Chapter 6, Problem 18

Operating Systems: Internals and Design Principles Systems, 7th Edition (Textbook Solutions)

Author: William Stallings

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Suppose that there are two types of philosphers. One type always picks up his left fork first (a "lefty"), and the other type always picks up his right fork first (a "righty"). The behavior of a left is defined in Figure 6.12. The behavior of a righty is as follows:

begin

repeat

think;

wait (fork[(i+1) mod 5]);

wait (fork[i]);

eat;

signal (fork[i]);

signal (fork[(i+1) mod 5]);

forever

end;

Prove the following:

a. Any seating arrangement of lefties and righties with at least one of each avoids deadlock.

b. Any seating arrangement of lefties and righties with at least one of each prevents starvation.

Figure 6.12

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/*program dining philopsheres*/

semaphore fork [5] = {1};

int i;

void philosopher (int i){

while(true){

think();

wait( fork [i]);

wait( fork [(i+1) mod 5]);

eat();

signal (fork [(i+1) mod 5]);

signal (fork[i]);

}

}

void main(){

parbegin (philosopher (0), philosopher (1), philosopher (2), philosopher (3), philosopher (4));

}

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