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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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).
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24 */
25
26 package java.lang.invoke;
27
28 import java.io.Serializable;
29 import java.util.Arrays;
30
31 /**
32 * <p>Bootstrap methods for converting lambda expressions and method references to functional interface objects.</p>
33 *
34 * <p>For every lambda expressions or method reference in the source code, there is a target type which is a
35 * functional interface. Evaluating a lambda expression produces an object of its target type. The mechanism for
36 * evaluating lambda expressions is to invoke an invokedynamic call site, which takes arguments describing the sole
37 * method of the functional interface and the implementation method, and returns an object (the lambda object) that
38 * implements the target type. Methods of the lambda object invoke the implementation method. For method
39 * references, the implementation method is simply the referenced method; for lambda expressions, the
40 * implementation method is produced by the compiler based on the body of the lambda expression. The methods in
41 * this file are the bootstrap methods for those invokedynamic call sites, called lambda factories, and the
42 * bootstrap methods responsible for linking the lambda factories are called lambda meta-factories.
43 *
44 * <p>The bootstrap methods in this class take the information about the functional interface, the implementation
45 * method, and the static types of the captured lambda arguments, and link a call site which, when invoked,
46 * produces the lambda object.
47 *
48 * <p>When parameterized types are used, the instantiated type of the functional interface method may be different
49 * from that in the functional interface. For example, consider
50 * {@code interface I<T> { int m(T x); }} if this functional interface type is used in a lambda
51 * {@code I<Byte>; v = ...}, we need both the actual functional interface method which has the signature
52 * {@code (Object)int} and the erased instantiated type of the functional interface method (or simply
53 * <I>instantiated method type</I>), which has signature
54 * {@code (Byte)int}.
55 *
56 * <p>The argument list of the implementation method and the argument list of the functional interface method(s)
57 * may differ in several ways. The implementation methods may have additional arguments to accommodate arguments
58 * captured by the lambda expression; there may also be differences resulting from permitted adaptations of
59 * arguments, such as casting, boxing, unboxing, and primitive widening. They may also differ because of var-args,
60 * but this is expected to be handled by the compiler.
61 *
62 * <p>Invokedynamic call sites have two argument lists: a static argument list and a dynamic argument list. The
63 * static argument list lives in the constant pool; the dynamic argument list lives on the operand stack at
64 * invocation time. The bootstrap method has access to the entire static argument list (which in this case,
65 * contains method handles describing the implementation method and the canonical functional interface method),
66 * as well as a method signature describing the number and static types (but not the values) of the dynamic
67 * arguments, and the static return type of the invokedynamic site.
68 *
69 * <p>The implementation method is described with a method handle. In theory, any method handle could be used.
70 * Currently supported are method handles representing invocation of virtual, interface, constructor and static
71 * methods.
72 *
73 * <p>Assume:
74 * <ul>
75 * <li>the functional interface method has N arguments, of types (U1, U2, ... Un) and return type Ru</li>
76 * <li>then the instantiated method type also has N arguments, of types (T1, T2, ... Tn) and return type Rt</li>
77 * <li>the implementation method has M arguments, of types (A1..Am) and return type Ra,</li>
78 * <li>the dynamic argument list has K arguments of types (D1..Dk), and the invokedynamic return site has
79 * type Rd</li>
80 * <li>the functional interface type is F</li>
81 * </ul>
82 *
83 * <p>The following signature invariants must hold:
84 * <ul>
85 * <li>Rd is a subtype of F</li>
86 * <li>For i=1..N, Ti is a subtype of Ui</li>
87 * <li>Either Rt and Ru are primitive and are the same type, or both are reference types and
88 * Rt is a subtype of Ru</li>
89 * <li>If the implementation method is a static method:
90 * <ul>
91 * <li>K + N = M</li>
92 * <li>For i=1..K, Di = Ai</li>
93 * <li>For i=1..N, Ti is adaptable to Aj, where j=i+k</li>
94 * </ul></li>
95 * <li>If the implementation method is an instance method:
96 * <ul>
97 * <li>K + N = M + 1</li>
98 * <li>D1 must be a subtype of the enclosing class for the implementation method</li>
99 * <li>For i=2..K, Di = Aj, where j=i-1</li>
100 * <li>For i=1..N, Ti is adaptable to Aj, where j=i+k-1</li>
101 * </ul></li>
102 * <li>The return type Rt is void, or the return type Ra is not void and is adaptable to Rt</li>
103 * </ul>
104 *
105 * <p>Note that the potentially parameterized implementation return type provides the value for the SAM. Whereas
106 * the completely known instantiated return type is adapted to the implementation arguments. Because the
107 * instantiated type of the implementation method is not available, the adaptability of return types cannot be
108 * checked as precisely at link-time as the arguments can be checked. Thus a loose version of link-time checking is
109 * done on return type, while a strict version is applied to arguments.
