1 /*
   2  * Copyright (c) 2008, 2021, 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 java.lang.constant.ClassDesc;
  29 import java.lang.constant.Constable;
  30 import java.lang.constant.MethodTypeDesc;
  31 import java.lang.ref.Reference;
  32 import java.lang.ref.ReferenceQueue;
  33 import java.lang.ref.WeakReference;
  34 import java.util.Arrays;
  35 import java.util.Collections;
  36 import java.util.List;
  37 import java.util.NoSuchElementException;
  38 import java.util.Objects;
  39 import java.util.Optional;
  40 import java.util.StringJoiner;
  41 import java.util.concurrent.ConcurrentHashMap;
  42 import java.util.concurrent.ConcurrentMap;

  43 import java.util.stream.Stream;
  44 
  45 import jdk.internal.vm.annotation.Stable;
  46 import sun.invoke.util.BytecodeDescriptor;
  47 import sun.invoke.util.VerifyType;
  48 import sun.invoke.util.Wrapper;
  49 import sun.security.util.SecurityConstants;
  50 
  51 import static java.lang.invoke.MethodHandleStatics.UNSAFE;
  52 import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException;
  53 import static java.lang.invoke.MethodType.fromDescriptor;
  54 
  55 /**
  56  * A method type represents the arguments and return type accepted and
  57  * returned by a method handle, or the arguments and return type passed
  58  * and expected  by a method handle caller.  Method types must be properly
  59  * matched between a method handle and all its callers,
  60  * and the JVM's operations enforce this matching at, specifically
  61  * during calls to {@link MethodHandle#invokeExact MethodHandle.invokeExact}
  62  * and {@link MethodHandle#invoke MethodHandle.invoke}, and during execution
  63  * of {@code invokedynamic} instructions.
  64  * <p>
  65  * The structure is a return type accompanied by any number of parameter types.
  66  * The types (primitive, {@code void}, and reference) are represented by {@link Class} objects.
  67  * (For ease of exposition, we treat {@code void} as if it were a type.
  68  * In fact, it denotes the absence of a return type.)
  69  * <p>
  70  * All instances of {@code MethodType} are immutable.
  71  * Two instances are completely interchangeable if they compare equal.
  72  * Equality depends on pairwise correspondence of the return and parameter types and on nothing else.
  73  * <p>
  74  * This type can be created only by factory methods.
  75  * All factory methods may cache values, though caching is not guaranteed.
  76  * Some factory methods are static, while others are virtual methods which
  77  * modify precursor method types, e.g., by changing a selected parameter.
  78  * <p>
  79  * Factory methods which operate on groups of parameter types
  80  * are systematically presented in two versions, so that both Java arrays and
  81  * Java lists can be used to work with groups of parameter types.
  82  * The query methods {@code parameterArray} and {@code parameterList}
  83  * also provide a choice between arrays and lists.
  84  * <p>
  85  * {@code MethodType} objects are sometimes derived from bytecode instructions
  86  * such as {@code invokedynamic}, specifically from the type descriptor strings associated
  87  * with the instructions in a class file's constant pool.
  88  * <p>
  89  * Like classes and strings, method types can also be represented directly
  90  * in a class file's constant pool as constants.
  91  * A method type may be loaded by an {@code ldc} instruction which refers
  92  * to a suitable {@code CONSTANT_MethodType} constant pool entry.
  93  * The entry refers to a {@code CONSTANT_Utf8} spelling for the descriptor string.
  94  * (For full details on method type constants, see sections {@jvms
  95  * 4.4.8} and {@jvms 5.4.3.5} of the Java Virtual Machine
  96  * Specification.)
  97  * <p>
  98  * When the JVM materializes a {@code MethodType} from a descriptor string,
  99  * all classes named in the descriptor must be accessible, and will be loaded.
 100  * (But the classes need not be initialized, as is the case with a {@code CONSTANT_Class}.)
 101  * This loading may occur at any time before the {@code MethodType} object is first derived.
 102  * <p>
 103  * <b><a id="descriptor">Nominal Descriptors</a></b>
 104  * <p>
 105  * A {@code MethodType} can be described in {@linkplain MethodTypeDesc nominal form}
 106  * if and only if all of the parameter types and return type can be described
 107  * with a {@link Class#describeConstable() nominal descriptor} represented by
 108  * {@link ClassDesc}.  If a method type can be described nominally, then:
 109  * <ul>
 110  * <li>The method type has a {@link MethodTypeDesc nominal descriptor}
 111  *     returned by {@link #describeConstable() MethodType::describeConstable}.</li>
 112  * <li>The descriptor string returned by
 113  *     {@link #descriptorString() MethodType::descriptorString} or
 114  *     {@link #toMethodDescriptorString() MethodType::toMethodDescriptorString}
 115  *     for the method type is a method descriptor (JVMS {@jvms 4.3.3}).</li>
 116  * </ul>
 117  * <p>
 118  * If any of the parameter types or return type cannot be described
 119  * nominally, i.e. {@link Class#describeConstable() Class::describeConstable}
 120  * returns an empty optional for that type,
 121  * then the method type cannot be described nominally:
 122  * <ul>
 123  * <li>The method type has no {@link MethodTypeDesc nominal descriptor} and
 124  *     {@link #describeConstable() MethodType::describeConstable} returns
 125  *     an empty optional.</li>
 126  * <li>The descriptor string returned by
 127  *     {@link #descriptorString() MethodType::descriptorString} or
 128  *     {@link #toMethodDescriptorString() MethodType::toMethodDescriptorString}
 129  *     for the method type is not a type descriptor.</li>
 130  * </ul>
 131  *
 132  * @author John Rose, JSR 292 EG
 133  * @since 1.7
 134  */
 135 public final
 136 class MethodType
 137         implements Constable,
 138                    TypeDescriptor.OfMethod<Class<?>, MethodType>,
 139                    java.io.Serializable {
 140     @java.io.Serial
 141     private static final long serialVersionUID = 292L;  // {rtype, {ptype...}}
 142 
 143     // The rtype and ptypes fields define the structural identity of the method type:
 144     private final @Stable Class<?>   rtype;
 145     private final @Stable Class<?>[] ptypes;
 146 
 147     // The remaining fields are caches of various sorts:
 148     private @Stable MethodTypeForm form; // erased form, plus cached data about primitives
 149     private @Stable Object wrapAlt;  // alternative wrapped/unwrapped version and
 150                                      // private communication for readObject and readResolve
 151     private @Stable Invokers invokers;   // cache of handy higher-order adapters
 152     private @Stable String methodDescriptor;  // cache for toMethodDescriptorString
 153 
 154     /**
 155      * Constructor that performs no copying or validation.
 156      * Should only be called from the factory method makeImpl
 157      */
 158     private MethodType(Class<?> rtype, Class<?>[] ptypes) {
 159         this.rtype = rtype;
 160         this.ptypes = ptypes;
 161     }
 162 
 163     /*trusted*/ MethodTypeForm form() { return form; }
 164     /*trusted*/ Class<?> rtype() { return rtype; }
 165     /*trusted*/ Class<?>[] ptypes() { return ptypes; }
 166 
 167     void setForm(MethodTypeForm f) { form = f; }
 168 
 169     /** This number, mandated by the JVM spec as 255,
 170      *  is the maximum number of <em>slots</em>
 171      *  that any Java method can receive in its argument list.
 172      *  It limits both JVM signatures and method type objects.
 173      *  The longest possible invocation will look like
 174      *  {@code staticMethod(arg1, arg2, ..., arg255)} or
 175      *  {@code x.virtualMethod(arg1, arg2, ..., arg254)}.
 176      */
 177     /*non-public*/
 178     static final int MAX_JVM_ARITY = 255;  // this is mandated by the JVM spec.
 179 
 180     /** This number is the maximum arity of a method handle, 254.
