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ThreadPoolExecutor.DiscardOldestPolicy
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
}}
Summary
Public constructors |
DiscardOldestPolicy()
Creates a DiscardOldestPolicy for the given executor.
|
Public methods |
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.
|
Inherited methods |
From class
java.lang.Object
Object
|
clone()
Creates and returns a copy of this object.
|
boolean
|
equals(Object obj)
Indicates whether some other object is "equal to" this one.
|
void
|
finalize()
Called by the garbage collector on an object when garbage collection
determines that there are no more references to the object.
|
final
Class<?>
|
getClass()
Returns the runtime class of this Object .
|
int
|
hashCode()
Returns a hash code value for the object.
|
final
void
|
notify()
Wakes up a single thread that is waiting on this object's
monitor.
|
final
void
|
notifyAll()
Wakes up all threads that are waiting on this object's monitor.
|
String
|
toString()
Returns a string representation of the object.
|
final
void
|
wait(long timeoutMillis, int nanos)
Causes the current thread to wait until it is awakened, typically
by being notified or interrupted, or until a
certain amount of real time has elapsed.
|
final
void
|
wait(long timeoutMillis)
Causes the current thread to wait until it is awakened, typically
by being notified or interrupted, or until a
certain amount of real time has elapsed.
|
final
void
|
wait()
Causes the current thread to wait until it is awakened, typically
by being notified or interrupted.
|
|
|
Public constructors
DiscardOldestPolicy
public DiscardOldestPolicy ()
Creates a DiscardOldestPolicy
for the given executor.
Public methods
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.
Parameters |
r |
Runnable : the runnable task requested to be executed |
e |
ThreadPoolExecutor : the executor attempting to execute this task |
Content and code samples on this page are subject to the licenses described in the Content License. Java and OpenJDK are trademarks or registered trademarks of Oracle and/or its affiliates.
Last updated 2025-02-10 UTC.
[null,null,["Last updated 2025-02-10 UTC."],[],[],null,["# ThreadPoolExecutor.DiscardOldestPolicy\n\nAdded in [API level 1](/guide/topics/manifest/uses-sdk-element#ApiLevels) \nSummary: [Ctors](#pubctors) \\| [Methods](#pubmethods) \\| [Inherited Methods](#inhmethods) \n\nThreadPoolExecutor.DiscardOldestPolicy\n======================================\n\n\n`\npublic\nstatic\n\n\nclass\nThreadPoolExecutor.DiscardOldestPolicy\n`\n\n\n`\n\nextends `[Object](/reference/java/lang/Object)`\n\n\n`\n\n`\n\n\nimplements\n\n`[RejectedExecutionHandler](/reference/java/util/concurrent/RejectedExecutionHandler)`\n\n\n`\n\n|---|-------------------------------------------------------------|\n| [java.lang.Object](/reference/java/lang/Object) ||\n| ↳ | java.util.concurrent.ThreadPoolExecutor.DiscardOldestPolicy |\n\n\u003cbr /\u003e\n\n*** ** * ** ***\n\nA handler for rejected tasks that discards the oldest unhandled\nrequest and then retries `execute`, unless the executor\nis shut down, in which case the task is discarded. This policy is\nrarely useful in cases where other threads may be waiting for\ntasks to terminate, or failures must be recorded. Instead consider\nusing a handler of the form: \n\n new RejectedExecutionHandler() {\n public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {\n Runnable dropped = e.getQueue().poll();\n if (dropped instanceof Future\u003c?\u003e) {\n ((Future\u003c?