gcc/libjava/classpath/java/nio/channels/spi/AbstractSelectableChannel.java

/* AbstractSelectableChannel.java
   Copyright (C) 2002, 2003, 2004 Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.

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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

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Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
02110-1301 USA.

Linking this library statically or dynamically with other modules is
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As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
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package java.nio.channels.spi;

import java.io.IOException;
import java.nio.channels.ClosedChannelException;
import java.nio.channels.SelectableChannel;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.IllegalBlockingModeException;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.ListIterator;

public abstract class AbstractSelectableChannel extends SelectableChannel
{
  private boolean blocking = true;
  private Object LOCK = new Object();
  private SelectorProvider provider;
  private LinkedList keys = new LinkedList();

  /**
   * Initializes the channel
   *
   * @param provider the provider that created this channel
   */
  protected AbstractSelectableChannel(SelectorProvider provider)
  {
    this.provider = provider;
  }

  /**
   * Retrieves the object upon which the configureBlocking and register
   * methods synchronize.
   *
   * @return the blocking lock
   */
  public final Object blockingLock()
  {
    return LOCK;
  }

  /**
   * Adjusts this channel's blocking mode.
   *
   * @param blocking true if blocking should be enabled, false otherwise
   *
   * @return this channel
   *
   * @exception IOException If an error occurs
   */
  public final SelectableChannel configureBlocking(boolean blocking)
    throws IOException
  {
    synchronized (blockingLock())
      {
        if (this.blocking != blocking)
          {
            implConfigureBlocking(blocking);
            this.blocking = blocking;
          }
      }

    return this;
  }

  /**
   * Closes this channel.
   *
   * @exception IOException If an error occurs
   */
  protected final void implCloseChannel() throws IOException
  {
    try
      {
        implCloseSelectableChannel();
      }
    finally
      {
        for (Iterator it = keys.iterator(); it.hasNext(); )
          ((SelectionKey) it.next()).cancel();
      }
  }

  /**
   * Closes this selectable channel.
   *
   * @exception IOException If an error occurs
   */
  protected abstract void implCloseSelectableChannel()
    throws IOException;

  /**
   * Adjusts this channel's blocking mode.
   *
   * @param blocking true if blocking should be enabled, false otherwise
   *
   * @exception IOException If an error occurs
   */
  protected abstract void implConfigureBlocking(boolean blocking)
    throws IOException;

  /**
   * Tells whether or not every I/O operation on this channel will block
   * until it completes.
   *
   * @return true of this channel is blocking, false otherwise
   */
  public final boolean isBlocking()
  {
    return blocking;
  }

  /**
   * Tells whether or not this channel is currently registered with
   * any selectors.
   *
   * @return true if this channel is registered, false otherwise
   */
  public final boolean isRegistered()
  {
    return ! keys.isEmpty();
  }

  /**
   * Retrieves the key representing the channel's registration with the
   * given selector.
   *
   * @param selector the selector to get a selection key for
   *
   * @return the selection key this channel is registered with
   */
  public final SelectionKey keyFor(Selector selector)
  {
    if (! isOpen())
      return null;

    try
      {
        synchronized (blockingLock())
          {
            return locate(selector);
          }
      }
    catch (Exception e)
      {
        return null;
      }
  }

  /**
   * Returns the provider that created this channel.
   *
   * @return the selector provider that created this channel
   */
  public final SelectorProvider provider()
  {
    return provider;
  }

  private SelectionKey locate(Selector selector)
  {
    ListIterator it = keys.listIterator();

    while (it.hasNext())
      {
        SelectionKey key = (SelectionKey) it.next();

        if (key.selector() == selector)
          return key;
      }

    return null;
  }

  /**
   * Registers this channel with the given selector, returning a selection key.
   *
   * @param selin the seletor to use
   * @param ops the interested operations
   * @param att an attachment for the returned selection key
   *
   * @return the registered selection key
   *
   * @exception ClosedChannelException If the channel is already closed.
   * @exception IllegalBlockingModeException If the channel is configured in
   * blocking mode.
   */
  public final SelectionKey register(Selector selin, int ops, Object att)
    throws ClosedChannelException
  {
    if (! isOpen())
      throw new ClosedChannelException();

    if ((ops & ~validOps()) != 0)
      throw new IllegalArgumentException();

    SelectionKey key = null;
    AbstractSelector selector = (AbstractSelector) selin;

    synchronized (blockingLock())
      {
        if (blocking)
          throw new IllegalBlockingModeException();

        key = locate(selector);

        if (key != null && key.isValid())
          {
            key.interestOps(ops);
            key.attach(att);
          }
        else
          {
            key = selector.register(this, ops, att);

            if (key != null)
              addSelectionKey(key);
          }
      }

    return key;
  }

  void addSelectionKey(SelectionKey key)
  {
    keys.add(key);
  }

  // This method gets called by AbstractSelector.deregister().
  void removeSelectionKey(SelectionKey key)
  {
    keys.remove(key);
  }
}