| (b) |
Describe,using examples,three situations
which may lead to deadlock.
One mark is available
for naming each situation,one mark is available for each satisfactory
elaboration,and one mark is available for a suitable example.
•Mutual exclusion
(1 mark).Only one process can use a particular resource;if another
process requests that resource,the requesting process ust be delayed
until the resource has been released (1 mark).
•Hold and wait (1 mark).One process already holds at least one resource,and
is waiting to acquire more resources which are held by other resources
(1 mark).
•No preemption (1 mark).Resources cannot be preempted:resources can
only be released voluntarily by the process holding it,after the process
has completed its task (1 mark). •Circular wait (1 mark).There is
a circular chain of two or more processes, each of which is waiting
for a resource held by the next member of the chain (1 mark).
|
[9] |
| (c) |
Refer to the scenario given below,in
which there are three processes,A,B and C, and three resources,R,S
and T.
|
Processes
|
A
|
B
|
C
|
|
|
Request R
|
Request S
|
Request T
|
|
|
Request S
|
Request T
|
Request R
|
Illustrate,using a Resource Allocation
Graph,how deadlock may be avoided.
One mark
should be awarded for the correct representation of processes and
resources; one mark should be awarded for the correct representation
of the holding of a resource;one mark should be awarded for the correct
representation of the request for a resource;and one mark should be
awarded if the overall representation is correct.
|
[4] |