《FreeRTOS任务删除篇》

1. 介绍FreeRTOS任务删除函数的执行过程，逐行分析源代码。
2. 要使用任务删除函数vTaskDelete，需要配置宏INCLUDE_vTaskDelete为1。
3. 删除任务函数vTaskDelete的参数为待删除任务的任务句柄（即任务控制块）。
4. 当函数参数为NULL时，代表删除的是调用函数的任务本身（即正在运行的任务）。

源码

/* 示例，在正在运行的任务中调用任务删除函数。*/
vTaskDelete(NULL); 

/* 任务删除 */
#if ( INCLUDE_vTaskDelete == 1 ) /* 需要INCLUDE_vTaskDelete宏配置为1 */void vTaskDelete( TaskHandle_t xTaskToDelete ) /* 函数参数为待删除任务的任务句柄，可以用NULL代替当前任务句柄。 */{TCB_t * pxTCB;taskENTER_CRITICAL(); /* 进入临界区，本质是关闭全局中断。 */{/* If null is passed in here then it is the calling task that is* being deleted.* 如果在此处传递NULL，则删除的是调用函数的任务本身。*/pxTCB = prvGetTCBFromHandle( xTaskToDelete );/* Remove task from the ready/delayed list.* 从就绪/延迟列表中删除任务* 如果删除后列表中没有列表项，则uxListRemove返回0*//* 将任务控制块的成员状态列表项xStateListItem从列表中移除 */if( uxListRemove( &( pxTCB->xStateListItem ) ) == ( UBaseType_t ) 0 ){taskRESET_READY_PRIORITY( pxTCB->uxPriority );}else{mtCOVERAGE_TEST_MARKER();}/* Is the task waiting on an event also?* 任务是否也在等待事件？* 任务控制块的成员xEventListItem是否挂载在其他列表中*/if( listLIST_ITEM_CONTAINER( &( pxTCB->xEventListItem ) ) != NULL ){/* 将事件列表项从等待事件列表中移出 */( void ) uxListRemove( &( pxTCB->xEventListItem ) );}else{mtCOVERAGE_TEST_MARKER();}/* Increment the uxTaskNumber also so kernel aware debuggers can* detect that the task lists need re-generating.  This is done before* portPRE_TASK_DELETE_HOOK() as in the Windows port that macro will* not return.* 同时自增uxTaskNumber，以便内核感知调试器可以检测到任务列表需要重新生成。* 这是在portPRE_TASK_DELETE_HOOK之前完成的，因为在Windows端口中，宏不会返回*/uxTaskNumber++; /* 任务列表需要重新生成 *//* 删除的是调用任务本身时 */if( pxTCB == pxCurrentTCB ){/* A task is deleting itself.  This cannot complete within the* task itself, as a context switch to another task is required.* Place the task in the termination list.  The idle task will* check the termination list and free up any memory allocated by* the scheduler for the TCB and stack of the deleted task.* 一个任务正在删除自己。* 这无法在任务本身内完成，因为需要切换到另一个任务的上下文。* 将任务放入等待结束列表中。* 空闲任务将检查等待结束列表，并释放调度器为准备删除任务分配的TCB和堆栈内存。*/vListInsertEnd( &xTasksWaitingTermination, &( pxTCB->xStateListItem ) );/* Increment the ucTasksDeleted variable so the idle task knows* there is a task that has been deleted and that it should therefore* check the xTasksWaitingTermination list.* 递增ucTasksDeleted变量，以便空闲任务知道有一个任务已被删除，* 因此它应该检查xTasksWaitingTermination列表。*/++uxDeletedTasksWaitingCleanUp;/* Call the delete hook before portPRE_TASK_DELETE_HOOK() as* portPRE_TASK_DELETE_HOOK() does not return in the Win32 port.* 在调用portPRE_TASK_delete_hook之前调用delete钩子，* 因为portPRE_TAS K_delete_ hook在Win32端口中不返回。*/traceTASK_DELETE( pxTCB );/* The pre-delete hook is primarily for the Windows simulator,* in which Windows specific clean up operations are performed,* after which it is not possible to yield away from this task -* hence xYieldPending is used to latch that a context switch is* required.* 预删除挂钩主要用于Windows模拟器，* 在该模拟器中执行特定于Windows的清理操作，之后不可能放弃此任务，* 因此xYieldPending用于锁定需要进行上下文切换。*/portPRE_TASK_DELETE_HOOK( pxTCB, &xYieldPending );}else{--uxCurrentNumberOfTasks; /* 当前任务个数自减一 */traceTASK_DELETE( pxTCB );/* Reset the next expected unblock time in case it referred to* the task that has just been deleted.* 重置下一个预期的解锁时间，以防它引用了刚刚被删除的任务*/prvResetNextTaskUnblockTime();}}taskEXIT_CRITICAL(); /* 退出临界区，本质是开启全局中断 *//* If the task is not deleting itself, call prvDeleteTCB from outside of* critical section. If a task deletes itself, prvDeleteTCB is called* from prvCheckTasksWaitingTermination which is called from Idle task.* 如果任务不是删除自己，请从临界区外部调用prvDeleteTCB。* 如果任务删除自己，则从空闲任务调用的prvCheckTasksWaitingTermination中调用prvDeleteTCB删除任务*/if( pxTCB != pxCurrentTCB ){prvDeleteTCB( pxTCB );}/* Force a reschedule if it is the currently running task that has just* been deleted.* 如果删除的是当前正在运行的任务，则强制重新开启一次任务调度*/if( xSchedulerRunning != pdFALSE ) /* 任务调度器正在运行中 */{if( pxTCB == pxCurrentTCB ) /* 删除的是当前正在运行的任务 */{configASSERT( uxSchedulerSuspended == 0 );portYIELD_WITHIN_API();}else{mtCOVERAGE_TEST_MARKER();}}}#endif /* INCLUDE_vTaskDelete */

