1 函数接口

1.1 函数接口

void vTaskDelete( TaskHandle_t xTaskToDelete )

1.2 函数参数简介

• TaskHandle_t xTaskToDelete 要删除任务的句柄，但这个句柄其实就是我们申请任务时创建的TCB，这个参数在传入的时候可以设置为NULL，表示要删除的是自己当前的任务。

2 vTaskDelete的调用关系

2.1 调用关系

|- vTaskDelete|- pxTCB = prvGetTCBFromHandle( xTaskToDelete );|- uxListRemove( &( pxTCB->xStateListItem ) )|- taskRESET_READY_PRIORITY( pxTCB->uxPriority );|- vListInsertEnd( &xTasksWaitingTermination, &( pxTCB->xStateListItem ) );|- taskYIELD_WITHIN_API();

2.2 调用关系示意图

3 函数源码分析

3.1 vTaskDelete

• pxTCB = prvGetTCBFromHandle( xTaskToDelete ); 获取要删除任务的TCB
• uxListRemove( &( pxTCB->xStateListItem ) ) == ( UBaseType_t ) 0 将当前要删除的任务从pxReadyTasksLists对应优先级的链表里面删除，并判断该优先级的任务数是不是为0了，如果当前该优先级的链表里已经没有任务则需要调用taskRESET_READY_PRIORITY( pxTCB->uxPriority );去做重置将该优先级在uxTopReadyPriority中mask掉。
• vListInsertEnd( &xTasksWaitingTermination, &( pxTCB->xStateListItem ) ); 如果当前的任务处于运行状态，则将当前要删除的任务放入到xTasksWaitingTermination列表，等到idle task执行的时候再去执行删除操作。任务是否处于调度状态的判断依据是xSchedulerRunning是否是pdTRUE，该状态位在执行vTaskStartScheduler函数时被置位，在执行vTaskEndScheduler函数时被置位pdFALSE，因此只要是当前的系统调度没有停就需要将要删除的任务的TCB加入到xTasksWaitingTermination链表中。
• ++uxDeletedTasksWaitingCleanUp 记录等待清理任务的数量，在idle task或者vTaskEndScheduler执行时，以该全局变量作为清理数量的标准。
• xDeleteTCBInIdleTask = pdTRUE; 标记当前任务要再idle task里面做删除工作。
• taskYIELD_WITHIN_API();或者prvYieldCore( pxTCB->xTaskRunState ); 将处理器让出去，调度其他的任务。

