SPDX-License-Identifier: CC-BY-SA-4.0 OR BSD-2-Clause
brief: |
Sets the priority by scheduler for the semaphore.
copyrights:
- Copyright (C) 2021 embedded brains GmbH (http://www.embedded-brains.de)
- Copyright (C) 1988, 2008 On-Line Applications Research Corporation (OAR)
definition:
default:
attributes: null
body: null
params:
- ${../../type/if/id:/name} ${.:/params[0]/name}
- ${../../type/if/id:/name} ${.:/params[1]/name}
- ${../../type/if/priority:/name} ${.:/params[2]/name}
- ${../../type/if/priority:/name} *${.:/params[3]/name}
return: ${../../status/if/code:/name}
variants: []
description: |
This directive sets the priority of the semaphore specified by
${.:/params[0]/name}. The priority corresponds to the scheduler specified by
${.:/params[1]/name}.
The special priority value ${../../task/if/current-priority:/name} can be
used to get the current priority without changing it.
The availability and use of a priority depends on the class and locking
protocol of the semaphore:
* For local, binary semaphores using the MrsP locking protocol, the ceiling
priority for each scheduler can be set by this directive.
* For local, binary semaphores using the priority ceiling protocol, the
ceiling priority can be set by this directive.
* For other semaphore classes and locking protocols, setting a priority is
undefined behaviour.
enabled-by: true
index-entries:
- set priority by scheduler for a semaphore
interface-type: function
links:
- role: interface-placement
uid: header
- role: interface-ingroup
uid: group
- role: constraint
uid: /constraint/directive-ctx-isr
- role: constraint
uid: /constraint/directive-ctx-devinit
- role: constraint
uid: /constraint/directive-ctx-task
- role: constraint
uid: /constraint/priority-may-preempt
name: rtems_semaphore_set_priority
notes: |
Please have a look at the following example:
.. code-block:: c
:linenos:
#include <assert.h>
#include <rtems.h>
#define SCHED_A rtems_build_name( ' ', ' ', ' ', 'A' )
#define SCHED_B rtems_build_name( ' ', ' ', ' ', 'B' )
static void Init( rtems_task_argument arg )
{
rtems_status_code sc;
rtems_id semaphore_id;
rtems_id scheduler_a_id;
rtems_id scheduler_b_id;
rtems_task_priority prio;
(void) arg;
// Get the scheduler identifiers
sc = rtems_scheduler_ident( SCHED_A, &scheduler_a_id );
assert( sc == RTEMS_SUCCESSFUL );
sc = rtems_scheduler_ident( SCHED_B, &scheduler_b_id );
assert( sc == RTEMS_SUCCESSFUL );
// Create a local, binary semaphore using the MrsP locking protocol
sc = rtems_semaphore_create(
rtems_build_name( 'M', 'R', 'S', 'P' ),
1,
RTEMS_BINARY_SEMAPHORE | RTEMS_PRIORITY |
RTEMS_MULTIPROCESSOR_RESOURCE_SHARING,
1,
&semaphore_id
);
assert( sc == RTEMS_SUCCESSFUL );
// The ceiling priority for each scheduler is equal to the priority
// specified for the semaphore creation.
prio = RTEMS_CURRENT_PRIORITY;
sc = rtems_semaphore_set_priority( semaphore_id, scheduler_a_id, prio, &prio );
assert( sc == RTEMS_SUCCESSFUL );
assert( prio == 1 );
// Check the old value and set a new ceiling priority for scheduler B
prio = 2;
sc = rtems_semaphore_set_priority( semaphore_id, scheduler_b_id, prio, &prio );
assert( sc == RTEMS_SUCCESSFUL );
assert( prio == 1 );
// Check the ceiling priority values
prio = RTEMS_CURRENT_PRIORITY;
sc = rtems_semaphore_set_priority( semaphore_id, scheduler_a_id, prio, &prio );
assert( sc == RTEMS_SUCCESSFUL );
assert( prio == 1 );
prio = RTEMS_CURRENT_PRIORITY;
sc = rtems_semaphore_set_priority( semaphore_id, scheduler_b_id, prio, &prio );
assert( sc == RTEMS_SUCCESSFUL );
assert( prio == 2 );
sc = rtems_semaphore_delete( semaphore_id );
assert( sc == RTEMS_SUCCESSFUL );
rtems_shutdown_executive( 0 );
}
#define CONFIGURE_APPLICATION_NEEDS_CLOCK_DRIVER
#define CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER
#define CONFIGURE_MAXIMUM_TASKS 1
#define CONFIGURE_MAXIMUM_SEMAPHORES 1
#define CONFIGURE_MAXIMUM_PROCESSORS 2
#define CONFIGURE_SCHEDULER_SIMPLE_SMP
#include <rtems/scheduler.h>
RTEMS_SCHEDULER_CONTEXT_SIMPLE_SMP( a );
RTEMS_SCHEDULER_CONTEXT_SIMPLE_SMP( b );
#define CONFIGURE_SCHEDULER_TABLE_ENTRIES \
RTEMS_SCHEDULER_TABLE_SIMPLE_SMP( a, SCHED_A ), \
RTEMS_SCHEDULER_TABLE_SIMPLE_SMP( b, SCHED_B )
#define CONFIGURE_SCHEDULER_ASSIGNMENTS \
RTEMS_SCHEDULER_ASSIGN( 0, RTEMS_SCHEDULER_ASSIGN_PROCESSOR_MANDATORY ), \
RTEMS_SCHEDULER_ASSIGN( 1, RTEMS_SCHEDULER_ASSIGN_PROCESSOR_MANDATORY )
#define CONFIGURE_RTEMS_INIT_TASKS_TABLE
#define CONFIGURE_INIT
#include <rtems/confdefs.h>
params:
- description: |
is the semaphore identifier.
dir: null
name: semaphore_id
- description: |
is the identifier of the scheduler corresponding to the new priority.
dir: null
name: scheduler_id
- description: |
is the new priority corresponding to the specified scheduler.
dir: null
name: new_priority
- description: |
is the pointer to a task priority variable. When the directive call is
successful, the old priority of the semaphore corresponding to the
specified scheduler will be stored in this variable.
dir: out
name: old_priority
return:
return: null
return-values:
- description: |
The requested operation was successful.
value: ${../../status/if/successful:/name}
- description: |
The ${.:/params[3]/name} parameter was ${/c/if/null:/name}.
value: ${../../status/if/invalid-address:/name}
- description: |
There was no scheduler associated with the identifier specified by
${.:/params[1]/name}.
value: ${../../status/if/invalid-id:/name}
- description: |
There was no semaphore associated with the identifier specified by
${.:/params[0]/name}.
value: ${../../status/if/invalid-id:/name}
- description: |
The semaphore resided on a remote node.
value: ${../../status/if/illegal-on-remote-object:/name}
- description: |
The ${.:/params[2]/name} parameter was invalid.
value: ${../../status/if/invalid-priority:/name}
- description: |
Setting a priority for the class or locking protocol of the semaphore is
undefined behaviour.
value: ${../../status/if/not-defined:/name}
type: interface