 181      *  It is derived from the absolute JVM-imposed arity by subtracting one,
 182      *  which is the slot occupied by the method handle itself at the
 183      *  beginning of the argument list used to invoke the method handle.
 184      *  The longest possible invocation will look like
 185      *  {@code mh.invoke(arg1, arg2, ..., arg254)}.
 186      */
 187     // Issue:  Should we allow MH.invokeWithArguments to go to the full 255?
 188     /*non-public*/
 189     static final int MAX_MH_ARITY = MAX_JVM_ARITY-1;  // deduct one for mh receiver
 190 
 191     /** This number is the maximum arity of a method handle invoker, 253.
 192      *  It is derived from the absolute JVM-imposed arity by subtracting two,
 193      *  which are the slots occupied by invoke method handle, and the
 194      *  target method handle, which are both at the beginning of the argument
 195      *  list used to invoke the target method handle.
 196      *  The longest possible invocation will look like
 197      *  {@code invokermh.invoke(targetmh, arg1, arg2, ..., arg253)}.
 198      */
 199     /*non-public*/
 200     static final int MAX_MH_INVOKER_ARITY = MAX_MH_ARITY-1;  // deduct one more for invoker
 201 
 202     /** Return number of extra slots (count of long/double args). */
 203     private static int checkPtypes(Class<?>[] ptypes) {
 204         int slots = 0;
 205         for (Class<?> ptype : ptypes) {
 206             Objects.requireNonNull(ptype);
 207             if (ptype == void.class)
 208                 throw newIllegalArgumentException("parameter type cannot be void");
 209             if (ptype == double.class || ptype == long.class) {
 210                 slots++;
 211             }
 212         }
 213         checkSlotCount(ptypes.length + slots);
 214         return slots;
 215     }
 216 
 217     static {
 218         // MAX_JVM_ARITY must be power of 2 minus 1 for following code trick to work:
 219         assert((MAX_JVM_ARITY & (MAX_JVM_ARITY+1)) == 0);
 220     }
 221     static void checkSlotCount(int count) {
 222         if ((count & MAX_JVM_ARITY) != count)
 223             throw newIllegalArgumentException("bad parameter count "+count);
 224     }
 225     private static IndexOutOfBoundsException newIndexOutOfBoundsException(Object num) {
 226         if (num instanceof Integer)  num = "bad index: "+num;
 227         return new IndexOutOfBoundsException(num.toString());
 228     }
 229 
 230     static final ConcurrentWeakInternSet<MethodType> internTable = new ConcurrentWeakInternSet<>();
 231 
 232     static final Class<?>[] NO_PTYPES = {};
 233 
 234     /**
 235      * Finds or creates an instance of the given method type.
 236      * @param rtype  the return type
 237      * @param ptypes the parameter types
 238      * @return a method type with the given components
 239      * @throws NullPointerException if {@code rtype} or {@code ptypes} or any element of {@code ptypes} is null
 240      * @throws IllegalArgumentException if any element of {@code ptypes} is {@code void.class}
 241      */
 242     public static MethodType methodType(Class<?> rtype, Class<?>[] ptypes) {
 243         return makeImpl(rtype, ptypes, false);
 244     }
 245 
 246     /**
 247      * Finds or creates a method type with the given components.
 248      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 249      * @param rtype  the return type
 250      * @param ptypes the parameter types
 251      * @return a method type with the given components
 252      * @throws NullPointerException if {@code rtype} or {@code ptypes} or any element of {@code ptypes} is null
 253      * @throws IllegalArgumentException if any element of {@code ptypes} is {@code void.class}
 254      */
 255     public static MethodType methodType(Class<?> rtype, List<Class<?>> ptypes) {
 256         boolean notrust = false;  // random List impl. could return evil ptypes array
 257         return makeImpl(rtype, listToArray(ptypes), notrust);
 258     }
 259 
 260     private static Class<?>[] listToArray(List<Class<?>> ptypes) {
 261         // sanity check the size before the toArray call, since size might be huge
 262         checkSlotCount(ptypes.size());
 263         return ptypes.toArray(NO_PTYPES);
 264     }
 265 
 266     /**
 267      * Finds or creates a method type with the given components.
 268      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 269      * The leading parameter type is prepended to the remaining array.
 270      * @param rtype  the return type
 271      * @param ptype0 the first parameter type
 272      * @param ptypes the remaining parameter types
 273      * @return a method type with the given components
 274      * @throws NullPointerException if {@code rtype} or {@code ptype0} or {@code ptypes} or any element of {@code ptypes} is null
 275      * @throws IllegalArgumentException if {@code ptype0} or {@code ptypes} or any element of {@code ptypes} is {@code void.class}
 276      */
 277     public static MethodType methodType(Class<?> rtype, Class<?> ptype0, Class<?>... ptypes) {
 278         Class<?>[] ptypes1 = new Class<?>[1+ptypes.length];
 279         ptypes1[0] = ptype0;
 280         System.arraycopy(ptypes, 0, ptypes1, 1, ptypes.length);
 281         return makeImpl(rtype, ptypes1, true);
 282     }
 283 
 284     /**
 285      * Finds or creates a method type with the given components.
 286      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 287      * The resulting method has no parameter types.
 288      * @param rtype  the return type
 289      * @return a method type with the given return value
 290      * @throws NullPointerException if {@code rtype} is null
 291      */
 292     public static MethodType methodType(Class<?> rtype) {
 293         return makeImpl(rtype, NO_PTYPES, true);
 294     }
 295 
 296     /**
 297      * Finds or creates a method type with the given components.
 298      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 299      * The resulting method has the single given parameter type.
 300      * @param rtype  the return type
 301      * @param ptype0 the parameter type
 302      * @return a method type with the given return value and parameter type
 303      * @throws NullPointerException if {@code rtype} or {@code ptype0} is null
 304      * @throws IllegalArgumentException if {@code ptype0} is {@code void.class}
 305      */
 306     public static MethodType methodType(Class<?> rtype, Class<?> ptype0) {
 307         return makeImpl(rtype, new Class<?>[]{ ptype0 }, true);
 308     }
 309 
 310     /**
 311      * Finds or creates a method type with the given components.
 312      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 313      * The resulting method has the same parameter types as {@code ptypes},
 314      * and the specified return type.
 315      * @param rtype  the return type
 316      * @param ptypes the method type which supplies the parameter types
 317      * @return a method type with the given components
 318      * @throws NullPointerException if {@code rtype} or {@code ptypes} is null
 319      */
 320     public static MethodType methodType(Class<?> rtype, MethodType ptypes) {
 321         return makeImpl(rtype, ptypes.ptypes, true);
 322     }
 323 
 324     /**
 325      * Sole factory method to find or create an interned method type. Will perform
 326      * input validation on behalf of factory methods
 327      *
 328      * @param rtype desired return type
 329      * @param ptypes desired parameter types
 330      * @param trusted whether the ptypes can be used without cloning
 331      * @throws NullPointerException if {@code rtype} or {@code ptypes} or any element of {@code ptypes} is null
 332      * @throws IllegalArgumentException if any element of {@code ptypes} is {@code void.class}
 333      * @return the unique method type of the desired structure
 334      */
 335     /*trusted*/
 336     static MethodType makeImpl(Class<?> rtype, Class<?>[] ptypes, boolean trusted) {
 337         if (ptypes.length == 0) {
 338             ptypes = NO_PTYPES; trusted = true;
 339         }
 340         MethodType primordialMT = new MethodType(rtype, ptypes);
 341         MethodType mt = internTable.get(primordialMT);
 342         if (mt != null)
 343             return mt;
 344 
 345         // promote the object to the Real Thing, and reprobe
 346         Objects.requireNonNull(rtype);
 347         if (trusted) {
 348             MethodType.checkPtypes(ptypes);
 349             mt = primordialMT;
 350         } else {
 351             // Make defensive copy then validate
 352             ptypes = Arrays.copyOf(ptypes, ptypes.length);
 353             MethodType.checkPtypes(ptypes);
 354             mt = new MethodType(rtype, ptypes);
 355         }
 356         mt.form = MethodTypeForm.findForm(mt);
 357         return internTable.add(mt);
 358     }
 359     private static final @Stable MethodType[] objectOnlyTypes = new MethodType[20];
 360 
 361     /**
 362      * Finds or creates a method type whose components are {@code Object} with an optional trailing {@code Object[]} array.
