content: /*
   * 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 alluxio.concurrent.jsr;
  
  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 <a href=
   * "../../../java9/util/concurrent/ForkJoinPool.html#ForkJoinPool-int-java9.util.concurrent.ForkJoinPool.ForkJoinWorkerThreadFactory-java.lang.Thread.UncaughtExceptionHandler-boolean-int-int-int-java.util.function.Predicate-long-java.util.concurrent.TimeUnit-">
   * use it</a> in a {@code ForkJoinPool}.
   *
   * @since 1.7
   * @author Doug Lea
   */
  public class ForkJoinWorkerThread extends Thread {
    // CVS rev. 1.76
    /*
     * 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.
     */
  
    // A placeholder name until a useful name can be set in registerWorker
    private static final String NAME_PLACEHOLDER = "aForkJoinWorkerThread";
  
    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(NAME_PLACEHOLDER);
      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(NAME_PLACEHOLDER);
      TLRandom.setContextClassLoader(this, ccl); // java9-concurrent-backport changed
      this.pool = pool;
      this.workQueue = pool.registerWorker(this);
    }
  
    /**
     * Version for InnocuousForkJoinWorkerThread.
     */
    ForkJoinWorkerThread(ForkJoinPool pool, ClassLoader ccl, ThreadGroup threadGroup,
        AccessControlContext acc) {
      super(threadGroup, NAME_PLACEHOLDER);
      super.setContextClassLoader(ccl);
      TLRandom.setInheritedAccessControlContext(this, acc);
      TLRandom.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<ThreadGroup>() {
            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() {
        TLRandom.eraseThreadLocals(this);
      }
  
      @Override // to silently fail
      public void setUncaughtExceptionHandler(UncaughtExceptionHandler x) {}
  
      @Override // paranoically
      public void setContextClassLoader(ClassLoader cl) {
        throw new SecurityException("setContextClassLoader");
      }
    }
  }
  