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The best way to handle exceptions at the application level is to use an exception handler. The handler can perform diagnostic actions, clean - up and shut down the JVMJava Virtual Machine, or simply log the details of the failure.

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This noncompliant code example consists of the PoolService class that encapsulates a thread pool and a runnable Task class. The Task.run() method can throw runtime exceptions, such as NullPointerException.

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final class PoolService {
  private final ExecutorService pool = Executors.newFixedThreadPool(10);

  public void doSomething() {
    pool.execute(new Task());
  }
}

final class Task implements Runnable {
  @Override public void run() {
    // ...
    throw new NullPointerException();
    // ...
  }
}

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Task-specific recovery or clean-up cleanup actions can be performed by overriding the afterExecute() hook of the java.util.concurrent.ThreadPoolExecutor class. This hook is called either when a task concludes successfully by executing all statements in its run() method or when the task halts because of an exception. Some implementations may fail to catch java.lang.Error. (See see Bug ID 6450211 for more information [SDN 2008]). ) When using this approach, substitute the executor service with a custom ThreadPoolExecutor that overrides the afterExecute() hook:

Code Block

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final class PoolService {
  // The values have been hard-coded for brevity
  ExecutorService pool = new CustomThreadPoolExecutor(
      10, 10, 10, TimeUnit.SECONDS, new ArrayBlockingQueue<Runnable>(10));
  // ...
}

class CustomThreadPoolExecutor extends ThreadPoolExecutor {
  // ... Constructor ...
  public CustomThreadPoolExecutor(
      int corePoolSize, int maximumPoolSize, long keepAliveTime, 
      TimeUnit unit, BlockingQueue<Runnable> workQueue) { 
    super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue);
  }


  @Override
  public void afterExecute(Runnable r, Throwable t) {
    super.afterExecute(r, t);
    if (t != null) {
      // Exception occurred, forward to handler
    }
    // ... Perform task-specific clean-upcleanup actions
  }

  @Override
  public void terminated() {
    super.terminated();
    // ... Perform final clean-up actions
  }
}

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This compliant solution sets an uncaught exception handler on behalf of the thread pool. A ThreadFactory argument is passed to the thread pool during construction. The factory is responsible for creating new threads and setting the uncaught exception handler on their behalf. The Task class is unchanged from the noncompliant code example.

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final class PoolService {
  private static final ThreadFactory factory =
      new ExceptionThreadFactory(new MyExceptionHandler());
  private static final ExecutorService pool =
      Executors.newFixedThreadPool(10, factory);

  public void doSomething() {
    pool.execute(new Task()); // Task is a runnable class
  }

  public static class ExceptionThreadFactory implements ThreadFactory  {
    private static final ThreadFactory defaultFactory =
        Executors.defaultThreadFactory();
    private final Thread.UncaughtExceptionHandler handler;

    public ExceptionThreadFactory(
        Thread.UncaughtExceptionHandler handler)
    {
      this.handler = handler;
    }

    @Override public Thread newThread(Runnable run) {
      Thread thread = defaultFactory.newThread(run);
      thread.setUncaughtExceptionHandler(handler);
      return thread;
    }
  }

  public static class MyExceptionHandler extends ExceptionReporter
      implements Thread.UncaughtExceptionHandler {
    // ...

    @Override public void uncaughtException(Thread thread, Throwable t) {
      // Recovery or logging code
    }
  }
}

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This compliant solution invokes the ExecutorService.submit() method to submit the task so that a Future object can be obtained. It uses the Future object to let the task rethrow the exception so that it can be handled locally.

Code Block

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final class PoolService {
  private final ExecutorService pool = Executors.newFixedThreadPool(10);

  public void doSomething() {
    Future<?> future = pool.submit(new Task());

    // ...

    try {
      future.get();
    } catch (InterruptedException e) {
      Thread.currentThread().interrupt(); // Reset interrupted status
    } catch (ExecutionException e) {
      Throwable exception = e.getCause();
      // Forward to exception reporter
    }
  }
}

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Rule	Severity	Likelihood	Remediation Cost	Priority	Level
TPS03-J	low Low	probable Probable	medium Medium	P4	L3

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Related Guidelines

MITRE CWE

CWE-392. , Missing report Report of error condition Error Condition

Bibliography

[API 20062014] Interfaces `ExecutorService`, `ThreadFactory`; class `Thread`	Class `Thread` Interface `ExecutorService` Interface `ThreadFactory`
[Goetz 2006a]	Chapter 7.3, "Handling Abnormal Thread Termination"

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