1 /*
   2  * Copyright (c) 2008, 2018, 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 jdk.internal.misc.Unsafe;
  29 import jdk.internal.vm.annotation.ForceInline;
  30 import jdk.internal.vm.annotation.Stable;
  31 import sun.invoke.util.ValueConversions;
  32 import sun.invoke.util.VerifyAccess;
  33 import sun.invoke.util.VerifyType;
  34 import sun.invoke.util.Wrapper;
  35 
  36 import java.lang.ref.WeakReference;
  37 import java.util.Arrays;
  38 import java.util.Objects;
  39 
  40 import static java.lang.invoke.LambdaForm.*;
  41 import static java.lang.invoke.LambdaForm.Kind.*;
  42 import static java.lang.invoke.MethodHandleNatives.Constants.*;
  43 import static java.lang.invoke.MethodHandleStatics.UNSAFE;
  44 import static java.lang.invoke.MethodHandleStatics.newInternalError;
  45 import static java.lang.invoke.MethodTypeForm.*;
  46 
  47 /**
  48  * The flavor of method handle which implements a constant reference
  49  * to a class member.
  50  * @author jrose
  51  */
  52 class DirectMethodHandle extends MethodHandle {
  53     final MemberName member;
  54 
  55     // Constructors and factory methods in this class *must* be package scoped or private.
  56     private DirectMethodHandle(MethodType mtype, LambdaForm form, MemberName member) {
  57         super(mtype, form);
  58         if (!member.isResolved())  throw new InternalError();
  59 
  60         if (member.getDeclaringClass().isInterface() &&
  61             member.getReferenceKind() == REF_invokeInterface &&
  62             member.isMethod() && !member.isAbstract()) {
  63             // Check for corner case: invokeinterface of Object method
  64             MemberName m = new MemberName(Object.class, member.getName(), member.getMethodType(), member.getReferenceKind());
  65             m = MemberName.getFactory().resolveOrNull(m.getReferenceKind(), m, null);
  66             if (m != null && m.isPublic()) {
  67                 assert(member.getReferenceKind() == m.getReferenceKind());  // else this.form is wrong
  68                 member = m;
  69             }
  70         }
  71 
  72         this.member = member;
  73     }
  74 
  75     // Factory methods:
  76     static DirectMethodHandle make(byte refKind, Class<?> refc, MemberName member, Class<?> callerClass) {
  77         MethodType mtype = member.getMethodOrFieldType();
  78         if (!member.isStatic()) {
  79             if (!member.getDeclaringClass().isAssignableFrom(refc) || member.isConstructor())
  80                 throw new InternalError(member.toString());
  81             mtype = mtype.insertParameterTypes(0, refc);
  82         }
  83         if (!member.isField()) {
  84             // refKind reflects the original type of lookup via findSpecial or
  85             // findVirtual etc.
  86             switch (refKind) {
  87                 case REF_invokeSpecial: {
  88                     member = member.asSpecial();
  89                     // if caller is an interface we need to adapt to get the
  90                     // receiver check inserted
  91                     if (callerClass == null) {
  92                         throw new InternalError("callerClass must not be null for REF_invokeSpecial");
  93                     }
  94                     LambdaForm lform = preparedLambdaForm(member, callerClass.isInterface());
  95                     return new Special(mtype, lform, member, callerClass);
  96                 }
  97                 case REF_invokeInterface: {
  98                     // for interfaces we always need the receiver typecheck,
  99                     // so we always pass 'true' to ensure we adapt if needed
 100                     // to include the REF_invokeSpecial case
 101                     LambdaForm lform = preparedLambdaForm(member, true);
 102                     return new Interface(mtype, lform, member, refc);
 103                 }
 104                 default: {
 105                     LambdaForm lform = preparedLambdaForm(member);
 106                     return new DirectMethodHandle(mtype, lform, member);
 107                 }
 108             }
 109         } else {
 110             LambdaForm lform = preparedFieldLambdaForm(member);
 111             if (member.isStatic()) {
 112                 long offset = MethodHandleNatives.staticFieldOffset(member);
 113                 Object base = MethodHandleNatives.staticFieldBase(member);
 114                 return new StaticAccessor(mtype, lform, member, base, offset);
 115             } else {
 116                 long offset = MethodHandleNatives.objectFieldOffset(member);
 117                 assert(offset == (int)offset);
 118                 return new Accessor(mtype, lform, member, (int)offset);
 119             }
 120         }
 121     }
 122     static DirectMethodHandle make(Class<?> refc, MemberName member) {
 123         byte refKind = member.getReferenceKind();
 124         if (refKind == REF_invokeSpecial)
 125             refKind =  REF_invokeVirtual;
 126         return make(refKind, refc, member, null /* no callerClass context */);
 127     }
 128     static DirectMethodHandle make(MemberName member) {
 129         if (member.isConstructor())
 130             return makeAllocator(member);
 131         return make(member.getDeclaringClass(), member);
 132     }
 133     private static DirectMethodHandle makeAllocator(MemberName ctor) {
 134         assert(ctor.isConstructor() && ctor.getName().equals("<init>"));
 135         Class<?> instanceClass = ctor.getDeclaringClass();
 136         ctor = ctor.asConstructor();
 137         assert(ctor.isConstructor() && ctor.getReferenceKind() == REF_newInvokeSpecial) : ctor;
 138         MethodType mtype = ctor.getMethodType().changeReturnType(instanceClass);
 139         LambdaForm lform = preparedLambdaForm(ctor);
 140         MemberName init = ctor.asSpecial();
 141         assert(init.getMethodType().returnType() == void.class);
 142         return new Constructor(mtype, lform, ctor, init, instanceClass);
 143     }
 144 
 145     @Override
 146     BoundMethodHandle rebind() {
 147         return BoundMethodHandle.makeReinvoker(this);
 148     }
 149 
 150     @Override
 151     MethodHandle copyWith(MethodType mt, LambdaForm lf) {
 152         assert(this.getClass() == DirectMethodHandle.class);  // must override in subclasses
 153         return new DirectMethodHandle(mt, lf, member);
 154     }
 155 
 156     @Override
 157     String internalProperties() {
 158         return "\n& DMH.MN="+internalMemberName();
 159     }
 160 
 161     //// Implementation methods.
