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/*
 * This file is available under and governed by the GNU General Public
 * License version 2 only, as published by the Free Software Foundation.
 * However, the following notice accompanied the original version of this
 * file, and Oracle licenses the original version of this file under the BSD
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/*
   Copyright 2009-2013 Attila Szegedi

   Redistribution and use in source and binary forms, with or without
   modification, are permitted provided that the following conditions are
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     notice, this list of conditions and the following disclaimer in the
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   * Neither the name of the copyright holder nor the names of
     contributors may be used to endorse or promote products derived from
     this software without specific prior written permission.

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*/

package jdk.dynalink.linker;

import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodType;
import java.util.List;
import jdk.dynalink.DynamicLinkerFactory;


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 the linking logic for their own language as one or more GuardingDynamicLinker classes. They will typically set them as prioritized linkers in the DynamicLinkerFactory they configure for themselves, and maybe also set some as fallback
linkers to handle language-specific "property not found" etc. conditions. 
 Consider implementing TypeBasedGuardingDynamicLinker interface instead of this interface for those linkers that are based on the Java class of the objects. If you need to implement language-specific type conversions, have your GuardingDynamicLinker also implement the GuardingTypeConverterFactory interface. 
 Languages can export linkers to other language runtimes for automatic discovery using a GuardingDynamicLinkerExporter. 
/**
 * 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
 * the linking logic for their own language as one or more
 * {@link GuardingDynamicLinker} classes. They will typically set them as
 * {@link DynamicLinkerFactory#setPrioritizedLinkers(List) prioritized linkers}
 * in the {@code DynamicLinkerFactory} they configure for themselves, and maybe also
 * set some as {@link DynamicLinkerFactory#setFallbackLinkers(List) fallback
 * linkers} to handle language-specific "property not found" etc. conditions.
 * <p>
 * Consider implementing {@link TypeBasedGuardingDynamicLinker} interface
 * instead of this interface for those linkers that are based on the Java class
 * of the objects. If you need to implement language-specific type conversions,
 * have your {@code GuardingDynamicLinker} also implement the
 * {@link GuardingTypeConverterFactory} interface.
 * <p>
 * Languages can export linkers to other language runtimes for
 * {@link DynamicLinkerFactory#setClassLoader(ClassLoader) automatic discovery}
 * using a {@link GuardingDynamicLinkerExporter}.
 */
public interface GuardingDynamicLinker {
    
Creates a guarded invocation appropriate for a particular invocation with
the specified arguments at a call site.

Params:
  • linkRequest – the object describing the request for linking a
particular invocation
  • linkerServices – linker services
Throws:
  • Exception – if the operation fails for whatever reason
Returns: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 any number of switch points for asynchronous invalidation of the linkage, as well as a Throwable subclass that describes an expected exception condition that also triggers relinking (often it is faster to rely on an infrequent but expected ClassCastException than on an always evaluated instanceof guard). 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 LinkerServices.asTypeLosslessReturn(MethodHandle, MethodType) for further explanation.
/**
     * 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 any
     * number of switch points 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). 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(MethodHandle, MethodType)} for
     * further explanation.
     * @throws Exception if the operation fails for whatever reason
     */
    public GuardedInvocation getGuardedInvocation(LinkRequest linkRequest, LinkerServices linkerServices)
            throws Exception;
}