我正在尝试使用Java的ThreadPoolExecutor类来运行具有固定线程数的大量重量级任务。每个任务都有很多地方，在这些地方可能因例外而失败。
我已经将ThreadPoolExecutor子类化了，并且我已经覆盖了afterExecute方法，该方法应该提供运行任务时遇到的任何未捕获的异常。但是，我似乎无法使其发挥作用。
例如：
public class ThreadPoolErrors extends ThreadPoolExecutor {
public ThreadPoolErrors() {
super( 1, // core threads
1, // max threads
1, // timeout
TimeUnit.MINUTES, // timeout units
new LinkedBlockingQueue<Runnable>() // work queue
);
}
protected void afterExecute(Runnable r, Throwable t) {
super.afterExecute(r, t);
if(t != null) {
System.out.println("Got an error: " + t);
} else {
System.out.println("Everything's fine--situation normal!");
}
}
public static void main( String [] args) {
ThreadPoolErrors threadPool = new ThreadPoolErrors();
threadPool.submit(
new Runnable() {
public void run() {
throw new RuntimeException("Ouch! Got an error.");
}
}
);
threadPool.shutdown();
}
}
这个程序的输出是“一切都很好 - 情况正常！”即使提交给线程池的唯一Runnable也会引发异常。这里有什么线索？
谢谢！
答案 0 :(得分：231)
警告：应该注意此解决方案将阻止调用线程。
如果您要处理任务抛出的异常，那么通常最好使用Callable而不是Runnable。
Callable.call()抛出已检查的异常，并将这些异常传播回调用线程：
Callable task = ...
Future future = executor.submit(task);
try {
future.get();
} catch (ExecutionException ex) {
ex.getCause().printStackTrace();
}
如果Callable.call()引发异常，则会将其包含在ExecutionException中并由Future.get()引发。
这可能比继承ThreadPoolExecutor要好得多。如果异常是可恢复的，它还为您提供重新提交任务的机会。
答案 1 :(得分：141)
来自docs：
注意：当包含操作时 任务（例如FutureTask） 明确地或通过诸如的方法 提交，这些任务对象捕获和 保持计算异常，和 所以他们不会引起突然 终止，内部 异常不会传递给此 方法
当你提交一个Runnable时，它将包含在Future中。
你的afterExecute应该是这样的：
public final class ExtendedExecutor extends ThreadPoolExecutor {
// ...
protected void afterExecute(Runnable r, Throwable t) {
super.afterExecute(r, t);
if (t == null && r instanceof Future<?>) {
try {
Future<?> future = (Future<?>) r;
if (future.isDone()) {
future.get();
}
} catch (CancellationException ce) {
t = ce;
} catch (ExecutionException ee) {
t = ee.getCause();
} catch (InterruptedException ie) {
Thread.currentThread().interrupt();
}
}
if (t != null) {
System.out.println(t);
}
}
}
答案 2 :(得分：16)
此行为的解释正好在javadoc for afterExecute：
中注意：当包含操作时 任务（例如FutureTask） 明确地或通过诸如的方法 提交，这些任务对象捕获和 保持计算异常，和 所以他们不会引起突然 终止，内部 异常不会传递给此 方法
答案 3 :(得分：9)
我通过将提交的runnable包装提交给执行者来解决它。
CompletableFuture.runAsync(
() -> {
try {
runnable.run();
} catch (Throwable e) {
Log.info(Concurrency.class, "runAsync", e);
}
},
executorService
);
答案 4 :(得分：6)
我正在使用VerboseRunnable中的jcabi-log类，它会吞下所有异常并记录它们。非常方便，例如：
import com.jcabi.log.VerboseRunnable;
scheduler.scheduleWithFixedDelay(
new VerboseRunnable(
Runnable() {
public void run() {
// the code, which may throw
}
},
true // it means that all exceptions will be swallowed and logged
),
1, 1, TimeUnit.MILLISECONDS
);
答案 5 :(得分：3)
另一种解决方案是使用 ManagedTask 和 ManagedTaskListener 。
您需要一个 Callable 或 Runnable ，它实现了 ManagedTask 接口。
方法getManagedTaskListener返回您想要的实例。
public ManagedTaskListener getManagedTaskListener() {
您在 ManagedTaskListener 中实现了taskDone方法：
@Override
public void taskDone(Future<?> future, ManagedExecutorService executor, Object task, Throwable exception) {
if (exception != null) {
LOGGER.log(Level.SEVERE, exception.getMessage());
}
}
答案 6 :(得分：1)
如果要监视任务的执行，可以旋转1或2个线程（可能更多，具体取决于负载）并使用它们从ExecutionCompletionService包装器中获取任务。
答案 7 :(得分：0)
如果您的ExecutorService来自外部来源（即无法继承ThreadPoolExecutor并覆盖afterExecute()），则可以使用动态代理来实现所需的行为：
public static ExecutorService errorAware(final ExecutorService executor) {
return (ExecutorService) Proxy.newProxyInstance(Thread.currentThread().getContextClassLoader(),
new Class[] {ExecutorService.class},
(proxy, method, args) -> {
