freeRTOS源碼解析4--tasks.c 3

4.2.6 任務刪除--vTaskDelete

這個介面並不複雜，主要是在判斷是否要放到xTasksWaitingTermination列表裡，還是直接處理。

  1 void vTaskDelete( TaskHandle_t xTaskToDelete )
  2 {
  3     TCB_t * pxTCB;
  4     BaseType_t xDeleteTCBInIdleTask = pdFALSE;
  5     BaseType_t xTaskIsRunningOrYielding;
  6 
  7     taskENTER_CRITICAL();
  8     {
  9         /* If null is passed in here then it is the calling task that is
 10          * being deleted. */
 11         /* 如果是NULL就是刪除自己，否則是刪除其他任務 */
 12         pxTCB = prvGetTCBFromHandle( xTaskToDelete );
 13 
 14         /* Remove task from the ready/delayed list. */
 15         if( uxListRemove( &( pxTCB->xStateListItem ) ) == ( UBaseType_t ) 0 )
 16         {
 17             taskRESET_READY_PRIORITY( pxTCB->uxPriority );
 18         }
 19         else
 20         {
 21             mtCOVERAGE_TEST_MARKER();
 22         }
 23 
 24         /* Is the task waiting on an event also? */
 25         if( listLIST_ITEM_CONTAINER( &( pxTCB->xEventListItem ) ) != NULL )
 26         {
 27             ( void ) uxListRemove( &( pxTCB->xEventListItem ) );
 28         }
 29         else
 30         {
 31             mtCOVERAGE_TEST_MARKER();
 32         }
 33 
 34         /* Increment the uxTaskNumber also so kernel aware debuggers can
 35          * detect that the task lists need re-generating.  This is done before
 36          * portPRE_TASK_DELETE_HOOK() as in the Windows port that macro will
 37          * not return. */
 38         /* 這個變數是用於TRACE相關的，調試用的，先不管，以後看trace的代碼再解析 */
 39         uxTaskNumber++;
 40 
 41         /* Use temp variable as distinct sequence points for reading volatile
 42          * variables prior to a logical operator to ensure compliance with
 43          * MISRA C 2012 Rule 13.5. */
 44         /* 確定是否正在運行或正在調度到這個任務 */
 45         xTaskIsRunningOrYielding = taskTASK_IS_RUNNING_OR_SCHEDULED_TO_YIELD( pxTCB );
 46 
 47         /* If the task is running (or yielding), we must add it to the
 48          * termination list so that an idle task can delete it when it is
 49          * no longer running. */
 50         if( ( xSchedulerRunning != pdFALSE ) && ( xTaskIsRunningOrYielding != pdFALSE ) )
 51         {
 52             /* A running task or a task which is scheduled to yield is being
 53              * deleted. This cannot complete when the task is still running
 54              * on a core, as a context switch to another task is required.
 55              * Place the task in the termination list. The idle task will check
 56              * the termination list and free up any memory allocated by the
 57              * scheduler for the TCB and stack of the deleted task. */
 58             /* 看註釋，不放到終止列表中，無法刪除。需要依賴空閑任務來處理
 59              * 具體原因暫時還不清楚，看來需要閱讀更多源碼才能明白。 */
 60             vListInsertEnd( &xTasksWaitingTermination, &( pxTCB->xStateListItem ) );
 61 
 62             /* Increment the ucTasksDeleted variable so the idle task knows
 63              * there is a task that has been deleted and that it should therefore
 64              * check the xTasksWaitingTermination list. */
 65             ++uxDeletedTasksWaitingCleanUp;
 66 
 67             /* Delete the task TCB in idle task. */
 68             xDeleteTCBInIdleTask = pdTRUE;
 69 
 70             /* The pre-delete hook is primarily for the Windows simulator,
 71              * in which Windows specific clean up operations are performed,
 72              * after which it is not possible to yield away from this task -
 73              * hence xYieldPending is used to latch that a context switch is
 74              * required. */
 75             /* 只有在Windows下才有用，先不分析了 */
 76             #if ( configNUMBER_OF_CORES == 1 )
 77                 portPRE_TASK_DELETE_HOOK( pxTCB, &( xYieldPendings[ 0 ] ) );
 78             #endif
 79         }
 80         else
 81         {
 82             /* 這裡是刪除阻塞任務(pxDelayedTaskList)的(xTaskIsRunningOrYielding = pdFALSE) */
 83             --uxCurrentNumberOfTasks;
 84 
 85             /* Reset the next expected unblock time in case it referred to
 86              * the task that has just been deleted. */
 87             /* 主要用於更新最久阻塞的剩餘阻塞時間，防止最近需要運行的就是刪除的這個任務 */
 88             prvResetNextTaskUnblockTime();
 89         }
 90     }
 91     taskEXIT_CRITICAL();
 92 
 93     /* If the task is not deleting itself, call prvDeleteTCB from outside of
 94      * critical section. If a task deletes itself, prvDeleteTCB is called
 95      * from prvCheckTasksWaitingTermination which is called from Idle task. */
 96     /* 如果刪除的是當前運行的任務在空閑任務中處理，阻塞任務在這裡處理 */
 97     if( xDeleteTCBInIdleTask != pdTRUE )
 98     {
 99         prvDeleteTCB( pxTCB );
100     }
101 
102     /* Force a reschedule if it is the currently running task that has just
103      * been deleted. */
104     /* 如果刪除的是當前運行的任務，需要調度，這很明顯。 */
105     #if ( configNUMBER_OF_CORES == 1 )
106     {
107         if( xSchedulerRunning != pdFALSE )
108         {
109             if( pxTCB == pxCurrentTCB )
110             {
111                 configASSERT( uxSchedulerSuspended == 0 );
112                 taskYIELD_WITHIN_API();
113             }
114             else
115             {
116                 mtCOVERAGE_TEST_MARKER();
117             }
118         }
119     }
120     #endif /* #if ( configNUMBER_OF_CORES == 1 ) */
121 }