 363      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 364      * All parameters and the return type will be {@code Object},
 365      * except the final array parameter if any, which will be {@code Object[]}.
 366      * @param objectArgCount number of parameters (excluding the final array parameter if any)
 367      * @param finalArray whether there will be a trailing array parameter, of type {@code Object[]}
 368      * @return a generally applicable method type, for all calls of the given fixed argument count and a collected array of further arguments
 369      * @throws IllegalArgumentException if {@code objectArgCount} is negative or greater than 255 (or 254, if {@code finalArray} is true)
 370      * @see #genericMethodType(int)
 371      */
 372     public static MethodType genericMethodType(int objectArgCount, boolean finalArray) {
 373         MethodType mt;
 374         checkSlotCount(objectArgCount);
 375         int ivarargs = (!finalArray ? 0 : 1);
 376         int ootIndex = objectArgCount*2 + ivarargs;
 377         if (ootIndex < objectOnlyTypes.length) {
 378             mt = objectOnlyTypes[ootIndex];
 379             if (mt != null)  return mt;
 380         }
 381         Class<?>[] ptypes = new Class<?>[objectArgCount + ivarargs];
 382         Arrays.fill(ptypes, Object.class);
 383         if (ivarargs != 0)  ptypes[objectArgCount] = Object[].class;
 384         mt = makeImpl(Object.class, ptypes, true);
 385         if (ootIndex < objectOnlyTypes.length) {
 386             objectOnlyTypes[ootIndex] = mt;     // cache it here also!
 387         }
 388         return mt;
 389     }
 390 
 391     /**
 392      * Finds or creates a method type whose components are all {@code Object}.
 393      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 394      * All parameters and the return type will be Object.
 395      * @param objectArgCount number of parameters
 396      * @return a generally applicable method type, for all calls of the given argument count
 397      * @throws IllegalArgumentException if {@code objectArgCount} is negative or greater than 255
 398      * @see #genericMethodType(int, boolean)
 399      */
 400     public static MethodType genericMethodType(int objectArgCount) {
 401         return genericMethodType(objectArgCount, false);
 402     }
 403 
 404     /**
 405      * Finds or creates a method type with a single different parameter type.
 406      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 407      * @param num    the index (zero-based) of the parameter type to change
 408      * @param nptype a new parameter type to replace the old one with
 409      * @return the same type, except with the selected parameter changed
 410      * @throws IndexOutOfBoundsException if {@code num} is not a valid index into {@code parameterArray()}
 411      * @throws IllegalArgumentException if {@code nptype} is {@code void.class}
 412      * @throws NullPointerException if {@code nptype} is null
 413      */
 414     public MethodType changeParameterType(int num, Class<?> nptype) {
 415         if (parameterType(num) == nptype)  return this;
 416         Class<?>[] nptypes = ptypes.clone();
 417         nptypes[num] = nptype;
 418         return makeImpl(rtype, nptypes, true);
 419     }
 420 
 421     /**
 422      * Finds or creates a method type with additional parameter types.
 423      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 424      * @param num    the position (zero-based) of the inserted parameter type(s)
 425      * @param ptypesToInsert zero or more new parameter types to insert into the parameter list
 426      * @return the same type, except with the selected parameter(s) inserted
 427      * @throws IndexOutOfBoundsException if {@code num} is negative or greater than {@code parameterCount()}
 428      * @throws IllegalArgumentException if any element of {@code ptypesToInsert} is {@code void.class}
 429      *                                  or if the resulting method type would have more than 255 parameter slots
 430      * @throws NullPointerException if {@code ptypesToInsert} or any of its elements is null
 431      */
 432     public MethodType insertParameterTypes(int num, Class<?>... ptypesToInsert) {
 433         int len = ptypes.length;
 434         if (num < 0 || num > len)
 435             throw newIndexOutOfBoundsException(num);
 436         int ins = checkPtypes(ptypesToInsert);
 437         checkSlotCount(parameterSlotCount() + ptypesToInsert.length + ins);
 438         int ilen = ptypesToInsert.length;
 439         if (ilen == 0)  return this;
 440         Class<?>[] nptypes = new Class<?>[len + ilen];
 441         if (num > 0) {
 442             System.arraycopy(ptypes, 0, nptypes, 0, num);
 443         }
 444         System.arraycopy(ptypesToInsert, 0, nptypes, num, ilen);
 445         if (num < len) {
 446             System.arraycopy(ptypes, num, nptypes, num+ilen, len-num);
 447         }
 448         return makeImpl(rtype, nptypes, true);
 449     }
 450 
 451     /**
 452      * Finds or creates a method type with additional parameter types.
 453      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 454      * @param ptypesToInsert zero or more new parameter types to insert after the end of the parameter list
 455      * @return the same type, except with the selected parameter(s) appended
 456      * @throws IllegalArgumentException if any element of {@code ptypesToInsert} is {@code void.class}
 457      *                                  or if the resulting method type would have more than 255 parameter slots
 458      * @throws NullPointerException if {@code ptypesToInsert} or any of its elements is null
 459      */
 460     public MethodType appendParameterTypes(Class<?>... ptypesToInsert) {
 461         return insertParameterTypes(parameterCount(), ptypesToInsert);
 462     }
 463 
 464     /**
 465      * Finds or creates a method type with additional parameter types.
 466      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 467      * @param num    the position (zero-based) of the inserted parameter type(s)
 468      * @param ptypesToInsert zero or more new parameter types to insert into the parameter list
 469      * @return the same type, except with the selected parameter(s) inserted
 470      * @throws IndexOutOfBoundsException if {@code num} is negative or greater than {@code parameterCount()}
 471      * @throws IllegalArgumentException if any element of {@code ptypesToInsert} is {@code void.class}
 472      *                                  or if the resulting method type would have more than 255 parameter slots
 473      * @throws NullPointerException if {@code ptypesToInsert} or any of its elements is null
 474      */
 475     public MethodType insertParameterTypes(int num, List<Class<?>> ptypesToInsert) {
 476         return insertParameterTypes(num, listToArray(ptypesToInsert));
 477     }
 478 
 479     /**
 480      * Finds or creates a method type with additional parameter types.
 481      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 482      * @param ptypesToInsert zero or more new parameter types to insert after the end of the parameter list
 483      * @return the same type, except with the selected parameter(s) appended
 484      * @throws IllegalArgumentException if any element of {@code ptypesToInsert} is {@code void.class}
 485      *                                  or if the resulting method type would have more than 255 parameter slots
 486      * @throws NullPointerException if {@code ptypesToInsert} or any of its elements is null
 487      */
 488     public MethodType appendParameterTypes(List<Class<?>> ptypesToInsert) {
 489         return insertParameterTypes(parameterCount(), ptypesToInsert);
 490     }
 491 
 492     /**
 493      * Finds or creates a method type with modified parameter types.
