Java线程同步类容器和并发容器（四）
同步类容器都是线程安全的，在某些场景下，需要枷锁保护符合操作，最经典ConcurrentModifiicationException，原因是当容器迭代的过程中，被并发的修改了内容。
for (Iterator iterator = tickets.iterator(); iterator.hasNext();) {
String string = (String) iterator.next();
tickets.remove(20);
}
//多线程使用Vector或者HashTable的示例（简单线程同步问题）
public class Tickets {
public static void main(String[] args) {
//初始化火车票池并添加火车票:避免线程同步可采用Vector替代ArrayList HashTable替代HashMap
final Vector<String> tickets = new Vector<String>();
Map<String, String> map = Collections.synchronizedMap(new HashMap<String, String>());
for(int i = 1; i<= 1000; i++){
tickets.add("火车票"+i);
}
// for (Iterator iterator = tickets.iterator(); iterator.hasNext();) {
// String string = (String) iterator.next();
// tickets.remove(20);
// }
for(int i = 1; i <=10; i ++){
new Thread("线程"+i){
public void run(){
while(true){
if(tickets.isEmpty()) break;
System.out.println(Thread.currentThread().getName() + "---" + tickets.remove(0));
}
}
}.start();
}
}
}
同步类容器：如古老的Vector、HashTable。都是通过Collections.synchronized等工厂方法去创建实现的，底层用传统的synchronized关键字对每个共用的方法进行同步，使得每次只能有一个线程访问容器的状态。
并发类容器是专门针对并发设计的。ConCurrentHashMap替代HashTable。使用CopyOnWriteArrayList代替Voctor，CopyonWriteArraySet，并发的Queue，ConcurrentLinkedQueue高性能队列，LinkedBlockingQueue阻塞形式的队列
ConCurrentHashMap接口有两个实现
ConcurentHashMap
ConcurentSkipListMap(支持排序功能)
ConcurentHashMap内部使用段（Segment）来表示不同的部分，每个段就是一个小的HashTable，有自己的锁，只要多个修改操作，发生在不同的段上，就可以并发进行。
把一个整体分成16个段，最高支持16个线程的并发修改操作，在多线程中减小锁的粒度，从而降低锁竞争的一种方案，共享变量使用了volatile关键字声明，目的是第一时间获取修改的内容。
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
public class UseConcurrentMap {
public static void main(String[] args) {
ConcurrentHashMap<String,Object> chm=new ConcurrentHashMap<String, Object>();
chm.put("k1", "v1");
chm.put("k1", "v7777");//覆盖
chm.put("k2", "v2");
chm.put("k3", "v3");
chm.putIfAbsent("k4", "vvvv"); //存在 就不放入了
chm.putIfAbsent("k4", "555");
System.out.println(chm.get("k2"));
System.out.println(chm.size());
for (Map.Entry<String,Object> me:chm.entrySet()){
System.out.println("key:" + me.getKey() + ",value:" + me.getValue());
}
}
}
import java.util.concurrent.TimeUnit;
public class TimeUinitTest {
private TimeUnit timeUnit = TimeUnit.DAYS;
public static void main(String[] TimeUinitTest) {
TimeUinitTest tut = new TimeUinitTest();
tut.outInfo();
}
public void outInfo() {
System.out.println(timeUnit.name());
System.out.println(timeUnit.toDays(1));
System.out.println(timeUnit.toHours(1));
System.out.println(timeUnit.toMinutes(1));
System.out.println(timeUnit.toSeconds(1));
System.out.println(timeUnit.toMillis(1));
System.out.println(timeUnit.toMicros(1));
System.out.println(timeUnit.toNanos(1));
System.out.println((timeUnit.convert(1, TimeUnit.DAYS)) + timeUnit.name());
System.out.println((timeUnit.convert(24, TimeUnit.HOURS)) + timeUnit.name());
System.out.println((timeUnit.convert(1440, TimeUnit.MINUTES)) + timeUnit.name());
System.out.println("-------------------");
}
}
public class Task implements Comparable<Task>{
private int id ;
private String name;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public int compareTo(Task task){
return this.id>task.id?1:(this.id<task.id?-1:0);
}
public String toString(){
return this.id + "," + this.name;
}
}
Copy-On-Write容器：程序设计中的优化策略
两种：CopyOneWriteArrayList和CopyOnWriteArraySet
Copy-On-Write容器为写时复制的容器，当往一个容器添加元素的时候，不直接往当前容器添加，而是将当前容器就行Copy，复制出一个新的容器，然后新的容器中添加元素，添加完元素之后，在将原容器的引用指向新容器。
可以对CopyOneWrite容器进行并发的读，不需要枷锁，当前容器不会添加任何元素，所以CopyOnWrite也是一种读写分离的思想，读和写在不同的容器中
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.CopyOnWriteArraySet;
public class UseCopyOnWrite {
public static void main(String[] args) {
CopyOnWriteArrayList<String> cwal=new CopyOnWriteArrayList<String>();
CopyOnWriteArraySet<String> cwas = new CopyOnWriteArraySet<String>();
}
}
并发Queue:
import java.util.ArrayList; import java.util.List; import java.util.concurrent.ArrayBlockingQueue; import java.util.concurrent.ConcurrentLinkedQueue; import java.util.concurrent.LinkedBlockingQueue; import java.util.concurrent.SynchronousQueue;
public class UseQueue {
public static void main(String[] args) throws Exception {
//高性能无阻塞无界队列：ConcurrentLinkedQueue offer和add是没有区别的
ConcurrentLinkedQueue<String> q = new ConcurrentLinkedQueue<String>();
q.offer("a");
q.offer("b");
q.offer("c");
q.offer("d");
q.add("e");
System.out.println(q.poll()); //a 从头部取出元素，并从队列里删除
System.out.println(q.size()); //4
System.out.println(q.peek()); //b
