Lock 接口
**公平锁:**十分的公平,可以先来后到
**非公平锁:**十分不公平,可以插队 (默认)
public class SaleTicketDemo02 {
public static void main(String[] args) {
Ticket2 ticket = new Ticket2();
new Thread(()->{for (int i = 0; i <60 ; i++) ticket.sale(); },"A").start();
new Thread(()->{for (int i = 0; i <60 ; i++) ticket.sale(); },"B").start();
new Thread(()->{for (int i = 0; i <60 ; i++) ticket.sale(); },"C").start();
}
}
/*
* 1、new ReentrantLock()
* 2.lock.lock() 加锁
* 3、 finally=>lock.unlock() 解锁
* */
//资源类OOP
class Ticket2 {
private int number = 50;
Lock lock = new ReentrantLock();
public void sale() {
lock.lock();
try {
if(number>0){
System.out.println(Thread.currentThread().getName()+"买到了第:"+number-- +"票");
}
}catch (Exception e){
}finally {
lock.unlock();
}
}
}
Synchronized 和 Lock 区别
- synchronized 内置的 java 的关键子,Lock 是一个 Java 类
- synchronized 无法判断获取所得状态,Lock 可以判断是否获取到了锁
- synchronized 会自动释放锁,lock 必须要手动释放锁!如果不释放锁那么就是个死锁
- synchronized 线程 1(获得锁,阻塞)、线程 2(等待,傻乎乎的等着),Lock 锁就不一定会等下去
- synchronized 可重入锁,不可以中断,非公平的;Lock,可重入锁 ,可以判断锁,非公平的锁,可以自己设置
- synchronized 适合锁少量的代码同步问题,Lock 适合锁大量的 同步代码!
生产者和消费者问题 synchronized 版
进行线程之间的通信
下面是两个线程之间的通信
package net.yscxy.pc;
/**
* @Author WangFuKun
* @create 2020/11/19 20:46
*/
/*
* 线程之间的通信问题,生产者和消费者问题! 等待唤醒,通知唤醒
* 线程交替执行A B 操作同一个变量 num = 0
* */
public class A {
public static void main(String[] args) {
Data data = new Data();
new Thread(()->{
for (int i = 0; i < 10; i++) {
try {
data.decrement();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
},"A").start();
new Thread(()->{
for (int i = 0; i < 10; i++) {
try {
data.increment();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
},"B").start();
}
}
//判断、等待、通知
class Data{
private int number = 0;
//+1
public synchronized void increment() throws InterruptedException {
if (number!=0){
this.wait();
}
number ++;
System.out.println(Thread.currentThread().getName()+"->"+number);
//通知其他线程,我+1完成了
this.notify();
}
//-1
public synchronized void decrement() throws InterruptedException {
if(number ==0){
//等待
this.wait();
}
number --;
System.out.println(Thread.currentThread().getName()+"->"+number);
//通知其他线程我-1完成了
this.notify();
}
}
问题出现,如果是多个线程的话就会出现问题!,例如纯在 ABCD 四个线程就会出现问题(虚假唤醒!)
