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comparison graal/com.oracle.max.base/src/com/sun/max/util/ArrayValueHistory.java @ 3733:e233f5660da4

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Added Java files from Maxine project.
author Thomas Wuerthinger <thomas.wuerthinger@oracle.com>
date Sat, 17 Dec 2011 19:59:18 +0100
parents
children bc8527f3071c
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3732:3e2e8b8abdaf 3733:e233f5660da4
1 /*
2 * Copyright (c) 2009, 2011, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 */
23 package com.sun.max.util;
24
25 import java.util.*;
26
27 import com.sun.max.program.*;
28
29 /**
30 * An array-based recording of the history of a value, with
31 * time expressed as the number of generations back from the current generation (0).
32 */
33 public final class ArrayValueHistory<E> {
34
35 private final ArrayDeque<E> generations;
36 private final int limit;
37 private int age = -1;
38
39 public ArrayValueHistory(int limit) {
40 this.generations = new ArrayDeque<E>();
41 this.limit = limit;
42 }
43
44 public ArrayValueHistory() {
45 this (Integer.MAX_VALUE);
46 }
47
48 /**
49 * Adds a new value, which becomes the current generation.
50 * The generation of all previously recorded values increases by 1.
51 */
52 public void addNew(E newValue) {
53 // if (generations.size() > 0) {
54 // if (newValue.equals(generations.getFirst())) {
55 // if (age >= 0) {
56 // age++;
57 // }
58 // } else {
59 // age = 0;
60 // }
61 // }
62 generations.addFirst(newValue);
63 if (generations.size() > limit) {
64 generations.removeLast();
65 }
66 this.age = currentAge();
67 }
68
69 /**
70 * Replaces the current value in the history.
71 *
72 * @param newValue value which becomes current
73 * @throws ProgramError if no values have been recorded.
74 */
75 public void updateCurrent(E newValue) {
76 if (generations.size() > 0) {
77 if (!newValue.equals(generations.getFirst())) {
78 generations.pop();
79 addNew(newValue);
80 }
81 } else {
82 throw ProgramError.unexpected("attempt to update empty history");
83 }
84 }
85
86 /**
87 * Gets the historical value at some generation, 0 is current.
88 *
89 * @return The value at a specified generation.
90 * @throws ProgramError if the index is out of range of the current history
91 */
92 public E value(int generation) {
93 if (generation == 0 && generations.size() > 0) {
94 return generations.getFirst();
95 }
96 final Iterator<E> iterator = generations.iterator();
97 int index = 0;
98 while (iterator.hasNext()) {
99 if (index == generation) {
100 return iterator.next();
101 }
102 index++;
103 }
104 throw ProgramError.unexpected("exceeded history");
105 }
106
107 /**
108 * @return the age, in generations, of the current value, since recording began.
109 * 0 if different from immediate predecessor; -1 if no different value ever recorded
110 * Comparison uses {@linkplain Object#equals(Object) equals}.
111 */
112 public int currentValueAge() {
113 return age;
114 }
115
116 /**
117 * @return the maximum number of generations that can be recorded.
118 */
119 public int getLimit() {
120 return limit;
121 }
122
123 /**
124 * @return the number of generations recorded; initially 0.
125 */
126 public int size() {
127 return generations.size();
128 }
129
130 /**
131 * @return iteration of the values recorded in the history, starting with the current
132 * generation and proceeding backward in time.
133 */
134 public Iterator<E> generations() {
135 return generations.iterator();
136 }
137
138 /**
139 * Computes the age of the current generation, defined to be the number of
140 * preceding values that are equal, or -1 if no different value exists.
141 */
142 private int currentAge() {
143 assert generations.size() > 0;
144 final Iterator<E> iterator = generations.iterator();
145 E currentValue = iterator.next();
146 int duplicates = 0;
147 while (iterator.hasNext()) {
148 if (iterator.next().equals(currentValue)) {
149 duplicates++;
150 } else {
151 return duplicates;
152 }
153 }
154 return -1;
155 }
156
157 }