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Diffstat (limited to 'c-user/task/background.rst')
| -rw-r--r-- | c-user/task/background.rst | 68 |
1 files changed, 63 insertions, 5 deletions
diff --git a/c-user/task/background.rst b/c-user/task/background.rst index a55f743..c7645b1 100644 --- a/c-user/task/background.rst +++ b/c-user/task/background.rst @@ -1,6 +1,6 @@ .. 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 & Co. KG .. Copyright (C) 1988, 2008 On-Line Applications Research Corporation (OAR) Background @@ -127,13 +127,19 @@ scheduling of a task is based on its current state and priority. .. index:: priority, task .. index:: rtems_task_priority +.. _TaskPriority: + Task Priority ------------- -A task's priority determines its importance in relation to the other tasks -executing on the same processor. RTEMS supports 255 levels of priority ranging -from 1 to 255. The data type ``rtems_task_priority`` is used to store task -priorities. +A task's :term:`priority` determines its importance in relation to the other +tasks executing on the processor set owned by a :term:`scheduler`. Normally, +RTEMS supports 256 levels of priority ranging from 0 to 255. The priority +level 0 represents a special priority reserved for the operating system. The +data type :c:type:`rtems_task_priority` is used to store task priorities. The +maximum priority level depends on the configured scheduler, see +:ref:`CONFIGURE_MAXIMUM_PRIORITY`, :ref:`ConfigurationSchedulersClustered`, and +:ref:`RTEMSAPIClassicScheduler`. Tasks of numerically smaller priority values are more important tasks than tasks of numerically larger priority values. For example, a task at priority @@ -227,6 +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 |