 162     @Override
 163     @ForceInline
 164     MemberName internalMemberName() {
 165         return member;
 166     }
 167 
 168     private static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
 169 
 170     /**
 171      * Create a LF which can invoke the given method.
 172      * Cache and share this structure among all methods with
 173      * the same basicType and refKind.
 174      */
 175     private static LambdaForm preparedLambdaForm(MemberName m, boolean adaptToSpecialIfc) {
 176         assert(m.isInvocable()) : m;  // call preparedFieldLambdaForm instead
 177         MethodType mtype = m.getInvocationType().basicType();
 178         assert(!m.isMethodHandleInvoke()) : m;
 179         int which;
 180         // MemberName.getReferenceKind represents the JVM optimized form of the call
 181         // as distinct from the "kind" passed to DMH.make which represents the original
 182         // bytecode-equivalent request. Specifically private/final methods that use a direct
 183         // call have getReferenceKind adapted to REF_invokeSpecial, even though the actual
 184         // invocation mode may be invokevirtual or invokeinterface.
 185         switch (m.getReferenceKind()) {
 186         case REF_invokeVirtual:    which = LF_INVVIRTUAL;    break;
 187         case REF_invokeStatic:     which = LF_INVSTATIC;     break;
 188         case REF_invokeSpecial:    which = LF_INVSPECIAL;    break;
 189         case REF_invokeInterface:  which = LF_INVINTERFACE;  break;
 190         case REF_newInvokeSpecial: which = LF_NEWINVSPECIAL; break;
 191         default:  throw new InternalError(m.toString());
 192         }
 193         if (which == LF_INVSTATIC && shouldBeInitialized(m)) {
 194             // precompute the barrier-free version:
 195             preparedLambdaForm(mtype, which);
 196             which = LF_INVSTATIC_INIT;
 197         }
 198         if (which == LF_INVSPECIAL && adaptToSpecialIfc) {
 199             which = LF_INVSPECIAL_IFC;
 200         }
 201         LambdaForm lform = preparedLambdaForm(mtype, which);
 202         maybeCompile(lform, m);
 203         assert(lform.methodType().dropParameterTypes(0, 1)
 204                 .equals(m.getInvocationType().basicType()))
 205                 : Arrays.asList(m, m.getInvocationType().basicType(), lform, lform.methodType());
 206         return lform;
 207     }
 208 
 209     private static LambdaForm preparedLambdaForm(MemberName m) {
 210         return preparedLambdaForm(m, false);
 211     }
 212 
 213     private static LambdaForm preparedLambdaForm(MethodType mtype, int which) {
 214         LambdaForm lform = mtype.form().cachedLambdaForm(which);
 215         if (lform != null)  return lform;
 216         lform = makePreparedLambdaForm(mtype, which);
 217         return mtype.form().setCachedLambdaForm(which, lform);
 218     }
 219 
 220     static LambdaForm makePreparedLambdaForm(MethodType mtype, int which) {
 221         boolean needsInit = (which == LF_INVSTATIC_INIT);
 222         boolean doesAlloc = (which == LF_NEWINVSPECIAL);
 223         boolean needsReceiverCheck = (which == LF_INVINTERFACE ||
 224                                       which == LF_INVSPECIAL_IFC);
 225 
 226         String linkerName;
 227         LambdaForm.Kind kind;
 228         switch (which) {
 229         case LF_INVVIRTUAL:    linkerName = "linkToVirtual";   kind = DIRECT_INVOKE_VIRTUAL;     break;
 230         case LF_INVSTATIC:     linkerName = "linkToStatic";    kind = DIRECT_INVOKE_STATIC;      break;
 231         case LF_INVSTATIC_INIT:linkerName = "linkToStatic";    kind = DIRECT_INVOKE_STATIC_INIT; break;
 232         case LF_INVSPECIAL_IFC:linkerName = "linkToSpecial";   kind = DIRECT_INVOKE_SPECIAL_IFC; break;
 233         case LF_INVSPECIAL:    linkerName = "linkToSpecial";   kind = DIRECT_INVOKE_SPECIAL;     break;
 234         case LF_INVINTERFACE:  linkerName = "linkToInterface"; kind = DIRECT_INVOKE_INTERFACE;   break;
 235         case LF_NEWINVSPECIAL: linkerName = "linkToSpecial";   kind = DIRECT_NEW_INVOKE_SPECIAL; break;
 236         default:  throw new InternalError("which="+which);
 237         }
 238 
 239         MethodType mtypeWithArg = mtype.appendParameterTypes(MemberName.class);
 240         if (doesAlloc)
 241             mtypeWithArg = mtypeWithArg
 242                     .insertParameterTypes(0, Object.class)  // insert newly allocated obj
 243                     .changeReturnType(void.class);          // <init> returns void
 244         MemberName linker = new MemberName(MethodHandle.class, linkerName, mtypeWithArg, REF_invokeStatic);
 245         try {