 494      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 495      * @param start  the position (zero-based) of the first replaced parameter type(s)
 496      * @param end    the position (zero-based) after the last replaced parameter type(s)
 497      * @param ptypesToInsert zero or more new parameter types to insert into the parameter list
 498      * @return the same type, except with the selected parameter(s) replaced
 499      * @throws IndexOutOfBoundsException if {@code start} is negative or greater than {@code parameterCount()}
 500      *                                  or if {@code end} is negative or greater than {@code parameterCount()}
 501      *                                  or if {@code start} is greater than {@code end}
 502      * @throws IllegalArgumentException if any element of {@code ptypesToInsert} is {@code void.class}
 503      *                                  or if the resulting method type would have more than 255 parameter slots
 504      * @throws NullPointerException if {@code ptypesToInsert} or any of its elements is null
 505      */
 506     /*non-public*/
 507     MethodType replaceParameterTypes(int start, int end, Class<?>... ptypesToInsert) {
 508         if (start == end)
 509             return insertParameterTypes(start, ptypesToInsert);
 510         int len = ptypes.length;
 511         if (!(0 <= start && start <= end && end <= len))
 512             throw newIndexOutOfBoundsException("start="+start+" end="+end);
 513         int ilen = ptypesToInsert.length;
 514         if (ilen == 0)
 515             return dropParameterTypes(start, end);
 516         return dropParameterTypes(start, end).insertParameterTypes(start, ptypesToInsert);
 517     }
 518 
 519     /** Replace the last arrayLength parameter types with the component type of arrayType.
 520      * @param arrayType any array type
 521      * @param pos position at which to spread
 522      * @param arrayLength the number of parameter types to change
 523      * @return the resulting type
 524      */
 525     /*non-public*/
 526     MethodType asSpreaderType(Class<?> arrayType, int pos, int arrayLength) {
 527         assert(parameterCount() >= arrayLength);
 528         int spreadPos = pos;
 529         if (arrayLength == 0)  return this;  // nothing to change
 530         if (arrayType == Object[].class) {
 531             if (isGeneric())  return this;  // nothing to change
 532             if (spreadPos == 0) {
 533                 // no leading arguments to preserve; go generic
 534                 MethodType res = genericMethodType(arrayLength);
 535                 if (rtype != Object.class) {
 536                     res = res.changeReturnType(rtype);
 537                 }
 538                 return res;
 539             }
 540         }
 541         Class<?> elemType = arrayType.getComponentType();
 542         assert(elemType != null);
 543         for (int i = spreadPos; i < spreadPos + arrayLength; i++) {
 544             if (ptypes[i] != elemType) {
 545                 Class<?>[] fixedPtypes = ptypes.clone();
 546                 Arrays.fill(fixedPtypes, i, spreadPos + arrayLength, elemType);
 547                 return methodType(rtype, fixedPtypes);
 548             }
 549         }
 550         return this;  // arguments check out; no change
 551     }
 552 
 553     /** Return the leading parameter type, which must exist and be a reference.
 554      *  @return the leading parameter type, after error checks
 555      */
 556     /*non-public*/
 557     Class<?> leadingReferenceParameter() {
 558         Class<?> ptype;
 559         if (ptypes.length == 0 ||
 560             (ptype = ptypes[0]).isPrimitive())
 561             throw newIllegalArgumentException("no leading reference parameter");
 562         return ptype;
 563     }
 564 
 565     /** Delete the last parameter type and replace it with arrayLength copies of the component type of arrayType.
 566      * @param arrayType any array type
 567      * @param pos position at which to insert parameters
 568      * @param arrayLength the number of parameter types to insert
 569      * @return the resulting type
 570      */
 571     /*non-public*/
 572     MethodType asCollectorType(Class<?> arrayType, int pos, int arrayLength) {
 573         assert(parameterCount() >= 1);
 574         assert(pos < ptypes.length);
 575         assert(ptypes[pos].isAssignableFrom(arrayType));
 576         MethodType res;
 577         if (arrayType == Object[].class) {
 578             res = genericMethodType(arrayLength);
 579             if (rtype != Object.class) {
 580                 res = res.changeReturnType(rtype);
 581             }
 582         } else {
 583             Class<?> elemType = arrayType.getComponentType();
 584             assert(elemType != null);
 585             res = methodType(rtype, Collections.nCopies(arrayLength, elemType));
 586         }
 587         if (ptypes.length == 1) {
 588             return res;
 589         } else {
 590             // insert after (if need be), then before
 591             if (pos < ptypes.length - 1) {
 592                 res = res.insertParameterTypes(arrayLength, Arrays.copyOfRange(ptypes, pos + 1, ptypes.length));
 593             }
 594             return res.insertParameterTypes(0, Arrays.copyOf(ptypes, pos));
 595         }
 596     }
 597 
 598     /**
 599      * Finds or creates a method type with some parameter types omitted.
 600      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 601      * @param start  the index (zero-based) of the first parameter type to remove
 602      * @param end    the index (greater than {@code start}) of the first parameter type after not to remove
 603      * @return the same type, except with the selected parameter(s) removed
 604      * @throws IndexOutOfBoundsException if {@code start} is negative or greater than {@code parameterCount()}
 605      *                                  or if {@code end} is negative or greater than {@code parameterCount()}
 606      *                                  or if {@code start} is greater than {@code end}
 607      */
 608     public MethodType dropParameterTypes(int start, int end) {
 609         int len = ptypes.length;
 610         if (!(0 <= start && start <= end && end <= len))
 611             throw newIndexOutOfBoundsException("start="+start+" end="+end);
 612         if (start == end)  return this;
 613         Class<?>[] nptypes;
 614         if (start == 0) {
 615             if (end == len) {
 616                 // drop all parameters
 617                 nptypes = NO_PTYPES;
 618             } else {
 619                 // drop initial parameter(s)
 620                 nptypes = Arrays.copyOfRange(ptypes, end, len);
 621             }
 622         } else {
 623             if (end == len) {
 624                 // drop trailing parameter(s)
 625                 nptypes = Arrays.copyOfRange(ptypes, 0, start);
 626             } else {
 627                 int tail = len - end;
 628                 nptypes = Arrays.copyOfRange(ptypes, 0, start + tail);
 629                 System.arraycopy(ptypes, end, nptypes, start, tail);
 630             }
 631         }
 632         return makeImpl(rtype, nptypes, true);
 633     }
 634 
 635     /**
 636      * Finds or creates a method type with a different return type.
 637      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 638      * @param nrtype a return parameter type to replace the old one with
 639      * @return the same type, except with the return type change
 640      * @throws NullPointerException if {@code nrtype} is null
 641      */
 642     public MethodType changeReturnType(Class<?> nrtype) {
 643         if (returnType() == nrtype)  return this;
 644         return makeImpl(nrtype, ptypes, true);
 645     }
 646 
 647     /**
 648      * Reports if this type contains a primitive argument or return value.
 649      * The return type {@code void} counts as a primitive.
 650      * @return true if any of the types are primitives
 651      */
 652     public boolean hasPrimitives() {
 653         return form.hasPrimitives();
 654     }
 655 
 656     /**
 657      * Reports if this type contains a wrapper argument or return value.
 658      * Wrappers are types which box primitive values, such as {@link Integer}.
 659      * The reference type {@code java.lang.Void} counts as a wrapper,
 660      * if it occurs as a return type.
 661      * @return true if any of the types are wrappers
 662      */
 663     public boolean hasWrappers() {
 664         return unwrap() != this;
 665     }
 666 
 667     /**
 668      * Erases all reference types to {@code Object}.
 669      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 670      * All primitive types (including {@code void}) will remain unchanged.
 671      * @return a version of the original type with all reference types replaced
 672      */
 673     public MethodType erase() {
 674         return form.erasedType();
 675     }
 676 
 677     /**
 678      * Erases all reference types to {@code Object}, and all subword types to {@code int}.
 679      * This is the reduced type polymorphism used by private methods
 680      * such as {@link MethodHandle#invokeBasic invokeBasic}.
 681      * @return a version of the original type with all reference and subword types replaced
 682      */
 683     /*non-public*/
 684     MethodType basicType() {
 685         return form.basicType();
 686     }
 687 
 688     private static final @Stable Class<?>[] METHOD_HANDLE_ARRAY
 689             = new Class<?>[] { MethodHandle.class };
 690 
 691     /**
 692      * @return a version of the original type with MethodHandle prepended as the first argument
 693      */
 694     /*non-public*/
 695     MethodType invokerType() {
 696         return insertParameterTypes(0, METHOD_HANDLE_ARRAY);
 697     }
 698 
 699     /**
 700      * Converts all types, both reference and primitive, to {@code Object}.
