Philadelphia University
Faculty of Information Technology
Lecturer
: Dr. M. Maouche
Coordinator
: Dr M. Maouche
Internal Examiner : Dr N. Nedam
Marking Schema
Department of Computer Science
Course Name: Advanced OS (750434)
Section: 1
Final Exam
First Semester
Academic Year: 2014/15
Date: February, 5th, 2015 Time: 120 minutes
Question1: (18 marks)
1. Access, Location, Migration, Replication transparency (1x4)
2. migration transparency: Distributed OS has the ability to move OS resources from
one location to another location in a way not visible to users.
(2)
3. Application programmers will program their centralized or their distributed
concurrent programs in a uniform way by using the same process communication
paradigm (read/write shared memory) (2)
4 load balancing (1); load sharing (1); Task assignment approach (1)
5. Remote File Access (1), Caching based Access (1)
6. Increase of Availability, of performance, of reliability.... (2)
7. Message Passing (1), RPC (1), DSM (1) mechanisms
.
Question2:
1. (3)
P3:
P4:
r(x) a
r (x) b
r(x)a
r(x)b
It is not satisfy strict consistency model because the first read value by P3 and P4 is
not the last update value of x (2)
It satisfies sequential consistency model because P3 and P4 see the same global order
when reading the values of x. (2)
3. No it does not satisfy the causal consistency model (4)
w(x)b is causally-related on r(x)a, which is causally-related on w(x)a
Therefore, system must enforce w(x)a < w(x)b ordering.
But P3 violates that ordering, because it reads a after reading b.
Question3: (6 marks)
Run T; U : x=10; ai = 55; aj= 66
Run U;T : ai =55; x=55; aj=44
Run (a) gives same results than T;U so (a) is serially equivalent (2)
Run (b) gives the same results than T;U so (b) is serially equivalent (2)
(a) does not respect the two-phase locking because the scenario does not apply the
growing phase and shrinking phase when locking and unlocking both ai and aj. (1)
b) respects the two-phase locking because the scenario applies the growing and
shriking phase when locking and unlocking both ai and aj. (1)
Question4: (6 marks)
Execution cost = E11 + E21 + E32 + E43 = 33 + 1 + 4 + 10 = 48 (2)
Communication cost= C13 + C23 + C14 + C24 + C34 = 3 + 6 + 8 + 4 + 23 = 44 (2)
Total cost = Execution cost + Communication cost = 48 +44 = 92 (2)
Question5 : (6 marks)
(i)
Sequential: 2(5 (prepare) + 4(0.5 (marsh/unmarsh) + 0.5 (local OS)) + 2*3 (net)) +
10 (serv)) = 50 ms
(ii) concurrent: because of the overlap, the total is that of the time for the first
operation’s request message to reach the server, for the server to perform all
processing of both request and reply messages without interruption, and for the
second operation’s reply message to reach the client.
This is: 5 + (0.5+0.5+3) + (0.5+0.5+10+0.5+0.5) + (0.5+0.5+10+0.5+0.5) + (3 +
0.5+0.5) = 37ms