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 * @since 1.7
86 */
87 abstract
88 public class CallSite {
89
90 // The actual payload of this call site:
91 /*package-private*/
92 MethodHandle target; // Note: This field is known to the JVM. Do not change.
93
94 /**
95 * Make a blank call site object with the given method type.
96 * An initial target method is supplied which will throw
97 * an {@link IllegalStateException} if called.
98 * <p>
99 * Before this {@code CallSite} object is returned from a bootstrap method,
100 * it is usually provided with a more useful target method,
101 * via a call to {@link CallSite#setTarget(MethodHandle) setTarget}.
102 * @throws NullPointerException if the proposed type is null
103 */
104 /*package-private*/
105 CallSite(MethodType type) {
106 target = makeUninitializedCallSite(type);
107 }
108
109 /**
110 * Make a call site object equipped with an initial target method handle.
111 * @param target the method handle which will be the initial target of the call site
112 * @throws NullPointerException if the proposed target is null
113 */
114 /*package-private*/
115 CallSite(MethodHandle target) {
116 target.type(); // null check
117 this.target = target;
118 }
119
120 /**
121 * Make a call site object equipped with an initial target method handle.
122 * @param targetType the desired type of the call site
123 * @param createTargetHook a hook which will bind the call site to the target method handle
124 * @throws WrongMethodTypeException if the hook cannot be invoked on the required arguments,
125 * or if the target returned by the hook is not of the given {@code targetType}
126 * @throws NullPointerException if the hook returns a null value
127 * @throws ClassCastException if the hook returns something other than a {@code MethodHandle}
128 * @throws Throwable anything else thrown by the hook function
129 */
130 /*package-private*/
131 CallSite(MethodType targetType, MethodHandle createTargetHook) throws Throwable {
132 this(targetType);
133 ConstantCallSite selfCCS = (ConstantCallSite) this;
134 MethodHandle boundTarget = (MethodHandle) createTargetHook.invokeWithArguments(selfCCS);
135 checkTargetChange(this.target, boundTarget);
136 this.target = boundTarget;
137 }
138
139 /**
140 * {@code CallSite} dependency context.
141 * JVM uses CallSite.context to store nmethod dependencies on the call site target.
142 */
143 private final MethodHandleNatives.CallSiteContext context = MethodHandleNatives.CallSiteContext.make(this);
144
145 /**
146 * Returns the type of this call site's target.
147 * Although targets may change, any call site's type is permanent, and can never change to an unequal type.
148 * The {@code setTarget} method enforces this invariant by refusing any new target that does
149 * not have the previous target's type.
150 * @return the type of the current target, which is also the type of any future target
151 */
152 public MethodType type() {
153 // warning: do not call getTarget here, because CCS.getTarget can throw IllegalStateException
154 return target.type();
155 }
156
157 /**
158 * Returns the target method of the call site, according to the
159 * behavior defined by this call site's specific class.
160 * The immediate subclasses of {@code CallSite} document the
161 * class-specific behaviors of this method.
162 *
163 * @return the current linkage state of the call site, its target method handle
164 * @see ConstantCallSite
165 * @see VolatileCallSite
166 * @see #setTarget
167 * @see ConstantCallSite#getTarget
168 * @see MutableCallSite#getTarget
169 * @see VolatileCallSite#getTarget
170 */
171 public abstract MethodHandle getTarget();
172
173 /**
174 * Updates the target method of this 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 * <p>
179 * The type of the new target must be {@linkplain MethodType#equals equal to}
180 * the type of the old target.
181 *
182 * @param newTarget the new target
183 * @throws NullPointerException if the proposed new target is null
184 * @throws WrongMethodTypeException if the proposed new target
185 * has a method type that differs from the previous target
186 * @see CallSite#getTarget
187 * @see ConstantCallSite#setTarget
188 * @see MutableCallSite#setTarget
189 * @see VolatileCallSite#setTarget
190 */
191 public abstract void setTarget(MethodHandle newTarget);
192
193 void checkTargetChange(MethodHandle oldTarget, MethodHandle newTarget) {
194 MethodType oldType = oldTarget.type();
195 MethodType newType = newTarget.type(); // null check!
196 if (!newType.equals(oldType))
197 throw wrongTargetType(newTarget, oldType);
198 }
199
200 private static WrongMethodTypeException wrongTargetType(MethodHandle target, MethodType type) {
201 return new WrongMethodTypeException(String.valueOf(target)+" should be of type "+type);
202 }
203
204 /**
205 * Produces a method handle equivalent to an invokedynamic instruction
206 * which has been linked to this call site.
