ExecutorCompletionService Class

Definition

[Android.Runtime.Register("java/util/concurrent/ExecutorCompletionService", DoNotGenerateAcw=true)]
[Java.Interop.JavaTypeParameters(new System.String[] { "V" })]
public class ExecutorCompletionService : Java.Lang.Object, IDisposable, Java.Interop.IJavaPeerable, Java.Util.Concurrent.ICompletionService

[<Android.Runtime.Register("java/util/concurrent/ExecutorCompletionService", DoNotGenerateAcw=true)>]
[<Java.Interop.JavaTypeParameters(new System.String[] { "V" })>]
type ExecutorCompletionService = class
    inherit Object
    interface ICompletionService
    interface IJavaObject
    interface IDisposable
    interface IJavaPeerable

Inheritance

Object

Object

ExecutorCompletionService

Attributes

RegisterAttribute JavaTypeParametersAttribute

Implements

IJavaObject IJavaPeerable ICompletionService IDisposable

Remarks

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.

<b>Usage Examples.</b>

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<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:

{@code
            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);
            }}

Added in 1.5.

Java documentation for java.util.concurrent.ExecutorCompletionService.

Portions of this page are modifications based on work created and shared by the Android Open Source Project and used according to terms described in the Creative Commons 2.5 Attribution License.