 1 static void prvDeleteTCB( TCB_t * pxTCB )
 2 {
 3     #if ( ( configSUPPORT_DYNAMIC_ALLOCATION == 1 ) && ( configSUPPORT_STATIC_ALLOCATION == 0 ) && ( portUSING_MPU_WRAPPERS == 0 ) )
 4     {
 5         /* The task can only have been allocated dynamically - free both
 6          * the stack and TCB. */
 7         vPortFreeStack( pxTCB->pxStack );
 8         vPortFree( pxTCB );
 9     }
10     #elif ( tskSTATIC_AND_DYNAMIC_ALLOCATION_POSSIBLE != 0 )
11     {
12         /* The task could have been allocated statically or dynamically, so
13          * check what was statically allocated before trying to free the
14          * memory. */
15         /* 按需釋放tcb和stack */
16         if( pxTCB->ucStaticallyAllocated == tskDYNAMICALLY_ALLOCATED_STACK_AND_TCB )
17         {
18             /* Both the stack and TCB were allocated dynamically, so both
19              * must be freed. */
20             vPortFreeStack( pxTCB->pxStack );
21             vPortFree( pxTCB );
22         }
23         else if( pxTCB->ucStaticallyAllocated == tskSTATICALLY_ALLOCATED_STACK_ONLY )
24         {
25             /* Only the stack was statically allocated, so the TCB is the
26              * only memory that must be freed. */
27             vPortFree( pxTCB );
28         }
29         else
30         {
31             /* Neither the stack nor the TCB were allocated dynamically, so
32              * nothing needs to be freed. */
33             configASSERT( pxTCB->ucStaticallyAllocated == tskSTATICALLY_ALLOCATED_STACK_AND_TCB );
34             mtCOVERAGE_TEST_MARKER();
35         }
36     }
37     #endif /* configSUPPORT_DYNAMIC_ALLOCATION */
38 }

 4.2.7 獲取任務狀態--eTaskGetState

這個介面可以大致看出任務在哪些情況下會處於什麼狀態。

首先是返回值的說明：

1 typedef enum
2 {
3     eRunning = 0, /* 運行態. */
4     eReady,       /* 就緒態, 任務在 ready or pending ready 列表. */
5     eBlocked,     /* 阻塞態. */
6     eSuspended,   /* 掛起態, 任務在 掛起列表, 或處於無限延遲的阻塞中. */
7     eDeleted,     /* 等待刪除. */
8     eInvalid      /* Used as an 'invalid state' value. */
9 } eTaskState;

