1 /* 2 * Copyright (c) 2012, 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 java.lang.invoke; 27 28 /** 29 * <p>Bootstrap methods for converting lambda expressions and method references to functional interface objects.</p> 30 * 31 * <p>For every lambda expressions or method reference in the source code, there is a target type which is a 32 * functional interface. Evaluating a lambda expression produces an object of its target type. The mechanism for 33 * evaluating lambda expressions is to invoke an invokedynamic call site, which takes arguments describing the sole 34 * method of the functional interface and the implementation method, and returns an object (the lambda object) that 35 * implements the target type. Methods of the lambda object invoke the implementation method. For method 36 * references, the implementation method is simply the referenced method; for lambda expressions, the 37 * implementation method is produced by the compiler based on the body of the lambda expression. The methods in 38 * this file are the bootstrap methods for those invokedynamic call sites, called lambda factories, and the 39 * bootstrap methods responsible for linking the lambda factories are called lambda meta-factories. 40 * 41 * <p>The bootstrap methods in this class take the information about the functional interface, the implementation 42 * method, and the static types of the captured lambda arguments, and link a call site which, when invoked, 43 * produces the lambda object. 44 * 45 * <p>When parameterized types are used, the instantiated type of the functional interface method may be different 46 * from that in the functional interface. For example, consider 47 * <code>interface I<T> { int m(T x); }</code> if this functional interface type is used in a lambda 48 * <code>I<Byte> v = ...</code>, we need both the actual functional interface method which has the signature 49 * <code>(Object)int</code> and the erased instantiated type of the functional interface method (or simply 50 * <I>instantiated method type</I>), which has signature 51 * <code>(Byte)int</code>. 52 * 53 * <p>While functional interfaces only have a single abstract method from the language perspective (concrete 54 * methods in Object are and default methods may be present), at the bytecode level they may actually have multiple 55 * methods because of the need for bridge methods. Invoking any of these methods on the lambda object will result 56 * in invoking the implementation method. 57 * 58 * <p>The argument list of the implementation method and the argument list of the functional interface method(s) 59 * may differ in several ways. The implementation methods may have additional arguments to accommodate arguments 60 * captured by the lambda expression; there may also be differences resulting from permitted adaptations of 61 * arguments, such as casting, boxing, unboxing, and primitive widening. They may also differ because of var-args, 62 * but this is expected to be handled by the compiler. 63 * 64 * <p>Invokedynamic call sites have two argument lists: a static argument list and a dynamic argument list. The 65 * static argument list lives in the constant pool; the dynamic argument list lives on the operand stack at 66 * invocation time. The bootstrap method has access to the entire static argument list (which in this case, 67 * contains method handles describing the implementation method and the canonical functional interface method), 68 * as well as a method signature describing the number and static types (but not the values) of the dynamic 69 * arguments, and the static return type of the invokedynamic site. 70 * 71 * <p>The implementation method is described with a method handle. In theory, any method handle could be used. 72 * Currently supported are method handles representing invocation of virtual, interface, constructor and static 73 * methods. 