Initial revision

From-SVN: r102074

libjava/classpath/java/io/PipedReader.java

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+/* 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., 51 Franklin Street, Fifth Floor, Boston, MA
+02110-1301 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 (arenn@urbanophile.com)
+  */
+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 source 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.
+    *
+    * @param buf The array containing chars to write to this stream
+    * @param offset The offset into the array to start writing from
+    * @param len The number of chars to write.
+    *
+    * @exception IOException If an error occurs
+    * @specnote This code should be in PipedWriter.write, but we
+    *           put it here in order to support that bizarre recieve(int)
+    *           method.
+    */  
+  void receive(char[] buf, int offset, int len)
+    throws IOException
+  {
+    synchronized (lock)
+    {
+      if (closed)
+	throw new IOException ("Pipe closed");
+
+      int bufpos = offset;
+      int copylen;
+
+      while (len > 0)
+	{
+          try
+	    {
+	      while (in == out)
+		{
+		  // The pipe is full. Wake up any readers and wait for them.
+		  lock.notifyAll();
+		  lock.wait();
+		  // The pipe could have been closed while we were waiting.
+	          if (closed)
+		    throw new IOException ("Pipe closed");
+		}
+	    }
+	  catch (InterruptedException ix)
+	    {
+              throw new InterruptedIOException ();
+	    }
+
+	  if (in < 0) // The pipe is empty.
+	    in = 0;
+
+	  // Figure out how many chars from buf can be copied without 
+	  // overrunning out or going past the length of the buffer.
+	  if (in < out)
+	    copylen = Math.min (len, out - in);
+	  else
+	    copylen = Math.min (len, buffer.length - in);
+
+	  // Copy chars until the pipe is filled, wrapping if necessary.
+	  System.arraycopy(buf, bufpos, buffer, in, copylen);
+	  len -= copylen;
+	  bufpos += copylen;
+	  in += copylen;
+	  if (in == buffer.length)
+	    in = 0;
+	}
+      // Notify readers that new data is in the pipe.
+      lock.notifyAll();
+    }
+  }
+  
+  /**
+    * This method reads chars from the stream into a caller supplied buffer.
+    * It starts storing chars at position <code>offset</code> into the 
+    * buffer and
+    * reads a maximum of <code>len</code> chars.  Note that this method 
+    * can actually
+    * read fewer than <code>len</code> chars.  The actual number of chars 
+    * read is
+    * returned.  A -1 is returned to indicated that no chars can be read
+    * because the end of the stream was reached.  If the stream is already
+    * closed, a -1 will again be returned to indicate the end of the stream.
+    * <p>
+    * This method will block if no char is available to be read.
+    */
+  public int read() throws IOException
+  {
+    // Method operates by calling the multichar overloaded read method
+    // Note that read_buf is an internal instance variable.  I allocate it
+    // there to avoid constant reallocation overhead for applications that
+    // call this method in a loop at the cost of some unneeded overhead
+    // if this method is never called.
+
+    int r = read(read_buf, 0, 1);
+    return r != -1 ? read_buf[0] : -1;
+  }
+  
+  /**
+    * This method reads characters from the stream into a caller supplied 
+    * buffer. It starts storing chars at position <code>offset</code> into 
+    * the buffer and reads a maximum of <code>len</code> chars.  Note that 
+    * this method can actually read fewer than <code>len</code> chars.  
+    * The actual number of chars read is
+    * returned.  A -1 is returned to indicated that no chars can be read
+    * because the end of the stream was reached - ie close() was called on the
+    * connected PipedWriter.
+    * <p>
+    * This method will block if no chars are available to be read.
+    *
+    * @param buf The buffer into which chars will be stored
+    * @param offset The index into the buffer at which to start writing.
+    * @param len The maximum number of chars to read.
+    *
+    * @exception IOException If <code>close()</code> was called on this Piped
+    *                        Reader.
+    */  
+  public int read(char[] buf, int offset, int len)
+    throws IOException
+  {
+    synchronized (lock)
+    {
+      if (source == null)
+	throw new IOException ("Not connected");
+      if (closed)
+	throw new IOException ("Pipe closed");
+
+      // If the buffer is empty, wait until there is something in the pipe 
+      // to read.
+      try
+	{
+	  while (in < 0)
+	    {
+	      if (source.closed)
+		return -1;
+	      lock.wait();
+	    }
+	}
+      catch (InterruptedException ix)
+	{
+          throw new InterruptedIOException();
+	}
+
+      int total = 0;
+      int copylen;
+
+      while (true)
+	{
+	  // Figure out how many chars from the pipe can be copied without 
+	  // overrunning in or going past the length of buf.
+	  if (out < in)
+	    copylen = Math.min (len, in - out);
+	  else
+	    copylen = Math.min (len, buffer.length - out);
+
+          System.arraycopy (buffer, out, buf, offset, copylen);
+	  offset += copylen;
+	  len -= copylen;
+	  out += copylen;
+	  total += copylen;
+
+	  if (out == buffer.length)
+	    out = 0;
+
+	  if (out == in)
+	    {
+	      // Pipe is now empty.
+	      in = -1;
+	      out = 0;
+	    }
+
+          // If output buffer is filled or the pipe is empty, we're done.
+	  if (len == 0 || in == -1)
+	    {
+	      // Notify any waiting Writer that there is now space
+	      // to write.
+	      lock.notifyAll();
+	      return total;
+	    }
+	}
+    }
+  }
+  
+  public boolean ready() throws IOException
+  {
+    // The JDK 1.3 implementation does not appear to check for the closed or 
+    // unconnected stream conditions here.  However, checking for a
+    // closed stream is explicitly required by the JDK 1.2 and 1.3
+    // documentation (for Reader.close()), so we do it.
+    
+    synchronized (lock)
+    {
+      if (closed)
+	throw new IOException("Pipe closed");
+
+      if (in < 0)
+	return false;
+
+      int count;
+      if (out < in)
+	count = in - out;
+      else
+	count = (buffer.length - out) - in;
+
+      return (count > 0);
+    }
+  }
+  
+  /**
+  * This methods closes the stream so that no more data can be read
+  * from it.
+  *
+  * @exception IOException If an error occurs
+  */
+  public void close() throws IOException
+  {
+    synchronized (lock)
+    {
+      closed = true;
+      // Wake any thread which may be in receive() waiting to write data.
+      lock.notifyAll();
+    }
+  }
+}
+