Java线程之间通讯（三）
使用wait和notify方法实现了线程间的通讯，都是Object 类的方法，java所有的对象都提供了这两个方法
1.wait和notify必须配合synchronized使用
2.wait方法释放锁，notify方法不释放锁
import java.util.ArrayList;
import java.util.List;
public class ListAdd1 {
private volatile static List list = new ArrayList();
public void add(){
list.add("laoshi");
}
public int size(){
return list.size();
}
public static void main(String[] args) {
final ListAdd1 list1 = new ListAdd1();
Thread t1 = new Thread(new Runnable() {
@Override
public void run() {
try {
for(int i = 0; i <10; i++){
list1.add();
System.out.println("当前线程：" + Thread.currentThread().getName() + "添加了一个元素..");
Thread.sleep(500);
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}, "t1");
Thread t2 = new Thread(new Runnable() {
@Override
public void run() {
while(true){
if(list1.size() == 5){
System.out.println("当前线程收到通知：" + Thread.currentThread().getName() + " list size = 5 线程停止..");
throw new RuntimeException();
}
}
}
}, "t2");
t1.start();
t2.start();
}
}
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.CountDownLatch;
/**
* wait notfiy 方法，wait释放锁，notfiy不释放锁
*/
public class ListAdd2 {
private volatile static List list = new ArrayList();
public void add(){
list.add("laoshi");
}
public int size(){
return list.size();
}
public static void main(String[] args) {
final ListAdd2 list2 = new ListAdd2();
// 1 实例化出来一个 lock
// 当使用wait 和 notify 的时候 ， 一定要配合着synchronized关键字去使用
final Object lock = new Object();
final CountDownLatch countDownLatch = new CountDownLatch(1);
Thread t1 = new Thread(new Runnable() {
@Override
public void run() {
try {
synchronized (lock) {
for(int i = 0; i <10; i++){
list2.add();
System.out.println("当前线程：" + Thread.currentThread().getName() + "添加了一个元素..");
Thread.sleep(500);
if(list2.size() == 5){
System.out.println("已经发出通知..");
countDownLatch.countDown();
lock.notify();
}
}
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}, "t1");
Thread t2 = new Thread(new Runnable() {
@Override
public void run() {
synchronized (lock) {
if(list2.size() != 5){
try {
System.out.println("t2进入...");
lock.wait();
countDownLatch.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
System.out.println("当前线程：" + Thread.currentThread().getName() + "收到通知线程停止..");
throw new RuntimeException();
}
}
}, "t2");
t2.start();
t1.start();
}
}
import java.util.LinkedList;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;
public class MyQueue {
//1 需要一个承装元素的集合
private LinkedList<Object> list=new LinkedList<Object>();
//2 需要一个计数器
private AtomicInteger count=new AtomicInteger(0);
//3 需要制定上限和下限
private final int minSize=0;
private final int maxSize ;
//4 构造方法
public MyQueue(int size){
this.maxSize = size;
}
//5 初始化一个对象 用于加锁
private final Object lock=new Object();
//put(anObject): 把anObject加到BlockingQueue里,如果BlockQueue没有空间,则调用此方法的线程被阻断，
// 直到BlockingQueue里面有空间再继续.
public void put(Object obj){
synchronized (lock){
while (count.get()==this.maxSize){
try {
lock.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
//1 加入元素
list.add(obj);
//2.计数器累加
count.incrementAndGet();
//3 通知另外一个线程（唤醒）
lock.notify();
System.out.println("新加入的元素为:" + obj);
}
}
//take: 取走BlockingQueue里排在首位的对象,若BlockingQueue为空,
// 阻断进入等待状态直到BlockingQueue有新的数据被加入.
