1 /* 2 * Copyright (c) 2008, 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 // Android-changed: Not using Empty. 29 //import sun.invoke.empty.Empty; 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>{@code 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 // Android-changed: not used. 89 // static { MethodHandleImpl.initStatics(); } 90 91 // The actual payload of this call site: 92 /*package-private*/ 93 MethodHandle target; // Note: This field is known to the JVM. Do not change. 94 95 /** 96 * Make a blank call site object with the given method type. 97 * An initial target method is supplied which will throw 98 * an {@link IllegalStateException} if called. 99 * <p> 100 * Before this {@code CallSite} object is returned from a bootstrap method, 101 * it is usually provided with a more useful target method, 102 * via a call to {@link CallSite#setTarget(MethodHandle) setTarget}. 103 * @throws NullPointerException if the proposed type is null 104 */ 105 /*package-private*/ CallSite(MethodType type)106 CallSite(MethodType type) { 107 // Android-changed: No cache for these. 108 // Instead create uninitializedCallSite target here using method handle transformations 109 // to create a method handle that has the expected method type but throws an 110 // IllegalStateException. 111 // target = makeUninitializedCallSite(type); 112 this.target = MethodHandles.throwException(type.returnType(), IllegalStateException.class); 113 this.target = MethodHandles.insertArguments( 114 this.target, 0, new IllegalStateException("uninitialized call site")); 115 if (type.parameterCount() > 0) { 116 this.target = MethodHandles.dropArguments(this.target, 0, type.ptypes()); 117 } 118 119 // Android-changed: Using initializer method for GET_TARGET instead of static initializer. 120 initializeGetTarget(); 121 } 122 123 /** 124 * Make a call site object equipped with an initial target method handle. 125 * @param target the method handle which will be the initial target of the call site 126 * @throws NullPointerException if the proposed target is null 127 */ 128 /*package-private*/ CallSite(MethodHandle target)129 CallSite(MethodHandle target) { 130 target.type(); // null check 131 this.target = target; 132 133 // Android-changed: Using initializer method for GET_TARGET instead of static initializer. 134 initializeGetTarget(); 135 } 136 137 /** 138 * Make a call site object equipped with an initial target method handle. 139 * @param targetType the desired type of the call site 140 * @param createTargetHook a hook which will bind the call site to the target method handle 141 * @throws WrongMethodTypeException if the hook cannot be invoked on the required arguments, 142 * or if the target returned by the hook is not of the given {@code targetType} 143 * @throws NullPointerException if the hook returns a null value 144 * @throws ClassCastException if the hook returns something other than a {@code MethodHandle} 145 * @throws Throwable anything else thrown by the hook function 146 */ 147 /*package-private*/ CallSite(MethodType targetType, MethodHandle createTargetHook)148 CallSite(MethodType targetType, MethodHandle createTargetHook) throws Throwable { 149 this(targetType); 150 ConstantCallSite selfCCS = (ConstantCallSite) this; 151 MethodHandle boundTarget = (MethodHandle) createTargetHook.invokeWithArguments(selfCCS); 152 checkTargetChange(this.target, boundTarget); 153 this.target = boundTarget; 154 155 // Android-changed: Using initializer method for GET_TARGET instead of static initializer. 156 initializeGetTarget(); 157 } 158 159 /** 160 * Returns the type of this call site's target. 161 * Although targets may change, any call site's type is permanent, and can never change to an unequal type. 162 * The {@code setTarget} method enforces this invariant by refusing any new target that does 163 * not have the previous target's type. 164 * @return the type of the current target, which is also the type of any future target 165 */ type()166 public MethodType type() { 167 // warning: do not call getTarget here, because CCS.getTarget can throw IllegalStateException 168 return target.type(); 169 } 170 171 /** 172 * Returns the target method of the call site, according to the 173 * behavior defined by this call site's specific class. 