Method downgrade

src/lock/lock.cpp:651–714

UCHAR LockManager::downgrade(thread_db* tdbb,
							 CheckStatusWrapper* statusVector,
							 const SRQ_PTR request_offset)
{
/**************************************
 *
 *	d o w n g r a d e
 *
 **************************************
 *
 * Functional description
 *	Downgrade an existing lock returning
 *	its new state.
 *
 **************************************/
	LOCK_TRACE(("LM::downgrade (%ld)\n", request_offset));

	LockTableGuard guard(this, FB_FUNCTION, DUMMY_OWNER);

	lrq* const request = get_request(request_offset);
	const SRQ_PTR owner_offset = request->lrq_owner;
	guard.setOwner(owner_offset);

	own* const owner = (own*) SRQ_ABS_PTR(owner_offset);
	if (!owner->own_count)
		return LCK_none;

	++(m_sharedMemory->getHeader()->lhb_downgrades);

	const lbl* lock = (lbl*) SRQ_ABS_PTR(request->lrq_lock);
	UCHAR pending_state = LCK_none;

	// Loop thru requests looking for pending conversions
	// and find the highest requested state

	srq* lock_srq;
	SRQ_LOOP(lock->lbl_requests, lock_srq)
	{
		const lrq* const pending = (lrq*) ((UCHAR*) lock_srq - offsetof(lrq, lrq_lbl_requests));
		if ((pending->lrq_flags & LRQ_pending) && pending != request)
		{
			pending_state = MAX(pending->lrq_requested, pending_state);
			if (pending_state == LCK_EX)
				break;
		}
	}

	UCHAR state = request->lrq_state;
	while (state > LCK_none && !compatibility[pending_state][state])
		--state;

	if (state == LCK_none || state == LCK_null)
	{
		internal_dequeue(request_offset);
		state = LCK_none;
	}
	else
	{