pjs/grendel/calypso/util/Atom.java

225 строки
6.0 KiB
Java
Исходник Обычный вид История

1998-09-09 04:52:38 +04:00
/* -*- Mode: Java; tab-width: 2; indent-tabs-mode: nil -*-
*
* The contents of this file are subject to the Mozilla Public License
* Version 1.0 (the "License"); you may not use this file except in
* compliance with the License. You may obtain a copy of the License at
* http://www.mozilla.org/MPL/
*
* Software distributed under the License is distributed on an "AS IS"
* basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
* the License for the specific language governing rights and limitations
* under the License.
*
* The Original Code is the Grendel mail/news client.
*
* The Initial Developer of the Original Code is Netscape Communications
* Corporation. Portions created by Netscape are Copyright (C) 1997
* Netscape Communications Corporation. All Rights Reserved.
*
* Contributors: Edwin Woudt <edwin@woudt.nl>
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*/
package calypso.util;
/**
* Atom's are unique objects that you can use the object address
* to perform equality tests. This class accepts variants on
* String's to create the Atom's from.
*/
public final class Atom {
String fString;
int fHashCode;
private static final AtomTable gAtoms = new AtomTable();
/**
* Private constructor used by static allocators.
*/
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protected Atom(String aString, int aHashCode) {
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fString = aString;
fHashCode = aHashCode;
}
public String toString() {
return fString;
}
public int hashCode() {
return fHashCode;
}
public boolean equals(Object aObject) {
return aObject == this;
}
protected void finalize() throws Throwable {
synchronized (gAtoms) {
gAtoms.remove(fString, fHashCode);
}
}
// XXX deprecated entry point. Use Find instead
static private int gNoisyUsageCount = 10;
static public Atom ForObject(Object aObject) {
synchronized (gAtoms) {
if (gNoisyUsageCount > 0) {
try {
throw new RuntimeException("Atom.ForObject: deprecated method called! Use Atom.Find instead. Object:" + aObject.toString());
}
catch(RuntimeException e){
e.printStackTrace();
}
gNoisyUsageCount--;
}
return gAtoms.find(aObject.toString());
}
}
/**
* Find the atom for the given argument string. If the atom doesn't
* already exist then it is created.
*/
static public Atom Find(String aString) {
synchronized (gAtoms) {
return gAtoms.find(aString);
}
}
/**
* Find the atom for the given argument string. If the atom doesn't
* already exist then it is created.
*/
static public Atom Find(StringBuf aString) {
synchronized (gAtoms) {
return gAtoms.find(aString);
}
}
private static int gNextAtomID;
static public Atom UniqueAtom(String aPrefix) {
synchronized (gAtoms) {
StringBuf sbuf = StringBuf.Alloc();
Atom atom = null;
for (;;) {
int id = ++gNextAtomID;
sbuf.setLength(0);
sbuf.append(aPrefix);
sbuf.append(id);
if (!gAtoms.contains(sbuf)) {
atom = gAtoms.find(sbuf);
break;
}
// Hmmm. Somebody else recorded an atom with this name. Try
// again with the next id
}
StringBuf.Recycle(sbuf);
return atom;
}
}
//----------------------------------------------------------------------
// key's are String's/StringBuf's
// value's are WeakLink's which hold a weak reference to Atom's
static final class AtomTable extends HashtableBase {
Atom find(String aKey) {
return find(aKey, HashCodeFor(aKey));
}
Atom find(StringBuf aKey) {
return find(aKey, HashCodeFor(aKey));
}
private Atom find(Object aKey, int aHash) {
if (hashCodes == null) {
// create tables
grow();
}
int index = tableIndexFor(aKey, aHash);
Atom atom = null;
WeakLink link = (WeakLink) elements[index];
if (link == null) {
if (hashCodes[index] == EMPTY) {
// If the total number of occupied slots (either with a real
// element or a removed marker) gets too big, grow the table.
if (totalCount >= capacity) {
grow();
return find(aKey, aHash);
}
totalCount++;
}
count++;
hashCodes[index] = aHash;
keys[index] = aKey.toString();
elements[index] = link = new WeakLink();
} else {
atom = (Atom) link.get();
}
// Create atom if necessary
if (atom == null) {
atom = new Atom(aKey.toString(), aHash);
link.setThing(atom);
}
return atom;
}
// XXX replace with a faster better function
static final int HashCodeFor(String aString) {
int h = 0;
int len = aString.length();
if (len < 16) {
for (int i = 0; i < len; i++) {
h = (h * 37) + aString.charAt(i);
}
} else {
// only sample some characters
int skip = len / 8;
for (int i = len, off = 0 ; i > 0; i -= skip, off += skip) {
h = (h * 39) + aString.charAt(off);
}
}
return h;
}
static final int HashCodeFor(StringBuf aString) {
int h = 0;
int len = aString.length();
if (len < 16) {
for (int i = 0; i < len; i++) {
h = (h * 37) + aString.charAt(i);
}
} else {
// only sample some characters
int skip = len / 8;
for (int i = len, off = 0 ; i > 0; i -= skip, off += skip) {
h = (h * 39) + aString.charAt(off);
}
}
return h;
}
boolean contains(StringBuf aKey) {
if (hashCodes == null) {
return false;
}
int index = tableIndexFor(aKey, HashCodeFor(aKey));
WeakLink link = (WeakLink) elements[index];
if (link != null) {
return link.get() != null;
}
return false;
}
void remove(String aKey, int aHashCode) {
int index = tableIndexFor(aKey, aHashCode);
count--;
hashCodes[index] = REMOVED;
keys[index] = null;
elements[index] = null;
}
}
}