Gabrielle Evaristo CSE 460. Lab Dining Philosophers and Deadlock

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1 Gabrielle Evaristo CSE 460 Lab 8 1. Dining Philosophers and Deadlock Try dine1.cpp. Type to check the number of philosophers eating. What conclusion can you draw on the number of philosophers that can eat at one time? The output shows that only one philosopher is allowed to eat at a time. Compile and run dine2.cpp, and repeat the experiment as above. What is the maximum number of philosophers who can eat simultaneously? A maximum of 2 philosophers can eat simultaneously. Output: [ @csusb.edu@jb359-4 cse460]$ g++ -o dine2 dine2.cpp -lsdl [ @csusb.edu@jb359-4 cse460]$./dine2 Taking chopstick 0 2 philospers eating 2 philospers eating

2 Philosoper 4 2 philospers eating Taking chopstick 0 2 philospers eating Taking chopstick 0 Philosopher 4 eating! ^\ Quitting, please wait... Unlocking 0 Unlocking 0 done Unlocking 1 Unlocking 1 done Unlocking 2 Unlocking 2 done Unlocking 3 Unlocking 3 done Unlocking 4 Unlocking 4 done Taking chopstick 0

3 cse460]$ Add a delay statement like SDL_delay(rand() % 2000); right after the take_chops(l) statement in the philosopher function. Run the program for a longer time. What do you observe? Before the delay statement addition, 2 philosophers could eat simultaneously. However, adding the delay statement resulted in deadlock, meaning that philosophers have to wait their turn to eat (only 1 philosopher can eat at a time). Thus, philosopher 2 and 3 are stuck waiting, never getting a chance to eat. Added function: Output: [ @csusb.edu@jb359-4 cse460]$ g++ -o dine2 dine2.cpp -lsdl [ @csusb.edu@jb359-4 cse460]$./dine2 Taking chopstick 0 Taking chopstick 0 Philosopher 4 eating!

4 ^\ Quitting, please wait... Unlocking 0 Unlocking 0 done Unlocking 1 Unlocking 1 done Unlocking 2 Unlocking 2 done Unlocking 3 Unlocking 3 done Taking chopstick 0 Philosopher 4 eating! Unlocking 4 Unlocking 4 done [ @csusb.edu@jb359-4 cse460]$ To avoid deadlock, you can use an array state to record the state of each philosopher, and one can pick up the chopsticks only if her neighbors are not eating. Implement this mechanism as discussed in class and call your program dine3.cpp. Repeat the above experiment to see whether deadlock occurs and what the maximum number of philosophers can dine simultaneously. In this example, deadlock did not occur because a philosopher was only able to pick up the chopsticks if their neighbor was not eating. The maximum number of philosophers that can dine simultaneously is 3.

5 Code: #include <SDL/SDL.h> #include <SDL/SDL_thread.h> #include <stdio.h> #include <stdlib.h> #include <math.h> #include <signal.h> #include <unistd.h> #define LEFT (i - 1) % 5 #define RIGHT (i + 1) % 5 #define HUNGRY 0 #define EATING 1 #define THINKING 2 SDL_sem *s[5]; bool quit = false; int neating = 0; SDL_mutex *mutex; int state[5]; //one semaphore per philospher //number of philosphers eating //keeps track of state void test (int i) { //eats as long as neighbors are not eating if (state[i] == HUNGRY && state[left]!= EATING && state[right]!= EATING) { state[i] = EATING; SDL_SemPost (s[i]); void think(int i ) { SDL_Delay (rand () % 2000); //delay statement void take_chops(int i) { SDL_LockMutex(mutex); state[i] = HUNGRY; printf("\ntaking choptsticks %d", i); test(i); SDL_UnlockMutex(mutex); void eat(int i) { printf("\nphilosopher %d eating!\n", i); SDL_Delay(rand () % 2000); void put_chops(int i ) { SDL_LockMutex(mutex); state[i] = THINKING; test(left); test(right); SDL_UnlockMutex(mutex); void checkcount(int sig) { if (sig == SIGINT) { printf("\n%d philospers eating\n", neating ); else if (sig == SIGQUIT) {

