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 * Copyright (c) 2019, 2019, 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.
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package com.oracle.svm.util;

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

Marker interface to identify threads that are only used by SubstateVM infrastructure and will not be present in the image heap at run time. Each of such threads has a way to obtain the terminated replacement of itself. 
 Not intented to be implemented by customer threads. Allowing background threads that are not terminated can lead to very hard to debug errors. If you have background threads running while the static analysis is running, then bad race conditions can happen: the static analysis looks at a heap snapshot at a "random" time from the point of view of the background thread. If the background thread makes new objects available after the last heap snapshot, then the static analysis misses objects of the image heap, which leads to either strange errors during image generation (when the image heap is written), or even worse strange behavior at run time (when a field is, e.g., constant folded to null because the static analysis only saw the null value). /**
 * Marker interface to identify threads that are only used by SubstateVM infrastructure and will not
 * be present in the image heap at run time. Each of such threads has a {@link #asTerminated() way}
 * to obtain the terminated replacement of itself.
 * <p>
 * Not intented to be implemented by customer threads. Allowing background threads that are not
 * terminated can lead to very hard to debug errors. If you have background threads running while
 * the static analysis is running, then bad race conditions can happen: the static analysis looks at
 * a heap snapshot at a "random" time from the point of view of the background thread. If the
 * background thread makes new objects available after the last heap snapshot, then the static
 * analysis misses objects of the image heap, which leads to either strange errors during image
 * generation (when the image heap is written), or even worse strange behavior at run time (when a
 * field is, e.g., constant folded to {@code null} because the static analysis only saw the
 * {@code null} value).
 */
@Platforms(Platform.HOSTED_ONLY.class)
public interface ImageGeneratorThreadMarker /* extends Thread */ {
    default Thread asTerminated() {
        return TerminatedThread.SINGLETON;
    }
}

final class TerminatedThread extends Thread {
    static final TerminatedThread SINGLETON;
    static {
        SINGLETON = new TerminatedThread("Terminated Infrastructure Thread");
        SINGLETON.start();
        try {
            SINGLETON.join();
        } catch (InterruptedException ex) {
            throw new IllegalStateException(ex);
        }
    }

    TerminatedThread(String name) {
        super(name);
    }
}