Added in API level 1

ExecutorCompletionService

open class ExecutorCompletionService<V : Any!> : CompletionService<V>
kotlin.Any
   ↳ java.util.concurrent.ExecutorCompletionService

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:

<code>void solve(Executor e,
             Collection&lt;Callable&lt;Result&gt;&gt; solvers)
      throws InterruptedException, ExecutionException {
    CompletionService&lt;Result&gt; cs
        = new ExecutorCompletionService&lt;&gt;(e);
    solvers.forEach(cs::submit);
    for (int i = solvers.size(); i &gt; 0; i--) {
      Result r = cs.take().get();
      if (r != null)
        use(r);
    }
  }</code>
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:
<code>void solve(Executor e,
             Collection&lt;Callable&lt;Result&gt;&gt; solvers)
      throws InterruptedException {
    CompletionService&lt;Result&gt; cs
        = new ExecutorCompletionService&lt;&gt;(e);
    int n = solvers.size();
    List&lt;Future&lt;Result&gt;&gt; futures = new ArrayList&lt;&gt;(n);
    Result result = null;
    try {
      solvers.forEach(solver -&gt; futures.add(cs.submit(solver)));
      for (int i = n; i &gt; 0; i--) {
        try {
          Result r = cs.take().get();
          if (r != null) {
            result = r;
            break;
          }
        } catch (ExecutionException ignore) {}
      }
    } finally {
      futures.forEach(future -&gt; future.cancel(true));
    }
 
    if (result != null)
      use(result);
  }</code>

Summary

Public constructors

Creates an ExecutorCompletionService using the supplied executor for base task execution and a LinkedBlockingQueue as a completion queue.

ExecutorCompletionService(executor: Executor!, completionQueue: BlockingQueue<Future<V>!>!)

Creates an ExecutorCompletionService using the supplied executor for base task execution and the supplied queue as its completion queue.

Public methods
open Future<V>!

open Future<V>!
poll(timeout: Long, unit: TimeUnit!)

open Future<V>!
submit(task: Callable<V>!)

open Future<V>!
submit(task: Runnable!, result: V)

open Future<V>!

Public constructors

ExecutorCompletionService

Added in API level 1
ExecutorCompletionService(executor: Executor!)

Creates an ExecutorCompletionService using the supplied executor for base task execution and a LinkedBlockingQueue as a completion queue.

Parameters
executor Executor!: the executor to use
Exceptions
java.lang.NullPointerException if executor is null

ExecutorCompletionService

Added in API level 1
ExecutorCompletionService(
    executor: Executor!,
    completionQueue: BlockingQueue<Future<V>!>!)

Creates an ExecutorCompletionService using the supplied executor for base task execution and the supplied queue as its completion queue.

Parameters
executor Executor!: the executor to use
completionQueue BlockingQueue<Future<V>!>!: 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.
Exceptions
java.lang.NullPointerException if executor or completionQueue are null

Public methods

poll

Added in API level 1
open fun poll(): Future<V>!
Return
Future<V>! the Future representing the next completed task, or null if none are present

poll

Added in API level 1
open fun poll(
    timeout: Long,
    unit: TimeUnit!
): Future<V>!
Parameters
timeout Long: how long to wait before giving up, in units of unit
unit TimeUnit!: a TimeUnit determining how to interpret the timeout parameter
Return
Future<V>! the Future representing the next completed task or null if the specified waiting time elapses before one is present
Exceptions
java.lang.InterruptedException if interrupted while waiting

submit

Added in API level 1
open fun submit(task: Callable<V>!): Future<V>!
Parameters
task Callable<V>!: the task to submit
Return
Future<V>! a Future representing pending completion of the task
Exceptions
java.util.concurrent.RejectedExecutionException if the task cannot be scheduled for execution
java.lang.NullPointerException if the task is null

submit

Added in API level 1
open fun submit(
    task: Runnable!,
    result: V
): Future<V>!
Parameters
task Runnable!: the task to submit
result V: the result to return upon successful completion
Return
Future<V>! a Future representing pending completion of the task, and whose get() method will return the given result value upon completion
Exceptions
java.util.concurrent.RejectedExecutionException if the task cannot be scheduled for execution
java.lang.NullPointerException if the task is null

take

Added in API level 1
open fun take(): Future<V>!
Return
Future<V>! the Future representing the next completed task
Exceptions
java.lang.InterruptedException if interrupted while waiting