Subj : Re: Deadlock theorem
To   : comp.programming.threads
From : David Schwartz
Date : Wed May 04 2005 05:04 am


"Uenal Mutlu" <520001085531-0001@t-online.de> wrote in message 
news:d59mgm$8k8$02$1@news.t-online.com...
>> > Locker L(o1.LV);
>> > while (!IsEnd())
>> > {
>> >    o1.DoStuff();
>> > }

>>     This won't work. If 'IsEnd' acquires and releases a lock, then your
>> rules are violated since 'IsEnd' is in the same block as 'DoStuff'. If
>> 'IsEnd' does not acquire any locks, then it can never return a different
>> value because no lock is released to allow another thread to change the
>> return value.
>
> Ok, the new rule d should have covered this now.

    Nope, this code is still illegal by your current rules. There are two 
possibilities:

    1) IsEnd acquires and releases a lock. In this case, your rule 'd' is 
violated.

    2) IsEnd acquires no locks. In this case, the code is unsafe and can 
never ensure 'IsEnd' returns the right value.

    In most cases, 'IsEnd' will have to acquire a lock of some kind. This 
violates rule 'd' of your hierarchy.

    DS

.