rtems提供了更新任务优先级的函数，最常用的场景是主动调用rtems_task_set_priority来调整任务的优先级，当前其他相关线程的操作都可以操作优先级，本文仅以最简单和通用的方式解释更新任务优先级

一、函数实现

rtems_task_set_priority的函数实现如下：


rtems_status_code rtems_task_set_priority(
  rtems_id             id,
  rtems_task_priority  new_priority,
  rtems_task_priority *old_priority_p
)_RTEMS_tasks_Set_priority
{
  Thread_Control          *the_thread;
  Thread_queue_Context     queue_context;
  const Scheduler_Control *scheduler;
  Priority_Control         old_priority;
  rtems_status_code        status;
 
  if ( old_priority_p == NULL ) {
    return RTEMS_INVALID_ADDRESS;
  }
 
  _Thread_queue_Context_initialize( &queue_context );
  _Thread_queue_Context_clear_priority_updates( &queue_context );
  the_thread = _Thread_Get( id, &queue_context.Lock_context.Lock_context );
 
  if ( the_thread == NULL ) {
#if defined(RTEMS_MULTIPROCESSING)
    return _RTEMS_tasks_MP_Set_priority( id, new_priority, old_priority_p );
#else
    return RTEMS_INVALID_ID;
#endif
  }
 
  _Thread_Wait_acquire_critical( the_thread, &queue_context );
 
  scheduler = _Thread_Scheduler_get_home( the_thread );
  old_priority = _Thread_Get_priority( the_thread );
 
  if ( new_priority != RTEMS_CURRENT_PRIORITY ) {
    status = _RTEMS_tasks_Set_priority(
      the_thread,
      scheduler,
      new_priority,
      &queue_context
    );
  } else {
    _Thread_Wait_release( the_thread, &queue_context );
    status = RTEMS_SUCCESSFUL;
  }
 
  *old_priority_p = _RTEMS_Priority_From_core( scheduler, old_priority );
  return status;
}

对于此函数，其作用主要是获取线程后加锁然后更新优先级，最后释放锁后返回旧的优先级，所以我们关心主要函数_RTEMS_tasks_Set_priority。其调用路径如下


_RTEMS_tasks_Set_priority--->_Thread_Priority_update--->_Scheduler_Update_priority

二、测试程序

测试调整优先级的方法是在task创建之后的任意时间，根据taskid来调整优先级，故部分代码如下


status = rtems_task_start( Task_id[ 1 ], Task_1, 0 );
directive_failed( status, "rtems_task_start of TA1" );
                                                                                                                                                                                             
rtems_task_priority previous_priority;                                                                                                                                                     
status = rtems_task_set_priority( Task_id[ 1 ], 253, &previous_priority );
printf("Kylin: set priority 254 ret=%d prev=%d \n", status, previous_priority );
                                                                                                                                                                                             
status = rtems_task_start( Task_id[ 2 ], Task_2, 0 );
directive_failed( status, "rtems_task_start of TA2" );
                                                                                                                                                                                             
status = rtems_task_set_priority( Task_id[ 2 ], 254, &previous_priority );
printf("Kylin: set priority 255 ret=%d prev=%d \n", status, previous_priority );

我们可以调整task1和task2的优先级，这样task1和task2的启动顺序会出现不一样。日志如下

task1 优于 task2


Kylin: set priority 254 ret=0 prev=4                                                                                         
Kylin: set priority 255 ret=0 prev=4                                                                                                                                                                                                                                                                   
TA1 - rtems_signal_send - RTEMS_SIGNAL_16 to self                                                                                                                                                                        
TA1 - rtems_signal_send - RTEMS_SIGNAL_0 to self                                                                                                                                                                                                                                                  
TA2 - rtems_signal_send - RTEMS_SIGNAL_17 to self                                                                                                                                                     
TA2 - rtems_signal_send - RTEMS_SIGNAL_18 and RTEMS_SIGNAL_19 to self

task2优于task1


Kylin: set priority 254 ret=0 prev=4                                                                                         
Kylin: set priority 255 ret=0 prev=4                                                                                           
TA2 - rtems_signal_send - RTEMS_SIGNAL_17 to self                                                                                                                                                     
TA2 - rtems_signal_send - RTEMS_SIGNAL_18 and RTEMS_SIGNAL_19 to self                                                                                                                                                                                 
TA1 - rtems_signal_send - RTEMS_SIGNAL_16 to self                                                                                                                                                                        
TA1 - rtems_signal_send - RTEMS_SIGNAL_0 to self

三、总结

本文简单的演示了调整任务优先级，由于目前未了解不同调度器的实现，故此实验比较简单

目录

一、函数实现

二、测试程序

三、总结