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/*
 * Copyright (c) 2014, 2022, 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 com.sun.glass.ui.monocle;

import com.sun.glass.ui.Application;

import java.util.LinkedList;
import java.util.concurrent.CountDownLatch;

/**
 * RunnableProcessor provides control over nested run loops in the JavaFX
 * event queue.
 */
class RunnableProcessor implements Runnable {

    private RunnableQueue queue = new RunnableQueue();

    private static class RunLoopControl {
        boolean active; // thread should continue to process events.
        Object release; // object to return with on leave nested
    }

    // our stack of nested run loops
    private LinkedList activeRunLoops = new LinkedList<>();

    @Override
    public void run() {
        runLoop();
    }

    /**
     * Posts a Runnable to the JavaFX event queue using this RunnableProcessor
     *
     * @param r an action to be performed on the JavaFX application thread.
     */
    void invokeLater(Runnable r) {
        queue.postRunnable(r);
    }

    /**
     * Posts a Runnable to the JavaFX event queue and waits for the Runnable
     * to complete.
     *
     * @param r an action to be performed on the JavaFX application thread.
     */
    void invokeAndWait(final Runnable r) {
        final CountDownLatch latch = new CountDownLatch(1);
        queue.postRunnable(() -> {
            try {
                r.run();
            } finally {
                latch.countDown();
            }
        });
        try {
            latch.await();
        } catch (InterruptedException e) { }
    }

    private Object runLoop() {
        final RunLoopControl control = new RunLoopControl();

        //push this new instance on the stack
        activeRunLoops.push(control);

        control.active = true;
        while (control.active) {
            try {
                queue.getNextRunnable().run();
            } catch (Throwable e) {
                Application.reportException(e);
            }
        }

        return control.release;

    }

    Object enterNestedEventLoop() {
        // we are being called on the current active event thread
        // via dispatch, so it is stalled until we return.

        // start our nested loop, which will block until that exits
        Object ret = runLoop();

        // and return the value that was passed into leaveNested
        return ret;
    }

    void leaveNestedEventLoop(Object retValue) {
        // we are being called from dispatch of the current running
        // event thread. We want to cause this thread to exit, and
        // restart the nested on.

        RunLoopControl current = activeRunLoops.pop();
        assert current != null;

        // let the current run loop die when we return to dispatch.
        current.active = false;
        // and give it the ret object so it will return it to the
        // blocked nesting call.
        current.release = retValue;

        // when we return from this dispatched event, we will exit
        // because we are no longer active, and then the nested
        // call can return the release value we just provided.
    }

    void shutdown() {
        synchronized (queue) {
            queue.clear();
            while (!activeRunLoops.isEmpty()) {
                RunLoopControl control = activeRunLoops.pop();
                control.active = false;
            }
            queue.notifyAll();
        }
    }

    /** Posts a Runnable to the JavaFX event queue using the global
     * RunnableProcessor.
     *
     * @param r an action to be performed on the JavaFX application thread.
     */
    static void runLater(Runnable r) {
        NativePlatformFactory.getNativePlatform()
                .getRunnableProcessor()
                .invokeLater(r);
    }

}