Java: set timeout on a certain block of code?

Is it possible to force Java to throw an Exception after some block of code runs longer than acceptable?

Here's the simplest way that I know of to do this:

final Runnable stuffToDo = new Thread() {
  @Override 
  public void run() { 
    /* Do stuff here. */ 
  }
};

final ExecutorService executor = Executors.newSingleThreadExecutor();
final Future future = executor.submit(stuffToDo);
executor.shutdown(); // This does not cancel the already-scheduled task.

try { 
  future.get(5, TimeUnit.MINUTES); 
}
catch (InterruptedException ie) { 
  /* Handle the interruption. Or ignore it. */ 
}
catch (ExecutionException ee) { 
  /* Handle the error. Or ignore it. */ 
}
catch (TimeoutException te) { 
  /* Handle the timeout. Or ignore it. */ 
}
if (!executor.isTerminated())
    executor.shutdownNow(); // If you want to stop the code that hasn't finished.

Alternatively, you can create a TimeLimitedCodeBlock class to wrap this functionality, and then you can use it wherever you need it as follows:

new TimeLimitedCodeBlock(5, TimeUnit.MINUTES) { @Override public void codeBlock() {
    // Do stuff here.
}}.run();

I compiled some of the other answers into a single utility method:

public class TimeLimitedCodeBlock {

  public static void runWithTimeout(final Runnable runnable, long timeout, TimeUnit timeUnit) throws Exception {
    runWithTimeout(new Callable<Object>() {
      @Override
      public Object call() throws Exception {
        runnable.run();
        return null;
      }
    }, timeout, timeUnit);
  }

  public static <T> T runWithTimeout(Callable<T> callable, long timeout, TimeUnit timeUnit) throws Exception {
    final ExecutorService executor = Executors.newSingleThreadExecutor();
    final Future<T> future = executor.submit(callable);
    executor.shutdown(); // This does not cancel the already-scheduled task.
    try {
      return future.get(timeout, timeUnit);
    }
    catch (TimeoutException e) {
      //remove this if you do not want to cancel the job in progress
      //or set the argument to 'false' if you do not want to interrupt the thread
      future.cancel(true);
      throw e;
    }
    catch (ExecutionException e) {
      //unwrap the root cause
      Throwable t = e.getCause();
      if (t instanceof Error) {
        throw (Error) t;
      } else if (t instanceof Exception) {
        throw (Exception) t;
      } else {
        throw new IllegalStateException(t);
      }
    }
  }

}

Sample code making use of this utility method:

  public static void main(String[] args) throws Exception {
    final long startTime = System.currentTimeMillis();
    log(startTime, "calling runWithTimeout!");
    try {
      TimeLimitedCodeBlock.runWithTimeout(new Runnable() {
        @Override
        public void run() {
          try {
            log(startTime, "starting sleep!");
            Thread.sleep(10000);
            log(startTime, "woke up!");
          }
          catch (InterruptedException e) {
            log(startTime, "was interrupted!");
          }
        }
      }, 5, TimeUnit.SECONDS);
    }
    catch (TimeoutException e) {
      log(startTime, "got timeout!");
    }
    log(startTime, "end of main method!");
  }

  private static void log(long startTime, String msg) {
    long elapsedSeconds = (System.currentTimeMillis() - startTime);
    System.out.format("%1$5sms [%2$16s] %3$s\n", elapsedSeconds, Thread.currentThread().getName(), msg);
  }

Output from running the sample code on my machine:

    0ms [            main] calling runWithTimeout!
   13ms [ pool-1-thread-1] starting sleep!
 5015ms [            main] got timeout!
 5016ms [            main] end of main method!
 5015ms [ pool-1-thread-1] was interrupted!

Yes, but its generally a very bad idea to force another thread to interrupt on a random line of code. You would only do this if you intend to shutdown the process.

What you can do is to use Thread.interrupt() for a task after a certain amount of time. However, unless the code checks for this it won't work. An ExecutorService can make this easier with Future.cancel(true)

Its much better for the code to time itself and stop when it needs to.

If it is test code you want to time, then you can use the time attribute:

@Test(timeout = 1000)  
public void shouldTakeASecondOrLess()
{
}

If it is production code, there is no simple mechanism, and which solution you use depends upon whether you can alter the code to be timed or not.

