2 * Copyright (c) 2019 PANTHEON.tech, s.r.o. and others. All rights reserved.
4 * This program and the accompanying materials are made available under the
5 * terms of the Eclipse Public License v1.0 which accompanies this distribution,
6 * and is available at http://www.eclipse.org/legal/epl-v10.html
8 package org.opendaylight.mdsal.binding.dom.codec.impl;
10 import static com.google.common.base.Verify.verify;
11 import static com.google.common.base.Verify.verifyNotNull;
12 import static java.util.Objects.requireNonNull;
13 import static net.bytebuddy.implementation.bytecode.member.MethodVariableAccess.loadThis;
14 import static org.opendaylight.mdsal.binding.dom.codec.impl.ByteBuddyUtils.getField;
15 import static org.opendaylight.mdsal.binding.dom.codec.impl.ByteBuddyUtils.invokeMethod;
16 import static org.opendaylight.mdsal.binding.dom.codec.impl.ByteBuddyUtils.putField;
18 import com.google.common.collect.ImmutableMap;
19 import java.lang.invoke.MethodHandles;
20 import java.lang.invoke.MethodHandles.Lookup;
21 import java.lang.invoke.VarHandle;
22 import java.lang.reflect.Method;
24 import java.util.Map.Entry;
25 import java.util.Optional;
26 import net.bytebuddy.ByteBuddy;
27 import net.bytebuddy.description.field.FieldDescription;
28 import net.bytebuddy.description.type.TypeDefinition;
29 import net.bytebuddy.description.type.TypeDescription;
30 import net.bytebuddy.description.type.TypeDescription.ForLoadedType;
31 import net.bytebuddy.description.type.TypeDescription.Generic;
32 import net.bytebuddy.dynamic.DynamicType.Builder;
33 import net.bytebuddy.dynamic.scaffold.InstrumentedType;
34 import net.bytebuddy.implementation.Implementation;
35 import net.bytebuddy.implementation.bytecode.ByteCodeAppender;
36 import net.bytebuddy.implementation.bytecode.StackManipulation;
37 import net.bytebuddy.implementation.bytecode.assign.TypeCasting;
38 import net.bytebuddy.implementation.bytecode.constant.ClassConstant;
39 import net.bytebuddy.implementation.bytecode.constant.TextConstant;
40 import net.bytebuddy.implementation.bytecode.member.MethodReturn;
41 import net.bytebuddy.implementation.bytecode.member.MethodVariableAccess;
42 import net.bytebuddy.jar.asm.Opcodes;
43 import org.eclipse.jdt.annotation.Nullable;
44 import org.opendaylight.mdsal.binding.dom.codec.impl.ClassGeneratorBridge.CodecContextSupplierProvider;
45 import org.opendaylight.mdsal.binding.dom.codec.impl.ClassGeneratorBridge.LocalNameProvider;
46 import org.opendaylight.mdsal.binding.loader.BindingClassLoader;
47 import org.opendaylight.mdsal.binding.loader.BindingClassLoader.ClassGenerator;
48 import org.opendaylight.mdsal.binding.loader.BindingClassLoader.GeneratorResult;
49 import org.opendaylight.yangtools.yang.binding.contract.Naming;
50 import org.slf4j.Logger;
51 import org.slf4j.LoggerFactory;
54 * Private support for generating {@link CodecDataObject} and {@link AugmentableCodecDataObject} specializations.
57 * Code generation here is probably more involved than usual mainly due to the fact we *really* want to express the
58 * strong connection between a generated class to the extent possible. In most cases (grouping-generated types) this
59 * involves one level of indirection, which is a safe approach. If we are dealing with a type generated outside of a
60 * grouping statement, though, we are guaranteed instantiation-invariance and hence can hard-wire to a runtime-constant
61 * {@link CodecContextSupplier} -- which provides significant boost to JITs ability to optimize code -- especially with
62 * inlining and constant propagation.
65 * The accessor mapping performance is critical due to users typically not taking care of storing the results acquired
66 * by an invocation, assuming the accessors are backed by a normal field -- which of course is not true, as the results
67 * are lazily computed.
