1 /*
   2  * Copyright (c) 2010, 2013, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 package jdk.nashorn.internal.runtime.linker;
  27 
  28 import static jdk.nashorn.internal.lookup.Lookup.MH;
  29 
  30 import java.lang.invoke.MethodHandle;
  31 import java.lang.invoke.MethodHandles;
  32 import java.lang.ref.WeakReference;
  33 import jdk.internal.dynalink.CallSiteDescriptor;
  34 import jdk.nashorn.api.scripting.JSObject;
  35 import jdk.nashorn.internal.codegen.ObjectClassGenerator;
  36 import jdk.nashorn.internal.objects.Global;
  37 import jdk.nashorn.internal.runtime.Property;
  38 import jdk.nashorn.internal.runtime.PropertyMap;
  39 import jdk.nashorn.internal.runtime.ScriptFunction;
  40 import jdk.nashorn.internal.runtime.ScriptObject;
  41 
  42 /**
  43  * Constructor of method handles used to guard call sites.
  44  */
  45 public final class NashornGuards {
  46     private static final MethodHandle IS_SCRIPTOBJECT   = findOwnMH("isScriptObject", boolean.class, Object.class);
  47     private static final MethodHandle IS_NOT_JSOBJECT   = findOwnMH("isNotJSObject", boolean.class, Object.class);
  48     private static final MethodHandle IS_SCRIPTFUNCTION = findOwnMH("isScriptFunction", boolean.class, Object.class);
  49     private static final MethodHandle IS_MAP            = findOwnMH("isMap", boolean.class, Object.class, PropertyMap.class);
  50     private static final MethodHandle SAME_OBJECT       = findOwnMH("sameObject", boolean.class, Object.class, WeakReference.class);
  51     private static final MethodHandle IS_INSTANCEOF_2   = findOwnMH("isInstanceOf2", boolean.class, Object.class, Class.class, Class.class);
  52 
  53     // don't create me!
  54     private NashornGuards() {
  55     }
  56 
  57     /**
  58      * Get the guard that checks if an item is a {@code ScriptObject}
  59      * @return method handle for guard
  60      */
  61     public static MethodHandle getScriptObjectGuard() {
  62         return IS_SCRIPTOBJECT;
  63     }
  64 
  65     /**
  66      * Get the guard that checks if an item is not a {@code JSObject}
  67      * @return method handle for guard
  68      */
  69     public static MethodHandle getNotJSObjectGuard() {
  70         return IS_NOT_JSOBJECT;
  71     }
  72 
  73     /**
  74      * Get the guard that checks if an item is a {@code ScriptFunction}
  75      * @return method handle for guard
  76      */
  77     public static MethodHandle getScriptFunctionGuard() {
  78         return IS_SCRIPTFUNCTION;
  79     }
  80 
  81     /**
  82      * Get the guard that checks if a {@link PropertyMap} is equal to
  83      * a known map, using reference comparison
  84      *
  85      * @param map The map to check against. This will be bound to the guard method handle
  86      *
  87      * @return method handle for guard
  88      */
  89     public static MethodHandle getMapGuard(final PropertyMap map) {
  90         return MH.insertArguments(IS_MAP, 1, map);
  91     }
  92 
  93     /**
  94      * Determine whether the given callsite needs a guard.
  95      * @param property the property, or null
  96      * @param desc the callsite descriptor
  97      * @return true if a guard should be used for this callsite
  98      */
  99     static boolean needsGuard(final Property property, final CallSiteDescriptor desc) {
 100         return property == null || property.isConfigurable()
 101                 || property.isBound() || !ObjectClassGenerator.OBJECT_FIELDS_ONLY
 102                 || !NashornCallSiteDescriptor.isFastScope(desc) || property.canChangeType();
 103     }
 104 
 105     /**
 106      * Get the guard for a property access. This returns an identity guard for non-configurable global properties
 107      * and a map guard for everything else.
 108      *
 109      * @param sobj the first object in the prototype chain
 110      * @param property the property
 111      * @param desc the callsite descriptor
 112      * @return method handle for guard
 113      */
 114     public static MethodHandle getGuard(final ScriptObject sobj, final Property property, final CallSiteDescriptor desc) {
 115         if (!needsGuard(property, desc)) {
 116             return null;
 117         }
 118         if (NashornCallSiteDescriptor.isScope(desc)) {
 119             if (property != null && property.isBound()) {
 120                 // This is a declared top level variables in main script or eval, use identity guard.
 121                 return getIdentityGuard(sobj);
 122             }
 123             if (!(sobj instanceof Global) && (property == null || property.isConfigurable())) {
 124                 // Undeclared variables in nested evals need stronger guards
 125                 return combineGuards(getIdentityGuard(sobj), getMapGuard(sobj.getMap()));
 126             }
 127         }
 128         return getMapGuard(sobj.getMap());
 129     }
 130 
 131 
 132     /**
 133      * Get a guard that checks referential identity of the current object.
 134      *
 135      * @param sobj the self object
 136      * @return true if same self object instance
 137      */
 138     public static MethodHandle getIdentityGuard(final ScriptObject sobj) {
 139         return MH.insertArguments(SAME_OBJECT, 1, new WeakReference<>(sobj));
 140     }
 141 
 142     /**
 143      * Get a guard that checks if in item is an instance of either of two classes.
 144      *
 145      * @param class1 the first class
 146      * @param class2 the second class
 147      * @return method handle for guard
 148      */
 149     public static MethodHandle getInstanceOf2Guard(final Class<?> class1, final Class<?> class2) {
 150         return MH.insertArguments(IS_INSTANCEOF_2, 1, class1, class2);
 151     }
 152 
 153     /**
 154      * Combine two method handles of type {@code (Object)boolean} using logical AND.
 155      *
 156      * @param guard1 the first guard
 157      * @param guard2 the second guard, only invoked if guard1 returns true
 158      * @return true if both guard1 and guard2 returned true
 159      */
 160     public static MethodHandle combineGuards(final MethodHandle guard1, final MethodHandle guard2) {
 161         return MH.guardWithTest(guard1, guard2, MH.dropArguments(MH.constant(boolean.class, false), 0, Object.class));
 162     }
 163 
 164     @SuppressWarnings("unused")
 165     private static boolean isScriptObject(final Object self) {
 166         return self instanceof ScriptObject;
 167     }
 168 
 169     @SuppressWarnings("unused")
 170     private static boolean isNotJSObject(final Object self) {
 171         return !(self instanceof JSObject);
 172     }
 173 
 174     @SuppressWarnings("unused")
 175     private static boolean isScriptFunction(final Object self) {
 176         return self instanceof ScriptFunction;
 177     }
 178 
 179     @SuppressWarnings("unused")
 180     private static boolean isMap(final Object self, final PropertyMap map) {
 181         return self instanceof ScriptObject && ((ScriptObject)self).getMap() == map;
 182     }
 183 
 184     @SuppressWarnings("unused")
 185     private static boolean sameObject(final Object self, final WeakReference<ScriptObject> ref) {
 186         return self == ref.get();
 187     }
 188 
 189     @SuppressWarnings("unused")
 190     private static boolean isInstanceOf2(final Object self, final Class<?> class1, final Class<?> class2) {
 191         return class1.isInstance(self) || class2.isInstance(self);
 192     }
 193 
 194     private static MethodHandle findOwnMH(final String name, final Class<?> rtype, final Class<?>... types) {
 195         return MH.findStatic(MethodHandles.lookup(), NashornGuards.class, name, MH.type(rtype, types));
 196     }
 197 
 198 }