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 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>{@code
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 = 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 * 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>{@code
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.bindArgumentL(0, this);
215 MethodHandle invoker = MethodHandles.exactInvoker(this.type());
216 return MethodHandles.foldArguments(invoker, getTarget);
217 }
218
219 private static final MethodHandle GET_TARGET;
220 private static final MethodHandle THROW_UCS;
221 static {
222 try {
223 GET_TARGET = IMPL_LOOKUP.
224 findVirtual(CallSite.class, "getTarget", MethodType.methodType(MethodHandle.class));
225 THROW_UCS = IMPL_LOOKUP.
226 findStatic(CallSite.class, "uninitializedCallSite", MethodType.methodType(Object.class, Object[].class));
227 } catch (ReflectiveOperationException e) {
228 throw newInternalError(e);
229 }
230 }
231
232 /** This guy is rolled into the default target if a MethodType is supplied to the constructor. */
233 private static Object uninitializedCallSite(Object... ignore) {
234 throw new IllegalStateException("uninitialized call site");
235 }
236
237 private MethodHandle makeUninitializedCallSite(MethodType targetType) {
238 MethodType basicType = targetType.basicType();
239 MethodHandle invoker = basicType.form().cachedMethodHandle(MethodTypeForm.MH_UNINIT_CS);
240 if (invoker == null) {
241 invoker = THROW_UCS.asType(basicType);
242 invoker = basicType.form().setCachedMethodHandle(MethodTypeForm.MH_UNINIT_CS, invoker);
243 }
244 // unchecked view is OK since no values will be received or returned
245 return invoker.viewAsType(targetType);
246 }
247
248 // unsafe stuff:
249 private static final long TARGET_OFFSET;
250 static {
251 try {
252 TARGET_OFFSET = UNSAFE.objectFieldOffset(CallSite.class.getDeclaredField("target"));
253 } catch (Exception ex) { throw new Error(ex); }
254 }
255
256 /*package-private*/
257 void setTargetNormal(MethodHandle newTarget) {
258 MethodHandleNatives.setCallSiteTargetNormal(this, newTarget);
259 }
260 /*package-private*/
261 MethodHandle getTargetVolatile() {
262 return (MethodHandle) UNSAFE.getObjectVolatile(this, TARGET_OFFSET);
263 }
264 /*package-private*/
265 void setTargetVolatile(MethodHandle newTarget) {
266 MethodHandleNatives.setCallSiteTargetVolatile(this, newTarget);
267 }
268
269 // this implements the upcall from the JVM, MethodHandleNatives.makeDynamicCallSite:
270 static CallSite makeSite(MethodHandle bootstrapMethod,
271 // Callee information:
272 String name, MethodType type,
273 // Extra arguments for BSM, if any:
274 Object info,
275 // Caller information:
276 Class<?> callerClass) {
277 MethodHandles.Lookup caller = IMPL_LOOKUP.in(callerClass);
278 CallSite site;
279 try {
280 Object binding;
281 info = maybeReBox(info);
282 if (info == null) {
283 binding = bootstrapMethod.invoke(caller, name, type);
284 } else if (!info.getClass().isArray()) {
285 binding = bootstrapMethod.invoke(caller, name, type, info);
286 } else {
287 Object[] argv = (Object[]) info;
288 maybeReBoxElements(argv);
289 switch (argv.length) {
290 case 0:
291 binding = bootstrapMethod.invoke(caller, name, type);
292 break;
293 case 1:
294 binding = bootstrapMethod.invoke(caller, name, type,
295 argv[0]);
296 break;
297 case 2:
298 binding = bootstrapMethod.invoke(caller, name, type,
299 argv[0], argv[1]);
300 break;
301 case 3:
302 binding = bootstrapMethod.invoke(caller, name, type,
303 argv[0], argv[1], argv[2]);
304 break;
305 case 4:
306 binding = bootstrapMethod.invoke(caller, name, type,
307 argv[0], argv[1], argv[2], argv[3]);
308 break;
309 case 5:
310 binding = bootstrapMethod.invoke(caller, name, type,
311 argv[0], argv[1], argv[2], argv[3], argv[4]);
312 break;
313 case 6:
314 binding = bootstrapMethod.invoke(caller, name, type,
315 argv[0], argv[1], argv[2], argv[3], argv[4], argv[5]);
316 break;
317 default:
318 final int NON_SPREAD_ARG_COUNT = 3; // (caller, name, type)
319 if (NON_SPREAD_ARG_COUNT + argv.length > MethodType.MAX_MH_ARITY)
320 throw new BootstrapMethodError("too many bootstrap method arguments");
321 MethodType bsmType = bootstrapMethod.type();
322 MethodType invocationType = MethodType.genericMethodType(NON_SPREAD_ARG_COUNT + argv.length);
323 MethodHandle typedBSM = bootstrapMethod.asType(invocationType);
324 MethodHandle spreader = invocationType.invokers().spreadInvoker(NON_SPREAD_ARG_COUNT);
325 binding = spreader.invokeExact(typedBSM, (Object)caller, (Object)name, (Object)type, argv);
326 }
327 }
328 //System.out.println("BSM for "+name+type+" => "+binding);
329 if (binding instanceof CallSite) {
330 site = (CallSite) binding;
331 } else {
332 throw new ClassCastException("bootstrap method failed to produce a CallSite");
333 }
334 if (!site.getTarget().type().equals(type))
335 throw wrongTargetType(site.getTarget(), type);
336 } catch (Throwable ex) {
337 BootstrapMethodError bex;
338 if (ex instanceof BootstrapMethodError)
339 bex = (BootstrapMethodError) ex;
340 else
341 bex = new BootstrapMethodError("call site initialization exception", ex);
342 throw bex;
343 }
344 return site;
345 }
346
347 private static Object maybeReBox(Object x) {
348 if (x instanceof Integer) {
349 int xi = (int) x;
350 if (xi == (byte) xi)
351 x = xi; // must rebox; see JLS 5.1.7
352 }
353 return x;
354 }
355 private static void maybeReBoxElements(Object[] xa) {
356 for (int i = 0; i < xa.length; i++) {
357 xa[i] = maybeReBox(xa[i]);
358 }
359 }
360 }