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

/* AbstractSelectableChannel.java
   Copyright (C) 2002, 2003 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.

GNU Classpath is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

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Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
02111-1307 USA.

Linking this library statically or dynamically with other modules is
making a combined work based on this library.  Thus, the terms and
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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
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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.util.LinkedList;
import java.util.List;
import java.util.ListIterator;

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

  /**
   * Initializes the channel
   */
  protected AbstractSelectableChannel (SelectorProvider provider)
  {
    this.provider = provider;
    this.keys = new LinkedList();
  }

  /**
   * Retrieves the object upon which the configureBlocking and register
   * methods synchronize.
   */
  public final Object blockingLock ()
  {
    return LOCK;
  }
    
  /**
   * Adjusts this channel's blocking mode.
   */
  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
  {
    implCloseSelectableChannel ();
  }

  /**
   * Closes this selectable channel.
   */
  protected abstract void implCloseSelectableChannel () throws IOException;
  
  /**
   * Adjusts this channel's blocking mode.
   */
  protected abstract void implConfigureBlocking (boolean block)
    throws IOException;

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

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

  /**
   * Retrieves the key representing the channel's registration with the
   * given selector.
   */
  public final SelectionKey keyFor(Selector selector)
  {
    try
      {
        return register (selector, 0, null);
      }
    catch (Exception e)
      {
        return null;
      }
  }

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

  private SelectionKey locate (Selector selector)
  {
    if (keys == null)
      return null;
    
    ListIterator it = keys.listIterator ();
    
    while (it.hasNext ())
      {
        SelectionKey key = (SelectionKey) it.next();
        
    	if (key.selector() == selector)
          return key;
      }
    
    return null;
  }

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

  /**
   * Registers this channel with the given selector, returning a selection key.
   *
   * @exception ClosedChannelException If the channel is already closed.
   */
  public final SelectionKey register (Selector selin, int ops, Object att)
    throws ClosedChannelException
  {
    if (!isOpen ())
      throw new ClosedChannelException();

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

    synchronized (blockingLock())
      {
        key = locate (selector);

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

    return key;
  }
}