ScheduledExecutorService Exception handling

Java Problem Overview

I use ScheduledExecutorService to execute a method periodically.

p-code:

ScheduledExecutorService scheduler = Executors.newSingleThreadScheduledExecutor();
ScheduledFuture<?> handle =
	    scheduler.scheduleWithFixedDelay(new Runnable() {
	         public void run() { 
	             //Do business logic, may Exception occurs
	         }
	    }, 1, 10, TimeUnit.SECONDS);

My question:

How to continue the scheduler, if run() throws Exception? Should I try-catch all Exception in method run()? Or any built-in callback method to handle the Exception? Thanks!

Java Solutions

Solution 1 - Java

tl;dr

Any exception escaping your run method halts all further work, without notice.

Always use a try-catch within your run method. Try to recover if you want scheduled activity to continue.

@Override
public void run ()
{
    try {
        doChore();
    } catch ( Exception e ) { 
        logger.error( "Caught exception in ScheduledExecutorService. StackTrace:\n" + t.getStackTrace() );
    }
}

The Problem

The question refers to the critical trick with a ScheduledExecutorService: Any thrown exception or error reaching the executor causes the executor to halt. No more invocations on the Runnable, no more work done. This work stoppage happens silently, you'll not be informed. This naughty-language blog posting entertainingly narrates the hard way to learn about this behavior.

The Solution

The answer by yegor256 and the answer by arun_suresh both seem to be basically correct. Two issues with those answers:

Catch errors as well as exceptions
A bit complicated

Errors and Exceptions ?

In Java we normally catch only exceptions, not errors. But in this special case of ScheduledExecutorService, failing to catch either will mean a work stoppage. So you may want to catch both. I'm not 100% sure about this, not knowing fully the implications of catching all errors. Please correct me if needed.

One reason to catch errors as well as exceptions might involve the use of libraries within your task. See the comment by jannis.

One way to catch both exceptions and errors is to catch their superclass, Throwable for an example.

} catch ( Throwable t ) {

…rather than…

} catch ( Exception e ) {

Simplest Approach: Just Add a `Try-Catch`

But both answers are a bit complicated. Just for the record, I'll show the simplest solution:

> Always wrap your Runnable's code in a Try-Catch to catch any and all exceptions and errors.

Lambda Syntax

With a lambda (in Java 8 and later).

final Runnable someChoreRunnable = () -> {
    try {
        doChore();
    } catch ( Throwable t ) {  // Catch Throwable rather than Exception (a subclass).
        logger.error( "Caught exception in ScheduledExecutorService. StackTrace:\n" + t.getStackTrace() );
    }
};

Old-Fashioned Syntax

The old-fashioned way, before lambdas.

final Runnable someChoreRunnable = new Runnable()
{
    @Override
    public void run ()
    {
        try {
            doChore();
        } catch ( Throwable t ) {  // Catch Throwable rather than Exception (a subclass).
            logger.error( "Caught exception in ScheduledExecutorService. StackTrace:\n" + t.getStackTrace() );
        }
    }
};

In Every Runnable/Callable

Regardless of a ScheduledExecutorService, it seems sensible to me to always use a general try-catch( Exception† e ) in any run method of a Runnable. Ditto for any call method of a Callable.

Complete example code

In real work, I would likely define the Runnable separately rather than nested. But this makes for neat all-in-one example.

package com.basilbourque.example;

import java.time.ZoneId;
import java.time.ZonedDateTime;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.TimeUnit;

/**
 *  Demo `ScheduledExecutorService`
 */
public class App {
    public static void main ( String[] args ) {
        App app = new App();
        app.doIt();
    }

    private void doIt () {

        // Demonstrate a working scheduled executor service.
        // Run, and watch the console for 20 seconds.
        System.out.println( "BASIL - Start." );