207 * <p>
208 * This method is equivalent to the following code:
209 * <blockquote><pre>{@code
210 * MethodHandle getTarget, invoker, result;
211 * getTarget = MethodHandles.publicLookup().bind(this, "getTarget", MethodType.methodType(MethodHandle.class));
212 * invoker = MethodHandles.exactInvoker(this.type());
213 * result = MethodHandles.foldArguments(invoker, getTarget)
214 * }</pre></blockquote>
215 *
216 * @return a method handle which always invokes this call site's current target
217 */
218 public abstract MethodHandle dynamicInvoker();
219
220 /*non-public*/ MethodHandle makeDynamicInvoker() {
221 MethodHandle getTarget = getTargetHandle().bindArgumentL(0, this);
222 MethodHandle invoker = MethodHandles.exactInvoker(this.type());
223 return MethodHandles.foldArguments(invoker, getTarget);
224 }
225
226 private static @Stable MethodHandle GET_TARGET;
227 private static MethodHandle getTargetHandle() {
228 MethodHandle handle = GET_TARGET;
229 if (handle != null) {
230 return handle;
231 }
232 try {
233 return GET_TARGET = IMPL_LOOKUP.
234 findVirtual(CallSite.class, "getTarget",
235 MethodType.methodType(MethodHandle.class));
236 } catch (ReflectiveOperationException e) {
237 throw newInternalError(e);
238 }
239 }
240
241 private static @Stable MethodHandle THROW_UCS;
242 private static MethodHandle uninitializedCallSiteHandle() {
243 MethodHandle handle = THROW_UCS;
244 if (handle != null) {
245 return handle;
246 }
247 try {
248 return THROW_UCS = IMPL_LOOKUP.
249 findStatic(CallSite.class, "uninitializedCallSite",
250 MethodType.methodType(Object.class, Object[].class));
251 } catch (ReflectiveOperationException e) {
252 throw newInternalError(e);
253 }
254 }
255
256 /** This guy is rolled into the default target if a MethodType is supplied to the constructor. */
257 private static Object uninitializedCallSite(Object... ignore) {
258 throw new IllegalStateException("uninitialized call site");
259 }
260
261 private MethodHandle makeUninitializedCallSite(MethodType targetType) {
262 MethodType basicType = targetType.basicType();
263 MethodHandle invoker = basicType.form().cachedMethodHandle(MethodTypeForm.MH_UNINIT_CS);
264 if (invoker == null) {
265 invoker = uninitializedCallSiteHandle().asType(basicType);
266 invoker = basicType.form().setCachedMethodHandle(MethodTypeForm.MH_UNINIT_CS, invoker);
267 }
268 // unchecked view is OK since no values will be received or returned
269 return invoker.viewAsType(targetType, false);
270 }
271
272 // unsafe stuff:
273 private static @Stable long TARGET_OFFSET;
274 private static long getTargetOffset() {
275 long offset = TARGET_OFFSET;
276 if (offset > 0) {
277 return offset;
278 }
279 offset = TARGET_OFFSET = UNSAFE.objectFieldOffset(CallSite.class, "target");
280 assert(offset > 0);
281 return offset;
282 }
283
284 /*package-private*/
285 void setTargetNormal(MethodHandle newTarget) {
286 MethodHandleNatives.setCallSiteTargetNormal(this, newTarget);
287 }
288 /*package-private*/
289 MethodHandle getTargetVolatile() {
290 return (MethodHandle) UNSAFE.getObjectVolatile(this, getTargetOffset());
291 }
292 /*package-private*/
293 void setTargetVolatile(MethodHandle newTarget) {
294 MethodHandleNatives.setCallSiteTargetVolatile(this, newTarget);
295 }
296
297 // this implements the upcall from the JVM, MethodHandleNatives.linkCallSite:
298 static CallSite makeSite(MethodHandle bootstrapMethod,
299 // Callee information:
300 String name, MethodType type,
301 // Extra arguments for BSM, if any:
302 Object info,
303 // Caller information:
304 Class<?> callerClass) {
305 CallSite site;
306 try {
307 Object binding = BootstrapMethodInvoker.invoke(
308 CallSite.class, bootstrapMethod, name, type, info, callerClass);
309 if (binding instanceof CallSite) {
310 site = (CallSite) binding;
311 } else {
312 // See the "Linking Exceptions" section for the invokedynamic
313 // instruction in JVMS 6.5.
314 // Throws a runtime exception defining the cause that is then
315 // in the "catch (Throwable ex)" a few lines below wrapped in
316 // BootstrapMethodError
317 throw new ClassCastException("CallSite bootstrap method failed to produce an instance of CallSite");
318 }
319 if (!site.getTarget().type().equals(type)) {
320 // See the "Linking Exceptions" section for the invokedynamic
321 // instruction in JVMS 6.5.
322 // Throws a runtime exception defining the cause that is then
323 // in the "catch (Throwable ex)" a few lines below wrapped in
324 // BootstrapMethodError
325 throw wrongTargetType(site.getTarget(), type);
326 }
327 } catch (Error e) {
328 // Pass through an Error, including BootstrapMethodError, any other
329 // form of linkage error, such as IllegalAccessError if the bootstrap
330 // method is inaccessible, or say ThreadDeath/OutOfMemoryError
331 // See the "Linking Exceptions" section for the invokedynamic
332 // instruction in JVMS 6.5.
333 throw e;
334 } catch (Throwable ex) {
335 // Wrap anything else in BootstrapMethodError
336 throw new BootstrapMethodError("CallSite bootstrap method initialization exception", ex);
337 }
338 return site;
339 }
340 }