 701      * Convenience method for {@link #genericMethodType(int) genericMethodType}.
 702      * The expression {@code type.wrap().erase()} produces the same value
 703      * as {@code type.generic()}.
 704      * @return a version of the original type with all types replaced
 705      */
 706     public MethodType generic() {
 707         return genericMethodType(parameterCount());
 708     }
 709 
 710     /*non-public*/
 711     boolean isGeneric() {
 712         return this == erase() && !hasPrimitives();
 713     }
 714 
 715     /**
 716      * Converts all primitive types to their corresponding wrapper types.
 717      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 718      * All reference types (including wrapper types) will remain unchanged.
 719      * A {@code void} return type is changed to the type {@code java.lang.Void}.
 720      * The expression {@code type.wrap().erase()} produces the same value
 721      * as {@code type.generic()}.
 722      * @return a version of the original type with all primitive types replaced
 723      */
 724     public MethodType wrap() {
 725         return hasPrimitives() ? wrapWithPrims(this) : this;
 726     }
 727 
 728     /**
 729      * Converts all wrapper types to their corresponding primitive types.
 730      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
 731      * All primitive types (including {@code void}) will remain unchanged.
 732      * A return type of {@code java.lang.Void} is changed to {@code void}.
 733      * @return a version of the original type with all wrapper types replaced
 734      */
 735     public MethodType unwrap() {
 736         MethodType noprims = !hasPrimitives() ? this : wrapWithPrims(this);
 737         return unwrapWithNoPrims(noprims);
 738     }
 739 
 740     private static MethodType wrapWithPrims(MethodType pt) {
 741         assert(pt.hasPrimitives());
 742         MethodType wt = (MethodType)pt.wrapAlt;
 743         if (wt == null) {
 744             // fill in lazily
 745             wt = MethodTypeForm.canonicalize(pt, MethodTypeForm.WRAP);
 746             assert(wt != null);
 747             pt.wrapAlt = wt;
 748         }
 749         return wt;
 750     }
 751 
 752     private static MethodType unwrapWithNoPrims(MethodType wt) {
 753         assert(!wt.hasPrimitives());
 754         MethodType uwt = (MethodType)wt.wrapAlt;
 755         if (uwt == null) {
 756             // fill in lazily
 757             uwt = MethodTypeForm.canonicalize(wt, MethodTypeForm.UNWRAP);
 758             if (uwt == null)
 759                 uwt = wt;    // type has no wrappers or prims at all
 760             wt.wrapAlt = uwt;
 761         }
 762         return uwt;
 763     }
 764 
 765     /**
 766      * Returns the parameter type at the specified index, within this method type.
 767      * @param num the index (zero-based) of the desired parameter type
 768      * @return the selected parameter type
 769      * @throws IndexOutOfBoundsException if {@code num} is not a valid index into {@code parameterArray()}
 770      */
 771     public Class<?> parameterType(int num) {
 772         return ptypes[num];
 773     }
 774     /**
 775      * Returns the number of parameter types in this method type.
 776      * @return the number of parameter types
 777      */
 778     public int parameterCount() {
 779         return ptypes.length;
 780     }
 781     /**
 782      * Returns the return type of this method type.
 783      * @return the return type
 784      */
 785     public Class<?> returnType() {
 786         return rtype;
 787     }
 788 
 789     /**
 790      * Presents the parameter types as a list (a convenience method).
 791      * The list will be immutable.
 792      * @return the parameter types (as an immutable list)
 793      */
 794     public List<Class<?>> parameterList() {
 795         return List.of(ptypes);
 796     }
 797 
 798     /**
 799      * Returns the last parameter type of this method type.
 800      * If this type has no parameters, the sentinel value
 801      * {@code void.class} is returned instead.
 802      * @apiNote
 803      * <p>
 804      * The sentinel value is chosen so that reflective queries can be
 805      * made directly against the result value.
 806      * The sentinel value cannot be confused with a real parameter,
 807      * since {@code void} is never acceptable as a parameter type.
 808      * For variable arity invocation modes, the expression
 809      * {@link Class#getComponentType lastParameterType().getComponentType()}
 810      * is useful to query the type of the "varargs" parameter.
 811      * @return the last parameter type if any, else {@code void.class}
 812      * @since 10
 813      */
 814     public Class<?> lastParameterType() {
 815         int len = ptypes.length;
 816         return len == 0 ? void.class : ptypes[len-1];
 817     }
 818 
 819     /**
 820      * Presents the parameter types as an array (a convenience method).
 821      * Changes to the array will not result in changes to the type.
 822      * @return the parameter types (as a fresh copy if necessary)
 823      */
 824     public Class<?>[] parameterArray() {
 825         return ptypes.clone();
 826     }
 827 
 828     /**
 829      * Compares the specified object with this type for equality.
 830      * That is, it returns {@code true} if and only if the specified object
 831      * is also a method type with exactly the same parameters and return type.
 832      * @param x object to compare
 833      * @see Object#equals(Object)
 834      */
 835     // This implementation may also return true if x is a WeakEntry containing
 836     // a method type that is equal to this. This is an internal implementation
 837     // detail to allow for faster method type lookups.
 838     // See ConcurrentWeakInternSet.WeakEntry#equals(Object)
 839     @Override
 840     public boolean equals(Object x) {
 841         if (this == x) {
 842             return true;
 843         }
 844         if (x instanceof MethodType) {
 845             return equals((MethodType)x);
 846         }
 847         if (x instanceof ConcurrentWeakInternSet.WeakEntry) {
 848             Object o = ((ConcurrentWeakInternSet.WeakEntry)x).get();
 849             if (o instanceof MethodType) {
 850                 return equals((MethodType)o);
 851             }
 852         }
 853         return false;
 854     }
 855 
 856     private boolean equals(MethodType that) {
 857         return this.rtype == that.rtype
 858             && Arrays.equals(this.ptypes, that.ptypes);
 859     }
 860 
 861     /**
 862      * Returns the hash code value for this method type.
 863      * It is defined to be the same as the hashcode of a List
 864      * whose elements are the return type followed by the
 865      * parameter types.
 866      * @return the hash code value for this method type
 867      * @see Object#hashCode()
 868      * @see #equals(Object)
 869      * @see List#hashCode()
 870      */
 871     @Override
 872     public int hashCode() {
 873         int hashCode = 31 + rtype.hashCode();
 874         for (Class<?> ptype : ptypes)
 875             hashCode = 31 * hashCode + ptype.hashCode();
 876         return hashCode;
 877     }
 878 
 879     /**
 880      * Returns a string representation of the method type,
 881      * of the form {@code "(PT0,PT1...)RT"}.
 882      * The string representation of a method type is a
 883      * parenthesis enclosed, comma separated list of type names,
 884      * followed immediately by the return type.
 885      * <p>
 886      * Each type is represented by its
 887      * {@link java.lang.Class#getSimpleName simple name}.
 888      */
 889     @Override
 890     public String toString() {
 891         StringJoiner sj = new StringJoiner(",", "(",
 892                 ")" + rtype.getSimpleName());
 893         for (int i = 0; i < ptypes.length; i++) {
 894             sj.add(ptypes[i].getSimpleName());
 895         }
 896         return sj.toString();
 897     }
 898 







 899     /** True if my parameter list is effectively identical to the given full list,
 900      *  after skipping the given number of my own initial parameters.
 901      *  In other words, after disregarding {@code skipPos} parameters,
 902      *  my remaining parameter list is no longer than the {@code fullList}, and
 903      *  is equal to the same-length initial sublist of {@code fullList}.