6 quit = true; printf("\nquitting, please wait...\n"); for (int i = 0; i < 5; i++) { // break any deadlock printf("\nunlocking %d ", i ); SDL_SemPost ( s[i] ); printf("\nunlocking %d done", i ); int philosopher(void *data) { int i, l, r; i = atoi ((char *) data); l = i; r = (i + 1) % 5; while (!quit) { think(i); printf("\nphilosoper %d ", i); SDL_SemWait (s[l]); take_chops (l); SDL_Delay(rand() % 2000); SDL_SemWait(s[r]); take_chops(r); neating++; eat(i); neating--; put_chops(r); SDL_SemPost(s[r]); put_chops(l); SDL_SemPost(s[l]); int main() { struct sigaction act, actq; act.sa_handler = checkcount; sigemptyset(&act.sa_mask); sigaction (SIGINT, &act, 0); actq.sa_handler = checkcount; sigaction(sigquit, &actq, 0); SDL_Thread *p[5]; //thread identifiers const char *names[] = { "0", "1", "2", "3", "4" ; for (int i = 0; i < 5; i++) { s[i] = SDL_CreateSemaphore(1); for (int i = 0; i < 5; i++) { p[i] = SDL_CreateThread(philosopher, (char *) names[i]); for (int i = 0; i < 5; i++) { SDL_WaitThread(p[i], NULL); for (int i = 0; i < 5; i++) { SDL_DestroySemaphore(s[i]);

7 return 0; Output: cse460]$ g++ -o dine3 dine3.cpp -lsdl cse460]$./dine3 Taking choptsticks 2 Taking choptsticks 1 Taking choptsticks 3 0 philospers eating Taking choptsticks 0 Taking choptsticks 4 Philosoper 4 Taking choptsticks 2 Taking choptsticks 3 Taking choptsticks 1 Taking choptsticks 1 2 philospers eating Taking choptsticks 4 Taking choptsticks 3 0 philospers eating 0 philospers eating Taking choptsticks 0 Philosopher 4 eating! Taking choptsticks 0 Taking choptsticks 2 Taking choptsticks 2

8 Taking choptsticks 3 Taking choptsticks 4 3 philospers eating Taking choptsticks 1 Philosoper 4 Taking choptsticks 4 Taking choptsticks 2 Taking choptsticks 1 Taking choptsticks 0 Taking choptsticks 1 ^\ Quitting, please wait... Unlocking 0 Unlocking 0 done Unlocking 1 Unlocking 1 done Unlocking 2 Unlocking 2 done Unlocking 3 Unlocking 3 done Unlocking 4 Unlocking 4 done Taking choptsticks 3 Taking choptsticks 3 Taking choptsticks 2 Taking choptsticks 0 Philosopher 4 eating! Taking choptsticks 4 [ @csusb.edu@jb359-4 cse460]$

9 2. XV6 Process Priority 1. Add priority to struct proc in proc.h. 2. Assign default priority in allocproc() in proc.c. 3. Modify cps() in proc.c discussed in the las lab to include the printout of the priority. 4. Modify foo.c discussed in Lab 6 so that it loops for a much longer time before it exits.

10 5. Add the function chpr() (meaning change priority) in proc.c. 6. Add sys_chpr() in sysproc.c. 7. Add chpr() as a system call to xv6 as discussed in the last lab. a. Add name to syscall.h b. Add function prototype to defs.h (under proc.c) c. Add function prototype to user.h

11 d. Add function call to sysproc.c e. Add call to usys.s f. Add call to syscall.c g. Add code to proc.c

12 8. Create the user file nice.c which calls chpr. Add nice to the system as discussed in lab 7. To add nice to the system, you have to modify the Makefile. 9. Test nice using foo. Run foo to create a few processes, which run in the background and check them using ps: ($ foo 4 &). As can be seen in the output below, the program works successfully. $ ls README cat echo forktest grep init kill ln ls mkdir rm sh

13 stressfs usertests wc zombie console ps nice //successfully added to command list $ foo 4 &.... $ ps Name pid State Priority init 1 SLEEPING 10 sh 2 SLEEPING 10 foo 4 RUNNING 10 foo 5 SLEEPING 10 foo 6 RUNNING 10 foo 7 SLEEPING 10 ps 18 RUNNING 10 Change the priority of a process using nice and check the status using ps again. As can be seen in the output below, the command successfully changed the priority from 10 to 18 of the process with pid: 4. $ nice 4 18 Name pid State Priority init 1 SLEEPING 10 sh 2 SLEEPING 10 foo 4 RUNNING 18 foo 5 SLEEPING 10 foo 6 RUNNING 10 foo 7 SLEEPING 10

Diego Gamboa. cse 460: Operating Systems. Dr. Yu. Lab 8: Dining Philosophers and XV6 Process Priority.

Diego Gamboa. cse 460: Operating Systems. Dr. Yu Lab 8: Dining Philosophers and XV6 Process Priority. 1] Dining Philosophers and Deadlock. ** Try the following program type ^C run it for some time to check