1. 进入临界区

taskENTER_CRITICAL(); /* 进入临界区，本质是关闭全局中断。 */

1.1 第一步

#define taskENTER_CRITICAL()               portENTER_CRITICAL() /* 从任务中进入临界区 */

1.2 第二步

#define portENTER_CRITICAL()  vPortEnterCritical()

1.3 第三步

void vPortEnterCritical( void )
{portDISABLE_INTERRUPTS();ulCriticalNesting++;
}

1.4 第四步

#define portDISABLE_INTERRUPTS() __asm(" setc INTM") /* 关闭全局中断 */

2. 获取待删除任务的任务控制块TCB

portDONT_DISCARD PRIVILEGED_DATA TCB_t * volatile pxCurrentTCB = NULL; /* 指向当前运行的任务控制块。 */

/** Several functions take a TaskHandle_t parameter that can optionally be NULL,* where NULL is used to indicate that the handle of the currently executing* task should be used in place of the parameter.  This macro simply checks to* see if the parameter is NULL and returns a pointer to the appropriate TCB.* 有几个函数接受一个TaskHandle_t参数，该参数可以选择设置为NULL，* 其中NULL用于表示使用当前正在执行的任务的句柄来代替该参数。* 此宏只是检查参数是否为NULL，并返回指向相应TCB的指针。*/
#define prvGetTCBFromHandle( pxHandle )    ( ( ( pxHandle ) == NULL ) ? pxCurrentTCB : ( pxHandle ) )

3. 从就绪/延迟列表中删除任务

/* Remove task from the ready/delayed list.* 从就绪/延迟列表中删除任务* 如果删除后列表中没有列表项，则返回0*/
if( uxListRemove( &( pxTCB->xStateListItem ) ) == ( UBaseType_t ) 0 )
{taskRESET_READY_PRIORITY( pxTCB->uxPriority );
}
else
{mtCOVERAGE_TEST_MARKER();
}

