bool LockManager::unlock(LockRequest* request) {
invariant(request->lock);
// Fast path for decrementing multiple references of the same lock. It is safe to do this
// without locking, because 1) all calls for the same lock request must be done on the same
// thread and 2) if there are lock requests hanging of a given LockHead, then this lock
// will never disappear.
request->recursiveCount--;
if ((request->status == LockRequest::STATUS_GRANTED) && (request->recursiveCount > 0)) {
return false;
}
LockHead* lock = request->lock;
LockBucket* bucket = _getBucket(lock->resourceId);
scoped_spinlock scopedLock(bucket->mutex);
invariant(lock->grantedQueue != NULL);
invariant(lock->grantedModes != 0);
if (request->status == LockRequest::STATUS_WAITING) {
// This cancels a pending lock request
invariant(request->recursiveCount == 0);
lock->removeFromConflictQueue(request);
lock->changeConflictModeCount(request->mode, LockHead::Decrement);
}
else if (request->status == LockRequest::STATUS_CONVERTING) {
// This cancels a pending convert request
invariant(request->recursiveCount > 0);
// Lock only goes from GRANTED to CONVERTING, so cancelling the conversion request
// brings it back to the previous granted mode.
request->status = LockRequest::STATUS_GRANTED;
lock->conversionsCount--;
lock->changeGrantedModeCount(request->convertMode, LockHead::Decrement);
request->convertMode = MODE_NONE;
_onLockModeChanged(lock, lock->grantedCounts[request->convertMode] == 0);
}
else if (request->status == LockRequest::STATUS_GRANTED) {
// This releases a currently held lock and is the most common path, so it should be
// as efficient as possible.
invariant(request->recursiveCount == 0);
// Remove from the granted list
lock->removeFromGrantedQueue(request);
lock->changeGrantedModeCount(request->mode, LockHead::Decrement);
_onLockModeChanged(lock, lock->grantedCounts[request->mode] == 0);
}
else {
// Invalid request status
invariant(false);
}
return (request->recursiveCount == 0);
}
void LockManager::downgrade(LockRequest* request, LockMode newMode) {
invariant(request->lock);
invariant(request->status == LockRequest::STATUS_GRANTED);
invariant(request->recursiveCount > 0);
// The conflict set of the newMode should be a subset of the conflict set of the old mode.
// Can't downgrade from S -> IX for example.
invariant((LockConflictsTable[request->mode] | LockConflictsTable[newMode])
== LockConflictsTable[request->mode]);
LockHead* lock = request->lock;
LockBucket* bucket = _getBucket(lock->resourceId);
SimpleMutex::scoped_lock scopedLock(bucket->mutex);
invariant(lock->grantedQueueBegin != NULL);
invariant(lock->grantedQueueEnd != NULL);
invariant(lock->grantedModes != 0);
lock->changeGrantedModeCount(newMode, LockHead::Increment);
lock->changeGrantedModeCount(request->mode, LockHead::Decrement);
request->mode = newMode;
_onLockModeChanged(lock, true);
}
