Package Summary Overview Summary

### class:ExecutorCompletionService [NONE]
Type Parameters: `V` - the type of values the tasks of this service produce and consume All Implemented Interfaces: `CompletionService<V>` public class ExecutorCompletionService<V>extends Object implements CompletionService<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<Callable<Result>> solvers)
         throws InterruptedException, ExecutionException {
       CompletionService<Result> cs
           = new ExecutorCompletionService<>(e);
       solvers.forEach(cs::submit);
       for (int i = solvers.size(); i > 0; i--) {
         Result r = cs.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<Callable<Result>> solvers)
         throws InterruptedException {
       CompletionService<Result> cs
           = new ExecutorCompletionService<>(e);
       int n = solvers.size();
       List<Future<Result>> futures = new ArrayList<>(n);
       Result result = null;
       try {
         solvers.forEach(solver -> futures.add(cs.submit(solver)));
         for (int i = n; i > 0; i--) {
           try {
             Result r = cs.take().get();
             if (r != null) {
               result = r;
               break;
             }
           } catch (ExecutionException ignore) {}
         }
       } finally {
         futures.forEach(future -> future.cancel(true));
       }

       if (result != null)
         use(result);
     }
Since: 1.5

### constructor:ExecutorCompletionService(java.util.concurrent.Executor) [NONE]
### ExecutorCompletionService public ExecutorCompletionService (Executor executor) Creates an ExecutorCompletionService using the supplied executor for base task execution and a `LinkedBlockingQueue` as a completion queue. Parameters: `executor` - the executor to use Throws: `NullPointerException` - if executor is `null`

### constructor:ExecutorCompletionService(java.util.concurrent.Executor,java.util.concurrent.BlockingQueue) [NONE]
### ExecutorCompletionService public ExecutorCompletionService (Executor executor, BlockingQueue<Future<V>> completionQueue) Creates an ExecutorCompletionService using the supplied executor for base task execution and the supplied queue as its completion queue. Parameters: `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 tasks cause them not to be retrievable. Throws: `NullPointerException` - if executor or completionQueue are `null`

### method:submit(java.util.concurrent.Callable) [NONE]
### submit public Future<V> submit (Callable<V> task) Description copied from interface: `CompletionService` 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. Specified by: `submit` in interface `CompletionService<V>` 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 Future<V> submit (Runnable task, V result) Description copied from interface: `CompletionService` Submits a Runnable task for execution and returns a Future representing that task. Upon completion, this task may be taken or polled. Specified by: `submit` in interface `CompletionService<V>` 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

### method:take() [NONE]
### take public Future<V> take() throws InterruptedException Description copied from interface: `CompletionService` Retrieves and removes the Future representing the next completed task, waiting if none are yet present. Specified by: `take` in interface `CompletionService<V>` Returns: the Future representing the next completed task Throws: `InterruptedException` - if interrupted while waiting

### method:poll() [NONE]
### poll public Future<V> poll() Description copied from interface: `CompletionService` Retrieves and removes the Future representing the next completed task, or `null` if none are present. Specified by: `poll` in interface `CompletionService<V>` Returns: the Future representing the next completed task, or `null` if none are present

### method:poll(long,java.util.concurrent.TimeUnit) [NONE]
### poll public Future<V> poll (long timeout, TimeUnit unit) throws InterruptedException Description copied from interface: `CompletionService` Retrieves and removes the Future representing the next completed task, waiting if necessary up to the specified wait time if none are yet present. Specified by: `poll` in interface `CompletionService<V>` 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 `null` if the specified waiting time elapses before one is present Throws: `InterruptedException` - if interrupted while waiting