/*

 * Copyright (c) 2015, 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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package jdk.dynalink.linker;

import java.security.Permission;

import java.util.List;

import java.util.ServiceLoader;

import java.util.function.Supplier;

import jdk.dynalink.DynamicLinkerFactory;

/**

 * A class acting as a supplier of guarding dynamic linkers that can be

 * automatically loaded by other language runtimes. Language runtimes wishing

 * to export their own linkers should subclass this class and implement the

 * {@link #get()} method to return a list of exported linkers and declare the

 * subclass in

 * {@code /META-INF/services/jdk.dynalink.linker.GuardingDynamicLinkerExporter}

 * resource of their distribution (typically, JAR file) so that dynamic linker

 * factories can discover them using the {@link ServiceLoader} mechanism. Note

 * that instantiating this class is tied to a security check for the

 * {@code RuntimePermission("dynalink.exportLinkersAutomatically")} when a

 * security manager is present, to ensure that only trusted runtimes can

 * automatically export their linkers into other runtimes.

 * @see DynamicLinkerFactory#setClassLoader(ClassLoader)

 */

public abstract class GuardingDynamicLinkerExporter implements Supplier<List<GuardingDynamicLinker>> {

    /**

     * The name of the runtime permission for creating instances of this class.

     * Granting this permission to a language runtime allows it to export its

     * linkers for automatic loading into other language runtimes.

     */

    public static final String AUTOLOAD_PERMISSION_NAME = "dynalink.exportLinkersAutomatically";

    private static final Permission AUTOLOAD_PERMISSION = new RuntimePermission(AUTOLOAD_PERMISSION_NAME);

    /**

     * Creates a new linker exporter. If there is a security manager installed

     * checks for the

     * {@code RuntimePermission("dynalink.exportLinkersAutomatically")} runtime

     * permission. This ensures only language runtimes granted this permission

     * will be allowed to export their linkers for automatic loading.

     * @throws SecurityException if the necessary runtime permission is not

     * granted.

     */

    protected GuardingDynamicLinkerExporter() {

        final SecurityManager sm = System.getSecurityManager();

        if (sm != null) {

            sm.checkPermission(AUTOLOAD_PERMISSION);

        }

    }

}