FreeRTOS学习笔记【11】-----任务列表

根据b站up freeRTOS源码

数据结构

1 TCB（task control block）

typedef struct tskTaskControlBlock /* The old naming convention is used to prevent breaking kernel aware debuggers. */
{
volatile StackType_t * pxTopOfStack; /**< Points to the location of the last item placed on the tasks stack. THIS MUST BE THE FIRST MEMBER OF THE TCB STRUCT. */
//指向任务栈顶部的指针
ListItem_t xStateListItem; /**< The list that the state list item of a task is reference from denotes the state of that task (Ready, Blocked, Suspended ). */
//用于将任务链接到不同状态列表（就绪、阻塞、挂起）的列表项。
ListItem_t xEventListItem; /**< Used to reference a task from an event list. */
//用于将任务链接到事件列表的列表项。
UBaseType_t uxPriority; /**< The priority of the task. 0 is the lowest priority. */
//任务的优先级，数值越小优先级越低。
StackType_t * pxStack; /**< Points to the start of the stack. */
//指向任务栈起始地址的指针
char pcTaskName[ configMAX_TASK_NAME_LEN ];
} tskTCB;

2 任务列表项

struct xLIST_ITEM
{
listFIRST_LIST_ITEM_INTEGRITY_CHECK_VALUE /**< Set to a known value if configUSE_LIST_DATA_INTEGRITY_CHECK_BYTES is set to 1. */

configLIST_VOLATILE TickType_t xItemValue; /**< The value being listed. In most cases this is used to sort the list in ascending order. */

struct xLIST_ITEM * configLIST_VOLATILE pxNext; /**< Pointer to the next ListItem_t in the list. */

struct xLIST_ITEM * configLIST_VOLATILE pxPrevious; /**< Pointer to the previous ListItem_t in the list. */

void * pvOwner; /**< Pointer to the object (normally a TCB) that contains the list item. There is therefore a two way link between the object containing the list item and the list item itself. */
//指向“拥有”该 list item 的对象。通常是一个任务控制块（TCB）。
struct xLIST * configLIST_VOLATILE pxContainer; /**< Pointer to the list in which this list item is placed (if any). */
//指列表项所处的列表（就绪列表、delay列表、挂起列表）
listSECOND_LIST_ITEM_INTEGRITY_CHECK_VALUE /**< Set to a known value if configUSE_LIST_DATA_INTEGRITY_CHECK_BYTES is set to 1. */

};
typedef struct xLIST_ITEM ListItem_t;

3 列表头

typedef struct xLIST
{
listFIRST_LIST_INTEGRITY_CHECK_VALUE /**< Set to a known value if configUSE_LIST_DATA_INTEGRITY_CHECK_BYTES is set to 1. */

configLIST_VOLATILE UBaseType_t uxNumberOfItems; /**< Number of items in the list. */

ListItem_t * configLIST_VOLATILE pxIndex; /**< Used to walk through the list. Points to the last item returned by a call to listGET_OWNER_OF_NEXT_ENTRY (). */
//指向列表的指针
MiniListItem_t xListEnd; /**< List item that contains the maximum possible item value meaning it is always at the end of the list and is therefore used as a marker. */
//尾节点
listSECOND_LIST_INTEGRITY_CHECK_VALUE /**< Set to a known value if configUSE_LIST_DATA_INTEGRITY_CHECK_BYTES is set to 1. */

} List_t;

列表代码

1 列表初始化

freeRTOS的列表变量：

PRIVILEGED_DATA static List_t pxReadyTasksLists[ configMAX_PRIORITIES ];
/**< 用于存储就绪态（Ready）的任务列表. */
PRIVILEGED_DATA static List_t xDelayedTaskList1;
/**< 用于存储延迟（Delayed）的任务 */
PRIVILEGED_DATA static List_t xDelayedTaskList2;
/**< xDelayedTaskList2 用于存储那些延迟时间超过了当前 tick 计数范围的任务. */
PRIVILEGED_DATA static List_t * volatile pxDelayedTaskList;
/**< 当前正在使用的延迟任务列表.延迟时间超过了当前 tick 计数器的范围时，这些任务会被放入 */
PRIVILEGED_DATA static List_t * volatile pxOverflowDelayedTaskList;
/**< 指向当前用于存储溢出延迟任务的列表. */
PRIVILEGED_DATA static List_t xPendingReadyList;
/**< 用于存储那些由于某些事件（如信号量释放、队列操作等）而变为就绪态的任务 */

2 列表初始化

pxList->pxIndex = ( ListItem_t * ) &( pxList->xListEnd );

pxList->xListEnd.xItemValue = portMAX_DELAY;
//0xffffffffU
pxList->xListEnd.pxNext = ( ListItem_t * ) &( pxList->xListEnd );

pxList->xListEnd.pxPrevious = ( ListItem_t * ) &( pxList->xListEnd );

pxList->uxNumberOfItems = ( UBaseType_t ) 0U;

3 Insert 函数

void vListInsert( List_t * const pxList,
ListItem_t * const pxNewListItem )

pxList 要插入的列表， pxNewListItem 要插入的列表项

ListItem_t * pxIterator;
//将新列表项插入在pxIterator指向位置的后面
pxNewListItem->pxNext = pxIterator->pxNext;
pxNewListItem->pxNext->pxPrevious = pxNewListItem;
pxNewListItem->pxPrevious = pxIterator;
pxIterator->pxNext = pxNewListItem;

那么，pxIterator的是如何定位的呢？

//如果value最大，就放在尾结点的前面
if( xValueOfInsertion == portMAX_DELAY )
{
pxIterator = pxList->xListEnd.pxPrevious;
}
else
{
//初始化，迭代器指向尾部
//停止条件，迭代器的下一个节点的值小于等于当前值
//否则 迭代器指向下一个节点
for( pxIterator = ( ListItem_t * ) &( pxList->xListEnd );
pxIterator->pxNext->xItemValue <= xValueOfInsertion;
pxIterator = pxIterator->pxNext )
{
/* There is nothing to do here, just iterating to the wanted
* insertion position. */
}

4 InsertEnd函数

这里的End是对于遍历而言的End， 在listGET_OWNER_OF_NEXT_ENTRY中，需要对list进行遍历

do { \\
List_t * const pxConstList = ( pxList ); \\
/* Increment the index to the next item and return the item, ensuring */ \\
/* we don't return the marker used at the end of the list. */ \\
( pxConstList )->pxIndex = ( pxConstList )->pxIndex->pxNext; \\
if( ( void * ) ( pxConstList )->pxIndex == ( void * ) &( ( pxConstList )->xListEnd ) ) \\
{ \\
( pxConstList )->pxIndex = ( pxConstList )->xListEnd.pxNext; \\
} \\
( pxTCB ) = ( pxConstList )->pxIndex->pvOwner; \\
} while( 0 )

InsertEnd 函数存在的含义是：

并不是把当前要插入的项插到列表尾 而是要把列表放在遍历时最后一个遍历的位置