/*

 * Copyright (c) 2010, 2013, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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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

 * license:

 */

/*

   Copyright 2009-2013 Attila Szegedi

*/

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

 * {@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.

     *

     * @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;

}