70 * The design is such that for a particular structure like:
78 * we end up generating a class with the following layout:
80 * public final class Foo$$$codecImpl extends CodecDataObject implements Foo {
81 * private static final VarHandle getBar$$$V;
82 * private volatile Object getBar;
84 * public Foo$$$codecImpl(DistinctNodeContainer data) {
88 * public Bar getBar() {
89 * return (Bar) codecMember(getBar$$$V, "bar");
95 * This strategy minimizes the bytecode footprint and follows the generally good idea of keeping common logic in a
96 * single place in a maintainable form. The glue code is extremely light (~6 instructions), which is beneficial on both
97 * sides of invocation:
99 * <li>generated method can readily be inlined into the caller</li>
100 * <li>it forms a call site into which codeMember() can be inlined with VarHandle being constant</li>
104 * The second point is important here, as it allows the invocation logic around VarHandle to completely disappear,
105 * becoming synonymous with operations on a field. Even though the field itself is declared as volatile, it is only ever
106 * accessed through helper method using VarHandles -- and those helpers are using relaxed field ordering
107 * of {@code getAcquire()}/{@code setRelease()} memory semantics.
110 * Furthermore there are distinct {@code codecMember} methods, each of which supports a different invocation style:
112 * <li>with {@code String}, which ends up looking up a {@link ValueNodeCodecContext}</li>
113 * <li>with {@code Class}, which ends up looking up a {@link DataContainerCodecContext}</li>
114 * <li>with {@code NodeContextSupplier}, which performs a direct load</li>
116 * The third mode of operation requires that the object being implemented is not defined in a {@code grouping}, because
117 * it welds the object to a particular namespace -- hence it trades namespace mobility for access speed.
120 * The sticky point here is the NodeContextSupplier, as it is a heap object which cannot normally be looked up from the
121 * static context in which the static class initializer operates -- so we need perform some sort of a trick here.
122 * Even though ByteBuddy provides facilities for bridging references to type fields, those facilities operate on
123 * volatile fields -- hence they do not quite work for us.
126 * Another alternative, which we used in Javassist-generated DataObjectSerializers, is to muck with the static field
127 * using reflection -- which works, but requires redefinition of Field.modifiers, which is something Java 9+ complains
128 * about quite noisily.
131 * We take a different approach here, which takes advantage of the fact we are in control of both code generation (here)
132 * and class loading (in {@link BindingClassLoader}). The process is performed in four steps:
134 * <li>During code generation, the context fields are pointed towards
135 * {@link ClassGeneratorBridge#resolveCodecContextSupplier(String)} and
136 * {@link ClassGeneratorBridge#resolveKey(String)} methods, which are public and static, hence perfectly usable
137 * in the context of a class initializer.</li>
138 * <li>During class loading of generated byte code, the original instance of the generator is called to wrap the actual
139 * class loading operation. At this point the generator installs itself as the current generator for this thread via
140 * {@link ClassGeneratorBridge#setup(CodecDataObjectGenerator)} and allows the class to be loaded.
141 * <li>After the class has been loaded, but before the call returns, we will force the class to initialize, at which
142 * point the static invocations will be redirected to {@link #resolveCodecContextSupplier(String)} and
143 * {@link #resolveKey(String)} methods, thus initializing the fields to the intended constants.</li>
144 * <li>Before returning from the class loading call, the generator will detach itself via
145 * {@link ClassGeneratorBridge#tearDown(CodecDataObjectGenerator)}.</li>
149 * This strategy works due to close cooperation with the target ClassLoader, as the entire code generation and loading
150 * block runs with the class loading lock for this FQCN and the reference is not leaked until the process completes.