110 *
111 * <p>A type Q is considered adaptable to S as follows:
112 * <table>
113 * <tr><th>Q</th><th>S</th><th>Link-time checks</th><th>Capture-time checks</th></tr>
114 * <tr>
115 * <td>Primitive</td><td>Primitive</td>
116 * <td>Q can be converted to S via a primitive widening conversion</td>
117 * <td>None</td>
118 * </tr>
119 * <tr>
120 * <td>Primitive</td><td>Reference</td>
121 * <td>S is a supertype of the Wrapper(Q)</td>
122 * <td>Cast from Wrapper(Q) to S</td>
123 * </tr>
124 * <tr>
125 * <td>Reference</td><td>Primitive</td>
126 * <td>strict: Q is a primitive wrapper and Primitive(Q) can be widened to S
127 * <br>loose: If Q is a primitive wrapper, check that Primitive(Q) can be widened to S</td>
128 * <td>If Q is not a primitive wrapper, cast Q to the base Wrapper(S); for example Number for numeric types</td>
129 * </tr>
130 * <tr>
131 * <td>Reference</td><td>Reference</td>
132 * <td>strict: S is a supertype of Q
133 * <br>loose: none</td>
134 * <td>Cast from Q to S</td>
135 * </tr>
136 * </table>
137 *
138 * The default bootstrap ({@link #metaFactory}) represents the common cases and uses an optimized protocol.
139 * Alternate bootstraps (e.g., {@link #altMetaFactory}) exist to support uncommon cases such as serialization
140 * or additional marker superinterfaces.
141 *
142 */
143 public class LambdaMetafactory {
144
145 /** Flag for alternate metafactories indicating the lambda object is
146 * must to be serializable */
147 public static final int FLAG_SERIALIZABLE = 1 << 0;
148
149 /**
150 * Flag for alternate metafactories indicating the lambda object implements
151 * other marker interfaces
152 * besides Serializable
153 */
154 public static final int FLAG_MARKERS = 1 << 1;
155
156 /**
157 * Flag for alternate metafactories indicating the lambda object requires
158 * additional bridge methods
159 */
160 public static final int FLAG_BRIDGES = 1 << 2;
161
162 private static final Class<?>[] EMPTY_CLASS_ARRAY = new Class<?>[0];
163 private static final MethodType[] EMPTY_MT_ARRAY = new MethodType[0];
164
165 /**
166 * Standard meta-factory for conversion of lambda expressions or method
167 * references to functional interfaces.
168 *
169 * @param caller Stacked automatically by VM; represents a lookup context
170 * with the accessibility privileges of the caller.
171 * @param invokedName Stacked automatically by VM; the name of the invoked
172 * method as it appears at the call site.
173 * Currently unused.
174 * @param invokedType Stacked automatically by VM; the signature of the
175 * invoked method, which includes the expected static
176 * type of the returned lambda object, and the static
177 * types of the captured arguments for the lambda.
178 * In the event that the implementation method is an
179 * instance method, the first argument in the invocation
180 * signature will correspond to the receiver.
181 * @param samMethod The primary method in the functional interface to which
182 * the lambda or method reference is being converted,
183 * represented as a method handle.
184 * @param implMethod The implementation method which should be called
185 * (with suitable adaptation of argument types, return
186 * types, and adjustment for captured arguments) when
187 * methods of the resulting functional interface instance
188 * are invoked.
189 * @param instantiatedMethodType The signature of the primary functional
190 * interface method after type variables
191 * are substituted with their instantiation
192 * from the capture site
193 * @return a CallSite, which, when invoked, will return an instance of the
194 * functional interface
195 * @throws ReflectiveOperationException
196 * @throws LambdaConversionException If any of the meta-factory protocol
197 * invariants are violated
198 */
199 public static CallSite metaFactory(MethodHandles.Lookup caller,
200 String invokedName,
201 MethodType invokedType,
202 MethodHandle samMethod,
203 MethodHandle implMethod,
204 MethodType instantiatedMethodType)
205 throws ReflectiveOperationException, LambdaConversionException {
206 AbstractValidatingLambdaMetafactory mf;
207 mf = new InnerClassLambdaMetafactory(caller, invokedType, samMethod,
208 implMethod, instantiatedMethodType,
209 false, EMPTY_CLASS_ARRAY, EMPTY_MT_ARRAY);
210 mf.validateMetafactoryArgs();
211 return mf.buildCallSite();
212 }
213
214 /**
215 * Alternate meta-factory for conversion of lambda expressions or method
216 * references to functional interfaces, which supports serialization and
217 * other uncommon options.
