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static char rcsid[] =
"$Id: sem.c,v 1.3 2001/09/25 17:07:33 pvmsrc Exp $";
/*
Semaphore control code for Binary Semaphores only
GEF UTK/ORNL
20 Jan 1997
*/
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <unistd.h> /* needed for usleep */
#include <stdio.h>
#ifdef XXX_IMA_LINUX
/* Seems to be O.K. on latest Linux systems now. JAK - 9/25/01 */
union semun forth_arg; /* XXXX optional under all OSs except Linux ! */
#endif
void unlock_sem_forced ();
int get_sem (key_t k, int n)
{
int semid;
for(;(semid=semget(k, n, 0)) == -1;) usleep (1000);
return semid;
}
void lock_sem (int sem, int n)
{
struct sembuf sop; /* 1 element array */
sop.sem_num = n; /* which sem are we operating on */
sop.sem_op = -1; /* -1 locks */
sop.sem_flg = SEM_UNDO; /* if I crash reset the semaphore */
/* this is a very important flag to set! */
semop (sem, &sop, 1); /* block until resource is free, then lock it */
}
int sem_is (int sem, int n)
{
#ifdef XXX_IMA_LINUX
/* Seems to be O.K. on latest Linux systems now. JAK - 9/25/01 */
return (semctl( sem, n, GETVAL, forth_arg));
#else
return (semctl( sem, n, GETVAL));
#endif
}
void unlock_sem (int sem, int n)
{
struct sembuf sop; /* 1 element array */
sop.sem_num = n; /* which sem are we operating on */
sop.sem_op = 1; /* +1 locks */
sop.sem_flg = SEM_UNDO;
semop (sem, &sop, 1); /* unblock resource */
}
void unlock_sem_forced (int sem, int n)
{
struct sembuf sop; /* 1 element array */
sop.sem_num = n; /* which sem are we operating on */
sop.sem_op = 1; /* +1 locks */
sop.sem_flg = 0; /* flag =0 NOT SEM_UNDO */
semop (sem, &sop, 1); /* unblock resource */
}
int init_sem (key_t k, int n)
{
int semid, i;
if((semid=semget (k, n, 0)) !=-1) {
printf("[init_sem] sem key %lx exists with id of %d\n",
(long) k, semid);
#ifdef XXX_IMA_LINUX
/* Seems to be O.K. on latest Linux systems now. JAK - 9/25/01 */
semctl (semid, 0, IPC_RMID, forth_arg); /* existing sem destroy */
#else
semctl (semid, 0, IPC_RMID); /* existing sem destroy */
#endif
}
if((semid=semget (k, n, IPC_CREAT | 0600)) !=-1) {
/* semaphore are init to zero, i.e. locked so we unlock them */
/* for(i=0;i<n;i++) unlock_sem (semid, i); */
/* as we have SEM_UNDO in unlock_sem, this causes problems when */
/* we reset, so... */
/* we use an explicit sem set, hoping of course than nobody has */
/* attempted to use the semaphore already */
for(i=0;i<n;i++) unlock_sem_forced (semid, i);
}
printf("[init_sem] sem key %lx is now id %d\n", (long) k, semid);
return semid;
}
void del_sem (int semid)
{
#ifdef XXX_IMA_LINUX
/* Seems to be O.K. on latest Linux systems now. JAK - 9/25/01 */
semctl (semid, 0, IPC_RMID, forth_arg); /* existing sem destroy */
#else
semctl (semid, 0, IPC_RMID); /* existing sem destroy */
#endif
}
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