# HW4-solution - Homework 4(Distributed File Systems...

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Homework 4 (Distributed File Systems, Self Stabilization, Transactions and Concurrency Control, Replication) 100 Points Solutions CS425/ECE 428 Distributed Systems, Fall 2009, Instructor: Klara Nahrstedt Out: Tuesday, November 10, Due Date : Tuesday, December 1 Instructions: (1) Please, hand in hardcopy solutions that are typed (you may use your favorite word processor). We will not accept handwritten solutions. Figures and equations (if any) may be drawn by hand. (2) Please, start each problem on a fresh sheet and type your name at the top of each sheet. (3) Homework will be due at the beginning of class on the day of the deadline. Problem 1 (15 Points) : Consider a Calendar composed of “week”, “days” and “hourly time slots”. Indicate what actions (block , grant lock, release lock) is taken and what type of locks are set for each of the following actions in the following sequence: (i) – Process A wants to insert an appointment for slot 11:00 am of Monday of week 10. (ii) – Before Process A completes, process B requires to read entries in week 10; (iii) – Process A finishes and commits. (iv) ‐‐ Process C wants to block off Monday of week 10 for a conference. Solutions: (i) – Process A wants to insert an appointment for slot 11:00 am of Monday of week-10. A acquires (action: grant Write Lock) - Write Lock on 11:00 AM time slot of Monday of Week-10; and - Write on Monday of week 10; and - Write on Week 10 (ii) – Before Process A completes, process B requires to read entries in week-10; B is blocked (waits) because the Read-Lock it needs is in conflict with the Write on Week 10; (i.e., B blocks until A releases the Write Lock)

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(iii) – Process A finishes and commits.
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