RelinkableCallSite.java

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/*
   Copyright 2009-2013 Attila Szegedi

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   * Neither the name of the copyright holder nor the names of
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package jdk.dynalink;

import java.lang.invoke.CallSite;
import java.lang.invoke.MethodHandle;
import jdk.dynalink.linker.GuardedInvocation;
import jdk.dynalink.support.ChainedCallSite;
import jdk.dynalink.support.SimpleRelinkableCallSite;

/**
 * Interface for call sites managed by a {@link DynamicLinker}. Users of
 * Dynalink must use subclasses of {@link CallSite} that also implement this
 * interface as their call site implementations. There is a readily usable
 * {@link SimpleRelinkableCallSite} subclass that implements monomorphic inline
 * caching strategy as well as {@link ChainedCallSite} that implements a
 * polymorphic inline caching strategy and retains a chain of previously linked
 * method handles. A relinkable call site will be managed by a
 * {@link DynamicLinker} object after being associated with it using its
 * {@link DynamicLinker#link(RelinkableCallSite)} method.
 */
public interface RelinkableCallSite {
    /**
     * Invoked by dynamic linker to initialize the relinkable call site by
     * setting a relink-and-invoke method handle. The call site implementation
     * is supposed to set this method handle as its target using
     * {@link CallSite#setTarget(MethodHandle)}. Relink-and-invoke is the
     * initial method handle set by
     * {@link DynamicLinker#link(RelinkableCallSite)} that will cause the call
     * site to be relinked to an appropriate target on its first invocation
     * based on its arguments, and that linked target will then be invoked
     * (hence the name). This linking protocol effectively delays linking until
     * the call site is invoked with actual arguments and thus ensures that
     * linkers can make nuanced linking decisions based on those arguments and
     * not just on the static method type of the call site.
     * @param relinkAndInvoke a relink-and-invoke method handle supplied by
     * Dynalink.
     */
    public void initialize(MethodHandle relinkAndInvoke);

    /**
     * Returns the descriptor for this call site.
     *
     * @return the descriptor for this call site.
     */
    public CallSiteDescriptor getDescriptor();

    /**
     * This method will be called by the dynamic linker every time the call site
     * is relinked (but see
     * {@link #resetAndRelink(GuardedInvocation, MethodHandle)} for an
     * exception). It will be passed a {@code GuardedInvocation} that the call
     * site should incorporate into its target method handle. When this method
     * is called, the call site is allowed to keep other non-invalidated
     * invocations around for implementation of polymorphic inline caches and
     * compose them with this invocation to form its final target.
     *
     * @param guardedInvocation the guarded invocation that the call site should
     * incorporate into its target method handle.
     * @param relinkAndInvoke a relink-and-invoke method handle. This is a
     * method handle matching the method type of the call site that is supplied
     * by the {@link DynamicLinker} as a callback. It should be used by this
     * call site as the ultimate fallback when it can't invoke its target with
     * the passed arguments. The fallback method is such that when it's invoked,
     * it'll try to obtain an adequate target {@link GuardedInvocation} for the
     * invocation, and subsequently invoke
     * {@link #relink(GuardedInvocation, MethodHandle)} or
     * {@link #resetAndRelink(GuardedInvocation, MethodHandle)}, and finally
     * invoke the target.
     */
    public void relink(GuardedInvocation guardedInvocation, MethodHandle relinkAndInvoke);

    /**
     * This method will be called by the dynamic linker every time the call site
     * is relinked <b>and</b> the linker wishes the call site to throw away any
     * prior linkage state (that is how it differs from
     * {@link #relink(GuardedInvocation, MethodHandle)}). It will be passed a
     * {@code GuardedInvocation} that the call site should use to build its new
     * target method handle. When this method is called, the call site is
     * discouraged from keeping any previous state, and is supposed to only
     * link the current invocation.
     *
     * @param guardedInvocation the guarded invocation that the call site should
     * use to build its target method handle.
     * @param relinkAndInvoke a relink-and-invoke method handle. This is a
     * method handle matching the method type of the call site that is supplied
     * by the {@link DynamicLinker} as a callback. It should be used by this
     * call site as the ultimate fallback when it can't invoke its target with
     * the passed arguments. The fallback method is such that when it's invoked,
     * it'll try to obtain an adequate target {@link GuardedInvocation} for the
     * invocation, and subsequently invoke
     * {@link #relink(GuardedInvocation, MethodHandle)} or
     * {@link #resetAndRelink(GuardedInvocation, MethodHandle)}, and finally
     * invoke the target.
     */
    public void resetAndRelink(GuardedInvocation guardedInvocation, MethodHandle relinkAndInvoke);
}