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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
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*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
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package jdk.nashorn.internal.runtime.linker;
import static jdk.nashorn.internal.lookup.Lookup.MH;
import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;
import java.lang.ref.WeakReference;
import jdk.dynalink.CallSiteDescriptor;
import jdk.dynalink.linker.LinkRequest;
import jdk.nashorn.api.scripting.JSObject;
import jdk.nashorn.internal.objects.Global;
import jdk.nashorn.internal.runtime.JSType;
import jdk.nashorn.internal.runtime.Property;
import jdk.nashorn.internal.runtime.PropertyMap;
import jdk.nashorn.internal.runtime.ScriptFunction;
import jdk.nashorn.internal.runtime.ScriptObject;
import jdk.nashorn.internal.runtime.options.Options;
/**
* Constructor of method handles used to guard call sites.
*/
public final class NashornGuards {
private static final MethodHandle IS_MAP = findOwnMH("isMap", boolean.class, ScriptObject.class, PropertyMap.class);
private static final MethodHandle IS_MAP_SCRIPTOBJECT = findOwnMH("isMap", boolean.class, Object.class, PropertyMap.class);
private static final MethodHandle IS_SCRIPTOBJECT = findOwnMH("isScriptObject", boolean.class, Object.class);
private static final MethodHandle IS_NOT_JSOBJECT = findOwnMH("isNotJSObject", boolean.class, Object.class);
private static final MethodHandle SAME_OBJECT = findOwnMH("sameObject", boolean.class, Object.class, WeakReference.class);
//TODO - maybe put this back in ScriptFunction instead of the ClassCastException.class relinkage
//private static final MethodHandle IS_SCRIPTFUNCTION = findOwnMH("isScriptFunction", boolean.class, Object.class);
private static final boolean CCE_ONLY = Options.getBooleanProperty("nashorn.cce");
// don't create me!
private NashornGuards() {
}
/**
* Given a callsite descriptor and a link request, determine whether we should use an instanceof
* check explicitly for the guard if needed, or if we should link it with a try/catch ClassCastException
* combinator as its relink criteria - i.e. relink when CCE is thrown.
*
* @param desc callsite descriptor
* @param request link request
* @return true of explicit instanceof check is needed
*/
public static boolean explicitInstanceOfCheck(final CallSiteDescriptor desc, final LinkRequest request) {
//THIS is currently true, as the inliner encounters several problems with sun.misc.ValueConversions.castReference
//otherwise. We should only use the exception based relink where we have no choice, and the result is faster code,
//for example in the NativeArray, TypedArray, ContinuousArray getters. For the standard callsite, it appears that
//we lose performance rather than gain it, due to JVM issues. :-(
return !CCE_ONLY;
}
/**
* Returns a guard that does an instanceof ScriptObject check on the receiver
* @return guard
*/
public static MethodHandle getScriptObjectGuard() {
return IS_SCRIPTOBJECT;
}
/**
* Get the guard that checks if an item is not a {@code JSObject}
* @return method handle for guard
*/
public static MethodHandle getNotJSObjectGuard() {
return IS_NOT_JSOBJECT;
}
/**
* Returns a guard that does an instanceof ScriptObject check on the receiver
* @param explicitInstanceOfCheck - if false, then this is a nop, because it's all the guard does
* @return guard
*/
public static MethodHandle getScriptObjectGuard(final boolean explicitInstanceOfCheck) {
return explicitInstanceOfCheck ? IS_SCRIPTOBJECT : null;
}
/**
* Get the guard that checks if a {@link PropertyMap} is equal to
* a known map, using reference comparison
*
* @param explicitInstanceOfCheck true if we should do an explicit script object instanceof check instead of just casting
* @param map The map to check against. This will be bound to the guard method handle
*
* @return method handle for guard
*/
public static MethodHandle getMapGuard(final PropertyMap map, final boolean explicitInstanceOfCheck) {
return MH.insertArguments(explicitInstanceOfCheck ? IS_MAP_SCRIPTOBJECT : IS_MAP, 1, map);
}
/**
* Determine whether the given callsite needs a guard.
