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	/*
	* 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.
	*/

	/*
	* This file is available under and governed by the GNU General Public
	* License version 2 only, as published by the Free Software Foundation.
	* However, the following notice accompanied the original version of this
	* file:
	*
	* Written by Doug Lea with assistance from members of JCP JSR-166
	* Expert Group and released to the public domain, as explained at
	* http://creativecommons.org/publicdomain/zero/1.0/
	*/

	package java.util.concurrent;

	import java.security.AccessControlContext;
	import java.security.AccessController;
	import java.security.PrivilegedAction;
	import java.security.ProtectionDomain;

	/**
	* A thread managed by a {@link ForkJoinPool}, which executes
	* {@link ForkJoinTask}s.
	* This class is subclassable solely for the sake of adding
	* functionality -- there are no overridable methods dealing with
	* scheduling or execution. However, you can override initialization
	* and termination methods surrounding the main task processing loop.
	* If you do create such a subclass, you will also need to supply a
	* custom {@link ForkJoinPool.ForkJoinWorkerThreadFactory} to
	* {@linkplain ForkJoinPool#ForkJoinPool(int, ForkJoinWorkerThreadFactory,
	* UncaughtExceptionHandler, boolean, int, int, int, Predicate, long, TimeUnit)
	* use it} in a {@code ForkJoinPool}.
	*
	* @since 1.7
	* @author Doug Lea
	*/
	public class ForkJoinWorkerThread extends Thread {
	/*
	* ForkJoinWorkerThreads are managed by ForkJoinPools and perform
	* ForkJoinTasks. For explanation, see the internal documentation
	* of class ForkJoinPool.
	*
	* This class just maintains links to its pool and WorkQueue. The
	* pool field is set immediately upon construction, but the
	* workQueue field is not set until a call to registerWorker
	* completes. This leads to a visibility race, that is tolerated
	* by requiring that the workQueue field is only accessed by the
	* owning thread.
	*
	* Support for (non-public) subclass InnocuousForkJoinWorkerThread
	* requires that we break quite a lot of encapsulation (via helper
	* methods in ThreadLocalRandom) both here and in the subclass to
	* access and set Thread fields.
	*/

	final ForkJoinPool pool; // the pool this thread works in
	final ForkJoinPool.WorkQueue workQueue; // work-stealing mechanics

	/**
	* Creates a ForkJoinWorkerThread operating in the given pool.
	*
	* @param pool the pool this thread works in
	* @throws NullPointerException if pool is null
	*/
	protected ForkJoinWorkerThread(ForkJoinPool pool) {
	// Use a placeholder until a useful name can be set in registerWorker
	super("aForkJoinWorkerThread");
	this.pool = pool;
	this.workQueue = pool.registerWorker(this);
	}

	/**
	* Version for use by the default pool. Supports setting the
	* context class loader. This is a separate constructor to avoid
	* affecting the protected constructor.
	*/
	ForkJoinWorkerThread(ForkJoinPool pool, ClassLoader ccl) {
	super("aForkJoinWorkerThread");
	super.setContextClassLoader(ccl);
	this.pool = pool;
	this.workQueue = pool.registerWorker(this);
	}

	/**
	* Version for InnocuousForkJoinWorkerThread.
	*/
	ForkJoinWorkerThread(ForkJoinPool pool,
	ClassLoader ccl,
	ThreadGroup threadGroup,
	AccessControlContext acc) {
	super(threadGroup, null, "aForkJoinWorkerThread");
	super.setContextClassLoader(ccl);
	ThreadLocalRandom.setInheritedAccessControlContext(this, acc);
	ThreadLocalRandom.eraseThreadLocals(this); // clear before registering
	this.pool = pool;
	this.workQueue = pool.registerWorker(this);
	}

	/**
	* Returns the pool hosting this thread.
	*
	* @return the pool
	*/
	public ForkJoinPool getPool() {
	return pool;
	}

	/**
	* Returns the unique index number of this thread in its pool.
	* The returned value ranges from zero to the maximum number of
	* threads (minus one) that may exist in the pool, and does not
	* change during the lifetime of the thread. This method may be
	* useful for applications that track status or collect results
	* per-worker-thread rather than per-task.
	*
	* @return the index number
	*/
	public int getPoolIndex() {
	return workQueue.getPoolIndex();
	}

	/**
	* Initializes internal state after construction but before
	* processing any tasks. If you override this method, you must
	* invoke {@code super.onStart()} at the beginning of the method.
	* Initialization requires care: Most fields must have legal
	* default values, to ensure that attempted accesses from other
	* threads work correctly even before this thread starts
	* processing tasks.
	*/
	protected void onStart() {
	}

	/**
	* Performs cleanup associated with termination of this worker
	* thread. If you override this method, you must invoke
	* {@code super.onTermination} at the end of the overridden method.
	*
	* @param exception the exception causing this thread to abort due
	* to an unrecoverable error, or {@code null} if completed normally
	*/
	protected void onTermination(Throwable exception) {
	}

	/**
	* This method is required to be public, but should never be
	* called explicitly. It performs the main run loop to execute
	* {@link ForkJoinTask}s.
	*/
	public void run() {
	if (workQueue.array == null) { // only run once
	Throwable exception = null;
	try {
	onStart();
	pool.runWorker(workQueue);
	} catch (Throwable ex) {
	exception = ex;
	} finally {
	try {
	onTermination(exception);
	} catch (Throwable ex) {
	if (exception == null)
	exception = ex;
	} finally {
	pool.deregisterWorker(this, exception);
	}
	}
	}
	}

	/**
	* Non-public hook method for InnocuousForkJoinWorkerThread.
	*/
	void afterTopLevelExec() {
	}

	/**
	* A worker thread that has no permissions, is not a member of any
	* user-defined ThreadGroup, uses the system class loader as
	* thread context class loader, and erases all ThreadLocals after
	* running each top-level task.
	*/
	static final class InnocuousForkJoinWorkerThread extends ForkJoinWorkerThread {
	/** The ThreadGroup for all InnocuousForkJoinWorkerThreads */
	private static final ThreadGroup innocuousThreadGroup =
	AccessController.doPrivileged(new PrivilegedAction<>() {
	public ThreadGroup run() {
	ThreadGroup group = Thread.currentThread().getThreadGroup();
	for (ThreadGroup p; (p = group.getParent()) != null; )
	group = p;
	return new ThreadGroup(
	group, "InnocuousForkJoinWorkerThreadGroup");
	}});

	/** An AccessControlContext supporting no privileges */
	private static final AccessControlContext INNOCUOUS_ACC =
	new AccessControlContext(
	new ProtectionDomain[] { new ProtectionDomain(null, null) });

	InnocuousForkJoinWorkerThread(ForkJoinPool pool) {
	super(pool,
	ClassLoader.getSystemClassLoader(),
	innocuousThreadGroup,
	INNOCUOUS_ACC);
	}

	@Override // to erase ThreadLocals
	void afterTopLevelExec() {
	ThreadLocalRandom.eraseThreadLocals(this);
	}

	@Override // to silently fail
	public void setUncaughtExceptionHandler(UncaughtExceptionHandler x) { }

	@Override // paranoically
	public void setContextClassLoader(ClassLoader cl) {
	throw new SecurityException("setContextClassLoader");
	}
	}
	}

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