本文依据的freeRTOS版本是V9.0.0版本，本文将分析链表文件的结构体，主要根据其list.c和list.h文件;
/*
* FreeRTOS Kernel V9.0.0a
* Copyright (C) 2018 Amazon.com, Inc. or its affiliates. All Rights Reserved.
*
* Permission is hereby granted, free of charge, to any person obtaining a copy of
* this software and associated documentation files (the "Software"), to deal in
* the Software without restriction, including without limitation the rights to
* use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
* the Software, and to permit persons to whom the Software is furnished to do so,
* subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in all
* copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
* FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
* COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
* IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*
* http://www.FreeRTOS.org
* http://aws.amazon.com/freertos
*
* 1 tab == 4 spaces!
*/
/*
* This is the list implementation used by the scheduler. While it is tailored
* heavily for the schedulers needs, it is also available for use by
* application code.
*
* list_ts can only store pointers to list_item_ts. Each ListItem_t contains a
* numeric value (xItemValue). Most of the time the lists are sorted in
* descending item value order.
*
* Lists are created already containing one list item. The value of this
* item is the maximum possible that can be stored, it is therefore always at
* the end of the list and acts as a marker. The list member pxHead always
* points to this marker - even though it is at the tail of the list. This
* is because the tail contains a wrap back pointer to the true head of
* the list.
*
* In addition to it's value, each list item contains a pointer to the next
* item in the list (pxNext), a pointer to the list it is in (pxContainer)
* and a pointer to back to the object that contains it. These later two
* pointers are included for efficiency of list manipulation. There is
* effectively a two way link between the object containing the list item and
* the list item itself.
*
*
* \page ListIntroduction List Implementation
* \ingroup FreeRTOSIntro
*/
#ifndef INC_FREERTOS_H
#error FreeRTOS.h must be included before list.h
#endif
#ifndef LIST_H
#define LIST_H
/*
* 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 */
#ifdef __cplusplus
extern "C" {
#endif
/* 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 */
/*
* Definition of the only type of object that a list can contain.
*/
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 descending 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. */
void * configLIST_VOLATILE pvContainer; /*< 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. */
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;
};
typedef struct xMINI_LIST_ITEM MiniListItem_t;
/*
* 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;
/*
* Access macro to set the owner of a list item. The owner of a list item
* is the object (usually a TCB) that contains the list item.
*
* \page listSET_LIST_ITEM_OWNER listSET_LIST_ITEM_OWNER
* \ingroup LinkedList
*/
#define listSET_LIST_ITEM_OWNER( pxListItem, pxOwner ) ( ( pxListItem )->pvOwner = ( void * ) ( pxOwner ) )
/*
* Access macro to get the owner of a list item. The owner of a list item
* is the object (usually a TCB) that contains the list item.
*
* \page listSET_LIST_ITEM_OWNER listSET_LIST_ITEM_OWNER
* \ingroup LinkedList
*/
#define listGET_LIST_ITEM_OWNER( pxListItem ) ( ( pxListItem )->pvOwner )
/*
* Access macro to set the value of the list item. In most cases the value is
* used to sort the list in descending order.
*
* \page listSET_LIST_ITEM_VALUE listSET_LIST_ITEM_VALUE
* \ingroup LinkedList
*/
#define listSET_LIST_ITEM_VALUE( pxListItem, xValue ) ( ( pxListItem )->xItemValue = ( xValue ) )
/*
* Access macro to retrieve the value of the list item. The value can
* represent anything - for example the priority of a task, or the time at
* which a task should be unblocked.
*
* \page listGET_LIST_ITEM_VALUE listGET_LIST_ITEM_VALUE
* \ingroup LinkedList
*/
#define listGET_LIST_ITEM_VALUE( pxListItem ) ( ( pxListItem )->xItemValue )
/*
* Access macro to retrieve the value of the list item at the head of a given
* list.
*
* \page listGET_LIST_ITEM_VALUE listGET_LIST_ITEM_VALUE
* \ingroup LinkedList
*/
#define listGET_ITEM_VALUE_OF_HEAD_ENTRY( pxList ) ( ( ( pxList )->xListEnd ).pxNext->xItemValue )
/*
* Return the list item at the head of the list.
*
* \page listGET_HEAD_ENTRY listGET_HEAD_ENTRY
* \ingroup LinkedList
*/
#define listGET_HEAD_ENTRY( pxList ) ( ( ( pxList )->xListEnd ).pxNext )
/*
* Return the list item at the head of the list.