174 * The immediate subclasses of {@code CallSite} document the 175 * class-specific behaviors of this method. 176 * 177 * @return the current linkage state of the call site, its target method handle 178 * @see ConstantCallSite 179 * @see VolatileCallSite 180 * @see #setTarget 181 * @see ConstantCallSite#getTarget 182 * @see MutableCallSite#getTarget 183 * @see VolatileCallSite#getTarget 184 */ getTarget()185 public abstract MethodHandle getTarget(); 186 187 /** 188 * Updates the target method of this call site, according to the 189 * behavior defined by this call site's specific class. 190 * The immediate subclasses of {@code CallSite} document the 191 * class-specific behaviors of this method. 192 * <p> 193 * The type of the new target must be {@linkplain MethodType#equals equal to} 194 * the type of the old target. 195 * 196 * @param newTarget the new target 197 * @throws NullPointerException if the proposed new target is null 198 * @throws WrongMethodTypeException if the proposed new target 199 * has a method type that differs from the previous target 200 * @see CallSite#getTarget 201 * @see ConstantCallSite#setTarget 202 * @see MutableCallSite#setTarget 203 * @see VolatileCallSite#setTarget 204 */ setTarget(MethodHandle newTarget)205 public abstract void setTarget(MethodHandle newTarget); 206 checkTargetChange(MethodHandle oldTarget, MethodHandle newTarget)207 void checkTargetChange(MethodHandle oldTarget, MethodHandle newTarget) { 208 MethodType oldType = oldTarget.type(); 209 MethodType newType = newTarget.type(); // null check! 210 if (!newType.equals(oldType)) 211 throw wrongTargetType(newTarget, oldType); 212 } 213 wrongTargetType(MethodHandle target, MethodType type)214 private static WrongMethodTypeException wrongTargetType(MethodHandle target, MethodType type) { 215 return new WrongMethodTypeException(String.valueOf(target)+" should be of type "+type); 216 } 217 218 /** 219 * Produces a method handle equivalent to an invokedynamic instruction 220 * which has been linked to this call site. 221 * <p> 222 * This method is equivalent to the following code: 223 * <blockquote><pre>{@code 224 * MethodHandle getTarget, invoker, result; 225 * getTarget = MethodHandles.publicLookup().bind(this, "getTarget", MethodType.methodType(MethodHandle.class)); 226 * invoker = MethodHandles.exactInvoker(this.type()); 227 * result = MethodHandles.foldArguments(invoker, getTarget) 228 * }</pre></blockquote> 229 * 230 * @return a method handle which always invokes this call site's current target 231 */ dynamicInvoker()232 public abstract MethodHandle dynamicInvoker(); 233 makeDynamicInvoker()234 /*non-public*/ MethodHandle makeDynamicInvoker() { 235 // Android-changed: Use bindTo() rather than bindArgumentL() (not implemented). 236 MethodHandle getTarget = GET_TARGET.bindTo(this); 237 MethodHandle invoker = MethodHandles.exactInvoker(this.type()); 238 return MethodHandles.foldArguments(invoker, getTarget); 239 } 240 241 // Android-changed: no longer final. GET_TARGET assigned in initializeGetTarget(). 242 private static MethodHandle GET_TARGET = null; 243 initializeGetTarget()244 private void initializeGetTarget() { 245 // Android-changed: moved from static initializer for GET_TARGET. 246 // This avoids issues with running early. Called from constructors. 247 // CallSite creation is not performance critical. 248 synchronized (CallSite.class) { 249 if (GET_TARGET == null) { 250 try { 251 GET_TARGET = IMPL_LOOKUP. 252 findVirtual(CallSite.class, "getTarget", 253 MethodType.methodType(MethodHandle.class)); 254 } catch (ReflectiveOperationException e) { 255 throw new InternalError(e); 256 } 257 } 258 } 259 } 260 261 // Android-changed: not used. 262 // /** This guy is rolled into the default target if a MethodType is supplied to the constructor. */ 263 // /*package-private*/ 264 // static Empty uninitializedCallSite() { 265 // throw new IllegalStateException("uninitialized call site"); 266 // } 267 268 // unsafe stuff: 269 private static final long TARGET_OFFSET; 270 static { 271 try { 272 TARGET_OFFSET = UNSAFE.objectFieldOffset(CallSite.class.getDeclaredField("target")); 273 } catch (Exception ex) { throw new Error(ex); } 274 } 275 276 /*package-private*/ setTargetNormal(MethodHandle newTarget)277 void setTargetNormal(MethodHandle newTarget) { 278 // Android-changed: Set value directly. 