FreeRTOS之鏈表操作相關接口

1 FreeRTOS源碼下載地址
2 任務控制塊TCB
- 2.1 任務控制塊TCB
- - 2.1.1 任務控制塊的關鍵成員
  - 2.1.2 TCB 的核心作用
- 2.2 ListItem_t
- 2.3 List_t
3 函數接口
- 3.1 vListInitialise
- 3.2 vListInitialiseItem

1 FreeRTOS源碼下載地址

https://www.freertos.org/
在這里插入圖片描述

2 任務控制塊TCB

2.1 任務控制塊TCB

2.1.1 任務控制塊的關鍵成員

volatile StackType_t * pxTopOfStack，上下文切換的核心依賴 —— 保存 / 恢復任務運行狀態（如 CPU 寄存器值壓棧 / 出棧）。指向任務棧中 “最后一個被使用的位置”（棧頂），存儲任務當前的上下文（如寄存器值、返回地址等）。
UBaseType_t uxCoreAffinityMask，條件編譯：（configUSE_CORE_AFFINITY == 1 && configNUMBER_OF_CORES > 1）在多核系統中，指定任務可運行的核心（核心親和性）。
ListItem_t xStateListItem，將任務鏈接到 FreeRTOS 的 “狀態鏈表” 中（如就緒鏈表、阻塞鏈表、掛起鏈表）。
ListItem_t xEventListItem，將任務鏈接到 “事件等待鏈表” 中（如信號量、消息隊列、事件組的等待鏈表）。當任務調用xSemaphoreTake()、xQueueReceive()等函數等待事件時，會通過xEventListItem加入對應事件的等待鏈表，直到事件觸發（如信號量被釋放）才被移回就緒鏈表。
UBaseType_t uxPriority，存儲任務的優先級（0 為最低優先級，最大值由configMAX_PRIORITIES定義）。
StackType_t * pxStack，指向任務棧的 “起始地址”（棧的最低地址，與pxTopOfStack配合標識棧的范圍）。
- 與pxTopOfStack的關系：
  - pxStack：棧的起點（固定不變）；
  - pxTopOfStack：棧的當前頂部（隨任務運行動態變化，如函數調用時棧頂上移）。
volatile BaseType_t xTaskRunState：標識任務的運行狀態 —— 若任務正在運行，存儲其所在的核心編號；若未運行，存儲狀態（如未運行、正在讓出 CPU）。
UBaseType_t uxTaskAttributes：存儲任務的屬性，目前主要用于標識 “空閑任務”（FreeRTOS 為每個核心創建一個空閑任務，用于核心空閑時運行）。
char pcTaskName[ configMAX_TASK_NAME_LEN ]，存儲任務的名稱（字符串），僅用于調試（如通過vTaskList()打印任務列表時顯示名稱）。由configMAX_TASK_NAME_LEN定義（默認 16 字節，含終止符\0）。
UBaseType_t uxCriticalNesting，記錄任務的 “臨界區嵌套深度”（進入臨界區時加 1，退出時減 1，0 表示不在臨界區）。
UBaseType_t uxTCBNumber：存儲 TCB 的創建序號（每次創建任務時遞增），用于調試時識別任務是否被刪除后重建（刪除后重建的任務序號不同）。
UBaseType_t uxTaskNumber：供第三方跟蹤工具使用，用于任務的唯一標識和性能分析。
UBaseType_t uxBasePriority：存儲任務的 “基礎優先級”（原始優先級），用于 “優先級繼承” 機制 —— 當任務持有互斥鎖時，若被高優先級任務等待，會臨時提升到等待任務的優先級（避免優先級反轉），釋放鎖后恢復為uxBasePriority。
UBaseType_t uxMutexesHeld：記錄任務當前持有的互斥鎖數量，用于確保任務刪除時釋放所有持有的鎖（避免死鎖）。

/** 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. */#endifListItem_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. */#endifchar 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 任務的 “數字身份證”，通過整合棧信息、優先級、狀態鏈表、同步機制等關鍵數據，實現了以下核心功能：

任務調度：操作系統通過uxPriority和xStateListItem選擇下一個運行的任務；
上下文切換：依賴pxTopOfStack保存 / 恢復任務的運行環境；
任務同步：通過xEventListItem和任務通知成員實現任務間的事件交互；
內存與安全管理：通過 MPU 配置、棧溢出檢測、臨界區控制確保任務安全運行；
可擴展性：條件編譯支持按需裁剪功能，適配從微控制器到多核處理器的各類場景。

2.2 ListItem_t

configLIST_VOLATILE TickType_t xItemValue;，節點的排序依據，通常存儲任務的優先級、超時時間（如xTaskDelay()的延時值）等。
- FreeRTOS 通過該值對鏈表進行升序排序
  - 就緒任務鏈表按優先級（uxPriority）排序，高優先級任務排在前面；
  - 延時任務鏈表按喚醒時間（當前時間 + 延時值）排序，最早喚醒的任務排在最前。
雙向鏈表指針，分別指向前驅節點和后繼節點，形成雙向鏈表結構。
- struct xLIST_ITEM * configLIST_VOLATILE pxNext;
- struct xLIST_ITEM * configLIST_VOLATILE pxPrevious;
void * pvOwner;，指向包含該鏈表節點的對象（通常是任務控制塊TCB）。通過鏈表節點快速定位到所屬任務。
struct xLIST * configLIST_VOLATILE pxContainer;，指向當前節點所在的鏈表（xLIST結構體）。

/** 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

這個結構體是 FreeRTOS 內核中用于管理鏈表的核心數據結構xLIST。鏈表在 FreeRTOS 中被廣泛用于任務調度、事件管理、資源分配等場景（如就緒任務鏈表、延時任務鏈表、信號量等待鏈表等）。

configLIST_VOLATILE UBaseType_t uxNumberOfItems;，記錄鏈表中節點數量。
ListItem_t * configLIST_VOLATILE pxIndex;，用于迭代訪問鏈表節點（支持循環遍歷）。
MiniListItem_t xListEnd;，特殊節點，始終位于鏈表尾部，作為遍歷終止標記。

/** 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 函數接口

3.1 vListInitialise

pxList->pxIndex = ( ListItem_t * ) &( pxList->xListEnd );，將遍歷指針pxIndex指向哨兵節點xListEnd。空鏈表中沒有有效節點，pxIndex指向尾部標記，確保首次遍歷時能正確定位到第一個有效節點。
pxList->xListEnd.xItemValue = portMAX_DELAY;，將哨兵節點的xItemValue設為最大值（通常是0xFFFFFFFF）。在插入節點時，按xItemValue升序排列，哨兵節點的值最大，因此始終位于鏈表尾部，作為遍歷終止標記。
pxList->xListEnd.pxNext = ( ListItem_t * ) &( pxList->xListEnd );，讓哨兵節點的pxNext和pxPrevious都指向自身，形成自循環。
pxList->xListEnd.pxPrevious = ( ListItem_t * ) &( pxList->xListEnd );，讓哨兵節點的pxNext和pxPrevious都指向自身，形成自循環。
pxList->uxNumberOfItems = ( UBaseType_t ) 0U;，將鏈表長度計數器置為 0，表示鏈表中沒有有效節點。

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 ) );}#endifpxList->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

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();
}