我对javascript承诺很好。所以我想尝试Java Futures(仍然停留在Java 7中)。但这些Java期货对我来说没有意义。以下是journaldev的修剪和修改版本:
import java.util.concurrent.*;
public class FutureTest {
static class MyCallable implements Callable<String> {
private long waitTime;
MyCallable(int timeInMillis){
this.waitTime=timeInMillis;
}
@Override
public String call() throws Exception {
Thread.sleep(waitTime);
return Thread.currentThread().getName();
}
}
public static void main(String[] args) throws Exception {
MyCallable callable1 = new MyCallable(500);
MyCallable callable2 = new MyCallable(1000);
FutureTask<String> futureTask1 = new FutureTask<String>(callable1);
FutureTask<String> futureTask2 = new FutureTask<String>(callable2);
ExecutorService executor = Executors.newFixedThreadPool(2);
executor.execute(futureTask2);
executor.execute(futureTask1);
while (true) {
try {
boolean done1 = futureTask1.isDone();
boolean done2 = futureTask2.isDone();
if(futureTask1.isDone() && futureTask2.isDone()){
System.out.println("Done");
executor.shutdown();
return;
}
System.out.println("Done1:" + done1 + " - 2:" + done2);
String x = futureTask1.get(100L, TimeUnit.MILLISECONDS);
if (x != null)
System.out.println("FutureTask1 output="+x);
else
System.out.println("Waiting for FutureTask1");
String s = futureTask2.get(200L, TimeUnit.MILLISECONDS);
if(s != null)
System.out.println("FutureTask2 output="+s);
else
System.out.println("Waiting for FutureTask2");
Thread.sleep(100);
} catch(TimeoutException e) {}
}
}
}
它的输出是:
Done1:false - 2:false
Done1:false - 2:false
Done1:false - 2:false
Done1:false - 2:false
Done1:false - 2:false
FutureTask1 output=pool-1-thread-2
Done1:true - 2:false
FutureTask1 output=pool-1-thread-2
Done1:true - 2:false
FutureTask1 output=pool-1-thread-2
FutureTask2 output=pool-1-thread-1
Done
为什么Waiting for FutureTaskX
系统没有执行?我希望主线程循环和系统输出Waiting for ...
,直到期货得到解决。
我对解决此问题的不同方法不感兴趣,仅在此代码的程序流程中。感谢。
答案 0 :(得分:1)
代码永远不会到达“Waiting for FutureTask1”行。
如果futureTask1.get
未在超时时间内返回值,则会引发TimeoutException
。
唯一一次返回而不抛出异常,x
和s
不再为空。
答案 1 :(得分:1)
由于futureTask1.get(100L, TimeUnit.MILLISECONDS)
会抛出TimeoutException
,因此futureTask1
睡眠时间为500
毫秒,futureTask2
会出现同样的问题。
也许您需要Waiting for FutureTask
catch子句中的输出TimeoutException
和sleep
块中的finally
,可能是这样的:
try {
...
} catch (TimeoutException e) {
System.out.println("Waiting for FutureTask");
} finally {
Thread.sleep(100);
}