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CS 1901473 Operating Systems; Exam 2; Saturday, May 15, 2004; 1 Hour
Student Name (CAPITAL LETTERS): _______________________________________
Student Number: __________________________________________
Section: ___________________
Problem 1(10 pts)
Answer yes or no, or with a single term or short answer, as appropriate.
a) Does the test-and-set instruction need to be a privileged instruction
b) A resource allocation graph that has a cycle in it always/sometimes/never means
that there is a deadlock
c) What approach to dealing with deadlock does the Banker’s algorithm implement
d) A system that meets the four deadlock conditions will always/sometimes/never
result in deadlock
.
Problem 2 (10 pts)
What is the advantage of using threads compared to processes (your answer should be
short. VERY SHORT)
Problem 3 LINUX (10 pts)
a) write down the command needed to change the file permission to be as shown
below:
Filename: file1, Required file permission :_r_x r_ _r_ _
b) write down the command that will give you long listing for the content for your
current directory
c) write down the command that will show you the process tree available on your
system
d) If you have a process P1 hanged in the system, what is the name of the
command used to terminate this process
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Problem 4 (30 pts)
a) (15 pts) Three processes share four resource units that can be reserved and
released only one at a time. Each process acquires and releases resources over
time but only needs a maximum of two resource units at any one time. Deadlock
can not occur. Why
b) (15 pts) Consider a system consisting of m resources of the same type, being
shared by n processes. Resources can be requested and released by processes
only 1 at a time. Show that the system is deadlock free if the following two
conditions hold:
(I) The max need for each process is between 1 and m resources.
(II) The sum of all max needs is less than n + m.
Problem 5 (15 pts)
In lecture we said that, if the semaphore operations Wait and Signal are not executed
atomically, then mutual exclusion may be violated. Assume that Wait and Signal are
implemented as below:
void Wait (Semaphore S) {
while (S.count

Problem 6 (25 Points)
Consider a system that has W workers and M managers that continuously enter and
leave an office. Work can only be done in teams consisting of 1 manager and 2 workers
in the office. The detailed requirements are:
• Managers arrive to a FCFS queue, and workers arrive to their own FCFS queue.
• When the manager at the front of the queue is ready, he/she picks the next two
workers for his team and tells them to begin working. Then, the next manager
can form his/her team in a similar manner.
• Workers tell their manager when they are done working and leave immediately.
• A manager does not leave until all team members have said they are leaving.
• After work is completed, the team members leave for a random amount of time
before re turning.
a) Describe the synchronization for the manager process by writing the manager
process in terms of the counting semaphore primitives Signal() and Wait() and
the semaphore and variable declarations. Note: You do not need to give the
worker process code; i.e., you can assume that the worker process is given.
b) Describe the use of each semaphore and the general logic of the manager
process. You can do that using comments in your code.
HINT: (Note: You may use the following skeleton.)
struct {
int manager;
int worker[2];
int n=0;
} newTeam;
// shared
// manager of new team
// which workers are forming a new team
// how many entries in worker[2]
... semaphore definitions ...
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process manager (i) {
int myTeam[2];
// who is on my team
}
do forever {
... code ...
}
process worker (i) {
... NOT NEEDED ...
}
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