74 * 75 * <p>Assume: 76 * <ul> 77 * <li>the functional interface method has N arguments, of types (U1, U2, ... Un) and return type Ru</li> 78 * <li>then the instantiated method type also has N arguments, of types (T1, T2, ... Tn) and return type Rt</li> 79 * <li>the implementation method has M arguments, of types (A1..Am) and return type Ra,</li> 80 * <li>the dynamic argument list has K arguments of types (D1..Dk), and the invokedynamic return site has 81 * type Rd</li> 82 * <li>the functional interface type is F</li> 83 * </ul> 84 * 85 * <p>The following signature invariants must hold: 86 * <ul> 87 * <li>Rd is a subtype of F</li> 88 * <li>For i=1..N, Ti is a subtype of Ui</li> 89 * <li>Either Rt and Ru are primitive and are the same type, or both are reference types and 90 * Rt is a subtype of Ru</li> 91 * <li>If the implementation method is a static method: 92 * <ul> 93 * <li>K + N = M</li> 94 * <li>For i=1..K, Di = Ai</li> 95 * <li>For i=1..N, Ti is adaptable to Aj, where j=i+k</li> 96 * </ul></li> 97 * <li>If the implementation method is an instance method: 98 * <ul> 99 * <li>K + N = M + 1</li> 100 * <li>D1 must be a subtype of the enclosing class for the implementation method</li> 101 * <li>For i=2..K, Di = Aj, where j=i-1</li> 102 * <li>For i=1..N, Ti is adaptable to Aj, where j=i+k-1</li> 103 * </ul></li> 104 * <li>The return type Rt is void, or the return type Ra is not void and is adaptable to Rt</li> 105 * </ul> 106 * 107 * <p>Note that the potentially parameterized implementation return type provides the value for the SAM. Whereas 108 * the completely known instantiated return type is adapted to the implementation arguments. Because the 109 * instantiated type of the implementation method is not available, the adaptability of return types cannot be 110 * checked as precisely at link-time as the arguments can be checked. Thus a loose version of link-time checking is 111 * done on return type, while a strict version is applied to arguments. 112 * 113 * <p>A type Q is considered adaptable to S as follows: 114 * <table> 115 * <tr><th>Q</th><th>S</th><th>Link-time checks</th><th>Capture-time checks</th></tr> 116 * <tr> 117 * <td>Primitive</td><td>Primitive</td> 118 * <td>Q can be converted to S via a primitive widening conversion</td> 119 * <td>None</td> 120 * </tr> 121 * <tr> 122 * <td>Primitive</td><td>Reference</td> 123 * <td>S is a supertype of the Wrapper(Q)</td> 124 * <td>Cast from Wrapper(Q) to S</td> 125 * </tr> 126 * <tr> 127 * <td>Reference</td><td>Primitive</td> 128 * <td>strict: Q is a primitive wrapper and Primitive(Q) can be widened to S 129 * <br>loose: If Q is a primitive wrapper, check that Primitive(Q) can be widened to S</td> 130 * <td>If Q is not a primitive wrapper, cast Q to the base Wrapper(S); for example Number for numeric types</td> 131 * </tr> 132 * <tr> 133 * <td>Reference</td><td>Reference</td> 134 * <td>strict: S is a supertype of Q 135 * <br>loose: none</td> 136 * <td>Cast from Q to S</td> 137 * </tr> 138 * </table> 139 * 140 * The default bootstrap ({@link #metaFactory}) represents the common cases and uses an optimized protocol. 141 * Alternate bootstraps (e.g., {@link #altMetaFactory}) exist to support uncommon cases such as serialization 142 * or additional marker superinterfaces. 143 * 144 */ 145 public class LambdaMetafactory { 146 147 /** Flag for alternate metafactories indicating the lambda object is must to be serializable */ 148 public static final int FLAG_SERIALIZABLE = 1 << 0; 149 150 /** 151 * Flag for alternate metafactories indicating the lambda object implements other marker interfaces 152 * besides Serializable 153 */ 154 public static final int FLAG_MARKERS = 1 << 1; 155 156 private static final Class<?>[] EMPTY_CLASS_ARRAY = new Class<?>[0]; 157 158 /** 159 * Standard meta-factory for conversion of lambda expressions or method references to functional interfaces. 160 * 161 * @param caller Stacked automatically by VM; represents a lookup context with the accessibility privileges 162 * of the caller. 163 * @param invokedName Stacked automatically by VM; the name of the invoked method as it appears at the call site. 164 * Currently unused. 165 * @param invokedType Stacked automatically by VM; the signature of the invoked method, which includes the 166 * expected static type of the returned lambda object, and the static types of the captured 167 * arguments for the lambda. In the event that the implementation method is an instance method, 168 * the first argument in the invocation signature will correspond to the receiver. 