FreeRTOS之链表关键数据结构和函数操作接口-1

FreeRTOS之链表操作相关接口

[1 FreeRTOS源码下载地址](#1 FreeRTOS源码下载地址)
[2 任务控制块TCB](#2 任务控制块TCB)
- [2.1 任务控制块TCB](#2.1 任务控制块TCB)
- - [2.1.1 任务控制块的关键成员](#2.1.1 任务控制块的关键成员)
  - [2.1.2 TCB 的核心作用](#2.1.2 TCB 的核心作用)
- [2.2 ListItem_t](#2.2 ListItem_t)
- [2.3 List_t](#2.3 List_t)
[3 函数接口](#3 函数接口)
- [3.1 vListInitialise](#3.1 vListInitialise)
- [3.2 vListInitialiseItem](#3.2 vListInitialiseItem)

1 FreeRTOS源码下载地址

https://www.freertos.org/

2 任务控制块TCB

2.1 任务控制块TCB

2.1.1 任务控制块的关键成员

c 复制代码

/*
 * Task control block.  A task control block (TCB) is allocated for each task,
 * and stores task state information, including a pointer to the task's context
 * (the task's run time environment, including register values)
 */
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. */

    #if ( portUSING_MPU_WRAPPERS == 1 )
        xMPU_SETTINGS xMPUSettings; /**< The MPU settings are defined as part of the port layer.  THIS MUST BE THE SECOND MEMBER OF THE TCB STRUCT. */
    #endif

    #if ( configUSE_CORE_AFFINITY == 1 ) && ( configNUMBER_OF_CORES > 1 )
        UBaseType_t uxCoreAffinityMask; /**< Used to link the task to certain cores.  UBaseType_t must have greater than or equal to the number of bits as configNUMBER_OF_CORES. */
    #endif

    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 ). */
    ListItem_t xEventListItem;                  /**< Used to reference a task from an event list. */
    UBaseType_t uxPriority;                     /**< The priority of the task.  0 is the lowest priority. */
    StackType_t * pxStack;                      /**< Points to the start of the stack. */
    #if ( configNUMBER_OF_CORES > 1 )
        volatile BaseType_t xTaskRunState;      /**< Used to identify the core the task is running on, if the task is running. Otherwise, identifies the task's state - not running or yielding. */
        UBaseType_t uxTaskAttributes;           /**< Task's attributes - currently used to identify the idle tasks. */
    #endif
    char pcTaskName[ configMAX_TASK_NAME_LEN ]; /**< Descriptive name given to the task when created.  Facilitates debugging only. */

    #if ( configUSE_TASK_PREEMPTION_DISABLE == 1 )
        BaseType_t xPreemptionDisable; /**< Used to prevent the task from being preempted. */
    #endif

    #if ( ( portSTACK_GROWTH > 0 ) || ( configRECORD_STACK_HIGH_ADDRESS == 1 ) )
        StackType_t * pxEndOfStack; /**< Points to the highest valid address for the stack. */
    #endif

    #if ( portCRITICAL_NESTING_IN_TCB == 1 )
        UBaseType_t uxCriticalNesting; /**< Holds the critical section nesting depth for ports that do not maintain their own count in the port layer. */
    #endif

    #if ( configUSE_TRACE_FACILITY == 1 )
        UBaseType_t uxTCBNumber;  /**< Stores a number that increments each time a TCB is created.  It allows debuggers to determine when a task has been deleted and then recreated. */
        UBaseType_t uxTaskNumber; /**< Stores a number specifically for use by third party trace code. */
    #endif

    #if ( configUSE_MUTEXES == 1 )
        UBaseType_t uxBasePriority; /**< The priority last assigned to the task - used by the priority inheritance mechanism. */
        UBaseType_t uxMutexesHeld;
    #endif

    #if ( configUSE_APPLICATION_TASK_TAG == 1 )
        TaskHookFunction_t pxTaskTag;
    #endif

    #if ( configNUM_THREAD_LOCAL_STORAGE_POINTERS > 0 )
        void * pvThreadLocalStoragePointers[ configNUM_THREAD_LOCAL_STORAGE_POINTERS ];
    #endif

    #if ( configGENERATE_RUN_TIME_STATS == 1 )
        configRUN_TIME_COUNTER_TYPE ulRunTimeCounter; /**< Stores the amount of time the task has spent in the Running state. */
    #endif

    #if ( configUSE_C_RUNTIME_TLS_SUPPORT == 1 )
        configTLS_BLOCK_TYPE xTLSBlock; /**< Memory block used as Thread Local Storage (TLS) Block for the task. */
    #endif

    #if ( configUSE_TASK_NOTIFICATIONS == 1 )
        volatile uint32_t ulNotifiedValue[ configTASK_NOTIFICATION_ARRAY_ENTRIES ];
        volatile uint8_t ucNotifyState[ configTASK_NOTIFICATION_ARRAY_ENTRIES ];
    #endif

    /* See the comments in FreeRTOS.h with the definition of
     * tskSTATIC_AND_DYNAMIC_ALLOCATION_POSSIBLE. */
    #if ( tskSTATIC_AND_DYNAMIC_ALLOCATION_POSSIBLE != 0 )
        uint8_t ucStaticallyAllocated; /**< Set to pdTRUE if the task is a statically allocated to ensure no attempt is made to free the memory. */
    #endif

    #if ( INCLUDE_xTaskAbortDelay == 1 )
        uint8_t ucDelayAborted;
    #endif

    #if ( configUSE_POSIX_ERRNO == 1 )
        int iTaskErrno;
    #endif
} tskTCB;

