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comparison: src/share/classes/com/sun/tools/javac/util/Context.java

src/share/classes/com/sun/tools/javac/util/Context.java

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1 /*
2 * Copyright (c) 2001, 2012, 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. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package com.sun.tools.javac.util;
27
28 import java.util.*;
29
30 /**
31 * Support for an abstract context, modelled loosely after ThreadLocal
32 * but using a user-provided context instead of the current thread.
33 *
34 * <p>Within the compiler, a single Context is used for each
35 * invocation of the compiler. The context is then used to ensure a
36 * single copy of each compiler phase exists per compiler invocation.
37 *
38 * <p>The context can be used to assist in extending the compiler by
39 * extending its components. To do that, the extended component must
40 * be registered before the base component. We break initialization
41 * cycles by (1) registering a factory for the component rather than
42 * the component itself, and (2) a convention for a pattern of usage
43 * in which each base component registers itself by calling an
44 * instance method that is overridden in extended components. A base
45 * phase supporting extension would look something like this:
46 *
47 * <p><pre>{@code
48 * public class Phase {
49 * protected static final Context.Key<Phase> phaseKey =
50 * new Context.Key<Phase>();
51 *
52 * public static Phase instance(Context context) {
53 * Phase instance = context.get(phaseKey);
54 * if (instance == null)
55 * // the phase has not been overridden
56 * instance = new Phase(context);
57 * return instance;
58 * }
59 *
60 * protected Phase(Context context) {
61 * context.put(phaseKey, this);
62 * // other intitialization follows...
63 * }
64 * }
65 * }</pre>
66 *
67 * <p>In the compiler, we simply use Phase.instance(context) to get
68 * the reference to the phase. But in extensions of the compiler, we
69 * must register extensions of the phases to replace the base phase,
70 * and this must be done before any reference to the phase is accessed
71 * using Phase.instance(). An extended phase might be declared thus:
72 *
73 * <p><pre>{@code
74 * public class NewPhase extends Phase {
75 * protected NewPhase(Context context) {
76 * super(context);
77 * }
78 * public static void preRegister(final Context context) {
79 * context.put(phaseKey, new Context.Factory<Phase>() {
80 * public Phase make() {
81 * return new NewPhase(context);
82 * }
83 * });
84 * }
85 * }
86 * }</pre>
87 *
88 * <p>And is registered early in the extended compiler like this
89 *
90 * <p><pre>
91 * NewPhase.preRegister(context);
92 * </pre>
93 *
94 * <p><b>This is NOT part of any supported API.
95 * If you write code that depends on this, you do so at your own risk.
96 * This code and its internal interfaces are subject to change or
97 * deletion without notice.</b>
98 */
99 public class Context {
100 /** The client creates an instance of this class for each key.
101 */
102 public static class Key<T> {
103 // note: we inherit identity equality from Object.
104 }
105
106 /**
107 * The client can register a factory for lazy creation of the
108 * instance.
109 */
110 public static interface Factory<T> {
111 T make(Context c);
112 };
113
114 /**
115 * The underlying map storing the data.
116 * We maintain the invariant that this table contains only
117 * mappings of the form
118 * {@literal Key<T> -> T }
119 * or
120 * {@literal Key<T> -> Factory<T> }
121 */
122 private Map<Key<?>,Object> ht = new HashMap<Key<?>,Object>();
123
124 /** Set the factory for the key in this context. */
125 public <T> void put(Key<T> key, Factory<T> fac) {
126 checkState(ht);
127 Object old = ht.put(key, fac);
128 if (old != null)
129 throw new AssertionError("duplicate context value");
130 checkState(ft);
131 ft.put(key, fac); // cannot be duplicate if unique in ht
132 }
133
134 /** Set the value for the key in this context. */
135 public <T> void put(Key<T> key, T data) {
136 if (data instanceof Factory<?>)
137 throw new AssertionError("T extends Context.Factory");
138 checkState(ht);
139 Object old = ht.put(key, data);
140 if (old != null && !(old instanceof Factory<?>) && old != data && data != null)
141 throw new AssertionError("duplicate context value");
142 }
143
144 /** Get the value for the key in this context. */
145 public <T> T get(Key<T> key) {
146 checkState(ht);
147 Object o = ht.get(key);
148 if (o instanceof Factory<?>) {
149 Factory<?> fac = (Factory<?>)o;
150 o = fac.make(this);
151 if (o instanceof Factory<?>)
152 throw new AssertionError("T extends Context.Factory");
153 Assert.check(ht.get(key) == o);
154 }
155
156 /* The following cast can't fail unless there was
157 * cheating elsewhere, because of the invariant on ht.
158 * Since we found a key of type Key<T>, the value must
159 * be of type T.
160 */
161 return Context.<T>uncheckedCast(o);
162 }
163
164 public Context() {}
165
166 /**
167 * The table of preregistered factories.
168 */
169 private Map<Key<?>,Factory<?>> ft = new HashMap<Key<?>,Factory<?>>();
170
171 public Context(Context prev) {
172 kt.putAll(prev.kt); // retain all implicit keys
173 ft.putAll(prev.ft); // retain all factory objects
174 ht.putAll(prev.ft); // init main table with factories
175 }
176
177 /*
178 * The key table, providing a unique Key<T> for each Class<T>.
179 */
180 private Map<Class<?>, Key<?>> kt = new HashMap<Class<?>, Key<?>>();
181
182 private <T> Key<T> key(Class<T> clss) {
183 checkState(kt);
184 Key<T> k = uncheckedCast(kt.get(clss));
185 if (k == null) {
186 k = new Key<T>();
187 kt.put(clss, k);
188 }
189 return k;
190 }
191
192 public <T> T get(Class<T> clazz) {
193 return get(key(clazz));
194 }
195
196 public <T> void put(Class<T> clazz, T data) {
197 put(key(clazz), data);
198 }
199 public <T> void put(Class<T> clazz, Factory<T> fac) {
200 put(key(clazz), fac);
201 }
202
203 /**
204 * TODO: This method should be removed and Context should be made type safe.
205 * This can be accomplished by using class literals as type tokens.
206 */
207 @SuppressWarnings("unchecked")
208 private static <T> T uncheckedCast(Object o) {
209 return (T)o;
210 }
211
212 public void dump() {
213 for (Object value : ht.values())
214 System.err.println(value == null ? null : value.getClass());
215 }
216
217 public void clear() {
218 ht = null;
219 kt = null;
220 ft = null;
221 }
222
223 private static void checkState(Map<?,?> t) {
224 if (t == null)
225 throw new IllegalStateException();
226 }
227 }

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