Hello,
I am a new user of the X.10 language. I have some questions about
the clocks construct in the X.10 language from the X.10 language manual:
1.) In clocks chapter, page-124, Advancing clocks (section-16.1.4) in the
third paragraph it says "Once the implementation has detected quiescence on
c...", shouldn't it say "Once the implementation has detected quiescence of
all registered activates on c, the system marks them as being able to
progress. Because, from what I understood of "clocks", I might well be
wrong, two activities registered on the same clock C1 act synchronously
(using the clock edge as the barrier). Is this correct?
2.) If my above observation is correct then that would mean the clocks in
X.10 are logical clocks, i.e., the period of a clock depends upon the
computational complexity of all the activities that are registered with this
clock. Since, a clock edge is considered complete (a new edge appears) when
all the activities complete computations and then call resume on that clock
(barrier synchronizing). How can one map this logical clock time to physical
time? Do we need some kind of worst case execution time analysis, which has
all the issues of loop bounds etc, to determine how long a clock's new edge
will appear (determining maximum clock periods)? I was wondering if X.10 is
a suitable language for modeling and implementing reactive systems with hard
real-time deadlines?
3.) Another thing that I wanted to know concerns the concept of activity
being registered with more than one clock; the system has a general
complexity of a cross product of the CCS style asynchronous operator (in the
most general case when every activity progresses at its own clock speed) but
when more than one activity is registered with the same clock the system
simplifies considerably, since parts of the system now act synchronously and
a number of transitions can be removed. Is there a mathematical formulation
describing the behaviors of activities and clocks in X.10, their temporal
relations, I really like the concept and wanted to study it further. Sorry
if there are pointers that I have missed from the website.
One other question
4.) Section 15.3 Place changes: Isn't this equivalent to a RMI in Java? How
are they different?
If my first observation about "clocks" is incorrect please explain how does
barrier synchronization with clocks work in X.10.
Thanks and Regards,
Avinash Malik
Post-Doc,
INRIA Grenoble,
Rhone-Alps
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