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
}}

Since:

1.5

Constructor Summary

Constructors

Constructor	Description
DiscardOldestPolicy()	Creates a DiscardOldestPolicy for the given executor.

Method Summary

Modifier and Type	Method	Description
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.

Methods declared in class Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Modifier and Type	Method	Description
protected Object	clone()	Answers a new instance of the same class as the receiver, whose slots have been filled in with the values in the slots of the receiver.
boolean	equals(Object o)	Compares the argument to the receiver, and answers true if they represent the same object using a class specific comparison.
protected void	finalize()	Deprecated, for removal: This API element is subject to removal in a future version. May cause performance issues, deadlocks and hangs.
final Class<? extends Object>	getClass()	Answers the unique instance of java.lang.Class which represents the class of the receiver.
int	hashCode()	Answers an integer hash code for the receiver.
final void	notify()	Causes one thread which is waiting on the receiver to be made ready to run.
final void	notifyAll()	Causes all threads which are waiting on the receiver to be made ready to run.
String	toString()	Answers a string containing a concise, human-readable description of the receiver.
final void	wait()	Causes the thread which sent this message to be made not ready to run pending some change in the receiver (as indicated by notify or notifyAll).
final void	wait(long time)	Causes the thread which sent this message to be made not ready to run either pending some change in the receiver (as indicated by notify or notifyAll) or the expiration of the timeout.
final void	wait(long time, int frac)	Causes the thread which sent this message to be made not ready to run either pending some change in the receiver (as indicated by notify or notifyAll) or the expiration of the timeout.

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