/* 从列表中移除待移除的列表项 */
UBaseType_t uxListRemove( ListItem_t * const pxItemToRemove )
{/* The list item knows which list it is in.  Obtain the list from the list* item.* 从列表项的成员pxContainer可以知道它在哪个列表中。从列表项中获取列表。* */List_t * const pxList = pxItemToRemove->pxContainer;/* 将列表项从列表中移除 */pxItemToRemove->pxNext->pxPrevious = pxItemToRemove->pxPrevious;pxItemToRemove->pxPrevious->pxNext = pxItemToRemove->pxNext;/* Only used during decision coverage testing.* 仅在决策覆盖率测试期间使用。*/mtCOVERAGE_TEST_DELAY();/* Make sure the index is left pointing to a valid item.* 确保索引指向有效项*/if( pxList->pxIndex == pxItemToRemove ) /* 如果列表的列表索引号指向待移除的列表项 */{pxList->pxIndex = pxItemToRemove->pxPrevious; /* 将索引号指向待移除列表项的前一个列表项 */}else{mtCOVERAGE_TEST_MARKER();}pxItemToRemove->pxContainer = NULL; /* 将待删除列表项的成员pxContainer设置为NULL，表示其不属于任何列表 */( pxList->uxNumberOfItems )--; /* 列表的列表项个数减一 */return pxList->uxNumberOfItems; /* 返回列表中剩余的列表项个数 */
}

4. 从事件列表中删除任务

/* Is the task waiting on an event also?* 任务是否也在等待事件？* 任务控制块的成员xEventListItem是否挂载在其他列表中*/
if( listLIST_ITEM_CONTAINER( &( pxTCB->xEventListItem ) ) != NULL )
{/* 将事件列表项从等待事件列表中移出 */( void ) uxListRemove( &( pxTCB->xEventListItem ) );
}
else
{mtCOVERAGE_TEST_MARKER();
}

/** Return the list a list item is contained within (referenced from).* 返回列表项所挂载的列表** @param pxListItem The list item being queried. pxListItem表示正在查询的列表项。* @return A pointer to the List_t object that references the pxListItem.  指向挂载pxListItem的List_t对象的指针*/
#define listLIST_ITEM_CONTAINER( pxListItem )            ( ( pxListItem )->pxContainer )

5. 如果待删除任务是当前运行的任务

1. 将列表项xStateListItem按尾部插入法挂载到xTasksWaitingTermination列表中
2. 变量uxDeletedTasksWaitingCleanUp自增一，以供空闲任务使用。

/* 删除的是调用任务本身时 */
if( pxTCB == pxCurrentTCB )
{/* A task is deleting itself.  This cannot complete within the* task itself, as a context switch to another task is required.* Place the task in the termination list.  The idle task will* check the termination list and free up any memory allocated by* the scheduler for the TCB and stack of the deleted task.* 一个任务正在删除自己。* 这无法在当前任务执行内部完成，因为还需要切换到另一个任务的上下文。* 因此将待删除任务放入等待结束任务列表中。* 空闲任务将检查等待结束任务列表，并释放调度器为待删除任务分配的TCB和堆栈内存。*/vListInsertEnd( &xTasksWaitingTermination, &( pxTCB->xStateListItem ) );/* Increment the ucTasksDeleted variable so the idle task knows* there is a task that has been deleted and that it should therefore* check the xTasksWaitingTermination list.* 递增ucTasksDeleted变量，以便空闲任务知道有一个任务已被删除，* 因此它应该检查xTasksWaitingTermination列表。* */++uxDeletedTasksWaitingCleanUp;/* Call the delete hook before portPRE_TASK_DELETE_HOOK() as* portPRE_TASK_DELETE_HOOK() does not return in the Win32 port.* 在调用portPRE_TASK_delete_hook之前调用delete钩子，* 因为portPRE_TAS K_delete_ hook在Win32端口中不返回。* */traceTASK_DELETE( pxTCB );/* The pre-delete hook is primarily for the Windows simulator,* in which Windows specific clean up operations are performed,* after which it is not possible to yield away from this task -* hence xYieldPending is used to latch that a context switch is* required.* 预删除挂钩主要用于Windows模拟器，* 在该模拟器中执行特定于Windows的清理操作，之后不可能放弃此任务，* 因此xYieldPending用于锁定需要进行上下文切换。* */portPRE_TASK_DELETE_HOOK( pxTCB, &xYieldPending );
}