if (method.getName().equals("submit")) {
final Object arg0 = args[0];
if (arg0 instanceof Runnable) {
args[0] = new Runnable() {
@Override
public void run() {
final Runnable task = (Runnable) arg0;
try {
task.run();
if (task instanceof Future<?>) {
final Future<?> future = (Future<?>) task;
if (future.isDone()) {
try {
future.get();
} catch (final CancellationException ce) {
// Your error-handling code here
ce.printStackTrace();
} catch (final ExecutionException ee) {
// Your error-handling code here
ee.getCause().printStackTrace();
} catch (final InterruptedException ie) {
Thread.currentThread().interrupt();
}
}
}
} catch (final RuntimeException re) {
// Your error-handling code here
re.printStackTrace();
throw re;
} catch (final Error e) {
// Your error-handling code here
e.printStackTrace();
throw e;
}
}
};
} else if (arg0 instanceof Callable<?>) {
args[0] = new Callable<Object>() {
@Override
public Object call() throws Exception {
final Callable<?> task = (Callable<?>) arg0;
try {
return task.call();
} catch (final Exception e) {
// Your error-handling code here
e.printStackTrace();
throw e;
} catch (final Error e) {
// Your error-handling code here
e.printStackTrace();
throw e;
}
}
};
}
}
return method.invoke(executor, args);
});
}
答案 8 :(得分：0)
这是因为AbstractExecutorService :: submit将runnable包裹到RunnableFuture（除了FutureTask之外），如下所示
AbstractExecutorService.java
public Future<?> submit(Runnable task) {
if (task == null) throw new NullPointerException();
RunnableFuture<Void> ftask = newTaskFor(task, null); /////////HERE////////
execute(ftask);
return ftask;
}
然后execute会将其传递给Worker，Worker.run()会调用以下内容。
ThreadPoolExecutor.java
final void runWorker(Worker w) {
Thread wt = Thread.currentThread();
Runnable task = w.firstTask;
w.firstTask = null;
w.unlock(); // allow interrupts
boolean completedAbruptly = true;
try {
while (task != null || (task = getTask()) != null) {
w.lock();
// If pool is stopping, ensure thread is interrupted;
// if not, ensure thread is not interrupted. This
// requires a recheck in second case to deal with
// shutdownNow race while clearing interrupt
if ((runStateAtLeast(ctl.get(), STOP) ||
(Thread.interrupted() &&
runStateAtLeast(ctl.get(), STOP))) &&
!wt.isInterrupted())
wt.interrupt();
try {
beforeExecute(wt, task);
Throwable thrown = null;
try {
task.run(); /////////HERE////////
} catch (RuntimeException x) {
thrown = x; throw x;
} catch (Error x) {
thrown = x; throw x;
} catch (Throwable x) {
thrown = x; throw new Error(x);
} finally {
afterExecute(task, thrown);
}
} finally {
task = null;
w.completedTasks++;
w.unlock();
}
}
completedAbruptly = false;
} finally {
processWorkerExit(w, completedAbruptly);
}
}
最后
task.run();在上面的代码调用中会调用FutureTask.run()。这是异常处理程序代码，因为 这是你没有得到预期的例外。
class FutureTask<V> implements RunnableFuture<V>
public void run() {
if (state != NEW ||
!UNSAFE.compareAndSwapObject(this, runnerOffset,
null, Thread.currentThread()))
return;
try {
Callable<V> c = callable;
if (c != null && state == NEW) {
V result;
boolean ran;
try {
result = c.call();
ran = true;
} catch (Throwable ex) { /////////HERE////////
result = null;
ran = false;
setException(ex);
}
if (ran)
set(result);
}
} finally {
// runner must be non-null until state is settled to
// prevent concurrent calls to run()
runner = null;
// state must be re-read after nulling runner to prevent
// leaked interrupts
int s = state;
if (s >= INTERRUPTING)
handlePossibleCancellationInterrupt(s);
}
}
答案 9 :(得分：0)
这有效