*
* \page listGET_NEXT listGET_NEXT
* \ingroup LinkedList
*/
#define listGET_NEXT( pxListItem ) ( ( pxListItem )->pxNext )
/*
* Return the list item that marks the end of the list
*
* \page listGET_END_MARKER listGET_END_MARKER
* \ingroup LinkedList
*/
#define listGET_END_MARKER( pxList ) ( ( ListItem_t const * ) ( &( ( pxList )->xListEnd ) ) )
/*
* Access macro to determine if a list contains any items. The macro will
* only have the value true if the list is empty.
*
* \page listLIST_IS_EMPTY listLIST_IS_EMPTY
* \ingroup LinkedList
*/
#define listLIST_IS_EMPTY( pxList ) ( ( BaseType_t ) ( ( pxList )->uxNumberOfItems == ( UBaseType_t ) 0 ) )
/*
* Access macro to return the number of items in the list.
*/
#define listCURRENT_LIST_LENGTH( pxList ) ( ( pxList )->uxNumberOfItems )
/*
* Access function to obtain the owner of the next entry in a list.
*
* The list member pxIndex is used to walk through a list. Calling
* listGET_OWNER_OF_NEXT_ENTRY increments pxIndex to the next item in the list
* and returns that entry's pxOwner parameter. Using multiple calls to this
* function it is therefore possible to move through every item contained in
* a list.
*
* The pxOwner parameter of a list item is a pointer to the object that owns
* the list item. In the scheduler this is normally a task control block.
* The pxOwner parameter effectively creates a two way link between the list
* item and its owner.
*
* @param pxTCB pxTCB is set to the address of the owner of the next list item.
* @param pxList The list from which the next item owner is to be returned.
*
* \page listGET_OWNER_OF_NEXT_ENTRY listGET_OWNER_OF_NEXT_ENTRY
* \ingroup LinkedList
*/
#define listGET_OWNER_OF_NEXT_ENTRY( pxTCB, pxList ) \
{ \
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 )->pxIndex->pxNext; \
} \
( pxTCB ) = ( pxConstList )->pxIndex->pvOwner; \
}
/*
* Access function to obtain the owner of the first entry in a list. Lists
* are normally sorted in ascending item value order.
*
* This function returns the pxOwner member of the first item in the list.
* The pxOwner parameter of a list item is a pointer to the object that owns
* the list item. In the scheduler this is normally a task control block.
* The pxOwner parameter effectively creates a two way link between the list
* item and its owner.
*
* @param pxList The list from which the owner of the head item is to be
* returned.
*
* \page listGET_OWNER_OF_HEAD_ENTRY listGET_OWNER_OF_HEAD_ENTRY
* \ingroup LinkedList
*/
#define listGET_OWNER_OF_HEAD_ENTRY( pxList ) ( (&( ( pxList )->xListEnd ))->pxNext->pvOwner )
/*
* Check to see if a list item is within a list. The list item maintains a
* "container" pointer that points to the list it is in. All this macro does
* is check to see if the container and the list match.
*
* @param pxList The list we want to know if the list item is within.
* @param pxListItem The list item we want to know if is in the list.
* @return pdTRUE if the list item is in the list, otherwise pdFALSE.
*/
#define listIS_CONTAINED_WITHIN( pxList, pxListItem ) ( ( BaseType_t ) ( ( pxListItem )->pvContainer == ( void * ) ( pxList ) ) )
/*
* Return the list a list item is contained within (referenced from).
*
* @param pxListItem The list item being queried.
* @return A pointer to the List_t object that references the pxListItem
*/
#define listLIST_ITEM_CONTAINER( pxListItem ) ( ( pxListItem )->pvContainer )
/*
* This provides a crude means of knowing if a list has been initialised, as
* pxList->xListEnd.xItemValue is set to portMAX_DELAY by the vListInitialise()
* function.
*/
#define listLIST_IS_INITIALISED( pxList ) ( ( pxList )->xListEnd.xItemValue == portMAX_DELAY )
/*
* Must be called before a list is used! This initialises all the members
* of the list structure and inserts the xListEnd item into the list as a
* marker to the back of the list.
*
* @param pxList Pointer to the list being initialised.
*
* \page vListInitialise vListInitialise
* \ingroup LinkedList
*/
void vListInitialise( List_t * const pxList ) PRIVILEGED_FUNCTION;
/*
* Must be called before a list item is used. This sets the list container to
* null so the item does not think that it is already contained in a list.
*
* @param pxItem Pointer to the list item being initialised.
