Module java.base
Package java.util.concurrent

Class ThreadPoolExecutor.DiscardOldestPolicy

java.lang.Object
java.util.concurrent.ThreadPoolExecutor.DiscardOldestPolicy
All Implemented Interfaces:
RejectedExecutionHandler
Enclosing class:
ThreadPoolExecutor
public static class ThreadPoolExecutor.DiscardOldestPolicy extends Object implements RejectedExecutionHandler
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
 }}

  • Constructor Details

    • DiscardOldestPolicy

      public DiscardOldestPolicy()
      Creates a DiscardOldestPolicy for the given executor.

  • Method Details

    • rejectedExecution

      public void rejectedExecution(Runnable r, ThreadPoolExecutor e)
      Obtains and ignores the next task that the executor would otherwise execute, if one is immediately available, and then retries execution of task r, unless the executor is shut down, in which case task r is instead discarded.
      Specified by:
      rejectedExecution in interface RejectedExecutionHandler
      Parameters:
      r - the runnable task requested to be executed
      e - the executor attempting to execute this task