/* SelectorImpl.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.

You should have received a copy of the GNU General Public License
along with GNU Classpath; see the file COPYING.  If not, write to the
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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combination.

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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terms of your choice, provided that you also meet, for each linked
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or based on this library.  If you modify this library, you may extend
this exception to your version of the library, but you are not
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exception statement from your version. */

package gnu.java.nio;

import java.io.IOException;
import java.nio.channels.ClosedSelectorException;
import java.nio.channels.SelectableChannel;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.spi.AbstractSelectableChannel;
import java.nio.channels.spi.AbstractSelector;
import java.nio.channels.spi.SelectorProvider;
import java.util.Collections;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;
import gnu.classpath.Configuration;

/**
 * This SelectorImpl, while based on the code from GNU classpath
 * differs in that we try to make the time spend on a select bounded
 * by O(m) where m is the number of now available operations.
 * Note that this was not quite achieved since the 'canceled' operation
 * check is still O(n) where n is the total number of elements in the
 * select-set.  Another major difference to classpath is that we build
 * the select set as we go, that is each time a client adds a selector
 * we directly go to the native layer and modify the sets.  The
 * classpath code did this in O(n) on entry to select.  Finally, the
 * native code (or in OVM, the LibraryGlue) is made responsible for
 * updating the selected set directly (and to update the ready-ops).
 * In classpath this was done in an O(n) pass over the ready-array
 * that was build and passed to select.
 *
 * @author Christian Grothoff (modifications from classpath)
 */
public class SelectorImpl extends AbstractSelector
{
  static
  {
    // load the shared library needed for native methods.
    if (Configuration.INIT_LOAD_LIBRARY)
      {
        System.loadLibrary ("javanio");
      }
  }
  
  private Set keys;
    Set selected;

  /**
   * A dummy object whose monitor regulates access to both our
   * selectThread and unhandledWakeup fields.
   */
  private Object selectThreadMutex = new Object ();
  
  /**
   * Any thread that's currently blocked in a select operation.
   */
  private Thread selectThread;
  
  /**
   * Indicates whether we have an unhandled wakeup call. This can
   * be due to either wakeup() triggering a thread interruption while
   * a thread was blocked in a select operation (in which case we need
   * to reset this thread's interrupt status after interrupting the
   * select), or else that no thread was on a select operation at the
   * time that wakeup() was called, in which case the following select()
   * operation should return immediately with nothing selected.
   */
  private boolean unhandledWakeup;

    
    Object nativeCookie_;


  public SelectorImpl (SelectorProvider provider)
  {
    super (provider);
    
    keys = new HashSet ();
    selected = new HashSet ();
    
    selectorImplInit();
  }

    private native void selectorImplInit();

    private native void selectorImplDone();

  protected void finalize() throws Throwable
  {
    close();
  }

  protected final void implCloseSelector()
    throws IOException
  {
    // Cancel any pending select operation.
    wakeup();
    
    synchronized (keys)
      {
        synchronized (selected)
          {
            synchronized (cancelledKeys ())
              {
		  selectorImplDone();
              }
          }
      }
  }

  public final Set keys()
  {
    if (!isOpen())
      throw new ClosedSelectorException();

    return Collections.unmodifiableSet (keys);
  }
    
  public final int selectNow()
    throws IOException
  {
    // FIXME: We're simulating an immediate select
    // via a select with a timeout of one millisecond.
    return select (1);
  }

  public final int select()
    throws IOException
  {
    return select (0);
  }

  // A timeout value of 0 means block forever.
  private static native int implSelect (long timeout)
    throws IOException;

  public synchronized int select (long timeout)
    throws IOException
  {
    if (!isOpen())
      throw new ClosedSelectorException();
      
    synchronized (keys)
      {
        synchronized (selected)
          {
            deregisterCancelledKeys();

            // Test to see if we've got an unhandled wakeup call,
            // in which case we return immediately. Otherwise,
            // remember our current thread and jump into the select.
            // The monitor for dummy object selectThreadMutex regulates
            // access to these fields.