  1 eTaskState eTaskGetState( TaskHandle_t xTask )
  2 {
  3     eTaskState eReturn;
  4     List_t const * pxStateList;
  5     List_t const * pxEventList;
  6     List_t const * pxDelayedList;
  7     List_t const * pxOverflowedDelayedList;
  8     const TCB_t * const pxTCB = xTask;
  9 
 10     configASSERT( pxTCB );
 11 
 12     #if ( configNUMBER_OF_CORES == 1 )
 13         if( pxTCB == pxCurrentTCB )
 14         {
 15             /* The task calling this function is querying its own state. */
 16             /* 當前任務是查詢的任務，則處於運行態 */
 17             eReturn = eRunning;
 18         }
 19         else
 20     #endif
 21     {
 22         taskENTER_CRITICAL();
 23         {
 24             pxStateList = listLIST_ITEM_CONTAINER( &( pxTCB->xStateListItem ) );
 25             pxEventList = listLIST_ITEM_CONTAINER( &( pxTCB->xEventListItem ) );
 26             pxDelayedList = pxDelayedTaskList;
 27             pxOverflowedDelayedList = pxOverflowDelayedTaskList;
 28         }
 29         taskEXIT_CRITICAL();
 30 
 31         if( pxEventList == &xPendingReadyList )
 32         {
 33             /* The task has been placed on the pending ready list, so its
 34              * state is eReady regardless of what list the task's state list
 35              * item is currently placed on. */
 36             /* 任務的事件項處於xPendingReadyList中就是就緒態
 37              * 說明xPendingReadyList里放的是任務的xEventListItem
 38              * 調度器掛起時，任務已ready，調度器運行後，
 39              * 會將xPendingReadyList中的任務移至就緒列表中 */
 40             eReturn = eReady;
 41         }
 42         else if( ( pxStateList == pxDelayedList ) || ( pxStateList == pxOverflowedDelayedList ) )
 43         {
 44             /* The task being queried is referenced from one of the Blocked
 45              * lists. */
 46             /* pxDelayedTaskList和pxOverflowDelayedTaskList放的是阻塞任務，xStateListItem */
 47             eReturn = eBlocked;
 48         }
 49 
 50         #if ( INCLUDE_vTaskSuspend == 1 )
 51         /* xSuspendedTaskList放的是掛起的任務，xStateListItem */
 52         else if( pxStateList == &xSuspendedTaskList )
 53         {
 54             /* The task being queried is referenced from the suspended
 55              * list.  Is it genuinely suspended or is it blocked
 56              * indefinitely? */
 57             /* xEventListItem不在任何列表裡 */
 58             if( listLIST_ITEM_CONTAINER( &( pxTCB->xEventListItem ) ) == NULL )
 59             {
 60                 #if ( configUSE_TASK_NOTIFICATIONS == 1 )
 61                 {
 62                     BaseType_t x;
 63 
 64                     /* The task does not appear on the event list item of
 65                      * and of the RTOS objects, but could still be in the
 66                      * blocked state if it is waiting on its notification
 67                      * rather than waiting on an object.  If not, is
 68                      * suspended. */
 69                     /* 說明等通知不是把xEventListItem放到某個列表裡，
 70                      * 而且等通知會把任務放到掛起的列表裡 */
 71                     eReturn = eSuspended;
 72 
 73                     for( x = ( BaseType_t ) 0; x < ( BaseType_t ) configTASK_NOTIFICATION_ARRAY_ENTRIES; x++ )
 74                     {
 75                         if( pxTCB->ucNotifyState[ x ] == taskWAITING_NOTIFICATION )
 76                         {
 77                             eReturn = eBlocked;
 78                             break;
 79                         }
 80                     }
 81                 }
 82                 #else /* if ( configUSE_TASK_NOTIFICATIONS == 1 ) */
 83                 {
 84                     eReturn = eSuspended;
 85                 }
 86                 #endif /* if ( configUSE_TASK_NOTIFICATIONS == 1 ) */
 87             }
 88             else
 89             {
 90                 /* 如果xStateListItem在掛起列表裡且xEventListItem處於某個列表裡，則任務會阻塞 */
 91                 eReturn = eBlocked;
 92             }
 93         }
 94         #endif /* if ( INCLUDE_vTaskSuspend == 1 ) */
 95 
 96         #if ( INCLUDE_vTaskDelete == 1 )
 97             else if( ( pxStateList == &xTasksWaitingTermination ) || ( pxStateList == NULL ) )
 98             {
 99                 /* The task being queried is referenced from the deleted
100                  * tasks list, or it is not referenced from any lists at
101                  * all. */
102                 /* 等著被刪除，這很明顯 */
103                 eReturn = eDeleted;
104             }
105         #endif
106 
107         else
108         {
109             #if ( configNUMBER_OF_CORES == 1 )
110             {
111                 /* If the task is not in any other state, it must be in the
112                  * Ready (including pending ready) state. */
113                 /* 剩下的就只能是在就緒列表裡(pxReadyTasksLists)
114                  * pxReadyTasksLists是個列表數組，通過排除法，可以
115                  * 免於進行遍歷操作。 */
116                 eReturn = eReady;
117             }
118             #else /* #if ( configNUMBER_OF_CORES == 1 ) */
119             {
120                 if( taskTASK_IS_RUNNING( pxTCB ) == pdTRUE )
121                 {
122                     /* Is it actively running on a core? */
123                     eReturn = eRunning;
124                 }
125                 else
126                 {
127                     /* If the task is not in any other state, it must be in the
128                      * Ready (including pending ready) state. */
129                     eReturn = eReady;
130                 }
131             }
132             #endif /* #if ( configNUMBER_OF_CORES == 1 ) */
133         }
134     }
135 
136     /* 簡單總結下：xStateListItem會在pxDelayedTaskList、pxOverflowDelayedTaskList、
137      * xSuspendedTaskList和xTasksWaitingTermination里
138      * xEventListItem會在xPendingReadyList里。
139      * 簡單分析就是事件、通知來了任務就放到xPendingReadyList里，其他情況就在其他列表裡
140      * 具體是不是這樣，看後面的源碼，會逐漸清晰 */
141 
142     return eReturn;
143 }

