CSC364 Lecture 09

Introduction to Networked, Distributed, and Parallel Computing
Concurrency Design Patterns
(202602)

Transcript

1. Dr. Javier Gonzalez-Sanchez javiergs@calpoly.edu www.javiergs.info o ffi ce: 14 -227 CSC 364 Introduction to Networked, Distributed, and Parallel Computing Lecture 09. Concurrency Design Patterns 1
2. 2 De f inition A Concurrency Design P a ttern is a reus a ble solution to a common coordin a tion problem between multiple thre a ds. They describe: • How thre a ds inter a ct • How sh a red d a t a is a ccessed • How execution is coordin a ted s a fely P a tterns a re a bout structure a nd intent
3. 3 Why Concurrency Patterns? Concurrency mech a nisms (sem a phore, lock, synchronize, pool, a tomic) tell us how to synchronize. P a tterns expl a in when a nd why. With p a tterns: • Code is e a sier to re a son a bout • Beh a vior is predict a ble • Systems sc a le more s a fely
4. Producer-Consumer Pattern 4
5. 5 De f inition
6. 6 Features • The Producer–Consumer p a ttern sep a r a tes the gener a tion of work from the processing of work. • One or more thre a ds produce t a sks. • One or more thre a ds consume t a sks. • They oper a te a t di ff erent speeds. • It provide decoupling between producers a nd consumers • S a fe sh a ring of a work bu ff er
7. 7 When to Use Producer–Consumer? Use when: • Work a rrives continuously • Processing is a synchronous • Producers a nd consumers should not block e a ch other unnecess a rily Ex a mples: • T a sk queues • Network mess a ge h a ndling
8. 8 Producer
9. 9 Consumer
10. 10 Main
11. 11 Buffer (1/2)
12. 12 Buffer (2/2)
13. Readers-Writers Pattern 13
14. 14 De f inition
15. 15 Features • Multiple thre a ds to re a d simult a neously • Re a ds do not block other re a ds. • Only one thre a d to write exclusively • Writes block everyone. • High perform a nce for re a d-he a vy worklo a ds • D a t a consistency during writes • Controlled a ccess b a sed on oper a tion type
16. 16 When to Use Readers–Writers? • Re a ds a re much more frequent th a n writes • Sh a red d a t a must rem a in consistent • Exclusive write a ccess is required Ex a mples: • Course C a t a log in a University System • Web server c a che • G a me st a tes • IDE - compiler
17. 17 ReadWriteLock A Re a dWriteLock is a lock with two di ff erent modes of a ccess: • Re a d lock → sh a red • Write lock → exclusive Why do we need it? • With a norm a l lock (synchronized or Reentr a ntLock) only one thre a d c a n a ccess the d a t a a t a time • Re a ders block other re a ders, even though they don’t modify a nything. Blocking re a ders from e a ch other is unnecess a ry a nd slow.
18. 18 Main
19. 19 Reader
20. 20 Writer
21. 21 CourseCatalog (1/2)
22. 22 CourseCatalog (2/2)
23. Immutable Object Pattern 23
24. 24 De f inition • An Immut a ble Object c a nnot be modi f ied a fter cre a tion. • Once constructed, its st a te never ch a nges. Wh a t does this p a ttern gu a r a ntee? • Thre a d s a fety by design • No synchroniz a tion required • No r a ce conditions When to Use Immut a ble Objects? • D a t a is sh a red a cross thre a ds • St a te does not need to ch a nge • Simplicity a nd s a fety a re priorities
25. 25 Code
26. 26 Code • final on a class prevents extension. • final on fields prevents mutation. • Immutability requires both — plus no setters.
27. Guarded Suspension Pattern 27
28. 28 Features The Gu a rded Suspension p a ttern forces a thre a d to w a it until a condition becomes true. Execution is suspended until it is s a fe to continue. Wh a t does this p a ttern gu a r a ntee? • Correct ordering of oper a tions • No busy w a iting • S a fe coordin a tion using conditions When to Use Gu a rded Suspension? • A thre a d depends on a condition • D a t a m a y not be re a dy yet • W a iting must be e ff icient
29. 29 Questions
30. Lab 09
31. 31 Path f inder
32. 32 Path f inder
33. 33 Path f inder
34. 34 Path f inder
35. 35 Path f inder 1 2 3 4 5 6 11 12 13 14 15 7 8 9 10
36. 36 Technical Speci f ication • Observer P a ttern (PropertyCh a ngeSupport a nd PropertyCh a ngeListener) • J a v a Swing for GUI • Allow a Big number of cells • Perform a nce is import a nt - cre a te multiple Thre a ds • It is a bout f inding the best (shortest dist a nce) p a th not just a ny p a th • Te a m of 2 or 3 (m a ximum 3)
37. CSC 364 Introduction to Introduction to Networked, Distributed, and Parallel Computing Javier Gonzalez-Sanchez, Ph.D. javiergs@calpoly.edu Winter 2026 Copyright. These slides can only be used as study material for the class CSC 364 at Cal Poly. They cannot be distributed or used for another purpose. 37