void vTaskDelete( TaskHandle_t xTaskToDelete )
{TCB_t * pxTCB;BaseType_t xDeleteTCBInIdleTask = pdFALSE;BaseType_t xTaskIsRunningOrYielding;traceENTER_vTaskDelete( xTaskToDelete );taskENTER_CRITICAL();{获取当前要删除任务的TCB，如果xTaskToDelete 为空则表示要删除当前正在运行的任务，否则就找到对应任务的TCB。pxTCB = prvGetTCBFromHandle( xTaskToDelete );configASSERT( pxTCB != NULL );把当前要删除的任务从ready/delayed 链表中删除，并判断任务优先级的链表任务数是否为0if( uxListRemove( &( pxTCB->xStateListItem ) ) == ( UBaseType_t ) 0 ){如果当前要删除的任务优先级所对应的链表任务数为0，则将该优先级在uxTopReadyPriority中mask掉。taskRESET_READY_PRIORITY( pxTCB->uxPriority );}else{mtCOVERAGE_TEST_MARKER();}判断当前的任务是否在一个event的链表，如果是则通过uxListRemove将其移除if( listLIST_ITEM_CONTAINER( &( pxTCB->xEventListItem ) ) != NULL ){( void ) uxListRemove( &( pxTCB->xEventListItem ) );}else{mtCOVERAGE_TEST_MARKER();}/* Increment the uxTaskNumber also so kernel aware debuggers can* detect that the task lists need re-generating.  This is done before* portPRE_TASK_DELETE_HOOK() as in the Windows port that macro will* not return. */uxTaskNumber++;通过taskTASK_IS_RUNNING_OR_SCHEDULED_TO_YIELD来判断当前的任务是否在运行状态，如果其xTaskRunState被设置为-1则表明其不处于运行状态，正常运行的任务其xTaskRunState值会被设置为所运行的core的id。xTaskIsRunningOrYielding = taskTASK_IS_RUNNING_OR_SCHEDULED_TO_YIELD( pxTCB );根据xSchedulerRunning 来判断当前的是否还处于正常的调度状态，该全局变量在vTaskStartScheduler函数被执行时设置为pdTRUE，在vTaskEndScheduler时被设置为pdFALSEif( ( xSchedulerRunning != pdFALSE ) && ( xTaskIsRunningOrYielding != pdFALSE ) ){为了防止该任务在其他core上还有运行的，所以将该任务添加到xTasksWaitingTermination链表上，等idle task运行时再做清理工作。vListInsertEnd( &xTasksWaitingTermination, &( pxTCB->xStateListItem ) );标记当前需要做清理的任务数++uxDeletedTasksWaitingCleanUp;/* Call the delete hook before portPRE_TASK_DELETE_HOOK() as* portPRE_TASK_DELETE_HOOK() does not return in the Win32 port. */traceTASK_DELETE( pxTCB );用以标记有任务需要删除，如果需要设置为pdTRUE，则在后面会调用prvDeleteTCB( pxTCB );释放掉这块内存空间。xDeleteTCBInIdleTask = pdTRUE;/* The pre-delete hook is primarily for the Windows simulator,* in which Windows specific clean up operations are performed,* after which it is not possible to yield away from this task -* hence xYieldPending is used to latch that a context switch is* required. */#if ( configNUMBER_OF_CORES == 1 )portPRE_TASK_DELETE_HOOK( pxTCB, &( xYieldPendings[ 0 ] ) );#elseportPRE_TASK_DELETE_HOOK( pxTCB, &( xYieldPendings[ pxTCB->xTaskRunState ] ) );#endif在SMP系统给按任务让出CPU，让其他任务去运行#if ( configNUMBER_OF_CORES > 1 ){if( taskTASK_IS_RUNNING( pxTCB ) == pdTRUE ){if( pxTCB->xTaskRunState == ( BaseType_t ) portGET_CORE_ID() ){configASSERT( uxSchedulerSuspended == 0 );taskYIELD_WITHIN_API();}else{prvYieldCore( pxTCB->xTaskRunState );}}}#endif /* #if ( configNUMBER_OF_CORES > 1 ) */}else{--uxCurrentNumberOfTasks;traceTASK_DELETE( pxTCB );/* Reset the next expected unblock time in case it referred to* the task that has just been deleted. */prvResetNextTaskUnblockTime();}}taskEXIT_CRITICAL();/* If the task is not deleting itself, call prvDeleteTCB from outside of* critical section. If a task deletes itself, prvDeleteTCB is called* from prvCheckTasksWaitingTermination which is called from Idle task. */if( xDeleteTCBInIdleTask != pdTRUE ){prvDeleteTCB( pxTCB );}/* Force a reschedule if it is the currently running task that has just* been deleted. */#if ( configNUMBER_OF_CORES == 1 ){if( xSchedulerRunning != pdFALSE ){if( pxTCB == pxCurrentTCB ){configASSERT( uxSchedulerSuspended == 0 );taskYIELD_WITHIN_API();}else{mtCOVERAGE_TEST_MARKER();}}}#endif /* #if ( configNUMBER_OF_CORES == 1 ) */traceRETURN_vTaskDelete();
}

3.2 uxListRemove

• pxList = pxItemToRemove->pxContainer; 通过pxContainer找到当前任务优先级所对应链表的链表头
• pxList->uxNumberOfItems 返回当前任务优先级链表还剩余的任务数，一般用于判断链表所挂任务是否为0，用以来确定当前任务的优先级是否需要mask掉。

UBaseType_t uxListRemove( ListItem_t * const pxItemToRemove )
{/* The list item knows which list it is in.  Obtain the list from the list* item. */List_t * const pxList = pxItemToRemove->pxContainer;traceENTER_uxListRemove( pxItemToRemove );pxItemToRemove->pxNext->pxPrevious = pxItemToRemove->pxPrevious;pxItemToRemove->pxPrevious->pxNext = pxItemToRemove->pxNext;/* Only used during decision coverage testing. */mtCOVERAGE_TEST_DELAY();/* Make sure the index is left pointing to a valid item. */if( pxList->pxIndex == pxItemToRemove ){pxList->pxIndex = pxItemToRemove->pxPrevious;}else{mtCOVERAGE_TEST_MARKER();}pxItemToRemove->pxContainer = NULL;( pxList->uxNumberOfItems ) = ( UBaseType_t ) ( pxList->uxNumberOfItems - 1U );traceRETURN_uxListRemove( pxList->uxNumberOfItems );return pxList->uxNumberOfItems;
}