99 lines
2.5 KiB
C
99 lines
2.5 KiB
C
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// Original version of dining philosphers. Rather that using a single
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// semaphore of size 5 to control the chopsticks, this version uses a
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// C array of 5 singular semaphores to control chopstick access
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//
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// Source: http://www.lisha.ufsc.br/~guto/teaching/os/exercise/phil.html
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#include <unistd.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <sys/types.h>
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#include <sys/wait.h>
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#include <sys/ipc.h>
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#include <sys/sem.h>
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const int ITERATIONS = 50;
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int chopstick[5];
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int philosopher(int n)
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{
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int i, j, first, second;
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struct sembuf op;
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op.sem_num = 0;
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op.sem_flg = 0;
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printf("Philosopher %d was born!\n", n);
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srand(n);
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first = (n < 4)? n : 0; /* left for phil 0 .. 3, right for phil 4 */
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second = (n < 4)? n + 1 : 4; /* right for phil 0 .. 3, left for phil 4 */
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for(i = 0; i < ITERATIONS; i++) {
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printf("%2d: Philosopher %d is thinking ...\n", i,n);
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/* get first chopstick */
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op.sem_op = -1;
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semop(chopstick[first], &op, 1);
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/* get second chopstick */
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op.sem_op = -1;
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semop(chopstick[second], &op, 1);
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printf("%2d: Philosopher %d is eating ...\n", i,n);
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/* release first chopstick */
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op.sem_op = +1;
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semop(chopstick[first], &op, 1);
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/* release second chopstick */
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op.sem_op = +1;
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semop(chopstick[second], &op, 1);
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int sleep_time = rand() % 10;
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usleep(sleep_time); // sleep for 0-9 microseconds
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}
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exit(n);
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}
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int main(){
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int i, status;
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pid_t phil[5];
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printf("The Dining-Philosophers Problem\n");
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// Parent process only:
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//
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// Allocate chopsticks: semaphores which are initially set to value
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// 1. 5 chopsticks total in an array.
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for(i = 0; i < 5; i++) {
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if((chopstick[i] = semget(IPC_PRIVATE, 1, IPC_CREAT | 0600)) < 0)
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return -1;
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if(semctl(chopstick[i], 0, SETVAL, 1) < 0)
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return -1;
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}
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// Parent generates child processes
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for(i = 0; i < 5; i++){
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int pid = fork();
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if(pid == 0){ // child has pid 0
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int ret = philosopher(i); // child acts as philosopher
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exit(ret); // then exits
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}
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else{ // parent gets pid > 0
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phil[i] = pid; // parent tracks children
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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 < 5; i++) {
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waitpid(phil[i], &status, 0);
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if(WEXITSTATUS(status) == i)
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printf("Philosopher %d went to heaven!\n", i);
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else
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printf("Philosopher %d went to hell!\n", i);
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}
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// Eliminate the chopsticks semaphores
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for(i = 0; i < 5; i++)
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semctl(chopstick[i], 0, IPC_RMID, 0);
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return 0;
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}
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