GuardingDynamicLinker.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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       distributed under the License is distributed on an "AS IS" BASIS,
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package jdk.internal.dynalink.linker;

/**
 * The base interface for language-specific dynamic linkers. Such linkers always have to produce method handles with
 * guards, as the validity of the method handle for calls at a call site inevitably depends on some condition (at the
 * very least, it depends on the receiver belonging to the language runtime of the linker). Language runtime
 * implementors will normally implement one for their own language, and declare it in the
 * <tt>META-INF/services/jdk.internal.dynalink.linker.GuardingDynamicLinker</tt> file within their JAR file.
 *
 * @author Attila Szegedi
 */
public interface GuardingDynamicLinker {
    /**
     * Creates a guarded invocation appropriate for a particular invocation with the specified arguments at a call site.
     *
     * @param linkRequest the object describing the request for linking a particular invocation
     * @param linkerServices linker services
     * @return a guarded invocation with a method handle suitable for the arguments, as well as a guard condition that
     * if fails should trigger relinking. Must return null if it can't resolve the invocation. If the returned
     * invocation is unconditional (which is actually quite rare), the guard in the return value can be null. The
     * invocation can also have a switch point for asynchronous invalidation of the linkage, as well as a
     * {@link Throwable} subclass that describes an expected exception condition that also triggers relinking (often it
     * is faster to rely on an infrequent but expected {@link ClassCastException} than on an always evaluated
     * {@code instanceof} guard). If the linker does not recognize any native language runtime contexts in arguments, or
     * does recognize its own, but receives a call site descriptor without its recognized context in the arguments, it
     * should invoke {@link LinkRequest#withoutRuntimeContext()} and link for that. While the linker must produce an
     * invocation with parameter types matching those in the call site descriptor of the link request, it should not try
     * to match the return type expected at the call site except when it can do it with only the conversions that lose
     * neither precision nor magnitude, see {@link LinkerServices#asTypeLosslessReturn(java.lang.invoke.MethodHandle,
     * java.lang.invoke.MethodType)}.
     * @throws Exception if the operation fails for whatever reason
     */
    public GuardedInvocation getGuardedInvocation(LinkRequest linkRequest, LinkerServices linkerServices)
            throws Exception;
}