4.2.8 任務延遲，釋放CPU--vTaskDelay

這個介面比較熟悉，至少是任務中最常用的介面了。但是正如介面的註釋所說的那樣，這個介面不提供準確的延遲時間，任務喚醒的周期會受中斷、其他任務的影響，並且計時起始於這個介面開始被調用的時候，且時間是大於等於給予的延遲時間。如果想要準確的周期性的任務，那就要調用xTaskDelayUntil介面，這個會在後面講到。

  1 void vTaskDelay( const TickType_t xTicksToDelay )
  2 {
  3     BaseType_t xAlreadyYielded = pdFALSE;
  4 
  5     /* A delay time of zero just forces a reschedule. */
  6     /* 如果延遲tick為0, 則表示強制執行調度 */
  7     if( xTicksToDelay > ( TickType_t ) 0U )
  8     {
  9         vTaskSuspendAll();    // 停止調度器
 10         {
 11             configASSERT( uxSchedulerSuspended == 1U );
 12 
 13             /* A task that is removed from the event list while the
 14              * scheduler is suspended will not get placed in the ready
 15              * list or removed from the blocked list until the scheduler
 16              * is resumed.
 17              *
 18              * This task cannot be in an event list as it is the currently
 19              * executing task. */
 20             /* 在調度器暫停時, 從事件列表中刪除的任務將不會被放置在就緒列表中
 21              * 或從阻塞列表中刪除, 直到調度器恢復。此任務不可能在事件列表中,
 22              * 因為它是當前正在執行的任務。 */
 23             prvAddCurrentTaskToDelayedList( xTicksToDelay, pdFALSE );
 24         }
 25         xAlreadyYielded = xTaskResumeAll();
 26     }
 27     else
 28     {
 29         mtCOVERAGE_TEST_MARKER();
 30     }
 31 
 32     /* Force a reschedule if xTaskResumeAll has not already done so, we may
 33      * have put ourselves to sleep. */
 34     /* xTaskResumeAll沒有調度, 那在這裡手動調度 */
 35     if( xAlreadyYielded == pdFALSE )
 36     {
 37         taskYIELD_WITHIN_API();
 38     }
 39     else
 40     {
 41         mtCOVERAGE_TEST_MARKER();
 42     }
 43 }
 44 
 45 void vTaskSuspendAll( void )
 46 {
 47     #if ( configNUMBER_OF_CORES == 1 )
 48     {
 49         /* A critical section is not required as the variable is of type
 50          * BaseType_t.  Please read Richard Barry's reply in the following link to a
 51          * post in the FreeRTOS support forum before reporting this as a bug! -
 52          * https://goo.gl/wu4acr */
 53 
 54         /* portSOFTWARE_BARRIER() is only implemented for emulated/simulated ports that
 55          * do not otherwise exhibit real time behaviour. */
 56         portSOFTWARE_BARRIER();
 57 
 58         /* The scheduler is suspended if uxSchedulerSuspended is non-zero.  An increment
 59          * is used to allow calls to vTaskSuspendAll() to nest. */
 60         /* uxSchedulerSuspended非0, 則調度器暫停, 加1是為了嵌套調用(中斷也調用) */
 61         uxSchedulerSuspended = ( UBaseType_t ) ( uxSchedulerSuspended + 1U );
 62 
 63         /* Enforces ordering for ports and optimised compilers that may otherwise place
 64          * the above increment elsewhere. */
 65         portMEMORY_BARRIER();
 66     }
 67     #endif /* #if ( configNUMBER_OF_CORES == 1 ) */
 68 }
 69 
 70 static void prvAddCurrentTaskToDelayedList( TickType_t xTicksToWait,
 71                                             const BaseType_t xCanBlockIndefinitely )
 72 {
 73     TickType_t xTimeToWake;
 74     const TickType_t xConstTickCount = xTickCount;
 75     List_t * const pxDelayedList = pxDelayedTaskList;
 76     List_t * const pxOverflowDelayedList = pxOverflowDelayedTaskList;
 77 
 78     #if ( INCLUDE_xTaskAbortDelay == 1 )
 79     {
 80         /* About to enter a delayed list, so ensure the ucDelayAborted flag is
 81          * reset to pdFALSE so it can be detected as having been set to pdTRUE
 82          * when the task leaves the Blocked state. */
 83         pxCurrentTCB->ucDelayAborted = ( uint8_t ) pdFALSE;
 84     }
 85     #endif
 86 
 87     /* Remo