java.lang.Object | |
↳ | java.util.concurrent.ExecutorCompletionService<V> |
A CompletionService
that uses a supplied Executor
to execute tasks. This class arranges that submitted tasks are,
upon completion, placed on a queue accessible using take
.
The class is lightweight enough to be suitable for transient use
when processing groups of tasks.
Usage Examples.
Suppose you have a set of solvers for a certain problem, each
returning a value of some type Result
, and would like to
run them concurrently, processing the results of each of them that
return a non-null value, in some method use(Result r)
. You
could write this as:
void solve(Executor e,
Collection> solvers)
throws InterruptedException, ExecutionException {
CompletionService ecs
= new ExecutorCompletionService(e);
for (Callable s : solvers)
ecs.submit(s);
int n = solvers.size();
for (int i = 0; i < n; ++i) {
Result r = ecs.take().get();
if (r != null)
use(r);
}}
Suppose instead that you would like to use the first non-null result
of the set of tasks, ignoring any that encounter exceptions,
and cancelling all other tasks when the first one is ready:
void solve(Executor e, Collection
} catch (ExecutionException ignore) {} } } finally { for (Future> solvers) throws InterruptedException { CompletionService ecs = new ExecutorCompletionService (e); int n = solvers.size(); List > futures = new ArrayList >(n); Result result = null; try { for (Callable s : solvers) futures.add(ecs.submit(s)); for (int i = 0; i < n; ++i) { try { Result r = ecs.take().get(); if (r != null) { result = r; break; f : futures) f.cancel(true); } if (result != null) use(result); }}
Public Constructors | |||||||||||
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Creates an ExecutorCompletionService using the supplied
executor for base task execution and a
LinkedBlockingQueue as a completion queue. | |||||||||||
Creates an ExecutorCompletionService using the supplied
executor for base task execution and the supplied queue as its
completion queue.
|
Public Methods | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Retrieves and removes the Future representing the next
completed task, or
null if none are present. | |||||||||||
Retrieves and removes the Future representing the next
completed task, waiting if necessary up to the specified wait
time if none are yet present.
| |||||||||||
Submits a value-returning task for execution and returns a Future
representing the pending results of the task.
| |||||||||||
Submits a Runnable task for execution and returns a Future
representing that task.
| |||||||||||
Retrieves and removes the Future representing the next
completed task, waiting if none are yet present.
|
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Inherited Methods | |||||||||||
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From class
java.lang.Object
| |||||||||||
From interface
java.util.concurrent.CompletionService
|
Creates an ExecutorCompletionService using the supplied
executor for base task execution and a
LinkedBlockingQueue
as a completion queue.
executor | the executor to use |
---|
NullPointerException | if executor is null
|
---|
Creates an ExecutorCompletionService using the supplied executor for base task execution and the supplied queue as its completion queue.
executor | the executor to use |
---|---|
completionQueue | the queue to use as the completion queue
normally one dedicated for use by this service. This
queue is treated as unbounded -- failed attempted
Queue.add operations for completed taskes cause
them not to be retrievable. |
NullPointerException | if executor or completionQueue are null
|
---|
Retrieves and removes the Future representing the next
completed task, or null
if none are present.
null
if none are present
Retrieves and removes the Future representing the next completed task, waiting if necessary up to the specified wait time if none are yet present.
timeout | how long to wait before giving up, in units of
unit |
---|---|
unit | a TimeUnit determining how to interpret the
timeout parameter |
null
if the specified waiting time elapses
before one is presentInterruptedException |
---|
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.
task | the task to submit |
---|
Submits a Runnable task for execution and returns a Future representing that task. Upon completion, this task may be taken or polled.
task | the task to submit |
---|---|
result | the result to return upon successful completion |
get()
method will return the given
result value upon completionRetrieves and removes the Future representing the next completed task, waiting if none are yet present.
InterruptedException |
---|