Solutions. CS241 Homework 2. Fall 2008. netid: _ _ _ _ _ _ _ _
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Question 1: (Game, Set and) Match it!
Part I. [7 points] 1-b,e (any one answer is ok too). 2-b,d,e. 3-a. 4-none. 5-d,e. 6-c,d,e.
Part II. [3 points] 1-i. 2-e. 3-a. 4-g. 5-h.
Question 2: Nobel Process Hierarchy [10 points]
One possible solution is as follows.
create_binary_tree_with_depth(int N){
int i;
for (i = 1; i < N; i++)
if (fork()) /* 1st child created – child goes to next for iteration */
if (fork()) /* 2nd child created – child goes to next for iteration */
break; /* parent done and exits */
}
Question 3: Does it Sync? [10 points]
Guarantees... Case a b c d e
Mutual
Exclusion(Yes/No)
No Yes Yes No Yes
Progress (Yes/No)
No No No Yes Yes
Question 4: Ping-Pong 1 [10 points]
i. [2 points] If pongthread is the fast one, it will execute mythread_start(pingthread)
before pingthread has executed mythread_stop(). Subsequently, both threads will
deadlock.
ii. [8 points] One possible solution is as follows.
Sempahores sping=0, spong=0; /* shared by both threads */
void ping() {
while(true) {
sping.wait();
printf("ping is here\n");
spong.signal();
}
}
void pong() {
while(true) {
printf("pong is here\n");
sping.signal();
spong.wait();
}
}