*
* \page vListInitialiseItem vListInitialiseItem
* \ingroup LinkedList
*/
void vListInitialiseItem( ListItem_t * const pxItem ) PRIVILEGED_FUNCTION;
/*
* Insert a list item into a list. The item will be inserted into the list in
* a position determined by its item value (descending item value order).
*
* @param pxList The list into which the item is to be inserted.
*
* @param pxNewListItem The item that is to be placed in the list.
*
* \page vListInsert vListInsert
* \ingroup LinkedList
*/
void vListInsert( List_t * const pxList, ListItem_t * const pxNewListItem ) PRIVILEGED_FUNCTION;
/*
* Insert a list item into a list. The item will be inserted in a position
* such that it will be the last item within the list returned by multiple
* calls to listGET_OWNER_OF_NEXT_ENTRY.
*
* The list member pxIndex is used to walk through a list. Calling
* listGET_OWNER_OF_NEXT_ENTRY increments pxIndex to the next item in the list.
* Placing an item in a list using vListInsertEnd effectively places the item
* in the list position pointed to by pxIndex. This means that every other
* item within the list will be returned by listGET_OWNER_OF_NEXT_ENTRY before
* the pxIndex parameter again points to the item being inserted.
*
* @param pxList The list into which the item is to be inserted.
*
* @param pxNewListItem The list item to be inserted into the list.
*
* \page vListInsertEnd vListInsertEnd
* \ingroup LinkedList
*/
void vListInsertEnd( List_t * const pxList, ListItem_t * const pxNewListItem ) PRIVILEGED_FUNCTION;
/*
* Remove an item from a list. The list item has a pointer to the list that
* it is in, so only the list item need be passed into the function.
*
* @param uxListRemove The item to be removed. The item will remove itself from
* the list pointed to by it's pxContainer parameter.
*
* @return The number of items that remain in the list after the list item has
* been removed.
*
* \page uxListRemove uxListRemove
* \ingroup LinkedList
*/
UBaseType_t uxListRemove( ListItem_t * const pxItemToRemove ) PRIVILEGED_FUNCTION;
#ifdef __cplusplus
}
#endif
#endif
上面的代码是freeRTOS v9.0.0的list.h文件，上面的文件经过简化如下，下面展示的是数据结构：
struct xLIST_ITEM
{
configLIST_VOLATILE TickType_t xItemValue; /*< The value being listed. In most cases this is used to sort the list in descending 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. */
void * configLIST_VOLATILE pvContainer; /*< Pointer to the list in which this list item is placed (if any). */
};
typedef struct xLIST_ITEM ListItem_t; /* For some reason lint wants this as two separate definitions. */
struct xMINI_LIST_ITEM
{
configLIST_VOLATILE TickType_t xItemValue;
struct xLIST_ITEM * configLIST_VOLATILE pxNext;
struct xLIST_ITEM * configLIST_VOLATILE pxPrevious;
};
typedef struct xMINI_LIST_ITEM MiniListItem_t;
/*
* Definition of the type of queue used by the scheduler.
*/
typedef struct xLIST
{
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. */
} List_t;
list文件中比较主要的几个函数如下（初始化、插入和删除）：
void vListInitialise( List_t * const pxList ) PRIVILEGED_FUNCTION;
void vListInitialiseItem( ListItem_t * const pxItem ) PRIVILEGED_FUNCTION;
void vListInsert( List_t * const pxList, ListItem_t * const pxNewListItem ) PRIVILEGED_FUNCTION;
void vListInsertEnd( List_t * const pxList, ListItem_t * const pxNewListItem ) PRIVILEGED_FUNCTION;
UBaseType_t uxListRemove( ListItem_t * const pxItemToRemove ) PRIVILEGED_FUNCTION;
根据list头文件我们可以看到其链表是双向链表，其数据结构的组织形式如下所示：
ListItem_t：
List_t：
MiniListItem_t：
list.c文件如下：
/*
* FreeRTOS Kernel V9.0.0a
* Copyright (C) 2018 Amazon.com, Inc. or its affiliates. All Rights Reserved.
*
* Permission is hereby granted, free of charge, to any person obtaining a copy of
* this software and associated documentation files (the "Software"), to deal in
* the Software without restriction, including without limitation the rights to
* use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
* the Software, and to permit persons to whom the Software is furnished to do so,
* subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in all
* copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
* FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
* COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
* IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*
* http://www.FreeRTOS.org
* http://aws.amazon.com/freertos
*
* 1 tab == 4 spaces!