 246             linker = IMPL_NAMES.resolveOrFail(REF_invokeStatic, linker, null, NoSuchMethodException.class);
 247         } catch (ReflectiveOperationException ex) {
 248             throw newInternalError(ex);
 249         }
 250         final int DMH_THIS    = 0;
 251         final int ARG_BASE    = 1;
 252         final int ARG_LIMIT   = ARG_BASE + mtype.parameterCount();
 253         int nameCursor = ARG_LIMIT;
 254         final int NEW_OBJ     = (doesAlloc ? nameCursor++ : -1);
 255         final int GET_MEMBER  = nameCursor++;
 256         final int CHECK_RECEIVER = (needsReceiverCheck ? nameCursor++ : -1);
 257         final int LINKER_CALL = nameCursor++;
 258         Name[] names = arguments(nameCursor - ARG_LIMIT, mtype.invokerType());
 259         assert(names.length == nameCursor);
 260         if (doesAlloc) {
 261             // names = { argx,y,z,... new C, init method }
 262             names[NEW_OBJ] = new Name(getFunction(NF_allocateInstance), names[DMH_THIS]);
 263             names[GET_MEMBER] = new Name(getFunction(NF_constructorMethod), names[DMH_THIS]);
 264         } else if (needsInit) {
 265             names[GET_MEMBER] = new Name(getFunction(NF_internalMemberNameEnsureInit), names[DMH_THIS]);
 266         } else {
 267             names[GET_MEMBER] = new Name(getFunction(NF_internalMemberName), names[DMH_THIS]);
 268         }
 269         assert(findDirectMethodHandle(names[GET_MEMBER]) == names[DMH_THIS]);
 270         Object[] outArgs = Arrays.copyOfRange(names, ARG_BASE, GET_MEMBER+1, Object[].class);
 271         if (needsReceiverCheck) {
 272             names[CHECK_RECEIVER] = new Name(getFunction(NF_checkReceiver), names[DMH_THIS], names[ARG_BASE]);
 273             outArgs[0] = names[CHECK_RECEIVER];
 274         }
 275         assert(outArgs[outArgs.length-1] == names[GET_MEMBER]);  // look, shifted args!
 276         int result = LAST_RESULT;
 277         if (doesAlloc) {
 278             assert(outArgs[outArgs.length-2] == names[NEW_OBJ]);  // got to move this one
 279             System.arraycopy(outArgs, 0, outArgs, 1, outArgs.length-2);
 280             outArgs[0] = names[NEW_OBJ];
 281             result = NEW_OBJ;
 282         }
 283         names[LINKER_CALL] = new Name(linker, outArgs);
 284         LambdaForm lform = new LambdaForm(ARG_LIMIT, names, result, kind);
 285 
 286         // This is a tricky bit of code.  Don't send it through the LF interpreter.
 287         lform.compileToBytecode();
 288         return lform;
 289     }
 290 
 291     /* assert */ static Object findDirectMethodHandle(Name name) {
 292         if (name.function.equals(getFunction(NF_internalMemberName)) ||
 293             name.function.equals(getFunction(NF_internalMemberNameEnsureInit)) ||
 294             name.function.equals(getFunction(NF_constructorMethod))) {
 295             assert(name.arguments.length == 1);
 296             return name.arguments[0];
 297         }
 298         return null;
 299     }
 300 
 301     private static void maybeCompile(LambdaForm lform, MemberName m) {
 302         if (lform.vmentry == null && VerifyAccess.isSamePackage(m.getDeclaringClass(), MethodHandle.class))
 303             // Help along bootstrapping...
 304             lform.compileToBytecode();
 305     }
 306 
 307     /** Static wrapper for DirectMethodHandle.internalMemberName. */
 308     @ForceInline
 309     /*non-public*/ static Object internalMemberName(Object mh) {
 310         return ((DirectMethodHandle)mh).member;
 311     }
 312 
 313     /** Static wrapper for DirectMethodHandle.internalMemberName.
 314      * This one also forces initialization.
 315      */
 316     /*non-public*/ static Object internalMemberNameEnsureInit(Object mh) {
 317         DirectMethodHandle dmh = (DirectMethodHandle)mh;
 318         dmh.ensureInitialized();
 319         return dmh.member;
 320     }
 321 
 322     /*non-public*/ static
 323     boolean shouldBeInitialized(MemberName member) {
 324         switch (member.getReferenceKind()) {
 325         case REF_invokeStatic:
 326         case REF_getStatic:
 327         case REF_putStatic:
 328         case REF_newInvokeSpecial:
 329             break;
 330         default:
 331             // No need to initialize the class on this kind of member.
 332             return false;
 333         }
 334         Class<?> cls = member.getDeclaringClass();
 335         if (cls == ValueConversions.class ||
 336             cls == MethodHandleImpl.class ||
 337             cls == Invokers.class) {
 338             // These guys have lots of <clinit> DMH creation but we know
 339             // the MHs will not be used until the system is booted.
