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_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