1/*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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10 *
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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
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25
26/*
27 * This file is available under and governed by the GNU General Public
28 * License version 2 only, as published by the Free Software Foundation.
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30 * file, and Oracle licenses the original version of this file under the BSD
31 * license:
32 */
33/*
34   Copyright 2009-2013 Attila Szegedi
35
36   Licensed under both the Apache License, Version 2.0 (the "Apache License")
37   and the BSD License (the "BSD License"), with licensee being free to
38   choose either of the two at their discretion.
39
40   You may not use this file except in compliance with either the Apache
41   License or the BSD License.
42
43   If you choose to use this file in compliance with the Apache License, the
44   following notice applies to you:
45
46       You may obtain a copy of the Apache License at
47
48           http://www.apache.org/licenses/LICENSE-2.0
49
50       Unless required by applicable law or agreed to in writing, software
51       distributed under the License is distributed on an "AS IS" BASIS,
52       WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
53       implied. See the License for the specific language governing
54       permissions and limitations under the License.
55
56   If you choose to use this file in compliance with the BSD License, the
57   following notice applies to you:
58
59       Redistribution and use in source and binary forms, with or without
60       modification, are permitted provided that the following conditions are
61       met:
62       * Redistributions of source code must retain the above copyright
63         notice, this list of conditions and the following disclaimer.
64       * Redistributions in binary form must reproduce the above copyright
65         notice, this list of conditions and the following disclaimer in the
66         documentation and/or other materials provided with the distribution.
67       * Neither the name of the copyright holder nor the names of
68         contributors may be used to endorse or promote products derived from
69         this software without specific prior written permission.
70
71       THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
72       IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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82*/
83
84package jdk.dynalink.linker;
85
86import java.lang.invoke.MethodHandle;
87import java.lang.invoke.MethodType;
88import java.util.List;
89import jdk.dynalink.DynamicLinkerFactory;
90
91/**
92 * The base interface for language-specific dynamic linkers. Such linkers
93 * always have to produce method handles with guards, as the validity of the
94 * method handle for calls at a call site inevitably depends on some condition
95 * (at the very least, it depends on the receiver belonging to the language
96 * runtime of the linker). Language runtime implementors will normally implement
97 * the linking logic for their own language as one or more
98 * {@link GuardingDynamicLinker} classes. They will typically set them as
99 * {@link DynamicLinkerFactory#setPrioritizedLinkers(List) prioritized linkers}
100 * in the {@code DynamicLinkerFactory} they configure for themselves, and maybe also
101 * set some as {@link DynamicLinkerFactory#setFallbackLinkers(List) fallback
102 * linkers} to handle language-specific "property not found" etc. conditions.
103 * <p>
104 * Consider implementing {@link TypeBasedGuardingDynamicLinker} interface
105 * instead of this interface for those linkers that are based on the Java class
106 * of the objects. If you need to implement language-specific type conversions,
107 * have your {@code GuardingDynamicLinker} also implement the
108 * {@link GuardingTypeConverterFactory} interface.
109 * <p>
110 * Languages can export linkers to other language runtimes for
111 * {@link DynamicLinkerFactory#setClassLoader(ClassLoader) automatic discovery}
112 * using a {@link GuardingDynamicLinkerExporter}.
113 */
114public interface GuardingDynamicLinker {
115    /**
116     * Creates a guarded invocation appropriate for a particular invocation with
117     * the specified arguments at a call site.
118     *
119     * @param linkRequest the object describing the request for linking a
120     * particular invocation
121     * @param linkerServices linker services
122     * @return a guarded invocation with a method handle suitable for the
123     * arguments, as well as a guard condition that if fails should trigger
124     * relinking. Must return null if it can't resolve the invocation. If the
125     * returned invocation is unconditional (which is actually quite rare), the
126     * guard in the return value can be null. The invocation can also have any
127     * number of switch points for asynchronous invalidation of the linkage, as
128     * well as a {@link Throwable} subclass that describes an expected exception
129     * condition that also triggers relinking (often it is faster to rely on an
130     * infrequent but expected {@link ClassCastException} than on an always
131     * evaluated {@code instanceof} guard). While the linker must produce an
132     * invocation with parameter types matching those in the call site
133     * descriptor of the link request, it should not try to match the return
134     * type expected at the call site except when it can do it with only the
135     * conversions that lose neither precision nor magnitude, see
136     * {@link LinkerServices#asTypeLosslessReturn(MethodHandle, MethodType)} for
137     * further explanation.
138     * @throws Exception if the operation fails for whatever reason
139     */
140    public GuardedInvocation getGuardedInvocation(LinkRequest linkRequest, LinkerServices linkerServices)
141            throws Exception;
142}
143