-/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
-
-struct s_lock_t {
- decl_simple_lock_data(,interlock) /* "hardware" interlock field */
- volatile unsigned int
- read_count:16, /* No. of accepted readers */
- want_upgrade:1, /* Read-to-write upgrade waiting */
- want_write:1, /* Writer is waiting, or
- locked for write */
- waiting:1, /* Someone is sleeping on lock */
- can_sleep:1; /* Can attempts to lock go to sleep? */
-};
-
-static struct s_lock_t gIORegistryLock;
-
-/* Time we loop without holding the interlock.
- * The former is for when we cannot sleep, the latter
- * for when our thread can go to sleep (loop less)
- * we shouldn't retake the interlock at all frequently
- * if we cannot go to sleep, since it interferes with
- * any other processors. In particular, 100 is too small
- * a number for powerpc MP systems because of cache
- * coherency issues and differing lock fetch times between
- * the processors
- */
-static unsigned int lock_wait_time[2] = { (unsigned int)-1, 100 } ;
-
-static void
-s_lock_init(
- s_lock_t *l,
- boolean_t can_sleep)
-{
- (void) memset((void *) l, 0, sizeof(s_lock_t));
-
- simple_lock_init(&l->interlock, 0);
- l->want_write = FALSE;
- l->want_upgrade = FALSE;
- l->read_count = 0;
- l->can_sleep = can_sleep;
-}
-
-static void
-s_lock_write(
- register s_lock_t * l)
-{
- register int i;
-
- simple_lock(&l->interlock);
-
- /*
- * Try to acquire the want_write bit.
- */
- while (l->want_write) {
-
- i = lock_wait_time[l->can_sleep ? 1 : 0];
- if (i != 0) {
- simple_unlock(&l->interlock);
- while (--i != 0 && l->want_write)
- continue;
- simple_lock(&l->interlock);
- }
-
- if (l->can_sleep && l->want_write) {
- l->waiting = TRUE;
- thread_sleep_simple_lock((event_t) l,
- simple_lock_addr(l->interlock), FALSE);
- simple_lock(&l->interlock);
- }
- }
- l->want_write = TRUE;
-
- /* Wait for readers (and upgrades) to finish */
-
- while ((l->read_count != 0) || l->want_upgrade) {
-
- i = lock_wait_time[l->can_sleep ? 1 : 0];
- if (i != 0) {
- simple_unlock(&l->interlock);
- while (--i != 0 && (l->read_count != 0 ||
- l->want_upgrade))
- continue;
- simple_lock(&l->interlock);
- }
-
- if (l->can_sleep && (l->read_count != 0 || l->want_upgrade)) {
- l->waiting = TRUE;
- thread_sleep_simple_lock((event_t) l,
- simple_lock_addr(l->interlock), FALSE);
- simple_lock(&l->interlock);
- }
- }
-
- simple_unlock(&l->interlock);
-}
projects / apple / xnu.git / blobdiff