1/*
2 * Written by Doug Lea with assistance from members of JCP JSR-166
3 * Expert Group and released to the public domain, as explained at
4 * http://creativecommons.org/publicdomain/zero/1.0/
5 */
6
7package java.util.concurrent.locks;
8
9/**
10 * A synchronizer that may be exclusively owned by a thread.  This
11 * class provides a basis for creating locks and related synchronizers
12 * that may entail a notion of ownership.  The
13 * <tt>AbstractOwnableSynchronizer</tt> class itself does not manage or
14 * use this information. However, subclasses and tools may use
15 * appropriately maintained values to help control and monitor access
16 * and provide diagnostics.
17 *
18 * @since 1.6
19 * @author Doug Lea
20 */
21public abstract class AbstractOwnableSynchronizer
22    implements java.io.Serializable {
23
24    /** Use serial ID even though all fields transient. */
25    private static final long serialVersionUID = 3737899427754241961L;
26
27    /**
28     * Empty constructor for use by subclasses.
29     */
30    protected AbstractOwnableSynchronizer() { }
31
32    /**
33     * The current owner of exclusive mode synchronization.
34     */
35    private transient Thread exclusiveOwnerThread;
36
37    /**
38     * Sets the thread that currently owns exclusive access. A
39     * <tt>null</tt> argument indicates that no thread owns access.
40     * This method does not otherwise impose any synchronization or
41     * <tt>volatile</tt> field accesses.
42     */
43    protected final void setExclusiveOwnerThread(Thread t) {
44        exclusiveOwnerThread = t;
45    }
46
47    /**
48     * Returns the thread last set by
49     * <tt>setExclusiveOwnerThread</tt>, or <tt>null</tt> if never
50     * set.  This method does not otherwise impose any synchronization
51     * or <tt>volatile</tt> field accesses.
52     * @return the owner thread
53     */
54    protected final Thread getExclusiveOwnerThread() {
55        return exclusiveOwnerThread;
56    }
57}
58