Re: About Figure 6.5 Chapter 6 (v 31.01.2015)

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

On Sun, May 10, 2015 at 09:42:53PM -0300, Jose Fernando Santos de Carvalho wrote:
> Dear Paul,
> thank you for feedback. FYI, we are using perfbook as a main reference
> in our discipline.

Hello, Jose,

That is very good to hear, and thank you for letting me know!

								Thanx, Paul

> best regards.
> 
> 
> On Sun, May 10, 2015 at 5:49 PM, Paul E. McKenney
> <paulmck@linux.vnet.ibm.com> wrote:
> > On Sat, May 09, 2015 at 12:01:01PM -0300, Jose Fernando Santos de Carvalho wrote:
> >> Link: http://ustore1.rnp.br/ustore/faces/publicFile.xhtml?code=35e4c269403136c4a9fdb9227b704409
> >>
> >> On Tue, May 5, 2015 at 11:40 PM, Jose Fernando Santos de Carvalho
> >> <jfsc@cin.ufpe.br> wrote:
> >> > Dear all,
> >> >
> >> > while writing chapter 6 (Partitioning and Synchronisation Design), Paul has
> >> > presented five special cases about Left - and Right-Hand Locks(Figure 6.5).
> >> > However, it is not clear for me the possible problem in the fourth case
> >> > (link).
> >> >
> >> >
> >> > If possible, could anyone send some feedback about it?
> >> >
> >> > Link:
> >> > http://ustore1.rnp.br/ustore/faces/publicFile.xhtml?code=35e4c269403136c4a9fdb9227b704409--
> >> >
> >> > --
> >> > Jose Fernando
> >
> > Hello, Jose,
> >
> > You could indeed claim that the second-to-last row is safe because the two
> > ends will be operating on different pointers for element 1.  Nevertheless,
> > the fact remains that both ends need to operate on element 1 simultaneously,
> > which should give us pause.  Especially given that we are in a concurrent
> > environment.
> >
> > For example, suppose that thread A holds the left-hand lock and wants to
> > remove element 0.  While thread A is comtemplating doing this, some other
> > thread B might hold the right-hand lock and remove element 2.  We are now
> > in the state shown in the third row, and thus completely unsafe.
> >
> >                                                         Thanx, Paul
> >
> 
> 
> 
> -- 
> -- 
> José Fernando Carvalho
> DSc Candidate in Computer Science
> Federal University of Pernambuco (UFPE) - Brazil
>