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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

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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

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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

       BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,

       WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR

       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;

import java.lang.invoke.MethodHandle;

import java.lang.invoke.MethodHandles;

import java.lang.invoke.MethodType;

import java.lang.invoke.MutableCallSite;

import java.util.List;

import jdk.internal.dynalink.linker.GuardedInvocation;

import jdk.internal.dynalink.linker.GuardingDynamicLinker;

import jdk.internal.dynalink.linker.LinkRequest;

import jdk.internal.dynalink.linker.LinkerServices;

import jdk.internal.dynalink.support.CallSiteDescriptorFactory;

import jdk.internal.dynalink.support.LinkRequestImpl;

import jdk.internal.dynalink.support.Lookup;

import jdk.internal.dynalink.support.RuntimeContextLinkRequestImpl;

/**

 * The linker for {@link RelinkableCallSite} objects. Users of it (scripting frameworks and language runtimes) have to

 * create a linker using the {@link DynamicLinkerFactory} and invoke its link method from the invokedynamic bootstrap

 * methods to set the target of all the call sites in the code they generate. Usual usage would be to create one class

 * per language runtime to contain one linker instance as:

 *

 * <pre>

 * class MyLanguageRuntime {

 *     private static final GuardingDynamicLinker myLanguageLinker = new MyLanguageLinker();

 *     private static final DynamicLinker dynamicLinker = createDynamicLinker();

 *

 *     private static DynamicLinker createDynamicLinker() {

 *         final DynamicLinkerFactory factory = new DynamicLinkerFactory();

 *         factory.setPrioritizedLinker(myLanguageLinker);

 *         return factory.createLinker();

 *     }

 *

 *     public static CallSite bootstrap(MethodHandles.Lookup caller, String name, MethodType type) {

 *         return dynamicLinker.link(new MonomorphicCallSite(CallSiteDescriptorFactory.create(lookup, name, type)));

 *     }

 * }

 * </pre>

 *

 * Note how there are three components you will need to provide here:

 * <ul>

 * <li>You're expected to provide a {@link GuardingDynamicLinker} for your own language. If your runtime doesn't

 * have its own language and/or object model (i.e. it's a generic scripting shell), you don't need to implement a

 * dynamic linker; you would simply not invoke the {@code setPrioritizedLinker} method on the factory, or even better,

 * simply use {@link DefaultBootstrapper}.</li>

 * <li>The performance of the programs can depend on your choice of the class to represent call sites. The above

 * example used {@link MonomorphicCallSite}, but you might want to use {@link ChainedCallSite} instead. You'll need to

 * experiment and decide what fits your language runtime the best. You can subclass either of these or roll your own if

 * you need to.</li>

 * <li>You also need to provide {@link CallSiteDescriptor}s to your call sites. They are immutable objects that contain

 * all the information about the call site: the class performing the lookups, the name of the method being invoked, and

 * the method signature. The library has a default {@link CallSiteDescriptorFactory} for descriptors that you can use,

 * or you can create your own descriptor classes, especially if you need to add further information (values passed in

 * additional parameters to the bootstrap method) to them.</li>

 * </ul>

 *

 * @author Attila Szegedi

 */

public class DynamicLinker {

    private static final String CLASS_NAME = DynamicLinker.class.getName();

    private static final String RELINK_METHOD_NAME = "relink";

    private final LinkerServices linkerServices;

    private final int runtimeContextArgCount;

    private final boolean syncOnRelink;

    private final int unstableRelinkThreshold;

    /**

     * Creates a new dynamic linker.

     *

     * @param linkerServices the linkerServices used by the linker, created by the factory.

     * @param runtimeContextArgCount see {@link DynamicLinkerFactory#setRuntimeContextArgCount(int)}

     */

    DynamicLinker(LinkerServices linkerServices, int runtimeContextArgCount, boolean syncOnRelink,

            int unstableRelinkThreshold) {

        if(runtimeContextArgCount < 0) {

            throw new IllegalArgumentException("runtimeContextArgCount < 0");

        }

        if(unstableRelinkThreshold < 0) {

            throw new IllegalArgumentException("unstableRelinkThreshold < 0");

        }

        this.runtimeContextArgCount = runtimeContextArgCount;

        this.linkerServices = linkerServices;

        this.syncOnRelink = syncOnRelink;

        this.unstableRelinkThreshold = unstableRelinkThreshold;

    }

    /**

     * Links an invokedynamic call site. It will install a method handle into the call site that invokes the relinking

     * mechanism of this linker. Next time the call site is invoked, it will be linked for the actual arguments it was

     * invoked with.

     *

     * @param callSite the call site to link.

     * @return the callSite, for easy call chaining.

     */

    public <T extends RelinkableCallSite> T link(final T callSite) {

        callSite.initialize(createRelinkAndInvokeMethod(callSite, 0));

        return callSite;

    }

    /**

     * Returns the object representing the lower level linker services of this class that are normally exposed to

     * individual language-specific linkers. While as a user of this class you normally only care about the

     * {@link #link(RelinkableCallSite)} method, in certain circumstances you might want to use the lower level services

     * directly; either to lookup specific method handles, to access the type converters, and so on.

