Presentation is loading. Please wait.

Presentation is loading. Please wait.

Synchronization Andy Wang Operating Systems COP 4610 / CGS 5765.

Published byRuby Copeland Modified over 9 years ago

Similar presentations

Presentation on theme: "Synchronization Andy Wang Operating Systems COP 4610 / CGS 5765."— Presentation transcript:

1 Synchronization Andy Wang Operating Systems COP 4610 / CGS 5765

2 Motivating Example: Too Much Milk Two robots are programmed to maintain the milk inventory at a store… They are not aware of each other’s presence… Robot: Dumb Robot: Dumber

3 Motivating Example: Too Much Milk Dumb 10:00Look into fridge: Out of milk Dumber

4 Motivating Example: Too Much Milk Dumb 10:00Look into fridge: Out of milk 10:05Head for the warehouse Dumber

5 Motivating Example: Too Much Milk Dumb 10:05Head for the warehouse Dumber 10:10Look into fridge: Out of milk

6 Motivating Example: Too Much Milk DumbDumber 10:10Look into fridge: Out of milk 10:15 Head for the warehouse

7 Motivating Example: Too Much Milk Dumb 10:20Arrive with milk Dumber 10:15 Head for the warehouse

8 Motivating Example: Too Much Milk Dumb 10:20Arrive with milk Dumber 10:15 Head for the warehouse

9 Motivating Example: Too Much Milk Dumb 10:20Arrive with milk 10:25Go party Dumber

10 Motivating Example: Too Much Milk Dumb 10:20Arrive with milk 10:25Go party Dumber 10:30Arrive with milk: “Uh oh…”

11 Definitions Synchronization: uses atomic operations to ensure cooperation among threads Mutual exclusion: ensures one thread can do something without the interference of other threads Critical section: a piece of code that only one thread can execute at a time

12 More on Critical Section A lock prevents a thread from doing something A thread should lock before entering a critical section A thread should unlock when leaving the critical section A thread should wait if the critical section is locked Synchronization often involves waiting

13 Too Much Milk: Solution 1 Two properties: Only one robot will go get milk Someone should go get the milk if needed Basic idea of solution 1 Leave a note (kind of like a lock) Remove the note (kind of like a unlock) Don’t go get milk if the note is around (wait)

14 Too Much Milk: Solution 1 if (no milk) { if (no note) { // leave a note; // go get milk; // remove the note; }

15 Too Much Milk: Solution 1 Dumb 10:00 if (no milk) { Dumber

16 Too Much Milk: Solution 1 Dumb 10:00 if (no milk) { Dumber 10:01 if (no milk) {

17 Too Much Milk: Solution 1 Dumb 10:00 if (no milk) { Dumber 10:01 if (no milk) { 10:02 if (no note) {

18 Too Much Milk: Solution 1 Dumb 10:00 if (no milk) { 10:03 if (no note) { Dumber 10:01 if (no milk) { 10:02 if (no note) {

19 Too Much Milk: Solution 1 Dumb 10:00 if (no milk) { 10:03 if (no note) { 10:04 // leave a note Dumber 10:01 if (no milk) { 10:02 if (no note) {

20 Too Much Milk: Solution 1 Dumb 10:03 if (no note) { 10:04 // leave a note Dumber 10:01 if (no milk) { 10:02 if (no note) { 10:05 // leave a note

21 Too Much Milk: Solution 1 Dumb 10:03 if (no note) { 10:04 // leave a note 10:06 // go get milk Dumber 10:02 if (no note) { 10:05 // leave a note

22 Too Much Milk: Solution 1 Dumb 10:03 if (no note) { 10:04 // leave a note 10:06 // go get milk Dumber 10:05 // leave a note 10:07 // go get milk

23 Too Much Milk: Solution 2 Okay…solution 1 does not work The notes are posted too late… What if both robots begin by leaving their own notes?