 340             return false;
 341         }
 342         if (VerifyAccess.isSamePackage(MethodHandle.class, cls) ||
 343             VerifyAccess.isSamePackage(ValueConversions.class, cls)) {
 344             // It is a system class.  It is probably in the process of
 345             // being initialized, but we will help it along just to be safe.
 346             if (UNSAFE.shouldBeInitialized(cls)) {
 347                 UNSAFE.ensureClassInitialized(cls);
 348             }
 349             return false;
 350         }
 351         return UNSAFE.shouldBeInitialized(cls);
 352     }
 353 
 354     private static class EnsureInitialized extends ClassValue<WeakReference<Thread>> {
 355         @Override
 356         protected WeakReference<Thread> computeValue(Class<?> type) {
 357             UNSAFE.ensureClassInitialized(type);
 358             if (UNSAFE.shouldBeInitialized(type))
 359                 // If the previous call didn't block, this can happen.
 360                 // We are executing inside <clinit>.
 361                 return new WeakReference<>(Thread.currentThread());
 362             return null;
 363         }
 364         static final EnsureInitialized INSTANCE = new EnsureInitialized();
 365     }
 366 
 367     private void ensureInitialized() {
 368         if (checkInitialized(member)) {
 369             // The coast is clear.  Delete the <clinit> barrier.
 370             if (member.isField())
 371                 updateForm(preparedFieldLambdaForm(member));
 372             else
 373                 updateForm(preparedLambdaForm(member));
 374         }
 375     }
 376     private static boolean checkInitialized(MemberName member) {
 377         Class<?> defc = member.getDeclaringClass();
 378         WeakReference<Thread> ref = EnsureInitialized.INSTANCE.get(defc);
 379         if (ref == null) {
 380             return true;  // the final state
 381         }
 382         Thread clinitThread = ref.get();
 383         // Somebody may still be running defc.<clinit>.
 384         if (clinitThread == Thread.currentThread()) {
 385             // If anybody is running defc.<clinit>, it is this thread.
 386             if (UNSAFE.shouldBeInitialized(defc))
 387                 // Yes, we are running it; keep the barrier for now.
 388                 return false;
 389         } else {
 390             // We are in a random thread.  Block.
 391             UNSAFE.ensureClassInitialized(defc);
 392         }
 393         assert(!UNSAFE.shouldBeInitialized(defc));
 394         // put it into the final state
 395         EnsureInitialized.INSTANCE.remove(defc);
 396         return true;
 397     }
 398 
 399     /*non-public*/ static void ensureInitialized(Object mh) {
 400         ((DirectMethodHandle)mh).ensureInitialized();
 401     }
 402 
 403     /** This subclass represents invokespecial instructions. */
 404     static class Special extends DirectMethodHandle {
 405         private final Class<?> caller;
 406         private Special(MethodType mtype, LambdaForm form, MemberName member, Class<?> caller) {
 407             super(mtype, form, member);
 408             this.caller = caller;
 409         }
 410         @Override
 411         boolean isInvokeSpecial() {
 412             return true;
 413         }
 414         @Override
 415         MethodHandle copyWith(MethodType mt, LambdaForm lf) {
 416             return new Special(mt, lf, member, caller);
 417         }
 418         Object checkReceiver(Object recv) {
 419             if (!caller.isInstance(recv)) {
 420                 String msg = String.format("Receiver class %s is not a subclass of caller class %s",
 421                                            recv.getClass().getName(), caller.getName());
 422                 throw new IncompatibleClassChangeError(msg);
 423             }
 424             return recv;
 425         }
 426     }
 427 
 428     /** This subclass represents invokeinterface instructions. */
 429     static class Interface extends DirectMethodHandle {
 430         private final Class<?> refc;
 431         private Interface(MethodType mtype, LambdaForm form, MemberName member, Class<?> refc) {
 432             super(mtype, form, member);
 433             assert refc.isInterface() : refc;
 434             this.refc = refc;
 435         }
 436         @Override
 437         MethodHandle copyWith(MethodType mt, LambdaForm lf) {
 438             return new Interface(mt, lf, member, refc);
 439         }
 440         @Override
 441         Object checkReceiver(Object recv) {
 442             if (!refc.isInstance(recv)) {
 443                 String msg = String.format("Receiver class %s does not implement the requested interface %s",
 444                                            recv.getClass().getName(), refc.getName());
 445                 throw new IncompatibleClassChangeError(msg);
 446             }
 447             return recv;
 448         }
 449     }
 450 
 451     /** Used for interface receiver type checks, by Interface and Special modes. */
 452     Object checkReceiver(Object recv) {
 453         throw new InternalError("Should only be invoked on a subclass");
 454     }
 455 
 456 
 457     /** This subclass handles constructor references. */
 458     static class Constructor extends DirectMethodHandle {
 459         final MemberName initMethod;
 460         final Class<?>   instanceClass;
 461 
 462         private Constructor(MethodType mtype, LambdaForm form, MemberName constructor,
 463                             MemberName initMethod, Class<?> instanceClass) {
 464             super(mtype, form, constructor);
 465             this.initMethod = initMethod;
 466             this.instanceClass = instanceClass;
 467             assert(initMethod.isResolved());
 468         }
 469         @Override
 470         MethodHandle copyWith(MethodType mt, LambdaForm lf) {
 471             return new Constructor(mt, lf, member, initMethod, instanceClass);
 472         }
 473     }
 474 
 475     /*non-public*/ static Object constructorMethod(Object mh) {
 476         Constructor dmh = (Constructor)mh;
 477         return dmh.initMethod;
 478     }
 479 
 480     /*non-public*/ static Object allocateInstance(Object mh) throws InstantiationException {
 481         Constructor dmh = (Constructor)mh;
 482         return UNSAFE.allocateInstance(dmh.instanceClass);
 483     }
 484 
 485     /** This subclass handles non-static field references. */
 486     static class Accessor extends DirectMethodHandle {
 487         final Class<?> fieldType;
 488         final int      fieldOffset;
 489         private Accessor(MethodType mtype, LambdaForm form, MemberName member,
 490                          int fieldOffset) {
 491             super(mtype, form, member);
 492             this.fieldType   = member.getFieldType();
 493             this.fieldOffset = fieldOffset;
 494         }
 495 
 496         @Override Object checkCast(Object obj) {
 497             return fieldType.cast(obj);
 498         }
 499         @Override
 500         MethodHandle copyWith(MethodType mt, LambdaForm lf) {
 501             return new Accessor(mt, lf, member, fieldOffset);
 502         }
 503     }
 504 
 505     @ForceInline
 506     /*non-public*/ static long fieldOffset(Object accessorObj) {
 507         // Note: We return a long because that is what Unsafe.getObject likes.
