1 /*

     2  * Copyright (c) 2018, Oracle and/or its affiliates. All rights reserved.

     3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

     4  *

     5  * This code is free software; you can redistribute it and/or modify it

     6  * under the terms of the GNU General Public License version 2 only, as

     7  * published by the Free Software Foundation.

     8  *

     9  * This code is distributed in the hope that it will be useful, but WITHOUT

    10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

    11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

    12  * version 2 for more details (a copy is included in the LICENSE file that

    13  * accompanied this code).

    14  *

    15  * You should have received a copy of the GNU General Public License version

    16  * 2 along with this work; if not, write to the Free Software Foundation,

    17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

    18  *

    19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

    20  * or visit www.oracle.com if you need additional information or have any

    21  * questions.

    22  */

    23 

    24 import java.lang.management.ManagementFactory;

    25 import java.lang.management.MonitorInfo;

    26 import java.lang.management.ThreadInfo;

    27 import java.nio.channels.Selector;

    28 

    29 public class SelectorUtils {

    30 

    31     /**

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

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

    34      * @param lock the Object

    35      * @return

    36      */

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

    38         long tid = t.getId();

    39         int hash = System.identityHashCode(lock);

    40         ThreadInfo ti = ManagementFactory.getThreadMXBean().

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

    42         if (ti != null) {

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

    44                 if (mi.getIdentityHashCode() == hash)

    45                     return true;

    46             }

    47         }

    48         return false;

    49     }

    50 

    51     /**

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

    53      * as selected operations are specified to synchronize on the

    54      * selected-key set.

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

    56      * @param sel the Selector

    57      * @throws Exception

    58      */

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

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

    61             Thread.sleep(50);

    62         }

    63     }

    64 }