        ScheduledExecutorService scheduler = Executors.newSingleThreadScheduledExecutor();
        ScheduledFuture < ? > handle =
                scheduler.scheduleWithFixedDelay( new Runnable() {
                    public void run () {
                        try {
                            // doChore ;   // Do business logic.
                            System.out.println( "Now: " + ZonedDateTime.now( ZoneId.systemDefault() ) );  // Report current moment.
                        } catch ( Exception e ) {
                            // … handle exception/error. Trap any unexpected exception here rather to stop it reaching and shutting-down the scheduled executor service.
                            // logger.error( "Caught exception in ScheduledExecutorService. StackTrace:\n" + e.getStackTrace() );
                        }   // End of try-catch.
                    }   // End of `run` method.
                } , 0 , 2 , TimeUnit.SECONDS );


        // Wait a long moment, for background thread to do some work.
        try {
            Thread.sleep( TimeUnit.SECONDS.toMillis( 20 ) );
        } catch ( InterruptedException e ) {
            e.printStackTrace();
        }

        // Time is up. Kill the executor service and its thread pool.
        scheduler.shutdown();

        System.out.println( "BASIL - Done." );

    }
}

When run.

>BASIL - Start. > >Now: 2018-04-10T16:46:01.423286-07:00[America/Los_Angeles] > >Now: 2018-04-10T16:46:03.449178-07:00[America/Los_Angeles] > >Now: 2018-04-10T16:46:05.450107-07:00[America/Los_Angeles] > >Now: 2018-04-10T16:46:07.450586-07:00[America/Los_Angeles] > >Now: 2018-04-10T16:46:09.456076-07:00[America/Los_Angeles] > >Now: 2018-04-10T16:46:11.456872-07:00[America/Los_Angeles] > >Now: 2018-04-10T16:46:13.461944-07:00[America/Los_Angeles] > >Now: 2018-04-10T16:46:15.463837-07:00[America/Los_Angeles] > >Now: 2018-04-10T16:46:17.469218-07:00[America/Los_Angeles] > >Now: 2018-04-10T16:46:19.473935-07:00[America/Los_Angeles] > >BASIL - Done.

Another example

Here is another example. Here our task is meant to run about twenty times, once every five seconds for a minute. But on the fifth run, we throw an exception.

public class App2
{
    public static void main ( String[] args )
    {
        ScheduledExecutorService ses = Executors.newSingleThreadScheduledExecutor();
        final AtomicInteger counter = new AtomicInteger( 0 );
        Runnable task = ( ) -> {
            int c = counter.incrementAndGet();
            if ( c > 4 )
            {
                System.out.println( "THROWING EXCEPTION at " + Instant.now() );
                throw new IllegalStateException( "Bogus exception. c = " + c + ". " + Instant.now() ); // Notice how this exception is silently swallowed by the scheduled executor service, while causing a work stoppage.
            }
            System.out.println( "Task running. c = " + c + ". " + Instant.now() );
        };
        ses.scheduleAtFixedRate( task , 0 , 5 , TimeUnit.SECONDS );

        try { Thread.sleep( Duration.ofMinutes( 1 ).toMillis() ); }catch ( InterruptedException e ) { e.printStackTrace(); }
        System.out.println( "Main thread done sleeping. " + Instant.now() );

        ses.shutdown();
        try { ses.awaitTermination( 1 , TimeUnit.MINUTES ); }catch ( InterruptedException e ) { e.printStackTrace(); }
    }
}

When run.

Task running. c = 1. 2021-10-14T20:09:16.317995Z
Task running. c = 2. 2021-10-14T20:09:21.321536Z
Task running. c = 3. 2021-10-14T20:09:26.318642Z
Task running. c = 4. 2021-10-14T20:09:31.318320Z
THROWING EXCEPTION at 2021-10-14T20:09:36.321458Z
Main thread done sleeping. 2021-10-14T20:10:16.320430Z

Notice:

The exception is silently swallowed by the scheduled executor service.
A work stoppage occurs. No further executions of our task are scheduled. Again, a silent problem.

So when your task throws an exception, you get the worst outcome possible: Silent work stoppage with no explanation.

The solution, as mentioned above: Always use a try-catch within your run method.

† Or perhaps Throwable instead of Exception to catch Error objects too.