 508         // We store a plain int because it is more compact.
 509         return ((Accessor)accessorObj).fieldOffset;
 510     }
 511 
 512     @ForceInline
 513     /*non-public*/ static Object checkBase(Object obj) {
 514         // Note that the object's class has already been verified,
 515         // since the parameter type of the Accessor method handle
 516         // is either member.getDeclaringClass or a subclass.
 517         // This was verified in DirectMethodHandle.make.
 518         // Therefore, the only remaining check is for null.
 519         // Since this check is *not* guaranteed by Unsafe.getInt
 520         // and its siblings, we need to make an explicit one here.
 521         return Objects.requireNonNull(obj);
 522     }
 523 
 524     /** This subclass handles static field references. */
 525     static class StaticAccessor extends DirectMethodHandle {
 526         private final Class<?> fieldType;
 527         private final Object   staticBase;
 528         private final long     staticOffset;
 529 
 530         private StaticAccessor(MethodType mtype, LambdaForm form, MemberName member,
 531                                Object staticBase, long staticOffset) {
 532             super(mtype, form, member);
 533             this.fieldType    = member.getFieldType();
 534             this.staticBase   = staticBase;
 535             this.staticOffset = staticOffset;
 536         }
 537 
 538         @Override Object checkCast(Object obj) {
 539             return fieldType.cast(obj);
 540         }
 541         @Override
 542         MethodHandle copyWith(MethodType mt, LambdaForm lf) {
 543             return new StaticAccessor(mt, lf, member, staticBase, staticOffset);
 544         }
 545     }
 546 
 547     @ForceInline
 548     /*non-public*/ static Object nullCheck(Object obj) {
 549         return Objects.requireNonNull(obj);
 550     }
 551 
 552     @ForceInline
 553     /*non-public*/ static Object staticBase(Object accessorObj) {
 554         return ((StaticAccessor)accessorObj).staticBase;
 555     }
 556 
 557     @ForceInline
 558     /*non-public*/ static long staticOffset(Object accessorObj) {
 559         return ((StaticAccessor)accessorObj).staticOffset;
 560     }
 561 
 562     @ForceInline
 563     /*non-public*/ static Object checkCast(Object mh, Object obj) {
 564         return ((DirectMethodHandle) mh).checkCast(obj);
 565     }
 566 
 567     Object checkCast(Object obj) {
 568         return member.getReturnType().cast(obj);
 569     }
 570 
 571     // Caching machinery for field accessors:
 572     static final byte
 573             AF_GETFIELD        = 0,
 574             AF_PUTFIELD        = 1,
 575             AF_GETSTATIC       = 2,
 576             AF_PUTSTATIC       = 3,
 577             AF_GETSTATIC_INIT  = 4,
 578             AF_PUTSTATIC_INIT  = 5,
 579             AF_LIMIT           = 6;
 580     // Enumerate the different field kinds using Wrapper,
 581     // with an extra case added for checked references.
 582     static final int
 583             FT_LAST_WRAPPER    = Wrapper.COUNT-1,
 584             FT_UNCHECKED_REF   = Wrapper.OBJECT.ordinal(),
 585             FT_CHECKED_REF     = FT_LAST_WRAPPER+1,
 586             FT_LIMIT           = FT_LAST_WRAPPER+2;
 587     private static int afIndex(byte formOp, boolean isVolatile, int ftypeKind) {
 588         return ((formOp * FT_LIMIT * 2)
 589                 + (isVolatile ? FT_LIMIT : 0)
 590                 + ftypeKind);
 591     }
 592     @Stable
 593     private static final LambdaForm[] ACCESSOR_FORMS
 594             = new LambdaForm[afIndex(AF_LIMIT, false, 0)];
 595     static int ftypeKind(Class<?> ftype) {
 596         if (ftype.isPrimitive())
 597             return Wrapper.forPrimitiveType(ftype).ordinal();
 598         else if (VerifyType.isNullReferenceConversion(Object.class, ftype))
 599             return FT_UNCHECKED_REF;
 600         else
 601             return FT_CHECKED_REF;
 602     }
 603 
 604     /**
 605      * Create a LF which can access the given field.
