使用ExecutorService时CancellationException [英] CancellationException when using ExecutorService
本文介绍了使用ExecutorService时CancellationException的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
我想等待两个任务完成然后返回它们的结果但有时我得到这个错误。为什么? CancellationException来自哪里?
I want to wait two tasks to finish then return the result of them but sometimes I get this error. Why? Where did CancellationException come from?
public class ShouldVoteTask extends AbstractWorkerTask<Void, Void, Boolean> {
private final int placeID;
private final int userID;
public ShouldVoteTask(final int placeID, final int userID) {
this.placeID = placeID;
this.userID = userID;
}
@Override
protected Boolean doInBackground(final Void... params) {
try {
// Prepare callables.
final IsMaxRatingCallable call1 = new IsMaxRatingCallable(placeID);
final DidVoteCallable call2 = new DidVoteCallable(placeID, userID);
final List<Callable<Boolean>> callables = new ArrayList<Callable<Boolean>>();
callables.add(call1);
callables.add(call2);
// Execute them.
final ExecutorService service = Executors.newFixedThreadPool(2);
final List<Future<Boolean>> futures = service.invokeAll(callables, 5, TimeUnit.SECONDS);
// Check the result.
boolean result = true;
for(final Future<Boolean> future : futures) {
if(future.get()) {
result = false;
}
}
return result;
} catch (final InterruptedException e) {
e.printStackTrace();
} catch (final ExecutionException e) {
e.printStackTrace();
}
return false;
}
}
private class IsMaxRatingCallable implements Callable<Boolean> {
private final int placeID;
public IsMaxRatingCallable(final int placeID) {
this.placeID = placeID;
}
@Override
public Boolean call() throws Exception {
return Places.isMaxRating(placeID);
}
}
private class DidVoteCallable implements Callable<Boolean> {
private final int placeID;
private final int userID;
public DidVoteCallable(final int placeID, final int userID) {
this.placeID = placeID;
this.userID = userID;
}
@Override
public Boolean call() throws Exception {
return Votes.didVote(placeID, userID);
}
}
错误
E/AndroidRuntime(19014): FATAL EXCEPTION: AsyncTask #1
E/AndroidRuntime(19014): java.lang.RuntimeException: An error occured while executing doInBackground()
E/AndroidRuntime(19014): at android.os.AsyncTask$3.done(AsyncTask.java:200)
E/AndroidRuntime(19014): at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:274)
E/AndroidRuntime(19014): at java.util.concurrent.FutureTask.setException(FutureTask.java:125)
E/AndroidRuntime(19014): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:308)
E/AndroidRuntime(19014): at java.util.concurrent.FutureTask.run(FutureTask.java:138)
E/AndroidRuntime(19014): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1088)
E/AndroidRuntime(19014): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:581)
E/AndroidRuntime(19014): at java.lang.Thread.run(Thread.java:1027)
E/AndroidRuntime(19014): Caused by: java.util.concurrent.CancellationException
E/AndroidRuntime(19014): at java.util.concurrent.FutureTask$Sync.innerGet(FutureTask.java:222)
E/AndroidRuntime(19014): at java.util.concurrent.FutureTask.get(FutureTask.java:83)
E/AndroidRuntime(19014): at com.vfa.android.planet.task.ShouldVoteTask.doInBackground(ShouldVoteTask.java:43)
E/AndroidRuntime(19014): at com.vfa.android.planet.task.ShouldVoteTask.doInBackground(ShouldVoteTask.java:1)
E/AndroidRuntime(19014): at android.os.AsyncTask$2.call(AsyncTask.java:185)
E/AndroidRuntime(19014): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:306)
E/AndroidRuntime(19014): ... 4 more
推荐答案
您要求执行程序服务执行您的callables,超时为5秒。根据 javadoc :
You ask your executor service to execute your callables with a timeout of 5 seconds. According to the javadoc:
$ b未完成[超时结束时]的$ b任务被取消
tasks that have not completed [by the end of the timeout] are cancelled
我的猜测是 future.get()
抛出 CancellationException
,因为已达到超时并且执行程序调用 future.cancel ()
。
My guess is that future.get()
throws a CancellationException
because the timeout has been reached and the executor calls future.cancel()
.
您可以:
- 增加超时
- 在你的callable中捕获
InterruptedException
以优雅地处理取消
- increase the timeout
- catch an
InterruptedException
in your callable to handle the cancellation gracefully
这篇关于使用ExecutorService时CancellationException的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!
查看全文