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Java/storage/ZZCacheDimension.java
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/*
ZZCacheDimension.java
*
* Copyright (c) 2000, Ted Nelson and Tuomas Lukka
*
* You may use and distribute under the terms of either the GNU Lesser
* General Public License, either version 2 of the license or,
* at your choice, any later version. Alternatively, you may use and
* distribute under the terms of the XPL.
*
* See the LICENSE.lgpl and LICENSE.xpl files for the specific terms of
* the licenses.
*
* This software is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the README
* file for more details.
*
*/
/*
* Written by Tuomas Lukka
*/
package org.gzigzag;
import java.util.*;
/** Dimension-centric implementation of a locally
* cached dimension.
* This class may be used as a cache to
* a dimension stored on disk, and includes facilities for tracking
* the changes.
* XXX Look into replacing hashtable with a more memory-saving constructions?
* <p>
* This, uglily, shares some code with ZZLocalDimension but making
* this an inheritance relationship would have been difficult, and
* the point is to keep ZZLocalDimension a truly simple basic
* example implementation of a dimension.
* <p>
* The mechanism for the undolist is quite interesting:
* we save each connect / disconnect operation with the two cells,
* so we know the inverse of each operation.
* We can then, at commit time, build a hash table by taking the first
* operation and seeing if it cancels an earlier operation (undolist does
* commits in reverse order) and if it does, we do nothing.
* This allows the user to move the cursor without wasting storage on all
* positions.
* Interestingly, although we store all connections bidirectionally as
* connect/disconnect pairs in the undolist, we cannot save them like that
* after compression: they must be saved as single-sided disconnects and
* pair connects.
*/
public class ZZCacheDimension extends ZZDimension implements ZZDimStorer {
public static final String rcsid = "$Id: ZZCacheDimension.java,v 1.11 2001/02/23 08:33:37 ajk Exp $";
public static final boolean dbg = true;
final static void p(String s) { if(dbg) System.out.println(s); }
final static void pa(String s) { System.out.println(s); }
UndoList undo;
public void setUndoList(UndoList l) { undo = l; }
protected boolean readonly;
public ZZCacheDimension() { this(false); }
public ZZCacheDimension(boolean readonly) {
this.readonly = readonly;
}
/** Connections to the positive direction. */
Hashtable cp = new Hashtable();
/** Connections to the negative direction. */
Hashtable cm = new Hashtable();
/** The earlier connection on each cell's poswards or negwards
* direction at commit time.
* This list is created at commit time by reversing all operations
* so we can then compare these values and the current values to
* see which have changed.
* Hmm.. do we really even need comm?
*/
Hashtable comp;
Hashtable comm;
/** A null marker for the hashtables. */
static final Object nolla = new Object();
synchronized public void startCommit() {
if (readonly) throw new ZZError("readonly dimension");
comp = new Hashtable();
comm = new Hashtable();
}
synchronized public void endCommit(ZZDimStorer sto) {
if (readonly) throw new ZZError("readonly dimension");
for(Enumeration e = comp.keys();
e.hasMoreElements();) {
String id = (String)e.nextElement();
Object oidto = comp.get(id);
String idto = (oidto == nolla ? null : (String)oidto);
String idwasto = (String)cp.get(id);
// If it's the same, then nevermind.
if(idto == idwasto || (
idto != null && idto.equals(idwasto)))
continue;
if(idwasto != null)
sto.storeConnect(id, idwasto);
else
sto.storeDisconnect(id, 1);
}
for(Enumeration e = comm.keys();
e.hasMoreElements();) {
String id = (String)e.nextElement();
Object oidto = comm.get(id);
String idto = (oidto == nolla ? null : (String)oidto);
String idwasto = (String)cm.get(id);
// If it's the same, then nevermind.
if(idto == idwasto || (
idto != null && idto.equals(idwasto)))
continue;
if(idwasto == null)
sto.storeDisconnect(id, -1);
// Not here: we only call connect once.
// else
// sto.connect(id, -1, idto);
}
comp = null;
comm = null;
}
ZZCellHandle ch(Object o) {
if(o instanceof ZZCellHandle) return (ZZCellHandle)o;
return (ZZCellHandle)space.getCellByID((String)o);
}
String cid(Object o) {
if(o instanceof ZZCellHandle) return ((ZZCellHandle)o).id;
return (String)o;
}
/** The abstracted operation of connecting two cells.
