DynamicLinkerFactory.java

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/*
   Copyright 2009-2013 Attila Szegedi

   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.
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     notice, this list of conditions and the following disclaimer in the
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   * Neither the name of the copyright holder nor the names of
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     this software without specific prior written permission.

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package jdk.dynalink;

import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodType;
import java.lang.invoke.MutableCallSite;
import java.security.AccessControlContext;
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.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.Objects;
import java.util.ServiceConfigurationError;
import java.util.ServiceLoader;
import java.util.Set;
import java.util.function.Supplier;
import jdk.dynalink.beans.BeansLinker;
import jdk.dynalink.internal.AccessControlContextFactory;
import jdk.dynalink.linker.GuardedInvocation;
import jdk.dynalink.linker.GuardedInvocationTransformer;
import jdk.dynalink.linker.GuardingDynamicLinker;
import jdk.dynalink.linker.GuardingDynamicLinkerExporter;
import jdk.dynalink.linker.GuardingTypeConverterFactory;
import jdk.dynalink.linker.LinkRequest;
import jdk.dynalink.linker.LinkerServices;
import jdk.dynalink.linker.MethodHandleTransformer;
import jdk.dynalink.linker.MethodTypeConversionStrategy;
import jdk.dynalink.linker.support.CompositeGuardingDynamicLinker;
import jdk.dynalink.linker.support.CompositeTypeBasedGuardingDynamicLinker;
import jdk.dynalink.linker.support.DefaultInternalObjectFilter;
import jdk.dynalink.linker.support.TypeUtilities;

/**
 * A factory class for creating {@link DynamicLinker} objects. Dynamic linkers
 * are the central objects in Dynalink; these are composed of several
 * {@link GuardingDynamicLinker} objects and coordinate linking of call sites
 * with them. The usual dynamic linker is a linker
 * composed of all {@link GuardingDynamicLinker} objects explicitly pre-created
 * by the user of the factory and configured with
 * {@link #setPrioritizedLinkers(List)}, as well as any
 * {@link #setClassLoader(ClassLoader) automatically discovered} ones, and
 * finally the ones configured with {@link #setFallbackLinkers(List)}; this last
 * category usually includes {@link BeansLinker}.
 */
public final class DynamicLinkerFactory {
    @SuppressWarnings("removal")
    private static final AccessControlContext GET_CLASS_LOADER_CONTEXT =
            AccessControlContextFactory.createAccessControlContext("getClassLoader");

    /**
     * Default value for {@link #setUnstableRelinkThreshold(int) unstable relink
     * threshold}.
     */
    private 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 boolean syncOnRelink = false;
    private int unstableRelinkThreshold = DEFAULT_UNSTABLE_RELINK_THRESHOLD;
    private GuardedInvocationTransformer prelinkTransformer;
    private MethodTypeConversionStrategy autoConversionStrategy;
    private MethodHandleTransformer internalObjectsFilter;

    private List<ServiceConfigurationError> autoLoadingErrors = Collections.emptyList();

    /**
     * Creates a new dynamic linker factory with default configuration. Upon
     * creation, the factory can be configured using various {@code setXxx()}
     * methods and used to create one or more dynamic linkers according to its
     * current configuration using {@link #createLinker()}.
     */
    public DynamicLinkerFactory() {
    }

    /**
     * Sets the class loader for automatic discovery of available guarding
     * dynamic linkers. {@link GuardingDynamicLinkerExporter} implementations
     * available through this class loader will be automatically instantiated
     * using the {@link ServiceLoader} mechanism and the linkers they provide
     * will be incorporated into {@code DynamicLinker}s that this factory
     * creates. This allows for cross-language interoperability where call sites
     * belonging to this language runtime can be linked by linkers from these
     * automatically discovered runtimes if their native objects are passed to
     * this runtime. If class loader is not set explicitly by invoking this
     * method, then the thread context class loader of the thread invoking
     * {@link #createLinker()} will be used. If this method is invoked
     * explicitly with null then {@link ServiceLoader#loadInstalled(Class)} will
     * be used to load the linkers.
     *
     * @param classLoader the class loader used for the automatic discovery of
     * available linkers.
     */
    public void setClassLoader(final ClassLoader classLoader) {
        this.classLoader = classLoader;
        classLoaderExplicitlySet = true;
    }

    /**
     * Sets the prioritized guarding dynamic linkers. Language runtimes using
     * Dynalink will usually have at least one linker for their own language.
     * These linkers will be consulted first by the resulting dynamic linker
     * when it is linking call sites, before any autodiscovered and fallback
     * linkers. If the factory also autodiscovers a linker class matching one
     * of the prioritized linkers, the autodiscovered class will be ignored and
     * the explicit prioritized instance will be used.
     *
     * @param prioritizedLinkers the list of prioritized linkers. Can be null.
     * @throws NullPointerException if any of the list elements are null.
     */
    public void setPrioritizedLinkers(final List<? extends GuardingDynamicLinker> prioritizedLinkers) {
        this.prioritizedLinkers = copyListRequireNonNullElements(prioritizedLinkers);
    }

