Use submit if your doing computation e. Creating a thread is an expensive operation and it should be minimized. Shutting Down an ExecutorService In general, the ExecutorService will not be automatically destroyed when there is not task to process. Remember, the key difference between them is that submit return a Future but execute return nothing. If you have to develop a program that runs a lot of concurrent tasks, this approach will present many disadvantages such as lots of boiler plate code create and manage threads , executing thread manually and keeping track of thread execution results.
But the real power of ExecutorService comes when we create a pool of threads and execute multiple tasks concurrently in the thread pool. Though you can use ThreadPoolExecutor and ScheduledThreadPoolExecutor directly, but the best way to get an executor is to use one of the static factory methods provided by the Executors utility class. Upon return, tasks that have not completed are cancelled. The Future's get method will return null upon successful completion. ExecutorService, represents an asynchronous execution mechanism which is capable of executing tasks concurrently in the background. Shutdown methods in ExecutorService You can shut down an ExecutorService which will cause it to reject new tasks.
The submit method returns a object which can be used to check when the Runnable has completed. The ExecutorService has the following implementation in the java. If you need to get a value back from the now-completed task, you must use a method outside the interface and wait for some kind of notification message that the task completed. Monitor waiting time in a queue Monitoring work queue depth is one side. Calling get on that Future will throw an ExecutionException with the original Throwable as its cause accessible by calling getCause on the ExecutionException. Additional tasks are waiting in a queue. If any thread terminates due to failure during execution, it will be replaced by a new one.
If you have any doubt or any suggestions to make please drop a comment. Exception: Client stack trace at com. There is one small difference between the Callable and Runnable interface though. It makes sense because thread dumps show classes and method names, not parameters and local variables. Still, programmers should be careful to avoid some common mistakes.
Its key methods are schedule , scheduleAtFixedRate and scheduleWithFixedDelay. Note that a completed task could have terminated either normally or by throwing an exception. If that time expires, the execution is stopped immediately: executorService. If additional tasks are submitted when all threads are active, they will wait in the queue until a thread becomes available. To support an immediate shutdown, tasks should handle interrupts correctly.
A thread-pool that is too large will cause unnecessary overhead just to create threads which mostly will be in the waiting mode. When the task is submitted via ExecutorService. If the order of the returned values needed to be preserved, a List could be used instead. There are no guarantees beyond best-effort attempts to stop processing actively executing tasks. We stop as soon as task was picked up and begins execution.
The task simply prints the thread name and terminates. This hook can be overridden to release resources acquired by the thread pool, much like a finally block. Conclusion Even despite the relative simplicity of ExecutorService, there are a few common pitfalls. And isCancelled is for cancellation. If you run the above program, you will notice that the program never exits, because, the executor service keeps listening for new tasks until we shut it down explicitly.
To give more information: in the case of the ExecutorService implementation, the core implementation being returned by the call to Executors. It can take both runnable and callable. Upon normal or exceptional return, tasks that have not completed are cancelled. For a task that was submitted with submit and that terminates with an exception, the Future. Instead of creating new threads when new tasks arrive, a thread pool keeps a number of idle threads that are ready for executing tasks as needed. Here is an example of cancelling a task by calling the Future. The Future's get method will return the task's result upon successful completion.