和之前的信号量释放相比,互斥量的释放要复杂一切,关键就在于修改优先级的问题。我们来梳理一下,
(1)判断参数合法性;
(2)判断线程是否为互斥量的占有线程,不是则返回;
(3)判断等待队列是否为空,为空的话则返回;
(4)判断占有任务的优先级有没有发生变化,如果有则需要重新修改优先级,重新加入调度队列中;
(5)选择下一个可以调度的线程;
(6)函数返回。
说了这么些,就剩下最后一个删除互斥量了,大家再接再厉,一起去学习。
RAW_U16 raw_mutex_delete(RAW_MUTEX *mutex_ptr) { LIST *block_list_head; RAW_TASK_OBJ *mutex_occupy; RAW_SR_ALLOC(); #if (RAW_MUTEX_FUNCTION_CHECK > 0) if (mutex_ptr == 0) { return RAW_NULL_OBJECT; } #endif block_list_head = &mutex_ptr->common_block_obj.block_list; RAW_CRITICAL_ENTER(); mutex_occupy = mutex_ptr->occupy; /*if mutex is occupied and occupy priority is not the original priority*/ if ((mutex_occupy) && (mutex_occupy->priority != mutex_ptr->occupy_original_priority)) { switch (mutex_occupy->task_state) { case RAW_RDY: /*remove from the ready list*/ remove_ready_list(&raw_ready_queue, mutex_ptr->occupy); /*raise the occupy task priority*/ mutex_occupy->priority = mutex_ptr->occupy_original_priority; /*readd to the ready list head*/ add_ready_list_end(&raw_ready_queue, mutex_ptr->occupy); break; case RAW_DLY: case RAW_SUSPENDED: case RAW_DLY_SUSPENDED: /*occupy task is not on any list, so just change the priority*/ mutex_occupy->priority = mutex_ptr->occupy_original_priority; break; case RAW_PEND: case RAW_PEND_TIMEOUT: case RAW_PEND_SUSPENDED: case RAW_PEND_TIMEOUT_SUSPENDED: /*occupy task is on the block list so change the priority on the block list*/ mutex_occupy->priority = mutex_ptr->occupy_original_priority; change_pend_list_priority(mutex_occupy); break; default: RAW_CRITICAL_EXIT(); return RAW_STATE_UNKNOWN; } } /*All task blocked on this queue is waken up*/ while (!is_list_empty(block_list_head)) { delete_pend_obj(list_entry(block_list_head->next, RAW_TASK_OBJ, task_list)); } RAW_CRITICAL_EXIT(); raw_sched(); return RAW_SUCCESS; } |
互斥量的操作在实际情形下未必是存在的,所以作者在设计的时候添加了一个编译宏。不过删除所做的工作也不难理解,一个是处理好当前占有者的关系,一个是处理好等待队列的关系。我们来细看一下流程,
(1)判断当前参数合法性;
(2)判断占有者的情况,修改任务优先级,这里的情形和上面申请互斥量的处理方式是一样的,不再赘述;
(3)唤醒所有的等待线程,如果线程已经suspend掉了,那么继续suspend;
(4)调度到其他线程,防止有优先级高的任务已经被释放出来了;
(5)函数返回,结束。
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