锁持有者管理器AbstractOwnableSynchronizer

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/*
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/publicdomain/zero/1.0/
 */

package java.util.concurrent.locks;

/**
 * A synchronizer that may be exclusively owned by a thread.  This
 * class provides a basis for creating locks and related synchronizers
 * that may entail a notion of ownership.  The
 * AbstractOwnableSynchronizer class itself does not manage or
 * use this information. However, subclasses and tools may use
 * appropriately maintained values to help control and monitor access
 * and provide diagnostics.
 *
 一个线程，可能独占一个同步锁。AbstractOwnableSynchronizer用于表示锁与持有者之间的关系；
AbstractOwnableSynchronizer不管理这种关系；主要是其子类，用于控制或监视锁的状态，提供
帮助。
 * @since 1.6
 * @author Doug Lea
 */
public abstract class AbstractOwnableSynchronizer
    implements java.io.Serializable {

    /** Use serial ID even though all fields transient. */
    private static final long serialVersionUID = 3737899427754241961L;

    /**
     * Empty constructor for use by subclasses.
     */
    protected AbstractOwnableSynchronizer() { }

    /**
     * The current owner of exclusive mode synchronization.
     */
     //独占模式，锁的持有者
    private transient Thread exclusiveOwnerThread;

    /**
     * Sets the thread that currently owns exclusive access. A
     * null argument indicates that no thread owns access.
     * This method does not otherwise impose any synchronization or
     * volatile field accesses.
     */
     //设置锁持有者
    protected final void setExclusiveOwnerThread(Thread t) {
        exclusiveOwnerThread = t;
    }

    /**
     * Returns the thread last set by
     * setExclusiveOwnerThread, or null if never
     * set.  This method does not otherwise impose any synchronization
     * or volatile field accesses.
     * @return the owner thread
     */
      //获取锁的持有线程
    protected final Thread getExclusiveOwnerThread() {
        return exclusiveOwnerThread;
    }
}