169 * @param samMethod The primary method in the functional interface to which the lambda or method reference is 170 * being converted, represented as a method handle. 171 * @param implMethod The implementation method which should be called (with suitable adaptation of argument 172 * types, return types, and adjustment for captured arguments) when methods of the resulting 173 * functional interface instance are invoked. 174 * @param instantiatedMethodType The signature of the primary functional interface method after type variables 175 * are substituted with their instantiation from the capture site 176 * @return a CallSite, which, when invoked, will return an instance of the functional interface 177 * @throws ReflectiveOperationException 178 * @throws LambdaConversionException If any of the meta-factory protocol invariants are violated 179 */ 180 public static CallSite metaFactory(MethodHandles.Lookup caller, 181 String invokedName, 182 MethodType invokedType, 183 MethodHandle samMethod, 184 MethodHandle implMethod, 185 MethodType instantiatedMethodType) 186 throws ReflectiveOperationException, LambdaConversionException { 187 AbstractValidatingLambdaMetafactory mf; 188 mf = new InnerClassLambdaMetafactory(caller, invokedType, samMethod, implMethod, instantiatedMethodType, 189 0, EMPTY_CLASS_ARRAY); 190 mf.validateMetafactoryArgs(); 191 return mf.buildCallSite(); 192 } 193 194 /** 195 * Alternate meta-factory for conversion of lambda expressions or method references to functional interfaces, 196 * which supports serialization and other uncommon options. 197 * 198 * The declared argument list for this method is: 199 * 200 * CallSite altMetaFactory(MethodHandles.Lookup caller, 201 * String invokedName, 202 * MethodType invokedType, 203 * Object... args) 204 * 205 * but it behaves as if the argument list is: 206 * 207 * CallSite altMetaFactory(MethodHandles.Lookup caller, 208 * String invokedName, 209 * MethodType invokedType, 210 * MethodHandle samMethod 211 * MethodHandle implMethod, 212 * MethodType instantiatedMethodType, 213 * int flags, 214 * int markerInterfaceCount, // IF flags has MARKERS set 215 * Class... markerInterfaces // IF flags has MARKERS set 216 * ) 217 * 218 * 219 * @param caller Stacked automatically by VM; represents a lookup context with the accessibility privileges 220 * of the caller. 221 * @param invokedName Stacked automatically by VM; the name of the invoked method as it appears at the call site. 222 * Currently unused. 223 * @param invokedType Stacked automatically by VM; the signature of the invoked method, which includes thefu 224 * expected static type of the returned lambda object, and the static types of the captured 225 * arguments for the lambda. In the event that the implementation method is an instance method, 226 * the first argument in the invocation signature will correspond to the receiver. 227 * @param args argument to pass, flags, marker interface count, and marker interfaces as described above 228 * @return a CallSite, which, when invoked, will return an instance of the functional interface 229 * @throws ReflectiveOperationException 230 * @throws LambdaConversionException If any of the meta-factory protocol invariants are violated 231 */ 232 public static CallSite altMetaFactory(MethodHandles.Lookup caller, 233 String invokedName, 234 MethodType invokedType, 235 Object... args) 236 throws ReflectiveOperationException, LambdaConversionException { 237 MethodHandle samMethod = (MethodHandle)args[0]; 238 MethodHandle implMethod = (MethodHandle)args[1]; 239 MethodType instantiatedMethodType = (MethodType)args[2]; 240 int flags = (Integer) args[3]; 241 Class<?>[] markerInterfaces; 242 int argIndex = 4; 243 if ((flags & FLAG_MARKERS) != 0) { 244 int markerCount = (Integer) args[argIndex++]; 245 markerInterfaces = new Class<?>[markerCount]; 246 System.arraycopy(args, argIndex, markerInterfaces, 0, markerCount); 247 argIndex += markerCount; 248 } 249 else 250 markerInterfaces = EMPTY_CLASS_ARRAY; 251 AbstractValidatingLambdaMetafactory mf; 252 mf = new InnerClassLambdaMetafactory(caller, invokedType, samMethod, implMethod, instantiatedMethodType, 253 flags, markerInterfaces); 254 mf.validateMetafactoryArgs(); 255 return mf.buildCallSite(); 256 } 257 } --- EOF ---