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	/*
	* Copyright (c) 2015, 2020, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/

	package jdk.internal.ref;

	import java.lang.ref.Cleaner;
	import java.lang.ref.Cleaner.Cleanable;
	import java.lang.ref.ReferenceQueue;
	import java.security.AccessController;
	import java.security.PrivilegedAction;
	import java.util.concurrent.ThreadFactory;
	import java.util.concurrent.atomic.AtomicInteger;
	import java.util.function.Function;

	import jdk.internal.misc.InnocuousThread;

	/**
	* CleanerImpl manages a set of object references and corresponding cleaning actions.
	* CleanerImpl provides the functionality of {@link java.lang.ref.Cleaner}.
	*/
	public final class CleanerImpl implements Runnable {

	/**
	* An object to access the CleanerImpl from a Cleaner; set by Cleaner init.
	*/
	private static Function<Cleaner, CleanerImpl> cleanerImplAccess = null;

	/**
	* Heads of a CleanableList for each reference type.
	*/
	final PhantomCleanable<?> phantomCleanableList;

	// The ReferenceQueue of pending cleaning actions
	final ReferenceQueue<Object> queue;

	/**
	* Called by Cleaner static initialization to provide the function
	* to map from Cleaner to CleanerImpl.
	* @param access a function to map from Cleaner to CleanerImpl
	*/
	public static void setCleanerImplAccess(Function<Cleaner, CleanerImpl> access) {
	if (cleanerImplAccess == null) {
	cleanerImplAccess = access;
	} else {
	throw new InternalError("cleanerImplAccess");
	}
	}

	/**
	* Called to get the CleanerImpl for a Cleaner.
	* @param cleaner the cleaner
	* @return the corresponding CleanerImpl
	*/
	static CleanerImpl getCleanerImpl(Cleaner cleaner) {
	return cleanerImplAccess.apply(cleaner);
	}

	/**
	* Constructor for CleanerImpl.
	*/
	public CleanerImpl() {
	queue = new ReferenceQueue<>();
	phantomCleanableList = new PhantomCleanableRef();
	}

	/**
	* Starts the Cleaner implementation.
	* Ensure this is the CleanerImpl for the Cleaner.
	* When started waits for Cleanables to be queued.
	* @param cleaner the cleaner
	* @param threadFactory the thread factory
	*/
	public void start(Cleaner cleaner, ThreadFactory threadFactory) {
	if (getCleanerImpl(cleaner) != this) {
	throw new AssertionError("wrong cleaner");
	}
	// schedule a nop cleaning action for the cleaner, so the associated thread
	// will continue to run at least until the cleaner is reclaimable.
	new CleanerCleanable(cleaner);

	if (threadFactory == null) {
	threadFactory = CleanerImpl.InnocuousThreadFactory.factory();
	}

	// now that there's at least one cleaning action, for the cleaner,
	// we can start the associated thread, which runs until
	// all cleaning actions have been run.
	Thread thread = threadFactory.newThread(this);
	thread.setDaemon(true);
	thread.start();
	}

	/**
	* Process queued Cleanables as long as the cleanable lists are not empty.
	* A Cleanable is in one of the lists for each Object and for the Cleaner
	* itself.
	* Terminates when the Cleaner is no longer reachable and
	* has been cleaned and there are no more Cleanable instances
	* for which the object is reachable.
	* <p>
	* If the thread is a ManagedLocalsThread, the threadlocals
	* are erased before each cleanup
	*/
	@Override
	public void run() {
	Thread t = Thread.currentThread();
	InnocuousThread mlThread = (t instanceof InnocuousThread)
	? (InnocuousThread) t
	: null;
	while (!phantomCleanableList.isListEmpty()) {
	if (mlThread != null) {
	// Clear the thread locals
	mlThread.eraseThreadLocals();
	}
	try {
	// Wait for a Ref, with a timeout to avoid getting hung
	// due to a race with clear/clean
	Cleanable ref = (Cleanable) queue.remove(60 * 1000L);
	if (ref != null) {
	ref.clean();
	}
	} catch (Throwable e) {
	// ignore exceptions from the cleanup action
	// (including interruption of cleanup thread)
	}
	}
	}

	/**
	* Perform cleaning on an unreachable PhantomReference.
	*/
	public static final class PhantomCleanableRef extends PhantomCleanable<Object> {
	private final Runnable action;

	/**
	* Constructor for a phantom cleanable reference.
	* @param obj the object to monitor
	* @param cleaner the cleaner
	* @param action the action Runnable
	*/
	public PhantomCleanableRef(Object obj, Cleaner cleaner, Runnable action) {
	super(obj, cleaner);
	this.action = action;
	}

	/**
	* Constructor used only for root of phantom cleanable list.
	*/
	PhantomCleanableRef() {
	super();
	this.action = null;
	}

	@Override
	protected void performCleanup() {
	action.run();
	}

	/**
	* Prevent access to referent even when it is still alive.
	*
	* @throws UnsupportedOperationException always
	*/
	@Override
	public Object get() {
	throw new UnsupportedOperationException("get");
	}

	/**
	* Direct clearing of the referent is not supported.
	*
	* @throws UnsupportedOperationException always
	*/
	@Override
	public void clear() {
	throw new UnsupportedOperationException("clear");
	}
	}

	/**
	* A ThreadFactory for InnocuousThreads.
	* The factory is a singleton.
	*/
	static final class InnocuousThreadFactory implements ThreadFactory {
	static final ThreadFactory factory = new InnocuousThreadFactory();

	static ThreadFactory factory() {
	return factory;
	}

	final AtomicInteger cleanerThreadNumber = new AtomicInteger();

	public Thread newThread(Runnable r) {
	return InnocuousThread.newThread("Cleaner-" + cleanerThreadNumber.getAndIncrement(),
	r, Thread.MIN_PRIORITY - 2);
	}
	}

	/**
	* A PhantomCleanable implementation for tracking the Cleaner itself.
	*/
	static final class CleanerCleanable extends PhantomCleanable<Cleaner> {
	CleanerCleanable(Cleaner cleaner) {
	super(cleaner, cleaner);
	}

	@Override
	protected void performCleanup() {
	// no action
	}
	}
	}

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