freeRTOS LIST代码解读 （二）

freeRTOS 采用的是双向链表

头文件定义内容

其他宏定义

configLIST_VOLATILE 可以不用定义，因为结构体成员的修改只在临界区内进行修改。所以不需要定义为volatile。

/*
 * The list structure members are modified from within interrupts, and therefore
 * by rights should be declared volatile.  However, they are only modified in a
 * functionally atomic way (within critical sections of with the scheduler
 * suspended) and are either passed by reference into a function or indexed via
 * a volatile variable.  Therefore, in all use cases tested so far, the volatile
 * qualifier can be omitted in order to provide a moderate performance
 * improvement without adversely affecting functional behaviour.  The assembly
 * instructions generated by the IAR, ARM and GCC compilers when the respective
 * compiler's options were set for maximum optimisation has been inspected and
 * deemed to be as intended.  That said, as compiler technology advances, and
 * especially if aggressive cross module optimisation is used (a use case that
 * has not been exercised to any great extend) then it is feasible that the
 * volatile qualifier will be needed for correct optimisation.  It is expected
 * that a compiler removing essential code because, without the volatile
 * qualifier on the list structure members and with aggressive cross module
 * optimisation, the compiler deemed the code unnecessary will result in
 * complete and obvious failure of the scheduler.  If this is ever experienced
 * then the volatile qualifier can be inserted in the relevant places within the
 * list structures by simply defining configLIST_VOLATILE to volatile in
 * FreeRTOSConfig.h (as per the example at the bottom of this comment block).
 * If configLIST_VOLATILE is not defined then the preprocessor directives below
 * will simply #define configLIST_VOLATILE away completely.
 *
 * To use volatile list structure members then add the following line to
 * FreeRTOSConfig.h (without the quotes):
 * "#define configLIST_VOLATILE volatile"
 */
#ifndef configLIST_VOLATILE
	#define configLIST_VOLATILE
#endif /* configSUPPORT_CROSS_MODULE_OPTIMISATION */

链表测试代码定义

链表测试代码,用于测试链表和链表节点的数据是否被破环，通过在链表结构体和节点结构体的头和尾添加两个指定的成员变量。通过监测成员变量是否被改变，来测试代码是否正常运行。

/* Macros that can be used to place known values within the list structures,
then check that the known values do not get corrupted during the execution of
the application.   These may catch the list data structures being overwritten in
memory.  They will not catch data errors caused by incorrect configuration or
use of FreeRTOS.*/
#if( configUSE_LIST_DATA_INTEGRITY_CHECK_BYTES == 0 )
	/* Define the macros to do nothing. */
	#define listFIRST_LIST_ITEM_INTEGRITY_CHECK_VALUE
	#define listSECOND_LIST_ITEM_INTEGRITY_CHECK_VALUE
	#define listFIRST_LIST_INTEGRITY_CHECK_VALUE
	#define listSECOND_LIST_INTEGRITY_CHECK_VALUE
	#define listSET_FIRST_LIST_ITEM_INTEGRITY_CHECK_VALUE( pxItem )
	#define listSET_SECOND_LIST_ITEM_INTEGRITY_CHECK_VALUE( pxItem )
	#define listSET_LIST_INTEGRITY_CHECK_1_VALUE( pxList )
	#define listSET_LIST_INTEGRITY_CHECK_2_VALUE( pxList )
	#define listTEST_LIST_ITEM_INTEGRITY( pxItem )
	#define listTEST_LIST_INTEGRITY( pxList )
#else
	/* Define macros that add new members into the list structures. */
	#define listFIRST_LIST_ITEM_INTEGRITY_CHECK_VALUE				TickType_t xListItemIntegrityValue1;
	#define listSECOND_LIST_ITEM_INTEGRITY_CHECK_VALUE				TickType_t xListItemIntegrityValue2;
	#define listFIRST_LIST_INTEGRITY_CHECK_VALUE					TickType_t xListIntegrityValue1;
	#define listSECOND_LIST_INTEGRITY_CHECK_VALUE					TickType_t xListIntegrityValue2;

	/* Define macros that set the new structure members to known values. */
	#define listSET_FIRST_LIST_ITEM_INTEGRITY_CHECK_VALUE( pxItem )		( pxItem )->xListItemIntegrityValue1 = pdINTEGRITY_CHECK_VALUE
	#define listSET_SECOND_LIST_ITEM_INTEGRITY_CHECK_VALUE( pxItem )	( pxItem )->xListItemIntegrityValue2 = pdINTEGRITY_CHECK_VALUE
	#define listSET_LIST_INTEGRITY_CHECK_1_VALUE( pxList )		( pxList )->xListIntegrityValue1 = pdINTEGRITY_CHECK_VALUE
	#define listSET_LIST_INTEGRITY_CHECK_2_VALUE( pxList )		( pxList )->xListIntegrityValue2 = pdINTEGRITY_CHECK_VALUE

