CS 241 Spring 2007: System Programming Midterm Review - Reader-Writer Problem, Study notes of Computer Science

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CS 241 Spring 2007System Programming

Classic Synchronization Problems (Reader-Writer Problem) Midterm Review Topics

Lecture 19 Klara Nahrstedt

CS241 Administrative

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Read Chapter 5.6 in Stallings

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Homework 1 due 3/2 4pm in Anda Ohlsson’sOffice

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MIDTERM – MONDAY, March 5, 11am (willtalk about Midterm at the end of lecture)

First Reader-Writer Problem •

readers: read data

writers: write data

Rule:

Multiple readers can read the data simultaneously

Only one writer can write the data at any time

A reader and a writer cannot in critical section together.

Locking table: whether any two can be in the critical sectionsimultaneously

Reader

Writer

Reader

OK

No

Writer

NO

No

First Readers-Writers Problem (Readers have priority) Let processes reading do so concurrently Let processes writing do so one at a time Introduce semaphores Semaphore mutex = 1; Semaphore wrt = 1; int readc = 0; /* reader counter */

First Reader-Writer Solution Does it work? What if?Problem with this solutionMutex m, wrt;int readcount;

// shared and initialized to 0

// Writer

// Reader

Lock(&m);

readcount:=readcount+1;

Lock(&wrt);

if (readcount == 1) lock(&wrt);

......

unlock(&m);

writing performed

....

.....

reading performedlock(&m);

Lock(&wrt);

readcount:=readcount-1;if (readcount == 0) unlock(&wrt);

Unlock(&m);

Midterm Review †

Review^ „

Lecture Notes

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All quizzes until today †

SMP Quizzes and Regular Quizzes

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Review homework 1 solutions

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Review Stallings and R&R book material

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Midterm

• Monday 11-11:50am, 1404 SC

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Review Session

• Sunday 2-3:30pm in 1404 SC

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You need to bring questions, TAs will respond

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Midterm^ „

closed book, closed notes,

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NO calculator or other calculating electronic devices

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No cell-phones

Topics: Processes †

Chapter 3.1-3.4 (Stallings)

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Chapter 2 and 3 (R&R)

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Keywords need to know „

What is process?

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What is the difference between process and program?

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What is the program image layout?

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Understand argument arrays

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What does it mean to have a thread-safe function?

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What is the difference between static and dynamic variables?

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What are the major process states?

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What is the difference between dispatcher and scheduler?

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What is PCB?

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What happens when process switches from running to readystate?

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What is process chain, process fan?

Topics: Threads †

Chapter 12.1-12.5 (R&R)

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Chapter 4.1, 4.5 (Stallings)

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Keywords need to know^ „

What is the difference between processes andthreads?

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What is the difference between user-level threadsand kernel-level threads?

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Detaching and joining threads

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What happens if you if you call exit(1) in a thread?

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What is a graceful way to exit a thread withoutcausing process termination?

Topics: Thread Synchronization †

Chapter 13.1-13.2 (R&R)

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Keywords to know^ „

What are mutex locks?

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How do you initialize mutex locks?

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When would you use mutex instead of countingsemaphore?

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When would you use counting semaphore instead ofmutex?

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Are mutex functions interrupted by signals?

Topics: Scheduling †

Chapter 9.1-9.2 Scheduling (Stallings)

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Keywords need to know^ „

Scheduling policies

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FCFC, SJF, Round Robin, Priority Scheduling

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Preemptive vs. Non-Preemptive Scheduling

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Queues in Process management – what is readyqueue? How are process states related to processmanagement queues?

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What is average waiting time?

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What is the difference between process waiting timeand turn-around time?

Topics: Timers †

Chapter 9.1-9.3 (R&R)

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Keywords need to know^ „

Understand what the various time functions are for

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Gettimeofday

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Understand the different clock resolutions

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Sleep function

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What are time intervals? What are they great for?

Topics: Classical Sync Problems †

Chapter 5.3 and 6.6 (Stallings )

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Keywords need to know^ „

What is the producer-consumer problem?

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What are the various semaphores in theproducer/consumer solution for?

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What is the dining philosopher problem?

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What is the danger of a simple solution for diningphilosopher problem?