C language Homework

#include <stdio.h> #include <stdlib.h> #include <pthread.h> #include <time.h> #include <unistd.h> // Change the constant below to change the number of philosophers // coming to lunch... // This is a known GOOD solution based on the Arbitrator // solution #define PHILOSOPHER_COUNT 20 // Each philosopher is represented by one thread. Each thread independenly // runs the same "think/start eating/finish eating" program. pthread_t philosopher[PHILOSOPHER_COUNT]; // Each chopstick gets one mutex. If there are N philosophers, there are // N chopsticks. That's the whole problem. There's not enough chopsticks // for all of them to be eating at the same time. If they all cooperate, // everyone can eat. If they don't... or don't know how.... well.... // philosophers are going to starve. pthread_mutex_t chopstick[PHILOSOPHER_COUNT]; // The arbitrator solution adds a "waiter" that ensures that only pairs of // chopsticks are grabbed. Here is the mutex for the waiter ;) pthread_mutex_t waiter; void *philosopher_program(int philosopher_number) { // In this version of the "philosopher program", the philosopher // will think and eat forever. while (1) { // Philosophers always think before they eat. They need to // build up a bit of hunger.... //printf ("Philosopher %d is thinking\n", philosopher_number); usleep(1); // That was a lot of thinking.... now hungry... this // philosopher (who knows his own number) grabs the chopsticks // to her/his right and left. The chopstick to the left of // philosopher N is chopstick N. The chopstick to the right // of philosopher N is chopstick N+1 //printf ("Philosopher %d wants chopsticks\n",philosopher_number); pthread_mutex_lock(&waiter); pthread_mutex_lock(&chopstick[philosopher_number]); pthread_mutex_lock(&chopstick[(philosopher_number+1)%PHILOSOPHER_COUNT]); pthread_mutex_unlock(&waiter); // Hurray, if I got this far I'm eating printf ("Philosopher %d is eating\n",philosopher_number); //usleep(1); // I spend twice as much time eating as thinking... // typical.... // I'm done eating. Now put the chopsticks back on the table //printf ("Philosopher %d finished eating\n",philosopher_number); pthread_mutex_unlock(&chopstick[philosopher_number]); pthread_mutex_unlock(&chopstick[(philosopher_number+1)%PHILOSOPHER_COUNT]); //printf("Philosopher %d has placed chopsticks on the table\n", philosopher_number); } return(NULL); } int main() { int i; srand(time(NULL)); for(i=0;i<PHILOSOPHER_COUNT;i++) pthread_mutex_init(&chopstick[i],NULL); pthread_mutex_init(&waiter,NULL); for(i=0;i<PHILOSOPHER_COUNT;i++) pthread_create(&philosopher[i],NULL,(void *)philosopher_program,(void *)i); for(i=0;i<PHILOSOPHER_COUNT;i++) pthread_join(philosopher[i],NULL); for(i=0;i<PHILOSOPHER_COUNT;i++) pthread_mutex_destroy(&chopstick[i]); return 0; }