Java并发编程系列之LockSupport的用法

public static void park();
public static void park(Object blocker);

public static void parkNanos(Object blocker, long nanos) {
    if (nanos > 0) { 
        // 获取当前线程
        Thread t = Thread.currentThread();
        // 设置Blocker
        setBlocker(t, blocker);
        // 获取许可，并设置了时间
        UNSAFE.park(false, nanos);
        // 设置许可，重新设置blocker为null，避免unpack，获取的blocker为之前设置的
        setBlocker(t, null);
    }
}

public static void parkUntil(Object blocker, long deadline) {
    // 获取当前线程
    Thread t = Thread.currentThread();
    // 设置Blocker
    setBlocker(t, blocker);
    UNSAFE.park(true, deadline);
    // 设置Blocker为null
    setBlocker(t, null);
}

import java.util.concurrent.locks.LockSupport;
public class LockSupportExample {
    private static final int total = 10;
    private  static int i = 0;
    static Thread t1 , t2;
    public static void main(String[] args) {
        t1 = new Thread(() ->{
            while (i < total) {
                System.out.println("t1:" + (++i));
                LockSupport.unpark(t2);
                LockSupport.park();
            }
        });
        t2 = new Thread(() -> {
            while (i < total) {
                LockSupport.park();
                System.out.println("t2:" + (++i));
                LockSupport.unpark(t1);
            }
        });
        t1.start();
        t2.start();
    }
}

public class LockSupport {
    // Hotspot implementation via intrinsics API
    private static final sun.misc.Unsafe UNSAFE;
    private static final long parkBlockerOffset;
    private static final long SEED;
    private static final long PROBE;
    private static final long SECONDARY;
    static {
        try {
            // 获取Unsafe实例
            UNSAFE = sun.misc.Unsafe.getUnsafe();
            // 线程类的class对象
            Class<?> tk = Thread.class;
            // 获取Thread的parkBlocker字段的内存偏移地址
            parkBlockerOffset = UNSAFE.objectFieldOffset
                (tk.getDeclaredField("parkBlocker"));
            // 获取Thread的threadLocalRandomSeed字段的内存偏移地址
            SEED = UNSAFE.objectFieldOffset
                (tk.getDeclaredField("threadLocalRandomSeed"));
            // 获取Thread的threadLocalRandomProbe字段的内存偏移地址
            PROBE = UNSAFE.objectFieldOffset
                (tk.getDeclaredField("threadLocalRandomProbe"));
            // 获取Thread的threadLocalRandomSecondarySeed字段的内存偏移地址
            SECONDARY = UNSAFE.objectFieldOffset
                (tk.getDeclaredField("threadLocalRandomSecondarySeed"));
        } catch (Exception ex) { throw new Error(ex); }
    }
}

public static void park(Object blocker) {
    // 获取当前线程
    Thread t = Thread.currentThread();
    // 设置Blocker
    setBlocker(t, blocker);
    // 获取许可
    UNSAFE.park(false, 0L);
    // 重新可运行后再此设置Blocker为null，避免unpack获取到上一个设置的setBlocker(t, blocker);
    setBlocker(t, null);
}

public static void unpark(Thread thread) {
    if (thread != null) // 线程为不空
        UNSAFE.unpark(thread); // 释放该线程许可
}