kern_return_t
lock_handoff_accept (lock_set_t lock_set, int lock_id)
{
ulock_t ulock;
int wait_result;
if (lock_set == LOCK_SET_NULL)
return KERN_INVALID_ARGUMENT;
if (lock_id < 0 || lock_id >= lock_set->n_ulocks)
return KERN_INVALID_ARGUMENT;
retry:
lock_set_lock(lock_set);
if (!lock_set->active) {
lock_set_unlock(lock_set);
return KERN_LOCK_SET_DESTROYED;
}
ulock = (ulock_t) &lock_set->ulock_list[lock_id];
ulock_lock(ulock);
lock_set_unlock(lock_set);
/*
* If there is another accepting thread that beat us, just
* return with an error.
*/
if (ulock->accept_wait) {
ulock_unlock(ulock);
return KERN_ALREADY_WAITING;
}
if (ulock->holder == current_thread()) {
ulock_unlock(ulock);
return KERN_LOCK_OWNED_SELF;
}
/*
* If the handoff thread (the sender) is already waiting to
* hand-off the lock to the accepting thread (the receiver),
* then perform the hand-off now.
*/
if (ulock->ho_wait) {
wait_queue_t wq = &ulock->wait_queue;
/*
* See who the lucky devil is, if he is still there waiting.
*/
assert(ulock->holder != THREAD_NULL);
if (wait_queue_wakeup64_thread(wq,
LOCK_SET_HANDOFF,
ulock->holder,
THREAD_AWAKENED) == KERN_SUCCESS) {
/*
* Holder thread was still waiting to give it
* away. Take over ownership.
*/
ulock_ownership_clear(ulock);
ulock_ownership_set(ulock, current_thread());
ulock->ho_wait = FALSE;
ulock_unlock(ulock);
return (ulock->unstable) ? KERN_LOCK_UNSTABLE :
KERN_SUCCESS;
}
/*
* OOPS. The owner was aborted out of the handoff.
* He will clear his own flag when he gets back.
* in the meantime, we will wait as if we didn't
* even see his flag (by falling thru).
*/
}
ulock->accept_wait = TRUE;
wait_result = wait_queue_assert_wait64(&ulock->wait_queue,
LOCK_SET_HANDOFF,
THREAD_ABORTSAFE, 0);
ulock_unlock(ulock);
if (wait_result == THREAD_WAITING)
wait_result = thread_block(THREAD_CONTINUE_NULL);
/*
* If the thread was woken-up via some action other than
* lock_handoff_accept or lock_set_destroy (i.e. thread_terminate),
* then we need to clear the ulock's handoff state.
*/
switch (wait_result) {
case THREAD_AWAKENED:
/*
* Take the lock to synchronize with the thread handing
* off the lock to us. We don't want to continue until
* they complete the handoff.
*/
ulock_lock(ulock);
assert(ulock->accept_wait == FALSE);
assert(ulock->holder == current_thread());
ulock_unlock(ulock);
return KERN_SUCCESS;
case THREAD_INTERRUPTED:
ulock_lock(ulock);
ulock->accept_wait = FALSE;
ulock_unlock(ulock);
return KERN_ABORTED;
case THREAD_RESTART:
goto retry;
}
panic("lock_handoff_accept");
return KERN_FAILURE;
}
kern_return_t
lock_handoff (lock_set_t lock_set, int lock_id)
{
ulock_t ulock;
int wait_result;
if (lock_set == LOCK_SET_NULL)
return KERN_INVALID_ARGUMENT;
if (lock_id < 0 || lock_id >= lock_set->n_ulocks)
return KERN_INVALID_ARGUMENT;
retry:
lock_set_lock(lock_set);
if (!lock_set->active) {
lock_set_unlock(lock_set);
return KERN_LOCK_SET_DESTROYED;
}
ulock = (ulock_t) &lock_set->ulock_list[lock_id];
ulock_lock(ulock);
lock_set_unlock(lock_set);
if (ulock->holder != current_thread()) {
ulock_unlock(ulock);
return KERN_INVALID_RIGHT;
}
/*
* If the accepting thread (the receiver) is already waiting
* to accept the lock from the handoff thread (the sender),
* then perform the hand-off now.
*/
if (ulock->accept_wait) {
wait_queue_t wq = &ulock->wait_queue;
thread_t thread;
spl_t s;
/*
* See who the lucky devil is, if he is still there waiting.
