/**@class java.util.concurrent.ExecutorCompletionService implements java.util.concurrent.CompletionService @extends java.lang.Object A {@link java.util.concurrent.CompletionService} that uses a supplied {@link java.util.concurrent.Executor} to execute tasks. This class arranges that submitted tasks are, upon completion, placed on a queue accessible using {@code take}. The class is lightweight enough to be suitable for transient use when processing groups of tasks. <p> <b>Usage Examples.</b> Suppose you have a set of solvers for a certain problem, each returning a value of some type {@code Result}, and would like to run them concurrently, processing the results of each of them that return a non-null value, in some method {@code use(Result r)}. You could write this as: <pre> {@code void solve(Executor e, Collection<Callable<Result>> solvers) throws InterruptedException, ExecutionException { CompletionService<Result> ecs = new ExecutorCompletionService<Result>(e); for (Callable<Result> 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); } }}</pre> 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: <pre> {@code void solve(Executor e, Collection<Callable<Result>> solvers) throws InterruptedException { CompletionService<Result> ecs = new ExecutorCompletionService<Result>(e); int n = solvers.size(); List<Future<Result>> futures = new ArrayList<>(n); Result result = null; try { for (Callable<Result> 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; } } catch (ExecutionException ignore) {} } } finally { for (Future<Result> f : futures) f.cancel(true); } if (result != null) use(result); }}</pre> */ var ExecutorCompletionService = { /** */ submit : function( ) {}, /** */ submit : function( ) {}, /** */ take : function( ) {}, /** */ poll : function( ) {}, /** */ poll : function( ) {}, };