1 /* 2 * Copyright (c) 2016, 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 /* 27 * This file is available under and governed by the GNU General Public 28 * License version 2 only, as published by the Free Software Foundation. 29 * However, the following notice accompanied the original version of this 30 * file, and Oracle licenses the original version of this file under the BSD 31 * license: 32 */ 33 /* 34 Copyright 2009-2013 Attila Szegedi 35 36 Redistribution and use in source and binary forms, with or without 37 modification, are permitted provided that the following conditions are 38 met: 39 * Redistributions of source code must retain the above copyright 40 notice, this list of conditions and the following disclaimer. 41 * Redistributions in binary form must reproduce the above copyright 42 notice, this list of conditions and the following disclaimer in the 43 documentation and/or other materials provided with the distribution. 44 * Neither the name of the copyright holder nor the names of 45 contributors may be used to endorse or promote products derived from 46 this software without specific prior written permission. 47 48 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS 49 IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 50 TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A 51 PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL COPYRIGHT HOLDER 52 BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 53 CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 54 SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR 55 BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, 56 WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR 57 OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF 58 ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 59 */ 60 61 package jdk.dynalink; 62 63 import java.lang.StackWalker.StackFrame; 64 import java.lang.invoke.MethodHandle; 65 import java.lang.invoke.MethodHandles; 66 import java.lang.invoke.MethodType; 67 import java.lang.invoke.MutableCallSite; 68 import java.util.Objects; 69 import jdk.dynalink.linker.GuardedInvocation; 70 import jdk.dynalink.linker.GuardedInvocationTransformer; 71 import jdk.dynalink.linker.GuardingDynamicLinker; 72 import jdk.dynalink.linker.LinkRequest; 73 import jdk.dynalink.linker.LinkerServices; 74 import jdk.dynalink.linker.support.Lookup; 75 import jdk.dynalink.linker.support.SimpleLinkRequest; 76 import jdk.dynalink.support.ChainedCallSite; 77 import jdk.dynalink.support.SimpleRelinkableCallSite; 78 79 /** 80 * The linker for {@link RelinkableCallSite} objects. A dynamic linker is a main 81 * objects when using Dynalink, it coordinates linking of call sites with 82 * linkers of available language runtimes that are represented by 83 * {@link GuardingDynamicLinker} objects (you only need to deal with these if 84 * you are yourself implementing a language runtime with its own object model 85 * and/or type conversions). To use Dynalink, you have to create one or more 86 * dynamic linkers using a {@link DynamicLinkerFactory}. Subsequently, you need 87 * to invoke its {@link #link(RelinkableCallSite)} method from 88 * {@code invokedynamic} bootstrap methods to let it manage all the call sites 89 * they create. Usual usage would be to create at least one class per language 90 * runtime to contain one linker instance as: 91 * <pre> 92 * 93 * class MyLanguageRuntime { 94 * private static final GuardingDynamicLinker myLanguageLinker = new MyLanguageLinker(); 95 * private static final DynamicLinker dynamicLinker = createDynamicLinker(); 96 * 97 * private static DynamicLinker createDynamicLinker() { 98 * final DynamicLinkerFactory factory = new DynamicLinkerFactory(); 99 * factory.setPrioritizedLinker(myLanguageLinker); 100 * return factory.createLinker(); 101 * } 102 * 103 * public static CallSite bootstrap(MethodHandles.Lookup lookup, String name, MethodType type) { 104 * return dynamicLinker.link( 105 * new SimpleRelinkableCallSite( 106 * new CallSiteDescriptor(lookup, parseOperation(name), type))); 107 * } 108 * 109 * private static Operation parseOperation(String name) { 110 * ... 111 * } 112 * } 113 * </pre> 114 * The above setup of one static linker instance is often too simple. You will 115 * often have your language runtime have a concept of some kind of 116 * "context class loader" and you will want to create one dynamic linker per 117 * such class loader, to ensure it incorporates linkers for all other language 118 * runtimes visible to that class loader (see 119 * {@link DynamicLinkerFactory#setClassLoader(ClassLoader)}). 120 * <p> 121 * There are three components you need to provide in the above example: 122 * <ul> 123 * 124 * <li>You are expected to provide a {@link GuardingDynamicLinker} for your own 125 * language. If your runtime doesn't have its own object model or type 126 * conversions, you don't need to implement a {@code GuardingDynamicLinker}; you 127 * would simply not invoke the {@code setPrioritizedLinker} method on the factory.