解决方案
if 换成 while,类似下面这样
package net.yscxy.pc;
/**
* @Author WangFuKun
* @create 2020/11/19 20:46
*/
/*
* 线程之间的通信问题,生产者和消费者问题! 等待唤醒,通知唤醒
* 线程交替执行A B 操作同一个变量 num = 0
* */
public class A {
public static void main(String[] args) {
Data data = new Data();
new Thread(()->{
for (int i = 0; i < 100; i++) {
try {
data.decrement();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
},"A").start();
new Thread(()->{
for (int i = 0; i < 100; i++) {
try {
data.increment();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
},"B").start();
new Thread(()->{
for (int i = 0; i < 100; i++) {
try {
data.decrement();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
},"C").start();
new Thread(()->{
for (int i = 0; i < 100; i++) {
try {
data.decrement();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
},"D").start();
}
}
//判断、等待、通知
class Data{
private int number = 0;
//+1
public synchronized void increment() throws InterruptedException {
while (number!=0){
this.wait();
}
number ++;
System.out.println(Thread.currentThread().getName()+"->"+number);
//通知其他线程,我+1完成了
this.notify();
}
//-1
public synchronized void decrement() throws InterruptedException {
while(number ==0){
//等待
this.wait();
}
number --;
System.out.println(Thread.currentThread().getName()+"->"+number);
//通知其他线程我-1完成了
this.notify();
}
}
JUC 版本的生产者和消费者问题
代码实现
package net.yscxy.pc;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
* @Author WangFuKun
* @create 2020/11/19 20:46
*/
/*
* 线程之间的通信问题,生产者和消费者问题! 等待唤醒,通知唤醒
* 线程交替执行A B 操作同一个变量 num = 0
* */
public class B {
public static void main(String[] args) {
Data2 data = new Data2();
new Thread(()->{
for (int i = 0; i < 10; i++) {
try {
data.decrement();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
},"A").start();
new Thread(()->{
for (int i = 0; i < 10; i++) {
try {
data.increment();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
},"B").start();
new Thread(()->{
for (int i = 0; i < 10; i++) {
try {
data.decrement();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
},"C").start();
new Thread(()->{
for (int i = 0; i < 10; i++) {
try {
data.increment();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
},"D").start();
}
}
//判断、等待、通知
class Data2{
private int number = 0;
Lock lock = new ReentrantLock();
Condition condition = lock.newCondition();
//+1
public void increment() throws InterruptedException {
lock.lock();
try {
//业务代码
while(number !=0){
//等待
condition.await();
}
number ++;
System.out.println(Thread.currentThread().getName()+"->"+number);
//通知其他线程,我+1完成了
condition.signalAll();
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
//-1
public void decrement() throws InterruptedException {
lock.lock();
try {
while(number ==0){
//等待
condition.await();
}
number --;
System.out.println(Thread.currentThread().getName()+"->"+number);
condition.signalAll();//唤醒全部
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
}
Condition 进准的通知和和唤醒线程
A、B、C、D 有序执行
代码测试
package net.yscxy.pc;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
* @Author WangFuKun
* @create 2020/11/19 20:46
*/
/*
* 让线程有序执行,A执行完成调用B,B执行完调用C,C执行完调用A
* */
public class C {
public static void main(String[] args) {
Data3 data = new Data3();
new Thread(() -> {
for (int i = 0; i <10 ; i++) {
data.PrintA();
}
},"A").start();
new Thread(() -> {
for (int i = 0; i <10 ; i++) {
data.PrintB();
}
},"B").start();
new Thread(() -> { for (int i = 0; i <10 ; i++) {
data.PrintC();
} },"C").start();
}
}
//判断、等待、通知
class Data3 {
private int number = 1;
Lock lock = new ReentrantLock();
Condition condition1 = lock.newCondition();
Condition condition2 = lock.newCondition();
Condition condition3 = lock.newCondition();
public void PrintA() {
lock.lock();
try {
//业务、判断、执行、通知
while (number!=1){
//等待
condition1.await();
}
System.out.println(Thread.currentThread().getName()+"-->AAAAAAAAAA");
//唤醒指定的人,唤醒2
number = 2;
condition2.signal();
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
public void PrintB() {
lock.lock();
try {
//业务、判断、执行、通知
while (number!=2){
//等待
condition2.await();
}
System.out.println(Thread.currentThread().getName()+"-->BBBBBBBBB");
//唤醒指定的人,唤醒2
number = 3;
condition3.signal();
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
public void PrintC() {
lock.lock();
try {
//业务、判断、执行、通知
while (number!=3){
//等待
condition3.await();
}
System.out.println(Thread.currentThread().getName()+"-->CCCCCCCCC");
//唤醒指定的人,唤醒2
number = 1;
condition1.signal();
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
}
8 锁现象
如何判断锁的是谁,锁的到底是谁
new this 锁的是具体的一个手机
static Class 唯一的一个模板
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