152 abstract class CodecDataObjectGenerator<T extends CodecDataObject<?>> implements ClassGenerator<T> {
153 // Not reusable definition: we can inline NodeContextSuppliers without a problem
154 // FIXME: MDSAL-443: wire this implementation, which requires that BindingRuntimeTypes provides information about
155 // types being generated from within a grouping
156 private static final class Fixed<T extends CodecDataObject<?>> extends CodecDataObjectGenerator<T>
157 implements CodecContextSupplierProvider<T> {
158 private final ImmutableMap<Method, CodecContextSupplier> properties;
160 Fixed(final TypeDescription superClass, final ImmutableMap<Method, CodecContextSupplier> properties,
161 final @Nullable Method keyMethod) {
162 super(superClass, keyMethod);
163 this.properties = requireNonNull(properties);
167 Builder<T> generateGetters(final Builder<T> builder) {
168 Builder<T> tmp = builder;
169 for (Method method : properties.keySet()) {
170 LOG.trace("Generating for fixed method {}", method);
171 final String methodName = method.getName();
172 final TypeDescription retType = ForLoadedType.of(method.getReturnType());
173 tmp = tmp.defineMethod(methodName, retType, PUB_FINAL).intercept(
174 new SupplierGetterMethodImplementation(methodName, retType));
180 public CodecContextSupplier resolveCodecContextSupplier(final String methodName) {
181 final Optional<Entry<Method, CodecContextSupplier>> found = properties.entrySet().stream()
182 .filter(entry -> methodName.equals(entry.getKey().getName())).findAny();
183 verify(found.isPresent(), "Failed to find property for %s in %s", methodName, this);
184 return verifyNotNull(found.orElseThrow().getValue());
188 // Reusable definition: we have to rely on context lookups
189 private static final class Reusable<T extends CodecDataObject<?>> extends CodecDataObjectGenerator<T>
190 implements LocalNameProvider<T> {
191 private final ImmutableMap<Method, ValueNodeCodecContext> simpleProperties;
192 private final Map<Class<?>, PropertyInfo> daoProperties;
194 Reusable(final TypeDescription superClass, final ImmutableMap<Method, ValueNodeCodecContext> simpleProperties,
195 final Map<Class<?>, PropertyInfo> daoProperties, final @Nullable Method keyMethod) {
196 super(superClass, keyMethod);
197 this.simpleProperties = requireNonNull(simpleProperties);
198 this.daoProperties = requireNonNull(daoProperties);
202 Builder<T> generateGetters(final Builder<T> builder) {
203 Builder<T> tmp = builder;
204 for (Method method : simpleProperties.keySet()) {
205 LOG.trace("Generating for simple method {}", method);
206 final String methodName = method.getName();
207 final TypeDescription retType = ForLoadedType.of(method.getReturnType());
208 tmp = tmp.defineMethod(methodName, retType, PUB_FINAL).intercept(
209 new SimpleGetterMethodImplementation(methodName, retType));
211 for (Entry<Class<?>, PropertyInfo> entry : daoProperties.entrySet()) {
212 final PropertyInfo info = entry.getValue();
213 final Method method = info.getterMethod();
214 LOG.trace("Generating for structured method {}", method);
215 final String methodName = method.getName();
216 final TypeDescription retType = ForLoadedType.of(method.getReturnType());
217 tmp = tmp.defineMethod(methodName, retType, PUB_FINAL).intercept(
218 new StructuredGetterMethodImplementation(methodName, retType, entry.getKey()));
220 if (info instanceof PropertyInfo.GetterAndNonnull orEmpty) {
221 final String nonnullName = orEmpty.nonnullMethod().getName();
222 tmp = tmp.defineMethod(nonnullName, retType, PUB_FINAL).intercept(
223 new NonnullMethodImplementation(nonnullName, retType, entry.getKey(), method));
231 public String resolveLocalName(final String methodName) {
232 final Optional<Entry<Method, ValueNodeCodecContext>> found = simpleProperties.entrySet().stream()
233 .filter(entry -> methodName.equals(entry.getKey().getName())).findAny();
234 verify(found.isPresent(), "Failed to find property for %s in %s", methodName, this);
235 return found.orElseThrow().getValue().getSchema().getQName().getLocalName();
239 private static final Logger LOG = LoggerFactory.getLogger(CodecDataObjectGenerator.class);
240 private static final Generic BB_BOOLEAN = TypeDefinition.Sort.describe(boolean.class);
