freeRTOS LIST代碼解讀 （二）

freeRTOS 採用的是雙向鏈表

頭文件定義內容

其他宏定義

configLIST_VOLATILE 可以不用定義，因爲結構體成員的修改只在臨界區內進行修改。所以不需要定義爲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 */

鏈表測試代碼定義

鏈表測試代碼,用於測試鏈表和鏈表節點的數據是否被破環，通過在鏈表結構體和節點結構體的頭和尾添加兩個指定的成員變量。通過監測成員變量是否被改變，來測試代碼是否正常運行。

/* 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 */

鏈表結構體

鏈表節點結構體

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. */
	//定義在鏈表節點中的值，用於鏈表節點排序
	configLIST_VOLATILE TickType_t xItemValue;			/*< The value being listed.  In most cases this is used to sort the list in descending order. */
	//鏈表下一個節點的指針
	struct xLIST_ITEM * configLIST_VOLATILE pxNext;		/*< Pointer to the next ListItem_t in the list. */
	//鏈表上一個節點的指針
	struct xLIST_ITEM * configLIST_VOLATILE pxPrevious;	/*< Pointer to the previous ListItem_t in the list. */
	//節點指向的TCB塊
	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. */
	//節點所處的鏈表指針
	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. */

最小的鏈表節點結構體，用於作爲鏈表的頭指針

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;
};

鏈表結構體

typedef struct xLIST
{
	listFIRST_LIST_INTEGRITY_CHECK_VALUE				/*< Set to a known value if configUSE_LIST_DATA_INTEGRITY_CHECK_BYTES is set to 1. */
	//鏈表的節點個數
	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 (). */
	//相當於鏈表的頭節點，但是節點中不包括任何數據
	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;

宏定義函數

//設置節點的內容
#define listSET_LIST_ITEM_OWNER(pxListItem, pxOwner) ((pxListItem)->pvOwner = (void *)(pxOwner))
//獲取節點的內容
#define listGET_LIST_TIEM_OWNER(pxListItem) ((pxListItem)->pvwner)
//設置節點的xItemValue
#define listSET_LIST_ITEM_VALUE(pxListItem, xValue) ((pxListItem)->xItemValue = (xValue))
//獲取節點的參數值
#define listGET_LIST_ITEM_VALUE(pxListItem) ((pxListItem)->xItemValue)
//獲取鏈表的頭節點參數值
#define listGET_ITEM_VALUE_OF_HEAD_ENTRY(pxList) (((pxList)->xListEnd).xItemValue)
//獲取鏈表的頭節點指針
#define listGET_HEAD_ENTRY(pxList) (((pxList)->xListEnd).pxNext)
//獲取下一個節點的指針
#define listGET_NEXT(pxListItem) ((pxListItem)->pxNext)
//獲取鏈表的MARKER 節點
#define listGET_END_MARKER(pxList) ((ListItem_t const *)(&((pxList)->xListEnd)))
//鏈表是否爲空
#define listLIST_IS_EMPTY(pxList) (((pxList)->uxNumberOfItems == (UBaseType_t)0) ? pdTRUE : pdFALSE)
//鏈表的長度
#define listCURRENT_LIST_LENGTH(pxList) ((pxList)->uxNumberOfItems)
//鏈表的內容
#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)
//節點是否在鏈表中
#define listIS_CONTAINED_WITHIN(pxList,pxListItem)  (((pxListItem)->pxContainer == (pxList)) ? (pdTRUE) : (pdFALSE))
//節點指向的鏈表
#define listLIST_ITME_CONTAINER(pxListItem) ((pxListItem)->pxContainer)
//鏈表是否初始化
#define listLIST_IS_INITIALISED(pxList)     ((pxList)->xListEnd.xItemValue == portMAX_DELAY)