-- File: DBStorageGroupScanImpl.mesa
-- This module exports group-related stuff to DBStorage.
-- Last edited by:
-- MBrown on December 2, 1982 3:17 pm
-- Cattell on November 2, 1983 3:19 pm
-- Willie-Sue on June 30, 1982 4:49 pm
DIRECTORY
DBCache USING [CacheHandle],
DBCommon USING [GetDebugStream],
DBEnvironment,
DBSegment,
DBStorage USING[FieldHandle, FirstLast, MaxSystemTupleID, TupleHandle],
DBStorageField USING[ CheckFieldHandleType, GroupIDOfField],
DBStorageGroup USING[GroupList, GroupListFromTuple, ReadGroupField, WriteGroupField,
WriteHeadField, CreateHeadEntry, DestroyHeadEntry],
DBStorageConcrete USING[GroupScanObject],
DBStorageGroupScan USING[],
DBStoragePrivate USING[TupleFromTID],
DBStorageTID,
DBStorageTuple USING[ConsTupleObject, EqualTuple, IsValidTuple, InvalidateTuple,
NullTupleHandle, PrintTupleObject],
IO;
DBStorageGroupScanImpl: PROGRAM
IMPORTS
DBCommon,
DBEnvironment,
DBSegment,
DBStorageField,
DBStorageGroup,
DBStoragePrivate,
DBStorageTuple,
IO
EXPORTS
DBStorage,
DBStorageGroupScan
= BEGIN OPEN IO, DBEnvironment, DBStorageGroup, DBStorageTuple;
TID: TYPE = DBStorageTID.TID;
NullTID: TID = DBStorageTID.NullTID;
TupleHandle: TYPE = DBStorage.TupleHandle;
-- Type exported to DBStorage
GroupScanObject: PUBLIC TYPE = DBStorageConcrete.GroupScanObject;
GroupScanHandle: TYPE = REF GroupScanObject;
-- Module global state
activeGroupScanList: GroupScanHandle;
-- 1st item on list is a permanent header node
nullTupleHandle: TupleHandle;
Init: PUBLIC PROC = {
activeGroupScanList ← NEW[GroupScanObject ← [
tidFieldHandle: NIL, headOfGroup: NIL]];
nullTupleHandle ← DBStorageTuple.NullTupleHandle[];
};
ReadTID: PUBLIC PROC[x: TupleHandle, f: DBStorage.FieldHandle]
RETURNS[TupleHandle] = {
-- If x belongs to an f-group, ReadTID returns the head of the group; otherwise it
--returns NIL.
RETURN[ReadGroupField[x, f, headTID]];
};--ReadTID
WriteTID: PUBLIC PROC[x: TupleHandle, r: GroupScanHandle] = {
-- Makes tuple x join the group specified by r at r's current position (i.e. between
-- the tuple just read and the next tuple that would be read by NextInGroup). A
-- NextInGroup following WriteTID returns the tuple following x; a PrevInGroup
-- returns x itself.
-- Note that: (1) if x's field y had a non-NIL value before the WriteTID call, then
-- WriteTID has the effect of deleting x from some group (using WriteTIDNIL below),
-- (2) WriteTID cannot delete a tuple from one group without inserting it into
-- another, so WriteTIDNil below is necessary for that case, and (3) inserting or
-- deleting a tuple from a group requires the storage level to check all outstanding
-- GroupScanHandles to assure that they stay consistent with the deletion.
-- For now, this works only when inserting at the front...
