Function check_precedence

src/jrd/cch.cpp:3179–3321

static void check_precedence(thread_db* tdbb, WIN* window, PageNumber page)
{
/**************************************
 *
 *	c h e c k _ p r e c e d e n c e
 *
 **************************************
 *
 * Functional description
 *	Given a window accessed for write and a page number,
 *	establish a precedence relationship such that the
 *	specified page will always be written before the page
 *	associated with the window.
 *
 *	If the "page number" is negative, it is really a transaction
 *	id.  In this case, the precedence relationship is to the
 *	database header page from which the transaction id was
 *	obtained.  If the header page has been written since the
 *	transaction id was assigned, no precedence relationship
 *	is required.
 *
 **************************************/
	SET_TDBB(tdbb);
	Database* dbb = tdbb->getDatabase();
	BufferControl* bcb = dbb->dbb_bcb;

	// If this is really a transaction id, sort things out

	switch(page.getPageSpaceID())
	{
		case DB_PAGE_SPACE:
			break;

		case TRANS_PAGE_SPACE:
			if (page.getPageNum() <= tdbb->getDatabase()->dbb_last_header_write)
				return;
			page = PageNumber(DB_PAGE_SPACE, 0);
			break;

		default:
			fb_assert(false);
			return;
	}

	// In the past negative value, passed here, meant not page, but transaction number.
	// When we finally move to 32 (not 31) bit page numbers, this should be removed,
	// but currently I add:
	fb_assert(!(page.getPageNum() & 0x80000000));
	// to help detect cases, when something possibly negative is passed.
	// AP - 2011.

	// Start by finding the buffer containing the high priority page

#ifndef HASH_USE_CDS_LIST
	Sync bcbSync(&bcb->bcb_syncObject, FB_FUNCTION);
	bcbSync.lock(SYNC_SHARED);
#endif