 904      */
 905     /*non-public*/
 906     boolean effectivelyIdenticalParameters(int skipPos, List<Class<?>> fullList) {
 907         int myLen = ptypes.length, fullLen = fullList.size();
 908         if (skipPos > myLen || myLen - skipPos > fullLen)
 909             return false;
 910         List<Class<?>> myList = Arrays.asList(ptypes);
 911         if (skipPos != 0) {
 912             myList = myList.subList(skipPos, myLen);
 913             myLen -= skipPos;
 914         }
 915         if (fullLen == myLen)
 916             return myList.equals(fullList);
 917         else
 918             return myList.equals(fullList.subList(0, myLen));
 919     }
 920 
 921     /** True if the old return type can always be viewed (w/o casting) under new return type,
 922      *  and the new parameters can be viewed (w/o casting) under the old parameter types.
 923      */
 924     /*non-public*/
 925     boolean isViewableAs(MethodType newType, boolean keepInterfaces) {
 926         if (!VerifyType.isNullConversion(returnType(), newType.returnType(), keepInterfaces))
 927             return false;
 928         if (form == newType.form && form.erasedType == this)
 929             return true;  // my reference parameters are all Object
 930         if (ptypes == newType.ptypes)
 931             return true;
 932         int argc = parameterCount();
 933         if (argc != newType.parameterCount())
 934             return false;
 935         for (int i = 0; i < argc; i++) {
 936             if (!VerifyType.isNullConversion(newType.parameterType(i), parameterType(i), keepInterfaces))
 937                 return false;
 938         }
 939         return true;
 940     }
 941     /*non-public*/
 942     boolean isConvertibleTo(MethodType newType) {
 943         MethodTypeForm oldForm = this.form();
 944         MethodTypeForm newForm = newType.form();
 945         if (oldForm == newForm)
 946             // same parameter count, same primitive/object mix
 947             return true;
 948         if (!canConvert(returnType(), newType.returnType()))
 949             return false;
 950         Class<?>[] srcTypes = newType.ptypes;
 951         Class<?>[] dstTypes = ptypes;
 952         if (srcTypes == dstTypes)
 953             return true;
 954         int argc;
 955         if ((argc = srcTypes.length) != dstTypes.length)
 956             return false;
 957         if (argc <= 1) {
 958             if (argc == 1 && !canConvert(srcTypes[0], dstTypes[0]))
 959                 return false;
 960             return true;
 961         }
 962         if ((!oldForm.hasPrimitives() && oldForm.erasedType == this) ||
 963             (!newForm.hasPrimitives() && newForm.erasedType == newType)) {
 964             // Somewhat complicated test to avoid a loop of 2 or more trips.
 965             // If either type has only Object parameters, we know we can convert.
 966             assert(canConvertParameters(srcTypes, dstTypes));
 967             return true;
 968         }
 969         return canConvertParameters(srcTypes, dstTypes);
 970     }
 971 
 972     /** Returns true if MHs.explicitCastArguments produces the same result as MH.asType.
 973      *  If the type conversion is impossible for either, the result should be false.
 974      */
 975     /*non-public*/
 976     boolean explicitCastEquivalentToAsType(MethodType newType) {
 977         if (this == newType)  return true;
 978         if (!explicitCastEquivalentToAsType(rtype, newType.rtype)) {
 979             return false;
 980         }
 981         Class<?>[] srcTypes = newType.ptypes;
 982         Class<?>[] dstTypes = ptypes;
 983         if (dstTypes == srcTypes) {
 984             return true;
 985         }
 986         assert(dstTypes.length == srcTypes.length);
 987         for (int i = 0; i < dstTypes.length; i++) {
 988             if (!explicitCastEquivalentToAsType(srcTypes[i], dstTypes[i])) {
 989                 return false;
 990             }
 991         }
 992         return true;
 993     }
 994 
 995     /** Reports true if the src can be converted to the dst, by both asType and MHs.eCE,
 996      *  and with the same effect.
 997      *  MHs.eCA has the following "upgrades" to MH.asType:
 998      *  1. interfaces are unchecked (that is, treated as if aliased to Object)
 999      *     Therefore, {@code Object->CharSequence} is possible in both cases but has different semantics
1000      *  2. the full matrix of primitive-to-primitive conversions is supported
1001      *     Narrowing like {@code long->byte} and basic-typing like {@code boolean->int}
1002      *     are not supported by asType, but anything supported by asType is equivalent
1003      *     with MHs.eCE.
1004      *  3a. unboxing conversions can be followed by the full matrix of primitive conversions
1005      *  3b. unboxing of null is permitted (creates a zero primitive value)
1006      * Other than interfaces, reference-to-reference conversions are the same.
1007      * Boxing primitives to references is the same for both operators.
1008      */
1009     private static boolean explicitCastEquivalentToAsType(Class<?> src, Class<?> dst) {
1010         if (src == dst || dst == Object.class || dst == void.class)  return true;
1011         if (src.isPrimitive()) {
1012             // Could be a prim/prim conversion, where casting is a strict superset.
1013             // Or a boxing conversion, which is always to an exact wrapper class.
1014             return canConvert(src, dst);
1015         } else if (dst.isPrimitive()) {
1016             // Unboxing behavior is different between MHs.eCA & MH.asType (see 3b).
1017             return false;
1018         } else {
1019             // R->R always works, but we have to avoid a check-cast to an interface.
1020             return !dst.isInterface() || dst.isAssignableFrom(src);
1021         }
1022     }
1023 
1024     private boolean canConvertParameters(Class<?>[] srcTypes, Class<?>[] dstTypes) {
1025         for (int i = 0; i < srcTypes.length; i++) {
1026             if (!canConvert(srcTypes[i], dstTypes[i])) {
1027                 return false;
1028             }
1029         }
1030         return true;
1031     }
1032 
1033     /*non-public*/
1034     static boolean canConvert(Class<?> src, Class<?> dst) {
1035         // short-circuit a few cases:
1036         if (src == dst || src == Object.class || dst == Object.class)  return true;
1037         // the remainder of this logic is documented in MethodHandle.asType
1038         if (src.isPrimitive()) {
1039             // can force void to an explicit null, a la reflect.Method.invoke
1040             // can also force void to a primitive zero, by analogy
1041             if (src == void.class)  return true;  //or !dst.isPrimitive()?
1042             Wrapper sw = Wrapper.forPrimitiveType(src);
1043             if (dst.isPrimitive()) {
1044                 // P->P must widen
1045                 return Wrapper.forPrimitiveType(dst).isConvertibleFrom(sw);
1046             } else {
1047                 // P->R must box and widen
1048                 return dst.isAssignableFrom(sw.wrapperType());
1049             }
1050         } else if (dst.isPrimitive()) {
1051             // any value can be dropped
1052             if (dst == void.class)  return true;
1053             Wrapper dw = Wrapper.forPrimitiveType(dst);
1054             // R->P must be able to unbox (from a dynamically chosen type) and widen
1055             // For example:
1056             //   Byte/Number/Comparable/Object -> dw:Byte -> byte.
1057             //   Character/Comparable/Object -> dw:Character -> char
1058             //   Boolean/Comparable/Object -> dw:Boolean -> boolean
1059             // This means that dw must be cast-compatible with src.
1060             if (src.isAssignableFrom(dw.wrapperType())) {
1061                 return true;
1062             }
1063             // The above does not work if the source reference is strongly typed
1064             // to a wrapper whose primitive must be widened.  For example:
1065             //   Byte -> unbox:byte -> short/int/long/float/double
1066             //   Character -> unbox:char -> int/long/float/double
1067             if (Wrapper.isWrapperType(src) &&
1068                 dw.isConvertibleFrom(Wrapper.forWrapperType(src))) {
1069                 // can unbox from src and then widen to dst
1070                 return true;
1071             }
1072             // We have already covered cases which arise due to runtime unboxing
1073             // of a reference type which covers several wrapper types:
1074             //   Object -> cast:Integer -> unbox:int -> long/float/double
1075             //   Serializable -> cast:Byte -> unbox:byte -> byte/short/int/long/float/double
1076             // An marginal case is Number -> dw:Character -> char, which would be OK if there were a
1077             // subclass of Number which wraps a value that can convert to char.
