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Department of Computer Science University of Virginia
CS686 - DEPENDABLE COMPUTING
ASSIGNMENT 7
DUE: APRIL 21
Please type the Reading and Individual Activity parts of the assignment single spaced, 12pt type
with 1” margins, and indented paragraphs with no space between paragraphs. Be sure to include a
face page with course number and course name, assignment number, date, and your name.
For the project part, follow the project document guidelines.
Individual Reading
Complete the readings from assignment 6. In the e-mail I sent out, I deferred several items from
the list, so the list for this assignment should be:
(i) Barnes chapter 2. Please work with the rest of your group to schedule the use of your group’s
copy of the book. (ii) Storey chapter 12. (iii) Paper 23 on the class Web site. Prepare a half-page
summary. Turn in your summary.
Individual Activity
As with the reading, two questions were deferred from assignment 6.
1. Complete whichever two questions from assignment 6 you deferred.
2. Consider the following piece of program:
i, max : integer;
values : array[1..100] of integer;
i := 2;
max := values[1];
while i <= 100 loop
if max < values[i] then
max := values[i];
i := i + 1;
end loop
Determine the loop invariant. State the invariant as a SPARK assertion.
3. Java uses a garbage collection approach to reclaiming dynamic storage. Is it possible for a
Java program to “leak” memory? If so, why? If not, why not?
4. Dynamic memory management is problematic for safety-critical systems, and SPARK Ada
specifically disallows it. What are the issues that make dynamic memory management prob-
lematic?
5. In full Ada, exceptions are propagated up the dynamic call chain until a handler is found.
SPARK Ada specifically disallows all exceptions because they are not easy to analyze. Would
the inclusion of exception handlers in every function and procedure along with a static check
of the handlers being there be a way to allow Ada exceptions in SPARK Ada? If so, why? If
not, why not?