	/* Define macros that will assert if one of the structure members does not
	contain its expected value. */
	#define listTEST_LIST_ITEM_INTEGRITY( pxItem )		configASSERT( ( ( pxItem )->xListItemIntegrityValue1 == pdINTEGRITY_CHECK_VALUE ) && ( ( pxItem )->xListItemIntegrityValue2 == pdINTEGRITY_CHECK_VALUE ) )
	#define listTEST_LIST_INTEGRITY( pxList )			configASSERT( ( ( pxList )->xListIntegrityValue1 == pdINTEGRITY_CHECK_VALUE ) && ( ( pxList )->xListIntegrityValue2 == pdINTEGRITY_CHECK_VALUE ) )
#endif /* configUSE_LIST_DATA_INTEGRITY_CHECK_BYTES */

链表结构体

链表节点结构体

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. */
	//定义在链表节点中的值，用于链表节点排序
	configLIST_VOLATILE TickType_t xItemValue;			/*< The value being listed.  In most cases this is used to sort the list in descending order. */
	//链表下一个节点的指针
	struct xLIST_ITEM * configLIST_VOLATILE pxNext;		/*< Pointer to the next ListItem_t in the list. */
	//链表上一个节点的指针
	struct xLIST_ITEM * configLIST_VOLATILE pxPrevious;	/*< Pointer to the previous ListItem_t in the list. */
	//节点指向的TCB块
	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. */
	//节点所处的链表指针
	struct xLIST * configLIST_VOLATILE pxContainer;		/*< Pointer to the list in which this list item is placed (if any). */
	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;					/* For some reason lint wants this as two separate definitions. */

最小的链表节点结构体，用于作为链表的头指针

struct xMINI_LIST_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;
	struct xLIST_ITEM * configLIST_VOLATILE pxNext;
	struct xLIST_ITEM * configLIST_VOLATILE pxPrevious;
};

链表结构体

typedef struct xLIST
{
	listFIRST_LIST_INTEGRITY_CHECK_VALUE				/*< Set to a known value if configUSE_LIST_DATA_INTEGRITY_CHECK_BYTES is set to 1. */
	//链表的节点个数
	volatile UBaseType_t uxNumberOfItems;
	//
	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 (). */
	//相当于链表的头节点，但是节点中不包括任何数据
	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. */
	listSECOND_LIST_INTEGRITY_CHECK_VALUE				/*< Set to a known value if configUSE_LIST_DATA_INTEGRITY_CHECK_BYTES is set to 1. */
} List_t;

宏定义函数

//设置节点的内容
#define listSET_LIST_ITEM_OWNER(pxListItem, pxOwner) ((pxListItem)->pvOwner = (void *)(pxOwner))
//获取节点的内容
#define listGET_LIST_TIEM_OWNER(pxListItem) ((pxListItem)->pvwner)
//设置节点的xItemValue
#define listSET_LIST_ITEM_VALUE(pxListItem, xValue) ((pxListItem)->xItemValue = (xValue))
//获取节点的参数值
#define listGET_LIST_ITEM_VALUE(pxListItem) ((pxListItem)->xItemValue)
//获取链表的头节点参数值
#define listGET_ITEM_VALUE_OF_HEAD_ENTRY(pxList) (((pxList)->xListEnd).xItemValue)
//获取链表的头节点指针
#define listGET_HEAD_ENTRY(pxList) (((pxList)->xListEnd).pxNext)
//获取下一个节点的指针
#define listGET_NEXT(pxListItem) ((pxListItem)->pxNext)
//获取链表的MARKER 节点
#define listGET_END_MARKER(pxList) ((ListItem_t const *)(&((pxList)->xListEnd)))
//链表是否为空
#define listLIST_IS_EMPTY(pxList) (((pxList)->uxNumberOfItems == (UBaseType_t)0) ? pdTRUE : pdFALSE)
//链表的长度
#define listCURRENT_LIST_LENGTH(pxList) ((pxList)->uxNumberOfItems)
//链表的内容
#define listGET_OWNER_OF_NEXT_ENTRY(pxTCB, pxList)                                  \
    {                                                                               \
        List_t *const pxConstList = (pxList);                                       \
        (pxConstList)->pxIndex = (pxConstList)->pxIndex->pxNext;                    \
        if ((void *)(pxConstList)->pxIndex == (void *)(&((pxconstList)->xListEnd))) \
        {                                                                           \
            (pxConstList)->pxIndex = (pxConstList)->pxIndex->pxNext;                \
        }                                                                           \
        (pxTCB) = (pxConstList)->pxIndex->pvOwner;                                  \
    }

#define listGET_OWNER_OF_HEAD_ENTRY(pxList)     ((&((pxList)->pxListEnd))->pxNext->pvOwner)
//节点是否在链表中
#define listIS_CONTAINED_WITHIN(pxList,pxListItem)  (((pxListItem)->pxContainer == (pxList)) ? (pdTRUE) : (pdFALSE))
//节点指向的链表
#define listLIST_ITME_CONTAINER(pxListItem) ((pxListItem)->pxContainer)
//链表是否初始化
#define listLIST_IS_INITIALISED(pxList)     ((pxList)->xListEnd.xItemValue == portMAX_DELAY)