 606      * Cache and share this structure among all fields with
 607      * the same basicType and refKind.
 608      */
 609     private static LambdaForm preparedFieldLambdaForm(MemberName m) {
 610         Class<?> ftype = m.getFieldType();
 611         boolean isVolatile = m.isVolatile();
 612         byte formOp;
 613         switch (m.getReferenceKind()) {
 614         case REF_getField:      formOp = AF_GETFIELD;    break;
 615         case REF_putField:      formOp = AF_PUTFIELD;    break;
 616         case REF_getStatic:     formOp = AF_GETSTATIC;   break;
 617         case REF_putStatic:     formOp = AF_PUTSTATIC;   break;
 618         default:  throw new InternalError(m.toString());
 619         }
 620         if (shouldBeInitialized(m)) {
 621             // precompute the barrier-free version:
 622             preparedFieldLambdaForm(formOp, isVolatile, ftype);
 623             assert((AF_GETSTATIC_INIT - AF_GETSTATIC) ==
 624                    (AF_PUTSTATIC_INIT - AF_PUTSTATIC));
 625             formOp += (AF_GETSTATIC_INIT - AF_GETSTATIC);
 626         }
 627         LambdaForm lform = preparedFieldLambdaForm(formOp, isVolatile, ftype);
 628         maybeCompile(lform, m);
 629         assert(lform.methodType().dropParameterTypes(0, 1)
 630                 .equals(m.getInvocationType().basicType()))
 631                 : Arrays.asList(m, m.getInvocationType().basicType(), lform, lform.methodType());
 632         return lform;
 633     }
 634     private static LambdaForm preparedFieldLambdaForm(byte formOp, boolean isVolatile, Class<?> ftype) {
 635         int ftypeKind = ftypeKind(ftype);
 636         int afIndex = afIndex(formOp, isVolatile, ftypeKind);
 637         LambdaForm lform = ACCESSOR_FORMS[afIndex];
 638         if (lform != null)  return lform;
 639         lform = makePreparedFieldLambdaForm(formOp, isVolatile, ftypeKind);
 640         ACCESSOR_FORMS[afIndex] = lform;  // don't bother with a CAS
 641         return lform;
 642     }
 643 
 644     private static final Wrapper[] ALL_WRAPPERS = Wrapper.values();
 645 
 646     private static Kind getFieldKind(boolean isGetter, boolean isVolatile, Wrapper wrapper) {
 647         if (isGetter) {
 648             if (isVolatile) {
 649                 switch (wrapper) {
 650                     case BOOLEAN: return GET_BOOLEAN_VOLATILE;
 651                     case BYTE:    return GET_BYTE_VOLATILE;
 652                     case SHORT:   return GET_SHORT_VOLATILE;
 653                     case CHAR:    return GET_CHAR_VOLATILE;
 654                     case INT:     return GET_INT_VOLATILE;
 655                     case LONG:    return GET_LONG_VOLATILE;
 656                     case FLOAT:   return GET_FLOAT_VOLATILE;
 657                     case DOUBLE:  return GET_DOUBLE_VOLATILE;
 658                     case OBJECT:  return GET_REFERENCE_VOLATILE;
 659                 }
 660             } else {
 661                 switch (wrapper) {
 662                     case BOOLEAN: return GET_BOOLEAN;
 663                     case BYTE:    return GET_BYTE;
 664                     case SHORT:   return GET_SHORT;
 665                     case CHAR:    return GET_CHAR;
 666                     case INT:     return GET_INT;
 667                     case LONG:    return GET_LONG;
 668                     case FLOAT:   return GET_FLOAT;
 669                     case DOUBLE:  return GET_DOUBLE;
 670                     case OBJECT:  return GET_REFERENCE;
 671                 }
 672             }
 673         } else {
 674             if (isVolatile) {
 675                 switch (wrapper) {
 676                     case BOOLEAN: return PUT_BOOLEAN_VOLATILE;
 677                     case BYTE:    return PUT_BYTE_VOLATILE;
 678                     case SHORT:   return PUT_SHORT_VOLATILE;
 679                     case CHAR:    return PUT_CHAR_VOLATILE;
 680                     case INT:     return PUT_INT_VOLATILE;
 681                     case LONG:    return PUT_LONG_VOLATILE;
 682                     case FLOAT:   return PUT_FLOAT_VOLATILE;
 683                     case DOUBLE:  return PUT_DOUBLE_VOLATILE;
 684                     case OBJECT:  return PUT_REFERENCE_VOLATILE;
 685                 }
 686             } else {
 687                 switch (wrapper) {
 688                     case BOOLEAN: return PUT_BOOLEAN;
 689                     case BYTE:    return PUT_BYTE;
 690                     case SHORT:   return PUT_SHORT;
 691                     case CHAR:    return PUT_CHAR;
 692                     case INT:     return PUT_INT;
 693                     case LONG:    return PUT_LONG;
 694                     case FLOAT:   return PUT_FLOAT;
 695                     case DOUBLE:  return PUT_DOUBLE;
 696                     case OBJECT:  return PUT_REFERENCE;
 697                 }
 698             }
 699         }
 700         throw new AssertionError("Invalid arguments");
 701     }
 702 
 703     static LambdaForm makePreparedFieldLambdaForm(byte formOp, boolean isVolatile, int ftypeKind) {
 704         boolean isGetter  = (formOp & 1) == (AF_GETFIELD & 1);
 705         boolean isStatic  = (formOp >= AF_GETSTATIC);
 706         boolean needsInit = (formOp >= AF_GETSTATIC_INIT);
 707         boolean needsCast = (ftypeKind == FT_CHECKED_REF);
 708         Wrapper fw = (needsCast ? Wrapper.OBJECT : ALL_WRAPPERS[ftypeKind]);
 709         Class<?> ft = fw.primitiveType();
 710         assert(ftypeKind(needsCast ? String.class : ft) == ftypeKind);
 711 
 712         // getObject, putIntVolatile, etc.
