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GraalVM is an ecosystem for compiling and running applications written in multiple languages. GraalVM removes the isolation between programming languages and enables interoperability in a shared runtime.

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/*
 * Copyright (c) 2017, 2017, 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
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */
package org.graalvm.nativeimage.impl;

import org.graalvm.nativeimage.ImageSingletons;
import org.graalvm.nativeimage.Platform;
import org.graalvm.nativeimage.Platforms;

@Platforms(Platform.HOSTED_ONLY.class)
public abstract class ImageSingletonsSupport {

    /** Implementation-specific singleton that stores the registration data. */
    private static ImageSingletonsSupport support;

    protected static void installSupport(ImageSingletonsSupport imageSingletonsSupport) {
        assert imageSingletonsSupport != null : "ImageSingletonsSupport cannot be null.";
        support = imageSingletonsSupport;
    }

    public static ImageSingletonsSupport get() {
        checkInstalled();
        return support;
    }

    private static void checkInstalled() {
        if (support == null) {
            throw new Error("The class " + ImageSingletons.class.getSimpleName() + " can only be used when building native images, i.e., when using the native-image command.");
        }
    }

    protected ImageSingletonsSupport() {
    }

    public abstract  void add(Class key, T value);

    public abstract  T lookup(Class key);

    public abstract boolean contains(Class key);
}