进程的状态位掩码

      每个进程有两个独立的状态标志：

              task->state:是关系进程的 runnability;

              task->exit_state:是关于 task exiting;

#define TASK_RUNNING        0

#define TASK_INTERRUPTIBLE  1

#define TASK_UNITERRUPTIBLE 2

#define __TASK_STOPPED      4

#define __TASK_TRACED       8

/* in task->exit_state*/

#define EXIT_ZOMBIE         16

#define EXIT_DEAD           32

/*in task->state*/

#define TASK_DEAD           64

#define TASK_WAKEKILL       128

#define TASK_WAKING         256

set_task_state()函数中用到的符号常量的宏定义：

#define TASK_KILLABLE (TASK_WAKEKILL | TASK_UNINTERRUPTIBLE)

#define TASK_STOPPED  (TASK_WAKEKILL | __TASK_STOPPED)

#define TASK_TRACED   (TASK_WAKEKILL | __TASK_TRACED)

wake_up()函数中用到的符号常量的宏定义：

#define TASK_NORMAL  (TASK_INTERRUPTIBLE | TASK_UNITERRUPTIBLE)

#define TASK_ALL     (TASK_NORMAL | __TASK_STOPPED | __TASK_TRACED)

get_task_state()函数中用到的符号常量的宏定义：

#define TASK_REPORT (TASK_RUNNING | TASK_INTERRUPTIBLE \

                      | TASK_UNINTERRUPTIBLE | __TASK_STOPPED\

                      | __TASK_TRACED)

set_task_state()方法的实现：

   #define set_task_state(task, state_value) \

         set_mb((task)->state, (state_value))

    set_mb()函数保证了指令的执行顺序；

   #define __set_task_state(task, state_value)  \

          do{ (task)->state = (state_value );}while(0)

set_current_stat()方法的实现：

    #define __set_current_state(state_value) \

       do{ current->state = (state_value);}while(0)

    #define set_current_state(state_value) \

       set_mb(current->state, (state_value))