* @param property the property, or null
* @param desc the callsite descriptor
* @return true if a guard should be used for this callsite
*/
static boolean needsGuard(final Property property, final CallSiteDescriptor desc) {
return property == null || property.isConfigurable()
|| property.isBound() || property.hasDualFields()
|| !NashornCallSiteDescriptor.isFastScope(desc) || property.canChangeType();
}
/**
* Get the guard for a property access. This returns an identity guard for non-configurable global properties
* and a map guard for everything else.
*
* @param sobj the first object in the prototype chain
* @param property the property
* @param desc the callsite descriptor
* @param explicitInstanceOfCheck true if we should do an explicit script object instanceof check instead of just casting
* @return method handle for guard
*/
public static MethodHandle getGuard(final ScriptObject sobj, final Property property, final CallSiteDescriptor desc, final boolean explicitInstanceOfCheck) {
if (!needsGuard(property, desc)) {
return null;
}
if (NashornCallSiteDescriptor.isScope(desc) && sobj.isScope()) {
if (property != null && property.isBound() && !property.canChangeType()) {
// This is a declared top level variables in main script or eval, use identity guard.
return getIdentityGuard(sobj);
}
if (!(sobj instanceof Global) && (property == null || property.isConfigurable())) {
// Undeclared variables in nested evals need stronger guards
return combineGuards(getIdentityGuard(sobj), getMapGuard(sobj.getMap(), explicitInstanceOfCheck));
}
}
return getMapGuard(sobj.getMap(), explicitInstanceOfCheck);
}
/**
* Get a guard that checks referential identity of the current object.
*
* @param sobj the self object
* @return true if same self object instance
*/
public static MethodHandle getIdentityGuard(final ScriptObject sobj) {
return MH.insertArguments(SAME_OBJECT, 1, new WeakReference<>(sobj));
}
/**
* Get a guard that checks if in item is a JS string.
*
* @return method handle for guard
*/
public static MethodHandle getStringGuard() {
return JSType.IS_STRING.methodHandle();
}
/**
* Get a guard that checks if in item is a JS number.
*
* @return method handle for guard
*/
public static MethodHandle getNumberGuard() {
return JSType.IS_NUMBER.methodHandle();
}
/**
* Combine two method handles of type {@code (Object)boolean} using logical AND.
*
* @param guard1 the first guard
* @param guard2 the second guard, only invoked if guard1 returns true
* @return true if both guard1 and guard2 returned true
*/
public static MethodHandle combineGuards(final MethodHandle guard1, final MethodHandle guard2) {
if (guard1 == null) {
return guard2;
} else if (guard2 == null) {
return guard1;
} else {
return MH.guardWithTest(guard1, guard2, MH.dropArguments(MH.constant(boolean.class, false), 0, Object.class));
}
}
@SuppressWarnings("unused")
private static boolean isScriptObject(final Object self) {
return self instanceof ScriptObject;
}
@SuppressWarnings("unused")
private static boolean isScriptObject(final Class<? extends ScriptObject> clazz, final Object self) {
return clazz.isInstance(self);
}
@SuppressWarnings("unused")
private static boolean isMap(final ScriptObject self, final PropertyMap map) {
return self.getMap() == map;
}
@SuppressWarnings("unused")
private static boolean isNotJSObject(final Object self) {
return !(self instanceof JSObject);
}
@SuppressWarnings("unused")
private static boolean isMap(final Object self, final PropertyMap map) {
return self instanceof ScriptObject && ((ScriptObject)self).getMap() == map;
}
@SuppressWarnings("unused")
private static boolean sameObject(final Object self, final WeakReference<ScriptObject> ref) {
return self == ref.get();
}
@SuppressWarnings("unused")
private static boolean isScriptFunction(final Object self) {
return self instanceof ScriptFunction;
}
private static MethodHandle findOwnMH(final String name, final Class<?> rtype, final Class<?>... types) {
return MH.findStatic(MethodHandles.lookup(), NashornGuards.class, name, MH.type(rtype, types));
}
}