24 Too Much Milk: Solution 2 // leave a note; if (no note from the other) { if (no milk) { // go get milk; } // remove the note;

25 Too Much Milk: Solution 2 Dumb 10:00 // leave a note Dumber

26 Too Much Milk: Solution 2 Dumb 10:00 // leave a note Dumber 10:01 // leave a note

27 Too Much Milk: Solution 2 Dumb 10:00 // leave a note 10:02 if (no note from Dumber) {…} Dumber 10:01 // leave a note

28 Too Much Milk: Solution 2 Dumb 10:00 // leave a note 10:02 if (no note from Dumber) {…} Dumber 10:01 // leave a note 10:03 if (no note from Dumb) {…}

29 Too Much Milk: Solution 2 Dumb 10:00 // leave a note 10:02 if (no note from Dumber) {…} 10:04 // remove the note Dumber 10:01 // leave a note 10:03 if (no note from Dumb) {…}

30 Too Much Milk: Solution 2 Dumb 10:00 // leave a note 10:02 if (no note from Dumber) {…} 10:04 // remove the note Dumber 10:01 // leave a note 10:03 if (no note from Dumb) {…}

31 Too Much Milk: Solution 2 Dumb 10:02 if (no note from Dumber) {…} 10:04 // remove the note Dumber 10:01 // leave a note 10:03 if (no note from Dumb) {…} 10:05 // remove the note

32 Too Much Milk: Solution 2 Dumb 10:02 if (no note from Dumber) {…} 10:04 // remove the note Dumber 10:01 // leave a note 10:03 if (no note from Dumb) {…} 10:05 // remove the note

33 Too Much Milk: Solution 3 Dumb // leave Dumb’s note while (Dumber’s note) { }; if (no milk) { // go get milk } // remove Dumb’s note Dumber // leave Dumber’s note if (no Dumb’s note) { if (no milk) { // go get milk } // remove Dumber’s note

34 Too Much Milk Solution 3 How do we verify the correctness of a solution? Test arbitrary interleaving of locking and checking locks In this case, leaving notes and checking notes

35 Dumber Challenges Dumb: Case 1 Dumb // leave Dumb’s note while (Dumber’s note) { }; if (no milk) { // go get milk } // remove Dumb’s note Dumber // leave Dumber’s note if (no Dumb’s note) { } // remove Dumber’s note Time

36 Dumber Challenges Dumb: Case 2 Dumb // leave Dumb’s note while (Dumber’s note) { }; if (no milk) { // go get milk } // remove Dumb’s note Dumber // leave Dumber’s note if (no Dumb’s note) { } // remove Dumber’s note Time

37 Dumber Challenges Dumb: Case 3 Dumb // leave Dumb’s note while (Dumber’s note) { }; if (no milk) { // go get milk } // remove Dumb’s note Dumber // leave Dumber’s note if (no Dumb’s note) { } // remove Dumber’s note Time

38 Dumb Challenges Dumber: Case 1 Dumb // leave Dumb’s note while (Dumber’s note) { }; if (no milk) { } // remove Dumb’s note Dumber // leave Dumber’s note if (no Dumb’s note) { if (no milk) { // go get milk } // remove Dumber’s note Time

39 Dumb Challenges Dumber: Case 2 Dumb // leave Dumb’s note while (Dumber’s note) { }; if (no milk) { // go get milk } // remove Dumb’s note Dumber // leave Dumber’s note if (no Dumb’s note) { } // remove Dumber’s note Time

40 Dumb Challenges Dumber: Case 3 Dumb // leave Dumb’s note while (Dumber’s note) { }; if (no milk) { // go get milk } // remove Dumb’s note Dumber // leave Dumber’s note if (no Dumb’s note) { } // remove Dumber’s note Time

41 Lessons Learned Although it works, Solution 3 is ugly Difficult to verify correctness Two threads have different code Difficult to generalize to N threads While Dumb is waiting, it consumes CPU time (busy waiting) More elegant with higher-level primitives lock  acquire(); if (no milk) { // go get milk } lock  release();

Download ppt "Synchronization Andy Wang Operating Systems COP 4610 / CGS 5765."

Similar presentations

Operating Systems Semaphores II

Operating Systems Semaphores II
1 Lecture 20: Synchronization & Consistency Topics: synchronization, consistency models (Sections 4.5-4.6)

1 Lecture 20: Synchronization & Consistency Topics: synchronization, consistency models (Sections )
Process Synchronization A set of concurrent/parallel processes/tasks can be disjoint or cooperating (or competing) With cooperating and competing processes.

Process Synchronization A set of concurrent/parallel processes/tasks can be disjoint or cooperating (or competing) With cooperating and competing processes.
PROCESS SYNCHRONIZATION READINGS: CHAPTER 5. ISSUES IN COOPERING PROCESSES AND THREADS – DATA SHARING Shared Memory Two or more processes share a part.