279 // MethodHandleNatives.setCallSiteTargetNormal(this, newTarget); 280 target = newTarget; 281 } 282 /*package-private*/ getTargetVolatile()283 MethodHandle getTargetVolatile() { 284 return (MethodHandle) UNSAFE.getObjectVolatile(this, TARGET_OFFSET); 285 } 286 /*package-private*/ setTargetVolatile(MethodHandle newTarget)287 void setTargetVolatile(MethodHandle newTarget) { 288 // Android-changed: Set value directly. 289 // MethodHandleNatives.setCallSiteTargetVolatile(this, newTarget); 290 UNSAFE.putObjectVolatile(this, TARGET_OFFSET, newTarget); 291 } 292 293 // Android-changed: not used. 294 // this implements the upcall from the JVM, MethodHandleNatives.makeDynamicCallSite: 295 // static CallSite makeSite(MethodHandle bootstrapMethod, 296 // // Callee information: 297 // String name, MethodType type, 298 // // Extra arguments for BSM, if any: 299 // Object info, 300 // // Caller information: 301 // Class<?> callerClass) { 302 // MethodHandles.Lookup caller = IMPL_LOOKUP.in(callerClass); 303 // CallSite site; 304 // try { 305 // Object binding; 306 // info = maybeReBox(info); 307 // if (info == null) { 308 // binding = bootstrapMethod.invoke(caller, name, type); 309 // } else if (!info.getClass().isArray()) { 310 // binding = bootstrapMethod.invoke(caller, name, type, info); 311 // } else { 312 // Object[] argv = (Object[]) info; 313 // maybeReBoxElements(argv); 314 // switch (argv.length) { 315 // case 0: 316 // binding = bootstrapMethod.invoke(caller, name, type); 317 // break; 318 // case 1: 319 // binding = bootstrapMethod.invoke(caller, name, type, 320 // argv[0]); 321 // break; 322 // case 2: 323 // binding = bootstrapMethod.invoke(caller, name, type, 324 // argv[0], argv[1]); 325 // break; 326 // case 3: 327 // binding = bootstrapMethod.invoke(caller, name, type, 328 // argv[0], argv[1], argv[2]); 329 // break; 330 // case 4: 331 // binding = bootstrapMethod.invoke(caller, name, type, 332 // argv[0], argv[1], argv[2], argv[3]); 333 // break; 334 // case 5: 335 // binding = bootstrapMethod.invoke(caller, name, type, 336 // argv[0], argv[1], argv[2], argv[3], argv[4]); 337 // break; 338 // case 6: 339 // binding = bootstrapMethod.invoke(caller, name, type, 340 // argv[0], argv[1], argv[2], argv[3], argv[4], argv[5]); 341 // break; 342 // default: 343 // final int NON_SPREAD_ARG_COUNT = 3; // (caller, name, type) 344 // if (NON_SPREAD_ARG_COUNT + argv.length > MethodType.MAX_MH_ARITY) 345 // throw new BootstrapMethodError("too many bootstrap method arguments"); 346 // MethodType bsmType = bootstrapMethod.type(); 347 // MethodType invocationType = MethodType.genericMethodType(NON_SPREAD_ARG_COUNT + argv.length); 348 // MethodHandle typedBSM = bootstrapMethod.asType(invocationType); 349 // MethodHandle spreader = invocationType.invokers().spreadInvoker(NON_SPREAD_ARG_COUNT); 350 // binding = spreader.invokeExact(typedBSM, (Object)caller, (Object)name, (Object)type, argv); 351 // } 352 // } 353 // //System.out.println("BSM for "+name+type+" => "+binding); 354 // if (binding instanceof CallSite) { 355 // site = (CallSite) binding; 356 // } else { 357 // throw new ClassCastException("bootstrap method failed to produce a CallSite"); 358 // } 359 // if (!site.getTarget().type().equals(type)) 360 // throw wrongTargetType(site.getTarget(), type); 361 // } catch (Throwable ex) { 362 // BootstrapMethodError bex; 363 // if (ex instanceof BootstrapMethodError) 364 // bex = (BootstrapMethodError) ex; 365 // else 366 // bex = new BootstrapMethodError("call site initialization exception", ex); 367 // throw bex; 368 // } 369 // return site; 370 // } 371 372 // private static Object maybeReBox(Object x) { 373 // if (x instanceof Integer) { 374 // int xi = (int) x; 375 // if (xi == (byte) xi) 376 // x = xi; // must rebox; see JLS 5.1.7 377 // } 378 // return x; 379 // } 380 // private static void maybeReBoxElements(Object[] xa) { 381 // for (int i = 0; i < xa.length; i++) { 382 // xa[i] = maybeReBox(xa[i]); 383 // } 384 // } 385 } 386