FREERTOS之任务的挂起和唤醒
2009-05-13 声明：本篇文章主要参考了http://blog.ednchina.com/bluehacker
它把所有挂起的任务加到
xSuspendedTaskList
中，而且一旦调用
vTaskSuspend()
函数挂起一个任务，该任务就将从所有它原先连入的链表中删除（包括就绪表，延时表和它等待的事件链表），也就是说，一旦一个任务被挂起，它将取消先前它的延时和对事件的等待。
void vTaskSuspend( xTaskHandle pxTaskToSuspend )
{
tskTCB *pxTCB;
taskENTER_CRITICAL();
{
/* Ensure a yield is performed if the current task is being
suspended. */
if( pxTaskToSuspend == pxCurrentTCB )
{
pxTaskToSuspend = NULL;
//token
}
/*
得到对应任务tcb */
pxTCB = prvGetTCBFromHandle( pxTaskToSuspend );
traceTASK_SUSPEND( pxTaskToSuspend );
/*
把任务从就绪表或者延时链表中删除 */
vListRemove( &( pxTCB->xGenericListItem ) );
/*
如果任务也在等待某事件，则取消等待 */
if( pxTCB->xEventListItem.pvContainer )
{
vListRemove( &( pxTCB->xEventListItem ) );
}
//
插到xSuspendedTaskList
vListInsertEnd( ( xList * ) &xSuspendedTaskList, &( pxTCB->xGenericListItem ) );
}
taskEXIT_CRITICAL();
/*
如果挂起的是当前任务，则调度 */
if( ( void * ) pxTaskToSuspend == NULL )
{
taskYIELD();
}
}
相反的唤醒就是把任务从xSuspendedTaskList中删除，加到对应的就绪链表中（根据任务的优先级），然后如果唤醒的任务优先级高于当前任务优先级，则调度。
void vTaskResume( xTaskHandle pxTaskToResume )
{
tskTCB *pxTCB;
/* Remove the task from whichever list it is currently in, and place
it in the ready list. */
pxTCB = ( tskTCB * ) pxTaskToResume;
/* The parameter cannot be NULL as it is impossible to resume the
currently executing task. */
if( pxTCB != NULL )
{
taskENTER_CRITICAL();
{
if( prvIsTaskSuspended( pxTCB ) == pdTRUE )
{
traceTASK_RESUME( pxTCB );
/* As we are in a critical section we can access the ready
lists even if the scheduler is suspended. */
vListRemove( &( pxTCB->xGenericListItem ) );
prvAddTaskToReadyQueue( pxTCB );
/* We may have just resumed a higher priority task. */
if( pxTCB->uxPriority >= pxCurrentTCB->uxPriority )
{
/* This yield may not cause the task just resumed to run, butwill leave the lists in the correct state for the next yield. */
taskYIELD();
}
}
}
taskEXIT_CRITICAL();
}
}