MissingMethodLinkerExporter.java revision 1805:7caf1f762f1d 
1/*
2 * Copyright (c) 2015, Oracle and/or its affiliates. All rights reserved.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
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7 *
8 *   - Redistributions of source code must retain the above copyright
9 *     notice, this list of conditions and the following disclaimer.
10 *
11 *   - Redistributions in binary form must reproduce the above copyright
12 *     notice, this list of conditions and the following disclaimer in the
13 *     documentation and/or other materials provided with the distribution.
14 *
15 *   - Neither the name of Oracle nor the names of its
16 *     contributors may be used to endorse or promote products derived
17 *     from this software without specific prior written permission.
18 *
19 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
20 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
21 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
22 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
23 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
24 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
25 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
26 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
27 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
28 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
29 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
30 */
31
32import java.lang.invoke.MethodHandle;
33import java.lang.invoke.MethodHandles;
34import java.lang.invoke.MethodType;
35import java.util.ArrayList;
36import java.util.List;
37import jdk.dynalink.CallSiteDescriptor;
38import jdk.dynalink.NamedOperation;
39import jdk.dynalink.NamespaceOperation;
40import jdk.dynalink.Operation;
41import jdk.dynalink.StandardNamespace;
42import jdk.dynalink.StandardOperation;
43import jdk.dynalink.beans.BeansLinker;
44import jdk.dynalink.linker.GuardedInvocation;
45import jdk.dynalink.linker.GuardingDynamicLinker;
46import jdk.dynalink.linker.GuardingDynamicLinkerExporter;
47import jdk.dynalink.linker.LinkRequest;
48import jdk.dynalink.linker.LinkerServices;
49import jdk.dynalink.linker.TypeBasedGuardingDynamicLinker;
50import jdk.dynalink.linker.support.Guards;
51import jdk.dynalink.linker.support.Lookup;
52
53/**
54 * This is a dynalink pluggable linker (see http://openjdk.java.net/jeps/276).
55 * This linker routes missing methods to Smalltalk-style doesNotUnderstand method.
56 * Object of any Java class that implements MissingMethodHandler is handled by this linker.
57 * For any method call, if a matching Java method is found, it is called. If there is no
58 * method by that name, then MissingMethodHandler.doesNotUnderstand is called.
59 */
60public final class MissingMethodLinkerExporter extends GuardingDynamicLinkerExporter {
61    static {
62        System.out.println("pluggable dynalink missing method linker loaded");
63    }
64
65    // represents a MissingMethod - just stores as name and also serves a guard type
66    public static class MissingMethod {
67        private final String name;
68
69        public MissingMethod(final String name) {
70            this.name = name;
71        }
72
73        public String getName() {
74            return name;
75        }
76    }
77
78    // MissingMethodHandler.doesNotUnderstand method
79    private static final MethodHandle DOES_NOT_UNDERSTAND;
80
81    // type of MissingMethodHandler - but "this" and String args are flipped
82    private static final MethodType FLIPPED_DOES_NOT_UNDERSTAND_TYPE;
83
84    // "is this a MissingMethod?" guard
85    private static final MethodHandle IS_MISSING_METHOD;
86
87    // MissingMethod object->it's name filter
88    private static final MethodHandle MISSING_METHOD_TO_NAME;
89
90    static {
91        DOES_NOT_UNDERSTAND = Lookup.PUBLIC.findVirtual(
92            MissingMethodHandler.class,
93            "doesNotUnderstand",
94            MethodType.methodType(Object.class, String.class, Object[].class));
95        FLIPPED_DOES_NOT_UNDERSTAND_TYPE =
96            MethodType.methodType(Object.class, String.class, MissingMethodHandler.class, Object[].class);
97        IS_MISSING_METHOD = Guards.isOfClass(MissingMethod.class,
98            MethodType.methodType(Boolean.TYPE, Object.class));
99        MISSING_METHOD_TO_NAME = Lookup.PUBLIC.findVirtual(MissingMethod.class,
100            "getName", MethodType.methodType(String.class));
101    }
102
103    @Override
104    public List<GuardingDynamicLinker> get() {
105        final ArrayList<GuardingDynamicLinker> linkers = new ArrayList<>();
106        final BeansLinker beansLinker = new BeansLinker();
107        linkers.add(new TypeBasedGuardingDynamicLinker() {
108            // only handles MissingMethodHandler and MissingMethod objects
109            @Override
110            public boolean canLinkType(final Class<?> type) {
111                return
112                    MissingMethodHandler.class.isAssignableFrom(type) ||
113                    type == MissingMethod.class;
114            }
115
116            @Override
117            public GuardedInvocation getGuardedInvocation(final LinkRequest request,
118                final LinkerServices linkerServices) throws Exception {
119                final Object self = request.getReceiver();
120                final CallSiteDescriptor desc = request.getCallSiteDescriptor();
121
122                // any method call is done by two steps. Step (1) GET_METHOD and (2) is CALL
123                // For step (1), we check if GET_METHOD can succeed by Java linker, if so
124                // we return that method object. If not, we return a MissingMethod object.
125                if (self instanceof MissingMethodHandler) {
126                    // Check if this is a named GET_METHOD first.
127                    final Operation namedOp = desc.getOperation();
128                    final Operation namespaceOp = NamedOperation.getBaseOperation(namedOp);
129                    final Operation op = NamespaceOperation.getBaseOperation(namespaceOp);
130
131                    final boolean isGetMethod = op == StandardOperation.GET && StandardNamespace.findFirst(namespaceOp) == StandardNamespace.METHOD;
132                    final Object name = NamedOperation.getName(namedOp);
133                    if (isGetMethod && name instanceof String) {
134                        final GuardingDynamicLinker javaLinker = beansLinker.getLinkerForClass(self.getClass());
135                        GuardedInvocation inv;
136                        try {
137                            inv = javaLinker.getGuardedInvocation(request, linkerServices);
138                        } catch (final Throwable th) {
139                            inv = null;
140                        }
141
142                        final String nameStr = name.toString();
143                        if (inv == null) {
144                            // use "this" for just guard and drop it -- return a constant Method handle
145                            // that returns a newly created MissingMethod object
146                            final MethodHandle mh = MethodHandles.constant(Object.class, new MissingMethod(nameStr));
147                            inv = new GuardedInvocation(
148                                MethodHandles.dropArguments(mh, 0, Object.class),
149                                Guards.isOfClass(self.getClass(), MethodType.methodType(Boolean.TYPE, Object.class)));
150                        }
151
152                        return inv;
153                    }
154                } else if (self instanceof MissingMethod) {
155                    // This is step (2). We call MissingMethodHandler.doesNotUnderstand here
156                    // Check if this is this a CALL first.
157                    final boolean isCall = NamedOperation.getBaseOperation(desc.getOperation()) == StandardOperation.CALL;
158                    if (isCall) {
159                        MethodHandle mh = DOES_NOT_UNDERSTAND;
160
161                        // flip "this" and method name (String)
162                        mh = MethodHandles.permuteArguments(mh, FLIPPED_DOES_NOT_UNDERSTAND_TYPE, 1, 0, 2);
163
164                        // collect rest of the arguments as vararg
165                        mh = mh.asCollector(Object[].class, desc.getMethodType().parameterCount() - 2);
166
167                        // convert MissingMethod object to it's name
168                        mh = MethodHandles.filterArguments(mh, 0, MISSING_METHOD_TO_NAME);
169                        return new GuardedInvocation(mh, IS_MISSING_METHOD);
170                    }
171                }
172
173                return null;
174            }
175        });
176        return linkers;
177    }
178}
179