If you can change the code being timed, then a simple approach is is to have your timed code remember it's start time, and periodically the current time against this. E.g.

long startTime = System.currentTimeMillis();
// .. do stuff ..
long elapsed = System.currentTimeMillis()-startTime;
if (elapsed>timeout)
   throw new RuntimeException("tiomeout");

If the code itself cannot check for timeout, you can execute the code on another thread, and wait for completion, or timeout.

    Callable<ResultType> run = new Callable<ResultType>()
    {
        @Override
        public ResultType call() throws Exception
        {
            // your code to be timed
        }
    };

    RunnableFuture<ResultType> future = new FutureTask<>(run);
    ExecutorService service = Executors.newSingleThreadExecutor();
    service.execute(future);
    ResultType result = null;
    try
    {
        result = future.get(1, TimeUnit.SECONDS);    // wait 1 second
    }
    catch (TimeoutException ex)
    {
        // timed out. Try to stop the code if possible.
        future.cancel(true);
    }
    service.shutdown();
}

EDIT: Peter Lawrey is completely right: it's not as simple as interrupting a thread (my original suggestion), and Executors & Callables are very useful ...

Rather than interrupting threads, you could set a variable on the Callable once the timeout is reached. The callable should check this variable at appropriate points in task execution, to know when to stop.

Callables return Futures, with which you can specify a timeout when you try to 'get' the future's result. Something like this:

try {
   future.get(timeoutSeconds, TimeUnit.SECONDS)
} catch(InterruptedException e) {
   myCallable.setStopMeAtAppropriatePlace(true);
}

See Future.get, Executors, and Callable ...

https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/Future.html#get-long-java.util.concurrent.TimeUnit-

https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/Callable.html

https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/Executors.html#newFixedThreadPool%28int%29

I can suggest two options.

1. Within the method, assuming it is looping and not waiting for an external event, add a local field and test the time each time around the loop.

    void method() {
    	long endTimeMillis = System.currentTimeMillis() + 10000;
    	while (true) {
    		// method logic
    		if (System.currentTimeMillis() > endTimeMillis) {
    			// do some clean-up
    			return;
    		}
    	}
    }
   

2. Run the method in a thread, and have the caller count to 10 seconds.

    Thread thread = new Thread(new Runnable() {
    		@Override
    		public void run() {
    			method();
    		}
    });
    thread.start();
    long endTimeMillis = System.currentTimeMillis() + 10000;
    while (thread.isAlive()) {
    	if (System.currentTimeMillis() > endTimeMillis) {
    		// set an error flag
    		break;
    	}
    	try {
    		Thread.sleep(500);
    	}
    	catch (InterruptedException t) {}
    }
   

The drawback to this approach is that method() cannot return a value directly, it must update an instance field to return its value.

I created a very simple solution without using any frameworks or APIs. This looks more elegant and understandable. The class is called TimeoutBlock.

public class TimeoutBlock {

 private final long timeoutMilliSeconds;
	private long timeoutInteval=100;
	
	public TimeoutBlock(long timeoutMilliSeconds){
		this.timeoutMilliSeconds=timeoutMilliSeconds;
	}
	
	public void addBlock(Runnable runnable) throws Throwable{
		long collectIntervals=0;
		Thread timeoutWorker=new Thread(runnable);
		timeoutWorker.start();
		do{ 
			if(collectIntervals>=this.timeoutMilliSeconds){
				timeoutWorker.stop();
				throw new Exception("<<<<<<<<<<****>>>>>>>>>>> Timeout Block Execution Time Exceeded In "+timeoutMilliSeconds+" Milli Seconds. Thread Block Terminated.");
			}
			collectIntervals+=timeoutInteval;           
			Thread.sleep(timeoutInteval);
			
		}while(timeoutWorker.isAlive());
		System.out.println("<<<<<<<<<<####>>>>>>>>>>> Timeout Block Executed Within "+collectIntervals+" Milli Seconds.");
	}

	/**
	 * @return the timeoutInteval
	 */
	public long getTimeoutInteval() {
		return timeoutInteval;
	}

	/**
	 * @param timeoutInteval the timeoutInteval to set
	 */
	public void setTimeoutInteval(long timeoutInteval) {
		this.timeoutInteval = timeoutInteval;
	}
}

example :

try {
        TimeoutBlock timeoutBlock = new TimeoutBlock(10 * 60 * 1000);//set timeout in milliseconds
        Runnable block=new Runnable() {

            @Override
            public void run() {
                //TO DO write block of code to execute
            }
        };
        
        timeoutBlock.addBlock(block);// execute the runnable block 
        
    } catch (Throwable e) {
        //catch the exception here . Which is block didn't execute within the time limit
    }

This was so much useful for me when i had to connect to a FTP account. Then download and upload stuff. sometimes FTP connection hangs or totally breaks. This caused whole system to go down. and i needed a way to detect it and prevent it from happening . So i created this and used it. Works pretty well.