241 private static final Generic BB_OBJECT = TypeDefinition.Sort.describe(Object.class);
242 private static final Generic BB_INT = TypeDefinition.Sort.describe(int.class);
243 private static final Generic BB_STRING = TypeDefinition.Sort.describe(String.class);
244 private static final TypeDescription BB_CDO = ForLoadedType.of(CodecDataObject.class);
245 private static final TypeDescription BB_ACDO = ForLoadedType.of(AugmentableCodecDataObject.class);
247 private static final StackManipulation FIRST_ARG_REF = MethodVariableAccess.REFERENCE.loadFrom(1);
249 private static final int PROT_FINAL = Opcodes.ACC_PROTECTED | Opcodes.ACC_FINAL | Opcodes.ACC_SYNTHETIC;
250 private static final int PUB_FINAL = Opcodes.ACC_PUBLIC | Opcodes.ACC_FINAL | Opcodes.ACC_SYNTHETIC;
252 private static final ByteBuddy BB = new ByteBuddy();
254 private final TypeDescription superClass;
255 private final Method keyMethod;
257 CodecDataObjectGenerator(final TypeDescription superClass, final @Nullable Method keyMethod) {
258 this.superClass = requireNonNull(superClass);
259 this.keyMethod = keyMethod;
262 static <T extends CodecDataObject<T>> Class<T> generate(final BindingClassLoader loader,
263 final Class<?> bindingInterface, final ImmutableMap<Method, ValueNodeCodecContext> simpleProperties,
264 final Map<Class<?>, PropertyInfo> daoProperties, final Method keyMethod) {
265 return CodecPackage.CODEC.generateClass(loader, bindingInterface,
266 new Reusable<>(BB_CDO, simpleProperties, daoProperties, keyMethod));
269 static <T extends CodecDataObject<T>> Class<T> generateAugmentable(final BindingClassLoader loader,
270 final Class<?> bindingInterface, final ImmutableMap<Method, ValueNodeCodecContext> simpleProperties,
271 final Map<Class<?>, PropertyInfo> daoProperties, final Method keyMethod) {
272 return CodecPackage.CODEC.generateClass(loader, bindingInterface,
273 new Reusable<>(BB_ACDO, simpleProperties, daoProperties, keyMethod));
277 public final GeneratorResult<T> generateClass(final BindingClassLoader loader, final String fqcn,
278 final Class<?> bindingInterface) {
279 LOG.trace("Generating class {}", fqcn);
281 final Generic bindingDef = TypeDefinition.Sort.describe(bindingInterface);
282 @SuppressWarnings("unchecked")
283 Builder<T> builder = (Builder<T>) BB.subclass(Generic.Builder.parameterizedType(superClass, bindingDef).build())
284 .name(fqcn).implement(bindingDef);
286 builder = generateGetters(builder);
288 if (keyMethod != null) {
289 LOG.trace("Generating for key {}", keyMethod);
290 final String methodName = keyMethod.getName();
291 final TypeDescription retType = ForLoadedType.of(keyMethod.getReturnType());
292 builder = builder.defineMethod(methodName, retType, PUB_FINAL).intercept(
293 new KeyMethodImplementation(methodName, retType));
297 return GeneratorResult.of(builder
298 // codecHashCode() ...
299 .defineMethod("codecHashCode", BB_INT, PROT_FINAL)
300 .intercept(codecHashCode(bindingInterface))
301 // ... equals(Object) ...
302 .defineMethod("codecEquals", BB_BOOLEAN, PROT_FINAL).withParameter(BB_OBJECT)
303 .intercept(codecEquals(bindingInterface))
304 // ... toString() ...
305 .defineMethod("toString", BB_STRING, PUB_FINAL)
306 .intercept(toString(bindingInterface))
311 abstract Builder<T> generateGetters(Builder<T> builder);
313 private static Implementation codecHashCode(final Class<?> bindingInterface) {
314 return new Implementation.Simple(
315 // return Foo.bindingHashCode(this);
317 invokeMethod(bindingInterface, Naming.BINDING_HASHCODE_NAME, bindingInterface),
318 MethodReturn.INTEGER);
321 private static Implementation codecEquals(final Class<?> bindingInterface) {
322 return new Implementation.Simple(
323 // return Foo.bindingEquals(this, obj);
326 invokeMethod(bindingInterface, Naming.BINDING_EQUALS_NAME, bindingInterface, Object.class),
327 MethodReturn.INTEGER);
330 private static Implementation toString(final Class<?> bindingInterface) {
331 return new Implementation.Simple(
332 // return Foo.bindingToString(this);
334 invokeMethod(bindingInterface, Naming.BINDING_TO_STRING_NAME, bindingInterface),
335 MethodReturn.REFERENCE);
338 private abstract static class AbstractMethodImplementation implements Implementation {
339 final TypeDescription retType;
