FreeRTOS/Source/include/list.h

   1 /*
   2     FreeRTOS V6.0.5 - Copyright (C) 2010 Real Time Engineers Ltd.
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  25     This file is part of the FreeRTOS distribution.
  26
  27     FreeRTOS is free software; you can redistribute it and/or modify it under
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  52 */
  53
  54 /*
  55  * This is the list implementation used by the scheduler.  While it is tailored
  56  * heavily for the schedulers needs, it is also available for use by
  57  * application code.
  58  *
  59  * xLists can only store pointers to xListItems.  Each xListItem contains a
  60  * numeric value (xItemValue).  Most of the time the lists are sorted in
  61  * descending item value order.
  62  *
  63  * Lists are created already containing one list item.  The value of this
  64  * item is the maximum possible that can be stored, it is therefore always at
  65  * the end of the list and acts as a marker.  The list member pxHead always
  66  * points to this marker - even though it is at the tail of the list.  This
  67  * is because the tail contains a wrap back pointer to the true head of
  68  * the list.
  69  *
  70  * In addition to it's value, each list item contains a pointer to the next
  71  * item in the list (pxNext), a pointer to the list it is in (pxContainer)
  72  * and a pointer to back to the object that contains it.  These later two
  73  * pointers are included for efficiency of list manipulation.  There is
  74  * effectively a two way link between the object containing the list item and
  75  * the list item itself.
  76  *
  77  *
  78  * \page ListIntroduction List Implementation
  79  * \ingroup FreeRTOSIntro
  80  */
  81
  82 /*
  83         Changes from V4.3.1
  84
  85         + Included local const within listGET_OWNER_OF_NEXT_ENTRY() to assist
  86           compiler with optimisation.  Thanks B.R.
  87 */
  88
  89 #ifndef LIST_H
  90 #define LIST_H
  91
  92 #ifdef __cplusplus
  93 extern "C" {
  94 #endif
  95 /*
  96  * Definition of the only type of object that a list can contain.
  97  */
  98 struct xLIST_ITEM
  99 {
 100         portTickType xItemValue;                                /*< The value being listed.  In most cases this is used to sort the list in descending order. */
 101         volatile struct xLIST_ITEM * pxNext;    /*< Pointer to the next xListItem in the list. */
 102         volatile struct xLIST_ITEM * pxPrevious;/*< Pointer to the previous xListItem in the list. */
 103         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. */
 104         void * pvContainer;                                             /*< Pointer to the list in which this list item is placed (if any). */
 105 };
 106 typedef struct xLIST_ITEM xListItem;            /* For some reason lint wants this as two separate definitions. */
 107
 108 struct xMINI_LIST_ITEM
 109 {
 110         portTickType xItemValue;
 111         volatile struct xLIST_ITEM *pxNext;
 112         volatile struct xLIST_ITEM *pxPrevious;
 113 };
 114 typedef struct xMINI_LIST_ITEM xMiniListItem;
 115
 116 /*
 117  * Definition of the type of queue used by the scheduler.
 118  */
 119 typedef struct xLIST
 120 {
 121         volatile unsigned portBASE_TYPE uxNumberOfItems;
 122         volatile xListItem * pxIndex;                   /*< Used to walk through the list.  Points to the last item returned by a call to pvListGetOwnerOfNextEntry (). */
 123         volatile xMiniListItem 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. */
 124 } xList;
 125
 126 /*
 127  * Access macro to set the owner of a list item.  The owner of a list item
 128  * is the object (usually a TCB) that contains the list item.
 129  *
 130  * \page listSET_LIST_ITEM_OWNER listSET_LIST_ITEM_OWNER
 131  * \ingroup LinkedList
 132  */
 133 #define listSET_LIST_ITEM_OWNER( pxListItem, pxOwner )          ( pxListItem )->pvOwner = ( void * ) pxOwner
 134
 135 /*
 136  * Access macro to set the value of the list item.  In most cases the value is
 137  * used to sort the list in descending order.
