從jdk1.5開始我們可以利用Future來跟蹤異步計算的結果。在此之前主線程要想獲得工作線程(異步計算線程)的結果是比較麻煩的事情,需要我們進行特殊的程序結構設計,比較繁瑣而且容易出錯。有了Future我們就可以設計出比較優雅的異步計算程序結構模型:根據分而治之的思想,我們可以把異步計算的線程按照職責分爲3類:
1. 異步計算的發起線程(控制線程):負責異步計算任務的分解和發起,把分解好的任務交給異步計算的work線程去執行,發起異步計算後,發起線程可以獲得Futrue的集合,從而可以跟蹤異步計算結果
2. 異步計算work線程:負責具體的計算任務
3. 異步計算結果收集線程:從發起線程那裏獲得Future的集合,並負責監控Future的狀態,根據Future的狀態來處理異步計算的結果。
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
public class AsyncController {
//線程池
private ExecutorService executorService;
//保存異步計算的Future
private FutureContext<String> context;
public AsyncController() {
this.executorService = Executors.newFixedThreadPool(100);
this.context = new FutureContext<String>();
}
public static void main(String[] args) {
//啓動異步計算
AsyncController controller = new AsyncController();
controller.startAsyncCompution();
//啓動異步計算結果輸出線程,該線程掃描異步計算Futrue的狀態,如果已經完成,則輸出異步計算結果
OutputResult output = new OutputResult();
output.setFutureContext(controller.getFutureContext());
Thread resultThread = new Thread(output);
resultThread.start();
}
public FutureContext<String> getFutureContext() {
return this.context;
}
public void startAsyncCompution() {
/**
* 開啓100個異步計算,每個異步計算線程隨機sleep幾秒來模擬計算耗時。
*/
final Random random = new Random();
for (int i = 0; i < 100; i++) {
Future<String> future = this.executorService
.submit(new Callable<String>() {
@Override
public String call() throws Exception {
int randomInt = random.nextInt(10);
Thread.sleep(randomInt * 1000);
return "" + randomInt;
}
});
//每個異步計算的結果存放在context中
this.context.addFuture(future);
}
}
public static class FutureContext<T> {
private List<Future<T>> futureList = new ArrayList<Future<T>>();
public void addFuture(Future<T> future) {
this.futureList.add(future);
}
public List<Future<T>> getFutureList() {
return this.futureList;
}
}
public static class OutputResult implements Runnable {
private FutureContext<String> context;
public void setFutureContext(FutureContext<String> context) {
this.context = context;
}
@Override
public void run() {
System.out.println("start to output result:");
List<Future<String>> list = this.context.getFutureList();
for (Future<String> future : list) {
this.outputResultFromFuture(future);
}
System.out.println("finish to output result.");
}
private void outputResultFromFuture(Future<String> future) {
try {
while (true) {
if (future.isDone() && !future.isCancelled()) {
System.out.println("Future:" + future + ",Result:"
+ future.get());
break;
} else {
Thread.sleep(1000);
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
}