    /**
     * Sets the prioritized guarding dynamic linkers. Identical to calling
     * {@link #setPrioritizedLinkers(List)} with
     * {@code Arrays.asList(prioritizedLinkers)}.
     *
     * @param prioritizedLinkers an array of prioritized linkers. Can be null.
     * @throws NullPointerException if any of the array elements are null.
     */
    public void setPrioritizedLinkers(final GuardingDynamicLinker... prioritizedLinkers) {
        setPrioritizedLinkers(prioritizedLinkers == null ? null : 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 NullPointerException if null is passed.
     */
    public void setPrioritizedLinker(final GuardingDynamicLinker prioritizedLinker) {
        this.prioritizedLinkers = Collections.singletonList(Objects.requireNonNull(prioritizedLinker));
    }

    /**
     * Sets the fallback guarding dynamic linkers. These linkers will be
     * consulted last by the resulting dynamic linker when it is linking call
     * sites, after any autodiscovered and prioritized linkers. If the factory
     * also autodiscovers a linker class matching one of the fallback linkers,
     * the autodiscovered class 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. Note that if this
     * method is not invoked explicitly or is passed null, then the factory
     * will create an instance of {@link BeansLinker} to serve as the default
     * fallback linker.
     * @throws NullPointerException if any of the list elements are null.
     */
    public void setFallbackLinkers(final List<? extends GuardingDynamicLinker> fallbackLinkers) {
        this.fallbackLinkers = copyListRequireNonNullElements(fallbackLinkers);
    }

    /**
     * Sets the fallback guarding dynamic linkers. Identical to calling
     * {@link #setFallbackLinkers(List)} with
     * {@code Arrays.asList(fallbackLinkers)}.
     *
     * @param fallbackLinkers an array of fallback linkers. Can be empty to
     * indicate the caller wishes to set no fallback linkers. Note that if this
     * method is not invoked explicitly or is passed null, then the factory
     * will create an instance of {@link BeansLinker} to serve as the default
     * fallback linker.
     * @throws NullPointerException if any of the array elements are null.
     */
    public void setFallbackLinkers(final GuardingDynamicLinker... fallbackLinkers) {
        setFallbackLinkers(fallbackLinkers == null ? null : Arrays.asList(fallbackLinkers));
    }

    /**
     * Sets whether the dynamic 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. Defaults to 8 when not set explicitly.
     * @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 transformer. This is a
     * {@link GuardedInvocationTransformer} 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, a default pre-link
     * transformer will be used that simply calls
     * {@link GuardedInvocation#asType(LinkerServices, MethodType)}. Customized
     * pre-link transformers are rarely needed; they are mostly used as a
     * building block for implementing advanced techniques such as code
     * deoptimization strategies.
     * @param prelinkTransformer the pre-link transformer for the dynamic
     * linker. Can be null to have the factory use the default transformer.
     */
    public void setPrelinkTransformer(final GuardedInvocationTransformer prelinkTransformer) {
        this.prelinkTransformer = prelinkTransformer;
    }

    /**
     * Sets an object representing the conversion strategy for automatic type
     * conversions. After
     * {@link LinkerServices#asType(MethodHandle, 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 MethodHandle#asType(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(MethodHandle, 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 that will be done internally as the
     * final step.
     * @param autoConversionStrategy the strategy for applying method invocation
     * conversions for the linker created by this factory. Can be null for no
     * custom strategy.
     */
    public void setAutoConversionStrategy(final MethodTypeConversionStrategy autoConversionStrategy) {
        this.autoConversionStrategy = autoConversionStrategy;
    }

    /**
     * Sets a method handle transformer that is supposed to act as the
     * implementation of
     * {@link LinkerServices#filterInternalObjects(MethodHandle)} for linker
     * services of dynamic linkers created by this factory. Some language
     * runtimes can have internal objects that should not escape their scope.
     * They can add a transformer here that will modify the method handle so
     * that any parameters that can receive potentially internal language
     * runtime objects will have a filter added on them to prevent them from
     * escaping, potentially by wrapping them. The transformer can also
     * potentially add an unwrapping filter to the return value.
     * {@link DefaultInternalObjectFilter} is provided as a convenience class
     * for easily creating such filtering transformers.
     * @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 based on the current configuration. This
     * method can be invoked more than once to create multiple dynamic linkers.
     * Automatically discovered linkers are newly instantiated on every
     * invocation of this method. It is allowed to change the factory's
     * configuration between invocations. The method is not thread safe. After
     * invocation, callers can invoke {@link #getAutoLoadingErrors()} to
     * retrieve a list of {@link ServiceConfigurationError}s that occurred while
     * trying to load automatically discovered linkers. These are never thrown
     * from the call to this method as it makes every effort to recover from
     * them and ignore the failing 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<? extends GuardingDynamicLinker>> knownLinkerClasses =
                new HashSet<>();
        addClasses(knownLinkerClasses, prioritizedLinkers);
        addClasses(knownLinkerClasses, fallbackLinkers);