 138  *
 139  * \page listSET_LIST_ITEM_VALUE listSET_LIST_ITEM_VALUE
 140  * \ingroup LinkedList
 141  */
 142 #define listSET_LIST_ITEM_VALUE( pxListItem, xValue )           ( pxListItem )->xItemValue = xValue
 143
 144 /*
 145  * Access macro the retrieve the value of the list item.  The value can
 146  * represent anything - for example a the priority of a task, or the time at
 147  * which a task should be unblocked.
 148  *
 149  * \page listGET_LIST_ITEM_VALUE listGET_LIST_ITEM_VALUE
 150  * \ingroup LinkedList
 151  */
 152 #define listGET_LIST_ITEM_VALUE( pxListItem )                           ( ( pxListItem )->xItemValue )
 153
 154 /*
 155  * Access macro to determine if a list contains any items.  The macro will
 156  * only have the value true if the list is empty.
 157  *
 158  * \page listLIST_IS_EMPTY listLIST_IS_EMPTY
 159  * \ingroup LinkedList
 160  */
 161 #define listLIST_IS_EMPTY( pxList )                             ( ( pxList )->uxNumberOfItems == ( unsigned portBASE_TYPE ) 0 )
 162
 163 /*
 164  * Access macro to return the number of items in the list.
 165  */
 166 #define listCURRENT_LIST_LENGTH( pxList )               ( ( pxList )->uxNumberOfItems )
 167
 168 /*
 169  * Access function to obtain the owner of the next entry in a list.
 170  *
 171  * The list member pxIndex is used to walk through a list.  Calling
 172  * listGET_OWNER_OF_NEXT_ENTRY increments pxIndex to the next item in the list
 173  * and returns that entries pxOwner parameter.  Using multiple calls to this
 174  * function it is therefore possible to move through every item contained in
 175  * a list.
 176  *
 177  * The pxOwner parameter of a list item is a pointer to the object that owns
 178  * the list item.  In the scheduler this is normally a task control block.
 179  * The pxOwner parameter effectively creates a two way link between the list
 180  * item and its owner.
 181  *
 182  * @param pxList The list from which the next item owner is to be returned.
 183  *
 184  * \page listGET_OWNER_OF_NEXT_ENTRY listGET_OWNER_OF_NEXT_ENTRY
 185  * \ingroup LinkedList
 186  */
 187 #define listGET_OWNER_OF_NEXT_ENTRY( pxTCB, pxList )                                                                    \
 188 {                                                                                                                                                                               \
 189 xList * const pxConstList = pxList;                                                                                                             \
 190         /* Increment the index to the next item and return the item, ensuring */                        \
 191         /* we don't return the marker used at the end of the list.  */                                          \
 192         ( pxConstList )->pxIndex = ( pxConstList )->pxIndex->pxNext;                                            \
 193         if( ( pxConstList )->pxIndex == ( xListItem * ) &( ( pxConstList )->xListEnd ) )        \
 194         {                                                                                                                                                                       \
 195                 ( pxConstList )->pxIndex = ( pxConstList )->pxIndex->pxNext;                                    \
 196         }                                                                                                                                                                       \
 197         pxTCB = ( pxConstList )->pxIndex->pvOwner;                                                                                      \
 198 }
 199
 200
 201 /*
 202  * Access function to obtain the owner of the first entry in a list.  Lists
 203  * are normally sorted in ascending item value order.
 204  *
 205  * This function returns the pxOwner member of the first item in the list.
 206  * The pxOwner parameter of a list item is a pointer to the object that owns
 207  * the list item.  In the scheduler this is normally a task control block.
 208  * The pxOwner parameter effectively creates a two way link between the list
 209  * item and its owner.
 210  *
 211  * @param pxList The list from which the owner of the head item is to be
 212  * returned.
