Introduction to Computer Systems Homework 8

cs154: Introduction to Computer Systems

Homework 8

Submit your work by committing files in the hw8 sub-directory of your CNETID-cs154-spr-20 svn
repository. The filename should be either hw8.txt or hw8.pdf for answers in plain ASCII text, or PDF,
respectively. PDFs of scanned hand-written pages must not exceed 6 megabytes. Not following directions
will result in losing points.
(1) (18 points)
1 #include "csapp.h"
2 #define N 2
3 void *thread(void *vargp);
4
5 char **ptr; /* global variable */
6
7 int main()
8 {
9 int i;
10 pthread_t tid;
11 char *msgs[N] = {
12 "Hello from foo",
13 "Hello from bar"
14 };
15
16 ptr = msgs;
17 for (i = 0; i < N; i++)
18 Pthread_create(& tid, NULL, thread, (void *)&i);
19 Pthread_exit(NULL);
20 }
21
22 void *thread(void *vargp)
23 {
24 int myid = *((int*)vargp);
25 int cnt = 0;
26 printf("[%d]: %s (cnt=%d)\n", myid, ptr[myid], ++cnt);
27 return NULL;
28 }
This question refers to the above modified version of the code in textbook Figure 12.15. Modifications were made to lines 18, 24, and 25.
Using the analysis from Section 12.4, fill each entry in the following table with “Yes” or “No” for
the code above. In the first column, the notation v.t denotes an instance of variable v residing
on the local stack for thread t, where t is either m (main thread), t0 (peer thread 0), or t1 (peer
thread 1). This is a modification of Practice Problem 12.6.A.
Variable instance Referenced by main
thread?
Referenced by peer
thread 0?
Referenced by peer
thread 1?
cnt.t0
cnt.t1
i.m
msgs.m
myid.t0
myid.t1
(2) (15 points)
Consider the following use of mutexes in two threads in light of the “Mutex lock ordering rule”
from textbook Section 12.7.
Initially: a = 1, b = 1, c = 1, d = 1.
Thread 1: Thread 2:
P(a); P(a);
P(b); V(a);
V(b); P(d);
P(c); P(c);
V(c); P(b);
P(d); V(b);
V(d); V(c);
V(a); V(d);
A. List all pairs of mutexes that Thread 1 can hold, and all pairs of mutexes that Thread 2 can hold.
B. Is there overlap between the sets of pairs of mutexes? If yes, are the mutexes (within the pair)
locked in the same order?
C. Given your analysis, is there a potential for deadlock (Yes or No)?