System.out.println(q.size()); //4
ArrayBlockingQueue<String> array = new ArrayBlockingQueue<String>(5);
array.put("a");
array.put("b");
array.add("c");
array.add("d");
array.add("e");
array.add("f");
//System.out.println(array.offer("a", 3, TimeUnit.SECONDS));
//阻塞队列
LinkedBlockingQueue<String> q = new LinkedBlockingQueue<String>();
q.offer("a");
q.offer("b");
q.offer("c");
q.offer("d");
q.offer("e");
q.add("f");
//System.out.println(q.size());
// for (Iterator iterator = q.iterator(); iterator.hasNext();) {
// String string = (String) iterator.next();
// System.out.println(string);
// }
List<String> list = new ArrayList<String>();
System.out.println(q.drainTo(list, 3));
System.out.println(list.size());
for (String string : list) {
System.out.println(string);
}
final SynchronousQueue<String> q = new SynchronousQueue<String>();
Thread t1 = new Thread(new Runnable() {
@Override
public void run() {
try {
System.out.println(q.take());
} catch (InterruptedException e) {
e.printStackTrace();
}
}
});
t1.start();
Thread t2 = new Thread(new Runnable() {
@Override
public void run() {
q.add("asdasd");
}
});
t2.start();
}
}
BlockingQueue接口:(下面的全是阻塞的)
import java.util.concurrent.PriorityBlockingQueue;
public class UsePriorityBlockingQueue {
public static void main(String[] args) throws Exception{
PriorityBlockingQueue<Task> q = new PriorityBlockingQueue<Task>();
Task t1 = new Task();
t1.setId(3);
t1.setName("id为3");
Task t2 = new Task();
t2.setId(4);
t2.setName("id为4");
Task t3 = new Task();
t3.setId(1);
t3.setName("id为1");
//return this.id > task.id ? 1 : 0;
q.add(t1); //3
q.add(t2); //4
q.add(t3); //1
// 1 3 4
System.out.println("容器：" + q);
System.out.println(q.take().getId());
System.out.println("容器：" + q);
System.out.println(q.take().getId());
System.out.println(q.take().getId());
}
}
//没有缓存的队列，生产者产生的数据会被消费者直接消费掉
final SynchronousQueue<String> q = new SynchronousQueue<String>();
Thread t1 = new Thread(new Runnable() {
@Override
public void run() {
try {
System.out.println("进入到t1线程中，阻塞等待获取元素");
System.out.println("消费"+q.take());
} catch (InterruptedException e) {
e.printStackTrace();
}
}
});
t1.start();
TimeUnit.SECONDS.sleep(2);
Thread t2 = new Thread(new Runnable() {
@Override
public void run() {
q.add("asdasd");
}
});
t2.start();
}
import java.util.concurrent.DelayQueue;
public class WangBa implements Runnable{
private DelayQueue<Wangmin> queue=new DelayQueue<Wangmin>();
public boolean yinye =true;
public void shangji(String name,String id,int money){
Wangmin man = new Wangmin(name, id, 1000 * money + System.currentTimeMillis());
System.out.println("网名"+man.getName()+" 身份证"+man.getId()+"交钱"+money+"块,开始上机...");
this.queue.add(man);
}
public void xiaji(Wangmin man){
System.out.println("网名"+man.getName()+" 身份证"+man.getId()+"时间到下机...");
}
@Override
public void run() {
while(yinye){
try {
Wangmin man = queue.take();
xiaji(man);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
public static void main(String args[]){
try{
System.out.println("网吧开始营业");
WangBa siyu = new WangBa();
Thread shangwang = new Thread(siyu);
shangwang.start();
siyu.shangji("路人甲", "123", 1);
siyu.shangji("路人乙", "234", 10);
siyu.shangji("路人丙", "345", 5);
}
catch(Exception e){
e.printStackTrace();
}
}
}
import java.util.concurrent.Delayed;
import java.util.concurrent.TimeUnit;
public class Wangmin implements Delayed {
private String name;
//身份证
private String id;
//截止时间
private long endTime;
//定义时间工具类
private TimeUnit timeUnit = TimeUnit.SECONDS;
public Wangmin(String name,String id,long endTime){
this.name=name;
this.id=id;
this.endTime = endTime;
}
public String getName(){
return this.name;
}
public String getId(){
return this.id;
}
/**
* 用来判断是否到了截止时间
*/
@Override
public long getDelay(TimeUnit unit) {
//return unit.convert(endTime, TimeUnit.MILLISECONDS) - unit.convert(System.currentTimeMillis(), TimeUnit.MILLISECONDS);
return endTime - System.currentTimeMillis();
}
/**
* 相互批较排序用
*/
@Override
public int compareTo(Delayed delayed) {
Wangmin w = (Wangmin)delayed;
return this.getDelay(this.timeUnit) - w.getDelay(this.timeUnit) > 0 ? 1:0;
}
}
AQS锁：
Thread A = new Thread(new Runnable() {
@Override
public void run() {
int sum = 0;
for(int i =0; i < 10; i ++){
sum += i;
}
try {
Thread.sleep(4000);
} catch (InterruptedException e) {
e.printStackTrace();
}
LockSupport.park(); //后执行
System.err.println("sum: " + sum);
}
});
A.start();
Thread.sleep(1000);
LockSupport.unpark(A); //先执行
