1 /*
   2  *  Copyright (c) 2020, 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 
  27 package java.lang.invoke;
  28 
  29 import jdk.internal.vm.annotation.ForceInline;
  30 import jdk.internal.vm.annotation.Stable;
  31 
  32 import java.util.List;
  33 import java.util.function.BiFunction;
  34 
  35 /**
  36  * An indirect var handle can be thought of as an aggregate of the method handles implementing its supported access modes.
  37  * Its varform contains no method name table (given that some of the method handles composing a bound var handle might
  38  * not be direct). The set of method handles constituting an inditrect var handle are retrieved lazily, to minimize
  39  * code spinning (since not all the access modes will be used anyway).
  40  * Indirect var handles are useful when constructing var handle adapters - that is, an adapter var handle
  41  * can be constructed by extracting the method handles constituting the target var handle, adapting them
  42  * (using the method handle combinator API) and then repackaging the adapted method handles into a new, indirect
  43  * var handle.
  44  */
  45 /* package */ class IndirectVarHandle extends VarHandle {
  46 
  47     @Stable
  48     private final MethodHandle[] handleMap = new MethodHandle[AccessMode.values().length];
  49     private final VarHandle directTarget; // cache, for performance reasons
  50     private final VarHandle target;
  51     private final BiFunction<AccessMode, MethodHandle, MethodHandle> handleFactory;
  52     private final Class<?> value;
  53     private final Class<?>[] coordinates;
  54 
  55     IndirectVarHandle(VarHandle target, Class<?> value, Class<?>[] coordinates, BiFunction<AccessMode, MethodHandle, MethodHandle> handleFactory) {
  56         super(new VarForm(value, coordinates));
  57         this.handleFactory = handleFactory;
  58         this.target = target;
  59         this.directTarget = target.asDirect();
  60         this.value = value;
  61         this.coordinates = coordinates;
  62     }
  63 
  64     @Override
  65     public Class<?> varType() {
  66         return value;
  67     }
  68 
  69     @Override
  70     public List<Class<?>> coordinateTypes() {
  71         return List.of(coordinates);
  72     }
  73 
  74     @Override
  75     MethodType accessModeTypeUncached(AccessMode accessMode) {
  76         return accessMode.at.accessModeType(directTarget.getClass(), value, coordinates);
  77     }
  78 
  79     @Override
  80     boolean isDirect() {
  81         return false;
  82     }
  83 
  84     @Override
  85     VarHandle asDirect() {
  86         return directTarget;
  87     }
  88 
  89     VarHandle target() {
  90         return target;
  91     }
  92 
  93     @Override
  94     @ForceInline
  95     MethodHandle getMethodHandle(int mode) {
  96         MethodHandle handle = handleMap[mode];
  97         if (handle == null) {
  98             MethodHandle targetHandle = target.getMethodHandle(mode); // might throw UOE of access mode is not supported, which is ok
  99             handle = handleMap[mode] = handleFactory.apply(AccessMode.values()[mode], targetHandle);
 100         }
 101         return handle;
 102     }
 103 
 104     @Override
 105     public MethodHandle toMethodHandle(AccessMode accessMode) {
 106         return getMethodHandle(accessMode.ordinal()).bindTo(directTarget);
 107     }
 108 }