/*
* Release a ticket lock by incrementing the head of the queue. Only generate
* a thread wakeup signal if at least one thread is waiting. If the queue tail
* matches the wakeup_ticket value, no threads have to be woken up.
*
* Note: tail will only be read after head has been incremented since both are
* declared as volatile and since the __sync...() functions imply a memory
* barrier.
*/
static void release_sched_lock(struct sched_lock *p, ThreadId tid, SchedLockKind slk)
{
unsigned wakeup_ticket, futex_value;
volatile unsigned *futex;
SysRes sres;
vg_assert(p->owner != 0);
p->owner = 0;
INNER_REQUEST(ANNOTATE_RWLOCK_RELEASED(p, /*is_w*/1));
wakeup_ticket = __sync_fetch_and_add(&p->head, 1) + 1;
if (p->tail != wakeup_ticket) {
futex = &p->futex[wakeup_ticket & TL_FUTEX_MASK];
futex_value = __sync_fetch_and_add(futex, 1);
if (s_debug)
VG_(printf)("[%d/%d] release: waking up ticket %d (futex[%ld] = %d)"
"\n", VG_(getpid)(), VG_(gettid)(), wakeup_ticket,
(long)(futex - p->futex), futex_value);
sres = VG_(do_syscall3)(__NR_futex, (UWord)futex,
VKI_FUTEX_WAKE | VKI_FUTEX_PRIVATE_FLAG,
0x7fffffff);
vg_assert(!sr_isError(sres));
} else {
if (s_debug)
VG_(printf)("[%d/%d] release: no thread is waiting for ticket %d\n",
VG_(getpid)(), VG_(gettid)(), wakeup_ticket);
}
}
static void rwlock_unlock(rwlock_t* p)
{
while (__sync_val_compare_and_swap(&p->locked, 0, 1) == 1)
;
if (p->reader_count > 0)
{
p->reader_count--;
ANNOTATE_RWLOCK_RELEASED(p, 0);
}
else
{
p->writer_count--;
ANNOTATE_RWLOCK_RELEASED(p, 1);
}
assert(p->reader_count >= 0);
assert(p->writer_count >= 0);
assert(p->reader_count == 0 || p->writer_count == 0);
__sync_fetch_and_sub(&p->locked, 1);
}
/* put token back */
void ML_(sema_up)( vg_sema_t *sema, Bool as_LL )
{
Int ret;
HChar buf[2];
vg_assert(as_LL == sema->held_as_LL);
buf[0] = sema_char;
buf[1] = 0;
vg_assert(sema->owner_lwpid != -1); /* must be initialised */
vg_assert(sema->pipe[0] != sema->pipe[1]);
vg_assert(sema->owner_lwpid == VG_(gettid)()); /* must have it */
sema->owner_lwpid = 0;
INNER_REQUEST(ANNOTATE_RWLOCK_RELEASED(sema, /*is_w*/1));
ret = VG_(write)(sema->pipe[1], buf, 1);
if (ret != 1)
VG_(debugLog)(0, "scheduler",
"VG_(sema_up):write returned %d\n", ret);
vg_assert(ret == 1);
}