*/
s = splsched();
wait_queue_lock(wq);
thread = wait_queue_wakeup64_identity_locked(
wq,
LOCK_SET_HANDOFF,
THREAD_AWAKENED,
TRUE);
/* wait queue unlocked, thread locked */
/*
* Transfer lock ownership
*/
if (thread != THREAD_NULL) {
/*
* The thread we are transferring to will try
* to take the lock on the ulock, and therefore
* will wait for us complete the handoff even
* through we set the thread running.
*/
thread_unlock(thread);
splx(s);
ulock_ownership_clear(ulock);
ulock_ownership_set(ulock, thread);
ulock->accept_wait = FALSE;
ulock_unlock(ulock);
return KERN_SUCCESS;
} else {
/*
* OOPS. The accepting thread must have been aborted.
* and is racing back to clear the flag that says is
* waiting for an accept. He will clear it when we
* release the lock, so just fall thru and wait for
* the next accept thread (that's the way it is
* specified).
*/
splx(s);
}
}
/*
* Indicate that there is a hand-off thread waiting, and then wait
* for an accepting thread.
*/
ulock->ho_wait = TRUE;
wait_result = wait_queue_assert_wait64(&ulock->wait_queue,
LOCK_SET_HANDOFF,
THREAD_ABORTSAFE, 0);
ulock_unlock(ulock);
if (wait_result == THREAD_WAITING)
wait_result = thread_block(THREAD_CONTINUE_NULL);
/*
* If the thread was woken-up via some action other than
* lock_handoff_accept or lock_set_destroy (i.e. thread_terminate),
* then we need to clear the ulock's handoff state.
*/
switch (wait_result) {
case THREAD_AWAKENED:
/*
* we take the ulock lock to syncronize with the
* thread that is accepting ownership.
*/
ulock_lock(ulock);
assert(ulock->holder != current_thread());
ulock_unlock(ulock);
return KERN_SUCCESS;
case THREAD_INTERRUPTED:
ulock_lock(ulock);
assert(ulock->holder == current_thread());
ulock->ho_wait = FALSE;
ulock_unlock(ulock);
return KERN_ABORTED;
case THREAD_RESTART:
goto retry;
}
panic("lock_handoff");
return KERN_FAILURE;
}
/*
* ROUTINE: lock_set_destroy [exported]
*
* Destroys a lock set. This call will only succeed if the
* specified task is the SAME task name specified at the lock set's
* creation.
*
* NOTES:
* - All threads currently blocked on the lock set's ulocks are awoken.
* - These threads will return with the KERN_LOCK_SET_DESTROYED error.
*/
kern_return_t
lock_set_destroy (task_t task, lock_set_t lock_set)
{
ulock_t ulock;
int i;
if (task == TASK_NULL || lock_set == LOCK_SET_NULL)
return KERN_INVALID_ARGUMENT;
if (lock_set->owner != task)
return KERN_INVALID_RIGHT;
lock_set_lock(lock_set);
if (!lock_set->active) {
lock_set_unlock(lock_set);
return KERN_LOCK_SET_DESTROYED;
}
/*
* Deactivate lock set
*/
lock_set->active = FALSE;
/*
* If a ulock is currently held in the target lock set:
*
* 1) Wakeup all threads blocked on the ulock (if any). Threads
* may be blocked waiting normally, or waiting for a handoff.
* Blocked threads will return with KERN_LOCK_SET_DESTROYED.
*
* 2) ulock ownership is cleared.
* The thread currently holding the ulock is revoked of its
* ownership.
*/
for (i = 0; i < lock_set->n_ulocks; i++) {
ulock = &lock_set->ulock_list[i];
ulock_lock(ulock);
if (ulock->accept_wait) {
ulock->accept_wait = FALSE;
wait_queue_wakeup64_one(&ulock->wait_queue,
LOCK_SET_HANDOFF,
THREAD_RESTART);
}
if (ulock->holder) {
if (ulock->blocked) {
ulock->blocked = FALSE;
wait_queue_wakeup64_all(&ulock->wait_queue,
LOCK_SET_EVENT,
THREAD_RESTART);
}
if (ulock->ho_wait) {
ulock->ho_wait = FALSE;
wait_queue_wakeup64_one(&ulock->wait_queue,
LOCK_SET_HANDOFF,
THREAD_RESTART);
}
ulock_ownership_clear(ulock);
}
ulock_unlock(ulock);
}
lock_set_unlock(lock_set);
lock_set_ownership_clear(lock_set, task);
/*
* Drop the lock set reference given to the containing task,
* which inturn destroys the lock set structure if the reference
* count goes to zero.
