Function get_dirty_buffer

src/jrd/cch.cpp:3615–3664

static BufferDesc* get_dirty_buffer(thread_db* tdbb)
{
	// This code is only used by the background I/O threads:
	// cache writer, cache reader and garbage collector.

	SET_TDBB(tdbb);
	Database* dbb = tdbb->getDatabase();
	BufferControl* bcb = dbb->dbb_bcb;
	int walk = bcb->bcb_free_minimum;
	int chained = walk;

	Sync lruSync(&bcb->bcb_syncLRU, FB_FUNCTION);
	lruSync.lock(SYNC_SHARED);

	for (QUE que_inst = bcb->bcb_in_use.que_backward;
		 que_inst != &bcb->bcb_in_use; que_inst = que_inst->que_backward)
	{
		BufferDesc* bdb = BLOCK(que_inst, BufferDesc, bdb_in_use);

		if (bdb->bdb_flags & BDB_lru_chained)
		{
			if (!--chained)
				break;
			continue;
		}

		if (bdb->bdb_use_count || (bdb->bdb_flags & BDB_free_pending))
			continue;

		if (bdb->bdb_flags & BDB_db_dirty)
		{
			//tdbb->bumpStats(RuntimeStatistics::PAGE_FETCHES); shouldn't it be here?
			return bdb;
		}

		if (!--walk)
			break;
	}

	if (!chained)
	{
		lruSync.unlock();
		lruSync.lock(SYNC_EXCLUSIVE);
		requeueRecentlyUsed(bcb);
	}
	else
		bcb->bcb_flags &= ~BCB_free_pending;

	return NULL;
}


static BufferDesc* get_oldest_buffer(thread_db* tdbb, BufferControl* bcb)