jdk/dynalink/RelinkableCallSite.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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       distributed under the License is distributed on an "AS IS" BASIS,
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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);
}