一.线程同步机制
1.三大不安全案例
1.买票，多个线程共同使用票数
2.银行，两个人取同一个账户的钱
3.不能保证线程同步的集合
2.synchronized的同步方法及方法块
1.买票
package syn;
//不安全的买票
public class UnsafeBuyTicket {
public static void main(String[] args) {
BuyTicket buyTicket = new BuyTicket();
new Thread(buyTicket,"me").start();
new Thread(buyTicket,"you").start();
new Thread(buyTicket,"other").start();
}
}
class BuyTicket implements Runnable{
int ticketNums = 100;
boolean flag = true;
@Override
public void run() {
//买票
while(flag){
//模拟延时
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
buy();
}
}
//synchronized同步方法，锁的是this
private synchronized void buy(){
//判断是否有票
if(ticketNums<=0){
flag = false;
return ;
}
System.out.println(Thread.currentThread().getName()+"拿到"+ticketNums--);
}
}2.银行，不能直接锁run方法，因为run方法的this是银行，而不是账户，锁了银行，两个人仍可以从不同的银行，取同一个账户的钱，导致并发问题,可以锁方法块来解决
package syn;
public class UnSafeBank {
public static void main(String[] args) {
Account account = new Account(100, "MONEY");
Drawing you = new Drawing(account,50,"你");
Drawing me = new Drawing(account,100,"我");
you.start();
me.start();
}
}
//账户
class Account{
int money;//余额
String name;//卡名
public Account(int money, String name) {
this.money = money;
this.name = name;
}
}
//银行
class Drawing extends Thread{
Account account;
int drawingMoney; //取了多少钱
int nowMoney; //手里有多少钱
public Drawing(Account account,int drawingMoney, String name){
super(name);
this.account = account;
this.drawingMoney = drawingMoney;
}
@Override
public void run(){
synchronized (account){
if(account.money-drawingMoney<0){
System.out.println(Thread.currentThread().getName()+"钱不够");
return ;
}
//sleep可以放大问题的发生性
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
account.money = account.money - drawingMoney;
nowMoney = nowMoney + drawingMoney;
System.out.println(account.name+"余额为"+account.money);
System.out.println(this.getName()+"手里的钱"+nowMoney);
}
}
}juc安全类型的集合
package syn;
import com.sun.xml.internal.ws.api.model.wsdl.WSDLOutput;
import java.util.concurrent.CopyOnWriteArrayList;
//测试JUC安全类型的集合
public class TestJUC {
public static void main(String[] args) {
CopyOnWriteArrayList<String> list = new CopyOnWriteArrayList<String>();
for (int i = 0; i < 100000; i++) {
new Thread(() -> {
list.add(Thread.currentThread().getName());
}).start();
}
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(list.size());
}
}
死锁
条件：互斥，不可抢占，循环等待，请求和保持
package DeadLock;
//死锁：多个线程互相只有对方需要的资源，形成僵持
public class DeadLock {
public static void main(String[] args) {
Makeup g1 = new Makeup(0,"xiao");
Makeup g2 = new Makeup(1,"da");
g1.start();
g2.start();
}
}
class Lipstick{
}
class Mirror{
}
class Makeup extends Thread{
//需要的资源只有一份，用static来保证互斥条件
static Lipstick lipstick =new Lipstick();
static Mirror mirror =new Mirror();
int choice; //选择
String girlName; //使用化妆品的人
Makeup(int choice , String girlName){
this.choice = choice;
this.girlName = girlName;
}
@Override
public void run(){
//化妆
try {
makeup();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
//化妆，互相持有对方的锁，需要拿到对方的资源
//满足了请求和保持，循环等待，不可抢占
//想要解决死锁，只需要在请求新资源的时候吧旧的资源的锁释放掉就可一了
private void makeup() throws InterruptedException {
if(choice==0){
synchronized (lipstick){ //获得口红的锁
System.out.println(this.girlName+"获得口红的锁");
Thread.sleep(1000);
//一秒钟后想获得镜子
synchronized (mirror){
System.out.println(this.girlName+"获得镜子的锁");
}
}
}
else{
synchronized (mirror){
System.out.println(this.girlName+"获得镜子的锁");
Thread.sleep(2000);
synchronized (lipstick){ //获得口红的锁
System.out.println(this.girlName+"获得口红的锁");
}
}
}
}
}lock锁
不能同步方法，juc
与syn对比
1.syn是隐式的，自动释放，lock是显式的
2.lock只有代码块锁
3.lock性能好
package advanced;
import java.util.concurrent.locks.ReentrantLock;