\u003e)dropped).cancel(false);\n // also consider logging the failure\n }\n e.execute(r); // retry\n }}\n\n\u003cbr /\u003e\n\nSummary\n-------\n\n| ### Public constructors ||\n|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---|\n| ` `[DiscardOldestPolicy](/reference/java/util/concurrent/ThreadPoolExecutor.DiscardOldestPolicy#DiscardOldestPolicy())`() ` Creates a `DiscardOldestPolicy` for the given executor. |\n\n| ### Public methods ||\n|---------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|\n| ` void` | ` `[rejectedExecution](/reference/java/util/concurrent/ThreadPoolExecutor.DiscardOldestPolicy#rejectedExecution(java.lang.Runnable,%20java.util.concurrent.ThreadPoolExecutor))`(`[Runnable](/reference/java/lang/Runnable)` r, `[ThreadPoolExecutor](/reference/java/util/concurrent/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. |\n\n| ### Inherited methods |\n|-----------------------|---|\n| From class ` `[java.lang.Object](/reference/java/lang/Object)` ` |---------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | ` `[Object](/reference/java/lang/Object) | ` `[clone](/reference/java/lang/Object#clone())`() ` Creates and returns a copy of this object. | | ` boolean` | ` `[equals](/reference/java/lang/Object#equals(java.lang.Object))`(`[Object](/reference/java/lang/Object)` obj) ` Indicates whether some other object is \"equal to\" this one. | | ` void` | ` `[finalize](/reference/java/lang/Object#finalize())`() ` Called by the garbage collector on an object when garbage collection determines that there are no more references to the object. | | ` final `[Class](/reference/java/lang/Class)`\u003c?\u003e` | ` `[getClass](/reference/java/lang/Object#getClass())`() ` Returns the runtime class of this `Object`. | | ` int` | ` `[hashCode](/reference/java/lang/Object#hashCode())`() ` Returns a hash code value for the object. | | ` final void` | ` `[notify](/reference/java/lang/Object#notify())`() ` Wakes up a single thread that is waiting on this object's monitor. | | ` final void` | ` `[notifyAll](/reference/java/lang/Object#notifyAll())`() ` Wakes up all threads that are waiting on this object's monitor. | | ` `[String](/reference/java/lang/String) | ` `[toString](/reference/java/lang/Object#toString())`() ` Returns a string representation of the object. | | ` final void` | ` `[wait](/reference/java/lang/Object#wait(long,%20int))`(long timeoutMillis, int nanos) ` Causes the current thread to wait until it is awakened, typically by being *notified* or *interrupted*, or until a certain amount of real time has elapsed. | | ` final void` | ` `[wait](/reference/java/lang/Object#wait(long))`(long timeoutMillis) ` Causes the current thread to wait until it is awakened, typically by being *notified* or *interrupted*, or until a certain amount of real time has elapsed. | | ` final void` | ` `[wait](/reference/java/lang/Object#wait())`() ` Causes the current thread to wait until it is awakened, typically by being *notified* or *interrupted*. | ||\n| From interface ` `[java.util.concurrent.RejectedExecutionHandler](/reference/java/util/concurrent/RejectedExecutionHandler)` ` |------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | ` abstract void` | ` `[rejectedExecution](/reference/java/util/concurrent/RejectedExecutionHandler#rejectedExecution(java.lang.Runnable,%20java.util.concurrent.ThreadPoolExecutor))`(`[Runnable](/reference/java/lang/Runnable)` r, `[ThreadPoolExecutor](/reference/java/util/concurrent/ThreadPoolExecutor)` executor) ` Method that may be invoked by a [ThreadPoolExecutor](/reference/java/util/concurrent/ThreadPoolExecutor) when [execute](/reference/java/util/concurrent/ThreadPoolExecutor#execute(java.lang.Runnable)) cannot accept a task. | ||\n\nPublic constructors\n-------------------\n\n### DiscardOldestPolicy\n\nAdded in [API level 1](/guide/topics/manifest/uses-sdk-element#ApiLevels) \n\n```\npublic DiscardOldestPolicy ()\n```\n\nCreates a `DiscardOldestPolicy` for the given executor.\n\n\u003cbr /\u003e\n\nPublic methods\n--------------\n\n### rejectedExecution\n\nAdded in [API level 1](/guide/topics/manifest/uses-sdk-element#ApiLevels) \n\n```\npublic void rejectedExecution (Runnable r, \n ThreadPoolExecutor e)\n```\n\nObtains and ignores the next task that the executor\nwould otherwise execute, if one is immediately available,\nand then retries execution of task r, unless the executor\nis shut down, in which case task r is instead discarded.\n\n\u003cbr /\u003e\n\n| Parameters ||\n|-----|---------------------------------------------------------------------------|\n| `r` | `Runnable`: the runnable task requested to be executed \u003cbr /\u003e |\n| `e` | `ThreadPoolExecutor`: the executor attempting to execute this task \u003cbr /\u003e |"]]