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freeRTOS 互斥量优先级继承机制函数实现xQueueGenericReceive()

news 来源：原创 2025/6/8 9:42:22

一接收到互斥量时，将互斥量的任务持有者赋值为当前任务

以下为xQueueGenericReceive()函数接收互斥量，互斥量不为空（未被别的任务持有），去除互斥量，并且将互斥量的持有者赋值为当前任务，紫色字体部分

if( uxMessagesWaiting > ( UBaseType_t ) 0 )
           {
               /* Remember the read position in case the queue is only being
               peeked. */
               pcOriginalReadPosition = pxQueue->u.pcReadFrom;

prvCopyDataFromQueue( pxQueue, pvBuffer );

               if( xJustPeeking == pdFALSE )
               {
                   traceQUEUE_RECEIVE( pxQueue );

/* Actually removing data, not just peeking. */
pxQueue->uxMessagesWaiting = uxMessagesWaiting - 1;

                   #if ( configUSE_MUTEXES == 1 )
                   {
                       if( pxQueue->uxQueueType == queueQUEUE_IS_MUTEX )
                       {
                           /* Record the information required to implement
                           priority inheritance should it become necessary. */
           pxQueue->pxMutexHolder = ( int8_t * ) pvTaskIncrementMutexHeldCount(); /*lint !e961 Cast is not redundant as TaskHandle_t is a typedef. */
                       }
                       else
                       {
                           mtCOVERAGE_TEST_MARKER();
                       }
                   }
                   #endif /* configUSE_MUTEXES */

二接收任务接收不到信号量时，提升互斥量持有者任务的优先级

还是xQueueGenericReceive()函数接收互斥量，互斥量为空（被别的任务持有），而且时间未超时时，就是第一次尝试接收时，进行优先级继承，紫色字体函数

/* Update the timeout state to see if it has expired yet. */
       if( xTaskCheckForTimeOut( &xTimeOut, &xTicksToWait ) == pdFALSE )
       {
           if( prvIsQueueEmpty( pxQueue ) != pdFALSE )
           {
               traceBLOCKING_ON_QUEUE_RECEIVE( pxQueue );

               #if ( configUSE_MUTEXES == 1 )
               {
                   if( pxQueue->uxQueueType == queueQUEUE_IS_MUTEX )
                   {
                       taskENTER_CRITICAL();
                       {
                           vTaskPriorityInherit( ( void * ) pxQueue->pxMutexHolder );
                       }
                       taskEXIT_CRITICAL();
                   }
                   else
                   {
                       mtCOVERAGE_TEST_MARKER();
                   }
               }
               #endif

               vTaskPlaceOnEventList( &( pxQueue->xTasksWaitingToReceive ), xTicksToWait );
               prvUnlockQueue( pxQueue );
               if( xTaskResumeAll() == pdFALSE )
               {
                   portYIELD_WITHIN_API();
               }
               else
               {
                   mtCOVERAGE_TEST_MARKER();
               }
           }

三最终实现函数TaskPriorityInherit（）解析

void vTaskPriorityInherit( TaskHandle_t const pxMutexHolder )
{
TCB_t * const pxTCB = ( TCB_t * ) pxMutexHolder;

       if( pxMutexHolder != NULL )
       {

           if( pxTCB->uxPriority < pxCurrentTCB->uxPriority )
           {
                 /* Adjust the mutex holder state to account for its new
               priority. Only reset the event list item value if the value is
               not   being used for anything else. */
               if( ( listGET_LIST_ITEM_VALUE( &( pxTCB->xEventListItem ) ) & taskEVENT_LIST_ITEM_VALUE_IN_USE ) == 0UL ) //获取互斥量持有任务的节点辅助值，用于迁移到新优先级就绪链表时的排序
               {
                   listSET_LIST_ITEM_VALUE( &( pxTCB->xEventListItem ), ( TickType_t ) configMAX_PRIORITIES - ( TickType_t ) pxCurrentTCB->uxPriority ); //设定互斥量持有任务的节点辅助值，用于迁移到新优先级就绪链表时的排序
               }
               else
               {
                   mtCOVERAGE_TEST_MARKER();
               }

               /* If the task being modified is in the ready state it will need
               to be moved into a new list. */
               if( listIS_CONTAINED_WITHIN( &( pxReadyTasksLists[ pxTCB->uxPriority ] ), &( pxTCB->xStateListItem ) ) != pdFALSE )//互斥量持有者任务现在处于就绪列表
               {
                   if( uxListRemove( &( pxTCB->xStateListItem ) ) == ( UBaseType_t ) 0 )//将互斥量持有者任务从其所在就绪列表移除
                   {
                       taskRESET_READY_PRIORITY( pxTCB->uxPriority );
                   }
                   else
                   {
                       mtCOVERAGE_TEST_MARKER();
                   }

                   /* Inherit the priority before being moved into the new list. */
                   pxTCB->uxPriority = pxCurrentTCB->uxPriority;//将互斥量持有者任务优先级赋值为当前任务优先级
                   prvAddTaskToReadyList( pxTCB );//将互斥量持有者任务移到相应优先级列表
               }
               else
               {
                   /* Just inherit the priority. */
                   pxTCB->uxPriority = pxCurrentTCB->uxPriority; //将互斥量持有者任务优先级赋值为当前任务优先级，只进行优先级上升级，因为现在不在就绪列表中
               }

               traceTASK_PRIORITY_INHERIT( pxTCB, pxCurrentTCB->uxPriority );
           }
           else
           {
               mtCOVERAGE_TEST_MARKER();
           }
       }
       else
       {
           mtCOVERAGE_TEST_MARKER();
       }
   }