DynamicLinker.java

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 * This file is available under and governed by the GNU General Public
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 * However, the following notice accompanied the original version of this
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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.
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         notice, this list of conditions and the following disclaimer in the
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*/

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 java.util.Objects;
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 lookup, 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 static final String INITIAL_LINK_CLASS_NAME = "java.lang.invoke.MethodHandleNatives";
    private static final String INITIAL_LINK_METHOD_NAME = "linkCallSite";

    private final LinkerServices linkerServices;
    private final GuardedInvocationFilter prelinkFilter;
    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 prelinkFilter see {@link DynamicLinkerFactory#setPrelinkFilter(GuardedInvocationFilter)}
     * @param runtimeContextArgCount see {@link DynamicLinkerFactory#setRuntimeContextArgCount(int)}
     */
    DynamicLinker(final LinkerServices linkerServices, final GuardedInvocationFilter prelinkFilter, final int runtimeContextArgCount,
            final boolean syncOnRelink, final int unstableRelinkThreshold) {
        if(runtimeContextArgCount < 0) {
            throw new IllegalArgumentException("runtimeContextArgCount < 0");
        }
        if(unstableRelinkThreshold < 0) {
            throw new IllegalArgumentException("unstableRelinkThreshold < 0");
        }
        this.linkerServices = linkerServices;
        this.prelinkFilter = prelinkFilter;
        this.runtimeContextArgCount = runtimeContextArgCount;
        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 <T> the particular subclass of {@link RelinkableCallSite} for
     *        which to create a link.
     * @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, final 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(final RelinkableCallSite callSite, final int relinkCount, final 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, callSite, relinkCount, callSiteUnstable, arguments) :
                        new RuntimeContextLinkRequestImpl(callSiteDescriptor, callSite, relinkCount, callSiteUnstable, arguments, runtimeContextArgCount);

        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);
            }
        }

        // Make sure we filter the invocation before linking it into the call site. This is typically used to match the
        // return type of the invocation to the call site.
        guardedInvocation = prelinkFilter.filter(guardedInvocation, linkRequest, linkerServices);
        Objects.requireNonNull(guardedInvocation);

        int newRelinkCount = relinkCount;
        // Note that the short-circuited "&&" evaluation below ensures we'll increment the relinkCount until
        // threshold + 1 but not 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.
        if(unstableDetectionEnabled && newRelinkCount <= unstableRelinkThreshold && newRelinkCount++ == unstableRelinkThreshold) {
            callSite.resetAndRelink(guardedInvocation, createRelinkAndInvokeMethod(callSite, newRelinkCount));
        } else {
            callSite.relink(guardedInvocation, createRelinkAndInvokeMethod(callSite, newRelinkCount));
        }
        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 linked 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 linked, or null if it is not invoked while a call
     *         site is being linked.
     */
    public static StackTraceElement getLinkedCallSiteLocation() {
        final StackTraceElement[] trace = new Throwable().getStackTrace();
        for(int i = 0; i < trace.length - 1; ++i) {
            final StackTraceElement frame = trace[i];
            if(isRelinkFrame(frame) || isInitialLinkFrame(frame)) {
                return trace[i + 1];
            }
        }
        return null;
    }

    /**
     * Deprecated because of imprecise name.
     *
     * @deprecated Use {@link #getLinkedCallSiteLocation()} instead.
     *
     * @return see non-deprecated method
     */
    @Deprecated
    public static StackTraceElement getRelinkedCallSiteLocation() {
        return getLinkedCallSiteLocation();
    }

    /**
     * Returns {@code true} if the frame represents {@code MethodHandleNatives.linkCallSite()},
     * the frame immediately on top of the call site frame when the call site is
     * being linked for the first time.
     *
     * @param frame the frame
     *
     * @return {@code true} if this frame represents {@code MethodHandleNatives.linkCallSite()}.
     */
    private static boolean isInitialLinkFrame(final StackTraceElement frame) {
        return testFrame(frame, INITIAL_LINK_METHOD_NAME, INITIAL_LINK_CLASS_NAME);
    }

    /**
     * Returns {@code true} if the frame represents {@code DynamicLinker.relink()},
     * the frame immediately on top of the call site frame when the call site is
     * being relinked (linked for second and subsequent times).
     *
     * @param frame the frame
     *
     * @return {@code true} if this frame represents {@code DynamicLinker.relink()}.
     */
    private static boolean isRelinkFrame(final StackTraceElement frame) {
        return testFrame(frame, RELINK_METHOD_NAME, CLASS_NAME);
    }

    private static boolean testFrame(final StackTraceElement frame, final String methodName, final String className) {
        return methodName.equals(frame.getMethodName()) && className.equals(frame.getClassName());
    }
}