DiscardOldestPolicy

A handler for rejected tasks that discards the oldest unhandled request and then retries execute, unless the executor is shut down, in which case the task is discarded. This policy is rarely useful in cases where other threads may be waiting for tasks to terminate, or failures must be recorded. Instead consider using a handler of the form:

 `new RejectedExecutionHandler() {
public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
Runnable dropped = e.getQueue().poll();
if (dropped instanceof Future<>) {
((Future<>)dropped).cancel(false);
// also consider logging the failure
}
e.execute(r);  // retry
}}`