java线程池(八)：ForkJoinPool源码分析之四（ForkJoinWorkerThread源码）

public class ForkJoinWorkerThread extends Thread {
    
}

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);
}

ForkJoinWorkerThread(ForkJoinPool pool, ThreadGroup threadGroup,
                     AccessControlContext acc) {
    super(threadGroup, null, "aForkJoinWorkerThread");
    U.putOrderedObject(this, INHERITEDACCESSCONTROLCONTEXT, acc);
    eraseThreadLocals(); // clear before registering
    this.pool = pool;
    this.workQueue = pool.registerWorker(this);
}

/**
 * Erases ThreadLocals by nulling out Thread maps.
 */
final void eraseThreadLocals() {
    U.putObject(this, THREADLOCALS, null);
    U.putObject(this, INHERITABLETHREADLOCALS, null);
}

public void run() {
     //如果workQueue为空，则抛出异常
    if (workQueue.array == null) { // only run once
        Throwable exception = null;
        try {
           //调用onStart方法
            onStart();
            //调用pool的runWorker方法，运行workQueue
            pool.runWorker(workQueue);
        } catch (Throwable ex) {
            exception = ex;
        } finally {
           //操作完之后处理
            try {
               //调用onTermination方法
                onTermination(exception);
            } catch (Throwable ex) {
               //如果出现异常，则进行异常处理
                if (exception == null)
                    exception = ex;
            } finally {
               //最终需要指向deregister方法
                pool.deregisterWorker(this, exception);
            }
        }
    }
}

/**
 * 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) {
}

static final class InnocuousForkJoinWorkerThread extends ForkJoinWorkerThread {
    /** The ThreadGroup for all InnocuousForkJoinWorkerThreads */
    private static final ThreadGroup innocuousThreadGroup =
        createThreadGroup();

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

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

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

    @Override // to always report system loader
    public ClassLoader getContextClassLoader() {
        return ClassLoader.getSystemClassLoader();
    }

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

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

    /**
     * Returns a new group with the system ThreadGroup (the
     * topmost, parent-less group) as parent.  Uses Unsafe to
     * traverse Thread.group and ThreadGroup.parent fields.
     */
    private static ThreadGroup createThreadGroup() {
        try {
            sun.misc.Unsafe u = sun.misc.Unsafe.getUnsafe();
            Class<?> tk = Thread.class;
            Class<?> gk = ThreadGroup.class;
            long tg = u.objectFieldOffset(tk.getDeclaredField("group"));
            long gp = u.objectFieldOffset(gk.getDeclaredField("parent"));
            ThreadGroup group = (ThreadGroup)
                u.getObject(Thread.currentThread(), tg);
            while (group != null) {
                ThreadGroup parent = (ThreadGroup)u.getObject(group, gp);
                if (parent == null)
                    return new ThreadGroup(group,
                                           "InnocuousForkJoinWorkerThreadGroup");
                group = parent;
            }
        } catch (Exception e) {
            throw new Error(e);
        }
        // fall through if null as cannot-happen safeguard
        throw new Error("Cannot create ThreadGroup");
    }
}

if (factory == null) {
    if (System.getSecurityManager() == null)
        factory = defaultForkJoinWorkerThreadFactory;
    else // use security-managed default
        factory = new InnocuousForkJoinWorkerThreadFactory();
}

ForkJoinWorkerThreadFactory fac = factory;
try {
        if (fac != null && (wt = fac.newThread(this)) != null) {
            wt.start();
            return true;
        }
    } catch (Throwable rex) {
        ex = rex;
    }

static final class InnocuousForkJoinWorkerThreadFactory
    implements ForkJoinWorkerThreadFactory {

    /**
     * An ACC to restrict permissions for the factory itself.
     * The constructed workers have no permissions set.
     */
    private static final AccessControlContext innocuousAcc;
    static {
        Permissions innocuousPerms = new Permissions();
        innocuousPerms.add(modifyThreadPermission);
        innocuousPerms.add(new RuntimePermission(
                               "enableContextClassLoaderOverride"));
        innocuousPerms.add(new RuntimePermission(
                               "modifyThreadGroup"));
        innocuousAcc = new AccessControlContext(new ProtectionDomain[] {
                new ProtectionDomain(null, innocuousPerms)
            });
    }

    public final ForkJoinWorkerThread newThread(ForkJoinPool pool) {
        return (ForkJoinWorkerThread.InnocuousForkJoinWorkerThread)
            java.security.AccessController.doPrivileged(
                new java.security.PrivilegedAction<ForkJoinWorkerThread>() {
                public ForkJoinWorkerThread run() {
                    return new ForkJoinWorkerThread.
                        InnocuousForkJoinWorkerThread(pool);
                }}, innocuousAcc);
    }
}

static final class DefaultForkJoinWorkerThreadFactory
    implements ForkJoinWorkerThreadFactory {
    public final ForkJoinWorkerThread newThread(ForkJoinPool pool) {
        return new ForkJoinWorkerThread(pool);
    }
}