f: DBStorage.FieldHandle ← r.tidFieldHandle;
WriteTIDNil[x, f];
WriteGroupField[x, f, headTID, r.headOfGroup];
SELECT TRUE FROM
(r.prevInScan=NIL) AND (r.nextInScan=NIL) => BEGIN --x is only tuple in group
CreateHeadEntry[r.headOfGroup, f];
WriteHeadField[r.headOfGroup, f, firstTID, x];
WriteHeadField[r.headOfGroup, f, lastTID, x];
WriteGroupField[x, f, prevTID, nullTupleHandle];
WriteGroupField[x, f, nextTID, nullTupleHandle];
END;
(r.prevInScan=NIL) AND (r.nextInScan#NIL) => BEGIN --x is at front of group
WriteHeadField[r.headOfGroup, f, firstTID, x];
WriteGroupField[x, f, prevTID, nullTupleHandle];
WriteGroupField[x, f, nextTID, r.nextInScan];
WriteGroupField[r.nextInScan, f, prevTID, x];
END;
(r.prevInScan#NIL) AND (r.nextInScan=NIL) => BEGIN --x is at rear of group
WriteHeadField[r.headOfGroup, f, lastTID, x];
WriteGroupField[x, f, nextTID, nullTupleHandle];
WriteGroupField[x, f, prevTID, r.prevInScan];
WriteGroupField[r.prevInScan, f, nextTID, x];
END;
(r.prevInScan#NIL) AND (r.nextInScan#NIL) => BEGIN --x is in middle of group
WriteGroupField[x, f, nextTID, r.nextInScan];
WriteGroupField[r.nextInScan, f, prevTID, x];
WriteGroupField[x, f, prevTID, r.prevInScan];
WriteGroupField[r.prevInScan, f, nextTID, x];
END;
ENDCASE => ERROR;
BEGIN --fix up active scans that are in identical position to scan (others are unaffected)
FOR p: GroupScanHandle ← activeGroupScanList.link, p.link UNTIL p = NIL DO
IF (DBStorageField.GroupIDOfField[p.tidFieldHandle] #
DBStorageField.GroupIDOfField[r.tidFieldHandle]) OR
(~EqualTuple[p.headOfGroup,r.headOfGroup]) OR
(~EqualTuple[p.prevInScan,r.prevInScan]) THEN LOOP;
-- p is effectively identical to scan
p.prevInScan ← x; -- no need for explicit free here anymore ...
ENDLOOP;
END;
};--WriteTID
WriteTIDNil: PUBLIC PROC[x: TupleHandle, f: DBStorage.FieldHandle] = {
-- Makes x's TID field point to the null tuple, i.e. removes x from whatever f-group
-- it currently belongs.
head, prev, next: TupleHandle;
head ← ReadGroupField[x, f, headTID];
IF head = NIL THEN RETURN;
prev ← ReadGroupField[x, f, prevTID];
next ← ReadGroupField[x, f, nextTID];
WriteGroupField[x, f, headTID, nullTupleHandle];
WriteGroupField[x, f, prevTID, nullTupleHandle]; --redundant
WriteGroupField[x, f, nextTID, nullTupleHandle]; --redundant
SELECT TRUE FROM
(prev=NIL) AND (next=NIL) => BEGIN --x was only tuple in group
DestroyHeadEntry[head, f];
END;
(prev=NIL) AND (next#NIL) => BEGIN --x was first tuple in group
WriteGroupField[next, f, prevTID, nullTupleHandle];
WriteHeadField[head, f, firstTID, next];
END;
(prev#NIL) AND (next=NIL) => BEGIN --x was last tuple in group
WriteGroupField[prev, f, nextTID, nullTupleHandle];
WriteHeadField[head, f, lastTID, prev];
END;
(prev#NIL) AND (next#NIL) => BEGIN --x was in middle of group
WriteGroupField[prev, f, nextTID, next];
WriteGroupField[next, f, prevTID, prev];
END;
ENDCASE => ERROR;
-- head is free now
BEGIN --fix up active scans that contain x (others are unaffected)
FOR p: GroupScanHandle ← activeGroupScanList.link, p.link UNTIL p = NIL DO
IF DBStorageField.GroupIDOfField[p.tidFieldHandle] #
DBStorageField.GroupIDOfField[f] THEN LOOP;
IF EqualTuple[p.prevInScan,x] THEN p.prevInScan ← prev;
IF EqualTuple[p.nextInScan,x] THEN p.nextInScan ← next;
ENDLOOP;
END;
-- prev, next are free now
};--WriteTIDNil
GetGroupIDs: PUBLIC PROC[x: TupleHandle] RETURNS[LIST OF TupleHandle] = {
-- Returns a list containing all GroupIDs g such that z is the head of a g-group.
-- The Tuple level is responsible for mapping from GroupIDs to FieldHandles, so that
-- OpenScanGroup can be called when necessary.
groupList: LONG DESCRIPTOR FOR DBStorageGroup.GroupList;
cacheHint: DBCache.CacheHandle;
result: LIST OF TupleHandle;
[groupList,cacheHint] ← GroupListFromTuple[x];
IF LENGTH[groupList] = 0 THEN result ← NIL
ELSE {
newCons, lastCons: LIST OF TupleHandle;
FOR i: CARDINAL IN [0..LENGTH[groupList]) DO
newCons ← LIST[
IF groupList[i].groupID <= DBStorage.MaxSystemTupleID THEN
DBStoragePrivate.TupleFromTID[groupList[i].groupID]
ELSE
DBStorageTuple.ConsTupleObject[tid: groupList[i].groupID, cacheHint: NIL]];
-- Append the cell just created to the list we're growing.
