/* Return locked block number {0, 1}, or -1 on error */
static int/*tri-state*/ s_Shmem_RLock(int which)
{
#ifdef LBSM_DEBUG
CORE_LOG(eLOG_Trace, "LBSM R-lock acquire (%d)", which + 1);
#endif /*LBSM_DEBUG*/
/* For block 1 then block 0: check [1] first, then continue with [2] */
if (s_Shmem_Lock(which, 1, which/*1:no-wait,0:wait*/) == 0)
return which/*block locked*/;
return !which || errno == EINVAL ? -1 : s_Shmem_Lock(0, 1, 0/*wait*/);
}
/* Return locked block number {0, 1}, or -1 in error */
static int/*tri-state*/ s_Shmem_RLock(void)
{
#ifdef LBSM_DEBUG
CORE_LOG(eLOG_Trace, "LBSM R-lock acquire");
#endif /*LBSM_DEBUG*/
/* For block 1, then block 0: check [1] first, then continue with [2] */
if (s_Shmem_Lock(1, 1, 1/*no-wait*/) == 0)
return 1/*block 1 locked*/;
return errno == EINVAL ? -1 : s_Shmem_Lock(0, 1, 0/*wait*/);
}
static int/*tri-state-bool, inverted*/ s_Shmem_TryWLock(int which)
{
int semnum = (which << 1) | 1;
int/*bool*/ no_undo = 0;
struct sembuf rwlock[2];
int i = 0;
for (;;) {
rwlock[0].sem_num = semnum;
rwlock[0].sem_op = 0; /* precondition: [1] == 0 */
rwlock[0].sem_flg = 0;
rwlock[1].sem_num = semnum;
rwlock[1].sem_op = 1; /* postcondition: [1] == 1 */
rwlock[1].sem_flg = no_undo ? 0 : SEM_UNDO;
if (semop(s_Muxid, rwlock, sizeof(rwlock)/sizeof(rwlock[0])) >= 0) {
/* No new read accesses are allowed after this point */
s_NoUndo[semnum - 1] = no_undo;
/* Look at [2] first, then continue with it */
if (s_Shmem_Lock(which, 2, 0/*wait*/) != 0)
return 1/*partially locked*/;
return 0/*okay*/;
}
if (i)
break;
i = errno;
if (i == ENOSPC) {
CORE_LOGF_X(8, eLOG_Warning,
("LBSM PreW-locking[%d] w/o undo", which + 1));
no_undo = 1;
continue;
}
if (i == EINTR)
continue;
if (i != ENOMEM)
break;
#ifdef LBSM_DEBUG
CORE_LOGF(eLOG_Trace,
("LBSM PreW-lock[%d] wait(ENOMEM)", which + 1));
#endif/*LBSM_DEBUG*/
sleep(1);
}
return -1/*not locked*/;
}