341 final String methodName;
343 AbstractMethodImplementation(final String methodName, final TypeDescription retType) {
344 this.methodName = requireNonNull(methodName);
345 this.retType = requireNonNull(retType);
349 private abstract static class AbstractCachedMethodImplementation extends AbstractMethodImplementation {
350 private static final Generic BB_HANDLE = TypeDefinition.Sort.describe(VarHandle.class);
351 private static final Generic BB_OBJECT = TypeDefinition.Sort.describe(Object.class);
352 private static final StackManipulation OBJECT_CLASS = ClassConstant.of(ForLoadedType.of(Object.class));
353 private static final StackManipulation LOOKUP = invokeMethod(MethodHandles.class, "lookup");
354 private static final StackManipulation FIND_VAR_HANDLE = invokeMethod(Lookup.class,
355 "findVarHandle", Class.class, String.class, Class.class);
357 static final int PRIV_CONST = Opcodes.ACC_PRIVATE | Opcodes.ACC_STATIC | Opcodes.ACC_FINAL
358 | Opcodes.ACC_SYNTHETIC;
359 private static final int PRIV_VOLATILE = Opcodes.ACC_PRIVATE | Opcodes.ACC_VOLATILE | Opcodes.ACC_SYNTHETIC;
362 final String handleName;
364 AbstractCachedMethodImplementation(final String methodName, final TypeDescription retType) {
365 super(methodName, retType);
366 handleName = methodName + "$$$V";
370 public InstrumentedType prepare(final InstrumentedType instrumentedType) {
371 final InstrumentedType tmp = instrumentedType
372 // private static final VarHandle getFoo$$$V;
373 .withField(new FieldDescription.Token(handleName, PRIV_CONST, BB_HANDLE))
374 // private volatile Object getFoo;
375 .withField(new FieldDescription.Token(methodName, PRIV_VOLATILE, BB_OBJECT));
377 return tmp.withInitializer(new ByteCodeAppender.Simple(
378 // TODO: acquiring lookup is expensive, we should share it across all initialization
379 // getFoo$$$V = MethodHandles.lookup().findVarHandle(This.class, "getFoo", Object.class);
381 ClassConstant.of(tmp),
382 new TextConstant(methodName),
385 putField(tmp, handleName)));
389 private static final class KeyMethodImplementation extends AbstractCachedMethodImplementation {
390 private static final StackManipulation CODEC_KEY = invokeMethod(CodecDataObject.class,
391 "codecKey", VarHandle.class);
393 KeyMethodImplementation(final String methodName, final TypeDescription retType) {
394 super(methodName, retType);
398 public ByteCodeAppender appender(final Target implementationTarget) {
399 return new ByteCodeAppender.Simple(
400 // return (FooType) codecKey(getFoo$$$V);
402 getField(implementationTarget.getInstrumentedType(), handleName),
404 TypeCasting.to(retType),
405 MethodReturn.REFERENCE);
409 private static final class NonnullMethodImplementation extends AbstractMethodImplementation {
410 private static final StackManipulation NONNULL_MEMBER = invokeMethod(CodecDataObject.class,
411 "codecMemberOrEmpty", Object.class, Class.class);
413 private final Class<?> bindingClass;
414 private final Method getterMethod;
416 NonnullMethodImplementation(final String methodName, final TypeDescription retType,
417 final Class<?> bindingClass, final Method getterMethod) {
418 super(methodName, retType);
419 this.bindingClass = requireNonNull(bindingClass);
420 this.getterMethod = requireNonNull(getterMethod);
424 public ByteCodeAppender appender(final Target implementationTarget) {
425 return new ByteCodeAppender.Simple(
426 // return (FooType) codecMemberOrEmpty(getFoo(), FooType.class)
429 invokeMethod(getterMethod),
430 ClassConstant.of(TypeDefinition.Sort.describe(bindingClass).asErasure()),
432 TypeCasting.to(retType),
433 MethodReturn.REFERENCE);
437 public InstrumentedType prepare(final InstrumentedType instrumentedType) {
439 return instrumentedType;
444 * A simple leaf method, which looks up child by a String constant. This is slightly more complicated because we
445 * want to make sure we are using the same String instance as the one stored in associated DataObjectCodecContext,
446 * so that during lookup we perform an identity check instead of comparing content -- speeding things up as well
447 * as minimizing footprint. Since that string is not guaranteed to be interned in the String Pool, we cannot rely
448 * on the constant pool entry to resolve to the same object.
