To keep things simple in this article, two primitive tasks will be used. Your callable waits for exactly 1 second, but if there was a little bit of random, you will probably notice that the get method, a blocking one, will slow down the execution in the for loop because some of the results are not ready yet. Upon termination, an executor has no tasks actively executing, no tasks awaiting execution, and no new tasks can be submitted. Obviously we can modify for better performance but if I will add too much implementation, we will loose focus on learning the Callable-Future usage. At any point, at most nThreads threads will be active processing tasks. Java ScheduledExecutorService interface ScheduledExecutorService interface extends ExecutorService interface and adds functionality to schedule commands to run after a given delay, or to execute periodically. Executors is a utility class that also provides useful methods to work with ExecutorService, ScheduledExecutorService, ThreadFactory, and Callable classes through various factory methods.
For example, the ThreadPoolExecutor class has a few constructors which can be used to configure an executor service and its internal pool. When a new task is submitted, the executor service picks one of the available threads from the pool and executes the task on that thread. In that case you should consider using scheduleWithFixedDelay instead. To find the best method for your needs, consult. The majority of concepts shown in this article also work in older versions of Java. Also notice that there are only 10 threads executing these tasks. The awaitTermination method is typically called after calling shutdown or shutdownNow.
TimeUnit is a useful enum for working with units of time. If any further request comes to the servlet, it should add new task to queue and servlet method should return from there. The worker threads execute Runnable threads from the queue. Invoking this method does not return a Future, but returns the result of one of the Callable objects. There are isDone and isCancelled methods to find out the current status of associated Callable task.
ThreadPoolExecutor Example Executors class provide simple implementation of ExecutorService using ThreadPoolExecutor but ThreadPoolExecutor provides much more feature than that. Shutdown methods in ExecutorService You can shut down an ExecutorService which will cause it to reject new tasks. After this delay has elapsed the task will be executed concurrently. Output should also change accordingly like pool-1, pool-2 etc. It is up to the developer to decide what to do with these tasks. In some cases this is very helpful; for example, if an app needs to process tasks which appear on an irregular basis or the quantity of these tasks is not known at compile time.
If one of the tasks complete or throws an exception , the rest of the Callable's are cancelled. It starts the execution of the given task after the specified delay and then executes it periodically on an interval specified by the period value. Executor gives the opportunity how we want to decouple the submitted task. If all n threads are busy performing the task and additional tasks are submitted, then they will have to be in the queue until a thread is available. In large scale applications it is better to separate the thread creation and thread management from the business logic.
These methods can block the whole application execution if not returned in small time. Which means that a newFixedThreadPool can be reconfigured later in the program by: ThreadPoolExecutor fixedThreadPool. The view name for the model is set to the specified view name. Now the future is finally done and we see the following result on the console: future done? Parameters: tasks - the collection of tasks timeout - the maximum time to wait unit - the time unit of the timeout argument Returns: a list of Futures representing the tasks, in the same sequential order as produced by the iterator for the given task list. Once the thread has delegated the task to the ExecutorService, the thread continues its own execution independent of the execution of that task. I so much appreciate your solutions, Pankaj.
Using pooled threads minimizes the overhead due to thread creation. This java program creates an ExecutorService with a pool size of two, then it submits five threads to it. This number controls the max number of worker threads that the underlying Netty library will use. Upon return, tasks that have not completed are cancelled. Executing Task2 inside : pool-1-thread-2 Executing Task1 inside : pool-1-thread-1 Executing Task3 inside : pool-1-thread-1 In the example above, we created an executor service with a fixed thread pool of size 2.
The above program executes the task after 5 seconds from the time of submission. A fixed thread pool is a very common type of thread pool that is frequently used in multi-threaded applications. If executorservice execute method has already one thread running, then it should add it to queue. The Java ExecutorService interface, java. This factory method is part of Java 8 and returns an executor of type ForkJoinPool which works slightly different than normal executors. We already saw an example of a thread pool in the previous section called a fixed thread-pool. This is not always the right decision, however.