1 /* 2 * Copyright (c) 2008, 2012, 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 static java.lang.invoke.MethodHandleStatics.*; 30 import static java.lang.invoke.MethodHandles.Lookup.IMPL_LOOKUP; 31 32 /** 33 * A {@code CallSite} is a holder for a variable {@link MethodHandle}, 34 * which is called its {@code target}. 35 * An {@code invokedynamic} instruction linked to a {@code CallSite} delegates 36 * all calls to the site's current target. 37 * A {@code CallSite} may be associated with several {@code invokedynamic} 38 * instructions, or it may be "free floating", associated with none. 39 * In any case, it may be invoked through an associated method handle 40 * called its {@linkplain #dynamicInvoker dynamic invoker}. 41 * <p> 42 * {@code CallSite} is an abstract class which does not allow 43 * direct subclassing by users. It has three immediate, 44 * concrete subclasses that may be either instantiated or subclassed. 45 * <ul> 46 * <li>If a mutable target is not required, an {@code invokedynamic} instruction 47 * may be permanently bound by means of a {@linkplain ConstantCallSite constant call site}. 48 * <li>If a mutable target is required which has volatile variable semantics, 49 * because updates to the target must be immediately and reliably witnessed by other threads, 50 * a {@linkplain VolatileCallSite volatile call site} may be used. 51 * <li>Otherwise, if a mutable target is required, 52 * a {@linkplain MutableCallSite mutable call site} may be used. 53 * </ul> 54 * <p> 55 * A non-constant call site may be <em>relinked</em> by changing its target. 56 * The new target must have the same {@linkplain MethodHandle#type() type} 57 * as the previous target. 58 * Thus, though a call site can be relinked to a series of 59 * successive targets, it cannot change its type. 60 * <p> 61 * Here is a sample use of call sites and bootstrap methods which links every 62 * dynamic call site to print its arguments: 63 <blockquote><pre><!-- see indy-demo/src/PrintArgsDemo.java --> 64 static void test() throws Throwable { 65 // THE FOLLOWING LINE IS PSEUDOCODE FOR A JVM INSTRUCTION 66 InvokeDynamic[#bootstrapDynamic].baz("baz arg", 2, 3.14); 67 } 68 private static void printArgs(Object... args) { 69 System.out.println(java.util.Arrays.deepToString(args)); 70 } 71 private static final MethodHandle printArgs; 72 static { 73 MethodHandles.Lookup lookup = MethodHandles.lookup(); 74 Class thisClass = lookup.lookupClass(); // (who am I?) 75 printArgs = lookup.findStatic(thisClass, 76 "printArgs", MethodType.methodType(void.class, Object[].class)); 77 } 78 private static CallSite bootstrapDynamic(MethodHandles.Lookup caller, String name, MethodType type) { 79 // ignore caller and name, but match the type: 80 return new ConstantCallSite(printArgs.asType(type)); 81 } 82 </pre></blockquote> 83 * @author John Rose, JSR 292 EG 84 */ 85 abstract 86 public class CallSite { 87 static { MethodHandleImpl.initStatics(); } 88 89 // The actual payload of this call site: 90 /*package-private*/ 91 MethodHandle target; // Note: This field is known to the JVM. Do not change. 92 93 /** 94 * Make a blank call site object with the given method type. 95 * An initial target method is supplied which will throw 96 * an {@link IllegalStateException} if called. 97 * <p> 98 * Before this {@code CallSite} object is returned from a bootstrap method, 99 * it is usually provided with a more useful target method, 100 * via a call to {@link CallSite#setTarget(MethodHandle) setTarget}. 101 * @throws NullPointerException if the proposed type is null 102 */ 103 /*package-private*/ 104 CallSite(MethodType type) { 105 target = type.invokers().uninitializedCallSite(); 106 } 107 108 /** 109 * Make a call site object equipped with an initial target method handle. 