Galvin Edition 9 Exercise 7 Question 16 (Page No. 342-343)

Question

In a real computer system, neither the resources available nor the demands of processes for resources are consistent over long periods (months). Resources break or are replaced, new processes come and go, and new resources are bought and added to the system. If deadlock is controlled by the banker’s algorithm, which of the following changes can be made safely (without introducing the possibility of deadlock), and under what circumstances ?

a. Increase $Available$ (new resources added).

b. Decrease $Available$ (resource permanently removed from system).

c. Increase $Max$ for one process (the process needs or wants more resources than allowed).

d. Decrease $Max$ for one process (the process decides it does not need that many resources).

e. Increase the number of processes.

f. Decrease the number of processes.

Comments

a) Increase Available (new resources added)- This could safely be changed without any problems.

b) Decrease Available (resource permanently removed from system)- This could have an effect on the system and introduce the possibility of deadlock as the safety of the system assumed there were a certain number of available resources.

c) Increase Max for one process (the process needs more resources than allowed, it may want more)-This could have an effect on the system and introduce the possibility of deadlock.

d) Decrease Max for one process (the process decides it does not need that many resources)—This could safely be changed without any problems.

e) Increase the number of processes—This could be allowed assuming that resources were allocated to the new process such that the system does not enter an unsafe state.

f) Decrease the number of processes—This could safely be changed without any problems.