读LockSupport源码

LockSupport类简介

LockSupport类是其他类实现锁和同步的基础

 * Basic thread blocking primitives for creating locks and other * synchronization classes.

读了源码就会知道，这个类主要利用了Unsafe类中提供的part和unpart两个方法．而LockSupport类暴露出来的两个核心接口也是part和unpart两个．

如果需要阅读Unsafe类源码，参考我的另一篇博文：读Unsafe类源码

读源码

//构造方法私有化private LockSupport() {} // Cannot be instantiated.// 引用Unsafe类private static final sun.misc.Unsafe UNSAFE;//Thread类中　parkBlocker 　字段的偏移量private static final long parkBlockerOffset;//Thread　类中　threadLocalRandomSeed　字段的偏移量private static final long SEED;//Thread　类中　threadLocalRandomProbe　字段的偏移量private static final long PROBE;//Thread　类中　threadLocalRandomSecondarySeed　字段的偏移量private static final long SECONDARY;//初始化上面4个字段的值static {    try {        UNSAFE = sun.misc.Unsafe.getUnsafe();        Class<?> tk = Thread.class;        parkBlockerOffset = UNSAFE.objectFieldOffset                (tk.getDeclaredField("parkBlocker"));        SEED = UNSAFE.objectFieldOffset                (tk.getDeclaredField("threadLocalRandomSeed"));        PROBE = UNSAFE.objectFieldOffset                (tk.getDeclaredField("threadLocalRandomProbe"));        SECONDARY = UNSAFE.objectFieldOffset                (tk.getDeclaredField("threadLocalRandomSecondarySeed"));    } catch (Exception ex) { throw new Error(ex); }}//把 Thread 实例 t 的 parkBlocker 字段的值设置为 argprivate static void setBlocker(Thread t, Object arg) {    // Even though volatile, hotspot doesn't need a write barrier here.    UNSAFE.putObject(t, parkBlockerOffset, arg);}//获取对象 t 中 parkBlocker 字段的值public static Object getBlocker(Thread t) {    if (t == null)        throw new NullPointerException();    return UNSAFE.getObjectVolatile(t, parkBlockerOffset);}// 取消阻塞线程，如果线程已经处于非阻塞状态，那么下次调用ｐark时不会阻塞线程public static void unpark(Thread thread) {    if (thread != null)        UNSAFE.unpark(thread);}// 使当前调用线程在给定对象上阻塞(不能保证一定阻塞，// 因为如果之前在非阻塞状态调用了unpar方法的话，此次调用ｐark方法就不会阻塞线程)public static void park(Object blocker) {    Thread t = Thread.currentThread();    setBlocker(t, blocker);    UNSAFE.park(false, 0L);    setBlocker(t, null);}// 阻塞线程public static void park() {        UNSAFE.park(false, 0L);}// 使当前线程在blocker对象上阻塞给定的纳秒时间public static void parkNanos(Object blocker, long nanos) {    if (nanos > 0) {        Thread t = Thread.currentThread();        setBlocker(t, blocker);        UNSAFE.park(false, nanos);        setBlocker(t, null);    }}// 使当前线程在blocker对象上阻塞到给定的时间点// 这个时间点是从Epoch time(1970-01-01 00:00:00 UTC)开始算起的某个具体的时间点。public static void parkUntil(Object blocker, long deadline) {    Thread t = Thread.currentThread();    setBlocker(t, blocker);    UNSAFE.park(true, deadline);    setBlocker(t, null);}