I faced a similar kind of issue where my task was to push a message to SQS within a particular timeout. I used the trivial logic of executing it via another thread and waiting on its future object by specifying the timeout. This would give me a TIMEOUT exception in case of timeouts.

final Future<ISendMessageResult> future = 
timeoutHelperThreadPool.getExecutor().submit(() -> {
  return getQueueStore().sendMessage(request).get();
});
try {
  sendMessageResult = future.get(200, TimeUnit.MILLISECONDS);
  logger.info("SQS_PUSH_SUCCESSFUL");
  return true;

} catch (final TimeoutException e) {
  logger.error("SQS_PUSH_TIMEOUT_EXCEPTION");
}

But there are cases where you can't stop the code being executed by another thread and you get true negatives in that case.

For example - In my case, my request reached SQS and while the message was being pushed, my code logic encountered the specified timeout. Now in reality my message was pushed into the Queue but my main thread assumed it to be failed because of the TIMEOUT exception. This is a type of problem which can be avoided rather than being solved. Like in my case I avoided it by providing a timeout which would suffice in nearly all of the cases.

If the code you want to interrupt is within you application and is not something like an API call then you can simply use

future.cancel(true)

However do remember that java docs says that it does guarantee that the execution will be blocked.

"Attempts to cancel execution of this task. This attempt will fail if the task has already completed, has already been cancelled,or could not be cancelled for some other reason. If successful,and this task has not started when cancel is called,this task should never run. If the task has already started,then the mayInterruptIfRunning parameter determines whether the thread executing this task should be interrupted inan attempt to stop the task."

Instead of having the task in the new thread and the timer in the main thread, have the timer in the new thread and the task in the main thread:

public static class TimeOut implements Runnable{
    public void run() {
        Thread.sleep(10000);
        if(taskComplete ==false) {
            System.out.println("Timed Out");
            return;
        }
        else {
            return;
        }
    }
}
public static boolean taskComplete = false;
public static void main(String[] args) {
    TimeOut timeOut = new TimeOut();
    Thread timeOutThread = new Thread(timeOut);
    timeOutThread.start();
    //task starts here
    //task completed
    taskComplete =true;
    while(true) {//do all other stuff }
}

If you want a CompletableFuture way you could have a method like

public MyResponseObject retrieveDataFromEndpoint() {

   CompletableFuture<MyResponseObject> endpointCall 
       = CompletableFuture.supplyAsync(() ->
             yourRestService.callEnpoint(withArg1, withArg2));

   try {
       return endpointCall.get(10, TimeUnit.MINUTES);
   } catch (TimeoutException 
               | InterruptedException 
               | ExecutionException e) {
       throw new RuntimeException("Unable to fetch data", e);
   }
}

If you're using spring, you could annotate the method with a @Retryable so that it retries the method three times if an exception is thrown.

There is a hacky way to do it.

Set some boolean field to indicate whether the work was completed. Then before the block of code, set a timer to run a piece of code after your timeout. The timer will check if the block of code had finished executing, and if not, throw an exception. Otherwise it will do nothing.

The end of the block of code should, of course, set the field to true to indicate the work was done.

There's a very simple option that nobody's mentioned yet:

Duration timeout = Duration.ofMinutes(5);
Thread thread = new Thread(() -> {
    // your code here
});
thread.start();
thread.join(timeout.toMillis());
if (thread.isAlive()) {
    thread.interrupt();
    throw new MyTimeoutException();
}

If the thread running your code block fails to complete within the timeout, it is interrupted and whatever exception you want can be thrown.

It is possible to write code that will simply ignore the interruption and carry on. If you're dealing with this can cannot fix it then there is thread.stop(), but that can break any synchronisation mechanisms that you are relying on. See its deprecation notice.

You can also capture exceptions from the thread:

AtomicReference<Throwable> uncaughtException = new AtomicReference<>();
thread.setUncaughtExceptionHandler((t, ex) -> uncaughtException.setRelease(ex));

// ...

Throwable ex = uncaughtException.getAcquire();
if (ex != null) {
    throw ex;
}