*/
#include <stdlib.h>
#include "FreeRTOS.h"
#include "list.h"
/*-----------------------------------------------------------
* PUBLIC LIST API documented in list.h
*----------------------------------------------------------*/
void vListInitialise( List_t * const 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 ); /*lint !e826 !e740 The mini list structure is used as the list end to save RAM. This is checked and valid. */
/* 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 ); /*lint !e826 !e740 The mini list structure is used as the list end to save RAM. This is checked and valid. */
pxList->xListEnd.pxPrevious = ( ListItem_t * ) &( pxList->xListEnd );/*lint !e826 !e740 The mini list structure is used as the list end to save RAM. This is checked and valid. */
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 );
}
/*-----------------------------------------------------------*/
void vListInitialiseItem( ListItem_t * const pxItem )
{
/* Make sure the list item is not recorded as being on a list. */
pxItem->pvContainer = 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 );
}
/*-----------------------------------------------------------*/
void vListInsertEnd( List_t * const pxList, ListItem_t * const pxNewListItem )
{
ListItem_t * const pxIndex = pxList->pxIndex;
/* Only effective when configASSERT() is also defined, these tests may catch
the list data structures being overwritten in memory. They will not catch
data errors caused by incorrect configuration or use of FreeRTOS. */
listTEST_LIST_INTEGRITY( pxList );
listTEST_LIST_ITEM_INTEGRITY( pxNewListItem );
/* Insert a new list item into pxList, but rather than sort the list,
makes the new list item the last item to be removed by a call to
listGET_OWNER_OF_NEXT_ENTRY(). */
pxNewListItem->pxNext = pxIndex;
pxNewListItem->pxPrevious = pxIndex->pxPrevious;
/* Only used during decision coverage testing. */
mtCOVERAGE_TEST_DELAY();
pxIndex->pxPrevious->pxNext = pxNewListItem;
pxIndex->pxPrevious = pxNewListItem;
/* Remember which list the item is in. */
pxNewListItem->pvContainer = ( void * ) pxList;
( pxList->uxNumberOfItems )++;
}
/*-----------------------------------------------------------*/
void vListInsert( List_t * const pxList, ListItem_t * const pxNewListItem )
{
ListItem_t *pxIterator;
const TickType_t xValueOfInsertion = pxNewListItem->xItemValue;
/* Only effective when configASSERT() is also defined, these tests may catch
the list data structures being overwritten in memory. They will not catch
data errors caused by incorrect configuration or use of FreeRTOS. */
listTEST_LIST_INTEGRITY( pxList );
listTEST_LIST_ITEM_INTEGRITY( pxNewListItem );
/* Insert the new list item into the list, sorted in xItemValue order.
If the list already contains a list item with the same item value then the
new list item should be placed after it. This ensures that TCB's which are
stored in ready lists (all of which have the same xItemValue value) get a
share of the CPU. However, if the xItemValue is the same as the back marker
the iteration loop below will not end. Therefore the value is checked
first, and the algorithm slightly modified if necessary. */
if( xValueOfInsertion == portMAX_DELAY )
{
pxIterator = pxList->xListEnd.pxPrevious;
}
else
{
/* *** NOTE ***********************************************************
If you find your application is crashing here then likely causes are
listed below. In addition see http://www.freertos.org/FAQHelp.html for
more tips, and ensure configASSERT() is defined!
http://www.freertos.org/a00110.html#configASSERT
1) Stack overflow -
see http://www.freertos.org/Stacks-and-stack-overflow-checking.html
2) Incorrect interrupt priority assignment, especially on Cortex-M
parts where numerically high priority values denote low actual
interrupt priorities, which can seem counter intuitive. See
http://www.freertos.org/RTOS-Cortex-M3-M4.html and the definition
of configMAX_SYSCALL_INTERRUPT_PRIORITY on
http://www.freertos.org/a00110.html
3) Calling an API function from within a critical section or when
the scheduler is suspended, or calling an API function that does
not end in "FromISR" from an interrupt.
4) Using a queue or semaphore before it has been initialised or
before the scheduler has been started (are interrupts firing
before vTaskStartScheduler() has been called?).
