1 | /* |
2 | * Copyright 2001-2006 Sun Microsystems, Inc. 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. Sun designates this |
8 | * particular file as subject to the "Classpath" exception as provided |
9 | * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, |
22 | * CA 95054 USA or visit www.sun.com if you need additional information or |
23 | * have any questions. |
24 | */ |
25 | |
26 | package com.sun.tools.javac.util; |
27 | |
28 | import com.sun.tools.javac.Main; |
29 | import java.util.*; |
30 | |
31 | /** |
32 | * Support for an abstract context, modelled loosely after ThreadLocal |
33 | * but using a user-provided context instead of the current thread. |
34 | * |
35 | * <p>Within the compiler, a single Context is used for each |
36 | * invocation of the compiler. The context is then used to ensure a |
37 | * single copy of each compiler phase exists per compiler invocation. |
38 | * |
39 | * <p>The context can be used to assist in extending the compiler by |
40 | * extending its components. To do that, the extended component must |
41 | * be registered before the base component. We break initialization |
42 | * cycles by (1) registering a factory for the component rather than |
43 | * the component itself, and (2) a convention for a pattern of usage |
44 | * in which each base component registers itself by calling an |
45 | * instance method that is overridden in extended components. A base |
46 | * phase supporting extension would look something like this: |
47 | * |
48 | * <p><pre> |
49 | * public class Phase { |
50 | * protected static final Context.Key<Phase> phaseKey = |
51 | * new Context.Key<Phase>(); |
52 | * |
53 | * public static Phase instance(Context context) { |
54 | * Phase instance = context.get(phaseKey); |
55 | * if (instance == null) |
56 | * // the phase has not been overridden |
57 | * instance = new Phase(context); |
58 | * return instance; |
59 | * } |
60 | * |
61 | * protected Phase(Context context) { |
62 | * context.put(phaseKey, this); |
63 | * // other intitialization follows... |
64 | * } |
65 | * } |
66 | * </pre> |
67 | * |
68 | * <p>In the compiler, we simply use Phase.instance(context) to get |
69 | * the reference to the phase. But in extensions of the compiler, we |
70 | * must register extensions of the phases to replace the base phase, |
71 | * and this must be done before any reference to the phase is accessed |
72 | * using Phase.instance(). An extended phase might be declared thus: |
73 | * |
74 | * <p><pre> |
75 | * public class NewPhase extends Phase { |
76 | * protected NewPhase(Context context) { |
77 | * super(context); |
78 | * } |
79 | * public static void preRegister(final Context context) { |
80 | * context.put(phaseKey, new Context.Factory<Phase>() { |
81 | * public Phase make() { |
82 | * return new NewPhase(context); |
83 | * } |
84 | * }); |
85 | * } |
86 | * } |
87 | * </pre> |
88 | * |
89 | * <p>And is registered early in the extended compiler like this |
90 | * |
91 | * <p><pre> |
92 | * NewPhase.preRegister(context); |
93 | * </pre> |
94 | * |
95 | * <p><b>This is NOT part of any API supported by Sun Microsystems. If |
96 | * you write code that depends on this, you do so at your own risk. |
97 | * This code and its internal interfaces are subject to change or |
98 | * deletion without notice.</b> |
99 | */ |
100 | public class Context { |
101 | /** The client creates an instance of this class for each key. |
102 | */ |
103 | public static class Key<T> { |
104 | // note: we inherit identity equality from Object. |
105 | } |
106 | |
107 | /** |
108 | * The client can register a factory for lazy creation of the |
109 | * instance. |
110 | */ |
111 | public static interface Factory<T> { |
112 | T make(); |
113 | }; |
114 | |
115 | /** |
116 | * The underlying map storing the data. |
117 | * We maintain the invariant that this table contains only |
118 | * mappings of the form |
119 | * Key<T> -> T or Key<T> -> Factory<T> */ |
120 | private Map<Key,Object> ht = new HashMap<Key,Object>(); |
121 | |
122 | /** Set the factory for the key in this context. */ |
123 | public <T> void put(Key<T> key, Factory<T> fac) { |
124 | checkState(ht); |
125 | Object old = ht.put(key, fac); |
126 | if (old != null) |
127 | throw new AssertionError("duplicate context value"); |
128 | } |
129 | |
130 | /** Set the value for the key in this context. */ |
131 | public <T> void put(Key<T> key, T data) { |
132 | if (data instanceof Factory) |
133 | throw new AssertionError("T extends Context.Factory"); |
134 | checkState(ht); |
135 | Object old = ht.put(key, data); |
136 | if (old != null && !(old instanceof Factory) && old != data && data != null) |
137 | throw new AssertionError("duplicate context value"); |
138 | } |
139 | |
140 | /** Get the value for the key in this context. */ |
141 | public <T> T get(Key<T> key) { |
142 | checkState(ht); |
143 | Object o = ht.get(key); |
144 | if (o instanceof Factory) { |
145 | Factory fac = (Factory)o; |
146 | o = fac.make(); |
147 | if (o instanceof Factory) |
148 | throw new AssertionError("T extends Context.Factory"); |
149 | assert ht.get(key) == o; |
150 | } |
151 | |
152 | /* The following cast can't fail unless there was |
153 | * cheating elsewhere, because of the invariant on ht. |
154 | * Since we found a key of type Key<T>, the value must |
155 | * be of type T. |
156 | */ |
157 | return Context.<T>uncheckedCast(o); |
158 | } |
159 | |
160 | public Context() {} |
161 | |
162 | private Map<Class<?>, Key<?>> kt = new HashMap<Class<?>, Key<?>>(); |
163 | |
164 | private <T> Key<T> key(Class<T> clss) { |
165 | checkState(kt); |
166 | Key<T> k = uncheckedCast(kt.get(clss)); |
167 | if (k == null) { |
168 | k = new Key<T>(); |
169 | kt.put(clss, k); |
170 | } |
171 | return k; |
172 | } |
173 | |
174 | public <T> T get(Class<T> clazz) { |
175 | return get(key(clazz)); |
176 | } |
177 | |
178 | public <T> void put(Class<T> clazz, T data) { |
179 | put(key(clazz), data); |
180 | } |
181 | public <T> void put(Class<T> clazz, Factory<T> fac) { |
182 | put(key(clazz), fac); |
183 | } |
184 | |
185 | /** |
186 | * TODO: This method should be removed and Context should be made type safe. |
187 | * This can be accomplished by using class literals as type tokens. |
188 | */ |
189 | @SuppressWarnings("unchecked") |
190 | private static <T> T uncheckedCast(Object o) { |
191 | return (T)o; |
192 | } |
193 | |
194 | public void dump() { |
195 | for (Object value : ht.values()) |
196 | System.err.println(value == null ? null : value.getClass()); |
197 | } |
198 | |
199 | public void clear() { |
200 | ht = null; |
201 | kt = null; |
202 | } |
203 | |
204 | private static void checkState(Map<?,?> t) { |
205 | if (t == null) |
206 | throw new IllegalStateException(); |
207 | } |
208 | } |