MissingMethodLinkerExporter.java revision 1786:80120e9b3273 
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
6 * are met:
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.CompositeOperation;
39import jdk.dynalink.NamedOperation;
40import jdk.dynalink.Operation;
41import jdk.dynalink.StandardOperation;
42import jdk.dynalink.beans.BeansLinker;
43import jdk.dynalink.linker.GuardedInvocation;
44import jdk.dynalink.linker.GuardingDynamicLinker;
45import jdk.dynalink.linker.GuardingDynamicLinkerExporter;
46import jdk.dynalink.linker.LinkRequest;
47import jdk.dynalink.linker.LinkerServices;
48import jdk.dynalink.linker.TypeBasedGuardingDynamicLinker;
49import jdk.dynalink.linker.support.Guards;
50import jdk.dynalink.linker.support.Lookup;
51
52/**
53 * This is a dynalink pluggable linker (see http://openjdk.java.net/jeps/276).
54 * This linker routes missing methods to Smalltalk-style doesNotUnderstand method.
55 * Object of any Java class that implements MissingMethodHandler is handled by this linker.
56 * For any method call, if a matching Java method is found, it is called. If there is no
57 * method by that name, then MissingMethodHandler.doesNotUnderstand is called.
58 */
59public final class MissingMethodLinkerExporter extends GuardingDynamicLinkerExporter {
60    static {
61        System.out.println("pluggable dynalink missing method linker loaded");
62    }
63
64    // represents a MissingMethod - just stores as name and also serves a guard type
65    public static class MissingMethod {
66        private final String name;
67
68        public MissingMethod(final String name) {
69            this.name = name;
70        }
71
72        public String getName() {
73            return name;
74        }
75    }
76
77    // MissingMethodHandler.doesNotUnderstand method
78    private static final MethodHandle DOES_NOT_UNDERSTAND;
79
80    // type of MissingMethodHandler - but "this" and String args are flipped
81    private static final MethodType FLIPPED_DOES_NOT_UNDERSTAND_TYPE;
82
83    // "is this a MissingMethod?" guard
84    private static final MethodHandle IS_MISSING_METHOD;
85
86    // MissingMethod object->it's name filter
87    private static final MethodHandle MISSING_METHOD_TO_NAME;
88
89    static {
90        DOES_NOT_UNDERSTAND = Lookup.PUBLIC.findVirtual(
91            MissingMethodHandler.class,
92            "doesNotUnderstand",
93            MethodType.methodType(Object.class, String.class, Object[].class));
94        FLIPPED_DOES_NOT_UNDERSTAND_TYPE =
95            MethodType.methodType(Object.class, String.class, MissingMethodHandler.class, Object[].class);
96        IS_MISSING_METHOD = Guards.isOfClass(MissingMethod.class,
97            MethodType.methodType(Boolean.TYPE, Object.class));
98        MISSING_METHOD_TO_NAME = Lookup.PUBLIC.findVirtual(MissingMethod.class,
99            "getName", MethodType.methodType(String.class));
100    }
101
102    // locate the first standard operation from the call descriptor
103    private static StandardOperation getFirstStandardOperation(final CallSiteDescriptor desc) {
104        final Operation base = NamedOperation.getBaseOperation(desc.getOperation());
105        if (base instanceof StandardOperation) {
106            return (StandardOperation)base;
107        } else if (base instanceof CompositeOperation) {
108            final CompositeOperation cop = (CompositeOperation)base;
109            for(int i = 0; i < cop.getOperationCount(); ++i) {
110                final Operation op = cop.getOperation(i);
111                if (op instanceof StandardOperation) {
112                    return (StandardOperation)op;
113                }
114            }
115        }
116        return null;
117    }
118
119    @Override
120    public List<GuardingDynamicLinker> get() {
121        final ArrayList<GuardingDynamicLinker> linkers = new ArrayList<>();
122        final BeansLinker beansLinker = new BeansLinker();
123        linkers.add(new TypeBasedGuardingDynamicLinker() {
124            // only handles MissingMethodHandler and MissingMethod objects
125            @Override
126            public boolean canLinkType(final Class<?> type) {
127                return
128                    MissingMethodHandler.class.isAssignableFrom(type) ||
129                    type == MissingMethod.class;
130            }
131
132            @Override
133            public GuardedInvocation getGuardedInvocation(final LinkRequest request,
134                final LinkerServices linkerServices) throws Exception {
135                final Object self = request.getReceiver();
136                final CallSiteDescriptor desc = request.getCallSiteDescriptor();
137
138                // any method call is done by two steps. Step (1) GET_METHOD and (2) is CALL
139                // For step (1), we check if GET_METHOD can succeed by Java linker, if so
140                // we return that method object. If not, we return a MissingMethod object.
141                if (self instanceof MissingMethodHandler) {
142                    // Check if this is a named GET_METHOD first.
143                    final boolean isGetMethod = getFirstStandardOperation(desc) == StandardOperation.GET_METHOD;
144                    final Object name = NamedOperation.getName(desc.getOperation());
145                    if (isGetMethod && name instanceof String) {
146                        final GuardingDynamicLinker javaLinker = beansLinker.getLinkerForClass(self.getClass());
147                        GuardedInvocation inv;
148                        try {
149                            inv = javaLinker.getGuardedInvocation(request, linkerServices);
150                        } catch (final Throwable th) {
151                            inv = null;
152                        }
153
154                        final String nameStr = name.toString();
155                        if (inv == null) {
156                            // use "this" for just guard and drop it -- return a constant Method handle
157                            // that returns a newly created MissingMethod object
158                            final MethodHandle mh = MethodHandles.constant(Object.class, new MissingMethod(nameStr));
159                            inv = new GuardedInvocation(
160                                MethodHandles.dropArguments(mh, 0, Object.class),
161                                Guards.isOfClass(self.getClass(), MethodType.methodType(Boolean.TYPE, Object.class)));
162                        }
163
164                        return inv;
165                    }
166                } else if (self instanceof MissingMethod) {
167                    // This is step (2). We call MissingMethodHandler.doesNotUnderstand here
168                    // Check if this is this a CALL first.
169                    final boolean isCall = getFirstStandardOperation(desc) == StandardOperation.CALL;
170                    if (isCall) {
171                        MethodHandle mh = DOES_NOT_UNDERSTAND;
172
173                        // flip "this" and method name (String)
174                        mh = MethodHandles.permuteArguments(mh, FLIPPED_DOES_NOT_UNDERSTAND_TYPE, 1, 0, 2);
175
176                        // collect rest of the arguments as vararg
177                        mh = mh.asCollector(Object[].class, desc.getMethodType().parameterCount() - 2);
178
179                        // convert MissingMethod object to it's name
180                        mh = MethodHandles.filterArguments(mh, 0, MISSING_METHOD_TO_NAME);
181                        return new GuardedInvocation(mh, IS_MISSING_METHOD);
182                    }
183                }
184
185                return null;
186            }
187        });
188        return linkers;
189    }
190}
191