1/*
2 * Copyright (c) 2014, 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 java.lang.invoke;
27
28import java.util.Arrays;
29import static java.lang.invoke.LambdaForm.*;
30import static java.lang.invoke.LambdaForm.Kind.*;
31import static java.lang.invoke.MethodHandleStatics.*;
32
33/**
34 * A method handle whose invocation behavior is determined by a target.
35 * The delegating MH itself can hold extra "intentions" beyond the simple behavior.
36 * @author jrose
37 */
38/*non-public*/
39abstract class DelegatingMethodHandle extends MethodHandle {
40    protected DelegatingMethodHandle(MethodHandle target) {
41        this(target.type(), target);
42    }
43
44    protected DelegatingMethodHandle(MethodType type, MethodHandle target) {
45        super(type, chooseDelegatingForm(target));
46    }
47
48    protected DelegatingMethodHandle(MethodType type, LambdaForm form) {
49        super(type, form);
50    }
51
52    /** Define this to extract the delegated target which supplies the invocation behavior. */
53    protected abstract MethodHandle getTarget();
54
55    @Override
56    abstract MethodHandle asTypeUncached(MethodType newType);
57
58    @Override
59    MemberName internalMemberName() {
60        return getTarget().internalMemberName();
61    }
62
63    @Override
64    boolean isInvokeSpecial() {
65        return getTarget().isInvokeSpecial();
66    }
67
68    @Override
69    Class<?> internalCallerClass() {
70        return getTarget().internalCallerClass();
71    }
72
73    @Override
74    MethodHandle copyWith(MethodType mt, LambdaForm lf) {
75        // FIXME: rethink 'copyWith' protocol; it is too low-level for use on all MHs
76        throw newIllegalArgumentException("do not use this");
77    }
78
79    @Override
80    String internalProperties() {
81        return "\n& Class="+getClass().getSimpleName()+
82               "\n& Target="+getTarget().debugString();
83    }
84
85    @Override
86    BoundMethodHandle rebind() {
87        return getTarget().rebind();
88    }
89
90    private static LambdaForm chooseDelegatingForm(MethodHandle target) {
91        if (target instanceof SimpleMethodHandle)
92            return target.internalForm();  // no need for an indirection
93        return makeReinvokerForm(target, MethodTypeForm.LF_DELEGATE, DelegatingMethodHandle.class, NF_getTarget);
94    }
95
96    static LambdaForm makeReinvokerForm(MethodHandle target,
97                                        int whichCache,
98                                        Object constraint,
99                                        NamedFunction getTargetFn) {
100        // No pre-action needed.
101        return makeReinvokerForm(target, whichCache, constraint, true, getTargetFn, null);
102    }
103    /** Create a LF which simply reinvokes a target of the given basic type. */
104    static LambdaForm makeReinvokerForm(MethodHandle target,
105                                        int whichCache,
106                                        Object constraint,
107                                        boolean forceInline,
108                                        NamedFunction getTargetFn,
109                                        NamedFunction preActionFn) {
110        MethodType mtype = target.type().basicType();
111        Kind kind = whichKind(whichCache);
112        boolean customized = (whichCache < 0 ||
113                mtype.parameterSlotCount() > MethodType.MAX_MH_INVOKER_ARITY);
114        boolean hasPreAction = (preActionFn != null);
115        LambdaForm form;
116        if (!customized) {
117            form = mtype.form().cachedLambdaForm(whichCache);
118            if (form != null)  return form;
119        }
120        final int THIS_DMH    = 0;
121        final int ARG_BASE    = 1;
122        final int ARG_LIMIT   = ARG_BASE + mtype.parameterCount();
123        int nameCursor = ARG_LIMIT;
124        final int PRE_ACTION   = hasPreAction ? nameCursor++ : -1;
125        final int NEXT_MH     = customized ? -1 : nameCursor++;
126        final int REINVOKE    = nameCursor++;
127        LambdaForm.Name[] names = LambdaForm.arguments(nameCursor - ARG_LIMIT, mtype.invokerType());
128        assert(names.length == nameCursor);
129        names[THIS_DMH] = names[THIS_DMH].withConstraint(constraint);
130        Object[] targetArgs;
131        if (hasPreAction) {
132            names[PRE_ACTION] = new LambdaForm.Name(preActionFn, names[THIS_DMH]);
133        }
134        if (customized) {
135            targetArgs = Arrays.copyOfRange(names, ARG_BASE, ARG_LIMIT, Object[].class);
136            names[REINVOKE] = new LambdaForm.Name(target, targetArgs);  // the invoker is the target itself
137        } else {
138            names[NEXT_MH] = new LambdaForm.Name(getTargetFn, names[THIS_DMH]);
139            targetArgs = Arrays.copyOfRange(names, THIS_DMH, ARG_LIMIT, Object[].class);
140            targetArgs[0] = names[NEXT_MH];  // overwrite this MH with next MH
141            names[REINVOKE] = new LambdaForm.Name(mtype, targetArgs);
142        }
143        form = new LambdaForm(ARG_LIMIT, names, forceInline, kind);
144        if (!customized) {
145            form = mtype.form().setCachedLambdaForm(whichCache, form);
146        }
147        return form;
148    }
149
150    private static Kind whichKind(int whichCache) {
151        switch(whichCache) {
152            case MethodTypeForm.LF_REBIND:   return BOUND_REINVOKER;
153            case MethodTypeForm.LF_DELEGATE: return DELEGATE;
154            default:                         return REINVOKER;
155        }
156    }
157
158    static final NamedFunction NF_getTarget;
159    static {
160        try {
161            NF_getTarget = new NamedFunction(DelegatingMethodHandle.class
162                                             .getDeclaredMethod("getTarget"));
163        } catch (ReflectiveOperationException ex) {
164            throw newInternalError(ex);
165        }
166        // The Holder class will contain pre-generated DelegatingMethodHandles resolved
167        // speculatively using MemberName.getFactory().resolveOrNull. However, that
168        // doesn't initialize the class, which subtly breaks inlining etc. By forcing
169        // initialization of the Holder class we avoid these issues.
170        UNSAFE.ensureClassInitialized(Holder.class);
171    }
172
173    /* Placeholder class for DelegatingMethodHandles generated ahead of time */
174    final class Holder {}
175}
176