Function CCH_fetch

src/jrd/cch.cpp:774–827

pag* CCH_fetch(thread_db* tdbb, WIN* window, int lock_type, SCHAR page_type, int wait,
	const bool read_shadow)
{
/**************************************
 *
 *	C C H _ f e t c h
 *
 **************************************
 *
 * Functional description
 *	Fetch a specific page.  If it's already in cache,
 *	so much the better.
 *
 * 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.
 *	NULL pointer if timeout occurred (only possible if wait <> 1).
 *
 **************************************/
	SET_TDBB(tdbb);

	const LockState lockState = CCH_fetch_lock(tdbb, window, lock_type, wait, page_type);
	BufferDesc* bdb = window->win_bdb;
	SyncType syncType = (lock_type >= LCK_write) ? SYNC_EXCLUSIVE : SYNC_SHARED;

	switch (lockState)
	{
	case lsLocked:
		CCH_TRACE(("FE PAGE %d:%06d", window->win_page.getPageSpaceID(), window->win_page.getPageNum()));
		CCH_fetch_page(tdbb, window, read_shadow);	// must read page from disk
		if (syncType != SYNC_EXCLUSIVE)
			bdb->downgrade(syncType);
		break;

	case lsLatchTimeout:
	case lsLockTimeout:
		return NULL;			// latch or lock timeout
	}

	adjust_scan_count(window, lockState == lsLocked);

	// Validate the fetched page matches the expected type

	if (bdb->bdb_buffer->pag_type != page_type && page_type != pag_undefined)
		page_validation_error(tdbb, window, page_type);

	return window->win_buffer;
}


LockState CCH_fetch_lock(thread_db* tdbb, WIN* window, int lock_type, int wait, SCHAR page_type)