wait queues

[ruben@mrbrklyn.com (Ruben Safir)]

I'm not pouring over Love's book in detail and the section in Chapter 4
on the wit queue is implemented  in the text completely surprised me.

He is recommending that you have to right your own wait queue entry
routine for every process?  Isn't that reckless?

He is suggesting

DEFINE_WAIT(wait) //what IS wait

add_wait_queue(q, &wait); // in the current kernel this invovled
                         //  flag   checking and a linked list

while(!condition){ /* an event we are weighting for
  prepare_to_wait(&q, &wait, TASK_INTERRUPTIBLE);
  if(signal_pending(current))
        /* SIGNAl HANDLE */
  schedule();
}

finish_wait(&q, &wait);

He also write how this proceeds to function and one part confuses me

5.  When the taks awakens, it again checks whether the condition is
true.  If it is, it exists the loop.  Otherwise it again calls schedule.


This is not the order that it seems to follow according to the code.

To me it looks like it should
1 - creat2 the wait queue
2 - adds &wait onto queue q
3 checks if condition is true, if so, if not, enter a while loop
4 prepare_to_wait which changes the status of our &wait to
TASK_INTERUPPABLE
5 check for signals ... notice the process is still moving.  Does it
stop and wait now?
6  schedule itself on the runtime rbtree... which make NO sense unless
there was a stopage I didn't know about.
7 check the condition again and repeat while look
	7a. if the loop ends fishish_waiting... take it off the queue.



Isn't this reckless to leave this to users to write the code.  Your
begging for a race condition.

Ruben