Operating Systems 173323 (3 cu)

Exercise 10

Week 51

Exercises 10 are in computer classes:

Group 1: on Monday Dec. 17 at 14-16 in T/B178
Group 2: on Monday Dec. 17 at 10-12 in T/B178

1. Consider the following resource allocation graph:

   P = {P1,P2,P3,P4}
   R = {R1,R2,R3}
   E = {R1 --> P1, P1 --> R2, R2 --> P2, P2 --> R3,
        R3 --> P3, P3 --> R1, R1 --> P4}
   

   - resource type R1 has two instances
   - resource type R2 has one instance
   - resource type R3 has one instance

   Draw a resource allocation graph and explain the possibility for a deadlock.

2. Consider the following resource allocation graph:

   P = {P1,P2,P3}
   R = {R1,R2,R3}
   E = {R1 --> P1, P1 --> R2, R2 --> P2, P2 --> R3,
        R3 --> P3, P3 --> R1}
   

   - resource type R1 has one instance
   - resource type R2 has one instance
   - resource type R3 has one instance

   Draw a resource allocation graph and explain the possibility for a deadlock.

3. Consider the following situation, in which there are 3 processes and the total number of recources is 12.

   Process   Current needs   Maximum needs
   ---------------------------------------
     P1            5              10 
     P2            2               4
     P3            2               9
   

   Is the state above safe or unsafe ?

   In the next state, process P1 needs two more resources. Is the state then safe or unsafe ?

4. Consider a disk that has 200 cylinders (from 0 to 199). Disk arm (read/write head) is currently in position 143 and before that it was in position 125. Consider a queue of requests: 86, 147, 91, 177, 94, 150, 102, 175, 130.

   Calculate the total number of disk arm movements needed, when the disk scheduling is done using:

   a) FCFS
   b) SSTF
   c) SCAN
   d) C-SCAN
   

   Draw also a figure to visualize the disk arm movement in every scheduling.

   The copies of the material for this task are available in Rekursio's room.