标签：多线程 lock reentrantreadwritelo 读写锁
本文可作为传智播客《张孝祥-Java多线程与并发库高级应用》的学习笔记。public class LockTest {
public static void main(String[] args){
final Outputer outputer = new Outputer();
new Thread(new Runnable(){
@Override
public void run() {
while(true){
try {
Thread.sleep(10);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
outputer.output("aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa");
}
}
}).start();
new Thread(new Runnable(){
@Override
public void run() {
while(true){
try {
Thread.sleep(10);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
outputer.output("bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb");
}//a的数量与b的数量一致
}
}).start();
}
static class Outputer{
public void output(String name){
int len = name.length();
try{
for(int i=0;i<len;i++){
System.out.print(name.charAt(i));
}
System.out.println();
}finally{
}
}
}
} static class Outputer{
public synchronized void output(String name){
int len = name.length();
//.....
}
}这样一来,我们就保证了Outputer类里的output方法是原子性的,不会有两个线程同时执行它。 static class Outputer{
Lock lock = new ReentrantLock();
public void output(String name){
int len = name.length();
lock.lock(); //标识1
try{
for(int i=0;i<len;i++){
System.out.print(name.charAt(i));
}
System.out.println();
}finally{
lock.unlock(); //标识2
}
}线程a执行到上面代码的标识1处加锁,当线程a在输出字符a时,线程b也执行到了标识1处。此时线程b是不能获得锁的。它被阻塞到标识1处,直到线程a打印完之后在标识2处释放了锁。(线程a线程b共用一把锁,也就是Lock lock = new ReentrantLock())上面的问题中output的主体(len是方法内部的局部变量,为每个线程自有,互不干涉)被全部互斥,它保证了任何时候,都只有一个线程执行标识1与标识2直接的代码。
但是我们得意识到:对共有数据的操作,基本可以分为两类,读与写。public class ReadWriteLockTest {
public static void main(String[] args) {
final Queue3 q3 = new Queue3();
for(int i=0;i<3;i++)
{
new Thread(){
public void run(){
while(true){
q3.get();
}
}
}.start();
new Thread(){
public void run(){
while(true){
q3.put(new Random().nextInt(10000));
}
}
}.start();
}
}
}
class Queue3{
private Object data = null;//共享数据，只能有一个线程能写该数据，但可以有多个线程同时读该数据。
public void get(){
try {
System.out.println(Thread.currentThread().getName() + " be ready to read data!");
Thread.sleep((long)(Math.random()*1000));
System.out.println(Thread.currentThread().getName() + "have read data :" + data);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
public void put(Object data){
try {
System.out.println(Thread.currentThread().getName() + " be ready to write data!");
Thread.sleep((long)(Math.random()*1000));
this.data = data;
System.out.println(Thread.currentThread().getName() + " have write data: " + data);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}结果如下public class ReentrantReadWriteLock extends Object implements ReadWriteLock, Serializable看看使用方法
class Queue3{
private Object data = null;//共享数据，只能有一个线程能写该数据，但可以有多个线程同时读该数据。
ReadWriteLock rwl = new ReentrantReadWriteLock();
public void get(){
rwl.readLock().lock();
try {
System.out.println(Thread.currentThread().getName() + " be ready to read data!");
Thread.sleep(20);
System.out.println(Thread.currentThread().getName() + " have read data :" + data);
} catch (InterruptedException e) {
e.printStackTrace();
}finally{
rwl.readLock().unlock();
}
}
public void put(Object data){
rwl.writeLock().lock();
try {
System.out.println(Thread.currentThread().getName() + " be ready to write data!");
Thread.sleep(20);
this.data = data;
System.out.println(Thread.currentThread().getName() + " have write data: " + data);
} catch (InterruptedException e) {
e.printStackTrace();
}finally{
rwl.writeLock().unlock();
}
}
}结果如下而线程2 4 0的读是可以同步进行的。
这是读写锁最简单的例子,下一节,我们看一个稍微复杂的,把读锁与写锁放到一个方法内的例子。
感谢glt
标签：多线程 lock reentrantreadwritelo 读写锁
原文地址：http://blog.csdn.net/dlf123321/article/details/42919085
