java.util.concurrent

## Class AbstractExecutorService

- java.lang.Object
- - java.util.concurrent.AbstractExecutorService

- All Implemented Interfaces:
    Executor, ExecutorService
  Direct Known Subclasses:
    ForkJoinPool, ThreadPoolExecutor

      public abstract class AbstractExecutorService
      extends Object
      implements ExecutorService

  Provides default implementations of `ExecutorService` execution methods. This class implements the `submit`, `invokeAny` and `invokeAll` methods using a `RunnableFuture` returned by `newTaskFor`, which defaults to the `FutureTask` class provided in this package. For example, the implementation of `submit(Runnable)` creates an associated `RunnableFuture` that is executed and returned. Subclasses may override the `newTaskFor` methods to return `RunnableFuture` implementations other than `FutureTask`.

  Extension example. Here is a sketch of a class that customizes `ThreadPoolExecutor` to use a `CustomTask` class instead of the default `FutureTask`:

       public class CustomThreadPoolExecutor extends ThreadPoolExecutor {

         static class CustomTask<V> implements RunnableFuture<V> {...}

         protected <V> RunnableFuture<V> newTaskFor(Callable<V> c) {
             return new CustomTask<V>(c);
         }
         protected <V> RunnableFuture<V> newTaskFor(Runnable r, V v) {
             return new CustomTask<V>(r, v);
         }
         // ... add constructors, etc.
       }

  Since:
    1.5
  Author:
    Doug Lea

- - ### Constructor Summary

    Constructors
    Constructor and Description
    `AbstractExecutorService()`

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `<T> List<Future<T>>` | `invokeAll(Collection<? extends Callable<T>> tasks)` Executes the given tasks, returning a list of Futures holding their status and results when all complete.
    `<T> List<Future<T>>` | `invokeAll(Collection<? extends Callable<T>> tasks, long timeout, TimeUnit unit)` Executes the given tasks, returning a list of Futures holding their status and results when all complete or the timeout expires, whichever happens first.
    `<T> T` | `invokeAny(Collection<? extends Callable<T>> tasks)` Executes the given tasks, returning the result of one that has completed successfully (i.e., without throwing an exception), if any do.
    `<T> T` | `invokeAny(Collection<? extends Callable<T>> tasks, long timeout, TimeUnit unit)` Executes the given tasks, returning the result of one that has completed successfully (i.e., without throwing an exception), if any do before the given timeout elapses.
    `protected <T> RunnableFuture<T>` | `newTaskFor(Callable<T> callable)` Returns a `RunnableFuture` for the given callable task.
    `protected <T> RunnableFuture<T>` | `newTaskFor(Runnable runnable, T value)` Returns a `RunnableFuture` for the given runnable and default value.
    `<T> Future<T>` | `submit(Callable<T> task)` Submits a value-returning task for execution and returns a Future representing the pending results of the task.
    `Future<?>` | `submit(Runnable task)` Submits a Runnable task for execution and returns a Future representing that task.
    `<T> Future<T>` | `submit(Runnable task, T result)` Submits a Runnable task for execution and returns a Future representing that task.

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

    - ### Methods inherited from interface java.util.concurrent.ExecutorService

      `awaitTermination, isShutdown, isTerminated, shutdown, shutdownNow`

    - ### Methods inherited from interface java.util.concurrent.Executor

      `execute`

- - ### Constructor Detail

    - #### AbstractExecutorService

          public AbstractExecutorService()

  - ### Method Detail

    - #### newTaskFor

          protected <T> RunnableFuture<T> newTaskFor(Runnable runnable,
                                                     T value)

      Returns a `RunnableFuture` for the given runnable and default value.
      Parameters:
        `runnable` - the runnable task being wrapped
        `value` - the default value for the returned future
      Returns:
        a `RunnableFuture` which when run will run the underlying runnable and which, as a `Future`, will yield the given value as its result and provide for cancellation of the underlying task.
      Since:
        1.6

    - #### newTaskFor

          protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable)

      Returns a `RunnableFuture` for the given callable task.
      Parameters:
        `callable` - the callable task being wrapped
      Returns:
        a `RunnableFuture` which when run will call the underlying callable and which, as a `Future`, will yield the callable's result as its result and provide for cancellation of the underlying task.
      Since:
        1.6

    - #### submit

          public Future<?> submit(Runnable task)

      Description copied from interface: `ExecutorService`
      Submits a Runnable task for execution and returns a Future representing that task. The Future's `get` method will return `null` upon successful completion.
      Specified by:
        `submit` in interface `ExecutorService`
      Parameters:
        `task` - the task to submit
      Returns:
        a Future representing pending completion of the task
      Throws:
        `RejectedExecutionException` - if the task cannot be scheduled for execution
        `NullPointerException` - if the task is null

