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sem2.c
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sem2.c
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/* creazione di due semafori con potenziale deadlock
*/
#include <unistd.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#define SEMKEY 75
#define S1 0
#define S2 0
int semid;
unsigned int count;
struct sembuf psembuf, vsembuf;
main (int argc, char **argv) {
int i, sem1, sem2;
short initvec[2], outvec[2];
if ( argc == 1 ) {
semid = semget(SEMKEY, 2, 0777|IPC_CREAT);
initvec[0] = initvec[1] = 1;
semctl (semid, SETALL, initvec[0]);
semctl (semid, GETALL, outvec[0]);
printf ("semaphore init values: %d %d\n", outvec[0],
outvec[1]);
pause();
}
else if ( ! strcmp (argv[1],"0") ) {
sem1 = S1;
sem2 = S1;
}
else {
sem1 = S2;
sem2 = S1;
}
semid = semget (SEMKEY, 2, 0777);
psembuf.sem_op = -1; // P
psembuf.sem_flg = SEM_UNDO;
vsembuf.sem_op = 1; // V
vsembuf.sem_flg = SEM_UNDO;
for ( count = 0 ; ; count++ ) {
psembuf.sem_num = sem1;
semop (semid, &psembuf, 1); // P(s1)
printf ("p(s1)\n");
psembuf.sem_num = sem2;
semop (semid, &psembuf, 1); // P(s2)
printf ("\tp(s2)\n");
// printf ("proc %d - count %d\n", getpid(), count);
printf ("resource usage: %d\n", psembuf.sem_num);
vsembuf.sem_num = sem2;
semop(semid, &vsembuf, 1); // V(s1) XXX
printf ("\tv(s2)\n");
vsembuf.sem_num = sem1;
semop(semid, &vsembuf, 1); // V(s2) XXX
printf ("v(s1)\n");
sleep (2);
}
}