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Midterm Review

Midterm Review . 4:00pm – 5:20pm, 11/10/11 Open book and notes Four problems. Midterm Review - 1. Overview

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Midterm Review

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

  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. 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. 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. 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 classCountingSemaphore { • privateint permits = 0; • BinarySemaphore mutex (1); • BinarySemaphore delayQ (0); • publicCoutingSemaphore (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) • } • } Advanced Topics in Software Engineering 6

  7. A scenario • T1T2T3T4 (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. 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. Exercises 3.5 • public final classCountingSemaphore { • privateint permits = 0; • BinarySemaphore mutex (1); • BinarySemaphore delayQ (0); • publicCoutingSemaphore (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) • } • } Advanced Topics in Software Engineering 9

  10. Questions? Advanced Topics in Software Engineering 10

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