threadgroup.java

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   * Copy all active ThreadGroups that are children of this ThreadGroup into
   * the specified array, and if desired, also all descendents.  If the array
   * is not large enough to hold all active ThreadGroups, extra ThreadGroups
   * simply will not be copied. There may be a security check,
   * <code>checkAccess</code>.
   *
   * @param array the array to put the ThreadGroups into
   * @param recurse whether to recurse into descendent ThreadGroups
   * @return the number of ThreadGroups copied into the array
   * @throws SecurityException if permission was denied
   * @throws NullPointerException if array is null
   * @throws ArrayStoreException if a group does not fit in the array
   * @see #activeCount()
   * @see #checkAccess()
   */
  public int enumerate(ThreadGroup[] array, boolean recurse)
  {
    return enumerate(array, 0, recurse);
  }

  /**
   * Stop all Threads in this ThreadGroup and its descendants.
   *
   * <p>This is inherently unsafe, as it can interrupt synchronized blocks and
   * leave data in bad states.  Hence, there is a security check:
   * <code>checkAccess()</code>, followed by further checks on each thread
   * being stopped.
   *
   * @throws SecurityException if permission is denied
   * @see #checkAccess()
   * @see Thread#stop(Throwable)
   * @deprecated unsafe operation, try not to use
   */
  public final synchronized void stop()
  {
    checkAccess();
    if (groups == null)
      return;
    int i = threads.size();
    while (--i >= 0)
      ((Thread) threads.get(i)).stop();
    i = groups.size();
    while (--i >= 0)
      ((ThreadGroup) groups.get(i)).stop();
  }

  /**
   * Interrupt all Threads in this ThreadGroup and its sub-groups. There may
   * be a security check, <code>checkAccess</code>.
   *
   * @throws SecurityException if permission is denied
   * @see #checkAccess()
   * @see Thread#interrupt()
   * @since 1.2
   */
  public final synchronized void interrupt()
  {
    checkAccess();
    if (groups == null)
      return;
    int i = threads.size();
    while (--i >= 0)
      ((Thread) threads.get(i)).interrupt();
    i = groups.size();
    while (--i >= 0)
      ((ThreadGroup) groups.get(i)).interrupt();
  }

  /**
   * Suspend all Threads in this ThreadGroup and its descendants.
   *
   * <p>This is inherently unsafe, as suspended threads still hold locks,
   * which can lead to deadlock.  Hence, there is a security check:
   * <code>checkAccess()</code>, followed by further checks on each thread
   * being suspended.
   *
   * @throws SecurityException if permission is denied
   * @see #checkAccess()
   * @see Thread#suspend()
   * @deprecated unsafe operation, try not to use
   */
  public final synchronized void suspend()
  {
    checkAccess();
    if (groups == null)
      return;
    int i = threads.size();
    while (--i >= 0)
      ((Thread) threads.get(i)).suspend();
    i = groups.size();
    while (--i >= 0)
      ((ThreadGroup) groups.get(i)).suspend();
  }

  /**
   * Resume all suspended Threads in this ThreadGroup and its descendants.
   * To mirror suspend(), there is a security check:
   * <code>checkAccess()</code>, followed by further checks on each thread
   * being resumed.
   *
   * @throws SecurityException if permission is denied
   * @see #checkAccess()
   * @see Thread#suspend()
   * @deprecated pointless, since suspend is deprecated
   */
  public final synchronized void resume()
  {
    checkAccess();
    if (groups == null)
      return;
    int i = threads.size();
    while (--i >= 0)
      ((Thread) threads.get(i)).resume();
    i = groups.size();
    while (--i >= 0)
      ((ThreadGroup) groups.get(i)).resume();
  }

  /**
   * Destroy this ThreadGroup.  The group must be empty, meaning that all
   * threads and sub-groups have completed execution. Daemon groups are
   * destroyed automatically. There may be a security check,
   * <code>checkAccess</code>.
   *
   * @throws IllegalThreadStateException if the ThreadGroup is not empty, or
   *         was previously destroyed
   * @throws SecurityException if permission is denied
   * @see #checkAccess()
   */
  public final synchronized void destroy()
  {
    checkAccess();
    if (! threads.isEmpty() || groups == null)
      throw new IllegalThreadStateException();
    int i = groups.size();
    while (--i >= 0)
      ((ThreadGroup) groups.get(i)).destroy();
    groups = null;
    if (parent != null)
      parent.removeGroup(this);
  }

  /**
   * Print out information about this ThreadGroup to System.out. This is
   * meant for debugging purposes. <b>WARNING:</b> This method is not secure,
   * and can print the name of threads to standard out even when you cannot
   * otherwise get at such threads.
   */
  public void list()
  {
    list("");
  }