public Object take(){
Object ret=null;
synchronized (lock){
while (count.get()==this.minSize){
try {
lock.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
//1 做移除元素操作
ret=list.removeFirst();
//2 计数器递减
count.decrementAndGet();
//3 唤醒另外一个线程
lock.notify();
}
return ret;
}
public int getSize(){
return this.count.get();
}
public static void main(String[] args) {
final MyQueue mq = new MyQueue(5);
mq.put("a");
mq.put("b");
mq.put("c");
mq.put("d");
mq.put("e");
System.out.println("当前容器的长度:" + mq.getSize());
Thread t1 = new Thread(new Runnable() {
@Override
public void run() {
mq.put("f");
mq.put("g");
}
},"t1");
t1.start();
Thread t2 = new Thread(new Runnable() {
@Override
public void run() {
Object o1 = mq.take();
System.out.println("移除的元素为:" + o1);
Object o2 = mq.take();
System.out.println("移除的元素为:" + o2);
}
},"t2");
try {
TimeUnit.SECONDS.sleep(2);
} catch (InterruptedException e) {
e.printStackTrace();
}
t2.start();
}
}
ThreadLocal：线程局部变量，是一种多线程间并发访问变量的解决方案，与synchronized枷锁的方式不同，ThreadLocal完全不提供锁，使用以空间换时间的手段，为每个线程提供变量的独立副本，以保证线程安全。
在高并发量或者竞争激烈的场景，使用ThreadLoacal可以一定程度少减少锁竞争。
public class ConnThreadLocal {
public static ThreadLocal<String> th=new ThreadLocal<String>();
public void setTh(String value){
th.set(value);
}
public void getTh(){
System.out.println(Thread.currentThread().getName() + ":" + this.th.get());
}
public static void main(String[] args) throws InterruptedException {
final ConnThreadLocal ct = new ConnThreadLocal();
Thread t1 = new Thread(new Runnable() {
@Override
public void run() {
ct.setTh("张三");
ct.getTh();
}
}, "t1");
Thread t2 = new Thread(new Runnable() {
@Override
public void run() {
try {
Thread.sleep(1000);
ct.getTh();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}, "t2");
t1.start();
t2.start();
}
}
单例模式：最常见的饥饿模式（直接实力化对象），懒汉模式（在调用方法时进行实例化对象）
在多线程中考虑性能和线程安全问题使用
dubble check instance
static inner class
public class DubbleSingleton {
private static DubbleSingleton ds;
public static DubbleSingleton getDs(){
if(ds == null){
try {
//模拟初始化对象的准备时间...
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
synchronized (DubbleSingleton.class) {
if(ds == null){
ds = new DubbleSingleton();
}
}
}
return ds;
}
public static void main(String[] args) {
Thread t1 = new Thread(new Runnable() {
@Override
public void run() {
System.out.println(DubbleSingleton.getDs().hashCode());
}
},"t1");
Thread t2 = new Thread(new Runnable() {
@Override
public void run() {
System.out.println(DubbleSingleton.getDs().hashCode());
}
},"t2");
Thread t3 = new Thread(new Runnable() {
@Override
public void run() {
System.out.println(DubbleSingleton.getDs().hashCode());
}
},"t3");
t1.start();
t2.start();
t3.start();
}
}
这种方法用的多
public class Singletion {
private static class InnerSingletion {
private static Singletion single = new Singletion();
}
public static Singletion getInstance(){
return InnerSingletion.single;
}
}
import java.util.concurrent.TimeUnit;
public class Demo3 {
private volatile int signal;
public synchronized void set(int value){
signal=1;
notifyAll(); //notifyAll叫醒所有的处于wait线程，争夺到时间片的线程只有一个
notify(); //notify方法会随机叫醒一个处于wait状态的线程
//notify 拿到锁
//this.signal=value;
}
public synchronized int get(){
System.out.println(Thread.currentThread().getName()+"方法执行了。。。");
if(signal!=1){
try {
wait(); //释放锁
} catch (InterruptedException e) {
e.printStackTrace();
}
}
System.out.println(Thread.currentThread().getName()+"方法执行完毕。。。");
return signal;
}
public static void main(String[] args) {
Demo3 demo=new Demo3();
Target t1=new Target(demo);
Target t2=new Target(demo);
new Thread(t2).start();
new Thread(t2).start();
new Thread(t2).start();
new Thread(t2).start();
try {
TimeUnit.SECONDS.sleep(1);
} catch (InterruptedException e) {
e.printStackTrace();
}
new Thread(t1).start();
}
}
