BufferCleaner supports PhantomReference-based management of native memory referred to by Direct-XXX-Buffers. Unreferenced DBBs may be garbage collected, deactivating the associated PRefs and making them available for cleanup here. There is a configured limit to the amount of memory that may be allocated by DBBs. When that limit is reached, the allocator may invoke the garbage collector directly to attempt to trigger cleaning here, hopefully permitting the allocation to complete. Only if that doesn't free sufficient memory does the allocation fail. See java.nio.Bits::reserveMemory() for details. One of the requirements for that approach is having a way to determine that deactivated cleaners have been cleaned. java.lang.ref.Cleaner doesn't provide such a mechanism, and adding such a mechanism to that class to satisfy this unique requirement was deemed undesirable. Instead, this class uses the underlying primitives (PhantomReferences, ReferenceQueues) to provide the functionality needed for DBB management.

Nested and Inner Type Summary

Modifier and Type	Class and Description
pack-priv static class	BufferCleaner.CleanerList
private static class	BufferCleaner.CleaningRunnable
private static class	BufferCleaner.PhantomCleaner

Modifier and Type	Field and Description
private static final BufferCleaner.CleanerList	cleanerList
private static Thread	cleaningThread
private static final ReferenceQueue<Object>	queue

Access	Constructor and Description
private	BufferCleaner()

Modifier and Type	Method and Description
public static Cleaner	Returns: associated cleaner. register(Object object to track. obj, Runnable cleanup action for obj. action) Construct a new Cleaner for obj, with the associated action.
private static void	startCleaningThreadIfNeeded()
public static boolean	Returns: true if a cleaner was found and executed, false if there weren't any cleaners in the queue. tryCleaning() Try to do some cleaning.

cleanerList	back to summary
private static final BufferCleaner.CleanerList cleanerList

cleaningThread	back to summary
private static Thread cleaningThread

queue	back to summary
private static final ReferenceQueue<Object> queue

BufferCleaner	back to summary
private BufferCleaner()

Method Detail

register	back to summary
public static Cleaner register(Object obj, Runnable action) Construct a new Cleaner for obj, with the associated action. Parameters obj:Object object to track. action:Runnable cleanup action for obj. Returns:Cleaner associated cleaner.

back to summary

public static Cleaner register(Object obj, Runnable action)

Construct a new Cleaner for obj, with the associated action.

Parameters

obj:Object: object to track.
action:Runnable: cleanup action for obj.

Returns:Cleaner

associated cleaner.

startCleaningThreadIfNeeded	back to summary
private static void startCleaningThreadIfNeeded()

tryCleaning	back to summary
public static boolean tryCleaning() Try to do some cleaning. Takes a cleaner from the queue and executes it. Returns:boolean true if a cleaner was found and executed, false if there weren't any cleaners in the queue.

tryCleaning

back to summary

public static boolean tryCleaning()

Try to do some cleaning. Takes a cleaner from the queue and executes it.

Returns:boolean: true if a cleaner was found and executed, false if there weren't any cleaners in the queue.

java.nio back to summary

pack-priv final Class BufferCleaner.CleanerList

Class Inheritance

extends Object

java.lang.Object
java.nio.BufferCleaner.CleanerList

Nested and Inner Type Summary

Modifier and Type	Class and Description
pack-priv static class	BufferCleaner.CleanerList.Node Segment node.

Field Summary

Modifier and Type	Field and Description
private BufferCleaner.CleanerList.Node	cache Cached node instance to provide better behavior near NODE_CAPACITY threshold: if list size flips around NODE_CAPACITY, it would reuse the cached node instead of wasting and re-allocating a new node all the time.
private BufferCleaner.CleanerList.Node	head Head node.
pack-priv static final int	NODE_CAPACITY Capacity for a single node in the list.

Constructor Summary

Access	Constructor and Description
public	CleanerList()

Method Summary

Modifier and Type	Method and Description
public synchronized void	insert(BufferCleaner.PhantomCleaner phc) Insert this PhantomCleaner in the list.
public synchronized boolean	Returns: true if Cleaner was removed or false if not because it had already been removed before remove(BufferCleaner.PhantomCleaner phc) Remove this PhantomCleaner from the list.

Inherited from java.lang.Object:: clone equals finalize getClass hashCode notify notifyAll toString wait wait wait

Field Detail

cache	back to summary
private BufferCleaner.CleanerList.Node cache Cached node instance to provide better behavior near NODE_CAPACITY threshold: if list size flips around NODE_CAPACITY, it would reuse the cached node instead of wasting and re-allocating a new node all the time.

head	back to summary
private BufferCleaner.CleanerList.Node head Head node. This is the only node where PhantomCleanabls are added to or removed from. This is the only node with variable size, all other nodes linked from the head are always at full capacity.