110 * @param target the method handle which will be the initial target of the call site 111 * @throws NullPointerException if the proposed target is null 112 */ 113 /*package-private*/ 114 CallSite(MethodHandle target) { 115 target.type(); // null check 116 this.target = target; 117 } 118 119 /** 120 * Make a call site object equipped with an initial target method handle. 121 * @param targetType the desired type of the call site 122 * @param createTargetHook a hook which will bind the call site to the target method handle 123 * @throws WrongMethodTypeException if the hook cannot be invoked on the required arguments, 124 * or if the target returned by the hook is not of the given {@code targetType} 125 * @throws NullPointerException if the hook returns a null value 126 * @throws ClassCastException if the hook returns something other than a {@code MethodHandle} 127 * @throws Throwable anything else thrown by the the hook function 128 */ 129 /*package-private*/ 130 CallSite(MethodType targetType, MethodHandle createTargetHook) throws Throwable { 131 this(targetType); 132 ConstantCallSite selfCCS = (ConstantCallSite) this; 133 MethodHandle boundTarget = (MethodHandle) createTargetHook.invokeWithArguments(selfCCS); 134 checkTargetChange(this.target, boundTarget); 135 this.target = boundTarget; 136 } 137 138 /** 139 * Returns the type of this call site's target. 140 * Although targets may change, any call site's type is permanent, and can never change to an unequal type. 141 * The {@code setTarget} method enforces this invariant by refusing any new target that does 142 * not have the previous target's type. 143 * @return the type of the current target, which is also the type of any future target 144 */ 145 public MethodType type() { 146 // warning: do not call getTarget here, because CCS.getTarget can throw IllegalStateException 147 return target.type(); 148 } 149 150 /** 151 * Returns the target method of the call site, according to the 152 * behavior defined by this call site's specific class. 153 * The immediate subclasses of {@code CallSite} document the 154 * class-specific behaviors of this method. 155 * 156 * @return the current linkage state of the call site, its target method handle 157 * @see ConstantCallSite 158 * @see VolatileCallSite 159 * @see #setTarget 160 * @see ConstantCallSite#getTarget 161 * @see MutableCallSite#getTarget 162 * @see VolatileCallSite#getTarget 163 */ 164 public abstract MethodHandle getTarget(); 165 166 /** 167 * Updates the target method of this call site, according to the 168 * behavior defined by this call site's specific class. 169 * The immediate subclasses of {@code CallSite} document the 170 * class-specific behaviors of this method. 171 * <p> 172 * The type of the new target must be {@linkplain MethodType#equals equal to} 173 * the type of the old target. 174 * 175 * @param newTarget the new target 176 * @throws NullPointerException if the proposed new target is null 177 * @throws WrongMethodTypeException if the proposed new target 178 * has a method type that differs from the previous target 179 * @see CallSite#getTarget 180 * @see ConstantCallSite#setTarget 181 * @see MutableCallSite#setTarget 182 * @see VolatileCallSite#setTarget 183 */ 184 public abstract void setTarget(MethodHandle newTarget); 185 186 void checkTargetChange(MethodHandle oldTarget, MethodHandle newTarget) { 187 MethodType oldType = oldTarget.type(); 188 MethodType newType = newTarget.type(); // null check! 189 if (!newType.equals(oldType)) 190 throw wrongTargetType(newTarget, oldType); 191 } 192 193 private static WrongMethodTypeException wrongTargetType(MethodHandle target, MethodType type) { 194 return new WrongMethodTypeException(String.valueOf(target)+" should be of type "+type); 195 } 196 197 /** 198 * Produces a method handle equivalent to an invokedynamic instruction 199 * which has been linked to this call site. 200 * <p> 201 * This method is equivalent to the following code: 202 * <blockquote><pre> 203 * MethodHandle getTarget, invoker, result; 204 * getTarget = MethodHandles.publicLookup().bind(this, "getTarget", MethodType.methodType(MethodHandle.class)); 205 * invoker = MethodHandles.exactInvoker(this.type()); 206 * result = MethodHandles.foldArguments(invoker, getTarget) 207 * </pre></blockquote> 208 * 209 * @return a method handle which always invokes this call site's current target 210 */ 211 public abstract MethodHandle dynamicInvoker(); 212 213 /*non-public*/ MethodHandle makeDynamicInvoker() { 214 MethodHandle getTarget = GET_TARGET.bindReceiver(this); 215 MethodHandle invoker = MethodHandles.exactInvoker(this.type()); 216 return MethodHandles.foldArguments(invoker, getTarget); 217 } 218 219 private static final MethodHandle GET_TARGET; 220 static { 221 try { 222 GET_TARGET = IMPL_LOOKUP. 223 findVirtual(CallSite.class, "getTarget", MethodType.methodType(MethodHandle.class)); 224 } catch (ReflectiveOperationException e) { 225 throw newInternalError(e); 226 } 227 } 228 229 /** This guy is rolled into the default target if a MethodType is supplied to the constructor. */ 230 /*package-private*/ 231 static Empty uninitializedCallSite() { 232 throw new IllegalStateException("uninitialized call site"); 233 } 234 235 // unsafe stuff: 236 private static final long TARGET_OFFSET; 237 static { 238 try { 239 TARGET_OFFSET = UNSAFE.objectFieldOffset(CallSite.class.getDeclaredField("target")); 240 } catch (Exception ex) { throw new Error(ex); } 241 } 242 243 /*package-private*/ 244 void setTargetNormal(MethodHandle newTarget) { 245 MethodHandleNatives.setCallSiteTargetNormal(this, newTarget); 246 } 247 /*package-private*/ 248 MethodHandle getTargetVolatile() { 249 return (MethodHandle) UNSAFE.getObjectVolatile(this, TARGET_OFFSET); 250 } 251 /*package-private*/ 252 void setTargetVolatile(MethodHandle newTarget) { 253 MethodHandleNatives.setCallSiteTargetVolatile(this, newTarget); 254 } 255 256 // this implements the upcall from the JVM, MethodHandleNatives.makeDynamicCallSite: 257 static CallSite makeSite(MethodHandle bootstrapMethod, 258 // Callee information: 259 String name, MethodType type, 260 // Extra arguments for BSM, if any: 261 Object info, 262 // Caller information: 263 Class<?> callerClass) { 264 Object caller = IMPL_LOOKUP.in(callerClass); 265 CallSite site; 266 try { 267 Object binding; 268 info = maybeReBox(info); 269 if (info == null) { 270 binding = bootstrapMethod.invoke(caller, name, type); 271 } else if (!info.getClass().isArray()) { 272 binding = bootstrapMethod.invoke(caller, name, type, info); 273 } else { 274 Object[] argv = (Object[]) info; 275 maybeReBoxElements(argv); 276 if (3 + argv.length > 255) 277 throw new BootstrapMethodError("too many bootstrap method arguments"); 278 MethodType bsmType = bootstrapMethod.type(); 279 if (bsmType.parameterCount() == 4 && bsmType.parameterType(3) == Object[].class) 280 binding = bootstrapMethod.invoke(caller, name, type, argv); 281 else 282 binding = MethodHandles.spreadInvoker(bsmType, 3) 283 .invoke(bootstrapMethod, caller, name, type, argv); 284 } 285 //System.out.println("BSM for "+name+type+" => "+binding); 286 if (binding instanceof CallSite) { 287 site = (CallSite) binding; 288 } else { 289 throw new ClassCastException("bootstrap method failed to produce a CallSite"); 290 } 291 if (!site.getTarget().type().equals(type)) 292 throw new WrongMethodTypeException("wrong type: "+site.getTarget()); 293 } catch (Throwable ex) { 294 BootstrapMethodError bex; 295 if (ex instanceof BootstrapMethodError) 296 bex = (BootstrapMethodError) ex; 297 else 298 bex = new BootstrapMethodError("call site initialization exception", ex); 299 throw bex; 300 } 301 return site; 302 } 303 304 private static Object maybeReBox(Object x) { 305 if (x instanceof Integer) { 306 int xi = (int) x; 307 if (xi == (byte) xi) 308 x = xi; // must rebox; see JLS 5.1.7 309 } 310 return x; 311 } 312 private static void maybeReBoxElements(Object[] xa) { 313 for (int i = 0; i < xa.length; i++) { 314 xa[i] = maybeReBox(xa[i]); 315 } 316 } 317 }