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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 IO, 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.
Method Summary | |
Future |
poll()
Retrieves and removes the Future representing the next completed task or null if none are present. |
Future |
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. |
Future |
submit(Callable task)
Submits a value-returning task for execution and returns a Future representing the pending results of the task. |
Future |
submit(java.lang.Runnable task,
java.lang.Object result)
Submits a Runnable task for execution and returns a Future representing that task.Upon completion, this task may be taken or polled. |
Future |
take()
Retrieves and removes the Future representing the next completed task, waiting if none are yet present. |
Method Detail |
public Future submit(Callable task)
task
- the task to submit
RejectedExecutionException
- if task cannot be scheduled
for execution
java.lang.NullPointerException
- if task nullpublic Future submit(java.lang.Runnable task, java.lang.Object result)
task
- the task to submitresult
- the result to return upon successful completion
RejectedExecutionException
- if task cannot be scheduled
for execution
java.lang.NullPointerException
- if task nullpublic Future take() throws java.lang.InterruptedException
java.lang.InterruptedException
- if interrupted while waiting.public Future poll()
public Future poll(long timeout, TimeUnit unit) throws java.lang.InterruptedException
timeout
- how long to wait before giving up, in units of
unitunit
- a TimeUnit determining how to interpret the
timeout parameter
java.lang.InterruptedException
- if interrupted while waiting.
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