嵌入式操作系统内核原理和开发（互斥量）

　　初始化的函数还是比较简单的，主要做了下面的流程，

　　（1）初始化互斥结构的公共属性，比如名字、阻塞方式等等；

　　（2）初始化当前资源数量；

　　（3）初始化占有资源的线程指针，还有是线程的优先级。

　　创建了互斥量之后，我们要看看互斥量是怎么申请的？代码有点长，同学们可以心理调整一下了，

RAW_U16 raw_mutex_get(RAW_MUTEX *mutex_ptr， RAW_U32 wait_option)
  {
   RAW_U16 error_status;
   RAW_SR_ALLOC();
 
   #if (RAW_MUTEX_FUNCTION_CHECK > 0)
 
 
   if (mutex_ptr == 0) {
    return RAW_NULL_OBJECT;
   }
 
   if (raw_int_nesting) {
   
    return RAW_NOT_CALLED_BY_ISR;
   
   }
  
   #endif
  
   RAW_CRITICAL_ENTER();
  
    /* mutex is available */
   if (mutex_ptr->count) { 
    mutex_ptr->occupy       =  raw_task_active;                               
    mutex_ptr->occupy_original_priority =  raw_task_active->priority;
    mutex_ptr->count   = 0;
 
    RAW_CRITICAL_EXIT();
 
    return RAW_SUCCESS;
   }
 
 
   /*if the same task get the same mutex again， it causes deadlock*/
   if (raw_task_active == mutex_ptr->occupy) {   
 
    #if (CONFIG_RAW_ASSERT > 0)
    RAW_ASSERT(0);
    #endif
   
      RAW_CRITICAL_EXIT(); 
    return RAW_MUTEX_DEADLOCK;
     }
 
   /*Cann't get mutex， and return immediately if wait_option is  RAW_NO_WAIT*/
   if (wait_option == RAW_NO_WAIT) {
 
    RAW_CRITICAL_EXIT();
 
    return RAW_NO_PEND_WAIT;
 
   }
 
   /*system is locked so task can not be blocked just return immediately*/
   if (raw_sched_lock) { 
    RAW_CRITICAL_EXIT();
    return RAW_SCHED_DISABLE;
   }
 
      /*if current task is a higher priority task and block on  the mutex
     *priority inverse condition happened， priority inherit method is used here*/
  
   if (raw_task_active->priority < mutex_ptr->occupy->priority) {
    switch (mutex_ptr->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_ptr->occupy->priority = raw_task_active->priority;
      /*readd to the ready list head*/
      add_ready_list_head(&raw_ready_queue， mutex_ptr->occupy);
      break;
    
 
     case RAW_DLY:
     case RAW_DLY_SUSPENDED:
     case RAW_SUSPENDED:
      /*occupy task is not on any list， so just change the priority*/
      mutex_ptr->occupy->priority = raw_task_active->priority;
      break;
 
     case RAW_PEND:                        /* Change the position of the task in the wait list       */
     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_ptr->occupy->priority = raw_task_active->priority;
      change_pend_list_priority(mutex_ptr->occupy);
      break;
 
     default:
      RAW_CRITICAL_EXIT();
      return RAW_INVALID_STATE;
    }
   
   }
 
   /*Any way block the current task*/
   raw_pend_object(&mutex_ptr->common_block_obj， raw_task_active， wait_option);
 
   RAW_CRITICAL_EXIT();
 
   /*find the next highest priority task ready to run*/
   raw_sched();                                           
 
   /*So the task is waked up， need know which reason cause wake up.*/
   error_status = block_state_post_process(raw_task_active， 0);
  
   return error_status;
  }