private static <T> Future<T> getFuture(final Callable<T> callable) {
        FutureTask<T> future = new FutureTask<>(callable);
        try {
            executorMain.execute(future);
        } catch (RejectedExecutionException e) {
            future.run();
        }
        return future;
    }
Performs an async processing. Note that the given request cannot be simultaneously
used in multiple such processings - a clone must be created for each.
container-core/src/main/java/com/yahoo/processing/execution/AsyncExecution.java