109 lines
3.3 KiB
C
109 lines
3.3 KiB
C
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// MODIFY THIS FILE to use pthreads rather than IPC. Lines marked with
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// **CHANGE** indicate lines that are higly likely to need alterations.
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#include <error.h>
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#include <pthread.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <sys/sem.h>
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#include <sys/types.h>
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#include <sys/wait.h>
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#include <time.h>
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#include <unistd.h>
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#define N_PHILOSOPHERS 5 // Number of philosophers
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const int MEALS_TO_FINISH = 2; // Number of iterations before finish
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const int MAX_DELAY = 50000; // Maximum delay in nanos between meal iterations
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pthread_mutex_t utensils[N_PHILOSOPHERS];
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void *philosopher(void *n);
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// **CHANGE** to have prototype compatible with thread entry points
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int main() {
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setvbuf(stdout, NULL, _IONBF, 0);
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int i, status;
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pthread_t phil[N_PHILOSOPHERS];
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printf("The Dining Swansons (Philosophers) Problem\n");
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// Parent thread only:
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//
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// Allocate utensils: mutexes
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for (i = 0; i < N_PHILOSOPHERS; i++) {
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pthread_mutex_init(&utensils[i], NULL);
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}
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// Parent generates child processes
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int numbers[N_PHILOSOPHERS];
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for (i = 0; i < N_PHILOSOPHERS; i++) {
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numbers[i] = i; // workaround for wrong numbers
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status = pthread_create(&phil[i], NULL, &philosopher, &numbers[i]);
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if (status) {
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fprintf(stderr, "Could not create thread: %s\n", strerror(status));
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exit(1);
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}
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}
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// Parent waits on all children to finish
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for (i = 0; i < N_PHILOSOPHERS; i++) {
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pthread_join(phil[i], NULL);
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}
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printf("JJ: All Swansons finished, cleaning up the diner\n");
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// Eliminate the utensils and table semaphores
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for (i = 0; i < N_PHILOSOPHERS; i++) {
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pthread_mutex_destroy(&utensils[i]);
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}
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return 0;
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}
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// Code for dining philosopher child processes
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void *philosopher(void *arg) {
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int n = *(int *)arg;
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int i, first, second;
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srand(time(NULL)); // Seed random number generator
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// Avoid deadlock via slightly different order of utensil requests
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// for last philospher
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// first utensil to get, most go for n first, last philospher goes for 0
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// first
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first = (n != N_PHILOSOPHERS - 1) ? n : 0;
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// second utensil to get, last philopher goes for n second
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second = (n != N_PHILOSOPHERS - 1) ? n + 1 : n;
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printf("Swanson %d wants utensils %d and %d\n", n, first, second);
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printf("Swanson %d at the table\n", n);
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// Main loop of thinking/eating cycles
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for (i = 0; i < MEALS_TO_FINISH; i++) {
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int sleep_time = rand() % MAX_DELAY;
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usleep(sleep_time); // sleep for for a short time
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printf("%2d: Swanson %d is contemplating his awesomeness ...\n", i, n);
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// get first utensil
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pthread_mutex_lock(&utensils[first]);
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printf("%2d: Swanson %d got utensil %d\n", i, n, first);
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// get second utensil
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pthread_mutex_lock(&utensils[second]);
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printf("%2d: Swanson %d got utensil %d\n", i, n, second);
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printf("%2d: Swanson %d is eating an egg ...\n", i, n);
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usleep(sleep_time); // sleep for for a short time
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// release first utensil
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pthread_mutex_unlock(&utensils[first]);
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// release second utensil
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pthread_mutex_unlock(&utensils[second]);
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}
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printf("Swanson %d leaving the diner\n", n);
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return NULL;
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}
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