一柬唯、方法如下

public native void unpark(Object var1);

public native void park(boolean var1, long var2);

二认臊、使用說明

park：將當(dāng)前線程掛起。unpark：精準(zhǔn)的喚醒某個(gè)線程锄奢。

park的參數(shù)失晴，表示掛起的到期時(shí)間冤议，第一個(gè)如果是true，表示絕對(duì)時(shí)間师坎，則var2為絕對(duì)時(shí)間值恕酸，單位是毫秒。第一個(gè)參數(shù)如果是false胯陋，表示相對(duì)時(shí)間蕊温，則var2為相對(duì)時(shí)間值，單位是納秒遏乔。

unpark的參數(shù)义矛，表示線程。

簡(jiǎn)單示例：

park(false,0) 表示永不到期盟萨，一直掛起凉翻，直至被喚醒

long time = System.currentTimeMillis()+3000;
park(true,time + 3000) 表示3秒后自動(dòng)喚醒

park(false,3000000000L) 表示3秒后自動(dòng)喚醒

三、測(cè)試示例

package com.suncy.article.article5;

import sun.misc.Unsafe;

import java.lang.reflect.Field;

public class ParkTest {
    public static void main(String[] args) throws NoSuchFieldException, IllegalAccessException, InterruptedException {
        Field f = Unsafe.class.getDeclaredField("theUnsafe");
        f.setAccessible(true);
        Unsafe unsafe = (Unsafe) f.get(null);

        //線程1必須等待喚醒
        Thread thread1 = new Thread(() -> {
            System.out.println("線程1:執(zhí)行任務(wù)");
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
            }
            System.out.println("線程1:掛起捻激，等待喚醒才能繼續(xù)執(zhí)行任務(wù)");
            unsafe.park(false, 0);
            System.out.println("線程1:執(zhí)行完畢");
        });
        thread1.start();

        //線程2必須等待喚醒
        Thread thread2 = new Thread(() -> {
            System.out.println("線程2:執(zhí)行任務(wù)");
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
            }
            System.out.println("線程2:掛起制轰，等待喚醒才能繼續(xù)執(zhí)行任務(wù)");
            unsafe.park(false, 0);
            System.out.println("線程2:執(zhí)行完畢");
        });
        thread2.start();

        Thread.sleep(5000);
        System.out.println("喚醒線程2");
        unsafe.unpark(thread2);
        Thread.sleep(1000);
        System.out.println("喚醒線程1");
        unsafe.unpark(thread1);

        //線程3自動(dòng)喚醒
        Thread thread3 = new Thread(() -> {
            System.out.println("線程3:執(zhí)行任務(wù)");
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
            }
            System.out.println("線程3:掛起，等待時(shí)間到自動(dòng)喚醒");
            unsafe.park(false, 3000000000L);
            System.out.println("線程3:執(zhí)行完畢");
        });
        thread3.start();

        //線程4自動(dòng)喚醒
        Thread thread4 = new Thread(() -> {
            System.out.println("線程4:執(zhí)行任務(wù)");
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
            }
            System.out.println("線程4:掛起胞谭，等待時(shí)間到自動(dòng)喚醒");
            long time = System.currentTimeMillis() + 3000;
            unsafe.park(true, time);
            System.out.println("線程4:執(zhí)行完畢");
        });
        thread4.start();
    }
}

測(cè)試結(jié)果：

image.png

四垃杖、目的

1、使用Unsafe中的park和unpark和上篇文章說的《Unsafe中的CAS》可以完成一個(gè)自己的鎖丈屹，這應(yīng)該是并發(fā)編程基礎(chǔ)的前提條件调俘。