NODE_CAPACITY	back to summary
pack-priv static final int NODE_CAPACITY Capacity for a single node in the list. This balances memory overheads vs locality vs GC walking costs.

Constructor Detail

CleanerList	back to summary
public CleanerList()

Method Detail

insert	back to summary
public synchronized void insert(BufferCleaner.PhantomCleaner phc) Insert this PhantomCleaner in the list.

remove	back to summary
public synchronized boolean remove(BufferCleaner.PhantomCleaner phc) Remove this PhantomCleaner from the list. Returns:boolean true if Cleaner was removed or false if not because it had already been removed before

remove

back to summary

public synchronized boolean remove(BufferCleaner.PhantomCleaner phc)

Remove this PhantomCleaner from the list.

Returns:boolean: true if Cleaner was removed or false if not because it had already been removed before

java.nio back to summary

pack-priv Class BufferCleaner.CleanerList.Node

Class Inheritance

extends Object

java.lang.Object
java.nio.BufferCleaner.CleanerList.Node

Segment node.

Field Summary

Modifier and Type	Field and Description
pack-priv final BufferCleaner.PhantomCleaner[]	arr
pack-priv BufferCleaner.CleanerList.Node	next
pack-priv int	size

Constructor Summary

Access	Constructor and Description
pack-priv	Node()

Method Summary

Inherited from java.lang.Object:: clone equals finalize getClass hashCode notify notifyAll toString wait wait wait

Field Detail

arr	back to summary
pack-priv final BufferCleaner.PhantomCleaner[] arr

next	back to summary
pack-priv BufferCleaner.CleanerList.Node next

size	back to summary
pack-priv int size

Constructor Detail

Node	back to summary
pack-priv Node()

java.nio back to summary

private final Class BufferCleaner.CleaningRunnable

Class Inheritance

extends Object
implements Runnable

java.lang.Object
java.nio.BufferCleaner.CleaningRunnable

All Implemented Interfaces

java.lang.Runnable

Constructor Summary

Access	Constructor and Description
public	CleaningRunnable()

Method Summary

Modifier and Type	Method and Description
public void	run() Implements java.lang.Runnable.run. Runs this operation.

Inherited from java.lang.Object:: clone equals finalize getClass hashCode notify notifyAll toString wait wait wait

Constructor Detail

CleaningRunnable	back to summary
public CleaningRunnable()

Method Detail

run	back to summary
public void run() Implements java.lang.Runnable.run. Doc from java.lang.Runnable.run. Runs this operation. Annotations @Override

run

back to summary

public void run()

Implements java.lang.Runnable.run.

Doc from java.lang.Runnable.run.

Runs this operation.

Annotations

@Override

java.nio back to summary

private final Class BufferCleaner.PhantomCleaner

Class Inheritance

extends PhantomReference<Object>
implements Cleaner

All Implemented Interfaces

sun.nio.Cleaner

Field Summary

Modifier and Type	Field and Description
private final Runnable	action
pack-priv int	index
pack-priv BufferCleaner.CleanerList.Node	node

Constructor Summary

Access	Constructor and Description
public	PhantomCleaner(Object obj, Runnable action)

Method Summary

Modifier and Type	Method and Description
public void	clean() Implements sun.nio.Cleaner.clean. Unregisters the cleaner and invokes the cleaning action.

Inherited from java.lang.ref.PhantomReference:: get

Field Detail

action	back to summary
private final Runnable action

index	back to summary
pack-priv int index

node	back to summary
pack-priv BufferCleaner.CleanerList.Node node

Constructor Detail

PhantomCleaner	back to summary
public PhantomCleaner(Object obj, Runnable action)

Method Detail

clean back to summary

clean	back to summary
public void clean() Implements sun.nio.Cleaner.clean. Doc from sun.nio.Cleaner.clean. Unregisters the cleaner and invokes the cleaning action. The cleaner's cleaning action is invoked at most once, regardless of the number of calls to `clean`. Annotations @Override

public void clean()

Implements sun.nio.Cleaner.clean.

Doc from sun.nio.Cleaner.clean.

Unregisters the cleaner and invokes the cleaning action. The cleaner's cleaning action is invoked at most once, regardless of the number of calls to clean.

Annotations

@Override