Java example source code file (GuardedInvocation.java)

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class, expected, guardedinvocation, list, methodhandle, methodtype, npe, switchpoint, util, wrongmethodtypeexception

The GuardedInvocation.java Java example source code

/*
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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,
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 *
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/*
 * This file is available under and governed by the GNU General Public
 * License version 2 only, as published by the Free Software Foundation.
 * However, the following notice accompanied the original version of this
 * file, and Oracle licenses the original version of this file under the BSD
 * license:
 */
/*
   Copyright 2009-2013 Attila Szegedi

   Licensed under both the Apache License, Version 2.0 (the "Apache License")
   and the BSD License (the "BSD License"), with licensee being free to
   choose either of the two at their discretion.

   You may not use this file except in compliance with either the Apache
   License or the BSD License.

   If you choose to use this file in compliance with the Apache License, the
   following notice applies to you:

       You may obtain a copy of the Apache License at

           http://www.apache.org/licenses/LICENSE-2.0

       Unless required by applicable law or agreed to in writing, software
       distributed under the License is distributed on an "AS IS" BASIS,
       WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
       implied. See the License for the specific language governing
       permissions and limitations under the License.

   If you choose to use this file in compliance with the BSD License, the
   following notice applies to you:

       Redistribution and use in source and binary forms, with or without
       modification, are permitted provided that the following conditions are
       met:
       * Redistributions of source code must retain the above copyright
         notice, this list of conditions and the following disclaimer.
       * Redistributions in binary form must reproduce the above copyright
         notice, this list of conditions and the following disclaimer in the
         documentation and/or other materials provided with the distribution.
       * Neither the name of the copyright holder nor the names of
         contributors may be used to endorse or promote products derived from
         this software without specific prior written permission.

       THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
       IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
       TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
       PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL COPYRIGHT HOLDER
       BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
       CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
       SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
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       OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
       ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/

package jdk.internal.dynalink.linker;

import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.MethodType;
import java.lang.invoke.SwitchPoint;
import java.lang.invoke.WrongMethodTypeException;
import java.util.List;
import jdk.internal.dynalink.CallSiteDescriptor;
import jdk.internal.dynalink.support.Guards;

/**
 * Represents a conditionally valid method handle. It is an immutable triple of an invocation method handle, a guard
 * method handle that defines the applicability of the invocation handle, and a switch point that can be used for
 * external invalidation of the invocation handle. The invocation handle is suitable for invocation if the guard
 * handle returns true for its arguments, and as long as the switch point is not invalidated. Both the guard and the
 * switch point are optional; neither, one, or both can be present.
 *
 * @author Attila Szegedi
 */
public class GuardedInvocation {
    private final MethodHandle invocation;
    private final MethodHandle guard;
    private final SwitchPoint switchPoint;

    /**
     * Creates a new guarded invocation.
     *
     * @param invocation the method handle representing the invocation. Must not be null.
     * @param guard the method handle representing the guard. Must have the same method type as the invocation, except
     * it must return boolean. For some useful guards, check out the {@link Guards} class. It can be null to represent
     * an unconditional invocation, although that is unusual.
     * @throws NullPointerException if invocation is null.
     */
    public GuardedInvocation(MethodHandle invocation, MethodHandle guard) {
        this(invocation, guard, null);
    }

    /**
     * Creates a new guarded invocation.
     *
     * @param invocation the method handle representing the invocation. Must not be null.
     * @param guard the method handle representing the guard. Must have the same method type as the invocation, except
     * it must return boolean. For some useful guards, check out the {@link Guards} class. It can be null. If both it
     * and the switch point are null, this represents an unconditional invocation, which is legal but unusual.
     * @param switchPoint the optional switch point that can be used to invalidate this linkage.
     * @throws NullPointerException if invocation is null.
     */
    public GuardedInvocation(MethodHandle invocation, MethodHandle guard, SwitchPoint switchPoint) {
        invocation.getClass(); // NPE check
        this.invocation = invocation;
        this.guard = guard;
        this.switchPoint = switchPoint;
    }

    /**
     * Creates a new guarded invocation.
     *
     * @param invocation the method handle representing the invocation. Must not be null.
     * @param switchPoint the optional switch point that can be used to invalidate this linkage.
     * @param guard the method handle representing the guard. Must have the same method type as the invocation, except
     * it must return boolean. For some useful guards, check out the {@link Guards} class. It can be null. If both it
     * and the switch point are null, this represents an unconditional invocation, which is legal but unusual.
     * @throws NullPointerException if invocation is null.
     */
    public GuardedInvocation(MethodHandle invocation, SwitchPoint switchPoint, MethodHandle guard) {
        this(invocation, guard, switchPoint);
    }
    /**
     * Returns the invocation method handle.
     *
     * @return the invocation method handle. It will never be null.
     */
    public MethodHandle getInvocation() {
        return invocation;
    }

    /**
     * Returns the guard method handle.
     *
     * @return the guard method handle. Can be null.
     */
    public MethodHandle getGuard() {
        return guard;
    }

    /**
     * Returns the switch point that can be used to invalidate the invocation handle.
     *
     * @return the switch point that can be used to invalidate the invocation handle. Can be null.
     */
    public SwitchPoint getSwitchPoint() {
        return switchPoint;
    }

    /**
     * Returns true if and only if this guarded invocation has a switchpoint, and that switchpoint has been invalidated.
     * @return true if and only if this guarded invocation has a switchpoint, and that switchpoint has been invalidated.
     */
    public boolean hasBeenInvalidated() {
        return switchPoint != null && switchPoint.hasBeenInvalidated();
    }

