PhiladelphiaUniversity

Lecturer : Dr Maouche Mourad

Coordinator : Dr Maouche Mourad

Internal Examiner:Dr. Raad. F. Alwan

Distributed Operating Systems (750732) Mid-Term Exam 2st Semester of 2009/2010

April 29, 2010 Time: 2.30 Hours

Information for Candidates

This examination paper contains 5 questions totaling 48 marks.

Advice to Candidates

You should attempt questions, such that the sum of their marks will be equal to 30.

  1. Basic Notions

Objectives: The aim of the questions in this part is to evaluate your required minimal knowledge and skills. Answers in the pass category represent the minimum acceptable standard.

Q1. (14 marks)

1. State the purpose of middleware in the context of distributed operating systems. Comment briefly on one of the studied distributed middleware(4 marks)

2. State the difference between a distributed operating system and a network operating system. (3 marks)

3. State briefly the characteristics (design issues) of OS microkernels when compared to monolithic OS kernels. (4 marks)

4. Compare, according to appropriate criteria, the concept of mailbox and the concept of port. (3 marks)

II.Familiar Problems Solving

Objectives. The aim of the questions in this part is to evaluate that you have some basic knowledge of the key aspects of the lecture material and can attempt to solve familiar problems.

Q2.Assume a distributed system with three sites, all of which are equipped with vector clocks that are initialized to (0, 0, 0). Assume further that each letter in the diagram represents an event as explained in the accompanying table.

Suppose messages are individually directed and the Schiper-Eggli-Sandoz protocol is used to maintain causal ordering of messages. Show all vector clock updates in the three sites as a result of these message sending activities. Please mark all your clock updates on the diagram. Show also the final content of the V_P sets at the end of all the given events. (10 marks)

LABEL| EVENT

(0,0,0) ------

P1 ------a------b------c------a| M3 arrives at P1

b| M4 arrives at P1

(0,0,0)c| M1 arrives at P1

P2 ------d------e------f------d| P2 sends M1 to P1 e | P2 sends M2 to P3

(0,0,0)f| P2 sends M4 to P1

P3 ------g------h------g| M2 arrives at P3

h| P3 sends M3 to P1

------

Q3. Assume that a distributed banking application is running over the nodes 1, 2 and 3.These nodesmaintain three bank accounts named as A, B, and C respectively with $10as the initial balance in each. Consider the following scenario: (12 marks)

•Site 1 sends $5 to site 2.

•Site2 sends $10 to site 1.

•Site 1 sends $4 to site 3.

•Site 2 receives $5 from site 1.

•Site 1 receives $10 from site 2.

•Site 3 sends $8 to site 2.

•Site 2 receives $8 from site 3.

•Site 3 receives $4 from site 1.

Node 1 launches the Chandy Lamport algorithm at the point 'Chandy-lamport launched

Assume total amount of money is conserved (no deposits or withdrawals).

Run the Chandy Lamport algorithm manually, and record a consistent global state for this scenario. Clearly show all the messages (both computation and marker) and the collected global state.

Q4. Given a distributed system with three processes P1, P2, and P3, in three different sites where mutual exclusion is enforced using Ricart-Agrawala's algorithm. Consider the scenario below and list in detail all the events that follow until both processes complete their critical sections. (6 marks)

  • Both P1 and P2 are requesting for critical section while P3 has no need at this time.
  • The timestamp of P1's request is 47, and that of P2 is 32.

III. Unfamiliar Problems Solving

Objectives. The aim of the questions in this part is to evaluate you can make progress towards the solution of unfamiliar problems, and can set out reasoning and explanation in a clear and coherent manner

Q5. If a site S has to broadcast message M to a set of sites, will the Schiper-Eggli-Sandoz protocol for causal ordering of messages work properly without modification? If your answer is yes, justify your answer and show a counter-example. (6 marks)

.