source: trunk/gcc/libjava/java/io/PipedReader.java@ 3951

/* PipedReader.java -- Read portion of piped character streams.
   Copyright (C) 1998, 1999, 2000, 2001 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
conditions of the GNU General Public License cover the whole
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
modules, and to copy and distribute the resulting executable under
terms of your choice, provided that you also meet, for each linked
independent module, the terms and conditions of the license of that
module.  An independent module is a module which is not derived from
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
obligated to do so.  If you do not wish to do so, delete this
exception statement from your version. */

package java.io;

// NOTE: This implementation is very similar to that of PipedInputStream. 
// If you fix a bug in here, chances are you should make a similar change to 
// the PipedInputStream code.

/**
  * An input stream that reads characters from a piped writer to which it is 
  * connected. 
  * <p>
  * Data is read and written to an internal buffer.  It is highly recommended
  * that the <code>PipedReader</code> and connected <code>PipedWriter</code>
  * be part of different threads.  If they are not, there is a possibility
  * that the read and write operations could deadlock their thread.
  *
  * @specnote The JDK implementation appears to have some undocumented 
  *           functionality where it keeps track of what thread is writing
  *           to pipe and throws an IOException if that thread susequently
  *           dies. This behaviour seems dubious and unreliable - we don't
  *           implement it.
  *
  * @author Aaron M. Renn ([email protected])
  */
public class PipedReader extends Reader
{
  /** PipedWriter to which this is connected. Null only if this 
    * Reader hasn't been connected yet. */
  PipedWriter source;

  /** Set to true if close() has been called on this Reader. */
  boolean closed;

  /**
    * The size of the internal buffer used for input/output.
    */
  static final int PIPE_SIZE = 2048;

  /**
    * This is the internal circular buffer used for storing chars written
    * to the pipe and from which chars are read by this stream
    */
  char[] buffer = new char[PIPE_SIZE];

  /**
    * The index into buffer where the next char from the connected
    * <code>PipedWriter</code> will be written. If this variable is 
    * equal to <code>out</code>, then the buffer is full. If set to < 0,
    * the buffer is empty.
    */
  int in = -1;

  /**
    * This index into the buffer where chars will be read from.
    */
  int out = 0;

  /** Buffer used to implement single-argument read/receive */
  char[] read_buf = new char[1];

  /**
    * Creates a new <code>PipedReader</code> that is not connected to a 
    * <code>PipedWriter</code>.  It must be connected before chars can 
    * be read from this stream.
    */
  public PipedReader()
  {
  }

  /**
    * This constructor creates a new <code>PipedReader</code> and connects
    * it to the passed in <code>PipedWriter</code>. The stream is then 
    * ready for reading.
    *
    * @param source The <code>PipedWriter</code> to connect this stream to
    *
    * @exception IOException If <code>source</code> is already connected.
    */
  public PipedReader(PipedWriter source) throws IOException
  {
    connect(source);
  }

  /**
    * This method connects this stream to the passed in <code>PipedWriter</code>.
    * This stream is then ready for reading.  If this stream is already
    * connected or has been previously closed, then an exception is thrown
    *
    * @param src The <code>PipedWriter</code> to connect this stream to
    *
    * @exception IOException If this PipedReader or <code>source</code> 
    *                        has been connected already.
    */
  public void connect(PipedWriter source) throws IOException
  {
    // The JDK (1.3) does not appear to check for a previously closed 
    // connection here.
    
    if (this.source != null || source.sink != null)
      throw new IOException ("Already connected");
    
    source.sink = this;
    this.source = source;
  }
  
  /**
    * This method is used by the connected <code>PipedWriter</code> to
    * write chars into the buffer.