Advanced Topics in Software Engineering 1

1
Midterm Review

• 400pm 520pm, 11/10/11
• Open book and notes
• Four problems

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,
  Petersons algorithm, Bakery algorithm,
  synchronization operation, SYN-sequence,
  RW-sequence, version-based tracing replay

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

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

5
Homework Problems

• Exercises 3.5
• Exercises 4.4, 4.11b., 4.18b, 4.24
• Exercises 6.6

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 lt 0) (3)
• mutex.V () (4)
• delayQ.P () (5)
• else
• mutex.V () (6)
• public void V ()

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)
8
Exercise 4.4

• public void waitC()
• numWaitingThreads
• threadQueue.VP(mutex)
• mutex.P()
• --numWaitingThreads
• public void signalC()
• if (numWaitingThreads gt 0)
• threadQueue.V()
• // continue in the monitor perhaps send more
  signals

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 lt 0) (3)
• mutex.V () (4)
• delayQ.P () (5)
• else
• mutex.V () (6)
• public void V ()

10
Questions?