1078             // Since there is none, we don't need an extra check here to cover char or boolean.
1079             return false;
1080         } else {
1081             // R->R always works, since null is always valid dynamically
1082             return true;
1083         }
1084     }
1085 
1086     /// Queries which have to do with the bytecode architecture
1087 
1088     /** Reports the number of JVM stack slots required to invoke a method
1089      * of this type.  Note that (for historical reasons) the JVM requires
1090      * a second stack slot to pass long and double arguments.
1091      * So this method returns {@link #parameterCount() parameterCount} plus the
1092      * number of long and double parameters (if any).
1093      * <p>
1094      * This method is included for the benefit of applications that must
1095      * generate bytecodes that process method handles and invokedynamic.
1096      * @return the number of JVM stack slots for this type's parameters
1097      */
1098     /*non-public*/
1099     int parameterSlotCount() {
1100         return form.parameterSlotCount();
1101     }
1102 
1103     /*non-public*/
1104     Invokers invokers() {
1105         Invokers inv = invokers;
1106         if (inv != null)  return inv;
1107         invokers = inv = new Invokers(this);
1108         return inv;
1109     }
1110 
1111     /**
1112      * Finds or creates an instance of a method type, given the spelling of its bytecode descriptor.
1113      * Convenience method for {@link #methodType(java.lang.Class, java.lang.Class[]) methodType}.
1114      * Any class or interface name embedded in the descriptor string will be
1115      * resolved by the given loader (or if it is null, on the system class loader).
1116      * <p>
1117      * Note that it is possible to encounter method types which cannot be
1118      * constructed by this method, because their component types are
1119      * not all reachable from a common class loader.
1120      * <p>
1121      * This method is included for the benefit of applications that must
1122      * generate bytecodes that process method handles and {@code invokedynamic}.
1123      * @param descriptor a bytecode-level type descriptor string "(T...)T"
1124      * @param loader the class loader in which to look up the types
1125      * @return a method type matching the bytecode-level type descriptor
1126      * @throws NullPointerException if the string is null
1127      * @throws IllegalArgumentException if the string is not well-formed
1128      * @throws TypeNotPresentException if a named type cannot be found
1129      * @throws SecurityException if the security manager is present and
1130      *         {@code loader} is {@code null} and the caller does not have the
1131      *         {@link RuntimePermission}{@code ("getClassLoader")}
1132      */
1133     public static MethodType fromMethodDescriptorString(String descriptor, ClassLoader loader)
1134         throws IllegalArgumentException, TypeNotPresentException
1135     {
1136         if (loader == null) {
1137             @SuppressWarnings("removal")
1138             SecurityManager sm = System.getSecurityManager();
1139             if (sm != null) {
1140                 sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
1141             }
1142         }
1143         return fromDescriptor(descriptor,
1144                               (loader == null) ? ClassLoader.getSystemClassLoader() : loader);
1145     }
1146 
1147     /**
1148      * Same as {@link #fromMethodDescriptorString(String, ClassLoader)}, but
1149      * {@code null} ClassLoader means the bootstrap loader is used here.
1150      * <p>
1151      * IMPORTANT: This method is preferable for JDK internal use as it more
1152      * correctly interprets {@code null} ClassLoader than
1153      * {@link #fromMethodDescriptorString(String, ClassLoader)}.
1154      * Use of this method also avoids early initialization issues when system
1155      * ClassLoader is not initialized yet.
1156      */
1157     static MethodType fromDescriptor(String descriptor, ClassLoader loader)
1158         throws IllegalArgumentException, TypeNotPresentException
1159     {
1160         if (!descriptor.startsWith("(") ||  // also generates NPE if needed
1161             descriptor.indexOf(')') < 0 ||
1162             descriptor.indexOf('.') >= 0)
1163             throw newIllegalArgumentException("not a method descriptor: "+descriptor);
1164         List<Class<?>> types = BytecodeDescriptor.parseMethod(descriptor, loader);
1165         Class<?> rtype = types.remove(types.size() - 1);
1166         Class<?>[] ptypes = listToArray(types);
1167         return makeImpl(rtype, ptypes, true);
1168     }
1169 
1170     /**
1171      * Returns a descriptor string for the method type.  This method
1172      * is equivalent to calling {@link #descriptorString() MethodType::descriptorString}.
1173      *
1174      * <p>
1175      * Note that this is not a strict inverse of {@link #fromMethodDescriptorString fromMethodDescriptorString}.
1176      * Two distinct classes which share a common name but have different class loaders
1177      * will appear identical when viewed within descriptor strings.
1178      * <p>
1179      * This method is included for the benefit of applications that must
1180      * generate bytecodes that process method handles and {@code invokedynamic}.
1181      * {@link #fromMethodDescriptorString(java.lang.String, java.lang.ClassLoader) fromMethodDescriptorString},
1182      * because the latter requires a suitable class loader argument.
1183      * @return the descriptor string for this method type
1184      * @jvms 4.3.3 Method Descriptors
1185      * @see <a href="#descriptor">Nominal Descriptor for {@code MethodType}</a>
1186      */
1187     public String toMethodDescriptorString() {
1188         String desc = methodDescriptor;
1189         if (desc == null) {
1190             desc = BytecodeDescriptor.unparseMethod(this.rtype, this.ptypes);
1191             methodDescriptor = desc;
1192         }
1193         return desc;
1194     }
1195 
1196     /**
1197      * Returns a descriptor string for this method type.
1198      *
1199      * <p>
1200      * If this method type can be <a href="#descriptor">described nominally</a>,
1201      * then the result is a method type descriptor (JVMS {@jvms 4.3.3}).
1202      * {@link MethodTypeDesc MethodTypeDesc} for this method type
1203      * can be produced by calling {@link MethodTypeDesc#ofDescriptor(String)
1204      * MethodTypeDesc::ofDescriptor} with the result descriptor string.
1205      * <p>
1206      * If this method type cannot be <a href="#descriptor">described nominally</a>
1207      * and the result is a string of the form:
1208      * <blockquote>{@code "(<parameter-descriptors>)<return-descriptor>"}</blockquote>
1209      * where {@code <parameter-descriptors>} is the concatenation of the
1210      * {@linkplain Class#descriptorString() descriptor string} of all
1211      * of the parameter types and the {@linkplain Class#descriptorString() descriptor string}
1212      * of the return type. No {@link java.lang.constant.MethodTypeDesc MethodTypeDesc}
1213      * can be produced from the result string.
1214      *
1215      * @return the descriptor string for this method type
1216      * @since 12
1217      * @jvms 4.3.3 Method Descriptors
1218      * @see <a href="#descriptor">Nominal Descriptor for {@code MethodType}</a>
1219      */
1220     @Override
1221     public String descriptorString() {
1222         return toMethodDescriptorString();
1223     }
1224 
1225     /*non-public*/
1226     static String toFieldDescriptorString(Class<?> cls) {
1227         return BytecodeDescriptor.unparse(cls);
1228     }
1229 
1230     /**
1231      * Returns a nominal descriptor for this instance, if one can be
1232      * constructed, or an empty {@link Optional} if one cannot be.
1233      *
1234      * @return An {@link Optional} containing the resulting nominal descriptor,
1235      * or an empty {@link Optional} if one cannot be constructed.
