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
26 package jdk.nashorn.internal.runtime.linker;
27
28 import java.lang.invoke.MethodHandle;
29
30 /**
31 * A tuple of method handles, one for dynamically getting function as a property of an object, and another for invoking
32 * a function with a given signature. A typical use for this class is to create method handles that can be used to
33 * efficiently recreate dynamic invocation of a method on an object from Java code. E.g. if you would have a call site
34 * in JavaScript that says
35 * <pre>
36 * value = obj.toJSON(key)
37 * </pre>
38 * then the efficient way to code an exact equivalent of this in Java would be:
39 * <pre>
40 * private static final InvokeByName TO_JSON = new InvokeByName("toJSON", Object.class, Object.class, Object.class);
41 * ...
42 * final Object toJSONFn = TO_JSON.getGetter().invokeExact(obj);
43 * value = TO_JSON.getInvoker().invokeExact(toJSONFn, obj, key);
44 * </pre>
45 * In practice, you can have stronger type assumptions if it makes sense for your code, just remember that you must use
46 * the same parameter types as the formal types of the arguments for {@code invokeExact} to work:
47 * <pre>
48 * private static final InvokeByName TO_JSON = new InvokeByName("toJSON", ScriptObject.class, Object.class, Object.class);
49 * ...
50 * final ScriptObject sobj = (ScriptObject)obj;
51 * final Object toJSONFn = TO_JSON.getGetter().invokeExact(sobj);
52 * if(toJSONFn instanceof ScriptFunction) {
53 * value = TO_JSON.getInvoker().invokeExact(toJSONFn, sobj, key);
54 * }
55 * </pre>
56 * Note that in general you will not want to reuse a single instance of this class for implementing more than one call
57 * site - that would increase the risk of them becoming megamorphic or otherwise hard to optimize by the JVM. Even if
58 * you dynamically invoke a function with the same name from multiple places in your code, it is advisable to create a
59 * separate instance of this class for every place.
60 */
61 public final class InvokeByName {
62 private final String name;
63 private final MethodHandle getter;
64 private final MethodHandle invoker;
65
66 /**
67 * Creates a getter and invoker for a function of the given name that takes no arguments and has a return type of
68 * {@code Object}.
69 * @param name the name of the function
70 * @param targetClass the target class it is invoked on; e.g. {@code Object} or {@code ScriptObject}.
71 */
72 public InvokeByName(final String name, final Class<?> targetClass) {
73 this(name, targetClass, Object.class);
74 }
75
76 /**
77 * Creates a getter and invoker for a function of the given name with given parameter types and a given return type
78 * of {@code Object}.
79 * @param name the name of the function
80 * @param targetClass the target class it is invoked on; e.g. {@code Object} or {@code ScriptObject}.
81 * @param rtype the return type of the function
82 * @param ptypes the parameter types of the function.
83 */
84 public InvokeByName(final String name, final Class<?> targetClass, final Class<?> rtype, final Class<?>... ptypes) {
85 this.name = name;
86 getter = Bootstrap.createDynamicInvoker(name, NashornCallSiteDescriptor.GET_METHOD_PROPERTY, Object.class, targetClass);
87
88 final Class<?>[] finalPtypes;
89 final int plength = ptypes.length;
90 if(plength == 0) {
91 finalPtypes = new Class<?>[] { Object.class, targetClass };
92 } else {
93 finalPtypes = new Class<?>[plength + 2];
94 finalPtypes[0] = Object.class;
95 finalPtypes[1] = targetClass;
96 System.arraycopy(ptypes, 0, finalPtypes, 2, plength);
97 }
98 invoker = Bootstrap.createDynamicCallInvoker(rtype, finalPtypes);
99 }
100
101 /**
102 * Returns the name of the function retrieved through this invoker.
103 * @return the name of the function retrieved through this invoker.
104 */
105 public String getName() {
106 return name;
107 }
108
109 /**
110 * Returns the property getter that can be invoked on an object to retrieve the function object that will be
111 * subsequently invoked by the invoker returned by {@link #getInvoker()}.
112 * @return the property getter method handle for the function.
113 */
114 public MethodHandle getGetter() {
115 return getter;
116 }
117
118 /**
119 * Returns the function invoker that can be used to invoke a function object previously retrieved by invoking
120 * the getter retrieved with {@link #getGetter()} on the target object.
121 * @return the invoker method handle for the function.
122 */
123 public MethodHandle getInvoker() {
124 return invoker;
125 }
126 }