</li> 128 * 129 * <li>The performance of the programs can depend on your choice of the class to 130 * represent call sites. The above example used 131 * {@link SimpleRelinkableCallSite}, but you might want to use 132 * {@link ChainedCallSite} instead. You'll need to experiment and decide what 133 * fits your runtime the best. You can further subclass either of these or 134 * implement your own.</li> 135 * 136 * <li>You also need to provide {@link CallSiteDescriptor}s to your call sites. 137 * They are immutable objects that contain all the information about the call 138 * site: the class performing the lookups, the operation being invoked, and the 139 * method signature. You will have to supply your own scheme to encode and 140 * decode operations in the call site name or static parameters, that is why 141 * in the above example the {@code parseOperation} method is left unimplemented.</li> 142 * 143 * </ul> 144 */ 145 public final class DynamicLinker { 146 private static final String CLASS_NAME = DynamicLinker.class.getName(); 147 private static final String RELINK_METHOD_NAME = "relink"; 148 149 private static final String INITIAL_LINK_CLASS_NAME = "java.lang.invoke.MethodHandleNatives"; 150 private static final String INITIAL_LINK_METHOD_NAME = "linkCallSite"; 151 private static final String INVOKE_PACKAGE_PREFIX = "java.lang.invoke."; 152 153 private static final StackWalker stackWalker = StackWalker.getInstance(StackWalker.Option.SHOW_HIDDEN_FRAMES); 154 155 private final LinkerServices linkerServices; 156 private final GuardedInvocationTransformer prelinkTransformer; 157 private final boolean syncOnRelink; 158 private final int unstableRelinkThreshold; 159 160 /** 161 * Creates a new dynamic linker. 162 * 163 * @param linkerServices the linkerServices used by the linker, created by the factory. 164 * @param prelinkTransformer see {@link DynamicLinkerFactory#setPrelinkTransformer(GuardedInvocationTransformer)} 165 * @param syncOnRelink see {@link DynamicLinkerFactory#setSyncOnRelink(boolean)} 166 * @param unstableRelinkThreshold see {@link DynamicLinkerFactory#setUnstableRelinkThreshold(int)} 167 */ DynamicLinker(final LinkerServices linkerServices, final GuardedInvocationTransformer prelinkTransformer, final boolean syncOnRelink, final int unstableRelinkThreshold)168 DynamicLinker(final LinkerServices linkerServices, final GuardedInvocationTransformer prelinkTransformer, 169 final boolean syncOnRelink, final int unstableRelinkThreshold) { 170 if(unstableRelinkThreshold < 0) { 171 throw new IllegalArgumentException("unstableRelinkThreshold < 0"); 172 } 173 this.linkerServices = linkerServices; 174 this.prelinkTransformer = prelinkTransformer; 175 this.syncOnRelink = syncOnRelink; 176 this.unstableRelinkThreshold = unstableRelinkThreshold; 177 } 178 179 /** 180 * Links an invokedynamic call site. It will install a method handle into 181 * the call site that invokes the relinking mechanism of this linker. Next 182 * time the call site is invoked, it will be linked for the actual arguments 183 * it was invoked with. 184 * 185 * @param <T> the particular subclass of {@link RelinkableCallSite} for 186 * which to create a link. 187 * @param callSite the call site to link. 188 * 189 * @return the callSite, for easy call chaining. 190 */ link(final T callSite)191 public <T extends RelinkableCallSite> T link(final T callSite) { 192 callSite.initialize(createRelinkAndInvokeMethod(callSite, 0)); 193 return callSite; 194 } 195 196 /** 197 * Returns the object representing the linker services of this class that 198 * are normally exposed to individual {@link GuardingDynamicLinker 199 * language-specific linkers}. While as a user of this class you normally 200 * only care about the {@link #link(RelinkableCallSite)} method, in certain 201 * circumstances you might want to use the lower level services directly; 202 * either to lookup specific method handles, to access the type converters, 203 * and so on. 204 * 205 * @return the object representing the linker services of this class. 206 */ getLinkerServices()207 public LinkerServices getLinkerServices() { 208 return linkerServices; 209 } 210 211 private static final MethodHandle RELINK = Lookup.findOwnSpecial(MethodHandles.lookup(), RELINK_METHOD_NAME, 212 MethodHandle.class, RelinkableCallSite.class, int.class, Object[].class); 213 createRelinkAndInvokeMethod(final RelinkableCallSite callSite, final int relinkCount)214 private MethodHandle createRelinkAndInvokeMethod(final RelinkableCallSite callSite, final int relinkCount) { 215 // Make a bound MH of invoke() for this linker and call site 216 final MethodHandle boundRelinker = MethodHandles.insertArguments(RELINK, 0, this, callSite, relinkCount); 217 // Make a MH that gathers all arguments to the invocation into an Object[] 218 final MethodType type = callSite.getDescriptor().getMethodType(); 219 final MethodHandle collectingRelinker = boundRelinker.asCollector(Object[].class, type.parameterCount()); 220 return MethodHandles.foldArguments(MethodHandles.exactInvoker(type), collectingRelinker.asType( 221 type.changeReturnType(MethodHandle.class))); 222 } 223 224 /** 225 * Relinks a call site conforming to the invocation arguments. 