*/
lock_set_dereference(lock_set);
return KERN_SUCCESS;
}
/*
* ROUTINE: ulock_release_internal [internal]
*
* Releases the ulock.
* If any threads are blocked waiting for the ulock, one is woken-up.
*
*/
kern_return_t
ulock_release_internal (ulock_t ulock, thread_t thread)
{
lock_set_t lock_set;
if ((lock_set = ulock->lock_set) == LOCK_SET_NULL)
return KERN_INVALID_ARGUMENT;
lock_set_lock(lock_set);
if (!lock_set->active) {
lock_set_unlock(lock_set);
return KERN_LOCK_SET_DESTROYED;
}
ulock_lock(ulock);
lock_set_unlock(lock_set);
if (ulock->holder != thread) {
ulock_unlock(ulock);
return KERN_INVALID_RIGHT;
}
/*
* If we have a hint that threads might be waiting,
* try to transfer the lock ownership to a waiting thread
* and wake it up.
*/
if (ulock->blocked) {
wait_queue_t wq = &ulock->wait_queue;
thread_t wqthread;
spl_t s;
s = splsched();
wait_queue_lock(wq);
wqthread = wait_queue_wakeup64_identity_locked(wq,
LOCK_SET_EVENT,
THREAD_AWAKENED,
TRUE);
/* wait_queue now unlocked, thread locked */
if (wqthread != THREAD_NULL) {
thread_unlock(wqthread);
splx(s);
/*
* Transfer ulock ownership
* from the current thread to the acquisition thread.
*/
ulock_ownership_clear(ulock);
ulock_ownership_set(ulock, wqthread);
ulock_unlock(ulock);
return KERN_SUCCESS;
} else {
ulock->blocked = FALSE;
splx(s);
}
}
/*
* Disown ulock
*/
ulock_ownership_clear(ulock);
ulock_unlock(ulock);
return KERN_SUCCESS;
}
/*
* ROUTINE: ulock_release_internal [internal]
*
* Releases the ulock.
* If any threads are blocked waiting for the ulock, one is woken-up.
*
*/
kern_return_t
ulock_release_internal (ulock_t ulock, thread_t thread)
{
lock_set_t lock_set;
if ((lock_set = ulock->lock_set) == LOCK_SET_NULL)
return KERN_INVALID_ARGUMENT;
lock_set_lock(lock_set);
if (!lock_set->active) {
lock_set_unlock(lock_set);
return KERN_LOCK_SET_DESTROYED;
}
ulock_lock(ulock);
lock_set_unlock(lock_set);
if (ulock->holder != thread) {
ulock_unlock(ulock);
return KERN_INVALID_RIGHT;
}
/*
* If we have a hint that threads might be waiting,
* try to transfer the lock ownership to a waiting thread
* and wake it up.
*/
if (ulock->blocked) {
wait_queue_t wq = &ulock->wait_queue;
thread_t wqthread;
spl_t s;
s = splsched();
wait_queue_lock(wq);
wqthread = wait_queue_wakeup64_identity_locked(wq,
LOCK_SET_EVENT,
THREAD_AWAKENED,
TRUE);
/* wait_queue now unlocked, thread locked */
if (wqthread != THREAD_NULL) {
/*
* JMM - These ownership transfer macros have a
* locking/race problem. To keep the thread from
* changing states on us (nullifying the ownership
* assignment) we need to keep the thread locked
* during the assignment. But we can't because the
* macros take an activation lock, which is a mutex.
* Since this code was already broken before I got
* here, I will leave it for now.
*/
thread_unlock(wqthread);
splx(s);
/*
* Transfer ulock ownership
* from the current thread to the acquisition thread.
*/
ulock_ownership_clear(ulock);
ulock_ownership_set(ulock, wqthread);
ulock_unlock(ulock);
return KERN_SUCCESS;
} else {
ulock->blocked = FALSE;
splx(s);
}
}
/*
* Disown ulock
*/
ulock_ownership_clear(ulock);
ulock_unlock(ulock);
return KERN_SUCCESS;
}
