NashornGuards.java revision 1751:9940204f504c
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 26package jdk.nashorn.internal.runtime.linker; 27 28import static jdk.nashorn.internal.lookup.Lookup.MH; 29 30import java.lang.invoke.MethodHandle; 31import java.lang.invoke.MethodHandles; 32import java.lang.ref.WeakReference; 33import jdk.dynalink.CallSiteDescriptor; 34import jdk.dynalink.linker.LinkRequest; 35import jdk.nashorn.api.scripting.JSObject; 36import jdk.nashorn.internal.objects.Global; 37import jdk.nashorn.internal.runtime.JSType; 38import jdk.nashorn.internal.runtime.Property; 39import jdk.nashorn.internal.runtime.PropertyMap; 40import jdk.nashorn.internal.runtime.ScriptFunction; 41import jdk.nashorn.internal.runtime.ScriptObject; 42import jdk.nashorn.internal.runtime.options.Options; 43 44/** 45 * Constructor of method handles used to guard call sites. 46 */ 47public final class NashornGuards { 48 private static final MethodHandle IS_MAP = findOwnMH("isMap", boolean.class, ScriptObject.class, PropertyMap.class); 49 private static final MethodHandle IS_MAP_SCRIPTOBJECT = findOwnMH("isMap", boolean.class, Object.class, PropertyMap.class); 50 private static final MethodHandle IS_SCRIPTOBJECT = findOwnMH("isScriptObject", boolean.class, Object.class); 51 private static final MethodHandle IS_NOT_JSOBJECT = findOwnMH("isNotJSObject", boolean.class, Object.class); 52 private static final MethodHandle SAME_OBJECT = findOwnMH("sameObject", boolean.class, Object.class, WeakReference.class); 53 //TODO - maybe put this back in ScriptFunction instead of the ClassCastException.class relinkage 54 //private static final MethodHandle IS_SCRIPTFUNCTION = findOwnMH("isScriptFunction", boolean.class, Object.class); 55 56 private static final boolean CCE_ONLY = Options.getBooleanProperty("nashorn.cce"); 57 58 // don't create me! 59 private NashornGuards() { 60 } 61 62 /** 63 * Given a callsite descriptor and a link request, determine whether we should use an instanceof 64 * check explicitly for the guard if needed, or if we should link it with a try/catch ClassCastException 65 * combinator as its relink criteria - i.e. relink when CCE is thrown. 66 * 67 * @param desc callsite descriptor 68 * @param request link request 69 * @return true of explicit instanceof check is needed 70 */ 71 public static boolean explicitInstanceOfCheck(final CallSiteDescriptor desc, final LinkRequest request) { 72 //THIS is currently true, as the inliner encounters several problems with sun.misc.ValueConversions.castReference 73 //otherwise. We should only use the exception based relink where we have no choice, and the result is faster code, 74 //for example in the NativeArray, TypedArray, ContinuousArray getters. For the standard callsite, it appears that 75 //we lose performance rather than gain it, due to JVM issues. :-( 76 return !CCE_ONLY; 77 } 78 79 /** 80 * Returns a guard that does an instanceof ScriptObject check on the receiver 81 * @return guard 82 */ 83 public static MethodHandle getScriptObjectGuard() { 84 return IS_SCRIPTOBJECT; 85 } 86 87 /** 88 * Get the guard that checks if an item is not a {@code JSObject} 89 * @return method handle for guard 90 */ 91 public static MethodHandle getNotJSObjectGuard() { 92 return IS_NOT_JSOBJECT; 93 } 94 95 /** 96 * Returns a guard that does an instanceof ScriptObject check on the receiver 97 * @param explicitInstanceOfCheck - if false, then this is a nop, because it's all the guard does 98 * @return guard 99 */ 100 public static MethodHandle getScriptObjectGuard(final boolean explicitInstanceOfCheck) { 101 return explicitInstanceOfCheck ? IS_SCRIPTOBJECT : null; 102 } 103 104 /** 105 * Get the guard that checks if a {@link PropertyMap} is equal to 106 * a known map, using reference comparison 107 * 108 * @param explicitInstanceOfCheck true if we should do an explicit script object instanceof check instead of just casting 109 * @param map The map to check against. This will be bound to the guard method handle 110 * 111 * @return method handle for guard 112 */ 113 public static MethodHandle getMapGuard(final PropertyMap map, final boolean explicitInstanceOfCheck) { 114 return MH.insertArguments(explicitInstanceOfCheck ? IS_MAP_SCRIPTOBJECT : IS_MAP, 1, map); 115 } 116 117 /** 118 * Determine whether the given callsite needs a guard. 