Java example source code file (DynamicLinkerFactory.java)

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arraylist, beanslinker, classloader, default_unstable_relink_threshold, dynamiclinkerfactory, guardingdynamiclinker, guardingtypeconverterfactory, hashset, illegalargumentexception, linkedlist, linkerservicesimpl, list, override, privilegedaction, security, util

The DynamicLinkerFactory.java Java example source code

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 * by Oracle in the LICENSE file that accompanied this code.
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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:
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/*
   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
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*/

package jdk.internal.dynalink;

import java.lang.invoke.MutableCallSite;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.Set;
import jdk.internal.dynalink.beans.BeansLinker;
import jdk.internal.dynalink.linker.GuardingDynamicLinker;
import jdk.internal.dynalink.linker.GuardingTypeConverterFactory;
import jdk.internal.dynalink.linker.LinkRequest;
import jdk.internal.dynalink.support.AutoDiscovery;
import jdk.internal.dynalink.support.BottomGuardingDynamicLinker;
import jdk.internal.dynalink.support.ClassLoaderGetterContextProvider;
import jdk.internal.dynalink.support.CompositeGuardingDynamicLinker;
import jdk.internal.dynalink.support.CompositeTypeBasedGuardingDynamicLinker;
import jdk.internal.dynalink.support.LinkerServicesImpl;
import jdk.internal.dynalink.support.TypeConverterFactory;

/**
 * A factory class for creating {@link DynamicLinker}s. The most usual dynamic linker is a linker that is a composition
 * of all {@link GuardingDynamicLinker}s known and pre-created by the caller as well as any
 * {@link AutoDiscovery automatically discovered} guarding linkers and the standard fallback {@link BeansLinker}. See
 * {@link DynamicLinker} documentation for tips on how to use this class.
 *
 * @author Attila Szegedi
 */
public class DynamicLinkerFactory {

    /**
     * Default value for {@link #setUnstableRelinkThreshold(int) unstable relink threshold}.
     */
    public static final int DEFAULT_UNSTABLE_RELINK_THRESHOLD = 8;

    private boolean classLoaderExplicitlySet = false;
    private ClassLoader classLoader;

    private List<? extends GuardingDynamicLinker> prioritizedLinkers;
    private List<? extends GuardingDynamicLinker> fallbackLinkers;
    private int runtimeContextArgCount = 0;
    private boolean syncOnRelink = false;
    private int unstableRelinkThreshold = DEFAULT_UNSTABLE_RELINK_THRESHOLD;

    /**
     * Sets the class loader for automatic discovery of available linkers. If not set explicitly, then the thread
     * context class loader at the time of {@link #createLinker()} invocation will be used.
     *
     * @param classLoader the class loader used for the autodiscovery of available linkers.
     */
    public void setClassLoader(ClassLoader classLoader) {
        this.classLoader = classLoader;
        classLoaderExplicitlySet = true;
    }

    /**
     * Sets the prioritized linkers. Language runtimes using this framework will usually precreate at least the linker
     * for their own language. These linkers will be consulted first in the resulting dynamic linker, before any
     * autodiscovered linkers. If the framework also autodiscovers a linker of the same class as one of the prioritized
     * linkers, it will be ignored and the explicit prioritized instance will be used.
     *
     * @param prioritizedLinkers the list of prioritized linkers. Null can be passed to indicate no prioritized linkers
     * (this is also the default value).
     */
    public void setPrioritizedLinkers(List<? extends GuardingDynamicLinker> prioritizedLinkers) {
        this.prioritizedLinkers =
                prioritizedLinkers == null ? null : new ArrayList<>(prioritizedLinkers);
    }

    /**
     * Sets the prioritized linkers. Language runtimes using this framework will usually precreate at least the linker
     * for their own language. These linkers will be consulted first in the resulting dynamic linker, before any
     * autodiscovered linkers. If the framework also autodiscovers a linker of the same class as one of the prioritized
     * linkers, it will be ignored and the explicit prioritized instance will be used.
     *
     * @param prioritizedLinkers a list of prioritized linkers.
     */
    public void setPrioritizedLinkers(GuardingDynamicLinker... prioritizedLinkers) {
        setPrioritizedLinkers(Arrays.asList(prioritizedLinkers));
    }

    /**
     * Sets a single prioritized linker. Identical to calling {@link #setPrioritizedLinkers(List)} with a single-element
     * list.
     *
     * @param prioritizedLinker the single prioritized linker. Must not be null.
     * @throws IllegalArgumentException if null is passed.
     */
    public void setPrioritizedLinker(GuardingDynamicLinker prioritizedLinker) {
        if(prioritizedLinker == null) {
            throw new IllegalArgumentException("prioritizedLinker == null");
        }
        this.prioritizedLinkers = Collections.singletonList(prioritizedLinker);
    }

    /**
     * Sets the fallback linkers. These linkers will be consulted last in the resulting composite linker, after any
     * autodiscovered linkers. If the framework also autodiscovers a linker of the same class as one of the fallback
     * linkers, it will be ignored and the explicit fallback instance will be used.
     *
     * @param fallbackLinkers the list of fallback linkers. Can be empty to indicate the caller wishes to set no
     * fallback linkers.
     */
    public void setFallbackLinkers(List<? extends GuardingDynamicLinker> fallbackLinkers) {
        this.fallbackLinkers = fallbackLinkers == null ? null : new ArrayList<>(fallbackLinkers);
    }