Solution 2 - Java

You should use the ScheduledFuture object returned by your scheduler.scheduleWithFixedDelay(...) like so :

ScheduledExecutorService scheduler = Executors.newSingleThreadScheduledExecutor();
ScheduledFuture<?> handle =
        scheduler.scheduleWithFixedDelay(new Runnable() {
             public void run() { 
                 throw new RuntimeException("foo");
             }
        }, 1, 10, TimeUnit.SECONDS);

// Create and Start an exception handler thread
// pass the "handle" object to the thread
// Inside the handler thread do :
....
try {
  handle.get();
} catch (ExecutionException e) {
  Exception rootException = e.getCause();
}

Solution 3 - Java

Old question but the accepted answer doesn't give explanations and provides a poor example and the most upvoted answer is right on some points but finally encourages you to add catch exceptions in every Runnable.run() method.
I disagree because :

it is not neat : not standard for a task to catch its own exceptions.
it is not robust : a new Runnable subclass could forget to perform the exception catch and the failover associated.
it defeats the low coupling promoted by tasks since that couples the tasks to execute with the way of handling the task result.
it mixes responsibilities : that is not the task responsibility to handle the exception or to communicate the exception to the caller. A task is something to execute.

I think that the exception propagation should be performed by the ExecutorService framework and actually it offers that feature.
Besides, trying to be too clever by trying to short-circuiting the ExecutorService way of working is not a good idea either : the framework may evolve and you want to use it in a standard way.
At last, letting the ExecutorService framework to make its job doesn't mean necessarily halting the subsequent invocations task.
If a scheduled task encounters an issue, that is the caller responsibility to re-schedule or not the task according to the issue cause.
Each layer has its its responsibilities. Keeping these make code both clear and maintainable.

ScheduledFuture.get() : the right API to catch exceptions and errors occurred in the task

ScheduledExecutorService.scheduleWithFixedDelay()/scheduleAtFixRate() state in their specification :

> If any execution of the task encounters an exception, subsequent > executions are suppressed. Otherwise, the task will only terminate via > cancellation or termination of the executor.

It means that ScheduledFuture.get() doesn't return at each scheduled invocation but that it returns for the last invocation of the task, that is a task cancelation : caused by ScheduledFuture.cancel() or a exception thrown in the task.
So handling the ScheduledFuture return to capture the exception with ScheduledFuture.get() looks right :

  try {
    future.get();

  } catch (InterruptedException e) {
    // ... to handle
  } catch (ExecutionException e) {
    // ... and unwrap the exception OR the error that caused the issue
    Throwable cause = e.getCause();       
  }

Example with the default behavior : halting the scheduling if one of the task execution encounters an issue

It executes a task that for the third executions thrown an exception and terminates the scheduling. In some scenarios, we want that.

import java.util.concurrent.ExecutionException;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;

public class ScheduledExecutorServiceWithException {

  public static void main(String[] args) {
    ScheduledExecutorService executor = Executors.newScheduledThreadPool(2);

    // variable used to thrown an error at the 3rd task invocation
    AtomicInteger countBeforeError = new AtomicInteger(3);

    // boolean allowing to leave the client to halt the scheduling task or not after a failure
    Future<?> futureA = executor
        .scheduleWithFixedDelay(new MyRunnable(countBeforeError), 1, 2, TimeUnit.SECONDS);
    try {
      System.out.println("before get()");
      futureA.get(); // will return only if canceled
      System.out.println("after get()");
    } catch (InterruptedException e) {
      // handle that : halt or no
    } catch (ExecutionException e) {
      System.out.println("exception caught :" + e.getCause());
    }

    // shutdown the executorservice
    executor.shutdown();
  }

  private static class MyRunnable implements Runnable {

    private final AtomicInteger invocationDone;

    public MyRunnable(AtomicInteger invocationDone) {
      this.invocationDone = invocationDone;
    }

    @Override
    public void run() {
      System.out.println(Thread.currentThread().getName() + ", execution");
      if (invocationDone.decrementAndGet() == 0) {
        throw new IllegalArgumentException("ohhh an Exception in MyRunnable");
      }
    }
  }
}

Output :

before get()
pool-1-thread-1, execution
pool-1-thread-1, execution
pool-1-thread-1, execution
exception caught :java.lang.IllegalArgumentException: ohhh an Exception in MyRunnable