    /**
     * Asserts that the invocation is of the specified type, and the guard (if present) is of the specified type with a
     * boolean return type.
     *
     * @param type the asserted type
     * @throws WrongMethodTypeException if the invocation and the guard are not of the expected method type.
     */
    public void assertType(MethodType type) {
        assertType(invocation, type);
        if(guard != null) {
            assertType(guard, type.changeReturnType(Boolean.TYPE));
        }
    }

    /**
     * Creates a new guarded invocation with different methods, preserving the switch point.
     *
     * @param newInvocation the new invocation
     * @param newGuard the new guard
     * @return a new guarded invocation with the replaced methods and the same switch point as this invocation.
     */
    public GuardedInvocation replaceMethods(MethodHandle newInvocation, MethodHandle newGuard) {
        return new GuardedInvocation(newInvocation, newGuard, switchPoint);
    }

    private GuardedInvocation replaceMethodsOrThis(MethodHandle newInvocation, MethodHandle newGuard) {
        if(newInvocation == invocation && newGuard == guard) {
            return this;
        }
        return replaceMethods(newInvocation, newGuard);
    }

    /**
     * Changes the type of the invocation, as if {@link MethodHandle#asType(MethodType)} was applied to its invocation
     * and its guard, if it has one (with return type changed to boolean, and parameter count potentially truncated for
     * the guard). If the invocation already is of the required type, returns this object.
     * @param newType the new type of the invocation.
     * @return a guarded invocation with the new type applied to it.
     */
    public GuardedInvocation asType(MethodType newType) {
        return replaceMethodsOrThis(invocation.asType(newType), guard == null ? null : Guards.asType(guard, newType));
    }

    /**
     * Changes the type of the invocation, as if {@link LinkerServices#asType(MethodHandle, MethodType)} was applied to
     * its invocation and its guard, if it has one (with return type changed to boolean, and parameter count potentially
     * truncated for the guard). If the invocation already is of the required type, returns this object.
     * @param linkerServices the linker services to use for the conversion
     * @param newType the new type of the invocation.
     * @return a guarded invocation with the new type applied to it.
     */
    public GuardedInvocation asType(LinkerServices linkerServices, MethodType newType) {
        return replaceMethodsOrThis(linkerServices.asType(invocation, newType), guard == null ? null :
            Guards.asType(linkerServices, guard, newType));
    }

    /**
     * Changes the type of the invocation, as if {@link MethodHandle#asType(MethodType)} was applied to its invocation
     * and its guard, if it has one (with return type changed to boolean for guard). If the invocation already is of the
     * required type, returns this object.
     * @param desc a call descriptor whose method type is adapted.
     * @return a guarded invocation with the new type applied to it.
     */
    public GuardedInvocation asType(CallSiteDescriptor desc) {
        return asType(desc.getMethodType());
    }

    /**
     * Applies argument filters to both the invocation and the guard (if there is one).
     * @param pos the position of the first argumen being filtered
     * @param filters the argument filters
     * @return a filtered invocation
     */
    public GuardedInvocation filterArguments(int pos, MethodHandle... filters) {
        return replaceMethods(MethodHandles.filterArguments(invocation, pos, filters), guard == null ? null :
            MethodHandles.filterArguments(guard, pos, filters));
    }

    /**
     * Makes an invocation that drops arguments in both the invocation and the guard (if there is one).
     * @param pos the position of the first argument being dropped
     * @param valueTypes the types of the values being dropped
     * @return an invocation that drops arguments
     */
    public GuardedInvocation dropArguments(int pos, List<Class valueTypes) {
        return replaceMethods(MethodHandles.dropArguments(invocation, pos, valueTypes), guard == null ? null :
            MethodHandles.dropArguments(guard, pos, valueTypes));
    }

    /**
     * Makes an invocation that drops arguments in both the invocation and the guard (if there is one).
     * @param pos the position of the first argument being dropped
     * @param valueTypes the types of the values being dropped
     * @return an invocation that drops arguments
     */
    public GuardedInvocation dropArguments(int pos, Class<?>... valueTypes) {
        return replaceMethods(MethodHandles.dropArguments(invocation, pos, valueTypes), guard == null ? null :
            MethodHandles.dropArguments(guard, pos, valueTypes));
    }


    /**
     * Composes the invocation, switchpoint, and the guard into a composite method handle that knows how to fall back.
     * @param fallback the fallback method handle in case switchpoint is invalidated or guard returns false.
     * @return a composite method handle.
     */
    public MethodHandle compose(MethodHandle fallback) {
        return compose(fallback, fallback);
    }

    /**
     * Composes the invocation, switchpoint, and the guard into a composite method handle that knows how to fall back.
     * @param switchpointFallback the fallback method handle in case switchpoint is invalidated.
     * @param guardFallback the fallback method handle in case guard returns false.
     * @return a composite method handle.
     */
    public MethodHandle compose(MethodHandle switchpointFallback, MethodHandle guardFallback) {
        final MethodHandle guarded =
                guard == null ? invocation : MethodHandles.guardWithTest(guard, invocation, guardFallback);
        return switchPoint == null ? guarded : switchPoint.guardWithTest(guarded, switchpointFallback);
    }

    private static void assertType(MethodHandle mh, MethodType type) {
        if(!mh.type().equals(type)) {
            throw new WrongMethodTypeException("Expected type: " + type + " actual type: " + mh.type());
        }
    }
}