    /**
     * Sets the fallback linkers. These linkers will be consulted last in the resulting composite linker, after any
     * autodiscovered linkers. If the framework also autodiscovers a linker of the same class as one of the fallback
     * linkers, it will be ignored and the explicit fallback instance will be used.
     *
     * @param fallbackLinkers the list of fallback linkers. Can be empty to indicate the caller wishes to set no
     * fallback linkers. If it is left as null, the standard fallback {@link BeansLinker} will be used.
     */
    public void setFallbackLinkers(GuardingDynamicLinker... fallbackLinkers) {
        setFallbackLinkers(Arrays.asList(fallbackLinkers));
    }

    /**
     * Sets the number of arguments in the call sites that represent the stack context of the language runtime creating
     * the linker. If the language runtime uses no context information passed on stack, then it should be zero
     * (the default value). If it is set to nonzero value, then every dynamic call site emitted by this runtime must
     * have the argument list of the form: {@code (this, contextArg1[, contextArg2[, ...]], normalArgs)}. It is
     * advisable to only pass one context-specific argument, though, of an easily recognizable, runtime specific type
     * encapsulating the runtime thread local state.
     *
     * @param runtimeContextArgCount the number of language runtime context arguments in call sites.
     */
    public void setRuntimeContextArgCount(int runtimeContextArgCount) {
        if(runtimeContextArgCount < 0) {
            throw new IllegalArgumentException("runtimeContextArgCount < 0");
        }
        this.runtimeContextArgCount = runtimeContextArgCount;
    }

    /**
     * Sets whether the linker created by this factory will invoke {@link MutableCallSite#syncAll(MutableCallSite[])}
     * after a call site is relinked. Defaults to false. You probably want to set it to true if your runtime supports
     * multithreaded execution of dynamically linked code.
     * @param syncOnRelink true for invoking sync on relink, false otherwise.
     */
    public void setSyncOnRelink(boolean syncOnRelink) {
        this.syncOnRelink = syncOnRelink;
    }

    /**
     * Sets the unstable relink threshold; the number of times a call site is relinked after which it will be
     * considered unstable, and subsequent link requests for it will indicate this.
     * @param unstableRelinkThreshold the new threshold. Must not be less than zero. The value of zero means that
     * call sites will never be considered unstable.
     * @see LinkRequest#isCallSiteUnstable()
     */
    public void setUnstableRelinkThreshold(int unstableRelinkThreshold) {
        if(unstableRelinkThreshold < 0) {
            throw new IllegalArgumentException("unstableRelinkThreshold < 0");
        }
        this.unstableRelinkThreshold = unstableRelinkThreshold;
    }

    /**
     * Creates a new dynamic linker consisting of all the prioritized, autodiscovered, and fallback linkers.
     *
     * @return the new dynamic Linker
     */
    public DynamicLinker createLinker() {
        // Treat nulls appropriately
        if(prioritizedLinkers == null) {
            prioritizedLinkers = Collections.emptyList();
        }
        if(fallbackLinkers == null) {
            fallbackLinkers = Collections.singletonList(new BeansLinker());
        }

        // Gather classes of all precreated (prioritized and fallback) linkers.
        // We'll filter out any discovered linkers of the same class.
        final Set<Class knownLinkerClasses =
                new HashSet<>();
        addClasses(knownLinkerClasses, prioritizedLinkers);
        addClasses(knownLinkerClasses, fallbackLinkers);

        final ClassLoader effectiveClassLoader = classLoaderExplicitlySet ? classLoader : getThreadContextClassLoader();
        final List<GuardingDynamicLinker> discovered = AutoDiscovery.loadLinkers(effectiveClassLoader);
        // Now, concatenate ...
        final List<GuardingDynamicLinker> linkers =
                new ArrayList<>(prioritizedLinkers.size() + discovered.size()
                        + fallbackLinkers.size());
        // ... prioritized linkers, ...
        linkers.addAll(prioritizedLinkers);
        // ... filtered discovered linkers, ...
        for(GuardingDynamicLinker linker: discovered) {
            if(!knownLinkerClasses.contains(linker.getClass())) {
                linkers.add(linker);
            }
        }
        // ... and finally fallback linkers.
        linkers.addAll(fallbackLinkers);
        final List<GuardingDynamicLinker> optimized = CompositeTypeBasedGuardingDynamicLinker.optimize(linkers);
        final GuardingDynamicLinker composite;
        switch(linkers.size()) {
            case 0: {
                composite = BottomGuardingDynamicLinker.INSTANCE;
                break;
            }
            case 1: {
                composite = optimized.get(0);
                break;
            }
            default: {
                composite = new CompositeGuardingDynamicLinker(optimized);
                break;
            }
        }

        final List<GuardingTypeConverterFactory> typeConverters = new LinkedList<>();
        for(GuardingDynamicLinker linker: linkers) {
            if(linker instanceof GuardingTypeConverterFactory) {
                typeConverters.add((GuardingTypeConverterFactory)linker);
            }
        }

        return new DynamicLinker(new LinkerServicesImpl(new TypeConverterFactory(typeConverters), composite),
                runtimeContextArgCount, syncOnRelink, unstableRelinkThreshold);
    }

    private static ClassLoader getThreadContextClassLoader() {
        return AccessController.doPrivileged(new PrivilegedAction<ClassLoader>() {
            @Override
            public ClassLoader run() {
                return Thread.currentThread().getContextClassLoader();
            }
        }, ClassLoaderGetterContextProvider.GET_CLASS_LOADER_CONTEXT);
    }

    private static void addClasses(Set<Class knownLinkerClasses,
            List<? extends GuardingDynamicLinker> linkers) {
        for(GuardingDynamicLinker linker: linkers) {
            knownLinkerClasses.add(linker.getClass());
        }
    }
}