     * @return the object representing the linker services of this class.

     */

    public LinkerServices getLinkerServices() {

        return linkerServices;

    }

    private static final MethodHandle RELINK = Lookup.findOwnSpecial(MethodHandles.lookup(), RELINK_METHOD_NAME,

            MethodHandle.class, RelinkableCallSite.class, int.class, Object[].class);

    private MethodHandle createRelinkAndInvokeMethod(final RelinkableCallSite callSite, int relinkCount) {

        // Make a bound MH of invoke() for this linker and call site

        final MethodHandle boundRelinker = MethodHandles.insertArguments(RELINK, 0, this, callSite, Integer.valueOf(

                relinkCount));

        // Make a MH that gathers all arguments to the invocation into an Object[]

        final MethodType type = callSite.getDescriptor().getMethodType();

        final MethodHandle collectingRelinker = boundRelinker.asCollector(Object[].class, type.parameterCount());

        return MethodHandles.foldArguments(MethodHandles.exactInvoker(type), collectingRelinker.asType(

                type.changeReturnType(MethodHandle.class)));

    }

    /**

     * Relinks a call site conforming to the invocation arguments.

     *

     * @param callSite the call site itself

     * @param arguments arguments to the invocation

     * @return return the method handle for the invocation

     * @throws Exception rethrows any exception thrown by the linkers

     */

    @SuppressWarnings("unused")

    private MethodHandle relink(RelinkableCallSite callSite, int relinkCount, Object... arguments) throws Exception {

        final CallSiteDescriptor callSiteDescriptor = callSite.getDescriptor();

        final boolean unstableDetectionEnabled = unstableRelinkThreshold > 0;

        final boolean callSiteUnstable = unstableDetectionEnabled && relinkCount >= unstableRelinkThreshold;

        final LinkRequest linkRequest =

                runtimeContextArgCount == 0 ? new LinkRequestImpl(callSiteDescriptor, callSiteUnstable, arguments)

                        : new RuntimeContextLinkRequestImpl(callSiteDescriptor, callSiteUnstable, arguments,

                                runtimeContextArgCount);

        // Find a suitable method handle with a guard

        GuardedInvocation guardedInvocation = linkerServices.getGuardedInvocation(linkRequest);

        // None found - throw an exception

        if(guardedInvocation == null) {

            throw new NoSuchDynamicMethodException(callSiteDescriptor.toString());

        }

        // If our call sites have a runtime context, and the linker produced a context-stripped invocation, adapt the

        // produced invocation into contextual invocation (by dropping the context...)

        if(runtimeContextArgCount > 0) {

            final MethodType origType = callSiteDescriptor.getMethodType();

            final MethodHandle invocation = guardedInvocation.getInvocation();

            if(invocation.type().parameterCount() == origType.parameterCount() - runtimeContextArgCount) {

                final List<Class<?>> prefix = origType.parameterList().subList(1, runtimeContextArgCount + 1);

                final MethodHandle guard = guardedInvocation.getGuard();

                guardedInvocation = guardedInvocation.dropArguments(1, prefix);

            }

        }

        if(unstableDetectionEnabled && relinkCount <= unstableRelinkThreshold && relinkCount++ == unstableRelinkThreshold) {

            // Note that we'll increase the relinkCount until threshold+1 and not increase it beyond that. Threshold+1

            // is treated as a special value to signal that resetAndRelink has already executed once for the unstable

            // call site; we only want the call site to throw away its current linkage once, when it transitions to

            // unstable.

            callSite.resetAndRelink(guardedInvocation, createRelinkAndInvokeMethod(callSite, relinkCount));

        } else {

            callSite.relink(guardedInvocation, createRelinkAndInvokeMethod(callSite, relinkCount));

        }

        if(syncOnRelink) {

            MutableCallSite.syncAll(new MutableCallSite[] { (MutableCallSite)callSite });

        }

        return guardedInvocation.getInvocation();

    }

    /**

     * Returns a stack trace element describing the location of the call site currently being relinked on the current

     * thread. The operation internally creates a Throwable object and inspects its stack trace, so it's potentially

     * expensive. The recommended usage for it is in writing diagnostics code.

     * @return a stack trace element describing the location of the call site currently being relinked, or null if it is

     * not invoked while a call site is being relinked.

     */

    public static StackTraceElement getRelinkedCallSiteLocation() {

        final StackTraceElement[] trace = new Throwable().getStackTrace();

        for(int i = 0; i < trace.length - 1; ++i) {

            final StackTraceElement frame = trace[i];

            if(RELINK_METHOD_NAME.equals(frame.getMethodName()) && CLASS_NAME.equals(frame.getClassName())) {

                return trace[i + 1];

            }

        }

        return null;

    }

}