* Parameters: cell1 cell2.
* The cells are explicitly assumed to be not connected before
* this.
*/
protected class Connect implements UndoList.Op {
public void undo(Object[] list, int nth) {
String c1 = (String)list[nth+1];
String c2 = (String)list[nth+2];
if(!s((ZZCellHandle)space.getCellByID(c1), 1, null).id.equals(c2))
throw new ZZError(
"Error when undoing change: disconnect assertion broken");
cp.remove(c1);
cm.remove(c2);
triggers.chg(c1);
triggers.chg(c2);
}
public void redo(Object[] list, int nth) {
String c1 = (String)list[nth+1];
String c2 = (String)list[nth+2];
if(cp.get(c1) != null ||
cm.get(c2) != null)
throw new ZZError(
"Error when redoing change: unconnected assertion broken");
cp.put(c1, c2);
cm.put(c2, c1);
triggers.chg(c1);
triggers.chg(c2);
}
public void commit(Object[] list, int nth) {
String c1 = (String)list[nth+1];
String c2 = (String)list[nth+2];
comp.put(c1, nolla);
comm.put(c2, nolla);
}
}
/** The abstracted operation of disconnecting two cells.
* Parameters: cell1 cell2.
*/
protected class Disconnect implements UndoList.Op {
public void undo(Object[] list, int nth) {
String c1 = (String)list[nth+1];
String c2 = (String)list[nth+2];
// Note we can't use disconnect() since that would make
// new undolist entries.
if(cp.get(c1) != null ||
cm.get(c2) != null)
throw new ZZError(
"Error when undoing change: unconnected assertion broken");
cp.put(c1, c2);
cm.put(c2, c1);
triggers.chg(c1);
triggers.chg(c2);
}
public void redo(Object[] list, int nth) {
String c1 = (String)list[nth+1];
String c2 = (String)list[nth+2];
if(!s((ZZCellHandle)space.getCellByID(c1), 1, null).id.equals(c2))
throw new ZZError(
"Error when redoing change: disconnect assertion broken");
cp.remove(c1);
cm.remove(c2);
triggers.chg(c1);
triggers.chg(c2);
}
public void commit(Object[] list, int nth) {
String c1 = (String)list[nth+1];
String c2 = (String)list[nth+2];
comp.put(c1, c2);
comm.put(c2, c1);
}
}
Connect myconnect = new Connect();
Disconnect mydisconnect = new Disconnect();
public ZZCellHandle s(ZZCellHandle c, int steps, ZZObs o) {
String s = c.id;
if(o != null) triggers.addObs(s, o);
if(steps>0)
while(steps-- > 0 && s != null) {
s = (String)cp.get(s);
if(o != null && s!=null) triggers.addObs(s, o);
}
else
while(steps++ < 0 && s != null) {
s = (String)cm.get(s);
if(o != null && s!=null) triggers.addObs(s, o);
}
if(s==null) return null;
return (ZZCellHandle)space.getCellByID(s);
}
public void connect(ZZCellHandle c0, ZZCellHandle d0) {
if (readonly) throw new ZZError("readonly dimension");
String c = c0.id;
String d = d0.id;
disconnect(c0, 1);
disconnect(d0, -1);
cp.put(c, d);
cm.put(d, c);
undo.add(myconnect, c, d);
triggers.chg(c);
triggers.chg(d);
}
public void disconnect(ZZCellHandle c0, int dir) {
if (readonly) throw new ZZError("readonly dimension");
String c = c0.id;
String o;
if(dir>0) {
o = (String)cp.get(c);
if(o!=null) {
undo.add(mydisconnect, c, o);
cp.remove(c);
cm.remove(o);
}
} else {
o = (String)cm.get(c);
if(o!=null) {
undo.add(mydisconnect, o, c);
cm.remove(c);
cp.remove(o);
}
}
triggers.chg(c);
if(o!=null) triggers.chg(o);
}
// ZZDimStorer implementation
public void storeConnect(String a, String b) {
cp.put(a, b);
cm.put(b, a);
}
public void storeDisconnect(String a, int dir) {
Hashtable h = (dir > 0 ? cp : cm);
h.remove(a);
}
}