Example with the possibility to go on the scheduling if one of the task execution encounters an issue

It executes a task that throws an exception at the two first executions and throws an error at the third one. We can see that the client of the tasks can choose to halt or not the scheduling : here I go on in cases of exception and I stop in case of error.

import java.util.concurrent.ExecutionException;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;

public class ScheduledExecutorServiceWithException {

  public static void main(String[] args) {
    ScheduledExecutorService executor = Executors.newScheduledThreadPool(2);

    // variable used to thrown an error at the 3rd task invocation
    AtomicInteger countBeforeError = new AtomicInteger(3);

    // boolean allowing to leave the client to halt the scheduling task or not after a failure
    boolean mustHalt = true;
    do {
      Future<?> futureA = executor
              .scheduleWithFixedDelay(new MyRunnable(countBeforeError), 1, 2, TimeUnit.SECONDS);
      try {
        futureA.get(); // will return only if canceled
      } catch (InterruptedException e) {
        // handle that : halt or not halt
      } catch (ExecutionException e) {
        if (e.getCause() instanceof Error) {
          System.out.println("I halt in case of Error");
          mustHalt = true;
        } else {
          System.out.println("I reschedule in case of Exception");
          mustHalt = false;
        }
      }
    }
    while (!mustHalt);
    // shutdown the executorservice
    executor.shutdown();
  }

  private static class MyRunnable implements Runnable {

    private final AtomicInteger invocationDone;

    public MyRunnable(AtomicInteger invocationDone) {
      this.invocationDone = invocationDone;
    }

    @Override
    public void run() {
      System.out.println(Thread.currentThread().getName() + ", execution");

      if (invocationDone.decrementAndGet() == 0) {
        throw new Error("ohhh an Error in MyRunnable");
      } else {
        throw new IllegalArgumentException("ohhh an Exception in MyRunnable");
      }
    }
  }
}

Output :

pool-1-thread-1, execution
I reschedule in case of Exception
pool-1-thread-1, execution
I reschedule in case of Exception
pool-1-thread-2, execution
I halt in case of Error

Solution 4 - Java

I know that this is old question, but if somebody is using delayed CompletableFuture with ScheduledExecutorService then should handle this in that way:

private static CompletableFuture<String> delayed(Duration delay) {
    CompletableFuture<String> delayed = new CompletableFuture<>();
    executor.schedule(() -> {
        String value = null;
        try {
            value = mayThrowExceptionOrValue();
        } catch (Throwable ex) {
            delayed.completeExceptionally(ex);
        }
        if (!delayed.isCompletedExceptionally()) {
            delayed.complete(value);
        }
    }, delay.toMillis(), TimeUnit.MILLISECONDS);
    return delayed;
}

and handling exception in CompletableFuture:

CompletableFuture<String> delayed = delayed(Duration.ofSeconds(5));
delayed.exceptionally(ex -> {
    //handle exception
    return null;
}).thenAccept(value -> {
    //handle value
});

Solution 5 - Java

Another solution would be to swallow an exception in the Runnable. You can use a convenient VerboseRunnable class from jcabi-log, for example:

import com.jcabi.log.VerboseRunnable;
scheduler.scheduleWithFixedDelay(
  new VerboseRunnable(
    Runnable() {
      public void run() { 
        // do business logic, may Exception occurs
      }
    },
    true // it means that all exceptions will be swallowed and logged
  ),
  1, 10, TimeUnit.SECONDS
);

Solution 6 - Java

Inspired by @MBec solution, I wrote a nice generic wrapper for the ScheduledExecutorService that:

will catch and print any unhandled thrown exception.
will return a Java 8 CompletableFuture instead of a Future.

import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

/**
 * This class use as a wrapper for the Native Java ScheduledExecutorService class.
 * It was created in order to address the very unpleasant scenario of silent death!
 * explanation: each time an unhandled exception get thrown from a running task that runs by ScheduledExecutorService
 * the thread will die and the exception will die with it (nothing will propagate back to the main thread).
 *
 * However, HonestScheduledExecutorService will gracefully print the thrown exception with a custom/default message,
 * and will also return a Java 8 compliant CompletableFuture for your convenience :)
 */
@Slf4j
public class HonestScheduledExecutorService {

    private final ScheduledExecutorService scheduledExecutorService;
    private static final String DEFAULT_FAILURE_MSG = "Failure occurred when running scheduled task.";

