/*
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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/*
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 *
 * 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");
 }
 }
}