1 /* 2 * Copyright (c) 2008, 2011, 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 import sun.invoke.empty.Empty; 29 import sun.misc.Unsafe; 30 import static java.lang.invoke.MethodHandleStatics.*; 31 import static java.lang.invoke.MethodHandles.Lookup.IMPL_LOOKUP; 32 33 /** 34 * A {@code CallSite} is a holder for a variable {@link MethodHandle}, 35 * which is called its {@code target}. 36 * An {@code invokedynamic} instruction linked to a {@code CallSite} delegates 37 * all calls to the site's current target. 38 * A {@code CallSite} may be associated with several {@code invokedynamic} 39 * instructions, or it may be "free floating", associated with none. 40 * In any case, it may be invoked through an associated method handle 41 * called its {@linkplain #dynamicInvoker dynamic invoker}. 42 * <p> 43 * {@code CallSite} is an abstract class which does not allow 44 * direct subclassing by users. It has three immediate, 45 * concrete subclasses that may be either instantiated or subclassed. 46 * <ul> 47 * <li>If a mutable target is not required, an {@code invokedynamic} instruction 48 * may be permanently bound by means of a {@linkplain ConstantCallSite constant call site}. 49 * <li>If a mutable target is required which has volatile variable semantics, 50 * because updates to the target must be immediately and reliably witnessed by other threads, 51 * a {@linkplain VolatileCallSite volatile call site} may be used. 52 * <li>Otherwise, if a mutable target is required, 53 * a {@linkplain MutableCallSite mutable call site} may be used. 54 * </ul> 55 * <p> 56 * A non-constant call site may be <em>relinked</em> by changing its target. 57 * The new target must have the same {@linkplain MethodHandle#type() type} 58 * as the previous target. 59 * Thus, though a call site can be relinked to a series of 60 * successive targets, it cannot change its type. 61 * <p> 62 * Here is a sample use of call sites and bootstrap methods which links every 63 * dynamic call site to print its arguments: 64 <blockquote><pre><!-- see indy-demo/src/PrintArgsDemo.java --> 65 static void test() throws Throwable { 66 // THE FOLLOWING LINE IS PSEUDOCODE FOR A JVM INSTRUCTION 67 InvokeDynamic[#bootstrapDynamic].baz("baz arg", 2, 3.14); 68 } 69 private static void printArgs(Object... args) { 70 System.out.println(java.util.Arrays.deepToString(args)); 71 } 72 private static final MethodHandle printArgs; 73 static { 74 MethodHandles.Lookup lookup = MethodHandles.lookup(); 75 Class thisClass = lookup.lookupClass(); // (who am I?) 76 printArgs = lookup.findStatic(thisClass, 77 "printArgs", MethodType.methodType(void.class, Object[].class)); 78 } 79 private static CallSite bootstrapDynamic(MethodHandles.Lookup caller, String name, MethodType type) { 80 // ignore caller and name, but match the type: 81 return new ConstantCallSite(printArgs.asType(type)); 82 } 83 </pre></blockquote> 84 * @author John Rose, JSR 292 EG 85 */ 86 abstract 87 public class CallSite { 88 static { MethodHandleImpl.initStatics(); } 89 90 // Fields used only by the JVM. Do not use or change. 91 private MemberName vmmethod; // supplied by the JVM (ref. to calling method) 92 private int vmindex; // supplied by the JVM (BCI within calling method) 93 94 // The actual payload of this call site: 95 /*package-private*/ 96 MethodHandle target; 97 98 /** 99 * Make a blank call site object with the given method type. 100 * An initial target method is supplied which will throw 101 * an {@link IllegalStateException} if called. 102 * <p> 103 * Before this {@code CallSite} object is returned from a bootstrap method, 104 * it is usually provided with a more useful target method, 105 * via a call to {@link CallSite#setTarget(MethodHandle) setTarget}. 106 * @throws NullPointerException if the proposed type is null 107 */ 108 /*package-private*/ 109 CallSite(MethodType type) { 110 target = type.invokers().uninitializedCallSite(); 111 } 112 113 /** 114 * Make a call site object equipped with an initial target method handle. 115 * @param target the method handle which will be the initial target of the call site 116 * @throws NullPointerException if the proposed target is null 117 */ 118 /*package-private*/ 119 CallSite(MethodHandle target) { 120 target.type(); // null check 121 this.target = target; 122 } 123 124 /** 125 * Make a call site object equipped with an initial target method handle. 