    HonestScheduledExecutorService(ScheduledExecutorService scheduledExecutorService) {
        this.scheduledExecutorService = scheduledExecutorService;
    }

    public CompletableFuture<Object> scheduleWithFixedDelay(Callable callable, String onFailureMsg, long initialDelay, long delay, TimeUnit unit) {
        final String msg = StringUtils.isEmpty(onFailureMsg) ? DEFAULT_FAILURE_MSG : onFailureMsg;
        CompletableFuture<Object> delayed = new CompletableFuture<>();

        scheduledExecutorService.scheduleWithFixedDelay(() -> {
            try {
                Object result = callable.call();
                delayed.complete(result);
            } catch (Throwable th) {
                log.error(msg, th);
                delayed.completeExceptionally(th);
            }
        }, initialDelay, delay, unit);

        return delayed;
    }

    public CompletableFuture<Void> scheduleWithFixedDelay(Runnable runnable, String onFailureMsg, long initialDelay, long delay, TimeUnit unit) {
        final String msg = StringUtils.isEmpty(onFailureMsg) ? DEFAULT_FAILURE_MSG : onFailureMsg;
        CompletableFuture<Void> delayed = new CompletableFuture<>();

        scheduledExecutorService.scheduleWithFixedDelay(() -> {
            try {
                runnable.run();
                delayed.complete(null);
            } catch (Throwable th) {
                log.error(msg, th);
                delayed.completeExceptionally(th);
            }
        }, initialDelay, delay, unit);

        return delayed;
    }

    public CompletableFuture<Object> schedule(Callable callable, String failureMsg, long delay, TimeUnit unit) {
        final String msg = StringUtils.isEmpty(failureMsg) ? DEFAULT_FAILURE_MSG : failureMsg;
        CompletableFuture<Object> delayed = new CompletableFuture<>();

        scheduledExecutorService.schedule(() -> {
            try {
                Object result = callable.call();
                delayed.complete(result);
            } catch (Throwable th) {
                log.error(msg, th);
                delayed.completeExceptionally(th);
            }
        }, delay, unit);

        return delayed;
    }

    public CompletableFuture<Void> schedule(Runnable runnable, String failureMsg, long delay, TimeUnit unit) {
        final String msg = StringUtils.isEmpty(failureMsg) ? DEFAULT_FAILURE_MSG : failureMsg;
        CompletableFuture<Void> delayed = new CompletableFuture<>();

        scheduledExecutorService.schedule(() -> {
            try {
                runnable.run();
                delayed.complete(null);
            } catch (Throwable th) {
                log.error(msg, th);
                delayed.completeExceptionally(th);
            }
        }, delay, unit);

        return delayed;
    }

    public CompletableFuture<Object> scheduleAtFixedRate(Callable callable, String failureMsg, long initialDelay, long period, TimeUnit unit) {
        final String msg = StringUtils.isEmpty(failureMsg) ? DEFAULT_FAILURE_MSG : failureMsg;
        CompletableFuture<Object> delayed = new CompletableFuture<>();

        scheduledExecutorService.scheduleAtFixedRate(() -> {
            try {
                Object result = callable.call();
                delayed.complete(result);
            } catch (Throwable th) {
                log.error(msg, th);
                delayed.completeExceptionally(th);
            }
        }, initialDelay, period, unit);

        return delayed;
    }

    public CompletableFuture<Void> scheduleAtFixedRate(Runnable runnable, String failureMsg, long initialDelay, long period, TimeUnit unit) {
        final String msg = StringUtils.isEmpty(failureMsg) ? DEFAULT_FAILURE_MSG : failureMsg;
        CompletableFuture<Void> delayed = new CompletableFuture<>();

