Cracking the Coding Interview, 4 Edition - 150 Programming Interview Questions and Solutions

Solutions to Chapter 18 | Threads and Locks
18.5 Suppose we have the following code:
class Foo {
public:
A(.....); /* If A is called, a new thread will be created and
* the corresponding function will be executed. */
B(.....); /* same as above */
C(.....); /* same as above */
}
Foo f;
f.A(.....);
f.B(.....);
f.C(.....);
i) Can you design a mechanism to make sure that B is executed after A, and C is executed
after B?
iii) Suppose we have the following code to use class Foo. We do not know how the
threads will be scheduled in the OS.
Foo f;
f.A(.....); f.B(.....); f.C(.....);
f.A(.....); f.B(.....); f.C(.....);
Can you design a mechanism to make sure that all the methods will be executed in
sequence?
SOLUTION
pg 86
i) Can you design a mechanism to make sure that B is executed after A, and C is executed after B?
1 Semaphore s_a(0);
2 Semaphore s_b(0);
3 A {
4 /***/
5 s_a.release(1);
6 }
7 B {
8 s_a.acquire(1);
9 /****/
10 s_b.release(1);
11 }
12 C {
13 s_b.acquire(1);
14 /******/
15 }
ii) Can you design a mechanism to make sure that all the methods will be executed in sequence?
1 Semaphore s_a(0);
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