 713         Kind kind = getFieldKind(isGetter, isVolatile, fw);
 714 
 715         MethodType linkerType;
 716         if (isGetter)
 717             linkerType = MethodType.methodType(ft, Object.class, long.class);
 718         else
 719             linkerType = MethodType.methodType(void.class, Object.class, long.class, ft);
 720         MemberName linker = new MemberName(Unsafe.class, kind.methodName, linkerType, REF_invokeVirtual);
 721         try {
 722             linker = IMPL_NAMES.resolveOrFail(REF_invokeVirtual, linker, null, NoSuchMethodException.class);
 723         } catch (ReflectiveOperationException ex) {
 724             throw newInternalError(ex);
 725         }
 726 
 727         // What is the external type of the lambda form?
 728         MethodType mtype;
 729         if (isGetter)
 730             mtype = MethodType.methodType(ft);
 731         else
 732             mtype = MethodType.methodType(void.class, ft);
 733         mtype = mtype.basicType();  // erase short to int, etc.
 734         if (!isStatic)
 735             mtype = mtype.insertParameterTypes(0, Object.class);
 736         final int DMH_THIS  = 0;
 737         final int ARG_BASE  = 1;
 738         final int ARG_LIMIT = ARG_BASE + mtype.parameterCount();
 739         // if this is for non-static access, the base pointer is stored at this index:
 740         final int OBJ_BASE  = isStatic ? -1 : ARG_BASE;
 741         // if this is for write access, the value to be written is stored at this index:
 742         final int SET_VALUE  = isGetter ? -1 : ARG_LIMIT - 1;
 743         int nameCursor = ARG_LIMIT;
 744         final int F_HOLDER  = (isStatic ? nameCursor++ : -1);  // static base if any
 745         final int F_OFFSET  = nameCursor++;  // Either static offset or field offset.
 746         final int OBJ_CHECK = (OBJ_BASE >= 0 ? nameCursor++ : -1);
 747         final int U_HOLDER  = nameCursor++;  // UNSAFE holder
 748         final int INIT_BAR  = (needsInit ? nameCursor++ : -1);
 749         final int PRE_CAST  = (needsCast && !isGetter ? nameCursor++ : -1);
 750         final int LINKER_CALL = nameCursor++;
 751         final int POST_CAST = (needsCast && isGetter ? nameCursor++ : -1);
 752         final int RESULT    = nameCursor-1;  // either the call or the cast
 753         Name[] names = arguments(nameCursor - ARG_LIMIT, mtype.invokerType());
 754         if (needsInit)
 755             names[INIT_BAR] = new Name(getFunction(NF_ensureInitialized), names[DMH_THIS]);
 756         if (needsCast && !isGetter)
 757             names[PRE_CAST] = new Name(getFunction(NF_checkCast), names[DMH_THIS], names[SET_VALUE]);
 758         Object[] outArgs = new Object[1 + linkerType.parameterCount()];
 759         assert(outArgs.length == (isGetter ? 3 : 4));
 760         outArgs[0] = names[U_HOLDER] = new Name(getFunction(NF_UNSAFE));
 761         if (isStatic) {
 762             outArgs[1] = names[F_HOLDER]  = new Name(getFunction(NF_staticBase), names[DMH_THIS]);
 763             outArgs[2] = names[F_OFFSET]  = new Name(getFunction(NF_staticOffset), names[DMH_THIS]);
 764         } else {
 765             outArgs[1] = names[OBJ_CHECK] = new Name(getFunction(NF_checkBase), names[OBJ_BASE]);
 766             outArgs[2] = names[F_OFFSET]  = new Name(getFunction(NF_fieldOffset), names[DMH_THIS]);
 767         }
 768         if (!isGetter) {
 769             outArgs[3] = (needsCast ? names[PRE_CAST] : names[SET_VALUE]);
 770         }
 771         for (Object a : outArgs)  assert(a != null);
 772         names[LINKER_CALL] = new Name(linker, outArgs);
 773         if (needsCast && isGetter)
 774             names[POST_CAST] = new Name(getFunction(NF_checkCast), names[DMH_THIS], names[LINKER_CALL]);
 775         for (Name n : names)  assert(n != null);
 776 
 777         LambdaForm form;
 778         if (needsCast || needsInit) {
 779             // can't use the pre-generated form when casting and/or initializing
 780             form = new LambdaForm(ARG_LIMIT, names, RESULT);
 781         } else {
 782             form = new LambdaForm(ARG_LIMIT, names, RESULT, kind);
 783         }
 784 
 785         if (LambdaForm.debugNames()) {
 786             // add some detail to the lambdaForm debugname,
 787             // significant only for debugging
 788             StringBuilder nameBuilder = new StringBuilder(kind.methodName);
 789             if (isStatic) {
 790                 nameBuilder.append("Static");
 791             } else {
 792                 nameBuilder.append("Field");
 793             }
 794             if (needsCast) {
 795                 nameBuilder.append("Cast");
 796             }
 797             if (needsInit) {
 798                 nameBuilder.append("Init");
 799             }
 800             LambdaForm.associateWithDebugName(form, nameBuilder.toString());
 801         }
 802         return form;
 803     }
 804 
 805     /**
 806      * Pre-initialized NamedFunctions for bootstrapping purposes.