        scheduledExecutorService.scheduleAtFixedRate(() -> {
            try {
                runnable.run();
                delayed.complete(null);
            } catch (Throwable th) {
                log.error(msg, th);
                delayed.completeExceptionally(th);
            }
        }, initialDelay, period, unit);

        return delayed;
    }

    public CompletableFuture<Object> execute(Callable callable, String failureMsg) {
        final String msg = StringUtils.isEmpty(failureMsg) ? DEFAULT_FAILURE_MSG : failureMsg;
        CompletableFuture<Object> delayed = new CompletableFuture<>();

        scheduledExecutorService.execute(() -> {
            try {
                Object result = callable.call();
                delayed.complete(result);
            } catch (Throwable th) {
                log.error(msg, th);
                delayed.completeExceptionally(th);
            }
        });

        return delayed;
    }

    public CompletableFuture<Void> execute(Runnable runnable, String failureMsg) {
        final String msg = StringUtils.isEmpty(failureMsg) ? DEFAULT_FAILURE_MSG : failureMsg;
        CompletableFuture<Void> delayed = new CompletableFuture<>();

        scheduledExecutorService.execute(() -> {
            try {
                runnable.run();
                delayed.complete(null);
            } catch (Throwable th) {
                log.error(msg, th);
                delayed.completeExceptionally(th);
            }
        });

        return delayed;
    }

    public boolean awaitTermination(long timeout, TimeUnit unit) throws InterruptedException {
        return scheduledExecutorService.awaitTermination(timeout, unit);
    }

    public List<Runnable> shutdownNow() {
        return scheduledExecutorService.shutdownNow();
    }

    public void shutdown() {
        scheduledExecutorService.shutdown();
    }

}

Solution 7 - Java

Any exception in the run() of a thread which is passed to (ScheduledExecutorService) is never thrown out and if we use future.get() to get status, then the main thread waits infinitely

Solution 8 - Java

An elegent way to catch the exception and keep scheduled tasks alive.

First, define a functional interface.

    @FunctionalInterface
    interface NoSuppressedRunnable extends Runnable {

        @Override
        default void run() {
            try {
                doRun();
            } catch (Exception e) {
                log.error("...", e);
            }
        }


        void doRun();

    }

Then, commit the job like this.

executorService.scheduleAtFixedRate((NoSuppressedRunnable) () -> {
    // Complier implies that this is an implement of doRun() once you put the cast above
}, 0, 60L, TimeUnit.SECONDS);

Solution 9 - Java

Personally, I disagree with all the answers here. The main issue with all of them is they provide the same solution in weird flavors. Instead, what you should be doing is creating your own thread factory that installs an uncaught exception handler on the thread that is being created. For example, this is the DefaultThreadFactory that is installed into any executor that would create threads on its own. Shamefully, it's still a private class as of Java 11, since I would like to extend it instead of copying it into my codebase. Below is a snippet how it appears in Executors.java file.

    private static class DefaultThreadFactory implements ThreadFactory {
        private static final AtomicInteger poolNumber = new AtomicInteger(1);
        private final ThreadGroup group;
        private final AtomicInteger threadNumber = new AtomicInteger(1);
        private final String namePrefix;

        DefaultThreadFactory() {
            SecurityManager s = System.getSecurityManager();
            group = (s != null) ? s.getThreadGroup() :
                                  Thread.currentThread().getThreadGroup();
            namePrefix = "pool-" +
                          poolNumber.getAndIncrement() +
                         "-thread-";
        }

        public Thread newThread(Runnable r) {
            Thread t = new Thread(group, r,
                                  namePrefix + threadNumber.getAndIncrement(),
                                  0);
            if (t.isDaemon())
                t.setDaemon(false);
            if (t.getPriority() != Thread.NORM_PRIORITY)
                t.setPriority(Thread.NORM_PRIORITY);
            return t;
        }
    }

As you can see, the interface itself is a single method that handles creating new threads. There isn't much magic to it besides figuring out the thread group where is the thread factory created in. The interesting bit is that threads are created as non-daemon.

