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63 lines
1.8 KiB
63 lines
1.8 KiB
/* Philosophers.c - Demonstrate the semaphore solution to the dining
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philosophers problem. The Room semaphore is neede to prevent all
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philosophers from entering the room and grabbing their left most fork
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at the same time, which would lead to deadlock. The Room sempahore
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can be enabled by specifying a command line argument. */
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#include <stdio.h>
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#include <pthread.h>
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#include <semaphore.h>
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typedef enum { False=0, True=1 } bool ;
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#define N 5 /* Number of times each philosopher tries to eat */
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#define P 3 /* Number of philosophers */
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sem_t Room;
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sem_t Fork[P];
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bool Switch ;
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void *tphilosopher(void *ptr) {
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int i, k = *((int *) ptr);
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for(i = 1; i <= N; i++) {
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printf("%*cThink %d %d\n", k*4, ' ', k, i);
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if(Switch) {
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sem_wait(&Room) ;
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}
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sem_wait(&Fork[k]) ;
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sem_wait(&Fork[(k+1) % P]) ;
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printf("%*cEat %d %d\n", k*4, ' ', k, i);
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sem_post(&Fork[k]) ;
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sem_post(&Fork[(k+1) % P]) ;
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if(Switch) {
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sem_post(&Room) ;
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}
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}
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pthread_exit(0);
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}
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int main(int argc, char * argv[]) {
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int i, targ[P];
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pthread_t thread[P];
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sem_init(&Room, 0, P-1);
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Switch = (argc > 1); /* Room semaphore on/off */
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printf("Switch=%s\n",(Switch?"true":"false"));
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for(i=0;i<P;i++) {
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sem_init(&Fork[i], 0, 1);
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}
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for(i=0;i<P;i++) {
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targ[i] = i;
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pthread_create(&thread[i], NULL, &tphilosopher,(void *) &targ[i]);
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}
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for(i=0;i<P;i++) {
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pthread_join(thread[i], NULL);
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}
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for(i=0;i<P;i++) {
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sem_destroy(&Fork[i]);
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}
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sem_destroy(&Room);
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return 0;
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}
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/* Please note that the checks on the return value of the system calls
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have been omitted to avoid cluttering the code. However, system calls
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can and will fail, in which case the results are unpredictable. */
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