Finally not executed after try block

[saurabhmehta mehta]

I am trying to run the below concurrency code:

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

public class TestThread {

   public static void main(final String[] arguments) throws InterruptedException {
      ExecutorService executor = Executors.newSingleThreadExecutor();

      try {
         executor.submit(new Task());
         System.out.println("Shutdown executor");
         executor.shutdown();
         executor.awaitTermination(5, TimeUnit.SECONDS);
      } catch (InterruptedException e) {
         System.err.println("tasks interrupted");
      } finally {

         if (!executor.isTerminated()) {
            System.err.println("cancel non-finished tasks");
         }
         executor.shutdownNow();
         System.out.println("shutdown finished");
      }
   }

   static class Task implements Runnable {
      
      public void run() {
         
         try {
            int duration = 6;
            System.out.println("Running Task!");
            TimeUnit.SECONDS.sleep(duration);
         } catch (InterruptedException e) {
            e.printStackTrace();
         }
      }
   }	   
}

and the output is :

Shutdown executor
Running Task!
shutdown finished
cancel non-finished tasks
java.lang.InterruptedException: sleep interrupted
	at java.lang.Thread.sleep(Native Method)
	at java.lang.Thread.sleep(Thread.java:340)
	at java.util.concurrent.TimeUnit.sleep(TimeUnit.java:386)
	at TestThread$Task.run(TestThread.java:34)
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:748)

According to the output it seems finally was not executed despite the try block getting completed. Am I right with the understanding? And why was the exception immediately thrown before going to the finally block?

[Henry Wong]

saurabhmehta mehta wrote:
According to the output it seems finally was not executed despite the try block getting completed. Am I right with the understanding? And why was the exception immediately thrown before going to the finally block?

Not sure how you draw that conclusion since there are messages in the output that can only be produced by the finally block...

Henry

[saurabhmehta mehta]

Henry Wong wrote:

saurabhmehta mehta wrote:
According to the output it seems finally was not executed despite the try block getting completed. Am I right with the understanding? And why was the exception immediately thrown before going to the finally block?

Not sure how you draw that conclusion since there are messages in the output that can only be produced by the finally block...

Henry

Yes I can see that, but after exiting the try block the control first goes to the statements outside the finally block and then to the statements inside the finally are executed. Is that the normal execution flow. Please help if I am missing something..

[Henry Wong]

saurabhmehta mehta wrote:
Yes I can see that, but after exiting the try block the control first goes to the statements outside the finally block and then to the statements inside the finally are executed. Is that the normal execution flow. Please help if I am missing something..

Keep in mind that you have more than one thread here. You need to follow the flow of each thread independently.

Also, you seem to be mixing standard out with standard error, so, it is possible for you messages to be out of order too.

Henry

[saurabhmehta mehta]

Henry Wong wrote:

Also, you seem to be mixing standard out with standard error, so, it is possible for you messages to be out of order too.

Henry

There are 2 threads in the program, the new thread executes statements inside the run method whereas the main thread runs inside the main method, is my understanding correct? From the output it seems the main thread after the line " executor.awaitTermination(5, TimeUnit.SECONDS);" skipped the finally block and directly executed the statements outside it. Then it came back inside the finally method. All this is done by the main thread.Is this a normal flow for a single thread?

[Henry Wong]

saurabhmehta mehta wrote:
There are 2 threads in the program, the new thread executes statements inside the run method whereas the main thread runs inside the main method, is my understanding correct? From the output it seems the main thread after the line " executor.awaitTermination(5, TimeUnit.SECONDS);" skipped the finally block and directly executed the statements outside it. Then it came back inside the finally method. All this is done by the main thread.Is this a normal flow for a single thread?

How did you draw that conclusion? That line doesn't have any output.  And also, how do you know the main thread "executed statements out of it"? Heck, what does that even mean?  

Are you referring to the "running task" output? This output is printed by the other thread -- not the main thread.

Henry

[saurabhmehta mehta]

Henry Wong wrote:

Are you referring to the "running task" output? This output is printed by the other thread -- not the main thread.

Henry

No I am not.

Henry Wong wrote:

How did you draw that conclusion? That line doesn't have any output.  And also, how do you know the main thread "executed statements out of it"? Heck, what does that even mean?  

Henry

Lets go by the line numbers. According to the output, lines 22 and 23 were executed and then the lines 19 and 20. My question is when the control left the try block at line 14 shouldn't it have first executed the finally block first since normally finally block has to be executed once the try/catch is complete? Why is the control going back to the line that should have been executed first?

[Paul Clapham]

saurabhmehta mehta wrote:Lets go by the line numbers. According to the output, lines 22 and 23 were executed and then the lines 19 and 20.

No, we don't know that from the output. The two lines which produce output use different output streams, and buffering could result in them writing output to the console in a different order than what they were run in.

So let's get rid of the System.out/System.err source of confusion and see what happens then.