| Known Indirect Subclasses |
A service that decouples the production of new asynchronous tasks
from the consumption of the results of completed tasks. Producers
submit tasks for execution. Consumers take
completed tasks and process their results in the order they
complete. A CompletionService can for example be used to
manage asynchronous I/O, in which tasks that perform reads are
submitted in one part of a program or system, and then acted upon
in a different part of the program when the reads complete,
possibly in a different order than they were requested.
Typically, a CompletionService relies on a separate
Executor to actually execute the tasks, in which case the
CompletionService only manages an internal completion
queue. The ExecutorCompletionService class provides an
implementation of this approach.
Memory consistency effects: Actions in a thread prior to
submitting a task to a CompletionService
happen-before
actions taken by that task, which in turn happen-before
actions following a successful return from the corresponding take().
Public Method Summary
| abstract Future<V> | |
| abstract Future<V> |
poll()
Retrieves and removes the Future representing the next
completed task, or
null if none are present. |
| abstract Future<V> | |
| abstract Future<V> | |
| abstract Future<V> |
take()
Retrieves and removes the Future representing the next
completed task, waiting if none are yet present.
|
Public Methods
public abstract Future<V> poll (long timeout, TimeUnit unit)
Retrieves and removes the Future representing the next completed task, waiting if necessary up to the specified wait time if none are yet present.
Parameters
| timeout | how long to wait before giving up, in units of
unit |
|---|---|
| unit | a TimeUnit determining how to interpret the
timeout parameter |
Returns
- the Future representing the next completed task or
nullif the specified waiting time elapses before one is present
Throws
| InterruptedException | if interrupted while waiting |
|---|
public abstract Future<V> poll ()
Retrieves and removes the Future representing the next
completed task, or null if none are present.
Returns
- the Future representing the next completed task, or
nullif none are present
public abstract Future<V> submit (Runnable task, V result)
Submits a Runnable task for execution and returns a Future representing that task. Upon completion, this task may be taken or polled.
Parameters
| task | the task to submit |
|---|---|
| result | the result to return upon successful completion |
Returns
- a Future representing pending completion of the task,
and whose
get()method will return the given result value upon completion
Throws
| RejectedExecutionException | if the task cannot be scheduled for execution |
|---|---|
| NullPointerException | if the task is null |
public abstract Future<V> submit (Callable<V> task)
Submits a value-returning task for execution and returns a Future representing the pending results of the task. Upon completion, this task may be taken or polled.
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 |
public abstract Future<V> take ()
Retrieves and removes the Future representing the next completed task, waiting if none are yet present.
Returns
- the Future representing the next completed task
Throws
| InterruptedException | if interrupted while waiting |
|---|