2.1.2 TCB 的核心作用

TCB 是 FreeRTOS 任务的 "数字身份证"，通过整合栈信息、优先级、状态链表、同步机制等关键数据，实现了以下核心功能：

任务调度：操作系统通过uxPriority和xStateListItem选择下一个运行的任务；
上下文切换：依赖pxTopOfStack保存 / 恢复任务的运行环境；
任务同步：通过xEventListItem和任务通知成员实现任务间的事件交互；
内存与安全管理：通过 MPU 配置、栈溢出检测、临界区控制确保任务安全运行；
可扩展性：条件编译支持按需裁剪功能，适配从微控制器到多核处理器的各类场景。

2.2 ListItem_t

configLIST_VOLATILE TickType_t xItemValue;，节点的排序依据，通常存储任务的优先级、超时时间（如xTaskDelay()的延时值）等。
- FreeRTOS 通过该值对链表进行升序排序
  - 就绪任务链表按优先级（uxPriority）排序，高优先级任务排在前面；
  - 延时任务链表按唤醒时间（当前时间 + 延时值）排序，最早唤醒的任务排在最前。
双向链表指针，分别指向前驱节点和后继节点，形成双向链表结构。
- struct xLIST_ITEM * configLIST_VOLATILE pxNext;
- struct xLIST_ITEM * configLIST_VOLATILE pxPrevious;
void * pvOwner;，指向包含该链表节点的对象（通常是任务控制块TCB）。通过链表节点快速定位到所属任务。
struct xLIST * configLIST_VOLATILE pxContainer;，指向当前节点所在的链表（xLIST结构体）。

c 复制代码

/*
 * Definition of the only type of object that a list can contain.
 */
struct xLIST;
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. */
    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;

2.3 List_t

这个结构体是 FreeRTOS 内核中用于管理链表的核心数据结构xLIST。链表在 FreeRTOS 中被广泛用于任务调度、事件管理、资源分配等场景（如就绪任务链表、延时任务链表、信号量等待链表等）。

configLIST_VOLATILE UBaseType_t uxNumberOfItems;，记录链表中节点数量。
ListItem_t * configLIST_VOLATILE pxIndex;，用于迭代访问链表节点（支持循环遍历）。
MiniListItem_t xListEnd;，特殊节点，始终位于链表尾部，作为遍历终止标记。

c 复制代码

/*
 * Definition of the type of queue used by the scheduler.
 */
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;
    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 (). */
    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;

3 函数接口

3.1 vListInitialise

pxList->pxIndex = ( ListItem_t * ) &( pxList->xListEnd );，将遍历指针pxIndex指向哨兵节点xListEnd。空链表中没有有效节点，pxIndex指向尾部标记，确保首次遍历时能正确定位到第一个有效节点。
pxList->xListEnd.xItemValue = portMAX_DELAY;，将哨兵节点的xItemValue设为最大值（通常是0xFFFFFFFF）。在插入节点时，按xItemValue升序排列，哨兵节点的值最大，因此始终位于链表尾部，作为遍历终止标记。
pxList->xListEnd.pxNext = ( ListItem_t * ) &( pxList->xListEnd );，让哨兵节点的pxNext和pxPrevious都指向自身，形成自循环。
pxList->xListEnd.pxPrevious = ( ListItem_t * ) &( pxList->xListEnd );，让哨兵节点的pxNext和pxPrevious都指向自身，形成自循环。
pxList->uxNumberOfItems = ( UBaseType_t ) 0U;，将链表长度计数器置为 0，表示链表中没有有效节点。

c 复制代码

void vListInitialise( List_t * const pxList )
{
    traceENTER_vListInitialise( pxList );

    /* The list structure contains a list item which is used to mark the
     * end of the list.  To initialise the list the list end is inserted
     * as the only list entry. */
    pxList->pxIndex = ( ListItem_t * ) &( pxList->xListEnd );

    listSET_FIRST_LIST_ITEM_INTEGRITY_CHECK_VALUE( &( pxList->xListEnd ) );

    /* The list end value is the highest possible value in the list to
     * ensure it remains at the end of the list. */
    pxList->xListEnd.xItemValue = portMAX_DELAY;

    /* The list end next and previous pointers point to itself so we know
     * when the list is empty. */
    pxList->xListEnd.pxNext = ( ListItem_t * ) &( pxList->xListEnd );
    pxList->xListEnd.pxPrevious = ( ListItem_t * ) &( pxList->xListEnd );

    /* Initialize the remaining fields of xListEnd when it is a proper ListItem_t */
    #if ( configUSE_MINI_LIST_ITEM == 0 )
    {
        pxList->xListEnd.pvOwner = NULL;
        pxList->xListEnd.pxContainer = NULL;
        listSET_SECOND_LIST_ITEM_INTEGRITY_CHECK_VALUE( &( pxList->xListEnd ) );
    }
    #endif

    pxList->uxNumberOfItems = ( UBaseType_t ) 0U;

    /* Write known values into the list if
     * configUSE_LIST_DATA_INTEGRITY_CHECK_BYTES is set to 1. */
    listSET_LIST_INTEGRITY_CHECK_1_VALUE( pxList );
    listSET_LIST_INTEGRITY_CHECK_2_VALUE( pxList );

    traceRETURN_vListInitialise();
}

3.2 vListInitialiseItem

c 复制代码

void vListInitialiseItem( ListItem_t * const pxItem )
{
    traceENTER_vListInitialiseItem( pxItem );

    /* Make sure the list item is not recorded as being on a list. */
    pxItem->pxContainer = NULL;

    /* Write known values into the list item if
     * configUSE_LIST_DATA_INTEGRITY_CHECK_BYTES is set to 1. */
    listSET_FIRST_LIST_ITEM_INTEGRITY_CHECK_VALUE( pxItem );
    listSET_SECOND_LIST_ITEM_INTEGRITY_CHECK_VALUE( pxItem );

    traceRETURN_vListInitialiseItem();
}