DynamicLinkerFactory.java

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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:

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       modification, are permitted provided that the following conditions are
       met:
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         notice, this list of conditions and the following disclaimer.
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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.linker.LinkerServices;
import jdk.internal.dynalink.linker.MethodHandleTransformer;
import jdk.internal.dynalink.linker.MethodTypeConversionStrategy;
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.DefaultPrelinkFilter;
import jdk.internal.dynalink.support.LinkerServicesImpl;
import jdk.internal.dynalink.support.TypeConverterFactory;
import jdk.internal.dynalink.support.TypeUtilities;

/**
 * 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} and a
 * {@link DefaultPrelinkFilter}. 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;
    private GuardedInvocationFilter prelinkFilter;
    private MethodTypeConversionStrategy autoConversionStrategy;
    private MethodHandleTransformer internalObjectsFilter;

    /**
     * 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(final 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(final 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(final 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(final 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(final 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(final 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(final 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(final 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(final int unstableRelinkThreshold) {
        if(unstableRelinkThreshold < 0) {
            throw new IllegalArgumentException("unstableRelinkThreshold < 0");
        }
        this.unstableRelinkThreshold = unstableRelinkThreshold;
    }

    /**
     * Set the pre-link filter. This is a {@link GuardedInvocationFilter} that will get the final chance to modify the
     * guarded invocation after it has been created by a component linker and before the dynamic linker links it into
     * the call site. It is normally used to adapt the return value type of the invocation to the type of the call site.
     * When not set explicitly, {@link DefaultPrelinkFilter} will be used.
     * @param prelinkFilter the pre-link filter for the dynamic linker.
     */
    public void setPrelinkFilter(final GuardedInvocationFilter prelinkFilter) {
        this.prelinkFilter = prelinkFilter;
    }

    /**
     * Sets an object representing the conversion strategy for automatic type conversions. After
     * {@link TypeConverterFactory#asType(java.lang.invoke.MethodHandle, java.lang.invoke.MethodType)} has
     * applied all custom conversions to a method handle, it still needs to effect
     * {@link TypeUtilities#isMethodInvocationConvertible(Class, Class) method invocation conversions} that
     * can usually be automatically applied as per
     * {@link java.lang.invoke.MethodHandle#asType(java.lang.invoke.MethodType)}.
     * However, sometimes language runtimes will want to customize even those conversions for their own call
     * sites. A typical example is allowing unboxing of null return values, which is by default prohibited by
     * ordinary {@code MethodHandles.asType}. In this case, a language runtime can install its own custom
     * automatic conversion strategy, that can deal with null values. Note that when the strategy's
     * {@link MethodTypeConversionStrategy#asType(java.lang.invoke.MethodHandle, java.lang.invoke.MethodType)}
     * is invoked, the custom language conversions will already have been applied to the method handle, so by
     * design the difference between the handle's current method type and the desired final type will always
     * only be ones that can be subjected to method invocation conversions. The strategy also doesn't need to
     * invoke a final {@code MethodHandle.asType()} as the converter factory will do that as the final step.
     * @param autoConversionStrategy the strategy for applying method invocation conversions for the linker
     * created by this factory.
     */
    public void setAutoConversionStrategy(final MethodTypeConversionStrategy autoConversionStrategy) {
        this.autoConversionStrategy = autoConversionStrategy;
    }

    /**
     * Sets a method handle transformer that is supposed to act as the implementation of this linker factory's linkers'
     * services {@link LinkerServices#filterInternalObjects(java.lang.invoke.MethodHandle)} method.
     * @param internalObjectsFilter a method handle transformer filtering out internal objects, or null.
     */
    public void setInternalObjectsFilter(final MethodHandleTransformer internalObjectsFilter) {
        this.internalObjectsFilter = internalObjectsFilter;
    }

    /**
     * Creates a new dynamic linker consisting of all the prioritized, autodiscovered, and fallback linkers as well as
     * the pre-link filter.
     *
     * @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<? extends GuardingDynamicLinker>> 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(final 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(final GuardingDynamicLinker linker: linkers) {
            if(linker instanceof GuardingTypeConverterFactory) {
                typeConverters.add((GuardingTypeConverterFactory)linker);
            }
        }

        if(prelinkFilter == null) {
            prelinkFilter = new DefaultPrelinkFilter();
        }

        return new DynamicLinker(new LinkerServicesImpl(new TypeConverterFactory(typeConverters,
                autoConversionStrategy), composite, internalObjectsFilter), prelinkFilter, 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(final Set<Class<? extends GuardingDynamicLinker>> knownLinkerClasses,
            final List<? extends GuardingDynamicLinker> linkers) {
        for(final GuardingDynamicLinker linker: linkers) {
            knownLinkerClasses.add(linker.getClass());
        }
    }
}