        final List<GuardingDynamicLinker> discovered = discoverAutoLoadLinkers();
        // 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 = (r, s) -> null; // linker that can't link anything
                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(prelinkTransformer == null) {
            prelinkTransformer = (inv, request, linkerServices) -> inv.asType(linkerServices, request.getCallSiteDescriptor().getMethodType());
        }

        return new DynamicLinker(new LinkerServicesImpl(new TypeConverterFactory(typeConverters,
                autoConversionStrategy), composite, internalObjectsFilter), prelinkTransformer,
                syncOnRelink, unstableRelinkThreshold);
    }

    /**
     * Returns a list of {@link ServiceConfigurationError}s that were
     * encountered while loading automatically discovered linkers during the
     * last invocation of {@link #createLinker()}. They can be any non-Dynalink
     * specific service configuration issues, as well as some Dynalink-specific
     * errors when an exporter that the factory tried to automatically load:
     * <ul>
     * <li>did not have the runtime permission named
     * {@link GuardingDynamicLinkerExporter#AUTOLOAD_PERMISSION_NAME} in a
     * system with a security manager, or</li>
     * <li>returned null from {@link GuardingDynamicLinkerExporter#get()}, or</li>
     * <li>the list returned from {@link GuardingDynamicLinkerExporter#get()}
     * had a null element.</li>
     * </ul>
     * @return an immutable list of encountered
     * {@link ServiceConfigurationError}s. Can be empty.
     */
    public List<ServiceConfigurationError> getAutoLoadingErrors() {
        return Collections.unmodifiableList(autoLoadingErrors);
    }

    private List<GuardingDynamicLinker> discoverAutoLoadLinkers() {
        autoLoadingErrors = new LinkedList<>();
        final ClassLoader effectiveClassLoader = classLoaderExplicitlySet ? classLoader : getThreadContextClassLoader();
        final List<GuardingDynamicLinker> discovered = new LinkedList<>();
        try {
            @SuppressWarnings("removal")
            final ServiceLoader<GuardingDynamicLinkerExporter> linkerLoader =
                    AccessController.doPrivileged((PrivilegedAction<ServiceLoader<GuardingDynamicLinkerExporter>>)()-> {
                        if (effectiveClassLoader == null) {
                            return ServiceLoader.loadInstalled(GuardingDynamicLinkerExporter.class);
                        }
                        return ServiceLoader.load(GuardingDynamicLinkerExporter.class, effectiveClassLoader);
                    });

            for(final Iterator<GuardingDynamicLinkerExporter> it = linkerLoader.iterator(); it.hasNext();) {
                try {
                    final GuardingDynamicLinkerExporter autoLoader = it.next();
                    try {
                        discovered.addAll(requireNonNullElements(
                                Objects.requireNonNull(autoLoader.get(),
                                        ()->(autoLoader.getClass().getName() + " returned null from get()")),
                                ()->(autoLoader.getClass().getName() + " returned a list with at least one null element")));
                    } catch (final ServiceConfigurationError|VirtualMachineError e) {
                        // Don't wrap a SCE in another SCE. Also, don't ignore
                        // any VME (e.g. StackOverflowError or OutOfMemoryError).
                        throw e;
                    } catch (final Throwable t) {
                        throw new ServiceConfigurationError(t.getMessage(), t);
                    }
                } catch (final ServiceConfigurationError e) {
                    // Catch SCE with an individual exporter, carry on with it.hasNext().
                    autoLoadingErrors.add(e);
                }
            }
        } catch (final ServiceConfigurationError e) {
            // Catch a top-level SCE; one either in ServiceLoader.load(),
            // ServiceLoader.iterator(), or Iterator.hasNext().
            autoLoadingErrors.add(e);
        }
        return discovered;
    }

    @SuppressWarnings("removal")
    private static ClassLoader getThreadContextClassLoader() {
        return AccessController.doPrivileged(
            (PrivilegedAction<ClassLoader>) () -> Thread.currentThread().getContextClassLoader(),
            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());
        }
    }

    private static <T> List<T> copyListRequireNonNullElements(final List<T> list) {
        if (list == null) {
            return null;
        }
        return new ArrayList<>(requireNonNullElements(list, ()->"List has at least one null element"));
    }

    private static <T> List<T> requireNonNullElements(final List<T> list, final Supplier<String> msgSupplier) {
        for(final T t: list) {
            Objects.requireNonNull(t, msgSupplier);
        }
        return list;
    }

}