Handling Exceptions for ThreadPoolExecutor

concurrency, exception, java, multithreading, threadpoolexecutor

Solution

When you submit a task to the executor, it returns you a `FutureTask` instance.

`FutureTask.get()` will re-throw any exception thrown by the task as an `ExecutorException`.

So when you iterate through the `List<Future>` and call get on each, catch `ExecutorException` and invoke an orderly shutdown.

Problem

I have the following code snippet that basically scans through the list of task that needs to be executed and each task is then given to the executor for execution. The `JobExecutor` in turn creates another executor (for doing db stuff...reading and writing data to queue) and completes the task. `JobExecutor` returns a `Future<Boolean>` for the tasks submitted. When one of the task fails, I want to gracefully interrupt all the threads and shutdown the executor by catching all the exceptions. What changes do I need to do? ``` 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 ; } } } ```

Original source

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