126 * @param targetType the desired type of the call site 127 * @param createTargetHook a hook which will bind the call site to the target method handle 128 * @throws WrongMethodTypeException if the hook cannot be invoked on the required arguments, 129 * or if the target returned by the hook is not of the given {@code targetType} 130 * @throws NullPointerException if the hook returns a null value 131 * @throws ClassCastException if the hook returns something other than a {@code MethodHandle} 132 * @throws Throwable anything else thrown by the the hook function 133 */ 134 /*package-private*/ 135 CallSite(MethodType targetType, MethodHandle createTargetHook) throws Throwable { 136 this(targetType); 137 ConstantCallSite selfCCS = (ConstantCallSite) this; 138 MethodHandle boundTarget = (MethodHandle) createTargetHook.invokeWithArguments(selfCCS); 139 checkTargetChange(this.target, boundTarget); 140 this.target = boundTarget; 141 } 142 143 /** 144 * Returns the type of this call site's target. 145 * Although targets may change, any call site's type is permanent, and can never change to an unequal type. 146 * The {@code setTarget} method enforces this invariant by refusing any new target that does 147 * not have the previous target's type. 148 * @return the type of the current target, which is also the type of any future target 149 */ 150 public MethodType type() { 151 // warning: do not call getTarget here, because CCS.getTarget can throw IllegalStateException 152 return target.type(); 153 } 154 155 /** Called from JVM (or low-level Java code) after the BSM returns the newly created CallSite. 156 * The parameters are JVM-specific. 157 */ 158 void initializeFromJVM(String name, 159 MethodType type, 160 MemberName callerMethod, 161 int callerBCI) { 162 if (this.vmmethod != null) { 163 // FIXME 164 throw new BootstrapMethodError("call site has already been linked to an invokedynamic instruction"); 165 } 166 if (!this.type().equals(type)) { 167 throw wrongTargetType(target, type); 168 } 169 this.vmindex = callerBCI; 170 this.vmmethod = callerMethod; 171 } 172 173 /** 174 * Returns the target method of the call site, according to the 175 * behavior defined by this call site's specific class. 176 * The immediate subclasses of {@code CallSite} document the 177 * class-specific behaviors of this method. 178 * 179 * @return the current linkage state of the call site, its target method handle 180 * @see ConstantCallSite 181 * @see VolatileCallSite 182 * @see #setTarget 183 * @see ConstantCallSite#getTarget 184 * @see MutableCallSite#getTarget 185 * @see VolatileCallSite#getTarget 186 */ 187 public abstract MethodHandle getTarget(); 188 189 /** 190 * Updates the target method of this call site, according to the 191 * behavior defined by this call site's specific class. 192 * The immediate subclasses of {@code CallSite} document the 193 * class-specific behaviors of this method. 194 * <p> 195 * The type of the new target must be {@linkplain MethodType#equals equal to} 196 * the type of the old target. 197 * 198 * @param newTarget the new target 199 * @throws NullPointerException if the proposed new target is null 200 * @throws WrongMethodTypeException if the proposed new target 201 * has a method type that differs from the previous target 202 * @see CallSite#getTarget 203 * @see ConstantCallSite#setTarget 204 * @see MutableCallSite#setTarget 205 * @see VolatileCallSite#setTarget 206 */ 207 public abstract void setTarget(MethodHandle newTarget); 208 209 void checkTargetChange(MethodHandle oldTarget, MethodHandle newTarget) { 210 MethodType oldType = oldTarget.type(); 211 MethodType newType = newTarget.type(); // null check! 