gcc/libjava/gnu/java/nio/SelectorImpl.java

/* SelectorImpl.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.

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
executable, regardless of the license terms of these independent
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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;

public class SelectorImpl extends AbstractSelector
{
  private Set keys;
  private 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;

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

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

  protected final void implCloseSelector()
    throws IOException
  {
    // Cancel any pending select operation.
    wakeup();
    
    synchronized (keys)
      {
        synchronized (selected)
          {
            synchronized (cancelledKeys ())
              {
                // FIXME: Release resources here.
              }
          }
      }
  }

  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);
  }

  private final int[] getFDsAsArray (int ops)
  {
    int[] result;
    int counter = 0;
    Iterator it = keys.iterator ();

    // Count the number of file descriptors needed
    while (it.hasNext ())
      {
        SelectionKeyImpl key = (SelectionKeyImpl) it.next ();

        if ((key.interestOps () & ops) != 0)
          {
            counter++;
          }
      }

    result = new int[counter];

    counter = 0;
    it = keys.iterator ();

    // Fill the array with the file descriptors
    while (it.hasNext ())
      {
        SelectionKeyImpl key = (SelectionKeyImpl) it.next ();

        if ((key.interestOps () & ops) != 0)
          {
            result[counter] = key.getNativeFD();
            counter++;
          }
      }

    return result;
  }

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

            // Set only keys with the needed interest ops into the arrays.
            int[] read = getFDsAsArray (SelectionKey.OP_READ
                                        | SelectionKey.OP_ACCEPT);
            int[] write = getFDsAsArray (SelectionKey.OP_WRITE
                                         | SelectionKey.OP_CONNECT);

            // FIXME: We dont need to check this yet
            int[] except = new int [0];

            // 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 = VMSelector.select (read, write, except, timeout);
              }
            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;
                    Thread.interrupted ();
                  }
                selectThread = null;
              }

            Iterator it = keys.iterator ();

            while (it.hasNext ())
              {
                int ops = 0;
                SelectionKeyImpl key = (SelectionKeyImpl) it.next ();

                // If key is already selected retrieve old ready ops.
                if (selected.contains (key))
                  {
                    ops = key.readyOps ();
                  }

                // Set new ready read/accept ops
                for (int i = 0; i < read.length; i++)
                  {
                    if (key.getNativeFD() == read[i])
                      {
                        if (key.channel () instanceof ServerSocketChannelImpl)
                          {
                            ops = ops | SelectionKey.OP_ACCEPT;
                          }
                        else
                          {
                            ops = ops | SelectionKey.OP_READ;
                          }
                      }
                  }

                // Set new ready write ops
                for (int i = 0; i < write.length; i++)
                  {
                    if (key.getNativeFD() == write[i])
                      {
                        ops = ops | SelectionKey.OP_WRITE;

        //                 if (key.channel ().isConnected ())
        //                   {
        //                     ops = ops | SelectionKey.OP_WRITE;
        //                   }
        //                 else
        //                   {
        //                     ops = ops | SelectionKey.OP_CONNECT;
        //                   }
                     }
                  }

                // FIXME: We dont handle exceptional file descriptors yet.

                // If key is not yet selected add it.
                if (!selected.contains (key))
                  {
                    selected.add (key);
                  }

                // Set new ready ops
                key.readyOps (key.interestOps () & ops);
              }
            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 ())
        {
          keys.remove ((SelectionKeyImpl) it.next ());
          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)
      result = new SocketChannelSelectionKey (ch, this);
    else if (ch instanceof DatagramChannelImpl)
      result = new DatagramChannelSelectionKey (ch, this);
    else if (ch instanceof ServerSocketChannelImpl)
      result = new ServerSocketChannelSelectionKey (ch, this);
    else
      throw new InternalError ("No known channel type");

    synchronized (keys)
      {
        keys.add (result);
      }

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