6. 如果待删除任务是其它任务

--uxCurrentNumberOfTasks; /* 当前任务个数自减一 */
traceTASK_DELETE( pxTCB );/* Reset the next expected unblock time in case it referred to* the task that has just been deleted.* 重置下一个预期的解锁时间，以防它引用了刚刚被删除的任务，即下一个解除等待准备运行的任务就是待删除任务。*/
prvResetNextTaskUnblockTime();

/* 重置下一个任务解锁时间 */
static void prvResetNextTaskUnblockTime( void )
{if( listLIST_IS_EMPTY( pxDelayedTaskList ) != pdFALSE ) /* 延迟任务列表是否为空 */{/* The new current delayed list is empty.  Set xNextTaskUnblockTime to* the maximum possible value so it is  extremely unlikely that the* if( xTickCount >= xNextTaskUnblockTime ) test will pass until* there is an item in the delayed list.* 当前新的延迟列表为空。将xNextTaskUnblockTime设置为最大可能值*/xNextTaskUnblockTime = portMAX_DELAY;}else{/* The new current delayed list is not empty, get the value of* the item at the head of the delayed list.  This is the time at* which the task at the head of the delayed list should be removed* from the Blocked state.* 当前新的延迟列表不为空，请获取延迟列表头部项目的值。* 此时，应将延迟列表开头的任务从“阻塞”状态中删除。* 即准备让下一个被阻塞的任务开始执行*/xNextTaskUnblockTime = listGET_ITEM_VALUE_OF_HEAD_ENTRY( pxDelayedTaskList );}
}

/** Access macro to determine if a list contains any items.  The macro will* only have the value true if the list is empty.* 访问宏以确定列表是否包含任何列表项。只有当列表为空时，宏才会具有值true。*/
#define listLIST_IS_EMPTY( pxList ) ( ( ( pxList )->uxNumberOfItems == ( UBaseType_t ) 0 ) ? pdTRUE : pdFALSE )

PRIVILEGED_DATA static List_t * volatile pxDelayedTaskList; /*< Points to the delayed task list currently being used. 指向当前正在使用的延迟任务列表*/

#define portMAX_DELAY ( TickType_t ) 0xffffffffUL

/** Access macro to retrieve the value of the list item at the head of a given list. * 访问宏以检索给定列表开头的列表项的值*/
#define listGET_ITEM_VALUE_OF_HEAD_ENTRY( pxList )        ( ( ( pxList )->xListEnd ).pxNext->xItemValue ) /* 末尾列表项的下一个列表项即为头部列表项。 */

PRIVILEGED_DATA static volatile TickType_t xNextTaskUnblockTime = ( TickType_t ) 0U; /* Initialised to portMAX_DELAY before the scheduler starts. 在调度程序启动之前，已初始化为portMAX_DELAY*/

7. 退出临界区

taskEXIT_CRITICAL(); /* 退出临界区，本质是开启全局中断 */

7.1 第一步

#define taskEXIT_CRITICAL()                portEXIT_CRITICAL()

7.2 第二步

#define portEXIT_CRITICAL()   vPortExitCritical()

7.3 第三步

void vPortExitCritical( void )
{ulCriticalNesting--;if( ulCriticalNesting == 0 ){portENABLE_INTERRUPTS();}
}

7.4 第四步

#define portENABLE_INTERRUPTS()   __asm(" clrc INTM") /* 打开全局中断 */

8. 如果待删除的任务不是当前运行的任务

/* If the task is not deleting itself, call prvDeleteTCB from outside of* critical section. If a task deletes itself, prvDeleteTCB is called* from prvCheckTasksWaitingTermination which is called from Idle task.* 如果任务不是删除自己，请从临界区外部调用prvDeleteTCB。* 如果任务删除自己，则从空闲任务调用的prvCheckTasksWaitingTermination中调用prvDeleteTCB删除任务*/
if( pxTCB != pxCurrentTCB )
{prvDeleteTCB( pxTCB );
}

