1 LockSupport类

• 底层使用Unsafe类

private static void block1(Thread thread) {    new Thread(() -> {        LockSupport.parkNanos(THREE_SECOND);        LockSupport.unpark(thread);    }).start();    LockSupport.park();}

2 Unsafe类

private static void block2(Thread thread) {    try {        Field f = Unsafe.class.getDeclaredField("theUnsafe");        f.setAccessible(true);        Unsafe unsafe = (Unsafe) f.get(null);        new Thread(() -> {            LockSupport.parkNanos(THREE_SECOND);            unsafe.unpark(thread);        }).start();        unsafe.park(false, 0L);    } catch (NoSuchFieldException | IllegalAccessException e) {        e.printStackTrace();    }}

3 Object类

private static void block3(Thread thread) {    new Thread(() -> {        LockSupport.parkNanos(THREE_SECOND);        synchronized (thread) {            thread.notify();        }    }).start();    synchronized (thread) {        try {            thread.wait(); // 释放锁        } catch (InterruptedException e) {            e.printStackTrace();        }    }}

4 CountDownLatch类

private static void block4() {    CountDownLatch latch = new CountDownLatch(1);    new Thread(() -> {        LockSupport.parkNanos(THREE_SECOND);        latch.countDown();    }).start();    try {        latch.await();    } catch (InterruptedException e) {        e.printStackTrace();    }}

5 自旋

private static void block5() {    AtomicBoolean flag = new AtomicBoolean(true);    new Thread(() -> {        LockSupport.parkNanos(THREE_SECOND);        flag.set(false);    }).start();    while (flag.get()) {    }}

6 测试

• 测试误差排行(非准确测试)： 自旋 < Unsafe < CountDownLatch < Object < LockSupport

public class Main {    private static final long THREE_SECOND = 3_000_000_000L;    private static final int times = 10;    public static void main(String[] args) {        System.out.println(System.currentTimeMillis() + ":start");        Thread thread = Thread.currentThread();        long diff = 0;        for (int i = 0; i < times; i++) {            long start = System.nanoTime();            block1(thread);//4364820            //block2(thread);//3881931            //block3(thread);//4358189            //block4(); // 4309549            //block5(); // 3473868            diff += Math.abs(System.nanoTime() - start - THREE_SECOND);        }        System.out.println("block diff Time:"+diff / times);        System.out.println(System.currentTimeMillis() + ":end");    }}