Function CCH_handoff

src/jrd/cch.cpp:1433–1543

pag* CCH_handoff(thread_db*	tdbb, WIN* window, ULONG page, int lock, SCHAR page_type,
	int wait, const bool release_tail)
{
/**************************************
 *
 *	C C H _ h a n d o f f
 *
 **************************************
 *
 * Functional description
 *	Follow a pointer handing off the lock.  Fetch the new page
 *	before retiring the old page lock.
 *
 * input
 *	wait:	1 => Wait as long as necessary to get the latch.
 *				This can cause deadlocks of course.
 *			0 => If the latch can't be acquired immediately,
 *				give up and return 0.
 *	      		<negative number> => Latch timeout interval in seconds.
 *
 * return
 *	PAG if successful.
 *	0 if a latch timeout occurred (only possible if wait <> 1).
 *		The latch on the fetched page is downgraded to shared.
 *		The fetched page is unmarked.
 *
 **************************************/

	// The update, if there was one, of the input page is complete.
	// The cache buffer can be 'unmarked'.  It is important to
	// unmark before CCH_unwind is (might be) called.

	SET_TDBB(tdbb);

	CCH_TRACE(("HANDOFF %d:%06d->%06d, %s",
		window->win_page.getPageSpaceID(), window->win_page.getPageNum(), page, (lock >= LCK_write) ? "EX" : "SH"));

	BufferDesc *bdb = window->win_bdb;

	// unmark
	if (bdb->bdb_writers == 1 && (bdb->bdb_flags & BDB_marked))
	{
		bdb->bdb_flags &= ~BDB_marked;
		bdb->unLockIO(tdbb);
	}

	// If the 'from-page' and 'to-page' of the handoff are the
	// same and the latch requested is shared then downgrade it.

	if ((window->win_page.getPageNum() == page) && (lock == LCK_read))
	{
		if (bdb->ourExclusiveLock())
			bdb->downgrade(SYNC_SHARED);

		return window->win_buffer;
	}

	WIN temp = *window;