Re: Protected Objects - eggshell model

[hesobreira <herrsobreira@gmail.com>]

It is all clear now.

Thank you (Adam and Bob) for the answers and thanks for the references
to the RM.

Hugo

On Dec 24, 1:43 am, Adam Beneschan <a...@irvine.com> wrote:
> On Dec 23, 2:08 pm, hesobreira <herrsobre...@gmail.com> wrote:
>
> > This was not clear to me while reading Barnes' book about protected
> > types.
>
> > There are two conditions that must be satisfied in order to execute
> > the entry call: no other task accessing the object at the same time
> > and the condition barrier evaluated to TRUE (eggshell, or two level
> > protection model). My question is: which one of these conditions is
> > evaluated first, the access lock or the condition barrier?
>
> > Thank you all in advance,
> > Hugo
>
> The access lock has to be obtained first, and in fact the task calling
> the protected entry has to have the protected object all to itself
> while it's evaluating the entry barrier.  If the barrier is closed
> (False), the entry call is added to a queue, and *then* the lock is
> relinquished.
>
> In the RM, the concept of access locking is expressed by the phrase
> "protected actions".  See 9.5.1(4-7) and 9.5.3(8-12).
>
>                             -- Adam