/* 删除任务控制块，根据分配内存的方式释放TCB和堆栈内存 */
#if ( INCLUDE_vTaskDelete == 1 )static void prvDeleteTCB( TCB_t * pxTCB ){/* This call is required specifically for the TriCore port.  It must be* above the vPortFree() calls.  The call is also used by ports/demos that* want to allocate and clean RAM statically.* 此调用是TriCore端口特有的。它必须位于vPortFree调用之上。* 该调用也被希望静态分配和清理RAM的端口/演示使用。* */portCLEAN_UP_TCB( pxTCB );#if ( ( configUSE_NEWLIB_REENTRANT == 1 ) || ( configUSE_C_RUNTIME_TLS_SUPPORT == 1 ) ){/* Free up the memory allocated for the task's TLS Block. */configDEINIT_TLS_BLOCK( pxCurrentTCB->xTLSBlock );}#endif#if ( ( configSUPPORT_DYNAMIC_ALLOCATION == 1 ) && ( configSUPPORT_STATIC_ALLOCATION == 0 ) && ( portUSING_MPU_WRAPPERS == 0 ) ){/* The task can only have been allocated dynamically - free both* the stack and TCB.* 该任务只能是被动态分配，需要释放堆栈和TCB* */vPortFreeStack( pxTCB->pxStack );vPortFree( pxTCB );}#elif ( tskSTATIC_AND_DYNAMIC_ALLOCATION_POSSIBLE != 0 ) /*lint !e731 !e9029 Macro has been consolidated for readability reasons. */{/* The task could have been allocated statically or dynamically, so* check what was statically allocated before trying to free the* memory.* 任务可以静态或动态分配，因此在尝试释放内存之前，请检查静态分配的内容* */if( pxTCB->ucStaticallyAllocated == tskDYNAMICALLY_ALLOCATED_STACK_AND_TCB ){/* Both the stack and TCB were allocated dynamically, so both* must be freed.* 堆栈和TCB都是动态分配的，因此必须释放它们。* */vPortFreeStack( pxTCB->pxStack );vPortFree( pxTCB );}else if( pxTCB->ucStaticallyAllocated == tskSTATICALLY_ALLOCATED_STACK_ONLY ){/* Only the stack was statically allocated, so the TCB is the* only memory that must be freed.* 只有堆栈是静态分配的，因此TCB是唯一必须释放的内存。* */vPortFree( pxTCB );}else{/* Neither the stack nor the TCB were allocated dynamically, so* nothing needs to be freed.* 堆栈和TCB都不是动态分配的，因此不需要释放任何内容* */configASSERT( pxTCB->ucStaticallyAllocated == tskSTATICALLY_ALLOCATED_STACK_AND_TCB );mtCOVERAGE_TEST_MARKER();}}#endif /* configSUPPORT_DYNAMIC_ALLOCATION */}#endif /* INCLUDE_vTaskDelete */

9. 如果待删除的任务不是当前运行的任务

/* Force a reschedule if it is the currently running task that has just* been deleted.* 如果删除的是当前正在运行的任务，则强制重新开启一次任务调度*/
if( xSchedulerRunning != pdFALSE ) /* 任务调度器正在运行中 */
{if( pxTCB == pxCurrentTCB ) /* 删除的是当前正在运行的任务 */{configASSERT( uxSchedulerSuspended == 0 );portYIELD_WITHIN_API();}else{mtCOVERAGE_TEST_MARKER();}
}

PRIVILEGED_DATA static volatile BaseType_t xSchedulerRunning = pdFALSE;

#ifndef portYIELD_WITHIN_API#define portYIELD_WITHIN_API    portYIELD
#endif

#define portYIELD() do{bYield = 1; __asm(" INTR INT14");}while(0)