  /**
   * When a Thread in this ThreadGroup does not catch an exception, the
   * virtual machine calls this method. The default implementation simply
   * passes the call to the parent; then in top ThreadGroup, it will
   * ignore ThreadDeath and print the stack trace of any other throwable.
   * Override this method if you want to handle the exception in a different
   * manner.
   *
   * @param thread the thread that exited
   * @param exception the uncaught exception
   * @throws NullPointerException if t is null
   * @see ThreadDeath
   * @see System#err
   * @see Throwable#printStackTrace()
   */
  public void uncaughtException(Thread thread, Throwable t)
  {
    if (parent != null)
      parent.uncaughtException(thread, t);
    else if (! (t instanceof ThreadDeath))
      {
        if (t == null)
          throw new NullPointerException();
        had_uncaught_exception = true;
        try
          {
            if (thread != null)
              System.err.print("Exception in thread \"" + thread.name + "\" ");
            t.printStackTrace(System.err);
          }
        catch (Throwable x)
          {
            // This means that something is badly screwed up with the runtime,
            // or perhaps someone overloaded the Throwable.printStackTrace to
            // die. In any case, try to deal with it gracefully.
            try
              {
                System.err.println(t);
                System.err.println("*** Got " + x
                                   + " while trying to print stack trace.");
              }
            catch (Throwable x2)
              {
                // Here, someone may have overloaded t.toString() or
                // x.toString() to die. Give up all hope; we can't even chain
                // the exception, because the chain would likewise die.
                System.err.println("*** Catastrophic failure while handling "
                                   + "uncaught exception.");
                throw new InternalError();
              }
          }
      }
  }

  /**
   * Originally intended to tell the VM whether it may suspend Threads in
   * low memory situations, this method was never implemented by Sun, and
   * is hence a no-op.
   *
   * @param allow whether to allow low-memory thread suspension; ignored
   * @return false
   * @since 1.1
   * @deprecated pointless, since suspend is deprecated
   */
  public boolean allowThreadSuspension(boolean allow)
  {
    return false;
  }

  /**
   * Return a human-readable String representing this ThreadGroup. The format
   * of the string is:<br>
   * <code>getClass().getName() + "[name=" + getName() + ",maxpri="
   * + getMaxPriority() + ']'</code>.
   *
   * @return a human-readable String representing this ThreadGroup
   */
  public String toString()
  {
    return getClass().getName() + "[name=" + name + ",maxpri=" + maxpri + ']';
  }

  /**
   * Implements enumerate.
   *
   * @param list the array to put the threads into
   * @param next the next open slot in the array
   * @param recurse whether to recurse into descendent ThreadGroups
   * @return the number of threads put into the array
   * @throws SecurityException if permission was denied
   * @throws NullPointerException if list is null
   * @throws ArrayStoreException if a thread does not fit in the array
   * @see #enumerate(Thread[])
   * @see #enumerate(Thread[], boolean)
   */
  private int enumerate(Thread[] list, int next, boolean recurse)
  {
    checkAccess();
    if (groups == null)
      return next;
    int i = threads.size();
    while (--i >= 0 && next < list.length)
      {
        Thread t = (Thread) threads.get(i);
        if (t.isAlive())
          list[next++] = t;
      }
    if (recurse)
      {
        i = groups.size();
        while (--i >= 0 && next < list.length)
          {
            ThreadGroup g = (ThreadGroup) groups.get(i);
            next = g.enumerate(list, next, true);
          }
      }
    return next;
  }

  /**
   * Implements enumerate.
   *
   * @param list the array to put the groups into
   * @param next the next open slot in the array
   * @param recurse whether to recurse into descendent ThreadGroups
   * @return the number of groups put into the array
   * @throws SecurityException if permission was denied
   * @throws NullPointerException if list is null
   * @throws ArrayStoreException if a group does not fit in the array
   * @see #enumerate(ThreadGroup[])
   * @see #enumerate(ThreadGroup[], boolean)
   */
  private int enumerate(ThreadGroup[] list, int next, boolean recurse)
  {
    checkAccess();
    if (groups == null)
      return next;
    int i = groups.size();
    while (--i >= 0 && next < list.length)
      {
        ThreadGroup g = (ThreadGroup) groups.get(i);
        list[next++] = g;
        if (recurse && next != list.length)
          next = g.enumerate(list, next, true);
      }
    return next;
  }

  /**
   * Implements list.
   *
   * @param indentation the current level of indentation
   * @see #list()
   */
  private void list(String indentation)
  {
    if (groups == null)
      return;
    System.out.print(indentation + this);
    indentation += "    ";
    int i = threads.size();
    while (--i >= 0)
      System.out.println(indentation + threads.get(i));
    i = groups.size();
    while (--i >= 0)
      ((ThreadGroup) groups.get(i)).list(indentation);
  }

  /**
   * Add a thread to the group. Called by Thread constructors.
   *
   * @param t the thread to add, non-null
   * @throws IllegalThreadStateException if the group is destroyed
   */
  final synchronized void addThread(Thread t)
  {
    if (groups == null)
      throw new IllegalThreadStateException("ThreadGroup is destroyed");
    threads.add(t);
  }

  /**
   * Called by the VM to remove a thread that has died.
   *
   * @param t the thread to remove, non-null
   * @XXX A ThreadListener to call this might be nice.
   */
  final synchronized void removeThread(Thread t)
  {
    if (groups == null)
      return;
    threads.remove(t);
    // Daemon groups are automatically destroyed when all their threads die.
    if (daemon_flag && groups.size() == 0 && threads.size() == 0)
      {
        // We inline destroy to avoid the access check.
        groups = null;
        if (parent != null)
          parent.removeGroup(this);
      }
  }

  /**
   * Called when a group is destroyed, to remove it from its parent.
   *
   * @param g the destroyed group, non-null
   */
  final synchronized void removeGroup(ThreadGroup g)
  {
    groups.remove(g);
    // Daemon groups are automatically destroyed when all their threads die.
    if (daemon_flag && groups.size() == 0 && threads.size() == 0)
      {
        // We inline destroy to avoid the access check.
        groups = null;
        if (parent != null)
          parent.removeGroup(this);
      }
  }
} // class ThreadGroup