/*

 * Copyright (c) 2018, 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.

 *

 * 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.

 */

import java.lang.management.ManagementFactory;

import java.lang.management.MonitorInfo;

import java.lang.management.ThreadInfo;

import java.nio.channels.Selector;

public class SelectorUtils {

    /**

     * tell if the monitor of an Object is held by a Thread.

     * @param t    the Thread to hold the monitor of the selected-key set

     * @param lock the Object

     * @return

     */

    public static boolean mightHoldLock(Thread t, Object lock) {

        long tid = t.getId();

        int hash = System.identityHashCode(lock);

        ThreadInfo ti = ManagementFactory.getThreadMXBean().

                getThreadInfo(new long[]{ tid} , true, false, 100)[0];

        if (ti != null) {

            for (MonitorInfo mi : ti.getLockedMonitors()) {

                if (mi.getIdentityHashCode() == hash)

                    return true;

            }

        }

        return false;

    }

    /**

     * Spin until the monitor of the selected-key set is likely held

     * as selected operations are specified to synchronize on the

     * selected-key set.

     * @param t   the Thread to hold the monitor of the selected-key set

     * @param sel the Selector

     * @throws Exception

     */

    public static void spinUntilLocked(Thread t, Selector sel) throws Exception {

        while (!mightHoldLock(t, sel.selectedKeys())) {

            Thread.sleep(50);

        }

    }

}