1236      * @since 12
1237      * @see <a href="#descriptor">Nominal Descriptor for {@code MethodType}</a>
1238      */
1239     @Override
1240     public Optional<MethodTypeDesc> describeConstable() {
1241         try {
1242             return Optional.of(MethodTypeDesc.of(returnType().describeConstable().orElseThrow(),
1243                                                  Stream.of(parameterArray())
1244                                                       .map(p -> p.describeConstable().orElseThrow())
1245                                                       .toArray(ClassDesc[]::new)));
1246         }
1247         catch (NoSuchElementException e) {
1248             return Optional.empty();
1249         }
1250     }
1251 
1252     /// Serialization.
1253 
1254     /**
1255      * There are no serializable fields for {@code MethodType}.
1256      */
1257     @java.io.Serial
1258     private static final java.io.ObjectStreamField[] serialPersistentFields = { };
1259 
1260     /**
1261      * Save the {@code MethodType} instance to a stream.
1262      *
1263      * @serialData
1264      * For portability, the serialized format does not refer to named fields.
1265      * Instead, the return type and parameter type arrays are written directly
1266      * from the {@code writeObject} method, using two calls to {@code s.writeObject}
1267      * as follows:
1268      * <blockquote><pre>{@code
1269 s.writeObject(this.returnType());
1270 s.writeObject(this.parameterArray());
1271      * }</pre></blockquote>
1272      * <p>
1273      * The deserialized field values are checked as if they were
1274      * provided to the factory method {@link #methodType(Class,Class[]) methodType}.
1275      * For example, null values, or {@code void} parameter types,
1276      * will lead to exceptions during deserialization.
1277      * @param s the stream to write the object to
1278      * @throws java.io.IOException if there is a problem writing the object
1279      */
1280     @java.io.Serial
1281     private void writeObject(java.io.ObjectOutputStream s) throws java.io.IOException {
1282         s.defaultWriteObject();  // requires serialPersistentFields to be an empty array
1283         s.writeObject(returnType());
1284         s.writeObject(parameterArray());
1285     }
1286 
1287     /**
1288      * Reconstitute the {@code MethodType} instance from a stream (that is,
1289      * deserialize it).
1290      * This instance is a scratch object with bogus final fields.
1291      * It provides the parameters to the factory method called by
1292      * {@link #readResolve readResolve}.
1293      * After that call it is discarded.
1294      * @param s the stream to read the object from
1295      * @throws java.io.IOException if there is a problem reading the object
1296      * @throws ClassNotFoundException if one of the component classes cannot be resolved
1297      * @see #readResolve
1298      * @see #writeObject
1299      */
1300     @java.io.Serial
1301     private void readObject(java.io.ObjectInputStream s) throws java.io.IOException, ClassNotFoundException {
1302         // Assign defaults in case this object escapes
1303         UNSAFE.putReference(this, OffsetHolder.rtypeOffset, void.class);
1304         UNSAFE.putReference(this, OffsetHolder.ptypesOffset, NO_PTYPES);
1305 
1306         s.defaultReadObject();  // requires serialPersistentFields to be an empty array
1307 
1308         Class<?>   returnType     = (Class<?>)   s.readObject();
1309         Class<?>[] parameterArray = (Class<?>[]) s.readObject();
1310 
1311         // Verify all operands, and make sure ptypes is unshared
1312         // Cache the new MethodType for readResolve
1313         wrapAlt = new MethodType[]{MethodType.methodType(returnType, parameterArray)};
1314     }
1315 
1316     // Support for resetting final fields while deserializing. Implement Holder
1317     // pattern to make the rarely needed offset calculation lazy.
1318     private static class OffsetHolder {
1319         static final long rtypeOffset
1320                 = UNSAFE.objectFieldOffset(MethodType.class, "rtype");
1321 
1322         static final long ptypesOffset
1323                 = UNSAFE.objectFieldOffset(MethodType.class, "ptypes");
1324     }
1325 
1326     /**
1327      * Resolves and initializes a {@code MethodType} object
1328      * after serialization.
1329      * @return the fully initialized {@code MethodType} object
1330      */
1331     @java.io.Serial
1332     private Object readResolve() {
1333         // Do not use a trusted path for deserialization:
1334         //    return makeImpl(rtype, ptypes, true);
1335         // Verify all operands, and make sure ptypes is unshared:
1336         // Return a new validated MethodType for the rtype and ptypes passed from readObject.
1337         MethodType mt = ((MethodType[])wrapAlt)[0];
1338         wrapAlt = null;
1339         return mt;
1340     }
1341 
1342     /**
1343      * Simple implementation of weak concurrent intern set.
1344      *
1345      * @param <T> interned type
1346      */
1347     private static class ConcurrentWeakInternSet<T> {
1348 
1349         private final ConcurrentMap<WeakEntry<T>, WeakEntry<T>> map;
1350         private final ReferenceQueue<T> stale;
1351 
1352         public ConcurrentWeakInternSet() {
1353             this.map = new ConcurrentHashMap<>(512);
1354             this.stale = new ReferenceQueue<>();
1355         }
1356 
1357         /**
1358          * Get the existing interned element.
1359          * This method returns null if no element is interned.
1360          *
1361          * @param elem element to look up
1362          * @return the interned element
1363          */
1364         public T get(T elem) {
1365             if (elem == null) throw new NullPointerException();
1366             expungeStaleElements();
1367 
1368             WeakEntry<T> value = map.get(elem);
1369             if (value != null) {
1370                 T res = value.get();
1371                 if (res != null) {
1372                     return res;
1373                 }
1374             }
1375             return null;
1376         }
1377 
1378         /**
1379          * Interns the element.
1380          * Always returns non-null element, matching the one in the intern set.
1381          * Under the race against another add(), it can return <i>different</i>
1382          * element, if another thread beats us to interning it.
1383          *
1384          * @param elem element to add
1385          * @return element that was actually added
1386          */
1387         public T add(T elem) {
1388             if (elem == null) throw new NullPointerException();
1389 
1390             // Playing double race here, and so spinloop is required.
1391             // First race is with two concurrent updaters.
1392             // Second race is with GC purging weak ref under our feet.
1393             // Hopefully, we almost always end up with a single pass.
1394             T interned;
1395             WeakEntry<T> e = new WeakEntry<>(elem, stale);
1396             do {
1397                 expungeStaleElements();
1398                 WeakEntry<T> exist = map.putIfAbsent(e, e);
1399                 interned = (exist == null) ? elem : exist.get();
1400             } while (interned == null);
1401             return interned;
1402         }
1403 
1404         private void expungeStaleElements() {
1405             Reference<? extends T> reference;
1406             while ((reference = stale.poll()) != null) {
1407                 map.remove(reference);
1408             }
1409         }
1410 
1411         private static class WeakEntry<T> extends WeakReference<T> {
1412 
1413             public final int hashcode;
1414 
1415             public WeakEntry(T key, ReferenceQueue<T> queue) {
1416                 super(key, queue);
1417                 hashcode = key.hashCode();
1418             }
1419 
1420             /**
1421              * This implementation returns {@code true} if {@code obj} is another
1422              * {@code WeakEntry} whose referent is equal to this referent, or
1423              * if {@code obj} is equal to the referent of this. This allows
1424              * lookups to be made without wrapping in a {@code WeakEntry}.
1425              *
1426              * @param obj the object to compare
1427              * @return true if {@code obj} is equal to this or the referent of this
1428              * @see MethodType#equals(Object)
1429              * @see Object#equals(Object)
1430              */
1431             @Override
1432             public boolean equals(Object obj) {
1433                 Object mine = get();
1434                 if (obj instanceof WeakEntry) {
1435                     Object that = ((WeakEntry) obj).get();
1436                     return (that == null || mine == null) ? (this == obj) : mine.equals(that);
1437                 }
1438                 return (mine == null) ? (obj == null) : mine.equals(obj);
1439             }
1440 
1441             @Override
1442             public int hashCode() {
1443                 return hashcode;
1444             }
1445 
1446         }
1447     }
1448 
1449 }
--- EOF ---