[cap-talk] Selling capabilities programming

James A. Donald jamesd at echeque.com
Sun Jul 29 21:25:21 EDT 2007


Karp, Alan H wrote:
 > > > The stated goal was that capabilities granted to a
 > > > process do not survive that process's demise. This
 > > > goal could be defeated if the process could fork
 > > > another process and hand it the bits representing
 > > > the capability it wanted to survive the parent
 > > > process's demise.

James A. Donald:
 >> That is not "defeat" of the goal, but correct
 >> functioning.

Karp, Alan H:
 > Now I'm totally confused.  This statement appears to
 > be counter to your earlier reply to my Word/Excel
 > example where you said Excel would lose the capability
 > when Word exited.

I offered you three different interpretations of your
Word/Excel example, with four different behaviors and
user intents, and you neglected to tell me which one you
had in mind.

"B spawns C" could refer to any one of them.  In the
containment scenario, Excel's capability depends on word
- its capability is in fact a file handle to a file
within a Word file.  Excel gets shut down by Word, or
the Excel window managing the contained data gets shut
down by Word when Word closes the containing file.  In
the project file scenario, Excel gets launched either by
word or by the project manager, or opens a new window at
word's prompting or the project manager's prompting but
the instance or window gets shut down at the prompting
of the project file manager.  If it should somehow not
shut down, perhaps due to bug or unsatifactory
file-modified interface between in and the project file
manager, then it would remain open, but no longer be
able to access the file.  But until the project manager
shuts stuff down, probably because of the user closing
the project, Excel can pass the capability to new
instances of itself - the user might command it to spawn
several instances so that he can view several aspects of
the data simultaneously, and then shut down some of
those instances.  In the project scenario, Excel's file
handle depends on the project manager.  No more project
manager, no more valid file handle, even if Excel still
running.  The Excel window to that file should be
closed.

As it happens, Excel *does* have hooks that allow
external programs to open Excel windows to files and
close them.


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