1 /*
2 * Copyright (c) 2008, 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 package java.lang.invoke;
27
28 import static java.lang.invoke.MethodHandleStatics.*;
29 import static java.lang.invoke.MethodHandles.Lookup.IMPL_LOOKUP;
30
31 import jdk.internal.vm.annotation.Stable;
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
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 = makeUninitializedCallSite(type);
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 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 * {@code CallSite} dependency context.
140 * JVM uses CallSite.context to store nmethod dependencies on the call site target.
141 */
142 private final MethodHandleNatives.CallSiteContext context = MethodHandleNatives.CallSiteContext.make(this);
143
144 /**
145 * Returns the type of this call site's target.
146 * Although targets may change, any call site's type is permanent, and can never change to an unequal type.
147 * The {@code setTarget} method enforces this invariant by refusing any new target that does
148 * not have the previous target's type.
149 * @return the type of the current target, which is also the type of any future target
150 */
151 public MethodType type() {
152 // warning: do not call getTarget here, because CCS.getTarget can throw IllegalStateException
153 return target.type();
154 }
155
156 /**
157 * Returns the target method of the call site, according to the
158 * behavior defined by this call site's specific class.
159 * The immediate subclasses of {@code CallSite} document the
160 * class-specific behaviors of this method.
161 *
162 * @return the current linkage state of the call site, its target method handle
163 * @see ConstantCallSite
164 * @see VolatileCallSite
165 * @see #setTarget
166 * @see ConstantCallSite#getTarget
167 * @see MutableCallSite#getTarget
168 * @see VolatileCallSite#getTarget
169 */
170 public abstract MethodHandle getTarget();
171
172 /**
173 * Updates the target method of this call site, according to the
174 * behavior defined by this call site's specific class.
175 * The immediate subclasses of {@code CallSite} document the
176 * class-specific behaviors of this method.
177 * <p>
178 * The type of the new target must be {@linkplain MethodType#equals equal to}
179 * the type of the old target.
180 *
181 * @param newTarget the new target
182 * @throws NullPointerException if the proposed new target is null
183 * @throws WrongMethodTypeException if the proposed new target
184 * has a method type that differs from the previous target
185 * @see CallSite#getTarget
186 * @see ConstantCallSite#setTarget
187 * @see MutableCallSite#setTarget
188 * @see VolatileCallSite#setTarget
189 */
190 public abstract void setTarget(MethodHandle newTarget);
191
192 void checkTargetChange(MethodHandle oldTarget, MethodHandle newTarget) {
193 MethodType oldType = oldTarget.type();
194 MethodType newType = newTarget.type(); // null check!
195 if (!newType.equals(oldType))
196 throw wrongTargetType(newTarget, oldType);
197 }
198
199 private static WrongMethodTypeException wrongTargetType(MethodHandle target, MethodType type) {
200 return new WrongMethodTypeException(String.valueOf(target)+" should be of type "+type);
201 }
202
203 /**
204 * Produces a method handle equivalent to an invokedynamic instruction
205 * which has been linked to this call site.
206 * <p>
207 * This method is equivalent to the following code:
208 * <blockquote><pre>{@code
209 * MethodHandle getTarget, invoker, result;
210 * getTarget = MethodHandles.publicLookup().bind(this, "getTarget", MethodType.methodType(MethodHandle.class));
211 * invoker = MethodHandles.exactInvoker(this.type());
212 * result = MethodHandles.foldArguments(invoker, getTarget)
213 * }</pre></blockquote>
214 *
215 * @return a method handle which always invokes this call site's current target
216 */
217 public abstract MethodHandle dynamicInvoker();
218
219 /*non-public*/ MethodHandle makeDynamicInvoker() {
220 MethodHandle getTarget = getTargetHandle().bindArgumentL(0, this);
221 MethodHandle invoker = MethodHandles.exactInvoker(this.type());
222 return MethodHandles.foldArguments(invoker, getTarget);
223 }
224
225 private static @Stable MethodHandle GET_TARGET;
226 private static MethodHandle getTargetHandle() {
227 MethodHandle handle = GET_TARGET;
228 if (handle != null) {
229 return handle;
230 }
231 try {
232 return GET_TARGET = IMPL_LOOKUP.
233 findVirtual(CallSite.class, "getTarget",
234 MethodType.methodType(MethodHandle.class));
235 } catch (ReflectiveOperationException e) {
236 throw newInternalError(e);
237 }
238 }
239
240 private static @Stable MethodHandle THROW_UCS;
241 private static MethodHandle uninitializedCallSiteHandle() {
242 MethodHandle handle = THROW_UCS;
243 if (handle != null) {
244 return handle;
245 }
246 try {
247 return THROW_UCS = IMPL_LOOKUP.