212 if (!newType.equals(oldType)) 213 throw wrongTargetType(newTarget, oldType); 214 } 215 216 private static WrongMethodTypeException wrongTargetType(MethodHandle target, MethodType type) { 217 return new WrongMethodTypeException(String.valueOf(target)+" should be of type "+type); 218 } 219 220 /** 221 * Produces a method handle equivalent to an invokedynamic instruction 222 * which has been linked to this call site. 223 * <p> 224 * This method is equivalent to the following code: 225 * <blockquote><pre> 226 * MethodHandle getTarget, invoker, result; 227 * getTarget = MethodHandles.publicLookup().bind(this, "getTarget", MethodType.methodType(MethodHandle.class)); 228 * invoker = MethodHandles.exactInvoker(this.type()); 229 * result = MethodHandles.foldArguments(invoker, getTarget) 230 * </pre></blockquote> 231 * 232 * @return a method handle which always invokes this call site's current target 233 */ 234 public abstract MethodHandle dynamicInvoker(); 235 236 /*non-public*/ MethodHandle makeDynamicInvoker() { 237 MethodHandle getTarget = MethodHandleImpl.bindReceiver(GET_TARGET, this); 238 MethodHandle invoker = MethodHandles.exactInvoker(this.type()); 239 return MethodHandles.foldArguments(invoker, getTarget); 240 } 241 242 private static final MethodHandle GET_TARGET; 243 static { 244 try { 245 GET_TARGET = IMPL_LOOKUP. 246 findVirtual(CallSite.class, "getTarget", MethodType.methodType(MethodHandle.class)); 247 } catch (ReflectiveOperationException ignore) { 248 throw new InternalError(); 249 } 250 } 251 252 /** This guy is rolled into the default target if a MethodType is supplied to the constructor. */ 253 /*package-private*/ 254 static Empty uninitializedCallSite() { 255 throw new IllegalStateException("uninitialized call site"); 256 } 257 258 // unsafe stuff: 259 private static final Unsafe unsafe = Unsafe.getUnsafe(); 260 private static final long TARGET_OFFSET; 261 262 static { 263 try { 264 TARGET_OFFSET = unsafe.objectFieldOffset(CallSite.class.getDeclaredField("target")); 265 } catch (Exception ex) { throw new Error(ex); } 266 } 267 268 /*package-private*/ 269 void setTargetNormal(MethodHandle newTarget) { 270 target = newTarget; 271 } 272 /*package-private*/ 273 MethodHandle getTargetVolatile() { 274 return (MethodHandle) unsafe.getObjectVolatile(this, TARGET_OFFSET); 275 } 276 /*package-private*/ 277 void setTargetVolatile(MethodHandle newTarget) { 278 unsafe.putObjectVolatile(this, TARGET_OFFSET, newTarget); 279 } 280 281 // this implements the upcall from the JVM, MethodHandleNatives.makeDynamicCallSite: 282 static CallSite makeSite(MethodHandle bootstrapMethod, 283 // Callee information: 284 String name, MethodType type, 285 // Extra arguments for BSM, if any: 286 Object info, 287 // Caller information: 288 MemberName callerMethod, int callerBCI) { 289 Class<?> callerClass = callerMethod.getDeclaringClass(); 290 Object caller = IMPL_LOOKUP.in(callerClass); 291 CallSite site; 292 try { 293 Object binding; 294 info = maybeReBox(info); 295 if (info == null) { 296 binding = bootstrapMethod.invoke(caller, name, type); 297 } else if (!info.getClass().isArray()) { 298 binding = bootstrapMethod.invoke(caller, name, type, info); 299 } else { 300 Object[] argv = (Object[]) info; 301 maybeReBoxElements(argv); 302 if (3 + argv.length > 255) 303 throw new BootstrapMethodError("too many bootstrap method arguments"); 304 MethodType bsmType = bootstrapMethod.type(); 305 if (bsmType.parameterCount() == 4 && bsmType.parameterType(3) == Object[].class) 306 binding = bootstrapMethod.invoke(caller, name, type, argv); 307 else 308 binding = MethodHandles.spreadInvoker(bsmType, 3) 309 .invoke(bootstrapMethod, caller, name, type, argv); 310 } 311 //System.out.println("BSM for "+name+type+" => "+binding); 312 if (binding instanceof CallSite) { 313 site = (CallSite) binding; 314 } else { 315 throw new ClassCastException("bootstrap method failed to produce a CallSite"); 316 } 317 if (!site.getTarget().type().equals(type)) 318 throw new WrongMethodTypeException("wrong type: "+site.getTarget()); 319 } catch (Throwable ex) { 320 BootstrapMethodError bex; 321 if (ex instanceof BootstrapMethodError) 322 bex = (BootstrapMethodError) ex; 323 else 324 bex = new BootstrapMethodError("call site initialization exception", ex); 325 throw bex; 326 } 327 return site; 328 } 329 330 private static Object maybeReBox(Object x) { 331 if (x instanceof Integer) { 332 int xi = (int) x; 333 if (xi == (byte) xi) 334 x = xi; // must rebox; see JLS 5.1.7 335 } 336 return x; 337 } 338 private static void maybeReBoxElements(Object[] xa) { 339 for (int i = 0; i < xa.length; i++) { 340 xa[i] = maybeReBox(xa[i]); 341 } 342 } 343 }