 213  *
 214  * \page listGET_OWNER_OF_HEAD_ENTRY listGET_OWNER_OF_HEAD_ENTRY
 215  * \ingroup LinkedList
 216  */
 217 #define listGET_OWNER_OF_HEAD_ENTRY( pxList )  ( ( pxList->uxNumberOfItems != ( unsigned portBASE_TYPE ) 0 ) ? ( (&( pxList->xListEnd ))->pxNext->pvOwner ) : ( NULL ) )
 218
 219 /*
 220  * Check to see if a list item is within a list.  The list item maintains a
 221  * "container" pointer that points to the list it is in.  All this macro does
 222  * is check to see if the container and the list match.
 223  *
 224  * @param pxList The list we want to know if the list item is within.
 225  * @param pxListItem The list item we want to know if is in the list.
 226  * @return pdTRUE is the list item is in the list, otherwise pdFALSE.
 227  * pointer against
 228  */
 229 #define listIS_CONTAINED_WITHIN( pxList, pxListItem ) ( ( pxListItem )->pvContainer == ( void * ) pxList )
 230
 231 /*
 232  * Must be called before a list is used!  This initialises all the members
 233  * of the list structure and inserts the xListEnd item into the list as a
 234  * marker to the back of the list.
 235  *
 236  * @param pxList Pointer to the list being initialised.
 237  *
 238  * \page vListInitialise vListInitialise
 239  * \ingroup LinkedList
 240  */
 241 void vListInitialise( xList *pxList );
 242
 243 /*
 244  * Must be called before a list item is used.  This sets the list container to
 245  * null so the item does not think that it is already contained in a list.
 246  *
 247  * @param pxItem Pointer to the list item being initialised.
 248  *
 249  * \page vListInitialiseItem vListInitialiseItem
 250  * \ingroup LinkedList
 251  */
 252 void vListInitialiseItem( xListItem *pxItem );
 253
 254 /*
 255  * Insert a list item into a list.  The item will be inserted into the list in
 256  * a position determined by its item value (descending item value order).
 257  *
 258  * @param pxList The list into which the item is to be inserted.
 259  *
 260  * @param pxNewListItem The item to that is to be placed in the list.
 261  *
 262  * \page vListInsert vListInsert
 263  * \ingroup LinkedList
 264  */
 265 void vListInsert( xList *pxList, xListItem *pxNewListItem );
 266
 267 /*
 268  * Insert a list item into a list.  The item will be inserted in a position
 269  * such that it will be the last item within the list returned by multiple
 270  * calls to listGET_OWNER_OF_NEXT_ENTRY.
 271  *
 272  * The list member pvIndex is used to walk through a list.  Calling
 273  * listGET_OWNER_OF_NEXT_ENTRY increments pvIndex to the next item in the list.
 274  * Placing an item in a list using vListInsertEnd effectively places the item
 275  * in the list position pointed to by pvIndex.  This means that every other
 276  * item within the list will be returned by listGET_OWNER_OF_NEXT_ENTRY before
 277  * the pvIndex parameter again points to the item being inserted.
 278  *
 279  * @param pxList The list into which the item is to be inserted.
 280  *
 281  * @param pxNewListItem The list item to be inserted into the list.
 282  *
 283  * \page vListInsertEnd vListInsertEnd
 284  * \ingroup LinkedList
 285  */
 286 void vListInsertEnd( xList *pxList, xListItem *pxNewListItem );
 287
 288 /*
 289  * Remove an item from a list.  The list item has a pointer to the list that
 290  * it is in, so only the list item need be passed into the function.
 291  *
 292  * @param vListRemove The item to be removed.  The item will remove itself from
 293  * the list pointed to by it's pxContainer parameter.
 294  *
 295  * \page vListRemove vListRemove
 296  * \ingroup LinkedList
 297  */
 298 void vListRemove( xListItem *pxItemToRemove );
 299
 300 #ifdef __cplusplus
 301 }
 302 #endif
 303
 304 #endif
 305