248 findStatic(CallSite.class, "uninitializedCallSite",
249 MethodType.methodType(Object.class, Object[].class));
250 } catch (ReflectiveOperationException e) {
251 throw newInternalError(e);
252 }
253 }
254
255 /** This guy is rolled into the default target if a MethodType is supplied to the constructor. */
256 private static Object uninitializedCallSite(Object... ignore) {
257 throw new IllegalStateException("uninitialized call site");
258 }
259
260 private MethodHandle makeUninitializedCallSite(MethodType targetType) {
261 MethodType basicType = targetType.basicType();
262 MethodHandle invoker = basicType.form().cachedMethodHandle(MethodTypeForm.MH_UNINIT_CS);
263 if (invoker == null) {
264 invoker = uninitializedCallSiteHandle().asType(basicType);
265 invoker = basicType.form().setCachedMethodHandle(MethodTypeForm.MH_UNINIT_CS, invoker);
266 }
267 // unchecked view is OK since no values will be received or returned
268 return invoker.viewAsType(targetType, false);
269 }
270
271 // unsafe stuff:
272 private static @Stable long TARGET_OFFSET;
273 private static long getTargetOffset() {
274 long offset = TARGET_OFFSET;
275 if (offset > 0) {
276 return offset;
277 }
278 try {
279 offset = TARGET_OFFSET = UNSAFE.objectFieldOffset(CallSite.class.getDeclaredField("target"));
280 assert(offset > 0);
281 return offset;
282 } catch (Exception ex) { throw newInternalError(ex); }
283 }
284
285 /*package-private*/
286 void setTargetNormal(MethodHandle newTarget) {
287 MethodHandleNatives.setCallSiteTargetNormal(this, newTarget);
288 }
289 /*package-private*/
290 MethodHandle getTargetVolatile() {
291 return (MethodHandle) UNSAFE.getObjectVolatile(this, getTargetOffset());
292 }
293 /*package-private*/
294 void setTargetVolatile(MethodHandle newTarget) {
295 MethodHandleNatives.setCallSiteTargetVolatile(this, newTarget);
296 }
297
298 // this implements the upcall from the JVM, MethodHandleNatives.linkCallSite:
299 static CallSite makeSite(MethodHandle bootstrapMethod,
300 // Callee information:
301 String name, MethodType type,
302 // Extra arguments for BSM, if any:
303 Object info,
304 // Caller information:
305 Class<?> callerClass) {
306 MethodHandles.Lookup caller = IMPL_LOOKUP.in(callerClass);
307 CallSite site;
308 try {
309 Object binding;
310 info = maybeReBox(info);
311 if (info == null) {
312 binding = bootstrapMethod.invoke(caller, name, type);
313 } else if (!info.getClass().isArray()) {
314 binding = bootstrapMethod.invoke(caller, name, type, info);
315 } else {
316 Object[] argv = (Object[]) info;
317 maybeReBoxElements(argv);
318 switch (argv.length) {
319 case 0:
320 binding = bootstrapMethod.invoke(caller, name, type);
321 break;
322 case 1:
323 binding = bootstrapMethod.invoke(caller, name, type,
324 argv[0]);
325 break;
326 case 2:
327 binding = bootstrapMethod.invoke(caller, name, type,
328 argv[0], argv[1]);
329 break;
330 case 3:
331 binding = bootstrapMethod.invoke(caller, name, type,
332 argv[0], argv[1], argv[2]);
333 break;
334 case 4:
335 binding = bootstrapMethod.invoke(caller, name, type,
336 argv[0], argv[1], argv[2], argv[3]);
337 break;
338 case 5:
339 binding = bootstrapMethod.invoke(caller, name, type,
340 argv[0], argv[1], argv[2], argv[3], argv[4]);
341 break;
342 case 6:
343 binding = bootstrapMethod.invoke(caller, name, type,
344 argv[0], argv[1], argv[2], argv[3], argv[4], argv[5]);
345 break;
346 default:
347 final int NON_SPREAD_ARG_COUNT = 3; // (caller, name, type)
348 if (NON_SPREAD_ARG_COUNT + argv.length > MethodType.MAX_MH_ARITY)
349 throw new BootstrapMethodError("too many bootstrap method arguments");
350
351 MethodType invocationType = MethodType.genericMethodType(NON_SPREAD_ARG_COUNT + argv.length);
352 MethodHandle typedBSM = bootstrapMethod.asType(invocationType);
353 MethodHandle spreader = invocationType.invokers().spreadInvoker(NON_SPREAD_ARG_COUNT);
354 binding = spreader.invokeExact(typedBSM, (Object) caller, (Object) name, (Object) type, argv);
355 }
356 }
357 if (binding instanceof CallSite) {
358 site = (CallSite) binding;
359 } else {
360 // See the "Linking Exceptions" section for the invokedynamic
361 // instruction in JVMS 6.5.
362 // Throws a runtime exception defining the cause that is then
363 // in the "catch (Throwable ex)" a few lines below wrapped in
364 // BootstrapMethodError
365 throw new ClassCastException("bootstrap method failed to produce a CallSite");
366 }
367 if (!site.getTarget().type().equals(type)) {
368 // See the "Linking Exceptions" section for the invokedynamic
369 // instruction in JVMS 6.5.
370 // Throws a runtime exception defining the cause that is then
371 // in the "catch (Throwable ex)" a few lines below wrapped in
372 // BootstrapMethodError
373 throw wrongTargetType(site.getTarget(), type);
374 }
375 } catch (Error e) {
376 // Pass through an Error, including BootstrapMethodError, any other
377 // form of linkage error, such as IllegalAccessError if the bootstrap
378 // method is inaccessible, or say ThreadDeath/OutOfMemoryError
379 // See the "Linking Exceptions" section for the invokedynamic
380 // instruction in JVMS 6.5.
381 throw e;
382 } catch (Throwable ex) {
383 // Wrap anything else in BootstrapMethodError
384 throw new BootstrapMethodError("call site initialization exception", ex);
385 }
386 return site;
387 }
388
389 private static Object maybeReBox(Object x) {
390 if (x instanceof Integer) {
391 int xi = (int) x;
392 if (xi == (byte) xi)
393 x = xi; // must rebox; see JLS 5.1.7
394 }
395 return x;
396 }
397 private static void maybeReBoxElements(Object[] xa) {
398 for (int i = 0; i < xa.length; i++) {
399 xa[i] = maybeReBox(xa[i]);
400 }
401 }
402 }