它将创建一个具有单个线程的Executor，可以完成很多任务;并将等待当前的一个结束执行以开始下一个
如果出现unaugth错误或异常， uncaughtExceptionHandler 将会抓住它
public final class SingleThreadExecutorWithExceptions {
public static ExecutorService newSingleThreadExecutorWithExceptions(final Thread.UncaughtExceptionHandler uncaughtExceptionHandler) {
ThreadFactory factory = (Runnable runnable) -> {
final Thread newThread = new Thread(runnable, "SingleThreadExecutorWithExceptions");
newThread.setUncaughtExceptionHandler( (final Thread caugthThread,final Throwable throwable) -> {
uncaughtExceptionHandler.uncaughtException(caugthThread, throwable);
});
return newThread;
};
return new FinalizableDelegatedExecutorService
(new ThreadPoolExecutor(1, 1,
0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue(),
factory){
protected void afterExecute(Runnable runnable, Throwable throwable) {
super.afterExecute(runnable, throwable);
if (throwable == null && runnable instanceof Future) {
try {
Future future = (Future) runnable;
if (future.isDone()) {
future.get();
}
} catch (CancellationException ce) {
throwable = ce;
} catch (ExecutionException ee) {
throwable = ee.getCause();
} catch (InterruptedException ie) {
Thread.currentThread().interrupt(); // ignore/reset
}
}
if (throwable != null) {
uncaughtExceptionHandler.uncaughtException(Thread.currentThread(),throwable);
}
}
});
}
private static class FinalizableDelegatedExecutorService
extends DelegatedExecutorService {
FinalizableDelegatedExecutorService(ExecutorService executor) {
super(executor);
}
protected void finalize() {
super.shutdown();
}
}
/**
* A wrapper class that exposes only the ExecutorService methods
* of an ExecutorService implementation.
*/
private static class DelegatedExecutorService extends AbstractExecutorService {
private final ExecutorService e;
DelegatedExecutorService(ExecutorService executor) { e = executor; }
public void execute(Runnable command) { e.execute(command); }
public void shutdown() { e.shutdown(); }
public List shutdownNow() { return e.shutdownNow(); }
public boolean isShutdown() { return e.isShutdown(); }
public boolean isTerminated() { return e.isTerminated(); }
public boolean awaitTermination(long timeout, TimeUnit unit)
throws InterruptedException {
return e.awaitTermination(timeout, unit);
}
public Future submit(Runnable task) {
return e.submit(task);
}
public Future submit(Callable task) {
return e.submit(task);
}
public Future submit(Runnable task, T result) {
return e.submit(task, result);
}
public List> invokeAll(Collection> tasks)
throws InterruptedException {
return e.invokeAll(tasks);
}
public List> invokeAll(Collection> tasks,
long timeout, TimeUnit unit)
throws InterruptedException {
return e.invokeAll(tasks, timeout, unit);
}
public T invokeAny(Collection> tasks)
throws InterruptedException, ExecutionException {
return e.invokeAny(tasks);
}
public T invokeAny(Collection> tasks,
long timeout, TimeUnit unit)
throws InterruptedException, ExecutionException, TimeoutException {
return e.invokeAny(tasks, timeout, unit);
}
}
private SingleThreadExecutorWithExceptions() {}
}
答案 10 :(得分：0)
这与mmm的解决方案相似，但更容易理解。让您的任务扩展一个抽象类，该抽象类包装run（）方法。
public abstract Task implements Runnable {
public abstract void execute();
public void run() {
try {
execute();
} catch (Throwable t) {
// handle it
}
}
}
public MySampleTask extends Task {
public void execute() {
// heavy, error-prone code here
}
}
答案 11 :(得分：-5)
我没有为ThreadPoolExecutor创建子类，而是提供一个ThreadFactory实例来创建新的Threads，并为它们提供UncaughtExceptionHandler