**********************************************************************/
for( pxIterator = ( ListItem_t * ) &( pxList->xListEnd ); pxIterator->pxNext->xItemValue <= xValueOfInsertion; pxIterator = pxIterator->pxNext ) /*lint !e826 !e740 The mini list structure is used as the list end to save RAM. This is checked and valid. */
{
/* There is nothing to do here, just iterating to the wanted
insertion position. */
}
}
pxNewListItem->pxNext = pxIterator->pxNext;
pxNewListItem->pxNext->pxPrevious = pxNewListItem;
pxNewListItem->pxPrevious = pxIterator;
pxIterator->pxNext = pxNewListItem;
/* Remember which list the item is in. This allows fast removal of the
item later. */
pxNewListItem->pvContainer = ( void * ) pxList;
( pxList->uxNumberOfItems )++;
}
/*-----------------------------------------------------------*/
UBaseType_t uxListRemove( ListItem_t * const pxItemToRemove )
{
/* The list item knows which list it is in. Obtain the list from the list
item. */
List_t * const pxList = ( List_t * ) pxItemToRemove->pvContainer;
pxItemToRemove->pxNext->pxPrevious = pxItemToRemove->pxPrevious;
pxItemToRemove->pxPrevious->pxNext = pxItemToRemove->pxNext;
/* Only used during decision coverage testing. */
mtCOVERAGE_TEST_DELAY();
/* Make sure the index is left pointing to a valid item. */
if( pxList->pxIndex == pxItemToRemove )
{
pxList->pxIndex = pxItemToRemove->pxPrevious;
}
else
{
mtCOVERAGE_TEST_MARKER();
}
pxItemToRemove->pvContainer = NULL;
( pxList->uxNumberOfItems )--;
return pxList->uxNumberOfItems;
}
/*-----------------------------------------------------------*/
void vListInitialise( List_t * const pxList )
{
pxList->pxIndex = ( ListItem_t * ) &( pxList->xListEnd );
pxList->xListEnd.xItemValue = portMAX_DELAY;
pxList->xListEnd.pxNext = ( ListItem_t * ) &( pxList->xListEnd );
pxList->xListEnd.pxPrevious = ( ListItem_t * ) &( pxList->xListEnd );
pxList->uxNumberOfItems = ( UBaseType_t ) 0U;
}
其对应的图示：
- void vListInsertEnd( List_t * const pxList, ListItem_t * const pxNewListItem )
{
ListItem_t * const pxIndex = pxList->pxIndex;
pxNewListItem->pxNext = pxIndex; //①
pxNewListItem->pxPrevious = pxIndex->pxPrevious; //②
pxIndex->pxPrevious->pxNext = pxNewListItem; //③
pxIndex->pxPrevious = pxNewListItem; //④
/* 记住该节点所在的链表 */
pxNewListItem->pvContainer = ( void * ) pxList; //⑤
/* 链表节点计数器++ */
( pxList->uxNumberOfItems )++; //⑥
}
其示意图如下所示：
void vListInsert( List_t * const pxList, ListItem_t * const pxNewListItem )
{
ListItem_t *pxIterator;
const TickType_t xValueOfInsertion = pxNewListItem->xItemValue;
if( xValueOfInsertion == portMAX_DELAY )
{
pxIterator = pxList->xListEnd.pxPrevious;
}
else
{
for( pxIterator = ( ListItem_t * ) &( pxList->xListEnd ); pxIterator->pxNext->xItemValue <= xValueOfInsertion; pxIterator = pxIterator->pxNext )
{
}
}
pxNewListItem->pxNext = pxIterator->pxNext; // 1
pxNewListItem->pxNext->pxPrevious = pxNewListItem; // 2
pxNewListItem->pxPrevious = pxIterator; // 3
pxIterator->pxNext = pxNewListItem; // 4
pxNewListItem->pvContainer = ( void * ) pxList; //5
( pxList->uxNumberOfItems )++; // 6
}
其示意图如下：
UBaseType_t uxListRemove( ListItem_t * const pxItemToRemove )
{
/* The list item knows which list it is in. Obtain the list from the list
item. */
List_t * const pxList = ( List_t * ) pxItemToRemove->pvContainer;
pxItemToRemove->pxNext->pxPrevious = pxItemToRemove->pxPrevious;
pxItemToRemove->pxPrevious->pxNext = pxItemToRemove->pxNext;
/* Only used during decision coverage testing. */
mtCOVERAGE_TEST_DELAY();
/* Make sure the index is left pointing to a valid item. */
if( pxList->pxIndex == pxItemToRemove )
{
pxList->pxIndex = pxItemToRemove->pxPrevious;
}
else
{
mtCOVERAGE_TEST_MARKER();
}
pxItemToRemove->pvContainer = NULL;
( pxList->uxNumberOfItems )--;
return pxList->uxNumberOfItems;
}
链表作为 C 语言中一种基础的数据结构，在freeRTOS系统中的作用非常重要，因此这一块内容必须要要完全掌握，以便深入阅读freeRTOS的内核代码。
参考资料：
《FreeRTOS内核实现与应用开发实战指南—基于野火 STM32 全系列（M3/4/7）开发板》