119 * @param property the property, or null 120 * @param desc the callsite descriptor 121 * @return true if a guard should be used for this callsite 122 */ 123 static boolean needsGuard(final Property property, final CallSiteDescriptor desc) { 124 return property == null || property.isConfigurable() 125 || property.isBound() || property.hasDualFields() 126 || !NashornCallSiteDescriptor.isFastScope(desc) || property.canChangeType(); 127 } 128 129 /** 130 * Get the guard for a property access. This returns an identity guard for non-configurable global properties 131 * and a map guard for everything else. 132 * 133 * @param sobj the first object in the prototype chain 134 * @param property the property 135 * @param desc the callsite descriptor 136 * @param explicitInstanceOfCheck true if we should do an explicit script object instanceof check instead of just casting 137 * @return method handle for guard 138 */ 139 public static MethodHandle getGuard(final ScriptObject sobj, final Property property, final CallSiteDescriptor desc, final boolean explicitInstanceOfCheck) { 140 if (!needsGuard(property, desc)) { 141 return null; 142 } 143 if (NashornCallSiteDescriptor.isScope(desc) && sobj.isScope()) { 144 if (property != null && property.isBound() && !property.canChangeType()) { 145 // This is a declared top level variables in main script or eval, use identity guard. 146 return getIdentityGuard(sobj); 147 } 148 if (!(sobj instanceof Global) && (property == null || property.isConfigurable())) { 149 // Undeclared variables in nested evals need stronger guards 150 return combineGuards(getIdentityGuard(sobj), getMapGuard(sobj.getMap(), explicitInstanceOfCheck)); 151 } 152 } 153 return getMapGuard(sobj.getMap(), explicitInstanceOfCheck); 154 } 155 156 157 /** 158 * Get a guard that checks referential identity of the current object. 159 * 160 * @param sobj the self object 161 * @return true if same self object instance 162 */ 163 public static MethodHandle getIdentityGuard(final ScriptObject sobj) { 164 return MH.insertArguments(SAME_OBJECT, 1, new WeakReference<>(sobj)); 165 } 166 167 /** 168 * Get a guard that checks if in item is a JS string. 169 * 170 * @return method handle for guard 171 */ 172 public static MethodHandle getStringGuard() { 173 return JSType.IS_STRING.methodHandle(); 174 } 175 176 /** 177 * Get a guard that checks if in item is a JS number. 178 * 179 * @return method handle for guard 180 */ 181 public static MethodHandle getNumberGuard() { 182 return JSType.IS_NUMBER.methodHandle(); 183 } 184 185 /** 186 * Combine two method handles of type {@code (Object)boolean} using logical AND. 187 * 188 * @param guard1 the first guard 189 * @param guard2 the second guard, only invoked if guard1 returns true 190 * @return true if both guard1 and guard2 returned true 191 */ 192 public static MethodHandle combineGuards(final MethodHandle guard1, final MethodHandle guard2) { 193 if (guard1 == null) { 194 return guard2; 195 } else if (guard2 == null) { 196 return guard1; 197 } else { 198 return MH.guardWithTest(guard1, guard2, MH.dropArguments(MH.constant(boolean.class, false), 0, Object.class)); 199 } 200 } 201 202 @SuppressWarnings("unused") 203 private static boolean isScriptObject(final Object self) { 204 return self instanceof ScriptObject; 205 } 206 207 @SuppressWarnings("unused") 208 private static boolean isScriptObject(final Class<? extends ScriptObject> clazz, final Object self) { 209 return clazz.isInstance(self); 210 } 211 212 @SuppressWarnings("unused") 213 private static boolean isMap(final ScriptObject self, final PropertyMap map) { 214 return self.getMap() == map; 215 } 216 217 @SuppressWarnings("unused") 218 private static boolean isNotJSObject(final Object self) { 219 return !(self instanceof JSObject); 220 } 221 222 @SuppressWarnings("unused") 223 private static boolean isMap(final Object self, final PropertyMap map) { 224 return self instanceof ScriptObject && ((ScriptObject)self).getMap() == map; 225 } 226 227 228 @SuppressWarnings("unused") 229 private static boolean sameObject(final Object self, final WeakReference<ScriptObject> ref) { 230 return self == ref.get(); 231 } 232 233 @SuppressWarnings("unused") 234 private static boolean isScriptFunction(final Object self) { 235 return self instanceof ScriptFunction; 236 } 237 238 private static MethodHandle findOwnMH(final String name, final Class<?> rtype, final Class<?>... types) { 239 return MH.findStatic(MethodHandles.lookup(), NashornGuards.class, name, MH.type(rtype, types)); 240 } 241} 242