226 * 227 * @param callSite the call site itself 228 * @param arguments arguments to the invocation 229 * 230 * @return return the method handle for the invocation 231 * 232 * @throws Exception rethrows any exception thrown by the linkers 233 */ 234 @SuppressWarnings("unused") relink(final RelinkableCallSite callSite, final int relinkCount, final Object... arguments)235 private MethodHandle relink(final RelinkableCallSite callSite, final int relinkCount, final Object... arguments) throws Exception { 236 final CallSiteDescriptor callSiteDescriptor = callSite.getDescriptor(); 237 final boolean unstableDetectionEnabled = unstableRelinkThreshold > 0; 238 final boolean callSiteUnstable = unstableDetectionEnabled && relinkCount >= unstableRelinkThreshold; 239 final LinkRequest linkRequest = new SimpleLinkRequest(callSiteDescriptor, callSiteUnstable, arguments); 240 241 GuardedInvocation guardedInvocation = linkerServices.getGuardedInvocation(linkRequest); 242 243 // None found - throw an exception 244 if(guardedInvocation == null) { 245 throw new NoSuchDynamicMethodException(callSiteDescriptor.toString()); 246 } 247 248 // Make sure we transform the invocation before linking it into the call site. This is typically used to match the 249 // return type of the invocation to the call site. 250 guardedInvocation = prelinkTransformer.filter(guardedInvocation, linkRequest, linkerServices); 251 Objects.requireNonNull(guardedInvocation); 252 253 int newRelinkCount = relinkCount; 254 // Note that the short-circuited "&&" evaluation below ensures we'll increment the relinkCount until 255 // threshold + 1 but not beyond that. Threshold + 1 is treated as a special value to signal that resetAndRelink 256 // has already executed once for the unstable call site; we only want the call site to throw away its current 257 // linkage once, when it transitions to unstable. 258 if(unstableDetectionEnabled && newRelinkCount <= unstableRelinkThreshold && newRelinkCount++ == unstableRelinkThreshold) { 259 callSite.resetAndRelink(guardedInvocation, createRelinkAndInvokeMethod(callSite, newRelinkCount)); 260 } else { 261 callSite.relink(guardedInvocation, createRelinkAndInvokeMethod(callSite, newRelinkCount)); 262 } 263 if(syncOnRelink) { 264 MutableCallSite.syncAll(new MutableCallSite[] { (MutableCallSite)callSite }); 265 } 266 return guardedInvocation.getInvocation(); 267 } 268 269 /** 270 * Returns a stack trace element describing the location of the 271 * {@code invokedynamic} call site currently being linked on the current 272 * thread. The operation is potentially expensive as it needs to generate a 273 * stack trace to inspect it and is intended for use in diagnostics code. 274 * For "free-floating" call sites (not associated with an 275 * {@code invokedynamic} instruction), the result is not well-defined. 276 * 277 * @return a stack trace element describing the location of the call site 278 * currently being linked, or null if it is not invoked while a call 279 * site is being linked. 280 */ getLinkedCallSiteLocation()281 public static StackTraceElement getLinkedCallSiteLocation() { 282 return stackWalker.walk(s -> s 283 // Find one of our linking entry points on the stack... 284 .dropWhile(f -> !(isRelinkFrame(f) || isInitialLinkFrame(f))) 285 .skip(1) 286 // ... then look for the first thing calling it that isn't j.l.invoke 287 .dropWhile(f -> f.getClassName().startsWith(INVOKE_PACKAGE_PREFIX)) 288 .findFirst() 289 .map(StackFrame::toStackTraceElement) 290 .orElse(null) 291 ); 292 } 293 294 /** 295 * Returns {@code true} if the frame represents {@code MethodHandleNatives.linkCallSite()}, 296 * the frame immediately on top of the call site frame when the call site is 297 * being linked for the first time. 298 * 299 * @param frame the frame 300 * 301 * @return {@code true} if this frame represents {@code MethodHandleNatives.linkCallSite()}. 302 */ isInitialLinkFrame(final StackFrame frame)303 private static boolean isInitialLinkFrame(final StackFrame frame) { 304 return testFrame(frame, INITIAL_LINK_METHOD_NAME, INITIAL_LINK_CLASS_NAME); 305 } 306 307 /** 308 * Returns {@code true} if the frame represents {@code DynamicLinker.relink()}, 309 * the frame immediately on top of the call site frame when the call site is 310 * being relinked (linked for second and subsequent times). 311 * 312 * @param frame the frame 313 * 314 * @return {@code true} if this frame represents {@code DynamicLinker.relink()}. 315 */ isRelinkFrame(final StackFrame frame)316 private static boolean isRelinkFrame(final StackFrame frame) { 317 return testFrame(frame, RELINK_METHOD_NAME, CLASS_NAME); 318 } 319 testFrame(final StackFrame frame, final String methodName, final String className)320 private static boolean testFrame(final StackFrame frame, final String methodName, final String className) { 321 return methodName.equals(frame.getMethodName()) && className.equals(frame.getClassName()); 322 } 323 } 324