[cs33211] OS Student question

[Mikhail Nesterenko]

> 
> I have two questions considering slide 11 from Lecture 11 LocksnCVs.
> The issue concerns the code used to implement condition variables
> using spinlocks.
> -------------------------------------------------------------------------------------------------------------------
> /* condition consists of:
>   list - waiting threads
>   listlock - lock protecting
>        operation on list*/
> 
> void wait(condition *c,
>           lock *s){
>    spinlock(c->listlock);
>    /* add self to list */
>    spinunlock(c->listlock);
>    unlock(s);
>    /* block current thread */
>    lock(s);
>    return;
> }
> 
> void signal(condition *c){
>    spinlock(c->listlock);
>    /* remove a thread from
>      list if list not empty */
>    spinunlock(c->listlock);
>    /* make removed thread
>      runnable */
> }
> -------------------------------------------------------------------------------------------------------------------
> 
> 1. When acquiring a spinlock, a boolean variable is given as an
> argument to use on a testnset operation. Here, c->listlock is given as
> an argument. Does c->listlock return some boolean value?

spinlock() is a function implemented as described in previous slides -
with testNset. spinlock() does not itself return anything, it just
spins until this process acquires the lock.

> 2. At the end of the wait() operation: unlock(s), /* block current
> thread */, lock(s). How is the current thread blocked?

Make it non-runnable, remove from fready queue. It will be made
runnable again by the signal() operation.

Thanks,
--
Mikhail