218 *
219 * The declared argument list for this method is:
220 *
221 * CallSite altMetaFactory(MethodHandles.Lookup caller,
222 * String invokedName,
223 * MethodType invokedType,
224 * Object... args)
225 *
226 * but it behaves as if the argument list is:
227 *
228 * CallSite altMetaFactory(MethodHandles.Lookup caller,
229 * String invokedName,
230 * MethodType invokedType,
231 * MethodHandle samMethod
232 * MethodHandle implMethod,
233 * MethodType instantiatedMethodType,
234 * int flags,
235 * int markerInterfaceCount, // IF flags has MARKERS set
236 * Class... markerInterfaces // IF flags has MARKERS set
237 * int bridgeCount, // IF flags has BRIDGES set
238 * MethodType... bridges // IF flags has BRIDGES set
239 * )
240 *
241 *
242 * @param caller Stacked automatically by VM; represents a lookup context
243 * with the accessibility privileges of the caller.
244 * @param invokedName Stacked automatically by VM; the name of the invoked
245 * method as it appears at the call site. Currently unused.
246 * @param invokedType Stacked automatically by VM; the signature of the
247 * invoked method, which includes the expected static
248 * type of the returned lambda object, and the static
249 * types of the captured arguments for the lambda.
250 * In the event that the implementation method is an
251 * instance method, the first argument in the invocation
252 * signature will correspond to the receiver.
253 * @param args flags and optional arguments, as described above
254 * @return a CallSite, which, when invoked, will return an instance of the
255 * functional interface
256 * @throws ReflectiveOperationException
257 * @throws LambdaConversionException If any of the meta-factory protocol
258 * invariants are violated
259 */
260 public static CallSite altMetaFactory(MethodHandles.Lookup caller,
261 String invokedName,
262 MethodType invokedType,
263 Object... args)
264 throws ReflectiveOperationException, LambdaConversionException {
265 MethodHandle samMethod = (MethodHandle)args[0];
266 MethodHandle implMethod = (MethodHandle)args[1];
267 MethodType instantiatedMethodType = (MethodType)args[2];
268 int flags = (Integer) args[3];
269 Class<?>[] markerInterfaces;
270 MethodType[] bridges;
271 int argIndex = 4;
272 if ((flags & FLAG_MARKERS) != 0) {
273 int markerCount = (Integer) args[argIndex++];
274 markerInterfaces = new Class<?>[markerCount];
275 System.arraycopy(args, argIndex, markerInterfaces, 0, markerCount);
276 argIndex += markerCount;
277 }
278 else
279 markerInterfaces = EMPTY_CLASS_ARRAY;
280 if ((flags & FLAG_BRIDGES) != 0) {
281 int bridgeCount = (Integer) args[argIndex++];
282 bridges = new MethodType[bridgeCount];
283 System.arraycopy(args, argIndex, bridges, 0, bridgeCount);
284 argIndex += bridgeCount;
285 }
286 else
287 bridges = EMPTY_MT_ARRAY;
288
289 boolean foundSerializableSupertype = Serializable.class.isAssignableFrom(invokedType.returnType());
290 for (Class<?> c : markerInterfaces)
291 foundSerializableSupertype |= Serializable.class.isAssignableFrom(c);
292 boolean isSerializable = ((flags & LambdaMetafactory.FLAG_SERIALIZABLE) != 0)
293 || foundSerializableSupertype;
294
295 if (isSerializable && !foundSerializableSupertype) {
296 markerInterfaces = Arrays.copyOf(markerInterfaces, markerInterfaces.length + 1);
297 markerInterfaces[markerInterfaces.length-1] = Serializable.class;
298 }
299
300 AbstractValidatingLambdaMetafactory mf
301 = new InnerClassLambdaMetafactory(caller, invokedType, samMethod,
302 implMethod, instantiatedMethodType,
303 isSerializable, markerInterfaces, bridges);
304 mf.validateMetafactoryArgs();
305 return mf.buildCallSite();
306 }
307 }