    - #### submit

          public <T> Future<T> submit(Runnable task,
                                      T result)

      Description copied from interface: `ExecutorService`
      Submits a Runnable task for execution and returns a Future representing that task. The Future's `get` method will return the given result upon successful completion.
      Specified by:
        `submit` in interface `ExecutorService`
      Parameters:
        `task` - the task to submit
        `result` - the result to return
      Returns:
        a Future representing pending completion of the task
      Throws:
        `RejectedExecutionException` - if the task cannot be scheduled for execution
        `NullPointerException` - if the task is null

    - #### submit

          public <T> Future<T> submit(Callable<T> task)

      Description copied from interface: `ExecutorService`
      Submits a value-returning task for execution and returns a Future representing the pending results of the task. The Future's `get` method will return the task's result upon successful completion.

      If you would like to immediately block waiting for a task, you can use constructions of the form `result = exec.submit(aCallable).get();`

      Note: The `Executors` class includes a set of methods that can convert some other common closure-like objects, for example, `PrivilegedAction` to `Callable` form so they can be submitted.

      Specified by:
        `submit` in interface `ExecutorService`
      Parameters:
        `task` - the task to submit
      Returns:
        a Future representing pending completion of the task
      Throws:
        `RejectedExecutionException` - if the task cannot be scheduled for execution
        `NullPointerException` - if the task is null

    - #### invokeAny

          public <T> T invokeAny(Collection<? extends Callable<T>> tasks)
                          throws InterruptedException,
                                 ExecutionException

      Description copied from interface: `ExecutorService`
      Executes the given tasks, returning the result of one that has completed successfully (i.e., without throwing an exception), if any do. Upon normal or exceptional return, tasks that have not completed are cancelled. The results of this method are undefined if the given collection is modified while this operation is in progress.
      Specified by:
        `invokeAny` in interface `ExecutorService`
      Parameters:
        `tasks` - the collection of tasks
      Returns:
        the result returned by one of the tasks
      Throws:
        `InterruptedException` - if interrupted while waiting
        `ExecutionException` - if no task successfully completes

    - #### invokeAny

          public <T> T invokeAny(Collection<? extends Callable<T>> tasks,
                                 long timeout,
                                 TimeUnit unit)
                          throws InterruptedException,
                                 ExecutionException,
                                 TimeoutException

      Description copied from interface: `ExecutorService`
      Executes the given tasks, returning the result of one that has completed successfully (i.e., without throwing an exception), if any do before the given timeout elapses. Upon normal or exceptional return, tasks that have not completed are cancelled. The results of this method are undefined if the given collection is modified while this operation is in progress.
      Specified by:
        `invokeAny` in interface `ExecutorService`
      Parameters:
        `tasks` - the collection of tasks
        `timeout` - the maximum time to wait
        `unit` - the time unit of the timeout argument
      Returns:
        the result returned by one of the tasks.
      Throws:
        `InterruptedException` - if interrupted while waiting
        `ExecutionException` - if no task successfully completes
        `TimeoutException` - if the given timeout elapses before any task successfully completes

    - #### invokeAll

          public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks)
                                        throws InterruptedException

      Description copied from interface: `ExecutorService`
      Executes the given tasks, returning a list of Futures holding their status and results when all complete. `Future.isDone()` is `true` for each element of the returned list. Note that a completed task could have terminated either normally or by throwing an exception. The results of this method are undefined if the given collection is modified while this operation is in progress.
      Specified by:
        `invokeAll` in interface `ExecutorService`
      Parameters:
        `tasks` - the collection of tasks
      Returns:
        A list of Futures representing the tasks, in the same sequential order as produced by the iterator for the given task list, each of which has completed.
      Throws:
        `InterruptedException` - if interrupted while waiting, in which case unfinished tasks are cancelled.

    - #### invokeAll

          public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks,
                                               long timeout,
                                               TimeUnit unit)
                                        throws InterruptedException

      Description copied from interface: `ExecutorService`
      Executes the given tasks, returning a list of Futures holding their status and results when all complete or the timeout expires, whichever happens first. `Future.isDone()` is `true` for each element of the returned list. Upon return, tasks that have not completed are cancelled. Note that a completed task could have terminated either normally or by throwing an exception. The results of this method are undefined if the given collection is modified while this operation is in progress.
      Specified by:
        `invokeAll` in interface `ExecutorService`
      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. If the operation did not time out, each task will have completed. If it did time out, some of these tasks will not have completed.
      Throws:
        `InterruptedException` - if interrupted while waiting, in which case unfinished tasks are cancelled

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