IF i = 0 THEN result ← newCons ELSE lastCons.rest ← newCons;
lastCons ← newCons;
ENDLOOP;
};--IF
DBSegment.UnlockPage[cacheHint];
RETURN[result];
};--GetGroupIDs
OpenScanGroup:
PUBLIC PROC[x: TupleHandle, f: DBStorage.FieldHandle, start: DBStorage.FirstLast]
RETURNS[GroupScanHandle] = {
-- Returns a GroupScanHandle positioned before the first (or after the last) tuple
-- of the f-group that has tuple x as head (first or last depending upon the value of
-- start). Returns a non-NIL GroupScanHandle even if there is no group (since the
-- scan handle is the only way to CREATE a group).
groupList: LONG DESCRIPTOR FOR DBStorageGroup.GroupList;
cacheHint: DBCache.CacheHandle;
result: GroupScanHandle;
DBStorageField.CheckFieldHandleType[f, Group];
result ← Alloc[f, x];
result.link ← activeGroupScanList.link;
activeGroupScanList.link ← result;
[groupList, cacheHint] ← DBStorageGroup.GroupListFromTuple[x];
IF LENGTH[groupList] # 0 THEN BEGIN
FOR i: CARDINAL IN [0..LENGTH[groupList]) DO
IF groupList[i].groupID = DBStorageField.GroupIDOfField[f] THEN GOTO FoundIt;
REPEAT
FoundIt =>
SELECT start FROM
First => result.nextInScan← DBStorageTuple.ConsTupleObject[groupList[i].firstTID, NIL];
Last => result.prevInScan← DBStorageTuple.ConsTupleObject[groupList[i].lastTID, NIL];
ENDCASE => ERROR;
FINISHED => NULL; -- this is ok, the scan is just empty
ENDLOOP;
END;--IF
DBSegment.UnlockPage[cacheHint];
RETURN[result];
};--OpenScanGroup
Alloc: PROC [f: DBStorage.FieldHandle, x: TupleHandle]
RETURNS [GroupScanHandle] = INLINE {
RETURN[NEW[GroupScanObject ← [
tidFieldHandle: f,
headOfGroup: x,
prevInScan: NIL, nextInScan: NIL, link: NIL]]] };
NextInGroup: PUBLIC PROC[r: GroupScanHandle] RETURNS[TupleHandle] = {
-- Returns the tuple x immediately following the position r in a group, and advances
-- r one position. Returns NIL if r was already positioned after the last tuple in
-- the group.
result: TupleHandle ← NIL;
IF r.tidFieldHandle = NIL THEN ERROR InternalError; -- InvalidGroupScan
IF r.nextInScan#NIL THEN {
r.prevInScan ← result ← r.nextInScan;
r.nextInScan ← DBStorageGroup.ReadGroupField[result, r.tidFieldHandle, nextTID];
};--IF
RETURN[result];
};--NextInGroup
PrevInGroup: PUBLIC PROC[r: GroupScanHandle] RETURNS[TupleHandle] = {
-- Returns the tuple x immediately preceding the position r in a group, and moves r
-- one position backwards. Returns NIL if r was already positioned before the first
-- tuple in the group.
result: TupleHandle ← NIL;
IF r.tidFieldHandle = NIL THEN ERROR InternalError; -- InvalidGroupScan
IF r.prevInScan # NIL THEN {
r.nextInScan ← result ← r.prevInScan;
r.prevInScan ← DBStorageGroup.ReadGroupField[result, r.tidFieldHandle, prevTID];
};--IF
RETURN[result];
};--PrevInGroup
CloseScanGroup: PUBLIC PROC[r: GroupScanHandle] = {
FOR scanPred: GroupScanHandle ← activeGroupScanList, scanPred.link
UNTIL scanPred=NIL DO
IF scanPred.link=r THEN {
scanPred.link ← r.link; r.link ← NIL;
FreeContents[r];
RETURN;
};
REPEAT
FINISHED => ERROR DBEnvironment.InternalError; -- [GroupScanNotFound];
ENDLOOP;
};--CloseScanGroup
CallAfterFinishTransaction: PUBLIC PROC [] = {
rPrev: GroupScanHandle ← activeGroupScanList;
UNTIL rPrev.link = NIL DO
r: GroupScanHandle ← rPrev.link;
IF NOT DBStorageTuple.IsValidTuple[r.headOfGroup] THEN {
DBStorageTuple.InvalidateTuple[r.prevInScan];
DBStorageTuple.InvalidateTuple[r.nextInScan];
FreeContents[r];
rPrev.link ← r.link; r.link ← NIL;
}
ELSE rPrev ← r;
ENDLOOP;
};
FreeContents: PROC[r: GroupScanHandle] = {
-- Frees all objects that are dependent on r. works even if r is invalid, i.e. FreeContents[r]
-- has been done before.
r.tidFieldHandle ← NIL;
r.headOfGroup ← r.prevInScan ← r.nextInScan ← NIL;
};--FreeContents
CheckState: PUBLIC PROC[doPrinting: BOOLEAN] = {
-- There isn't really much to check, except that the lists are well-formed.
