jdk/dynalink/CallSiteDescriptor.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.

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   License or the BSD License.

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       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
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package jdk.dynalink;

import java.lang.invoke.MethodHandles;
import java.lang.invoke.MethodHandles.Lookup;
import java.lang.invoke.MethodType;
import java.util.Objects;

/**
 * Call site descriptors contain all the information necessary for linking a
 * call site. This information is normally passed as parameters to bootstrap
 * methods and consists of the {@code MethodHandles.Lookup} object on the caller
 * class in which the call site occurs, the dynamic operation at the call
 * site, and the method type of the call site. {@code CallSiteDescriptor}
 * objects are used in Dynalink to capture and store these parameters for
 * subsequent use by the {@link DynamicLinker}.
 * <p>
 * The constructors of built-in {@link RelinkableCallSite} implementations all
 * take a call site descriptor.
 * <p>
 * Call site descriptors must be immutable. You can use this class as-is or you
 * can subclass it, especially if you need to add further information to the
 * descriptors (typically, values passed in additional parameters to the
 * bootstrap method. Since the descriptors must be immutable, you can set up a
 * cache for equivalent descriptors to have the call sites share them.
 */
public class CallSiteDescriptor {
    private final MethodHandles.Lookup lookup;
    private final Operation operation;
    private final MethodType methodType;

    /**
     * The name of a runtime permission to invoke the {@link #getLookup()}
     * method.
     */
    public static final String GET_LOOKUP_PERMISSION_NAME = "dynalink.getLookup";

    private static final RuntimePermission GET_LOOKUP_PERMISSION = new RuntimePermission(GET_LOOKUP_PERMISSION_NAME);

    /**
     * Creates a new call site descriptor.
     * @param lookup the lookup object describing the class the call site belongs to.
     * @param operation the dynamic operation at the call site.
     * @param methodType the method type of the call site.
     */
    public CallSiteDescriptor(final Lookup lookup, final Operation operation, final MethodType methodType) {
        this.lookup = Objects.requireNonNull(lookup, "lookup");
        this.operation = Objects.requireNonNull(operation, "name");
        this.methodType = Objects.requireNonNull(methodType, "methodType");
    }

    /**
     * Returns the operation at the call site.
     * @return the operation at the call site.
     */
    public final Operation getOperation() {
        return operation;
    }

    /**
     * The type of the method at the call site.
     *
     * @return type of the method at the call site.
     */
    public final MethodType getMethodType() {
        return methodType;
    }

    /**
     * Returns the lookup that should be used to find method handles to set as
     * targets of the call site described by this descriptor. When creating
     * descriptors from a {@link java.lang.invoke} bootstrap method, it should
     * be the lookup passed to the bootstrap.
     * @return the lookup that should be used to find method handles to set as
     * targets of the call site described by this descriptor.
     * @throws SecurityException if the lookup isn't the
     * {@link MethodHandles#publicLookup()} and a security manager is present,
     * and a check for {@code RuntimePermission("dynalink.getLookup")} fails.
     */
    public final Lookup getLookup() {
        final SecurityManager sm = System.getSecurityManager();
        if (sm != null && lookup != MethodHandles.publicLookup()) {
            sm.checkPermission(GET_LOOKUP_PERMISSION);
        }
        return lookup;
    }

    /**
     * Returns the value of {@link #getLookup()} without a security check. Can
     * be used by subclasses to access the lookup quickly.
     * @return same as returned value of {@link #getLookup()}.
     */
    protected final Lookup getLookupPrivileged() {
        return lookup;
    }

    /**
     * Creates a new call site descriptor from this descriptor, which is
     * identical to this, except it changes the method type. Invokes
     * {@link #changeMethodTypeInternal(MethodType)} and checks that it returns
     * a descriptor of the same class as this descriptor.
     *
     * @param newMethodType the new method type
     * @return a new call site descriptor, with the method type changed.
     * @throws RuntimeException if {@link #changeMethodTypeInternal(MethodType)}
     * returned a descriptor of different class than this object.
     * @throws NullPointerException if {@link #changeMethodTypeInternal(MethodType)}
     * returned null.
     */
    public final CallSiteDescriptor changeMethodType(final MethodType newMethodType) {
        final CallSiteDescriptor changed = Objects.requireNonNull(
                changeMethodTypeInternal(newMethodType),
                "changeMethodTypeInternal() must not return null.");

        if (getClass() != changed.getClass()) {
            throw new RuntimeException(
                    "changeMethodTypeInternal() must return an object of the same class it is invoked on.");
        }

        return changed;
    }

    /**
     * Creates a new call site descriptor from this descriptor, which is
     * identical to this, except it changes the method type. Subclasses must
     * override this method to return an object of their exact class.
     *
     * @param newMethodType the new method type
     * @return a new call site descriptor, with the method type changed.
     */
    protected CallSiteDescriptor changeMethodTypeInternal(final MethodType newMethodType) {
        return new CallSiteDescriptor(lookup, operation, newMethodType);
    }

    /**
     * Returns true if this call site descriptor is equal to the passed object.
     * It is considered equal if the other object is of the exact same class,
     * their operations and method types are equal, and their lookups have the
     * same {@link java.lang.invoke.MethodHandles.Lookup#lookupClass()} and
     * {@link java.lang.invoke.MethodHandles.Lookup#lookupModes()}.
     */
    @Override
    public boolean equals(final Object obj) {
        if (obj == this) {
            return true;
        } else if (obj == null) {
            return false;
        } else if (obj.getClass() != getClass()) {
            return false;
        }
        final CallSiteDescriptor other = (CallSiteDescriptor)obj;
        return operation.equals(other.operation) &&
               methodType.equals(other.methodType) &&
               lookupsEqual(lookup, other.lookup);
    }

    /**
     * Compares two lookup objects for value-based equality. They are considered
     * equal if they have the same
     * {@link java.lang.invoke.MethodHandles.Lookup#lookupClass()} and
     * {@link java.lang.invoke.MethodHandles.Lookup#lookupModes()}.
     * @param l1 first lookup
     * @param l2 second lookup
     * @return true if the two lookups are equal, false otherwise.
     */
    private static boolean lookupsEqual(final Lookup l1, final Lookup l2) {
        return l1.lookupClass() == l2.lookupClass() && l1.lookupModes() == l2.lookupModes();
    }

    /**
     * Returns a value-based hash code of this call site descriptor computed
     * from its operation, method type, and lookup object's lookup class and
     * lookup modes.
     * @return value-based hash code for this call site descriptor.
     */
    @Override
    public int hashCode() {
        return operation.hashCode() + 31 * methodType.hashCode() + 31 * 31 * lookupHashCode(lookup);
    }

    /**
     * Returns a value-based hash code for the passed lookup object. It is
     * based on the lookup object's
     * {@link java.lang.invoke.MethodHandles.Lookup#lookupClass()} and
     * {@link java.lang.invoke.MethodHandles.Lookup#lookupModes()} values.
     * @param lookup the lookup object.
     * @return a hash code for the object..
     */
    private static int lookupHashCode(final Lookup lookup) {
        return lookup.lookupClass().hashCode() + 31 * lookup.lookupModes();
    }

    /**
     * Returns the string representation of this call site descriptor, of the
     * format {@code name(parameterTypes)returnType@lookup}.
     */
    @Override
    public String toString() {
        final String mt = methodType.toString();
        final String l = lookup.toString();
        final String o = operation.toString();
        final StringBuilder b = new StringBuilder(o.length() + mt.length() + 1 + l.length());
        return b.append(o).append(mt).append('@').append(l).toString();
    }
}