runtime/linker/BoundCallableLinker.java

/*
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * 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).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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package jdk.nashorn.internal.runtime.linker;

import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.MethodType;
import java.util.Arrays;
import jdk.internal.dynalink.CallSiteDescriptor;
import jdk.internal.dynalink.linker.GuardedInvocation;
import jdk.internal.dynalink.linker.LinkRequest;
import jdk.internal.dynalink.linker.LinkerServices;
import jdk.internal.dynalink.linker.TypeBasedGuardingDynamicLinker;
import jdk.internal.dynalink.support.Guards;

/**
 * Links {@link BoundCallable} objects. Passes through to linker services for linking a callable (for either
 * "dyn:call" or "dyn:new"), and modifies the returned invocation to deal with the receiver and argument binding.
 */
final class BoundCallableLinker implements TypeBasedGuardingDynamicLinker {
    @Override
    public boolean canLinkType(final Class<?> type) {
        return type == BoundCallable.class;
    }

    @Override
    public GuardedInvocation getGuardedInvocation(final LinkRequest linkRequest, final LinkerServices linkerServices) throws Exception {
        final Object objBoundCallable = linkRequest.getReceiver();
        if(!(objBoundCallable instanceof BoundCallable)) {
            return null;
        }

        final CallSiteDescriptor descriptor = linkRequest.getCallSiteDescriptor();
        if (descriptor.getNameTokenCount() < 2 || !"dyn".equals(descriptor.getNameToken(CallSiteDescriptor.SCHEME))) {
            return null;
        }
        final String operation = descriptor.getNameToken(CallSiteDescriptor.OPERATOR);
        // We need to distinguish "dyn:new" from "dyn:call" because "dyn:call" sites have parameter list of the form
        // "callee, this, args", while "dyn:call" sites have "callee, args" -- they lack the "this" parameter.
        final boolean isCall;
        if ("new".equals(operation)) {
            isCall = false;
        } else if ("call".equals(operation)) {
            isCall = true;
        } else {
            // Only dyn:call and dyn:new are supported.
            return null;
        }
        final BoundCallable boundCallable = (BoundCallable)objBoundCallable;
        final Object callable = boundCallable.getCallable();
        final Object boundThis = boundCallable.getBoundThis();

        // We need to ask the linker services for a delegate invocation on the target callable.

        // Replace arguments (boundCallable[, this], args) => (callable[, boundThis], boundArgs, args) when delegating
        final Object[] args = linkRequest.getArguments();
        final Object[] boundArgs = boundCallable.getBoundArgs();
        final int argsLen = args.length;
        final int boundArgsLen = boundArgs.length;
        final Object[] newArgs = new Object[argsLen + boundArgsLen];
        newArgs[0] = callable;
        final int firstArgIndex;
        if (isCall) {
            newArgs[1] = boundThis;
            firstArgIndex = 2;
        } else {
            firstArgIndex = 1;
        }
        System.arraycopy(boundArgs, 0, newArgs, firstArgIndex, boundArgsLen);
        System.arraycopy(args, firstArgIndex, newArgs, firstArgIndex + boundArgsLen, argsLen - firstArgIndex);

        // Use R(T0, T1, T2, ...) => R(callable.class, boundThis.class, boundArg0.class, ..., boundArgn.class, T2, ...)
        // call site type when delegating to underlying linker (for dyn:new, there's no this).
        final MethodType type = descriptor.getMethodType();
        // Use R(T0, ...) => R(callable.class, ...)
        MethodType newMethodType = descriptor.getMethodType().changeParameterType(0, callable.getClass());
        if (isCall) {
            // R(callable.class, T1, ...) => R(callable.class, boundThis.class, ...)
            newMethodType = newMethodType.changeParameterType(1, boundThis.getClass());
        }
        // R(callable.class[, boundThis.class], T2, ...) => R(callable.class[, boundThis.class], boundArg0.class, ..., boundArgn.class, T2, ...)
        for(int i = boundArgs.length; i-- > 0;) {
            newMethodType = newMethodType.insertParameterTypes(firstArgIndex, boundArgs[i] == null ? Object.class : boundArgs[i].getClass());
        }
        final CallSiteDescriptor newDescriptor = descriptor.changeMethodType(newMethodType);

        // Delegate to target's linker
        final GuardedInvocation inv = linkerServices.getGuardedInvocation(linkRequest.replaceArguments(newDescriptor, newArgs));
        if(inv == null) {
            return null;
        }

        // Bind (callable[, boundThis], boundArgs) to the delegate handle
        final MethodHandle boundHandle = MethodHandles.insertArguments(inv.getInvocation(), 0,
                Arrays.copyOf(newArgs, firstArgIndex + boundArgs.length));
        final Class<?> p0Type = type.parameterType(0);
        final MethodHandle droppingHandle;
        if (isCall) {
            // Ignore incoming boundCallable and this
            droppingHandle = MethodHandles.dropArguments(boundHandle, 0, p0Type, type.parameterType(1));
        } else {
            // Ignore incoming boundCallable
            droppingHandle = MethodHandles.dropArguments(boundHandle, 0, p0Type);
        }
        // Identity guard on boundCallable object
        final MethodHandle newGuard = Guards.getIdentityGuard(boundCallable);
        return inv.replaceMethods(droppingHandle, newGuard.asType(newGuard.type().changeParameterType(0, p0Type)));
    }
}