[英]Handling Exceptions for ThreadPoolExecutor
我有以下代码片段,它基本上扫描需要执行的任务列表,然后将每个任务提供给执行程序执行。
JobExecutor
依次创建另一个执行程序(用于执行数据库内容...读取和写入数据到队列)并完成任务。
JobExecutor
为提交的任务返回Future<Boolean>
。 当其中一个任务失败时,我想优雅地中断所有线程并通过捕获所有异常来关闭执行程序。 我需要做哪些改变?
public class DataMovingClass {
private static final AtomicInteger uniqueId = new AtomicInteger(0);
private static final ThreadLocal<Integer> uniqueNumber = new IDGenerator();
ThreadPoolExecutor threadPoolExecutor = null ;
private List<Source> sources = new ArrayList<Source>();
private static class IDGenerator extends ThreadLocal<Integer> {
@Override
public Integer get() {
return uniqueId.incrementAndGet();
}
}
public void init(){
// load sources list
}
public boolean execute() {
boolean succcess = true ;
threadPoolExecutor = new ThreadPoolExecutor(10,10,
10, TimeUnit.SECONDS, new ArrayBlockingQueue<Runnable>(1024),
new ThreadFactory() {
public Thread newThread(Runnable r) {
Thread t = new Thread(r);
t.setName("DataMigration-" + uniqueNumber.get());
return t;
}// End method
}, new ThreadPoolExecutor.CallerRunsPolicy());
List<Future<Boolean>> result = new ArrayList<Future<Boolean>>();
for (Source source : sources) {
result.add(threadPoolExecutor.submit(new JobExecutor(source)));
}
for (Future<Boolean> jobDone : result) {
try {
if (!jobDone.get(100000, TimeUnit.SECONDS) && success) {
// in case of successful DbWriterClass, we don't need to change
// it.
success = false;
}
} catch (Exception ex) {
// handle exceptions
}
}
}
public class JobExecutor implements Callable<Boolean> {
private ThreadPoolExecutor threadPoolExecutor ;
Source jobSource ;
public SourceJobExecutor(Source source) {
this.jobSource = source;
threadPoolExecutor = new ThreadPoolExecutor(10,10,10, TimeUnit.SECONDS, new ArrayBlockingQueue<Runnable>(1024),
new ThreadFactory() {
public Thread newThread(Runnable r) {
Thread t = new Thread(r);
t.setName("Job Executor-" + uniqueNumber.get());
return t;
}// End method
}, new ThreadPoolExecutor.CallerRunsPolicy());
}
public Boolean call() throws Exception {
boolean status = true ;
System.out.println("Starting Job = " + jobSource.getName());
try {
// do the specified task ;
}catch (InterruptedException intrEx) {
logger.warn("InterruptedException", intrEx);
status = false ;
} catch(Exception e) {
logger.fatal("Exception occurred while executing task "+jobSource.getName(),e);
status = false ;
}
System.out.println("Ending Job = " + jobSource.getName());
return status ;
}
}
}
当您向执行程序提交任务时,它会返回一个FutureTask
实例。
FutureTask.get()
将重新抛出任务抛出的任何异常作为ExecutorException
。
因此,当您遍历List<Future>
并在每个上调用get时,捕获ExecutorException
并调用有序关闭。
由于您要向ThreadPoolExecutor
提交任务,因此FutureTask
会吞下异常。
看看这段代码
**Inside FutureTask$Sync**
void innerRun() {
if (!compareAndSetState(READY, RUNNING))
return;
runner = Thread.currentThread();
if (getState() == RUNNING) { // recheck after setting thread
V result;
try {
result = callable.call();
} catch (Throwable ex) {
setException(ex);
return;
}
set(result);
} else {
releaseShared(0); // cancel
}
}
protected void setException(Throwable t) {
sync.innerSetException(t);
}
从上面的代码中可以看出, setException
方法捕获了Throwable
。 由于这个原因,如果在ThreadPoolExecutor
上使用“ submit()
”方法,则FutureTask
会吞下所有异常
根据java 文档 ,您可以在ThreadPoolExecutor
扩展afterExecute()
方法
protected void afterExecute(Runnable r,
Throwable t)
根据文档的示例代码:
class ExtendedExecutor extends ThreadPoolExecutor {
// ...
protected void afterExecute(Runnable r, Throwable t) {
super.afterExecute(r, t);
if (t == null && r instanceof Future<?>) {
try {
Object result = ((Future<?>) r).get();
} catch (CancellationException ce) {
t = ce;
} catch (ExecutionException ee) {
t = ee.getCause();
} catch (InterruptedException ie) {
Thread.currentThread().interrupt(); // ignore/reset
}
}
if (t != null)
System.out.println(t);
}
}
您可以通过三种方式捕获Exceptions
Future.get()
如接受的答案中所建议的那样 try{}catch{}Exceptoion{}
块中包装整个run()
或call()
方法 ThreadPoolExecutor
方法的afterExecute
要优雅地中断其他线程,请看下面的SE问题:
子类ThreadPoolExecutor
并覆盖其protected afterExecute (Runnable r, Throwable t)
方法。
如果你是通过java.util.concurrent.Executors
方便类(你不是)创建一个线程池,那么看一下它的来源,看看它是如何调用ThreadPoolExecutor的 。
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