1 /*
   2  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   3  *
   4  * This code is free software; you can redistribute it and/or modify it
   5  * under the terms of the GNU General Public License version 2 only, as
   6  * published by the Free Software Foundation.  Oracle designates this
   7  * particular file as subject to the "Classpath" exception as provided
   8  * by Oracle in the LICENSE file that accompanied this code.
   9  *
  10  * This code is distributed in the hope that it will be useful, but WITHOUT
  11  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  12  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  13  * version 2 for more details (a copy is included in the LICENSE file that
  14  * accompanied this code).
  15  *
  16  * You should have received a copy of the GNU General Public License version
  17  * 2 along with this work; if not, write to the Free Software Foundation,
  18  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  19  *
  20  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  21  * or visit www.oracle.com if you need additional information or have any
  22  * questions.
  23  */
  24 
  25 /*
  26  * This file is available under and governed by the GNU General Public
  27  * License version 2 only, as published by the Free Software Foundation.
  28  * However, the following notice accompanied the original version of this
  29  * file:
  30  *
  31  * Written by Doug Lea with assistance from members of JCP JSR-166
  32  * Expert Group and released to the public domain, as explained at
  33  * http://creativecommons.org/publicdomain/zero/1.0/
  34  */
  35 
  36 package java.util.concurrent.locks;
  37 
  38 /**
  39  * A synchronizer that may be exclusively owned by a thread.  This
  40  * class provides a basis for creating locks and related synchronizers
  41  * that may entail a notion of ownership.  The
  42  * {@code AbstractOwnableSynchronizer} class itself does not manage or
  43  * use this information. However, subclasses and tools may use
  44  * appropriately maintained values to help control and monitor access
  45  * and provide diagnostics.
  46  *
  47  * @since 1.6
  48  * @author Doug Lea
  49  */
  50 public abstract class AbstractOwnableSynchronizer
  51     implements java.io.Serializable {
  52 
  53     /** Use serial ID even though all fields transient. */
  54     private static final long serialVersionUID = 3737899427754241961L;
  55 
  56     /**
  57      * Empty constructor for use by subclasses.
  58      */
  59     protected AbstractOwnableSynchronizer() { }
  60 
  61     /**
  62      * The current owner of exclusive mode synchronization.
  63      */
  64     private transient Object exclusiveOwner;
  65 
  66     /**
  67      * Sets the strand that currently owns exclusive access.
  68      * A {@code null} argument indicates that no strand owns access.
  69      * This method does not otherwise impose any synchronization or
  70      * {@code volatile} field accesses.
  71      * @param owner the owner thread or fiber
  72      */
  73     protected final void setExclusiveOwner(Object owner) {
  74         if (owner != null && !(owner instanceof Thread || owner instanceof Fiber))
  75             throw new IllegalArgumentException();
  76         exclusiveOwner = owner;
  77     }
  78 
  79     /**
  80      * Returns the strand last set by {@code setExclusiveOwnerStrand}
  81      * or {@code setExclusiveOwnerThread}, or {@code null} if never set.
  82      * This method does not otherwise impose any synchronization or {@code
  83      * volatile} field accesses.
  84      * @return the owner thread
  85      */
  86     protected final Object getExclusiveOwner() {
  87         return exclusiveOwner;
  88     }
  89 
  90     /**
  91      * Sets the thread that currently owns exclusive access.
  92      * A {@code null} argument indicates that no thread owns access.
  93      * This method does not otherwise impose any synchronization or
  94      * {@code volatile} field accesses.
  95      * @param thread the owner thread
  96      */
  97     protected final void setExclusiveOwnerThread(Thread thread) {
  98         exclusiveOwner = thread;
  99     }
 100 
 101     /**
 102      * Returns the thread last set by {@code setExclusiveOwnerThread},
 103      * or {@code null} if never set.  This method does not otherwise
 104      * impose any synchronization or {@code volatile} field accesses.
 105      * @return the owner thread
 106      * @throws ClassCastException if the synchronizer is owned by a Fiber
 107      */
 108     protected final Thread getExclusiveOwnerThread() {
 109         return (Thread) exclusiveOwner;
 110     }
 111 }