 807      */
 808     static final byte NF_internalMemberName = 0,
 809             NF_internalMemberNameEnsureInit = 1,
 810             NF_ensureInitialized = 2,
 811             NF_fieldOffset = 3,
 812             NF_checkBase = 4,
 813             NF_staticBase = 5,
 814             NF_staticOffset = 6,
 815             NF_checkCast = 7,
 816             NF_allocateInstance = 8,
 817             NF_constructorMethod = 9,
 818             NF_UNSAFE = 10,
 819             NF_checkReceiver = 11,
 820             NF_LIMIT = 12;
 821 
 822     private static final @Stable NamedFunction[] NFS = new NamedFunction[NF_LIMIT];
 823 
 824     private static NamedFunction getFunction(byte func) {
 825         NamedFunction nf = NFS[func];
 826         if (nf != null) {
 827             return nf;
 828         }
 829         // Each nf must be statically invocable or we get tied up in our bootstraps.
 830         nf = NFS[func] = createFunction(func);
 831         assert(InvokerBytecodeGenerator.isStaticallyInvocable(nf));
 832         return nf;
 833     }
 834 
 835     private static final MethodType OBJ_OBJ_TYPE = MethodType.methodType(Object.class, Object.class);
 836 
 837     private static final MethodType LONG_OBJ_TYPE = MethodType.methodType(long.class, Object.class);
 838 
 839     private static NamedFunction createFunction(byte func) {
 840         try {
 841             switch (func) {
 842                 case NF_internalMemberName:
 843                     return getNamedFunction("internalMemberName", OBJ_OBJ_TYPE);
 844                 case NF_internalMemberNameEnsureInit:
 845                     return getNamedFunction("internalMemberNameEnsureInit", OBJ_OBJ_TYPE);
 846                 case NF_ensureInitialized:
 847                     return getNamedFunction("ensureInitialized", MethodType.methodType(void.class, Object.class));
 848                 case NF_fieldOffset:
 849                     return getNamedFunction("fieldOffset", LONG_OBJ_TYPE);
 850                 case NF_checkBase:
 851                     return getNamedFunction("checkBase", OBJ_OBJ_TYPE);
 852                 case NF_staticBase:
 853                     return getNamedFunction("staticBase", OBJ_OBJ_TYPE);
 854                 case NF_staticOffset:
 855                     return getNamedFunction("staticOffset", LONG_OBJ_TYPE);
 856                 case NF_checkCast:
 857                     return getNamedFunction("checkCast", MethodType.methodType(Object.class, Object.class, Object.class));
 858                 case NF_allocateInstance:
 859                     return getNamedFunction("allocateInstance", OBJ_OBJ_TYPE);
 860                 case NF_constructorMethod:
 861                     return getNamedFunction("constructorMethod", OBJ_OBJ_TYPE);
 862                 case NF_UNSAFE:
 863                     MemberName member = new MemberName(MethodHandleStatics.class, "UNSAFE", Unsafe.class, REF_getField);
 864                     return new NamedFunction(
 865                             MemberName.getFactory()
 866                                     .resolveOrFail(REF_getField, member, DirectMethodHandle.class, NoSuchMethodException.class));
 867                 case NF_checkReceiver:
 868                     member = new MemberName(DirectMethodHandle.class, "checkReceiver", OBJ_OBJ_TYPE, REF_invokeVirtual);
 869                     return new NamedFunction(
 870                         MemberName.getFactory()
 871                             .resolveOrFail(REF_invokeVirtual, member, DirectMethodHandle.class, NoSuchMethodException.class));
 872                 default:
 873                     throw newInternalError("Unknown function: " + func);
 874             }
 875         } catch (ReflectiveOperationException ex) {
 876             throw newInternalError(ex);
 877         }
 878     }
 879 
 880     private static NamedFunction getNamedFunction(String name, MethodType type)
 881         throws ReflectiveOperationException
 882     {
 883         MemberName member = new MemberName(DirectMethodHandle.class, name, type, REF_invokeStatic);
 884         return new NamedFunction(
 885             MemberName.getFactory()
 886                 .resolveOrFail(REF_invokeStatic, member, DirectMethodHandle.class, NoSuchMethodException.class));
 887     }
 888 
 889     static {
 890         // The Holder class will contain pre-generated DirectMethodHandles resolved
 891         // speculatively using MemberName.getFactory().resolveOrNull. However, that
 892         // doesn't initialize the class, which subtly breaks inlining etc. By forcing
 893         // initialization of the Holder class we avoid these issues.
 894         UNSAFE.ensureClassInitialized(Holder.class);
 895     }
 896 
 897     /* Placeholder class for DirectMethodHandles generated ahead of time */
 898     final class Holder {}
 899 }