public class TestLock {
public static void main(String[] args) {
TestLock2 testLock2 = new TestLock2();
new Thread(testLock2).start();
new Thread(testLock2).start();
new Thread(testLock2).start();
}
}
class TestLock2 implements Runnable{
int ticketNums = 10;
//定义lock锁
private final ReentrantLock lock = new ReentrantLock();
@Override
public void run() {
while(true){
try{
lock.lock();
if(ticketNums>0){
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(ticketNums--);
}else{
break;
}
}finally{
lock.unlock();
}
}
}
}生产者消费者问题
wait释放锁，常用来线程通信
noitfyALL唤醒所有线程
生产者消费者问题中用while而不用if，排除假唤醒
###管程法
package advanced;
//测试生产者消费者模型->利用缓冲区解决：管程法
//生产者，消费者，缓冲区
public class TestPC {
public static void main(String[] args) {
SynContainer container = new SynContainer();
new Productor(container).start();
new Consumer(container).start();
}
}
class Productor extends Thread{
SynContainer container;
public Productor(SynContainer container){
this.container = container;
}
//生产
@Override
public void run(){
for (int i = 0; i < 100; i++) {
container.push(new Chicken(i));
}
}
}
class Consumer extends Thread{
SynContainer container;
public Consumer(SynContainer container){
this.container = container;
}
@Override
public void run(){
for (int i = 0; i < 100; i++) {
container.pop();
}
}
}
class Chicken{
int id;
public Chicken(int id) {
this.id = id;
}
}
//缓冲区
class SynContainer{
//容器大小
Chicken[] chickens = new Chicken[10];
//计数器
int count = 0;
//生产者丢入产品
public synchronized void push(Chicken chiken){
//如果容器慢了就需要等待消费者消费
while(count == 10){
//通知消费者消费,生产者等待
try {
this.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
//如果没有满就需要丢入产品
chickens[count] = chiken;
count++;
System.out.println("生产了"+chiken.id+"只鸡");
//可以通知消费者消费了
this.notifyAll();
}
//消费者消费产品
public synchronized Chicken pop(){
while(count == 0){
//等待生产者生产，消费者等待
try {
this.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
//如果可以消费
count--;
Chicken chicken = chickens[count];
System.out.println("消费了"+chicken.id+"只鸡");
this.notifyAll();
return chicken;
}
}信号灯法
package advanced;
//测试生产者消费者问题2：信号灯法
public class TestPC2 {
public static void main(String[] args) {
TV tv = new TV();
new Player(tv).start();
new Watcher(tv).start();
}
}
//生产者--演员
class Player extends Thread{
TV tv;
public Player(TV tv){
this.tv = tv;
}
@Override
public void run(){
for (int i = 0; i < 20; i++) {
if(i%2 == 0){
this.tv.play("haha");
}else{
this.tv.play("hehe");
}
}
}
}
//消费者--观众
class Watcher extends Thread{
TV tv;
public Watcher(TV tv){
this.tv = tv;
}
@Override
public void run(){
for (int i = 0; i < 20; i++) {
tv.watch();
}
}
}
//产品
class TV{
//演员表演，观众等待
//观众观看，演员等待
String voice; //表演的节目
boolean flag = true;
//表演
public synchronized void play(String voice){
while(flag==false){
try {
this.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
System.out.println("演员表演了:"+voice);
this.notifyAll();
this.voice = voice;
this.flag = !this.flag;
}
//观看
public synchronized void watch(){
while(flag){
try {
this.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
System.out.println("观看了："+voice);
//通知演员表演
this.notifyAll();
this.flag = !this.flag;
}
}线程池
package advanced;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class TestPool {
public static void main(String[] args) {
//1.创建服务,创建线程池，参数为线程池大小
ExecutorService ser = Executors.newFixedThreadPool(10);
ser.execute(new MyThread());
ser.execute(new MyThread());
ser.execute(new MyThread());
ser.shutdown();
}
}
class MyThread implements Runnable{
@Override
public void run() {
System.out.println(Thread.currentThread().getName());
}
}
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