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处理Java ExecutorService任务中的异常

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我'm trying to use Java' s ThreadPoolExecutor 类用固定数量的线程运行大量重量级任务 . 每个任务都有许多地方，在这些地方可能因异常而失败 .

我已经子类化 ThreadPoolExecutor 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 . 有什么线索在这里发生了什么？

谢谢！

java multithreading exception executorservice threadpoolexecutor

11 回答

  • 218

    我正在使用jcabi-log中的VerboseRunnable类，它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
);
    回复于
  • 1

    来自docs：

    注意：当任务明确地或通过诸如submit之类的方法包含在任务（例如FutureTask）中时，这些任务对象会捕获并维护计算异常，因此它们不会导致突然终止，并且内部异常不会传递给此方法 .

    当你提交一个Runnable时，它将被包含在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);
        }
    }
}
    回复于
  • 0

    WARNING ：应该注意，此解决方案将阻止调用线程 .

    如果要处理任务抛出的异常，则通常最好使用 Callable 而不是 Runnable .

    允许 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() 抛出异常，则会将其包装在 ExecutionException 中并由 Future.get() 抛出 .

    这可能比继承 ThreadPoolExecutor 更为可取 . 如果异常是可恢复的，它还为您提供重新提交任务的机会 .

    回复于
  • 6

    这种行为的解释正好在_1692168中：

    注意：当任务明确地或通过诸如submit之类的方法包含在任务（例如FutureTask）中时，这些任务对象会捕获并维护计算异常，因此它们不会导致突然终止，并且内部异常不会传递给此方法 .

    回复于
  • -5

    我通过将提交的runnable包装提交给执行程序来解决它 .

    CompletableFuture.runAsync(

        () -> {
                try {
                        runnable.run();
                } catch (Throwable e) {
                        Log.info(Concurrency.class, "runAsync", e);
                }
        },

        executorService
);
    回复于
  • 3

    另一种解决方案是使用ManagedTask和ManagedTaskListener .

    您需要一个Callable或Runnable来实现ManagedTask接口 .

    方法 getManagedTaskListener 返回所需的实例 .

    public ManagedTaskListener getManagedTaskListener() {

    并在ManagedTaskListener中实现 taskDone 方法：

    @Override
public void taskDone(Future<?> future, ManagedExecutorService executor, Object task, Throwable exception) {
    if (exception != null) {
        LOGGER.log(Level.SEVERE, exception.getMessage());
    }
}

    有关managed task lifecycle and listener的更多详细信息 .

    回复于
  • 16

    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 .

    回复于
  • 0

    如果您的 ExecutorService 来自外部源（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);
            });
}
    回复于
  • 0

    这是因为 AbstractExecutorService :: submit 将 runnable 包装成 RunnableFuture （只有 FutureTask ），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将调用FutureTask.run（） . 这是异常处理程序代码，因此您没有得到预期的异常 .

    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);
    }
}
    回复于
  • 9

    这有效

    • 它派生自SingleThreadExecutor，但您可以轻松地进行调整

    • Java 8 lamdas代码，但易于修复

    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从下一个开始

    如果出现unaugth错误或异常，则uncaughtExceptionHandler将捕获它

    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() {}
}
    回复于
  • 134

    而不是继承ThreadPoolExecutor，我会提供一个创建新线程的ThreadFactory实例并为它们提供UncaughtExceptionHandler

    回复于

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