sync和lock的区别

本文已参与「新人创作礼」活动， 一起开启掘金创作之路。

题目: synchronized 和ock有什么区别?用新的Lock有什么好处?你举例说说

1原始构成

synchronized是关键字属于JVM层面,monitorenter(底层是通过monitor对象来完成，其实wait/notify等方法也依赖Fmonitor对象只有在同步块或方法中才能漏wait/notify等方monitorexit

Lock是具体类(java. util. concurrent. locks . Lock)是api层面的锁

2使用方法

synchronized不需要用户去手动释放锁，|当synchronized代码执 行完后系统会自动让线程释放对锁的占用 ReentrantLock,则需要用户去手动释放锁若没有主动释放锁，就有可能导致出现死锁现象。

需要lock() unlock()方法配合try/finally语句块来完成。

3等待是否可中断

synchronized.不可中断，除非抛出异常或者正常运行完成

ReentrantLock可中断，1. 设置超时方法tryLock(long timeout, TimeUnit unit)

lockInterruptibly()放代码块中，调用interrupt() 方法可中断

加锁是否公平. synchronized非公平锁

ReentrantLock两者都可以，默认非公平锁，构造方法可以传入boolean值，true 为公平锁，false为非公平锁

锁绑定多个条件Condition

synchronized没有

ReentrantLock用来实现分组唤醒需要唤醒的线程们，可以精确唤醒， 而不是像synchronized 要么随机唤醒一个线程要 么唤醒全部线程。 sync两次退出，第一次正常退出第二次异常退出

package juc;

import sun.awt.windows.ThemeReader;

import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;

        class ShareResource{

            private int flag = 1;

            private ReentrantLock lock = new ReentrantLock();

            private Condition condition1 = lock.newCondition();

            private Condition condition2 = lock.newCondition();

            private Condition condition3 = lock.newCondition();

            //ctrl+alt+t是try catch

            public void print5(int totalLoop){
                lock.lock();
                try {
                    //1.判断
                    while (flag != 1){
                        condition1.await();
                    }
                    //干活

                    for (int i = 1;i <= 5; i++) {
                        System.out.println("线程名字:"+Thread.currentThread().getName()+"\t次数:"+i+"\t轮数:"+totalLoop);
                    }

                    //唤醒+通知
                    flag = 2;
                    condition2.signal();

                } catch (Exception e) {
                    e.printStackTrace();
                } finally {
                    lock.unlock();
                }
            }

            public void print10(int totalLoop){
                lock.lock();
                try {
                    //1.判断
                    while (flag != 2){
                        condition2.await();
                    }
                    //干活

                    for (int i = 1;i <= 10; i++) {
                        System.out.println("线程名字:"+Thread.currentThread().getName()+"\t次数:"+i+"\t轮数:"+totalLoop);
                    }

                    //唤醒+通知
                    flag = 3;
                    condition3.signal();

                } catch (Exception e) {
                    e.printStackTrace();
                } finally {
                    lock.unlock();
                }
            }

            public void print15(int totalLoop){
                lock.lock();
                try {
                    //1.判断
                    while (flag != 3){
                        condition3.await();
                    }
                    //干活

                    for (int i = 1;i <= 15; i++) {
                        System.out.println("线程名字:"+Thread.currentThread().getName()+"\t次数:"+i+"\t轮数:"+totalLoop);
                    }

                    //唤醒+通知
                    flag = 1;
                    condition1.signal();

                } catch (Exception e) {
                    e.printStackTrace();
                } finally {
                    lock.unlock();
                }
            }



        }

        public class ConditionLockDemo {
            public static void main(String[] args) {

                ShareResource sr = new ShareResource();

                new Thread(()->{
                    for(int i = 1 ; i<=10 ; i++){
                        sr.print5(i);
                    }
                },"A").start();

                new Thread(()->{
                    for(int i = 1 ; i<=10 ; i++){
                        sr.print10(i);
                    }
                },"B").start();

                new Thread(()->{
                    for(int i = 1 ; i<=10 ; i++){
                        sr.print15(i);
                    }
                },"C").start();
            }
        }