-- if this runs forever, one isn't.
activeGroupScanListLen: CARDINAL ← 0;
FOR r: GroupScanHandle ← activeGroupScanList.link, r.link UNTIL r=NIL DO
activeGroupScanListLen ← activeGroupScanListLen + 1;
DBStorageField.CheckFieldHandleType[r.tidFieldHandle, Group];
IF r.headOfGroup = NIL THEN ERROR;
ENDLOOP;
IF doPrinting THEN {
DBCommon.GetDebugStream[].PutF["list of active group scans contains %d elements*n", card[activeGroupScanListLen]];
FOR r: GroupScanHandle ← activeGroupScanList, r.link UNTIL r=NIL DO
PrintGroupScanObject[r];
ENDLOOP;
DBCommon.GetDebugStream[].PutF["*n"];
};--IF
};--CheckState
PrintGroupScanObject: PROC[scan: GroupScanHandle] = {
pscan: POINTER TO GroupScanHandle = @scan;
debugStream: IO.STREAM← DBCommon.GetDebugStream[];
debugStream.PutF["groupScanHdl: %12bB, tidFieldHdl: ", card[LOOPHOLE[pscan, CARDINAL]]];
--DBStorageField.PrintFieldObject[scan.tidFieldHandle];
debugStream.PutF["*n headOfGroup: "];
DBStorageTuple.PrintTupleObject[scan.headOfGroup];
debugStream.PutF["*n prevInScan: "];
DBStorageTuple.PrintTupleObject[scan.prevInScan];
debugStream.PutF["*n nextInScan: "];
DBStorageTuple.PrintTupleObject[scan.nextInScan];
debugStream.PutF["*n"];
};--PrintGroupScanObject
END.--DBStorageGroupScanImpl
CHANGE LOG
Created by MBrown on June 17, 1980 1:00 PM
-- Moved code here from StorageImplB.
Changed by MBrown on June 20, 1980 4:19 PM
-- Added explicit management of free GroupScanObjects.
Changed by MBrown on July 23, 1980 10:10 PM
-- FirstLast changed from {First, Last} to {first, last}.
Changed by MBrown on August 4, 1980 11:50 PM
-- Added NoticeCloseDatabase. Changed ListofGroupID to ListOfGroupID.
Changed by MBrown on August 20, 1980 9:15 PM
-- Added CheckState.
Changed by MBrown on September 12, 1980 2:13 PM
-- Added Finalize.
Changed by MBrown on September 14, 1980 11:27 PM
-- NullTupleObject went away during Finalize! Now it is kept in the global frame, which requires us
--to export TupleHandle, etc...
Changed by MBrown on September 26, 1980 12:33 PM
-- Converted to new DBException.
Changed by MBrown on November 12, 1980 4:09 PM
-- In NoticeCloseDatabase, set activeGroupScanList ← NIL after deallocation.
--This is a hack; it leaves garbage around, and doing a CloseScanGroup on a
--deleted scan will cause InternalBug[GroupScanNotFound] to be generated.
Changed by MBrown on December 11, 1980 2:26 PM
-- Undid the above hack, and modified Finalize to not raise any signals. Made NextInGroup
--and PrevInGroup ERROR BadOperation[InvalidGroupScan] when invoked on a group scan with
--r.tidFieldHandle = NIL.
Changed by MBrown on December 20, 1980 6:04 PM
-- Added cleanup code in NextInGroup and PrevInGroup, to avoid error in finalization.
Changed by MBrown on February 27, 1981 3:58 PM
-- Use zone for storage allocation.
Changed by MBrown on 9-Jun-81 18:13:50
-- Converting to use collectable storage for GroupScanObject, TupleObject.
Changed by Willie-Sue on June 24, 1982 12:19 pm
-- IOStream => IO
Changed by Willie-Sue on June 30, 1982 4:49 pm
-- PrivateIO.DebugStream => DBCommon.GetDebugStream[]
Changed by MBrown on November 30, 1982 10:07 pm
-- Changes for new segment scheme.