PROCESS SYNCHRONIZATION READINGS: CHAPTER 5. ISSUES IN COOPERING PROCESSES AND THREADS – DATA SHARING Shared Memory Two or more processes share a part.
Chapter 6 Process Synchronization Bernard Chen Spring 2007.

Chapter 6 Process Synchronization Bernard Chen Spring 2007.
Background Concurrent access to shared data can lead to inconsistencies Maintaining data consistency among cooperating processes is critical What is wrong.

Background Concurrent access to shared data can lead to inconsistencies Maintaining data consistency among cooperating processes is critical What is wrong.
5.1 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts with Java – 8 th Edition Chapter 5: CPU Scheduling.

5.1 Silberschatz, Galvin and Gagne ©2009 Operating System Concepts with Java – 8 th Edition Chapter 5: CPU Scheduling.
Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition, Chapter 6: Process Synchronization.

Silberschatz, Galvin and Gagne ©2009 Operating System Concepts – 8 th Edition, Chapter 6: Process Synchronization.
Process Synchronization. Module 6: Process Synchronization Background The Critical-Section Problem Peterson’s Solution Synchronization Hardware Semaphores.

Process Synchronization. Module 6: Process Synchronization Background The Critical-Section Problem Peterson’s Solution Synchronization Hardware Semaphores.
Parallel Processing (CS526) Spring 2012(Week 6).  A parallel algorithm is a group of partitioned tasks that work with each other to solve a large problem.

Parallel Processing (CS526) Spring 2012(Week 6).  A parallel algorithm is a group of partitioned tasks that work with each other to solve a large problem.
Monitors Chapter 7. The semaphore is a low-level primitive because it is unstructured. If we were to build a large system using semaphores alone, the.

Monitors Chapter 7. The semaphore is a low-level primitive because it is unstructured. If we were to build a large system using semaphores alone, the.
CS 162 Discussion Section Week 3. Who am I? Mosharaf Chowdhury Office 651 Soda 4-5PM.

CS 162 Discussion Section Week 3. Who am I? Mosharaf Chowdhury Office 651 Soda 4-5PM.
CS444/CS544 Operating Systems Synchronization 2/16/2006 Prof. Searleman

CS444/CS544 Operating Systems Synchronization 2/16/2006 Prof. Searleman
U NIVERSITY OF M ASSACHUSETTS, A MHERST Department of Computer Science Emery Berger University of Massachusetts, Amherst Operating Systems CMPSCI 377 Lecture.

U NIVERSITY OF M ASSACHUSETTS, A MHERST Department of Computer Science Emery Berger University of Massachusetts, Amherst Operating Systems CMPSCI 377 Lecture.
Computer Science 162 Discussion Section Week 3. Agenda Project 1 released! Locks, Semaphores, and condition variables Producer-consumer – Example (locks,

Computer Science 162 Discussion Section Week 3. Agenda Project 1 released! Locks, Semaphores, and condition variables Producer-consumer – Example (locks,
Concurrency Recitation – 2/24 Nisarg Raval Slides by Prof. Landon Cox.

Concurrency Recitation – 2/24 Nisarg Raval Slides by Prof. Landon Cox.
9/8/2015cse410-23-synchronization-p1 © 2006-07 Perkins DW Johnson and University of Washington1 Synchronization Part 1 CSE 410, Spring 2008 Computer Systems.

9/8/2015cse synchronization-p1 © Perkins DW Johnson and University of Washington1 Synchronization Part 1 CSE 410, Spring 2008 Computer Systems.
1 Lecture 9: Synchronization  concurrency examples and the need for synchronization  definition of mutual exclusion (MX)  programming solutions for.

1 Lecture 9: Synchronization  concurrency examples and the need for synchronization  definition of mutual exclusion (MX)  programming solutions for.
1 Thread Synchronization: Too Much Milk. 2 Implementing Critical Sections in Software Hard The following example will demonstrate the difficulty of providing.

1 Thread Synchronization: Too Much Milk. 2 Implementing Critical Sections in Software Hard The following example will demonstrate the difficulty of providing.
Pthread (continue) General pthread program structure –Encapsulate parallel parts (can be almost the whole program) in functions. –Use function arguments.

Pthread (continue) General pthread program structure –Encapsulate parallel parts (can be almost the whole program) in functions. –Use function arguments.

Similar presentations

Ads by Google