多线程模式（五）-Future模式2009-04-07 20:41:41
1引论
2 思想
一個簡單的Java程式片段示範可能像是這樣：
....
public Future request() {
final Future future = new Future();
new Thread() {
public void run() {
// 下面這個動作可能是耗時的
RealSubject subject = new RealSubject();
future.setRealSubject(subject);
}
}.start();
return future;
}
public void run() {
// 下面這個動作可能是耗時的
RealSubject subject = new RealSubject();
future.setRealSubject(subject);
}
}.start();
}
可是我要怎么判断我要的数据已经准备好？
通过自定义一个结果类，负责结果持有。
private String result;
private boolean isFinish = false;
public String getResult(){
return result;
}
public synchronized void setResult (String result){
this.result = result;
this.isFinish = true;
}
public synchronized boolean isFinish(){
return isFinish;
}
}
3 Just do it
- 希望能看到这个对象可用，并完成一些相关的后续流程。如果实在不可用，也可以进入其它分支流程。
- “没有你我的人生就会失去意义，所以就算海枯石烂，我也要等到你。”（当然，如果实在没有毅力枯等下去，设一个超时也是可以理解的）
总之，FutureTask封装了对realObject(Callable实例)的异步和同步操作，持有Callable实例，线程执行FutureTask对象。
下面的例子模拟的是一个会计算账的过程，主线程中已经获得其他帐户的总额了，为了不让主线程等待PrivateAccount 返回而启用新的线程去处理，并使用 FutureTask 对象来监控，最后需要计算总额的时候再尝试去获得PrivateAccount 的信息。
-
SumAccountExample.java
package com.gc.pattern;
import java.util.Random;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.FutureTask;
public class SumAccountExample {
public static void main(String[] args) {
// Init callable object and future task
Callable pAccount = new PrivateAccount();
FutureTask futureTask = new FutureTask(pAccount);
// Create a new thread to do so
Thread pAccountThread = new Thread(futureTask);
pAccountThread.start();
// Do something else in the main thread
System.out.println("Doing something else here.");
// Get the total money from other accounts
int totalMoney = new Random().nextInt(100000);
System.out.println("You have "+totalMoney+" in your other Accounts.");
System.out.println("Waiting for data from Private Account");
// If the Future task is not finished, we will wait for it
while (!futureTask.isDone()){
try{
Thread.sleep(5);
}
catch(InterruptedException e){
e.printStackTrace();
}
}
Integer privataAccountMoney = null ;
// Since the future task is done, get the object back
try{
privataAccountMoney = (Integer)futureTask.get();
}
catch(InterruptedException e){
e.printStackTrace();
}
catch(ExecutionException e){
e.printStackTrace();
}
System.out.println("The total moeny you have is "+(totalMoney+privataAccountMoney.intValue()));
}
}
-
PrivateAccount.java
package com.gc.pattern;
import java.util.Random;
import java.util.concurrent.Callable;
class PrivateAccount implements Callable{
Integer totalMoney;
public Integer call() throws Exception {
// Simulates a time conusimg task, sleep for 10s
//与Callable 不同，它有返回值
Thread.sleep( 10000 );
totalMoney = new Integer(new Random().nextInt(10000));
System.out.println("You have "+totalMoney+" in your private Account. " );
return totalMoney;
}
}
2009-04-07 19:19:04
1.示例
-
Host.java
package com.gc.pattern;
public final class Host {
private final Helper m_helper = new Helper();
public Host(){
}
public void request(final int count,
final char c) {
System.out.println(" request(" + count + " , " + c + ") Begin ");
Thread t_tempThread = new Thread(){
public void run(){
m_helper.handle(count, c);
}
};
t_tempThread.start();
System.out.println(" request(" + count + " , " + c + ") End ");
}
}
-
Helper.java
package com.gc.pattern;
public final class Helper{
public Helper(){
}
public void handle(int count,char c){
System.out.println(" handle(" + count + " , " + c + " ) Begin ");
for (int i = 0 ; i < count ; i++ ){
slowly(1000);
System.out.print(c);
}
System.out.println("");
System.out.println(" handle(" + count + " , " + c + " ) End ");
}
private void slowly(long sleepTime){
try {
Thread.sleep(sleepTime);
} catch (InterruptedException e){
// TODO: handle exception
}
}
}
-
ThreadPerMessaageTest.java
package com.gc.pattern;
public final class ThreadPerMessageTest{
public ThreadPerMessageTest(){
}
public static void main(String[] args){
System.out.println("main Begin");
Host t_host = new Host();
t_host.request(10,'c');
t_host.request(12,'b');
t_host.request(8, 'a');
System.out.println("main End");
}
}
2.观念
简单的说，Thread Per Message 模式是在某个请求发生时，新增一个线程来处理该请求，主线程继续往下执行。像文档载入，搜寻，字串转换之类需要一些时间来执行时，使用该模式可以提高主线程（界面）的响应。例如：
menuOpenFile.addActionListener(
new ActionListener() {
public void actionPerformed(ActionEvent e) {
new Thread(new Runnable(){
public void run() {
openFile();
}
}).start();
}
}
);
2009-04-07 19:37:20
1 示例
- ClientTjread.java
package com.gc.language;
public class ClientThread extends Thread{
private Channel channel;
public ClientThread(Channel channel) {
this.channel = channel;
}
public void run (){
for(int i =0;i<15;i++)
{
try{
Thread.sleep(50);
}
catch(InterruptedException e){
}
channel.putRequest(new Request());
}
}
}
- Request.java
package com.gc.language;
import java.util.Date;
public class Request {
// ....
public void execute() {
// do some work....
System.out .println(new Date());
}
}
- WorkerThread.java
package com.gc.language;
public class WorkerThread extends Thread {
private Channel channel;
public WorkerThread(Channel channel) {
this.channel = channel;
}
// ...
public void run() {
while(true) {
try{
Thread.sleep(5000);
}
catch(InterruptedException e){
}
Request request = channel.getRequest();
request.execute();
}
}
}
- Channel.java
package com.gc.language;
import java.util.LinkedList;
public class Channel {
private LinkedList requests;
private WorkerThread[] workerThreads;
public Channel(int threadNumber) {
requests = new LinkedList();
ClientThread cthread = new ClientThread (this);
cthread.start();
workerThreads = new WorkerThread[threadNumber];
for(int i = 0; i < workerThreads.length; i++) {
workerThreads[i] = new WorkerThread(this);
workerThreads[i].start();
}
}
public synchronized void putRequest(Request request) {
while(requests.size() >= 2) { // 容量限制為 2
try {
wait();
}
catch(InterruptedException e) {}
}
requests.addLast(request);
notifyAll();
}
public synchronized Request getRequest() {
while(requests.size() <= 0) {
try {
wait();
}
catch(InterruptedException e) {}
}
Request request = (Request) requests.removeFirst();
notifyAll();
return request;
}
}
- Test.java
package com.gc.language;
public class Test {
public static void main(String[] args){
Channel channel = new Channel(10);
}
}