            // FIXME: Not sure from the spec at what point we should
            // return "immediately". Is it here or immediately upon
            // entry to this function?
            
            // NOTE: There's a possibility of another thread calling
            // wakeup() immediately after our thread releases
            // selectThreadMutex's monitor here, in which case we'll
            // do the select anyway. Since calls to wakeup() and select()
            // among different threads happen in non-deterministic order,
            // I don't think this is an issue.
            synchronized (selectThreadMutex)
              {
                if (unhandledWakeup)
                  {
                    unhandledWakeup = false;
                    return 0;
                  }
                else
                  {
                    selectThread = Thread.currentThread ();
                  }
              }

            // Call the native select() on all file descriptors.
            int result = 0;
            try
              {
                begin();
                result = implSelect(timeout);
		// side-effects 'selected'!
              }
            finally
              {
                end();
              }

            // If our unhandled wakeup flag is set at this point,
            // reset our thread's interrupt flag because we were
            // awakened by wakeup() instead of an external thread
            // interruption.
            //
            // NOTE: If we were blocked in a select() and one thread
            // called Thread.interrupt() on the blocked thread followed
            // by another thread calling Selector.wakeup(), then race
            // conditions could make it so that the thread's interrupt
            // flag is reset even though the Thread.interrupt() call
            // "was there first". I don't think we need to care about
            // this scenario.
            synchronized (selectThreadMutex)
              {
                if (unhandledWakeup)
                  {
                    unhandledWakeup = false;
                    selectThread.interrupted ();
                  }
                selectThread = null;
              }
            deregisterCancelledKeys();
            
            return result;
          }
        }
  }
    
  public final Set selectedKeys()
  {
    if (!isOpen())
      throw new ClosedSelectorException();

    return selected;
  }

  public final Selector wakeup()
  {
    // IMPLEMENTATION NOTE: Whereas the specification says that
    // thread interruption should trigger a call to wakeup, we
    // do the reverse under the covers: wakeup triggers a thread
    // interrupt followed by a subsequent reset of the thread's
    // interrupt status within select().
    
    // First, acquire the monitor of the object regulating
    // access to our selectThread and unhandledWakeup fields.
    synchronized (selectThreadMutex)
      {
        unhandledWakeup = true;
        
        // Interrupt any thread which is currently blocked in
        // a select operation.
        if (selectThread != null)
          selectThread.interrupt ();
      }
      
    return this;
  }

  private final void deregisterCancelledKeys()
  {
    Set ckeys = cancelledKeys ();
    synchronized (ckeys)
    {
      Iterator it = ckeys.iterator();

      while (it.hasNext ())
        {
	    SelectionKeyImpl ski = (SelectionKeyImpl) it.next ();
	    unregisterNative(ski);
	    keys.remove(ski);
	    it.remove ();
        }
    }
  }

  protected SelectionKey register (SelectableChannel ch, int ops, Object att)
  {
    return register ((AbstractSelectableChannel) ch, ops, att);
  }

  protected final SelectionKey register (AbstractSelectableChannel ch, int ops,
                                         Object att)
  {
    SelectionKeyImpl result;
    
    if (ch instanceof SocketChannelImpl)
      {
        SocketChannelImpl sc = (SocketChannelImpl) ch;
        result = new SocketChannelSelectionKey (ch, this);
      }
    else if (ch instanceof DatagramChannelImpl)
      {
        DatagramChannelImpl dc = (DatagramChannelImpl) ch;
        result = new DatagramChannelSelectionKey (ch, this);
      }
    else if (ch instanceof ServerSocketChannelImpl)
      {
        ServerSocketChannelImpl ssc = (ServerSocketChannelImpl) ch;
        result = new ServerSocketChannelSelectionKey (ch, this);
      }
    else
      {
        throw new InternalError ("No known channel type");
      }

    synchronized (keys)
      {
	  if (keys.contains(result)) {
	      keys.add (result);	
	      registerNative(result);
	  }
      }

    result.interestOps (ops);
    result.attach (att);
    return result;
  }

    private native void registerNative(SelectionKeyImpl key);

    private native void unregisterNative(SelectionKeyImpl key);

}