450 private static final class SimpleGetterMethodImplementation extends AbstractCachedMethodImplementation {
451 private static final StackManipulation CODEC_MEMBER = invokeMethod(CodecDataObject.class,
452 "codecMember", VarHandle.class, String.class);
453 private static final StackManipulation BRIDGE_RESOLVE = invokeMethod(ClassGeneratorBridge.class,
454 "resolveLocalName", String.class);
455 private static final Generic BB_STRING = TypeDefinition.Sort.describe(String.class);
458 private final String stringName;
460 SimpleGetterMethodImplementation(final String methodName, final TypeDescription retType) {
461 super(methodName, retType);
462 stringName = methodName + "$$$S";
466 public InstrumentedType prepare(final InstrumentedType instrumentedType) {
467 final InstrumentedType tmp = super.prepare(instrumentedType)
468 // private static final String getFoo$$$S;
469 .withField(new FieldDescription.Token(stringName, PRIV_CONST, BB_STRING));
471 return tmp.withInitializer(new ByteCodeAppender.Simple(
472 // getFoo$$$S = CodecDataObjectBridge.resolveString("getFoo");
473 new TextConstant(methodName),
475 putField(tmp, stringName)));
479 public ByteCodeAppender appender(final Target implementationTarget) {
480 final TypeDescription instrumentedType = implementationTarget.getInstrumentedType();
481 return new ByteCodeAppender.Simple(
482 // return (FooType) codecMember(getFoo$$$V, getFoo$$$S);
484 getField(instrumentedType, handleName),
485 getField(instrumentedType, stringName),
487 TypeCasting.to(retType),
488 MethodReturn.REFERENCE);
492 private static final class StructuredGetterMethodImplementation extends AbstractCachedMethodImplementation {
493 private static final StackManipulation CODEC_MEMBER = invokeMethod(CodecDataObject.class,
494 "codecMember", VarHandle.class, Class.class);
496 private final Class<?> bindingClass;
498 StructuredGetterMethodImplementation(final String methodName, final TypeDescription retType,
499 final Class<?> bindingClass) {
500 super(methodName, retType);
501 this.bindingClass = requireNonNull(bindingClass);
505 public ByteCodeAppender appender(final Target implementationTarget) {
506 return new ByteCodeAppender.Simple(
507 // return (FooType) codecMember(getFoo$$$V, FooType.class);
509 getField(implementationTarget.getInstrumentedType(), handleName),
510 ClassConstant.of(TypeDefinition.Sort.describe(bindingClass).asErasure()),
512 TypeCasting.to(retType),
513 MethodReturn.REFERENCE);
517 private static final class SupplierGetterMethodImplementation extends AbstractCachedMethodImplementation {
518 private static final StackManipulation CODEC_MEMBER = invokeMethod(CodecDataObject.class,
519 "codecMember", VarHandle.class, CodecContextSupplier.class);
520 private static final StackManipulation BRIDGE_RESOLVE = invokeMethod(ClassGeneratorBridge.class,
521 "resolveNodeContextSupplier", String.class);
522 private static final Generic BB_NCS = TypeDefinition.Sort.describe(CodecContextSupplier.class);
525 private final String contextName;
527 SupplierGetterMethodImplementation(final String methodName, final TypeDescription retType) {
528 super(methodName, retType);
529 contextName = methodName + "$$$C";
533 public InstrumentedType prepare(final InstrumentedType instrumentedType) {
534 final InstrumentedType tmp = super.prepare(instrumentedType)
535 // private static final NodeContextSupplier getFoo$$$C;
536 .withField(new FieldDescription.Token(contextName, PRIV_CONST, BB_NCS));
538 return tmp.withInitializer(new ByteCodeAppender.Simple(
539 // getFoo$$$C = CodecDataObjectBridge.resolve("getFoo");
540 new TextConstant(methodName),
542 putField(tmp, contextName)));
546 public ByteCodeAppender appender(final Target implementationTarget) {
547 final TypeDescription instrumentedType = implementationTarget.getInstrumentedType();
548 return new ByteCodeAppender.Simple(
549 // return (FooType) codecMember(getFoo$$$V, getFoo$$$C);
551 getField(instrumentedType, handleName),
552 getField(instrumentedType, contextName),
554 TypeCasting.to(retType),
555 MethodReturn.REFERENCE);