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c-user: Replace pre-emption with preemption

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Sebastian Huber 2017-05-11 09:25:04 +02:00
parent 4cc5fcf012
commit 39773ce8bd
2 changed files with 8 additions and 8 deletions
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4
c-user/key_concepts.rst
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@ -271,7 +271,7 @@ Priority Inversion
.. index:: priority inversion .. index:: priority inversion
Priority inversion is a form of indefinite postponement which is common in Priority inversion is a form of indefinite postponement which is common in
multitasking, pre-emptive executives with shared resources. Priority inversion multitasking, preemptive executives with shared resources. Priority inversion
occurs when a high priority tasks requests access to shared resource which is occurs when a high priority tasks requests access to shared resource which is
currently allocated to a low priority task. The high priority task must block currently allocated to a low priority task. The high priority task must block
until the low priority task releases the resource. This problem is exacerbated until the low priority task releases the resource. This problem is exacerbated
@ -333,7 +333,7 @@ scheduler instance. In case the thread owning the mutex releases the mutex,
then the normal priority of the thread is restored. Threads that wait for then the normal priority of the thread is restored. Threads that wait for
mutex ownership are not blocked with respect to the scheduler and instead mutex ownership are not blocked with respect to the scheduler and instead
perform a busy wait. The MrsP uses temporary thread migrations to foreign perform a busy wait. The MrsP uses temporary thread migrations to foreign
scheduler instances in case of a pre-emption of the mutex owner. This locking scheduler instances in case of a preemption of the mutex owner. This locking
protocol is available since RTEMS 4.11. It was re-implemented in RTEMS 4.12 to protocol is available since RTEMS 4.11. It was re-implemented in RTEMS 4.12 to
overcome some shortcomings of the original implementation overcome some shortcomings of the original implementation
:cite:`Catellani:2015:MrsP`. :cite:`Catellani:2015:MrsP`.

12
c-user/symmetric_multiprocessing_services.rst
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@ -347,15 +347,15 @@ executed in a uni-processor configuration and should be assumed to have data
synchronization conflicts with what was formerly the highest priority task synchronization conflicts with what was formerly the highest priority task
which executed without conflict. which executed without conflict.
Disabling of Thread Pre-Emption Disabling of Thread Preemption
------------------------------- ------------------------------
A thread which disables pre-emption prevents that a higher priority thread gets A thread which disables preemption prevents that a higher priority thread gets
hold of its processor involuntarily. In uni-processor configurations, this can hold of its processor involuntarily. In uni-processor configurations, this can
be used to ensure mutual exclusion at thread level. In SMP configurations, be used to ensure mutual exclusion at thread level. In SMP configurations,
however, more than one executing thread may exist. Thus, it is impossible to however, more than one executing thread may exist. Thus, it is impossible to
ensure mutual exclusion using this mechanism. In order to prevent that ensure mutual exclusion using this mechanism. In order to prevent that
applications using pre-emption for this purpose, would show inappropriate applications using preemption for this purpose, would show inappropriate
behaviour, this feature is disabled in SMP configurations and its use would behaviour, this feature is disabled in SMP configurations and its use would
case run-time errors. case run-time errors.
@ -706,7 +706,7 @@ creation. The home scheduler instance can be changed with
:ref:`rtems_task_set_scheduler() <rtems_task_set_scheduler>`. Due to the :ref:`rtems_task_set_scheduler() <rtems_task_set_scheduler>`. Due to the
locking protocols a thread may gain access to scheduler nodes of other locking protocols a thread may gain access to scheduler nodes of other
scheduler instances. This allows the thread to temporarily migrate to another scheduler instances. This allows the thread to temporarily migrate to another
scheduler instance in case of pre-emption. scheduler instance in case of preemption.
The scheduler infrastructure is based on an object-oriented design. The The scheduler infrastructure is based on an object-oriented design. The
scheduler operations for a thread are defined as virtual functions. For the scheduler operations for a thread are defined as virtual functions. For the
@ -724,7 +724,7 @@ variants. Up to now, only priority-based schedulers are implemented.
In case a thread is allowed to use more than one scheduler node it will ask In case a thread is allowed to use more than one scheduler node it will ask
these nodes for help these nodes for help
* in case of pre-emption, or * in case of preemption, or
* an unblock did not schedule the thread, or * an unblock did not schedule the thread, or
* a yield was successful. * a yield was successful.