1. Advanced Topics in Software Engineering 1
Midterm Review
4:00pm – 5:20pm, 11/10/11
Open book and notes
Four problems
Advanced Topics in Software Engineering 1

2. Advanced Topics in Software Engineering 2
Midterm Review - 1
Overview
What, why, concurrent vs sequential computation, models of concurrency (interleaving-based/true concurrency), semantics of correctness (safety & liveness), unique challenges in testing and debugging
Shared variables
The CS problem, correctness requirements, Peterson’s algorithm, Bakery algorithm, synchronization operation, SYN-sequence, RW-sequence, version-based tracing & replay
Advanced Topics in Software Engineering 2

3. Advanced Topics in Software Engineering 3
Midterm Review - 2
Semaphore & Locks
Binary semaphore, counting semaphore, lock, semaphores in Java, common patterns in semaphore-based programming, semaphore-based solutions to classical synchronization problems, fine-grained locking, PV-sequence, Lock/Unlock-sequence, permission-based tracing & replay
Advanced Topics in Software Engineering 3

4. Advanced Topics in Software Engineering 4
Midterm Review - 3
Monitor
Graphic representation, different signaling disciplines, monitor implementation, Java monitors, monitor-based solutions (dinning philosophers, bounded buffer, reader/writers), tracing/replay monitors (entry-based execution, simple and complete M-sequence)
Message Passing
Link/port/mailbox, synchronous vs asynchronous, rendezvous, selective wait, happened-before relation, integer/vector timestamps
Advanced Topics in Software Engineering 4

5. Advanced Topics in Software Engineering 5
Homework Problems
Exercises 3.5
Exercises 4.4, 4.11b., 4.18b, 4.24
Exercises 6.6
Advanced Topics in Software Engineering 5

6. Simulating Counting Semaphores
public final class CountingSemaphore {
private int permits = 0;
BinarySemaphore mutex (1);
BinarySemaphore delayQ (0);
public CoutingSemaphore (int initialPermits) {
permits = initialPermits; }
public void P () {
mutex.P (); (1)
-- permits; (2)
if (permits < 0) { (3)
mutex.V (); (4)
delayQ.P (); (5)
else
mutex.V (); (6)
public void V () {
mutex.P (); (7)
++ permits; (8)
if (permits <= 0) { (9)
delayQ.V (); (10)
mutex.V (); (11)
Assume that we have a system which only provides binary semaphores. This class shows how to simulate counting semaphores using binary semaphores.
Advanced Topics in Software Engineering 6

7. Advanced Topics in Software Engineering 7
A scenario
T1 T2 T3 T4
(1)
(2)
(3)
(4)
(1)
(2)
(3)
(4)
(7)
(8)
(9)
(10)
(7)
(8)
(9)
*(10)
(5)
*(10)
(5)
Advanced Topics in Software Engineering 7

8. Advanced Topics in Software Engineering 8
Exercise 4.4
public void waitC() { ++numWaitingThreads; threadQueue.VP(mutex); mutex.P(); --numWaitingThreads; } public void signalC() { if (numWaitingThreads > 0) threadQueue.V(); // continue in the monitor; perhaps send more signals
Advanced Topics in Software Engineering 8

9. Advanced Topics in Software Engineering 9
Exercises 3.5
public final class CountingSemaphore {
private int permits = 0;
BinarySemaphore mutex (1);
BinarySemaphore delayQ (0);
public CoutingSemaphore (int initialPermits) {
permits = initialPermits; }
public void P () {
mutex.P (); (1)
-- permits; (2)
if (permits < 0) { (3)
mutex.V (); (4)
delayQ.P (); (5)
else
mutex.V (); (6)
public void V () {
mutex.P (); (7)
++ permits; (8)
if (permits <= 0) { (9)
delayQ.V (); (10)
mutex.V (); (11)
Assume that we have a system which only provides binary semaphores. This class shows how to simulate counting semaphores using binary semaphores.
Advanced Topics in Software Engineering 9

10. Advanced Topics in Software Engineering 10
Questions?
Advanced Topics in Software Engineering 10