Docsity
Docsity
Prepare for your exams
Prepare for your exams

Study with the several resources on Docsity

Earn points to download
Earn points to download

Earn points by helping other students or get them with a premium plan

Guidelines and tips
Guidelines and tips
Sell on Docsity
Sell on Docsity
Docsity AI
Docsity AI
Log inSign up

Prepare for your exams

Study with the several resources on Docsity

Find documents

Prepare for your exams with the study notes shared by other students like you on Docsity

Search for your university

Find the specific documents for your university's exams

Docsity AINEW

Summarize your documents, ask them questions, convert them into quizzes and concept maps

Explore questions

Clear up your doubts by reading the answers to questions asked by your fellow students

Earn points to download

Earn points by helping other students or get them with a premium plan

Share documents
download point icon20 Points

For each uploaded document

Answer questions
download point icon5 Points

For each given answer (max 1 per day)

All the ways to get free points
Get points immediately

Choose a premium plan with all the points you need

Study Opportunities

Choose your next study program

Get in touch with the best universities in the world. Search through thousands of universities and official partners

Community

Ask the community

Ask the community for help and clear up your study doubts

Free resources

Our save-the-student-ebooks!

Download our free guides on studying techniques, anxiety management strategies, and thesis advice from Docsity tutors

Deadlocks - Applied Operating System - Lecture Slides, Slides of Computer Science

University of AllahabadComputer Science

These are the Lecture Slides of Applied Operating System which includes Swapping, Virtual Memory, Page Replacement Algorithms, Modeling Page Replacement Algorithms, Design Issues for Paging Systems, Implementation Issues, Segmentation etc. Key important points are: Deadlocks, Ostrich Algorithm, Deadlock Detection, Deadlock Recovery, Deadlock Avoidance, Deadlock Prevention, Computer Resources, Preemptable Resources, Sequence of Events, Conditions for Deadlock

Typology: Slides

2012/2013

Uploaded on 03/21/2013

dheeraj
dheeraj 🇮🇳

5

(4)

101 documents

1 / 22

Toggle sidebar

This page cannot be seen from the preview

Don't miss anything!

bg1
Deadlocks
Chapter 3
3.1. Resource
3.2. Introduction to deadlocks
3.3. The ostrich algorithm
3.4. Deadlock detection and recovery
3.5. Deadlock avoidance
3.6. Deadlock prevention
3.7. Other issues
Docsity.com
pf3
pf4
pf5
pf8
pf9
pfa
pfd
pfe
pff
pf12
pf13
pf14
pf15
pf16

Partial preview of the text

Download Deadlocks - Applied Operating System - Lecture Slides and more Slides Computer Science in PDF only on Docsity!

Deadlocks

Chapter 3

3.1. Resource 3.2. Introduction to deadlocks 3.3. The ostrich algorithm 3.4. Deadlock detection and recovery 3.5. Deadlock avoidance 3.6. Deadlock prevention 3.7. Other issues

Resources

  • Examples of computer resources
    • printers
    • tape drives
    • tables
  • Processes need access to resources in reasonable order
  • Suppose a process holds resource A and requests

resource B

  • at same time another process holds B and requests A
  • both are blocked and remain so

Resources (2)

  • Sequence of events required to use a resource
    1. request the resource
    2. use the resource
    3. release the resource
  • Must wait if request is denied
    • requesting process may be blocked
    • may fail with error code

Introduction to Deadlocks

  • Formal definition : A set of processes is deadlocked if each process in the set is waiting for an event that only another process in the set can cause
  • Usually the event is release of a currently held resource
  • None of the processes can …
    • run
    • release resources
    • be awakened

Deadlock Modeling (2)

  • Modeled with directed graphs
    • resource R assigned to process A
    • process B is requesting/waiting for resource S
    • process C and D are in deadlock over resources T and U

Deadlock Modeling (3)

Strategies for dealing with Deadlocks

  1. just ignore the problem altogether
  2. detection and recovery
  3. dynamic avoidance
    • careful resource allocation
  4. prevention
    • negating one of the four necessary conditions

Detection with One Resource of Each Type (1)

  • Note the resource ownership and requests
  • A cycle can be found within the graph, denoting deadlock

Detection with One Resource of Each Type (3)

An example for the deadlock detection algorithm

Recovery from Deadlock (2)

  • Recovery through killing processes
    • crudest but simplest way to break a deadlock
    • kill one of the processes in the deadlock cycle
    • the other processes get its resources
    • choose process that can be rerun from the beginning

Banker's Algorithm for Multiple Resources

Example of banker's algorithm with multiple resources

Attacking the Hold and Wait Condition

  • Require processes to request resources before starting
    • a process never has to wait for what it needs
  • Problems
    • may not know required resources at start of run
    • also ties up resources other processes could be using
  • Variation:
    • process must give up all resources
    • then request all immediately needed

Attacking the No Preemption Condition

  • This is not a viable option
  • Consider a process given the printer
    • halfway through its job
    • now forcibly take away printer
    • !!??

Attacking the Circular Wait Condition (1)

Summary of approaches to deadlock prevention

Other Issues

Two-Phase Locking

  • Phase One
    • process tries to lock all records it needs, one at a time
    • if needed record found locked, start over
    • (no real work done in phase one)
  • If phase one succeeds, it starts second phase,
    • performing updates
    • releasing locks
  • Note similarity to requesting all resources at once
  • Algorithm works where programmer can arrange
    • program can be stopped, restarted