1/*
2 * Copyright (c) 2010, 2013, 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
26package jdk.nashorn.internal.runtime.linker;
27
28import static jdk.nashorn.internal.runtime.ECMAErrors.typeError;
29
30import java.security.AccessControlContext;
31import java.security.AccessController;
32import java.security.Permissions;
33import java.security.PrivilegedAction;
34import java.security.ProtectionDomain;
35import java.util.Collection;
36import java.util.Iterator;
37import java.util.LinkedHashMap;
38import java.util.LinkedList;
39import java.util.List;
40import java.util.Map;
41
42/**
43 * A tuple of a class loader and a single class representative of the classes that can be loaded through it. Its
44 * equals/hashCode is defined in terms of the identity of the class loader. The rationale for this class is that it
45 * couples a class loader with a random representative class coming from that loader - this representative class is then
46 * used to determine if one loader can see the other loader's classes.
47 */
48final class ClassAndLoader {
49    static AccessControlContext createPermAccCtxt(final String... permNames) {
50        final Permissions perms = new Permissions();
51        for (final String permName : permNames) {
52            perms.add(new RuntimePermission(permName));
53        }
54        return new AccessControlContext(new ProtectionDomain[] { new ProtectionDomain(null, perms) });
55    }
56
57    private static final AccessControlContext GET_LOADER_ACC_CTXT = createPermAccCtxt("getClassLoader");
58
59    private final Class<?> representativeClass;
60    // Don't access this directly; most of the time, use getRetrievedLoader(), or if you know what you're doing,
61    // getLoader().
62    private ClassLoader loader;
63    // We have mild affinity against eagerly retrieving the loader, as we need to do it in a privileged block. For
64    // the most basic case of looking up an already-generated adapter info for a single type, we avoid it.
65    private boolean loaderRetrieved;
66
67    ClassAndLoader(final Class<?> representativeClass, final boolean retrieveLoader) {
68        this.representativeClass = representativeClass;
69        if(retrieveLoader) {
70            retrieveLoader();
71        }
72    }
73
74    Class<?> getRepresentativeClass() {
75        return representativeClass;
76    }
77
78    boolean canSee(final ClassAndLoader other) {
79        try {
80            final Class<?> otherClass = other.getRepresentativeClass();
81            return Class.forName(otherClass.getName(), false, getLoader()) == otherClass;
82        } catch (final ClassNotFoundException e) {
83            return false;
84        }
85    }
86
87    ClassLoader getLoader() {
88        if(!loaderRetrieved) {
89            retrieveLoader();
90        }
91        return getRetrievedLoader();
92    }
93
94    ClassLoader getRetrievedLoader() {
95        assert loaderRetrieved;
96        return loader;
97    }
98
99    private void retrieveLoader() {
100        loader = representativeClass.getClassLoader();
101        loaderRetrieved = true;
102    }
103
104    @Override
105    public boolean equals(final Object obj) {
106        return obj instanceof ClassAndLoader && ((ClassAndLoader)obj).getRetrievedLoader() == getRetrievedLoader();
107    }
108
109    @Override
110    public int hashCode() {
111        return System.identityHashCode(getRetrievedLoader());
112    }
113
114    /**
115     * Given a list of types that define the superclass/interfaces for an adapter class, returns a single type from the
116     * list that will be used to attach the adapter to its ClassValue. The first type in the array that is defined in a
117     * class loader that can also see all other types is returned. If there is no such loader, an exception is thrown.
118     * @param types the input types
119     * @return the first type from the array that is defined in a class loader that can also see all other types.
120     */
121    static ClassAndLoader getDefiningClassAndLoader(final Class<?>[] types) {
122        // Short circuit the cheap case
123        if(types.length == 1) {
124            return new ClassAndLoader(types[0], false);
125        }
126
127        return AccessController.doPrivileged(new PrivilegedAction<ClassAndLoader>() {
128            @Override
129            public ClassAndLoader run() {
130                return getDefiningClassAndLoaderPrivileged(types);
131            }
132        }, GET_LOADER_ACC_CTXT);
133    }
134
135    static ClassAndLoader getDefiningClassAndLoaderPrivileged(final Class<?>[] types) {
136        final Collection<ClassAndLoader> maximumVisibilityLoaders = getMaximumVisibilityLoaders(types);
137
138        final Iterator<ClassAndLoader> it = maximumVisibilityLoaders.iterator();
139        if(maximumVisibilityLoaders.size() == 1) {
140            // Fortunate case - single maximally specific class loader; return its representative class.
141            return it.next();
142        }
143
144        // Ambiguity; throw an error.
145        assert maximumVisibilityLoaders.size() > 1; // basically, can't be zero
146        final StringBuilder b = new StringBuilder();
147        b.append(it.next().getRepresentativeClass().getCanonicalName());
148        while(it.hasNext()) {
149            b.append(", ").append(it.next().getRepresentativeClass().getCanonicalName());
150        }
151        throw typeError("extend.ambiguous.defining.class", b.toString());
152    }
153
154    /**
155     * Given an array of types, return a subset of their class loaders that are maximal according to the
156     * "can see other loaders' classes" relation, which is presumed to be a partial ordering.
157     * @param types types
158     * @return a collection of maximum visibility class loaders. It is guaranteed to have at least one element.
159     */
160    private static Collection<ClassAndLoader> getMaximumVisibilityLoaders(final Class<?>[] types) {
161        final List<ClassAndLoader> maximumVisibilityLoaders = new LinkedList<>();
162        outer:  for(final ClassAndLoader maxCandidate: getClassLoadersForTypes(types)) {
163            final Iterator<ClassAndLoader> it = maximumVisibilityLoaders.iterator();
164            while(it.hasNext()) {
165                final ClassAndLoader existingMax = it.next();
166                final boolean candidateSeesExisting = maxCandidate.canSee(existingMax);
167                final boolean exitingSeesCandidate = existingMax.canSee(maxCandidate);
168                if(candidateSeesExisting) {
169                    if(!exitingSeesCandidate) {
170                        // The candidate sees the the existing maximum, so drop the existing one as it's no longer maximal.
171                        it.remove();
172                    }
173                    // NOTE: there's also the anomalous case where both loaders see each other. Not sure what to do
174                    // about that one, as two distinct class loaders both seeing each other's classes is weird and
175                    // violates the assumption that the relation "sees others' classes" is a partial ordering. We'll
176                    // just not do anything, and treat them as incomparable; hopefully some later class loader that
177                    // comes along can eliminate both of them, if it can not, we'll end up with ambiguity anyway and
178                    // throw an error at the end.
179                } else if(exitingSeesCandidate) {
180                    // Existing sees the candidate, so drop the candidate.
181                    continue outer;
182                }
183            }
184            // If we get here, no existing maximum visibility loader could see the candidate, so the candidate is a new
185            // maximum.
186            maximumVisibilityLoaders.add(maxCandidate);
187        }
188        return maximumVisibilityLoaders;
189    }
190
191    private static Collection<ClassAndLoader> getClassLoadersForTypes(final Class<?>[] types) {
192        final Map<ClassAndLoader, ClassAndLoader> classesAndLoaders = new LinkedHashMap<>();
193        for(final Class<?> c: types) {
194            final ClassAndLoader cl = new ClassAndLoader(c, true);
195            if(!classesAndLoaders.containsKey(cl)) {
196                classesAndLoaders.put(cl, cl);
197            }
198        }
199        return classesAndLoaders.keySet();
200    }
201}
202