【JAVA多线程编程核心技术】第四章 Lock(ReentrantLock)
一、ReentrantLock简介
ReentrantLock：可重入锁。
- 分路分支通知功能
package com.hfview.reentrantLock.base;
import java.util.concurrent.locks.ReentrantLock;
/**
* ReentrantLock的基本使用
*
* @author: zhw
* @since: 2019/3/12 11:41
*/
public class Demo1 {
public static void main(String[] args) {
final ReentrantLock lock = new ReentrantLock();
new Thread(new Runnable() {
@Override
public void run() {
try {
lock.lock();
System.out.println("a begin");
Thread.sleep(2000);
System.out.println("a end");
} catch (Exception e) {
e.printStackTrace();
}finally {
lock.unlock();
}
}
}).start();
new Thread(new Runnable() {
@Override
public void run() {
try {
lock.lock();
System.out.println("b begin");
Thread.sleep(2000);
System.out.println("b end");
} catch (Exception e) {
e.printStackTrace();
}finally {
lock.unlock();
}
}
}).start();
}
}
使用分为2步，第一步lock锁定 第二步unlock解锁
二、ReentrantLock分路分支通知功能
下面就是演示如何解决notifyAll浪费性能的问题
package com.hfview.reentrantLock;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;
/**
* 修改多消费者和生产者
*
* @author: zhw
* @since: 2019/3/12 11:50
*/
public class Demo2 {
public static void main(String[] args) {
Service service = new Service();
for(int i=0;i<20;i++){
Produce p = new Produce(service);
Consumer c = new Consumer(service);
p.start();
c.start();
}
}
}
class Service{
private ReentrantLock lock = new ReentrantLock();
private Condition pCondition = lock.newCondition();
private Condition sCondition = lock.newCondition();
private List list = new ArrayList<>();
public void push(){
try {
lock.lock();
while(list.size()>0){
pCondition.await();
}
list.add("zhw");
System.out.println("push zhw :"+Thread.currentThread().getName());
sCondition.signal();
} catch (Exception e) {
e.printStackTrace();
}finally {
lock.unlock();
}
}
public void pop(){
try {
lock.lock();
while(list.size()==0){
sCondition.await();
}
list.remove(0);
System.out.println(" pop zhw :"+Thread.currentThread().getName());
pCondition.signal();
} catch (Exception e) {
e.printStackTrace();
}finally {
lock.unlock();
}
}
}
class Produce extends Thread{
private Service service;
public Produce(Service service){
this.service = service;
}
@Override
public void run(){
service.push();
}
}
class Consumer extends Thread{
private Service service;
public Consumer(Service service){
this.service = service;
}
@Override
public void run(){
service.pop();
}
}
三、ReentrantLock公平锁和非公平锁
简单来说就是先进先出
package com.hfview.reentrantLock.Fair;
import java.lang.invoke.LambdaConversionException;
import java.util.concurrent.locks.ReentrantLock;
/**
* 公平锁和非公平锁
* @author: zhw
* @since: 2019/3/12 14:18
*/
public class Service implements Runnable{
private final ReentrantLock lock;
public Service(boolean isFair){
lock = new ReentrantLock(isFair);
}
@Override
public void run(){
try {
System.out.println("线程:"+Thread.currentThread().getName()+" 运行了");
lock.lock();
System.out.println(" 线程:"+Thread.currentThread().getName()+" 获得了锁");
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
public static void main(String[] args) {
Service service = new Service(true);
Thread[] arr = new Thread[20];
for(int i=0;i<20;i++){
arr[i] = new Thread(service);
}
for(Thread t:arr){
t.start();
}
}
}
公平锁: 顾名思义，先来排队的先去获得锁。就行食堂吃饭
非公平锁： 看CPU心情随机的去获得锁，默认是非公平的(残忍的人生啊)
四、ReentrantReadWriteLock锁
该锁是ReentrantLock的一种改进，这是读写分离的思想，都是读的时候是可以共享锁的，是读读 或者是读写 就要设计到写都要是互斥锁。
package com.hfview.reentrantReadWriteLock.read;
import java.io.Serializable;
import java.util.concurrent.locks.ReentrantReadWriteLock;
/**
* //TODO 写注释
*
* @author: zhw
* @since: 2019/3/12 15:08
*/
public class Demo1 {
public static void main(String[] args) {
Service service = new Service();
Thread t1 = new Thread(new Runnable() {
@Override
public void run() {
service.read1();
//service.write1();
}
});
Thread t2 = new Thread(new Runnable() {
@Override
public void run() {
//service.read2();
service.write2();
}
});
t1.start();
t2.start();
}
}
class Service {
private final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
public void read1() {
try {
/**
* 共享读锁
*/
lock.readLock().lock();
System.out.println(Thread.currentThread().getName()+" 获得read锁 "+System.currentTimeMillis());
Thread.sleep(2000);
}catch (Exception e){
}finally {
lock.readLock().unlock();
}
}
public void read2() {
try {
lock.readLock().lock();
System.out.println(Thread.currentThread().getName()+" 获得read锁 "+System.currentTimeMillis());
Thread.sleep(2000);
}catch (Exception e){
}finally {
lock.readLock().unlock();
}
}
public void write1() {
try {
lock.writeLock().lock();
System.out.println(Thread.currentThread().getName()+" 获得write锁 "+System.currentTimeMillis());
Thread.sleep(2000);
}catch (Exception e){
}finally {
lock.writeLock().unlock();
}
}
public void write2() {
try {
lock.writeLock().lock();
System.out.println(Thread.currentThread().getName()+" 获得write锁 "+System.currentTimeMillis());
Thread.sleep(2000);
}catch (Exception e){
}finally {
lock.writeLock().unlock();
}
}
}