task life states
Task Life States
----------------
Independent of the task state with respect to the scheduler, the task life is
determined by several orthogonal states:
* *protected* or *unprotected*
* *deferred life changes* or *no deferred life changes*
* *restarting* or *not restarting*
* *terminating* or *not terminating*
* *detached* or *not detached*
While the task life is *protected*, asynchronous task restart and termination
requests are blocked. A task may still restart or terminate itself. All tasks
are created with an unprotected task life. The task life protection is used by
the system to prevent system resources being affected by asynchronous task
restart and termination requests. The task life protection can be enabled
(``PTHREAD_CANCEL_DISABLE``) or disabled (``PTHREAD_CANCEL_ENABLE``) for the
calling task through the ``pthread_setcancelstate()`` directive.
While *deferred life changes* are enabled, asynchronous task restart and
termination requests are delayed until the task performs a life change itself
or calls ``pthread_testcancel()``. Cancellation points are not implemented in
RTEMS. Deferred task life changes can be enabled (``PTHREAD_CANCEL_DEFERRED``)
or disabled (``PTHREAD_CANCEL_ASYNCHRONOUS``) for the calling task through the
``pthread_setcanceltype()`` directive. Classic API tasks are created with
deferred life changes disabled. POSIX threads are created with deferred life
changes enabled.
A task is made *restarting* by issuing a task restart request through the
:ref:`InterfaceRtemsTaskRestart` directive.
A task is made *terminating* by issuing a task termination request through the
:ref:`InterfaceRtemsTaskExit`, :ref:`InterfaceRtemsTaskDelete`,
``pthread_exit()``, and ``pthread_cancel()`` directives.
When a *detached* task terminates, the termination procedure completes without
the need for another task to join with the terminated task. Classic API tasks
are created as not detached. The detached state of created POSIX threads is
determined by the thread attributes. They are created as not detached by
default. The calling task is made detached through the ``pthread_detach()``
directive. The :ref:`InterfaceRtemsTaskExit` directive and self deletion
though :ref:`InterfaceRtemsTaskDelete` directive make the calling task
detached. In contrast, the ``pthread_exit()`` directive does not change the
detached state of the calling task.
.. index:: task arguments
.. index:: task prototype