When the thread is created, you can call setThreadUncaughtExceptionHandler which accepts a handler where you should be handling any uncaught exceptions that had happened in that thread. By default, it will be inherited from your thread group, which has the following

    public void uncaughtException(Thread t, Throwable e) {
        if (parent != null) {
            parent.uncaughtException(t, e);
        } else {
            Thread.UncaughtExceptionHandler ueh =
                Thread.getDefaultUncaughtExceptionHandler();
            if (ueh != null) {
                ueh.uncaughtException(t, e);
            } else if (!(e instanceof ThreadDeath)) {
                System.err.print("Exception in thread \""
                                 + t.getName() + "\" ");
                e.printStackTrace(System.err);
            }
        }
    }

By default, it will attempt to delegate handling to parent thread group if it exists, and only then test for platform default uncaught exception handler. Usually it is not explicitly installed. If you want to do some real damage to poor codebases that are not aware of this, you can install one via Thread#setDefaultUncaughtExceptionHandler. Don't worry, you won't get to do that if the runtime has Security manager in place.

If you were to install your own handler, that handler will be called instead of the group one.

Now with that out of the way, to your question: How do you handle exceptions in Executors. By default, a thread is considered dead if code is unable to handle its own errors. And I think you should adhere to that. Uncaught exception handler won't save your thread. Instead it will help you diagnose what happened. To segway into ScheduledExecutor implementations, which permit periodic execution of a runnable, the same rules apply: if one execution fails, the thread is killed, along with the runnable that was supposed to get run.

In short, handle your own errors. We have checked exceptions for a reason.

But what about unchecked exceptions?

Funny, since I will commit the same sin as other posters do: use try/catch on Throwable, but assert that it's not a ThreadDeath error. If you do get one, you must rethrow it to ensure the thread actually does die.

Content Type	Original Author	Original Content on Stackoverflow
Question	卢声远 Shengyuan Lu	View Question on Stackoverflow
Solution 1 - Java	Basil Bourque	View Answer on Stackoverflow
Solution 2 - Java	arun_suresh	View Answer on Stackoverflow
Solution 3 - Java	davidxxx	View Answer on Stackoverflow
Solution 4 - Java	MBec	View Answer on Stackoverflow
Solution 5 - Java	yegor256	View Answer on Stackoverflow
Solution 6 - Java	dorony	View Answer on Stackoverflow
Solution 7 - Java	Guru	View Answer on Stackoverflow
Solution 8 - Java	Anderson	View Answer on Stackoverflow
Solution 9 - Java	Dragas	View Answer on Stackoverflow

ScheduledExecutorService Exception handling

Java Problem Overview

Java Solutions

Solution 1 - Java

tl;dr

The Problem

The Solution

Errors and Exceptions ?

Simplest Approach: Just Add a `Try-Catch`

Lambda Syntax

Old-Fashioned Syntax

In Every Runnable/Callable

Complete example code

Another example

Solution 2 - Java

Solution 3 - Java

ScheduledFuture.get() : the right API to catch exceptions and errors occurred in the task

Example with the default behavior : halting the scheduling if one of the task execution encounters an issue

Example with the possibility to go on the scheduling if one of the task execution encounters an issue

Solution 4 - Java

Solution 5 - Java

Solution 6 - Java

Solution 7 - Java

Solution 8 - Java

Solution 9 - Java

PyQt or PySide - which one to use

How do I delete till non-whitespace in vim?

Attributions

Java Problem Overview

Java Solutions

Solution 1 - Java

tl;dr

The Problem

The Solution

Errors and Exceptions ?

Simplest Approach: Just Add a Try-Catch

Lambda Syntax

Old-Fashioned Syntax

In Every Runnable/Callable

Complete example code

Another example

Solution 2 - Java

Solution 3 - Java

ScheduledFuture.get() : the right API to catch exceptions and errors occurred in the task

Example with the default behavior : halting the scheduling if one of the task execution encounters an issue

Example with the possibility to go on the scheduling if one of the task execution encounters an issue

Solution 4 - Java

Solution 5 - Java

Solution 6 - Java

Solution 7 - Java

Solution 8 - Java

Solution 9 - Java

PyQt or PySide - which one to use

How do I delete till non-whitespace in vim?

Attributions

Simplest Approach: Just Add a `Try-Catch`